Reinforced polishing pad for linear chemical mechanical...

Details Reinforced polishing pad for linear chemical mechanical... Reinforced polishing pad for linear chemical mechanical...

2001-06-25

2003-10-21

Staicovici, Stefan (Department: 1732)

Plastic and nonmetallic article shaping or treating: processes

With severing, removing material from preform mechanically,...

Making hole or aperture in article

C264S255000, C264S257000, C264S258000, C264S271100, C264S299000, C264S319000, C264S324000, C264S327000, C156S245000

Reexamination Certificate

active

06635211

ABSTRACT:

FIELD OF THE INVENTION
The present invention generally relates to a polishing pad for linear chemical mechanical polishing and method for forming and more particularly, relates to a polishing pad for linear chemical mechanical polishing that is reinforced by reinforcing fillers for improved creep resistance and a method for forming the reinforced polishing pad.
BACKGROUND OF THE INVENTION
In the fabrication of semiconductor devices from a silicon wafer, a variety of semiconductor processing equipment and tools are utilized. One of these processing tools is used for polishing thin, flat semiconductor wafers to obtain a planarized surface. A planarized surface is highly desirable on a shallow trench isolation (STI) layer, on an inter-layer dielectric (ILD) or on an inter-metal dielectric (IMD) layer which are frequently used in memory devices. The planarization process is important since it enables the use of a high resolution lithographic process to fabricate the next level circuit. The accuracy of a high resolution lithographic process can be achieved only when the process is carried out on a substantially flat surface. The planarization process is therefore an important processing step in the fabrication of semiconductor devices.
A global planarization process can be carried out by a technique known as chemical mechanical polishing or CMP. The process has been widely used on ILD or IMD layers in fabricating modern semiconductor devices. A CMP process is performed by using a rotating platen in combination with a pneumatically actuated polishing head. The process is used primarily for polishing the front surface or the device surface of a semiconductor wafer for achieving planarization and for preparation of the next level processing. A wafer is frequently planarized one or more times during a fabrication process in order for the top surface of the wafer to be as flat as possible. A wafer can be polished in a CMP apparatus by being placed on a carrier and pressed face down on a polishing pad covered with a slurry of colloidal silica or aluminum.
A polishing pad used on a rotating platen is typically constructed in two layers overlying a platen with a resilient layer as an outer layer of the pad. The layers are typically made of a polymeric material such as polyurethane and may include a filler for controlling the dimensional stability of the layers. A polishing pad is typically made several times the diameter of a wafer, in a conventional rotary CMP, while the wafer is kept off-center on the pad in order to prevent polishing a non-planar surface onto the wafer. The wafer itself is also rotated during the polishing process to prevent polishing a tapered profile onto the wafer surface. The axis or rotation of the wafer and the axis of rotation of the pad are deliberately not collinear, however, the two axes must be parallel. It is known that uniformity in wafer polishing by a CMP process is a function of pressure, velocity and concentration of the slurry used.
The polishing or the removal of surface layers is accomplished by a polishing slurry consisting mainly of colloidal silica suspended in deionized water or KOH solution. The slurry is frequently fed by an automatic slurry feeding system in order to ensure the uniform wetting of the polishing pad and the proper delivery and recovery of the slurry. For a high volume wafer fabrication process, automated wafer loading/unloading and a cassette handler are also included in a CMP apparatus.
As the name implies, a CMP process executes a microscopic action of polishing by both chemical and mechanical means. While the exact mechanism for material removal of an oxide layer is not known, it is hypothesized that the surface layer of silicon oxide is removed by a series of chemical reactions which involve the formation of hydrogen bonds with the oxide surface of both the wafer and the slurry particles in a hydrogenation reaction; the formation of hydrogen bonds between the wafer and the slurry; the formation of molecular bonds between the wafer and the slurry; and finally, the breaking of the oxide bond with the wafer or the slurry surface when the slurry particles moves away from the wafer surface. It is generally recognized that the CMP polishing process is not a mechanical abrasion process of slurry against a wafer surface.
While the rotary CMP process provides a number of advantages over the traditional mechanical abrasion type polishing process, a serious drawback for the rotary CMP process is the difficulty in controlling polishing rates and different locations on a wafer surface. Since the polishing rate applied to a wafer surface is generally proportional to the relative velocity of the polishing pad, the polishing rate at a specific point on the wafer surface depends on the distance from the axis of rotation. In other words, the polishing rate obtained at the edge portion of the wafer that is closest to the rotational axis of the polishing pad is less than the polishing rate obtained at the opposite edge of the wafer. Even though this is compensated by rotating the wafer surface during the polishing process such that a uniform average polishing rate can be obtained, the wafer surface, in general, is exposed to a variable polishing rate during the CMP process.
More recently, a new chemical mechanical polishing method has been developed in which the polishing pad is not moved in a rotational manner but instead, in a linear manner. It is therefore known as a linear chemical mechanical polishing process in which a polishing pad is moved in a linear manner in relation to a rotating wafer surface. The linear polishing method provides a more uniform polishing rate across a wafer surface throughout a planarization process for uniformly removing a film layer on the surface of a wafer. One added advantage of the linear CMP system is the simpler construction of the apparatus and therefore not only reducing the cost of the apparatus but also reduces the floor space required in a clean room environment.
A typical linear CMP apparatus
10
is shown in
FIGS. 1A and 1B
. The linear CMP apparatus
10
is utilized for polishing a semiconductor wafer
24
, i.e., a silicon wafer for removing a film layer of either an insulating material or a wafer from the wafer surface. For instance, the film layer to be removed may include insulating materials such as silicon oxide, silicon nitrite or spin-on-glass material or a metal layer such as aluminum, copper or tungsten. Various other materials such as metal alloys or semi-conducting materials such as polysilicon may also be removed.
As shown in
FIGS. 1A and 1B
, the wafer
24
is mounted on a rotating platform, or wafer holder
18
which rotates at a pre-determined speed. The major difference between the linear polisher
10
and a conventional CMP is that a continuous, or endless belt
12
is utilized instead of a rotating polishing pad. The belt
12
moves in a linear manner in respect to the rotational surface of the wafer
24
. The linear belt
12
is mounted in a continuous manner over a pair of rollers
14
which are, in turn, driven by a motor means (not shown) at a pre-determined rotational speed. The rotational motion of the rollers
14
is transformed into a linear motion
26
in respect to the surface of the wafer
24
. This is shown in FIG.
1
B.
In the linear polisher
10
, a polishing pad
30
is adhesively joined to the continuous belt
12
on its outer surface that faces the wafer
24
. A polishing assembly
38
is thus formed by the continuous belt
12
and the polishing pad
30
glued thereto. As shown in
FIG. 1A
, a plurality of polishing pads
30
are utilized which are frequently supplied in rectangular-shaped pieces with a pressure sensitive layer coated on the back side.
The wafer platform
18
and the wafer
24
form an assembly of a wafer carrier
28
. The wafer
24
is normally held in position by a mechanical retainer, commonly known as a retaining ring
16
, as shown in FIG.
1
B. The major function of the retaining ring
16
is to fix the wafer in position in the wafer carri

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