Abrading – Machine – Rotary tool
Reexamination Certificate
2000-08-25
2003-01-21
Eley, Timothy V. (Department: 3723)
Abrading
Machine
Rotary tool
C451S286000, C451S289000, C451S029000
Reexamination Certificate
active
06508696
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a wafer-polishing head which is used in an apparatus for polishing the surface of wafers such as a semiconductor wafer or the like, and a polishing apparatus having the same.
2. Description of the Related Art
Recently, fineness of patterning of wafers has become important, in accordance with high level of integration thereof. It has become especially important to flatten semiconductor wafers where the patterning is formed and to flatten the surface of semiconductor wafers as much as possible in the process of forming the patterning, such that the formation of a fine pattern having a multi-layer structure can be carried out easily and surely. For example, the formation of a pattern is carried out using optical lithography, and the depth of focus in the optical lithography becomes shallow in proportion to the fineness of a pattern. In order to increase the accuracy of a pattern and to easily control focus during exposure, it is required that a difference of unevenness on a wafer surface is no greater than the depth of focus (that is, flatness).
Further, with regard to polishing bare wafers, a requirement for flatness has become severe in proportion to the increased size of the wafer. In this case, a chemical and mechanical polishing method (CPM method) is known which provides a high flatness to the polished surface of semiconductor wafers (referred to as a wafer, hereunder). In the CMP method, the surface of the wafer is polished chemically and mechanically to obtain a flatness of the surface using an alkaline slurry containing SiO
2
, a neutral slurry containing CeO
2
, an acid slurry containing Al
2
O
3
or a slurry containing abrasive grains (hereunder, these slurries are generally referred to as abrasive grain-containing slurries). For example, a polishing apparatus shown in
FIG. 4
is known for polishing the surface of wafers according to the CPM method.
As schematically shown in
FIG. 4
, which is an enlarged perspective view of an important part of the CPM, a polishing pad
104
comprising, for example, hard urethane, is provided on a disc-shaped platen
103
attached to a center shaft
102
in a polishing apparatus
100
, and a wafer-polishing head
105
which holds a wafer W is disposed facing the polishing pad
104
and in a position eccentric to the center shaft
102
of the polishing pad
104
such that the polishing head can be rotated on its own axis. In the polishing apparatus
100
, the polishing pad
104
and the wafer W are moved relatively to each other while the wafer W is pressed against the surface of the polishing pad
104
by the wafer-polishing head
105
. The above-mentioned abrasive grain-containing slurry S is interposed between the wafer W and the polishing pad
104
, thereby to polish one surface of the wafer W. The polishing apparatus
100
as shown in
FIG. 4
is only one example. There are known polishing apparatuses having a plurality of wafer-polishing heads
105
.
Next, one example of wafer-polishing pad
105
is schematically shown in front sectional view in FIG.
5
(
a
). The wafer-polishing head
105
a
shown in FIG.
5
(
a
) comprises a principal head
106
having a lower opening portion
106
a
and having an approximately circular shape. A flexible membrane
108
is positioned inside the principal head
106
for closing the opening portion
106
a
and for holding a wafer W at the underside of an inward peripheral portion
108
a
. A sealed pressurizing chamber
107
is formed by closing the opening portion
106
a
with the flexible membrane
108
. A pressure regulator
109
is connected to the pressurizing chamber
107
to control the internal pressure thereof.
The flexible membrane
108
comprises a flexible film and is fixed to the principal head
106
so as to be approximately planar over the full face thereof, for example by putting the outer peripheral portion of the flexible membrane between the principal head
106
and a guide ring
110
which has an approximately annular shape and is attached to the end of the opening portion of the principal head
106
, as shown in FIG.
5
(
b
) which is a partially enlarged view of FIG.
5
(
a
).
The pressure regulator is used for adjusting a force for displacing the flexible membrane
108
in the axial direction of the head by controlling the internal pressure of the pressurizing chamber
107
. In the wafer-polishing head
105
a
, a force for displacing the flexible membrane
108
in the axial direction of the head, that is a force by which the flexible membrane
108
presses a wafer W against a polishing pad
104
(polishing pressure), is adjusted such that the polishing pressure for the wafer W is controlled within a proper range thereof.
A guide ring
110
is attached to the principal head
106
, surrounding the end of the opening portion of the principal head. When the wafer W is polished, the guide ring protects the wafer W from dropping out from the wafer-polishing head
105
a
while it is pressed against the polishing pad
104
, and decreases the deformation of the polishing pad
104
by pressing the polishing pad in a portion surrounding the wafer W, with the result that the working accuracy at the outer peripheral edge of the wafer W is increased.
A wafer-polishing head having a structure mentioned above is disclosed in JP-A 5-69310, for example.
Other wafer-polishing heads are also known. FIG.
6
(
a
) is a front sectional view schematically illustrating a wafer-polishing head
105
b
and FIG.
6
(
b
) is a partially enlarged view of FIG.
6
(
a
). The wafer-polishing head
105
b
of these figures comprises a principal head
111
having a lower opening portion
111
a
and having an approximately circular shape; a holding member
112
is disposed inside of the principal head
111
; a flexible membrane
114
having an outer peripheral portion
114
b
is held by the holding member
112
so that the outer peripheral portion
114
b
of the membrane is turned up and inward toward the peripheral portion
114
a
; and a pressurizing chamber
113
is formed inside the opening portion
111
a
by the flexible membrane
114
. Here, a pressure regulator
115
is connected to the pressurizing chamber
113
to control the internal pressure thereof. Further, in this example a retaining ring
116
having an approximately annular shape is provided in the lower end of the wafer-polishing head
105
b
, surrounding the periphery of the opening portion
111
a
. The flexible membrane comprises a flexible film and holds a wafer W underneath the lower surface thereof. In the same manner as in the wafer-polishing head
105
a
, a force by which the flexible membrane
114
presses the wafer W against a polishing pad
104
(polishing pressure) is adjusted by controlling the internal pressure of the pressurizing chamber
113
with the pressure regulator
115
. The retaining ring
116
has almost the same function as the guide ring
110
of the wafer-polishing head
105
a.
A wafer-polishing head having the structure mentioned above is disclosed in JP-A 10-337658, for example.
The above-mentioned wafer-polishing heads
105
a
and
105
b
apply polishing pressure to the wafer W by transferring the internal pressure of the pressurizing chamber to the wafer W thorough the flexible membrane, and so the membrane is required to be as thin as possible so that the elasticity of the flexible membrane has no influence on the polishing pressure to the wafer W.
However, as the flexible membrane is apt to deform due to its thinness, it can enter a gap formed between the peripheral end of the wafer W and the inward peripheral portion of the guide ring
110
(or the inward peripheral portion of the retaining ring
116
) when the wafer W is pressed against the polishing pad by the internal pressure of the pressurizing chamber. See FIGS.
7
(
a
) and
7
(
b
). In this case, as the underside of the membrane is not pressed against other members such as the wafer W and the guide ring
110
(or the retaining ring
116
), and since the membrane receiv
Kajiwara Jiro
Kobayashi Tatsunori
Tanaka Hiroshi
Eley Timothy V.
Grant Alvin J
Mitsubishi Materials Corporation
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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