Ultraviolet laser beam output mirror, ultraviolet laser device, and method for manufacturing electronic device

Abstract

SOLUTION: To provide an output mirror 400 for ultraviolet laser light, which includes a plate-shaped sapphire substrate 410, and in which at least a portion of one main surface 411 of the sapphire substrate is exposed and is a partially reflective surface 401 that reflects a portion of the ultraviolet laser light and transmits another portion, and the other main surface 412 of the sapphire substrate is provided with a reflection suppression structure 402 that suppresses reflection of the ultraviolet laser light.EFFECT: Since an output mirror 400 does not have a multilayer film formed on the partially reflecting surface 401, the multilayer film does not deteriorate and the output mirror 400 can be made highly durable against the high-power ultraviolet laser light L with a high energy density.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present disclosure relates to an output mirror for ultraviolet laser light, an ultraviolet laser device, 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 248.0 nm, and ArF excimer laser devices, which output laser light with a wavelength of approximately 193.4 nm, are used as gas laser devices for exposure.

[0003] The spectral linewidth of the spontaneously oscillating light of KrF excimer laser devices and ArF excimer laser devices is as wide as 350 pm 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 a 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] U.S. Patent No. 6,642,989 [Patent Document 2] U.S. Patent No. 5,507,175 [Patent Document 3] U.S. Patent No. 7,756,189 [Patent Document 4] Summary of the specification of U.S. Patent No. 11,784,452

[0005] One aspect of the present disclosure is an output mirror for ultraviolet laser light, the output mirror including a plate-shaped sapphire substrate, at least a portion of one main surface of the sapphire substrate being exposed and being a partially reflective surface that reflects a portion of the ultraviolet laser light and transmits another portion, and the other main surface of the sapphire substrate may be provided with a reflection suppression structure that suppresses reflection of the ultraviolet laser light.

[0006] Another aspect of the present disclosure is an ultraviolet laser device including an amplifier that amplifies ultraviolet laser light, wherein the amplifier includes an output mirror for the ultraviolet laser light, the output mirror including a plate-shaped sapphire substrate, at least a portion of one main surface of the output mirror being a partially reflective surface where the sapphire substrate is exposed and which reflects a portion of the ultraviolet laser light and transmits another portion, and the other main surface of the output mirror may be provided with a reflection suppression structure that suppresses reflection of the ultraviolet laser light.

[0007] Furthermore, yet another aspect of the present disclosure may include a method for manufacturing an electronic device, the method including: outputting ultraviolet laser light generated by an ultraviolet laser apparatus, wherein the output mirror for ultraviolet laser light includes a plate-shaped sapphire substrate, at least a portion of one main surface of the output mirror being a partially reflective surface where the sapphire substrate is exposed and which reflects a portion of the ultraviolet laser light and transmits another portion, and the other main surface of the output mirror being provided with a reflection suppression structure that suppresses reflection of the ultraviolet laser light, to an exposure apparatus; and exposing the ultraviolet laser light onto a photosensitive substrate in the exposure apparatus to manufacture the 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 schematic diagram showing an example of the overall configuration of an electronic device manufacturing apparatus. [Figure 2] FIG. 2 is a schematic diagram showing an example of the overall configuration of an ultraviolet laser device of a comparative example. [Figure 3] FIG. 3 is a schematic diagram showing an example of the schematic configuration of an output mirror provided in an ultraviolet laser device of a comparative example. [Figure 4] FIG. 4 is a schematic diagram showing an example of the schematic configuration of the output mirror of the first embodiment. [Figure 5] FIG. 5 is a graph showing the relationship between the refractive index of the substrate and the surface reflectance due to Fresnel reflection. [Figure 6] FIG. 6 is a schematic diagram showing the arrangement of output mirrors in a first modification of the first embodiment. [Figure 7] FIG. 7 is a schematic diagram showing the arrangement of output mirrors in Modification 2 of Embodiment 1. In FIG. [Figure 8] FIG. 8 is a schematic diagram showing the arrangement of output mirrors in Modification 3 of Embodiment 1. In FIG. [Figure 9] FIG. 9 is a schematic diagram showing the positional relationship between the output mirror and the window of the chamber device in the fourth modification of the first embodiment. [Figure 10] FIG. 10 is a schematic diagram of an ultraviolet laser device according to the second embodiment having a moth-eye structure as the reflection suppressing structure of the output mirror. [Figure 11] FIG. 11 is an explanatory diagram of the moth-eye structure. [Figure 12] FIG. 12 is a schematic diagram showing an example of the schematic configuration of a part of an amplifier included in the ultraviolet laser device of the third embodiment. [Figure 13] FIG. 13 is a graph showing the incidence angle dependency of the reflectance of Fresnel reflection. Embodiment

[0009] 1. Explanation of the electronic device manufacturing equipment used in the exposure process of electronic devices 2. Description of the ultraviolet laser device as a comparative example 2.1 Configuration 2.2 Operation 2.3 Challenges 3. Description of the ultraviolet laser device of embodiment 1 3.1 Configuration 3.2 Operation 3.3 Actions and Effects 3.4 Explanation of Variation 1 3.5 Explanation of Variation 2 3.6 Explanation of Variation 3 3.7 Explanation of Variation 4 4. Description of the ultraviolet laser device of embodiment 2 4.1 Configuration 4.2 Actions and Effects 5. Description of the ultraviolet laser device of embodiment 3 5.1 Configuration 5.2 Operation 5.3 Actions and Effects

