Pulse stretcher and method for manufacturing electronic device

Abstract

This pulse expander comprises: a beam splitter for splitting a pulsed laser beam in two; a plurality of first concave mirrors that are arranged side by side in a prescribed direction; and a plurality of second concave mirrors that are arranged side by side in a prescribed direction, the second concave mirrors being equal in number to the first concave mirrors and individually facing the first concave mirrors. One pulsed laser beam that is split by the beam splitter proceeds toward any one first concave mirror among the plurality of first concave mirrors, is reflected alternately by the plurality of first concave mirrors and the plurality of second concave mirrors an even number of times equal to or greater than 12, and returns to the beam splitter. At each of a plurality of convergence points where at least parts of the one pulsed laser beam overlap each other in the beam waist of the one pulsed laser beam, the number of overlaps of the one pulsed laser beam is two.

Description

[Technical Field]

[0001] The present disclosure relates to a method for manufacturing a pulse stretcher and 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 of KrF excimer laser devices and ArF excimer laser devices is as wide as 350 pm 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 a 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] Summary of the specification of U.S. Patent No. 7,369,597

[0005] A pulse stretcher according to one aspect of the present disclosure includes a beam splitter that splits a pulsed laser beam into two beams, a plurality of first concave mirrors that are arranged side by side in a predetermined direction, and a plurality of second concave mirrors, the number of which is the same as the number of the first concave mirrors, that individually face the first concave mirrors and are arranged side by side in the predetermined direction, wherein one pulsed laser beam split by the beam splitter travels to any one of the plurality of first concave mirrors, is reflected alternately by the plurality of first concave mirrors and the plurality of second concave mirrors an even number of 12 or more times, and returns to the beam splitter, and at each of a plurality of focusing points where the one pulsed laser beams at least partially overlap with each other at the beam waist of the one pulsed laser beam, the number of overlaps of the one pulsed laser beam may be two.

[0006] A pulse stretcher according to one aspect of the present disclosure includes a beam splitter that splits a pulsed laser beam into two beams, a plurality of first concave mirrors that are arranged side by side in a predetermined direction, and a plurality of second concave mirrors, the number of which is the same as that of the first concave mirrors, that individually face the first concave mirrors and are arranged side by side in the predetermined direction, wherein one of the pulsed laser beams split by the beam splitter travels to any one of the plurality of first concave mirrors and is reflected alternately by the plurality of first concave mirrors and the plurality of second concave mirrors an even number of times, i.e., 12 or more, before returning to the beam splitter, and the first concave mirror or the second concave mirror may be shifted around an axis perpendicular to the predetermined direction so that the beam waists of the one pulsed laser beams are shifted from each other.

[0007] a gas laser apparatus including a gas laser device and a gas laser beam expander configured to expand the first pulsed laser beam at a plurality of focal points where the first pulsed laser beams at least partially overlap with each other at a beam waist of the gas laser device; a gas laser apparatus including a gas laser device and a gas laser beam expander configured to expand the first pulsed laser beam at a plurality of focal points where the first pulsed laser beams at least partially overlap with each other at a beam waist of the gas laser device; a gas laser apparatus including a gas laser device and a gas laser device configured to expand the gas laser beam at a plurality of focal points where the first pulsed laser beams at least partially overlap with each other at a beam waist of the gas laser device; a gas laser apparatus including a gas laser device and a gas laser device configured to expand the gas laser beam at a plurality of focal points where the first pulsed laser beams at least partially overlap with each other at a beam waist of the gas laser 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 schematic diagram showing an example of the overall configuration of an electronic device manufacturing apparatus. [Figure 2] FIG. 2 is a schematic diagram showing an example of the overall configuration of a gas laser device of a comparative example. [Figure 3] FIG. 3 is a diagram illustrating a schematic configuration example of a pulse stretcher of a comparative example. [Figure 4] FIG. 4 is a diagram showing the positions of reflection points 1 to 12 and the reflection directions of laser light in the pulse stretcher of the first embodiment. [Figure 5] FIG. 5 is a diagram showing the positions of reflection points 1 to 12 and the reflection directions of laser light in the pulse stretcher of the second embodiment. [Figure 6] FIG. 6 is a diagram showing the concave mirror, reflection points 1 to 12, and the reflection direction of the laser light shown in FIG. 5, viewed along a predetermined direction. [Figure 7]FIG. 7 is a diagram showing a schematic configuration example of a pulse stretcher according to the third embodiment, the positions of reflection points 1 to 12, and the reflection direction of laser light. [Figure 8] FIG. 8 is a diagram showing the concave mirror, reflection points 1 to 12, and the reflection direction of the laser light shown in FIG. 7, viewed along a predetermined direction. [Figure 9] FIG. 9 is a diagram showing the positions of reflection points 1 to 20 and the reflection directions of laser light in a pulse stretcher according to a modification of the third embodiment. [Figure 10] FIG. 10 is a schematic perspective view showing the positional relationship of reflection points 1 to 12 in the concave mirror of the fourth embodiment. [Figure 11] FIG. 11 is a diagram illustrating the position of the beam waist of the laser light according to the fourth embodiment. [Figure 12] FIG. 12 is a schematic perspective view showing the positional relationship of reflection points 1 to 12 in a concave mirror according to a first modification of the fourth embodiment. [Figure 13] FIG. 13 is a diagram illustrating the position of the beam waist of the laser beam in the first modification of the fourth embodiment. [Figure 14] FIG. 14 is a schematic perspective view showing the positional relationship of reflection points 1 to 12 in a concave mirror according to Modification 2 of Embodiment 4. In FIG. [Figure 15] FIG. 15 is a diagram illustrating the position of the beam waist of the laser beam in the second modification of the fourth embodiment. Embodiment

[0009] 1. Explanation of the electronic device manufacturing equipment used in the exposure process of electronic devices 2. Description of the gas laser device of the comparative example 2.1 Configuration 2.2 Operation 2.3 Challenges 3. Description of the Pulse Stretcher of Embodiment 1 3.1 Configuration 3.2 Operation 3.3 Actions and Effects 4. Description of the Pulse Stretcher of Embodiment 2 4.1 Configuration 4.2 Operation 4.3 Actions and Effects 5. Description of the pulse stretcher of embodiment 3 5.1 Configuration 5.2 Operation 5.3 Actions and Effects 6. Description of the pulse stretcher of embodiment 4 6.1 Configuration 6.2 Actions and Effects

[0010] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. The embodiments described below are examples of the present disclosure and are not intended to limit the scope of the present disclosure. Furthermore, not all of the configurations and operations described in each embodiment are necessarily essential to the configurations and operations of the present disclosure. Identical components are designated by the same reference numerals, and redundant descriptions will be omitted.

[0011] 1. Explanation of the electronic device manufacturing equipment used in the exposure process of electronic devices FIG. 1 is a schematic diagram showing an example of the overall configuration of an electronic device manufacturing apparatus used in an exposure process for electronic devices. As shown in FIG. 1, the manufacturing apparatus used in the exposure process includes a gas laser apparatus 100 and an exposure apparatus 200. The exposure apparatus 200 includes an illumination optical system 210, which includes multiple mirrors 211, 212, and 213, and a projection optical system 220. The illumination optical system 210 illuminates a reticle pattern on a reticle stage RT with laser light incident from the gas laser apparatus 100. The projection optical system 220 reduces and projects the laser light transmitted through the reticle onto a workpiece (not shown) placed on a workpiece table WT. The workpiece is a photosensitive substrate such as a semiconductor wafer coated with photoresist. The exposure apparatus 200 synchronously translates the reticle stage RT and the workpiece table WT to expose the workpiece with laser light reflecting the reticle pattern. Semiconductor devices, which are electronic devices, can be manufactured by transferring a device pattern onto a semiconductor wafer using the exposure process described above.

[0012] 2. Description of the gas laser device of the comparative example 2.1 Configuration A gas laser device as a comparative example will be described. Note that the comparative example in the present disclosure is a configuration that the applicant recognizes as being known only by the applicant, and is not a publicly known example that the applicant acknowledges.

[0013] FIG. 2 is a schematic diagram showing an example of the overall configuration of a gas laser apparatus 100 of a comparative example. The gas laser apparatus 100 is, for example, an ArF excimer laser apparatus that uses a mixed gas containing argon (Ar), fluorine (F), and neon (Ne). This gas laser apparatus 100 outputs laser light with a center wavelength of approximately 193 nm. Note that the gas laser apparatus 100 may be a gas laser apparatus other than an ArF excimer laser apparatus, such as a KrF excimer laser apparatus that uses a mixed gas containing krypton (Kr), F, and Ne. In this case, the gas laser apparatus 100 emits laser light with a center wavelength of approximately 248 nm. A mixed gas containing Ar, F, and Ne as a laser medium, or a mixed gas containing Kr, F, and Ne as a laser medium, is sometimes called a laser gas.

[0014] Gas laser device 100 mainly comprises a housing 110, a laser oscillator 130 arranged in the interior space of housing 110, a pulse stretcher 150, a monitor module 160, a shutter 170, and a laser processor 190.

[0015] The laser oscillator 130 includes a laser chamber 131, a charger 141, a pulse power module 143, a line narrowing module 145, and an output coupling mirror 147. Fig. 2 shows the internal configuration of the laser chamber 131 as viewed from a direction substantially perpendicular to the traveling direction of the laser light.

[0016] Laser chamber 131 includes an internal space where light is generated by excitation of the laser medium in the laser gas. The light travels to windows 139a and 139b, which will be described later. Laser gas is supplied to the internal space of laser chamber 131 from a laser gas supply source (not shown) through piping (not shown). The laser gas in laser chamber 131 is subjected to processing such as removal of F2 gas using a halogen filter, and is then exhausted to housing 110 through piping (not shown) by an exhaust pump (not shown).

[0017] In the internal space of the laser chamber 131, a pair of electrodes 133a and 133b are arranged facing each other, with their respective longitudinal directions aligned with the direction of light travel. The electrodes 133a and 133b are discharge electrodes for exciting the laser medium by glow discharge. In this example, the electrode 133a is a cathode, and the electrode 133b is an anode.

[0018] The electrode 133a is supported by an electrical insulator 135. The electrical insulator 135 closes an opening formed in the laser chamber 131. A conductive part (not shown) is embedded in the electrical insulator 135, and the conductive part applies a high voltage supplied from the pulse power module 143 to the electrode 133a. The electrode 133b is supported by a return plate 137, and the return plate 137 is connected to the inner surface of the laser chamber 131 by wiring (not shown).

[0019] Charger 141 is a DC power supply device that charges a charging capacitor (not shown) in pulse power module 143 with a predetermined voltage. Pulse power module 143 includes switch 143a controlled by laser processor 190. When switch 143a is turned from OFF to ON, pulse power module 143 generates a pulsed high voltage from the electrical energy held in charger 141 and applies this high voltage between electrode 133a and electrode 133b.

[0020] When a high voltage is applied between electrodes 133a and 133b, a discharge occurs between electrodes 133a and 133b. The energy of this discharge excites the laser medium in laser chamber 131, and the excited laser medium emits light when it transitions to the ground state.

[0021] The laser chamber 131 is provided with windows 139a and 139b. The window 139a is located at one end of the laser chamber 131 in the traveling direction of the laser light, and the window 139b is located at the other end in the traveling direction, and the windows 139a and 139b sandwich a space between the electrodes 133a and 133b. The windows 139a and 139b are inclined at a Brewster angle with respect to the traveling direction of the laser light so as to suppress reflection of P-polarized laser light. As described below, the oscillated laser light is emitted to the outside of the laser chamber 131 via the windows 139a and 139b. As described above, a pulsed high voltage is applied between the electrodes 133a and 133b by the pulse power module 143, and therefore the laser light is pulsed laser light.

[0022] The line narrowing module 145 includes a housing 145a, a prism 145b arranged in the internal space of the housing 145a, a grating 145c, and a rotation stage (not shown). An opening is formed in the housing 145a, and the housing 145a is connected to the rear side of the laser chamber 131 via the opening.

[0023] Prism 145b expands the beam width of light emitted from window 139a and makes the light incident on grating 145c. Prism 145b also reduces the beam width of light reflected from grating 145c and returns the light to the internal space of laser chamber 131 via window 139a. Prism 145b is supported on a rotation stage and rotates by the rotation stage. Rotation of prism 145b changes the angle of incidence of light with respect to grating 145c. Therefore, rotation of prism 145b makes it possible to select the wavelength of light returning from grating 145c to laser chamber 131 via prism 145b. While FIG. 2 shows an example in which one prism 145b is arranged, it is sufficient that at least one prism is arranged.

[0024] The surface of the grating 145c is made of a highly reflective material and has numerous grooves formed at regular intervals. The cross-sectional shape of each groove is, for example, a right-angled triangle. Light incident on the grating 145c from the prism 145b is reflected by these grooves and diffracted in a direction corresponding to the wavelength of the light. The grating 145c is Littrow-oriented so that the angle of incidence of the light incident on the grating 145c from the prism 145b matches the angle of diffraction of the diffracted light of the desired wavelength. This allows light near the desired wavelength to be returned to the laser chamber 131 via the prism 145b.

[0025] Output coupling mirror 147 is disposed in the internal space of optical path pipe 147a connected to the other end of laser chamber 131, and faces window 139b. Output coupling mirror 147 transmits a portion of the laser light emitted from window 139b toward pulse stretcher 150, and reflects the other portion back into the internal space of laser chamber 131 via window 139b. In this way, grating 145c and output coupling mirror 147 form a Fabry-Perot type laser resonator, and laser chamber 131 is disposed on the optical path of the laser resonator.

[0026] Pulse stretcher 150 is disposed between output coupling mirror 147 and monitor module 160 in the internal space of optical path tube 147a. Pulse stretcher 150 stretches the pulse width of the laser light from output coupling mirror 147, and emits the laser light with the stretched pulse width toward monitor module 160. FIG. 2 simply illustrates pulse stretcher 150, and the configuration of pulse stretcher 150 will be described later. Note that an amplifier may be disposed between pulse stretcher 150 and output coupling mirror 147 of laser oscillator 130, and the laser light emitted from output coupling mirror 147 may be amplified by the amplifier before traveling to pulse stretcher 150.

[0027] Monitor module 160 is disposed on the optical path of the laser light emitted from pulse stretcher 150. Monitor module 160 includes a housing 161, and a beam splitter 163 and an optical sensor 165 that are disposed in the internal space of housing 161. An opening is formed in housing 161, and the internal space of housing 161 communicates with the internal space of optical path pipe 147a through this opening.

[0028] Beam splitter 163 transmits a portion of the laser light emitted from pulse stretcher 150 toward shutter 170, and reflects another portion of the laser light toward the light-receiving surface of optical sensor 165. Optical sensor 165 measures the energy E of the laser light incident on the light-receiving surface. Optical sensor 165 outputs a signal indicating the measured energy E to laser processor 190.

[0029] The laser processor 190 of the present disclosure is a processing device including a storage device 190a storing a control program and a CPU (Central Processing Unit) 190b that executes the control program. The laser processor 190 is specially configured or programmed to execute various processes included in the present disclosure. The laser processor 190 also controls the entire gas laser apparatus 100.

[0030] The laser processor 190 transmits and receives various signals to and from the exposure processor 230 of the exposure apparatus 200. For example, the laser processor 190 receives signals indicating a light emission trigger Tr (described later) and a target energy Et from the exposure processor 230. The target energy Et is a target value for the energy of the laser light used in the exposure process. The laser processor 190 controls the charging voltage of the charger 141 based on the energy E and the target energy Et received from the optical sensor 165 and the exposure processor 230. The energy of the laser light is controlled by controlling this charging voltage. The laser processor 190 also transmits a command signal to the pulse power module 143 to turn on or off a switch 143a. The laser processor 190 is also electrically connected to the shutter 170 and controls the opening and closing of the shutter 170.

[0031] The laser processor 190 closes the shutter 170 until the difference ΔE between the energy E received from the monitor module 160 and the target energy Et received from the exposure processor 230 falls within an allowable range. When the difference ΔE falls within the allowable range, the laser processor 190 sends a reception ready signal to the exposure processor 230, notifying the exposure processor 230 that it is ready to receive the light emission trigger Tr. Upon receiving the reception ready signal, the exposure processor 230 sends a signal indicating the light emission trigger Tr to the laser processor 190, and upon receiving the signal indicating the light emission trigger Tr, the laser processor 190 opens the shutter 170. The light emission trigger Tr is defined by a predetermined repetition frequency f of the laser light and a predetermined pulse number P, and is a timing signal that the exposure processor 230 uses to cause the laser oscillator 130 to oscillate the laser, and is an external trigger. The repetition frequency f of the laser light is, for example, 1 kHz or more and 10 kHz or less.

[0032] The shutter 170 is disposed in the optical path of the laser light that has passed through the beam splitter 163 of the monitor module 160 and an opening formed in the housing 161 on the side opposite to the side to which the optical path pipe 147a is connected. The shutter 170 is disposed in the internal space of the optical path pipe 171. The optical path pipe 171 is connected to the housing 161 so as to surround the opening and is in communication with the housing 161. A purge gas is supplied to and filled in the internal spaces of the optical path pipe 171 and the optical path pipe 147a, as well as the internal spaces of the housing 161 and the housing 145a. The purge gas includes an inert gas such as nitrogen (N2). The purge gas is supplied from a purge gas supply source (not shown) through piping (not shown). The optical path pipe 171 is in communication with the exposure apparatus 200 through an opening in the housing 110 and an optical path pipe 500 that connects the housing 110 to the exposure apparatus 200. The laser light that has passed through the shutter 170 enters the exposure device 200 .

[0033] The exposure processor 230 of the present disclosure is a processing device including a storage device 230a that stores a control program and a CPU 230b that executes the control program. The exposure processor 230 is specially configured or programmed to execute the various processes included in the present disclosure. The exposure processor 230 also controls the entire exposure apparatus 200.

[0034] 3 is a diagram showing a schematic configuration example of a comparative example pulse stretcher 150. Pulse stretcher 150 includes a beam splitter 51, a first mirror unit 53a, and a second mirror unit 53b.

[0035] Beam splitter 51 is disposed on the optical path of the laser light that has passed through output coupling mirror 147. Beam splitter 51 splits the laser light that has entered beam splitter 51 into two beams, reflects one of the split laser beams toward first mirror unit 53a, and transmits the other laser beam toward beam splitter 163.

[0036] The first mirror unit 53a includes a plurality of first concave mirrors, and the second mirror unit 53b includes a plurality of second concave mirrors equal in number to the plurality of first concave mirrors. In Fig. 3, two concave mirrors 55a and 55b are shown as the first concave mirrors, and two concave mirrors 55c and 55d are shown as the second concave mirrors.

[0037] In mirror units 53a and 53b, concave mirrors 55a and 55b are arranged side by side in a predetermined direction, and concave mirrors 55c and 55d are also arranged side by side in the predetermined direction, i.e., the direction in which concave mirrors 55a and 55b are arranged. Concave mirror 55a is arranged on the opposite side of concave mirror 55d with respect to beam splitter 51 and faces concave mirror 55d. Concave mirror 55b faces concave mirror 55c. Therefore, concave mirrors 55a and 55b face concave mirrors 55c and 55d, respectively. Beam splitter 51 and concave mirrors 55a to 55d arranged in this manner constitute a delay optical path that extends the pulse width of the laser light.

[0038] 3, the reflection points of the laser light on concave mirrors 55a to 55d are shown as reflection points 1 to 12. In pulse stretcher 150, part of the laser light is reflected by beam splitter 51 and travels to concave mirror 55a, is alternately reflected by the first concave mirror and the second concave mirror, travels through reflection points 1 to 12 in this order, and returns to beam splitter 51 after passing through reflection point 12.

[0039] Reflection points 1, 3, 7, and 9 are located on concave mirror 55a, reflection points 5 and 11 are located on concave mirror 55b, reflection points 2 and 8 are located on concave mirror 55c, and reflection points 4, 6, 10, and 12 are located on concave mirror 55d.

[0040] On concave mirror 55a, reflection point 1 is located at the same position as reflection point 9, reflection point 3 is located at the same position as reflection point 7, and reflection points 1 and 9 are shifted in a predetermined direction from reflection points 3 and 7 and are farther from concave mirror 55b than reflection points 3 and 7. On concave mirror 55b, reflection point 5 is shifted in a predetermined direction from reflection point 11 and is closer to concave mirror 55a than reflection point 11. On concave mirror 55c, reflection point 2 is shifted in a predetermined direction from reflection point 8 and is farther from concave mirror 55d than reflection point 8. Furthermore, on concave mirror 55d, reflection point 4 is located at the same position as reflection point 12, reflection point 6 is located at the same position as reflection point 10, and reflection points 4 and 12 are shifted in a predetermined direction from reflection points 6 and 10 and are farther from concave mirror 55c than reflection points 6 and 10.

[0041] On concave mirrors 55a and 55d, reflection points 1 and 9 face reflection points 4 and 12, and reflection points 3 and 7 face reflection points 6 and 10. On concave mirrors 55b and 55c, reflection point 5 faces reflection point 8, and reflection point 11 faces reflection point 2.

[0042] Pulse stretcher 150 causes the laser light to travel within pulse stretcher 150, with one cycle being the laser light traveling from beam splitter 51 through reflection points 1 to 12 in order and returning to beam splitter 51. Beam splitter 51 reflects a portion of the laser light reflected at reflection point 12 of concave mirror 55d toward beam splitter 163, and transmits another portion of the laser light toward reflection point 1 of concave mirror 55a. In this way, in pulse stretcher 150, the laser light is alternately reflected 12 times by concave mirrors 55a to 55d during one cycle, making one or more revolutions around pulse stretcher 150.

[0043] 2.2 Operation Next, the operation of the gas laser device 100 of the comparative example will be described.

[0044] Before gas laser device 100 emits laser light, the internal spaces of optical path pipes 147a, 171, and 500 and housings 145a and 161 are filled with purge gas from a purge gas supply source (not shown). Laser gas is also supplied to the internal space of laser chamber 131 from a laser gas supply source (not shown).

[0045] When the gas laser apparatus 100 emits laser light, the laser processor 190 receives a signal indicating the target energy Et and a signal indicating the light emission trigger Tr from the exposure processor 230. Upon receiving the signal indicating the target energy Et and the signal indicating the light emission trigger Tr, the laser processor 190 closes the shutter 170 and drives the charger 141. The laser processor 190 also turns on the switch 143a of the pulse power module 143. This causes the pulse power module 143 to apply a pulsed high voltage between the electrodes 133a and 133b from the electrical energy stored in the charger 141. This high voltage causes a discharge between the electrodes 133a and 133b, and the laser medium contained in the laser gas between the electrodes 133a and 133b is excited, emitting light when the laser medium returns to its ground state. This light resonates between grating 145c and output coupling mirror 147, and the light is amplified, causing laser oscillation, every time it passes through a discharge space in the internal space of laser chamber 131. A portion of the laser light then passes through output coupling mirror 147 as pulsed laser light and travels to pulse stretcher 150.

[0046] Beam splitter 51 of pulse stretcher 150 transmits a portion of the laser light that has passed through output coupling mirror 147 toward beam splitter 163, and reflects the other portion of the laser light toward concave mirror 55a. The laser light that travels to concave mirror 55a is alternately reflected by the first concave mirror and the second concave mirror, and travels through reflection points 1 to 12 in order. The laser light then travels from reflection point 12 to beam splitter 51 and makes one circuit through pulse stretcher 150. The portion of the laser light that travels to beam splitter 51 is reflected by beam splitter 51 toward beam splitter 163 and is emitted from pulse stretcher 150. The other portion of the laser light transmits through beam splitter 51 and travels again toward reflection point 1 of concave mirror 55a, entering a second cycle.

[0047] The laser light that has made one circuit through pulse stretcher 150 and is output from pulse stretcher 150 is delayed by a predetermined delay time compared to the laser light that has passed through beam splitter 51 and output from pulse stretcher 150 without traveling to concave mirror 55a. Furthermore, the laser light that has made two circuits through pulse stretcher 150 and is output from pulse stretcher 150 is delayed by a predetermined delay time compared to the laser light that has made one circuit through pulse stretcher 150 and is output from pulse stretcher 150. The intensity of the laser light decreases as the number of circuits through pulse stretcher 150 increases. When the laser light repeatedly circulates in pulse stretcher 150, the laser light that is output later from pulse stretcher 150 overlaps with part of the laser light that was output from pulse stretcher 150 earlier than the laser light. As a result, the laser light whose pulse width has been expanded to a predetermined pulse width proceeds to the beam splitter 163 .

[0048] A portion of the laser light that has traveled to the beam splitter 163 is reflected by the beam splitter 163 and received by the optical sensor 165. The optical sensor 165 measures the energy E of the received laser light and outputs a signal indicating the energy E to the laser processor 190. The laser processor 190 controls the charging voltage so that the difference ΔE between the energy E and the target energy Et falls within an allowable range, and after the difference ΔE falls within the allowable range, it sends a reception preparation completion signal to the exposure processor 230 indicating that preparation for receiving the light emission trigger Tr has been completed.

