JPH0580982B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention is directed to 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. A particle detection device that detects particles such as dust on a surface by detecting scattered light from a surface, and in particular, a detection limit particle size of particles without reducing the scanning efficiency of a light beam on the surface to be inspected. The present invention relates to an apparatus configuration that can be made small and that can obtain accurate particulate information without reducing the particulate detection rate even if the light intensity distribution in the cross section of the light beam is non-uniform.

[Conventional technology]

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 beam that irradiates the surface of the sample placed on the sample stage. an irradiation mechanism; a light beam scanning mechanism that drives at least one of the sample stage and the light irradiation mechanism to relatively scan a surface to be inspected with a light beam; The particle detection device is equipped with a light receiving mechanism that receives reflected light, directly scattered light, fluorescent light scattered light, etc. In such a particle detection device, the surface to be inspected is scanned over its entire surface by a light beam scanning mechanism. ,
A light spot smaller than the size of the surface to be inspected is relatively scanned by a light beam generated on the surface to be inspected,
Fine particles are then 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, and in the former case, continuous scanning in the X-axis direction is repeated in the Y-axis direction. In the latter case, scanning is performed in a spiral manner. In either case, based on the output signal of the light receiving mechanism obtained by uniformly scanning the surface to be inspected with the light beam,
We are trying to obtain information such as composition and 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.

[Problem to be solved by the invention]

In the particle detection device described above, in order to minimize the size of detectable particles (hereinafter this size may be referred to as the detection limit particle size), the intensity of the light beam on the surface to be detected is made as strong as possible. There is a need to. For this purpose, it is necessary to efficiently condense the light from the light source to form a light beam, and to reduce the diameter of the light spot formed on the surface to be inspected by this light beam. 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.
3a and 3b are both fine particles attached to the surface 2 to be inspected. Reference numeral 4 denotes a light beam whose optical axis X-X is orthogonal to the surface 2 to be inspected, and whose light source is a laser beam.
Each part is arranged so that X penetrates 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 surface to be inspected 2 by the light beam 4 has a circular shape. 6 is a light intensity distribution characteristic line of each part of this light spot 5. A He/Ne laser, a He/Cd laser, or an Ar ion laser is usually used as a light source for the light beam 4, and the transverse mode of the light beam 4 generated by these light sources, that is, the characteristic line 6, is normally As shown in the figure, it is a unimodal Gaussian distribution, so-called TEM ₀₀ mode.
In other words, the light intensity distribution within the light spot 5 is non-uniform.

As shown, the particles 3a and 3b are exposed to the light beam 4.
When irradiated with light, these particles produce scattered light. In this way, the intensity of this scattered light is
It is customary to be proportional to the particle size of particles a and 3b, the intensity of light irradiating these particles, and the like. Therefore, by detecting such scattered light and measuring the intensity of the scattered light, it is possible to obtain information such as the presence and particle size of the fine particles 3a and 3b. The light intensity distribution is non-uniform. Therefore, in this case, the particle size information of the fine particles based on the detection of scattered light may contain a large error. For example, even if fine particles 3a and 3b both have the same particle size, fine particle 3b
Since it is located away from the optical axis XX, it will be erroneously observed that it is a fine particle with a smaller particle size than the fine particle 3a. Furthermore, in FIG. 4, since the light intensity is very low near the outline 5a of the light spot 5, a phenomenon occurs in which small particles existing in this vicinity may not be detected. In other words, in the conventional particulate detection device that irradiates the surface 2 with a light beam 4 as shown in the figure, the light intensity distribution within the light spot 5 is non-uniform, so that the particles of the detected particulate matter cannot be detected. There is a problem that the accuracy of diameter information is low, and there is also a problem that the detection rate of fine particles is low. Furthermore, the fourth
In the case shown in the figure, if the diameter of the light spot 5 is increased in an attempt to shorten the macro scanning time, the light intensity will become weaker and the detection limit particle size of fine particles will increase.
If the diameter of the optical spot 5 is made smaller and the light intensity is increased in order to reduce the detection limit particle size, there is also the problem that the macro scanning time becomes longer.

