JPH0266433A - Defect detecting machine - Google Patents

Abstract

PURPOSE:To accurately detect a defective part by converting light from a light source into parallel beams, converting the parallel beams into polarized beams through a polarizer, irradiating an object to be inspected through a polarized beam splitter, and inputting reflected light into a solid image pickup element. CONSTITUTION:Light from a light source 10 is converted into parallel beams by a collimeter lens 13 through a flexible light guide 11 and a condensor lens 12 and converted into polarized beams by a polarizer 14. The polarized beams are reflected by a polarized beam splitter 16 and an object 19 to be inspected is irradiated with the reflected beams through a 1/4 wavelength plate 15. The polarized beams reflected by the object 9 are straight transmitted through the 1/4 wavelength plate 15 and the beam splitter 16 and then inputted to an analyzer 17. The analyzer 17 transmits only positive reflected light obtained from a normal part, interrupts irregular reflection light from a defective part and inputs the transmitted light to the solid image pickup element 2 through an acromat lens 18 to execute image processing. Consequently, a fine defect can be accurately detected, the movement of the light source can be omitted by a flexible light guide and the device can be simplified.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a defect detector particularly effective for detecting defects in a transparent substrate, particularly in a transparent film formed over one surface of the transparent substrate.

[Prior Art] Conventionally, defect detectors for the surfaces of semiconductor wafers, photomasks, glass disks, etc. are widely known. For example, as a typical example, as shown in FIG. 4, a laser beam 41 is irradiated onto a spinal surface 42 to be examined, and specularly reflected light 43 from the spinal surface 42 to be examined is received by a photomultiplier tube 44. An optical system (a) that measures a decrease in the amount of light received due to scattering at a defect and detects the presence or absence of a defect, or an optical system (b) that detects the presence of a defect by receiving scattered light 45 scattered by the defect. The equipment used is known. Further, as shown in FIG. 5, the transmitted light (c) or reflected light (d) from the light source 51 is received by the CCD camera 52, and the amount of decrease in the transmitted light (c) or reflected light (d) due to the defect is detected. There is a known device that detects the presence or absence of a defect by doing this.

[Problem to be solved by the invention] However, if the defect to be detected is one in which the direction of reflected light cannot be determined uniquely or has a reflectance that is not very different from that of a normal part, If the defect is in a transparent film formed on a substrate, it is possible to perform accurate inspection using a defect detector that simply detects the difference in reflected or transmitted light as described above. was not possible.

[Means for Solving the Problems] The present invention has been made to solve the above-mentioned problems, and includes a light source, a light guide that guides the light emitted from the light source, and a collimator that directs the light emitted from the light guide. A condenser lens that focuses light on the focal point of the lens, a collimator lens that converts the light that has passed through the condenser lens into one destination, a polarizer that converts the parallel light into polarized light, and a polarizer that reflects the polarized light to a 174-wave plate. , and a polarizing beam splitter that transmits the light that has passed through the 174-wave plate; the polarized light reflected by the polarizing beam splitter is directed to the surface of the object to be inspected; and the specularly reflected light from the surface of the object to be inspected is converted into a polarized beam. A 174 wavelength plate that transmits a phase change equivalent to 174 wavelengths to the splitter, an analyzer that transmits only a predetermined polarized light of the light that has passed through the polarizing beam splitter, and a polarized light that has passed through the analyzer. An optical system consisting of an achromatic lens that focuses light on a light receiving surface of a solid-state image sensor, a solid-state image sensor that captures light incident from the optical system and photoelectrically converts it, and converts the output from the solid-state image sensor into color gradation, The present invention provides a defect detector characterized by having an image processing device that then performs binarization.

Hereinafter, the optical system in the defect detector of the present invention will be explained using FIG. 1, following the optical path of the light emitted from the light source.

The light source 10 of the present invention is not particularly limited, and mercury lamps, fluorescent lamps, white light, lasers, etc. can be used, but halogen lamps are preferred for reasons of safety, equipment cost, ease of handling, etc. preferable.

The light emitted from the light source 10 is guided by a flexible light guide 11, and the light emitted from the light guide 11 is condensed by a condenser lens 12 to the focal point of a collimator lens 13, and then enters the collimator lens 13. The collimator lens 13 converts the light into parallel light. The parallel light is polarized by a polarizer 14, reflected by a polarizing beam splitter 16 at a reflection angle of 45'', transmitted through a 174-wave plate 15, and irradiated perpendicularly onto the surface of the object 9 to be inspected.

The specularly reflected light from the inspected object 9 is a 1/4 wavelength plate! 5. The light passes through the polarizing beam splitter 16 and enters the analyzer 17. Of the light entering the analyzer 17, only predetermined polarized light is transmitted through the analyzer 17, and other light is blocked. The polarized light that has passed through the analyzer 17 is focused by the achromatic lens 18 on the light receiving surface of the solid-state image sensor 2 regardless of the wavelength.

The specularly reflected light from the object to be inspected, which is taken into the solid-state image sensor 2 by the optical system as described above, is photoelectrically converted by the solid-state image sensor 2 and sent to the image processing device 3 as an electrical signal.

In the image processing device 3, the electric signal for each pixel of the solid-state image sensor 2 is converted into a color gradation from light to dark, and is binarized with a predetermined appropriate threshold I11 as the boundary.
The presence or absence of defects on the surface of the object to be inspected is output.

Next, a step-by-step explanation will be given of the process from when the object to be inspected is carried into the defect detector of the present invention until it is inspected for the presence or absence of defects and is carried out. (See FIG. 2) First, the object 9 to be inspected is carried in and positioned by the X controller 6 at a predetermined point on a straight line including the moving direction of the object 9 to be inspected.

Next, the optical system 1 including everything from the light guide to the solid-state image sensor is positioned by the XY controller 5 at a predetermined X and Y coordinate point on the upper surface of a section of the object to be inspected 9 . Therefore, the specularly reflected light from the object to be inspected 9 is taken into the solid-state image sensor, and is sent as an electrical signal to the image processing device 3, and is sent to the image processing device 3 for each microsection of the object to be inspected corresponding to each pixel of the solid-state image sensor. The presence or absence of defects is output to the monitor 4.

An optical system 1 including a light guide to a solid-state image sensor is caused to scan in the XY direction by an XY controller 5, and the entire surface of the object 9 to be inspected is inspected.

All test results are displayed on monitor 4.

After the inspection of the entire surface of the object to be inspected 9 is completed, the object to be inspected is carried out.

The above operating procedure is displayed on the CRT 8, and even beginners can easily input commands into the host computer 7 and operate it. The host computer 7 supervises the above-mentioned testing procedure.

In the host computer, the size of the defect is determined by combining the adjacent parts of the micro-sections of the object to be inspected 9 that have been determined to have defects, and an NG judgment is made based on the size of the defect for each object to be inspected. It is also possible to make an NG judgment based on the number of defects. In this case, the inspection ends when an NG determination is made.

The type of light source and the type of solid-state image sensor in the present invention are selected in consideration of the absorption wavelength characteristics of the object to be inspected.

[Operation] The present invention is characterized in that defects are detected using polarized light.

The optical system of the present invention irradiates the surface of the object to be inspected 9 with polarized light,
It is designed to take advantage of changes in the polarization state of reflected light. That is, some of the light irradiated onto the defective area is scattered, but some of it returns to the light receiving section of the solid-state image sensor or the like as specularly reflected light, similar to the light reflected from the normal area. In the present invention, in order to avoid misidentifying such light as reflected light from a normal area, the reflected light from a normal area is distinguished from the reflected light from a defect based on the difference in polarization state. Specifically, the analyzer 17 blocks light with a polarization state different from that from the normal area, thereby avoiding confusion between the specularly reflected light from the defect and the specularly reflected light from the normal area. By doing this, a very accurate inspection is possible, unlike the conventional method of simply inspecting the amount of light reflected from the object to be inspected.

Therefore, in the present invention, defects in which the direction of reflected light cannot be determined uniquely and defects in which the reflectance is not significantly different from the reflectance of a normal region can be detected with great precision. In particular, when detecting defects in a transparent film formed on a transparent substrate, such as a tin-doped indium oxide (ITOI film) formed on a glass substrate, a fluorine- or antimony-doped tin oxide film, etc. Optimal.

Furthermore, in the present invention, since the light entering from the above-mentioned optical system is photoelectrically converted by the solid-state image sensor, even very minute defects can be detected. For example, as shown in FIG. 3, a two-layer coating in which a first layer 32 and a second layer 33 are formed on a substrate 31 is coated with a coating as shown in FIGS. 3(a), (b), and (c). Even if various minute defects X, Y, and Z exist, they can be detected.

In addition, if dust that can be removed by cleaning is attached to a transparent object to be inspected, the light from the dust that would normally pass through will be reflected by the dust, and the amount of reflection will be greater than that of a normal part.
As more light passes through the analyzer, more reflected light enters the solid-state image sensor than in the normal area, and as a result of color gradation conversion, the image may appear darker than in the normal area. By appropriately setting and binarizing, it is possible to detect and display the presence or absence of dust that can be removed by such cleaning, and to distinguish it from defects.

[Example] The performance of the defect detector of the present invention was investigated using a glass substrate on which two transparent conductive films made of tin-doped indium oxide were formed as an object to be inspected. Comparing the results of inspecting the same object with an optical microscope, the defect detector of the present invention detects 100% of defects with a major axis of 100 μm or more, and detects defects with a major axis of 70 μm or more.
It was found that the detection performance was 70% for defects of μm to 00 μm. In addition, dust that can be removed by washing,
80% or more was detectable in a class 1000 clean room.

1 Comparative Example 1] When the same object to be inspected as in the above example was inspected using the defect detection device of the method shown in FIG. It was impossible to determine whether the detected signal was due to defects or noise.

[Ratio f bite example 2] When the same object as in the above example was inspected using the reflection type defect detection device shown in Fig. 5, 70% of the defects had a major diameter of 100 μm or more, and 50% had a major diameter of 70 μm to 100 μm. Only % could be detected. In addition, it has been found that since dust that can be removed by cleaning is detected in the same way as defects, areas where the membrane is actually normal are incorrectly determined as defects.

[Effects] The present invention employs an optical system that uses polarized light to process a single image, making it possible to very accurately distinguish between defective areas and normal areas.Also, since a solid-state imaging device is used, ,
The surface of the object to be inspected can be inspected by dividing it into minute areas, and the position of defects can be accurately determined.

Therefore, when detecting a defect where the difference in reflectance between the normal part and the defect is small and the direction of the reflected light cannot be determined uniquely,
For example, when detecting defects in transparent films formed on transparent substrates, especially defects in transparent conductive films formed on glass substrates, compared to conventional defect detectors that do not use polarized light,
This has the excellent effect of making it possible to obtain very accurate defect detection performance.

In addition, in the present invention, since the light from the light source is guided by a flexible light guide, there is no need to move the light source itself when inspecting the entire surface of the non-inspection object 9.
, the equipment becomes simple, and dust generation can be prevented as much as possible.

[Brief explanation of the drawing]

Fig. 1 is a configuration diagram of the optical system (1 in Fig. 2) in the defect detector of the present invention, Fig. 2 is an explanatory diagram showing the interconnection of each device of the defect detector of the present invention, and Fig. 3 is a board FIGS. 4 and 5 are cross-sectional views showing the types of defects that may exist when two layers of films are formed on top, and are schematic illustrations of a conventional defect detector. 1...Optical system 2...Solid-state image sensor 3...Image processing device 4...Hydrogen 5...XY controller 6...-X controller 7...Host computer 8...CRT 9 ...Object to be inspected 10...Light source ++...Light guide 12...Condenser lens 13...Collimator lens 14...Polarizer 15...174 Wave plate i6...Polarizing beam splitter 17... Analyzer 18... Achromatic lens 31... Substrate 32... First layer 33... Second layer X, Y, Z... Defect 41... Laser beam 42... Covered Inspection surface 43... Specularly reflected light 44... Photomultiplier tube 45... Scattered light Fig. 4? Figure 4

Claims (1)

[Claims] (1) A light source, a light guide that guides the light emitted from the light source, a condenser lens that focuses the light emitted from the light guide onto the focal point of a collimator lens, and a parallel light that converts the light that has passed through the condenser lens. a polarizer that changes the parallel light into polarized light, a polarizing beam splitter that reflects the polarized light to a quarter-wave plate and transmits the light that has passed through the quarter-wave plate, and A 1/4 wavelength plate that transmits the polarized light reflected by the beam splitter to the surface of the object to be inspected, and specularly reflected light from the surface of the object to be inspected to the polarizing beam splitter with a phase change equivalent to 1/4 wavelength. , an optical system comprising an analyzer that transmits only predetermined polarized light out of the light that has passed through the polarizing beam splitter, and an achromatic lens that focuses the polarized light that has passed through the analyzer onto a light receiving surface of a solid-state image sensor;
a solid-state image sensor that captures light incident from the optical system and converts it into electricity; a solid-state image sensor that converts the output from the solid-state image sensor into color gradation;
1. A defect detector comprising: an image processing device that then performs binarization.