Laser apparatus, and method for manufacturing electronic device

Abstract

To provide a laser apparatus that prevents a variation in the direction of travel of a laser beam.SOLUTION: A laser apparatus comprises a line narrowing module and an output coupling mirror. The line narrowing module includes: a prism that includes a transmission surface through which a laser beam transmits, a bottom face in contact with the transmission surface, and a top face opposite to the bottom face; and a holder that holds the prism on the bottom face. The output coupling mirror includes a partial reflection film whose reflectance changes in a direction in which the bottom face and the top face are opposite to each other.SELECTED DRAWING: Figure 7

Description

[Technical Field]

[0001] The present disclosure relates to 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] U.S. Patent No. 7,903,700 [Patent Document 2] Patent No. 3638110 [Patent Document 3] Overview of Patent No. 3591360

[0005] A laser device according to one aspect of the present disclosure is a laser device comprising a line narrowing module and an output coupling mirror, wherein the line narrowing module includes a prism including a transmission surface through which laser light passes, a bottom surface in contact with the transmission surface, and an upper surface opposite the bottom surface, and a holder that holds the prism at the bottom surface, and the output coupling mirror includes a partially reflective film whose reflectivity changes in the direction in which the bottom surface and the upper surface face each other.

[0006] A method for manufacturing an electronic device according to one aspect of the present disclosure includes a line narrowing module and an output coupling mirror, wherein the line narrowing module includes a prism having a transmission surface through which laser light passes, a bottom surface in contact with the transmission surface, and a top surface opposite the bottom surface, and a holder for holding the prism at the bottom surface, and the output coupling mirror includes a partially reflective film whose reflectivity changes in the direction in which the bottom surface and the top surface face each other, generating laser light using a laser device, outputting the laser light to an exposure device, and exposing the laser light to a photosensitive substrate in the exposure device to manufacture an electronic device. [Brief explanation of the drawings]

[0007] 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 laser device according to a comparative example. [Figure 2] FIG. 2 is a diagram schematically showing the configuration of a laser device according to a comparative example. [Figure 3] FIG. 3 is a diagram showing a schematic configuration of a prism. [Figure 4] FIG. 4 is a diagram showing an example of a change in Pointing V over time during continuous operation of a laser device according to a comparative example. [Figure 5] FIG. 5 is a diagram schematically illustrating an example of a temperature gradient occurring in a magnifying optical system in a comparative example. [Figure 6] FIG. 6 is a diagram showing the temperature coefficient of the refractive index of materials that make up the magnifying optical system. [Figure 7] FIG. 7 is a diagram schematically showing the configuration of the laser device according to the first embodiment. [Figure 8] FIG. 8 is a diagram schematically showing the configuration of the output coupling mirror according to the first embodiment. [Figure 9] FIG. 9 is a diagram showing an example of the relationship between the internal load and the reflectance of the output coupling mirror. [Figure 10] FIG. 10 is a diagram schematically showing an example of a temperature gradient that occurs in the magnifying optical system in the first embodiment. [Figure 11] FIG. 11 is a diagram showing an example of the change over time in Pointing V during continuous operation of the laser device according to the first embodiment. [Figure 12] FIG. 12 is a diagram schematically showing the V-direction dependence of various characteristics of the optical resonator according to the first embodiment. [Figure 13] FIG. 13 is a diagram showing the relationship between the extraction efficiency and the reflectance of the output coupling mirror when g0 / α=20. [Figure 14] FIG. 14 is a diagram showing the relationship between the extraction efficiency and the reflectance of the output coupling mirror when g0 / α=10. [Figure 15] FIG. 15 is a diagram schematically showing the V-direction dependence of various characteristics of the optical resonator according to the first modification. [Figure 16] FIG. 16 is a diagram showing an example in which the first partially reflective film and the second partially reflective film are formed so that the boundary passes through the +V direction side of the center of the irradiation area. [Figure 17] FIG. 17 is a diagram showing an example in which the first partially reflective film and the second partially reflective film are formed so that the boundary passes through the −V direction side of the center of the irradiation area. [Figure 18] FIG. 18 is a diagram schematically showing the V-directional dependence of various characteristics of an optical resonator when the boundaries are set as shown in FIG. [Figure 19] FIG. 19 is a diagram schematically showing the V-directional dependence of various characteristics of an optical resonator when the boundaries are set as shown in FIG. [Figure 20] FIG. 20 is a diagram schematically illustrating an example of the relationship between the amount of variation in PointingV and the boundary position. [Figure 21]FIG. 21 is a diagram schematically showing the configuration of an output coupling mirror according to the second embodiment. [Figure 22] FIG. 22 is a diagram schematically showing the V-direction dependence of various characteristics of the optical resonator according to the second embodiment. [Figure 23] FIG. 23 is a diagram showing an example of the change over time in Pointing V during continuous operation of the laser device according to the second embodiment. [Figure 24] FIG. 24 is a diagram schematically showing an example of the configuration of an exposure apparatus. Embodiment

[0008] <Contents> 1. Comparative Example 1.1 Configuration 1.2 Operation 1.3 Challenges 2. First embodiment 2.1 Configuration 2.2 Operation 2.3 Effects 3. Modification of the First Embodiment 3.1 First Modification 3.2 Second Modification 4. Second embodiment 4.1 Configuration 4.2 Operation 4.3 Effects 5. Electronic Device Manufacturing Method

[0009] 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.

