U.S. patent application number 09/725595 was filed with the patent office on 2001-10-18 for method for improved chamber bake-out and cool-down.
Invention is credited to Ding, Peijun, Gogh, James van, Saigal, Dinesh, Sundarrajan, Arvind.
Application Number | 20010029888 09/725595 |
Document ID | / |
Family ID | 22994480 |
Filed Date | 2001-10-18 |
United States Patent
Application |
20010029888 |
Kind Code |
A1 |
Sundarrajan, Arvind ; et
al. |
October 18, 2001 |
Method for improved chamber bake-out and cool-down
Abstract
A method and apparatus for baking-out and for cooling a vacuum
chamber are provided. In a first aspect, an inert gas which
conducts heat from the vacuum chamber's bake-out lamps to the
shield and from the shield to the other parts within the vacuum
chamber is introduced to the chamber during chamber bake-out. The
inert gas preferably comprises argon, helium or nitrogen and
preferably raises the chamber pressure to about 500 Torr during
chamber bake-out. A semiconductor processing apparatus also is
provided having a controller programmed to perform the inventive
bake-out method. In a second aspect, a process chamber is provided
having at least one source of a cooling gas. The cooling gas is
input to the chamber and is allowed to thermally communicate with
the chamber body and components. The cooling gas may reside in the
chamber for a period of time or may be continuously flowed through
the chamber. Once the chamber reaches a target temperature the
cooling gas is evacuated.
Inventors: |
Sundarrajan, Arvind; (Santa
Clara, CA) ; Saigal, Dinesh; (San Jose, CA) ;
Ding, Peijun; (San Jose, CA) ; Gogh, James van;
(Sunnyvale, CA) |
Correspondence
Address: |
PATENT COUNSEL
APPLIED MATERIALS, INC.
Legal Affairs Department
P.O.BOX 450A
Santa Clara
CA
95052
US
|
Family ID: |
22994480 |
Appl. No.: |
09/725595 |
Filed: |
November 29, 2000 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09725595 |
Nov 29, 2000 |
|
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|
09261700 |
Mar 3, 1999 |
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6193811 |
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Current U.S.
Class: |
118/715 ;
118/724; 432/198; 432/51 |
Current CPC
Class: |
H01L 21/67103 20130101;
C23C 14/564 20130101; C23C 16/4411 20130101; Y10S 438/905 20130101;
C23C 16/4408 20130101 |
Class at
Publication: |
118/715 ;
118/724; 432/51; 432/198 |
International
Class: |
C23C 016/00 |
Claims
The invention claimed is:
1. A semiconductor processing apparatus comprising: a semiconductor
processing chamber having an inlet and an outlet; a semiconductor
wafer support located within the semiconductor processing chamber
for supporting a semiconductor wafer during processing within the
semiconductor processing chamber; a vacuum pump operatively coupled
to the semiconductor processing chamber's outlet for evacuating the
semiconductor processing chamber; an inert gas source operatively
coupled to the semiconductor processing chamber's inlet for
injecting an inert gas into the semiconductor processing chamber; a
bake-out mechanism located within the semiconductor processing
chamber for baking-out the semiconductor processing chamber; and a
bake-out controller operatively coupled to the semiconductor
processing chamber's inlet and outlet and to the bake-out
mechanism, the bake-out controller programmed for: evacuating the
semiconductor processing chamber via the vacuum pump; isolating the
semiconductor processing chamber from the vacuum pump; injecting
inert gas from the inert gas source into the semiconductor
processing chamber so as to raise the pressure within the
semiconductor processing chamber to a bake-out pressure; and
baking-out the semiconductor processing chamber via the bake-out
mechanism in the presence of the inert gas.
2. The semiconductor processing apparatus of claim 1 wherein the
inert gas comprises an inert gas selected from the group consisting
of argon, helium and nitrogen.
3. The semiconductor processing apparatus of claim 1 wherein the
bake-out pressure is about 500 Torr.
4. The semiconductor processing apparatus of claim 1 wherein the
semiconductor processing chamber comprises an HDP chamber, the HDP
chamber comprising: an adapter located within the HDP chamber for
supporting and cooling a target during semiconductor wafer
processing within the HDP chamber; a cooling system operatively
coupled to the adapter for supplying cooling fluid to the adapter;
and a shield operatively coupled to the adapter and surrounding the
adapter and the semiconductor wafer support; and wherein the
bake-out controller is further operatively coupled to the cooling
system and is programmed for baking-out the semiconductor
processing chamber by: turning off the supply of cooling fluid to
the adapter; turning on the bake-out mechanism for a first time
period sufficient to bake-out the semiconductor processing chamber;
turning off the bake-out mechanism for a second time period
sufficient to allow the bake-out to cool; and turning on the supply
of cooling fluid to the adapter during the cooling of the bake-out
mechanism.
5. The apparatus of claim 4 wherein the bake-out mechanism
comprises at least one bake-out lamp.
6. The apparatus of claim 4 wherein the HDP chamber comprises a
copper target and a copper wire coil.
7. A semiconductor wafer processing tool comprising: a load port
for loading wafers into the tool; a wafer handler chamber
operatively coupled to the load port and having a wafer handler
therein; a plurality of processing chambers wherein at least one of
the plurality of processing chambers comprises the semiconductor
processing apparatus of claim 1; and a tool controller operatively
coupled to the load port, the wafer handler chamber, the wafer
handler and the plurality of processing chambers, the controller
programmed to transfer a wafer between the plurality of processing
chambers and to perform processes within the chambers.
