JPH04351941A - Particulate measuring device - Google Patents

Abstract

PURPOSE:To improve precision of particulate size measurement by a particulate measuring device which utilizes scattered light. CONSTITUTION:Photodiodes 32-1, 32-2 which receive laser beam and photodiodes 35-1, 35-2 which receive scattered light are arranged in pairs at each of laser beam reflection points 27-1, 27-2 of a half mirror 22. In order that amplitude scattered light signals d1, d2 which limit their variation factors to scattered light arising positions are obtained by correcting the strength difference of scattered light resulting from the strength deviation of laser beam in accordance with the output of the photodiodes 32-1, 32-2 which receive laser beam, a laser beam strength deviation signal output means 40 and a scattered light arising signal amplitude means 41 are provided. Also, a means 42 of selecting a maximum level signal each time is provided to pick up a true scattered light signal.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a particle measuring device for measuring particles in a vacuum.

Semiconductors are manufactured by processing wafers in processing equipment in a vacuum atmosphere. The cleanliness inside the processing equipment is related to the yield, and management of the cleanliness is important.

[0003] A particulate measuring device is used to determine the cleanliness level.

[0004] In order to properly manage the above-mentioned cleanliness level, it is necessary that the particulate measuring device be capable of accurately measuring the number and size of particulates.

[0005] The measurement of fine particles is generally carried out using scattered light.

[0006]

2. Description of the Related Art FIG. 9 shows a conventional particulate measuring device 1 disclosed in Japanese Patent Application Laid-Open No. 1-129138.

This device 1 reflects a laser beam 5 from a laser 4 multiple times in a zigzag pattern as shown by reference numeral 6 between a pair of opposing reflecting mirrors 2 and 3, and scatters one photodiode 7. It is arranged approximately in the center so as to receive light, and the output of the photodiode 7 is processed by a processing circuit 8.

[0008] Here, fine particles 1 having a particle size on the order of microns
0 passes between mirrors 2 and 3 as indicated by arrow 11.

When the particles 10 pass between the mirrors 2 and 3, the laser beam 6 is scattered by the particles 10, and scattered light 12 is generated.

A photodiode 7 detects a portion of this scattered light 12 and outputs a signal.

Here, the intensity of the scattered light 12 is approximately proportional to the particle size of the fine particles 10.

Therefore, the processing circuit 8 uses the photodiode 7
The number of particles is calculated from the number of signals output from the sensor, and the size of the particles is determined from the signal level.

[0013]

The intensity of the laser beam decreases each time it is reflected by the mirrors 2 and 3, albeit slightly.

Therefore, there is a difference in intensity between the portion of the laser beam 6a that has been reflected less frequently and the portion of the laser beam 6b that has been reflected many times, with the latter being weaker than the former. The intensity of the scattered light is approximately proportional to the intensity of the laser beam that impinges on the particles.

Therefore, even if the particles have the same particle size,
In the space sandwiched between the mirrors 2 and 3, the intensity of the scattered light detected by the photodiode 7 differs depending on where the particles pass.

For example, as shown in FIG.
Even if particles a and 13b have the same particle size, the intensity of the scattered light 15 is strong when it passes through the upper part of the space 14 between the mirrors 2 and 3, and the intensity of the scattered light 15 is strong when it passes through the lower part. In this case, the intensity of the scattered light 16 becomes weaker.

For this reason, the processing circuit 8 in FIG.
3a is determined to be a fine particle with a particle size larger than the actual particle size, and conversely, fine particle 13b is determined to be a fine particle with a particle size smaller than the actual particle size.

For this reason, although no error occurs in the total number of fine particles, an error occurs when determining the number of fine particles for each size.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a particle measuring device that can accurately measure the size of particles by correcting the difference in the intensity of laser beams.

[0020]

[Means for Solving the Problems] FIG. 1 shows a principle diagram of a particle measuring device 20 of the present invention. 21 is a reflecting mirror, and 22 is a half mirror, which are arranged to face each other. Between the reflective mirror 21 and the half mirror 22, a particulate measurement region 23 is formed through which particulates pass in a direction perpendicular to the plane of the drawing.

Furthermore, within this particulate measurement region 23, a zigzag optical path 26 is formed within one plane, in which a laser beam 25 emitted from a laser 24 is reflected a plurality of times.

27-1 and 27-2 are reflection points of the laser beam on the half mirror 22.

28-1 and 28-2 are reflection points of the laser beam on the reflection mirror 21.

