Inductively Coupled Plasma Light Source

Abstract

A plasma chamber for a UV light source includes a plasma generation region defining a plasma confinement region. A port that allows generated light to be transmitted out of the chamber is positioned adjacent a side of the plasma generation region. A high voltage region is coupled to the plasma generation region. A ground region is coupled to the high voltage region, the ground region defining an outer surface configured to be coupled to ground and dimensioned to receive an enclosing inductor core. A width of the high voltage region is greater than a width of the ground region.

Description

[Technical field]

[0001]

[0001] The section headings used herein are for organizational purposes only and are not to be construed as limiting the subject matter described in the present application in any way.

[0002] [introduction]

[0002] Many commercial and academic applications require high brightness light in the extreme ultraviolet (EUV) region of the spectrum. For example, EUV light is required for many industrial applications such as metrology, accelerated testing, photoresists, defect inspection, and microscopy. Other uses of EUV light include microscopy, spectroscopy, area imaging, and blank mask inspection. These and other applications require EUV sources that have high reliability, small physical size, low fixed costs, low operating costs, and low complexity from these important sources of extreme ultraviolet photons. Summary of the Invention

[0003] A plasma chamber according to the present teachings, which may be a plasma chamber for an ultraviolet light source, includes a plasma generation region defining a plasma confinement region. A port that allows the generated ultraviolet radiation to be transmitted out of the chamber is positioned adjacent a side of the plasma generation region. A gas supply port may be positioned proximate to the plasma generation region. A vacuum pump port may be positioned proximate to the plasma generation region.

[0004]

[0004] A high voltage region is coupled to the plasma generation region. A ground region is coupled to the high voltage region, the ground region defining an outer surface configured to be coupled to ground and dimensioned to receive the surrounding inductor core. A width of the high voltage region is greater than a width of the ground region. In various embodiments, the width of the high voltage region may be at least two times greater than the width of the ground region. The width of the plasma generation region may also be less than the width of the ground region.

[0005]

[0005] The insulating region may be coupled to the ground region and may be configured to be coupled to a ground potential. The insulating region may also have an aperture for passing ultraviolet light. The insulating region may be configured to reduce a negative potential in proximity to the ground region to reduce attraction of ions generated in the plasma generation region. A gas supply port for providing gas to the plasma generation region may be located in the insulating region. A plasma diagnostic port may also be located in the insulating region. The port in the insulating region may include an aperture for passing ultraviolet light.

[0006] A mirror may be positioned adjacent to the ground region and oriented to reflect at least some of the light generated in the plasma generation region back to the plasma generation region. The mirror may be partially transmissive such that some of the light generated in the plasma passes through an output port.

[0007]

[0007] An inner inductor core may be positioned around the plasma generation region to couple the current into the plasma loop. An outer inductor core may be positioned around the inner inductor core. An inductor core may be positioned around a portion of the ground region and configured to prevent current from flowing through the ground region. [Brief description of the drawings]

[0008]

[0008] The present teachings, in accordance with preferred and exemplary embodiments, together with further advantages thereof, are more particularly described in the following detailed description taken in conjunction with the accompanying drawings. Those skilled in the art will appreciate that the drawings described below are for illustrative purposes only. The drawings are not necessarily to scale, rather emphasis is generally placed on illustrating the principles of the teachings. The drawings are not intended to limit the scope of the applicant's teachings in any way. [Figure 1] FIG. 1 illustrates a plasma chamber according to the present teachings for a Z-pinch ultraviolet light source. [Figure 2A]1 illustrates an ultraviolet light source including a plasma confinement region, a high voltage region, a ground region, and an insulating region in accordance with the present teachings. [Figure 2B] 1 illustrates a graph from an oscilloscope showing the pulsed operation of an embodiment of an ultraviolet light source of the present teachings. [Diagram 3] 1 illustrates an embodiment of an ultraviolet light source in accordance with the present teachings including a gas supply port coupled to an insulating region. [Figure 4A] 1 illustrates an embodiment of an ultraviolet light source according to the present teachings including a diagnostic probe port coupled to an insulating region. [Figure 4B] 1 illustrates another embodiment of an ultraviolet light source in accordance with the present teachings, including a laser source having an output optically coupled to an insulating region. [Diagram 5] 1 illustrates an embodiment of an ultraviolet light source according to the present teachings, including a port with a transparent region for passing generated ultraviolet light coupled to an insulating region. [Figure 6] 1 illustrates an embodiment of an ultraviolet light source in accordance with the present teachings that includes a mirror for reflecting the generated ultraviolet light back into the plasma confinement region. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Description of Various Embodiments

