U.S. patent application number 09/961152 was filed with the patent office on 2002-01-24 for method and apparatus for reducing contamination in a wafer loadlock of a semiconductor wafer processing system.
Invention is credited to Davis, Matthew F., Evans, David, McAllister, Douglas R..
Application Number | 20020008099 09/961152 |
Document ID | / |
Family ID | 24150037 |
Filed Date | 2002-01-24 |
United States Patent
Application |
20020008099 |
Kind Code |
A1 |
Davis, Matthew F. ; et
al. |
January 24, 2002 |
Method and apparatus for reducing contamination in a wafer loadlock
of a semiconductor wafer processing system
Abstract
A method and apparatus for heating a loadlock to inhibit the
formation of contaminants within the loadlock. At least one heater
is attached to the walls of the loadlock to boil contaminants from
the surfaces within the loadlock. These desorbed contaminants are
exhausted from the loadlock by a vacuum pump. Alternatively, a
purge gas can be supplied to the loadlock while the loadlock is
being heated. The flow of purge gas flushes the desorbed
contaminants from the loadlock.
Inventors: |
Davis, Matthew F.;
(Brookdale, CA) ; McAllister, Douglas R.;
(Pleasanton, CA) ; Evans, David; (Santa Clara,
CA) |
Correspondence
Address: |
Mr. Robert W. Mulcahy
Applied Materials, Inc.
PO Box 450A
Santa Clara
CA
95052
US
|
Family ID: |
24150037 |
Appl. No.: |
09/961152 |
Filed: |
September 21, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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09961152 |
Sep 21, 2001 |
|
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|
09539158 |
Mar 29, 2000 |
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6323463 |
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Current U.S.
Class: |
219/390 ;
219/391; 219/395; 392/416 |
Current CPC
Class: |
C23C 16/4408 20130101;
C23C 14/566 20130101; H01L 21/67028 20130101 |
Class at
Publication: |
219/390 ;
392/416; 219/391; 219/395 |
International
Class: |
F27D 011/00; F27B
005/14 |
Claims
What is claimed is:
1. A method of controlling contaminants in a loadlock comprising
the steps of: heating an atmosphere in said loadlock; and pumping
said atmosphere from said loadlock to remove contaminants from the
loadlock.
2. The method of claim 1 further comprising the step of:
continuously supplying purge gas to said loadlock
3. The method of claim 2 wherein said purge gas is an inert
gas.
4. The method of claim 3 wherein the inert gas is nitrogen.
5. The method of claim 1 wherein said heating step heats the
atmosphere within the loadlock to about 50.degree. C.
6. The method of claim 2 wherein a plurality of loadlocks are
provided and said method further comprises the steps of:
selectively supplying purge aas to said loadlocks; and selectively
pumping said purge gas from said loadlocks.
7. The method of claim 6 further comprising the step of: isolating
a select loadlock from said purge gas and said pumping; and venting
an atmosphere of said select loadlock.
8. The method of claim 1 wherein said heating inhibits a corrosive
reaction within said loadlock.
9. The method of claim 1 wherein said heating is independently
applied to a plurality of heating zones.
10. The method of claim 1 wherein said heating inhibits the
formation of corrosion particles within said loadlock.
11. The method of claim 1 wherein a temperature of said loadlock
resulting from said heating is dynamically controlled.
12. A method for controlling contaminants in a pair of loadlocks
comprising the steps of: heating a first loadlock while
simultaneously flowing purge gas through said first loadlock, where
an atmosphere of said first loadlock is at a first pressure;
stopping the flow of purge gas to said first loadlock by isolating
said first loadlock from a source of purge gas and a vacuum pump;
isolating said first loadlock from said second load lock; heating
said second loadlock while simultaneously flowing purge gas through
said second loadlock, where an atmosphere of said second loadlock
in at a second pressure; and when said first pressure and said
second pressure are the same, connecting said first chamber to said
vacuum pump and said source of purge gas.
13. The method of claim 12 wherein said purge gas is an inert
gas.
14. The method of claim 13 wherein the inert gas is nitrogen.
15. The method of claim 12 wherein said heating step heats the
atmosphere within each of the loadlocks to about 50.degree. C.
16. The method of claim 12 further comprising the step of:
isolating a select loadlock from said purge gas source and said
vacuum pump; and venting an atmosphere of said select loadlock.
