Wafer processing architecture including load locks

Details Wafer processing architecture including load locks Wafer processing architecture including load locks

1999-09-30

2002-04-23

Dang, Thi (Department: 1763)

Coating apparatus

Gas or vapor deposition

Multizone chamber

C118S724000, C156S345420

Reexamination Certificate

active

06375746

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention generally relates to semiconductor device manufacturing equipment.
2. Description of the Related Art
In the semiconductor industry, special wafer processing systems are used to convert bare semiconductor wafers into working devices. Typically, the wafer processing system has a reactor for processing wafers and a wafer handling system for moving wafers to and from the reactor. The reactor or process module is where wafer processing such as film deposition or etching occurs. The wafer handling system is mechanically coupled to the reactor and has a loading station on which wafers can be loaded from the factory floor. Once loaded onto the loading station, wafers are transferred to and from reactors using mechanical manipulators such as robots.
FIG. 1
shows a wafer processing system in the prior art. Wafer processing system
1
includes a reactor
2
and a wafer handler
3
. Wafer handler
3
further includes a user interface
4
, a loading station
5
, load locks
7
A and
7
B, and a transfer chamber
6
. User interface
4
has a display terminal for entering and reading information and a computer system (not shown) for controlling the operation of wafer processing system
1
.
A typical wafer handling sequence for wafer processing system
1
is as follows. Wafer cassette or carrier
10
is moved from loading station
5
into load lock
7
A by an indexer robot
28
A. Pressure within load lock
7
A is decreased using a vacuum pump (not shown). When the desired pressure differential between transfer chamber
6
and load lock
7
A is reached, load lock
7
A is opened to transfer chamber
6
and a wafer
11
is picked up from wafer carrier
10
and then transferred to reactor
2
by vacuum robot
9
. Wafer
11
is then processed inside reactor
2
. When processing is completed, wafer
11
is moved from reactor
2
and placed into a cooling station
8
by vacuum robot
9
. Cooling of wafer
11
is required because wafer processing temperatures can reach as high as 650° C. whereas wafer carrier
10
typically has a limitation of 70° C., beyond which deformation begins. When cooled, vacuum robot
9
transfers wafer
11
from cooling station
8
and into its original wafer carrier (carrier
10
) inside load lock
7
A. The other wafers in carrier
10
are processed in a similar manner. After all wafers originally contained in wafer carrier
10
have been processed, load lock
7
A is vented to atmospheric pressure, after which cassette
10
is transferred from load lock
7
A back to loading station
5
.
Load locks
7
A and
7
B function as transition chambers between transfer chamber
6
, which is maintained under vacuum, and loading station
5
, which is at atmospheric pressure. Load locks
7
A and
7
B are referred to as batch load locks because they accommodate multiple wafers, typically in a carrier, at a time. Because load locks
7
A and
7
B do not have an integral cooling unit, cooling station
8
must be provided within transfer chamber
6
. Providing cooling station
8
outside load lock
7
A significantly cuts down on the number of wafers that can be processed within a given amount of time because vacuum robot
9
has to move a processed wafer to cooling station
8
before moving the processed wafer into load lock
7
A.
In a batch load lock, pump down and vent operations take time because batch load locks must have a volume large enough to accommodate multiple wafers. The long pump down and vent times of the batch load lock adversely affect the wafer processing system's throughput or the number of wafers that the system can process within a given amount of time. This throughput problem is compounded when the system is used with partially filled wafer carriers, as is the case in many factories, specially those involved in custom device fabrication.
The large volume and large internal surface area of batch load locks raise micro-contamination problems. The walls of a load lock adsorb moisture every time the load lock is vented and exposed to atmospheric pressure. This moisture outgasses at operating pressures, creating partial pressure build-up of gases such as, for example, H
2
O, N
2
, or O
2
in the transfer chamber and the reactor. The larger the load lock, the greater the chance of micro-contaminants entering the transfer chamber and reactor. Further, the load lock must be pumped down to a pressure slightly lower than that of the transfer chamber to prevent micro-contaminants from getting into the transfer chamber. Obtaining this lower pressure takes additional time in a batch load lock because of its large volume.
In order to alleviate the throughput problems associated with batch load locks, some batch load lock systems transfer multiple wafers at a time from the loading station to the load locks. A problem with this approach is that moving multiple wafers at a time increases the chance of wafer handling errors or breakage. Further, all ancillary wafer operations such as wafer alignment, wafer ID reading, and metrology must be performed inside the load lock or transfer chamber under vacuum. This leads to increased complexity and implementation cost.
U.S. Pat. No. 5,512,320 to Turner et. al., incorporated herein by reference, discloses a batch load lock with an integral metallic carrier for cooling processed wafers. In Turner, as in any batch load locks, an elevator is required for incrementally raising each shelf of the metallic carrier to the same level as the vacuum robot or an external atmospheric robot. Because the elevator must be precisely controlled for proper wafer exchange with the vacuum and atmospheric robots, the elevator is essentially a robot which not only complicates but also raises the cost of the wafer processing system. Further, Turner suffers from the same problems associated with batch load locks in the prior art.
Thus, there is a clear need for a wafer processing system that has better throughput, has better contamination control, and is less expensive to implement than those in the prior art.
SUMMARY OF THE INVENTION
The invention provides for a modular wafer processing system. In one embodiment, the modular wafer processing system includes a single-wafer load lock having a cooling unit within. Having a cooling unit within the single-wafer load lock provides for increased system throughput because processed wafers can be directly transferred from the reactor and into the load lock. Throughput is further increased by reducing the volume of the single-wafer load lock to allow for fast pump down and vent times.
In another embodiment of the invention, the modular wafer processing system includes a load lock having the capability to heat and cool a wafer within the load lock. In processes requiring the wafer to be pre-heated before moving the wafer into a reactor, the capability to heat the wafer in the load lock increases throughput because the wafer can be directly moved from the load lock and into the reactor without having to move the wafer into an intermediate pre-heating station. Having a cooling unit within the load lock further increases throughput because processed wafers can be directly transferred from the reactor and into the load lock.


REFERENCES:
patent: 5135608 (1992-08-01), Okutani
patent: 5186594 (1993-02-01), Toshima et al.
patent: 5314541 (1994-05-01), Saito et al.
patent: 5512320 (1996-04-01), Turner et al.
patent: 5855681 (1999-01-01), Maydan et al.
patent: 5882165 (1999-03-01), Maydan et al.
patent: 5951770 (1999-09-01), Perlov et al.
patent: 6048154 (2000-04-01), Wytman
patent: 0834907 (1998-04-01), None
patent: WO99/03133 (1999-01-01), None

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