JPH0833354B2 - Defect inspection equipment - Google Patents

Description

TECHNICAL FIELD The present invention relates to a defect inspection apparatus for detecting minute scratches, dust, etc. on a flat substrate to be inspected. For example, an optical disc, a magneto-optical disc, The present invention relates to a defect inspection apparatus suitable for inspecting a surface defect in a transparent body such as a hard disk.

[Prior Art] In a manufacturing process of a transparent body such as an optical disc, a glass substrate having a predetermined outer diameter is polished, and then a recording pattern or the like is formed.

In this polishing step, grainy rough scratches may occur on the glass substrate due to polishing with an abrasive. The size of such a scratch is, for example, several μm to 1 μm.
Below, but in some cases even larger.

Further, as the shape mode, there are an isolated scratch and a series of many scratches.

On the other hand, in addition to the above-mentioned polishing scratches, foreign matter may be attached to the disk substrate after polishing.

However, among these, foreign matters can be removed by a cleaning step after polishing, but polishing scratches cannot be removed. The glass substrate on which polishing scratches are found is either re-polished or discarded depending on the degree of the scratches.

The present condition is that visual judgment depends on the quality judgment of the glass substrate after polishing as described above, that is, the detection of polishing scratches and the presence or absence of foreign matter.

[Problems to be Solved by the Invention] However, such a visual inspection has a disadvantage that it takes a lot of time and labor and that it is difficult to find a minute defect.

In addition, it is not possible to reliably judge whether the found defect is a polishing scratch or a foreign matter. In particular, in the case of isolated polishing scratches, it is almost indistinguishable from the foreign substances attached to the glass substrate by visual inspection. For this reason, the manufacturing efficiency of the glass substrate is significantly reduced.

As described above, although it is important to judge whether the defect on the glass substrate is a polishing scratch or a foreign substance, the conventional visual inspection can give only an ambiguous result.

The present invention has been made in view of the above problems, and improves the above-mentioned drawbacks of the prior art by inspecting a defect on a transparent body such as a glass substrate and determining whether the defect is a scratch or a foreign substance. It is an object of the present invention to provide a defect inspection apparatus capable of automatically making a determination with high accuracy.

[Means for Solving Problems] A defect inspection apparatus according to the invention described in claim 1 is a defect inspection apparatus for optically detecting a defect present in an inspection object having light transmittance. An irradiation means for irradiating the object to be inspected with an inspection light, and a light which propagates in a direction different from a transmission direction and a regular reflection direction of the inspection light among scattered light generated from the defect by the irradiation of the inspection light Of the scattered light generated from the defect by the irradiation of the inspection light and scattered inside the inspection object, the inside of the inspection object is located in the transmission direction of the inspection light. Second light receiving means for receiving light propagating in one direction, a signal output obtained by the first light receiving means, and the second light receiving means.
And a determination means for determining the state of the defect by comparing with the signal output obtained by the light receiving means.

A defect inspection apparatus according to the invention described in claim 2 is the defect inspection apparatus described in claim 1, wherein the determination means is a signal obtained by the first light receiving means. It is characterized in that whether the defect exists on the outer side or the inner side of the inspection object is determined based on the magnitude of the output and the signal output obtained by the second light receiving means. .

The defect inspection apparatus according to the third aspect of the invention is the defect inspection apparatus according to the first aspect of the invention, and the determination means is a signal obtained by the first light receiving means. It is characterized in that whether or not the defect is a scratch formed on the inspection object is determined based on the magnitudes of the output and the signal output obtained by the second light receiving means.

[Operation] According to the present invention, of the scattered light of the inspection light generated by the defect existing in the inspection object, the light that travels in a direction different from the transmission direction and the regular reflection direction of the inspection light, for example, the forward scattered light is , And is received by the first light receiving means.

Further, of the scattered light generated from the defect due to the irradiation of the inspection light and scattered inside the inspection object by the second light receiving means, it propagates inside the inspection object laterally with respect to the transmission direction of the inspection light. Light, for example edge light, is received.

The signal outputs obtained by the first and second light receiving means are input to the determining means.