17. The method of claim 12 wherein said heating inhibits a
corrosive reaction within said loadlocks.
18. The method of claim 12 wherein said heating is independently
applied to a plurality of heating zones.
19. The method of claim 12 wherein said heating inhibits the
formation of corrosion particles within said loadlocks.
20. The method of claim 12 wherein a temperature of said loadlocks
resulting from said heating is dynamically controlled.
21. Apparatus for controlling contaminants in a loadlock
comprising: a heater attached to said loadlock; and a pump coupled
to said loadlock.
22. The apparatus of claim 21 further comprising: a purge gas
source coupled to said loadlock.
23. The apparatus of claim 22 further comprising: a first source
isolation valve between said purge gas source and said loadlock;
and a first pump isolation valve between said pump and said
loadlock.
24. The apparatus of claim 21 wherein said heater comprises a
heater controller and at least one heater element.
25. The apparatus of claim 24 wherein said heater controller
dynamically controls the at least one heater element.
26. The apparatus of claim 25 wherein said at least one heater
element is a resistive heater.
27. The apparatus of claim 26 wherein the heater controller further
comprises a temperature sensor.
28. The apparatus of claim 22 further comprising: a second loadlock
being coupled to said purge gas source through a second source
isolation valve and being coupled to said pump through a second
pump isolation valve.
29. The apparatus of claim 28 further comprising a main source
valve located between a each of said first and second source
isolation valves and said gas source.
Description
BACKGROUND OF THE DISCLOSURE
[0001] 1. Field of the Invention
[0002] The invention relates to semiconductor wafer process systems
and, more particularly, the invention relates to a method and
apparatus for controlling contamination in a loadlock of a
semiconductor wafer processing system.
[0003] 2. Description of the Background Art
[0004] Semiconductor wafer processing systems comprise a loadlock
wherein a plurality of wafers are stacked that are awaiting
processing within a system. These wafers are removed from the
loadlock one at a time by a robot and transported to various
processing chambers within the system. Once processed, the wafers
are returned from the process chambers to the wafer cassette in the
loadlock for removal from the system.
[0005] During wafer processing within the system contaminants
adsorb onto the wafers. Typically the reactant gases adsorb onto
the wafer surface and when the wafer is returned to the loadlock
the adsorbed material will desorb. The desorbed gases combine with
moisture in the loadlock to form a corrosive film that coats the
interior surfaces of the loadlock and the wafers. Such coating of
the interior surfaces causes corrosion of the surfaces within the
loadlock, and causes the formation of condensation particles upon
the wafers. The surface corrosion creates tremendous quantities of
corrosion by product particulates that disperse throughout the
loadlock to contaminate the wafers.
[0006] Therefore, a need exists in the art for a method and
apparatus that controls corrosive contaminants within a
loadlock.
SUMMARY OF THE INVENTION
[0007] The disadvantages associated with the prior art are overcome
by a method and apparatus that heats the atmosphere of a loadlock.
Specifically, the apparatus heats the loadlock to inhibit the
formation of corrosive by product particles. In addition, the
apparatus may supply a purge gas to the loadlock to dilute and
remove both moisture and corrosive gases from the loadlock. To
provide, de heat to the loadlock, at least one heater is attached
to the walls of the loadlock to desorb the contaminants from the
surfaces within the loadlock. These desorbed contaminants are
exhausted from the loadlock by a vacuum pump or flushed from the
loadlock by a flow of the purge gas. As such a combination of
heating and purging effectively eliminates both the moisture and
corrosive gases from the loadlock to eliminate a source of wafer
contamination.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] The teachings of the present invention can be readily
understood by considering the following detailed description in
conjunction with the accompanying drawings, in which:
[0009] FIG. 1 depicts a semiconductor processing system including
apparatus for removing contaminants from one or more loadlocks;
[0010] FIG. 2 depicts a perspective view of a loadlock having a
plurality of blanket heaters attached to the exterior surfaces of
loadlock; and
[0011] FIG. 3 depicts a cross-sectional view of the loadlock of
FIG. 2 taken along line 3-3;
[0012] FIG. 4 depicts a schematic design of a heater arrangement;
and
[0013] FIG. 5 depicts a flow diagram representing operation of the
present invention.
[0014] To facilitate understanding, identical reference numerals
have been used, where possible, to designate identical elements
that are common to the figures.
DETAILED DESCRIPTION
[0015] FIG. 1 depicts a semiconductor wafer processing system 100
comprising a system hardware 102 coupled to a loadlock contaminant
control system 104 of the present invention. The system hardware
operates in a manner that is generally known in the art while the
contaminant control system provides a unique technique for heating
and exhausting an atmosphere in the loadlock(s) to eliminate a
source of wafer contamination. A purge gas may be supplied to the
loadlock during heating.
[0016] Specifically, the wafer processing hardware 102 comprises a
plurality of process chambers 112 and 110, and a pair of loadlocks
122 and 124 coupled to a central platform 113 that contains a
transfer chamber 103. Within transfer chamber 104 is a robot 106
having a blade 18 located at the distal of the robot arms and
adapted for carrying semiconductor wafers from one process chamber
to another and between the loadlocks and the process chambers. The
robot's blade 108 has access to the chambers 112 and 110 through
respective slit valves 114 and 116. The platform is also coupled to
at least one loadlock 122. In the depicted platform there are two
loadlocks 122 and 124. Each of the loadlocks 122 and 124 are
respectively coupled to the transfer chamber 104 via slit valves
118 and 120.
[0017] In operation, wafers 128 and 126 within the loadlocks are
accessed by the robot's blade 108 through the respective slit
valves 118 and 124. The wafers are carried to a particular process
chamber 112 or 110 wherein they are processed and then returned to
the loadlock for removal from the system. Typically corrosives and
other processing byproducts adsorb upon the wafers as they are
processed within chambers 112 and 110 and the loadlock
contamination control system 104 removes these corrosives. As such,
the corrosives are prevented from attacking the interior surfaces
of the loadlocks and combining with loadlock moisture to form
condensation particles on unprocessed wafers in the loadlock.
[0018] In one embodiment of the invention, the contamination
control system 104 comprises a gas input subsystem 160, a gas
exhaust subsystem 162 and a loadlock heating subsystem 164. The gas
input subsystem 160 is optional. The gas input subsystem 160
comprises a gas source 140, a plurality valves 136A, 136B and 136C,
and a plurality of set screws 138A and 138B. The exhaust subsystem
comprises a pair of valves 134A and 134B and a pump 144. The heater
subsystem comprises a heater controller 146, a thermocouple 130 and
at least one heater element 132 that is attached or embedded in the
side wall or side walls of the loadlock 122 and/or 124.
[0019] In operation, the gas source 140 supplies an inert gas such
as nitrogen through valves 136C through the set screws 138A and
138B and valves 136A and 136B to the loadlocks 122 and 124. The set
screws 138A and 138B are needle valves that, upon a system
initialization, are used to set the flow rates into the chamber
such that the flow of gas is balanced between one loadlock and the
other such that the pressure within the loadlocks is in the correct
regime for efficient removal of moisture and corrosives. The
plurality of valves 136A, 136B and 136C are used to control the
flow of gas to the respective loadlocks such that the gas can be
decoupled from a loadlock that is being opened to remove or add
additional wafers to the loadlock.
[0020] The pumping system comprises a pair of exhaust valves 134A
and 134B that are coupled to a manifold 135 that carries the
exhaust gases to the pump 144. In this manner the inert gas is
supplied to the loadlock, flows through the loadlock causing
contaminants to be removed from the loadlock via the gas flow to
the pump 144. The gas flow is maintained at approximately 250 sccm
where a pressure of 400-500 mT is maintained within each of the
loadlocks.
[0021] To inhibit the formation of corrosive particles on loadlock
surfaces, at least one heater element 132 is attached or embedded
in the side wall of each of the loadlocks 122 and 124. A heater
controller applies electric current to the heater element to heat
the interior gas in the loadlock 122. The interior of the loadlock
is maintained at approximately 50-55.degree. C. or more. To
facilitate dynamic control of the heating process at least one
thermocouple 130 is attached to the loadlock wall. The output
voltage from the thermocouple 130 is coupled to the heater
controller 146 which, in response to the signal from the
thermocouple, modifies the voltage applied to the heater to
maintain a constant temperature within the loadlock. The
temperature change from top to bottom within the loadlock is
approximately 5-6.degree. C. To facilitate this stringent
temperature differential the heater controller 146 is used to
control a plurality of zones of heater elements and a plurality of
thermocouples are used to provide feedback voltage with respect to
each zone. A detailed description of the zonal heater control
system is provided with respect to FIG. 4.
[0022] The contaminant control system 104 comprises a controller
150 which may form part of the wafer processing system controller
148. The controller 150 comprises a central processing unit (CPU)
152, a memory 158, support circuits 156 and input/output (I/O)
circuits 154. The CPU 152 is a general purpose computer which when
programmed by executing software 159 contained in memory 158
becomes a specific purpose computer for controlling the hardware
components of the contaminant control system 104. The memory 158
may comprise read only memory, random access memory, removable
storage, a hard disk drive, or any form of digital memory device.
The I/O circuits comprise well known displays for output of
information and keyboards, mouse, track ball, or input of
information. The support circuits 156 are well known in the art and
include circuits such as cache, clocks, power supplies, and the
like.
[0023] The memory 158 contains control software 159 that when
executed by the CPU 152 enables the controller to digitally control
the various components of the contaminant control system 104. A
detailed description of the process that is implemented by the
control software is described with respect to FIG. 5.
[0024] Although the heater controller 146 is generally autonomous,
the heater controller 146 provides the controller with fault and
error information regarding the heater operation. Alternatively,
the heater controller may be a portion of the controller 150 of the
digital system. In fact, the controller 148 of the semiconductor
wafer processing system 102 that controls the processes that occur
within system 102 as well as the contaminant control system 104 may
also incorporate the heater controller 146 as depicted by the
dashed box that circumscribes the controller 150 as well as the
heater controller 146.
[0025] FIG. 2 depicts a perspective view of an individual loadlock
122, while FIG. 3 depicts a cross-sectional view of the loadlock
122 taken along lines 3-3 in FIG. 2. FIGS. 2 and 3 should be
referred to simultaneously to best understand the invention.
[0026] Loadlock 122 comprises a top 122T, a bottom 122B, and four
sides 122S.sub.1-22S.sub.4. The side 122S.sub.4 contains an
aperture that is covered by a door 200. The door 200, the top side
122T, the bottom side 122B as well as sides 122S.sub.1 and
122S.sub.3. have attached thereto a heater element 132. The heater
elements 132 in the embodiment depicted are self-adhesive resistive
blanket heaters. Alternatively, the resistive blanket heaters 132
can be replaced by embedded heater cartridges as well as conduits
carrying heated fluid. Other external heaters such as infra-red
lamps are also considered within the scope of the invention. The
heaters are required to heat the internal atmosphere of the
loadlock 122 to a temperature that will desorb the contaminants
that are contained within the loadlock. An adsorbed molecule of
corrosive gas (represented at reference 310) is desorbed by the
heating of the atmosphere within the loadlock 122 and exhausted
from the loadlock by the purge gas flow. A typical adsorbed
material comprises hydrogen bromide (HBr) and is desorbed by a
temperature of 50-55.degree. C. or more.
[0027] Gas is provided through a porous ceramic element 204. The
element 204 comprises an electro-polished stainless steel mounting
flange 300 and an alumina portion 302 having a 0.5 micron pore
size. The ceramic element 204 is mounted to the side wall
122S.sub.3 via the flange 300 and a conduit carrying the inert gas
is coupled to the element 204. The flange 300 is sealed to the wall
122S.sub.3. The gas enters the chamber and is dispersed by the
ceramic element such that the gas does not enter at a high velocity
and the gas is distributed through the wafers 308 contained in the
wafer cassette 306. To ensure that recondensation of corrosives
does not occur in the exhaust manifold, heater elements may be
placed on the conduits that lead to the pump to maintain the
conduits at elevated temperatures.
[0028] FIG. 4 depicts a schematic diagram of the heating system 164
comprising the heater controller 146 as well a plurality of heating
zone circuitry 400, 402 and 404. Each zone comprises a thermocouple
130.sub.1, 130.sub.2 and 130.sub.3 and a heating element 132.sub.1,
132.sub.2 and 132.sub.3. Any given zone may comprise multiple
heating elements such that multiple regions of the loadlock are
heated in response to one or more thermocouple signals. For
example, zone 400 may comprise a thermocouple on one side of the
loadlock and heating elements on sides 122S.sub.1, 122S.sub.2 and
122S.sub.4. While a second zone 402 may comprise a thermocouple
1302 on the door 200 and a heating pad 132 also located on the
door. The third zone may comprise a thermocouple on the top 122T of
the chamber and a heating pad 132 located on the top. Each zone is
independently controlled to adjust the temperature such that an
attempt is made to uniformly heat the atmosphere within the
loadlock. Through use of a standard feedback circuit to monitor a
voltage that is generated with respect to the temperature of the
thermocouple, the current driven to the heater is controlled. As
such, the temperature throughout the loadlock is held uniform to
within plus or minus 5.degree. C. while the overall temperature is
about 50.degree. C. Higher temperatures mav also be used.
[0029] When two chambers are simultaneously used as shown in FIG.
1, the valve assemblies are used to enable one loadlock to be used
for supplying wafers to the hardware while the second loadlock is
open to atmosphere. As such, any combination of venting and pumping
between the two chambers 122 and 124 can be provided. With the
selective opening and closing of the valves, the system of the
present invention avoids back streaming of gases from one chamber
to another.
[0030] FIG. 5 depicts a flow diagram of a process used by thre
invention. This process provides any combination of pumping and
venting either or both loadlocks 122 and 124 cf FIG. 1. The process
550 is implemented by executing control software 159 upon CPU 152.
The process 550 begins with the system 104 in an initial state
where the loadlocks 122 and 124 are open, valves 136A, B, C are
closed and all the heaters are active. At step 502, a cassette of
wafers is placed in the loadlock 122 and the door is closed when
the loadlock issues a "LOAD/UNLOAD" command. At step 504, the valve
134A is opened. Ag step 506, the routine queries whether the
pressure in loadlock 122 (P.sub.122) is less than the base loadlock
pressure (P.sub.B) When the loadlock pressure attains the base
pressure, the routine proceeds to step 508. At step 508, the valves
136A and 136C are opened and the loadlock 122 is evacuated to a
nominal pressure of 400-500 mT. At step 510, as the gas and heat
remove contaminants, the wafers are transferred one by one into and
out of the wafer processing hardware 102. At step 512, the process
queries whether the second loadlock 124 is to be used. Generally,
this query is answered by a cassette being placed in loadlock 124
and a "LOAD" button being depressed. If the LOAD request is not
made, the process ends at step 514. If the LOAD request is made,
the process 550 proceeds to step 516.
[0031] At step 516, valve 1360 is closed to temporarily stop the
flow of inert gas. Then, at step 518, valve 136A is closed to
isolate the loadlocks from one another. A delay of about one second
occurs at step 520 before, at step 522, the valve 134A is closed to
isolate the pump from loadlock 122. After a delay of about one
second occurs at step 524, step 526 opens valve 134B. At step 528,
the routine queries whether the pressure in loadlock 124 is less
than the pressure in loadlock 122. When the pressure in loadlock
124 (P.sub.124) is greater than or equal to the pressure in
loadlock 122 (P.sub.122) the routine proceeds to step 530. Then, at
step 530, the valve 134A is opened to pump the loadlock 124 to
400-500 mT. At step 531, valves 136A and 136B are opened. Then, at
step 532, the routine waits for a delay of about one second. To
apply inert purge gas, valve 136C is opened at step 534 and the
process 550 ends at step 536. At this time, both loadlocks 550 are
being heated and purged of contaminants.
[0032] To unload a wafer cassette, an operator generally depresses
an "UNLOAD" button corresponding to one of the loadlocks, e.g.,
loadlock 122. An automatic unload sequence may also be executed by
the software. In either instance, the valve 136A is closed, then
valve 134A is closed. The loadlock atmosphere is then vented to
atmospheric pressure with nitrogen. In this manner either loadlock
can be isolated from the contaminant control system to allow a
cassette to be removed, while the other loadlock is used. Once a
new cassette is loaded, the loadlock 122 can be pumped and purged
using steps 516 through 536 of process 550; however valve 136B is
substituted for 136A and valves 134B is substituted for 134A and so
on. Also, to unload loadlock 124, the process described above for
unloading loadlock 122 can be used, except valves 134B and 136B are
used to isolate loadlock 124.
[0033] Although various embodiments which incorporate the teachings
of the present invention have been shown and described in detail
herein, those skilled in the art can readily devise many other
varied embodiments that still incorporate these teachings.
* * * * *