Cassette and workpiece handler characterization tool

Details Cassette and workpiece handler characterization tool Cassette and workpiece handler characterization tool

2002-12-17

2004-08-17

Paladini, Albert W. (Department: 2125)

Data processing: generic control systems or specific application

Specific application, apparatus or process

Product assembly or manufacturing

C700S218000, C700S228000, C414S937000

Reexamination Certificate

active

06778874

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to automated workpiece handling systems, and more particularly, to methods and devices for aligning a cassette for workpieces in an automated workpiece handling system.
BACKGROUND OF THE INVENTION
In order to decrease contamination and to enhance throughput, semiconductor processing systems often utilize one or more robots to transfer semiconductor wafers, substrates and other workpieces between a number of different vacuum chambers which perform a variety of tasks. An article entitled “Dry Etching Systems: Gearing Up for Larger Wafers”, in the October, 1985 issue of Semiconductor International magazine, pages 48-60, describes a four-chamber dry etching system in which a robot housed in a pentagonal-shaped mainframe serves four plasma etching chambers and a loadlock chamber mounted on the robot housing. In order to increase throughput, it has been proposed to utilize two loadlock chambers as described in U.S. Pat. No. 5,186,718. In such a two-loadlock system, both loadlock chambers are loaded with full cassettes of unprocessed wafers.
FIG. 1
of the present application illustrates two typical loadlock chambers LLA and LLB, each having a cassette
190
therein for holding unprocessed wafers
192
to be unloaded by a robot
194
and transferred to various processing chambers
196
attached to a mainframe
198
.
The loadlock chamber LLA, for example, is a pressure-tight enclosure which is coupled to the periphery of the mainframe
198
by interlocking seals which permit the loadlock chamber to be removed and reattached to the mainframe as needed. The cassette
190
is loaded into the loadlock chamber LLA through a rear door which is closed in a pressure-tight seal. The wafers are transferred between the mainframe
198
and the loadlock chamber LLA through a passageway
199
which may be closed by a slit valve to isolate the loadlock chamber volume from the mainframe volume.
As shown in
FIG. 2
, a typical cassette
190
is supported by a platform
200
of a cassette handler system
208
which includes an elevator
210
which elevates the platform
200
and the cassette
190
. The platform
200
has a top surface which defines a base plane
220
on which the cassette
190
rests. As the cassette includes a plurality of “slots”
204
or wafer support locations, the elevator moves the cassette to sequentially position each of the slots with the slit valves to allow a robot blade to pass from the mainframe, through the slit valve, and to a location to “pick” or deposit a wafer in a wafer slot.
The slots
204
of the cassette may be initially loaded with as many as
25
or more unprocessed wafers or other workpieces before the cassette is loaded into the loadlock chamber LLA. After the loadlock access door is closed and sealed, the loadlock chamber is then pumped by a pump system down to the vacuum level of the mainframe
198
before the slit valve is opened. The robot
194
which is mounted in the mainframe
198
then unloads the wafers from the cassette one at a time, transferring each wafer in turn to the first processing chamber. The robot
194
includes a robot hand or blade
206
which is moved underneath the wafer to be unloaded. The robot
194
then “lifts” the wafer from the wafer slot supports supporting the wafers in the cassette
190
. By “lifting,” it is meant that either the robot blade
206
is elevated or the cassette
190
is lowered by the handler mechanism
208
such that the wafer is lifted off the cassette wafer supports. The wafer may then be withdrawn from the cassette
190
through the passageway and transferred to the first processing chamber.
Once a wafer has completed its processing in the first processing chamber, that wafer is transferred to the next processing chamber (or back to a cassette) and the robot
194
unloads another wafer from the cassette
190
and transfers it to the first processing chamber. When a wafer has completed all the processing steps of the wafer processing system, and two cassettes full of wafers are loaded in the loadlocks, the robot
194
returns the processed wafer back to the cassette
190
from which it came. Once all the wafers have been processed and returned to the cassette
190
, the cassette in the loadlock chamber is removed and another full cassette of unprocessed wafers is reloaded. Alternatively, a loaded cassette may be placed in one loadlock, and an empty one in the other loadlock. Wafers are thus moved from the full cassette, processed, and then loaded into the (initially) empty cassette in the other loadlock. Once the initially empty cassette is full, the initially full cassette will be empty. The full “processed” cassette is exchanged for a full cassette of unprocessed wafers, and these are then picked from the cassette, processed, and returned to the other cassette. The movements of the robot
194
and the cassette handler
208
are controlled by an operator system controller
222
(
FIG. 1
) which is often implemented with a programmed workstation.
As shown in
FIGS. 2 and 3
, the wafers are typically very closely spaced in many wafer cassettes. For example, the spacing between the upper surface of a wafer carried on a moving blade and the lower surface of an adjacent wafer in the cassette may be as small as 0.050 inches. Thus, the wafer blade must be very thin, to fit between wafers as cassettes are loaded or unloaded. As a consequence, it is often important in many processing systems for the cassette and the cassette handler
208
to be precisely aligned with respect to the robot blade and wafer to avoid accidental contact between either the robot blade or the wafer carried by the blade and the walls of the cassette or with other wafers held within the cassette.
However, typical prior methods for aligning the handler and cassette to the robot blade have generally been relatively imprecise, often relying upon subjective visual inspections of the clearances between the various surfaces. Some tools have been developed to assist the operator in making the necessary alignments. These tools have included special wafers, bars or reference “pucks” which are placed upon the robot blade and are then carefully moved into special slotted or pocketed receptacles which are positioned to represent the tolerance limits for the blade motions. However, many of these tools have a number of drawbacks. For example, some tools rely upon contact between the blade or a tool on the blade and the receptacle to indicate a condition of nonalignment. Such contact can be very detrimental to high precision mechanisms for moving the blade as well as the blade itself. Also, many such tools do not indicate the degree of alignment or nonalignment but merely a “go
o-go” indication of whether contact is likely.
In aligning the handler mechanism to the robot blade, one procedure attempts to orient the cassette to be as level as possible with respect to the robot blade. One tool that has been developed to assist in the leveling procedure has dual bubble levels in which one bubble level is placed on the blade and the other is placed on the cassette. The operator then attempts to match the level orientation of the blade to that of the cassette. In addition to being very subjective, such bubble tools have also often been difficult to see in the close confines of the cassette and handler mechanisms.
As a consequence of these and other deficiencies of the prior alignment procedures and tools, alignments have often tended to be not only imprecise but also inconsistent from application to application. These problems have frequently lead to the breakage or scratching of very expensive wafers and equipment as well as the generation of damaging particulates in the systems.
A cassette alignment tool which addresses these problems is described in copending application Ser. No.: 09/294,301, filed Apr. 19, 1999, entitled “METHOD AND APPARATUS FOR ALIGNING A CASSETTE,” assigned to the assignee of the present application and incorporated by reference in its entirety. However, further improvement is useful in

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