JPH04238255A - Defect inspecting device - Google Patents

Abstract

PURPOSE:To realize a defect inspecting device which can provide space filters easily coping with various inspection objects. CONSTITUTION:A defect inspecting device using a space filter has both a reloadable space filter which can change the area to delete the reflected/ diffracted light and a fixed space filter with the fixed area to delete the reflected/diffracted light.

Description

[Detailed description of the invention]

[Purpose of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a defect inspection apparatus, and more particularly to an improvement in an inspection apparatus for inspecting for defects or adhesion of foreign matter on an object to be inspected, such as a semiconductor, which has a periodic pattern on its surface.

0002

2. Description of the Related Art Conventionally, some inspection apparatuses for inspecting objects having periodic patterns on their surfaces, such as semiconductors, use spatial filters. The concept of a device using such a spatial filter will be explained using FIG. 6.

A collimating lens 52 and a half mirror 53 are located on the optical axis of the laser beam emitted from the laser oscillator 51.
is placed on the XY stage 54 on the optical axis reflected by the half mirror 53. A Fourier transform lens 55, a spatial filter 56 on which a Fourier transform image of a normal semiconductor wafer is recorded in advance, an inverse Fourier transform lens 57, and a CCD camera 58 are sequentially arranged on the extension of the half mirror 53 of the optical axis reflected by the half mirror 53. has been done. The CCD camera 58 is connected to an image processing device 59 so as to be able to transmit its imaging data.

[0004] The operation of the device having such a configuration will be explained. A laser beam oscillated by a laser oscillator 51 is expanded by a collimator lens 52, reflected by a half mirror 53, and irradiated onto an object to be inspected a placed on an XY stage 54. The laser beam irradiated onto the object to be inspected forms an image of the object to be inspected, is regularly reflected, passes through the half mirror 53, the Fourier transform lens 55, the spatial filter 56, and the inverse Fourier transform lens 57, and is then sent to the CCD camera. The image is taken at 58. At this time, the image of the inspected object a transmitted through the Fourier transform lens 55 is Fourier transformed, and the spatial filter 56
Transmit. At this time, it is superimposed on a Fourier transformed image of a normal semiconductor wafer stored in advance in the spatial filter 56, the pattern portion of the normal semiconductor wafer is erased, and only the defective components of the semiconductor wafer a are transmitted. The transmitted light of the defect component is subjected to inverse Fourier transform by an inverse Fourier transform lens 57, thereby forming an image at a position corresponding to the position on the image of the object to be inspected. This image is captured by CCD camera 58
The image processing device 59 processes the image to process the noise component and recognize the necessary position and size of the defect.

[0005] Now, a defect inspection apparatus using a spatial filter uses a spatial filter created by Fourier transforming the reflected and diffracted light of the object to be inspected using a Fourier transform lens and recording it on a recording plate. In addition to this, there is also one that uses a cross filter that cuts only the low frequency components of the periodic components of reflected and diffracted light.

[0006] This is because the reflected and diffracted light from the periodic pattern of the object to be inspected appears at positions on the periodic grating in the vertical and horizontal directions, so the filter is placed at the cross-shaped position where the points of this light appear most conspicuously. The purpose is to remove the periodic pattern component of the lever. To explain this using FIG. 7, the n-th order diffracted lights diffracted for each pattern have the same diffraction angle, so they become parallel lights. Since the object to be inspected has a periodic pattern, when the light is focused through the lens, it appears as periodic light points at positions on the grid on the imaging plane.

[0007]

[Problems to be Solved by the Invention] Regarding the spatial filters used in the above-mentioned inspection devices, the former requires creating a spatial filter for each object to be inspected, and when performing multiple types of inspections, It was necessary to prepare as many spatial filters as there were objects to be inspected. In addition, when having such a plurality of inspection objects, alignment with respect to the spatial positioning of the spatial filter is also required, so there is a problem in that having a plurality of inspection objects requires a lot of preparation.

