Electrodes for a discharge chamber

Abstract

An electrode for the discharge chamber is provided. A discharge chamber for a deep ultraviolet (DUV) light source includes a housing and first and second electrodes within the housing. The first and second electrodes are separated from each other to form a discharge region between the first and second electrodes, and the discharge region is configured to receive a gain medium including at least one noble gas and a halogen gas. At least one of the first and second electrodes includes a metal alloy including greater than 33% by weight and less than 50% by weight of zinc.

Description

[Technical Field]

[0001] (CROSS-REFERENCE TO RELATED APPLICATIONS)

[0001] This application claims priority to U.S. Provisional Patent Application No. 62 / 616,357, filed January 11, 2018, which is incorporated herein by reference in its entirety.

[0002] FIELD OF THE DISCLOSURE

[0002] The present disclosure relates to electrodes for discharge chambers, which may form part of, for example, deep ultraviolet light (DUV) sources. [Background technology]

[0003] Photolithography is the process of patterning semiconductor circuits on substrates such as silicon wafers. Photolithography light sources provide deep ultraviolet (DUV) light, which is used to expose photoresist on the wafer. One type of gas discharge light source used in photolithography is known as an excimer light source or laser. Excimer light sources typically use a combination of one or more noble gases, such as argon, krypton, or xenon, with a reactive, such as fluorine or chlorine. The name excimer light source comes from the fact that under the appropriate conditions of electrical stimulation (supplied energy) and high pressure (of the gas mixture), pseudo-molecules called excimers are produced, which exist only in an excited state and emit amplified light in the ultraviolet range. Excimer light sources generate a light beam with a wavelength in the deep ultraviolet (DUV) range, which is used in a photolithography tool to pattern semiconductor substrates (or wafers). Excimer light sources can be constructed using a single gas discharge chamber or multiple gas discharge chambers. Summary of the Invention

[0004] In one general aspect, a discharge chamber for a deep ultraviolet (DUV) light source includes an enclosure and first and second electrodes within the enclosure. The first and second electrodes are separated from one another to form a discharge region between the first and second electrodes, the discharge region being configured to receive a gain medium including at least one noble gas and a halogen gas. At least one of the first and second electrodes includes a metal alloy including greater than 33% by weight and less than 50% by weight of zinc.

[0005]

[0005] Implementations may include one or more of the following features. The first electrode is a cathode and the second electrode is an anode, and the second electrode may include a metal alloy including greater than 33% and less than 50% zinc by weight. The metal alloy may also include copper. The halogen gas may include fluorine. The noble gas may include argon, krypton, neon, and / or xenon. The metal alloy of the second electrode may include 35% to 50% zinc by weight. The metal alloy of the second electrode may include 37% to 50% zinc by weight. The metal alloy of the second electrode may include 40% to 50% zinc by weight. The metal alloy of the second electrode may include greater than 33% and less than 45% zinc by weight.

[0006]

[0006] The first electrode may comprise greater than 33% and less than 40% by weight zinc, and the second electrode may comprise greater than 33% and less than 50% by weight zinc.

[0007] In another general aspect, a deep ultraviolet (DUV) light source includes a master oscillator including a first master oscillator electrode and a second master oscillator electrode, the first master oscillator electrode and the second master oscillator electrode separated from one another to form a master oscillator discharge region, the master oscillator discharge region configured to receive a gain medium including a noble gas and a halogen gas, at least one of the first master oscillator electrode and the second master oscillator electrode including a metal alloy including greater than 33% and less than 50% zinc by weight, and a power amplifier on a beam path, wherein, in operational use, the master oscillator generates seed light that propagates on the beam path and is amplified by the power amplifier.

[0008] Implementations may include one or more of the following features. The power amplifier may include a first power amplifier electrode and a second power amplifier electrode separated from the first power amplifier electrode to form a power amplifier discharge region. The power amplifier discharge region is configured to receive a gain medium including a noble gas and a halogen gas. At least one of the first power amplifier electrode and the second power amplifier electrode includes a metal alloy including greater than 33% and less than 50% zinc by weight.

[0009] In another general aspect, an anode for a deep ultraviolet (DUV) light source includes a substrate of a metal alloy material including at least one metal component, and a surface on one side of the substrate, wherein, in operational use, the surface is positioned facing a cathode and a discharge region having a gain medium including a halogen gas, the metal component on the surface reacts with the halogen gas to form a protective material layer on the surface, and the protective material layer covers the entire surface after at least 30 billion discharges have occurred between the anode and the cathode.

[0010]

[0010] Implementations may include one or more of the following features: After at least 30 billion discharges occur between the anode and the cathode, the protective material layer may have a substantially uniform electrical conductivity. The protective material layer may have a substantially uniform thickness along a direction parallel to a normal to the surface. At least one metal component of the substrate may include zinc. The metal component of the substrate may be greater than 33% by weight and less than 50% by weight zinc. The substrate and the surface may form a single bulk structure of a metal alloy. The metal alloy may include a second metal component, and the second metal component may include copper. The metal alloy may also include nickel.

[0011]

[0011] In another general aspect, a method of operating a discharge chamber of a deep ultraviolet light source includes applying a voltage to a discharge chamber including a first electrode and a second electrode, the voltage being sufficient to generate a population inversion in a gaseous gain medium including a halogen gas in a discharge region between the first electrode and the second electrode; reacting a metal component in the first electrode and / or the second electrode with the halogen gas to form a protective material layer on a surface facing the discharge region; and continuing to apply and remove the voltage to the discharge chamber at timed intervals a total of at least 30 billion times sufficient to generate a pulsed light beam.

[0012] In another general aspect, an electrode configured for use in an excimer laser source includes a metal alloy including greater than 33% and less than 50% zinc by weight.

[0013]

[0013] Implementations of any of the techniques described above and herein may include processes, apparatus, electrodes, photolithography systems, DUV light sources, and / or methods. The details of one or more implementations are set forth in the accompanying drawings and the description below. Other features will be apparent from the description and drawings, and from the claims. [Brief explanation of the drawings]

[0014] [Figure 1] FIG. 1 is a block diagram of an example discharge chamber. [Figure 2]

[0015] FIG. 2A is a block diagram of an example discharge chamber.

