U.S. patent application number 09/211998 was filed with the patent office on 2001-12-27 for high temperature chemical vapor deposition chamber.
Invention is credited to CHEN, JAMES J, CHIAO, STEVE H, HUSTON, JOEL, LEI, LAWRENCE CHUNG-LAI, NGUYEN, ANH N, UMOTOY, SALVADOR P, VO, BE V.
Application Number | 20010054381 09/211998 |
Document ID | / |
Family ID | 22789133 |
Filed Date | 2001-12-27 |
United States Patent
Application |
20010054381 |
Kind Code |
A1 |
UMOTOY, SALVADOR P ; et
al. |
December 27, 2001 |
HIGH TEMPERATURE CHEMICAL VAPOR DEPOSITION CHAMBER
Abstract
An apparatus for wafer processing, which comprises a chamber
body and a heated liner which are thermally isolated from each
other by isolating pins. During wafer processing, e.g., deposition
of titanium nitride film by thermal reaction between titanium
tetrachloride and ammonia, a wafer substrate is heated to a
reaction temperature in the range of 600-700.degree. C. by a heated
support pedestal. The chamber liner and the interior chamber walls
are maintained at a temperature between 150-250.degree. C. to
prevent deposition of undesirable by-products inside the chamber.
This facilitates the chamber cleaning procedure, which can be
performed using an in-situ chlorine-based process. The excellent
thermal isolation between the heated liner and the chamber body
allows the chamber exterior to be maintained at a safe operating
temperature of 60-65.degree. C. A heated exhaust assembly is also
used in conjunction with the process chamber to remove exhaust
gases and reaction by-products. External heaters are used to
maintain the exhaust assembly at a temperature of about
150-200.degree. C. to minimize undesirable deposits on the interior
surfaces of the exhaust assembly.
Inventors: |
UMOTOY, SALVADOR P;
(ANTIOCH, CA) ; CHIAO, STEVE H; (FREMONT, CA)
; NGUYEN, ANH N; (MILPITAS, CA) ; VO, BE V;
(SUNNYVALE, CA) ; HUSTON, JOEL; (SAN JOSE, CA)
; CHEN, JAMES J; (SAN JOSE, CA) ; LEI, LAWRENCE
CHUNG-LAI; (MILPITAS, CA) |
Correspondence
Address: |
APPLIED MATERIALS, INC
PATENT COUNSEL
LEGAL AFFAIRS DEPT
P O BOX 450A
SANTA CLARA
CA
95052
|
Family ID: |
22789133 |
Appl. No.: |
09/211998 |
Filed: |
December 14, 1998 |
Current U.S.
Class: |
118/715 ;
118/725; 427/248.1 |
Current CPC
Class: |
C23C 16/4412 20130101;
C23C 16/4405 20130101; C23C 16/45565 20130101; C23C 16/45514
20130101; C23C 16/4401 20130101; C23C 16/5096 20130101; C23C
16/4584 20130101; C23C 16/45574 20130101 |
Class at
Publication: |
118/715 ;
118/725; 427/248.1 |
International
Class: |
C23C 016/00; H01L
021/44 |
Claims
What is claimed is:
1. Apparatus for wafer processing, comprising: a chamber body; and
a liner being substantially enclosed in said chamber body, where
said liner is maintained at a first temperature T1, and said
chamber body is maintained at a second temperature T2, where said
second temperature T2 is lower than said first temperature T1.
2. The apparatus as in claim 1, wherein said liner and said chamber
body are spaced apart from one another.
3. The apparatus as in claim 2, wherein said liner and said chamber
body are separated from one another by an isolating member.
4. The apparatus as in claim 3, wherein said isolating member is a
plurality of pins.
5. The apparatus as in claim 4, wherein said pins are made of
stainless steel or nickel.
6. The apparatus as in claim 1, wherein said wafer processing
comprises depositing titanium nitride film from a reaction of
titanium tetrachloride and ammonia.
7. The apparatus as in claim 1, wherein said first temperature T1
is approximately between 150.degree. C. and 250.degree. C.; and
said second temperature T2 is approximately between 60.degree. C.
and 65.degree. C.
8. The apparatus as in claim 1, wherein said liner further
comprises a heater embedded therein.
9. The apparatus as in claim 1, further comprising: a pedestal
positioned centrally within said liner to support a substrate
within the chamber, where said pedestal is maintained at a third
temperature T3 approximately between 600.degree. C. and 800.degree.
C.
10. The apparatus as in claim 9, wherein said pedestal further
comprises a heating element disposed inside said pedestal.
11. The apparatus as in claim 9, wherein said pedestal is made of a
ceramic material.
12. The apparatus as in claim 11, wherein said ceramic material is
aluminum nitride.
13. The apparatus as in claim 9, wherein said pedestal further
comprises an electrode disposed inside said pedestal, and said
electrode is capable of imparting radio frequency power to a volume
proximate said pedestal.
14. The apparatus as in claim 1, further comprising: an exhaust
assembly connected to said chamber body; and at least one heater
element positioned proximate said exhaust assembly to maintain said
exhaust assembly at a temperature T4.
