JPS61228332A - Apparatus for optical inspection of flaw - Google Patents

Abstract

PURPOSE:To make it possible to detect a flaw having unevenness and a flaw changing only in reflectivity, by using not only illumination beam allowed to obliquely irradiate an object to be inspected but also illumination beam having a spot diameter near to a diffraction limit and allowed to vertically irradiate the object to be inspected. CONSTITUTION:The semiconductive laser beam from a beam source 20 is allowed to obliquely irradiate an object 25 to be inspected. When there is a flaw on the object 25 to be inspected, the illumination beam is scattered to be guided to a beam detector 41 and condensed thereto to be converted to a flow detection signal A. The remaining scattered beam is guided to a shaping circuit 46 to be converted to a flaw detection signal C. The beam from a beam source 30 is focused to the object 25 to be inspected and a part of the reflected beam thereof is guided to a focus error drive circuit 42 and the illumination beam from the beam source 30 is controlled by the output signal of said circuit 42 so as to be always focused to the object 25 to be inspected. Reflected beam is guided to shaping circuits 44, 43 to be respectively converted to flaw detection signals B', B. By this method, both or either one of a flaw having unevenness and a flaw changing in reflectivity can be detected by the same apparatus and detection accuracy is also enhanced.

Description

[Detailed Description of the Invention] Industrial Application Fields Optical disks (VLPs), compact disks (CDs),
Various systems such as recordable discs have been developed and commercialized.

The disks used in such systems are images.

Information such as voice, address data, and digital data is recorded primarily optically on the master disc as changes in the unevenness, a mold is made from the master disc through a plating process, and this mold is used to mass-produce duplicate discs. .

The causes of defects that occur in the manufacturing process of this duplicate disk are 1. Scratches on the surface of the glass master, 2. Cleaning condition of the glass master (adhesion of foreign matter), 3. Foreign matter in the resist, 4. Pinholes in the resist, and 6. Lack of care during process operations. Miss, 6
There are various possible causes such as adhesion of the replication material to the mold. Defect inspection equipment and inspection techniques that detect these defects early and prevent defective devices from being sent to the next process are extremely important when considering process yield and cost reduction.

Although the optical disc manufacturing process has been described here, similar inspections are also required in the disc manufacturing process using mechanical recording, for example. Furthermore, it is important to inspect not only disks but also silicon wafers, steel plates, and aluminum plates for defects and scratches on their surfaces.

The present invention relates to an optical defect inspection device that optically inspects the surface of an object to be inspected for defects, scratches, and adhesion of foreign matter.

Conventional technology An example of a conventional master disk surface defect inspection device is the Japanese Patent Publication No. 52
There is a defect inspection device as shown in Japanese Patent No.-146601. Fig. 6 shows the principle diagram.

Coherent light from a light source 1 (for example, a laser) is passed through a lens 3 so that it converges at a certain point beyond the reflective surface of a mirror 2.
focused by. The focused beam incident on this mirror surface is reflected by the mirror surface and projected onto the first relay lenses 4 and 6. The light beam passing through the lenses 4 and 6 is reflected by the mirror 6 and passes through the second relay lens 7.8 to the motor 9.
to the surface of the object to be inspected 11 on the turntable 10 which is rotating. The light beam emerging from the relay lens 7.8 is focused to a focal point at a certain position beyond the surface of the object to be inspected 110, and forms a light spot on the surface of the object to be inspected that blocks this. The spot diameters are parallel to each other by approximately 100 μm, and are placed at a selected angle (for example, 4
6 degrees), intersects the surface of the object to be inspected along the radius of the disk, and is preferably on a plane that includes the central axis of the object to be inspected.

The incident light is reflected by the surface of the object to be inspected and passes through the beam splitter 12.
is incident on the This beam splitter 12 transmits a portion of the incident light to travel toward the first photodetector 13 and reflects the remainder toward the second photodetector 14 . The light shielding plate 16 is for cutting off the 0th order diffracted light of the disk which acts as a diffraction grating, and if there is no defect on the disk, the light will not be detected by the detector 13. The photodetector 14 is used to maintain a constant light spot on the disk, and the detection output moves the mirrors 2 and 6, so that the spot on the detector 14 is moved in the radial and tangential directions on the disk surface. Correct so that it does not move.

Problems to be Solved by the Invention However, the defect inspection apparatus having the conventional configuration described above has the following problems.

(1) The illumination light is irradiated obliquely onto the object to be inspected, and if there is a large foreign object or scratch on the object, the detection sensitivity is high, but there are no irregularities and only the reflectance changes. Detection sensitivity for defects is low.

(2) It is difficult to focus the spot diameter of illumination light to 10 μm or less, and the detection accuracy for defects is low.

In view of these points, the present invention aims to provide an optical defect detection device that is capable of detecting defects that have no irregularities and only changes in reflectance, and has high defect detection accuracy.

