JPH10170830A - Pattern reader - Google Patents

Abstract

(57) [Problem] A conventional filtering optical system cannot optically enlarge or reduce a pattern because an image magnification cannot be changed. 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 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. Of the light reflected from the surface 1a, the scattered reflection component transmitted through the spatial filter 31 enters the imaging lens 32. The imaging lens 32
It has a power to conjugate the surface 1a of the silicon wafer 1 and the image sensor 33, and a differential image of the surface 1a is formed on the image sensor 33 by a scattered reflection component. The objective lens 20 is arranged such that light emitted from one point on the target surface and emitted from the objective lens becomes non-parallel light, and the imaging lens 32
And the imaging element 33 are movable in the direction of the optical axis Ax2 for adjusting the magnification.

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.

[0003]

However, in the above-described pattern reading apparatus using the conventional filtering optical system, the magnification of the pattern image to be formed cannot be changed. There was a problem that you can not. That is,
In the conventional optical system, since the target surface is located at the focal point of the objective lens, the light beam emitted from the objective lens is afocal, and the imaging magnification cannot be changed even if the imaging lens is moved. In order to change the magnification, it was necessary to compose the imaging lens with a plurality of lens groups.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems of the prior art, and has as its object to provide a pattern reading apparatus capable of changing the magnification of a pattern image with a simple configuration.

[0005]

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. The light emitted from the objective lens is arranged to be non-parallel light, and the imaging lens and the imaging surface can be moved along the optical axis direction of the imaging lens to change the imaging magnification. I do.

In order to satisfy the above-mentioned non-parallel condition and to provide a change in magnification with a small amount of movement, the distance X between the target surface and the objective lens must be 0 <0, where the focal length of the objective lens is fo. It is desirable to satisfy the condition of X <0.7fo.

When the target surface is a reflection surface, the light source is
The light beam emitted from the light source and reaching the target surface via the objective lens can be arranged to be reflected on the target surface, transmitted again through the objective lens, and incident on the imaging lens. Further, in this case, the light source and the imaging lens can be arranged on opposite sides with respect to the optical axis of the objective lens, and the light source is provided at a position where the illumination light is obliquely incident on the target surface. be able to.

In order to obtain a predetermined filtering effect, a spatial filter having a light-blocking region for blocking on-axis light can be arranged in an optical path between the objective lens and the imaging lens. When the objective lens has a spherical aberration, it is desirable that the spatial filter be disposed closer to the objective lens than the paraxial image point of the light source formed via the objective lens.
In addition, in order to process the read image or display it on another display device, at the image forming position of the pattern image,
What is necessary is just to arrange the imaging element which reads a pattern.

When the light source is disposed farther from the objective lens than the front focal point of the objective lens, the light flux from the light source to the target surface via the objective lens becomes convergent light, and the position where the image of the light source is formed is more focused on the objective. As the lens becomes closer to the lens, the spatial filter and the imaging lens can be closer to the objective lens by that much, and the adjustment range of the image magnification can be expanded.

[0010]

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 diagrams 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 flux transmitted through the test object O enters the spatial filter 31 via the objective lens 22, passes through the spatial filter 31, and forms an image of the test object on the imaging surface 33 a by the imaging lens 32. The spatial filter 31 is used to
This is a filter having a light-blocking region for blocking a light beam that forms an image of a light source that is not scattered by the light source, and is disposed closer to the objective lens 22 than the paraxial image plane IM of the light source. The light source formed by the pinhole plate 12 is located at the front focal point of the illumination lens 21, and the test object O is illuminated by parallel light.

In an optical system using a conventional Fourier transform lens, the test object O is located at the front focal point of the objective lens 22 which is a Fourier transform lens, and further, the rear focal point of the objective lens 22 and the front side of the imaging lens 32. The focal point matches, and the imaging surface 33a is located at the focal point of the imaging lens 32. However, in this case, since the light beam emitted from one point of the test object becomes parallel light, the magnification cannot be changed even if the imaging lens 32 is moved.

In the embodiment, the test object O and the objective lens 22
Is set to be shorter than the focal length of the objective lens. Accordingly, light emitted from one point of the test object O and emitted from the objective lens 22 becomes non-parallel light, and the imaging magnification can be changed by moving the imaging lens 32 and the imaging surface 33a. The distance X desirably satisfies the condition of 0 <X <0.7fo, where fo is the focal length of the objective lens. Note that, by bringing the objective lens 22 close to the test object O, the image forming position I of the light source is formed.
Since M also approaches the test object, the spatial filter 31 can also be closer to the test object O than a conventional optical system. Thereby, the movable range of the imaging lens 32 is widened, which is advantageous for expanding the range of magnification adjustment.

