Laser device and method for manufacturing electronic device

Abstract

A laser device according to one aspect of the present disclosure comprises: an optical isolator disposed on an optical path between an oscillation stage laser and an amplification stage laser that amplifies, as seed light, pulse laser light of linearly polarized light of an ultraviolet wavelength output from the oscillation stage laser, the optical isolator including a first Faraday rotator that causes the polarization direction of the pulse laser light output from the oscillation stage laser to rotate by a first angle in a first rotation direction by means of a magnetic field in the first direction, a first polarizer that has a normalized transmittance of 0.9 or more with respect to the pulse laser light output from the first Faraday rotator, and a second Faraday rotator that causes the polarization direction of the pulsed laser light transmitted through the first polarizer to rotate by a second angle in a second rotation direction opposite to the first rotation direction by means of a magnetic field in the second direction opposite to the first direction; and a second polarizer that is disposed in an optical resonator of the amplification stage laser and has a normalized transmittance of 0.9 or more with respect to the seed light.

Description

Laser device and method for manufacturing electronic device

[0001] The present disclosure relates to a laser apparatus and a method for manufacturing an electronic device.

[0002] In recent years, semiconductor exposure apparatuses 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 that output laser light with a wavelength of approximately 248 nm and ArF excimer laser devices that 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, constructing a projection lens using a material that transmits ultraviolet light, such as KrF and ArF laser light, can result in chromatic aberration. This can result in a decrease in resolution. Therefore, it is necessary to narrow the spectral linewidth of the laser light output from a 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 within 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.

[0004] International Publication No. 2022 / 195893 Japanese Patent Application Laid-Open No. 2006-165484 overview

[0005] A laser device according to one aspect of the present disclosure comprises an oscillation-stage laser, an amplification-stage laser that amplifies linearly polarized pulsed laser light of an ultraviolet wavelength output from the oscillation-stage laser using as seed light, an optical isolator arranged on an optical path between the oscillation-stage laser and the amplification-stage laser, the optical isolator including: a first Faraday rotator that rotates the polarization direction of the pulsed laser light output from the oscillation-stage laser by a first angle in a first rotation direction by a magnetic field in a first direction, a first polarizer having a normalized transmittance of 0.9 or more for the pulsed laser light output from the first Faraday rotator, and a second Faraday rotator that rotates the polarization direction of the pulsed laser light that has passed through the first polarizer by a second angle in a second rotation direction opposite to the first rotation direction by a magnetic field in a second direction opposite to the first direction, and a second polarizer arranged within an optical resonator of the amplification-stage laser, the second polarizer having a normalized transmittance of 0.9 or more for the seed light.

[0006] A laser device according to another aspect of the present disclosure comprises an oscillation-stage laser, an amplification-stage laser that amplifies linearly polarized pulsed laser light of an ultraviolet wavelength output from the oscillation-stage laser using as seed light, an optical isolator arranged on an optical path between the oscillation-stage laser and the amplification-stage laser, the optical isolator including: a first Faraday rotator that rotates the polarization direction of the pulsed laser light output from the oscillation-stage laser by a first angle in a first rotation direction using a magnetic field in a first direction, a first polarizer that has a normalized transmittance of 0.9 or more for the pulsed laser light output from the first Faraday rotator, and a second Faraday rotator that rotates the polarization direction of the pulsed laser light that has passed through the first polarizer by a second angle in the same direction as the first rotation direction using a magnetic field in the same direction as the first direction, and a second polarizer that is arranged in an optical resonator of the amplification-stage laser and has a normalized transmittance of 0.9 or more for the seed light.

[0007] A method for manufacturing an electronic device according to another aspect of the present disclosure includes an oscillation-stage laser, an amplification-stage laser that amplifies linearly polarized pulsed laser light of an ultraviolet wavelength output from the oscillation-stage laser using the linearly polarized pulsed laser light of an ultraviolet wavelength output from the oscillation-stage laser as seed light, an optical isolator arranged on an optical path between the oscillation-stage laser and the amplification-stage laser, the optical isolator including a first Faraday rotator that rotates the polarization direction of the pulsed laser light output from the oscillation-stage laser by a first angle in a first rotation direction using a magnetic field in a first direction, a first polarizer that has a normalized transmittance of 0.9 or more for the pulsed laser light output from the first Faraday rotator, and a first The method includes generating laser light amplified by the amplification stage laser using a laser apparatus including: an optical isolator including a second Faraday rotator that rotates the polarization direction of pulsed laser light that has passed through the polarizer by a second angle in a second rotation direction opposite to the first rotation direction by a magnetic field in a second direction opposite to the first direction; and a second polarizer that is placed in an optical resonator of the amplification stage laser and has a normalized transmittance for seed light of 0.9 or more; outputting the amplified laser light to an exposure apparatus; and exposing the laser light onto a photosensitive substrate in the exposure apparatus to manufacture an electronic device.

[0008] Some embodiments of the present disclosure are described below, by way of example only, with reference to the accompanying drawings. FIG. 1 is an explanatory diagram of polarization. FIG. 2 is a graph showing the relationship between the angle of incidence of light incident on calcium fluoride from air and the reflectance of each polarization component of S-polarized light and P-polarized light. FIG. 3 is an explanatory diagram showing an example in which a window of an excimer laser chamber is arranged at Brewster's angle within an optical resonator. FIG. 4 is a schematic diagram showing the configuration of a laser apparatus according to a comparative example. FIG. 5 is a diagram showing problems with the laser apparatus according to the comparative example. FIG. 6 is a schematic diagram showing the configuration of an optical isolator according to a comparative example that suppresses optical feedback. FIG. 7 is a schematic cross-sectional diagram showing the configuration of a laser apparatus according to the first embodiment. FIG. 8 is a schematic cross-sectional diagram showing the configuration of a Faraday rotator. FIG. 9 is a diagram showing preferred ranges of magnetic field and Faraday material thickness when the wavelength of pulsed laser light is the oscillation wavelength of an ArF excimer laser. FIG. 10 is a diagram showing preferred ranges of magnetic field and Faraday material thickness when the wavelength of pulsed laser light is the oscillation wavelength of a KrF excimer laser. FIG. 11 is a graph showing the relationship between the extinction ratio and the angular difference between the transmission axis of a polarizer and the polarization direction of pulsed laser light, and a graph converting the extinction ratio into a normalized transmittance. FIG. 12 is a schematic diagram showing the configuration of a laser device according to a second embodiment. FIG. 13 is a schematic diagram showing the configuration of an amplification-stage laser of a laser device according to the second embodiment. FIG. 14 is a graph showing the relationship between the transmittance Tp of P-polarized light and the ratio (Ts / Tp) of the transmittance Ts of S-polarized light to the transmittance Tp of P-polarized light, with respect to the angle of incidence on a window arranged in the optical resonator of the amplification-stage laser shown in FIG. 13. FIG. 15 is an explanatory diagram showing the optical path of the S-polarized component of pulsed laser light propagating through a window when the window is positioned at Brewster's angle. FIG. 16 is a schematic diagram showing the configuration of a laser device according to a third embodiment. FIG. 17 is a schematic diagram showing the configuration of a laser device according to a fourth embodiment. FIG. 18 is a schematic diagram showing the configuration of an amplification-stage laser of a laser device according to the fourth embodiment. Fig. 19 is an explanatory diagram showing the optical path of the S-polarized component of pulsed laser light propagating through a plane-parallel substrate and a window when the plane-parallel substrate and the window are arranged at the Brewster angle. Fig. 20 shows a schematic configuration of an exposure apparatus. Embodiment

[0009] -Table of Contents- 1. Explanation of Terms 1.1 Polarizer 1.2 Polarization 1.3 Brewster Angle 1.4 Normalized Transmittance 2. Overview of Laser Device According to Comparative Example 2.1 Configuration 2.2 Operation 3. Issues 4. First Embodiment 4.1 Configuration 4.2 Operation 4.3 Specific Example of Faraday Rotator 4.4 Allowable Angle Difference Between Transmission Axis of Polarizer and Polarization Direction of Laser Light 4.5 Actions and Effects 5. Second Embodiment 5.1 Configuration 5.2 Operation 5.3 Actions and Effects 6. Third Embodiment 6.1 Configuration 6.2 Operation 6.3 Actions and Effects 7. Fourth Embodiment 7.1 Configuration 7.2 Operation 7.3 Actions and Effects 8. Regarding Manufacturing Method of Electronic Device 9. Others Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. The embodiments described below are examples of the present disclosure and are not intended to limit the scope of the present disclosure. Furthermore, not all of the configurations and operations described in each embodiment are necessarily essential to the configurations and operations of the present disclosure. Identical components are designated by the same reference numerals, and redundant descriptions will be omitted.

[0010] 1. Explanation of terms 1.1 Polarizer A "polarizer" is an optical element that separates light with a specific polarization direction (transmission axis direction) from light with a polarization direction perpendicular to that direction.

[0011] 1.2 Polarized light "Polarized light" refers to light with a regular vibration direction of the electric and magnetic fields. Figure 1 is an explanatory diagram of polarized light, and the refractive index n A From medium A to refractive index n B This figure shows an example in which light is incident on a medium B. When light is incident on a medium with a different refractive index as shown in Figure 1, the electric field component perpendicular to the plane of incidence is called S-polarized light, and the electric field component parallel to the plane of incidence is called P-polarized light. According to Fresnel's law, the reflectance and transmittance of each polarization component change with the angle of incidence as shown in Figure 2.

[0012] 2 is a graph showing the reflectance of S-polarized light and P-polarized light relative to the incident angle α. A = 1) to CaF2 (refractive index n for wavelength 248 nm B Graphs are shown for the case where the incident angle is 1.468.

[0013] 1.3 Brewster angle As shown in Figure 2, in the case of P-polarized light, there exists an incident angle at which the reflectance is 0 and the transmittance is 100%, and this angle is called the Brewster angle. Figure 3 shows an example of a window WD placed in the chamber of an excimer laser. Discharge electrodes DE in the chamber are placed opposite each other in a direction perpendicular to the paper surface, and discharge occurs between the electrodes. The window WD is located within the laser resonator at a Brewster angle α as shown in Figure 3. B When the optical waveguide is arranged such that the wavelength is 100 nm, the output beam is transmitted multiple times during resonance and becomes almost entirely P-polarized with respect to the window WD.

[0014] 1.4 Normalized Transmittance The "normalized transmittance" is a value normalized so that the transmittance is 1.0 when the angular difference between the transmission axis of the polarizer and the polarization direction of the pulsed laser light is 0, or a value normalized so that the transmittance of P-polarized light of a window positioned at Brewster angle is 1.0.

[0015] 4 is a side view showing a schematic configuration of a laser device 20 according to a comparative example. The comparative example of 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.

[0016] The laser device 20 is an excimer laser device including a master oscillator (MO) 22, which is an oscillation stage laser, an MO beam steering unit 24, and an amplification stage laser, a power oscillator (PO) 26. The MO 22 includes a line narrowing module (LNM) 30, a chamber 32, and an output coupling mirror 34.

[0017] The LNM 30 includes a prism beam expander 36 for narrowing the spectral width, and a grating 38. The prism beam expander 36 and the grating 38 are arranged in a Littrow configuration in which the angle of incidence and the angle of diffraction match. The output coupling mirror 34 is a partial reflection mirror with a reflectivity of 40% to 60%. The output coupling mirror 34 is arranged so as to form an optical resonator together with the LNM 30.

[0018] The chamber 32 is disposed on the optical path of the optical resonator. The chamber 32 includes a pair of discharge electrodes 40a, 40b and two windows 42, 44 through which the laser light passes. The chamber 32 is filled with a laser gas. The laser gas includes a rare gas, a halogen gas, and a buffer gas. The rare gas may be, for example, argon (Ar) or krypton (Kr) gas. The halogen gas may be, for example, fluorine (F2) gas. The buffer gas may be, for example, neon (Ne) gas. A voltage is applied between the discharge electrodes 40a, 40b by a power supply (not shown). The power supply may be a pulse power module (PPM) including a switch and a charging capacitor.

[0019] The MO beam steering unit 24 includes a high-reflection mirror 50 and a high-reflection mirror 52 and is arranged so that the laser light output from the MO 22 is incident on the PO 26 .

[0020] An MO pulse energy monitor 54 is disposed between high-reflection mirror 50 and high-reflection mirror 52. MO pulse energy monitor 54 includes a beam splitter (BS) 55 and an optical sensor 56. BS 55 is disposed on the optical path of the pulsed laser light output from MO 22, and is disposed so that reflected light from BS 55 enters optical sensor 56.

[0021] The PO 26 includes a rear mirror 60, a chamber 62, and an output coupling mirror 64. The rear mirror 60 and the output coupling mirror 64 form an optical resonator, and the chamber 62 is disposed on the optical path of this optical resonator.

[0022] The configuration of the chamber 62 may be similar to that of the chamber 32. The chamber 62 includes a pair of discharge electrodes 70a, 70b and two windows 72, 74. The chamber 62 is filled with laser gas. The rear mirror 60 may be, for example, a partial reflection mirror with a reflectance of 50% to 90%. The output coupling mirror 64 may be a partial reflection mirror with a reflectance of 10% to 30%.

[0023] 2.2 Operation A high-voltage pulse is applied between the discharge electrodes 40a and 40b in the chamber 32 from a power supply (not shown). When a discharge occurs between the discharge electrodes 40a and 40b in the chamber 32, the laser gas is excited, and pulsed laser light with an ultraviolet wavelength of 150 nm to 380 nm is output from the output coupling mirror 34, the line of which has been narrowed by the optical resonator formed by the output coupling mirror 34 and the LNM 30.

[0024] The energy of the pulsed laser light output from the output coupling mirror 34 is measured by an MO pulse energy monitor 54. The pulsed laser light is also incident on a rear mirror 60 of the PO 26 by the MO beam steering unit 24 as a pulsed seed light.

[0025] At the timing when the pulsed seed light transmitted through the rear mirror 60 enters the chamber 62, a high-voltage pulse is applied between the discharge electrodes 70a and 70b in the chamber 62 from a power supply (not shown). When a discharge occurs between the discharge electrodes 70a and 70b in the chamber 62, the laser gas is excited, and the pulsed seed light is amplified by a Fabry-Perot optical resonator formed by the output coupling mirror 64 and the rear mirror 60, and the amplified pulsed laser light is output from the output coupling mirror 64. In FIG. 4, the direction perpendicular to the paper surface is defined as the X direction. The traveling direction of the pulsed laser light output from the output coupling mirror 64 is defined as the Z direction, and the direction perpendicular to the Z direction and the X direction is defined as the Y direction.

[0026] 3. Issues Figure 5 illustrates an issue with the laser device 20 according to the comparative example. When light returning from the PO 26 reaches the MO 22, laser performance deteriorates. The term "returned light" here refers to the sum of two types of light: MO-returned light and PO-escape light. Light emitted from the MO 22 enters the PO 26, but because the rear mirror 60 inside the PO 26 is a partially reflective mirror (reflectivity 50% to 90%), some of the light incident on the rear mirror 60 returns directly to the MO 22 without entering the PO 26. The light that is reflected by the rear mirror 60 and returns to the MO 22 without entering the chamber 62 of the PO 26 is called "MO-returned light."

[0027] On the other hand, light that is incident on the PO 26 from the MO 22 and passes through the rear mirror 60 is resonated and amplified within the PO 26 and then output. As described above, the rear mirror 60 within the PO 26 is a partial reflection mirror, so some of the light that is incident on the chamber 62 of the PO 26 and amplified returns to the MO 22. Of the light amplified by the PO 26, the light that passes through the rear mirror 60 and returns to the MO 22 is called "PO-leaving light."

[0028] The returning light becomes a thermal load on the LNM 30 and the like, and may cause deterioration in the stability of the linewidth, the stability of the pulse energy, etc. In order to suppress the returning light entering the MO 22, an optical isolator may be placed between the MO 22 and the PO 26.

[0029] Fig. 6 shows a configuration example of an optical isolator 80 according to a comparative example that suppresses returning light. The upper part of Fig. 6 shows the operation of the optical isolator 80 with respect to pulsed laser light (MO injection light: outgoing light) traveling from the MO 22 to the PO 26. The lower part of Fig. 6 shows the operation of the optical isolator 80 with respect to laser light (returning light) traveling from the PO 26 to the MO 22.

[0030] The optical isolator 80 includes a half-wave plate 81, a first polarizer 83, a Faraday rotator 84, and a second polarizer 88 arranged in this order from the MO22 side. The Faraday rotator 84 includes a Faraday material 85 and a magnet 86. In FIG. 6, the right-pointing arrow shown in the Faraday rotator 84 indicates the direction of the magnetic field generated by the magnet 86. The double-headed arrow shown in the dashed circle in the figure indicates the direction of the polarization plane of the pulsed laser light when the line of sight is aligned in the direction in which the pulsed laser light travels, i.e., the polarization direction. The same applies to FIG. 7 and other drawings.

[0031] In the optical isolator 80, pulsed laser light linearly polarized in a specific direction from the MO 22 passes through a first polarizer 83, and the polarization direction is rotated 45 degrees clockwise by a Faraday rotator 84 to which a magnetic field is applied. Then, after passing through a second polarizer 88, the light enters the PO 26.

[0032] The half-wave plate 81 adjusts the polarization direction of the pulsed laser light from the MO 22 so that the polarization direction of the pulsed laser light output from the MO 22 is the same as the polarization direction of the pulsed laser light incident on the PO 26. This eliminates the need to change other modules that depend on the polarization direction.

[0033] 6, the returning light from the PO 26 passes through the second polarizer 88 in the same polarization direction as the incident light to the PO 26, and the polarization direction is rotated 45 degrees clockwise by the Faraday rotator 84 to which a magnetic field is applied. The polarization direction of the returning light that has passed through the Faraday rotator 84 is perpendicular to the transmission axis of the first polarizer 83, and the returning light is reflected by the first polarizer 83 and does not enter the MO 22.

[0034] Here, the half-wave plate 81 that adjusts the polarization direction has low durability at short wavelengths such as those of an excimer laser, making it difficult to use it stably for a long period of time. One of the problems to be solved by the present disclosure is to provide an optical isolator that can be used stably for a long period of time even with pulsed laser light of a short wavelength such as an excimer laser.

[0035] 4. First Embodiment 4.1 Configuration FIG. 7 schematically illustrates an example configuration of a laser device 100 according to the first embodiment. Differences between the configuration illustrated in FIG. 7 and that illustrated in FIG. 4 will be described. The laser device 100 differs from the configuration illustrated in FIG. 4 in that an optical isolator 120 is disposed between the MO 22 and the PO 26 and a second polarizer 89 is disposed on the optical path of the optical resonator of the PO 26. The optical isolator 120 includes a first Faraday rotator 110, a first polarizer 83, a second Faraday rotator 112, and a damper 116 for terminating the return light. While the optical isolator 80 according to the comparative example illustrated in FIG. 6 includes two polarizers (83, 88), the optical isolator 120 according to the first embodiment includes only one first polarizer 83.

[0036] The first Faraday rotator 110 and the second Faraday rotator 112 each have a magnet, and by reversing the direction of the applied magnetic field, the rotation direction of the polarization direction is reversed. The direction of the magnetic field applied to the first Faraday rotator 110 shown in Figure 7 (the direction indicated by the downward arrow in Figure 7) is an example of the "first direction" in this disclosure. The direction of the magnetic field applied to the second Faraday rotator 112 shown in Figure 7 (the direction indicated by the upward arrow in Figure 7) is an example of the "second direction" in this disclosure.

[0037] The Faraday material, size, and magnetic field of the first Faraday rotator 110 and the second Faraday rotator 112 are selected so that the rotation angle of the polarization direction of each is 45 degrees. Preferred selection conditions will be described in detail later (FIGS. 8 to 10).

[0038] The damper 116 is disposed so that the returning light reflected by the first polarizer 83 enters the damper 116 .

[0039] The second polarizer 89 is positioned so that pulsed laser light polarized in a specific direction incident on the PO 26 passes through. The second polarizer 89 may be a flat-plate polarizing beam splitter having a multilayer film formed on the surface of a flat glass plate, a glass-cube polarizing beam splitter having a multilayer film sandwiched between right-angle glass cubes, a crystal polarizer using birefringence, or a plane-parallel substrate positioned at the Brewster angle. Other configurations may be the same as those shown in FIG. 4.

[0040] 7 also shows the polarization direction of the pulsed laser beam at points a, b, c, and d on the optical path between the MO 22 and the PO 26. Fig. 7 shows the polarization direction of the pulsed laser beam propagating from the MO 22 to the PO 26 at points a to d, and the polarization direction of the return beam traveling from the PO 26 to the MO 22 at points d and c.

[0041] 4.2 Operation First, we will explain the pulsed laser light propagating from the MO 22 to the PO 26. In the laser device 100, the optical isolator 120 is arranged so that the polarization direction of the pulsed laser light output from the MO 22 is the same as the polarization direction of the pulsed laser light incident on the PO 26. In this case, the polarization directions being the same means that the angle difference is within 10 degrees.

[0042] The linearly polarized pulsed laser light (point a) output from the MO 22 and polarized in a specific direction has its polarization direction rotated 45 degrees counterclockwise (point b) by the first Faraday rotator 110. The counterclockwise direction is an example of the "first rotation direction" in this disclosure, and 45 degrees is an example of the "first angle" in this disclosure.

[0043] The first polarizer 83 is arranged so that its transmission axis is parallel to the polarization direction of the pulsed laser light output from the first Faraday rotator 110. The pulsed laser light, whose polarization direction has been rotated by the first Faraday rotator 110, passes through the first polarizer 83 (point c).

[0044] The pulsed laser light transmitted through the first polarizer 83 enters the second Faraday rotator 112, where the polarization direction is rotated 45 degrees clockwise by the second Faraday rotator 112 (point d). The clockwise direction is an example of the "second rotation direction" in this disclosure, and 45 degrees is an example of the "second angle" in this disclosure. The pulsed laser light whose polarization direction has been rotated by the second Faraday rotator 112 is injected into the PO 26. The polarization direction of the pulsed laser light at points a and d is the same.

[0045] The pulsed laser light (pulsed seed light) injected into the PO 26 passes through the second polarizer 89, and the pulsed laser light amplified by the optical resonator consisting of the output coupling mirror 64 and the rear mirror 60 is output from the output coupling mirror 64.

[0046] Next, we will explain the pulsed laser light returning from the PO 26 to the MO 22. At point d in Fig. 7, the polarization direction of the pulsed laser light propagating from the MO 22 to the PO 26 is the same as the polarization direction of the pulsed laser light (return light) returning from the PO 26 to the MO 22, because the second polarizer 89 is present on the optical path of the optical resonator of the PO 26.

[0047] The polarization direction of the returning light from PO26 is then rotated 45 degrees clockwise by the second Faraday rotator 112 (point c). At point c, the polarization direction of the pulsed laser light propagating from MO22 to PO26 is perpendicular to the polarization direction of the pulsed laser light returning from PO26 to MO22. Therefore, the pulsed laser light returning from PO26 to MO22 is reflected without passing through the first polarizer 83 and enters the damper 116. The damper 116 absorbs and blocks the light reflected by the first polarizer 83.

[0048] 4.3 Specific Examples of Faraday Rotators Figure 8 is a cross-sectional view schematically showing a configuration example of the Faraday rotator 130. The Faraday rotator 130 can be used as each of the first Faraday rotator 110 and the second Faraday rotator 112. The Faraday rotator 130 includes a Faraday material 135 and a magnet 136. The Faraday material 135 is transparent in the ultraviolet wavelength range and has a large Verdet constant. The term "transparent" means that the material is optically transparent.

[0049] The Verdet constant depends on the type of material and the wavelength. Suitable materials for the Faraday material 135 include calcium fluoride (CaF), synthetic quartz (SiO), and magnesium fluoride (MgF). The Faraday material 135 is held in a holder 137.

[0050] The magnet 136 has a hollow structure, and a Faraday material 135 is placed inside via a holder 137. The direction of the magnetic field penetrating the Faraday material 135 is parallel to the direction of light propagation. The direction of rotation of the polarization plane (polarization direction) by the Faraday rotator 130 depends on the sign of the Verdet constant and the direction of the applied magnetic field.

[0051] 9 shows the magnetic field and the preferred range of the thickness of the Faraday material 135 when the wavelength of the pulsed laser light is the oscillation wavelength of an ArF excimer laser. The oscillation wavelength of an ArF excimer laser includes a wavelength of approximately 193 nm. FIG. 9 shows the cases where the Faraday material 135 is CaF2 and SiO2, respectively. The thickness of the Faraday material 135 is evaluated based on the thickness in the optical axis direction.

[0052] 10 shows a preferable range of the magnetic field and the thickness of the Faraday material 135 when the wavelength of the pulsed laser light is the oscillation wavelength of a KrF excimer laser. The oscillation wavelength of a KrF excimer laser includes a wavelength of approximately 248 nm. FIG. 10 shows the cases where the Faraday material 135 is CaF2 and SiO2, respectively.

[0053] 9 and 10 are selected based on the ease of realizing the magnetic field. The most preferable range of the magnetic field is the magnetic flux density when a neodymium magnet or the like with strong magnetic force is used. The thickness of the Faraday material 135 is calculated based on the selected material, the magnetic flux density of the magnetic field, and the Verdet constant, to determine the thickness at which the polarization plane is rotated by 45 degrees.

[0054] 9 , when the Faraday material 135 is calcium fluoride and the wavelength of the pulsed laser light is the oscillation wavelength of an ArF excimer laser, the preferred ranges for the magnetic field applied to the Faraday rotator 130 and the thickness of the Faraday material 135 in the optical axis direction are 0.5 T to 3.0 T and 6 mm to 40 mm, respectively. More preferably, they are 0.75 T to 2.9 T and 10 mm to 30 mm, and most preferably, they are 0.8 T to 1.5 T and 15 mm to 25 mm. Note that notations indicating a numerical range, such as "0.5 T to 3.0 T," indicate a range that includes the numerical values ​​before and after "to." For example, the notation "0.5 T to 3.0 T" means "0.5 T or more and 3.0 T or less."

[0055] When the Faraday material 135 is made of synthetic quartz and the wavelength of the pulsed laser light is the oscillation wavelength of an ArF excimer laser, the preferable ranges of the magnetic field applied to the Faraday rotator 130 and the thickness of the Faraday material 135 in the optical axis direction are 0.5 T to 3 T and 3 mm to 25 mm, more preferably 0.75 T to 2.9 T and 6 mm to 20 mm, and most preferably 0.8 T to 1.5 T and 8 mm to 15 mm.

[0056] 10, when the Faraday material is calcium fluoride and the wavelength of the pulsed laser light is the oscillation wavelength of a KrF excimer laser, the preferable ranges of the magnetic field applied to the Faraday rotator 130 and the thickness of the Faraday material 135 in the optical axis direction are 0.5 T to 3.0 T and 13 mm to 83 mm, more preferably 0.75 T to 2.9 T and 20 mm to 55 mm, and most preferably 0.8 T to 1.5 T and 30 mm to 50 mm.

[0057] When the Faraday material is synthetic quartz and the wavelength of the pulsed laser light is the oscillation wavelength of a KrF excimer laser, the preferable ranges of the magnetic field applied to the Faraday rotator 130 and the thickness of the Faraday material 135 in the optical axis direction are 0.5 T to 3.0 T and 8 mm to 53 mm, more preferably 0.75 T to 2.9 T and 10 mm to 40 mm, and most preferably 0.8 T to 1.5 T and 15 mm to 30 mm.

[0058] The Faraday material 135 may be divided into multiple pieces, the total of which may satisfy the above thickness. The number of pieces may be, for example, two, three, or four. It is also possible to use different types of Faraday rotators for the first Faraday rotator 110 and the second Faraday rotator 112, such as those made of different Faraday materials, with different thicknesses in the optical axis direction, and with different magnetic field strengths. On the other hand, using the same Faraday material, the same thickness in the optical axis direction, and the same magnetic field strength for the first Faraday rotator 110 and the second Faraday rotator 112 is preferable because it is easy to handle, since the polarization planes of the first and second Faraday rotators 110 and 112 rotate in opposite directions by the same rotation amount (angle).

[0059] 4.4 Allowable Angle Difference Between the Transmission Axis of the Polarizer and the Polarization Direction of the Laser Light It is most preferable that the transmission axes of the first polarizer 83 and the second polarizer 89 are parallel to the polarization direction of the pulsed laser light incident on each polarizer. However, they do not necessarily have to be strictly parallel, and an angular difference between the two is allowable within a range that allows the intended function to be achieved in practice.

[0060] FIG. 11 shows a graph showing the relationship between the extinction ratio (dB) and the angular difference between the transmission axis of a polarizer and the polarization direction of a pulsed laser beam, and a graph showing the extinction ratio converted into normalized transmittance. The left vertical axis of FIG. 11 represents the extinction ratio, and the right vertical axis represents the normalized transmittance. The normalized transmittance is a value normalized so that the transmittance is 1.0 when the angular difference is 0 degrees. The first polarizer 83, which transmits the pulsed laser beam output from the first Faraday rotator 110, and the second polarizer 89, which transmits the pulsed laser beam output from the second Faraday rotator 112, can function effectively for practical purposes if their normalized transmittances for the incident pulsed laser beam are 0.9 or greater. Therefore, according to FIG. 11, the preferred allowable range of the angular difference between the transmission axis of the first polarizer 83 or the second polarizer 89 and the polarization direction of the pulsed laser beam is ±17.5 degrees, within which the normalized transmittance is 0.9 or greater.

[0061] According to the above considerations, the angle by which the polarization direction of the pulsed laser beam output from the MO 22 is rotated by the first Faraday rotator 110 and the angle by which the polarization direction of the pulsed laser beam transmitted through the first polarizer 83 is rotated by the second Faraday rotator 112 may each be within a range of 45 degrees ± 17.5 degrees. Furthermore, the polarization direction of the pulsed laser beam traveling from the MO 22 toward the PO 26 when it enters the first polarizer 83 may intersect with the polarization direction of the pulsed laser beam returning from the PO 26 toward the MO 22 when it passes through the second Faraday rotator 112 and enters the first polarizer 83 at an angle within a range of 90 degrees ± 17.5 degrees. As a result, the pulsed laser beam that passes through the second Faraday rotator 112 and enters the first polarizer 83 is reflected by the first polarizer 83 and absorbed by the damper 116.

[0062] 4.5 Actions and Effects According to the laser device 100 according to the first embodiment, the following effects can be obtained.

[0063] [1] The optical isolator 120 of the laser device 100 does not use the half-wave plate 81, which has low durability at short wavelengths, and therefore can be used stably for a long period of time even with short-wavelength pulsed laser light such as an excimer laser.

[0064] [2] According to the laser device 100, the pulsed laser light returning from the PO 26 toward the MO 22 is reflected by the first polarizer 83 and absorbed by the damper 116, thereby preventing the light from entering the MO 22. This reduces the thermal load on the MO 22, and improves the energy stability, linewidth stability, and other properties compared to the configuration of the comparative example.

[0065] [3] According to the laser device 100, since the second polarizer 89 is located inside the PO26, the transmission efficiency from the MO22 to the PO26 is improved compared to when the second polarizer 88 is placed between the MO22 and the PO26 (Figure 6), and pulsed seed light can be efficiently injected into the PO26.

[0066] [4] According to the laser device 100, the polarization direction of the pulsed laser light can be made the same before and after passing through the optical isolator 120 without using the half-wave plate 81, which has low durability at short wavelengths. Therefore, it is possible to suppress the return light without changing other modules that depend on the polarization direction.

[0067] [5] According to the laser device 100, by placing the second polarizer 89 inside the optical resonator of the amplification stage laser, the polarization purity can be increased compared to when a polarizer is placed outside the optical resonator so that the light passes through the second polarizer 89 on each round trip in the optical resonator.

[0068] 5. Second Embodiment 5.1 Configuration Fig. 12 schematically shows the configuration of a laser device 102 according to a second embodiment. Fig. 13 schematically shows the configuration of the PO 26 in the laser device 102. Differences between the configurations shown in Figs. 12 and 13 and that shown in Fig. 7 will be described. The laser device 102 shown in Fig. 12 differs from the configuration shown in Fig. 7 in that the second polarizer 89 is not provided and that the windows 72 and 74 are arranged so that the angles of incidence on the windows 72 and 74 are Brewster's angles as shown in Fig. 13. Other configurations may be the same as those shown in Fig. 7.

[0069] The windows 72 and 74 are each arranged so that the pulsed laser light is incident as P-polarized light. As a result, the pulsed laser light is highly transmitted through the windows 72 and 74. Therefore, the windows 72 and 74 can also function as the second polarizer 89. The windows 72 and 74 may be, for example, calcium fluoride substrates.

[0070] 14 is a graph showing the relationship between the transmittance Tp of P-polarized light and the ratio (Ts / Tp) of the transmittance Ts of S-polarized light to the transmittance Tp of P-polarized light, versus the angle of incidence on the window 72 and the window 74. Note that the transmittance in Fig. 14 is the value when light passes through the window 72 and the window 74 twice, respectively, i.e., when light makes one round trip through the optical resonator.

[0071] As shown in Figure 14, P-polarized light is highly transmitted even when the incident angle is not the Brewster angle. The transmittance Tp of P-polarized light is 0.9 or greater when the incident angle is in the range of 45 degrees or greater and 65 degrees or less. However, as the incident angle becomes smaller, the ratio Ts / Tp increases, and the transmission rate of S-polarized light increases. For this reason, an incident angle greater than 45 degrees, at which the ratio Ts / Tp becomes less than 0.5, is preferable. Therefore, as long as the incident angle on window 72 and window 74 is greater than 45 degrees and equal to or less than 65 degrees, they can also function as second polarizer 89.

[0072] 15 is an explanatory diagram showing the optical path of the S-polarized component of pulsed laser light propagating through window 72 when window 72 is positioned at Brewster's angle. In Fig. 15, the solid arrows indicate the optical path of transmitted light, and the dashed arrows indicate the optical path of multiple-reflected light due to surface reflections of the substrate.

[0073] In order to increase the polarization split ratio of the window 72 arranged at the Brewster angle, it is desirable that the optical paths of the transmitted light (solid arrow) and the multiple reflected light (dashed arrow) are spatially separated.

[0074] If these two optical paths are spatially separated, the multiple-reflected light does not pass through the discharge region in chamber 62 and is not amplified. This results in a high polarization separation ratio. The transmitted light of the P-polarized component and S-polarized component of the pulsed laser light passes through the discharge region in chamber 62, is amplified, and is output as pulsed laser light.

[0075] The spatial distance between the optical paths of the transmitted light and the multiple-reflected light (distance between the optical paths) varies depending on the thickness of the window 72. By increasing the thickness of the window 72, the two optical paths can be spatially separated.

[0076] The first optical path distance x1 between the transmitted light and the multiple-reflected light can be expressed by the following equation (1), where t is the thickness of the window 72, θ is the angle of incidence, and n is the refractive index.

[0077]

[0078] The width in the direction perpendicular to the discharge direction of the pulsed laser light (1 / e 2 When the width of the multi-reflected light beam is D, if x1>D, the multi-reflected light beam is not amplified.

[0079] The thickness t of the window 72 is, for example, 5 mm or more.

[0080] The same applies to the window 74 as to the window 72. The thicknesses of the window 72 and the window 74 may be the same or different.

[0081] 5.3 Actions and Effects The laser device 102 according to embodiment 2 can achieve the same effects as the laser device 100 according to embodiment 1. Furthermore, the laser device 102 can reduce the number of optical elements inside the PO 26 compared to the laser device 100, which is expected to result in longer life and higher transmittance of the optical elements.

[0082] Furthermore, according to the laser device 102, by arranging the windows 72 and 74 at the Brewster angle within the optical resonator of the PO 26, the light passes through the windows 72 and 74 on each round trip within the optical resonator, thereby increasing the polarization purity compared to when a polarizer or window is arranged outside the optical resonator.

[0083] 6. Embodiment 3 6.1 Configuration Figure 16 schematically shows the configuration of a laser device 103 according to embodiment 3. Differences between the configuration shown in Figure 16 and embodiment 2 (Figures 12 and 13) will be described below. The laser device 103 shown in Figure 16 differs from the laser device 102 in that an optical isolator 120 is arranged so that the polarization direction of the pulsed laser light output from the MO 22 and the polarization direction of the pulsed laser light incident on the PO 26 are orthogonal. In this case, the polarization directions being orthogonal means that the angle difference is between 85 degrees and 95 degrees.

[0084] 16 , for example, the direction of the magnetic field applied to the second Faraday rotator 112 is the same as the direction of the magnetic field applied to the first Faraday rotator 110. As a result, the polarization direction of the pulsed seed beam incident on the PO 26 is orthogonal to the polarization direction of the pulsed seed beam incident on the PO 26 of the laser device 102.

[0085] Therefore, the incident planes of the windows 72 and 74 of the laser device 103 are perpendicular to the incident planes of the windows 72 and 74 of the laser device 102 according to the second embodiment.

[0086] The angle of incidence of the pulsed laser light on the windows 72 and 74 of the laser device 103 is preferably the Brewster angle, similar to the laser device 102. Note that, similar to the second embodiment, the angle of incidence of the pulsed laser light on the windows 72 and 74 does not necessarily have to be the Brewster angle, and as long as it is greater than 45 degrees and equal to or less than 65 degrees, it can also function as the second polarizer 89. The other configurations may be similar to those of the laser device 102.

[0087] 6.2 Operation The operation of the optical isolator 120 ( FIG. 16 ) of the laser device 103 according to embodiment 3 that differs from that of FIG. 12 will be described below. In the optical isolator 120 shown in FIG. 16 , the pulsed laser light (point c) that has passed through the first polarizer 83 enters the second Faraday rotator 112, and the polarization direction of the pulsed laser light is rotated by 45 degrees counterclockwise by the second Faraday rotator 112 (point d). The polarization directions of the pulsed laser light at points a and d in FIG. 16 are orthogonal to each other.

[0088] The pulsed laser light whose polarization direction has been rotated by the second Faraday rotator 112 is injected into the PO 26 , and the pulsed laser light amplified by the optical resonator of the PO 26 is output from the output coupling mirror 64 .

[0089] As for the pulsed laser light returning from PO26 to MO22, at point d in Figure 16, the polarization direction of the pulsed laser light propagating from MO22 to PO26 is the same as the polarization direction of the pulsed laser light (return light) returning from PO26 to MO22.

[0090] The polarization direction of the return light from the PO 26 is rotated 45 degrees counterclockwise by the second Faraday rotator 112 (point c). That is, the direction of rotation of the polarization direction by the second Faraday rotator 112 is the same as the direction of rotation of the polarization direction by the first Faraday rotator 110. Other operations are the same as those of the laser device 102.

[0091] 6.3 Actions and Effects According to the laser device 103 of the third embodiment, the same effects as those of the laser device 102 of the second embodiment can be obtained.

[0092] 7. Fourth Embodiment 7.1 Configuration FIG. 17 schematically illustrates the configuration of a laser device 104 according to a fourth embodiment. FIG. 18 schematically illustrates the configuration of the PO 26 in the laser device 104. Differences between the configurations illustrated in FIGS. 17 and 18 and those of the second embodiment (FIGS. 12 and 13) will be described below. The laser device 104 differs from the configuration illustrated in FIG. 12 in that it includes a plane-parallel substrate 92 disposed parallel to the window 72 between the rear mirror 60 of the PO 26 and the window 72. The angle of incidence between the plane-parallel substrate 92 and the window 72 is not limited to the Brewster angle and may be greater than 45 degrees and equal to or less than 70 degrees.

[0093] The plane-parallel substrate 92 may be, for example, a calcium fluoride substrate, similar to the windows 72 and 74. The other configurations may be the same as those in the second embodiment.

[0094] 19 is an explanatory diagram showing the optical path of the S-polarized component of pulsed laser light propagating through the plane-parallel substrate 92 and the window 72 when the plane-parallel substrate 92 and the window 72 are arranged at the Brewster angle. In Fig. 19, the solid arrows indicate the optical path of the transmitted light, the dashed arrows indicate the optical path of the multiple-reflected light due to surface reflection of the substrate, and the thick wavy arrows indicate the optical path of the multiple-reflected light reflected by the window 72 and the plane-parallel substrate 92.

[0095] In order to increase the polarization separation ratio of the window 72 arranged at the Brewster angle, it is desirable that the optical paths of the transmitted light (solid arrow) and the multiple-reflected light (thick wavy arrow) reflected by the window 72 and the parallel plane substrate 92 are spatially separated.

[0096] If these two optical paths are spatially separated, the multiple-reflected light does not pass through the discharge region in chamber 62 and is not amplified. This results in a high polarization separation ratio. The transmitted light of the P-polarized component and S-polarized component of the pulsed laser light passes through the discharge region in chamber 62, is amplified, and is output as pulsed laser light.

[0097] The spatial distance between the optical paths of the transmitted light and the multiple-reflected light varies depending on the distance d between the window 72 and the plane-parallel substrate 92. By increasing the distance d, the two optical paths can be spatially separated.

[0098] The second optical path distance x, which is the spatial distance between the optical paths of the transmitted light and the multiple-reflected light (thick wavy arrows), can be expressed by the following equation (2), where θ is the angle of incidence onto the parallel plane substrate 92.

[0099]

[0100] The width in the direction perpendicular to the discharge direction of the pulsed laser light (1 / e 2 When x1>D and x2>D, the multiple reflected light is not amplified.

[0101] The distance d between the window 72 and the plane-parallel substrate 92 is, for example, 3 mm or more. The thicknesses of the window 72 and the plane-parallel substrate 92 may be the same or different.

[0102] 7.3 Actions and Effects The laser device 104 according to the fourth embodiment can provide the same effects as those of the second embodiment. Furthermore, the laser device 104 can provide pulsed laser light with a higher polarization purity than that of the second embodiment.

[0103] 8. Regarding the Manufacturing Method of Electronic Devices Figure 20 shows a schematic configuration example of an exposure apparatus 300. The exposure apparatus 300 includes an illumination optical system 304 and a projection optical system 306. The illumination optical system 304 uses laser light incident from the laser apparatus 100 to illuminate a reticle pattern on a reticle (not shown) placed on a reticle stage RT. The projection optical system 306 reduces and projects the laser light 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.

[0104] The exposure apparatus 300 exposes the workpiece with laser light reflecting the reticle pattern by synchronously translating the reticle stage RT and the workpiece table WT. After the reticle pattern is transferred to the 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. Instead of the laser apparatus 100, the laser light may be generated using the laser apparatus 102, 103, or 104 described in embodiments 2 to 4.

[0105] 9. Other The above description is intended to be illustrative and not restrictive. Therefore, 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.

[0106] Terms used throughout this specification and claims should be construed as "open ended" terms unless expressly stated otherwise. For example, terms such as "comprise," "have," "comprise," and "equip" should be construed as meaning "without excluding the presence of elements other than those listed." In addition, the modifier "a" should be construed as meaning "at least one" or "one or more." In addition, the term "at least one of A, B, and C" should be construed as "A," "B," "C," "A+B," "A+C," "B+C," or "A+B+C." Furthermore, it should be construed to include combinations of these with elements other than "A," "B," and "C."

Claims

1. A laser device comprising: an oscillation stage laser; an amplification stage laser that amplifies linearly polarized ultraviolet wavelength pulsed laser light output from the oscillation stage laser using as seed light; an optical isolator arranged on an optical path between the oscillation stage laser and the amplification stage laser, the optical isolator including: a first Faraday rotator that rotates the polarization direction of the pulsed laser light output from the oscillation stage laser by a first angle in a first rotation direction by a magnetic field in a first direction; a first polarizer having a normalized transmittance of 0.9 or more for the pulsed laser light output from the first Faraday rotator; and a second Faraday rotator that rotates the polarization direction of the pulsed laser light that has passed through the first polarizer by a second angle in a second rotation direction opposite to the first rotation direction by a magnetic field in a second direction opposite to the first direction; and a second polarizer arranged in an optical resonator of the amplification stage laser, the second polarizer having a normalized transmittance of 0.9 or more for the seed light.

2. A laser device according to claim 1, wherein the second polarizer is a flat plate type polarizing beam splitter, a glass cube type polarizing beam splitter, or a calcium fluoride substrate.

3. A laser device according to claim 1, wherein the second polarizer is a calcium fluoride substrate, and the angle of incidence of the pulsed laser light incident on the calcium fluoride substrate is greater than 45 degrees and equal to or less than 65 degrees.

4. A laser device according to claim 1, wherein the polarization direction of the pulsed laser light output from the oscillation-stage laser and the pulsed laser light incident on the amplification-stage laser are the same.

5. A laser device as claimed in claim 1, wherein the amplification stage laser comprises a chamber including a window through which the pulsed laser light passes, and the window has an incident angle of the pulsed laser light incident thereon that is greater than 45 degrees and not greater than 65 degrees, and also serves as the second polarizer.

6. A laser device according to claim 5, wherein, when the thickness of the window is t, the angle of incidence to the window is θ, and the refractive index of the window is n, a first optical path distance x1 calculated by the following formula is greater than the width of the pulsed laser light in a direction perpendicular to the discharge direction. Laser device.

7. A laser device according to claim 5, wherein said amplification stage laser further comprises a parallel plane substrate arranged parallel to said window.

8. A laser device according to claim 7, wherein, when the distance between the window and the parallel plane substrate is d and the angle of incidence on the parallel plane substrate is θ, a second optical path distance x2 calculated by the following formula is greater than a width in a direction perpendicular to the discharge direction of the pulsed laser light: Laser device.

9. A laser device according to claim 7, wherein said window and said parallel plane substrate are calcium fluoride substrates.

10. A laser device as described in claim 1, wherein the angular difference between the polarization direction of the pulsed laser light output from the first Faraday rotator and the transmission axis of the first polarizer is within 17.5 degrees, and the angular difference between the polarization direction of the pulsed laser light output from the second Faraday rotator and the transmission axis of the second polarizer is within 17.5 degrees.

11. A laser device according to claim 1, wherein the angular difference between the first angle and the second angle is within 17.5 degrees.

12. A laser device as described in claim 1, wherein the first angle and the second angle are each within the range of 45 degrees ±17.5 degrees, the polarization direction of the pulsed laser light traveling from the oscillation stage laser in the direction of the amplification stage laser when it is incident on the first polarizer intersects with the polarization direction of the pulsed laser light returning from the amplification stage laser in the direction of the oscillation stage laser when it passes through the second Faraday rotator and is incident on the first polarizer at an angle within the range of 90 degrees ±17.5 degrees, and the pulsed laser light that passes through the second Faraday rotator and is incident on the first polarizer is reflected by the first polarizer.

13. A laser device according to claim 12, wherein the wavelength of the pulsed laser light is the oscillation wavelength of an ArF excimer laser, the Faraday material contained in each of the first Faraday rotator and the second Faraday rotator is calcium fluoride, and the thickness of the Faraday material in the optical axis direction is 6 mm or more and 40 mm or less.

14. A laser device according to claim 12, wherein the wavelength of the pulsed laser light is the oscillation wavelength of an ArF excimer laser, the Faraday material contained in each of the first Faraday rotator and the second Faraday rotator is synthetic quartz, and the thickness of the Faraday material in the optical axis direction is 3 mm or more and 25 mm or less.

15. A laser device according to claim 12, wherein the wavelength of the pulsed laser light is the oscillation wavelength of a KrF excimer laser, the Faraday material contained in each of the first Faraday rotator and the second Faraday rotator is calcium fluoride, and the thickness of the Faraday material in the optical axis direction is 13 mm or more and 83 mm or less.

16. A laser device according to claim 12, wherein the wavelength of the pulsed laser light is the oscillation wavelength of a KrF excimer laser, the Faraday material contained in each of the first Faraday rotator and the second Faraday rotator is synthetic quartz, and the thickness of the Faraday material in the optical axis direction is 8 mm or more and 53 mm or less.

17. A laser device comprising: an oscillation stage laser; an amplification stage laser that amplifies linearly polarized ultraviolet wavelength pulsed laser light output from the oscillation stage laser using as seed light; an optical isolator arranged on an optical path between the oscillation stage laser and the amplification stage laser, the optical isolator including: a first Faraday rotator that rotates the polarization direction of the pulsed laser light output from the oscillation stage laser by a first angle in a first rotation direction by a magnetic field in a first direction; a first polarizer having a normalized transmittance of 0.9 or more for the pulsed laser light output from the first Faraday rotator; and a second Faraday rotator that rotates the polarization direction of the pulsed laser light that has passed through the first polarizer by a second angle in the same direction as the first rotation direction by a magnetic field in the same direction as the first direction; and a second polarizer that is arranged in an optical resonator of the amplification stage laser, and has a normalized transmittance of 0.9 or more for the seed light.

18. A laser device according to claim 17, wherein the polarization direction of the pulsed laser light output from the oscillation-stage laser is perpendicular to the polarization direction of the pulsed laser light incident on the amplification-stage laser.

19. A laser device as described in claim 17, wherein the amplification stage laser comprises a chamber including a window that transmits the pulsed laser light, and the window has an incident angle of the pulsed laser light incident on it that is greater than 45 degrees and not greater than 65 degrees, and also serves as the second polarizer.

20. A method for manufacturing an electronic device, comprising: an oscillation stage laser; an amplification stage laser that amplifies linearly polarized ultraviolet wavelength pulsed laser light output from the oscillation stage laser using as seed light; an optical isolator arranged on an optical path between the oscillation stage laser and the amplification stage laser, the optical isolator including: a first Faraday rotator that rotates the polarization direction of the pulsed laser light output from the oscillation stage laser by a first angle in a first rotation direction by a magnetic field in a first direction; a first polarizer having a normalized transmittance of 0.9 or more for the pulsed laser light output from the first Faraday rotator; and a second Faraday rotator that rotates the polarization direction of the pulsed laser light that has passed through the first polarizer by a second angle in a second rotation direction opposite to the first rotation direction by a magnetic field in a second direction opposite to the first direction; and a second polarizer that is arranged in an optical resonator of the amplification stage laser and has a normalized transmittance of 0.9 or more for the seed light. generating laser light amplified by the amplification stage laser using a laser apparatus comprising: outputting the amplified laser light to an exposure apparatus; and exposing a photosensitive substrate in the exposure apparatus with the laser light to manufacture an electronic device.

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