JPS61296243A - Method for inspecting object to be inspected in non-contact state - Google Patents

Abstract

PURPOSE:To enable inspection with good resolving power without limiting a visual field, by applying indirect laser scanning to the image of an object to be inspected through a liquid crystal light valve. CONSTITUTION:The laser beam oscillated from a laser oscillation is controlled in its irradiation angle by a laser X-Y scanning mechanism 12. Said laser beam passes through a polarizer 11 and transmits through a half mirror 9 while the luminous flux thereof is converged by a condensing lens 10 to irradiate the optical image on a liquid crystal 5b at every coordinates. Subsequently, the laser beam issued to the liquid crystal 5b is reflected to the direction at a right angle to an advance path, for example, by the mirror 9 and subsequently passes through an analyser 8 to be incident to a beam receiving part 7. If the quantity of this laser beam is measured, the polarizing state in the liquid crystal 5b can be analyzed and the optical state thereof can be further specified. The information of laser beam incident to the light receiving part 7 is converted to an electric signal which is, in turn, outputted to an image processor 6 to receive digital processing. By this method, the flaw area on the surface of an object to be inspected can be inspected.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for non-contact testing of a specimen, and more particularly to a method for non-contact testing of the surface properties of any specimen or the internal properties of a translucent specimen.

Conventionally, when inspecting circuits such as printed circuit boards, ICs, and LSI chips, the subject is imaged using an image pickup tube or a fixed image sensor, and then the shape of the subject displayed on a display is visually inspected. The surface texture was inspected by obtaining image information corresponding to the shape and analyzing it using a computer, but since the structure of the inspection part of IC and LSI chips is extremely precise, it is difficult to optically examine the shape of the object to be inspected. It was necessary to enlarge the image. However, with conventional image pickup tubes, there is a limit to the field of view that can be imaged at one time due to its resolution dependence, so the only way to do so is to divide the surface of the subject into pieces of a size that can be imaged and inspect them one by one.

For example, the number of scanning lines in conventional image pickup tubes used for surface inspection is usually 525 or less, and even high-resolution models have 1,200 or less, whereas in order to identify the circuits of ICs and LSI chips, the number of scanning lines is at least 0. A resolution of about 5 μm/pixel is required. In order to achieve this resolution, conventionally the subject image was optically magnified using a lens and input into the image pickup tube, but in that case, the field of view that could be captured at one time was 0.2
It will be narrow, about 5 mm square, for example 4 mm x 5
If you want to conduct a circuit inspection on the entire surface of an LSI measuring approximately mm square, it is necessary to divide the enlarged surface image of the object into pieces that fit within the field of view of the image pickup tube, and then move the image tube or the object to a predetermined position. It was necessary to repeat the process several hundred times. Furthermore, in order to recognize the entire image, a complicated processing step is required to reunite the image information obtained by dividing, making surface inspection a time-consuming and complicated task. Conversely, if the magnification of the optical system lens is adjusted so that the entire surface of the object to be inspected can be imaged at once, the resolution will drop and it will become impossible to identify fine details, making it impossible to expect high-precision surface inspection. This method was extremely unsatisfactory as a chip circuit inspection method.

The present invention was conceived in view of the above situation, and by projecting the image of the subject on a liquid crystal light valve for inspection,
For example, the purpose is to provide an inspection method that can perform inspections on the surface properties of arbitrary specimens, internal properties of translucent specimens, etc. over a wide range and with high resolution. By projecting an image of the image onto a photoconductive layer of a liquid crystal light valve, which is a light modulation element, and scanning the optical image of the liquid crystal formed corresponding to the projected image with a laser, an electric signal corresponding to the projected image is obtained. It is characterized by the following.

Hereinafter, the main structure of the present invention will be explained with reference to the simplified conceptual diagram shown in FIG.

B in the figure is a reflective liquid crystal light valve, and the photoconductive layer B
1. It is mainly constructed by polymerizing liquid crystal B3 via a light reflective layer B2, and is used with a voltage applied in series to photoconductive layer B1 and liquid crystal B3. A writing light source E and a subject A are arranged in front of the photoconductive layer B1 on the left side of the figure, and a projection lens F of an optical system is arranged between the subject A and the liquid crystal light valve 8, and is illuminated by the writing light source E. The projected image of the subject A is displayed on the photoconductive layer Bl at the same magnification or magnification.
The image is formed in a reduced size.

