Abrading – Machine – Endless band tool
Reexamination Certificate
2001-12-28
2003-09-16
Rose, Robert A. (Department: 3723)
Abrading
Machine
Endless band tool
C451S442000, C451S059000
Reexamination Certificate
active
06620035
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to chemical mechanical planarization (CMP) techniques and, more particularly, to the efficient, cost effective, and improved CMP operations.
2. Description of the Related Art
In the fabrication of semiconductor devices, there is a need to perform chemical mechanical planarization (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. As more metallization levels and associated dielectric layers are formed, the need to planarize the dielectric material grows. Without planarization, fabrication of further metallization layers becomes substantially more difficult due to the 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.
A CMP system is typically utilized to polish a wafer as described above. A CMP system typically includes system components for handling and polishing the surface of a wafer. Such components can be, for example, an orbital polishing pad, or a linear belt polishing pad. The pad itself is typically made of a polyurethane material or polyurethane in conjunction with other materials such as, for example a stainless steel belt. In operation, the belt pad is put in motion and then a slurry material is applied and spread over the surface of the belt pad. Once the belt pad having slurry on it is moving at a desired rate, the wafer is lowered onto the surface of the belt pad. In this manner, wafer surface that is desired to be planarized is substantially smoothed, much like sandpaper may be used to sand wood. The wafer may then be cleaned in a wafer cleaning system.
FIG. 1A
shows a linear polishing apparatus
10
which is typically utilized in a CMP system. The linear polishing apparatus
10
polishes away materials on a surface of a semiconductor wafer
16
. The material being removed may be a substrate material of the wafer
16
or one or more layers formed on the wafer
16
. Such a layer typically includes one or more of any type of material formed or present during a CMP process such as, for example, dielectric materials, silicon nitride, metals (e.g., aluminum and copper), metal alloys, semiconductor materials, etc. Typically, CMP may be utilized to polish the one or more of the layers on the wafer
16
to planarize a surface layer of the wafer
16
.
The linear polishing apparatus
10
utilizes a polishing belt
12
in the prior art, which moves linearly in respect to the surface of the wafer
16
. The belt
12
is a continuous belt rotating about rollers (or spindles)
20
. The rollers
20
each have a plurality of parallel grooves
30
where a groove direction is parallel to the polishing belt
12
travel direction. The rollers are typically driven by a motor so that the rotational motion of the rollers
20
causes the polishing belt
12
to be driven in a linear motion
22
with respect to the wafer
16
. Typically, the polishing belt
12
has seams
14
in different sections of the polishing belt
12
.
The wafer
16
is held by a wafer carrier
18
. The wafer
16
is typically held in position by mechanical retaining ring and/or by vacuum. The wafer carrier positions the wafer atop the polishing belt
12
so that the surface of the wafer
16
comes in contact with a polishing surface of the polishing belt
12
.
FIG. 1B
shows a side view of the linear polishing apparatus
10
. As discussed above in reference to
FIG. 1A
, the wafer carrier
18
holds the wafer
16
in position over the polishing belt
12
. The polishing belt
12
is a continuous belt typically made up of a polymer material such as, for example, the IC
1000
made by Rodel, Inc. layered upon a supporting layer. The support layer is generally made from a firm material such as stainless steel. The polishing belt
12
is rotated by the rollers
20
which drives the polishing belt in the linear motion
22
with respect to the wafer
16
. In one example, an air bearing platen
24
supports a section of the polishing belt under the region where the wafer
16
is applied. The platen
24
can then be used to apply air against the under surface of the supporting layer. The applied air thus forms an controllable air bearing that assists in controlling the pressure at which the polishing belt
12
is applied against the surface of the wafer
16
.
FIG. 1C
shows an overhead view of the rollers
20
in the linear polishing apparatus
10
. During the CMP process, liquid substances such as, for example, slurry or aqueous substances may be applied. Consequently, liquids may come between the rollers
20
and the polishing belt
12
(as shown by the dotted lines). When this happens, hydroplaning may be occur resulting in slippage between the polishing belt
12
and the rollers
20
. Such slippage may result in inaccurate and inconsistent polishing of the wafer
16
. To help reduce this problems, the rollers
20
have a plurality of parallel grooves
30
that enable liquids to be removed from the contact areas between the rollers
20
and the polishing belt
12
. Each of the plurality of parallel grooves
30
are parallel to each other and non-spiraling. Unfortunately, due to each one of the plurality of grooves
30
forming separate, distinct, and unconnected rings around the rollers
20
, certain portions of the polishing belt
12
is always over one of the plurality of grooves and is not supported during the rolling of the polishing belt
12
.
Because the grooves
30
on the rollers
20
are parallel, the center of the wafer polishing position is lined up with groove sections on both rollers. Without a rigid support such as a stainless steel band, the polishing belt
12
is not evenly stretched across the roller surface. The uneven tension profile directly transfers to the uneven polishing pressure on the belt
12
. Because of the parallel pattern on the rollers
20
, when the belt
12
is rolling during polish, the uneven tension pattern does not change across the belt
12
(perpendicular to the belt travel direction) at any given time. As the wafer
16
spins, this effect may average out. However, even with the wafer spinning, the center of the wafer
16
always “sees” low pressure, therefore, the removal is the lowest at wafer center.
FIG. 1D
shows uneven polish profile is directly transferred to the uneven polishing pressure on the polishing belt
12
. The y-axis is a polishing pressure and the x-axis is distance from the center of the wafer
16
. Curve
32
shows the distance from the radius of the wafer
16
plotted against the polishing pressure. Because of the parallel pattern on the rollers
20
, when the belt
12
is rolling during polishing, the uneven tension pattern does not change across the belt. Due to the lack of support over areas of the plurality of parallel grooves
30
, a set of concentric rings separated by, in one example, 0.5″ is observed on a polished wafer. Generally, oscillation in removal rate from wafer center to edge corresponds to the rings visually detected on the polishing belt
12
. Even if the wafer is spun during polishing, the center of the wafer
16
typically has a minimal polishing rate compared to other areas of the wafer
16
.
Therefore, different sections of the polishing belt
12
may have differing tensions which may result in differing polishing rates on certain portions of the wafer
16
. Consequently, wafer processing may be less consistent and more wafers may be damaged.
SUMMARY OF THE INVENTION
Broadly speaking, the present invention fills these needs by providing an improved apparatus for rotating a p
Lam Research Corporation
Martine & Penilla LLP
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