Laser system, method for generating pulsed laser light, and method for manufacturing an electronic device

Abstract

This laser system is provided with: a first laser for outputting continuously-oscillating first laser light; a variable optical intensity controller for pulsing the first laser light to output first pulsed laser light; a modulator for widening the spectral linewidth of the first laser light or first pulsed laser light in accordance with a modulated signal; an optical fiber amplifier for amplifying the first pulsed laser light and outputting second pulsed laser light; a second laser that has a center wavelength which is variable and that is for outputting continuously-oscillating second laser light; an optical parametric amplifier for pulsing and amplifying the second laser light and outputting third pulsed laser light; a wavelength conversion unit for using the second pulsed laser light and the third pulsed laser light to output fourth pulsed laser light; an amplification unit for amplifying the fourth pulsed laser light and outputting fifth pulsed laser light; and a processor for controlling the modulated signal so that fifth pulsed laser light of a target spectral linewidth can be obtained and controlling the center wavelength of the second laser light so that fifth pulsed laser light of a target center wavelength will be obtained.

Description

Technical Field

[0001] The present disclosure relates to a laser system, a method for generating pulsed laser light, and a method for manufacturing an electronic device.

Background Art

[0002] In recent years, in semiconductor exposure apparatuses, with the miniaturization and high integration of semiconductor integrated circuits, improvement in resolution has been demanded. For this reason, the wavelength of light emitted from the exposure light source has been shortened. For example, as a gas laser device for exposure, a KrF excimer laser device that outputs laser light with a wavelength of about 248 nm and an ArF excimer laser device that outputs laser light with a wavelength of about 193 nm are used.

[0003] The spectral linewidth of the spontaneous emission light of a KrF excimer laser device and an ArF excimer laser device is as wide as 350 to 400 pm. Therefore, when a projection lens is configured with a material that transmits ultraviolet light such as KrF and ArF laser light, chromatic aberration may occur. As a result, the resolution may decrease. Therefore, it is necessary to narrow the spectral linewidth of the laser light output from the gas laser device to such an extent that chromatic aberration can be ignored. For this reason, a narrowbanding module (Line Narrowing Module: LNM) including a narrowbanding element (etalon, grating, etc.) may be provided in the laser resonator of the gas laser device in order to narrow the spectral linewidth. Hereinafter, a gas laser device whose spectral linewidth is narrowed is referred to as a narrowbanded gas laser device.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

[0005] A laser system according to one aspect of the present disclosure includes a first laser that outputs a first laser beam with continuous oscillation, an optical intensity variator that pulses the first laser beam to output a first pulsed laser beam, a modulator that broadens the spectral linewidth of the first laser beam or the first pulsed laser beam according to a modulation signal, an optical fiber amplifier that amplifies the first pulsed laser beam to output a second pulsed laser beam, a second laser with variable center wavelength that outputs a second laser beam with continuous oscillation, an optical parametric amplifier that pulses and amplifies the second laser beam to output a third pulsed laser beam, and a wavelength conversion unit that outputs a fourth pulsed laser beam using the second pulsed laser beam and the third pulsed laser beam, the wavelength conversion unit including a first nonlinear crystal, a second nonlinear crystal, a third nonlinear crystal, and a fourth nonlinear crystal, wherein the first nonlinear crystal outputs a first harmonic light when the second pulsed laser beam is input, the second nonlinear crystal outputs a second harmonic light when the first harmonic light is input, the third nonlinear crystal outputs a first sum-frequency light and the third pulsed laser beam when the second harmonic light and the third pulsed laser beam are input, and the fourth nonlinear crystal outputs the fourth pulsed laser beam, which is the second sum-frequency light, when the first sum-frequency light and the third pulsed laser beam are input; an amplification unit that amplifies the fourth pulsed laser beam to output a fifth pulsed laser beam; and a processor that receives commands for a target spectral linewidth and a target center wavelength, controls the modulation signal so that a fifth pulsed laser beam with the commanded target spectral linewidth is obtained, and controls the center wavelength of the second laser beam so that a fifth pulsed laser beam with the commanded target center wavelength is obtained.

[0006] A method for generating pulsed laser light according to another aspect of the present disclosure includes: a first laser outputting first laser light with continuous oscillation; an optical intensity variator pulsing the first laser light to output first pulsed laser light; a modulator broadening the spectral linewidth of the first laser light or the first pulsed laser light according to a modulation signal; an optical fiber amplifier amplifying the first pulsed laser light to output second pulsed laser light; a second laser with variable center wavelength outputting second laser light with continuous oscillation; an optical parametric amplifier pulsing and amplifying the second laser light to output third pulsed laser light; inputting the second pulsed laser light into a first non-linear crystal of a wavelength conversion unit including a first non-linear crystal, a second non-linear crystal, a third non-linear crystal, and a fourth non-linear crystal, so that the first non-linear crystal outputs first harmonic light; inputting the first harmonic light into the second non-linear crystal, so that the second non-linear crystal outputs second harmonic light; inputting the second harmonic light and the third pulsed laser light into the third non-linear crystal, so that the third non-linear crystal outputs first sum-frequency light and the third pulsed laser light; inputting the first sum-frequency light and the third pulsed laser light into the fourth non-linear crystal, so that the fourth non-linear crystal outputs fourth pulsed laser light which is second sum-frequency light; an amplifier amplifying the fourth pulsed laser light to output fifth pulsed laser light; a processor controlling the modulation signal so that fifth pulsed laser light with a target spectral linewidth commanded by an external device is obtained; and the processor controlling the center wavelength of the second laser light so that fifth pulsed laser light with a target center wavelength commanded by an external device is obtained.

[0007] A method for manufacturing an electronic device according to another aspect of the present disclosure includes a first laser that outputs a first laser beam of continuous oscillation, an optical intensity variator that pulses the first laser beam to output a first pulsed laser beam, a modulator that broadens the spectral linewidth of the first laser beam or the first pulsed laser beam according to a modulation signal, an optical fiber amplifier that amplifies the first pulsed laser beam to output a second pulsed laser beam, a second laser with a variable center wavelength that outputs a second laser beam of continuous oscillation, an optical parametric amplifier that pulses and amplifies the second laser beam to output a third pulsed laser beam, and a wavelength conversion unit that outputs a fourth pulsed laser beam using the second pulsed laser beam and the third pulsed laser beam. The wavelength conversion unit includes a first non-linear crystal, a second non-linear crystal, a third non-linear crystal, and a fourth non-linear crystal. When the second pulsed laser beam is input into the first non-linear crystal, the first non-linear crystal outputs a first harmonic light beam. When the first harmonic light beam is input into the second non-linear crystal, the second non-linear crystal outputs a second harmonic light beam. When the second harmonic light beam and the third pulsed laser beam are input into the third non-linear crystal, the third non-linear crystal outputs a first sum-frequency light beam and the third pulsed laser beam. When the first sum-frequency light beam and the third pulsed laser beam are input into the fourth non-linear crystal, the fourth non-linear crystal outputs a fourth pulsed laser beam that is a second sum-frequency light beam. The method further includes an amplification unit that amplifies the fourth pulsed laser beam to output a fifth pulsed laser beam, and a processor that receives commands for a target spectral linewidth and a target center wavelength, controls the modulation signal so that a fifth pulsed laser beam with the commanded target spectral linewidth is obtained, and controls the center wavelength of the second laser beam so that a fifth pulsed laser beam with the commanded target center wavelength is obtained. The fifth pulsed laser beam is generated by a laser system including the above components, the fifth pulsed laser beam is output to an exposure apparatus, and in order to manufacture an electronic device, the fifth pulsed laser beam is used to expose a photosensitive substrate in the exposure apparatus.

Brief Description of the Drawings

[0008] Some embodiments of the present disclosure will be described below by way of example only with reference to the accompanying drawings.

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[0009] -Table of Contents- 1. Overview of the Laser System According to the Comparative Example 1.1 Configuration 1.2 Operation 1.3 Problems 2. Embodiment 1 2.1 Configuration 2.2 Operation 2.3 Example of Spectrum Linewidth Control 2.4 Examples of Central Wavelength Control 2.5 Effects 2.6 Modification Examples 2.6.1 Configuration 2.6.2 Operation 2.6.3 Examples of Spectral Linewidth Control 2.6.4 Effects 3. Embodiment 2 3.1 Configuration 3.2 Operation 3.3 Examples of Spectral Linewidth Control 3.4 Effects 4. Regarding the Manufacturing Method of an Electronic Device 5. Others Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. The embodiments described below show some examples of the present disclosure and do not limit the content of the present disclosure. Also, not all of the configurations and operations described in each embodiment are essential as the configurations and operations of the present disclosure. Note that the same reference numerals are assigned to the same components, and redundant descriptions are omitted.