29-1 is a laser beam directed from the reflection point 27-1 to the reflection mirror 21, and 29-2 is a laser beam directed from the reflection point 28-1.
Laser beam heading from to the half mirror 22, 29-3
is a laser beam directed toward the reflection mirror 21 from the reflection point 27-2.

Reference numerals 30-1 and 30-2 are light receiving means, and the laser beam reflection point 2 on the back surface of the half mirror 22 is
7-1 and 27-2 are arranged correspondingly.

The light-receiving means 30-1 is paired with a first light-receiving element 32-1 that receives the laser beam 31 of the laser beam 25 that has passed through the half mirror 22. It consists of a second light receiving element 35-1 that receives light 34. Similarly, the light receiving means 3
0-2 is the half mirror 2 of the laser beam 29-2.
a first light receiving element 32-2 that receives the laser beam 36 that has passed through the laser beam 32;
2 and more.

40 is a laser beam intensity deviation signal output means, which outputs a laser beam signal a1 from each first light receiving element 32-1, 32-2 of each light receiving means 30-1, 30-2.
, a2 are compared with a reference level, and deviation signals b1, b2 of levels corresponding to the deviations are output for each light receiving means 30-1, 30-2.

41 is a scattered light signal amplifying means, which converts the scattered light signal c1 from the second light receiving element 35-1 of the light receiving means 30-1 into a deviation signal b1 corresponding to the light receiving means 30-1.
The amplified scattered light signal d is amplified with a gain determined by
1 and amplifies the scattered light signal c2 from the second light receiving element 35-2 of another light receiving means 30-2 with a gain determined by the deviation signal b2 corresponding to the light receiving means 30-2. A scattered light signal d2 is output.

42 is maximum level signal selection means,
Of the amplified scattered light signals d1 and d2, the amplified scattered light signal (for example, d1) having the highest level is output as the original scattered light signal.

[0030]

[Operation] The laser beam intensity deviation signal output means 40 and the scattered light signal amplification means 41 are connected to each of the light receiving means 30-1, 30-.
The second light receiving element 35-1, 35-2 acts to correct the influence of the difference in laser beam intensity on the scattered light signals c1, c2 from the second light receiving elements 35-1, 35-2.

The selection means 42 functions to select the original scattered light signal from among the plurality of amplified scattered light signals obtained at the same time.

[0032]

Embodiment FIG. 2 shows an optical system of a particle measuring device according to an embodiment of the present invention. In the figure, parts corresponding to those shown in FIG. 1 are given the same reference numerals.

[0033] The particle measurement area 23 is several tens of mm x several tens of mm.
The width is mm.

On the back surface of the half mirror 22, first to nth light receiving means 30-1 and 30-n are arranged in line, corresponding to the reflection points on the surface of the half mirror 22. The second to n-1th intermediate light receiving means are omitted for convenience of illustration.

50-1 is a photodiode, and the first
constitutes the first light receiving element 32-1 of the light receiving means 30-1.

51-1 is a photodiode, and the first
The second light receiving element 35-1 of the light receiving means 30-1 is arranged at a side portion of the photodiode 50-1.

50-n is a photodiode, and the nth
constitutes the first light receiving element of the light receiving means 30-n.

51-n is a photodiode, and the nth
It constitutes the second light receiving element of the light receiving means 30-n, and is disposed at a side portion of the photodiode 50-n.

The photodiodes 50-1 and 50-n are
The reflecting mirror 21 is disposed between the half mirror 22 and an extended surface of a plane 52 that includes the optical path of the zigzag laser beam.
The laser beams focused by the laser beams are efficiently received and laser beam signals a1 and an are output.

The photodiodes 51-1 and 51-n are
Since the position is deviated from the plane 52, the laser beam is not received, and only the light scattered by the particles is received.

FIG. 3 shows a signal processing system of a particle measuring device according to an embodiment of the present invention. In the figure, parts corresponding to those shown in FIG. 1 are given the same reference numerals.

The laser beam intensity deviation signal output means 40 outputs the first to nth deviation detection circuits 60-1, 60-n second
to n-1th deviation detection circuit are omitted for convenience of illustration), and a reference voltage generation circuit 61 which outputs a reference voltage Vref at a reference level and applies it to each circuit 60-1 to 60-n.
It becomes more.

First to nth deviation detection circuits 60-1 to 60-6
0-n output deviation signals c1 and c2, respectively.

The scattered light signal amplifying means 41 includes first to nth
It consists of gain control amplifier circuits 62-1 to 62-n. Second
The (n-1)th gain control type amplifier circuits are omitted for convenience of illustration.

