Multi-mirror laser-sustained plasma light source system and method

Abstract

A multi-mirror laser sustained plasma broadband light source is disclosed.SOLUTION: The light source may include a gas containment structure for containing a gas. The light source includes a pump source 202 configured to generate pump illumination 204 and a first reflector element 206 configured to direct a portion of the pump illumination 204 into a gas to sustain a plasma. The first reflector is configured to collect a portion of the broadband light emitted from the plasma. The light source also includes one or more additional reflector elements 214 disposed opposite the first reflector. The one or more additional reflector elements 214 are configured to reflect unabsorbed pump illumination 204 and broadband light not collected by the first reflector element 206 back to the plasma.SELECTED DRAWING: Figure 2A

Description

[Technical Field]

[0001] The present invention relates generally to laser-sustained plasma (LSP) broadband light sources, and more particularly to an LSP lamphouse having multiple reflector elements. [Background technology]

[0002] There is a growing need for improved light sources for use in inspecting increasingly miniaturized semiconductor devices. One such light source is the laser-sustained plasma (LSP) broadband light source. LSP broadband light sources include LSP lamps that can produce high-power broadband light. LSP lamps operate by using an elliptical mirror to focus laser radiation into a gas volume, thereby igniting and / or sustaining a plasma. Current elliptical mirrors have low collection efficiency due to a large collection polarization angle (e.g., 120 degrees) and a small collection solid angle (e.g., less than 3π). Additionally, a large collection polarization angle (e.g., a polarization angle of 120 degrees) results in a larger-than-ideal focused spot size at the collection aperture. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] U.S. Patent Application Publication No. 2016 / 0097513 [Patent Document 2] U.S. Patent Application Publication No. 2017 / 0315369 Summary of the Invention [Problem to be solved by the invention]

[0004] Therefore, it would be advantageous to provide a system and method that ameliorate the shortcomings of conventional methods such as those discussed above. [Means for solving the problem]

[0005] According to one or more embodiments of the present disclosure, a system is disclosed. In one embodiment, the system includes a gas confinement structure for containing a gas. In another embodiment, the system includes a pump light 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, thereby sustaining 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 opposite 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 unabsorbed pump illumination and broadband light not collected by the first reflector element back to the plasma.

[0006] According to one or more embodiments of the present disclosure, a system is disclosed. In one embodiment, the system includes a gas confinement structure for containing a gas. In another embodiment, the system includes a pump light 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, thereby sustaining 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 a portion of the broadband light to one or more downstream applications. In another embodiment, the system includes one or more spherical mirrors disposed 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 unabsorbed pump illumination and broadband light not collected by the elliptical mirror back to the plasma.

[0007] According to one or more embodiments of the present disclosure, a method 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 confinement structure, thereby sustaining a plasma via a first reflector element. In another embodiment, the method includes collecting a portion of broadband light emitted from the plasma via the first reflector element and directing a portion of the broadband light to one or more downstream applications. In another embodiment, the method includes reflecting unabsorbed pump illumination and broadband light not collected by the first reflector element back to the plasma via one or more additional reflector elements.

[0008] It is to be understood that both the foregoing general description 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 general description, serve to explain the principles of the invention.

[0009] The many advantages of the present disclosure may be better understood by those skilled in the art by reference to the accompanying drawings. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a schematic diagram of a conventional LSP broadband light source in accordance with one or more embodiments of the present disclosure. [Figure 2A] FIG. 1 is a schematic diagram of an LSP broadband light source in accordance with one or more embodiments of the present disclosure. [Figure 2B] FIG. 1 is a schematic diagram of one or more pump sources of an LSP broadband light source that sustains and heats a plasma in accordance with one or more embodiments of the present disclosure. [Figure 2C] FIG. 1 is a schematic diagram of light collection in an LSP broadband light source, in accordance with one or more embodiments of the present disclosure. [Figure 2D]1 is a schematic diagram 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 confinement structure. [Figure 3A] 2B is a graph comparing the LSP broadband light source shown in FIG. 1 with the LSP broadband light source shown in FIG. 2A in accordance with one or more embodiments of the present disclosure. [Figure 3B] 2B is a diagram of a focused spot corresponding to the LSP broadband light source shown in FIG. 1 and the LSP broadband light source shown in FIG. 2A in accordance with one or more embodiments of the present disclosure. [Figure 3C] 2B is a graph illustrating the collected light efficiency of the LSP broadband light source shown in FIG. 1, the collected light efficiency of the LSP broadband light source shown in FIG. 2A, and the solid angle derivative of the LSP broadband light source shown in FIG. 2A as a function of polarized emission angle, in accordance with one or more embodiments of the present disclosure. [Figure 4] FIG. 1 is a schematic diagram of an LSP broadband light source with two additional reflector elements in a stacked configuration, in accordance with one or more embodiments of the present disclosure. [Figure 5] FIG. 1 is a schematic diagram of an LSP broadband light source with three additional reflector elements in a stacked configuration, in accordance with one or more embodiments of the present disclosure. [Figure 6] FIG. 1 is a schematic diagram of an LSP broadband light source in accordance with one or more embodiments of the present disclosure. [Figure 7] FIG. 7 is a schematic diagram of an optical characterization system implementing the LSP broadband light source shown in any one (or a combination) of FIGS. 2A-6, in accordance with one or more embodiments of the present disclosure. [Figure 8] FIG. 1 is a simplified schematic diagram of an optical characterization system arranged in a reflectometry and / or ellipsometry configuration, in accordance with one or more embodiments of the present disclosure. [Figure 9] 2A-8 are schematic diagrams of optical characterization systems implementing an LSP broadband light source (eg, any of the LSP broadband light sources shown in FIGS. 2A-8 or any combination thereof) in accordance with one or more embodiments of the present disclosure. [Figure 10] FIG. 1 is a flow diagram illustrating a method for implementing an LSP broadband light source in accordance with one or more embodiments of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0011] Reference will now be made in detail to the disclosed subject matter, which is illustrated in the accompanying drawings.

