Spatial Modulation of Light Beam

Abstract

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

Description

[0001] Cross - Reference to Related Applications

[0002] This application claims priority to U.S. Application No. 62 / 651,928, filed on Apr. 3, 2018, the entire content of which is incorporated herein by reference. Technical Field

[0003] The present disclosure relates to techniques for spatially modulating a light beam. Such techniques can be used, for example, in an extreme ultraviolet (EUV) light source. The light beam can be, for example, a beam that irradiates a target material or a fuel material. Background Art

[0004] Extreme ultraviolet (EUV) light - which is electromagnetic radiation having a wavelength of 100 nanometers (nm) or shorter (sometimes also referred to as soft x-rays), and includes light having a wavelength, for example, of 20 nm or shorter, between 5 nm and 20 nm, or between 13 nm and 14 nm - can be used in a lithography process to create extremely small features in a substrate such as a silicon wafer by initiating polymerization in a resist layer.

[0005] 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 includes elements having emission spectral lines in the EUV range, such as xenon, lithium, or tin. In one such method, often referred to as laser-produced plasma (LPP), the desired plasma can be generated by irradiating a target including the target material with an amplified light beam that can be referred to as a drive laser. For this purpose, the plasma is typically generated in a sealed container such as a vacuum chamber and observed using various types of metrology instruments. The target material can be in the form of droplets, plates, ribbons, streams, or clusters. Summary of the Invention

[0006] In one general aspect, a system includes a spatial modulation device configured to interact with a light beam to create a modified light beam that includes a spatial pattern of light having a non-uniform intensity along a direction perpendicular to the propagation direction of the modified light beam, the spatial pattern of light including one or more light components; and a target supply system configured to supply a target to a target region, the target including 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.

[0007] Embodiments may include one or more of the following features. The spatial modulation device may be a diffractive optical element. The diffractive optical device may be a spatial light modulator (SLM), an adaptive optical device, a reticle, and / or a grating. The spatial modulation device may be a refractive optical element. The refractive optical device may be a lens, a microlens array, and / or a reticle.

[0008] The spatial pattern of the 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 the light may include two or more light components arranged in a linear grid. The spatial modulation device may include at least one Dammann grating.

[0009] The spatial modulation device may also be configured to interact with a second light beam to create a second modified light beam that includes a second spatial pattern of light having a non-uniform intensity in a direction perpendicular to the propagation direction of the second modified light beam, and the second spatial pattern of light includes one or more second light components.

[0010] In some embodiments, the system further includes a first light generation module configured to emit a light beam and a second light generation module configured to emit a second light beam.

[0011] In another general aspect, a method of forming a target for an extreme ultraviolet (EUV) light source includes 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 that includes a spatial pattern of light having a non-uniform intensity in a direction perpendicular to the propagation direction of the modified light beam, and the spatial pattern of light includes one or more light components; and causing the modified light beam to interact with a target including 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 an attribute of the region of the target.

[0012] Embodiments 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 attribute may be the surface area of the target, and in these embodiments, modifying the attribute of any part 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.

[0013] The spatial pattern of the 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 discrete such that the portion of the target between any two light components does not interact with any component of the modified beam. In some embodiments, the method further includes causing the modified beam to interact with a focusing component before causing the modified beam to interact with the target.

[0014] In some embodiments, the method further includes causing an initial target to interact with a second beam to form a modified target that has a greater extent in a first direction and a smaller 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 to interact with a target comprising a target material that emits EUV light when in a plasma state includes causing the modified beam to interact with the modified target, and each of the one or more light components interacts with a region of the modified target to modify an attribute of the region of the modified target. Additionally, in some embodiments, after causing the modified beam to interact with the modified target, the modified target interacts with a third beam that has an energy sufficient to convert at least some of the target material in the modified target into a plasma that emits EUV light.

[0015] The method may also include, after causing the target to interact with the modified beam, causing the target to interact with another beam that has an energy sufficient to convert at least some of the target material in a second modified target into a plasma that emits EUV light. The beam and the other beam may be temporally connected and part of a single light pulse. The attribute may include a conversion efficiency related to the amount of EUV light emitted and the energy of the other beam, and modifying an attribute of a portion of the target includes increasing the conversion efficiency associated with the entire target.

[0016] Causing the modified beam to interact with a target comprising a target material that emits EUV light when in a plasma state includes causing the modified beam to interact with a target having a substantially spherical shape.

[0017] Implementations 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. Details of one or more implementations are given in the drawings and the following description. Other features will be apparent from the description and drawings, and from the claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1A is a block diagram of an example of an EUV light source.

[0019] Figure 1B is an intensity plot of an example of a light beam as a function of position in a direction perpendicular to the propagation direction before spatial modulation.

[0020] Figure 1C is, after spatial modulation, of Figure 1B an example of a light beam as a function of position in a direction perpendicular to the propagation direction.

[0021] Figure 1D is of an example of a target interacting with Figure 1C a light beam.

[0022] Figure 2A is a block diagram of another example of an EUV light source.

[0023] Figure 2B is a block diagram of another example of a target.

[0024] Figure 2C is an intensity plot of another example of a light beam as a function of position in a direction perpendicular to the propagation direction after spatial modulation.

[0025] Figure 2D is a block diagram of an example of a modified target.

[0026] Figures 2E - 2G is an example of a light pattern in a target region.

[0027] Figures 3 - 6 is a block diagram of an additional example of an EUV light source.

[0028] Figure 7 is an illustration of a target region varying with time.

[0029] Figure 8 is of Figure 7 a target region varying with Figure 7 a time scale of

[0030] Figure 9 is a block diagram of an example of a lithographic apparatus.

[0031] Figure 10 A block diagram of an example of an EUV lithography system.

[0032] Figure 11 A block diagram of an example of an EUV light source. DETAILED DESCRIPTION

[0033] Techniques for spatially modulating a light beam are disclosed. The spatially modulated light beam is used to irradiate a target material or a fuel material.

[0034] REFERENCE Figure 1A , a side view of an extreme ultraviolet (EUV) light source 100 is shown. The EUV light source 100 includes a light generation module 105 that emits a light beam 106 onto a beam path 107 and towards a spatial modulation device 120 that includes a modulation element 122. The interaction between the modulation element 122 and the light beam 106 forms a modified light beam 132. The modified light beam 132 interacts with a target 140 in a target region 142. The light beam 106 can be a pulsed light beam that includes light pulses that are temporally separated from each other. In these embodiments, the modified light beam 132 is also a pulsed light beam.

[0035] The target 140 includes a target material or a fuel material that emits EUV light when in a plasma state. The target material includes a target substance and can also include impurities such as non-target particles. The target substance is a substance that is converted into a plasma state having emission spectral lines in the EUV range. For example, the target substance can be water, tin, lithium, xenon, or any material that has emission spectral lines in the EUV range when converted into a plasma state. For example, the target substance can be elemental tin, which can be used as pure tin (Sn); as a tin compound, such as SnBr4, SnBr2, SnH4; as a tin alloy, such as a tin-gallium alloy, a tin-indium alloy, a tin-indium-gallium alloy, or any combination of these alloys. In the absence of impurities, the target material includes only the target substance.

[0036] The target 140 can take any form that is beneficial for the generation of a plasma that emits EUV light. For example, the target 140 can be a droplet of a liquid or a molten metal, a portion of a liquid stream, a solid particle or cluster, a solid particle contained within a droplet, a foam of the target material, or a solid particle contained within a portion of a liquid stream. The target 140 can take other forms. For example, the target 140 can be a continuous segment of a molten metal that is substantially dish-shaped. The target 140 can be a collection of particles that occupy a substantially dish-shaped volume or a hemispherical volume. The target 140 is a continuous segment of the target material that does not have gaps or voids, a fog of nano- or micro-particles, or a cloud of atomic vapor.