In this determination means, for example, a ratio of both inputs is obtained as a comparison of both inputs. Then, the state of the defect existing in the inspection object is determined from this ratio. In particular,
It is determined whether the defect exists on the outer side or the inner side of the inspection object, or whether the defect is a scratch formed on the inspection object.

Embodiments Embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

Basic Principle First, in order to facilitate understanding of the present invention, the basic principle of defect type discrimination in the present invention will be described with reference to FIG.

The figure (A) shows the state of scattered light when the foreign matter D _A adheres to the surface to be inspected of the glass substrate such as an optical desk, and the figure (B) shows the state of the inspected light. The appearance of scattered light when a scratch D _B is present on the surface is shown. In both cases, the inspection light is emitted obliquely from above as indicated by the arrow FA.

First, the case of FIG. When the foreign matter D _A attached on the surface 12 to be inspected of the glass substrate 10 is irradiated with light as indicated by an arrow FA, forward scattered light LF _A is emitted in the traveling direction of this light.
Occurs.

Further, part of the scattered light due to the foreign matter D _A propagates while being reflected inside the glass substrate 10 like a waveguide, and diverges outward from the end face 14 of the glass substrate 10 (hereinafter referred to as “end face light”). It will be LE _A.

Similarly, in the case shown in FIG. 6B, the forward scattered light LF _B and the end surface light LE _B are generated due to the light scattering by the scratch D _B.

In such a case, according to the experiment conducted for the present invention, it is confirmed that the ratio of the forward scattered light and the end face light is different between the foreign matter D _A and the flaw D _B.

That is, the amount of light on the end face is larger than the amount of forward scattered light in the case of the flaw D _{B in} FIG. 9B than in the case of the foreign matter D _A in FIG. In other words, the forward scattered light amount LF and the end face light amount LE
Considering the ratio LF / LE with the value of the foreign matter D _A , the value of the flaw D _B is smaller than that of the foreign matter D _A.

This tends to be common to foreign matter and scratches attached on a transparent substrate.

Therefore, a transparent disk substrate such as an optical disk is scanned with a light beam, and at this time, the forward scattered light and the end surface light of the scattered light generated by the presence of defects are measured,
By determining these light intensity ratios, it is possible to determine whether the defect is a foreign substance or a scratch.

Incidentally, so-called back-scattered light LR _A scattered on the light incident side,
The LR _B acts on the foreign matter D _A and the flaw D _B , and is generated, like the forward scattered lights LF _A and LF _B.

Therefore, when it is difficult to receive the forward scattered light LF due to the device configuration, the same effect can be obtained by receiving the back scattered light LR.

This method is particularly effective when, for example, the light incident side of the glass substrate 10, that is, the surface 12 to be inspected is light transmissive, but the light emitting side is covered with a light shielding film such as a chromium film. Is.

Further, in the example of FIG. 1, the light is made incident on the object from the upper left, but if the light is illuminated from the lower left to detect the defect on the light emitting side of the glass substrate 10, The effect can be obtained.

First Embodiment Next, a first embodiment of the present invention will be described with reference to FIGS. 2 and 3.

First, referring to FIG. 2, a mechanical or optical portion of the configuration of the first embodiment will be described.

In FIG. 2, the disk substrate 20 is supported at its center by a supporting portion 22, and the supporting portion 22 is joined to the rotating shaft of a motor 24. That is, the rotation of the motor 24 causes the disk substrate 20 to rotate in the fixed direction indicated by the arrow FB.

The rotation amount of the support portion 22 at this time is configured to be measured by, for example, a rotary encoder or the like (not shown).

Next, the light beam, for example, the laser beam 26 is output from an appropriate oscillating means (not shown), converted into an arbitrary beam diameter by a beam expander (not shown), and condenser lenses 28 and 30. , Is obliquely incident on the disk substrate 20.

Here, the condenser lenses 28 and 30 are the light receiving lens 34, which will be described later.
It is preferable that the optical system is a telecentric optical system so that the effective diameter of is not large. Also, the disk substrate 20
The incident angle of the laser beam 26 with respect to is preferably between 0 ° and 80 °.

Next, the laser beam 26 as described above is scanned by a scanning mirror, for example, a resonant scanner mirror arranged in the optical axis thereof.
By 32, the disk substrate 20 is scanned within a predetermined range (hereinafter referred to as “scan range”) S in the diametrical direction.

