JPH0340802B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a defect inspection device for detecting defects occurring in an object having fine scales, such as the main scale plate of an angle-measuring rotary encoder.

In recent years, defect inspection equipment that uses coherent light and a spatial frequency filter instead of visual inspection has been used to search for defects in fine scales, that is, regularly arranged regular patterns, on objects to be inspected. A device has been developed that detects and displays the defect position, size, etc. by separating the non-periodic information caused by the defect from the non-periodic information caused by the defect.

Conventionally, this type of device utilizes the property that the Fourier transformed image of a regular pattern is regularly distributed in a lattice shape, and uses a spatial frequency filter having light-opaque regions distributed in a lattice shape to detect the period of the regular pattern. There is a method that blocks information and detects aperiodic defect information from the transparent part of a spatial frequency filter.

This type of apparatus includes a transmission type defect inspection apparatus as shown in FIG.

This defect inspection device converts coherent light emitted from a laser light source 1 into parallel light using a beam expander 2, illuminates a regular pattern 3 of an object to be inspected with the parallel light, and then uses the parallel light to transmit and illuminate a regular pattern 3 on the object to be inspected. An objective lens 4 forms an image, and a spatial frequency filter 5 placed at the focal point of the objective lens 4 separates periodic information from aperiodic information. The aperiodic information, ie, defect information, separated by the spatial frequency filter 5 is observed by a defect observation device 10 consisting of an eyepiece lens 6, a relay lens 7, a TV image pickup tube 8, and a TV monitor 9.

By the way, there are some regular patterns of the object to be inspected that cannot be subjected to transmission illumination, and a transmission-type defect inspection apparatus cannot detect defects that occur in such regular patterns of the object to be inspected. Therefore, there is a reflection type defect inspection apparatus as shown in FIG. 2, in which epi-illumination is applied to a regular pattern of an object to be inspected to obtain light diffracted from the regular pattern.

This defect inspection device converts coherent light emitted from a laser light source 1 into parallel light using an illumination lens 12, and converts the parallel light into parallel light using an oblique half mirror 13 installed obliquely between a regular pattern 14 and an objective lens 15. The regular pattern 14 of the object to be inspected is reflected and epi-illuminated, and the light reflected and diffracted by the regular pattern 14 is passed through the diagonal half mirror 13 and then illuminated by the objective lens 1.
5, and a spatial frequency filter 16 placed at the focal point of the objective lens 15 separates periodic information from aperiodic information. Reference numeral 10 denotes a defect observation device, which includes an eyepiece lens 6, an imaging lens 7, a TV camera 8, and a TV monitor 9, as described above.

However, in such a conventional reflective defect inspection device, since the oblique half mirror 13 is disposed between the regular pattern 14 and the objective lens 15, the working distance WD of the objective lens 15 is It is necessary to take a large value.

In particular, in recent years, the fine scale of the specimen has become increasingly finer,
Accordingly, a defect inspection device with high magnification is required, but in order to increase the magnification of the defect inspection device, it is necessary to increase the magnification of the objective lens 15. As the lens group constituting the lens group becomes more complex and the total length becomes longer, the working distance WD of the objective lens 15 is increasingly restricted and shortened due to various optical design requirements. Since it becomes very difficult to arrange the half mirror 13,
There has been a problem in that it has become increasingly difficult to provide defect inspection devices with higher magnification.

This invention was made by focusing on these conventional problems, and involves forming a reflection diffraction image from a light emitting body that emits coherent light and a test object having a regular pattern irradiated with coherent light. The above-mentioned problems can be solved by providing a defect inspection device consisting of an objective lens for imaging and a spatial frequency filter placed at the focal position of the objective lens, and in which a light emitting body is placed on the spatial frequency filter. It aims to solve the problem.

The present invention will be explained below based on the drawings.

FIGS. 3 and 4 are diagrams showing a first embodiment of the present invention. The defect inspection device of this embodiment is of a transmission type.

In the figure, reference numeral 21 is a regular pattern formed on a reflection type test object, and 22 is a regular pattern 21.
The objective lens 23 is a spatial frequency filter placed at the focal point of the objective lens 22 for forming an image of the reflected and diffracted light from the objective lens 22.