[0008] Furthermore, the latter method using a cross-shaped filter has the disadvantage that not only the periodic component of the object to be inspected cannot be completely removed, but also the defect component that is imaged on the cross-shaped filter is removed. Furthermore, it is clear that even if the above-mentioned two filters are combined, these basic individual problems cannot be solved.

It is an object of the present invention to solve these problems and to realize a defect inspection device that can easily provide a spatial filter that can handle various changes in the object to be inspected. . [Structure of the invention]

0010

[Means for Solving the Problems] The present invention irradiates parallel light onto an object to be inspected having a periodic pattern formed on its surface, and converts reflected and diffracted light from the object into a Fourier transform lens. The image is formed through a spatial filter that removes the Fourier transform image of the reflected and diffracted light of the inspection reference object, which is placed on the Fourier transform surface and has a normal pattern, and from this formed image, defects in the pattern are detected. In defect inspection equipment that performs inspection, the spatial filter has a configuration that combines a rewritable spatial filter that can change the area from which reflected and diffracted light is removed and a fixed spatial filter whose area from which reflected and diffracted light is removed is fixed. This is a certain defect inspection device. Further, the rewritable spatial filter at this time is a defect inspection device that is an optical rewritable type or an electronic rewritable type. Furthermore, the rewritable spatial filter and the fixed spatial filter change the polarization of the reflected/diffracted light of the normal pattern and the reflected/diffracted light of the defect component, or delete the reflected/diffracted light of the normal pattern, and This is a defect inspection device that transmits or reflects reflected and diffracted light of components.

Further, the present invention irradiates parallel light onto an object to be inspected having a periodic pattern formed on its surface, and passes the reflected and diffracted light from the object through a Fourier transform lens to transform the object into a Fourier transformer. Defects in which the reflected and diffracted light of an inspection reference object placed on the conversion surface and having a normal pattern is imaged through a spatial filter that removes the Fourier transform image, and the pattern defects are inspected from this formed image. This is a defect inspection device in which the spatial filter is a rewritable spatial filter that can change the area from which reflected and diffracted light is removed. Further, the rewritable spatial filter at this time is an optical rewritable type or an electronic rewritable type defect inspection device.

0012

[Operation] With this configuration, it is possible to realize a defect detection device with good detection accuracy and which can quickly respond to changes in the object to be inspected. First, a laser beam emitted from a laser oscillator is expanded through a collimating lens, reflected by a half mirror, and irradiated onto an object to be inspected. The irradiated laser light is reflected from the object to be inspected, passes through the half mirror, and enters the Fourier transform lens. The laser light that has passed through the Fourier transform lens is incident on the spatial filter. Periodic components with strong diffracted light are blocked by the fixed filter, and other periodic components with relatively weak reflected/diffracted light intensity are blocked by the rewritable filter. The reflected and diffracted light of other defective components is guided to the imaging device without being removed by these spatial filters. Further, as long as the contrast of the rewritable filter is sufficient, the fixed filter may be omitted and only the rewritable filter may be used.

[0013]

[Embodiment] An embodiment of the above-mentioned defect inspection apparatus will be explained with reference to the drawings.

FIG. 1a shows a spatial filter 1 used in this embodiment.
FIG. 2 is a configuration diagram showing the configuration of. It is composed of a spatial light modulator 1a, which is an optically rewritable spatial filter, and a fixed spatial filter 1b, which is a translucent member coated with light-absorbing paint in a cross shape. This spatial light modulator 1a has the function of rotating the polarization direction of light incident on a portion where information is written by 90 degrees and transmitting the light. Of course, it goes without saying that the polarization direction of the light incident on the portion where no information is written is not changed and is transmitted. 2 and 3 show the configuration of an embodiment of a defect inspection apparatus using the spatial filter 1 of the embodiment of the present invention.

A collimating lens 3 and a half mirror 4 are arranged on the optical axis of the laser beam oscillated by the laser oscillator 2. Also, on the optical axis reflected by the half mirror 4,
An XYθ table 5 is arranged, and a polarizing plate 6 and a Fourier transform lens 7 are arranged on the opposite side of the XYθ table 5 with the half mirror 4 interposed therebetween, and on the extension of the optical axis. Further, a spatial filter 1 is arranged at the focal position of the Fourier transform lens 7, an inverse Fourier transform lens 8 and a polarizing plate 9 are arranged on the optical axis of the light transmitted from the spatial filter 1, and the focal position of the inverse Fourier transform lens 8 is A CCD camera 10 is arranged at. An image processing device 11 is connected to be able to receive image signals from this CCD camera 10. Further, the polarizing plate 6 and the polarizing plate 9 are arranged so as to transmit light having the same polarization direction. Further, the spatial filter 1 is supported by a support column 12, and a CCD camera 13 supported by the support column 12 is installed so as to have a light receiving surface on the imaging plane of the Fourier transform lens 7. A rotatable drive unit 14 is installed. By driving this drive unit 14 and rotating the support column 12, the positions of the spatial filter 1 and the CCD camera 13 can be exchanged. Further, the image processing device 11 is connected to a monitor 15 so as to be able to output data, and a projector lens 16 is provided above the display surface of the monitor 15. In addition, the monitor 15 and the projector lens 16 provide CC to the spatial filter 1 when the spatial filter 1 is positioned on the display surface of the monitor 15.
It is set and arranged so that the monitor screen can be formed in the same size as the image taken by the D camera 13. The operation of the defect inspection apparatus of the first embodiment will be explained below.

First, a spatial filter is created. The polarization modulation spatial light modulator 1a of the spatial light modulator 1a, which is an optically rewritable filter, transmits light other than the part where information is written as it is, and the part where information is written changes the polarization of the incident light. This is an optical writing type spatial filter that has the effect of polarizing light by 90 degrees and transmitting it. An object to be inspected a is placed on the XYθ table 5. Subsequently, the laser beam oscillated by the laser oscillator 2 is expanded by the collimator lens 3, reflected by the half mirror 4, and irradiated onto the inspection object a on the XYθ table 5. The reflected light of the irradiated laser light passes through the half mirror 4 and the polarizing plate 6, and is focused by the Fourier transform lens 7. At this time, the position of the polarizing plate 6 is adjusted so that the reflected and diffracted light of the object to be inspected a can be transmitted therethrough. Furthermore, the reflected light including the reflected and diffracted light that has passed through the polarizing plate 6 is Fourier transformed, and a spectral image appears. Here, the driving section 14 is driven, and the CCD camera 12 is placed as shown in FIG. 3 at the position where the spatial filter 1 would normally be placed as shown in FIG. This CCD camera 12 captures a spectral image of the object to be inspected a, and transmits it to the image processing device 11. In order to remove noise caused by scratches in the optical system from the transmitted spectrum image, binarization processing is performed to extract only the normal component spectrum. The extracted image is further subjected to inversion processing and displayed on the monitor 15. The displayed inverted spectral image is imaged onto the spatial light modulator 1a via the projector lens 16, and the spatial light modulator 1a records this image, completing the creation of the spatial filter 1.

Spatial filter 1 created in this way
If the type of the object to be inspected does not change, the resulting spectral image will not change either, so there is no need to create it each time the object to be inspected is replaced. Furthermore, since image processing is performed in the image processing device 11 to delete spectra other than normal spectra, the reference object to be inspected as a sample when capturing the spectral image into the spatial light modulator 1a may have some defects. . Furthermore, by changing the width of the spectral image when displayed on the monitor 15, the frequency band cut by the spatial light modulator 1a can be arbitrarily changed, making it possible to perform special inspections.

Next, an inspection is performed using the created spatial filter 1. First, the spatial filter 1 is rearranged as shown in FIGS. 3 and 2 so that it is located on the image plane of the Fourier transform lens 7. Here, the laser oscillator 2 oscillates a laser beam. The oscillated laser light passes through the collimating lens 3, is expanded, is reflected by the half mirror 4, and is irradiated onto the inspection object a placed on the XY table 5. The irradiated laser light is reflected and diffracted on the surface of the object to be inspected a, passes through the half mirror 4, and further passes through the polarizing plate 6. When passing through this polarizing plate 6, only the light having the same polarization direction as that of the polarizing plate 6 is transmitted among the reflected light from the inspection object a, and the other light is blocked. Further, the reflected light from the inspected object a that has passed through the polarizing plate 6 passes through the Fourier transform lens 7, and forms a spectral image on the spatial filter 1 by the reflected light from the inspected object a. Here, the strong reflected light is completely blocked by the fixed spatial filter 1b. moreover,
The normal spectrum of the other inspected object a is transmitted with the polarization direction rotated by 90 degrees by the spatial light modulator 1a, and the spectrum of defective components of the other inspected object a is transmitted with the same polarization direction. do. The light that has passed through the spatial filter 1 in this manner further passes through an inverse Fourier transform lens 8 and a polarizing plate 9, and is imaged on a CCD camera 10. Here, since the polarizing plate 9 is arranged to have the same polarization direction as the polarizing plate 6, the normal spectrum of the object to be inspected whose polarization direction is polarized by 90 degrees by the optical spatial modulator 1a of the spatial filter 1 is The light is blocked by the polarizing plate 9, and only the spectrum of the defect component passes through the polarizing plate 9. That is, what is imaged by the CCD camera 10 here is only the image of the defect transmitted through the inverse Fourier transform lens 8. Here, the video signal captured by the CCD camera 10 is transmitted to the image processing device 11, and the image processing device 11 detects the type, size, position, etc. of the defect.

By configuring the defect inspection device in this way, even if there are multiple types of objects to be inspected and the objects to be inspected are changed at any time, there is no need to change the spatial filter as in the conventional case, and it is possible to use the already installed spatial filter. This can be easily handled by simply rewriting the spatial filter information. Further, in the above-described embodiment, it is not necessary to change the spatial filter 1 when the type of the inspected object a does not change, but the spatial filter 1 may be recreated each time the inspected object a is replaced. This makes it possible to configure a defect inspection device that does not require precise alignment.

Next, a second embodiment of the present invention will be described. In the first embodiment, an optically rewritable spatial light modulator 1a was used as the rewritable spatial filter, but in the second embodiment, a defect inspection apparatus using an electronically rewritable one is shown. A second embodiment will be described with reference to FIGS. 1b, 4 and 5. Components having the same configuration as those in the first embodiment are designated by the same reference numerals, and therefore their description will be omitted. Here, the difference between the second embodiment and the first embodiment is that the rewritable spatial filter 1a of the spatial filter 1 is changed from an optical rewritable type to an electronic rewritable type as described above. The monitor 15 and projector lens 16 that were necessary for writing to the spatial light modulator 1a in the embodiment are no longer necessary, and instead, the information on the filter surface of the electronically rewritable spatial filter 1a can be rewritten by the image processing device 11. A driver 1c is provided, and this driver 1c is connected to be able to receive write information from the image processing device 11. A spatial light modulator 1, which is an electronically rewritable filter,
In the polarization modulation spatial light modulator 1a of a, when the driver 1c receives information sent from the image processing device 11, an information portion is written based on this information, and the information is written. The direction of polarization is rotated by 90 degrees at the portion where the light passes through the beam, and the other portions have the effect of allowing the incident light to pass through without being rotated. Below is the second
The effect of the embodiment is shown below.

First, a spatial filter is created. First, the object to be inspected a is placed on the XYθ table 5. Subsequently, the laser beam oscillated by the laser oscillator 2 is expanded by the collimator lens 3, reflected by the half mirror 4, and irradiated onto the inspection object a on the XYθ table 5. The reflected light of the irradiated laser light passes through the half mirror 4 and the polarizing plate 6, and is focused by the Fourier transform lens 7. At this time, the position of the polarizing plate 6 is adjusted so that the reflected and diffracted light of the object to be inspected a can be transmitted therethrough. Furthermore, the reflected light including the reflected and diffracted light that has passed through the polarizing plate 6 is Fourier transformed, and a spectral image appears. Here, the driving unit 14 is driven, and the CCD camera 12 is placed at the position where the spatial filter 1 would normally be placed, as shown in FIG. 5, as shown in FIG. This CCD camera 12 captures a spectral image of the object to be inspected a, and transmits it to the image processing device 11. In order to remove noise caused by scratches in the optical system from the transmitted spectrum image, binarization processing is performed to extract only the normal component spectrum. The extracted image information is further subjected to inversion processing and sent to the driver 1c. The driver 1c that has received this image information forms this image information on the spatial light modulator 1a, completing the creation of the spatial filter 1.

Spatial filter 1 created in this way
If the type of the object to be inspected does not change, the resulting spectral image will not change either, so there is no need to create it each time the object to be inspected is replaced. Furthermore, since image processing is performed in the image processing device 11 to delete spectra other than normal spectra, the reference object to be inspected as a sample when capturing the spectral image into the spatial light modulator 1a may have some defects. . Furthermore, by changing the width of the spectral image through image processing when transmitting image information to the driver 1c, the frequency band cut by the spatial light modulator 1a can be arbitrarily changed, making it possible to perform special inspections. .

Next, an inspection is performed using the created spatial filter 1. First, the spatial filter 1 is rearranged as shown in FIGS. 5 and 4 so that it is located on the image plane of the Fourier transform lens 7. Here, the laser oscillator 2 oscillates a laser beam. The oscillated laser light passes through the collimating lens 3, is expanded, is reflected by the half mirror 4, and is irradiated onto the inspection object a placed on the XY table 5. The irradiated laser light is reflected and diffracted on the surface of the object to be inspected a, passes through the half mirror 4, and further passes through the polarizing plate 6. When passing through this polarizing plate 6, only the light having the same polarization direction as that of the polarizing plate 6 is transmitted among the reflected light from the inspection object a, and the other light is blocked. Further, the reflected light from the inspected object a that has passed through the polarizing plate 6 passes through the Fourier transform lens 7, and forms a spectral image on the spatial filter 1 by the reflected light from the inspected object a. Here, the strong reflected light is completely blocked by the fixed spatial filter 1b. moreover,
The normal spectrum of the other inspected object a is transmitted with the polarization direction rotated by 90 degrees by the spatial light modulator 1a, and the spectrum of defective components of the other inspected object a is transmitted with the same polarization direction. do. The light that has passed through the spatial filter 1 in this manner further passes through an inverse Fourier transform lens 8 and a polarizing plate 9, and is imaged on a CCD camera 10. Here, since the polarizing plate 9 is arranged to have the same polarization direction as the polarizing plate 6, the normal spectrum of the object to be inspected whose polarization direction is polarized by 90 degrees by the optical spatial modulator 1a of the spatial filter 1 is The light is blocked by the polarizing plate 9, and only the spectrum of the defect component passes through the polarizing plate 9. That is, what is imaged by the CCD camera 10 here is only the image of the defect transmitted through the inverse Fourier transform lens 8. Here, the video signal captured by the CCD camera 10 is transmitted to the image processing device 11, and the image processing device 11 detects the type, size, position, etc. of the defect. By configuring the defect inspection apparatus in this way, the same effects as in the first embodiment can be obtained.

It should be noted that the defect inspection apparatus of the present invention is not limited to the above embodiment. As in the first and second embodiments, information on the object to be inspected a may be stored in the image processing device 11, and a spatial filter may be created based on this stored information. Further, although a transmissive spatial filter is used in the above embodiment, the present invention is not limited to a spatial filter using a transmissive spatial light modulator, and a reflective spatial light modulator may also be used. . In addition, in this embodiment, the polarization direction of the light incident on the part where information is written is 90°.
In this example, the polarization direction of the two polarizing plates placed before and after the spatial filter may be adjusted to allow the spectrum of normal components to pass through as is and to polarize the defective components. In addition to changing the polarization direction and removing normal components using a polarizing plate, a spatial filter may be used that changes the direction of reflection of the spectrum of normal components so that they do not enter the light receiving element. In addition, in the above embodiment, the cross filter was used in combination with the rewritable spatial filter in order to eliminate particularly strong diffracted light, but if the contrast of the rewritable spatial filter is sufficiently strong, the cross filter can be omitted. You can stay there.

[0025]

As described above, by using the above-described defect inspection apparatus, a defect inspection apparatus can be realized that can easily and quickly follow changes in the inspected object even in an environment where the inspected objects are changed one after another. This is because spatial filters can be created in real time by using a rewritable spatial filter.
This eliminates the conventional waiting time from the completion of the inspected object to the completion of the spatial filter, making it possible to inspect the inspected object at the same time it is completed. It is possible to make artificial changes to perform various tests, and it is possible to greatly expand the range of tests.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram showing the configuration of an embodiment of the present invention.

FIG. 2 is a configuration diagram showing the configuration of an embodiment of the present invention.

FIG. 3 is a configuration diagram showing the configuration of an embodiment of the present invention.

FIG. 4 is a configuration diagram showing the configuration of an embodiment of the present invention.

FIG. 5 is a configuration diagram showing the configuration of an embodiment of the present invention.

FIG. 6 is a configuration diagram showing the basic configuration of a conventional defect inspection device.

FIG. 7 is an explanatory diagram for explaining problems in the conventional technology.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1...Spatial filter, 1a...Spatial light modulator, 1b...Fixed spatial filter, 1c...Driver, 2...Laser oscillator, 3
...Collimating lens, 4...Half mirror, 5...XYθ table, 6...Polarizing plate, 7...Fourier transform lens, 8...Inverse Fourier transform lens, 9...Polarizing plate, 10,
13...CCD camera, 11...image processing device, 15...monitor, 16...projector lens.

Claims (8)

[Claims] Claim 1: An object to be inspected having a periodic pattern formed on its surface is irradiated with parallel light, and reflected and diffracted light from the object to be inspected is passed through a Fourier transform lens and placed on its Fourier transform surface. The image is formed through a spatial filter that deletes the Fourier transform image of the reflected and diffracted light of the inspection reference object that has a normal pattern and is detected by the light receiving element. In a defect inspection device that inspects defects, the spatial filter includes a rewritable spatial filter in which the area from which reflected and diffracted light is removed can be changed, and a fixed spatial filter in which the area from which reflected and diffracted light is removed is fixed. A defect inspection device characterized by having the following configuration. 2. The defect inspection apparatus according to claim 1, wherein the rewritable spatial filter is of an optical rewritable type. 3. The defect inspection apparatus according to claim 1, wherein the rewritable spatial filter is an electronic rewritable spatial filter. Claim 4: The rewritable spatial filter and the fixed spatial filter change the polarization of the reflected/diffracted light of a normal pattern and the reflected/diffracted light of a defective component.
Defect inspection equipment described. 5. Defect inspection according to claim 1, in which the rewritable spatial filter and the fixed spatial filter eliminate reflected and diffracted light of normal patterns and transmit or reflect reflected and diffracted light of defective components. Device. 6. An object to be inspected having a periodic pattern formed on its surface is irradiated with parallel light, and the reflected and diffracted light from the object to be inspected is passed through a Fourier transform lens and placed on the Fourier transform surface. In a defect inspection device that images a Fourier transformed image of reflected and diffracted light of an inspection reference object having a normal pattern through a spatial filter that deletes it, and inspects the pattern for defects from this formed image, A defect inspection device characterized in that the spatial filter is a rewritable spatial filter that can change the area from which reflected and diffracted light is removed. 7. The defect inspection apparatus according to claim 6, wherein the rewritable spatial filter is of an optical rewritable type. 8. The defect inspection apparatus according to claim 6, wherein the rewritable spatial filter is an electronic rewritable spatial filter.