[0010] 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.

[0011] 1.1 Configuration 1 and 2 show a schematic configuration of a laser device 1 according to a comparative example. The laser device 1 is an excimer laser device that outputs ultraviolet laser light Lb.

[0012] The laser device 1 includes a laser chamber 10, a pair of discharge electrodes 11a and 11b, a line narrowing module 14, and an output coupling mirror 15. The laser device 1 further includes a beam splitter 20, a monitor 21 capable of measuring the wavelength and energy intensity of the laser light Lb, a control processor 22, and a driver 23. The line narrowing module 14 and the output coupling mirror 15 constitute an optical resonator. The laser chamber 10 is disposed in the optical path of the optical resonator.

[0013] In the present disclosure, the traveling direction of the laser light Lb output from the output coupling mirror 15 is defined as the Z direction. The direction of discharge occurring between the pair of discharge electrodes 11a and 11b is defined as the V direction. The Z direction and the V direction are perpendicular to each other. The direction perpendicular to the Z direction and the V direction is defined as the H direction. Figure 1 shows the laser device 1 as viewed from the V direction. Figure 2 shows the laser device 1 as viewed from the H direction. The V direction is an example of a "first direction" according to the technology of the present disclosure. The H direction is an example of a "second direction" according to the technology of the present disclosure.

[0014] The laser chamber 10 is a chamber in which a laser gas containing components of a laser medium is sealed. The laser gas includes, for example, argon gas or krypton gas as a rare gas, fluorine gas as a halogen gas, and neon gas as a buffer gas. Windows 10a and 10b are provided on both ends of the laser chamber 10.

[0015] The discharge electrodes 11a and 11b are disposed in a laser chamber 10. The discharge electrode 11a is connected to a power supply 30, and the discharge electrode 11b is applied with a ground potential.

[0016] As shown in FIG. 1, the windows 10a and 10b are arranged so that the incident plane of the laser light Lb on these windows is approximately parallel to the HZ plane, and the incident angle of the laser light Lb is approximately the Brewster angle.

[0017] The line narrowing module 14 includes an expanding optical system 14e, a grating 14f, and a housing 12. The expanding optical system 14e includes four prisms 14a to 14d.

[0018] Each of the prisms 14a to 14d is made of calcium fluoride crystals. Each of the prisms 14a to 14d includes two transmission surfaces 18 and 19 through which the laser light Lb passes. The transmission surfaces 18 and 19 are parallel to the V direction.

[0019] Each of the prisms 14a to 14d is arranged so that the traveling direction of the laser light Lb passing through the transmitting surface 18 is non-perpendicular to the transmitting surface 18, and the traveling direction of the laser light Lb passing through the transmitting surface 19 is approximately perpendicular to the transmitting surface 19. The laser light Lb is refracted at the transmitting surface 18, and travels approximately straight at the transmitting surface 19. The transmitting surface 18 is coated with a film that suppresses reflection of the P-polarized component of the laser light Lb. The transmitting surface 19 is coated with a film that suppresses reflection of the laser light Lb.

[0020] The volume of each of the prisms 14a to 14d can be set to match the beam width of the laser light Lb passing through it, thereby reducing the amount of material used. If the volumes of two or more of the prisms 14a to 14d are set to be equal, the same components may be used as long as they are made of the same material. Note that the magnifying optical system 14e only needs to include at least one prism.

[0021] Housing 12 houses magnifying optical system 14e and grating 14f. Prism 14a is held by holder 16a, prism 14b is held by holder 16b, prism 14c is held by holder 16c, prism 14d is held by holder 16d, and grating 14f is held by holder 16f. Holder 16c includes rotation mechanism 17, which is driven by driver 23, and rotates prism 14c around an axis parallel to the V direction.

[0022] Specifically, as shown in FIG. 3, prism 14a is a triangular prism including transmitting surfaces 18 and 19, a bottom surface 31 in contact with transmitting surfaces 18 and 19, and a top surface 32 facing bottom surface 31. Holder 16a holds prism 14a at bottom surface 31. Top surface 32 is held down by a fixing member (not shown). The other prisms 14b to 14d have the same configuration as prism 14a. The direction in which bottom surface 31 and top surface 32 face each other corresponds to the V direction. In particular, the direction from bottom surface 31 toward top surface 32 is referred to as the "+V direction," and the opposite direction from top surface 32 toward bottom surface 31 is referred to as the "-V direction."

[0023] The grating 14f is an echele grating that includes a highly reflective material on its surface and has a large number of grooves formed at predetermined intervals.

[0024] The housing 12 is connected to the laser chamber 10 by an optical path pipe 24. The inside of the optical path pipe 24 is in communication with the inside of the housing 12. An inert gas such as nitrogen gas is introduced into the inside of the housing 12 and the inside of the optical path pipe 24 through an inert gas inlet pipe (not shown) and exhausted through an inert gas exhaust pipe (not shown). In this way, the inside of the housing 12 and the inside of the optical path pipe 24 are purged with the inert gas.