An optical fiber optical element 24 is located above the center of the spatial frequency filter 23, that is, at the focal point of the objective lens 22.
A light exit end 24a, which is one end of the lens, is disposed with its end face facing the objective lens 22. This light emitting end portion 24a becomes a light emitting body that emits coherent light. The other end of the optical fiber optical element 24, the incident light end 24b, has an end surface that is connected to the laser light source 2.
It is arranged so as to face the focal position of the condenser lens 26 that condenses the coherent light emitted from the condenser lens 5 . 27 is a laser light source 25 and a condensing lens 26
This is the shutter that is interposed between the The optical fiber optical element 24 has a core diameter as small as possible,
In addition, the optical fiber optical element 24 is used which has a large numerical aperture (NA) and low transmission loss.
The end faces of the exit end 24a and the entrance end 24b are polished.

Further, reference numeral 28 denotes an illumination light source consisting of a tungsten bulb for illumination during visual observation of the regular pattern 21. The illumination light emitted from the illumination light source 28 is collected by an illumination lens 29, and in the figure, a spatial frequency filter 23 Half mirror 3 placed above
0, passes through the spatial frequency filter 23, is converted into parallel light by the objective lens 22, and illuminates the regular pattern 21 with the parallel light. A shutter 31 is interposed between the illumination light source 28 and the illumination lens 29.

Furthermore, 35 is a defect observation device for observing aperiodic information, that is, defect information separated by the spatial frequency filter 23, and includes an eyepiece lens 36 and an imaging lens 3.
7. Consists of a TV image pickup tube 38 and a TV monitor 39.

Next, the effect will be explained.

Laser light, which is coherent light emitted from the laser light source 25, is focused by a condenser lens 26, received at the end face of the input end 24b of the optical fiber optical element 24, and guided by the optical fiber optical element 24. and the light exit end 2 of the optical fiber optical element 24
The light is emitted from the end face of 4a toward the objective lens 22. At this time, the laser beam from the laser light source 25 guided by the optical fiber optical element 24 spreads from the focal position of the objective lens 22 by the numerical aperture.

The light transmitted through the objective lens 22 becomes parallel light and irradiates the regular pattern 21 in parallel. When the regular pattern 21 is irradiated with parallel light, a diffraction phenomenon occurs, and the diffracted light reflected by the regular pattern 21 and indicated by the arrow in FIG. 4 is imaged by the objective lens 22 as a diffraction image. At this time, if the regular pattern 21 is a pattern as shown in FIG. 4, the diffraction images _I1 by the objective lens 22 are regularly arranged in a line as shown in FIG. Since the spatial frequency filter 23 is placed at the focal point of the objective lens 22, the diffraction images _I1 , that is, the Fourier transform images regularly arranged in a row, are blocked by the spatial frequency filter 23 having a light-opaque region. Eyepiece 3
6. It does not go toward the TV image pickup tube 38.

In addition, if there is a defective part of the regular pattern 21, it will be reflected by the regular pattern 21, and the objective lens 2
The diffraction images formed by the pattern 2 are not arranged in a straight line like the regular pattern 21 but appear irregularly around the spatial frequency filter 23, that is, the regular pattern 2
Since diffracted light without directionality is emitted from the defective portion 1, the Fourier transform image also becomes complicated and scattered within the spatial frequency plane of the spatial frequency filter.
Therefore, the Fourier transform image of the regular pattern 21 without defects is blocked by the spatial frequency filter 23, and only the light from the defective portions leaking from the spatial frequency filter 23 is transmitted. Therefore, only the light from this defective area is sent to the TV image pickup tube 38 through the eyepiece lens 36.
A diffraction image I ₂ of the defective part is formed by the imaging lens 37 and a TV connected to the TV image pickup tube 38.
The monitor 39 allows the diffraction image I ₂ of the defective portion to be observed on the screen.

In the defect inspection device of this embodiment, the incident end 24b of the optical fiber optical element 24 that emits the laser beam is disposed on the spatial frequency filter 23, and between the regular pattern 21 to which the laser beam is irradiated and the objective lens 22. Since the oblique half mirror 13 is not provided as in the conventional case, the working distance WD of the objective lens 22 is
It is possible to use the objective lens 22 with a small magnification and a high magnification of the defect inspection apparatus.

In addition, by using the optical fiber optical element 24, the optical energy transmission efficiency becomes better than that using the conventional oblique half mirror 13, and the optical path becomes flexible, so the laser light source 24
5 and the condenser lens 26 are not limited. Furthermore, by using the optical fiber optical element 24 with a small fiber core diameter,
The light source is close to a point light source, and good parallel light can be obtained through the objective lens 22.

On the other hand, when it is desired to visually observe the regular pattern 21, the laser light emitted from the laser light source 25 is blocked by the shutter 27, the shutter 31 on the illumination light source 28 side is opened, and the light emitted from the illumination light source 28 is used to The regular pattern 21 is illuminated. That is, the illumination light emitted from the illumination light source 28 passes through the illumination lens 29.
After being focused, it is reflected by a half mirror 30,
It passes through the spatial frequency filter 23 and passes through the objective lens 2.
2, a regular pattern 21 is used to focus and illuminate. The light reflected by the regular pattern 21 is again condensed by the objective lens 22 and is transmitted through the half mirror 30 this time. Then, the light transmitted through the half mirror 30 is imaged on the TV image pickup tube 38 by the eyepiece lens 36 and the relay lens 37.
The monitor 39 allows the image of the regular pattern 21 to be visually observed on the screen.

FIG. 5 shows a modification of the spatial frequency filter 23 used in the first embodiment of the invention.

As shown in FIGS. 3 and 4, the spatial frequency filter 23 of the first embodiment is a straight line with a certain width, but the regular pattern 21 of the object to be examined is arranged in a right angle direction. Therefore, the diffracted light reflected by the regular pattern 21 is also aligned in the perpendicular direction. Therefore, to block this, the spatial frequency filter 23 must be rotated 90 degrees. Therefore, if the cross-shaped spatial frequency filter 33 is made in advance, even if the direction of the regular pattern 21 is rotated by 90 degrees, there is no need to rotate the spatial frequency filter 33. For this purpose, a cross-shaped spatial frequency filter 33 as shown in FIG.
It is arranged at the focal position of 2.

6 to 8 show a second embodiment of the present invention, and are block diagrams including a speckle noise reduction device 40 and a defect discrimination circuit 41. In the drawings, parts or members that are the same or equivalent to those in the first embodiment are given the same reference numerals and redundant explanations will be omitted. The defect determination circuit 41 determines whether or not there is a defect in the regular pattern 21, stores the defect, and determines the position, size, and shape of the defective portion.

The configuration of the speckle noise reduction device 40 used in this embodiment is shown in FIGS. 7 and 8.

The speckle noise reduction device 40 is designed to prevent speckle noise from occurring in the laser beam when the laser beam emitted from the laser light source 25 passes through the optical fiber optical element 24, and even if parallel illumination is performed using the objective lens 22. This device eliminates unevenness in light intensity caused by speckle noise. The speckle noise reduction device ₄₀₁ shown in FIG. 7 uses a high frequency oscillator 42 to vibrate the optical fiber optical element 24 to reduce speckle noise. In addition, the speckle noise reduction device ₄₀₂ shown in FIG.
The speckle noise is reduced by a rotating diffuser plate 44 which is interposed between the two. The speckle noise reduction device 40 in FIG.
Either of the speckle noise reduction devices 40 ₁ , 40 ₂ shown in FIG. 8 or 8 is used.

Next, the defect determination circuit 41 shown in FIG. 6 will be explained.

Regular pattern 21 imaged on TV image pickup tube 38
The diffraction image of the defective part is displayed on a TV monitor 39 via a camera control unit (hereinafter referred to as CCU) 45.
It can be observed in FIG. 9 shows the diffraction image. Further, a video signal of the diffraction image can be taken out from the CCU 45, and FIG. 10 shows the video signal. The approximately circular portion in FIG. 9 is a defective portion of the regular pattern 21. In FIG. In FIG. 10, the rising portion of the waveform is the peak voltage obtained corresponding to the position and brightness of the diffraction image of the defective portion. Therefore, by dividing the peak voltage according to the size of the defective portion into those above and below a certain level, it is possible to classify the defects into levels.

Defect levels are classified as follows.

First, the processing control device 46 drives the stage controller 47 to move the scale plate 49 having the regular pattern 21 of an object to be measured, such as a rotary encoder for angle measurement, placed on the stage 48 in the X-Y direction.
direction, rotate it in the θ direction, and set it at the O position.

