Laser apparatus and method for manufacturing electronic device

Abstract

A laser apparatus according to one aspect of the present disclosure comprises: an oscillator that outputs a pulse laser beam having an ultraviolet wavelength; an amplifier that amplifies the pulse laser beam; an optical pulse stretches that includes a beam splitter and a plurality of mirrors, and expands the pulse width of the pulse laser beam; a beam divergence angle adjuster for adjusting a beam divergence angle of the expanded pulse laser beam, said beam divergence angle adjuster including an upstream-side lens that is disposed on the upstream side in the optical path of the pulse laser beam, a downstream-side lens that is disposed downstream of the upstream-side lens, and an optical path length changing mechanism that changes the inter-lens optical path length between the upstream-side lens and the downstream-side lens; and a processor for controlling the beam divergence angle adjuster, the processor determining a repetition frequency or a duty of the pulse laser beam, and, when the repetition frequency or the duty of the pulse laser beam has changed by a preset threshold value or more, changing the inter-lens optical path length so that the beam divergence angle of the expanded pulse laser beam becomes smaller in accordance with the repetition frequency or the duty after the change.

Description

Laser device and method for manufacturing electronic device

[0001] The present disclosure relates to a laser apparatus and a method for manufacturing an electronic device.

[0002] In recent years, semiconductor exposure apparatuses 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 that output laser light with a wavelength of approximately 248 nm and ArF excimer laser devices that 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 broad, ranging from 350 to 400 pm. Therefore, constructing a projection lens using a material that transmits ultraviolet light, such as KrF and ArF laser light, can result in chromatic aberration. This can result in a decrease in resolution. Therefore, it is necessary to narrow the spectral linewidth of the laser light output from a 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 within 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-narrowed gas laser device.

[0004] JP 2008-168323 A JP 2009-141186 A overview

[0005] a beam divergence angle adjuster that adjusts the beam divergence angle of the stretched pulsed laser beam; and a processor that controls the beam divergence angle adjuster, the processor determining a repetition frequency or duty of the pulsed laser beam, and, when the repetition frequency or duty has changed by more than a predetermined threshold, changing the inter-lens optical path length so as to reduce the beam divergence angle of the stretched pulsed laser beam.

[0006] According to one aspect of the present disclosure, there is provided a method for manufacturing an electronic device, the method including: outputting pulsed laser light output from a laser apparatus including an oscillator that outputs pulsed laser light of an ultraviolet wavelength, an amplifier that amplifies the pulsed laser light, and an optical pulse stretcher including a beam splitter and a plurality of mirrors that stretches the pulse width of the pulsed laser light to an exposure apparatus; and exposing a photosensitive substrate in the exposure apparatus to the pulsed laser light to manufacture an electronic device, the laser apparatus including an upstream lens arranged upstream in an optical path of the pulsed laser light, a downstream lens arranged downstream of the upstream lens, and an optical path length changing mechanism that changes an inter-lens optical path length between the upstream lens and the downstream lens, the method including: a beam divergence angle adjuster that adjusts the beam divergence angle of the stretched pulsed laser light; and a processor that controls the beam divergence angle adjuster, the processor determining a repetition frequency or duty of the pulsed laser light, and, when the repetition frequency or duty has changed by more than a predetermined threshold, changing the inter-lens optical path length so that the beam divergence angle of the stretched pulsed laser light becomes smaller in accordance with the changed repetition frequency or duty.

[0007] Some embodiments of the present disclosure are described below, by way of example only, with reference to the accompanying drawings. FIG. 1 is a front view schematically illustrating an exemplary configuration of a laser device according to a comparative example. FIG. 2 is a top view schematically illustrating an exemplary configuration of a laser device according to a comparative example. FIG. 3 is an explanatory diagram of a beam divergence angle. FIG. 4 is a diagram illustrating a cross-sectional shape of a beam spot of pulsed laser light. FIG. 5 is a front view schematically illustrating an exemplary configuration of a laser device according to a first embodiment. FIG. 6 is a top view schematically illustrating an exemplary configuration of a laser device according to the first embodiment. FIG. 7 is a diagram schematically illustrating an exemplary configuration of a beam divergence angle adjuster. FIG. 8 is a diagram schematically illustrating an exemplary configuration of an optical path length changing mechanism. FIG. 9 is a graph illustrating the relationship between the inter-lens optical path length and the beam divergence angle for each repetition frequency. FIG. 10 is an example of table data used to control the adjustment of the beam divergence angle. FIG. 11 is a flowchart illustrating the procedure of operation of the laser device according to the first embodiment. FIG. 12 is a graph illustrating the relationship between the inter-lens optical path length and the beam divergence angle for each repetition frequency. FIG. 13 is a diagram showing a state in which the focusing position of the pulsed laser beam does not coincide with the focus of the downstream lens. FIG. 14 is a diagram showing a state in which the focusing position of the pulsed laser beam coincides with the focus by changing the optical path length between the lenses. FIG. 15 is an example of table data used for controlling the adjustment of the beam divergence angle in the second embodiment. FIG. 16 is a flowchart showing the procedure of the operation of the laser apparatus according to the second embodiment. FIG. 17 is a front view showing an outline of an example configuration of a laser apparatus according to a first modified example. FIG. 18 is a top view showing an outline of an example configuration of a laser apparatus according to the first modified example. FIG. 19 is a front view showing an outline of an example configuration of a laser apparatus according to a second modified example. FIG. 20 is a top view showing an outline of an example configuration of a laser apparatus according to the second modified example. FIG. 21 is a diagram showing a modified example of the optical path length changing mechanism. FIG. 22 is a diagram showing an outline of an example configuration of an exposure apparatus. Embodiment

[0008] <Contents> 1. Comparative Example 1.1 Configuration 1.2 Operation 1.3 Issues 2. First Embodiment 2.1 Configuration 2.2 Operation 2.3 Effects 3. Second Embodiment 3.1 Configuration 3.2 Operation 3.3 Effects 4. Modifications 4.1 First Modification 4.2 Second Modification 4.3 Other Modifications 5. Method for Manufacturing Electronic Device

[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 each embodiment 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 and 2 schematically show a configuration example of a laser device 2 according to a comparative example. The comparative example of 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.

[0011] 1 and 2, the height direction of the laser device 2 is defined as the V-axis direction, the length direction is defined as the Z-axis direction, and the depth direction is defined as the H-axis direction.

[0012] The laser device 2 includes a master oscillator (MO) 10, an MO beam steering unit 20, a power oscillator (PO) 30, a PO beam steering unit 40, a first optical pulse stretcher (OPS) 100 (see FIG. 2 ), a second optical pulse stretcher (OPS) 50, a monitor module 60, and a laser processor 70. The laser device 2 is an excimer laser device that outputs pulsed laser light PL to be incident on the exposure device 3.

[0013] The master oscillator 10 includes a line narrowing module (LNM) 11, a chamber 14, and an output coupler (OC) 17. The master oscillator 10 is an example of the "oscillator that outputs pulsed laser light with an ultraviolet wavelength" in this disclosure.

[0014] The LNM 11 includes a prism beam expander 12 for narrowing the spectral linewidth, and a grating 13. The prism beam expander 12 and the grating 13 are arranged in a Littrow configuration so that the angle of incidence and the angle of diffraction are the same.

[0015] The output coupling mirror 17 is a reflecting mirror with a reflectance in the range of 40% to 60%. The output coupling mirror 17 and the LNM 11 are arranged to form an optical resonator.

[0016] The chamber 14 is disposed on the optical path of the optical resonator. The chamber 14 includes a pair of discharge electrodes 15a, 15b and two windows 16a, 16b through which the pulsed laser light PL passes. The chamber 14 contains an excimer laser gas therein. The excimer laser gas may include, for example, Ar gas or Kr gas as a rare gas and F as a halogen gas. ２ The gas may contain Ne gas as a buffer gas.

[0017] The MO beam steering unit 20 includes a high-reflection mirror 21a and a high-reflection mirror 21b. The high-reflection mirror 21a and the high-reflection mirror 21b are arranged so that the pulsed laser light PL output from the master oscillator 10 is incident on the power oscillator 30. The high-reflection mirror in the present disclosure is made of, for example, synthetic quartz or calcium fluoride (CaF ２ The highly reflective film is a dielectric multilayer film, such as a film containing fluoride.

[0018] The power oscillator 30 includes a rear mirror 31, a chamber 32, and an output coupling mirror 35. The rear mirror 31 and the output coupling mirror 35 are arranged to form an optical resonator. The power oscillator 30 is an example of an "amplifier that amplifies pulsed laser light" in this disclosure.

[0019] The chamber 32 is disposed on the optical path of the optical resonator. The chamber 32 may have a configuration similar to that of the chamber 14 of the master oscillator 10. That is, the chamber 32 includes a pair of discharge electrodes 33 a, 33 b and two windows 34 a, 34 b through which the pulsed laser light PL passes. The chamber 32 contains an excimer laser gas therein.

[0020] The rear mirror 31 is a reflective mirror with a reflectance in the range of 50% to 90%, and the output coupling mirror 35 is a reflective mirror with a reflectance in the range of 10% to 30%.

[0021] The PO beam steering unit 40 includes a high-reflection mirror 44 a, a high-reflection mirror 44 b, and a high-reflection mirror 44 c. The high-reflection mirrors 44 a and 44 b are arranged so that the pulsed laser beam PL output from the power oscillator 30 is incident on the first OPS 100. The high-reflection mirror 44 c is arranged so that the pulsed laser beam PL output from the first OPS 100 is reflected and incident on the second OPS 50.

[0022] The first OPS 100 is an optical pulse stretcher having a long delay optical path for generating a long-distance optical path difference that stretches the pulse width compared to the second OPS 50. The first OPS 100 is disposed on the rear surface of the laser device 2. The "rear surface" is the back side when viewed from the front surface of the laser device 2.

[0023] The first OPS 100 includes a beam splitter 104, four concave mirrors 102a to 102d, and a housing 100a that houses the beam splitter 104 and the concave mirrors 102a to 102d.

[0024] The beam splitter 104 is disposed on the optical path of the pulsed laser beam PL output from the PO beam steering unit 40. The beam splitter 104 is a reflective mirror that transmits a portion of the incident pulsed laser beam PL and reflects the remaining pulsed laser beam PL. The reflectance of the beam splitter 104 is preferably within a range of 40% to 70%, and more preferably approximately 60%. The beam splitter 104 outputs the pulsed laser beam PL that has transmitted through the beam splitter 104 toward the high-reflection mirror 106a.

[0025] The high-reflection mirror 106 a and the high-reflection mirror 106 b are arranged so that the pulsed laser beam PL expanded by the first OPS 100 re-enters the PO beam steering unit 40 .

[0026] The four concave mirrors 102a to 102d constitute a delay optical path for the pulsed laser beam PL reflected by the first surface of the beam splitter 104. The pulsed laser beam PL reflected by the first surface of the beam splitter 104 is reflected by the four concave mirrors 102a to 102d and is again imaged by the beam splitter 104.

[0027] The four concave mirrors 102a to 102d may all have approximately the same focal length f, which may correspond to the distance from the beam splitter 104 to the concave mirror 102a, for example.

[0028] The concave mirrors 102a and 102b are arranged so that the pulsed laser beam PL reflected by the first surface of the beam splitter 104 is reflected by the concave mirror 102a and incident on the concave mirror 102b. The concave mirrors 102a and 102b are arranged so that the pulsed laser beam PL reflected by the first surface of the beam splitter 104 forms an image on the first surface of the beam splitter 104 as a first image at an equal magnification (1:1).

[0029] The concave mirrors 102c and 102d are arranged so that the pulsed laser beam PL reflected by the concave mirror 102b is reflected by the concave mirror 102c and incident on the concave mirror 102d. Furthermore, the concave mirror 102d is arranged so that the pulsed laser beam PL reflected by the concave mirror 102d is incident on a second surface of the beam splitter 104 opposite to the first surface. The concave mirrors 102c and 102d are arranged so that the first image is formed as a second image on the second surface of the beam splitter 104 at a 1:1 ratio.

[0030] Although the first OPS 100 has four concave mirrors 102a to 102d in the example shown, in reality, the number may be in the range of 16 to 34. The delay optical path length of the first OPS 100 is, for example, in the range of 30 m to 75 m.

[0031] The second OPS 50 has a configuration substantially similar to that of the first OPS 100, except that the delay optical path length is relatively short. The second OPS 50 includes a beam splitter 52 and four concave mirrors 54a to 54d. The beam splitter 52 is disposed on the optical path of the pulsed laser beam PL output from the PO beam steering unit 40. The beam splitter 52 is a reflective mirror that transmits a portion of the incident pulsed laser beam PL and reflects the remaining pulsed laser beam PL. The reflectivity of the beam splitter 52 is preferably within a range of 40% to 70%, and more preferably approximately 60%. The beam splitter 52 outputs the pulsed laser beam PL that has passed through the beam splitter 52 from the laser device 2.

[0032] The four concave mirrors 54a to 54d constitute a delay optical path for the pulsed laser beam PL reflected by the first surface of the beam splitter 52. The pulsed laser beam PL reflected by the first surface of the beam splitter 52 is reflected by the four concave mirrors 54a to 54d and is again positioned so that the beam is imaged by the beam splitter 52.

[0033] The four concave mirrors 54a to 54d may all have approximately the same focal length f, which may correspond to the distance from the beam splitter 52 to the concave mirror 54a, for example.

[0034] The concave mirrors 54a and 54b are arranged so that the pulsed laser beam PL reflected by the first surface of the beam splitter 52 is reflected by the concave mirror 54a and incident on the concave mirror 54b. The concave mirrors 54a and 54b are arranged so that the pulsed laser beam PL reflected by the first surface of the beam splitter 52 forms an image on the first surface of the beam splitter 52 as a first image at an equal magnification (1:1).

[0035] The concave mirrors 54c and 54d are arranged so that the pulsed laser beam PL reflected by the concave mirror 54b is reflected by the concave mirror 54c and incident on the concave mirror 54d. Furthermore, the concave mirror 54d is arranged so that the pulsed laser beam PL reflected by the concave mirror 54d is incident on a second surface of the beam splitter 52 opposite the first surface. The concave mirrors 54c and 54d are arranged so that the first image is formed as a second image on the second surface of the beam splitter 52 at a 1:1 ratio.

[0036] Although the number of concave mirrors 54a to 54d of the second OPS 50 is shown as four in this example, the number may actually be in the range of 4 to 12. The delay optical path length of the second OPS 50 is, for example, in the range of 5 m to 25 m.

[0037] The monitor module 60 includes beam splitters 60 a and 60 b, a pulse energy measuring device 60 c, and a spectrum measuring device 60 d. The beam splitter 60 a is disposed on the optical path of the pulsed laser beam PL output from the second OPS 50, and reflects a portion of the pulsed laser beam PL and transmits the other portion. The pulsed laser beam PL that has transmitted through the beam splitter 60 a is incident on the exposure device 3.

[0038] The beam splitter 60b is disposed on the optical path of the pulsed laser beam PL reflected by the beam splitter 60a. The pulse energy measuring device 60c is disposed on the optical path of the pulsed laser beam PL reflected by the beam splitter 60b and measures the pulse energy of the pulsed laser beam PL. The spectrum measuring device 60d is disposed on the optical path of the pulsed laser beam PL transmitted through the beam splitter 60b and measures the spectrum of the pulsed laser beam PL. The measurement data of the pulse energy and spectrum are transmitted to the laser processor 70.

[0039] The laser processor 70 is communicatively connected via a signal line to the exposure apparatus controller 3a of the exposure apparatus 3. The laser processor 70 receives signals from the exposure apparatus controller 3a. The signals received by the laser processor 70 include a target pulse energy, a target wavelength, a target spectral linewidth, and a light emission trigger signal.

[0040] The exposure device 3 is a device that exposes a photosensitive substrate, such as a semiconductor wafer (not shown), by way of example, using a pulsed laser beam PL.

[0041] 1.2 Operation The laser processor 70 of the laser device 2 receives the target pulse energy, target wavelength, target spectral linewidth, and light emission trigger signal from the exposure device controller 3 a. The light emission trigger signal is transmitted from the exposure device controller 3 a to the laser processor 70 at a repetition frequency corresponding to the operation of the exposure device 3.

[0042] In synchronization with the light emission trigger signal, the laser processor 70 applies a high voltage between the discharge electrodes 15a and 15b of the master oscillator 10. When a discharge occurs in the chamber 14 of the master oscillator 10, the laser gas is excited, and laser oscillation is initiated by an optical resonator formed by the output coupling mirror 17 and the LNM 11. When laser oscillation is initiated, narrowband pulsed laser light PL with a center wavelength of 150 nm to 380 nm in ultraviolet light is output from the output coupling mirror 17. This pulsed laser light PL is incident as seed light on the rear mirror 31 of the power oscillator 30 by the MO beam steering unit 20.

[0043] A discharge occurs in the chamber 32 in synchronization with the incidence of the seed light that has passed through the rear mirror 31. As a result, the laser gas is excited, the seed light is amplified by a Fabry-Perot optical resonator formed by the output coupling mirror 35 and the rear mirror 31, and the amplified pulsed laser light PL is output from the output coupling mirror 35. The pulsed laser light PL output from the output coupling mirror 35 passes through the PO beam steering unit 40 and enters the first OPS 100.

[0044] A portion of the pulsed laser beam PL that is incident on the first OPS 100 passes through the beam splitter 104 and is output, and a portion of the pulsed laser beam PL is reflected by the beam splitter 104. The pulsed laser beam PL that is reflected by the beam splitter 104 travels around a delay optical path formed by the first to fourth concave mirrors 102a to 102d and is incident on the beam splitter 104 again. Then, a portion of the pulsed laser beam PL that is incident on the beam splitter 104 is reflected and output from the first OPS 100. The pulsed laser beam PL that is transmitted through the beam splitter 104 travels around the delay optical path again.

[0045] In this way, the pulsed laser light PL repeatedly circulates through the delay optical path, and as a result, the pulsed laser light PL is output from the first OPS 100 as 0th circumnavigation light, 1st circumnavigation light, 2nd circumnavigation light, 3rd circumnavigation light, etc. The light intensity of the pulsed laser light PL output from the first OPS 100 decreases as the number of circumnavigations through the delay optical path increases.

[0046] The pulsed laser beam PL from the first orbit onwards is delayed relative to the pulsed laser beam PL of the 0th orbit by an integer multiple of a delay time determined by the optical path length of the delay optical path, and then combined and output. That is, the pulse waveform of the pulsed laser beam PL of the 0th orbit light is sequentially superimposed on the pulse waveform of the pulsed laser beam PL of the 0th orbit light, with each pulse waveform being delayed by the delay time. In this way, the pulse width of the pulsed laser beam PL is extended by the first OPS 100.

[0047] By extending the pulse width of the pulsed laser beam PL using the first OPS 100, the coherence is reduced, thereby suppressing the occurrence of speckles. Speckles are bright and dark spots that occur due to interference when laser beams are scattered in a random medium.

[0048] The pulsed laser beam PL whose pulse width has been expanded by the first OPS 100 is incident on the second OPS 50 via the PO beam steering unit 40. In the second OPS 50, the pulsed laser beam PL is expanded by the same action as in the first OPS 100.

[0049] The pulsed laser beam PL, whose pulse width has been expanded by the second OPS 50, enters the monitor module 60. A portion of the pulsed laser beam PL that entered the monitor module 60 is reflected by the beam splitter 60a. A portion of the pulsed laser beam PL reflected by the beam splitter 60a is reflected by the beam splitter 60b and enters the pulse energy measuring device 60c, whereby the pulse energy is measured. A portion of the pulsed laser beam PL reflected by the beam splitter 60a passes through the beam splitter 60b and enters the spectrum measuring device 60d, whereby the spectrum is measured.

[0050] The laser processor 70 controls the voltage applied to the pair of discharge electrodes 33 a and 33 b of the power oscillator 30 so that the difference between the target pulse energy and the measured pulse energy approaches zero.

[0051] The laser processor 70 calculates the wavelength from the measured spectrum and controls the angle of the prism beam expander 12 of the LNM 11 so that the wavelength of the pulsed laser light PL output from the laser device 2 becomes the target wavelength. The laser processor 70 also calculates the spectral linewidth from the measured spectrum and controls a wavefront adjuster (not shown) so that the wavelength of the pulsed laser light PL output from the laser device 2 becomes the target spectral linewidth.

[0052] The pulsed laser light PL output from the laser device 2 enters the exposure device 3 and is irradiated onto a photosensitive substrate such as a semiconductor wafer (not shown).

[0053] 1.3 Issues The repetition frequency or duty, which is determined according to the period of the light emission trigger signal transmitted from the exposure apparatus 3, may change depending on the operating state of the exposure apparatus 3. When the repetition frequency or duty changes, thermal deformation or the like occurs in the optical elements, and this thermal deformation or the like causes a change in the beam divergence angle of the pulsed laser beam PL. When the beam divergence angle increases, beam vignetting or the like occurs within the exposure apparatus 3, resulting in a loss of energy in the pulsed laser beam PL. The change in the beam divergence angle is greater, for example, when the pulsed laser beam PL is stretched using an optical pulse stretcher than when an optical pulse stretcher is not used. In particular, the change in the beam divergence angle becomes more pronounced with an optical pulse stretcher that has more optical elements, such as a concave mirror, and also becomes more pronounced with an optical pulse stretcher that has a longer delay path length, such as the first OPS 100 shown in the comparative example.

[0054] Here, as shown in FIG. 3 , pulsed laser light PL is focused by a focusing lens LZ, and the value obtained by dividing the size of a beam spot BS at a position of focal length F of the focusing lens LZ by the focal length F is defined as the beam divergence angle. The size of the beam spot BS is its diameter or full width. The size of the beam spot BS is measured by a two-dimensional image sensor IS placed at the position of focal length F. When the wavefront is a plane WF0 as in the case of pulsed laser light PL shown in FIG. 3 , the position at which the pulsed laser light PL is focused by the focusing lens LZ coincides with the focal point corresponding to the focal length F of the focusing lens LZ, and the size of the beam spot BS formed at the focal point is minimized, and the beam divergence angle is also minimized.

[0055] On the other hand, when the pulsed laser beam PL diverges and the wavefront thereof becomes a convex curved surface toward the condenser lens LZ, the focusing position of the pulsed laser beam PL focused by the condenser lens LZ is located downstream of the focal point. In this case, the size of the beam spot BS measured by the two-dimensional image sensor IS increases, and the beam divergence angle also increases.

[0056] The duty is a value corresponding to the cycle of a plurality of light emission trigger signals repeatedly output by the exposure device 3. If the duty is DC, it is defined by the following equation (1): DC (%) = (Np / Np_max) x 100 (1)

[0057] Here, Np is the number of pulses oscillated within a preset time Tc after the start of laser oscillation. Np_max is the product of the maximum repetition frequency RR_max determined according to the performance of the laser device 2 and the set time Tc, and is the maximum number of pulses that the laser device 2 can output within the set time Tc. In other words, the duty cycle DC indicates the ratio of the number of pulses that are actually output to the maximum number of pulses that the laser device 2 can output within a unit time.

[0058] 4, the cross-sectional shape of the beam spot BS of the pulsed laser light PL is a substantially rectangular shape with the longer side in the discharge direction (V-axis direction). Therefore, the beam divergence angle in the discharge direction is different from that in the direction perpendicular to the discharge direction (H-axis direction), with the beam divergence angle in the discharge direction being larger.

[0059] 5 and 6 schematically show an example configuration of a laser device 2A according to a first embodiment of the present disclosure. Differences between the configuration of the laser device 2A shown in FIGS. 5 and 6 and the configuration of the laser device 2 according to the comparative example shown in FIGS. 1 and 2 will be described. The laser device 2A according to the first embodiment differs from the configuration of the laser device 2 according to the comparative example in that it includes a beam divergence angle adjuster 80 and that a laser processor 70 has a function of controlling the beam divergence angle adjuster 80.

[0060] 5 and 6 , the beam divergence angle adjuster 80 is disposed in the optical path of the pulsed laser beam PL between the first OPS 100 and the second OPS 50. The first OPS 100 is an example of the “optical pulse stretcher” or the “first optical pulse stretcher” in the present disclosure, and the second OPS 50 is an example of the “second optical pulse stretcher” in the present disclosure.

[0061] The beam divergence angle adjuster 80 includes an upstream lens 80a arranged upstream in the optical path of the pulsed laser light PL, a downstream lens 80b arranged downstream of the upstream lens 80a, and an optical path length changing mechanism 90 that changes the inter-lens optical path length L between the upstream lens 80a and the downstream lens 80b, and adjusts the beam divergence angle of the expanded pulsed laser light PL.

[0062] The laser processor 70 determines the repetition frequency RR of the pulsed laser light PL, and when the repetition frequency RR changes by a predetermined first threshold value Th1 or more, changes the inter-lens optical path length L according to the changed repetition frequency RR so as to reduce the beam divergence angle of the expanded pulsed laser light PL. The laser processor 70 is an example of a "processor" in the present disclosure. The laser processor 70 is provided with a memory 70a. The memory 70a stores reference information that the laser processor 70 refers to in order to adjust the beam divergence angle. The reference information will be described later.

[0063] 7 , in the beam divergence angle adjuster 80, the upstream lens 80a and the downstream lens 80b function as relay lenses that relay the beam spot BS of the pulsed laser beam PL, which is focused by the upstream lens 80a, to the downstream lens 80b. As shown as an example, the upstream lens 80a is a plano-convex lens having a convex spherical surface on the incident side of the pulsed laser beam PL and a flat surface on the exit side, while the downstream lens 80b is a plano-convex lens having a flat surface on the incident side and a convex spherical surface on the exit side. Furthermore, the cross sections of the upstream lens 80a and the downstream lens 80b in a direction perpendicular to the optical axis OA are circular.

[0064] In addition, as an example, the upstream lens 80a and the downstream lens 80b have the same focal length F. As an example, the focal lengths of the upstream lens 80a and the downstream lens 80b are in the range of 500 mm to 1000 mm.

[0065] In the initial state, the upstream lens 80a and the downstream lens 80b are arranged so that the downstream focal point FP of the upstream lens 80a coincides with the upstream focal point FP of the downstream lens 80b. That is, in the initial state, the inter-lens optical path length L between the upstream lens 80a and the downstream lens 80b is 2F, which is twice the focal length F. When pulsed laser light PL having a flat wavefront WF0 is incident on the upstream lens 80a arranged in this manner, the focal point FP of the upstream lens 80a coincides with the focusing position C of the pulsed laser light PL, and the beam divergence angle at the focal point FP is minimized. Furthermore, by arranging the inter-lens optical path length L to be twice the focal length F of the upstream lens 80a and the downstream lens 80b in this manner, an image of the pulsed laser light PL at the upstream focal point of the upstream lens 80a is formed at the downstream focal point of the downstream lens 80b at the same magnification (1:1). The image of the pulsed laser beam PL before it enters the upstream lens 80a and the image of the pulsed laser beam PL after it exits the downstream lens 80b are inverted vertically and horizontally.

[0066] As an example, the downstream lens 80b is freely movable along the direction of the optical axis OA by an optical path length changing mechanism 90, and the optical path length changing mechanism 90 changes the inter-lens optical path length L by changing the position of the downstream lens 80b.

[0067] 8 , the optical path length changing mechanism 90 includes a lens holder 91 that holds the downstream lens 80b, a linear stage 92, and a pedestal 93. The pedestal 93 fixes the linear stage 92. The linear stage 92 moves the lens holder 91 in the direction of the optical axis OA. The linear stage 92 is driven by a motor M. The laser processor 70 changes the position of the downstream lens 80b in the direction of the optical axis OA by moving the linear stage 92 via the motor M. Note that instead of the linear stage 92, a mechanism that pushes and pulls the lens holder 91 in the direction of the optical axis OA using an actuator may be provided.

[0068] As shown in Fig. 9, the inter-lens optical path length L and the beam divergence angle in the discharge direction have a downward parabolic relationship for each repetition frequency RR. The graph in Fig. 9 can be obtained by simulating or experimenting to determine the beam divergence angle when the inter-lens optical path length L is changed for each repetition frequency RR.

[0069] In graph G1 of the repetition frequency RR1, the inter-lens optical path length L at the minimum point where the beam divergence angle is minimum is Lr1_min. Increasing or decreasing the inter-lens optical path length L based on Lr1_min means moving the position of the downstream lens 80b back or forth in the direction of the optical axis OA. Because the position where the beam divergence angle is minimum is determined at one point, moving the downstream lens 80b back or forth from that position to change the inter-lens optical path length L increases the beam divergence angle. Therefore, the inter-lens optical path length L and the beam divergence angle in the discharge direction have a relationship resembling a downward parabola.

[0070] In graph G2 for repetition frequency RR2, the inter-lens optical path length L at the minimum point where the beam divergence angle is smallest is Lr2_min. In graph G3 for repetition frequency RR3, the inter-lens optical path length L at the minimum point where the beam divergence angle is smallest is Lr3_min. The magnitude relationship between repetition frequencies RR1 to RR3 is such that RR1 is the smallest, RR3 is the largest, and RR2 is intermediate. According to the graph shown in FIG. 9, the inter-lens optical path lengths Lr1_min to Lr3_min at which the beam divergence angle is smallest for each of repetition frequencies RR1 to RR3 tend to increase as the repetition frequency RR increases. This is presumably because, as the repetition frequency RR increases, the amount of thermal deformation of the optical element increases, resulting in a corresponding increase in the beam divergence angle.

[0071] Based on the relationship between the beam divergence angle and the inter-lens optical path length L, the laser processor 70 controls the inter-lens optical path length L so that the beam divergence angle becomes smaller when the repetition frequency RR changes.

[0072] Fig. 10 shows table data generated based on the relationship shown in Fig. 9 . The table data shown in Fig. 10 is information in which each of a plurality of repetition frequencies RR is associated with the inter-lens optical path length Lr_min at which the beam divergence angle of the expanded pulsed laser beam PL is minimized. The table data shown in Fig. 10 also records the downstream lens position Pr corresponding to each inter-lens optical path length Lr_min. The inter-lens optical path length Lr_min and the downstream lens position Pr are each an example of "information related to the inter-lens optical path length" in the present disclosure. The intervals between the plurality of repetition frequencies RR recorded in the table data are, for example, in the range of 100 Hz to 500 Hz.

[0073] The memory 70a of the laser processor 70 stores the table data shown in Fig. 10 as reference information. Of the table data, one of the inter-lens optical path length Lr_min and the downstream lens position Pr may be stored, and the other may be calculated from the value of the other. Furthermore, because the laser processor 70 ultimately performs control based on the downstream lens position Pr, the information stored in the memory 70a may be only the downstream lens position Pr for each repetition frequency RR.

[0074] As described above, the beam divergence angle of the pulsed laser light PL is larger in the discharge direction than in the direction perpendicular to the discharge direction. In controlling the beam divergence angle, it is often highly necessary to control the discharge direction in which the beam divergence angle is relatively large. The laser processor 70 controls the inter-lens optical path length L based on data on the discharge direction in which the beam divergence angle is relatively large. The beam divergence angle that forms the basis of the graph shown in FIG. 9 and the table data shown in FIG. 10 is data on the discharge direction. That is, in controlling the beam divergence angle adjuster 80, the laser processor 70 controls the inter-lens optical path length L based on the beam divergence angle in the discharge direction of the discharge electrodes 33 a, 33 b.

[0075] Of course, because the cross sections of the upstream lens 80a and the downstream lens 80b are circular, the beam divergence angle in the direction perpendicular to the discharge direction as well as the discharge direction is adjusted. However, with emphasis on the beam divergence angle in the discharge direction, the laser processor 70 controls the inter-lens optical path length L so that the beam divergence angle in the discharge direction is minimized.

[0076] 2.2 Operation The operation of the laser device 2A will be described with reference to the flowchart shown in Fig. 11. When starting control of the beam divergence angle, the laser processor 70 first moves the downstream lens 80b to a preset initial position in step ST1000. As an example, the initial position is a position where the inter-lens optical path length L is twice the focal length F (2F), as shown in Fig. 7.

[0077] In step ST1100, when a light emission trigger signal is received from the exposure apparatus 3, laser processor 70 proceeds to step ST1200 and starts laser oscillation of laser apparatus 2A. After starting laser oscillation, in step ST1300, laser processor 70 waits for reception of the next light emission trigger signal.

[0078] In step ST1300, if the next light emission trigger signal is received (Y in step ST1300), the process proceeds to step ST1400, where laser processor 70 starts laser oscillation.

[0079] Then, in step ST1500, the laser processor 70 calculates the repetition frequency RR based on the time interval between two consecutively received light emission trigger signals.

[0080] Meanwhile, while waiting for reception of the next light emission trigger signal in step ST1300 (N in step ST1300), laser processor 70 measures a first elapsed time from the time the previous light emission trigger signal was received in step ST1600. Then, in step ST1700, laser processor 70 determines whether the first elapsed time is equal to or greater than a first set time, and while the first elapsed time is less than the first set time (N in step ST1700), laser processor 70 returns to step ST1300 and waits for reception of the next light emission trigger signal.

[0081] In step ST1700, if the first elapsed time has reached or exceeded the first set time (Y in step ST1700), the laser processor 70 returns to step ST1100. This is for the following reason. In step ST1500, the repetition frequency RR is calculated based on the time interval between two consecutively received light emission trigger signals. However, depending on the operating state of the exposure apparatus 3, there may be periods during which exposure is paused, in which case the light emission trigger signal may not be received for a relatively long period of time. If the time interval between two consecutively received light emission trigger signals is equal to or greater than the first set time, this is not an appropriate time interval for calculating the repetition frequency RR. In this case, it is considered preferable to not calculate the repetition frequency RR and instead re-measure the first elapsed time from the reception of the first light emission trigger signal. Therefore, if the first elapsed time has reached or exceeded the first set time, the first elapsed time is re-measured. The first set time is, for example, in the range of 1 to 10 seconds.

[0082] After calculating the repetition frequency RR in step ST1500, the laser processor 70 proceeds to step ST1800. In step ST1800, the laser processor 70 determines whether the change in the repetition frequency RR is equal to or greater than a first threshold value Th1. If the determination result is less than the first threshold value Th1 (N in step ST1800), the laser processor 70 returns to step ST1300. If the determination result is equal to or greater than the first threshold value Th1 (Y in step ST1800), the laser processor 70 proceeds to step ST1900.

[0083] The reason for setting the first threshold Th1 is that when the change is very small, there may be little need to change the inter-lens optical path length L. Therefore, by setting the first threshold Th1, a dead zone is created in which the inter-lens optical path length L is not changed when the change in the repetition frequency RR is less than the first threshold Th1. A value considered appropriate as a standard for the dead zone is set in advance as the first threshold Th1. Note that there may be cases in which it is desirable to change the inter-lens optical path length L even with a slight change. Therefore, as an example, the first threshold Th1 is set to a value in the range of 0 Hz to 200 Hz. To substantially provide a dead zone, it is preferable to set the value of the first threshold Th1 to a value greater than 0 Hz. The first threshold Th1 is an example of a "threshold" in this disclosure.

[0084] In step ST1900, the laser processor 70 refers to the table data (see FIG. 10) stored in the memory 70a to find the inter-lens optical path length Lr_min at which the beam divergence angle is minimum at the changed repetition frequency RR.

[0085] In step ST2000, the laser processor 70 changes the inter-lens optical path length L to the obtained inter-lens optical path length Lr_min. Specifically, the laser processor 70 reads out the downstream lens position Pr corresponding to the obtained inter-lens optical path length Lr_min from the table data in the memory 70a. Then, by controlling the optical path length changing mechanism 90, the position of the downstream lens 80b is moved to the read downstream lens position Pr. As a result, the inter-lens optical path length L is changed to "Lr_min."

[0086] Laser processor 70 continues the above operations until laser oscillation is stopped (step ST2100).

[0087] 12 to 14, the control of the beam divergence angle adjustment will be described in more detail. For example, consider a case where the repetition frequency RR before the change is "RR1" and the repetition frequency RR is changed to "RR2." As shown in FIG. 12, since the repetition frequency RR before the change is "RR1," the inter-lens optical path length Lr_min at which the beam divergence angle is minimum is "Lr1_min." The position of the downstream lens 80b is also set to the corresponding "Pr1."

[0088] When the repetition rate RR is changed to "RR2," as shown by the arrow in (1) of Fig. 12, if the inter-lens optical path length L remains at "Lr1_min," the beam divergence angle increases at "RR2." Therefore, as shown by the arrow in (2) of Fig. 12, the laser processor 70 changes the inter-lens optical path length L to the inter-lens optical path length Lr2_min at which the beam divergence angle is minimized at "RR2," which is the new repetition rate RR. The change in inter-lens optical path length L is performed by changing the position of the downstream lens 80b to "Pr2."

[0089] 13 and 14 , a change in the focusing position C of the pulsed laser beam PL by the upstream lens 80a in response to a change in the repetition frequency RR and the meaning of changing the position of the downstream lens 80b will be explained schematically, similar to Fig. 7 . First, the inter-lens optical path length L between the upstream lens 80a and the downstream lens 80b shown in Fig. 13 is "2F," which is twice the focal length F similar to the initial state shown in Fig. 7 . In this state, if there is no thermal deformation or the like, the wavefront of the pulsed laser beam PL incident on the upstream lens 80a is a plane WF0, as shown in Fig. 7 , and therefore the focusing position C of the pulsed laser beam PL coincides with the focal point FP of the upstream lens 80a.

[0090] However, when the repetition frequency RR changes, as shown in Fig. 13 , the wavefront of the pulsed laser beam PL becomes a curved surface WF1 that is convex toward the downstream side due to thermal deformation of the optical element, etc., and the focusing position C of the pulsed laser beam PL moves downstream of the focal point FP of the upstream lens 80a. Since the beam divergence angle of the pulsed laser beam PL is minimum at the focusing position C, when the focusing position C is displaced from the focal point FP, the beam divergence angle at the focal point FP increases. In the state shown in Fig. 13 , the position of the downstream lens 80b has not changed, so the upstream focal point of the downstream lens 80b is aligned with the focal point FP of the upstream lens 80a, and the downstream lens 80b relays an image with a large beam divergence angle.

[0091] Therefore, when the focusing position C moves as shown in Figure 13, the position of the downstream lens 80b is moved downstream by an amount ΔL corresponding to the deviation between the focusing position C and the focal point FP, as shown in Figure 14, thereby changing the inter-lens optical path length L to "2F + ΔL". This causes the upstream focal point of the downstream lens 80b to coincide with the focusing position C where the beam divergence angle is minimum. In this state, the downstream lens 80b can relay an image with the minimum beam divergence angle. This control achieves adjustment of the beam divergence angle.

[0092] 2.3 Effects The laser apparatus 2A according to the first embodiment is equipped with the beam divergence angle adjuster 80 and the laser processor 70 that controls the beam divergence angle adjuster 80, thereby making it possible to suppress an increase in the beam divergence angle due to thermal deformation of optical elements, etc. By suppressing an increase in the beam divergence angle, beam vignetting in the exposure device 3 is also suppressed, and energy loss is also suppressed.

[0093] In the above embodiment, the inter-lens optical path length Lr_min at which the beam divergence angle is minimized is a concept that includes an error in the range of ±10%. It is sufficient for the laser processor 70 to control it within the error range. Furthermore, in controlling the beam divergence angle adjustment, it is not necessary to change the inter-lens optical path length Lr_min at which the beam divergence angle is minimized; it is sufficient to suppress an increase in the beam divergence angle due to a change in the repetition frequency RR. In other words, when the repetition frequency RR changes, the laser processor 70 can obtain the above effect by changing the inter-lens optical path length L so that the beam divergence angle of the expanded pulsed laser light PL becomes smaller.

[0094] In the above embodiment, the adjustment of the beam divergence angle is controlled using the table data shown in FIG. 10. However, instead of the table data, the adjustment of the beam divergence angle may be controlled by calculation using a function corresponding to the graph shown in FIG. 9.

[0095] 3. Second Embodiment Next, a laser device according to a second embodiment of the present disclosure will be described. Note that, hereinafter, the laser device according to the second embodiment has substantially the same configuration as the laser device 2A according to the first embodiment, except that the duty cycle DC defined by the above formula (1) is used instead of the repetition rate RR in controlling the beam divergence angle adjuster 80. The differences will be described below.

[0096] 3.1 Configuration FIG. 15 shows an example of table data used by the laser processor 70 of the laser device according to the second embodiment. For each of a plurality of duties DC, the correspondence between the inter-lens optical path length Ld_min at which the beam divergence angle is minimum and the corresponding downstream lens position Pd is recorded. This table data is stored in the memory 70a. The table data shown in FIG. 15 can be obtained by simulation or experiment, similar to the table data shown in FIG. 10. In the table data, the interval between the duties DC is, for example, in the range of 1% to 10%.

[0097] 15, one of the inter-lens optical path length Ld_min and the downstream lens position Pd may be stored, and the other may be calculated from the value of the other. Furthermore, since the laser processor 70 ultimately performs control based on the downstream lens position Pd, the information stored in the memory 70a may be only the downstream lens position Pd for each duty DC.

[0098] 3.2 Operation The operation of the laser apparatus of the second embodiment will be described with reference to the flowchart shown in Fig. 16. As with the laser apparatus 2A of the first embodiment shown in Fig. 11, when starting control of the beam divergence angle, the laser processor 70 first moves the downstream lens 80b to a preset initial position in step ST3000. As an example, the initial position is a position where the inter-lens optical path length L is twice the focal length F (2F), as shown in Fig. 7.

[0099] In step ST3100, when laser processor 70 starts receiving a light emission trigger signal from exposure apparatus 3, laser processor 70 proceeds to step ST3200 and starts laser oscillation. Laser oscillation is performed every time a light emission trigger signal is received.

[0100] In step ST3300, laser processor 70 measures a second elapsed time from the start of laser oscillation.

[0101] In step ST3400, it is determined whether the second elapsed time is equal to or greater than the second set time, and if the second elapsed time is less than the second set time (N in step ST3400), the process returns to step ST3300, and laser processor 70 continues measuring the second elapsed time. On the other hand, if the second elapsed time is equal to or greater than the second set time (Y in step ST3400), laser processor 70 calculates duty DC.

[0102] The second set time corresponds to the set time Tc related to the above equation (1). In calculating the duty cycle DC, if the second elapsed time is equal to or greater than the second set time, the laser processor 70 counts Np, which is the number of pulses of the pulsed laser light PL output within the second elapsed time. Furthermore, the laser processor 70 calculates Np_max, which is the maximum number of pulses that the laser device of the second embodiment can output within the second elapsed time, based on a preset maximum repetition frequency RR_max and the second elapsed time. The laser processor 70 calculates the duty cycle DC based on Np and Np_max in accordance with the duty cycle DC equation (1). The second set time is, for example, in the range of 45 to 90 seconds.

[0103] In step ST3600, laser processor 70 determines whether the change from the previous duty DC is equal to or greater than second threshold Th2. If the result of the determination is less than second threshold Th2 (N in step ST3600), laser processor 70 returns to step ST3300, and if the result is equal to or greater than second threshold Th2 (Y in step ST3600), laser processor 70 proceeds to step ST3700.

[0104] The reason for setting the second threshold value Th2 is the same as the reason for setting the first threshold value Th1 in the first embodiment. As an example, the second threshold value Th2 is set to a value in the range of 0% to 2%. In order to substantially provide a dead zone, it is preferable to set the value of the second threshold value Th2 to a value greater than 0%. The second threshold value Th2 is an example of a "threshold value" in the present disclosure.

[0105] In step ST3700, the laser processor 70 refers to the table data (see FIG. 15) stored in the memory 70a to find the inter-lens optical path length Ld_min at which the beam divergence angle is minimum at the changed duty DC.

[0106] In step ST3800, the laser processor 70 changes the inter-lens optical path length L to the obtained inter-lens optical path length Ld_min. Specifically, the laser processor 70 reads out the downstream lens position Pd corresponding to the obtained inter-lens optical path length Ld_min from the table data in the memory 70a. Then, by controlling the optical path length changing mechanism 90, the position of the downstream lens 80b is moved to the read downstream lens position Pd. As a result, the inter-lens optical path length L is changed to "Ld_min."

[0107] Laser processor 70 continues the above operation until laser oscillation is stopped (step ST3900).

[0108] 3.3 Effects The effects of the laser apparatus according to the second embodiment are the same as those of the laser apparatus 2A according to the first embodiment. Depending on the operation of the exposure apparatus 3, there may be cases where the beam divergence angle adjuster 80 can be more appropriately controlled by using the duty cycle DC rather than the repetition rate RR. It is preferable to select whether to use the repetition rate RR or the duty cycle DC depending on the actual situation.

[0109] 17 and 18 is an example in which the position of the beam divergence angle adjuster 80 in the laser device 2A of the first embodiment is changed. Specifically, in the first modification, the upstream lens 80a is disposed inside the housing 100a of the first OPS 100, and the downstream lens 80b is disposed outside the housing 100a and upstream of the second OPS 50.

[0110] The upstream lens 80a is disposed within the housing 100a between the beam splitter 104 and the high-reflection mirror 106a. The optical path between the beam splitter 104 and the high-reflection mirror 106a is an optical path through which the pulsed laser beam PL, whose pulse width has been expanded, travels around the delay optical path, even though it is within the housing 100a. Therefore, the pulsed laser beam PL, whose pulse width has been expanded by the first OPS 100, is incident on the upstream lens 80a, and the beam divergence angle adjuster 80 can adjust the beam divergence angle of the pulsed laser beam PL, whose pulse width has been expanded.

[0111] According to the first modified example, it is possible to increase the inter-lens optical path length L between the upstream lens 80a and the downstream lens 80b, which makes it easy to arrange the upstream lens 80a and the downstream lens 80b even when the focal length F of the upstream lens 80a and the downstream lens 80b is long. As a lens characteristic, the longer the focal length F, the less the influence of aberration tends to be. According to the first modified example, it is easy to use lenses that are relatively less affected by aberration as the upstream lens 80a and the downstream lens 80b.

[0112] 19 and 20 is an example in which the position of the beam divergence angle adjuster 80 in the laser apparatus 2A of the first embodiment is changed, as in the first modified example. Specifically, in the second modified example, the beam divergence angle adjuster 80 is disposed downstream of the second OPS 50.

[0113] If space can be secured downstream of the second OPS 50, the second modified example can be used.

[0114] 4.3 Other Modifications The optical path length change mechanism 90A shown in FIG. 21 is a modification of the optical path length change mechanism 90 shown in FIG. 8. The optical path length change mechanism 90A moves the lens holder 91 using an actuator 94 and a spring 95 instead of a linear stage 92. The actuator 94 is, for example, a solenoid having a plunger that is movable between a protruding position and a retracted position. The actuator 94 is controlled by the laser processor 70. The actuator 94 is fixed to a base 93, and the plunger abuts against the lens holder 91. When the plunger protrudes, the lens holder 91 is pressed and moved in one direction along the optical axis OA. The spring 95 has a biasing force that pulls the lens holder 91 in the direction in which the plunger retracts. Therefore, when the plunger retracts, the lens holder 91 moves while maintaining contact with the plunger due to the biasing force of the spring 95. The configuration of the optical path length change mechanism can be modified in various ways, and may be selected as appropriate.

[0115] Furthermore, in the above embodiment, the optical path length change mechanism has been described as changing the position of the downstream lens 80b, but it may also be changed as changing the position of the upstream lens 80a. For example, in the state shown in Fig. 13, by moving the position of the upstream lens 80a further upstream, it is possible to achieve the state shown in Fig. 14, in which the focus position C of the pulsed laser beam PL and the focus of the downstream lens 80b coincide. Whether to move the upstream lens 80a or the downstream lens 80b is appropriately selected taking into consideration the space required for placement, etc.

[0116] 5. Electronic Device Manufacturing Method Figure 22 shows a schematic configuration example of an exposure apparatus 200. The exposure apparatus 200 includes an illumination optical system 204 and a projection optical system 206. The illumination optical system 204 illuminates a reticle pattern of a reticle (not shown) placed on a reticle stage RT with pulsed laser light PL incident thereon, for example, from the laser apparatus 2A according to the first embodiment. The projection optical system 206 reduces and projects the pulsed laser light PL that has passed through the reticle, forming an image on a workpiece (not shown) placed on a workpiece table WT. The workpiece is a photosensitive substrate such as a semiconductor wafer coated with photoresist.

[0117] The exposure apparatus 200 exposes the workpiece with pulsed laser light PL reflecting the reticle pattern by synchronously translating the reticle stage RT and the workpiece table WT. After the reticle pattern is transferred to the 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. Note that the laser apparatus 2A may be the laser apparatus according to the second embodiment or a laser apparatus to which the various modifications described above are applied.

[0118] 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.

[0119] Terms used throughout this specification and the appended claims should be interpreted as "open-ended" terms. For example, the terms "including" 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" or "an" used in this specification and the appended claims should be interpreted as meaning "at least one" or "one or more."

Claims

1. A laser apparatus comprising: an oscillator that outputs pulsed laser light of an ultraviolet wavelength; an amplifier that amplifies the pulsed laser light; an optical pulse stretcher including a beam splitter and a plurality of mirrors and stretching a pulse width of the pulsed laser light; a beam divergence angle adjuster including an upstream lens arranged upstream in an optical path of the pulsed laser light, a downstream lens arranged downstream of the upstream lens, and an optical path length change mechanism that changes an inter-lens optical path length between the upstream lens and the downstream lens, and adjusts a beam divergence angle of the stretched pulsed laser light; and a processor that controls the beam divergence angle adjuster, determining a repetition frequency or duty of the pulsed laser light, and, when the repetition frequency or the duty has changed by more than a predetermined threshold value, changing the inter-lens optical path length in accordance with the changed repetition frequency or duty so that the beam divergence angle of the stretched pulsed laser light becomes smaller.

2. The laser device according to claim 1, wherein the amplifier includes a pair of discharge electrodes, and in controlling the beam divergence angle adjuster, the processor changes the inter-lens optical path length based on the beam divergence angle in the discharge direction of the discharge electrodes.

3. The laser device according to claim 1, wherein the processor changes the inter-lens optical path length to a length that minimizes the beam divergence angle in accordance with the changed repetition frequency or duty.

4. The laser device of claim 1, wherein the processor includes a memory unit that stores a correspondence between each of the multiple repetition frequencies or multiple duties and information related to the inter-lens optical path length at which the beam divergence angle of the expanded pulsed laser light is minimized, and the processor obtains from the memory unit the information related to the inter-lens optical path length at which the beam divergence angle is minimized in accordance with the changed repetition frequency or duty.

5. The laser device according to claim 4, wherein the information relating to the inter-lens optical path length is the inter-lens optical path length or the position of the upstream lens or the downstream lens for achieving the inter-lens optical path length.

6. The laser device according to claim 1, wherein the optical path length changing mechanism changes the inter-lens optical path length by changing the position of the downstream lens.

7. The laser device according to claim 1, wherein the upstream lens and the downstream lens function as a relay lens that relays the beam spot of the pulsed laser light focused by the upstream lens to the downstream lens.

8. The laser device according to claim 7, wherein the upstream lens is a plano-convex lens having a convex surface on the incident side, and the downstream lens is a plano-convex lens having a flat surface on the incident side.

9. The laser device of claim 1, wherein the optical pulse stretcher includes a first optical pulse stretcher and a second optical pulse stretcher disposed downstream of the first optical pulse stretcher, and the first optical pulse stretcher has a longer delay path than the second optical pulse stretcher.

10. The laser device of claim 9, wherein the beam divergence angle adjuster is disposed between the first optical pulse stretcher and the second optical pulse stretcher.

11. The laser device of claim 9, wherein the upstream lens is disposed within a housing of the first optical pulse stretcher, and the downstream lens is disposed outside the housing of the first optical pulse stretcher and upstream of the second optical pulse stretcher.

12. The laser device of claim 9, wherein the beam divergence angle adjuster is disposed downstream of the second optical pulse stretcher.

13. A method for manufacturing an electronic device, comprising: outputting a pulsed laser beam output from a laser apparatus including an oscillator that outputs a pulsed laser beam of an ultraviolet wavelength, an amplifier that amplifies the pulsed laser beam, and an optical pulse stretcher including a beam splitter and a plurality of mirrors that stretches a pulse width of the pulsed laser beam to an exposure apparatus; and exposing a photosensitive substrate in the exposure apparatus with the pulsed laser beam to manufacture an electronic device, wherein the laser apparatus includes: an upstream lens that is arranged upstream in an optical path of the pulsed laser beam, a downstream lens that is arranged downstream of the upstream lens, and an optical path length changing mechanism that changes an inter-lens optical path length between the upstream lens and the downstream lens, and adjusts a beam divergence angle of the stretched pulsed laser beam; and a processor that controls the beam divergence angle adjuster, the processor determining a repetition frequency or duty of the pulsed laser beam, and, when the repetition frequency or the duty has changed by equal to or more than a preset threshold value, changing the inter-lens optical path length so that the beam divergence angle of the stretched pulsed laser beam becomes smaller in accordance with the changed repetition frequency or duty. A method for manufacturing an electronic device.

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