Line narrowing module, laser device, and method of manufacturing electronic device

Abstract

To provide a line narrowing module, a laser device, and a method of manufacturing an electronic device, capable of suppressing deterioration in beam divergence and spectral line width caused by distortion of a wavefront.SOLUTION: A line narrowing module includes a grating and an expansion optical system including a plurality of prisms. In the expansion optical system, a first closest prism which is closest to the grating and a second closest prism which is second closest to the grating have temperature coefficients of refractive indices opposite in sign to each other, and an amount of change of an optical path length difference between a case in which a temperature difference in the second closest prism is 0.2°C or less and a case in which the temperature difference is 0.5°C or more and 10°C or less is less than half the wavelength of pulse laser light, as defining a light ray at one end of the pulse laser light in an expansion direction as a first light ray, a light ray at the other end as a second light ray, and a difference between a sum of optical path lengths of the first light ray in the first closest prism and the second closest prism and a sum of optical path lengths of the second light ray in the first closest prism and the second closest prism as the optical path length difference.SELECTED DRAWING: Figure 8

Description

[Technical Field]

[0001] The present disclosure relates to a line-narrowing module, a laser apparatus, and a method for manufacturing an electronic device. [Background technology]

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

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

[0004] [Patent Document 1] International Publication No. 2006 / 060360 [Patent Document 2] European Patent Application Publication No. 1041689 Overview

[0005] A line narrowing module according to one aspect of the present disclosure is a line narrowing module that narrows the line of pulsed laser light having a wavelength in the ultraviolet region, and includes a grating that reflects the incident pulsed laser light and an expansion optical system including a plurality of prisms that expand the beam width of the pulsed laser light and make it incident on the grating, wherein the expansion optical system has a first near prism that is closest to the grating and a second near prism that is second closest to the grating, and the temperature coefficients of the refractive index of the first near prism and the second near prism are opposite in sign, and when a ray at one end in the expansion direction of the pulsed laser light is defined as the first ray and a ray at the other end as the second ray, and the difference between the sum of the optical path lengths of the first ray in the first near prism and the second near prism and the sum of the optical path lengths of the second ray in the first near prism and the second near prism is defined as the optical path length difference, the change in the optical path length difference between when the temperature difference in the second near prism is 0.2°C or less and when it is 0.5°C or more and 10°C or less is less than 1 / 2 the wavelength of the pulsed laser light.

[0006] A laser device according to one aspect of the present disclosure is a line narrowing module that narrows the line of pulsed laser light having a wavelength in the ultraviolet region, and includes a grating that reflects the incident pulsed laser light and an expansion optical system including a plurality of prisms that expand the beam width of the pulsed laser light and make it incident on the grating, wherein the expansion optical system has a first nearest prism that is closest to the grating and a second nearest prism that is second closest to the grating, and the temperature coefficients of the refractive index of the first nearest prism and the second nearest prism are opposite in sign, and when a ray at one end in the expansion direction of the pulsed laser light is defined as the first ray and a ray at the other end as the second ray, and the difference between the sum of the optical path lengths of the first ray within the plurality of prisms and the sum of the optical path lengths of the second ray within the plurality of prisms is defined as the optical path length difference, the amount of change in the optical path length difference between when the temperature difference within the second nearest prism is 0.2°C or less and when it is 0.5°C or more and 10°C or less is less than 1 / 2 the wavelength of the pulsed laser light.

[0007] A method for manufacturing an electronic device according to one aspect of the present disclosure is a laser apparatus including: a line narrowing module for narrowing the line of pulsed laser light having a wavelength in the ultraviolet region, the line narrowing module including a grating that reflects the incident pulsed laser light and an expansion optical system including a plurality of prisms that expand the beam width of the pulsed laser light and make it incident on the grating; an output coupling mirror; and a laser chamber including a pair of discharge electrodes and disposed in an optical path of an optical resonator formed by the line narrowing module and the output coupling mirror, wherein the expansion optical system is configured to adjust the refractive index of a first closest prism that is closest to the grating and a second closest prism that is second closest to the grating. The optical path length difference is defined as the difference between the sum of the optical path lengths of the first ray in the first near prism and the second near prism and the sum of the optical path lengths of the second ray in the first near prism and the second near prism, and the change in the optical path length difference between a case where the temperature difference in the second near prism is 0.2°C or less and a case where the temperature difference is 0.5°C or more and 10°C or less is less than 1 / 2 the wavelength of the pulsed laser beam. The method includes generating pulsed laser beam by a laser apparatus in which the optical path length difference is less than 1 / 2 the wavelength of the pulsed laser beam, outputting the pulsed laser beam to an exposure apparatus, and exposing a photosensitive substrate with the pulsed laser beam in the exposure apparatus to manufacture an electronic device. [Brief explanation of the drawings]