On the other hand, behind the liquid crystal B3 on the right side of the figure, a laser oscillation/control mechanism is arranged as a reading light source via a half mirror G, and a light receiving/image processing mechanism C is provided. Changes in the optical state of the liquid crystal B3 are read by receiving and image-processing the reading light that is oscillated and reflected by the liquid crystal B3. Note that as a writing light source, it is advantageous to use ultraviolet light with a short wavelength to improve resolution, and the photoconductive layer B1
As the material, zinc sulfide, cadmium sulfide, cadmium selenide, amorphous silicon, polyvinylcarbazole, etc. can be used arbitrarily, but it is preferable to use zinc sulfide, which is highly sensitive to ultraviolet rays, especially when ultraviolet rays are used as the writing light. It is something.

Next, the operation of the above configuration will be explained. For example, the image on the object illuminated by the writing light source E is the projection lens F.
The light enters the liquid crystal light valve B after being magnified or enlarged/reduced, and is imaged on the photoconductive layer B1, but since the impedance of the photoconductive layer B1 changes in accordance with the intensity of the light at each coordinate, The optical pattern projected onto the photoconductive layer B1 is converted into a charge pattern and immediately transmitted to the liquid crystal B3. The charge pattern transmitted to the liquid crystal B3 changes the optical state of the liquid crystal B3 due to the electro-optic effect, and when reading light is irradiated, the image of the subject is detected as its intensity distribution. Therefore, for example, if the polarization direction of the reading light incident on the liquid crystal is defined in advance by a polarizer, and the reading light after passing through the liquid crystal is measured via an analyzer arranged in an appropriate polarization relationship with the polarizer, the polarization direction of the liquid crystal B3 can be measured. The optical state can now be determined. The accuracy of the optical image of the subject formed on the liquid crystal B3 in this way depends on the resolution of the liquid crystal light valve, but even with the current technology it is 501 p/mm.
It is already possible to produce a device with a size of about 200 mm x 200 mm, so it is fully expected that about 10,000 x lO,000 pixels can be obtained on one light receiving surface. This number of pixels is much larger than the 480 x 512 pixels of a conventional standard image pickup tube.For example, if the resolution is the same as that of a conventional image pickup tube, you can view an area hundreds of times larger at once. On the other hand, if the field of view is limited, it is possible to achieve a resolution 2 to 30 times that of the conventional method, and it is understood that inspection of the object can be performed with high accuracy and a wide field of view. The optical image formed on the liquid crystal B3 is irradiated to each coordinate unit via the half mirror G by a laser beam whose polarization direction is defined by a polarizer and whose traveling direction is controlled by an appropriate mechanism.
The laser beam incident on the liquid crystal B3 is polarized according to the optical state of the liquid crystal B3, and then reflected by the light reflection NB2 and exits from the liquid crystal.

The laser light that exits the liquid crystal goes straight, for example, following the same return path as the outgoing path, and after being reflected by the half mirror G, it enters the light receiving and image processing mechanism via an analyzer and is analyzed. be. As described above, by scanning all the coordinates with a laser beam, an electrical signal corresponding to the optical state of each coordinate of the liquid crystal can be obtained, and after digitally processing the obtained electrical signal, it is analyzed by a computer etc. This means that the surface condition of the object can be accurately inspected. Laser light has excellent directivity, high resolution, and scanning operations can be easily realized by controlling mirrors, etc., so that highly accurate image information that accurately corresponds to the optical image on the liquid crystal B3 can be obtained.

Figure 2 is a simplified conceptual diagram when a transmission type liquid crystal light valve is used. Light is received on the left side of the center. In this case, it is essential that the reading light does not rewrite the projected image of the subject projected onto the photoconductive layer B1, and therefore the reading light has no sensitivity to zinc sulfide, which is the material of the photoconductive layer B1. It is preferred to use light, for example a visible laser such as a helium ion laser. In addition, in the transmission type, it is easy to select whether the optical image obtained is a positive image or a negative image by appropriately adjusting the arrangement angle of the polarizer and analyzer. Various applications are being considered, such as placing a standard light image in an appropriate location to form a comparison, and then optically polymerizing the two in a positive/negative relationship, making the differences between the two optically obvious. It will be done.

Next, details of the present invention will be explained based on illustrated embodiments. FIG. 3 is a schematic diagram of a surface inspection method using a reflective liquid crystal light valve. With the liquid crystal light valve 5 in the center of the figure, the projection lens 2 and the subject 1 are arranged side by side in a straight line through a half mirror 4 on the left side in the figure, that is, in front of the photoconductive layer 5a, and writing is performed close to the straight line. light 1f
iX3 is arranged so that the illumination light reflected by the half mirror 4 can illuminate the subject l. On the other hand, on the right side in the figure, that is, behind the liquid crystal 5b, a laser oscillator 13 as a reading light source is preceded by a laser X-Y scanning mechanism 12, a polarizer 11, and a condensing lens 10, arranged so that the optical path thereof is a straight line. The half mirror 9 is provided so that the laser beam transmitted through the half mirror 9 can irradiate an optical image of the liquid crystal 5b in each coordinate unit. Also liquid crystal 5
An analyzer is placed in front of the analyzer at a position where it can receive the reflected light from the laser beam, and a light receiving section using a highly sensitive photomultiplier tube that can respond quickly to the wavelength of the laser beam is installed. Furthermore, the light receiving section is connected to an image processing device that digitally processes the electrical signals output from the light receiving section and then executes various processes.

Next, the operating mode in this embodiment will be described.

A subject 1, such as a tC chip or a 7° lint substrate, placed at a predetermined position is irradiated with, for example, ultraviolet light emitted from a writing light source 3, and a projected image of its surface is formed on a photoconductive layer Sa. Depending on the size of the subject and the content of the test, it is appropriate to select whether this projected image is a same-size image of the subject 1, an enlarged image, or a reduced image.For example, by adjusting the projection lens 2, a printed circuit board with a low magnification year,
In IC and LSI chips, the photoconductive layer 5 is
It is sufficient to project it onto a. As mentioned above, the number of pixels of the liquid crystal light valve is 1oooo xi even with the current technology.

Since OOO pixels can be realized, even if the image of the object to be examined is enlarged and projected, the image of the object to be examined usually does not deviate from the field of view of the liquid crystal light valve, and the image of the object to be examined is collectively projected onto the photoconductive layer 5a.
It can be projected onto the surface. When the image of the object 1 is projected onto the photoconductive layer 5a, an optical image corresponding to the projected image is formed on the liquid crystal 5b due to the electro-optic effect, and the surface of the object 1 can be inspected by laser scanning the optical image. Although it is possible to scan the optical image on the liquid crystal 5b indirectly, the following method is used to scan the optical image on the liquid crystal 5b. For example, a laser beam such as a helium neon laser oscillated by a laser oscillator 13 has its irradiation angle controlled by a laser X-Y scanning mechanism 12, passes through a polarizer to become linearly polarized light, and is converged by a condensing lens. After passing through half mirror 9,
An optical image on the liquid crystal 5b is irradiated for each coordinate. LCD 5b
The incident laser light is optically modulated in accordance with the optical state of each part of the liquid crystal, and then reflected by the light reflection layer and exits the liquid crystal 5b, for example, through the same path as the forward path in the opposite direction.

The laser beam emitted to the liquid crystal 5b is reflected by the half mirror 9, for example, in a direction perpendicular to its path, and then passes through the analyzer 8 and enters the light receiving section 7. Since the analyzer 8 is arranged in a unique relationship with the polarizer 11, the polarization state within the liquid crystal 5b can be analyzed by measuring the amount of laser light that passes through the analyzer 8 and enters the light receiving section 7. Furthermore, the optical state of the liquid crystal 5b can be specified. Information on the laser light incident on the light receiving unit 7 is converted into an electrical signal and output to the image processing device 6 connected to the subsequent stage, where it is digitally processed to detect, for example, defects or stains on the surface of the object. It is possible. Although not shown, if the object to be inspected is a translucent material, the writing light source 3 is moved to the left side in the figure to illuminate the object from behind, and the transmitted light that has passed through the object is used to illuminate the photoconductive layer 5a. If a projected image is formed on the top, the projected image becomes a two-dimensional representation of the internal properties of the subject, so the optical image appearing on the liquid crystal 5b corresponding to the projected image is analyzed by appropriate means. This makes it possible to inspect the internal properties of a translucent specimen, such as detecting scratches inside glass or impurities in an aqueous solution. In addition, if all or part of the image processing process is managed on software and the software can be replaced as appropriate, it will be possible to handle various inspections by replacing the software, and IC
It can be expected to be applicable not only to inspections such as circuit inspections and LSI chip inspections, but also to a wide variety of inspections such as inspection of printed matter and identification of specific objects on objects. Also, although not shown,
Furthermore, a method may be arbitrarily adopted in which the necessary parts of the above-mentioned apparatus sections of the set are installed side by side and compared with the image information obtained from the subject to detect differences between the two.

