JPH04143640A - Apparatus for inspecting foreign matter - Google Patents

Abstract

PURPOSE:To enhance the yield in an exposure process by receiving the scattering beam from foreign matter by an optical detection system passing through the center of the beam irradiating a foreign matter adhesion preventing film and arranged so as to form a specific angle to said light. CONSTITUTION:The laser beam from a laser oscillator 14 is totally reflected by a reciprocally rotating and vibrating glavano-mirror 17 to be incident on the surface of a foreign matter adhesion preventing film 23 as a laser spot through a collimator lens 18 in an oblique direction. A detection means consisting of an image forming lens 26 and a photoelectric converter 27 is provided so as to observe scanning beam 22 in an oblique upper direction and the laser spot image on the scanning beam 22 is formed on the converter 27 and, when there is foreign matter 20, the scattering beam 21 therefrom is detected. Then, the surface of the film 23 is scanned over the entire region thereof while a glass substrate 39 is sent in a Y-direction. By this method, the yield in an exposure process can be enhanced.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention is applicable to substrates such as reticles and photomasks used for exposure in an exposure process using a reduction projection exposure apparatus or a 1:1 reflective projection exposure apparatus. This foreign matter inspection device prevents a decrease in the yield of semiconductor devices, etc. by inspecting large foreign matter that interferes with exposure and has adhered to the foreign matter adhesion prevention film while a frame with the foreign matter adhesion prevention film is mounted.

[Conventional technology]

For example, in a reduction projection exposure apparatus (hereinafter abbreviated as RA), a circuit pattern formed on a substrate such as a reticle or photomask is reduced/IXed, transferred onto a wafer, and exposed one chip at a time. If present, the foreign object image will be transferred and all chips on the wafer will be defective. Therefore, inspection of foreign substances on the substrate before exposure is essential for improving the yield of the exposure process. Related devices of this type include, for example, JP-A-57-80546 and JP-A-58-79.
No. 240, JP-A-59-82727, and the like.

If these devices are built into the RA, they are expensive devices, and a large amount of investment will be required in a mass production line that requires a large number of RAs.

On the other hand, recently, in order to prevent foreign matter from directly adhering to the surface of the substrate, an IJ shell (a transparent thin film of 21-hole cellulose pasted on a metal frame) has been installed to prevent foreign matter from adhering to the substrate surface. After the foreign matter adhesion prevention film is attached to the substrate, in principle, new foreign matter can be prevented from adhering to the substrate. Further, since the foreign matter adhesion prevention film and the surface of the substrate are separated from each other, even if a relatively small foreign matter exists on the foreign matter adhesion prevention film, the foreign matter image is not transferred onto the wafer. Therefore, when a foreign matter adhesion prevention film is used, the steps from substrate cleaning to exposure are as follows.

First, the substrate is cleaned and inspected for foreign matter such as dust on the surface where the pattern is present and the surface where the pattern is not present. If there is no foreign matter such as dust, attach a foreign matter adhesion prevention film using a jig. This foreign matter adhesion prevention film is also attached to the surface where the pattern is present. After applying the foreign matter adhesion prevention film, the presence of foreign matter on the surface of the substrate is inspected using the method disclosed in Japanese Patent Laid-Open No. 59-82727. If there are no foreign objects, it is stored in a cassette and sent to a reduction exposure device for the exposure process.

By installing a foreign matter adhesion prevention film, 20 to 30
Since foreign matter adhering to the film of .mu.m or less can be ignored, the yield can be improved.

[Problem to be solved by the invention]

It is generally believed that the probability of foreign matter adhesion is inversely proportional to the square of the foreign matter size, so the probability of foreign matter adhesion of 20 to 30 μm or more cannot be completely ignored. Therefore, in order to further improve the yield, it has become necessary to inspect the presence or absence of relatively large foreign matter on the foreign matter adhesion prevention film.

SUMMARY OF THE INVENTION An object of the present invention is to provide a foreign matter inspection device that further improves the yield in the exposure process by inspecting only large foreign matter that interferes with exposure that has adhered to a foreign matter adhesion prevention film attached to a substrate via a frame. There is something to do.

