Optical isolator, ultraviolet laser device, and method for manufacturing electronic device

Abstract

An optical isolator of one aspect of the present disclosure has: a first polarizer that transmits linearly polarized incident light of an ultraviolet wavelength; a Faraday rotator that rotates a polarization direction of light that has transmitted through the first polarizer by a magnetic field; and a second polarizer that transmits incident light that has transmitted through the Faraday rotator. A Faraday material of the Faraday rotator is a calcium fluoride crystal, and when a direction of a crystal axis of [001] is set as an a-axis, a direction of [100] is set as a b-axis, and a direction of [010] is set as a c-axis, in a case where the three axes are rotated by a first angle with the c-axis as a center, and axes after the b-axis is rotated by a second angle after the first angle are set as an x-axis, a y-axis, and a z-axis, respectively, the first angle is 40 degrees or more and 50 degrees or less, the second angle is 45 degrees or more and 75 degrees or less, the z-axis is parallel to a propagation direction of the incident light, and the calcium fluoride crystal is disposed in a manner that an angle difference between a transmission axis of the first polarizer and the x-axis is in a range of 0 degrees or more and 45 degrees or less.

Description

Technical Field

[0001] This disclosure relates to methods for manufacturing optical isolators, ultraviolet laser devices, and electronic devices. Background Technology

[0002] In recent years, with the miniaturization and high integration of semiconductor integrated circuits, there has been a demand for higher resolution in semiconductor exposure equipment. Therefore, the use of shorter wavelengths of light emitted from exposure light sources has been developed. For example, as gas laser devices for exposure, there are KrF excimer lasers that use lasers with an output wavelength of approximately 248 nm, and ArF excimer lasers that use lasers with an output wavelength of approximately 193 nm.

[0003] The naturally oscillating light from KrF and ArF excimer lasers has a relatively wide spectral linewidth, approximately 350 pm to 400 pm. Therefore, when using projection lenses made of materials that allow ultraviolet light to pass through KrF and ArF lasers, chromatic aberration sometimes occurs. As a result, resolution may be reduced. Therefore, it is necessary to narrow the spectral linewidth of the laser output from the gas laser device to a level that eliminates chromatic aberration. Thus, in the laser resonator of a gas laser device, a line-narrowing module (LNM) containing narrowing elements (etalon, grating, etc.) is sometimes included to narrow the spectral linewidth. Hereinafter, gas laser devices with narrowed spectral linewidths will be referred to as narrow-bandgap gas laser devices.

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: Japanese Patent Application Publication No. 2006-73921

[0007] Patent Document 2: Japanese Patent Application Publication No. 61-141189

[0008] Patent Document 3: Japanese Patent Application Publication No. 2011-225400

[0009] Non-patent literature

[0010] Non-patent literature 1: Vyatkin, Anton&Snetkov, Ilya&Palashov, Oleg&Khazanov, Efim. "Specificity of Thermally Induced Depolarization in CaF2." 2013Conference onLasers and Electro-Optics, CLEO 2013.10.1364 / CLEO_SI.2013.CTu1O.5. Summary of the Invention

[0011] One aspect of this disclosure is an optical isolator comprising: a first polarizer whose transmission axis is configured such that the normalized transmittance of the first polarizer for linearly polarized incident light of ultraviolet wavelength is 0.9 or more; a Faraday rotor comprising a Faraday material, which rotates the polarization direction of light transmitted through the first polarizer by a magnetic field; and a second polarizer whose transmission axis is configured such that the normalized transmittance of the second polarizer for incident light transmitted through the Faraday rotor is 0.9 or more, wherein the Faraday material is a calcium fluoride crystal, and the direction

[001] , which is the crystal axis of the calcium fluoride crystal, is set as the a-axis, [100... When the direction of

[010] is set as the b-axis and the direction of

[010] is set as the c-axis, the axes after rotating the three axes a-axis, b-axis and c-axis by a first angle around the c-axis and rotating the axes after rotating the first angle around the b-axis by a second angle are respectively set as the x-axis, y-axis and z-axis. The first angle is 40 degrees or more and 50 degrees or less, the second angle is 45 degrees or more and 75 degrees or less, and the z-axis is parallel to the propagation direction of light incident on the calcium fluoride crystal from the first polarizer. The calcium fluoride crystal is configured such that the angle difference between the transmission axis of the first polarizer and the x-axis is within the range of 0 degrees or more and 45 degrees or less.

[0012] Another aspect of this disclosure discloses an ultraviolet laser device comprising: an oscillating laser that outputs linearly polarized pulsed laser light of ultraviolet wavelength; an amplifier that amplifies and outputs the pulsed laser light; and an optical isolator disposed in the optical path between the oscillating laser and the amplifier, the optical isolator comprising: a first polarizer whose transmission axis is configured such that the normalized transmittance of the first polarizer for linearly polarized incident light of ultraviolet wavelength is 0.9 or more; a Faraday rotor comprising a Faraday material that rotates the polarization direction of light transmitted through the first polarizer by a magnetic field; and a second polarizer whose transmission axis is configured such that the normalized transmittance of the second polarizer for incident light transmitted through the Faraday rotor is 0.9 or more, wherein... The Faraday material is calcium fluoride crystal. When the direction of

[001] , which is the crystal axis of calcium fluoride crystal, is set as the a-axis, the direction of

[100] is set as the b-axis, and the direction of

[010] is set as the c-axis, the axes of a, b, and c are rotated by a first angle around the c-axis and by a second angle around the b-axis after the first angle is rotated as the x-axis, y-axis, and z-axis, respectively. The first angle is 40 degrees or more and 50 degrees or less, the second angle is 45 degrees or more and 75 degrees or less, and the z-axis is parallel to the propagation direction of light incident on the calcium fluoride crystal from the first polarizer. The calcium fluoride crystal is configured such that the angle difference between the transmission axis of the first polarizer and the x-axis is within the range of 0 degrees or more and 45 degrees or less.

[0013] Another aspect of this disclosure discloses a method for manufacturing an electronic device comprising the following steps: generating a laser amplified by an amplifier using an ultraviolet laser device; outputting the amplified laser to an exposure device; and exposing the laser on a photosensitive substrate within the exposure device to manufacture the electronic device. The ultraviolet laser device comprises: an oscillating laser that outputs linearly polarized pulsed laser light of ultraviolet wavelength; an amplifier that amplifies and outputs the pulsed laser light; and an optical isolator disposed in the optical path between the oscillating laser and the amplifier. The optical isolator comprises: a first polarizer whose transmission axis is configured such that the normalized transmittance of the first polarizer for linearly polarized incident light of ultraviolet wavelength is 0.9 or higher; a Faraday rotor comprising a Faraday material that rotates the polarization direction of light transmitted through the first polarizer by a magnetic field; and a second polarizer whose transmission axis is configured... The second polarizer has a normalized transmittance of 0.9 or higher for incident light after passing through the Faraday rotor. The Faraday material is calcium fluoride crystal. When the direction of

[001] , which is the crystal axis of the calcium fluoride crystal, is set as the a-axis, the direction of

[100] is set as the b-axis, and the direction of

[010] is set as the c-axis, the three axes of a-axis, b-axis and c-axis are rotated by a first angle around the c-axis and rotated by a second angle around the b-axis after the first angle is rotated as the x-axis, y-axis and z-axis, respectively. The first angle is 40 degrees or more and 50 degrees or less, the second angle is 45 degrees or more and 75 degrees or less, and the z-axis is parallel to the propagation direction of light incident from the first polarizer to the calcium fluoride crystal. The calcium fluoride crystal is configured such that the angle difference between the transmission axis and the x-axis of the first polarizer is in the range of 0 degrees or more and 45 degrees or less. Attached Figure Description

[0014] Hereinafter, several embodiments of the present disclosure will be described as simple examples with reference to the accompanying drawings.