Means for Solving the Problems In order to solve the above-mentioned problems, the optical defect inspection apparatus of the present invention uses two types of light: one that is irradiated obliquely to the object to be inspected, and the other that is irradiated almost perpendicularly and has a spot diameter. A means of irradiating irradiation light close to the diffraction limit to almost the same position on the object to be inspected, light scattered by defects in light irradiated obliquely, light reflected from the object to be inspected, and light irradiated almost perpendicularly. means for detecting defects on the object to be inspected by each of the reflected light or transmitted light;
The apparatus includes a focus position control means for keeping the nearly perpendicularly irradiated light focused on the object to be inspected, and means for relatively scanning the irradiation light over the object to be inspected.

Effect The present invention has the above-described configuration, and the object to be inspected is irradiated with illumination light obliquely, has a spot diameter close to the diffraction limit, and is irradiated almost perpendicularly to the object to be inspected. Using illumination light, defects with irregularities and defects without irregularities but with changes in reflectance or transmittance can be detected with the same device, and with high defect detection accuracy and stable optics. The purpose of this invention is to provide a defect detection device that can detect defects.

EXAMPLES Hereinafter, examples of the present invention will be described based on the accompanying drawings.

FIG. 1 shows a first embodiment of the invention. In FIG. 1, reference numeral 20 denotes a first light source, which is, for example, a semiconductor laser with a wavelength of 8,000. The light from the light source 2o passes through the shirt p-21 and the beam expander system 22-23, becomes parallel light, is reflected by the mirror 24, and is irradiated onto the inspection object 26, which is rotated by the spindle motor 26, and becomes illumination light. Become. The light reflected from the object to be inspected 26 is guided by a mirror 27 and then condensed onto a photodetector 29 by a converging lens 28. If there is a defect on the object 25 to be inspected, this illumination light is scattered, and the scattered light is focused by a lens 34 mounted on a voice coil and guided to a beam splitter 33. The light transmitted through the beam splitter 33 passes through the dichroic mirror 35, is guided to the lens 4o, and is focused on the photodetector 41, where it becomes a defect detection signal A. On the other hand, it becomes a defect detection signal C after being led to a shaping circuit 46 having a scattering. The object to be inspected 26 is mounted on a turntable 26a and rotates. Also turntable 26a
is transported in the direction of arrow P (radial direction) in the figure by the carry tool. The surface runout of the object to be inspected 26 usually ranges from several tens of micrometers to several hundreds of micrometers. In this case, the light reflected by the object to be inspected 26 moves on the mirror 27, but by designing the mirror 27 and the condenser lens 28 in consideration of the amount of movement caused by the surface deflection of the object to be inspected 25, Shaking does not prevent reflected light from being received.

The second light source 30 is, for example, a He-No laser, and the light from the second light source is a beam expander system.

32, the beam is guided and reflected by the beam splitter 33, enters the lens 34, and the object to be inspected 25
Focus on the top. For example, the NA of the lens 34 is NA.
= approximately 0.5 is used.

The light reflected by the object to be inspected 25 returns through the forward path and the four-way path, passes through the beam splitter 33, is totally reflected by the dichroic mirror 35, and is condensed by the condensing lens 36. The mirror 37 is a total reflection mirror for configuring the knife focus detection method. Half of the light focused by the lens 36 is guided to a photoelectric conversion element 38 which is a photodetection element for detecting focus error. This output signal is led to the focus error drive circuit 42, which drives the focus actuator 34 so that the illumination light from the second light source 3o is always focused on the object to be inspected 26. controlled.

The light reflected by the mirror 37 is photoelectrically converted by the photoelectric conversion element 39, and its output is guided to a shaping circuit 44 having an amplification/level detection function and a shaping circuit 43 having an addition/amplification/level detection function. . The output of the shaping circuit 44 becomes the defect detection signal B'.

Further, a part of the output signal of the photoelectric conversion element 38 is transmitted to the shaping circuit 43.
After being added to the output signal of the photoelectric conversion element 39, it becomes the defect detection signal B. The output level of the output signals of the photoelectric conversion elements 38 and 39 decreases when an uneven defect exists on the object to be inspected and the illumination light is scattered. Furthermore, when there is no unevenness on the object to be inspected but there is a change in reflectance, the output level increases or decreases depending on the reflectance. Therefore, by designing the shaping circuits 43 and 44 in consideration of the levels when the illumination light is scattered by a defect and when there is a change in the reflectance of the defect, it is possible to detect it with a detector of the same level. It is possible. For example, the level detector of the shaping circuit 44 is set to a level suitable for detecting scattering, and the detection level of the shaping circuit 43 is set to a level suitable for detecting a change in reflectance, and the defect detection signals B, B' It is also possible to make each defect detection signal. Further, in this embodiment, the second light source 3
Although the embodiment in which the illumination light from 0 is reflected on the object to be inspected is used, it is also possible to detect by transmitted light using a known technique, and this can be taken into consideration based on the reflectance of the object to be inspected. By opening and closing the shutter 21, the diagonal illumination light is 0N10.
FF becomes possible.

A second embodiment of the present invention will be described using FIG. 2. Here, the constituent elements described in the configuration of the first embodiment are given the same numbers in the drawings, and only points different from the first embodiment will be explained.

The light source 3o is, for example, a He-N e laser, and the light from the light source is separated at an appropriate ratio by a semi-transparent mirror 49, and the first and second light sources are configured with the same wavelength as described in the first embodiment. It has the same function as when The polarization plane of the light source is S
A total reflection mirror 60 arranged to polarize the light is added to guide the light split by the semi-transparent mirror 49 to the lens 22.

The illumination light that passes through the expander systems 22 and 23 and is totally reflected by the mirror 24 is irradiated onto the object 26 to be inspected.

If there is an uneven defect on the object to be inspected, this illumination light is scattered, and this scattered light is focused by a lens 34 and then transmitted through a beam splitter (hereinafter abbreviated as BS) 51. , and is guided to a polarized beam splinter (hereinafter abbreviated as PBS) 52. Here, the polarization plane of the light from the light source is set to be S polarization, but if it is scattered by uneven defects, the polarization plane of the scattered light will increase the P polarization component, so it will be transmitted to the PBS 52. The light is focused by the lens 40 and guided onto the photoelectric conversion element 41 .

On the other hand, the light from the light source 3o that has passed through the semi-transparent mirror 49 is
It is reflected by B561, condensed onto the object to be inspected by lens 34, then reflected, returns along the same path as the outgoing path, passes through B551, and then is reflected by PBS 62. The output of each photoelectric conversion element is processed in the same manner as in the first embodiment, and becomes each defect detection signal.

Next, a third embodiment of the present invention will be described using FIG. 3.

Here again, the constituent elements explained in the configuration of the first embodiment are given the same numbers in the drawings, and only the points different from the first embodiment will be explained.

The light source 42 is, for example, a He-N o laser, and is arranged so that the plane of polarization is S polarized with respect to PBSel. After the light from the light source 42 is guided to the lens 6o, the light from the PB
It is totally reflected by Sel, transmitted through the dichroic mirror 62, and guided to the lens 34. The lens 6o and the lens 34 constitute a beam expander system, and the light source 4
The light from the lens 34 enters the lens 34 at a position shifted from the optical axis, and the light emitted from the lens 34 becomes parallel light. After the light reflected from the object to be inspected 26 returns along the same route as the outgoing route,
After being totally reflected by the PBSel and condensed by the lens 63, the light is divided into two photoelectric conversion elements 38A.

38B. This system constitutes an off-axis focused detection system, and heat is radiated onto the object to be inspected at approximately the same position as the focused spot of the other light source 30.
It has the same function as the illumination light that is obliquely irradiated onto the object to be inspected as in the previous embodiment. There is a defect on the object to be inspected, and the scattered light returns to the PBSel along the same path as the light from the light source, but due to the rotation of the plane of polarization due to scattering, the scattered light returns to the PBSel.
Since it has P polarization with respect to S61, after passing through PBS61 and being focused by lens 40, it is transmitted to photoelectric conversion element 41.
incident on . The other light source 30 is, for example, a semiconductor laser, and after passing through the shutter 21, the beam expander
The beam passes through systems 31 and 32, passes through a rear mirror 63 that has been expanded to a desired beam diameter, is totally reflected by a dichroic ink mirror 62, is focused by a lens 34, and is placed on the object to be inspected at the diffraction limit. It has a spot diameter narrowed down to . The light reflected by the object to be inspected passes through a semi-transparent mirror 63 along the same optical path as the forward path.
After returning to this point, the light is reflected by a semi-transparent mirror 63 and condensed by a lens 64, and then guided to a photoelectric conversion element 66. This photoelectric conversion element output is the photoelectric conversion element 38 in the first embodiment.
It is equivalent to the sum of the numbers 39 and 39. Shaping circuit 6
6 is composed of an amplification/level detection circuit. On the other hand, the photoelectric conversion element outputs 38A and 38B are led to a shaping circuit 67 composed of an amplifier circuit/addition circuit/level detection circuit/differential circuit, and the added signal is the photoelectric conversion element of the first embodiment. This is equivalent to the output of the element 29, and the differential signal becomes a focus error signal. Further, the shutter 21 is placed immediately after the light source 30, and by opening and closing this shunter 21, the 0N-O of the vertically irradiated illumination light is removed.
FF becomes possible.

Next, post-processing of the defect detection signal will be explained using FIG. 4. FIG. 4(-) shows the shaping circuit and subsequent parts of the first embodiment. In this case, each defect detection signal is output independently. However, as actual inspection result information, for example, defect detection information in which the desired defect detection matches among the respective defect detection signals, and defect detection information in the case where all the respective defect detection signals match are important. Such defect detection information can be processed using known techniques. FIG. 4(b) shows an embodiment of this processing circuit.

In each example, it was assumed that the object to be inspected was disk-shaped and the scanning direction was radial feed and rotation with respect to the object to be inspected, but in this example, the shape of the object to be inspected and the scanning direction It is not limited to.

By applying means capable of scanning in the X-Y directions to the present invention, the shape of the object to be inspected can be square or long strip-like. Furthermore, the object to be inspected is not limited to glass or resist master disks.

Components such as a light source and optical elements, as well as focus detection means, etc. are not limited as long as the configuration can realize this embodiment.

Effects of the Invention As described above, the present invention allows light that is irradiated obliquely to the object to be inspected and light that is irradiated almost perpendicularly to the object to be inspected to have a spot diameter close to the diffraction limit. means for irradiating the light to the position, and scattered light due to defects in the obliquely irradiated light;
The structure of the means for detecting defects on the object to be inspected using each of the reflected light from the object to be inspected and the reflected light or transmitted light of light irradiated almost perpendicularly to the object to be inspected detects defects with irregularities and irregularities on the object to be inspected. However, it is possible to detect defects with reflectance or transmittance changes using the same device, and by processing each defect detection signal, it is possible to detect both or either defect using the same device. It is also possible to provide an optical defect inspection device that can generate all desired defect detection signals with high accuracy and has a stable and simple configuration.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an optical defect inspection apparatus according to a first embodiment of the present invention, FIG. 2 is a block diagram of the second embodiment, and FIG. 3 is a block diagram of a third embodiment of the present invention. FIG. 4 is a block diagram showing an embodiment of post-processing of defect detection signals according to the present invention, and FIG. 6 is a block diagram of a conventional optical defect inspection apparatus. 1.20, 30.42... Light source, 3.4.5
. 7.8, 22, 23, 28, 31. 32, 33° 36.
40... Lens, 34... Lens mounted on actuator, 21... Shutter, 2.6, 24, 27.37... Mirror, 11 , 26... object to be inspected, 26...
Spindle motor, 13°29...-Photodetector, 3
8,39.41...Photoelectric conversion element, 43,44
．． 45... Shaping circuit, 67... Shaping and focus error detection circuit, 33.51... Beam splitter 135, 62... Dichroic mirror, 52. 61...Polarizing beam splitter-0 Name of agent Patent attorney Toshio Nakao and 1 other person20
, 30--Ikko U5 site, 43, 44.45--Single-shaped circuit Figure 2 and 4' Figure 3 Figure 4 (a) (b) Figure 5 /-Light source 3-m = Objective Lens U-Liquid Investigation Object I3- Light Detection Joy

Claims (8)

[Claims] (1) A first light source for illuminating the surface of the object to be inspected, a first irradiation means for irradiating light from the first light source obliquely to the object to be inspected, and a first light source for illuminating the surface of the object to be inspected; a first optical means for guiding at least a portion of the light scattered by the defect to the detection system, a first detection means for detecting the scattered light, a second light source, and a second light source. a second irradiation means for condensing light from the object to be inspected and irradiating it almost perpendicularly to the same position as the irradiation light from the first light source; and reflection or transmission from the object to be inspected. A second optical means for guiding light to the detection system, a second detection means for detecting the reflected or transmitted light, and a second light source for keeping the light focused on the object to be inspected. An optical defect inspection apparatus comprising: a focal position control means; and a scanning means for relatively scanning the irradiation light over an object to be inspected. (2) The means for condensing obliquely irradiated illumination light scattered by defects on the inspected object and the means for concentrating the light irradiated almost perpendicularly to the inspected object are integrated into the same lens. The optical defect inspection device according to claim 1, characterized in that it is also used as an optical defect inspection device. (3) A patent claim characterized by having means for selecting to irradiate only one of the irradiation light from the first light source or the irradiation light from the second light source onto the object to be inspected. The optical defect inspection device according to scope 1. (4) The optical defect inspection apparatus according to claim 1, further comprising means for detecting only P-polarized light of light scattered by defects on the object to be inspected. (5) The optical defect inspection apparatus according to claim 1, further comprising means for detecting reflected light from the object to be inspected of light irradiated obliquely onto the object to be inspected. (6) The optical defect inspection device according to claim 1, which outputs a logical sum of any or all of the detected defect signals. (7) The optical defect inspection device according to claim 1, wherein the first light source and the second light source have different wavelengths. (8) The optical defect inspection device according to claim 1, characterized in that the first light source and the second light source are used in combination.