[0010] 1. Outline of the Laser System According to the Comparative Example 1.1 Configuration FIG. 1 schematically shows the configuration of a laser system 2 according to the comparative example. The comparative example of the present disclosure is a form recognized by the applicant as being known only to the applicant and is not a known example recognized by the applicant.

[0011] The laser system 2 shown in FIG. 1 is a solid laser system using a semiconductor laser that generates pulsed laser light with a wavelength of 194.3 nm and amplifies the pulsed laser light with an excimer amplifier. Note that the numerical values of the wavelengths described in this specification are representative values, and are not limited to the numerical values of the wavelengths described, and may be wavelengths near the numerical values of those wavelengths. For example, the description of a wavelength of 194.3 nm includes the meaning of a wavelength of approximately 194.3 nm unless otherwise specified.

[0012] The laser system 2 includes a solid-state laser system 10, an excimer amplifier 20, a monitor module 30, and a laser control unit 40. The solid-state laser system 10 includes a first semiconductor laser 101, a second semiconductor laser 102, a first semiconductor optical amplifier (Semiconductor Optical Amplifier: SOA) 111, a second semiconductor optical amplifier 112, a first optical fiber amplifier 121, a second optical fiber amplifier 122, and a wavelength conversion unit 130. In the drawings, for example, the first semiconductor laser 101 is denoted as "semiconductor laser 1", the first semiconductor optical amplifier 111 is denoted as "SOA1", and so on.

[0013] The first semiconductor laser 101 is, for example, a semiconductor laser that continuously oscillates at a wavelength of 1030 nm and oscillates in a single longitudinal mode.

[0014] The second semiconductor laser 102 is, for example, a semiconductor laser that continuously oscillates at a wavelength of 1553 nm and oscillates in a single longitudinal mode. The first semiconductor laser 101 and the second semiconductor laser 102 may be distributed feedback laser diodes (Distributed Feedback - Laser Diode: DFB - LD), distributed Bragg reflector laser diodes (Distributed Bragg Reflector - Laser Diode: DBR - LD), or external resonator type DBR lasers.

[0015] The first semiconductor optical amplifier 111 performs pulse formation and amplification of the continuously oscillating laser light output from the first semiconductor laser 101. The second semiconductor optical amplifier 112 performs pulse formation and amplification of the continuously oscillating laser light output from the second semiconductor laser 102.

[0016] The first optical fiber amplifier 121 amplifies the energy of the pulsed laser light output from the first semiconductor optical amplifier 111. The second optical fiber amplifier 122 amplifies the energy of the pulsed laser light output from the second semiconductor optical amplifier 112. The first optical fiber amplifier 121 and the second optical fiber amplifier 122 may be Yb fiber amplifiers, Yb - YAG crystals, or the like.

[0017] The pulsed laser light amplified by the first optical fiber amplifier 121 is reflected by, for example, the first high reflection mirror HR1, the second high reflection mirror HR2, the third high reflection mirror HR3, and the fourth high reflection mirror HR4, and introduced into the wavelength conversion unit 130.

[0018] The wavelength conversion unit 130 converts the laser light with a near-infrared wavelength output from the first semiconductor laser 101 and the second semiconductor laser 102 into laser light with an ultraviolet wavelength. Here, the near-infrared wavelength is 780 nm to 2500 nm, and the ultraviolet wavelength is 150 nm to 380 nm. The wavelength conversion unit 130 may include an LBO crystal 132, a first CLBO crystal 141, a first dichroic mirror DC1, a second CLBO crystal 142, a second dichroic mirror DC2, a third dichroic mirror DC3, a fourth dichroic mirror DC4, a fifth high reflection mirror HR5, a sixth high reflection mirror HR6, a third CLBO crystal 143, and a fifth dichroic mirror DC5. LBO is represented by the chemical formula LiB3O5. CLBO is represented by the chemical formula CsLiB6O 10 represented by. Each of the LBO crystal and the CLBO crystal is a nonlinear crystal for wavelength conversion. The term "nonlinear crystal" is synonymous with "nonlinear optical crystal".

[0019] The LBO crystal 132 is arranged such that the pulsed laser light with a wavelength of 1030 nm output from the first optical fiber amplifier 121 is incident thereon.

[0020] The first CLBO crystal 141 is arranged such that the pulsed laser light with a wavelength of 515 nm from the LBO crystal 132 is incident thereon.

[0021] The first dichroic mirror DC1 is arranged between the first CLBO crystal 141 and the second CLBO crystal 142, and is coated with a film that highly reflects the pulsed laser light with a wavelength of 1553 nm from the second optical fiber amplifier 122 and highly transmits the pulsed laser light with a wavelength of 257.5 nm from the first CLBO crystal 141.

[0022] The second CLBO crystal 142 is arranged such that the pulsed laser light with a wavelength of 257.5 nm that has passed through the first dichroic mirror DC1 and the pulsed laser light with a wavelength of 1553 nm that has been reflected by the first dichroic mirror DC1 are incident thereon.

[0023] The second dichroic mirror DC2 is arranged between the second CLBO crystal 142 and the third dichroic mirror DC3, and is coated with a film that highly reflects the pulsed laser light with a wavelength of 1553 nm (the third pulsed laser light PL3) from the second CLBO crystal 142 and highly transmits the pulsed laser light with a wavelength of 257.5 nm and the pulsed laser light with a wavelength of 220.9 nm.

[0024] The third dichroic mirror DC3 is arranged between the second dichroic mirror DC2 and the fourth dichroic mirror DC4, and is coated with a film that highly reflects the pulsed laser light with a wavelength of 257.5 nm from the second dichroic mirror DC2 and highly transmits the pulsed laser light with a wavelength of 220.9 nm.

[0025] The fourth dichroic mirror DC4 is arranged between the third dichroic mirror DC3 and the third CLBO crystal 143, and is coated with a film that highly reflects the pulsed laser light with a wavelength of 1553 nm from the sixth high reflection mirror HR6 and highly transmits the pulsed laser light with a wavelength of 220.9 nm from the third dichroic mirror DC3.

[0026] The third CLBO crystal 143 is arranged such that the pulsed laser light with a wavelength of 220.9 nm and the pulsed laser light with a wavelength of 1553 nm from the fourth dichroic mirror DC4 are incident thereon.

[0027] The fifth dichroic mirror DC5 is arranged between the third CLBO crystal 143 and the excimer amplifier 20, and is coated with a film that highly reflects the pulsed laser light with a wavelength of 193.4 nm from the third CLBO crystal 143 and highly transmits the pulsed laser light with a wavelength of 220.9 nm and the pulsed laser light with a wavelength of 1553 nm.

[0028] The excimer amplifier 20 includes a rear mirror RM, a chamber 22, and an output coupler OC. The rear mirror RM and the output coupler OC constitute an optical resonator, and the chamber 22 is disposed on the optical path of this optical resonator. The optical resonator is a Fabry - Perot type optical resonator, and is composed of a rear mirror RM that partially reflects and transmits a part of the laser light, and an output coupler OC that partially reflects and transmits a part of the laser light. Here, the reflectivity of the output coupler OC may be, for example, 10% - 30%, and the reflectivity of the rear mirror RM may be, for example, 80% - 90%. Also, the optical resonator may be a ring resonator, and the amplifier may be a multi - pass amplifier such as a three - pass amplifier that amplifies by reflecting the seed light with a cylindrical mirror and passing it through the discharge space three times.

[0029] The chamber 22 includes a pair of discharge electrodes 25a, 25b and two windows 26, 27 through which the laser light passes. An excimer laser gas is introduced into the chamber 22. The excimer laser gas includes, for example, a rare gas, a halogen gas, and a buffer gas. The rare gas may be Ar or Kr. The halogen gas may be, for example, F2 gas. The buffer gas may be, for example, Ne gas.

