JPH0812061B2 - Surface inspection device - Google Patents

Description

Description: TECHNICAL FIELD OF THE INVENTION The present invention relates to a surface inspection apparatus for inspecting a surface state of a substrate, and in particular, it is possible to perform the inspection under the same condition on substrates having different optical reflectances. Regarding improvements made.

[Technical background of the invention and its problems] When inspecting the surface state of a substrate, for example, the state of generation of scratches and the size of surface deposits, conventionally, the substrate surface is irradiated with light and then the surface of the substrate is inspected. Collects scattered light from
A method generally performed by detecting this intensity change. Particularly in recent years, as a surface inspection device, a device that detects the size of deposits such as dust and dust on the surface of a semiconductor wafer has been emphasized. The surface inspection device for such an application scans the surface of a semiconductor wafer with a laser beam, collects scattered light due to dust, dust, etc. on the surface of the wafer, and collects this photomultiplier tube (photomultiplier tube, photomultiplier tube, Hereinafter, it is general that the detection is performed by PMT). The amplitude (peak value) of the scattered light signal from the standard particles on the silicon semiconductor wafer has a monotonically increasing relationship with the particle size. Therefore, the size of dust, dust, etc. is determined by setting the signal level for a specific particle size to the slice level. Then, dust having a specific particle size or more and dust having a specific number or more attached thereto are rewashed.

In Fig. 11, the horizontal axis is the particle size D of surface deposits such as dust and dust.
(Μm) and the vertical axis is a characteristic curve diagram in which the peak value P (V) of the scattered light signal is taken. In FIG. 11, a curve a is a silicon substrate whose underlying substrate is the same, a curve b is a silicon substrate surface covered with a polycrystalline silicon film, and a curve c is a silicon substrate surface covered with a silicon oxide film. The curve d represents the case where the surface of the silicon substrate is covered with the silicon nitride film, and the curve d is the case in each case. Such a curve diagram is generally called a sensitivity characteristic curve diagram, and the sensitivity characteristic depends on the optical property, particularly the reflectance, of the film formed on the surface of the silicon substrate. Therefore, when detecting dust, dust, etc. on a silicon substrate having a film formed on its surface, the sensitivity characteristics are different from those of the silicon substrate, and it is very difficult to set the slice level. As a result, conventionally, there is a drawback in that it is impossible to detect deposits on a silicon substrate on which various films are formed with the same sensitivity as in the case of the silicon substrate.

[Object of the Invention] The present invention has been made in consideration of the above circumstances, and an object thereof is to detect scattered light from particles on a substrate surface having different light reflectances with the same sensitivity. The object is to provide a surface inspection device capable of detecting particles under the same conditions.

[Summary of the Invention] A surface inspection apparatus of the present invention irradiates a surface of a substrate with light that is narrowed down, collects scattered light from the surface of the substrate, detects the light with a light detection system, and detects the detected light. In the surface inspection apparatus for detecting a minute specimen on the substrate surface according to the intensity, the photodetection system includes a photomultiplier tube for outputting a signal according to the intensity of scattered light from the substrate surface, and the photomultiplier. Before the detection of the minute sample and the amplifier that amplifies the signal output from the tube, the whole system so that the output signal level of the amplifier based on the scattered light by the substrate itself becomes constant regardless of the type of substrate. And sensitivity setting means for setting the sensitivity according to the intensity of scattered light from the substrate surface.

Further, the surface inspection apparatus of the invention irradiates the surface of the substrate with light that is narrowed down and collects scattered light from the surface of the substrate,
This is detected by a light detection system, and in a surface inspection device that detects a minute sample on the substrate surface according to the detected light intensity, the light detection system outputs a signal according to the intensity of scattered light from the substrate surface. A first photomultiplier tube for output, a first amplifier for amplifying a signal output from the first photomultiplier tube, and a signal according to the intensity of specularly reflected light from the surface of the substrate. A second photomultiplier tube, a second amplifier for amplifying the signal output from the second photomultiplier tube, and the first amplifier based on scattered light from the substrate itself before detecting the minute sample. And a sensitivity setting means for setting the sensitivity of the entire system according to the output signal of the second amplifier so that the output signal level of the first amplifier becomes constant regardless of the type of the substrate. To do.