[0017] The present teachings will now be described in more detail with reference to exemplary embodiments thereof as illustrated in the accompanying drawings. While the present teachings are described in conjunction with various embodiments and examples, it is not intended that the present teachings be limited to such embodiments. On the contrary, the present teachings encompass various alternatives, modifications, and equivalents, as will be understood by those skilled in the art. Those skilled in the art and having access to the teachings herein will recognize additional implementations, modifications, and embodiments, and other fields of use, that are within the scope of the present disclosure as described herein.

[0010]

[0018] References herein to "one embodiment" or "one embodiment" mean that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present teachings. The appearances of the phrase "in one embodiment" in various places in the specification are not necessarily all referring to the same embodiment.

[0011]

[0019] It should be understood that the individual steps of the methods of the present teachings may be performed in any order and / or simultaneously so long as the present teachings remain operable.Further, it should be understood that the apparatus and methods of the present teachings may include any number of the described embodiments or all of the described embodiments so long as the present teachings remain operable.

[0012]

[0020] Extreme ultraviolet light sources play an important role in many optical metrology and exposure applications. It is desirable for these sources to be configured to address many use cases. One challenge is to generate high power and high brightness EUV light in a configuration that allows integration with many applications and yet exhibits high stability and reliability.

[0013]

[0021] Extreme ultraviolet radiation is referred to by various names by those skilled in the art. Some have sometimes referred to extreme ultraviolet radiation as high energy ultraviolet radiation, which may be abbreviated as XUV. Extreme ultraviolet radiation generally refers to electromagnetic radiation that is a part of the electromagnetic spectrum that nominally spans wavelengths from 124 nm to 10 nm. There is some overlap between extreme ultraviolet radiation and what is considered to be the optical spectrum. One particular EUV wavelength of interest is 13.5 nm, as that wavelength is commonly used for lithography. Extreme ultraviolet radiation sources according to the present teachings are not limited to the production of EUV radiation. As is known in the art, plasmas can be used to generate photons in a wide spectral range. For example, plasmas generated according to the present teachings can also be used to generate soft x-ray photons (SXR). This includes, for example, photons having wavelengths less than 10 nm.

[0014]

[0022] So-called Z-pinch plasmas with axial current have been shown to be effective in producing EUV and SXR light. However, most known sources have employed electrodes to conduct the high discharge current to the plasma. These electrodes, which are typically in contact with the hot plasma, can melt and create significant debris, which is highly undesirable as it can greatly reduce the useful lifetime of the source.

[0015]

[0023] An electrodeless approach to generating EUV would be desirable and would fill a significant market need. Such sources are available, for example, from Energetiq, a Hamamatsu Company, Wilmington, MA. These sources are based on Z-pinch plasma, but avoid electrodes entirely by inductively coupling current into the plasma. The plasma in these EUV sources is magnetically confined away from the walls of the source to minimize heat load, reduce debris, provide excellent open-loop spatial stability, and provide a stable, repeatable power output. One challenge with known Z-pinch plasma chambers is that the high voltage region of the chamber wall obscures one side of the Z-pinch region (referred to herein as the backside). This makes it difficult or impossible to modify the chamber to provide backside access, since ground potential cannot be achieved in the high voltage region while the plasma is running.

[0016]

[0024] One feature of the EUV sources of the present teachings is that they are versatile and support a variety of applications. For example, EUV source operating conditions are user adjustable. In particular, the EUV sources of the present teachings improve upon known Z-pinch designs since they can be optimized for peak power or peak brightness as required by the user for a specific application. The plasma size may typically be less than 1 mm in diameter under typical operating conditions. This design supports a simple and flexible optical interface provided to the user on one side of the system housing to connect to application equipment. Custom interfaces may also be accommodated for specific applications.

[0017]

[0025] Another feature of the EUV sources of the present teachings is that they accommodate two-sided optical access to the plasma chamber, which is provided, at least in part, by appropriate modifications to the high voltage chamber used to generate the Z-pinch system conditions.

[0018]

[0026] 1 illustrates a plasma chamber 100 in accordance with the present teachings for a Z-pinch ultraviolet light source. The chamber 100 includes an interface 102 that passes a target gas 104 into the chamber 100. A pump 106 is used to evacuate a chamber region 108 to a desired operating pressure and / or to control gas flow in the chamber 100.

