U.S. patent application number 08/805018 was filed with the patent office on 2001-11-15 for method and apparatus for controlling rate of pressure change in a vacuum process chamber.
Invention is credited to HOCHHALTER, ELTON, ROLFSON, J. BRETT.
Application Number | 20010039921 08/805018 |
Document ID | / |
Family ID | 25190504 |
Filed Date | 2001-11-15 |
United States Patent
Application |
20010039921 |
Kind Code |
A1 |
ROLFSON, J. BRETT ; et
al. |
November 15, 2001 |
METHOD AND APPARATUS FOR CONTROLLING RATE OF PRESSURE CHANGE IN A
VACUUM PROCESS CHAMBER
Abstract
A method, apparatus and system for controlling a rate of
pressure change in a vacuum process chamber during pump down and
vent up cycles of a vacuum process are provided. The method
includes sensing the pressure in the process chamber, and then
controlling the rate of pressure change to achieve a desired rate
for a particular vacuum process. For a pump down cycle, the
apparatus can include a control valve in flow communication with
the process chamber and with an evacuation pump. For a vent up
cycle, the apparatus can include a control valve in flow
communication with the process chamber and with an inert gas
supply. With either embodiment controllers can be programmed to
adjust positions of the control valves based upon feedback from
pressure sensors. The system can include multiple chambers each
having an associated pump down and vent up control apparatus
configured to match the rates of pressure change between
chambers.
Inventors: |
ROLFSON, J. BRETT; (BOISE,
ID) ; HOCHHALTER, ELTON; (BOISE, ID) |
Correspondence
Address: |
STEPHEN A GRATTON
2764 SOUTH BRAUN WAY
LAKEWOOD
CO
80228
US
|
Family ID: |
25190504 |
Appl. No.: |
08/805018 |
Filed: |
February 21, 1997 |
Current U.S.
Class: |
118/715 ;
118/718; 118/728; 156/345.26; 438/689 |
Current CPC
Class: |
H01J 37/32431 20130101;
C23C 16/4412 20130101; C23C 16/52 20130101 |
Class at
Publication: |
118/715 ;
118/718; 118/728; 156/345; 438/689 |
International
Class: |
C23C 016/00 |
Claims
What is claimed is:
1. A method for controlling a rate of pressure change in a vacuum
process chamber during a vacuum process comprising: determining a
desired rate of pressure change for the chamber during the vacuum
process; providing a valve in flow communication with the chamber;
sensing a pressure within the chamber; and controlling a flow
through the valve responsive to the pressure to achieve the desired
rate of pressure change.
2. The method as claimed in claim 1 and wherein the vacuum process
comprises an etching process.
3. The method as claimed in claim 1 and wherein the vacuum process
comprises a deposition process.
4. A method for controlling a rate of pressure change during a pump
down cycle for a vacuum process chamber comprising: determining a
desired rate of pressure change for the chamber during the pump
down cycle; providing a valve in flow communication with the
chamber and with a pump; and controlling a flow through the valve
to the pump by sensing pressure in the chamber and adjusting a
position of the valve responsive to the pressure to achieve the
desired rate of pressure change.
5. The method as claimed in claim 4 wherein adjusting the position
of the valve is performed with a controller.
6. The method as claimed in claim 5 wherein the controller is
programmable to store the desired rate of pressure change.
7. A method for controlling a rate of pressure change during a vent
up cycle for a vacuum process chamber comprising: determining a
desired rate of pressure change for the chamber during the vent up
cycle; providing a valve in flow communication with the chamber and
with a gas supply; and controlling a flow through the valve to the
chamber by sensing pressure in the chamber and adjusting a position
of the valve responsive to the pressure to achieve the desired rate
of pressure change.
8. The method as claimed in claim 7 wherein adjusting the position
of the valve is performed with a controller.
9. The method as claimed in claim 8 wherein the controller is
programmable to store the desired rate of pressure change.
10. A method for controlling a rate of pressure change in a process
chamber during a vacuum process comprising: providing a pressure
sensor in the chamber; providing a valve in flow communication with
the chamber; providing a programmed controller in electrical
communication with the pressure sensor configured to adjust a flow
rate through the valve responsive to signals from the pressure
sensor; sensing a pressure in the chamber and communicating the
pressure to the controller; and controlling a flow rate through the
valve such that the rate of pressure change in the chamber matches
a desired rate of pressure change programmed into the
controller.
11. The method as claimed in claim 10 wherein the method controls
the rate of pressure change during a pump down cycle for the vacuum
process.
12. The method as claimed in claim 10 wherein the method controls
the rate of pressure change during a vent up cycle for the vacuum
process.
13. A method for controlling a vacuum process comprising: providing
a plurality of vacuum process chambers; providing a plurality of
valves in flow communication with the chambers; providing at least
one controller for the valves configured to control flow rates
through the valves; providing a plurality of pressure sensors in
the chambers in electrical communication with the controller; and
matching rates of pressure change in the chambers by controlling
flow rates through the valves using the controller and feedback
from the pressure sensors.
14. The method as claimed in claim 13 and further comprising
providing the controller with desired rates of pressure change and
matching the rates of pressure change to the desired rates of
pressure change.
15. The method as claimed in claim 13 wherein the vacuum process
comprises an etching process or a deposition process.
16. A method for controlling a plurality of vacuum process chambers
comprising: providing a pressure sensor in each chamber; providing
a plurality of control valves for controlling flow rates into and
out of each chamber; providing a plurality of controllers for the
control valves, with each controller in electrical communication
with a respective pressure sensor and valve; programming each
controller with a desired rate of pressure change; and adjusting
the flow rate through the valves using the controllers and pressure
sensors, such that a rate of pressure change in each chamber
matches the desired rate of pressure change.
17. The method as claimed in claim 16 wherein the desired rate of
pressure change is for a pump down cycle of a vacuum process.
18. The method as claimed in claim 16 wherein the desired rate of
pressure change is for a vent up cycle of a vacuum process.
19. The method as claimed in claim 16 wherein the vacuum process
chambers are contained on a same frame.
20. The method as claimed in claim 16 wherein the vacuum process
chambers are contained on separate pieces of equipment.
21. A method for controlling a vacuum process during processing o f
a semiconductor wafer comprising: providing a vacuum process
chamber; determining a desired rate of pressure change in the
chamber during the vacuum process; sensing a pressure in the
chamber; providing a valve in gaseous flow communication with the
chamber; and controlling a gas flow through the valve by adjusting
a position of the valve responsive to sensing the pressure, to
substantially match the rate of pressure change in the chamber
during the vacuum process with the desired rate of pressure
change.
22. The method as claimed in claim 21 wherein the vacuum process
comprises an etching process.
23. The method as claimed in claim 21 wherein the vacuum process
comprises a deposition process.
24. An apparatus for controlling a rate of pressure change in a
vacuum process chamber during a pump down cycle of a vacuum process
comprising: a pressure sensor configured to sense a pressure within
the chamber; a control valve in flow communication with the chamber
and with a pump; and a controller for the control valve in
electrical communication with the sensor, said controller
configured to control flow from the chamber through the control
valve to the pump, said controller responsive to input from the
sensor to achieve a desired rate of pressure change in the
chamber.
25. The apparatus as claimed in claim 24 wherein the controller
comprises a programmable memory wherein the desired rate of
pressure change is stored.
26. The apparatus as claimed in claim 24 wherein the chamber is
contained in a multi chambered system and the rate of pressure
change during the vacuum process is matched between the
chambers.
27. The apparatus as claimed in claim 24 wherein the multi
chambered system comprises a plurality of chambers contained on a
same frame.
28. The apparatus as claimed in claim 24 wherein the multi
chambered system comprises a plurality of chambers contained on
separate pieces of equipment.
29. An apparatus for controlling a rate of pressure change in a
vacuum process chamber during a vent up cycle of a vacuum process
comprising: a pressure sensor configured to sense a pressure within
the chamber; a control valve in flow communication with the chamber
and with an inert gas supply; and a controller for the control
valve, said controller in electrical communication with the sensor,
said controller configured to control flow from the gas supply
through the control valve to the chamber, said controller
responsive to input from the sensor to achieve a desired rate of
pressure change in the chamber.
30. The apparatus as claimed in claim 29 wherein the controller
comprises a programmable memory wherein the desired rate of
pressure change is stored.
31. The apparatus as claimed in claim 29 wherein the chamber is
part of a multi chambered system and the rate of pressure change
during the vacuum process is matched between the chambers.
32. An apparatus for controlling a vacuum process in a process
chamber comprising: a pressure sensor configured to sense a
pressure within the chamber; a flow control valve in flow
communication with the chamber; and a controller for the control
valve in electrical communication with the sensor, said controller
programmable with a desired rate of pressure change for the vacuum
process, said controller configured to adjust a position of the
control valve responsive to the pressure to achieve the desired
rate of pressure change in the chamber during the vacuum
process.
33. The apparatus as claimed in claim 32 wherein the vacuum process
comprises a pump down cycle wherein the chamber is evacuated to an
operating pressure.
34. The apparatus as claimed in claim 32 wherein the vacuum process
comprises a vent up cycle wherein the chamber is pressurized.
35. The apparatus as claimed in claim 32 wherein the control valve
is in flow communication with a vacuum pump.
