Data processing: generic control systems or specific application – Specific application – apparatus or process – Product assembly or manufacturing
Reexamination Certificate
2000-03-10
2003-02-11
Picard, Leo (Department: 2125)
Data processing: generic control systems or specific application
Specific application, apparatus or process
Product assembly or manufacturing
C700S100000, C700S112000, C700S213000
Reexamination Certificate
active
06519498
ABSTRACT:
BACKGROUND OF THE DISCLOSURE
1. Field of the Invention
The present invention relates to a multiple chamber wafer processing system and, more particularly, to a method and apparatus for managing scheduling in a multiple cluster tool.
2. Description of the Background Art
Semiconductor wafers are processed to produce integrated circuits using a plurality of sequential process steps. These steps are performed using a plurality of process chambers. An assemblage of process chambers served by a wafer transport robot is known as a multiple chamber semiconductor wafer processing tool or cluster tool. In a single cluster tool, wafers are moved from one chamber to the next by means of a transfer mechanism (one or more robots). This wafer movement is known as a wafer transfer. The transfer mechanism can only move wafers among chambers that are within the transfer mechanism's “space”. The set of chambers that are reachable by a given transfer mechanism are referred to as the transfer space or the robot space. A cluster tool may be comprised of one or more transfer spaces, i.e., one or more transfer mechanisms in different spaces having access to several chambers in each of the spaces.
When a wafer processing system is comprised of two or more transfer spaces, the system is referred to as a multiple cluster tool or a multi-cluster tool. In a multi-cluster tool, wafers visit chambers from different transfer spaces and thus they are moved both within transfer spaces as well as between different (adjacent) transfer spaces. Wafers may be transferred from one space to another via a common chamber that is accessible from adjacent transfer spaces. The chamber that forms a connection between adjacent transfer spaces is known as a pass-through chamber. The pass-through chamber may also perform wafer processing.
Suppose that a pass-through chamber A connects transfer spaces R
1
and R
2
. If chamber A is the only pass-through chamber, then chamber A must facilitate a “double-pass”, i.e., chamber A is used to transfer the wafer in both directions between transfer spaces R
1
and R
2
. If there is at least one more pass-through chamber, then chamber A may be either single-pass (one direction) or double-pass (bi-directional) type of chamber. Furthermore, a pass-through chamber may have either single or multiple capacity (i.e., the chamber could hold one or more wafers).
Pass-through chambers may severely limit a tool's throughput in that the pass-through chamber may form a bottleneck with respect to wafers being transferred from one transfer space to another. An example of a system that has limited throughput is a multi-cluster tool system that has only a single capacity pass-through chamber. Such a system requires that one transfer mechanism in one of the transfer spaces wait for access to the transfer chamber while the other transfer mechanism accesses the transfer chamber. Another example of a system that has limited throughput because of the transfer chamber is a system where the pass-through chambers have long processing times and/or frequent cleaning processes. Thus, to avoid making the pass-through chamber a bottleneck and to achieve optimal throughput in a multi-cluster tool, management of the pass-through chambers (i.e., which wafer enters/leaves and when) is considered when designing scheduling logic for multi-cluster tools.
As an illustration of a multi-cluster tool,
FIG. 1
depicts a schematic diagram of an illustrative multiple chamber semiconductor wafer processing tool known as the Endura® System manufactured by Applied Materials, Inc. of Santa Clara, Calif. This multi-cluster tool
100
comprises, for example, a preclean chamber
114
, a buffer chamber
116
(a first transfer space R
1
), a wafer orienter/degas chamber
118
, a cooldown chamber
102
, four process chambers
104
,
106
,
108
,
110
, a transfer chamber
112
(a second transfer space R
2
), and a pair of loadlock chambers
120
and
122
. The buffer chamber
116
is centrally located with respect to the loadlock chambers
120
and
122
, the wafer orienter/degas chamber
118
, the preclean chamber
114
and the cooldown chamber
102
. To effectuate wafer transfer amongst these chambers, the buffer chamber
116
contains a first robotic wafer transfer mechanism
124
. A collection of wafers
128
is typically carried from a previous location (storage or other tools) to the system in a plastic transport cassette
126
that is placed within one of the loadlock chambers
120
or
122
. The first robotic wafer transport mechanism
124
transports wafers from collection
128
, one at a time, from the cassette
126
to a designated chamber of the three chambers
118
,
102
, or
114
. Typically, a given wafer is first placed in the wafer orienter/degas chamber
118
, then moved to the preclean chamber
114
. The cooldown chamber
102
is generally not used until after the wafer is processed within the process chambers
104
,
106
,
108
,
110
. Individual wafers are carried upon a wafer transport blade
130
that is located at the distal end of the first robotic mechanism
124
. The transport operation is controlled by a sequencer
136
.
The transfer chamber
112
(transfer space R
2
) is surrounded by and has access to the four process chambers
104
,
106
,
108
and
110
as well as the preclean chamber
114
and the cooldown chamber
102
. The preclean chamber
114
and the cool down chamber
102
form the pass-through chambers that couple one transfer space R
1
to another transfer space R
2
. The pass-through chambers are described here as uni-directional in that the preclean chamber
114
is used to move wafers into the transfer chamber
112
and the cooldown chamber
102
is used to move wafers out of the transfer chamber
112
. However, these transfer chambers can be bi-directional.
To effectuate transport of a wafer amongst the chambers, the transfer chamber
112
contains a second robotic transport mechanism
132
. The mechanism
132
has a wafer transport blade
134
attached to its distal end for carrying the individual wafers. In operation, the wafer transport blade
134
of the second transport mechanism
132
retrieves a wafer from the preclean chamber
114
and carries that wafer to a first stage of processing, for example, a physical vapor deposition (PVD) process within chamber
104
. Once the wafer is processed (e.g., the PVD process deposits material upon the wafer), the wafer can then be moved to a subsequent stage of processing.
Once required processing is completed within the process chambers
104
,
106
,
108
, and
110
, the transport mechanism
132
removes the wafer from the last process chamber and transports the wafer to the cooldown chamber
102
. The wafer is then removed from the cooldown chamber
102
using the first transport mechanism
124
within the buffer chamber
116
. Lastly, the wafer is placed in the transport cassette
126
within the loadlock chamber
122
.
To ensure an optimal schedule that facilitates a high throughput, a priority-based scheduling routine may be executed by the sequencer
136
. The routine prioritizes the chambers within the cluster tool and computes the optimal schedule for movement of each wafer such that the wafer is fully processed in a minimal amount of time. Empirical testing to determine an optimal schedule is both expensive and time consuming. Present schedule development consists of having to “hard code” each possible scheduling algorithm into the scheduler. Hard coding requires each scheduling algorithm to be individually considered and tested. The number of priority based routine possibilities that can be used to process a given wafer is staggering. For example, for a 5-stage cluster tool there would be at least 5!=120 different scheduling routines (each routine would have to be independently designed, developed and tested). This number of scheduling routines is for a single cluster tool and does not consider the impact of pass through chambers that connect the individual cluster tools.
Therefore, a need exists in the art for a
Jevtic Dusan
Pool Mark
Sunkara Raja
Applied Materials Inc.
Jarrett Ryan
Moser Patterson & Sheridan LLP
Picard Leo
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