JPH041849B2 - - 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 spatial filters instead of visual inspection has been developed 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 it from non-periodic information.

Conventionally, this type of device takes advantage of 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 obtain periodic information of the regular pattern. There is a method that detects non-periodic defect information from the transparent part of the 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 transmits the light diffracted by the regular pattern 3 to an objective. An image is formed by a lens 4, and periodic information and aperiodic information are separated by a spatial frequency filter 5 placed at the focal position of the objective lens 4. The aperiodic information separated by the spatial frequency filter 5, that is, the defect information, is sent to the eyepiece 6,
Relay lens 7, TV image pickup tube 8 and TV monitor 9
The defects are observed by a defect observation device 10 consisting of:

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 also a reflection-type defect inspection apparatus (not shown) in which epi-illumination is applied to a regular pattern of an object to be inspected to obtain light diffracted from the regular pattern.

Incidentally, in recent years, the optical scales incorporated in optical instruments have been rapidly becoming finer. For example, the regular patterns of the scale plates of angle-measuring rotary encoders are becoming finer due to the demand for high resolution brains and miniaturization. , Some degree scales for surveying instruments have a line width of 2 μm or less, and in the semiconductor field, mask patterns,
Regular patterns on IC wafers are becoming increasingly finer. Defect inspection equipment has become indispensable for manufacturers because even the slightest defect in these various miniaturized regular patterns can be fatal, and the detected defect size is extremely large. Because of their small size, high magnification defect inspection equipment is now required.

However, in such a conventional defect inspection device, in order to have a high magnification defect inspection device, the objective lens 4 must have a high magnification.
As the magnification of the objective lens 4 increases, the lens groups that make up the objective lens 4 become more complex, and the total length of the objective lens 4 becomes longer.
The working distance of the machine is limited and shortened, making it difficult to automate and speed up defect inspection.

Furthermore, as the magnification of the objective lens 4 increases, the back focus position of the objective lens when viewed from the test object side will be located inside the objective lens 4 rather than outside, so a spatial frequency filter 5 is installed. There was a problem in that it became impossible to inspect defects on regular patterns, and it became impossible to provide a defect inspection device with even higher magnification.

This invention was made by focusing on such conventional problems, and includes a test object mounting table on which a test object having a regular pattern is placed, and a coherent light irradiated onto the regular pattern of the test object. a light source that
an objective lens system that forms a diffraction image in a lens system by diffracted light generated when coherent light from the light source is irradiated onto the regular pattern; and an objective lens system that relays the diffraction image formed in the lens system to a focal position. a relay lens to be re-formed; a spatial frequency filter disposed at the focal position of the relay lens and having a spatial frequency selected to correspond to the diffraction image formed within the lens system; Provided is a defect inspection device comprising: an image pickup tube installed at a conjugate position to receive a beam of light transmitted through the spatial frequency filter based on the defective portion of the regular pattern; and a defect observation device for observing the defective portion. The aim is to solve the above problems by doing so.

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

FIGS. 2 and 3 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 11 is a regular pattern that is irradiated with coherent light from a transmission type test object, 12 is a laser light source that emits coherent light to the regular pattern 11, and the laser light source 12 and the regular pattern 1 are
A collimator lens 13 is interposed between the lens 1 and the lens 1. Reference numeral 14 denotes an objective lens system for forming an image of the diffracted light by the regular pattern 11, and has therein a rear focal plane f located at a rear focal position when viewed from the regular pattern 11 side. 15 is a relay lens that relays and reimages the diffraction image formed on the rear focal plane f of the objective lens system 14; 16 is a spatial frequency filter disposed at the focal position of the relay lens 15.

17 is a defect observation device for observing aperiodic information, that is, defect information separated by the spatial frequency filter 16, and includes an eyepiece lens 18, an imaging lens 19, and a TV.
Image pickup tube 20, camera control unit (hereinafter referred to as
(CCU) 21 and a TV monitor 22.

Next, the effect will be explained.

