Active gimbal ring with internal gel and methods for making...

Details Active gimbal ring with internal gel and methods for making... Active gimbal ring with internal gel and methods for making...

2001-12-26

2003-07-15

Hail, III, Joseph J. (Department: 3723)

Abrading

Machine

Rotary tool

C451S398000, C451S288000

Reexamination Certificate

active

06592437

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to chemical mechanical planarization (CMP) systems and techniques for improving the performance and effectiveness of CMP operations. Specifically, the present invention relates to a hollow annular gimbal ring having internal gel suitable for providing gimbal movement of a wafer carrier plate relative to a carrier head.
2. Description of the Related Art
In the fabrication of semiconductor devices, there is a need to perform CMP operations. Typically, integrated circuit devices are in the form of multi-level structures. At the substrate level, transistor devices having diffusion regions are formed. In subsequent levels, interconnect metallization lines are patterned and electrically connected to the transistor devices to define the desired functional device. As is well known, patterned conductive layers are insulated from other conductive layers by dielectric materials, such as silicon dioxide. At each metallization level and/or associated dielectric layer, there is a need to planarize the metal and/or dielectric material. Without planarization, fabrication of additional metallization layers becomes substantially more difficult due to higher variations in the surface topography. In other applications, metallization line patterns are formed in the dielectric material, and then metal CMP operations are performed to remove overburden materials, such as copper metallization.
In the prior art, CMP systems typically implement belt, orbital, or brush stations in which belts, pads, or brushes are used to polish, buff, and scrub one or both sides of a wafer. Slurry is used to facilitate and enhance the CMP operation, and may be distributed by a combination of the movement of the preparation surface, the movement of the semiconductor wafer and the friction created between the semiconductor wafer and the preparation surface.
In a typical CMP system, a wafer is mounted on a carrier head, which rotates in a direction of rotation. The CMP process is achieved when an exposed surface of the rotating wafer is applied with force against a polishing pad, which moves or rotates in a polishing pad direction. Some CMP processes require that a significant force be used at the time the rotating wafer is being polished by the polishing pad.
Normally, the polishing pads used in the CMP systems are composed of porous or fibrous materials. Depending on the type of the polishing pad used, slurry composed of an aqueous solution containing different types of dispersed abrasive particles such as SiO
2
and/or Al
2
O
3
may be applied to the polishing pad, thereby creating an abrasive chemical solution between the polishing pad and the wafer.
FIG. 1A
depicts a schematic cross-sectional view of an exemplary prior art CMP system. In this CMP system a carrier head
100
engages a retaining ring mounting plate
101
provided with a retaining ring
102
. The retaining ring
102
centers a wafer
103
relative to a vertical axis of rotation
104
of the carrier head
100
. The carrier head
100
is urged toward a surface
106
of a polishing pad
107
with a force F. As shown, an outer surface
108
of the retaining ring
102
is positioned above an exposed surface
109
of the wafer
103
. Thus, while the exposed surface
109
of the wafer
103
is in contact with the polishing pad surface
106
, the outer surface
108
of the retaining ring
101
is configured to not come into contact with the polishing pad surface
106
, and is thus spaced from the polishing pad surface
106
. The spacing of the ring
102
from the surface
106
allows room for the wafer
103
, the mounting plate
101
, and the ring
102
to tilt relative to the vertical axis
104
on which the carrier head
100
rotates. A typical gimbal
111
is provided as a spherical member
112
mounted in spherical sockets
113
a
and
113
b
of the respective carrier head
100
and mounting plate
101
. One or the other of the sockets
113
a
or
113
b
is configured to secure the member
112
to the respective carrier head
100
or mounting plate
101
.
FIG. 1B
shows the tilt of the wafer
103
, the mounting plate
101
, and the retaining ring
102
allowed by the gimbal
111
in terms of an angle
116
between the vertical axis
104
and an axis of rotation
117
of the retaining ring mounting plate
101
. The tilt allows movement of the mounting plate
101
for parallelism of a plane (represented by a line
118
) of the exposed surface
109
of the wafer
103
and a plane (represented by a line
119
) of the surface
106
of the pad
107
.
Several problems may be encountered while using an “edge-effect” caused by the CMP system polishing the edge of the wafer
103
at a different rate than other regions, thereby creating a non-uniform profile on the surface of the wafer
103
. The problems associated with edge-effect are twofold, namely “pad rebound effect” and “edge burn-off effect.”
FIG. 1C
is an enlarged illustration of the pad rebound effect associated with the prior art. The pad rebound effect occurs when the polishing pad surface
106
initially comes into contact with the edge of the wafer
103
, causing the polishing pad surface
106
to bounce off the exposed surface
109
of the wafer
103
. As the moving polishing pad surface
106
shifts under the exposed surface
109
of the wafer
103
(see arrow
120
), the edge of the wafer
103
cuts into the polishing pad
107
at an edge contact zone
121
. The cutting causes the polishing pad
106
to bounce off the wafer
103
, thereby creating a wave on the polishing pad
106
as shown in FIG.
1
C. Ideally, the polishing pad
107
is configured to be applied to the wafer
103
at a specific uniform pressure and to remain flat (planar). However,
FIG. 1C
shows that the wave created on the polishing pad
103
creates a series of low-pressure regions of the exposed surface
109
of the wafer
103
. Such regions may include an edge non-contact zone
122
and an inner non-contact zone
123
, wherein the removal rate is lower than the average removal rate. Thus, the edge contact zone
121
and an inner contact zone
124
of the wafer
103
are polished more than the other zones. As a result, the CMP processed wafer
103
will tend to show a non-uniform profile.
Further illustrated in
FIG. 1D
is the “edge burn-off” effect. As the polishing pad surface
106
comes into contact with the sharper edge of the wafer
103
at the edge contact zone
121
, the edge of the wafer
103
cuts into the polishing pad
107
, thereby creating an area defined as a “hot spot,” wherein the pressure exerted by the polishing pad
107
is higher than the average polishing pressure. Thus, the polishing pad surface
106
excessively polishes the edge of the wafer
103
and the area around the edge contact zone
121
(i.e., the hot spots). By the burn-off effect, a substantially high removal rate is exhibited at the area within about 1 millimeter to about 3 millimeters of the edge of the wafer
103
. Moreover, depending on the polisher and the hardware construction, a substantially low removal rate is detected within the edge non-contact zone
122
, an area between about 3 millimeters to about 20 millimeters of the edge of the wafer
103
. Accordingly, as a cumulative result of the edge-effects, an area of about 1 millimeter to about 20 millimeters of the edge of the resulting post-CMP wafers
103
sometimes could be rendered unusable, thereby wasting silicon device area.
One way to compensate against edge effects is to use a gimbal, such as the gimbal
111
. However, such gimbals
111
also suffer problems in that the complexity of the mechanical components of such gimbals makes them difficult to design and implement for symmetric repetitive CMP environments. For example, some typical gimbals
111
tend to vibrate in response to the forces of the polishing pad
107
and the wafer
103
. The vibrations may introduce numerous potential problems to troubleshot when inappropriate CMP results start appearing in processed wafers
103
.

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