NL2021155B1

NL2021155B1 - Optical Membrane

Info

Publication number: NL2021155B1
Application number: NL2021155A
Authority: NL
Inventors: Mohammadi Vahid; Janssen Paul; Van Zwol Pieter-Jan; Nihtianov Stoyan; Adrianus Van De Kerkhof Marcus; Nikolov Zdravkov Alexandar
Original assignee: Asml Netherlands Bv
Priority date: 2017-07-21
Filing date: 2018-06-20
Publication date: 2019-05-20
Also published as: CN110945432A; TW201908120A; NL2023116B1; KR20200026902A; CN110945432B; WO2019015905A1; NL2023116A; NL2021155A

Abstract

An optical membrane for use in or with a lithographic apparatus, the membrane comprising a first layer comprising a first material, and a second layer comprising a second material, the first layer being arranged on the second layer, wherein the first and second materials are selected such that a space charge region or depletion region is formed in the membrane, the space charge region or depletion region inducing an electric field in the membrane.

Description

Optical Membrane

FIELD

[0001] The present invention relates to an optical membrane for use in or with a lithographic apparatus and associated apparatus and methods.

BACKGROUND

[0002] A lithographic apparatus is a machine constructed to apply a desired pattern onto a substrate. A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (l'Cs). A lithographic apparatus may for example project a pattern from a patterning device (e.g. a mask) onto a layer of radiation-sensitive material (resist) provided on a substrate.

[0003] The wavelength of radiation used by a lithographic apparatus to project a pattern onto a substrate determines the minimum size of features which can be formed on that substrate. A lithographic apparatus which uses EUV radiation, being electromagnetic radiation having a wavelength within the range 4-20 ran, may be used to form smaller features on a substrate than a conventional lithographic apparatus (which may for example use electromagnetic radiation with a wavelength of 193 nm).

[0004] A membrane may be used in the lithographic apparatus to protect one or more components of the lithographic apparatus from contamination. The membrane may act as a spectral filter to reduce or even eliminate unwanted non-EUV radiation, such as deep ultra-violet (DUV) radiation and/or infrared (IR radiation), which may cause heat damage to one or more components of the lithographic apparatus. Additionally, the membrane may be arranged in the lithographic apparatus to reduce or prevent contamination of one or more components of the lithographic apparatus.

[0005] The membrane may additionally or alternatively be provided as part of a patterning device assembly comprising the patterning device. The membrane may be arranged to protect the patterning device from contamination, such as for example particulate contamination.

[0006] In use, the membrane may have to withstand high local heat loads. For example, when the membrane is part of the patterning device, a temperature on at least some parts of the membrane may be about 500°C. Such temperatures may cause damage to the membrane and decrease a life time of the membrane.

[0007] The article “Thickness analysis of silicon membranes for stencil masks'’, in J. Vac. Sci. Technol. B 18(6), Nov/Dec 2000, by Sossna, Herzinger and Wagner, discloses a stencil membrane mask used in ion projection lithography. In ion projection lithography the stencil membrane mask is the mask that defines a pattern in the ion beam projected onto a the substrate in order to impart this pattern to the substrate. The membrane of this article has a thickness of 4-7 pm and is not transparent for EUV radiation.

SUMMARY

[0008] According to a first aspect of the invention there is provided an optical membrane for use in or with a lithographic apparatus, the membrane comprising a first layer comprising a first material, and a second layer comprising a second material, the first layer being arranged on the second layer, wherein the first and second materials are selected such that a space charge region or depletion region is formed in the membrane, the space charge region or depletion region inducing an electric field in the membrane. The induced electrical field may cause a separation and/or distribution of charge carriers that may, for example be generated during irradiation of the optical membrane with radiation. This may reduce local heating of the optical membrane, e.g. one or more parts thereof, during irradiation of the membrane. The distribution and/or separation of the generated charge carriers may allow a heat load acting on the membrane to be spread over an area, e.g. an increased area, of the optical membrane.

[0009] The first and second materials may be selected such that the space charge region or depletion extends into a part of all of the membrane.

[00010] The first and second materials may be selected based on one or more properties of the first material and/or the second material.

[00011] The electrical field may extend in a direction perpendicular or substantially perpendicular to the first layer and/or the second layer.

[00012] The first and second materials may be selected such that the electrical field induced by the space charge region or depletion region may cause a separation of the generated charge carriers. The separation of the generated charge carriers may reduce the probability of recombination of the generated charge carriers. This may reduce the local heating of the membrane, e.g. during irradiation of the membrane.

[00013] The first and second materials may be selected such that the electrical field induced by the space charge region or depletion region may cause an accumulation of the generated charge carriers on or near opposing sides of the space charge region or depletion region.

[00014] The separation and/or accumulation of the generated charge carriers may induce another electrical field.

[00015] The other electrical field may extend in a direction parallel or substantially parallel to the first layer and/or the second layer.

[00016] The other electrical field may cause movement of the generated charge carriers, for example outwards and/or away from a part or region of the membrane that is irradiated.

[00017] The other electrical field may cause movement of the generated charge carriers, for example towards a periphery or peripheral area of the membrane.

[00018] The other electrical field may be such that the generated charge carriers may move at a velocity or speed that may be higher than a velocity or speed of a radiation beam moving across the membrane.

[00019] At least one of the first and second materials may comprise a semiconductor material. This may allow for the formation of a space charge region or depletion region, e.g. when the first layer is arranged on the second layer.

[00020] At least one other of the first and second materials may comprise a semiconductor material and/or a metal. This may allow the formation of a pn junction or a Schottky-junction.

[00021] At least one of the first and second materials may comprise Boron.

[00022] At least one other of the first and second materials comprises at least one of crystalline Silicon, polycrystalline Silicon, Silicon Carbide, Silicon Nitride, Germanium and Graphene. For example, the first material may comprise Boron and the second material may comprise Silicon for the formation of a Boron-Silicon junction. The Boron-Silicon junction may provide a nearly damage-free interface or interface region between the first and second layers. This in turn may provide an increase of conductivity at or near the interface or interface region between the first and second layers. 100023] The first material may comprise a first semiconductor material. The second material may comprise a second semiconductor material. The first and second semiconductor materials may be the same or different.

[00024] At least one of the first and second materials may be negatively doped. At least one other of the first and second materials may be positively doped.

[00025] The membrane may comprise an electrode. The electrode may be configured to allow for application of a voltage to the membrane. The voltage may induce yet another electrical field, such as for example an external electrical field, in the optical membrane. The voltage may be selected so that the application of the voltage to the optical membrane results in an increase of the width of the space charge region or depletion region.

[00026] The electrode may be arranged on the membrane, for example such that the voltage may induce a yet another electric field. The yet other electric field may extend in a direction perpendicular or substantially perpendicular to the first layer and/or the second layer.

[00027] The membrane may comprise a third layer. The third layer may comprise a third material.

[00028] The third material may comprise a metal, such as Zirconium, Molybdenum and/or

Ruthenium.

[00029] At least one of the first and second materials may comprise a fluorescent dopant. The fluorescent dopant may increase radiative emission from the optical membrane. The fluorescent dopant may act as a heat sink and/or reduce local heating of the optical membrane.

[00030] According to a second aspect of the invention there is provided a method of manufacture of an optical membrane for use in or with a lithographic apparatus, the method comprising forming a first layer comprising a first material, and forming or providing a second layer comprising a second material, the first layer being formed on the second layer, wherein the first and second materials are selected such that a space charge region or depletion region is formed in the membrane, the space charge region or depletion region inducing an electric field in the membrane. The optical membrane may comprise any of the features defined in the first aspect.

[00031] According to a third aspect of the invention there is provided an optical membrane for use in or with a lithographic apparatus, the membrane comprising a semiconductor material, the semiconductor material comprising a doping material, wherein a concentration of the doping material is selected such that an electric field is induced in the membrane. By selecting a concentration of the doping material such that an electric field is induced in the semiconductor material, a sheet resistance of the membrane may be reduced. A reduction in the sheet resistance of the membrane may result in a longer or increased travel distance of the generated charge carriers. This may allow for faster removal of the generated charge carriers from at least a part of the membrane that is irradiated with radiation and/or may reduce local heating of one or more parts of the optical membrane. An increased travel distance of the generated charge carriers may additionally allow and/or facilitate the removal of at least a portion of the generated charge carriers from the membrane.

[00032] The concentration of the doping material may be non-uniform in the semiconductor material. The concentration of the doping material may define a doping gradient in the semiconductor material.

[00033] A first portion or side the membrane may comprise a first concentration of the doping material. A second portion or side of the membrane may comprise a second concentration of the doping material. The first concentration of the doping material may be higher than the second concentration of the doping material.

[00034] The concentration of the doping material may be selected to vary in the semiconductor material between 1022cm 'and 10i4cnri\ [00035] The concentration of the doping material may be selected such that the induced electric field is about or larger than 107 V/m.

[00036] The concentration of the doping material may be selected such that the induced electrical field causes a separation of charge carriers that may be generated during irradiation of the membrane with radiation.

[00037] The concentration of the doping material may be selected such that the induced electrical field causes an accumulation of the generated charge carriers on or near' opposing sides of membrane.

[00038] The separation and/or accumulation of the generated charge carriers may induce another electrical field.

[00039] The semiconductor material may comprise at least one of at least one of crystalline Silicon, polycrystalline Silicon, Silicon Carbide, Silicon Nitride, Graphene and a I1I-V compound semiconductor.

[00040] The doping material may comprise at least one of Boron, Arsenic, Antimony and Phosphor.

[00041] According to a fourth aspect of the invention there is provided a method of manufacture of an optical membrane for use in or with a lithographic apparatus, the method comprising forming or providing a semiconductor material, and doping the semiconductor material with a doping material, wherein a concentration of the doping material is selected such that an electric field is induced in the membrane. The optical membrane may comprise any of the features defined in the third aspect.

[00042] According to a fifth aspect of the invention there is provided a system for reducing heating of an optical membrane, the system comprising an optical membrane according to the first and/or tltird aspect, wherein the system is configured for removal of charge carriers from the membrane, the charge carriers being generated during irradiation of the membrane, e.g. with radiation, such as for example EUV radiation.

[00043] The system may be configured for removal of the generated charge carriers from one or more peripheral portions or a periphery of the membrane.

[00044] The system may be configured to provide a sink for the generated charge carriers.

[00045] The system may be configured to short-circuit the membrane. The short-circuiting of the membrane may allow for the membrane to be discharged, such as for example continuously discharged. In other words, the generated charge carriers may be continuously removed from the membrane. This may allow continuous distribution of the charge carriers generated in the membrane, thereby reducing heating of the membrane (e.g. one or more portions or pails thereof).

[00046] A first portion or side of the membrane may be connected, such as electrically connected, to a second portion or side of the membrane. The first side and/or second sides or portions may be electrically grounded. Tire electrical grounding of the first and/or second sides or portions may provide the sink for the generated charge carriers. This may allow for the generated charge carriers to be removed from the membrane. The removal of the charge earners from the membrane may prevent or reduce recombination of the charge carriers, which may generate heat in the membrane.

[00047] The first portion or side of the membrane may be connected to the second portion or side of the membrane at or near a periphery of the membrane.

[00048] The system may comprise a load, such as a resistive element. The load may be connected to the membrane.

[00049] A resistance of the load may be selected based on at least one further property of the membrane. The at least one further property may comprise a sheet resistance of the membrane.

[00050] The resistance of the load may be selected to match (e.g. substantially match) the sheet resistance of the membrane. By selecting the resistance of the load to match (e.g. substantially match) the sheet resistance, heat (or at least a portion thereof) that is generated in the membrane, e.g. during irradiation of the optical membrane (e.g. one or more parts or portions thereof) with radiation, may be removed from the membrane.

[00051] According to a sixth aspect there is provided a patterning device assembly for use with a lithographic apparatus, the assembly comprising a patterning device, and a pellicle comprising an optical membrane according to the first and/or third aspect or a system for reducing heating of an optical membrane according to the fifth aspect.

[00052] According to a seventh aspect there is provided a lithographic apparatus comprising one or more of: an illumination system configured to condition a radiation beam; a support structure constructed to support a patterning device, the patterning device being capable of imparting the radiation beam with a pattern in its cross-section to form a patterned radiation beam, a substrate table constructed to hold a substrate, a projection system configured to project the patterned radiation beam onto the substrate; and an optical membrane according to the first and/or third aspect, the membrane being arranged adjacent the substrate table, or a system for reducing heating of an optical membrane according to the fifth aspect.

[00053] The apparatus may comprise a debris mitigation device. The debris mitigation device may be configured to direct a gas flow towards the substrate. The membrane may be part of or comprised in the debris mitigation device.

[00054] According to an eight aspect there is provided a method comprising projecting a patterned beam of radiation onto a substrate, wherein the beam of radiation is passed through an optical membrane according to the first or third aspect.