8. The semiconductor wafer processing tool of claim 7 wherein the
tool controller and the bake-out controller are the same
controller.
9. An apparatus, comprising: a) a chamber defining an enclosure; b)
one or more process gas sources fluidly connected to the chamber;
c) one or more cooling gas sources fluidly connected to the chamber
adapted to cool the chamber after processing; d) a vacuum pump; e)
an exhaust line fluidly connecting the vacuum pump to the
enclosure; and f) a gate valve disposed in the exhaust line.
10. The apparatus of claim 9, wherein the chamber is selected from
the group consisting of a physical vapor deposition chamber, a
chemical vapor deposition chamber, and an ion metal plasma.
11. The apparatus of claim 9, wherein the one or more cooling gas
sources comprises an inert gas source.
12. The apparatus of claim 9, wherein the one or more cooling gas
sources comprises a gas selected from the group consisting of
nitrogen, argon, helium, and any combination thereof.
13. The apparatus of claim 9, wherein the chamber is a
semiconductor processing chamber.
14. The apparatus of claim 9, further comprising a cooling system
in fluid communication with the enclosure to cool the cooling gases
after delivery into the chamber.
15. A method for cooling a processing chamber after a processing
period, the method comprising: a) pumping the chamber to a first
pressure; b) flowing a cooling gas into the chamber to raise the
chamber pressure to a second pressure greater than the first
pressure; and c) lowering a chamber temperature by allowing for
thermal exchange between the cooling gas and chamber.
16. The method of claim 15, further comprising: d) closing a gate
valve after a) and before b); e) terminating flowing the cooling
gas when the second pressure is reached; and f) flowing the cooling
gas into the chamber to raise the chamber pressure to the second
pressure if the chamber pressure is less than the second
pressure.
17. The method of claim 15, further comprising: d) repeating steps
a) through c).
18. The method of claim 15, wherein the cooling gas is input to the
chamber at a temperature below 30.degree. C. and above a
condensation temperature of the cooling gas.
19. The method of claim 15, wherein the first pressure is less than
about 1 Torr and the second pressure is between 200 Torr and 600
Torr.
20. The method of claim 15, further comprising: d) purging the
chamber prior to flowing the cooling gas into the chamber.
21. The method of claim 15, wherein the cooling gas is allowed to
reside in the chamber for a period of time until a desired chamber
temperature is reached.
22. The method of claim 15, wherein the one or more cooling gas
sources comprises an inert gas source.
23. The method of claim 15, wherein the cooling gas comprises a gas
selected from the group consisting of nitrogen, argon, and
helium.
24. The method of claim 15, further comprising: d) exhausting the
cooling gas from the chamber; and e) cooling the cooling gas; and
f) returning the cooling gas to the chamber.
25. The method of claim 15, wherein (e) comprises: (i) flowing the
cooling gas through a cooling system.
Description
[0001] This application is a divisional of U.S. patent application
Ser. No. 09/261,700, filed Mar. 3, 1999, which is incorporated
herein in its entirety by reference.
FIELD OF THE INVENTION
[0002] The present invention relates to semiconductor vacuum
chambers, and mores specifically to an improved method and
apparatus for baking-out and cooling-down a semiconductor vacuum
chamber.
BACKGROUND OF THE INVENTION
[0003] Many semiconductor device fabrication processes such as
physical vapor deposition (PVD), high density plasma (HDP)
deposition, etc., employ high vacuum chambers (e.g.,
10.sup.-8-10.sup.-9 Torr) to affect the deposition of thin films on
a semiconductor wafer. To reach such high vacuum levels after a
vacuum chamber has been vented to atmosphere (e.g., for
maintenance, cleaning, etc.) and to prevent film contamination due
to the desorption of moisture and other gaseous elements and
compounds (i.e., potential contaminants) from the chamber's
interior surfaces (e.g., the chamber's shield, wafer pedestal,
etc.) during elevated temperature processing, the vacuum chamber's
interior surfaces must be heated to an elevated temperature (e.g.,
about 200.degree. C.) for a time period sufficient to desorb the
potential contaminants (i.e., chamber bake-out). Improper chamber
bake-out manifests itself in a degraded pre-process or "idle"
chamber pressure (i.e., base pressure), an enhanced rate of
pressure rise from the base pressure when the chamber's vacuum pump
is shut-off (i.e., rate of rise or "ROR"), and poor deposited film
quality (e.g., poor film resistivity), as described below with
reference to FIG. 1.
[0004] FIG. 1 is a side diagrammatic illustration, in section, of
the pertinent portions of a conventional high density plasma
sputtering chamber 21. The sputtering chamber 21 contains a wire
coil 23 which is operatively coupled to a first RF power supply 25.
The wire coil 23 may comprise a plurality of coils, a single turn
coil as shown in FIG. 1, a single turn material strip, or any other
similar configuration. The wire coil 23 is positioned along the
inner surface of the sputtering chamber 21, between a sputtering
target 27 and a wafer pedestal 29. The wafer pedestal 29 is
positioned in the lower portion of the sputtering chamber 21 and
typically comprises a pedestal heater (not shown) for elevating the
temperature of a semiconductor wafer supported by the wafer
pedestal 29 during processing within the sputtering chamber 21. The
sputtering target 27 is mounted to a water cooled adapter 31 in the
upper portion of the sputtering chamber 21 so as to face the
substrate receiving surface of the wafer pedestal 29. A cooling
system 31a is coupled to the adapter 31 and delivers cooling fluid
(e.g., water) thereto.
[0005] The sputtering chamber 21 generally includes a vacuum
chamber enclosure wall 33 having at least one gas inlet 35 and
having an exhaust outlet 37 operatively coupled to an exhaust pump
39 (e.g., a cryopump). A removable shield 41 that surrounds the
wire coil 23, the target 27 and the wafer pedestal 29 is provided
within the sputtering chamber 21. The shield 41 may be removed for
cleaning during chamber maintenance, and the adapter 31 is coupled
to the shield 41 (as shown). The sputtering chamber 21 also
includes a plurality of bake-out lamps 49 located between the
shield 41 and the chamber enclosure wall 33 for baking-out the
sputtering chamber 21 as described below.
[0006] The sputtering target 27 and the wafer pedestal 29 are
electrically isolated from the shield 41. The shield 41 preferably
is grounded so that a negative voltage (with respect to grounded
shield 41) may be applied to the sputtering target 27 via a DC
power supply 43 operatively coupled between the target 27 and
ground, and a negative bias may be applied to the wafer pedestal 29
via a second RF power supply 45 operatively coupled between the
pedestal 29 and ground. A controller 47 is operatively coupled to
the first RF power supply 25, the DC power supply 43, the second RF
power supply 45, the gas inlet 35 and the exhaust outlet 37.
[0007] To bake-out the sputtering chamber 21, conventionally the
bake-out lamps 49 are switched on between about 90% to 100% power
when the chamber is at high vacuum. The pedestal heater (not shown)
of the wafer pedestal 29 is set at about 200.degree. C., and the
water supply to the adapter may or may not be shut-off. The chamber
then is allowed to bake-out for about eight hours during which time
degassed material will raise the chamber pressure.
[0008] For chambers in which titanium, titanium nitride or tantalum
nitride are deposited, the above bake-out procedure is sufficient
to produce a good base pressure (e.g., low 10.sup.-8 Torr range),
ROR (e.g., about 10 to 20 nTorr/min), and good deposited film
quality.
[0009] The reason for the success of this bake-out procedure is
that both titanium and tantalum are excellent gettering materials
and, therefore, once deposited on the chamber surfaces during wafer
processing, can absorb (or "getter") moisture and other gaseous
elements and compounds from the sputtering chamber's atmosphere.
Typically, these gettered contaminants do not desorb, even during
elevated temperature processing, so that the chamber's base
pressure and ROR are not affected by the gettered contaminants. As
well, the gettered contaminants do not significantly affect
deposited film quality. An eight hour bake-out, however, results in
significant process downtime for the chamber being baked-out, as
well as for processing equipment upstream and downstream from the
processing chamber. Overall fabrication throughput thereby is
greatly degraded by conventional bake-out techniques.
[0010] When the conventional bake-out procedure is employed within
a chamber for copper deposition (e.g., a copper HDP chamber) the
results are less satisfactory due to copper's poor gettering
properties. For instance, even after an eight hour bake-out, a
copper HDP chamber can exhibit a high base pressure (e.g., low
10.sup.-7 Torr), a rapid ROR (e.g., about 200 nTorr/min) and a poor
deposited copper film quality (e.g., poor resistivity).
Accordingly, a need exists for an improved bake-out method that can
be performed more rapidly then conventional bake-out methods (e.g.,
so as to improve chamber throughput), and that sufficiently bakes
out even a copper chamber.
[0011] A process related to and often used in conjunction with
processing chamber bake-out is processing chamber cooling or
"cool-down". As chamber cool-down often is performed following high
temperature processing or following chamber bake-out, and can
result in significant process downtime for the processing chamber
being cooled, as well as for processing equipment upstream and
downstream from the processing chamber. For example, the time
required to perform chamber maintenance and repair is initially
determined by the temperature of the various chamber components
which must be sufficiently cooled before handling. Opening a
chamber at elevated temperatures exposes personnel to safety
hazards and may result in oxidation and contamination of the
chamber.
[0012] In order to mitigate the effects of contamination, chambers
are typically cooled under high vacuum conditions. Because some
processing chamber components are operated at temperatures in
excess of 600.degree. C., cool-down time may be on the order of
hours. The exact time required to reach a desired temperature
depends on the chamber. For example, chamber components having high
thermal conductivity (such as aluminum components) are capable of
cooling more rapidly than components having low thermal
conductivity (such as stainless steel components).
[0013] FIG. 2 shows a cooling curve for a typical ionized metal
plasma chamber cooled according to current practice. The chamber
was operated under normal conditions and then allowed to cool under
vacuum. The temperatures of a clamp ring, a coil, and a shield were
measured and recorded. For comparison, the temperature of the
shield was measured in two locations, zero (0) degrees from the RF
feedthrough and one hundred thirty-five (135) degrees from the
feedthrough. Because significant oxidation can occur at
temperatures at or above 100.degree. C., the desired temperature
before opening the chamber is preferably below about 50.degree. C.
As can be seen from FIG. 2, the time required for all components to
reach the desired temperature is at least three (3) hours. Thus,
the chamber remains idle and nonproductive during this cooling
period plus the time required to perform the routine maintenance or
repair, and to bake-out the chamber thereafter.
[0014] One attempt to cool a chamber (specifically, a Czochralski
silicon growth chamber) is found in U.S. Pat. No. 5,676,751,
entitled, "Rapid Cooling of CZ Silicon Crystal Growth System," by
Banan et al. The approach disclosed therein involves disposing a
porous insulating ring within the chamber and then saturating the
ring with a gas. The gas is intended to improve the thermal
conductivity of the insulating ring and to provide an annular
cooling medium for efficient heat exchange. Because the cooling
ring is believed to transfer heat more rapidly than other chamber
components the overall cooling time is reduced.
