Abrading – Machine – Rotary tool
Reexamination Certificate
2000-10-02
2002-08-20
Eley, Timothy V. (Department: 3723)
Abrading
Machine
Rotary tool
C451S005000, C451S041000, C451S008000
Reexamination Certificate
active
06435956
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a substrate holding apparatus, and more particularly to a substrate holding apparatus suitable for use in a polishing apparatus for polishing a surface of a substrate such as a semiconductor wafer to a flat mirror finish.
BACKGROUND ART
Recent rapid progress in semiconductor device integration has demanded smaller and smaller wiring patterns or interconnections and also narrower spaces between interconnections. In case of photolithography which can form interconnections that are at most 0.5 &mgr;m wide, it requires that surfaces of semiconductor wafers on which pattern images are to be focused by a stepper should be as flat as possible because the depth of focus of the optical system is relatively small. As a means for planarizing the semiconductor wafer, it is polished by a polishing apparatus.
Conventionally, this kind of polishing apparatus has a turntable with a polishing cloth constituting a polishing surface thereon, and a top ring for holding a substrate with a surface, to be polished, facing the turntable. The substrate is pressed against the turntable under a certain pressure by the top ring while the turntable and the top ring are being rotated, and the substrate is polished to a flat mirror finish while a polishing liquid is being supplied.
FIG. 8
is a schematic view showing main parts of an example of a conventional polishing apparatus. The conventional polishing apparatus comprises a turntable
102
with a polishing cloth
100
attached to an upper surface thereof, a top ring
104
for holding a semiconductor wafer W to be polished so as to allow the semiconductor wafer W to be rotated and to be pressed, a polishing liquid supply nozzle
106
for supplying a polishing liquid Q onto the polishing cloth
100
. The top ring
104
is connected to a top ring shaft
108
, which is supported by a top ring head (not shown) via an air cylinder so as to be vertically movable.
The top ring
104
comprises an elastic pad
110
of polyurethane or the like on its lower surface. The semiconductor wafer W is held in contact with the elastic pad
110
by the top ring
104
. The top ring
104
further comprises a cylindrical guide ring
112
on an outer circumferential edge thereof for holding the semiconductor wafer W on the lower surface of the top ring
104
during a polishing process. The guide ring
112
is fixed to the top ring
104
, and has a lower end projecting downwardly from the holding surface of the top ring
104
. A recess is formed inside the guide ring
112
. The semiconductor substrate W to be polished is held in the recess so as not to be removed from the top ring
104
during the polishing process.
In the conventional polishing apparatus thus constructed, the semiconductor wafer W is held against the lower surface of the elastic pad
110
which is attached to the lower surface of the top ring
104
. The semiconductor wafer W is then pressed against the polishing cloth
100
on the turntable
102
by the top ring
104
, and the turntable
102
and the top ring
104
are rotated to move the polishing cloth
100
and the semiconductor wafer W relatively to each other, for thereby polishing the semiconductor wafer W. At this time, the polishing liquid Q is supplied onto the polishing cloth
100
from the polishing liquid supply nozzle
106
. The polishing liquid Q comprises an alkaline solution containing abrasive particles of fine particles suspended therein, for example. The semiconductor wafer W is polished by a composite action comprising a chemical polishing action of the alkaline solution and a mechanical polishing action of the abrasive particles.
In order to planarize the substrate with high accuracy by the conventional polishing apparatus, it is considered to be desirable that a substrate holding surface of the top ring
104
for holding the semiconductor substrate, and the polishing surface of the polishing cloth
100
, and thus the surface of the turntable
100
to which the polishing cloth
100
is attached and which affects the polishing surface have a flatness with high accuracy, respectively.
However, during a polishing process, the top ring
104
is rotated about its own axis in sliding contact with the turntable
102
which is rotated about its own axis independently of the top ring
104
. The top ring
104
is deformed by a load transmitted via the air cylinder and a complex reaction force transmitted from the polishing cloth
100
to the top ring
104
, and hence the flatness of the substrate holding surface deteriorates. A part of heat generated during the polishing process is removed by the supplied polishing liquid, another part of heat is transferred to the turntable
102
, and the remaining heat is transferred to the top ring
104
to increase a temperature thereof and to deform the top ring
104
. Therefore, in some cases, the flatness of the substrate holding surface cannot constantly be maintained. Further, in some case, it is inevitable that the polishing rate at the central portion of the substrate is different from that at the peripheral portion of the substrate, for example, because of factors hard to be controlled, such as an amount, a position, or a temperature of the polishing liquid supplied from the polishing liquid supply nozzle.
The applicant of the present invention proposed, in the Japanese laid-open Patent Publication No. 9-225821, a substrate holding apparatus as shown in FIG.
9
. In this substrate holding apparatus, a plurality of pressure spaces C
1
, C
2
, C
3
defined by walls
114
are formed inside a top ring
104
. In
FIG. 9
, the pressure spaces C
1
, C
2
, C
3
are concentrically formed. A plurality of through-holes
118
communicating with both surfaces of a holding plate
116
are formed in the holding plate
116
, and through-holes
120
are similarly formed in an elastic pad
110
. There is provided a back pressure control mechanism capable of supplying a pressure fluid to each of the pressure spaces C
1
, C
2
, C
3
while controlling the pressure of the pressure fluid. Thus, pressing forces on the backside surface of the substrate are individually controlled at each of areas on the substrate holding surface corresponding to each of the pressure spaces C
1
, C
2
, C
3
for thereby pressing the substrate uniformly, thus improving the planarization of the polished surface. The numeral
122
denotes a presser ring disposed around the outer periphery of the top ring
104
for pressing the polishing cloth
100
by another pressing air cylinder different from the air cylinder for the top ring.
However, in the method utilizing a pressing force of a pressurized fluid as described above, an open space is basically formed between the backside surface of the substrate and the holding surface. Therefore, it is difficult to maintain the open space under high pressure not less than a pressure applied by the top ring. As a result, a non uniform pressing force due to the deformation of the holding plate cannot be corrected, so that the degree of the planarization of the polished surface is lowered. Similarly, since each of the areas between the backside surface of the substrate and the holding surface is not hermetically sealed, air passes through a gap produced by pressurizing the backside surface of the substrate. Therefore, it is difficult to individually control each of the pressures in the areas. Further, in the apparatus thus constructed, it is difficult to change the settings of the areas in which the back pressure is controlled depending on an actual polishing state, or to properly control the pressure in accordance with the polishing state.
DISCLOSURE OF THE INVENTION
The present invention has been made in view of the above drawbacks. It is therefore an object of the present invention to provide a substrate holding apparatus which can adjust a holding state of a substrate in accordance with a polishing state, and maintain uniformity of a polishing amount over an entire surface of the substrate, or control the polishing amount intentionally.
According to the present i
Ichimura Teruhiko
Ohwada Shin
Ebara Corporation
Eley Timothy V.
Thomas David B.
Wenderoth , Lind & Ponack, L.L.P.
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