[00055] According to a ninth aspect there is provided a use of an optical membrane according to the first and/or third aspect in or with a lithographic apparatus.

[00056] Various aspects and features of the invention set out above or below may be combined with various other aspects and features of the invention as will be readily apparent to the skilled person.

BRIEF DESCRIPTION OF THE DRAWINGS

[00057] Embodiments of the invention will now be described, by way of example only, with reference to the accompanying schematic drawings, in which:

Figure 1 depicts a lithographic system comprising a lithographic apparatus and a radiation source according to an embodiment of the invention;

Figure 2 depicts an optical membrane according to an embodiment of the invention;

Figure 3 A depicts the optical membrane of Figure 2 prior to irradiation of the optical membrane; Figure 3B depicts a graph of a distribution of one or more heat sinks and one or more heat sources in the optical membrane of Figure 3A;

Figure 4A depicts the optical membrane of Figure 3A during irradiation;

Figure 4B depicts a graph of a distribution of the one or more heat sinks and the one or more heat sources in the optical membrane of Figure 4A;

Figure 5A depicts the optical membrane of Figure 4A during irradiation, wherein an electric field is induced in the optical membrane;

Figure 5B depicts a graph of a distribution of the one or more heat sinks and the one or more heat sources in the optical membrane of Figure 5 A;

Figure 6 depicts the optical membrane of Figure 5A during irradiation, wherein another electric field is induced in the optical membrane;

Figure 7 A depicts the optical membrane of Figure 6 during irradiation, wherein the other electric field causes charge carriers to spread in the optical membrane;

Figure 7B depicts a graph of a distribution of the one or more heat sinks and the one or more heat sources in the optical membrane of Figure 7 A;

Figures 8A and 8B depict an exemplary optical membrane for use with or in the lithographic apparatus of Figure 1;

Figure 8C depicts a distribution of a charge density and electric field intensity in the optical membrane of Figures 8A and 8B ;

Figure 9 depicts a graph of the responsivity over wavelength of a photodiode comprising first and second layers of the optical membrane Figures 8 A and 8B;

Figure 10 depicts a top view of another exemplary optical membrane for use with or in a lithographic apparatus of Figure 1;

Figure 11 depicts another exemplary optical membrane for use with or in the lithographic apparatus of Figure 1;

Figure 12 depicts another exemplary optical membrane for use with or in the lithographic apparatus of Figure 1;

Figure 13 depicts another exemplary optical membrane for use with or in the lithographic apparatus of Figure 1;

Figure 14 depicts another exemplary optical membrane for use with or in the lithographic apparatus of Figure 1;

Figure 15 depicts a lithographic system comprising a lithographic apparatus and a radiation source according to another embodiment of the invention;

Figure 16A depicts another exemplary optical membrane for use with or in the lithographic apparatus of Figure 1 or Figure 15;

Figure 16B depicts an exemplary graph of a donor atom concentration Nn in dependence of a thickness ,v of the optical membrane of Figure 16A;

Figure 16C depicts the optical membrane of Figure 16A prior irradiation;

Figures 17A to 17C depict the optical membrane of Figure 16A during irradiation;

Figure 18A depicts a system for reducing heating of an optical membrane according to an embodiment of the present invention;

Figure 18B depicts a distributed electrical model of the optical membrane of Figure 18A;

Figure 19A depicts another exemplary system for reducing heating of an optica] membrane; and

Figure 19B depicts a distributed electrical model of the optical membrane of Figure 19A. DETAILED DESCRIPTION

[00058] Figure 1 shows a lithographic system. The lithographic system comprises a radiation source SO and a lithographic apparatus LA. The radiation source SO is configured to generate an extreme ultraviolet (EUV) radiation beam B. The lithographic apparatus LA comprises an illumination system 1L, a support structure MT configured to support a patterning device MA (e.g. a mask), a projection system PS and a substrate table WT configured to support a substrate W. The illumination system IL is configured to condition the radiation beam B before it is incident upon the patterning device MA. The projection system is configured to project the radiation beam B (now patterned by the mask MA) onto the substrate W. The substrate W may include previously formed patterns. Where this is the case, the lithographic apparatus aligns the patterned radiation beam B with a pattern previously formed on the substrate W.

[00059] The radiation source SO, illumination system IL, and projection system PS may all be constructed and arranged such that they can be isolated from the external environment. A gas at a pressure below atmospheric pressure (e.g. hydrogen) may be provided in the radiation source SO. A vacuum may be provided in illumination system IL and/or the projection system PS. A small amount of gas (e.g. hydrogen) at a pressure well below atmospheric pressure may be provided in the illumination system IL and/or the projection system PS.

[00060] The radiation source SO shown in Figure 1 is of a type which may be referred to as a laser produced plasma (LPP) source). A laser 1, which may for example be a CO2 laser, is arranged to deposit energy via a laser beam 2 into a fuel, such as tin (Sn) which is provided from a fuel emitter 3. Although tin is referred to in the following description, any suitable fuel may be used. The fuel may for example be in liquid form, and may for example be a metal or alloy. The fuel emitter 3 may comprise a nozzle configured to direct tin, e.g. in the form of droplets, along a trajectory towards a plasma formation region 4. The laser beam 2 is incident upon the tin at the plasma formation region 4. The deposition of laser energy into the tin creates a plasma 7 at the plasma formation region 4. Radiation, including EUV radiation, is emitted from the plasma 7 during de-excitation and recombination of ions of the plasma.

[00061] The EUV radiation is collected and focused by a near normal incidence radiation collector 5 (sometimes referred to more generally as a normal incidence radiation collector). The collector 5 may have a multilayer structure which is arranged to reflect EUV radiation (e.g. EUV radiation having a desired wavelength such as 13.5 nm). The collector 5 may have an ellipsoidal configuration, having two ellipse focal points. A first focal point may be at the plasma formation region 4, and a second focal point may be at an intermediate focus 6, as discussed below.

[00062] The laser 1 may be remote from the radiation source SO. Where this is the case, the laser beam 2 may be passed from the laser 1 to the radiation source SO with the aid of a beam delivery system (not shown) comprising, for example, suitable directing mirrors and/or a beam expander, and/or other optics. The laser 1 and the radiation source SO may together be considered to be a radiation system.

[00063] Radiation that is reflected by the collector 5 forms a radiation beam B. The radiation beam B is focused at point 6 to form an image of the plasma formation region 4, which acts as a virtual radiation source for the illumination system 1L. The point 6 at which the radiation beam B is focused may be referred to as the intermediate focus. Tire radiation source SO is arranged such that the intermediate focus 6 is located at or near to an opening 8 in an enclosing structure 9 of the radiation source.

[G0064] The radiation beam B passes from the radiation source SO into the illumination system IL, which is configured to condition the radiation beam. The illumination system IL may include a facetted field mirror device 10 and a facetted pupil mirror device 11. The faceted field mirror device 10 and faceted pupil mirror device 11 together provide the radiation beam B with a desired cross-sectional shape and a desired angular intensity distribution. The radiation beam B passes from the illumination system IL and is incident upon the patterning device MA held by the support structure MT. The patterning device MA reflects and patterns the radiation beam B. The illumination system IL may include other minors or devices in addition to or instead of the faceted field mirror device 10 and faceted pupil mirror device 11.

[00065] Following reflection from the patterning device MA the patterned radiation beam B enters the projection system PS. The projection system comprises a plurality of mirrors which are configured to project the radiation beam B onto a substrate W held by the substrate table WT. The projection system PS may apply a reduction factor to the radiation beam, forming an image with features that are smaller than corresponding features on the patterning device MA. A reduction factor of 4 may for example be applied. Although the projection system PS has two mirrors in Figure 1, the projection system may include any number of mirrors (e.g. six mirrors).

[00066] Figure l schematically depicts an optical membrane 16 for use in or with a lithographic apparatus according to an embodiment of the present invention. The optical membrane may be part of or comprised in a patterning device assembly PA for use with a lithographic apparatus. The patterning device assembly PA may comprise the patterning device MA depicted in Figure 1 and a pellicle PL (indicated in Figure 1 by a dashed line). The pellicle PL may be or comprise the optical membrane 16. The pellicle PL may be arranged to protect the patterning device MA from contamination, such as for example particulate contamination, and/or damage. For example, the pellicle PL may be arranged so as to extend over or cover the patterning device MA. However, it will be appreciated that the optical membrane described herein is not limited to being part of or comprised in a patterning assembly. For example, as will be described below, in other embodiments the optical membrane may be provided as part of a debris mitigation system.

[00067] f igure 2 schematically depicts the optical membrane 16. The optical membrane 16 may be provided in the form of a filter, spectral filter or spectral purity filter. The optical membrane 16 may be configured to transmit EUV radiation and/or to be transparent, e.g. substantially transparent, to EUV radiation. The optical membrane 16 may be configured to filter, e.g. reduce or substantially eliminate, deep ultra-violet (D1JV) radiation and/or infra-red (1R) radiation. T he optical membrane 16 may be or comprise a film, such as a thin film, or a flexible sheet, e.g. a thin flexible sheet. The optical membrane 16 may comprise a thickness of about 20 to 80nm.

[00068] The optical membrane 16 comprises a first layer 18 composing a first material and a second layer 20 comprising a second material. The first layer 18 is arranged on the second layer 20. The first and second materials are selected such that a space charge region or depletion region 22 is formed in the membrane 16. The space charge region or depletion region 22 induces an electric field E in the optical membrane 16. The induced electrical field may cause a separation and/or distribution of charge carriers that may be generated during irradiation of the optical membrane with the radiation beam B. This may reduce local heating of one or more parts of the optical membrane 16. The distribution and/or separation of the generated charge carriers may allow the heat load acting on the optical membrane 16 to be spread over an increased area of the optical membrane 16. This may reduce heating of one or more parts of the optical membrane 16 during irradiation with the radiation beam B.

[00069] The term “generated charge carriers” may be considered as encompassing photo-generated charge carriers, such as for example electron-hole pairs that are generated during absorption of some of the radiation beam B by the optical membrane 16.

[00070] The terms “space charge region or depletion region” may be understood as a region from wliich mobile charge carrier, such as electrons and/or holes, have diffused away. Any positive and/or negative net charges that remain induce an electric field E at or near an interface 23 between the first layer 18 and the second layer 20. The positive and/or negative net charges may include ionised impurities, such as ionized donors and/or acceptors, and are indicated by “+” and in Figure 2. The term “interface” may be considered as encompassing an interface region.

[00071] The first and second materials of the first and second layers 18, 20, respectively, may be selected based on one or more properties of the first and/or second materials. The one or more properties of the first and/or second materials may comprise a type of material, a defect concentration, type of dopant, and/or a doping concentration of the first and/or second materials. The one or more properties may comprise one or more optical properties of the first and/or second materials, such as for example a transmission coefficient, a reflection coefficient and/or an absorption coefficient, of the first and/or second materials. The one or more properties may comprise one or more physical properties, such as for example radiation hardness and/or illumination stability, of the first and/or second materials.

[00072] The first and second materials may be selected such that the space charge region or depletion region 22 extends into at least a part or al 1 of the optical membrane 16. For example, the first and second materials may be selected such that the space charge region or depletion region 22 extends at least from the interface 23 between the first layer 18 and second layer 20 into at least one of or both of the first and second layers 18, 20, e.g. the first and second materials. The first and second materials may be selected such that an extent of the space charge region or depletion region 22 into the second layer 20, e.g. the second material, is larger than an extent of the space charge region or depletion region 22 into the first layer 18, e.g. the first material. Alternatively, the first and second materials may he selected such that the extent of the space charge region or depletion region 22 into the second layer 20, e.g. the second material, is equal (e.g. substantially equal) to or smaller than the extent of the space charge region or depletion region 22 into the first layer 18, e.g. the first material.

[G0073] In the embodiment depicted in Figure 2, the first material of the first layer 18 comprises a first semiconductor material and the second material of the second layer 20 comprises a second semiconductor material. The first and second semiconductor materials may be the same or different. At least one of the first semiconductor material and second semiconductor material may be negatively doped and at least one other of the first semiconductor material and the second semiconductor material may be positively doped. In the embodiment depicted in Figure 2, the first and second layers 18, 20 may be considered as forming a pn-junction. The space charge region or depletion region 22 extends into both the first and second layers 18, 20. However, it will be appreciated that the first and second layers described herein are not limited to forming a pn-junction. For example, in other embodiments the first and second materials of the first and second layers may be selected such that the first and second layers form a Schottky-junction or a Boron-Silicon junction, as will be described below. In such embodiments, the space charge region or depletion region may be considered as extending into only one of the first and second layers.

