Discharge electrode, method for manufacturing discharge electrode, and method for manufacturing electronic device

Abstract

A discharge electrode according to one perspective of the present disclosure is used in a gas laser device that excites a laser gas including fluorine via discharging, and comprises a cathode electrode that extends in one direction, and an anode electrode that extends in the one direction and that is disposed facing the cathode electrode in a discharging direction that is orthogonal to the one direction. The cathode electrode and / or the anode electrode has an electrode base material that includes a metal, and a dielectric that is provided to a pair of side surfaces of the electrode base material and that includes a first layer having voids. The porosity of the first layer is 0.5 to 25%.

Description

[Technical Field]

[0001] The present disclosure relates to a discharge electrode, a method for manufacturing a discharge electrode, and a method for manufacturing an electronic device. [Background technology]

[0002] In recent years, semiconductor exposure devices have been required to improve their resolution in response to the miniaturization and high integration of semiconductor integrated circuits. To this end, the wavelength of light emitted from exposure light sources has been shortened. For example, KrF excimer laser devices, which output laser light with a wavelength of approximately 248 nm, and ArF excimer laser devices, which output laser light with a wavelength of approximately 193 nm, are used as gas laser devices for exposure.

[0003] The spectral linewidth of the spontaneously oscillating light from KrF excimer laser devices and ArF excimer laser devices is as wide as 350 to 400 pm. Therefore, if a projection lens is constructed using a material that transmits ultraviolet light, such as KrF and ArF laser light, chromatic aberration may occur. As a result, resolution may decrease. Therefore, it is necessary to narrow the spectral linewidth of the laser light output from the gas laser device to a level where chromatic aberration is negligible. Therefore, a line narrowing module (LNM) containing a line narrowing element (e.g., an etalon or grating) may be installed inside the laser resonator of the gas laser device to narrow the spectral linewidth. Hereinafter, a gas laser device with a narrowed spectral linewidth is referred to as a line narrowing gas laser device. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Summary of JP 2004-179599 A

[0005] A discharge electrode according to one aspect of the present disclosure is a discharge electrode used in a gas laser device that excites a fluorine-containing laser gas by discharge, and comprises a cathode electrode that extends in one direction and an anode electrode that extends in one direction and is arranged opposite the cathode electrode in a discharge direction that is perpendicular to the one direction, at least one of the cathode electrode and the anode electrode has an electrode base material that includes a metal and a dielectric that includes a first layer having voids provided on a pair of side surfaces of the electrode base material, and the porosity of the first layer is within the range of 0.5% or more and 25% or less.

[0006] A method for manufacturing a discharge electrode according to one aspect of the present disclosure is a method for manufacturing a discharge electrode used in a gas laser device, and includes a step of forming a dielectric on a side surface of an electrode substrate containing a metal, the step of forming the dielectric including a first step of forming a first layer having voids by thermally spraying a dielectric material on the side surface of the electrode substrate, and a second step of forming a second layer having a porosity different from that of the first layer by thermally spraying a dielectric material on the surface of the first layer formed on the side surface of the electrode substrate.

[0007] A method for manufacturing an electronic device according to one aspect of the present disclosure is a method for manufacturing an electronic device, the method comprising: generating laser light using a gas laser device that excites a laser gas containing fluorine by discharge using a discharge electrode comprising: a cathode electrode extending in one direction; and an anode electrode extending in one direction and arranged opposite the cathode electrode in a discharge direction perpendicular to the one direction, at least one of the cathode electrode and the anode electrode having an electrode base material containing metal and a dielectric including a first layer having voids provided on a pair of side surfaces of the electrode base material, the porosity of the first layer being within the range of 0.5% or more and 25% or less; outputting the laser light to an exposure device; and exposing a photosensitive substrate to the laser light in the exposure device to manufacture an electronic device. [Brief explanation of the drawings]

[0008] Some embodiments of the present disclosure will now be described, by way of example only, with reference to the accompanying drawings, in which: [Figure 1] FIG. 1 is a side view schematically showing the configuration of a gas laser device according to a comparative example. [Figure 2] FIG. 2 is a cross-sectional view schematically showing the configuration of a gas laser device according to a comparative example. [Figure 3] FIG. 3 is a cross-sectional view showing in detail the configuration in the vicinity of the discharge electrode. [Figure 4] FIG. 4 is a contour diagram showing the simulation results of the electric field intensity. [Figure 5] FIG. 5 is a graph showing the electric field intensity at each position in the X direction. [Figure 6] FIG. 6 is a cross-sectional view that schematically shows the configuration of the discharge electrode according to the first embodiment. [Figure 7] FIG. 7 is a diagram showing the principle of thermal spraying of a dielectric material. [Figure 8] FIG. 8 is a graph showing a schematic diagram of the relationship between the porosity and the wear rate of a low-density ceramic. [Figure 9] FIG. 9 is a diagram showing the process of wear between the discharge surface and the dielectric. [Figure 10] FIG. 10 is a diagram showing the process of wear between the discharge surface and the dielectric. [Figure 11] FIG. 11 is a graph showing the relationship between porosity and wear rate. [Figure 12] FIG. 12 is a graph showing the relationship between the number of shots and the amount of wear. [Figure 13] FIG. 13 is a cross-sectional view that schematically shows the configuration of a discharge electrode according to the second embodiment. [Figure 14] FIG. 14 is a diagram showing steps included in a method for manufacturing a discharge electrode according to the second embodiment. [Figure 15] FIG. 15 is a graph showing the relationship between the number of shots and the amount of wear when the first layer and the second layer are laminated. [Figure 16] FIG. 16 is a diagram schematically showing an example of the configuration of an exposure apparatus. Embodiment

[0009] <Contents> 1. Comparative Example 1.1 Configuration 1.2 Operation 1.3 Challenges 2. First embodiment 2.1 Configuration and operation 2.2 Discharge electrode manufacturing method 2.3 Effects 2.3.1 Factors that cause wear 2.3.2 Relationship between porosity and wear rate 2.3.3 Process of wear between discharge surface and dielectric 2.4 Issues with the first embodiment 3. Second embodiment 3.1 Configuration and operation 3.2 Discharge electrode manufacturing method 3.3 Effects 4. Variations 5. Electronic Device Manufacturing Method

[0010] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. The embodiments described below show some examples of the present disclosure and do not limit the content of the present disclosure. Furthermore, not all of the configurations and operations described in the embodiments are necessarily essential as the configurations and operations of the present disclosure. Note that the same components are given the same reference symbols, and redundant explanations will be omitted.

[0011] 1. Comparative Example First, a comparative example of the present disclosure will be described. The comparative example of the present disclosure is a form that the applicant recognizes as being known only by the applicant, and is not a publicly known example that the applicant acknowledges.

[0012] 1.1 Configuration The configuration of a gas laser device 2 according to a comparative example is shown schematically in Figures 1 and 2. Figure 1 shows the configuration of the gas laser device 2. Figure 2 is a cross-sectional view of the gas laser device 2 shown in Figure 1 as viewed from the Z direction. The gas laser device 2 is a discharge excitation type gas laser device that excites laser gas by electric discharge, such as an excimer laser device.

[0013] 1, the traveling direction of pulsed laser light PL output from gas laser device 2 is defined as the Z direction. The discharge direction, which will be described later, is defined as the Y direction. The direction perpendicular to the Z direction and the Y direction is defined as the X direction. The Z direction corresponds to the "one direction" according to the technology of the present disclosure.

[0014] 1, the gas laser device 2 includes a laser chamber 10, a charger 11, a pulse power module (PPM) 12, a pulse energy measurement unit 13, a control unit 14, a pressure sensor 17, and a laser resonator. The laser resonator is composed of a line narrowing module 15 and an output coupling mirror (OC) 16.

[0015] The laser chamber 10 is a metal container made of, for example, aluminum metal with a nickel-plated surface. As shown in Figures 1 and 2, the laser chamber 10 contains a discharge electrode 20, a ground plate 21, wiring 22, a fan 23, a heat exchanger 24, a preionization discharge unit 19, an electrical insulating guide 32, and a metal damper 33. The preionization discharge unit 19 includes a preionization outer electrode 19a, a dielectric pipe 19b, and a preionization inner electrode 19c.

[0016] A laser gas is sealed as a laser medium inside the laser chamber 10. The laser gas includes, for example, rare gases such as argon, krypton, and xenon, buffer gases such as neon and helium, and halogen gases such as fluorine and chlorine.

[0017] An opening is also formed in the laser chamber 10. An electrical insulating plate 26 is provided to close this opening via an O-ring 18 serving as a sealing member. A plurality of feedthroughs 25 are embedded in the electrical insulating plate 26. A plurality of peaking capacitors 27 and a holder 28 that holds these are arranged on the electrical insulating plate 26. The PPM 12 is arranged on this holder 28. The laser chamber 10 and the holder 28 are grounded.

[0018] The discharge electrode 20 comprises a cathode electrode 20a and an anode electrode 20b. The cathode electrode 20a and the anode electrode 20b are arranged in the laser chamber 10 so that their discharge surfaces face each other. The space between the discharge surface of the cathode electrode 20a and the discharge surface of the anode electrode 20b is called the discharge space 30. The surface of the cathode electrode 20a opposite the discharge surface is supported by an electrically insulating plate 26. The surface of the anode electrode 20b opposite the discharge surface is supported by a ground plate 21.

[0019] The feedthrough 25 is connected to the cathode electrode 20a. As shown in Fig. 2, the feedthrough 25 is connected to a peaking capacitor 27 held by a holder 28 via a connection part 29. The connection part 29 is a member for connecting the peaking capacitor 27 to other components.

[0020] Wall 28a forming the internal space of holder 28 is made of a metal material such as aluminum. A plurality of peaking capacitors 27, a connection portion 29, and a high-voltage terminal 12b of PPM 12 are arranged inside holder 28. Peaking capacitor 27 is a capacitor that receives and stores electrical energy from PPM 12 and supplies it to discharge electrode 20. Peaking capacitor 27 is a ceramic capacitor whose dielectric material is, for example, strontium titanate.

[0021] The peaking capacitors 27 are arranged in a matrix, two in the X direction and a plurality in the Z direction. The plurality of peaking capacitors 27 are connected in parallel via connecting portions 29. In each peaking capacitor 27, one electrode 27a is connected to the high-voltage terminal 12b and the feedthrough 25 via connecting portion 29, and the other electrode 27b is connected to the wall 28a of the holder 28 via connecting portion 29.

[0022] The connection portion 29 includes a connection plate 29a and connection terminals 29b and 29c. The connection plate 29a is formed of a conductive plate having a U-shaped cross section, and is connected to the high-voltage terminal 12b and the feedthrough 25.

[0023] The ground plate 21 is connected to the laser chamber 10 via wiring 22. The laser chamber 10 is grounded to the ground. The ground plate 21 is grounded to the ground via wiring 22. An end of the ground plate 21 in the Z direction is fixed to the laser chamber 10.

[0024] Fan 23 is a cross-flow fan for circulating laser gas within laser chamber 10, and is disposed on the opposite side of ground plate 21 from discharge space 30. A motor 23a that rotates fan 23 is connected to laser chamber 10.

[0025] The laser gas blown out from fan 23 flows into discharge space 30. The flow direction of the laser gas flowing into discharge space 30 is approximately parallel to the X direction. The laser gas flowing out from discharge space 30 can be sucked into fan 23 via heat exchanger 24. Heat exchanger 24 exchanges heat between the laser gas and a refrigerant supplied inside heat exchanger 24.

[0026] Electrical insulating guide 32 is disposed on the surface of electrical insulating plate 26 facing discharge space 30, sandwiching cathode electrode 20a therebetween. Electrical insulating guide 32 is formed in a shape that guides the flow of laser gas so that the laser gas from fan 23 flows efficiently between cathode electrode 20a and anode electrode 20b. Electrical insulating guide 32 and electrical insulating plate 26 are formed of ceramic such as alumina (Al2O3), which has low reactivity with fluorine gas.

[0027] The metal damper 33 is disposed on the surface of the ground plate 21 facing the discharge space 30, so as to sandwich the anode electrode 20b therebetween. The metal damper 33 is made of, for example, porous nickel metal that has low reactivity with fluorine gas.

[0028] Laser chamber 10 is provided with a laser gas supply device and a laser gas exhaust device (not shown). The laser gas supply device includes a valve and a flow control valve, and is connected to a gas cylinder containing laser gas. The laser gas exhaust device includes a valve and an exhaust pump.

[0029] Windows 10a and 10b are provided at the ends of the laser chamber 10 to emit light generated within the laser chamber 10 to the outside. The laser chamber 10 is arranged so that the optical path of the optical resonator passes through the discharge space 30 and the windows 10a and 10b.

[0030] The line narrowing module 15 includes a prism 15a and a grating 15b. The prism 15a expands the beam width of the light emitted from the laser chamber 10 through the window 10a and transmits the expanded beam toward the grating 15b.

[0031] Grating 15b is arranged in a Littrow configuration, where the angle of incidence and the angle of diffraction are the same. Grating 15b is a wavelength selection element that selectively extracts light near a specific wavelength depending on the diffraction angle. The spectral width of the light returning from grating 15b to laser chamber 10 via prism 15a is narrowed.

[0032] The output coupling mirror 16 transmits a portion of the light emitted from the laser chamber 10 via the window 10b and reflects the other portion back into the laser chamber 10. The surface of the output coupling mirror 16 is coated with a partially reflective film.

[0033] The light emitted from the laser chamber 10 travels back and forth between the line narrowing module 15 and the output coupling mirror 16, and is amplified each time it passes through the discharge space 30. A portion of the amplified light is output as pulsed laser light PL via the output coupling mirror 16. The pulsed laser light PL is an example of the "laser light" according to the technology of the present disclosure.

[0034] The pulse energy measuring unit 13 is disposed in the optical path of the pulsed laser light PL output via the output coupling mirror 16. The pulse energy measuring unit 13 includes a beam splitter 13a, a focusing optical system 13b, and an optical sensor 13c.

[0035] The beam splitter 13a transmits the pulsed laser light PL with high transmittance and reflects a portion of the pulsed laser light PL toward the focusing optical system 13b. The focusing optical system 13b focuses the light reflected by the beam splitter 13a on the light-receiving surface of the optical sensor 13c. The optical sensor 13c measures the pulse energy of the light focused on the light-receiving surface and outputs the measurement value to the control unit 14.

[0036] The pressure sensor 17 detects the gas pressure inside the laser chamber 10 and outputs the detected value to the control unit 14. The control unit 14 determines the gas pressure of the laser gas inside the laser chamber 10 based on the detected gas pressure value and the charging voltage of the charger 11.

[0037] The charger 11 is a high-voltage power supply that supplies a charging voltage to a charging capacitor included in the PPM 12. The PPM 12 includes a solid-state switch SW controlled by the control unit 14. When the solid-state switch SW is turned from OFF to ON, the PPM 12 generates a high-voltage pulse from the electrical energy stored in the charging capacitor and applies it to the discharge electrode 20.

[0038] The control unit 14 is a processor that transmits and receives various signals to and from an exposure apparatus control unit 110 provided in the exposure apparatus 100. For example, signals related to the target pulse energy and target oscillation timing of the pulsed laser light PL output to the exposure apparatus 100 are transmitted to the control unit 14 from the exposure apparatus control unit 110.

[0039] The control unit 14 comprehensively controls the operation of each component of the gas laser device 2 based on various signals sent from the exposure tool control unit 110, measured values ​​of pulse energy, detected values ​​of gas pressure, and the like.

[0040] 3 shows in detail the configuration in the vicinity of the discharge electrode 20. In FIG. 3, the preionization discharge part 19, the electrical insulating guide 32, the metal damper 33, etc. are omitted from the illustration.

[0041] The cathode electrode 20a includes a cathode holder 40, an electrode substrate 41, and a dielectric 42. The cathode holder 40 is made of a metal such as aluminum, and is fixed to an electrical insulating plate 26 by bolts 60. The cathode holder 40 is also connected to the PPM 12 outside the laser chamber 10 via the bolts 60. The electrical insulating plate 26 is fixed to the laser chamber 10 by clamps 61 and bolts 62.

[0042] The electrode substrate 41 is made of a metal such as copper or brass, and its bottom is embedded in the cathode holder 40. The electrode substrate 41 extends in the Z direction and has a discharge surface 41a that faces the anode electrode 20b in the Y direction and a pair of side surfaces 41b that face each other in the X direction. The cross-sectional shape of the discharge surface 41a in the XY plane is formed by a straight line, a quadratic curve such as an ellipse, or a curve expressed by a special function. The pair of side surfaces 41b are parallel to each other, and the distance between them is equal to the width W of the discharge surface 41a in the X direction. The pair of side surfaces 41b are each parallel to the YZ plane.

[0043] The dielectric 42 is made of ceramic such as alumina and is disposed so as to be in close contact with the pair of side surfaces 41b. One end of the dielectric 42 is formed close to the discharge surface 41a so as not to cover the discharge surface 41a, and the other end is in contact with the cathode holder 40.

[0044] The anode electrode 20b includes an anode holder 50, an electrode substrate 51, and a dielectric 52. The anode holder 50 is made of a metal such as aluminum, and is held by the ground plate 21.

[0045] The electrode substrate 51 is made of a metal such as copper or brass, and its bottom is embedded in the anode holder 50. The electrode substrate 51 extends in the Z direction and has a discharge surface 51a that faces the cathode electrode 20a in the Y direction and a pair of side surfaces 51b that face each other in the X direction. The cross-sectional shape of the discharge surface 51a in the XY plane is formed by a straight line, a quadratic curve such as an ellipse, or a curve expressed by a special function. The pair of side surfaces 51b are parallel to each other, and the distance between them is equal to the width W of the discharge surface 51a in the X direction. The pair of side surfaces 51b are each parallel to the YZ plane.

[0046] Dielectric 52 is made of ceramic such as alumina and is disposed so as to be in close contact with pair of side surfaces 51b. One end of dielectric 52 is formed close to discharge surface 51a so as not to cover discharge surface 51a, and the other end is in contact with anode holder 50.

[0047] The discharge surface 41a and the discharge surface 51a face each other and are disposed apart by a distance G in the Y direction so as to form a discharge space 30.

[0048] 1.2 Operation The control unit 14 controls the laser gas supply device to supply laser gas into the laser chamber 10, and drives the motor 23a to rotate the fan 23. This causes the laser gas inside the laser chamber 10 to circulate.

[0049] The control unit 14 receives signals relating to the target pulse energy Et and the target oscillation timing transmitted from the exposure tool control unit 110 .

[0050] The control unit 14 sets a charging voltage Vhv corresponding to the target pulse energy Et in the charger 11. The control unit 14 stores the value of the charging voltage Vhv set in the charger 11. The control unit 14 operates the solid-state switch SW of the PPM 12 in synchronization with the target oscillation timing.

[0051] When the solid-state switch SW of the PPM 12 is turned from OFF to ON, a voltage is applied between the preionization inner electrode 19c and the preionization outer electrode 19a of the preionization discharge unit 19, and between the cathode electrode 20a and the anode electrode 20b. This causes a corona discharge in the preionization discharge unit 19, generating UV (Ultraviolet) light. The laser gas in the discharge space 30 is irradiated with UV light, causing the laser gas to be preionized.

[0052] Thereafter, when the voltage between the cathode electrode 20a and the anode electrode 20b reaches the breakdown voltage, a main discharge occurs in the discharge space 30. If the discharge direction of the main discharge is the direction in which electrons flow, the discharge direction is from the cathode electrode 20a to the anode electrode 20b. When the main discharge occurs, the laser gas in the discharge space 30 is excited and emits light.

[0053] Metal damper 33 prevents acoustic waves generated by the main discharge from being reflected and returning to discharge space 30. In addition, as laser gas circulates within laser chamber 10, discharge products generated in discharge space 30 move downstream.

[0054] Light emitted from the laser gas is reflected by the line narrowing module 15 and the output coupling mirror 16 and travels back and forth within the laser resonator, resulting in laser oscillation. The light narrowed in line by the line narrowing module 15 is output from the output coupling mirror 16 as pulsed laser light PL.

[0055] A portion of the pulsed laser light PL output from the output coupling mirror 16 is incident on the pulse energy measuring unit 13. The pulse energy measuring unit 13 measures the pulse energy E of the incident pulsed laser light PL and outputs the measurement value to the control unit 14.

[0056] The control unit 14 stores the measurement value of the pulse energy E measured by the pulse energy measurement unit 13. The control unit 14 calculates the difference ΔE between the measured value of the pulse energy E and the target pulse energy Et. Based on the difference ΔE, the control unit 14 feedback-controls the charging voltage Vhv so that the measured value of the pulse energy E becomes the target pulse energy Et.

[0057] When charging voltage Vhv becomes higher than the maximum value of the allowable range, control unit 14 controls the laser gas supply device to supply laser gas into laser chamber 10 until a predetermined pressure is reached. Also, when charging voltage Vhv becomes lower than the minimum value of the allowable range, control unit 14 controls the laser gas exhaust device to exhaust laser gas from laser chamber 10 until a predetermined pressure is reached.

[0058] 1.3 Challenges As the number of shots increases, the discharge surfaces 41a, 51a of the electrode base materials 41, 51 wear, and the gap G between the discharge surfaces 41a, 51a increases. The dielectrics 42, 52 are provided to prevent the width W from increasing as the discharge surfaces 41a, 51a wear. Here, the number of shots refers to the number of pulses of the pulsed laser light PL generated by the main discharge. Hereinafter, the width W of the discharge surfaces 41a, 51a is referred to as the discharge width W. The discharge width W is, for example, approximately 8 mm.

[0059] As the number of shots increases, the discharge surfaces 41a, 51a wear away, while the shapes of the dielectrics 42, 52 change very little. To be precise, the main discharge causes sputtering and etching of the dielectrics 42, 52, which causes deterioration and wear of the dielectrics 42, 52, but the amount of wear is small. Because the wear rates of the discharge surfaces 41a, 51a and the dielectrics 42, 52 differ in this way, the discharge surfaces 41a, 51a sink as the number of shots increases, and the electric field concentrates at the ends of the discharge surfaces 41a, 51a.