On the other hand, the rotation of the disk substrate 20 described above is performed at a speed lower than the scanning speed of the laser beam 20 in the diameter direction, that is, the vibration speed of the resonant scanner mirror 32.

By the laser beam scanning and the disk rotation, the entire surface of the disk substrate 20 is optically scanned.

The irradiation position of the laser beam 26 at this time can be known by the deflection angle detector (not shown) of the resonant scanner mirror 32 in the diameter direction and by the rotary encoder (not shown) in the rotation direction. It is possible.

Next, on the optical axis of the condenser lenses 28, 30 and on the opposite side of the disk substrate 20, a light receiving lens 34 for receiving the forward scattered light LF generated by a defect on the disk substrate 20 is arranged. There is.

A perforated mirror 36 is arranged on the pupil plane of the light receiving lens 34, and the laser beam 26 transmitted through the light receiving lens 34 has a hole 36 of the perforated mirror 36 as shown by a solid line in the figure.
It passes through H as 0th-order light and travels further forward.

On the other hand, the forward scattered light LF generated by the defect on the disk substrate 20 is received by the light receiving lens 34 as shown by the broken line in the figure.
The light is converged after being received by, and most of it is reflected by the perforated mirror 36.

The forward scattered light LF, after passing through the slit 38 placed at a position conjugate with the disk substrate 20, is converged and incident on the photoelectric detector 42 by the converging lens 40, whereby the photoelectric signal corresponding to the light amount of the forward scattered light LF is obtained. Is obtained.

Here, the slit 38 is for cutting stray light generated by the edge portion of the hole 36H of the perforated mirror 36, and has a slit length corresponding to the scanning range S.

On the other hand, on the end surface of the disk substrate 20, the laser beam
A slit 44 for detecting the end face light LE, a light receiving lens 46, and a photoelectric detector 48 are arranged on the side of the traveling direction of 26, that is, substantially on the extension of the scanning range S described above.

Among these, the slits 44 are arranged to cut scattered light diverging toward the upper and lower surfaces of the disk substrate 20 and to transmit only the end surface light.

With the above-described configuration, the entire surface of the inspected surface of the disk substrate 20 is optically inspected, and the front scattered light LF and the end surface light LE of the scattered light generated by the defect can be detected at the same time.

Next, with reference to FIG. 3, a signal processing circuit for determining the type of defect based on the outputs of the photoelectric detectors 42 and 48 shown in FIG. 2 will be described.

In FIG. 3, the output sides of the photoelectric detectors 42 and 48 are connected to the input sides of the amplifiers 50 and 52. The output sides of these amplifiers 50 and 52 are connected to the input sides of the amplification degree converters 54 and 56, respectively. A control unit 58 is connected to each of the amplification degree converters 54 and 56, and the amplification degree of each of the amplification degree converters 54 and 56 is controlled by a control signal from the control unit 58. There is.

The output photoelectric signals of the photoelectric detectors 42 and 48 described above have different signal magnitudes depending on the position of the defect on the disk substrate 20 even if the defect has the same shape or size.

That is, for photoelectric detector 42, laser beam 26
Beam diameter on the disk substrate 20 and the light receiving lens
Defect detection sensitivity in the scanning range S varies depending on the aberration of 34 and the like.

In addition to the above reason, the photoelectric detector 48 has a lower detection sensitivity because the amount of the end face light LE decreases as the distance from the end face of the disc substrate 20, that is, the inner side of the disc substrate 20 decreases.

The amplification degree converting groups 54 and 56 are used for the laser beam 26 as described above.
It is provided in order to correct the change in the detection sensitivity due to the difference in the scanning position. Then, these amplification degree converters 54 and 56 start operation when the laser beam 26 starts scanning on the scanning range S by the resonant scanner mirror 32 according to a control signal from the control unit 58, and scans during scanning. The amplification degree conversion is performed so as to correspond to the position, and the operation ends at the same time as the scanning ends.

Then, the laser beam 26 is applied in the diameter direction of the disk substrate 20.
Every time the scanning is performed, the above series of operations is repeated.

As a result, forward scattered light LF and edge light LE generated from defects
Thus, the photoelectric signals S _A and S _{B, which} are respectively proportional to the light amount of, are obtained regardless of the defect position.