[00074] Figure 3A schematically depicts the optical membrane 16 of Figure 2 before irradiation with the radiation beam B. In the embodiment depicted in Figure 3A, the space charge region or depletion region 22 is considered to extend into all of the optical membrane 16. However, it will be appreciated that in other embodiments, the space charge may only extend into a part of the optical membrane. Figure 3B depicts a graph of a contribution of one or more heat sinks and one or more heat sources acting on the optical membrane 16 in dependency on a position, e.g. a position in the y-direction, on the optical membrane 16. In can be seen in Figure 3B that the contribution 30 of one or more heat sinks acting on the optical membrane 16 is substantially constant and that there tire no heat sources acting on the optical membrane 16, prior to irradiation of the optical membrane 16.

[00075] The term “heat source” may be considered as encompassing one or more mechanisms that generate heat on or in the optical membrane. The one or more mechanisms that generate heat on or in the optical membrane will be described below. The terms “one or more heat sources” may be interchangeably used with the terms “heat sources.” [00076] The term “heat sink” may be considered as encompassing one or more mechanisms that transfer heat from the optical membrane, for example to the surrounding environment of the optical membrane. The one or more mechanisms that transfer heat from the optical membrane will be described below. The terms “one or more heat sinks” may be interchangeably used with the terms “heat sinks.” [00077] Figure 4A schematically depicts the optical membrane 16 during irradiation. Figure 4B is similar to Figure 3B. During irradiation of the optical membrane 16 a plurality of charge earners 24 is generated. In other words, a plurality of electron-hole pairs 24 is generated due to the absorption of some of the radiation of the radiation beam B by the first and second materials of the optical membrane 16. The plurality of electron-hole pairs 24 are generated in apart or region of the optical membrane that is irradiated by the radiation beam B. The part or region of the optical membrane 1.6 that is iiradiated by the radiation beam B may also be referred to as an illumination volume 26. The irradiation of the optical membrane 16 with the radiation beam B causes heat to be generated in the optical membrane 16. In other words, the irradiation of the optical membrane 16 with the radiation beam B can be considered as one of the one or more heat sources.

[00078] Other heat sources that generate heat in or on the optical membrane 16 may include one or more of: recombination of the generated electron-hole pairs, e.g. radiative and/or non-radiative recombination of the generated electron-hole pairs, and thennalisation of the electron-hole pairs. Thermalisation of the electron-hole pairs may comprise relaxation of the generated electrons and holes towards the lowest level of the conduction band and valence band, respectively, for example under emission of one or more phonons, e.g. lattice vibrations. Other heat sources that generate heat in or on the optical membrane 16 may further include Joule heating or the Joule effect, which may be due to a current flowing through the optical membrane 16. The current may be caused by the generated electron-hole pairs, w hich move through the optical membrane 16. Other heat sources may further include the Peltier effect, which may be due to a current flowing through a junction between two different conductors.

[00079] Heat sinks that may transfer heat from the optical membrane 16 may include the Thompson effect, which may be due to the current flowing though the optical membrane 16. Another heat sink that may transfer heat from the optical membrane 16 may include convection, e.g. a transfer of heat between the optical membrane and the environment of the optical membrane 16, such as for example a gas flow that may be present at or near the optical membrane 16 [00080] Figure 4B depicts the contribution 28 of the one or more heat sources to the heating of the optical membrane 16 in comparison with the contribution 30 of the one or more heat sinks in the illumination volume 26 of the optical membrane 16. It can be seen from Figure 4B that in the illumination volume 26 the contribution 28 of the one or more heat source is larger than the contribution 30 of the one or more heat sinks. The difference between the contribution 28 of the heat sources and the contribution 30 of the heat sinks is indicated in Figure 4B by reference numeral D l. This difference D1 between the contribution 28 of the heat source and the contribution 30 of the heat sinks may cause local heating of the optical membrane 16 in the illumination volume 26. For example, a power of 200W of the radiation beam B measured at the intermediate focus 6 may cause a temperature of about 500°C of the optical membrane 16, w'hen the optical membrane 16 is used as a pellicle of the patterning device. MA. Alternatively or additionally, in some embodiments, the optical membrane 16 is part of the debris mitigation device 15, as will be described below. In such embodiments, a pow’er of 200W of the radiation beam B measured at the intermediate focus 6 may cause a temperature of about 100°C of the optical membrane. As described above, heating of the optical membrane 16 may reduce the lifetime of the optical membrane 16 and/or cause damages to the optical membrane 16. It can be seen from Figure 4B that outside of the illumination volume 26 the heat sinks are more dominant than inside the illumination volume 26. Ill other words, outside the illumination volume 26, heat is transferred from the optical membrane 16, for example to the surrounding environment of the optical membrane 16.

[00081] Figure 5A schematically depicts the optical membrane 16 during irradiation. Figure 4B is similar to Figures 3B and 4B. As discussed above, the first and second materials are selected such that a space charge region or depletion region 22 is formed in the membrane 16. The space charge region or depletion region 22 induces the electric field E in the optical membrane 16. The first and second materials of the first and second layer 18, 20, respectively, may be selected such that electric field E induced by the space charge region or depletion region 22 is sufficient to cause the separation of the generated charge carriers 24. For example, the first and second materials of the first and second layers, 18, 20, respectively, may be selected such that the electric field E induced by the space charge region 22 is about 107 V/m. It will be appreciated that the larger the induced electric field is, the more efficient, e.g. the larger and/or faster, the separation of the generated charge carrier 24 may be. For example, an increase in the induced electric field, e.g. above 107V/m, may provide an increased potential barrier for the generated charge carrier 24. This may provide an effective separation of the charge carriers 24 and/or may reduce the number of charge carriers that may overcome the potential hairier. The separation of the generated charge carriers 24 may reduce the probability of recombination of the generated charge carriers 24. This may reduce the local heating, of the optical membrane 16 in the illumination volume 26. Additionally, an increase in the induced electric field E, e.g. above 107V/m, may lead to a separation of an increased amount of the generated charge carriers.

[00082] The electric field E may be considered as extending in a direction perpendicular, e.g. substantially perpendicular, to the first and/or second layers 18, 20. The electric field E may be considered as a built-in electric field or vertical built-in electrical field. The interface 23 between the first and second layers 18, 20 is indicated by a dashed line in Figure 5A.

[00083] The separation of the generated charged carrier 24 may be instant. In other words, the generated charge carriers 24 may be separated by the electric field E before the charge carrier can recombine.

[00084] As can be seen in Figure 5A, the separated charge carriers 24a, 24b may accumulate at or near opposing sides 22a, 22b of the space charge region or depletion region 22. For example, the electrons 24a may accumulate on or near a bottom side 22b of the space charge region or depletion region 22and the holes 24b may accumulate on or near a top side 22a of the space charge region or depletion region 22. It will be appreciated that in other examples, the first and second materials may be selected such that the electrons accumulate on or near a top side of the space charge region or depletion region 22 and the holes accumulate on or near a bottom side of the space charge region or depletion region 22. In examples where the space charge region or depletion region extends into all of the optical membrane, the electrons may accumulate on or near a bottom side of the first layer 18 and the holes may accumulate on or near a top side of the second layer 20, or vice versa.

[00085] As discussed above, the separation between the generated charge carriers 24 may reduce or prevent recombination of the generated charge carrier, whereby recombination of the generated charge carriers may be considered as one of the heat sources that generates heat in or on the optical membrane 16. Figure 5B is similar to Figure 4B and depicts the contribution of the heat sources 28b with the electric field E present in the optical membrane 16 compared to the contributi on of the heat sources 28a without an electrie field being present. As can be seen in Figure 5B, the contribution of the heat sources 28b with the electric field E present in the optical membrane 16 is decreased relative to the contribution of the heat sources 28a without an electric field being present Additionally, a difference D2 between the contribution of the heat sources 28b with the electric field E present and the contribution of the heat sinks 30 is decreased relative to the difference D1 between the contribution of the heat sources 28a without an electric field present and the contribution of the heat sinks 30. A width, e.g. full width at half maximum (FWH'M), of the contribution of the heat source 28b with the electric field E present may be the same (e.g. substantially the same) as a width, e.g. full width at half maximum (FWHM), of the contribution of the heat sources 28a without an electric field present.

[00086] Figure 6 schematically depicts the optical membrane 16 during irradiation. As discussed above, the separated charge carriers 24a, 24b accumulate on or near opposing sides 22a, 22b of the space charge region or depletion region 22. The separation and/or accumulation of the generated charge carriers 24a, 24b may induce another electrical field. The other electric field may be caused by a potential difference between the charge carriers 24a, 24b accumulated in the illumination volume 26 and a region outside of the illumination volume 26. The other electric field may extend in a direction parallel, e.g. substantial parallel, to the first and/or second layers 18, 20. The other electric field may be considered as a lateral built-in electric field. The other electric field may cause movement of the accumulated charge carrier 24a, 24b outwards and/or away from the illumination volume 26. For example, the other electrical field may cause movement of the charge carrier 24a, 24b towards a periphery or peripheral area of the optical membrane 16. The movement of the charge carriers 24a, 24b is indicated in Figure 6 by the arrows labelled M. The accumulated charge carriers 24a, 24b may additionally experience a repelling force, such as for example a repelling Coulomb force. The repelling force may also cause the charge carriers 24a, 24b to move outwards and/or away from the illumination volume 26.

[00087] Figure 7A schematically depicts the optical membrane 16 in which some of the accumulated charge carriers 24a, 24b have moved outwards and/or away from the illumination volume 26. In the region outside of the illumination volume 26, the charge earners 24a, 24b may recombine. This may result in spreading of the heat over an area or volume 32 of the optical membrane 16 and/or may reduce the local heating of the optical membrane 16. Additionally, this may allow' the optical membrane 16 to be used at higher powers of the radiation beam B, such as for example powers above 200W.

[00088] The other electric field may be about 104V/m. This may result in a velocity or speed of the charge earners 24a, 24b of about 105 m/s. The movement of the radiation beam B across the optical membrane 16 may comprise a velocity or speed of about 0.5 m/s. This may allow the accumulated charge carriers 24a, 24b to spread or move at a velocity or speed that is higher than the velocity or speed of the radiation beam B across the optical membrane.

[00089] Figure 7B depicts the contribution 28a of the heat sources without an electric field present in the optical membrane 16 compared to the contribution 28b of the heat sources with the electric field E and the other electric field present in the optical membrane 16. It can be seen that the contribution 28b of the heat sources with the electric field E and the other electric field present is decreased compared to the contribution 28a of the heat sources without an electric field present in the optical membrane 16. Additionally, a width, e.g. a full width at half maximum (FWHM), of the contribution 28b of the heat sources with the electric field E and the other electric field present is increased compared to a width, e.g. a full width at half maximum (FWHM). of the contribution 28a of the heat sources without an electric field present in the optical membrane 16. In other words, the local heating of the optical membrane 16 can be considered to be spread, as discussed above. The difference D2 between the contribution 28b of the heat sources with the electric field E and the other electric field E present and the contribution of the heat sinks 30 is decreased compared the difference D1 between the contribution 28a of the heat sources without an electric field present and the contribution 30 of the heat sinks. In other words, the local heating of the optical membrane may be considered to be reduced, when the electrical field and the other electrical field are present.

[00090] Figures 8A and 8B schematically depict an embodiment of the optical membrane 16 in which the first material comprises Boron and the second material comprises negalively-doped Silicon, such as for example negatively doped polycrystalline Silicon. It will be appreciated that in other embodiments, the second material may comprise undoped (e.g. intrinsic) Silicon. It should also be understood that in other embodiments, the first material may comprise Silicon and the second material may comprise Boron. Additionally, the first material comprising Boron may be positively or negatively doped. By doping the first and/or second materials, a conductivity of the first and/or second materials may be increased. This may enhance the movement the generated charge carriers and/or reduce the heating of the optical membrane 16.

[00091] Figure 8A schematically depicts the optical membrane 16 before arrangement of the first layer 18 on the second layer 20. Figure 8B schematically depicts the optical membrane 16 subsequent to the arrangement of the first fayer 18 on the second layer 20. The arrangement of the first layer 18 comprising Boron on the second layer 20 comprising Silicon may lead to the formation of a Boron-Silicon-junction. It can be seen from Figure 8B that a space charge region or depletion region 22 is formed in the second layer 20, when the first layer 18 is arranged on the second layer 20. Figures 8A and 8B additionally schematically depict an interface region or system 19, which is formed between the first layer 18 and the second layer 20, e.g. at or near an interface between the first and second layers 18, 20, as will be described below. The formation of the space charge region or depletion region 22 in an embodiment where the first material comprises Boron and the second material comprises negatively doped Silicon (or intrinsic Silicon) differs from the formation of a space charge region or depletion region in a pn-junction or a Schottky-junction. The formation of the space charge region or depletion region 22 can be considered as being caused by a transfer of charge earners at the interface between the first and second layers 18, 20.

