Abrading – Machine – Combined
Reexamination Certificate
2000-08-22
2003-07-01
Nguyen, George (Department: 3723)
Abrading
Machine
Combined
C451S291000, C451S286000, C451S285000
Reexamination Certificate
active
06585572
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 wafer carrier utilized in a subaperture CMP system.
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. As more metallization levels and associated dielectric layers are formed, the need to planarize the dielectric material increases. 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 scrub, buff, and polish 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. However, in some CMP systems, the polishing pads may contain fixed abrasive particles throughout their surfaces. Depending on the form of the polishing pad used, a slurry composed of an aqueous solution such as NH
4
OH or DI water containing dispersed abrasive particles may be applied to the polishing pad, thereby creating an abrasive chemical solution between the polishing pad and the wafer.
Several problems may be encountered while using a typical CMP system. One recurring problem is called “edge-effect,” which is caused when the CMP system polishes the edge of the wafer at a different rate than other regions, thereby causing a non-uniform profile on the surface of the wafer. The problems associated with edge-effect can be divided to two distinct categories. The first category relates to the so-called “pad rebound effect” caused as a result of the initial contact of the polishing pad with the edge of the wafer. The second category will be described below.
FIG. 1A
is an illustration of the pad rebound effect associated with the prior art. A wafer
202
is mounted on a carrier
100
. Subsequently, the wafer
202
is applied against the pad surface
102
with a force F to accomplish a CMP process. At a certain point in time, the pad surface
102
contacts the edge of the wafer
202
at an edge contact zone
104
c, and the pad surface is shown bouncing off the edge of the wafer, thereby creating a non-contact zone
104
a
. Thereafter, the pad surface comes into contact with the wafer
202
at a contact zone
104
b
. However, the pad surface
102
bounces off the surface of the wafer
202
again, so as to create another non-contact zone
104
a
. Then, once more the pad surface comes into contact with the wafer
202
at another contact zone
104
b
. However, it bounces off again. Thus, the regions of the wafer
202
, which came into contact with the pad surface
102
like the contact zones
104
b
, are polished more than other regions. As a result, the CMP processed wafer will tend to show a non-uniform profile.
The “burn-off” effect, which constitutes the second category of problems associated with the edge-effect is shown in FIG.
1
B. As illustrated, the burn-off effect occurs when the sharper edge of a wafer
202
is excessively polished as it makes contact with the pad surface
102
(e.g., at the edge contact zone
104
c
). This happens because a considerable amount of pressure is exerted on the edge of the wafer
202
as a result of the surface pad
102
applying the force F on an infinitely small contact area defined as the edge contact zone
104
c
. As a consequence of the burn-off effect, the edge of the resulting polished wafers exhibit a burn ring that renders the edge region unusable, thereby wasting silicon device area.
Another shortcoming of conventional CMP systems is their inability to polish the surface of the wafer
202
along a desired finishing layer profile. Ordinarily, the surface of a wafer
202
that has undergone some fabrication tends to be of a different thickness in the center region and varies in thickness out to the edge. As illustrated in
FIG. 1C-1
, in a typical conventional CMP system, the pad surface
102
, which covers the entire wafer surface, is designed to apply a force on a finishing layer
202
a
surface. As a result, all the regions of the finishing layer
202
a
are polished until the finishing layer
202
a
is substantially flat. Thus, as shown in
FIG. 1C-2
, the pad surface
102
polishes the finishing layer
202
a
, irrespective of its wavy profile, thereby causing the thickness of the finishing layer
202
a
to be non-uniform (i.e., at points
202
a
1
,
202
a
2
,
202
a
3
, and
202
a
4
). As is well known, some circuit fabrication applications require that a certain thickness of material be maintained in order to build a working device. For instance, if the finishing layer
202
a
were a dielectric layer, a certain thickness would be needed in order to define metal lines and conductive vias therein.
In view of the foregoing, a need therefore exists in the art for a chemical mechanical polishing system that enables precision and controlled polishing of specifically targeted wafer surface regions, while substantially eliminating damaging edge-effects, pad rebound effects, and edge burn-off effects.
SUMMARY OF THE INVENTION
Broadly speaking, the present invention fills these needs by providing a system which implements precision controlled polishing of layer surfaces of a wafer. In one implementation, the CMP system can be made to follow the topography of the layer surfaces of the wafer so as to create a layer surface, which has a uniform thickness throughout. In a preferred embodiment, the CMP system is designed to implement a rotating carrier in a subaperture polishing configuration, thereby eliminating the above-mentioned drawbacks, edge-effects, pad rebound effects, and edge burn-off effects. It should be appreciated that the present invention can be implemented in numerous ways, including as a process, an apparatus, a system, a device, or a method. Several inventive embodiments of the present invention are described below.
In one embodiment, a chemical mechanical polishing (CMP) system is disclosed. The CMP system includes a carrier, which has a top surface and a bottom region. The top surface of the carrier is designed to hold and rotate a wafer having a one or more formed layers to be prepared. Further included is a
Boyd John M.
Gotkis Yehiel
Owczarz Aleksander A.
Saldana Miguel A.
Lam Research Corporation
Martine & Penilla LLP
Nguyen George
LandOfFree
Subaperture chemical mechanical polishing system does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Subaperture chemical mechanical polishing system, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Subaperture chemical mechanical polishing system will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3013001