15. The apparatus as in claim 14, where said temperature T4 is
approximately between 150.degree. C. and 200.degree. C.
16. The apparatus as in claim 14, where said at least one heater
element is disposed around an exterior surface of said exhaust
assembly.
17. The apparatus as in claim 1, further comprising: a pedestal
having a top surface, a bottom surface, an outer perimeter and an
outside edge; a substantially annular edge ring having a top
surface, a bottom surface, an inside surface, an outside surface,
and a protruded portion; and said bottom surface, said inside
surface and said protruded portion of said edge ring are disposed
adjacent to and in close proximity to said outer perimeter and
outside edge of said pedestal.
18. Apparatus for wafer processing, comprising: a substantially
bucket-shaped chamber body having a chamber side and a
substantially annular-shaped chamber base having an inside bottom
surface and defining a bottom opening in said chamber body, said
chamber body capable of being maintained at a temperature T2; a
liner being substantially enclosed by said chamber body having a
top end and a bottom end, an inside surface and an outside surface;
where said liner is maintained at a temperature T1 which is higher
than said temperature T2 of said chamber body; an isolating member
disposed between said bottom end of said liner and said inside
surface of said chamber base that maintains said liner and said
chamber base in a spaced apart relation; a pedestal assembly
positioned centrally within said bottom opening of said chamber
body and within said liner; said pedestal assembly comprising: a
pedestal with a top surface, a bottom surface and a circumferential
edge having a heater and at least one electrode embedded therein,
said pedestal capable of being maintained at a temperature T3 which
is higher than temperatures T1 and T2; a shaft-like portion
connected to said bottom surface of said pedestal; a showerhead
disposed above said pedestal having a top surface and a bottom
surface; an edge ring disposed at said circumferential edge of said
pedestal; and an exhaust assembly connected to said chamber body
having an interior surface and an exterior surface, with at least
one heater element disposed around said exterior surface to
maintain said exhaust assembly at a temperature T4.
19. The apparatus as in claim 18, where said liner has a heater
embedded therein.
20. The apparatus as in claim 18, where said isolating member is a
plurality of pins.
21. The apparatus as in claim 18, wherein said temperature T1 is
approximately between 150.degree. C. and 250.degree. C.; said
temperature T2 is approximately between 60.degree. C. and
65.degree. C.; said temperature T3 is approximately between
600.degree. C. and 800.degree. C.; and said temperature T4 is
approximately between 150.degree. C. and 200.degree. C.
22. The apparatus as in claim 18, wherein said showerhead is
capable of being coupled to a radio-frequency source for imparting
radio-frequency to said showerhead.
23. A method of wafer processing comprising the steps of: a)
heating a pedestal to temperature T3; b) maintaining a liner at
temperature T1 and a chamber at temperature T2; and c) injecting
process gases into said chamber for film deposition, where
T3>T1>T2.
24. The method as in claim 23, where said temperature T1 is
approximately between 150.degree. C. and 250.degree. C., said
temperature T2 is approximately between 60.degree. C. to 65.degree.
C., and said temperature T3 is approximately between 600.degree. C.
to 800.degree. C.
25. The method as in claim 24, further comprising the step of
introducing a first purge gas to flow past said bottom surface of
said pedestal and a second purge gas to flow between said liner and
an inside surface of said chamber.
26. The method as in claim 25, wherein said purge gas is nitrogen
or argon.
27. The method as in claim 23, further comprising the step of
annealing said wafer after film deposition.
28. The method as in claim 27, wherein said annealing step
comprises heating said wafer to a temperature higher than T3.
29. The method as in claim 27, wherein said annealing step
comprises subjecting said wafer to a plasma inside said
chamber.
30. The method as in claim 23, wherein said injecting step
comprises introducing at least two process gases without pre-mixing
the process gases prior to entry into said chamber.
31. The method as in claim 23, wherein said liner is heated to said
temperature T1 by a heater embedded in said liner.
32. The method as in claim 23, further comprising the step of
cleaning said chamber after said film deposition.
33. The method as in claim 32, wherein said cleaning step comprises
the steps of: maintaining said pedestal at a temperature between
600-700.degree. C.; maintaining said chamber at a temperature
between 150-250.degree. C.; and introducing chlorine gas into said
chamber.
34. The method as in claim 33, wherein said cleaning step comprises
creating a plasma containing chlorine species inside said chamber.
Description
BACKGROUND OF THE DISCLOSURE
[0001] 1. Field of the Invention
[0002] The present invention relates to semiconductor wafer
processing systems and, more particularly, to a high temperature
chemical vapor deposition (CVD) chamber with a heated inside liner,
and a temperature-controlled outer chamber body.
[0003] 2. Description of the Background Art
[0004] Titanium nitride (TiN) film has found wide applications in
ultra large-scale integrated circuits (ULSI) as a diffusion barrier
and as an adhesion layer for tungsten contacts. Low temperature
reactive sputtering of Ti in the presence of nitrogen has been used
in the past to deposit TiN films upon semiconductor wafers.