[00092] Boron has an electronegativity of about 2 and Silicon has an electronegativity of about 1.9. The difference in electronegativity between Boron and Silicon may cause an ionic character of the bond between the Boron and Silicon atoms. The ionic bond between the Boron and Silicon atoms may lead to the formation of a dipole at the interface between the first layer 18 and the second layer 20. The dipole may define or form the interface region or system 19. The interface region or system 19 may be considered as defining a positively charged side 19a at or near the Silicon side and a negatively charged side 19b at or near the Boron side. When the first layer 18 is arranged on the second layer 20 and the interface region or system 19 is formed, for example between at least one monolayer of Silicon atoms and at least one monolayer of Boron atoms, and a transfer of electrons from the Silicon atoms at the interface region or system 19 to the neighbouring Boron atoms may occur. This may be due to the ionic bond between the Boron atoms and Silicon atoms, w’hich is able to accept additional electrons. This may lead to an increase in the bond length of the bond between the Boron and Silicon atoms. The increase in the bond length of the bond between Boron and Silicon may allow·1 further electrons to be accepted by Boron. This may cause a decrease in the positive charges in the positively charged side 19a of the interface region or system 19, which is indicated in Figure 8B. The electrons may diffuse towards die positively charged side 19a of the interface region or system 19, for example due to Coulomb forces acting on the electrons. The diffusion of the electrons towards the interface system 19, e.g. the positively charged side 19a thereof, may leave behind positive net charges and lead to the formation of the space charge region or depletion region 22. The net positive net charges may induce the electric field E near the interface region or system 19 between the first layer 18 and the second layer 20. The diffusion of the electrons towards the interface system 19 may lead to the formation of the space charge region or depletion region 22 in the second layer 20, e.g. the Silicon.

[00093] The first layer 18 may comprise a thickness of at least one monolayer of Boron atoms to form the space charge region or depletion region with the second layer 20. Tn some examples, the thickness of the first layer 18 may be about lnm to 2nm, such as for example 1.5nm. The first layer 18 comprising Boron may be formed by any deposition technique that leads to the formation of a space charge region or depletion region 22 in the second layer 20, as described above. Exemplary deposition techniques that may lead to the formation of the space charge region or depletion region 22 in the second layer 20 may comprise Chemical Vapour Deposition (CVD) or Atomic Layer Deposition (ALD) techniques. The formation of the space charge region or depletion region and/or exemplary deposition techniques for the formation of the Boron-Silicon-junction is further described in, for example in V. Mohammad i “Low Temperature PureB Technology for CMOS Compatible Photodetectors", Doctoral Thesis, TU Delft (http://repository.tudelft.nlJ), 2015. Boron formed using CVD or ALD may also be referred to as “PureB.” The use of Boron, e.g. formed using CVD or ALD, as the first material of the first layer 18 and Silicon as the second material of the second layer 20, may allow for the formation of a nearly damage-free interface region or system 19 between the first and second layers 18, 20. This is turn may provide an increased conductivity along or at the interface region or system 19 compared to other materials.

[00094] The second layer 20 may comprise a thickness of about 20 to 50nm, such as for example 40nm.

[00095] Boron and Silicon may be considered as transmissive for EUV radiation (e.g. radiation having a wavelength of about 13.5nm). The use of Boron as the first material of the first layer and Silicon as the second material of the second layer may allow a transmission of the optical membrane 16 to EUV radiation to be above 90%.

[00096] As described above and schematically depicted in Figure 8B, the space charge region or depletion region 22 extends from the interface region or system 19 into the second material of the second layer 20. The space charge region or depletion region 22 may comprise a width in the micrometer range or less than lpm. For example, the space charge region or depletion region 22 may comprise a width of about lOOnm to 500nm. Although the space charge region or depletion region 22 is depicted in Figure 8B as extending into part of the second layer 20, it will be appreciated that in other embodiments the space charge region or depletion region to may instead or additionally extend into the first layer or substantially all of the optical membrane. In other words, the whole optical membrane may be depleted from mobile charge carriers.

[00097] Figure 8C schematically depicts the charge density and electric field intensity across the space charge region or depletion region 22. As described above, the diffusion of the electrons towards the interface system or region 19, e.g. the positively charged side 19a thereof, may leave behind positive net charges and lead to the formation of the space charge region or depletion region 22. Additionally, negative charge may be present or accumulate at or near the negatively charged side 19b of the interface region or system 19, as indicated in Figure 8C. The electric field intensity has a maximum at the interface region or system 19 between the first and second layers 18, 20. For example, the electric field may comprise a maximum strength of about 107 V/m at the interface system or region 19 between the first and second layers.

[00098] Figure 9 depicts a graph of the responsivity over wavelength of a photodiode comprising the first and second layers 18, 20 of the optical membrane 16 described in relation to Figure 8A and 8B. In other words, the photodiode comprises a first layer comprising Boron, which is arranged on a second layer comprising negatively-doped Silicon. The responsivity of the photodiode was measured for three photodiodes formed from the same substrate. The measured responsivity MR for the three samples is close to a theoretical responsivity TR of Silicon, which is about 0.27, for wavelengths of about or larger than 13.5nm. This may lead to quantum efficiency of nearly 100% for the photodiodes. The quantum efficiency corresponds to the ratio of the measured responsivity of the theoretical responsivity. The theoretical responsivity TR depicted in Figure 9 was calculated based on 26 electron holes pair being generated per photon having a wavelength of about 13.5nm and a near loss-less and/or ideal system was assumed. Exemplary calculations of the theoretical responsivity may be found in, for example, F. Schalie, et.al. "Mean energy required to produce an electron-hole pair in silicon for photons of energies between 50 and 1500 eV," Journal of Applied Physics, vol 84, no 4, pp.2926-2939,1998 and F. Scholze, et.al. "Determination of the electron-hole pair creation energy for semiconductors from the spectral responsivity of photodiodes," Nuclear Instruments and Methods in Physics Research A 439, pp. 208-215, 2000. The quantum efficiency may be considered as being indicative of the generated electron-hole pairs per photon of a given energy. In other words, the quantum efficiency may be considered as a ratio of charge carriers collected by the photodiode to the number of photons of a gi ven energy incident on the photodiode. Therefore, an optical membrane comprising a first layer comprising Boron and a second layer comprising Silicon, as described above, may be considered to be efficient in converting photons into electron-hole pairs, which are subsequently separated and moved away from the illumination volume 26 by the induced electric field E and the other electric field. This may reduce the local heating of the optical membrane 16.

[00099] Although in the embodiment of Figures 8a to 8C, Boron was described as the first material of the first layer and negatively-doped Silicon was described as the second material of the second layer, it should be understood that the optical membrane disclosed herein is not limited to these materials. For example, the second material may comprise at least one of crystalline Silicon, e.g. monocrystalline Silicon, Silicon Carbide, Silicon Nitride and Graphene, which may be positively or negatively doped or undoped (e.g. intrinsic).

[000100] it will be appreciated that at least one of the first and second materials described herein may comprise a semiconductor material. This may allow for the formation of a space charge region or depletion region, when the first layer is arranged on the second layer. The other one of the first and second material may also comprise a semiconductor material. Exemplary semiconductor materials of at least one of or both of the first and second layers may comprise at least one of crystalline Silicon, e.g. monocrystalline Silicon, Silicon Carbide, Silicon Nitride. Germanium and Graphene, which may be positively or negatively doped. Exemplary materials that may be used to negatively dope at least Silicon may comprise Arsenic (As) (e.g. with a concentration of about 101S to 1020 cm'3). Antimony (Sb) (e.g. with a concentration of about 1018to 1020 cm'3) or Phosphor (P) (e.g. with a concentration of about 10iSto 1020 cm'3). An exemplary material (hat may be used to positively dope Silicon may comprise Boron (B) (e.g. with a concentration of about 1018 to 5x l020 cm'3). The exemplary semiconductor materials may be doped so that there is abrupt change or a gradual change in the dopant concentration.

For example as described above in relation to Figures 2 to 7B, the first and second layers 18, 20 may be considered as forming a pn-junction.

[000101] In other embodiments, at least one of the first and second materials may comprise a metal and at least one other of the first and second materials comprises the semiconductor material. The semiconductor material may be positively or negatively doped. In such examples, the first and second layers may be considered as forming a Schottky-junction. In such embodiments, the space charge region or depletion region may be considered as extending into the semiconductor material. Exemplary metals for forming the Schottky-junction may comprise Platinum and/or Iridium. A voltage, such as for example a reverse-bias voltage, may be applied to the optical membrane 16, for example, to increase a width of the space charge region or depletion region. The optical membrane may comprise an electrode to allow for the application of the voltage, as will be described below.

[000102] Additionally or alternatively, the first and/or second materials comprise a fluorescent dopant. The fluorescent dopant may increase radiative emission from the optical membrane 16. Exemplary fluorescent dopants may comprise Europium and/or Terbium. A concentration of the fluorescent dopant may be about or less than 1020 cm"3. For example, the fluorescent dopants may absorb at least some radiation of the radiation beam B. This may excite the fluorescent dopant to a higher energy state from which it can relax non-radiatively, e.g. under emission of one or more phonons, and emit radiation having a longer wavelength than that of the absorbed radiation. This may allow the fluorescent dopant to act as a heat sink and/or reduce local heating of the optical membrane 16.

[000103] Figure 10 schematically depicts a top view of an exemplary optical membrane 1.6 for use in or with a lithographic apparatus. The optical membrane 16 may be similar to that depicted in any one of Figures 2 to 8B and may comprise any of the features of the optical membrane described in relation to any one of Figures 2 to 8B. In the embodiment depicted in Figure 10, the optical membrane 16 comprises an electrode 34. The electrode 34 may be configured to allow for application of a voltage to the optical membrane 16. The voltage may induce yet another electrical field, such as for example an external electrical field, in the optical membrane 16. The voltage may be selected so that the application of the voltage to the optical membrane results in an increase of the width of the space charge region or depletion region22. The voltage may be selected based on one or more requirements or conditions, such as for example a required increase of the space charge region or depletion region 22, a size of a current flowing through the optical membrane due to the applied voltage, heat induced by the current and/or interference effects between the yet other electric field with the generated plasma in the radiation source or other components of the lithographic apparatus. The voltage may be or comprise a reverse-bias voltage. The yet another electrical field may extend in the substantially the same direction as the electrical field E. As can be seen in Figure 10, the electrode 34 is arranged along the periphery' 16c of the optical membrane 16. It will be appreciated that the optical membrane disclosed herein is not limited to comprising an electrode that is arranged along the periphery of the optical membrane. For example. in other embodiments, the electrode may be provided one or more sides of the optical membrane and/or may be embedded in at least part or all of the optical membrane.

[000104] The electrode 34 may comprise a conductive material, such as for example a metal. The conductive material may be selected based on one or more properties, such as for example a relatively high transmission to EUV radiation, relatively low reflectivity to EUV radiation and/or chemical stability in a hydrogen environment. Exemplary materials for the electrode may comprise Ruthenium (Ru), Zirconium (Zr) or Molybdenum (Mo). An electrode 34 comprising Zirconium or Molybdenum may additionally comprise a capping layer.

[000105] The electrode 34 may be arranged on the optical membrane 16 such that the external electric field extends in a direction perpendicular to the first layer and/or the second layer. The external electric field may be applied to increase the vertical and/or lateral built-in electric fields E. This may increase and/or accelerate the separation of the generated charge carriers 24. In addition, the applied external electric field may increase the speed or velocity of the generated charge carriers 24. This may allow the generated charge carriers to move away from the illumination volume 26 at a higher speed or velocity compared to embodiments where no external electrical field is applied to the optical membrane. This may lead to reduced local heating of the optical membrane 16.

[000106] Figure 11 schematically depicts another exemplary optical membrane 16 for use in or with a lithographic apparatus. The optical membrane 16 depicted in Figure 11 may comprise any of the features of the optical membrane described above in relation to Figures 2 to 8B and/or 10. The optical membrane 16 depicted in Figure 11 comprises a third layer 36 comprising a third material. The third layer 36 may be arranged between the first and second layers 18, 20. The third layer 36 may be configured to act as an emission layer. In other words, the third layer 36 may be configured to allow' for emission of radiation from the optical membrane. The third layer 36 may comprise an emissive coefficient that is higher than an emissive coefficient of the first and/or second layers 18,20. This may allow the third layer 36 to act as a heat sink and/or reduce local heating of the optical membrane 16. The third material may comprise a metal, such as for example Zirconium, Molybdenum and/or Ruthenium. The third layer may comprise a thickness of about 3 to 4 nm.

