CN110945432B

CN110945432B - Optical diaphragm

Info

Publication number: CN110945432B
Application number: CN201880048782.2A
Authority: CN
Inventors: V·穆罕默迪; 保罗·詹森; 斯通扬·尼蒂安沃夫; 马库斯·艾德里纳斯·范德柯克霍夫; 彼得-詹·范兹沃勒; A·N·兹德瑞乌卡夫
Original assignee: ASML Holding NV
Current assignee: ASML Holding NV
Priority date: 2017-07-21
Filing date: 2018-06-20
Publication date: 2022-12-27
Anticipated expiration: 2038-06-20
Also published as: NL2023116A; WO2019015905A1; KR20200026902A; TW201908120A; CN110945432A; NL2021155A; NL2021155B1; NL2023116B1

Abstract

An optical membrane (16) for use in or with a lithographic apparatus, the membrane comprising a first layer (18) comprising a first material, and a second layer (20) 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 (22) or depletion region is formed in the membrane, the space charge region or depletion region inducing an electric field (E) in the membrane.

Description

Optical diaphragm

Cross Reference to Related Applications

This application claims priority from european application 17182609.2 filed on 21/7/2017 and european application 17189037.9 filed on 1/9/2017, the entire contents of which are incorporated herein by reference.

Technical Field

The present invention relates to an optical diaphragm for use in or with a lithographic apparatus and associated apparatus and methods.

Background

A lithographic apparatus is a machine that is configured to apply a desired pattern onto a substrate. For example, lithographic apparatus can be used to manufacture Integrated Circuits (ICs). The 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 the substrate.

The wavelength of radiation used by a lithographic apparatus to project a pattern onto a substrate determines the minimum size of features that can be formed on the substrate. Lithographic apparatus using EUV radiation (electromagnetic radiation having a wavelength in the range of 4-20 nm) may be used to form features on a substrate that are smaller than conventional lithographic apparatus (e.g. electromagnetic radiation having a wavelength of 193nm may be used).

A membrane may be used in a 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 Ultraviolet (DUV) radiation and/or Infrared (IR) radiation, which may cause thermal damage to one or more components of the lithographic apparatus. In addition, a membrane may be arranged in the lithographic apparatus to reduce or prevent contamination of one or more components of the lithographic apparatus.

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 particle contamination.

In use, the diaphragm may have to withstand high local thermal loads. For example, when the membrane is part of a patterning device, the temperature may be about 500 ℃ on at least some portions of the membrane. Such temperatures may damage the membrane and shorten the useful life of the membrane.

Disclosure of Invention

According to a first aspect of the present 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 or depletion region is formed in the membrane, the space charge or depletion region inducing an electric field in the membrane. The induced electric field may cause a separation and/or distribution of charge carriers that may be generated, for example, during irradiation of the optical membrane with radiation. This may reduce local heating of the optical membrane (e.g., one or more portions thereof) during irradiation of the membrane. The distribution and/or separation of the generated charge carriers may allow the thermal load acting on the membrane to be spread over an area (e.g., an increased area) of the optical membrane.

The first material and the second material may be selected such that the space charge region or depletion extends into a portion or all of the optical membrane.

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

The electric field may extend in a direction perpendicular or substantially perpendicular to the first layer and/or the second layer.

The first and second materials may be selected such that an electric field induced by the space charge region or the depletion region may cause separation of the generated charge carriers. The separation of the generated charge carriers may reduce the likelihood of recombination of the generated charge carriers. This may reduce local heating of the membrane, for example during irradiation of the membrane.

The first and second materials may be selected such that an electric field induced by the space charge region or depletion region may cause generated charge carriers to accumulate on or near opposite sides of the space charge region or depletion region.

The separation and/or accumulation of the generated charge carriers may induce another electric field.

The further electric field may extend in a direction parallel or substantially parallel to the first layer and/or the second layer.

The further electric field may cause a movement of the generated charge carriers, for example outwards and/or away from a portion or region of the membrane that is irradiated.

Another electric field may cause the generated charge carriers to move, for example, towards the periphery or peripheral region of the membrane.

The further electric field may be such that the generated charge carriers may move at a higher speed or velocity than a speed or velocity of a radiation beam moving across the membrane.

At least one of the first material and the second material may include a semiconductor material. This may allow for the formation of space charge regions or depletion regions, for example, when the first layer is disposed on the second layer.

At least the other of the first material and the second material may comprise a semiconductor material and/or a metal. This may allow formation of a pn junction or a schottky junction.

At least one of the first material and the second material may include boron.

At least one other of the first material and the second material includes at least one of crystalline silicon, polycrystalline silicon, silicon carbide, silicon nitride, germanium, and graphene. For example, the first material may include boron and the second material may include silicon to form a boron-silicon junction. The boron-silicon junction may provide a nearly damage free interface or interfacial region between the first layer and the second layer. This in turn may provide an increase in electrical conductivity at or near the interface or interface region between the first and second layers.

The first material may include a first semiconductor material. The second material may include a second semiconductor material. The first semiconductor material and the second semiconductor material may be the same or different.

At least one of the first material and the second material may be negatively doped. At least the other of the first material and the second material may be positively doped.

The separator may include an electrode. The electrodes may be configured to allow a voltage to be applied to the membrane. The voltage may induce a further electric field in the optical membrane, such as for example an external electric field. The voltage may be selected such that application of the voltage to the optical membrane causes the width of the space charge region or depletion region to increase.

The electrodes may be arranged on the membrane, for example such that a voltage may induce a further electric field. The further electric field may extend in a direction perpendicular or substantially perpendicular to the first layer and/or the second layer.

The separator may include a third layer. The third layer may comprise a third material.

The third material may include a metal, such as zirconium, molybdenum, and/or ruthenium.

At least one of the first material and the second material may include a fluorescent dopant. The fluorescent dopant may increase the emission of radiation from the optical septum. The fluorescent dopant may act as a heat sink and/or reduce localized heating of the optical membrane.

According to a second aspect of the invention, there is provided a method of manufacturing an optical diaphragm 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 material and the second material 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 septum may comprise any of the features defined in the first aspect.

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

The concentration of the dopant material may be non-uniform in the semiconductor material. The concentration of the dopant material may define a dopant gradient in the semiconductor material.

The first portion or first side of the diaphragm may include a first concentration of a dopant material. The second portion or the second side of the diaphragm may include a second concentration of the dopant material. The first concentration of the dopant material may be higher than the second concentration of the dopant material.

The concentration of the dopant material may be selected to be at 10 in the semiconductor material ²² cm ^-3 And 10 ¹⁴ cm ^-3 To change between.

The concentration of the doping material may be selected such that the induced electric field is about 10 ⁷ V/m or greater than 10 ⁷ V/m。

The concentration of the doping material may be chosen such that the induced electric field causes a separation of charge carriers that may be generated during irradiation of the membrane with radiation.

The concentration of the doping material may be selected such that the induced electric field causes the generated charge carriers to accumulate on or near opposite sides of the membrane.

The semiconductor material may include at least one of crystalline silicon, polycrystalline silicon, silicon carbide, silicon nitride, graphene, and a group III-V compound semiconductor.

The doping material may include at least one of boron, arsenic, antimony and phosphorus.

According to a fourth aspect of the invention, there is provided a method of manufacturing an optical diaphragm 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 the concentration of the doping material is selected such that an electric field is induced in the membrane. The optical diaphragm may comprise any of the features defined in the third aspect.

According to a fifth aspect of the present 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 third aspect, wherein the system is configured for removing charge carriers from the membrane, the charge carriers being generated during irradiation of the membrane, for example with radiation, such as for example EUV radiation.

The system may be configured to remove the generated charge carriers from one or more peripheral portions or peripheries of the membrane.

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

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

The first portion or side of the diaphragm may be connected (e.g., electrically connected) to the second portion or side of the diaphragm. The first side and/or the second side or portion may be electrically grounded. Electrical grounding of the first side or portion and/or the second side or portion may provide a sink for generated charge carriers. This may allow for removal of the generated charge carriers from the membrane. Removing the charge carriers from the membrane may prevent or reduce recombination of the charge carriers, which may generate heat in the membrane.

The first portion or side of the diaphragm may be connected to the second portion or side of the diaphragm at or near the periphery of the diaphragm.

The system may include a load, such as a resistive element. A load may be coupled to the diaphragm.

The resistance of the load may be selected based on at least one other property of the diaphragm. The at least one other property may include a sheet resistance of the separator.

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

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 aspects, or a system for reducing heating of an optical membrane according to the fifth aspect.

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 configured 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 beam of radiation onto the substrate; and an optical diaphragm according to the first and/or third aspect, the diaphragm being arranged adjacent to the substrate table, or a system for reducing heating of the optical diaphragm according to the fifth aspect.

The apparatus may include a debris mitigation device. The debris mitigation device may be configured to direct the gas flow toward the substrate. The membrane may be part of or included in the debris mitigation device.

According to an eighth aspect, there is provided a method comprising projecting a patterned beam of radiation onto a substrate, wherein the beam of radiation passes through an optical membrane according to the first or third aspects.

According to a ninth aspect, there is provided use of an optical diaphragm in or with a lithographic apparatus, the optical diaphragm being an optical diaphragm according to the first and/or third aspects.

Various aspects and features of the invention set forth above or below may be combined with various other aspects and features of the invention that will be apparent to those skilled in the art.

