Abrading – Abrading process – With tool treating or forming
Reexamination Certificate
2000-03-30
2001-10-16
Eley, Timothy V. (Department: 3723)
Abrading
Abrading process
With tool treating or forming
C451S041000, C451S060000, C451S287000, C451S288000, C451S443000
Reexamination Certificate
active
06302772
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
The present application claims priority under 35 U.S.C. §119 to Japanese Patent Applications No. HEI 11-095565, filed Apr. 1, 1999 and No. HEI 11-283560, filed Oct. 4, 1999. The contents of these applications are incorporated herein by reference in their entirety.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an apparatus and a method for dressing a polishing pad for use in a wafer polishing apparatus.
2. Description of the Related Art
A rotary wafer polishing apparatus for polishing surfaces of semiconductor wafers is generally constructed as follows. A wafer polishing head for holding a wafer and a platen including a polishing pad affixed to the platen are arranged in opposed relation. The polishing pad is rotated while the surface of the wafer is pressed against the polishing pad and a slurry containing polishing abrasive grains is supplied. Simultaneously, the wafer polishing head is rotated to perform planetary or oscillatory motion on the polishing pad, whereby the wafer is polished.
It is known in the above wafer polishing apparatus that repeating the process of polishing a wafer reduces roughness of the polishing pad and gradually deteriorates the polishing performance. For this reason, each time the wafer polishing process is finished, the polishing pad is dressed by using polishing-pad dressing apparatus as shown in FIG.
7
.
Referring to
FIG. 7
, the dressing apparatus comprises a dresser
11
affixed to a dresser support
10
, and an arm
12
for supporting the dresser
11
rotatably in the circumferential direction with a dressing surface
11
a
facing downward. A ball joint (not shown) is provided at a joint portion between the arm
12
and the dresser support
10
so that the dressing surface
11
a
of the dresser
11
is held parallel to a polishing pad
14
regardless of an angle at which the arm
12
inclines. Also, the dresser
11
is movable in the vertical and horizontal directions toward or away from the polishing pad
14
affixed to a platen
13
with operation of an arm elevating/lowering mechanism and an arm advancing/retracting mechanism (both not shown) which are coupled to a base end of the arm
12
.
In the above dressing apparatus, by rotating the polishing pad
14
while the dresser
11
is pressed against the polishing pad
14
, frictional force generated between the dresser
11
and the polishing pad
14
causes the dresser
11
to rotate in the same direction as the polishing pad
14
, and brings the dresser
11
into slide contact with the surface of the polishing pad
14
. As a result, the surface of the polishing pad
14
is dressed.
However, a conventional dressing apparatus has such a tendency that the amount of dressing (i.e., the amount by which the polishing pad is dressed) in each step of dressing increases gradually, though by small degrees, toward the center of the polishing pad. In other words, each time the polishing pad is subjected to dressing, the surface of the polishing pad is cut in the form conically recessed toward the center, and an extent of excessive cutting on the inner side increases gradually.
The reason is thought to reside in that a dresser is arranged to locate entirely within an area covered by the radius R of the polishing pad when viewed from above vertically.
On condition that the contact pressure of the dresser is uniform, the amount of dressing of the polishing pad is determined depending on a sliding length of dresser abrasive grains at radial positions of the polishing pad, as seen from the following formula (I):
z(x)=k·L(x)·P(x) (I)
z(x): amount of dressing at position spaced distance x from the center of the polishing pad
k: proportional coefficient
L(x): sliding length of abrasive grains at position spaced distance x from the center of the polishing pad
P(x): contact pressure of the dresser at position spaced distance x from the center of the polishing pad
Further, the sliding length L(x) is determined depending on the rotational speed of the dresser, the surface configuration of the dresser abrasive grains, and the density of the dresser abrasive grains. Usually, the sliding length L(x) tends to have a larger value in an area closer to the center of the polishing pad.
In the conventional dressing apparatus, because the dresser is arranged to locate entirely within an area covered by the radius R of the polishing pad, the contact pressure of the dresser against the polishing pad is substantially uniform. As seen from the formula (1), therefore, the amount of dressing is increased on the inner peripheral side of the polishing pad in which the sliding length of the abrasive grains is comparatively long, thus resulting in a phenomenon of inner-side excessive cutting. Accordingly, repeating the dressing increases gradually a minus gradient of the surface configuration of the polishing pad toward the center from the outer periphery thereof, and hence increases the gradient of the pad surface in the conically recessed form.
This eventually raises a problem of impairing uniformity in each wafer polishing process.
Such a variation of uniformity in each wafer polishing process has been hitherto regarded to be so small as falling in sufficiently allowable range, but a demand for higher uniformity has become keen in recent years.
At present, the above problem is dealt with, for example, by frequently replacing the polishing pad with a fresh one. This solution however gives rise to the secondary problems that an operation cost is pushed up and the operation must be suspended for a while for replacement of the polishing pad.
Moreover, in the conventional dressing apparatus, because the dressing surface of a dresser is clogged with pad chippings cut by the dresser and slurry particles during the dressing of a polishing pad, the polishing pad is unevenly dressed. Accordingly, the machining accuracy of a wafer polished by the polishing pad deteriorates.
At present, therefore, the above problem is dealt with by cleaning the dresser after being used for the dressing, for example, with a method of spraying pure water to the dressing surface of the dresser or keeping the dresser in water to rinse the dressing surface. However, the problem of clogging of the dresser occurred during the dressing cannot be overcome at the current state of the art.
SUMMARY OF THE INVENTION
In view of the above-described situations in the art, an object of the present invention is to provide an apparatus and a method for dressing a wafer polishing pad, which can hold uniform the amount of dressing of the polishing pad at any radial positions, and can prevent a phenomenon of inner-side or outer-side excessive cutting of the polishing pad from progressing gradually, thereby improving uniformity in each wafer polishing process. Another object of the present invention is to provide an apparatus and a method for dressing a wafer polishing pad, which can effectively prevent clogging of a dresser to make the polishing pad dressed uniformly, and can improve the machining accuracy of a wafer.
The above objects are achieved by providing an apparatus for dressing a wafer polishing pad, which is constructed as follows. Specifically, the present invention provides an apparatus for dressing a wafer polishing pad, in which a disk-shaped dresser is pressed from above against a circular polishing pad rotating in a circumferential direction, and the dresser is rotated in the same direction as the polishing pad due to frictional force generated between the dresser and the polishing pad, thereby dressing a surface of the polishing pad, the dressing apparatus comprising an arm for supporting the dresser rotatably and pressing the dresser against the polishing pad from above, and a control unit for controlling operation of the arm and arranging a peripheral edge portion of the dresser to shift off a predetermined distance radially outward of the polishing pad from an entirely overlapped relation.
When the dresser is pressed against the polishing pad, the polishing pad
Hosoki Kanji
Kobayashi Hiroyuki
Komasaki Masahito
Sano Jiro
Shibaya Hiroshi
Eley Timothy V.
McDonald Shantese
Mitsubishi Materials Corporation
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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