[0037] The present technology relates to spatially modulating a beam 106 prior to its interaction with a target 140. As discussed below, spatially modulating the beam 106 can result in an increase in conversion efficiency (CE) and / or a reduction in debris generation.

[0038] The modulation element 122 is an optical element capable of spatially modulating the beam 106 to form a modified beam 132. The modulation element 122 can be a diffractive optical element, which is any structure capable of modulating the beam 106 by diffraction. The diffractive optical element can be, for example, a grating, a spatial light modulator (SLM), an acousto-optic modulator (AOM), an acousto-optic deflector (AOD), an aperture or collection of apertures arranged in a plane to create a specific diffraction pattern, and / or a mask. The modulation element 122 can be a refractive optical element, such as a two-dimensional array of lenses or other arrangements of lenses, a phase plate, a deformable mirror, and / or a refractive mask. The modulation element 122 can include 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 can be placed serially on the beam path 107 and rotated relative to each other about the beam path 107 to form a more complex diffraction pattern corresponding to a more complex spatial modulation of the beam 106. In some embodiments, the modulation element 122 includes both refractive and diffractive optical elements. Additionally, the modulation element 122 can be any type of adaptive optical device, such as, by way of example, a deformable mirror.

[0039] Furthermore, the modulation element 122 can be static or dynamic. A static modulation element is one in which the structure of the modulation element 122 is fixed at the time the modulation element 122 is manufactured and does not change after the modulation element 122 is formed. A dynamic modulation element is one in which the spatial modulation imposed by the interaction between the beam 106 and the modulation element 122 can change or be adjusted during the lifetime of the modulation element 122. For example, the spatial modulation imposed by an AOM on an incident beam depends on the properties of an acoustic wave propagating in a medium (such as quartz) through which the incident beam passes. Thus, by changing the amplitude and / or period of the acoustic wave, the characteristics of the modulation provided by the AOM can also be changed. In this way, an AOM can be considered a dynamic modulation element. An SLM can also be used as a dynamic modulation element. A deformable mirror or any other type of adaptive optical element can also be used as a dynamic modulation element. On the other hand, a small lens array and a blazed diffraction grating formed from classical or traditional refractive and / or reflective materials, whose optical and mechanical properties are not intended to be changed by the end user, are examples of static modulation elements.

[0040] Due to the optical modulation, the spatial profile of the modified beam 132 is different from the spatial profile of the beam 106. The spatial profile of a beam is a property of the beam (e.g., intensity and / or phase) as a function of position along a direction that is in a plane perpendicular to the propagation direction. Thus, the modified beam 132 can have an intensity and / or phase profile that is different from that of the beam 106. The characteristics of the profile of the modified beam 132 depend on the characteristics and / or arrangement of the modulation element 122. For example, in an embodiment where the modulation element 122 is a diffraction grating, the angle at which the diffraction orders propagate away from the modulation element 122 (and thus the position at which the diffraction orders are in the target region 142) depends on the spacing between the grooves on the diffraction element.

[0041] In Figure 1A the example of, the beams 106 and the modified beam 132 generally propagate along the Z direction. Figure 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. Figure 1C is a plot of the intensity (in arbitrary units) of the modified beam 132 at the target region 141 as a function of position along the direction X. In Figures 1A - 1C the example of, the intensity profile of the beam 106 is substantially Gaussian. Due to the interaction between the beam 106 and the modulation element 122, the intensity profile of the modified beam 132 is different from the intensity profile of the beam 106. Figure 1C The intensity profile shown in is along a single line in the X-Y plane. The intensity profiles of the modified beam 132 at other lines in the X-Y plane along the X direction can be the same as or different from the intensity profile shown in Figure 1C In other words, the spatial profile of the modified beam 132 can vary along the X direction, along the Y direction, or along both the X and Y directions.

[0042] The properties of the spatial profile of the modified beam 132 depend on the configuration of the modulation element 122. For example, the modified beam 132 can have a profile in which the intensity of the modified beam 132 varies continuously as a function of position in the X-Y plane and there are no regions that do not include light, such as the example shown in Figure 1C In some embodiments, the modified beam 132 is formed of discrete components that are separated from each other, such that the profile of the modified beam 132 includes regions that are substantially devoid of light. An example of such a modified beam 132 is shown in Figure 2C In any case, the profile of the modified beam 132 is different from the profile of the beam 106 due to the interaction between the modulation element 122 and the beam 106.

[0043] The modified beam 132 illuminates the target 140. Figure 1CThe intensity profile of the modified beam 132 shown in interacts with the target 140 at line C-C'. Figure 1D ) Since the spatial profile of the modified beam 132 is different from that of the beam 106, the modified beam 132 interacts with the target 140 in a different manner than the beam 106. For example, compared to the beam 106, the modified beam 132 provides relatively more light to portions 140a and 140c near the outer edges of the target 140 than to the portion 140 near the center of the target 140.

[0044] As discussed below, using the modulation element 122 allows the spatial profile of the light interacting with the target 140 to be customized to consume more 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 a separate beam that converts the target material in the target 140 into a plasma emitting EUV light. Additionally, by increasing the amount of target material consumed, using the modified beam 132 also reduces debris generated by the interaction between the target 140 and the beam.

[0045] Furthermore, the modulation element 122 can be configured such that the modified beam 132 has a profile 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 its lower edge than near its center or upper edge. For such a target, the modulation element 122 can be configured to produce a modified beam having a spatial profile such as Figure 1C shown in.

[0046] Figure 1A Only a single beam 106 is illustrated in the example of. However, the light source 100 can use more than one beam, and each of the more than one beam can interact with a different form of the target 140. For example, the light source 100 can use one or more "pre-pulse" beams that shape, change, or otherwise modify one or more properties of the target 140 (without necessarily generating a plasma emitting EUV light) to produce a modified target or an intermediate target. These embodiments can also use a "main pulse" beam having an energy sufficient to convert the target material in the modified or intermediate target into a plasma emitting EUV light. Figure 3 、 4Figs. 6 show examples of embodiments of EUV light source 100 using more than one pulsed beam. Any or all of the beams used in EUV light source 100 can interact with modulation element 122 to modify the spatial profile of the beam. In embodiments where light source 100 uses more than one grating, light source 100 can include more than one spatial modulation device 120. For example, in these embodiments, light source 100 can include separate spatial modulation devices 120 positioned to interact with each of more than one beam.

[0047] Reference Figure 2A , shows a side view of EUV light source 200. EUV light source 200 is an example of an embodiment of EUV light source 100 ( Figure 1A ).

[0048] EUV light source 200 includes modulation device 220. Modulation device 220 includes modulation element 222 that spatially modulates beam 106 to produce modified beam 232 including components 233, where each component 233 is also a beam. Components 233 can be separated from each other such that there is a region of no light (or significantly reduced light) between each component and one or more of its adjacent components. Modified beam 233 includes a number of individual components, and the individual components are collectively referred to as components 233. Figure 2A Components 233a, 233b, 233c, 233d, 233e are shown in. Modulation element 222 can be a diffraction grating. In these embodiments, each of components 233a, 233b, 233c, 233d, 233e is a diffraction order. Component 233c can be the zero order that is not diffracted by modulation element 222. In these embodiments, component 233c generally propagates in the same direction as beam 106. In Figure 2A 's example, each of components 233a, 233b, 233c, 233d, 233e propagates away from the diffraction grating in a different direction.

[0049] Modified beam 232 also includes other components that, together with components 233a, 233b, 233c, 233d, and 233e, form a two-dimensional grid pattern in the X-Y plane at target region 232. Figure 2B Shows target region 242 in the X-Y plane. In Figure 2B , the solid circles represent components 233 in target region 242. In Figure 2B 's example, all components 233 interact with corresponding parts of target 140. Element labeled 243 represents the part that interacts with component 233a. For simplicity, Figure 2BOnly one part 243 is marked out. However, other components 233 interact with other parts of the target 140. Part 243 is illustrated as a circular area on the target 140. However, the interaction between component 233a and the target 140 can affect parts of the target 140 other than those marked as 243 in Figure 2B and part 243 is not necessarily a circular area.

[0050] Figure 2C is a plot of the intensities of components 233a - 233e of the modified beam 232 as a function of the position along direction X. In Figure 2C the example, the intensities of components 233a - 233e vary. In other embodiments, the modulation element 222 is a diffractive element that produces diffractive orders of equal intensity. For example, in these embodiments, the modulation element 222 can be a Dammann grating.

[0051] The interaction between component 233 and the target 140 produces a modified target 245 ( Figure 2D ). The modified target 245 has a modified area 244 formed by interacting component 233 with the target 140. For simplicity, only the interaction between the target material in part 243 and component 233a is discussed and only one modified area 244 is marked out. However, other components interact with the target material in other parts of the target 140 in a similar manner and form other modified areas. Figure 2D The other modified areas are shown as dashed circular areas.

[0052] The interaction between the target material in portion 242 and component 233a changes the physical properties of portion 243. For example, the interaction can change the geometric distribution of portion 243 by removing some of the target material from portion 243 to thereby form a recessed region. In this example, the modified region 244 is the recessed region. The recessed region is a region lacking the target material. The recessed region can be a void. The target material can be removed, for example, by ablation, sputtering, and / or conversion to a plasma that does not emit EUV light or emits only a minimal amount of EUV light. The recessed region can be an opening, a pocket, or an aperture in the modified target 245. The recessed region can pass through the modified target 245. Additionally, the recessed region can have any shape. For example, the recessed region can be a cone or a 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 the recessed region depend on the intensity and diameter of component 233a and the properties of the target material in portion 243. The interaction between component 233a and portion 243 can change the properties of portion 243 in other ways. For example, the interaction can reduce the density of portion 243. In this example, the modified region 244 is a region where the density of the target material may be reduced.

[0053] As discussed above, although Figure 2D only one modified region 244 is marked in, other modified regions are formed to produce the modified target 245. The various modified regions on the modified target 245 can have different characteristics from each other.

[0054] Regardless of how the interaction changes the specific properties of portion 243 (or other unmarked portions), the interaction between component 233 and target 130 forms the modified target 245, which is more easily converted into 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 greater amount of target material being exposed to the incident light beam, thereby allowing more target material to be converted into a plasma that emits EUV light.

[0055] Component 233 in Figure 2B The two-dimensional grid pattern formed in is only one possible pattern that can be formed in the target region 242. Other patterns can be generated according to the configuration and characteristics of the modulation element 222. Figures 2E - 2G Examples of components in other patterns are shown. Figure 2E Includes component 233_E, which is concentric rings separated by lightless regions. Component 233_E can be formed, for example, in an embodiment where the modulation element 222 is a circular aperture. Figure 2F Shows component 233_F arranged in a one-dimensional array. InFigure 2F In the example, component 233_F has a rectangular cross-section. Figure 2G FIG. illustrates yet another example of the arrangement of component 233_G. Component 233_G is represented as a solid circle. Figure 2G The target regions 142 in the X-Y and X-Z planes are shown. In Figure 2G the example, component 233_G propagates generally in the Z direction and the -X direction. Thus, component 233_G reaches the target region 142 from more than one direction and interacts with the target 140 at the surfaces of the X-Y plane and the X-Z plane.

[0056] Figure 3 is a block diagram of an EUV light source 300. The EUV light source 300 is Figure 1A an example of an embodiment of the light source 100. The EUV light source 300 includes a first light generation module 305a and a second light generation module 305b. The first light generation module 305a emits a first light beam 306a onto a beam path 307a, and the light generation module 305b emits a second light beam 306b onto a beam path 307b. The first light beam 306a is used to form a modified light beam 332a. The modified light 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 light beam 306a may be referred to as a "pre-pulse" light beam. The second light beam 306b is a light beam having an energy sufficient to convert the target material in the modified region 345 into a plasma that emits EUV light 399. The second light beam 306b may be referred to as a "main pulse" light beam or a heating light beam. The first light generation module 305a and / or the second light generation module 305b are controlled such that for a specific pairing of the pre-pulse and the main pulse - where the pre-pulse forms the modified target 345 and the main pulse converts the modified target 345 into a plasma that emits EUV light - the pre-pulse occurs before the main pulse.

[0057] The light generation module 305b can be, for example, a carbon dioxide (CO2) laser, and the wavelength of the second light beam 306b can be, for example, 10.59 micrometers (μm). The first light generation module 305a can 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 can be, for example, 1.06 μm. In some embodiments, the first light generation module 305a and the second light generation module 305b are light sources of the same type. For example, the first and second light generation modules 305a, 305b can both be CO2 lasers. In these embodiments, the first and second light generation modules 305a, 305b can have the same spectral content. For example, the first and second light generation modules 305a, 305b can both have a wavelength of 10.59 μm. In yet another example, the first and second light generation modules 305a, 305b can both be solid-state lasers. In these embodiments, the first and second light generation modules 305a, 305b can both have a wavelength of, for example, 1.06 μm.

[0058] In one embodiment, light sources of the same type are used for the first and second light generation modules 305a, 305b, but the spectral content of the first and second light beams 306a, 306b is different. For example, the first and second light generation modules 305a, 305b can be implemented as a single module including two CO2 seed laser subsystems and an amplifier. One of the seed laser subsystems generates a first light beam 306a having a wavelength of, for example, 10.26 μm, while the other seed laser subsystem generates a second light beam 306b having a wavelength of, for example, 10.59 μm. These two wavelengths can be from different spectral lines of the CO2 laser.

[0059] In addition, wavelengths other than those provided in the examples above can be used. For example, either or both of the first light beam 306a and the second light beam 306b can have a wavelength less than 1 μm. Using a relatively short wavelength (such as a wavelength less than 1 μm) can be advantageous in some cases. For example, a relatively short wavelength enables a smaller focal spot size to be obtained, which allows for improved control of beam shaping.

[0060] The first light beam 306a interacts with the modulation element 322 to generate a modified light beam 332a. The modulation element 322 is any optical component or collection of components capable of spatially modulating the first light beam 306a. The modified light beam 332a has a spatial profile different from that of the first light beam 306a. The spatial profile of the modified light beam 332a depends on the configuration of the modulation element 322. The modified light beam 332a can have a spatial profile that varies continuously as a function of position (e.g., as Figure 1Cas shown), or the modified beam 332a can include components of light separated by lightless regions (e.g., as shown in Figure 2B and 2E -2G). In embodiments where the spatial profile varies continuously as a function of position, the components are not discrete and can be considered any part of the spatial profile.

[0061] The EUV light source 30 also includes a beam combiner 324, which is positioned to direct the modified beam 332a and the second beam 306b towards the beam delivery system 325. The beam combiner 324 is any optical element or collection of optical elements capable of interacting with the modified beam 332a and the second beam 306b. For example, the beam combiner 324 can include one or more mirrors or one or more beam splitters, some of which are positioned to direct the modified beam 332a towards the beam delivery system 325, while others of them are positioned to direct the second beam 306b towards the beam delivery system 325. In embodiments where the modified beam 332a and the second beam 306b have different spectral contents, the beam combiner 324 can be a dichroic element (such as a dichroic beam splitter), which is configured to transmit the wavelengths in the second beam 306b and reflect the wavelengths in the modified beam 332a. In Figure 3 the example, the beam combiner 324 directs the modified beam 332a and the second beam 306b towards the beam delivery system 325 on spatially separated beam paths.

[0062] The beam delivery system 325 also includes a focusing system 326. The focusing system 326 includes any combination of optical elements arranged to focus the modified beam 332a and the second beam 306b. For example, the focusing system 326 can include lenses and / or mirrors. The modified beam 332a is focused at or near the initial target area 342a, and the second beam 306b is focused at or near the modified target area 342b. In Figure 3 the example shown, the focusing system 326 focuses the modified beam 332a and the second beam 306b even though these beams do not follow the same beam path through the focusing system 326. However, in some embodiments, the optical elements that focus the modified beam 332a are independent of the optical elements that focus the second beam 306b. For example, discrete optical components can be used when the spectral content of the modified beam 332a is different from that of the second beam 306b.

[0063] The initial target area 342a receives the target 340 from the target material supply system 350. In Figure 3In the example, the target 340 is a spherical droplet of molten metal. The components in the modified beam 332a interact with the target 340 to form a modified target 345. The interaction between the modified beam 332a and the target 340 changes one or more properties of the target 340. For example, the modified target 345 may have a recessed area and / or an area with a reduced density as discussed with respect to the modified area 245 of Figure 2D The modified target 345 travels to the modified target area 342b and interacts with the second beam 306b. The interaction between the second beam 306b converts at least some of the target material in the modified target 345 into a plasma that emits EUV light 399.

[0064] Figure 4 FIG. is a block diagram of an EUV light source 400. The EUV light source 400 is another example of an embodiment of the EUV light source 100. The EUV light source 400 is similar to the EUV light source 300, except that the EUV light source 400 uses two "pre-pulse" beams to generate a modified target 445.

[0065] The EUV light source 400 includes light generation modules 405a, 405b, and 405c. The light generation module 405a emits a first beam 406a. The light generation module 405b emits a second beam 406b. The light generation module 405c emits a third beam 406c. The light generation module 405c can be, for example, a CO2 laser. All of the beams 405a, 405b, 405c may have the same spectral content, or the spectral content of at least one of the beams 405a, 405b, 405c may be different from that of the other beams. The beams 405a and 405b can be two different emission lines of a CO2 laser. The emission lines of a CO2 laser include, for example, light at 9.4 μm, 10.26 μm, and 10.59 μm. In some embodiments, either the beam 405a or the beam 405b is a beam formed by the 10.26 μm emission line of a CO2 laser. In these embodiments, the other of the beams 405a and 405b can be a beam having a wavelength of 1.06 μm generated by a solid-state laser (as an example, such as a Q-switched Nd:YAG laser). In other embodiments, both the beams 405a and 405b are generated by solid-state lasers.

[0066] The first and second beams 406a, 406b change one or more physical properties of the target 440 to produce a modified target 445. In Figure 4In the illustrated embodiment, the first beam 406a interacts with the target 440 to spatially expand the target 440 and form an intermediate target 447. The intermediate target 447 can be a disk-shaped segment of molten metal that has a greater extent along the X axis (which includes the X direction and the -X direction opposite the X direction) than the target 440. Additionally, the intermediate target 447 has a smaller extent along the Z axis than the target 440. The intermediate target 447 moves in the X direction.

[0067] The EUV light source 400 also includes a modulation element 422 positioned to interact with a second beam 406b. The modulation element 422 is any optical element or collection of elements capable of spatially modulating the second beam 406b. For example, the modulation element 422 can be similar to the modulation element 122 discussed with respect to Figure 1A or the modulation element 222 discussed with respect to Figure 2A . The interaction between the modulation element 422 and the second beam 406b produces a modified beam 432b. The modified beam 432b has a spatial profile different from that of the second beam 406b. The modified beam 432b and the first beam 406a are directed by a beam combiner 424 towards a focusing system 425a. The beam combiner 424 can be any optical element or collection of optical elements capable of directing the modified beam 432b and the first beam 406a towards the focusing system 425a. The focusing system 425a focuses the first beam 406a at or near a target area 442a that receives the target 440 from a target supply system 450, and focuses the modified beam 432b at or near a target area 442b that receives the intermediate target 447 from the target area 442a.

[0068] The intermediate target 447 and the modified beam 432b interact at the target 442b to form a modified target 445. In the illustrated example, the interaction between the modified beam 432b and the intermediate target 447 forms a recessed area 444 in the modified target 445. After interacting with the modified beam 432b, the modified target 445 moves into a target area 442c that receives a third beam 406c. The third beam 406c is focused by a focusing system 426c and has an energy sufficient to convert at least some of the target material in the modified target 445 into a plasma that emits EUV light. The recessed area 444 can cause more of the target material in the modified target 445 to be converted into plasma. Thus, compared to a target lacking the recessed area 444 (such as the target 440 or the intermediate target 447), more EUV light and less debris are generated by the interaction between the modified target 445 and the third beam 406c.

[0069] Figure 5 is a block diagram of an EUV light source 500. The EUV light source 500 isFigure 1A Another example of an embodiment of the EUV light source 100. In the EUV light source 500, a single beam is used to generate the modified target 545 and a plasma that emits EUV light is formed from the modified target 545.

[0070] The EUV light source 500 includes a light generation module 505. The light generation module 505 can be, for example, a CO2 laser. The light generation module 505 emits a beam 506 onto a beam path 507 that is directed towards the modulation device 520. The modulation device 520 includes a modulation element 522. The modulation element 522 is any optical element that is capable of spatially modulating the beam 506 into components that do not all have the same intensity. The modulation element 522 can be similar to the modulation element 222 ( Figure 2A ). The interaction between the modulation element 522 and the beam 506 modulates the beam 506 and generates components 533a - 533g. The components 533a - 533g are separated from each other by regions that are devoid of light.

[0071] The components 533a - 533g propagate away from the modulation element 522 in different directions. 533a - 533g propagate towards the beam trap 528 and do not leave the modulation device 520. The components 533a - 533g propagate towards the target region 542a of the target 540. The target 540 can be a spherical droplet provided by a target material supply system such as Figure 4 the system 450, or the target 540 can be an intermediate target (such as Figure 4 the intermediate target 447) that is produced by a previous interaction of another beam. The components 533a - 533c have an intensity sufficient to modify the properties of the target 540 without generating a plasma that emits EUV light. Thus, regardless of the form of the target 540, the interaction between 533a - 533c produces the modified target 545. In Figure 5 the example, three recessed regions 544 are illustrated. Each recessed region 544 is formed by the interaction between one of the components 533a - 533c and the target 540.

[0072] Component 533d propagates towards the focusing system 525. The focusing system 525 focuses component 533d at or near the modified target area 542b that receives the modified target 545. The focusing system 525 also includes an optical delay 529 that causes component 533d to arrive at the modified target area 542b at a time after components 533a - 533c and at a time when the modified target 545 is within the modified target area 542b. The optical delay 529 can be, for example, an arrangement including a plurality of reflective elements (such as mirrors) that fold component 533d multiple times in a relatively compact volume. Such an optical delay 529 can cause component 533d to travel an additional several hundred meters, thereby enabling a delay of several hundred nanoseconds.

[0073] Component 533d has a greater intensity than 533a - 533c, and component 533d has an energy sufficient to convert at least some of the target material in the modified target 545 into a plasma that emits EUV light. For example, the total energy of the component can be approximately 2 kilowatts (kW), while the energy in component 533d can be greater than 100 kW.

[0074] Figure 6 is a block diagram of EUV light source 600. EUV light source 600 is another example of an embodiment of EUV light source 100. EUV light source 600 is similar to EUV light source 300 ( Figure 3 ), except that EUV light source 600 includes a modulation device 620 that spatially modulates a portion of the second beam 306b instead of the first beam 306a. In Figure 6 the illustrated embodiment, the target area 642 receives the target 640 from the target material supply 350. Figure 7 is an illustration of the target area 642 as a function of time. Figure 8 is as Figure 7 an illustration of the light intensity in the target area 642 as a function of the time scale.