Next, the output sides of the amplification degree converters 54 and 56 are respectively divided by the division unit 60.
, And the photoelectric signals S _A and S _B output from the amplification degree converters 54 and 56 are input to the division unit 60. By this division unit 60, the forward scattered light LF
And the light quantity ratio S _A / S _{B of the} edge light LE is obtained.

The light quantity ratio S _A / S _B is connected so as to be input to the determination unit 62. In this determination unit 62, the light amount ratio S _A
/ S _B is the determination of whether larger or smaller than a predetermined threshold value is performed.

As described above, the foreign matter D _A and scratches D _B, different light intensity ratio S _A / S _B of the forward scattered light LF and the end face light LE, generally wound D value smaller than it is in the foreign matter D _A in the case of _B Becomes

The determination unit 62 determines whether the light amount ratio S _A / S _B with respect to a predetermined threshold value (reference voltage) is large or small.
If it is D _A , and if it is small, the judgment result of scratch D _B is obtained. The result is output to the outside as, for example, a binarized digital signal S2.

On the other hand, the output side of the above-mentioned amplification degree converter 54 is the comparison unit 64.
Is connected to the input side of the
The photoelectric signal S _A proportional to is input to the comparison unit 64.

Generally, the larger the defect, the larger the light amount of the forward scattered light LF.
Therefore, it is possible to know the approximate size of the defect from the light quantity of the forward scattered light LF.

Therefore, in the comparison unit 64, data about the relationship between the size of the defect and the photoelectric signal S _A , which is statistically obtained in advance and stored, for example, the approximate size of the defect is obtained using a table, and the size thereof is calculated. The analog signal S1 corresponding to is output.

Next, the operation of the first embodiment configured as above will be described.

First, the laser beam 26 scans the disk substrate 20 by vibrating the resonant scanner mirror 32 and rotating the disk substrate 20 by the motor 24.

When the defect D exists in the scanning range S, the forward scattered light LF and the end surface light LE are generated, respectively, as shown in FIG.
These are detected by the photoelectric detectors 42 and 48, respectively. And
A photoelectric signal corresponding to the light amount of the forward scattered light LF and the edge light LE is
The signals are output from the photoelectric detectors 42 and 48, respectively.

On the other hand, the beam scanning position at this time is detected by the deflection angle detector of the resonant scanner mirror 32 and the rotary encoder of the motor 24, respectively, as described above.

Next, the photoelectric signals output from the photoelectric detectors 42 and 48 are amplified by the amplifiers 50 and 52, respectively, and then the amplification degree converter 54,
Each of the 56 is entered.

By the way, the amplification degree of the amplification degree converters 54 and 56 is
Is controlled in accordance with the beam scanning position. Therefore, signal amplification is performed by the amplification degree converters 54 and 56 in accordance with the controlled amplification degree, and the photoelectric signal S
Output as _A and S _B respectively.

Of these photoelectric signals S _A and S _B , the photoelectric signal S _A is
4, the size of the defect D is obtained from the size of the signal, and the detection signal S1 is output.

On the other hand, the photoelectric signals S _A and S _B are input to the dividing unit 60 and S _A / S _B
Is calculated. This calculation result is input to the determination unit 62, where it is determined whether the defect D is a foreign substance or a scratch, and the detection signal S2 indicating the type of defect is output.

From these detection signals S1 and S2, the approximate size and type of the defect (D) can be obtained together with the position on the disk substrate 20 described above.

Second Embodiment Next, a second embodiment of the present invention will be described with reference to FIGS. 4 and 5. The same reference numerals will be used for the same or corresponding parts as in the first embodiment described above.

FIG. 4 shows the mechanical or optical components of the second embodiment. In this structure, the drive system for the disk substrate 20, the light-transmitting incidence system for the laser beam 26, and the light-receiving and detecting system for the forward scattered light LF are the same as those in the first embodiment. However, edge light LE
The light receiving detection system of is different from that of the first embodiment.

In the above-described first embodiment, the end surface light LE is received by the light receiving lens 46 and the photoelectric detector 48 which are arranged substantially in the extending direction of the scanning range S.