[0019]

[0027] A port 110 is provided for passing EUV radiation generated by the plasma. The port 110 may include an EUV output port that passes desired EUV radiation. The port 110 may also be configured to include a filter structure that blocks undesired radiation. In some embodiments, the port 110 is configured to block visible light. For example, in various embodiments, the EUV transparent port 110 is an aperture that may include a spectral purifying foil. Typically, the port 110 is a beamline aperture port that passes radiation propagating along the beamline. The port may also be configured to have a desired diameter to physically block light propagating in a particular direction. Furthermore, the diameter of the aperture may be selected to provide a desired pressure differential.

[0020]

[0028] In various systems, the port 110 is configured to be adaptable for a user to attach to an application system (not shown) where EUV radiation passes directly through the port 110. The plasma generation region 112 uses magnetic induction to define a plasma confinement region 113, described in more detail below. The plasma confinement region 113 is formed by a pulse shaping and power delivery section 115 which passes a current that excites a core (not shown) during operation. A high voltage region 114 is attached to the plasma generation region 112.

[0021]

[0029] A grounded region 116 is attached to the high voltage region 114. The grounded region 116 has an outer surface that is coupled to ground at a first location 118. An insulating vacuum pipe 120 including a dielectric breakdown 122 is positioned adjacent to the first location 118. The insulating material forming the dielectric breakdown 122 may be formed of ceramic or one or more other high temperature insulating materials such as polytetrafluoroethylene (PTFE), or similar materials. The vacuum pipe 120 is grounded at a location 124 after the dielectric breakdown 122 near an input / output port 126 of the chamber 100. The insulating vacuum pipe 120 serves to provide a dielectric breakdown that reduces the negative potential in order to attract ions to further downstream components (not shown) during operation as desired.

[0022]

[0030] The chamber 100 also includes regions 128, 130 for positioning magnets that provide induced currents for the chamber 100 during operation. The last or first location 118 of the regions of the chamber 100 is also grounded. Collectively, the grounded insulating vacuum pipe 120 with the dielectric breakdown 122 and the grounded region 124 at the output port 126 may be referred to as the insulating region 129. One feature of the insulating region 129 of the chambers described herein is that it provides a safe grounded exterior region of the chamber that allows access by users and / or other downstream equipment from outside the chamber 100.

[0023]

[0031] One feature of the present teachings is that the input / output ports 126 defined by the insulated vacuum pipes 120 are configured for flexible connection of various downstream components (not shown). This feature supports various custom and semi-custom configurations of the chamber 100 to address different applications. For example, the input / output ports 126 may form gas supply ports that provide gas to the plasma generation region 112. The input / output ports 126 may form plasma diagnostic ports. This allows, for example, optical imaging, spectroscopy, and / or electron probing of the plasma in the plasma generation region 112 from the input / output ports 126 during operation. The input / output ports 126 may form an aperture for passing ultraviolet light generated from the plasma. The input / output ports 126 may include a mirror positioned adjacent the ground location 124. The mirror (not shown) may be fully or partially reflective and oriented as desired to reflect at least a portion of the light generated in the plasma generation region 112 back to the plasma generation region 112. In some embodiments, the mirror is partially transmissive such that some light generated in the plasma generation region 112 passes through the input / output port 126 and some light is reflected back. In some embodiments, this light is EUV radiation generated in the plasma generation region, and in some embodiments this light may also include laser light or other light, for example, that interacts with and / or probes the plasma.

[0024]

[0032] 2A illustrates an ultraviolet light source 200 including a plasma confinement region 202, a high voltage region 204, a ground region 206, and an insulating region 208 in accordance with the present teachings. The source 200 is an inductive design that uses magnetic confinement of the plasma in the plasma confinement region 202 away from the components of the chamber 210 to provide high reliability and stability. A target gas 212 enters the chamber 210 through an interface 214. In some embodiments, the target gas is xenon. A pump 216 is used to evacuate the chamber region 218 to a desired operating pressure. A port 220 is provided for passing EUV radiation, i.e., EUV light 236 generated by the plasma.

