Abrading – Abrading process – Utilizing fluent abradant
Reexamination Certificate
2000-08-30
2002-08-27
Eley, Timothy V. (Department: 3724)
Abrading
Abrading process
Utilizing fluent abradant
C451S059000, C451S533000, C451S550000
Reexamination Certificate
active
06439965
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a polishing pad and a surface polishing method, which are suitable for a rotary surface polishing apparatus that polishes a surface of a workpiece such as a disk substrate of a magnetic storage medium for a fixed magnetic disk unit, a silicon wafer for a semiconductor, and liquid crystal glass and the like by a chemo-mehanical-polishing (CMP) method.
2. Description of Related Art
To obtain a flat surface of the disk substrate of the magnetic storage medium, the surface of a disc-shaped substrate made of an aluminum alloy is plated with Ni—P of about 10 &mgr;m, and then both sides of the disk substrate are polished (lapped) before the formation of a magnetic layer. Likewise, the flat surfaces of the silicon wafer and the liquid crystal glass and the like are obtained by polishing both sides of their substrates.
On the other hand, a rotary surface polishing machine for polishing the disk substrate, the silicon wafer and the like is widely used which comprises a pair of upper and lower platens, polishing pads attached to the inner surfaces of the platens, and a carrier that is mounted between the upper and lower platens to hold the workpiece. The workpieces, which are inserted into set holes formed in the carrier, are pinched by the polishing pads attached to the platens from above and below. In this state, a slurry is dropped between the polishing pads and the workpiece from the direction of the upper platen while the upper and lower sides of the workpiece are simultaneously polished by rotating the upper and lower platens and the carrier.
Next, there will be described the structure of the rotary surface polishing machine (lapping machine) and the polishing operation with reference to
FIGS. 4 through 6
. In FIGS.
4
(
a
),
4
(
b
) and
FIG. 5
, reference numeral
1
denotes an upper platen;
2
, a lower platen;
3
, a carrier mounted between the upper platen
1
and the lower platen
2
;
4
, a workpiece (e.g., the disk substrate and the silicon wafer and the like) to be polished; and
5
, polishing pads attached to the inner surfaces of the upper and lower platens
1
and
2
.
As shown in the drawing, the carrier
3
is constructed as a planetary gear that rotates and revolves a disc
3
a
through a gear mechanism
3
b
. A plurality of set holes are formed in the disc
3
a
(four set holes are formed in FIG.
4
(
b
)), and the workpieces
4
are inserted into the set holes one by one.
With this arrangement, the workpieces
4
, which are inserted one by one into the set holes formed in the disc
3
a
of the carrier
3
, are pinched by the polishing pads
5
attached to the inner surfaces of the platens
1
and
2
from above and below. In this state, a slurry
6
is dropped through a slurry supply hole
1
a
formed in the upper platen
1
while the upper and lower platens
2
are rotated in reverse directions with the rotation and revolution of each carrier. Therefore, the workpiece
4
as well as the carrier
3
moves on a plane between the upper and lower platens
1
and
2
, and the upper and lower sides of the workpiece
4
are polished by the polishing pads
5
and the slurry
6
. In the prior art, the slurry
6
is ordinarily produced by finely crushing a hard solid matter composed mainly of metal oxide and carbon by a mill or the like, and dispersing the classified fine powder with a predetermined grain size as abrasive grains in a chemical with an etching function.
On the other hand, the polishing pads
5
are now ordinarily made of soft plastic foam. As shown in a conceptual drawing of
FIG. 6
, the polishing pads
5
are conventionally structured in such a manner that a nap layer
5
b
made of plastic foam is deposited on a sheet-shaped base layer
5
a
. A honeycomb pore structure is constructed in the nap layer
5
b
in the following manner. Polyethylene, polyurethane resin, and the like are foamed and spread in the shape of a sheet, and skin layers (non-foaming layers which form the surface of the plastic foam) which form the surface of the nap layer
5
b
are buffed to horizontally cut pores (foam)
5
b
-
1
in the layer. This forms pore cavities in the surface of the nap layer
5
b.
In the polishing pads
5
with the above-mentioned structure, the nap layer
5
b
rubbing the workpiece
4
has an uneven surface having the honeycomb pore structure. Crater-shaped cavities of the pores
5
b
-
1
hold the slurry
6
dropped from the outside during the polishing. As shown in
FIG. 6
, when the workpiece
4
moves relatively to the upper and lower polishing pads
5
, the slurry held in the pores is squeezed out to polish the surface of the workpiece
4
. The sludge deposited with the progress of the polishing and other mixed alien matters are captured into and held in the cavities of the pores
5
b
-
1
in order to prevent the surface of the workpiece from being scratched and the like.
The above-mentioned method, in which the workpiece is polished by a combination of the polishing pads and the slurry with the conventional structure, has the following problems to be solved:
1) As shown in the conceptual drawing of
FIG. 6
, the surface of the nap layer
5
b
made of the plastic foam in the conventional polishing pad
5
is uneven, and only cut parts of a wall surrounding the pores
5
b
-
1
locally contact with and slide on the workpiece
4
during the polishing. Thus, the polishing pads
5
cannot uniformly contact with the entire surface of the workpiece
4
. Therefore, the workpiece
4
cannot be polished uniformly, and this results in a fine “waviness” on the polished surface of the workpiece
4
. It is therefore difficult to ensure a surface quality required by a product specification. The “waviness” as well as “surface roughness” is an item to be measured for evaluating the surface quality with respect to the disk substrate, the silicon wafer and the like. The “waviness” is represented by a waving amount (Wa) of a surface image per unit area observed by an optical non-contact surface roughness gauge (ZYGO) in an angstrom (Å). Particularly, if the “waviness” is increased on the disk substrate for use in the fixed magnetic disk unit used in combination with a floating magnetic head, a floating characteristic of the magnetic head is deteriorated. It is therefore important to reduce the “waviness” as much as possible during the polishing.
2) The abrasive grains of micro powder (whose particles have square surfaces) obtained by crushing and classifying a solid matter as mentioned previously are ordinarily mixed in the conventional slurry
6
. The abrasive grains, the sludge and the like easily sediment and agglutinate in the slurry of this kind. If this slurry is used in combination with the conventional polishing pads
5
described with reference to
FIG. 6
, the alien matters such as the abrasive grains and the sludge in the slurry are caked in the pores
5
b
-
1
formed in the surface of the nap layer
5
b
during the polishing although a large amount of slurry can be held on the polishing pads. If the caked alien matters are left as they are, they may rub the surface of the workpiece during the polishing to thereby form scratches, which may cause troubles. Therefore, in the prior art, a brush, a jet stream or the like frequently cleans the surfaces of the polishing pads
5
in a short cycle in order to remove the alien matters (caked matters) adhered to the polishing pads. This maintaining (cleaning) operation, however, requires a lot of time and effort, and it is necessary to stop running the polishing machine during the maintaining operation. This affects the operating rate of the polishing machine.
3) The conventional polishing pad has much unevenness in the nap layer thereof after the manufacture. In order to polish a product mounted on the surface polishing machine, a running-in is performed in advance to fair the surface of the polishing pad by polishing a dummy workpiece. The running-in requires a lot of time, which is one of the causes of the decrease in the operat
Fujisawa Yuichiro
Ichino Mitsuyoshi
Ikemori Gosuke
Ishizawa Yoshiaki
Ito Yasushi
Fuji Electric & Co., Ltd.
Rossi & Associates
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