FIG. 4 shows an embodiment using a transmissive liquid crystal light valve, and the difference from FIG. 3 is the reading position of the laser beam. In this embodiment, after the laser beam is incident on the liquid crystal 5b, it is polarized according to the optical state of the liquid crystal 5b, and travels straight, passing through the photoconductive Nb3 and exiting the liquid crystal light valve. Therefore, the half mirror 9 for reflecting and guiding the laser beam to the light receiving section 7 is disposed between the liquid crystal light valve 5 and the half mirror 4 for reflecting and guiding the writing light. Since the same optical path is taken between -9 and 9, it is desirable that the photoconductive layer 5a has sensitivity to laser light, and that the light receiving section 7 has no sensitivity to writing light. Although there are many other possible arrangements for both reflective and transmissive devices, it is possible to write the shape of the object on the liquid crystal light valve and read the corresponding optical image formed on the liquid crystal using laser scanning. If possible, the number, arrangement, and type of various lenses, polarizers, analyzers, devices, writing light sources, and reading light sources may be arbitrarily adopted.

According to the present invention, by indirect laser scanning of the object image using a liquid crystal light valve, inspection of the object with good resolution, which was difficult with conventional image pickup tubes and solid-state image sensors, is possible due to the limited field of view. This is easily possible without having to do so.

In addition, since laser scanning is performed continuously and at high speed by operating mirrors, there is no need to mechanically move the positional relationship between the image pickup tube and the subject as in the past, and the inspection time can be significantly shortened. Furthermore, by analyzing and processing the obtained electrical signals using a computer or the like, real-time inspection becomes possible depending on the inspection content. In addition, since the inspection method is non-contact, the image of the subject can be projected onto the photoconductive layer, and the subject to be inspected is not limited by the size, shape, or surface condition of the subject. If it is translucent, it is possible to inspect not only surface properties but also internal properties, so a wide range of inspections that were previously performed using separate devices due to differences in inspection content and attributes of the test object can now be performed using the same device. It is possible.

[Brief explanation of the drawing]

Fig. 1 is a simplified conceptual diagram of the present invention when a reflective liquid crystal light valve is used, Fig. 2 is a conceptual diagram of the present invention when a transmissive liquid crystal light valve is used, and Fig. 3 is a conceptual diagram of the present invention when a transmissive liquid crystal light valve is used. 4 shows an example in which a reflective liquid crystal light valve is used, and FIG. 4 shows an example in which a transmissive liquid crystal light valve is used. A: Object, B: Liquid crystal light valve, B1: Photoconductive layer, Bl light reflective layer, B3: Liquid crystal, C: Light reception/image processing mechanism, D=Laser oscillation/control mechanism, E: Writing light source, F: Projection Lens, G: half mirror, 1: object, 2: projection lens, 3: writing light source, 4: half mirror, 5: liquid crystal light valve, 5a: photoconductive layer, 5b: liquid crystal, 6: image processing mechanism, 7 : Light receiving section, 8; Analyzer, 9: Half mirror, IO: Condensing lens, 11: Polarizer, 12: Laser X-Y scanning mechanism, 13: Laser oscillator. Patent applicant Duck Engineering Co., Ltd. Figure 3 Figure 4 Figure 1 Figure 2 Date

Claims (1)

[Scope of Claims] 1) A non-contact inspection method for a subject, which comprises projecting the subject onto a liquid crystal light valve, scanning the projected image with a laser, and obtaining an electrical signal corresponding to the projected image. 2) A non-contact inspection method for a subject as claimed in claim 1, characterized in that the internal property inspection is performed by illuminating the translucent subject from behind and projecting the transmitted light onto a liquid crystal light valve. . 3) A non-contact inspection method for a test object according to claim 1, wherein the test object is a pattern of a wafer or a printed circuit board on which an IC circuit, an LSI circuit, or the like is drawn. 4) A non-contact inspection method for a subject as claimed in claim 1, characterized in that a reflective type or a transmissive type is used as the liquid crystal light valve. 5) Non-contact testing of a subject according to claim 1, characterized in that zinc sulfide is used as the photoconductive layer of the liquid crystal light valve, ultraviolet rays are used as writing light, and visible light is used as reading light. Inspection method. 6) A method for non-contact inspection of a subject according to claim 1, characterized in that the subject is inspected by comparing a projected image on a liquid crystal light valve with information obtained from a standard product. .