[Means to solve the problem]

That is, in order to achieve the above object, the present invention applies the foreign matter adhesion prevention film to an object to be inspected, which is equipped with a frame having a foreign matter adhesion prevention film attached to a substrate such as a reticle or a photomask used for exposure. The detection optical axis is set at an angle ψ≧ with respect to the irradiation light flux d so that it does not intersect with the light flux on the substrate surface caused by the light that passes through the optical center and passes through the foreign matter adhesion prevention film.
t a n-1d/2t (where t is the distance between the substrate surface and the foreign matter adhesion prevention film), and optically detects the scattered light from only the foreign matter adhering to the foreign matter adhesion prevention film. A foreign matter inspection device comprising a detection optical system and a photoelectric conversion means for receiving scattered light from only foreign matter adhering to a foreign matter adhesion prevention film detected by the detection optical system and converting it into a signal. be.

[Effect]

With the above configuration, it is possible to optically inspect only large foreign particles that have adhered to the foreign particle adhesion prevention film and interfere with exposure without detecting scattered light generated from the edges of the circuit pattern formed on the substrate. It is possible to significantly improve the yield of semiconductor devices and the like during exposure and the like.

[Embodiments of the invention]

The present invention will be explained below with reference to FIGS. 1 to 12.

First, FIG. 1 shows the structure of an embodiment of a reduction projection exposure apparatus equipped with a foreign matter inspection device on a foreign matter adhesion prevention film. After washing,
In the absence of any foreign matter, the substrate 39 with the foreign matter adhesion prevention film 23 mounted thereon via the frame 24 is stored in the magazine 6 in a cassette. In the exposure process, the substrates are taken out one by one from the cassette and returned to their original positions after exposure.

That is, the board 39 is moved from the cassette in the magazine 6 by the arrow 5a.
It is pulled out in the direction of arrow 4a and moved by the transport arm 3 in the direction of arrow 4a. Foreign matter inspection on the foreign matter adhesion prevention film 23 attached to the field surface of the substrate 39 is performed by the upper foreign matter inspection device 1 and the lower foreign matter inspection device M2 installed above and below the transfer arm 3. If foreign matter (for example, 2
If a foreign substance (0 μm to 30 μm or more) is present, the substrate is returned to its original cassette and the foreign matter is removed. On the other hand, if there is no foreign matter, the transfer arm 3 is rotated by the rotating machine 8 in the direction of the arrow 7a, placed at the exposure position 9, and transferred one chip at a time onto the wafer 11 via the exposure optical system 10. .

When the exposure process using this substrate is completed, the substrate 39 is again stored in the cassette within the magazine 6.

Further, FIG. 2 shows a second embodiment of the present invention. Here, the substrate 39 is transported by a transport mechanism using, for example, a belt 12 driven by a motor 13. An example of a foreign matter inspection device used in the above embodiment will be described below.

FIG. 3 shows a frame 2 on a substrate 39 such as a photomask or reticle.
Foreign matter adhesion prevention film (pellicle film) 23 pasted through 4
1 shows an apparatus for detecting foreign objects on a surface. According to this, the laser beam from the laser oscillator 14 is transmitted to the polarizing plate 1
6. After successively passing through the condensing lens 15, the laser beam is totally reflected by the galvanometer mirror 17, which is vibrated in a reciprocating rotation by a triangular wave signal, and then passes through the collimator lens 18 to become a laser spot on the surface of the foreign matter adhesion prevention film 23. It is designed so that the light is incident from an oblique direction. In this case, the galvano mirror
Since the laser beam 17 is driven by a triangular wave-shaped electric signal and rotates and oscillates at a constant period, the laser spot scans back and forth in the X direction at a constant speed on the surface of the foreign matter adhesion prevention film 23, thereby forming a linear scanning line 22. It is something that will be done.

On the other hand, the means for detecting the scattered light 21 from the foreign object 20 is a self-scanning accumulation type photoelectric conversion element including an imaging lens 26, a light shielding plate (not shown), and a -dimensional linear sensor (CCD, photodiode array, etc.). 27, and is provided so as to look at the scanning line 22 of the laser spot from diagonally above.

That is, the scanning line 2 of the laser spot that is linearly scanned on the surface of the foreign matter adhesion prevention film 23 by the imaging lens 26
2 is formed on a photoelectric conversion element 27. Therefore, the motor 48 and the feed screw 4
9, if the surface of the foreign matter adhesion prevention film 23 is scanned over the entire area while moving the glass substrate 39 at a constant speed in the Y direction, if a foreign matter 20 is present on the scanning line 22, the foreign matter 20 will be removed. The intensity of the scattered light 21 is accumulated and detected.

To explain the laser beam irradiation system in more detail with reference to FIG. 4, the laser beam from the laser oscillator 14 passes through a polarizing plate 16 (the polarizing plate is not necessary when using a polarizing laser such as a semiconductor laser). The laser beam is focused on the surface of the galvano mirror 17 by the condenser lens 15, but this laser light is totally reflected on the surface of the galvano mirror 17 and then reaches the collimator lens 18. Since the collimator lens 18 is installed so that its focal point is located on the rotation center axis of the galvanometer mirror 17, the laser beam passing through the collimator lens 18 becomes a parallel beam of light,
As a result of the rotational vibration of the galvanometer mirror 17, which vibrates back and forth in the direction 35 as shown, the surface of the foreign matter adhesion prevention film 23 is reciprocated in a linear manner. In this case, if the focal length of the collimator lens 18 is f, the deflection angle of the laser beam is θ, and the scanning amount of the laser spot is h, then the scanning amount is expressed as follows.

h=f-tanθHf-θ (tanθ#θ if θ is small) (1) Assuming that the rotation speed of the galvano mirror 17 is constant, the parallel focused laser spot will be on the surface of the foreign matter adhesion prevention film 23. It will move at a constant speed above.

FIG. 5 shows the triangular wave signal as a signal for driving the galvano mirror 17 and the light amount accumulation time for each photoelectric conversion element 27. As shown in the figure, the photoelectric conversion element 27
The amount of light accumulated in the photoelectric conversion element 27 is increased by setting the scanning time T to an integral multiple in synchronization with the period t of the galvano mirror 17, but the scanning conditions at each scanning position are the same. Therefore, as shown in FIG. 6, the intensity of the scattered light from the foreign matter existing near the center on the surface of the foreign matter adhesion prevention film 23 is the same as the intensity of the scattered light from the foreign matter present at the edges, and the scattering is almost uniform. A light intensity distribution 28 is obtained. Therefore, there is no need to change the threshold level depending on the location as in the past, and even if the foreign matter adhesion prevention film 23 moves up and down, the threshold level remains constant at 4.
This means that stable foreign matter detection can be performed with only 3.

FIG. 7 shows factors that generate scattered light from sources other than foreign objects. Frame 2 to which a foreign matter adhesion prevention film 23 is attached is likely to be mistakenly detected as scattered light 21 from foreign matter 20.
Scattered light 31 from 4 and light passing through the foreign matter adhesion prevention film 23 form a pattern 2 on the surface 5 of the glass substrate 39.
It is possible that the scattered light 30 is generated by hitting the light beam 9. By the way, as shown in FIGS. 8(a) and 8(b), when a transparent material such as a glass substrate is generally irradiated with light such as a laser beam from an oblique direction, the surface 5 of the substrate is irradiated, although this varies depending on the irradiation angle a. On the other hand, a wave (S-polarized wave) 44 in which the magnetic interface vibrates in a parallel direction (horizontal direction) has many reflected components, whereas a wave in which the magnetic interface vibrates in a direction perpendicular to the substrate surface 5 (p In the case of polarized light wave) 45, there is a property that the number of transmitted components increases. Based on this fact, in order to prevent the influence of scattered light from the pattern 29 formed on the substrate surface 5 as much as possible, the polarizing plate 16 irradiates the foreign matter adhesion prevention film 23 with S-polarized light waves, which pass through the foreign matter adhesion prevention film 23. It can be said that it is desirable to minimize light. However, even a very small amount of laser light passing through the foreign matter adhesion prevention film 23 causes scattered light from the pattern 29, so as shown in FIGS. 9 and 10, the optical axis 4 of the scattered light detection system
It is preferable to set the pattern 29 so that it is inclined by Φ with respect to the vertical 41 of the substrate surface 5 so that the location where the scattered light 30 from the pattern 29 is generated cannot be seen. Note that FIG. 9 shows the case where the top of the foreign matter adhesion prevention film 23 is being inspected, and FIG. 10 shows the case where the surface of a relatively thick glass substrate 39 having the same function as the foreign matter adhesion prevention film 23 is being inspected. The generation states of scattered light 30 from the pattern 29 are shown respectively. In addition, the symbol d in the figure indicates the beam diameter of the irradiated laser beam, t indicates the thickness of the glass substrate 39 or the thickness of the frame 24 to which the foreign matter adhesion prevention film 23 is attached, and φ indicates the refraction angle with respect to ψ. show.

In any case, the condition for the scattered light detection system not to detect the scattered light 30 from the pattern 29 is that after the optical axis 42 of the detection system passes the substrate surface 5 or the surface of the foreign matter adhesion prevention film 23,
The point where the laser beam is refracted or goes straight and intersects with the pattern forming surface of the glass substrate 39 is not included in the beam diameter d of the irradiated laser beam. That is, it is necessary to set ψ that satisfies the following equation.

ψ≧5in-1(n 5in(tan-”d/2t)
) - (2) However, n indicates a refractive index. In the case of FIG. 9, n is set to 1 because the foreign matter adhesion prevention film 23 is thin and moves straight.

However, in reality, since the amount of aberration of the imaging lens 26 is also affected, ψ varies slightly from Φ determined by the above formula, but ψ is set within a range of approximately 0° or more and 20' or less.

On the other hand, the frame 24 to which the foreign matter adhesion prevention film 23 is attached
The scattered light 31 generated from the photoelectric conversion element 27 can be blocked by additionally installing a light-blocking bag w32 at the imaging position of the photoelectric conversion element 27, as shown in FIG. Imaging lens 2
When a light blocking device is appropriately provided near the frame 24, the scattered light 31 from the frame 24 cannot be detected by the photoelectric conversion element 27.

Now, as for the configuration of the foreign matter inspection device, there are other
Something like 80546 is also possible.

Furthermore, it is also possible to install a TV camera or the like during transportation and visually observe the product in a state where there is a low possibility of foreign matter adhering. The foreign matter inspection device can be installed not only while the substrate is being transported, but also by providing an inspection station on the reduction projection exposure device and installing it there.

Further, it is also possible to juxtapose a device for removing foreign matter on the foreign matter adhesion prevention film.

Furthermore, the present invention can be used not only in reduction projection exposure apparatuses but also in 1:1 reflective projection exposure apparatuses.

〔Effect of the invention〕

As explained above, according to the present invention, it is possible to detect large foreign particles that have adhered to the foreign particle adhesion prevention film and interfere with exposure by substantially detecting the scattered light generated from the edges of the circuit pattern formed on the substrate. This has the effect that it can be inspected without any problems, and can greatly contribute to improving the yield in the exposure process.

[Brief explanation of drawings]

FIG. 1 is a diagram showing one embodiment of the present invention, FIG. 2 is a diagram showing another embodiment, FIG. 3 is a diagram showing the configuration of an example of a foreign object detection device according to the present invention, and FIG. FIG. 5 is a diagram for explaining the operation of the laser beam irradiation system in the configuration, FIG. A diagram for explaining the foreign object detection process according to the present invention, FIG. 7 is a diagram showing the factors of scattered light generation from sources other than foreign objects, FIG. 8 (a),
(b) is a diagram showing the reflection states of S-polarized light waves and p-polarized light waves on the substrate surface, respectively, and FIGS. 9 and 10 are diagrams showing the desirable optical axis of the scattered light detection system that makes it impossible to detect unnecessary scattered light. FIG. 11, which is a diagram for explaining the setting state, is a diagram showing a desirable configuration of a scattered light detection system that similarly makes it impossible to detect unnecessary scattered light. 1.2... Foreign object inspection device 3... Transport arm 10... Exposure optical system 14.
- Laser oscillator 15... Condensing lens 16... Polarizing plate 17... Galvano mirror 18... Collimator lens 26 - Imaging lens 27... Photoelectric conversion element 32.
・Shading device number! Figure 1 (? Figure 1)

Claims (1)

[Claims] 1. For an object to be inspected, which has a frame on which a foreign matter adhesion prevention film is attached to a substrate such as a reticle or photomask used for exposure, a light beam is irradiated onto the foreign matter adhesion prevention film. The light beam passes approximately through the center of the light irradiation optical system and the light beam irradiated by the light irradiation optical system on the foreign matter adhesion prevention film, and does not intersect with the light beam on the substrate surface due to the light that has passed through the foreign matter adhesion prevention film. The detection optical axis is at an angle ψ≧ with respect to the irradiation light flux d.
a detection optical system arranged at tan^-^1d/2t (where t is the distance between the substrate surface and the foreign matter adhesion prevention film) to detect scattered light only from foreign matter adhering to the foreign matter adhesion prevention film; , a photoelectric conversion means for receiving scattered light from only the foreign matter adhering to the foreign matter adhesion prevention film detected by the detection optical system and converting it into a signal; A foreign matter inspection device characterized in that it is configured to inspect a certain large foreign matter. 2. The foreign matter inspection device according to claim 1, wherein the detection optical system is provided with a light shielding device for shielding scattered light generated from the frame.