JP4214547B2 - Beam shaping optical element and pattern writing apparatus having the same - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a pattern drawing apparatus for forming a drawing pattern such as a circuit pattern on a drawing object such as a photomask (rectile) or a direct printed board or a silicon wafer as an original plate.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, drawing apparatuses that form circuit patterns by photolithography on the surface of an object to be drawn such as silicon wafers, LCDs (Liquid Crystal Displays), and PWBs (Printed Wiring Boards) have been known. The exposure surface is scanned with an electron beam or a laser beam. A photosensitive material such as a photographic material or a photoresist reacts with light on the surface of the photomask, and as a result, a circuit pattern is formed. In addition, a drawing device (exposure device) that directly forms a circuit pattern on a drawing object such as a printed circuit board or a silicon wafer without using a photomask has been realized, and a DMD (Digital Micro-mirror Device) is used as a light intensity modulation element. ) Is known (for example, see Japanese Patent Application Laid-Open No. 2001-168003). When the DMD is used, the light emitted from the light source enters the DMD via the illumination optical system. The light incident on the DMD is selectively reflected for each micromirror, and a circuit pattern is formed based on the reflected light.
[0003]
[Problems to be solved by the invention]
The cross-sectional shape of a light beam emitted from a light source such as a laser is generally circular or elliptical. On the other hand, the overall size of a light modulation unit such as a DMD is determined according to a television screen display standard or the like, and the size is not determined according to the cross-sectional shape of the light beam. Therefore, when the size of the light beam cross-sectional shape does not correspond to the DMD size, only a part of the illumination light is irradiated onto the DMD, so that the light from the light source cannot be effectively used, and the illumination efficiency is lowered.
[0004]
Therefore, an object of the present invention is to obtain a pattern drawing apparatus that can effectively use light from a light source regardless of the aspect ratio in the vertical and horizontal directions in a light modulation unit such as a DMD.
[0005]
[Means for Solving the Problems]
The pattern writing apparatus of the present invention is a device for forming a pattern on the exposure surface of a pattern forming body, and emits light having symmetrical intensity distributions along two axial directions that pass through the center and are orthogonal to each other in the light beam cross section. A drawing apparatus that uses a light source to perform. For example, the light source is a laser oscillator that emits a laser beam, and emits light having a Gaussian distribution of light intensity along each of the two axial directions. An LED (Light Emitting Diode) may be used instead of the laser oscillator. The drawing apparatus includes: a light modulation unit that regularly arranges a plurality of light modulation elements each of which is in one of a first state for guiding light from a light source to an exposure surface and a second state for guiding light to other than the exposure surface; And a beam shaping optical element for correcting the cross-sectional shape of the light beam. Then, the beam shaping optical element of the present invention has a beam cross-section while maintaining the similarity of the intensity distribution in each of the two axial directions independently so that the aspect ratio in the two axial directions matches the aspect ratio of the light modulation unit. Correct the shape. As a result, substantially all of the light emitted from the light source is irradiated onto the light modulation unit. The light modulation unit is, for example, a DMD (Digital Micro-mirror Device) composed of a micromirror as a light modulation element. Alternatively, an LCD (Liquid Crystal Display) may be applied.
[0006]
With respect to a light modulation unit in which minute light modulation elements such as DMD are arranged, the aspect ratio in the vertical and horizontal directions according to the two-axis directions is determined according to a predetermined standard. For example, a television display standard (color TV standard system) , VGA, XGA, Hi-Vision, etc.). Usually, since the light modulation unit has a rectangular shape, the length and width of the light modulation unit do not match. If the aspect ratio and the ratio of the beam cross-sectional shape in the two-axis directions do not match, if the illumination shape is sufficiently larger than the light modulation unit, only the light at the central part with high intensity is used and the light at the peripheral part with low intensity is Must be cut. Alternatively, if the illumination shape is smaller than that of the light modulation unit, a portion that does not receive light is generated in the minute light modulation element on the outer peripheral portion, and the entire element cannot be used effectively. become longer. In the present invention, since the beam shaping optical element is provided, the light from the light source can be guided to the light modulation unit without being substantially cut. In other words, since the cross-sectional shape of the light beam is corrected while maintaining the similarity of the intensity distribution, the beam is shaped so that the entire light is within the DMD area. Accordingly, it is possible to form a pattern with sufficient illumination light while effectively using the minute light modulation element of the light modulation unit.
[0007]
In order to perform beam shaping, it is desirable to correct the cross-sectional shape of the light beam with a simple optical system configuration. Therefore, the beam shaping optical element is preferably a diffusing plate in which divergence angles along two axial directions can be set separately. That is, when the light is diverged, the cross-sectional shape of the light beam can be changed by separately setting the divergence angles in the two axial directions. The divergence angle in the biaxial direction is determined according to the aspect ratio of the light modulation unit. For example, a frost diffusion plate is preferably used as the diffusion plate. The frost diffusing plate is usually used for the purpose of simply diffusing light in a liquid crystal display or the like, but in the present invention, the divergence angle may be determined according to the aspect ratio of the light modulation unit.
[0008]
Since the beam shaping optical element for a pattern writing apparatus of the present invention forms a pattern on the exposure surface of the pattern forming body, each has a symmetrical intensity distribution along two axial directions that pass through the center and are orthogonal to each other in the light beam cross section. A plurality of light modulation elements regularly arranged in either a first state for guiding light from the light source to the exposure surface or a second state for guiding light from the light source to other than the exposure surface. An optical element provided in a pattern writing apparatus comprising a light modulation unit, wherein the light modulation unit is irradiated with substantially all the light emitted from the light source. Beam shaping that corrects the cross-sectional shape of the light beam while maintaining the similarity of the intensity distribution in each of the two axial directions independently to match the aspect ratio of the light modulation unit Characterized by comprising the academic element.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, a pattern drawing apparatus according to an embodiment of the present invention will be described with reference to the drawings.
[0010]
FIG. 1 is a perspective view schematically showing a pattern drawing apparatus according to this embodiment, and FIG. 2 is a view schematically showing an exposure unit provided in the pattern drawing apparatus. FIG. 3 shows the movement of the exposure area accompanying the movement of the stage. The pattern drawing apparatus of this embodiment is a drawing apparatus that forms a circuit pattern by directly irradiating light onto a substrate such as a printed board or a silicon wafer coated with a photoresist.
[0011]
The pattern drawing apparatus 10 includes a gate-like structure 12 and a base 14, and an XY stage driving mechanism 19 that supports an XY stage 18 is mounted on the base 14. A substrate SW is installed on the top. The gate-like structure 12 is provided with an exposure unit 20 for forming a circuit pattern on the surface of the substrate SW, and the exposure unit 20 operates in accordance with the movement of the XY stage 18. Further, the drawing apparatus 10 includes a drawing control unit (not shown here) that controls the movement of the XY stage 18 and the operation of the exposure unit 20.
[0012]
As shown in FIG. 2, the exposure unit 20 includes a DMD (Digital Micro-mirror Device) 22, an illumination optical system 24, and an imaging optical system 26, and is arranged between an argon laser 21 used as a light source and the DMD 22. The illumination optical system 24 is disposed, and the imaging optical system 26 is disposed between the DMD 22 and the substrate SW. Light (laser beam) emitted continuously from the argon laser 21 at a constant intensity is guided to the illumination optical system 24.
[0013]
The illumination optical system 24 includes a diffusing plate 24A and a collimator lens 24B. When the laser beam LB passes through the illumination optical system 24, light composed of a light beam that totally illuminates the DMD 22 is formed. The DMD 22 is a light modulation unit in which minute micromirrors having an order of μm are arranged in a matrix, and each micromirror rotates and fluctuates due to an electrostatic field effect. In the present embodiment, the DMD 22 is configured by arranging M × N micromirrors in a matrix. In the following description, a micromirror corresponding to the position of the array (i, j) is designated as “X _ij ” (1 (Indicated as i (M, 1 (j (N).