[0049] When the exposure processor 230 receives the ready-to-receive signal, it transmits a light emission trigger Tr to the laser processor 190. When the laser processor 190 opens the shutter 170 in synchronization with the reception of the light emission trigger Tr, the laser light that has passed through the shutter 170 enters the exposure device 200. This laser light is, for example, a pulsed laser light with a center wavelength of 193 nm.

[0050] 2.3 Challenges In the pulse stretcher 150 of the comparative example, the pulsed laser beams traveling from the concave mirrors 55c and 55d to the concave mirrors 55a and 55b are parallel beams, whereas the pulsed laser beams traveling from the concave mirrors 55a and 55b to the concave mirrors 55c and 55d are focused beams that are focused during their travel. Among the focused beams, the pulsed laser beams traveling from reflection point 1 to reflection point 2, from reflection point 5 to reflection point 6, from reflection point 7 to reflection point 8, and from reflection point 11 to reflection point 12 will be described. In the pulse stretcher 150 of the comparative example, a focus point 301 is formed at the beam waist of each of these pulsed laser beams, where the pulsed laser beams at least partially overlap each other. The focus point 301 is located between the first mirror unit 53a and the second mirror unit 53b. Furthermore, a focus point 303 is also formed for the pulsed laser beams traveling from reflection point 3 to reflection point 4 and from reflection point 9 to reflection point 10. Thus, in the pulse stretcher 150 of the comparative example, two focusing points 301 and 303 are formed, with the number of overlaps of the pulsed laser beams at four and two, respectively. By forming the focusing points 301 and 303, even if there is a deviation in the pulsed laser beam incident on the pulse stretcher 150 or a deviation in the alignment of the concave mirrors 55a to 55d, changes in the characteristics of the pulsed laser beam emitted from the gas laser apparatus 100 are suppressed. One example of such a change in characteristics is a deviation in the pointing, which is the direction of propagation of the pulsed laser beam.

[0051] The more times the pulsed laser beam is reflected by the concave mirrors 55a to 55d, the more overlapping the pulsed laser beam is at each focal point. The more overlapping the pulsed laser beam, the higher the energy density of the pulsed laser beam at the focal point, and the more energy of the pulsed laser beam is absorbed by oxygen. This can cause a temperature rise near the focal point of the pulse stretcher 150, and plasma can be generated due to the temperature rise. The temperature rise and plasma generation can cause a refractive index distribution in the pulse stretcher 150, distorting the wavefront of the pulsed laser beam. Wavefront distortion can cause pointing deviation, resulting in vignetting of the pulsed laser beam in one of the optical systems in the exposure apparatus 200 and fluctuations in the energy of the pulsed laser beam. Energy fluctuations can reduce the processing accuracy of the workpiece in the exposure apparatus 200. In other words, the exposure apparatus 200 may not emit a pulsed laser beam that meets the required performance, which can lead to concerns about a reduction in the reliability of the gas laser apparatus 100.

[0052] Therefore, in the following embodiment, a pulse stretcher 150 that can suppress a decrease in the reliability of the gas laser device 100 will be exemplified.

[0053] 3. Description of the Pulse Stretcher of Embodiment 1 Next, a description will be given of the pulse stretcher 150 of the first embodiment. Note that the same components as those described above are given the same reference numerals, and redundant description will be omitted unless otherwise specified.

[0054] 3.1 Configuration

[0055] FIG. 4 is a diagram showing the positions of reflection points 1 to 12 and the reflection directions of pulsed laser light in the pulse stretcher 150 of this embodiment.

[0056] In the pulse stretcher 150 of this embodiment, three focusing points 401, 403, and 405 are formed, and two or more of the concave mirrors 55a to 55d are shifted around an axis perpendicular to a predetermined direction compared to the comparative example so that the number of overlapping pulsed laser beams is two at each of the focusing points 401, 403, and 405. In the pulse stretcher 150 of this embodiment, an example is shown in which the concave mirrors 55a to 55c are shifted, and due to this shift, the positions of the reflection points 1 to 12 in the pulse stretcher 150 and the reflection direction of the pulsed laser beam change from those in the comparative example. In FIG. 4, the shifting of the concave mirrors 55a to 55c is omitted to avoid complicating the drawing.

[0057] In this embodiment, reflection points 1 and 7 are located on concave mirror 55a, reflection points 3, 5, 9 and 11 on concave mirror 55b, reflection points 4 and 10 on concave mirror 55c, and reflection points 2, 6, 8 and 12 on concave mirror 55d.

[0058] On concave mirror 55a, reflection point 1 is shifted in a predetermined direction from reflection point 7 and is farther from concave mirror 55b than reflection point 7. On concave mirror 55b, reflection point 3 is located at the same position as reflection point 11, reflection point 5 is located at the same position as reflection point 9, and reflection points 3 and 11 are shifted in a predetermined direction from reflection points 5 and 9 and are farther from concave mirror 55a than reflection points 5 and 9. On concave mirror 55c, reflection point 4 is shifted in a predetermined direction from reflection point 10 and is closer to concave mirror 55d than reflection point 10. Furthermore, on concave mirror 55d, reflection point 2 is located at the same position as reflection point 6, reflection point 8 is located at the same position as reflection point 12, and reflection points 2 and 6 are shifted in a predetermined direction from reflection points 8 and 12 and are closer to concave mirror 55c than reflection points 8 and 12.

[0059] On concave mirrors 55a and 55d, reflection point 1 faces reflection points 8 and 12, and reflection point 7 faces reflection points 2 and 6. On concave mirrors 55b and 55c, reflection points 5 and 9 face reflection point 4, and reflection points 3 and 11 face reflection point 10. When viewing concave mirrors 55a and 55b from the front, reflection points 1, 3, 5, 7, 9, and 11 of concave mirrors 55a and 55b are located on a line passing through the centers of concave mirrors 55a and 55b, respectively. When viewing concave mirrors 55c and 55d from the front, reflection points 2, 4, 6, 8, 10, and 12 of concave mirrors 55c and 55d are located on a line passing through the centers of concave mirrors 55c and 55d, respectively. Reflection points 1 to 12 are located offset from the centers of concave mirrors 55a to 55d where reflection points 1 to 12 are located. In the concave mirrors 55a to 55d of this embodiment, the same plane passes through the reflection points 1 to 12.

[0060] In pulse stretcher 150 of this embodiment, during one period, concave mirrors 55a and 55c, which are one of the first and second concave mirrors, reflect the pulsed laser beam once at two reflection points on each mirror. Also, during one period, concave mirrors 55b and 55d, which are the other of the first and second concave mirrors, reflect the pulsed laser beam twice at two reflection points on each mirror. In pulse stretcher 150 of this embodiment, the pulsed laser beam is alternately reflected by concave mirrors 55a to 55d 12 times and returned to beam splitter 51, but may be alternately reflected an even number of times greater than 12 times and returned to beam splitter 51.

[0061] In pulse stretcher 150 of this embodiment, each of concave mirrors 55a to 55d has the same radius of curvature R and the same diameter D. The distance between concave mirrors 55a and 55d facing each other and the distance between concave mirrors 55b and 55c facing each other are distance L. R=L and L>>D.

[0062] 3.2 Operation Next, the operation of the pulse stretcher 150 in this embodiment will be described.

[0063] As in the comparative example, a portion of the pulsed laser beam travels from beam splitter 51 to concave mirror 55a and is alternately reflected by the first and second concave mirrors. As described above, at the first and second concave mirrors, reflection point 1 is located on a line passing through the centers of concave mirrors 55a and 55b and is shifted from the center of concave mirror 55a, so the pulsed laser beam travels through reflection points 1 to 12 in order. As described above, the same plane passes through reflection points 1 to 12, so the pulsed laser beam travels along the plane passing through reflection points 1 to 12. The pulsed laser beam then returns from reflection point 12 to beam splitter 51 and makes one circuit through pulse stretcher 150.

