Laser-Sustained Plasma Light Source with Gas Vortex

Abstract

A laser-sustained plasma (LSP) light source having a vortex gas flow is disclosed. The LSP source comprises: a gas containment structure for containing a gas; one or more gas inlets configured to flow a gas into the gas containment structure; and one or more gas outlets configured to flow a gas out of the gas containment structure. The one or more gas inlets and the one or more gas outlets are arranged to generate a vortex gas flow within the gas containment structure. The LSP source also comprises a laser pump source configured to generate an optical pump to maintain a plasma within an internal gas flow within the vortex gas flow in a region of the gas containment structure. The LSP source comprises a light collector element configured to collect at least a portion of broadband light emitted from the plasma.

Description

[0001] CROSS REFERENCE TO RELATED APPLICATIONS

[0002] This application claims the benefit of U.S. Provisional Application Serial No. 63 / 008,840, filed on April 13, 2020, under 35 U.S.C. §119(e), which is incorporated herein by reference in its entirety. Technical Field

[0003] The present invention generally relates to a laser-sustained plasma (LSP) broadband light source, and in particular to an LSP source including a gas vortex to organize an LSP region throughout the LSP source. Background Art

[0004] There is a growing need for improved light sources for inspecting ever-shrinking semiconductor devices. 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. The gas in the container is typically not flowing because most current LSP lamps do not have any mechanism to force gas flow through the lamp other than natural convection caused by the buoyancy of the hot plasma plume. Previous attempts to flow gas through an LSP lamp resulted in instabilities within the LSP lamp caused by unstable turbulent gas flow. These instabilities are amplified at higher powers and at the location of mechanical elements (e.g., nozzles), thereby creating high radiant heat loads on these mechanical elements, resulting in overheating and melting. Thus, it would be advantageous to provide a system and method to correct the shortcomings of previous approaches identified above. Summary of the invention

[0005] A laser sustained plasma (LSP) light source is disclosed. In an illustrative embodiment, the LSP source includes a gas containment structure for containing a gas. In another illustrative embodiment, the LSP source includes one or more gas inlets fluidly coupled to the gas containment structure and configured to flow the gas into the gas containment structure. In another illustrative embodiment, the LSP source includes one or more gas outlets fluidly coupled to the gas containment structure and configured to flow the gas out of the gas containment structure, wherein the one or more gas inlets and the one or more gas outlets are arranged to generate a vortex gas flow within the gas containment structure. In another illustrative embodiment, the LSP source includes a laser pump source configured to generate an optical pump to maintain a plasma within an internal gas flow within the vortex gas flow in a region of the gas containment structure. In another illustrative embodiment, the LSP source includes a light collector element configured to collect at least a portion of the broadband light emitted from the plasma.

[0006] In another illustrative embodiment, the one or more gas inlets and the one or more gas outlets are arranged to generate a vortex gas flow within the gas containment structure such that the direction of the vortex gas flow through the plasma region is in the same direction as the inlet gas flow from the one or more inlets (i.e., a co-current vortex).

[0007] In another illustrative embodiment, the one or more gas inlets and the one or more gas outlets are arranged to generate a vortex gas flow within the gas containment structure such that the vortex gas flow direction through the plasma region is in a direction opposite to the inlet gas flow from the one or more inlets (i.e., a counter-vortex flow).

[0008] It should 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. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Those skilled in the art may better understand the numerous advantages of the present invention with reference to the accompanying drawings, in which:

[0010] Figure 1 is a schematic illustration of an LSP broadband light source according to one or more embodiments of the present invention;

[0011] Figure 2 is a schematic illustration of a vortex-generating gas cell for use in a LSP broadband light source according to one or more embodiments of the present invention;

[0012] Figure 3 is a schematic illustration of a gas cell for generating a counter-flow vortex for use in a LSP broadband light source according to one or more embodiments of the present invention;

[0013] Figure 4A and 4B is a schematic illustration of a single-inlet vortex-generating gas cell for use in an LSP broadband light source according to one or more embodiments of the present invention;

[0014] Figure 4C is a schematic illustration of a single-inlet vortex-generating gas chamber for use in an LSP broadband light source according to one or more embodiments of the present invention;

[0015] Figure 5A and 5B is a schematic illustration of a multi-inlet vortex-generating gas cell for use in a LSP broadband light source according to one or more embodiments of the present invention;

[0016] Figure 5C is a schematic illustration of a multi-inlet vortex-generating gas chamber for use in an LSP broadband light source according to one or more embodiments of the present invention;

[0017] Figure 6 is a schematic illustration of a gas cell for generating a counter-flow vortex including a plurality of side-located gas inlets for use in a LSP broadband light source according to one or more embodiments of the present invention;

[0018] Fig. 7A and 7B is a schematic illustration of a vortex-generating gas cell including a gas inlet for introducing a plurality of gases for use in a LSP broadband light source according to one or more embodiments of the present invention;

[0019] Figure 8 is a schematic illustration of a vortex-generating glass unit for use in an LSP broadband light source according to one or more embodiments of the present invention;

[0020] Fig.9A is a schematic illustration of a converging nozzle for use in an inlet of a vortex generating unit of an LSP broadband light source according to one or more embodiments of the present invention;

[0021] Fig. 9B is a schematic illustration of an annular flow nozzle for use in the inlet of a vortex generating unit of an LSP broadband light source according to one or more embodiments of the present invention;

[0022] Fig.10 depicting a comparative line graph comparing the gas flow velocity of an annular flow nozzle to the gas flow velocity of a converging nozzle as a function of axial distance from the nozzle;

[0023] Fig.11A and 11B is a schematic illustration of a multiple annular flow nozzle according to one or more embodiments of the present invention;

[0024] Fig.12 According to one or more embodiments of the present invention, Figures 5A to 5C A simplified schematic illustration of an optical characterization system for an LSP broadband light source as illustrated in any one of the embodiments;

[0025] Fig.13 Illustrated 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 invention. DETAILED DESCRIPTION

[0026] The present invention has been particularly shown and described with respect to certain embodiments and specific features thereof. The embodiments set forth herein are considered to be illustrative and not restrictive. It should be apparent to those skilled in the art that various changes and modifications may be made in form and detail without departing from the spirit and scope of the present invention. Reference will now be made in detail to the disclosed subject matter illustrated in the accompanying drawings.

[0027] Embodiments of the present invention are directed to an LSP light source that implements a vortex or counter-vortex to organize gas flow throughout the LSP region of the LSP light source. Embodiments of the present invention are directed to a transparent bulb, cell or chamber for containing high pressure gas required for LSP operation, a gas inlet nozzle and a gas outlet for producing a vortex gas flow or a counter-vortex gas flow. In one embodiment, the inlet and outlet are positioned on opposite sides of the cell, thereby forcing the general direction of the gas flow to be the same. In another embodiment, the inlet and outlet are positioned on the same side of the cell, which forms a counter-vortex pattern in which the general direction of the flow changes within the cell.

[0028] Embodiments of the present invention can be used to form two gas flow regions - an outer region located near the cell wall and an inner region located near the central axis of the cell. The LSP can be maintained in a central position near the axis of symmetry of the cell and is affected by the inner part of the flow. There are various advantages to the configuration of the present invention. For example, a fast gas flow is formed through the plasma region, resulting in a smaller plasma size and therefore higher plasma brightness. The hot plume generated from the plasma is removed from the pump laser propagation path and does not form an "air swing" aberration, thus resulting in a more stable plasma operation. The gas flow is stabilized in a vortex arrangement, allowing for more stable plasma operation. The hot plasma plume is kept away from the cell wall, which reduces the thermal heat load on the wall and allows the use of optical materials that are sensitive to overheating. The separation of the inner flow and the outer flow allows the cell wall to cool, thereby forming a favorable photochemical environment and radiation blocking.

[0029] The generation of light-sustaining plasmas is also generally described in U.S. Pat. No. 7,435,982, issued on October 14, 2008, which is incorporated herein by reference in its entirety. The generation of plasmas is also generally described in U.S. Pat. No. 7,786,455, issued on August 31, 2010, which is incorporated herein by reference in its entirety. The generation of plasmas is also generally described in U.S. Pat. No. 7,989,786, issued on August 2, 2011, which is incorporated herein by reference in its entirety. The generation of plasmas is also generally described in U.S. Pat. No. 8,182,127, issued on May 22, 2012, which is incorporated herein by reference in its entirety. The generation of plasma is also generally described in U.S. Patent No. 8,309,943, issued on November 13, 2012, which is incorporated herein by reference in its entirety. The generation of plasma is also generally described in U.S. Patent No. 8,525,138, issued on February 9, 2013, which is incorporated herein by reference in its entirety. The generation of plasma is also generally described in U.S. Patent No. 8,921,814, issued on December 30, 2014, which is incorporated herein by reference in its entirety. The generation of plasma is also generally described in U.S. Patent No. 9,318,311, issued on April 19, 2016, which is incorporated herein by reference in its entirety. The generation of plasma is also generally described in U.S. Patent No. 9,390,902, issued on July 12, 2016, which is incorporated herein by reference in its entirety. In a general sense, the various embodiments of the present invention should be interpreted as extending to any plasma-based light source known in the art. Optical systems used in the context of plasma generation are generally described in U.S. Patent No. 7,1205,331, issued April 27, 2010, which is incorporated herein by reference in its entirety.

[0030] Figure 11 is a schematic illustration of an LSP light source 100 having a vortex according to one or more embodiments of the present invention. The LSP source 100 includes a pump source 102 configured to generate an optical pump 104 for maintaining a plasma 110. For example, the pump source 102 may emit a laser radiation beam suitable for pumping the plasma 110. In an embodiment, a light collector element 106 is configured to direct a portion of the optical pump 104 to a gas contained in a vortex-generating gas containment structure 108 to ignite and / or maintain the plasma 110. The pump source 102 may include any pump source known in the art that is suitable for igniting and / or maintaining a plasma. For example, the pump source 102 may include one or more lasers (i.e., pump lasers). The pump beam may include radiation of any wavelength or range of wavelengths known in the art, including but not limited to visible radiation, IR radiation, NIR radiation, and / or UV radiation.

[0031] The light collector element 106 is configured to collect a portion of the broadband light 115 emitted from the plasma 110. The gas containment structure 108 may include one or more gas inlets 120 and one or more gas outlets 122 arranged to form a vortex gas flow 124 within the interior of the gas containment structure 108. The broadband light 115 emitted from the plasma 110 may be collected via one or more additional optical devices (e.g., cold mirror 112) for use in one or more downstream applications (e.g., inspection, metrology, or lithography). The LSP light source 100 may include any number of additional optical elements, such as, but not limited to, a filter 117 or a homogenizer 119 for conditioning the broadband light 115 prior to one or more downstream applications. The gas containment structure 108 may include a plasma cell, a plasma bulb (or lamp), or a plasma chamber.

[0032] Figure 2A simplified schematic diagram of a vortex unit 200 suitable for use as a gas containment structure 108 for generating a vortex according to one or more embodiments of the present invention is illustrated. In an embodiment, the vortex unit 200 includes one or more gas inlets configured to flow gas into the vortex unit 200 and one or more gas outlets configured to flow gas out of the vortex unit 200. For example, the vortex unit 200 includes a first gas inlet 202a located at a peripheral position (e.g., bottom corner) of the vortex unit 200 and a second gas inlet 202b located at a central position (e.g., bottom center) of the vortex unit 200. The vortex unit 200 also includes a first gas outlet 204a located at a peripheral position (e.g., top corner) of the vortex unit 200 and a second gas outlet 204b located at a central position (e.g., top center) of the vortex unit 200. In an embodiment, the one or more gas inlets and the one or more first gas outlets are arranged to generate a vortex 206 within the vortex unit 200. In this embodiment, the inlets 202a, 202b are located on one side (eg, bottom side) of the swirl unit 200 and the outlets 204a, 204bb are located on the opposite side (eg, top side) of the swirl unit 200, which ensures that the gas passes through the swirl unit 200 in a unidirectional swirling motion.

[0033] In an embodiment, the vortex is a spiral vortex having a drift velocity between 1 m / s and 100 m / s at a location near the plasma 110. It should be noted that the tangential velocity within the gas can exceed the drift velocity by several times. The vortex gas flow 206 of the vortex unit 200 includes an inner flow region 208 and an outer flow region 210. In this embodiment, the vortex unit 200 acts as a downstream vortex unit, whereby the inner gas flow 208 flows in the same direction as the outer gas flow 210 ( Figure 2 In this regard, the vortex gas flow direction through the plasma region can be in the same direction as the inlet gas flow from one or more inlets. In an embodiment, the pump source 102 directs the optical pump illumination 104 to the central region of the vortex cell 200 so that the pump illumination is affected by the inner flow region 208. The separation of the inner flow 208 from the outer flow 210 allows the cell wall to cool, thereby forming a favorable photochemical environment and radiation blocking.

[0034] The vortex unit 200 includes an optical transmission element 106 configured to contain the gas that forms the plasma and transmit the optical pump radiation 104 and the broadband light 115. For example, the transparent wall 212 may include a cylinder formed of a material that is transparent to at least a portion of the pump radiation 104 and the broadband light 115. The transparent optical element 106 of the vortex unit 200 may be formed of any number of different optical materials. For example, the optical transmission element 106 may be formed of, but not limited to, sapphire, crystalline quartz, CaF2, MgF2, or fused silica. It should be noted that the vortex 206 of the vortex unit 200 keeps the heat plume of the plasma 110 away from the walls of the vortex unit 200, which reduces the thermal head load on the wall and allows the use of optical materials that are sensitive to overheating (e.g., glass, CaF2, MgF2, crystalline quartz, etc.).

[0035] In an embodiment, the vortex unit 200 includes one or more flanges for terminating / sealing the transparent optical element 106. For example, the vortex unit 200 may include, but is not limited to, a top flange 214 and a bottom flange 216. In an embodiment, the top flange 214 and / or the bottom flange 216 may secure inlet and / or outlet pipes or tubes and additional mechanical and electronic components. The use of a flanged plasma unit is described in at least the following: U.S. Patent Application No. 9,775,226, issued on September 26, 2017, and U.S. Patent No. 9,185,788, issued on November 10, 2015, each of which is previously incorporated herein by reference in its entirety.

[0036] Figure 3 A simplified schematic diagram of a reverse flow vortex unit 300 suitable for use as a vortex-generating gas containment structure 108 according to one or more embodiments of the present invention is illustrated. Figure 2 The associated instructions should be interpreted as extending to Figure 3 In an embodiment, the reverse flow vortex unit 300 includes a gas inlet 302 and a gas outlet 304. In addition, the reverse flow vortex unit 300 includes a bottom flange 216 and a top flange 214. In this example, the top flange 214 may include a blind flange or a cover.

[0037] In this embodiment, vortex unit 300 is arranged in countercurrent configuration. In countercurrent vortex configuration, outer vortex 310 propagates in the direction opposite to inner vortex 308a, 308b. Countercurrent configuration can be produced by placing gas inlet 302 and gas outlet 304 on the same side (e.g., bottom) of countercurrent vortex unit 300. In addition, gas inlet 302 can be positioned at the periphery or one side of bottom flange 216, which promotes the formation of vortex in the gas flow of unit 300. In this embodiment, vortex gas flow moves upward at the periphery of vortex unit 300. Then, the narrowed cavity of top flange 316 works to roll outer vortex 310 back to the central area of ​​vortex unit 300 downward. Since gas is a continuous flow through vortex unit 300, this forms an outer vortex region 310 moving upward and an inner vortex region 308a, 308b moving downward through outer vortex region 310. In this arrangement, top internal vortex 308a is directed toward plasma 110, with bottom internal vortex 308b carrying downwardly the plume of plasma 110. In this regard, the swirling gas flow direction through the plasma region may be in an opposite direction to the inlet gas flow from one or more inlets.

[0038] Figure 4A Illustrated is a simplified schematic diagram of a single inlet vortex unit 400 suitable for use as a vortex-generating gas containment structure 108 according to one or more embodiments of the present invention. In this embodiment, a single centrally located inlet 402 and outlet 404 are used to form a fast gas flow (e.g., 1 m / s to 100 m / s) through the plasma-forming region of the vortex unit 400. Due to the central location of the single inlet 402 and outlet 404, the gas flow has a relatively minimal vortex. In other embodiments, such as Figure 4B , a single inlet 402 is located at a peripheral position (e.g., an edge) of the unit 410 and directed into the unit at an oblique angle, and is used to form a fast high vorticity gas flow (e.g., 1 m / s to 100 m / s) through the plasma forming region of the vortex unit 400. Due to the peripheral position of the single inlet 402 and the central position of the single outlet 404, the gas flow has a relatively high vorticity.

[0039] Figure 4C A simplified schematic diagram of a single inlet vortex chamber 410 suitable for use as a vortex-generating gas containment structure 108 is illustrated in accordance with one or more embodiments of the present invention. Figure 1 The plasma unit shown in FIG. 4 can be replaced by the plasma chamber 410. It should be noted that, unless otherwise stated, the previous references herein to Figures 1 to 4B The described embodiments should be interpreted as extending to Figure 4CThe use of a gas chamber as a gas containment structure is described in U.S. Pat. No. 9,099,292, issued Aug. 4, 2015, U.S. Pat. No. 9,263,238, issued Feb. 16, 2016, and U.S. Pat. No. 9,390,902, issued Jul. 12, 2016, each of which is incorporated herein by reference in its entirety.

[0040] In this embodiment, the light collector element 106, together with the window 412, can be configured to form a gas containment structure. For example, the light collector element 106 can be sealed using the window 412 to contain the gas within the volume defined by the surfaces of the light collector element 106 and the window 412. In this example, no internal gas containment structure such as a plasma cell or plasma bulb is required because the surfaces of the light collector element 106 and the one or more windows 412 form the plasma chamber 410. In this case, the opening of the light collector element 106 can be sealed using the window 412 (e.g., a glass window) to allow both the pump illumination 104 and the plasma broadband light 115 to pass through the window.

[0041] In an embodiment, the plasma chamber 410 includes a single inlet 402 and an outlet 404. The single inlet 402 and outlet 404 are used to form a fast gas flow (e.g., 1 m / s to 20 m / s) through the plasma forming region of the vortex chamber 410. Due to the alignment of the single inlet 402 and outlet 404, the gas flow has a relatively minimal swirl. It should be noted that the inlet 402 and outlet 404 can be located along any portion of the light collector element 106. It should be noted that any nozzle configuration of the present invention as further discussed herein can be used Figures 4A to 4C 402 of the entrance.

[0042] Figure 5A The diagram illustrates a simplified schematic diagram of a multi-inlet vortex unit 500 suitable for use as a vortex-generating gas containment structure 108 according to one or more embodiments of the present invention. In this embodiment, multiple centrally located inlets 502 and outlets 504 are used to form a fast gas flow (e.g., 1 m / s to 20 m / s) through the plasma-forming region of the vortex unit 500. Due to the central location of the inlets 502 and outlets 504, the gas flow has a relatively minimal vortex. It should be noted that the vortex unit 500 may include any number of inlets. For example, if Figure 5A In the top view of FIG. 5 , the vortex includes 4 inlets. The vortex unit 500 may include other numbers of inlets, such as but not limited to 2 inlets, 3 inlets, 5 inlets, etc. In other embodiments, such as Figure 5B500, a plurality of inlets 502 are located at peripheral locations (e.g., edges) of the unit 510 and are oriented obliquely into the unit and are used to form a fast high vorticity gas flow (e.g., 1 m / s to 100 m / s) through the plasma forming region of the vortex unit 510. Due to the peripheral location of the inlets 502 and the central location of the outlets 504, the gas flow has a relatively high vorticity. Positioning the inlets around the perimeter of the unit 500 enhances the vorticity within the vortex unit 510.

