OPTICAL MODULE FOR EXTREME ULTRAVIOLET LIGHT SOURCE

An optical module is configured to pass an optical beam. The optical module includes: a plurality of lenses through which the optical beam passes, the plurality of lenses including at least one aspheric toroid lens; and an optical mount apparatus in which the plurality of lenses is mounted. The plurality of lenses is placed relative to a linearly focused curtain of the optical beam, the linearly focused curtain intersecting a region of interest. The optical mount apparatus is arranged in or fixed to a wall of a chamber of an extreme ultraviolet (EUV) light source such that an optical path is defined that passes through the EUV light source chamber and intersects the region of interest inside the chamber.

TECHNICAL FIELD

The disclosed subject matter relates to an optical module for passing an optical beam into or out of a chamber of an extreme ultraviolet (EUV) light source.

BACKGROUND

Extreme ultraviolet (EUV) light, for example, electromagnetic radiation having wavelengths of around 50 nm or less (also sometimes referred to as soft x-rays), and including light at a wavelength of about 13 nm, can be used in photolithography processes to produce extremely small features in substrates, for example, silicon wafers.

Methods to produce EUV light include, but are not necessarily limited to, converting a material that has an element, for example, xenon, lithium, or tin, with an emission line in the EUV range in a plasma state. In one such method, often termed laser produced plasma (“LPP”), the required plasma can be produced by irradiating a target material, for example, in the form of a droplet, plate, tape, stream, or cluster of material, with an amplified light beam that can be referred to as a drive laser. For this process, the plasma is typically produced in a sealed vessel, for example, a vacuum chamber, and monitored using various types of metrology equipment.

Extreme ultraviolet (EUV) light, for example, electromagnetic radiation having wavelengths of around 50 nanometers (nm) or less (also sometimes referred to as soft x-rays), and including light at a wavelength of about 13 nm, can be used in or with a lithographic apparatus to produce extremely small features in substrates, for example, silicon wafers. Methods to produce EUV light include, but are not necessarily limited to, converting a material that has an element, for example, xenon (Xe), lithium (Li), or tin (Sn), with an emission line in the EUV range to a plasma state. For example, in one such method called laser produced plasma (LPP), the plasma can be produced by irradiating a target material, which is interchangeably referred to as fuel in the context of LPP sources, for example, in the form of a droplet, plate, tape, stream, or cluster of material, with an amplified light beam that can be referred to as a drive laser. For this process, the plasma is typically produced in a sealed vessel, for example, a vacuum chamber, and monitored using various types of metrology equipment.

SUMMARY

In some general aspects, an optical module is configured to pass an optical beam. The optical module includes: a plurality of lenses through which the optical beam passes, the plurality of lenses including at least one aspheric toroid lens; and an optical mount apparatus in which the plurality of lenses is mounted. The plurality of lenses is placed relative to a linearly focused curtain of the optical beam, the linearly focused curtain intersecting a region of interest. The optical mount apparatus is arranged in or fixed to a wall of a chamber of an extreme ultraviolet (EUV) light source such that an optical path is defined that passes through the EUV light source chamber and intersects the region of interest inside the chamber.

Implementations can include one or more of the following features. For example, the plurality of lenses can include at least one toroid lens. The at least one toroid lens can include a first plano-concave cylindrical lens and a second plano-concave cylindrical lens. The at least one aspheric toroid lens can be a single lens that is plano-convex, plano-concave, meniscus with one face being aspheric toroid, or meniscus with both faces being aspheric toroid. The second plano-concave cylindrical lens and the aspheric toroid lens can be fixed in position relative to each other and moveable together relative to the first plano-concave cylindrical lens. Adjustment of the first plano-concave cylindrical lens relative to the second plano-concave cylindrical lens and the aspheric toroid lens can thereby adjust a position and/or a width of the linearly focused curtain. The linearly focused curtain of the optical beam can be focused along an axis of the chamber; The first plano-concave cylindrical lens can have a radius of curvature along the axis that is −19 mm to −25 mm. The second plano-concave cylindrical lens can have a radius of curvature along the axis that is −31 mm to −39 mm. The aspheric toroid lens can have a base radius of curvature along the axis that is −26 mm to −32 mm. The distance from an adjacent mechanical output face and an outer face of the aspheric toroid lens can be less than 80 millimeters (mm), less than 70 mm, less than 60 mm, or less than 50 mm. The adjacent mechanical output face can be an output face of an optical collimator The linearly focused curtain can be formed from the optical beam passing through the plurality of lenses and to the region of interest inside the chamber. The aspheric toroid lens can be the lens that is closest to the region of interest. The at least one aspheric toroid lens can be a single lens that is plano-convex, plano-concave, meniscus with one face being aspheric toroid, or meniscus with both faces being aspheric toroid. The aspheric toroid lens can be an acylindrical lens. The plurality of lenses can be configured and arranged to thereby reduce optical aberrations such that their actual resolution is diffraction limited. The optical beam can travel along an optical axis of the chamber, and the linearly focused curtain of the optical beam can have a beam profile along a first axis perpendicular to the optical axis of the chamber that is at least 10, at least 20, at least 30, at least 40, at least 50, or at least 60 times a beam profile along the a second axis perpendicular to the optical of the chamber within the region of interest inside the chamber. The optical mount apparatus can be arranged in a wall of the EUV light source chamber. The optical path can pass through an optically-transparent window fixed within the chamber wall.