[0030] The monitor module 30 is arranged to measure the central wavelength, the spectral linewidth, and the pulse energy of the pulsed laser light output from the excimer amplifier 20. The monitor module 30 includes a first beam splitter BS1, a wavelength monitor 34, a second beam splitter BS2, a linewidth monitor 35, a third beam splitter BS3, and a pulse energy monitor 36.

[0031] The first beam splitter BS1 is arranged on the optical path of the pulsed laser light output from the excimer amplifier 20. The second beam splitter BS2 and the third beam splitter BS3 are arranged on the optical path of the pulsed laser light reflected by the first beam splitter BS1. The wavelength monitor 34 is arranged so that the pulsed laser light reflected by the second beam splitter BS2 is incident thereon. The wavelength monitor 34 measures the wavelength of the pulsed laser light. The wavelength monitor 34 is, for example, an etalon spectroscope.

[0032] The third beam splitter BS3 is arranged between the second beam splitter BS2 and the pulse energy monitor 36. The linewidth monitor 35 is arranged so that the pulsed laser light reflected by the third beam splitter BS3 is incident thereon. The linewidth monitor 35 measures the spectral linewidth of the pulsed laser light with high precision. The linewidth monitor 35 is, for example, an etalon spectroscope. The pulse energy monitor 36 is arranged so that the pulsed laser light transmitted through the third beam splitter BS3 is incident thereon. The pulse energy monitor 36 detects the pulse energy of the pulsed laser light. The pulse energy monitor 36 may be, for example, a pulse energy sensor including a photodiode or a pyroelectric element.

[0033] 1.2 Operation The laser control unit 40 continuously oscillates the first semiconductor laser 101 and the second semiconductor laser 102 at all times. The first semiconductor optical amplifier 111 performs pulse formation and amplification of the laser light with a continuous oscillation wavelength of 1030 nm output from the first semiconductor laser 101. The pulse width of the pulsed laser light after pulse formation is, for example, 10 ns to 40 ns.

[0034] The pulsed laser light output from the first semiconductor optical amplifier 111 is incident on the first optical fiber amplifier 121 and amplified. The pulsed laser light amplified by the first optical fiber amplifier 121 is incident on the LBO crystal 132. The incident angle of the LBO crystal 132 is adjusted so that the pulsed laser light with a wavelength of 1030 nm satisfies the phase matching condition for generating the second harmonic light with a wavelength of 1030 nm. As a result, pulsed laser light with a wavelength of 515 nm, which is the second harmonic of the pulsed laser light with a wavelength of 1030 nm, is generated.

[0035] The pulsed laser light with a wavelength of 515 nm is incident on the first CLBO crystal 141. The incident angle of the first CLBO crystal 141 is adjusted so that the pulsed laser light with a wavelength of 515 nm satisfies the phase matching condition for generating the second harmonic light with a wavelength of 515 nm. As a result, pulsed laser light with a wavelength of 257.5 nm, which is the second harmonic of the pulsed laser light with a wavelength of 515 nm, is generated.

[0036] The second semiconductor optical amplifier 112 pulses and amplifies the continuous-wave laser light with a wavelength of 1553 nm output from the second semiconductor laser 102. The pulse width of the pulsed laser light is, for example, 10 ns to 40 ns. The pulsed laser light output from the second semiconductor optical amplifier 112 is incident on the second optical fiber amplifier 122 and amplified.

[0037] The pulsed laser light with a wavelength of 257.5 nm and the pulsed laser light with a wavelength of 1553 nm are combined by the first dichroic mirror DC1 and incident on the second CLBO crystal 142. The incident angles of the second CLBO crystal 142 are adjusted so that the pulsed laser light with a wavelength of 257.5 nm and the pulsed laser light with a wavelength of 1553 nm satisfy the phase matching condition for generating the sum-frequency light. As a result, pulsed laser light with a wavelength of 220.9 nm, which is the sum frequency of the pulsed laser light with a wavelength of 257.5 nm and the pulsed laser light with a wavelength of 1553 nm, is generated. Note that, together with the pulsed laser light with a wavelength of 220.9 nm, the pulsed laser light with a wavelength of 257.5 nm and the pulsed laser light with a wavelength of 1553 nm are also output from the second CLBO crystal 142.

[0038] The pulsed laser light with a wavelength of 257.5 nm passes through the second dichroic mirror DC2, is then reflected by the third dichroic mirror DC3, and is deflected out of the optical path. The pulsed laser light with a wavelength of 1553 nm output from the second CLBO crystal 142 is reflected by the second dichroic mirror DC2 and then enters the fourth dichroic mirror DC4 through the fifth high-reflection mirror HR5 and the sixth high-reflection mirror HR6. The pulsed laser light with a wavelength of 220.9 nm and the pulsed laser light with a wavelength of 1553 nm are combined by the fourth dichroic mirror DC4 and enter the third CLBO crystal 143. The third CLBO crystal 143 has its respective incident angles adjusted so that the pulsed laser light with a wavelength of 220.9 nm and the pulsed laser light with a wavelength of 1553 nm satisfy the phase matching condition for sum-frequency light generation. As a result, pulsed laser light with a wavelength of 193.4 nm, which is the sum frequency of the pulsed laser light with a wavelength of 220.9 nm and the pulsed laser light with a wavelength of 1553 nm, is generated.

[0039] The pulsed laser light with a wavelength of 193.4 nm, which is highly reflected by the fifth dichroic mirror DC5, enters the excimer amplifier 20 through the eighth high-reflection mirror HR8.

[0040] At the timing when the pulsed laser light transmitted through the rear mirror RM enters the chamber 22, a high-voltage pulse is applied between the discharge electrodes 25a and 25b in the chamber 22 from a power supply (not shown). When a discharge occurs between the discharge electrodes 25a and 25b in the chamber 22, the laser gas is excited, and the pulsed laser light is amplified by a Fabry - Perot type optical resonator composed of the output coupler OC and the rear mirror RM, and is output from the output coupler OC.

[0041] The pulsed laser light amplified by the excimer amplifier 20 has its spectral linewidth, central wavelength, and pulse energy measured by the monitor module 30. The measurement results of the monitor module 30 are sent to the laser control unit 40.

[0042] The laser control unit 40 receives the target pulse energy Et, the target spectral linewidth Δλt, the target center wavelength λct, and the emission trigger signal Tr from the exposure control unit 82 of the exposure apparatus 80. The laser control unit 40 controls the spectral linewidth of the laser light output from the first semiconductor laser 101 so that the difference ΔΔλ between the spectral linewidth Δλ of the pulsed laser light measured by the linewidth monitor 35 and the target spectral linewidth Δλt becomes small. Specifically, the laser control unit 40 controls the AC component value of the current flowing through the semiconductor laser element of the first semiconductor laser 101 so that ΔΔλ approaches 0.

[0043] The laser control unit 40 may change the wavelength of the laser light output from the first semiconductor laser 101 so that the difference δλc between the wavelength λc of the pulsed laser light measured by the wavelength monitor 34 and the target center wavelength λct becomes small. Specifically, the laser control unit 40 controls the DC component value of the current flowing through the semiconductor laser element of the first semiconductor laser 101 or the temperature of the semiconductor laser element so that the difference δλc approaches 0.

[0044] The laser control unit 40 calculates the difference ΔE between the pulse energy E measured by the pulse energy monitor 36 and the target pulse energy Et. Then, the excimer amplifier 20 is controlled so that the difference ΔE approaches 0.

[0045] 1.3 Problems

[0046] [1]When attempting to amplify the laser light output from the first semiconductor laser 101 using the first optical fiber amplifier 121, since the spectral linewidth is narrow, there is a possibility that amplification up to the target power may not be achievable due to the occurrence of stimulated Brillouin scattering (SBS). Also, there is a risk of damaging the first semiconductor optical amplifier 111 and the first semiconductor laser 101 due to SBS traveling in the direction opposite to that of the laser light. To suppress the occurrence of this SBS, it is necessary to arrange a mechanism for broadening the spectral linewidth of the laser light. Similarly, for the laser light output from the second semiconductor laser 102 as well, a mechanism for broadening the spectral linewidth is required, and it is necessary to arrange two mechanisms with the same function. Also, since the minimum spectral linewidth is restricted in both devices, the minimum spectral linewidth of the pulsed laser light output from the laser system 2 becomes broad.

