Abrading – Abrading process – Glass or stone abrading
Reexamination Certificate
1999-05-17
2002-01-01
Banks, Derris H. (Department: 3723)
Abrading
Abrading process
Glass or stone abrading
C451S042000
Reexamination Certificate
active
06334808
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for processing a peripheral portion of a thin plate, such as a silicon wafer and an apparatus therefor.
2. Description of the Related Art
A shock (impact) load is applied to a peripheral portion of a silicon wafer when a lapping step or a double side polishing step is carried out in a process of manufacturing silicon wafers. A shock load is applied to a peripheral portion of a wafer in a process of manufacturing semiconductor elements because of a thermal stress caused by a heating and cooling treatment between room temperature and one thousand and several hundred degrees centigrade or because of a film forming treatment, such as an oxidation. Further, a shock load is applied to a peripheral portion of a wafer locally and frequently because a wafer is positioned, a wafer is transferred inside an apparatus, a wafer is transferred between one apparatus and another, a wafer is supported or the like by using a peripheral portion of the wafer in the process of manufacturing silicon wafers and in the process of manufacturing semiconductor elements.
When the shock load is applied to a peripheral portion of a wafer locally, the peripheral portion of the wafer is liable to be chipped off. Because the Si wafer which is a material for semiconductor elements is made of a silicon and is a single crystal, the wafer has a cleavage depending on a crystal orientation thereof and is brittle. When the wafer is chipped off, small fragments thereof fly. Because the small fragments adhere to the surface of the wafer, on which the semiconductor elements are formed, the characteristics of the semiconductor elements and the yield thereof are deteriorated.
The peripheral portion of the wafer has been chamfered in order to avoid or relieve these problems according to an earlier development.
Next, the typical three types of the chamfering apparatus will be explained below.
The first chamfering apparatus is a formed chamfering apparatus shown in FIG.
7
. The chamfering apparatus
100
comprises a grinding wheel
101
(a so-called formed grinding wheel) having a groove of which shape is the same as that of a chamfered portion. The wafer W is held on the holding table
102
by using a vacuum chuck. In this chamfering apparatus
100
, the grinding wheel
101
is pushed to the wafer W by applying a constant load thereto in order to process the peripheral portion of the wafer W. According to the chamfering apparatus
100
, the shape of the chamfered portion of the wafer W is determined by the shape of the groove of the grinding wheel
101
.
The second chamfering apparatus is a copy chamfering apparatus shown in FIG.
8
. The chamfering apparatus
200
comprises a grinding wheel
201
having a groove
201
a
of which width is larger than the thickness of the wafer W. The wafer W is sandwiched by a pair of holding bodies
202
and
203
disposed at upper and lower positions of the wafer W to be sandwiched in order to hold the wafer W. In the chamfering apparatus
200
, a copy model
204
is disposed on the same axis as the upper holding body
202
. The copy model
204
and the upper holding body
202
rotate together and move in a vertical direction. A copy roller
205
is disposed on the same axis as the grinding wheel
201
. The copy roller
205
and the grinding wheel
201
rotate independently of each other.
The process of chamfering the peripheral portion of the wafer is carried out by using the chamfering apparatus
200
as follows. That is, after the wafer W was sandwiched, the copy roller
205
moves in a direction of the copy model
204
. The copy roller
205
and the copy model
204
roll in order to contact with each other. While the copy roller
205
moves, the grinding wheel
201
contacts the wafer W in order to start chamfering the peripheral portion of the wafer W. In the chamfering process, the peripheral portion of the wafer W is processed by rotating the wafer W by one rotation. The wafer W is moved upwardly and is rotated by one rotation in order to chamfer the upper surface of the peripheral portion of the wafer W. The wafer W is moved downwardly and is rotated by one rotation in order to chamfer the lower surface of the peripheral portion of the wafer W.
In the chamfering apparatus
200
, because the diameter of the grinding wheel
201
, which is measured on the basis of the bottom of the groove
201
a
is the same as that of the copy roller
205
, the diameter of the wafer W is the same as that of the copy model
204
. The upper surface of the peripheral portion of the wafer W is processed by the upper wall of the groove
201
a
. The lower surface of the peripheral portion of the wafer W is processed by the lower wall of the groove
201
a
. As a result, the shape of the upper part of the chamfered portion corresponds to that of the upper wall of the groove
201
a
. Similarly, the shape of the lower part of the chamfered portion corresponds to that of the lower wall of the groove
201
a
. Further, the width of the chamfered portion is determined by the positions in which the wafer W is disposed when the wafer W is moved upwardly and when the wafer W is moved downwardly.
The third chamfering apparatus is an NC (numerical control) chamfering apparatus which is not shown in the drawings. The chamfering apparatus carries out the control of the relative positions of the wafer and the grinding wheel not by using the copy roller and the copy model like the copy chamfering apparatus, but by the NC control. The process of chamfering the peripheral portion of the wafer is carried out similarly to the copy chamfering apparatus.
The function of the chamfered portion of the wafer is not only that the wafer is prevented from being chipped off. In particular, in case of a wafer for making an epitaxial wafer, the chamfered portion of the wafer prevents an extraordinary growth of an Si single crystal at the peripheral portion of the wafer. Further, the chamfered portion of the wafer drains liquid during a spin coat in a resisting step. It is decided by the cross-sectional shape of the chamfered portion of the wafer (hereinafter, referred to as “chamfer shape”) and by the size thereof which function of the chamfered portion is superior to another. It is necessary to select the chamfer shape and the size of the chamfered portion suitably by considering which function is important. For example, the chamfer shape is a semicircular shape, a trapezoidal shape, a shape in which an end of a trapezoid is round or the like. There are various sizes of the chamfered portion.
However, in the three types of chamfering apparatus, because the chamfer shape is determined by the shape of the groove of the grinding wheel, it is necessary that one grinding wheel should be changed for another having a different groove from one grinding wheel when the shape of the chamfered portion is changed. Several types of grinding wheels must be prepared in order to change one grinding wheel for another. It is troublesome to change one grinding wheel for another. Further, there is a problem that a chamfering apparatus cannot be operated while one grinding wheel is changed for another.
SUMMARY OF THE INVENTION
The present invention was developed in view of these problems.
An object of the present invention is to provide a processing method for processing several types of chamfered portions or the like without changing one tool for another and a processing apparatus therefor.
That is, in accordance with one aspect of the present invention, the method for processing a peripheral portion of a thin plate, comprises the steps of; contacting the thin plate with a processing part of a tool, which has a round free end and projects to the thin plate in order to process the contacted peripheral portion of the thin plate, and moving at least one selected from the tool and the thin plate in a direction of the other, which is parallel to a main surface of the thin plate and in a direction of the other, which is normal to the main surface of the thin plate, i
Banks Derris H.
Shin-Etsu Handotai & Co., Ltd.
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