[0016] FIG. 2B is a block diagram of the anode of the discharge chamber of FIG. 2A during steady-state operation.

[0017] FIG. 2C is a block diagram of the anode of FIG. 2B after 20 billion discharge events. [Figure 3]

[0018] FIG. 2 is a block diagram of another example of a discharge chamber. [Figure 4]

[0019] 4A-4C are photographs of exemplary electrodes.

[0020] 4D-4F are line drawings corresponding to the electrodes of FIGS. 4A-4C, respectively. [Figure 5]

[0021] FIG. 5A is a block diagram of an example photolithography system.

[0022] FIG. 5B is a block diagram of an example of a projection optical system that may be used, for example, in the photolithography system of FIG. 5A. [Figure 6]

[0023] 6A and 6B relate to exemplary experimental results for material loss in metal alloys with various weights of zinc. [Figure 7]

[0024] FIG. 2 is a block diagram of another example of a photolithography system. [Figure 8]

[0025] FIG. 8A is the amplitude of an example wafer exposure signal as a function of time.

[0026] FIG. 8B is the amplitude of an example gating signal as a function of time.

[0027] FIG. 8C is the amplitude of an example trigger signal as a function of time. [Figure 9]

[0028] 1 is an example of measured beam quality (BQ) rates as a function of discharge events. DETAILED DESCRIPTION OF THE INVENTION

[0015]

[0029] Referring to FIG. 1, a block diagram of a discharge chamber 110 is shown. Discharge chamber 110 is an example of a discharge chamber that can be part of a deep ultraviolet (DUV) light source such as those shown in FIGS. 5A and 7. Discharge chamber 110 includes an energy source 115 and a gas mixture 118 within an enclosure 112. Gas mixture 118 includes a gain medium formed from a noble gas and a halogen gas. Energy source 115 provides sufficient energy to gas mixture 118 to cause population inversion in the gain medium and generate output light beam 111 by stimulated emission. Output light beam 111 can be provided to a photolithography system such as those shown in FIGS. 5A and 7 or to another discharge chamber. Energy source 115 can be controlled to provide energy to gas mixture 118 at regular time intervals such that light beam 111 is a pulsed light beam including multiple light pulses that are separated in time from one another.

[0016]

[0030] Energy source 115 includes electrodes 114, at least one of which includes metal alloy 119. Electrodes 114 may be a pair of electrodes, one an anode and the other a cathode. The chemical composition of metal alloy 119 allows energy source 115 (and thus discharge chamber 110) to have a longer life than discharge chambers utilizing electrodes made from metal alloys conventionally used in discharge chambers of DUV light sources.

[0017]

[0031] Details of metal alloy 119 are discussed in connection with, for example, Figures 3, 4, 6A, and 6B. Operation of a discharge chamber of a DUV light source using an anode formed from conventional materials is discussed in connection with Figures 2A through 2C.

[0018]

[0032] 2A is a side cross-sectional block diagram of discharge chamber 210. Discharge chamber 210 is an example of an existing or known discharge chamber 210 that may be used in a DUV light source. Discharge chamber 210 includes cathode 214a and anode 214b. Cathode 214a and anode 214b extend generally in the xz plane along longitudinal axis 209 of discharge chamber 210. Electrodes 214a and 214b are made from a conventional metal alloy 219. Conventional metal alloy 219 may be, for example, an alloy of copper and zinc, containing 30% or less than 30% zinc by weight.

[0019]

[0033] Cathode 214a and anode 214b are separated from each other by a distance d along the y-axis, with a discharge region 216 between cathode 214a and anode 214b. Discharge region 216 includes a gas mixture 218, represented by a dotted pattern in FIG. 2A. Gas mixture 218 includes a gain medium formed from a noble gas and a halogen gas. The noble gas may be, for example, argon, krypton, and / or xenon. The halogen gas may be, for example, fluorine. Gas mixture 218 may also include a buffer gas.

[0020]

[0034] A voltage source 220 is used to create a potential difference and electric field between cathode 214a and anode 214b. The potential difference is large enough to create a discharge (electron flow, charge, or current) in gas mixture 218, ionizing at least a portion of the halogen gas in gas mixture 218. A "discharge event" is the application of a voltage that creates a potential difference sufficient to create a discharge in gas mixture 218. The electric field accelerates electrons in the gain medium, causing them to collide with neutral atoms in gas mixture 218. This collision causes electrons from a lower energy state to jump to a higher energy state, creating a population inversion within the gain medium that allows for the generation of output light beam 211 by stimulated emission.

[0021]

[0035] The ionization of the gas mixture 218 forms a halogen-containing plasma containing halogen ions that react with the metal alloy 219. The ionized gas mixture 218 is also referred to as a reactive gas. A layer 213b is formed on the surface of the anode 214b facing the discharge region 216. The layer 213b includes reaction products formed by the reaction between the metal alloy 219 and the reactive gas. The layer 213b forms after the first few discharge events. For example, the layer 213b may form after 10 or 100 discharge events.

[0022]

[0036] Layer 213b is less conductive than metal alloy 219. Compared to metal alloy 219, layer 213b is also less reactive with halogen-containing plasmas. Therefore, layer 213b acts as a passivation or protective layer. In implementations where alloy 219 includes zinc and copper and gas mixture 218 includes fluorine, fluorine ions react with zinc before reacting with copper (because zinc has a higher affinity for reaction with fluorine than copper). Therefore, protective layer 213b in these implementations is primarily zinc fluoride (ZnF2), but also includes CuF2. Also, protective layer 213a is formed on cathode 214a.

[0023]

[0037] 2B shows a side block diagram of anode 214b during steady-state operation of discharge chamber 210. During steady-state operation, discharge events occur at regular time intervals to form light pulses. Protective layer 213b may crack due to discharge events, exposing large areas of the underlying metal alloy 219. However, the exposed surface of metal alloy 219 is recoated with a new protective layer 213b', primarily ZnF, so that substantially the entire surface of electrode 214b facing discharge region 216 remains covered during steady-state operation, and the output of discharge chamber 210 is unaffected.

[0024]

[0038] Referring to FIG. 2C , which is a side block diagram of anode 214b, after many discharge events (e.g., 20 billion), protective layer 213b thickens in the y-direction. The thickening can be caused by high current and / or high temperature in protective layer 213b. As protective layer 213b thickens, mechanical stress in protective layer 213b increases. Portions of protective layer 213b begin to crumble or peel, exposing small areas (e.g., area 225) of uncoated metal alloy 219. Because metal alloy 219 in area 225 is significantly more reactive than the adjacent layer 213b, area 225 attracts nearby current, resulting in a significant temperature increase in area 225. The high local temperature in area 225 increases the reaction of metal alloy 219 with reactive gases, thereby causing a corrosion layer to begin to build up at a high rate, resulting in the growth or accumulation of corrosion products on protective layer 213b. The corrosion layer and accumulated corrosion products resulting from this runaway corrosion process are represented in Figure 2C as 224 and can be referred to as a "reef." Reef 224 is made of the same material as protective layer 213b and is believed to be a localized accumulation of corrosion products produced by the halogen-containing plasma. Reef 224 extends toward cathode 214a and is made of the same material as protective layer 213b.

[0025]

[0039] Metal alloy 219 has a higher electrical conductivity than protective layer 213b. Therefore, small exposed area 225 attracts arcs formed during a discharge event more strongly than protective layer 213b, resulting in a non-uniform electric field and arc formation in discharge region 216. Arc formation is undesirable because it can absorb energy from the gain medium that would otherwise be used to form optical beam 211. Accelerated degradation of protective layer 213b causes protective layer 213b to become spatially and electrically non-uniform, preventing it from reliably generating beam 211. When beam 211 can no longer be reliably generated, discharge chamber 210 cannot function properly and has reached the end of its life. Thus, the formation of rocks 224 shortens the life of discharge chamber 210. Discharge chambers 210 including cathode 214a and anode 214b fabricated from conventional metal alloy 219 begin to develop rocks after approximately 18 billion discharge events and have a life of approximately 30 billion discharge events or less.

[0026]

[0040] Referring to Figure 3, a cross-sectional side block diagram of discharge chamber 310 is shown. Discharge chamber 310 is an example of a discharge chamber that may be part of a deep ultraviolet (DUV) light source such as those shown in Figures 5A and 7. Discharge chamber 310 includes electrodes 314a and 314b within housing 312. In the example of Figure 3, electrode 314a is a cathode and electrode 314b is an anode. Anode 314b includes metal alloy 319b. The chemical composition of metal alloy 319b provides a more robust protective layer, thereby extending the life of discharge chamber 310 compared to discharge chamber 210.

[0027]

[0041] Cathode 314a and anode 314b extend generally in the xz plane along a direction parallel to longitudinal axis 309 of discharge chamber 310. Cathode 314a is separated from anode 314b by a distance d along the y axis, and between cathode 314a and anode 314b is discharge region 316. Discharge region 316 contains gas mixture 218.

[0028]

[0042] Ionization of gas mixture 218 forms a halogen-containing plasma containing halogen ions that react with metal alloy 319b. The reaction of metal alloy 319b with the halogen ions forms a protective layer 313b on the surface of electrode 314b facing discharge region 316.

[0029]

[0043] The metal alloy 319b has a chemical composition that results in a more robust protective layer 313b than the protective layer 219b discussed in connection with FIGS. 2A-2C. For example, compared to the protective layer 219b, the protective layer 313b adheres more strongly to the bulk metal alloy 319b, making it less susceptible to cracking. This reduces or eliminates exposure of the underlying bulk metal alloy 319b. Furthermore, the layer 313b can remain spatially and / or electrically uniform over many more discharge events than electrodes made of metal alloys conventionally used in the discharge chambers of DUV light sources. The protective layer 313b can cover substantially all of the portion of the electrode 314b facing the discharge region 316 and / or have uniform conductivity, even after 30-60 billion discharge events. In contrast, protective layers formed by electrodes made of conventional metal alloys typically crack and have non-uniform conductivity after approximately 20 billion discharge events. In this manner, the use of metal alloy 319b increases the number of discharge events that electrode 314b can withstand, thereby extending the life of discharge chamber 310.

[0030]

[0044] Metal alloy 319b may be, for example, a copper-zinc alloy containing 33%-50% zinc, 33.5%-40% zinc, 35%-50% zinc, 37%-50% zinc, 40%-50% zinc, or 33%-45% zinc by weight. Metal alloy 319b may be, for example, 33.5% zinc, 37% zinc, or 45% zinc by weight. In some implementations, metal alloy 319b also includes nickel.

[0031]

[0045] Additionally or alternatively, cathode 314a may include a metal alloy 319a having a different chemical composition than the conventional metal alloy 219 discussed in connection with Figures 2A-2C, such as a copper-zinc alloy containing 33% to 40% zinc by weight.

[0032]

[0046] These compositions differ from typical metal alloys used in electrodes in discharge chambers of DUV light sources, such as alloy 219 discussed in connection with FIGS. 2A-2C. Typical metal alloys for electrodes in DUV discharge chambers include copper and zinc alloys, but with a lower zinc weight percentage than metal alloy 319b. For example, a typical anode used in the discharge chambers of DUV light sources is made of a copper and zinc alloy with 30% zinc by weight. Applicant has discovered that increasing the zinc weight percentage produces an electrode that supports a more robust protective layer. Zinc reacts more readily with fluorine than copper with halogen gases. For example, a protective layer formed from a copper and zinc alloy in the presence of ionized fluorine is zinc fluoride. Increasing the zinc percentage in the metal alloy is believed to increase the zinc exposure to the halogen-containing plasma formed in discharge region 316. This results in more zinc fluoride being formed, resulting in a more robust protective layer 313b. However, because zinc has a relatively high vapor pressure, alloys with more than about 50 wt. % zinc evaporate easily and do not form a robust protective layer. Thus, although the zinc content of metal alloy 319b is higher than that of conventional electrodes, the zinc concentration in metal alloy 319b is not so high that evaporation dominates over the formation of a protective layer.