[0043] In another embodiment, if Figure 5C As shown in FIG. 5 , multiple inlets 502 may be implemented within a plasma chamber 510. The inlets 502 may be positioned anywhere along the light collector element 106 and their relative positions may be used to establish a desired degree of swirl within the plasma chamber 510. It should be noted that any nozzle configuration of the present invention as further discussed herein may be used Figures 5A to 5C in the entrance.

[0044] Any number of peripheral or central inlet settings may be utilized in a cell or chamber of the present invention. The inlets and outlets and the flow rates through the inlets and outlets will be configured depending on the desired flow conditions. For example, to establish a reverse vortex flow, the primary outlet may be centrally located on the same side of the cell as the primary inlet. Additional inlets and outlets may be located on opposite sides of the cell / chamber to achieve the desired flow conditions.

[0045] Figure 6 Illustrated is a simplified schematic diagram of a reverse flow vortex unit 600 including a sidewall positioned gas inlet for use as a gas containment structure 108 of the system 100 according to one or more embodiments of the present invention. In an embodiment, the reverse flow vortex unit 600 includes a first inlet 602a located in the bottom flange 216 and a second inlet 602b located in the top flange 214. It should be noted that the inlets can be positioned in the end flanges and / or sidewalls of the unit 600. The outlet inlet 604 is positioned at the center of the unit 604. The side locations of the inlets 602a, 602b and the center location of the outlet create a significant degree of swirl within the unit 600. It should be noted that although Figure 6 Inlets 602a, 602b are depicted as being located on the periphery of unit 600, but this arrangement is not a limitation on the scope of the invention. In alternative embodiments, one or more outlets may be located at the periphery of unit 600 with one or more inlets centrally located at the top or bottom of unit 600.

[0046] Fig. 7A and 7B Illustrated is a simplified schematic diagram of a counter-flow vortex unit 700 including multiple gas inlets for use as the gas containment structure 108 of the system 100 according to one or more embodiments of the present invention. In an embodiment, each of the inlets may carry a different gas or gas mixture into the unit 700. Fig. 7A and 7B , a first gas 710a can be introduced into the cell 700 via a first inlet 702a and a second gas 710b can be introduced into the cell 700 via a second inlet 702b. In this regard, the gas composition near the cell wall and near the plasma can be independently controlled. The inner gas region 708a is the gas flow directed into the plasma 110, while the inner gas flow 708b is the gas flow that carries away the heat plume of the plasma 110. For example, Fig. 7A As shown in FIG. 7 , the first inlet 702a and the second inlet 702b are arranged in a co-propagating configuration, whereby the first gas and the second gas flow through the cell 700 in the same direction. Figure 7B As shown in FIG. 7 , the first inlet 702a and the second inlet 702b are arranged in a counter-propagation configuration, whereby the first gas and the second gas flow through the cell 700 in opposite directions.

[0047] It should be noted that any combination of gases or gas mixtures may be used in the cell 700. For example, the first gas may be pure Ar, while the second gas is Ar with an O2 addition. In this example, the oxygen addition may be used to absorb a portion of the Ar plasma radiation that damages the glass wall, thereby forming a beneficial chemical environment near the glass wall. Non-limiting examples of first gas 710a / second gas 710b combinations are as follows: Xe-Ar, air (N2 / O2)-Ar, Ar / Xe-Ar, Ar / O2-Ar, Ar / Xe / O2-Ar, Ar / Xe / F2-Ar, Ar / CF6-Ar, Ar / CF6-Ar / Xe, and the like.

[0048] Figure 8Illustrated is a simplified schematic diagram of a glass counterflow vortex unit 800 used as a gas containment structure 108 of the system 100 according to one or more embodiments of the present invention. The unit 800 includes a gas inlet 802 and a gas outlet 804 located on the same side of the unit 800 (e.g., bottom flange 810). In an embodiment, the unit 800 is formed of glass (e.g., blown glass). In an embodiment, the unit 800 is formed of a transparent glass (e.g., fused silica) body that is sealed to a metal flange 810 for the inlet and outlet, and cooling of the metal parts may be required to control the gas flow 806. The internal gas flow 808a is directed downward toward the plasma 110 and the internal gas flow 808b carries away the hot plume of the plasma 110. It should be noted that the advantage of using such units compared to conventional lamps is that the convective plume originating from the LSP 110 is carried by the internal vortex gas flow 808b and does not contact the glass wall, thus reducing the heat load on the glass wall of the unit 800. Fabricating the downstream cell from glass allows for a variety of shapes that can be obtained through standard glass shaping techniques. These shapes can aid in convection and also help reduce optical aberrations of the laser pump and collected light.

[0049] Fig.9A and 9B Illustrated is a schematic diagram of a nozzle suitable for use in one or more of the inlets of the unit of the present invention. In an embodiment, as Fig.9A As shown in FIG. 1 , the converging nozzle 900 may be used in one or more inlets of various units of the system 100. In other embodiments, such as Fig. 9B As shown in FIG. 1 , an annular flow nozzle 910 may be used in one or more inlets of various units of the system 100. The annular flow nozzle 910 may include a flow guide nose 914. Utilizing the annular flow nozzle 910 allows the LSP 110 to be placed at a sufficient distance from the nozzle to avoid overheating of the component. Fig.9A and 9B As shown in , the flow stream 912 of the annular flow nozzle 910 is significantly extended relative to the flow stream 902 of the converging nozzle 900. The flow stream of the annular flow nozzle 910 is formed by adding a guide nose near the bottom end of the pressurization unit. Compared with the operating pressure in these cases, the additional pressure head required to form the flow rate of interest is quite insignificant. For converging jets, the flow rate decays rapidly. However, by using an annular flow inlet and directing the flow along the converging nose, the flow rate can be maintained at a greater distance. In this configuration, the plasma can be ignited at a farther and safer distance from the guide. In addition, the nozzle can be water-cooled and operated at a safe operating temperature without worrying about melting.

[0050] Fig.10A comparative line graph is depicted indicating that plasma can be ignited about 50 mm away from the nose guide and still maintain a flow rate greater than 50% of the tip speed for the flow nose configuration of the annular flow nozzle 910. It should be noted that the converging nozzle 900 and / or the annular flow nozzle 910 can be implemented in any of the gas inlets of the vortex or counter-flow vortex units discussed throughout the present invention.

[0051] Fig.11A and 11B Illustrated is a schematic diagram of an annular nozzle arrangement including multiple jets in accordance with one or more embodiments of the present invention. Fig.11A Depicts a cross section of an annular flow nozzle with multiple jets, and Fig. 11B A top view of an annular flow nozzle with multiple jets is depicted. In an embodiment, the annular flow nozzle 1100 includes a nozzle head 1106 located within an inlet passage 1102. In an embodiment, multiple outflow jets 1104 spiral around an underlying conical guide 1108, thereby forming an outflow vortex pattern in the outflow gas 1110. It should be noted that the multi-jet annular flow nozzle 1100 can be implemented in any of the gas inlets of the vortex or counter-flow vortex units discussed throughout the present invention.

[0052] Generally speaking Figures 1 to 11B , the pump source 102 may include any laser system known in the art that is capable of acting as an optical pump for maintaining a plasma. For example, the pump source 102 may include any laser system known in the art that is capable of emitting radiation in the infrared, visible, and / or ultraviolet portions of the electromagnetic spectrum.

[0053] In an embodiment, the pump source 102 may include a laser system configured to emit continuous wave (CW) laser radiation. For example, the pump source 102 may include one or more CW infrared laser sources. In an embodiment, the pump source 102 may include one or more lasers configured to provide laser light to the plasma 110 at a substantially constant power. In an embodiment, the pump source 102 may include one or more modulated lasers configured to provide modulated laser light to the plasma 110. In an embodiment, the pump source 102 may include one or more pulsed lasers configured to provide pulsed laser light to the plasma. In an embodiment, the pump source 102 may include one or more diode lasers. For example, the pump source 102 may include one or more diode lasers that emit radiation at a wavelength corresponding to any one or more absorption lines of a species of gas contained within the gas containment structure. The diode laser of the pump source 102 may be selected for an embodiment such that the wavelength of the diode laser is tuned to any absorption line of any plasma known in the art (e.g., an ion transition line) or any absorption line of the gas from which the plasma is produced (e.g., a highly excited neutral transition line). Thus, the selection of a given diode laser (or set of diode lasers) will depend on the type of gas used in the light source 100. In an embodiment, the pump source 102 may include an ion laser. For example, the pump source 102 may include any noble gas ion laser known in the art. For example, in the case of an argon-based plasma, the pump source 102 for pumping argon ions may include an Ar+ laser. In an embodiment, the pump source 102 may include one or more frequency converted laser systems. In an embodiment, the pump source 102 may include a disk laser. In an embodiment, the pump source 102 may include a fiber laser. In an embodiment, the pump source 102 may include a broadband laser. In an embodiment, the pump source 102 may include one or more non-laser sources. The pump source 102 may include any non-laser source known in the art. For example, the pump source 102 may include any non-laser system known in the art that can discretely or continuously emit radiation in the infrared, visible, or ultraviolet portions of the electromagnetic spectrum.

[0054] In an embodiment, the pump source 102 may include two or more light sources. In an embodiment, the pump source 102 may include two or more lasers. For example, the pump source 102 (or "source") may include a plurality of diode lasers. In an embodiment, each of the two or more lasers may emit laser radiation tuned to a different absorption line of a gas or plasma within the source 100.

[0055] The light collector element 106 may include any light collector element known in the art of plasma generation. For example, the light collector element 106 may include one or more elliptical reflectors, one or more spherical reflectors, and / or one or more parabolic reflectors. The light collector element 106 may be configured to collect broadband light of any wavelength known in the art of plasma-based broadband light sources from the plasma 110. For example, the light collector element 106 may be configured to collect infrared light, visible light, ultraviolet (UV) light, near ultraviolet light (NUV), vacuum UV (VUV) light, and / or deep UV (DUV) light from the plasma 110.

[0056] The transmission portion (e.g., transmission element, bulb, or window) of the gas containment structure of the source 100 may be formed of any material known in the art that is at least partially transparent to the broadband light 115 generated by the plasma 110 and / or the pump light 104. In embodiments, one or more transmission portions (e.g., transmission element, bulb, or window) of the gas containment structure may be formed of any material known in the art that is at least partially transparent to VUV radiation, DUV radiation, UV radiation, NUV radiation, and / or visible light generated within the gas containment structure. Additionally, one or more transmission portions of the gas containment structure may be formed of any material known in the art that is at least partially transparent to IR radiation, visible light, and / or UV light from the pump source 102. In embodiments, one or more transmission portions of the gas containment structure may be formed of any material known in the art that is transparent to radiation from the pump source 102 (e.g., an IR source) and radiation emitted by the plasma 110 (e.g., VUV radiation, DUV radiation, UV radiation, NUV radiation, and / or visible light).

[0057] The gas containment structure 108 may contain any selected gas known in the art to be suitable for generating a plasma upon absorption of pump radiation (e.g., argon, xenon, mercury, etc.). In embodiments, pump radiation 510 is focused from the pump source 102 into the volume of gas such that energy is absorbed by the gas or plasma within the gas containment structure (e.g., through one or more selected absorption lines), thereby "pumping" the gas species to generate and / or maintain the plasma 110. In embodiments, although not shown, the gas containment structure may include a set of electrodes for initiating the plasma 110 within the interior volume of the gas containment structure 108, whereby radiation from the pump source 102 sustains the plasma 110 after it is ignited by the electrodes.

[0058] Source 100 may be used to initiate and / or maintain plasma 110 in various gas environments. In embodiments, the gas used to initiate and / or maintain plasma 110 may include an inert gas (e.g., a noble gas or a non-noble gas), or a non-inert gas (e.g., mercury). In embodiments, the gas used to initiate and / or maintain plasma 110 may include a gas mixture (e.g., an inert gas mixture, an inert gas mixture with a non-inert gas, or a non-inert gas mixture). For example, gases suitable for implementation in source 100 may include, but are not limited to: Xe, Ar, Ne, Kr, He, N2, H2O, O2, H2, D2, F2, CH4, CF6, one or more metal halides, halogens, Hg, Cd, Zn, Sn, Ga, Fe, Li, Na, Ar:Xe, ArHg, KrHg, XeHg, and any mixtures thereof. The present invention should be construed to extend to any gas suitable for maintaining a plasma within a gas containment structure.

[0059] In an embodiment, the LSP light source 100 further includes one or more additional optical devices configured to direct the broadband light 115 from the plasma 110 to one or more downstream applications. 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, etc. The light collector element 106 may collect one or more of the visible radiation, NUV radiation, UV radiation, DUV radiation, and / or VUV radiation emitted by the plasma 110 and direct the broadband light 115 to one or more downstream optical elements. For example, the light collector element 106 may deliver infrared radiation, visible radiation, NUV radiation, UV radiation, DUV radiation, and / or VUV radiation to downstream optical elements of any optical characterization system known in the art, such as but not limited to an inspection tool, a metrology tool, or a lithography tool. In this regard, the broadband light 115 may be coupled to the illumination optics of the inspection tool, the metrology tool, or the lithography tool.

[0060] Fig.12 is a schematic illustration of an optical characterization system 1200 implementing the LSP broadband light source 100 illustrated in any of FIG. 11 (or any combination thereof) in accordance with one or more embodiments of the present invention.

[0061] It should be noted herein that the system 1200 may include any imaging, inspection, metrology, lithography, or other characterization / fabrication system known in the art. In this regard, the system 1200 may be configured to perform inspection, optical metrology, lithography, and / or imaging on a sample 1207. The sample 1207 may include any sample known in the art, including but not limited to a wafer, a reticle / photomask, and the like. It should be noted that the system 1200 may be incorporated into one or more of the various embodiments of the LSP broadband light source 100 described throughout the present disclosure.

[0062] In an embodiment, the sample 1207 is disposed on a stage assembly 1212 to facilitate movement of the sample 1207. The stage assembly 1212 may include any stage assembly 1212 known in the art, including but not limited to an XY stage, an R-theta stage, etc. In an embodiment, the stage assembly 1212 is capable of adjusting the height of the sample 1207 to maintain focus on the sample 1207 during inspection or imaging.

[0063] In an embodiment, the set of illumination optics 1203 is configured to direct illumination from the broadband light source 100 to the sample 1207. The set of illumination optics 1203 may include any number and type of optical components known in the art. In an embodiment, the set of illumination optics 1203 includes one or more optical elements, such as but not limited to one or more lenses 1202, a beam splitter 1204, and an objective lens 1206. In this regard, the set of illumination optics 1203 may be configured to focus illumination from the LSP broadband light source 100 onto the surface of the sample 1207. The one or more optical elements 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.

[0064] In an embodiment, the set of collection optics 1205 is configured to collect light reflected, scattered, diffracted, and / or emitted from the sample 1207. In an embodiment, the set of collection optics 1205, such as but not limited to the focusing lens 710, may direct and / or focus the light from the sample 1207 to the sensor 1216 of the detector assembly 1214. It should be noted that the sensor 1216 and the detector assembly 1214 may include any sensor and detector assembly known in the art. For example, the sensor 1216 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), and the like. Furthermore, the sensor 1216 may include but is not limited to a line sensor or an electron bombardment line sensor.

[0065] In an embodiment, the detector assembly 1214 is communicatively coupled to a controller 1218, which includes one or more processors 1220 and a memory medium 1222. For example, the one or more processors 1220 may be communicatively coupled to the memory 1222, wherein the one or more processors 1220 are configured to execute a set of program instructions stored on the memory 1222. In an embodiment, the one or more processors 1220 are configured to analyze the output of the detector assembly 1214. In an embodiment, the set of program instructions are configured to cause the one or more processors 1220 to analyze one or more characteristics of the sample 1207. In an embodiment, the set of program instructions are configured to cause the one or more processors 1220 to modify one or more characteristics of the system 1200 in order to maintain focus on the sample 1207 and / or the sensor 1216. For example, the one or more processors 1220 may be configured to adjust the objective lens 1206 or the one or more optical elements 1202 in order to focus the illumination from the LSP broadband light source 100 onto the surface of the sample 1207. By way of another example, the one or more processors 1220 may be configured to adjust the objective lens 1206 and / or the one or more optical elements 1202 in order to collect illumination from the surface of the sample 1207 and focus the collected illumination onto the sensor 1216 .

[0066] It should be noted that system 1200 may be configured in any optical configuration known in the art, including but not limited to dark field configuration, bright field orientation, and the like.

[0067] Fig.13 Illustrated is a simplified schematic diagram of an optical characterization system 1300 arranged in a reflectometry and / or elliptical polarization configuration in accordance with one or more embodiments of the present invention. Figures 1 to 12 The various embodiments and components described may be interpreted as extending to Fig.13 System 1300 may include any type of metering system known in the art.

[0068] In an embodiment, the system 1300 includes the LSP broadband light source 100 , a set of illumination optics 1316 , a set of collection optics 1318 , a detector assembly 1328 , and a controller 1218 , which includes one or more processors 1220 and a memory 1222 .

[0069] In this embodiment, broadband illumination from the LSP broadband light source 100 is directed to the sample 1207 via the set of illumination optics 1316. In an embodiment, the system 1300 collects the illumination emitted from the sample via the set of collection optics 1318. The set of illumination optics 1316 may include one or more beam conditioning components 1320 suitable for modifying and / or conditioning the broadband beam. For example, the one or more beam conditioning components 1320 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.

[0070] In embodiments, the set of illumination optics 1316 may utilize a first focusing element 1322 to focus and / or direct a beam onto a sample 207 disposed on a sample carrier 1312. In embodiments, the set of collection optics 1318 may include a second focusing element 1326 to collect illumination from the sample 1207.

[0071] In an embodiment, the detector assembly 1328 is configured to capture the illumination emitted from the sample 1207 through the set of collection optics 1318. For example, the detector assembly 1328 may receive illumination reflected or scattered (e.g., via specular reflection, diffuse reflection, etc.) from the sample 1207. By way of another example, the detector assembly 1328 may receive illumination generated by the sample 1207 (e.g., luminescence associated with absorption of a light beam, etc.). It should be noted that the detector assembly 1328 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.

[0072] The set of collection optical devices 1318 may further include any number of collection beam conditioning elements 1330 for directing and / or modifying the radiation collected by the second focusing element 1326, including but not limited to one or more lenses, one or more filters, one or more polarizers, or one or more phase plates.

[0073] System 1300 can 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.

[0074] Descriptions of inspection / metrology tools suitable for implementation in various embodiments of the present invention are provided in the following: U.S. Patent No. 7,957,066, entitled “Split Field Inspection System Using Small Catadioptric Objectives,” issued on June 7, 2011; U.S. Patent No. 7,345,825, entitled “Beam Delivery System for Laser Dark-Field Illumination in a Catadioptric Optical System,” issued on March 18, 2018; U.S. Patent No. 5,999,310, entitled “Ultra-broadband UV Microscope Imaging System with Wide Range Zoom Capability,” issued on December 7, 1999; U.S. Patent No. 5,999,310, entitled “Surface Inspection System Using Laser Line Illumination and Two-Dimensional Imaging,” issued on April 28, 2009; No. 7,525,649, entitled “Laser Line Illumination with Two Dimensional Imaging”, U.S. Patent No. 9,228,943, issued on January 5, 2016, entitled “Dynamically Adjustable Semiconductor Metrology System”, U.S. Patent No. 5,608,526, issued on March 4, 1997, entitled “Focused Beam Spectroscopic Ellipsometry Method and System” to Piwonka-Corle et al., and U.S. Patent No. 6,297,880, issued on October 2, 2001, entitled “Apparatus for Analyzing Multi-Layer Thin Film Stacks on Semiconductors”, each of which is incorporated herein by reference in its entirety.

[0075] The one or more processors 1220 of the controller 1218 may include any processor or processing element known in the art. For the purposes of the present invention, the term "processor" or "processing element" may be broadly defined to include any device having one or more processing or logic elements (e.g., one or more microprocessor devices, one or more application specific integrated circuit (ASIC) devices, one or more field programmable gate arrays (FPGAs), or one or more digital signal processors (DSPs)). In this sense, the one or more processors 1220 may include any device configured to execute algorithms and / or instructions from the storage medium 1222 (e.g., program instructions stored in memory). The storage medium 1222 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 1220.

[0076] In an embodiment, as described herein, the LSP light source 100 and systems 1200, 1300 may be configured as a "stand-alone tool," which is interpreted herein as a tool that is not physically coupled to a process tool. In other embodiments, this inspection or metrology system may be coupled to a process tool (not shown) via a transmission medium (which 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 etching tool, a deposition tool, a polishing tool, a plating tool, a cleaning tool, or an ion implantation tool. The results of the inspection or measurement performed by the systems described herein may be used to change the parameters of a process or process tool using feedback control techniques, feedforward control techniques, and / or in-situ control techniques. The parameters of a process or process tool may be changed manually or automatically.

[0077] Those skilled in the art will recognize that for the purpose of conceptual clarity, the components, operations, devices, objects, and accompanying discussions described herein are used as examples, and various configuration modifications are contemplated. Therefore, as used herein, the specific examples set forth and the accompanying discussions are intended to represent their more general class. In general, the use of any specific example is intended to represent its class, and the exclusion of specific components, operations, devices, and objects should not be considered limiting.

[0078] With respect to the use of substantially any plural and / or singular terms herein, those skilled in the art can translate from the plural to the singular and / or from the singular to the plural as is appropriate to the context and / or application. For clarity, the various singular / plural arrangements are not explicitly set forth herein.

[0079] The subject matter described herein sometimes illustrates different components that are housed in or connected to other components. It should be understood that these depicted architectures are only exemplary, and in fact many other architectures that realize the same functionality can be implemented. In a conceptual sense, any component arrangement that realizes the same functionality is effectively "associated" so that the desired functionality is realized. Therefore, any two components that are combined to realize a specific functionality herein can be considered to be "associated" with each other so that the desired functionality is realized, regardless of the architecture or intermediate components. Similarly, any two components so associated can also be considered to be "connected" or "coupled" to each other to realize the desired functionality, and any two components that can be so associated can also be considered to be "coupleable" to each other to realize the desired functionality. Specific examples that can be coupled include but are not limited to components that can physically cooperate and / or physically interact and / or components that can interact wirelessly and / or interact wirelessly and / or components that interact logically and / or components that can interact logically.

[0080] In addition, it should be understood that the present invention is defined by the appended claims. It will be understood by those skilled in the art 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 "at least having"; the term "include" should be interpreted as "including but not limited to", etc.). It should be further understood by those skilled in the art that if there is an intention to express the introduced technical solution narrative as a specific number, then this intention will be explicitly stated in the technical solution, and when there is no such statement, there is no such intention. For example, as an aid to understanding, the appended claims may contain the use of the introductory phrases "at least one" and "one or more" to introduce the technical solution narrative. However, the use of these phrases should not be interpreted as implying that a technical solution statement introduced by the indefinite article "a or an" limits any particular technical solution containing this introduced technical solution statement to an invention containing only one such statement, even when the same technical solution includes the introductory phrase "one or more" or "at least one", and the indefinite article such as "a or an" (for example, "a and / or an" should generally be interpreted as meaning "at least one" or "one or more"); the same is true for the use of definite articles used to introduce technical solution statements. In addition, even if a specific number of introduced technical solution statements is explicitly stated, a person skilled in the art will recognize that this statement should generally be interpreted as meaning at least the stated number (for example, the plain statement of "two statements", without other modifiers, generally means at least two statements, or two or more statements). Furthermore, in those instances where a convention similar to “at least one of A, B, and C, etc.” is used, generally speaking, this construction is intended to mean that one skilled in the art will understand the meaning of the convention (e.g., “a system having at least one of A, B, and C” will include, 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 both A, B, and C, etc.). In those instances where a convention similar to “at least one of A, B, or C, etc.” is used, generally speaking, this construction is intended to mean that one skilled in the art will understand the meaning of the convention (e.g., “a system having at least one of A, B, or C” will include, 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 both A, B, and C, etc.).It will be further understood by those skilled in the art that any transitional word and / or phrase (whether in the description, claims or drawings) that indicates two or more alternative terms should be understood to contemplate the possibility of including one of the terms, any of the terms, or both of the terms. For example, the phrase "A or B" will be understood to include the possibility of "A" or "B" or "A and B".

[0081] It is believed that the present invention and its many attendant advantages will be appreciated from the foregoing description, and it will be apparent that various changes may be made in the form, construction, and arrangement of components without departing from the disclosed subject matter or sacrificing all of its substantial advantages. The forms described are merely illustrative, and it is intended that such changes be encompassed and included by the appended claims. Furthermore, it should be understood that the present invention is defined by the appended claims.

Claims

1. A laser-maintained plasma light source, comprising: Gas containment structures, which are used to contain gas; one or more gas inlets fluidly coupled to the gas containment structure and configured to flow the gas into the gas containment structure; one or more gas outlets fluidly coupled to the gas containment structure and configured to flow gas out of the gas containment structure, wherein the one or more gas inlets and the one or more gas outlets are arranged to generate a swirling gas flow within the gas containment structure, wherein the swirling gas flow comprises a helical vortex having a drift velocity between 1 m / s and 100 m / s; a laser pump source configured to generate an optical pump to sustain a plasma within an inner gas flow within the vortexing gas flow in a region of the gas containment structure; and A light collector element is configured to collect at least a portion of the broadband light emitted from the plasma.

2. The laser-sustained plasma light source of claim 1, wherein the one or more gas inlets include at least a first gas inlet, and wherein the one or more gas outlets include at least a first gas outlet.

3. The laser-sustained plasma light source of claim 2, wherein the one or more gas inlets comprises a first gas inlet and a second gas inlet, and wherein the one or more gas outlets comprises a first gas outlet and a second gas outlet.

4. The laser-sustained plasma light source of claim 1, wherein the one or more gas inlets are positioned on a side of the gas containment structure opposite the one or more gas outlets.

5. A laser-sustained plasma light source as claimed in claim 4, wherein the swirling gas flow direction through the plasma region is in the same direction as the inlet gas flow from the one or more inlets.

6. The laser-sustained plasma light source of claim 1, wherein the one or more gas inlets and the one or more gas outlets are positioned on the same side of the gas containment structure.

7. A laser-sustained plasma light source as claimed in claim 6, wherein the swirling gas flow direction through the plasma region is in an opposite direction to the inlet gas flow from the one or more inlets.

8. The laser-sustained plasma light source of claim 1, wherein one or more of the gas inlets are positioned at a peripheral portion of the gas containment structure and one or more of the gas outlets are positioned at a central portion of the gas containment structure.

9. The laser-sustained plasma light source of claim 1, wherein one or more of the gas outlets are positioned at a peripheral portion of the gas containment structure and one or more of the gas inlets are positioned at a central portion of the gas containment structure.

10. The laser-sustained plasma light source of claim 1, wherein one or more of the gas inlets are positioned at a peripheral portion of the gas containment structure and one or more of the gas outlets are positioned at an additional peripheral portion of the gas containment structure.

11. The laser-sustained plasma light source of claim 1 , wherein the one or more gas inlets comprise a gas nozzle for flowing a gas through the gas containment structure.

12. The laser-sustained plasma light source of claim 11, wherein the gas nozzle comprises a converging gas nozzle for generating a gas jet.

13. The laser-sustained plasma light source of claim 11, wherein the gas nozzle comprises an annular flow nozzle for producing an annular gas jet having a gas velocity sufficient to sustain a plasma 25 mm to 75 mm from the annular flow nozzle.

14. The laser-sustained plasma light source of claim 13, wherein the annular flow nozzle comprises a flow nose section.

15. The laser-sustained plasma light source of claim 1, wherein gas flow from the one or more inlets and gas flow into the one or more outlets propagate in the same direction.

16. The laser-sustained plasma light source of claim 1, wherein gas flow from the one or more inlets and gas flow into the one or more outlets propagate in opposite directions.

17. The laser-sustained plasma light source of claim 1, wherein the gas containment structure comprises at least one of: a plasma cell, a plasma bulb, or a plasma chamber.

18. The laser-sustained plasma light source of claim 1, wherein the gas contained within the gas containment structure comprises at least one of the following: Xe, Ar, Ne, Kr, He, N2, H2O, O2, H2, D2, F2, CF6, or a mixture of two or more of the following: Xe, Ar, Ne, Kr, He, N2, H2O, O2, H2, D2, F2, or CF6.

19. The laser-sustained plasma light source of claim 1, wherein the light collector elements comprise elliptical, parabolic, or spherical light collector elements.

20. The laser-sustained plasma light source of claim 1, wherein the pump source comprises: One or more lasers.

21. The laser-sustained plasma light source of claim 20, wherein the pump source comprises: At least one of an infrared laser, a visible laser, or an ultraviolet laser.

22. The laser-sustained plasma light source of claim 1, wherein the light collector element is configured to collect at least one of: broadband infrared light, visible light, UV light, VUV light, or DUV light from the plasma.

23. The laser-sustained plasma light source 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.

24. The laser-sustained plasma light source of claim 23, wherein the one or more downstream applications include at least one of inspection or metrology.

25. An optical characterization system, comprising: A laser sustaining light source comprising: Gas containment structures, which are used to contain gas; one or more gas inlets fluidly coupled to the gas containment structure and configured to flow the gas into the gas containment structure; one or more gas outlets fluidly coupled to the gas containment structure and configured to flow gas out of the gas containment structure, wherein the one or more gas inlets and the one or more gas outlets are arranged to generate a swirling gas flow within the gas containment structure, wherein the swirling gas flow comprises a helical vortex having a drift velocity between 1 m / s and 100 m / s; a laser pump source configured to generate an optical pump to sustain a plasma within an inner gas flow within the vortexing gas flow in a region of the gas containment structure; and a light collector element configured to collect at least a portion of the broadband light emitted from the plasma; a set of illumination optics configured to direct broadband light from the laser sustaining light source to one or more samples; a set of collection optics configured to collect light emitted from the one or more samples; and Detector assembly.

26. A plasma cell comprising: Gas containment structures, which are used to contain gas; one or more gas inlets fluidly coupled to the gas containment structure and configured to flow the gas into the gas containment structure; one or more gas outlets fluidly coupled to the gas containment structure and configured to flow gas out of the gas containment structure, wherein the one or more gas inlets and the one or more gas outlets are arranged to generate a vortex gas flow within the gas containment structure, wherein the vortex gas flow comprises a helical vortex having a drift velocity between 1 m / s and 100 m / s, wherein the direction of the vortex gas flow through a plasma region is in the same direction as an inlet gas flow from the one or more inlets, wherein the gas containment structure is configured to receive an optical pump so as to maintain a plasma within an internal gas flow within the vortex gas flow.

27. A plasma cell comprising: Gas containment structures, which are used to contain gas; one or more gas inlets fluidly coupled to the gas containment structure and configured to flow the gas into the gas containment structure; one or more gas outlets fluidly coupled to the gas containment structure and configured to flow gas out of the gas containment structure, wherein the one or more gas inlets and the one or more gas outlets are arranged to generate a vortex gas flow within the gas containment structure, wherein the vortex gas flow comprises a helical vortex having a drift velocity between 1 m / s and 100 m / s, wherein the direction of the vortex gas flow through a plasma region is in a direction opposite to an inlet gas flow from the one or more inlets, wherein the gas containment structure is configured to receive an optical pump to maintain a plasma within an internal gas flow within the vortex gas flow.

28. An optical characterization method, comprising: generating a vortex gas flow within a gas containment structure of a laser sustaining light source, wherein the vortex gas flow comprises a spiral vortex having a drift velocity between 1 m / s and 100 m / s; Producing pump irradiation; directing a portion of the pump illumination into an internal gas flow within the swirling gas flow in the gas containment structure using a light collector element to sustain a plasma; and A portion of the broadband light emitted from the plasma is collected using the light collector element and directed to one or more downstream applications.

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