Wafer out-of-pocket detection method

Details Wafer out-of-pocket detection method Wafer out-of-pocket detection method

2000-06-06

2001-08-14

Lee, John R. (Department: 2878)

Radiant energy

Photocells; circuits and apparatus

Photocell controls its own optical systems

C250S222100, C250S559290

Reexamination Certificate

active

06274878

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates generally to semiconductor processing and particularly to a tool for detecting the position of a wafer in a semiconductor processing chamber.
BACKGROUND OF THE INVENTION
Deposition of a film on the surface of a semiconductor wafer is a common step in semiconductor processing. The process of depositing layers on a semiconductor wafer (or substrate) usually involves placing the substrate within a processing chamber and holding the wafer within a stream of a reactant gas flowing across the surface of a wafer. Usually, heat is applied to drive the chemical reaction of the gases in the chamber and to heat the surface of the wafer on which the film is deposited. The processing chamber is typically heated by external lamps which pass infra-red radiation into the processing chamber through a quartz window that is transparent to the infra-red radiation.
Referring now to
FIG. 1
, there is shown a multiple-chamber integrated process system
100
including an enclosed main frame or housing
102
having sidewalls that define an enclosed vacuum transfer chamber
104
.
A number of individual processing chambers
106
a-f
are mounted one each on an associated sidewall of the transfer chamber
104
. Two load lock cassette elevators
108
a
and
108
b
are adapted for vertically stacking a multiplicity of cassettes which in turn hold wafers
110
horizontally. The load lock cassette elevator assemblies
108
a
and
108
b
selectively position each cassette directly opposite and aligned with a transfer chamber entrance slit or opening
112
a
and
112
b
, respectively. Each cassette holds multiple wafers. Wafers
110
are held within the cassette by a set of support structures
111
having a diameter that is slightly larger than the diameter of the wafers being housed.
Processing chambers
106
a-f
and the associated main frame side walls also have communicating slits
114
a-f
, respectively, which are similar to the load lock entrance slits
112
a
and
112
b
. Doors or slit valves (not shown) are provided for sealing the access slits.
A robotic wafer transfer system
120
is mounted within transfer chamber
104
for transferring wafers
110
between load locks
108
a
and
108
b
and the individual processing chambers
106
a-f
. Robot assembly
120
includes a blade
122
and a driver (not shown) that imparts both rotational and reciprocating movement to blade
122
for affecting the desired cassette-to-chamber, chamber-to-chamber and chamber-to-cassette wafer transfer. The reciprocating movement (straight line extension and retraction) is indicated by arrow
130
, while the pivotal or rotational movement is indicated by arrow
140
.
FIG. 2
illustrates a cross-sectional view of an exemplary semiconductor processing chamber, such as processing chamber
106
a
depicted in FIG.
1
. Processing chamber
106
a
includes an inner chamber
202
for facilitating the flow of a process gas over the surface of a wafer. The housing includes a baseplate
204
having a gas inlet port
206
and a gas exhaust port
208
. An upper clamp ring
210
and a lower clamp ring
212
act to hold a quartz cover member
214
and a quartz lower member
216
in place, respectively. Process gas is injected into chamber
202
through gas inlet port
206
which is connected to a gas source. Residual process gas and various waste products are continuously removed from the interior of chamber
202
through exhaust port
208
. Arrows F indicate the typical flow path of a reactant gas passing through the chamber.
Wafers are placed into and removed from chamber
202
by the robotic wafer handling system
120
through an opening
203
formed in the side wall of the chamber.
A susceptor
224
holds the wafer in position during the semiconductor layer deposition process. As shown in
FIG. 2
, susceptor
224
includes a pocket
225
that is defined by at least one annular or planar bottom surface
226
and a cylindrical side wall
227
. The depth of pocket
225
is generally chosen so that the top surface of the wafer being processed is approximately level with the top surface of the susceptor. Susceptor support
229
is coupled to susceptor
224
for rotating the wafer during the semiconductor fabrication process. Susceptor
224
also includes a plurality of through holes
240
for receiving at least three pins
242
. Loading position pins
242
are attached to a support shaft
244
that provides vertical movement to raise and lower pins
242
. Pins
242
are used to raise a wafer above susceptor surface
226
while the wafer is being loaded or unloaded into the chamber. Raising of the wafer prevents the robot blade from scraping or otherwise damaging the susceptor surface during the wafer loading or unloading procedure.
Heating lamps
228
and
230
provide infra-red radiant heat into the chamber through window portion
214
and quartz lower member
216
which are transparent to infra-red radiation.
In deposition processes, it is desirable to maximize wafer throughput while depositing film layers that have uniform thickness. With the increasing miniaturization of electronic circuits, there is a need to more accurately control the thickness of the deposition layers during semiconductor wafer processing. Among other requirements, in order to obtain uniform deposition layer thicknesses, it is important that the angular orientation of the wafer with that of the gas flow be essentially equal at all points along the wafer surface during the deposition process.
As discussed above, a robotic wafer handling system is often used to position a wafer within the pocket of a semiconductor processing chamber susceptor. As shown in
FIGS. 3A and 3B
, in some instances a wafer
300
is improperly placed on the susceptor
302
. As a result, a portion of the wafer will reside outside of the susceptor pocket
304
causing the wafer to be out of alignment with the reactant gas flow stream. Currently, there is no method for detecting whether a wafer has been properly placed within the susceptor pocket.
The slant or tilt of the out-of-pocket wafer will result in an uneven film deposition across the surface of the wafer and a non-uniform resistivity. If the film deposition thickness or resistivity of a wafer is found to be non-uniform during post-process testing, that wafer and every wafer residing within the same cassette is discarded. This adversely affects throughput and results in higher processing costs.
Therefore, what is needed is a method and an apparatus for accurately determining the angular position of a wafer within a semiconductor processing chamber.
SUMMARY OF THE INVENTION
An apparatus and method for monitoring the inclination of a wafer residing within a pocket of a semiconductor processing chamber susceptor is disclosed. The apparatus of the present invention includes a light beam transmitter that is positioned to direct a light beam, such as a laser beam, onto the top surface of a wafer that has been positioned within a susceptor pocket. A light beam receiver is positioned to detect the light beam after it has been reflected off the surface of the wafer. The light beam receiver emits an output signal to a visual or audible indicator that indicates whether or not the wafer is properly positioned within the pocket of the susceptor.


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