JPS6247073Y2 - - Google Patents

Description

[Detailed description of the invention] [Industrial application field] The present invention is designed to eliminate scratches and other defects (hereinafter referred to as surface defects) on the surface of various materials such as silicon wafer face plates.
This invention relates to an optical surface defect detector that detects surface defects.

[Prior Art] Conventional methods for detecting surface defects on silicon wafer face plates and other metals and non-metals used as semiconductor product materials have been manual methods, that is, visual inspection with the naked eye or a microscope. Such a method is not only inefficient, but also has variations in detection results due to individual differences, and is not suitable for a mass production line. In response, progress is being made in the development of automatic inspection methods in which surface defects are detected using an optical detection method and the electrical signals detected in this manner are processed by a computer.

In the optical surface defect detection described above, many methods can be considered for selecting the light source, light receiving method, and light receiving element to be used. For example, an ordinary illumination lamp can be used as a light source, and a lens system can be used to form a small spot on the face plate, and as a light receiver,
The simplest method is to place a condenser lens on one side of the face plate, for example in an obliquely upward direction, to capture scattered light caused by defects. However, it is not always easy to create a spot with a small diameter and high intensity using such a normal illumination lamp, and the detection ability is not good. In addition, the direction and angle of scattered light due to a defect vary depending on the type, shape, size, etc. of the defect, and as mentioned above, the light scattered by a condenser lens placed on one side simply captures a narrow angle. However, the disadvantage is that it is difficult to accurately capture such scattered light.

Here, what is required of an optical surface defect detector that specifically detects minute defects on a test object is, first of all, to make the spot irradiated onto the test object as small as possible. Second, the light receiving section that receives reflected light from the subject must have good light collection efficiency at a position as close as possible to the subject. Thirdly, it must be possible to finely adjust the position of the irradiation part of the illumination light, and fourthly, in order to automate defect detection of the object to be detected, the configuration of the device must be changed. Miniaturization·
Needs to be simplified.

The present invention was developed in view of the above points, and its purpose is to achieve good detection accuracy of the object to be detected through a simple configuration, and to easily adjust the mechanism that constitutes the detector. An object of the present invention is to provide an optical surface defect detector capable of performing the following steps.

[Means for Solving the Problems] In order to achieve the above-mentioned object, the present invention provides a holder that supports a laser oscillation tube that irradiates the object with a laser beam, in which the laser beam from the laser oscillation tube is attached. The lower end of the holder is provided with a plurality of insertion holes that extend diagonally outward from the laser spot position, and each insertion hole receives the scattered light from the object. By inserting an optical fiber that receives light and supporting the holder on a vertical movement adjustment member, the distance between the laser oscillation tube and the subject can be adjusted, and the focal length of the lens can be adjusted. A feature of the lens is that the distance between the lens and the laser oscillation tube can be adjusted by supporting the lens with a member.

[Function] As described above, by configuring the laser beam to be irradiated onto the subject, the spot diameter on the subject can be reduced, and
The intensity of that light can be increased. In addition, by placing an optical fiber around the laser beam spot, it is possible not only to place it as close to the surface of the object as possible, but also to improve the light collection efficiency. will also be good. Moreover, since a plurality of optical fibers are provided, if each of these optical fibers is connected to a detection section using a photoelectric conversion means, etc., the direction and intensity of scattered light in each direction can be measured. It becomes possible to analyze the type, shape, size, etc. of the gap.

Furthermore, by adjusting the height position of the holder using the vertical movement adjustment member and adjusting the position of the lens by operating the focal length adjustment member, the position of the laser oscillation tube with respect to the subject and the focal position of the lens can be adjusted. Fine adjustments can now be made, the detection accuracy of surface defects is significantly improved, and the device can be easily disassembled and assembled, resulting in good maintainability.

[Example] Hereinafter, an example of the present invention will be described in detail based on the drawings.

Before going into a specific explanation of the present invention, some explanations will be given regarding its principle.

That is, the optical surface defect detector according to the present invention has the following features:
By using continuous wave laser light as a light source, focusing this laser light into a narrow beam using a condensing lens, and irradiating the object with a high intensity spot, it is possible to Surface defects on the mirror-like surface of the object are detected. For this purpose, a laser beam is irradiated onto the object from a perpendicular direction, and surface defects are detected by detecting the scattering of the reflected light.