[0015] However, such an insulating system requires entirely new
chambers having enlarged capacities to accommodate the insulating
ring. Further, the porosity of the ring makes it unsuitable for
chambers wherein process gases are needed such as CVD chambers or
wherein a plasma is used such as a PVD, a CVD, or an IMP chamber.
In such chambers, the process and plasma gases would be absorbed by
the ring and/or outgassed during lower vacuum conditions thereby
upsetting the deposition process and contaminating substrates.
[0016] Therefore, there remains a need for an apparatus and method
which provides rapid cool-down of a vacuum chamber and its
components from an elevated temperature which protects the chamber
from contamination and oxidation while also ensuring the safety of
personnel. Preferably, such a method may be easily adopted by
existing vacuum chambers.
SUMMARY OF THE INVENTION
[0017] To address the needs of the prior art a novel method and
apparatus for baking-out and for cooling-down a vacuum chamber are
provided. In a first aspect of the invention, rather than maintain
the chamber to a low pressure, a dry inert gas (e.g., semiconductor
grade argon, helium, nitrogen, etc.) which conducts heat from the
vacuum chamber's bake-out lamps to the shield and from the shield
to the other parts within the vacuum chamber is introduced during
chamber bake-out. The dense inert gas behaves as a conduction path
between the bake-out lamps and the shield and between the shield
and the chamber parts surrounded by the shield (e.g., the target,
the coil, the pedestal, etc.) so that the shield and other parts
are heated more rapidly and to a higher temperature than
conventional bake-out techniques that are performed under high
vacuum conditions. With use of the present invention, even copper
chambers are sufficiently baked-out in a fraction of the time
required to bake-out a chamber by conventional techniques.
Applicants have found that the inert gas does not adversely become
trapped in chamber components or later outgas, and due to the
uniform heating of chamber components, contaminants desorbed from
one chamber surface do not reabsorb on another chamber surface.
[0018] To bake-out a vacuum chamber the chamber is pumped out and
is then isolated from the chamber's vacuum pump. A volume of inert
gas such as argon, helium or nitrogen is injected into the chamber,
the chamber's bake-out lamps are turned on and the cooling fluid
flow to the adapter is turned off. The inert gas may be injected,
the baking lamps may be turned on and the cooling fluid flow to the
adapter may be turned off simultaneously or in any order.
[0019] Preferably, the amount of inert gas injected raises the
chamber pressure to about 500 Torr (e.g., close to but less than
atmospheric pressure).
[0020] Because of the rapid transfer of heat between the bake-out
lamps and the shield and between the shield and the other chamber
parts through the gas as a heat transfer medium, adequate chamber
bake-out occurs quickly (e.g., typically in about two hours
depending on the chamber involved, the pressure of the inert gas,
the inert gas employed--gasses of smaller atomic mass conduct heat
faster, etc.). After the chamber is sufficiently baked-out, the
baking lamps are turned off and cooling fluid is flowed to the
adapter so as to cool the inert gas before it is pumped from the
vacuum chamber (e.g., to prevent overheating of the cryopump).
Because the adapter and the shield are coupled, the adapter cools
the shield, and the shield cools the inert gas. The inert gas is
quickly cooled thereby (e.g., typically in about one hour). After
the inert gas has cooled, it is pumped from the vacuum chamber, and
the bake-out of the chamber is complete.
[0021] With use of the inventive bake-out method, chamber bake-out
can be performed in far less than half the time of conventional
bake-out techniques. Specifically, the present inventor have found
that using the conventional bake-out technique described with
reference to FIG. 1, the aluminum shield of a copper HDP chamber
reaches only a temperature of about 120.degree. C. even for an
eight hour bake-out. However, by employing the inventive bake-out
method, the same aluminum shield can reach 200 to 300.degree. C.
during bake-out. In fact, care must be taken not to melt the
aluminum shield due to the rapid conduction of heat between the
bake-out lamps and the shield. Accordingly, a highly improved
bake-out method is provided.
[0022] In a second aspect of the invention, a process chamber is
provided having at least one source of a cooling gas having a high
thermal conductivity. The gas is input into the chamber and allowed
to reside therein for a period of time. Once a target temperature
is reached for the chamber and its components, the cooling gas is
evacuated.
[0023] In another aspect of the invention, a cooling gas having a
high thermal conductivity is input into a process chamber until a
desired pressure is reached. The chamber is allowed to cool for a
period of time and then the cooling gas is evacuated. During the
cooling stage, a pressure equilibrium may be maintained by
periodically flowing additional cooling gas into the chamber.
[0024] In yet another aspect of the invention, a cooling gas is
charged into a process chamber until a desired pressure is
established in the chamber. The cooling gas in brought into contact
with chamber components to allow for thermal conduction
therebetween. During the cooling stage, a pressure equilibrium is
maintained in the chamber by providing a constant flow of the
cooling gas into the chamber while simultaneously evacuating the
chamber at a substantially equal rate by engaging a vacuum
pump.
[0025] In still another aspect of the present invention, a process
chamber is purged by a purge gas and a cooling gas is then input
into the chamber. Thereafter, the cooling gas is evacuated, cooled,
and returned to the chamber. The cooling gas is permitted to reside
within the chamber for a period of time or, alternatively,
continuously recycled. Any of the above cooling aspects may be used
to affect more rapid cooling of a processing chamber following
chamber bake-out.
[0026] Other objects, features and advantages of the present
invention will become more fully apparent from the following
detailed description of the preferred embodiments, the appended
claims and the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0027] FIG. 1 is a side diagrammatic illustration, in section, of
the pertinent portions of a conventional high density plasma
sputtering chamber, as previously described;
[0028] FIG. 2 is a graphical representation of the cooling curve
for a typical ion metal plasma process chamber;
[0029] FIG. 3A is a side diagrammatic illustration, in section, of
the pertinent portions of an inventive high density plasma
sputtering chamber configured for performing the inventive bake-out
method;
[0030] FIG. 3B is a flowchart of an inventive bake-out method for
baking-out a vacuum chamber;
[0031] FIG. 4 is a top plan view of an automated semiconductor
manufacturing tool employing the inventive high density plasma
sputtering chamber of FIG. 3;
[0032] FIG. 5 is cross sectional view of an ion metal plasma
process chamber;
[0033] FIG. 6 is a flow chart representing the steps of an
inventive cooling method in accordance with the present invention;
and
[0034] FIG. 7 is a graphical representation of the cooling curve
for a chamber employing the inventive cooling method.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0035] FIG. 3A is a side diagrammatic illustration, in section, of
the pertinent portions of an inventive high density plasma
sputtering chamber 21' configured for performing the bake-out
method of the present invention. In addition to the components
23-49 of the conventional sputtering chamber 21, the inventive
sputtering chamber 21' comprises a source of inert gas 51
operatively coupled to the gas inlet 35 and to the controller 47.
Additionally, the controller 47 is operatively coupled to the
cooling system 31a and comprises a memory 53 preferably having a
program stored therein for automatically performing the inventive
bake-out method as described below.
[0036] FIG. 3B is a flowchart of an inventive bake-out method 300
that may be performed on any vacuum chamber, but which is described
with reference to the inventive sputtering chamber 211 of FIG. 3A.
The inventive bake-out method 300 starts at step 301.
[0037] In step 303, the sputtering chamber 21' is evacuated or
"pumped out" via the exhaust pump 39. Typically the sputtering
chamber 211 is pumped out following chamber maintenance and
cleaning. The sputtering chamber 21' is preferably pumped to its
"pre-bake-out" base level (e.g., the lowest level it can be pumped
to prior to bake-out).
[0038] In step 305, the sputtering chamber 211 is isolated from the
pump 39 in preparation for the introduction of inert gas into the
sputtering chamber 21' in step 307.
[0039] In step 307, an inert gas such as argon, helium, nitrogen or
the like is injected into the sputtering chamber 21' from the
source of inert gas 51 (through the gas inlet 35). Preferably
sufficient inert gas is flowed into the sputtering chamber 21' to
raise the chamber's pressure to slightly below atmospheric pressure
(to ensure the chamber is not inadvertently opened and exposed to
atmosphere due to a positive pressure within the chamber). Most
preferably chamber pressure is raised to about 500 Torr.
[0040] Thereafter, in step 309 the bake-out lamps 49 are turned on
(e.g., at about 90% to 100% power), and in step 311 the cooling
fluid supply to the adapter 31 is shut off. Turning off the cooling
fluid supply to the adapter 31 allows the shield 41 to heat to a
higher and more uniform temperature because the shield is
operatively coupled to the adapter and looses heat thereto. It will
be understood that steps 307-311 may be performed simultaneously or
in any order.
[0041] The dense inert gas within the sputtering chamber 21'
behaves as a conduction path between the bake-out lamps 49 and the
shield 41, and between the shield 41 and the coil 23, the target
27, the wafer pedestal 29, the adapter 31 and any other components
within the sputtering chamber 211. Because of the rapid transfer of
heat through the chamber and between isolated chamber components
via the inert gas, the sputtering chamber 21' is baked-out quickly
(e.g., typically in about two hours depending on the chamber size,
the pressure of the inert gas, the inert gas employed, etc.).
Preferably the shield 41 reaches a temperature of at least
200.degree. C. to 300.degree. C. during chamber bake-out to ensure
adequate desorption of potential contaminants from chamber
surfaces.
[0042] In step 313, bake-out of the sputtering chamber 21' is
continued until enough moisture and other gaseous elements and
compounds have been desorbed from the chamber's surface to achieve
the desired base pressure, rate of rise and deposited film quality
for the sputtering chamber 21'. Thereafter, in step 315, to cool
the inert gas (e.g., to prevent overheating of the pump 39 when the
inert gas is pumped from the sputtering chamber 21') cooling fluid
is flowed to the adapter 31, and in step 317 the bake-out lamps 49
are turned off. Step 315 and 317 may be performed simultaneously or
in any order.
[0043] Because the adapter 31 and the shield 41 are coupled, the
adapter 31 cools the shield 41, and the shield 41 cools the inert
gas. The inert gas thereby is cooled quickly (e.g., typically in
about one hour). Accordingly, in step 319, a sufficient time is
provided to allow the inert gas to cool.
[0044] Thereafter, in step 321, the inert gas is evacuated from the
sputtering chamber 21' via the pump 39. In step 323 the inventive
bake-out method 300 ends.
[0045] The higher temperatures to which the shield 41, the coil 23,
the target 27 and/or the adapter 31 are heated, significantly
improves chamber bake-out, even for chambers employing poor
gettering materials such as copper, and even though bake-out time
is significantly reduced. Therefore, following the inventive
bake-out method 300, the sputtering chamber 21' has a lower base
pressure, a lower rate of rise and produces a higher quality
deposited film than that achieved by conventional bake-out
methods.