Embodiments of the Invention Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing the configuration of the first embodiment of the surface inspection apparatus according to the present invention. The substrate 12 to be inspected by the laser light emitted from the light source 11, that is, the light that is narrowed down.
The surface of is scanned sequentially. This board 12
The specularly reflected light 13 from the surface of the is emitted to the outside from one opening of the integrating sphere 14. In addition, scattered light 15 from the surface of the substrate 12
Is integrated by the integrating sphere 14 and is led out from the other opening of the integrating sphere 14. The derived scattered light is incident on the light receiving surface of a PMT (photomultiplier tube) 16 and is converted into a voltage signal corresponding to the light intensity here. The voltage signal converted here is amplified by the head amplifier 17 having a fixed amplification factor and supplied to a measurement circuit (not shown). In this measuring circuit, a slice level corresponding to a specific grain size is set, and by detecting the output of the head amplifier 17 at this slice level, dust and dust having a specific grain size or more are detected.

On the other hand, the output voltage from the head amplifier 17 is supplied to the averaging unit 18. The averaging unit 18 averages the output voltage of the head amplifier 17 in a predetermined period and holds it. The averaging process in the averaging unit 18 is the average value of the output voltage of the head amplifier 17 within a certain fixed time due to the in-plane variation of the reflectance due to the non-uniformity of the in-plane film thickness of the inspected substrate 12. Is obtained and the value is given as the relative reflectance of the inspected substrate 12. Examples of this averaging process include a method of obtaining an average value of the output voltage of the head amplifier 17 through an integrating circuit, or A / D conversion of the output voltage of the head amplifier 17, and sampling of the voltage within a certain period at multiple points. Well-known methods such as a method of obtaining the average value can be used. This averaging part 18
The holding voltage of is supplied to the high voltage power supply controller 19. The high-voltage power supply control unit 19 supplies a control signal according to the voltage held in the averaging unit 18 to the high-voltage power supply unit (HV) 20. The high-voltage power supply unit 20 supplies a high DC voltage to the PMT 16, and its value is set according to the control signal. In addition, the above PMT1
The head amplifier 17, the averaging unit 18, the high-voltage power supply control unit 19, and the high-voltage power supply unit 20 constitute a photodetection system that detects the scattered light intensity of the substrate 12.

In such a configuration, before detecting dust, dust, etc., first, the surface of the substrate 12 is irradiated with laser light from the light source 11 for a predetermined period, and the scattered light 15 from the surface of the substrate 12 at this time is detected.
Is converted into a voltage signal by the PMT 16 and further averaged by the averaging unit 18. As a laser beam scanning method in this case, for example, as shown in FIG. 2, the laser beam is focused on a substantially central point a of the substrate 12 to be measured, and in this state, the substrate 12 is moved to an arrow b in the drawing. And is translated in the direction of arrow c. Then, during the period when the substrate 12 makes one rotation, for example, PM
The averaging unit 18 averages the converted signals of T16. Then, the DC high voltage corresponding to the voltage signal held by the averaging unit 18 at this time is output from the high voltage power supply unit 20. This makes PMT16
The sensitivity of is set according to the light scattering rate of the surface of the substrate 12 at that time. Here, the high-voltage power supply control unit 19 controls the high-voltage power supply unit 20 so that the converted voltage signal level of the PMT 16 obtained when the surface of the substrate 12 is scanned with laser light is constant regardless of the type of the substrate 12. Preprogrammed to control.