[0015] Figure 1 This is a side view that schematically shows the structure of the ultraviolet laser device of the comparative example.

[0016] Figure 2 This is a diagram illustrating the subject of a comparative example of an ultraviolet laser device.

[0017] Figure 3 The structure of a comparative example of an optical isolator that suppresses returning light is shown in a schematic diagram.

[0018] Figure 4 The structure of the optical isolator in Embodiment 1 is shown in outline.

[0019] Figure 5 This is a diagram illustrating the definitions of the x-axis, y-axis, and z-axis after rotating the crystal axis, as well as the rotation angles α and β.

[0020] Figure 6This is a perspective view illustrating an example of preferred configuration conditions for Faraday materials.

[0021] Figure 7 This is a schematic diagram showing the relationship between the transmission axis of the first polarizer and the crystal axis of the Faraday material.

[0022] Figure 8 Shown in Figure 7 The relationship between the transmission axis of the first polarizer and the x-axis and y-axis of the Faraday material when viewed along the direction of incident light propagation.

[0023] Figure 9 The graph, transcribed from Non-Patent Document 1, shows the relationship between depolarization γ and rotation angle β, where depolarization γ is the proportion of the polarization component in the transmitted light orthogonal to the polarization direction of the incident light relative to the total incident power of the light incident on the CaF2 crystal.

[0024] Figure 10 It is a graph showing the relationship between depolarization γ and rotation angle β when the wavelength of the incident light is estimated to be 193 nm.

[0025] Figure 11 It is a graph showing the preferred range of magnetic fields applied to the Faraday rotor and the thickness of the Faraday material.

[0026] Figure 12 It is a graph showing the relationship between the angle difference between the transmission axis of the polarizer and the polarization direction of the pulsed laser and the extinction ratio, as well as a graph converting the extinction ratio into normalized transmittance.

[0027] Figure 13 The structure of the optical isolator in Embodiment 2 is shown in outline.

[0028] Figure 14 This is a front view of the Faraday rotor applied in Embodiment 2.

[0029] Figure 15 yes Figure 14 A sectional view at line 15-15.

[0030] Figure 16 The structure of the optical isolator in Embodiment 3 is shown in outline.

[0031] Figure 17 The structure of the ultraviolet laser device of Embodiment 4 is shown in outline.

[0032] Figure 18 The structure of the ultraviolet laser device of Embodiment 5 is shown in outline.

[0033] Figure 19 The structure of the ultraviolet laser device of Embodiment 6 is shown in outline.

[0034] Figure 20 The structure of the ultraviolet laser device of Embodiment 7 is shown in outline.

[0035] Figure 21 This is a top view that schematically shows the structure of the amplification stage laser applied in Embodiment 7.

[0036] Figure 22 A structural example of an exposure apparatus is shown in general. Detailed Implementation

[0037] -Table of contents-

[0038] 1. Explanation of terminology

[0039] 2. Overview of the comparative ultraviolet laser device

[0040] 2.1 Structure

[0041] 2.2 Actions

[0042] 3. Research Topic

[0043] 4. Implementation Method 1

[0044] 4.1 Structure

[0045] 4.2 Relationship between the transmission axis of the first polarizer and the crystal axis of the Faraday material

[0046] 4.3 Regarding rotation angles α and β

[0047] 4.4 Preferred range of magnetic field and Faraday material thickness

[0048] 4.5 The allowable angular difference between the transmission axis of the polarizer and the polarization direction of the laser.

[0049] 4.6 Actions

[0050] 4.7 Functions / Effects

[0051] 4.8 Verification method for crystal axes

[0052] 4.9 Variation Example

[0053] 5. Implementation Method 2

[0054] 5.1 Structure

[0055] 5.2 Actions

[0056] 5.3 Functions / Effects

[0057] 6. Implementation Method 3

[0058] 6.1 Structure

[0059] 6.2 Actions

[0060] 6.3 Functions / Effects

[0061] 7. Implementation Method 4

[0062] 7.1 Structure

[0063] 7.2 Actions

[0064] 7.3 Functions / Effects

[0065] 7.4 Variation Example

[0066] 8. Implementation Method 5

[0067] 8.1 Structure

[0068] 8.2 Actions

[0069] 8.3 Functions / Effects

[0070] 9. Implementation Method 6

[0071] 9.1 Structure

[0072] 9.2 Actions

[0073] 9.3 Functions / Effects

[0074] 10. Implementation Method 7

[0075] 10.1 Structure

[0076] 10.2 Actions

[0077] 10.3 Functions / Effects

[0078] 11. Manufacturing methods for electronic devices

[0079] 12. Another application example of optical isolators

[0080] 13. Other

[0081] The embodiments of this disclosure will now be described in detail with reference to the accompanying drawings. The embodiments described below illustrate several examples of this disclosure and do not limit its scope. Furthermore, the structures and operations described in each embodiment are not necessarily all necessary for the structures and operations of this disclosure. Additionally, the same reference numerals are used to denote the same structural elements, and repeated descriptions are omitted.

[0082] 1. Explanation of terminology

[0083] A polarizer is an optical element that separates light with a specific polarization direction (transmission axis direction) from light with a polarization direction or orthogonal to it.

[0084] In this specification, the term "parallel" is used, unless explicitly stated otherwise, to mean not only strictly parallel, but also includes the concept of approximately parallel, encompassing a range of practically permissible angular differences without losing technical significance. Similarly, the terms "orthogonal" or "perpendicular" in this specification are also used, unless explicitly stated otherwise, to mean not only strictly orthogonal or perpendicular, but also to include the concept of approximately orthogonal or approximately perpendicular, encompassing a range of practically permissible angular differences without losing technical significance.

[0085] 2. Overview of the comparative ultraviolet laser device

[0086] 2.1 Structure

[0087] Figure 1 This is a side view schematically showing the structure of the ultraviolet laser device 20 of the comparative example. The comparative examples disclosed herein are in a manner known only to the applicant and are not publicly known examples acknowledged by the applicant.

[0088] The ultraviolet laser device 20 is an excimer laser device comprising a master oscillator (MO) 22, an MO beam steering unit 24, and a power oscillator (PO) 26. The MO 22 includes a narrowband module (LNM) 30, a cavity 32, and an output coupling mirror 34.

[0089] The LNM30 includes a prism expander 36 and a grating 38 for narrowing the spectral width. The prism expander 36 and the grating 38 are configured in a Litterrow configuration with consistent incident and diffraction angles. The output coupling mirror 34 is a partial reflector with a reflectivity of 40%–60%. The output coupling mirror 34 is configured to form an optical resonator together with the LNM30.

[0090] Cavity 32 is positioned in the optical path of the optical resonator. Cavity 32 includes a pair of discharge electrodes 40a and 40b and two windows 42 and 44 for laser transmission. Cavity 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). The halogen gas may be, for example, fluorine (F2). The buffer gas may be, for example, neon (Ne). A voltage is applied between the discharge electrodes 40a and 40b by a power supply (not shown). The power supply may be a pulsed power module (PPM) including a switch and a charging capacitor.

[0091] MO beam steering unit 24 includes high reflectivity mirrors 50 and 52, and is configured to direct laser light output from MO22 onto PO26.

[0092] An MO pulse energy monitor 54 is disposed between high reflectivity mirror 50 and high reflectivity mirror 52. The MO pulse energy monitor 54 includes a beam splitter (BS) 55 and a photodetector 56. The BS 55 is positioned in the optical path of the pulsed laser output from MO22, and the reflected light from the BS 55 is configured to be incident on the photodetector 56.

[0093] PO26 is an amplification stage laser comprising a rear mirror 60, a cavity 62, and an output coupling mirror 64. The rear mirror 60 and the output coupling mirror 64 constitute an optical resonator, and the cavity 62 is arranged in the optical path of the optical resonator.

[0094] The structure of cavity 62 can be the same as that of cavity 32. Cavity 62 includes a pair of discharge electrodes 70a and 70b and two windows 72 and 74. Cavity 62 is filled with laser gas. The rear mirror 60 can be, for example, a partial reflector with a reflectivity of 50% to 90%. The output coupling mirror 64 can be a partial reflector with a reflectivity of 10% to 30%.

[0095] 2.2 Actions

[0096] A high-voltage pulse is applied between the discharge electrodes 40a and 40b inside cavity 32 by a power source not shown in the diagram. When a discharge occurs between the discharge electrodes 40a and 40b inside cavity 32, the laser gas is excited and outputs a pulsed laser with a wavelength of 150nm to 380nm, which is narrowed by the optical resonator composed of the output coupling mirror 34 and LNM30.

[0097] The energy of the pulsed laser output from the output coupling mirror 34 is measured by the MO pulse energy monitor 54. Furthermore, this pulsed laser is incident as a seed light onto the rear mirror 60 of PO26 via the MO beam steering unit 24.

[0098] At the moment when the seed light, after passing through the rear mirror 60, is incident on the cavity 62, a high-voltage pulse is applied between the discharge electrodes 70a and 70b inside the cavity 62 by a power source not shown. When a discharge occurs between the discharge electrodes 70a and 70b inside the cavity 62, the laser gas is excited and amplified by the Fabry-Perot type optical resonator formed by the output coupling mirror 64 and the rear mirror 60. The amplified pulsed laser is then output from the output coupling mirror 64 as the output laser.

[0099] 3. Research Topic

[0100] Figure 2This diagram illustrates the problem of the comparative example ultraviolet laser device 20. Laser performance deteriorates when the return light from PO26 returns to MO22. Here, "return light" refers to the sum of the MO return light and the PO leakage light. Light emitted from MO22 is incident on PO26; however, the rear mirror 60 within PO26 is a partial reflector (reflectivity 50%–90%), therefore, a portion of the light incident on the rear mirror 60 does not return towards the interior of PO26 but directly returns to the MO22 side. The light that does not enter the cavity 62 of PO26 and is reflected by the rear mirror 60 back to the MO22 side is called "MO return light."

[0101] On the other hand, the light incident from MO22 onto PO26 and passing through the rear mirror 60 is resonated / amplified within PO26 and output. As described above, the rear mirror 60 within PO26 is a partial reflector; therefore, a portion of the light amplified in cavity 62 of PO26 returns to MO22. The light amplified in PO26 that passes through the rear mirror 60 and returns to MO22 is called "PO leak light".

[0102] Return light becomes a thermal load on LNM30 and other components, potentially causing deterioration in linewidth stability, pulse energy stability, and other aspects. To suppress return light entering MO22, a method exists to place an optical isolator between MO22 and PO26.

[0103] Figure 3 An example of the structure of an optical isolator 80, which is a comparative example of suppressing returned light, is shown. Figure 3 The upper section shows the operation of the optical isolator 80 for a pulsed laser (MO injection light: the advancing light) moving from MO22 toward PO26. Figure 3 The lower section shows the operation of the optical isolator 80 for the laser (returning light) traveling from PO26 toward MO22.

[0104] Optical isolators 80, starting from the MO22 side, are sequentially configured with a first polarizer 83, a Faraday rotor 84, and a second polarizer 88. The Faraday rotor 84 comprises a Faraday material 85 and a magnet 86. Additionally, in... Figure 3 In the diagram, the right-pointing arrow shown in Faraday rotor 84 indicates the direction of the magnetic field based on magnet 86. The double-headed arrow inside the dashed circle in the diagram indicates the direction of the polarization plane of the pulsed laser when the line of sight is aligned with the direction of the pulsed laser's propagation, i.e., the polarization direction.

[0105] like Figure 3As shown in the upper section, a linearly polarized pulsed laser is output from MO22, polarized in the horizontal direction. Passing through a half-wavelength plate 81, the polarization direction of the pulsed laser output from MO22 is rotated 45 degrees counterclockwise. A first polarizer 83 is configured such that its transmission axis is parallel to the polarization direction of the pulsed laser output from the half-wavelength plate 81, and the pulsed laser output from the half-wavelength plate 81 passes through the first polarizer 83.

[0106] The polarization direction of the pulsed laser light, after passing through the first polarizer 83 via the Faraday rotor 84 which is subjected to a magnetic field, rotates 45 degrees clockwise. Thus, the pulsed laser light output from the Faraday rotor 84 becomes horizontally polarized light. The second polarizer 88 is configured such that its transmission axis is parallel to the polarization direction of the pulsed laser light output from the Faraday rotor 84, and the pulsed laser light output from the Faraday rotor 84, after passing through the second polarizer 88, is incident on PO26.

[0107] The 1 / 2 wavelength plate 81 adjusts the polarization direction of the pulsed laser from MO22 so that the polarization direction of the pulsed laser output from MO22 is the same as the polarization direction of the pulsed laser incident on PO26. Therefore, no changes need to be made to other modules that depend on the polarization direction.

[0108] On the other hand, such as Figure 3 As shown in the lower section, the returning light from PO26 passes through the second polarizer 88 with the same polarization direction as the incident light incident on PO26, and then passes through the Faraday rotor 84, which is subjected to a magnetic field, rotating the polarization direction by 45 degrees clockwise. The polarization direction of the returning light after passing through the Faraday rotor 84 is orthogonal to the transmission axis of the first polarizer 83, and the returning light is reflected by the first polarizer 83 without incident on MO22.

[0109] Here, in order to suppress the return light of short-wavelength light such as that of an excimer laser with a wavelength of about 193 nm, calcium fluoride (CaF2) crystal is used as the Faraday material 85 for the Faraday rotor 84.

[0110] When a high-output laser, such as one with a power of 10W or more, is incident on a CaF2 crystal, the effect of thermally induced birefringence cannot be ignored, leading to a deterioration in polarization purity. This deterioration in polarization purity reduces the proportion of reflected light from the first polarizer 83, thus worsening the isolation ratio of the optical isolator 80.

[0111] 4. Implementation Method 1

[0112] 4.1 Structure

[0113] Figure 4 The structure of the optical isolator 120 in Embodiment 1 is shown in outline. Regarding... Figure 4 The structure shown is for... Figure 3The differences will be explained. Optical isolator 120 replaces... Figure 3 The Faraday rotor 84 has a Faraday rotor 112 comprising a Faraday material 135. The Faraday material 135 is a CaF2 crystal, and in Embodiment 1, it is... Figure 3 The difference in the structure is that the Faraday rotor 112 is configured in such a way that the deterioration of the polarization purity of the laser decreases before and after passing through the Faraday material 135.

[0114] Specifically, the Faraday rotor 112 is configured such that the crystal axis of the Faraday material 135 and the propagation direction of the incident light are related as follows. That is, in the case where the Faraday material 135 is a CaF2 crystal, as... Figure 5 As shown, when the direction of

[001] , which serves as the crystal axis, is set as the a-axis, the direction of

[100] as the b-axis, and the direction of

[010] as the c-axis, the axes a, b, and c are rotated by α around the c-axis and by β around the b-axis after the rotation by α, respectively, and then set as the x-axis, y-axis, and z-axis. The rotation angles α and β will be described later.

[0115] Moreover, such as Figure 6 As shown, the Faraday material 135 is configured such that its z-axis is parallel to the laser propagation direction, and the laser polarization direction becomes parallel to the x-axis approximately at the center of the dielectric length of the Faraday material 135. Other structures can be similar. Figure 3 same.

[0116] 4.2 Relationship between the transmission axis of the first polarizer and the crystal axis of the Faraday material

[0117] Figure 7 This is a side view that schematically shows the relationship between the transmission axis TA1 of the first polarizer 83 and the x-axis and y-axis of the Faraday material 135. Figure 8 The diagram shows the relationship between the transmission axis TA1 of the first polarizer 83 and the x-axis and y-axis of the Faraday material 135 when viewed along the direction of incident light propagation (z-axis). The polarization direction of the light incident on the Faraday rotor 112 through the first polarizer 83 is parallel to the x-axis. Furthermore, in Figure 8 In this configuration, the polarization direction of the incident light rotates clockwise through the Faraday rotor 112. In the direction in which the polarization direction of the incident light rotates through the Faraday rotor 112, the preferred range of the angle difference θ between the transmission axis TA1 of the first polarizer 83 and the polarization direction of the incident light is 0 degrees or more and 45 degrees or less.

[0118] 4.3 Regarding rotation angles α and β

[0119] Figure 9 It is a graph based on Fig. 1 as described in Non-Patent Document 1. Figure 9 The diagram illustrates the dependence of the rotation angle β on the depolarization γ, which is the proportion of the polarization component in the transmitted light orthogonal to the polarization direction of the incident light relative to the total incident power of the light incident on the CaF2 crystal. Figure 9 In this case, the rotation angle α is 45 degrees. According to... Figure 9 The solid line in the graph shows that when β is between 50 and 60 degrees, the change in polarization direction is small and the deterioration of polarization purity is small.

[0120] Should Figure 9 This is a graph showing the situation when the incident light wavelength is 1074 nm. Therefore, when estimating the relationship between the value of γ and the rotation angle β when the incident light wavelength is 193 nm, as shown... Figure 10 As shown. Figure 10 The vertical axis normalizes the value of γ to "1" when β is 0 degrees.

[0121] according to Figure 10 The preferred range for β is 45°–75°, a more preferred range is 54°–66°, and the most preferred range is 58°–62°. According to... Figure 10 Regarding the preferred rotation angle, when α is 45 degrees, β is estimated to be between 45 degrees and 75 degrees. Furthermore, the permissible range of α is 45 degrees ± 5 degrees. Additionally, expressions indicating a numerical range, such as "45 degrees to 75 degrees," indicate a range including the values ​​before and after the "~". For example, the expression "45 degrees to 75 degrees" means "above 45 degrees and below 75 degrees". Rotation angle α is an example of a "first angle" in this disclosure, and rotation angle β is an example of a "second angle" in this disclosure.

[0122] Figure 10 The graph shows the result when the incident light wavelength is 193 nm. However, when the incident light wavelength is 248 nm or other ultraviolet wavelengths, although it is similar to... Figure 10 The curve has slight deviations, but it can be roughly compared to... Figure 10 The curve is the same as the curve. Therefore, according to Figure 10 The aforementioned preferred ranges of rotation angles α and β have also been applied to incident light of other ultraviolet wavelengths such as 248 nm.

[0123] 4.4 Preferred range of magnetic field and Faraday material thickness

[0124] Regarding the cases where the incident light wavelength is 193 nm and 248 nm, Figure 11 The preferred ranges for the magnetic field and thickness of the Faraday material 135 when it is a CaF2 crystal are shown. The oscillation wavelength of the ArF excimer laser includes a wavelength of 193 nm. The oscillation wavelength of the KrF excimer laser includes a wavelength of 248 nm.

[0125] The preferred range is selected based on the ease of achieving the magnetic field. The optimal range of magnetic fields is the magnetic flux density when using a strong neodymium magnet or the like. The thickness of the Faraday material 135 is a value obtained by calculating the thickness based on the rotation of the polarization plane to 45 degrees, achieved through the Faraday effect, using the selected material, the magnetic flux density of the magnetic field, and the Feld constant.

[0126] When the Faraday material 135 is a CaF2 crystal and the wavelength of the incident light is the oscillation wavelength of the ArF excimer laser, i.e., 193 nm, then... Figure 11 As shown, the selectable ranges for the magnetic field applied to the Faraday rotor 112 and the thickness of the Faraday material 135 along the optical axis are 0.5T to 3.0T and 6mm to 40mm, respectively. More preferably, they are 0.75T to 2.9T and 10mm to 30mm, and most preferably, they are 0.8T to 1.5T and 15mm to 25mm.

[0127] Furthermore, when the wavelength of the incident light is the oscillation wavelength of the KrF excimer laser, i.e., 248 nm, the selectable ranges for the magnetic field applied to the Faraday rotor 112 and the thickness of the Faraday material 135 along the optical axis are 0.5 T to 3.0 T and 13 mm to 83 mm, respectively. More preferably, these ranges are 0.75 T to 2.9 T and 20 mm to 55 mm, and most preferably, they are 0.8 T to 1.5 T and 30 mm to 50 mm.

[0128] During the processing of the CaF2 crystal incorporated into the Faraday rotor 112, the Faraday rotor 112 is fabricated based on parameters such as the direction of the crystal axis and the thickness in the optical axis direction.

[0129] Alternatively, the Faraday material 135 can be divided into multiple portions, the total of which satisfies the aforementioned thickness. The number of portions can be, for example, 2, 3, 4, etc.

[0130] 4.5 The allowable angular difference between the transmission axis of the polarizer and the polarization direction of the laser.

[0131] Ideally, the transmission axes of the first polarizer 83 and the second polarizer 88 are parallel to the polarization direction of the pulsed laser incident on each polarizer. However, they are not limited to being strictly parallel; within the range that can achieve the target function in a practical way, the angle difference between the two is allowed.

[0132] Figure 12 It is a graph showing the relationship between the angle difference between the transmission axis of the polarizer and the polarization direction of the pulsed laser and the extinction ratio (dB), as well as a graph converting the extinction ratio into normalized transmittance. Figure 12The left vertical axis represents the extinction ratio, and the right vertical axis represents the normalized transmittance. The normalized transmittance is obtained by normalizing the transmittance to 1.0 when the angular difference is 0 degrees.

[0133] In the first polarizer 83 that allows pulsed laser light output from MO22 to pass through, and the second polarizer 88 that allows pulsed laser light output from Faraday rotor 112 to pass through, if the normalized transmittance for the incident pulsed laser light is 0.9 or higher, then it can function sufficiently effectively in practical applications. Therefore, according to Figure 12 The preferred allowable range of the angle difference between the transmission axis of the first polarizer 83 or the second polarizer 88 and the polarization direction of the pulsed laser is ±17.5 degrees, where the normalized transmittance is 0.9 or higher.

[0134] 4.6 Actions

[0135] The polarization direction of the linearly polarized pulsed laser output from MO22 and passing through the first polarizer 83, via the Faraday rotor 112 which is subjected to a magnetic field, rotates 45 degrees clockwise before and after passing through the Faraday rotor 112. The second polarizer 88 is configured such that its transmission axis is parallel to the polarization direction of the pulsed laser output from the Faraday rotor 112, and the pulsed laser output from the Faraday rotor 112 passes through the second polarizer 88 and is incident on PO26.

[0136] On the other hand, the returning light from PO26 passes through the second polarizer 88 and then through the Faraday rotor 112, which is subjected to a magnetic field, causing its polarization direction to rotate 45 degrees clockwise. The polarization direction of the returning light after passing through the Faraday rotor 112 is orthogonal to the transmission axis of the first polarizer 83, and the returning light is reflected by the first polarizer 83. Thus, the returning light from PO26 is reflected by the first polarizer 83 after passing through the Faraday rotor 112, suppressing its incidence on MO22.