FIG. 1B shows a modification of the optical system of FIG. 1A for adjusting the imaging magnification. In the example of FIG.
The position of the light source is arranged away from the illumination lens 21 from the front focal point of the illumination lens 21. With this arrangement,
The illumination light emitted from the illumination lens becomes convergent light, and therefore, the position of the light source formed via the objective lens 22 can be made closer to the test object O. Thereby, the spatial filter 31 is closer to the test object O than the optical system of FIG. 2A, and the movable range of the imaging lens 32 is further expanded. Therefore, the range of magnification adjustment can be further expanded.

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 the 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 the 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 drawing 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 a plane perpendicular to the principal ray Ax1 of the illumination light and a 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 1a passes through the objective lens 20 again, becomes convergent light toward the detection unit 30 side, 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. 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, as described above, the detecting 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 by 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 changed to 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 length of the character string of the serial number to be read and the size of the image pickup surface of the image pickup 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 when it is assumed that 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 mounted at a reference position T shown 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 vertical support 202 vertically raised from the horizontal support plate 201 is provided. 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 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 commercially available optical fiber having a diameter of about 5 mm, and a pinhole is used to make it a light source having a very small area. 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 a center of the first step portion 205a in the width direction passes through the vertical holding plate 203 from the first step portion to have a width. A narrow second step portion 205b is formed. The imaging unit 320 is formed with two arms 322 for attachment, and a bolt 321 is provided at the tip of each arm 322 with a washer 323 smaller in diameter than the first step 205a 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 positioned 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 inclination of the silicon wafer itself may be adjusted. However, the inclination 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 not only the light source side but also the position of the spatial filter 31 is adjusted. 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 of FIG. 10, the spatial filter 31 fitted in the movable frame is movable with respect to the movable frame in the Y direction in the figure, and the movable frame is further mounted on 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.

[0052]

As described above, according to the present invention, the light emitted from one point on the target surface and emitted from the objective lens is arranged as non-parallel light, and the imaging lens and the imaging surface are formed. Since the image lens can be moved in the optical axis direction, the magnification of the pattern image formed on the imaging surface can be changed optically, and the size of the image is enlarged or reduced according to the size of the pattern. be able to.

[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 (13)

[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 the objective lens is arranged such that light emitted from one point of the target surface and emitted from the objective lens becomes non-parallel light. ,
A pattern reading apparatus, wherein the imaging lens and the imaging surface are movable along the optical axis direction of the imaging lens to change an imaging magnification. 2. A distance X between the object plane and the objective lens.
Is 0 <X <, where fo is the focal length of the objective lens.
2. The pattern reading apparatus according to claim 1, wherein a condition of 0.7fo is satisfied. 3. The object surface is a reflection surface, and the light source transmits a light beam emitted from the light source, reaches the object surface via the objective lens, and is reflected by the object surface again through the objective lens. 2. The pattern reading device according to claim 1, wherein the pattern reading device is disposed so as to be incident on the imaging lens. 4. 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 3, wherein the light source is provided at a position where the illumination light is obliquely incident on the target surface. 5. The pattern according to claim 1, wherein a spatial filter having a light blocking region for blocking on-axis light is disposed in an optical path between the objective lens and the imaging lens. Reader. 6. The pattern reading apparatus according to claim 5, wherein the spatial filter is arranged on a side of the objective lens from a paraxial image point of the light source formed through the objective lens. . 7. The pattern reading device according to claim 3, wherein the light source is disposed farther from the objective lens than a front focal point of the objective lens. 8. An illumination lens is disposed between the light source and the target surface, and the light source is disposed farther from the illumination lens than a front focal point of the illumination lens. 2. The pattern reading device according to 1. 9. An image pickup device arranged on the image plane and reading the pattern.
9. The pattern reading device according to any one of 8. 10. A light source having a small area, an illumination lens from the light source being incident on a target surface provided with a pattern to be read, and an objective lens for converging light reflected on the target surface, A spatial filter that extracts a scattered and reflected component in the reflected light flux transmitted through the objective lens, an imaging lens that forms an image of the pattern by a component that has passed through the spatial filter, and an imaging lens that is disposed at an imaging position of the pattern image; A pattern reading device, comprising: an imaging element for reading the pattern, wherein the imaging lens and the imaging element are movable along an optical axis direction of the imaging lens to change an imaging magnification. . 11. The distance X between the target surface and the objective lens is 0 <X, where fo is the focal length of the objective lens.
2. The condition of <0.7 fo is satisfied.
0. The pattern reading device according to 0. 12. 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 target surface. The pattern reading device according to claim 10, wherein the pattern reading device is provided at a position. 13. The spatial filter according to claim 10, wherein the spatial filter is disposed closer to the objective lens than a paraxial image point of the light source formed through the objective lens.
The pattern reading device according to item 1.