[0012] 2A-10, a multi-mirror laser-sustained plasma broadband light source according to the present disclosure will be described.

[0013] 1 is a schematic diagram illustrating a conventional LSP broadband light source 100. The broadband light source 100 includes a pump light source 102 configured to generate pump illumination 104 and an elliptical reflector element 106 configured to direct a portion of the pump illumination 104 toward a gas contained in a gas confinement structure 108, thereby igniting and / or sustaining a plasma 110. The elliptical reflector element 106 is configured to collect a portion of broadband light 115 (e.g., the 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 elements (e.g., a cold mirror 112) for one or more downstream applications (e.g., inspection or metrology).

[0014] 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 polarization angle of 120 degrees) to collect the broadband light 115 emitted from the plasma 110. However, such a light source 100 has a large source etendue and requires a high magnification for the first reflector element. The large source etendue and high magnification result in a large focused spot size at the collection aperture and low collection efficiency. It should be noted that the broadband light source 100 cannot recycle the broadband radiation 115 emitted from the plasma, and therefore the plasma is heated only via the primary thermal light source.

[0015] Based on the shortcomings of light source 100, embodiments of the present disclosure are directed to realizing a multi-mirror LSP broadband light source configured to increase the total collection solid angle to 3π or more (e.g., 3π-4π), thereby improving the collection efficiency and reducing the focused spot size of the light source. Furthermore, by increasing the collection efficiency, it is possible to obtain 1.5 times the amount of light with the same laser output as light source 100 with a polarization angle of 120 degrees.

[0016] 2A is a schematic diagram of an LSP broadband light source 200 in accordance with one or more embodiments of the present disclosure. In one embodiment, the broadband light source 200 includes one or more pump light sources 202 for generating one or more beams of pump illumination 204. The one or more pump light sources 202 may include any pump light source known in the art suitable for igniting and / or sustaining a plasma. For example, the one or more pump light sources 202 may include one or more lasers (i.e., pump lasers). For example, the one or more pump light sources 202 may include at least one of an infrared (IR) laser, a visible laser, an ultraviolet (UV) laser, etc.

[0017] In another embodiment, broadband light source 200 includes a first reflector element 206 configured to focus a portion of pump illumination 204 into gas contained within gas confinement structure 208 at a focal point of first reflector element 206 to ignite and / or sustain plasma 210.

[0018] In another embodiment, the first reflector element 206 has a collection polarization angle of less than 120 degrees. For example, the first reflector element 206 may have a collection polarization angle of 90 degrees or approximately 90 degrees. It should be noted that the collection angles shown in FIG. 2A are provided herein for illustrative purposes only and should not be construed as limiting the scope of the present disclosure.

[0019] 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 be positioned above the first reflector element 206, but this is not required. In this specification, the one or more additional reflector elements 214 may be referred to as an upper reflector element(s), and the first reflector element 206 may be referred to as a lower reflector element, although it should be noted that such designations are not limiting.

[0020] The one or more additional reflector elements 214 include one or more apertures 220 configured to pass pump illumination 204 from the pump light source 202 to the plasma 210 and / or to one or more components from the focal point of the first reflector element 206. For example, the one or more apertures 220 may be configured to pass broadband light 215 to one or more additional optical elements (e.g., entrance apertures of an optical characterization system, etc.).

[0021] 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 generation. In one embodiment, the first reflector element 206 may include a reflective elliptical section (i.e., an elliptical reflector), and the one or more additional reflector elements 214 may include one or more spherical sections (i.e., spherical reflectors). Note that, herein, the first reflector element 206 and the one or more additional reflector elements 214 are not limited to an elliptical reflector and a spherical reflector, 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 generation. 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.

[0022] In one embodiment, the one or more additional reflector elements 214 include a single reflective spherical section 214. The single reflective spherical section may be centered at the focal point of the first reflector element 206.

[0023] In another embodiment, the first reflector element 206 has a smaller radius of curvature than 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 that, herein, the one or more additional reflector elements 214 may have any conic constant k known in the art. For example, the one or more additional reflector elements 214 may have a conic constant k=0 (i.e., spherical mirrors). As another example, the one or more additional reflector elements 214 may have a conic constant k=-1 (i.e., parabolic mirrors).