However, as device geometries become increasingly smaller, the
resulting step coverage from a sputtered TiN film is no longer
adequate. Therefore, chemical vapor deposition (CVD) techniques
have become the methods of choice in ULSI applications. For
example, TiN film from a titanium tetrachloride based CVD process
can be used as a high aspect ratio contact barrier, a capacitor top
electrode or in plug fill processes below 0.18 .mu.m.
[0005] Both cold wall and hot wall low pressure chemical vapor
deposition (LPCVD) processes have been used for depositing TiN
films using a reaction between titanium tetrachloride (TiCl.sub.4)
and ammonia (NH.sub.3). A cold wall reactor contains a wafer that
is heated to a temperature above the reaction temperature of the
process gases, e.g., over 650.degree. C., by a halogen lamp that is
located external to the chamber. However, since the chamber walls
are cold (unheated), process by-products such as adduct ammonia
salts will detrimentally form on the interior surfaces of the cold
chamber walls or other cold surfaces. During thermal cycling of the
chamber, these deposits may flake and fall on a wafer causing
contamination and reducing wafer yield. Since these reaction
by-products cannot be removed by in-situ chamber cleaning
processes, frequent chamber disassembly and cleaning is required.
This necessitates the opening of the chamber to the atmosphere, and
results in considerable down time for the chamber.
[0006] Alternatively, quartz hot wall reactors have been used to
form high quality TiN films. The heated walls of these reactors
help reduce accumulation of undesirable deposits, such as adduct
ammonia salts, on the interior chamber walls. However, hot wall
chambers can be dangerous to operate because of the high
temperature of the walls, e.g., 150-200.degree. C. Furthermore, it
is difficult to achieve uniform heating of the chamber walls and
other interior surfaces such that no undesirable deposits form.
[0007] One possible solution is the use of a chamber liner, such as
that disclosed in U.S. Pat. No. 5,348,587, issued on Sep. 20, 1994,
to Eichman et al., entitled "Apparatus for Elimination of Low
Temperature Ammonia Salts in TiCl.sub.4 NH.sub.3 CVD Reaction,"
which is a continuation of U.S. Pat. No. 5,271,963, issued on Dec.
21, 1993. Both patents are herein incorporated by reference.
Eichman et al. discloses an inside liner which is partly heated by
lamps external to the chamber, and partly heated by a secondary
plasma. This heated liner is located within a cold reactor wall
enclosure. The heated liner lies against the inner surface of the
cold reactor wall, and, as such, is only partially insulated from
the reactor wall. Not only does this contact promote excessive
thermal conduction to the reactor wall resulting in the chamber
wall becoming dangerously hot, but additional heating of the liner
will be needed to compensate for the heat lost to the wall.
[0008] Therefore, a need exists in the art for a CVD chamber having
a heated liner which substantially defines a chamber cavity and is
thermally isolated from the external chamber body.
SUMMARY OF THE INVENTION
[0009] The disadvantages of the prior art are overcome by an
apparatus for processing a wafer having a chamber body that
encloses a chamber liner, where the liner is maintains a spaced
apart distance from the chamber body such that the liner is
maintained at a higher temperature than the chamber body. As such,
the liner can be maintained at a temperature that reduces the
amount of deposition on the liner while maintaining a safe
temperature for the chamber body.
[0010] More specifically, the present invention relates to a
process chamber system for high temperature film deposition, e.g.,
using a reaction between titanium tetrachloride (TiCl.sub.4) and
ammonia (NH.sub.3) to deposit titanium nitride (TiN). The system
comprises a process chamber and an exhaust assembly. The process
chamber has an inside liner which is maintained at a temperature of
approximately 150-250.degree. C., while the chamber body is
maintained at a temperature of approximately 60-65.degree. C. or
below. The liner can either be heated directly by a resistive
heater embedded in the liner, or indirectly by a heated wafer
support pedestal. The liner, which is substantially cylindrical, is
enclosed within the bucket-shaped chamber body having a cylindrical
wall and a base. Isolating pins are located between the bottom of
the liner and the inside surface of the chamber base such that a
spacing is maintained between the liner and the chamber body, i.e.,
the liner only contacts the chamber body through the isolating
pins. Excellent thermal isolation is achieved between the liner and
the chamber body because of the low thermal conductivity resulting
from the small contact area between the isolating pins and the
liner.
[0011] The process chamber further comprises a heated wafer support
pedestal for supporting and heating a semiconductor wafer and a
showerhead for separately introducing TiCl.sub.4 and NH.sub.3 into
the process chamber into a space above the wafer. The wafer is
maintained at a temperature of approximately 600-700.degree. C.
such that a thermal reaction occurs at the surface of the wafer
between TiCl.sub.4 and NH.sub.3, resulting in the formation of a
TiN film upon the wafer.
[0012] The exhaust assembly is connected to the process chamber to
allow for continuous pumping of gases away from the process
chamber. In one embodiment, a substantial portion of the exhaust
assembly is maintained at approximately 150.degree. C.-200.degree.