In other general aspects, an illumination module is configured for an extreme ultraviolet (EUV) light source. The illumination module includes: a light source configured to produce an optical beam; and an optical module configured to pass the optical beam through a wall of or within a chamber of the EUV light source and to focus the optical beam as a linear curtain at a region of interest inside the chamber. The optical module includes a plurality of lenses through which the optical beam passes and defining an optical path from the light source to the region of interest, the plurality of lenses including at least one aspheric toroid lens.

Implementations can include one or more of the following features. For example, the plurality of lenses can include at least one toroid lens. The at least one toroid lens can include a first plano-concave cylindrical lens and a second plano-concave cylindrical lens. The at least one aspheric toroid lens can be a single lens that is plano-convex, plano-concave, meniscus with one face being aspheric toroid, or meniscus with both faces being aspheric toroid. The second plano-concave cylindrical lens and the aspheric toroid lens can be fixed in position relative to each other and moveable together relative to the first plano-concave cylindrical lens. Adjustment of the first plano-concave cylindrical lens relative to the second plano-concave cylindrical lens and the aspheric toroid lens can thereby adjust a position and/or a width of the linearly focused curtain in the region of the interest. The optical module can have a focus sensitivity of at least 1 μm, at least 10 μm, at least 20 μm, at least 30 μm, or between 32-44 μm per adjustment of the first plano-concave cylindrical lens relative to the second plano-concave cylindrical lens and the aspheric toroid lens of 1 μm. The optical module can have a focus sensitivity that is sensitive enough to allow the optical beam to be focused as the linear curtain at the region of interest inside the chamber using an adjustment range on the order of a micron.

The linearly focused curtain of the optical beam can be focused along an axis of the chamber. The first plano-concave cylindrical lens can have a radius of curvature along the axis that is −19 mm to −25 mm. The second plano-concave cylindrical lens can have a radius of curvature along the axis that is −31 mm to −39 mm. The aspheric toroid lens can have a base radius of curvature along the axis that is −26 mm-−32 mm. The distance from an adjacent mechanical output face and an outer face of the aspheric toroid lens can be less than 80 millimeters (mm), less than 70 mm, less than 60 mm, or less than 50 mm. The adjacent mechanical output face can be an output face of an optical collimator. The aspheric toroid lens can be the lens that is closest to the region of interest. The aspheric toroid lens can be an acylindrical lens. The optical beam can travel along an optical axis of the chamber, and the linearly focused curtain of the optical beam can have a beam profile along a first axis perpendicular to the optical axis of the chamber that is at least 10, at least 20, at least 30, at least 40, at least 50, or at least 60 times a beam profile along a second axis perpendicular to the optical axis of the chamber within the region of interest inside the chamber. The optical beam can be a continuous wave light beam. Each of the lenses can be made of fused silica, optical glass, optical ceramic, or optical crystals.

In other general aspects, an extreme ultraviolet (EUV) light source includes: a chamber including a plurality of walls that together define a cavity, and a region of interest is defined inside the cavity; and an optical module for passing an optical beam. The optical module includes: a plurality of lenses through which the optical beam passes, the plurality of lenses including at least one aspheric toroid lens; and an optical mount apparatus in which the plurality of lenses is mounted. The plurality of lenses is placed relative to a linearly focused curtain of the optical beam, the linearly focused curtain intersecting a region of interest. The optical mount apparatus is arranged in or fixed to a wall of a chamber such that an optical path is defined that intersects the region of interest inside the chamber.

Implementations can include one or more of the following features. For example, plurality of lenses can include at least one toroid lens. The EUV light source can further include an illumination module including a light source configured to produce the optical beam and the optical module configured to receive the produced optical beam from the light source.