[0060] 4 and 5 show the results of a simulation of the electric field strength 30 billion shots after replacing the discharge electrode 20. FIG. 4 is a contour diagram of the electric field strength on the XY plane. FIG. 5 is a graph showing the electric field strength at each position in the X direction. In FIG. 5, the dotted line A indicates the electric field strength at the center of the discharge space 30. The solid line B indicates the electric field strength near the discharge surface 41a of the discharge space 30. The dashed line C indicates the electric field strength near the discharge surface 51a of the discharge space 30. In this simulation, the dielectric constant of the dielectrics 42 and 52 is set to 10.

[0061] 5, it can be seen that the discharge width W remains almost unchanged from the initial state even as the number of shots increases, but the electric field concentrates at the ends of the discharge surfaces 41a and 51a. When the electric field concentrates at the ends of the discharge surfaces 41a and 51a in this way, the main discharge is split into two, and the uniformity of the beam profile of the pulsed laser light PL is lost, making it unsuitable for exposure or processing. As a result, the discharge electrode 20 is deemed to have reached the end of its life and must be replaced.

[0062] Therefore, it is required to suppress the electric field concentration that occurs with an increase in the number of shots and to extend the life of the discharge electrode 20.

[0063] 2. First embodiment 2.1 Configuration and operation The gas laser device 2 according to the first embodiment of the present disclosure has the same configuration as the gas laser device 2 according to the comparative example, except for the configuration of the discharge electrode 20. Furthermore, the operation of the gas laser device 2 according to the first embodiment is the same as the operation of the gas laser device 2 according to the comparative example.

[0064] 6 schematically shows the configuration of the discharge electrode 20 according to the first embodiment. The discharge electrode 20 according to this embodiment differs from the discharge electrode 20 according to the comparative example only in that the dielectrics 42, 52 are made of low-density ceramic.

[0065] 6 shows a partially enlarged view of the configuration of the dielectric 52. In this embodiment, the dielectric 52 is a low-density ceramic formed as an aggregate of a plurality of ceramic particles 52a, and has voids. The ceramic particles 52a are formed of an oxide such as alumina or yttria (YO), or a two-dimensional or three-dimensional compound made of yttrium (Y), oxygen (O), and fluorine (F).

[0066] The porosity of the dielectric 52 affects the wear rate of the dielectric 52. As will be described in detail later, the larger the porosity, the faster the wear rate. Therefore, by adjusting the porosity, the wear rate of the dielectric 52 can be made closer to the wear rate of the discharge surface 51a. The porosity is the ratio of the volume of voids to the volume of the dielectric 52. In this disclosure, the porosity refers to a value measured by underwater gravimetry.

[0067] In order to make the wear rate of the dielectric 52 close to the wear rate of the discharge surface 51a, the porosity is preferably in the range of 0.5% to 25%, more preferably in the range of 2% to 15%.

[0068] The dielectric 42 has a similar structure to the dielectric 52 .

[0069] 2.2 Discharge electrode manufacturing method The dielectric 42 is formed by thermally spraying a dielectric material onto the side surface 41b of the electrode substrate 41 and the surface of the electrode holder 30 facing the discharge space 30. Similarly, the dielectric 52 is formed by thermally spraying a dielectric material onto the side surface 51b of the electrode substrate 51 and the surface of the electrode holder 40 facing the discharge space 30.

[0070] FIG. 7 shows a schematic diagram of the principle of thermal spraying of a dielectric material. The thermal spraying of the dielectric material is carried out using a thermal spray gun 70. A powdered dielectric material such as alumina or yttria and an assist gas, which is an inert gas such as nitrogen or argon, are supplied to the thermal spray gun 70. The thermal spray gun 70 carries the dielectric material on the assist gas to an outlet 71. An electrode 72 that generates an arc discharge is disposed at the outlet 71. The dielectric material is molten by the arc current and is then ejected from the thermal spray gun 70 toward the base material 73 to be sprayed. Note that the molten state also includes a semi-molten state.

[0071] When the dielectric material sprayed from the thermal spray gun 70 reaches the base material 73, it adheres to the surface of the base material 73 due to the anchor effect. A thermal sprayed film is formed by a plurality of dielectric materials adhering to the surface of the base material 73. Note that if a thermal sprayed film made of a dielectric material has already been formed on the surface of the base material 73 when the dielectric material sprayed from the thermal spray gun 70 reaches the base material 73, the dielectric material bonds to the thermal sprayed film due to the anchor effect. The anchor effect refers to the bonding force obtained when the molten dielectric material penetrates into tiny holes or irregularities and solidifies.

[0072] The base material 73 is used as the electrode substrates 41, 51 and the electrode holders 40, 50, and a dielectric material is sprayed onto the base material 73 to form a sprayed film of a predetermined thickness, thereby forming the dielectrics 42, 52 having voids.

[0073] The porosity can be adjusted by controlling the energy of the dielectric material ejected from the thermal spray gun 70. The greater the energy of the dielectric material, the lower the porosity of the sprayed film. Conversely, the lower the energy of the dielectric material, the higher the porosity of the sprayed film. The energy of the dielectric material can be controlled using the flow rate of the assist gas and the arc current as parameters. The higher the flow rate of the assist gas or the arc current, the higher the energy of the dielectric material.

[0074] 2.3 Effects 2.3.1 Factors that cause wear By making the dielectrics 42, 52 low-density ceramics having voids, the rate of wear caused by the main discharge increases for the dielectrics 42, 52. The wear of the dielectrics 42, 52 is caused by the above-mentioned sputtering and etching.

[0075] Sputtering is a phenomenon in which accelerated charged particles contained in the discharge plasma generated by the main discharge collide with ceramic particles, breaking the bonds between the ceramic particles and scattering the ceramic particles, causing physical wear to the dielectrics 42 and 52.

[0076] Etching is a phenomenon in which a discharge plasma of halogen gas containing fluorine, chlorine, etc. causes a chemical reaction in ceramic particles, resulting in chemical wear of the dielectrics 42, 52. For example, when alumina is exposed to a plasma containing fluorine, aluminum fluoride (AlF3) is generated on the alumina surface, and etching progresses as this aluminum fluoride volatilizes from the surface. In other words, it is believed that the chemical reaction expressed by the following formula (1) occurs: Al2O3+6F2→ 2AlF3+3F2O ···(1) However, the chemical reaction is not limited to this, and it is also possible that the form of fluorine is a radical or ion, or that the product is oxygen fluoride (FO).

[0077] 2.3.2 Relationship between porosity and wear rate Figure 8 shows a schematic diagram of the relationship between the porosity and wear rate of a low-density ceramic. The wear rate is defined as the amount of wear (mm / Bpls) caused by sputtering and etching when a low-density ceramic is exposed to a discharge plasma for billions of shots. Bpls stands for "Billion pulses."

[0078] As shown by point P in Figure 8, when the porosity is 0%, i.e., in the case of dense ceramics, the amount of wear is negligible and the wear rate is low. This is because in dense ceramics, the ceramic molecules are bound by intermolecular forces greater than the energy of the discharge plasma.

[0079] On the other hand, when the porosity is greater than 0%, i.e., in the case of a low-density ceramic with voids, the wear rate increases with increasing porosity. This is because the sprayed ceramic particles 52a are only attached to the base material 73 by the anchor effect, and are easily sputtered and etched by the energy of the discharge plasma. Since the same amount of sputtering and etching occurs for discharge plasma with the same energy, the wear rate of the low-density ceramic increases with increasing porosity.

[0080] Therefore, the wear rate of the low-density ceramic can be controlled by adjusting the porosity, which can be set so that the wear rates of the discharge surfaces 41a and 51a and the dielectrics 42 and 52 become closer to each other.

[0081] 2.3.3 Process of wear between discharge surface and dielectric 9 and 10 show the process by which the discharge surface 51a and the dielectric 52 wear away in this embodiment. As shown in FIG. 9, as with the comparative example, the discharge surface 51a wears away and sinks as the number of shots increases. When the discharge surface 51a sinks, the wall surface 52b of the dielectric 52 is exposed and exposed to the discharge plasma. The wear of the dielectric 52 progresses due to the above-mentioned sputtering and etching occurring near the wall surface 52b exposed to the discharge plasma.

[0082] 10, as the wear of the dielectric 52 progresses, the surface of the dielectric 52 drops. As a result, the discharge surface 51a and the surface of the dielectric 52 wear while maintaining their initial relationship, which reduces the difference in the wear rates between the discharge surface 51a and the dielectric 52. Therefore, sinking of the discharge surface 51a relative to the surface of the dielectric 52 is reduced.

[0083] In this embodiment, the process by which the discharge surface 41a and the dielectric 42 wear away is similar, and the sinking of the discharge surface 41a relative to the surface of the dielectric 42 is suppressed.

[0084] In this way, in this embodiment, the difference in wear rate between the discharge surfaces 41 a, 51 a and the dielectrics 42, 52 is suppressed, thereby suppressing electric field concentration at the ends of the discharge surfaces 41 a, 51 a. As a result, the uniformity of the beam profile is maintained, and the life of the discharge electrode 20 is extended.

[0085] 2.4 Issues with the first embodiment As mentioned above, the wear rate of low-density ceramics increases with increasing porosity, but the greater the porosity, the greater the variability in the porosity. Therefore, as shown in Figure 11, the greater the porosity, the greater the variability in the wear rate relative to the average wear rate. In other words, it is easy to control the wear rate when the porosity is low, but it becomes difficult to control the wear rate when the porosity is high.

[0086] When the dielectrics 42 and 52 are formed from low-density ceramics with a single porosity, as in the first embodiment, the desired wear rate may not be achieved depending on the porosity. Therefore, as shown in FIG. 12, a large difference may occur between the wear rate of the dielectrics 42 and 52 and the wear rate of the discharge surfaces 41a and 51a. This difference increases as the number of shots increases, so depending on the porosity, the effect of using low-density ceramics may not be fully realized. While FIG. 12 shows a case where the wear rate of the dielectrics 42 and 52 is smaller than that of the discharge surfaces 41a and 51a, the wear rate of the dielectrics 42 and 52 may also be larger than that of the discharge surfaces 41a and 51a.

[0087] 3. Second embodiment 3.1 Configuration and operation Next, a gas laser device 2 according to a second embodiment will be described. The gas laser device 2 according to the second embodiment has the same configuration as the gas laser device 2 according to the first embodiment, except for the configuration of the discharge electrode 20. The operation of the gas laser device 2 according to the second embodiment is similar to that of the gas laser device 2 according to the comparative example.

[0088] 13 schematically shows the configuration of a discharge electrode 20 according to the second embodiment. In the discharge electrode 20 according to this embodiment, the dielectrics 42, 52 are formed from low-density ceramic, but differ from the discharge electrode 20 according to the first embodiment in that the dielectrics 42, 52 include multiple layers with different porosities.

[0089] FIG. 13 shows a partially enlarged view of the configuration of the dielectric 52. In this embodiment, the dielectric 52 includes a first layer 81 having voids and a second layer 82 having a porosity different from that of the first layer 81. The first layer 81 is formed of a low-density ceramic. The porosity of the first layer 81 is the same as that of the low-density ceramic constituting the dielectric 52 of the first embodiment, and is preferably in the range of 0.5% to 25%, and more preferably in the range of 2% to 15%. That is, the dielectric 52 of the first embodiment is constituted by the first layer 81.

[0090] The second layer 82 has the same configuration as the first layer 81, except for the difference in porosity. The porosity of the second layer 82 is smaller than that of the first layer 81. That is, the second layer 82 is formed of a ceramic that is denser than the first layer 81. The difference in porosity between the first layer 81 and the second layer 82 is preferably 1% or more, and more preferably 3% or more. The porosity of the second layer 82 is, for example, less than 0.3%.

[0091] A plurality of first layers 81 and a plurality of second layers 82 are provided. The first layers 81 and the second layers 82 are alternately stacked. In this embodiment, the first layer 81 is the uppermost layer of the dielectric 52. The plurality of first layers 81 each have the same porosity. The plurality of second layers 82 each have the same porosity. The plurality of first layers 81 each have the same thickness. The plurality of second layers 82 each have the same thickness. In this disclosure, "equal" means that the difference is within a range of ±15%.

[0092] In this embodiment, the thickness of the first layer 81 is greater than the thickness of the second layer 82. In FIG. 13, the thickness of the first layer 81 is designated as t1, and the thickness of the second layer 82 is designated as t2. The thicknesses t1 and t2 are, for example, 0.2 mm or less. The thickness of the bottom layer of the dielectric 52 shown in FIG. 13 is greater than the thicknesses of the first layer 81 and the second layer 82.

[0093] The dielectric 42 has the same configuration as the dielectric 52, and includes first layers 81 and second layers 82 that are alternately laminated. The porosity, thickness, etc. of the first layers 81 and second layers 82 of the dielectric 42 may be the same as the porosity, thickness, etc. of the first layers 81 and second layers 82 of the dielectric 52. Furthermore, the porosity, thickness, etc. of the first layers 81 and second layers 82 of the dielectric 42 may be values ​​selected so that the wear rates of the discharge surface 41a of the electrode base material 41 and the dielectric 42 are equal.

[0094] 3.2 Discharge electrode manufacturing method The dielectrics 42 and 52 of the second embodiment can be formed by thermal spraying, similarly to the first embodiment.

[0095] FIG. 14 shows steps included in a method for manufacturing a discharge electrode 20 according to the second embodiment. The method for manufacturing a discharge electrode 20 includes a step of forming dielectrics 42, 52 on the side surfaces 41b, 51b of electrode base materials 41, 51. The step of forming the dielectrics 42, 52 includes a first step and a second step shown in FIG. 14. The first step is a step of forming a first layer 81 by thermally spraying a dielectric material on the side surfaces 41b, 51b of the electrode base materials 41, 51. The second step is a step of forming a second layer 82 having a porosity different from that of the first layer 81 by thermally spraying a dielectric material on the surface of the first layer 81 formed on the side surfaces 41b, 51b of the electrode base materials 41, 51. The first step and the second step are performed alternately.

[0096] The first and second steps include a thermal spraying step in which an arc current is applied to the dielectric material to melt it, and the molten dielectric material is then transported by an assist gas. The porosity of the first layer 81 and the second layer 82 is adjusted by controlling the energy of the dielectric material through at least one of the flow rate of the assist gas and the arc current. Therefore, in order to make the porosity of the first layer 81 and the second layer 82 different, at least one of the flow rate of the assist gas and the arc current is different between the first and second steps.

[0097] The porosity of the first layer 81 and the second layer 82 is set so that the wear rates of the discharge surfaces 41 a, 51 a of the electrode substrates 41, 51 and the dielectrics 42, 52 are equal when the discharge electrode 20 repeatedly performs main discharge. The thickness of the first layer 81 and the second layer 82 is set so that the wear rates of the discharge surfaces 41 a, 51 a of the electrode substrates 41, 51 and the dielectrics 42, 52 are equal when the discharge electrode 20 repeatedly performs main discharge.

[0098] 3.3 Effects The second layer 82 has a smaller porosity than the first layer 81, and therefore has a lower wear rate, but the variation in the wear rate is also small. Therefore, by stacking the first layer 81 and the second layer 82, the variation in the overall wear rate can be suppressed, and the wear rate can be made closer to the target wear rate. In other words, by stacking the first layer 81 and the second layer 82, the wear rate can be made closer to the wear rate of the discharge surfaces 41a, 51a.

[0099] Figure 15 shows the relationship between the number of shots and the amount of wear when a first layer 81 and a second layer 82 are laminated. The solid line shows the amount of wear between the first layer 81 and the second layer 82, and the dashed line shows the amount of wear between the discharge surfaces 41a and 51a. As shown in Figure 15, due to the different wear rates between the first layer 81 and the second layer 82, the amount of wear between the dielectrics 42 and 52 does not locally match the amount of wear between the discharge surfaces 41a and 51a, but over a long period of time spanning several billion shots, it approaches the amount of wear between the discharge surfaces 41a and 51a.

[0100] As described above, according to the second embodiment, the problems of the first embodiment are solved, and the life of the discharge electrode 20 can be extended.

[0101] 4. Variations Next, various modified examples of the first and second embodiments will be described. In the first and second embodiments, both the dielectrics 42, 52 are low-density ceramic, but only one of the dielectrics 42, 52 may be low-density ceramic. For example, since it is known that the anode electrode 20b wears faster than the cathode electrode 20a, only the dielectric 52 of the anode electrode 20b may be low-density ceramic. That is, it is sufficient that the dielectric 42, 52 including voids is provided on the side surface 41b, 51b of the electrode base material 41, 51 of at least one of the cathode electrode 20a and the anode electrode 20b.

[0102] In the first and second embodiments, the gas laser device 2 is a line-narrowing laser device, but the present invention is not limited to this and may be a gas laser device that outputs spontaneously oscillated light. For example, a high-reflection mirror may be provided instead of the line-narrowing module 15.

[0103] In the first and second embodiments, the gas laser device 2 is an excimer laser device, but instead, it may be an F molecular laser device that uses a laser gas containing fluorine gas and a buffer gas. In other words, the gas laser device according to the present disclosure may be any gas laser device that excites a laser gas containing fluorine by electric discharge.

