Multi-mirror laser maintained plasma light source

Abstract

The embodiment of the invention relates to a multi-mirror laser-maintained plasma light source. The light source may include a gas containment structure for containing a gas. The light source includes a pump source configured to generate pump illumination and a first reflector element configured to direct a portion of the pump illumination into the gas to maintain a plasma. The first reflector is configured to collect a portion of broadband light emitted from the plasma. The light source also includes one or more additional reflector elements positioned opposite the first reflector. The one or more additional reflector elements are configured to reflect back to the plasma unabsorbed pump illumination and broadband light not collected by the first reflector element.

Description

[0001] Information about divisional applications

[0002] This application is a divisional application of the invention patent application with application date of June 29, 2020, application number 202080049165.1, and invention name “Multi-mirror laser maintained plasma light source”. Technical Field

[0003] The present invention generally relates to a laser-sustained plasma (LSP) broadband light source and, in particular, to a LSP lamphouse having a plurality of reflector elements. Background Art

[0004] The need for improved light sources for inspecting ever-shrinking semiconductor devices continues to grow. One such light source includes a laser-sustained plasma (LSP) broadband light source. An LSP broadband light source includes an LSP lamp capable of producing high-power broadband light. An LSP lamp operates by using an elliptical mirror to focus laser radiation into a gas volume in order to ignite and / or sustain a plasma. Current elliptical mirrors have large collection angles (e.g., 120 degrees) and low collection solid angles (e.g., less than 3π), which results in low collection efficiency. Furthermore, due to the large collection angles (e.g., 120 degree angles), the focused spot size at the collection aperture is larger than ideal.

[0005] It would therefore be advantageous to provide a system and method for remedying the shortcomings of the conventional approaches identified above. Summary of the invention

[0006] A system according to one or more embodiments of the present disclosure is disclosed. In one embodiment, the system includes a gas containment structure for containing a gas. In another embodiment, the system includes a pump source configured to generate pump illumination. In another embodiment, the system includes a first reflector element configured to direct a portion of the pump illumination into the gas to maintain a plasma. In another embodiment, the first reflector is configured to collect at least a portion of broadband light emitted from the plasma. In another embodiment, the system includes one or more additional reflector elements positioned relative to the first reflector. In another embodiment, a reflective surface of the first reflector element faces a reflective surface of the one or more additional reflector elements. In another embodiment, the one or more additional reflector elements are configured to reflect broadband light that is not absorbed by the pump illumination and is not collected by the first reflector element back to the plasma.

[0007] A system according to one or more embodiments of the present disclosure is disclosed. In one embodiment, the system includes a gas containment structure for containing a gas. In another embodiment, the system includes a pump source configured to generate pump illumination. In another embodiment, the system includes an elliptical mirror configured to direct a portion of the pump illumination into the gas to maintain a plasma. In another embodiment, the elliptical mirror is configured to collect at least a portion of broadband light emitted from the plasma and direct the portion of the broadband light to one or more downstream applications. In another embodiment, the system includes one or more spherical mirrors positioned above the elliptical mirror. In another embodiment, a reflective surface of the elliptical mirror faces a reflective surface of the one or more spherical mirrors. In another embodiment, the one or more spherical mirrors are configured to reflect broadband light that is not absorbed by the pump illumination and is not collected by the elliptical mirror back to the plasma.

[0008] A method according to one or more embodiments of the present disclosure is disclosed. In one embodiment, the method includes generating pump illumination. In another embodiment, the method includes directing a portion of the pump illumination into a gas in a gas containment structure via a first reflector element to sustain a plasma. In another embodiment, the method includes collecting a portion of broadband light emitted from the plasma via the first reflector element and directing the portion of the broadband light to one or more downstream applications. In another embodiment, the method includes reflecting broadband light that is not absorbed by the pump illumination and not collected by the first reflector element back to the plasma via one or more additional reflector elements.

[0009] It should be understood that both the foregoing summary and the following detailed description are exemplary and explanatory only and do not necessarily limit the invention as claimed.The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the summary, serve to explain the principles of the invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Several advantages of the present disclosure may be better understood by those skilled in the art by referring to the accompanying drawings, in which:

[0011] FIG. 1 is a schematic illustration of a conventional LSP broadband light source according to one or more embodiments of the present disclosure;

[0012] Figure 2A is a schematic illustration of an LSP broadband light source according to one or more embodiments of the present disclosure;

[0013] Figure 2B is a schematic illustration of one or more pump sources of an LSP broadband light source that sustains and heats a plasma according to one or more embodiments of the present disclosure;

[0014] Figure 2C is a schematic illustration of light collection in an LSP broadband light source according to one or more embodiments of the present disclosure;

[0015] Figure 2D is a schematic illustration of an LSP broadband light source including a first reflector element and one of one or more additional reflector elements configured to form a gas containment structure;

[0016] Figure 3A The LSP broadband source shown in FIG. 1 is compared with the LSP broadband source shown in FIG. 1 according to one or more embodiments of the present disclosure. Figure 2A A diagram of the LSP broadband source shown in;

[0017] Figure 3B According to one or more embodiments of the present disclosure, the LSP broadband light source and Figure 2A Illustration of the focused light spot corresponding to the LSP broadband source shown in;

[0018] Figure 3C is a graph depicting the light collection efficiency of the LSP broadband light source shown in FIG. 1 as a function of the emitter angle according to one or more embodiments of the present disclosure, Figure 2A The light collection efficiency and Figure 2A Solid angle derivative of the LSP broadband source shown in;

[0019] Figure 4 is a schematic illustration of an LSP broadband light source with two additional reflector elements in a stacked configuration according to one or more embodiments of the present disclosure;

[0020] Figure 5 is a schematic illustration of an LSP broadband light source with three additional reflector elements in a stacked configuration according to one or more embodiments of the present disclosure;

[0021] Figure 6 is a schematic illustration of an LSP broadband light source according to one or more embodiments of the present disclosure;

[0022] Figure 7 According to one or more embodiments of the present disclosure, Figures 2A to 6 A schematic diagram of an optical characterization system for an LSP broadband light source as described in any of (or any combination thereof);

[0023] Figure 8 A simplified schematic diagram illustrating an optical characterization system arranged in a reflectometry and / or ellipsometric configuration according to one or more embodiments of the present disclosure;

[0024] Fig. 9 is an implementation of an LSP broadband light source (e.g., in Figures 2A to 8Schematic illustration of an optical characterization system for an LSP broadband light source as described in any one of or any combination of

[0025] Fig.10 is a flow chart illustrating a method for implementing an LSP broadband light source according to one or more embodiments of the present disclosure. DETAILED DESCRIPTION

[0026] Reference will now be made in detail to the disclosed subject matter which is illustrated in the accompanying drawings.