[0047] [2]The optimum phase matching conditions (conditions of incident angle or crystal temperature) for the four non-linear crystals, namely the LBO crystal 132, the first CLBO crystal 141, the second CLBO crystal 142, and the third CLBO crystal 143, differ for each center wavelength. When the center wavelength is controlled by changing the wavelength of the laser light output from the first semiconductor laser 101, since it affects the phase matching conditions of all four crystals, it is necessary to control so as to satisfy the phase matching conditions of all four crystals.

[0048] 2. Embodiment 1 2.1 Configuration FIG. 2 schematically shows the configuration of the laser system 2A according to Embodiment 1. Regarding the laser system 2A shown in FIG. 2, the differences from the configuration shown in FIG. 1 will be described.

[0049] The laser system 2A includes a solid-state laser system 11 instead of the solid-state laser system 10 shown in FIG. 1. In the solid-state laser system 11, an optical frequency modulator 114 and an optical intensity variator 116 are arranged between a first semiconductor laser 101 and a first optical fiber amplifier 121, and a wavelength conversion unit 131 is provided instead of the wavelength conversion unit 130 shown in FIG. 1. In the wavelength conversion unit 131, a sixth dichroic mirror DC6 is arranged between an LBO crystal 132 and a first CLBO crystal 141.

[0050] Also, instead of the second semiconductor optical amplifier 112 and the second optical fiber amplifier 122 shown in FIG. 1, a seventh dichroic mirror DC7 and an optical parametric amplifier (OPA) 125 using a periodically poled lithium niobate (PPLN) crystal are arranged in the solid-state laser system 11.

[0051] The first semiconductor laser 101 in the solid-state laser system 11, for example, continuously oscillates at a wavelength of 1030 nm and oscillates in a single longitudinal mode, and outputs a first laser beam L1. The first semiconductor laser 101 may be, for example, a DFB-LD, a DBR-LD, or an external resonator type DBR laser. The first semiconductor laser 101 is an example of the "first laser" in the present disclosure.

[0052] The solid-state laser system 11 includes an optical intensity variator 116 that pulses the first laser beam L1 output from the first semiconductor laser 101 to output a first pulsed laser beam PL1. The optical intensity variator 116 may be a semiconductor optical amplifier (SOA) or an optical intensity modulator using an electro-optic effect. The optical intensity modulator using an electro-optic effect may be an optical shutter combining a Pockels cell and a polarizer, or a Mach-Zehnder type optical intensity modulator.

[0053] In the solid-state laser system 11, an optical frequency modulator 114 is disposed between the first semiconductor laser 101 and the optical intensity variator 116. The optical frequency modulator 114 may be, for example, an AO frequency modulator using an acousto-optic element (Acousto-Optics: AO). Instead of the optical frequency modulator 114, an optical phase modulator may be disposed. The optical phase modulator may be, for example, a phase modulator using an electro-optic effect. The optical frequency modulator 114 may be disposed downstream of the optical intensity variator 116. The optical frequency modulator 114 is an example of the "modulator" in the present disclosure.

[0054] The first optical fiber amplifier 121 amplifies the energy of the first pulsed laser beam PL1 output from the optical intensity variator 116 and outputs a second pulsed laser beam PL2. When the energy is still insufficient even after amplification by the first optical fiber amplifier 121, a Yb-doped solid-state amplifier may be disposed downstream of the first optical fiber amplifier 121.

[0055] The second semiconductor laser 102 is, for example, a laser with a variable center wavelength that can be freely changed between 1551 nm and 1555 nm, continuously oscillates at the commanded wavelength, and oscillates in a single longitudinal mode to output a second laser beam L2. The second semiconductor laser 102 may be a DFB-LD, a DBR-LD, or an external resonator type DBR laser. The DBR-LD may be an SG-DBR-LD (Sampled Grating Distributed Bragg Reflector Laser Diode) or an SSG-DBR-LD (Super Structure Grating Distributed Bragg Reflector Laser Diode). The second semiconductor laser 102 is an example of the "second laser" in the present disclosure.

[0056] The seventh dichroic mirror DC7 is disposed upstream of the OPA125 and is coated with a film that highly reflects a pulsed laser beam with a wavelength of 1030 nm (the second pulsed laser beam PL2) and highly transmits the laser beam with a wavelength of 1553 nm (the second laser beam L2) from the second semiconductor laser 102.

[0057] OPA125 performs the pulsing and amplification of the second laser beam L2 and outputs the third pulsed laser beam PL3. OPA125 uses a plurality of PPLN crystals, installs a partial reflection mirror that branches the pulsed laser beam with a wavelength of 1030 nm between the sixth dichroic mirror DC6 and the seventh dichroic mirror DC7, installs dichroic mirrors between each of the serially installed PPLN crystals, and inputs the branched pulsed laser beam with a wavelength of 1030 nm to each PPLN crystal, and OPA125 may be installed in multiple stages for amplification.

[0058] The wavelength conversion unit 131 includes an LBO crystal 132, a sixth dichroic mirror DC6, a first CLBO crystal 141, a first dichroic mirror DC1, a second CLBO crystal 142, a second dichroic mirror DC2, a third dichroic mirror DC3, a fourth dichroic mirror DC4, a fifth high reflection mirror HR5, a sixth high reflection mirror HR6, a third CLBO crystal 143, and a fifth dichroic mirror DC5.

[0059] The LBO crystal 132 is arranged such that the pulsed laser beam with a wavelength of 1030 nm (the second pulsed laser beam PL2) output from the first optical fiber amplifier 121 is incident thereon.

[0060] The sixth dichroic mirror DC6 is arranged between the LBO crystal 132 and the first CLBO crystal 141, and is coated with a film that highly reflects the pulsed laser beam with a wavelength of 1030 nm (the second pulsed laser beam PL2) and highly transmits the pulsed laser beam with a wavelength of 515 nm (the first harmonic light) from the LBO crystal 132.

[0061] The pulsed laser light with a wavelength of 1030 nm (the second pulsed laser light PL2) reflected by the sixth dichroic mirror DC6 and the laser light with a wavelength of 1553 nm (the second laser light L2) from the second semiconductor laser 102 are combined by the seventh dichroic mirror DC7, and the seventh dichroic mirror DC7 and the OPA125 are arranged so as to be incident on the OPA125. Alternatively, without arranging the sixth dichroic mirror DC6, a beam splitter may be arranged instead of the fourth high-reflection mirror HR4, and the pulsed laser light (the second pulsed laser light PL2) transmitted through this beam splitter is combined by the seventh dichroic mirror DC7, and the seventh dichroic mirror DC7 and the OPA125 may be arranged so as to be incident on the OPA125.

[0062] The first CLBO crystal 141 may be arranged so that the pulsed laser light with a wavelength of 515 nm (the first harmonic light) from the LBO crystal 132 is incident thereon.

[0063] The first dichroic mirror DC1 is arranged between the first CLBO crystal 141 and the second CLBO crystal 142, and may be coated with a film that highly reflects the pulsed laser light with a wavelength of 1553 nm (the third pulsed laser light PL3) from the OPA125 and highly transmits the pulsed laser light with a wavelength of 257.5 nm (the second harmonic light) from the first CLBO crystal 141. Alternatively, the first dichroic mirror DC1 is arranged between the sixth dichroic mirror DC6 and the first CLBO crystal 141, and may be coated with a film that highly reflects the pulsed laser light with a wavelength of 1553 nm (the third pulsed laser light PL3) from the OPA125 and highly transmits the pulsed laser light with a wavelength of 515 nm (the second harmonic light) from the sixth dichroic mirror DC6.

[0064] The second CLBO crystal 142 may be arranged such that the pulsed laser light with a wavelength of 257.5 nm (second harmonic light) that has passed through the first dichroic mirror DC1 and the pulsed laser light with a wavelength of 1553 nm (third pulsed laser light PL3) that has been reflected by DC1 are incident thereon. The second CLBO crystal 142 may be arranged on a rotation stage (not shown) and configured to be able to change the incident angle to the crystal and the temperature in order to meet the phase matching conditions.

[0065] The second dichroic mirror DC2 is arranged between the second CLBO crystal 142 and the third dichroic mirror DC3, and may be coated with a film that highly reflects the pulsed laser light with a wavelength of 1553 nm (third pulsed laser light PL3) from the second CLBO crystal 142 and highly transmits the pulsed laser light with a wavelength of 257.5 nm (second harmonic light) and the pulsed laser light with a wavelength of 220.9 nm (first sum frequency light) from the first CLBO crystal 141.