[0008] Some embodiments of the present disclosure will now be described, by way of example only, with reference to the accompanying drawings, in which: [Figure 1] FIG. 1 is a diagram schematically showing the configuration of a gas laser device according to a comparative example. [Figure 2] FIG. 2 is a view of the line-narrowing module as seen from the Y direction. [Figure 3] FIG. 3 is a view of the line narrowing module as seen from the X direction. [Figure 4] FIG. 4 is a diagram showing an example of a method for fixing a prism. [Figure 5] FIG. 5 shows the beam profile and wavelength spectrum 5 minutes and 2 hours after the start of laser oscillation. [Figure 6]FIG. 6 is a diagram defining the direction of each prism. [Figure 7] FIG. 7 is a diagram schematically showing the twist of the wavefront that occurs in the third prism. [Figure 8] FIG. 8 is a view of the line narrowing module according to the first embodiment as viewed from the Y direction. [Figure 9] FIG. 9 is a diagram defining the optical path length. [Figure 10] FIG. 10 is a view of a line narrowing module according to a modified example, viewed from the Y direction. [Figure 11] FIG. 11 is a diagram schematically showing an example of the configuration of an exposure apparatus. Embodiment

[0009] <Contents> 1. Comparative Example 1.1 Gas laser device 1.1.1 Configuration 1.1.2 Operation 1.2 Band-narrowing module 1.3 Challenges 2. First embodiment 2.1 Configuration 2.2 Operation 2.3 Effects 3. Modification of the First Embodiment 4. Manufacturing method of electronic devices

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

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

[0012] 1.1 Gas laser device 1.1.1 Configuration The configuration of a gas laser device 2 according to a comparative example will be described. FIG. 1 shows a schematic configuration of the gas laser device 2. The gas laser device 2 is a discharge excitation type gas laser device that discharges and excites laser gas, such as an excimer laser device. The gas laser device 2 is an example of a "laser device" according to the technology of the present disclosure.

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

[0014] The gas laser device 2 includes a laser chamber 10, a charger 11, a pulse power module (PPM) 12, a monitor module 13, a processor 14, and a laser resonator. The laser resonator is composed of a line narrowing module 15 and an output coupling mirror 16.

[0015] The laser chamber 10 is a metal container made of, for example, aluminum metal with a nickel-plated surface. Inside the laser chamber 10, a main electrode 20, a ground plate 21, a fan 23, etc. are provided.

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

[0017] An opening is formed in the laser chamber 10. An electrical insulating plate 26 with a feedthrough 25 embedded therein is attached to the laser chamber 10 via an O-ring (not shown) so as to close the opening. The PPM 12 is placed on the electrical insulating plate 26. The laser chamber 10 is grounded.

[0018] The PPM 12 includes a charging capacitor (not shown) and is connected to the main electrode 20 via a feedthrough 25. The PPM 12 includes a switch SW for discharging the main electrode 20. The charger 11 is connected to the charging capacitor of the PPM 12.

[0019] The main electrodes 20 are a pair of discharge electrodes consisting of a cathode electrode 20a and an anode electrode 20b. The cathode electrode 20a and the anode electrode 20b are arranged in the laser chamber 10 so that their discharge surfaces face each other. The space between the discharge surface of the cathode electrode 20a and the discharge surface of the anode electrode 20b is called a discharge space 27. The surface of the cathode electrode 20a opposite the discharge surface is supported by an electrically insulating plate 26 and connected to a feedthrough 25. The surface of the anode electrode 20b opposite the discharge surface is supported by a ground plate 21.

[0020] Fan 23 is a cross-flow fan for circulating laser gas within laser chamber 10, and is disposed on the opposite side of ground plate 21 from discharge space 27. A motor 23a that rotates fan 23 is connected to laser chamber 10.

[0021] Windows 10a and 10b are provided at the ends of the laser chamber 10 for emitting the pulsed laser light PL generated within the laser chamber 10 to the outside. The windows 10a and 10b are positioned so that the pulsed laser light PL is incident at a Brewster angle. The laser chamber 10 is positioned so that the optical path of the optical resonator passes through the discharge space 27 and the windows 10a and 10b.

[0022] The line narrowing module 15 includes an expansion optical system 15a and a grating 15b. The expansion optical system 15a expands the beam width of the pulsed laser light PL emitted from the laser chamber 10 through the window 10a and transmits the pulsed laser light PL to the grating 15b side.

[0023] The grating 15b is arranged in a Littrow configuration, where the angle of incidence and the angle of diffraction are the same. The grating 15b is a wavelength selection element that selectively extracts light near a specific wavelength depending on the diffraction angle. The spectral linewidth of the pulsed laser light PL returning from the grating 15b to the laser chamber 10 via the magnifying optical system 15a is narrowed.

[0024] Furthermore, the line narrowing module 15 is provided with a rotation stage 15c that rotates one of the prisms included in the magnifying optical system 15a. The rotation of the prism by the rotation stage 15c changes the angle of incidence of the pulsed laser light PL incident on the grating 15b.

[0025] The output coupling mirror 16 is a partial reflection mirror that transmits a part of the pulsed laser light PL emitted from the laser chamber through the window b and reflects the other part back to the laser chamber .

[0026] The pulsed laser light PL emitted from the laser chamber 10 travels back and forth between the line-narrowing module 15 and the output-coupling mirror 16. Most of the P-polarized component of the pulsed laser light PL passes through the windows 10a and 10b without Fresnel reflection. On the other hand, most of the S-polarized component is Fresnel reflected and is attenuated while passing through the windows 10a and 10b multiple times. The P-polarized component is amplified by passing through the laser medium with almost no attenuation. As a result, the pulsed laser light PL is output from the output-coupling mirror 16 as linearly polarized light. The wavelength of the pulsed laser light PL is in the ultraviolet region of 150 nm to 380 nm, which is the oscillation wavelength of an excimer laser device, for example.

[0027] The monitor module 13 includes beam splitters 13a and 13b, a pulse energy measuring instrument 13c, and a spectrometer 13d. The beam splitter 13a is disposed on the optical path of the pulsed laser beam PL output from the output coupling mirror 16 and reflects a portion of the pulsed laser beam PL. The beam splitter 13b is disposed on the optical path of the pulsed laser beam PL reflected by the beam splitter 13a and reflects a portion of the pulsed laser beam PL.

[0028] The pulse energy measuring instrument 13c is disposed on the optical path of the pulsed laser beam PL reflected by the beam splitter 13b. The pulse energy measuring instrument 13c is, for example, a photodiode, and is configured to be able to measure the pulse energy of the pulsed laser beam PL output from the gas laser device 2.

[0029] The spectrum measuring instrument 13d is disposed on the optical path of the pulsed laser light PL that has passed through the beam splitter 13b. The spectrum measuring instrument 13d is, for example, a monitor etalon spectroscope, and is configured to be able to measure the wavelength and spectral linewidth of the pulsed laser light PL by measuring the shape of interference fringes with a line sensor or the like.

[0030] The charger 11 is a high-voltage power supply that supplies a charging voltage to a charging capacitor included in the PPM 12. The switch SW of the PPM 12 is controlled by the processor 14. When the switch SW changes from off to on, the PPM 12 generates a high-voltage pulse from the electrical energy stored in the charging capacitor and applies it to the main electrode 20.

[0031] The processor 14 is a processing device that transmits and receives various signals to and from an exposure apparatus controller 110 provided in the exposure apparatus 100. For example, the processor 14 receives from the exposure apparatus controller 110 the target pulse energy of the pulsed laser light PL output to the exposure apparatus 100, a measured value of the wavelength, an oscillation trigger signal, and the like.

[0032] The processor 14 comprehensively controls the operation of each component of the gas laser device 2 based on various signals sent from the exposure tool controller 110, measured values ​​of pulse energy, measured values ​​of wavelength, and the like.

[0033] The processor 14 functions as a controller for the gas laser device 2. For example, the processor 14 is a processing device including a storage device in which a control program is stored and a CPU (Central Processing Unit) that executes the control program. The processor 14 is specially configured or programmed to execute various processes included in the present disclosure. The storage device is a non-transitory computer-readable storage medium, and includes, for example, a memory that is a primary storage device and a storage that is an auxiliary storage device. The storage device may be a semiconductor memory, a hard disk drive (HDD) device, a solid-state drive (SSD) device, or a combination of two or more of these.

[0034] 1.1.2 Operation Next, the operation of the gas laser apparatus 2 according to the comparative example will be described. First, the processor 14 receives a target pulse energy, a target wavelength, and an oscillation trigger signal from the exposure apparatus controller 110. The oscillation trigger signal is a signal that instructs the gas laser apparatus 2 to output one pulse of pulsed laser light PL.

[0035] The processor 14 sets a charging voltage according to the target pulse energy in the charger 11. The processor 14 operates the switch SW of the PPM 12 in synchronization with the oscillation trigger signal.

[0036] When the switch SW of the PPM 12 is turned on, a voltage is applied between the cathode electrode 20a and the anode electrode 20b, which causes a discharge between the cathode electrode 20a and the anode electrode 20b, and the laser gas in the discharge space 27 is excited to emit light.

[0037] Light emitted from the laser gas is reflected by the line narrowing module 15 and the output coupling mirror 16 and travels back and forth within the laser resonator, resulting in laser oscillation. The light narrowed in line by the line narrowing module 15 is output from the output coupling mirror 16 as pulsed laser light PL.

[0038] The pulsed laser light PL output from the output coupling mirror 16 enters the monitor module 13, where a portion of the light is reflected by the beam splitter 13a and enters the beam splitter 13b. The pulsed laser light PL is split by the beam splitter 13b and enters the pulse energy measuring instrument 13c and the spectrometer 13d, respectively. The pulse energy is measured by the pulse energy measuring instrument 13c, and the wavelength and spectral linewidth are measured by the spectrometer 13d. The pulsed laser light PL that has passed through the beam splitter 13a enters the exposure apparatus 100.