[0075] The beam combiner 324 directs the first beam 306a towards the target 640. The interaction between the first beam 306a and the target 640 forms an intermediate target 547. The second beam 306b passes through the beam combiner 324 and interacts with the modulation device 620 to form a single optical pulse 604. The modulation device 620 includes a temporal modulation device 662 and a spatial modulation element 622. The spatial modulation element 622 is a dynamic modulation element that can be controlled by a controller 660. The temporal modulation device 662 can also be controlled by the controller 660. The controller 660 can include an electronic processor and an electronic memory or storage. The electronic processor can store instructions that direct the processor to perform actions - perhaps as a computer program. For example, the electronic processor can generate signals that, when provided by the controller 660 to the modulation device 620, the modulation element 622, and / or the temporal modulation device 662, cause the modulation device 620, the modulation element 622, and / or the temporal modulation device 662 to perform specific actions.

[0076] The temporal modulation device 662 is any optical element that can control the temporal profile (intensity as a function of time) of the second beam 306b. For example, the temporal modulation device 662 can be an electro-optic modulator (EOM). The temporal modulation device 662 is controlled to form an optical pulse 604 including a substrate 608 and a heating portion 609 from the second beam 605b. The substrate 608 and the heating portion 609 are shown in Figure 8 FIG. The substrate 608 is temporally connected to the heating portion 609 such that the substrate 608 and the heating portion 609 are part of a single optical pulse 604 ( Figure 6 and 8 ).

[0077] The temporal profile of the substrate 608 can have any shape. For example, the intensity of the substrate 608 can increase and decrease over time such that the substrate 608 has a shape somewhat similar to a pulse. Figure 8 FIG. illustrates an example of such a substrate. In other examples, the intensity of the substrate 608 can increase and decrease over time without having a pulse-like profile. In still other examples, the substrate 608 can have an intensity that monotonically increases until the heating portion 609 begins. Regardless of the shape of the substrate 608, the substrate 608 and the heating portion 609 together form a single pulse 604. That is, there is no region without light between the start and the end of the pulse 604.

[0078] The spatial modulation element 622 is controlled such that only the substrate 608 is spatially modulated. Accordingly, the spatial profile of the substrate 608 is varied. In some embodiments, the substrate focus size in the x-y plane is modulated to achieve different intensities. For example, the focus size can be modulated to heat the outer edge of the target before heating the material closer to the center of the target.

[0079] As Figure 7 and Figure 8 shown, the substrate 608 reaches the target region 642 before the heating portion 609. The spatially modulated substrate 608 interacts with the intermediate target 647 and forms a modified target 645. The heating portion 609 reaches the target region 642 after the substrate 608. The heating portion 609 has a much greater intensity than the substrate 608 and is capable of converting the target material in the modified target 645 into a plasma that emits EUV light 399. Accordingly, the EUV light source 600 uses two separate pulses - the first beam 306a and the second beam 306b. However, the second beam 306b is acted upon by the modulation device 620 such that the second beam 306b generates a pulse 608 that modifies the intermediate target 647 and converts the modified target 645 into a plasma that emits EUV light 399.

[0080] Figure 9 and Figure 10 Examples of EUV lithography systems 900 are discussed. EUV light generated by any of the EUV light sources 100, 200, 300, 400, 500, and 600 can be used with the lithography system 900. Additionally, a system including any of the EUV light sources 100, 200, 300, 400, 500, and 600 also includes a lithography system such as the lithography system 900. Figure 11 Examples of EUV light sources are discussed. The EUV light sources 100, 200, 300, 400, 500, and 600 can include additional components and systems such as those discussed with respect to Figure 10 and Figure 11 For example, the EUV light sources 100, 200, 300, 400, 500, and 600 include a vacuum chamber such as the vacuum chamber 1130 discussed with respect to Figure 11 shown.

[0081] Figure 9 A lithographic apparatus 900 including a source collector module SO according to an embodiment is schematically depicted. The lithographic apparatus 900 includes:

[0082] · An illumination system (illuminator) IL configured to condition a radiation beam B (e.g., EUV radiation);

[0083] · A support structure (e.g., a mask table) MT, which is configured to support a patterning device (e.g., a mask or a reticle) MA and is connected to a first positioner PM configured to accurately position the patterning device;

[0084] · A substrate table (e.g., a wafer table) WT, which is configured to hold a substrate (e.g., a resist - coated wafer) W and is connected to a second positioner PW configured to accurately position the substrate; and

[0085] · A projection system (e.g., a reflective projection system) PS, which is configured to project the pattern applied by the patterning device MA to a radiation beam B onto a target portion C (e.g., including one or more dies) of the substrate W.

[0086] The illumination system can include various types of optical components, such as refractive, reflective, magnetic, electromagnetic, electrostatic, or other types of optical components, or any combination thereof, for guiding, shaping, or controlling the radiation.

[0087] The support structure MT holds the patterning device MA in a manner depending on the orientation of the patterning device, the design of the lithographic apparatus, and other conditions, such as, by way of example, whether the patterning device is held in a vacuum environment. The support structure can use mechanical, vacuum, electrostatic, or other clamping techniques to hold the patterning device. The support structure can be a frame or a table, for example, which can be fixed or movable as required. The support structure can ensure that the patterning device is, for example, in a desired position with respect to the projection system.

[0088] The term "patterning device" should be broadly interpreted as meaning any device that can be used to impart a pattern in a cross - section of a radiation beam so as to create a pattern in a target portion of a substrate. The pattern imparted to the radiation beam can correspond to a particular functional layer in a device, such as an integrated circuit, created in the target portion.

[0089] The patterning device can 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 tilted individually so as to reflect an incoming radiation beam in a different direction. The tilted mirrors impart a pattern in the radiation beam reflected by the mirror matrix.

[0090] Like the illumination system IL, the projection system PS may include various types of optical components, such as refractive, reflective, magnetic, electromagnetic, electrostatic, or other types of optical components, or any combination thereof, depending on the exposure radiation used or other factors such as the use of a vacuum. Since other gases may absorb too much radiation, it may be desirable to use a vacuum for EUV radiation. Therefore, a vacuum environment can be provided to the entire beam path by means of a vacuum wall and a vacuum pump.

[0091] As depicted herein, the apparatus is of the reflective type (e.g., employing a reflective mask). The lithographic apparatus may be of the type having two (dual-stage) or more substrate tables (and / or two or more patterning device tables). In such a “multi-stage” machine, additional tables may be used in parallel, or preparation steps may be carried out on one or more tables while one or more other tables are used for exposure.

[0092] Reference Figure 9 , the illuminator IL receives an extreme ultraviolet radiation beam from the source collector 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), the at least one element having one or more emission spectral lines in the EUV range. In one such method, often referred to as laser-produced plasma (LPP), the desired plasma can be generated by irradiating a fuel with a laser beam, the fuel being, for example, droplets, streams, or clusters of a material having an element that emits the required spectral lines. The source collector module SO may be part of an EUV radiation system that includes Figure 9 a laser (not shown in ) for providing a laser beam to excite the fuel. The resulting plasma emits output radiation, such as EUV radiation, which is collected using a radiation collector and deposited in the source collector module. The laser and the source collector module may be separate entities, for example when a carbon dioxide (CO2) laser is used to provide the laser beam for fuel excitation.

[0093] In such a case, the laser is not considered to form part of the lithographic apparatus, and the radiation beam is transmitted from the laser to the source collector module by means of a beam delivery system, which may include, for example, appropriate guiding mirrors and / or beam expanders. 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).

[0094] The illuminator IL may include a regulator for adjusting the angular intensity distribution of the radiation beam. Generally, at least the outer and / or inner radial ranges of the intensity distribution on the pupil plane of the illuminator (which are typically referred to as σ outer and σ inner, respectively) may be adjusted. In addition, the illuminator IL may include various other components, such as a facetted field and a pupil mirror device. The illuminator IL can be used to adjust the radiation beam so as to have a desired uniformity and intensity distribution in its cross-section.

[0095] The radiation beam B is incident on a patterning device (e.g., a mask) MA held on a support structure (e.g., a mask table) MT and is patterned by the patterning device. After being reflected by the patterning device (e.g., the mask) MA, the radiation beam B passes through a projection system PS, which focuses the beam onto a target portion C of the substrate W. By means of a second positioner PW and a position sensor PS2 (e.g., an interferometric device, a linear encoder, or a capacitive sensor), the substrate table WT can be accurately moved so as to, for example, position different target portions C in the path of the radiation beam B. Similarly, a first positioner PM and another position sensor PS1 can be used to accurately position the patterning device (e.g., the mask) MA with respect to the path of the radiation beam B. The patterning device (e.g., the mask) MA and the substrate W can be aligned using patterning device alignment marks M1, M2 and substrate alignment marks P1, P2.

[0096] The depicted apparatus can be used in at least one of the following modes:

[0097] 1. In the step mode, the support structure (e.g., the mask table) MT and the substrate table WT are substantially stationary while the entire pattern applied to the radiation beam is projected onto the target portion C at once (i.e., a single static exposure). The substrate table WT is then shifted in the X and / or Y directions so that different target portions C can be exposed.

[0098] 2. In the scan mode, the support structure (e.g., the mask table) MT and the substrate table WT are scanned simultaneously while the pattern applied to the radiation beam is projected onto the target portion C (i.e., a single static exposure). The speed and direction of the substrate table WT relative to the support structure (e.g., the mask table) MT can be determined by the magnification (reduction) and image flipping characteristics of the projection system PS.

[0099] 3. In another mode, the support structure (e.g., a mask table) MT remains substantially stationary, holding a programmable patterning device, and the substrate table WT is moved or scanned while the pattern applied to the radiation beam is projected onto the target portion C. In this mode, a pulsed radiation source is typically employed and the programmable patterning device is updated as required after each movement of the substrate table WT or between successive radiation pulses during scanning. This operating mode can be readily applied to maskless lithography employing a programmable patterning device such as a programmable mirror array of the type mentioned above.

[0100] Combinations and / or variations of the usage modes described above may also be employed, or entirely different usage modes.

[0101] Figure 10 An embodiment of a lithographic apparatus 900 is shown in more detail, which includes a source collector module SO, an illumination system IL, and a projection system PS. The source collector module SO is constructed and arranged such that a vacuum environment can be maintained within the enclosure structure 1020 of the source collector module SO. The systems IL and PS are likewise contained within their own vacuum environments. A plasma 2 emitting EUV radiation can be formed by a laser-produced LPP plasma source. The function of the source collector module SO is to deliver an EUV radiation beam 20 from the plasma 2 such that it is focused at a virtual source point. This virtual source point is generally referred to as the intermediate focus (IF), and the source collector module is arranged such that this intermediate focus IF lies at or near the opening 1021 in the enclosure structure 1020. The virtual source point IF is an image of the plasma 2 emitting the radiation.

[0102] From the opening 1021 at the intermediate focus IF, the radiation passes through the illumination system IL, which in this example includes a faceted field mirror device 22 and a faceted pupil mirror device 24. These devices form a so-called "fly's eye" illuminator, which is arranged to provide the desired angular distribution of the radiation beam 21 at the patterning device MA, as well as the desired radiation intensity uniformity at the patterning device MA (as indicated by reference numeral 1060). When the beam 21 is reflected at the patterning device MA 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 reflection elements 28, 30 onto a substrate W held by the substrate table WT. To expose the target portion C on the substrate W, pulsed radiation is generated while the substrate table WT and the patterning device table MT perform synchronous movements to scan the pattern on the patterning device MA through an illumination slit.

[0103] Each of the systems IL and PS is arranged in its own vacuum or near-vacuum environment defined by an enclosure similar to the enclosure 1020. There may generally be more elements in the illumination system IL and the projection system PS than shown. Additionally, 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 Figure 10 .

[0104] Considering the source collector module SO in more detail, the laser energy source including the laser 1023 is arranged to deposit the laser energy 1024 onto a fuel including a target material. The target material can 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 can be generated using other fuel materials such as terbium (Tb) and gadolinium (Gd). The energy radiation generated during the de-excitation and recombination of these ions is emitted from the plasma, collected by the near-normal incidence collector 3, and focused on the aperture 1021. The plasma 2 and the aperture 1021 are located at the first and second foci of the collector CO, respectively.

[0105] Although Figure 10 the collector 3 shown in is a single-curved mirror, the collector can take other forms. For example, the collector can be a Schwarzschild collector having two radiation collection surfaces. In one embodiment, the collector can be a grazing incidence collector including a plurality of substantially cylindrical reflectors nested with each other.

[0106] To deliver a fuel such as liquid tin, the 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, the laser energy 1024 is delivered while the droplet generator 1026 is operating to deliver a radiation pulse to turn each fuel droplet into the plasma 2. The delivery frequency of the droplets can be several kilohertz, for example 50 kHz. In practice, the laser energy 1024 is delivered in at least two pulses: a pre-pulse with limited energy is delivered to the droplet before it reaches the plasma location to evaporate the fuel material into a small-scale cloud, and then the main pulse of the laser energy 1024 is delivered to the cloud at the desired location to generate the plasma 2. A trap 1030 is provided on the opposite side of the enclosure 1020 to capture the fuel that has not been turned into plasma for any reason.

[0107] The droplet generator 1026 includes a reservoir 1001 containing a fuel liquid (e.g., molten tin), a filter 1069, and a nozzle 1002. The nozzle 1002 is configured to eject droplets of the fuel liquid towards the formation location of the plasma 2. The droplets of the fuel liquid can be ejected from the nozzle 1002 by a combination of the pressure within the reservoir 1001 and the vibration applied to the nozzle by a piezoelectric actuator (not shown).

[0108] As will be appreciated by those skilled in the art, reference axes X, Y, and Z can be defined to measure and describe the geometry and behavior of the device, its various components, and the radiation beams 20, 21, 26. In each part of the device, a local reference frame for the X, Y, and Z axes can be defined. In Figure 10 the example, the Z-axis at a given point in the system generally coincides with the direction optical axis O, and is generally perpendicular to the plane of the patterning device (mask) MA and perpendicular to the plane of the substrate W. In the source collector module, the X-axis generally coincides with the direction of the fuel stream 1028, while the Y-axis is orthogonal thereto, as Figure 10 pointing out of the page in. On the other hand, in the vicinity of the support structure MT holding the mask MA, the X-axis is generally transverse to the scanning direction aligned with the Y-axis. For convenience, in Figure 10 the schematic diagram of this region, also as marked, the X-axis points out of the page. These designations are conventional in the art and are adopted herein for convenience. In principle, any reference frame can be chosen to describe the device and its behavior.

[0109] A number of additional components are present in a conventional device and are used in the operation of the source collector module and the lithographic apparatus 900 as a whole, but are not described herein. These additional components include arrangements for reducing or eliminating the effects of contamination within the enclosed vacuum, such as for preventing the deposition of fuel material from damaging or degrading the performance of the collector 3 and other optical components. Other features that are present but not described in detail are all the sensors, controllers, and actuators involved in the control of the various components and subsystems of the lithographic apparatus 900.

[0110] Reference Figure 11 , shows an embodiment of an LPP EUV light source 1100. The light source 1100 can be used as the source collector module SO in the lithographic apparatus 900. In addition, Figure 1A and Figure 2A the light generation module 105 in Figure 5 the light generation module 505 in Figure 3 the light generation module 305b in Figure 4 or the light generation module 405b in Figure 10 can be part of the drive laser 1115. The drive laser 1115 can be used as the laser 1023( Figure 10 ).

[0111]

[0111] The LPP EUV light source 1100 is formed by irradiating a target mixer 1114 at a plasma formation position 1105 with an amplified beam 1110 traveling along a beam path toward the target mixture 1114. The plasma formation position 1105 is within the interior 1107 of a vacuum chamber 1130. When the amplified beam 1110 strikes the target mixture 1114, the target material within the target mixture 1114 is converted to a plasma state that has elements with emission spectral lines in the EUV range. The created plasma has certain characteristics that depend on the composition of the target material within the target mixture 1114. These characteristics include the wavelength of the EUV light generated by the plasma and the type and amount of debris released from the plasma.

[0112]

[0112] The light source 1100 also includes a supply system 1125 that delivers, controls, and guides the 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 includes a target material that is, for example, water, tin, lithium, xenon, or any material that has emission spectral lines in the EUV range when converted to a plasma state. For example, the element tin can be used as pure tin (Sn); as a tin compound, such as SnBr4, SnBr2, SnH4; as a tin alloy, such as a tin-gallium alloy, a tin-indium alloy, a tin-indium-gallium alloy, or any combination of these alloys. The target mixture 1114 can also include impurities of non-target particles. Thus, in the absence of impurities, the target mixture 1114 consists only of the target substance. The target mixture 1114 is delivered by the supply system 1125 into the interior 1107 of the chamber 1130 and to the plasma formation position 1105.

[0113]

[0113] The light source 1100 includes a drive laser system 1115 that generates the amplified 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 position 1105, the beam delivery system including a beam transport system 1120 and a focusing assembly 1122. The beam transport system 1120 receives the amplified beam 1110 from the laser system 1115, manipulates and modifies the amplified beam 1110 as needed and outputs the amplified beam 1110 to the focusing assembly 1122. The focusing assembly 1122 receives the amplified beam 1110 and focuses the beam 1110 onto the plasma formation position 1105.

[0114] In some embodiments, the laser system 1115 may include one or more optical amplifiers, lasers, and / or lamps for providing one or more main 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 laser mirrors or other feedback devices forming a laser cavity. Thus, the laser system 1115 generates an amplified beam 1110 due to population inversion in the gain medium of the laser amplifier even in the absence of a laser cavity. Additionally, if a laser cavity is present to provide sufficient feedback to the laser system 1115, the laser system 1115 may generate the amplified beam 1110 as a coherent laser beam. The term "amplified beam" encompasses one or more of the following: light from the laser system 1115 that is only amplified but not necessarily coherent laser oscillation, and light from the laser system 1115 that is amplified and also coherent laser oscillation.

[0115] The optical amplifier in the laser system 1115 may include a fill gas including CO2 as the gain medium and may amplify light at a wavelength between approximately 9100 nm and approximately 11000 nm - particularly approximately 10600 nm - with a gain of greater than or equal to 800 times. Suitable amplifiers and lasers in the laser system 1115 may include pulsed laser devices, such as pulsed gas discharge CO2 laser devices, which generate radiation at approximately 9300 nm or approximately 10600 nm, for example, using DC or RF excitation and operate at a relatively high power of, for example, 10 kW or higher and a high pulse repetition rate of, for example, 40 kHz or higher. The pulse repetition rate may be, for example, 50 kHz. 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 a higher power.

[0116] The light source 1100 includes a collector mirror 1135 having an aperture 1140 to allow the amplified beam 1110 to pass through and reach the plasma formation location 1105. The collector mirror 1135 can be, for example, an ellipsoidal mirror having a primary focus at the plasma formation location 1105 and a secondary focus (also referred to as an intermediate focus) at an intermediate location 1145 where EUV light can be output from the light source 1100 and, for example, input into an integrated circuit lithography tool (not shown). The light source 1100 can also include an open-ended hollow conical shroud 1150 (e.g., a 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 the beam delivery system 1120 while allowing the amplified beam 1110 to reach the plasma formation location 1105. For this purpose, an air flow directed toward the plasma formation location 1105 can be provided in the shroud.

[0117] The light source 1100 can also include a main controller 1155 that is connected to a droplet position detection feedback system 1156, a laser control system 1157, and a beam control system 1158. The light source 1100 can include one or more target or droplet imagers 1160 that provide an output indicative of the position of a droplet, e.g., relative to the plasma formation location 1105, and provide this output to the droplet position detection feedback system 1156. The droplet position detection feedback system 1156 can, for example, calculate the droplet position and trajectory, based on which the droplet position error can be calculated on a droplet-by-droplet basis or on average. The droplet position detection feedback system 1156 thus provides this droplet position error as an input to the main controller 1155. The main controller 1155 can thus, for example, provide laser position, direction, and timing correction signals to the laser control system 1157, which can be used to control a laser timing circuit, and / or to the beam control system 1158 to control the amplified beam position and the shaping of the beam delivery system 1120 to change the position and / or the optical power of the beam focus within the chamber 1130.

[0118] The supply system 1125 includes a target material delivery control system 126 that can operate in response to a signal from the main controller 1155 to, for example, modify the release point of droplets released by the target material supply device 1127 in order to correct for errors in the droplets reaching the desired plasma formation location 1105.

[0119] In addition, the light source 1100 may 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 specific wavelength band, energy outside a specific wavelength band, and the angular distribution of EUV intensity and / or average power. The light source detector 1165 generates a feedback signal for use by the main controller 1155. The feedback signal may indicate, for example, errors in parameters such as the timing and focus of the laser pulses, so as to intercept the droplets at the correct place and time for effective and efficient EUV light generation.

[0120] The light source 1100 may further include a guiding laser 1175, which may be used to align the various segments of the light source 1100 or assist in manipulating the amplified beam 1110 to the plasma formation position 1105. In combination with the guiding laser 1175, the light source 1100 includes a metrology system 1124 disposed within the focusing assembly to sample a portion of the light from the guiding laser 1175 and the amplified beam 1110. In other embodiments, the metrology system 1124 is disposed within the beam delivery system 1120. The metrology system 1124 may include optical elements that sample or redirect a subset of the light, and such optical elements are made of any material that can withstand the power of the guiding laser beam and the amplified beam 1110. Since the main controller 1155 analyzes the sampled light from the guiding laser 1175 and uses this information to adjust the components within the focusing assembly 1122 through the beam control system 1158, the metrology system 1124 and the main controller 1155 form a beam analysis system.

[0121] Thus, in summary, the light source 1100 generates an amplified beam 1110 that is guided along a beam path to irradiate a target mixture 1114 at the plasma formation position 1105 to convert the target material within the mixture 1114 into a plasma that emits light in the EUV range. The amplified 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. In addition, the amplified beam 1110 may be a laser beam when the target material provides sufficient feedback to the laser system 115 to generate a coherent laser or when the drive laser system 1115 includes appropriate optical feedback to form a laser cavity.

[0122] Other embodiments are within the scope of the claims. The modulation elements discussed above may be implemented to generate any type of pattern on the target. For example, the modulation element 222 may generate a pattern that is Figure 2AThe different component patterns shown in the examples of. In some embodiments, the modulation element 222 is implemented such that all components are on one side of the zeroth order. Additionally, the modulation element 522 can also be implemented in such a way that all components other than the component 533d propagate towards the target area 542a without the need for the beam trap 528.

[0123] Other aspects of the present invention are given in the following numbered clauses.