[0137] use Figure 6 The condition described, "the polarization direction of the laser becomes parallel to the x-axis at the center of the Faraday material 135," is one of the preferred conditions. It is not required that the Faraday rotor 112 be configured so that the polarization direction becomes parallel to the x-axis at the center of the length of the Faraday material 135 medium. Regarding light incident on the Faraday material 135, the polarization plane rotates due to the Faraday effect. Therefore, if the polarization direction becomes parallel to the x-axis midway through the light path of the light traveling in the medium of the Faraday material 135 (at some point in the medium), the suppression effect on the deterioration of polarization purity is enhanced. It is particularly preferred that the Faraday rotor 112 be configured so that the polarization direction becomes parallel to the x-axis near the center of the thickness of the Faraday material 135, thereby averaging the effect on suppressing the deterioration of polarization purity.

[0138] 4.7 Functions / Effects

[0139] According to the optical isolator 120 of Embodiment 1, even if a high-output laser is incident on the Faraday rotor 112, the deterioration of polarization purity caused by the effect of thermal birefringence is suppressed, and a high isolation ratio can be maintained.

[0140] The Faraday rotor 112 is configured in a manner that satisfies the above conditions, thereby reducing the strain caused by the photoelastic effect and suppressing the effect of thermal birefringence even with the same input heat.

[0141] 4.8 Verification method for crystal axes

[0142] As a method for verifying whether the structure of the optical isolator meets the conditions described in Embodiment 1, there is, for example, the following method.

[0143] [Step 1] Regarding the Faraday material (CaF2 crystal) 135 placed in the Faraday rotor 112, the crystal orientation analysis is performed by back reflection Laue method and transmission Laue method to determine the crystal axis of Faraday material 135.

[0144] [Step 2] Determine the transmission axis of the first polarizer 83 based on the markings etched on the first polarizer 83. Alternatively, determine the direction of the transmission axis using a linearly polarized laser.

[0145] Through steps 1 and 2 above, the relationship between the crystal axis of Faraday material 135 and the propagation direction of the incident light can be determined. Furthermore, the relationship between the crystal axis of Faraday material 135 and the transmission axis of the first polarizer 83 can be determined.

[0146] 4.9 Variation Example

[0147] In Embodiment 1, an example is described where the polarization direction of the light incident on the Faraday rotor 112 through the first polarizer 83 is maintained before and after passing through the Faraday rotor 112, and the polarization direction of the returning light incident on the Faraday rotor 112 through the second polarizer 88 is rotated by 90 degrees before and after passing through the Faraday rotor 112. However, this example is not limited to; within the scope of achieving the intended practical function, an angular difference in the polarization direction before and after passing through the Faraday rotor 112 is permissible. Figure 12Alternatively, the polarization direction of the light incident on the Faraday rotor 112 through the first polarizer 83 can be maintained within an angle difference of 17.5 degrees before and after passing through the Faraday rotor 112, while the polarization direction of the returning light incident on the Faraday rotor 112 through the second polarizer 88 can rotate within an angle of 90 degrees ± 17.5 degrees before and after passing through the Faraday rotor 112. Based on the structure where the polarization direction of the light incident on the first polarizer 83 and the polarization direction of the returning light returning from PO26 intersect at an angle of 90 degrees ± 17.5 degrees when incident on the first polarizer 83, the returning light is reflected at the first polarizer 83, and the incident light onto MO22 is suppressed.

[0148] 5. Implementation Method 2

[0149] 5.1 Structure

[0150] Figure 13 The structure of the optical isolator 122 in Embodiment 2 is shown in outline. Regarding... Figure 13 The structure shown is for... Figure 3 and Figure 4 The differences will be explained. The optical isolator 122 of Embodiment 2 differs from that of Embodiment 1 in that it uses a temperature-adjustable Faraday rotor 113 instead of the Faraday rotor 112 in Embodiment 1, and has a structure that controls the temperature of the Faraday rotor 113 to a constant temperature.

[0151] Figure 14 This is a front view that roughly shows the structure of the Faraday rotor 113. Figure 15 yes Figure 14 A cross-sectional view at line 15-15. Faraday material 135 is held in a cage 137 and disposed inside a hollow magnet 136. The Faraday rotor 113 includes heaters 138a and 138b and a temperature sensor 139. Heaters 138a and 138b and the temperature sensor 139 are mounted in the cage 137. Preferably, heaters 138a and 138b are configured to extend parallel to the optical axis and are symmetrically positioned across the Faraday material 135. The temperature sensor 139 detects the temperature of the Faraday rotor 113.

[0152] Optical isolator 122 has heater power supply 142 and processor 144 (see reference) for controlling the temperature of Faraday rotor 113. Figure 13 Heater power supply 142 supplies power to heaters 138a and 138b.

[0153] Processor 144 controls heater power supply 142 based on information obtained from temperature sensor 139 to maintain a constant temperature for Faraday rotor 113. Furthermore, the description "maintain constant" includes keeping it within an acceptable range. Processor 144 controls heaters 138a and 138b via heater power supply 142 to suppress temperature variations in Faraday material 135. Processor 144 is a processing device including a storage device storing control programs and a CPU (Central Processing Unit) that executes the control programs.

[0154] Other structures can be the same as in Implementation 1. To satisfy... Figures 5-11 The Faraday rotor 113 is configured in accordance with the conditions and other specifications described herein.

[0155] 5.2 Actions

[0156] The processor 144 drives heaters 138a and 138b via heater power supply 142, monitors the temperature of Faraday rotor 113 via temperature sensor 139, and adjusts the temperature of Faraday rotor 113 to maintain a predetermined temperature. The predetermined temperature is preferably, for example, below 100°C and at room temperature. Furthermore, the preferred temperature control range is ±1°C. Other operations are the same as in Embodiment 2.

[0157] 5.3 Functions / Effects

[0158] Figure 10 The preferred angle β shown is temperature-dependent. Therefore, according to embodiment 2, the optical isolator 122 can maintain a high isolation ratio by controlling the temperature to a constant, suppressing the deterioration of polarization purity caused by the change of preferred β.

[0159] Furthermore, according to the structure of Embodiment 2, by controlling the temperature to a constant, the change in optical path length caused by temperature variation is suppressed, the polarization rotation angle can be kept constant, and the deterioration of the isolation ratio can be suppressed.

[0160] 6. Implementation Method 3

[0161] 6.1 Structure

[0162] Figure 16 The structure of a portion of the Faraday rotor 112 in the optical isolator 123 of Embodiment 3 is shown schematically. Additionally, with... Figure 4 Similarly, optical isolator 123 includes optical isolator 120. Figure 16 The first polarizer 83 and the second polarizer 88 are not shown in the diagram. Regarding... Figure 16 The structure shown is for... Figure 4 The differences will be explained.

[0163] The optical isolator 123 of embodiment 3 has a rotary table 150 for rotating the Faraday rotor 112 about the y-axis. Other structures can be similar. Figure 4 same.

[0164] 6.2 Actions

[0165] By moving the rotary table 150, the Faraday rotor 112 rotates about the y-axis. By rotating the Faraday rotor 112 around the y-axis, the rotation angle α can be maintained, and the rotation angle β can be adjusted. The y-axis is obtained by rotating the b-axis around the c-axis by α.

[0166] 6.3 Functions / Effects

[0167] According to the optical isolator 123 of embodiment 3, the rotation angle of β can be adjusted to a smaller angle before and after the transmission of polarization purity to the Faraday rotor 112. As a result, the isolation ratio can be improved.

[0168] 7. Implementation Method 4

[0169] 7.1 Structure

[0170] Figure 17 A structural example of the ultraviolet laser device 100 according to Embodiment 4 is shown in general. Regarding... Figure 17 The structure shown is for... Figure 1 The differences will be explained. The ultraviolet laser device 100 and... Figure 1 The difference in structure lies in that a half-wavelength plate 81 and an optical isolator 120 are arranged in the optical path between MO22 and PO26. The structure of the optical isolator 120 is the same as that described in Embodiment 1, including a first polarizer 83, a Faraday rotor 112 and a second polarizer 88. As described in Embodiment 1, the Faraday rotor 112 is configured to arrange the crystal axis of the CaF2 crystal in a manner that satisfies specific conditions.

[0171] The optical isolator 120 also includes an attenuator 116 for the return light terminator. The attenuator 116 is configured such that the return light, reflected by the first polarizer 83, is incident on the attenuator 116. Other configurations may be compatible with... Figure 1 and Figure 4 same.

[0172] exist Figure 17 The diagram also shows the polarization direction of the pulsed laser at points a, b, c, and d along the optical path between MO22 and PO26. Figure 17 The diagram shows the polarization directions at points a to d of the pulsed laser propagating from MO22 to PO26, and the polarization directions at points d and c of the returning light traveling from PO26 to MO22.

[0173] 7.2 Actions

[0174] The operation of the 1 / 2 wavelength plate 81 and the optical isolator 120 and Figure 3 Same as in Implementation Method 1. Through the 1 / 2 wavelength plate 81, the polarization direction of the pulsed laser output from MO22 and polarized in a specific direction (point a) is rotated 45 degrees counterclockwise (point b).

[0175] The first polarizer 83 is configured such that its transmission axis becomes parallel to the polarization direction of the pulsed laser output from the half-wave plate 81. Therefore, the pulsed laser whose polarization direction has been rotated by the half-wave plate 81 passes through the first polarizer 83 (point c).

[0176] The pulsed laser light, after passing through the first polarizer 83, is incident on the Faraday rotor 112. As it passes through the Faraday rotor 112, its polarization direction rotates 45 degrees clockwise (point d). The second polarizer 88 is configured such that its transmission axis becomes parallel to the polarization direction of the pulsed laser light after its polarization direction has been rotated by the Faraday rotor 112. Therefore, the pulsed laser light after its polarization direction has been rotated by the Faraday rotor 112 passes through the second polarizer 88. The polarization direction of the pulsed laser light traveling from MO22 to PO26 at point a is the same as the polarization direction at point e.

[0177] exist Figure 17 At point e, the polarization direction of the pulsed laser propagating from MO22 to PO26 is the same as the polarization direction of the pulsed laser returning from PO26 to MO22 (return light). Therefore, the return light traveling from PO26 to MO22 passes through the second polarizer 88.

[0178] Next, the polarization direction of the returning light after passing through the second polarizer 88 is rotated 45 degrees clockwise (point c) via the Faraday rotor 112. At point c, the polarization direction of the pulsed laser propagating from MO22 to PO26 is orthogonal to the polarization direction of the pulsed laser returning from PO26 to MO22. Therefore, the pulsed laser returning from PO26 to MO22 is reflected by the first polarizer 83 and incident on the attenuator 116. The attenuator 116 absorbs and blocks the light reflected by the first polarizer 83.

[0179] 7.3 Functions / Effects

[0180] According to the ultraviolet laser device 100 of embodiment 4, even if a high-output laser is incident on the Faraday rotor 112, the deterioration of polarization purity caused by thermal birefringence is suppressed, and a high isolation ratio can be maintained.

[0181] Furthermore, according to the structure of Embodiment 4, the pulsed laser returning in the direction of MO22 is reflected by the first polarizer 83, and the incident light onto MO22 is suppressed. Therefore, the thermal load on MO22 is reduced, compared with the structure of the comparative example ( Figure 1 Compared to [previous version], energy stability and linewidth stability are improved.

[0182] 7.4 Variation Example

[0183] Regarding the configuration of the MO pulse energy monitor 54, it can be configured on either the upstream or downstream side of the optical isolator 120, however, as Figure 17 Therefore, it is preferable to configure it to be located on the upstream side of the optical isolator 120.

[0184] 8. Implementation Method 5

[0185] 8.1 Structure

[0186] Figure 18 The structure of the ultraviolet laser device 105 of Embodiment 5 is shown in outline. Regarding... Figure 18 The structure shown is for... Figure 17 The differences will be explained. Figure 18 The ultraviolet laser device 105 shown is... Figure 17 The difference in the structure shown is that a parallel planar substrate 202 capable of two-axis adjustment and a high-reflectivity mirror 52 capable of two-axis adjustment are arranged in the optical path between the second polarizer 88 and PO26. The parallel planar substrate 202 is held in a two-axis angle adjustment holder 204 that can adjust the angle of the two orthogonal axes as rotation axes respectively.

[0187] A parallel planar substrate 202 is disposed in the optical path between the second polarizer 88 and the high-reflectivity mirror 52. The parallel planar substrate 202 may be a calcium fluoride substrate. The 2-axis angle adjustment holder 204 may be, for example, capable of adjusting the angle of the polarizer to the optical path. Figure 18 The paper surface perpendicular to the axis and the substrate surface of the parallel plane substrate 202 and Figure 18 The paper-parallel axes serve as the rotation axes for angle adjustment of the retainers.

[0188] The high-reflectivity mirror 52 is held in a two-axis angle adjustment holder 208, which is capable of adjusting the angles of two orthogonal axes as rotation axes. The two-axis angle adjustment holder 208, for example, can be a device capable of adjusting the angles of two orthogonal axes as rotation axes. Figure 18 The axis perpendicular to the paper and the reflecting surface of the high-reflectivity mirror 52 and Figure 18 The paper-parallel axes serve as the rotation axes for angle adjustment of the retainers.

[0189] 8.2 Actions

[0190] The optical axis is adjusted by adjusting the parallel planar substrate 202, which is capable of 2-axis adjustment, and the high-reflectivity mirror 52, which is capable of 2-axis adjustment, so that the pulsed laser from MO22 can be incident on PO26 with the most efficient efficiency.

[0191] The parallel planar substrate 202, which is capable of 2-axis adjustment, is adjusted so that the pulsed laser from MO22 is shifted parallel to the direction of travel, thereby maximizing the efficiency of the pulsed laser incident on PO26.

[0192] The highly reflective mirror 52, which is capable of two-axis adjustment, is adjusted to change the angle at which the pulsed laser from MO22 is incident on PO26, thereby maximizing the efficiency of the pulsed laser incident on PO26.

[0193] The two-axis angle adjustment holder 204 and the two-axis angle adjustment holder 208 are examples of the "optical axis adjustment mechanism" in this disclosure. A structure having both a parallel planar substrate 202 capable of two-axis adjustment and a high-reflectivity mirror 52 capable of two-axis adjustment is preferred, but a structure having only one of them is also possible.

[0194] 8.3 Functions / Effects

[0195] The ultraviolet laser device 105 according to Embodiment 5 achieves the same effect as Embodiment 4. Furthermore, according to the structure of Embodiment 5, the optical axis adjustment of the injected light incident on PO26 becomes easier compared to the structure of Embodiment 4.

[0196] 9. Implementation Method 6

[0197] 9.1 Structure

[0198] Figure 19 The structure of the ultraviolet laser device 106 in Embodiment 6 is shown in outline. Regarding... Figure 19 The structure shown is for... Figure 17 The differences will be explained. Figure 19 The ultraviolet laser device 106 shown replaces Figure 17 The MO22 in the laser has an ultraviolet solid-state laser device 232 as the oscillating stage laser, and the PO26 has an excimer amplifier 236 instead of PO26. Other structures can be combined with Figure 17 The structures shown are the same.

[0199] The ultraviolet solid-state laser device 232 is, for example, a 4th, 5th, or 6th harmonic (wavelength range of 150 nm to 380 nm) outputting a solid-state laser with a near-infrared band (wavelength 780 nm to 2500 nm) as its fundamental wavelength. For example, the ultraviolet solid-state laser device 232 is configured to output seed light with a wavelength of approximately 193 nm, which is incident on the excimer amplifier 236.

[0200] As an example, the ultraviolet solid-state laser device 232 can also be configured to include a semiconductor laser system, a Ti:sapphire amplifier, and a wavelength conversion system. The semiconductor laser system can also be configured to include a distributed feedback (DFB) semiconductor laser that outputs a CW laser with an output wavelength of approximately 773.6 nm and a semiconductor optical amplifier (SOA) that pulses the CW laser. The wavelength conversion system includes multiple nonlinear optical crystals that perform wavelength conversion on the incident pulsed laser to output a fourth-harmonic pulsed laser. The wavelength conversion system may include, for example, LBO crystals and KBBF crystals. An LBO crystal is a nonlinear optical crystal represented by the chemical formula LiB3O5. A KBBF crystal is a nonlinear optical crystal represented by the chemical formula KBa2BO3F2.

[0201] The excimer amplifier 236 includes a cavity 242, a convex cylindrical mirror 244, and a concave cylindrical mirror 246.

[0202] Cavity 242 includes a pair of discharge electrodes 250a and 250b and two windows 252 and 254 for laser transmission. The discharge electrodes 250a and 250b are arranged opposite each other across a discharge space 256. The space between the discharge electrodes 250a and 250b is called the discharge space 256. The orientation of the discharge electrodes 250a and 250b across the discharge space 256 corresponds to the discharge direction. Cavity 242 is filled with... Figure 1 The laser gas described herein is the same as the laser gas.

[0203] The convex surface of the convex cylindrical mirror 244 and the concave surface of the concave cylindrical mirror 246 are coated with high-reflectivity films for light with a wavelength of approximately 193 nm.

[0204] The convex cylindrical mirror 244 and the concave cylindrical mirror 246 are configured such that the seed light from the ultraviolet solid-state laser device 232 passes through the discharge space 256 of the excimer amplifier 236 three times, thereby expanding and amplifying the beam in the discharge direction.

[0205] 9.2 Actions

[0206] Seed light output from the ultraviolet solid-state laser device 232 is incident on the excimer amplifier 236 through the optical isolator 120. The seed light, with a wavelength of approximately 193 nm, incident on the excimer amplifier 236 is reflected by the convex cylindrical mirror 244 and the concave cylindrical mirror 246, thereby passing three times through the discharge space 256 between the discharge electrodes 250a and 250b. Thus, the seed light beam is amplified. The excimer amplifier 236 is an example of a "multi-pass amplifier" in this disclosure. It is not limited to a three-pass excimer amplifier 236; various multi-pass amplifiers can be used.

[0207] The operation of the optical isolator 120 is the same as in Embodiment 1. The optical isolator 120 suppresses the incident ultraviolet solid-state laser device 232 from amplified spontaneous emission (ASE) generated by the excimer amplifier 236.

[0208] 9.3 Functions / Effects

[0209] According to the ultraviolet laser device 106 of Embodiment 6, the light returning from the excimer amplifier 236 to the ultraviolet solid-state laser device 232 does not incident on the ultraviolet solid-state laser device 232. Therefore, the thermal load on the ultraviolet solid-state laser device 232 is reduced, and the energy stability, linewidth stability, etc. are improved compared with the structure of the comparative example.

[0210] 10. Implementation Method 7

[0211] 10.1 Structure

[0212] Figure 20 The structure of the ultraviolet laser device 107 in Embodiment 7 is shown in outline. Regarding... Figure 20 The structure shown is for... Figure 17 The differences will be explained. In Embodiment 7, the structure of the amplification stage laser and the structure of the high-reflectivity mirror that guides the laser from MO22 into the amplification stage laser are different from those in Embodiment 4.

[0213] Figure 17 The amplification stage laser shown in Embodiment 4 is a PO26 having a Fabry-Perot type optical resonator composed of a rear mirror 60 and an output coupling mirror 64. In contrast, Figure 20 The amplification stage laser in Embodiment 7 shown is a PO266 with a ring resonator 270, which is different.

[0214] Figure 21 This is a top view schematically showing the structure of PO266 applied in Embodiment 7. The ring resonator 270 is configured to include a high-reflectivity mirror 284, a high-reflectivity mirror 285, a high-reflectivity mirror 286, and a partial reflector 290.

[0215] The ultraviolet laser device 107 is equipped with a high-reflectivity mirror 283 to guide the laser output from MO22 and reflected by high-reflectivity mirrors 50 and 52 into the ring resonator 270. The high-reflectivity mirror 283 is positioned in the optical path between high-reflectivity mirror 52 and partial reflector 290 so that the laser reflected by high-reflectivity mirror 52 is incident on partial reflector 290.

[0216] 10.2 Actions

[0217] The laser output from MO22 is reflected sequentially by high-reflectivity mirrors 50, 52 and 283, and then incident on the ring resonator 270 through partial reflector 290.

[0218] The laser light, after passing through partial reflector 290, is reflected by high reflector 284 and then incident into cavity 62 for amplification. It is then reflected again by high reflectors 285 and 286 and incident into cavity 62 for amplification once more. A portion of the laser light output from cavity 62 passes through partial reflector 290, while the other portion is reflected and amplified again in ring resonator 270.

[0219] The amplified pulsed laser, after passing through a partial reflector 290, is output from the ultraviolet laser device 107.

[0220] Optical isolator 120 suppresses the return light from PO266 incident on MO22. The operation of the 1 / 2 wavelength plate 81 and optical isolator 120 is related to... Figure 3 and Figure 17 The same as the implementation method 4 described in the text.

[0221] 10.3 Functions / Effects

[0222] According to the ultraviolet laser device 107 of Embodiment 7, the same effect as that of Embodiment 4 is obtained.

[0223] 11. Manufacturing methods for electronic devices

[0224] Figure 22 An example of the structure of the exposure apparatus 300 is shown schematically. The exposure apparatus 300 includes an illumination optics system 304 and a projection optics system 306. The illumination optics system 304 illuminates a mask pattern (not shown) disposed on a mask stage RT using laser light incident from the ultraviolet laser device 100. The projection optics system 306 projects the laser light after it has passed through the mask in a reduced manner, so that it images onto a workpiece (not shown) disposed on a workpiece stage WT. The workpiece is a photosensitive substrate such as a semiconductor wafer coated with photoresist.

[0225] The exposure apparatus 300 moves the mask stage RT and the workpiece stage WT synchronously and parallelly, thereby exposing the workpiece to laser light reflecting the mask pattern. After transferring the mask pattern onto the semiconductor wafer through this exposure process, a semiconductor device can be manufactured through multiple processes. The semiconductor device is an example of the "electronic device" in this disclosure. Alternatively, the ultraviolet laser apparatus 105, 106, or 107 described in embodiments 5-7 can be used to generate laser light instead of the ultraviolet laser apparatus 100.

[0226] 12. Another application example of optical isolators

[0227] The optical isolators 120, 122, and 123 illustrated in embodiments 1-7 are not limited to ultraviolet laser devices and can be applied to various purposes. For example, the incident light incident on optical isolator 120 is not limited to pulsed lasers, but can also be CW lasers or radioactive light. For example, optical isolator 120 can also be configured at the exit of radioactive light in an accelerator. Furthermore, optical isolator 120 can also be configured to suppress stray light of ultraviolet wavelengths in a beam splitter using a deuterium lamp. The same applies to optical isolators 122 and 123.

[0228] 13. Other

[0229] The foregoing description is not a limitation but a simple illustration. Therefore, those skilled in the art will understand that modifications can be made to embodiments of this disclosure without departing from the claims. Furthermore, those skilled in the art will understand the use of embodiments of this disclosure in combination.

[0230] Unless explicitly stated otherwise, all terms used in this specification and claims should be interpreted as "non-limiting." For example, terms such as "comprising," "having," "possessing," and "comprise" should be interpreted as "excluding the presence of structural elements other than the described structural elements." Furthermore, the modifier "a" should be interpreted as meaning "at least one" or "one or more." Additionally, terms such as "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." Moreover, it should be interpreted as also including combinations of these elements with portions other than "A," "B," and "C."