[000107] Figure 12 depicts tin exemplary optical membrane 16 for use in or with a lithographic apparatus. The optical membrane 16 depicted in Figure 12 may comprise any of the features of the optical membrane described above in relation to Figures 2 to 8 A, 10 and/or 11. The optical membrane 16 comprises a first layer 18, which comprises Boron, .e.g. PureB. and a second layer 20, which comprises negatively-doped Silicon. The first layer may be formed by a deposition method such as for example CVD or ALD, which allows for the formation of the space charge region or depletion region in the first and/or second materials, as described above. The first layer 18 may comprise a thickness of about 1 to 2nm, such as for example 1,5nm. The second layer 20 may comprise a thickness about 20 to 50nm, such as for example 40nm. The optical membrane 16 comprises two capping layers 28a, 28b. The first and second layers 18, 20 are arranged between in the capping layers 28a, 28b. In this embodiment, the capping layers 28a, 28a comprise Boron, which may be formed by another deposition technique, such as for example Physical Vapour Deposition (PVD). Each capping layer 28a, 28b may comprise a thickness of about 2 to 4nm. In this embodiments the capping layer 28b that is arranged adjacent the second layer 20 comprises a thickness of about 4nm and the capping layer that is arranged adjacent the first layer 18 comprises a thickness of 3nm. The capping layers 28a, 28b may be provided to protect the first and/or second layers 18, 20. It will be appreciated that in other embodiments, the optical membrane may comprise less or more than two capping layers.

[000108] Figure 13 depicts another exemplary optical membrane 16 for use in or with a lithographic apparatus. The optical membrane 16 depicted in Figure 13 may comprise any of the features of the optical membrane described above in relation to Figures 2 to 8B, 10, 11 and/or 12. The optical membrane 16 depicted in Figure 13 comprise first and second layers 18, 20 that are the same as those described in relation to Figure 12. The optical membrane further comprises the third layer 36. In this embodiment, the third layer comprises Zirconium. The third layer 36 comprises a thickness of about 3 to 4nm. The optical membrane 16 comprises two capping layers 28a, 28b. The first of the two capping layers 28a is arranged between the second layer 20 and the third layer 26. The first of the two capping layers 28a comprises Boron, which may be formed by the other deposition technique, such as for example PVD. The first of the two capping layers 28a comprises a thickness of about 1 to 2nm, such as for example 1.5nm. The second of the two capping layers 28b is arranged beneath the third layer 36. The second of the two capping layers 28b comprises Boron, which may be formed by the other deposition technique, such as for example PVD. The second of the two capping layers 28b comprises a thickness of about 4nm.

[000109] Figure 14 depicts another exemplary optical membrane 16 for use in or with a lithographic apparatus. The optical membrane 16 depicted in Figure 14 is similar to that depicted in Figure 13. Howe ver, instead of the first capping layer 28a, the optical membrane comprises a fourth foyer 40. The fourth layer 40 may provide a barrier, e.g. to avoid intermixing of the materials of the second layer 20 and the third layer 36. The fourth layer 40 may comprise Silicon Nitride. The fourth layer comprises a thickness of about 1 to 3 nm.

[000110] It will be appreciated that the optical membrane disclosed herein is not limited to being provided as or comprised in the pellicle. In other embodiments the optical membrane may be arranged in the lithographic apparatus, such as for example the projection system.

[000111] Figure 15 shows another embodiment of a lithographic system. In the embodiment depicted in Figure 15, the optical membrane is part of or comprised in the lithographic apparatus LA. It will he appreciated that the optical membrane may be provided in the lithographic apparatus instead or in addition to being provided in the patterning assembly. For example, the optical membrane 16 may be airanged adjacent the substrate table WT. The optical membrane 16 may be arranged to at least partially or fully close an opening of the projection system PS through which the radiation beam B is projected on the substrate W, as depicted in Figure 15.

[000112] The lithographic apparatus may include a debris mitigation device 15. The debris mitigation device 15 may be arranged in the projection system PS, such as for example in the vicinity of the substrate W. The debris mitigation device 15 may be configured to direct a flow of gas towards the substrate W, e.g. to reduce or prevent contamination from entering the projection system PS.

[Ö00113] The optical membrane 16 may be part of or comprised in the debris mitigation device 15. The optical membrane 16 may be arranged to reduce or prevent contamination from entering the projections system of the lithographic apparatus. It will be appreciated that the optical membrane disclosed herein is not limited to being arranged adjacent the substrate table. For example, in other embodiments the optical membrane may be arranged at other locations in the lithographic apparatus, such as for example in the illumination system and/or other positions in the projection system.

[000114] The optical membrane depicted in Figure 15 may comprise any of the features of the optical membrane described in relation to any one of Figure 2 to 8B and/or any one of Figures 10 to 14.

[000115] The optical membrane 16 for use in or with a lithographic may be manufactured by forming the first layer 18 comprising the first material. The first layer 18 may be formed by a deposition technique that allows for the formation of a space charge region or depletion region in the optical membrane. Exemplary techniques for forming the first layer may comprise Chemical Vapour Deposition (CVD) or Atomic Layer Deposition (ALD). For example, the first layer 18 may be formed by a CVD process comprising a temperature range of about 400°C to about 700°C. A CVD process comprising such a temperature range may be suitable for formation of a space charge region between a first layer comprising Boron and a second layer comprising Silicon, as described above. It will be appreciated that the method described herein is not limited to such deposition techniques. For example, in other embodiments an epitaxial technique may be used to form the first layer.

[000116] The first layer 18 may be formed on the second layer 20 comprising the second material. The second layer may be formed by any of the deposition techniques disclosed herein. Alternatively, the second layer may be provided, e.g. pre-formed or separately from the first layer. For example, the second layer may be provided in the form of a substrate or the like. As discussed above, the first and second materials are selected such that a space charge region or depletion region is formed in the optical membrane 16. As described above, the space charge region or depletion region induces tut electric field in the optical membrane 16.

[000117] Prior to forming the first layer 18, contaminates and/or oxides may be removed from the second layer and/or the second layer 20 may be passivated, e.g. against oxide formation. Additionally, prior to forming the first layer 18, hydrogen may be removed from the second layer 20. A process of forming a first layer comprising Boron on a second layer comprising Silicon is described for example in “Low Temperature PureB Technology for CMOS Compatible Photocletectors ”, Doctoral Thesis, TU Delft (http://repository.tudeift.nl/), 2015.

[000118] Figures 16A, 16C and 17A to 17C schematically depict another exemplary optical membrane 16 for use in or with a lithographic apparatus. Figures I6A and 16C depict the optical membrane prior to irradiation with the radiation beam B and Figures 17A to 17C depict the optical membrane 16 during irradiation with the radiation beam B. The optical membrane 16 comprises a semiconductor material. The semiconductor material comprises a doping material. A concentration of the doping material may be selected such that an electric field E is induced in the optical membrane 16, as will be described below. The induced electrical field may cause a separation and/or distribution of charge carriers that may be generated during irradiation of the optical membrane 16 with the radiation beam B. This may reduce local heating of one or more parts of the optical membrane 16. The distribution and/or separation of the generated charge carriers may allow the heat load acting on the optical membrane 16 to be spread over an increased area of the optical membrane 16. This may reduce heating of one or more parts of the optical membrane 16 during irradiation with the radiation beam B.

[000119] By selecting a concentration of the doping material such that an electric field is induced in the semiconductor material, a sheet resistance of the optical membrane may be reduced. The term “sheet resistance” may be understood as referring to a measure of resistance of thin films, which may be uniform in thickness. A reduction in the sheet resistance of the optical membrane may allow separated charge earner to move away from the illumination volume 26 of the optical membrane by an increased distance, e.g. before recombining. In other words, the reduction in the sheet resistance of the optical membrane may result in a longer or increased travel distance of the generated charge carriers. This may allow for faster removal of the generated charge earners from the illumination volume 26 and/or may reduce local heating of one or more parts of the optical membrane 16. An increased travel distance of the generated charge earners may also allow the removal of at least a portion of the generated charge carriers from the optical membrane 16, as will be described below.

[000120] The concentration of the doping material may be non-uniform in the semiconductor material. In other words, the doping material may define a doping gradient in the semiconductor material. The doping gradient may comprise a steep doping gradient. A first portion or side of the optical membrane 16 may comprise a first concentration of the doping material. A second portion or side of the optical membrane 16 may comprise a second concentration of the doping material. The first concentration of the doping material may be higher than the second concentration of the doping material. The sheet resistance of the optical membrane 16 may be considered to be inversely proportional to a doping level, e.g. at the surface, of the semiconductor material. In other words, an increase in the doping level may lead to a decrease in the sheet resistance of the optical membrane 16.

[000121] Figure 16B schematically depicts an exemplary graph of a donor atom concentration Nd in dependence of a thickness x of the optical membrane 16. It will be understood that the gradient of the donor atom concentration No is not limited to that depicted in Figure 16B. In this example, the donor atoms may define or be comprised in the doping material. Referring to Figures 16A and 16B, a top portion or side 16a of the optical membrane 16 comprises a higher donor atom concentration than a bottom portion or side 16b of the optical membrane 16. In between the top portion or side 16a and the bottom portion or side 16b of the optical membrane 16, the donor atom concentration may decrease. such as for example gradually decrease. It will he appreciated that the optical membrane disclosed herein is not limited to such as distribution of the donor atom concentration. For example, in other embodiments, the donor atom concentration of the top portion or side may be lower than the donor concertation of the bottom portion or side of the optical membrane.

[000122] The doping gradient may cause a diffusion of mobile charge carriers (or majority charge carriers), which may be in the form of electrons 42. For examples, the electrons 42 may diffuse from the top portion or side 16a of the optical membrane 16 towards the bottom portion or side 16b of the optical membrane. The diffusion of the electrons 42 leaves behind positive net charges, which may be in the form of ionised donors. The separation of the positive and negative charges, which tire indicated in Figure 16C by “+” and induces an electric field E.

[000123] The induced electric field E extends in a direction opposite to the diffusion process. The electrical field E may be considered as a built-in electrical field or a vertical built-in electrical field. The electrical field E extends in this embodiment in direction perpendicular (e.g. substantially perpendicular) to the top portion or side 16a and/or bottom portion or side 16b of the optical membrane 16.

[000124] Although the above example refers to a donor atom concentration, it will be appreciated that in other embodiments, the doping material may be provided in the form of acceptor atoms in addition or instead of the donor atoms.

[000125] Tire concentration of the doping material may be selected such that the induced electrical field E causes a separation of charge carriers 24a, 24b that are generated during irradiation of the optical membrane 16 with tire radiation beam B. Additionally or alternatively, the concentration of the doping material may be selected such that the induced electric field is about or larger than 107V/m. For example, the concentration of the doping material may be selected to vary between about 1022cm ’ and 1014 cm" 3 [000126] The separation of the generated charge carriers 24 is schematically depicted in Figure 17A. The separated charge carriers may accumulate on or near opposing sides or portions 16a, 16b of the optical membrane 16. For example, the electrons 24a may accumulate on or near the top portion or side 16a of the optical membrane 16 and the holes 24b may accumulate on or near the bottom portion or side 16b of the optical membrane 16.

[000127] As described above in relation to Figure 6, the separation and/or accumulation of the generated charge carriers 24a, 24b may induce another electrical field. The other electric field may be caused by a potential difference between the charge carriers 24a, 24b accumulated in the illumination volume 26 and a region outside of the illumination volume 26. The other electric field may extend in a direction parallel, e.g. substantial parallel, to the top portion or side 16a and/or the bottom portion or side 16b of the optical membrane 16. The other electiic field may be considered as a lateral built-in electric field. The other electric field may cause movement of the accumulated charge carrier 24a, 24b outwards and/or away from the illumination volume 26. For example, the other electrical field may cause movement of the charge carrier 24a, 24b towards a periphery or peripheral area of the optical membrane 16. The movement of the charge carriers 24a, 24b is indicated in Figure 17B by the arrows labelled M. The accumulated charge carriers 24a, 24b may additionally experience a repelling force, such as for example a repelling Coulomb force. The repelling force may also cause the charge carriers 24a, 24b to move outwards and/or away from the illumination volume 26.

[000128] Figure 17C schematically depicts the optical membrane 16 in which some of the accumulated charge carriers 24a, 24b have moved outwards and/or away from the illumination volume 26. In the region outside of the illumination volume 26, the charge carriers 24a, 24b may recombine. This may result in spreading of the heat over an area or volume 32 of the optical membrane 16 and/or may reduce the local heating of the optical membrane 16. Alternatively or additionally, the charge carriers 24a, 24b may be removed from the optical membrane 16, as will be described below.

[000129] Figures 17A to 17C are similar to Figures 5A, 6 and 7A. It will be appreciated that any features described above, e.g. in relation to Figures 5A, 6 and 7A, may also apply to the embodiments described in relation to Figures 17A to 17C.

[000130] The optical membrane 16 depicted in Figures 16A, 16C, and 17A to 17C may be manufactured by forming or providing the semiconductor material. For example, the semiconductor material may be formed using any of the deposition techniques disclosed herein. Alternatively, the semiconductor material may be provided, e.g. pie-formed. The semiconductor material may be doped with the doping material. A concentration of the doping material may be selected such that an electric field is induced in the membrane.

[000131] The semiconductor material may be doped as part of the step of forming the semiconductor material. Alternatively, the semiconductor material may be doped subsequently to the formation of the semiconductor material, for example using a diffusion or implantation process, such as for example ion implantation.

[000132] An exemplary step of doping the semiconductor material may comprise depositing the doping material on the semiconductor material, e.g. using one of the deposition techniques disclosed herein, such as for example CVD. During the deposition of the doping material on the semiconductor material, some of the doping material may diffuse into the semiconductor material. The diffusion of the doping material into the semiconductor material may be dependent on a temperature of the deposition technique.

[000133] For example, the semiconductor material may comprise Silicon, such as for example crystalline or poly-crystalline Silicon The semiconductor material comprises negatively-doped (e.g. n-type) Silicon, e.g. using Phosphor, and the Phosphor doping concentration may be about 1014 cm'3. In other words, the semiconductor material may already be doped with another doping material. The doping material may comprise Boron, which may be used to introduce a positive doping (e.g. p-type doping) into the Silicon.

[000134] Boron, such as for example amorphous Boron, may be deposited on the n-type Silicon at a temperature of about 700°C, for example using the CVD technique. This process may lead to the formation of a layer of Boron, such as a layer of Pure-Boron, at the surface of the Silicon. During the deposition of Boron on the n-type Silicon some of the Boron may diffuse into Silicon. The Boron concentration may be about 1021 to 1022 c-m'3 at or near the top portion or side 16a of the optical membrane. The Boron concentration may decrease to about 1014 cm'5 at or near the bottom portion or side 16b of the optical membrane 16.

[000135] It will be appreciated that Boron may be deposited on Silicon at temperatures larger or less than 700°C, for example to achieve a pre-determined or desired doping gradient in the semiconductor material.

[000136] It will be appreciated that optical membrane disclosed herein is not limited to comprising Silicon as the semiconductor material. For example, in other embodiments, the semiconductor material may comprise at least one of Silicon Carbide, Silicon Nitride and Graphene. Alternatively, the semiconductor material may comprise a 1II-V compound semiconductor.

[000137] It will also be appreciated that the optical membrane disclosed herein is not limited to comprising Boron as the doping material. For example, in other embodiments, at least one of Arsenic (As), Antimony (Sb) and Phosphor (P) may be used to as a doping material, for example to negatively dope Silicon.

[000138] Figures 18A to 19B schematically depict a system for reducing heating of an optical membrane 16 according to an embodiment of the present invention. The optical membrane 16 may comprise any of the features of the exemplary optical membranes described above. The system 44 is configured for removal of charge carriers 24a, 24b (e.g. at least a portion thereof) from the optical membrane 16 (e.g. one or more parts or portions thereof). The charge carriers 24a, 24b are generated during irradiation of the membrane 16, e.g. with the radiation beam B.

[000139] The system may comprise a conducting element 45, such as for example an electrical conductor, for dissipating or removing the generated charge carriers 24a, 24b from the optical membrane 16.

[000140] The system 44 may be configured for removal of the generated charge carriers 24a, 24b from one or more peripheral portions or a periphery of the optical membrane 1.6, as will be described below'. The system 44 may be configured to provide a sink 46 for the generated charge carriers 24a, 24b.

[000141] The system 44 may be configured to short-circuit the optical membrane 16. For example, the conducting element 45 may be arranged to short-circuit the optical membrane 16. As depicted in Figure 18A, a first side or portion 16a, e.g. a top portion or side 16a, of the optical membrane 16 may be connected, e.g. electrically connected, to a second or portion 16b, e.g. a bottom portion of or side 16b, of the optical membrane 16. The first and/or second sides or portions 16a, 16b of the optical membrane 16 may be considered as portions or sides towards which the charge carriers 24a, 24b move. e.g. due to the electric field E, e.g. the vertical built-in electrical field, as described above. The first side or portion 16a of the optical membrane 16 may be connected, e.g. electrically connected, to the second side or portion 16b of the optical membrane 16 at or near a periphery 16c of the optical membrane 16. For example, the first side or portion 16a of the optical membrane 16 may be connected, e.g. electrically connected, to the second side or portion 16b along at least a part or all of the periphery 16c of the optical membrane 16. The term “periphery” may be considered as encompassing a peripheral area or region.

[000142] Alternatively, the first side or portion 16a of the optical membrane 16 may be connected, e.g. electrically connected, to the second side or portion 16b of the optical membrane 16 at or near one or more peripheral portions 16c of the optical membrane 16. The one or more peripheral portions 16c may be closely spaced relative to each other.

[000143] The conducting element 45 may be arranged to connect, e.g. electrically connect the first side or portion 16a of the optical membrane 16 to the second side or portion 16b of the optical membrane 16, as described above.

[000144] The first and/or second sides or portions 16a, 16b may be electrically grounded. For example, the conducting element 45 may be connected the first and/or second sides or portions 16a, 16b of the optical membrane 16 to an electrical ground. The electrical ground may provide the sink 46 for the generated charge carriers 24a, 24b. This may allow for the generated charge carriers 24a, 24b to be removed from the optical membrane 16. The removal of the charge carriers 24a, 24b from the optical membrane 16 may prevent or reduce recombination of the charge carriers 24a, 24b, which may generate heat in the optical membrane. The electrical grounding of the first and/or second sides or portion 16a, 16b of the optical membrane 16 may protect the optical membrane 16 from being statically charged and/or may prevent an increase of an electrical potential of the optical membrane with relative to other and/or neighbouring components or objects, e.g. of the patterning device assembly or the lithographic apparatus, it should be understood that the system described herein is no( limited to electrically grounding the optical membrane, e.g. the first and/or second side or portions thereof. For example, in other embodiments, the membrane may not be electrically grounded.

[000145] Although Figure 18A depicts both the first and second sides or portions 16a. 16b as being connected to a common electrical ground, which may provide the sink 46, it will be appreciated that in other embodiments the first and second sides or portions of the optical membrane may be each connected to a respective electrical ground. This may additionally allow for short-circuiting of the optical membrane.

[000146] A voltage or potential, e.g. electrical potential, may additionally be applied to the optical membrane, e.g. relative to the electrical ground. For example, when the optical membrane is mounted to a mounting or supporting element (not depicted), such as for example a frame, support or the like, the voltage or potential applied to the optical membrane may be selected to correspond or match (e.g. substantially correspond or match) a voltage or potential, e.g. relative to the electrical ground, that has been applied to the mounting or supporting element. This may allow the optical membrane to have the same (e.g. substantially the same) voltage or potential as the mounting or supporting element. Tn other words, electrical isolation of the optical membrane from the mounting or supporting element may be reduced or prevented.

[000147] Figure 18B schematically depicts a distributed electrical model of the optical membrane 16. The optical membrane 16 may be considered as a photodiode comprising a plurality of capacitors Ci, C2, C3, Cn, a plurality of first resistors, which may be provided in the form of series resistors Rs, and a plurality of second resistors, which may be provided in form of shunt resistors Rsh. The generated charge carriers 24a, 24b may be considered as being stored in at least one capacitor of the plurality of capacitors Ci, C2, C3, Cn. Each capacitor of the plurality of capacitors Ci, C2, C3, Cn may be associated with a respective part or region of the optical membrane 16. The pans or regions of the optical membrane 16 are indicated in Figure 18B by the concentrically arranged circles.

[000148] The series resistors Rs may be considered to represent the sheet resistance of the optical membrane 16. The series resistors R„ are arranged to connect two or more capacitors of the plurality of capacitors Ci, C2, C3, Cn- The generated carriers 24a, 24b may be removed from the at least one capacitor of the plurality of capacitors Ci, C2, Ci, Cn through or via the series resistors Rs in the form of current or photocurrent.

[000149] The shunt resistors R.ss may be considered to represent a loss of the charge carriers 24a, 24b, such as for example an internal loss of the charge carriers 24a, 24b, e.g. due to recombination of the charge carriers 24a, 24b.

[000150] Referring to Figure 18B, a pail or region of the optical membrane 16 is irradiated by the radiation beam B and is referred to as the illumination volume 26. Charge carriers 24a, 24b that are generated due to the irradiation of the optical membrane 16 with the radiation beam B may be represented as a current I over a photodiode P. The charge carriers 24a, 24b are charging the capacitor Ci of the optical membrane 16, which is associated with the illumination volume 26 of the optical membrane 16.

[000151] The generated charge carriers may be distributed over one or more other portions of the optical membrane. As described above, due to the other electric field the charge carriers 24a, 24b move away and/or outwards from the illumination volume 26, such as for example towards the periphery or one or more peripheral portions 16c of the optical membrane 16. The charge carriers 24a, 24b may be considered as moving away from the illumination volume 26 through or via the sheet resistors Rs, thereby moving successively from the capacitor Ci that is associated with the illumination volume 26 towards the remaining capacitors C2, C3, Cn- This may allow the generated charge carriers 24a, 24b to become distributed across the optical membrane 16.

[000152] in an ideal case, heat that may be generated in the optical membrane 16 due to the current flowing through the sheet resistors R,. A decrease in the sheet resistance, e.g. due to a selected doping concentration of the semiconductor material of the optical membrane 16, as described above, may lead to a decrease in the generated heat. For example, by reducing the sheet resistance, e.g. the resistance of the series resistors R , and/or reducing the recombination, e.g. the local recombination, of generated charge carriers 24a, 24b, for example by increasing the resistance of the shunt resistors R», an increased amount of generated charge carriers 24a, 24b may move away from the illumination volume 26, before recombining, and reach the periphery or one or more peripheral portions 16c of the optical membrane 16. Tliis may allow the heat generation to be at least distributed over or across the optical membrane 16, such as for example a part or all of the optical membrane 16. As will be described below, a pail of the generated heat may be removed by transferring the part of the heat to a load.

[000153] The above described process may be repeated each time a part or region of the optical membrane 16 is irradiated with the radiation beam B. When the irradiation of the part or region of the optical membrane 16 is repeated, new charge carriers may be generated. The newly generated charge carriers may contribute to the charging of the capacitor Ci that is associated with the illumination volume 26. The newly generated charge carriers may accumulate at one or more capacitors of the plurality of capacitors Cl, C2, C?, Cn. This may lead to the one or more capacitors of the plurality of capacitors Ci, C2, C3. Cn exceeding a threshold level. Above the threshold level, the charge earners 24a, 24b may recombine before moving away and/or outwards from the illumination volume 26. In other words, if the charge of the capacitor C( is not removed before the new charge carriers are generated, a voltage level over the photodiode P (which is associated with the illumination volume 26) increases and may reach a threshold level. Above the threshold level, the photodiode P may become conductive and the charge carriers may recombine, e.g. to discharge (he photodiode P. This may lead to heat being generated in the illumination volume 26.

[000154] Referring to Figure 18B, by short-circuiting the optical membrane 16, for example as described above, the capacitors Ci, C>, C;. Cn and/or shunt resistors R.sh may be considered as being short-circuited. This may allow the charge carriers 24a, 24b to be removed or discharged from the optical membrane 16, e.g. from the one or more peripheral portions or periphery 16c thereof. This in turn may allow removal of the charge carriers that are stored in the one or more capacitors of the plurality of capacitors Cl, C2, C3, Cn, thereby preventing or reducing the accumulation of charge carriers at the one or more capacitors of the plurality of capacitors Ci, C2, C3, Cn· Newly generated charge carriers may be able to move away and/or outwards from the illumination volume 26, thereby becoming distributed in the optical membrane 16. The distribution of the charge carriers in or across the optical membrane 16 may reduce heating, e.g. local heating, of the optical membrane 16 (e.g. one or more portions or parts thereof).

[000155] By short-circuiting the optical membrane 16, as described above, the shunt resistors R* may be associated with a finite value that may be considered to be increased. In other words, loss of charge carriers, e.g. due to recombination, may be considered to be decreased.

[000156] The short-circuiting of the optical membrane 16 may allow for the optical membrane to be discharged, such as for example continuously discharged, in other words, the generated charge carriers 24a, 24b may be removed, e.g. continuously removed, from the optical membrane 16. This may allow continuous distribution of the charge carriers generated in the optical membrane 16, thereby reducing heating, e.g, local heating, of the optical membrane (e.g. one or more portions or parts thereof).

[000157] Figures 19A and 19B are similar to Figures 18A and I8B and any features described in relation to Figures 18A and 18B may also apply to the system depicted in Figures 19A and 19B. The system 44 depicted in Figures 19A and 19B may comprise a load, which may be provided in the form of a resistive element Rl. However, it will be appreciated that in other embodiments the load may be provided in the form of another device or element to which power may be delivered. In the embodiment depicted in Figures 19A and I9B, the load is provided instead of the short-circuiting of the optical membrane 16, described above.

[000158] The resistive element Rl is connected to the optical membrane 16, as for example depicted in Figure 19A. For example, the first and/or second portions or sides 16a, 16b of the optical membrane 16 may be connected to the resistive element Rl, e.g. by the conducting element 45. The first and/or second sides or portions 16a, 16b may be connected to the resistive element Rl along at least a part or all of the periphery 16c of the optical membrane 16. Alternatively, the first and/or second side or portions 16a, 16b of the optical membrane 16 may be connected to the resistive element Rl at or near one or more peripheral portions 16c of the optical membrane 16. The one or more peripheral portions 16c may be closely spaced relative to each other.