[0124] 1. A system, comprising:

[0125] 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 the propagation direction of the modified light beam, the spatial pattern of light including one or more light components; and

[0126] A target supply system configured to supply a target to a target area, the target including a target material that emits EUV light when in a plasma state, wherein the target area 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.

[0127] 2. The system according to clause 1, wherein the spatial modulation device includes a diffractive optical element.

[0128] 3. The system according to clause 2, wherein the diffractive optical device includes a spatial light modulator (SLM), adaptive optics, a mask, and / or a grating.

[0129] 4. The system according to clause 1, wherein the spatial modulation device includes a refractive optical element.

[0130] 5. The system according to clause 4, wherein the spatial modulation device includes a lens, a microlens array, and / or a mask.

[0131] 6. The system according to clause 1, wherein the spatial pattern of light includes two or more light components, and each of the two or more light components has substantially the same intensity.

[0132] 7. The system according to clause 1, wherein the spatial pattern of light includes two or more light components arranged in a linear grid.

[0133] 8. The system according to clause 2, wherein the spatial modulation device includes at least one Dammann grating.

[0134] 9. The system according to clause 1, further comprising:

[0135] A first light generation module configured to emit the light beam; and

[0136] A second light generation module configured to emit a second light beam.

[0137] 10. The system according to 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 including a second spatial pattern of light having a non-uniform intensity in a direction perpendicular to the propagation direction of the second modified light beam, the second spatial pattern of light including one or more second light components.

[0138] 11. A method of forming a target for an extreme ultraviolet (EUV) light source, the method comprising:

[0139] Directing a light beam onto a beam path;

[0140] 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 including a spatial pattern of light having a non-uniform intensity in a direction perpendicular to the propagation direction of the modified light beam, the spatial pattern of light including one or more light components; and

[0141] Causing the modified light beam to interact with a target including 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 an attribute of the region of the target.

[0142] 12. The method according to clause 11, wherein the attribute includes density, and modifying the attribute includes reducing the density.

[0143] 13. The method according to clause 11, wherein the spatial pattern of light includes two or more light components.

[0144] 14. The method according to clause 13, wherein all the light components have the same intensity.

[0145] 15. The method according to clause 13, wherein the light components are arranged in a grid, and the regions of the target that directly interact with the light components are arranged in a grid.

[0146] 16. The method according to clause 11, further comprising causing the modified light beam to interact with a focusing component before causing the modified light beam to interact with the target.

[0147] 17. The method according to clause 13, wherein the optical components are spatially separated and discrete, such that the portion of the target between any two optical components does not interact with any component in the modified beam.

[0148] 18. The method according to clause 11, further comprising:

[0149] causing an initial target to interact with a second beam to form a modified target, the modified target having a greater extent in a first direction and a smaller extent in a second direction than the initial target, the first direction and the second direction being orthogonal to each other, and wherein

[0150] 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 beam to interact with the modified target, and each optical component in the one or more optical components to interact with a region of the modified target to modify an attribute of the region of the modified target.

[0151] 19. The method according to clause 18, further comprising, after causing the modified beam to interact with the modified target, causing the modified target to interact with a third beam, the third beam having an energy sufficient to convert at least some of the target material in the modified target into the plasma that emits EUV light.

[0152] 20. The method according to clause 11, further comprising, after interacting the target with the modified beam, interacting the target with another beam, the other beam having an energy sufficient to convert at least some of the target material in a second modified target into the plasma that emits EUV light.

[0153] 21. The method according to clause 20, wherein the attribute comprises a conversion efficiency related to the amount of EUV light emitted and the energy of the other beam, and modifying the attribute of a portion of the target comprises increasing the conversion efficiency associated with the entire target.

[0154] 22. The method according to clause 20, wherein the beam and the other beam are temporally connected and are part of a single optical pulse.

[0155] 23. The method according to clause 11, wherein the attribute comprises the surface area of the target, and modifying the attribute of any portion of the target comprises increasing the surface area of the entire target.

[0156] 24. The method according to clause 23, wherein the amount of increase in the surface area is related to the number of light components in the modified beam.

[0157] 25. The method according to clause 11, wherein interacting the modified beam with a target comprising a target material that emits EUV light when in a plasma state comprises: causing the modified beam to interact with a target having a substantially spherical shape.

[0158] Other embodiments are within the scope of the following claims.

Claims

1. A system for forming a target for an extreme ultraviolet (EUV) light source, comprising: A spatial modulation device configured to interact with a beam of light to create a modified beam of light, the modified beam of light including a spatial pattern of light having a non-uniform intensity in a direction perpendicular to the propagation direction of the modified beam of light, the spatial pattern of light including light components that are spatially separated and spatially discrete and are arranged in a grid; and A target supply system configured to supply a target to a target region, the target including 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 light components in the modified beam of light interact with a portion of the target.

2. The system according to claim 1, wherein the spatial modulation device comprises a diffractive optical element or a refractive optical element.

3. The system according to claim 2, wherein the diffractive optical element comprises a spatial light modulator (SLM), adaptive optics, a mask, and / or a grating.

4. The system according to claim 1, wherein the spatial modulation device comprises a lens, a microlens array, and / or a mask.

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

6. The system according to claim 1, wherein the spatial pattern of the light comprises two or more light components arranged in a linear grid.

7. The system according to claim 2, wherein the diffractive optical device comprises at least one Dammann grating.

8. The system according to claim 1, further comprising: A first light generation module configured to emit the beam of light; and A second light generation module configured to emit a second beam of light.

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

10. A method for forming a target for an extreme ultraviolet (EUV) light source, the method comprising: Direct the beam of light onto the beam path; Cause the beam of light to interact with a spatial modulation device located on the beam path to form a modified beam of light, the modified beam of light including a spatial pattern of light having a non-uniform intensity in a direction perpendicular to the propagation direction of the modified beam of light, the spatial pattern of light including light components that are spatially separated and spatially discrete and are arranged in a grid; and Cause the modified beam of light to interact with a target including a target material that emits EUV light when in a plasma state, wherein at least some of the light components in the spatial pattern interact with a region of the target to modify an attribute of the region of the target.

11. The method according to claim 10, wherein the spatial modulation device comprises a diffractive optical element or a refractive optical element.

12. The method according to claim 10, wherein the property comprises density, and modifying the property comprises reducing the density.

13. The method according to claim 10, wherein the spatial pattern of the light comprises two or more light components.

14. The method according to claim 13, wherein all the optical components have the same intensity.

15. The method according to claim 13, wherein the optical components are arranged in a grid, and the regions of the target that directly interact with the optical components are arranged in a grid.

16. The method according to claim 10, further comprising: Before causing the modified beam of light to interact with the target, cause the modified beam of light to interact with a focusing component.

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

18. The method according to claim 10, further comprising: Cause an initial target to interact with the second beam of light to form a modified target that has a greater extent in a first direction and a smaller extent in a second direction than the initial target, the first direction and the second direction being orthogonal to each other, and wherein Causing the modified beam of light to interact with a target including a target material that emits EUV light when in a plasma state includes: causing the modified beam of light to interact with the modified target, and each of the one or more light components interacting with a region of the modified target to modify an attribute of the region of the modified target.

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

20. The method according to claim 10, further comprising: After interacting the target with the modified beam of light, interact the target with another beam of light having an energy sufficient to convert at least some of the target material in a second modified target into the plasma that emits EUV light.

21. The method according to claim 20, wherein the property includes 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: Increase the conversion efficiency associated with the entire target.

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

23. The method according to claim 10, wherein the property includes the surface area of the target, and modifying the property of any portion of the target includes: Increase the surface area of the entire target.

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

25. The method according to claim 10, wherein interacting the modified beam with a target comprising a target material that emits EUV light when in a plasma state includes: Cause the modified beam to interact with a target having a substantially spherical shape.

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