Claims

1. An optical isolator, comprising: The first polarizer, whose transmission axis is configured such that the normalized transmittance of the first polarizer for linearly polarized incident light of ultraviolet wavelength is 0.9 or more. A Faraday rotor, comprising a Faraday material, rotates the polarization direction of light transmitted through the first polarizer via a magnetic field; and A second polarizer, whose transmission axis is configured such that the normalized transmittance of the second polarizer for the incident light after passing through the Faraday rotor is 0.9 or higher. in, The Faraday material is calcium fluoride crystal. When the direction of [001], which is the crystal axis of the calcium fluoride crystal, is set as the a-axis, the direction of [100] as the b-axis, and the direction of [010] as the c-axis, and the axes after rotating the a-axis, the b-axis, and the c-axis by a first angle around the c-axis and by a second angle around the b-axis (after the first angle rotation) are respectively set as the x-axis, y-axis, and z-axis, respectively. The first angle is greater than 40 degrees and less than 50 degrees. The second angle is greater than 45 degrees and less than 75 degrees. The z-axis is parallel to the propagation direction of light incident from the first polarizer onto the calcium fluoride crystal. The calcium fluoride crystal is configured such that the angular difference between the transmission axis of the first polarizer and the x-axis is within the range of 0 degrees or more and 45 degrees or less.

2. The optical isolator according to claim 1, wherein, The second angle is above 54 degrees and below 66 degrees.

3. The optical isolator according to claim 1, wherein, The second angle is above 58 degrees and below 62 degrees.

4. The optical isolator according to claim 1, wherein, The calcium fluoride crystal is configured such that the polarization direction of light incident from the first polarizer onto the Faraday material and propagating in the medium of the Faraday material becomes parallel to the x-axis within the medium of the Faraday material due to the Faraday effect.

5. The optical isolator according to claim 1, wherein, The angular difference between the polarization direction of the incident light and the transmission axis of the first polarizer is within 17.5 degrees. The angle difference between the polarization direction of the incident light after passing through the Faraday rotor and the transmission axis of the second polarizer is within 17.5 degrees.

6. The optical isolator according to claim 1, wherein, The polarization direction of the returning light incident from the second polarizer through the Faraday rotor onto the first polarizer intersects the transmission axis of the first polarizer at an angle within 90 degrees ± 17.5 degrees, and the returning light is reflected by the first polarizer.

7. The optical isolator according to claim 1, wherein, The wavelength of the incident light is the oscillation wavelength of the ArF excimer laser or the oscillation wavelength of the KrF excimer laser.

8. The optical isolator according to claim 1, wherein, The magnetic flux density of the magnetic field applied to the Faraday rotor is above 0.5T and below 3.0T.

9. The optical isolator according to claim 8, wherein, When the wavelength of the incident light is the same as the oscillation wavelength of the ArF excimer laser, the thickness of the Faraday material along the optical axis is 6 mm or more and 40 mm or less.

10. The optical isolator according to claim 8, wherein, When the wavelength of the incident light is the same as the oscillation wavelength of the KrF excimer laser, the thickness of the Faraday material along the optical axis is 13 mm or more and 83 mm or less.

11. The optical isolator according to claim 1, wherein, The Faraday material is composed of multiple segments.

12. The optical isolator according to claim 1, wherein, The Faraday rotor has a heater and a temperature sensor, and is controlled so that the temperature of the Faraday material is maintained within an allowable temperature range.

13. The optical isolator according to claim 1, wherein, The optical isolator has a rotary table that allows the Faraday rotor to rotate about the y-axis.

14. An ultraviolet laser device, comprising: An oscillating laser that outputs linearly polarized pulsed laser light with an ultraviolet wavelength; An amplifier that amplifies and outputs the pulsed laser; and An optical isolator is positioned in the optical path between the oscillator-stage laser and the amplifier. The optical isolator has the following features: The first polarizer, whose transmission axis is configured such that the normalized transmittance of the first polarizer for linearly polarized incident light of ultraviolet wavelength is 0.9 or more. A Faraday rotor, comprising a Faraday material, rotates the polarization direction of light transmitted through the first polarizer via a magnetic field; and A second polarizer, whose transmission axis is configured such that the normalized transmittance of the second polarizer for the incident light after passing through the Faraday rotor is 0.9 or higher. in, The Faraday material is calcium fluoride crystal. When the direction of [001], which is the crystal axis of the calcium fluoride crystal, is set as the a-axis, the direction of [100] as the b-axis, and the direction of [010] as the c-axis, and the axes after rotating the a-axis, the b-axis, and the c-axis by a first angle around the c-axis and by a second angle around the b-axis (after the first angle rotation) are respectively set as the x-axis, y-axis, and z-axis, respectively. The first angle is greater than 40 degrees and less than 50 degrees. The second angle is greater than 45 degrees and less than 75 degrees. The z-axis is parallel to the propagation direction of light incident from the first polarizer onto the calcium fluoride crystal. The calcium fluoride crystal is configured such that the angular difference between the transmission axis of the first polarizer and the x-axis is within the range of 0 degrees or more and 45 degrees or less.

15. The ultraviolet laser device according to claim 14, wherein, The ultraviolet laser device has the following features: A heater, which is configured on the Faraday rotor; A temperature sensor that detects the temperature of the Faraday rotor; and The processor controls the heater based on information from the temperature sensor to suppress temperature changes in the Faraday material.

16. The ultraviolet laser device according to claim 14, wherein, The ultraviolet laser device has a rotary table that rotates the Faraday rotor about the y-axis.

17. The ultraviolet laser device according to claim 14, wherein, An optical axis adjustment mechanism comprising at least two axes is provided between the second polarizer and the amplifier.

18. The ultraviolet laser device according to claim 14, wherein, The oscillating laser and the amplifier each have a cavity filled with laser gas.

19. The ultraviolet laser device according to claim 14, wherein, The oscillating stage laser is an ultraviolet solid-state laser.

20. A method for manufacturing an electronic device, comprising the following steps: A laser beam, amplified by an amplifier, is generated using an ultraviolet laser device. The amplified laser beam is then output to the exposure device. The laser is exposed on a photosensitive substrate within the exposure apparatus to manufacture electronic devices. The ultraviolet laser device has the following features: An oscillating laser that outputs linearly polarized pulsed laser light with an ultraviolet wavelength; The amplifier amplifies and outputs the pulsed laser; and An optical isolator is positioned in the optical path between the oscillator-stage laser and the amplifier. The optical isolator has the following features: The first polarizer, whose transmission axis is configured such that the normalized transmittance of the first polarizer for linearly polarized incident light of ultraviolet wavelength is 0.9 or more. A Faraday rotor, comprising a Faraday material, rotates the polarization direction of light transmitted through the first polarizer via a magnetic field; and A second polarizer, whose transmission axis is configured such that the normalized transmittance of the second polarizer for the incident light after passing through the Faraday rotor is 0.9 or higher. in, The Faraday material is calcium fluoride crystal. When the direction of [001], which is the crystal axis of the calcium fluoride crystal, is set as the a-axis, the direction of [100] as the b-axis, and the direction of [010] as the c-axis, and the axes after rotating the a-axis, the b-axis, and the c-axis by a first angle around the c-axis and by a second angle around the b-axis (after the first angle rotation) are respectively set as the x-axis, y-axis, and z-axis, respectively. The first angle is greater than 40 degrees and less than 50 degrees. The second angle is greater than 45 degrees and less than 75 degrees. The z-axis is parallel to the propagation direction of light incident from the first polarizer onto the calcium fluoride crystal. The calcium fluoride crystal is configured such that the angular difference between the transmission axis of the first polarizer and the x-axis is within the range of 0 degrees or more and 45 degrees or less.

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