[0025] The output coupling mirror 15 is a partial reflection mirror formed by coating a partial reflection film 151 on the surface of a substrate 150 facing the window 10b. The substrate 150 is a glass substrate made of, for example, calcium fluoride. The partial reflection film 151 is coated so that the reflectance of the output coupling mirror 15 is uniform within the surface, and the reflectance is, for example, 10%.

[0026] In addition, a slit 13 is disposed between the window 10b and the output coupling mirror 15. The slit 13 has a width narrower than the distance between the pair of discharge electrodes 11a and 11b, and limits the beam width of the laser light Lb emitted from the window 10b of the laser chamber 10 in the discharge direction.

[0027] The beam splitter 20 is disposed in the optical path of the laser light Lb output from the output coupling mirror 15. One surface of the beam splitter 20 is coated with a partially reflective film. A monitor 21 is disposed in the optical path of the laser light Lb reflected by the beam splitter 20. The monitor 21 includes an energy sensor, a spectroscope such as an etalon, and an image sensor, all of which are not shown.

[0028] The control processor 22 is a processing device including, for example, a memory 22a in which a control program is stored and a CPU (Central Processing Unit) 22b that executes the control program. The control processor 22 is specially configured or programmed to execute various processes included in the present disclosure.

[0029] 1.2 Operation Next, the operation of the laser device 1 according to the comparative example will be described. When a high voltage is applied between the discharge electrodes 11a and 11b by the power supply 30, a discharge occurs between the discharge electrodes 11a and 11b. The energy of this discharge excites the laser medium in the laser chamber 10, causing it to transition to a high energy level. When the excited laser medium transitions to a low energy level, it emits laser light Lb with a wavelength corresponding to the difference between the high energy level and the low energy level.

[0030] Laser light Lb generated within the laser chamber 10 is emitted to the outside of the laser chamber 10 through windows 10a and 10b. The laser light Lb emitted from the window 10a of the laser chamber 10 is refracted within a plane parallel to the HZ plane by the magnifying optical system 14e, thereby expanding the beam width in the H direction and entering the grating 14f.

[0031] Laser light Lb incident on the grating 14f from the magnifying optical system 14e is reflected by the grating 14f and diffracted in a direction according to its wavelength. As a result, the laser light Lb reflected by the grating 14f is dispersed in a plane parallel to the HZ plane. The grating 14f is configured in a Littrow configuration so that the angle of incidence of the laser light Lb incident on the grating 14f from the magnifying optical system 14e matches the diffraction angle of the diffracted light of the desired wavelength. As a result, laser light Lb near the desired wavelength returns to the laser chamber 10 via the magnifying optical system 14e.

[0032] The expansion optical system 14e reduces the beam width of the laser light Lb incident from the grating 14f in the H direction, and returns the laser light Lb to the inside of the laser chamber 10 through the window 10a.

[0033] The output coupling mirror 15 transmits and outputs a portion of the laser light Lb that is emitted from the window 10b of the laser chamber 10 and has a beam width limited by the slit 13, and reflects the other portion back into the laser chamber 10.

[0034] In this way, the laser light Lb emitted from the laser chamber 10 travels back and forth between the line narrowing module 14 and the output coupling mirror 15, and is amplified each time it passes through the discharge space between the discharge electrodes 11a and 11b. This laser light Lb is narrowed in line each time it is reflected by the line narrowing module 14. Furthermore, the H-directional polarization component is selected by the arrangement of the windows 10a and 10b and the coatings of the prisms 14a to 14d described above. The amplified laser light Lb is output from the output coupling mirror 15. This laser light Lb has a wavelength in the vacuum ultraviolet region.

[0035] The beam splitter 20 transmits a part of the laser light Lb output from the output coupling mirror 15 with high transmittance and reflects the other part. The laser light Lb transmitted through the beam splitter 20 enters an exposure device.

[0036] The laser light Lb reflected by the beam splitter 20 enters a spectroscope included in the monitor 21. The spectroscope forms interference fringes of the laser light Lb on the light receiving surface of an image sensor included in the monitor 21. The image sensor generates image data of the interference fringes and transmits the generated image data to the control processor 22.

[0037] The control processor 22 receives target wavelength data indicating the target wavelength from a control unit of the exposure apparatus or the like. The control processor 22 also receives image data from the monitor 21 and calculates the wavelength of the laser light Lb based on the received image data. The control processor 22 sends a control signal to the driver 23 based on the target wavelength data and the calculated wavelength of the laser light Lb. The driver 23 sends a drive signal to the rotation mechanism 17 based on the control signal.

[0038] Rotation mechanism 17 rotates holder 16c together with prism 14c in response to a drive signal from driver 23. Rotation of prism 14c changes the angle of incidence of laser light Lb on grating 14f, thereby adjusting the wavelength. Note that in this comparative example, prism 14c is rotatable for wavelength control, but this is not limiting, and any of prisms 14a to 14d may be rotatable.

[0039] 1.3 Challenges When the laser device 1 according to the comparative example is continuously operated, the traveling direction of the laser light Lb reflected by the grating 14f and emitted from the line-narrowing module 14 via the magnifying optical system 14e may fluctuate. In the present disclosure, the traveling direction of the laser light Lb is referred to as pointing, and the angle of pointing with respect to the reference direction in the V direction is defined as "PointingV." The unit of PointingV is mrad. The reference direction is, for example, the Z direction.

[0040] Fig. 4 shows an example of the change in Pointing V over time during continuous operation of the laser device 1 according to the comparative example. According to Fig. 4, the traveling direction of the laser light Lb emitted from the line-narrowing module 14 fluctuates in the -V direction as time passes from the start of continuous operation.

[0041] Referring again to FIG. 2, a possible cause of the fluctuation in Pointing V will be explained. When the laser device 1 is operated continuously, the magnifying optical system 14e absorbs part of the energy of the laser light Lb, causing the temperature to rise. This causes the temperature inside the magnifying optical system 14e to become non-uniform, resulting in a temperature gradient. For example, the prisms 14a to 14d have high temperatures in the areas far from the holders 16a to 16d, while the areas close to the holders 16a to 16d have low temperatures.

[0042] Fig. 5 schematically shows an example of a temperature gradient occurring in the magnifying optical system 14e in the comparative example. In Fig. 5, Pt indicates the contact position in the V direction between the prisms 14a to 14d and the fixing member, and Pb indicates the contact position in the V direction between the prisms 14a to 14d and the holders 16a to 16d. Furthermore, Tt indicates the maximum temperature at the contact surface between the prisms 14a to 14d and the fixing member, and Tb0 indicates the maximum temperature at the contact surface between the prisms 14a to 14d and the holders 16a to 16d. In the present disclosure, the temperature gradient refers to the rate of change of the temperature T in the V direction. Furthermore, A indicates the area of the output coupling mirror 15 that is irradiated with the laser light Lb.

[0043] One possible cause of such a temperature gradient is that the thermal energy of the prisms 14a to 14d in the portions close to the holders 16a to 16d is lost due to thermal conduction to the holders 16a to 16d. Another possible cause is that the temperature of the prisms 14a to 14d in the portions far from the holders 16a to 16d increases due to thermal conduction from the fixing members heated by the scattered light of the laser beam Lb to the prisms 14a to 14d.

[0044] The refractive index of the calcium fluoride crystals that make up the prisms 14a-14d is temperature-dependent, with the refractive index decreasing as the temperature increases. Generally, the lower the refractive index, the faster the speed of light passing through a medium. Therefore, when the direction of light intersects with the direction of the temperature gradient, the wavefront of the light tilts toward the lower temperature. Therefore, as shown in Figure 2, it is estimated that the direction of laser light Lb fluctuates toward the lower temperature, i.e., the -V direction. If the absolute value of PointingV increases over time and exceeds a threshold, vignetting of laser light Lb may occur in the optical system of the exposure tool, potentially resulting in reduced throughput and poor imaging performance.

[0045] The material forming the prisms 14a to 14d must have high transparency to the laser light Lb. In addition to the above-mentioned calcium fluoride CaF2, quartz crystal QC or synthetic quartz SQ can be used as the material forming the prisms 14a to 14d. In addition to the material forming the prisms 14a to 14d, the material forming the magnifying optical system 14e also includes nitrogen gas N2 as an inert gas present on the optical path.

[0046] Figure 6 shows the temperature coefficients dn / dT of the refractive index of materials that make up the magnifying optical system 14e. The temperature coefficient dn / dT is the amount of change in the refractive index n of light with a wavelength of 248.4 nm when the temperature T changes by 1°C. Figure 6 shows that quartz crystal QC has a smaller absolute value of the temperature coefficient dn / dT than calcium fluoride CaF2. Furthermore, both quartz crystal QC and calcium fluoride CaF2 have negative temperature coefficients dn / dT, while synthetic quartz SQ has a positive temperature coefficient dn / dT.

[0047] For this reason, it is conceivable to suppress fluctuations in Pointing V by configuring the expanding optical system 14e by combining calcium fluoride CaF2, which has a negative temperature coefficient dn / dT, with synthetic quartz SQ, which has a positive temperature coefficient dn / dT. However, because quartz QC and synthetic quartz SQ have low resistance to ultraviolet light, configuring the expanding optical system 14e in this manner would shorten the life of the line-narrowing module 14.

[0048] It is also conceivable to suppress fluctuations in PointingV by providing a temperature regulator to suppress the temperature gradient in the V direction inside the housing 12, but this would result in an increase in costs.

[0049] Therefore, an object of the present disclosure is to suppress fluctuations in Pointing V by suppressing the temperature gradient in the V direction of the magnifying optical system 14e without increasing costs.

[0050] 2. First embodiment 2.1 Configuration Fig. 7 schematically illustrates the configuration of a laser device 1a according to the first embodiment of the present disclosure. Fig. 7 illustrates the laser device 1a as viewed from the H direction. The laser device 1a as viewed from the V direction is not illustrated. The laser device 1a has the same configuration as the laser device 1 according to the comparative example, except that the configuration of the output coupling mirror 15 is different.

[0051] In the comparative example, the output coupling mirror 15 has a partial reflection film 151 having a uniform reflectance formed on the surface of the substrate 150 facing the window 10b. In contrast, in the present embodiment, the output coupling mirror 15 has a first partial reflection film 151a having a first reflectance R1 and a second partial reflection film 151b having a second reflectance R2 higher than the first reflectance R1 formed on the surface of the substrate 150 facing the window 10b. That is, the first partial reflection film 151a and the second partial reflection film 151b form a partial reflection film whose reflectance changes in the direction in which the bottom surface 31 and the top surface 32 face each other.

[0052] The substrate 150 is a glass substrate made of, for example, calcium fluoride. The first partially reflective film 151a and the second partially reflective film 151b are dielectric multilayer films that achieve a predetermined reflectance by alternately stacking high-refractive-index dielectric materials and low-refractive-index dielectric materials. The high-refractive-index material may be selected from, for example, lanthanum fluoride (LaF), gadolinium fluoride (GdF), and alumina (AlO). The low-refractive-index material may be selected from, for example, aluminum fluoride (AlF), magnesium fluoride (MgF), and silicon oxide (SiO).

[0053] In this embodiment, as in the comparative example, the prisms 14a to 14d are made of calcium fluoride CaF2, which has a negative temperature coefficient dn / dT.

[0054] FIG. 8 schematically shows the configuration of the output coupling mirror 15 according to the first embodiment. FIG. 8 shows the output coupling mirror 15 as viewed from the Z direction, and the position dependence of the reflectance R of the output coupling mirror 15. The first partially reflective film 151a and the second partially reflective film 151b are adjacent to each other in the V direction, with a boundary B between them. The boundary B extends linearly in the H direction. Furthermore, the boundary B passes through an irradiation area A of the laser light Lb. In this embodiment, the irradiation area A is the area that is irradiated with the laser light Lb when the first partially reflective film 151a is formed on the entire surface of the output coupling mirror 15 on the window 10b side.

[0055] In this embodiment, boundary B passes through center C of irradiation area A. With boundary B as a reference, first partially reflective film 151a is provided on the +V direction side, and second partially reflective film 151b is provided on the -V direction side. That is, the reflectance R of output coupling mirror 15 changes at boundary B, and is relatively higher on the -V direction side of boundary B than on the +V direction side.

[0056] In this embodiment, it is estimated that a temperature gradient will occur during continuous operation of the laser device 1a, with the +V direction side of the magnifying optical system 14e being higher in temperature and the −V direction side being lower in temperature. Based on this estimation, the first partial reflection film 151a and the second partial reflection film 151b are arranged so that the laser light Lb passing through the higher temperature side irradiates the first partial reflection film 151a, which has a low reflectivity, and the laser light Lb passing through the lower temperature side irradiates the second partial reflection film 151b, which has a high reflectivity. Note that if the estimated temperature gradient is reversed, the second partial reflection film 151b is arranged on the +V direction side, and the first partial reflection film 151a is arranged on the −V direction side.

[0057] 2.2 Operation The operation of the laser device 1a according to this embodiment is the same as that of the comparative example, except for the difference in the function of the output coupling mirror 15. The function of the output coupling mirror 15 according to this embodiment will be described below.

[0058] In the optical resonator of the laser device 1a according to this embodiment, as in the comparative example, laser light Lb is reflected by the output coupling mirror 15 and passes through the high-temperature side of the magnifying optical system 14e, and laser light Lb passes through the low-temperature side. The laser light Lb passing through the high-temperature side is reflected by the first partially reflective film 151a with low reflectivity, so its light intensity is lower than the light intensity of the laser light Lb on the low-temperature side. Conversely, the laser light Lb passing through the low-temperature side is reflected by the second partially reflective film 151b with high reflectivity, so its light intensity is higher than the light intensity of the laser light Lb on the high-temperature side.

[0059] The temperature of the magnifying optical system 14e rises as it absorbs the laser light Lb, but in this embodiment, the light intensity of the laser light Lb on the low-temperature side is relatively higher than that on the high-temperature side, so the temperature of the magnifying optical system 14e on the low-temperature side rises more. This suppresses the temperature gradient in the V direction of the magnifying optical system 14e. As a result, fluctuations in Pointing V are suppressed.

[0060] Next, the relationship between the reflectance R of the output coupling mirror 15 and the temperature rise of the magnifying optical system 14e will be described in detail. When the light intensity of the laser light Lb reflected by the output coupling mirror 15 is within the range of light intensity at which stimulated emission light is proportionally generated within the optical resonator, the laser light Lb reflected by the output coupling mirror 15 is considered to impart energy to the optical resonator. Hereinafter, the energy imparted to the optical resonator by the laser light Lb reflected by the output coupling mirror 15 is referred to as the internal load.

[0061] The light intensity of the laser light Lb output from the output coupling mirror 15 is I out , the reflectance of the line-narrowing module 14 is R LNM Then, the internal load I LNM and the reflectance R of the output coupling mirror 15 can be expressed by the following formula (1) based on modeling of an optical resonator.

[0062]

number

[0063] Figure 9 shows the internal load I LNM 9 shows an example of the relationship between the internal load I LNM is R in the above equation (1). LNM = 0.8, and the light intensity I out 9, the higher the reflectance R of the output coupling mirror 15, the greater the internal load I LNM As a result, it can be seen that the amount of laser light Lb absorbed by the magnifying optical system 14e increases.

[0064] In this embodiment, the reflectance R of the output coupling mirror 15 is relatively high on the −V direction side, so the internal load I LNM For example, if R1=10% and R2=20%, the internal load I LNM is the internal load I on the high temperature side LNM This is about 1.3 times the original amount.

[0065] 2.3 Effects FIG. 10 schematically illustrates an example of a temperature gradient occurring in the magnifying optical system 14e in the first embodiment. In this embodiment, as described above, the light intensity of the laser light Lb on the low-temperature side within the optical resonator is relatively increased, causing a relative increase in the temperature of the low-temperature side of the magnifying optical system 14e. As a result, as shown in FIG. 10, a temperature boundary corresponding to the boundary B between the first partially reflective film 151a and the second partially reflective film 151b is generated in the temperature gradient in the V direction occurring in the magnifying optical system 14e, and the temperature at position Pb of the magnifying optical system 14e rises from Tb0 in the comparative example to Tb1. In reality, the temperature gradient would be more gradual due to factors such as thermal conduction; however, for simplicity of explanation, a schematic shape is shown that eliminates the effects of thermal conduction.

[0066] As a result, the temperature change from Tt to Tb1, which is the substantial temperature gradient, is lower than the temperature change from Tt to Tb0 in the comparative example, and therefore the fluctuation of Pointing V is suppressed as shown in Fig. 11. In Fig. 11, the solid line shows an example of the fluctuation of Pointing V in this embodiment, and the dashed line shows an example of the fluctuation of Pointing V in the comparative example.

[0067] Therefore, according to this embodiment, fluctuations in Pointing V can be suppressed by suppressing the temperature gradient in the V direction of the magnifying optical system 14e without increasing costs.

[0068] 3. Modification of the First Embodiment Next, various modifications of the first embodiment will be described.

[0069] 3.1 First Modification According to the first embodiment, fluctuations in Pointing V can be suppressed, but the light intensity I out The symmetry in the V direction may be reduced.

[0070] 12 is a graph showing the V-directional dependence of various characteristics of the optical resonator according to the first embodiment. The graph shows the V-directional dependence of various characteristics of the optical resonator according to the first embodiment, which is a function of the temperature T of the magnifying optical system 14e, the light intensity I of the laser light Lb in the optical resonator, and the V-directional dependence of various characteristics of the optical resonator according to the first embodiment. in , the reflectance R of the output coupling mirror 15, and the light intensity I of the laser light Lb output from the output coupling mirror 15. out As described above, in the first embodiment, the V-direction dependency of the light intensity I out Asymmetry may occur in the

[0071] In this modification, the fluctuation of PointingV is suppressed and the light intensity I out suppresses the asymmetry of

[0072] The laser device 1a according to this modification has a light intensity I out The second embodiment is similar to the first embodiment except that the first reflectance R1 of the first partially reflective film 151a and the second reflectance R2 of the second partially reflective film 151b are determined so as to suppress the asymmetry.

[0073] In this modification, the first reflectance R1 and the second reflectance R2 are set to a value that is equal to the extraction efficiency E of the laser light Lb from the output coupling mirror 15. effect The extraction efficiency E is determined based on effect is an index that indicates how efficiently the output of the laser light Lb can be extracted as an optical resonator.

[0074] Extraction efficiency E effect The relationship between the reflectance R of the output coupling mirror 15 and the reflectance R of the output coupling mirror 15 is expressed by the following equation (2). Furthermore, the following equation (2) can be transformed into the following equation (3). Here, g0 is the small signal gain coefficient, α is the unsaturated absorption coefficient, L is the gain length, and I s is the saturation intensity.

[0075]

number

[0076]

number

[0077] According to the above formula (3), the extraction efficiency E effect The relationship between the reflectance R of the output coupling mirror 15 and the ratio g0 / α of the small signal gain coefficient g0 to the unsaturated absorption coefficient α and the product g0L of the small signal gain coefficient g0 and the gain length L is determined by the design value of the discharge length. The small signal gain coefficient g0 is determined by the gas pressure of the laser gas, the voltage applied to the discharge electrode 11a, and other factors. When the laser device 1a is an excimer laser device, the ratio g0 / α often takes a value within a range of 10 to 20, and the product g0L often takes a value within a range of 5 to 20.

[0078] Figure 13 shows the extraction efficiency E effect and the reflectance R of the output coupling mirror 15. Figure 14 shows the relationship between the extraction efficiency E effect and the reflectance R of the output coupling mirror 15. Figures 13 and 14 show three characteristic curves for g0L=5, g0L=10, and g0L=20, respectively.

[0079] In this modification, at a specific ratio g0 / α and product g0L, the extraction efficiency E effect Two different reflectivities R with equal reflectance are determined as the first reflectivity R1 and the second reflectivity R2. FIG. 13 shows a method for determining the first reflectivity R1 and the second reflectivity R2. First, one characteristic curve is selected, and the extraction efficiency E effect The reflectance R at which is maximized is called the reflectance R Emax Next, the reflectance R Emax The extraction efficiency E effect are approximately equal, and the two specified reflectances R are determined as the first reflectance R1 and the second reflectance R2.

[0080] As shown in Fig. 13, the characteristic curve corresponding to g0 / α=20 and g0L=5 is selected, and the extraction efficiency E effectWhen 53% is selected as the reflectivity R1, the first reflectivity R1 is approximately 10% and the second reflectivity R2 is approximately 40%. When g0 / α=20 and g0L=10, the first reflectivity R1 can be approximately 5% and the second reflectivity R2 can be approximately 20%. When g0 / α=20 and g0L=20, the first reflectivity R1 can be approximately 3% and the second reflectivity R2 can be approximately 10%. For example, the extraction efficiency E at the first reflectivity R1 is effect and the extraction efficiency E at the second reflectivity R2 effect may vary within a range of ±5%.

[0081] The operation of the laser device 1a according to this modification is the same as that of the first embodiment, except for the function of the output coupling mirror 15. In this modification, the output coupling mirror 15 has an extraction efficiency E effect The first reflectance R1 and the second reflectance R2 are determined so that the light intensity I out and the light intensity I of the laser light Lb transmitted through the second partially reflective film 151b and output from the output coupling mirror 15. out It is preferable to determine the first reflectance R1 and the second reflectance R2 so that the ratio between them falls within a range of 90% to 110%.

[0082] 15 is a graph showing the V-directional dependence of various characteristics of the optical resonator according to the first modification. The graph shows the V-directional dependence of various characteristics of the optical resonator according to the first modification. The V-directional dependence of various characteristics of the optical resonator is shown in FIG. 15 as a function of the temperature T of the magnifying optical system 14e, the light intensity I of the laser light Lb in the optical resonator, and the V-directional dependence of the temperature T of the magnifying optical system 14e. in , the reflectance R of the output coupling mirror 15, and the light intensity I of the laser light Lb output from the output coupling mirror 15. out As described above, according to this modification, the V-direction dependence of the light intensity I out That is, according to this modification, the asymmetry of the light intensity I is suppressed while the fluctuation of the PointingV is suppressed. out This can suppress the asymmetry.

[0083] 3.2 Second Modification In the first embodiment, the first partially reflective film 151a and the second partially reflective film 151b are formed so that the boundary B passes through the center C of the irradiation area A. In contrast, in this modified example, the first partially reflective film 151a and the second partially reflective film 151b are formed so that the boundary B passes through a position other than the center C of the irradiation area A.

[0084] 16 shows an example in which the first partial reflection film 151a and the second partial reflection film 151b are formed so that the boundary B passes through the +V direction side of the center C of the irradiation area A. Specifically, when the irradiation area A is divided into three in the V direction, the first partial reflection film 151a and the second partial reflection film 151b are formed so that the boundary B passes through the division point on the +V direction side of the center C.

[0085] 17 shows an example in which the first partial reflection film 151a and the second partial reflection film 151b are formed so that the boundary B passes through the −V direction side of the center C of the irradiation area A. Specifically, when the irradiation area A is divided into three in the V direction, the first partial reflection film 151a and the second partial reflection film 151b are formed so that the boundary B passes through the division point on the −V direction side of the center C.

[0086] Fig. 18 shows a schematic diagram of the V-directional dependence of various characteristics of an optical resonator when boundary B is set as shown in Fig. 16. Fig. 19 shows a schematic diagram of the V-directional dependence of various characteristics of an optical resonator when boundary B is set as shown in Fig. 17.

[0087] The position of boundary B is determined based on, for example, the amount of variation in Pointing V. Hereinafter, the position of boundary B will be referred to as the "boundary position." The amount of variation in Pointing V refers to the absolute value of the amount of variation in Pointing V when the laser device 1a is operated continuously for a certain period of time.

[0088] 20 is a schematic diagram showing an example of the relationship between the amount of variation in PointingV and the boundary position. As shown in FIG. 20, the amount of variation in PointingV is not necessarily smallest when the boundary position coincides with the center C of the irradiation area A. Therefore, it is preferable to determine in advance the boundary position at which the amount of variation in PointingV is smallest, and form the first partially reflective film 151a and the second partially reflective film 151b based on the determined boundary position. This can further suppress the variation in PointingV.

[0089] It should be noted that the present invention is not limited to either the first modified example or the second modified example, and both the first modified example and the second modified example may be applied to the first embodiment.

[0090] 4. Second embodiment Next, a laser device 1a according to a second embodiment of the present disclosure will be described. The laser device 1a according to this embodiment differs from the first embodiment only in the configuration of the output coupling mirror 15.

[0091] 4.1 Configuration 21 is a schematic diagram illustrating the configuration of an output coupling mirror 15 according to the second embodiment. The output coupling mirror 15 is shown in FIG. 21 as viewed from the Z direction, and the position dependence of the reflectance R of the output coupling mirror 15. In this embodiment, a partially reflective film 152 whose reflectance R changes continuously in the V direction is formed on the surface of the substrate 150 facing the window 10b. That is, the partially reflective film 152 forms a partially reflective film whose reflectance changes in the direction in which the bottom surface 31 and the top surface 32 face each other.

[0092] In this embodiment, it is estimated that a temperature gradient will occur during continuous operation of the laser device 1a, with the +V direction side of the magnifying optical system 14e being hotter and the −V direction side being colder. Based on this estimation, in this embodiment, the partially reflective film 152 is formed so that the reflectance R continuously increases at a constant rate of change toward the −V direction. Note that, if the estimated temperature gradient is reversed, the partially reflective film 152 is formed so that the reflectance R continuously increases at a constant rate of change toward the +V direction. In either case, the rate of change of the reflectance R does not need to be constant. It is sufficient that the partially reflective film 152 is formed so that the reflectance R continuously and monotonically increases toward the +V direction or the −V direction depending on the estimated temperature gradient.

[0093] 4.2 Operation The operation of the laser device 1a according to this embodiment is the same as that of the comparative example, except for the function of the output coupling mirror 15. FIG. 22 schematically shows the V-directional dependence of various characteristics of the optical resonator according to the second embodiment. As described above, by forming the partially reflective film 152 whose reflectance R changes continuously in accordance with the temperature gradient estimated in the magnifying optical system 14e, the light intensity I of the laser light Lb in the optical resonator can be reduced. in changes continuously in the V direction, thereby canceling the temperature gradient of the magnifying optical system 14e.

[0094] 4.3 Effects According to this embodiment, the temperature gradient of the magnifying optical system 14e is canceled out, and therefore the fluctuation of Pointing V can be almost completely eliminated, as shown in Fig. 23. In Fig. 23, the solid line shows an example of the fluctuation of Pointing V in this embodiment, and the dashed line shows an example of the fluctuation of Pointing V in the comparative example.

[0095] 5. Electronic Device Manufacturing Method 24 shows a schematic configuration example of exposure apparatus 100. Exposure apparatus 100 includes an illumination optical system 104 and a projection optical system 106. Illumination optical system 104 illuminates a reticle pattern of a reticle (not shown) placed on a reticle stage RT with laser light Lb incident from, for example, laser device 1a. Projection optical system 106 reduces and projects the laser light Lb 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.

[0096] Exposure apparatus 100 exposes a workpiece with laser light Lb reflecting a reticle pattern by synchronously translating reticle stage RT and 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.

[0097] The laser device 1a is not limited to being used for manufacturing electronic devices, but can also be used for laser processing such as drilling.

[0098] In the first and second embodiments, the laser device 1a is shown as a laser device having one laser chamber, but the laser device 1a may be a two-stage laser device having two laser chambers. In this case, the laser device 1a includes an oscillation-stage laser device and an amplification-stage laser device that amplifies the laser light emitted from the oscillation-stage laser, and is, for example, a MOPO (Master Oscillator Power Oscillator).

[0099] 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.

[0100] 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 laser device comprising a line narrowing module and an output coupling mirror, The narrowband module comprises: a prism including a transmission surface through which the laser light passes, a bottom surface in contact with the transmission surface, and an upper surface opposite to the bottom surface; a holder that holds the prism at the bottom surface; Including, The output coupling mirror is A partially reflective film whose reflectance changes in the direction in which the bottom surface and the top surface face each other. Including, Laser device.

2. 2. The laser device according to claim 1, the partially reflective film includes a first partially reflective film having a first reflectance and a second partially reflective film having a second reflectance; The first partially reflective film and the second partially reflective film are formed adjacent to each other in a first direction in which the bottom surface and the top surface face each other.

3. 3. The laser device according to claim 2, A boundary exists between the first partially reflective film and the second partially reflective film.

4. 4. The laser device according to claim 3, The boundary extends in a second direction perpendicular to the first direction.

5. 5. The laser device according to claim 4, The boundary passes through an irradiation area, which is an area on the output coupling mirror where the laser light is irradiated.

6. 6. The laser device according to claim 5, The boundary passes through the center of the illuminated area.

7. 7. The laser device according to claim 6, The boundary passes through the upper surface side of the center.

8. 7. The laser device according to claim 6, The boundary passes through the bottom surface side from the center.

9. 3. The laser device according to claim 2, the first partially reflective film is formed closer to the upper surface than the second partially reflective film, The first reflectance is less than the second reflectance.

10. 3. The laser device according to claim 2, The first reflectivity and the second reflectivity are determined so that the ratio between the light intensity of the laser light that passes through the first partially reflective film and is output from the output coupling mirror and the light intensity of the laser light that passes through the second partially reflective film and is output from the output coupling mirror is within a range of 90% to 110%.

11. 2. The laser device according to claim 1, The reflectance changes continuously in the direction from the top surface to the bottom surface.

12. 12. The laser device according to claim 11, The reflectance increases in a direction from the top surface to the bottom surface.

13. 2. The laser device according to claim 1, The direction in which the bottom surface and the top surface face each other corresponds to the discharge direction.

14. 2. The laser device according to claim 1, The line narrowing module includes an expansion optical system including at least one of the prisms, and a grating onto which the laser light whose beam width has been expanded by the expansion optical system is incident.

15. A method for manufacturing an electronic device, comprising: a line narrowing module and an output coupling mirror; The narrowband module comprises: a prism including a transmission surface through which the laser light passes, a bottom surface in contact with the transmission surface, and an upper surface opposite to the bottom surface; a holder that holds the prism at the bottom surface; Including, The output coupling mirror is A partially reflective film whose reflectance changes in the direction in which the bottom surface and the top surface face each other. Including, generating laser light by a laser device; outputting the laser light to an exposure device; exposing a photosensitive substrate to the laser light in the exposure apparatus to manufacture an electronic device; A method for manufacturing electronic devices.

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