Here, when a laser beam is irradiated onto the object from a perpendicular direction as described above, if there are no defects on the surface of the object, the reflected light returns with a slight divergence angle along the irradiation optical axis of the laser beam. However, if there is a defect on the surface of the object, the light will be scattered in a direction and intensity depending on factors such as the type, shape, and size of the defect. Therefore, by analyzing this scattering pattern, it becomes possible to estimate each of these elements. Furthermore, when looking at defects of the same type and shape, the intensity of scattered light (the sum of scattered light in each direction) changes as a function of the size of the defect, so it is not necessary to simply find out the size of the defect. For example, it is sufficient to detect only the intensity of the aforementioned scattered light.

Here, it is desirable to arrange the detection element for scattered light as close to the subject as possible from the viewpoint of light reception efficiency. Therefore, in the present invention, in order to effectively capture scattered light by arranging a plurality of optical fibers close to the laser spot, the laser light source and the light receiving optical fiber are integrated. structure and maintain a certain relationship with each other.

Here, regarding the arrangement of multiple optical fibers, in order to improve the efficiency, two
It is necessary to consider the following points.

First, assuming that light scattered by a defect is uniformly scattered in each direction, it is ideal to arrange enough optical fibers to cover all directions. However, as optical fibers, there are molded products on the market in which a large number of extremely thin fiber wires are made into a circular cross section with a diameter of several mm, and the optical transmission loss is reduced by applying the required treatment to both ends. It is preferable to use such a molded product from the viewpoint of simplification of the mechanism. However, such optical fiber molded products (hereinafter simply referred to as optical fibers)
When using, in order to obtain good detection efficiency,
Important issues include the number of units used and their placement.

FIG. 1 is an explanatory diagram of the optical fiber arrangement of the optical surface defect detector according to the present invention.
A subject 1 is placed horizontally, and a laser beam 2 is irradiated onto the subject 1 from a vertical direction. The tip 3' of the optical fiber 3 is provided so as to face the laser spot point P of the laser beam 2.
Here, the detection efficiency of scattered light is influenced by the angle α between the subject 1 and the central axis of the optical fiber 3 and the angle 20 that the tip 3' of the optical fiber 3 makes with respect to the point P.

Now, assuming that the scattered light is uniform in each direction according to the above assumption, and that the angle α is 45°, when a plurality of optical fibers 3 are arranged on the circumference at this angle, the adjacent optical fibers 3
There is an access limit between the tips 3' and the subject 1 to prevent the tips 3' from touching each other. Therefore, when six optical fibers 3 are used, the projection 3'' of the tip 3' of the optical fiber 3 onto the subject 1 is positioned close to this approach limit, as shown in FIG. It is preferable to do so.

On the other hand, in FIG. 1, if we consider a hemispherical surface whose radius is the distance R from the point P to the tip 3', the tip 3 of the n optical fiber group at the approach limit position mentioned above with respect to its surface area. If we take the ratio of the total area of ', this can be considered to be approximately equal to the detection efficiency of scattered light. Therefore, by using n as a variable (angle α=45°), the approximate calculation of the area ratio is as shown in FIG. As is clear from the figure, the larger n is, the smaller the area ratio becomes, so it is better not to make the value of n too large. In addition, as a characteristic of optical fiber 3,
There is a certain limit to the incident angle of light incident on the tip 3', and if the incident angle becomes larger than the limit, the light reception efficiency will deteriorate due to reflection on the surface of the tip 3'. Here, as shown in Figure 4,
As the number n of optical fibers 3 increases, the angle θ shown in FIG. 1 becomes smaller. The relationship between the angle θ and the light receiving rate is as shown in FIG. 2, and as the number n of optical fibers 3 is increased, the amount of ineffective reflection is reduced. Therefore, from these points, it is preferable to set n to about 4 to 6. For example, if n=6, the area ratio is 40%, but
Since θ is about 20°, it is possible to reduce ineffective reflections, which is efficient.

Next, regarding the light receiving section, by using the optical fiber 3, it is possible to guide the detected scattered light to a remote position without attenuating it much, so there is a photoelectric converter that converts the amount of this scattered light into an electrical signal. This has the advantage that it becomes possible to arrange the detector at an arbitrary position, which is advantageous in that it becomes possible to reduce the burden on the movable parts when configuring the detector. This photoelectric converter combines all optical fibers into one
However, if each optical fiber 3 is connected to an individual photoelectric converter, the direction of the dispersed light can be detected. By detecting the direction of the dispersed light in this manner, the accuracy of detecting the type, shape, size, etc. of defects is significantly improved.

Note that in order to inspect the entire surface of the object for surface defects, it is necessary to move either the object or the detector, or both. Configuring the sample to move is more advantageous than moving the detector.

Considering the above points, the specific configuration adopted by the present invention is shown in FIGS. 6a, b, and c.

As shown in the figure, a laser oscillation tube 4 to which a power cord 10 is connected is attached to a holder 5 made of a light metal such as aluminum, and positioned by a set screw 6. An optical fiber fixture 9 made of aluminum or the like is attached to the lower part of the holder 5, similar to the holder 5.
A plurality of holes are formed radially in an oblique direction toward the laser beam spot position P from the laser beam, and an optical fiber 3 is inserted into each of these holes so as to be individually defined by a set screw 17. ing. These optical fibers 3 can be fixed by the set screw 17 after finely adjusting their axial positions.

Further, a condensing lens 22 is mounted on the optical axis of the laser beam from the laser oscillation tube 4.
This lens 22 is provided with a fixing ring 18 firmly fixed to the upper surface of the optical fiber fixture 9 at a lower position inside the holder 5, and a lens outer cylinder 23 is installed inside the fixing ring 18. A lens inner cylinder 21 is fixed within the lens 23 with a screw 24, and is attached to a lens mount 22' mounted on the lens inner cylinder 21. An adjustment screw 25 is carved on the outer peripheral surface of the lens outer cylinder 23, and this adjustment screw 25 meshes with a rotating ring 19 having a dial 8, and by rotating the dial 8, the lens can be adjusted. The cylinder 23 can be moved up and down in the direction of the optical axis of the laser beam, thereby forming a lens focal length adjustment member that adjusts the focal length of the lens 22. As shown in FIG. 6a, this dial 8 faces a window 7 formed in the holder 5, and by rotating the dial 8 from the outside through this window 7, the focus of the lens 22 Adjustment can be made, and a scale 8' is provided for convenience of the focus adjustment operation.

Furthermore, a pinhole plate 26 is provided at the upper part of the lens inner cylinder 21, which constitutes a diaphragm for the laser beam. The pinhole plate 26 is for cutting unnecessary side waves in the laser beam and improving the S/N ratio, and the diameter of this pinhole can be changed as appropriate.

Next, the detector having the above-mentioned configuration is supported so that its position can be adjusted in the vertical direction, and this support mechanism includes a stand 14, and the holder 5 is supported on the stand 14 via a roller guide 13. has been done. This roller guide 13 is the stand 1
Consisting of a fixed part 13-1 provided on the 4 side and a movable part 13-2 connected to the holder 5, the fixed part 13
By interposing the roller 13-4 between -1 and the movable part 13-2, the movable part 13-2 to which the holder 5 is connected can be raised and lowered without causing play. There is. And holder 5
In order to adjust the height position of the holder 5, a fine adjustment threaded rod 12 having a knob 11 is inserted into the movable part 13-2, and by rotating the knob 11, the holder 5 is moved together with the movable part 13-2. can be moved up and down. In order to fix this holder 5 at a desired position, a fixing member consisting of a slide pin 15 and a clamp 16 is provided.

Next, FIG. 7 shows the structure of the light receiving element portion of this optical surface defect detector. As is clear from the figure, the terminal end of the optical fiber 3 is connected to the fixing member 3.
The optical fibers 3 are inserted into the holes 32 provided in the optical fibers 1, and the optical fibers 3 are assembled together. And the fixing member 3
1 is attached to the magnetic shield case 29 of the photo multiplier 28, so that the tip 3' of the optical fiber 3 is placed close to the effective surface of the photo multiplier 28, and is photoelectrically converted by the photo multiplier 28. It is composed of

This embodiment has the above-mentioned configuration, and its operation will be explained next.

First, the subject 1 is installed in the subject installation section, and in order to be able to irradiate the subject 1 with the optimum laser beam, the knob 11 that constitutes the vertical movement adjustment member is rotated. , the height position of the holder 5 is adjusted, and the dial 8 serving as the operating part of the lens focal length adjustment member is rotated to adjust the position of the lens 22 so that the laser beam is focused on the surface of the subject 1. Adjust as follows. Then,
Depending on the characteristics and placement position of this lens 22,
It becomes possible to form a beam spot with a spot diameter of about 10-odd microns to several tens of microns, which is convenient for detecting minute defects in the object 1.