[0039] Processor 14 controls the charging voltage so that the difference between the measured pulse energy value and the target pulse energy approaches 0. Processor 14 also drives rotation stage 15c so that the difference between the measured wavelength value and the target wavelength approaches 0, thereby controlling the angle of incidence of pulsed laser light PL incident on grating 15b.

[0040] 1.2 Band-narrowing module Next, a configuration of the line narrowing module 15 according to a comparative example will be described. Fig. 2 is a view of the line narrowing module 15 as seen from the Y direction. Fig. 3 is a view of the line narrowing module 15 as seen from the X direction.

[0041] The housing of the line narrowing module 15 is filled with nitrogen gas. The expanding optical system 15a includes first to fourth prisms P1 to P4 and a mirror M. The first to fourth prisms P1 to P4 are arranged so that the pulsed laser light PL emitted from the laser chamber 10 passes through the first prism P1, the second prism P2, the third prism P3, and the fourth prism P4 in this order before entering the grating 15b. The mirror M is arranged between the third prism P3 and the fourth prism P4, and reflects the pulsed laser light PL that has passed through the third prism P3 so that it enters the fourth prism P4. The beam width of the pulsed laser light PL is expanded each time it passes through each of the first to fourth prisms P1 to P4.

[0042] Each of the first to fourth prisms P1 to P4 is made of calcium fluoride (CaF2) and is held by a holder 30. The grating 15b is held by a holder 40. Each of the first to fourth prisms P1 to P4 includes two transmission surfaces 31 and 32 through which the pulsed laser beam PL passes. The transmission surfaces 31 and 32 are parallel to the Y direction. Each of the first to fourth prisms P1 to P4 is, for example, a triangular prism.

[0043] Each of the first to fourth prisms P1 to P4 is arranged so that the propagation direction of the pulsed laser light PL passing through the transmitting surface 31 is non-perpendicular to the transmitting surface 31, and the propagation direction of the pulsed laser light PL passing through the transmitting surface 32 is approximately perpendicular to the transmitting surface 32. For example, the angle of incidence of the pulsed laser light PL with respect to the transmitting surface 31 is larger than the Brewster's angle. The pulsed laser light PL is refracted at the transmitting surface 31, and travels approximately straight at the transmitting surface 32. The transmitting surface 31 is coated with a film that suppresses reflection of the P-polarized component of the pulsed laser light PL. The transmitting surface 32 is coated with a film that suppresses reflection of the pulsed laser light PL.

[0044] Assuming that the volumes of the first to fourth prisms P1 to P4 are VP1 to VP4 respectively, three magnitude relationships of "VP1 < VP2 < VP3 < VP4", "VP1 = VP2 < VP3 < VP4", and "VP1 = VP2 = VP3 < VP4" can be obtained. In the examples shown in FIGS. 2 and 3, the relationship of "VP1 < VP2 < VP3 < VP4" is satisfied.

[0045] The holder 30 that holds the third prism P3 is disposed on the above-described rotary stage 15c. The rotary stage 15c rotates the third prism P3 about an axis parallel to the Y axis.

[0046] Each of the first to fourth prisms P1 to P4 is held by the holder 30 on the lower surface side, while being supported by the support member 35 on the upper surface side. For example, as shown in FIG. 4, the entire lower surface 33 of the first prism P1 is held by contacting the holder 30, and a part of the upper surface 34 is supported by contacting the support member 35. Thus, for each of the first to fourth prisms P1 to P4, the contact area on the lower surface side with respect to the holder 30 is larger than the contact area on the upper surface side with respect to the support member 35.

[0047] 1.3 Problems Next, problems of the gas laser device 2 according to the comparative example will be described. The applicant has confirmed that when the operation of the gas laser device 2 is started, the beam profile and wavelength spectrum of the pulsed laser light PL change according to the elapsed time from the start of laser oscillation.

[0048] FIG. 5 shows the beam profile and wavelength spectrum 5 minutes and 2 hours after the start of laser oscillation. Comparing the beam profiles 5 minutes and 2 hours after, it can be seen that the beam divergence increases after a long time has elapsed. BDH shown in FIG. 5 indicates the beam divergence in the X direction. The beam divergence refers to the width of a region where the light intensity is at a certain ratio with respect to the peak value.

[0049] Furthermore, comparing the wavelength spectra after 5 minutes and 2 hours, we can see that the spectral linewidth increases after a long time has passed. The FWHM shown in Figure 5 is one index of the spectral linewidth and is the full width at half maximum of the wavelength spectrum.

[0050] The deterioration of the beam divergence and the spectral linewidth is thought to be caused by the distortion of the wavefront of the pulsed laser light PL due to the temperature difference that occurs inside each of the first to fourth prisms P1 to P4 due to laser oscillation.

[0051] The applicant has considered the cause of the distortion of the wavefront of the pulsed laser light PL, which will be explained below. First, as shown in Fig. 6, for each of the first to fourth prisms P1 to P4, the Y direction is defined as the V direction, the direction perpendicular to the transmitting surface 32 is defined as the L direction, and the direction perpendicular to the V direction and the L direction is defined as the H direction. The H direction is the direction in which the beam width expands.

[0052] Each of the first to fourth prisms P1 to P4 absorbs a portion of the pulsed laser beam PL as it passes through it and generates heat. Portions of each of the first to fourth prisms P1 to P4 that are in contact with the holder 30 and the support member 35 are cooled via the holder 30 and the support member 35, while other portions are cooled via nitrogen gas. Cooling via the holder 30 and the support member 35 is more efficient than cooling via nitrogen gas. Furthermore, the holder 30 and the support member 35 have different contact areas and heat capacities with each of the first to fourth prisms P1 to P4. Therefore, as time elapses after the start of laser oscillation, a temperature difference occurs within each of the first to fourth prisms P1 to P4. As described above, the holder 30 has a larger contact area and heat capacity than the support member 35. Therefore, the temperature of the upper surface of each of the first to fourth prisms P1 to P4 is higher than that of the lower surface, resulting in a temperature gradient in the V direction.

[0053] Figure 7 shows a schematic diagram of the wavefront twist that occurs in the third prism P3. The ray at one end of the beam width in the H direction of the pulsed laser light PL that passes through the third prism P3 is referred to as the first ray R1, and the ray at the other end is referred to as the second ray R2. Since the second ray R2 passes through a thicker portion of the third prism P3 than the first ray R1, the transmission length of the second ray R2 is longer than the transmission length of the first ray R1. In this way, the transmission lengths differ in the H direction. Here, the transmission length refers to the physical distance of the optical path that passes through the prism.

[0054] Furthermore, when the third prism P3 has a temperature gradient in the V direction, the optical path length changes in the V direction. Here, the optical path length refers to the optical distance obtained by multiplying the transmission length by the refractive index. The third prism P3 is made of calcium fluoride, which has a negative temperature coefficient of refractive index, so the refractive index decreases as the temperature increases. Therefore, the optical path length is shorter at the upper part of the third prism P3 than at the lower part. Therefore, the first light ray R1 and the second light ray R2 have different optical path lengths in the V direction, and the second light ray R2 has a longer transmission length than the first light ray R1, so the change in optical path length is greater.

[0055] As a result, the wavefront of the pulsed laser light PL that has passed through the third prism P3 is twisted. In Fig. 7, wavefront 50 schematically shows the wavefront when twisting occurs. Wavefront 51 schematically shows the wavefront when no twisting occurs. For example, wavefront 51 five minutes after the start of laser oscillation changes and becomes twisted like wavefront 50 two hours later.

[0056] A similar wavefront distortion occurs when the pulsed laser light PL passes through the first prism P1, the second prism P2, and the fourth prism P4. Since the larger the beam width of the incident pulsed laser light PL in the H direction, the greater the effect on the wavefront distortion, the greater the wavefront distortion in the third prism P3 and the fourth prism P4 than in the first prism P1 and the second prism P2. Such wavefront distortion is thought to cause beam divergence and degradation of the spectral linewidth.

[0057] Therefore, an object of the present disclosure is to provide a line narrowing module, a laser apparatus, and a method for manufacturing an electronic device that can suppress beam divergence and degradation of the spectral linewidth due to distortion of the wavefront.

[0058] 2. First embodiment 2.1 Configuration The gas laser device 2 according to the first embodiment of the present disclosure has the same configuration as the gas laser device 2 according to the comparative example, except that the configuration of the line-narrowing module 15 is different.

[0059] 8 is a view of the line narrowing module 15 according to the first embodiment as viewed from the Y direction. In this embodiment, of the first to fourth prisms P1 to P4, the fourth prism P4 and the third prism P3 are thought to have a large effect on the distortion of the wavefront, and are formed from materials with opposite positive and negative temperature coefficients of refractive index, thereby suppressing changes in the optical path length due to temperature changes. The fourth prism P4 is the "first nearest prism" closest to the grating 15b. The third prism P3 is the "second nearest prism" second closest to the grating 15b.

[0060] Materials with a positive temperature coefficient of refractive index include synthetic quartz (SiO2) and sapphire. Materials with a negative temperature coefficient of refractive index include calcium fluoride (CaF2) and quartz. The temperature coefficient of refractive index of synthetic quartz is 1.02 x 10 -5 The temperature coefficient of refractive index of calcium fluoride is -1.08×10 -5 is.

[0061] The third prism P3 has a smaller transmission cross-sectional area for the pulsed laser light PL than the fourth prism P4, and is therefore required to have higher resistance to the pulsed laser light PL than the fourth prism P4. For this reason, in this embodiment, the third prism P3 is made of calcium fluoride, which has high resistance to the pulsed laser light PL, and the fourth prism P4 is made of synthetic quartz.

[0062] The first prism P1 and the second prism P2 have a smaller transmission cross-sectional area than the third prism P3, and are therefore preferably made of calcium fluoride.

[0063] The sum of the optical path lengths of the first light ray R1 in the third prism P3 and the fourth prism P4 is defined as the first optical path sum, the sum of the optical path lengths of the second light ray R2 in the third prism P3 and the fourth prism P4 is defined as the second optical path sum, and the difference between the first and second optical path sums is defined as the optical path difference. In this embodiment, the amount of change in the optical path difference between when the elapsed time from the start of laser oscillation is in the first time zone and when it is in the second time zone is set to be less than a reference value. Here, the reference value is a value obtained by multiplying the wavelength of the pulsed laser light PL by 1 / 2.

[0064] The first time period is a time period during which the temperature difference inside the third prism P3 is 0.2°C or less, for example, 5 minutes or less. The second time period is a time period during which the temperature difference inside the third prism P3 is 0.5°C or more and 10°C or less, for example, longer than 5 minutes, including 2 hours. The temperature difference inside the prism refers to the value obtained by subtracting the minimum temperature from the maximum temperature inside the prism.

[0065] As described above, the first light ray R1 and the second light ray R2 are light rays at one end and the other end of the beam width of the pulsed laser beam PL in the H direction. In this embodiment, the first light ray R1 and the second light ray R2 are two light rays that pass through the same position in the V direction.

[0066] In this embodiment, in order to keep the amount of change in the optical path length difference at or below a reference value, the third prism P3 and the fourth prism P4 are arranged so that the transmission length of the first light ray R1 is shorter than the transmission length of the second light ray R2 within the third prism P3 and the fourth prism P4. Note that the third prism P3 and the fourth prism P4 may also be arranged so that the transmission length of the first light ray R1 is longer than the transmission length of the second light ray R2 within the third prism P3 and the fourth prism P4.

[0067] The condition for making the change in the optical path length difference equal to or less than the reference value will be described in more detail with reference to Fig. 9. As shown in Fig. 9, when the transmission length of the first light ray R1 in the first prism P1 is set to L1R1 , the transmission length in the second prism P2 is L2 R1 , the transmission length in the third prism P3 is L3 R1 , the transmission length in the fourth prism P4 is L4 R1 The transmission length of the second light ray R2 in the first prism P1 is L1 R2 , the transmission length in the second prism P2 is L2 R2 , the transmission length in the third prism P3 is L3 R2 , the transmission length in the fourth prism P4 is L4 R2 Let's say.

[0068] In addition, the first optical path length sum in the first time zone is LC R1 , the second optical path length sum is LC R2 The first optical path length sum in the second time zone is LH R1 , the second optical path length sum is LH R2 In addition, the refractive index of the third prism P3 in the first time period is set to n1, and the refractive index of the fourth prism P4 is set to n2.

[0069] First optical path length sum LC in the first time zone R1 is expressed by the following equation (1).

[0070]

number

[0071] Second optical path length sum LC in the first time zone R2 is expressed by the following equation (2).

[0072]

number

[0073] If the optical path length difference in the first time zone is ΔLC, the optical path length difference ΔLC is expressed by the following formula (3).

[0074]

number

[0075] The temperature coefficient of the refractive index n1 of the third prism P3 is dn1 / dT, and the temperature coefficient of the refractive index n2 of the fourth prism P4 is dn2 / dT. The temperature change from the first time period at the transmission point of the first light ray R1 in the third prism P3 during the second time period is ΔT. 31 The temperature change from the first time period at the point where the first light ray R1 passes through the fourth prism P4 is ΔT 41 In addition, the temperature change from the first time period at the point in the third prism P3 where the second light ray R2 passes is ΔT 32 The temperature change from the first time period at the point where the second light ray R2 passes through the fourth prism P4 is ΔT 42 Let's say.

[0076] First optical path length sum LH in the second time zone R1 is expressed by the following equation (4).

[0077]

number

[0078] Second optical path length sum LH in the second time zone R2 is expressed by the following equation (5).

[0079]

number

[0080] If the optical path length difference in the second time zone is ΔLH, the optical path length difference ΔLH is expressed by the following equation (6).

[0081]

number

[0082] In this embodiment, the transmission length L3 is set to satisfy the following formula (7): R1 ,L3 R2 ,L4 R1 ,L4 R2where λ is the wavelength of the pulsed laser light PL, and λ / 2 is the reference value mentioned above.

[0083]

number

[0084] The above equation (7) can be transformed into the following equation (8).

[0085]

number

[0086] In order for the above formula (8) to be satisfied regardless of temperature changes, the temperature coefficient dn1 / dT and the temperature coefficient dn2 / dT must have opposite signs. R1 <L3 R2 , and L4 R1 <L4 R2 " and "L3 R1 >L3 R2 , and L4 R1 >L4 R2 It is preferable that either of the relationships "a" and "b" is satisfied.

[0087] In addition, the temperature change ΔT 31 ,ΔT 32 ,ΔT 41 ,ΔT 42 differs depending on the method for fixing the third prism P3 and the fourth prism P4, the pulse energy of the pulsed laser light PL that passes through, and the like.

[0088] 2.2 Operation The operation of the gas laser device 2 according to this embodiment is the same as that of the comparative example, except that the function of the line-narrowing module 15 is different.

[0089] The fourth prism P4 and the third prism P3 are formed of materials whose temperature coefficients of refractive index are opposite in sign, and the transmission length L3 is set to satisfy the above formula (7). R1 ,L3 R2 ,L4 R1 ,L4 R2By setting the above, the change in the optical path length due to the temperature change can be suppressed.

[0090] 2.3 Effects According to this embodiment, the change in optical path length due to temperature change is suppressed, and therefore distortion of the wavefront is suppressed, thereby making it possible to suppress beam divergence and deterioration of the spectral linewidth.

[0091] 3. Modification of the First Embodiment Various modifications of the first embodiment will be described below.

[0092] In the above embodiment, the sum of the optical path lengths of the first light ray R1 in the third prism P3 and the fourth prism P4 is defined as the first optical path sum, but the sum of the optical path lengths of the first light ray R1 in the first to fourth prisms P1 to P4 may also be defined as the first optical path sum. Similarly, the sum of the optical path lengths of the second light ray R2 in the first to fourth prisms P1 to P4 may also be defined as the first optical path sum.

[0093] In this case, the above formulas (1) and (2) become the following formulas (1a) and (2a).

[0094]

number

[0095]

number

[0096] The above formulas (4) and (5) become the following formulas (4a) and (5a): The temperature change from the first time zone at the point in the first prism P1 where the first light ray R1 passes is ΔT 11 The temperature change from the first time period at the point where the first light ray R1 passes through the second prism P2 is ΔT 21 The temperature change from the first time period at the point where the second light ray R2 passes through the first prism P1 is ΔT 12 The temperature change from the first time period at the point where the second light ray R2 passes through the second prism P2 is ΔT22 Let's say.

[0097]

number

[0098]

number

[0099] As a result, the above equation (8) becomes the following equation (8a).

[0100]

number

[0101] The above formula (8a) takes into account the influence of temperature changes in the first prism P1 and the second prism P2, in addition to temperature changes in the third prism P3 and the fourth prism P4. Therefore, by setting the optical path lengths of the first light ray R1 and the second light ray R2 that pass through the first to fourth prisms P1 to P4 so as to satisfy the above formula (8a), it is possible to more accurately suppress deterioration of beam divergence and spectral linewidth.

[0102] In the above embodiment, the mirror M is disposed between the third prism P3 and the fourth prism P4, but as shown in Fig. 10, the mirror M may be disposed between the fourth prism P4 and the grating 15b. In this case, the mirror M reflects the pulsed laser light PL that has passed through the fourth prism P4 so that it is incident on the grating 15b. The other configurations of the line narrowing module 15 shown in Fig. 10 are the same as those of the above embodiment.

[0103] In the above embodiment, the line narrowing module 15 includes four prisms, but may include five or more prisms. The line narrowing module 15 may be configured to include a plurality of prisms.

[0104] 4. Manufacturing method of electronic devices 11 shows a schematic configuration example of an exposure apparatus 100. The exposure apparatus 100 includes an illumination optical system 104 and a projection optical system 106. The illumination optical system 104 illuminates a reticle pattern of a reticle (not shown) placed on a reticle stage RT with pulsed laser light PL incident thereon, for example, from a gas laser device 2. The projection optical system 106 reduces and projects the pulsed laser light PL that has passed through the reticle, forming an image on a workpiece (not shown) placed on a workpiece table WT. The workpiece is a photosensitive substrate such as a semiconductor wafer coated with photoresist.

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

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

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

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

Claims

1. A line narrowing module for narrowing the line of pulsed laser light having a wavelength in the ultraviolet region, a grating that reflects incident pulsed laser light; an expanding optical system including a plurality of prisms that expand the beam width of the pulsed laser light and cause the pulsed laser light to enter the grating; Equipped with The magnifying optical system includes: The temperature coefficients of the refractive index of a first close prism nearest to the grating and a second close prism nearest to the grating have opposite positive and negative values, a first ray is a ray at one end in the expansion direction of the pulsed laser beam, and a second ray is a ray at the other end, and the difference between the sum of the optical path lengths of the first ray in the first near prism and the second near prism and the sum of the optical path lengths of the second ray in the first near prism and the second near prism is an optical path length difference, when a temperature difference in the second near prism is 0.2°C or less and a temperature difference in the second near prism is 0.5°C or more and 10°C or less is less than 1 / 2 times the wavelength of the pulsed laser beam Narrowband module.

2. 2. The band-narrowing module according to claim 1, an optical path length of the first light ray in the first near prism is shorter than an optical path length of the second light ray in the first near prism; The optical path length of the first light ray in the second near prism is shorter than the optical path length of the second light ray in the second near prism.

3. 2. The band-narrowing module according to claim 1, the first near prism is formed of a material having a positive temperature coefficient of refractive index; The second near prism is made of a material whose temperature coefficient of refractive index is negative.