[000159] A resistance of the resistive element Rl may be selected based on at least one further property of the optical membrane 16. For example, the resistance of the resistive element Rl may be selected based on the sheet resistance of the optical membrane 16, .e.g. a resistance of one or more series resistors of the plurality of series resistors Rs. The resistance of the resistive element Rl may be selected to match (e.g. substantially match) the sheet resistance. This may allow a transfer of power from the optical element 16 to the resistive element Rl to be increased or maximised. For example, the optical membrane 16 may convert energy, e.g. photon energy, of the radiation beam B into power. The power may cause heating of the optical membrane 16. By selecting the resistance of the resistive element Rl to match (e.g. substantially match) the sheet resistance, heat (or at least a portion thereof) that is generated in the optical membrane 16 during irradiation of the optical membrane (e.g. one or more portions thereof) may be transferred to the resistive element Rl, and thereby may be removed from the optical membrane 16. In other words, at least a part of the kinetic energy of the generated charge earners 24a, 24b, e.g. the recombination of the charge carriers 24a, 24b, may be converted into heat outside of the optical membrane 16, such as for example over the resistive element Rl.

[000160] ft will be appreciated that the power that may be transferred to the resistive element Rl may be considered to be proportional to the product of a current / and a voltage V. The current I may be considered as a current that may be due, e.g. at least partially due, to the generated charge carriers 24a, 24b flowing towards the resistive element Rl. The current I may cause the voltage V across the resistive element Rl. The provision of a load, e.g. a resistive element Rl, may allow' for the removal of the generated charge carriers 24a, 24b (e.g. a portion thereof) from the optical membrane 16.

[000161] Although Figures 19A and 19B depict no electrical ground of the optical membrane 16, it will be appreciated that in other embodiments the optical membrane may be connected to an electrical ground. For example, by electrical grounding of the optical membrane, the optical membrane may be protected from being statically charged and/or an increase of an electrical potential of the optical membrane relative to other and/or neighbouring components or objects, e.g. of the patterning device assembly or the lithographic apparatus, may be reduced or prevented. Additionally, a voltage or potential may be applied to the optical membrane, e.g. relative to the electrical ground, as described above.

[000162] Although specific reference may be made in this text to embodiments of the invention in the context of a lithographic apparatus, embodiments of the invention may be used in other apparatus. Embodiments of the invention may form pa it of a mask inspection apparatus, a metrology apparams, or any apparatus that measures or processes an object such as a wafer (or other substrate) or mask (or other patterning device). These apparatus may be generally referred to as lithographic tools. Such a lithographic tool may use vacuum conditions or ambient (non-vacuum) conditions.

[000163] In an embodiment, the invention may form part of a metrology apparatus. The metrology apparatus may be used to measure alignment of a projected pattern formed in resist on a substrate relative to a pattern already present on the substrate. This measurement of relative alignment may be referred to as overlay. The metrology apparatus may for example be located immediately adjacent to a lithographic apparatus and may be used to measure the overlay before the substrate (and the resist) has been processed.

[000164] The term “EUV radiation” may be considered to encompass electromagnetic radiation having a wavelength within the range of 4-20 nm, for example within the range of 13-14 nm. EUV radiation may have a wavelength of less than 10 nm, for example within the range of 4-10 nm such as 6.7 nm or 6.8 nm.

[000165] Although Figure 1 depicts the radiation source SO as a laser produced plasma LPP source, any suitable source may be used to generate EUV radiation. For example, EUV emitting plasma may be produced by using an electrical discharge to convert fuel (e.g. tin) to a plasma state. A radiation source of this type may be referred to as a discharge produced plasma (DPP) source. The electrical discharge may be generated by a power supply which may form part of the radiation source or may be a separate entity that is connected via tin electrical connection to the radiation source SO.

[000166] Although specific reference may be made in this text to the use of lithographic apparatus in the manufacture of TCs, it should be understood that the lithographic apparatus described herein may have other applications. Possible other applications include the manufacture of integrated optical systems, guidance and detection patterns for magnetic domain memories, flat-panel displays, liquid-crystal displays (LCDs), thin-filni magnetic heads, etc.

[000167] Although specific reference may have been made above to the use of embodiments of the invention in the context of optical lithography, it will be appreciated that the invention may be used in other applications, for example imprint lithography, and where the context allows, is not limited to optical lithography. In imprint lithography a topography in a patterning device defines the pattern created on a substrate. The topography of the patterning device may be pressed into a layer of resist supplied to the substrate whereupon the resist is cured by applying electromagnetic radiation, heat, pressure or a combination thereof. The patterning device is moved out of the resist leaving a pattern in it after the resist is cured.

[000168] While specific embodiments of the invention have been described above, it will be appreciated that die invention may be practiced otherwise than as described. The descriptions above are intended to be illustrative, not limiting. Thus it will be apparent to one skilled in the art that modifications may be made to the invention as described without departing from the scope of the claims set out below.

Claims

1. Optisch, voor EUV-straling transparant membraan voor gebruik in of met een lithografische inrichting, waarbij het membraan omvat: een eerste laag die een eerste materiaal omvat, en een tweede laag die een tweede materiaal omvat, waarbij de eerste laag is aangebracht op de tweede laag, waarbij de eerste en tweede materialen zodanig geselecteerd zijn dat een ruimteladingsgebied of depletiegebied in het membraan gevormd wordt, waarbij het ruimteladingsgebied of depletiegebied een elektrisch veld opwekt in het membraan.An EUV radiation transparent membrane for use in or with a lithographic device, the membrane comprising: a first layer comprising a first material, and a second layer comprising a second material, the first layer being applied to the second layer, the first and second materials being selected such that a space charge region or depletion region is formed in the membrane, the space charge region or depletion region generating an electric field in the membrane.

2. Membraan volgens conclusie 1, waarbij de eerste en tweede materialen zodanig geselecteerd zijn dat het ruimteladingsgebied of depletiegebied zich uitstrekt in een deel of geheel van het membraan.A membrane according to claim 1, wherein the first and second materials are selected such that the space charge region or depletion region extends in part or all of the membrane.

3. Membraan volgens conclusie 1 of 2, waarbij de eerste en tweede materialen geselecteerd zijn op basis van een of meer eigenschappen van het eerste materiaal en/of het tweede materiaal.A membrane according to claim 1 or 2, wherein the first and second materials are selected on the basis of one or more properties of the first material and / or the second material.

4. Membraan volgens een van de voorgaande conclusies, waarbij het elektrisch veld zich uitstrekt in een richting loodrecht op de eerste laag en/of de tweede laag.A membrane according to any one of the preceding claims, wherein the electric field extends in a direction perpendicular to the first layer and / or the second layer.

5. Membraan volgens een van de voorgaande conclusies, waarbij de eerste en tweede materialen zodanig geselecteerd zijn dat het door het ruimteladingsgebied of depletiegebied opgewekte elektrische veld een scheiding veroorzaakt van ladingdragers die gegenereerd worden tijdens bestraling van het membraan.A membrane according to any one of the preceding claims, wherein the first and second materials are selected such that the electric field generated by the space charge region or depletion region causes a separation of charge carriers that are generated during irradiation of the membrane.

6. Membraan volgens conclusie 5, waarbij de eerste en tweede materialen zodanig geselecteerd zijn dat het door het ruimteladingsgebied of depletiegebied opgewekte elektrische veld een opeenhoping veroorzaakt van de ladingdragers op of bij tegenoverliggende zijden van het ruimteladingsgebied of depletiegebied.The membrane of claim 5, wherein the first and second materials are selected such that the electric field generated by the space charge region or depletion region causes an accumulation of the charge carriers on or at opposite sides of the space charge region or depletion region.

7. Membraan volgens conclusie 5 of 6, waarbij de scheiding en/of opeenhoping van de gegenereerde ladingdragers een ander elektrisch veld opwekt.Membrane according to claim 5 or 6, wherein the separation and / or accumulation of the generated charge carriers generates a different electric field.

8. Membraan volgens conclusie 7, waarbij het andere elektrisch veld zich uitstrekt in een richting parallel aan de eerste laag en/of de tweede laag.The membrane of claim 7, wherein the other electric field extends in a direction parallel to the first layer and / or the second layer.

9. Membraan volgens conclusie 7 of 8, waarbij een ander elektrisch veld verplaatsing veroorzaakt van de gegenereerde ladingdragers naar buiten toe en/of weg van een deel of gebied van het membraan dat bestraald wordt.A membrane according to claim 7 or 8, wherein a different electric field causes displacement of the generated charge carriers to the outside and / or away from a part or area of the membrane that is being irradiated.

10. Membraan volgens een van de conclusies 7 tot en met 9, waarbij het andere elektrische veld verplaatsing veroorzaakt van de gegenereerde ladingdragers richting een omtrek of omtrekgebied van het membraan.A membrane according to any of claims 7 to 9, wherein the other electric field causes displacement of the generated charge carriers towards a perimeter or perimeter region of the membrane.

11. Membraan volgens een van de conclusies 9 of 10, waarbij het andere elektrische veld zodanig is dat de gegenereerde ladingdragers met een snelheid bewegen die hoger is dan een snelheid van een stralingsbundel die door het membraan beweegt.A membrane according to any of claims 9 or 10, wherein the other electric field is such that the generated charge carriers move at a speed that is higher than a speed of a radiation beam moving through the membrane.

12. Membraan volgens een van de voorgaande conclusies, W'aarbij ten minste een van de eerste en tweede materialen een halfgeleider materiaal omvat.A membrane according to any one of the preceding claims, wherein at least one of the first and second materials comprises a semiconductor material.

13. Membraan volgens een van de voorgaande conclusies, waarbij ten minste een ander van de eerste en tweede materialen een halfgeleider materiaal en/of een metaal omvat.A membrane according to any one of the preceding claims, wherein at least one of the first and second materials comprises a semiconductor material and / or a metal.

14. Membraan volgens een van de voorgaande conclusies, w'aarbij ten minste een van de eerste en tweede materialen Boor omvat.A membrane according to any of the preceding claims, wherein at least one of the first and second materials comprises Boron.

15. Membraan volgens een van de voorgaande conclusies, waarbij ten minste een ander van de eerste en tweede materialen ten minste een van kristallijn Silicium, polykristallijn Silicium, Siliciumcarbide, Siliciumnitride en grafeen omvat.A membrane according to any of the preceding claims, wherein at least one of the first and second materials comprises at least one of crystalline silicon, polycrystalline silicon, silicon carbide, silicon nitride and graphene.

16. Membraan volgens een van de conclusies, waarbij het eerste materiaal een eerste halfgeleidermateriaal omvat en het tweede materiaal een tweede halfgeleidermateriaal omvat, waarbij de eerste en tweede halfgeleidermaterialen hetzelfde of verschillend zijn.A membrane according to any one of the claims, wherein the first material comprises a first semiconductor material and the second material comprises a second semiconductor material, the first and second semiconductor materials being the same or different.

17. Membraan volgens een van de voorgaande conclusies, waarbij ten minste een van de eerste en tweede materiaal negatief gedoteerd is en/of ten minste een ander van de eerste en tweede materialen positief gedoteerd is.A membrane according to any one of the preceding claims, wherein at least one of the first and second material is negatively doped and / or at least another of the first and second materials is positively doped.

18. Membraan volgens een van de voorgaande conclusies, waarbij het membraan een elektrode omvat die geconfigureerd is om toepassing van een elektrische spanning op het membraan mogelijk te maken.A membrane as claimed in any one of the preceding claims, wherein the membrane comprises an electrode configured to allow application of an electrical voltage to the membrane.

19. Membraan volgens conclusie 18, waarbij de elektrode zodanig ingericht is op het membraan dat de elektrische spanning nog een ander elektrisch veld opwekt dat zich uitstrekt in een richting loodrecht op de eerste laag en/of de tweede laag.A membrane according to claim 18, wherein the electrode is arranged on the membrane such that the electrical voltage generates yet another electric field that extends in a direction perpendicular to the first layer and / or the second layer.

20. Membraan volgens een van de voorgaande conclusies, waarbij het membraan een derde laag omvat die een derde materiaal omvat.The membrane of any one of the preceding claims, wherein the membrane comprises a third layer comprising a third material.

21. Membraan volgens conclusie 20, waarbij het derde materiaal een metaal zoals Zirkonium, Molybdeen en/of Ruthenium omvat.The membrane of claim 20, wherein the third material comprises a metal such as Zirconium, Molybdenum and / or Ruthenium.

22. Membraan volgens een van de voorgaande conclusies, waarbij ten minste een van de eerste en tweede materialen een fluorescerend doteermateriaal omvat.A membrane according to any one of the preceding claims, wherein at least one of the first and second materials comprises a fluorescent dopant material.

23. Optisch, voor EUV-straling transparant membraan voor gebruik in of met een lithografische inrichting, waarbij het membraan een halfgeleidermateriaal omvat, waarbij het halfgeleidermateriaal een doteermateriaal omvat, waarbij een concentratie van het doteermateriaal zodanig geselecteerd is dat een elektrisch veld opgewekt wordt in het membraan.23. An EUV-radiation transparent membrane for use in or with a lithographic device, wherein the membrane comprises a semiconductor material, the semiconductor material comprising a dopant, a concentration of the dopant being selected such that an electric field is generated in the membrane.

24. Membraan volgens conclusie 23, waarbij de concentratie van het doteermateriaal niet-uniform is in het halfgeleidermateriaal en/of een doteergradiënt in het halfgeleidermateriaal definieert.The membrane of claim 23, wherein the concentration of the dopant material is non-uniform in the semiconductor material and / or defines a dopant gradient in the semiconductor material.

25. Membraan volgens conclusie 23 of 24, waarbij een eerste deel of zijde van het membraan een eerste concentratie van het doteermateriaal omvat en een tweede deel of zijde van het membraan een tweede concentratie van het doteermateriaal omvat, waarbij de eerste concentratie van het doteermateriaal hoger is dan de tweede concentratie van het doteermateriaal.The membrane of claim 23 or 24, wherein a first portion or side of the membrane comprises a first concentration of the dopant material and a second portion or side of the membrane comprises a second concentration of the dopant material, the first concentration of the dopant material being higher is then the second concentration of the dopant material.

26. Membraan volgens een van de conclusies 23 tot en met 25, waarbij de concentratie van het doteermateriaal geselecteerd is om in het halfgeleidermateriaal te variëren tussen 1022cm3 en 10l4cm3.The membrane of any one of claims 23 to 25, wherein the concentration of the dopant material is selected to vary between 1022 cm 3 and 10 14 cm 3 in the semiconductor material.

27. Membraan volgens een van de conclusies 23 tot en met 26, waarbij de concentratie van het doteermateriaal zodanig geselecteerd is dat het opgewekte elektrische veld ongeveer of groter dan 107 V/m is.The membrane of any one of claims 23 to 26, wherein the concentration of the dopant is selected such that the electric field generated is approximately or greater than 107 V / m.

28. Membraan volgens een van de conclusies 23 tot en met 27, waarbij de concentratie van het doteermateriaal zodanig geselecteerd is dat het opgewekte elektrische veld een scheiding veroorzaakt van ladingdragers die gegenereerd worden tijdens bestraling van het membraan met straling.A membrane according to any of claims 23 to 27, wherein the concentration of the dopant is selected such that the generated electric field causes a separation of charge carriers that are generated during irradiation of the membrane with radiation.

29. Membraan volgens een van de conclusies 23 tot en met 28, waarbij de concentratie van het doteermateriaal zodanig geselecteerd is dat het opgewekte elektrische veld een opeenhoping van de gegenereerde ladingdragers veroorzaakt op of bij tegenoverliggende membraanzijden.A membrane according to any of claims 23 to 28, wherein the concentration of the dopant material is selected such that the generated electric field causes an accumulation of the generated charge carriers on or at opposite membrane sides.

30. Membraan volgens conclusie 28 of 29, waarbij de scheiding en/of opeenhoping van de gegenereerde ladingdragers een ander elektrisch veld opwekt.The membrane according to claim 28 or 29, wherein the separation and / or accumulation of the generated charge carriers generates a different electric field.

31. Membraan volgens een van de conclusies 23 tot 30, waarbij het halfgeleidermateriaal ten minste een van ten minste een van kristallijn Silicium, polykristallijn Silicium, Siliciumcarbide, Siliciumnitride, grafeen en een I1I-V halfgeleidersamenstelling omvat.The membrane of any one of claims 23 to 30, wherein the semiconductor material comprises at least one of at least one of crystalline Silicon, polycrystalline Silicon, Silicon carbide, Silicon nitride, graphene and an II-V semiconductor composition.

32. Membraan volgens een van de conclusies 23 tot 31, waarbij het doteermateriaal ten minsteeen van Boor, Arsenicum, Antimonium en Fosfor omvat.The membrane of any one of claims 23 to 31, wherein the dopant material comprises at least one of Boron, Arsenic, Antimony and Phosphorus.

33. Membraan volgens een van de conclusies 1 tot en met 32, waarbij het membraan een dikte heeft van ongeveer 20 tot 80 nm.The membrane of any one of claims 1 to 32, wherein the membrane has a thickness of about 20 to 80 nm.

34. Membraan volgens een van de conclusies 1 tot en met 33, waarbij het membraan transparant is voor straling met een golflengte in het bereik van 4-20 nm.The membrane of any one of claims 1 to 33, wherein the membrane is transparent to radiation with a wavelength in the range of 4-20 nm.

35. Werkwijze voor vervaardiging van een optisch, voor EUV-straling transparant membraan voor gebruik in of met een lithografische inrichting, waarbij de werkwijze omvat: het vormen van een eerste laag die een eerste materiaal omvat, en het vormen of verschaffen van een tw'eede laag die een tweede materiaal omvat, waarbij de eerste laag gevormd is op de tweede laag; waarbij de eerste en tweede materialen zodanig geselecteerd zijn dat een ruimteladingsgebied of depletiegebied gevormd wordt in het membraan, waarbij het ruimteladingsgebied of depletiegebied een elektrisch veld opwekt in het membraan.35. A method of manufacturing an optical, EUV-radiation transparent membrane for use in or with a lithographic device, the method comprising: forming a first layer comprising a first material, and forming or providing a tw ' the layer comprising a second material, the first layer being formed on the second layer; wherein the first and second materials are selected such that a space charge region or depletion region is formed in the membrane, the space charge region or depletion region generating an electric field in the membrane.

36. Werkwijze voor het vervaardigen van een optisch, voor EUV-straling transparant membraan voor gebruik in of met een lithografische inrichting, waarbij de werkwijze omvat: het vormen of verschaffen van een halfgeleidermateriaal; en het doteren van het halfgeleidermateriaal met een doteermateriaal; waarbij een concentratie van het doteermateriaal zodanig wordt geselecteerd dat een elektrisch veld wordt opgewekt in het membraan.36. A method for manufacturing an EUV radiation transparent membrane for use in or with a lithographic device, the method comprising: forming or providing a semiconductor material; and doping the semiconductor material with a dopant material; wherein a concentration of the dopant material is selected such that an electric field is generated in the membrane.

37. Werkwijze volgens conclusie 35 of 36, waarbij het vervaardigde membraan een dikte heeft van ongeveer 20 to 80 nm.The method of claim 35 or 36, wherein the manufactured membrane has a thickness of about 20 to 80 nm.

38. Werkwijze volgens een van de conclusies 35 tot en met 37, waarbij het vervaardigde membraan transparant is voor straling met een golflengte in het bereik van 4-20 nm.The method of any one of claims 35 to 37, wherein the manufactured membrane is transparent to radiation with a wavelength in the range of 4-20 nm.

39. Systeem voor het reduceren van verwarming van een optisch membraan, waarbij het systeem omvat: een optisch membraan volgens een van de conclusies 1 tot en met 34; waarbij het systeem is geconfigureerd voor het verwijderen van ladingdragers uit het membraan, waarbij de ladingdragers gegenereerd worden tijdens bestraling van het membraan.A system for reducing heating of an optical membrane, the system comprising: an optical membrane according to any of claims 1 to 34; wherein the system is configured to remove charge carriers from the membrane, the charge carriers being generated during irradiation of the membrane.

40. Systeem volgens conclusie 39, waarbij het systeem geconfigureerd is voor het verv-'ijderen van de gegenereerde ladingdragers uit een of meer omtrekdelen of een omtrek van het membraan.The system of claim 39, wherein the system is configured to remove the generated charge carriers from one or more peripheral portions or a periphery of the membrane.

41. Systeem volgens conclusie 39 of 40, waarbij het systeem geconfigureerd is om een koellichaam te verschaffen voor de gegenereerde ladingdragers.The system of claim 39 or 40, wherein the system is configured to provide a heat sink for the generated load carriers.

42. Systeem volgens een van de conclusies 39 tot en met 41, waarbij het systeem geconfigureerd is om het optisch membraan kort te sluiten.The system of any one of claims 39 to 41, wherein the system is configured to short-circuit the optical membrane.

43. Systeem volgens een van de conclusies 39 tot en met 42, waarbij een eerste deel of zijde van het membraan is verbonden met een tweede deel of zijde van het membraan.A system according to any of claims 39 to 42, wherein a first part or side of the membrane is connected to a second part or side of the membrane.

44. Systeem volgens conclusie 43, waarbij de eerste zijde en/of tweede omtrekzijden of delen elektrisch geaard zijn.The system of claim 43, wherein the first side and / or second peripheral sides or parts are electrically grounded.

45. Systeem volgens conclusie 42 of 43, waarbij het eerste deel of zijde van het membraan verbonden is met het tweede deel of zijde van het membraan aan of nabij een omtrek van het membraan.The system of claim 42 or 43, wherein the first part or side of the membrane is connected to the second part or side of the membrane at or near a periphery of the membrane.

46. Systeem volgens een van de conclusies 39 tot en met 45, waarbij het systeem een belasting omvat, waarbij de belasting verbonden is met het membraan.The system of any one of claims 39 to 45, wherein the system comprises a load, the load being connected to the membrane.

47. Systeem volgens conclusie 46, waarbij een weerstand van de belasting is geselecteerd op basis van ten minste een verdere eigenschap van het membraan, waarbij de ten minste ene verdere eigenschappen een velweerstand van het membraan omvat.The system of claim 46, wherein a load resistance is selected based on at least one further characteristic of the membrane, the at least one further characteristics comprising a sheet resistance of the membrane.

48. Systeem volgens conclusie 47, waarbij de weerstand van de belasting wordt geselecteerd om overeen te komen met de velweerstand van het membraan.The system of claim 47, wherein the resistance of the load is selected to correspond to the sheet resistance of the membrane.

49. Een modelleerinrichting-samenstel voor gebruik met een lithografische inrichting, het samenstel omvattende: een modelleerinrichting; en een vlies omvattende een optisch membraan volgens een van de conclusies 1 tot en met 34 of een systeem voor het reduceren van verwarming van een optisch membraan volgens een van de conclusies 39 tot en met 48.49. A modeling device assembly for use with a lithographic device, the assembly comprising: a modeling device; and a film comprising an optical membrane according to one of claims 1 to 34 or a system for reducing heating of an optical membrane according to one of claims 39 to 48.

50. Lithografische inrichting, omvattende: een verlichtingssysteem dat is geconfigureerd om een stralingsbundel te conditioneren; een steunstructuur die is vervaardigd om een modelleerinrichting te ondersteunen, waarbij de modelleerinrichting in staat is om de stralingsbundel te voorzien van een patroon in de dwarsdoorsnede daarvan teneinde een gemodelleerde stralingsbundel te vormen; een substraattafel die vervaardigd is om een substraat vast te houden; een projectiesysteem dat is geconfigureerd om de gemodelleerde stralingsbundel te projecteren op het substraat; en een optisch membraan volgens een van de conclusies 1 tot en met 34, waarbij het membraan grenzend aan de substraattafel is ingericht; of een systeem voor het verminderen van verwarming van een optisch membraan volgens een van de conclusies 39 tot en met 48.A lithographic apparatus comprising: an illumination system configured to condition a radiation beam; a support structure made to support a modeling device, the modeling device being able to provide the radiation beam with a cross-sectional pattern thereof to form a modeled radiation beam; a substrate table made to hold a substrate; a projection system configured to project the modeled radiation beam onto the substrate; and an optical membrane according to any of claims 1 to 34, wherein the membrane is arranged adjacent to the substrate table; or a system for reducing heating of an optical membrane according to any of claims 39 to 48.

51. De inrichting volgens conclusie 50, omvattende een puin-matigende inrichting, ingericht om een gasstroom naar het substraat te richten, waarbij het membraan deel is van of omvat in de puin-matigende inrichting.The device of claim 50, comprising a debris-modifying device adapted to direct a gas stream toward the substrate, wherein the membrane is part of or included in the debris-modifying device.

52, Werkwijze omvattende het projecteren van een gemodelleerde EUV stralenbundel op een substraat, waarbij de stralenbundel dooi' een optisch membraan volgens een van de conclusies 1 tot en met 34 gaat.A method comprising projecting a modeled EUV ray beam onto a substrate, wherein the ray beam passes through an optical membrane according to any of claims 1 to 34.

53. Gebruik van een optisch membraan volgens een van de conclusies I tot en met 34 in of met een lithografische inrichting.Use of an optical membrane according to any of claims I to 34 in or with a lithographic device.