Data processing: measuring – calibrating – or testing – Calibration or correction system – Position measurement
Reexamination Certificate
2000-03-16
2003-09-30
Hoff, Marc S. (Department: 2857)
Data processing: measuring, calibrating, or testing
Calibration or correction system
Position measurement
C702S035000, C702S149000, C702S150000, C702S152000
Reexamination Certificate
active
06629053
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to transferring wafers among modules of semiconductor processing equipment, and more particularly to dynamic alignment of each wafer with a support blade that carries the wafer, wherein dynamic alignment apparatus and methods define, as a statement of an optimization program, the determination of an approximate value of an offset of the wafer with respect to a desired location of the wafer in a module.
2. Description of the Related Art
In the manufacture of semiconductor devices, process chambers are interfaced to permit transfer of wafers or substrates, for example, between the interfaced chambers. Such transfer is via transport modules that move the wafers, for example, through slots or ports that are provided in the adjacent walls of the interfaced chambers. Transport modules are generally used in conjunction with a variety of wafer processing modules, which may include semiconductor etching systems, material deposition systems, and flat panel display etching systems. Due to the growing demands for cleanliness and high processing precision, there has been a growing need to reduce the amount of human interaction during and between processing steps. This need has been partially met with the implementation of vacuum transport modules which operate as an intermediate wafer handling apparatus (typically maintained at a reduced pressure, e.g., vacuum conditions). By way of example, a vacuum transport module may be physically located between one or more clean room storage facilities where wafers are stored, and multiple wafer processing modules where the wafers are actually processed, e.g., etched or have deposition performed thereon. In this manner, when a wafer is required for processing, a robot arm located within the transport module may be employed to retrieve a selected wafer from storage and place it into one of the multiple processing modules.
As is well known to those skilled in the art, the arrangement of transport modules to “transport” wafers among multiple storage facilities and processing modules is frequently referred to as a “cluster tool architecture” system.
FIG. 1
depicts a typical semiconductor process cluster architecture
100
illustrating the various chambers that interface with a vacuum transport module
106
. Vacuum transport module
106
is shown coupled to three processing modules
108
a
-
108
c
which may be individually optimized to perform various fabrication processes. By way of example, processing modules
108
a
-
108
c
may be implemented to perform transformer coupled plasma (TCP) substrate etching, layer depositions, and/or sputtering.
Connected to vacuum transport module
106
is a load lock
104
that may be implemented to introduce wafers into vacuum transport module
106
. Load lock
104
may be coupled to a clean room
102
where wafers are stored. In addition to being a retrieving and serving mechanism, load lock
104
also serves as a pressure-varying interface between vacuum transport module
106
and clean room
102
. Therefore, vacuum transport module
106
may be kept at a constant pressure (e.g., vacuum), while clean room
102
is kept at atmospheric pressure.
Consistent with the growing demands for cleanliness and high processing precision, the amount of human interaction during and between processing steps has been reduced by the use of robots for wafer transfer. Such transfer may be from the clean room
102
to the load lock
104
, or from the load lock
104
to the vacuum transport module
106
, or from the vacuum transport module
106
to a processing module
108
a
, for example. While such robots substantially reduce the amount of human contact with each wafer, problems have been experienced in the use of robots for wafer transfer. For example, in a clean room a blade of a robot may be used to pick a wafer from a cassette and place it on fingers provided in the load lock
104
. However, the center of the wafer may not be accurately positioned relative to the fingers. As a result, when the blade of the robot of the vacuum transport module
106
picks the wafer from the fingers of the load lock
104
, the center of the wafer may not be properly located, or aligned, relative to the center of the blade. This improper wafer center-blade center alignment, also referred to as “wafer-blade misalignment” or simply “wafer misalignment,” continues as the robot performs an “extend” operation, by which the blade (and the wafer carried by the blade) are moved through a slot in the processing module and by which the wafer is placed on pins in the processing module
108
a
, for example.
Even if there was proper original wafer-blade alignment when the wafer was initially placed in the exemplary processing module
108
a
, and even though the wafer may have thus been properly aligned during processing in the exemplary processing module
108
a
, the proper alignment may be interfered with. For example, electrostatic chucks generally used in the exemplary processing modules
108
a
may have a residual electrostatic field that is not completely discharged after completion of the processing. In this situation, the processed wafer may suddenly become detached from the chuck. As a result, the wafer may become improperly positioned with respect to the robot blade that picks the processed wafer off the chuck. Thus, when the blade of the robot of the vacuum transport module
106
picks the processed wafer off the chuck, the center of the wafer may not be properly located, or aligned, relative to the center of the blade. This wafer misalignment may continue as the robot performs a “retract” operation, by which the blade (and the wafer carried by the blade) are moved through the slot in the processing module
108
a
. Such wafer misalignment may also continue during a subsequent extend operation by which the wafer is placed in another one of the processing modules
108
b
, or in the load lock
104
.
The above-described wafer misalignment before an extend operation (which may continue to the time at which the wafer is placed on pins in the processing module
108
a
), and the above-described wafer misalignment before a retract operation (which may continue during a subsequent extend operation by which the wafer is placed in another one of the processing modules
108
b
, or in the load lock
104
) results in placement of the wafer at a location that is offset from a desired location on the pins of the module
108
a
or module
108
b
or in the load lock
104
.
Wafer misalignment, and resulting offset, are sources of wafer processing errors, and are of course to be avoided. It is also clear that the amount of time the robots take to transfer a wafer among the modules (the “wafer transfer time period”) is an amount of time that is not available for performing processing on the wafer, i.e., the wafer transfer time period is wasted time. Thus, there is an unfilled need to both monitor the amount of such wafer misalignment, and to perform such monitoring without increasing the wafer transfer time period. One aspect of monitoring the amount of wafer misalignment, or of determining the amount of such wafer offset, is the period of time required to compute the offset (the “offset computation time period”). If increases in the wafer transfer time period are to be avoided yet the amount of such wafer offset is to be determined to a sufficient degree of offset accuracy before the wafer is placed relative to the desired location, the offset computation time period must be no more than a portion of the wafer transfer time period.
A problem complicating such monitoring of wafer misalignment is that a wafer may be transferred from (or to) the one vacuum transport module
106
to (or from) as many as six, for example, processing modules, e.g.,
108
a
. In the past, attempts to determine whether a wafer is properly aligned on the blade of a robot have included use of many sensors between adjacent modules. Sensors on opposite sides of a wafer transfer path have been located symmetrica
Hoff Marc S.
Lam Research Corporation
Martine & Penilla LLP
Suarez Felix
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