[0066] The third dichroic mirror DC3 is arranged between the second dichroic mirror DC2 and the fourth dichroic mirror DC4, and is coated with a film that highly reflects the pulsed laser light with a wavelength of 257.5 nm (second harmonic light) from the second dichroic mirror DC2 and highly transmits the pulsed laser light with a wavelength of 220.9 nm (first sum frequency light).

[0067] The fourth dichroic mirror DC4 is arranged between the third dichroic mirror DC3 and the third CLBO crystal 143, and is coated with a film that highly reflects the pulsed laser light with a wavelength of 1553 nm (third pulsed laser light PL3) from the sixth high reflection mirror HR6 and highly transmits the pulsed laser light with a wavelength of 220.9 nm (first sum frequency light) from the third dichroic mirror DC3.

[0068] The third CLBO crystal 143 is arranged such that the pulsed laser light with a wavelength of 220.9 nm (the first sum-frequency light) and the pulsed laser light with a wavelength of 1553 nm (the third pulsed laser light PL3) from the fourth dichroic mirror DC4 are incident thereon. The third CLBO crystal 143 is arranged on a rotation stage (not shown) and may be configured to be able to change the incident angle to the crystal and the temperature in order to meet the phase matching conditions.

[0069] The fifth dichroic mirror DC5 is arranged between the third CLBO crystal 143 and the excimer amplifier 20 and may be coated with a film that highly reflects the pulsed laser light with a wavelength of 193.4 nm (the second sum-frequency light, the fourth pulsed laser light PL4) from the third CLBO crystal 143 and highly transmits the pulsed laser light with a wavelength of 220.9 nm (the first sum-frequency light) and the pulsed laser light with a wavelength of 1553 nm (the third pulsed laser light PL3).

[0070] The LBO crystal 132 is an example of the "first non-linear crystal" in the present disclosure. The first CLBO crystal 141 is an example of the "second non-linear crystal" in the present disclosure, and the second CLBO crystal 142 and the third CLBO crystal 143 are examples of the "third non-linear crystal" and the "fourth non-linear crystal" in the present disclosure.

[0071] The laser control unit 40 is configured using a processor. The processor in the present disclosure is a processing device including a storage device storing a control program and a CPU (Central Processing Unit) that executes the control program. The processor is specially configured or programmed to execute various processes included in the present disclosure. The processor may include an integrated circuit represented by an FPGA (Field Programmable Gate Array) or an ASIC (Application Specific Integrated Circuit). Note that the functions of the laser control unit 40 may be realized by a plurality of processors.

[0072] The configurations of the excimer amplifier 20 and the monitor module 30 in the laser system 2A may be the same as those in FIG. 1.

[0073] 2.2 Operation The laser control unit 40 continuously oscillates the first semiconductor laser 101 and the second semiconductor laser 102 at all times. The first laser beam L1 output from the first semiconductor laser 101 is wavelength (frequency) - modulated by the modulation signal received from the laser control unit 40 by the optical frequency modulator 114, and according to the principle of frequency modulation, the spectral linewidth spreads.

[0074] The optical intensity variable 116 pulses the continuous - oscillation laser beam (the first laser beam L1) with a wavelength of 1030 nm output from the optical frequency modulator 114. The pulse width of the pulsed laser beam (the first pulsed laser beam PL1) is, for example, 10 ns to 40 ns.

[0075] The first pulsed laser beam PL1 output from the optical intensity variable 116 enters the first optical fiber amplifier 121, is amplified, and outputs the second pulsed laser beam PL2.

[0076] The second pulsed laser beam PL2 amplified by the first optical fiber amplifier 121 enters the LBO crystal 132. The incident angle of the LBO crystal is adjusted by a rotation stage (not shown) so that the pulsed laser beam with a wavelength of 1030 nm (the second pulsed laser beam PL2) satisfies the phase - matching condition for the generation of the second - harmonic light with a wavelength of 1030 nm. As a result, a pulsed laser beam with a wavelength of 515 nm (the first harmonic light), which is the second - harmonic of the pulsed laser beam with a wavelength of 1030 nm (the second pulsed laser beam PL2), is generated.

[0077] A pulsed laser beam with a wavelength of 515 nm (first harmonic light) is incident on the first CLBO crystal 141. The incident angle of the first CLBO crystal 141 is adjusted so that the pulsed laser beam with a wavelength of 515 nm (first harmonic light) satisfies the phase matching condition for generating the second harmonic light with a wavelength of 515 nm. As a result, a pulsed laser beam with a wavelength of 257.5 nm (second harmonic light), which is the second harmonic of the pulsed laser beam with a wavelength of 515 nm (first harmonic light), is generated.

[0078] The pulsed laser beam with a wavelength of 1030 nm (second pulsed laser beam PL2) reflected by the sixth dichroic mirror DC6 and the laser beam with a wavelength of 1553 nm (second laser beam L2) output from the second semiconductor laser 102 are combined by the seventh dichroic mirror DC7 and incident on the OPA125. In the OPA125, a pulsed laser beam with a wavelength of 1553 nm (third pulsed laser beam PL3) having a pulse width equal to or slightly shorter than the pulse width of the pulsed laser beam with a wavelength of 1030 nm (second pulsed laser beam PL2) is generated and amplified by optical parametric amplification. That is, the OPA125 pulses the continuous-wave laser beam output from the second semiconductor laser 102.

[0079] The third pulsed laser beam PL3 output from the OPA125 is incident on the first dichroic mirror DC1 via the seventh high-reflection mirror HR7. The pulsed laser beam with a wavelength of 257.5 nm (second harmonic light) output from the first CLBO crystal 141 and the pulsed laser beam with a wavelength of 1553 nm (third pulsed laser beam PL3) output from the OPA125 are combined by the first dichroic mirror DC1 and incident on the second CLBO crystal 142.

[0080] The second CLBO crystal 142 has the incident angles of the pulsed laser beam with a wavelength of 257.5 nm (second harmonic light) and the pulsed laser beam with a wavelength of 1553 nm (third pulsed laser beam PL3) adjusted so as to satisfy the phase matching condition for sum frequency light generation. As a result, a pulsed laser beam with a wavelength of 220.9 nm (first sum frequency light), which is the sum frequency light of the pulsed laser beam with a wavelength of 257.5 nm (second harmonic light) and the pulsed laser beam with a wavelength of 1553 nm (third pulsed laser beam PL3), is generated. Note that from the second CLBO crystal 142, a pulsed laser beam with a wavelength of 257.5 nm (second harmonic light) and a pulsed laser beam with a wavelength of 1553 nm (third pulsed laser beam PL3) are also output together with the pulsed laser beam with a wavelength of 220.9 nm (first sum frequency light).

[0081] The pulsed laser beam with a wavelength of 257.5 nm (second harmonic light) is reflected by the third dichroic mirror DC3 and is removed from the optical path. The pulsed laser beam with a wavelength of 220.9 nm (first sum frequency light) and the pulsed laser beam with a wavelength of 1553 nm (third pulsed laser beam PL3) are incident on the third CLBO crystal 143. The third CLBO crystal 143 has the incident angles of the pulsed laser beam with a wavelength of 220.9 nm (first sum frequency light) and the pulsed laser beam with a wavelength of 1553 nm (third pulsed laser beam PL3) adjusted so as to satisfy the phase matching condition for sum frequency light generation. As a result, a pulsed laser beam with a wavelength of 193.4 nm (second sum frequency light, fourth pulsed laser beam PL4), which is the sum frequency of the pulsed laser beam with a wavelength of 220.9 nm (first sum frequency light) and the pulsed laser beam with a wavelength of 1553 nm (third pulsed laser beam PL3), is generated.

[0082] The pulsed laser beam with a wavelength of 193.4 nm (fourth pulsed laser beam PL4), which is highly reflected by the fifth dichroic mirror DC5, is incident on the excimer amplifier 20.

[0083] At the timing when the fourth pulsed laser beam PL4 transmitted through the rear mirror RM enters the chamber 22, a high-voltage pulse is applied between the discharge electrodes 25a and 25b in the chamber 22 from a power supply (not shown). When a discharge occurs between the discharge electrodes 25a and 25b in the chamber 22, the laser gas is excited, and the fourth pulsed laser beam PL4 is amplified by a Fabry - Perot type optical resonator composed of the output coupler OC and the rear mirror RM, and the fifth pulsed laser beam PL5 is output from the output coupler OC. The excimer amplifier is an example of the "amplifying section" in the present disclosure.

