Abrading – Abrading process – Glass or stone abrading
Reexamination Certificate
1999-10-22
2001-02-06
Gerrity, Stephen F. (Department: 3723)
Abrading
Abrading process
Glass or stone abrading
C451S060000, C451S287000, C451S285000, C451S397000, C451S398000, C451S446000
Reexamination Certificate
active
06183350
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to semiconductor fabrication technologies, and more particularly, to an improved structure for the retainer ring used on the polishing head of a chemical-mechanical polish (CMP) machine to retain a semiconductor wafer in position while performing the CMP process.
2. Description of Related Art
In semiconductor fabrications, the chemical-mechanical polish (CMP) technique is widely used for the global planarization of semiconductor wafers that are used for the fabrication of VLSI (very large-scale integration) and ULSI (ultra large-scale integration) integrated circuits.
FIGS. 1A and 1B
are schematic diagrams showing a conventional CMP machine. The CMP machine comprises a polishing table
10
on which a polishing pad
12
is layered, a polishing head
14
for holding a semiconductor wafer
16
in position, and a nozzle
18
for applying a mass of slurry to the semiconductor wafer
16
during the CMP process.
FIG. 1C
shows a respective view of the structure inside of the polishing head
14
. As shown, the polishing head
14
includes an air-pressure means
20
which applies air pressure to a wafer loader
22
used to hold the wafer
16
. In addition, a retainer ring
24
is mounted around the loader
22
and the wafer
16
, which can retain the wafer
16
in fixed position during the CMP process. Moreover, a cushion pad (not shown) is placed between the wafer
16
and the loader
22
.
FIGS. 2A-2B
show a conventional structure for the retainer ring
24
. Through the retainer ring structure of
FIGS. 2A-2B
, the slurry is supplied for polishing under the polishing head
14
, that is, over the surface of a wafer to be polished. However, without a proper conduit or passage of the retainer head, the slurry is non-uniformly distributed over the surface of the wafer. It is found that the slurry can not circulating fluently over the wafer surface. Thus, drawbacks such as a large wafer-edge exclusion range, a low refuse removing rate, an inefficient use of the slurry, and a reduced life of use of the cushion pad are caused. The resultant surface flatness of the wafer after undergoing a CMP process using the retainer ring of
FIGS. 2A-2B
is shown in FIG.
3
. The graph of
FIG. 3
shows the thickness of the wafer in relation to the various points of a straight line passing through the spinning center of the wafer. From the plot shown in
FIG. 3
, it can be seen that the flatness is not quite satisfactory. The standard deviation of the thickness data is about 5.06%.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a new retainer ring for used on the polishing head of a CMP machine. The new retainer ring in the CMP machine allows the slurry supplying more uniformly over the surface of a wafer. Thus, the above mentioned problems by using the conventional CMP machine, such as a large wafer-edge exclusion range, a low refuse removing rate, an inefficient use of the slurry, and a reduced life of use of the cushion pad, are solved.
It is another objective of the invention to provide a fabrication process for a wafer. The wafer is planarized by CMP method using the CMP machine with a new retainer ring to obtain a much improved flatness is obtained.
In accordance with the foregoing and other objectives of the present invention, a retainer ring for used on the polishing head of a CMP machine is provided. The retainer ring comprises a plurality of slurry passages formed at the bottom edge of the retainer ring. The slurry passages are substantially equally spaced, and each of the slurry passages is radically inclined in such a manner to form an acute angle of attack against the slurry outside of the retainer ring when the retainer ring spins.
In accordance with a first embodiment of the invention, a retainer ring is formed with a plurality of straight grooves equally spaced around the bottom of the retainer ring. Each of the straight grooves is radially inclined in such a manner so as to form an acute angle of attack against the slurry on the outside of said retainer ring when said retainer ring spins.
In accordance with a second embodiment of the invention, the retainer ring further comprises a circular path at the bottom between the inner perimeter and the outer perimeter of the retainer ring. The equally spaced arrangement of the straight grooves causes the slurry to be drawn into the inside of the retainer ring from all radical directions, thus allowing the slurry to be spread uniformly over the wafer held on the inside of the retainer ring. Furthermore, the provision of the circular path allows the slurry buffered by and circulating in, thus allowing those edge portions of the wafer proximate to the inner ends of the straight grooves to receive a buffered flow of slurry.
In the third embodiment, the slurry passages are designed with a gradually expanding path for slurry from an inlet to an outlet thereof, a diffusion angle between 0° to 10°, and an angle of attack &ohgr;, calculated from the equation:
sin&phgr;
1
=x/l
wherein the x is the minimum distance between a tangent line of an inlet point and a tangent line of an outlet point, and l is a path length of each of the slurry passages.
In the fourth embodiment, the retainer ring is formed with a combination of the slurry passages in the second embodiment and the circular path in the second embodiment.
To achieve the objectives of the invention, a fabrication process is also provided. To planarize a wafer having a deposition layer thereon, the wafer is disposed within a polishing head with the deposition layer facing down the polishing table. The wafer is retained within the polishing head by a retainer ring, and the retainer ring comprises a plurality of slurry passage. A slurry is supplied from a slurry supplier to be evenly distributed over the deposition layer through the retainer ring. The polishing is rotating and the polishing head is spinning to achieve the objective and the invention, a fabrication process is also provided.
In another embodiment, a chemical mechanical process is provided. A deposition layer is formed on a wafer. A chemical mechanical process is performed to the deposition layer using a chemical mechanical polishing machine with a retainer ring having a plurality of slurry passages at the bottom thereof.
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Chiu Daniel
Chiu Hao-Kuang
Lai Chien-Hsin
Lin Juen-Kuen
Peng Peng-Yih
Gerrity Stephen F.
McDonald Shantese
Thomas Kayden Horstemeyer & Risley
United Microelectronics Corp.
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