JPH02194352A - Inspection device for surface of transparent substrate - Google Patents

Abstract

PURPOSE:To inspect the surface of a substrate without being affected by a defect or foreign matter on the reverse surface of the substrate by cutting off scattered light by a light shield plate which is arranged on the object-point side of the condenser lens of a scattered light photodetection part or a slit arranged at the image point. CONSTITUTION:A light beam 11 which is emitted by a laser oscillator 10 is converged by a scanning lens 14 to irradiate the surface 16a of the transparent substrate as a sample at a low angle. The scattered light 17 generated by the foreign matter or defect on the surface 16a is photodetected by a scattered light photodetection part 21 and converted into an electric signal, which is a scattered light signal 30 corresponding to the quantity of photodetection. Further, the sample 16 is moved by a moving mechanism 25 in a direction P perpendicular to the scanning direction of the beam 11. Then the scattered light which is transmitted through the sample 16 and generated by the foreign matter or defect on the reverse surface 16b is cut off by the light shield plate 50 arranged on the object point side of the condenser lens 18 or the slit arranged at the image point of the lens 18. Therefore, the inspection is affected by neither the foreign matter nor defect on the reverse surface 16b.

Description

[Detailed description of the invention] [Industrial application field]

The present invention inspects the surface condition by scanning the surface of a transparent substrate such as a glass substrate used for a liquid crystal display board or a photomask for semiconductor processing with a light beam and detecting scattered light caused by defects or attached foreign matter on the surface. The present invention relates to a transparent substrate surface inspection device.

[Conventional technology]

Conventionally, devices for detecting defects and attached foreign matter on solid surfaces include wafer surface foreign matter detection devices for wafers used in semiconductor processes, various films such as chrome films, chromium oxide films, resist coatings, and mask blanks. There is a mask inspection device targeted for this purpose. These devices are all 1
A scattered light detection method using a /- laser as a light source is adopted. FIG. 7 shows the optical system of the detection section of the mask inspection apparatus described above. Laser beam 1 is focused onto mask surface 9a by scanning lens 2, and further scanned in a direction perpendicular to the plane of the paper as shown. If there is any foreign matter on the mask surface 9a, scattered light 4 is generated, which is received by the side scattered light detector 3. Further, if the mask 9 has a pinhole, the transmitted light 7 and the diffracted light 8 are received by the mirror 5 and the transmitted light receiving section 6 provided at the lower part of the mask. Note that the detection section of the wafer surface inspection apparatus described above is basically the transmitted light detection mechanism (5,
6) is excluded. In any case, these conventional inspection devices are intended to inspect opaque mirror-surfaced (or patterned) substrates.

[Problem to be solved by the invention]

When attempting to inspect a transparent substrate using these devices, it is impossible to distinguish between foreign matter attached to the front side of the substrate and foreign matter attached to the back side of the substrate. This is because a laser beam focused on the front surface of the substrate is scattered by foreign objects on the front surface, passes through the substrate, reaches the back surface, and is also scattered by foreign objects attached to the back surface. Scattered light from the back surface passes through the substrate and is detected by the scattered light receiver 3. The present invention has been made in view of the above points, and an object of the present invention is to provide a transparent substrate surface inspection device that can inspect only the surface of the substrate without being affected by foreign matter or defects attached to the back surface of the transparent substrate. With the goal.

[Means to solve the problem]

In order to achieve the above object, the present invention provides a transparent substrate surface inspection apparatus with a light projecting means that irradiates a light beam onto the surface of a transparent substrate at a low angle to form a light bubble on the surface of the substrate. , a moving means for moving the light spot north of the substrate surface, and a method for receiving scattered light generated when the light beam is scattered by a scattering center such as a defect or foreign object on the substrate surface on which the light spot is formed, and detecting the amount of received light. Scattered light receiver that outputs an electric signal according to the current value, and a scatterer that prevents the scattered light generated when the light beam transmitted through the substrate is scattered by a scattering center such as a defect or foreign object on the back side of the substrate from reaching the scattered light receiver. light blocking means;
It was composed of According to the present invention, the scattered light blocking means is arranged on the light blocking plate disposed on the object point side of the condensing lens of the scattered light receiving means or at the image point of the condensing lens of the scattered light receiving means. slit.

[For use]

By irradiating the light beam at a low angle close to parallel to the substrate surface, the passage positions of the light beam on the front surface and the back surface of the substrate are greatly separated. Among the scattered light from scattering centers such as defects and foreign objects existing at the passing positions of the respective light beams, the scattered light from the back surface of the substrate is collected by the scattered light blocking means, for example, the scattered light receiving means. It is blocked by a light-shielding plate placed on the object point side of the lens or a slit placed at the image point of the condensing lens of the scattered light receiving means, and does not enter the scattered light receiving means, causing defects on the back side of the substrate and It is possible to inspect the substrate surface for defects and foreign matter without being affected by foreign matter.

【Example】

FIG. 1 is a schematic explanatory diagram for explaining one embodiment of the present invention, in which FIG. 1A is a front view and FIG. 1B is a side view. In FIG. 1, a light beam 11 emitted from a laser oscillator 10 is deflected and scanned by a deflector 12, reflected by a mirror 13, and incident on a scanning lens 14 where it is converged. The focused light beam is reflected by the mirror 15 and irradiated at a low angle onto the surface 16a of the transparent substrate 16, which is the sample. Scattered light 17 generated by foreign matter or defects on the substrate surface 16a is collected by a scattered light receiving section 21 consisting of a condensing lens 18, a light guide 19, and a photoelectric conversion element 20.
It receives light and converts it into an electrical signal. In this embodiment, the scattered light receiving section 21 is arranged in two directions of the base 16;
It is arranged to receive side scattered light from the substrate surface 16δ in a direction substantially perpendicular to the light beam incident on the substrate 16 from the mirror 15. Further, the specularly reflected light 22 from the substrate surface 16a is received by the light guide 23 and converted into an electrical signal by the photoelectric conversion element 24, and this electrical signal is provided as a signal 31 for detecting the presence or absence of a sample and the sample area. Ru. Further, a moving mechanism 25 is provided that moves the sample 16 in a direction P perpendicular to the scanning direction of the laser beam. A block diagram of a processing circuit for the scattered light signal 30 and sample area signal 31 output from the scattered light receiver 21 is shown in FIG. The scattered light signal 30 is input to a pulse height discrimination circuit 40 consisting of a plurality of comparators 40a to 40n with different threshold voltages in order to identify the pulse height, and the result is outputted to the I10 boat 42 via a decoding circuit 41. be done. At the same time, the clock 4 from the rising edge of the sample area signal 31
A counter 44 integrates the number of pulses generated at 3, and outputs the integrated value to the I10 boat 42. The sample area signal 31 is obtained by binarizing the analog electrical signal obtained by the photoelectric conversion element 24 in FIG. 1(B) by an appropriate means not shown. The CPU 45 receives wave height data of the scattered light signal 30 and position data within the sample.
via the I10 port 42 to the appropriate address in memory 46. Further, the CPU 45 resets the contents of the counter 44 when the sample area signal 31 falls, and waits until the next rise of the sample area signal 31. If the rising edge of the sample area signal 31 does not appear even after waiting longer than the scanning period of the light beam, it is assumed that the measurement has ended, and the CPU
45 organizes the pulse height data and position data stored in the memory 46 and sends them to the display 4 via the I10 port 47.
8 shows the number of foreign objects and defects for each map and pulse height. Note that 49 is a keyboard used for inputting data from the outside, such as setting threshold voltages of the comparators 40a to 40n. FIG. 3 is an explanatory diagram for explaining an example of a scattered light blocking means and its arrangement in an embodiment of the present invention. When the laser beam 11 irradiates the point S1 on the surface 16a of the sample 16,
Specularly reflected light 22a and transmitted light 22b are generated. Furthermore, multiple reflection lights R2, R3, etc. are generated by reflection of the light beam R1 that has entered the sample at points 33, 34, and S5 of the sample. Here, point S
If there is a scattering center such as a foreign object or a defect at points 1 and S2, scattered light will be generated around each point.
The light enters the condenser lens 18 at a condensing solid angle of 32B. Therefore, if the light shielding plate 50 is provided at the illustrated position, the scattered light 17b from the point S2 will be blocked, and only the scattered light 17a from the point S1 will reach the condenser lens 18. Also, S3
, 34. Scattered light generated at a reflection point of multiple reflected light such as S5 is also blocked. FIG. 4 shows analog signal waveforms obtained by measuring the host mask glass substrate, in which (A) shows the case where the light shielding plate 50 is not provided, and (B) shows the case where the light shielding plate 50 is provided. Each case is shown. As shown in FIG. 5, half of the polystyrene latex standard particles 60 with a diameter of 10.28 μm are attached to the front and back surfaces of the glass substrate, and the signal waveform regions A and B and points E and F shown in FIG. 4 are obtained. correspond to areas A and B and points E and F in FIG. 5, respectively. The signal shown in Figure 4 (A) includes pulses corresponding to the particles on the front side as well as pulses corresponding to the particles on the back side, but in Figure 4 (B), the signal height due to the particles on the front side is It can be seen that the signal in the B region corresponding to the particles on the back side disappears without any change in the intensity. From this, it can be confirmed that the optical system shown in FIG. 3 inspects only the surface of the transparent substrate. FIG. 6 is an explanatory diagram for explaining another example of the scattered light blocking means and its arrangement. The difference between Figure 6 and Figure 3 is that
A short focusing lens 18 of the scattered light receiving means is used to form an image of the received scattered light and then make it enter the light guide. In this case as well, the method of providing the light shielding plate 50 used in the first embodiment can be applied, but in this embodiment, a slit-shaped spatial filter 52 is provided at the image point Sl' of the scattered light from the point S1, and a slit-shaped spatial filter 52 is provided at the image point Sl' of the scattered light from the point S1 Separate the images corresponding to the scattered light from the In order to confirm the effect of this spatial filter 52, an experiment similar to that of the first embodiment was conducted, and the same result as the signal waveform shown in FIG. 4 was obtained. The present invention has been described above using two embodiments, but when inspecting a wide area of the sample surface, it is difficult to inspect the sample surface in addition to fixing the sample and applying the optical heater 1 as described above.
It is clear that the present invention is also effective when the irradiation beam is fixed and only the sample is moved in the XY direction or rotated. Furthermore, although the present invention discloses an apparatus specifically for measuring transparent substrates, it goes without saying that it can also be applied to inspecting opaque mirror samples.

【Effect of the invention】

As explained above (1), according to the present invention, the optical beam is irradiated at a low angle close to parallel to the substrate surface, and the passing positions of the light beam on the front and back surfaces of the substrate are greatly separated. Of the scattered light from the passing position of the light beam,
Scattered light from the back surface of the substrate is blocked by a scattered light blocking means, for example, a light blocking plate placed on the object point side of the condensing lens of the scattered light receiving means, or a light blocking plate placed at the image point of the condensing lens at the lower stage of the scattered light receiving means. Since the scattered light is prevented from entering the light receiving means by the slit, it is possible to inspect the surface of the board for defects and foreign matter without being affected by defects and foreign matter on the back side of the board. .

[Brief explanation of the drawing]

Fig. 1 is a schematic explanatory diagram for explaining one embodiment of the present invention, in which Fig. 1A is a front view, Fig. 3 is a side view, and Fig.
The figure is a block circuit diagram of a processing circuit for the scattered light signal 30 and sample area signal 31 in FIG. 1, and FIG. 3 is an explanatory diagram for explaining an example of the scattered light blocking means and its arrangement in FIG. 1. Figure 4 is a waveform diagram showing the AB-log signal waveform obtained by measuring a glass substrate for a photomask. Figure 4 (A) is a waveform diagram when no scattered light blocking means is provided, and Figure 4 (B)
5 is an explanatory diagram of the photomask glass substrate used to measure the waveform diagram in FIG. 4, and FIG. 6 is a waveform diagram when a scattered light blocking means is provided. FIG. 7 is an explanatory diagram for explaining another example of the stage arrangement, and FIG. 7 is a schematic explanatory diagram for explaining the prior art. II light beam, I2 deflector, 13, 1.5
Mira, 16 Sample, 16a - Back side of sample, 1
7.17a, 17b scattered light, 18- condensing lens, 1
9.23 - Light guide, 20.24 ---- Photoelectric conversion element, 211Pi scattered light] 2 Light receiving section, 25 Sample moving mechanism, 40 - Wave height discrimination circuit, 41 - Decoding circuit, 42. 47 - 110 Port, 43 - Rio, 7ri, 45 CPIJ
, 46 memory, 50- light shielding plate, 52- slit.

Claims (1)

[Scope of Claims] 1) Light projecting means for irradiating a light beam at a low angle onto the surface of a transparent substrate to form a light spot on the surface of the substrate; and movement for moving the light spot on the surface of the substrate. means; a scattered light receiving means for receiving scattered light generated when the light beam is scattered by a scattering center on the surface of the substrate on which the light spot is formed, and outputting an electric signal according to the amount of the received light; A transparent substrate surface comprising: a scattered light blocking means for blocking scattered light generated when a light beam transmitted through the substrate is scattered by a scattering center on the back surface of the substrate from reaching the scattered light receiving section. Inspection equipment. 2) In the transparent substrate surface inspection apparatus according to claim 1, the scattered light blocking means is a light shielding plate disposed on the object point side of the condensing lens of the scattered light receiving means. Board surface inspection equipment. 3) The transparent substrate surface inspection device according to claim 1, wherein the scattered light blocking means is a slit arranged at the image point of the condensing lens of the scattered light receiving means. Surface inspection equipment.