Classifying – separating – and assorting solids – Sifting – Special applications
Reexamination Certificate
2000-11-29
2003-07-22
Nguyen, Tuan N. (Department: 3653)
Classifying, separating, and assorting solids
Sifting
Special applications
C209S643000, C118S719000, C414S217000
Reexamination Certificate
active
06595370
ABSTRACT:
FIELD OF THE INVENTION
The present invention generally relates to a wafer transfer chamber for use in a semiconductor processing apparatus and more particularly, relates to a wafer transfer chamber for a semiconductor process machine that can be operated with reduced particle contamination by utilizing a particle filter for isolating wafers in the transfer chamber and a method for operating the wafer transfer chamber equipped with such particle filter.
BACKGROUND OF THE INVENTION
In the fabrication process for a semiconductor device, numerous processing steps must be performed on a semi-conducting substrate to form various circuits. The process may consist of as many as several hundred processing steps. Each processing step is executed in a process chamber such as an etcher, a physical vapor deposition chamber (PVD), a chemical vapor deposition chamber, etc.
In the vast majority of the processing steps, a special environment of either a high vacuum, a low vacuum, a gas plasma or other chemical environment must be provided for the process. For instance, in a PVD (or sputter) chamber, a high vacuum environment must first be provided that surrounds the wafer such that particles sputtered from a metal target can travel to and deposit on an exposed surface of the wafer. In other process chambers, such as in a plasma enhanced chemical vapor deposition chamber (PECVD), a plasma cloud of a reactant gas or gases is formed over a wafer positioned in a chamber such that deposition of a chemical substance can occur on the wafer. During any processing step, the wafer must also be kept in an extremely clean environment without the danger of being contaminated. The processing of a wafer therefore is normally conducted in a hermetically sealed environment that is completely isolated from the atmosphere. Numerous processing equipment has been provided for such purpose. One of such widely used cluster-type fabrication equipment is marketed by the Applied Materials Corporation of Santa Clara, Calif., i.e., the Centura® 5000 system.
In a typical Centura® 5000 cluster-type wafer handling system, as shown in
FIG. 1
, the basic system
10
consists of two independent vacuum cassette load-locks
12
and
14
, a capacity for one to four independent process chambers (two of such chambers
16
and
18
are shown in FIG.
1
), a capacity for two service chambers which includes an orienter
22
, and a vacuum transfer chamber
20
which is isolated from vacuum cassette load-locks
12
,
14
and process chambers
16
,
18
by slit valves (not shown). The modular design of the basic system
10
is such that up to three high-temperature deposition chambers may be installed in the system. The basic system
10
can be used for fully automatic high-throughput processing of wafers by utilizing a magnetically coupled robot. The basic system
10
is further capable of transferring wafers which are maintained at a temperature as high as 700° C. The basic system
10
also allows cross-chamber pressure equalization and through-the-wall factory installation. The vacuum pumps for the process chambers
16
,
18
, the transfer chamber
20
and the cassette load-locks
12
,
14
are mounted at a remote location to prevent mechanical vibration from affecting the operation of the system.
The vacuum cassette load-locks
12
,
14
, the process chambers
16
,
18
and the orienter
22
are bolted to the vacuum transfer chamber
20
and are self-aligned for ease of expansion or modification. Each of the process chambers
16
,
18
is capable of processing a single wafer for achieving wafer-to-wafer repeatability and control. The temperatures in the process chambers
16
,
18
are controlled in a closed-loop circuit for accuracy.
A plane view of the basic system
10
of
FIG. 1
is shown in FIG.
2
. In the basic wafer processing system
10
shown in
FIGS. 1 and 2
, the transporting of wafers between the various load-lock chambers
12
,
14
, the process chambers
16
,
18
and the orienter
22
must be carefully conducted to avoid damages from occurring to the wafers. To accomplish such task, the wafer is transported by a wafer transfer system
24
. The wafer transfer system
24
consists mainly of a robotic handler which handles all wafer transfers by a single, planar, two-axis, random access, cassette-to-cassette motion. A magnetically coupled robot permits good vacuum integrity and service without interrupting chamber integrity. The major component of the wafer transfer system
24
is a robot blade
28
. The robot blade
28
permits high-temperature transfer of wafers without incurring contamination. A non-contact optical wafer centering process is also performed during the wafer transfer process. A constant flow of filtered inert gas such as nitrogen is used in the cassette load-locks
12
,
14
and the vacuum transfer chamber
20
. A conventional robot blade
28
can be fabricated of a non-magnetic type metal such as aluminum.
One of the process chambers
16
,
18
is frequently used as an etch chamber for performing an etching process on a wafer. For instance, when he formation of alignment marks on the surface of a wafer is necessary, an etching process utilizing a corrosive gas is used for etching the marks (or holes) in the wafer surface. The surface layer etched may be a polysilicon layer. After the completion of the etching process, the robot lade
28
transfers the etched wafer from the etch chamber back into one of the load-lock chambers
12
,
14
. When such direct transfer of wafers between an etch chamber and a load-lock chamber occurs, contaminating particles are were left on the surface of the wafer is carried into the load-lock chamber. While the number of contaminating particles left on a single wafer surface does not present a serious problem to load-lock chamber, the total number of particles carried on as many as 25 wafers stored in a wafer cassette situated in the load-lock chamber produces a cumulative effect an causes a serious contaminating problem.
FIGS. 3 and 4
are lane views and cross-sectional view of a load-lock chamber that has a different design when compared to the load-lock chamber of
FIGS. 1 and 2
. The different configuration of the load-lock chamber
30
which, similar to the load-lock chamber of
FIG. 1
, is equipped with a wafer cassette elevator
32
. However, the wafer cassette elevator
32
is situated in load-lock chamber
30
which is part of the vacuum transfer chamber
20
. The operation of the load-lock chamber
30
is similar to that shown previously. For instance, a wafer is first transferred from the load-lock chambers
12
,
14
to a wafer orienter
22
(not shown in
FIG. 3
) to locate the wafer flat side an the wafer center. The wafer is then transferred to a process chamber to carry out a process such as etching, physical vapor deposition or chemical vapor deposition. After the process is completed, the wafer may be transferred to a cool-down chamber for cooling if the process is conducted at a high temperature, otherwise, the wafer is transferred back into the load-lock chamber, i.e. into the wafer cassette. After all the wafers are processed, the wafer cassette elevator is lowered to its unload position and the chamber is vented to atmospheric pressure.
The venting of the chamber is conducted similar to the pumping process for the chamber with the wafer cassette situated on a platform of the elevator positioned in a lowermost position. During the pumping process for the load-lock chamber, as shown in
FIG. 4
, the process is carried out slowly, i.e. for a time duration of about 5 min. in order to avoid the creation of turbulent flow inside the load-lock chamber. This is to avoid the loosening of contaminating particles that may have attached to the chamber interior components from falling on the wafers. Similarly, during the venting process of the chamber interior, the venting must also be carried out slowly, i.e. for a time duration of about 5 min., in order to avoid turbulent flow in the chamber interior and the further distribution of contaminating particles on the wafer surfac
Chuang Yao-Fey
Lin Mu-Tsang
Lin Yu-Lun
Nguyen Tuan N.
Taiwan Semiconductor Manufacturing Co. Ltd
Tung & Associates
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