[0014]
The micromirror X _ij is positioned in one of a first posture for reflecting the light LB from the argon laser 21 in the direction of the exposure surface SU of the substrate SW and a second posture for reflecting the light LB in the direction outside the exposure surface SU. Then, the posture is switched according to the control signal from the drawing control unit. When the micromirror X _ij is positioned in the first posture, the light reflected on the micromirror X _ij is guided toward the imaging optical system 26. The imaging optical system 26 includes two convex lenses 26A and 26C and a reflector lens 26B, and light passing through the imaging optical system 26 irradiates a predetermined spot on the exposure surface SU. On the other hand, when the micromirror X _ij is positioned in the second attitude, the light reflected by the micromirror X _ij is guided toward the light absorbing plate 29 and deviates from the imaging optical system 26 to the exposure surface SU. Is not illuminated. Hereinafter, the state in which the micromirror X _ij is supported in the first posture is defined as the ON state, and the state in which the micromirror X _ij is supported in the second posture is defined as the OFF state. In the present embodiment, the magnification of the imaging optical system 26 is set to 1. The size (width, height) of the projection spot Y _ij irradiated with light by one micromirror X _ij is micro. It matches the size of the mirror _Xij .
[0015]
When all the micromirrors are in the ON state with the XY stage 18 stopped, the entire exposure area EA having a size of (M × h) × (N × l) is irradiated on the exposure surface SU. Is done. However, the height and the width of the micromirror X _ij are represented by h and l, respectively. In the DMD 22, the micromirrors X _ij are independently turned on / off, so that the light irradiated on the entire DMD 22 is divided into light composed of light beams selectively reflected by the micromirrors. The As a result, the spot corresponding to the exposure area EA on the exposure surface SU is irradiated with light corresponding to the circuit pattern to be formed at that spot. As the XY stage 18 moves, the exposure area EA relatively moves on the exposure surface SU along the scanning direction. Thereby, a circuit pattern is formed along the scanning direction. Note that a photosensitive photoresist layer is formed in advance on the surface SU of the substrate SW.
[0016]
In the present embodiment, the XY stage 18 moves at a constant speed along the scanning direction according to raster scanning (see FIG. 3). The micro mirrors X _{ij of the} DMD 22 are independently controlled based on raster data corresponding to the circuit pattern, so that a predetermined circuit pattern is formed with respect to the projection spot within the exposure area EA. The mirror X _ij is positioned in the first posture or the second posture, respectively. In accordance with the relative movement of the exposure area EA accompanying the movement of the XY stage 18, the micromirrors _Xij are sequentially turned ON / OFF. When the scanning for one line is completed, the XY stage 18 moves in the sub-scanning direction (Y direction) so that the next line can be exposed, and the folded XY stage 18 moves along the scanning direction. By exposing all the lines, a circuit pattern is formed on the substrate SW.
[0017]
The size of the DMD 22 is determined in accordance with the television display standard. The scanning direction (X direction) of the DMD 22 is defined as the horizontal direction, the sub-scanning direction (Y direction) is defined as the vertical direction, and the width (lateral length) and When the height (length in the vertical direction) is represented by “W” and “K”, respectively, the aspect ratio (aspect ratio W: K) of the DMD 22 of this embodiment is determined to be 3: 4.
[0018]
FIG. 4 is a plan view showing the diffusion plate 24A.
[0019]
As shown in FIG. 4, the diffusion plate 24A is a frost type diffusion plate in which predetermined irregularities are formed and arranged on glass, film, resin, or the like. As will be described later, the light beam cross section of the light emitted from the argon laser 21 In order to correct the shape, the incident light is diverged at a predetermined angle along the vertical and horizontal directions. However, the vertical and horizontal directions “Z1” and “Z2” of the diffusion plate 24A correspond to the height and width directions (K, W) of the DMD 22, respectively. Further, the divergence angle is determined according to the uneven shape, pitch, and the like. In the present embodiment, the divergence angles in the vertical and horizontal directions are determined so that substantially all the light from the argon laser 21 is irradiated on the entire surface of the DMD 22.
[0020]
FIG. 5 is a diagram showing a cross section of the light beam when the DMD 22 is irradiated with light, and FIG. 6 is a diagram showing a graph of light intensity distribution. The correction of the light beam sectional shape by the diffusion plate 24A will be described with reference to FIGS.