36. The apparatus as claimed in claim 32 wherein the control valve
is in flow communication with a gas supply.
37. A vacuum system comprising: a first process chamber and a
second process chamber; a first pressure sensor in the first
process chamber and a second pressure sensor in the second process
chamber; and a controller coupled to the first and second pressure
sensors configured to control flow rates from the first and second
chambers such that a rate of pressure change in the first and
second chambers during a vacuum process matches.
38. The system as claimed in claim 37 wherein the vacuum process
includes a pump down cycle and the controller causes the process
chambers to have matching rates of pressure change during the pump
down cycle.
39. A vacuum system comprising: a first process chamber and a
second process chamber; a first pressure sensor in the first
process chamber and a second pressure sensor in the second process
chamber; and a first controller coupled to the first pressure
sensor; a second controller coupled to the second pressure sensor;
said first and second controllers configured to control flow rates
into the first and second chambers such that a rate of pressure
change in the first and second chambers during a vacuum process
matches.
40. The system as claimed in claim 39 wherein the vacuum process
includes a vent up cycle and the first and second controllers cause
the first and second process chambers to have matching rates of
pressure change during the vent up cycle.
41. The system as claimed in claim 39 wherein the first and second
process chambers are contained on a same frame.
42. The system as claimed in claim 39 wherein the first and second
process chambers are contained on separate pieces of equipment.
43. A system for controlling pressure for a plurality of vacuum
processes comprising: a first process chamber and a second process
chamber; a first pressure sensor in the first process chamber and a
second pressure sensor in the second process chamber; a first
control valve in flow communication with the first process chamber
and a second control valve in flow communication with the second
process chamber; and a first controller coupled to the first
control valve and first pressure sensor, and a second controller
coupled to the second control valve and the second pressure sensor,
said controllers responsive to the sensors to match a rate of
pressure change in the first and second process chambers during the
vacuum processes.
44. The system as claimed in claim 43 wherein the controllers are
programmable with a desired rate of pressure change.
45. The system as claimed in claim 43 wherein the vacuum processes
include a pump down cycle and a vent up cycle.
46. The system as claimed in claim 43 wherein the vacuum processes
comprises a deposition or etching process.
47. The system as claimed in claim 43 wherein the first process
chamber and the second process chamber are contained on a same
frame.
48. The system as claimed in claim 43 wherein the first process
chamber and the second process chamber are contained on separate
pieces of equipment.
49. A vacuum system for semiconductor wafers comprising: a wafer
handler configured to transport the wafers; a plurality of vacuum
process chambers configured to receive wafers from the wafer
handler; a pressure sensor in each process chamber; a flow control
valve associated with each chamber for controlling a flow rate into
or out of each chamber; and a controller for controlling each
control valve, said controllers configured to control the control
valves such that a rate of pressure change in the chambers during a
vacuum process substantially matches a desired rate of pressure
change.
50. The system as claimed in claim 49 wherein the flow control
valves are in flow communication with evacuation pumps for a pump
down cycle.
51. The system as claimed in claim 49 wherein the flow control
valves are in flow communication with an inert gas supply for a
vent up cycle.
52. A vacuum system for semiconductor wafers comprising: a first
process chamber and a second process chamber configured to perform
a same vacuum process; a first pressure sensor for sensing pressure
in the first process chamber and a second pressure sensor for
sensing pressure in the second process chamber; a first control
valve for controlling a first flow rate from the first process
chamber and a second control valve for controlling a second flow
rate from the second process chamber; a first controller responsive
to the first pressure sensor for controlling the first flow rate
and a second controller responsive to the second pressure sensor
for controlling the second flow rate; wherein said first and second
controllers are programmed such that the first and second flow
rates comprise substantially a same value.
53. The vacuum system as claimed in claim 52 wherein the first
process chamber and the second process chamber are contained on a
same frame.
54. The vacuum system as claimed in claim 52 wherein the first
process chamber and the second process chamber are contained on
separate pieces of equipment.
55. The vacuum system as claimed in claim 52 wherein the same
vacuum process comprises a deposition process.
56. The vacuum system as claimed in claim 52 wherein the same
vacuum process comprises an etching process.
Description
FIELD OF THE INVENTION
[0001] This invention relates generally to vacuum processes, such
as dry etching and chemical vapor deposition particularly for
semiconductor manufacture. More specifically, this invention
relates to a method and apparatus for controlling a rate of
pressure change in a vacuum process chamber during pump down and
vent up cycles of a vacuum process.
BACKGROUND OF THE INVENTION
[0002] Various etching and deposition processes for semiconductor
manufacture are performed in vacuum process chambers. For example,
dry etching and chemical vapor deposition (CVD) processes utilize
vacuum process chambers. Conventional dry etching processes include
plasma etching and reactive ion etching (RIE). Conventional
chemical vapor deposition processes include plasma enhanced
chemical vapor deposition (PECVD) and low pressure chemical vapor
deposition (LPCVD).
