Abrading – Precision device or process - or with condition responsive... – With indicating
Reexamination Certificate
2000-12-29
2003-11-25
Hail, III, Joseph J. (Department: 3723)
Abrading
Precision device or process - or with condition responsive...
With indicating
C451S009000, C451S262000, C451S264000, C451S265000
Reexamination Certificate
active
06652358
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field
The present invention relates to a double sided simultaneous grinding method for plate-like workpieces such as a semiconductor wafer or a quartz substrate for an exposure original, a double side simultaneous grinding machine, a double side simultaneous lapping method, and a double side simultaneous lapping machine.
2. Background Art
Surface grinding has been used conventionally in precision processing of plate-like workpieces such as semiconductor wafers or quartz substrates. Surface grinding has come to be used instead of lapping, or the like, because the grinding rate is high, a wafer having high flatness is easily obtained, and so forth.
When a single side surface grinding machine is used in the grinding step, a problem exists that waviness generated in the previous step, i.e., a slicing step, cannot be removed because one side of a wafer is held by a vacuum suction while the other side is ground. In order to solve the problem, a double side simultaneous grinding machine (also referred to as “double head grinding machine”) has been developed as a technique for simultaneous grinding both sides of a wafer.
Regarding double head grinding methods for simultaneously grinding the surfaces of a wafer, various methods exist. For example, in a creepfeed grinding method, a wafer is passed between a pair of cylindrical grinding stones and thereby ground. In an infeed grinding method, a wafer is ground using a pair of cup-type grinding stones such that the grinding stones pass along the center of the wafer with the grinding stones and the wafer rotating together.
An infeed-type double side simultaneous grinding machine
1
a
used for grinding a semiconductor wafer, illustrated in
FIG. 6
, comprises a pair of cup-type grinding stones
20
,
21
that rotate in the same direction, two pairs of plate-like workpiece press rollers
4
for supporting a plate-like workpiece W on each side, four plate-like workpiece guide rollers
5
for supporting a circumference of the plate-like workpiece W, and a pair of plate-like workpiece driving-holding rollers
3
for rotating the plate-like workpiece W in an opposite direction to the direction of the grinding stones and holding the workpiece. The cup type grinding stones
20
,
21
consist of a cup-shaped stock
2
a
, a grinding stone portion
2
b
and a grinding stone rotating shaft
2
c
. Grinding stone segments (not shown) are connected to a grinding surface of the grinding stone portion
2
b
. The plate-like workpiece W and the cup type grinding stones
20
,
21
are rotated at a predetermined rotational speed. Grinding fluid is generally fed from a central hole (not shown) of the grinding stone rotating shaft
2
c
, or poured onto outer periphery or an inside portion of the grinding stone.
Along with the development of the double side simultaneous grinding machine, a double side simultaneous lapping machine for single wafer processing has been developed in place of conventional batch processing lapping machines which have low accuracy and low productivity. The lapping process using this single wafer processing lapping machine has the advantages of the surface grinding, such as high efficiency in processing and automation with high accuracy. Further, this lapping process has the advantages of conventional lapping, obtaining the same surface condition and an equal back surface condition.
A double side simultaneous lapping machine of the infeed-type
1
a
is shown in FIG.
6
. The pair of cup-type grinding stones
20
,
21
is replaced with flat lapping turn tables. For driving a plate-like workpiece, the lapping machine adopts the same mechanism as that of the double side simultaneous grinding machine. However, there is a wide variance in terms of feeding the grinding stones or the turn tables. Feeding the grinding stones in the grinding machine is accomplished by controlling a servomotor or the like, which is a so-called “infeed”. On the other hand, since the turn tables of the lapping machine are basically controlled at a constant pressure, the turn tables are always supported by a pressurizing mechanism such as air cylinder.
As to a difference in actual processing of the plate-like workpiece, the material operating in the grinding machine is bonded abrasives of the cup type grinding stones, while the lapping machine uses a lapping fluid (slurry) containing alumina abrasives and the like which are loose abrasives.
In recent years, the above-mentioned infeed-type grinding method has been used generally because of the advantage of easily obtaining high flatness as compared to the creep-feed type. However, in the infeed-type method, a problem exists that warpage (hereinafter also referred to as “warp”) is apt to be generated in the ground workpiece due to an unbalance of cutting loads on each side, and so forth.
A technique is known wherein coolant is injected from static pressure pads such that a plate-like workpiece is stably supported (for example, see Japanese Patent Laid-open Publication (Kokai) No. 9-262747). However, it has been found that this technique necessarily cannot sufficiently suppress the generation of warpage. Moreover, it has been found that the warpage of the wafer after double head grinding is apt to be worse (degrade) than the warpage before the grinding. Since it is difficult to remove warpage in processing steps subsequent to the grinding step, such problems should be solved in the grinding step to achieve a higher flatness.
SUMMARY OF THE INVENTION
The present invention has been accomplished in view of the above-mentioned problems, and its major object is to provide a double side simultaneous grinding method using a double side simultaneous grinding machine wherein the generation of warpage of a plate-like workpiece is suppressed and or the degradation of warpage generated in a previous step is prevented. Thereby the plate-like workpiece can be processed to have high flatness on both sides. An object of the present invention is also to provide a double side simultaneous grinding machine having such characteristics.
Another object is to provide a double side simultaneous grinding method, wherein a plate-like workpiece is ground while a degree of warpage is controlled. Thereby, the workpiece can be processed to have a desired warpage. Another object is to provide a double side simultaneous grinding machine having such a characteristic.
A double side simultaneous lapping machine having a similar structure as the double side simultaneous grinding machine has similar problems as those of the double side simultaneous grinding machine described above. Another object of the present invention is to provide a double side simultaneous lapping method, wherein the generation of warpage of a workpiece is suppressed and/or the degradation of warpage generated in a previous step is prevented. Thereby, the workpiece can be lapped to have high flatness on both sides. Another object is to provide a lapping method wherein the workpiece is lapped while a degree of warpage is controlled. Thereby, the workpiece can be processed to have a desired warpage. Another object is to provide a double side simultaneous lapping machine having such characteristics.
In order to solve the aforementioned problems, the present invention provides a method for simultaneously grinding both a front surface and a back surface of a plate-like workpiece that is held and simultaneously ground on both sides using a pair of grinding stones opposed at both sides of the workpiece, wherein a relative position of at least one of a center between stone surfaces of the pair of grinding stones and at least one of a center of thickness of the plate-like workpiece and a center of the holding means for holding the workpiece is controlled while performing the grinding.
The center of thickness of a plate-like workpiece is a reference for defining a position of the plate-like workpiece and may be, for example, a line or plane passing points (center) of one half of the thickness at two or more points on a surface of the plate-like workpie
Ikeda Shun-ichi
Kato Tadahiro
Okuni Sadayuki
Grant Alvin J.
Hail III Joseph J.
Oliff & Berridg,e PLC
Shin-Etsu Handotai & Co., Ltd.
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