[0021]
As shown in FIG. 6, the intensity distribution of the laser beam LB emitted from the argon laser 21 generally follows a Gaussian distribution (normal distribution). That is, when the light intensity at the center is I ₀ and the spot size indicating the effective radius of the light beam cross section is ω, the light intensity is expressed by the following equation.
I = I ₀ e ^{−2 α} (α = (x / ω) ² ) (1)
However, x represents the distance from the optical axis, and the spot size ω is defined by the intensity of I = I ₀ × 1 / e ² = 0.135I _{0. In} FIG. 6, I ₀ = 1, ω = The intensity distribution in the case of 1 is graphed.
[0022]
Further, the intensity distribution of the laser beam LB from the argon laser 21 coincides with the biaxial direction defined in the beam cross section. Here, the biaxial direction is a direction that passes through the center of the light beam cross section and is orthogonal to each other, and corresponds to the vertical and horizontal directions of the diffusion plate 24A. In the following, the biaxial directions are represented as “x” and “y”. However, x corresponds to the horizontal (X) direction of the DMD 22, and y corresponds to the vertical (Y) direction of the DMD 22. Since the intensity distribution is the same in both the x and y directions, the light beam cross section of the laser beam LB is circular, and the light beam cross section is formed with the spot size ω as the diameter. Therefore, the ratio of the biaxial directions x and y in the light beam cross section (hereinafter referred to as the aspect ratio of the light beam cross section) substantially maintains a 1: 1 relationship.
[0023]
When the diffusing plate 24A is not arranged in the exposure unit 20, the aspect ratio of the DMD 22 and the aspect ratio of the light beam cross section do not match. Therefore, regarding the laser beam LB enlarged and shaped in the process of passing through the commonly used diffusing lens and collimator lens 24B, the light beam cross section on the plane including the surface of the DMD 22 is expressed as “LF0”. The aspect ratio (L: H) is 1: 1. Therefore, a part of the laser beam LB is not irradiated into the area of the DMD 22 (see FIG. 5).
[0024]
In this embodiment, the diffusion plate 24A is disposed in the exposure unit 20, and the divergence angle in the vertical and horizontal directions of the diffusion plate 24A is such that the aspect ratio (aspect ratio) of the beam cross section corresponds to the aspect ratio of the DMD 22. It has been established. That is, the laser beam LB is expanded at different conversion rates in the vertical direction and the horizontal direction while maintaining the similarity relationship of the intensity distribution, and the spot size ω in the x direction is corrected to ω ′. Thereby, the aspect ratio (= L1 / H1) of the beam cross section of the laser beam LB that has passed through the diffusion plate 24A is substantially equal to the aspect ratio (= W / K) of the DMD 22, and on the plane including the surface of the DMD 22 The beam cross-section LF1 of the laser beam LB is all within the area of the DMD 22 (see FIG. 5).
[0025]
FIG. 7 is a view showing a cross section of the laser beam LB with respect to the DMD 22, and FIG. 8 is a view showing a graph showing the light amount fluctuation and the acquisition rate.
[0026]
As shown in FIG. 7, the width and height of the DMD 22 are represented as Sx and Sy, the length along the x direction of the light beam cross section corrected by the diffusion plate 24A is represented as Bx, and the length along the y direction is represented as By. To do. However, Bx and By follow the spot size (I ₀ / e ² ). Bx and By can be arbitrarily set according to the width and height Sx and Sy of the DMD 22 as long as the condition for the light to substantially enter the DMD 22 is satisfied.
[0027]
In FIG. 8, when the amount of movement in the Y direction after the end of one scan is overlapped with Sy / 2, the amount of light in the scanning direction (X direction) is 100%, and the sub scanning direction (Y direction) is 100%. The light quantity variation rate and the light quantity capture rate depending on the illumination ratio are shown. The horizontal axis represents the ratio of By and Sy (By / Sy), and the vertical axis represents the light quantity variation rate and the light quantity capture rate in percentage. As can be seen from the curve J representing the light quantity fluctuation rate shown in FIG. 8, when the By / Sy ratio is about 0.9, the light quantity fluctuation rate is about 3%, and the light quantity capture rate is high. Therefore, the divergence angles in the vertical and horizontal directions of the diffusion plate 24A are preferably determined so that the ratio By / Sy is 0.9.
