Abrading – Abrading process – Glass or stone abrading
Reexamination Certificate
2000-09-18
2002-10-29
Morgan, Eileen P. (Department: 3723)
Abrading
Abrading process
Glass or stone abrading
C451S286000, C451S287000, C451S060000
Reexamination Certificate
active
06471566
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to chemical mechanical polishing (CMP) systems and techniques for improving the performance and effectiveness of CMP operations. Specifically, the present invention relates to a substrate carrier having an active sacrificial retaining ring.
2. Description of the Related Art
In the fabrication of semiconductor devices, there is a need to perform CMP operations, including polishing, buffing and wafer cleaning. 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 the 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 excess 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. Slurry is most usually introduced onto a moving preparation surface, e.g., belt, pad, brush, and the like, and distributed over the preparation surface as well as the surface of the semiconductor wafer being buffed, polished, or otherwise prepared by the CMP process. The distribution is generally accomplished 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, which rotates in a direction of rotation. The CMP process is achieved when the 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 cross-sectional view of an exemplary prior art CMP system. The CMP system of
FIG. 1A
depicts a carrier head
100
engaging a wafer
102
utilizing a retaining ring
101
. The carrier head
100
is applied against the polishing pad surface
103
a
of a polishing pad
103
with a force F. As shown, the top surface of the retaining ring
101
is positioned above the front surface of the wafer
102
. Thus, while the front surface of the wafer
102
is in contact with the polishing pad surface
103
a
, the surface of the retaining ring
101
is configured not to come into contact with the polishing pad surface
103
a.
Several problems may be encountered while using a typical prior art CMP system. One recurring problem is called “edge-effect” caused by the CMP system polishing the edge of the wafer
102
at a different rate than other regions, thereby creating a non-uniform profile on the surface of the wafer
102
. The problems associated with edge-effect can be divided into two distinct categories of the “pad rebound effect” and “edge burn-off effect.”
FIG. 1B
is an enlarged illustration of the pad rebound effect associated with the prior art. The pad rebound effect occurs when the polishing pad surface
103
a
initially comes into contact with the edge of the wafer
102
causing the polishing pad surface
103
to bounce off the wafer
102
. As the moving polishing pad surface
103
a
shifts under the surface of the wafer
102
, the edge of the wafer
102
cuts into the polishing pad
103
at the edge contact zone
104
c
, causing the polishing pad
103
a
to bounce off the wafer
102
, thereby creating a wave on the polishing pad
103
.
Ideally, the polishing pad
103
is configured to be applied to the wafer
102
at a specific uniform pressure. However, the waves created on the polishing pad
103
create a series of low-pressure regions such as an edge non-contact zone
104
a
and a non-contact zone
104
a
, wherein the removal rate is lower than the average removal rate. Thus, the regions of the wafer
102
which came into contact with the polishing pad surface
103
a
such as the edge contact zone
104
c
and a contact zone
104
b
, are polished more than the other regions. As a result, the CMP processed wafer will tend to show a non-uniform profile.
Further illustrated in
FIG. 1B
is the edge “burn-off.” As the polishing pad surface
103
a
comes into contact with the sharper edge of the wafer
102
at the edge contact zone
104
c
, the edge of the wafer
102
cuts into the polishing pad
103
, thereby creating an area defined as a “hot spot,” wherein the pressure exerted by the polishing pad
103
is higher than the average polishing pressure. Thus, the polishing pad surface
103
a
excessively polishes the edge of the wafer
102
and the area around the edge contact zone
104
(i.e., the hot spots). The excessive polishing of the edge of the wafer
102
occurs because a considerable amount of pressure is exerted on the edge of the wafer
102
as a result of the polishing pad surface
103
a
applying pressure on a small contact area defined as the edge contact zone
104
c
. As a consequence of 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
102
. Moreover, depending on the polisher and the hardware construction, a substantially low removal rate is detected within the edge non-contact zone
104
a
′, an area between about 3 millimeters to about 20 millimeters of the edge of the wafer
102
. 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 sometimes could be rendered unusable, thereby wasting silicon device area.
Although, occasionally, an air bearing has been implemented in an attempt to compensate for the different levels of pressure applied by the polishing pad
103
, air bearings have almost never been able to completely compensate for the difference in the pressure levels. Particularly, at the edge contact zone
104
c
, the edge non-contact zone
104
a
′, the contact zone
104
b
, and the non-contact zone
104
a
the use of air bearings do not completely compensate for the difference in the exerted pressure, as the air can easily escape.
A common problem associated with the pad rebound effect and the edge burn off effect is the non-uniformity of the wafer
102
caused by the lack of uniform distribution of slurry between the polishing pad surface
103
a
and the surface of the wafer
102
. As the edge of the wafer
102
cuts into the polishing pad surface
103
a
, it causes the slurry to be squeezed out of the polishing pad
103
, thereby preventing the polishing pad surface
103
a
from performing a thorough polishing operation on the edge of the wafer
102
. Thus, to accomplish a proper polishing operation, additional slurry must be supplied to the polishing interface. Consequently, a significant amount of slurry is wasted as a result of the combined effects of the pad rebound effect and edge burn-off ef
Boyd John M.
Mikhaylich Katrina A.
Martine & Penilla LLP
Morgan Eileen P.
Shakeri Hadi
LandOfFree
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