C. by the use of several heaters disposed on the outside walls of
the exhaust assembly. Such heating reduces reaction by-product
accumulation within the exhaust assembly.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] The teachings of the present invention can be readily
understood by considering the following detailed description in
conjunction with the accompanying drawings, in which:
[0014] FIG. 1 is a partial cross-sectional perspective view of the
high temperature CVD chamber system of the present invention,
showing a process chamber and an exhaust assembly;
[0015] FIG. 2a is a cross-sectional view of the process chamber,
showing details of various components inside the process chamber of
FIG. 1;
[0016] FIG. 2b shows an enlarged cross-sectional view around the
area of the inside liner, the isolating pin and the chamber body of
FIG. 2a;
[0017] FIG. 3a shows a cross-sectional view of the showerhead
assembly;
[0018] FIG. 3b shows a cross-sectional view of the dual-gas
faceplate of the showerhead assembly of FIG. 3a;
[0019] FIG. 4a is a top view of the cooling plate;
[0020] FIG. 4b is a cross-sectional view showing the channel inside
the cooling plate of FIG. 4a;
[0021] FIG. 4c is a side view of the cooling plate of FIG. 4a;
[0022] FIG. 5a is a cross-sectional view of the process chamber
showing the bottom purge arrangement;
[0023] FIG. 5b is a perspective view of another embodiment of an
edge ring;
[0024] FIG. 5c is a partial cross-sectional view of the edge ring
(line 5c in FIG. 5b) resting atop of the liner;
[0025] FIG. 5d is a partial cross-sectional view of the edge ring
(line 5d in FIG. 5b) resting atop of the liner;
[0026] FIG. 6 shows a partial cross-sectional view of the exhaust
assembly; and
[0027] FIG. 7a shows a conceptual design of a process chamber
modified for plasma application; and
[0028] FIG. 7b is a cross-sectional view illustrating the RF
connections to the chamber of FIG. 7a.
[0029] To facilitate understanding, identical reference numerals
have been used, where possible, to designate identical elements
that are common to the figures.
DETAILED DESCRIPTION OF THE INVENTION
[0030] FIG. 1 shows a partial cross-sectional perspective view of a
high temperature chemical vapor deposition (HT CVD) system,
including a process chamber 100 and an exhaust assembly 600. A
chamber mounting plate 110 is provided for mounting this process
chamber 100 onto a wafer transfer chamber (not shown) which
interfaces the process chamber 100 to the rest of a complete wafer
processing system, such as a Centura 5200 system (not shown)
manufactured by Applied Materials, Inc. of Santa Clara, Calif.
Cross-sectional views illustrating various components in the
process chamber 100 are shown in FIGS. 2-5. To best understand the
process chamber 100 of the present invention and its operation, the
reader should simultaneously refer to all these figures.
[0031] The process chamber 100 of the present invention performs,
for example, high temperature deposition of titanium nitride upon a
semiconductor wafer using a TiCl.sub.4+NH.sub.3 chemistry. Since
the thermal decomposition of TiCl.sub.4 and NH.sub.3 occurs at high
temperature, the wafer should preferably be maintained at a
temperature range of 600-700.degree. C. to facilitate deposition
upon the wafer.
[0032] The process chamber 100 comprises a chamber body 250, a
liner 200, a pedestal assembly 160 and a showerhead assembly 300.
The pedestal assembly 160 contains a pedestal 180 that supports the
wafer in the chamber 100. The dual-gas showerhead assembly 300 is
positioned in a parallel, spaced apart relation with respect to the
pedestal 180 such that the wafer support surface of the pedestal
180 and a faceplate 330 of the showerhead assembly 300 define a
reaction zone. To achieve deposition, the wafer is heated by a
heated pedestal 180 while the showerhead assembly 300 introduces
the two reactant gases (TiCl.sub.4 and NH.sub.3) into the process
chamber 100 such that reaction occurs only above the wafer,
resulting in TiN deposition onto the wafer. In order to minimize
unwanted TiN deposition on the inside surface of the chamber, the
interior wall of the chamber, i.e., the chamber liner 200, is
maintained at a temperature between 150.degree. C. to 250.degree.
C. An improved bottom purge arrangement is also provided to reduce
undesirable adduct reaction by-products which may form on cold
areas of the chamber. The heated exhaust assembly 600 also prevents
the formation of powder deposits on the interior walls of the
exhaust assembly 600. This powder deposit is a reaction by-product
between TiCl.sub.4 and NH.sub.3 which forms at a temperature below
150.degree. C. At a temperature above 150.degree. C. but below
600.degree. C., minimal amounts of TiN is deposited on interior
chamber components. The TiN film that is inadvertently deposited on
chamber components can readily be removed by an in-situ thermal
chlorine cleaning process performed within chamber 100 of the
present invention.
Chamber Body and Heated Inside Liner
[0033] As shown in FIG. 2a, the chamber body 250 is substantially
bucket-shaped, with a cylindrical side 254 and a base 252. There is
an opening 256 at one portion of the cylindrical side 254, which is
connected to the exhaust assembly 600 for the removal of process
and product gases. The chamber base 252 has a centrally-located
opening 258, which is provided to accommodate a pedestal assembly
160, as well as a gas purging arrangement to be described below. An
inside liner 200, which is substantially cylindrical, is located on
the inside, but spaced apart from the chamber body 250. The chamber
body 250, which substantially encloses this inside liner 200, is
made of nickel-plated aluminum. In this particular application,
nickel plating is needed to protect the aluminum components from
corrosion by chlorine gas, which is used in an in-situ chamber
cleaning process to be described below. Of course, for other
applications with different cleaning processes, alternative
metal-plating may be used as long as it is compatible with the
chemical species used in the reaction or cleaning processes.
[0034] To avoid an exterior temperature of the chamber body 250
that may harm a user/operator, the chamber body temperature is
maintained at approximately 60.degree. C.-65.degree. C. or less by
thermally isolating the chamber body 250 from the inside heated
liner 200. The inside liner 200, which is also made of
nickel-plated aluminum, has an embedded resistive heater 215 for
establishing a fixed liner temperature. A thermal conductive paste
is applied to the resistive heater 215 and enclosed within a cover
plate 207 which is welded to the liner 200 to ensure good thermal
conductivity between the heater 215 and the liner 200. An AC
voltage is coupled to the heater 215 using AC connectors inside a
feedthrough portion 214 of the liner 200. This heater 215 can
optionally be used to dynamically control the temperature of the
liner 200. For example, the heater 215 may be used to maintain the
liner temperature at approximately 150 to 250.degree. C. to avoid
the formation of adduct ammonia salt or other process by-products
on the interior surface of liner 200. To facilitate dynamic thermal
control of the liner 200, a Type K thermocouple 212 is removably
inserted in the liner 200 approximately half the distance along its
cylindrical wall 204. Thus, the liner temperature can be measured
at approximately half way from the bottom 202 of the liner 200.
Connectors (not shown) for the thermocouple 212 and the resistive
heater 215 are located inside the feedthrough portion 214 of the
liner 200. A clamping plate 216 seats an O-ring 201 against the
chamber base 252 and the feedthrough portion 214 to seal the
interior of the chamber 100 from the outside atmosphere.
[0035] In practice, independent heating by the resistive heater 215
is not always necessary to achieve an appropriate liner temperature
since the operation of the heated pedestal 180 (see FIG. 2a) alone
is generally sufficient to maintain the temperature of the liner
200 within the desired range of 150-250.degree. C. Of course, this
heater 215 may be used, alone or in conjunction with the heated
pedestal 180, for other processes with different temperature
requirements.
[0036] The inside liner 200 and the chamber body 250 are
substantially isolated from each other by means of three dowel pins
220, one of which is shown in the cross-sectional view in FIG. 2a.
These isolating pins 220 are located between the bottom 202 of the
inside liner 200 and the inside surface 253 of the chamber base
252. The area around the inside liner 200, dowel pin 220 and the
chamber base 252 is shown in an enlarged cross-sectional view in
FIG. 2b. The three pins 220 are arranged to lie equidistant from
each other on the circumference of a circle, subtending angles of
120 degrees at the center of the circle. Each dowel pin 220 has a
central portion 221 having a diameter d.sub.1 and two smaller ends
222 and 223, each having a diameter d.sub.2, where d.sub.2 is less
than d.sub.1. As is typical in vacuum applications, a
drilled-through hole 225 is provided along the longitudinal axis of
the pin 220 to allow for pump-out of any trapped gases. The pins
220 are press-fit into corresponding receiving holes 224 in the
bottom 202 of the liner 200, such that the liner 200 rests against
one side of the larger central portion 221 of each pin 220. There
are also three corresponding holes 226 on the inside surface 253 of
the chamber base 252 to accommodate these pins 220. One of these
holes 226 is round, and the other two are slotted (not shown) to
provide for additional assembly tolerance.
[0037] When the liner 200, with the dowel pins 220 in place, is set
to rest in these holes 226 inside the chamber base 252, the pins
220 serve to maintain a proper spacing (s) between the liner 200
and the chamber base 252. This spacing (s) corresponds to the
thickness of the larger central portion 221 of the pin 220, which
is about 0.135" (3.4 mm). Four 1/4-20 nickel screws (not shown),
which also lie on the circumference of the same diameter circle as
the dowel pins 220, are used to secure the liner 200 in place by
screwing into corresponding tapped holes (not shown) on the inside
surface 253 of the chamber base 252. The small contact areas of the
nickel pins 220 and screws ensure very good thermal isolation
between the heated liner 200 and the chamber body 250, and allows
the chamber body 250 to be kept at around 65.degree. C. while
maintaining the heated liner at 150-250.degree. C.
[0038] These dowel pins 220 can be made of a variety of materials
that can withstand high temperatures and have a relatively high
thermal resistivity (low thermal conductivity), such as stainless
steel or nickel. The choice of material depends on the specific
processing applications. For example, nickel (200 or 201 grade), is
the preferred material because of its chemical resistance to
chlorine and high thermal resistance. It is understood that the
dimensions and specific layouts for the various components are for
illustrative purpose only. For example, the liner 200 could be
spaced from the body 250 by intermittently spaced ribs formed in
the bottom 252 of chamber body 250, a continuous annular ridge
formed in the bottom 252 of the chamber body 250, a spacer ring
positioned on the bottom 252 of the chamber body 250 and the like.
As such, the present invention encompasses many other
chamber/liner/spacer combinations that facilitate thermal isolation
between the liner 200 and the chamber body 250. Such isolation
enables separate temperature control of these components.
Lid/Gas Box and Dual-Gas Faceplate
[0039] FIG. 3a shows a cross-sectional view of the dual-gas
showerhead assembly 300, comprising a nickel-plated aluminum
lid/gas box (manifold assembly 310) and a faceplate 330. The
showerhead assembly 300 provides a dual-gas separate entry for
TiCl.sub.4 and NH.sub.3 into the process chamber 100 without
premixing of the gases. The gas manifold assembly 310 also serves
as the lid of the chamber 100. The faceplate 330 is described in a
commonly-assigned patent application by Umotoy et al. entitled
"Dual Gas Faceplate for a Showerhead in a Semiconductor Wafer
Processing System," Ser. No. 09/098,969, filed Jun. 16, 1998; which
is herein incorporated by reference. The showerhead assembly 300
allows two gases, for example, NH.sub.3 and TiCl.sub.4, to be
separately introduced into the reaction region, or processing zone
515. The processing zone 515 is roughly defined by the space
between the bottom 332 of the faceplate 330 and the heated pedestal
180, which is the top portion of a pedestal assembly 160 to be
described below. (See FIG. 5a.) In order to avoid the formation of
undesirable deposits inside the showerhead assembly 300, separate
flow paths or passageways are established through different
channels 320 or chambers 322 inside the showerhead assembly 300.
These channels 320 and chambers 322 prevent mixing of the two gases
prior to reaching the process zone 515. Briefly, the gas manifold
or lid 310 comprises three plates--bottom 312, middle 314 and top
316, which have been fused together by vacuum brazing their mating
surfaces 334 and 336 using a silicon-rich aluminum film, clamping
the entire assembly and placing the assembly in a furnace at a
temperature of approximately 550.degree. C. to form a unitary
manifold assembly 310. As such, no O-rings are necessary to provide
isolation between the process gases as they flow through the
manifold assembly 310. These plates 312, 314 and 316, contain a
combination of channels 320 and chambers 322, such that when the
faceplate 330 is bolted to the manifold assembly 310, the myriad of
channels 320 and chambers 322 provide proper passageways, or flow
paths, for introducing two gases separately from their supply
sources (not shown) outside the chamber 100 into the process zone
515 without pre-mixing of the gases.
[0040] The faceplate 330 further comprises a lower gas distribution
plate 340 and a upper gas distribution plate 350, as shown in FIG.
3b. The specific arrangement of channels 343 and holes (351, 352,
341, 342 and 344) that together define distinct passageways or flow
paths for the two process gases are described in detail in the
above-referenced patent application Ser. No. 09/098,969. Suffice to
say that when the two plates, 340 and 350, are fused together using
the same technique as previously described for the gas manifold
plates 312, 314 and 316, the resulting unitary faceplate 330
provides separate passageways, or flow paths, for uniformly
introducing two gases into the processing zone 515 without
pre-mixing of the gases.
[0041] For example, there are two sets of holes, 341 and 342, in
the lower plate 340, one for each gas. As shown in FIG. 3b, one set
of holes 341 aligns with holes 351 in the upper plate to form one
flow path (from 351, via 344 to 341) for one gas, e.g., TiCl.sub.4.
The other set of holes 342 are connected to channels 343 within the
lower plate 340. These channels 343 are in turn connected to a
circumferential plenum 390, which is formed between the upper and
lower plates, 350 and 340, when they are fused together. The plenum
390 is further connected to another hole 352 in the upper plate
350, which provides an inlet for a second gas, e.g., NH.sub.3. This
configuration allows the first gas to pass through the first
passageway (e.g., from 351, via 344 to 341) and the second gas to
pass through the second passageway (e.g., from 352, via 390 to 343
and 342) within the faceplate 330 without mixing until the gases
enter the process zone 515 after exiting from these holes 341 and
342 at the bottom 332 of the faceplate 330. It should be noted that
the choice of hole size for each gas and hole distribution are
functions of process conditions. For example, the hole size will
vary depending upon gas flow rate, gas pressure, gas type, chamber
pressure and the faceplate 330 such that gas flow rates through the
holes are correlated with the locations of the holes in the
faceplate 330.
[0042] The showerhead assembly 300 is formed by affixing the
faceplate 330 directly to the bottom of the gas distribution
manifold 310 using a plurality of bolts (not shown) through the
mounting holes (hole 396 is shown in FIG. 3b) in the faceplate 330.
An O-ring groove 325 (see FIG. 3a) is provided in the gas manifold
310 to accommodate an O-ring 326 which is used to provide sealing
between the gas manifold 310 and the faceplate 330. Different types
of O-ring materials, such as Viton, may be used, as long the
material is compatible with the operating temperature and
chemically resistant to the gases used in the process. Both the
faceplate 330 and the gas distribution manifold 310 are made of
nickel-plated aluminum or some other thermally conductive and
chlorine compatible materials such as nickel. Of course, other
material choices are possible as long as they provide the thermal
conductivity and/or chemical compatibility which are necessary for
the specific process.
[0043] The showerhead assembly 300 can be coupled to a cold plate
assembly 400 or other cooling apparatus that will maintain the
entire lid/gas box 310 at a uniform and constant temperature.
During wafer processing, the showerhead assembly 300 is heated by
the heated pedestal 180 through thermal radiation in the reaction
zone 515. Therefore, to avert deposition of TiN or by-products of
the TiN deposition process upon and/or within the showerhead, a
cold plate assembly 400 is necessary to maintain the faceplate
temperature within a range of 150-250.degree. C. The cold plate
assembly 400 serves a dual-purpose of preventing the showerhead
assembly 300 from temperature drift, as well as keeping the areas
around the O-ring seal to within specification for proper
sealing.
Cold Plate Assembly
[0044] A detachable cold plate assembly 400 is designed to maintain
temperature of the lid/gas box 310 to prevent it from temperature
drift. FIG. 4a is a schematic illustration of the top view of the
cold plate assembly 400. This cold plate assembly 400 is
substantially annular in shape, except for a rectangular protruded
portion 402. FIG. 4b shows a cross-sectional view of the cold plate
assembly 400, comprising a top plate 440 and a bottom plate 420,
which are brazed together and then nickel-plated as an assembly.
The top plate 440 has a coil-shaped channel 410 passing through the
plate 440 for circulating coolant, as illustrated in FIG. 4a. The
two ends, 412 and 414, of the coil-shaped channel 410 are located
at the rectangular protruded portion 402, and serve as the inlet
and outlet for the coolant. The channel 410 has a rectangular
cross-section and is open on its bottom side 415. This is
illustrated in the cross-sectional view shown in FIG. 4b and the
side view shown in FIG. 4c. The top surface 425 of the bottom plate
420, when brazed together with the top plate 440, defines a closed
channel 445 through which a coolant can circulate. The bottom plate
420 has two apertures 422 and 424, close to the end of the
rectangular protruded portion 402. These apertures 422 and 424 are
aligned respectively with the two ends 412 and 414 of the top plate
channel 410 to provide for coolant inlet and outlet. The coolant,
typically water, is connected in series with the coolant for the
chamber 100.
[0045] The cold plate assembly 400 is attached onto the top of the
lid/gas box (310 in FIG. 3a) using screws at locations 430 around
the circumference of the cold plate assembly 400. Note that one
annular portion 421 of the bottom plate 420 is recessed such that
only an inner 426 and an outer 428 portion of the bottom plate 420
actually come into physical contact with the chamber lid 310. The
cooling plate assembly 400, lid/gas box 310 and the faceplate 330
are sometimes collectively referred to as a lid assembly. With an
inlet water temperature of about 45-55.degree. C., the lid/gas box
310 can readily be maintained within a temperature range of
60-65.degree. C.
[0046] As a detachable component, this cold plate assembly 400 is a
cost-effective design feature which allows for ease of maintenance
as well as design and process flexibility. For example, different
temperature control scenarios for the faceplate 330 may be achieved
by a suitable interchange with a different cooling (or heating)
plate that provide more or less heating or cooling. To most
effectively process a wafer or wafers, the cold plate assembly 400
that is best suited for a particular process can be easily
installed onto the chamber lid.
Pedestal Assembly
[0047] FIG. 5a illustrates a pedestal assembly 160 in a
cross-sectional view within the process chamber 100. The pedestal
assembly 160 comprises a flat circular portion 180 at the top,
sometimes referred to as a susceptor or pedestal; and a bottom
cylindrical shaft-like portion 560 which extends downwards through
the centrally-located opening 258 at the bottom 252 of the chamber
body 250. The upper surface 185 of the pedestal 180 has a wafer
pocket 563 to support a wafer 564 (shown in phantom in FIG. 5a),
and four clearance holes to accommodate wafer lift pins 285. These
wafer lift pins 285 are made of ceramic, and are used for
wafer-handling and transport. They are slidably mounted within
bores in the pedestal 180 and can be lifted above the pedestal's
upper surface 185 by engaging a wafer lift ring 580, in order to
raise and lower the wafer with respect to the support surface 185
of the pedestal 180. These lift pins 285 are kept from falling out
from the pedestal 180 by conical heads 585 located on their upper
ends. The current pedestal assembly 160 and chamber design can
accommodate wafer diameters of 125 mm, 150 mm and 200 mm,
respectively. Those skilled in the art can perform proper design
scale-up to encompass applications to larger wafer diameters such
as 300 mm as well.