The present invention solves the problems in conventional particulate detection devices as described above, and improves the scanning efficiency of the light beam (effective scanning per unit time), which is defined as the irradiated area of the surface to be inspected per unit macro scanning distance by the light beam. As a result, the detection limit particle size of fine particles can be reduced without actually prolonging the detection time, and even if the light intensity distribution in the cross section of the light beam is uneven, fine particle detection is possible. It is an object of the present invention to provide a particulate detection device that can obtain accurate particulate information without causing a decrease in particle efficiency.

[Means to solve the problem]

In order to achieve the above object, the present invention includes a sample stand on which a sample having a planar test surface is placed, and a light irradiation mechanism that irradiates the test surface of the sample placed on the sample stand with a light beam. , a light beam scanning mechanism that drives the sample stage and scans the test surface two-dimensionally with a light beam; A light receiving mechanism that outputs a light receiving signal, and a light irradiation mechanism of a particle detection device that detects particles on a surface to be inspected based on the light receiving signal. It has an optical deflector that performs micro-scanning that performs reciprocating vibrational scanning at high frequency and small amplitude in a direction intersecting the scanning path, and the light-receiving mechanism is configured such that at least one of the particles is scanned multiple times by micro-scanning. Envelope detection is performed on a series of optical pulse trains emitted by the laser beam, and a received light signal is output based on the result of the envelope detection.

[Effect]

With the above technical means, it is equivalent to performing macro scanning with a light beam of a large cross-sectional area with a nearly uniform light intensity distribution, and the detection limit of fine particles can be reached without causing a decrease in the scanning efficiency of the light beam. The particle size can be reduced, and even if the light intensity distribution in the cross section of the light beam is non-uniform, the light beam can be narrowed down to increase its intensity and a decrease in the particle detection rate can be easily avoided.

〔Example〕

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 a sample stage on which the sample 1 is placed, and 7 is a sample stage driving device that drives the sample stage 6 so that the surface to be examined 2 is macro-scanned in a spiral shape by the light beam 4. In FIG. 1, a loader and an unloader for loading and unloading the sample 1 on the sample stage 6 are omitted. 8 is a laser light source, 9 is a light deflector that deflects the beam-shaped laser light 8a emitted from the laser light source 8, 10 is a deflected laser light emitted from the light deflector 9, and 11 is a light deflector that focuses the deflected laser light 10. This is a focusing lens that converts the light beam into a light beam 4. 12 is a light irradiation mechanism consisting of a laser light source 8, a light deflector 9, and a focusing lens 11, and irradiates the test surface 2 of the sample 1 placed on the sample stage 6 with a light beam 4 as shown in the figure. be. The optical deflector 9 is made of heavy flint glass or
This deflector 9 is an acousto-optic deflector comprising an acousto-optic element formed using an optically transparent crystal such as TeO ₂ or PbMoO ₄ and an ultrasonic oscillator bonded to this element. When an ultrasonic oscillator 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 This method utilizes the phenomenon that light is diffracted and emitted at a diffraction angle that corresponds to the frequency of the ultrasonic wave, and that such diffraction is performed oscillatingly at a frequency that is equal to the frequency of the ultrasonic wave. Reference numeral 13 denotes an optical deflection drive device using a voltage-controlled frequency variable oscillator. The device is configured to be excited at a frequency.

1 and 2, the optical deflector 9 is configured as described above, and the laser beam 8a incident on the deflector 9 is directed along the axis Y perpendicular to the test surface 2 of the sample 1.
-Y is configured to be incident at an angle θ ₀ , so when the ultrasonic oscillator of the optical deflector 9 is excited with the output voltage 13a, the beam from the deflector 9 is diffracted by the deflector. Zero-order diffracted light 10 that will never be
a. Due to the diffraction effect of the deflector 9, first-order diffracted light 10b and the like that vibrate at a deflection angle θ ₁ about the axis Y-Y are emitted. The diffracted light 10a is light whose optical axis coincides with that of the laser light 8a, and the diffracted light 10b is the light that is reflected by the focusing lens 11.
This is the light used as the light beam 4 by.
The polarized laser beam 10 is a laser beam formed by the diffracted light 10b deflected as described above. In this case, the deflection angle θ ₁ is an angle of several degrees. If the zero-order diffracted light 10a is left unattended, it will irradiate the sample 1, etc., so there is a possibility that reflected light etc. from this irradiation may enter the light receiving mechanism 19, which will be described later, as interference light for particle detection. 14 is a zero-order diffracted light 10 arranged to prevent such a phenomenon.
This is a beam stopper for a. The stopper 14 has a function of absorbing the incident diffracted light 10a. Although the optical deflector 9 is configured as described above, it may also be configured using an electro-optic deflector.
The lens 11 may be a normal fixed focus lens, and if the deflection angle θ ₁ of the diffracted light 10b is large, the optical path length between the lens 11 and the test surface 2 based on the deflection of the diffracted light 10b can be changed. The diameter of the optical spot 5 does not change even if there is a change F・θ (F・θ)
It may also be a lens.