4. 4. The band-narrowing module according to claim 3, the first near prism is made of synthetic quartz, The second near prism is made of calcium fluoride.

5. 2. The band-narrowing module according to claim 1, The magnifying optical system includes a mirror disposed between the first near prism and the second near prism.

6. 2. The band-narrowing module according to claim 1, The magnifying optical system includes a mirror disposed between the grating and the first near prism.

7. 2. The band-narrowing module according to claim 1, The plurality of prisms is four prisms.

8. A line narrowing module for narrowing the line of pulsed laser light having a wavelength in the ultraviolet region, a grating that reflects incident pulsed laser light; an expanding optical system including a plurality of prisms that expand the beam width of the pulsed laser light and cause the pulsed laser light to enter the grating; Equipped with The magnifying optical system includes: The temperature coefficients of the refractive index of a first close prism nearest to the grating and a second close prism nearest to the grating have opposite positive and negative values, a first light ray is a light ray at one end in the expansion direction of the pulsed laser beam, and a second light ray is a light ray at the other end, and the difference between the sum of the optical path lengths of the first light ray within the plurality of prisms and the sum of the optical path lengths of the second light ray within the plurality of prisms is an optical path length difference, wherein an amount of change in the optical path length difference between a case where the temperature difference within the second closest prism is 0.2°C or less and a case where the temperature difference is 0.5°C or more and 10°C or less is less than 1 / 2 times the wavelength of the pulsed laser beam. Narrowband module.

9. 9. The band narrowing module according to claim 8, an optical path length of the first light ray in the first near prism is shorter than an optical path length of the second light ray in the first near prism; The optical path length of the first light ray in the second near prism is shorter than the optical path length of the second light ray in the second near prism.

10. 9. The band narrowing module according to claim 8, the first near prism is formed of a material having a positive temperature coefficient of refractive index; The second near prism is made of a material whose temperature coefficient of refractive index is negative.

11. 11. The line narrowing module of claim 10, the first near prism is made of synthetic quartz, The second near prism is made of calcium fluoride.

12. 9. The band narrowing module according to claim 8, The magnifying optical system includes a mirror disposed between the first near prism and the second near prism.

13. 9. The band narrowing module according to claim 8, The magnifying optical system includes a mirror disposed between the grating and the first near prism.

14. 9. The band narrowing module according to claim 8, The plurality of prisms is four prisms.

15. a line narrowing module for narrowing the line of pulsed laser light having a wavelength in the ultraviolet region, the line narrowing module including: a grating for reflecting incident pulsed laser light; and an expansion optical system including a plurality of prisms for expanding the beam width of the pulsed laser light and causing it to enter the grating; an output coupling mirror; a laser chamber including a pair of discharge electrodes, the laser chamber being disposed in an optical path of an optical resonator configured by the line-narrowing module and the output coupling mirror; A laser device comprising: The magnifying optical system includes: The temperature coefficients of the refractive index of a first close prism nearest to the grating and a second close prism nearest to the grating have opposite positive and negative values, a first ray is a ray at one end in the expansion direction of the pulsed laser beam, and a second ray is a ray at the other end, and the difference between the sum of the optical path lengths of the first ray in the first near prism and the second near prism and the sum of the optical path lengths of the second ray in the first near prism and the second near prism is an optical path length difference, when a temperature difference in the second near prism is 0.2°C or less and a temperature difference in the second near prism is 0.5°C or more and 10°C or less is less than 1 / 2 times the wavelength of the pulsed laser beam Laser device.

16. A method for manufacturing an electronic device, comprising: a line narrowing module for narrowing the line of pulsed laser light having a wavelength in the ultraviolet region, the line narrowing module including: a grating for reflecting incident pulsed laser light; and an expansion optical system including a plurality of prisms for expanding the beam width of the pulsed laser light and causing it to enter the grating; an output coupling mirror; a laser chamber including a pair of discharge electrodes, the laser chamber being disposed in an optical path of an optical resonator configured by the line-narrowing module and the output coupling mirror; A laser device comprising: The magnifying optical system includes: The temperature coefficients of the refractive index of a first close prism nearest to the grating and a second close prism nearest to the grating have opposite positive and negative values, a first ray is a ray at one end in the expansion direction of the pulsed laser beam, and a second ray is a ray at the other end, and the difference between the sum of the optical path lengths of the first ray in the first near prism and the second near prism and the sum of the optical path lengths of the second ray in the first near prism and the second near prism is an optical path length difference, when a temperature difference in the second near prism is 0.2°C or less and a temperature difference in the second near prism is 0.5°C or more and 10°C or less is less than 1 / 2 times the wavelength of the pulsed laser beam generating the pulsed laser light by a laser device; outputting the pulsed laser light to an exposure device; and exposing a photosensitive substrate to the pulsed laser light in the exposure apparatus to manufacture an electronic device. A method for manufacturing electronic devices.

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