[0084] The fifth pulsed laser beam PL5 output from the excimer amplifier 20 has its spectral linewidth, central wavelength, and pulse energy measured by the monitor module 30.

[0085] The laser control unit 40 receives the target pulse energy Et, the target spectral linewidth Δλt, the target central wavelength λct, and the emission trigger signal Tr from the exposure control unit 82 of the exposure apparatus 80. The exposure apparatus 80 is an example of the "external device" in the present disclosure. The laser control unit 40 determines and outputs a modulation signal to the optical frequency modulator 114 so that the difference ΔΔλ between the spectral linewidth Δλ of the fifth pulsed laser beam PL5 measured by the linewidth monitor 35 and the target spectral linewidth Δλt becomes small. In this case, the control of the AC component value of the current flowing through the semiconductor laser element of the first semiconductor laser 101 is not performed.

[0086] The first laser beam L1 output from the first semiconductor laser 101 has its wavelength (frequency) modulated by the received modulation signal in the optical frequency modulator 114, and according to the principle of frequency modulation, the spectral linewidth broadens.

[0087] Also, the laser control unit 40 calculates the difference δλc between the wavelength λc of the fifth pulsed laser beam PL5 measured by the wavelength monitor 34 and the target central wavelength λct. Then, a control signal to the second semiconductor laser 102 is determined and output so that the difference δλc becomes small.

[0088] In the case of the second semiconductor laser 102 being, for example, an SG-DBR-LD or an SSG-DBR-LD, the center wavelength of the output second laser beam L2 may be changed by controlling the current to each diffraction grating and the adjustment amount of the current to the phase adjustment region. Alternatively, in the case of an external resonator type DBR laser, the center wavelength of the output second laser beam L2 may be changed by controlling the angle and position of the diffraction grating or mirror constituting the resonator according to the received control signal. In these cases, the DC component value of the current flowing through the active layer of the semiconductor laser element of the second semiconductor laser 102 or the variable control of the temperature of the semiconductor laser element is not performed.

[0089] The above-described spectrum linewidth control and center wavelength control may be performed for each pulse in the same manner as the wavelength control, or may be performed for each predetermined number of pulses. Further, the wavelength control and the spectrum linewidth control may be independently controlled in parallel, or may be alternately controlled in series.

[0090] The laser control unit 40 adjusts the rotation angles of the second CLBO crystal 142 and the third CLBO crystal 143 according to the target center wavelength λct so as to phase-match the incident angle of the incident light. Alternatively, the laser control unit 40 adjusts the crystal temperatures of the second CLBO crystal 142 and the third CLBO crystal 143 so as to perform phase matching.

[0091] 2.3 Example of Spectrum Linewidth Control FIG. 3 is a flowchart showing an example of spectrum linewidth control implemented in the laser system 2A according to Embodiment 1.

[0092] In step S11, the laser control unit 40 receives the target spectrum linewidth Δλt from the exposure apparatus 80.

[0093] In step S12, the laser control unit 40 receives the spectrum linewidth Δλ of the fifth pulsed laser beam PL5 from the linewidth monitor 35.

[0094] In step S13, the laser control unit 40 calculates the difference ΔΔλ between the spectral linewidth Δλ and the target spectral linewidth Δλt.

[0095] In step S14, the laser control unit 40 determines and outputs a modulation signal to the optical frequency modulator 114 so that the difference ΔΔλ becomes smaller.

[0096] In step S15, the spectral linewidth of the first laser light L1 output from the first semiconductor laser 101 by the optical frequency modulator 114 is changed by the modulation signal.

[0097] In step S16, the laser control unit 40 determines whether to end the spectral linewidth control. If the determination result in step S16 is a No determination, the laser control unit 40 returns to step S11 and repeats steps S11 to S16. If the determination result in step S16 is a Yes determination, the laser control unit 40 ends the flowchart in FIG. 3.

[0098] 2.4 Example of Center Wavelength Control FIG. 4 is a flowchart showing an example of center wavelength control implemented in the laser system 2A according to Embodiment 1.

[0099] In step S21, the laser control unit 40 receives the target center wavelength λct from the exposure device 80. In step S22, the laser control unit 40 receives the wavelength λc of the fifth pulsed laser light PL5 from the wavelength monitor 34.

[0100] In step S23, the laser control unit 40 calculates the difference δλc between the wavelength λc and the target center wavelength λct.

[0101] In step S24, the laser control unit 40 determines and outputs a control signal to the second semiconductor laser 102 so that the difference δλc becomes smaller.

[0102] In step S25, the center wavelength of the second laser beam L2 output from the second semiconductor laser 102 is changed by a control signal.

[0103] In step S26, the laser control unit 40 determines whether to end the spectral linewidth control. If the determination result in step S26 is a No determination, the laser control unit 40 returns to step S21 and repeats steps S21 to S26. If the determination result in step S26 is a Yes determination, the laser control unit 40 ends the flowchart of FIG. 4.

[0104] 2.5 Effects According to Embodiment 1, since the second laser beam L2 output from the second semiconductor laser 102 is not amplified using an optical fiber amplifier, it is not necessary to suppress SBS. For this reason, it is not necessary to arrange a mechanism for broadening the spectral linewidth of the second laser beam L2 output from the second semiconductor laser 102.

[0105] Also, the minimum spectral linewidth of the fifth pulsed laser beam PL5 output from the laser system 2A according to Embodiment 1 is limited only by the mechanism for broadening the spectral linewidth of the first laser beam L1. And the spectral linewidth of the fifth pulsed laser beam PL5 can be controlled by this mechanism for broadening the spectral linewidth.

[0106] According to Embodiment 1, only the center wavelength of the second semiconductor laser 102 is controlled. In this case, the non-linear crystals that affect the optimum phase matching condition are only the two, the second CLBO crystal 142 and the third CLBO crystal 143. For this reason, only these two non-linear crystals are required to control the phase matching condition when controlling the center wavelength.

[0107] In the configuration of the wavelength conversion unit 131 in Embodiment 1, second harmonic generation is performed twice on the second pulsed laser beam PL2 obtained by pulse-amplifying the first laser beam L1, and second sum frequency generation is performed twice between the harmonic light and the third pulsed laser beam PL3 obtained by pulse-amplifying the second laser beam L2. In such a configuration of the wavelength conversion unit 131, the ratio of the spectral linewidth change amount (linewidth fluctuation sensitivity) of the fifth pulsed laser beam PL5 to the spectral linewidth change amount of the first laser beam L1 output from the first semiconductor laser 101 is about 4.6 times larger than the ratio when changing the spectral linewidth of the second laser beam L2 output from the second semiconductor laser 102. Therefore, it is possible to adjust a wider range by controlling the spectral linewidth of the first laser beam L1 or the first pulsed laser beam PL1 output from the first semiconductor laser 101 with the optical frequency modulator 114 than by controlling the spectral linewidth of the second laser beam L2 output from the second semiconductor laser 102.

[0108] Also, the method of controlling the center wavelength with an SG-DBR-LD or an SSG-DBR-LD has a wider control range than the method of controlling with the DC component value of the current flowing through the active layer of a normal semiconductor laser element, or has a wider control range and a faster response speed than the method of controlling the temperature of the semiconductor laser element.

[0109] 2.6 Variation 2.6.1 Configuration FIG. 5 schematically shows the configuration of a laser system 2B according to a variation of Embodiment 1. Regarding the configuration shown in FIG. 5, the differences from FIG. 2 will be described.

[0110] The laser system 2B includes a monitor module 30B instead of the monitor module 30 in FIG. 2. The monitor module 30B is different from the monitor module 30 in FIG. 2 in that the third beam splitter BS3 and the linewidth monitor 35 are not arranged therein. Other configurations may be the same as those in FIG. 2.

[0111] 2.6.2 Operation The laser control unit 40 stores relationship data indicating the relationship between the spectral linewidth and the modulation signal to the optical frequency modulator 114. The relationship data is stored, for example, as a function or table representing the relationship (corresponding relationship) between the spectral linewidth and the modulation signal.

[0112] The laser control unit 40 determines a modulation signal corresponding to the target spectral linewidth Δλt from the target spectral linewidth Δλt and a function or table defining the relationship between the spectral linewidth and the modulation signal to the optical frequency modulator 114. The laser control unit 40 outputs the determined modulation signal to the optical frequency modulator 114.

[0113] The spectral width of the first laser beam L1 input to the optical frequency modulator 114 expands according to the modulation signal. When the target spectral linewidth Δλt commanded from the exposure apparatus 80 is changed, the laser control unit 40 determines a modulation signal from the target spectral linewidth Δλt and a function or table representing the relationship between the spectral linewidth and the modulation signal to the optical frequency modulator 114, and outputs the determined modulation signal to the optical frequency modulator 114. Other operations may be the same as those in the first embodiment.

[0114] 2.6.3 Example of Spectral Linewidth Control FIG. 6 is a flowchart showing an example of spectral linewidth control implemented in the laser system 2B according to a modified example of the first embodiment.

[0115] In step S30, the laser control unit 40 stores a function representing the relationship between the spectral linewidth and the modulation signal to the optical frequency modulator 114. Note that a table may be stored instead of the function.

[0116] In step S31, the laser control unit 40 receives the target spectral linewidth Δλt from the exposure apparatus 80.

[0117] In step S32, the laser control unit 40 determines a modulation signal corresponding to the target spectral linewidth Δλt from the target spectral linewidth Δλt and the function representing the relationship.

[0118] In step S34, the laser control unit 40 outputs a modulation signal to the optical frequency modulator 114.

[0119] In step S35, the spectral linewidth of the first laser beam L1 output from the first semiconductor laser 101 by the optical frequency modulator 114 is changed by the modulation signal.

[0120] In step S36, the laser control unit 40 determines whether to end the spectral linewidth control. If the determination result in step S36 is a No determination, the laser control unit 40 returns to step S31 and repeats steps S31 to S36. If the determination result in step S36 is a Yes determination, the laser control unit 40 ends the flowchart of FIG. 6.

[0121] 2.6.4 Effects According to the laser system 2B according to the modification of Embodiment 1, the control of the spectral linewidth is simplified. Further, it is not necessary to measure the spectral linewidth of the fifth pulsed laser beam PL5 with the monitor module 30B.

[0122] 3. Embodiment 2 3.1 Configuration FIG. 7 schematically shows the configuration of the laser system 2C according to Embodiment 2. Differences from FIG. 2 in the configuration shown in FIG. 7 will be described.

[0123] The laser system 2C includes a solid-state laser system 12 instead of the solid-state laser system 11. The solid-state laser system 12 includes an optical phase modulator 115 and a modulation signal generation unit 150 instead of the optical frequency modulator 114. The optical phase modulator 115 is an example of the "modulator" in the present disclosure. The optical phase modulator 115 may be disposed between the first semiconductor laser 101 and the optical intensity variable device 116, or may be disposed between the optical intensity variable device 116 and the first optical fiber amplifier 121, as shown in FIG. 7. Other configurations may be the same as those in Embodiment 1.

[0124] The details of the modulation signal generation unit 150 are shown in FIG. 8. The modulation signal generation unit 150 includes a white noise generation unit 152, a variable low-pass filter 154, and a power adjuster 156. The white noise generation unit 152 may be a white noise generator such as a noise source module. The variable low-pass filter 154 passes the low-frequency components of the signal generated by the white noise generation unit 152 and limits the high-frequency components. The power adjuster 156 adjusts the signal passed through the variable low-pass filter 154 to an appropriate power. The power adjuster 156 may be configured, for example, by an attenuator, an amplifier, or a combination of an attenuator and an amplifier.

[0125] 3.2 Operation The laser control unit 40 receives the target spectral linewidth Δλt from the exposure apparatus 80. The white noise generation unit 152 generates white noise. The laser control unit 40 calculates the difference ΔΔλ between the spectral linewidth Δλ of the pulsed laser light measured by the linewidth monitor 35 and the target spectral linewidth Δλt. Then, the laser control unit 40 determines a band control signal to the variable low-pass filter 154 and an attenuation rate control signal or an amplification rate control signal to the power adjuster 156 so that the difference ΔΔλ becomes small, and outputs these signals.

[0126] The variable low-pass filter 154 passes the low-frequency side signal of the white noise signal according to the band control signal. The power of the signal passed through the variable low-pass filter 154 is adjusted by the power adjuster 156 so as to compensate for the power attenuated by the variable low-pass filter 154.

[0127] The white noise signal whose power is adjusted by the power adjuster 156 is input to the optical phase modulator 115.

[0128] According to the band of the white noise signal input to the optical phase modulator 115, the spectral linewidth of the first laser light L1 output from the first semiconductor laser 101 is broadened.

[0129] Fig. 9 shows the spectral linewidth and typical spectral shape of the laser light output from the optical phase modulator 115 when the cut-off frequency fc of the variable low-pass filter 154 is changed. As shown in Fig. 9, the laser light output from the optical phase modulator 115 in Embodiment 2 can have a spectral shape close to a Gaussian distribution.

[0130] Also, even if only the power of the white noise signal input to the optical phase modulator 115 is changed by the power adjuster 156, the spectral linewidth of the output laser light from the optical phase modulator 115 changes slightly. Therefore, it is also possible to finely adjust the spectral linewidth with the power adjuster 156.

[0131] 3.3 Examples of Spectral Linewidth Control Fig. 10 is a flowchart showing an example of spectral linewidth control applied to the laser system 2C according to Embodiment 2.

[0132] In step S40, the modulation signal generation unit 150 generates a white noise signal with the white noise generation unit 152.

[0133] In step S41, the laser control unit 40 receives the target spectral linewidth Δλt from the exposure apparatus 80.

[0134] In step S42, the laser control unit 40 receives the spectral linewidth Δλ of the fifth pulsed laser light PL5 from the linewidth monitor 35.

[0135] In step S43, the laser control unit 40 calculates the difference ΔΔλ between the spectral linewidth Δλ and the target spectral linewidth Δλt.

[0136] In step S44, the laser control unit 40 outputs a band control signal to the variable low-pass filter 154 and an attenuation rate control signal or an amplification rate control signal to the power adjuster 156 so that the difference ΔΔλ becomes smaller.

[0137] In step S45, the white noise signal that has been band-limited by the variable low-pass filter 154 and adjusted by the power adjuster 156 is input to the optical phase modulator 115. Then, in step S46, the spectral linewidth of the first laser light L1 output from the first semiconductor laser 101 by the optical phase modulator 115 is changed by the white noise signal.

[0138] In step S47, the laser control unit 40 determines whether to end the spectral linewidth control. If the determination result in step S47 is a No determination, the laser control unit 40 returns to step S41 and repeats steps S41 to S47. If the determination result in step S47 is a Yes determination, the laser control unit 40 ends the flowchart of FIG. 10.

[0139] 3.4 Effects According to Embodiment 2, when white noise is superimposed on the optical phase modulator 115, the spectral linewidth can be widened in a spectral shape close to a Gaussian distribution (see FIG. 9). Therefore, the incoherence is also high, and interference noise and speckle noise of the wavelength-converted light can be reduced.

[0140] In the case of frequency modulation by a single frequency shown in Embodiment 1, the optical frequency modulator 114 broadens the spectrum of the continuously oscillating laser light into a comb-shaped spectrum composed of the fundamental frequency and its harmonics (see FIG. 11). FIG. 11 shows an example where the frequency of the modulation signal is 90 MHz and the phase shift is 2π.

[0141] 4. Regarding the manufacturing method of the electronic device FIG. 12 schematically shows a configuration example of the exposure apparatus 80. The exposure apparatus 80 includes an illumination optical system 804 and a projection optical system 806. The laser system 2A generates a fifth pulsed laser beam PL5 and outputs the fifth pulsed laser beam PL5 to the exposure apparatus 80. The illumination optical system 804 illuminates a reticle pattern of a reticle (not shown) disposed on the reticle stage RT with the laser beam incident from the laser system 2A. The projection optical system 806 reduces and projects the laser beam that has passed through the reticle and forms an image on a workpiece (not shown) disposed on the workpiece table WT. The workpiece is a photosensitive substrate such as a semiconductor wafer coated with a photoresist.