[0028]
As described above, according to the present embodiment, by providing the diffusion plate 24 in the exposure unit 20, the beam cross-sectional shape of the laser beam LB emitted from the argon laser 21 is corrected, and the light from the laser 21 is substantially reduced. All can be accommodated in the reflection area of the DMD 22.
[0029]
In this embodiment, an argon laser that emits light whose Gaussian distributions in the vertical and horizontal directions match (circular beam cross section) is applied, but a laser that emits light having unique Gaussian distribution characteristics in both vertical and horizontal directions is applied. May be. In this case, the divergence angle in the vertical and horizontal directions of the frost diffusion plate 24A is determined so that substantially all light is incident on the entire surface of the DMD 22. Further, a light source other than a laser (for example, an LED) may be applied, or a light source that emits light having intensity distribution characteristics that are symmetrical with respect to an axis may be used instead of a Gaussian distribution. Good. In the present embodiment, the beam cross section is defined with the spot size ω as the radius. However, the diffuser plate 24A may be applied by defining the beam cross section so as to capture all light.
[0030]
When the aspect ratio of the DMD 22 is determined according to a standard other than the television screen display standard, the divergence angle may be determined according to the aspect ratio.
[0031]
An optical element other than the frost diffusion plate may be used to adjust the aspect ratio in the cross section of the light beam while maintaining the similarity relationship of the intensity distribution. For example, an optical system for reducing and projecting along one direction of two axes may be arranged in front of a diffuser plate that enlarges and projects at the same magnification along the vertical and horizontal directions. As the light modulation unit, an SLM (Spatial Light Modulators) device may be applied instead of the DMD 22.
[0032]
【The invention's effect】
As described above, according to the present invention, the light from the light source can be effectively used regardless of the size of the light modulation unit.
[Brief description of the drawings]
FIG. 1 is a perspective view schematically showing a pattern drawing apparatus according to an embodiment of the present invention.
FIG. 2 is a diagram schematically showing an exposure unit provided in the pattern drawing apparatus.
FIG. 3 is a view showing movement of an exposure area accompanying movement of a stage.
FIG. 4 is a plan view showing a diffusion plate.
FIG. 5 is a diagram showing a cross section of a light beam when light is applied to a DMD.
FIG. 6 is a graph showing a light intensity distribution graph;
FIG. 7 is a diagram showing a beam cross section of a laser beam with respect to DMD.
FIG. 8 is a graph showing a light amount variation and an acquisition rate.
[Explanation of symbols]
10 Pattern drawing device 21 Argon laser (light source)
22 DMD (Light Modulation Unit)
24A Diffuser (Beam shaping optical element)
_Xij micromirror (light modulation element)
x, y Biaxial direction

Claims (5)

A light source that emits light having symmetrical intensity distributions along two axial directions that pass through the center and are orthogonal to each other in order to form a pattern on the exposure surface of the pattern forming body;
A light modulation in which a plurality of light modulation elements, each of which is set in one of a first state for guiding light from the light source to the exposure surface and a second state for guiding light other than the exposure surface, are regularly arranged in two dimensions Unit,
In order to irradiate substantially all of the light emitted from the light source to the light modulation unit, the aspect ratio in the biaxial direction is matched with the aspect ratio in the vertical and horizontal directions of the light modulation unit. A beam shaping optical element for correcting the cross-sectional shape of the light beam while maintaining the similarity of the intensity distribution independently;
A pattern drawing apparatus , wherein a pattern is formed by moving an exposure area by the light modulation unit relative to the exposure surface .   The pattern drawing apparatus according to claim 1, wherein the light modulation unit is a DMD (Digital Micro-mirror Device) including a micromirror as the light modulation element. The beam shaping optical element is a diffuser plate capable of individually setting a divergence angle along the two axial directions;
The pattern drawing apparatus according to claim 1, wherein a divergence angle in the biaxial direction is determined according to an aspect ratio of the light modulation unit.   The pattern drawing apparatus according to claim 3, wherein the diffusion plate is a frost type diffusion plate.   The pattern drawing apparatus according to claim 1, wherein the light source is a laser oscillator that emits a laser beam, and emits light having a Gaussian distribution of light intensity along each of the two axial directions.

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