JPS62220842A - Particulate detector - Google Patents

Abstract

PURPOSE:To reduce the detection limit of particle size of particulates without causing a decrease in the scanning efficiency of a light beam on a surface to be detected by making a microscan reciprocally in a direction crossing the two-dimensional macroscan path of a light beam. CONSTITUTION:A sample table driving device 7 allows a light beam 4 to make a macroscan spirally on the surface 2 to be inspected, but a microscan is made simultaneously through an optical deflector 9 at right angles to the path of the macroscan. this scanning speed is faster than that of the macroscan, so a particulate is irradiated with a light sport plural times according to the macroscan. Reflected light and scattered light from the surface 2 to be inspected as a result of the irradiation of the light beam 4 are photodetected by a photoelectric converter 17 through a lens 15 and an aperture 16 and the output signal 18a of an amplifier 18 is inputted to a signal processing part 22. This signal processing part 22 performs signal processing to decide whether the particulate is present or not and determine the particle size and position of the particulate on the basis of the envelope detection result of the signal 18a.

Description

Detailed Description of the Invention [Technical field to which the invention pertains] The present invention involves scanning the surface of a sample having a flat surface, such as the surface of a silicon wafer for semiconductor device manufacturing, with a light beam, and A particle detection device that detects particles such as dust on the surface by detecting scattered light from the surface, in particular, detecting the detection limit of particles without reducing the scanning efficiency of the light beam on the surface to be inspected. The present invention relates to an apparatus configuration that can reduce the diameter of the light beam and obtain accurate particle information without causing a decrease in particle detection rate even if the light intensity distribution in the cross section of the light beam is non-uniform.

[Prior art and its problems]

The above-mentioned particle detection device for detecting particles on the surface of a silicon wafer generally includes a sample stage on which a sample such as a silicon wafer is placed, and a light irradiation mechanism that irradiates the test surface of the sample placed on the sample stage with a light beam. and a light beam scanning mechanism that drives one of the sample stages and a light irradiation mechanism to relatively scan the surface to be inspected with a light beam, and a light beam scanning mechanism that drives one of the sample stages and a light irradiation mechanism to relatively scan the surface to be inspected with a light beam, and the reflected light emitted from the surface to be inspected by the irradiation of the light beam. , direct scattering, 1ff
In such a particle detection device, a light beam scanning mechanism scans a light spot smaller than the size of the surface to be detected over the entire surface of the surface to be detected. The particles are relatively scanned by the light beam generated by the light beam, and the particles are detected based on the output signal of the light receiving mechanism.

The scanning of the light beam on the surface to be inspected is usually performed along each coordinate axis of a two-axis orthogonal coordinate system or a two-dimensional polar coordinate system.
In the case of t1, continuous scanning in the X-axis direction is repeated in the Y-axis direction VC, and in the latter case, scanning is performed in a spiral pattern.

In each case, based on the output signal of the light receiving mechanism obtained by uniformly scanning the surface to be inspected with the light beam, the number, particle size, composition,
We are trying to obtain information such as its location. Hereinafter, the above-described two-dimensional scanning of the surface to be inspected with the light beam will be referred to as macro scanning.

In the particle detection device described above, the intensity of the light beam on the surface to be detected is made as strong as possible in order to minimize the size of the detectable particles (hereinafter this size may be referred to as the detection limit particle size). There is a need. In order to achieve this goal, the light from the light source is efficiently focused to form a light beam.
It is necessary to reduce the diameter of the light spot formed by this light beam on the surface to be inspected. For these reasons, the above-mentioned particle detection device employs a laser light source with high brightness and good focusing as the light source of the normal light beam.

FIG. 4 is an explanatory diagram of the detection operation in a conventional particle detection device using a light beam as described above. In FIG. 1, numeral 1 indicates a plate-shaped sample having a flat test surface 2.

3a+3b are both fine particles attached to the surface 2 to be tested. 4 was arranged such that its optical axis X--X was perpendicular to the surface to be inspected 2 to irradiate the converging surface 2. The light beam uses a laser beam as a light source, and in this case, each part is arranged so that the optical axis XX passes through the fine particles 3a. The light beam 4 has a circular cross section perpendicular to the X-X axis, and therefore the light spot 5 formed on the test surface 2 by the light beam 4 has a circular shape. 6 is a light intensity distribution characteristic line of each part in this light spot 5. The light source of the light beam 4 is usually a He@Ne laser or a He@Cd L/-the%A ion laser, and the ejection mode, or characteristic, of the light beam 4 emitted from these light sources is line 6
is usually a unimodal Gaussian distribution as shown in the figure, so-called TF
It is in liMoo mode.

In other words, the light intensity distribution within the light spot 5 is non-uniform.

As shown in the figure, when fine particles 3a and 3b are irradiated with a light beam 4, scattered light is generated by these fine particles. The intensity of this scattered light is usually proportional to the coarseness of the fine particles 3a, 3b, the intensity of the light irradiating these fine particles, and the like. Therefore, by detecting such scattered light and measuring the intensity of the scattered light, information such as the presence and particle size of the fine particles 3a*3b can be obtained. The intensity distribution is uneven.

Therefore, in this case, there is a possibility that the particle+information of the micro-particles based on the detection of scattered light contains a large error. For example, even if fine particles 3a and 3b both have the same particle size, since fine particle 3b is located away from the optical axis will be observed incorrectly. Furthermore, in FIG. 4, the light intensity is very low near the outline 5a of the light spot 5, so fine particles with small diameters existing in this vicinity may not be detected.
A phenomenon occurs. In other words, in the conventional particulate detection device which irradiates the surface 2 to be detected with the light beam 4 as shown in Figure 1, the light intensity distribution within the light spot 5 is non-uniform.
There is a problem that the accuracy of the particle size information of the detected fine particles is low, and there is also a problem that the detection rate of fine particles is low. Furthermore, in the case of Fig. 4, if the diameter of the light spot 5 is increased in an attempt to shorten the macro scanning time, the light intensity becomes weaker, and the detection limit particle size of fine particles increases; If the diameter of the optical slot is made smaller and the light intensity is increased, there is also the problem that the macro scanning time becomes longer.

[Purpose of the invention]

The present invention solves the problems in conventional particle detection devices as described above and uses a light beam. This makes it possible to reduce the particle detection limit particle size without actually increasing the detection time without reducing the scanning efficiency of the light beam, which is defined as the irradiated area of the surface to be inspected per unit macro scanning distance. Further, even if the light intensity distribution in the cross section of the light beam is non-uniform, accurate particle information can be obtained without reducing the particle detection rate.An object of the present invention is to provide a particle detection device.

[Key points of the invention]

In order to achieve the above object, the present invention provides a particle detection device that detects particles on a surface to be inspected by scanning a surface to be inspected with a light beam and receiving scattered light obtained by scanning the surface to be inspected with a light beam. In addition to macro-scanning the surface in a two-dimensional manner as in conventional particulate detection devices, the light beam also performs micro-scanning in a direction intersecting this macro-scanning path in a small-amplitude oscillating manner. With what I did.

In this way, macro scanning can be performed using a light beam with a large cross-sectional area that has an isometrically almost uniform light intensity distribution, and as a result, fine particles can be detected without reducing the scanning efficiency of the light beam. The critical particle size can be reduced to a minimum, and even if the light intensity distribution in the cross section of the light beam is non-uniform, the detection rate of particles does not decrease, and accurate particle information can be obtained.

[Embodiments of the invention]

FIG. 1 is a block diagram of an embodiment of the present invention, and FIG. 2 is an explanatory diagram of the operation of the main parts in FIG. In both figures, 6 is the sample stage on which the sample 1 is placed, and 7 is the sample surface 2 that is exposed to the light beam 4.
This is a sample stage driving device that drives the sample stage 6 so that it is macro-scanned in a spiral manner. In Figure 1, the sample l is placed on the sample stage 6.
The loader and unloader used to load and unload the vehicle are omitted. 8 is a laser light source; 9 is an optical deflector that deflects the beam-shaped laser light 8a emitted from the laser light source 8; I;
O is a polarized laser beam emitted from the optical deflector 9, and 11 is a focusing lens that focuses the polarized laser beam 10 into a light beam 4. Reference numeral 12 denotes a light irradiation mechanism that includes a laser light source 8, a light deflector 9, and a focusing lens 11, and irradiates the surface 2 to be examined of the sample 1 placed on the sample stage 6 with a light beam 4 as shown in the figure. The optical deflector 9 is made of heavy 7 lint glass or T
This deflector 9 is an acousto-optic deflector comprising an acousto-optic element formed using a crystal having optical transparency such as eO, PbMoO4, etc. and an ultrasonic exciter bonded to this element. When an ultrasonic excavator is excited to generate ultrasonic waves in the acousto-optic element, the compression waves in the acousto-optic element caused by the ultrasonic waves act as a diffraction grating on the light incident on the element, and the incident light is is diffracted and emitted at a diffraction angle that corresponds to the frequency of the ultrasonic wave, and this type of diffraction takes advantage of the phenomenon that such diffraction is performed oscillatingly at a frequency equal to the frequency of the ultrasonic wave. Reference numeral 13 denotes an optical deflector driving device using a voltage-controlled frequency variable oscillator. It is configured to be excited by

In FIGS. 1 and 2, the optical deflector 9 is configured as described above, and the laser beam 8a incident on the deflector 9 is directed relative to the axis Y-Y perpendicular to the test surface 2 of the sample l. angle θo
Since the ultrasonic oscillator of the optical deflector 9 is excited by the output voltage 13a, the zero-order diffracted light 10a that is not diffracted by the deflector is emitted from the deflector 9. By the diffraction action of the deflector 90, first-order diffracted light tab etc. which vibrate at a deflection angle θ1 with @YY as the center are emitted. The diffracted light 10a is light whose optical axis coincides with that of the laser light 8a, and the diffracted light tab is used as the light beam 4 by the focusing lens 11.

The optically deflected laser beam lO is a laser beam formed by the diffracted light tab deflected as described above. In this case, the deflection angle θ1 is several degrees. Zero-order diffracted light t
If Oa is left unattended, sample 1 etc. will be irradiated, so
There is a possibility that reflected light and the like from this irradiation may enter a light receiving mechanism 19, which will be described later, as light that interferes with particle detection. 14
is a beam stopper for the zero-order diffracted light 10a provided to prevent such a phenomenon. The stopper 14 has a function of absorbing the incident diffracted light tOa.

Although the optical deflector 9 is configured as σ) above, it may also be configured using an electro-optic deflector. The lens 11 may be a normal fixed focus lens, and may also be a diffracted light lens.
If the deflection angle is large.

An F-theta (F-theta) lens may be used in which the diameter of the light spot 5 does not change even if the optical path length between the lens 11 and the surface to be measured 2 changes due to the deflection of the diffracted light tab.

15 is a condenser lens that collects reflected light and scattered light from the test surface 2 based on the irradiation of the light beam 4; 17 is a photoelectric converter that receives the light focused by the lens 15; and 16 is a photoelectric converter. An aperture 18 placed between the photoelectric converter 17 and the lens 15 amplifies the output signal of the photoelectric converter 17 and converts it into a signal 1.
This is an amplifier that outputs 8a. 19 is the lens 1 mentioned above.
5, an aperture 16, a converter 17, and an amplifier 18. The aperture 16, together with the lens 15 and the photoelectric converter 17, is provided to reduce the effective light receiving area of the light receiving mechanism 19 by no. Output signal 18a is f detector 1
In other words, the signal corresponds to the amount of light received by the light receiving mechanism 19.
This is the light reception signal output by .

In FIGS. 1 and 2, it is assumed that the diffracted light tab oscillates around the intersection point Z of the optical axis of the laser light 8a incident on the optical polarizer 9 and the axis Y-Y. Assuming that the distance between point Z and the surface to be inspected 2 is lOO [parrot], when θ1 is 1°, the light spot 5 is on both sides of the axis Y-Y at t=approximately 1.
I ended up shooting with a shooting width of 8 [4]. Hereinafter, the oscillating scan of the single beam width t on the surface to be inspected 2 performed by the polarized laser beam 10 photographed as described above will be referred to as micro-scanning.

As mentioned above, in FIG. 1, the sample stage driving device 7 causes the surface to be examined 2 to be macro-scanned in a spiral manner by the light beam 4, but in this case, at the same time, the optical deflector 9 is used to scan the surface 2 perpendicularly to the macro-scanning path. The above-mentioned micro-scanning is performed. Therefore, the light spot 5 moves on the surface to be inspected 2 along the composite path of the macro-scanning path and the micro-scanning path. 20 is the surface to be inspected 2 by the light beam 4;
be scanned relatively as described above. This is a light beam scanning mechanism consisting of drive devices 7 and 13.

FIG. 3 is an explanatory diagram of the operation of the main parts in FIG. 1 when the surface to be inspected 2 is scanned by the light beam 4 along the synthetic scanning path as described above. A plan view of the section;
3 is a waveform diagram of the light reception signal tea corresponding to the state shown in the figure. In Figure 3, W is the axis Y in Figure 2.
-Y and the surface to be inspected 2 Which intersection P is the moving line that moves on the surface to be inspected 2 due to the above-mentioned macro scanning, and the arrow Q indicates the direction opposite to the moving direction of the intersection P, that is, the advancing direction of the macro scanning. It shows. Macro-scanning of the light beam 4 with respect to the surface to be inspected 2 is performed by the sample stage driving device 7Vc shown in FIG. At the same time, it will move in the opposite direction to the Q arrow.

In this case, the surface 2 to be inspected is micro-scanned vibrationally at a high speed by the light spot 5 so as to be perpendicular to the line of movement W. t is the half amplitude of the vibration motion of the center of the light spot 5 in this vibration scanning. The surface 2 to be inspected is thus scanned center 1 by the light spot 5, and the scanning speed is faster than that of macro scanning, so the particles 3a on the movement line W move along the macro scanning. The light spots 5&C will be irradiated multiple times. Therefore, in Figure 3, the fine particles 3a are
While the approximate circular irradiation area 21 formed by the vibrating light spot 5 is stacked upward, scattered light by the fine particles 31 is generated multiple times. FIG. 30 shows the waveform of the signal tSa obtained by such scattered light.

As is clear from the above, this waveform is a series of pulse trains. In the figure, the number of pulses in this pulse train is five, but it is clear that the number of nonolus can be increased by increasing the vibration frequency of micro-scanning, and the pulse train in Figure 3 is formed as described above, it is also clear that the envelope of this pulse train exhibits a shape approximately corresponding to the shape of the light intensity distribution characteristic line within the light spot 5. In other words, the shape of the envelope of the 00 pulse train in FIG. 3 becomes bell-shaped if the light intensity distribution at the light spot 5Vc is like the characteristic gland 6 shown in FIG. 4. Then, a pulse train having such a shape can be generated by increasing the micro-scanning frequency so that the fine particles 3a can move along the movement line W as long as the fine particles 3a have a width of L=2t shown in It occurs in the same shape no matter where it is, including the top. In other words, one particle 3a can be detected by performing envelope detection of the above-mentioned pulse train in the signal tea shown in FIG. It is clear from the above that the light intensity distribution characteristic at the light spot 5 is not affected as long as . Therefore, in this case, the surface 2 to be inspected is % equivalently treated by a light spot having a larger area than the light spot 5, in which the light intensity distribution in the direction perpendicular to the movement line W is uniform over the width. It will be macro scanned.

In FIG. 1, a surface to be inspected 2 is scanned by a light beam 4 along a composite scanning path of the above-mentioned macro scanning path and micro scanning path. Therefore, in this case, the irradiation area of the surface to be inspected per unit macro-scanning distance by the light beam 4, that is, the scanning efficiency of the light beam 4, is improved compared to a conventional particulate detection device that does not perform micro-scanning. Since the above-mentioned macro-scanning using the sample stage driving device [7] is performed mechanically, the speed of this macro-scanning cannot be made extremely high. According to the particle detection device shown in FIG. 1, the time required to scan the entire surface 2 to be detected with the light beam 4 can be reduced compared to the conventional detection device. 2 in Figure 1
2 receives the light reception signal 18a, the macro scanning position signal 7a by the light beam 4vC output from the sample stage driving device 7, and the micro scanning position signal 13b by the light beam 4 output from the 2-light deflector driving device 13. In the signal processing section,
This signal processing unit 22 performs envelope detection for the above-mentioned pulse train in the signal tSa, determines whether or not particles are present on the test surface 2 based on the detection results, determines the particle size of the particles, and outputs the signals 7a and 13b. It is configured to perform signal processing such as determining the position of the particles used, and to store and display the determination and determination results as appropriate.

In FIG. 1, the particle detection device is constructed as described above. Therefore, in such an apparatus, a laser light source is used as a light source to increase the intensity of irradiation of the surface 2 to be inspected by the light spot 5, and even if the light intensity distribution in the light spot 5 becomes uneven as a result, the above-mentioned Due to micro-scanning, the surface to be inspected 2 is equivalently macro-scanned with a light spot with a uniform light intensity distribution, which results in a decrease in the accuracy of the particle size information of detected particles and a decrease in the detection rate of particles. There isn't. In addition, according to such a particle detection device, macro scanning is performed using a light spot with strong light intensity and equivalently large diameter for the micro scanning, which improves the efficiency of macro scanning and improves the efficiency of macro scanning in practice. The detection limit particle size of fine particles can be increased by increasing the light intensity of the light spot 5. It can be easily made small, and in this case, the light intensity distribution of the light spot 5 does not become non-uniform and the scanning efficiency of the light beam 4 does not decrease.

In FIG. 1, macro-scanning of the test surface 2 by the light beam 4 is performed by the sample stage driving device t7.

Further, the micro-scanning by the beam is performed by the optical deflector 9 and the optical deflector driving device 13. In the present invention, the above-mentioned macro-scanning and micro-scanning by the optical beam 4 are defined as the sample stage 6 and the light irradiation. The scanning may be performed by a light beam scanning mechanism that drives at least one of the mechanism 12 and the mechanism 12.

In addition, in FIGS. 2 and 3, the light spot 5 intersects the moving line W to perform micro-scanning, but 1
In the present invention, the main parts may be configured so that the light spot 5 performs micro-scanning on one side of the moving line W.

〔Effect of the invention〕

As described above, in one aspect of the present invention, in a particle detection device that detects particles on a horizontal surface by scanning a surface to be detected with a light beam and receiving scattered light obtained by scanning the surface to be detected with a light beam, In addition to macro-scanning in a two-dimensional manner, micro-scanning is also performed using a light beam in a direction intersecting the macro-scanning path in a reciprocating manner with a small loss width. Therefore, in this case, even if a light beam whose light intensity distribution on the jet surface is inherently non-uniform is used, macro scanning can be performed using a light beam with a large cross-sectional area and a nearly uniform light intensity distribution in one equivalent sense. As a result, the present invention has the effect of reducing the detection limit particle size of fine particles without causing a decrease in the scanning efficiency of the light beam. Since the detection can be carried out with high light intensity, the present invention has the effect of increasing the detection rate of particles and obtaining more accurate particle information.

[Brief explanation of drawings]

Fig. 1 is a configuration diagram of an embodiment of the present invention, Fig. 2 is an explanatory diagram of the main parts of the wJ1 diagram, and Fig. 1m3 is an explanatory diagram of the operation corresponding to Fig. 2. 3 is a plan view of the different part in the figure, and FIG. 3 is a waveform diagram of a received light signal. FIG. 4 is an explanatory diagram of a detection operation in a conventional particle detection device. 1...Sample% 2...Test surface, 3a,
3b...Fine particles, 4...Light beam, 6
... Sample stage, 12 ... Light irradiation mechanism, 19 ... Light receiving mechanism, 20 ... Light beam scanning mechanism. Blindness 1 Notebook 2 Illustrated wealth 4 Mouth

Claims (1)

[Claims] 1) a sample stand on which a sample having a planar test surface is placed; a light irradiation mechanism that irradiates the test surface of the sample placed on the sample stand with a light beam; and the sample stand and the light irradiation. a light beam scanning mechanism that drives at least one of the light beam and the light beam to scan the surface to be inspected with the light beam; and a light receiving mechanism that outputs a light reception signal, and detects particles on the test surface based on the light reception signal, and the light beam scanning mechanism scans the test surface with the light beam, Particle detection is carried out along a composite scanning path consisting of a macro scanning path that scans two-dimensionally and a micro scanning path that scans back and forth in a small-amplitude oscillating manner in a direction that intersects the macro scanning path. Device.