[0104] 5. Electronic Device Manufacturing Method 16 shows a schematic configuration example of exposure apparatus 100. Exposure apparatus 100 includes an illumination optical system 104 and a projection optical system 106. Illumination optical system 104 illuminates a reticle pattern of a reticle (not shown) placed on a reticle stage RT with pulsed laser light PL incident thereon, for example, from a gas laser device 2. Projection optical system 106 reduces and projects the pulsed laser light PL that has passed through the reticle, forming an image on a workpiece (not shown) placed on a workpiece table WT. The workpiece is a photosensitive substrate such as a semiconductor wafer coated with photoresist.

[0105] Exposure apparatus 100 exposes a workpiece to pulsed laser light PL reflecting a reticle pattern by synchronously translating a reticle stage RT and a workpiece table WT. After transferring the reticle pattern to a semiconductor wafer through the exposure process described above, a semiconductor device can be manufactured through multiple processes. A semiconductor device is an example of an "electronic device" in this disclosure.

[0106] The gas laser device 2 is not limited to use in the manufacture of electronic devices, but can also be used for laser processing such as drilling.

[0107] The above description is intended to be illustrative rather than limiting. Thus, it will be apparent to those skilled in the art that modifications may be made to the embodiments of the present disclosure without departing from the scope of the appended claims.

[0108] Terms used throughout this specification and the appended claims should be interpreted as "open ended" terms. For example, the terms "include" or "including" should be interpreted as "not limited to what is stated as including." The term "having" should be interpreted as "not limited to what is stated as having." Additionally, the modifier "a" used in this specification and the appended claims should be interpreted as "at least one" or "one or more." Additionally, the term "at least one of A, B, and C" should be interpreted as "A," "B," "C," "A+B," "A+C," "B+C," or "A+B+C," and should also be interpreted as including combinations other than "A," "B," and "C."

Claims

1. A discharge electrode used in a gas laser device that excites a laser gas containing fluorine by discharge, a cathode electrode extending in one direction; an anode electrode extending in the one direction and disposed opposite to the cathode electrode in a discharge direction perpendicular to the one direction; Equipped with At least one of the cathode electrode and the anode electrode is an electrode substrate including a metal; and a dielectric including a first layer having a gap provided on a pair of side surfaces of the electrode substrate; the porosity of the first layer is in the range of 0.5% or more and 25% or less, the dielectric material includes a second layer having a porosity different from that of the first layer; The first layer and the second layer are each provided in plural numbers and are alternately stacked. discharge electrode.

2. The discharge electrode according to claim 1, Both the cathode electrode and the anode electrode include the electrode substrate and the dielectric.

3. The discharge electrode according to claim 1, The porosity of the first layer is in the range of 2% to 15%.

4. The discharge electrode according to claim 1, The porosity of the first layer is a value measured by underwater gravimetry.

5. The discharge electrode according to claim 1, The plurality of first layers each have the same porosity, The second layers each have the same porosity.

6. The discharge electrode according to claim 5, The first layers each have the same thickness, The second layers each have the same thickness.

7. The discharge electrode according to claim 1, The top layer of the dielectric is the first layer.

8. The discharge electrode according to claim 1, The thickness of the first layer is greater than the thickness of the second layer.

9. The discharge electrode according to claim 1, The porosity of the second layer is less than the porosity of the first layer.

10. The discharge electrode according to claim 5, The difference in porosity between the first layer and the second layer is 1% or more.

11. The discharge electrode according to claim 10, The difference in porosity between the first layer and the second layer is 3% or more.

12. A method for manufacturing a discharge electrode used in a gas laser device, comprising: forming a dielectric on a side surface of an electrode substrate containing a metal; The step of forming the dielectric includes: a first step of forming a first layer having voids by thermally spraying a dielectric material on a side surface of the electrode base material; a second step of spraying the dielectric material onto the surface of the first layer formed on the side surface of the electrode base material to form a second layer having a porosity different from that of the first layer; A method for manufacturing a discharge electrode comprising:

13. The method for producing a discharge electrode according to claim 12, The porosity of the first layer and the second layer is set so that the wear rates of the discharge surface of the electrode substrate and the dielectric are equal when the discharge electrode repeatedly performs main discharge.

14. The method for producing a discharge electrode according to claim 12, The thicknesses of the first layer and the second layer are set so that the wear rates of the discharge surface of the electrode substrate and the dielectric are equal when the discharge electrode repeatedly generates main discharges.

15. The method for producing a discharge electrode according to claim 12, The first and second steps include a thermal spraying step in which an arc current is applied to a dielectric material to melt the dielectric material, and the molten dielectric material is carried by an assist gas.

16. The method for producing a discharge electrode according to claim 15, At least one of the flow velocity of the assist gas and the arc current is different between the first step and the second step.

17. A method for manufacturing an electronic device, comprising: a cathode electrode extending in one direction; an anode electrode extending in the one direction and disposed opposite to the cathode electrode in a discharge direction perpendicular to the one direction; Equipped with At least one of the cathode electrode and the anode electrode is an electrode substrate including a metal; and a dielectric including a first layer having a gap provided on a pair of side surfaces of the electrode substrate; the porosity of the first layer is in the range of 0.5% or more and 25% or less, the dielectric material includes a second layer having a porosity different from that of the first layer; The first layer and the second layer are each provided in plural numbers and are alternately stacked. A laser beam is generated by a gas laser device that uses a discharge electrode to excite a laser gas containing fluorine by discharge; outputting the laser light to an exposure device; exposing a photosensitive substrate to the laser light in the exposure apparatus to manufacture an electronic device; A method for manufacturing electronic devices.

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