[0064] In the pulse stretcher 150 of this embodiment, at least a portion of the pulsed laser beams overlap at their respective beam waists, namely, the pulsed laser beam traveling from reflection point 1 to reflection point 2 and the pulsed laser beam traveling from reflection point 7 to reflection point 8, and a focal point 401 is formed by the overlap. Furthermore, at least a portion of the pulsed laser beams overlap at their respective beam waists, namely, the pulsed laser beam traveling from reflection point 3 to reflection point 4 and the pulsed laser beam traveling from reflection point 9 to reflection point 10, and a focal point 403 is formed by the overlap. Furthermore, at least a portion of the pulsed laser beams overlap at their respective beam waists, namely, the pulsed laser beam traveling from reflection point 5 to reflection point 6 and the pulsed laser beam traveling from reflection point 11 to reflection point 12, and a focal point 403 is formed by the overlap. Therefore, in the pulse stretcher 150 of this embodiment, three focal points 401, 403, and 405 are formed, and the number of overlaps of the pulsed laser beams at each of the focal points 401, 403, and 405 is two. Since the same plane passes through reflection points 1 to 12, the same plane passes through condensing points 401, 403, and 405.

[0065] 3.3 Actions and Effects In the pulse stretcher 150 of this embodiment, the number of overlapping pulsed laser beams at each of the focusing points 401, 403, and 405 is two.

[0066] According to the above configuration, the energy density of the pulsed laser beam at the focal point is lower than at focal point 301 where the number of overlapping pulsed laser beams is four, and the energy of the pulsed laser beam absorbed by oxygen is reduced. This suppresses temperature rise and plasma generation near the focal point of pulse stretcher 150. Suppressing these suppresses the generation of refractive index distribution in pulse stretcher 150, and can suppress distortion of the wavefront of the pulsed laser beam. Therefore, exposure apparatus 200 can emit pulsed laser beam that satisfies the required performance, and a decrease in the reliability of gas laser apparatus 100 can be suppressed.

[0067] 4. Description of the Pulse Stretcher of Embodiment 2 Next, a description will be given of the configuration of the pulse stretcher 150 of embodiment 2. Note that the same components as those described above are given the same reference numerals, and redundant description will be omitted unless otherwise specified.

[0068] 4.1 Configuration Fig. 5 is a diagram showing the positions of reflection points 1 to 12 and the reflection direction of pulsed laser light in pulse stretcher 150 of this embodiment. For ease of viewing, Fig. 5 does not show beam splitter 51, the pulsed laser light traveling from output coupling mirror 147 to beam splitter 51, and the pulsed laser light traveling from beam splitter 51 to beam splitter 163. In pulse stretcher 150 of this embodiment, the positions of reflection points 1 to 12 in pulse stretcher 150 and the reflection direction of pulsed laser light are different from those in embodiment 1.

[0069] In this embodiment, reflection points 1, 5, 7, and 11 are located on concave mirror 55a, reflection points 3 and 9 on concave mirror 55b, reflection points 2, 4, 8, and 10 on concave mirror 55c, and reflection points 6 and 12 on concave mirror 55d.

[0070] On concave mirror 55a, reflection point 1 is located at the same position as reflection point 5, and reflection point 7 is located at the same position as reflection point 11. Furthermore, reflection points 1 and 5 are shifted from reflection points 7 and 11 in a direction perpendicular to a predetermined direction, and are further separated from concave mirror 55b by the same distance as reflection points 7 and 11.

[0071] On concave mirror 55b, reflection point 3 is shifted from reflection point 9 in a direction perpendicular to the predetermined direction, and is further separated from concave mirror 55a by the same distance as reflection point 9.

[0072] On concave mirror 55c, reflection point 2 is located at the same position as reflection point 10, and reflection point 4 is located at the same position as reflection point 8. Furthermore, reflection points 2 and 10 are shifted in a direction perpendicular to the predetermined direction from reflection points 4 and 8, and are further separated from concave mirror 55d by the same distance as reflection points 4 and 8.

[0073] In concave mirror 55d, reflection point 6 is shifted from reflection point 12 in a direction perpendicular to the predetermined direction, and is further separated from concave mirror 55c by the same distance as reflection point 12.

[0074] On concave mirrors 55a and 55d, reflection points 1 and 5 face reflection point 12, and reflection points 7 and 11 face reflection point 6. On concave mirrors 55b and 55c, reflection point 9 faces reflection points 4 and 8, and reflection point 3 faces reflection points 2 and 10. When viewing concave mirrors 55a and 55b from the front, reflection points 1, 3, 5, 7, 9, and 11 of concave mirrors 55a and 55b are shifted in a direction perpendicular to the predetermined direction from a line passing through the centers of concave mirrors 55a and 55b. When viewing concave mirrors 55c and 55d from the front, reflection points 2, 4, 6, 8, 10, and 12 of concave mirrors 55c and 55d are shifted in a direction perpendicular to the predetermined direction from a line passing through the centers of concave mirrors 55c and 55d. Reflection points 1 to 12 are located offset from the centers of the concave mirrors on which they are located. The same plane passes through reflection points 1, 5, 7, and 11 of concave mirror 55a and reflection points 6 and 12 of concave mirror 55d, and the same plane passes through reflection points 3 and 9 of concave mirror 55b and reflection points 2, 4, 8, and 10 of concave mirror 55c. When concave mirrors 55a and 55b are viewed along a predetermined direction, reflection points 1, 5, and 9 overlap with each other, and reflection points 3, 7, and 11 overlap with each other. Furthermore, on concave mirrors 55c and 55d, reflection points 2, 6, and 10 overlap with each other, and reflection points 4, 8, and 12 overlap with each other.

[0075] In this embodiment as well, the pulsed laser beam is alternately reflected by the first concave mirror and the second concave mirror during one period, and travels through reflection points 1 to 12 in order. Therefore, in the pulse stretcher 150 of this embodiment, the first and second concave mirrors (concave mirrors 55b and 55d) on one side reflect the pulsed laser beam once each at two reflection points during one period. Furthermore, the other first and second concave mirrors (concave mirrors 55a and 55c) reflect the pulsed laser beam twice each at two reflection points during one period. Furthermore, as described above, the reflection points of the concave mirrors 55a to 55d are shifted in a direction perpendicular to the predetermined direction.

[0076] 4.2 Operation Next, the operation of the pulse stretcher 150 in this embodiment will be described.

[0077] As with the pulse stretcher 150 of the first embodiment, a portion of the pulsed laser beam travels from the beam splitter 51 to the concave mirror 55a and is alternately reflected by the first and second concave mirrors. As described above, the reflection point 1 is positioned at a position offset in a direction perpendicular to a predetermined direction from a line passing through the centers of the concave mirrors 55a and 55b. Therefore, the pulsed laser beam travels through the reflection points 1 to 12 in order. Then, the pulsed laser beam returns from the reflection point 12 to the beam splitter 51 and makes one circuit through the pulse stretcher 150.

[0078] In the pulse stretcher 150 of this embodiment, similarly to the pulse stretcher 150 of the first embodiment, three focusing points 401, 403, and 405 are formed, and the number of overlapping pulsed laser beams at each of the focusing points 401, 403, and 405 is two. Unlike the first embodiment, the plane passing through the reflection points 1, 7, 2, and 8, the plane passing through the reflection points 9, 3, 10, and 4, and the plane passing through the reflection points 5, 11, 6, and 12 are arranged to be shifted in a predetermined direction. Therefore, the focusing points 401, 403, and 405 are located at different positions in the predetermined direction.

[0079] 6 is a diagram showing concave mirrors 55a to 55d, reflection points 1 to 12, and the reflection direction of pulsed laser light shown in FIG. 5, viewed along a predetermined direction. When first mirror unit 53a and second mirror unit 53b are viewed along the predetermined direction, there are two optical paths of pulsed laser light passing through focal points 401, 403, and 405. The pulsed laser light passing through focal points 401, 403, and 405 intersects with a plane where the centers of concave mirrors 55a to 55d overlap, while the pulsed laser light that does not pass through focal points 401, 403, and 405 travels along this plane. Furthermore, focal points 401, 403, and 405 overlap with each other. Note that at least a portion of some focal points may overlap with other focal points.

[0080] 4.3 Actions and Effects In the pulse stretcher 150 of this embodiment, the number of overlapping pulsed laser beams is also two at each of the focusing points 401, 403, and 405. Therefore, the exposure apparatus 200 can emit a pulsed laser beam that satisfies the required performance, and a decrease in the reliability of the gas laser apparatus 100 can be suppressed.

[0081] 5. Description of the pulse stretcher of embodiment 3 Next, a description will be given of the configuration of the pulse stretcher 150 of embodiment 3. Note that the same components as those described above are given the same reference numerals, and redundant description will be omitted unless otherwise specified.