[0046] As previously stated, the memory 53 preferably contains a
program for automatically performing the inventive bake-out method
300 on the sputtering chamber 21' of FIG. 3A. Specifically, the
memory 53 directs the controller 47 to control the cooling system
31a, the gas inlet 35, the gas outlet 37, the pump 39, the bake-out
lamps 49 and the inert gas source 51 so as to perform the inventive
bake-out method 300.
[0047] FIG. 4 is a top plan view of an automated semiconductor
manufacturing tool 55 useful for performing the inventive method.
Specifically, the automated semiconductor manufacturing tool 55
comprises a pair of chambers, a buffer chamber 57 and a transfer
chamber 59 which house a first and a second wafer handler 61, 63,
respectively. The buffer chamber 57 is operatively coupled to a
pair of load locks 65, 67 and to a pair of pass-through chambers 69
and 71. Other chambers such as degassing or cool-down chambers also
may be coupled to the buffer chamber 57.
[0048] The transfer chamber 59 is coupled to the pass-through
chambers 69, 71, and to a plurality of processing chambers 73, 75
and 77. Most importantly the transfer chamber 59 is coupled to the
inventive sputtering chamber 21' of FIG. 3A.
[0049] A controller 79 comprising a microprocessor 81 and a memory
83 is operatively coupled to the first and second wafer handlers
61, 63, to the load locks 65, 67, to the four processing chambers
21', 73-77, and to the various slit valves (not shown) for
selectively sealing the load locks, pass-through chambers and
processing chambers. The memory 83 contains a program for
performing transfers between and processing within each of the
processing chambers. The memory 83 also may be programmed to
perform the inventive bake-out method on any of the processing
chambers 21', 73-77. Note that because of the significant decrease
in bake-out time achieved with the inventive bake-out method, the
overall productivity of the tool 55 is significantly increased, as
less downtime is experienced by chambers employing the inventive
bake-out method, as well as by chambers upstream and downstream
therefrom.
[0050] FIG. 5 is a schematic cross-sectional view of an inductively
coupled ion metal plasma chamber 110 suitable for performing a PVD
process. As shown in this figure, chamber 110 is defined
principally by a chamber wall 112 and a target backing plate 114. A
PVD target 116, having a composition comprising at least part of
the material being sputter deposited, is mounted to the target
backing plate 114 and defines an upper boundary of a processing
region 115. The lateral boundary of the processing region 115 is
defined by a shield 119 which supports a clamp ring 117 in the
chamber 110. A substrate 118 is shown supported on a movable
pedestal 120 disposed opposite the target 116. A high vacuum pump
134, such as a cryogenic pump, communicates with the chamber 110
through an exhaust line 136 having a throttle valve 133 disposed
therein. A thermocouple 135 disposed in the chamber wall 112
monitors the operating temperature of the chamber 110. A high
purity sputtering gas, such as argon, is supplied to the chamber
110 via a first gas line 122 from a first gas source 124 as metered
by mass flow controller 125. A second gas source 126 supplies a
venting gas via gas line 127 at a rate determined by a flow
controller 128. A cooling gas source 129 and mass flow controller
130 are shown coupled to the chamber 110 to supply a
post-processing cooling gas. Although the cooling gas source 129 is
shown here having a dedicated second gas line 132 leading to the
chamber, in another embodiment the gas source 129 may communicate
with the chamber 110 via the first gas line 122. Additional gas
sources may be provided to supply more than one post-processing
cooling gas.
[0051] An inductive coil 138 is helically disposed along the
chamber wall 112 adjacent the processing region 115. Three
independent power supplies are used to achieve the desired
electrical conditions in the chamber 110. A DC power supply 140 is
coupled to the target 116 while an RF power source 142 supplies
electrical power in the megahertz range to the inductive coil 138.
Another RF power source 144 applies electrical power in the
frequency range of 100 KHz to a few megahertz to the pedestal 120
in order to bias it with respect to the plasma. Magnets 146 are
disposed behind the target 116 to create a magnetic field adjacent
to the target 116. Each of the various chamber components are
connected to a controller 137.
[0052] In operation, the pedestal 120 raises the substrate 118 to a
processing position at which position the substrate 118 is secured
to the pedestal by the clamp ring 117. An inert gas, such as argon,
is then flowed from the first gas source 124. The DC power supply
140 negatively biases the target 116 with respect to the pedestal
120 and causes the argon gas to ionize and form a plasma. The RF
coil 138 increases the plasma flux, that is, increases the density
of ionized particles. The magnets 146 act to significantly increase
the density of the plasma adjacent to the target 116 thereby
improving the sputtering efficiency. The positively charged ions
are attracted to the negatively biased target 116 with enough
energy that the ions sputter particles from the target 116. The
sputtered particles travel primarily along ballistic paths, and
some of them strike the substrate 118 to deposit on the substrate.
The RF power source 144 provides an additional attractive force to
the particles dislodged from the target 116 by capacitively
coupling the pedestal and the plasma.
[0053] In a dynamic system, such as in the process chamber 110
described above, gas is flowed into the chamber 110 and the
pressure is preferably held constant at a pre-determined process
pressure. The pump 134 is operated concurrently to achieve
stabilization of the pressure and to maintain a steady pressure
during the processing steps. The mass flow controller 125 allows
the gas to be flowed into the chamber 110 at a constant rate or at
a variable rate as needed. Once a desired amount of deposition is
achieved, the flow of gas from the first gas source 124 and the
power from the power supplies is terminated. The pump 134 and the
second gas source 126 then cooperate to vent the chamber 110 after
which the substrate 118 is removed.
[0054] Upon removal of the substrate 118, the chamber 110 is cooled
according to the present invention as depicted in the flow chart of
FIG. 6. At step 150, the chamber 110 is sealed and the gas sources
124 and 126 are isolated from the chamber 110 by their respective
mass flow controllers 125, 128. At step 152, the pump 134 is
engaged in order to evacuate the chamber 110 to a pressure
preferably less than about 1 Torr. Most preferably, a high vacuum
condition (e.g., on the order of 10.sup.-9 Torr) is achieved so
that the subsequently introduced cooling gas, described below, is
not diluted by the presence of gases having inferior thermal
conductivity. At steps 154 and 156 , the pump 134 is terminated and
the mass flow controller 130 opens the cooling gas source 129 to
the chamber 110 to backfill the chamber 110 with a cooling gas
therein until a desired pressure is achieved. The cooling gas (or
gases) preferably has a high thermal conductivity and includes such
gases as nitrogen (thermal conductivity of 7.18.times.10.sup.5
g.-cal/(sec..multidot.cm.sup.2) (.degree. C./cm) at 100.degree.
C.), argon (thermal conductivity of 5.087.times.10.sup.5
g.-cal/(sec..multidot.cm.sup.2) (.degree. C./cm) at 100.degree.
C.), or helium (thermal conductivity of 39.85.times.10.sup.5
g.-cal/(sec..multidot.cm.sup.2) (.degree. C./cm) at 100.degree.
C.). While helium and nitrogen are preferred, any gas having a
thermal conductivity greater than 5.times.10.sup.5
g.-cal/(sec..multidot.cm.sup.2- ) (.degree. C,/cm) at 100.degree.
C. may be used in accordance with the present invention. Gases with
thermal conductivities lower than 5.times.10.sup.5
g.-cal/(sec..multidot.cm.sup.2) (.degree. C.,/cm) may be used, but
are not preferred because the cooling rate will be lower. The
temperature of the cooling gas prior to its introduction into the
chamber depends upon the particular gas used. The gases are
preferably cooled to a lower limit above a condensation
temperature. In general, the temperature will be ambient
temperature, or between about 25 and about 30.degree. C. The
desired pressure may be between about 1 and 760 Torr and preferably
about 500 Torr. Although pressures below 1 Torr may be used, in
general higher pressures are preferred because thermal exchange
between the gas medium and the vacuum system is proportionally
increased. However, at pressures above approximately 500-550 Torr,
the concentration of contaminants in the cooling gases (all
purified gases still contain some level of contaminants) increases
thereby contaminating the chamber and components. The presence of
contaminants results in a critical pressure level, or saturation
level, above which the increase in thermal exchange is negligible
and danger of contamination becomes prohibitive. Thus, decreasing
thermal exchange provides a lower pressure limitation and
contamination provides an upper pressure limitation.
[0055] Once the desired chamber pressure is achieved, the flow of
cooling gas is terminated, as indicated at step 158, and the
cooling gas is permitted to reside in the chamber for a period of
time as determined by the desired temperature. During the cool down
cycle, the cooling gas flow is optionally resumed periodically to
compensate for pressure reduction due to cooling as indicated by
step 158a. At step 158b, the temperature is checked against the
target temperature; if the chamber temperature is equal to or less
than the target temperature the chamber is backfilled to ambient
pressure and may then be opened as indicated by step 165. The
processing parameters such as gas flow rates and pressures as well
as the positioning of the substrate are controlled by a computer
control described below.
[0056] The present invention also contemplates other alternatives
which may be used to maintain a desired pressure while cooling the
chamber after step 156. In each case, the chamber 110 is cooled to
a target temperature at which point the chamber 110 is backfilled
to ambient pressure and may be opened as indicated by steps 164 and
165. Step 160 indicates one alternative where the cooling gas flow
is reduced to a flow rate sufficient to maintain the chamber
pressure within the desired range, accounting for pressure
reduction due to cooling. The pressure may be continuously
monitored and adjusted by controlling the gas flow rate according
to the computer control described in detail below.
[0057] Another alternative, indicated at step 162, provides
continuously flowing the cooling gas into the chamber 110 while
simultaneously operating the pump 134 such that the cooling gas is
continuously introduced and evacuated from the chamber 10 at a rate
sufficient to hold the pressure substantially constant. As in each
of the preceding embodiments, the gas flow rate is controlled and
adjusted by the computer control which responds to the chamber
pressure.
[0058] Those skilled in the art will recognize alternative methods
of cooling the chamber 110 which are contemplated by the present
invention. For instance, the chamber 110 may initially be purged of
residual processing gases by flowing the cooling gas through the
chamber 110 while evacuating the cooling gas from the lower end of
the chamber 110 by the pump 134 as indicated by step 166 in FIG. 6.
The present invention may be further enhanced by providing a
cooling system 141 through which the cooling gas may be flowed and
then recycled to the chamber 110. A further optional step is to
monitor the chamber temperature, evacuate the chamber 110 once the
cooling gas reaches some predetermined temperature greater than the
final target temperature, and then backfill the chamber with a new
supply of cooling gas. This cycle is repeated until the target
temperature is reached. Additionally, the cooling curve of present
invention may be improved by equipping the chamber 110 with
multiple cooling gas sources and introducing a mixture of cooling
gases (such as argon, nitrogen, helium, etc.) into the chamber
110.
[0059] Because the thermal conductivity of gases varies with
temperature, the present invention may be optimized by selectively
introducing different gases according to their thermal conductivity
at a given temperature range. For example, a first cooling gas may
be introduced to cool the chamber from a first temperature to a
second temperature. Subsequently, a second cooling gas having a
thermal conductivity greater than the first cooling gas at
temperatures below the second temperature is introduced to cool the
chamber from the second temperature to a third temperature. In a
final stage, a third cooling gas having a thermal conductivity
greater than both the first and the second cooling gases at
temperatures below the third temperature is introduced to cool the
chamber to a desired temperature at which the chamber may be safely
opened without risk to personnel and at which oxidation is
minimized. These series of steps are merely illustrative of one
embodiment of the present invention. Other approaches using two or
more gases having varying thermal conductivities may be without
departing from the spirit and scope of the present invention. This
multi-stage approach allows for a rapid chamber cool-down by
selecting the most thermally conductive gas at a particular
temperature.
[0060] The total time required to cool down a chamber is a function
of many factors. Therefore cool-down time may be reduced by
streamlining each of the steps recited above. For example, because
the cooling curve is improved at higher pressures, the time
required to backfill the chamber to a particular pressure with the
cooling gas should be minimized. The precise times are, of course,
dependent on the particular chamber capacity. However, a pressure
of 500 Torr is preferably reached in approximately 1 minute or
less.
[0061] The described embodiment is only representative of invention
and should not be considered limiting of its scope. Although the
above description discusses the present invention in the context of
an ionized metal plasma chamber, other chambers which operate at
elevated temperatures such as CVD chambers, RTP chambers, and PVD
chambers may use the present invention to advantage.
[0062] The processes described above can be implemented using a
computer program product that runs on a conventional computer
system comprising a central processor unit (CPU) connected to a
memory system with peripheral control components, such as for
example a 68400 microprocessor, commercially available from
Synenergy Microsystems, California. The computer program code can
be written in any conventional computer readable programming
language such as for example 68000 assembly language, C, C++, or
Pascal. Suitable program code is entered into a single file, or
multiple files, using a conventional text editor, and stored or
embodied in a computer usable medium, such as a memory system of
the computer. If the entered code text is in a high level language,
the code is compiled, and the resultant compiler code is then
linked with an object code of precompiled windows library routines.
To execute the linked compiled object code, the system user invokes
the object code, causing the computer system to load the code in
memory from which the CPU reads and executes the code to perform
the tasks identified in the program.
[0063] A gas control subroutine has program code for controlling
gas composition and flow rates. Generally, the gas supply lines
122, 132 for each of the gases comprise one or more components that
can be used to measure and control the flow of gas into the chamber
110 such as the mass flow controllers 125, 128, 130 shown in FIG.
5. The gas control subroutine ramps up/down the mass flow
controllers 125, 128, 130 to obtain the desired gas flow rate. The
gas control subroutine is invoked by the chamber manager
subroutine, as are all chamber component subroutines, and receives
from the chamber manager subroutine parameters related to the
desired gas flow rates. Typically, the gas control subroutine
operates by opening the gas supply lines 122, 132, and repeatedly
(i) reading the necessary mass flow controllers 125, 128, 130, (ii)
comparing the readings to the desired flow rates received from the
chamber manager subroutine, and (iii) adjusting the flow rates of
the gas supply lines 122, 132 as necessary. Furthermore, the gas
control subroutine includes steps for monitoring the gas flow rates
for unsafe rates and activating the mass flow controllers when an
unsafe condition is detected.
[0064] When the pressure control subroutine is invoked, the desired
or target pressure level is received as a parameter from the
chamber manager subroutine. The pressure control subroutine
operates to measure the pressure in the chamber 110 by reading one
or more conventional pressure manometers connected to the chamber
110, compare the measure value(s) to the target pressure, obtain
PID (proportional, integral, and differential) values from a stored
pressure table corresponding to the target pressure, and adjust the
throttle valve 133 according to the PID values obtained from the
pressure table.
[0065] FIG. 7 is a graphical representation of the results obtained
by a method of the present invention in the same ionized metal
plasma chamber used to obtain the data shown in FIG. 2. The chamber
is an IMP chamber available from Applied Materials, Inc. located in
Santa Clara, Calif. The chamber was operated under normal
conditions and then vented with an inert gas. Nitrogen was then
flowed into the chamber for about one minute until a pressure of
approximately 550 Torr was reached. Prior to its introduction into
the chamber, the nitrogen was maintained above condensation
temperature and at about 25 to 30.degree. C. (i.e., ambient
temperature). The cooling gas was then allowed to reside in
chamber. FIG. 7 shows the decreasing temperature over time of three
components: a clamp ring, a coil, and a shield (for comparison the
temperature of the shield was measured at zero (0) degrees from the
RF feedthrough and one hundred thirty-five (135) degrees from the
RF feedthrough). As can be seen from comparison with FIG. 2, the
method of the present achieved a significant reduction in the time
needed to cool the chamber components on the order of hours.
[0066] The foregoing description discloses only the preferred
embodiments of the invention, modifications of the above disclosed
apparatus and method which fall within the scope of the invention
will be readily apparent to those of ordinary skill in the art. For
instance, the inventive bake-out may be performed with any vacuum
chamber. Specific bake-out times, cooling times, inert gas pressure
and the like will vary widely depending on the pre-bake-out
condition of the vacuum chamber, the size of the chamber, the
various shields, pedestals, targets, etc., within the chamber, and
with other similar factors. Further, the process may be performed
manually, automatically or semi-automatically.
[0067] Accordingly, while the present invention has been disclosed
in connection with the preferred embodiments thereof, it should be
understood that other embodiments may fall within the spirit and
scope of the invention, as defined by the following claims.
* * * * *