JPH10170831A - Pattern reader - Google Patents

Abstract

(57) [Problem] When an object to be read has a function of deflecting a light beam, there is a possibility that an image of a light source is formed off-axis instead of on-axis, so that it cannot be blocked by a spatial filter. is there. SOLUTION: Light emitted from a lighting unit 10 is an objective lens 2.
By passing through 0, the light becomes parallel light and illuminates the surface 1a of the silicon wafer 1 from an oblique direction. The light beam reflected by the surface 1a passes through the objective lens 20 again, becomes convergent light toward the detection unit 30 side, and reaches the spatial filter 31. The spatial filter 31 of the reflected light from the surface 1a
The scattered reflection component transmitted through is incident on the imaging lens 32. The imaging lens 32 is provided on the surface 1 a of the silicon wafer 1.
And the imaging element 33 have a power to make them conjugate. On the imaging element 33, a differential image of the pattern imprinted on the surface 1a is formed by the scattered reflection component transmitted through the spatial filter 31. The light source unit 10 is adjustable in a plane perpendicular to the principal ray of the illumination light.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for reading a pattern provided on an object surface.

[0002]

2. Description of the Related Art A filtering optical system using a Fourier transform lens has been conventionally used as an optical system for reading a pattern formed on a transmission type target surface by performing a predetermined filtering process. The optical system transmits light from the object through an objective lens through a spatial filter disposed at a rear focal point. When an imaging lens having the position of the filter as the front focal point is disposed further behind the filter, an object image is formed on the rear focal plane by the change by the filter.

For example, when it is desired to output a differential image of a pattern formed on a target surface, a high-pass filter that blocks on-axis light flux corresponding to an image of a point light source is used as a spatial filter. Further, in order to process the read image and display the processed image on another display device, an image sensor for reading the pattern may be arranged at an image forming position of the pattern image.

[0004]

However, in the pattern reading apparatus using the above-mentioned conventional filtering optical system, if the object to be read has a prism function of deflecting a light beam, the image of the point light source is not axial. There is a possibility that it cannot be blocked by the spatial filter because it is formed off-axis instead of above, in which case components other than the scattered light component will enter the imaging lens and the desired filtered output image will be formed. There is a problem that cannot be obtained. A similar problem may occur when the device of this type reads a pattern formed on a reflective object and the reflective surface is inclined.

The present invention has been made in view of the above-mentioned problems of the prior art, and is intended to provide a point light source even when the object has a prismatic function or when the reflection surface of a reflective object is inclined. It is an object of the present invention to provide a pattern reading device capable of making the image of the image and the light shielding area of the spatial filter coincide with each other.

[0006]

SUMMARY OF THE INVENTION In order to achieve the above object, a pattern reading apparatus according to the present invention impinges illumination light emitted from a light source having a very small area on a target surface provided with a pattern to be read. In a pattern reading apparatus, a light beam having pattern information is converged by an objective lens and made incident on an imaging lens, and a pattern image is formed and read by the imaging lens. It is characterized in that an adjusting mechanism for adjusting within an intersecting plane is provided.

The light source has a pinhole for transmitting a part of the light from the light source. In this case, it is desirable that the adjusting mechanism moves the light source and the pinhole together. Further, the above light source can be constituted by a lamp and an optical fiber for guiding light from the lamp to a pinhole.
In this case, it is desirable that the adjusting mechanism moves both the end of the optical fiber on the emission side and the pinhole. The direction of movement by the adjustment mechanism can be in a plane substantially perpendicular to the principal ray of the illumination light.

When the object surface is a reflection surface, the illumination lens and the objective lens can be configured as the same objective lens. In this case, the luminous flux emitted from the light source and reaching the target surface via the objective lens (functioning as an illumination lens)
Objective lens that reflects off the target surface (acts as an objective lens)
Is transmitted again and is incident on the imaging lens. Further, the adjustment mechanism may move the light source in a plane perpendicular to the optical axis of the objective lens.

Further, when the target surface is a reflection surface,
The light source and the imaging lens can be arranged on opposite sides of the optical axis of the objective lens, and the light source can be provided at a position where the illumination light is obliquely incident on the target surface.