[0033]

[0047] 4A to 4C, scanning electron microscope photographs are shown of protective layers 413_1, 413_2, and 413_3 formed on electrodes 414_1, 414_2, and 414_3, respectively. Protective layers 413_1, 413_2, and 413_3 are formed on boundaries 422_1, 422_2, and 422_3 on bulk substrate 419 of electrodes 414_1, 414_2, and 414_3, respectively. FIG. 4D is an approximate line drawing of electrode 414_1. FIG. 4E is an approximate line drawing of electrode 414_2. FIG. 4F is an approximate line drawing of electrode 414_3.

[0034]

[0048] Electrode 414_1 was formed from a metal alloy containing zinc and copper, with 5% zinc by weight. Electrode 414_2 was formed from a metal alloy containing zinc and copper, with 30% zinc by weight. Electrode 414_3 was formed from a metal alloy containing zinc and copper, with 45% zinc by weight. Each of electrodes 414_1, 414_2, and 414_3 was exposed to ionized fluorine gas at a temperature of 450°C for two hours. Because the thicknesses of the protective layers formed on electrodes 414_1, 414_2, and 414_3 were similar to those formed on electrodes used in discharge chambers, the temperature of 450°C is considered to be approximately the same as the surface temperature of the electrodes in an actual discharge chamber during chamber operation.

[0035]

[0049] As shown in the photograph, the protective layer 413_3 is more spatially uniform than the protective layers 413_1 and 413_2. The protective layer 413_3 is also denser than the protective layers 413_1 and 413_2 and is firmly bonded to the underlying bulk metal alloy. The appearance of the protective layer 413_3 indicates that it is more robust than the protective layers 413_1 and 413_2 formed on the electrodes 414_1 and 414_3, respectively.

[0036]

[0050] 5A and 7 provide examples of DUV light sources that can use electrodes comprising metal alloys such as alloy 119 or 319b.

[0037]

[0051] 5A and 5B, photolithography system 500 includes an optical (or light) source 505 that provides a light beam 511 to a lithography exposure apparatus 569. Lithography exposure apparatus 569 processes a wafer 570 supported by a wafer holder or stage 571. Light source 505 includes a discharge chamber 510 that houses a cathode 514a and an anode 514b. Although only one gas discharge chamber 510 is shown in FIG. 5A, light source 505 may include more than one discharge chamber.

[0038]

[0052] Light beam 511 is a pulsed light beam that includes light pulses that are separated in time from one another. Lithography exposure apparatus 569 includes a projection optical system 575 through which light beam 511 passes before reaching wafer 570. Lithography exposure apparatus 569 also includes a metrology system 572. Metrology system 572 may include, for example, a camera or other device capable of capturing an image of wafer 570 and / or light beam 511 at wafer 570, or an optical detector capable of capturing data describing characteristics of light beam 511, such as the intensity of light beam 511 in the x-y plane at wafer 570. Lithography exposure apparatus 569 may be an immersion system or a dry system. Photolithography system 500 also includes a control system 550 for controlling light source 505 and / or lithography exposure apparatus 569.

[0039]

[0053] For example, microelectronic features are formed on wafer 570 by exposing a layer of radiation-sensitive photoresist material on wafer 570 with light beam 511. Referring also to FIG. 5B, projection optical system 575 includes a slit 576, a mask 574, and a projection objective including a lens system 577. Lens system 577 includes one or more optical elements. Light beam 511 enters optical system 575 and strikes slit 576, with at least a portion of beam 511 passing through slit 576. In the example of FIGS. 5A and 5B, slit 576 is rectangular and shapes light beam 511 into an elongated, rectangular light beam. Mask 574 has a pattern formed thereon, which determines which portions of the shaped light beam are transmitted through mask 574 and which portions are blocked by mask 574. The design of the pattern is determined by the particular microelectronic circuit design to be formed on wafer 570.

[0040]

[0054] The cathode 514a and / or the anode 514b include a metal alloy having a composition that forms a more robust protective layer than metal alloys conventionally used in the discharge chambers of DUV light sources. For example, the anode 514b may be a copper-zinc alloy containing 33% to 50% zinc by weight, 33.5% to 40% zinc by weight, 35% to 50% zinc by weight, 37% to 50% zinc by weight, 40% to 50% zinc by weight, or 33% to 45% zinc by weight. The metal alloy used in the anode 514b may be, for example, 33.5% zinc by weight, 37% zinc by weight, or 45% zinc by weight. It is further believed that electrode compositions suitable for various applications may include about 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 40%, 42%, 44%, 46%, 48%, or 50% zinc, or any range therebetween (e.g., 33%-38%).

[0041]

[0055] In some implementations, only the anode uses a metal alloy with an increased zinc content. In other implementations, both the cathode 514a and the anode 514b include a metal alloy with a higher zinc content by weight than metal alloys traditionally used in DUV light source discharge chambers. Increasing the amount of zinc in the cathode 514a reduces the material loss rate of the cathode 514a. However, increasing the amount of zinc in the cathode 514a increases the material loss rate of the anode 514b. Therefore, to achieve optimal performance of the discharge chamber 510, the amount of zinc in the metal alloy used for the cathode 514a and the anode 514b may differ from the amount expected to result in the lowest material loss rate.

[0042]

[0056] 6A and 6B examine experimental results related to the rate of material loss for metal alloy segments containing various amounts of zinc after exposure to ionized fluorine gas. The rate of material loss represents a measure of the amount of material lost along the y-axis from the segment due to exposure to ionized fluorine gas. Higher amounts of material loss indicate higher reactivity of the metal alloy-containing segments.

[0043]

[0057] FIG. 6A shows a side view block diagram of cathode 614a and anode 614b. Cathode 614a and anode 614b are parallel to each other and extend along the x-axis. Cathode 614a includes segments 1-7, which are in physical contact with each other and extend along the x-axis. Anode 614b includes a copper and zinc metal alloy, with zinc being 37% by weight of the metal alloy. Segments 1-7 were also copper and zinc metal alloys. To assess the effect of zinc content in the cathode, the amount of zinc in each of segments 1-7 was varied. Segments 2 and 5 included 15% by weight zinc, segment 3 included 33.5% by weight zinc, segment 4 included 37% by weight zinc, and segments 1, 6, and 7 included 30% by weight zinc. The amount of zinc in anode 614b was 37% throughout anode 614b.

[0044]

[0058] After 10.035 billion discharge events (or generated pulses), the amount of corrosion or material loss was measured. An electrode scanner was used to measure the height profiles of segments 1-7. The heights of segments 1-7 are the range along the y-axis. For each segment, the height profile was measured at two or more locations along the x-axis. The measured heights of a segment were averaged, and this average was used as the measured height for that segment. Material loss was determined from the initial height of the segment and the measured height of that segment after exposure to ionized fluorine gas.

[0045]

[0059] Figure 6B shows the measured material loss rate in microns (μm) per billion pulses (BP) for cathode segments 2-4 and 6 and anode 614b. In Figure 6B, the material loss rate is plotted as a function of segment identifier. Plot 680 represents the material loss rate for cathode 614a, and plot 681 represents the material loss rate for anode 614b.

[0046]

[0060] The material loss rate of anode 614b for a particular cathode segment is the material loss rate measured for the portion of anode 614b aligned on the y-axis with the cathode segment. Although anode 614b has a constant zinc content along the x-axis, the material loss rate of anode 614b varies with the change in zinc content in segments 1 through 7. Segment 2 (15 wt% zinc) had a cathode material loss rate of 27 μm / BP and an anodic material loss rate of 43 μm / BP. Segment 6 (30 wt% zinc) had a cathode material loss rate of 18 μm / BP and an anodic material loss rate of 49 μm / BP. Segment 3 (33.5 wt% zinc) had a cathode material loss rate of 13 μm / BP and an anodic corrosion rate of 51 μm / BP. Segment 4 (37 wt% zinc) had a cathode corrosion rate of 11 μm / BP and an anodic corrosion rate of 55 μm / BP.

[0047]

[0061] Thus, as the amount of zinc in cathode 614a increased, the cathode material loss rate decreased. A reduced material loss rate is generally beneficial and leads to a longer discharge chamber life. However, increasing the amount of zinc in the cathode also resulted in an increased material loss rate in anode 614b. Therefore, in some implementations where both the anode and cathode contain a metal alloy with a higher zinc content by weight than metal alloys traditionally used in discharge chambers of DUV light sources, the amount of zinc in the cathode can be less than the amount of zinc in the anode to balance cathode and anodic corrosion. For example, referring again to FIG. 5A , anode 514b can be made from a metal alloy containing copper and zinc, with the zinc content ranging from 33% to 50% by weight, and cathode 514a can be made from a metal alloy containing copper and zinc, with the zinc content ranging from 33% to 40% by weight. In some implementations, the anode 514b may be made from a metal alloy including copper and zinc, with the zinc being 37% by weight, and the cathode 514a may be made from a metal alloy including copper and zinc, with the zinc being 33% by weight.

[0048]

[0062] The amount of material loss for two segments with the same amount of zinc but located in different parts of the discharge chamber may differ due to non-uniformity in the discharge chamber. For example, segments 2 and 5 both contain a copper-zinc metal alloy with 15% zinc by weight. The material loss rate for segment 2 was 27 μm / BP, and the material loss rate for segment 5 was 24 μm / BP. However, the difference in material loss rate due to location was observed to be less significant than the difference in material loss rate due to zinc content, so the conclusion regarding the effect of zinc content on material loss rate remains unchanged.

[0049]

[0063] Referring to FIG. 7, a block diagram of photolithography system 700 is shown. System 700 is one example of an implementation of system 500 (FIG. 5A). For example, photolithography system 700 uses light source 705 as light source 505 (FIG. 5A). Light source 705 generates a pulsed light beam 711, which is provided to lithography exposure apparatus 569. Photolithography system 700 also includes a control system 750. In the example of FIG. 7, control system 750 is connected to components of light source 705 and lithography exposure apparatus 569 to control various operations of system 700. In other implementations, control system 750 can be implemented as two separate control systems, one controlling various aspects of light source 705 and the other controlling the lithography exposure apparatus.

[0050]

[0064] 7, the light source 705 is a two-stage laser system and includes a master oscillator (MO) 701 that provides a seed light beam 706 to a power amplifier (PA) 702. The MO 701 and PA 702 can be considered subsystems of the light source 705, or systems that are part of the light source 705. The power amplifier 702 receives the seed light beam 706 from the master oscillator 701 and amplifies the seed light beam 706 to generate a light beam 711 for use in the lithography exposure tool 569. For example, the master oscillator 701 may emit a pulsed seed light beam having a seed pulse energy of about 1 millijoule (mJ) per pulse, and these seed pulses may be amplified by the power amplifier 702 to about 10-15 mJ.

[0051]

[0065] The master oscillator 701 includes a discharge chamber 710_1 having two elongated electrodes 714a_1 and 714b_1, a gain medium 718_1 that is a gas mixture, and a fan (not shown) for circulating the gas mixture between the electrodes 714a_1 and 714b_1. The electrodes 714a_1 and / or 714b_1 are formed from a metal alloy containing copper and zinc, with a higher zinc concentration by weight than metal alloys typically used in DUV master oscillator discharge chambers. In the illustrated example, the electrode 714a_1 is the cathode and the electrode 714b_1 is the anode. The cathode 714a_1 may contain 33% to 40% zinc by weight, and the anode 714b_1 may contain 33% to 50% zinc by weight.

[0052]

[0066] A resonator is formed between a line narrowing module 780 on one side of the discharge chamber 710_1 and an output coupler 781 on the second side of the discharge chamber 710_1. The line narrowing module 780 may include a diffractive optical element, such as a grating, that fine-tunes the spectral output of the discharge chamber 710_1. The light source 705 also includes a line center analysis module 784 that receives the output light beam from the output coupler 781 and a beam combining optical system 738. The line center analysis module 784 is a measurement system that can be used to measure or monitor the wavelength of the seed light beam 706. The line center analysis module 784 may be located elsewhere within the light source 705 or at the output of the light source 705.

[0053]

[0067] The gas mixture 718_1 can be any gas suitable for producing a light beam of the wavelength and bandwidth required for the application. In an excimer source, the gas mixture can include a noble gas, such as argon or krypton, a halogen, such as fluorine or chlorine, and a trace amount of xenon in addition to a buffer gas, such as helium. Specific examples of gas mixtures include argon fluoride (ArF), which emits light at a wavelength of approximately 193 nm, krypton fluoride (KrF), which emits light at a wavelength of approximately 248 nm, or xenon chloride (XeCl), which emits light at a wavelength of approximately 351 nm. The excimer gain medium (gas mixture) is excited with short (e.g., nanosecond) current pulses of a high-voltage discharge generated by applying a voltage to the elongated electrodes 714a_1 and 714b_1.

[0054]

[0068] Power amplifier 702 includes a beam combining optical system 783 that receives seed light beam 706 from master oscillator 701 and directs it through discharge chamber 710_2 to beam conditioning optical element 782. Beam conditioning optical element 782 redirects or changes seed light beam 706 so as to return it to discharge chamber 710_2. The beam conditioning optical element and beam combining optical system 783 form a circulating closed loop path in which the input to the ring amplifier intersects with the output of the ring amplifier at beam combining device 783.

[0055]

[0069] Discharge chamber 710_2 includes a pair of elongated electrodes 714a_2 and 714b_2, a gas mixture 718_2, and a fan (not shown) for circulating gas mixture 718_2 between electrodes 714a_2 and 714b_2. Gas mixture 718_2 may be identical to gas mixture 718_1. Electrode 714a_2 and / or electrode 714b_2 may be fabricated from a metal alloy containing copper and zinc, with a higher zinc concentration by weight than metal alloys typically used in DUV master oscillator discharge chambers. In the illustrated example, electrode 714a_2 is the cathode and electrode 714b_2 is the anode. Cathode 714a_2 may include 33% to 40% zinc by weight, and anode 714b_2 may include 33% to 50% zinc by weight.

[0056]

[0070] The output light beam 711 may reach the lithography exposure apparatus 569 after being directed through a beam conditioning system 785. The beam conditioning system 785 may include a bandwidth analysis module that measures various parameters (such as bandwidth or wavelength) of the beam 711. The beam conditioning system 785 may also include a pulse stretcher (not shown) that stretches each pulse in time of the output light beam 711. The beam conditioning system 785 may also include other components that can act on the beam 711, such as reflective and / or refractive optical elements (such as lenses and mirrors), filters, and optical apertures (including automatic shutters).

[0057]

[0071] Photolithography system 700 also includes a control system 750. Control system 750 can send one or more signals to light source 705 to control when light source 705 emits a light pulse or a light pulse burst containing one or more light pulses. Control system 750 is also connected to lithography exposure apparatus 569. Thus, control system 750 can also control various aspects of lithography exposure apparatus 569. For example, control system 750 can control the exposure of wafer 570 (FIG. 5B) and therefore can be used to control how electronic features are printed on wafer 570. In some implementations, control system 750 can control the scanning of wafer 570 by controlling the movement of slit 576 in the x-y plane (FIG. 5B). Control system 750 can also exchange data with metrology system 572 and / or optical system 575 (FIG. 5B).

[0058]

[0072] The lithography exposure apparatus 569 may also include, for example, temperature control devices (such as air conditioning and / or heating devices) and / or power supplies for various electrical components. The control system 750 may also control these components. In some implementations, the control system 750 includes two or more sub-control systems, and is implemented such that at least one sub-control system (lithography controller) is dedicated to controlling aspects of the lithography exposure apparatus 569. In these implementations, the control system 750 may be used to control aspects of the lithography exposure apparatus 569 instead of or in addition to using a lithography controller.

[0059]

[0073] Control system 750 includes an electronic processor 751, electronic storage 752, and an I / O interface 753. Electronic processor 751 includes one or more processors suitable for executing computer programs, such as general-purpose or special-purpose microprocessors, and one or more processors of any type of digital computer. Typically, an electronic processor receives instructions and data from a read-only memory, a random-access memory, or both. Electronic processor 751 may be any type of electronic processor.

[0060]

[0074] Electronic storage 752 may be volatile memory, such as RAM, or non-volatile memory. In some implementations, electronic storage 752 includes both non-volatile and volatile portions or components. Electronic storage 752 may store data and information used in the operation of control system 750, components of control system 750, and / or systems controlled by control system 750. This information may be stored, for example, in a lookup table or database.

[0061]

[0075] The electronic storage 752 may also store instructions, possibly as a computer program, that when executed cause the processor 751 to communicate with the control system 750, the optical system 705, and / or components within the lithographic exposure apparatus 569.

[0062]

[0076] I / O interface 753 is any type of electronic interface that allows control system 750 to receive and / or provide data and signals from an operator, optical system 705, lithography exposure apparatus 569, any component or system within optical system 705 and / or lithography exposure apparatus 569, and / or an automated process running on another electronic device. For example, I / O interface 753 may include one or more of a visual display, a keyboard, and a communications interface.

[0063]

[0077] 8A-8C illustrate an overview of pulse and burst generation in light source 705. Light beam 711 is a pulsed light beam and may include one or more pulse bursts separated in time from one another. Each burst may include one or more light pulses. In some implementations, a burst may include hundreds of pulses, e.g., 100-400 pulses. FIG. 8A illustrates the amplitude of wafer exposure signal 800 as a function of time, FIG. 8B illustrates the amplitude of gating signal 815 as a function of time, and FIG. 8C illustrates the amplitude of a trigger signal as a function of time.

[0064]

[0078] Control system 850 can be configured to send wafer exposure signal 800 to light source 705 to control light source 705 to generate light beam 711. In the example shown in Figure 7A, wafer exposure signal 800 has a high value 805 (e.g., 1) during time periods 807 when light source 705 generates light pulse bursts. Wafer exposure signal 800 has a low value 810 (e.g., 0) when wafer 570 is not being exposed.

[0065]

[0079] 8B, the light beam 711 is a pulsed light beam, and the light beam 711 includes pulse bursts. The control system 750 also controls the duration and frequency of the pulse bursts by sending a gating signal 815 to the light source 705. The gating signal 815 has a high value 820 (e.g., 1) during the pulse bursts and a low value 825 (e.g., 0) for the time between successive bursts. In the illustrated example, the duration that the gating signal 815 has a high value is also the duration of a burst 816. The bursts are separated in time by an inter-burst time interval. During the inter-burst time interval, the lithography exposure apparatus 569 can position the next die on the wafer 570 for exposure.

[0066]

[0080] 8C, control system 750 also controls the repetition rate of the pulses within each burst via trigger signal 830. Trigger signal 830 includes triggers 840, one of which is provided to light source 705 to cause light source 705 to generate one light pulse. Control system 750 can send trigger 840 to light source 705 each time a pulse is to be generated. Thus, the repetition rate of the pulses generated by light source 705 (the time between two consecutive pulses) can be set by trigger signal 830.

[0067]

[0081] When the gain medium of gas mixture 718_1 or gas mixture 718_2 is excited by applying a voltage to electrodes 714a_1, 714b_1, or 714a_2, 714b_2, the gain medium of the gas mixture emits light. As discussed above, this application of voltage is a discharge event. When a voltage is applied to the electrodes at regular time intervals, light beam 711 is pulsed. The repetition rate of pulsed light beam 711 is therefore determined by the rate at which the voltage is applied to the electrodes. For example, trigger signal 830 can be used to control the application of voltage to the electrodes and the pulse repetition rate. The pulse repetition rate can range from about 500 to about 6,000 Hz for most applications. In some implementations, the repetition rate can be greater than 6,000 Hz, for example, 12,000 Hz or greater.

[0068]

[0082] FIG. 9 is a plot showing a measured master oscillator beam quality (BQ) rate as a function of generated pulse or discharge events. The data in FIG. 9 was obtained from a master oscillator such as MO 701 in FIG. 7. The BQ rate indicates how many beam quality events occurred in the source 705. A beam quality event occurs when any aspect of the seed light beam 706 or beam 711 does not meet predetermined specifications. For example, a beam quality event occurs when the optical energy, spectral bandwidth, and / or wavelength of beam 706 or 711 is outside of acceptable ranges. The BQ rate in FIG. 9 is the number of beam quality events (or BQ counts) per billion generated pulses or discharge events. In the example of FIG. 9, the upper limit of the acceptable BQ rate for MO 701 was 50.

[0069]

[0083] In the example of Figure 9, plot 991 (dashed line) represents the BQ rate (BQ counts per billion pulses) for a system in which anode 714a_1 and anode 714b_1 of MO701 were made from a conventional copper-zinc alloy with 30 wt% zinc. Plot 992 (dashed line) represents the BQ rate for a system in which anode 714b_1 was made from a copper-zinc alloy with 33.5 wt% zinc. Plot 993 (solid line) represents the BQ rate for a system in which anode 714b_1 was made from a copper-zinc alloy with 37 wt% zinc.

[0070]

[0084] As shown by comparing plots 992 and 993 with plot 991, increasing the zinc content of electrode 714b_1 allows MO701 to generate more pulses of seed light beam 706 without exceeding the BQ rate limit. For example, a system with an anode made from a conventional alloy exceeds the BQ rate limit near 22 BP. Systems with anodes having 33.5 wt. % zinc and 37 wt. % zinc had poor beam quality rates up to and above 40 BP. The electrode with 33.5 wt. % zinc formed rocks near 35 BP, while the electrode with 37 wt. % zinc did not form rocks at 50 BP. Thus, increasing the amount of zinc in the discharge chamber electrodes improved the performance of MO701 compared to using conventional metal alloys.

[0071]

