JPH0430574B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a foreign matter inspection device for inspecting foreign matter adhering to the surface of a photomask or reticle (hereinafter referred to as a substrate). The present invention relates to a foreign matter inspection device having an optical system that is not easily affected.

When forming a layer of chromium or other material on a transparent thin plate such as glass or quartz and etching it to form a fine transparent or opaque circuit pattern (hereinafter referred to as a pattern), the presence of foreign matter on the surface of the substrate may cause exposure. During this process, the shadow of the foreign object is also transferred and defects occur. Therefore, it is essential to inspect for foreign substances before exposure.

FIG. 1 is a diagram showing the principle of a conventional foreign matter inspection device. In the figure, when a substrate 1 is irradiated with S-polarized laser light 2, only the S-polarized light component 4 is reflected if no foreign matter is present. If a foreign object 3 is present as shown in the figure, the P-polarized light component 5 will also be reflected due to its irregular shape. When this light is focused by a lens 6 and transmitted through a polarizing plate 7, only the P-polarized light component 5 enters the light receiver 8, and the presence of the foreign object 3 is detected.

At this time, in order to reduce the influence of the pattern on the substrate 1, it is necessary to make the angle ψ between the laser beam 2 and the substrate 1 as small as possible. FIG. 2 is a diagram showing the direction of patterns often used on the substrate 1. FIG. For laser beam 2, pattern A is 0°, pattern B is 90°, pattern C is ±45°, pattern D
is at an angle of ±30°, and pattern E is at an angle of ±60°.

Now, as patterns become finer, a pellicle protective film as shown in FIG. 3 has come to be installed to prevent foreign matter from adhering after inspection. In Figure 3,
10 is a metal frame, and 11 is a thin film made of nitrocellulose.

By the way, since there is a high possibility that foreign matter will adhere even when the pellicle protective film is attached after the foreign matter inspection, it is necessary to perform the foreign matter inspection also after the pellicle protective film is attached.
However, as shown in FIG. 3, since the frame 10 exists on the substrate 1 after the pellicle protective film is attached, it is not possible to reduce the angle ψ between the laser beam 2 and the substrate 1 as shown in FIG. There is a problem that detection sensitivity further decreases. Further, there is a problem that detection sensitivity is further reduced because foreign matter on the pellicle protective film and reflected light from the frame enter the light receiver 8.

An object of the present invention is to solve the above-mentioned problems of the prior art by eliminating foreign particles present on the substrate surface without being affected by complicated circuit patterns or pellicle protective films formed with directionality on the substrate surface. An object of the present invention is to provide a foreign matter inspection device that can inspect foreign matter with high sensitivity.

That is, in order to achieve the above object, the present invention has the following features:
An irradiation means for condensing and irradiating a laser beam onto the substrate surface from an oblique direction inclined with respect to a vertical direction in a foreign matter inspection installation for inspecting foreign matter attached to a substrate surface on which a circuit pattern is formed with directionality; A scanning means for relatively scanning the condensed irradiated laser beam and the substrate; a first lens provided on the Fourier transform surface of the first lens and configured to release regularly reflected light from the irradiation point and condense reflected scattered light; and a first lens provided on the Fourier transform surface of the first lens and formed on the surface of the substrate. A light-shielding optical system that blocks regular reflected and scattered light that has directionality from a circuit pattern and passes reflected and scattered light that does not have directionality from foreign matter on a substrate surface, and a direction from the foreign matter that is obtained through the light-shielding optical system. a second lens that performs an inverse Fourier transform on reflected and scattered light that has no properties, and a light shielding means that is provided at an imaging point of the second lens and that blocks incident scattered light from other than the irradiation point on the substrate surface. , and a light receiving means for receiving reflected and scattered light that has passed through the light shielding means, and is configured to inspect foreign matter present on the surface of a circuit pattern-bearing substrate based on a signal detected from the light receiving means. This is a foreign object inspection device with special features.

Next, the principle of the present invention will be explained. In the optical system shown in FIG. 4, when the focal point 17 of the lens 15 is arranged so as to overlap the irradiation point of the laser beam 18 on the substrate 1, the Fourier transform surface 16 has the pattern shown in FIG. Bright lines are formed.
Bright line 20 is based on pattern B (90°) in Figure 2, and bright line 21 is based on pattern E (±60°) in Figure 2.
This is due to Therefore, by shielding these bright line areas, only the reflected light from other irregular patterns (foreign objects) can be extracted. In FIG. 5, 22 indicates a light shielding plate.

Further, considering an optical system as shown in FIG. 6, the reflected light of the laser beam 18 from a point 36 on the substrate 1 is imaged by the lens system 30 at the position of a point 33. On the other hand, the reflected light from the foreign matter 31 on the pellicle protective film 11 is imaged at a point 32 because the laser light 18 is irradiated obliquely. Therefore, point 33
By arranging the pinhole or slit 35 at the position, only the reflected light from the substrate 1 can enter the light receiver 34.

The foreign object detection device of the present invention is characterized by eliminating the influence of the pattern and the influence of the pellicle protective film by combining the principles shown in FIGS. 5 and 6.

The present invention will be described in more detail below with reference to embodiments shown in the accompanying drawings. FIG. 7 and FIG. 8 are diagrams showing one embodiment of the present invention. In FIG. 7, it is assumed that the laser beam 18 is irradiated from diagonally above the substrate 1, and a small spot is formed on the foreign object 36. The light reflected from the foreign object 36 is collected by a lens 40 and separated from the light reflected from the pattern by a light shielding plate as shown in FIG. 5 placed on the Fourier transform surface 16. This is inversely Fourier transformed by the lens 41, and in this case, the lens 40 and the lens 41
Since the synthetic optical system is equivalent to the lens system 30 shown in FIG. 6, if a slit 35 is provided that allows only the conjugate point 33 of the point where the foreign object 36 is placed to pass through, only the reflected light from the foreign object 36 will be received. The light enters the vessel 34. Since the laser beam 18 is scanned in a direction perpendicular to the plane of the paper, the slit 35 is also formed to be elongated in the direction perpendicular to the plane of the paper to accommodate this.

FIG. 8 is a perspective view of the embodiment shown in FIG. 7.
In the figure, the light shielding plate 22 is designed to shield 90° and 60° patterns, but this may vary depending on the situation.
You can block light only at 90° (if the pattern is 0°, ±45°,
(If the light is formed from only 90°), a light shielding plate other than 90° or 60° can also be inserted. The laser beam 18 is focused to a spot of about 20 to 100 μm by a scanning optical system 51, and scans the substrate 1 in the direction indicated by an arrow 50. Since the lens 40 takes in a lot of scattered light,
A lens as bright as F1.2 is desirable. Light receiver 34
For this purpose, it is sufficient to use a photomal, and at this time, in order to prevent disturbance light of wavelengths other than laser light, the 9th
It is preferable to place a lens 55 between the light receiver 34 and the slit 35 as shown in the figure, or to place an interference filter 56 as shown in FIG. Note that in FIGS. 9 and 10, reference numeral 52 indicates a light beam passing through the slit 35.

Since the laser beam is irradiated obliquely at an angle ψ,
Spots on substrate 1 are generally not circular. Therefore, a correction optical system using a cylindrical lens is used as the scanning optical system 51 shown in FIG. 1st
FIG. 1 is a diagram showing a specific example thereof. Laser light irradiated from a laser oscillator 60 is expanded by a beam expander 61, and then enters a cylindrical lens 62. As a result, the laser beam is converted into a beam having a long elliptical cross section, and is passed through the galvano mirror 63 and lens 64 to the point 50 on the substrate 1.
The light is focused on. In this way, the laser beam is focused on the substrate 1 in a substantially circular shape. Scanning of the laser beam is performed by a galvano mirror 63.
A polygon mirror may be used instead of 3.

In the embodiments shown in FIGS. 7 and 8, since the scanning distance of the optical system is short, table feeding and scanning are repeated as shown in FIG. 12 in order to inspect the entire surface of a large substrate. In the figure, 70 indicates scanning by an optical system, and 71 indicates scanning by table feeding.

FIG. 13 is a diagram showing an example of a circuit that detects the presence or absence of a foreign object by receiving the output of the light receiver 34 shown in FIG. 7. In the figure, numeral 34 is a photoreceiver composed of a photomultiplier, 100 is a microcomputer, and 1
01 is a timing generation circuit, 102 is a table address counter, 103 is a motor drive circuit, 10
4 is a motor, 105 is a galvano mirror angle counter, 106 is a galvano mirror drive circuit, 63 is a galvano mirror, 107 is an input buffer, 110 is an amplifier, 111 is a comparator, 120 is a start signal, 121 is a timing pulse, 122 is an interrupt 123 is address data, and 124 is foreign object detection data.

As explained above, according to the present invention, circuit patterns and It is possible to detect foreign matter adhering to the surface of the substrate with high sensitivity by eliminating the influence of the Percle protective film, etc., and as a result, it is possible to perform exposure using a substrate free of foreign matter, and it is possible to detect non-defective semiconductor products. This has the advantage of being able to be manufactured with high yield.

[Brief explanation of drawings]

Fig. 1 is a perspective view showing an example of a conventional foreign matter inspection device, Fig. 2 is an explanatory drawing showing the direction of the pattern on the substrate, Fig. 3 is a perspective view showing the state of the pellicle protective film device, and Fig. 4 is An explanatory diagram showing the Fourier transform method which is the principle of the present invention, FIG. 5 is an explanatory diagram showing the state of the light shielding plate which is the principle of the present invention, and FIG. 6 is a sectional view showing the slit method which is the principle of the present invention. FIG. 7 is a sectional view showing an embodiment of the present invention, FIG. 8 is a perspective view of the embodiment shown in FIG. 7, and FIGS. 9 and 10 show that light other than laser light is removed from the incident light of the light receiver. 11 is a perspective view showing an overview of the scanning optical system, FIG. 12 is an explanatory diagram showing an example of a substrate scanning method, and FIG. 13 is a block diagram showing an example of an inspection circuit. be. 1... Substrate, 2, 18, 52... Laser light,
3, 31, 36... Foreign matter, 6, 15, 40, 4
1, 55, 64... Lens, 7, 22... Polarizing plate, 8, 34... Light receiver, 10... Frame, 1
1... Pellicle protective film, 16... Fourier transform surface, 30... Lens system, 35... Slit, 51
...Scanning optical system, 56...Interference filter, 60...
...Laser oscillator, 61...Beam expander,
62...Cylindrical lens, 63...Galvano mirror.

Claims (1)

[Claims] 1. A foreign matter inspection device for inspecting foreign matter attached to the surface of a substrate on which a circuit pattern is formed with directionality, comprising: an irradiation means for condensing and irradiating the surface of the substrate with laser light from an oblique direction inclined with respect to the vertical direction; , a scanning means for relatively scanning the condensed irradiated laser beam and the substrate, and an upper part of the substrate so that the irradiation point of the condensed and irradiated laser beam by the irradiation means and the focal plane substantially coincide with each other. a first lens provided on the Fourier transform surface of the first lens and configured to release regularly reflected light from the irradiation point and condense reflected scattered light; and a first lens provided on the Fourier transform surface of the first lens and formed on the surface of the substrate. A light-shielding optical system that blocks regular reflected and scattered light that has directionality from a circuit pattern formed on a substrate, and also transmits reflected and scattered light that has no directionality from foreign matter on a substrate surface; a second lens that performs inverse Fourier transform on reflected and scattered light that has no directionality, and a light shielding means that is provided at the imaging point of the second lens and that shields incident scattered light from other than the irradiation point on the substrate surface. and a light-receiving means for receiving reflected and scattered light that has passed through the light-shielding means, and is configured to inspect foreign matter present on the surface of a substrate having a circuit pattern based on a signal detected from the light-receiving means. A foreign object inspection device featuring: