Active retaining ring support

Details Active retaining ring support Active retaining ring support

2001-03-30

2004-04-13

HassanZadeh, P. (Department: 1763)

Adhesive bonding and miscellaneous chemical manufacture

Differential fluid etching apparatus

For liquid etchant

C451S041000

Reexamination Certificate

active

06719874

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 compressible ring suitable for use carriers having active retaining rings.
2. Description of the Related Art
In the fabrication of semiconductor devices, there is a need to perform CMP operations, including topography planarization, 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 transistors to define the desired functional devices. 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 over-burden materials, such as copper metallization.
In the prior art, CMP systems typically implement rotary, belt, orbital, or brush stations in which rotating tables (platens), 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 to provide uniform and symmetrical material removal. 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
, CeO
2
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, namely “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 edge non-contact zone
104
a
′ and 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 undulating surface 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 higher than the average removal rate is exhibited at the area within about 4 millimeters of the wafer edge area.
102
. Moreover, depending on the polisher and the hardware construction, a substantially low removal rate is detected within the edge next lower contact pressure 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 20 millimeters of the edge of the resulting post CMP wafers sometimes could be rendered unusable, thereby wasting silicon device area.
One way to compensate against edge effects is to use an active retaining ring. An active retaining rings is one that can be controlled so that the under surface of the retaining rings is about even with surface of the wafer being polished. To accomplish this, prior art active retaining rings utilize complex force application mechanisms that apply a reactive force to the retaining ring. These systems commonly use springs, air, or a combination of both, and are coupled to feedback electronics. Based on the feedback, the reactive force, which is commonly in terms of pressure, is fed to the active retaining ring.
Although such systems work relatively well, these systems also suffer in that their complexity makes them difficult to design and implement for symmetric repetitive CMP environments. As is well known, a retaining ring typically is round. As such, a system implementing springs or air must arrange a number of spring or air locations around the retaining ring. In doing so, circumstances will arise where the pressure being applied by one spring or air bladders will not match the pressure being applied by another spring or bladder. This difference can, of course, be

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