Drawings

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

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

FIG. 2 depicts an optical diaphragm according to an embodiment of the invention;

figure 3A depicts the optical membrane of figure 2 before irradiating the optical membrane;

FIG. 3B depicts a distribution diagram of one or more cold sources and one or more heat sources in the optical membrane of FIG. 3A;

figure 4A depicts the optical septum of figure 3A during irradiation;

FIG. 4B depicts a distribution diagram of one or more heat sources and one or more cold sources in the optical membrane of FIG. 4A;

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

FIG. 5B depicts a distribution diagram of one or more cold sources and one or more heat sources in the optical membrane of FIG. 5A;

FIG. 6 depicts the optical membrane of FIG. 5A during irradiation, wherein a further electric field is induced in the optical membrane;

fig. 7A depicts the optical membrane of fig. 6 during irradiation, wherein a further electric field causes diffusion of charge carriers in the optical membrane;

FIG. 7B depicts a distribution diagram of one or more heat sources and one or more cold sources in the optical membrane of FIG. 7A;

FIGS. 8A and 8B depict an exemplary optical diaphragm for use with or in the lithographic apparatus of FIG. 1;

FIG. 8C depicts the distribution of charge density and electric field strength in the optical membrane of FIGS. 8A and 8B;

figure 9 depicts the responsivity versus wavelength curve of a photodiode comprising the first and second layers of the optical membrane of figures 8A and 8B;

FIG. 10 depicts a top view of another exemplary optical diaphragm for use with or in the lithographic apparatus of FIG. 1;

FIG. 11 depicts another exemplary optical diaphragm for use with or in the lithographic apparatus of FIG. 1;

FIG. 12 depicts another exemplary optical diaphragm for use with or in the lithographic apparatus of FIG. 1;

FIG. 13 depicts another exemplary optical diaphragm for use with or in the lithographic apparatus of FIG. 1;

FIG. 14 depicts another exemplary optical diaphragm for use with or in the lithographic apparatus of FIG. 1;

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

FIG. 16A depicts another exemplary optical diaphragm for use with or in the lithographic apparatus of FIG. 1 or 15;

FIG. 16B depicts the donor atom concentration N _D An exemplary graph of the variation in thickness x depending on the optical membrane of FIG. 16A;

FIG. 16C depicts the optical septum of FIG. 16A before irradiation;

17A to 17C depict the optical septum of FIG. 16A during irradiation;

FIG. 18A depicts a system for reducing heat generation of an optical membrane according to an embodiment of the invention;

FIG. 18B depicts a distributed electrical model of the optical septum of FIG. 18A;

FIG. 19A depicts another exemplary system for reducing the heating of an optical diaphragm; and

FIG. 19B depicts the distributed electrical model of the optical membrane of FIG. 19A.

Detailed Description

FIG. 1 illustrates a lithography system. The lithographic system comprises a radiation source SO and a lithographic apparatus LA. The radiation source SO is configured to generate a beam B of Extreme Ultraviolet (EUV) radiation. The lithographic apparatus LA comprises an illumination system IL, 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 on the patterning device MA. The projection system is configured to project a radiation beam B (which has now been patterned by mask MA) onto the substrate W. The substrate W may include a previously formed pattern. In this case, the lithographic apparatus aligns the patterned radiation beam B with a pattern previously formed on the substrate W.

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

The type of radiation source SO shown in fig. 1 may be referred to as a Laser Produced Plasma (LPP) source. Laser 1 (which may be, for example, CO) ₂ A laser) is arranged to deposit energy into the fuel, for example tin (Sn) provided from a fuel emitter 3, by means of a laser beam 2. Although tin is mentioned 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 an alloy. The fuel emitter 3 may include a nozzle configured to direct tin (e.g., in the form of droplets) along a trajectory toward the plasma formation region 4. The laser beam 2 is incident on the tin at the plasma formation region 4. Laser energy is deposited into the tin, generating a plasma 7 at the plasma formation region 4. During deexcitation and recombination or recombination of ions of the plasma, radiation comprising EUV radiation is emitted from the plasma 7.

EUV radiation is collected and focused by a near normal incidence radiation collector 5 (sometimes more generally referred to as a normal incidence radiation collector). The collector 5 may have a multi-layer structure arranged to reflect EUV radiation (e.g. EUV radiation having a desired wavelength, such as 13.5 nm). The collector 5 may have an elliptical configuration with two elliptical foci. The first focus may be at the plasma formation region 4 and the second focus may be at the intermediate focus 6, as described below.

The laser 1 may be remote from the radiation source SO. In this case, the laser beam 2 may be delivered from the laser 1 to the radiation source SO by means 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 a radiation system.

The radiation 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 IL. The spot 6 at which the radiation beam B is focused may be referred to as an intermediate focus. The radiation source SO is arranged such that the intermediate focus 6 is located at or near the opening 8 in the enclosing structure 9 of the radiation source.

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 comprise a facet field lens device 10 and a facet pupil lens device 11. The facet field lens arrangement 10 and the facet pupil lens arrangement 11 together provide a radiation beam B having a desired cross-sectional shape and a desired angular intensity distribution. The radiation beam B passes from the illumination system IL and is incident on the patterning device MA, which is held by the support structure MT. The patterning device MA reflects and patterns the radiation beam B. The illumination system IL may comprise other mirrors or devices in addition to or instead of the facet field lens device 10 and the facet pupil lens device 11.

After being reflected by the patterning device MA, the patterned radiation beam B enters the projection system PS. The projection system PS comprises a plurality of mirrors configured to project a radiation beam onto a substrate W held by the substrate table WT. The projection system PS may apply a reduction factor to the radiation beam to form an image having features smaller than corresponding features on the patterning device MA. For example, a reduction factor of 4 may be applied. Although the projection system PS has two mirrors in FIG. 1, the projection system can include any number of mirrors (e.g., six mirrors).

FIG. 1 schematically depicts an optical diaphragm 16 for use in or with a lithographic apparatus according to an embodiment of the invention. The optical diaphragm may be part of or included in a patterning device assembly PA used with the lithographic apparatus. The patterning device assembly PA may comprise the patterning device MA and the pellicle PL (indicated by the dashed line in fig. 1) shown in fig. 1. Pellicle PL may be or include an optical membrane 16. The pellicle PL may be arranged to protect the patterning device MA from contamination, such as for example particle contamination and/or damage. For example, the pellicle PL may be arranged to extend over or cover the patterning device MA. However, it will be understood that the optical membranes described herein are not limited to being part of or included in the patterning assembly. For example, as will be described below, in other embodiments, an optical membrane may be provided as part of a debris mitigation system.

Fig. 2 schematically illustrates the optical diaphragm 16. The optical membrane 16 may be provided in the form of a filter, a spectral filter or a spectral purity filter. The optical diaphragm 16 may be configured to transmit EUV radiation and/or 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 Ultraviolet (DUV) radiation and/or Infrared (IR) radiation. The optical diaphragm 16 may be or include a film (e.g., a film) or a flexible sheet, such as a thin flexible sheet. Optical membrane 16 may include a thickness of about 20 to 80 nm.

The optical membrane 16 includes a first layer 18 comprising a first material and a second layer 20 comprising a second material. The first layer 18 is disposed on the second layer 20. The first material and the second material are selected such that a space charge region or depletion region 22 is formed in the membrane 16. The space charge or depletion region 22 induces an electric field E in the optical membrane 16. The induced electric 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 localized heating of one or more portions of optical membrane 16. The distribution and/or separation of the generated charge carriers may allow the thermal load acting on optical membrane 16 to be spread over an increased area of optical membrane 16. This may reduce heating of one or more portions of optical membrane 16 during irradiation with radiation beam B.

The term "generated charge carriers" may be considered to include photogenerated charge carriers, such as, for example, electron-hole pairs generated during absorption of some of the radiation beam B by the optical membrane 16.

The term "space charge region or depletion region" can be understood as a region: mobile charge carriers (e.g., electrons and/or holes) diffuse from the region. Any positive and/or negative net charge remaining at or near the interface 23 between the first layer 18 and the second layer 20 induces an electric field E. The positive and/or negative net charge may contain ionized impurities, such as ionized donors and/or acceptors, represented by "+" and "-" in fig. 2. The term "interface" may be considered to encompass an interfacial region.

The first material and/or the second material of first layer 18 and second layer 20 may be selected based on one or more properties of the first material and the second material, respectively. The one or more properties of the first material and/or the second material may include a material type, a defect concentration, a dopant type, and/or a doping concentration of the first material and/or the second material. The one or more properties may include one or more optical properties of the first material and/or the second material, such as a transmission coefficient, a reflection coefficient, and/or an absorption coefficient of the first material and/or the second material. The one or more properties may include one or more physical properties of the first material and/or the second material, such as, for example, radiation resistance and/or radiation stability.

The first and second materials may be selected such that the space charge or depletion region 22 extends into at least a portion or all of the optical membrane 16. For example, the first and second materials may be selected such that the space charge or depletion region 22 extends at least from the interface 23 between the first and

second layers

18, 20 into at least one 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 the extent of the space charge or depletion region 22 into the second layer 20 (e.g., the second material) is greater than the extent of the space charge or depletion region 22 into the first layer 18 (e.g., the first material). Alternatively, the first and second materials may be selected such that the extent of the space charge or depletion region 22 into the second layer 20 (e.g., the second material) is equal to (e.g., substantially equal to) or less than the extent of the space charge or depletion region 22 into the first layer 18 (e.g., the first material).

In the embodiment shown in fig. 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 semiconductor material and the second semiconductor material may be the same or different. At least one of the first semiconductor material and the second semiconductor material may be negatively doped and at least the other of the first semiconductor material and the second semiconductor material may be positively doped. In the embodiment shown in fig. 2, the first layer 18 and the second layer 20 may be considered to form a pn junction. A space charge region or depletion region 22 extends into both the first layer 18 and the second layer 20. However, it will be understood 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 described below. In such embodiments, the space charge region or depletion region may be considered to extend into only one of the first layer and the second layer.

Fig. 3A schematically shows the optical diaphragm 16 of fig. 2 before being irradiated with a radiation beam B. In the embodiment shown in fig. 3A, the space charge region or depletion region 22 is considered to extend into the entire optical membrane 16. However, it will be understood that in other embodiments, the space charge may extend only into a portion of the optical membrane. Fig. 3B depicts a graph of the contribution of one or more heat sinks or heat sinks and one or more heat sources acting on optical membrane 16 as a function of position on optical membrane 16 (e.g., position in the y-direction). As can be seen in fig. 3B, the contribution 30 of the one or more heat sinks acting on the optical membrane 16 is substantially constant and no heat source acts on the optical membrane 16 before irradiating the optical membrane 16.

The term "heat source" may be considered to include one or more mechanisms that generate heat on or in the optical membrane. One or more mechanisms for generating heat on or in the optical membrane will be described below. The term "one or more heat sources" may be used interchangeably with the term "heat source".

The term "heat sink" may be considered to include one or more mechanisms that transfer heat from the optical septum to the surrounding environment, e.g., the optical septum. One or more mechanisms for transferring heat from the optical membrane will be described below. The term "one or more heat sinks" may be used interchangeably with the term "heat sinks".

Fig. 4A schematically shows the optical membrane 16 during irradiation. Fig. 4B is similar to fig. 3B. During irradiation of the optical membrane 16, a plurality of charge carriers 24 are generated. In other words, a plurality of electron-hole pairs 24 are generated as the first and second materials of the optical membrane 16 absorb some of the radiation beam B. A plurality of electron-hole pairs 24 are generated in a portion or region of the optical membrane that is irradiated by the radiation beam B. The portion or region of the optical membrane 16 irradiated by the radiation beam B may also be referred to as an illumination volume 26. Irradiation of optical diaphragm 16 by radiation beam B causes heat to be generated in optical diaphragm 16. In other words, the irradiation of optical membrane 16 by radiation beam B may be considered one of the one or more heat sources.

Other sources of heat that generate heat in or on optical membrane 16 may include one or more of the following: recombination of the generated electron-hole pairs, e.g., radiative and/or non-radiative recombination of the generated electron-hole pairs, and thermalization of the electron-hole pairs. Thermalization of electron-hole pairs may include, for example, in the case of emission of one or more phonons (e.g., lattice vibrations), relaxation of the generated electrons and holes toward minimum levels of the conduction and valence bands, respectively. Other sources of heat that generate heat in or on the optical diaphragm 16 may also include joule heating or the joule effect, which may be due to current flowing through the optical diaphragm 16. The current may be caused by the generation of electron-hole pairs that move through the optical membrane 16. Other heat sources may also include the peltier effect, which may be due to current flowing through a junction between two different conductors.

The heat sink that may transfer heat from the optical membrane 16 may include the thompson effect, which may be due to current flowing through the optical membrane 16. Another source of heat that may transfer heat from optical membrane 16 may include convection, e.g., heat transfer between the optical membrane and the environment of optical membrane 16, such as, for example, air flow that may be present at or near optical membrane 16.

Fig. 4B depicts a contribution 28 of one or more heat sources in the illuminated volume 26 of the optical diaphragm 16 to the heating of the optical diaphragm 16 as compared to a contribution 30 of one or more heat sources in the illuminated volume 26 of the optical diaphragm 16. As can be seen from fig. 4B, the contribution 28 of the one or more heat sources is greater than the contribution 30 of the one or more heat sinks in the illuminated volume 26. The difference between the contribution 28 of the heat source and the contribution 30 of the heat source is indicated by reference numeral D1 in fig. 4B. The difference D1 between the contribution 28 of the heat source and the contribution 30 of the heat sink may cause local heating of the optical membrane 16 in the illuminated volume 26. For example, when using the optical diaphragm 16 as a pellicle of the patterning device MA, a power of 200W of the radiation beam B measured at the intermediate focus 6 may cause a temperature of the optical diaphragm 16 of about 500 ℃. Alternatively or additionally, in some embodiments, the optical membrane 16 is part of the debris mitigation device 15, as described below. In such an embodiment, a power of 200W of the radiation beam B measured at the intermediate focus 6 may cause a temperature of about 100 ℃ of the optical membrane. As discussed above, heating of optical membrane 16 may shorten the life of optical membrane 16 and/or cause damage to optical membrane 16. As can be seen from fig. 4B, the cold source is more dominant outside the irradiation volume 26 than inside the irradiation volume 26. In other words, outside of the illuminated volume 26, heat is transferred from the optical diaphragm 16 to, for example, the ambient environment of the optical diaphragm 16.

Fig. 5A schematically shows the optical membrane 16 during irradiation. Fig. 4B is similar to fig. 3B and 4B. As described above, the first material and the second material are selected such that a space charge region or depletion region 22 is formed in the membrane 16. The space charge or depletion region 22 induces an electric field E in the optical membrane 16. The first and second materials of the first and

second layers

18 and 20, respectively, may be selected such that the electric field E induced by the space charge or depletion region 22 is sufficient to cause separation of the generated charge carriers 24. For example, the first and second materials of first layer 18 and second layer 20 may be selected, respectively, such thatThe electric field E induced by the space charge region 22 is about 10 ⁷ V/m. It will be appreciated that the greater the induced electric field, the more efficient, e.g., greater and/or faster, the separation of the generated charge carriers 24 may be. E.g. an increase in induced electric field, e.g. above 10 ⁷ V/m, may provide an increased potential barrier for the generated charge carriers 24. This may provide for efficient separation of charge carriers 24 and/or may reduce the number of charge carriers that may overcome the potential barrier. The separation of the generated charge carriers 24 may reduce the likelihood of recombination of the generated charge carriers 24. This may reduce local heating of the optical membrane 16 in the illuminated volume 26. In addition, an increase in the induced electric field E, for example higher than 10 ⁷ V/m, may result in a separation of an increased number of generated charge carriers.

The electric field E may be considered to extend in a direction perpendicular (e.g., substantially perpendicular) to the first layer 18 and/or the second layer 20. The electric field E may be considered a built-in electric field or a vertical built-in electric field. The interface 23 between the first layer 18 and the second layer 20 is indicated by a dashed line in fig. 5A.

The separation of the generated charge carriers 24 may be instantaneous. In other words, the generated charge carriers 24 may be separated by the electric field E before the charge carriers are able to recombine.

As can be seen in fig. 5A, the separated

charge carriers

24a, 24b may collect at or near

opposite sides

22a, 22b of the space charge or depletion region 22. For example, electrons 24a may collect on or near the bottom side 22b of the space charge or depletion region 22, while holes 24b may collect on or near the top side 22a of the space charge or depletion region 22. It will be understood that in other examples, the first and second materials may be selected such that electrons collect on or near the top side of the space charge or depletion region 22 and holes collect on or near the bottom side of the space charge or depletion region 22. In examples where the space charge or depletion region extends into the entire optical membrane, electrons may collect on or near the bottom side of the first layer 18, while holes may collect on or near the top side of the second layer 20, and vice versa.

As described above, the separation between the generated charge carriers 24 may reduce or prevent recombination of the generated charge carriers, which may thus be considered one of the heat sources that generates heat in or on the optical membrane 16. FIG. 5B is similar to FIG. 4B and depicts the contribution of heat source 28B in the presence of electric field E in optical membrane 16 as compared to the contribution of heat source 28a in the absence of an electric field. As can be seen in fig. 5B, the contribution of heat source 28B in the presence of electric field E in optical membrane 16 is reduced relative to the contribution of heat source 28a in the absence of an electric field. In addition, a difference D2 between the contribution of the heat source 28b and the contribution of the heat sink 30 in the presence of the electric field E is reduced relative to a difference D1 between the contribution of the heat source 28a and the contribution of the heat sink 30 in the absence of the electric field. The width, e.g., full width at half maximum (FWHM), of the contribution of the heat source 28b in the presence of the electric field E may be the same (e.g., substantially the same) as the width, e.g., FWHM, of the contribution of the heat source 28a in the absence of the electric field.

Fig. 6 schematically shows the optical membrane 16 during irradiation. As described above, the separated

charge carriers

24a, 24b accumulate on or near

opposite sides

22a, 22b of the space charge or depletion region 22. The separation and/or accumulation of the generated

charge carriers

24a, 24b may induce another electric field. Another electric field may be caused by a potential difference between the

charge carriers

24a, 24b collected in the illuminated volume 26 and a region outside the illuminated volume 26. The further electric field may extend in a direction parallel (e.g. substantially parallel) to the first layer 18 and/or the second layer 20. The other electric field can be considered as a laterally built-in electric field. Another electric field may cause the collected

charge carriers

24a, 24b to move outwards and/or away from the irradiated volume 26. For example, another electric field may cause the

charge carriers

24a, 24b to move toward the perimeter or peripheral region of the optical membrane 16. The movement of the

charge carriers

24a, 24b is indicated in fig. 6 by the arrows labeled M. The accumulated

charge carriers

24a, 24b may additionally be subjected to a repulsive force, such as, for example, a repulsive coulomb force. The repulsive force may also cause the

charge carriers

24a, 24b to move outwards and/or away from the irradiation volume 26.

Fig. 7A schematically illustrates the optical membrane 16 in which some of the collected

charge carriers

24a, 24b have moved outwards and/or away from the irradiated volume 26. In regions outside the irradiated volume 26,

charge carriers

24a, 24b may recombine. This may result in heat spreading over the area or volume 32 of the optical membrane 16 and/or may reduce localized heating of the optical membrane 16. In addition, this may allow the optical membrane 16 to be used at higher powers of the radiation beam B, such as, for example, at powers above 200W.

The other electric field may be about 10 ⁴ V/m. This may result in a velocity or velocity of the

charge carriers

24a, 24b of about 10 ⁵ m/s. The movement of the radiation beam B across the optical diaphragm 16 may comprise a velocity or velocity of about 0.5 m/s. This may allow the collected charge carriers 24a, 24B to diffuse or move at a higher speed or rate than the speed or rate at which the radiation beam B passes through the optical membrane.

FIG. 7B shows that the contribution 28a of the heat source in the absence of an electric field in the optical membrane 16 is compared to the contribution 28B of the heat source in the presence of an electric field E and another electric field in the optical membrane 16. It can be seen that the contribution 28b of the heat source is reduced in the presence of the electric field E and the further electric field compared to the contribution 28a of the heat source in the absence of the electric field in the optical membrane 16. In addition, the width of the contribution of the heat source 28b in the presence of the electric field E and another electric field (e.g., full width at half maximum (FWHM)) is increased compared to the width of the contribution of the heat source 28a in the absence of the electric field in the optical diaphragm 16 (e.g., full width at half maximum (FWHM)). In other words, as described above, the local heating of the optical diaphragm 16 can be considered to be diffused. The difference D2 between the contribution 28b of the heat source and the contribution 30 of the heat sink in the presence of the electric field E and the further electric field E is reduced relative to the difference D1 between the contribution 28a of the heat source and the contribution 30 of the heat sink in the absence of the electric field. In other words, when an electric field and another electric field are present, it is considered that local heat generation of the optical diaphragm is reduced.

Fig. 8A and 8B schematically illustrate an embodiment of the optical diaphragm 16 in which the first material comprises boron and the second material comprises negatively doped silicon, such as, for example, negatively doped polysilicon. It should be understood 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 include silicon and the second material may include boron. In addition, the first material including boron may be positively doped or negatively doped. By doping the first material and/or the second material, the electrical conductivity of the first material and/or the second material may be increased. This may enhance the movement of the generated charge carriers and/or reduce heating of the optical membrane 16.

Fig. 8A schematically illustrates optical membrane 16 prior to disposing first layer 18 on second layer 20. Fig. 8B schematically illustrates optical septum 16 after first layer 18 is disposed on second layer 20. The placement of the first layer 18 comprising boron on the second layer 20 comprising silicon may result in the formation of a boron-silicon junction. As can be seen from fig. 8B, when the first layer 18 is disposed on the second layer 20, a space charge region or depletion region 22 is formed in the second layer 20. Fig. 8A and 8B further schematically depict an interface region or system 19 formed between first layer 18 and second layer 20, such as at or near the interface between first layer 18 and second layer 20, as described below. In embodiments where the first material comprises boron and the second material comprises negatively doped silicon (or intrinsic silicon), the formation of the space charge or depletion region 22 is different from the formation of the space charge or depletion region in a pn junction or schottky junction. The formation of space charge region or depletion region 22 may be thought of as being due to the transfer of charge carriers at the interface between first layer 18 and second layer 20.

The electronegativity of boron is about 2 and that of silicon is about 1.9. The electronegativity difference between boron and silicon may result in the bond between the boron and silicon atoms having ionic character. The ionic bond between the boron and silicon atoms may cause a dipole to form at the interface between first layer 18 and second layer 20. The dipoles may define or form an interface region or system 19. The interface region or system 19 can be considered to define a positively charged side 19a at or near the silicon side and a negatively charged side 19b at or near the boron side. When first layer 18 is disposed on second layer 20 and forms interface region or system 19, for example, between at least one monolayer of silicon atoms and at least one monolayer of boron atoms, transfer of electrons from the silicon atoms at interface region or system 19 to adjacent boron atoms may occur. This may be due to ionic bonds between the boron atoms and the silicon atoms, which are able to accept additional electrons. This may result in an increase in the bond length of the bond between the boron and silicon atoms. An increase in the bond length of the bond between boron and silicon may cause boron to accept more electrons. This may result in a reduction of positive charge in the interface region or positively charged side 19a of system 19, as shown in fig. 8B. For example, due to coulomb forces acting on the electrons, the electrons can diffuse toward the interface region or positively charged side 19a of the system 19. The diffusion of electrons to the interface system 19 (e.g., to its positively charged side 19 a) can leave a net positive charge and result in the formation of a space charge or depletion region 22. The net positive net charge may induce an electric field E near the interface region or system 19 between the first layer 18 and the second layer 20. The diffusion of electrons to the interface system 19 may result in the formation of a space charge region or depletion region 22 in the second layer 20 (e.g. silicon).

The first layer 18 may include a thickness of at least one monolayer of boron atoms to form a space charge or depletion region with the second layer 20. In some examples, the thickness of the first layer 18 may be about 1nm to 2nm, such as, for example, 1.5nm. As described above, the first layer 18 comprising boron may be formed by any deposition technique that results in the formation of a space charge or depletion region 22 in the second layer 20. Exemplary deposition techniques that can result in the formation of space charge regions or depletion regions 22 in the second layer 20 can include Chemical Vapor Deposition (CVD) or Atomic Layer Deposition (ALD) techniques. The formation of space charge or depletion regions and/or exemplary deposition techniques for forming boron-silicon junctions are further described, for example, in v.mohammadi "Low Temperature pure b Technology for CMOS Compatible photodynamics", docoral Thesis, TU Delft (http:// redundancy. Tudelft. Nl /), 2015. Boron formed using CVD or ALD may also be referred to as "PureB. Using boron, for example formed by CVD or ALD, as the first material for first layer 18 and silicon as the second material for second layer 20 may allow for the formation of an almost damage-free interface region or system 19 between first layer 18 and second layer 20. This in turn may provide increased conductivity along or at the interface region or system 19 compared to other materials.

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

Boron and silicon may be considered to be transmissive to EUV radiation (e.g., radiation having a wavelength of about 13.5 nm). Using boron as the first material of the first layer and silicon as the second material of the second layer may allow the transmittance of the optical membrane 16 for EUV radiation to be higher than 90%.

As described above and schematically depicted in fig. 8B, a 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 width of the space charge or depletion region 22 may be in the micrometer range or less than 1 μm. For example, the space charge region or depletion region 22 may comprise a width of about 100nm to 500 nm. Although the space charge or depletion region 22 is depicted in fig. 8B as extending into a portion of the second layer 20, it should be understood that in other embodiments the space charge or depletion region may alternatively or additionally extend into the first layer or substantially all of the optical membrane. In other words, the entire optical membrane may be depleted from mobile charge carriers.

Fig. 8C schematically depicts charge density and electric field strength across the space charge region or depletion region 22. As described above, the diffusion of electrons to the interface system or region 19 (e.g., its positively charged side 19 a) can leave a net positive charge and result in the formation of a space charge or depletion region 22. Additionally, as shown in fig. 8C, negative charge may be present or accumulated at or near the negatively charged side 19b of the interface region or system 19. The electric field strength has a maximum at the interface region or system 19 between the first layer 18 and the second layer 20. For example, at the interface system or region 19 between the first and second layers, the electric field may comprise about 10 ⁷ Maximum intensity of V/m.

Fig. 9 depicts a plot of responsivity versus wavelength for a photodiode including the first layer 18 and the second layer 20 of the optical membrane 16 described with respect to fig. 8A and 8B. In other words, the photodiode includes a first layer comprising boron disposed on a second layer comprising negatively doped silicon. The responsivity of a photodiode of three photodiodes formed from the same substrate was measured. For wavelengths around 13.5nm or above 13.5nm, the measured responsivity MR for the three samples is close to the theoretical responsivity TR of silicon, which is around 0.27. This may result in a quantum efficiency of the photodiode approaching 100%. The quantum efficiency corresponds to the ratio of the measured responsivity to the theoretical responsivity. The theoretical responsivity TR depicted in fig. 9 is calculated based on the generation of 26 electron-hole pairs per photon of wavelength about 13.5nm and assumes a near lossless and/or ideal system. Exemplary calculations of theoretical responsiveness may be found, for example, in "Mean induced required to product an electron-hole pair in silicon for photons of energies between 500eV," Journal of Applied Physics, vol 84, no 4, pp.2926-2939,1998, and "Determination of the electron-hole pair evolution energy for semiconductor from the spectra responses, in" Nuclear Instruments and Methods in Physics Research A439, pp.208-215,2000, by F.Scholze et al. Quantum efficiency can be considered to be indicative of the electron-hole pairs generated per photon of a given energy. In other words, quantum efficiency can be considered as the ratio of the charge carriers collected by the photodiode to the number of photons of a given energy incident on the photodiode. Thus, as described above, an optical diaphragm comprising a first layer comprising boron and a second layer comprising silicon may be considered to efficiently convert photons into electron-hole pairs, which are subsequently separated by the induced electric field E and another electric field and moved away from the irradiation volume 26. This may reduce localized heating of the optical membrane 16.

Although in the embodiment of fig. 8 a-8C, boron is described as the first material of the first layer and negatively doped silicon is described as the second material of the second layer, it should be understood that the optical membranes disclosed herein are not limited to these materials. For example, the second material may comprise at least one of crystalline silicon, such as single crystal silicon, silicon carbide, silicon nitride and graphene, which may be positively or negatively doped or undoped (e.g. intrinsic).

It will be understood that at least one of the first and second materials described herein may comprise a semiconductor material. This may allow for the formation of space charge regions or depletion regions when the first layer is disposed on the second layer. The other of the first material and the second material may also comprise a semiconductor material. Exemplary semiconductor materials of at least one or both of the first and second layers may include crystallineAt least one of the silicon, such as single crystal silicon, silicon carbide, silicon nitride, germanium, and graphene, may be positively or negatively doped. An exemplary material that may be used to negatively dope at least silicon may include arsenic (As) (e.g., at a concentration of about 10 a) ¹⁸ To 10 ²⁰ cm ^-3 ) Antimony (Sb) (e.g. at a concentration of about 10) ¹⁸ To 10 ²⁰ cm ^-3 ) Or phosphorus (P) (e.g., at a concentration of about 10) ¹⁸ To 10 ²⁰ cm ^-3 ). An exemplary material that may be used for positively doped silicon may include boron (B) (e.g., at a concentration of about 10 a) ¹⁸ To 5x10 ²⁰ cm ^-3 ). Exemplary semiconductor materials may be doped to produce abrupt or graded changes in dopant concentration. For example, as described above with reference to fig. 2-7B, the first layer 18 and the second layer 20 may be considered to form a pn junction.

In other embodiments, at least one of the first and second materials may comprise a metal and at least the other of the first and second materials comprises a semiconductor material. The semiconductor material may be positively or negatively doped. In such an example, the first layer and the second layer may be considered to form a schottky junction. In such embodiments, the space charge region or depletion region may be considered to extend into the semiconductor material. Exemplary metals for forming schottky junctions may include 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 the width of the space charge region or depletion region. The optical membrane may include electrodes to allow application of a voltage, as described below.

Additionally or alternatively, the first material and/or the second material comprise a fluorescent dopant. The fluorescent dopant may increase the radiation emission from optical septum 16. Exemplary fluorescent dopants may include europium and/or terbium. The concentration of the fluorescent dopant may be about 10 ²⁰ cm ^-3 Or less than 10 ²⁰ cm ^-3 . For example, the fluorescent dopant may absorb at least some radiation of radiation beam B. This may excite the fluorescent dopant to a higher energy state from which the fluorescent dopant may relax radiationless, e.g., emit one or morePhonons and emits radiation of longer wavelength than the absorbed radiation. This may allow the fluorescent dopant to act as a heat sink and/or reduce localized heating of optical membrane 16.

FIG. 10 schematically depicts a top view of an exemplary optical diaphragm 16 used in or with a lithographic apparatus. Optical septum 16 may be similar to that depicted in any of fig. 2-8B and may include any of the features of the optical septum described with respect to any of fig. 2-8B. In the embodiment shown in FIG. 10, optical membrane 16 includes an electrode 34. The electrode 34 may be configured to allow a voltage to be applied to the optical diaphragm 16. The voltage may induce a further electric field in the optical diaphragm 16, such as, for example, an external electric field. The voltage may be selected such that application of a voltage to the optical membrane causes the width of the space charge or depletion region 22 to increase. The voltage may be selected based on one or more requirements or conditions, such as, for example, an increase in the required space charge region or depletion region 22, the magnitude of the current flowing through the optical membrane due to the applied voltage, the current between the further electric field and the plasma generated in the radiation source or other component of the lithographic apparatus, and/or interference effects. The voltage may be or include a reverse bias voltage. The further electric field may extend in substantially the same direction as the electric field E. As shown in fig. 10, electrode 34 is disposed along perimeter 16c of optical membrane 16. It will be understood that the optical membranes disclosed herein are not limited to including electrodes disposed along the perimeter of the optical membrane. For example, in other embodiments, the electrodes may be disposed on one or more sides of the optical membrane and/or may be embedded in at least a portion or all of the optical membrane.

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, relatively high transmittance to EUV radiation, relatively low reflectance to EUV radiation, and/or chemical stability in a hydrogen environment. Exemplary materials for the electrode may include ruthenium (Ru), zirconium (Zr), or molybdenum (Mo). The electrode 34 comprising zirconium or molybdenum may additionally comprise a capping layer.

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. An external electric field may be applied to increase the vertical and/or lateral built-in electric field 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 rate or velocity of the generated charge carriers 24. This may allow the generated charge carriers to move away from the illuminated volume 26 at a higher rate or higher speed than in embodiments where no external electric field is applied to the optical membrane. This may result in reduced localized heating of the optical membrane 16.

FIG. 11 schematically depicts another example optical diaphragm 16 for use in or with a lithographic apparatus. The optical septum 16 depicted in fig. 11 may include any of the features of the optical septum described above with respect to fig. 2-8B and/or fig. 10. The optical membrane 16 depicted in fig. 11 includes a third layer 36 comprising a third material. The third layer 36 may be disposed between the first layer 18 and the second layer 20. The third layer 36 may be configured to act as an emissive layer. In other words, the third layer 36 may be configured to allow radiation to be emitted from the optical membrane. The third layer 36 may include an emission coefficient that is higher than the emission coefficient of the first layer 18 and/or the second layer 20. This may allow third layer 36 to act as a heat sink and/or reduce localized heating of optical membrane 16. The third material may include a metal such as, for example, zirconium, molybdenum, and/or ruthenium. The third layer may comprise a thickness of about 3 to 4 nm.

FIG. 12 depicts an exemplary optical diaphragm 16 for use in or with a lithographic apparatus. The optical septum 16 depicted in fig. 12 may include any of the features of the optical septum described above with respect to fig. 2-8A, 10, and/or 11. Optical diaphragm 16 includes a first layer 18 (which includes boron, such as PureB) and a second layer 20 (which includes negatively doped silicon). As mentioned above, the first layer may be formed by a deposition method, such as for example CVD or ALD, which allows the formation of space charge regions or depletion regions in the first material and/or the second material. The first layer 18 may comprise a thickness of about 1-2nm, for example 1.5nm. The second layer 20 may comprise a thickness of about 20 to 50nm, for example 40nm. The optical diaphragm 16 includes two

cover layers

28a, 28b. The first layer 18 and the second layer 20 are disposed between the

cap layers

28a, 28b. In this embodiment, the capping

layers

28a, 28b comprise boron, which may be formed by another deposition technique, such as, for example, physical Vapor Deposition (PVD). Each

capping layer

28a, 28b may comprise a thickness of about 2-4 nm. In this embodiment, the cap layer 28b disposed adjacent the second layer 20 comprises a thickness of approximately 4nm, and the cap layer disposed adjacent the first layer 18 comprises a thickness of 3 nm. Cover layers 28a, 28b may be provided to protect first layer 18 and/or second layer 20. It will be understood that in other embodiments, the optical septum may include fewer or more than two cap layers.

FIG. 13 depicts another exemplary optical diaphragm 16 for use in or with a lithographic apparatus. The optical septum 16 depicted in fig. 13 may include any of the features of the optical septum described above with respect to fig. 2-8B, 10, 11, and/or 12. The optical membrane 16 depicted in fig. 13 includes first and

second layers

18, 20 that are the same as those described with respect to fig. 12. The optical membrane also includes a third layer 36. In this embodiment, the third layer comprises zirconium. The third layer 36 comprises a thickness of about 3 to 4 nm. The optical membrane 16 includes two

cover layers

28a, 28b. A first cap layer 28a of the two cap layers is disposed between the second layer 20 and the third layer 26. The first 28a of the two cap layers comprises boron, which may be formed by another deposition technique, such as PVD, for example. The first 28a of the two cap layers comprises a thickness of about 1-2nm, such as, for example, 1.5nm. The second of the two cap layers 28b is disposed below the third layer 36. The second cap layer 28b of the two cap layers comprises boron, which may be formed by another deposition technique, such as PVD, for example. The second 28b of the two cap layers comprises a thickness of about 4 nm.

FIG. 14 depicts another exemplary optical diaphragm 16 for use in or with a lithographic apparatus. The optical septum 16 shown in fig. 14 is similar to that shown in fig. 13. However, instead of the first cap layer 28a, the optical diaphragm includes a fourth layer 40. The fourth layer 40 may provide a barrier layer, for example to avoid mixing 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.

It should be understood that the optical membranes disclosed herein are not limited to being provided as or included in a pellicle. In other embodiments, the optical diaphragm may be arranged in a lithographic apparatus, such as for example in a projection system.

FIG. 15 depicts another embodiment of a lithography system. In the embodiment shown in fig. 15, the optical diaphragm is part of or comprised in the lithographic apparatus LA. It will be appreciated that the optical diaphragm may be provided in the lithographic apparatus instead of, or in addition to, the patterning device. For example, the optical diaphragm 16 may be arranged adjacent to the substrate table WT. The optical membrane 16 may be arranged to at least partially or completely enclose an opening of the projection system PS through which the radiation beam B is projected onto the substrate W, as shown in fig. 15.

The lithographic apparatus may comprise a debris mitigation device 15. The debris mitigation device 15 may be arranged in the projection system PS, such as for example near the substrate W. The debris mitigation device 15 may be configured to direct a gas flow towards the substrate W, for example to reduce or prevent contaminants from entering the projection system PS.

The optical membrane 16 may be part of the debris mitigation device 15 or comprised in the debris mitigation device 15. The optical diaphragm 16 may be arranged to reduce or prevent contaminants from entering the projection system of the lithographic apparatus. It will be understood that the optical diaphragm disclosed herein is not limited to being arranged adjacent to the substrate table. For example, in other embodiments, the optical diaphragm may be arranged elsewhere in the lithographic apparatus, such as for example in the illumination system and/or elsewhere in the projection system.

The optical septum depicted in fig. 15 may include any of the features of the optical septum described with respect to any of fig. 2-8B and/or any of fig. 10-14.

An optical diaphragm 16 for use with or in connection with photolithography may be fabricated by forming a first layer 18 comprising a first material. The first layer 18 may be formed by a deposition technique that allows the formation of a space charge region or depletion region in the optical membrane. Exemplary techniques for forming the first layer may include Chemical Vapor Deposition (CVD) or Atomic Layer Deposition (ALD). For example, the first layer 18 may be formed by a CVD process or process that includes a temperature range of about 400 ℃ to about 700 ℃. As described above, a CVD process including such a temperature range may be suitable for forming a space charge region between a first layer including boron and a second layer including silicon. It will be understood that the methods described herein are not limited to such deposition techniques. For example, in other embodiments, the first layer may be formed using epitaxial techniques.

The first layer 18 may be formed on a second layer 20 comprising a second material. The second layer may be formed by any of the deposition techniques disclosed herein. Alternatively, the second layer may be provided, for example, preformed or separate from the first layer. For example, the second layer may be provided in the form of a substrate or the like. As described above, the first material and the second material 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 an electric field in the optical membrane 16.

Before forming the first layer 18, contaminants and/or oxides may be removed from the second layer and/or the second layer 20 may be passivated, for example, to prevent oxide formation. In addition, hydrogen may be removed from second layer 20 prior to forming first layer 18. For example, a process of forming a first layer including boron on a second layer including silicon is described in the following documents: "Low Temperature pure B Technology for CMOS Compatible photomodeectors", doctoral Thesis, TU Delft (http:// reprositor. Tudelft. Nl /), 2015.

16A, 16C and 17A to 17C schematically illustrate another example optical diaphragm 16 for use in or with a lithographic apparatus. Fig. 16A and 16C depict the optical diaphragm before irradiation with radiation beam B, and fig. 17A to 17C depict the optical diaphragm 16 during irradiation with radiation beam B. The optical diaphragm 16 comprises a semiconductor material. The semiconductor material comprises a doped material. The concentration of the doping material may be selected such that an electric field E is induced in the optical diaphragm 16, as described below. The induced electric 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 localized heating of one or more portions of optical membrane 16. The distribution and/or separation of the generated charge carriers may allow the thermal load acting on optical membrane 16 to be spread over an increased area of optical membrane 16. This may reduce heating of one or more portions of optical membrane 16 during irradiation with radiation beam B.

By selecting the concentration of the doping material such that an electric field is induced in the semiconductor material, the sheet resistance of the optical membrane can be reduced. The term "sheet resistance" is understood to mean a measure of the resistance of a thin film that may be uniform in thickness. The reduction in sheet resistance of the optical membrane may allow separated charge carriers to move an increased distance away from the illuminated volume 26 of the optical membrane, e.g., prior to recombination. In other words, a decrease in the sheet resistance of the optical membrane may result in a longer or more distant travel distance of the generated charge carriers. This may allow for faster removal of generated charge carriers from the illuminated volume 26 and/or may reduce local heating of one or more portions of the optical membrane 16. The increased travel distance of the generated charge carriers may also allow for removal of at least a portion of the generated charge carriers from optical membrane 16, as will be described below.

The concentration of the dopant 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. The first portion or first side of optical membrane 16 may include a first concentration of a dopant material. The second portion or side of the optical membrane 16 may include a second concentration of the dopant material. The first concentration of the dopant material may be higher than the second concentration of the dopant material. The sheet resistance of the optical membrane 16 may be considered to be inversely proportional to the doping level at, for example, the surface of the semiconductor material. In other words, an increase in the doping level may result in a decrease in the sheet resistance of optical membrane 16.

FIG. 16B schematically depicts the donor atom concentration N _D Exemplary graph of the variation in thickness x depending on optical membrane 16. It will be understood that the donor atom concentration N _D Is not limited to that shown in fig. 16B. In this example, the donor atoms may define or be included in the dopant material. Referring to FIGS. 16A and 16B, of optical membrane 16The top or topside 16a includes a higher concentration of donor atoms than the bottom or bottom side 16b of the optical membrane 16. Between the top or topside 16a and the bottom or bottom side 16b of the optical membrane 16, the donor atom concentration may decrease, e.g., gradually decrease. It should be understood that the optical membranes disclosed herein are not limited to such a distribution of donor atom concentrations. For example, in other embodiments, the donor atom concentration at the top or topside may be lower than the donor concentration at the bottom or bottom side of the optical membrane.

The doping gradient may cause diffusion of mobile charge carriers (or majority charge carriers), which may be in the form of electrons 42. For example, electrons 42 may diffuse from the top or topside 16a of optical membrane 16 to the bottom or underside 16b of the optical membrane. The diffusion of the electrons 42 leaves a positive net charge, which may be in the form of an ionized donor. The separation of positive and negative charges (indicated by "+" and "-" in fig. 16C) induces an electric field E.

The induced electric field E extends in the opposite direction to the diffusion process. The electric field E may be considered a built-in electric field or a vertical built-in electric field. In this embodiment, the electric field E extends in a direction perpendicular (e.g., substantially perpendicular) to the top or topside 16a and/or the bottom or bottom side 16b of the optical diaphragm 16.

Although the above examples refer to donor atom concentrations, it should be understood that in other embodiments, the dopant material may be provided in the form of acceptor atoms in addition to or instead of donor atoms.

The concentration of the doping material may be chosen such that the induced electric field E causes a separation of the charge carriers 24a, 24B generated during irradiation of the optical membrane 16 with the radiation beam B. Additionally or alternatively, the concentration of the doping material may be selected such that the induced electric field is about 10 ⁷ V/m or greater than 10 ⁷ V/m. For example, the concentration of the dopant material may be selected to be about 10 ²² cm ^-3 And 10 ¹⁴ cm ^-3 To change between.

The separation of the generated charge carriers 24 is schematically depicted in fig. 17A. The separated charge carriers may collect on or near opposite sides or

portions

16a, 16b of the optical membrane 16. For example, electrons 24a may collect on or near the top or topside 16a of optical membrane 16, while holes 24b may collect on or near the bottom or underside 16b of optical membrane 16.

As described above with respect to fig. 6, the separation and/or aggregation of the generated

charge carriers

24a, 24b collected in the illuminated volume 26 and a region outside the illuminated volume 26. The other electric field may extend in a direction parallel (substantially parallel) to the top or topside 16a and/or the bottom or bottom side 16b of the optical diaphragm 16. The other electric field can be considered as a laterally built-in electric field. Another electric field may cause the collected

charge carriers

24a, 24b to move toward the perimeter or peripheral region of the optical membrane 16. The movement of the charge carriers 24a, 24B is indicated in fig. 17B by the arrows labeled M. The accumulated

charge carriers

24a, 24b to move outwards and/or away from the irradiation volume 26.

Fig. 17C schematically shows the optical membrane 16, wherein some of the collected

charge carriers

24a, 24b have moved outwards and/or away from the irradiation volume 26. In regions outside the irradiated volume 26, the

charge carriers

24a, 24b may recombine. This may result in heat spreading over an area or volume 32 of optical membrane 16 and/or may reduce localized heating of optical membrane 16. Alternatively or additionally,

charge carriers

24a, 24b may be removed from optical membrane 16, as described below.

Fig. 17A to 17C are similar to fig. 5A, 6, and 7A. It should be understood that any of the features described above, for example, the features described with respect to fig. 5A, 6, and 7A, may also be applied to the embodiments described with respect to fig. 17A through 17C.

The optical diaphragm 16 shown in fig. 16A, 16C, and 17A to 17C may be manufactured by forming or providing a 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 as, for example, a preform. The semiconductor material may be doped with a dopant material. The concentration of the doping material may be chosen such that an electric field is induced in the membrane.

The doped semiconductor material may be formed as part of the step of forming the semiconductor material. Alternatively, the semiconductor material may be doped after it is formed, for example using a diffusion or implantation process, such as for example ion implantation.

An exemplary step of doping the semiconductor material may include depositing the doping material on the semiconductor material, for example using one of the deposition techniques disclosed herein, such as, for example, CVD. During deposition of the dopant material on the semiconductor material, some of the dopant material may diffuse into the semiconductor material. The diffusion of the dopant material into the semiconductor material may depend on the temperature of the deposition technique.

For example, the semiconductor material may comprise silicon, such as, for example, crystalline or polycrystalline silicon. The semiconductor material comprises negatively doped (e.g., n-type) silicon, e.g., with phosphorus, which may be doped to a concentration of about 10 ¹⁴ cm ^-3 . In other words, the semiconductor material may already be doped with another doping material. The dopant material may include boron, which may be used to introduce positive doping (e.g., p-type doping) into the silicon.

Boron, such as, for example, amorphous boron, may be deposited on n-type silicon, for example, using CVD techniques, at a temperature of about 700 ℃. This process may result in the formation of a layer of boron, such as a layer of pure boron, on the surface of the silicon. During the deposition of boron on n-type silicon, some boron may diffuse into the silicon. The boron concentration may be about 10 at or near the top or topside 16a of the optical membrane ²¹ To 10 ²² cm ^-3 . At or near the bottom or bottom side 16b of the optical diaphragm 16, the boron concentration may be reduced to about 10 ¹⁴ cm ^-3 。

It should be understood that boron may be deposited on silicon at temperatures greater than or less than 700 ℃, for example, to achieve a predetermined or desired doping gradient in the semiconductor material.

It should be understood that the optical membranes disclosed herein are not limited to including silicon as the semiconductor material. For example, in other embodiments, the semiconductor material may include at least one of silicon carbide, silicon nitride, and graphene. Alternatively, the semiconductor material may comprise a group III-V compound semiconductor.

It should also be understood that the optical membranes disclosed herein are not limited to including boron as the dopant material. For example, in other embodiments, at least one of arsenic (As), antimony (Sb), and phosphorus (P) may be used As a doping material, for example to negatively dope silicon.

Fig. 18A-19B schematically depict a system for reducing heat generation of optical membrane 16, in accordance with an embodiment of the present invention. Optical membrane 16 may include any of the features of the exemplary optical membranes described above. System 44 is configured to remove

charge carriers

24a, 24b (e.g., at least a portion thereof) from optical membrane 16 (e.g., one or more portions or portions thereof). The charge carriers 24a, 24B are generated during irradiation of the membrane 16, for example with a radiation beam B.

The system may include an electrically conductive element 45, such as, for example, an electrical conductor, for dissipating or removing the generated

charge carriers

24a, 24b from the optical membrane 16.

System 44 may be configured to remove generated

charge carriers

24a, 24b from one or more peripheral portions or peripheries of optical membrane 16, as described below. The system 44 may be configured to provide a sink 46 for the generated

charge carriers

24a, 24b.

System 44 may be configured to short circuit optical diaphragm 16. For example, the conductive element 45 may be arranged to short circuit the optical diaphragm 16. As shown in fig. 18A, a first side or portion 16a (e.g., top or topside 16 a) of optical membrane 16 may be connected (e.g., electrically connected) to a second side or portion 16b (e.g., bottom or bottom side 16 b) of optical membrane 16. The first side or portion 16a and/or the second side or portion 16b of the optical membrane 16 may be considered as the side or portion to which the

charge carriers

24a, 24b move, e.g. due to an electric field E (e.g. a vertically built-in electric field as described above). A first side or portion 16a of optical membrane 16 may be connected (e.g., electrically connected) to a second side or portion 16b of optical membrane 16 at or near a perimeter 16c of optical membrane 16. For example, a first side or portion 16a of optical septum 16 may be connected (e.g., electrically connected) to a second side or portion 16b along at least a portion or all of a perimeter 16c of optical septum 16. The term "perimeter" may be considered to encompass a perimeter region or zone.

