JP5209946B2 - Focus position detection method and drawing apparatus - Google Patents

Description

  The present invention relates to an exposure apparatus and a drawing apparatus that can form a pattern on a substrate or the like, and more particularly, to a focus position detection method for an optical system that guides illumination light to a substrate.

  In the manufacturing process of an object to be drawn such as an electronic circuit board, a drawing process for forming a pattern on the object to be drawn is applied or coated with a photosensitive material such as a photoresist. As a drawing apparatus, a drawing apparatus using a spatial light modulator in which cells (spatial light modulation elements) such as micromirrors such as LCD and DMD (Digital Micro-mirror Device) are two-dimensionally arranged in a matrix is known. . There, the illumination light from the light source is modulated by controlling each cell. The light passing through the spatial light modulator passes through the projection optical system, whereby a drawing pattern is imaged on the exposure surface of the drawing object.

In order to make the exposure surface coincide with the focal plane of the projection optical system, the position of the drawing table on which the substrate is mounted is adjusted before drawing processing. In order to form a high-resolution pattern, it is necessary to accurately adjust the position of the drawing table. Conventionally, the test pattern is projected onto the substrate while gradually shifting the position of the substrate in the optical axis direction, and the formed pattern is Select the pattern with the highest resolution while visually recognizing or measuring the contrast of the reflected light. Then, the position where the pattern is obtained is determined as the focal position, and the position of the table is adjusted. On the other hand, a method is also known in which a light detection device in which light receiving elements are arranged one-dimensionally or two-dimensionally is placed at a temporary focal position to detect a deviation between the imaging position and the focal position (for example, Patent Document 1). 2).
Japanese Patent Laid-Open No. 10-227971 JP 2003-233199 A

  In a drawing apparatus that emits light of a specific wavelength such as ultraviolet light, it is extremely important to place the substrate at an accurate focal position in order to obtain a high-resolution pattern. However, in the conventional focus position detection method involving manual work, the focus position detection work is labor intensive and takes time. Further, since the detection is performed while gradually moving the table in the direction of the optical axis, it is difficult to accurately detect the focal position.

  On the other hand, incorporating the photodetectors described in Patent Documents 1 and 2 into the drawing apparatus has problems in terms of space and cost. As in Patent Document 1, in order to arrange the light receiving elements at the conjugate positions on the imaging plane, the half mirror must be arranged on the optical path, which becomes an obstacle during the drawing process.

  The focus position detection method of the present invention is a focus position detection method of a pattern forming apparatus including a projection optical system such as a drawing apparatus having a DMD and an exposure apparatus such as a stepper. In the focus position detection method, first, a focus detection device in which a plurality of light receiving elements (photoelectric cells) are arranged is arranged in the exposure area so that the light receiving surface is inclined with respect to the focal plane of the projection optical system. When a plurality of projection optical systems are arranged in the exposure apparatus, a focus detection device may be arranged in one projection area. For example, the focus detection device may be arranged on the drawing table so that the inclined light receiving surface and the focal plane of the projection optical system intersect. As the focus detection device, for example, a CCD line sensor or a two-dimensional CCD sensor is used.

  When the focus detection device is arranged, a focus detection pattern, which is a pattern with repeated contrast, is projected onto the light receiving surface via the projection optical system. As the focus detection pattern, if a pattern such as a barcode in which vertical lines are repeated regularly (for example, at regular intervals) along the arrangement direction of the light receiving elements is used as the focus detection pattern (here, referred to as a line pattern). Good. In this case, the pattern pitch is larger than the pitch of the light receiving elements, and the spatial frequency is determined to be close to the resolution limit. For example, a line pattern in which black and white are arranged at equal intervals is used. In this case, the drawing apparatus inputs drawing data corresponding to the focus detection pattern, and the exposure apparatus only has to arrange a dedicated mask and reticle.

  When the focus detection pattern is projected, a pattern having repeated contrast is formed on the entire light receiving surface. Since the MTF value is the highest at the focal position and the MTF value decreases as the distance from the focal position increases, the image of the portion having the highest contrast, that is, the highest resolution in the entire pattern, is the focus of the projection optical system. It corresponds to the image on the surface. In the present invention, when a series of image signals are read from the plurality of light receiving elements, the focal position of the projection optical system is detected from the read series of image signals. For example, among the series of image signals, the image signal corresponding to the in-focus state with the most contrast difference is detected, and the arrangement position of the light-receiving element that outputs the image signal according to the in-focus state, Based on the above, the focal position of the projection optical system is detected.