On the other hand, the irradiation side of the laser beam can be adjusted as described above. ′
must be located at equal distances from the position P. For this reason, it may be necessary to adjust the position of each optical fiber 3, but this position adjustment can be done by loosening the set screw 17 and moving the optical fiber 3 in the axial direction. This can be done by adjusting and fixing again by tightening the set screw 17.

As described above, a state is established in which the test can be performed under optimal conditions, and the test subject 1 is mounted on the test subject mounting section. By moving the subject 1, defects on the surface of the subject 1 are detected. Therefore, if there are no defects on the surface, the irradiated laser beam will be reflected in the same direction as the direction of incidence, and therefore almost no reflected light will be incident on the optical fiber 3. . However, if there is a defect on the surface of the object 1,
The reflected light of the laser beam is scattered depending on the nature, shape, size, etc. of the defect. This scattered light is then incident on the optical fiber 3, transmitted through the optical fiber 3 to a photomultiplier 28 constituting a light receiving element section, and converted into an electrical signal corresponding to the amount of light received. Therefore, this electrical signal can be input to data processing means such as a computer, and the defect can be analyzed by this data processing means.

Here, the laser beam irradiated onto the object 1 needs to be adjusted to have an appropriate spot diameter depending on the type of defect to be inspected. Therefore, in order to adjust the spot diameter,
Rotate the dial 8 to change the distance between the lens 22 and the laser oscillation tube 4, and turn the knob 11.
There is no need to change the distance between the lens 22 and the subject 1 by adjusting the height of the holder 5. Furthermore, when replacing the lens or when using the output beam of the laser oscillation tube 4 as is (usually about 1 mmφ), the lens 22 can be removed from the lens mount 22'.

In the above-mentioned embodiment, the angle α of the optical fiber 3 with respect to the position P of the laser spot was approximately 45 degrees, but this angle α can be arbitrarily set to 30 degrees, 60 degrees, etc. Also, as mentioned above, the number of optical fibers is 4 to 4.
It is preferable to use any one of six.

[Effects of the invention] As detailed above, according to the invention, since a laser beam is used as a light source for detecting defects in the object to be inspected, the spot diameter can be reduced, and a strong beam can be used. This makes it possible to detect minute defects, and increases the amount of scattered light caused by the defects, significantly improving inspection accuracy.
Furthermore, the vertical position of the holder can be adjusted using the vertical movement adjustment member, and the focal length of the lens can be adjusted using the lens focal length adjustment member, allowing for smooth optical adjustment. And you will be able to do it in minute detail. Furthermore, since the laser oscillation tube and the optical fiber are integrated into the holder, various effects such as the ability to simplify and downsize the structure of the detector are achieved.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram of the arrangement of optical fibers in the optical surface defect detector according to the present invention, Fig. 2 is a projection of the tip of the optical fiber onto the test object, and Fig. 3 is the tip surface and hemispherical area of the optical fiber. FIG. 4 is a curve diagram showing an example of the incident angle characteristics of optical fibers, and FIG. 5 is a graph showing the number and maximum number of optical fibers in the array of optical fibers in the optical surface defect detector according to the present invention. Characteristic diagram showing the relationship with the incident angle, No. 6
Figures a, b, and c are explanatory diagrams showing the specific configuration of the optical surface defect detector according to the present invention, and Fig. 7 is an explanatory diagram of the configuration of the light receiving element section. 1... Subject, 2... Laser light, 3... Optical fiber, 4... Laser oscillation tube, 5... Holder, 6, 17, 27... Set screw, 7...
... window, 8 ... dial, 9 ... optical fiber fixture, 11 ... knob, 12 ... fine adjustment threaded rod, 13-1 ... fixed part, 13-2 ... movable part,
13-4...Roller, 18...Fixing ring, 19
... Rotating ring, 20 ... Presser ring, 21 ...
Lens inner tube, 22... lens, 23... lens outer tube, 28... photo multiplier.

Claims (1)

[Scope of utility model registration request] A holder that supports a laser oscillation tube that irradiates a laser beam onto a subject is equipped with a lens that focuses the laser beam from the laser oscillation tube. A plurality of insertion holes extending radially diagonally outward are provided, an optical fiber for receiving scattered light from the subject is inserted into each of the insertion holes, and the holder is supported by a vertical movement adjustment member. , the distance between the laser oscillation tube and the subject is adjustable, and the distance between the lens and the laser oscillation tube is adjusted by supporting the lens on a focal length adjustment member. An optical surface defect detector characterized by the following features: