JP3037671B2 - Transparent substrate inspection method and transparent substrate inspection device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for inspecting a transparent substrate, and more particularly to a method for inspecting a transparent substrate in which the appearance of transparent substrates having the same cross section and different thicknesses can be inspected in real time by image processing. The present invention relates to a transparent substrate inspection apparatus that can select an optimal observation method according to inspection contents.

[0002]

2. Description of the Related Art As a technique for improving the characteristics of a crystal resonator, beveling (chamfering) the periphery of a flat-plate type crystal blank has been performed. Further, a flat plate type crystal blank is formed into a lens shape by convex processing. In order to perform beveling processing and convex processing, a cylindrical barrel method capable of mass processing is commonly adopted. As shown in FIG. 17, an abrasive g is put in a cylindrical barrel 41 together with a large number of crystal blanks 1 and polishing is performed while rotating the cylindrical barrel 41. Polishing in a relatively short time tends to beveling processing, and polishing in a long time tends to convex processing, but cannot be concluded because various conditions work. In order to improve the characteristics of the crystal unit with good reproducibility, it is necessary to increase the dimensional accuracy of the beveling and the convex by the above-mentioned method so that the crystal unit is symmetrical left and right and up and down.

In the cylindrical barrel method, beveling and convex processing conditions are different depending on the number of quartz substrates to be charged, the type of abrasive, the number of rotations, the temperature, and the like. Even if these conditions are the same, the same beveling state or convex state is always used. Shape is not always obtained. Quartz substrate manufacturers often rely on their own know-how, but the know-how also has uncertain factors, and it does not work well, so it is not always possible to maintain the same beveling and convex dimensional accuracy. At present, elements are also mixed. In order to improve beveling or convex dimensional accuracy, it is necessary to establish an inspection method capable of evaluating the beveling state and convex shape of the quartz crystal blank surface and feeding back the results to beveling processing and convex processing.

[0004] Beveling is performed by making very small scratches and shaving off a part of the surface, so that there is no significant difference from a non-beveled part in ordinary bright-field observation, and the crystal blank surface The beveling state cannot be inspected by visual inspection of an operator or image processing technology. Convex processing is also achieved by shaving off a part of the surface in the same way, but ordinary bright-field observation does not make it possible to grasp the degree of surface polishing. And cannot be inspected with conventional image processing techniques.

For this reason, the conventional beveling inspection or convex finishing inspection is carried out by (1) pen recorder method,
Physical methods such as (2) level measurement and (3) projection have to be relied on.

(1) Pen Recorder Method This is a method in which a quartz blank surface is scanned by a probe and its locus is recorded using a pen recorder, and the surface height of the probe along the scanning direction can be measured. In the case of the convex type, since the stability is poor, fixing to the mounting table with an adhesive is performed.

(2) Level measuring method This method uses a laser height measuring machine. A silver film for reflection is vapor-deposited on the back of a quartz blank, and a laser beam is irradiated on the front of the quartz blank in the radial direction (linear direction). ), And the level on a straight line is measured from the reflected light. According to this, as shown in FIG. 18, the surface height of the crystal blank along the linear direction can be continuously measured, and the state of beveling or convex processing can be known from the surface height. In the figure, the solid line is beveling,
The dashed line indicates the convex. In the case of the convex type, since the stability is poor, fixing to the mounting table with an adhesive is performed.

(3) Projection method Carbon powder (black) is applied to the surface of a quartz blank,
This is a method in which a semi-transparent film or thin paper is pressed thereon, and the carbon powder is transferred to the film or thin paper. The transferred film is enlarged and projected on a screen. Since carbon adheres to the non-beveled part, the beveling state can be visually recognized from the transfer state of the carbon powder. This method is not applicable to convex type.

[0009]

However, the above-mentioned conventional method has the following problems.

(1) Pen Recorder Method Since the accuracy of measuring the height of the polished surface is poor and only data on a straight line obtained by scanning a quartz blank is obtained, beveling or convex inspection cannot be performed on the entire quartz blank. In addition, since the sampling inspection is performed, it takes time for the inspection, and the inspected sample cannot be used. Further, in the case of the convex type, a troublesome operation of fixing with an adhesive is required.

(2) Level Measuring Method The height of the polished surface can be measured with high accuracy, but since only data on a straight line obtained by scanning a quartz blank can be obtained, the entire surface of the quartz blank cannot be subjected to beveling or convex inspection. . If the scanning in the horizontal direction is shifted in the vertical direction, surface data will not be obtained, but missing data corresponding to the vertical pitch width cannot be avoided. Therefore, it becomes difficult to inspect the entire surface of the crystal blank. In addition, since it is necessary to deposit silver on the back surface, the inspection becomes a sampling inspection, which takes a long time, and the inspected sample cannot be used. In the case of the convex type, a troublesome operation of further fixing with an adhesive is required.

(3) Projection method Although inspection can be performed over the entire surface of a quartz blank, it is necessary to extract, transfer, and project, so that a sampling inspection is required, and the inspection takes a very long time. In addition, inspection data cannot be obtained due to visual observation. Inspection of convex processing is not possible.

As described above, any of the methods (1), (2) and (3) cannot be inspected in real time, and it takes time. In addition, since a unified inspection method cannot be established, beveling inspection or standardization of convex processing cannot be performed. In addition, since appropriate data cannot be obtained, feedback cannot be effectively provided to the beveling processing technology or the convex processing technology.

In addition, since the beveling or convex processing is a batch method in which a large amount is processed, the state of beveling or convex processing differs for each crystal blank, and variations occur even in the subsequent etching by an acid treatment. Nevertheless, since the inspection standard has not been determined, it is difficult to determine the allowable range, and there has been a problem that a non-defective product is treated as a defective product or a defective product is made a non-defective product.

By the way, in addition to the beveling inspection, a flaw inspection and an outline (dimension) inspection are also required for the quartz substrate. Recently, it has been proposed that a dark field observation method is effective for these inspections (Japanese Patent No. 282460). Then, when this method was applied to the beveling inspection, it was found that the method was effective even after the beveling process but before the etching, since the minute flaws formed during the beveling process remained on the surface. However, it was found that the dark-field observation method could not be applied because the surface was smoothed after etching and fine scratches disappeared from the surface. In addition, it was found that the method cannot be applied to a convex type quartz substrate having different thicknesses at the center and the periphery. This is because the convex type quartz substrate has a flatter surface than that of the beveling process, and is difficult to detect by the dark field observation method.

An object of the present invention is to provide a method of inspecting a transparent substrate capable of objectively inspecting the state of the transparent substrate by image processing while solving the problems of the prior art.
It is another object of the present invention to provide an apparatus for inspecting a transparent substrate in which an optimum inspection result can be obtained by one unit according to the inspection content.

[0017]

SUMMARY OF THE INVENTION The gist of the present invention is to make it possible to image the finished condition of transparent substrates having different thicknesses by introducing a polarization observation method, and to provide a dark field observation method by a polarization observation method. Then, the finished state of the transparent substrate having a different thickness, which cannot be inspected, can be inspected by image processing.

According to a first aspect of the present invention, light from a light source is polarized by a polarizer to a transparent substrate made of a birefringent medium having the same cross section and different thickness by processing, and the light passed through the transparent substrate is analyzed by an analyzer. By passing light in a polarization state forming a predetermined angle with respect to the polarized light, a phase difference due to a difference in the thickness of the transparent substrate is visualized by polarization interference, and the cross-sectional shape of the transparent substrate is inspected. This is a method for inspecting a transparent substrate. Processing generally includes polishing and etching. On the transparent substrate, besides a crystal resonator and a crystal blank for a filter, a video camera and a DV
A crystal lens for D and the like are included.

In the case where the transparent substrate is processed to have the same cross section and different thickness, it is necessary to inspect the finished state of the processing. Polarized light from a light source is given to the processed transparent substrate, and light in a polarization state that forms a predetermined angle with respect to the polarized light from the light that has passed through the transparent substrate is passed through. A phase difference occurs due to the difference in thickness, and an interference fringe composed of light and dark appears on an image of the transparent substrate, so that the finished state of the transparent substrate can be distinguished from the image.

It is preferable that the inspection of the cross-sectional shape of the transparent substrate is performed based on the shape of an isoluminance line connecting points of equal luminance of interference fringes appearing by visualizing the phase difference.

Further, the thickness of the transparent substrate between interference fringes, which appears by visualizing the phase difference due to the difference in the thickness of the transparent substrate, is determined by the following equation, and the sectional shape of the transparent substrate is determined based on the determined thickness. Preferably, an inspection is performed.

[0022] _{P = (n e -n 0)} t · 2π / λ However lambda: wavelength of the light source n _0: the ordinary refractive index n _e: refractive index of extraordinary ray t: thickness of the transparent substrate P: fringe When the cross-sectional shape of a convex type transparent substrate is inspected, the above-described first invention is particularly useful because a dark field observation method useful for inspecting a flaw cannot be applied.
Also, in the case of inspecting the beveling process of the transparent substrate which is polished and etched by the peripheral portion by the beveling process, the polishing damage disappears when the etching process is performed, so that the inspection cannot be performed by the dark field observation method. Is particularly effective. The transparent substrate is particularly preferable when it is a quartz blank for a quartz oscillator.

According to a second aspect of the present invention, there is provided a polarized light source for irradiating unpolarized light toward the transparent substrate, a polarizer for irradiating the transparent substrate with the polarized light from the polarized light source. An analyzer for detecting light in a polarization state at a predetermined angle transmitted through the transparent substrate; and an image of the transparent substrate of the polarization observation light having passed through the analyzer, and a position due to a difference in thickness of the transparent substrate due to polarization interference. The transparent substrate inspection apparatus includes an imaging unit that visualizes a phase difference, and an image processing unit that performs image processing on an image of the transparent substrate captured by the imaging unit and inspects a cross-sectional shape of the transparent substrate. This allows the above method to be properly implemented with a simple structure,
Equipment costs and maintenance operation costs can be reduced.

According to a third aspect of the present invention, there is provided a polarization observation light source for irradiating unpolarized light toward a transparent substrate, and a light source for diffusing light within an irradiation angle of ± 30 ° vertically with respect to a reference plane of the transparent substrate. A dark-field observation light source for irradiating the scattered light from the entire circumferential side of the transparent substrate, a switch for switchably connecting the polarization observation light source and the dark-field observation light source, and a switch for the polarization observation. A polarizer that irradiates the transparent substrate with irradiation light from a light source instead of polarized light, an analyzer that detects light in a polarized state at a predetermined angle transmitted through the transparent substrate, and a polarization switch that switches to a polarization observation light source with the switch. Insertion / extraction means for inserting the polarizer and the analyzer into an optical path, and for switching the polarizer and the analyzer from the optical path during dark-field observation in which the switch is switched to the dark-field observation light source. And, image the transparent substrate of the polarized observation light that has passed the analyzer, visualize the phase difference due to the difference in the thickness of the transparent substrate due to polarization interference, or the transparent substrate of the dark field observation light that does not pass the analyzer The transparent substrate inspection apparatus includes: an imaging unit that captures an image; and an image processing unit that performs image processing on an image of the transparent substrate captured by the imaging unit to inspect the transparent substrate.

The reference surface of the transparent substrate is defined as a plane passing through the average thickness when the transparent substrate has the same cross section and different thickness, the surface when the plate is flat, and the surface perpendicular to the optical axis when the convex type. It is a horizontal plane that intersects.

When performing a flaw or contour inspection of a transparent substrate or a beveling inspection before etching, a dark field observation method is selected by switching to a dark field observation light source by a switch.
When a transparent substrate having the same cross section and a different thickness is to be inspected or a beveling inspection after etching is performed, the light source is switched to a polarization observation light source, and a polarizer and an analyzer by insertion / extraction means are inserted into an optical path to select a polarization observation method.
As described above, since one inspection apparatus can select an optimum observation method according to the inspection contents, two inspection apparatuses having different observation methods can be used.
Compared to the case where a table is prepared, the structure can be simplified and it is economical.

[0027]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic configuration diagram showing an embodiment in which an inspection apparatus for performing an inspection method of a transparent substrate according to the present invention is applied to a convex type crystal blank for a crystal unit.

The inspection apparatus includes a monochromatic light source 26 having no polarization.
And a diffuser plate 2 for diffusing the light of the light source 26 and irradiating the light uniformly.
3 and a polarizer 21 for polarizing light from the diffusion plate 23
A mounting table 2 on which a quartz blank 1 as a transparent substrate made of a birefringent medium is placed; an analyzer 22 for passing light having a predetermined angle with respect to the polarized light from light passing through the quartz blank 1; It comprises a lens 12, a CCD camera 13 as an image pickup means, and an image processing device 14. Here, as the monochromatic light source 26, a 660 nm red LED having a high luminance and a long life is used.
The polarizer 21, the mounting table 2, the analyzer 22
Are provided rotatably, and after adjusting the rotation angle,
It is configured so that it can be fixed. The shorter the distance between the polarizer 21 and the mounting table 2 and the shorter the distance between the analyzer 22 and the mounting table 2, the better. If necessary, a condenser lens for condensing light on the quartz blank 1 is provided on the diffusion plate 2.
Alternatively, a compensator provided between the analyzer 22 and the mounting table 2 may be provided between the analyzer 3 and the polarizer 21, or a compensator for clearly embossing the crystal blank image from the background.

As shown in FIG. 2, a quartz blank mainly to be inspected by the inspection apparatus is a biconvex convex type having a thinner peripheral portion and a thicker central portion as shown in FIG. 2 (a). In addition to the crystal blank 1 described above, as shown in FIG. 2B, a substantially flat type is wrapped (step 101), and the peripheral portion is polished by beveling (step 1).
02) and further etching (step 10)
3) There is a crystal blank 17 which is beveled and whose entire surface is smooth except for the peripheral portion. For example, in the case of a strip-shaped quartz blank having a beveled shape, the size is usually 1 × 3 mm to 3 × 10 mm and the thickness is about 30 μm to 500 μm. Crystal blank 17
Is not limited to a rectangular shape or a rectangular shape, but may be a circular shape having a diameter of about 4 to 8 mm or other shapes. The shape of the convex type is almost the same.

The image processing device 14 shown in FIG.
An image of the crystal blank 1 captured by the D camera 13 is taken in, features are extracted as in, for example, a binarization process, and processing data is stored or processing finish determination processing is performed based on the extracted features.

The illumination light from the light source 26 is diffused by the diffusion plate 23, is converted into linearly polarized light by passing through the polarizer 21, and is incident on the crystal blank 1 on the mounting table 2. The linearly polarized light incident on the quartz blank 1 is divided into an ordinary ray and an extraordinary ray. Of these transmitted lights, only the polarization components of the ordinary ray and the extraordinary ray whose polarization direction is perpendicular to the irradiation light are extracted, and interference occurs because one of these polarization components has a phase delay with respect to the other. The interference differs depending on the phase difference and the intensity (amplitude). The phase difference is determined by the thickness t and the wavelength λ of the quartz blank 1 (see FIG. 4B), and the intensity is determined by the linear polarization from the polarizer 21 and the quartz blank 1. Is determined by the angle θ formed with the main surface of

For example, the peripheral area becomes a dark area and the central area becomes a light area, and a phase difference due to a difference in thickness is visualized.
Therefore, the light emitted from the analyzer 22 becomes strong and weak interference light due to the strengthening light and the canceling light in the white light. This interference light passes through the objective lens 12 and enters the CCD camera 13. The image of the crystal blank 1 is converted into an electric signal by the CCD camera 13 and transferred to the image processing device 14. The image processing device 14 performs statistical processing so that a dark portion generated in a peripheral portion and a bright portion generated in a central portion can be clearly distinguished. For example, a contrast enhancement process between a dark portion and a bright portion is performed by a binarization process (FIG. 4A). By measuring the dark area or the light area after the processing, the processing finish such as excessive shaving, insufficient shaving or symmetry is inspected.

As the observation method applicable to the inspection of the finished work, other observation methods such as a phase difference observation method, a differential interference observation method, and a modulation contrast observation method can be considered in addition to the polarization observation method described above. The reason for adopting the polarization observation method in the above mode is that the light source may be an LED, and the polarizing filter such as a polarizer or an analyzer may be of such a size that a polarizing film is attached to a glass plate, and is the cheapest and simplest.

FIG. 3A schematically shows an image of the crystal blank 1 obtained by the polarization observation method shown in FIG. The crystal blank 1 is a convex type as described above. Using monochromatic light as the light source 26, the polarizer 21, the analyzer 22, and the mounting table 2 are rotated with respect to each other, and
Is an image when interference fringes appear most clearly at the periphery of the image. The peripheral portion having a small thickness becomes “dark” because the phase difference Δφ is an odd multiple of π, and the central portion having a large thickness becomes “bright” because the phase difference Δφ is an even multiple of π. In addition, crystal blank 1
It is considered that the four corners become "bright" because the birefringence increases due to stress due to processing, lens effect, and the like, and is a phenomenon different from the above-described interference fringes due to the thickness.

On the other hand, FIG. 3B shows a picked-up image of the quartz blank 1 by the dark field method. Here, the dark field method is a method according to the aforementioned Japanese Patent No. 282460. In this case, only the outline is raised white, the inside of the outline is uniformly gray, and the difference in thickness is visualized inside. I can't find an image that does it. In this way, the convex type has no scratches on the surface, so for inspection of the processing finish of the curved surface of the crystal blank,
An effective dark-field method for wounds is not suitable.

Polarized light from a light source is given to a convex type quartz blank by a polarizer, and light having a predetermined angle with respect to the polarized light from the light passing through the quartz blank is extracted from the analyzer. A fringe pattern (contour pattern) appears around the blank. Many interference fringes occur when the blank size is large and thick. However, the interference fringes decrease when the blank size is small and thin. The long side is 4 mm, the short side is 2 mm, and the thickness is 100 to 200 μm.
With a small rectangular blank, only one dark interference fringe is formed on the outer periphery. In addition, the main force of the crystal blank has shifted to a small one by the downsizing of the mounting equipment.

In the embodiments, it is assumed that there is a correlation between the shape of the interference fringes and the thickness of the quartz blank. This makes it possible to visualize the phase difference due to the difference in thickness due to the interference fringes, and to inspect the shape of the interference fringes to inspect the polished state of the convex type crystal blank. Give feedback for improvement.

In order to verify the above premise, the relationship between the interference fringes and the thickness will be considered below. For this consideration, a method is used in which a theoretical value is obtained and the theoretical value is confirmed by experiments. However, the sample used in this experiment should originally be able to use a small crystal blank according to the actual situation. However, in practice, a large convex type crystal blank was used instead of the small crystal blank. This is because the larger one is clearer and produces multiple interference fringes,
This is because the size (thickness) of the pen recorder can be measured more easily with a large size than with a small size. FIG.
FIG. 6 shows a large sample (long side 8.25 mm to 7.0 mm,
Short side 1.5mm ~ 2.0mm, thickness 400μm ~ 450
(μm) shows images in which two and three black stripes are respectively formed. FIG. 7 shows a small sample (long side of 5.0 mm to 4.0 mm).
0mm, short side 1.5mm ~ 2.5mm, thickness 100μm
(Up to 200 μm), each showing an image having one black stripe. [1] Theoretical value Quartz is a birefringent device, and the light incident on it is split into an ordinary ray and an extraordinary ray whose polarization planes are orthogonal to each other and propagates.

The quartz blank has a function as a phase plate, and gives a predetermined phase difference by a difference in phase speed between the ordinary ray and the extraordinary ray. The quarter-wave plate converts linearly polarized light to circularly polarized light,
Alternatively, the half-wave plate has the function of rotating the circularly polarized light into linearly polarized light and rotating the linearly polarized light by (2θ) with respect to the angle θ between the incident polarization plane and the optical axis of the wave plate.

The wavelength of the light source is λ, the refractive index of the ordinary ray is n ₀ ,
The refractive index of the extraordinary ray When n _e, the relationship between the thickness t and the phase difference P of the crystal blank, P = a _{(n e -n 0) t ·} 2π / λ (1).

From Equation 1, it can be seen that the thickness of the quartz blank can be determined if the phase difference, the difference between the refractive indices of the ordinary ray and the extraordinary ray, and the wavelength of the light source are known. The following data is obtained by determining the refractive index of the quartz crystal in the Y-axis cut for a specific wavelength.

The lambda (Å) inspection of the crystal blank refractive index _{n e 5080 1.54822 1.55746 5893 1.54424 1.55335} 7680 1.53903 1.54794 embodiment of a refractive index n ₀ extraordinary ray ordinary ray Is 660 nm for the light source
Use red LED. The above data is shown in FIG.
The wavelength is plotted on the horizontal axis, and the refractive index is plotted on the vertical axis.
When determining the difference between the refractive index of the ordinary ray and the extraordinary ray in the 0 nm, the n _e -n ₀ = 0.009. The quartz device is not an Y-axis cut, but an AT cut having a good frequency-temperature characteristic. Therefore, the difference between the refractive index of the ordinary ray and the extraordinary ray on the Y-axis indicates that AT
It is necessary to find the difference between the cut (about 35 °) quartz pieces.

The refractive index of the ordinary ray and the extraordinary ray of the AT-cut quartz plate can be obtained from FIG. 9 in which the refractive index distribution of the ordinary ray and the extraordinary ray is drawn on the YZ axis plane. X perpendicular to the paper
A circle 51 around which the refractive index distribution of the ordinary ray is drawn.
And the ellipse 52 on which the refractive index distribution of the extraordinary ray is drawn intersects the y-axis at points n _e and n ₀ , respectively, which represent the extraordinary ray refractive index and the ordinary ray refractive index on the Y axis, respectively. , The aforementioned Y
The difference between the axis of the extraordinary ray refractive index and the ordinary refractive index (n _e -n
₀ ).

Further, the AT cut surface comes at an angular position deviated by about 35 ° counterclockwise from the Z axis. In the polarization observation method for a quartz blank, light passes in a direction perpendicular to this plane. Straight line 5 indicating the direction of light passing through the origin (X axis)
Each point n _e ′, n at which 3 intersects the circle 51 and the ellipse 52
₀ 'is the extraordinary ray refractive index and the ordinary ray refractive index of the AT cut quartz plate, respectively, and the length between both points is the difference between the extraordinary ray refractive index and the ordinary ray refractive index of the AT cut quartz plate (AT plate). a _{(n e '-n 0')} . First, the intersection between the ellipse and the straight line is determined, and then the intersection between the perfect circle and the straight line is determined.

The equation of the ellipse is z ² / a ² + y ² / b ² = 1 (2). Where a = n _e, a b = n _0.

The equation for the straight line of light is y = cz (3) Here, c = tan 35 °.

[0047] When determining the intersection of the ellipse formula (2) and the linear equation (3), z = ± n e · n 0 / (n 0 2 + n e 2 · tan 2 35) (4) y = ± n e · _{n 0 · tan35 ° / (n} 0 2 + n e 2 · tan 2 35 °) (5) is obtained.

Similarly, in the elliptic equation (2), a = b = n
₀ and the true circle equation obtained by substituting, if obtaining the intersection point of the straight line equation (3), z = ± n 0 / (1 + tan 2 35 °) 1/2 (6) y = ± 1 / tan35 ° (7) is obtained Can be

From [0049] Equation (4) to (7), the difference between both the refractive index in a direction perpendicular to the AT plate _{(n e -n 0) = 0.006} (8) is obtained.

Substituting equation (8), the phase difference between interference fringes P = 2π, and the light source wavelength λ = 660 nm into equation (1), t = 660 nm / 0.006 = 110 μm Is obtained. Since the sample is a biconvex convex type, t '= 110/2 = 55 μm (10) is obtained by calculating the thickness of one side. Therefore, the change amount of the phase difference of 2π, that is, the thickness between the interference fringes is 55 μm. [2] Experimental value As shown in FIG. 10, the luminance of the striped pattern of the sample image 61 of the rectangular crystal blank reflected on the display was measured.
The measured striped pattern was an outermost dark part 63 (the point where the luminance dropped the most) and a dark part 62 that was one inside from the outermost (the point where the luminance dropped the most). Dark area 6 one inside from the sample center
The distance L ₁ to L ₂ , the distance L ₂ from the innermost dark part 62 to the outermost dark part 63, and the distance to the edge were L ₀ . L ₀ × 2 is the long side of the sample. The same samples were bonded to the base was measured L ₁ and L between the _second height (thickness) H a pen recorder. Note that the dark portion was the portion where the luminance distribution along the center line in the longitudinal direction was the lowest. The measurement samples are the following three.

[0051] (1) Sample _{A L 1 = 2.85mm L 2 =} 0.95mm L = 8.25mm H = 55μm (2) Sample _{B L 1 = 2.8mm L 2 =} 1.05mm L = 8.25mm H = 55 μm (3) Sample C L ₁ = 3.15 mm L ₂ = 0.7 mm L = 8.00 mm H = 55 μm The samples (1) to (3) described above all have a height H between the dark portions. It showed 55 μm which is the same as the theoretical value. Here, because the adhesive was used to fix the sample to the base, the horizontality of the sample could not be secured due to the variation in the applied thickness of the adhesive, but since the relative height between the dark parts was determined,
The level of the sample is not an error. 5
The surface roughness of the sample surface was measured in order to examine how much error was included in 5 μm. FIG.
As shown in the figure, half of the peak-to-peak is about 1 μm
Therefore, it was found that there was no problem if the accuracy of the thickness was about 10%. Therefore, it was confirmed that the stripe pattern had a correlation with the thickness of the sample. [Inference] The theoretical value and the experimental value are as follows:
Although applied to large samples of the order of 400 μm thick, and without any exclusions, the results should be applicable to small samples. 4mm long side, 1m short side
As shown in FIG. 7, only one striped pattern (dark portion) occurs in a small sample of m units and a thickness of 100 μm to 200 μm. Therefore, the thickness cannot be measured based on the above results.
However, since it was found that there was a correlation between the sample thickness and the luminance appearing in the sample image, the luminance was observed when only one stripe pattern was generated by the polarization observation method, or even when no clear stripe pattern was generated. If there is a change, set an optimal threshold value and draw an isoluminance line (corresponding to a contour line of mountainous terrain) connecting points with the same intensity of interference fringes, so that the isoluminance line is the same It will indicate the thickness. FIG. 12 is a sample diagram depicting such an equal luminance line.
These samples are approximately 416 μm thick and have a blank frequency of 4 MHz. (A) Sample (Fig. 12 (a)) Long side = 04.324mm Short side = 01.807mm Isoluminance line shape: beautiful ellipse (b) Sample (Fig. 12 (b)) Long side = 04.328mm Short side = 01.807mm isoluminance line shape: slightly distorted ellipse (c) Sample (FIG. 12 (c)) Long side = 04.332mm Short side = 01.806mm Isoluminance line shape: largely distorted ellipse (a) When the oscillation test was performed by assembling the strip-shaped convex oscillators of (a) to (c), (a) and (b) had good and stable frequency characteristics, high Q values were obtained, and good temperature characteristics and good products. there were. On the other hand, in (c), the frequency characteristics were unstable and poor, the Q value was low, and the temperature characteristics were poor and poor. From these results, it was found that the polarization observation method is effective for thickness measurement and shape measurement even for a small sample.

Although the convex type has been described as an object to be inspected by the polarization observation method, the present invention can also be applied to a beveled version of a substantially flat type. This is because the beveled substantially flat-plate type crystal blank is also polished at its peripheral portion and thinned, so that it has substantially the same cross section and a different thickness as the convex type.

Incidentally, not all the inspections of the quartz blank can be covered by the above-mentioned polarization observation method.
Although the polarization observation method is effective for the convex type or the substantially flat type etched after beveling, it is possible to find the optimum light source wavelength or rotate the polarizer 21, the analyzer 22, and the mounting table 2 only for the first time. Since it is necessary to find the optimal angle, operability and reproducibility are somewhat difficult. Further, it is impossible to detect a flaw or an outline generated in the quartz blank 1. Therefore, the inspection finish (thickness) of a quartz blank using the dark field method for inspection of scratches and dimensions and the polarization observation method
It would be very convenient if the inspection could be selected by simple switching.

FIG. 13 illustrates a schematic configuration of a crystal blank 1 inspection apparatus provided with such a switching device. As for the light source, a ring-shaped dark-field observation light source 6 and a dot-shaped polarization observation light source 26 are incorporated in the same light source box (not shown) provided below the mounting table 2 (FIG. 13).
(A)) One of the light sources 6, 26 can be selected by the changeover switch 29 (FIG. 13 (c)).
On the other hand, since the dark-field observation light sources 6 are arranged in a ring shape, a space is created in the center of the light source box. The other polarization observation light source 26 may be provided in the center space.

Further, as for the analyzer 22 and the polarizer 21 which are the polarization filters shown in FIG. 13 (a), the rotary shaft 2 rotatably provided on a stand 28 as an insertion / extraction means.
The analyzer 22 and the polarizer 21 are attached to the optical disk 7 and inserted into the optical path when observing polarized light, and removed from the optical path when observing dark field (FIG. 13).
(B)). With such a configuration, one switch is shared by one inspection device, and the changeover switch 29 and the rotating shaft 2 of the stand 28 are used.
If the rotation of 7 is linked, it is possible to switch between dark field observation and polarization observation with one touch. In addition, the polarizer 21 and the analyzer 22 may be able to advance and retreat with a cylinder.

FIG. 14 is a system configuration diagram of a crystal blank inspection apparatus. The system consists of the following elements.
The parts feeder 51 as a substrate supply device accommodates a large number of crystal blanks 1 at random and aligns them with the linear feeder 52 while rotating to supply the quartz blanks 1 to the external measurement stage 57 in one or more units. The transfer robot 53 has a suction arm, and sucks and holds one or a plurality of crystal blanks supplied from the linear feeder 52 to the measurement stage 57 and transfers it to the mounting table 2 provided on the measurement stage 57. After the inspection, the quartz blank 1 on the mounting table 2 is held and transported to the downstream side of the measurement stage 57.

The mounting table 2 is formed of a sapphire substrate or the like, and is formed of a transparent member on which the crystal blank 1 transferred by the transfer robot 53 is mounted substantially horizontally. The light source is provided with a light source for dark field observation 6 and a light source for polarization observation 26 so as to be freely switchable. The dark-field observation light source 6 is constituted by a fluorescent lamp or the like, and is scattered in a range of an irradiation angle of ± 30 ° vertically with respect to the horizontal blank surface of the quartz blank 1 mounted on the mounting table 2. Light is irradiated from the entire circumferential side of the crystal blank so as to just surround the crystal blank 1. The polarization observation light source 26 is configured by a red LED or the like, and irradiates the crystal blank 1 so as to project the quartz blank 1 from a direction perpendicular to the blank surface. Although not shown, the polarizer and the analyzer are inserted into the optical path during polarization observation as described above.

The image pickup means 11 is constituted by a CCD camera or the like, and is set just above the mounting table 2 so that the light source 6 or 2
The crystal blank 1 is imaged from a direction perpendicular to the blank surface of the crystal blank 1 illuminated by 6. The image processing device 14 displays the image captured by the image capturing means 11 on the display 54, and extracts a flaw or a contour (dimension) existing in the quartz blank 1 and a dark portion caused by a difference in thickness from the image signal, Statistical processing is performed based on the extracted signal so that the scratches and outlines on the crystal blank can be clearly distinguished and the degree of the convex finishing can be clearly inspected. The personal computer 55 inputs set values to the image processing apparatus 14, performs statistical processing on data obtained by the image processing apparatus 14 by using known spreadsheet software, and stores the processing results.

The crystal blank 1 is sucked by a vacuum chuck (not shown), carried into the mounting table 2 by the transfer robot 53, inspected, sucked again by the vacuum chuck, and unloaded by the transfer robot 53. .

In order to inspect the finish of the convex type crystal blank 1 in the above-described configuration, the light source 26 is switched to the polarization observation light source 26 in advance, and a polarizer and an analyzer are inserted into the optical path. If this inspection is described including the convex processing for forming a convex type crystal blank from a plate type crystal blank, the steps shown in FIG. 15 will be performed. The wrapped quartz blank is subjected to convex processing by a cylindrical barrel method (step 401). An etching process using hydrofluoric acid or the like is performed to smooth the surface (step 402).

In the case of treating with an acid, a large amount is performed in batches as in the case of the convex processing. For this reason, the threshold value for binarization performed later differs one by one and needs to be set according to the variation within an allowable range. The crystal blank 1 which has been wrapped and further subjected to an acid treatment is supplied to the parts feeder 51 in lot units, and is supplied from the linear feeder 52 to the measurement stage 57 in an aligned manner (step 403). The supplied robot 1 sucks the crystal blank 1 onto the vacuum chuck and transports it.
The wafer is transported to the mounting table 2 by step 3 (step 404). Next, a work finish inspection by a polarization observation method is performed (steps 405 to 408).

The light from the light source 26 is polarized by a polarizer and applied to a quartz blank 1 made of a convexly processed birefringent medium. The light passing through the quartz blank 1 passes a polarized light having a predetermined angle to the polarized light. Let it. As a result, as shown in FIG. 4, a phase difference due to a difference in thickness due to polarization interference can be visualized with light and dark contrast, and a contrast image of the crystal blank 1 of the polarized light that has passed therethrough is taken as a video image. Transfer to
In order to perform a contrast enhancement process, the binarized data is statistically processed in order to obtain data for processing finish inspection (step 408).

When inspecting the finish of processing,
The light amount of the light source 26 and the rotation angles of the polarizer 21, the analyzer 22, and the mounting table 2 are adjusted with each other in advance so that interference fringes appearing on the image are optimal for the processing finish inspection.
Calibration for adjusting these light amounts and angles is performed.

In order to inspect the finish of processing on the entire blank surface, a threshold value is determined so as to reflect the image result of FIG. 3A, and a binarized image corresponding to FIG. Obtain a)). From FIG. 4A, it can be seen that the finished state of processing can be grasped quantitatively. Here, the finished processing state can be grasped by measuring the inner major axis, the inner minor axis dimension, the center shift, and the like of the ring-shaped dark portion. The contents to be grasped include deviation of the polishing amount in the peripheral part of the crystal blank (difference in the band width of the ring-shaped dark part), curvature of the convex or cross-sectional shape (number of interference fringes), excessive shaving or insufficient shaving (interference fringe width) ), Eccentricity of polishing (center shift), and the like.

Regardless of the convex type or the flat type whose peripheral portion is thinned by beveling, the interference fringes generated in the image of the crystal blank and the cross-sectional shape or beveling region of the crystal blank are determined by the light amount. (1) does not correspond to 1: 1 because there is a balance with the (wavelength) and the rotation angles of the polarizer, the analyzer, and the mounting table. However, since there is a clear correspondence, the obtained image data can be used as a control index for convex processing or beveling processing, and further, the image signal is statistically processed to 1: 1.
It is also possible to correspond to.

Next, when performing a flaw inspection of the quartz blank 1, the light source is switched to the dark-field observation light source 6 and the polarizer and the analyzer are removed from the optical path.
When the scattered light diffused from the light source 6 arranged in a ring shape below the mounting table 2 toward the quartz blank 1 is irradiated, the scattered light covers the entire side surface of the quartz blank 1. Here, the principle of determining a flaw in dark-field observation will be described. As shown in FIG. 16, when the crystal blank 1 is irradiated with light from the entire side surface, the reflected light energy at the scratches (or defective portions) 31 of the crystal blank 1 and the edge processed portion increases. The direction of light emitted from around the quartz blank 1 is omnidirectional in the horizontal direction due to scattering.
If the quartz blank 1 is not damaged, the optical path is not blocked, and the scattered light passes through as transmitted light.

On the other hand, if there is an edge or a flaw 31, the light hits the edge or flaw 31, and becomes a reflected light 33 and is emphasized. When the scattered light 32 hits the flaw 31, it is reflected and a flaw appears on the surface of the quartz blank 1. Since the light 32 is radiated from all directions to the scratch 31, the energy of the reflected light of the scratch 31 is emphasized,
When viewed from above the quartz blank 1, the scratches 31 appear to float clearly. Inspect this wound. In addition, the shape and dimensions of the quartz crystal blank are measured using the reflection on the edge processed surface.

In this way, the crystal blank 1 that has been finished with the same mounting table 2 and has been finished and inspected for scratches or contours,
The transfer robot 53 is sucked again by the vacuum chuck and
Is transported to the next step. In the next step, GO / NO GO can be selected based on the above-described inspection results.

As described above, in this embodiment, one inspection apparatus is provided with the light source switching means and the polarization filter insertion / extraction means, so that one inspection apparatus can be used for darkness suitable for flaw or contour inspection. It is possible to selectively perform a visual field observation and a polarization observation suitable for a convex type appearance or finished work inspection. If the switching of the light source and the insertion / removal of the polarizing filter can be performed with one touch, the operability will be remarkably improved. Furthermore, since a plurality of inspections can be performed at once on the same mounting table, there is no need to re-enter the parts feeder after completing one inspection and perform the inspection on the second day. And the reliability of the inspection is improved.

Further, it is possible to inspect all the scratches and contours, or the finished state of the work using image processing, and to grasp the condition in real time and instantaneously, and to obtain a large amount of data through statistical processing. Become. In particular, by making use of convex type processing finish data at the time of polarization observation, it is possible to standardize convex processing, and thus to select GO / NO GO with high reliability. In addition, since statistical methods can be used, even if there is variation in flaw detection, convex processing, beveling processing and subsequent acid treatment, the optimum threshold value can be determined, and the tolerance can be flexibly taken. By setting such an allowable value as an inspection standard, a non-defective product is not regarded as a defective product, and a defective product is not regarded as a non-defective product.

In the embodiment, the image is monochrome, but may be color. In addition, although monochromatic light of a specific wavelength is used as the light source for polarization observation, a white light source may be used. In addition, 660 nm red L
Although ED was used, it is not limited to this. It is preferable to use light having a shorter wavelength than this in order to improve measurement accuracy because more interference fringes appear.

In the embodiment, it is assumed that interference fringes occur. However, since there is a correlation between the luminance and the thickness, it is sufficient that a luminance distribution is generated, and the same luminance value is plotted. By inspecting the shape of the luminance line, it is possible to determine the quality of the processed finish of the quartz blank.

[0073]

According to the method of the present invention, a convex type appearance inspection which cannot be inspected by the dark field observation method can be performed by the polarization observation method, and the image data obtained by the polarization observation method can be used as a control index. it can. Further, according to the apparatus of the present invention, an optimal observation method according to the inspection content can be simultaneously realized by one apparatus.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of an inspection apparatus for carrying out a convex inspection method for a transparent substrate according to an embodiment.

FIGS. 2A and 2B are explanatory diagrams of a case optimal for the inspection method of the embodiment, in which FIG. 2A is a cross-sectional view of a convex type crystal blank, and FIG.

3A and 3B show images of a convex type crystal blank before binarization, wherein FIG. 3A shows an image of the crystal blank observed by the polarization observation method of the embodiment, and FIG. 3B shows an image of the crystal blank observed by the dark field observation method. This is the blank image.

FIGS. 4A and 4B are explanatory diagrams by polarization observation, wherein FIG. 4A is a binarized image, and FIG. 4B is a cross-sectional view illustrating the thickness of a quartz blank.

5A and 5B are explanatory diagrams showing an image of a stripe pattern and luminance of a large sample, wherein FIG. 5A is a plan view and FIG. 5B is a luminance distribution diagram along a center line.

6A and 6B are explanatory diagrams showing an image of a stripe pattern and luminance of a large sample, wherein FIG. 6A is a plan view and FIG. 6B is a luminance distribution diagram along a center line.

7A and 7B are explanatory diagrams showing an image of a striped pattern and luminance of a small sample, wherein FIG. 7A is a plan view and FIG. 7B is a luminance distribution diagram along a center line.

FIG. 8 is a plot diagram showing a Y-axis refractive index of a quartz crystal blank with respect to a specific wavelength.

FIG. 9 is a refractive index distribution diagram of an ordinary ray and an extraordinary ray on the YZ axis plane of the AT cut quartz plate.

FIG. 10 is an explanatory diagram showing a position where a stripe pattern of a sample image of a rectangular crystal blank reflected on a display is generated;
(A) is a plan view, and (b) is an enlarged sectional view of a main part.

FIG. 11 is an explanatory diagram showing the surface roughness of the sample surface.

FIG. 12 is a plan view showing an image of a small sample in which isoluminance lines are drawn.

13A and 13B show a common inspection apparatus for dark field observation and polarization observation according to the embodiment, wherein FIG. 13A is a schematic configuration diagram, and FIG.
FIG. 4 is an explanatory diagram of switching of a polarizing filter, and FIG. 4C is an explanatory diagram of switching between a light source for dark-field observation and a light source for polarization observation.

FIG. 14 is an overall system configuration diagram according to an embodiment.

FIG. 15 is a series of flowcharts from a convex working to a convex finishing inspection of the embodiment.

FIG. 16 is a view showing the principle that a flaw rises when light is irradiated toward the entire periphery of a side surface of a quartz blank;
(A) is a plan view and (b) is a side view.

FIG. 17 is an explanatory diagram of a cylindrical barrel system for performing convex (beveling) processing.

FIG. 18 is a characteristic diagram in which height data obtained by a conventional level measurement method is plotted in the length direction of a quartz blank.

[Explanation of symbols]

 Reference Signs List 1 crystal blank (transparent substrate) 2 mounting table 12 objective lens 13 CCD camera 14 image processing device 21 polarizer 22 analyzer 23 diffusion plate 26 light source

Continuation of the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G01B 11/00-11/30 G01B 9/02

Claims (8)

(57) [Claims] 1. A polarized light from a light source is applied to a transparent substrate made of a birefringent medium having the same cross section and different thicknesses by processing by a polarizer. Pass the polarized light at a predetermined angle,
A transparent substrate inspection method, wherein a phase difference due to a difference in thickness of the transparent substrate is visualized by polarization interference, and an inspection of a cross-sectional shape of the transparent substrate is performed. 2. The method according to claim 1, wherein the inspection of the cross-sectional shape of the transparent substrate is performed based on the shape of an isoluminance line connecting points of equal luminance of interference fringes appearing by visualizing the phase difference.
The method for inspecting a transparent substrate according to claim 1. 3. The thickness of the transparent substrate between interference fringes, which is manifested by visualizing a phase difference due to the difference in the thickness of the transparent substrate, is determined by the following equation, and the thickness of the transparent substrate is determined based on the determined thickness.
The method for inspecting a transparent substrate according to claim 1, wherein the inspection of the cross-sectional shape is performed. _{P = (n e -n 0)} t · 2π / λ However lambda: wavelength of the light source n _0: the ordinary refractive index n _e: refractive index of extraordinary ray t: thickness of the transparent substrate P: position of interference fringes Difference 4. The method for inspecting a transparent substrate according to claim 1, wherein said transparent substrate is a convex type transparent substrate. 5. The transparent substrate according to claim 1, wherein the transparent substrate is a transparent substrate having a peripheral portion polished by beveling, and an inspection of the finish of the beveling of the transparent substrate is performed. Inspection method. 6. The beveling inspection method for a transparent substrate according to claim 1, wherein said transparent substrate is a crystal blank for a crystal unit. 7. A light source for polarization observation for irradiating unpolarized light toward a transparent substrate, a polarizer for irradiating irradiation light from the light source for polarization observation with polarized light to the transparent substrate, and An analyzer that detects transmitted light in a polarization state at a predetermined angle, and an image of a transparent substrate of polarized observation light that has passed through the analyzer, and visualizes a phase difference due to a difference in the thickness of the transparent substrate due to polarization interference. An apparatus for inspecting a transparent substrate, comprising: an imaging unit; and an image processing unit that inspects a cross-sectional shape of the transparent substrate by performing image processing on an image of the transparent substrate captured by the imaging unit. 8. A polarization observation light source for irradiating unpolarized light toward a transparent substrate, and scattering diffused within an irradiation angle of ± 30 ° in a vertical direction with respect to a reference plane of the transparent substrate. A light source for dark-field observation that irradiates light from the entire side of the side surface of the transparent substrate; a switch that switches between the light source for polarization observation and the light source for dark-field observation; and a switch from the light source for polarization observation. A polarizer for irradiating the transparent substrate with the irradiation light instead of polarized light; an analyzer for detecting light in a polarized state at a predetermined angle transmitted through the transparent substrate; and the polarizer for polarization observation when switching to a polarization observation light source with the switch. And inserting the analyzer into the optical path, and inserting and removing means for extracting the polarizer and the analyzer from the optical path during dark field observation by switching to the dark field observation light source with the switch, Image the transparent substrate of the polarized observation light that has passed through the analyzer, visualize the phase difference due to the difference in the thickness of the transparent substrate due to polarization interference, or image the transparent substrate of the dark field observation light that does not pass through the analyzer. An apparatus for inspecting a transparent substrate, comprising: an imaging unit; and an image processing unit that inspects the transparent substrate by performing image processing on an image of the transparent substrate captured by the imaging unit.