CN110914760B

CN110914760B - Reflection system, extreme ultraviolet exposure tool and lithography exposure tool

Info

Publication number: CN110914760B
Application number: CN201880030036.0A
Authority: CN
Inventors: 丹尼尔·基恩·史密斯; 大卫·M·威尔森; 多尼斯·G·弗拉杰罗; 麦可·B·宾纳德
Original assignee: Nikon Corp
Current assignee: Nikon Corp
Priority date: 2017-05-11
Filing date: 2018-05-09
Publication date: 2024-06-18
Anticipated expiration: 2038-05-09
Also published as: WO2018208912A3; TW201901308A; CN110914760A; WO2018208912A2; TWI785041B

Abstract

A reflection system, an extreme ultraviolet exposure tool and a lithography exposure tool. The reflective system has a reference axis and comprises a reflective pattern source (carrying a one-dimensional pattern) and a combination of two optical mirrors, which are arranged in sequence to transfer EUV radiation incident on a first optical assembly onto the pattern source, the one-dimensional pattern of the pattern source being arranged in a curved surface. In one case, such a combination includes only two optical mirrors (each optical mirror may contain multiple constituent components). The combination is disposed in a fixed spatial and optical relationship relative to the pattern source and represents an illumination unit of a one-dimensional extreme ultraviolet exposure tool that additionally includes a projection optical subsystem configured to form an optical image of the pattern source with only two beams of radiation on an image plane. The only two beams of radiation originate at the pattern source from extreme ultraviolet radiation transferred onto the pattern source.

Description

Reflection system, extreme ultraviolet exposure tool and lithography exposure tool

Cross reference to related applications

The present application claims priority and rights to U.S. provisional patent application No. 62/504,908 filed on 5/11/2017, U.S. patent application No. 15/599,148 filed on 18/5/2017, and international patent application PCT/US2018/027785 and international patent application PCT/US2018/029160 filed on 16/4/2018. The disclosure of each of the above applications is incorporated by reference.

Technical Field

The present invention relates to optical designs of spatially dense printers (space-DENSE LINE PRINTER) configured to operate in the extreme ultraviolet (extreme ultraviolet, EUV) and/or ultraviolet portion of the spectrum, and more particularly to illumination subsystems of lithographic exposure tools configured to such printers.

Background

Structures of currently commercially available EUV lithography equipment (hereinafter referred to as a generic EUV system) are configured to image a reticle mask carrying thereon an arbitrary two-dimensional (2D) pattern onto a rectangular field (rectangular field) on a workpiece (e.g., a semiconductor wafer, substrate). Due to the two-dimensional nature of such patterns that must be optically transferred from the reticle and imaged onto the workpiece, it is necessary to implement a generic EUV system as a scanning system to provide relative displacement between the substrate and the reticle. Currently, such an implementation is achieved with one mobile station for the reticle and at least one further mobile station for the substrate, without which it is quite difficult and in practice impossible to transfer all features of the reticle pattern onto the substrate with sufficient accuracy and resolution. The structural and operational complexity of the currently used systems inevitably and greatly increases the operating costs and reduces the number of exposures of the substrate per unit time, in part because the transmission of EUV light through the optical system is limited. Furthermore, because transferring a pattern onto a workpiece requires a process of optical imaging in two dimensions, the series of optical components of existing generic EUV systems require and are characterized by high complexity. For example, the series of optical components may include: six parabolas in the projection section (or projection optics) of the series of optical components, with a mirror roughness of less than 0.1 nanometers root mean square (rms) and a mirror alignment tolerance of less than 1 nanometer, etc.; -a structurally complex and fine-tunable illumination section of the series of optical assemblies; and large reticles or masks with complex reflective coatings. Furthermore, proper pattern transfer requires the use of complex combinations of alignment masks. All these factors inevitably lead to high design and manufacturing costs for a generic EUV system.

Disclosure of Invention

Embodiments provide a reflection system having a reference axis. The reflection system includes: a reflective pattern source carrying a substantially one-dimensional (1D) pattern defined in a spatially curved surface; and a combination of only two optical components, which are arranged in sequence relative to each other to transfer EUV radiation (incident on a first optical component of the only two optical components) onto the pattern source. Each of the only two optical components has a non-zero optical power. The combination is disposed in a substantially fixed spatial and optical relationship relative to the pattern source and represents an illumination unit (illumination unit, IU) of an EUV exposure tool that includes a Projection Optics (PO) subsystem having a reference axis and configured to form an optical image of the pattern source (with a reduction factor of N >1 on an image plane that is a plane optically conjugate to the pattern source) with only two beams of radiation. The only two beams of radiation originate at the pattern source as a result of diffracting the EUV radiation transferred onto the pattern source. In a specific embodiment, the PO subsystem is a reflective PO subsystem comprising only a primary mirror and a secondary mirror. It should be noted that the illumination unit IU may further be interchangeably referred to as an illumination lens, IL or simply as an illuminator. The projection optics subsystem or PO of the exposure tool used to supplement the IU may be interchangeably referred to herein as the "PO subsystem" or "projection lens" or "PL".

Related embodiments provide a lithographic exposure tool having a string of optical elements positioned to deliver EUV radiation to a target workpiece via the string of optical elements. The optical element string includes: (i) a reflective lighting unit (IU); (ii) A reflective pattern source configured to receive the EUV radiation from the IU and diffract such EUV radiation at the substantially one-dimensional pattern of the pattern source (such pattern being defined in a curved surface) to form first and second diffracted beams of the EUV radiation; and (iii) a reflective Projection Optics (PO) subsystem positioned to receive the first and second diffracted beams from the pattern source and to form an optical image of the pattern source with only the first and second diffracted beams (with a reduction factor of N >1 in an image plane optically conjugated to the pattern source). In a specific case, the substantially one-dimensional pattern forms a one-dimensional (1D) diffraction grating configured as one of: (i) a phase diffraction grating; (ii) an amplitude diffraction grating; and (iii) an attenuated phase-shift diffraction grating.

The lithographic exposure tool is generally configured to form the image to include a spatial frequency up to twice the spatial frequency characterizing the substantially one-dimensional pattern.

In operation of such a lithographic exposure tool, the first and second diffracted beams represent respective corresponding diffraction orders formed from the EUV radiation at the spatially curved substantially one-dimensional pattern of the pattern source, and have equal absolute values but different signs. Alternatively or additionally, the optical element string may be configured to forward the first and second diffracted beams from the pattern source to a first element of the PO subsystem such that the first and second diffracted beams are spatially separated from each other by a last element of the IU without any of the first and second diffracted beams being truncated by the last element of the IU. Here, the IU includes first and second fly-eye (FE) mirrors, and each of these first and second fly-eye mirrors contains a respective corresponding array of individually constituent reflective elements, the first fly-eye mirror being positioned to image a distribution of the EUV radiation from an entrance pupil of the IU to the second fly-eye mirror. Here, the last element of the IU is represented by the second fly's eye mirror.

In a related embodiment, the IU includes a first fly-eye (FE) mirror and a second fly-eye mirror, each of the first fly-eye mirror and the second fly-eye mirror containing a respective corresponding array of individually constituent reflective elements, and the first fly-eye mirror is positioned to image a distribution of the EUV radiation from an entrance pupil of the IU to the second fly-eye mirror. Alternatively or additionally, i) the pattern source is disposed in a substantially fixed spatial relationship with respect to the IU and/or ii) the substantially one-dimensional pattern has an outer boundary, and a first contrast value remains substantially equal to a second contrast value (where the first contrast value is a value representing an optical contrast of a first portion of the image formed at the target workpiece that represents a portion of the one-dimensional pattern that is within the outer boundary), and the second contrast value is a value representing an optical contrast of a second portion of such image). Alternatively or in addition, the optical elements of the IU may be positioned to block propagation of a third beam of EUV radiation to a surface located between such optical elements and the first optical element of the PO subsystem (here, the third beam represents zeroth order diffraction of the EUV radiation formed at the pattern source). When the substantially one-dimensional pattern is associated with a surface that is curved in space, such optical elements are represented by Fly Eye (FE) mirrors that contain arrays of individually constructed reflective elements.

In one embodiment of the lithographic exposure tool, the PO subsystem comprises a primary mirror and a secondary mirror, and at least one of the primary mirror and the secondary mirror contains two identical reflective elements spatially disconnected from each other. Here, the reflective surface of either one of the first reflective element and the second reflective element of the two identical reflective elements may be configured congruent with a portion of the rotationally symmetric surface.

Drawings

The invention will be more fully understood by reference to the following detailed description of specific embodiments in conjunction with the drawings, which are not to scale, in which:

FIG. 1A provides a generalized schematic of a one-dimensional EUV exposure tool of an embodiment;

FIG. 1B and FIG. 1C schematically illustrate related embodiments of a one-dimensional EUV exposure tool in more detail;

Fig. 2A shows a configuration of a light collection system for a laser driven plasma light source having an ellipsoidal mirror for refocusing EUV radiation from the laser driven plasma LPP to an "intermediate focus" (IF) (which in turn acts as a light source for an embodiment of IU and is referred to as a secondary light source). For comparison, a 5sr collector and 1.6sr sub-aperture configuration is schematically shown;

FIG. 2B is a schematic diagram of a light-based model of the laser-driven plasma source shown in FIG. 2A, showing a collector 210 having a central opening 210A, a tin ejection orifice 214, and a secondary light source IF 216;

fig. 2C and 2D show assumed substantially gaussian distributions (Gaussian distribution) of the plasma of the laser driven plasma source according to the model used for the calculation.

Fig. 3A and 3B show, respectively, the distribution of radiation as a function of the angle of the laser-driven plasma source model as viewed along the optical axis, and the angular distribution of radiation of the same source in an identified cross-sectional plane transverse to the optical axis;

FIGS. 4A and 4B show the distribution of light rays produced by a modeled laser driven plasma source and the directional cosine of such light rays at the plane of a secondary light source passing through the point of convergence of the light rays reflected by the collector of the plasma source, respectively;

5A, 5B, 5C, 5D, 5E, 5F, and 5G illustrate a process sequence for performing a light-to-light construction to optimize image contrast for a desired shape of illumination light;

FIGS. 6A, 6B illustrate a first level layout of IUs of an optical system containing an embodiment of a flat or planar reticle (pattern source);

FIG. 7A is a schematic diagram showing the overlapping of the "tiling" multiplicity of sub-apertures of a first "fly-eye" mirror of an IU receiving light from a laser-driven plasma source for the source itself, as viewed along the optical axis;

FIG. 7B shows the angular distribution of individual mirror elements (sub-apertures) of the first fly's eye mirror shown in FIG. 7A;

FIG. 7C is a plot of the uniformity of irradiance distribution formed by the embodiment of the first fly's eye mirror shown in FIGS. 7A and 7B;

FIG. 8 is a schematic diagram of a second fly-eye mirror receiving an IU of light from the first fly-eye mirror when viewed along the optical axis;

FIG. 9 is a schematic diagram of a related embodiment of an IU of an embodiment configured to operate with multiple light sources;

FIGS. 10A and 10B are diagrams showing dimensions of embodiments of fly eye mirrors FE1 and FE2 of an embodiment of an IU;

FIG. 11A is a schematic diagram of an embodiment of a monolithic optical element string of a one-dimensional EUV tool constructed in accordance with the present principles;

FIG. 11B provides an illustration of an optical path within an embodiment of an IU;

Fig. 12A, 12B are diagrams supplementing each of fig. 1B and 1C and showing the spatial coordinates of an EUV beam incident on a pattern source (reticle) of a one-dimensional EUV system from the last mirror of an IU of the one-dimensional EUV system, and the first diffracted beam and the second diffracted beam represent different diffraction orders formed at the pattern source as a result of diffracting the incident EUV beam on the light source. The last mirror of an IU may be either the relay mirror of an IU (e.g., the third mirror in the three mirror embodiment of an IU shown in fig. 1B in the case where the pattern source is substantially flat) or the second mirror (e.g., in the two mirror embodiment of an IU shown in fig. 1C in the case where the pattern source is spatially curved);

13A, 13B present a flow chart summarizing a process for manufacturing a device utilizing the disclosed embodiments;

14A, 14B are schematic diagrams of related embodiments of elements of an illumination unit containing an example of a one-dimensional EUV system of a spatially curved reticle or pattern source;

FIG. 15 illustrates a related embodiment of a monolithic optical element string of a one-dimensional EUV tool containing a curved reticle or pattern source;

FIGS. 16A, 16B illustrate a first level layout of IUs of an optical system containing an embodiment of a spatially curved reticle (pattern source);

fig. 17A, 17B, 17C and 17D show the optical path of propagation of EUV radiation through IU and PO subsystems of a one-dimensional EUV system in a plane parallel to a plane containing a radiation beam representing diffraction orders formed at a spatially curved reticle.

Generally, the sizes and relative proportions of the elements in the drawings may be set to be different from the actual sizes and relative proportions, in order to properly facilitate the brevity, clarity, and understanding of the drawings. For the same reason, it may not be necessary to show all elements presented in one figure in another figure.

Detailed Description

The discussed embodiments set forth an optical system configured as an IU of a one-dimensional EUV exposure tool and disclose a method of lithographically marking a selected substrate (which may be referred to generally as a workpiece or wafer and may have carried a preformed spatially distorted pattern in specific cases) with a new one-dimensional pattern containing spatially densely packed parallel lines.

As already mentioned above, the generic EUV system presents various problems, among which there is a problem of ensuring that the generic EUV system remains commercially competitive. These problems include: (A) The optical power produced by EUV light sources typically equipped with a generic EUV system is insufficient. Currently, typical outputs are about 40 to 80 watts. This problem is exacerbated by the fact that: the optical power delivered by the illumination subsystem of the EUV system from the EUV light source to the reticle is further reduced due to the limited (about 70% for each mirror) reflectivity of the EUV mirrors. This illumination subsystem may be further interchangeably referred to as an illumination unit, IU (or illumination lens, IL or simply as an illuminator). (B) The operation of a generic EUV system is sensitive to defects and/or particles on a reticle mask. Indeed, since a generic EUV system is configured to image a two-dimensional pattern from a reticle to a wafer at high resolution, the pattern transferred to the wafer may be susceptible to damage from defects or particles on the reticle. Stated another way, each defect or particle on the reticle that is greater than tens of nanometers can disrupt the pattern printed on the wafer. (C) The extremely stringent requirements imposed on the optical aberrations of the projection subsystem by the two-dimensional nature and high resolution of any pattern to be printed. The projection subsystem may be more interchangeably referred to as Projection Optics (PO) or Projection Lenses (PL).

Alternative processes to EUV lithography processes currently used (and in particular-including processes that sometimes utilize immersion lenses to pattern substrates multiple times with Deep Ultra Violet (DUV) light at wavelengths of approximately 193 nm) can be cheaper but involve complex wafer processing between multiple exposures. Eventually, as the resolution required for the features increases, it will reach a level where the multiple patterning process costs are similar to the common EUV exposure costs.

For any of the above reasons, printing patterns with simplified geometries using a generic EUV system and/or an alternative immersion system is economically unattractive. The described scenario thus presents the problem of configuring an EUV exposure tool that is specifically and intelligently configured and optimized for imaging a pattern comprising densely spaced lines; in particular-in the extreme ultraviolet spectral region (e.g., at a wavelength of about 13.5 nanometers). Not only will the design and operational characteristics of such tools meet the optomechanical requirements involved in imaging the transfer of a one-dimensional pattern of a simplified reticle onto a semiconductor substrate, but the reduced cost of such tools would also be beneficial to the industry. An important part of such a simplified EUV system is its illumination subsystem or unit (abbreviated IU) which delivers light from the light source of the exposure tool to a mask whose pattern is intended to be imaged onto an image plane and printed on a workpiece located at this imaging plane, which is the subject of the present disclosure. (projection optics subsystem or PO of the exposure tool for supplementing IU may be interchangeably referred to herein as a "PO subsystem" or "projection lens" or "PL")

The term "one-dimensional pattern" (or "1D pattern") as used herein, unless otherwise specified, refers to a geometric pattern defined on a surface of a photomask or reticle (for transfer to a photosensitive photoresist (e.g., a semiconductor wafer) on a selected substrate using photolithographic methods to generate an image of such one-dimensional pattern) and extending across such surface generally along two axes transverse to one another. The one-dimensional pattern may vary along the first axis of the pattern while remaining substantially unchanged along the second axis (i.e., the one-dimensional pattern may be characterized by a value of the geometric variation along the second axis that is no more than 50% of the variation observed along the first axis, preferably no more than 20% of the variation observed along the first axis, more preferably no more than 10% of the variation observed along the first axis, even more preferably within 5% or less than 5% of the variation observed along the first axis, and most preferably within 1% or less than 1% of the variation observed along the first axis). Examples of one-dimensional patterns are provided by any collection of spatially-spaced-apart substantially identical, parallel, elongated pattern elements, such as, for example, a combination of parallel lines or slits in an otherwise opaque screen defined at a photomask. In a particular case, the one-dimensional pattern under consideration may form a linear (one-dimensional) grating (e.g., a one-dimensional diffraction grating) characterized by an amplitude that varies periodically along a first selected axis and an amplitude that is constant along a second axis selected to be transverse to the first axis. Furthermore, as will be appreciated by those skilled in the art, to correct for imaging distortions caused by deformation of the optical system or the substrate, the one-dimensional pattern may nevertheless have small variations along the first axis and/or the second axis. For the purposes of this disclosure, an element or component containing a substantially one-dimensional pattern (and regardless of the particular configuration of such element or component, e.g., as a reticle or mask) may be interchangeably referred to as a pattern source.

In contrast, the term "two-dimensional pattern (2D pattern)" is defined to mean a set of pattern elements that changes or changes must be defined along two axes that are transverse to each other. One of the simplest examples of a two-dimensional pattern is provided by a grid (grid) or mesh (mesh) that forms a two-dimensional grating when having a spatial period defined along two lateral axes. The one-dimensional pattern and the two-dimensional pattern are considered as such with reference to the patterns of the photomask of the reticle disclosed herein, regardless of the curvature of the surface of the substrate (or photomask) on which they are formed. For brevity, the structure of an EUV system (in which embodiments of the illumination unit discussed herein are intended to be used) configured in accordance with the inventive concepts is specifically and purposefully configured to image a one-dimensional reticle pattern, and is referred to herein as a "one-dimensional EUV system. For brevity and in contrast, an EUV system (e.g., a generic EUV system) configured to image a two-dimensional patterned reticle may be referred to as a "two-dimensional EUV system.

The term "optically conjugate" and related terms are understood to be defined by the principle of optical reversibility according to which light rays will travel along an initial path if the direction of travel of the light is reversed. Thus, these terms are defined by two surfaces when referring to two surfaces, a point of one of which is imaged onto a point of the other surface with a given optical system. If an object is moved to a point occupied by its image, a new image of the moved object will appear at the point where the object originally appeared. The point across the optically conjugate surface is referred to and defined as the optically conjugate point. When a first layer is disposed directly on a given surface or substrate or second layer, or when the first layer is disposed on an intermediate third layer which is in turn disposed on the given surface or substrate or second layer, the first layer or pattern is defined as being carried by (or on) the given surface or substrate or second layer.

The design of an IU according to the inventive concept and the co-optimization of the IU with the PO subsystem of a one-dimensional EUV exposure tool enables the practical realization of an exposure tool or machine configured to optically transfer dense line patterns (this corresponds to a pitch or period of, for example, ten to twenty nanometers, preferably less than ten nanometers, more preferably a few nanometers, e.g., 5 nanometers or less than 5 nanometers, in the case of periodic line patterns) in a cost-effective manner with high spatial resolution to enable 10-nanometer and 7-nanometer node semiconductor devices (defined according to the international semiconductor technology map (e.g., ITRS 2.0)). The disclosed concepts stem from the realization that modern high density semiconductor chip designs are increasingly based on one-dimensional geometric patterns. The embodiment of IU in which the structure is specifically configured to illuminate or irradiate a one-dimensional pattern (e.g., a pattern representing a one-dimensional grating) carried by an optical substrate and used in conjunction with an embodiment of a PO subsystem (also specifically configured to image a set of densely packed lines) presents clear structural and operational advantages over the corresponding optical system of a general two-dimensional EUV system in the following respects:

The combination of IU and PO portions (of a one-dimensional EUV system implemented in accordance with the present invention) is substantially simplified as compared to a two-dimensional EUV system, and is affordable and does include fewer reflective surfaces, which in effect provides good quality exposure with less optical power (e.g., tens of watts, as low as about 20 watts in one example) required from the light source;

Because some or even many optical surfaces are eliminated from the system's PO (as compared to a two-dimensional EUV system), the cost of scanning reticle stages, pellicle, other components, and the proposed EUV raster machine can be substantially reduced.

Embodiments utilizing dense line one-dimensional EUV lithography systems solve this long standing problem of insufficient illumination levels typical of exposure tools utilizing EUV light by providing an illumination optics assembly with: (1) A first mirror and a second mirror comprising an array of facet fly's eye mirrors, and (2) a relay mirror disposed between such mirrors and the reticle. In such a one-dimensional EUV system, the shape of one of the fly's eye array mirrors preferably matches the shape of the incident light of a projection optics assembly that is optimized for two-beam interference (two-beam interference) over the entire range of pitch values characterizing the one-dimensional reticle pattern.

Illustrative examples of one-dimensional EUV exposure tools.

In fig. 1B and 1C, a more generalized schematic of a possible embodiment 102, 170 of a part 100 of the one-dimensional EUV system shown in fig. 1A, configured according to the inventive concept, is shown. The system 102, 170 may include one or more light sources (as shown-light source 114). In an embodiment, the system 102 is shown as comprising: an optical illumination subsystem or unit (IU) containing first and second mirrors 118, 122, and a relay mirror 126; and a PO subsystem (reflective objective) comprising two or more mirrors, at least one of which has a region defining an optical visual barrier (optical obscuration) (the dual-mirror objective of example 102 is shown as containing a first mirror 130 and a second mirror 134, the first mirror 130 and the second mirror 134 each having a corresponding central visual barrier 130A, 134A). The term "optical vision barrier" is used herein to refer to at least a portion (of an optical element) within the confines of which further transfer of light incident on the optical element to the next optical element is hindered, inhibited or even blocked. Examples of vision barriers in the case of the reflective objective lens shown are provided by: (i) A through opening in the base of a curved mirror, such as, for example, curved primary mirror 130A, within the confines of which light incident on this mirror is not further reflected toward curved secondary mirror 130B but is transmitted through the through opening, or (ii) the lack of a reflective coating (defining substantially the same optical effect) within a predetermined region of the mirror. The term central vision barrier defines a vision barrier centered at a reference axis of the optical system. For the purposes of this disclosure, the term "on-axis illumination" is a shorthand notation for illumination where (i) the illumination generally propagates parallel to the optical axis and/or the propagation direction of the illumination includes a direction parallel to the optical axis (excluding dipole or annular illumination where there is no axial direction), (ii) the center of the illumination location is located at a point where the optical axis pierces the object plane.

Referring to FIG. 1B, the mirror 118 collects radiation 150 emitted by the light source 114 and transfers the radiation 150 to the relay mirror 126 as radiation 140 via reflection off the mirror 122. The system also includes a reticle 144 that is placed in optical communication with the IU and the PO. Reticle 144 carries a spatially dense one-dimensional pattern and is positioned to be irradiated by radiation 148 delivered from light source 114 and reflected by relay mirror 126 to reticle 144 via vision barrier 134A. As shown, reticle 144 is a photomask that operates in reflection (in a related embodiment, the reticle may optionally be configured as a transmissive reticle). It is also intended that the surface of the substrate of the reticle 144, 144' bearing the one-dimensional pattern may be spatially curved (in which case the reflective reticle has non-zero optical power) or spatially flat (with substantially zero optical power), depending on the particular implementation of the systems 100 and 102. In the example shown in fig. 1B, this surface of reticle 144 is substantially planar. In the example shown in fig. 1C, such a surface of reticle 144' is spatially substantially curved.

Furthermore, the one-dimensional pattern on the reticle may judiciously be distorted in a manner suitable for compensating for the undesirable distortion of the PO. When the one-dimensional pattern carried by the reticle is configured as a linear diffraction grating of appropriately sized, the reticle 144 diffracts radiation 148 incident thereon to form diffracted beams comprising spatially distinct beams 152A, 152B, the beams 152A, 152B representing different diffraction orders (in one example, +1 diffraction order and-1 diffraction order), respectively, and propagating toward the mirror 130 of the PO (which may appropriately block zeroth order diffraction from doing so). The first mirror 130 and the second mirror 134 of the PO in combination redirect the diffracted beams through the vision barrier 130A to the workpiece or substrate 156 of interest to expose at least one layer of photoresist bearing an image of the one-dimensional pattern of the reticle 144 thereon.

It should be appreciated that in accordance with the present inventive concept, the reticle is disposed in a substantially fixed spatial and optical relationship with respect to the IU and PO subsystems, since once the reticle is selected and defined within the one-dimensional EUV exposure tool, both the position and orientation of the reticle are fixed (except for some small adjustments that may be required to maintain focus and alignment). The term "substantially fixed relationship" refers to and defines the situation when the position of the reticle is still likely to be subject to some small adjustment, the mechanical support of the reticle lacking structure configured to scan the reticle in motion synchronized with the motion of the wafer stage during operation of the exposure tool, the small adjustment being of sufficient magnitude to correct errors in any of focus, magnification and alignment during operation of the exposure tool.

The systems 100, 102 may also include in some embodiments: a fixed or variable size aperture 160 (e.g., having a particular shape of variable slit; interchangeably referred to as a "pattern shutter (pattern blind)" or a "shutter field stop (blind field stop)" or simply a "field stop") appropriately disposed within the IU (as shown-between the mirrors 122, 126), which IU may be disposed to be substantially optically conjugate with the reticles 144, 144'; light stops or apertures 164 (sized to match the desired shape of the incident light of PO; a stage/mounting unit (not shown) that supports the reticle; wafer stage 156A, equipped with an appropriate stage mover (not shown) to provide scanning of wafer 156 relative to reticle 144 and beams 152A, 152B as required by the photolithographic exposure process; and other auxiliary components as needed (e.g., vacuum chamber, metrology system, and temperature control system). The x-axis is defined as being perpendicular to the axis along which the system is scanned during operation, and the y-axis is defined as being parallel to this scanning axis. In embodiment 102, the one-dimensional pattern includes lines parallel to the Y-axis.

As shown in the generalized schematic 100 shown in fig. 1A, the system further comprises a control unit (control electronics circuitry) optionally equipped with a programmable processor and configured to manage operation of at least the wafer stage, and in some embodiments at least one of the light source, IU and PO subsystem.

FIG. 1C schematically illustrates an embodiment 170 of the one-dimensional EUV system 100, wherein-compared to the embodiment 102 illustrated in FIG. 1B-the relay mirror 126 is removed. When the structure of reticle 144 'is configured to operate in reflection, reticle 144' images mirror 122 into the incident light of the PO subsystem. Upon transmission from the light source 114, a beam of radiation 180 traverses the field stop 160', the field stop 160' being disposed against the reticle 144' (as shown) or alternatively against the wafer 156 (as shown schematically in dashed line EE) across a beam of radiation diffracted by the reticle pattern toward the PO subsystem. The approximate distance separating the field stop 160' (when present) from the reticle is generally less than 3 millimeters, preferably less than 1 millimeter, more preferably less than 100 micrometers, and even more preferably less than 50 micrometers. In the example shown in fig. 1C, the surface of the reticle (pattern source) 144' may be spatially curved. The size of the field stop 160 'may be adjusted such that the diffracted beams 152A, 152B pass through the opening of the field stop 160'.

The one-dimensional EUVD exposure tool is further supplemented with a control unit (control electronics circuitry) optionally equipped with a programmable processor and configured to manage operation of at least the wafer stage, and in some embodiments at least one of the light source, IU, and PO subsystem, as shown in fig. 1A, 1B. (for purposes of illustration brevity, FIG. 1C does not show control units otherwise presented.)

Coordination between light sources, IU subsystem, and PO subsystem.

Those skilled in the art will readily appreciate that in accordance with the disclosed concepts, in one example, an embodiment of the IU as a whole is configured to operatively correspond to and be optically optimized with an embodiment of the PO containing reflection astigmatism, as discussed in detail in PCT/US2018/027785, the disclosure of which is incorporated herein by reference. The IU includes at least one mirror unit having a "fly eye" structure. (in one example, both mirrors 118, 122 shown in FIGS. 1B, 1C are configured as fly's eye mirrors, as discussed below).

Furthermore, IU should also be optimized for use with a light source (radiation source) formed from a laser-driven plasma-based source. An example of a light collection schematic of such a source (configured for use with an embodiment of the optical system of a one-dimensional EUV exposure tool) is shown in fig. 2A, 2B. Fig. 2A shows a configuration of a laser driven plasma light source with an ellipsoidal mirror ("collection mirror") sized to refocus EUV radiation received from the LPP to a secondary light source IF (which in turn acts as a light source for an embodiment of IU). A 5sr collector and 1.6sr sub-aperture configuration is schematically shown.

Fig. 2B is a schematic diagram of a light-based model of the laser-driven plasma source shown in fig. 2A, showing a collector 210 with a central opening 210A, a tin ejection orifice 214, and a secondary light source IF 216. The model of the source shown in fig. 2A, 2B includes an aperture and a vision block mask (formed by a combination of two reticles and rectangles) that set the boundaries of the gaussian irradiance distribution of the light scaled with distance from the location of the IF 216.

The model of the source further includes the following effects: i) Three-dimensional (3D) distribution of plasma emissions 218; (ii) elliptical specular aberrations, vision impairment, and reflectivity variations; (iii) visual impairment caused by tin ejection orifice 214. Further assume that the model of the source has: a) An ellipsoid collection mirror 210 of 650 mm diameter; b) A source having a numerical aperture NA defined by a 5sr solid angle; c) A roughly gaussian projected plasma 218 radiation profile with a 90 micron diameter (or about 210 microns at 1/e ² level) at Full Width Half Maximum (FWHM). Has the following characteristics ofThe results of such a simulated projection of plasma distribution 218 are presented in fig. 2C. In the plot shown in fig. 2C, the irradiance of the EUV source is plotted along the vertical and horizontal axes representing coordinates on the local XY plane (the plane in which IF216 lies and is substantially perpendicular to the optical axis). FIG. 2D includes two plots showing the distribution of irradiance of an EUV source in two cross-sectional planes; d) IF216 with NA of 0.25; e) 20% of the central dish-shaped visual barrier 210A (formed as an axially symmetrical opening in the collection mirror 210 at a diameter of about 130 mm); and f) 15% of the linear visual barrier (100 mm width) caused by the tin jet 214. The reflectivity of the reflective surface of collector 210 is assumed to be about 50%; the effective diameter of the IF216 that allows for instability of the laser driven plasma source is assumed to be about 2 millimeters. The modeled spatial distribution of light generated by the plasma source and the modeled spatial distribution of light at the plane of the IF216 can be assessed from: a) fig. 3A, 3B, which show intensity distribution, and B) a light spot diagram (ray-spot diagram) at the plane of the IF216 shown in fig. 4A, and c) a diagram of light ray directions at the same plane as shown in fig. 4B.

The illumination light is TONG.

In order to determine parameters of the illumination subsystem of the overall optical system of a one-dimensional EUV exposure tool, it is appropriate to construct ideal or target illumination conditions. To this end, a construction of the illumination light dose has to be performed (i.e. with an embodiment of IU, the angular distribution of light is forwarded to the substrate/reticle/pattern source 144, 144' carrying the one-dimensional pattern/one-dimensional diffraction grating). Details of the construction of light are disclosed in PCT/US 2018/027785.

To this end, fig. 5A-5G illustrate an example of a process for photofabrication of the disclosed optical system for a one-dimensional EUVD exposure tool. The purpose of this process is to define the opto-electronic geometry of the PO subsystem of the embodiment that facilitates optimizing (increasing) the contrast of imaging a substantially one-dimensional pattern located between the IU of the exposure tool and its PO subsystem onto a selected workpiece. To this end, an image is formed as a result of 2-beam interference (optical interference between +1 and-1 diffraction orders formed from light incident on a substantially one-dimensional pattern of the pattern sources 144, 144' (such as, for example, a one-dimensional diffraction grating) via an IU of an exposure tool) to the image plane when such a one-dimensional pattern is imaged onto the image plane, with the workpiece 156 placed therein. Zero order diffraction is minimized by proper design of the one-dimensional diffraction grating and/or blocked by an opaque component (e.g., element 160') in another embodiment. Since the etendue of ultraviolet light source 114 is much smaller than the required illumination/imaging etendue, the constructable region (solid angle) is maximized for achieving 100% contrast of illumination light. This should allow for a wider margin in the process of fabricating the patterned workpiece 156.

Referring to fig. 5A and 5B, the construction begins with illumination on the intersecting axis assuming a one-dimensional (single frequency) diffraction grating. Here, the beam 504 illuminating the one-dimensional diffraction grating of the element 144, 144' is shown on-axis (as viewed along the reference axis 204). Then, the +1 diffraction order beam formed at the grating (grating pitch Λ _min) appears at a point P (+1) separated by a distance λ/Λ _min from the center of the optical axis or reference axis. The light build process continues with the following operations: the circle 508 drawn with respect to the line pair passing through the point P (+1) is "reflected" with a radius equal to the numerical aperture NA required in image space (i.e. in the space of the workpiece on which the one-dimensional diffraction grating is imaged from the elements 144, 144' by the PO subsystem) to obtain a borderline 510, shown in dashed lines in fig. 5A. The ideal shape of the illumination field that maximizes Ω _IU and image contrast, i.e. the spatially distributed light delivered to the elements 144, 144' via the IU of the one-dimensional EUV exposure tool, is then exhibited by the overlapping region of the two circles 508, 510. The area 514 outlined by the overlap between circles 508, 510 represents Ω _IU and corresponds to the illumination light field (i.e., the angular distribution of light incident on the substrate/reticle 144 shown in fig. 1 carrying the one-dimensional pattern/one-dimensional diffraction grating). The geometric parameters of the illumination light flux 514 relative to the parameters of the curve 508 are indicated in fig. 5B.

Indeed, it may be of interest not to a single value but to a series of values of the period of the substantially one-dimensional pattern on the elements 144, 144'. Thus, in addition to Λ _min (which represents the minimum value of the one-dimensional grating period of interest), a value Λ _max is also introduced which refers to the maximum value of this period. (when and if propagation of the zero order diffracted beam between the elements 144 and 144 'and the workpiece via the PO subsystem is blocked, as a result of imaging the one-dimensional grating from the elements 144, 144' onto the workpiece 156 via embodiments of the PO subsystem, the one-dimensional grating period value is halved, as will be readily appreciated by those skilled in the art.)

Referring now to fig. 5C and 5D, each of fig. 5C and 5D shows an outer boundary 508 of the imaging light, the earlier determined lobular illumination light 514 operating as a light source for the PO subsystem is shown centered substantially on the reference axis 204. The imaging light intensities corresponding to the imaging of the one-dimensional grating at the period Λ _min are shown as regions 532A and 532B within boundary 508 for the +1 diffraction order beam and the-1 diffraction order beam, respectively. The imaging light intensities corresponding to the imaging of the one-dimensional grating with a period of Λ _max are shown as regions 534A, 534B for the +1 diffraction order beam and the-1 diffraction order beam, respectively. In fig. 5E, boundary 540 outlines two regions 544A, 544B of overall aggregate imaging light configured to represent imaging of a one-dimensional grating at any period lying within a range between Λ _min and Λ _max, inclusive of Λ _min and Λ _max. The same two regions 544A and 544B (shown as regions a and B in fig. 5F) correspond to a combined solid angle Ω _PO that is encompassed by the aggregate imaging light of the PO subsystem. Fig. 5 additionally sets forth, column by column, the values and/or dimensions of specific examples of imaging light of the PO subsystem for the cases na=0.4, λ=13.5 nanometers, Λ _max =60 nanometers, and Λ _min =40 nanometers. Here, circle 508 with radius na=0.4 represents the numerical aperture of the distribution of light incident on the image plane via an embodiment of the PO subsystem. (the workpiece on which the image of the one-dimensional diffraction grating of the pattern source 144, 144' is formed is disposed at this image plane). Region 514 represents illumination light TOT including solid angle Ω _IU. The combined region A, B represents the aggregate imaging light fraction of the PO subsystem that includes solid angle Ω _PO.

First level layout of IU.

Fig. 6A schematically illustrates a first stage unfolded layout of an embodiment of an illumination unit comprising a relay mirror 126 and configured to operate with a substantially flat or planar reticle 144, wherein each of the mirrors FE1 and FE2 in an array (corresponding to and representing the mirrors 118, 122 illustrated in fig. 1B and 1C, respectively) is shown as containing a plurality of sub-aperture mirror elements (and, for simplicity of illustration, as three operatively equivalent sub-aperture lens elements). An embodiment of the IU is configured to operate with a single secondary light source IF 216. For simplicity of illustration, the sub-apertures of mirrors FE1, FE2, each having a designated area a _i and focal length f _i (or optical power Φ _i), are drawn as equivalent lens elements.

Fig. 6B shows a first level layout of a single channel (i.e., illumination channel defined by the respective corresponding fly-eye elements or sub-apertures of the FE1 and FE2 mirrors) of the overall embodiment of the IU shown in fig. 6A. Here, the chief ray is selected as the ray passing through the center of the incident light of the PO subsystem from the off-axis point of the one-dimensional pattern, and the edge ray is defined as the ray passing through the maximum aperture of the incident light of the PO subsystem from the axial point of the object (one-dimensional pattern).

In contrast, fig. 16A schematically shows a first stage unfolded layout of an embodiment of IU, the illumination unit comprising only two mirrors (mirrors or mirror arrays of which FE1, FE2 are arrayed) and configured to operate with a reticle 144' in which a substantially one-dimensional pattern is provided at a curved surface. Here, each of the mirrors FE1 and FE2 in an array (corresponding to and representing the mirrors 118, 122 shown in fig. 1B, 1C, respectively) is shown as containing a plurality of sub-aperture mirror elements (and, for simplicity of illustration, as three operationally equivalent sub-aperture lens elements). An embodiment of the IU is configured to operate with a single secondary light source IF 216. For simplicity of illustration, the sub-apertures of mirrors FE1, FE2, each having a designated area a _i and focal length f _i (or optical power Φ _i), are drawn as equivalent lens elements.

Fig. 16B shows a single channel first order layout of the overall embodiment of IU shown in fig. 16A (i.e., illumination channels defined by corresponding fly-eye reflective elements or sub-apertures of FE1, FE2 mirrors, respectively). In this embodiment, no relay mirrors are required, as the curved reticle of pattern source 144' images the FE2 mirror array onto the entrance pupil of the PO subsystem. Here, the chief ray is selected as the ray passing through the center of the incident light of the PO subsystem from the off-axis point of the one-dimensional pattern, and the edge ray is defined as the ray passing through the maximum aperture of the incident light of the PO subsystem from the axial point of the object (one-dimensional pattern).

In practice, the values h ₁、h₂、h₃、t₀ to t ₃ -and the optical powers of FE1, FE2 and relay mirrors are determined based on: i) The size of the image of FE1 at the optically conjugate surface 144, 144' and the size of the image of FE2 at the optically conjugate surface of the incident light of the PO subsystem; ii) the propagation angle of the chief ray and the edge ray; iii) The size h ₀ of the light source 216; iv) the size of the one-dimensional pattern h ₄; v) the size h ₅ of the incident light TONG EP; and vi) a separation distance t ₄ from the surface 144, 144' to the EP.

Examples of IU: reflecting mirror

One embodiment of the IU assumes a 16.5 mm wide diamond exposure field (in one specific case-16.6 mm wide diamond field) on the workpiece/wafer that enables proper engagement of the exposure field. It is also assumed that zero order diffracted light from the one-dimensional pattern (diffraction grating) on the reticle 144, 144 'is blocked such that optical interference of the beams 152A, 152B (representing +1 diffraction orders and-1 diffraction orders at the elements 144, 144') doubles the spatial frequency at the workpiece/wafer and also enables near normal incidence illumination (near normal incidence illumination) to be achieved. (proper blocking of the zero-order diffracted beam may be achieved by the central vision barrier of the PO subsystem, if desired).

Each of the fly's eye arrays (FE 1, FE 2) of mirrors 118, 122 is configured to capture and reflect radiant energy acquired from a radiant object (e.g., light source 216) with a respectively corresponding two-dimensional array of mirror elements (alternatively referred to as "facets" or "eyes"). Such an array of mirror elements or facets may be referred to as a "fly-eye mirror" (or even as a "fly-eye lens", as sometimes practiced in the art), normally without the aid of additional larger viewing lenses and/or mirrors.

The arrangement and orientation of array FE1 (optical element 118 in fig. 1B and 1C) is a result of a tradeoff between the number of constituent elements (sub-apertures) of the array, the luminous flux, and the dose uniformity. When a single (secondary) light source 216 is employed with a one-dimensional EUVD system employing an embodiment of an IU configured in accordance with the inventive concepts, the IU generally contains a single array FE1. However, in some embodiments, as described below, an IU may employ multiple FE1 arrays.

The schematic diagram shown in fig. 7A illustrates the size and orientation (as compared to the distribution shown in fig. 3A) of a sub-aperture 710 (shown as a grid) superimposed on the plot of irradiance distribution produced by IF 216 at a distance of about 100 millimeters below (along) the optical axis; the final size of the sub-aperture is scaled to match the actual IF distance. Fig. 7B provides a corresponding schematic diagram of neutron aperture 710 in angular space. Sub-apertures 710 located outside the outer boundary 714 of the irradiance distribution and sub-apertures located within the boundary 716 of the central vision barrier are not included in the FE1 array actually implemented, as they are intended to reduce radiation dose uniformity. The arrayed mirrors FE1 are optically conjugated to the surface of the pattern source or reticle 144 (see fig. 6B), so the diamond shape of the selected sub-apertures 710 is a primary indication of the shape of the irradiance distribution at the surface 144. Such a shape of the individual sub-apertures of fly's eye mirror FE1 is chosen based on the following idea: the exposure field on the workpiece 156 (during operation of the one-dimensional EUVD exposure tool) is offset by half the field width at a time such that each point at the workpiece 156 is exposed twice and receives the same radiation dose. The actual object here is to provide a uniform radiation dose on the workpiece while maximizing the light efficiency of the optical system of the one-dimensional EUV tool. The characteristics of some of the column-by-column traces of an embodiment of an FE1 array mirror are summarized in FIG. 7A.

Evaluation of the FE1 array also included calculating the static irradiance distribution at the reticle by summing the distribution within each element with a blue profile and estimating the scanned dose of radiation by integrating the reticle irradiance in the y-direction. The step of estimating dose uniformity while "stitching" the sub-apertures together and the step of determining operationally acceptable non-uniformities (in one case-about 1%) end up evaluating the FE1 array mirrors. The assessment of the uniformity of irradiance distribution at the optically conjugate surface 144 is shown in fig. 7C to be better than about 0.5% across the surface of the FE1 array.

A schematic 800 of an FE2 array mirror (e.g., optical assembly 122 in fig. 1B, 1C) configured to forward light from the FE1 array to reticle 144 is shown in fig. 8. When a single light source 216 is used with a one-dimensional EUV system, the number of elements (sub-apertures) in FE2 array 800 is the same as the number of elements in FE1 array 700, so the process of designing FE2 800 is essentially a problem of identifying elements 810 such that individual images of secondary source IF 216 (formed by the combination of each element 710 with a respective corresponding element 810) are substantially uniformly distributed within optimal illumination light 514 at the surface of pattern source 144. Thus, the shape of the outer boundary 824 of embodiment 800 substantially corresponds to the shape of the outer boundary of illumination light 514.

The hexagonal shape of the sub-apertures 810 is in fact a reasonable choice, and thus the shape provides dense uniform tiling of the surface of the FE2 array 800. Fig. 8 shows 200 sub-apertures or elements 810 (each 0.0136 radians wide in image space) that fill 88% of the optimal etendue.

It will be appreciated that when the only single light source is used in an embodiment of a one-dimensional EUV system, each subelement or sub-aperture of the FE 1-arrayed mirror projects an image of that source into the associated/corresponding subelement or sub-aperture of the FE 2-arrayed mirror. In other words, there is a one-to-one correspondence between the elements of the two arrays that satisfies two requirements: a) Two (or at least once about the y-axis) symmetries to maintain zero image offset about the z-axis motion of the workpiece on which the reticles 144, 144' are imaged by the PO subsystem, and b) maximum light uniformity to reduce the coherence of the source (at FE 2).

Embodiments of IUs for use with multiple radiation sources

It should be noted, however, that embodiments of IU may be configured to operate with multiple light sources instead of one light source based at least in part on optical power considerations. For example, in contrast to the embodiments shown in fig. 1B and 1C (where a single light source 114 is schematically indicated) and with further reference to fig. 9, a specific example of an IU900 is shown configured to operate with multiple light sources. Here (and with reference to fig. 2B for an illustration of secondary light source IF 216) two light sources are shown that provide light to the IU: 216-a and 216-B.

Specific examples of illuminator 900 are configured to provide:

A blade-like illumination pattern (for a one-dimensional pattern with a period of tens of nanometers) selected for maximum incoherence of light suitable for no contrast loss;

Two first "fly's eye" mirror arrays FE1-a and FE1-B (shown as 910-a and 910-B, each containing sub-apertures with diamond-shaped perimeters or individually constituting mirror elements 910);

A single second "fly's eye" mirror array FE2, 922, a tile configuration formed by individual hexagonally structured mirror elements 922-i to define a leaf-like aperture (shown as 824 in fig. 8) and to effectively combine light inputs LA, LB received from multiple light sources 216-a, 216-B while maintaining etendue, and

Curved relay mirrors 126, 926 as part of the lighting unit (relay 926 is not shown in fig. 9 when configured according to the design shown in fig. 1B);

As shown, light from light source 216-A is captured by mirror FE 1-A; light from light source 216-B is captured by mirrors FE 1-B; light reflected by FE1-A and FE1-B is captured by FE 2. As can be seen from the perspective of the position of the individual sub-apertures, each individual mirror element or sub-aperture forms an image of the corresponding radiation object. Stated differently, in this embodiment, there is one unique element in FE1-A or FE1-B associated with each element of FE2 (but not in both). Thus, as implemented, each of the individual mirrors of FE1-A and FE1-B has a respective corresponding mirror element in the mirrors of the array of FE 2. For example, individual mirrors 910-i of array FE1-A form an image of light source 216-A at individual mirrors 922-i of array FE2, while individual mirrors 910-j of array FE1-B form an image of light source 216-B at individual mirrors 922-j of array FE 2.

It should be appreciated that the embodiment 900 of the proposed IU provides an image plane 934 between the FE-2 mirror 922 and the relay mirrors 126, 926 (if present). This plane is optically conjugate to both the pattern source 144 and the plane of the workpiece/wafer 156 (see fig. 1B, 1C), and provides the appropriate location to position the (optionally variable size) aperture 160 to control the dose of radiation power delivered to the reticle 144 and define the boundaries of the exposure field formed at the wafer. If no relay mirrors (126, 926) are present, then the pattern sources 144 and 144' with diffraction gratings present thereon are placed at plane 934. For additional information regarding this design, the reader is referred to the examples disclosed in U.S. patent application 15/599,148, for example.

As shown, fig. 9 shows tilted elements (sub-apertures) 922-i of FE 2-arrayed mirror 922, tilted elements (sub-apertures) 922-i being configured to produce overlapping images of elements (sub-apertures) 918-i, 918-j of FE1-A, FE-B-arrayed mirror on reticle/pattern source 144 (possibly via some additional relay optics, such as relay mirror 126). However, the same effect can be achieved by placing the elements 922-i of the FE2 array of mirrors 922 on a properly curved convex surface. In practice, it may additionally be desirable to "scramble (scramble)" the fly's eye mirror optical channels (so that both mirrors in arrays of FE1 and FE2 in the constituent sub-mirror elements have many different inclinations) to create uniformity of the optical power.

The aperture 824 defined by the second fly's eye mirror array 800, 922 is not necessarily limited to only a blade shape. For example, in a related embodiment, may be bowtie-shaped (rectangular-shaped). At this time, the mirror arrays 800, 922 may have different sizes in two orthogonal directions.

Those skilled in the art will readily recognize that in each of the above designs (one containing a single light source 216 and a single FE 1-arrayed mirror, and one containing more than one light source and corresponding more than one FE 1-arrayed mirror, respectively), there are no more than three consecutive reflections of a beam of light (EUV radiation) propagating from the EUV source via the IU towards the reticle/pattern source (and only two reflections in the absence of the relay mirror 126, see the embodiment shown in fig. 1C), which yields a significant improvement in optical transmission over the more complex designs of the related art. Each mirror employed in the EUV spectral region typically has a reflectivity of only 65% to 70%. The number of reflections is thus reduced by about half compared to existing designs used in generic EUV machines, and thus the amount of light transmitted via the IU of an embodiment of the present invention is roughly doubled compared to generic EUV systems. Indeed, the transmission through the system can be estimated as the value of X≡where X is the typical reflectivity (65-70%) and N is the number of reflections. In a conventional generic EUV system, an IU has at least five (or more) mirrors arranged in sequence, while one embodiment includes as few as three or fewer mirrors. Thus, for embodiments of the present invention, the transport of an embodiment of IU increases from about 11% to 17% (for a general EUV system with five mirrors) to about 27% to 34%.

Once the existence of the PO subsystem is considered, the operational improvement effect will be more pronounced. Indeed, a typical PO subsystem for a typical universal EUV tool employs about six mirrors, while only two mirrors (primary and secondary) are used in embodiments of the present invention. See, e.g., PCT/US2018/027785. In this case, the transmission rate of 0.9% to 2% for a typical generic EUV system (which includes transmissions via IU and PO, but does not include the presence of a reticle) increases by an order of magnitude to about 12% to 17% when using embodiments of the present invention.

Embodiments of monolithic optical element strings.

Use of a flat pattern source.

Fig. 11A provides a schematic diagram of a global on-optical-axis optical train 1100 of a one-dimensional EUV system configured to image a substantially one-dimensional pattern (e.g., a diffraction grating having a period of tens of nanometers) disposed on a planar substrate of a pattern source 144 onto a workpiece 156. (for this reason, the diagram shown in FIG. 11A substantially corresponds to the diagram shown in FIG. 1B). In FIG. 11A, rays connecting the "edge" of source 210 with the "edge" of relay mirror 126 are shown and may be considered as chief rays. The function of the relays 126, 926 is to image a uniform distribution of irradiance on the arrayed mirror FE2 onto the pattern source 144. Numeral 1120 designates the location of a plane optically conjugated to the flat pattern source 144.

Referring again to fig. 11A, the optical path of EUV radiation (represented by the dash-dot line) propagating from the radiation source to IF 216 to FE1 118 to FE 2122 and then to relay mirror 126 to form an EUV beam directed to irradiate pattern source (reticle) 144 is folded in a first plane. Two beams of EUV formed at a substantially one-dimensional pattern of the pattern source 144 and representing different diffraction orders propagate in a second plane that is substantially transverse (and in the specific case-orthogonal) to the first plane as a result of diffracting the EUV beam incident on the pattern source from the relay mirror.

It should be noted that-with reference to the embodiments shown in fig. 1B, 1C and according to the schematic diagram shown in fig. 11A-the plane of symmetry of the one-dimensional EUV system 102, 170, 1100 is preferably parallel to the yz plane (as shown in the local coordinate system) to reduce the angle of incident EUV radiation on each mirror, which increases the reflectivity values that can be achieved during operation of the system. Such an arrangement is advantageous in minimizing the overall number of mirrors disposed in the optical path from the light source to the reflective reticle. It should be noted that in such a configuration, the axis along which the FE2 mirror array has a larger extent (shown as the Y-coordinate in fig. 8) and along which the lines of the substantially one-dimensional pattern of the pattern source extend may lie in a first plane.

Although specific values and examples have been selected in this disclosure, it should be understood that the values of all parameters can be varied over a wide range to accommodate different applications within the scope of the claimed invention. For example, in a related embodiment, the pattern source 144 may be located in a sub-aperture of the array 118, 700 (i.e., in the constituent individual reflective elements of the arrays 118 and 700) -e.g., in a space provided in the center 1010 of the array FE1, as seen in fig. 10A.

Fig. 11B is a schematic diagram showing the optical path of EUV radiation within an IU portion of optical train 1100 in a plane perpendicular to the plane in which the diffracted beam of radiation is formed at pattern source 144. Here, the relay mirror 126 operates at a magnification of-1; and the mirrors 134, 130 of the PO objective are shown in dashed lines. As is apparent from fig. 11B, the divergent light beam from the intermediate focus IF (light source 114, secondary light source 216) is incident on FE 1. Each reflective element of FE1 reflects and converges this incident beam to form a convergence point on or near the reflective surface of FE 2. These points are substantially optically conjugate to the intermediate focus IF. The beams reflected by the reflective surfaces of FE2 overlap each other on surface 1120. Such surface 1120 may be a surface that is optically conjugated to the surface of the pattern source 144. The light beam that passes through surface 1120 is reflected by relays 126, 926 and reaches pattern source 144. Here, the location (a portion of surface 1120) optically conjugate to pattern source 144 may be located on one side of pattern source 144. Furthermore, the beam reaching the relay 126, 926 from FE2 may be close to the optical axis in its propagation (in the figure, one-dot CHAIN LINE). The beam reaching FE2 from FE1 may approach the optical axis (in the figure, the dashed-dotted line) as it advances. The relays 126, 926 may be positioned with their axes tilted with respect to the optical axis of the projection objective PO (indicated by the two optical elements 134, 130 shown in dashed lines). In other words, the reflective surfaces of the relays 126, 926 may be tilted with respect to the optical axis of the PO. The principal ray of light (chief ray) may be substantially parallel to the optical axis of the projection objective PO along its direction from the relay 126, 926 to the pattern source 144.

Use of a curved pattern source.

The use of a curved pattern source 144' (i.e., a pattern source whose substantially one-dimensional pattern is disposed in a curved surface as compared to the use of a substantially planar pattern source 144) may result in a substantially reduced length of the PO subsystem of a one-dimensional EUV lithography tool (and a variation of the PO subsystem as discussed with reference to fig. 12 of 62/487,245 may then be employed, for example).

To this end, referring to fig. 14A and 14B, in one specific design of an optical element string of a one-dimensional EUV system, there is a curved pattern source provided in the individual reflective elements of the first mirror of IU 1400, in which case the radiation received by mirror 1400 from radiation source 126 is transferred to mirror array 1450 (which is substantially identical to mirror 800 and in turn directly forwards the radiation to pattern source 144', there being no relay mirror element 126 in the system when the pattern source is substantially flat). In the particular design shown in fig. 14A, 14B, about forty reflective elements 1410 of fly's eye array mirrors FE1, 1400 are optically imaged onto pattern source 144' at unit magnification by about forty reflective elements 1460 (of fly's eye mirrors FE2, 1450). The elements 1410 of FE1 are generally configured to have an elliptical or spherical surface. In one embodiment, the curved pattern source 144' may comprise a one-dimensional phase diffraction grating that is about 20 millimeters to 30 millimeters wide (angle to angle; in one case-about 25 millimeters) having a radius of curvature of about 450 millimeters to 490 millimeters (in one case-about 473 millimeters) and having a sag of about 400 micrometers to 800 micrometers (in one case-about 660 micrometers). The individual reflective elements 1460 of FE2 are spherical with substantially equal radii of curvature, but are tilted at different angles with respect to the selected reference to place the image of the individual elements 1410 on the pattern source 144'. Specifically designed element 1460 has a radius of curvature of about 410 millimeters to about 430 millimeters (in one case-about 419 millimeters) and a diameter of several millimeters (in one case-about 2.3 millimeters). In fig. 14B, the reflective surface of the reflective element 1460 may be hexagonal in shape. The plurality of reflective elements 1460 may be formatted as a spatially closely packed array.

In fig. 15 a specific non-limiting embodiment 1500 of a string of optical elements of a one-dimensional EUV system with a curved pattern source 144' (arranged in the center of the FE1 mirror array) is shown. Here, EUV radiation flux 1520 received from the EUV radiation source is diverted toward mirror 1400 using fold mirror 1510, mirror 1400 further reflecting EUV radiation toward mirror 1450, mirror 1450 in turn imaging mirror 1400 onto pattern source 144'. The pattern source 144 'projects the radiation toward the primary mirror M1 and further toward the secondary mirror M2 of the PO subsystem by diffracting the radiation, which forms an optical image of the pattern source 144' on the surface of the workpiece 156. In this design, mirror 1450 serves the additional purpose of blocking the propagation of the zeroth order diffraction of EUV radiation formed at pattern source 144' towards the projection optics subsystem and into the PO subsystem.

It should be appreciated that, as in the case of the embodiment shown in FIG. 11A, the mirror array 1400 containing the pattern source 144 'in its individual mirror elements 1410 is optically conjugate to the pattern source 144' (see the optical system shown in FIG. 15). Thus, the shape of the individual mirror elements 1410 of the array 1400 is a primary indication of the shape of the irradiance distribution of EUV radiation at the pattern source 144'. When the overall shape of the pattern source 144' and the individual elements 1410 is rhomboid, for each pass of the scanner of the one-dimensional EUV system over the workpiece, the exposure of the workpiece 156 to EUV radiation is offset by half the exposure field so that each point at the workpiece is exposed twice and receives the same radiation dose. By configuring the exposure system and process in this manner, the aim is to provide an extremely uniform dose of radiation on the workpiece while maximizing the radiation efficiency of the overall system.

Further, it should be appreciated with reference to FIG. 15 that the preferred location of FE2 mirror array 1450 can be on an axis of the system. In related embodiments, the substrate supporting the FE2 mirror array may be a substantially planar substrate or a spatially curved substrate. In general, the curved pattern source or reticle 144' may be aligned on or off the optical axis of the system. Although the schematic diagram shown in fig. 15 shows that the angle at which radiation 1520 is incident on fold mirror 1510 is substantially different from normal incidence, in related embodiments, a one-dimensional EUV system may be configured to ensure that the flux of radiation 1520 is incident on fold mirror 1510 at an angle as close as possible to normal incidence to increase reflectivity over a specified wavelength range. In another related embodiment, the one-dimensional EUV system may optionally be configured such that the incidence of the radiation 1520 onto the fold mirror 1510 is substantially grazing incidence (grazing incidence). In yet another related embodiment, a one-dimensional EUV system may be configured to avoid the use of folding mirrors and deliver radiation from an EUV source directly onto the FE1 mirror 1400 array.

In general, it should be appreciated that the radiation relayed by the substantially one-dimensional pattern (e.g., diffraction grating pattern) of the pattern source 144, 144' is projected onto an image plane (surface of the workpiece 156) by an embodiment of the PO objective lens (such as discussed in PCT/US 2018/027785). In this embodiment (see the specific designs shown in fig. 7A, 7B, 8, 10A, 10B, 14A, 14B), in general

The spatial extent FE1-D of the mirrors of the array of FE1 sub-apertures in rhomboid form with a side of about 14 mm is in the range of about 220 mm and 270 mm (in one embodiment-about 240 mm);

The spatial extent FE2-D of the mirrors corresponding to the array FE2 and FE2-D lie between about 60 and 85 mm along the long axis of the "blade" of the mirrors, and between about 20 and 30mm along the short axis of the "blade", respectively. (in one embodiment-78 mm and 25 mm, respectively). In such an example, the range of individual hexagonal mirror elements 810 of the FE 2-arrayed mirrors is about 3 millimeters; and

Concave relay mirror 126 has a radius of curvature between about 1900 mm and about 2300 mm (about 2190 mm in the example), a major axis diameter between about 140 mm and 180 mm (about 160mm in the example), and a minor axis diameter between about 65 mm and 85 mm (about 75 mm in the example).

In one embodiment, the overall length of the system measured from the vertex of collector 210 to the location of image plane 156 is about 3 meters.

In one embodiment, the power requirement of the secondary light source 216 is estimated to be about 51 watts based on the following assumption: a) Having a reflectivity of about 65% on each of the six mirrors of the optical system-FE 1, FE2, relay mirror, reticle with one-dimensional pattern, and primary and secondary mirrors-of the PO subsystem; b) A resistance of 30mJ/cm ² at the image plane at the workpiece/substrate; c) IU has a geometric efficiency of 85%; d) The grating of the one-dimensional pattern of the mask plate has a diffraction efficiency of 25%; e) A one-dimensional EUVD exposure system has a throughput of 100 workpieces per hour; and f) acceleration and overhead of 10 seconds per workpiece or wafer.

Referring again to fig. 11B, 11A, 15 and with further reference to fig. 12A, 12B, EUV radiation beam 148 from the radiation source is delivered by the last mirror in the order of mirrors presented in a given embodiment of IU to an axial point of the pattern source 144, 144' (i.e., a point of the pattern source 144, 144' lying on the optical axis AX, see fig. 12A) or an off-axis point of the pattern source 144, 144' (see fig. 12B). (in embodiments employing a flat pattern source 144, such last mirror in the sequence is typically a relay mirror 126, while in embodiments employing a curved pattern source 144', such last mirror is typically a second fly's eye mirror 122). The radiation is then diffracted at the substantially one-dimensional pattern of the pattern source 144, 144' to form two diffracted beams 152A, 152B propagating on opposite sides of the beam 148. (in other words, the EUV radiation beam incident on the pattern source from the last mirror of the IU unit propagates between two diffracted beams formed at the pattern source as a result of diffracting this incident beam in a substantially one-dimensional pattern of the pattern source).

Referring now to fig. 15, 17A, 17B, 17C and 17D, fig. 17A to 17D illustrate a portion of an embodiment of a one-dimensional EUV system, which shows: IU containing first fly-eye mirror array FE1 and second fly-eye mirror array FE 2; a pattern source 144' containing a substantially one-dimensional pattern on the curved surface; and a PO subsystem including mirror elements M1 and M2. Here, fig. 17A shows the optical path of EUV radiation from the FE2 mirror array to the curved reticle 144'; FIG. 17B shows the optical path of EUV radiation from the FE1 mirror array to mirror M1 of the PO subsystem via curved reticle 144'; FIG. 17C illustrates the optical path of radiation from the FE1 mirror array to the image plane at the workpiece 156 (here, only the chief ray is shown in the optical path from FE1 to the curved reticle 144'); and FIG. 17D illustrates the optical path of radiation from the curved reticle 144' to the image plane 156. These optical path diagrams appear in planes parallel to the plane in which the EUV radiation beam diffracted at the curved reticle 144' propagates.

Thus, those skilled in the art will readily appreciate that the disclosed embodiments of IU and one-dimensional EUV lithography systems employing such IU illumination units represent an overall reflective system configured for use in conjunction with a spatially curved reflective pattern source bearing a substantially one-dimensional pattern thereon:

When a single EUV radiation source is used, such a reflective IU system comprises a combination of only two (no other) optical mirrors arranged in sequence with respect to each other to transfer EUV radiation incident on the first optical component (from the only three optical components) onto the pattern source. The first optical mirror is a first fly's eye array constituting individual reflective elements. The second optical mirror is a further second array of fly's eye mirrors constituting individual reflective elements which in operation receive EUV radiation from the first fly's eye mirror. Each of these only two optical mirrors has a corresponding non-zero optical power. Such a combination of only three mirrors is disposed in a substantially fixed spatial and optical relationship with respect to the pattern source. Reflection IU represents an illumination unit of a one-dimensional EUV exposure tool (grouping of optical elements comprising a combination of the only two optical components and a pattern source also forms and defines another reflection system.) the tool comprises a projection optics subsystem having a reference axis and configured to form an optical image of the pattern source with only two beams of radiation with a reduction factor of N >1 on an image plane optically conjugated to the pattern source. When EUV radiation is transferred via an IU onto a flat pattern source, this only two beams of radiation originate at the spatially curved pattern source. The PO subsystem of the supplemental IU is a reflective PO subsystem that includes only a primary mirror and a secondary mirror. At least one of the only two optical components of the IU includes a Fly Eye (FE) mirror. In one embodiment, the pattern source is positioned in (at least partially surrounded by) the constituent individual reflective elements of such fly's eye mirrors. The pattern source may comprise a phase shift mask.

In addition, the above system can be used to fabricate semiconductor devices using the process schematically illustrated in fig. 13A. In step 1301, the functional and performance characteristics of the device are planned. Next, in step 1302, a mask (reticle) having a substantially one-dimensional pattern (as described above) is designed according to the previous design step 1301, and in a parallel step 1303, a workpiece is made of a silicon material. In step 1304, a mask pattern formed according to the result of step 1302 is exposed to illumination radiation and an image of this pattern is transferred onto and formed in a workpiece using a lithography system employing one-dimensional EUV optics as described above. In step 1305, the semiconductor device is assembled (including dicing, bonding and packaging processes), and finally in step 1306, the device is then inspected.

Fig. 13B provides an example of a detailed flow chart detailing the step 1304 described above. As shown, at step 1311 (oxidation step), the workpiece surface is oxidized. In step 1312 (CVD step), an insulating film is formed on the workpiece surface. In step 1313 (electrode forming step), an electrode is formed on the workpiece using vapor deposition. In step 1314 (ion implantation step), ions are implanted into the body of the workpiece. The above steps 1311 to 1314 form pretreatment steps for the workpiece during processing of the workpiece, and selection of the operating parameters is made at each step according to the processing requirements.

At each stage of workpiece processing, when the above-described pretreatment steps have been completed, the following post-processing steps may be implemented. During post-processing, photoresist is first applied to a workpiece in step 1315 (photoresist formation step). Next, in step 1316 (exposure step), the circuit pattern of the mask (reticle) is transferred to the workpiece using the above-described exposure apparatus. The exposed workpiece is then developed in step 1317 (development step), and in step 1318 (etching step), the portions other than the remaining photoresist (exposed material surface) are removed by etching. In step 1319 (photoresist removal step), unnecessary photoresist remaining after etching is removed. A plurality of circuit patterns are formed by repeating these preprocessing and post-processing steps.

For purposes of this disclosure and the appended claims, the use of the terms "substantially," "approximately," "about," and the like when used in connection with a description of a value, element, property, or characteristic is intended to emphasize that those skilled in the art will understand that the referenced value, element, property, or characteristic, while not necessarily identical to that stated, may be considered identical to that stated for practical purposes. These terms, when applied to a specified characteristic or quality description, mean, for example, "almost", "mainly", "equivalent", "substantially", "essentially", "to a large extent", "substantially identical but not necessarily identical in whole" to reasonably represent the approximate language, and set forth the specified characteristic or description so that its scope will be understood by those skilled in the art. In a particular case, the terms "approximately," "substantially," and "about" as used in reference to a numerical value refer to a range of plus or minus 20% relative to the specified value, more preferably plus or minus 10% relative to the specified value, even more preferably plus or minus 5%, most preferably plus or minus 2%. As a non-limiting example, two values being "substantially equal" to each other implies that the difference between the two values may be within +/-20% of the value itself, preferably within +/-10% of the value itself, more preferably within +/-5% of the value itself, and even more preferably within +/-2% or less of the value itself.

The use of such terms in describing a selected feature or concept does not imply nor provide any basis for uncertainty and adding numerical limitations to the specified feature or description. As will be appreciated by one of ordinary skill in the art, the actual deviation of the exact value, element, or characteristic from the stated value, or characteristic, may fall within and vary from the numerical range defined by the experimental measurement errors that would normally exist using measurement methods accepted in the art for such purposes.

For example, reference to an identified vector or line or plane being substantially parallel to a reference line or plane should be understood as one vector or line or plane being the same as or very close to the reference line or plane (there is an angular deviation from the reference line or plane that is considered typical in the related art as being, for example, between 0 and 15 degrees, preferably between 0 and 10 degrees, more preferably between 0 and 5 degrees, even more preferably between 0 and 2 degrees, and most preferably between 0 and 1 degree). For example, reference to an identified vector or line or plane being substantially perpendicular to a reference line or plane should be understood as the normal to the surface of one vector or line or plane being located at or very close to the reference line or plane (there is an angular deviation from the reference line or plane that is considered typical in the related art as being, for example, between 0 and 15 degrees, preferably between 0 and 10 degrees, more preferably between 0 and 5 degrees, even more preferably between 0 and 2 degrees, and most preferably between 0 and 1 degree). For example, the term "substantially planar" or "planar" as used in reference to a given surface means that such surface may have certain irregularities and/or roughness that are sized and expressed, as will be generally understood by those of skill in the art in the particular situation under consideration.

Other specific examples of the meaning of the terms "substantially", "about" and/or "approximately" as applied to different actual scenarios may have been provided elsewhere in this disclosure.

Embodiments of the system generally include electronic circuitry (e.g., a computer processor) controlled by instructions stored in a memory to perform the specific data collection/processing and computing steps described above. The memory may be random access memory (random access memory, RAM), read-only memory (ROM), flash memory, or any other memory suitable for storing control software or other instructions and data, or a combination thereof. Those skilled in the art will readily appreciate that instructions or programs defining the operation of embodiments of the present invention may be delivered to a processor in many forms, including but not limited to the following: information permanently stored on non-writable storage media (e.g., read-only memory devices within a computer (e.g., ROM) or devices readable by an INPUT/OUTPUT (I/O) accessory of a computer (e.g., CD-ROM or DVD disks)), information stored on writable storage media (e.g., floppy disks, removable flash memory and hard disk drives), or information delivered to a computer via a communication medium including a wired or wireless computer network. Furthermore, although the present invention may be implemented as software, the functions necessary to implement the methods of the present invention may optionally or alternatively be implemented in part or in whole using firmware and/or hardware components (e.g., combinational logic, application SPECIFIC INTEGRATED Circuits (ASICs), field-Programmable gate arrays (Field-Programmable GATE ARRAY, FPGA), or other hardware) or some combination of hardware, software, and/or firmware components.

The scope of the invention recited in the claims attached to this disclosure is intended to be assessed in light of the overall disclosure. Various changes in the details, steps and components that have been described may be made by those skilled in the art within the spirit and scope of the invention.

Various modifications and changes may be made to the illustrated embodiments without departing from the disclosed inventive concepts. Furthermore, the disclosed aspects, or portions of aspects, may be combined in ways not listed above. Therefore, the invention should not be construed as being limited to the disclosed embodiments.

Claims

1. A reflective system having a reference axis and for use with a pattern source carrying a one-dimensional pattern thereon, the reflective system comprising:

A combination of only two reflective optical components, which are sequentially optically disposed with respect to each other to transfer extreme ultraviolet radiation onto the pattern source,

Each of the only two reflective optical components has a non-zero optical power,

The combination is disposed in a fixed spatial and optical relationship relative to the pattern source;

wherein the only two reflective optical components include a first reflective optical component and a second reflective optical component closest to the pattern source,

A first radiation path from the second reflective optical component to the pattern source, positioned between a second radiation path from the first reflective optical component to the second reflective optical component and a third radiation path originating from the pattern source,

The combination represents an illumination unit of an extreme ultraviolet exposure tool, a projection optics subsystem of the extreme ultraviolet exposure tool configured to form an optical image of the pattern source with only two beams of radiation with a reduction factor of N >1 on an image plane optically conjugated to the pattern source, an

The only two beams of radiation originate at the pattern source from the extreme ultraviolet radiation transferred onto the pattern source,

The only two beams of radiation originating at the pattern source pass along a first beam path and a second beam path, the first beam path and the second beam path being located in the third radiation path,

The direction of departure of the first radiation path from the second radiation path intersects the direction of departure of the first beam path from the second beam path at right angles.

2. The reflective system of claim 1 wherein at least one of the only two reflective optical components comprises a fly's eye mirror comprising an array of individual reflective elements.

3. The reflective system according to any one of claims 1 to 2, wherein the pattern source is positioned in a constituent individual reflective element of one of the only two reflective optical components.

4. The reflective system of claim 2 wherein the individual mirror elements of said one of the only two reflective optical components have a rhomboid shape.

5. The reflective system of any one of claims 1 to 2, wherein the pattern source comprises a phase shift mask.

6. The reflective system of any one of claims 1 to 2, wherein the pattern source is characterized by a non-zero optical power.

7. An extreme ultraviolet exposure tool, characterized by containing the reflection system according to any one of claims 1 to 5, the reflection system being configured as the illumination unit of the extreme ultraviolet exposure tool.

8. The euv exposure tool of claim 7, further comprising a workpiece positioned at the image plane and configured to be laterally movable in response to the reference axis.

9. The euv exposure tool of claim 7, wherein said one-dimensional pattern has a first spatial frequency, said optical image has a second spatial frequency, and wherein said euv exposure tool is configured to ensure that said second spatial frequency is at least twice said first spatial frequency.

10. A lithographic exposure tool having a string of optical elements positioned to deliver euv radiation to a target workpiece and for use with a pattern source, the string of optical elements comprising:

a lighting unit having two mirrors; and

A projection optics subsystem having a reference axis and positioned to receive first and second diffracted beams from the pattern source and to form an optical image of the pattern source with only the first and second diffracted beams at an image plane optically conjugate to the pattern source with a reduction factor of N >1,

Wherein the pattern source carries a one-dimensional pattern thereon and is configured to receive the extreme ultraviolet radiation delivered to the pattern source via the illumination unit and diffract the extreme ultraviolet radiation at the one-dimensional pattern to form the first diffracted beam and the second diffracted beam of the extreme ultraviolet radiation, wherein the one-dimensional pattern is disposed in a spatially curved surface,

Wherein the projection optics subsystem comprises a primary mirror and a secondary mirror,

Wherein at least one of the primary mirror and the secondary mirror contains two identically shaped reflective elements spatially disconnected from each other,

Wherein the two mirrors comprise a first mirror and a second mirror closest to the pattern source, an

A first radiation path from the second mirror to the pattern source, positioned between a second radiation path from the first mirror to the second mirror and a third radiation path of the first diffracted beam and the second diffracted beam,

Wherein the second mirror of the illumination unit is positioned to block propagation of a third beam of extreme ultraviolet radiation to a surface between the secondary mirror and the primary mirror,

Wherein the third beam of extreme ultraviolet radiation represents a zeroth order diffraction of the extreme ultraviolet radiation formed at the pattern source.

11. The lithographic exposure tool of claim 10, wherein:

Wherein the one-dimensional pattern has a first spatial frequency, the optical image has a second spatial frequency, and

Wherein the second spatial frequency is at least twice the first spatial frequency.

12. A lithographic exposure tool according to any one of claims 10 to 11, wherein the illumination unit contains only two mirrors.

13. The lithographic exposure tool according to any one of claims 10 to 11, wherein the pattern source is arranged in a fixed spatial relationship with respect to the illumination unit and the projection optics subsystem.

14. A lithographic exposure tool according to any one of claims 10 to 11, wherein the first and second diffracted beams represent respectively corresponding diffraction orders formed from the euv radiation, the diffraction orders having equal absolute values but different signs.

15. The lithographic exposure tool according to any one of claims 10 to 11, wherein the string of optical elements is configured to relay the first and second diffracted beams from the pattern source to the main mirror and the second mirror is positioned between the first and second diffracted beams such that the first and second diffracted beams are spatially separated from each other by the second mirror without any of the first and second diffracted beams being truncated by the second mirror.

16. The lithographic exposure tool of claim 15, wherein:

wherein the lighting unit contains only two mirrors;

Wherein the first one of the only two mirrors of the illumination unit is a first fly-eye mirror, wherein the second one of the only two mirrors of the illumination unit is a second fly-eye mirror, each of the first fly-eye mirror and the second fly-eye mirror containing a respective corresponding array of individually constituent reflective elements, the first fly-eye mirror being positioned to image a distribution of the extreme ultraviolet radiation from an entrance pupil of the illumination unit to the second fly-eye mirror.

17. The lithographic exposure tool according to claim 13, wherein the one-dimensional pattern has an outer boundary, wherein a first contrast value is equal to a second contrast value, wherein the first contrast value is a value of the image that represents an optical contrast of a first portion of the outer boundary, and wherein the second contrast value is a value of an optical contrast of a second portion of the image that represents a portion of the one-dimensional pattern that is within the outer boundary.

18. The lithographic exposure tool according to any one of claims 10 to 11, wherein the illumination unit comprises a fly's eye mirror comprising an array of individually constituent reflective elements, and wherein the fly's eye mirror is each of the two mirrors of the illumination unit.

19. The lithographic exposure tool according to any one of claims 10 to 11, wherein the reflective surface of any one of the first and second reflective elements of the two identical reflective elements is part of a rotationally symmetric surface.