[0045] First to nth gain control type amplifier circuits 62-
1 to 62-n have amplified scattered light signals d1 to dn whose gains are controlled by the deviation signals c1 and cn, respectively.
Output.

The maximum level signal selection means 42 is constituted by a maximum level signal selection circuit 63 which selects the one having the maximum level from among the amplified scattered light signals d1 to dn inputted at the same time and outputs it.

Next, the operation of the particle measuring device having the above structure will be explained.

As shown in FIGS. 4 and 5, at time T1,
The fine particles 70 move vertically on the paper in the vicinity of the first light receiving means 30-1 in the fine particle measuring region 23, and at time T2, the fine particles 71, which are slightly smaller in diameter than the fine particles 70, move in the vicinity of the first light receiving means 30-1.
An example will be explained in which the vicinity of n is moved perpendicularly to the plane of the paper.

The intensity of the laser beam is lost each time it is reflected by a half mirror.

Therefore, as shown in FIG. 6, the level of the laser beam signal from the photodiodes 50-1 to 50-n gradually weakens as the subscript increases, and the laser beam signal an from the photodiode 50-n increases. The level Ln of is lower than the level L1 of the laser beam signal a1 from the photodiode 50-1.

Laser beam signals a2 to an-1 are omitted for convenience of illustration. - This laser beam signal a1
, an are the first and nth deviation detection circuits 60-1,
60-n, it is compared with the reference voltage Vref (see FIG. 6) from the reference voltage generation circuit 61, and the deviations 80, 81
is detected.

Each of the circuits 60-1 and 60-n outputs deviation signals c1 and 60-n corresponding to the deviations 80 and 81 as shown in FIG.
Continuously outputs c2.

At time T1, the particles 7 near the laser 24
0, a scattered light 82 is generated as shown in FIG. 4, and this is detected by the photodiodes 51-1 and 51-n.

Since the photodiode 51-1 is close to the source of the scattered light 82, and the photodiode 51-n is far away,
As shown in FIGS. 8(A) and 8(B), the photodiode 5
From 1-1, the scattered light signal b with a high peak value (L1-1)
1-T1 is output, and a scattered light signal bn-T1) having a low peak value (Ln-1) is output from the photodiode 51-n.

This scattered light signal b1-T1, bn-T1
are the first and nth gain control type amplifier circuits 62-1 and 62-1, respectively.
2-n, the deviation signals c1 and c2 are amplified with an amplification degree corresponding to the deviation signals c1 and c2.

[0056] As a result, each photodiode 51-1
.
1-1 and 51-n, that is, scattered light signals are obtained when the intensity of the laser beam is equal over the entire particulate measurement region 23.

That is, the difference in intensity of the laser beam is corrected,
A pure scattered light signal with only intensity differences based on the distance and direction from the scattered light source can be obtained.

The amplified scattered light signal corresponding to the photodiode 51-1 near the particle 70 (scattered light generation source) is shown in FIG.
The amplified scattered light signal corresponding to the photodiode 51-n which is farther from the particle 70 is shown as d1-T1 in FIG. 8(C), and is shown as dn-T1 in FIG. 8(D).

This amplified scattered light signal d1-T1, dn-
T1, etc. are simultaneously supplied to the maximum level signal selection circuit 63, and as shown in FIG. 8(E), only the signal d1-T1 having the maximum peak value is extracted as the original scattered light signal of the fine particles 70. .

At time T2, as shown in FIG.
When the light passes through, scattered light 83 is generated, and the scattered light signal b1-T of FIG. 8(A) is output from the photodiode 51-1.
2 is output, and another photodiode 51-n outputs a scattered light signal bn-T2 shown in FIG. 8(B). The respective peak values are L3-1 and L3-n.

[0061] These scattered signals b1-T2, bn-T2 are
Similarly to the above, the first and n-th gain control type amplifier circuits 62
-1, 62-n, the deviation signals c1 and c2 are amplified with a degree of amplification, and the intensity difference of the scattered light based on the intensity difference of the laser beams within the measurement area 23 is corrected. Amplified scattered light signal d1-T2,d shown in D)
It becomes n-T2.

These signals d1-T2 and dn-T2 are pure scattered light signals having intensity differences based on the distance and direction from the scattered light generation source, and the peak value of the former is L4-1, and the peak value of the latter is L4. -n, and the latter is higher than the former.

Since the fine particles 71 have a smaller diameter than the fine particles 70, the wave height value L4-n is lower than the wave height value L2-1.

These signals d1-T2, dn-T2, etc. are simultaneously supplied to the maximum level signal selection circuit 63, and as shown in FIG.
As shown in , the dn-T of the signal with the maximum peak value is
2 is extracted as the original scattered light signal of the fine particles 71.

As can be seen from the above, no matter what position within the measurement area 23 the fine particles pass, that is, regardless of the position within the measurement area 23 where the fine particles pass, the size of the fine particles A scattered light signal of a corresponding level can be obtained.

[0066] As a result, the size of fine particles can be measured with higher accuracy than in the past, and when the number of fine particles is classified according to particle size, the number of fine particles in each category can be accurately measured. .

Therefore, by using the measuring device of this embodiment, it is possible to more accurately grasp the cleanliness inside the semiconductor manufacturing equipment, and it is also effective in improving the yield of semiconductors.

[0068]

As explained above, according to the invention of claim 1, particles actually pass through regardless of the position within the measurement area between the reflecting mirror and the half mirror. It is possible to extract the original scattered light signal having a level that correctly corresponds to the size of the particulate, and therefore the size of the particulate can be accurately measured, and as a result, the size of the particulate can be classified accurately. .

[Brief explanation of drawings]

FIG. 1 is a diagram showing the principle of a particle measuring device of the present invention.

FIG. 2 is a diagram showing an optical system of a particle measuring device according to an embodiment of the present invention.

FIG. 3 is a diagram showing a signal processing system of a particle measuring device according to an embodiment of the present invention.

[Figure 4] Situation when particles pass near the laser (
FIG. 4 is a diagram showing time T1).

FIG. 5 is a diagram showing a situation (time T2) when fine particles pass through a part farther from the laser.

FIG. 6 is a diagram showing a laser beam signal in FIG. 3;

FIG. 7 is a diagram showing a deviation signal in FIG. 3;

FIG. 8 is a diagram showing the scattered light signal and processed signal in FIG. 3;

FIG. 9 is a diagram showing an example of a conventional particle measuring device.

10 is a diagram showing the state of scattering by fine particles in the apparatus of FIG. 9. FIG.

[Explanation of symbols]

20 Particulate measurement device 21 Reflection mirror 22 Half mirror 23 Particulate measurement area 24 Laser 25 Laser beam 26 Zigzag optical path 27-1, 27-2, 28-1, 28-2 Reflection point 2
9-1, 29-2, 29-3 Laser beam 30-1
, 30-2 Light receiving means 31, 36 Laser beam 3 transmitted through the half mirror
2-1, 32-2 First light receiving element 33 Fine particles 34, 37 Scattered light 35-1, 35-2 Second light receiving element 40 Laser beam intensity deviation signal output means 41 Scattered light signal amplification means 42 Maximum level signal selection Means 51-1, 50-2 One plane 52 including the optical path of the zigzag laser beam One plane 53 including the optical path of the zigzag laser beam Condenser lenses 60-1, 60-n Deviation detection circuit 61 Reference voltage Generation circuits 62-1, 62-n Gain control type amplifier circuit 63 Maximum level signal selection circuits 70, 71 Fine particles 80, 81 Deviations 82, 83 Scattered light

Claims (1)

[Claims] Claim 1: A particulate measurement area (23) in which a zigzag optical path (26) is formed in which a laser beam from a laser (24) is reflected multiple times by (25, 29-1, 29-2). A reflecting mirror (21) and a half mirror (22) are arranged to face each other to form a laser beam, and each reflection point (27-
127-2), and receives the laser beam and outputs the laser beam signal (a1, a2).
2), and a second light receiving element (35-1, 35-2, 51-) which is paired with this and receives the scattered light of the laser beam by the fine particles and outputs the scattered light signal (c1, c2).
1, 51-2) and a plurality of light receiving means (30-1,
30-2) and the level of the laser beam signal (a1, a2) from each first light receiving element (32-1, 32-2) of each light receiving means (30-1, 30-2) is set to a reference level ( V
ref), and each light receiving means (30-1, 30-2
), the deviation signal (b1, b2
) for outputting a laser beam intensity deviation signal output means (4
0) and the scattered light signal (c
1, c2) of the corresponding light receiving means obtained by the laser beam intensity deviation signal output means (40).
a scattered light signal amplifying means (41) that amplifies with a gain determined by b1, b2);
41), each light receiving means (30-1, 30
A particulate measuring device comprising maximum level signal selection means (42) for selecting and outputting the maximum level signal among the amplified scattered light signals (d1, d2) for -2).