[0142] The exposure apparatus 80 exposes the workpiece with the laser beam reflecting the reticle pattern by synchronously translating the reticle stage RT and the workpiece table WT in parallel. After transferring the reticle pattern to the semiconductor wafer by the exposure process as described above, a semiconductor device can be manufactured through a plurality of processes. The semiconductor device is an example of the "electronic device" in the present disclosure. Not limited to the laser system 2A, the laser systems 2B, 2C, etc. may also be used.

[0143] 5. Others 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.

[0144] The terms used throughout this specification and the claims should be construed as "non-limiting" terms unless otherwise specified. For example, terms such as "comprising", "having", "including", and "containing" should be construed as not excluding the presence of elements other than those described. Also, the modifier "one" should be construed to mean "at least one" or "one or more". Also, 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 with things other than "A", "B", and "C".

Claims

1. A first laser that outputs a first laser beam with continuous oscillation, An optical intensity variator that pulses the first laser beam to output a first pulsed laser beam, A modulator that broadens the spectral linewidth of the first laser beam or the first pulsed laser beam according to a modulation signal, An optical fiber amplifier that amplifies the first pulsed laser beam to output a second pulsed laser beam, A second laser with variable center wavelength that outputs a second laser beam with continuous oscillation, An optical parametric amplifier that pulses and amplifies the second laser beam to output a third pulsed laser beam, A wavelength conversion unit that outputs a fourth pulsed laser beam using the second pulsed laser beam and the third pulsed laser beam, including a first nonlinear crystal, a second nonlinear crystal, a third nonlinear crystal, and a fourth nonlinear crystal. When the second pulsed laser beam is input to the first nonlinear crystal, the first harmonic light is output, When the first harmonic light is input to the second nonlinear crystal, the second harmonic light is output, When the second harmonic light and the third pulsed laser beam are input to the third nonlinear crystal, the first sum-frequency light and the third pulsed laser beam are output, The fourth nonlinear crystal outputs the fourth pulsed laser beam, which is the second sum-frequency light, when the first sum-frequency light and the third pulsed laser beam are input. The wavelength conversion unit, An amplification unit that amplifies the fourth pulsed laser beam to output a fifth pulsed laser beam, A processor that receives commands for a target spectral linewidth and a target center wavelength, controls the modulation signal so that the fifth pulsed laser beam with the commanded target spectral linewidth is obtained, and controls the center wavelength of the second laser beam so that the fifth pulsed laser beam with the commanded target center wavelength is obtained, A laser system comprising the above.

2. The laser system according to Claim 1, wherein The modulator is an optical frequency modulator using an acousto-optic element, Laser system.

3. The laser system according to Claim 1, wherein The modulator is an optical phase modulator using the electro-optic effect, Laser system.

4. The laser system according to Claim 3, further comprising A modulation signal generation unit that outputs the modulation signal to the optical phase modulator, The modulation signal generation unit, A white noise generation unit that generates a white noise signal, A variable low-pass filter that limits the high-frequency components of the white noise signal; A power regulator that controls the attenuation rate or amplification rate of the white noise signal, and includes: The processor outputs a band control signal that limits the high-frequency components to the variable low-pass filter, and outputs an attenuation rate control signal or an amplification rate control signal to the power regulator. A laser system.

5. The laser system according to claim 1, further comprising: A wavelength monitor that measures the central wavelength of the fifth pulsed laser light; The processor controls the central wavelength of the second laser light based on the measurement result of the wavelength monitor. A laser system.

6. The laser system according to claim 1, further comprising: A linewidth monitor that measures the spectral linewidth of the fifth pulsed laser light; The processor controls the modulation signal based on the measurement result of the linewidth monitor. A laser system.

7. The laser system according to claim 1, The processor stores relationship data indicating the relationship between the spectral linewidth of the fifth pulsed laser light and the modulation signal, and controls the modulation signal based on the relationship data. A laser system.

8. The laser system according to claim 1, The first nonlinear crystal is an LBO crystal. A laser system.

9. The laser system according to claim 1, Each of the second nonlinear crystal, the third nonlinear crystal, and the fourth nonlinear crystal is a CLBO crystal. A laser system.

10. The laser system according to claim 1, further comprising: A dichroic mirror that combines the second pulsed laser light and the second laser light; The second pulsed laser light and the second laser light combined by the dichroic mirror are incident on the optical parametric amplifier. A laser system.

11. The laser system according to claim 1, The optical intensity variator is a semiconductor optical amplifier. A laser system.

12. The laser system according to claim 1, The optical intensity variator is an optical intensity modulator using the electro-optic effect. A laser system.

13. The laser system according to claim 1, Each of the first laser and the second laser is a semiconductor laser oscillating in a single longitudinal mode. A laser system.

14. The laser system according to claim 1, The wavelengths of the first laser light and the second laser light are each near-infrared wavelengths. Laser system.

15. The laser system according to claim 1, wherein the wavelength of the fourth pulsed laser light is an ultraviolet wavelength. Laser system.

16. A method for generating pulsed laser light, comprising: outputting, by a first laser, first laser light with continuous oscillation; pulsing, by an optical intensity variator, the first laser light to output first pulsed laser light; broadening, by a modulator, the spectral linewidth of the first laser light or the first pulsed laser light according to a modulation signal; amplifying, by an optical fiber amplifier, the first pulsed laser light to output second pulsed laser light; outputting, by a second laser with variable center wavelength, second laser light with continuous oscillation; pulsing and amplifying, by an optical parametric amplifier, the second laser light to output third pulsed laser light; inputting the second pulsed laser light into the first non-linear crystal of a wavelength conversion unit including a first non-linear crystal, a second non-linear crystal, a third non-linear crystal, and a fourth non-linear crystal, so that the first non-linear crystal outputs first harmonic light; inputting the first harmonic light into the second non-linear crystal, so that the second non-linear crystal outputs second harmonic light; inputting the second harmonic light and the third pulsed laser light into the third non-linear crystal, so that the third non-linear crystal outputs first sum-frequency light and the third pulsed laser light; inputting the first sum-frequency light and the third pulsed laser light into the fourth non-linear crystal, so that the fourth non-linear crystal outputs fourth pulsed laser light which is second sum-frequency light; amplifying, by an amplification unit, the fourth pulsed laser light to output fifth pulsed laser light; controlling, by a processor, the modulation signal so that fifth pulsed laser light with a target spectral linewidth commanded from an external device is obtained; controlling, by the processor, the center wavelength of the second laser light so that fifth pulsed laser light with a target center wavelength commanded from the external device is obtained; A method for generating pulsed laser light including the above steps.

17. A method for manufacturing an electronic device, comprising: a first laser that outputs first laser light with continuous oscillation; An optical intensity variator that pulses the first laser beam to output a first pulsed laser beam; A modulator that broadens the spectral linewidth of the first laser beam or the first pulsed laser beam according to a modulation signal; An optical fiber amplifier that amplifies the first pulsed laser beam to output a second pulsed laser beam; A second laser with a variable center wavelength that outputs a continuously oscillating second laser beam; An optical parametric amplifier that pulses and amplifies the second laser beam to output a third pulsed laser beam; A wavelength conversion unit that outputs a fourth pulsed laser beam using the second pulsed laser beam and the third pulsed laser beam, including a first nonlinear crystal, a second nonlinear crystal, a third nonlinear crystal, and a fourth nonlinear crystal. When the second pulsed laser beam is input into the first nonlinear crystal, the first harmonic light is output; When the first harmonic light is input into the second nonlinear crystal, the second harmonic light is output; When the second harmonic light and the third pulsed laser beam are input into the third nonlinear crystal, the first sum-frequency light and the third pulsed laser beam are output; The fourth nonlinear crystal outputs the fourth pulsed laser beam, which is the second sum-frequency light, when the first sum-frequency light and the third pulsed laser beam are input; the wavelength conversion unit; An amplification unit that amplifies the fourth pulsed laser beam to output a fifth pulsed laser beam; A processor that receives commands for a target spectral linewidth and a target center wavelength, controls the modulation signal so that the fifth pulsed laser beam with the commanded target spectral linewidth is obtained, and controls the center wavelength of the second laser beam so that the fifth pulsed laser beam with the commanded target center wavelength is obtained; A laser system comprising the above generates the fifth pulsed laser beam; Output the fifth pulsed laser beam to an exposure apparatus; A method for manufacturing an electronic device, including exposing a photosensitive substrate in the exposure apparatus with the fifth pulsed laser beam in order to manufacture the electronic device.

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