JPS63238454A - Foreign matter inspecting apparatus - Google Patents

Abstract

PURPOSE:To detect the presence of the foreign matter on a substrate with high accuracy, by transmitting laser beam through a pellicle to perform scanning on a substrate and preliminarily measuring the transmissivity of the pellicle when the scattering beam therefrom is detected to calibrate a measured detection value. CONSTITUTION:A pellicle 1 is provided to each of two frames 2, 3 under tension and said frames are mounted on the upper and under surfaces of a substrate 4. Laser beam 7a is transmitted through the pellicle 1 from a laser beam source 5 through a mirror 6 to perform the scanning on the scanning lines Y1, Y2 of the upper surface of the substrate 4. In the same way, the laser beam 8a is transmitted through the film from the opposite side to perform scanning on the upper surface of the substrate 4 and, further, laser beams 9a, 10a are transmitted through the pellicle 1 from mutually opposite sides to perform scanning on the under surface of the substrate 4. The scattering beams from the substrate 4 are transmitted through the pellicle 1 to be received by photoelectric elements 11-14 and foreign matter is detected from the change of the scattering beams. At this time, the transmissivity of the pellicle is preliminarily measured and the detected value of the substrate 4 is calibrated on the basis of said transmissivity. Since the detection value is calibrated, foreign matter can be detected with high reliability even when the thickness of the pellicle 1 is non-uniform.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a foreign matter inspection device, and is particularly suitable for inspecting the presence or absence of foreign matter adhering to the surface of a substrate such as a reticle or mask with a pellicle film attached. This invention relates to a foreign matter inspection device.

[Conventional technology]

Conventional devices, as described in Japanese Unexamined Patent Publication No. 59-82727, have been effective in detecting foreign matter on a substrate with a pellicle attached. However, no consideration was given to compensating for differences in transmittance due to variations in pellicle type or film thickness. Note that there is also Japanese Patent Application Laid-Open No. 59-82726 related to this type of device.

[Problem that the invention seeks to solve]

The above-mentioned conventional technology does not compensate for differences in transmittance due to variations in pellicle type or film thickness, and has a problem with accuracy.

An object of the present invention is to provide a foreign matter inspection device that can compensate for differences in transmittance due to variations in pellicle type or film thickness and can inspect the presence of foreign matter with high accuracy.

[Means for solving problems]

The above purpose is to pass a laser beam through the pellicle film into the frame of the pellicle film made of metal material or into the concave or convex portions formed on the substrate before inspecting a substrate such as a reticle or mask on which the pellicle film is attached. irradiation and detect the scattered light to automatically calibrate differences in detected values due to differences in the transmittance of the pellicle film, as well as improve the decrease in transmittance by using a short wavelength laser in the exposure wavelength range. I tried to achieve it.

[Effect]

When inspecting the presence or absence of foreign matter on a substrate, a laser beam is irradiated through a pellicle film and the scattered light from the foreign matter is received to detect the foreign matter, but there are differences in the type or thickness of the pellicle film. Since the transmittance of the laser beam differs depending on the type of test, the transmittance of the pellicle film is measured in advance and the detected value of foreign matter on the substrate is calibrated using this measurement, so the presence or absence of foreign matter can be detected with high precision.

〔Example〕

The present invention will be explained in detail below using the embodiments shown in FIGS. 1 to 6.

FIG. 1 is a configuration diagram showing an embodiment of the detection system of the foreign matter inspection device of the present invention. The configuration of the detection system is shown.

In FIG. 1, a substrate 4 such as a reticle or a mask is shown.
A pellicle film (having a thickness of 0.8 mm is attached to the upper and lower surfaces of the substrate 4 at a distance of several mm to about 10 mm).

Here, the purpose of using the pellicle film 1 is to prevent foreign matter such as dust from adhering to the surface of the substrate 4, and to make minute foreign matter adhering to the pellicle film 1 harmless during exposure due to transfer blur during exposure. Although it may be effective (however, it may be harmful if foreign particles of the same size are attached to the substrate 4), cleaning of the substrate 4 may be inadequate, or foreign particles attached to the inner surface of the pellicle membrane 1 may fall. However, the problem of foreign matter adhering to the substrate 4 still remains. This is why it is necessary to inspect the substrate 4 for foreign substances even after the pellicle film 1 is attached. Therefore, as shown in the figure, the laser beam emitted from the laser light source 5 is guided to the galvanometer mirror 6, and the laser beam is scanned in the range of 7b to 7c with 7a as the center, and scans on the line Yl and Yz on the upper surface of the substrate 4. Make it. Furthermore, the laser beam emitted from the same light source 5 is guided to the opposite side by ordinary optical means, and the laser beam is directed in the direction of 8a (7a is 180
The upper surface of the substrate 4 is irradiated from different directions) and scanned by the same means as described above. Further, the lower surface side of the substrate 4 is also irradiated with laser light from the directions 9a and 10a, respectively, and the lower surface is scanned by the same means as described above. Here, the laser beam 7a,
9a is responsible for scanning the inner half of the entire scanning area from YL and Yz, and 8a and 10a is responsible for scanning the front half of the area from Yt and Yz.

On the other hand, the light receiving system includes a photoelectric element 11 for receiving scattered light 11a generated from a foreign object in the process of scanning the Yl side on the upper surface side.
and a photoelectric element 12 for receiving scattered light 12a generated from a foreign object during the scanning process on the Y2 side.

Regarding the light receiving system on the lower surface side, the photoelectric element 13 receives the scattered light 13a on the Yl side in the same way as above, and the scattered light 14a on the Yl side is received by the photoelectric element 13.
The photoelectric element 14 is configured to receive the light. Here, the reason why the laser beam is scanned from two directions each on the upper surface and the lower surface of the substrate 4 and is configured to be received by two photoelectric elements each is that the laser beam is scanned from two directions on the upper surface and the lower surface of the substrate 4, and the laser beam is received by two photoelectric elements each. This is to widen the scanning area above 4.

In the detection system configured as described above, the laser light source 5 is one that emits a short wavelength laser having approximately the same wavelength as the exposure wavelength. The reason for using a short wavelength laser here is as follows.

The purpose of conventional foreign object inspection equipment is to inspect foreign objects such as reticles without beads, and the laser light source is a general He-Ne laser (wavelength: 662.8 nm).
m) was used. However, in inspecting foreign objects on a substrate with a pellicle attached, which is the object of the present invention, the laser beam must pass through the pellicle film 1 and irradiate the substrate 4, and the scattered light transmitted through the pellicle film 1 must be received. Therefore, the quality and dispersion of the transmittance of the laser beam through the pellicle film 1 determines the ability to detect foreign objects.

That is, the pellicle film 1 is manufactured to have the best light transmittance in the exposure wavelength range (currently, the exposure wavelength is mainly 436 nm, and the exposure wavelength range is generally 350 to 450 nm), and the quality is also high. However, the laser wavelength (662.8 nm) used in conventional foreign object inspection is
) is out of the exposure wavelength range, so the transmittance of the pellicle film 1 is poor, and the transmittance also varies due to non-uniform quality, causing problems in foreign matter inspection. Furthermore, this difference in wavelength also leads to the problem described below. That is, among the foreign substances attached to the substrate 4,
Items that are transparent at the exposure wavelength are not transferred onto the wafer and are therefore harmless from the exposure point of view, so when inspecting reticles and masks for foreign objects, such foreign objects are determined to be absent, or even if present, are determined to be harmless from the exposure point of view. matching the process needs. However, since conventional equipment uses a wavelength that is significantly different from the exposure wavelength, the properties of the foreign particles vary, and the results are not necessarily the same. There have been cases where the result has been overlooked, and the original purpose of the foreign body inspection has not been achieved. As is clear from the above explanation, the cause of the above problem is that the laser wavelength of the foreign object inspection device is significantly different from the exposure wavelength. Therefore, the first point of the present invention is to solve the above problem by using a short wavelength laser (for example, a He-Cd laser with a wavelength of 442 nm) that is almost the same wavelength as the exposure wavelength as the laser wavelength of the foreign matter inspection device as described above. The reason is that we tried to solve the problem.

Figures 2 and 3 show an embodiment for explaining the second point of the present invention. Figure 2 is an explanatory diagram of the detection method, and is representative of a part of the detection system in Figure 1. Shown as an example. Further, FIG. 3 is an explanatory view of the capture in FIG. 2 with frames 2 and 3 in FIG. 2 cut away. Before giving a detailed explanation of the embodiments, the necessity and solution of the second point of the present invention will be explained.

It was made clear in the explanation of the first point of the present invention that the variation in the transmittance of the pellicle membrane 1 affects the foreign object detection ability, but another reason for the variation in transmittance is the type of the pellicle membrane 1. There are differences in film thickness. There are many types of pellicles currently on the market, and there are approximately three types of pellicles that are frequently used. That is, there is a film thickness of 0.9 μm for reticles, a film thickness of 2.9 μm for reticles coated with a special coating, and a film thickness of 2.9 μm for masks. When measuring the transmittance of these three types, there is a difference of 10 to 20%, and if this is done, the sensitivity will be different for the same foreign matter, causing a problem in determining the size of the foreign matter. Furthermore, depending on the type of pellicle film ↓, the film thickness variation may be as large as ±0.2 μm, causing the same problem as above.

The only way to solve the above-mentioned problems is to use a board with a pellicle attached, which is the target to be inspected, and irradiate a laser beam onto the target that emits the reference scattered light using a method equivalent to foreign matter inspection. The purpose is to receive the scattered light and automatically calibrate the device based on this value. Specific means will be explained below based on the embodiments shown in FIGS. 2 and 3.

When the laser beam 7d is scanned to the position Y1' and irradiated onto the frame 2 of the pellicle film 1, scattered light 11b is generated in the frame 2 as shown in FIG. 3, and is received by the photoelectric element 11. Since the intensity of the scattered light 11b is constant for both the material and shape of the frame 2, it is constant if the transmittance of the pellicle film 1 is constant.

Therefore, by determining the intensity of the scattered light 11b for the reference pellicle in advance, it is possible to calibrate the difference in the scattered light intensity due to the difference in transmittance of the pellicle film 1. Furthermore, as shown in FIG. 3, the pellicle film 1' on the lower surface side of the substrate 4 is also irradiated with the laser beam 9d, and the scattered light intensity is determined by the difference in transmittance of the pellicle film 1' using the scattered light 13b from the frame 3. Differences can be calibrated.

Other embodiments are shown in FIGS. 4 and 5. FIG. 4 shows a substrate with a pellicle film similar to that shown in FIG.
is provided. FIG. 5 is a side view of the convex portion 43 sectioned through the frames 2 and 3.

When the laser beam 7e is irradiated onto the convex portion 43, scattered light is generated at the convex portion 43, and a part of the scattered light 11c is transmitted to the photoelectric element 11.
The light is received by If the shape of the convex portion 43 is kept constant, this scattered light 11c can be made to have a constant intensity as in the above embodiment.

Therefore, if the scattered light intensity is determined in advance for a reference pellicle, even if the transmittance of the pellicle film 1 is different and the scattered light intensity of the scattered light 11c is different, the difference can be adjusted to the reference value of the light. Calibration becomes possible. Also for the lower pellicle film 1', the laser beam 9e is irradiated onto the convex portion 43 through the transparent substrate 4, and the scattered light 13c emitted from this can be obtained.
3c can be used to calibrate the difference in scattered light intensity due to the difference in transmittance of the pellicle film 1' in the same way as described above.

FIG. 6 is a block diagram of the main configuration of an embodiment of the detection circuit of the foreign object inspection apparatus of the present invention. In FIG. 6, the analog signals of the photoelectric elements 11, 12, 13, 14 are passed through electrical amplifiers 19, 20, 21° 22 to a multiplexer 23.
Enter. The multiplexer 23 receives a gate signal (not shown) from a galvano mirror controller 34 and a gate signal from the substrate 4.
is operated by a gate signal issued from a control system (not shown) of a stage that moves in the X-axis direction in FIG. It operates to pass a signal from one of the photoelectric elements, and its output is input to the comparator 24. The comparator 24 compares the output of the threshold generation circuit 25 and considers the signal above the threshold as valid.
The signal is inputted to an arithmetic processing unit 27 via a converter 26. Here, the voltage applied to the photoelectric elements 11, 12, 13, 14 is supplied from high-voltage electricity [15, 16, 17, 1B], and the voltage is determined by the voltage control circuit 28, 29, 30, 31. A control command is issued from the arithmetic processing unit 27.

On the other hand, a laser beam (not shown) is applied to Y of the substrate 4 in FIG.
The galvanometer mirror 6 that scans in the axial direction is a galvanometer mirror that scans in the axial direction.
It is driven by a drive device 33 and controlled by a galvanometer mirror control device 34.

The operation of the embodiment configured as above will be explained next. A pellicle film 1.1' that serves as a calibration standard for the device is attached to the substrate 4, and the laser beam is applied to the pellicle films 1 and 1 as shown in 7d and 9d.
Scattered lights 11b and 13 obtained by irradiating frames 2 and 3 of '
b is detected through the pellicle films 1 and 1', and the intensity of the scattered light is input to the arithmetic processing unit 27 and stored. On the other hand, the foreign matter inspection device is calibrated with standard particles 79' (mainly using polystyrene latex) A equivalent to the foreign matter deposited on the substrate 4 with the pellicle films 1 and 1' installed. Next, the test substrate equipped with the unknown pellicle film to be calibrated is inspected. First, the frames 2 and 3 of the pellicle film are irradiated with a laser beam as shown in 7d and 9d in the manner described above, and the laser beam is passed through the pellicle film. The scattered lights 11b and 13b are detected and compared with the scattered light intensity at the calibration pellicle film, and a correction value is provided by the arithmetic processing unit 27 so as to be the same as the above-mentioned scattered light intensity. 31 to correct the sensitivity of the photoelectric elements 11, 12, 13, and 14.

After this, if the laser beam is scanned over the substrate 4 and the scattered light from the foreign object is detected, the difference in sensitivity due to the pellicle film has been calibrated as described above, so the foreign object can be accurately detected and its size determined. be able to.

The method shown in the other embodiment is a method in which a convex portion 43 on the substrate 4 shown in FIG. Can be done.

Furthermore, according to this method, it is needless to say that an effect equivalent to 5 can be obtained by using another means of obtaining scattered light through the periphery film to be calibrated.

〔Effect of the invention〕

According to the present invention described above, differences in laser light transmittance due to non-uniform film thickness or quality variations of the pellicle are calibrated for each foreign object inspection, so that the above-mentioned error factors are determined in the vapor deposition state of the pellicle film. Even if foreign matter is present, foreign matter can always be detected with a constant sensitivity, and there is an effect that a highly reliable device with no error factors can be provided.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram showing an embodiment of a detection system of a foreign object inspection apparatus according to the present invention, FIGS. 2 and 4 are explanatory diagrams showing an embodiment of a laser irradiation state, and FIG. FIG. 5 is a partial sectional view of FIGS. 2 and 4, respectively, and FIG. 6 is a block diagram of the main components showing an embodiment of the detection circuit of the foreign object inspection apparatus of the present invention. 1.1'... Pellicle membrane, 2,3... Frame, 4...
Substrate, 5... Laser light source, 6... Galvano mirror 1
11-14... Photoelectric element, 15-18... High voltage power supply, 19-22... Voltage amplifier, 23... Multiplexer, 24... Comparator, 25... Threshold generation circuit, 26 ...A/D converter, 27... Arithmetic processing unit, 28-31... Voltage control circuit, 33... Galvano mirror drive rate 1 country δ l, N recycle 2.5... scale 2nd mouth 3rd mouth Y modified 1'... public full summons S mouth

Claims (1)

[Scope of Claims] 1. With a foreign matter adhesion prevention means in which a pellicle film is formed on a frame attached to a substrate, a light beam is transmitted through the pellicle film and scanned onto the substrate to remove foreign matter adhering to the substrate. In the apparatus for detecting the foreign object based on scattered light from the pellicle film, the light beam is transmitted through the pellicle film and irradiated onto a frame on which the pellicle film is formed, and the scattered light emitted from the frame is detected through the pellicle film. . A foreign matter inspection apparatus, characterized in that the foreign matter inspection apparatus is configured to calibrate a detected value of foreign matter adhering to the substrate by determining a difference in the transmittance of the light beam of the pellicle film. 2. The foreign matter inspection device according to claim 1, wherein the wavelength of the light beam is close to the exposure wavelength. 3. With a foreign matter adhesion prevention means in which a pellicle film is formed on the frame attached to the substrate, a light beam is transmitted through the pellicle film and scanned onto the substrate, and based on the scattered light from the foreign matter adhering to the substrate. In the device for detecting foreign objects, the light beam is transmitted through the pellicle film and irradiated onto a recess or a protrusion provided on the substrate, and scattered light emitted from the recess or protrusion is detected through the pellicle film. A foreign matter inspection apparatus characterized in that the detection value of foreign matter adhering to the substrate is calibrated by determining the difference in the transmittance of the light beam of the pellicle film. 4. The foreign matter inspection device according to claim 3, wherein the wavelength of the light beam is close to the exposure wavelength.