[0024] In one embodiment, the first reflector element 206 and the one or more additional reflector elements 214 are configured to have a combined collection solid angle of 3π to 4π. For example, the first reflector element 206 and the one or more additional reflector elements 214 may have a combined collection solid angle of 3.4π to 3.6π. For example, the first reflector element 206 and the one or more additional reflector elements 214 have a combined collection solid angle of 3.5π. It should be noted that herein, the emission solid angle of a plasma light source (e.g., near 4π) is divided into an upper 2π and a lower 2π.

[0025] 2B is a schematic diagram illustrating how one or more pump light sources 202 of an LSP broadband light source 200 sustain and heat a plasma 210, according to one or more embodiments of the present disclosure. For simplicity, broadband light 215 emitted from the plasma 210 is not shown in FIG. 2B.

[0026] 2B , one or more pump light sources 202 are positioned at one of the focal points of the first reflector element 206, and pump illumination 204 from the pump light sources 202 is focused at a second focal point of the first reflector element 206 to maintain the plasma 210. One or more additional reflector elements 214 may be configured to reflect unabsorbed pump illumination 218 back into 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 light source 200.

[0027] 2C is a schematic diagram of light collection in an LSP broadband light source 200 in accordance with one or more embodiments of the present disclosure. For simplicity, the initial pump illumination 204 and the recycled pump illumination 218 are not shown in FIG. 2C. The first reflector element 206 may be configured to collect the lower 2π light for use in downstream applications. For example, the first reflector element 206 may focus the lower 2π light to a second focal point of the first reflector element 206.

[0028] 2A , during operation, plasma 210 absorbs a portion of pump illumination 204, 218 and emits broadband light 215. In this embodiment, approximately half of broadband light 215 is refocused at the focal point of first reflector element 206 and returned to plasma 210, providing additional heating power to plasma 210. Note that at least a portion of the light emitted in the upper 2π solid angle (i.e., upper 2π broadband light 215 and upper 2π unabsorbed pump illumination 218) is continuously recycled to help promote efficient utilization of photon energy for heating plasma 210. In this embodiment, one or more additional reflector elements 214 are configured to collect the upper 2π light not collected by first reflector element 206. For example, broadband light 215 emitted into the upper 2π solid angle may first be focused back to a focal point (e.g., where plasma 210 is located) of both first reflector element 206 and one or more additional reflector elements 214. In this example, first reflector element 206 may then relay the broadband light 215 that has been refocused from the one or more additional reflectors 214 back to first reflector element 206 to a second focal point (e.g., at the location of the collection aperture) of first reflector element 206. It is noted herein that in this embodiment, the upper 2π and lower 2π light may be focused within the same collection etendue, resulting in an increased collection solid angle (e.g., near 4π).

[0029] In some embodiments, the pump illumination 204 includes IR light. In this embodiment, the IR light focused into the plasma 210 occupies a solid angle of 2π. For example, a significant portion of the IR light is absorbed by the plasma 210 on its initial path through the plasma 210, and the remaining IR light propagates through the plasma 210 and is refocused into the plasma 210 by the top reflector element(s) 214. Furthermore, a significant portion of the returned IR light is again reabsorbed by the plasma 210, and a small portion of the remaining IR light escapes the broadband light source 200. In this embodiment, the one or more additional optical elements can include a cold mirror 212 configured to reflect the spectrum of interest of the broadband light 215 from the plasma 210 to the plasma collection surface 217, with another portion of the light spectrum (including the unabsorbed pump illumination) transmitting through the cold mirror 212. It is noted herein that this process increases the overall IR absorption efficiency through double absorption.

[0030] The gas confinement structure 208 may include any gas confinement structure known in the art, including, but not limited to, a plasma / gas valve, a plasma / gas cell, a plasma / gas chamber, etc. Additionally, the gas contained within the gas confinement 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 (N), etc.

[0031] In one embodiment, broadband light source 200 includes an open access hole 209 configured to allow insertion of a lamp (e.g., a plasma cell or plasma bulb). For example, gas confinement structure 208 of light source 200 may include open access hole 209. As another example, first reflector element 206 may include open access hole 209. It is noted herein that when gas confinement structure 208 is a plasma bulb or plasma cell, the transparent portion (e.g., glass) of gas confinement structure 208 may be any number of shapes. For example, gas confinement structure 208 may be cylindrical, spherical, cardioid, etc.

[0032] 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 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 ultraviolet (DUV) light, and / or extreme ultraviolet (EUV) light.

[0033] In another embodiment, broadband light source 200 further includes one or more additional optical elements configured to direct broadband light output 215 from plasma 210 to one or more downstream applications (shown by ellipses in FIGS. 2A-2C ). The one or more additional optical elements may include any optical element 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, etc.

[0034] While many of the embodiments of the present disclosure have been illustrated as including a plasma cell or plasma bulb, such as the embodiment shown in FIG. 2A , such a configuration should not be construed as limiting the scope of the present disclosure. In one or more alternative embodiments, the first reflector element 206 and one of the one or more additional reflector elements 214 may themselves be configured to form the gas confinement structure 208, as shown in FIG. 2D . For example, the first reflector element 206 and one or more additional reflector elements 214 may be sealed to contain a gas within a volume defined by the surfaces of the first reflector element 206 and one or more additional reflector elements 214. In this example, an internal gas confinement structure, such as a plasma cell or plasma bulb, is not required, and the surfaces of the first reflector element 206 and one or more additional reflector elements 214 function as a gas chamber. In this case, the opening 220 is sealed by a window 230 (e.g., a glass window) that allows both the pump light 204 and the plasma broadband light 215 to pass through. In one embodiment, the first reflector element 206 may be a structure without an opening 209. The opening between the first reflector element 206 and the additional reflector element 214 may be sealed with a seal 232.

[0035] 3A shows a graph 300 comparing broadband light source 100 and broadband light source 200. In this example, the reflector element 106 of light source 100 has a larger collection angle than the first reflector element 206 of broadband light source 200. For example, the first reflector element 106 of light source 100 may have a collection polarization angle of 120 degrees, while the first reflector element 206 of broadband light source 200 may have a collection polarization angle of 90 degrees. Furthermore, in this example, the collection numerical aperture (NA) of the downstream optical elements at collection surface 217 is the same for both light source 100 and light source 200.

[0036] 3B is a diagram of focused spots 310 and 320 corresponding to broadband light source 100 and broadband light source 200, respectively, in accordance with one or more embodiments of the present disclosure. In one embodiment, reflector element 106 of light source 100 generates focused spot 310, and first reflector element 206 of broadband light source 200 generates focused spot 320. In this example, focused spot 310 of broadband light source 100 is larger (e.g., approximately 2000 μm) than focused spot 320 of broadband light source 200 (e.g., approximately 1000 μm). This is due to the larger collection polarization angle (e.g., 120 degrees) of light source 100 (compared to light source 200). It should be noted herein that the smaller size of spot 320 of broadband light source 200 may allow broadband light source 200 to exhibit higher collection efficiency (e.g., approximately 4π for broadband light source 200 and approximately 3π for light source 100).

[0037] FIG. 3C is a graph 350 showing the collection efficiency 380 of light source 100, the collection efficiency 370 of broadband light source 200, and the solid angle derivative 360 ​​of both light source 100 and light source 200 as a function of polarized emission angle, in accordance with one or more embodiments of the present disclosure.

[0038] In one embodiment, the solid angle derivative 360 ​​of light source 200 shown in graph 350 is the derivative of the solid angle with respect to the polarization angle. In this embodiment, the solid angle derivative 360 ​​is greatest at a polarization angle Ψ=90 degrees.

[0039] In another embodiment, graph 350 shows collection efficiency per solid angle 370 for light source 200 and collection efficiency per solid angle 380 for light source 100. In this embodiment, collection efficiencies 370 and 380 are functions of polarization emission angle for the new and old designs, respectively. Also, collection efficiency per solid angle is higher for the new design (collection efficiency 370) relative to the old design (collection efficiency 380) at nearly all polarization angles. For the new design, collection efficiency per solid angle 370 is maximized at polarization angle Ψ=90 degrees, where the solid angle derivative is maximized. Meanwhile, for the old design, collection efficiency per solid angle 380 is maximized at polarization angles where the solid angle derivative is not maximized. Therefore, the overall collection efficiency of the new design is higher than that of the old design.

[0040] 4 is a schematic diagram of an LSP broadband light source 200 having two additional reflector elements in a stacked configuration in accordance with one or more embodiments of the present disclosure. In one embodiment, the one or more additional reflector elements include a first reflective spherical section 414a and a second spherical section 414b. The first reflective spherical section 414a and the second spherical section 414b may be co-centered at the focal point of the first reflector element 406. This double-mirror structure allows the second section 414b to collect the upper 2π of light not collected by the first section, thereby increasing the collection solid angle of the light source. Additionally, this double-mirror structure reduces the lateral diameter to allow for the manufacture of larger reflective spherical sections.

[0041] The first reflective spherical section 414a and the second spherical section 414b can include one or more openings 420 configured to allow the pump illumination 204 to pass through the spherical sections 414a, 414b and further configured to pass the broadband light 215 to one or more downstream components. For example, the second spherical section 414b can include a second opening 420b configured to pass the pump illumination 204 from the pump light source 202 to the plasma 210 through the first opening 420a of the first spherical section 414a. The first opening 420a can also be configured to pass the collected broadband light 215 from the focal point of the first reflector element 406 through the second opening 420b to one or more downstream components. Additionally, the second spherical section 414b can provide additional recycling of the pump illumination 218 and the broadband light 215.

[0042] In one embodiment, the radius of curvature of the second spherical section 414b is greater than the radius of curvature of the first spherical section 414a, and at least one of the first spherical section 414a or the second spherical section 414b has a radius of curvature greater than the radius of curvature of the first reflector element 406.

[0043] 5 is a schematic diagram of an LSP broadband light source 500 having three additional reflector elements 514 in a stacked configuration in accordance with one or more embodiments of the present disclosure. In one embodiment, the one or more reflector elements include a first reflective spherical section 514a, a second spherical section 514b, and a third spherical section 514c. The first reflective spherical section 514a, the second spherical section 514b, and the third spherical section 514c may be co-centered at the focal point of the first reflector element 506.