Alternatively, a first side or portion 16a of optical septum 16 may be connected (e.g., electrically connected) to a second side or portion 16b of optical septum 16 at or near one or more peripheral portions 16c of optical septum 16. One or more peripheral portions 16c may be closely spaced relative to one another.

The conductive element 45 may be arranged to connect (e.g., electrically connect) the first side or portion 16a of the optical diaphragm 16 with the second side or portion 16b of the optical diaphragm 16, as described above.

The first and/or second sides or

portions

16a, 16b may be electrically grounded. For example, the conductive element 45 may connect the first side or portion 16a and/or the second side or portion 16b of the optical diaphragm 16 to electrical ground. Electrical grounding may provide a sink 46 for the generated

charge carriers

24a, 24b. This may allow the generated

charge carriers

24a, 24b to be removed from the optical membrane 16. Removing 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 side or portion 16a and/or the second side or portion 16b of the optical membrane 16 may protect the optical membrane 16 from static charging and/or may prevent an increase in the electrical potential of the optical membrane relative to other and/or adjacent components or objects, for example, relative to components or objects of a patterning device assembly or a lithographic apparatus. It should be understood that the systems described herein are not limited to electrically grounding the optical membrane, such as electrically grounding the first side or portion and/or the second side or portion of the optical membrane. For example, in other embodiments, the membrane may not be electrically grounded.

Although fig. 18A depicts both the first side or portion 16a and the second side or portion 16b as being connected to a common electrical ground that may provide a junction 46, it should be understood that in other embodiments, the first side or portion and the second side or portion of the optical diaphragm may each be connected to a respective electrical ground. This may additionally allow for short circuiting of the optical membrane.

A voltage or potential, e.g. an electrical potential, may additionally be applied to the optical membrane, e.g. with respect to electrical ground. For example, when mounting the optical diaphragm to a mounting or support element (not shown), such as, for example, a frame, support, etc., the voltage or potential applied to the optical diaphragm may be selected to correspond or match (e.g., substantially correspond or match) the voltage or potential that has been applied to the mounting or support element, for example, relative to electrical ground. This may allow the optical membrane to have the same (e.g., substantially the same) voltage or potential as the mounting or support element. In other words, electrical isolation of the optical diaphragm from the mounting or support element may be reduced or prevented.

FIG. 18B schematically shows a distributed electrical model of optical membrane 16. The optical diaphragm 16 may be considered as a photodiode comprising a plurality of capacitors C ₁ 、C ₂ 、C ₃ 、C _N Can be connected in series with a resistor R _S A plurality of first resistors provided in the form of and possibly a shunt resistor R _Sh A plurality of second resistors provided in the form of. The generated

charge carriers

24a, 24b may be considered to be stored in a plurality of capacitors C ₁ 、C ₂ 、C ₃ 、C _N At least one capacitor. A plurality of capacitors C ₁ 、C ₂ 、C ₃ 、C _N May be associated with a respective portion or region of the optical diaphragm 16. Portions or regions of optical membrane 16 are represented in FIG. 18B by concentrically arranged circles.

Series resistance R _S May be considered to represent the sheet resistance of the optical diaphragm 16. Series resistance R _s Arranged to connect a plurality of capacitors C ₁ 、C ₂ 、C ₃ 、C _N Two or more capacitors. Can be selected from a plurality of capacitors C ₁ 、C ₂ 、C ₃ 、C _N Through or via a series resistance R in at least one of the capacitors _S The generated

carriers

24a, 24b are removed in the form of a current or photocurrent.

Shunt resistor R _Sh Can be considered to represent examplesSuch as a loss of

charge carriers

24a, 24b due to recombination of

charge carriers

24a, 24b, such as, for example, an internal loss of

charge carriers

24a, 24b.

Referring to FIG. 18B, a portion or region of the optical diaphragm 16 is irradiated by the radiation beam B and is referred to as an illumination volume 26. The charge carriers 24a, 24B generated as a result of the optical membrane 16 being irradiated by the radiation beam B may be represented as a current I on the photodiode P. Capacitor C of

charge carriers

24a, 24b to optical diaphragm 16 ₁ Charging, capacitor C ₁ Associated with the illuminated volume 26 of the optical diaphragm 16.

The generated charge carriers may be distributed over one or more other portions of the optical membrane. As described above, due to the further electric field, the

charge carriers

24a, 24b move away and/or outwards from the irradiation 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 to be moved away from the irradiated volume 26 by or via the sheet resistance Rs, thereby being removed from the capacitor C associated with the irradiated volume 26 ₁ To the rest of the capacitor C ₂ 、C ₃ 、C _N And then removed sequentially. This may allow the generated

charge carriers

24a, 24b to become distributed across the optical membrane 16.

Ideally, the sheet resistance R is caused to flow through _s May generate heat in the optical membrane 16. A reduction in sheet resistance, for example due to the doping concentration of the semiconductor material of the optical diaphragm 16 selected as described above, may result in a reduction in the amount of heat generated. For example, by reducing sheet resistance (e.g., series resistance R) _s E.g., by increasing the shunt resistance R) and/or reducing recombination (e.g., localized recombination) of the generated

charge carriers

24a, 24b, e.g., by increasing the shunt resistance R _Sh The increased number of generated

charge carriers

24a, 24b may move away from the illuminated volume 26 and reach the perimeter or one or more perimeter portions 16c of the optical membrane 16 before recombination. This may allow for the generation of heat to be distributed at least across optical membrane 16 or across optical membrane 16, such as, for example, a portion or all of optical membrane 16. As described below, a portion of the generated heat may be transferredTo the load to remove this portion of the generated heat.

The above process may be repeated each time a portion or region of optical membrane 16 is irradiated by radiation beam B. When a portion or region of optical membrane 16 is repeatedly irradiated, new charge carriers may be generated. The newly generated charge carriers may contribute to the capacitor C associated with the irradiated volume 26 ₁ Charging of (2). Newly generated charge carriers can be accumulated in a plurality of capacitors C ₁ 、C ₂ 、C ₃ 、C _N On one or more capacitors. This may result in a plurality of capacitors C ₁ 、C ₂ 、C ₃ 、C _N Exceeds a threshold level. Above a threshold level, the

charge carriers

24a, 24b may recombine before moving away and/or outward from the irradiation volume 26. In other words, if the capacitor C is not removed before new charge carriers are generated ₁ The voltage level across the photodiode P (associated with the illuminated volume 26) will increase and may reach a threshold level. Above a threshold level, the photodiode P may become conductive and charge carriers may recombine, for example, to discharge the photodiode P. This may result in heat being generated in the irradiation volume 26.

Referring to FIG. 18B, a capacitor C, for example by shorting the optical diaphragm 16 as described above ₁ 、C ₂ 、C ₃ 、C _N And/or shunt resistance R _Sh May be considered short-circuited. This may allow for removal or discharge of

charge carriers

24a, 24b from optical membrane 16, such as from one or more peripheral portions or peripheries 16c of optical membrane 16. This in turn may allow for the removal of stored in multiple capacitors C ₁ 、C ₂ 、C ₃ 、C _N Thereby preventing or reducing charge carriers in the plurality of capacitors C ₁ 、C ₂ 、C ₃ 、C _N Of one or more capacitors of (a). The newly generated charge carriers may be able to move away from the irradiation volume 26 and/or outwards, thereby becoming distributed in the lightIn the septum 16. The distribution of charge carriers in or across the optical membrane 16 may reduce heating, e.g., localized heating, of the optical membrane 16 (e.g., one or more portions or components of the optical membrane 16).

As described above, by short-circuiting the optical diaphragm 16, the shunt resistance R can be made _sh Associated with a finite value that can be considered to be increased. In other words, the loss of charge carriers (e.g., due to recombination) may be considered reduced.

The short circuit of the optical diaphragm 16 may allow the optical diaphragm to be discharged, such as continuously, for example. In other words, the generated

charge carriers

24a, 24b may be continuously removed from the optical membrane 16, for example. This may allow for a continuous distribution of charge carriers generated in the optical membrane 16, thereby reducing heating, e.g., localized heating, of the optical membrane (e.g., one or more portions or components thereof).

Fig. 19A and 19B are similar to fig. 18A and 18B, and any of the features described with respect to fig. 18A and 18B may also be applied to the system shown in fig. 19A and 19B. The system 44 depicted in fig. 19A and 19B may include a load, which may be a resistive element R _L Is provided in the form of (1). 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 shown in fig. 19A and 19B, a load is provided instead of the short-circuiting of the optical diaphragm 16 as described above.

Resistance element R _L Attached to the optical diaphragm 16, for example as shown in fig. 19A. For example, the first portion or first side 16a and/or the second portion or second side 16b of the optical membrane 16 may be connected to the resistive element R, e.g., by a conductive element 45 _L . First portion or first side 16a and/or second portion or second side 16b may be connected to resistive element R along at least a portion or all of perimeter 16c of optical membrane 16 _L . Alternatively, the first portion or first side 16a and/or the second portion or second side 16b of the optical diaphragm 16 may be connected to the resistive element R at or near one or more peripheral portions 16c of the optical diaphragm 16 _L . One or more peripheral portions 16c may be opposite to each otherThis is closely spaced.

The resistive element R may be selected based on at least one other property of the optical diaphragm 16 _L The resistance of (2). For example, the sheet resistance (e.g., the plurality of series resistances R) of the optical diaphragm 16 may be based _S Resistance of one or more series-connected resistors) to select the resistive element R _L The resistance of (2). The resistance element R can be selected _L To match (e.g., substantially match) the sheet resistance. This may allow for the passage from the optical element 16 to the resistive element R _L Is increased or maximized. For example, the optical diaphragm 16 may convert energy (e.g., energy of photons) of the radiation beam B into power. The power may cause heating of the optical diaphragm 16. By selecting the resistive element R _L To match (e.g., substantially match) the sheet resistance, heat (or at least a portion of the heat) 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 R _L And thus may be removed from optical membrane 16. In other words, at least a portion of the kinetic energy of the generated

charge carriers

24a, 24b (e.g., recombination of the

charge carriers

24a, 24 b) may be external to the optical membrane 16 (such as, for example, at the resistive element R) _L Upper) into heat.