[0027] Generally speaking Figures 2A to 10 , describing a multi-mirror laser-maintained plasma broadband light source according to the present disclosure.

[0028] 1 is a schematic illustration of a conventional LSP broadband light source 100. The broadband light source 100 includes a pump source 102 configured to generate pump illumination 104 and an elliptical reflector element 106 configured to direct a portion of the pump illumination 104 to a gas contained in a gas containment structure 108 to ignite and / or maintain a plasma 110. The elliptical reflector element 106 is configured to collect a portion of the broadband light 115 (e.g., lower 2π light) emitted from the plasma 110. The broadband light 115 emitted from the plasma 110 can be collected via one or more additional optical devices (e.g., cold mirror 112) for one or more downstream applications (e.g., inspection or metrology).

[0029] It should be noted herein that the broadband light source 100 has a total collection angle of 3π (or less). The broadband light source 100 utilizes a 120 degree elliptical mirror (i.e., an elliptical mirror with a polar angle of 120 degrees) to collect the broadband light 115 emitted from the plasma 110. However, this source 100 has a large source etendue and a high magnification is required for the first reflector element. Due to the large source etendue and high magnification, the focused spot size at the collection aperture is large and the collection efficiency is low. It should be noted that the broadband light source 100 cannot recycle the broadband radiation 115 emitted from the plasma, which causes the plasma to be heated only via the primary thermal light source.

[0030] Based on the shortcomings of source 100, embodiments of the present disclosure are directed to a multi-mirror LSP broadband light source configured to increase the total light collection solid angle to greater than 3π (e.g., 3π to 4π), which in turn increases the light collection efficiency and reduces the focused spot size of the source. Increasing the light collection efficiency can also result in a 1.5X gain in light using the same laser power as the 120 degree polar angle source 100.

[0031] Figure 2A2 is a schematic illustration of an LSP broadband light source 200 according to one or more embodiments of the present disclosure. In one embodiment, the broadband light source 200 includes one or more pump sources 202 for generating one or more beams of pump illumination 204. The one or more pump sources 202 may include any pump source known in the art suitable for igniting and / or maintaining a plasma. For example, the one or more pump sources 202 may include one or more lasers (i.e., pump lasers). For example, the one or more pump sources 202 may include at least one of an infrared (IR) laser, a visible light laser, an ultraviolet (UV) laser, or the like.

[0032] In another embodiment, the broadband light source 200 includes a first reflector element 206 configured to focus a portion of the pump illumination 204 into a gas contained within a gas containment structure 208 at a focal point of the first reflector element 206 to ignite and / or sustain a plasma 210 .

[0033] In another embodiment, the first reflector element 206 has a collection angle of less than 120 degrees. For example, the first reflector element 206 may have a collection angle of 90 degrees or about 90 degrees. It should be noted herein that Figure 2A The collection angles shown in are provided for illustrative purposes only and should not be construed as limiting the scope of the present disclosure.

[0034] In another embodiment, the broadband light source 200 includes one or more additional reflector elements 214 positioned opposite the first reflector element 206. For example, a reflective surface of the first reflector element 206 may face a reflective surface of the one or more additional reflector elements 214. The one or more additional reflector elements 214 may (but need not) be positioned above the first reflector element 206. It should be noted herein that the one or more additional reflector elements 214 may be referred to as top reflector element(s) and the first reflector element 206 may be referred to as a bottom reflector element, however, this designation is non-limiting.

[0035] The one or more additional reflector elements 214 include one or more openings 220 configured to pass pump illumination 204 from the pump source 202 to the plasma 210 and / or from the focus of the first reflector element 206 to one or more components. For example, the one or more openings 220 may be configured to pass broadband light 215 to one or more additional optics (e.g., an entrance aperture of an optical characterization system or the like).

[0036] The first reflector element 206 and the one or more additional reflector elements 214 may include any reflector element known in the art of plasma production. In one embodiment, the first reflector element 206 may include a reflective ellipsoid segment (i.e., an elliptical reflector) and the one or more additional reflector elements 214 may include one or more spherical segments (i.e., a spherical reflector). It should be noted herein that the first reflector element 206 and the one or more additional reflector elements 214 are not limited to elliptical reflectors and spherical reflectors, respectively. Rather, the first reflector element 206 and the one or more additional reflector elements 214 may include any reflector shape known in the art of plasma production. For example, the first reflector element 206 and / or the one or more additional reflector elements 214 may include one or more elliptical reflectors, one or more spherical reflectors, and / or one or more parabolic reflectors.

[0037] In one embodiment, the one or more additional reflector elements 214 include a single reflective spherical segment 214. The single reflective spherical segment may be centered at the focus of the first reflector element 206.

[0038] In another embodiment, the first reflector element 206 has a radius of curvature that is smaller than the radius of curvature of the one or more additional reflector elements 214. For example, the first reflector element 206 may have a radius of curvature R1 that is smaller than the radius of curvature R2 of the one or more additional reflector elements 214. For example, the first reflector element 206 may have a radius of curvature R1=100 mm, while the one or more additional reflector elements 214 may have a radius of curvature R2=160 mm. It should be noted herein that the one or more additional reflector elements 214 may have any cone constant k known in the art. For example, the one or more additional reflector elements 214 may have a cone constant k=0 (i.e., a spherical mirror). By way of another example, the one or more additional reflector elements 214 may have a cone constant k=-1 (i.e., a parabolic mirror).

[0039] In one embodiment, the first reflector element 206 and the one or more additional reflector elements 214 are configured such that they have a combined light collection solid angle between 3π and 4π. For example, the first reflector element 206 and the one or more additional reflector elements 214 may have a combined light collection solid angle between 3.4π and 3.6π. For example, the first reflector element 206 and the one or more additional reflector elements 214 have a combined light collection solid angle of 3.5π. It should be noted herein that the emission solid angle of the plasma light source (e.g., close to 4π) is divided into an upper 2π and a lower 2π.

[0040] Figure 2BFIG. 1 is a schematic illustration of one or more pump sources 202 of an LSP broadband light source 200 that maintains and heats a plasma 210 according to one or more embodiments of the present disclosure. Figure 2B Not depicted is the broadband light 215 emitted from the plasma 210.

[0041] like Figure 2B 2, one or more pump sources 202 are arranged at one of the focal points of a first reflector element 206 and pump illumination 204 from the pump source 202 is focused to a second focal point of the first reflector element 206 to sustain a plasma 210. One or more additional reflector elements 214 may be configured to reflect unabsorbed pump illumination 218 back to the plasma 210 at the focal point of the first reflector element 206. In this embodiment, the refocused pump illumination 218 may have an additional opportunity to be absorbed by the plasma 210, thereby further heating the plasma 210 and increasing the efficiency of the source 200.

[0042] Figure 2C is a schematic illustration of light collection in an LSP broadband light source 200 according to one or more embodiments of the present disclosure. Figure 2C The initial pump illumination 204 and the recycled pump illumination 218 are not depicted. The first reflector element 206 can be configured to collect the lower 2π light for use in downstream applications. For example, the first reflector element 206 can focus the lower 2π light to a second focal point of the first reflector element 206.

[0043] Reference again Figure 2A, during operation, the plasma 210 absorbs a portion of the pump illumination 204, 218 and emits the broadband light 215. In this embodiment, approximately half of the broadband light 215 is refocused back to the plasma 210 at the focus of the first reflector element 206 to provide additional heating power to the plasma 210. It should be noted that at least a portion of the light emitted to the upper 2π solid angle (i.e., the upper 2π broadband light 215 and the upper 2π non-absorbed pump illumination 218) is continuously recycled to help enhance the efficient use of photon energy to heat the plasma 210. In this embodiment, the one or more additional reflector elements 214 are configured to collect the upper 2π light that is not collected by the first reflector element 206. For example, the broadband light 215 emitted to the upper 2π solid angle is first focused back to the focus of both the first reflector element 206 and the one or more additional reflector elements 214 (e.g., where the plasma 210 is located). In this example, the first reflector element 206 may then relay the broadband light 215 refocused back to the first reflective element 206 from the one or more additional reflector elements 214 to a second focal point (e.g., the location of the collection aperture) of the first reflector element 206. It should be noted herein that in this embodiment, the upper 2π light and the lower 2π light may be collected within the same collection etendue, which results in an increased collection solid angle (e.g., close to 4π).

[0044] In some embodiments, the pump illumination 204 includes IR light. In this embodiment, the IR light focused to the plasma 210 occupies a 2π solid angle. For example, a majority of the IR light is absorbed by the plasma 210 on its first path through the plasma 210, while the remaining IR light propagates through the plasma 210 and is refocused to the plasma 210 by the top reflector element(s) 214. In addition, a majority of the returned IR light is again reabsorbed by the plasma 210, leaving a very small portion of the IR light to leak out of the broadband light source 200. In this embodiment, one or more additional optics may include a cold mirror 212 configured to reflect a spectrum of interest of the broadband light 215 from the plasma 210 to the plasma light collecting plane 217, while other portions of the spectrum (including the non-absorbed pump illumination) are transmitted through the cold mirror 212. It should be noted herein that this process increases the overall IR absorption efficiency via double absorption.

[0045] The gas containment structure 208 may include any gas containment structure known in the art, including but not limited to a plasma / gas bulb, a plasma / gas cell, a plasma / gas chamber, or the like. Furthermore, the gas contained in the gas containment structure 208 may include any gas known in the art, including but not limited to at least one of argon (Ar), krypton (Kr), xenon (Xe), neon (Ne), nitrogen (N2), or the like.

[0046] In one embodiment, the broadband light source 200 includes an open access hole 209 configured to allow insertion of a lamp, such as a plasma cell or a plasma bulb. For example, the gas containment structure 208 of the light source 200 may include an open access hole 209. By way of another example, the first reflector element 206 may include an open access hole 209. It is noted herein that in the case where the gas containment structure 208 is a plasma bulb or a plasma cell, the transparent portion (e.g., glass) of the gas containment structure 208 may take any number of shapes. For example, the gas containment structure 208 may have a cylindrical shape, a spherical shape, a heart shape, or the like.

[0047] The first reflector element 206 and the one or more additional reflector elements 214 are configured to collect broadband light of any wavelength from the plasma 210 as is known in the art of plasma-based broadband light sources. For example, the first reflector element 206 and the one or more additional reflector elements 214 may be configured to collect ultraviolet (UV) light, vacuum UV (VUV) light, deep UV (DUV) light, and / or extreme UV (EUV) light.

[0048] In another embodiment, the broadband light source 200 further includes a device configured to direct the broadband light output 215 from the plasma 210 to one or more downstream applications (by Figures 2A to 2C The one or more additional optical devices may include any optical elements known in the art, including but not limited to one or more mirrors, one or more lenses, one or more filters, one or more beam splitters, or the like.

[0049] Although many embodiments of the present disclosure (e.g. Figure 2A The embodiments shown in FIG. 1 and FIG. 2 have been shown as having a plasma cell or a plasma bulb, but this configuration should not be interpreted as limiting the scope of the present disclosure. Figure 2D208. In one or more alternative embodiments shown in , one of the first reflector element 206 and the one or more additional reflector elements 214 may be configured to itself form a gas containment structure 208. For example, the first reflector element 206 and the one or more additional reflector elements 214 may be sealed so as to contain a gas within a volume defined by the surfaces of the first reflector element 206 and the one or more additional reflector elements 214. In this example, no internal gas containment structure (such as a plasma cell or plasma bulb) is required, where the surfaces of the first reflector element 206 and the one or more additional reflector elements 214 serve as a gas chamber. In this case, the opening 220 would be sealed using a window 230 (e.g., a glass window) to allow both the pump light 204 and the plasma broadband light 215 to travel through it. In one embodiment, the first reflector element 206 may be constructed without an opening 209. The opening between the first reflector element 206 and the additional reflector element 214 may be sealed using a seal 232.

[0050] Figure 3A Graph 300 comparing broadband source 100 and broadband light source 200 is illustrated. In this example, reflector element 106 of source 100 has a larger collection angle than first reflector element 206 of broadband light source 200. For example, first reflector element 106 of source 100 may have a 120 degree collection angle, while first reflector element 206 of broadband light source 200 may have a 90 degree collection angle. Furthermore, in this example, the collection numerical aperture (NA) of the downstream optics in collection plane 217 is the same for both source 100 and source 200.

[0051] Figure 3B 3 is an illustration of focused light spots 310, 320 corresponding to broadband light source 100 and broadband light source 200, respectively, according to one or more embodiments of the present disclosure. In one embodiment, reflector element 106 of source 100 produces focused light spot 310 and first reflector element 206 of broadband light source 200 produces focused light spot 320. In this example, the focused light spot 310 of broadband light source 100 (e.g., approximately 2000 μm) is larger than the focused light spot 320 of broadband light source 200 (e.g., approximately 1000 μm) due to the larger collection angle (e.g., 120 degrees) of source 100 (relative to source 200). It should be noted herein that the smaller size of the light spot 320 of broadband light source 200 allows broadband light source 200 to exhibit a higher collection efficiency (e.g., at or near 4π for broadband light source 200 and 3π for source 100).

[0052] Figure 3Cis a graph 350 depicting the collection efficiency 380 of source 100, the collection efficiency 370 of broadband light source 200, and the solid angle derivative 360 ​​of both light sources 100 and 200 as a function of emitter angle in accordance with one or more embodiments of the present disclosure.

[0053] In one embodiment, the solid angle derivative 360 ​​of the light source 200 shown in the graph 350 is the derivative of the solid angle with respect to the polar angle. In this embodiment, the solid angle derivative 360 ​​reaches a maximum value at the polar angle Ψ=90 degrees.

[0054] In another embodiment, graph 350 illustrates the light collection efficiency 370 according to the solid angle of light source 200 and the light collection efficiency 380 according to the solid angle of light source 100. In this embodiment, the light collection efficiencies 370, 380 vary according to the emission polar angle of the new design and the old design, respectively. In addition, at almost all polar angles, the light collection efficiency according to the solid angle of the new design (light collection efficiency 370) is higher than that of the old design (light collection efficiency 380). In the new design, the light collection efficiency according to the solid angle 370 reaches a maximum value at a polar angle Ψ=90 degrees where the solid angle has the highest derivative. On the other hand, in the old design, the maximum light collection efficiency according to the solid angle 380 reaches a maximum value at a polar angle where the solid angle derivative is not at its maximum value. Therefore, the overall light collection efficiency of the new design is higher than the overall light collection efficiency of the previous method.

[0055] Figure 4 is a schematic illustration of an LSP broadband light source 400 with two additional reflector elements in a stacked configuration according to one or more embodiments of the present disclosure. In one embodiment, the one or more additional reflector elements include a first reflective spherical segment 414a and a second spherical segment 414b. The first reflective spherical segment 414a and the second spherical segment 414b can be co-centered at the focus of the first reflector element 406. This dual mirror configuration increases the light collection solid angle of the source because the second segment 414b is able to collect the upper 2π light that is not collected by the first segment. In addition, this dual mirror configuration reduces the lateral diameter for manufacturability of larger reflective spherical segments.

[0056] The first reflective spherical segment 414a and the second spherical segment 414b may include one or more openings 420 configured to allow the pump illumination 204 to travel through the spherical segments 414a, 414b and further configured to pass the broadband light 215 to one or more downstream components. For example, the second spherical segment 414b may include a second opening 420b configured to pass the pump illumination 204 from the pump source 202 to the plasma 210 through the first opening 420a of the first spherical segment 414a. In addition, the first opening 420a may be configured to pass the collected broadband light 215 from the focus of the first reflector element 406 to one or more components through the second opening 420b. Again, the second spherical segment 414b may provide additional recycling of the pump illumination 218 and the broadband light 215.

[0057] In one embodiment, the radius of curvature of the second spherical segment 414b is greater than the radius of curvature of the first spherical segment 414a. In addition, at least one of the first spherical segment 414a or the second spherical segment 414b has a radius of curvature greater than the radius of curvature of the first reflector element 406.

[0058] Figure 5 is a schematic illustration of an LSP broadband light source 500 with three additional reflector elements 514 in a stacked configuration according to one or more embodiments of the present disclosure. In one embodiment, the one or more reflector elements include a first reflective spherical segment 514a, a second spherical segment 514b, and a third spherical segment 514c. The first reflective spherical segment 514a, the second spherical segment 514b, and the third spherical segment 514c may be co-centered at the focus of the first reflector element 506.

[0059] The first reflective spherical segment 514a, the second spherical segment 514b, and the third spherical segment 514c can include one or more openings 520 configured to allow the pump illumination 204 to travel through the spherical segments 514a, 514b, and 514c and further configured to pass the broadband light 215 to one or more downstream components. For example, the third spherical segment 514c can include a third opening 520c, the second spherical segment 514b can include a second opening 520b, and the first spherical segment 514a can include a first spherical opening 520a. In this regard, the second spherical segment 514b can provide additional recycling of the pump illumination 218 and the broadband light 215 for light not collected by the first reflector element 506, while the third spherical segment 514c provides recycling of the pump illumination 218 not collected by the second spherical segment 514b. In another embodiment, the radius of curvature of the third spherical segment 514c is greater than the radius of curvature of the second spherical segment 514b and the first spherical segment 514a.

[0060] It should be noted in this article that Figure 4 and5 The stacked configuration of multiple additional reflector elements shown in FIG. 4 allows us to reduce the size of the additional reflector elements 414a-414b and 514a-514c. This reduction in size improves the light collection efficiency of one or more embodiments of the present disclosure. In addition, this reduction in mirror size improves the manufacturability of the mirror allowing for larger light collection solid angles for higher light collection efficiency.

[0061] It should be further noted that although the maximum number of additional reflector elements in source 200 has been shown as three, this should not be construed as limiting the scope of the present disclosure. For example, source 200 may be equipped with any number of additional reflector elements, including but not limited to one, two, three, four, five, or six additional reflector elements (etc.).

[0062] Figure 6 is a schematic illustration of a broadband light source 200 according to one or more alternative and / or additional embodiments of the present disclosure.

[0063] In this embodiment, the first reflector element 606 has a radius of curvature that is greater than a radius of curvature of the one or more additional reflector elements 614. In this embodiment, the one or more additional reflector elements 614 are arranged in the shadow and collection path 217 of the pump illumination 204. Furthermore, in this embodiment, the one or more additional reflector elements 614 are configured to refocus the plasma broadband radiation 215 back to the plasma 610.

[0064] Figure 7 According to one or more embodiments of the present disclosure, Figures 2A to 6 Schematic illustration of an optical characterization system 700 for an LSP broadband light source 200 as described in any of (or any combination thereof).

[0065] It should be noted herein that the system 700 may include any imaging, inspection, metrology, lithography, or other characterization / manufacturing system known in the art. In this regard, the system 700 may be configured to perform inspection, optical metrology, lithography, and / or imaging on a sample 707. The sample 707 may include any specimen known in the art, including, but not limited to, a wafer, a reticle / photomask, and the like. It should be noted that the system 700 may be incorporated into one or more of the various embodiments of the LSP broadband light source 200 described throughout this disclosure.

[0066] In one embodiment, the sample 707 is placed on a stage assembly 712 to facilitate movement of the sample 707. The stage assembly 712 may include any stage assembly 712 known in the art, including but not limited to an XY stage, an R-theta stage, and the like. In another embodiment, the stage assembly 712 is capable of adjusting the height of the sample 707 to maintain focus on the sample 707 during inspection or imaging.

[0067] In another embodiment, the illumination arm 703 is configured to direct illumination from the broadband light source 200 to the sample 707. The illumination arm 703 may include any number and type of optical components known in the art. In one embodiment, the illumination arm 703 includes one or more optical elements 702, a beam splitter 704, and an objective lens 706. In this regard, the illumination arm 703 may be configured to focus illumination from the LSP broadband light source 200 onto the surface of the sample 707. The one or more optical elements 702 may include any optical element or combination of optical elements known in the art, including, but not limited to, one or more mirrors, one or more lenses, one or more polarizers, one or more gratings, one or more filters, one or more beam splitters, and the like.

[0068] In another embodiment, the light collecting arm 705 is configured to collect light reflected, scattered, diffracted, and / or emitted from the sample 707. In another embodiment, the light collecting arm 705 can direct and / or focus the light from the sample 707 to the sensor 716 of the detector assembly 714. It should be noted that the sensor 716 and the detector assembly 714 can include any sensor and detector assembly known in the art. For example, the sensor 716 can include, but is not limited to, a charge coupled device (CCD) detector, a complementary metal oxide semiconductor (CMOS) detector, a time delay integration (TDI) detector, a photomultiplier tube (PMT), an avalanche photodiode (APD), and the like. In addition, the sensor 716 can include, but is not limited to, a line sensor or an electron bombardment line sensor.

[0069] In another embodiment, the detector assembly 714 is communicatively coupled to a controller 718 including one or more processors 720 and a memory 722. For example, the one or more processors 720 may be communicatively coupled to the memory 722, wherein the one or more processors 720 are configured to execute a set of program instructions stored on the memory 722. In one embodiment, the one or more processors 720 are configured to analyze the output of the detector assembly 714. In one embodiment, the set of program instructions are configured to cause the one or more processors 720 to analyze one or more characteristics of the sample 707. In another embodiment, the set of program instructions are configured to cause the one or more processors 720 to modify one or more characteristics of the system 700 in order to maintain focus on the sample 707 and / or the sensor 716. For example, the one or more processors 720 may be configured to adjust the objective lens 706 or the one or more optical elements 702 in order to focus the illumination from the LSP broadband light source 200 onto the surface of the sample 707. By way of another example, the one or more processors 720 may be configured to adjust the objective lens 706 and / or the one or more optical elements 702 in order to collect illumination from the surface of the sample 707 and focus the collected illumination onto the sensor 716 .

[0070] It should be noted that system 700 may be configured in any optical configuration known in the art, including, but not limited to, dark field configurations, bright field orientations, and the like.

[0071] Figure 8 A simplified schematic diagram illustrating an optical characterization system 800 arranged for reflectometry and / or ellipsometric configuration according to one or more embodiments of the present disclosure. Figures 2A to 7 The various embodiments and components described may be interpreted as extending to Figure 8 System 800 may include any type of metering system known in the art.

[0072] In one embodiment, system 800 includes LSP broadband light source 200 , illumination arm 816 , collection arm 818 , detector assembly 828 , and controller 718 including one or more processors 720 and memory 722 .

[0073] In this embodiment, broadband illumination from the LSP broadband light source 200 is directed to the sample 707 via an illumination arm 816. In another embodiment, the system 800 collects illumination emitted from the sample via a light collecting arm 818. The illumination arm path 816 may include one or more beam conditioning components 820 adapted to modify and / or condition the broadband light beam. For example, the one or more beam conditioning components 820 may include, but are not limited to, one or more polarizers, one or more filters, one or more beam splitters, one or more diffusers, one or more homogenizers, one or more apodizers, one or more beam shapers, or one or more lenses.

[0074] In another embodiment, the illumination arm 816 can utilize a first focusing element 822 to focus and / or direct the light beam onto a sample 207 disposed on the sample stage 812. In another embodiment, the collection arm 818 can include a second focusing element 826 to collect illumination from the sample 707.

[0075] In another embodiment, the detector assembly 828 is configured to capture illumination emitted from the sample 707 through the light collecting arm 818. For example, the detector assembly 828 may receive illumination reflected or scattered from the sample 707 (e.g., via specular reflection, diffuse reflection, and the like). By way of another example, the detector assembly 828 may receive illumination generated by the sample 707 (e.g., luminescence associated with absorption of a light beam, and the like). It should be noted that the detector assembly 828 may include any sensor and detector assembly known in the art. For example, the sensor may include, but is not limited to, a CCD detector, a CMOS detector, a TDI detector, a PMT, an APD, and the like.

[0076] The collecting arm 818 may further include any number of collecting beam conditioning elements 830 for directing and / or modifying the illumination collected by the second focusing element 826, including but not limited to one or more lenses, one or more filters, one or more polarizers, or one or more phase plates.

[0077] System 800 may be configured as any type of metrology tool known in the art, such as, but not limited to, a spectroscopic ellipsometer with one or more illumination angles, a spectroscopic ellipsometer for measuring Mueller matrix elements (e.g., using a rotational compensator), a single-wavelength ellipsometer, an angle-resolved ellipsometer (e.g., a beam profile ellipsometer), a spectroscopic reflectometer, a single-wavelength reflectometer, an angle-resolved reflectometer (e.g., a beam profile reflectometer), an imaging system, a pupil imaging system, a spectral imaging system, or a scatterometer.

[0078] Descriptions of inspection / metrology tools suitable for implementation in various embodiments of the present disclosure are provided in the following: U.S. Patent Application No. 13 / 554,954, entitled “Wafer Inspection System,” filed on July 9, 2012; U.S. Published Patent Application No. 2009 / 0180176, entitled “Split Field Inspection System Using Small Catadioptric Objectives,” published on July 16, 2009; U.S. Published Patent Application No. 2007 / 0002465, entitled “Beam Delivery System for Laser Dark-Field Illumination in a Catadioptric Optical System,” published on January 4, 2007; U.S. Published Patent Application No. 2007 / 0002465, entitled “Beam Delivery System for Laser Dark-Field Illumination in a Catadioptric Optical System,” published on December 7, 1999; and U.S. Published Patent Application No. 2007 / 0002465, entitled “Ultra-broadband UV Microscope Imaging System with Wide Range Zoom Capability,” published on December 7, 1999. No. 5,999,310, entitled “Surface Inspection System Using Laser Line Illumination with Two Dimensional Imaging”, issued on April 28, 2009; No. 7,525,649, entitled “Surface Inspection System Using Laser Line Illumination with Two Dimensional Imaging”, issued on April 28, 2009; U.S. Published Patent Application No. 2013 / 0114085, entitled “Dynamically Adjustable Semiconductor Metrology System”, issued on May 9, 2013 by Wang et al.; No. 5,608,526, entitled “Focused Beam Spectroscopic Ellipsometry Method and System”, issued on March 4, 1997 by Piwonka-Corle et al.;and U.S. Patent No. 6,297,880, issued on October 2, 2001 to Rosencwaig et al., entitled “Apparatus for Analyzing Multi-Layer Thin Film Stacks on Semiconductors,” each of which is incorporated herein by reference in its entirety. ;

[0079] The one or more processors 720 of the present disclosure may include any one or more processing elements known in the art. In this sense, the one or more processors 720 may include any microprocessor type device configured to execute software algorithms and / or instructions. It should be recognized that the steps described throughout the present disclosure may be implemented by a single computer system or alternatively by multiple computer systems. In general, the term "processor" can be broadly defined to cover any device having one or more processing and / or logic elements that execute program instructions from non-temporary memory media 722. Furthermore, different subsystems of the various systems disclosed may include processors and / or logic elements suitable for implementing at least a portion of the steps described throughout the present disclosure.

[0080] The memory medium 722 may include any storage medium known in the art suitable for storing program instructions that can be executed by the associated one or more processors 720. For example, the memory medium 722 may include a non-transitory memory medium. For example, the memory medium 722 may include (but is not limited to) a read-only memory, a random access memory, a magnetic or optical storage device (e.g., a disk), a tape, a solid-state drive, and the like. In another embodiment, the memory 722 is configured to store one or more results and / or outputs of the various steps described herein. It should be further noted that the memory 722 may be housed in a common controller housing with the one or more processors 720. In an alternative embodiment, the memory 722 may be remotely located relative to the physical location of the one or more processors 720. For example, the one or more processors 720 may access a remote memory (e.g., a server) that can be accessed through a network (e.g., the Internet, an intranet, and the like). In this regard, the one or more processors 720 of the controller 718 may perform any of the various processing steps described throughout this disclosure. It should be noted herein that one or more components of the system 700 may be communicatively coupled to various other components of the system 700 in any manner known in the art. For example, the lighting system 700, the detector assembly 714, the controller 718, and the one or more processors 720 may be communicatively coupled to each other and other components via a wired connection (e.g., copper wire, fiber optic cable, and the like) or a wireless connection (e.g., RF coupling, IR coupling, data network communications (e.g., WiFi, WiMax, Bluetooth, and the like)).

[0081] In some embodiments, the LSP broadband light source 200 and systems 700, 800 as described herein may be configured as a "stand-alone tool," which is interpreted herein as a tool that is not physically coupled to a processing tool. In other embodiments, this inspection or metrology system may be coupled to a processing tool (not shown) via a transmission medium that may include wired and / or wireless portions. The processing tool may include any processing tool known in the art, such as a lithography tool, an etching tool, a deposition tool, a polishing tool, a plating tool, a cleaning tool, or an ion implantation tool. Feedback control techniques, feedforward control techniques, and / or in-situ control techniques may be used to change the parameters of a process or processing tool using the results of the inspection or measurement performed by the system described herein. The parameters of a process or processing tool may be changed manually or automatically.

[0082] Fig. 9 is an implementation of an LSP broadband light source 200 (e.g., in Figures 2A to 8 9 (a) and (b) a schematic illustration of an optical characterization system 900 for an LSP broadband light source as described in any one of or any combination of . In one embodiment, the system 900 includes an illumination arm 950 coupled to a light collecting aperture 934 for receiving broadband light 215 from the broadband light source 200. It should be noted that the illumination arm 950 can be used as an illuminator for any inspection, metrology, or other imaging system known in the art and is provided herein for illustrative purposes only.

[0083] In another embodiment, system 900 includes an NA lens 922, a compensation plate 924, and a cylindrical lens 926 along the illumination path (i.e., the path of pump illumination 204). Additionally, system 900 includes a window 930 and a color filter (CF) 932 along the collection path 217 (i.e., the path of broadband light 215).

[0084] In one embodiment, the illumination arm 950 includes one or more components for shaping and / or conditioning the broadband light 215. For example, the one or more components may include one or more lenses 952, 956, one or more mirrors, one or more filters, or one or more beam shaping elements 954 (e.g., homogenizers, beam shapers, or the like) to provide selected illumination conditions (e.g., illumination field size, beam shape, angle, spectral content, or the like).

[0085] Fig.101 is a flow chart illustrating a method 1000 for implementing an LSP broadband light source 200-800 according to one or more embodiments of the present disclosure. It should be noted herein that the steps of the method 1000 may be implemented in whole or in part by the broadband light source 200 and / or the system 700, 800, or 900. However, it should be further recognized that the method 1000 is not limited to the broadband light source 200 and / or the system 700, 800, or 900 in that additional or alternative system-level embodiments may implement all or part of the steps of the method 1000.

[0086] In step 1002, a pump source generates pump illumination.

[0087] In step 1004, a first reflector element is configured to direct a portion of pump illumination into a gas in a gas containment structure to sustain a plasma.

[0088] In step 1006, a first reflector element collects a portion of the broadband light emitted from the plasma and directs the portion of the broadband light to one or more downstream applications. The one or more downstream applications may include at least one of inspection or metrology.

[0089] In step 1008, one or more additional reflector elements are configured to reflect broadband light that is not absorbed pump illumination and not collected by the first reflector element back into the plasma.

[0090] During operation, the pump source 202 generates pump illumination 204. The first reflector element 206 directs the pump illumination 204 into the gas containment structure 208 to maintain the plasma 210. The plasma 210 emits broadband light 215 that is collected by the first reflector element 206, and the first reflector element 206 directs the broadband light 215 to one or more downstream applications (e.g., metrology or inspection). One or more additional optical devices may assist in directing the broadband light 215 to one or more downstream applications. The one or more additional reflector elements 214 reflect the broadband light that is not absorbed by the pump illumination and not collected by the first reflector element 206 back to the plasma 210 to further heat the plasma. The plasma 210 absorbs a portion of the pump illumination 204 and emits broadband radiation 215, which is also refocused back to the plasma 210 to heat the plasma.

[0091] Those skilled in the art will recognize that the components, devices, objects, and the accompanying discussions described herein are used as examples for the sake of conceptual clarity and that various configuration modifications are contemplated. Therefore, as used herein, the specific examples and the accompanying discussions set forth are intended to represent their more general categories. In general, the use of any specific example is intended to represent its category, and the non-inclusion of specific components, devices, and objects should not be considered limiting.

[0092] With respect to the use of substantially any plural and / or singular terms herein, those skilled in the art may translate from the plural to the singular and / or from the singular to the plural, depending on the context and / or application. For clarity, various singular / plural arrangements are not explicitly set forth herein.

[0093] The subject matter described herein sometimes illustrates different components contained in other components or connected to other components. It should be understood that the architecture described in this way is only exemplary, and many other architectures that realize the same function can actually be implemented. In a conceptual sense, any arrangement of components that realize the same function is effectively "associated" so that the desired function is realized. Therefore, any two components combined to realize a specific function herein can be regarded as "associated" with each other so that the desired function is realized, regardless of the architecture or intermediate components. Similarly, any two components so associated can also be regarded as "connected" or "coupled" to each other to realize the desired function, and any two components that can be so associated can also be regarded as "coupleable" to each other to realize the desired function. Specific examples that can be coupled include but are not limited to physically compatible and / or physically interactive components and / or wirelessly interactive and / or wirelessly interactive components and / or logically interactive and / or logically interactive components.

[0094] In addition, it should be understood that the present invention is defined by the appended claims. Those skilled in the art will understand that, in general, the terms used herein and particularly in the appended claims (e.g., the body of the appended claims) are generally intended to be "open" terms (e.g., the term "including" should be interpreted as "including but not limited to", the term "having" should be interpreted as "having at least", the term "includes" should be interpreted as "including but not limited to" and the like). Those skilled in the art will further understand that if a specific number of introduced claim recitations is intended, such intent will be explicitly recited in the claims, and in the absence of such a recitation, such intent does not exist. For example, to aid understanding, the appended claims below may contain the use of the introductory phrases "at least one" and "one or more" to introduce claim recitations. However, the use of such phrases should not be construed as implying that the introduction of a claim recitation by the indefinite article "a" or "an" limits any particular claim containing such introduced claim recitation to the invention containing only one such recitation, even when the same claim contains the introductory phrases "one or more" or "at least one" and an indefinite article such as "a" or "an" (e.g., "a" and / or "an" should generally be construed to mean "at least one" or "one or more"); the same is true of the use of the definite article used to introduce the claim recitation. In addition, even if a specific number of introduced claim recitations is explicitly recited, one skilled in the art will recognize that such recitation should generally be construed to mean at least the recited number (e.g., the mere recitation of "two recitations" without other modifiers generally means at least two recitations, or two or more recitations). Moreover, in those instances where a convention similar to "at least one of A, B, and C, and the like" is used, generally such a construction is intended to have a meaning that one skilled in the art would interpret as The meaning of the convention is understood (e.g., "a system having at least one of A, B, and C" would include, but is not limited to, systems having only A, only B, only C, A and B together, A and C together, B and C together, and / or A, B, and C together, and the like). In those instances where a convention similar to "at least one of A, B, or C, and the like" is used, generally such construction is intended to have a person skilled in the art understand the meaning of the convention (e.g., "a system having at least one of A, B, or C" would include, but is not limited to, systems having only A, only B, only C, A and B together, A and C together, B and C together, and / or A, B, and C together, and the like). Persons skilled in the art will further understand that virtually any transitional word and / or phrase presenting two or more alternative terms, whether in the description, claims, or drawings, should be understood to contemplate the possibility of including one of the terms, either of the terms, or both of the terms.For example, the phrase "A or B" will be understood to include the possibilities of "A" or "B" or "A and B."

[0095] It is believed that the present disclosure and many of its attendant advantages will be understood from the foregoing description, and it will be apparent that various changes may be made to the form, construction, and arrangement of components without departing from the disclosed subject matter or without sacrificing all of its important advantages. The described form is illustrative only, and the following claims are intended to cover and encompass such changes.

Claims

1. A system comprising: a gas containing structure for containing gas; a pump source configured to generate pump illumination; a first reflector element configured to direct a portion of the pump illumination into the gas to sustain a plasma, wherein the first reflector element is configured to collect at least a portion of broadband light emitted from the plasma; and one or more additional reflector elements positioned opposite the first reflector element, wherein a reflective surface of the first reflector element faces a reflective surface of the one or more additional reflector elements, wherein the one or more additional reflector elements are configured to reflect broadband light that is not absorbed pump illumination and not collected by the first reflector element back into the plasma; wherein the one or more additional reflector elements include: a first reflective spherical segment and a second spherical segment, the first reflective spherical segment and the second spherical segment form a stacked configuration, and the one or more additional reflector elements have a window that allows the pump illumination from the pump source and the broadband light emitted from the plasma to pass therethrough.

2. The system of claim 1 , wherein the one or more additional reflector elements are configured to reflect a portion of the upper 2π light not collected by the first reflector element, when viewed from the direction of the first reflector element and the direction in which the pump source is located being an upper side.

3. The system of claim 2, wherein the one or more additional reflector elements are configured to focus the portion of the upper 2π light to a first focal point of the first reflector element.

4. The system of claim 3, wherein a portion of the upper 2π light is further relayed to a second focus of the first reflector element. 5 . The system of claim 1 , wherein a radius of curvature of the first reflective spherical segment is smaller than a radius of curvature of the second spherical segment.

6. The system of claim 1, wherein the first reflector element has a radius of curvature that is less than a radius of curvature of the one or more additional reflector elements.

7. The system of claim 1, wherein the first reflector element has a radius of curvature that is greater than a radius of curvature of the one or more additional reflector elements.

8. The system of claim 1, wherein the first reflector element and the one or more additional reflector elements have a collection solid angle between 3π and 4π.

9. The system of claim 8, wherein the first reflector element and the one or more additional reflector elements have a collection solid angle between 3.4π and 3.6π.

10. The system of claim 1, wherein the one or more additional reflector elements are positioned above the first reflector element, as viewed from the direction of the first reflector element and in the direction where the pump source is located.

11. The system of claim 1 , wherein the one or more additional reflector elements comprise an aperture configured to pass pump illumination from the pump source to the plasma.

12. The system of claim 1, wherein the pump source comprises: One or more lasers.

13. The system of claim 12, wherein the pump source comprises: At least one of an infrared laser, a visible light laser, or an ultraviolet laser.

14. The system of claim 1, wherein the first reflector element and the one or more additional elements are configured to collect at least one of broadband UV, VUV, DUV, or EUV light from the plasma.

15. The system of claim 1, wherein the gas comprises: At least one of argon, krypton, or xenon.

16. The system of claim 1, wherein the gas containment structure comprises: At least one of a plasma bulb, a plasma cell, or a plasma chamber.

17. The system of claim 1, further comprising: One or more additional light collection optics configured to direct broadband light output from the plasma to one or more downstream applications.

18. The system of claim 17, wherein the one or more downstream applications include: At least one of inspection or measurement.

19. A system comprising: a gas containing structure for containing gas; a pump source configured to generate pump illumination; an elliptical mirror configured to direct a portion of the pump illumination into the gas to sustain a plasma, wherein the elliptical mirror is configured to collect at least a portion of broadband light emitted from the plasma and direct the portion of the broadband light to one or more downstream applications; and one or more spherical mirrors, viewed from the direction of the elliptical mirror and the direction in which the pump source is located, positioned above the elliptical mirror, wherein a reflective surface of the elliptical mirror faces a reflective surface of the one or more spherical mirrors, wherein the one or more spherical mirrors are configured to reflect broadband light that is not absorbed by the pump illumination and is not collected by the elliptical mirror back to the plasma; wherein the one or more spherical mirrors include: a first reflective spherical segment and a second spherical segment, the first reflective spherical segment and the second spherical segment form a stacked configuration, and the one or more additional reflector elements have a window that allows the pump illumination from the pump source and the broadband light emitted from the plasma to pass therethrough.

20. A method comprising: Generate pump illumination; directing a portion of the pump illumination into a gas in a gas containment structure via a first reflector element to sustain a plasma; collecting a portion of broadband light emitted from the plasma via the first reflector element and directing the portion of the broadband light to one or more downstream applications; and reflecting broadband light that is not absorbed pump illumination and not collected by the first reflector element back into the plasma via one or more additional reflector elements; wherein the one or more additional reflector elements include: a first reflective spherical segment and a second spherical segment, the first reflective spherical segment and the second spherical segment form a stacked configuration, and the one or more additional reflector elements have a window that allows the pump illumination from a pump source and the broadband light emitted from the plasma to pass therethrough.

21. The method of claim 20, wherein the one or more downstream applications include: At least one of inspection or measurement.

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