Abrading – Machine – Combined
Reexamination Certificate
1999-12-16
2001-06-26
Hail, III, Joseph J. (Department: 3723)
Abrading
Machine
Combined
C451S044000, C451S057000, C451S194000
Reexamination Certificate
active
06250995
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an apparatus for mirror-polishing a chamfered outer peripheral portion of a substantially disk-shaped workpiece such as a semiconductor wafer or a magnetic disk substrate.
BACKGROUND ART
For example, semiconductor wafers such as silicon wafers are usually subjected to chamfering of their peripheries mainly to prevent their edges from chipping or to prevent crowns during epitaxial growth. The chamfering is performed by grinding with a diamond grinding wheel; however, distorted layers are apt to remain after grinding. The remaining distorted layers lead to crystal defects in some cases when heat treatment is repeated in a device process.
For that reason, the distorted layers are normally removed by etching. Etched surfaces, however, tend to develop undulated or scale-like irregularities which tend to retain soil. The soil spreads over an entire wafer in the device process, contributing greatly to deterioration of characteristics.
In recent years, a technique for smoothing chamfered edges of wafers by mirror polishing has been established as a technique completely different from that for polishing the surfaces of wafers. The applicants of the present invention have already proposed a technique for polishing edges as disclosed, for example, in Japanese Unexamined Patent Publication No. 1-71656. According to the polishing technique, a wafer having a chamfered edge on its outer periphery is rotated, and the outer periphery edge is pressed against a working plane of the outer periphery of a rotating polishing drum thereby to polish the outer periphery edge. This method enables wafer edges to be polished easily and reliably, and solves all the problems caused by the chamfering mentioned above.
However, this type of polishing apparatus is designed to perform polishing by bringing wafers into point contact with polishing drums; hence, machining efficiency is not always high, taking a considerable time for the machining. In these days, therefore, contrivance has been added. An example of such contrivance is increasing the diameter of a polishing drum to maximize the length of contact with a wafer so as to shorten the machining time.
However, a method in which a round wafer is brought into circumferential contact with a cylindrical working plane is disadvantageous in that there is limitation in extending the contact length, so that reducing the machining time is accordingly limited. In addition, increasing the diameter of the polishing drum means a larger space required for installation, inevitably resulting in an increased size of the apparatus including the drum. Especially because demands for larger wafers having diameters ranging from 30 cm to 40 cm are expected in the future, which means larger spaces occupied by the wafers, the polishing apparatuses would undesirably be even larger.
DISCLOSURE OF INVENTION
An object of the present invention is to provide a small polishing means featuring high machining efficiency that is capable of performing mirror polishing efficiently and quickly by simultaneously bringing chamfered outer peripheries of workpieces into uniform contact with a plurality of polishing drums.
To this end, according to one aspect of the present invention, there is provided an apparatus for polishing an outer periphery of a workpiece, comprising: a workpiece retaining means for rotatably retaining a disk-shaped workpiece having a chamfered edge on its outer periphery; a set of rotatable polishing drums which simultaneously polishes the outer periphery of the workpiece retained by the workpiece retaining means, a set being formed of two polishing drums; an aligning means that supports the workpiece retaining means and two polishing drums so that they can be relatively shifted in a direction in which the two polishing drums are arranged, and performs positional adjustment to bring a workpiece into uniform contact with the two polishing drums; and loading means for absorbing an action force in an eccentric direction produced between the workpiece retaining means and the polishing drums due to contact between a rotating workpiece and the polishing drums.
The polishing apparatus in accordance with the present invention is adapted to simultaneously polish an outer periphery of a workpiece by a plurality of polishing drums, thus permitting improved polishing efficiency and a shorter polishing time. Moreover, polishing drums of considerably smaller diameters than those of conventional polishing drums are employed, so that a smaller polishing apparatus can be achieved.
Furthermore, freedom in the direction in which the two polishing drums are arranged is provided between the workpiece retaining means and the polishing drums so as to automatically correct uneven contact by aligning action even if a workpiece comes in uneven contact with the two polishing drums, and the action force in an eccentric direction generated due to contact between a rotating workpiece and the polishing drums is absorbed by the loading means. This arrangement makes it possible to positively bring a workpiece into contact with the two polishing drums under even contact pressure.
According to a specific composition mode of the present invention, the aligning means is formed of a sliding mechanism that supports the workpiece retaining means such that it may move in the direction in which the two polishing drums are arranged, and the loading means is coupled to the workpiece retaining means so that the workpiece retaining means is urged in a direction opposite from a direction of the action force.
The loading means may be formed of a weight.
According to another specific composition mode of the present invention, the workpiece retaining means is supported by the sliding mechanism in a direction to move toward or away from the polishing drums, and also coupled to the loading means for applying contact pressure to press a workpiece against the polishing drums under a fixed contact pressure.
According to a specific composition mode of the present invention, the workpiece retaining means can be tilted and an axis of a retained workpiece is tilted in a plane, which is at right angles to a plane that includes axes of two polishing drums, thereby to simultaneously bring a chamfered edge of the workpiece into contact with the two polishing drums.
According to another specific composition mode of the present invention, the workpiece retaining means can be tilted, and an axis of a retained workpiece is tilted in a plane, which is slanted with respect to a plane that includes axes of two polishing drums, thereby to bring a chamfered edge of the workpiece into contact with one of the polishing drums, and to bring a non-chamfered peripheral side surface into contact with the other polishing drum.
According to still another specific composition mode, a polishing apparatus has two, namely, a first and a second, sets of workpiece retaining means, these workpiece retaining means being disposed at positions where they oppose each other with two polishing drums located therebetween, and a workpiece transporting means that reverses the front/rear side of a workpiece of the first workpiece retaining means and transports the workpiece to the second workpiece retaining means.
REFERENCES:
patent: 5040342 (1991-08-01), McGuire et al.
patent: 5094037 (1992-03-01), Hakomori et al.
patent: 5097630 (1992-03-01), Maeda et al.
patent: 5514025 (1996-05-01), Hasegawa et al.
patent: 5658189 (1997-08-01), Kagamida et al.
patent: 5674110 (1997-10-01), Cuoghi
patent: 6159081 (2000-12-01), Hakomori
Hail III Joseph J.
Kelly Michael K.
Nguyen George
Snell & Wilmer LLP
Speedfam Co., Ltd.
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