JP2845041B2 - Particle counting 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 particle counting apparatus for counting particles such as dust and dirt adhering to the surface of a semiconductor wafer, and more particularly to a particle counting apparatus having a high detection sensitivity for minute particles.

[0002]

2. Description of the Related Art Conventionally, this kind of particle counting apparatus for a semiconductor wafer surface has a structure as shown in FIG. 5 or FIG.

In FIG. 5, reference numeral 501 denotes a semiconductor wafer;
02 is a table, 503 is a motor, 504 is a translation unit, 505 is a laser, 506 is a laser beam, 507 is a condenser lens, 508 is a photodetector, and 509 is a counter.

On the other hand, in FIG. 6, 601 is a semiconductor wafer, 602 is a table, 603 is a motor, 604 is a parallel shifter, 605 is a laser, 606 is a laser beam, 607 is a condenser lens, 608 is a photodetector, 609 Is a counter.

The difference between the structure of the particle counting device in FIGS. 5 and 6 is that the angle of incidence of the laser beam on the surface of the semiconductor wafer is different. That is, FIG. 5 shows only oblique incidence and FIG. 6 shows only vertical incidence.

Next, the operation will be described. 5 and 6
In the particle counting device of the above, only the incident angle of the laser beam is different and the other points are the same, so only FIG. 5 will be described.

First, a semiconductor wafer 501 is placed on a table 502.
And a laser 505 on the surface of the semiconductor wafer 501.
Is irradiated with a laser beam 506. Then, the laser beam 50
6 is reflected on the surface of the semiconductor wafer 501. At this time, when the table 502 is rotated by the motor 503 and the table 502 is simultaneously moved in the x direction or the y direction by the parallel shifter 504, the laser beam 506 scans the entire surface of the semiconductor wafer 501 in a spiral shape. become.

Next, counting of particles such as dust and dust on the surface of a semiconductor wafer will be described. Semiconductor wafer 5
If no particles exist on the laser beam 506
Are all reflected on the surface of the semiconductor wafer 501 and no scattered light is detected by the photodetector 508, so that there is no output due to the scattered light from the photodetector 508. On the other hand, the semiconductor wafer 501
If there is a particle on top, the laser light 506 is scattered by the particle. The scattering intensity is correlated with the size of the particles, with large particles being strongly scattered and small particles being weakly scattered. Therefore, the scattered light of the laser light 506 due to the particles detected by the photodetector 508 is detected more in large particles and less in small particles, and the output from the photodetector 508 is large. Larger for particles, smaller for smaller ones.

FIG. 7 shows the relationship between the size of the particles on the surface of the semiconductor wafer and the output from the photodetector. The output of the photodetector 508 is classified and counted by the counter 509 for each output size of the photodetector 508, that is, for each particle size.

[0010]

Heretofore, in this type of particle counting apparatus, since a part of the scattered light due to the particles of the laser light has been detected, the size of the particles is reduced and the intensity of the scattered light is reduced. In particular, when the particle diameter of the particles is smaller than 0.1 μm, there is a problem that the detection sensitivity of the particles is extremely reduced.

[0011]

Particle counting device of the present invention SUMMARY OF THE INVENTION includes a laser for irradiating a laser beam to a semiconductor wafer surface, a photodetector for detecting the scattered light of the laser beam, photodetector
Condenser lens provided between the vessel and the surface of the semiconductor wafer
When the inner circumference the current between the photodetector and the semiconductor wafer surface
A cylindrical light reflecting structure is provided in contact with the outer periphery of the optical lens .

According to the present invention, it is possible to improve the detection sensitivity by reflecting all the scattered light of the laser light by the particles on the light reflecting structure and introducing the reflected light into the photodetector.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram of a first embodiment of the present invention. In FIG. 1, 101 is a semiconductor wafer, 102 is a table,
103 is a motor, 104 is a translator, 105 is a laser, 106 is a laser beam, 107 is a condenser lens, 108 is a photodetector, 109 is a counter, 110 is a cylindrical reflecting structure, and 111 and 112 are small. Hole. Semiconductor wafer 101
For example, in order to manage an air-conditioning room, the device is left in a predetermined place in the air-conditioning room for a predetermined time and investigates how much dust or dust particles adhere to the surface during the time.

Next, the operation will be described. The semiconductor wafer 101 is fixed to a table 102, and the surface of the semiconductor wafer 101 is irradiated with laser light 106 from a laser 105.
At this time, when the table 102 is rotated by the motor 103 and simultaneously moved in the x or y direction by the parallel shifter 104, the laser beam 106 scans the entire surface of the semiconductor wafer 101.

When no particles exist on the surface of the semiconductor wafer 101, the laser beam 106 incident from the small holes 111 formed on the side wall of the cylindrical reflecting structure 110 is entirely reflected on the surface of the semiconductor wafer 101, The light exits from the small hole 112 formed in the side wall on the side. Therefore, nothing is detected by the photodetector 108, and the count by the counter 109 becomes 0 (zero). On the other hand, when particles are present on the surface of the semiconductor wafer 101, the laser beam 106 incident from the small holes 111 is partially scattered by the particles, and the rest is emitted from the small holes 112. In the case of the prior art shown in FIGS. 5 and 6 described above, a part of the scattered light is detected by the photodetectors 508 and 608, but in the case of the present invention shown in FIG. Since the reflection structure 110 that reflects light is provided, almost all of the scattered light scattered by the particles is detected by the photodetector 108.

Here, it is calculated how much the amount of scattered light detected by the photodetector 108 differs between the case where the light reflecting structure 110 exists and the case where the light reflecting structure 110 does not exist. Assume the scattering as shown in FIG. That is, the laser light is scattered at the point 0 on the semiconductor wafer 201, and the scattered light is uniformly scattered in a hemispherical shape with the point 0 as a center. Also, of the scattered light,
It is assumed that a solid angle defined by θ is detected by the photodetector 202. Then, the ratio of the amount of scattered light in the case where the light reflecting structure 110 is present to the case where the light reflecting structure 110 is not present is the area ratio (1−cos θ). Therefore, Table 1 shown below
As is clear from FIG. 7, when the angle θ is equal to or less than 60 °, the light detector
Increases the scattered light received by more than two times, and the detection sensitivity is remarkably improved.

[0018]

[Table 1]

FIG. 3 is a diagram comparing the particle counting device of the present invention with the particle counting device of the prior art.
The detection limit of the prior art particle counter is about 0.1
In contrast, the particle counter of the present invention can detect a particle diameter of about 0.05 μm.

FIG. 4 is a block diagram of a second embodiment of the present invention. In the above-described first embodiment, the laser beam 106 is obliquely incident, whereas in the second embodiment, the laser beam 106 is vertically incident. In FIG. 4, 401 is a semiconductor wafer, 402 is a table, 403 is a motor, 404 is a translator, 405
Is a laser, 406 is a laser beam, 407 is a condenser lens, 4
08 is a photodetector, 409 is a counter, 410 is a cylindrical reflection structure, and 411 is a small hole. In this embodiment, the laser light 4
Since the entrance and exit of the 06 are the same small hole, the processing and installation of the reflection structure are extremely easy, and at the same time, the miniaturization of the apparatus is easy and the stability of particle counting is improved. The other operations are the same as those of the first embodiment, and the description is omitted.

[0021]

As described above, the present invention provides a laser for irradiating a laser beam to a semiconductor wafer surface, a photodetector for detecting scattered laser beam, and a photodetector between the photodetector and the semiconductor wafer surface. The provision of the cylindrical light reflecting structure allows the photodetector to receive almost all of the scattered light due to particles on the surface of the semiconductor wafer. As a result, the output of the photodetector increases, and a large output can be obtained, especially for minute particles smaller than 0.1 μm, so that the detection sensitivity for minute particles is significantly improved.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a first embodiment of the present invention.

FIG. 2 is a diagram for calculating the effect of the present invention.

FIG. 3 is a diagram comparing the photodetector outputs of the present invention and the prior art.

FIG. 4 is a configuration diagram of a second embodiment of the present invention.

FIG. 5 is a configuration diagram of a conventional technique.

FIG. 6 is a configuration diagram of another conventional technique.

FIG. 7 is a correlation diagram between a particle diameter and an output of a photodetector.

[Explanation of symbols]

 Reference Signs List 101 semiconductor wafer 102 table 103 motor 104 translator 105 laser 106 laser beam 107 condenser lens 108 photodetector 109 counter 110 reflecting structure 111, 112 small hole 201 semiconductor wafer 202 photodetector 401 semiconductor wafer 402 table 403 motor 404 Parallel mover 405 Laser 406 Laser light 407 Focusing lens 408 Photodetector 409 Counter 410 Reflective structure 411 Small hole 501 Semiconductor wafer 502 Table 503 Motor 504 Parallel mover 505 Laser 506 Laser light 507 Focusing lens 508 Light detection Device 509 Counter 601 Semiconductor wafer 602 Table 603 Motor 604 Translator 605 Laser 606 Laser light 607 Condensing lens 608 Photodetector 609 Counter

Claims (1)

(57) [Claims] 1. A laser for irradiating a laser beam onto a semiconductor wafer surface, a photodetector for detecting scattered light of the laser beam, and a photodetector provided between the photodetector and the semiconductor wafer surface.
A counting lens for counting particles such as dust and dust on the surface of the semiconductor wafer, wherein an inner circumference of the focusing lens is between the photodetector and the surface of the semiconductor wafer . A particle counting device provided with a cylindrical light reflecting structure in contact with an outer periphery .