20. The lithographic exposure tool according to any one of claims 10 to 11, wherein the one-dimensional pattern forms a one-dimensional diffraction grating configured as one of: a phase diffraction grating; an amplitude diffraction grating; an attenuated phase-shift diffraction grating.

21. The lithographic exposure tool according to any one of claims 10 to 11, configured to form the image to comprise a spatial frequency up to twice the spatial frequency characterizing the one-dimensional pattern.

22. The lithographic exposure tool of claim 10, wherein the pattern source comprises a surface having a first finite radius of curvature defined in a first plane transverse to the surface.

23. The lithographic exposure tool according to claim 22, wherein the surface has a second limited radius of curvature defined in a second plane transverse to both the surface and the first plane.

24. The lithographic exposure tool of claim 10, wherein:

wherein the projection optics subsystem comprises two pairs of reflective elements,

Wherein a first pair of said reflective elements is arranged to receive said extreme ultraviolet radiation that has been reflected by said pattern source and reflect said extreme ultraviolet radiation towards a second pair of said reflective elements,

Wherein the second pair of the reflective elements is configured to transfer the extreme ultraviolet radiation received from the first pair in a spatially converging manner between the first pair of reflective elements to form the optical image,

Wherein the image plane is separated from the second pair by the first pair.

25. The lithographic exposure tool of claim 10, wherein each of the only two mirrors comprises a fly's eye mirror array constituting individual reflective elements, and wherein each of the first fly's eye mirror array constituting individual reflective elements has a reflective surface that is elliptical or spherical.

26. The lithographic exposure tool of claim 25, wherein:

wherein the pattern source carries a one-dimensional diffraction grating thereon, the surface of the one-dimensional diffraction grating being curved;

wherein the pattern source, the second array of fly's eye mirrors, and the first mirror and the second mirror of the projection optics subsystem are symmetrically disposed about the reference axis;

Wherein first and second beams are transferred to the first mirror of the projection optics subsystem on opposite sides of the second fly's eye mirror array without impinging on the second fly's eye mirror array, the first and second beams representing the extreme ultraviolet radiation reflected by the second fly's eye mirror array and then diffracted into diffraction orders of the same absolute value but opposite sign on the one-dimensional diffraction grating.

27. The lithographic exposure tool of claim 26, wherein the third beam of extreme ultraviolet radiation is blocked by the second fly-eye mirror array to a plane on an opposite side of the second fly-eye mirror array relative to the first fly-eye mirror array.

28. A lithographic exposure tool according to any one of claims 25 to 27, wherein the pattern source carries a one-dimensional diffraction grating, and wherein individual constituent reflective elements of the first fly's eye mirror array have curved reflective surfaces.

29. The lithographic exposure tool of claim 28, wherein the reflective surface of the individual constituent reflective elements of the second fly's eye mirror array is a spherical reflective surface.

30. The lithographic exposure tool of claim 29, wherein the first and second optical axes of the first and second individual constituent reflective elements of the second fly's eye mirror array are not parallel to each other.

31. The lithographic exposure tool of claim 30, further comprising a source of the euv radiation comprising one of a laser driven plasma light source, a discharge driven plasma light source, a free electron laser, and a synchrotron-based light source.

32. A lithographic exposure tool having a string of optical elements positioned to deliver extreme ultraviolet radiation entering the string of optical elements to a target workpiece via the string of optical elements, the lithographic exposure tool for use with a pattern source, the string of optical elements comprising:

a lighting unit;

a projection optics subsystem positioned to receive the diffracted beam from the pattern source and form an optical image of the pattern source at an image plane optically conjugate to the pattern source with a reduction factor of N > 1; and

An element opaque to the extreme ultraviolet radiation and disposed between the pattern source and a primary mirror to block zeroth order diffraction of the diffracted beam at the pattern source from reaching a surface disposed between the optically opaque element and a mirror of the projection optics subsystem, the diffracted beam representing zeroth order diffraction at the pattern source,

Wherein the pattern source is configured to receive the extreme ultraviolet radiation from the illumination unit and diffract the extreme ultraviolet radiation to form the diffracted beam of the extreme ultraviolet radiation, the pattern source carrying thereon a one-dimensional pattern disposed on a spatially curved surface, the illumination unit comprising only two mirrors, the only two mirrors comprising a first mirror and a second mirror, and

Wherein a first radiation path from the second mirror to the pattern source is positioned between a second radiation path from the first mirror to the second mirror and a third radiation path originating from the pattern source,

Wherein the second mirror of the illumination unit is positioned to block a zeroth order diffraction of the extreme ultraviolet radiation from propagating to a surface between the optical element train and the mirror of the projection optics subsystem.

33. The lithographic exposure tool of claim 32, wherein:

The one-dimensional pattern has a first spatial frequency,

The optical image has a second spatial frequency, and

The second spatial frequency is at least twice the first spatial frequency.

34. The lithographic exposure tool of claim 33, wherein the first mirror is a first fly's eye mirror array comprising individually constructed reflective elements.

35. The lithographic exposure tool according to claim 34, wherein the pattern source is disposed in a respective constituent reflective element of the first fly's eye mirror.

36. A lithographic exposure tool according to any one of claims 34 to 35, wherein each of the individual reflective elements of the first fly's eye mirror array comprises a reflective surface that is elliptical or spherical.

37. The lithographic exposure tool according to claim 35, wherein the second mirror of the illumination unit comprises a second fly's eye mirror array comprising individually constituent reflective elements.

38. The lithographic exposure tool according to claim 33, wherein the mirror of the illumination unit is configured as an opaque element.

39. The lithographic exposure tool of claim 35, wherein the pattern source is positioned to form an image of the second mirror of the illumination unit at an entrance pupil of the projection optics subsystem.

40. The lithographic exposure tool of claim 31, wherein the pattern source is disposed in a fixed spatial relationship relative to the illumination unit and the projection optics subsystem.

41. The lithographic exposure tool of claim 31, wherein at least one of the mirror systems of the projection optics subsystem comprises two identical reflective elements disconnected from each other.

42. The lithographic exposure tool according to claim 41, wherein the reflective surface of either of the first and second reflective elements of the two identical reflective elements is part of a rotationally symmetric surface.

43. A lithographic exposure tool configured to irradiate a workpiece with extreme ultraviolet radiation and for use with a reflective pattern source carrying a one-dimensional pattern thereon, the one-dimensional pattern disposed in a curved surface; the lithographic exposure tool includes:

an illumination unit having an optical axis and configured to receive extreme ultraviolet radiation and irradiate the reflection pattern source with the extreme ultraviolet radiation, the illumination unit comprising a plurality of optical surfaces at a pupil of the illumination unit; and

A projection optical system configured to form an image of the reflection pattern source on a surface of the workpiece,

Wherein the plurality of optical surfaces are oriented such that, in operation of the tool, a first beam of extreme ultraviolet radiation reflected from a first surface of the plurality of optical surfaces diverges from the optical axis as it propagates toward the reflective pattern source, and a second beam of the extreme ultraviolet radiation reflected from a second surface of the plurality of optical surfaces approaches the optical axis as it propagates toward the reflective pattern source, the illumination unit comprising only two fly-eye mirror arrays including a first fly-eye mirror array and a second fly-eye mirror array closest to the pattern source, and

Wherein a first radiation path from the second fly-eye mirror array to the pattern source is positioned between a second radiation path from the first fly-eye mirror array to the second fly-eye mirror array and a third radiation path of the first diffracted beam and the second diffracted beam,

Wherein the projection optical system is a reflecting system comprising a main mirror and a sub-mirror, and

Wherein one of the only two fly's eye mirror arrays is positioned to block a zero-order diffracted beam from reaching the primary mirror, the first diffracted beam, the second diffracted beam, and the zero-order diffracted beam being formed as a result of diffracting the extreme ultraviolet radiation delivered via the illumination unit at the reflection pattern source.

44. The lithographic exposure tool of claim 43, wherein the projection optical system is configured to form the image having a spatial frequency that is at least twice the spatial frequency of the one-dimensional pattern.

45. The lithographic exposure tool according to any one of claims 43 to 44, wherein:

Wherein the projection optical system comprises two pairs of reflective elements,

Wherein a first pair of said reflective elements is arranged to receive said extreme ultraviolet radiation that has been reflected by said reflective pattern source and reflect said extreme ultraviolet radiation towards a second pair of said reflective elements,

Wherein the second pair of the reflective elements is configured to transfer the extreme ultraviolet radiation received from the first pair in a spatially converging manner between the first pair of reflective elements to form the optical image at an image plane,

Wherein the image plane is separated from the second pair by the first pair.

46. The lithographic exposure tool of claim 44, wherein the first and second optical axes of the first and second individual constituent reflective elements of one of the only two fly's eye mirror arrays are not parallel to each other.

47. A reflective system having an optical axis and configured to irradiate a one-dimensional pattern carried by an object, the reflective system comprising:

a first set of reflective elements disposed in a first region of a first substrate, the first substrate being planar;

a second set of reflective elements disposed in a second region of the first substrate; and

A third set of reflective elements disposed on a second substrate spaced apart from the first substrate along the optical axis; and

The reflective projection optical subsystem comprises a main mirror and a secondary mirror,

Wherein the first set of reflective elements is symmetrically arranged with respect to the second set of reflective elements about a plane containing the optical axis,

Wherein the reflection system is configured to irradiate a one-dimensional pattern carried by the object when the object is positioned on the optical axis between the first region and the second region, an

Wherein the first set of reflective elements and the second set of reflective elements together form a first fly-eye mirror and the third set of reflective elements form a second fly-eye mirror, the first fly-eye mirror and the second fly-eye mirror defining an illumination unit of a one-dimensional extreme ultraviolet lithography exposure tool, the first fly-eye mirror and the second fly-eye mirror being the only two mirrors of the illumination unit, a first radiation path from the second fly-eye mirror to a one-dimensional pattern carried by the object being positioned between a second radiation path from the first fly-eye mirror to the second fly-eye mirror and a third radiation path diffracting a one-dimensional pattern carried by the object,

Wherein the third set of reflective elements is positioned to block a zero-order diffracted beam, which is formed by diffracting extreme ultraviolet radiation delivered to the one-dimensional pattern, from reaching the primary mirror.

48. The reflective system of claim 47 wherein the first and second optical axes of the first and second sets of reflective elements are not parallel to each other.

49. The reflective system of claim 47, wherein said reflective projection optics subsystem comprises two pairs of reflective elements,

Wherein a first pair of said reflective elements is arranged to receive said extreme ultraviolet radiation which has been diffracted by said pattern and reflect said extreme ultraviolet radiation towards a second pair of said reflective elements,

Wherein the second pair of the reflective elements is configured to transfer the extreme ultraviolet radiation received from the first pair in a spatially converging manner between the first pair of reflective elements to form an optical image of the pattern at an image plane,

Wherein the image plane is separated from the second pair by the first pair.

50. The reflective system of claim 47, wherein:

wherein the optical image is formed on the image plane optically conjugated to the pattern source with only two beams of radiation with a reduction factor of N >1,

The only two beams of radiation originate at the pattern source as a result of diffracting the extreme ultraviolet radiation at the pattern.