Optics: measuring and testing – Inspection of flaws or impurities – Surface condition
Reexamination Certificate
2001-05-30
2004-04-27
Font, Frank G. (Department: 2877)
Optics: measuring and testing
Inspection of flaws or impurities
Surface condition
C356S237100, C250S559270
Reexamination Certificate
active
06726319
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a method for inspecting a semiconductor wafer surface and, more particularly, to a method for inspecting a semiconductor wafer surface for dividing, to detect according to types of defects present on and near a semiconductor wafer surface, particles adherent to the semiconductor wafer surface and the like (hereinafter referred to as occurrences associated with the semiconductor wafer), which affect electrical properties such as dielectric breakdown strength of LSIs and the like being manufactured using semiconductor wafers, so as to evaluate semiconductor wafer quality.
BACKGROUND ART
Hitherto, extraneous substances such as particles adherent on a semiconductor wafer, and crystal defects on and near a surface of the semiconductor wafer, or surface flaws, scratches, shallow pits and the like (hereinafter referred to as surface flaws) have been known as light point defects (LPDs) to be detected using a semiconductor wafer surface inspection apparatus. The extraneous substances are observed in a shape of a convex on the semiconductor wafer surface. The crystal defects are observed mainly as a quadrangular-pyramidal pit or projection [(100) wafer], or a triangular or hexagonal pit or projection [(111) wafer] on a mirror-finished wafer surface, while these defects are observed mainly in a shape of a square or a square that is partly concave or convex [(100) wafer], or in a shape of a triangle or a triangle that is partly concave or convex [(111) wafer] on an epitaxial wafer surface.
From a viewpoint of evaluation of semiconductor wafer quality, it is desirable that the extraneous substances, crystal defects and surface flaws be strictly divided according to their types to be detected. However, in a conventional method for inspecting a semiconductor wafer surface, a wafer is scanned with a laser beam, a scattered light having a prescribed angle reflected from the wafer surface is detected, and a result is compared with measurement results of standard particles having prescribed grain sizes previously obtained, whereby the number of LPDs of every size including all of the extraneous substances and crystal defects is obtained.
In order to determine the types of extraneous substances and crystal defects or surface flaws (hereinafter referred to as defects) in the above method, a possibility of separation by unevenness recognition based on a premise that grown-in defects are pit-shaped while particles are convex, for example, in separation of particles and grown-in defects (COPs) in a mirror-finished wafer was reported. However, since the unevenness recognition is actually imperfect, it has been evident that it is difficult to separate particles from grown-in defects (COPs). In addition, it has been evident that all of grown-in defects are not concave.
There are many types of crystal defects in an epitaxial wafer such as stacking faults (SFs), mounds, and dislocations (hereinafter referred to as epi defects), and some of the epi defects have concave shapes, some have convex shapes, and others have both concave and convex shapes. Therefore, since separation probability in a method wherein separation is conducted depending on concave and convex shapes is low, and all of the epi defects are not concave, it has been physically impossible to separate the epi defects from particles; moreover, to determine types of the defects.
Determination of the types of occurrences associated with the semiconductor wafer is possible using an atomic force microscope (AFM) or a scanning electron microscope on a research level. However, in order to observe these occurrences using these microscopes, coordinate positions where the occurrences exist must be detected first on a wafer surface having an enormously large area compared with the occurrences. This detecting activity is very difficult, and then, points where the occurrences exist must be brought into focus of the AFM or scanning electron microscope. These activities cost vast labor and time, and furthermore, there is a possibility that quality of a product might be lowered, even though inspection techniques used are not destructive. As a result, it has been actually impossible to conduct inspection using a microscope of this type on every product. Therefore, a visual distinction method performed by an inspector (a method wherein a high-intensity spotlight is irradiated in a darkroom and scatterers are detected by a visual check) has been actually adopted.
An occurrence size measured using only one light optic of a laser surface inspection apparatus is a standard particle conversion size, which may be very different from an actual size depending on shapes of the occurrences associated with the semiconductor wafer. Accordingly, a problem remains from a viewpoint of reliability with regard to distinction of types of the occurrences based on size of the occurrences. Not only does the method, wherein particles and defects are separated by judging whether shapes are concave or convex, have a low reliability, but also it cannot be applied at all to wafers wherein convex defects exist. In the visual distinction method performed by an inspector, distinction capacity greatly depends on the inspector's competence for the task, which is not stable, and it is difficult to respond to higher-level requirements in a future wafer inspection. Furthermore, as wafers have larger diameters, possibility that occurrences escape the inspectors attention becomes larger. In the visual distinction method performed by an inspector, ability of the inspector must be estimated first, leading to increases in the number of steps and costs.
SUMMARY OF THE INVENTION
The present invention was developed in order to solve the above problems, and it is an object to provide a method for inspecting a semiconductor wafer surface, wherein particles adherent to a semiconductor wafer surface and, for example, surface flaws in a mirror-finished wafer which exist near the semiconductor wafer surface, or grown-in defects in bulk near the surface can be separated to be detected, or adherent particles and defects such as SFs, mounds, and dislocations in an epitaxial wafer can be accurately divided according to types at a low cost, without being influenced by an inspector's ability.
In order to achieve the above object, a first method for inspecting a semiconductor wafer surface according to the present invention is characterized by a wafer being scanned with a laser beam, scattered or reflected light from the wafer surface being detected by multiple light optics having different detecting angles relative to an incident light, respectively, and an occurrence being classified into some characteristics based on the ratio of the detected light intensities from the multiple light optics.
In the above first method for inspecting a semiconductor wafer surface, since a wafer is scanned with a laser beam, scattered or reflected light from the wafer surface is detected by multiple light optics having different detecting angles relative to an incident light, respectively, and the occurrence is classified into some characteristics based on the ratio of the detected light intensities from the multiple light optics, the method can be utilized when there is a wide difference in detected defect sizes between a low-angle light optic and a high-angle light optic depending on types of the occurrences. Therefore, it becomes possible to quite accurately determine the types of the occurrences. Since determination is not conducted by an inspector, inspection can be automated. Without depending on an inspector's ability, the inspection can be stable and it is possible to deal with higher-level requirements in a future wafer inspection and with wafers having larger diameters. Moreover, it is unnecessary to estimate an inspector beforehand, leading to substantial reductions in the number of inspection steps and costs.
A second method for inspecting a semiconductor wafer surface according to the present invention is character
Koike Takashi
Kudo Noboru
Nakamura Osamu
Yanase Yoshio
Font Frank G.
Nguyen Sang Hoang
Sumitomo Mitsubishi Silicon Corporation
Wenderoth , Lind & Ponack, L.L.P.
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