CN111955058A

CN111955058A - Spatial modulation of light beams

Info

Publication number: CN111955058A
Application number: CN201980024259.0A
Authority: CN
Inventors: K·W·张; M·A·珀维斯; C·A·斯廷森
Original assignee: ASML Netherlands BV
Current assignee: ASML Netherlands BV
Priority date: 2018-04-03
Filing date: 2019-03-20
Publication date: 2020-11-17
Also published as: TWI820102B; TW201945792A; WO2019192841A1; JP7356439B2; NL2022769A; KR20200138728A; JP2021517662A

Abstract

A system includes a spatial modulation device configured to interact with a light beam to create a modified light beam, the modified light beam including a spatial pattern of light having a non-uniform intensity along a direction perpendicular to a direction of propagation of the modified light beam, the spatial pattern of light including one or more light components; and a target supply system configured to provide a target to a target region, the target comprising a target material that emits EUV light when in a plasma state. The target region overlaps the beam path such that at least some of the one or more light components in the modified beam interact with a portion of the target.

Description

Spatial modulation of light beams

Cross Reference to Related Applications

This application claims priority to U.S. application 62/651,928 filed on 03/04/2018, and is incorporated herein by reference in its entirety.

Technical Field

The present disclosure relates to techniques for spatially modulating an optical beam. This technique may be used, for example, in Extreme Ultraviolet (EUV) light sources. The beam may be, for example, a beam that irradiates a target material or a fuel material.

Background

Extreme Ultraviolet (EUV) light, such as electromagnetic radiation having a wavelength of 100 nanometers (nm) or less (sometimes also referred to as soft x-rays), and including light at wavelengths between, for example, 20nm or less, 5nm and 20nm, or 13nm and 14nm, may be used in a lithographic process to create extremely small features in a substrate, such as a silicon wafer, by initiating polymerization in a resist layer.

Methods for generating EUV light include, but are not necessarily limited to, converting a target material into a plasma that emits EUV light. The target material comprises an element having an emission line in the EUV range, for example xenon, lithium or tin. In one such method, often referred to as laser plasma (LPP), the desired plasma may be generated by irradiating a target comprising a target material with an amplified beam, which may be referred to as a drive laser. For this purpose, the plasma is usually generated in a sealed container such as a vacuum chamber, and observed using various types of measuring instruments. The target material may be in the form of droplets, plates, ribbons, streams or clusters.

Disclosure of Invention

In one general aspect, a system includes a spatial modulation device configured to interact with a light beam to create a modified light beam, the modified light beam including a spatial pattern of light having a non-uniform intensity along a direction perpendicular to a direction of propagation of the modified light beam, the spatial pattern of light including one or more light components; and a target supply system configured to provide a target to a target region, the target comprising a target material that emits EUV light when in a plasma state. The target region overlaps the beam path such that at least some of the one or more light components in the modified beam interact with a portion of the target.

Implementations may include one or more of the following features. The spatial modulation device may be a diffractive optical element. The diffractive optics may be a Spatial Light Modulator (SLM), adaptive optics, a reticle, and/or a grating. The spatial modulation device may be a refractive optical element. The refractive optics may be a lens, a lenslet array, and/or a reticle.

The spatial pattern of light may include two or more light components, and each of the two or more light components has substantially the same intensity. The spatial pattern of light may include two or more light components arranged in a rectilinear grid. The spatial modulation device may comprise at least one dammann grating.

The spatial modulation device may also be configured to interact with the second light beam to create a second modified light beam comprising a second spatial pattern of light having a non-uniform intensity along a direction perpendicular to a direction of propagation of the second modified light beam, the second spatial pattern of light comprising one or more second light components.

In some embodiments, the system further comprises a first light generation module configured to emit a light beam, and a second light generation module configured to emit a second light beam.

In another general aspect, a method of forming a target for an Extreme Ultraviolet (EUV) light source includes directing a beam of light onto a beam path; causing the light beam to interact with a spatial modulation device located on the beam path to form a modified light beam, the modified light beam comprising a spatial pattern of light having a non-uniform intensity along a direction perpendicular to a direction of propagation of the modified light beam, the spatial pattern of light comprising one or more light components; and causing the modified beam to interact with a target comprising a target material that emits EUV light when in a plasma state. At least some of the one or more light components in the spatial pattern interact with a region of the target to modify a property of the region of the target.

Implementations may include one or more of the following features. The attribute may be density, and in these embodiments, modifying the attribute includes reducing the density. The property may be a surface area of the target, and in these embodiments, modifying the property of any portion of the target includes increasing the surface area of the entire target. The amount of increase in surface area may be related to the number of light components in the modified light beam.

The spatial pattern of light may include two or more light components. All light components may have the same intensity. The light components may be arranged in a grid, and the regions of the target that directly interact with the light components may be arranged in a grid. The light components may be spatially separated and spatially discrete such that the portion of the target between any two light components does not interact with any of the components in the modified light beam. In some embodiments, the method further comprises interacting the modified beam with a focusing assembly prior to interacting the modified beam with the target.

In some embodiments, the method further comprises interacting the initial target with the second beam to form a modified target having a greater extent in a first direction than the initial target and a lesser extent in a second direction than the initial target, the first and second directions being orthogonal to each other. In these embodiments, causing the modified beam of light to interact with a target comprising a target material that emits EUV light when in a plasma state comprises causing the modified beam of light to interact with the modified target, and each of the one or more light components to interact with a region of the modified target to modify a property of the region of the modified target. Further, in some embodiments, after interacting the modified beam with the altered target, the altered target interacts with a third beam of light having an energy sufficient to convert at least some target material in the altered target to a plasma that emits EUV light.

The method may further include, after interacting the target with the modified beam, interacting the target with another beam having an energy sufficient to convert at least some target material in a second altered target into a plasma that emits EUV light. The beam and the other beams may be temporally connected and part of a single light pulse. The property may include a conversion efficiency related to the amount of EUV light emitted and the energy of the other beam, and modifying the property of a portion of the target includes increasing the conversion efficiency associated with the entire target.

Interacting the modified beam with a target comprising a target material that emits EUV light when in a plasma state comprises interacting the modified beam with a target having a substantially spherical shape.

Embodiments of any of the techniques described above may include an EUV light source, a system for an EUV light source, instructions stored on a non-transitory electronic storage medium, a method, a process, an apparatus, or a device. The details of one or more implementations are set forth in the accompanying drawings and the description below. Other features will be apparent from the description and drawings, and from the claims.

Drawings

Fig. 1A is a block diagram of an example of an EUV light source.

FIG. 1B is a plot of the intensity of an example of a beam as a function of position in a direction perpendicular to the direction of propagation, prior to spatial modulation.

FIG. 1C is a plot of the intensity of the example beam of FIG. 1B after spatial modulation as a function of position along a direction perpendicular to the propagation direction.

FIG. 1D is a block diagram of an example of a target interacting with the optical beam of FIG. 1C.

Fig. 2A is a block diagram of another example of an EUV light source.

Fig. 2B is a block diagram of another example of a target.

Fig. 2C is a plot of the intensity of another example of a beam as a function of position along a direction perpendicular to the direction of propagation after spatial modulation.

Fig. 2D is a block diagram of an example of a modified target.

Fig. 2E-2F are examples of light patterns in a target area.

Figures 3-6 are block diagrams of additional examples of EUV light sources.

Fig. 7 is a graphical representation of a target area over time.

Fig. 8 is a graphical representation of light intensity in the target region of fig. 7 as a function of the time scale of fig. 7.

FIG. 9 is a block diagram of an example of a lithographic apparatus.

FIG. 10 is a block diagram of an example of an EUV lithography system.

FIG. 11 is a block diagram of an example of an EUV light source.

Detailed Description

Techniques for spatially modulating an optical beam are disclosed. The spatially modulated light beam is used to illuminate a target material or a fuel material.

Referring to FIG. 1A, a side view of an Extreme Ultraviolet (EUV) light source 100 is shown. The EUV light source 100 comprises a light generation module 105 which emits a light beam 106 onto a beam path 107 and towards a spatial modulation device 120 comprising a modulation element 122. The interaction between the modulating element 122 and the light beam 106 forms a modified light beam 132. Modified beam 132 interacts with target 140 at target area 142. The beam 106 may be a pulsed beam comprising pulses of light spaced apart in time from each other. In these embodiments, modified beam 132 is also a pulsed beam.

The target 140 includes a target material or fuel material that emits EUF light when in a plasma state. The target material includes a target substance, and may also include impurities such as non-target particles. The target substance is a substance that is converted into a plasma state having an emission line in the EUV range. For example, the target substance may be water, tin, lithium, xenon, or any material having an emission line in the EUV range when converted into a plasma state. For example, the target substance may be elemental tin, which may be used as pure tin (Sn); as tin compounds, e.g. SnBr₄、SnBr₂、SnH₄(ii) a As a tin alloy, for example a tin-gallium alloy, a tin-indium-gallium alloy, or any combination of these alloys. In the absence of impurities, the target material includes only the target species.

The target 140 may take any form conducive to the generation of a plasma that emits EUV light. For example, the target 140 may be a droplet of liquid or molten metal, a portion of a liquid stream, a solid particle or cluster, a solid particle contained within a droplet, a foam of a target material, or a solid particle contained within a portion of a liquid stream. The target 140 may take other forms. For example, the target 140 may be a continuous segment of substantially disk-shaped molten metal. The target 140 may be a collection of particles that occupy a substantially disk-shaped volume or a hemispherical volume. The target 140 is a cloud of atomic vapor or a fog of nano-or micro-particles, continuous segments of target material without gaps or voids.

The present technique involves spatially modulating the light beam 106 prior to interaction with the target 140. As discussed below, spatially modulating the light beam 106 may result in an increase in Conversion Efficiency (CE) and/or a reduction in debris generation.

Modulating element 122 is an optical element capable of spatially modulating light beam 106 to form modified light beam 132. The modulation element 122 may be a diffractive optical element, which is any structure capable of modulating the optical beam 106 by diffraction. The diffractive optical element may be, for example, a grating, a Spatial Light Modulator (SLM), an acousto-optic modulator (AOM), an acousto-optic deflector (AOD), an aperture or set of apertures arranged in a plane to create a specific diffraction pattern, and/or a reticle. The modulation element 122 may be a refractive optical element, such as a two-dimensional array of lenses or other arrangement of lenses, a phase plate, a deformable mirror, and/or a refractive reticle. The modulation element 122 may comprise more than one instance of a particular type of modulation element or a collection of various different modulation elements. In these embodiments, more complex spatial modulation can be achieved by combining the effects of more than one modulation element. For example, two identical diffraction gratings may be placed in series on beam path 107 and rotated relative to each other about beam path 107 to form a more complex diffraction pattern corresponding to a more complex spatial modulation of optical beam 106. In some embodiments, modulation element 122 includes both refractive and diffractive optical elements. Furthermore, the modulation element 122 may be any type of adaptive optics, such as a deformable mirror, for example.

Furthermore, the modulation element 122 may be static or dynamic. A static modulating element is one in which the structure of the modulating element 122 is fixed at the time of manufacture of the modulating element 122 and does not change after the modulating element 122 is formed. A dynamic modulating element is one in which the spatial modulation imposed by the interaction between the light beam 106 and the modulating element 122 may change or be adjusted over the lifetime of the modulating element 122. For example, the spatial modulation imparted by an AOM on an incident beam depends on the properties of the acoustic wave propagating in the medium (such as quartz) through which the incident beam passes. Thus, by varying the amplitude and/or period of the acoustic wave, the characteristics of the modulation provided by the AOM may also be varied. In this way, the AOM can be considered a dynamic modulation element. SLMs can also be used as dynamic modulation elements. A deformable mirror or any other type of adaptive optical element may also be used as the dynamic modulation element. On the other hand, lenslet arrays and blazed diffraction gratings (which cause optical and mechanical properties not to be altered by the end user) formed from classical or conventional refractive and/or reflective materials are examples of static modulation elements.

The spatial profile of modified light beam 132 differs from the spatial profile of light beam 106 due to optical modulation. The spatial profile of a light beam is a property (e.g., intensity and/or phase) of the light beam as a function of position along a direction that is in a plane perpendicular to the direction of propagation. Thus, modified beam 132 may have an intensity and/or phase profile that is different from beam 106. The characteristics of the profile of the modified light beam 132 depend on the characteristics and/or arrangement of the modulating element 122. For example, in embodiments where the modulating element 122 is a diffraction grating, the angle at which the diffracted orders propagate away from the modulating element 122 (and thus the position at which the diffracted orders are at the target region 142) depends on the spacing between the grooves on the diffractive element.

In the example of fig. 1A, beam 106 and modified beam 132 propagate generally in the Z-direction. Fig. 1B is a plot of the intensity (in arbitrary units) of the beam 106 as a function of position along the direction X, which is perpendicular to the direction Z. Fig. 1C is a plot of the intensity (in arbitrary units) of modified light beam 132 as a function of position along direction X at target region 141. In the example of fig. 1A-1C, the intensity profile of the beam 106 is substantially gaussian. The intensity profile of the modified light beam 132 is different from the intensity profile of the light beam 106 due to the interaction between the light beam 106 and the modulating element 122. The intensity profile shown in FIG. 1C is along a single line in the X-Y plane. The intensity profile of the modified light beam 132 in the X-Y plane at other lines along the X-direction may be the same as that shown in fig. 1C or may be different. In other words, the spatial profile of the modified light beam 132 may vary along the X-direction, along the Y-direction, or along both the X-and Y-directions.

The properties of the spatial profile of the modified light beam 132 depend on the configuration of the modulating element 122. For example, the modified light beam 132 may have a profile in which the intensity of the modified light beam 132 varies continuously as a function of position in the X-Y plane and without regions that do not include light, such as the example shown in fig. 1C. In some embodiments, modified light beam 132 is formed from discrete components that are separated from one another such that the profile of modified light beam 132 includes regions that are substantially devoid of light. An example of such a modified beam 132 is shown in fig. 2C. In any event, the profile of the modified light beam 132 differs from the profile of the light beam 106 due to the interaction between the modulating element 122 and the light beam 106.

The modified beam 132 illuminates the target 140. The intensity profile of the modified beam 132 shown in FIG. 1C interacts with the target 140 (FIG. 1D) at line C-C'. Since the spatial profile of modified beam 132 is different from the profile of beam 106, modified beam 132 interacts with target 140 in a different manner than beam 106. For example, modified beam 132 provides relatively more light to

portions

140a and 140c near the outer edges of target 140 than to portion 140 near the center of target 140 as compared to beam 106.

As discussed below, the use of the modulating element 122 allows the spatial profile of the light interacting with the target 140 to be customized to consume more of the target material in the target 140. This in turn increases the amount of EUV light generated due to the interaction between the modified beam 132 and the target 140 and/or results in more efficient preparation of the target 140 prior to interaction with the separate beam, which converts the target material in the target 140 into a plasma that emits EUV light. Furthermore, the use of modified beam 132 also reduces debris generated by the interaction between target 140 and the beam by increasing the amount of target material consumed.

Further, the modulation element 122 may be configured such that the modified light beam 132 has a profile that is optimized based on known, assumed, or estimated properties of the target. For example, the target 140 may be known to contain more target material near the lower edge of the target 140 than near the center or top edge. For such a target, the modulating element 122 may be configured to produce a modified light beam having a spatial profile such as that shown in fig. 1C.

Only a single light beam 106 is illustrated in the example of fig. 1A. However, the light source 100 may use more than one light beam, and each of the more than one light beams may interact with a different form of target 140. For example, the light source 100 may use one or more "pre-pulsed" beams that shape, alter, or otherwise modify one or more properties of the target 140 (without necessarily producing a plasma that emits EUV light) to produce a modified target or an intermediate target. These embodiments may also use a "main pulse" beam of light having an energy sufficient to convert target material in the modified or intermediate target into a plasma that emits EUV light. Figures 3, 4 and 6 show examples of embodiments of EUV light sources 100 using more than one pulsed light beam. Any or all of the beams used in the EUV light source 100 may interact with the modulation element 122 to modify the spatial profile of the beam. In embodiments where the light source 100 uses more than one grating, the light source 100 may include more than one spatial modulation device 120. For example, in these embodiments, the light source 100 may include a separate spatial modulation device 120 positioned to interact with each of the more than one light beams.

Referring to FIG. 2A, a side view of an EUV light source 200 is shown. EUV light source 200 is an example of one implementation of EUV light source 100 (FIG. 1A).

The EUV light source 200 includes a modulation device 220. Modulation device 220 includes a modulation element 222 that spatially modulates light beam 106 to produce a modified light beam 232 that includes components 233, each component 233 also being a light beam. Components 233 may be separated from each other such that there are areas of no light (or significantly reduced light) between each component and its adjacent component or components. Modified light beam 233 includes a number of individual components, and the individual components are collectively referred to as components 233. The

components

233a, 233b, 233c, 233d, 233e are shown in FIG. 2A. The modulating element 222 may be a diffraction grating. In these embodiments, each

component

233a, 233b, 233c, 233d, 233e is a diffraction order. Component 233c may be the zeroth order that is not diffracted by modulation element 222. In these embodiments, component 233c propagates generally in the same direction as beam 106. In the example of fig. 2A, each of the

components

233a, 233b, 233c, 233d, 233e propagates away from the diffraction grating in a different direction.

Modified beam 232 also includes other components that, along with

components

233a, 233b, 233c, 233d, and 233e, form a two-dimensional grid pattern in the X-Y plane at target area 232. Fig. 2B shows the target area 242 in the X-Y plane. In fig. 2B, the solid circle represents component 233 in target region 242. In the example of fig. 2B, all components 233 interact with respective portions of target 140. The element labeled 243 represents the portion that interacts with component 233 a. For simplicity, only one portion 243 is labeled in FIG. 2B. However, other components 233 interact with other portions of target 140. Portion 243 is illustrated as a circular area on target 140. However, the interaction between component 233a and target 140 may affect portions of target 140 other than that labeled 243 in FIG. 2B, and portion 243 is not necessarily a circular area.

FIG. 2C is a plot of the intensities of the components 233a-233e of the modified beam 232 as a function of position along direction X. In the example of FIG. 2C, the intensities of components 233a-233e vary. In other embodiments, the modulating element 222 is a diffractive element that produces diffraction orders of equivalent intensity. For example, in these embodiments, the modulating element 222 may be a Dammann (Dammann) grating.

The interaction between component 233 and target 140 produces modified target 245 (fig. 2D). Modified target 245 has modified region 244 formed by interacting component 233 with target 140. For simplicity, only the interaction between the target material in portion 243 and component 233a is discussed, and only one modified region 244 is labeled. However, other components interact with the target material in other portions of the target 140 and form other modified regions in a similar manner. Fig. 2D shows the other modified regions as dashed circular regions.

The interaction between the target material in portion 242 and component 233a changes the physical properties of portion 243. For example, the interaction may alter the geometric distribution of portion 243 by removing some target material from portion 243 to thereby form a recessed region. In this example, modified region 244 is the recessed region. The recessed region is a region that is devoid of the target material. The recessed region may be a void. The target material may be removed, for example, by ablating, ejecting, and/or converting to a plasma that does not emit EUV light or emits only minimal EUV light. The recessed area may be an opening, pocket, or opening in the modified target 245. The recessed region may pass through the modified target 245. Furthermore, the recessed region may have any shape. For example, the recessed region may be a conical or rectangular slit that extends into the modified target 245 but does not ultimately pass through the modified target 245. The characteristics (e.g., shape, depth, and cross-section) of this recessed region depend on the strength and diameter of component 233a and the properties of the target material in portion 243. The interaction between component 233a and portion 243 may change the characteristics of portion 243 in other ways. For example, the interaction may reduce the density of portion 243. In this example, modified region 244 is a region that may include a reduction in the density of the target material.

As discussed above, while only one modified region 244 is labeled in fig. 2D, other modified regions are formed to produce modified target 245. The various modified regions on modified target 245 may have different characteristics from one another.

Regardless of how the interaction changes the specific characteristics of portion 243 (or other portions not labeled), the interaction between member 233 and target 130 forms a modified target 245 that is more easily converted to a plasma that emits EUV light. For example, forming the recessed region results in a modified target 245 having a larger surface area than target 140. The larger surface area corresponds to a larger amount of target material exposed to the incident beam, thereby allowing more target material to be converted into a plasma that emits EUV light.

The two-dimensional grid pattern formed by component 233 in FIG. 2B is only one possible pattern that may be formed in target area 242. Other patterns may be generated depending on the configuration and characteristics of the modulating member 222. Fig. 2E-2G show examples of components at other patterns. Fig. 2E includes a component 233_ E, which is a concentric circle separated by no light areas. Component 233_ E can be formed, for example, in embodiments in which modulating element 222 is a circular aperture. Fig. 2F shows components 233_ F arranged in a one-dimensional array. In the example of fig. 2F, component 233_ F has a rectangular cross-section. Fig. 2G illustrates yet another example of the arrangement of components 233_ G. The component 233_ G is represented as a solid circle. FIG. 2G shows target area 142 in the X-Y and X-Z planes. In the example of FIG. 2G, the component 233_ G propagates generally in the Z-direction and the-X direction. Thus, component 233_ G reaches target region 142 from more than one direction and interacts with target 140 at the surface of the X-Y plane and the X-Z plane.

Fig. 3 is a block diagram of an EUV light source 300. The EUV light source 300 is one example of an implementation of the light source 100 of fig. 1A. The EUV light source 300 includes a first light generation module 305a and a second light generation module 305 b. The first light generating module 305a emits a first light beam 306a onto beam path 307a and the light generating module 305b emits a second light beam 306b onto beam path 307 b. First beam 306a is used to form modified beam 332 a. The modified beam 332a interacts with the target 340 to form a modified target 345, but generally does not form a plasma that emits EUV light (or forms a plasma that emits only a small or negligible amount of EUV light). The first beam 306a may be referred to as a "pre-pulse" beam. Second beam 306b is a beam having energy sufficient to convert the target material in modified region 345 into a plasma that emits EUV light 399. The second beam 306b may be referred to as the "main pulse" beam or the heating beam. The first light generating module 305a and/or the second light generating module 305b are controlled such that for a specific pair of pre-pulse and main pulse, wherein the pre-pulse forms the modified target 345 and the main pulse converts the modified target 345 into a plasma emitting EUV light, the pre-pulse occurs before the main pulse.

The light generating module 305b may be, for example, carbon dioxide (CO)₂) A laser, and the wavelength of the second beam 306b may be, for example, 10.59 micrometers (μm). The first light generating module 305a may be, for example, a solid state laser such as an erbium doped fiber (Er: glass) laser or a Q-switched Nd: YAG laser. In these embodiments, the wavelength of the first light beam 306a may be, for example, 1.06 μm. In some embodiments, the first light generating module 305a and the second light generating module 305b are the same type of light source. For example, the first and second

light generating modules

305a, 305b may both be CO₂A laser. In these embodiments, the first and second

light generating modules

305a, 305b may have the same spectral content. For example, the first and second

light generating modules

305a, 305b may both have a wavelength of 10.59 μm. In yet further examples, the first and second

light generating modules

305a, 305b may both be solid state lasers. In these embodiments, the first and second

light generating modules

305a, 305b may both have a wavelength of, for example, 1.06 μm.

In one embodiment, the same type of light source is used for the first and second

light generating modules

305a, 305b, but the first and second

light beams

306a, 306b have spectral contentThe difference is that. For example, the first and second

light generating modules

305a, 305b may be implemented to include two COs₂A seed laser subsystem and a single module of an amplifier. One of the seed laser subsystems produces a first beam 306a of, for example, 10.26 μm wavelength, while the other seed laser subsystem produces a second beam 306b of, for example, 10.59 μm wavelength. The two wavelengths may be from CO₂The different spectral lines of the laser.

Further, wavelengths other than the examples provided above may be used. For example, either or both of first light beam 306a and second light beam 306b may have a wavelength less than 1 μm. Using relatively short wavelengths (such as wavelengths less than 1 μm) may be advantageous in some situations. For example, the relatively short wavelength enables a smaller focus size, which allows improved control of the beam shaping

First light beam 306a interacts with modulating element 322 to produce modified light beam 332 a. Modulating element 322 is any optical component or collection of components capable of spatially modulating first light beam 306 a. Modified light beam 332a has a different spatial profile than first light beam 306 a. The spatial profile of modified light beam 332a depends on the configuration of modulating element 322. The modified light beam 332a may have a spatial profile that varies continuously as a function of position (e.g., as shown in fig. 1C), or the modified light beam 332a may include components of light separated by no light regions (e.g., as shown in fig. 2B and 2E-2G). In embodiments where the spatial profile varies continuously as a function of position, the components are not discrete and may be considered any portion of the spatial profile.

The EUV light source 30 also includes a beam combiner 324 positioned to direct the modified light beam 332a and the second light beam 306b toward a beam delivery system 325. Beam combiner 324 is any optical element or collection of optical elements capable of interacting with modified light beam 332a and second light beam 306 b. For example, beam combiner 324 may include one or more mirrors or one or more beam splitters, some of which are positioned to direct modified light beam 332a toward beam delivery system 325, and others of which are positioned to direct second light beam 306b toward beam delivery system 325. In embodiments where the modified light beam 332a and the second light beam 306b have different spectral content, the beam combiner 324 may be a dichroic element (such as a dichroic beam splitter) configured to transmit wavelengths in the second light beam 306b and reflect wavelengths in the modified light beam 332 a. Beam combiner 324 directs modified light beam 332a and second light beam 306b in spatially separated beam paths toward beam delivery system 325 in the example of fig. 3.

The beam delivery system 325 also includes a focusing system 326. Focusing system 326 includes any combination of optical elements arranged to focus modified light beam 332a and second light beam 306 b. For example, the focusing system 326 may include lenses and/or mirrors. Modified beam 332a is focused at or near initial target area 342a and second beam 306b is focused at or near modified target area 342 b. In the example shown in fig. 3, focusing system 326 focuses modified light beam 332a and second light beam 306b even though these light beams do not follow the same beam path through focusing system 326. However, in some implementations, the optical element that focuses modified light beam 332a is independent of the optical element that focuses second light beam 306 b. For example, separate optical components may be used when the spectral content of modified light beam 332a is different from second light beam 306 b.

The initial target area 342a receives the target 340 from the target material supply system 350. In the example of fig. 3, the target 340 is a spherical droplet of molten metal. The components in modified light beam 332a interact with target 340 to form modified target 345. The interaction between the modified light beam 332a and the target 340 changes one or more properties of the target 340. For example, the modified target 345 may have recessed regions and/or regions of reduced density, such as discussed with respect to modified region 245 of fig. 2D. Modified target 345 travels to modified target region 342b and interacts with second light beam 306 b. The interaction between the second beams 306b converts at least some target material in the modified target 345 into a plasma that emits EUV light 399.

Fig. 4 is a block diagram of an EUV light source 400. EUV light source 400 is another example of an embodiment of EUV light source 100. EUV light source 400 is similar to EUV light source 300 except that EUV light source 400 uses two "pre-pulsed" beams to produce modified target 445.

The EUV light source 400 includes

light generating modules

405a, 405b, and 405 c. The light generating module 405a emits a first light beam 406 a. The light generating module 405b emits a second light beam 406 b. The light generating module 405c emits a third light beam 406 c. The light generating module 405c may be, for example, CO₂A laser. All of the

light beams

405a, 405b, 405c may have the same spectral content, or the spectral content of at least one of the

light beams

405a, 405b, 405c may be different from the spectral content of the other light beams.

Beams

405a and 405b may be CO₂Two different emission lines of the laser. CO 2₂The emission lines of the lasers include, for example, light of 9.4 μm, 10.26 μm and 10.59 μm. In some embodiments, either beam 405a or beam 405b is CO₂The laser forms a beam at an emission line of 10.26 μm. In these embodiments, the other of

beams

405a and 405b may be a beam having a wavelength of 1.06 μm produced by a solid-state laser (such as, by way of example, a Q-switched Nd: YAG laser). In other embodiments, both beam 405a and beam 405b are generated by solid state lasers.

The first and second

light beams

406a, 406b change one or more physical properties of the target 440 to produce a modified target 445. In the embodiment shown in fig. 4, first beam 406a interacts with target 440 to spatially expand target 440 and form intermediate target 447. The intermediate target 447 may be a disk-shaped segment of molten metal having a greater extent along the X-axis (which includes the X direction and the-X direction opposite the X direction) than the target 440. Further, intermediate target 447 has a smaller extent along the Z-axis than target 440. The intermediate target 447 moves in the X direction.

The EUV light source 400 also includes a modulating element 422 positioned to interact with the second light beam 406 b. Modulating element 422 is any optical element or collection of elements capable of spatially modulating second light beam 406 b. For example, the modulation element 422 may be similar to the modulation element 122 discussed with respect to fig. 1A or the modulation element 222 discussed with respect to fig. 2A. The interaction between the modulating element 422 and the second light beam 406b produces a modified light beam 432 b. Modified light beam 432b has a different spatial profile than second light beam 406 b. Modified light beam 432b and first light beam 406a are directed by beam combiner 424 toward focusing system 425 a. Beam combiner 424 may be any optical element or collection of optical elements capable of directing modified light beam 432b and first light beam 406a toward focusing system 425 a. The focusing system 425a focuses the first beam 406a at or near a target region 442a that receives the target 440 from the target delivery system 450 and focuses the modified beam 432b at or near a target region 442b that receives the intermediate target 447 from the target region 442 a.

Intermediate target 447 and modified beam 432b interact at target 442b to form modified target 445. In the example shown, the interaction between modified light beam 432b and intermediate target 447 forms a recessed region 444 on modified target 445. After interacting with modified light beam 432b, modified target 445 moves into target region 442c that receives third light beam 406 c. Third beam 406c is focused by focusing system 426c and has an energy sufficient to convert at least some target material in modified target 445 into a plasma that emits EUV light. The recessed region 444 may cause more of the target material in the modified target 445 to be converted to plasma. Thus, more EUV light and less debris is generated by the interaction between modified target 445 and third beam 406c as compared to a target lacking recessed region 444 (such as target 440 or intermediate target 447).

Fig. 5 is a block diagram of an EUV light source 500. EUV light source 500 is another example of an implementation of EUV light source 100 of fig. 1A. In the EUV light source 500, a single beam of light is used to produce the modified target 545 and form an EUV light-emitting plasma from the modified target 545.

The EUV light source 500 includes a light generation module 505. The light generating module 505 may be, for example, a CO₂A laser. The light generation module 505 emits a light beam 506 onto a beam path 507 towards a modulation device 520. The modulation device 520 comprises a modulation element 522. The modulating element 522 is capable of spatially modulating the light beam 506 to not all have the same intensityAny optical element of the component (b). The modulating member 522 may be similar to the modulating member 222 (fig. 2A). The interaction between modulating element 522 and optical beam 506 modulates optical beam 506 and produces components 533a-533 g. Components 533a-533g are separated from each other by regions without light.

Components 533a-533g propagate away from modulating element 522 in different directions. 533a-533g propagate toward beam dump 528 and do not exit modulation device 520. Components 533a-533g propagate toward target region 542a of receiving target 540. Target 540 may be a spherical droplet provided by a target material supply system, such as system 450 of fig. 4, or target 540 may be an intermediate target (such as intermediate target 447 of fig. 4) resulting from a previous interaction of another beam. Components 533a-533c have an intensity sufficient to modify a property of target 540 without producing an EUV light-emitting plasma. Thus, regardless of the form of target 540, the interaction between 533a-533c results in a modified target 545. In the example of fig. 5, three recessed regions 544 are illustrated. Each recessed region 544 is formed by the interaction between one of components 533a-533c and target 540.

Component 533d propagates toward focusing system 525. Focusing system 525 focuses component 533d at or near modified target region 542b, which receives modified target 545. Focusing system 525 also includes optical delay 529, which causes component 533d to reach modified target region 542b at a time after components 533a-533c and at a time when modified target 545 is within modified target region 542 b. Optical delay 529 can be, for example, an arrangement that includes multiple reflective elements (such as mirrors) that fold component 533d in multiple passes in a relatively compact volume. Such an optical delay 529 may cause component 533d to travel an additional hundreds of meters so that delays of hundreds of nanoseconds may be achieved.

Component 533d has a greater intensity than 533a-533c, and component 533d has an energy sufficient to convert at least some target material in modified target 545 into a plasma that emits EUV light. For example, the total energy of the components may be approximately 2 kilowatts (kW), while the energy in component 533d may be greater than 100 kW.

Fig. 6 is a block diagram of an EUV light source 600. EUV light source 600 is another example of an embodiment of EUV light source 100. The EUV light source 600 is similar to the EUV light source 300 (fig. 3) except that the EUV light source 600 includes a modulation device 620 that spatially modulates a portion of the second light beam 306b instead of modulating the first light beam 306 a. In the embodiment shown in fig. 6, the target region 642 receives the target 640 from the target material supply 350. Fig. 7 is a graphical representation of the target region 642 over time. Fig. 8 is a graphical representation of the light intensity in the target region 642 as a function of the time scale of fig. 7.

Beam combiner 324 directs first light beam 306a toward target 640. The interaction between the first beam 306a and the target 640 forms an intermediate target 547. The second light beam 306b passes through a beam combiner 324 and interacts with a modulation device 620 to form a single light pulse 604. The modulation device 620 includes a temporal modulation device 662 and a spatial modulation element 622. Spatial modulation element 622 is a dynamic modulation element that can be controlled by controller 660. The time modulation device 662 may also be controlled by the controller 660. Controller 660 may include an electronic processor and electronic memory or storage. The electronic processor may store instructions, perhaps as a computer program, that instruct the processor to perform actions. For example, the electronic processor may generate signals that, when provided to modulation device 620, modulation element 622, and/or time modulation device 662 by controller 660, cause modulation device 620, modulation element 622, and/or time modulation device 662 to perform particular actions.

Temporal modulation device 662 is any optical element capable of controlling the temporal profile (intensity as a function of time) of second light beam 306 b. For example, the time modulation device 662 may be an electro-optic modulator (EOM). The temporal modulation device 662 is controlled to form the light pulses 604 from the second light beam 605b, which comprise the substrate 608 and the heated portion 609. Substrate 608 and heating portion 609 are shown in fig. 8. Substrate 608 is temporally connected to heating portion 609 such that substrate 608 and heating portion 609 are part of a single light pulse 604 (fig. 6 and 8).

The temporal profile of the substrate 608 may have any shape. For example, the intensity of the substrate 608 may increase and decrease over time, such that the substrate 608 has a shape somewhat similar to a pulse. The example of fig. 8 illustrates an example of such a substrate. In other examples, the intensity of the substrate 608 may increase and decrease over time without having a pulse-like profile. In still other examples, substrate 608 may have a monotonically increasing intensity until heating portion 609 begins. Regardless of the shape of the substrate 608, the substrate 608 and the heating portion 609 collectively form a single pulse 604. That is, there is no region of no light between the beginning of pulse 604 and the end of pulse 604.

The spatial modulation element 622 is controlled such that only the substrate 608 is spatially modulated. Thus, the spatial profile of the substrate 608 varies. In some embodiments, the substrate focus size in the x-y plane is modulated to achieve different intensities. For example, the focal spot size may be modulated to heat the outer edge of the target before the heating material is closer to the center of the target.

As shown in fig. 7 and 8, the substrate 608 reaches the target area 642 before the heating portion 609. The spatially modulated substrate 608 interacts with an intermediate target 647 and forms a modified target 645. The heated portion 609 reaches the target area 642 after the substrate 608. Heating portion 609 has a much greater intensity than substrate 608 and is capable of converting target material in modified target 645 into plasma that emits EUV light 399. Thus, the EUV light source 600 uses two separate pulses-a first beam 306a and a second beam 306 b. However, second beam 306b is acted upon by modulation device 620 such that second beam 306b produces pulse 608, which modifies intermediate target 647 and converts modified target 645 into a plasma that emits EUV light 399.

Fig. 9 and 10 discuss an example of an EUV lithography system 900. EUV light generated by any of EUV

light sources

100, 200, 300, 400, 500, and 600 may be used with lithography system 900. Further, a system including any of EUV

light sources

100, 200, 300, 400, 500, and 600 also includes a lithography system such as lithography system 900. FIG. 11 discusses an example of an EUV light source. The EUV

light sources

100, 200, 300, 400, 500, and 600 may include additional components and systems such as discussed with respect to fig. 10 and 11. For example, EUV

light sources

100, 200, 300, 400, 500, and 600 include a vacuum chamber, such as vacuum chamber 1130 discussed with respect to fig. 11.

FIG. 9 schematically depicts a lithographic apparatus 900 that includes a source collector module SO according to an embodiment. The lithographic apparatus 900 includes:

an illumination system (illuminator) IL configured to condition a radiation beam B (e.g. EUV radiation);

a support structure (e.g. a mask table) MT constructed to support a patterning device (e.g. a mask or reticle) MA and connected to a first positioner PM configured to accurately position the patterning device;

a substrate table (e.g. a wafer table) WT constructed to hold a substrate (e.g. a resist-coated wafer) W and connected to a second positioner PW configured to accurately position the substrate; and

a projection system (e.g. a reflective projection system) PS configured to project a pattern imparted to the radiation beam B by patterning device MA onto a target portion C (e.g. comprising one or more dies) of the substrate W.

The illumination system may include various types of optical components, such as refractive, reflective, magnetic, electromagnetic, electrostatic or other types of optical components, or any combination thereof, for directing, shaping, or controlling radiation.

The support structure MT holds the patterning device MA in a manner that depends on the orientation of the patterning device, the design of the lithographic apparatus, and other conditions, such as for example whether or not the patterning device is held in a vacuum environment. The support structure may use mechanical, vacuum, electrostatic or other clamping techniques to hold the patterning device. The support structure may be a frame or a table, for example, which may be fixed or movable as required. The support structure may ensure that the patterning device is at a desired position, for example with respect to the projection system.

The term "patterning device" should be broadly interpreted as referring to any device that can be used to impart a radiation beam with a pattern in its cross-section, such as to create a pattern in a target portion of the substrate. The pattern imparted to the radiation beam may correspond to a particular functional layer in a device being created in the target portion, such as an integrated circuit.

The patterning device may be transmissive or reflective. Examples of patterning devices include masks, programmable mirror arrays, and programmable LCD panels. Masks are well known in lithography, and include mask types such as binary, alternating phase-shift, and attenuated phase-shift, as well as various hybrid mask types. An example of a programmable mirror array employs a matrix arrangement of small mirrors, each of which can be individually tilted so as to reflect an incoming radiation beam in different directions. The tilted mirrors impart a pattern in a radiation beam which is reflected by the matrix of mirrors.

Like the illumination system IL, the projection system PS can include various types of optical components, such as refractive, reflective, magnetic, electromagnetic, electrostatic or other types of optical components, or any combination thereof, as appropriate for the exposure radiation being used or other factors such as the use of a vacuum. It may be desirable to use a vacuum for EUV radiation since other gases may absorb too much radiation. Thus, a vacuum environment may be provided to the entire beam path by means of the vacuum wall and the vacuum pump.

As depicted herein, the apparatus is of a reflective type (e.g. employing a reflective mask). The lithographic apparatus may be of a type having two (dual stage) or more substrate tables (and/or two or more patterning device tables). In such "multiple stage" machines the additional tables may be used in parallel, or preparatory steps may be carried out on one or more tables while one or more other tables are being used for exposure.

Referring to fig. 9, the illuminator IL receives an euv radiation beam from a source collection module SO. Methods for generating EUV light include, but are not necessarily limited to, converting a material into a plasma state having at least one element (e.g., xenon, lithium, or tin) with one or more emission lines in the EUV range. In one such method, often referred to as laser plasma (LPP), the desired plasma may be generated by irradiating the fuel with a laser beamSuch as droplets, streams or clusters of material having elements that emit the desired spectral lines. The source collector module SO may be part of an EUV radiation system comprising a laser, not shown in fig. 9, for providing a laser beam for exciting the fuel. The resulting plasma emits output radiation, e.g., EUV radiation, which is collected using a radiation collector, deposited in the source collector module. The laser and source collector module may be separate entities, for example using carbon dioxide (CO)₂) A laser to provide a laser beam for fuel stimulation.

In such cases, the laser is not considered to form part of the lithographic apparatus and the radiation beam is passed from the laser to the source collector module by means of a beam delivery system comprising, for example, suitable directing mirrors and/or a beam expander. In other cases, the source may be an integral part of the source collector module, for example when the source is a discharge plasma EUV generator (which is often referred to as a DPP source).

The illuminator IL may comprise an adjuster to adjust the angular intensity distribution of the radiation beam. Generally, at least the outer and/or inner radial extent (commonly referred to as σ -outer and σ -inner, respectively) of the intensity distribution in a pupil plane of the illuminator can be adjusted. In addition, the illuminator IL may include various other components, such as a faceted field (facetted field) and pupil mirror device. The illuminator IL may be used to condition the radiation beam, to have a desired uniformity and intensity distribution in its cross-section.

The radiation beam B is incident on, and patterned by, a patterning device (e.g., a mask) MA, which is held on a support structure (e.g., a mask table) MT. After being reflected by the patterning device (e.g. mask) MA, the radiation beam B passes through the projection system PS, which focuses the beam onto a target portion C of the substrate W. With the aid of the second positioner PW and position sensor PS2 (e.g. an interferometric device, linear encoder or capacitive sensor), the substrate table WT can be moved accurately, e.g. so as to position different target portions C in the path of the radiation beam B. Similarly, the first positioner PM and another position sensor PS1 can be used to accurately position the patterning device (e.g. mask) MA with respect to the path of the radiation beam B. Patterning device (e.g. mask) MA and substrate W may be aligned using patterning device alignment marks M1, M2 and substrate alignment marks P1, P2.

The depicted apparatus may be used in at least one of the following modes:

1. in step mode, the support structure (e.g. mask table) MT and the substrate table WT are kept essentially stationary, while an entire pattern imparted to the radiation beam is projected onto a target portion C at one time (i.e. a single static exposure). The substrate table WT is then shifted in the X and/or Y direction so that a different target portion C can be exposed.

2. In scan mode, the support structure (e.g. mask table) MT and the substrate table WT are scanned simultaneously, while a pattern imparted to the radiation beam is projected onto a target portion C (i.e. a single static exposure). The velocity and direction of the substrate table WT relative to the support structure (e.g. mask table) MT may be determined by the (de-) magnification and image reversal characteristics of the projection system PS.

3. In another mode, the support structure (e.g., mask table) MT is kept essentially stationary holding a programmable patterning device, and the substrate table WT is moved or scanned while a pattern imparted to the radiation beam is projected onto a target portion C. In this mode, generally a pulsed radiation source is employed and the programmable patterning device is updated as required after each movement of the substrate table WT or in between successive radiation pulses during a scan. This mode of operation can be readily applied to maskless lithography that utilizes programmable patterning device, such as a programmable mirror array of a type as referred to above.

Combinations and/or variations on the above described modes of use or entirely different modes of use may also be employed.

FIG. 10 depicts an embodiment of lithographic apparatus 900 in more detail, including source collector module SO, illumination system IL, and projection system PS. The source collector module SO is constructed and arranged such that a vacuum environment may be maintained in the enclosure 1020 of the source collector module SO. The systems IL and PS are also contained within their own vacuum environment. The EUV radiation-emitting plasma 2 may be formed by a laser-produced LPP plasma source. The function of the source collector module SO is to deliver a beam 20 of EUV radiation from the plasma 2 such that it is focused to a virtual source point. The virtual source point is generally referred to as an Intermediate Focus (IF), and the source collector module is arranged such that the intermediate focus IF is located at or near an aperture 1021 in the enclosure 1020. The virtual source point IF is an image of the radiation-emitting plasma 2.

From an aperture 1021 at the intermediate focus IF, the radiation passes through an illumination system IL, which in this example comprises a faceted field mirror device 22 and a faceted pupil mirror device 24. These devices form a so-called "fly's eye" illuminator arranged to provide a desired angular distribution of the radiation beam 21 at the patterning device MA, and a desired uniformity of radiation intensity at the patterning device MA (as indicated by reference numeral 1060). When the beam 21 is reflected at the patterning device MA, which is held by the support structure (mask table) MT, a patterned beam 26 is formed and the patterned beam 26 is imaged by the projection system PS via

reflective elements

28, 30 onto a substrate W held by the substrate table WT. To expose a target portion C on the substrate W, pulsed radiation is generated to scan the pattern on the patterning device MA through the illumination slit while the substrate table WT and patterning device table MT perform a synchronized movement.

Each system IL and PS is disposed in its own vacuum or near-vacuum environment defined by an enclosure similar to enclosure 1020. There may generally be more elements in the illumination system IL and the projection system PS than shown. In addition, there may be more mirrors than shown. For example, there may be one to six additional reflective elements in the illumination system IL and/or the projection system PS in addition to those shown in FIG. 10.

Considering the source collector module SO in more detail, the laser energy source comprising the laser 1023 is arranged to deposit laser energy 1024 onto the fuel comprising the target material. The target material may be any material that emits EUV radiation in a plasma state, such as xenon (Xe), tin (Sn), or lithium (Li). The plasma 2 is a highly ionized plasma having an electron temperature of several tens of electron volts (eV). Higher energy EUV radiation may be generated using other fuel materials such as terbium (Tb) and gadolinium (Gd). Energetic radiation generated during de-excitation and recombination of these ions is emitted from the plasma, collected by near normal incidence collector 3 and focused on aperture 1021. The plasma 2 and the aperture 1021 are located at the first and second focus of the collector CO, respectively.

Although the collector 3 shown in fig. 10 is a single curved mirror, the collector may take other forms. For example, the collector may be a Schwarzschild collector having two radiation collecting surfaces. In one embodiment, the collector may be a grazing incidence collector comprising a plurality of substantially cylindrical reflectors nested within one another.

For delivering fuel, for example liquid tin, a droplet generator 1026 is arranged within the enclosure 1020, which is arranged to direct a high frequency stream 1028 of droplets towards a desired location of the plasma 2. In operation, laser energy 1024 is delivered simultaneously with the operation of the drop generator 1026 to deliver pulses of radiation to turn each fuel drop into a plasma 2. The drop delivery frequency may be several kilohertz, for example 50 kHz. In practice, the laser energy 1024 is delivered in at least two pulses: before the droplets reach the plasma location, a pre-pulse with limited energy is delivered to the droplets to vaporize the fuel material into a small-scale cloud, and then a main pulse of laser energy 1024 is delivered to the cloud at the desired location to generate the plasma 2. On the opposite side of the enclosing structure 1020 there are provided traps 1030 to trap fuel that for any reason has not been changed into plasma.

The droplet generator 1026 includes a reservoir 1001 containing a fuel liquid (e.g., molten tin), as well as a filter 1069 and a nozzle 1002. The nozzle 1002 is configured to eject droplets of the fuel liquid toward a formation position of the plasma 2. Droplets of fuel liquid may be ejected from nozzle 1002 by a combination of pressure within reservoir 1001 and vibration applied to the nozzle by a piezoelectric actuator (not shown).

As will be appreciated by those skilled in the art, reference axes X, Y and Z may be defined in order to measure and describe the geometry and behavior of the device, its various components, and the beams of

radiation

20, 21, 26. At each part of the device, X, Y local reference frames for the Z axis may be defined. In the example of fig. 10, the Z-axis generally coincides with the directional optical axis O at a given point in the system and is generally perpendicular to the plane of the patterning device (reticle) MA and to the plane of the substrate W. In the source collector module, the X-axis generally coincides with the direction of fuel flow 1028, while the Y-axis is orthogonal thereto, which is directed out of the page in FIG. 10. On the other hand, in the vicinity of the support structure MT holding the reticle MA, the X-axis is generally transverse to the scan direction aligned with the Y-axis. For convenience, in this region of the schematic of fig. 10, the X-axis points out of the page, also as labeled. These designations are conventional in the art and are employed herein for convenience. In principle, any frame of reference may be chosen to describe the device and its behavior.

A number of additional components used in the operation of the source collector module and lithographic apparatus 900 as a whole are present in conventional apparatus, but are not described herein. These additional components include arrangements for reducing or eliminating the effects of contamination within the enclosed vacuum, for example to prevent deposition of fuel material from damaging or impairing the performance of the collector 3 and other optics. Other features that are present but not described in detail are all sensors, controllers, and actuators involved in the control of the various components and subsystems of lithographic apparatus 900.

Referring to fig. 11, an embodiment of an LPP EUV light source 1100 is shown. The light source 1100 may be used as a source collector module SO in the lithographic apparatus 900. Furthermore, light generation module 105 in fig. 1A and 2A, light generation module 505 in fig. 5, light generation module 305b in fig. 3, or light generation module 405b in fig. 4 may be part of drive laser 1115. A drive laser 1115 may be used as the laser 1023 (fig. 10).

The LPP EUV light source 1100 is formed by irradiating a target mixture 1114 at a plasma formation location 1105 with an amplified light beam 1110 that travels along a beam path toward the target mixture 1114. The plasma formation site 1105 is within the interior 1107 of the vacuum chamber 1130. When the amplified light beam 1110 strikes the target mixture 1114, the target material within the target mixture 1114 is converted to a plasma state, which possesses elements having emission lines in the EUV range. The plasma created has certain characteristics that depend on the composition of the target material within the target mixture 1114. These characteristics include the wavelength of EUV light generated by the plasma and the type and amount of debris released from the plasma.

The light source 1100 also includes a supply system 1125 that delivers, controls, and directs a target mixture 1114 in the form of liquid droplets, liquid streams, solid particles or clusters, solid particles contained within droplets, or solid particles contained within liquid streams. The target mixture 1114 comprises a target material, which is, for example, water, tin, lithium, xenon, or any material that has an emission line in the EUV range when converted to a plasma state. For example, elemental tin may be used as pure tin (Sn); as tin compounds, e.g. SnBr₄、SnBr₂、SnH₄(ii) a As a tin alloy, for example a tin-gallium alloy, a tin-indium-gallium alloy, or any combination of these alloys. The target mixture 1114 may also include impurities other than the target particles. Thus, the target mixture 1114 consists of only the target substance without impurities. A target mixture 1114 is delivered by a supply system 1125 into the interior 1107 of the chamber 1130 and into the plasma formation location 1105.

The optical source 1100 includes a driven laser system 1115 that generates an amplified optical beam 1110 due to population inversion within one or more gain media of the laser system 1115. The light source 1100 includes a beam delivery system between the laser system 1115 and the plasma formation location 1105, including a beam delivery system 1120 and a focusing assembly 1122. The beam delivery system 1120 receives the amplified light beam 1110 from the laser system 1115, manipulates and modifies the amplified light beam 1110 as desired, and outputs the amplified light beam 1110 to the focusing assembly 1122. The focusing assembly 1122 receives the amplified light beam 1110 and focuses the beam 1110 to the plasma formation location 1105.

In some embodiments, the laser system 1115 may include one or more optical amplifiers, lasers, and/or lamps to provide one or more primary pulses, and in some cases one or more pre-pulses. Each optical amplifier includes a gain medium capable of optically amplifying a desired wavelength with high gain, an excitation source, and internal optics. The optical amplifier may or may not have a laser mirror or other feedback device that forms the laser cavity. Thus, the laser system 1115 generates the amplified light beam 1110 due to population inversion in the gain medium of the laser amplifier even in the absence of a laser cavity. Further, if a laser cavity is present to provide sufficient feedback to the laser system 1115, the laser system 1115 may generate the amplified light beam 1110 as a coherent laser beam. The term "amplified light beam" encompasses one or more of the following: light from the laser system 1115 that is only amplified but not necessarily coherent laser light oscillation, and light from the laser system 1115 that is amplified and also coherent laser light oscillation.

The optical amplifier in the laser system 1115 may include a CO as a gain medium₂And may amplify light of a wavelength between about 9100nm and about 11000nm, and particularly about 10600nm, with a gain of greater than or equal to 800 times. Suitable amplifiers and lasers for use in the laser system 1115 may include pulsed laser devices, such as pulsed gas discharge CO₂Laser apparatus, for example using DC or RF excitation, producing radiation of about 9300nm or about 10600nm, operating at a relatively high power, for example 10kW or more, and a high pulse repetition rate, for example 40kHz or more. The pulse repetition rate may be 50kHz, for example. The optical amplifier in the laser system 1115 may also include a cooling system, such as water, which may be used when operating the laser system 1115 at higher power.

The light source 1100 includes a collector mirror 1135 having an aperture 1140 to allow the amplified light beam 1110 to pass through and reach the plasma formation location 1105. Collector mirror 1135 may be, for example, an ellipsoidal mirror having a primary focus at plasma formation location 1105 and a secondary focus (also referred to as an intermediate focus) at an intermediate location 1145 where EUV light may be output from light source 1100 and may be input, for example, to an integrated circuit lithography tool (not shown). The light source 1100 may also include an open-ended hollow conical shroud 1150 (e.g., gas cone) that tapers from the collector mirror 1135 toward the plasma formation location 1105 to reduce the amount of debris generated by the plasma entering the focusing assembly 1122 and/or beam delivery system 1120 while allowing the amplified light beam 1110 to reach the plasma formation location 1105. For this purpose, a gas flow may be provided in the shield leading to the plasma formation site 1105.

The light source 1100 may also include a master controller 1155 that is connected to the droplet position detection feedback system 1156, the laser control system 1157, and the beam control system 1158. The light source 1100 may include one or more target or droplet imagers 1160 that provide an output indicative of the position of a droplet, for example, relative to the plasma formation location 1105 and provide that output to a droplet position detection feedback system 1156, which droplet position detection feedback system 1156 may, for example, calculate droplet position and trajectory from which droplet position errors may be calculated on a droplet-by-droplet basis or on average. The drop position detection feedback system 1156 thus provides this drop position error as an input to the master controller 1155. The main controller 1155 may thus, for example, provide laser position, orientation, and timing correction signals to a laser control system 1157, which may be used, for example, to control laser timing circuitry, and/or to a beam control system 1158 to control the position of the amplified light beam and the shaping of the beam delivery system 1120 to change the position and/or power of the beam focus within the chamber 1130.

Supply system 1125 includes a target material delivery control system 126 that is operable in response to signals from main controller 1155, for example, to modify the release point of droplets as released by target material supply 1127 in order to correct for errors in droplets arriving at the desired plasma formation location 1105.

In addition, the light source 1100 can include

light source detectors

1165 and 1170 that measure one or more EUV light parameters including, but not limited to, pulse energy, energy distribution as a function of wavelength, energy within a particular wavelength band, energy outside of a particular wavelength band, and angular distribution of EUV intensity and/or average power. The light source detector 1165 generates a feedback signal for use by the master controller 1155. The feedback signal may, for example, indicate errors in parameters such as timing and focus of the laser pulses to intercept the droplet at the correct place and time for efficient and effective production of EUV light.

The light source 1100 may also include a steering laser 1175 that may be used to align the various segments of the light source 1100 or to assist in steering the amplified light beam 1110 to the plasma formation location 1105. In conjunction with the pilot laser 1175, the light source 1100 includes a metrology system 1124 positioned within the focusing assembly to sample a portion of the light from the pilot laser 1175 and the amplified light beam 1110. In other embodiments, metrology system 1124 is positioned within beam delivery system 1120. Metrology system 1124 can include optical elements that sample or redirect a subset of the light, such optical elements being made of any material that is resistant to the power of the directed laser beam and the amplified light beam 1110. The metrology system 1124 and the main controller 1155 form a beam analysis system because the main controller 1155 analyzes the sampled light from the pilot laser 1175 and uses this information to adjust the components within the focusing assembly 1122 via the beam control system 1158.

Thus, in summary, the light source 1100 produces an amplified light beam 1110 that is directed along a beam path to irradiate a target mixture 1114 at a plasma formation location 1105 to convert target material within the mixture 1114 into a plasma that emits light in the EUV range. The amplified light beam 1110 operates at a specific wavelength (which is also referred to as the drive laser wavelength) determined based on the design and properties of the laser system 1115. Further, the amplified light beam 1110 may be a laser beam when the target material provides sufficient feedback to the laser system 115 to produce a coherent laser or where the drive laser system 1115 includes appropriate optical feedback to form a laser cavity.

Other implementations are within the scope of the following claims. The modulation elements discussed above may be implemented to produce any type of pattern on the target. For example, the modulation element 222 may produce different component patterns than shown in the example of fig. 2A. In some embodiments, the modulation element 222 is implemented such that all components are on the zeroth order side. Furthermore, modulating element 522 may also be implemented in such a way that all but component 533d propagates toward target region 542a without requiring beam dump 528.

Other aspects of the invention are given in the following numbered clauses.

1. A system, comprising:

a spatial modulation device configured to interact with a light beam to create a modified light beam comprising a spatial pattern of light having a non-uniform intensity along a direction perpendicular to a direction of propagation of the modified light beam, the spatial pattern of light comprising one or more light components; and

a target supply system configured to provide a target to a target region, the target comprising a target material that emits EUV light when in a plasma state, wherein the target region overlaps a beam path such that at least some of the one or more light components in the modified beam interact with a portion of the target.

2. The system of clause 1, wherein the spatial modulation device comprises a diffractive optical element.

3. The system of clause 2, wherein the diffractive optics comprise a Spatial Light Modulator (SLM), adaptive optics, a reticle, and/or a grating.

4. The system of clause 1, wherein the spatial modulation device comprises a refractive optical element.

5. The system of clause 4, wherein the spatial modulation device comprises a lens, a lenslet array, and/or a reticle.

6. The system of clause 1, wherein the spatial pattern of light comprises two or more light components, and each of the two or more light components has substantially the same intensity.

7. The system of clause 1, wherein the spatial pattern of light comprises two or more light components arranged in a rectilinear grid.

8. The system of clause 2, wherein the spatial modulation device comprises at least one dammann grating.

9. The system of clause 1, further comprising:

a first light generating module configured to emit the light beam; and

a second light generating module configured to emit a second light beam.

10. The system of clause 1, wherein the spatial modulation device is further configured to interact with the second light beam to create a second modified light beam, the second modified light beam comprising a second spatial pattern of light having a non-uniform intensity along a direction perpendicular to a direction of propagation of the second modified light beam, the second spatial pattern of light comprising one or more second light components.

11. A method of forming a target for an Extreme Ultraviolet (EUV) light source, the method comprising:

directing a light beam onto a beam path;

causing the light beam to interact with a spatial modulation device located on the beam path to form a modified light beam comprising a spatial pattern of light having a non-uniform intensity along a direction perpendicular to a direction of propagation of the modified light beam, the spatial pattern of light comprising one or more light components; and is

Causing the modified beam of light to interact with a target comprising a target material that emits EUV light when in a plasma state, wherein at least some of the one or more light components in the spatial pattern interact with a region of the target to modify a property of the region of the target.

12. The method of clause 11, wherein the attribute comprises a density and modifying the attribute comprises reducing the density.

13. The method of clause 11, wherein the spatial pattern of light comprises two or more light components.

14. The method of clause 13, wherein all light components have the same intensity.

15. The method of clause 13, wherein the light components are arranged in a grid and the region of the target that directly interacts with light components is arranged in a grid.

16. The method of clause 11, further comprising interacting the modified beam with a focusing component prior to interacting the modified beam with the target.

17. The method of clause 13, wherein the light components are spatially separated and spatially discrete such that the portion of the target between any two light components does not interact with any of the components in the modified light beam.

18. The method of clause 11, further comprising:

causing an initial target to interact with a second beam of light to form a modified target having a greater extent in a first direction than the initial target and a lesser extent in a second direction than the initial target, the first and second directions being orthogonal to each other, and wherein

Causing the modified beam to interact with a target comprising a target material that emits EUV light when in a plasma state comprises: causing the modified light beam to interact with the modified target and each of the one or more light components to interact with a region of the modified target to modify a property of the region of the modified target.

19. The method of clause 18, further comprising after interacting the modified beam with the altered target, interacting the altered target with a third beam of light having an energy sufficient to convert at least some target material in the altered target to the plasma that emits EUV light.

20. The method of clause 11, further comprising, after interacting the target with the modified beam, interacting the target with another beam having an energy sufficient to convert at least some of the target material in a second altered target to the plasma that emits EUV light.

21. The method of clause 20, wherein the attributes comprise conversion efficiency related to the amount of EUV light emitted and the energy of the other beam, and modifying the attributes of a portion of the target comprises increasing the conversion efficiency associated with the entire target.

22. The method of clause 20, wherein the beam and the other beam are temporally connected and are part of a single light pulse.

23. The method of clause 11, wherein the attribute comprises a surface area of the target, and modifying the attribute of any portion of the target comprises increasing the surface area of the entire target.

24. The method of clause 23, wherein the amount of increase in the surface area is related to the number of light components in the modified light beam.

25. The method of clause 11, wherein interacting the modified beam with a target comprising a target material that emits EUV light while in a plasma state comprises: such that the modified light beam interacts with a target having a substantially spherical shape.

Other implementations are within the scope of the following claims.

Claims

1. A system, comprising:

2. The system of claim 1, wherein the spatial modulation device comprises a diffractive optical element.

3. The system of claim 2, wherein the diffractive optics comprise a Spatial Light Modulator (SLM), adaptive optics, a reticle, and/or a grating.

4. The system of claim 1, wherein the spatial modulation device comprises a refractive optical element.

5. The system of claim 4, wherein the spatial modulation device comprises a lens, a lenslet array, and/or a reticle.

6. The system of claim 1, wherein the spatial pattern of light comprises two or more light components, and each of the two or more light components has substantially the same intensity.

7. The system of claim 1, wherein the spatial pattern of light comprises two or more light components arranged in a rectilinear grid.

8. The system of claim 2, wherein the spatial modulation device comprises at least one dammann grating.

9. The system of claim 1, further comprising:

a first light generating module configured to emit the light beam; and

a second light generating module configured to emit a second light beam.

10. The system of claim 1, wherein the spatial modulation device is further configured to interact with the second light beam to create a second modified light beam comprising a second spatial pattern of light having a non-uniform intensity along a direction perpendicular to a direction of propagation of the second modified light beam, the second spatial pattern of light comprising one or more second light components.

directing a light beam onto a beam path;

12. The method of claim 11, wherein the attribute comprises a density and modifying the attribute comprises reducing the density.

13. The method of claim 11, wherein the spatial pattern of light comprises two or more light components.

14. The method of claim 13, wherein all light components have the same intensity.

15. The method of claim 13, wherein the light components are arranged in a grid and the region of the target with which the light components directly interact is arranged in a grid.

16. The method of claim 11, further comprising: interacting the modified beam with a focusing component prior to interacting the modified beam with the target.

17. The method of claim 13, wherein the light components are spatially separated and spatially discrete such that the portion of the target between any two light components does not interact with any component in the modified light beam.

18. The method of claim 11, further comprising:

19. The method of claim 18, further comprising: after interacting the modified beam with the altered target, the altered target interacts with a third beam of light having an energy sufficient to convert at least some target material in the altered target to the plasma that emits EUV light.

20. The method of claim 11, further comprising: after interacting the target with the modified beam, interacting the target with another beam having an energy sufficient to convert at least some of the target material in a second altered target to the plasma that emits EUV light.

21. The method of claim 20, wherein the properties include conversion efficiency related to an amount of EUV light emitted and energy of the other beam, and modifying the properties of a portion of the target comprises: increasing the conversion efficiency associated with the overall target.

22. The method of claim 20, wherein the beam and the other beam are temporally connected and are part of a single light pulse.

23. The method of claim 11, wherein the property comprises a surface area of the target, and modifying the property of any portion of the target comprises: increasing the surface area of the entire target.

24. The method of claim 23, wherein the amount of increase in the surface area is related to the number of light components in the modified light beam.

25. The method of claim 11, wherein interacting the modified beam with a target comprising a target material that emits EUV light while in a plasma state comprises: such that the modified light beam interacts with a target having a substantially spherical shape.