DESCRIPTION

Referring toFIG.1, an optical module100is arranged relative to a chamber140of an extreme ultraviolet (EUV) light source. The optical module100is configured to pass an optical beam120such that the optical beam120is focused to a region of interest135. Space is limited for components within or affixed to the EUV light source chamber140. Thus, there is a benefit to reducing the size of components that are used in conjunction with the EUV light source chamber140, and specifically those components that are within or affixed to the EUV light source chamber140. With this in mind, the optical module100is designed with a significant reduction in its overall length relative to prior optical designs that pass the optical beam120such that the optical beam120is focused to the region of interest135. Moreover, the optical module100does not include additional powered optical elements such as lenses to achieve the significant reduction (for example, a 30% reduction, a 40% reduction, or a 50% reduction) in its overall length. Thus, the optical module100provides a more cost-effective solution than one that adds one or more powered optical elements. And, even though the overall length of the optical module100is reduced relative to prior optical designs, the optical module100maintains its diffraction-limited optical performance. In particular, as discussed in detail below, the optical module100is able to achieve the significant reduction in its overall length by replacing at least one of its existing toroid surfaces with an aspheric toroid surface101.

A toroid surface is a surface that has different radii of curvature in the perpendicular transverse axes. The perpendicular transverse axes are the axes that are transverse to the optical path through the toroid surface. Thus, for example, a toroid surface can be a cylindrical surface, in which the radius of curvature in a first transverse axis is infinite (the curvature is 0) and the radius of curvature in a second transverse axis is finite (and the curvature can be spheric). An aspheric toroid surface (such as the aspheric toroid surface101) is a toroid surface in which the curvature along one of the transverse axes is non-spherical or aspheric. In this example, the optical path of the aspheric toroid surface101aligns or is parallel with a Y axis of the drawing. Thus, the perpendicular transverse axes of the aspheric toroid surface101are in the XZ plane of the drawing. Moreover, the optical path of the aspheric toroid surface101is aligned with and parallel with the overall optical path of the lens plurality102.

In some implementations, the optical module100is a part of a target metrology apparatus that detects, measures and/or analyzes one or more moving properties (such as speed, velocity, and acceleration) of a target as the target travels generally along the —X direction (but also possibly along the Z or Y directions) through the region of interest135on its way toward an illumination space. The optical module100can be a part of an illumination module of the target metrology apparatus and the optical beam120can be a probing light beam.

The optical module100includes a plurality102of lenses through which the optical beam120passes. The lens plurality102includes at least one aspheric toroid lens103, the aspheric toroid surface101being one of the optically-interacting surfaces of the aspheric toroid lens103. The lens plurality102is placed relative to the linearly focused curtain121of the optical beam, such curtain121intersecting or overlapping the region of interest135. Because of the aspheric toroid lens103, the lens plurality102is configured and arranged relative to the region of interest135to thereby reduce optical aberrations such that the actual resolution is diffraction limited. Optical aberrations arise from interactions between the optical beam120and the physical size/shape and material of the lenses within the plurality102. The aberration-reducing characteristics of the aspheric toroid lens103enables the achievement of the diffraction limited performance despite the reduction in overall length of the optical module100.

The optical module100also includes an optical mount apparatus115in which the lens plurality102is mounted. In some implementations, the optical mount apparatus115is arranged inside the EUV light source chamber140and fixed to an interior wall or object. In other implementations, as shown inFIG.1, the optical mount apparatus115is fixed to a wall141of the EUV light source chamber140. In these implementations, the optical mount apparatus115includes a chamber mount portion116configured to be fixed to the wall141.

The lenses within the lens plurality102(including the aspheric toroid lens103) are made of a material that is transparent to (and therefore has a high transmission for) the wavelength of the optical beam120. Additionally, the lenses within the lens plurality102can be made of a material that is hard enough to withstand polishing to thereby obtain high optical quality optically-interacting surfaces. The lenses within the lens plurality102(as well as the aspheric toroid lens103) can be made of, for example, fused silica, optical glass, optical ceramic, or optical crystals. The one or more lenses in the lens plurality102other than the aspheric toroid lens103can include toroid lenses such as plano-concave cylindrical lenses. The aspheric toroid lens103can be a single lens. The aspheric toroid lens103can be a plano-convex lens, a plano-concave lens, a meniscus lens with one face (the surface101) being aspheric toroid, or a meniscus lens with both faces (the surface101and the surface opposite to the surface101) being aspheric toroid. Different implementations for the lenses in the plurality102are discussed below.

Each of the lenses in the lens plurality102defines its own optical axis, which is a line that defines the optical path along which the optical beam120propagates through the plurality102, to a first approximation. The optical axis passes through a center of curvature of at least one transverse axis. The optical axis can have an extent along the other transverse axis if the lenses lack curvature in the other transverse axis.

The optical mount apparatus115includes one or more optical mounts configured to hold or retain the lenses within the lens plurality102. Thus, for example, the optical mount apparatus115can include one or more lens barrels, with a lens barrel consisting of a threaded body and a retainer ring that, when screwed together, securely hold the lens or lenses in place. Moreover, two or more lens barrels can be threaded end-to-end in the optical mount apparatus115, depending on how many lenses need to be mounted. The optical mount apparatus115is held or retained by the chamber mount portion116. The chamber mount portion116can be any rigid mounting element that is compatible with the material of the wall141. For example, the chamber mount portion116can include one or more flexures, flexure mounts, kinematic balls, bases, plates, strain relief elements, gaskets or O-rings, and screws or other suitable connection mechanisms.

The optical beam120can be a continuous wave light beam, a continuous wave laser beam, a pulsed light beam, or a pulsed laser beam.

Referring toFIG.2, an implementation200of the optical module100is a part of an illumination module250for the EUV light source chamber240. The optical module200includes an optical mount apparatus215that is similar to the optical mount apparatus115and that holds or fixes a lens plurality202. Like the lens plurality102, the lens plurality202includes at least one aspheric toroid lens203, with an aspheric toroid surface201being one of the optically-interacting surfaces of the aspheric toroid lens203. The lens plurality202is placed relative to a linearly focused curtain221of an optical beam220, such curtain221intersecting or overlapping a region of interest235.

The optical mount apparatus215includes a chamber mount portion216configured to be fixed to a wall241of the EUV light source chamber240. The chamber mount portion216acts as a pass-through optical pathway that defines an interior that provides an optical passage for the optical beam220. Additionally, in these implementations, the optical path of the lens plurality202passes through the EUV light source chamber240, and intersects the region of interest235.

The illumination module250includes a light source251configured to produce the optical beam220and the optical module200is configured to pass the optical beam220through the wall241or within the EUV light source chamber240. The optical module200is configured to focus the optical beam220as the linear curtain at the region of interest235inside the chamber240. In this way, the optical path defined by the lens plurality202extends from the light source251to the region of interest235. The illumination module250also includes optical components252that receive the optical beam220from the light source251, and redirect and/or modify the optical beam220for input into the lens plurality202. For example, the optical components252can include a fiber optic apparatus for transporting the optical beam220from a remote light source251to the chamber mount portion216.

In some implementations350of the illumination module250, such as shown inFIG.3, an optical module300includes a chamber mount portion316that houses an optical mount apparatus315in which the lens plurality202is arranged. The chamber mount portion316is fixed within a wall341of the EUV light source chamber240.

An implementation400of the optical module300and an implementation450of the illumination module350is shown in perspective view inFIG.4. The optical module400includes an implementation402of the lens plurality102within an optical mount apparatus415that is fixed in a chamber mount portion416. The chamber mount portion416is fixed to the wall341of the EUV light source chamber240.

The illumination module450includes a remote (from the EUV light source chamber240) light source451that produces the optical beam420(shown inFIG.5) and optical components452that redirect and/or modify the optical beam420for input into the lens plurality402. The optical components452include a portion453that is configured transport the optical beam420from the remote light source to the lens plurality402. The portion453is a fiber collimator lens assembly that includes collimating optics that direct and collimate the optical beam420produced from the light source451.

The lens plurality402includes an aspheric toroid lens403having an aspheric toroid surface401. The aspheric toroid surface401is the closest surface and the aspheric toroid lens401is the closest lens of the plurality402to the region of interest235(which is not shown inFIG.4). The lens plurality402also includes at least one toroid lens. In this particular implementation, the lens plurality402includes two toroid lenses404,405arranged between the fiber collimator lens assembly453and the aspheric toroid lens403. The lenses403,404,405are arranged so that their optical axes are parallel with an optical path that extends along an optical axis that is parallel with the Y axis. Because of the design of the lenses403,404,405, as discussed below, the optical axes can have an extent along the Z axis.

Specifically, the optical beam420is focused into a line (as opposed to a point) and the line extends along the Z axis. In this particular implementation, the lenses403,404,405compress the optical beam420in the direction perpendicular to the line and thus the optical beam420is compressed along the X axis. The lenses403,404,405can leave the optical beam420unaltered or minimally altered in the Z direction.

In order to pass the optical beam420through the wall241of the EUV light source chamber240, the illumination module450can include additional windows454,455positioned within the chamber mount portion416and configured to seal an interior of the EUV light source chamber240from an exterior. The windows454,455are able to withstand a pressure differential between an interior of and an exterior to the EUV light source chamber240. The windows454,455also need to be transparent to the wavelength of the optical beam420.

FIG.5shows a side cross-sectional view of the optical module400, along with the fiber collimator lens assembly453and the windows454,455. The lens plurality402is held by an optical mount apparatus415. The optical mount apparatus415includes a pair of lens barrels417,418that are coupled together at an interface419. The interface419can be formed from a friction fit between an inner surface of the lens barrel418and an outer surface of the lens barrel417. In this way, the lens barrels417,418can be moveable relative to each other along a direction parallel with the Y axis by way of the interface419. The lens barrel417holds or retains the lens404. For example, the lens404can be held in place within a cavity of the lens barrel417by way of a retaining ring and an internal threaded body. The lens barrel418holds or retains the lens405and the aspheric toroid lens403. Each lens403,405can be held in place within a cavity of the lens barrel418by way of a respective retaining ring and internal threaded body. Moreover, the lens barrel417is configured to mate with the fiber collimator lens assembly453. The lens barrels417,418can be made from a suitable rigid material that is non-reactive to air such as stainless steel.

Referring toFIGS.6A-6C, in some implementations, the toroid lens404is a plano-concave cylindrical lens. Specifically, the lens404includes a flat side (plano)404aand a concave cylindrical side404bopposite the plano side404a. When placed in the lens barrel417, and the lens barrel417is fixed in the chamber mount portion416, the local optical axis YLof the lens404aligns with the Y axis of the EUV light source chamber140. The concave cylindrical side404bcurves along the XLaxis of the lens404and is flat along the ZLaxis of the lens404.

Referring toFIGS.7A-7C, in some implementations, the toroid lens405is also a plano-concave cylindrical lens. Specifically, the lens405includes a flat side (plano)405aand a concave cylindrical side405bopposite the plano side405a. When placed in the lens barrel418, and the lens barrel418is fixed in the chamber mount portion416, the local optical axis YLof the lens405aligns with the Y axis of the EUV light source chamber140. The concave cylindrical side405bcurves along the XLaxis of the lens405and is flat along the ZLaxis of the lens405.

Referring toFIGS.8A-8C, in some implementations, the aspheric toroid lens403is a single lens that is plano-convex. Specifically, the lens403includes a flat side (plano)403aand a convex aspheric toroid side403b(which provides the aspheric toroid surface401) opposite the plano side403a. When placed in the lens barrel418, and the lens barrel418is fixed in the chamber mount portion416, the local optical axis YLof the lens403aligns with the Y axis of the EUV light source chamber140. The convex aspheric toroid side403bcurves along the XLaxis of the lens403and is flat along the ZLaxis of the lens403.

In other implementations, the lens403can be plano-concave, meniscus with one face being aspheric toroid, or meniscus with both faces being aspheric toroid.

Because the plano-concave cylindrical lens405and the aspheric toroid lens403are fixed to the lens barrel418, they are fixed in position relative to each other. Moreover, the plano-concave cylindrical lens404is movable relative to the pair of the plano-concave cylindrical lens405and the aspheric toroid lens403because the lens barrel417is movable relative to the lens barrel418along the Y axis (at the interface419) and the plano-concave cylindrical lens404is fixed to the lens barrel417. The adjustment between the lens barrels417,418can occur during set up to adjust the position of the lens404relative to lenses403,405to compensate for manufacturing tolerances that can vary from nominal.

Referring toFIG.9A, adjustment of the plano-concave cylindrical lens404relative to the pair of the plano-concave cylindrical lens405and the aspheric toroid lens403adjusts a position PY along the Y axis and/or a width WX along the X axis of the linearly focused curtain of the optical beam420at the region of interest935. The focus sensitivity of the optical module400(FIG.4) is measured by how much the width WX along the X axis changes relative to a particular adjustment to the position of the plano-concave cylindrical lens404relative to the pair of lenses403,405. The focus sensitivity of the optical module400can be at least 1 μm, at least 10 μm, at least 20 μm, at least 30 μm, or between 32-44 μm for an adjustment to the relative position of 1 μm. That is, the width WX changes by at least 1 μm, at least 10 μm, at least 20 μm, at least 30 μm, or between 32-44 μm for an adjustment to the relative position between the lens404and the pair of lenses403,405of 1 μm. The optical module400has a focus sensitivity that is large enough (or sensitive enough) to allow the optical beam420to be focused as the linear curtain at the region of interest935using an adjustment range to the relative position of the lens404and the pair of lenses403,405on the order of 1 μm.

Once the adjustment is completed, the lens barrels417,418can then be fixed in place to thereby fix the positions of the lenses403,404,405relative to each other. Moreover, with reference toFIG.9B, a width WZ along the Z axis of the linearly focused curtain of the optical beam420generally remains unchanged. In this implementation, as shown inFIGS.9A and9B, the linearly focused curtain of the optical beam420is thereby focused along the X axis of the EUV light source chamber140. Additionally, the aspheric toroid lens403is the lens that is closest to the region of interest935.

In other implementations, the linearly focused curtain of the optical beam420can be focused along a different axis of the EUV light source chamber140, depending on the orientation of the lenses403,404,405relative to the EUV light source chamber140coordinate system. Moreover, in other implementations, the aspheric toroid lens403can be arranged at other locations or it may not be the lens that is closest to the region of interest135.

In one specific implementation, the plano-concave cylindrical lens404has a radius of curvature (for example, along its XLaxis) that is 19-25 millimeters (mm); the plano-concave cylindrical lens405has a radius of curvature (for example, along its XLaxis) that is 31-39 mm; and the aspheric toroid lens403has a base radius of curvature (for example, along its XLaxis) that is 26-32 mm.