[0003] During these processes the process chamber can be evacuated
from an initial pressure to an operating pressure. For example, the
process chamber may initially be at atmospheric pressure for
loading wafers, then evacuated to an operational pressure in the
milli-torr range. The initial evacuation cycle for a process is
sometimes referred to as a "pump down cycle". Typically, a pump
down cycle is accomplished using a vacuum pump in flow
communication with the process chamber.
[0004] Subsequently, the pressure in the process chamber can be
increased from the operating pressure back to the initial pressure
(e.g., back to atmospheric pressure). The subsequent pressurization
cycle is sometimes referred to as a "vent up cycle". Typically, a
vent up cycle is accomplished by injecting an inert gas into the
process chamber to a desired pressure.
[0005] Recently, etching and deposition systems having more than
one vacuum process chamber have been employed for semiconductor
manufacture. These multi-chamber systems improve production rates
and provide increased efficiency over single chamber systems. An
example of a multi-chambered etching or deposition system is sold
under the trademark "APPLIED MATERIALS 5000", by Applied Materials,
Inc., of Santa Clara, Calif.
[0006] Such a multi chambered system can include a wafer handler, a
load lock chamber and multiple process chambers. The wafer handler
can include cassettes for holding the wafers and cassette ports for
loading the wafers. During an etching or deposition process, the
wafers can be moved from the load lock chamber and into or out of
the process chambers as required. The process chambers can be
pumped down and vented up to different pressures during various
cycles of the process.
[0007] One limitation of multi chamber systems is that wafer
defects can sometimes occur more frequently in a particular process
chamber relative to the other process chambers. For example, some
types of wafer defects can be detected using optical detectors such
as those manufactured by KLA Instruments Corporation, Santa Clara,
Calif. These types of defects are sometimes termed "KLA defects".
The inventors have observed variations in KLA defects among wafers
processed in different process chambers of multi chamber vacuum
systems. In particular, some process chambers in multi chamber
systems produce wafers with more defects.
[0008] One possible source of defect variation between the process
chambers is that the rate of pressure change for the chambers
during pump down and vent up cycles may not be the same. This
difference in rate of pressure change can cause the pressures in
the process chambers to be different for significant time
increments. The pressure rate differences may be due to variations
between conduction lines, pumps, valves and associated equipment
for the different chambers. These variations can be caused by
residue build up and other factors.
[0009] The same situation can occur among different single chamber
systems adapted to perform the same process. Specifically,
variations can occur between the different process chambers causing
differences in the wafers. In this situation it would be
advantageous to control the rate of pressure change during pump
down and vent up in the process chambers in order to achieve
process uniformity.
[0010] Prior art attempts to regulate pump down cycles in vacuum
process chambers include "soft-start" valves, which open at a
linear rate (i.e., at a certain percentage per second). Prior art
attempts to regulate vent up cycles in vacuum process chambers
include needle valves and mass flow controllers which control the
flow rate into a particular chamber during vent up. However, these
prior art systems do not compensate for system variables and are
inherently linear in response. Accordingly, significant pressure
differentials can still occur between different process chambers
causing differences in the semiconductor wafers being
processed.
[0011] The present invention provides a method and apparatus for
achieving an optimal rate of pressure change in a vacuum process
chamber during pump down and vent up cycles of a vacuum process.
For multi chamber vacuum systems, the rate of pressure change
between different process chambers can be matched such that one
process variable can be eliminated and wafer uniformity can be
improved. Similarly, for multiple single chamber systems adapted to
perform the same process, one process variable can be eliminated
and the uniformity of the wafers produced by the different vacuum
process chambers can be improved.
SUMMARY OF THE INVENTION
[0012] In accordance with the present invention, a method and
apparatus for controlling the rate of pressure change in a process
chamber during pump down and vent up cycles of a vacuum process are
provided. The method, simply stated, comprises, determining a
desired rate of pressure change for the process chamber, and then,
controlling the gas flow out of, or into, the process chamber to
achieve the desired rate of pressure change. The gas flow can be
controlled using a flow control valve and programmed controller
responsive to feed back from pressure sensors within the process
chamber. The desired rate of pressure change can be determined
empirically for a particular vacuum process, expressed
mathematically, and then programmed into the controller.
[0013] An apparatus constructed in accordance with the invention,
comprises: a pressure sensor for sensing pressure in the process
chamber; a control valve in flow communication with the process
chamber; and a programmed controller for controlling the control
valve responsive to the pressure sensor. Separate controllers and
control valves can be operably associated with the process chamber
for the pump down and vent up cycles of a vacuum process. For
controlling the pump down cycle, a control valve can be in flow
communication with a vacuum pump. For controlling the vent up
cycle, a control valve can be in flow communication with an inert
gas supply.
[0014] A system constructed in accordance with the invention
comprises multiple process chambers configured for a vacuum process
such as depositing or etching layers of semiconductor wafers. The
multiple process chamber can be contained on the same frame or can
be contained on separate pieces of equipment configured to perform
the same process. Each process chamber includes a pressure sensor,
and separate control valves and controllers for controlling pump
down and vent up cycles during the vacuum processes. The
controllers and control valves can be configured to match the rates
of pressure change in the process chambers during the pump down and
vent up cycles. The matched rates permit more process uniformity
between the process chambers so that excessive defects do not occur
in any one process chamber.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] FIG. 1A is a flow diagram of a method for controlling a rate
of pressure change in a vacuum process chamber during a pump down
cycle of a vacuum process;
[0016] FIG. 1B is a flow diagram of a method for controlling a rate
of pressure change in a vacuum process chamber during a vent up
cycle of a vacuum process;
[0017] FIG. 2A is a schematic diagram of an apparatus constructed
in accordance with the invention for controlling the rate of
pressure change in a vacuum process chamber during a pump down
cycle of a vacuum processes;
[0018] FIG. 2B is a schematic diagram of an apparatus constructed
in accordance with the invention for controlling the rate of
pressure change in a vacuum process chamber during a vent up cycle
of a vacuum process;
[0019] FIG. 2C is a graph illustrating the pressure within the
vacuum process chamber as a function of time during pump down,
operational and vent up cycles of a vacuum process;
[0020] FIG. 3A is a schematic diagram of a multi chambered system
constructed in accordance with the invention with multiple process
chambers contained on a same frame, wherein the rate of pressure
change in the different process chambers during pump down and vent
up can be matched;
[0021] FIG. 3B is a schematic diagram of a multi chambered system
constructed in accordance with the invention with multiple process
chambers on separate pieces of equipment but configured to perform
the same process, wherein the rate of pressure change in the
different process chambers during pump down and vent up can be
matched;
[0022] FIG. 4 is a graph of pressure vs. time in a process chamber
during a pump down cycle illustrating a rate of pressure change
comprising a series of linear segments;
[0023] FIG. 5 is a graph of pressure vs. time in a process chamber
during a pump down cycle illustrating another rate of pressure
change comprising a series of linear segments; and
[0024] FIG. 6 is a graph of pressure vs. time in a process chamber
during a vent up cycle illustrating a rate of pressure change
comprising an exponential curve.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0025] Referring to FIG. 1A, broad steps in a method for
controlling the rate of pressure change in a vacuum process chamber
during a pump down cycle of an etching or deposition process are
shown. For a pump down cycle the method includes the steps of:
[0026] A. Providing a vacuum process chamber in flow communication
with a vacuum pump.
[0027] B. Providing an evacuation control valve in flow
communication with the process chamber and with the vacuum
pump.
[0028] C. Providing a controller for controlling the evacuation
control valve.
[0029] D. Providing a pressure sensor in the process chamber in
electrical communication with the controller.
[0030] E. Sensing a pressure in the process chamber using the
pressure sensor.
[0031] F. Controlling the rate of pressure change by inputting
signals from the pressure sensor to the controller to control a
flow rate through the control valve out of the chamber.
[0032] Referring to FIG. 1B, broad steps in a method for
controlling the rate of pressure change in a vacuum process chamber
during a vent up cycle are shown. For a vent up cycle the method
includes the steps of:
[0033] A. Providing a vacuum process chamber in flow communication
with a vent source such as an inert gas supply.
[0034] B. Providing a vent control valve in flow communication with
the process chamber and vent source.
[0035] C. Providing a controller for controlling the vent control
valve.
[0036] D. Providing a pressure sensor in the process chamber in
electrical communication with the controller.
[0037] E. Sensing a pressure in the process chamber using the
pressure sensor.
[0038] F. Controlling the rate of pressure change by inputting
signals from the pressure sensor to the controller to control a
flow rate from the vent source through the control valve into the
chamber.
[0039] Referring to FIG. 2A, a pump down apparatus 10P for
controlling a rate of pressure change in a vacuum process chamber
12 during a pump down cycle is illustrated. The pump down apparatus
10P includes a pressure sensor 14P configured to sense a pressure
within the process chamber; a controller 16P in electrical
communication with the pressure sensor 14P configured to receive
feedback from the pressure sensor 14P; and a pump down control
valve 18P coupled to the controller 16P in flow communication with
the process chamber 12.