It is understood that transfer to the resistive element R is possible _L Can be considered to be proportional to the product of the current I and the voltage V. The current I may be considered to be due, for example at least in part, to flowing to the resistive element R _L Resulting in generated

charge carriers

24a, 24b. The current I may cross the resistance element R _L Generating a voltage V. Providing a load (e.g. a resistive element R) _L ) The generated

charge carriers

24a, 24b (e.g., a portion thereof) may be allowed to be removed from the optical membrane 16.

Although fig. 19A and 19B do not show the electrical ground of the optical diaphragm 16, it should be understood that in other embodiments, the optical diaphragm may be connected to electrical ground. For example, by electrical grounding of the optical membrane, the optical membrane may be protected from static charging and/or an increase in the electrical potential of the optical membrane relative to other and/or adjacent components or objects (e.g., of a patterning device assembly or a lithographic apparatus) may be reduced or prevented. Additionally, as described above, a voltage or potential may be applied to the optical membrane, for example with respect to electrical ground.

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

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

The term "EUV radiation" may be considered to include electromagnetic radiation having a wavelength in the range of 4-20nm, for example in the range of 13-14 nm. The EUV radiation may have a wavelength of less than 10nm, for example in the range 4-10nm, such as 6.7nm or 6.8nm.

Although fig. 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 generated by converting a fuel (e.g., tin) into a plasma state using an electrical discharge. This type of radiation source may be referred to as a Discharge Produced Plasma (DPP) source. The discharge may be generated by a power source, which may form part of the radiation source, or may be a separate entity connected to the radiation source SO by an electrical connection.

Although specific reference may be made in this text to the use of lithographic apparatus in the manufacture of ICs, 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 film magnetic heads, etc.

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 is not limited to optical lithography where the context allows. In imprint lithography, a topography or topography in a patterning device defines the pattern created on a substrate. The topography of the patterning device may be printed into a layer of resist supplied to the substrate and the resist cured by applying electromagnetic radiation, heat, pressure or a combination thereof. The patterning device is removed from the resist leaving a pattern after the resist is cured.

While specific embodiments of the invention have been described above, it will be appreciated that the invention may be practiced otherwise than as described. The above description is intended to be illustrative and not restrictive. 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. 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 disposed on the second layer,

wherein the first and second materials are selected such that a space charge or depletion region is formed in the membrane, the space charge or depletion region inducing an electric field in the membrane, the induced electric field being capable of causing separation and/or distribution of charge carriers generated during irradiation of the optical membrane with a radiation beam.

2. The membrane of claim 1, wherein the first material and the second material are selected such that the space charge or depletion region extends into a portion or all of the membrane.

3. A diaphragm according to claim 1 or 2, wherein the first and second materials are selected based on one or more properties of the first and/or second materials.

4. A membrane according to claim 1 or 2, wherein the electric field extends in a direction perpendicular to the first and/or second layer.

5. A membrane according to claim 1 or 2, wherein the first and second materials are selected such that an electric field induced by the space charge or depletion region causes separation of charge carriers generated during irradiation of the membrane.

6. The membrane of claim 5, wherein the first and second materials are selected such that the electric field induced by the space charge or depletion region causes the generated charge carriers to collect on or near opposite sides of the space charge or depletion region.

7. A membrane according to claim 5, wherein the separation and/or accumulation of generated charge carriers induces a further electric field.

8. A membrane according to claim 7, wherein the further electric field extends in a direction parallel to the first and/or second layer.

9. A membrane according to claim 7, wherein the further electric field causes the generated charge carriers to move outwards and/or away from a portion or region of the membrane that is irradiated.

10. A diaphragm according to claim 7, wherein the further electric field causes the generated charge carriers to move towards a periphery or peripheral region of the diaphragm.

11. A diaphragm according to claim 9, wherein the further electric field causes the generated charge carriers to move at a speed or velocity higher than that of a radiation beam moving across the diaphragm.

12. A membrane according to claim 1 or 2, wherein at least one of the first and second materials comprises a semiconductor material.

13. A membrane according to claim 1 or 2, wherein at least one other of the first and second materials comprises a semiconductor material and/or a metal.

14. The diaphragm of claim 1 or 2, wherein at least one of the first material and the second material comprises boron.

15. The diaphragm of claim 1 or 2, wherein at least one other of the first and second materials comprises at least one of crystalline silicon, polysilicon, silicon carbide, silicon nitride and graphene.

16. The membrane of claim 1 or 2, 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. A membrane according to claim 1 or 2, wherein at least one of the first and second materials is negatively doped and/or at least the other of the first and second materials is positively doped.

18. A diaphragm according to claim 1 or 2, wherein the diaphragm comprises an electrode configured to allow a voltage to be applied to the diaphragm.

19. A membrane according to claim 18, wherein the electrodes are arranged on the membrane such that the voltage induces a further electric field extending in a direction perpendicular to the first and/or second layers.

20. A membrane according to claim 1 or 2, wherein the membrane comprises a third layer comprising a third material.

21. A membrane according to claim 20, wherein the third material comprises a metal such as zirconium, molybdenum and/or ruthenium.

22. A membrane according to claim 1 or 2, wherein at least one of the first and second materials comprises a fluorescent dopant.

23. A method of manufacturing an optical diaphragm 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 material and the second material are selected such that a space charge or depletion region is formed in the membrane, the space charge or depletion region inducing an electric field in the membrane, the induced electric field being capable of causing separation and/or distribution of charge carriers generated during irradiation of the optical membrane with a radiation beam.

24. An optical membrane for use in or with a lithographic apparatus, the membrane comprising a semiconductor material comprising a dopant material, wherein the concentration of the dopant material is selected such that an electric field is induced in the membrane, reducing the sheet resistance of the membrane, resulting in a longer or more distant travel distance of charge carriers generated in the membrane.

25. The membrane of claim 24, wherein the concentration of the doping material is non-uniform in the semiconductor material and/or defines a doping gradient in the semiconductor material.

26. A diaphragm according to claim 24 or 25, wherein a first portion or side of the diaphragm comprises a first concentration of doped material and a second portion or side of the diaphragm comprises a second concentration of doped material, wherein the first concentration of doped material is higher than the second concentration of doped material.

27. A membrane as claimed in claim 24 or 25 wherein the concentration of the dopant material is selected to be at 10 in the semiconductor material ²² cm ^-3 And 10 ¹⁴ cm ^-3 To change between.

28. A diaphragm according to claim 24 or 25, wherein the concentration of the doping material is selected such that the induced electric field is about 10 ⁷ V/m or greater than 10 ⁷ V/m。

29. A membrane according to claim 24 or 25 in which the concentration of the dopant material is selected such that the induced electric field causes separation of charge carriers generated during irradiation of the membrane with radiation.

30. A membrane according to claim 24 or 25 in which the concentration of the doping material is selected such that the induced electric field causes the generated charge carriers to collect on or near opposite sides of the membrane.

31. A membrane according to claim 29, wherein the separation and/or accumulation of generated charge carriers induces a further electric field.

32. The membrane of claim 24 or 25, wherein the semiconductor material comprises at least one of crystalline silicon, polysilicon, silicon carbide, silicon nitride, graphene, and a III-V compound semiconductor.

33. The membrane of claim 24 or 25, wherein the dopant material comprises at least one of boron, arsenic, antimony and phosphorus.

34. A method of manufacturing an optical diaphragm 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 the concentration of the doping material is selected such that an electric field is induced in the membrane, reducing the sheet resistance of the membrane, resulting in a longer or more distant travel distance of charge carriers generated in the membrane.

35. A system for reducing optical diaphragm heating, the system comprising:

an optical membrane according to any one of claims 1 to 22 or 24 to 33; wherein the system is configured for removing charge carriers from the membrane, the charge carriers being generated during irradiation of the membrane.

36. The system of claim 35, wherein the system is configured for removing the generated charge carriers from one or more peripheral portions or peripheries of the membrane.

37. A system according to claim 35 or 36, wherein the system is configured to provide a sink for the generated charge carriers.

38. The system of claim 35 or 36, wherein the system is configured to short circuit the optical membrane.

39. The system of claim 35 or 36, wherein the first portion or side of the diaphragm is connected to the second portion or side of the diaphragm.

40. The system of claim 39, wherein the first and/or second perimeter side or portion is electrically grounded.

41. A system as defined in claim 39, wherein the first portion or side of the diaphragm is connected to the second portion or side of the diaphragm at or near a periphery of the diaphragm.

42. The system of claim 35 or 36, wherein the system comprises a load, the load being connected to the diaphragm.

43. The system of claim 42, wherein the resistance of the load is selected based on at least one other property of the diaphragm, the at least one other property comprising a sheet resistance of the diaphragm.

44. The system of claim 43, wherein the resistance of the load is selected to match the sheet resistance of the diaphragm.

45. A patterning device assembly for use with a lithographic apparatus, the assembly comprising:

a pattern forming device; and

a pellicle comprising an optical membrane according to any of claims 1 to 22 or claims 24 to 33 or a system for reducing heating of an optical membrane according to any of claims 35 to 44.

46. A lithographic apparatus, comprising:

an illumination system configured to condition a radiation beam;

a support structure configured 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 beam of radiation onto the substrate; and

an optical diaphragm according to any of claims 1 to 22 or claims 24 to 33 arranged adjacent the substrate table; or

The system for reducing heating of an optical membrane of any one of claims 35 to 44.

47. The apparatus of claim 46, comprising a debris mitigation device configured to direct a gas flow toward the substrate, the membrane being part of or included in the debris mitigation device.

48. A method comprising projecting a patterned beam of radiation onto a substrate, wherein the beam of radiation passes through an optical membrane according to any one of claims 1 to 22 or claims 24 to 33.

49. Use of an optical diaphragm in or with a lithographic apparatus, the optical diaphragm being in accordance with any one of claims 1 to 22 or 24 to 33.