With these particular specifications, and with reference again toFIG.5, a distance D from an adjacent mechanical output face (such as an output face453oof the fiber collimator lens assembly453) and the aspheric toroid surface401of the lens403can be maintained at or below 80 mm, at or below 70 mm, at or below 60 mm, or at or below 50 mm. As discussed above, the optical module100is designed with a significant reduction in its overall length relative to prior optical designs that pass the optical beam120such that the optical beam120is focused to the region of interest135.

Moreover, the optical module100provides this space-saving reduction in length without the addition of powered optical elements such as lenses. As an example, in prior optical designs, the distance D from an output face453oof the fiber collimator lens assembly453and an outer surface of the lens that is closest to the region of interest135is greater than 80 mm or greater than 90 mm. Moreover, the optical module100provides this space-saving reduction in length while still maintaining its diffraction-limited optical performance by replacing at least one of its existing toroid surfaces with the aspheric toroid surface401of the lens403.

Referring again toFIGS.9A and9B, as discussed above, the optical beam420is a linearly focused curtain at the region of interest935. Specifically, a beam profile BP of the optical beam420has an extent along the Z axis that is much larger than an extent along the X axis of the EUV light source chamber140. As shown inFIG.10A, the beam profile BP extends in the XZ plane. The beam profile BP across the Z axis is shown by the graph1036B inFIG.10Band the beam profile BP across the X axis is shown by the graph1036C inFIG.10C. The extent EZ along the Z axis (FIG.10B) can be estimated by a width EZ_W of the graph1036B and the extent EX along the X axis (FIG.10C) can be estimated by a width EX_W of the graph1036C. The widths EZ_W and EX_W can be the full width at half maximum of the respective graphs1036B,1036C. For example, the beam profile BP across the Z axis (given by width EZ_W) can be between 2500 micrometers (μm) and 3500 μm and the beam provide BP across the X axis (given by width EX_W) can be less than 60 μm. In general, in some implementations, the beam profile BP across the Z axis is at least 10, at least 20, at least 30, at least 40, at least 50, or at least 60 times the beam profile BP across the X axis. Thus, written in math form, EZ_W≥10×EX_W; EZ_W≥20×EX_W; EZ_W≥30×EX_W; EZ_W≥40×EX_W; EZ_W≥50×EX_W; or EZ_W≥60×EX_W.

Referring toFIG.11, an implementation1100of the optical module100is incorporated into an EUV light source1170that, when in operation, supplies an EUV light beam1171to an output apparatus1172, which can be a lithography exposure apparatus. The EUV light source1170includes a vacuum chamber1140that defines a first target space at which each target1173in a stream of targets interacts with a first operational light beam1174A to form a modified target1173mand a second target space at which each modified target1173minteracts with a second operational light beam1174B. The first and second target spaces are in a target region1175. The first and second operational light beams1174A,1174B are produced by an operational light source1176.

The vacuum chamber1140is an implementation of the EUV light source chamber140, and it includes a plurality of walls that together define a cavity1145and the target region1175is within the cavity1145. Moreover, a region of interest1135is defined inside the cavity1145.

In some implementations, the region of interest1135is a probe region through which each target1173passes on its way to the target region1175. The optical module1100is arranged for passing an optical beam1120that interacts with the target1173in the probe region1135prior to the target1173entering the target region1175. An illumination module1150includes the optical module1100.

The EUV light source1170includes an EUV light collector (such as a mirror)1177arranged relative to the second target space. The EUV light collector1177collects EUV light1178emitted from a plasma1179that is produced when the modified target1173minteracts with the second operational light beam1174B. The EUV light collector1177redirects that collected EUV light1178as the EUV light beam1171toward the output apparatus1172. The EUV light collector1177can be a reflective optical device such as a curved mirror that is able to reflect light having EUV wavelength (that is, the EUV light1178) to form the produced EUV light beam1171.

The EUV light source1170includes a target supply apparatus1180that forms a stream of the targets1173directed to the first target space for interaction with the first operational light beam1174A. The targets1173are formed from target material that produces the EUV light1178when in a plasma state, such as after interaction with the second operational light beam1174B. The second target space is, for example, a location at which the modified targets1173mare converted to the plasma state. The target supply apparatus1180includes a reservoir1181defining a hollow interior that is configured to contain a fluid target material. The target supply apparatus1180includes a nozzle structure1182having an opening (or orifice)1183in fluid communication with the interior of the reservoir1181at one end. The target material, in a fluid state, being under the force of a pressure P (as well as other possible forces such as gravity), flows from the interior of the reservoir1181and through the opening1183to form the stream of targets1173. The trajectory (the target axial path) of the targets1173that are ejected from the opening1183generally extends along the −X direction or axis, although it is possible for the trajectory of the targets1173to include components along the plane perpendicular to the −X direction (that is, Y and Z components).

Each modified target1173mis converted at least partially or mostly to plasma through its interaction with the pulses in the second operational light beam1174B produced by the operational light source1176, such interaction occurring in the second target space. Each target1173is a target mixture that includes a target material and optionally impurities such as non-target particles. The target1173can be, for example, a droplet of liquid or molten metal, a portion of a liquid stream, solid particles or clusters, solid particles contained within liquid droplets, a foam of target material, or solid particles contained within a portion of a liquid stream. The target1173can include, for example, water, tin, lithium, xenon, or any material that, when converted to a plasma state, has an emission line in the EUV range. For example, the target1173can include the element tin, which can be used as pure tin (Sn); as a tin compound such as SnBr4, SnBr2, SnH4; as a tin alloy such as tin-gallium alloys, tin-indium alloys, tin-indium-gallium alloys, or any combination of these alloys.

The EUV light source1170can include a dedicated controller1184in communication with the components (such as the target supply apparatus1180and the operational light source1176) of the EUV light source1170. The controller1184can also communicate with the illumination module1150(such as the light source251of the illumination module1150).

The X, Y, Z coordinate system of the EUV light source1170can be fixed or determined based on an aspect of the vacuum chamber1140. For example, the chamber1140can be defined by a set of walls, and three points on one or more walls of the chamber1140or within the space of the chamber1140can provide reference for the X, Y, Z coordinate system. It is possible to fix one or more of the components of the illumination module1150to one or more walls of the chamber1140. As discussed above, the illumination module1150includes the optical module1100, which also includes a chamber mount portion (such as116) that fixes to one or more walls of the chamber1140).

The illumination module1150can function in combination with a detection module1190, which is arranged relative to the region of interest1135to detect light produced due to the interaction between the optical beam1120and the targets1173in the region of interest1135.

The implementations and/or embodiments can be further described using the following clauses:

1. An optical module for passing an optical beam, the optical module comprising:a plurality of lenses through which the optical beam passes, the plurality of lenses including at least one aspheric toroid lens, the plurality of lenses placed relative to a linearly focused curtain of the optical beam, the linearly focused curtain intersecting a region of interest; andan optical mount apparatus in which the plurality of lenses is mounted, wherein the optical mount apparatus is arranged in or fixed to a wall of a chamber of an extreme ultraviolet (EUV) light source such that an optical path is defined that passes through the EUV light source chamber and intersects the region of interest inside the chamber.

2. The optical module of clause1, wherein the plurality of lenses comprises at least one toroid lens.

3. The optical module of clause2, wherein:the at least one toroid lens comprises a first plano-concave cylindrical lens and a second plano-concave cylindrical lens; andthe at least one aspheric toroid lens is a single lens that is plano-convex, plano-concave, meniscus with one face being aspheric toroid, or meniscus with both faces being aspheric toroid.

4. The optical module of clause3, wherein the second plano-concave cylindrical lens and the aspheric toroid lens are fixed in position relative to each other and moveable together relative to the first plano-concave cylindrical lens.

5. The optical module of clause4, wherein adjustment of the first plano-concave cylindrical lens relative to the second plano-concave cylindrical lens and the aspheric toroid lens adjusts a position and/or a width of the linearly focused curtain.

6. The optical module of clause3, wherein:the linearly focused curtain of the optical beam is focused along an axis of the chamber;the first plano-concave cylindrical lens has a radius of curvature along the axis that is −19 mm to −25 mm;the second plano-concave cylindrical lens has a radius of curvature along the axis that is −31 mm to −39 mm; andthe aspheric toroid lens has a base radius of curvature along the axis that is −26 mm to −32 mm.

7. The optical module of clause6, wherein the distance from an adjacent mechanical output face and an outer face of the aspheric toroid lens is less than 80 millimeters (mm), less than 70 mm, less than 60 mm, or less than 50 mm.

8. The optical module of clause7, wherein the adjacent mechanical output face is an output face of an optical collimator.

9. The optical module of clause1, wherein the linearly focused curtain is formed from the optical beam passing through the plurality of lenses and to the region of interest inside the chamber.

10. The optical module of clause1, wherein the aspheric toroid lens is the lens that is closest to the region of interest.

11. The optical module of clause1, wherein the at least one aspheric toroid lens is a single lens that is plano-convex, plano-concave, meniscus with one face being aspheric toroid, or meniscus with both faces being aspheric toroid.

12. The optical module of clause1, wherein the aspheric toroid lens is an acylindrical lens.

13. The optical module of clause1, wherein the plurality of lenses is configured and arranged to thereby reduce optical aberrations such that their actual resolution is diffraction limited.

14. The optical module of clause1, wherein the optical beam travels along an optical axis of the chamber, and the linearly focused curtain of the optical beam has a beam profile along a first axis perpendicular to the optical axis of the chamber that is at least 10, at least 20, at least 30, at least 40, at least 50, or at least 60 times a beam profile along the a second axis perpendicular to the optical of the chamber within the region of interest inside the chamber.

15. The optical module of clause1, wherein the optical mount apparatus is arranged in a wall of the EUV light source chamber.

16. The optical module of clause15, wherein the optical path passes through an optically-transparent window fixed within the chamber wall.

17. An illumination module for an extreme ultraviolet (EUV) light source, the illumination module comprising:a light source configured to produce an optical beam; andan optical module configured to pass the optical beam through a wall of or within a chamber of the EUV light source and to focus the optical beam as a linear curtain at a region of interest inside the chamber, the optical module comprising a plurality of lenses through which the optical beam passes and defining an optical path from the light source to the region of interest, the plurality of lenses including at least one aspheric toroid lens.

18. The illumination module of clause17, wherein the plurality of lenses comprises at least one toroid lens.

19. The illumination module of clause18, wherein:the at least one toroid lens comprises a first plano-concave cylindrical lens and a second plano-concave cylindrical lens; andthe at least one aspheric toroid lens is a single lens that is plano-convex, plano-concave, meniscus with one face being aspheric toroid, or meniscus with both faces being aspheric toroid.

20. The illumination module of clause19, wherein the second plano-concave cylindrical lens and the aspheric toroid lens are fixed in position relative to each other and moveable together relative to the first plano-concave cylindrical lens.

21. The illumination module of clause20, wherein adjustment of the first plano-concave cylindrical lens relative to the second plano-concave cylindrical lens and the aspheric toroid lens adjusts a position and/or a width of the linearly focused curtain in the region of the interest.

22. The illumination module of clause21, wherein the optical module has a focus sensitivity of at least 1 μm, at least 10 μm, at least 20 μm, at least 30 μm, or between 32 to 44 μm per adjustment of the first plano-concave cylindrical lens relative to the second plano-concave cylindrical lens and the aspheric toroid lens of 1 μm.

23. The illumination module of clause21, wherein the optical module has a focus sensitivity that is sensitive enough to allow the optical beam to be focused as the linear curtain at the region of interest inside the chamber using an adjustment range on the order of a micron.

24. The illumination module of clause19, wherein:the linearly focused curtain of the optical beam is focused along an axis of the chamber;the first plano-concave cylindrical lens has a radius of curvature along the axis that is −19 mm to −25 mm;the second plano-concave cylindrical lens has a radius of curvature along the axis that is −31 mm to −39 mm; andthe aspheric toroid lens has a base radius of curvature along the axis that is −26 mm to −32 mm.

25. The illumination module of clause24, wherein the distance from an adjacent mechanical output face and an outer face of the aspheric toroid lens is less than 80 millimeters (mm), less than 70 mm, less than 60 mm, or less than 50 mm.

26. The illumination module of clause25, wherein the adjacent mechanical output face is an output face of an optical collimator.

27. The illumination module of clause17, wherein the aspheric toroid lens is the lens that is closest to the region of interest.

28. The illumination module of clause17, wherein the aspheric toroid lens is an acylindrical lens.

29. The illumination module of clause17, wherein the optical beam travels along an optical axis of the chamber, and the linearly focused curtain of the optical beam has a beam profile along a first axis perpendicular to the optical axis of the chamber that is at least 10, at least 20, at least 30, at least 40, at least 50, or at least 60 times a beam profile along a second axis perpendicular to the optical axis of the chamber within the region of interest inside the chamber.

30. The illumination module of clause17, wherein the optical beam is a continuous wave light beam.

31. The illumination module of clause17, wherein each of the lenses is made of fused silica, optical glass, optical ceramic, or optical crystals.

32. An extreme ultraviolet (EUV) light source comprising:a chamber comprising a plurality of walls that together define a cavity, wherein a region of interest is defined inside the cavity; andan optical module for passing an optical beam, the optical module comprising:a plurality of lenses through which the optical beam passes, the plurality of lenses including at least one aspheric toroid lens, the plurality of lenses placed relative to a linearly focused curtain of the optical beam, the linearly focused curtain intersecting a region of interest; andan optical mount apparatus in which the plurality of lenses is mounted, wherein the optical mount apparatus is arranged in or fixed to a wall of a chamber such that an optical path is defined that intersects the region of interest inside the chamber.

33. The EUV light source of clause32, wherein the plurality of lenses comprises at least one toroid lens.

34. The EUV light source of clause32, further comprising an illumination module comprising a light source configured to produce the optical beam and the optical module configured to receive the produced optical beam from the light source.

Other implementations are within the scope of the claims.