Valve/sensor assemblies

Details Valve/sensor assemblies Valve/sensor assemblies

2001-06-30

2003-04-22

Tran, Khoi H. (Department: 3651)

Data processing: generic control systems or specific application

Specific application, apparatus or process

Robot control

C700S218000, C700S213000, C414S935000, C414S936000, C414S939000

Reexamination Certificate

active

06553280

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to detection technology, and more specifically to detection technology that is used to detect a semiconductor wafer.
BACKGROUND OF THE INVENTION
Semiconductor wafers are processed within automated fabrication tools comprising a plurality of chambers.
FIG. 1A
is a schematic top plan view, in pertinent part, of an automated semiconductor device fabrication tool
11
. The exemplary fabrication tool
11
of
FIG. 1A
comprises a first transfer chamber
13
and a second transfer chamber
15
. A first and a second wafer handler
17
,
19
, each having a blade (not shown) that may support a wafer, are housed in the first transfer chamber
13
and the second transfer chamber
15
, respectively. The first transfer chamber
13
and the second transfer chamber
15
are both monolithic and have various chambers coupled thereto.
A pair of loadlocks
21
,
23
and a pair of pass-through chambers
25
,
27
are coupled to the first transfer chamber
13
. Other chambers such as degassing or oxide-etch chambers (shown in phantom) also may be coupled to the first transfer chamber
13
. The pass-through chambers
25
,
27
and a plurality of processing chambers
29
,
31
,
33
, and
35
, which are configured to perform various semiconductor device fabrication processes (e.g., chemical vapor deposition, sputter deposition, etc.), are coupled to the second transfer chamber
15
. A controller
36
controls wafer transfer and processing within the fabrication tool
11
.
Typically the environment of each chamber must be selectively isolated from the environments of neighboring chambers to prevent cross contamination, and to enable the various chambers to be maintained at pressures that differ according to the process to be performed therein. To achieve such selective isolation, each chamber is provided with a slit (not shown) through which one of the wafer handlers
17
,
19
may extend to transport wafers to and from the chamber. The slit of each chamber is selectively sealed with a door assembly
37
(typically referred to as a slit valve for vacuum applications, and as a gate valve for non-vacuum applications).
As the wafer handlers
17
,
19
transport a wafer through slits and through various chambers, the wafer must be accurately positioned on the blade of each wafer handler
17
,
19
to avoid breaking or damaging the wafer (by the wafer falling or striking a chamber component), to ensure proper placement of the wafer on a wafer pedestal so as to prevent deposition of material on the wafer pedestal during processing and to ensure complete coverage during deposition of a material layer on the wafer, etc. Accordingly, to ensure accurate wafer positioning (so as to avoid wafer damage/breakage or deposition on a wafer pedestal, so as to ensure complete material layer coverage on a wafer, etc.), numerous wafer detection devices (e.g., sensor systems) exist in fabrication tools to determine a wafer's position. Such sensor systems are typically located in the transfer chambers
13
,
15
, although sensor systems may be located in other chambers as well. A fabrication tool may employ multiple sensor systems.
Two main types of sensor systems are conventionally used within fabrication tools. Both systems employ sensors to detect a wafer's position as the wafer enters and/or leaves a chamber. In the first system, a sensor is mounted to the outside of a processing chamber and monitors wafer position via a quartz window formed in the processing chamber. That is, a wafer is observed through the quartz window as the wafer enters and exits the processing chamber. In the second system, a sensor is mounted within a transfer chamber and monitors a wafer's position as the wafer enters and exits the transfer chamber. The two conventional sensor systems may be used individually or jointly in the fabrication tool
11
.
Both types of sensor systems have disadvantages. With regard to the first sensor system, material may deposit on the quartz window during processing and affect sensor resolution/accuracy. With regard to the second system, sensor mounting locations typically must be machined within the transfer chamber (e.g., a potentially difficult and time consuming process).
FIG. 1B
is a partially exploded perspective view of the transfer chamber
15
of
FIG. 1A
that is useful in explaining another conventional sensor system. The transfer chamber
13
of
FIG. 1A
may be similarly configured.
As stated, in one conventional sensor system, a sensor may be mounted within a transfer chamber and monitor a wafer's position as the wafer enters and exits the transfer chamber. For example, in
FIG. 1B
, a plurality of light transmitters
39
a-b
(shown in phantom) are mounted to a lid
41
of the transfer chamber
15
(e.g., to one or more quartz windows or viewports not shown) and generate light beams
44
a-b
(shown in phantom) that are directed toward a bottom
43
of the transfer chamber
15
. A plurality of receivers
45
a-b
(e.g., photodetectors) are mounted to the bottom
43
of the transfer chamber
15
(e.g., the bottom
43
is machined to accept the receivers
45
a-b
), and are positioned to receive the light beams
44
a-b
generated by the transmitters
39
a-b.
By monitoring when the light beams
44
a-b
are broken by a wafer W positioned on a blade B (shown in phantom) of the wafer handler
19
(e.g., as the wafer W is positioned for entry through a slit
47
of the transfer chamber
15
and/or as the wafer W travels through the slit
47
of the transfer chamber
15
), the position of the wafer W on the blade B may be determined by conventional techniques.
A reflection based system wherein light beams
44
a-b
are reflected off of the wafer W toward the receivers
45
a-b
also may be employed to determine wafer position (e.g., if both the transmitters
39
a-b
and the receivers
45
a-b
are mounted to either the lid
41
or the bottom
43
). In either case, machining of one or more of the lid
41
and the bottom
43
may be required.
In one conventional system termed an on-the-fly (OTF) center finder, the transmitters
39
a-b
and the receivers
45
a-b
are employed to sense the wafer W as the wafer handler
19
rotates, and to determine wafer center information based thereon. Typically three light transmitters and three receivers are employed. The three light transmitters conventionally are mounted to the bottom
43
of the transfer chamber
15
, outside the transfer chamber
15
. Holes are machined in the bottom
43
to allow the light beams from the transmitters to travel into the transfer chamber
15
. The three receivers typically are mounted to the lid
41
, outside the transfer chamber
15
. Holes are machined in the lid
41
to allow the light beams from the transmitters to travel to the receivers.
In operation, the OTF center finder monitors (via the receivers mounted to the lid
41
of the transfer chamber
15
) when light beams emitted by the transmitters mounted to the bottom
43
of the transfer chamber
15
are blocked by the wafer W (e.g., as during such time periods, no light beams are detected by the receivers mounted to the lid
41
). A corresponding “blocked” light beam signal is sent to a controller (not shown), and the controller determines a step count of a motor (not shown) that rotates the wafer handler
19
. The controller then employs an algorithm to determine the center of the wafer W in relation to the center of the wafer handler
19
. The wafer W thereby may be placed in an exact location as it travels through the slit
47
.
As well as requiring machining of holes in the transfer chamber
15
, the OTF center finder suffers from other drawbacks. For example, the wafer W may move on the blade B during rotation (after passing the light beams
44
a-b
). Wafer position determinations thereby may be inaccurate.
Accordingly, an improved method and apparatus is needed for detecting wafer position during wafer transfer.
SUMMARY OF THE INVENTION
In accordance with a first aspect of the invention, a valve/sensor as

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