Abrading – Machine – Rotary tool
Reexamination Certificate
2000-11-22
2003-04-15
Nguyen, George (Department: 3723)
Abrading
Machine
Rotary tool
C451S060000, C451S242000, C451S443000, C451S446000
Reexamination Certificate
active
06547652
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the field of Chemical Mechanical Polishing (CMP). More particularly, the present invention relates to methods and apparatus for chemical mechanical polishing of substrates, such as semiconductor substrates, on a rotating polishing pad in the presence of a chemically and/or physically abrasive slurry, and providing fresh supply of slurry onto the surface of the substrate which is mounted on the polishing pad while the substrate is being polished. Additionally, the present invention includes a pad conditioning apparatus to condition the polishing pad while the polishing pad is being used to polish semiconductor substrates. Additionally, the present invention includes a new slurry delivery system where multi-component slurries can be used that can be metered very accurately during slurry flow and which completely eliminates the use of the conventional peristaltic pump.
DESCRIPTION OF THE PRIOR ART
Chemical Mechanical Polishing is a method of polishing materials, such as semiconductor substrates, to a high degree of planarity and uniformity. The process is used to planarize semiconductor slices prior to the fabrication of semiconductor circuitry thereon, and is also used to remove high elevation features created during the fabrication of the microelectronic circuitry on the substrate. One typical chemical mechanical polishing process uses a large polishing pad that is located on a rotating platen against which a substrate is positioned for polishing, and a positioning member which positions and biases the substrate on the rotating polishing pad. Chemical slurry, which may also include abrasive materials therein, is maintained on the polishing pad to modify the polishing characteristics of the polishing pad in order to enhance the polishing of the substrate.
The use of chemical mechanical polishing to planarize semiconductor substrates has not met with universal acceptance, particularly where the process is used to remove high elevation features created during the fabrication of microelectronic circuitry on the substrate. One primary problem which has limited the used of chemical the polishing pad is difficult. Providing a fresh supply of slurry to all positions of the substrate is even more difficult. As a result, the uniformity and the overall rate of polishing are significantly affected as the slurry reacts with the substrate.
The polishing process is carried out until the surface of the wafer is ground to a highly planar state. During the polishing process, both the wafer surface and the polishing pad become abraded. After numerous wafers have been polished, the polishing pad becomes worn to the point where the efficiency of the polishing process is diminished and the rate of removal of material from the wafer surface is significantly decreased. It is usually at this point that the polishing pad is treated and restored to its initial state so that a high rate of uniform polishing can once again be obtained.
In the conventional approach, the wafer is held in a circular carrier, which rotates. The polishing pads are mounted on a polish platen which has a flat surface and which rotates. The rotating wafer is brought into physical contact with the rotating polishing pad; this action constitutes the Chemical Mechanical Polishing process. Slurry is dispensed onto the polishing pad typically using a peristaltic pump. The excess slurry typically goes to a drain, which means that the CMP process has an open loop slurry flow. In addition, the conventional approach uses orbital motion where there is a relative motion at any point of the wafer that poses severe problems of non-uniformity across the die and across the wafer in addition to problems of planarity. Also, the conventional approach uses and dispenses with an excessive amount of slurry that adds significantly to the processing cost. There also is no method for exactly controlling slurry flow. The present invention addresses and solves the indicated problems. Since both the wafer and the polishing pad are rotating there exists a velocity differential across the wafer. This velocity differential wafer polishing uniformity and planarity suffer across the die and across the wafer. This limits the application of the conventional CMP approach especially in Shallow Trench Applications, copper damascene, etc., which are involved in sub-quarter micron technology modes.
FIG. 1
shows a Prior Art CMP apparatus. A polishing pad
20
is affixed to a circular polishing table
22
which mechanical polishing in the semiconductor industry is the limited ability to predict, much less control, the rate and uniformity at which the process will remove material from the substrate. As a result, CMP is labor intensive process because the thickness and uniformity of the substrate must be constantly monitored to prevent overpolishing or inconsistent polishing of the substrate surface.
One factor, which contributes to the unpredictability and non-uniformity of the polishing rate of the CMP process, is the non-homogeneous replenishment of slurry at the surface of the substrate and the polishing pad. The slurry is primarily used to enhance the rate at which selected materials are removed from the substrate surface. As a fixed volume of slurry in contact with the substrate reacts with the selected materials on the surface of the substrate, this fixed volume of slurry becomes less reactive and the polishing enhancing characteristics of that fixed volume of slurry is significantly reduced. One approach to overcoming this problem is to continuously provide fresh slurry onto the polishing pad. This approach presents at least two problems. Because of the physical configuration of the polishing apparatus, introducing fresh slurry into the area of contact between the substrate and rotates in a direction indicated by arrow
24
at a rate in the order of 1 to 100 m RPM. A wafer carrier
26
is used to hold wafer
18
face down against the polishing pad
20
. The wafer
18
is held in place by applying a vacuum to the backside of the wafer (not shown). The wafer carrier
26
also rotates as indicated by arrow
32
, usually in the same direction as the polishing table
22
, at a rate on the order of 1 to 100 RPM. Due to the rotation of the polishing table
22
, the wafer
18
traverses a circular polishing path over the polishing pad
20
. A force
28
is also applied in the downward or vertical direction against wafer
18
and presses the wafer
18
against the polishing pad
20
as it is being polished. The force
28
is typically in the order of 0 to 15 pounds per square inch and is applied by means of a shaft
30
that is attached to the back of wafer carrier
26
. Slurry
21
is deposited on top of the polishing pad
20
.
FIG. 2
shows a typical Prior Art slurry delivery system. Slurry
21
of uniform chemical and mechanical composition is contained in the slurry vat
34
from where the slurry
21
is pumped by the diaphragm pump
36
in direction
38
. The peristaltic pump
40
deposits controlled and intermittent amounts of slurry
21
onto the polishing pad
20
while the balance
44
of the slurry that had been pumped by the diaphragm pump
36
is returned to the slurry vat
34
. The rate at which the slurry
42
is provided by the two pumps
36
and
40
can be under control of conditions of operation and environment such as type of surface being polished, rate of rotation of either the wafer
18
and/or the polishing table, etc.
U.S. Pat. No. 5,688,360 (Jairath) shows cylindrical and conical polishing pads.
U.S. Pat. No. 5,709,593 (Guthrie et al.) shows a slurry delivery system and slurry wiper bar.
U.S. Pat. No. 5,785,585 (Manfredi et al.) discloses a polishing pad conditioner with radical compensation.
U.S. Pat. No. 5,792,709 (Robinson et al.) shows a polishing pad disk.
U.S. Pat. No. 5,782,675 (Southwick) discloses an apparatus to recondition a polishing pad.
U.S. Pat. No. 5,679,039 (Talieh) discloses a polishing pad with grooves to deliver slurry.
U.S. Pat. No. 5,775,983 (Shendon et al.) teaches a co
Chartered Semiconductor Manufacturing Ltd.
Nguyen George
Pike Rosemary L. S.
Saile George O.
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