Abrading – Accessory – Dressing
Reexamination Certificate
1998-06-11
2001-10-23
Eley, Timothy V. (Department: 3723)
Abrading
Accessory
Dressing
C451S056000
Reexamination Certificate
active
06306025
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a dressing tool for the surface of an abrasive cloth, more particularly to a dressing tool for dressing the surface of a polishing cloth for use in a mechanochemical polishing process.
DISCUSSION ON THE RELATED ART
The following considerations have been by the inventors during their eager investigations toward the present invention on the conventional techniques.
Recently, the high integration of the semiconductor device, the focus margin of the exposing unit for transferring a pattern has gotten narrower and narrower so that the conventional flattening process of reflowing, coating such as Spin On Glass (SOG) coating or etching back is hard to provide for a wide range of flattening. In this respect, a Chemical Mechanical Polishing or mechanochemical polishing (hereinafter shortly referred to as “CMP”) process for polishing a semiconductor substrate by mechanical and chemical actions has been mainly employed recently. A conventional polishing apparatus used in the CMP process will be explained below in reference to the accompanying drawings.
FIG. 13
is a side view showing an essential part of the polishing apparatus. As shown in
FIG. 13
, this polishing apparatus includes a turn table
10
with a flattened, leveled surface. This table
10
has a diameter of around 50 to 100 cm and is made of a highly rigid material. On the surface of the table
10
, an abrasive (polishing) cloth
11
of around 1 to 3 mm in thickness is affixed. The polishing apparatus further includes over the table
10
a carrier
13
of a size corresponding to the diameter of a semiconductor wafer
12
whose surface faces the face of the table
10
in parallel. The carrier
13
can be driven by means of a spindle
14
. The polishing apparatus moreover includes near the table
10
a dressing mechanism
15
for recovering the surface of the abrasive cloth
11
.
After providing the carrier
13
with the semiconductor wafer
12
, the carrier
13
is made to be lowered onto the abrasive cloth
11
, then to the semiconductor wafer
12
a load of around 300 to 600 g/cm
2
is applied while a polishing agent
16
is being supplied, and at the same time the table
10
and the carrier
13
are rotated to the same direction at around 20 to 50 rpm, thereby polishing is performed.
In the CMP process for an intercalative insulating film, as the abrasive cloth
11
, for example, IC1000 (trademark of Rodel Co., Ltd., U.S.A.) of hard foamed polyurethane is generally used, and as the polishing agent
16
, SC-1 (trademark of Cabot Co., Ltd., U.S.A.) basically containing fumed silica is used.
Polishing a semiconductor wafer by the same way as disclosed above, using these materials, causes phenomena that foams (pores), existing on the surface of the abrasive cloth
11
become clogged with the silica contained in the polishing agent so that a polishing rate becomes decreased.
For this reason, there has been put into practice a recovery treatment of the abrasive cloth
11
surface by means of the dressing mechanism
15
simultaneously or at given intervals with polishing the semiconductor wafer
12
. Refer to, for example, Solid State Technology, October 1994, left column, line 2 to right column, line 9.
The dressing mechanism
15
generally includes a disk-like dressing tool onto which diamond grains are fixed by nickel plating, a dressing tool holder and a drive arm for moving the dressing tool on the abrasive cloth.
The work of the dressing mechanism
15
is to remove clogging from the surface of the abrasive cloth
11
, and recover the surface roughness of the abrasive cloth
11
into the beginning state before polishing.
FIG. 16
is a graph showing the change of the polishing speed (or rate) in polishing a semiconductor wafer under insufficiently dressed conditions. The abscissa expresses the number of treated pieces, and the ordinate expresses the polishing speed (relative ratio). It is observed that under the insufficiently dressed conditions the polishing speed of the semiconductor wafer tends to decrease in proportion to the number of treated pieces, which causes a marked lowering of the productivity.
It is the most important in the CMP process to maintain a stable polishing speed stable, and in order to maintain this polishing stability the surface treatment of the abrasive cloth with the dressing mechanism is most effective. Especially, prominent effects are given by the dressing tool in terms of its surface roughness such as the intervals of the diamond grains and their grain sizes.
The following is the description of a conventional dressing tool.
FIG. 12
illustrates the cross-sectional view of a conventional dressing tool. At first,
FIG. 12
(a) shows that diamond grains
3
′ are embedded into nickel plating
2
and fixed so as not to be released. The diamond grains
3
′ generally used in the CMP process have an average particle diameter of around 120 to 240 &mgr;m, and the thickness of the nickel plating
2
is set to about 60 to 70% of the average particle diameter of the diamond grains.
In fixing diamond grains
3
′, sedimentation fixing and bag fixing methods are employed. In any of these methods, the diamond grains
3
′ are fixed onto all over the surface of a material to be fixed, thereby the diamond grains
5
floated from (i.e., floatingly retained by) a substrate
1
exist.
Such floated diamond grains
5
can be brought into contact with the interior of foams existing on the wavy surface of an abrasive cloth
11
so that aggregates of a polishing agent clogging the foams can be effectively removed.
However, the floated diamond grains
5
cause the problem that they are covered with nickel plating
2
in a ratio of not more than 50%, and accordingly, their retainability is low so that they are easily released out onto the surface of the abrasive cloth
11
, consequently, unrecoverable scratches of several tens microns in depth are produced on the surface of the semiconductor wafer
12
.
To this end, recently, as disclosed in, for example, Unexamined Japanese Patent Publication JP-A-4-318198 (1992 ) and etc., the floated diamond grains have been removed in the course of manufacturing. More concretely, there has been put into practice a process including steps of nickel plating in a vessel filled with diamond grains to develop first thin nickel plating, removing the floated diamond grains after taking out of the vessel, and then nickel plating in a vessel containing no dispersed diamond grains to develop second nickel plating until a total of the first and second nickel platings becomes the predetermined thickness.
By applying such a process as disclosed above, as shown in FIG.
12
(
b
), an almost uniform surface with little floated diamond grains can be obtained. However, the dressing tool having such a uniform surface prevents the diamond grains from sufficiently making contact with the interior of the foamed body existing on the surface of the abrasive cloth so that the polishing speed becomes lowered.
FIG. 15
is a cross-sectional view showing the contact state of an abrasive cloth with a dressing tool. On account that the surface of the abrasive cloth
11
is waved and the abrasive cloth is considerably hard, for example, IC1000 (trademark of Rodel Co., Ltd.) has a hardness of around 60 (Shore D), when the diamond grains
3
′ are embedded so as to have nearly the same projection height and close intervals as shown in FIG.
15
(
a
), a pressure becomes deconcentrated and biting-in of the diamond grains into the abrasive cloth is inhibited.
For this reason, it is preferable to decrease the number of the embedded diamond grains as shown in FIG.
15
(
b
).
However, simple reduction of diamond grains to be fixed accompanies the poor reproducibility with respect to the embedded number and the extreme difficulty in arranging at equivalent intervals, though it may be effective for decreasing the number of the embedded diamond grains under the surface of the dressing tool.
To this end, for example, the aforementioned Japanes
Eley Timothy V.
NEC Corporation
Nguyen Dung Van
Sughrue Mion Zinn Macpeak & Seas, PLLC
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