[0025]

[0033] The pulse forming and power delivery section 222 is driven using a parallel connected capacitor 224 and a pulse generator 226 that drives a current through the section 222 to ground. The pulse generator 226 applies a negative high voltage pulse to the capacitor. In some embodiments, the capacitor 224 is a collection of multiple capacitors. Thus, the pulse forming and power delivery section 222 of the chamber 210 has a high voltage side 228 and a ground side 230. The inner magnetic core 232 and the outer magnetic core 234, excited by a current pulse flowing through the pulse forming and power delivery section 222, generate at least three inductively coupled plasma loops (not shown) that meet at the plasma generation region 202 forming a magnetically confined Z-pinch. The loops flow through the region between the inner core 232 and the outer core 234 and through the plasma generation region 202.

[0026]

[0034] During operation, a voltage pulse from the pulse generator 226 charges the capacitor 224. During the charging time, a small amount of leakage current from the cores 232, 234 sustains the plasma loop. The pinch action requires a sustained loop because it requires ionized gas for proper function. The outer core 234 saturates, driving the impedance to zero. The capacitor then discharges. This results in beneficial pulse compression. The inner core 232 couples the current pulse into the plasma loop, resulting in a large pulse in the plasma current known as a Z-pinch.

[0027]

[0035] The plasma generation region 202 generates and emits nearly 100% of the EUV radiation produced by the plasma. The plasma loop does not generate EUV light. As a result, the source 200 produces a high quality, relatively compact source of EUV light 236 from a well-defined and stable pinched plasma confinement region 238 in the plasma generation region 202. By using the pulse shaping and power delivery section 222 to drive and contain the plasma, the source 200 operates without the use of electrodes commonly used in known systems to conduct discharge current to the plasma.

[0028]

[0036] Known Z-pinch plasma chambers have electrical continuity between the high voltage region 204 and the plasma generation region 202. As a result, when the outside of the chamber 210 is at a high potential voltage, it is difficult or impossible to have backside access to the chamber.

[0029]

[0037] 2A, the high voltage region 204 is electrically connected to the high voltage side 228 of the pulse forming and power delivery section 222, while the ground region 206 is coupled to the high voltage region 204. In particular, the ground region 206 has an outer surface that is coupled to ground at a first location 240. Additionally, there is an insulating vacuum pipe in the insulating region 208 that includes a dielectric breakdown 242. In this configuration, the insulating region 208 is grounded at a location 244 after the dielectric breakdown 242 near the output 246 of the chamber 210. As a result, the insulating region 208 serves to provide a dielectric breakdown that reduces the negative potential that attracts ions to components further downstream during operation, as desired.

[0030]

[0038] The current blocking inductor core 248 is positioned at the boundary between the high voltage region 204 and the ground region 206 of the chamber 210. The hard ground connected to the locations 240, 244 of the ground region 206 and the ground connected to the ground side 230 are electrically connected. A bias current is applied to the current blocking inductor core 248. This bias current reduces the current flowing from the high voltage region 204 to the ground region 206.

[0031]

[0039] During operation, some pulse leakage current flows through the inductive core 248 along the pipe (118 or 240) close to the end of the chamber. The time variation of the current in the pipe (118, 240) results in a time variation of the magnetic flux flowing around the core 248. The time variation of the magnetic flux causes a reverse current to flow in the pipe (118 or 240) close to the end of the chamber. As a result, the leakage current is countered by the resulting induced current, thus preventing the leakage current from flowing further. When the voltage on the high voltage side 228 swings from negative to positive, the current prevention core 248 automatically resets.

[0032]

[0040] Various embodiments may use different sized elements in the chamber 210. Typically, the width of the ground area is 250W. G is the width 251W of the plasma generation region 202 PGIn some embodiments, the cross-sectional area of ​​the current prevention inductor core 248 perpendicular to the magnetic flux in the current prevention inductor core 248 is greater than that of the inner core 232. In some embodiments, the cross-sectional area of ​​the current prevention inductor core 248 is at least twice the cross-sectional area of ​​the inner core 232. In this case, the width 252 of the high voltage region is HV The width of the ground area is 250W G In some configurations, the width of the high voltage region is 252W. HV The width of the ground area is 250W G is at least twice as large.

[0033]

[0041] Like the input / output ports 126 described in connection with FIG. 1, the input / output ports 246 may be configured for multi-purpose connection of various downstream components to support custom and semi-custom configurations of the source 200 to address a number of different applications. The generated EUV radiation 236 may also be directed to the backside of the pinched confinement region 238 (backside EUV radiation not shown). The output 246 may be configured to collect this backside EUV radiation and project it to downstream components. For example, the input / output ports 246 may be configured to enhance the EUV radiation using a multi-layer mirror at the output. The input / output ports 246 may also be used for optical access and gas fuel supply purposes. All or some of these configurations of the input / output ports 246 may be combined as well. Some of these configurations are described in more detail below.

[0034]

[0042] For example, in one particular embodiment, source 200 has a power rating of 8 W / mm 2The source is configured to generate about 20 watts of 13.5 nm wavelength EUV radiation at 2-pi steradians with a brightness of -sr. The source radiation may be relatively highly pulsed, such as at about 2.5 kHz, and the emissivity may be user configurable. The plasma confinement region 238 for such a source may be less than 1 mm in diameter, or even less than 0.5 mm in diameter. In some methods of operation, the actual position of the plasma confinement region 238 varies by less than a few microns from pulse to pulse.

[0035]

[0043] 2B illustrates a graph 290 from an oscilloscope showing the pulsed operation of an embodiment of an ultraviolet light source of the present teachings. The first trace 292 illustrates the capacitor discharge used to create the Z-pinch plasma. The second trace 294 illustrates the voltage measured at the pipe location 240 (FIG. 2A) to ground. Both voltages are large, negative high voltage amplitudes of over 500V. The third trace 296 is the voltage measured at the pipe location 244 (FIG. 2A) to ground.

[0036]

[0044] 2A has thus reduced the leakage voltage at pipe location 244 to a relatively low voltage level that is safe for operator maintenance and reconfiguration. Because plasma current only flows when the voltage swings from low to high, the main current pulse is always in the same direction. Because the negative voltage is always greater while the capacitor voltage swings positive, the current prevention inductor core 248 becomes negatively charged after each pulse and may be reset by a positive applied voltage.

[0037]

[0045] 3 illustrates an embodiment of an ultraviolet light source 300 in accordance with the present teachings, including a gas supply port 302 coupled to an insulating region 308. Similar to source 200 described in connection with FIG. 2A and chamber 100 described in connection with FIG. 1, source 300 includes many common components, such as a chamber 301, a high voltage region 304, a ground region 306, an insulating region 308, a plasma confinement region 310, a port 314 for passing EUV radiation 312, an inner core 316, an outer core 318, a current prevention core 320, and a pump 322.

[0038]

[0046] Gas 324 is supplied to the plasma confinement region through a gas supply port 302 to the chamber 301. In some embodiments, the gas 324 is xenon gas. The gas 324 flows through the chamber 301 and out of a pump 322 as illustrated by dashed line 326. In some embodiments, the gas supply port 302 supports the insertion of a gas jet that delivers the gas 324 to the plasma generation region. One advantage of attaching the gas supply port 302 to the insulating region 308 is that such a configuration improves the fueling of the plasma created in the plasma confinement region 310. Such an improvement may lead to a higher plasma density, which results in a higher power and / or higher brightness of the EUV radiation 312. In some embodiments, the gas supply port 302 is the only gas port in the chamber 301. In some embodiments, two or more gas ports are used.

[0039]

[0047] 4A illustrates an embodiment of an ultraviolet light source 400 in accordance with the present teachings, including a diagnostic probe port 402 coupled to an insulating region 408. Similar to source 200 described in connection with FIG. 2A and chamber 100 described in connection with FIG. 1, source 400 includes many common components, such as a chamber 401, a high voltage region 404, a ground region 406, an insulating region 408, a plasma confinement region 410, a port 414 transmitting EUV radiation 412, an inner core 416, an outer core 418, a current prevention core 420, and a pump 422.

[0040]

[0048] The diagnostic probe port 402 includes an optical port 424. The optical port 424 passes light 426 that is collected from the backside of the plasma generation region 410. This light 426 can be useful for detecting plasma characteristics, such as, for example, optical output power as a function of position and / or time. The port 424 may also pass a probe light 428 to the chamber 401. The probe light 428 may be directed into the plasma confinement region, and the resulting light 426 that is collected from the backside of the plasma generation region 410 back to the port 424 may be detected to determine various plasma characteristics. The probe light 428 may also be used for a number of other purposes, such as determining gas characteristics. One feature of the chamber according to the present teachings is that it is highly desirable to have the optical port 424 at ground potential for safety reasons.

[0041]

[0049] 4B illustrates another embodiment of an ultraviolet light source 450 in accordance with the present teachings, including a laser source 430 having an output optically coupled to an insulating region 408 such that light passes through the chamber and into the plasma confinement region. Similar to source 200 described in connection with FIG. 2A, chamber 100 described in connection with FIG. 1, and source 400 described in connection with FIG. 4A, source 450 includes many common components, such as a chamber 401, a high voltage region 404, a ground region 406, an insulating region 408, a plasma confinement region 410, a port 414 for passing EUV radiation 412, an inner core 416, an outer core 418, a current prevention core 420, and a pump 422.

[0042]

[0050] As in the configuration described in connection with FIGURE 4A, the diagnostic probe port 402 includes an optical port 424 that passes radiation at a desired frequency. The optical port may include a filter that passes only the desired radiation. The optical port 424 in FIGURE 4B is generally configured to pass laser radiation generated by a laser 430. Additionally, the optical port 402 may be used for diagnostic purposes to detect properties and / or probe the plasma as described in connection with FIGURE 4A.

[0043]

[0051] The laser optics 423 are positioned relative to the output of the laser 430 to direct the laser radiation generated by the laser 430 to the plasma confinement region. For example, the laser optics 432 may be a mirror or a collection of mirrors as shown that directs the laser radiation from the output of the laser 430 to the plasma confinement region. In other embodiments, the laser optics 430 may include a transmissive lens that passes and focuses the laser radiation to the plasma confinement region. In various embodiments, the laser 430 generates sufficient power at a desired wavelength to heat the plasma to form a Z-pinch plasma. As described in connection with FIG. 4A, one feature of the chamber is that it includes an optical port 424 that is at ground potential for safety reasons.

[0044]

[0052] 5 illustrates an embodiment of an ultraviolet light source 500 in accordance with the present teachings, including a port 502 having a transparent region for passing generated ultraviolet light coupled to an insulating region 508. Similar to source 200 described in connection with FIG. 2A and chamber 100 described in connection with FIG. 1, source 500 includes many common components, such as a chamber 501, a high voltage region 504, a ground region 506, an insulating region 508, a plasma confinement region 510, a port 514 for passing EUV radiation 512, an inner core 516, an outer core 518, a current prevention core 520, and a pump 522.

[0045]

[0053] The port 502 is configured to pass EUV radiation 524 generated in the plasma generation region 510 from the backside. The port 502 is also configured to interface with a beamline assembly system, which may be a customer supply system to the chamber 501. In some embodiments, this system may be a sealed system that interfaces with the port 520 to maintain a desired pressure in the chamber during operation. In other embodiments, a transparent port seals the port and light is transmitted through the port to an attached system. One feature of the source 500 is that the EUV radiation appears as both frontside EUV radiation 512 and backside EUV radiation 524. This feature allows two systems to be supplied from the same source 500, one with frontside access and one with backside access. In various embodiments, the two systems may be the same system or different systems.

[0046]

[0054] FIG. 6 illustrates an embodiment of an ultraviolet light source 600 according to the present teachings, including a mirror 602 for reflecting the generated ultraviolet light back to the plasma confinement region. Similar to the source 200 described in connection with FIG. 2A and the chamber 100 described in connection with FIG. 1, the source 600 includes many common components, such as a chamber 601, a high voltage region 604, a ground region 606, an insulating region 608, a plasma confinement region 610, a port 614 for passing EUV radiation 612, an inner core 616, an outer core 618, a current prevention core 620, and a pump 622. The mirror 602 reflects at least a portion of the emitted EUV radiation 624 from the plasma generation region 610 back toward the front of the chamber to co-propagate with the EUV radiation 612 from the front side. In some configurations, the mirror 602 is formed with a parabolic shape or some other curved shape that focuses the reflected light back to the plasma generation region. Mirror 602 may be configured to be highly reflective to EUV radiation 624. In these configurations, mirror 602 can provide a significant improvement in the optical power available from source 600 at port 614. This improvement can be nearly a factor of two. In other configurations, mirror 602 is a partially reflective mirror.

[0047]

[0055] The mirror 602 may be constructed in a number of ways, such as by using a multi-layer structure of molybdenum and silicon. The mirror 602 may be held and / or positioned by a fixture 626 that is attached to the insulating region 608. The fixture 626 may include a port that is transparent to EUV radiation 624.