Next, as described above, regardless of the type of substrate 12, PMT1
The above program for setting the sensitivity so that the converted voltage signal level of 6 is constant will be described. here,
Relative reflectance of various substrates (ratio of the reflectance of the substrate when the underlying substrate is the reflectance of the silicon substrate itself is 1.0) and the PMT16 due to dust and dust with the same particle size adhered on it. It is known that there is a proportional relationship with the detected output voltage as shown in FIG. It is also known that there is a proportional relationship between the applied voltage of the PMT16 and the detection output voltage when irradiating laser light on dust or dust having the same particle size (for example, 2.0 μm) as shown in FIG. Has been. From the characteristics shown in FIGS. 3 and 4, when measuring various substrates, PMT1 against dust and dust with the same particle size is obtained.
It is possible to obtain the applied voltage of the PMT 16 so that the detection output voltages of 6 become the same. FIG. 5 shows this characteristic. Such characteristics can be obtained as follows. For example, in FIG. 3, the detected output voltage is 7.0 V when the relative reflectance is 1.0. Then, the detection output voltage is 4.0 V when the substrate having the same particle size and dust and dust and a relative reflectance of 0.5 is measured. When the applied voltage of PMT16 for both detection output voltages is calculated from Fig. 4, it is V
1, V2. Then, in order to obtain the same detection output voltage as in the case of the substrate having the relative reflectance of 0.5 and the substrate having the relative reflectance of 1.0, as is apparent from FIG. 4, V2 is the difference voltage between V1 and V2. It suffices to apply a voltage added with Vd to the PMT16. Therefore, as shown in FIG. 5, the relative reflectance is 0.5.
In order to obtain the same detection output voltage as in the case of the substrate having the relative reflectance of 1.0, the voltage obtained by adding the above voltage Vd to the voltage applied to the substrate having the relative reflectance of 1.0 may be applied to the PMT16. It will be. FIG. 5 is obtained by obtaining the increase / decrease in the voltage with respect to the applied voltage of the substrate having the relative reflectance of 1.0 in the substrates having the various relative reflectances as described above. Then, such characteristics are stored in the high-voltage power supply controller 19 as a table.

Further, the detected output voltage from the PMT 16 obtained when the underlying substrate on which dust or dust having a specific particle diameter is attached scans the surface of the silicon substrate itself is stored in the high-voltage power supply control unit 19 as V0.

Then, before performing detection, the surface of the substrate 12 is irradiated with laser light for a predetermined period as described above, and the scattered light 15 from the surface of the substrate 12 at this time is converted into a voltage signal by the PMT 16, and further by the averaging unit 18. Average out. Assuming that the voltage obtained in this case is V, the high-voltage power supply controller 19 obtains a ratio V / V0 between the stored voltage V0 and the voltage V and obtains the relative reflectance of the substrate surface. Then, the sensitivity is set by determining the applied voltage in the high-voltage power supply unit 20 from the obtained relative reflectance by using the characteristic shown in FIG.

Next, after the sensitivity of the PMT 16 is set, the particles adhering to the surface of the substrate 12 are detected. This detection is performed as follows. That is, the surface of the substrate 12 is sequentially scanned by the laser light of the light source 11, and each time, the PMT 16 of the scattered light 15 from the surface of the substrate 12 is detected. Then, a measuring circuit (not shown) detects the output of the head amplifier 17 at a slice level corresponding to dust and dust having a specific particle size to be detected, thereby detecting dust and dust having a specific particle size or more. Then, every time the type of substrate 12 changes, the PMT1
By resetting the sensitivity of 6 and correcting the sensitivity of the entire photodetection system, scattered light from particles on the substrate surface having different light reflectances can be detected with the same sensitivity.

FIG. 6 is a block diagram showing the configuration of the second embodiment of the surface inspection apparatus according to the present invention. In this embodiment, PM
A light modulating device 21 made of liquid crystal is provided on the light receiving surface of T16, and the sensitivity of the entire photodetecting system is changed by controlling the light modulating device 21 by the output of the light modulation control unit 22 to change the light blocking ratio. Is. The light modulation control unit 22 is supplied with the holding voltage signal of the averaging unit 18 that averages the output of the head amplifier 17. In the case of the device of this embodiment, PM
A constant high DC voltage is constantly supplied to the T16 from the high-voltage power supply unit 20, so that the sensitivity of the PMT 16 itself is constant. In the device of this embodiment, an optical modulator corresponding to the scattered light intensity of the substrate 12 is used.
By changing the shading rate in 21, the sensitivity of the entire photodetection system including the PMT 16, the head amplifier 17, the averaging unit 18, the high-voltage power supply control unit 19, the high-voltage power supply unit 20, the optical modulator 21, and the optical modulation control unit 22 can be increased. I am trying to correct it.

In this case, instead of the characteristics of the PMT detection output voltage and applied voltage as shown in FIG. 4, the characteristics of the PMT detection output voltage and the light blocking ratio in the optical modulator 21 are used.

FIG. 7 is a block diagram showing the configuration of the third embodiment of the surface inspection apparatus according to the present invention. In this embodiment, PM
A constant high DC voltage from the high voltage power supply unit 20 is supplied to T16 to keep the sensitivity of PMT16 constant. Instead, an amplification factor control unit 23 that determines the amplification factor of the head amplifier 17 is inserted in the feedback loop of the head amplifier 17, and the value of the feedback resistance in the amplification factor control unit 23 is set to the holding voltage of the averaging unit 18. It is controlled accordingly. That is, by changing the resistance value in the amplification factor control unit 23 according to the intensity of scattered light on the surface of the substrate 12 and thereby changing the amplification factor of the head amplifier 17, the light is attached to the substrate surface having different light reflectance. Light scattered by particles having the same diameter is extracted as a voltage signal at the same level.

In this case, the characteristics of the detection output voltage of the PMT and the amplification factor of the head amplifier 17 are used instead of the characteristics of the detection output voltage of the PMT and applied voltage as shown in FIG.

FIG. 8 is a block diagram showing the configuration of the fourth embodiment of the surface inspection apparatus according to the present invention. Although the detection sensitivity of the photodetection system is set in accordance with the scattered light intensity on the substrate surface in each of the embodiments of FIGS. 1, 6 and 7 described above, in this embodiment the substrate surface is It is set according to the intensity of the specular reflection light. This is because the intensity of scattered light and the intensity of specular reflection each have a linearly increasing relationship with the reflectance of the surface of the silicon semiconductor substrate.

In this embodiment, a new device for measuring the intensity of specular reflected light 13 is used.
A PMT 24 is provided, converted by the PMT 24, and a voltage signal proportional to the intensity of specular reflection light is amplified by the head amplifier 25 and then supplied to the averaging unit 18. The voltage signal averaged and held by the averaging unit 18 is supplied to the high-voltage power supply control unit 19. Although not shown, the PMT 24 is supplied with a constant high DC voltage generated in the high-voltage power supply section.

FIG. 9 is a block diagram showing the configuration of the fifth embodiment of the surface inspection apparatus according to the present invention. In this embodiment, as shown in FIG. 6, a light modulator 21 is provided on the light receiving surface of the PMT 16, and the light modulator 21 is controlled by the output of the light modulation controller 22 to change the light blocking rate. In this case, the detection sensitivity of the light detection system is set according to the intensity of specular reflection light on the substrate surface. That is, the PMT 24 for measuring the intensity of the specularly reflected light 13 is also provided in the apparatus of this embodiment.
The voltage signal converted by 24 and proportional to the intensity of specular reflection light is amplified by the head amplifier 25 and then supplied to the averaging unit 18. The voltage signal averaged and held by the averaging unit 18 is supplied to the optical modulation control unit 22. In this case as well, although not shown, the PMT 24 is supplied with a constant high DC voltage generated in the high-voltage power supply section.

FIG. 10 is a block diagram showing the configuration of the sixth embodiment of the surface inspection apparatus according to the present invention. In this embodiment, the detection sensitivity is set by changing the amplification factor of the head amplifier 17 as shown in FIG. 7, and the detection sensitivity of the photodetection system is set to the specular reflection light intensity on the substrate surface. This is set according to the setting. That is, the PMT 24 for measuring the intensity of the specular reflection light 13 is also provided in the device of this embodiment, the PMT 24 converts the voltage signal, and the voltage signal proportional to the specular reflection light intensity is amplified by the head amplifier 25 and then supplied to the averaging unit 18. To be done. The voltage signal averaged and held by the averaging unit 18 is supplied to the amplification factor control unit 23. In addition,
Although not shown, the two PMTs 16 and 24 are supplied with constant high DC voltages generated by the two high voltage power supply units.

As described above, in each of the above-described embodiments, scattered light due to particles such as dust and dust adhering to the surface of the substrate having different reflectances can be detected with a certain sensitivity characteristic. As a result, even if the material of the substrate, the type of thin film formed on the surface, and the film thickness are different, particles having a certain diameter can be detected with the same sensitivity.