[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 each embodiment 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. Explanation of the electronic device manufacturing equipment used in the exposure process of electronic devices FIG. 1 is a schematic diagram showing an example of the overall configuration of an electronic device manufacturing apparatus used in an exposure process for electronic devices. As shown in FIG. 1, the manufacturing apparatus used in the exposure process includes an ultraviolet laser device 100 and an exposure apparatus 200. The exposure apparatus 200 includes an illumination optical system 210, which includes multiple mirrors 211, 212, and 213, and a projection optical system 220. The illumination optical system 210 illuminates a reticle pattern on a reticle stage RT with laser light incident from the ultraviolet laser device 100. The projection optical system 220 reduces and projects the laser light transmitted through the reticle onto a workpiece (not shown) placed on a workpiece table WT. The workpiece is a photosensitive substrate such as a semiconductor wafer coated with photoresist. The exposure apparatus 200 synchronously translates the reticle stage RT and the workpiece table WT to expose the workpiece with laser light reflecting the reticle pattern. Semiconductor devices, which are electronic devices, can be manufactured by transferring a device pattern onto a semiconductor wafer through the exposure process described above.

[0012] 2. Description of the ultraviolet laser device as a comparative example 2.1 Configuration The following describes an ultraviolet laser device as a comparative example. Note that the comparative example in the present disclosure is a configuration that the applicant recognizes as being known only by the applicant, and is not a publicly known example that the applicant acknowledges.

[0013] FIG. 2 is a schematic diagram showing an example of the overall configuration of an ultraviolet laser device 100 of this embodiment. The ultraviolet laser device 100 is, for example, an ArF excimer laser device that uses a mixed gas containing argon (Ar), fluorine (F2), and neon (Ne). This ultraviolet laser device 100 outputs laser light L with a center wavelength of approximately 193.4 nm. Note that, in this specification, the term "laser light" refers to ultraviolet laser light. The ultraviolet laser device 100 may be a gas laser device other than an ArF excimer laser device, such as a KrF excimer laser device that uses KrF gas containing krypton (Kr) and fluorine (F2). In this case, the ultraviolet laser device 100 emits pulsed laser light with a center wavelength of approximately 248 nm. The laser medium, ArF gas or KrF gas, is sometimes called a laser gas. Therefore, the ultraviolet laser light may be ArF laser light with a center wavelength of approximately 193.4 nm or KrF laser light with a center wavelength of 248 nm.

[0014] The ultraviolet laser device 100 of this example mainly includes a housing 110, a laser oscillator 130 which is a master oscillator arranged in the internal space of the housing 110, an optical transmission unit 141, an amplifier 160 which is a power oscillator, a detection unit 153, a display unit 180, and a processor 190.

[0015] The laser oscillator 130 includes a chamber device CH1, a charger 41, a pulse power module 43, a line narrowing module 60, and an output mirror 70 as its main components.

[0016] 2 shows the internal configuration of the chamber apparatus CH1 as viewed from a direction substantially perpendicular to the traveling direction of the laser light L. The chamber apparatus CH1 mainly includes a housing 30, a pair of windows 31a and 31b, a pair of electrodes 32a and 32b, an insulating section 33, a feedthrough 34, and an electrode holder section 36.

[0017] The housing 30 has a laser gas sealed in its internal space. The internal space is a space where light is generated by excitation of the laser medium in the laser gas. This light travels to the windows 31a and 31b.

[0018] The window 31a is arranged on the front wall of the housing 30 in the traveling direction of the laser light L from the ultraviolet laser device 100 to the exposure device 200, and the window 31b is arranged on the rear wall of the housing 30 in the traveling direction. The windows 31a and 31b are made of, for example, a calcium fluoride substrate, and the surfaces of the windows 31a and 31b facing the inside and outside of the housing 30 are flat. Note that the windows 31a and 31b are not limited to being calcium fluoride substrates as long as they are capable of transmitting the laser light L.

[0019] The electrodes 32a and 32b are arranged opposite each other in the internal space of the housing 30, and the longitudinal direction of the electrodes 32a and 32b is aligned with the direction of travel of light generated by a high voltage applied between the electrodes 32a and 32b. The discharge space between the electrodes 32a and 32b in the housing 30 is sandwiched between the windows 31a and 31b. The electrodes 32a and 32b are discharge electrodes for exciting the laser medium by glow discharge. In this example, the electrode 32a is the cathode, and the electrode 32b is the anode.

[0020] The electrode 32a is supported by an insulating part 33. The insulating part 33 closes an opening formed in the housing 30. The insulating part 33 includes an insulator. A feedthrough 34 made of a conductive member is also disposed in the insulating part 33. The feedthrough 34 applies a voltage supplied from a pulse power module 43 to the electrode 32a. The electrode 32b is supported by an electrode holder part 36 and is electrically connected to the electrode holder part 36, which is at ground potential.

[0021] Charger 41 is a DC power supply device that charges a capacitor (not shown) provided inside PPM 43 at a predetermined voltage. Charger 41 is located outside housing 30 and connected to PPM 43. PPM 43 includes a switch (not shown) controlled by processor 190. When the switch is turned on by this control, PPM 43 boosts the voltage applied from charger 41 to generate a pulsed high voltage and applies this high voltage to electrodes 32a and 32b. When the high voltage is applied, a discharge occurs between electrodes 32a and 32b. The energy of this discharge excites the laser medium inside housing 30. When the excited laser gas transitions to the ground state, light is emitted. The emitted light passes through windows 31a and 31b and exits housing 30. The windows 31a and 31b are tilted at a Brewster angle with respect to the propagation direction of the laser light L so as to suppress reflection of P-polarized light of the laser light L. In this example, the windows 31a and 31b are tilted with respect to a direction perpendicular to the propagation direction of the laser light L and the direction in which the electrodes 32a and 32b face each other. Therefore, the laser light L emitted from the chamber apparatus CH1 contains first linearly polarized light whose polarization direction is perpendicular to the direction in which the electrodes 32a and 32b face each other, and linearly polarized light whose polarization direction is different from that of the first linearly polarized light is reduced from the laser light L. In other words, the windows 31a and 31b are tilted with respect to the polarization direction of the first linearly polarized light, and also function as polarizers that reduce linearly polarized light whose polarization direction is different from that of the first linearly polarized light from the laser light L.

[0022] In this specification and claims, "perpendicular" refers to a state in which the angle formed is between 89 degrees and 91 degrees, and "parallel" refers to a state in which the angle formed is within 1 degree.

[0023] The line narrowing module 60 includes a housing 65, a prism 61, a grating 63, and a rotation stage (not shown) that are arranged in the internal space of the housing 65. An opening is formed in the housing 65, and the housing 65 is connected to the rear side of the housing 30 via the opening.

[0024] Prism 61 expands the beam width of light emitted from window 31b and makes the light incident on grating 63. Prism 61 also reduces the beam width of light reflected from grating 63 and returns the light to the internal space of housing 30 via window 31b. Prism 61 is supported on a rotation stage and rotates by the rotation stage. Rotation of prism 61 changes the angle of incidence of light with respect to grating 63, making it possible to select the wavelength of light that returns from grating 63 to housing 30 via prism 61. Although FIG. 2 shows an example in which one prism 61 is arranged, two or more prisms may be arranged.

[0025] The surface of the grating 63 is made of a highly reflective material, and numerous grooves are provided at regular intervals on the surface. The grating 63 is a dispersive optical element. The cross-sectional shape of each groove is, for example, a right-angled triangle. Light incident on the grating 63 from the prism 61 is reflected by these grooves and diffracted in a direction according to the wavelength of the light. The grating 63 is Littrow-oriented so that the angle of incidence of the light incident on the grating 63 from the prism 61 matches the angle of diffraction of the diffracted light of the desired wavelength. This allows the light of the desired wavelength to be returned to the housing 30 via the prism 61.

[0026] Output mirror 70 faces window 31a and transmits a portion of the laser light L emitted from window 31a and reflects the other portion back into the internal space of housing 30 via window 31a. Output mirror 70 is fixed to a holder (not shown) and is disposed in the internal space of housing 110.

[0027] A Fabry-Perot resonator is formed by the grating 63 and the output mirror 70, which are disposed on either side of the housing 30, and the housing 30 is disposed on the optical path of the resonator. Therefore, the resonator resonates light between the output mirror 70 and the grating 63, which sandwich the chamber device CH1.

[0028] The optical transmission unit 141 mainly includes high-reflection mirrors 141b and 141c. The high-reflection mirrors 141b and 141c are fixed to holders (not shown) with their respective tilt angles adjusted, and are arranged in the internal space of the housing 110. The high-reflection mirrors 141b and 141c highly reflect the laser light L. The high-reflection mirrors 141b and 141c are arranged on the optical path of the laser light L from the output mirror 70. The laser light L is reflected by the high-reflection mirrors 141b and 141c and enters the amplifier 160.

[0029] The amplifier 160 amplifies the energy of the laser light L output from the laser oscillator 130. The amplifier 160 is basically configured to mainly include a chamber device CH2 having a configuration generally similar to that of the laser oscillator 130, a charger 341, a rear mirror 380, and an output mirror 400. Note that components similar to those of the laser oscillator 130 are denoted by the same reference numerals and detailed description thereof will be omitted unless otherwise noted.

[0030] The electrodes 32a and 32b generate a discharge for amplifying the laser light L from the laser oscillator 130. The direction in which the electrodes 32a and 32b face each other is perpendicular to the polarization direction of the first linearly polarized light in the laser light L from the laser oscillator 130. The windows 31a and 31b are tilted with respect to the polarization direction of the first linearly polarized light so that the first linearly polarized light in the laser light L enters as P-polarized light and the incident angle θ of the laser light L becomes the Brewster angle. Therefore, the laser light L emitted from the chamber apparatus CH2 contains the first linearly polarized light, and linearly polarized light having a polarization direction different from the polarization direction of the first linearly polarized light is reduced from the laser light L.

[0031] Furthermore, the amplifier 160 differs from the laser oscillator 130 in that it does not include the line narrowing module 60 but includes a rear mirror 380 .

[0032] The rear mirror 380 is provided between the high-reflection mirror 141c and the window 31b and faces them. The rear mirror 380 transmits and emits the laser light L from the laser oscillator 130 toward the discharge space between the electrodes 32a and 32b, and reflects a portion of the laser light L that is amplified by the electrodes 32a and 32b and emitted from the chamber device CH2 toward the discharge space between the electrodes 32a and 32b.

[0033] The output mirror 400 is disposed on the opposite side of the chamber device CH2 from the rear mirror 380. The output mirror 400 reflects a portion of the laser light L from the chamber device CH2 and transmits another portion of the laser light L. The surface of the output mirror 400 facing the chamber device CH2 is coated with a partially reflective film having a predetermined reflectance. In addition, the surface of the output mirror 400 facing away from the chamber device CH2 is coated with a non-reflective film whose reflectance is almost zero.

[0034] FIG. 3 is a schematic diagram showing an example of the general configuration of the output mirror 400 included in the ultraviolet laser device 100 of the comparative example. The output mirror 400 may be disk-shaped. The surface of the output mirror 400 facing the chamber CH2 and the opposite surface may be flat. The output mirror 400 includes a plate-shaped substrate 410. One main surface 411 of the substrate 410 is provided with a partial reflection coating 420 having a reflectance of 10% to 20%, and the other main surface is provided with an anti-reflection coating 430 having a reflectance of approximately 0%. The substrate 410 is made of, for example, CaF2, MgF2, or synthetic quartz. The partial reflection coating 420 and the anti-reflection coating 430 each have a dielectric multilayer structure in which high-refractive index material layers and low-refractive index material layers are alternately stacked. The desired reflectances of the partial reflection coating 420 and the anti-reflection coating 430 are achieved by adjusting the thicknesses of the high-refractive index material layers and the low-refractive index material layers. Examples of materials for the high refractive index layer include dielectric materials such as LaF3 and GdF3, and examples of materials for the low refractive index layer include dielectric materials such as MgF2.

[0035] The detection unit 153 mainly includes a beam splitter 153b and an optical sensor 153c.

[0036] Beam splitter 153b is disposed on the optical path of laser light L transmitted through output mirror 400. Beam splitter 153b transmits laser light L transmitted through output mirror 400 toward output window 173 with high transmittance, and also reflects a portion of laser light L toward the light-receiving surface of optical sensor 153c.

[0037] The optical sensor 153c measures the pulse energy of the laser light L incident on the light receiving surface of the optical sensor 153c. The optical sensor 153c is electrically connected to the processor 190 and outputs a signal indicating the measured pulse energy to the processor 190. The processor 190 controls the voltage applied to the electrodes 32a, 32b of the laser oscillator 130 and / or the amplifier 160 based on the signal.

[0038] An exit window 173 is provided on the opposite side of the output mirror 400 with respect to the beam splitter 153b of the detection unit 153. The exit window 173 is provided on the wall of the housing 110. The light that passes through the beam splitter 153b is emitted from the exit window 173 to the exposure device 200 outside the housing 110. This laser light L is, for example, a pulsed laser light with a center wavelength of 193.4 nm.

[0039] The display unit 180 is a monitor that displays the state of control by the processor 190 based on a signal from the processor 190. The display unit 180 may be disposed outside the housing 110.

[0040] The processor 190 of the present disclosure is a processing device including a storage device in which a control program is stored and a CPU (Central Processing Unit) that executes the control program. The processor 190 is specially configured or programmed to execute various processes included in the present disclosure. The processor 190 also controls the entire ultraviolet laser device 100. The processor 190 is also electrically connected to an exposure processor (not shown) of the exposure device 200, and transmits and receives various signals to and from the exposure processor.

[0041] 2.2 Operation Next, the operation of the ultraviolet laser device 100 of the comparative example will be described.

[0042] When the ultraviolet laser device 100 emits laser light L, the processor 190 receives a signal indicating a target energy Et and a light emission trigger signal from an exposure processor (not shown) of the exposure device 200. The target energy Et is a target value for the energy of the laser light L used in the exposure process. The processor 190 sets a predetermined charging voltage in the charger 341 so that the energy E becomes the target energy Et, and turns on the pulse power module 43 in synchronization with the light emission trigger signal. This causes the pulse power module 43 to generate a pulsed high voltage from the electrical energy stored in the charger 41, and the high voltage is applied between the electrodes 32a and 32b. When the high voltage is applied, a discharge occurs between the electrodes 32a and 32b, exciting the laser medium contained in the laser gas between the electrodes 32a and 32b. The laser medium emits light when it returns to its ground state. The emitted light resonates between the grating 63 and the output mirror 70 and is amplified each time it passes through a discharge space within the interior space of the housing 30, resulting in laser oscillation. The laser light L contains a first linearly polarized light, and when passing through windows 31a and 31b, linearly polarized light having a polarization direction different from the polarization direction of the first linearly polarized light is reduced from the laser light L. A portion of the laser light L passes through the output mirror 70, is reflected by high-reflection mirrors 141b and 141c, and proceeds into the amplifier 160. In the amplifier 160, the laser light L passes through the rear mirror 380 and window 31b, and proceeds into the housing 30 of the chamber apparatus CH2.

[0043] The processor 190 turns on the switch of the pulse power module 43 of the amplifier 160 so that a discharge occurs when the laser light L from the laser oscillator 130 travels into the discharge space in the housing 30 of the amplifier 160. That is, the processor 190 controls the pulse power module 43 so that a high voltage is applied to the electrodes 32 a, 32 b of the amplifier 160 after a predetermined delay time has elapsed from the timing when the switch of the pulse power module 43 is turned on.

[0044] As a result, the laser light L incident on the amplifier 160 is amplified in the amplifier 160. Furthermore, the laser light L that has traveled into the internal space of the housing 30 travels to the output mirror 400 via the window 31a as described above, and a portion of the laser light L is reflected by the partially reflective film 420 of the output mirror 400. The laser light L reflected by the output mirror 400 travels into the internal space of the housing 30 via the window 31a, where it is amplified and emitted from the window 31b. The light that has traveled from the window 31b is reflected by the rear mirror 380 and travels into the internal space of the housing 30 via the window 31b. In this way, the laser light L of a predetermined wavelength travels back and forth between the rear mirror 380 and the output mirror 400. The laser light L contains a first linearly polarized light, and linearly polarized light having a polarization direction different from the polarization direction of the first linearly polarized light is reduced from the laser light L when it passes through the windows 31a and 31b. Furthermore, the laser light L is amplified each time it passes through the discharge space inside the housing 30.

[0045] Another part of the laser light L that is amplified in the chamber device CH2 and emitted from the window 31a passes through the output mirror 400 and travels to the beam splitter 153b.

[0046] A part of the laser light L that has traveled to the beam splitter 153b passes through the beam splitter 153b and travels to the exit window 173, and the other part is reflected by the beam splitter 153b and travels to the optical sensor 153c.

[0047] The optical sensor 153c measures the energy E of the received laser light L. The optical sensor 153c outputs a signal indicating the measured energy E to the processor 190. The processor 190 feedback-controls the charging voltage of the charger 341 so that the difference ΔE between the energy E and the target energy Et falls within an allowable range. At this time, the processor 190 may close a shutter (not shown) disposed in front of the exit window 173 to prevent the laser light L from entering the exposure device 200 until the difference ΔE falls within the allowable range.

[0048] 2.3 Challenges As the throughput of the exposure tool 200 increases, there is an increasing demand for higher output from the ultraviolet laser device 100, which is the light source. The ultraviolet laser light L that passes through the output mirror 400 of the amplifier 160 is amplified light and therefore has a high energy density. Therefore, as the output power of the light source increases, there is a possibility that the deterioration of the dielectric multilayer film that constitutes the partial reflection film 420 will accelerate. For this reason, there is a demand for a more durable output mirror that can withstand the demand for higher output power.

[0049] In the following embodiments, a highly durable output mirror and a highly durable ultraviolet laser device are exemplified.

[0050] 3. Description of the ultraviolet laser device of embodiment 1 The output mirror 400 and the ultraviolet laser device 100 of this embodiment will be described. Note that the same components as those described above are given the same reference numerals, and redundant description will be omitted unless otherwise specified.

[0051] 3.1 Configuration The ultraviolet laser device 100 of this embodiment differs from the ultraviolet laser device 100 of the comparative example only in the configuration of the output mirror 400. Therefore, a description of the overall configuration of the ultraviolet laser device 100 will be omitted.

[0052] FIG. 4 is a schematic diagram showing an output mirror 400 in this embodiment. In this embodiment, the substrate 410 of the output mirror 400 is a sapphire substrate made of sapphire crystal. Hereinafter, the substrate 410 will be described as the sapphire substrate 410. At least a portion of one principal surface 411 of the sapphire substrate 410 is exposed. In other words, at least a portion of the one principal surface 411 is an uncoated surface that is not provided with a layer made of a material different from that of the sapphire substrate 410. The one principal surface 411 is a partially reflective surface 401 that reflects a portion of the ultraviolet laser light L and transmits the other portion. Note that, although the example in FIG. 4 shows an example in which the entire one principal surface 411 is exposed, it is sufficient that only a portion of the one principal surface 411, which is the partially reflective surface 401, is exposed, and the other portion of the one principal surface 411 may be coated.

[0053] The ultraviolet light transmittance of the sapphire crystal constituting the sapphire substrate 410 may not currently be sufficiently high compared to CaF2, one of the materials used for the substrate 410 in the output mirror 400 of the comparative example. For this reason, it is preferable that the thickness of the sapphire substrate 410 be as thin as possible, but strength and surface precision must also be maintained. From these perspectives, the thickness of the sapphire substrate 410 is preferably 1 mm or more and 7 mm or less, and more preferably 1 mm or more and 5 mm or less.

[0054] FIG. 5 is a graph showing the relationship between the substrate refractive index and the surface reflectance due to Fresnel reflection. The ordinary refractive index of sapphire crystal for ultraviolet light with a wavelength of 193 nm is 1.929, and the extraordinary refractive index is 1.917. As shown by the dotted line in FIG. 5, the Fresnel reflection on one main surface 411 of the sapphire substrate 410 for ultraviolet light with a wavelength of 193 nm is found to have a reflectance of approximately 10%. Therefore, the reflectance of the partially reflective surface 401 in a configuration in which one main surface 411 of the sapphire substrate 410 is exposed is approximately 10% for ultraviolet light with a wavelength of 193 nm. Therefore, when the ultraviolet laser device 100 is an ArF excimer laser device, the reflectance of the partially reflective surface 401 of the output mirror 400 is approximately 10%.

[0055] Furthermore, the ordinary refractive index of sapphire crystal for ultraviolet light with a wavelength of 248 nm is 1.8467. As shown by the dashed-dotted line in Figure 5, the Fresnel reflection on one main surface 411 of the sapphire substrate 410 for ultraviolet light with a wavelength of 248 nm is approximately 9%. Therefore, the reflectance of the partially reflective surface 401 in which one main surface 411 of the sapphire substrate 410 is exposed is approximately 9% for ultraviolet light with a wavelength of 248 nm. Therefore, when the ultraviolet laser device 100 is a KrF excimer laser device, the reflectance of the partially reflective surface 401 of the output mirror 400 is approximately 9%.

[0056] An antireflection structure 402 that suppresses reflection of ultraviolet laser light L is provided on the other main surface 412 opposite to one main surface 411 of the sapphire substrate 410. In this embodiment, the antireflection structure 402 has the same configuration as the antireflection film 430 of the comparative example, and includes a structure made of a dielectric multilayer film.

[0057] The output mirror 400 is arranged so that the partially reflective surface 401 faces the chamber device CH2 side and the anti-reflection structure 402 faces the output window 173 side so that the partially reflective surface 401 is perpendicular to the ultraviolet laser light L emitted from the chamber device CH2.

[0058] 3.2 Operation As described above, the reflectance of the partially reflective surface 401, which is configured such that one main surface 411 of the sapphire substrate 410 is exposed, is approximately 10% for ultraviolet light with a wavelength of 193 nm, so when the ultraviolet laser light L is emitted from the ultraviolet laser device 100, part of the ultraviolet laser light L incident on the output mirror 400 is reflected by the partially reflective surface 401 and the other part is transmitted. Then, similar to the ultraviolet laser device 100 of the comparative example, the amplifier 160 amplifies the ultraviolet laser light L and emits it.

[0059] 3.3 Actions and Effects The output mirror 400 of this embodiment includes a plate-shaped sapphire substrate 410, and at least a portion of one main surface 411 of the sapphire substrate 410 is exposed and serves as a partially reflective surface 401 that reflects a portion of the ultraviolet laser light L and transmits another portion, and the other main surface 412 of the sapphire substrate 410 is provided with a reflection suppressing structure 402 that suppresses reflection of the ultraviolet laser light L. As such, the output mirror 400 of this embodiment does not have a multilayer film formed on the partially reflective surface 401, so there is no deterioration of the multilayer film and the output mirror 400 can be made highly durable against high-power ultraviolet laser light L with a high energy density. Furthermore, the ultraviolet laser device 100 including the output mirror 400 of this embodiment can be made highly durable.

[0060] 3.4 Explanation of Variation 1 The following describes Modification 1 of the ultraviolet laser device 100 of Embodiment 1. Note that the same components as those described above are given the same reference numerals, and redundant description will be omitted unless otherwise specified.

[0061] As described above, the output mirror 400 has a sapphire substrate 410, and the sapphire crystal that is the material of the substrate 410 is a birefringent material. Therefore, the influence of birefringence can be reduced by appropriately selecting the crystal orientation and the polarization direction of the incident light.

[0062] FIG. 6 is a schematic diagram showing the arrangement of the output mirror 400 in this modification. As shown in FIG. 6, in this modification, the c-axis of the sapphire crystal, which is the material of the sapphire substrate 410, is oriented perpendicular to the paper surface. Therefore, the c-axis of the sapphire crystal, which is the material of the sapphire substrate 410, is parallel to the partially reflective surface 401, which is one of the main surfaces. In addition, in this modification, the polarization direction of the ultraviolet laser light L emitted from the chamber device CH2 of the amplifier 160 is oriented in the H direction. In other words, the output mirror 400 is arranged so that the polarization direction of the ultraviolet laser light L incident on the output mirror 400 is parallel to the c-axis of the sapphire crystal, which is the material of the sapphire substrate 410. Note that the optical axis of the ultraviolet laser light L and the partially reflective surface 401 of the output mirror 400 are perpendicular to each other. By arranging the output mirror 400 in this manner, the influence of birefringence due to the sapphire substrate 410 can be reduced.

[0063] 3.5 Explanation of Variation 2 The following describes Modification 2 of the ultraviolet laser device 100 of Embodiment 1. Note that the same components as those described above are given the same reference numerals, and redundant description will be omitted unless otherwise specified.

[0064] FIG. 7 is a schematic diagram showing the arrangement of the output mirror 400 in this modification. As shown in FIG. 7, in this modification, the c-axis of the sapphire crystal, which is the material of the sapphire substrate 410, is parallel to the V direction. Therefore, the c-axis of the sapphire crystal, which is the material of the sapphire substrate 410, is parallel to the partially reflective surface 401, which is one of the main surfaces. Also in this modification, the polarization direction of the ultraviolet laser light L emitted from the chamber device CH2 of the amplifier 160 is the same as in Modification 1. That is, the output mirror 400 is arranged so that the polarization direction of the ultraviolet laser light L incident on the output mirror 400 is perpendicular to the c-axis of the sapphire crystal, which is the material of the sapphire substrate 410. Note that the optical axis of the ultraviolet laser light L and the partially reflective surface 401 of the output mirror 400 are perpendicular to each other. By arranging the output mirror 400 in this manner, the influence of birefringence due to the sapphire substrate 410 can be reduced.

[0065] 3.6 Explanation of Variation 3 A description will be given of Modification 3 of the ultraviolet laser device 100 of Embodiment 1. Note that the same components as those described above are given the same reference numerals, and redundant description will be omitted unless otherwise specified.

[0066] FIG. 8 is a schematic diagram showing the arrangement of the output mirror 400 in this modification. As shown in FIG. 8, in this modification, the c-axis of the sapphire crystal, which is the material of the sapphire substrate 410, is parallel to the Z direction. In other words, the output mirror 400 is arranged so that the optical axis of the ultraviolet laser light L incident on the output mirror 400 is parallel to the c-axis of the sapphire crystal, which is the material of the sapphire substrate 410. Therefore, the c-axis of the sapphire crystal, which is the material of the sapphire substrate 410, is perpendicular to the partially reflecting surface 401, which is one of the main surfaces. The optical axis of the ultraviolet laser light L and the partially reflecting surface 401 of the output mirror 400 are perpendicular to each other. By arranging the output mirror 400 in this manner, the influence of birefringence due to the sapphire substrate 410 can be reduced.

[0067] 3.7 Explanation of Variation 4 A fourth modified example of the ultraviolet laser device 100 of the first embodiment will be described. Note that the same components as those described above are given the same reference numerals, and redundant description will be omitted unless otherwise specified.

[0068] FIG. 9 is a schematic diagram showing the positional relationship between the output mirror 400 and the window 31a of the chamber apparatus CH2 in this modification. In this modification, the window 31a, which is provided in the chamber apparatus CH2 and through which the ultraviolet laser light L is emitted, is tilted so that the angle θ between the normal N to the main surface of the window 31a and the optical axis of the ultraviolet laser light L forms the Brewster angle. The tilt axis S of the window 31a is the rotation axis when the main surface of the window 31a tilts from a state perpendicular to the optical axis of the ultraviolet laser light L to form the Brewster angle as described above, and is parallel to the V axis as shown in FIG. 9. Therefore, the tilt axis S is perpendicular to the optical axis of the ultraviolet laser light L incident on the output mirror 400. Furthermore, as shown in FIG. 9, in this modification, the c-axis of the sapphire crystal, which is the material of the sapphire substrate 410, is oriented in a direction parallel to the H direction. That is, in this modification, the output mirror 400 is arranged so that the c-axis of the sapphire crystal that is the material of the sapphire substrate 410 is perpendicular to the tilt axis S of the window 31a provided in the chamber apparatus CH2 and the propagation direction of the ultraviolet laser light L. By arranging the output mirror 400 in this manner, it is possible to reduce the amount of window-reflected light of the ultraviolet laser light L emitted from the chamber apparatus CH2 and also to reduce the influence of birefringence caused by the sapphire substrate 410.

[0069] 4. Description of the ultraviolet laser device of embodiment 2 Next, a description will be given of the output mirror 400 of embodiment 2. Note that the same components as those described above are given the same reference numerals, and redundant description will be omitted unless otherwise specified.

[0070] 4.1 Configuration Fig. 10 is a schematic diagram showing output mirror 400 in this embodiment, similar to Fig. 4. Output mirror 400 in this embodiment differs from output mirror 400 in embodiment 1 in that antireflection structure 402 is a moth-eye structure provided on the other main surface 412 of sapphire substrate 410.

[0071] 11 is a schematic diagram showing a moth-eye structure. The moth-eye structure has a large number of protruding structures 415 arranged at regular intervals, and the pitch P of the structures 415 is smaller than the wavelength of the ultraviolet laser light L. That is, when the ultraviolet laser light L generated by the ultraviolet laser device 100 of this embodiment has a wavelength of 193 nm, the pitch P of the structures 415 is smaller than 193 nm.

[0072] The protruding structures 415 are, for example, conical. However, the structures 415 are not limited to cones, and may be spindle-shaped or pyramidal. The height of the structures 415 is preferably greater than the pitch P. Note that dry etching, for example, can be used as a method for forming the moth-eye structure on the other main surface 412 of the sapphire substrate 410.

[0073] 4.2 Actions and Effects In this embodiment, the output mirror 400 can realize the incident surface and the exit surface of the ultraviolet laser light L without using a dielectric multilayer film. Therefore, the output mirror 400 of this embodiment can be made more durable against high-power ultraviolet laser light L, and the ultraviolet laser device 100 including the output mirror 400 of this embodiment can be made more durable.

[0074] The anti-reflection function of the moth-eye structure is not limited to being applied to the output mirror 400, but may also be used in other optical elements of the ultraviolet laser device 100.

[0075] 5. Description of the ultraviolet laser device of embodiment 3 Next, an ultraviolet laser device 100 according to embodiment 3 will be described. Note that the same components as those described above are given the same reference numerals, and redundant description will be omitted unless otherwise specified.

[0076] 5.1 Configuration 12 is a schematic diagram showing a schematic configuration example of a part of the amplifier 160 included in the ultraviolet laser device 100 of this embodiment. In the ultraviolet laser device 100 of this embodiment, the amplifier 160 is configured to include a ring-type resonator. Note that the ultraviolet laser device 100 may be, for example, an ArF excimer laser device or a KrF excimer laser device.

[0077] In this embodiment, the amplifier 160 amplifies the energy of the ultraviolet laser light L. The amplifier 160 of this embodiment differs from the amplifier 160 of the first embodiment in that it includes high-reflection mirrors 605, 610, and 615.

[0078] In this embodiment, the output mirror 400 is inclined at 45° with respect to the optical axis of the ultraviolet laser light L emitted from the chamber apparatus CH2 and is positioned opposite the window 31a of the chamber apparatus CH2. The high-reflection mirror 605 is positioned next to the output mirror 400 and opposite the window 31a of the chamber apparatus CH2 so as to form a 90° angle with the output mirror 400. The high-reflection mirror 610 is positioned on the opposite side of the chamber apparatus CH2 from the output mirror 400 and opposite the window 31b so as to be inclined at 45° with respect to the ultraviolet laser light L emitted from the chamber apparatus CH2. The high-reflection mirror 615 is positioned next to the high-reflection mirror 610 and opposite the window 31b of the chamber apparatus CH2 so as to form a 90° angle with the high-reflection mirror 610.

[0079] The configuration of the output mirror 400 is the same as that of the output mirror 400 of the ultraviolet laser device 100 of the first embodiment, the modified example of the first embodiment, or the second embodiment.

[0080] 5.2 Operation Ultraviolet laser light L from the laser oscillator 130 enters through the main surface 412 on which the reflection suppressing structure 402 is provided, and passes through the output mirror 400. The ultraviolet laser light L that passes through the output mirror 400 is reflected by the high-reflection mirror 605 so as to pass from the window 31a to between the electrodes 32a and 32b. The ultraviolet laser light L that has passed through the chamber device CH2 and is amplified exits from the window 31b, is reflected by the high-reflection mirror 610 and the high-reflection mirror 615, passes again from the window 31b to between the electrodes 32a and 32b of the chamber device CH2, is amplified, and exits from the window 31a. The ultraviolet laser light L then enters the output mirror 400. The output mirror 400 is tilted at 45° with respect to the traveling direction of the ultraviolet laser light L that is emitted from the chamber device CH2, so the ultraviolet laser light L enters the output mirror 400 from the partially reflective surface 401 side at an incident angle of 45°. A portion of the ultraviolet laser light L incident on the output mirror 400 is reflected by the partially reflecting surface 401 of the output mirror 400, is incident on the high-reflection mirror 605, is reflected there, and again enters the chamber device CH2 and is amplified. The other portion of the ultraviolet laser light L incident on the output mirror 400 passes through the output mirror 400 and is emitted from the amplifier 160.

[0081] 5.3 Actions and Effects Fig. 13 is a graph showing the relationship between Fresnel reflectivity and incident angle for each polarization direction at a wavelength of 193 nm. As shown in Fig. 13, when the incident angle is 45°, the Fresnel reflectivity for S-polarized light is 18.8%, and the Fresnel reflectivity for P-polarized light is 3.6%. Therefore, the output mirror 400 has a reflectivity of approximately 19% for S-polarized light. As with the other embodiments, the output mirror 400 in this embodiment is not provided with a partially reflective film including a dielectric multilayer film, so that a high-output, highly durable ultraviolet laser device 100 can be realized.

[0082] The configuration of the amplifier 160 in the above embodiment may be applied to a laser oscillator that is the first stage of an ultraviolet laser device using a multistage amplification system, or may be applied to multiple amplifiers. Also, the configuration of the output mirror 400 may be applied to the output mirror of a single laser oscillator.

[0083] The above description is intended to be illustrative, not limiting. Accordingly, it will be apparent to those skilled in the art that modifications can be made to the embodiments of the present disclosure without departing from the scope of the claims. It will also be apparent to those skilled in the art that the embodiments of the present disclosure can be used in combination. Terms used throughout this specification and claims should be construed as "open-ended" terms unless expressly stated. For example, terms such as "comprise," "have," "comprise," and "equip" should be interpreted as meaning "without excluding the presence of elements other than those listed." The modifier "a" or "an" should be interpreted as meaning "at least one" or "one or more." 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," including combinations other than "A," "B," and "C."

Claims

1. An output mirror for ultraviolet laser light, the output mirror includes a plate-shaped sapphire substrate, at least a part of one main surface of the sapphire substrate is an exposed partially reflective surface that reflects a part of the ultraviolet laser light and transmits another part of the ultraviolet laser light; The other main surface of the sapphire substrate is provided with an anti-reflection structure that suppresses reflection of the ultraviolet laser light.

2. 2. The output mirror of claim 1, The antireflection structure includes a moth-eye structure provided on the other main surface of the sapphire substrate.

3. 2. The output mirror of claim 1, The anti-reflection structure includes a structure made of a dielectric multilayer film.

4. 2. The output mirror of claim 1, The ultraviolet laser light is an ArF laser light or a KrF laser light.

5. 2. The output mirror of claim 1, The c-axis of the sapphire crystal that is the material of the sapphire substrate is parallel to the one main surface.

6. 2. The output mirror of claim 1, The c-axis of the sapphire crystal that is the material of the sapphire substrate is perpendicular or parallel to the polarization direction of the ultraviolet laser light.

7. 2. The output mirror of claim 1, The c-axis of the sapphire crystal that is the material of the sapphire substrate is perpendicular to the one main surface.

8. 2. The output mirror of claim 1, The c-axis of the sapphire crystal that is the material of the sapphire substrate is parallel to the direction in which the ultraviolet laser light travels.

9. 2. The output mirror of claim 1, The c-axis of the sapphire crystal that is the material of the sapphire substrate is perpendicular to the tilt axis of a window that is provided in a chamber device and that emits the ultraviolet laser light and is tilted around the tilt axis with respect to the emission direction of the ultraviolet laser light, and to the propagation direction of the ultraviolet laser light.

10. 2. The output mirror of claim 1, The thickness of the sapphire substrate is 1 mm or more and 7 mm or less.

11. 2. The output mirror of claim 1, The thickness of the sapphire substrate is 1 mm or more and 5 mm or less.

12. An ultraviolet laser device including an amplifier for amplifying ultraviolet laser light, the amplifier includes an output mirror for the ultraviolet laser light, the output mirror includes a plate-shaped sapphire substrate, at least a part of one main surface of the output mirror is a partially reflective surface on which the sapphire substrate is exposed and which reflects a part of the ultraviolet laser light and transmits another part of the ultraviolet laser light; The other main surface of the output mirror is provided with a reflection suppressing structure that suppresses reflection of the ultraviolet laser light.

13. 13. The ultraviolet laser device according to claim 12, The output mirror is arranged so that the c-axis of the sapphire crystal that is the material of the sapphire substrate is perpendicular or parallel to the polarization direction of the ultraviolet laser light.

14. 13. The ultraviolet laser device according to claim 12, The output mirror is disposed so that the c-axis of the sapphire crystal that is the material of the sapphire substrate is parallel to the direction in which the ultraviolet laser light travels.

15. 13. The ultraviolet laser device according to claim 12, The output mirror is positioned so that the c-axis of the sapphire crystal, which is the material of the sapphire substrate, is perpendicular to the tilt axis of a window that is provided in a chamber device and emits the ultraviolet laser light and is tilted around the tilt axis with respect to the emission direction of the ultraviolet laser light, and to the propagation direction of the ultraviolet laser light.

16. 13. The ultraviolet laser device according to claim 12, The amplifier is a ring resonator.

17. 17. The ultraviolet laser device according to claim 16, The output mirror of the amplifier is positioned at an angle of 45° with respect to the direction of travel of the ultraviolet laser light emitted from a chamber device included in the amplifier, and the ultraviolet laser light incident on the output mirror is incident from the other main surface.

18. A method for manufacturing an electronic device, comprising: the output mirror for the ultraviolet laser light includes a plate-shaped sapphire substrate; at least a part of one main surface of the output mirror is a partially reflective surface on which the sapphire substrate is exposed and which reflects a part of the ultraviolet laser light and transmits another part of the ultraviolet laser light; The other main surface of the output mirror is provided with a reflection suppressing structure that suppresses reflection of the ultraviolet laser light. The ultraviolet laser light generated by the ultraviolet laser device is output to an exposure device. In order to manufacture an electronic device, a photosensitive substrate is exposed to the ultraviolet laser light in the exposure apparatus. A method for manufacturing an electronic device, comprising:

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