Interferometric exposure apparatus and interferometric exposure method

Abstract

To provide an interference exposure apparatus and interference exposure method that can improve the accuracy of interference exposure using coherent pulsed light without increasing the size of the apparatus. [Solution] An interference exposure apparatus according to one embodiment of the present invention is an interference exposure apparatus that performs interference exposure on an object to be irradiated arranged along the exposure surface by superimposing a first beam and a second beam obtained by splitting coherent pulsed light in an irradiation area on the exposure surface, and comprises a beam splitter, an incident optical system, and an optical path adjustment unit. The beam splitter causes the first beam and the second beam to be emitted in different directions from each other. The incident optical system causes the first beam and the second beam emitted from the beam splitter to be incident in the irradiation area so that they overlap with each other at an incident angle set for each. The optical path adjustment unit is capable of moving the beam splitter so that the first beam and the second beam interfere in the irradiation area.

Description

Technical Field

[0001] The present invention relates to an interference exposure apparatus and an interference exposure method for performing interference exposure.

Background Art

[0002] Conventionally, a technique for performing interference exposure using a pulsed laser has been developed. A pulsed laser is, for example, attracting attention as a light source that has higher energy than a continuous wave (CW) laser and enables exposure in a short time. On the other hand, a pulsed laser has a shorter coherence length than a CW laser, and an optical path difference between two beams is likely to affect the accuracy of interference exposure.

[0003] In contrast, Patent Document 1 describes a method of providing an optical delay circuit in the optical path of one of two beams split by a splitter in an interference exposure apparatus using a pulsed laser. This optical delay circuit is composed of a pair of mirrors that reflect one beam so as to be folded back, and the optical path length of one beam is adjusted by moving the pair of mirrors integrally. Thereby, the optical path difference between the two beams is suppressed, and it is possible to improve the exposure accuracy.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] Optical delay circuits that fold back the optical path can extend or shorten the original optical path by moving the entire optical delay circuit. However, to sufficiently extend the optical path, for example, it is necessary to ensure a sufficient range of motion for the optical delay circuit. Depending on the incidence conditions of the two beams and the configuration of the optical system, the optical path difference between the two beams may become large, and the method using the optical delay circuit described above may result in a larger device.

[0006] In view of the above circumstances, the object of the present invention is to provide an interference exposure apparatus and an interference exposure method that can improve the accuracy of interference exposure using coherent pulsed light without increasing the size of the apparatus. [Means for solving the problem]

[0007] To achieve the above objective, an interference exposure apparatus according to one embodiment of the present invention is an interference exposure apparatus that performs interference exposure on an object to be irradiated arranged along the exposure surface by superimposing a first beam and a second beam obtained by splitting coherent pulsed light in an irradiation area on the exposure surface, and comprises a beam splitter, an incident optical system, and an optical path adjustment unit. The beam splitter causes the first beam and the second beam to be emitted in different directions. The incident optical system causes the first beam and the second beam emitted from the beam splitting section to be incident on the irradiation area so that they overlap with each other at the respective set incident angles. The optical path adjustment unit is capable of moving the beam branching unit so that the first beam and the second beam interfere with each other in the irradiation area.

[0008] In this interference exposure apparatus, a beam splitter that emits a first beam and a second beam, which are obtained by splitting coherent pulsed light, in different directions, is moved so that the first beam and the second beam interfere with each other in the irradiation area. By moving the beam splitter, it is possible to adjust, for example, extending one of the optical paths of the first beam and the second beam while simultaneously shortening the other. As a result, it is possible to improve the accuracy of interference exposure using coherent pulsed light without increasing the size of the apparatus.

[0009] The incident optical system may have a variable incident angle of at least one of the first beam or the second beam with respect to the exposure surface. In this case, the optical path adjustment unit may move the beam splitter in accordance with the change in the incident angle of at least one of the first beam or the second beam.

[0010] The incident optical system may cause the first beam and the second beam to be incident on the irradiation area in such a manner that they are asymmetrical with respect to the normal to the exposure surface in the irradiation area.

[0011] The beam splitter may include a demultiplexing element that splits the pulsed light into a first beam and a second beam, and at least one optical element that sets at least one of the following: the incident direction of the pulsed light on the demultiplexing element, the exit direction of the first beam from the beam splitter, or the exit direction of the second beam from the beam splitter.

[0012] The beam splitter may emit the first beam and the second beam in opposite directions along a predetermined linear axis. In this case, the optical path adjustment unit may move the beam splitter along the linear axis.

[0013] The incident optical system may include a first mirror that moves along the linear axis and rotates with respect to the linear axis to reflect the first beam emitted from the beam bifurcation section, and a second mirror that moves along the linear axis and rotates with respect to the linear axis to reflect the second beam emitted from the beam bifurcation section.

[0014] The incident optical system may include a third mirror that moves along and rotates with respect to the first drive axis and reflects the first beam reflected by the first mirror toward the irradiation area, and a fourth mirror that moves along and rotates with respect to the second drive axis and reflects the second beam reflected by the second mirror toward the irradiation area.

[0015] The first drive shaft and the second drive shaft may each be an arc shaft surrounding the irradiation area.

[0016] The at least one optical element may include a fifth mirror that reflects the pulsed light incident along the linear axis toward the beam splitting element.

[0017] The beam branching section may set the emission axes of the first beam and the second beam on the same axis along the linear axis.

[0018] The beam splitting element may be either a beam splitter or a diffraction grating.

[0019] The optical path adjustment section may include a moving mechanism that moves the beam branching section and a control section that controls the moving mechanism to control the position of the beam branching section.

[0020] The optical path adjustment section may include a sensor section that detects the interference state of the first beam and the second beam in the irradiation area. In this case, the control section may control the moving mechanism based on the detection result of the sensor section.

[0021] The sensor section may detect interference fringes generated by the overlap of the first beam and the second beam. In this case, the control section may move the beam branching section so that the contrast of the interference fringes becomes high.

[0022] The sensor section may detect higher harmonics generated by the overlap of the first beam and the second beam. In this case, the control section may move the beam branching section so that the intensity of the higher harmonics becomes high.

[0023] The pulse width of the pulsed light may be 100 nsec or less.

[0024] An interference exposure method according to one embodiment of the present invention is an interference exposure method using the interference exposure apparatus, and includes detecting an interference state of the first beam and the second beam in the irradiation area. Based on the detection result of the interference state, the position of the beam splitter is controlled.

Advantages of the Invention

[0025] As described above, according to the present invention, it is possible to improve the accuracy of interference exposure using interferable pulsed light without increasing the size of the apparatus. Note that the effects described here are not necessarily limited, and any of the effects described in the present disclosure may be applicable.

Brief Description of the Drawings

[0026] [Figure 1] It is a schematic diagram showing a configuration example of an interference exposure apparatus according to an embodiment of the present invention. [Figure 2] It is a schematic diagram for explaining interference exposure. [Figure 3] It is a schematic diagram for explaining the relationship between the optical path difference of the first beam and the second beam and interference exposure. [Figure 4] It is a schematic diagram for explaining the relationship between the optical path difference of the first beam and the second beam and interference exposure. [Figure 5] It is a graph showing the relationship between the optical path difference of the first beam and the second beam and the contrast of interference fringes. [Figure 6] It is a schematic diagram showing a configuration example of a beam splitting section. [Figure 7] It is a schematic diagram showing another configuration example of a beam splitting section. [Figure 8] It is a schematic diagram showing a configuration example of a sensor section. [Figure 9] It is a flowchart showing an operation example of a control section. [Figure 10] It is a schematic diagram showing a specific configuration example of an interference exposure apparatus. [Figure 11] It is a schematic diagram showing a configuration example of a beam splitting section according to another embodiment. [Figure 12]This is a schematic diagram showing an example of the configuration of a beam branching section according to another embodiment. [Figure 13] This is a schematic diagram showing an example of the configuration of a beam branching section according to another embodiment. [Figure 14] This is a schematic diagram showing an example of the configuration of a beam branching section according to another embodiment. [Figure 15] This is a schematic diagram showing an example of the configuration of a beam branching section according to another embodiment. [Modes for carrying out the invention]

[0027] Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[0028] [Configuration of an interferometry lithography system] Figure 1 is a schematic diagram showing an example of the configuration of an interference exposure apparatus according to one embodiment of the present invention. The interference exposure apparatus 100 is an apparatus that performs interference exposure on a workpiece W arranged along the exposure surface 4 by superimposing a first beam B1 and a second beam B2, which are obtained by splitting coherent pulsed light, in the irradiation area 5 on the exposure surface 4.

[0029] The workpiece W of the interference exposure apparatus 100 is, for example, a substrate on which a photosensitive material is provided on the surface. Any substrate can be used as the substrate, such as a glass substrate, a resin substrate, or a semiconductor substrate. The photosensitive material can be a material coated on the substrate or a sheet-like material bonded to the substrate. In addition, the types of substrates and photosensitive materials are not limited. In this embodiment, the workpiece W corresponds to the object to be irradiated.

[0030] The coherent pulsed light that forms the basis of the first beam B1 and the second beam B2 is coherent light with a pulsed waveform. Typically, pulsed laser light can be used as the pulsed light. The pulsed laser light is emitted from the pulsed light source 20. In the following, the pulsed laser light before splitting may be referred to as beam B0. The first beam B1 and the second beam B2 are light beams generated by splitting the pulsed laser light (beam B0) into two by a demultiplexing element 25 such as a beam splitter or diffraction grating.

[0031] Thus, interference exposure using two light beams (first beam B1 and second beam B2) is generally also called two-beam interference exposure, and is a method of exposing a workpiece W by utilizing interference fringes (see Figure 2) that are produced by superimposing the light beams. In the interference exposure apparatus 100, the photosensitive material of the workpiece W placed in the irradiation area 5 is exposed to the interference fringes of the first beam B1 and the second beam B2.

[0032] The exposure surface 4 is a virtual plane in the interference exposure apparatus 100 where interference exposure is performed. For example, each part of the interference exposure apparatus 100 is arranged with respect to the exposure surface 4. The workpiece W is also arranged such that, for example, its surface coincides with the exposure surface 4. The irradiation area 5 is an area set on the exposure surface 4 as the target region for interference exposure. The first beam B1 and the second beam B2 are irradiated such that their respective irradiation spots overlap in the irradiation area 5.

[0033] In the following, directions that are orthogonal to each other on the exposure surface 4 are defined as the X direction and the Y direction, and the direction that is orthogonal to the XY plane is defined as the Z direction. The X direction, Y direction, and Z direction correspond to the left-right direction, front-back direction, and up-down direction, respectively, in the interference exposure apparatus 100.

[0034] As shown in Figure 1, the interference exposure apparatus 100 includes an optical system 10, a stage mechanism 11, a sensor unit 12, and a control unit 13. The optical system 10 also includes a pulse light source 20, a beam splitter 21, a moving mechanism 22, and an incident optical system 23.

[0035] The pulsed light source 20 is a light source device that emits pulsed laser light (beam B0). The pulsed light source 20 emits pulses having a predetermined pulse width and wavelength at regular intervals. As the pulsed light source 20, laser light sources using direct modulation, external modulation, Q-switching, mode-locking, etc. are used. In addition, the type of pulsed light source 20, the wavelength of the pulsed laser light, the pulse width, the emission interval, etc. are not limited.

[0036] The beam splitter 21 causes the first beam B1 and the second beam B2 to be emitted in different directions. In other words, the beam splitter 21 is an optical system that splits the optical paths of the first beam B1 and the second beam B2 in different directions. As shown in Figure 1, the beam splitter 21 has an incident direction control mirror 24 and a demultiplexer element 25.

[0037] The incident direction control mirror 24 is a mirror that relays the beam B0 emitted from the pulsed light source 20 to the demultiplexer 25. Here, the incident direction control mirror 24 reflects the beam B0 emitted from the pulsed light source 20 toward the right in the figure to the demultiplexer 25 located below the incident direction control mirror 24. The incident direction control mirror 24 is an example of an optical element that sets the incident direction of the pulsed laser light (beam B0) toward the demultiplexer 25.

[0038] The demultiplexer 25 splits the pulsed laser light (beam B0) into a first beam B1 and a second beam B2. Therefore, the demultiplexer 25 becomes the starting point for the optical paths of the first beam B1 and the second beam B2. A beam splitter, diffraction grating, or the like can be used as the demultiplexer 25.

[0039] In the example shown in Figure 1, a beam B0 incident on the demultiplexer 25 from above is schematically illustrated as being split into a first beam B1 directed to the left and a second beam B2 directed to the right. In reality, the first beam B1 and the second beam B2 are not necessarily split in opposite directions at the demultiplexer 25. For this reason, the beam splitter 21 is provided with an optical element to set the exit direction of the first beam B1 from the beam splitter 21, or the exit direction of the second beam B2 from the beam splitter 21.

[0040] The beam splitter 21 also has a support member 27 that integrally supports the demultiplexing element 25 and other optical elements such as the incident direction control mirror 24. In other words, the beam splitter 21 is an optical unit provided on the support member 27. This makes it possible to move the entire beam splitter 21 as a single unit. The specific configuration of the beam splitter 21 will be described later with reference to Figure 6, etc.

[0041] The moving mechanism 22 is a mechanism that moves the beam splitter 21. Specifically, the moving mechanism 22 moves the support member 27 that supports the demultiplexing element 25, etc., in a predetermined direction within the beam splitter 21. As the moving mechanism 22, for example, a linear actuator that moves the support member using a motor or the like, or a stage mechanism can be used.

[0042] The incident optical system 23 directs the first beam B1 and the second beam B2, emitted from the beam bifurcation section 21, into the irradiation area 5 so that they overlap at their respective set incidence angles. In other words, the incident optical system 23 is an optical system that sets the optical paths of the first beam B1 and the second beam B2 for performing two-beam interference exposure in the irradiation area 5. The incidence angles of the first beam B1 and the second beam B2 are set individually according to the exposure pattern conditions for interference exposure (slant angle, pitch width, etc.).

[0043] As shown in Figure 1, the incident optical system 23 has two relay drive mirrors 28a and 28b and two irradiation drive mirrors 29a and 29b. For example, the first beam B1 emitted from the beam splitter 21 is reflected by the relay drive mirror 28a and the irradiation drive mirror 29a and incident on the irradiation area 5. Similarly, the second beam B2 emitted from the beam splitter 21 is reflected by the relay drive mirror 28b and the irradiation drive mirror 29b and incident on the irradiation area 5.

[0044] In the incident optical system 23, the incident angles of the first beam B1 and the second beam B2 are appropriately set by adjusting the position and orientation of these mirrors (relay drive mirrors 28a and 28b, and illumination drive mirrors 29a and 29b). The configuration of the incident optical system 23 and the operation of each part will be explained in detail later.

[0045] The stage mechanism 11 has a stage 50 on which the workpiece W is placed, and is a mechanism for moving the stage 50. The stage 50 holds the workpiece W by a vacuum suction mechanism or a clamping mechanism. The stage mechanism 11 is configured so that the stage 50 can move in the X and Y directions. The stage mechanism 11 may also be configured so that the position of the stage 50 in the Z direction (height position of the workpiece W) can be adjusted, or the stage 50 may be configured so that it can rotate around a rotation axis along the Z direction.

[0046] The sensor unit 12 detects the interference state of the first beam B1 and the second beam B2 in the irradiation area 5. The interference state refers to the state of interference fringes that occur, for example, when the first beam B1 and the second beam B2 are superimposed in the irradiation area 5. The sensor unit 12 uses an element capable of measuring parameters that represent the presence or absence of interference fringes and the state of the generated interference fringes. The specific configuration of the sensor unit 12 will be described later with reference to Figure 8, etc.

[0047] The control unit 13 is a control device that controls the operation of the entire interference exposure apparatus 100, and has the necessary hardware configuration for a computer, such as a CPU (Central Processing Unit) and memory. The control unit 13 controls the position and orientation of the mirrors (relay drive mirrors 28a and 28b, irradiation drive mirrors 29a and 29b) that constitute the incident optical system 23 according to input values ​​related to the conditions of the exposure pattern of interference exposure formed on the workpiece W (such as slant angle and pitch width).

[0048] The control unit 13 also controls the position of the beam splitter 21 by controlling the moving mechanism 22. For example, by outputting a predetermined control signal to the moving mechanism 22, the direction and amount of movement of the beam splitter 21 are controlled. In this embodiment, the control unit 13 controls the moving mechanism based on the detection results of the sensor unit 12. By using the detection results of the sensor unit 12, it becomes possible to automatically move the beam splitter 21, for example.

[0049] In this embodiment, the optical path adjustment unit 19 is composed of the moving mechanism 22, sensor unit 12, and control unit 13 described above. The optical path adjustment unit 19 adjusts the optical paths of the first beam B1 and the second beam B2 by moving the beam branching unit 21. In the following, descriptions of the moving mechanism 22, sensor unit 12, and control unit 13 may be described as descriptions of the optical path adjustment unit 19.

[0050] [Interferometry] Figure 2 is a schematic diagram illustrating interference lithography. As described above, the first beam B1 and the second beam B2 are generated by splitting the pulsed laser light (beam B0). Therefore, the first beam B1 and the second beam B2 become pulsed laser light with pulses of the same waveform. In this case, in the region where the pulses of the first beam B1 and the second beam B2 overlap, interference fringes (hereinafter referred to as exposure interference fringes 6) are generated, in which regions where the beams reinforce each other (black regions) and regions where they cancel each other out (white regions) are alternately formed. In interference lithography, the photosensitive material provided on the surface of the workpiece W is exposed by these exposure interference fringes 6. As a result, a periodic pattern similar to, for example, the exposure interference fringes 6 is formed on the workpiece W.

[0051] As shown in Figure 2, the pattern of the exposure interference fringes 6 can be represented by the slant angle α and the pitch width p. Here, the slant angle α is the inclination angle of the exposure interference fringes 6 with respect to the normal L (Z direction) of the exposure surface 4. For example, in the incident planes of the two beams (here, the XZ plane), the angle between the direction in which the stripes of the exposure interference fringes 6 extend and the normal L of the exposure surface 4 is the slant angle α. The period of the stripes of the exposure interference fringes 6 (the period of the region where each beam reinforces (or cancels out) interference) is the pitch width p. Note that the pitch width p is the period in the direction perpendicular to each stripe.

[0052] Here, the angles of incidence of the first beam B1 (left beam) incident from the upper left and the second beam B2 (right beam) incident from the upper right are denoted as θ1 and θ2, respectively, with respect to the exposure surface 4 (XY plane). The optical axes of the first beam B1 and the second beam B2 toward the irradiation area 5 are denoted as the incidence axes.

[0053] The incident angle θ1 is the angle between the incident axis of the first beam B1 and the normal L (in the Z direction), and the incident angle θ2 is the angle between the incident axis of the second beam B2 and the normal L (in the Z direction). In the following, for incident angles θ1 and θ2, the case where the incident axis of the beam (B1 or B2) coincides with the normal L is defined as 0°, and the direction counterclockwise with respect to the normal L is defined as the positive direction. For example, in Figure 2, θ1 is a negative value and θ2 is a positive value. Using incident angles θ1 and θ2, the slant angle α is expressed by the following equation (1).

[0054]

number

[0055] Furthermore, if we let λ be the wavelength of the first beam B1 and the second beam B2 (the wavelength of pulsed laser light), and n be the refractive index of the medium in which the exposure interference fringes 6 are formed (for example, the photosensitive material on the workpiece W in which the exposure interference fringes 6 are exposed), then the pitch width p of the exposure interference fringes 6 can be expressed using the following equation (2).

[0056]

number

[0057] From equation (1), the slant angle α is the angle obtained by bisecting the sum of the incident angles (θ1 + θ2), and is the angle that the bisectors of each incident axis on the incident plane make with the normal L. Also, from equation (2), the pitch width p changes according to the angle between each incident axis (|θ1 - θ2|). In this way, the slant angle α and the pitch width p can be adjusted by appropriately setting the incident angles θ1 and θ2 of the first beam B1 and the second beam B2.

[0058] [Coherence length of pulsed laser light] Generally, pulsed laser light has a higher output than continuous wave (CW) laser light because its energy is concentrated at time intervals defined by the pulse width. On the other hand, pulsed laser light has a wider linewidth (bandwidth of the frequency spectrum), resulting in a shorter coherence length compared to single-wavelength CW laser light. Therefore, to perform interference lithography using pulsed laser light, it is important to properly set the optical path lengths of the two beams. This point will be explained below.

[0059] Figures 3 and 4 are schematic diagrams illustrating the relationship between the optical path difference between the first beam B1 and the second beam B2 and interference exposure. In the upper diagrams of Figures 3 and 4, the positions of each pulse 1 in the first beam B1 and the second beam B2, as viewed from the Y direction, are schematically illustrated using dotted lines representing equiphase surfaces. The four equiphase surfaces represent the positions where the waveform of pulse 1 has the same phase, starting from the front in the direction of beam propagation. In the lower diagrams of Figures 3 and 4, the state of the irradiation area 5 on the exposure surface 4 (XY plane) corresponding to the upper diagrams is schematically illustrated.

[0060] Figure 3 shows a state in which the optical path lengths of the first beam B1 and the second beam B2 are equal. In this disclosure, the optical path length of the first beam B1 is the length of the optical path that the first beam B1 travels from the demultiplexer 25 to the irradiation area 5. Similarly, the optical path length of the second beam B2 is the length of the optical path that the second beam B2 travels from the demultiplexer 25 to the irradiation area 5. Typically, the optical path length is the length of the optical axis (central axis of the spot) in the optical path through which each beam travels.

[0061] When the optical path lengths of the first beam B1 and the second beam B2 are equal, the timing at which pulse 1 of each beam reaches the irradiation area 5 is the same. In this case, as shown in the lower part of Figure 3, pulse 1 of the first beam B1 and pulse 1 of the second beam B2 interfere appropriately in the irradiation area 5, generating exposure interference fringes 6.

[0062] Furthermore, since the first beam B1 and the second beam B2 are incident at an angle, as shown in the upper part of Figure 3, the timing at which the corresponding equiphase planes of each beam reach the irradiation area 5 (exposure surface 4) is staggered at the outer edge of the irradiation area 5 (spot of each beam). In other words, the optical path difference between the first beam B1 and the second beam B2 is larger at the outer edge of the irradiation area 5 compared to the central part. As a result, interference between each pulse becomes less likely at the outer edge of the irradiation area 5. For this reason, for example, if the optical path lengths of the first beam B1 and the second beam B2 are equal, exposure interference fringes 6 will be generated in the central region of the irradiation area 5.

[0063] Figure 4 shows a state where the optical path lengths of the first beam B1 and the second beam B2 are different. Here, since the optical path length of the second beam B2 is longer than that of the first beam B1, pulse 1 of the second beam B2 arrives at the irradiation area 5 later than pulse 1 of the first beam B1. For this reason, if the difference in the optical path lengths of the first beam B1 and the second beam B2 (optical path difference) becomes large enough to exceed a certain level, pulse 1 of the first beam B1 and pulse 1 of the second beam B2 will no longer interfere with each other in the irradiation area 5. As a result, as shown in the lower part of Figure 4, exposure interference fringes 6 will not be generated in the irradiation area 5.

[0064] Figure 5 is a graph showing the relationship between the optical path difference between the first beam B1 and the second beam B2 and the contrast of the interference fringes. Here, to show the effect of coherence length on exposure quality, the visibility of the interference fringes against the optical path difference for typical CW laser light and pulsed laser light is shown. The visibility of the interference fringes is, for example, the contrast between the light and dark of the interference fringes. The horizontal axis of the graph is the optical path difference [mm], and the vertical axis is the visibility of the interference fringes produced by the interference of the first beam B1 and the second beam B2 in the irradiation area 5.

[0065] Here, the contrast of the interference fringes (measurement interference fringes) formed by a combined beam (see Figure 8, etc.) obtained by combining the first beam B1 and the second beam B2 was measured as a parameter representing the visibility of the exposure interference fringes 6. In the measurement, for both CW laser light and pulsed laser light, each laser light was split into two beams, a delay mechanism was added to the optical path of one of the beams to change the optical path length, and interference fringes were formed by superimposing the two beams.

[0066] As shown in Figure 5, the visibility of CW laser light does not significantly decrease even if the optical path length of one beam changes. In contrast, the visibility of pulsed laser light is maximum when the optical path difference is 0, and the contrast decreases sensitively when the optical path length of one beam changes. This is thought to be because the coherence length of pulsed laser light is short. In the example shown in Figure 5, the visibility of the interference fringes can be maintained at more than 50% of the peak value only when the optical path difference is within the range of ±1.5 mm.

[0067] For example, a decrease in visibility means that the difference in brightness between interference fringes becomes smaller. In other words, in interference fringes with low visibility, the amount of light illuminating the area that should be illuminated decreases, and the amount of light illuminating the area that should not be illuminated increases. As a result, exposure accuracy may decrease. Also, when the optical path difference exceeds a certain level, the interference fringes themselves will not be generated, as shown in Figure 4.

[0068] Thus, when using pulsed laser light, even a slight deviation in the optical path lengths of the first beam B1 and the second beam B2 can make it impossible to maintain exposure quality. In other words, when performing interference lithography using pulsed laser light, it is necessary to precisely adjust the optical path lengths of the first beam B1 and the second beam B2.

[0069] [Adjustment of optical path length in interferometric exposure apparatus] Returning to Figure 1, the configuration for adjusting the optical path lengths of the first beam B1 and the second beam B2 in the interference exposure apparatus 100 will be described. As described above, the interference exposure apparatus 100 is provided with an optical path adjustment unit 19 (movement mechanism 22, sensor unit 12, and control unit 13) that moves the beam branching unit 21.

[0070] The optical path adjustment unit 19 can move the beam splitter 21 so that the first beam B1 and the second beam B2 interfere with each other in the irradiation area 5. Here, the state in which the first beam B1 and the second beam B2 interfere in the irradiation area 5 is typically a state in which exposure interference fringes 6 are generated in the irradiation area 5, enabling interference exposure. Therefore, for example, the movement range and movement accuracy of the beam splitter 21 by the optical path adjustment unit 19 are set so that appropriate exposure interference fringes 6 can be generated within the irradiation area 5.

[0071] As shown in Figure 1, the beam splitter 21 is an optical unit that splits the optical paths of the first beam B1 and the second beam B2 in front of the incident optical system 23. Therefore, by moving the beam splitter 21, it is possible to adjust the optical path lengths of the first beam B1 and the second beam B2 simultaneously. This makes it possible to easily eliminate even relatively large optical path differences while maintaining a compact configuration.

[0072] Typically, the optical path adjustment unit 19 moves the beam splitter 21 so that the optical path length of the first beam B1 from the demultiplexer 25 to the irradiation area 5 is substantially equal to the optical path length of the second beam B2 from the demultiplexer 25 to the irradiation area 5. This makes it possible to generate appropriate exposure interference fringes 6 within the irradiation area 5 (the region where the spots of the two beams overlap), as shown in Figure 3, for example.

[0073] Furthermore, if it is possible to achieve interference between the first beam B1 and the second beam B2 in the irradiation area 5, it is not necessary to strictly match the optical path lengths of the first beam B1 and the second beam B2. For example, the beam splitter 21 may be moved so that the visibility of the interference fringes of the first beam B1 and the second beam B2 in the irradiation area 5 is above a predetermined threshold. The threshold for determining visibility (contrast) is set appropriately according to the accuracy required for interference exposure, etc.

[0074] Furthermore, the pulse width of the pulsed laser light is preferably 100 nsec or less. For example, if the pulse width is greater than 100 nsec, the coherence length becomes relatively large, and interference fringes can be generated in the irradiation area 5 without strictly adjusting the optical path length. On the other hand, if the pulse width is 100 nsec or less, the decrease in visibility corresponding to the optical path difference, as explained with reference to Figure 5, becomes significant. In this region, improvement in interference accuracy can be expected by moving the beam bifurcation section 21. From this viewpoint, the pulse width of the pulsed laser light is more preferably 10 nsec or less, and even more preferably 1 nsec or less.

[0075] [Beam branching section] Figure 6 is a schematic diagram showing an example of the configuration of a beam splitter. The beam splitter 21 includes an incident direction control mirror 24, a demultiplexing element 25, an exit direction control mirror 26, and a support member 27. A moving mechanism 22, which functions as an optical path adjustment unit 19, is also connected to the beam splitter 21.

[0076] The support member 27 is arranged in the following order from the top of the figure: an incident direction control mirror 24, a demultiplexer 25, and an exit direction control mirror 26. The incident direction control mirror 24 converts the optical path of the pulsed laser light (beam B0) from the pulsed light source 20 toward the demultiplexer 25. Specifically, the incident direction control mirror 24 is positioned with its reflective surface facing downward to the left and tilted at 45° with respect to the Z direction, and reflects the pulsed laser light (beam B0) incident in the X direction to the right toward the Z direction toward downward.

[0077] The demultiplexing element 25 is a beam splitter having a dividing surface 7 that reflects or transmits incident light. In Figure 6, an intensity-type beam splitter is used. The beam splitter may also be a prism type or a plate type such as a half mirror. Here, the pulsed laser light transmitted through the dividing surface 7 is designated as the first beam B1, and the pulsed laser light reflected by the dividing surface 7 is designated as the second beam B2. The dividing surface 7 of the demultiplexing element 25 is positioned at a 45° inclination with respect to the Z direction, with its upper end tilted to the left. In this case, the first beam B1 is emitted downwards from the dividing surface 7, and the second beam B2 is emitted to the right.

[0078] The emission direction control mirror 26 controls the emission direction of the first beam B1 by reflecting the first beam B1 emitted from the demultiplexing element 25 (splitting surface 7). The emission direction control mirror 26 is an example of an optical element that sets the emission direction of the first beam B1 from the beam bifurcation section 21. The emission direction control mirror 26 is positioned with its reflective surface facing upper left and tilted at 45° with respect to the Z direction, and reflects the first beam B1 incident downward in the Z direction to the left in the X direction.

[0079] In this way, the beam splitter 21 emits the first beam B1 and the second beam B2 in opposite directions along a predetermined linear axis 8. In other words, the demultiplexer 25 (beam splitter) and the emission direction control mirror 26 convert the optical path of each beam into an optical path parallel to the linear axis 8. The linear axis 8 is, for example, a hypothetical axis used to represent the direction of beam emission. Here, the axis extending in the X direction is the linear axis 8.

[0080] Furthermore, the optical path adjustment unit 19 (moving mechanism 22) moves the beam splitter 21 along the linear axis 8. That is, the beam splitter 21 moves parallel to the two beams emitted from the beam splitter 21 in opposite directions. In this case, the linear axis 8 becomes the axis that defines the movement path of the beam splitter 21 (moving mechanism 22). For example, when using a moving mechanism 22 such as a linear stage, the guide members constituting the linear stage can be considered as the linear axis 8.

[0081] With this configuration, even if the beam splitter 21 moves, the exit directions of the first beam B1 and the second beam B2 do not change. This makes it possible to change the optical path lengths of the first beam B1 and the second beam B2 without changing the optical path in the incident optical system 23 located downstream of the beam splitter 21.

[0082] Furthermore, when the beam splitter 21 is moved along the linear axis 8, the optical path of one beam becomes shorter and the optical path of the other beam becomes longer, depending on the direction of movement. For example, as shown in Figure 6, suppose the beam splitter 21 is moved to the right by a distance d. If the optical path length L1 of the first beam B1 before the movement was L1=a, then the optical path length L1 after the movement becomes L1=a+d, and the optical path length L1 becomes longer by the distance d. Conversely, if the optical path length L2 of the second beam B2 before the movement was L2=b, then the optical path length L2 after the movement becomes L2=bd, and the optical path length L2 becomes shorter by the distance d.

[0083] Therefore, if the optical path difference between the first beam B1 and the second beam B2 is ΔL (=L1-L2), the amount of change that the travel distance d has on the optical path difference ΔL is 2d. In other words, it is possible to change the optical path difference ΔL over a length twice the travel distance of the beam splitter 21. This makes it possible to easily eliminate the optical path difference even when a relatively large optical path difference occurs.

[0084] Furthermore, in Figure 6, the incident direction control mirror 24 reflects the pulsed laser light (beam B0) incident along the linear axis 8 toward the demultiplexing element 25. This makes it possible to move the beam splitter 21 while maintaining the incident position and incident angle of beam B0 relative to the demultiplexing element 25. As a result, it becomes unnecessary to adjust the position and orientation of each optical element as the beam splitter 21 moves, and the beam splitter 21 can be moved easily. In this embodiment, the incident direction control mirror 24 corresponds to the fifth mirror.

[0085] Figure 7 is a schematic diagram showing another example of the beam splitter configuration. The beam splitter 21a shown in Figure 7 is configured by adding output direction control mirrors 26b and 26c for setting the output direction of the second beam B2 to the beam splitter 21 shown in Figure 6. Note that the output direction control mirror 26 shown in Figure 6 will be referred to as output direction control mirror 26a here.

[0086] The emission direction control mirror 26b is positioned with its reflective surface facing downward to the left and tilted at 45° with respect to the Z direction, and reflects the second beam B1 emitted from the demultiplexing element 25 (splitting surface 7) in the rightward direction in the X direction downward in the Z direction. The emission direction control mirror 26c is positioned with its reflective surface facing upward to the right and tilted at 45° with respect to the Z direction, and reflects the second beam B1 emitted from the emission direction control mirror 26b in the downward direction in the Z direction in the rightward direction in the X direction. In Figure 7, the emission direction control mirrors 26b and 26c are examples of optical elements that set the emission direction of the second beam B2 from the beam splitter 21a.

[0087] As shown in Figure 7, the beam direction control mirror 26c is positioned to reflect the second beam B2 at the same height as the reflection position of the first beam B1 by the beam direction control mirror 26a. In this way, the beam splitter 21a sets the beam output axis of the first beam B1 and the beam output axis of the second beam B2 to the same axis along the linear axis 8. This makes it possible to design the optical elements that receive the first beam B1 and the second beam B2 (such as the relay drive mirrors 28a and 28b shown in Figure 1) in a similar manner, thereby reducing manufacturing and maintenance costs.

[0088] [Configuration of the incident optical system] Now, referring to Figure 1, the configuration of the incident optical system 23 provided downstream of the beam splitter 21 will be described. As described above, the incident optical system 23 has relay drive mirrors 28a and 28b and irradiation drive mirrors 29a and 29b.

[0089] The relay drive mirrors 28a and 28b are drive mirrors in the incident optical system 23 that receive the first beam B1 and beam B2 emitted from the beam splitter 21 and relay them to the subsequent irradiation drive mirrors 29a and 29b.

[0090] The relay drive mirror 28a is positioned to the left of the beam splitter 21, moves along the linear axis 8 and rotates relative to the linear axis 8, and reflects the first beam B1 emitted from the beam splitter 21. The relay drive mirror 28b is positioned to the right of the beam splitter 21, moves along the linear axis 8 and rotates relative to the linear axis 8, and reflects the second beam B2 emitted from the beam splitter 21. In this embodiment, the relay drive mirrors 28a and 28b correspond to the first mirror and the second mirror, respectively.

[0091] As explained with reference to Figure 6, the linear axis 8 defines the direction of emission of each beam from the beam splitter 21 and the direction of movement of the beam splitter 21. For example, if a linear motion stage is used as the moving mechanism 22 for moving the beam splitter 21, the relay drive mirrors 28a and 28b are moved using the same linear motion stage.

[0092] Furthermore, the rotation of the mirrors (relay drive mirrors 28a and 28b) with respect to the linear axis 8 includes rotation around the Y direction (rotational drive). It may also include rotation that tilts relative to the XZ plane (tilt drive). The rotational drive controls the reflection direction of the beam along the XZ plane, and the tilt drive controls the tilt of the reflection direction of the beam relative to the XZ plane. The mechanisms for moving and rotating the relay drive mirrors 28a and 28b are not limited.

[0093] In this embodiment, the relay drive mirrors 28a and 28b move in the direction along the linear axis 8 (X direction), similar to the beam splitter 21. The direction along the linear axis 8 is also the direction of beam emission from the beam splitter 21. Therefore, regardless of whether the beam splitter 21, relay drive mirrors 28a, or relay drive mirrors 28b are moved, the incidence direction and incidence position of the first beam B1 and second beam B2 to the relay drive mirrors 28a and 28b can be maintained.

[0094] The illumination drive mirrors 29a and 29b are drive mirrors in the incident optical system 23 that cause the first beam B1 and beam B2 to be incident on the illumination area 5 at their respective set incident angles.

[0095] The illumination drive mirror 29a moves along the first drive axis 9a and rotates relative to the first drive axis 9a, reflecting the first beam B1 reflected by the relay drive mirror 28a toward the illumination area 5. The illumination drive mirror 29b moves along the second drive axis 9b and rotates relative to the second drive axis 9b, reflecting the second beam B2 reflected by the relay drive mirror 28b toward the illumination area 5. In this embodiment, the illumination drive mirrors 29a and 29b correspond to the third mirror and the fourth mirror, respectively.

[0096] Here, the drive shafts (first drive shaft 9a and second drive shaft 9b) refer to axes that define the movement path of, for example, the mirrors (illumination drive mirror 29a and illumination drive mirror 29b). For example, suppose a mirror is mounted on a base that moves along a guide member. In this case, since the mirror moves along the guide member, the guide member can be considered the drive shaft of the mirror.

[0097] Furthermore, the rotation of the mirrors (illumination drive mirrors 29a and 29b) relative to the drive shaft includes rotational drive and tilt drive, similar to the case of the intermediate drive mirrors 28a and 28b. The mechanisms for moving and rotating the illumination drive mirrors 29a and 29b are not limited.

[0098] The first drive shaft 9a and the second drive shaft 9b are positioned along a common reference plane 2 set perpendicular to the exposure surface 4. For example, the reference plane 2 is the surface of the optical table on which the incident optical system 23 is provided (the so-called optical surface). As a result, the first drive shaft 9a and the second drive shaft 9b become axes aligned with the incident planes (XZ planes) of the first beam B1 and the second beam B2. This makes it possible to sufficiently avoid situations where, for example, the incident axis of each beam shifts significantly in the Y direction (deviates significantly from the XZ plane) even if the irradiation drive mirror 29a or the irradiation drive mirror 29b moves, thereby improving the stability of interference exposure.

[0099] Furthermore, the first drive shaft 9a and the second drive shaft 9b are provided such that both the irradiation drive mirror 29a and the irradiation drive mirror 29b can be positioned on one side of the normal L on the reference plane 2. This makes it possible to inject the first beam B1 and the second beam B2 from one side (in this case, the left side) of the normal L, and makes it possible to easily achieve a relatively large slant angle α.

[0100] In Figure 1, the first drive shaft 9a and the second drive shaft 9b are shown as straight shafts, but other shafts, such as arc-shaped shafts, may also be used. Furthermore, the first drive shaft 9a and the second drive shaft 9b do not need to be individually configured shafts; they can be configured as a common shaft.

[0101] Thus, the incident optical system 23 has variable incident angles θ1 and θ2 of the first beam B1 and the second beam B2 with respect to the exposure surface 4. For example, changing the incident angles θ1 and θ2 changes the optical path lengths of the first beam B1 and the second beam B2. As a result, an optical path difference occurs between the first beam B1 and the second beam B2, which is expected to make it difficult to generate exposure interference fringes 6 in the irradiation area 5.

[0102] The positions of the relay drive mirrors 28a and 28b are determined by the irradiation conditions, such as the position and angle of the irradiation drive mirrors 29a and 29b, which define the incident angles θ1 and θ2. Therefore, although the relay drive mirrors 28a and 28b can move along the linear axis 8, it is difficult for them to perform an optical path length adjustment function. Thus, in the incident optical system 23, the position and angle of each drive mirror are set in order to achieve the set incident angles θ1 and θ2, making it difficult to adjust the optical path length of each beam within the incident optical system 23.

[0103] Therefore, in this embodiment, the optical path adjustment unit 19 moves the beam splitter 21 in accordance with changes in the incident angles θ1 and θ2 of the first beam B1 and the second beam B2. That is, when the incident angles θ1 and θ2 are changed, the optical path adjustment unit 19 adjusts the position of the beam splitter 21 so that the first beam and the second beam interfere with each other in the irradiation area 5.

[0104] This adjustment is performed so that the optical path difference associated with each change in incidence angle is eliminated, or so that the optical path difference is reduced to a level where appropriate interference fringes 6 for exposure can be obtained. This makes it possible to achieve accurate interference exposure even when incidence angles θ1 and θ2 are changed.

[0105] In this embodiment, the incident optical system 23 incidents the first beam B1 and the second beam B2 onto the irradiation area 5 in a manner asymmetrical with respect to the normal L to the exposure surface 4 in the irradiation area 5. Hereinafter, the mode in which the first beam B1 and the second beam B2 are incident onto the irradiation area 5 in a manner asymmetrical with respect to the normal L will be referred to as the asymmetric mode. The mode in which the first beam B1 and the second beam B2 are incident onto the irradiation area 5 in a manner symmetrical with respect to the normal L will be referred to as the symmetric mode. The incident optical system 23 is configured to be switchable between interference exposure in these asymmetric modes and interference exposure in the symmetric mode.

[0106] Symmetric mode refers to a mode in which the incident axes of the first beam B1 and the second beam B2 directed toward the irradiation area 5 are set substantially symmetrically with respect to the normal L to the exposure surface 4 in the irradiation area 5. This is, for example, a state in which the incident axes of the first beam B1 and the second beam B2 are set rotationally symmetrically with respect to the normal L. Asymmetric mode refers to a mode in which the incident axes of the first beam B1 and the second beam B2 are set substantially asymmetrically with respect to the normal L to the exposure surface 4 in the irradiation area 5. For example, a state in which the incident axes are set in an arrangement different from the symmetric mode described above is an asymmetric mode.

[0107] For example, the incident optical system 23 is configured so that the first beam B1 and the second beam B2 can illuminate the irradiation area 5 along substantially the same plane (hereinafter referred to as the incident plane). In this case, in symmetric mode, the incident angles θ1 and θ2 are the same magnitude but opposite in direction, while in asymmetric mode, the incident angles θ1 and θ2 are angles of different magnitudes. In Figure 1, the incident optical system 23 is set to asymmetric mode.

[0108] In asymmetric mode, exposure interference fringes 6 tilted at a slant angle α are exposed to a photosensitive material such as a photoresist or sheet material on the surface of a workpiece W. This makes it possible to form a diffraction grating that bends light incident from the front (Z direction) by a slant angle α through diffraction. Such diffraction gratings can be used, for example, in augmented reality (AR) display devices (such as transmissive AR glasses) or combiners for in-vehicle displays.

[0109] For example, in symmetric mode, the optical paths of the first beam B1 and the second beam B2 in the incident optical system 23 are symmetric with respect to the normal L. On the other hand, in asymmetric mode, as shown in Figure 1, the optical paths of the first beam B1 and the second beam B2 in the incident optical system 23 are not symmetric with respect to the normal L, but are optical paths set independently according to the incident angles θ1 and θ2. For this reason, in asymmetric mode, a relatively large optical path difference is expected to occur within the incident optical system 23.

[0110] In contrast, in this embodiment, by moving the beam splitter 21, it is possible to easily eliminate or reduce the optical path difference of each beam without changing the optical arrangement of the incident optical system 23, even when interference exposure is performed in asymmetric mode. Thus, the configuration of adjusting the optical paths of the first beam B1 and the second beam B2 by moving the beam splitter 21 is particularly effective in a device that performs interference exposure in asymmetric mode using pulsed laser light.

[0111] [Configuration of the sensor unit] Figure 8 is a schematic diagram showing an example of the configuration of the sensor unit. The upper and lower diagrams of Figure 8 show examples of the arrangement of the sensor unit 12 in symmetric mode and asymmetric mode. In each mode shown in Figure 8, the incidence angle θ1 of the first beam B1 is the same, while the incidence angle θ2 of the second beam B2 is different.

[0112] As shown in Figure 8, the sensor unit 12 includes a beam multiplexing element 66, an attitude adjustment element 67, and an image sensor 68. The beam multiplexing element 66 receives the first beam B1 and the second beam B2 directed toward the irradiation area 5 and combines the first beam B1 and the second beam B2. The beam multiplexing element 66 emits a combined beam BA, which is the combined beam of the first beam B1 and the second beam B2. For example, a beam splitter (also called a beam combiner) can be used as the beam multiplexing element 66. However, other elements such as diffraction gratings may be used as long as they are capable of combining the first beam B1 and the second beam B2.

[0113] The multiplexing element 66 is positioned where the first beam B1 and the second beam B2 intersect. It transmits the beam incident from one incident surface (in this case, the first beam B1 incident on the left incident surface) and reflects the beam incident from the other incident surface (in this case, the second beam B2 incident on the right incident surface). The combined beam BA is formed when the optical paths of the transmitted beam (first beam B1) and the reflected beam (second beam B2) coincide.

[0114] The attitude adjustment element 67 adjusts the attitude of the multiplexing element 66 according to the slant angle α. For example, a drive mechanism that rotates a holder to which the multiplexing element 66 is fixed is used as the attitude adjustment element 67. In this case, the attitude adjustment element 67 rotates the multiplexing element 66 around a rotation axis along the Y direction. The rotation angle (amount of rotation) of the multiplexing element 66 is controlled by the control unit 13, which acquires the input value of the slant angle α.

[0115] The image sensor 68 is positioned in the optical path of the combined beam BA and measures the intensity distribution of the combined beam BA, which has been combined by the combined element 66. Alternatively, the combined beam BA may be guided to the image sensor 68 via a reflective mirror or the like. As the image sensor 68, a beam-detecting sensor such as a CMOS camera or CCD camera can be used. The intensity distribution measured by the image sensor 68 will be interference fringes with a longer pitch width (period) than the exposure interference fringes 6 described with reference to Figure 2. Hereafter, the interference fringes formed by the combined beam BA will be referred to as measurement interference fringes. Thus, the sensor unit 12 can also be described as a rotationally driven interference measurement camera.

[0116] In the sensor unit 12, the angle of the multiplexing element 66 is adjusted to properly generate the multiplexed beam BA. For example, as shown in the upper part of Figure 8, in symmetric mode, the multiplexing element 66 is positioned so that the incident surface is aligned with the normal L. This ensures that the transmission direction of the first beam B1 and the reflection direction of the second beam B2 coincide, allowing the beams to overlap properly. Also, as shown in the lower part of Figure 8, when the incident angle θ2 of the second beam B2 is changed, the attitude adjustment element 67 changes the inclination angle of the multiplexing element 66 so that the multiplexed beam BA can be generated. Specifically, the multiplexing element 66 is tilted so that its inclination angle with respect to the normal L matches the slant angle α.

[0117] Here, we will explain the characteristics of the interference fringes (interference fringes of the combined beam BA) measured by the image sensor 68. In the following, we will assume that the measurement surface of the image sensor 68 is the xy plane, and that interference fringes with a period in the x direction (i.e., stripes extending in the y direction) are formed. If the deviations of the incident angles θ1 and θ2 with respect to the normal L of the first beam B1 and the second beam B2 are Δθ1 and Δθ2, respectively, then the pitch width px in the x direction of the interference fringes is expressed by equation (3).

number

[0118] For example, the pitch width in the X direction of the exposure interference fringes 6 shown in Figure 2 is the length obtained by projecting the pitch width p shown in equation (2) onto the exposure surface 4, but its scale is determined by the laser wavelength λ and is on the order of submicrometers. For this reason, it is difficult to photograph the exposure interference fringes 6 with sufficient resolution.

[0119] In contrast, the pitch width px in the x-direction of the interference fringes for measurement is relatively large, exceeding the laser wavelength λ, because the denominator contains the difference between the sine values ​​of the incident angles, as shown in equation (6). Therefore, the interference fringes for measurement can be sufficiently captured even with the resolution of the image sensor 68. Thus, in this embodiment, the sensor unit 12 detects interference fringes (interference fringes for measurement) that are generated when the first beam B1 and the second beam B2 overlap.

[0120] Furthermore, the contrast of the measurement interference fringes and the exposure interference fringes 6 correspond to each other; the higher the contrast of the measurement interference fringes, the higher the contrast of the exposure interference fringes 6. Therefore, by detecting the measurement interference fringes, it becomes possible to monitor the state of the exposure interference fringes 6.

[0121] [Control Unit Operation] Figure 9 is a flowchart showing an example of the operation of the control unit. The process shown in Figure 9 is an optical path adjustment process that is performed, for example, after the incident angles θ1 and θ2 are set in the incident optical system 23. It is also possible to perform a calibration process for the incident angles θ1 and θ2 after performing the optical path adjustment process shown in Figure 9, and then perform the optical path adjustment process again. During the optical path adjustment process, the sensor unit 12 is moved so that it overlaps with the illumination area 5.

[0122] First, the sensor unit 12 detects interference fringes for measurement (step 101). Specifically, the interference fringes for measurement are captured by the image sensor 68. Depending on the optical arrangement of the incident optical system 23, it is conceivable that the optical path difference between the two beams may be large, and the interference fringes for measurement may not be detected. In that case, the control unit 13 may appropriately move the beam splitter 21 so that the interference fringes for measurement are detected. Alternatively, the beam splitter 21 may be moved manually via a control UI or the like.

[0123] Next, the control unit 13 measures the contrast of the interference fringes for measurement (step 102). The contrast measured here is the contrast in the initial state before the optical path adjustment is performed by the beam splitter 21.

[0124] Next, the control unit 13 controls the movement mechanism 22, and the beam splitter 21 is moved in the first direction (step 103). Here, the first direction is a preset initial movement direction, and is set to either the right or left direction. The amount of movement of the beam splitter 21 is appropriately set to a value that allows for the detection of changes in the contrast of the interference fringes for measurement, for example.

[0125] Next, the control unit 13 measures the contrast of the interference fringes for measurement again (step 104). The contrast measured here is the contrast after optical path adjustment by the beam splitter 21.

[0126] Next, the control unit 13 determines whether the contrast is above a threshold (step 105). The threshold for determining the contrast is set so that proper interference exposure is possible. For example, if the maximum contrast value is 1, the threshold is set to about 0.4. If the contrast is 0.4 or higher, interference exposure can be performed. Furthermore, by setting a higher threshold (e.g., 0.9), the exposure accuracy can be significantly improved. Alternatively, the threshold may be set relatively. For example, a data table recording the peak contrast values ​​for each incidence angle θ1 and θ2 may be prepared in advance, and a threshold set based on each peak value (e.g., 90% of the peak value) may be used. The method for setting the threshold for determining the contrast is not limited to these methods.

[0127] If the contrast is below the threshold (NO in step 105), the control unit 13 determines whether the contrast has increased or not (step 106). For example, in the first loop, the initial contrast measured in step 102 is compared with the current contrast measured in step 104. In subsequent loops, the contrast measured in the previous loop is compared with the current contrast.

[0128] If the contrast is increasing (YES in step 106), the control unit 13 controls the movement mechanism 22, assuming that the first direction is the direction that reduces the optical path difference, and the beam splitter 21 is moved further in the first direction (step 107). On the other hand, if the contrast is decreasing (NO in step 106), the control unit 13 controls the movement mechanism 22, assuming that the first direction is the direction that increases the optical path difference, and the beam splitter 21 is moved in the second direction, which is opposite to the first direction (step 108).

[0129] When step 107 or step 108 is executed, the processing from step 104 onwards is executed again. By repeating this loop, the contrast increases. That is, the position of the beam splitter 21 is adjusted so that the brightness and darkness of the interference fringes for measurement captured by the image sensor 68 become clearer. Then, if the contrast is above the threshold (YES in step 105), the optical path adjustment process ends.

[0130] In this way, the control unit 13 moves the beam splitter 21 so that the contrast of the interference fringes (measurement interference fringes) is increased. This can be described as a process of aligning the optical paths of the first beam B1 and the second beam B2 by moving the beam splitter 21 so that the interference quality (contrast) evaluated using the sensor unit 12 is within an acceptable range. This makes it possible to automatically adjust the position of the beam splitter 21 so that a high contrast can be obtained. As a result, the optical path difference between the first beam B1 and the second beam B2 is sufficiently eliminated, and the accuracy of interference exposure can be improved.

[0131] Furthermore, the amount of movement of the beam branching section 21 in step 107 or step 108 may be set according to the amount of change in contrast. For example, it is possible to set the amount of movement to be small when the amount of change in contrast is small, and to be large when the amount of change is large. This makes it possible to perform coarse position adjustment in areas where the contrast is far from the peak value, and fine position adjustment in areas where the contrast is close to the peak value. The method of setting the amount of movement is not limited; the amount of movement may be set according to the contrast value, or the amount of movement may be set to a constant value.

[0132] [Specific configuration of an interferometric exposure system] Figure 10 is a schematic diagram showing a specific example of the configuration of an interference exposure apparatus. In the following, parts common to the configuration described with reference to Figure 1 will be described using the same reference numerals.

[0133] As shown in Figure 10, in this embodiment, the first drive shaft 9a and the second drive shaft 9b are each arc axes surrounding the illumination area 5. The arc axes are arranged, for example, so as to be centered on the illumination area 5. By using arc axes, the positions of the illumination drive mirrors 29a and 29b in the X and Z directions can be easily changed. This makes it possible to sufficiently widen the control range of the incident angle θ1 and the incident angle θ2. It also makes it possible to configure the incident optical system 23 in a compact manner.

[0134] Here, a common arc-shaped shaft (an arc-shaped drive shaft 35, described later) is used as the first drive shaft 9a and the second drive shaft 9b. This simplifies the device configuration and reduces manufacturing and maintenance costs. Alternatively, the first drive shaft 9a and the second drive shaft 9b may be provided individually as concentric arc-shaped shafts. In this case, for example, the second drive shaft 9b may be positioned outside or inside the first drive shaft 9a.

[0135] The interference exposure apparatus 100 includes a frame section 14, an optical system 10, a stage mechanism 11, a sensor section 12, and a control unit 13 (not shown).

[0136] The frame section 14 is the frame of the interference exposure apparatus 100 and supports the optical system 10 and the stage mechanism 11. The frame section 14 includes a stage support base 15, an optical table support frame 16, a light source support base 17, and a connecting frame 18.

[0137] The stage support base 15 is a plate-shaped member that supports the stage mechanism 11. The stage support base 15 may have, for example, legs with a suspension function. The optical table support frame 16 is provided on the upper surface of the stage support base 15 and supports the optical table 30 of the optical system 10, which will be described later. The light source support base 17 is a plate-shaped member that supports the pulse light source 20 of the optical system 10, which will be described later, and is positioned above the optical table 30. The connecting frame 18 connects the optical table support frame 16 and the light source support base 17 and supports the light source support base 17, and is provided on the front and rear surfaces of the interference exposure apparatus 100. Note that the connecting frame 18 provided on the front surface is not shown in Figure 10.

[0138] The optical system 10 includes an exit optical system 37, a linear bench optical system 38, and an arc arm optical system 39. Of these, the linear bench optical system 38 is provided with a beam splitter 21. In addition, a portion of the linear bench optical system 38 and the arc arm optical system 39 constitute the incident optical system 23.

[0139] The emission optical system 37 is an optical system that emits beam B0, which is the source of the first beam B1 and the second beam B2, toward the linear bench optical system 38. The emission optical system 37 is configured on the light source support base 17 and includes a pulse light source 20, an exposure shutter S, a relay mirror 33a, and a relay mirror 33b.

[0140] The pulse light source 20 is provided on the upper surface of the light source support base 17 and emits pulsed laser light (beam B0) toward the relay mirror 33a. The exposure shutter S is a shutter for blocking the beam B0 and is provided between the pulse light source 20 and the relay mirror 33a. A rotary shutter is used here, but other types of shutters may be used. The relay mirror 33a is provided on the upper surface of the light source support base 17 and reflects the beam B0 toward the relay mirror 33b. The relay mirror 33b is provided on the lower surface of the light source support base 17 and reflects the beam B0 toward the incident direction control mirror 24, which will be described later.

[0141] In the example shown in Figure 10, the beam B0 emitted from the pulse light source 20 is reflected on the upper surface of the light source support base 17 by relay mirrors 33a and 33b located to the right of the light source support base 17 so that it travels to the left on the lower surface of the light source support base 17.

[0142] Next, the parts of the optical system 10 provided on the optical table 30 (linear bench optical system 38, arc arm optical system 39) will be described. The optical table 30 is a rectangular plate member as a whole. The rear surface of the optical table 30 is connected to the optical table support frame 16 and is supported along the XZ plane such that one pair of edges (in this case, the long side) is parallel to the X direction. The front surface of the optical table 30 is the reference plane 2, as explained with reference to Figure 1. The optical paths of the first beam B1 and the second beam B2 are basically set to be parallel to the reference plane 2.

[0143] The linear bench optical system 38 generates a first beam B1 and a second beam B2 and supplies each beam toward the arc arm optical system 39. The linear bench optical system 38 includes an incident direction control mirror 24, an exit direction control mirror 26, a demultiplexer 25, relay drive mirrors 28a and 28b, linear motion units 32a to 32c, and a linear drive axis 31, and is configured along the upper edge of the optical table 30.

[0144] The linear drive shaft 31 is a linear drive shaft provided along the X direction on the upper edge of the optical table 30. The linear motion sections 32a to 32c are bases that can move along the linear drive shaft 31. Optical components are arranged on the surfaces of each linear motion section 32a to 32c that face forward.

[0145] Each of the linear motion units 32a to 32c moves independently along the linear drive shaft 31. The configuration of the linear motion mechanism is not limited; any mechanism that allows the base to move along a predetermined guide such as a rail or groove can be used.

[0146] As shown in Figure 10, the front surface of the linear motion unit 32c is arranged in the following order from top to bottom: an incident direction control mirror 24, a demultiplexing element 25, and an exit direction control mirror 26. These optical units provided on the linear motion unit 32c constitute the beam splitter 21. The linear motion unit 32c and the linear drive shaft 31 constitute the moving mechanism 22. The beam splitter 21 shown in Figure 10 is configured similarly to the beam splitter 21 described with reference to Figure 6, for example.

[0147] The incident direction control mirror 24 reflects the beam B0 incident from the relay mirror 33b toward the demultiplexer element 25 located below it. The demultiplexer element 25 splits the beam B0 (coherent emitted light) into a first beam B1 and a second beam B2. Here, the demultiplexer element 25 is positioned at a 45° tilt with respect to the ZY plane, with its upper end tilted to the right. As a result, of the beam B0 incident on the demultiplexer element 25, a portion is reflected by the demultiplexer element 25 and becomes the first beam B1, which travels to the left, and another portion passes through the demultiplexer element 25 and becomes the second beam B2, which travels downward. The second beam B2 is reflected by the output direction control mirror 26 located directly below the demultiplexer element 25 so that it travels to the right.

[0148] The relay drive mirror 28a is rotatably mounted on the front of the left linear motion section 32a of the demultiplexing element 25. The relay drive mirror 28b is rotatably mounted on the front of the right linear motion section 32b of the demultiplexing element 25.

[0149] Thus, in the linear bench optical system 38, the beam splitter 21 and the two relay drive mirrors 28a and 28b can move independently of each other along a single linear drive axis 31. This makes it possible to make detailed adjustments to the optical path length of each beam within the linear bench optical system 38 without moving the arm sections 36a and 36b of the arc arm optical system 39, which will be described later.

[0150] The arc-arm optical system 39 is an optical system that illuminates the first beam B1 and the second beam B2 toward the illumination area 5. The arc-arm optical system 39 has illumination drive mirrors 29a and 29b, arm sections 36a and 36b, and an arc drive shaft 35, and is configured along the front surface (reference plane 2) of the optical table 30. In the example shown in Figure 10, the incident optical system 23 is configured by the arc-arm optical system 39 and the relay drive mirrors 28a and 28b of the linear bench optical system 38.

[0151] The arc drive shaft 35 is an arc-shaped drive shaft provided along the reference plane 2 (XZ plane) of the optical table 30. The arm portions 36a and 36b are bases that can move along the arc drive shaft 35.

[0152] Each arm section 36a and 36b moves independently along the arc drive shaft 35. The configuration of the arc drive mechanism is not limited; any mechanism that allows the base to move along a predetermined guide (arc drive shaft 35), such as a rail or groove, can be used.

[0153] The arc drive axis 35 is typically positioned around the irradiation area 5. For example, when viewed in the XZ plane, the arc drive axis 35 is positioned on the optical table 30 such that its center coincides with the center point of the irradiation area 5 (such as the intersection point of the first beam B1 and the second beam B2). This makes it easy to associate the respective incident angles θ1 and θ2 of the first beam B1 and the second beam B2 with the positions on the arc drive axis 35 of the irradiation drive mirrors 29a and 29b.

[0154] The illumination drive mirrors 29a and 29b reflect the first beam B1 and the second beam B2 toward the illumination area 5. Irradiation drive mirror 29a is rotatably mounted on the front of the left arm portion 36a, and illumination drive mirror 29b is rotatably mounted on the front of the right arm portion 36b. As a result, illumination drive mirrors 29a and 29b each move independently along the arc drive axis 35 and rotate relative to the arc drive axis 35.

[0155] Arm sections 36a and 36b are longitudinal bases on which optical components are mounted. In addition to the illumination drive mirrors 29a and 29b, adjustment optical systems 40a and 40b are provided on arm sections 36a and 36b, respectively. Adjustment optical system 40a is an optical system that adjusts the first beam B1 reflected by the illumination drive mirror 29a, and adjustment optical system 40b is an optical system that adjusts the second beam B2 reflected by the illumination drive mirror 29b. For example, the adjustment optical systems 40a and 40b are arranged along the longitudinal direction of arm sections 36a and 36b. Therefore, the longitudinal direction of each arm section 36a and 36b is the direction of the incident axis of the first beam B1 and the second beam B2.

[0156] As shown in Figure 10, the arm portion 36a moves along the arc drive axis 35 so that the adjustment optical system 40a faces the irradiation area 5. Similarly, the arm portion 36b moves along the arc drive axis 35 so that the adjustment optical system 40b faces the irradiation area 5. For example, the arms 36a and 36b are moved so that their longitudinal direction coincides with the radial direction (direction toward the center) of the arc drive axis 35. This is achieved, for example, by using a mechanism to maintain the attitude of the arms 36a and 36b relative to the arc drive axis 35, or by using guides formed concentrically with the arc drive axis 35. As a result, regardless of the position of the arms 36a and 36b (irradiation drive mirrors 29a and 29b) on the arc drive axis 35, the incident axes of the first beam B1 and the second beam B2 are directed toward the irradiation area 5.

[0157] The adjustment optical systems 40a and 40b are equipped with, for example, an expander (objective lens, etc.) to widen the beam spot, a spatial filter (pinhole element, etc.) to form the beam wavefront, and a collimating lens to parallelize the beam. This allows the first beam B1 and the second beam B2 to be irradiated onto the irradiation area 5 as parallel light with a predetermined spot. Sensors for monitoring the beam intensity and spot may also be provided.

[0158] The stage mechanism 11 is provided with a sensor unit 12. For example, the sensor unit 12 is appropriately positioned on the outer edge of the stage 50. This makes it possible to easily move the sensor unit 12 to the irradiation area 5 using the stage mechanism 11. The specific configuration of the stage mechanism 11 is not limited, and any mechanism capable of positioning with the precision required for interference exposure can be used.

[0159] In the interference exposure apparatus 100 according to this embodiment, the beam splitter 21, which emits the first beam B1 and second beam B2 (obtained by splitting the pulsed laser light (beam B0)) in different directions, is moved so that the first beam B1 and second beam B2 interfere with each other in the irradiation area 5. By moving the beam splitter 21, it becomes possible to adjust, for example, extending one of the optical paths of the first beam B1 and second beam B2 while simultaneously shortening the other optical path. As a result, it becomes possible to improve the accuracy of interference exposure using pulsed laser light without increasing the size of the apparatus.

[0160] <Other Embodiments> The present invention is not limited to the embodiments described above, and various other embodiments can be realized.

[0161] Figures 11 to 15 are schematic diagrams showing examples of beam branching configurations according to other embodiments.

[0162] Figure 11 shows an example of the configuration of a beam splitter 21b using a polarizing beam splitter 43 as the demultiplexing element 25. The beam splitter 21b is configured such that, for example, the demultiplexing element 25 is replaced with a polarizing beam splitter 43 and a half-wave plate 44 is added to the beam splitter 21 shown in Figure 6. The polarizing beam splitter 43 reflects or transmits incident light according to the polarization direction of the incident light. For example, the reflected light becomes S-polarized light with a polarization direction perpendicular to the incident plane (in this case, the XZ plane), and the transmitted light becomes P-polarized light perpendicular to the S-polarized light.

[0163] A pulsed laser beam (beam B0) containing, for example, S-polarized and P-polarized light is incident on the incident direction control mirror 24. Beam B0 is, for example, light whose polarization direction is tilted at 45° with respect to the XZ plane. The beam B0 reflected by the incident direction control mirror 24 is incident on the splitting surface 7 of the polarizing beam splitter 43. At this time, the P-polarized component is transmitted through the splitting surface 7 and emitted as the first beam B1. The S-polarized component is reflected by the splitting surface 7 and emitted as the second beam B2.

[0164] Note that interference between the two beams occurs only when they have the same polarization; no interference occurs when the polarization directions of the first beam B1 and the second beam B2 are orthogonal. Therefore, in order to rotate the polarization direction of one of the beams by 90°, a half-wave plate 44 is placed on either the optical path of the first beam B1 or the second beam B2. In this case, the half-wave plate 44 is placed on the optical path of the first beam B1 reflected by the output direction control mirror 26, and the first beam B1 is converted to S-polarization. Of course, the half-wave plate 44 may also be placed on the optical path of the second beam B2 to convert the second beam B2 to P-polarization.

[0165] Furthermore, the half-wave plate 44 does not necessarily need to be located within the beam splitter unit 21b. Also, if an optical film that rotates the polarization direction by 90° is formed on the polarizing beam splitter 43, the half-wave plate 44 does not need to be provided. In this way, by using the polarizing beam splitter 43 as the demultiplexing element 25, it becomes possible to control the light intensity of the first beam B1 and the second beam B2 with high precision.

[0166] Figure 12 shows an example of the configuration of a beam splitter 21c that uses a polarizing beam splitter 43 as the demultiplexing element 25 to emit two beams on the same axis. The beam splitter 21c is configured such that, for example, the demultiplexing element 25 is changed to a polarizing beam splitter 43 and a half-wave plate 44 is added to the beam splitter 21 shown in Figure 7. As shown in Figure 12, by cranking the second beam B2 with two emission direction control mirrors 26b and 26c, it is possible to set the optical path of the second beam B2 on the same axis as the optical path of the first beam B1 reflected by the emission direction control mirror 26a.

[0167] Figure 13 shows an example of the configuration of a beam splitter 21d using a diffraction grating 45 as a demultiplexing element 25. As shown in Figure 13, the beam splitter 21d has an incident direction control mirror 24, a diffraction grating 45 (demultiplexing element 25), and two exit direction control mirrors 26d and 26e.

[0168] The diffraction grating 45 is configured as an element on a plate, and diffracts light incident from one surface and emits it in two directions from the other surface. Here, pulsed laser light (beam B0) reflected by the incident direction control mirror 24 is incident perpendicularly to the upper surface of the diffraction grating 45, which is arranged parallel to the XY plane. The beam B0 incident on the diffraction grating 45 is split into a first beam B1 that points downward to the left and a second beam B2 that points downward to the right. The first beam B1 and the second beam B2 are first-order diffracted light, and the emission direction of each beam is symmetric with respect to the incident axis of beam B0.

[0169] The first beam B1 emitted from the diffraction grating 45 is reflected by the emission direction control mirror 26d so that it is emitted to the left in the X direction. The second beam B2 emitted from the diffraction grating 45 is reflected by the emission direction control mirror 26e so that it is emitted to the right in the X direction. The positions of the emission direction control mirrors 26d and 26e are set, for example, so that the optical paths of the first beam B1 and the second beam B2 are on the same axis.

[0170] In this way, by using the diffraction grating 45, it becomes possible to set the output axis of the first beam B1 and the output axis of the second beam on the same axis with a small number of parts, and for example, it becomes possible to miniaturize the beam bifurcation section 21d. In Figure 13, the primary light emitted symmetrically from the diffraction grating 45 is used, but for example, it is also possible to use light that has been transmitted through the diffraction grating 45 along the incident axis without being diffracted by the diffraction grating 45 (so-called zero-order light). For example, it is also possible to use one of the primary and zero-order light as the first beam B1 and the other as the second beam B2.

[0171] Figure 14 shows an example configuration of a beam splitter 21e using a prism unit 46 as a demultiplexing element 25. The prism unit 46 is an optical element that combines two prisms 47a and 47b to achieve the function of splitting the beam.

[0172] Prisms 47a and 47b are prisms with an equilateral triangular cross-section in the XZ plane. Prism 47a has a first surface 51a, a second surface 52a, and a third surface 53a, and prism 47b has a first surface 51b, a second surface 52b, and a third surface 53b. Prisms 47a and 47b are joined at their respective second surfaces 52a and 52b. In this case, the first surfaces 51a and 51b (or the third surfaces 53a and 53b) are parallel to each other.

[0173] In the prism unit 46, a beam-splitting coating 54 (beam-splitting surface) is formed at the interface where the two prisms 47a and 47b are joined (the interface of the second surfaces 52a and 52b). In addition, a total reflection coating 55 (total reflection surface) is formed on the third surface 53a of prism 47a. Here, the prism unit 46 is positioned such that the first surfaces 51a and 51b are parallel to the YZ plane.

[0174] At the beam splitting section 21e, pulsed laser light (beam B0) is incident perpendicularly to the first surface 51a of the prism 47a. The beam B0 incident on the prism 47a is split into reflected light and transmitted light by the splitting coating 54 on the second surface 52a (or second surface 52b). Here, the reflected light is referred to as the first beam B1 and the transmitted light as the second beam B2. The first beam B1 is incident on the third surface 53a, reflected by the total internal reflection coating 55, and exits perpendicularly from the first surface 51a. The second beam B2 passes through the splitting coating 54 and enters the prism 47b, and then exits perpendicularly from the first surface 51b.

[0175] As a result, the beam splitter 21e (prism unit 46) can emit the first beam B1 to the left in the X direction and the second beam B2 to the right in the X direction. This makes it possible to significantly reduce the number of parts. In addition, as shown in Figures 7 and 12, two mirrors may be added to the beam splitter 21e to make the emission axes of each beam the same axis.

[0176] Figure 15 shows an example configuration of a beam splitter 21f in which a demultiplexing element 25 is provided externally. The beam splitter 21f has incident direction control mirrors 24a and 24b and outgoing direction control mirrors 26f and 26g. In addition, a demultiplexing element 25 (e.g., a beam splitter) and a reflection mirror 48 are provided upstream of the beam splitter 21f.

[0177] A pulsed laser beam (beam B0) is incident on the demultiplexer 25 from above and split into a first beam B1 (transmitted light) and a second beam B2 (reflected light). The first beam B1 is reflected by a reflection mirror 48 located below the demultiplexer 25 so that it travels parallel to and in the same direction as the second beam B2. Here, the first beam B1 and the second beam B2 are emitted toward the beam splitter 21 as parallel light traveling to the right in the X direction.

[0178] The first beam B1, incident on the beam splitter 21f, is reflected downward in the Z direction by the incident direction control mirror 24a, and further reflected to the left in the X direction by the exit direction control mirror 26f. The second beam B2 is reflected downward in the Z direction by the incident direction control mirror 24b, and further reflected to the right in the X direction by the exit direction control mirror 26g. The positions of the exit direction control mirrors 26f and 26g are set, for example, so that the optical paths of the first beam B1 and the second beam B2 are on the same axis.

[0179] Thus, even with a beam splitter 21f that does not include a demultiplexing element 25, it is possible to emit the first beam B1 and the second beam B2 in opposite directions along a predetermined linear axis, similar to the other beam splitters described above. By moving such a beam splitter 21f, it is also possible to adjust the optical path lengths of the first beam B1 and the second beam B2 in the preceding stage of the incident optical system 23.

[0180] In the above embodiment, a sensor that primarily detects the interference state of the first and second beams in the irradiation area was described as a sensor that detects contrast by photographing interference fringes. The type of sensor is not limited to this, and for example, a sensor that utilizes the autocorrelation of pulsed laser light may be used.

[0181] The method of detecting the interference state of pulsed laser light using autocorrelation is a method that utilizes the second-order nonlinear optical effect that occurs when pulsed laser light interferes. For example, when the autocorrelation of two pulsed laser beams occurs within a nonlinear optical crystal, a second harmonic, which is one of the nonlinear optical effects, is generated. For example, it is known that when pulsed laser light overlaps spatially and temporally within a nonlinear optical crystal, light with half the wavelength of the input is generated. For example, when pulsed laser light with a wavelength of 1064 nm is used, light with a wavelength of 532 nm is generated due to the second-order nonlinear optical effect.

[0182] Spatially overlapping pulsed laser light means that the two beams (pulses) are focused at the same location. Temporarily overlapping means that the two beams (pulses) arrive at the focus point at the same time, i.e., the optical path lengths of each beam are the same. When both of these conditions are met, the interference conditions for interference lithography are satisfied.

[0183] Thus, the degree of spatial and temporal overlap between the first beam B1 and the second beam B2 can be observed using the light intensity of the second harmonic. Furthermore, by adjusting the optical path length, the intensity of the second harmonic increases or decreases, allowing for results similar to those obtained with regard to contrast measurements, as explained with reference to Figure 8, for example. In other words, by detecting the second harmonic, it becomes possible to detect the interference state of pulsed laser light.

[0184] This can be used to construct a sensor unit. That is, the sensor unit provided in the interference exposure apparatus may detect higher harmonics (in this case, second harmonic) generated when the first and second beams overlap. In this case, the sensor unit is constructed using a nonlinear optical crystal and a photodetector. As the nonlinear optical crystal, for example, barium β-borate crystal (BBO), lithium triborate crystal (LBO), potassium dihydrogen phosphate crystal (KDP), potassium titanyl phosphate crystal (KTP), germanium selenide crystal (GeSe), etc., can be appropriately selected based on the measurement wavelength range and nonlinear conversion efficiency. As the photodetector, a sensor is appropriately selected according to the wavelength of the generated second harmonic, etc.

[0185] Furthermore, when using a sensor unit that detects higher harmonics, the control unit may move the beam splitter so that the intensity of the second harmonic increases. This makes it possible to adjust the position of the beam splitter so that the optical path difference of each beam is sufficiently small, similar to the case of optical path adjustment using contrast, and interference exposure can be performed properly.

[0186] In the above embodiment, a beam splitter was described in which the first beam and the second beam are emitted in opposite directions along a linear axis. The emission directions of the first beam and the second beam do not necessarily have to be parallel. In this case, the optical path to the incident optical system can be appropriately adjusted by using an external mirror or the like that moves independently of the beam splitter.

[0187] Furthermore, in the above embodiment, a configuration was described in which the beam splitter moves parallel to the emission direction (linear axis) of the first beam and the second beam. The direction of movement of the beam splitter is not limited; for example, if it is possible to change the optical path difference between the first beam and the second beam, the beam splitter may be moved in a direction oblique or perpendicular to the linear axis.

[0188] The above embodiment describes a case where both the incident angles of the first beam and the second beam with respect to the exposure surface are variable. However, it is not limited to this, and for example, at least one of the incident angles of the first beam or the second beam may be variable. In this case, the beam bifurcation section may be moved in accordance with the change in at least one of the incident angles of the first beam or the second beam. In this way, even with a configuration in which only the incident angle of one beam is changed, the accuracy of interference exposure can be improved by moving the beam bifurcation section.

[0189] The above embodiment mainly describes a configuration for performing interference lithography using pulsed laser light. The light used for interference lithography can be any coherent pulsed light, and pulsed light other than pulsed laser light may be used. For example, pulsed light may be generated by splitting incoherent light using a chopper or the like. In this case, the incoherent light may be converted into coherent light by passing it through a filter that aligns the phase and wavelength. In addition, the type of pulsed light used for interference lithography is not limited.

[0190] It is also possible to combine at least two of the feature features of the present invention described above. In other words, the various feature features described in each embodiment may be combined arbitrarily without distinction between embodiments. Furthermore, the various effects described above are merely examples and are not limiting, and other effects may also be exhibited. [Explanation of Symbols]

[0191] B1...First beam B2... Second beam 4… Exposure surface 5… Irradiation area 6… Interference fringes for exposure 8…Linear axis 12...Sensor section 13…Control Unit 19...Optical path adjustment section 20... Pulsed light source 21, 21a~21f...beam branching section 22…Movement mechanism 23...Incidence optical system 25... Diplexer 100... Interferometric exposure system

Claims

1. An interference exposure apparatus that performs interference exposure on an object to be irradiated, arranged along the exposure surface, by superimposing a first beam and a second beam obtained by splitting coherent pulsed light in an irradiation area on the exposure surface, A beam splitter that causes the first beam and the second beam to be emitted in different directions from each other, An incident optical system that causes the first beam and the second beam emitted from the beam splitting section to overlap with each other at a set incidence angle and incident into the irradiation area, An optical path adjustment unit that can move the beam branching portion so that the first beam and the second beam interfere in the irradiation area. An interference exposure apparatus equipped with the following:

2. An interference exposure apparatus according to claim 1, The incident optical system has a variable incident angle of at least one of the first beam or the second beam with respect to the exposure surface. The optical path adjustment unit moves the beam splitter in response to a change in at least one of the incident angles of the first beam or the second beam. Interference exposure system.

3. An interference exposure apparatus according to claim 2, The incident optical system causes the first beam and the second beam to be incident on the irradiation area in such a manner that they are asymmetrical with respect to the normal to the exposure surface in the irradiation area. Interference exposure system.

4. An interference exposure apparatus according to claim 1, The beam splitter includes a demultiplexing element that splits the pulsed light into a first beam and a second beam, and at least one optical element that sets at least one of the following: the incident direction of the pulsed light to the demultiplexing element, the exit direction of the first beam from the beam splitter, or the exit direction of the second beam from the beam splitter. Interference exposure system.

5. An interference exposure apparatus according to claim 4, The beam splitter emits the first beam and the second beam in opposite directions along a predetermined linear axis. The optical path adjustment unit moves the beam branching unit along the linear axis. Interference exposure system.

6. An interference exposure apparatus according to claim 5, The incident optical system is A first mirror moves along the linear axis and rotates relative to the linear axis, and reflects the first beam emitted from the beam branching section, A second mirror moves along the linear axis and rotates relative to the linear axis, and reflects the second beam emitted from the beam branching section. has Interference exposure system.

7. An interference exposure apparatus according to claim 6, The incident optical system is A third mirror moves along the first drive shaft and rotates relative to the first drive shaft, and reflects the first beam reflected by the first mirror toward the irradiation area, A fourth mirror moves along the second drive shaft and rotates relative to the second drive shaft, and reflects the second beam reflected by the second mirror toward the irradiation area. has Interference exposure system.

8. An interference exposure apparatus according to claim 7, The first drive shaft and the second drive shaft are each arc axes that surround the irradiation area. Interference exposure system.

9. An interference exposure apparatus according to claim 5, The at least one optical element includes a fifth mirror that reflects the pulsed light incident along the linear axis toward the demultiplexer. Interference exposure system.

10. An interference exposure apparatus according to claim 5, The beam branching section sets the exit axis of the first beam and the exit axis of the second beam to the same axis along the linear axis. Interference exposure system.

11. An interference exposure apparatus according to claim 4, The demultiplexing element is either a beam splitter or a diffraction grating. Interference exposure system.

12. An interference exposure apparatus according to claim 1, The optical path adjustment unit includes a moving mechanism that moves the beam splitter and a control unit that controls the moving mechanism to control the position of the beam splitter. Interference exposure system.

13. An interference exposure apparatus according to claim 12, The optical path adjustment unit has a sensor unit that detects the interference state of the first beam and the second beam in the irradiation area. The control unit controls the movement mechanism based on the detection results of the sensor unit. Interference exposure system.

14. An interference exposure apparatus according to claim 13, The sensor unit detects interference fringes generated when the first beam and the second beam overlap, The control unit moves the beam splitter so that the contrast of the interference fringes is increased. Interference exposure system.

15. An interference exposure apparatus according to claim 13, The sensor unit detects higher harmonics generated when the first beam and the second beam overlap. The control unit moves the beam splitter so that the intensity of the higher harmonics increases. Interference exposure system.

16. An interference exposure apparatus according to claim 1, The pulse width of the pulsed light is 100 nsec or less. Interference exposure system.

17. An interference exposure method using the interference exposure apparatus described in claim 1, The interference state of the first beam and the second beam in the irradiation area is detected, The position of the demultiplexer is controlled based on the detection result of the interference state. Interference exposure method.

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