Abrading – Precision device or process - or with condition responsive... – With indicating
Reexamination Certificate
2000-01-14
2001-04-24
Eley, Timothy V. (Department: 3723)
Abrading
Precision device or process - or with condition responsive...
With indicating
C451S286000, C451S287000
Reexamination Certificate
active
06220930
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a chemical mechanical polishing (CMP) device, and in particular to a wafer polishing head controlled by gas and liquid pressures.
2. Description of the Related Art
Chemical mechanical polishing (CMP) is a global planarization technique. In chemical mechanical polishing, the rear surface of a semiconductor wafer is fixed by a wafer polishing head. Then, the front surface of the semiconductor wafer is pressed against a polishing pad which is installed on a removable platen. When polishing, a chemical agent conducive to CMP is continuously supplied to the platen. By the chemical reaction between the chemical agent and the front surface of the semiconductor wafer and mechanical polishing, the front surface of the semiconductor wafer can be completely planarized.
The wafer polishing head is used to safely and firmly hold the semiconductor wafer without any damage or contamination on the semiconductor wafer. In an early phase, a semiconductor wafer was adhered on a carrier with a material like wax. After polishing, the wax must be completely removed or the semiconductor wafer is contaminated. Currently, a wafer adhering layer is additionally disposed on the bottom of the carrier. Since the wafer adhering layer is made of a porous material, a semiconductor wafer can be firmly held on the carrier by creating a vacuum environment. However, a high-speed rotation could cause the semiconductor wafer slipping during polishing. Therefore, a retaining ring is additionally installed to surround the semiconductor wafer, thereby preventing the semiconductor wafer from slip. The retaining ring must be rigid and uneasily react with any chemical agent. Typically, Delrin and Tecktron are used to make the retaining ring.
FIG. 1A
is a cross-sectional view illustrating a wafer polishing head
10
. Referring to
FIG. 1A
, a carrier
12
is a main body of the wafer polishing head
10
. A wafer adhering layer
14
, is disposed on the bottom of the carrier
12
. The rear surface of a semiconductor wafer
16
is firmly held on the wafer adhering layer
14
by creating a vacuum environment during wafer loading. A retaining ring
18
surrounds the carrier
12
and the semiconductor wafer
16
, wherein the bottom of the retaining ring
18
must have a lower position than that of the carrier
12
, such that the semiconductor wafer
16
can be prevented from damage during polishing. Furthermore, a first pressure chamber
20
is disposed directly above the retaining ring
18
. A diaphragm
22
is disposed on the bottom the first pressure chamber
20
and contact the retaining ring
18
. When a gas flows into the first pressure chamber
20
, the diaphragm
22
is deformed to press again the retaining ring
18
, thereby fixing the retaining ring
18
. A second pressure chamber
24
is disposed directly on the carrier
12
. When a gas flows into the second pressure chamber
24
, a force is created to push the semiconductor wafer
16
via the carrier
12
.
FIG. 1B
is a flow chart illustrating a pressure control of the wafer polishing head
10
of FIG.
1
A. In
FIG. 1B
, a gas source
26
supplies a gas with a fixed pressure value to the first pressure chamber
20
. The second pressure chamber
24
and the carrier
12
.
During polishing, the retaining ring
18
always contacts the diaphragm
22
, resulting in an abrasion therebetween. Under this condition, it is easy to cause the semiconductor wafer
16
slipping if the bottom of the carrier
12
is lower than that of the retaining ring
18
. Therefore, the slipping wafer is easily broken. It is necessary to regularly and manually adjust the retaining ring
18
thereby to maintain the bottom of the retaining ring
18
at a lower position than that of the carrier
12
and to prevent the wafer from being broken.
Additionally, the wafer polishing head uses a gas pressure to provide a vertical force to the semiconductor wafer and the polishing pad, thereby alleviating wabble during polishing. However, the gas pressure depends on the stability of the gas source. As a result, it is easy to cause wabble on the semiconductor wafer and the polishing pad, resulting in a poor polishing uniformity. In order to improve the polishing uniformity, the pressures generated by a gas to press the carrier and the retaining ring are also manually adjusted to different proper pressure values even though the gas comes from the same gas source.
SUMMARY OF THE INVENTION
The invention provides a wafer polishing head for planarizing a wafer. The wafer polishing head comprises a carrier, a retaining ring, a first pressure chamber, a second pressure chamber and an automatic control system. The retaining ring is surrounding the carrier. The first pressure chamber having a first inner pressure is disposed above the retaining ring. The second pressure chamber having a second inner pressure is disposed on the carrier. The automatic control system for adjusting a relative height between the carrier and the retaining ring is respectively coupled to the first pressure chamber and the second pressure chamber.
According to preferred embodiment of the invention, the automatic control pressure device comprises a first converter, a second converter, a controller, a counter, a first regulator and a second regulator. The first and the second converters are respectively coupled to the first and the second pressure chambers but are both coupled to the controller. The controller is respectively coupled to the first and the second regulators. The first and the second regulators are respectively coupled to the first and the second pressure chambers. Additionally, the second pressure chamber is partly filled by a liquid with a relatively low volatility and a relatively low chemical reactivity.
By comparing the feedback pressures of the first and the second pressure chambers, the controller transmits pressure values to the first and the second pressure chambers respectively through the first and the second regulators to adjust the inner pressures of the first and the second pressure chambers. By adjusting the inner pressures of the first and the second pressure chambers, the relative height between the carrier and the retaining ring can be automatically controlled. Hence, the polished wafer does not slip away. In addition, the wafer polishing head can greatly alleviate wabble on the carrier by using a liquid pressure to press the carrier. Accordingly, the wafer polishing head of the invention can greatly improve a polishing uniformity.
REFERENCES:
patent: 5584751 (1996-12-01), Kobayashi et al.
patent: 5762539 (1998-06-01), Nakashiba et al.
patent: 5795215 (1998-08-01), Guthrie et al.
patent: 5803799 (1998-08-01), Volodarsky et al.
Chang Chia-Jui
Lai Chien-Hsin
Lin Juen-Kuen
Peng Peng-Yih
Eley Timothy V.
Nguyen Dung Van
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
United Microelectronics Corp.
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