[0044] The first reflective spherical section 514a, the second spherical section 514b, and the third spherical section 514c may include one or more openings 520. The openings 520 are configured to allow the pump illumination 204 to pass through the spherical sections 514a, 514b, and 514c and to pass the broadband light 215 to one or more downstream components. For example, the third spherical section 514c may include a third opening 520c, the second spherical section 514b may include a second opening 520b, and the first spherical section 514a may include a first spherical opening 520a. In this regard, the second spherical section 514b may provide additional recycling of the pump illumination 218 and the broadband light 215 for light not collected by the first reflector element 506. Additionally, the third spherical section 514c provides recycling of the pump illumination 218 not collected by the second spherical section 514c. In another embodiment, the radius of curvature of the third spherical section 514c is greater than the radius of curvature of the second spherical section 514b and the first spherical section 514a.

[0045] It is noted herein that stacking multiple additional reflector elements as shown in Figures 4 and 5 allows for a reduction in 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. Furthermore, this reduction in mirror size increases the manufacturability of the mirror, which allows for a larger collection solid angle for higher light collection efficiency.

[0046] Also, it should be noted that while the maximum number of additional reflector elements in light source 200 is shown as three, this should not be construed as limiting the scope of the present disclosure. For example, light source 200 can include any number of additional reflector elements, including, but not limited to, one, two, three, four, five, or six (etc.) additional reflector elements.

[0047] FIG. 6 is a schematic diagram of a broadband light source 200 in accordance with one or more alternative and / or additional embodiments of the present disclosure.

[0048] In this embodiment, the first reflector element 606 has a radius of curvature that is larger than the radius of curvature of the one or more additional reflector elements 614. In this embodiment, the one or more additional reflector elements 614 are positioned in the shadow of the pump illumination 204 and collection path 217. Furthermore, in this embodiment, the one or more additional reflector elements 614 are configured to refocus the plasma broadband radiation 215 back into the plasma 210.

[0049] FIG. 7 is a schematic diagram of an optical characterization system 700 implementing the LSP broadband light source 200 shown in any one (or a combination) of FIGS. 2A-6, in accordance with one or more embodiments of the present disclosure.

[0050] It is noted herein that system 700 may comprise any imaging, inspection, metrology, lithography, or other characterization / fabrication system known in the art. In this regard, system 700 may be configured to perform inspection, optical metrology, lithography, and / or imaging on specimen 707. Specimen 707 may include any sample known in the art, including, but not limited to, wafers, reticles / photomasks, etc. It is noted that system 700 may incorporate one or more of the various embodiments of LSP broadband light source 200 described throughout this disclosure.

[0051] In one embodiment, the sample 707 is placed on a stage assembly 712 to facilitate movement of the sample 707. The stage assembly 712 can include any stage assembly 712 known in the art, including, but not limited to, an XY stage, an R-Theta stage, etc. In another embodiment, the stage assembly 712 can adjust the height of the sample 707 during inspection or imaging, thereby keeping the sample 707 in focus.

[0052] In another embodiment, illumination arm 703 is configured to direct illumination from broadband light source 200 toward sample 707. Illumination arm 703 may include any number and type of optical components known in the art. In one embodiment, illumination arm 703 includes one or more optical elements 702, a beam splitter 704, and an objective lens 706. In this regard, illumination arm 703 may be configured to focus illumination from LSP broadband light source 200 onto the plane of sample 707. 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, etc.

[0053] In another embodiment, the collection arm 705 is configured to collect light reflected, scattered, diffracted, and / or emitted from the sample 707. In another embodiment, the collection arm 705 may direct and / or focus light from the sample 707 onto a sensor 716 of the detector assembly 714. It should be noted that the sensor 716 and the detector assembly 714 may include any sensor and detector assembly known in the art. For example, the sensor 716 may 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), etc. Additionally, the sensor 716 may include, but is not limited to, a line sensor or an electron-bombarded line sensor.

[0054] In another embodiment, the detector assembly 714 is communicatively coupled to a controller 718 that includes one or more processors 720 and a memory 722. For example, the one or more processors 720 can be communicatively coupled to the memory 722, where the one or more processors 720 are configured to execute a set of program instructions stored in 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 is 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 is configured to cause the one or more processors 720 to alter one or more characteristics of the system 700 to maintain focus on the sample 707 and / or the sensor 716. For example, the one or more processors 720 can be configured to adjust the objective lens 706 or one or more optical elements 702 to focus illumination from the LSP broadband light source 200 onto the plane of the sample 707. As another example, the one or more processors 720 may be configured to adjust the objective lens 706 and / or one or more optical elements 702 to collect illumination from the surface of the sample 707 and focus the collected illumination onto the sensor 716.

[0055] It should be noted that system 700 can be configured in any optical configuration known in the art, including but not limited to dark-field configurations, bright-field orientations, and the like.

[0056] Figure 8 shows a simplified schematic diagram of an optical characterization system 800 arranged in a reflectometry and / or ellipsometry configuration, in accordance with one or more embodiments of the present disclosure. It should be noted that the various embodiments and components described with respect to Figures 2A-7 may be construed as extending to the system of Figure 8. System 800 may include any type of metrology system known in the art.