[0082] 5.1 Configuration 7 is a diagram showing a schematic configuration example of the pulse stretcher 150 of this embodiment, the positions of reflection points 1 to 12, and the reflection direction of the pulse laser beam. For ease of viewing, FIG. 7 omits the illustration of the beam splitter 51, the pulse laser beam traveling from the output coupling mirror 147 to the beam splitter 51, and the pulse laser beam traveling from the beam splitter 51 to the beam splitter 163. In the pulse stretcher 150 of this embodiment, the first mirror unit 53a of the second embodiment is further provided with a concave mirror 55e as a first concave mirror, and the second mirror unit 53b is further provided with a concave mirror 55f as a second concave mirror. Therefore, the pulse stretcher 150 of this embodiment differs from the pulse stretcher 150 of the second embodiment in that each of the first mirror unit 53a and the second mirror unit 53b has three concave mirrors.

[0083] In the first mirror unit 53a, concave mirrors 55a, 55b, and 55e are arranged in this order in a predetermined direction, and in the second mirror unit 53b, concave mirrors 55d, 55c, and 55f are arranged in this order in a predetermined direction, with concave mirror 55f facing concave mirror 55e. The positions of reflection points 1 to 12 and the reflection direction of the pulsed laser beam change according to the arrangement of concave mirrors 55e and 55f.

[0084] In pulse stretcher 150 of this embodiment, the positions of reflection points 5 and 11 are changed to concave mirror 55e, and the positions of reflection points 4 and 10 are changed to concave mirror 55f. The other reflection points 1 to 3, 6 to 9, and 12 are located at the same positions as in the second embodiment.

[0085] In concave mirror 55e, reflection point 5 is shifted from reflection point 11 in a direction perpendicular to the predetermined direction, and is further separated from concave mirror 55b by the same distance as reflection point 11. In addition, in concave mirror 55f, reflection point 4 is shifted from reflection point 10 in a direction perpendicular to the predetermined direction, and is further separated from concave mirror 55c by the same distance as reflection point 10.

[0086] On concave mirrors 55e and 55f, reflection point 5 faces reflection point 4, and reflection point 11 faces reflection point 10. The same plane passes through reflection points 5 and 11 of concave mirror 55e and 4 and 10 of concave mirror 55f.

[0087] In this embodiment as well, the pulsed laser beam is alternately reflected by the first concave mirror and the second concave mirror during one period, and travels through reflection points 1 to 12 in order. Therefore, in the pulse stretcher 150 of this embodiment, the concave mirrors 55a to 55f each reflect the pulsed laser beam once at two reflection points during one period. Furthermore, as described above, the reflection points on the concave mirrors 55a to 55f are shifted in a direction perpendicular to the predetermined direction.

[0088] 5.2 Operation The operation of the pulse stretcher 150 in this embodiment is the same as that in the second embodiment, except that the pulsed laser beam is reflected at reflection points 4, 5, 10, and 11 of the concave mirrors 55e and 55f and is reflected once at two reflection points on each of the concave mirrors 55a to 55f during one period. Therefore, in the pulse stretcher 150 in this embodiment, as in the pulse stretcher 150 in the second embodiment, three focusing points 401, 403, and 405 are formed, and the number of overlapping pulsed laser beams at each of the focusing points 401, 403, and 405 is two. Also, as in the pulse stretcher 150 in the second embodiment, the focusing points 401, 403, and 405 are located at different positions in a predetermined direction.

[0089] 8 is a diagram showing concave mirrors 55a to 55f, reflection points 1 to 12, and the reflection direction of pulsed laser light shown in FIG. 7 as viewed along a predetermined direction. As in the second embodiment, when first mirror unit 53a and second mirror unit 53b are viewed along the predetermined direction, there are two optical paths of pulsed laser light passing through focal points 401, 403, and 405. Furthermore, focal points 401, 403, and 405 overlap with one another. Note that at least a portion of some focal points may overlap with other focal points.

[0090] 5.3 Actions and Effects In the pulse stretcher 150 of this embodiment, the first mirror unit 53a and the second mirror unit 53b each have three concave mirrors, and each of the concave mirrors 55a to 55f reflects the pulsed laser beam once at two reflection points during one period.

[0091] With the above configuration, the reflection points are dispersed, so that heat concentration at the reflection points and the temperature rise of concave mirrors 55a-55f due to the heat concentration can be suppressed. Suppressing the temperature rise can suppress deformation of concave mirrors 55a-55f, and distortion of the wavefront of the pulsed laser beam due to the deformation can be suppressed. Therefore, exposure device 200 can emit pulsed laser beams that satisfy the required performance, and a decrease in the reliability of gas laser device 100 can be suppressed.

[0092] Next, a modification of this embodiment will be described. Fig. 9 is a diagram showing the positions of reflection points 1 to 20 and the reflection direction of a pulse laser beam in a pulse stretcher 150 of this modification. For ease of viewing, Fig. 9 does not show the beam splitter 51, the pulse laser beam traveling from the output coupling mirror 147 to the beam splitter 51, and the pulse laser beam traveling from the beam splitter 51 to the beam splitter 163. The pulse stretcher 150 of this modification differs from the pulse stretcher 150 of the third embodiment in that the pulse laser beam is reflected 20 times by concave mirrors 55a to 55f during one period. Therefore, the pulse stretcher 150 of this modification is provided with reflection points 1 to 20, and the pulse laser beam is alternately reflected by the first concave mirror and the second concave mirror and travels through the reflection points 1 to 20 in order.

[0093] In this modification, concave mirror 55a has reflection points 1, 9, 11, and 19, concave mirror 55b has reflection points 3, 7, 13, and 17, and concave mirror 55e has reflection points 5 and 15. Furthermore, concave mirror 55f has reflection points 4, 6, 14, and 16, concave mirror 55c has reflection points 2, 8, 12, and 18, and concave mirror 55d has reflection points 10 and 20.

[0094] On concave mirror 55a, reflection point 1 is located at the same position as reflection point 9, and reflection point 11 is located at the same position as reflection point 19. Furthermore, reflection points 1 and 9 are shifted from reflection points 11 and 19 in a direction perpendicular to a predetermined direction, and are the same distance from concave mirror 55b as reflection points 11 and 19.

[0095] On concave mirror 55b, reflection point 3 is located at the same position as reflection point 7, and reflection point 13 is located at the same position as reflection point 17. Furthermore, reflection points 3 and 7 are shifted from reflection points 13 and 17 in a direction perpendicular to a predetermined direction, and are further separated from concave mirrors 55a and 55e by the same distance as reflection points 11 and 19.

[0096] In the concave mirror 55e, the reflection point 5 is shifted from the reflection point 15 in a direction perpendicular to the predetermined direction, and is the same distance away from the concave mirror 55b as the reflection point 15.

[0097] On concave mirror 55f, reflection point 4 is located at the same position as reflection point 16, and reflection point 6 is located at the same position as reflection point 14. Furthermore, reflection points 4 and 16 are shifted from reflection points 6 and 14 in a direction perpendicular to a predetermined direction, and are further separated from concave mirror 55c by the same distance as reflection points 6 and 14.

[0098] On concave mirror 55c, reflection point 2 is located at the same position as reflection point 18, and reflection point 8 is located at the same position as reflection point 12. Furthermore, reflection points 2 and 18 are shifted from reflection points 8 and 12 in a direction perpendicular to a predetermined direction, and are the same distance away from concave mirrors 55d and 55f as reflection points 8 and 12.

[0099] In concave mirror 55d, reflection point 10 is shifted from reflection point 20 in a direction perpendicular to the predetermined direction, and is the same distance away from concave mirror 55c as reflection point 20.

[0100] On concave mirrors 55a and 55d, reflection points 1 and 9 face reflection point 20, and reflection points 11 and 19 face reflection point 10. On concave mirrors 55b and 55c, reflection points 13 and 17 face reflection points 8 and 12, and reflection points 3 and 7 face reflection points 2 and 18. On concave mirrors 55e and 55f, reflection point 5 faces reflection points 4 and 16, and reflection point 15 faces reflection points 6 and 14. The same plane passes through reflection points 1, 9, 11, and 19 on concave mirror 55a and reflection points 10 and 20 on concave mirror 55d. Furthermore, the same plane passes through reflection points 3, 7, 13, and 17 of concave mirror 55b and reflection points 2, 8, 12, and 18 of concave mirror 55c, and the same plane passes through reflection points 5 and 15 of concave mirror 55e and reflection points 4, 6, 14, and 16 of concave mirror 55f. When concave mirrors 55a, 55b, and 55e are viewed along a predetermined direction, reflection points 1, 5, 9, 13, and 17 overlap with each other on concave mirrors 55a, 55b, and 55e, and reflection points 3, 7, 11, 15, and 19 overlap with each other on concave mirrors 55c, 55d, and 55f. Furthermore, reflection points 2, 6, 10, 14, and 18 overlap with each other, and reflection points 4, 8, 12, 16, and 20 overlap with each other on concave mirrors 55c, 55d, and 55f.

[0101] In pulse stretcher 150 of this modified example, at least a portion of the pulsed laser beam in the beam waist of the pulsed laser beam traveling from reflection point 1 to reflection point 2 and a portion of the pulsed laser beam traveling from reflection point 11 to reflection point 12 overlap with each other, forming a focal point 411. Furthermore, at least a portion of the pulsed laser beam in the beam waist of the pulsed laser beam traveling from reflection point 3 to reflection point 4 and a portion of the pulsed laser beam traveling from reflection point 13 to reflection point 14 overlap with each other, forming a focal point 413. Furthermore, at least a portion of the pulsed laser beam in the beam waist of the pulsed laser beam traveling from reflection point 5 to reflection point 6 and a portion of the pulsed laser beam traveling from reflection point 15 to reflection point 16 overlap with each other, forming a focal point 415. Furthermore, at least a portion of the pulsed laser beam in the beam waist of the pulsed laser beam traveling from reflection point 7 to reflection point 8 and a portion of the pulsed laser beam traveling from reflection point 17 to reflection point 18 overlap with each other, forming a focal point 417. Furthermore, at least a portion of the beam waist of the pulsed laser beam traveling from reflection point 9 to reflection point 10 and the beam waist of the pulsed laser beam traveling from reflection point 19 to reflection point 20 overlap each other, forming a focal point 419.

[0102] Therefore, in the pulse stretcher 150 of this modification, five focal points 411, 413, 415, 417, and 419 are generated, and the number of overlaps of the pulsed laser beam at each of the focal points 411, 413, 415, 417, and 419 is two. The focal points 411, 413, 415, 417, and 419 are located at different positions in a predetermined direction. When the first mirror unit 53a and the second mirror unit 53b are viewed along the predetermined direction, two optical paths of the pulsed laser beam pass through the focal points 411, 413, 415, 417, and 419. Furthermore, the focal points 411, 413, 415, 417, and 419 overlap with each other. Note that at least a portion of some focal points may overlap with other focal points.

[0103] 6. Description of the pulse stretcher of embodiment 4 Next, a description will be given of the configuration of the pulse stretcher 150 of the fourth embodiment. Note that the same components as those described above are given the same reference numerals, and redundant description will be omitted unless otherwise specified.

[0104] 6.1 Configuration FIG. 10 is a schematic perspective view showing the positional relationship of reflection points 1 to 12 on concave mirrors 55a to 55d of this embodiment. For ease of viewing, FIG. 10 does not show the beam splitter 51, the pulsed laser beam traveling from the output coupling mirror 147 to the beam splitter 51, and the pulsed laser beam traveling from the beam splitter 51 to the beam splitter 163. The configuration of the pulse stretcher 150 of this embodiment is the same as the configuration of the pulse stretcher 150 of the first embodiment, and the reflection points 1 to 12 located on the concave mirrors 55a to 55d, respectively, are also the same. However, in the pulse stretcher 150 of this embodiment, one concave mirror is shifted around an axis perpendicular to the arrangement direction of the concave mirrors compared to the first embodiment so that the beam waists of the pulsed laser beams are shifted from each other. This embodiment illustrates an example in which one concave mirror 55c of the second mirror unit 53b, which reflects the pulsed laser beam twice, is shifted.

[0105] Concave mirror 55c of this embodiment shifts around the vertical axis as described above so that the reflection direction of the pulsed laser beam changes at reflection points 4 to 10, the change in the reflection angle is canceled by reflection at reflection point 10, and the traveling direction of the pulsed laser beam returns to its original state. When concave mirror 55c shifts, reflection points 5 and 9 move lower than reflection point 4, and reflection point 7 moves higher than reflection points 2 and 6 in a direction perpendicular to the predetermined direction. Even if concave mirror 55c shifts, reflection points 1 to 4, 6, 8, and 10 to 12 other than reflection points 5, 7, and 9 do not shift.

[0106] 11 is a diagram illustrating the positions of the beam waists of pulsed laser beams when viewing concave mirrors 55a and 55b from concave mirrors 55c and 55d of this embodiment. In FIG. 11, reflection points 1 to 12 are indicated by black circles, and beam waists are indicated by white circles. When concave mirror 55c is misaligned as described above, beam waist 425 of pulsed laser beam traveling from reflection point 5 to reflection point 6 is lower than beam waist 431 of pulsed laser beam traveling from reflection point 11 to reflection point 12. Furthermore, beam waist 427 of pulsed laser beam traveling from reflection point 7 to reflection point 8 is higher than beam waist 421 of pulsed laser beam traveling from reflection point 1 to reflection point 2. Furthermore, beam waist 429 of pulsed laser beam traveling from reflection point 9 to reflection point 10 is lower than beam waist 423 of pulsed laser beam traveling from reflection point 3 to reflection point 4. Therefore, when one concave mirror 55c of the second mirror unit 53b is shifted, the beam waists 421, 423, 425, 427, 429, and 431 are shifted from one another and do not overlap.

[0107] 6.2 Actions and Effects According to the above configuration, beam waists 421, 423, 425, 427, 429, and 431 are offset from one another. Therefore, the energy of the pulsed laser beam absorbed by oxygen is smaller than when beam waists 421, 423, 425, 427, 429, and 431 overlap. This suppresses temperature rise and plasma generation near the focal point of pulse stretcher 150. Suppressing these issues suppresses the occurrence of refractive index distribution in pulse stretcher 150, thereby suppressing wavefront distortion of the pulsed laser beam. Therefore, exposure apparatus 200 can emit pulsed laser beams that satisfy the required performance, and a decrease in the reliability of gas laser apparatus 100 can be suppressed.

[0108] Next, as Modification 1 of this embodiment, an example in which the concave mirror 55a of the first mirror unit 53a, which reflects the pulsed laser beam twice, is misaligned will be described. FIG. 12 is a schematic perspective view showing the positional relationship of reflection points 1 to 12 on the concave mirrors 55a to 55d of Modification 1. The concave mirror 55a is misaligned around the vertical axis as described above so that the reflection direction of the pulsed laser beam at reflection points 1 to 7 changes, the change in the reflection angle is canceled by reflection at reflection point 7, and the traveling direction of the pulsed laser beam returns to its original direction. Due to the misalignment of the concave mirror 55a, reflection points 2 and 6 are elevated relative to reflection point 7, and reflection point 4 is lower relative to reflection points 5 and 9 in the direction perpendicular to the predetermined direction. Even if the concave mirror 55a is misaligned, reflection points 1, 3, 5, 7 to 12 other than reflection points 2, 4, and 6 do not shift.

[0109] 13 is a diagram illustrating the positions of the beam waists of pulsed laser beams when viewing concave mirrors 55a and 55b from concave mirrors 55c and 55d of this modified example. When concave mirror 55a is misaligned as described above, beam waist 421 of pulsed laser beam traveling from reflection point 1 to reflection point 2 is higher than beam waist 427 of pulsed laser beam traveling from reflection point 7 to reflection point 8. Also, beam waist 425 of pulsed laser beam traveling from reflection point 5 to reflection point 6 is higher than beam waist 431 of pulsed laser beam traveling from reflection point 11 to reflection point 12. Also, beam waist 423 of pulsed laser beam traveling from reflection point 3 to reflection point 4 is lower than beam waist 429 of pulsed laser beam traveling from reflection point 9 to reflection point 10. Therefore, when one concave mirror 55a of first mirror unit 53a is misaligned, beam waists 421, 423, 425, 427, 429, and 431 are misaligned with one another and do not overlap.

[0110] Next, as a second modification of this embodiment, an example will be described in which the concave mirror 55d of the second mirror unit 53b, which reflects the pulsed laser beam four times, is misaligned. FIG. 14 is a schematic perspective view showing the positional relationship of reflection points 1 to 12 on the concave mirrors 55a to 55d of the second modification. The concave mirror 55d is misaligned around the vertical axis as described above so that the reflection direction of the pulsed laser beam at reflection points 2 to 12 changes, the change in the reflection angle is canceled by reflection at reflection point 12, and the traveling direction of the pulsed laser beam returns to its original state. Due to the misalignment of the concave mirror 55d, reflection points 3 and 11 are lowered relative to reflection point 10, reflection points 5 and 9 are higher relative to reflection point 4, and reflection point 7 is lowered relative to reflection points 2 and 6. Even if the concave mirror 55d is misaligned, reflection points 1, 2, 4, 6, 8, 10, and 12, other than reflection points 3, 5, 7, 9, and 11, do not shift.

[0111] 15 is a diagram illustrating the positions of the beam waists of pulsed laser beams when concave mirrors 55a and 55b are viewed from concave mirrors 55c and 55d. When concave mirror 55d is misaligned as described above, beam waist 423 of pulsed laser beam traveling from reflection point 3 to reflection point 4 decreases, and beam waist 429 of pulsed laser beam traveling from reflection point 9 to reflection point 10 increases. Furthermore, beam waist 425 of pulsed laser beam traveling from reflection point 5 to reflection point 6 increases, and beam waist 431 of pulsed laser beam traveling from reflection point 11 to reflection point 12 decreases. Furthermore, beam waist 427 of pulsed laser beam traveling from reflection point 7 to reflection point 8 decreases from beam waist 421 of pulsed laser beam traveling from reflection point 1 to reflection point 2. Therefore, when the other concave mirror 55d of second mirror unit 53b is misaligned, beam waists 421, 423, 425, 427, 429, and 431 are misaligned and do not overlap with each other.

[0112] The above description is intended to be illustrative rather than limiting. Thus, it will be apparent to one skilled in the art that modifications can be made to the disclosed embodiments without departing from the scope of the claims. It will also be apparent to one skilled in the art that the disclosed embodiments can be used in combination. Terms used throughout this specification and claims should be construed as "open ended" unless expressly stated otherwise. For example, words such as "comprise," "have," "comprise," and "equip" should be construed as meaning "without excluding the presence of elements other than those listed." In addition, the modifier "a" should be construed as meaning "at least one" or "one or more." In addition, the term "at least one of A, B, and C" should be construed as "A," "B," "C," "A+B," "A+C," "B+C," or "A+B+C," and should also be construed as including combinations other than "A," "B," and "C."

Claims

1. a beam splitter that splits the pulsed laser light into two beams; a plurality of first concave mirrors arranged side by side in a predetermined direction; a plurality of second concave mirrors, the number of which is equal to the number of the first concave mirrors, individually facing the first concave mirrors and arranged side by side in the predetermined direction; Equipped with one of the pulsed laser beams split by the beam splitter travels to any one of the plurality of first concave mirrors, is reflected alternately by the plurality of first concave mirrors and the plurality of second concave mirrors an even number of times, which is equal to or greater than 12, and returns to the beam splitter; the number of overlaps of the one pulsed laser beam is two at each of a plurality of focusing points at which the one pulsed laser beam at least partially overlaps with each other in a beam waist of the one pulsed laser beam, the number of the first concave mirrors and the number of the second concave mirrors are each two, during one cycle in which the one pulse laser beam returns from the beam splitter to the beam splitter via the plurality of first concave mirrors and the plurality of second concave mirrors, the one pulse laser beam is reflected once at two reflection points on one of the first concave mirrors and one of the second concave mirrors, During one period, the one pulse laser beam is reflected twice at two reflection points on each of the other first concave mirror and the other second concave mirror. Pulse stretcher.

2. 2. A pulse stretcher according to claim 1, The first concave mirror and the second concave mirror have the same radius of curvature.

3. 3. A pulse stretcher according to claim 2, The distance between the first concave mirror and the second concave mirror facing each other is equal to the radius of curvature.

4. 2. A pulse stretcher according to claim 1, The number of the light-converging points is three.

5. 2. A pulse stretcher according to claim 1, The same plane passes through the reflection points on the first concave mirror and the second concave mirror.

6. 2. A pulse stretcher according to claim 1, Each of the reflection points on the first concave mirror is shifted in a direction perpendicular to the predetermined direction, The reflection points on the second concave mirror are shifted in a direction perpendicular to the predetermined direction.

7. 7. A pulse stretcher according to claim 6, The respective light-collecting points are located at different positions in the predetermined direction.

8. 7. A pulse stretcher according to claim 6, When the plurality of first concave mirrors and the plurality of second concave mirrors are viewed along the predetermined direction, the one pulse laser beam passes through the focal point along two optical paths.

9. a beam splitter that splits the pulsed laser light into two beams; a plurality of first concave mirrors arranged side by side in a predetermined direction; a plurality of second concave mirrors, the number of which is equal to the number of the first concave mirrors, individually facing the first concave mirrors and arranged side by side in the predetermined direction; Equipped with one of the pulsed laser beams split by the beam splitter travels to any one of the plurality of first concave mirrors, is reflected alternately by the plurality of first concave mirrors and the plurality of second concave mirrors an even number of times, which is equal to or greater than 12, and returns to the beam splitter; the number of overlaps of the one pulsed laser beam is two at each of a plurality of focusing points at which the one pulsed laser beam at least partially overlaps with each other in a beam waist of the one pulsed laser beam, the number of the first concave mirrors and the number of the second concave mirrors are each three, During one cycle in which the one pulse laser beam returns from the beam splitter to the beam splitter via the plurality of first concave mirrors and the plurality of second concave mirrors, the one pulse laser beam is reflected once at two reflection points on each of the first concave mirror and the second concave mirror. Pulse stretcher.

10. 10. A pulse stretcher according to claim 9, The number of the light-converging points is three.

11. a beam splitter that splits the pulsed laser light into two beams; a plurality of first concave mirrors arranged side by side in a predetermined direction; a plurality of second concave mirrors, the number of which is equal to the number of the first concave mirrors, individually facing the first concave mirrors and arranged side by side in the predetermined direction; Equipped with one of the pulsed laser beams split by the beam splitter travels to any one of the plurality of first concave mirrors, is reflected alternately by the plurality of first concave mirrors and the plurality of second concave mirrors an even number of times, which is equal to or greater than 12, and returns to the beam splitter; generating a laser beam by a gas laser apparatus including a pulse stretcher in which the number of overlaps of the one pulse laser beam is two at each of a plurality of focusing points at which the one pulse laser beam at least partially overlaps with each other in a beam waist of the one pulse laser beam; outputting the laser light to an exposure device; exposing the laser light onto a photosensitive substrate in the exposure apparatus to manufacture an electronic device. Including, the number of the first concave mirrors and the number of the second concave mirrors are each two, during one cycle in which the one pulse laser beam returns from the beam splitter to the beam splitter via the plurality of first concave mirrors and the plurality of second concave mirrors, the one pulse laser beam is reflected once at two reflection points on one of the first concave mirrors and one of the second concave mirrors, During one period, the one pulse laser beam is reflected twice at two reflection points on each of the other first concave mirror and the other second concave mirror. A method for manufacturing electronic devices.

12. a beam splitter that splits the pulsed laser light into two beams; a plurality of first concave mirrors arranged side by side in a predetermined direction; a plurality of second concave mirrors, the number of which is equal to the number of the first concave mirrors, individually facing the first concave mirrors and arranged side by side in the predetermined direction; Equipped with one of the pulsed laser beams split by the beam splitter travels to any one of the plurality of first concave mirrors, is reflected alternately by the plurality of first concave mirrors and the plurality of second concave mirrors an even number of times, which is equal to or greater than 12, and returns to the beam splitter; generating a laser beam by a gas laser apparatus including a pulse stretcher in which the number of overlaps of the one pulse laser beam is two at each of a plurality of focusing points at which the one pulse laser beam at least partially overlaps with each other in a beam waist of the one pulse laser beam; outputting the laser light to an exposure device; exposing the laser light onto a photosensitive substrate in the exposure apparatus to manufacture an electronic device. Including, the number of the first concave mirrors and the number of the second concave mirrors are each three, During one cycle in which the one pulse laser beam returns from the beam splitter to the beam splitter via the plurality of first concave mirrors and the plurality of second concave mirrors, the one pulse laser beam is reflected once at two reflection points on each of the first concave mirror and the second concave mirror. A method for manufacturing electronic devices.

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