JPH02102404A - Inspecting method for periodic pattern - Google Patents

Abstract

PURPOSE:To detect a defect of an optional periodic pattern without emphasizing the outer peripheral part of the periodic pattern by using an optical system wherein the shear quantity of a common optical path type dual light beam interferometer is equalized to the array pitch of unit patterns. CONSTITUTION:The common optical path type dual light beam interferometer consists of a polarizer 1, Wollaston prisms 2 and 5, lenses 3, 4, and an analyzer 6. Then linear polarized light passed through the polarizer 1 becomes two light beams which shift by SP at right angles to the optical axis through the prism 2 and lens 3 and the intensity distribution is varied by a sample 7 which has periodic openings. Then only the SP is returned by the lens 4 and prism 5 to cause interference on the analyzer 6. Then if the sample 7 has no defect, the light beam of interference 2 becomes equal in pitch with the shear quantity SP, so the phase and intensity are equal and the polarizer 1 and analyzer 6 are in orthogonal relation, so that the light beams cancel each other and become dark. If the sample has a defect 8 or it there is a transparent material 9 at an opening part, the light beams do not cancel each other completely and a bright point is observed.

Description

Detailed Description of the Invention [Industrial Field of Application] The present invention relates to shadow masks used in cathode ray tubes for color televisions, color separation filters for color explosion devices, color filters for liquid crystal display panels, and mesh-like filters used in electron tubes. Electric scraper, ■DT filter, mesh filter for filtration equipment, rotary encoder, linear encoder, IC
Industrial products in which units (hereinafter referred to as unit patterns) with certain optical properties and shapes are regularly and repeatedly arranged in one-dimensional or two-dimensional directions, such as photomasks, or unit patterns have certain optical properties and shapes. and one-dimensional direction, 2
It can be used to detect defects such as scratches, pinholes, sunspots, dust, and uneven transmittance of industrial products, which are repeatedly arranged with a gradually changing pitch in the dimensional direction, as well as unpatterned glass, colored films, etc. The present invention relates to a method for automatically inspecting periodic patterns.

[Traditional techniques, techniques]

Conventionally, defect inspections of industrial products in which unit patterns are periodically and repeatedly arranged are usually carried out by visual or microscopic observation, but such methods require a large amount of time to inspect a large number of products. Various testing methods have been proposed because it requires a lot of manpower and lacks test accuracy and reliability since it is a sensory test.

For example, for industrial products with periodic patterns arranged at equal pitches, pattern recognition may be performed by examining a video signal obtained by a microscope imaging device that sufficiently resolves the arrangement unit and the shape of the defect. Defects are detected by means such as comparing with signals obtained by similarly photographing patterns without defects.

Next, conventionally proposed methods for inspecting periodic patterns efficiently and with high accuracy will be explained with reference to FIGS. 4 to 6.

In order to detect an abnormality in the aperture area of a pattern with periodic apertures as a unit pattern 51 as shown in FIG. The pattern to be inspected 46 is
is illuminated, and the inspection area is photographed with a TV camera 41. The image processing device 42 A/D converts the output signal of the T''V camera into digital image data, and performs various image processing including addition and subtraction on the screen at high speed using a frame memory and an arithmetic unit.Control device 43 moves the pattern by controlling the image processing device 42 and a pattern moving mechanism composed of an XY stage 50 and a drive mechanism 45.

In addition, in FIG. 5, 52 and 53 are unit patterns with defects.

In FIG. 4, a video taken by the TV camera 41 (shooting conditions where changes due to the unit aperture of No. 8 can be ignored, for example, the pattern area corresponding to one pixel has a degree aperture 11 of 1041!A)
A case will be described with reference to FIG. 6 in which the direction in which the pattern is moved and displaced is the scanning line direction of the TV camera 41, and the pattern displacement distance is an integral multiple of the pixel pinch.

The light transmission weight distribution on a straight line passing through a defective part of the pattern is as shown in FIG. 6(a), for example, and 53 in FIG.
A change in light transmittance 54 due to a defect such as 5 in which the opening area is larger than the normal pattern 51, that is, a white defect, or a pattern 51 in which the opening area is normal as shown in 52 in FIG.
Change in light transmittance due to defects smaller than 5, that is, black defects
5 is detected. In addition, when the video signal is scanned on the same line as in the case of Fig. 6 (a), it becomes as shown in Fig. 6 (b), and the gradual signal change (shading) due to uneven illumination of the pattern, uneven sensitivity of the imaging surface, etc. ), random noise generated in the video signal processing device, and local changes 56 in the signal due to dust adhering to the optical system.

By adding multiple frames of such video signals, the ratio of random noise components can be reduced to 115, where the number of additions is N (Figure 6 (C)).
), then when the pattern is displaced and similar screen addition processing is performed, as shown in FIG. 6(d), the signal due to the defect on the pattern also moves as the pattern moves.
Signal 5 due to shading in the imaging system, dust in the optical system, etc.
The position of 6 has not changed, so if we subtract the data shown in Figure 6(d) from the data shown in Figure 6(c), we get
Signals 56 due to shading, dust, etc. included in both data are erased, and only signals due to changes in light transmittance of the pattern and reduced random noise components remain. As a result, signals due to defects are transmitted to pixels according to the amount of movement of the pattern. At several positions apart, the difference in value from the average value in the vicinity is almost the same, and the sign appears reversed, and the order of reversal depends on the type of defect (
(white defects, black defects).

In the image data processed as above, the brightness changes locally only in the defective area, so it can be easily recognized as a defect by observing it on a monitor, and the brightness of the defective area relative to its surroundings can be easily recognized as a defect. The type of defect can also be identified by the order of inversion.

Next, a conventional method for inspecting periodic patterns of color separation filters will be described.

FIG. 7 is a diagram showing an example of a color separation filter, and FIG. 8 is a diagram for explaining a method of inspecting a periodic pattern of a conventional color separation filter.

As a color separation filter, for example, as shown in FIG. 7, a stripe-like (FIG. 7(a)) or dot-like filter having color tones of R, GXB, Y, M, C, etc. is formed on a transparent substrate such as glass. This is a filter having a pattern in which minute elements shown in FIGS. 7(b) and 7(c) are periodically arranged one-dimensionally or two-dimensionally as a unit pattern.

In the eighth time, the emitted light from the lamp 61 is transmitted to the lens 62.
The light that is focused on the pinhole plate 63 and passed through the pinhole is turned into parallel light by the lens 64, and illuminates the color separation filter 65. The parallel light transmitted through the color separation filter 65 is diffracted by the periodic pattern of the color separation filter, forming a diffraction pattern on the back focal plane of the objective lens 66.

The parallel light transmitted through the normal pattern part is blocked by the spatial filter 67 having a light blocking part corresponding to this diffraction pattern, whereas the defective part goes against the periodicity of the pattern and has the effect of scattering light. Therefore, it passes through the spatial filter 67 and is imaged. Therefore, when observed through the eyepiece lens 68, only the defective portion is observed as a bright spot in the dark field, and the defect can be detected.

[Problem to be solved by the invention]

However, the conventional defect detection methods shown in FIGS. 4 to 6 require high-precision imaging devices and detection circuits, which makes the devices expensive, and the method shown in FIG. However, since the outer periphery of the periodic pattern portion is emphasized, it becomes difficult to detect defects near the outer periphery, and there are also drawbacks such as the need to prepare a spatial filter vacuum for each filter pattern.

The present invention is intended to solve the above-mentioned problems, and has an hour wheel configuration, does not emphasize the outer periphery of the periodic pattern part, and has periodicity that allows detection of defects in any periodic pattern. The purpose is to provide a pattern inspection method.

[Means to solve the problem]

To this end, the present invention provides a method for inspecting defects in a periodic pattern in which unit patterns are periodically and repeatedly arranged, in which the share of the common optical path type two-beam interferometer is made to match the arrangement pinch of the degree pattern or an integral multiple thereof. The present invention is characterized in that the inspection is carried out based on images obtained by an optical system, that the interference section is a polarization type common optical path beam interferometer, and that an interferometer whose shear amount can be changed is used.

[Effect]

The present invention makes the shear amount of the common optical path type two-beam interferometer match the arrangement pitch of the unit pattern of the sample or an integral multiple thereof, and makes the transmitted light or reflected light of the sample interfere, and the light beam is emitted at two corresponding points on the sample. Defects are detected by detecting bright spots obtained when there is a difference in intensity or phase between the defects, and the sample or device can be detected while in a stationary state. Since the light rays cancel each other out, the periphery of the pattern is not emphasized, and by making the shear amount variable, it is possible to inspect any periodic pattern.

〔Example] Examples will be described below based on the drawings.

FIG. 1 is a diagram showing an embodiment of the periodic pattern inspection method of the present invention, in which 1 is a polarizer, 2.5 is a Wollaston prism, 3.4 is a lens, 6 is an analyzer, and 7 is a subject. An inspection pattern, 8 is a defect, and 9 is a phase material.

In FIG. 1(a), a polarizer 1, a Wollaston prism 2, a lens 3.4, a Wollaston prism 5, and an analyzer 6 constitute a polarization type common optical path two-beam interferometer. Note that for convenience of explanation, the light source is assumed to be a monochromatic light source.

Parallel light from a light source (not shown) is irradiated, and linearly polarized light 8 obtained through the polarizer 1 is irradiated onto the Wollaston prism 2. The Wollaston prism 2 is made by laminating two model birefringent crystal plates 2a and 2b with optical axes parallel to the plane of incidence, and the incident light on the crystal plate 2b is oriented with respect to the optical axis of the crystal plate 2b. For example, the light is incident at an angle of 45°. As a result, it is divided into extraordinary rays with a plane of polarization parallel to the main cross section and ordinary rays with a plane of polarization perpendicular to the main cross section.
The beam is emitted at an angle of θ in the direction of travel. The two light beams are parallel to each other and pass through the test gold repeating pattern 7 with a shear (lateral shift) of MtSp by the lens 3 whose front focal point is the intersection point of the two light beams. In this case, the share amount SP is set to be the same as the repeating pitch of the pattern or an integral multiple thereof. Then, the two light beams whose intensity and phase distribution have been changed by the pattern 7 are focused by the lens 4.

As it is, the traveling directions of the two rays are different, so the lens 4
A Wollaston prism 5 similar to the Wollaston prism 2 placed at the rear focal position matches the traveling direction, and an analyzer 6 whose plane of polarization is orthogonal to the polarizer l separates the components of the two light beams polarized in the same plane. Take it out and let the two interfere.

Next, to explain the state of each part of the two light beams with reference to FIG. They become two light beams, the intensity distribution of which is changed by the sample 7 with a periodic aperture, and only SP is returned to its original state by the lens 4 and the Wollaston prism 5, and then the analyzer 6
This will cause interference. In this case, if there is no defect in the sample, the two interfering beams will have the same phase and intensity because the shear ff1sp and the repetition pitch are the same, and since the analyzer and the polarizer are arranged orthogonally, the two will cancel out. It becomes dark. On the other hand, if there is a light-shielding defect 8 or a pinhole in the light-shielding part, even if the phases match, the amplitude of the light will be different, so it will not be completely erased, and if there is a transparent substance 9 in the opening, Even if the amplitudes match, the phases change, so they are not erased in the same way and are observed as bright spots.

The amount of shear is determined by the separation angle θ of the Wollaston prism 2 and the focal length of the lens 3.
If a zoom lens is used, the shear amount can be adjusted by changing the focal length of the lens, and it is possible to accommodate samples with various array pitches.

Further, in the above embodiment, a transmission type in which the sample is transparent has been described, but the sample may be opaque, and in that case, a reflection type differential interferometer is used as shown in FIG.

FIG. 2 is a diagram showing another embodiment of the present invention using a reflective differential interferometer, in which 21 is a condenser lens, 22 is a polarizer, 23 is a half mirror, 124 is a Nomarski prism, and 25 is an objective lens. , 26 is a sample, 27 is an analyzer,
The 2nd is an ordinary ray, and the 29th is an extraordinary ray.

In this embodiment, when light from a monochromatic light source (not shown) is linearly polarized through a condenser lens 21 and a polarizer 22, reflected by a half mirror 23, and incident on a Nomarski prism, two ordinary rays 2 and an extraordinary ray 29 are generated. Two linearly polarized lights are obtained. When the rear focus of the objective lens 25 is made to coincide with the point where the two linearly polarized lights intersect, two beams of light that are coherent and whose polarization planes are perpendicular to each other are incident on the sample surface. After being reflected by the sample surface, the light enters the Nomarski prism again and generally exits the prism as elliptically polarized light. When this is passed through a half mirror 23 to an analyzer 27 which is perpendicular to the polarizer 22, the same polarized light components are taken out and interfered with. If there is an optical path difference due to unevenness on the sample surface, it is detected as a bright spot as in the case of Fig. 1. can do. It goes without saying that the polarizing prism may be a Wollaston prism instead of the Nomarski prism.

In each of the above embodiments, the light used was explained as monochromatic light for convenience, but the present invention is also possible with white light. In that case, two light beams corresponding to an optical path difference of an integral multiple of the wavelength pass through the analyzer. When these wavelengths cancel each other out, an interference color is obtained by adding the remaining wavelengths. Therefore, changes in spectral intensity can also be detected, and defects in colored periodic patterns can also be inspected.

Furthermore, as a method of obtaining the shear amount of the two light rays, it is also possible to use a Savart plate in which two birefringent materials whose optical axes are orthogonal are bonded together as shown in FIG. In the figure,
31 is a Savard plate, 31a is a first birefringent body, and 31b is a second birefringent body.

In FIG. 3(a), light incident perpendicularly to the surface of the first birefringent body 31a and obliquely to the optical axis becomes two polarized lights perpendicular to each other, that is, an ordinary ray 32 and an extraordinary ray 33.

The ordinary ray 32 travels straight, and the extraordinary ray 33 travels obliquely, contrary to Snell's law. The light that has passed through the first birefringent body 31a enters the second birefringent body 32b, but its optical axis is different from the first birefringent body by 90 degrees, so the ordinary ray 32 is different from the extraordinary ray. 35 and progress diagonally,
The extraordinary ray 33 becomes an ordinary ray 34 and travels straight. As a result, as shown in the figure, there are two completely parallel light rays, and it is also possible to eliminate the optical path difference between the two light rays. In this way, two light beams with a predetermined share amount can be obtained.

In addition, as shown in FIG. 3(b), two Savard plates 36
．． It is also possible to make the shear maximum variable by forming 37 into a model and making both relatively movable in the direction perpendicular to the optical axis.

[Effects of the Invention] As described above, according to the present invention, two-beam interference is performed at the unit pattern arrangement pitch of the periodic pattern or at an integral multiple thereof, so that two-beam interference is performed at two corresponding points on the sample. If there is a difference in the intensity or phase of the light, the brightness will be different from the surroundings due to interference, and defects can be detected by focusing only on the change in brightness. Therefore, the sample or device can be detected while it is in a stationary state. In addition, since the two interfering beams cancel each other except for defective areas, the peripheral areas of the pattern are not emphasized, and by making the shear amount variable, any pattern can be inspected. becomes possible. If the illumination light is not monochromatic light, changes in spectral intensity can also be detected, making it possible to inspect defects in colored periodic patterns.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing one embodiment of the periodic pattern inspection method of the present invention, FIG. 2 is a diagram showing another embodiment of the present invention, and FIG.
The figure shows the configuration of the Savard plate, Figure 4 is a diagram to explain the conventional periodic pattern inspection method, Figure 5 is a diagram to explain the periodic pattern and its defects, and Figure 6 is a diagram to explain the conventional periodic pattern inspection method. FIG. 7 is a diagram for explaining a conventional defect detection method, FIG. 7 is a diagram showing an example of a color separation filter, and FIG. 8 is a diagram for explaining a conventional defect detection method for a color separation filter. 1... Polarizer, 2.5... Wollaston prism, 3.4... Lens, 6... Analyzer, 7...
・Pattern to be inspected. Figure 4 Applicant

Claims (4)

[Claims] (1) In a method for inspecting defects in a periodic pattern in which unit patterns are periodically and repeatedly arranged, an optical system in which the shear amount of a common optical path type two-beam interferometer is made to match the arrangement pitch of the unit patterns or an integral multiple thereof A method for inspecting a periodic pattern, characterized in that inspection is performed based on an image obtained by. (2) The method for inspecting a periodic pattern according to claim 1, wherein the interference section is a polarization type common optical path two-beam interferometer. (3) Claim 1 using an interferometer whose shear amount can be changed
Method for inspecting the periodicity pattern described. (4) The periodic pattern inspection method according to claim 1, wherein a white light source is used as the light source.