[0048]

[0056] One feature of the high voltage chamber configuration for an EUV source according to the present teachings is that it allows safe and flexible access to one end of a Z-pinch plasma source that emits radiation from the other end. Another feature of the chamber configuration according to the present teachings is that it supports the necessary high voltage driving protocols and system components required to create and sustain the Z-pinch and associated plasma loop using an inductive coil to drive the plasma current.

[0049]

[0057] It should be appreciated that EUV sources according to the present teachings can support a wide range of test and measurement capabilities that can be initially supplied with the source or added at a later point in the system life cycle. Another advantage of the EUV sources of the present teachings is that they can support very flexible access to the EUV radiation generated by the plasma, resulting in many more possible configurations than known EUV systems. In addition, the EUV sources of the present teachings can provide more interaction with and control of the plasma using one or more optical excitation, optical probes, and feed gas management. Furthermore, the EUV sources of the present teachings can support more flexible EUV optical beam shaping and management by incorporating various types of optical elements in and / or near the backside access area of ​​the configuration.

[0050]

[0058] Those skilled in the art will appreciate that there are numerous methods of generating ultraviolet light according to the present teachings. These methods generally provide a feed gas to a plasma confinement region in a plasma chamber. Some methods also apply the gas to a port located in one or more of a variety of locations, such as adjacent to an insulating region. A high voltage is applied to a high voltage region connected to the plasma confinement region in the plasma chamber. A ground region is electrically connected to the high voltage region. A series of voltage pulses is applied to at least one capacitor electrically connected to an outer magnetic core surrounding an inner magnetic core positioned around the plasma confinement region. The voltage pulses charge the at least one capacitor such that the outer magnetic core becomes saturated, resulting in the discharging capacitor(s) coupling a current pulse to the inner core to the plasma confinement region, thereby forming a plasma in a loop where the plasma is sustained between voltage pulses by leakage current. The plasma generates ultraviolet light that propagates through a transparent port located adjacent to the plasma confinement region.

[0051]

[0059] A number of performance advantages are achieved by providing an insulating region that is grounded and coupled to the ground region to reduce attraction of ions generated in the plasma loop to the ground region. To reduce current flow to the ground region, a current is applied to an inductor core that surrounds a portion of the ground region of the plasma chamber.

[0052]

[0060] Additionally, some methods include retro-reflecting a portion of the generated ultraviolet light entering the ground region back to the plasma generation region to increase the brightness of the ultraviolet light passing through a transparent port positioned adjacent to the plasma confinement region. Some methods also include passing a portion of the generated ultraviolet light entering the ground region through a transparent port positioned adjacent to the insulating region. Some methods also include characterizing the generated ultraviolet light that passes through the transparent port positioned adjacent to the insulating region. Some methods also pass a diagnostic probe beam through a transparent port positioned adjacent to the insulating region into the plasma generation region. Some methods measure properties of the plasma in response to an interaction of the diagnostic probe beam and the plasma. Equivalent

[0061] While the applicant's teachings are described in conjunction with various embodiments, it is not intended that the applicant's teachings be limited to such embodiments. On the contrary, the applicant's teachings encompass various alternatives, modifications, and equivalents, as will be appreciated by those skilled in the art, that may be made herein without departing from the spirit and scope of the present teachings.

Claims

1. 1. A plasma chamber comprising: a) a plasma generation region defining a plasma confinement region; b) a port positioned adjacent a first side of the plasma generation region that allows generated light to pass out of the chamber; and c) a high voltage region coupled to the plasma generation region; d) a ground region coupled to the high voltage region, the ground region defining an outer surface configured to be coupled to a ground and dimensioned to receive an enclosing inductive core.

2. The plasma chamber of claim 1 , wherein a width of the high voltage region is greater than a width of the ground region.

3. The plasma chamber of claim 1 , wherein a width of the high voltage region is at least two times greater than a width of the ground region.

4. The plasma chamber of claim 1 , wherein a width of the plasma generation region is less than a width of the ground region.

5. 10. The plasma chamber of claim 1 further comprising an insulating region having a first end coupled to the ground region and a second end configured to be coupled to a ground potential.

6. The plasma chamber of claim 5 , wherein the second end of the insulating region comprises a port.

7. 7. The plasma chamber of claim 6, further comprising a gas supply port positioned at the port at the second end of the insulating region, the gas supply port providing gas to the plasma generation region.

8. The plasma chamber of claim 6 , wherein the port at the second end of the isolation region comprises a plasma diagnostic port.

9. 7. The plasma chamber of claim 6, wherein the port at the second end of the insulating region comprises an aperture for the passage of light.

10. 10. The plasma chamber of claim 1, further comprising a mirror positioned adjacent to the ground region oriented to reflect at least a portion of the light generated in the plasma generation region back to the plasma generation region.

11. 11. The plasma chamber of claim 10, wherein the mirror is partially transmissive such that some light generated in the plasma passes through the port at the second end of the insulating region.

12. The plasma chamber of claim 1 further comprising a gas supply port positioned proximate to the plasma generation region.

13. The plasma chamber of claim 1 further comprising a vacuum pump port positioned proximate to the plasma generation region.

14. a) a plasma chamber, i) a plasma generation region defining a plasma confinement region; ii) a port positioned adjacent a first end of the plasma generation region that allows generated light to pass out of the chamber; and iii) a high voltage region coupled to a second end of the plasma generation region; and iv) a ground region coupled to the high voltage region. b) an insulating region having a first end coupled to the ground region and a second end configured to be coupled to a ground potential, the insulating region reducing a negative potential proximate the ground region to reduce attraction of ions generated in the plasma generation region; c) an inner inductor core positioned around the plasma generation region that couples the current into a plasma loop; d) an outer inductor core positioned about the inner inductor core; and e) A light source comprising an inductive core positioned around a portion of said grounded area and configured to prevent current from flowing through said grounded area.

15. 15. The light source of claim 14, wherein the width of the high voltage region is greater than the width of the ground region.

16. 15. The light source of claim 14, wherein the width of the high voltage region is at least two times greater than the width of the ground region.

17. The light source of claim 14 , wherein a width of the plasma generation region is less than a width of the ground region.

18. The light source of claim 14 , wherein the second end of the insulating region comprises a port.

19. 20. The light source of claim 18, further comprising a gas supply port positioned at the port at the second end of the insulating region, the gas supply port providing gas to the plasma generation region.

20. 20. The light source of claim 18, wherein the port at the second end of the insulating region comprises a plasma diagnostic port.

21. 20. The light source of claim 18, wherein the port at the second end of the insulating region comprises an aperture for the passage of light.

22. 15. The light source of claim 14, further comprising a mirror positioned adjacent the ground region and oriented to reflect at least some light generated in the plasma generation region back to the plasma generation region.

23. 23. The light source of claim 22, wherein the mirror is partially transmissive such that some light generated in the plasma passes through the port.

24. The light source of claim 14 further comprising a gas supply port positioned proximate to the plasma generation region.

25. The light source of claim 14 further comprising a vacuum pump port positioned proximate to the plasma generation region.

26. 1. A method for generating light, comprising: a) providing a feed gas to a plasma confinement region in a plasma chamber; b) applying a high voltage pulse to a high voltage region connected to the plasma confinement region in the plasma chamber; c) grounding a ground region electrically connected to the high voltage region; d) applying a series of voltage pulses to at least one capacitor electrically connected to an outer magnetic core surrounding an inner magnetic core positioned around the plasma confinement region, the voltage pulses charging the at least one capacitor such that the outer magnetic core saturates, and the at least one capacitor discharging as a result couples a current pulse to the inner core into the plasma confinement region, thereby forming a plasma in a loop that is sustained between voltage pulses by leakage current, the plasma generating light that propagates through a transparent port positioned adjacent to the plasma confinement region; e) grounding an insulating region coupled to the ground region, thereby reducing attraction of ions generated in the plasma loop to the ground region; f) applying a current to an inductive core surrounding a portion of the grounded area of ​​the plasma chamber, thereby reducing current to the grounded area.

27. 27. The method of claim 26, further comprising retro-reflecting a portion of the generated light that enters the ground region back toward the plasma generation region to increase the brightness of the light passing through a transparent port positioned adjacent to the plasma confinement region.

28. 27. The method of claim 26, further comprising passing a portion of the generated light that enters the ground region through a transparent port positioned adjacent the insulating region.

29. 30. The method of claim 28, further comprising characterizing the generated light that passes through the transparent port positioned adjacent the insulating region.

30. 27. The method of claim 26, further comprising passing a diagnostic probe beam into the plasma generation region through a transparent port positioned adjacent the insulating region.

31. 31. The method of claim 30, further comprising measuring a characteristic of the plasma in response to an interaction of the diagnostic probe beam and the plasma.

32. 27. The method of claim 26, further comprising applying a gas to a port positioned adjacent the insulating region.

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