JP2004191660A - Exposure apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exposure apparatus which extends the life of a spatial modulation element without exchanging spatial modulation elements against deterioration in the spatial modulation element due to light energy or the like. <P>SOLUTION: A DMD (digital micromirror device) 42 is held by a DMD guide frame 60 and is made slidable (in the plane direction of the DMD 42) relative to the DMD guide frame 60 by using a screw 62 so that the irradiation region 68 of a light beam entering from a reflection mirror 40 can be varied in accordance with the screwing depth of the screw 62. Even when the irradiation region 68 of the DMD 42 deteriorates to render the DMD 42 no more usable, the DMD 42 can be continuously used by changing the irradiation region 68 of the light beam entering from the reflection mirror 40 onto the DMD 42. Thus, the life of the DMD 42 is improved several times and the running cost can be significantly decreased. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an exposure apparatus using a spatial modulation element.
[0002]
[Prior art]
Several exposure apparatuses using spatial light modulation elements such as DMD have been proposed. Among them, when the modulation speed of the spatial light modulation element becomes a rule and productivity is limited, the data transfer speed can be reduced by using only a part of the total number of pixels of the spatial light modulation element. Methods have been proposed that increase speed, increase modulation speed, and as a result, improve productivity. In the first place, the total number of pixels of the spatial light modulator is not necessary, and only a small number of pixels may be sufficient.
[0003]
On the other hand, improvement in productivity is a constantly required item, and therefore, the exposure power of the exposure apparatus tends to increase. And the power density of the light irradiated to each element of the optical system also tends to increase. Also, PWB exposure apparatuses, stereolithography apparatuses, and the like have been announced / suggested as exposure apparatuses in the near ultraviolet wavelength region.
[0004]
Among these optical elements, spatial light modulation elements are particularly affected by these large power densities or high energy short wavelengths. That is, since the spatial light modulation element generally has a small area, the energy density becomes higher and the modulation portion of the spatial light modulation element deteriorates.
[0005]
Specifically, in the case of a reflective spatial light modulator, the reflectivity decreases due to a change in the reflective surface, the operation of the movable part is poor, and in the case of a transmissive spatial light modulator, due to a change in the properties of the transmissive part. There is a decrease in transmittance. As described above, when the spatial light modulation element deteriorates, it becomes unusable and the spatial light modulation element needs to be replaced. For this reason, running cost will become high.
[0006]
[Patent Document 1]
Japanese Patent Application No. 2002-149886 [0007]
[Problems to be solved by the invention]
In view of the above facts, an object of the present invention is to obtain an exposure apparatus that extends the lifetime of a spatial modulation element without replacing the spatial modulation element against deterioration of the spatial modulation element due to light energy or the like.
[0008]
[Means for Solving the Problems]
The invention according to claim 1 includes an exposure head that moves relative to the drawing medium and exposes the drawing medium, and includes a plurality of pixel units that are arranged in the exposure head and whose modulation state changes according to drawing information. A spatial modulation element arranged two-dimensionally on a substrate, a first optical system that is disposed on the exposure head and that irradiates the spatial modulation element with a light beam emitted from a light source, and is disposed on the exposure head. A second optical system that forms an image of the light beam modulated by the spatial modulation element on the drawing medium, and an irradiation area changing unit that changes the irradiation area of the light beam in the spatial modulation element. It is a feature.
[0009]
According to the first aspect of the present invention, the light beam emitted from the light source is irradiated to the spatial modulation element by the first optical system. In the spatial modulation element, a plurality of pixel portions whose modulation states change according to drawing information are two-dimensionally arranged on the substrate, and the light beam modulated by the spatial modulation element is transmitted by the second optical system. An image is formed on the drawing medium, and a drawing is formed on the drawing medium.
[0010]
Here, in the spatial modulation element, the irradiation region of the light beam is changed by the irradiation region changing means. Even if the irradiation area of the spatial modulation element deteriorates and the spatial modulation element becomes unusable, the spatial modulation element can be continuously used as it is by changing the irradiation area. Thereby, the lifetime as a spatial modulation element can be improved several times, and a running cost can be reduced significantly.
[0011]
In the invention according to claim 2, the spatial modulation element is guided in the in-plane direction of the spatial modulation element by the guide means, and the spatial modulation element is slid along the guide means. Thereby, the irradiation area | region of a spatial modulation element can be changed.
[0012]
According to the third aspect of the present invention, a mask that divides the irradiation region of the spatial modulation element is disposed on the incident side of the light beam, the mask is guided in the in-plane direction of the spatial modulation element by the guide means, and the guide means Slide the spatial modulation element along In this way, by sliding the mask, the irradiation area of the spatial modulation element irradiated through the mask can be changed.
[0013]
In the invention according to claim 4, there is provided a deterioration state measuring means for measuring the deterioration state of the spatial modulation element. By linking the deterioration state measuring means and the irradiation area changing means, the irradiation area of the light beam of the spatial modulation element can be changed according to the deterioration state of the spatial modulation element. As a result, there is no waste such as changing the irradiation area even though the spatial modulation element is not deteriorated, and the lifetime of the spatial modulation element can be extended efficiently.
[0014]
In the fifth aspect of the present invention, the irradiation region of the light beam in the spatial modulation element is changed in accordance with the deterioration state of the spatial modulation element or the usage elapsed time.
[0015]
In the invention described in claim 6, the elapsed use time is the operation time of the light source or the time for which the spatial modulation element is irradiated.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[0017]
First, the configuration of the exposure apparatus will be described.
[0018]
As shown in FIG. 1, an exposure apparatus 10 according to an embodiment of the present invention includes a rectangular parallelepiped installation table 14 supported by four legs 12, and an upper surface of the installation table 14. Are provided with a pair of guides 16 extending along the longitudinal direction of the installation table 14.
[0019]
A flat stage 18 is placed on the upper surface of the guide 16 in a state where the guide 16 is bridged. A printed circuit board 20 is held on the upper surface of the stage 18.
[0020]
On the other hand, a substantially U-shaped gate 22 is fixed across the installation table 14 in a state where a gap is provided between the upper surface of the stage 18 and a central portion in the longitudinal direction of the installation table 14. A scanner 24 is provided on one side surface of the gate 22, and a plurality (for example, two) of side edges of the printed circuit board 20 held on the upper surface of the stage 18 are detected on the other side surface. A detection sensor 26 is provided.
[0021]
Here, the stage 18 can be moved along the guide 16 by driving means (not shown), and the scanner 24 and the detection sensor 26 are connected to a controller (not shown).
[0022]
As shown in FIGS. 2 and 3, the scanner 24 includes a plurality of exposure heads 28. Each exposure head 28 has a light source wavelength of 350 to 450 nm (however, the wavelength range is set in the heat mode). A fiber array light source 30 having a spread of 350 to 950 nm is provided.
[0023]
Laser light emitted from the fiber array light source 30 is converted into parallel light by a pair of combination lenses 34 constituting a lens system 32 and is incident on a pair of combination lenses 36.
[0024]
In the arrangement direction of the laser emitting ends, the combination lens 36 spreads the light beam at a portion close to the optical axis of the lens and contracts the light beam at a portion away from the optical axis, and in a direction orthogonal to the arrangement direction. The laser beam has a function to pass through as it is, and the laser beam is corrected so that the light quantity distribution is uniform.
[0025]
The laser light corrected so that the light quantity distribution is made uniform by the combination lens 36 is condensed by the condenser lens 38, and the incident laser light is converted into each pixel according to the image data via the reflection mirror 40. The light is incident on a digital micromirror device 42 (hereinafter referred to as “DMD 42”), which is a spatial light modulation element that modulates each time. The laser light incident on the DMD 42 is imaged on the printed circuit board 20 by the lens systems 44 and 46.
[0026]
Here, as shown in FIG. 4, the DMD 42 is configured by a micromirror (micromirror) 50 supported by a support column on an SRAM cell (memory cell) 48 and constitutes a pixel. This is a mirror device configured by arranging a large number (for example, 600 × 800) of micromirrors in a lattice pattern.
[0027]
Each pixel is provided with a micromirror 50 supported by a support at the top, and a material having high reflectivity such as aluminum is deposited on the surface of the micromirror 50, and the reflectivity of the micromirror 50 is 90%. That's it.
[0028]
A silicon gate CMOS SRAM cell 48 manufactured on a normal semiconductor memory manufacturing line is disposed directly below the micromirror 50 via a support including a hinge and a yoke, and is entirely monolithic (integrated type). ).
[0029]
When a digital signal is written to the SRAM cell 48 of the DMD 42, the micromirror 50 supported by the support is tilted in a range of ± α degrees (for example, ± 10 degrees) with respect to the substrate side on which the DMD 42 is disposed with the diagonal line as the center. It is done.
[0030]
Here, FIG. 5A shows a state in which the micromirror 50 is tilted to + α degrees when the micromirror 50 is in an on state, and FIG. 5B shows a state in which the micromirror 50 is tilted to −α degrees that is in an off state. Show.
[0031]
Each micromirror 50 controls the inclination of the micromirror 50 in each pixel of the DMD 42 according to an image signal from a control unit (not shown) provided in the exposure apparatus 10, and the light incident on the DMD 42 is transmitted to each micromirror 50. Reflected in the tilt direction of the mirror 50. Note that a light absorber (not shown) is arranged in the direction in which the light beam is reflected by the micromirror 50 in the off state.
[0032]
Here, the DMD 42 has 800 micromirrors 50 arranged in the longitudinal direction and 600 micromirrors 50 arranged in the short direction. It is preferable that the short direction is slightly inclined with respect to the sub-scanning direction by a predetermined angle θ (for example, 1 ° to 5 °).
[0033]
6A shows the scanning trajectory of the reflected light image (exposure beam) 54 by each micromirror 50 (see FIG. 4) when the DMD 42 is not tilted, and FIG. 6B shows the exposure when the DMD 42 is tilted. The scanning trajectory of the beam 54 is shown. Here, since the tilt angle of the DMD 42 is very small, the scan width W ₂ when the DMD 42 is tilted and the scan width W ₁ when the DMD 42 is not tilted are substantially the same.
[0034]
As shown in FIG. 6B, when the DMD 42 is tilted, the pitch P ₂ of the scanning locus (scanning line) of the exposure beam 54 by each micromirror 50 is equal to the pitch P ₁ of the scanning line when the DMD 42 is not tilted. It becomes narrower and the resolution can be greatly improved.
[0035]
Further, the same scanning line is overlapped and exposed (multiple exposure) by different micromirror 50 rows. In this way, by performing multiple exposure, it is possible to control a minute amount of the exposure position and to realize high-definition exposure. Further, the joints between the plurality of exposure heads 28 arranged in the main scanning direction can be connected without any step by a very small exposure position control.
[0036]
Note that the same effect can be obtained by arranging the micromirrors 50 in a staggered manner by shifting the micromirrors 50 by a predetermined interval in a direction orthogonal to the sub-scanning direction instead of inclining the DMD 42.
[0037]
Incidentally, the DMD 42 is held by a rectangular DMD guide frame 60 (guide means) as shown in FIGS. The DMD guide frame 60 is disposed so as to have the same angle as that provided between the reflection mirror 40 and the DMD 42.
[0038]
In addition, on the upper and lower sides of the inner surface side of the DMD guide frame 60, groove portions 60A are formed along the longitudinal direction of the DMD guide frame 60 (the left-right direction of the DMD guide frame 60), and the upper and lower edges of the DMD 42 Is engageable with the groove 60A.
[0039]
A ball screw 62 (sliding means) is screwed into the center of the right side wall of the DMD guide frame 60, and a substantially U-shaped clamp portion 64 is provided at the tip of the ball screw 62. The side edges of the DMD 42 are clamped by the clamp 64, and the DMD 42 can slide in the in-plane direction of the DMD 42 along the groove 60A through the clamp 64 by screwing the ball screw 62 manually.
[0040]
Here, since the DMD guide frame 60 is disposed so as to have the same angle as that provided between the reflection mirror 40 and the DMD 42, the DMD guide frame 60 is separated from the reflection mirror 40 even if the DMD 42 is slid in the DMD guide frame 60. The incident angle of is not changed.
[0041]
On the other hand, as shown in FIG. 7 and FIG. 10A, the fiber array light source 30 is connected with a light beam emission time accumulation counter 66 (hereinafter referred to as “counter 66”) as a deterioration state measuring means. The degradation state of DMD 42 is measured.
[0042]
Specifically, the emission time from the fiber array light source 30 is accumulated, and when this emission time exceeds a predetermined time, it is reported to the outside that the DMD 42 has deteriorated.
[0043]
As another means for detecting the aging state, the optical power is measured at a position corresponding to the drawing medium to detect a change such as a decrease in the optical power, or the scattered light is detected by a photodetector provided for each drawing area. It is also possible to measure the change and detect the change in the increase.
[0044]
Next, the operation of the exposure apparatus according to this embodiment will be described.
[0045]
As shown in FIG. 7, the DMD 42 is held on the DMD guide frame 60, and the DMD 42 can be slid with respect to the DMD guide frame 60 by the ball screw 62 (slidable in the in-plane direction of the DMD 42). The irradiation area 68 of the light beam incident from the reflection mirror 40 can be changed according to the amount.
[0046]
For example, as shown in FIGS. 7 and 9A, 9B, and 9C, when the ball screw 62 is rotated clockwise, the DMD 42 slides to the left with respect to the DMD guide frame 60. Since the incident angle of the reflection mirror 40 with respect to the DMD 42 does not change, the irradiation area 68 of the light beam of the DMD 42 incident by the reflection mirror 40 slides to the right.
[0047]
Even if the irradiation area 68 of the DMD 42 is deteriorated and the DMD 42 becomes unusable, the DMD 42 can be used as it is by changing the irradiation area 68 of the light beam of the DMD 42 incident from the reflection mirror 40. Can do. Thereby, the lifetime as DMD42 can be improved several times, and a running cost can be reduced significantly.
[0048]
On the other hand, by providing the counter 66 for measuring the degradation state of the DMD 42, the degradation state of the DMD 42 can be determined, and the irradiation area 68 of the DMD 42 can be changed according to the degradation of the DMD 42. For this reason, there is no waste such as changing the irradiation region 68 even though the DMD 42 is not deteriorated, and it is possible to efficiently extend the life of the DMD 42.
[0049]
Here, the DMD 42 is slid according to the amount of the ball screw 62 screwed in manually, but the present invention is not limited to this. For example, as shown in FIGS. 7 and 10B, the counter 66 and the driving device 67 are connected, and the driving device 67 is coupled to the ball screw 62.
[0050]
Then, when the emission time from the fiber array light source 30 reaches a predetermined time or longer, the driving device 67 may be driven to rotate the ball screw 62 and change the irradiation area of the DMD 42.
[0051]
The counter 66 is not limited to this as long as the degradation state of the DMD 42 is known. For example, the reflectivity of the DMD 42 is measured, and when the reflectivity of the DMD 42 falls below a predetermined value, the counter 66 notifies the outside by lighting the lamp. You may make it do. Furthermore, the counter 66 is not necessarily required because it is sufficient that the irradiation area 68 of the DMD 42 can be efficiently changed according to the deterioration state of the DMD 42.
[0052]
In the present embodiment, the DMD 42 is slid with respect to the left-right direction of the DMD guide frame 60. However, the present invention is not limited to this as long as it can slide in the in-plane direction of the DMD 42.
[0053]
For example, as shown in FIG. 11, the DMD 70 may be slidable in the vertical direction using a DMD 70 that is about twice as large in the height direction as the DMD 42 (see FIG. 7).
[0054]
In this case, as in the case of the DMD 42, the DMD guide frame 72 that allows the DMD 70 to slide in the left-right direction is used, and a frame that surrounds the DMD guide frame 72 in a state of being longer than the DMD guide frame 72 in the height direction. A body 74 is used.
[0055]
Here, an elongated hole 74A is passed through one side wall of the frame body 74 so that the ball screw 76 can move up and down along the elongated hole 74A. A groove 74B is recessed in the other side wall of the frame body 74, and a projecting portion (not shown) that projects from the outer surface of the side wall of the DMD guide frame 72 is engaged with the groove portion 74B to Try to guide the movement.
[0056]
On the other hand, a ball screw 78 is screwed into the center of the lower surface of the frame 74, and the tip of the ball screw 78 is fixed to the lower surface of the DMD guide frame 72. Accordingly, the DMD guide frame 72 is slid in the vertical direction of the frame body 74 in accordance with the screwing amount of the ball screw 78.
[0057]
Thus, when the ball screw 76 is rotated clockwise, the DMD 70 slides leftward in the DMD guide frame 72 as shown in FIGS. 11 and 12A, 12B, and 12C. For this reason, the irradiation region 68 of the light beam incident by the reflection mirror 40 slides from the left side of the DMD 70 to the right side.
[0058]
When the ball screw 78 is rotated clockwise, the DMD 70 slides upward in the frame body 74 via the DMD guide frame 72 as shown in FIGS. 11 and 12C and 12D. As a result, the irradiation area 68 of the light beam incident by the reflection mirror 40 slides from the upper side to the lower side of the DMD 70.
[0059]
When the ball screw 76 is rotated counterclockwise, the DMD 70 slides to the right in the DMD guide frame 72 as shown in FIGS. 11 and 12D, 12E, and 12F. As a result, the irradiation area 68 of the light beam incident by the reflection mirror 40 slides from the right side to the left side of the DMD 70. As described above, the DMD 70 may be slid vertically and horizontally to change the light beam irradiation area 68.
[0060]
In this embodiment, the DMD 42 and 70 are slid to change the light beam irradiation area 68, but the present invention is not limited to this.
[0061]
For example, as shown in FIG. 13, a mask 80 that divides the irradiation region 84 of the DMD 82 is arranged in parallel with the DMD 82 on the incident side of the light beam incident by the reflecting mirror 40, and the mask 80 is arranged with respect to the surface of the DMD 82. Alternatively, it may be slid in a parallel plane.
[0062]
In this case, as in the case of the DMD 42 (see FIG. 7), the mask 80 is slidably held by the mask guide frame 86, and the mask 80 is parallel to the surface of the DMD 82 via the mask guide frame 86. Slide to. In this way, by sliding the mask 80, the irradiation area 84 of the DMD 82 irradiated through the mask 80 can be changed.
[0063]
In addition to the printed circuit board, the exposure apparatus described above exposes a dry film resist (DFR) in a manufacturing process of a flat panel display (FPD) and a printed wiring board (PWB). It can be suitably used for applications such as color filter formation in liquid crystal display (LCD) manufacturing processes, DFR exposure in TFT manufacturing processes, and DFR exposure in plasma display panel (PDP) manufacturing processes. .
[0064]
When exposing a liquid resist used for patterning a TFT and a liquid resist used for patterning a color filter, in order to eliminate sensitivity reduction (desensitization) due to oxygen inhibition, the exposure is performed in a nitrogen atmosphere. It is preferable to expose the exposure material. Exposure in a nitrogen atmosphere suppresses oxygen inhibition of the photopolymerization reaction, increases the sensitivity of the resist, and enables high-speed exposure.
[0065]
In the exposure apparatus, either a photon mode photosensitive material in which information is directly recorded by exposure or a heat mode photosensitive material in which information is recorded by heat generated by exposure can be used.
[0066]
When using a photon mode photosensitive material, a GaN-based semiconductor laser, a wavelength conversion solid-state laser, or the like is used for the laser device. When using a heat mode photosensitive material, an AlGaAs-based semiconductor laser (infrared laser), A solid state laser is used.
[0067]
Furthermore, in the above embodiment, the exposure head provided with the DMD has been described. For example, a micro electro mechanical systems (SMEM) type spatial modulation element (SLM; Spatial Light Modulator) or transmitted light by an electro-optic effect is used. A modulating optical element (PLZT element), a liquid crystal optical shutter (FLC), or the like may be used.
[0068]
Further, even when a spatial modulation element other than the MEMS type is used, by using a part of the pixel portions for all the pixel portions arranged on the substrate, the modulation speed per pixel and per main scanning line is used. The same effect can be obtained.
[0069]
Note that MEMS is a general term for micro systems that integrate micro-sized sensors, actuators, and control circuits based on micro-machining technology based on the IC manufacturing process. It means a spatial modulation element that is driven by the electromechanical operation used.
[0070]
【The invention's effect】
Since the present invention is configured as described above, in the invention according to claim 1, even if the irradiation area of the spatial modulation element deteriorates and the spatial modulation element becomes unusable, the irradiation area is changed. Since the spatial modulation element can be continuously used as it is, the lifetime as the spatial modulation element can be improved several times, and the running cost can be greatly reduced.
[0071]
In the second aspect of the invention, the irradiation area of the spatial modulation element can be changed by sliding the holding body. According to the third aspect of the present invention, the irradiation area of the spatial modulation element irradiated through the mask can be changed by sliding the mask.
[0072]
In the inventions according to claims 4 to 6, since the irradiation region of the light beam of the spatial modulation element can be changed at least according to the degradation state of the spatial modulation element, the spatial modulation element is not degraded. Regardless of this, there is no waste such as changing the irradiation region, and the lifetime of the spatial modulation element can be increased efficiently.
[Brief description of the drawings]
FIG. 1 is a perspective view showing an exposure apparatus according to an embodiment of the present invention.
FIG. 2 is a perspective view showing a configuration of a scanner of the exposure apparatus according to the embodiment of the present invention.
3A is a front view showing a configuration of an exposure head constituting the scanner of FIG. 2, and FIG. 3B is a plan view of FIG.
FIG. 4 is a partially enlarged view showing a configuration of a digital micromirror device (DMD).
FIGS. 5A and 5B are explanatory diagrams of DMD operation. FIGS.
6A is a plan view showing a case where the DMD is not inclined, and FIG. 6B is a plan view showing a case where the DMD is inclined.
FIG. 7 is a perspective view showing a configuration of an exposure head and showing a DMD and a DMD guide frame.
FIG. 8 is a cross-sectional view showing a DMD and a DMD guide frame.
FIGS. 9A to 9C are explanatory views showing a sliding state of the DMD.
FIGS. 10A and 10B are explanatory diagrams when a light beam emission accumulation counter is used.
FIG. 11 is a perspective view showing a configuration of the exposure head and a modification of the DMD and the DMD guide frame.
FIGS. 12A to 12F are explanatory views showing a sliding state of the DMD.
FIG. 13 is a perspective view showing a DMD and a mask guide frame.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 Exposure apparatus 28 Exposure head 32 Lens system (1st optical system)
42 DMD (Spatial Modulation Element)
44 Lens system (second optical system)
46 Lens system (second optical system)
60 DMD guide frame (guide means, irradiation area changing means)
62 Ball screw (sliding means, irradiation area changing means)
66 Light beam emission time accumulation counter (deterioration state measuring means)
68 Irradiation area 72 DMD guide frame (guide means, irradiation area changing means)
74 Frame (guide means, irradiation area changing means)
76 Ball screw (sliding means, irradiation area changing means)
78 Ball screw (sliding means, irradiation area changing means)
80 Mask 84 Irradiation area 86 Mask guide frame (guide means, irradiation area changing means)

Claims (6)

An exposure head that moves relative to the drawing medium and exposes the drawing medium;
A spatial modulation element disposed in the exposure head and having a plurality of pixel portions whose modulation states change according to drawing information arranged in a two-dimensional manner on a substrate;
A first optical system disposed in the exposure head and irradiating the spatial light modulator with a light beam emitted from a light source;
A second optical system that is disposed in the exposure head and forms an image of the light beam modulated by the spatial modulation element on the drawing medium;
Irradiation region changing means for changing the irradiation region of the light beam in the spatial modulation element;
An exposure apparatus comprising: The irradiation region changing means is
Guide means for guiding the spatial modulation element in an in-plane direction of the spatial modulation element;
Slide means for sliding the spatial modulation element along the guide means;
The exposure apparatus according to claim 1, comprising: The irradiation region changing means is
A mask disposed on the incident side of the light beam and defining an irradiation region of the spatial modulation element;
Guide means for guiding the mask in an in-plane direction of the spatial modulation element;
Slide means for sliding the mask along the guide means;
The exposure apparatus according to claim 1, comprising: The exposure apparatus according to claim 1, further comprising a deterioration state measuring unit that measures a deterioration state of the spatial modulation element. The exposure apparatus according to claim 1, wherein an irradiation area of the light beam in the spatial modulation element is changed according to a deterioration state of the spatial modulation element or a usage elapsed time. 6. The exposure apparatus according to claim 5, wherein the elapsed use time is an operation time of the light source or a time during which the spatial modulation element is irradiated.

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