[0057] In one embodiment, system 800 includes an LSP broadband light source 200 , an illumination arm 816 , a collection arm 818 , a detector assembly 828 , and a controller 718 including one or more processors 720 and memory 722 .

[0058] In this embodiment, broadband illumination from LSP broadband light source 200 is directed toward sample 707 via illumination arm 816. In another embodiment, system 800 collects illumination emitted from the sample via collection arm 818. Illumination arm path 816 may include one or more beam conditioning components 820 suitable for modifying and / or conditioning the broadband beam. For example, 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.

[0059] In another embodiment, the illumination arm 816 may utilize a first focusing element 822 to focus and / or direct the beam onto the sample 207 disposed on the sample stage 812. In another embodiment, the collection arm 818 may include a second focusing element 826 to focus the illumination from the sample 707.

[0060] In another embodiment, the detector assembly 828 is configured to capture illumination emitted from the sample 707 via the collection 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, etc.). As another example, the detector assembly 828 may receive illumination generated by the sample 707 (e.g., luminescence associated with absorption of the beam, etc.). 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, etc.

[0061] The collection arm 818 may further include any number of collected beam conditioning elements 830 that direct and / or modify the illumination collected by the second focusing element 826. The collected beam conditioning elements 830 include, but are not limited to, one or more lenses, one or more filters, one or more polarizers, or one or more phase plates.

[0062] System 800 may be configured as any type of metrology tool known in the art, including, 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.

[0063] Descriptions of inspection / metrology tools suitable for implementation with various embodiments of the present disclosure are found in U.S. patent application Ser. No. 13 / 554,954, filed July 9, 2012, entitled "Wafer Inspection System"; U.S. published patent application Ser. No. 2009 / 0180176, published July 16, 2009, entitled "Split Field Inspection System Using Small Catadioptric Objectives"; U.S. published patent application Ser. No. 2007 / 0002465, published January 4, 2007, entitled "Beam Delivery System for Laser Dark-Field Illumination in a Catadioptric Optical System"; U.S. Patent No. 5,999,310, published December 7, 1999, entitled "Ultra-broadband UV Microscope Imaging System with Wide Range Zoom Capability"; U.S. Patent No. 5,999,310, published April 28, 2009, entitled "Surface Inspection System Using Laser Line Illumination with Two Dimensional No. 7,525,649, entitled "Dynamically Adjustable Semiconductor Metrology System," published May 9, 2013; U.S. Patent Application No. 2013 / 0114085, by Wang et al., entitled "Dynamically Adjustable Semiconductor Metrology System," published May 9, 2013; U.S. Patent No. 5,608,526, by Piwonka-Corle et al., entitled "Focused Beam Spectroscopic Ellipsometry Method and System," published March 4, 1997; and U.S. Patent No. 6,297,880, by Rosencwaig et al., entitled "Apparatus for Analyzing Multi-Layer Thin Film Stacks on Semiconductors," published October 2, 2001, each of which is incorporated herein by reference in its entirety.

[0064] 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 will be understood that the steps described throughout this disclosure may be performed by a single computer system, or alternatively, multiple computer systems. Overall, the term "processor" may be broadly defined to encompass any device having one or more processing and / or logic elements that execute program instructions from a non-transitory memory medium 722. Furthermore, different subsystems of the various disclosed systems may include processors and / or logic elements suitable for performing at least some of the steps described throughout this disclosure.

[0065] The memory medium 722 may include any storage medium known in the art suitable for storing program instructions executable 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, read-only memory, random access memory, magnetic or optical memory devices (e.g., disks), magnetic tape, solid-state drives, etc. In another embodiment, the memory 722 is configured to store one or more results and / or outputs of the various steps described herein. Furthermore, it should be 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 located remotely from 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) accessible via a network (e.g., the Internet, an intranet, etc.). In this regard, the one or more processors 720 of the controller 718 may perform any of the various process steps described throughout this disclosure. It should be noted herein that one or more components of system 700 may be communicatively coupled to various other components of system 700 in any manner known in the art. For example, illumination system 700, detector assembly 714, controller 718, and one or more processors 720 may be communicatively coupled to each other and to the other components via wired (e.g., copper wire, fiber optic cable, etc.) or wireless connections (e.g., RF connections, IR coupling, data network communications (e.g., WiFi, WiMax, Bluetooth, etc.)).

[0066] In some embodiments, the LSP broadband light source 200 and systems 700, 800 described herein may be configured as a "standalone tool," which is herein interpreted as a tool that is not physically connected to a process tool. In another embodiment, such an inspection or metrology system may be connected to a process tool (not shown) by a transmission medium that may include wired and / or wireless portions. The process tool may include any process tool known in the art, such as a lithography tool, an etch tool, a deposition tool, a polishing tool, a plating tool, a cleaning tool, or an ion implantation tool. Results of the inspection or measurement performed by the systems described herein may be used to modify process or process tool parameters using feedback, feedforward, and / or in situ control techniques. The process or process tool parameters may be modified manually or automatically.

[0067] 9 is a schematic diagram of an optical characterization system 900 implementing an LSP broadband light source 200 (e.g., any of the LSP broadband light sources shown in FIGS. 2A-8 or any combination thereof) in accordance with one or more embodiments of the present disclosure. In one embodiment, system 900 includes an illuminator arm 950 connected to a collection aperture 934 for receiving broadband light 215 from broadband light source 200. It should be noted that illumination arm 950 can serve as an illuminator for any inspection, metrology, or other imaging system known in the art and is provided herein for illustrative purposes only.

[0068] In another embodiment, the system 900 includes a NA lens 922, a compensation plate 924, and a cylinder lens 926 along the illumination path (i.e., the path of the pump illumination 204). Additionally, the system 900 includes a window 930 and a color filter (CF) 932 along the collection path 217 (i.e., the path of the broadband light 215).

[0069] In one embodiment, the illuminator 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, etc.) to provide a selected illumination condition (e.g., illumination field size, beam shape, angle, spectral content, etc.).

[0070] 10 is a flow diagram illustrating a method 1000 for implementing an LSP broadband light source 200-800 in accordance with one or more embodiments of the present disclosure. It is noted herein that all or a portion of the steps of method 1000 may be performed by broadband light source 200 and / or systems 700, 800, or 900. However, it will be further recognized that method 1000 is not limited to broadband light source 200 and / or systems 700, 800, or 900, as additional or alternative system-level embodiments may also perform all or a portion of the steps of method 1000.

[0071] In step 1002, a pump light source generates pump illumination.

[0072] In step 1004, a first reflector element is configured to direct a portion of the pump illumination toward the gas within the gas confinement structure to sustain a plasma.

[0073] In step 1006, the 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, which may include at least one of inspection or metrology.

[0074] In step 1008, one or more additional reflector elements are configured to reflect unabsorbed pump illumination and broadband light not collected by the first reflector element back into the plasma.

[0075] During operation, the pump light source 202 generates pump illumination 204. The first reflector element 206 directs the pump illumination 204 into the gas confinement structure 208, thereby sustaining the plasma 210. The plasma 210 emits broadband light 215, which is collected by the first reflector element 206, which directs the broadband light 215 toward one or more downstream applications (e.g., metrology or inspection). One or more additional optical elements may assist in directing the broadband light 215 toward one or more downstream applications. The one or more additional reflector elements 214 reflect unabsorbed pump illumination and broadband light not collected by the first reflector element 206 back to the plasma 210, thereby further heating the plasma. The plasma 210 absorbs a portion of the pump illumination 204 and emits broadband radiation 215, which is also refocused and directed back to the plasma 210, thereby heating the plasma.

[0076] Those skilled in the art will understand that the components, devices, objects, and accompanying discussion described herein are used as examples for conceptual clarity, and that various configuration modifications are contemplated. Thus, as used herein, the specific examples described and accompanying discussion are intended to be representative of their more general classes. In general, the use of any specific example is intended to be representative of that class, and the absence of a particular component, device, or object should not be construed as a limitation.

[0077] With respect to the use of substantially any plural and / or singular term herein, those of skill in the art will be able to interpret the plural to the singular and / or the singular to the plural as appropriate depending on the context and / or application. The various singular / plural permutations are not explicitly stated herein for the sake of clarity.

[0078] The subject matter described herein may depict different components contained within or connected to other components. It will be understood that such depicted architectures are merely exemplary, and that in fact many alternative architectures that achieve the same functionality are possible. Conceptually, any arrangement of components to achieve the same functionality is effectively "associated" such that the desired functionality is achieved. Thus, any two components combined in the specification to achieve a particular function may be considered to be "associated" with each other such that the desired functionality is achieved, regardless of the architecture or intermediate components. Similarly, any two components so associated may also be considered to be "connected" or "coupled" with each other to achieve the desired functionality, and any two components that can be associated in this manner may also be considered to be "couplable" with each other to achieve the desired functionality. Specific examples of what can be coupled include, but are not limited to, physically interlockable and / or physically interacting components, wirelessly interoperable and / or wirelessly interacting components, and / or logically interoperable and / or logically interacting components.

[0079] It will be further understood that the present invention is defined by the appended claims. In general, those skilled in the art will understand that the terms used herein, and particularly in the appended claims (e.g., the body of the appended claims), are generally intended as "open" terms (e.g., the term "including" should be interpreted as "including but limited to," the term "having" should be interpreted as "having at least," the term "includes" should be interpreted as "includes but is not limited to," etc.). Those skilled in the art will also understand that where a specific number of introduced claim recitations are intended, such intention will be clearly stated in the claim, and that, absent such recitation, such intention does not exist. For example, as an aid to understanding, the following appended claims may include 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 to mean that introducing a claim recitation with the indefinite article "a" or "an" means that any particular claim including a claim recitation so introduced is limited to embodiments containing only one such recitation, even if the same claim also includes the introductory phrase "at least one" or "one or more" and an indefinite article such as "a" or "an" (e.g., "a" and / or "an" should be construed to mean "at least one" or "one or more"). The same applies with respect to the use of definite articles used to introduce claim recitations.Additionally, even when a specific number is explicitly recited in an introduced claim recitation, a person skilled in the art would understand that such recitation should be interpreted to mean at least the recited number (e.g., the mere recitation of "two recitations," without any other modifier, means at least two recitations, or more than two recitations). Furthermore, when a phrase similar to "at least one of A, B, and C and the like" is used, such a configuration is generally intended to mean what a person skilled in the art would understand the phrase (e.g., "a system having at least one of A, B, and C" includes, but is not limited to, a system having only A, only B, only C, both A and B, both A and C, both B and C, and / or all of A, B, and C, etc.). When phrases similar to "at least one of A, B, or C and the like" are used, such a configuration is generally intended to have the meaning that one of ordinary skill in the art would understand the phrase (e.g., "a system having at least one of A, B, or C" includes, but is not limited to, systems having only A, only B, only C, both A and B, both A and C, both B and C, and / or all of A, B, and C, etc.). Those of ordinary skill in the art will also understand that substantially all disjunctions and / or phrases expressing two or more alternative terms, whether in the description, claims, or drawings, contemplate the possibility of including one of the terms, either of the terms, or both terms. For example, the phrase "A or B" will be understood to include the possibilities of "A" ("A") or "B" ("B") or "A and B" ("A and B").

