JPS5965428A - Foreign substance detector - Google Patents

Abstract

PURPOSE:To detect a foreign substance on a substrate with excellent accuracy without being disturbed by a complex pattern or pellicle protective film by providing a screening plate which screens a regularly dispersed light from the pattern on the substrate and a slit which screens a dispersed light coming from other points than the point on the substrate irradiated by a laser beam. CONSTITUTION:A laser beam 18 is radiated on a substrate from an inclined direction. The reflected light from a foreign substance 36 is condensed by a lense 40 and separated from the reflected light from a pattern by a screening plate 22 placed on a Fourier transformation plain 16 and transformed by inverse-Fourier trasnformation by a lense 41 and passes through a slit 35 through which only the light from a conjugate point 33 of the point 36 where the foreign substance exists can pass and is injected into a photodetector 34. A reflected light from a foreign substance on a pillicle protective film 11 is focused on the point other than the point 33 because the laser beam 18 is radiated from the inclined direction. Thus, if a pin-hole or a slit 35 is provided to the point 33, only the reflected light from the substrate 1 is received by the photodetector 34.

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), and more specifically to a pellicle protective film for preventing adhesion of patterns and foreign matter. The present invention relates to a foreign matter inspection device having an optical system that is not easily influenced by foreign matter.

When a fine transparent-opaque pattern is formed by forming a layer of chromium or the like on a transparent thin plate such as glass or quartz and etching it.

If foreign matter is present on the substrate surface, the shadow of the foreign matter will also be transferred during exposure, resulting in defects. Therefore, it is essential to inspect for foreign substances before exposure.

FIG. 1 is a diagram showing the principle of a conventional object inspection device. In the figure, when a substrate 1 is irradiated with an S-polarized laser beam 2, only the S-polarized light component 4 is reflected when there is no foreign object. The P-polarized light component 5 is also reflected. ``When all of the lenses 6 collect the light and transmit it through the polarizing plate 7, only the P-polarized light component 5 enters the light receiver 8, and the presence of the foreign object 5 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 ±456, pattern D is ±30@, pattern E is ±60
It forms the angle U of @.

Now, as patterns become finer, a pellicle protective film as shown in FIG. 3 has been installed to prevent foreign matter from adhering after inspection. In FIG. 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. 6, after attaching the pellicle protective film, the frame 10 is placed on the substrate 1.
1, it is not possible to reduce the angle ψ between the laser beam 2 and the substrate 1 as shown in FIG. 1, resulting in a disadvantage that the detection sensitivity is reduced. In addition, since foreign matter on the pellicle protective film and reflected light from the frame enter the light receiver 8, there is a drawback that the detection sensitivity is further reduced.

The present invention was made in view of the above-described shortcomings of the conventional foreign matter inspection device, and an object of the present invention is to provide a foreign matter inspection device that can detect foreign matter on a substrate with high sensitivity without being affected by a complicated pattern or a pellicle protective film. It is said that

The foreign matter inspection device of the present invention is a device for inspecting foreign matter adhering to the surface of a substrate used in semiconductor manufacturing, and includes means for obliquely irradiating and scanning a substrate with a laser beam, and a laser beam irradiation point and focus. A first lens is provided above the substrate so that the surfaces thereof almost coincide with each other to collect the scattered light of the laser beam, and a first lens is provided on the Fourier transform surface of the first lens to collect the regularly scattered light from the substrate pattern. 'f: A light-shielding plate that blocks light.

a second lens that performs inverse Fourier transform on scattered light from a foreign substance obtained through a light shielding plate; and a slit provided at the imaging point of the second lens to block scattered light from sources other than the laser beam irradiation point on the substrate. It is characterized by being comprised of a light receiver that receives scattered light (C) from foreign objects that have passed through it.

Next, the principle of the present invention will be explained. In the optical system shown in FIG. 4, if the focal point 17 of the lens 15 is arranged so as to be in contact with the irradiation point of the laser beam 18 on the substrate 1, the Fourier transform surface 16 will have the pattern shown in FIG. A line as shown is formed.

Bright line 20 is based on pattern B (90°) in Figure 2, and bright line 21 is based on pattern J'' in Figure 2 (±60°).
This is due to Therefore, by shielding these bright line parts, only the reflected light from other irregular patterns (foreign objects) can be extracted. In FIG. 5, 22 indicates a light shielding plate.

Also, considering the various optical systems shown in Fig. 6, the laser beam 1
The reflected light from the point 36 on the substrate 1 of 8 is reflected from the lens system 30.
An image is formed at the position of point 33. On the other hand, the reflected light from the foreign matter 31 on the pellicle protective film 11 is reflected by the laser beam 1.
8 is irradiated from an angle 1. Therefore, the image is formed at the position of point 32. Therefore, a pinhole or slit 3 is placed at the position of point 33.
5, the reflected light from the substrate 1 can be transferred to the receiver 34.
can be put in.

The foreign object detection device of the present invention is characterized by the combination of the principles shown in FIGS. 5 and 6, and in that the influence of the pattern and the influence of the pellicle protective film are completely eliminated.

The present invention will be described in more detail below with reference to embodiments shown in the accompanying drawings. FIGS. 7 and 8 are views 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 reflected light from the foreign object 36 is focused by a lens 40, and is separated from the reflected light from the pattern by a light blocking 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 combined optical system of the lenses 40 and 41 becomes equivalent to the lens system 30 shown in FIG.
If a slit 35 is provided that allows only the conjugate point 33 of the point where the
4.

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 further perspective view of the embodiment shown in FIG. 7.

In the same figure, the light shielding plate 22 is designed to shield the 90" and 60@ patterns, but in some cases, the light shielding plate 22 is designed to shield the light of υ90° (patterns from 0°, ±45°, 90° only) (if formed), a light shielding plate other than 90" or 60" can be inserted.The laser beam 182 is used by the scanning optical system 51 to spot a spot on the river of about 20 to 100 μm,
The substrate 1 is scanned in the direction indicated by the arrow 5o. lens 4
Since the lens 0 allows a lot of scattered light to enter, a lens as bright as FL2 is desirable. A photomultiplier may be used as the light receiver 34. At this time, in order to prevent disturbance light of wavelengths other than laser light, the light receiver 34 and the slit 35 are connected as shown in FIG.
It is preferable to place the lens 55'f between the lenses and the interference filter 56 as shown in FIG. Power,
In FIGS. 9 and 10, reference numeral 52 indicates a light beam passing through the slit 35. In FIG.

Since the laser beam is irradiated obliquely at an angle ψ, the spot on the substrate 1 is generally not circular.

Therefore, a correction optical system using a cylindrical lens is used as the scanning optical system 51 shown in FIG.

FIG. 11 is a diagram showing a specific example of the laser oscillator 6.
Laser light irradiated from 0 is expanded by a beam expander 61, and is incident on a cylindrical lens 62. As a result, the laser beam is converted into a beam having an elongated elliptical cross section, and is focused on a point 50 on the substrate 1 via the galvanometer mirror 63 and the lens 64. 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.
3. In the embodiments shown in FIGS. 7 and 8, the scanning distance of the optical system is short, so in order to inspect the entire surface of a large substrate, it is necessary to use a polygon mirror.
As shown in Figure 2, table feeding and scanning are repeated. In the figure, 7o indicates scanning by the optical system, and 71 indicates scanning by table feed.

FIG. 13 is a diagram showing an example of a detection circuit that detects the presence or absence of a foreign object by receiving the output from the light receiver 34 shown in FIG. 7. In the same figure, 34 is a photoreceiver composed of a photomultiplier, and 10
0 is a microcomputer, 101 is a timing generation circuit, 102 is a table address counter, 103 is a motor drive circuit, 104 is a motor, and 105 is a galvano mirror.
angle counter.

106 is a galvano mirror drive circuit, 63 is a galvano mirror, 1107 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 signal, 123 is address data, 124 is foreign object detection It is data.

As is clear from the above description, according to the present invention, foreign matter inspection on a substrate can be performed with high accuracy regardless of the presence or absence of a pellicle protective film.

Therefore, it has the great effect of suppressing the occurrence of defective products during semiconductor manufacturing and improving throughput.

[Brief explanation of the drawing]

Fig. 1 is a perspective view showing an example of a conventional foreign matter inspection device;
The figure is an explanatory diagram showing the direction of the pattern on the substrate, Figure 3 is a perspective view showing the state of the pellicle peritoneal retention membrane attached, Figure 4 is an explanatory diagram showing the Fourier transform method which is the principle of the present invention, and the fifth factor is FIG. 6 is an explanatory view showing the state of a 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, and FIG. 12 is an explanation showing an example of a substrate scanning method. FIG. 16 is a block diagram showing an example of an inspection circuit. be. 1... Substrate 2, 18.52... Laser beam 5, 31.36... Foreign matter 415, 40.41.55.64... Lens 7.
22... Polarizing plate 8.34... Light receiver 10... Frame 11... Pellicle &
[Membrane 16...Fourier transform surface 30...Lens system 35...Slit 51...Scanning optical system 56...Interference filter 60...Laser oscillator 61...Beam expander 62... Shirin Tori Lens 63... Galvano mirror - Figure 1 〒2 Illustration 5 Figure 4? i6 Figure Punishment Figure 7 Thousand Eight Figures ε Figure No. 107 Punishment Figure 11 ＼ Meng 1? figure

Claims (1)

[Claims] In an apparatus for inspecting foreign matter adhering to the surface of a substrate used in semiconductor manufacturing, there is a means for irradiating and scanning a substrate with a laser beam from an oblique direction, and a means for scanning the substrate by irradiating the substrate with a laser beam from an oblique direction. a first lens provided above and condensing the scattered light of the laser beam; a light shielding plate provided on the 7-layer conversion surface of the first lens to block regularly scattered light from the substrate pattern; A second lens that performs inverse Fourier transform on the scattered light from the foreign matter obtained by the light shielding plate, and a second lens provided at the imaging point of the second lens to block scattered light from other than the laser beam irradiation point on the substrate. A foreign object inspection device comprising a slit and a light receiver that receives scattered light from the foreign object that has passed through the slit.