[0040] The vacuum process chamber 12 can be a component of an
etching system such as a plasma etcher or a reactive ion etcher
(RIE). Alternately the vacuum process chamber 12 can be a component
of a CVD deposition system such as a plasma enhanced chemical vapor
deposition (PECVD) apparatus, or a low pressure chemical vapor
deposition (LPCVD) reactor.
[0041] The vacuum process chamber 12 is adapted to contain a
gaseous etching or deposition species. The vacuum process chamber
12 is in flow communication with an evacuation pump 20. The
evacuation pump 20 is configured to pump down (i.e., evacuate) and
then to maintain the process chamber 12 at a desired vacuum
pressure. For vacuum etching or deposition processes, the vacuum
process chamber 12 can be evacuated to pressures of from 760 torr
to 10.sup.-8 torr or less. Suitable conduits, such as tubes or
pipes, can be formed between the vacuum process chamber 12 and the
evacuation pump 20 to form conduction lines for the etching or
deposition gases.
[0042] The pump down control valve 18P is located in the flow path
of the etching or deposition gases from the process chamber 12 to
the evacuation pump 20. The pump down control valve 18P is
configured to regulate a flow rate of gases from the vacuum process
chamber 12 to the evacuation pump 20 during a pump down cycle. The
pump down control valve 18P can be a standard flow control valve
such as a throttle valve or butterfly valve that is responsive to
electrical signals from the controller 16P.
[0043] The controller 16P is configured to receive electrical
signals from the pressure sensor 14P. This provides real time feed
back to the controller 16P of the pressure within the process
chamber 12. In addition, the controller 16P is configured to input
electrical signals into the pump down control valve 18P for
adjusting the pump down control valve 18P to achieve a desired flow
rate at a particular pressure.
[0044] The controller 16P can include a microprocessor and
programmable memory that is programmable to achieve a desired mode
of operation for the controller 16P. For example, the controller
16P can be programmed such that the pump down control valve 18P
achieves a desired rate of pressure change in the process chamber
12 during the pump down cycle. The controller 16P can also include
a calibration cycle wherein the rate of pressure change at a given
pressure versus a valve position for the control valve 18P at that
pressure is determined. The calibration step is optional but makes
the response of the control valve 18P more rapid and accurate.
[0045] As will be further explained, the desired rate of pressure
change can be an empirically determined optimal rate. In addition,
for multiple chamber systems, the desired rate of pressure change
can be matched to the rate in another chamber. The multiple
chambers can be included in the same system, or frame, or can be
included in separate systems adapted to perform the same
process.
[0046] Preferably, the desired rate of pressure change can be
expressed mathematically such as illustrated in FIGS. 4-6. In these
figures, pressure is plotted as a function of time and the rate of
pressure change AP comprises the slope of the resultant curve.
[0047] Referring to FIG. 2B, a vent up apparatus 10V for
controlling a rate of pressure change in the process chamber 12
during a vent up cycle of a vacuum process is shown. During the
vent up cycle the pressure within the process chamber 12 can be
increased to a level that is higher than the operating pressure for
a particular vacuum process. This increased pressure level can be
atmospheric pressure, or can be an intermediate pressure level,
such as the vacuum pressure of a load lock chamber for the process
chamber 12.
[0048] The vent up apparatus 10V comprises a pressure sensor 14V
configured to sense a pressure within the process chamber; a
controller 16V in electrical communication with the pressure sensor
14V configured to receive feedback from the pressure sensor 14V;
and a vent up flow control valve 18V coupled to the controller 16V
in flow communication with the process chamber 12.
[0049] In the vent up apparatus 10V, the vacuum process chamber 12
is in flow communication with an inert gas supply 28. The inert gas
supply 28 can be maintained at a higher pressure than the operating
pressure of the process chamber 12. The inert gas supply 28 is
configured to inject an inert gas into the process chamber 12
during the vent up cycle. The vent up control valve 18V is
configured to regulate a flow rate of gas from the inert gas supply
28 to the vacuum process chamber 12 during the vent up cycle. The
controller 16V can be constructed as previously described for
controller 16P and can include a microprocessor and programmable
memory. Feed back from the pressure sensor 14V to the controller
16V enables the controller 16V to adjust the positions of the vent
up control valve 18V to achieve a desired gas flow and rate of
pressure change during the vent up cycle. Again this desired rate
of pressure change can be empirically determined and can be matched
in a multi chamber system. In addition, the controller 16V can
include a periodic calibration cycle to determine the rate of
pressure change at a given pressure and valve position.
[0050] FIG. 2C illustrates the pressure in the process chamber 12
as a function of time during an etching or deposition process.
During the pump down cycle, the pressure in the process chamber 12
is decreased as indicated by the pump down portion 22 of the
pressure curve. The rate of pressure change (.DELTA.P) during the
pump down cycle (i.e., slope of portion 22) is controlled by the
controller 16P (FIG. 2A) and the pump down control valve 18P (FIG.
2A). During the operating cycle, the pressure in the process
chamber 12 is maintained at a desired operating pressure as
indicated by the operating portion 24 of the pressure curve. During
the vent up cycle, the pressure in the process chamber 12 is
increased as indicated by the vent up portion 26 of the pressure
curve. During the vent up cycle, the rate of pressure change
(.DELTA.P) is controlled by the controller 16V (FIG. 2B) and vent
up control valve 18V.
[0051] Referring to FIG. 3A, a multi chamber system 30A constructed
in accordance with the invention with multiple chambers on a same
frame is shown. As used herein, the term "same frame" refers to a
single piece of equipment. For example, the system 30A can be based
on a commercially available multi chamber frame, such as an
"APPLIED MATERIALS 5000" manufactured by Applied Materials, Inc. of
Santa Clara, Calif.
[0052] The system 30A can be configured for etching or depositing
layers on semiconductor wafers during semiconductor fabrication
processes. The system 30A includes a first process chamber 12A, a
second process chamber 12B, and a third process chamber 12C. The
system 30A can also include a wafer handler 32 configured to
transport semiconductor wafers loaded in cassettes from a load lock
station into the process chambers 12A-12C for etching or deposition
processes.
[0053] Each process chamber 12A-12C includes an associated pump
down apparatus 10PA-10PC. Each pump down apparatus 10PA-10PC
includes a pump down pressure sensor 14PA-14PC, a pump down
controller 16PA-16PC, a pump down control valve 18PA-18PC, and an
evacuation pump 20A-20C. These elements function the same as the
equivalent elements previously described. In the multi chamber
system 30A, the rate of pressure change in the different process
chambers 12A-12C during the pump down cycle can be an optimal rate
as previously described. In addition, the rate of pressure change
(.DELTA.P) can be substantially the same (i.e., matched) for each
process chamber 12A-12C.
[0054] Each process chamber 12A-12C also includes an associated
vent up apparatus 10VA-10VC. Each vent up apparatus 10VA-10VC
includes a vent up pressure sensor 14VA-14VC, a vent up controller
16VA-16VC, a vent up control valve 18VA-18VC, and an inert gas
supply 28A-28C. These elements function the same as the equivalent
elements previously described. In the multi chamber system 30A, the
rate of pressure change (.DELTA.P) in the different process
chambers 12A-12C during the vent up cycle can be an optimal rate as
previously described. In addition, the rate of pressure change can
be substantially the same (i.e., matched) for each process chamber
12A-12C.
[0055] Referring to FIG. 3B, a system 30B includes separate process
chambers 12D-12F that are not contained on the same frame. For
example, the process chambers 12D-12F can be similar pieces of
equipment that are not clustered together, but which perform the
same processes (e.g., polysilicon deposition, metal etching,
silicon nitride deposition and etching etc.). Since these process
chambers 12D-12F may be in different areas of the semiconductor
manufacturing plant, process variables can occur between the
process chambers 12D-12F. For example, these process variables can
include differences in pumping speeds, conduction line resistance,
preventative maintenance schedules as well as others.
[0056] In accordance with the invention, each process chamber
includes an associated vent up apparatus 10VD-10VF. Each vent up
apparatus 10VD-10VF includes a vent up pressure sensor 14VD-14VF, a
vent up controller 16VD-16VF, a vent up control valve 18VD-18VF,
and an inert gas supply 28D-28F. These elements function the same
as the equivalent elements previously described. In the multi
chamber system 30B the rate of pressure change (.DELTA.P) in the
different process chambers 12D-12F during the vent up cycle can be
an optimal rate as previously described. In addition, the rate of
pressure change can be substantially the same (i.e., matched) for
each process chamber 12D-12F.
[0057] As also shown in FIG. 3B, each process chamber 12D-12F
includes an associated pump down apparatus 10PD-10PF. Each pump
down apparatus 10PD-10PF includes a pump down pressure sensor
14PD-14PF, a pump down controller 16PD-16PF, a pump down control
valve 18PD-18PF, and an evacuation pump 20D-20F. These elements
function the same as the equivalent elements previously described.
In the multi chamber system 30B, the rate of pressure change in the
different process chambers 12D-12F during the pump down cycle can
be an optimal rate as previously described. In addition, the rate
of pressure change (.DELTA.P) can be substantially the same value
(i.e., matched) for each process chamber 12D-12F.
[0058] In the multi chamber system 30B shown in FIG. 3B, each of
the process chambers 12D-12F can be configured to perform the same
process or "recipe". In addition, the vent up and pump down cycles
for each recipe can be matched. Still further, the process chambers
12D-12F can comprise stock equipment from different equipment
vendors but still use the same pump down and vent up cycles for a
given process recipe.
EXAMPLE 1
[0059] Referring to FIG. 4, an exemplary pump down cycle for the
pump down apparatus 10P (FIG. 2) is shown. In FIG. 4, the pressure
in the process chamber 12 (FIG. 2) is plotted as a function of time
as the pump down cycle progresses. Initially, the process chamber
12 (FIG. 2) has a pressure of approximately 760 torr. An optimal
rate of pressure drop during the pump down cycle includes three
(pressure v time) segments.
[0060] In a first segment the pressure is to be reduced to 100 torr
in 20 seconds. In a second segment the pressure is to be reduced
from 100 torr to 1 torr in 15 seconds. In a third segment the
pressure is to be reduced from 1 torr to 500 milli-torr in 15
seconds. The rate of pressure change during each segment is
represented by .DELTA.P1, .DELTA.P2 and .DELTA.P3. Each rate of
pressure change for a respective segment is linear for that
segment. In other words, the change in pressure for each segment is
directly proportional to the change in time. However, the rate of
change .DELTA.P1, .DELTA.P2 and .DELTA.P3 is different for each
segment.
[0061] The (pressure vs. time) segments can be empirically
determined and then programmed into the controller 16P (FIG. 2A).
During each pressure segment the controller 16P (FIG. 2A) based
upon input from the pressure sensor 14P (FIG. 2A) adjusts the
position of the pump down control valve 18P (FIG. 2) to meet the
desired rate of pressure change.
EXAMPLE 2
[0062] Referring to FIG. 5, another example of a pump down cycle is
illustrated. In this example the process chamber 12 (FIG. 2A) is
adjacent to a staging area, such as a load lock, wherein transfer
of the wafers into the process chamber 12 (FIG. 2A) takes place.
The staging area is at a pressure that is less than atmosphere,
which in this example is 10 torr. On the other hand, the desired
steady state processing pressure in the process chamber (FIG. 2A)
is to be 150 milli-torr.
[0063] It is desired to pump down in a linear fashion from 10 torr
to 1 torr in ten seconds, then from 1 torr to 500 millitorr in 15
seconds, then from 500 milli-torr to the operating pressure of 150
milli torr in 20 seconds. These rates of pressure change are
represented by segments 4, 5 and 6 respectively. Segment 7
represents the steady state operating pressure.
[0064] Based upon these predetermined rates of pressure change, the
controller 16P (FIG. 2A) can be programmed to adjust the positions
of the pump down control valve 18P (FIG. 2A) responsive to input
from the pressure sensor 14P (FIG. 2A) to achieve the desired rate.
Prior to the pump down cycle, a calibration cycle can be performed
to determine the rate of pressure drop at a given pressure for
different positions of the control valve 18P.
EXAMPLE 3
[0065] Referring to FIG. 6, an exemplary vent up cycle is
illustrated. During the vent up cycle the pressure in the process
chamber 12 (FIG. 2B) is increased from a steady state operating
pressure 34 to atmospheric pressure. In this case it is desired to
increase the pressure in the process chamber 12 (FIG. 2B) in a non
linear or exponential manner. An exponential curve 36 represents
the desired rate of pressure change during the vent up cycle. The
exponential curve 36 can be empirically determined.
[0066] In accordance with the invention, the vent up controller 16V
(FIG. 2B) is programmed to achieve a rate of pressure change in the
process chamber 12 (FIG. 2B) that is equivalent to the exponential
curve 36. Accordingly, the vent up controller 16V (FIG. 2B) based
upon feedback from the pressure sensor 14V, (FIG. 2B) adjusts the
positions of the vent up control valve 18V (FIG. 2B). The vent up
control valve 18V meters the flow of inert gas from the inert gas
supply 28 (FIG. 2B) to achieve the desired rate of pressure
change.
[0067] Thus the invention provides an improved method, apparatus
and system for controlling the rate of pressure change in a vacuum
process chamber during pump down and vent up cycles of a vacuum
etching or deposition process. In addition, the invention permits
an optimal rate of pressure change to be achieved in a single
chamber or multi chamber etching or deposition system. For a multi
chamber system the rate of pressure change between different
chambers of the system can be made substantially the same. This
improves process uniformity because at least one variable is
eliminated, and permits semiconductor wafers to be fabricated with
fewer defects.
[0068] While the invention has been described with reference to
certain preferred embodiments, as will be apparent to those skilled
in the art, certain changes and modifications can be made without
departing from the scope of the invention as defined by the
following claims.
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