JPH11142127A - Wafer surface inspecting method and equipment therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To distinguish a foreign matter and a crack on a wafer surface from a dot type recessed part existing on the surface, by independently photoelectrically converting two wavelengths of scattered lights from a light convergence point, and using the difference of intensities of the respective signals. SOLUTION: By detecting the difference in the intensities of scattered lights when the incident angles are changed, i.e., by detecting the magnitude of change of signals when the incident angles are changed, whether a scattering object is a foreign matter or a recessed part can be distinguished. Laser lights outputted from light sources 21, 22 are converged on the surface of a wafer with independent optical systems 24, 25. The lights outputted from the two light sources 21, 22 are converged on the surface of the wafer, in order to be measured at the same time at the same point. Two illuminating lights which have comparatively nearby different wavelengths are used, and the wafer is illuminated with two different incident angles. Two photoelectric converters 27, 28 receive the two scattered lights of comparatively nearby two different wavelengths at the same azimuth and angle to an incident surface, and output signals. A discriminating circuit 30 discriminates the foreign matter from a dot type recessed part by using the signals.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates generally to a method and an apparatus for inspecting a wafer surface of various objects, and more particularly to a wafer surface inspection method for inspecting foreign matters and scratches on the surface of a semiconductor wafer.

[0002]

2. Description of the Related Art Generally, a semiconductor integrated circuit is manufactured by forming a circuit on a wafer of a semiconductor substrate by a photolithography process. At this time, a large number of identical integrated circuits are formed on the surface of one wafer, and are finally cut off to form a single integrated circuit chip.

[0003] If foreign matter or scratches exist on the surface of the wafer, a defect occurs in a circuit pattern formed in that portion,
The integrated circuit becomes unusable. As a result, the number of integrated circuits that can be obtained from one wafer is reduced, and the yield is reduced.

Therefore, before entering the lithography process,
Inspection of a wafer as a material of a semiconductor integrated circuit has confirmed that no foreign matter exists.

[0005] As a method of this inspection, a method is generally used in which a laser beam is focused on the wafer surface, scattered light from the focused point is received, and a foreign substance or the like is detected based on the received light signal. .

FIG. 1 shows a conventional wafer surface inspection apparatus. The light source 10 uses a laser. Light emitted from the light source 10 is condensed on the surface of the wafer 12 by the optical system 11 at an incident angle of about 20 degrees. The scattered light from the focal point 13 is received by the photoelectric converter 15 by the lens 14. The wafer 12 is rotated by a motor 16 and simultaneously moved by a translation mechanism (not shown) so that the focal point 13 scans the entire surface of the wafer 12.

[0007] The photoelectric converter 15 for receiving the scattered light outputs a pulse-like signal corresponding to the intensity of the scattered light when the converging point 13 crosses a foreign substance or the like. Therefore, the pulse-like signal is detected by the signal detection circuit 17, and the presence and size of a scattering object, that is, a foreign substance, is determined based on the magnitude of the signal output.

On the other hand, the increase in the degree of integration of integrated circuits has promoted the miniaturization of circuit patterns, thereby miniaturizing the size of foreign substances to be inspected and, at the same time, improving the sensitivity of inspection apparatuses.

Against this background, some of the foreign matter detected by this inspection may include a small point-like concave portion that does not hinder the production of a circuit pattern. In recent years it has been known.

That is, since a concave portion which does not cause a problem in manufacturing an integrated circuit is erroneously recognized as a foreign substance, a usable wafer may be determined to be defective. Since the recess cannot be removed by re-cleaning, it is determined that the wafer is unusable and wasted. This will be
This means that as the size of the wafer increases, the waste increases.

[0011]

SUMMARY OF THE INVENTION An object of the present invention is to detect a foreign substance or a scratch on a wafer surface and a point-like concave portion present on the wafer surface in the inspection of the surface of a semiconductor substrate or other wafers. It is an object of the present invention to provide an inspection method and apparatus which can perform the inspection.

[0012]

This problem is solved by a wafer surface inspection method and apparatus described in the claims.

For example, one of the solutions of the present invention is to condense light from a light source on a wafer surface, scan a light converging point, receive scattered light from the light converging point by a photoelectric converter, In a wafer surface inspection method for detecting foreign matter and scratches on a wafer surface by detecting a signal from a photoelectric converter, two different wavelengths of light are collected at the same point at different angles of incidence and collected. It is characterized in that scattered light from a point is photoelectrically converted into two wavelengths separately, and the difference in the intensity of each signal is used to distinguish foreign matter or scratches on the wafer surface from dot-like recesses on the wafer surface. Wafer surface inspection method.

Another solution of the present invention is to provide a light source,
An optical system that focuses light from the light source on the wafer surface,
Scanning means for scanning the focal point over a predetermined area of the wafer surface, a light receiving section having a photoelectric converter for receiving scattered light from the focal point, and a signal detector for detecting a signal from the light receiving section Wherein the light source is a light source of two different wavelengths and the optical system is
Light of two wavelengths is condensed at the same point on the wafer surface at different angles of incidence, and the light receiving unit is configured to separately receive the two wavelengths, and the output from the signal detector is And a discrimination circuit for discriminating a foreign substance or a scratch on the wafer surface from a point-like concave portion existing on the wafer surface by utilizing the method.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention provides a wafer surface inspection method and apparatus for inspecting the surface of a wafer, for example, a semiconductor substrate or other wafers used in various technical fields.

The intensity of scattered light reflected from a foreign substance or the like attached to the wafer surface or a scratch or the like formed on the wafer surface changes depending on the relationship between the wavelength of the light from the light source and the size of the foreign substance or flaw.
Further, it is known that it changes depending on the incident angle and the azimuth / angle at which light is received. That is, the intensity of the scattered light changes depending on the wavelength of the light, the size of the foreign matter, the incident angle of the light, and the azimuth / angle at which the light is received.

For example, as described above, a point-like concave portion on the wafer surface may be mistaken for a foreign substance.
This occurs in a region that is considerably smaller than the wavelength in the visible region and generates scattered light equivalent to that of a foreign substance. In such a region, when the azimuth and angle of the light receiving unit are fixed, the change in the intensity of the scattered light with respect to the change in the incident angle is smaller in the minute concave portions of the surface than in the case of the foreign matter attached to the wafer surface. Is big. Therefore, by increasing the incident angle, that is, by making the incident angle closer to the inspection surface, and adjusting the sensitivity so that the scattered light from the foreign matter does not change, the scattered light from the concave portion is obtained. Is getting weaker. This was confirmed by experiments.

Therefore, when the difference in the scattered light intensity is examined by changing the incident angle, that is, when the magnitude of the signal change when the incident angle is changed is examined, it is determined whether the scattered object is a foreign substance or a concave part. I can distinguish them.

Based on such knowledge, in the present invention, two different wavelengths of light are condensed at the same point at different angles of incidence, and the scattered light from the converging point is separately converted into two wavelengths by photoelectric conversion. Then, using the difference in the intensity of each signal, a foreign substance or a scratch on the wafer surface is distinguished from a point-like concave portion present on the wafer surface.

For example, according to the present invention, when two light sources having different wavelengths and light from the two light sources are condensed on the wafer surface, the light having the two wavelengths is incident on the wafer surface at different incident angles. An optical system configured to focus light at the same point, scanning means for scanning the focus point over a predetermined area of the wafer surface, and two wavelengths for receiving scattered light from the focus point. Two photoelectric converters that are configured to receive light separately, a signal detector that detects signals from the two photoelectric converters, and the use of an output from the signal detector to detect a foreign substance or the like on the wafer surface. A discriminating circuit is provided for discriminating a flaw or the like from a dot-shaped recess present on the wafer surface.

[0021]

FIG. 2 shows an embodiment of the present invention. this is,
This is an example in which a conventional wafer surface inspection device is improved.

As shown in FIG. 2, in the wafer surface inspection apparatus according to the present invention, two light sources 2 having different wavelengths are used.
When the light from the two light sources 21 and 22 and the light from the two light sources 21 and 22 are collected on the surface of the wafer 23, the light of the two wavelengths is collected at the same point on the surface of the wafer 23 at different incident angles. , A scanning unit (not shown) for scanning the focal point 26 over a predetermined area (for example, the entire area) of the surface of the wafer 23, and a focal point 2
The two photoelectric converters 27 and 2 configured to separately receive two wavelengths when receiving the scattered light from
8, a signal detector 29 for detecting signals from the two photoelectric converters 27 and 28, and a foreign matter or a flaw on the wafer surface using the output from the signal detector 29 and present on the wafer surface. A discriminating circuit 30 for distinguishing from a dot-shaped recess is provided.

As the light sources 21 and 22, lasers are used. Light emitted from the light sources 21 and 22 is separated into separate optical systems 24 and 2
5 condenses on the surface of the wafer 23. These two
Light emitted from the two light sources 21 and 22 is condensed on the surface of the wafer 23 for measurement at the same time and at the same point.
Moreover, two relatively different wavelengths (for example, 4
Wafer 2 at two different angles of incidence (eg, 20 degrees and 70 degrees) using illumination light of 88 nm and 514.5 nm).
3 is configured to be illuminated. Then, the two photoelectric converters 27 and 28 receive the scattered lights of two different wavelengths which are relatively close to each other with the same azimuth and cuticle on the incident surface,
Output a signal. The signal detector 29 detects signals from the two photoelectric converters 27 and 28, and the discrimination circuit 30 uses the output signal from the signal detector 29 to detect foreign matter and scratches on the wafer surface, A distinction is made between point-like recesses present on the wafer surface.

FIG. 3 shows an example of a signal output from a foreign substance having the same scattered light intensity level and an example of a signal output from a concave portion.

The distinction between the point-like concave portions on the wafer surface and the foreign matters is performed as follows. That is, the azimuth and angle of the two photoelectric converters 27 and 28 are fixed, and the change in the intensity of the scattered light with respect to the change in the incident angle is detected. A change in the intensity of the scattered light with respect to the foreign matter attached to the wafer surface is detected, and a change in the intensity of the scattered light with respect to the minute concave portion on the wafer surface is detected. Comparing the two, as shown in FIG. 3, when the incident angle is small, the signals of the two are relatively large, and it is difficult to distinguish between the two. While the signal is relatively large, the signal in the concave portion is relatively small, and it is easy to distinguish between the two.

By comparing the difference in the intensity of the scattered light, ie, the magnitude of the change in the signal when the angle of incidence is changed, by changing the angle of incidence, it is possible to determine whether the scattered object is a foreign substance or a recess. It comes.

Although there is a possibility that it is not possible to distinguish the point-shaped recess from the recess-shaped scratch, the scratch is generally larger (longer) than the foreign material or the dot-shaped recess, and the signal is present in isolation. By checking whether they are present on a plurality of adjacent scanning lines as well.

In the above-described embodiment, different incident angles are set within the same incident plane. However, different incident planes may be used as long as light is received at the same azimuth and angle with respect to the incident plane.

Further, in the above-described embodiment, a scanning method called spiral scanning using a rotation and translation mechanism of a wafer is adopted. However, the present invention is not limited to this, and the laser beam is converted into two-dimensional XY. The present invention can be applied to a method and an apparatus for scanning.

When the incident angle is increased, the scattered light from the concave portion is reduced. Therefore, if attention is paid to the fact that the scattered light from the concave portion is not detected, the incident angle is increased by using only one wavelength and the signal is increased. If the detection circuit is devised, it is possible to distinguish foreign matters and scratches on the wafer surface from point-like concave portions present on the wafer surface, but in this case, when the size of the foreign matter becomes very small, The signal also needs to be detected. Then, a signal from the concave portion will be detected. On the other hand, when the signal strength is compared as in the present invention, even if the size of the foreign matter becomes very small, the foreign matter and the concave portion can be distinguished.

[0031]

According to the present invention, a semiconductor substrate or other wafer surface detecting apparatus can remove foreign matter and scratches adhering to the wafer surface except for minute concave portions which do not pose a problem when fabricating a semiconductor integrated circuit. It can be detected separately from the dot-shaped concave portions. As a result, waste of the wafer as the material can be eliminated.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a conventional U.S. wafer surface inspection apparatus.

FIG. 2 is a schematic configuration diagram showing a preferred embodiment according to the present invention.

FIG. 3 is a schematic diagram showing an example of a signal used to discriminate a foreign substance and a concave portion according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Light source 11 Optical system 12 Wafer 13 Focus point 14 Lens 15 Photoelectric converter 16 Motor 17 Signal detection circuit 21, 22 Light source 23 Wafer 24, 25 Optical system 26 Focus point 27, 28 Photoelectric converter 29 Signal detector 30 Discrimination circuit

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Yoichiro Iwa 75-1 Hasunumacho, Itabashi-ku, Tokyo Inside Topcon Co., Ltd.

Claims (4)

[Claims] 1. A method for condensing light from a light source on a wafer surface,
In the wafer surface inspection method of inspecting foreign matter and scratches on the wafer surface by scanning the focal point and receiving scattered light from the focal point with a photoelectric converter and detecting a signal from the photoelectric converter. The light of two different wavelengths is condensed at the same point at different angles of incidence, and the scattered light from the converging point is photoelectrically converted into two wavelengths separately.
A wafer surface inspection method characterized in that a difference in the intensity of each signal is used to distinguish a foreign substance or a scratch on the wafer surface from a point-like concave portion present on the wafer surface. 2. The light receiving device according to claim 1, wherein when receiving the scattered light beams of two different wavelengths, the light receiving positions thereof have the same relative positional relationship with respect to the incident surface of the illumination light beam of each wavelength. Wafer surface inspection method. 3. A light source, an optical system for condensing light from the light source on a wafer surface, a scanning unit for scanning a converging point over a predetermined area on the wafer surface, and a scattered light from the converging point. In a wafer surface inspection apparatus having a light receiving unit provided with a photoelectric converter for receiving light and a signal detector for detecting a signal from the light receiving unit, the light source is a light source having two different wavelengths, and the optical system has two light sources. The light receiving unit is configured to collect light having different wavelengths at the same point on the wafer surface at different incident angles.
Discriminator circuit that is configured to receive two wavelengths separately and uses the output from the signal detector to distinguish foreign matter or scratches on the wafer surface from dot-shaped recesses on the wafer surface Wafer surface inspection equipment characterized by having a. 4. The wafer surface inspection according to claim 3, wherein the light receiving units that receive the scattered lights of two different wavelengths are arranged so as to have the same relative positional relationship with respect to the incident surface of the illumination light of each wavelength. apparatus.