Next, when the scale plate 49 is set to the O position, a measurement start signal from the processing control device 46
The TV image pickup tube 38 is activated to detect the presence or absence of a defect in the regular pattern 21 on the scale plate 49 set at the O position. That is, a diffraction image of the defective portion of the regular pattern 21 is formed on the TV image pickup tube 38, and the diffraction image is converted into a video signal by the CCU 45.
Comparator 50 receives the video signal sent from 45 and detects the presence or absence of a defect by comparing whether the peak voltage in the video signal is above a predetermined level (defect image present) or below the level (no defect image). do. Then, the output from the comparator 50 is stored in the defect memory 51 at the next stage.

In this way, the scale plate 4 is set to the O position.
When the presence or absence of a defect in the rule pattern 21 in 9 is detected, the processing control device 46 drives the stage controller 47 again to rotate the scale plate 49 on the stage 48 by a predetermined angle, and the rule of the next area on the scale plate 49 is detected. The presence or absence of a defect in the pattern 21 is detected in the same manner as described above, and the output from the comparator 50 is stored in the corresponding defect memory 51.

In this way, the presence or absence of defects is checked over the entire circumference of the scale plate 49, and the defect information of the regular pattern 21 corresponding to each area is stored in the corresponding address of the defect memory 51.

Next, the processing control device 46 reads the information from the defect memory 51, searches out the area of the scale plate 49 where the defect is present, determines the position, size, and shape of the defect in the regular pattern 21 in that area, and An image is displayed on the tube 52. At this time, the data can also be printed by the printer 53. At the same time, the processing control device 46 drives the stage controller 47 to set the scale plate 4 so that the defective area is imaged on the TV image pickup tube 38.
Rotate 9.

When the scale plate 49 has rotated to a predetermined position, the shutter controller 54 is driven to close the shutter 27 on the laser light source 25 side, which has been open until now, to block the laser light, and to close the shutter 31 on the illumination light source 28 side. When opened, the scale plate 49 is illuminated with light emitted from the illumination light source 28. That is, the illumination light from the illumination light source 28 is focused by the illumination lens 29, reflected by the half mirror 30, and then passed through the spatial frequency filter 23.
The light passes through and is focused by the objective lens 22 on the scale plate 49 for illumination. The light reflected by the scale plate 49 is again condensed by the objective lens 22 and is transmitted through the half mirror 30 this time. Then, the light transmitted through the half mirror 30 is imaged on the TV image pickup tube 38 by the eyepiece lens 36 and the imaging lens 37, and the CCU
Dial plate 49 by TV monitor 39 via 45
Visually observe the image on the screen.

FIG. 11 shows a third embodiment of the invention.

In this embodiment, a coherent light beam is emitted onto the central portion of the spatial frequency filter 23, that is, at the focal point of the objective lens 22, rather than at the light emitting end 24a of the optical fiber optical element 24 as in the first embodiment. A semiconductor laser 60, which is an ejector, is provided. Since the other configurations are the same as those in the first embodiment, the same reference numerals are given and the explanation will be omitted.

A light emitting portion of the semiconductor laser 60 that emits coherent light is directed toward the objective lens 22 . 61 is a cord connected to the semiconductor laser 60, and 62 is a connector provided on the cord 61. This semiconductor laser 60 emits laser light from a light emitting portion when energized.

In this embodiment, the light source is placed directly at the focal position of the objective lens 22 without using the optical fiber optical element 24 as in the first embodiment, so there is no light energy transmission loss due to the optical fiber optical element 24. Light energy transfer efficiency is good. Also,
Measures against speckle noise, such as when using the optical fiber optical element 24, are also not required. Therefore, if the speckle noise reduction device 40 is provided as a countermeasure against speckle noise, it takes time for the speckle noise reduction device 40 to perform averaging to eliminate light unevenness when it is desired to detect defects at high speed.
There is no longer a problem that defects cannot be detected at high speed due to long measurement time. Furthermore, the semiconductor laser 60
is provided in the spatial frequency filter 23, and the spatial frequency filter 23 is located at the focal position of the objective lens 22. Therefore, the objective lens 22 and the spatial frequency filter 23 are incorporated in an objective lens barrel (not shown), and the spatial frequency filter 23 is provided in the spatial frequency filter 23. Since the cord 61 and connector 62 connected to the provided semiconductor laser 60 will be attached to the objective lens barrel, the attachment and detachment of the objective lens 22 will be performed only when the optical fiber optical element 24 is provided on the spatial frequency filter 23. This can be done more easily by attaching and detaching the objective lens barrel than in the first embodiment.