15 is a condenser lens that condenses the opposite light and scattered light from the test surface 2 based on the irradiation of the light beam 4; 17;
16 is an aperture arranged between the photoelectric converter 17 and the lens 15; 18 is a photoelectric converter that amplifies the output signal of the photoelectric converter 17 and converts the signal into a signal; 18a. Reference numeral 19 denotes a light receiving mechanism consisting of the above-mentioned lens 15, aperture 16, converter 17, and amplifier 18. The aperture 16 is provided together with the lens 15 and photoelectric converter 17 to adjust the effective light receiving area of the light receiving mechanism 19. . Output signal 1
8a is a signal corresponding to the amount of light received by the converter 17; in other words, it is a light reception signal output by the light reception mechanism 19. In FIGS. 1 and 2, the optical deflector 9
Assuming that the diffracted light 10b oscillates around the intersection Z of the optical axis of the laser light 8a incident on the laser beam 8a and the axis Y-Y, the distance between this point Z and the test surface 2 is
Assuming 100 [mm], when θ ₁ is 1°, the optical spot 5 will vibrate on both sides of the axis Y-Y with an amplitude of l = about 1.8 [mm]. Hereinafter, the oscillating scan with half amplitude l on the surface to be inspected 2 performed by the polarized laser beam 10 oscillating as described above will be referred to as micro-scanning.

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

FIG. 3 is an explanatory diagram of the operation of the main part 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, and FIG. 3A is an explanatory diagram of the main part in FIG. FIG. 3B is a waveform diagram of the received light signal 18a corresponding to the state shown in FIG. A. In FIG. 3, W is a moving line along which the intersection P of the axis Y-Y and the surface to be inspected 2 in FIG. It shows the direction opposite to the movement direction, that is, the direction in which macro scanning progresses. Macro-scanning of the light beam 4 with respect to the surface to be inspected 2 is performed by the sample stage driving device 7 shown in FIG. It will move together with surface 2 in the direction opposite 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 orthogonal to the line of movement W. l is the half amplitude of the vibration motion of the center of the optical spot 5 in this vibration scanning. The surface to be inspected 2 is thus scanned by the light spot 5, and the scanning speed is faster than macro scanning, so that the fine particles 3a on the movement line W are
is irradiated multiple times by the light spot 5 during macro scanning. Therefore, in FIG. 3A, while the fine particles 3a cross upwardly the approximate elliptical irradiation area 21 formed by the vibrating light spot 5, scattered light by the fine particles 3a is generated multiple times. . FIG. 3B shows the waveform of the signal 18a obtained by such scattered light, and 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 this number of pulses can be increased by increasing the vibration frequency of micro-scanning, and the number of pulses in this pulse train in Figure 3B can be increased. 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 pulse train shown in FIG. 3B becomes bell-shaped if the light intensity distribution at the light spot 5 is as shown in the characteristic line 6 shown in FIG. The pulse train having such a shape can be generated by increasing the vibration frequency of the micro-scanning so long as the particle 3a is within the width of L=2l shown in the figure. It occurs in the same shape no matter the location. That is, one particle 3a can be detected by performing envelope detection of the above-mentioned pulse train in the signal 18a 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 the light intensity is . Therefore, in this case, on the surface 2 to be inspected, the light intensity distribution in the direction perpendicular to the movement line W is uniform over the width L. A light spot having a larger area than the light spot 5 will equivalently perform macro scanning.

In FIG. 1, a surface to be inspected 2 is scanned by a light beam 4 along a composite scanning path of the above-described 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 inspected with the light beam 4 can be reduced compared to the conventional detection device. Reference numeral 22 in FIG. 1 indicates a macro-scanning position signal 7a based on the light receiving signal 18a, the light beam 4 output from the sample stage drive device 7, and a micro-scanning device 13b using the light beam 4 output from the optical deflector drive device 13. This signal processing unit 22 performs envelope detection for the above-mentioned pulse train in the signal 18a, determines whether or not particles are present on the test surface 2 based on this detection result, and processes the detection of the particles. It is configured to perform signal processing such as determination of particle size and determination of particle position using signals 7a and 13b, and to store and display these determination and determination results as appropriate.

In FIG. 1, the particle detection device is constructed as described above. Therefore, in such an apparatus, even if 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 as a result, the light intensity distribution at the light spot 5 becomes non-uniform, The surface to be inspected 2 is
is equivalently macro-scanned by a light spot with a uniform light intensity distribution, so there will be no reduction in the accuracy of the particle size information of the detected particles or a reduction in the detection rate of the particles. 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. Even without increasing the upper detection limit particle size, the time required to inspect the surface to be inspected for particles can be shortened. In this case, by increasing the light intensity of the light spot 5, the detection limit particle size of the fine particles can be easily reduced. It can also be said that the scanning efficiency does not decrease.

In FIG. 1, the surface to be inspected 2 by the light beam 4 is
Macro scanning is performed by the sample stage driving device 7,
Further, the micro-scanning by the beam is performed by the optical deflector 9 and the optical deflector driving device 13, but in the present invention, the above-mentioned macro-scanning and micro-scanning by the optical beam 4 are performed by the sample stage 6. The light beam scanning mechanism may be used to drive at least one of the light irradiation mechanism 12 and the light beam scanning mechanism. Furthermore, in FIGS. 2 and 3, the optical spot 5 crosses the moving line W to perform micro-scanning, but in the present invention, the optical spot 5 performs micro-scanning only on one side of the moving line W. There is no problem in configuring the main parts as follows.

〔Effect of the invention〕

As described above, in the present invention, in a particle detection device that detects particles on a surface to be inspected by scanning the surface to be inspected with a light beam and receiving scattered light obtained by scanning the surface to be inspected, In addition to two-dimensional macro-scanning of the surface to be inspected, micro-scanning is performed in which the inspection surface is vibrated back and forth at high frequency and small amplitude in a direction that intersects this macro-scanning path, with the macro-scanning path as the center. At least one of the microparticles is scanned multiple times by this microscanning, and an envelope detection is performed on a series of light pulse trains emitted.
Since particle detection (inspection of presence, particle size, and position) is performed based on the results of this envelope detection, even if a light beam whose light intensity distribution in the cross section is inherently non-uniform is used, it is possible to obtain equivalent Macro scanning can be performed using a light beam with a large cross-sectional area and a substantially uniform light intensity distribution.As a result, the present invention can achieve the detection limit particle size of fine particles without reducing the scanning efficiency of the light beam. This has the effect of making it smaller. Further, since the equivalent macro scan as described above can be performed 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 operation of the main parts in Fig. 1, and Fig. 3 is a diagram showing the operation of the main parts in Fig.
FIG. 3A is a plan view of the main part in FIG. 2, and FIG. 3B 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...Particles, 4...Light beam, 6...Sample stage, 12...
Light irradiation mechanism, 19... Light receiving mechanism, 20... Light beam scanning mechanism.

Claims (1)

[Scope of Claims] 1. A sample stage 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 a light beam scanning mechanism that drives a table to macro scan the surface to be inspected in a two-dimensional manner with the light beam;
a light-receiving mechanism that receives light emitted from the surface to be measured by irradiation with the light beam and outputs a light-receiving signal according to the amount of received light, and detects fine particles on the surface to be measured based on the light-receiving signal. In the particulate detection device that performs detection, the light irradiation mechanism scans the light beam in a reciprocating manner in a vibrating manner at a high frequency and with a small amplitude in a direction that intersects with the macro scanning path, with the light beam as the center. The light receiving mechanism performs envelope detection of a series of optical pulse trains emitted after at least one of the fine particles is scanned multiple times by the micro-scanning, and A particle detection device, characterized in that the device outputs the light reception signal based on the result of envelope detection.