However, the light on the disk substrate 20 is almost isotropically scattered from the defect. For this reason, in the first embodiment, the amount of light received on the end face is limited by the numerical aperture of the light receiving lens 46.

On the other hand, in the second embodiment, two annular concave mirrors 70, 7 are used.
The provision of 2 makes it possible to collect more end face light LE on the photoelectric detector 48 than in the first embodiment.

FIG. 5 is a cross section of the disk substrate 20 when viewed from the side, and only the end face light receiving and detecting system is shown. As shown in this figure, the edge light LE generated from the defect on the disk substrate 20 is focused on the photoelectric detector 48 along the optical path 74 by the action of the two annular concave mirrors 70 and 72. There is.

A slit 76 is arranged near the end face of the disk substrate 20 so as to cut scattered light other than the end face light LE so as to face the annular concave mirror 70.

The processing circuit for the scattered light signals from the defects detected by the photoelectric detectors 42 and 48 is the same as that of the first embodiment shown in FIG. 3, and the same signal processing is performed.

The operation of the second embodiment configured as described above is almost the same as that of the first embodiment described above, but the end surface light LE from the defect is LE.
Is detected by being condensed by the annular concave mirrors 70 and 72, the defect can be detected and the type can be discriminated with high sensitivity.

Other Embodiments Note that the present invention is not limited to the above embodiments. For example, in the above embodiments, the case of defect inspection of a disk substrate such as an optical disk is shown, but it is always necessary to have a plate shape. Instead, it may have a three-dimensional spread.

That is, the light beam may be made incident from any surface, and the end face light LE emitted from the surface other than the incident surface and the transmission surface of the beam may be received and detected.

EFFECTS OF THE INVENTION As described above, according to the present invention, scattered light generated by a defect travels in a direction different from the transmission direction and the regular reflection direction of the inspection light, and the inside of the inspection object generated by the defect. Of the scattered light scattered on the inside, the inside of the object to be inspected is divided into the light propagating laterally with respect to the transmission direction of the inspection light and the light is received separately. Comparison of received light signals, for example, determination of the state of defects from the ratio of each light amount,
That is, it is possible to automatically determine with high accuracy whether the defect exists on the outer side or the inner side of the inspection object or whether the defect is a scratch formed on the inspection object. There is an effect.

Further, there is also an effect that the approximate size of the defect can be known at the same time from the light amount of the front or back scattered light.

[Brief description of drawings]

FIG. 1 is an explanatory view showing the basic principle of the present invention, FIG. 2 is a perspective view showing an optical component of the first embodiment of the present invention, and FIG. 3 is an electrical component of the first embodiment. 4 is a perspective view showing an optical component of the second embodiment of the present invention, and FIG. 5 is a sectional view showing an end face light receiving portion of the second embodiment. . [Explanation of symbols for main parts] 20 …… disk substrate, 26 …… laser beam, 28,30 ……
Condensing lens, 32 …… Resonant scanner mirror, 34,4
6 …… Receiving lens, 36 …… Perforated mirror, 38,44,76 ……
Slit, 42, 48 ... Photoelectric detector, 70, 72 ... Annular concave mirror.

Claims (3)

[Claims] 1. A defect inspection apparatus for optically detecting a defect existing in a light-transmissive inspection object, comprising: illumination means for irradiating the inspection object with inspection light; and the defect by irradiation of the inspection light. The scattered light generated from the first light receiving means for receiving light traveling in a direction different from the transmission direction and the specular reflection direction of the inspection light; Of the scattered light scattered in the inside of the object to be inspected by the second light receiving means for receiving light propagating laterally in the inspected object in the transmission direction of the inspection light, and the first light receiving means. A defect inspection apparatus comprising: a determination unit that determines the state of the defect by comparing the obtained signal output with the signal output obtained by the second light receiving unit. 2. The outside of the object to be inspected is determined based on a magnitude of a signal output obtained by the first light receiving means and a signal output obtained by the second light receiving means. The defect inspection apparatus according to claim 1, wherein it is determined which of the inner side the defect exists. 3. The determining means determines, based on the magnitudes of the signal output obtained by the first light receiving means and the signal output obtained by the second light receiving means, that the defect is the inspected object. The defect inspection apparatus according to claim 1, wherein it is determined whether or not it is a scratch formed on an object.