  In this way, by arranging the light receiving surface of the focus detection device obliquely and projecting a pattern having a contrast, a part of the entire pattern image projected on the light receiving surface is brought into focus. The focal position of the projection optical system is obtained based on the position of the light receiving element in the in-focus portion and the inclination angle of the light receiving surface. When the focal position is detected, the relative position of the drawing table on which the drawing target is mounted with respect to the projection optical system may be adjusted based on the detected focal position.

  In the drawing apparatus of the present invention, an optical modulator composed of a plurality of spatial light modulation elements, a projection optical system that projects illumination light that has passed through the light modulator onto a drawing object, and a plurality of light receiving elements are arranged. A drawing table on which the focus detection device is mounted, a drawing control unit that controls the light modulator and projects a focus detection pattern on the light receiving surface of the focus detection device inclined with respect to the focal plane of the projection optical system; And a focus position detecting means for detecting a focus position based on a series of image signals read from the light receiving element. A focus position adjustment unit that adjusts the position of the drawing table based on the detected focus position may be provided.

  According to the present invention, a focus position can be accurately detected with a simple configuration, and a highly accurate pattern can be formed.

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

  FIG. 1 is a perspective view schematically showing a drawing apparatus according to the present embodiment. FIG. 2 is a schematic sectional view of the exposure head.

  The drawing apparatus 10 is an apparatus that forms a pattern by irradiating light onto a substrate SW on which a photosensitive material such as a photoresist is formed, and includes a gate-like structure 12 and a base 14. An XY stage drive mechanism (not shown here) that supports the drawing table 18 is mounted on the base 14, and a substrate SW is installed on the drawing table 18.

A gate-like structure 12, the eight exposure heads 20 ₁ to 20 ₈ to form a circuit pattern on the surface of the substrate SW are provided, each of the exposure heads, the first and second illumination optical system, an exposure unit, a projection An optical system (not shown here) is provided. Further, the upper portion of the gate-like structure 12, the two light source units 16A, 16B are arranged so as to face the light source unit 16A is the exposure head ₂₀ 1 to 20 _4, the illumination light source unit 16B is to ₂₀ 5 to 20 ₈ Send.

  The rectangular substrate SW is a substrate for an electronic circuit such as a silicon wafer, a dry film, or a glass substrate, for example, and is mounted on the drawing table 18 in a blank state that has been subjected to processing such as pre-baking and photoresist coating. . An XY coordinate system orthogonal to each other is defined for the drawing table 18, and the drawing table 18 is movable along the X and Y directions. Here, the negative direction of the Y direction is defined as the scanning direction. Further, as will be described later, the drawing table 18 is also movable in a direction perpendicular to the XY plane.

2 shows the internal structure of the exposure unit 20 ₁ is illustrated schematically, an exposure unit 20 _1, the first illumination optical system (not shown), the second illumination optical system 22, DMD (Digital Micro-mirror device) 24 and a projection optical system 26. The second illumination optical system 22 is disposed on the support plate 19 projecting from the gate-like structure 12 in parallel with the drawing table 18, while the imaging optical system 26 is disposed above the substrate SW. The DMD 24, the mirror 25, and the optical system 27 are disposed between the second illumination optical system 22 and the projection optical system 26.

Light source 16A is a light source with an ultra-high pressure mercury lamp (not shown), part of the illumination light emitted from the lamp IL is guided to the first illumination optical system in accordance with the exposure unit 20 _1. The first illumination optical system converts the diffused light emitted from the lamp into a parallel light beam having a uniform light intensity. The illumination light that has become a parallel light beam enters the second illumination optical system 22, and the illumination light has a predetermined light amount and a predetermined light beam shape suitable for exposure to the DMD 24 via the mirror 25 and the optical system 27. Led.

  The DMD 24 is an optical modulator in which micro rectangular micromirrors of several μm to several tens of μm are two-dimensionally arranged in a matrix, and here, it is composed of 1024 × 768 micromirrors. Each micromirror rotates and varies due to an electrostatic field effect, and a first posture (ON state) for reflecting the beam from the light source toward the exposure surface direction of the substrate SW and a second posture (ON state) for reflecting the beam toward the direction outside the exposure surface ( OFF state) Positioning is performed in any posture, and the posture is switched according to the control signal.

  In the DMD 24, each micromirror is selectively ON / OFF controlled, and the light reflected on the micromirror in the ON state passes through the projection optical system 26 and irradiates the substrate SW. Thereby, a predetermined pattern is imaged on the exposure surface of the substrate SW. The light irradiated onto the substrate SW is composed of a light beam selectively reflected by each micromirror, and becomes illumination light corresponding to a circuit pattern to be formed on the exposure surface. When all the micromirrors are in the ON state, a rectangular projection spot EA having a predetermined size is defined on the substrate SW (hereinafter, this projection area is referred to as an exposure area).

As the exposure method, for example, a multiple exposure method by a step & repeat method is applied, and the drawing table 18 intermittently moves along the Y direction. As the exposure area EA relatively moves along the scanning direction, a pattern is formed on the substrate SW along the scanning direction. Also in the exposure head ₂₀ 2-20 _8, similar exposure operation is performed. The exposure head 20 ₁ to 20 ₈ in a row along the X direction perpendicular to the scanning direction, the drawing table 18 along with the movement along the scanning direction, overall exposing the substrate SW.

  FIG. 3 is a block diagram of a drawing control unit provided in the drawing apparatus 10.

  The drawing control unit 30 is connected to an external workstation (not shown) and includes a system control circuit 32. The system control circuit 32 controls the drawing process and outputs a control signal to each circuit such as the DMD driving circuit 34, the read address control circuit 37, and the drawing table control circuit 38. A program for controlling the drawing process is stored in advance in a ROM (not shown) in the system control circuit 32.

  The raster conversion circuit 36 converts the pattern data into raster data that is image data for drawing. Raster data is generated for each exposure head DMD and stored in the buffer memory 38. The raster data stored in the buffer memory 38 is sent to the DMD driving circuit 34 in accordance with the exposure operation. The read address control circuit 37 controls the read timing of raster data from the buffer memory 38 and the write timing to the DMD drive circuit 34.

  The drawing table control circuit 38 outputs a control signal to the drive circuit 44 to control the movement of the XY stage mechanism and the Z direction mechanism 47. The Z direction mechanism 47 is a mechanism for adjusting the drawing table 18 in the Z direction perpendicular to the XY plane, and the drawing table 18 moves in the Z direction according to the focal plane of the projection optical system 26. The projection optical system 26 is mounted so that its optical axis is parallel to the Z direction.

  The position detection sensor 48 detects the relative position of the exposure area EA by detecting the position of the drawing table 18. The position detection sensor 48 can also detect the position of the drawing table 18 along the Z direction. The system control circuit 32 controls the DMD drive circuit 34, the read address control circuit 37, and the like based on the relative position of the exposure area EA detected through the drawing table control circuit 42.

  The DMD driving circuit 34 includes a bitmap memory for storing raster data for all micromirrors of the DMD, and selectively outputs the raster data to each DMD. When raster data corresponding to the relative position of the exposure area is sent from the buffer memory 38, a drawing signal for controlling the micromirror is output to each DMD in synchronization with a clock pulse signal for matching the drawing timing. Thereby, the micromirror of each DMD is ON / OFF controlled.

  The drawing apparatus 10 in this embodiment can be connected to a CCD line sensor 60 for focus detection. When the focal position is detected before the drawing process, the CCD line sensor 60 is mounted on the drawing table 18, and the drawing table 18 is adjusted in position along the XY direction so as to be within the exposure area of the projection optical system 24. Then, a focus detection pattern stored in advance in the ROM of the system control circuit 32 is read, and raster data is sent to the DMD drive circuit 34. As a result, the focus detection pattern is projected onto the CCD line sensor 60.

  The system control circuit 32 detects the focal position along the Z direction of the projection optical system 26 based on the image signal read from the CCD line sensor 60. Based on the detected focal position, the drawing table control circuit 42 drives the Z direction mechanism 47 so that the focal plane of the projection optical system 26 coincides with the exposure plane of the substrate SW. It is assumed that the thickness of the substrate SW is predetermined.

  FIG. 4 is a diagram showing the arrangement of the CCD line sensor 60 when the focal position is detected.

  The focal length of the projection optical system 26 is determined in advance, and the position along the Z direction of the drawing table 18 is adjusted according to the focal length. However, due to an assembly error or the like, it is necessary to confirm an accurate focal position while actually projecting a pattern. In addition, when the focal position is shifted during operation, it is necessary to detect the focal position again. In the present embodiment, the focal position is obtained as follows.

  First, the CCD line sensor 60 is connected to the drawing processing unit 30 of the drawing apparatus 10. The CCD line sensor 60 is disposed below the projection optical system 26, and its light receiving surface 60A is positioned in parallel along the X direction or the Y direction. One end of the CCD line sensor 60 is placed on a rectangular parallelepiped bar 62. As a result, the CCD line sensor 60 is inclined with respect to the drawing table 18 by a predetermined angle α. Here, the angle α is set to 1 to 2 degrees. In consideration of the size of the bar 62 and the dimensions of the CCD line sensor 60, the position of the drawing table 18 is adjusted in advance so that the center position R of the light receiving surface is placed on the reference exposure surface TM. Here, the reference exposure surface TM represents a provisional focal plane planned from the focal length.

  FIG. 5 is a diagram showing a pattern projected on the CCD line sensor 60. The focus detection pattern M is a black and white striped pattern (hereinafter referred to as a line pattern) in which lines perpendicular to the arrangement direction of the light receiving elements are arranged in one direction at equal intervals. Black and white patterns are repeatedly arranged at a pitch larger than the pitch. For example, in the CCD line sensor 60, when the light receiving elements are arranged at a 50 μm pitch on the light receiving surface 60A having a width of 5 mm and a length of 40 mm, the line pattern M has a full width of 0.05 mm and a line width of 0.05 mm. The pattern is set to 5 mm.

  As shown in FIG. 5, the line pattern M projected onto the CCD line sensor 60 through the projection optical system 26 extends over the entire light receiving surface 60A. The line pattern M is a pattern with repeated contrast because the line portions Q1 and the space portions Q2 continue alternately. The image signal detected from the CCD line sensor 60 by such a line pattern M is composed of a high-frequency component signal.

  As described above, the light receiving surface 60A of the CCD line sensor 60 is inclined with respect to the reference exposure surface TM of the drawing table 18, that is, the focal plane of the projection optical system 26. The CCD line sensor 60 is arranged so that the focal plane intersects the light receiving surface 60A. Therefore, when the line pattern M is projected on the entire light receiving surface 60A, the most contrasted part of the line pattern M corresponds to the focal position. That is, the position of the light receiving element that outputs a signal having the largest amplitude corresponds to the position of the focal plane FP along the Z direction. FIG. 5 is a diagram showing the amount of light received by the light receiving element at positions A to E of the light receiving surface 60A. In FIG. 5, an image having the highest contrast is formed at the position B, and the position B becomes the focal position.

  The system control circuit 32 detects a signal having the largest amplitude, that is, a high MTF value in a series of image signals output from the CCD 60, and calculates a focal position from the signal of the high frequency component. Then, the position of the light receiving element (position B in FIG. 5) that outputs the signal is obtained. Here, the position of the light receiving element near the center is obtained from a series of light receiving elements within a certain range that outputs a signal having the largest amplitude.

  The inclination angle α of the CCD line sensor 60 and the position information along the Z direction of the drawing table 18 are input in advance. In addition, here, the CCD line sensor 60 is installed so that the intersection of the reference exposure surface TM and the light receiving surface 60 is the center position of the arranged light receiving elements. When the distance to the position of the light receiving element corresponding to the in-focus state is L (see FIG. 5), the displacement ΔU from the reference plane TM is Lsin α.

  Thereby, the position of the focal plane FP, that is, the focal position is detected. When performing the drawing process, the position of the drawing table 18 is adjusted based on the thickness of the substrate and the focal position so that the exposure surface of the substrate SW coincides with the focal plane FP.

FIG. 6 shows the sensitivity magnification. The ratio between the focal position movement A1 along the Z direction and the focal position movement A2 along the light receiving surface 60A of the CCD line sensor 60 is expressed as the sensitivity magnification k by the following equation.

k = A2 / A1 (1)

By tilting the CCD line sensor 60, even if the focal position is shifted by a small distance in the Z direction, a shift amount due to a large distance is detected on the light receiving surface 60A of the CCD line sensor 60. As a result, the focal position of the projection optical system 24 can be detected with high accuracy.

  As described above, according to the present embodiment, when the focal position is detected, the CCD line sensor 60 is mounted on the drawing table 18 in a state where the CCD line sensor 60 is inclined by the angle α, and the focus detection pattern M having repetitive contrast is obtained. 60 on the light receiving surface 60A. Based on the detected series of image signals, the focal position of the projection optical system 26 is detected. When the focal position is detected, the position of the drawing table 18 is adjusted, whereby a highly accurate pattern is formed on the exposure surface.

  An accurate focal position can be detected simply by inclining the CCD line sensor 60, and the focal position can be detected even during operation. In addition, since the drawing apparatus forms the focus detection pattern M, the pattern can be changed in accordance with the characteristics of the CCD line sensor and the like, and an optimum pattern for focus detection can be projected.

  A CCD line sensor may be disposed on the substrate. Moreover, you may use optical inspection devices other than a CCD line sensor. As the focus detection pattern, the line width and pitch of the line pattern may be changed to adjust the degree of contrast, and a regular pattern with contrast other than the line pattern may be used. The shape of the bar 62 is arbitrary, and the bar 62 may be configured so that the inclination angle of the light receiving surface can be adjusted. Further, the CCD line sensor 60 may be configured such that the light receiving surface of the CCD line sensor 60 is inclined in advance.

  In the present embodiment, the drawing apparatus 10 is configured to automatically detect the focal position and automatically adjust the position of the drawing table 18. However, only the focal position is automatically detected and the drawing table 18 is manually operated. The position may be adjusted. Further, a processor (such as a PC) other than the drawing apparatus 10 may be connected to the CCD line sensor 60 so that the focal position is detected by the processor.

It is the perspective view which showed typically the drawing apparatus which is this embodiment. It is a schematic sectional drawing of an exposure head. It is a block diagram of the drawing control part provided in the drawing apparatus. It is the figure which showed arrangement | positioning of the CCD line sensor at the time of detecting a focus position. It is the figure which showed the pattern projected on a CCD line sensor. It is the figure which showed the sensitivity magnification.

Explanation of symbols

10 drawing device 18 drawing table 20 ₁ to 20 ₈ exposure head 24 DMD (exposure unit)
26 Projection Optical System 30 Drawing Control Unit 32 System Control Circuit 34 DMD Drive Circuit 36 Raster Conversion Circuit 42 Drawing Table Control Circuit 46 XY Stage Mechanism 47 Z Direction Mechanism 60 CCD Line Sensor (Focus Detection Device)
60A light receiving surface 62 bar SW substrate (object to be drawn)
EA Exposure area M Line pattern (focus detection pattern)
FP focal plane TM standard exposure surface

Claims (6)

A focus position detection method for a pattern forming apparatus including a projection optical system,
A focus detection device in which a plurality of light receiving elements are arranged is arranged in the exposure area so that the light receiving surface is inclined with respect to the focal plane of the projection optical system,
A focus detection pattern with repeated contrast , wherein a line pattern having a pattern pitch larger than the pitch of the plurality of light receiving elements is projected onto the light receiving surface via the projection optical system,
A focus position detection method for detecting a position of a light receiving element that outputs a signal having the largest amplitude in a series of image signals read from the plurality of light receiving elements as a focus position of the projection optical system. 2. The focal position detection according to claim 1, wherein the position of a light receiving element near the center of a series of light receiving elements within a certain range that outputs a signal having the largest amplitude is detected as a focal position. Method. The focal position detection method according to claim 1, wherein the focal position of the projection optical system is detected based on an arrangement position of light receiving elements that output a signal having the largest amplitude and an inclination angle of the light receiving surface.   The focus position detection method according to claim 1, wherein the focus detection device is a CCD sensor.   5. The focus position detection according to claim 1, wherein a relative position of the drawing table on which the drawing target is mounted with respect to the projection optical system is adjusted based on the detected focus position. Method. A light modulator composed of a plurality of spatial light modulation elements;
A projection optical system that projects illumination light via the light modulator onto a drawing object;
A drawing table on which a focus detection device in which a plurality of light receiving elements are arranged, and
Controls the optical modulator, the against the receiving surface of the focus detection device which is inclined with respect to the focal plane of the projection optical system, a large pattern pitch than the pitch of said plurality of light receiving elements a pattern for focus detection Drawing control means for projecting a line pattern via the projection optical system ;
A focus position detecting unit that detects a position of a light receiving element that outputs a signal having the largest amplitude in a series of image signals read from the plurality of light receiving elements as a focus position of the projection optical system. A drawing device.

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