Optics: measuring and testing – Inspection of flaws or impurities
Reexamination Certificate
1999-03-30
2001-07-24
Pham, Hoa Q. (Department: 2877)
Optics: measuring and testing
Inspection of flaws or impurities
C356S237400, C356S338000
Reexamination Certificate
active
06266137
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a particle detecting apparatus for a substrate with a film on its surface, and more particularly a particle detecting apparatus which can distinguish and detect a foreign substance on or in the film.
2. Description of the Related Art
With high integration of a semiconductor device, formation of a fine wiring pattern and fine gate pattern is requested. When there is a foreign substance on the pattern, a short circuit is sometimes formed due to the foreign substance. Also, the flatness of an interlayer insulating film is sometimes degraded by the foreign substance so that an upper wiring pattern is broken. With the high integration of the semiconductor device, even if the foreign substance has a small diameter, the foreign substance influences severely on the break of the wiring pattern.
In order to prevent such an influence, a particle detecting method is requested which can detect a particle with a smaller size. The particle with the smaller size could be detected by use of a laser beam with a shorter wavelength. For example, a particle with the size of 0.1 &mgr;M can be detected by an Ar laser beam. However, when there is a film of a material such as SiO
2
and SiN formed on a Si substrate, a scattered light beam by the foreign substance is hidden in a scattered light beam by the film, because the laser beam is reflected, absorbed or refracted. As a result, the scattered light beam by the film functions as noise so that it is difficult to detect the foreign substance in a high precision.
It is supposed that the maximum voltage corresponding to a quantity of scattered light beam by the foreign substance is represented by V
1
and the maximum voltage of the noise is represented by V
2
. In this case, the foreign substance cannot be distinguished from the noise, if V
1
/V
2
is not larger than 1 at least. This value is desirably equal to or more than 3. Therefore, the laser wavelength should be changed in accordance with the film thickness and the material of the film. However, it is impossible to cope with problems such as different light absorption and reflectivity depending on the film thickness and the film material only by changing the laser wavelength.
When the wavelength is made short, the light beam quantity transmitting a silicon film formed on a wafer surface sometimes decreases remarkably, so that the existence of a foreign substance particle in the silicon film cannot be detected. A laser unit with at least 2 wavelengths must be used to detect the existence of the foreign substance particle with a small size from the scattered light beam which is influenced by 2 variables of the film thickness and the particle diameter.
A method of detecting a particle by use of such a laser unit with 2 wavelengths is described in Japanese Laid Open Patent Application (JP-A-Heisei 6-148085). In this method, the degradation of the detection precision of a foreign substance particle in the wafer surface due to the interference depending upon the change of the film thickness can be prevented. That is, the method can obtain information relating to the change of the film thickness, but can not obtain information in the direction of the depth in the film. The information which is more important than the film thickness change is existence or non-existence of a foreign substance particle in the film, e.g., a hole in the film. Because the intensity of a light beam scattered by the hole is local but large, it is a detection object which is more important than the film thickness change. When the light beam is scattered by the hole, the film thickness information is not substantively gotten. A method of detecting the existence or non-existence of a foreign substance particle in the substrate surface can be surely is demanded even if the film thickness information is not obtained.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a particle detecting apparatus which can obtain information of a foreign substance particle in a film to reliably detect the foreign substance particle in a substrate surface.
Another object of the present invention is to provide a particle detecting apparatus which can reliably detect a foreign substance particle in a substrate surface by removing information in the direction of the thickness of the substrate.
Still another object of the present invention is to provide a particle detecting apparatus which can reliably detect a foreign substance particle in a film and a foreign substance particle on a film surface.
Yet still another object of the present invention is to provide a particle detecting apparatus which can obtain information of a foreign substance particle in a film formed on a substrate to detect the foreign substance particle with the size equal to or less than 0.1 &mgr;m on a film surface.
In order to achieve an aspect of the present invention, a particle detecting apparatus for testing a substrate with a film on its surface includes a light source section, an optical system, a light quantity measuring section and an operation section. The light source section emits first and second light beams respectively having first and second wavelengths which are different from each other. The optical system directs the first and second light beams to an incident point on the substrate, wherein the first and second light beams are scattered on the substrate to produce first and second scattered light beams. The light quantity measuring section measures a quantity of the first scattered light beam and a quantity of the second scattered light beam. The operation section detects a foreign particle on or in the film based on the first scattered light beam quantity and the second scattered light beam quantity measured by the light quantity measuring section.
The first and second light beams may be directed to the substrate at a same time. In this case, the light quantity measuring section includes a beam collecting section for collecting the first scattered light beam and the second scattered light beam, a light wave guide for guiding the first scattered light beam and the second scattered light beam, a spectroscope for separating the first scattered light beam and the second scattered light beam guided by the light wave guide, a first measuring section for measuring the quantity of the first scattered light beam separated by the spectroscope, and a second measuring section for measuring the quantity of the second scattered light beam separated by the spectroscope. The beam collecting section may include a set of optical fibers, wherein an end of each of the optical fibers is arranged on a semi-spherical surface having the incident point as a center and the other end is connected to the light wave guide. Also, the beam collecting section and the light wave guide are made as a unit, and the light wave guide includes the set of optical fibers. Instead, the beam collecting section may include a set of optical fibers and a set of lenses, each of which is provided for one of the optical fibers in front of the end. An end of each of the optical fibers is provided on a semi-spherical surface having the incident point as a center and the other end is connected to the light wave guide.
The first and second light beams may be alternatively directed to the substrate. In this case, it is desirable that the light quantity measuring section includes a beam collecting section for collecting the first scattered light beam and the second scattered light beam, a light wave guide for guiding the first scattered light beam and the second scattered light beam, and a measuring section for measuring the quantity of the first scattered light beam and the quantity of the second scattered light beam by the light wave guide. Also, the beam collecting section may include a set of optical fibers. An end of each of the optical fibers is arranged on a semi-spherical surface having the incident point as a center and the other end is connected to the light wave guide. Instead, the beam collecti
McGinn & Gibb PLLC
NEC Corporation
Pham Hoa Q.
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