Adhesive bonding and miscellaneous chemical manufacture – Differential fluid etching apparatus – For liquid etchant
Reexamination Certificate
2002-12-20
2004-06-22
Mills, Gregory (Department: 1763)
Adhesive bonding and miscellaneous chemical manufacture
Differential fluid etching apparatus
For liquid etchant
C451S008000, C451S081000, C451S066000
Reexamination Certificate
active
06752898
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to chemical mechanical planarization apparatuses, and more particularly to methods and apparatuses for improved edge performance using an air bearing with a raised topography to constrain airflow under a wafer.
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 material.
A chemical mechanical planarization (CMP) system typically is utilized to polish a wafer as described above. A CMP system generally includes system components for handling and polishing the surface of a wafer. Such components can be, for example, a rotary polishing pad, an orbital polishing pad, or a linear belt polishing pad. The pad itself typically is 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 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 is substantially planarized. The wafer may then be cleaned in a wafer cleaning system.
FIG. 1A
shows a linear polishing apparatus
10
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. Generally, 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
, which moves linearly with respect to the surface of the wafer
16
. The belt
12
is a continuous belt. A motor typically drives the rollers 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
.
A wafer carrier
18
holds the wafer
16
, which is 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
while applying pressure to the polishing belt. 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 rollers
20
rotate, moving the polishing belt in the linear motion
22
with respect to the wafer
16
. In one example, a fluid 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 fluid against the under surface of the supporting layer of the belt pad. The applied fluid thus forms a fluid bearing that creates a polishing pressure on the underside of the polishing belt
12
that is applied against the surface of the wafer
16
.
The above described linear polishing apparatus
10
functions well for most CMP operations when used with a supported polishing belt
12
, such as a stainless steel belt having a polymer material covering. However, more efficient polishing belts
12
are currently available that are not supported. Since supporting material, such as stainless steel, does not form part of an unsupported polishing belt
12
, unsupported polishing belts
12
often are easier to ship, higher quality, and less expensive to construct. As a result, unsupported polishing belts
12
generally are desirable to use in linear polishing systems.
Unfortunately, current linear polishing apparatuses
10
often perform poorly when polishing copper layers using an unsupported polishing belt
12
. For example,
FIG. 1C
is an illustration showing an edge of a wafer
16
having a copper layer. The exemplary wafer
16
edge includes a copper layer
50
disposed over a dielectric layer
52
. As is well known in the art, a slight raised section
54
occurs on copper layers
50
near the edge of the wafer
16
because of the particular properties of copper. As a result, it is desirable to increase the removal rate of the polishing process near the edge of the wafer during planarization of copper layers
50
to planarize the raised section
54
.
Prior art linear polishing apparatuses generally can achieve an increased removal rate along the edge of the wafer
16
using a supported polishing belt, as illustrated in FIG.
2
A.
FIG. 2A
is a graph
200
showing a removal rate using a supported polishing belt as a function of the distance from the center to the edge of a wafer. When using a supported polishing belt, such as a stainless steel supported polishing belt, the removal rate at the edge of the wafer can be increased dramatically, as shown in graph
200
. In particular, the removal rate can be increased at a wafer radius of about 90 mm, which is about the radius of the slight raised section, which occurs on copper layers near the edge of the wafer.
However, as discussed previously, more efficient polishing belts are currently available that are not supported. As a result, unsupported polishing belts generally are desirable to use in linear polishing systems. Unfortunately, as mentioned above, conventional linear polishing apparatuses often perform poorly when polishing copper layers using an unsupported polishing belt, as illustrated in FIG.
2
B.
FIG. 2B
is a graph
250
showing removal rate using an unsupported polishing belt as a function of the distance from the center to the edge of a wafer. As shown in graph
250
, when using an unsupported belt in a conventional linear polishing apparatus, the removal rate at a wafer radius of about 90 mm is still slow and does not increase significantly until about 95-97 mm, which is beyond the radius of the slight raised section in the copper layer
50
. As a result, it is difficult to effectively polish a copper layer
50
using an unsupported belt in a conventional linear polishing apparatus.
In view of the foregoing, there is a need for an apparatus that allows effective polishing of copper layers using unsupported polishing belts.
SUMMARY OF THE INVENTION
Broadly speaking, the present invention fills these needs by providing an air bearing platen with a raised topography to constrain airflow under a wafer. The raised topography of the platen allows enhanced edge removal rate uniformity control when using an unsupported polishing belt. In one embodiment, a CMP apparatus for enhancing removal rate uniformity is disclosed. The CMP apparatus include
Anderson, II Robert L.
Charatan Robert
Taylor Travis Robert
Lam Research Corporation
MacArthur Sylvia R.
Martine & Penilla LLP
Mills Gregory
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