Data processing: generic control systems or specific application – Specific application – apparatus or process – Product assembly or manufacturing
Reexamination Certificate
2001-06-26
2004-01-27
Gandhi, Jayprakash N. (Department: 2125)
Data processing: generic control systems or specific application
Specific application, apparatus or process
Product assembly or manufacturing
C700S095000, C700S117000, C438S800000, C414S935000, C414S940000
Reexamination Certificate
active
06684123
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to a multiple chamber semiconductor wafer processing system and, more specifically, the present invention relates to a method and apparatus for accessing a multiple chamber semiconductor wafer processing system.
2. Description of the Related Art
In integrated circuit (IC) manufacturing systems that handle 200 mm wafers, the interface to the factory is a 25-wafer load-lock. The load-lock forms an entry and exit point for the IC manufacturing system. In use, a cassette carrying 25 wafers is placed into a load-lock and the air in the load-lock is removed to form a vacuum in the load-lock. The wafer cassette is vertically positioned in the load-lock to align a particular wafer with a wafer transport mechanism, e.g., a wafer transport robot.
The time required to produce a vacuum in the load-lock is referred to herein as T
pump
. After processing within the IC manufacturing system, the processed wafer is returned to the cassette. When all the wafers have been processed and returned, the air in the load-lock is then let into the load-lock at a controlled rate in what is referred to as a vent operation. The time required to perform a vent operation is referred to herein as T
vent
. Once venting is complete, the cassette is removed from the load-lock. The maximum achievable load-lock throughput is represented as:
S
LL
=
2
K
T
pump
+
T
vent
+
T
load
+
T
unload
where:
K is the maximum number of wafers in the load-lock;
T
pump
is the time required to evacuate the load-lock;
T
vent
is the time required to fill the load-lock with air;
T
load
is the time required to load a cassette into the load-lock; and
T
unload
is the time required to unload a cassette from the load-lock.
Load-locks are generally double-buffered by using a pair of parallel load-locks that feed wafers to a wafer processing system. As such, loading, pumping, venting, and unloading of one cassette is overlapped with processing of wafers from another cassette. Without double-buffering, no overlap is possible and the time required to pump and vent a load-lock can be almost as long as the wafer processing time.
FIG. 1
depicts a semiconductor wafer processing system or cluster tool
100
for 300 mm wafers comprising a plurality of process chambers
110
1
,
110
2
,
110
3
, and a transfer chamber
112
. The cluster tool
100
is coupled to a factory interface
104
. The FI
104
comprises a pair of single wafer load-locks (SWLLs)
102
A and
102
B, FI transfer space
105
containing a wafer transport agent
106
, and at least one load port (two are depicted as ports
108
A and
108
B). The FI
104
may optionally comprise a wafer orientor, a pass-through slot, one or more cool down positions, a metrology station, or defect control station.
A tool transfer agent
114
(commonly referred to as a robot) accesses the chambers
110
1
,
110
2
,
110
3
and the load-locks
102
A,
102
B to move wafers amongst the chambers and load-locks. The SWLL
102
A and
102
B are used as the entry and exit points to the tool
100
. The load-locks
102
A and
102
B each retain only one wafer at a time during the pump/vent cycle.
The FI load ports
108
A and
108
B are supplied with wafer cassettes that hold up to 25 wafers each. When a transfer agent
106
having a single wafer transport blade is used in either the tool
100
or in the FI
104
, the SWLLs have two slots each. Using two slots enables a single blade robot (SBR) to wait for an SWLL to either pump or vent while being pre-positioned in front of the SWLL with a wafer on its blade. The robot then puts the wafer in an empty slot first before taking a wafer out of the SWLL. With two slots, the load and unload times are substantially decreased. However, the load-lock volume is increased to accommodate the second slot which increases pump and vent times.
When dual blade robots are used in both the tool
100
and the FI
104
, then only a single slot SWLL is used and load-lock volume is reduced. The second blade serves as a buffer that accepts a wafer from the SWLL before placing a new wafer from the other blade of the robot into the SWLL.
Wafers from the FI load ports
108
A or
108
B are directed toward either SWLL
102
A or
102
B depending upon which SWLL is available to be loaded. If both SWLLs are available, the wafer enters the nearest SWLL to the current position of the transfer agent
106
. Wafers leaving the transfer chamber
112
of the tool
100
are directed into either SWLL
102
A or
102
B depending upon which SWLL is available. If both SWLL are available, the wafer enters the one nearest the present position of the tool transfer agent
114
. The FI
104
returns the wafer to the source cassette into its original position, i.e., preserving slot integrity. Wafers that enter the transfer chamber
112
through SWLL
102
A are not restricted to exiting the transfer chamber
112
through SWLL
102
A. Similarly, wafers from one cassette can enter either SWLL
102
A or
102
B depending on the load-lock availability. In other words, unless explicitly restricted by the system controller software, wafers from one cassette are not restricted from entering and leaving the tool via a particular load-lock.
The fixed nature of the number of slots to either one or two can result in substantial transfer delays for wafers entering and leaving a cluster tool. Therefore, there is a need in the art for a method and apparatus to improve wafer throughput in semiconductor wafer processing systems that use load-locks.
SUMMARY OF THE INVENTION
The present invention is a factory interface for a semiconductor wafer processing cluster tool having a K-wafer load-lock (KWLL) to facilitate accessing a multiple chamber semiconductor wafer processing system. The KWLL comprises a variable number of K+1 wafer slots assigned as inbound and outbound slots. Inbound slots are used to send up to K+1 wafers into the cluster tool and the same physical slots, denoted as outbound slots, are used for receiving up to K+1 wafers from the cluster tool. The K+1 slots are in the same volume that has to be pumped for wafers to enter the tool and vented for wafers to leave the tool. These K+1 slots accommodate up to K wafers when accessed by a single blade robot from the tool or the factory interface, and up to K+1 wafers when the tool and factory interface are equipped with dual blade robots. Various KWLL loading methods can be selected to optimize the throughput of a wafer processing system using the KWLL. Such methods illustratively include a wafer packing method, a reactive method and a gamma tolerant method.
REFERENCES:
patent: 5928389 (1999-07-01), Jevtic
patent: 6157866 (2000-12-01), Conboy et al.
patent: 6340405 (2002-01-01), Park
patent: 6382895 (2002-05-01), Konishi et al.
Copy of International Search Report dated May 30, 2003 for corresponding PCT application, PCT/US02/20090.
Jevtic Dusan
Sunkara Raja
Applied Materials Inc.
Gandhi Jayprakash N.
Moser Patterson & Sheridan
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