[Effect of the Invention] As described above, according to the present invention, it is possible to provide a surface inspection apparatus capable of detecting scattered light from particles on a substrate surface having different light reflectances with the same sensitivity.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a first embodiment of the present invention, FIG. 2 is a plan view for explaining the apparatus of the above embodiment,
FIGS. 3 to 5 are characteristic diagrams for explaining the apparatus of the above embodiment, and FIGS. 6 to 10 are block diagrams showing the configurations of different embodiments of the present invention.
The figure is a characteristic curve diagram showing the relationship between the particle size of particles adhering to the substrate surface and the scattered light signal. 11 ... Light source, 12 ... Substrate, 13 ... Specular reflection light, 14 ... Integrating sphere, 15 ...
Scattered light, 16 ... PMT (photomultiplier tube), 17 ... Head amplifier, 18 ... Average part, 19 ... High voltage power supply control part, 20 ... High voltage power supply part (HV), 21 ... Optical modulator, 22 ... Optical modulation control Section, 23 ... Amplification factor control section, 24 ... PMT, 25 ... Head amplifier.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Katsuya Okumura 1 Komukai Toshiba-cho, Sachi-ku, Kawasaki-shi, Kanagawa Inside the Toshiba Research Institute Co., Ltd. (72) Inventor Shigeru Ogawa 8 Shinsugita-cho, Isogo-ku, Yokohama-shi, Kanagawa (56) Reference JP-A-52-111742 (JP, A) JP-A-54-97484 (JP, A) JP-A-57-165743 (JP, A) JP-A-57- 33306 (JP, A) JP 59-180313 (JP, A) JP 60-56208 (JP, A)

Claims (10)

[Claims] 1. A surface of a substrate is irradiated with light that is finely squeezed, the scattered light from the surface of the substrate is condensed, and this is detected by a photodetection system, and a minute amount of the substrate surface is detected according to the intensity of the detected light. In the surface inspection apparatus for detecting various specimens, the photodetection system amplifies the signal output from the photomultiplier tube, which outputs a signal according to the intensity of scattered light from the substrate surface. Before detecting the minute sample with the amplifier, the sensitivity of the entire system is adjusted so that the output signal level of the amplifier based on the scattered light by the substrate itself becomes constant regardless of the type of substrate. And a sensitivity setting means for setting according to the intensity of scattered light of the surface inspection apparatus. 2. The sensitivity setting means sets the sensitivity of the entire system by adjusting the voltage applied to the photomultiplier tube according to the intensity of scattered light from the surface of the substrate. The surface inspection apparatus according to claim 1. 3. The sensitivity setting means sets the sensitivity of the entire system by adjusting the light blocking rate of light incident on the photomultiplier tube according to the intensity of scattered light from the surface of the substrate. The surface inspection apparatus according to claim 1. 4. The sensitivity setting means sets the sensitivity of the entire system by adjusting the amplification factor of the amplifier according to the intensity of scattered light from the surface of the substrate. The surface inspection apparatus according to item 1. 5. The sensitivity setting means has an averaging unit for averaging output signals from the amplifier obtained when the surface of the substrate is irradiated with light that has been narrowed down for a predetermined period while being scanned. The surface inspection apparatus according to claim 1. 6. The surface of the substrate is irradiated with light that is finely squeezed, the scattered light from the surface of the substrate is condensed, and this is detected by a photodetection system, and a minute amount of the substrate surface is detected according to the detected light intensity. In the surface inspection apparatus for detecting various specimens, the photodetection system includes a first photomultiplier tube that outputs a signal according to the intensity of scattered light from the substrate surface, and the first photomultiplier tube. A first amplifier that amplifies the output signal, a second photomultiplier tube that outputs a signal according to the intensity of the specularly reflected light from the substrate surface, and a second photomultiplier tube that outputs the signal. A second amplifier for amplifying a signal which is amplified by the second amplifier, and an output signal level of the first amplifier based on scattered light by the substrate itself so as to be constant regardless of the type of the substrate before detecting the minute sample. Depending on the output signal of the second amplifier, the sensitivity of the entire system Setting surface inspection apparatus characterized by comprising a sensitivity setting means for. 7. The sensitivity setting means sets the sensitivity of the entire system by adjusting the voltage applied to the first photomultiplier tube according to the output signal of the second amplifier. The surface inspection device according to claim 6. 8. The sensitivity setting means sets the sensitivity of the entire system by adjusting the light blocking rate of the light incident on the first photomultiplier tube according to the output signal of the second amplifier. The surface inspection apparatus according to claim 6, wherein 9. The sensitivity setting means sets the sensitivity of the entire system by adjusting the amplification factor of the first amplifier according to the output signal of the second amplifier. The surface inspection apparatus according to claim 6. 10. The averaging unit for averaging an output signal from the second amplifier, which is obtained when the sensitivity setting means scans light that is narrowed down on the surface of the substrate and irradiates the light for a predetermined period. The surface inspection apparatus according to claim 6, further comprising: