Abrading – Machine – Rotary tool
Reexamination Certificate
1999-09-17
2002-05-21
Hail, III, Joseph J. (Department: 3723)
Abrading
Machine
Rotary tool
C451S287000, C451S288000, C451S041000
Reexamination Certificate
active
06390901
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a polishing apparatus for polishing a workpiece such as a semiconductor wafer or the like with a grinding plate to a flat, mirror finish, and more particularly to a polishing apparatus with a mechanism for installing a grinding plate easily and reliably on a turntable.
2. Description of the Related Art
Recent rapid progress in semiconductor device integration demands smaller and smaller device and wiring patterns or interconnections and also narrower spaces between interconnections which connect active areas. One of the processes available for forming such interconnections is photolithography. Though the photolithographic process can form interconnections that are at most 0.5 &mgr;m wide, it requires that surfaces on which pattern images are to be focused by a stepper be as flat as possible because the depth of focus of the optical system is relatively small. It is therefore necessary to make the surfaces of semiconductor wafers flat for photolithography. One customary way of flattening the surface of semiconductor wafers on which integrated circuit devices are formed has been to polish semiconductor wafers with polishing a apparatus.
Heretofore, polishing apparatus for polishing planar workpieces, generally referred to as CMP (Chemical Mechanical Polishing) apparatus, comprise a turntable with a polishing pad attached thereto and a top ring for holding a planar workpiece to be polished. The top ring which holds a workpiece to be polished presses the workpiece against the polishing pad on the turntable. While an abrasive liquid is being supplied to the polishing pad, the top ring and the turntable are rotated about their own axes to polish the lower surface of the workpiece to a planar mirror finish. In particular, the planar workpiece to be polished is a device wafer with a circuit pattern formed thereon.
FIG. 1
of the accompanying drawings shows a conventional polishing apparatus. As shown in
FIG. 1
, the conventional polishing apparatus comprises a turntable
5
with a polishing pad
6
attached to an upper surface thereof, a top ring
1
for holding a semiconductor wafer
4
which is a workpiece to be polished while rotating and pressing the semiconductor wafer
4
against the polishing pad
6
, and an abrasive liquid supply nozzle
9
for supplying an abrasive liquid Q to the polishing pad
6
. The top ring
1
is connected to a top ring drive shaft
8
, and supports on its lower surface a resilient mat
2
such as of polyurethane or the like. The semiconductor wafer
4
is held on the top ring
1
in contact with the resilient mat
2
. The top ring
1
also has a cylindrical guide ring
3
mounted on a lower outer circumferential surface thereof and having a lower end projecting downwardly beyond the lower supporting surface of the top ring
1
for preventing the semiconductor wafer
4
from being dislodged from the lower surface of the top ring
1
while the semiconductor wafer
4
is being polished. The top ring
1
is tiltably supported on the lower end of the top ring drive shaft
8
by a ball bearing
In operation, the semiconductor wafer
4
is held against the lower surface of the resilient mat
2
on the top ring
1
, and pressed against the polishing pad
6
by the top ring
1
. The turntable
5
and the top ring
1
are rotated about their own axes to move the polishing pad
6
and the semiconductor wafer
4
relatively to each other in sliding contact for thereby polishing the semiconductor wafer
4
. At this time, the abrasive liquid Q is supplied from the abrasive liquid supply nozzle
9
to the polishing pad
6
. The abrasive liquid Q comprises, for example, an alkaline solution with fine abrasive grain particles of silica or the like suspended therein. Therefore, the semiconductor wafer
4
is polished by both a chemical action of the alkaline solution and a mechanical action of the fine abrasive grain particles. Such a polishing process is referred to as a CMP process.
The conventional CMP process in which the abrasive slurry of fine abrasive grain particles is supplied to the polishing pad suffers the following two problems.
The first problem is that the polished surface may not be fully planarized and may have undulations depending on the types of patterns and the states of steps on the polished surface. Generally, patterns on semiconductor wafers have various dimensions and steps. Some of the steps include smaller convexities and concavities spaced at a pitch of a few &mgr;m and having heights ranging from 0.5 to 1 &mgr;m, and larger convexities and concavities spaced at a pitch ranging from 100 &mgr;m to 1 mm. When the surface of such a semiconductor wafer with those steps, which is covered with a film of silicon dioxide or aluminum, is planarized, both convexities and concavities of the pattern are polished such that the polishing rate is higher in regions where smaller convexities and concavities are present and lower in regions where larger convexities and concavities are present. As a result, large undulations are developed on the polished surface. The reason for such large undulations is that since the surface of the semiconductor wafer is chemically and mechanically polished by the relatively soft polishing pad of polyurethane or the like and the abrasive liquid, not only the convexities but also the concavities of the surface are polished.
The second problem is that the polishing apparatus incurs a high running cost and needs special care to avoid environmental contamination. The abrasive liquid comprises an alkaline solution with fine abrasive grain particles of silica or the like suspended therein, for example. In order to polish the semiconductor wafer to a highly uniform planar finish, the abrasive liquid needs to be supplied in a sufficient quantity onto the polishing pad. However, most of the supplied abrasive liquid does not contribute to the actual polishing operation, but is discharged as a waste liquid. Because the abrasive liquid used in polishing highly dense semiconductor wafers is highly costly, it makes the polishing process also highly costly. Furthermore, since the abrasive liquid is in the form of a slurry containing fine abrasive grain particles of silica or the like, its waste liquid requires special attention to keep the working environment clean. Specifically, a system for supplying the abrasive liquid and a system for discharging the waste liquid tend to be greatly contaminated, and a system for processing the waste liquid is highly complicated.
There is known a process of polishing semiconductor wafers with a grinding plate. The grinding plate, which is also referred to as a fixed abrasive polisher, comprises a flat plate of abrasive grain particles of silica or the like which are coupled together by a binder. The grinding plate is applied to a turntable, and a semiconductor wafer held by a top ring is pressed against the grinding plate and polished thereby in sliding movement relative thereto.
Since the grinding plate is harder than the polishing pad, only convexities on the surface of the semiconductor are polished, and the polished surface is free of any appreciable undulations and is sharply defined. As no slurry containing fine abrasive grain particles is used, the cost of the polishing process is lower, and any special care to avoid environmental contamination is not necessary.
A polishing apparatus which employs the grinding plate requires that the grinding plate and the turntable be fixed to each other easily and reliably.
A conventional polishing pad is attached to a turntable by an adhesive applied to the reverse surface of the polishing pad. The polishing pad is bonded to the turntable continuously from an end of the turntable while being elastically deformed in order not to trap air bubbles in the bonded surface. The bonded polishing pad can be peeled off from an end of the turntable while being elastically deformed.
A grinding plate, however, cannot be elastically deformed when it is installed on and detached from a turn
Hirokawa Kazuto
Hiyama Hirokuni
Matsuo Hisanori
Togawa Tetsuji
Wada Yutaka
Ebara Corporation
Hail III Joseph J.
Wenderoth , Lind & Ponack, L.L.P.
Wilson Lee
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