FIG. 12 shows a fourth embodiment of the invention.

FIG. 12 is a block diagram of a defect inspection apparatus including a defect discrimination circuit 41 and a semiconductor laser 60 provided in the spatial frequency filter 23. In this embodiment, there is no speckle noise reduction device 40.
Unlike the second embodiment, the other configurations are substantially the same as the second embodiment, so the same reference numerals are given and the explanation will be omitted.

In the figure, 63 is a shutter that blocks the laser light from the semiconductor laser 60. Note that the objective lens 2 is not provided with the speckle noise reduction device 40.
This is because the semiconductor laser 60 that directly emits laser light is disposed at the second focal point, so the problem of speckle noise occurring in the optical fiber optical element 24 as in the second embodiment does not occur.

Furthermore, in the embodiments described above, the spatial frequency filters 23 and 33 must be provided at the focal position of the objective lens 22. However, if there is not enough room to provide the spatial frequency filters 23, 33 at the focal position of the objective lens 22, they must be provided at a position slightly shifted from the original focal position.
A slight deviation in the optical axis direction of the spatial frequency filters 23 and 33 causes only a slight blurring of the image and a decrease in the amount of light, and has almost no practical effect. Therefore,
The positions where the spatial frequency filters 23 and 33 are provided are not necessarily exact, and some deviation is allowed.

As explained above, according to this invention,
The structure includes a light emitting body for emitting coherent light, an objective lens for forming an image of reflected diffracted light from a test object having a regular pattern irradiated with the coherent light, and a focal position of the objective lens. It consists of a spatial frequency filter arranged,
Since the light emitting body is disposed on the spatial frequency filter, there is no need to provide an oblique half mirror between the regular pattern irradiated with laser light and the objective lens, which is required in the past, and the working distance of the objective lens can be reduced. A small objective lens with high magnification can be used, and the effect of increasing the magnification can be obtained.

Moreover, by using the light emitting body as the light emitting end of the optical fiber optical element that guided the laser light source,
The optical energy transmission efficiency is better than that using conventional oblique half mirrors, and the optical path is flexible, so there are no restrictions on where the laser light source and condensing lens can be installed. .

Furthermore, by using a semiconductor laser as the light emitting body, it is possible to obtain the effect that the light energy transmission efficiency is even better than that using an optical fiber optical element, and there is no need for speckle noise countermeasures.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of a conventional transmission-type defect inspection device, FIG. 2 is a schematic diagram of a conventional reflection-type defect inspection device, and FIGS. 3 and 4 are diagrams of a defect inspection device of the present invention. Fig. 3 is a schematic configuration diagram of a defect inspection device, Fig. 4 is a perspective view of a regular pattern through which laser light passes, an objective lens and a spatial frequency filter, and Fig. 5 is a modification of the spatial frequency filter. 6 to 10 show a second embodiment of the present invention, and FIG. 6 is a block diagram of a defect inspection device equipped with a speckle noise reduction device and a defect discrimination circuit. Fig. 7 is a schematic diagram showing a speckle noise reduction device, Fig. 8 is a schematic diagram showing another speckle noise reduction device, Fig. 9 is a diagram showing a diffraction image of a defective part, and Fig. 10 is a schematic diagram showing a speckle noise reduction device. A diagram showing a video signal of a diffraction image of a defective part, FIG. 11 shows a third embodiment of the present invention, a schematic configuration diagram of a defect inspection apparatus, and FIG. 12 shows a fourth embodiment of the present invention, and a defect discrimination FIG. 2 is a block diagram of a defect inspection device equipped with a circuit. 21...Regular pattern, 22...Objective lens,
23...Spatial frequency filter, 24a...Light emission end of optical fiber optical element (light emission body), 25...
...Laser light source, 60...Semiconductor laser (light emitting body).

Claims (1)

[Scope of Claims] 1. A light emitting body that emits coherent light, an objective lens for forming an image of reflected diffracted light from a test object having a regular pattern irradiated with the coherent light, and 1. A defect inspection device comprising: a spatial frequency filter disposed at a focal position; and the light emitting body is disposed on the spatial frequency filter. 2. The defect inspection device according to claim 1, wherein the light emitting body is an emitting end of an optical fiber optical element through which a laser light source is guided. 3. The defect inspection device according to claim 1, wherein the light emitting body is a semiconductor laser.