Abrading – Abrading process – With tool treating or forming
Reexamination Certificate
2001-11-09
2003-08-19
Morgan, Eileen P. (Department: 3723)
Abrading
Abrading process
With tool treating or forming
C451S443000, C451S024000
Reexamination Certificate
active
06607426
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a polishing apparatus using a light-load dresser, the load of which is controlled by its own weight in combination with a fluid pressure.
A manufacturing process of a semiconductor wafer utilizes a polishing apparatus for planarizing and mirror-polishing a surface of the semiconductor wafer.
FIG. 4
is a perspective view, illustrating a general configuration of such a polishing apparatus. The polishing apparatus shown in
FIG. 4
comprises a turntable
100
equipped with a polishing cloth adhered to its upper surface, defining a polishing cloth face
103
, a top ring
111
arranged above said turntable
100
, with a semiconductor wafer W being held thereto or sucked under vacuum against a lower surface thereof, and a dresser
121
also arranged above said turntable
100
for dressing the polishing cloth face
103
.
In a polishing operation, a polishing slurry is supplied from a slurry supply nozzle
105
onto the polishing cloth face
103
of the turntable
100
driven rotationally by a driving shaft
101
, while the semiconductor wafer W held by the top ring
111
is compressed against the polishing cloth face
103
for polishing to a mirror-surface.
In such an apparatus, if slurry collects on and clogs the surface of the polishing cloth forming the polishing cloth face
103
, deterioration in polishing performance will result. Thus, pure water, as required, is supplied onto the polishing cloth face
103
of the rotating turntable
100
from a supply means (not shown), while the dresser
121
is rotated and compressed against the polishing cloth face
103
, thereby preventing slurry from clogging (i.e. regenerating the polishing cloth), and maintaining a working condition of the polishing cloth face
103
. In such an apparatus, the dresser
121
serves as a tool for abrading the polishing cloth face
103
slightly by a unit of &mgr;m (10
−6
m) or as a tool-for cleaning the polishing cloth face
103
.
FIG. 3
shows a dresser driving mechanism of a pneumatic balance control type according to a conventional technology. As shown in
FIG. 3
, the conventional dresser
121
has its driving shaft
123
operatively attached to an end portion of a swing arm
125
so as to be moved up and down freely with respect to the swing arm
125
, and the entire unit of the mechanism can be swingably moved together with the swing arm
125
upon a swinging motion of a support pole
127
of the swing arm
125
. The driving shaft
123
is rotationally driven by a motor
129
through a driving belt
131
. Further, a dresser driving cylinder
132
is mounted on the swing arm
125
, and pneumatic pipes
135
and
137
are respectively connected to chambers “a” and “b” defined within the cylinder
132
on opposite sides of a piston
133
. The upper pneumatic pipe
137
is connected to a three-way electromagnetic valve
139
via a throttle valve
138
for restricting an air flow rate. A pneumatic pipe
137
a
for supplying compressed air and a pneumatic pipe
137
b
for exhausting the air are connected to the three-way electromagnetic valve
139
; and further the pneumatic pipe
137
a
is connected to a pressure control unit
141
; while the lower pneumatic pipe
135
is connected to a relief valve
147
via throttle valves
143
and
145
. The relief valve
147
also functions to control a fluid pressure at a constant level.
The pressure control unit
141
functions to decrease a pressure of the supplied compressed air at a predetermined level, and supplying it to the chamber “b” of the cylinder
132
, while the relief valve
147
functions to relieve the air gradually from the chamber “a” of the cylinder
132
. The pressure control unit
141
also has a function similar to that of the relief valve
147
.
When the dresser
121
is moved up, the compressed air at the predetermined level is supplied through the pneumatic pipe
135
into the chamber “a” of the cylinder
132
while the chamber “b” of the cylinder
132
being in communication with the exhaust pipe
137
b
through the three-way electromagnetic valve
139
. When the dresser
121
is to be moved down, the chamber “b” is in communication with the pressure control unit
141
through the three-way valve
139
and the compressed air is supplied into the chamber “b” so that the piston
133
, and thus the dresser
121
, is moved downward. The pressure of the dresser
121
applied to the polishing cloth face
103
of the turntable
100
may be adjusted by controlling a pressure balance of the compressed air supplied into both of chamber “a” and “b” of the cylinder
132
.
If the dresser
121
abrades the polishing cloth face
103
of the turntable
121
by a large amount, the polishing cloth face
103
is likely to become worn rapidly and be required to replaced frequently. Thus, preferably the dresser
121
should abrade the polishing cloth face
103
by only a small amount so as to extend the life of the polishing cloth. In addition, if the load applied to the polishing cloth face
103
changes during dressing, amount of abrasion of the polishing cloth face
103
will vary, and the condition on the polishing cloth face
103
will be subject to variation resulting in a serious affection to the ability to polish the semiconductor wafer properly. From that point of view, such a dresser
121
has been desired that can maintain the light-load condition stably and can make an amount of abrasion of the polishing cloth face
103
to be as small as possible and also constant.
However, in the conventional dresser driving mechanism of a pneumatic balance control type described above, two pneumatic circuits consisting of two compressed air supplying systems are used and the load applied to the dresser
121
is determined by the balance in air pressure between the two systems. Therefore, the air pressure in the two systems cannot easily be controlled simultaneously with a high degree of precision, and accordingly, it has been difficult to maintain the dresser
121
in a constant light-load condition stably during dressing.
Further, there have been other problems such that upon moving the dresser
121
down, the relief valve
147
moves out of its operational limit due to very light air pressure applied thereto and which prohibits air relief and results in a failure of the downward movement of the dresser
121
. Additionally upon moving the dresser
121
down, the chamber “a” of the cylinder
132
is scarcely exhausted and thus the dresser
121
exhibits a discontinuous downward motion in a repetitive downward and stopping motions, cyclically.
SUMMARY OF THE INVENTION
The present invention has been made in the light of the problems described above, and an object thereof is to provide a polishing apparatus equipped with a light-load dresser capable of a precisely controlled light-load and achieving a smooth downward movement operation.
The present invention takes advantage of the mass of a dresser itself having a constant load in combination with a force provided by a single variable fluid pressure and thereby achieves precise control of the light load of the dresser.
That is, in order to solve the problems described above, the present invention provides a polishing apparatus comprising a turntable, a top ring and a dresser, each of which is rotatable independently, with an object to be polished being interposed between the turntable and the top ring so that a surface of the interposed object can be polished by a polishing cloth face defined on said turntable surface, wherein the polishing cloth face can be regenerated by compressing the dresser against the turntable, the apparatus characterized in that: a dresser unit including the dresser and a shaft for rotatably supporting the dresser is operatively mounted to a dresser supporting mechanism so as to be moved up and down freely with respect to the dresser supporting mechanism, and a push-up mechanism is installed between the dresser unit and said dresser supporting mechanism for pushing the dresser unit with an upward force, wherein a compress
Ebara Corporation
Wenderoth , Lind & Ponack, L.L.P.
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