In order to obtain a predetermined filtering effect, a spatial filter having a light-blocking region for blocking axial light can be arranged in an optical path between the objective lens and the imaging lens. In this case, the adjusting mechanism can be configured to adjust the relative positional relationship between the position of the light source formed by the objective lens and the light shielding area of the spatial filter in a plane intersecting the optical axis of the imaging lens. That is, either the case where the position of the light source itself is adjusted or the case where the spatial filter side is adjusted may be used.

When the objective lens has a spherical aberration, it is desirable that the spatial filter is disposed closer to the objective lens than the paraxial image point of the light source formed via the objective lens. In order to process the read image or to display the read image on another display device, an image sensor for reading the pattern may be arranged at the image forming position of the pattern image.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a pattern reading optical system according to the present invention will be described below. Here, a basic configuration of the present invention will be described first with reference to FIG. 1, and subsequently, an embodiment in which the pattern reading optical system of the present invention is applied to an apparatus for reading a reflective object based on FIG. 2 to FIG. And a mechanical configuration example of a device to which the optical system according to the embodiment is applied will be described with reference to FIGS.

FIGS. 1A and 1B are explanatory views of a filtering optical system for showing a basic configuration of the present invention. A light beam from a light source (not shown) becomes a light source having a very small area by the pinhole plate 12, and is incident on a transmission type inspection object O via the illumination lens 21. The light beam transmitted through the test object O enters the spatial filter 31 via the objective lens 22, passes through the spatial filter 31, and forms a differential image of the test object on the imaging surface 33 a by the imaging lens 32. The spatial filter 31 is a filter having a light-blocking region for blocking a light beam forming an image of the light source, and is disposed closer to the objective lens 22 than the geometric optical image plane IM of the light source.

In an optical system using a Fourier transform lens, as shown in FIG. 1A, a light source formed by a pinhole plate 12 is located at a front focal point of an illumination lens 21 and an object O is parallel. Illuminated by light. Further, the test object O is located at the front focal point of the objective lens 22 which is a Fourier transform lens, and the rear focal point of the objective lens 22 and the front focal point of the imaging lens 32 coincide with each other. The imaging surface 33a is located.

In the present invention, the light source (not shown) and the pinhole plate 12 are movably supported in a plane perpendicular to the optical axis as indicated by the arrow in the figure.

FIGS. 1B and 1C show the case where the test object O has a prism action. In this case, since the light beam emitted from the test object O is deflected upward in the figure, the image of the light source moves upward in the figure while the pinhole plate 12 remains as shown in FIG. However, there is a possibility that the light cannot be blocked by the light blocking area of the spatial filter 31. Therefore, in the example of FIG. 1B, the light source and the pinhole plate 12 are moved upward by a predetermined amount in the figure. This movement can offset the movement of the image position of the light source due to the prism action of the test object O, and the light beam forming the light source image is shielded by the spatial filter 31 as in the case without the prism action. The solid line indicating the light beam in FIG. 1B indicates the case where the pinhole is on the optical axis, and the one-dot chain line indicating the light beam indicates the case where the pinhole plate is moved upward in the figure. In the example of FIG. 1C, instead of moving the pinhole plate 12, the spatial filter 31 is moved upward by a predetermined amount in a plane orthogonal to the optical axis. This also allows the position of the image of the light source to coincide with the light shielding area of the spatial filter.

In this example, the spread of the light source image is smaller than the spread at the paraxial image point in consideration of the spherical aberration of the objective lens 22, the coma caused by off-axis light, and the influence of field curvature. A spatial filter 31 is arranged at a position. Thereby, while blocking light rays in a range where an image of the light source is formed in a light-shielding region smaller than the conventional one,
Scattered components from the test object O can be transmitted. Specifically, the distance L from the final surface of the objective lens 22 to the spatial filter 31 is arranged at a position that satisfies the condition of 0.60 fo <L <0.95 fo with respect to the focal length fo of the objective lens 22. . In this range, the spread of the light source image is smaller than the spread at the paraxial image point, so that the light-shielding region can be made smaller than before. When applied to an actual optical system, it is desirable to obtain a position where the size of the image of the light source is minimized by ray tracing, and to arrange the position at that position.

FIG. 2 is a schematic diagram showing a configuration of a pattern reading optical system according to an embodiment in which the present invention is applied to a reflection type object reading optical system. Here, a silicon wafer is to be read.

In a semiconductor component manufacturing process, a semiconductor layer is laminated on a semiconductor substrate such as a silicon wafer by repeating processes such as etching and vapor deposition. In general, a serial number is given to a silicon wafer by laser etching at a stage prior to the component generation process, and the following steps are managed by the serial number. The silicon wafer is mirror-finished, and when reading the serial number, it cannot be fully recognized unless the wafer is viewed from an angle by holding the wafer over light, and processes such as etching and vapor deposition are not possible. As the character quality deteriorates as the process proceeds, the serial number of the wafer near the final process becomes particularly difficult to read.

The optical system according to the embodiment is configured to be able to read an unclear pattern such as a serial number formed on such a silicon wafer, particularly a pattern deteriorated through processes such as etching and vapor deposition. .

Reference numeral 1 in the figure denotes a silicon wafer,
A serial number is engraved on the mirror-finished surface 1a by laser etching as a pattern to be read. The optical system of the apparatus includes an illumination unit 10, an objective lens 20, and a detection unit 30. The objective lens 20 has a surface 1 whose optical axis Ax is a reflection surface in a reference state.
It is arranged so as to be perpendicular to “a”, and is rotatable around a rotation axis Rx perpendicular to the optical axis of the objective lens 20 as indicated by an arrow in the figure. The illumination unit 10 and the detection unit 30 are disposed substantially symmetrically with respect to the optical axis Ax of the objective lens 20 in the reference state.

The illumination unit 10 includes a light source 11 using a halogen lamp or the like, and a pinhole plate 12 having a pinhole 12a for transmitting a part of light from the light source.
The light source has a very small area. A diffusion plate 13 is arranged between the light source 11 and the pinhole plate 12 to eliminate the influence of the filament image of the lamp. The detection unit 30 includes a spatial filter 31, an imaging lens 32, and an image sensor 33 such as a CCD image sensor. In the example of FIG. 2, the detection unit 30 is disposed on the extension of the direction of reflection of the specular reflection component from the surface 1a.

In this example, the rotation axis Rx is parallel to the intersection of the plane perpendicular to the principal ray Ax1 of the illumination light and the plane perpendicular to the optical axis Ax2 of the imaging lens 32. is there. It is sufficient that the rotation range of the objective lens 20 be about ± 45 degrees around the reference state.

The light beam emitted from the light source and reaching the surface 1a via the objective lens 20 is reflected by the surface 1a, passes through the objective lens 20 again, and enters the spatial filter 31.
In this example, a pinhole 12 a serving as a light source having a small area is arranged at a front focal position of the objective lens 20 so that the illumination light is incident on the silicon wafer 1 as parallel light. The light emitted from the light source passes through the objective lens 20 and becomes parallel light, and the surface 1a of the silicon wafer 1
Is illuminated from an oblique direction. The illumination light reaching the surface 1a is
The light is scattered and reflected at the engraved pattern portion, and specularly reflected at other portions.

The light beam reflected by the surface 1 a passes through the objective lens 20 again, becomes convergent light toward the detection unit 30, and reaches the spatial filter 31. Spatial filter 31
Is located closer to the objective lens 20 than the light source image formed by the objective lens 20 in the optical path between the imaging lens 32 and the objective lens 20. Spatial filter 31
Has a light-shielding region 31b that covers the center of the pupil of the imaging lens 32, as shown in FIG. The component of the illumination light emitted from the illumination unit 10, which is a light source having a very small area, is specularly reflected on the surface 1 a.
1b.

The scattered reflection component transmitted through the spatial filter 31 of the light reflected from the surface 1a enters the imaging lens 32. The imaging lens 32 has a power to conjugate the surface 1a of the silicon wafer 1 and the image sensor 33, and is stamped on the surface 1a on the image sensor 33 by a scattered reflection component transmitted through the spatial filter 31. The image of the pattern is formed. The image sensor 33 converts the information of the image of the formed pattern into an electric signal, outputs the electric signal, and inputs the electric signal to an image processing device (not shown). The image processing apparatus displays an image of a pattern on a display screen based on an input image signal, and analyzes the contents of the pattern using a character recognition algorithm.

The light source unit 10 adjusts the position of the image of the light source with respect to the light shielding area 31b of the spatial filter 31, so that the light source unit 10 is located within a plane intersecting with the principal ray Ax1 of the illumination light, in this example, at the reference time of the objective lens. Can be adjusted in a direction away from or approaching the optical axis Ax in a plane perpendicular to the optical axis Ax.

Further, the imaging lens 32 and the image pickup device 33 are connected to the optical axis Ax of the imaging lens in order to change the imaging magnification.
It is configured to be able to move along 2. Further, in order to enable the magnification change by moving the imaging lens, the distance X between the objective lens and the surface 1a which is the target surface is 0 <X <
It is set to satisfy the condition of 0.7fo. That is, in the configuration of FIG. 1A described above, X = fo, and a light beam emitted from one point of the test object indicated by a broken line becomes parallel light, so that the magnification is changed even when the imaging lens 32 is moved. However, by satisfying the above condition, the light beam emitted from one point of the test object becomes non-parallel, and the imaging magnification can be changed by moving the imaging lens 32 in the optical axis direction. Become.

In the example of FIG. 2, the detection unit 30
Are arranged on the extension of the reflection direction of the specular reflection component from the surface 1a, and when the spatial filter 31 is not provided, the specular reflection component enters the imaging lens. However, the specular reflection component is a component having little information on the pattern and has a large intensity.
The / N ratio decreases, making it difficult to detect patterns. Therefore, in this example, the specular reflection component is removed by using the spatial filter 31, and only the scattered reflection component is taken into the image pickup device, so that the S / N of the information regarding the pattern is improved.
The ratio is improved so that the pattern can be easily recognized and identified. The emphasized image formed on the image sensor is an image formed mainly by high-frequency components while suppressing low-frequency components of the spectrum, and is actually an image in which a pattern portion is emphasized.

The ghost light generated when the illumination light from the light source 11 is reflected on the surface of the objective lens 20 is converted into an image forming lens 32.
When the ghost light overlaps with the position of the pattern image on the image sensor 33, the contrast of the pattern image is reduced and reading becomes difficult. In such a case,
By adjusting the ghost light so that the ghost light does not overlap the pattern image by rotating the objective lens 20, it is possible to prevent a decrease in contrast and to accurately read the pattern.

If the distribution of the scattered and reflected light on the surface 1a is biased, the shape of the image of the light source may change and deviate from the light shielding area 31b of the spatial filter 31. Even in such a case, the shape of the image of the light source can be changed by controlling the coma aberration by rotating the objective lens 20. When the surface 1a has an inclination, the position of the image of the light source is adjusted by adjusting the position of the light source unit 10 so that the position where the image of the light source can be formed is shielded by the light shielding area 31.
b.

FIG. 4 is an optical path diagram showing the optical system of FIG. 2 in an expanded manner. The luminous flux emitted from the pinhole plate 12 becomes parallel light by the objective lens 20, is reflected (transmitted in the figure) by the surface 1a, reenters the objective lens 20, passes through the spatial filter 31 as convergent light, and forms an image. An image of the pattern is formed on the image sensor 33 via the lens 32. FIG.
Is constructed by folding one side of the optical system shown in FIG. In this example, the surface 1a is closer to the objective lens than the focal position of the objective lens 20, and the reflected light from one point of the surface 1a is
The light enters the imaging lens 32 as divergent light instead of parallel light as shown in FIG.

The focal length of the imaging lens 32 is determined by the angle of view and the photographing magnification determined by the length of the character string of the serial number to be read and the size of the imaging surface of the imaging device.
It is obtained from the overall size (movement amount) and the like. On the other hand, the focal length of the objective lens 20 is determined based on the focal length of the imaging lens 32 and the distance between the imaging lens 32 and the surface 1a determined by the imaging magnification.

FIG. 5 is an explanatory diagram of an optical system showing a design example in a case where the length of a character string is 2 cm and the size of the imaging surface of the imaging device is 1/2 inch diagonally. In this example, the focal length of the imaging lens 32 is 50 mm, and the focal length fo of the objective lens 20 is 220 mm. The distance a from the pinhole 12a to the surface 1a of the silicon wafer 1 is about 270 mm, the distance b from the objective lens 20 to the surface 1a is about 50 mm, and the distance L from the final surface of the objective lens 20 to the spatial filter 31 is about It becomes 190 mm.
Therefore, in this example, the condition 0.60fo <L <0.95fo that determines the distance L between the surface of the objective lens 20 closest to the spatial filter and the spatial filter is approximately 130
mm <L <210 mm. Further, a condition 0 <X <0.0 that defines a distance X between the objective lens and the surface 1a as the target surface.
7fo is 0 <X <154 mm.

Next, a specific mechanical configuration of a device incorporating the above-described optical system will be described with reference to FIGS. For the sake of explanation, the x direction parallel to the optical axis in the reference state of the objective lens and the y direction and the z direction orthogonal to each other in a plane perpendicular to the x direction are defined in the drawing. Principal ray A of illumination light
x1 and the optical axis Ax2 of the imaging lens are included in the xz plane.

The pattern reading apparatus according to the embodiment is provided with a base frame 100 on which a silicon wafer to be inspected is placed at a reference position T indicated by a dashed line, and a bearing 110 on the base frame 100. And a movable frame 200 provided slidably with respect to the base frame 100 in the y direction in the figure.

The movement of the movable frame 200 is realized by a frame driving mechanism 210 using a ball screw shown in FIG. The frame driving mechanism 210 is a base frame 1
The ball screw 211 is arranged on the screw support portion 102 fixed to 00 so as to be adjustable in rotation, and a screw member 212 fixed to the horizontal holding plate 201 (parallel to the yz plane) of the movable frame 200. I have. The ball screw 211 is
Operation knob 21 formed on the base side and operated by the inspector
1a and a screw portion 211b formed at a portion protruding toward the movable frame. The screw portion 211b of the ball screw 211 is screwed into a screw hole formed in the screwing member 212, and the operation knob 21 on the base frame 100 side.
When the ball screw 211 is rotated while holding 1a, the movable frame 200 slides in the y direction in the figure.

A tilt mechanism 220 for rotatably holding the objective lens 20 is disposed on a horizontal holding plate 201 of the movable frame 200, and a column 202 vertically raised from the horizontal supporting plate 201 is vertically attached to the column 202. Holding plate 203
(parallel to the xz plane) is fixed. Vertical holding plate 20
3 is an optical fiber 1 constituting a light source having a very small area.
1d, a pinhole plate 12, a lens barrel 32A in which the imaging lens 32 is incorporated, and a CC in which an image sensor 33 is provided.
The imaging unit 320 including the D unit 33A is fixed. Horizontal holding plate 2 of movable frame 200
01, the base frame 100, and the substrate 221 of the tilt mechanism 220, optical path holes 100a, 201a, 221 for guiding the silicon wafer from the light source 11 and guiding the reflected light from the silicon wafer to the imaging unit 320.
a are formed at positions where they coincide with each other.

The tilt mechanism 220 includes a substrate 221 erected between the column 202 and a support member 204 (see FIG. 6) erected on the horizontal holding plate 201 in parallel with the column 202, and is provided below the substrate 221. The extended bearing portion 222 (FIG. 7)
See). The objective lens 20 is housed in a lens frame 223 having a rotation axis 223a in the z direction.
The lens frame 223 is rotatably attached to the bearing 222 by a rotation shaft 223a. Lens frame 22
Both ends of the rotation shaft 3 project from the bearing 222, and a driven pulley 224 is fixed to an end protruding toward the frame drive mechanism 210, and a rotary plate for an encoder is mounted on an end protruding to the other side. 225 is fixed.

A lens drive motor 226 is mounted on the substrate 221 of the lens support mechanism 220.
The drive pulley 2 fixed to the rotation shaft of the motor 226
A timing belt 227 is stretched between the driven pulley 224 and the driven pulley 224. The encoder includes a rotating plate 225 attached to a rotating shaft, and a photo interrupter 228 having a light emitting element and a light receiving element arranged with the rotating plate 225 interposed therebetween. Rotating plate 22
5, a slit is formed at one location in the circumferential direction,
The light beam emitted from the light emitting element when the objective lens 20 is set at the initial position is adjusted so as to be detected by the light receiving element via the slit. In this example, the initial position of the objective lens 20 is a position at which the optical axis Ax of the objective lens 20 is perpendicular to an ideal target surface (a plane without inclination).

The light source 11 includes a halogen lamp 11a, an infrared cut filter 11b for cutting a heat ray of the convergent light emitted from the halogen lamp 11a, a negative lens 11c for converting the convergent light transmitted through the filter into substantially parallel light, and a negative lens 11c. It is composed of an optical fiber 11d through which light enters. The pinhole plate 12 is configured as a pinhole unit 120 integrally formed with a holding portion 121 for holding an end of the optical fiber on the emission side, and a mounting plate formed perpendicular to the pinhole plate 12 in this unit. The bolt 1 is attached to the vertical holding plate 203 through the portion 122.
23, 123 attached. The fixing long holes 124, 124 formed in the mounting plate 122 extend in a plane perpendicular to the principal ray Ax1 of the illumination light,
By loosening the bolt 123, the unit 120 can be integrally moved in the plane toward or away from the imaging unit 320 in this plane.

In this example, the fiber 11d is a generally commercially available optical fiber having a diameter of about 5 mm, and a pinhole for using this as a light source having a very small area is used. 2mm
If so, no pinhole is required. When the density of the light beam emitted from the end face of the fiber 11d is uneven, it is desirable to dispose a diffusion plate between the fiber end face and the pinhole.

In this example, the spatial filter 31 is fixedly provided via a filter holder 130 fixed to the vertical holding plate 203. In the case where the objective lens 20 is a spherical single lens as in the embodiment, spherical aberration always remains. Further, since the light beam is obliquely incident on the lens, both coma and field curvature occur. Under the influence of these aberrations, light rays forming an image of the light source are diffused without converging at one point, and the degree of the diffusion is considerably large at the paraxial image point of the light source. Therefore, when the spatial filter 31 is arranged at this paraxial image point, it is necessary to secure a large light-shielding area for reliable filtering, and the light amount of the image decreases. Therefore, in the apparatus according to the embodiment, the spatial filter 31 is disposed at a position closer to the objective lens 20 than the paraxial image point and at which the spread of the image of the light source formed by the objective lens 20 is minimized.

The imaging unit 320 includes a vertical holding plate 203
The vertical holding plate 20 is bolted by a bolt 321 through an elongated hole 205 formed along the optical axis Ax2 direction of the imaging lens 32.
3, and can be slid along the optical axis Ax2 by loosening the bolt 321.
That is, as shown in FIG.
A step portion 205a is formed on the imaging unit 320 side at a depth of approximately half the plate thickness, and the first step portion 205a has a width extending through the vertical holding plate 203 from the first step portion at the center in the width direction. A narrow second step portion 205b is formed. Two arms 322 for attachment are formed in the imaging unit 320, and a bolt 321 is provided at the tip of each arm 322 with a washer 323 smaller in diameter than the first step 205 a and larger in diameter than the second step. Are screwed from the opposite side of the vertical holding plate 203. With the above configuration, the imaging unit 320 is integrally formed with the imaging lens 32.
Can be moved in the direction of the optical axis Ax2, and the imaging lens 32 can be adjusted in the direction of the optical axis by a lens barrel adjustment mechanism (not shown). By the above two adjustments, the imaging magnification can be changed.

In the apparatus according to the embodiment, the position T is determined so that the silicon wafer is located before the focal point of the imaging lens 20. The reflected light from one point on the surface of the silicon wafer is converted into divergent light by the imaging lens. At 32.
For this reason, according to the configuration of the embodiment, the imaging magnification can be changed by moving the imaging lens 32 in the optical axis direction. When the imaging lens is moved to change the magnification, the focus state of the pattern on the image sensor 33 also changes.

Therefore, in order to change the magnification while maintaining the focused state of the pattern, the imaging lens 32 and the image pickup device 33
Are moved along the locus shown in FIG. FIG. 8 shows a position where the magnification gradually increases from the upper side to the lower side in the figure. The imaging lens 32 and the image sensor 33 should be set with the surface of the silicon wafer as the object plane immobile. Indicates the position. That is, when the imaging lens 32 and the imaging device 33 are respectively located at positions where an arbitrary horizontal straight line intersects with each locus line, a pattern image focused at that magnification is formed by the imaging device 3.
3 means that it is formed on

When reading the pattern, the silicon wafer is placed at the reference position T shown by the alternate long and short dash line in FIGS.
To read an image signal. Light emitted from the end face on the emission side of the optical fiber 11d passes through a pinhole 12a formed in the center of the pinhole plate 12, enters the objective lens 20 obliquely as illumination light, passes through the objective lens, and passes through the objective lens at the target surface. Reach a certain silicon wafer. Patterns such as characters and symbols are formed on the silicon wafer. When setting the pattern on the apparatus, positioning is performed so that the longitudinal direction of the pattern arrangement coincides with the y direction.

The light beam reflected on the surface of the silicon wafer passes through the objective lens 20 again and passes through the imaging unit 320.
Head to the side. Light rays passing through the on-axis region in the light beam at the position of the spatial filter 31 are blocked by the light shielding portion 31 b of the spatial filter 31, and only the surrounding portion enters the imaging unit 320. On the imaging device 33 of the imaging unit 320,
An off-axis light forms an enhanced image of the pattern. When the ghost light due to the surface reflection of the objective lens 20 overlaps the pattern image, the lens drive motor 226 is controlled to change the inclination of the objective lens 20.

When the surface of the silicon wafer is inclined, the direction of reflection changes as compared with the case where the surface is not inclined, so that the image of the light source may not coincide with the light shielding area 31 b of the spatial filter 31. is there. In such a case, since the specular reflection component from the surface of the silicon wafer reaches the image sensor 33, an accurate emphasized image cannot be formed, and it may be difficult to read the pattern. In such a case, the influence of the error can be compensated by adjusting the pinhole unit 120. That is, in this example, since the pinhole unit 120 can move away from and approach the imaging unit 320 in a plane perpendicular to the principal ray Ax1 of the illumination light, the position of the pinhole unit 120 is appropriately adjusted. By adjusting the position of the light source, an image of the light source can be formed on the light shielding area 31b.

In order to adjust the position of the image of the light source, the tilt of the silicon wafer itself may be adjusted. However, the tilt mechanism is provided on the side of the object to be inspected after being replaced one after another. In the apparatus of the embodiment, the control of the direction of reflection of the light beam by adjusting the inclination of the reflection surface is difficult because the sensitivity of the adjustment is too high and the fine adjustment is difficult. Hall unit 120
Is adjusted.

FIG. 9 is an explanatory view showing another example of the structure for adjusting the pinhole unit. In this example, the rail member 1 in which the guide groove 125a extending in the z direction is formed.
25 is fixed to a movable frame (not shown), and the pinhole unit 120a to which the pinhole plate 12 and the end of the fiber 11d on the emission side are fixed moves in the z direction along the guide groove 125a. It is attached so that it can be done. The pinhole unit may be movable in a plane perpendicular to the principal ray Ax1 of the illumination light as in the example of FIG. 6, or may be moved with respect to the optical axis Ax of the objective lens 20 as in this example. It may be possible to move in a vertical plane.

The purpose of adjusting the light source is to adjust the mutual positional relationship between the image of the light source and the light shielding area 31b of the spatial filter 31, so that the position of the spatial filter 31 is adjusted not only on the light source side. Is also good. Spatial filter 31
FIGS. 10 and 11 show an example of a mechanism for enabling the position to be adjusted. 10A is a plan view of the movable frame, FIG. 10B is a cross-sectional view along the line BB, and FIG. 11 is a plan view showing a state where the movable frame is assembled to a fixed rail. As shown in the figure, two rail members 131a and 131b having a “U” -shaped cross section are arranged in parallel with their openings facing each other at a predetermined distance, and near both ends between these rail members. A rectangular movable frame is formed from the two beam members 132a, 132b passed by the above, and the spatial filter 31 is inserted into the U-shaped opening of the rail members 131a, 131b and fixed with the holding screw 133. Guide pins 134 are provided on four ends of the movable frame, and these guide pins 134 are engaged with and fixed to two fixed rails 135a and 135b having guide grooves 136a and 136b, respectively.

According to the configuration shown in FIG. 10, the spatial filter 31 fitted in the movable frame can be moved in the Y direction in the figure with respect to the movable frame, and this movable frame is further attached to a fixed rail to be moved in the Z direction. Can be moved to Therefore, by combining these functions, the spatial filter becomes Y
The position can be adjusted in the -Z plane. With this adjustment,
By adjusting the position of the light shielding area 31b of the spatial filter 31,
An image of the light source can be formed on the light shielding area 31b.

[0054]

As described above, according to the present invention, by adjusting the position of the light source or the position of the spatial filter, when the object has a prismatic function, or the reflection surface of a reflective object, Can be made to coincide with the light shielding area of the spatial filter even when the image is inclined.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of an optical system showing a basic configuration of the present invention.

FIG. 2 is an explanatory view conceptually showing an optical system of the pattern reading apparatus according to the embodiment.

FIG. 3 is a plan view showing an example of a spatial filter.

FIG. 4 is an optical path diagram showing the optical system of FIG. 2 developed on a reflection surface.

FIG. 5 is an explanatory diagram showing a design example of the optical system according to the embodiment.

FIG. 6 is a front view showing a specific mechanical system configuration of the pattern reading apparatus to which the optical system of FIG. 5 is applied.

FIG. 7 is a side view of the device of FIG. 6 viewed from a direction different by 90 degrees.

FIG. 8 is an explanatory diagram showing the movement trajectory of the imaging lens for adjusting the magnification and the image sensor.

FIG. 9 is an explanatory diagram showing another configuration example for adjusting the pinhole unit.

FIGS. 10A and 10B are explanatory views showing another configuration example of a mounting portion of a spatial filter, wherein FIG. 10A is a plan view of a movable frame, and FIG. 10B is a cross-sectional view taken along line BB.

FIG. 11 is a plan view showing the entire mounting portion of the spatial filter of FIG. 10;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 Light source 12 Pinhole plate 12a Pinhole 20 Objective lens 31 Spatial filter 32 Imaging lens 33 Image sensor

Claims (15)

[Claims] 1. An illumination light emitted from a light source having a very small area is made incident on a target surface provided with a pattern to be read, and a light beam having information on the pattern is converged by an objective lens and made incident on an imaging lens. A pattern reading device that forms and reads the image of the pattern with the imaging lens, wherein an adjustment mechanism that adjusts the position of the light source in a plane that intersects with the principal ray of the illumination light is provided. Characteristic pattern reading device. 2. The apparatus according to claim 1, wherein the light source includes a pinhole for transmitting a part of light from the light source, and the adjusting mechanism moves the light source and the pinhole together. The pattern reading device according to item 1. 3. The light source includes a lamp and an optical fiber for guiding light from the lamp to a pinhole, and the adjusting mechanism moves the end of the optical fiber on the emission side and the pinhole together. The pattern reading device according to claim 2, wherein: 4. The pattern reading apparatus according to claim 1, wherein the adjustment mechanism moves the light source in a plane substantially perpendicular to a principal ray of the illumination light. 5. The object surface is a reflection surface, and a light beam emitted from the light source and reaching the object surface via the objective lens is reflected by the object surface and transmitted again through the object lens, and The pattern reading device according to claim 1, wherein the pattern reading device is arranged so as to be incident on an imaging lens. 6. The light source and the imaging lens are disposed on opposite sides of the optical axis of the objective lens,
The pattern reading device according to claim 5, wherein the light source is provided at a position where the illumination light is obliquely incident on the target surface. 7. The pattern reading apparatus according to claim 1, wherein the adjusting mechanism moves the light source in a plane substantially perpendicular to an optical axis of the objective lens. 8. An image forming apparatus, comprising:
The pattern reading device according to claim 1, further comprising an image sensor that reads the pattern. 9. Illumination light emitted from a light source having a very small area is made incident on a target surface provided with a pattern to be read, a light beam having information on the pattern is converged by an objective lens, and transmitted through the objective lens. In the pattern reading optical system that forms the image of the pattern by the imaging lens and reads the light beam through a spatial filter through a spatial filter, wherein the spatial filter has a light-blocking region that blocks on-axis light. An adjusting mechanism that adjusts a relative positional relationship between a position of an image of the light source formed by the objective lens and a light shielding area of the spatial filter in a plane that intersects an optical axis of the imaging lens. A pattern reading device, comprising: 10. The pattern reading apparatus according to claim 9, wherein said adjusting means moves a position of said light source. 11. The light source includes a pinhole for transmitting a part of light from the light source, and the light source adjusting mechanism moves the light source and the pinhole together. The pattern reading device according to claim 10. 12. The pattern reading apparatus according to claim 9, wherein said adjusting means moves a light shielding portion of said spatial filter. 13. The object surface is a reflection surface, and a light beam emitted from the light source and reaching the object surface via the objective lens is reflected by the object surface and transmitted again through the object lens, and The pattern reading device according to claim 9, wherein the pattern reading device is arranged to be incident on the imaging lens. 14. The light source and the imaging lens are arranged on different sides with respect to an optical axis of the objective lens, and the light source makes the illumination light obliquely enter the object plane. The pattern reading device according to claim 13, wherein the pattern reading device is provided at a position. 15. The pattern reading apparatus according to claim 9, wherein the spatial filter is arranged on the side of the objective lens from a paraxial image point of the light source formed via the objective lens. .