The laser light, which is coherent light emitted from the laser light source 12, is converted into parallel light by the collimator lens 13 and irradiates the regular pattern 11. When the regular pattern 11 is irradiated with parallel light shown by the arrow in FIG. 3, a diffraction phenomenon occurs, and the regular pattern 1
The diffracted light that has passed through the optical system 1 is imaged by the objective lens system 14 as a diffraction image, that is, a Fourier transform image. In the diffraction image I ₁ at this time, assuming that the regular pattern 11 is a pattern as shown in FIG.
4, they are formed inside the objective lens system 14 and are regularly arranged in a line as shown in FIG. Therefore, the light transmitted through the objective lens 14 does not form an image on the spatial frequency filter 16 as it is.
Therefore, a relay lens 15 interposed between the objective lens system 14 and the spatial frequency filter 16 relays the diffracted light focused on the rear focal plane f of the objective lens system 14, and the focal point of the relay lens 15 is Since the spatial frequency filter 16 is placed in
The diffraction image I ₂ is re-imaged on the spatial frequency filter 16 . The spatial frequency filter 16 has a light-opaque region that blocks the diffraction image _I2 . Therefore, the diffraction image I ₂ re-imaged on the spatial frequency filter 16 is blocked by the spatial frequency filter 16 and
8. It does not go toward the TV image pickup tube 20.

In addition, if the regular pattern 11 has a defective part, the diffracted light by the regular pattern 11 is focused by the objective lens system 14, and the relay lens 15
The diffraction images re-imaged by the diffraction images are not aligned in a straight line like the regular pattern 11 but appear irregularly around the regular pattern 11 to the spatial frequency filter 16. That is, rule pattern 1
Since diffracted light without directionality is emitted from the defective part of 1, the Fourier transform image becomes complicated.
are scattered within the spatial frequency plane of the spatial frequency filter 16. Therefore, the Fourier transform image of the regular pattern 11 without defects is blocked by the spatial frequency filter 16, and only the light from the defective portions leaking from the spatial frequency filter 16 is transmitted. Therefore, only the light from this defective portion is imaged on the TV image pickup tube 20 by the eyepiece lens 18 and the imaging lens 19 as a diffraction image I ₃ of the defective portion, and is transmitted to the TV image pickup tube 20 via the camera control unit 21. connected
The diffraction image I ₃ of the defective portion can be observed on the screen of the TV monitor 22 .

In the defect inspection device of this embodiment, the back focal plane f is located inside the objective lens system 14 with high magnification, and if this is done, the light transmitted through the objective lens system 14 will not form an image on the spatial frequency filter 16, but the objective lens system 1
4 and the spatial frequency filter 16 to re-image the diffracted light imaged by the objective lens system 14 on the spatial frequency filter 16. system 14 can be used, the distance between the regular pattern 11 and the spatial frequency filter 16 is large, and the working distance of the objective lens system 14 is also large,
It is easy to increase the magnification of the defect inspection device.

FIG. 4 shows a modification of the spatial frequency filter 16 used in the first embodiment of the invention.

As shown in FIG. 3, the spatial frequency filter 16 of the first embodiment uses a straight line with a certain width, but there is also a filter in which the regular pattern 11 of the non-test object is provided in a right angle direction. Therefore, the diffracted lights transmitted through the regular pattern 11 are also aligned in the right angle direction. Therefore, to block this, the spatial frequency filter 16 must be rotated 90 degrees. Therefore, if the cross-shaped spatial frequency filter 26 is made in advance, there is no need to rotate the spatial frequency filter 16 even if the direction of the regular pattern 10 is rotated by 90 degrees. For this purpose, a cross-shaped spatial frequency filter 26 as shown in FIG. 4 is arranged at the focal point of the relay lens 15.

FIG. 5 is a diagram showing a second embodiment of the invention. The defect inspection device of this embodiment is of a reflective type.

In the figure, reference numeral 31 denotes a regular pattern irradiated with coherent light from a reflection type test object, and 32 denotes an objective lens system for forming an image of the reflected and diffracted light from the regular pattern 31. It has a rear focal plane f located at the rear focal position inside. 33 is a relay lens that relays the diffracted light imaged on the rear focal plane f of the objective lens system 32 and reimages it, and 34 is a spatial frequency filter disposed at the focal position of the relay lens 33.

35 is a laser light source that emits coherent light onto the regular pattern 31; 36 is a condenser lens that focuses the laser light emitted from the laser light source 35; 37;
is an oblique half mirror that is interposed between the objective lens system 32 and the relay lens 33 and reflects the laser beam focused by the condenser lens 36 toward the objective lens system 32. The laser light emitted from the laser light source 35 passes through the objective lens system 32 and the relay lens 33.
By providing an oblique half mirror 37 between the regular pattern 31 and the regular pattern 31, the regular pattern 31 is epi-illuminated.

40 is a defect observation device for observing aperiodic information, that is, defect information separated by the spatial frequency filter 34, and includes an eyepiece lens 41, an imaging lens 42, and a TV.
Image pickup tube 43, camera control unit (hereinafter referred to as
(CCU) 44 and a TV monitor 45.

In this embodiment, laser light, which is coherent light emitted from a laser light source 35, is focused by a condenser lens 36, reflected by an oblique half mirror 37, and directed toward an objective lens system 32. Objective lens system 32
The light that passes through becomes parallel light and forms a regular pattern 31.
irradiate in parallel. When the regular pattern 31 is irradiated with parallel light, a diffraction phenomenon occurs, and the diffracted light reflected by the regular pattern 31 is imaged by the objective lens system 32 as a diffraction image, that is, a Fourier transformed image.
The diffraction images at this time are formed inside the objective lens system 32 similarly to the first embodiment, and are regularly arranged in a line. Since the subsequent steps are the same as those in the first embodiment, the explanation will be omitted.

In the defect inspection device of this embodiment, an oblique half mirror 37 is interposed between the objective lens system 32 and the relay lens 33, but a relay lens is installed between the objective lens system 32 and the spatial frequency filter 34. 3
3, a high magnification objective lens system 32 can be used, and the distance between the regular pattern 31 and the spatial frequency filter 34 is large, and the working distance of the objective lens system 32 is also large.
It is easy to increase the magnification of the defect inspection device.

FIG. 6 shows a third embodiment of the present invention, and is a block diagram of a defect inspection apparatus equipped with a defect discrimination circuit.

This embodiment is of a reflective type like the second embodiment, and in the drawings, parts or members that are the same or equivalent to those of the second embodiment are given the same reference numerals and redundant explanations will be omitted.

The defect determination circuit 50 determines whether or not there is a defect in the regular pattern 31, stores the defect, and determines the position, size, and shape of the defective portion.

This defect discrimination circuit 50 first starts with the regular pattern 31 imaged on the TV image pickup tube 43 as in the second embodiment.
A diffraction image of the defective portion can be observed on a TV monitor 45 via a camera control unit 44. FIG. 7 shows the diffraction image. Also,
A video signal of the diffraction image can be taken out from the CCU 45, and FIG. 8 shows the video signal. The approximately circular portion in FIG. 7 is a defective portion of the regular pattern 21. In FIG. The rising portion of the waveform in FIG. 8 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 51 drives the stage controller 52 to move the scale plate 54 having the regular pattern 31 of a test object placed on the stage 53, for example, a rotary encoder for angle measurement, to the X-
Move it in the Y direction and rotate it in the θ direction, and
Set to position.

Next, when the scale plate 54 is set to the O position, a measurement start signal from the processing/control device 51
The TV image pickup tube 43 is activated to detect the presence or absence of a defect in the regular pattern 31 on the scale plate 54 set at the O position. That is, a diffraction image of the defective part of the regular pattern 31 is formed on the TV image pickup tube 43, and the diffraction image is converted into a video signal by the CCU 44.
Comparator 55 receives the video signal sent from 44 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 a predetermined level (defect image not present). do. Then, the output from the comparator 55 is stored in the defect memory 56 at the next stage.

In this way, the scale plate 5 is set to the O position.
4, the processing/control device 51 drives the stage controller 52 again to rotate the scale plate 54 on the stage 53 by a predetermined angle, and the next area on the scale plate 54 is detected. The presence or absence of a defect in the regular pattern 31 is detected in the same manner as described above, and the output from the comparator 55 is stored in the corresponding defect memory 56.

In this way, the presence or absence of defects is checked over the entire circumference of the scale plate 54, and the defect information of the regular pattern 31 corresponding to each area is stored in the corresponding address of the defect memory 56.

Next, the processing/control device 51
reads the information from , finds the area where the scale plate 54 has a defect, determines the position, size, and shape of the defect in the regular pattern 31 in that area,
An image is displayed on the cathode ray tube 57. At this time, the data can also be printed by the printer 58. At the same time, the processing/control device 51 drives the stage controller 52 to rotate the scale plate 54 so that the defective area is imaged on the TV image pickup tube 43.

When the scale plate 54 has rotated to a predetermined position, the light source switching device 59 stops the laser light emitted from the laser light source 35 and switches on the illumination light from the illumination light source consisting of a tungsten bulb (not shown) for regular pattern illumination. Switch to eject,
The scale plate 54 is illuminated with the illumination light. Scale plate 54
The reflected light is again focused by the objective lens system 32, and this time passes through the oblique half mirror 37. Then, the light transmitted through the oblique half mirror 37 passes through the relay lens 33 and the spatial frequency filter 34, and is focused on the TV image pickup tube 43 by the eyepiece lens 41 and the imaging lens 42, and is then displayed on the TV monitor via the CCU 44. 45, the image of the scale plate 54 is visually observed on the screen.

Further, in the above embodiments, the objective lens systems 14, 32 and the spatial frequency filters 16, 26,
34, and the objective lens systems 14, 32 and the spatial frequency filters 16, 26, 34 are arranged completely independently, so the objective lens system can be attached and detached. In the conventional objective lens 4 in which the rear focal plane f is located outside, the rear focal plane f is close to the objective lens 4,
There are times when the spatial frequency filter 5 has to be integrated with the objective lens 4, and at that time, there is a risk that the Fourier transformed image of the regular pattern 3 and the direction of the spatial frequency filter 5 will not match due to the attachment and detachment of the objective lens 4. However, in these embodiments, the regular patterns 11, 31 and the spatial frequency filters 16, 2
Since the relative relationship with 6 and 34 does not change, there is no such fear.

As described above, the defect inspection apparatus according to the present invention includes: a test object mounting table on which a test object having a regular pattern is placed; a light source that irradiates the regular pattern of the test object with coherent light; an objective lens system that forms a diffraction image in a lens system by diffracted light generated when coherent light from the light source is irradiated onto the regular pattern; and an objective lens system that relays the diffraction image formed in the lens system to a focal position. a relay lens to be re-formed; a spatial frequency filter disposed at the focal position of the relay lens and having a spatial frequency selected to correspond to the diffraction image formed within the lens system; It has an image pickup tube that is installed at a conjugate position and receives the light flux that has passed through the spatial frequency filter based on the defective portion of the regular pattern, and a defect observation device that observes the defective portion. Use of a high-magnification objective lens system that has an internal back focal position, allowing the diffracted light focused on the back focal position inside the system to be reimaged onto a spatial frequency filter by a relay lens. The distance between the regular pattern and the spatial frequency filter can be increased, and the working distance of the objective lens system can also be increased, resulting in higher magnification.

In addition, since a relay lens is interposed between the objective lens system and the spatial frequency filter, the objective lens system and the spatial frequency filter are placed completely independently. Since the relative relationship between the regular pattern and the spatial frequency filter does not change when the objective lens is attached or removed, the Fourier transformed image of the regular pattern and the direction of the spatial frequency filter do not become mismatched when the objective lens is attached or detached. Effects can also be obtained.

[Brief explanation of drawings]

FIG. 1 is a schematic configuration diagram of a conventional transmission type defect inspection device, FIGS. 2 and 3 show a first embodiment of the defect inspection device of the present invention, and FIG. 2 is a diagram of a transmission type defect inspection device. A schematic configuration diagram; FIG. 3 is a perspective view of a regular pattern through which laser light passes, an objective lens system, a spatial frequency filter, etc.; FIG. 4 is a perspective view similar to FIG. 3 showing a modified example of the spatial frequency filter; FIG. 5 shows a second embodiment of the present invention, which is a schematic configuration diagram of a reflective defect inspection device, and FIG. 6 shows a third embodiment of the present invention, which is a reflective defect inspection device equipped with a defect discrimination circuit. FIG. 7 is an explanatory diagram showing a diffraction image of the defective part, and FIG. 8 is an explanatory diagram showing a video signal of the diffraction image of the defective part. 11, 13... rule pattern, 12, 35...
Laser light source, 14, 32...Objective lens system, 1
5, 33... Relay lens, 16, 26, 34...
...spatial frequency filter.

Claims (1)

[Scope of Claims] 1. A test object mounting table on which a test object having a regular pattern is placed; a light source that irradiates the regular pattern of the test object with coherent light; and the coherent light from the light source emits the regular pattern. an objective lens system that forms a diffraction image in a lens system by diffracted light generated by irradiating the pattern; a relay lens that relays the diffraction image formed in the lens system and re-forms it at a focal position; and the relay. a spatial frequency filter disposed at the focal point of the lens, the spatial frequency of which is selected in accordance with the diffraction image formed within the lens system; and a spatial frequency filter disposed at a position optically conjugate with the object to be inspected and adapted to the rule What is claimed is: 1. A defect inspection device comprising: an image pickup tube that receives a beam of light transmitted through the spatial frequency filter based on a defective portion of a pattern; and a defect observation device that observes the defective portion.