[0080] The present disclosure and many of its attendant advantages will be understood from the foregoing description. It will also be apparent that various changes in form, construction, and arrangement of the elements may be made without departing from the disclosed subject matter and without sacrificing all of its important advantages. The described embodiments are merely illustrative, and the following claims are intended to permit and cover such modifications.

Claims

1. 1. A system comprising: a gas containment structure for containing the gas; a pump light source configured to generate pump illumination; a first reflector element configured to direct a portion of the pump illumination into the gas, thereby sustaining a plasma, the first reflector element configured to collect at least a portion of the broadband light emitted from the plasma; and one or more additional reflector elements disposed opposite the first reflector element, a reflective surface of the first reflector element facing a reflective surface of the one or more additional reflector elements, the one or more additional reflector elements configured to reflect unabsorbed pump illumination and broadband light not collected by the first reflector element back to the plasma, the one or more additional reflector elements including a first reflective spherical section having a first opening and a second spherical section having a second opening, the first reflective spherical section and the second reflective spherical section being stacked, the second opening of the second spherical section is configured to pass the pump illumination from the pump light source through the first opening of the first reflective spherical section to the plasma, the first opening of the first reflective spherical section passes the broadband light collected from a focal point of the first reflector element through the second opening, the first opening and the second opening together pass both the pump illumination from the pump light source and broadband light emitted from the plasma, and the second spherical section provides additional recycling of the pump illumination and the broadband light.

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

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

5. The system of claim 1 , wherein the radius of curvature of the first reflective spherical section is smaller than the radius of curvature of the second spherical section.

6. The system of claim 1 , wherein the first reflector element has a radius of curvature that is smaller 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 of between 3π and 4π.

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

10. The system of claim 1 , wherein the direction in which the pump light source is positioned is considered to be the top when viewed from the first reflector element, and the one or more additional reflector elements are positioned above the first reflector element.

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

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

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

14. 10. 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 confinement 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 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 metrology.

19. 1. A system comprising: a gas containment structure for containing the gas; a pump light source configured to generate pump illumination; an elliptical mirror configured to direct a portion of the pump illumination into the gas, thereby sustaining a plasma, the elliptical mirror configured to collect at least a portion of broadband light emitted from the plasma and direct a portion of the broadband light to one or more downstream applications; and one or more spherical mirrors arranged above the elliptical mirror, with the direction in which the pump light source is arranged as viewed from the elliptical mirror as an upper side, wherein a reflective surface of the elliptical mirror faces a reflective surface of the one or more spherical mirrors, and the one or more spherical mirrors are configured to reflect unabsorbed pump illumination and broadband light not collected by the elliptical mirror back to the plasma, and the one or more spherical mirrors include a first reflective spherical section having a first opening and a second spherical section having a second opening, and the first reflective spherical section and the second spherical section are stacked. a layered arrangement, wherein the second opening of the second spherical section is configured to pass the pump illumination from the pump light source to the plasma through the first opening of the first reflective spherical section, the first opening of the first reflective spherical section passes the broadband light collected from the focal point of the ellipsoidal mirror through the second opening, the first opening and the second opening pass both the pump illumination from the pump light source and broadband light emitted from the plasma, and the second spherical section provides additional recycling of the pump illumination and the broadband light.

20. 1. A method comprising: generating pump illumination; directing a portion of the pump illumination into a gas within a gas confinement structure, thereby sustaining a plasma through a first reflector element; collecting a portion of the 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 unabsorbed pump illumination and broadband light not collected by the first reflector element back to the plasma via one or more additional reflector elements, wherein the one or more additional reflector elements include a first reflective spherical section having a first opening and a second spherical section having a second opening, the first reflective spherical section and the second spherical section being configured to pass the pump illumination from a pump light source through the first opening of the first reflective spherical section to the plasma, the first opening of the first reflective spherical section passing the broadband light collected from the focal point of the first reflector element through the second opening, the first opening and the second opening passing both the pump illumination from the pump light source and broadband light emitted from the plasma, and the second spherical section providing additional recycling of the pump illumination and the broadband light.

21. 21. The method of claim 20, wherein the one or more downstream applications include at least one of inspection or metrology.

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