[0085] The following clauses can be used to further describe the embodiments. 1. A discharge chamber for a deep ultraviolet (DUV) light source, comprising: The housing and a first electrode and a second electrode within the housing, the first electrode and the second electrode being separated from one another to form a discharge region between the first electrode and the second electrode, the discharge region being configured to receive a gain medium including at least one noble gas and a halogen gas; A discharge chamber wherein at least one of the first electrode and the second electrode comprises a metal alloy comprising greater than 33% and less than 50% by weight zinc. 2. The discharge chamber of clause 1, wherein the first electrode is a cathode and the second electrode is an anode, and the second electrode comprises a metal alloy containing greater than 33% by weight and less than 50% by weight zinc. 3. The discharge chamber of clause 2, wherein the metal alloy further comprises copper. 4. The discharge chamber of clause 3, wherein the halogen gas comprises fluorine. 5. The discharge chamber of clause 4, wherein the noble gas comprises argon, krypton, neon, and / or xenon. 6. The discharge chamber of clause 5, wherein the metal alloy of the second electrode comprises 35% to 50% zinc by weight. 7. The discharge chamber of clause 5, wherein the metal alloy of the second electrode comprises 37% to 50% zinc by weight. 8. The discharge chamber of clause 5, wherein the metal alloy of the second electrode comprises 40% to 50% zinc by weight. 9. The discharge chamber of clause 5, wherein the metal alloy of the second electrode comprises greater than 33% and less than 45% by weight zinc. 10. The discharge chamber of clause 2, wherein the first electrode comprises greater than 33% and less than 40% by weight zinc, and the second electrode comprises greater than 33% and less than 50% by weight zinc. 11. A deep ultraviolet (DUV) light source, comprising: a master oscillator including a first master oscillator electrode and a second master oscillator electrode, the first master oscillator electrode and the second master oscillator electrode being separated from one another to form a master oscillator discharge region, the master oscillator discharge region being configured to receive a gain medium including a noble gas and a halogen gas, and at least one of the first master oscillator electrode and the second master oscillator electrode including a metal alloy including greater than 33% and less than 50% zinc by weight; a power amplifier on the beam path, wherein in operational use the master oscillator generates seed light that propagates on the beam path and is amplified by the power amplifier. DUV light source. 12. A power amplifier is a first power amplifier electrode; a second power amplifier electrode separated from the first power amplifier electrode to form a power amplifier discharge region, the power amplifier discharge region configured to receive a gain medium including a noble gas and a halogen gas, and at least one of the first power amplifier electrode and the second power amplifier electrode includes a metal alloy including greater than 33% by weight and less than 50% by weight of zinc. 13. An anode for a deep ultraviolet (DUV) light source, comprising: a substrate of a metal alloy material including at least one metal component; a surface of one side of the substrate; wherein, in operational use, the surface is positioned opposite a cathode and a discharge region having a gain medium including a halogen gas; the metal components at the surface react with the halogen gas to form a protective material layer on the surface; After at least 30 billion discharges occur between the anode and cathode, a protective material layer covers the entire surface, the anode. 14. The anode of clause 13, wherein the protective material layer has a substantially uniform electrical conductivity after at least 30 billion discharges occur between the anode and the cathode. 15. The anode of clause 13, wherein the protective material layer has a substantially uniform thickness along a direction parallel to the normal to the surface. 16. The anode of clause 13, wherein at least one metal component of the substrate comprises zinc. 17. The anode of clause 16, wherein the metal content of the substrate is greater than 33% by weight and less than 50% by weight zinc. 18. The anode of clause 13, wherein the substrate and the surface form a single bulk structure of the metal alloy. 19. The anode of clause 16, wherein the metal alloy comprises a second metal component, and the second metal component comprises copper. 20. The anode of claim 19, wherein the metal alloy further comprises nickel. 21. A method of operating a discharge chamber of a deep ultraviolet light source, comprising: applying a voltage to a discharge chamber including a first electrode and a second electrode, the voltage being sufficient to generate a population inversion in a gaseous gain medium including a halogen gas in a discharge region between the first electrode and the second electrode; reacting a metal component in the first electrode and / or the second electrode with a halogen gas to form a protective material layer on the surface facing the discharge region; applying and removing a voltage sufficient to generate a population inversion to the discharge chamber at timed intervals totaling at least 30 billion times to generate a pulsed light beam; A method comprising: 22. An electrode configured for use in an excimer laser source, the electrode comprising a metal alloy containing greater than 33% and less than 50% by weight zinc.

[0072]

[0086] Other implementations are within the scope of the claims.

Claims

1. 1. A discharge chamber for a deep ultraviolet (DUV) light source, comprising: The housing and an anode and a cathode within the housing, the anode and the cathode being separated from one another to form a discharge region between the anode and the cathode, the discharge region being configured to receive a gain medium comprising at least one noble gas and a fluorine gas; the anode consists of only a single anode bulk material, and the cathode consists of only a single cathode bulk material; the anode bulk material comprises a metal alloy comprising copper and 35% to 50% by weight of zinc; Discharge chamber.

2. 10. The discharge chamber of claim 1, wherein the cathode bulk material comprises a metal alloy containing 33% to 40% zinc by weight.

3. 10. The discharge chamber of claim 1, wherein the anode bulk material comprises a metal alloy containing 36% to 48% zinc by weight.

4. A discharge chamber as described in claim 1, wherein the noble gas includes argon, krypton, neon, and / or xenon.

5. 1. A deep ultraviolet (DUV) light source, comprising: a master oscillator including a master oscillator anode and a master oscillator cathode, the master oscillator anode and the master oscillator cathode being separated from one another to form a master oscillator discharge region, the master oscillator discharge region being configured to receive a gain medium including a noble gas and a fluorine gas; the main oscillator anode is comprised of only a single anode bulk material, and the main oscillator cathode is comprised of only a single cathode bulk material; a master oscillator, wherein the anode bulk material comprises a metal alloy including copper and 35% to 50% by weight of zinc; a power amplifier on the beam path, wherein in operational use the master oscillator generates seed light that propagates on the beam path and is amplified by the power amplifier. DUV light source.

6. The output amplifier an output amplifier anode; a power amplifier cathode separated from the power amplifier anode to form a power amplifier discharge region, the power amplifier discharge region configured to receive a gain medium comprising a noble gas and a fluorine gas, the power amplifier anode consisting of only a single anode bulk material, the power amplifier cathode consisting of only a single cathode bulk material, the anode bulk material of the power amplifier anode comprising a metal alloy including copper and 35 to 50 weight percent zinc.

7. 1. An anode for a deep ultraviolet (DUV) light source, comprising: a substrate consisting of only a single bulk material comprising a metal alloy containing copper and 33% to 50% by weight of zinc; a surface on one side of the substrate; wherein, in operational use, the surface is positioned opposite a cathode and a discharge region having a gain medium comprising fluorine gas; metal components on the surface react with the fluorine gas to form a protective material layer on the surface; an anode, wherein the protective material layer covers the entire surface after at least 30 billion discharges have occurred between the anode and the cathode;

8. 8. The anode of claim 7, wherein after at least 30 billion discharges occur between the anode and the cathode, the protective material layer has a substantially uniform electrical conductivity, and the protective material layer has a substantially uniform thickness along a direction parallel to a normal to the surface.

9. 8. The anode of claim 7, wherein the metal alloy comprises 35% to 50% by weight zinc.

10. 10. The anode of claim 9, wherein the metal alloy further comprises nickel.

11. 1. A discharge chamber for a deep ultraviolet (DUV) light source, comprising: The housing and an anode and a cathode within the housing, the anode and the cathode being separated from one another to form a discharge region between the anode and the cathode, the discharge region being configured to receive a gain medium comprising at least one noble gas and a fluorine gas; the anode consists of only a single anode bulk material, and the cathode consists of only a single cathode bulk material; the anode bulk material comprises a metal alloy comprising copper and 35% to 50% by weight of zinc; the cathode bulk material comprises a metal alloy comprising copper and 33% to 40% by weight of zinc; the metal alloy further comprises copper; Discharge chamber.

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