[0048] The pedestal 180, preferably made of a ceramic material such
as aluminum nitride (AlN), is further equipped with two embedded
electrodes 571 and 572. In general, these electrodes 571 and 572,
made of different types of conducting materials, can be of various
thicknesses and shapes. In the present invention, one of these
electrodes is a radio-frequency (RF) grid 571 for performing plasma
clean and other plasma processes such as plasma annealing of the
wafer. The mesh-type grid 571, made of molybdenum, is located
slightly below the pedestal's top surface 185. Slightly below the
RF electrode is an alternating current (AC) grid 572 for heating
purpose. The pedestal 180 currently in use is made of a dark gray,
high resistivity AlN of 99.9% purity. Of course, other similar
heaters may also be used, depending on the specific process
requirements. This heated pedestal 180 allows the wafer temperature
to be controlled within a range of approximately 600-800.degree. C.
Although TiN film deposition can also be performed between
200-600.degree. C., the resulting TiN film tends to have an
undesirably high chlorine content. Therefore, the wafer temperature
is preferably maintained within a range of 600-700.degree. C. for
optimal deposition results. During wafer processing, there is also
a center-to-edge temperature difference in the pedestal 180 of
about 10.degree. C., with the edge 186 being cooler because of a
purge gas flow around the pedestal's edge 186.
[0049] The pedestal assembly 160 moves vertically within the
chamber cavity by a lift mechanism (not shown) between a first
(top) position 501 and a second (bottom) position 502. This second
position 502 of the pedestal assembly 160 is illustrated in phantom
in FIG. 5a. During wafer processing, e.g., for film deposition onto
the wafer substrate 564, the pedestal assembly 160 is placed in the
first position 501. A reaction zone, or process zone 515, within
the chamber cavity 280 can be defined roughly as the space between
the bottom 332 of the faceplate 330 and the pedestal top surface
185, and confined on the side by the edge ring 290. A wafer
substrate 564 is positioned in the wafer pocket 563 during wafer
processing, and the distance between the wafer and the bottom of
the faceplate 330 is approximately 0.360" (9.1 mm). Note that this
distance is for illustrative purpose only, and it may be different
for other process applications. The spacing 530 between the outside
edge 186 of the pedestal 180 to the inside surface 286 of the liner
200 is about 0.125" (3.2 mm). The choice of this spacing 530 is
determined both by the specified temperature of the liner 200 and
the need to prevent purge gas from entering the process zone
515.
[0050] Before and after film deposition for each wafer, the
pedestal assembly 160 is moved to a second position 502 for wafer
loading or unloading. In this second position 502, the pedestal top
surface 185 is slightly below a slit valve opening 260, which is
located on the side, or cylindrical wall, 204 of the chamber liner
200 and the cylindrical side 254 of the chamber body 250. A wafer
can be transported in and out of the process chamber 100 through
the slit valve opening 260 to an adjacent transfer chamber and/or
load-lock chamber (not shown), or another chamber within a cluster
tool. A cluster tool of a type that can be coupled to the process
chamber 100 is described in a commonly assigned U.S. Pat. No.
5,186,718, entitled "Staged-Vacuum Wafer Processing System and
Method", issued Feb. 16, 1993, and is herein incorporated by
reference.
[0051] Wafer-handling and transport is accomplished by the wafer
lift pins 285 in the pedestal 180 in conjunction with a robotic
transfer assembly (not shown) which has been described in a
commonly assigned U.S. Pat. No. 4,951,601, entitled "Multi-chamber
Integrated Process System," issued Aug. 28, 1990; the complete
disclosure of which is incorporated herein by reference. Briefly,
the sequence for wafer loading involves the pedestal being placed
in position 502, and a robotic arm transporting a wafer through the
slit valve opening 260 into the process chamber 100. With the wafer
564 poised above the pedestal surface 185, the wafer lift ring 580
rises to engage pin bottoms such that the wafer lift pins 285 are
raised above the pedestal top surface 185 to lift the wafer 564 off
the robotic arm. After the retraction of the robotic arm away from
the pedestal surface 185, the pedestal assembly 160 is raised to
receive the wafer 564 in the wafer pocket 563, and the lift ring
580 lowers to its original position. The pedestal assembly 160 is
subsequently moved into its first position 501 for wafer
processing. The wafer unloading sequence is a reverse of the
loading sequence. The self-adjusting mechanism for the vertical
movement of the pedestal assembly 160 has also been described in a
commonly assigned U.S. patent application Ser. No. 08/738,240,
filed on Oct. 25, 1996, and entitled "Self-Aligning Lift
Mechanism," the disclosure of which is herein incorporated by
reference.
Improved Purge Arrangement
[0052] FIG. 5a also illustrates details of an edge ring 290 and a
backside gas purge arrangement. The edge ring 290 is disposed
around the outer perimeter 187 of the pedestal 180 of the pedestal
assembly 160. This edge ring 290 is substantially annular, with a
protruding portion 292 at the bottom 294 of the ring 290. As such,
this protruding portion 292 essentially divides the bottom 294 of
the ring 290 into an inside bottom surface 297 and an outside
bottom surface 298. When the pedestal assembly 160 is in its first
position 501, the edge ring 290 rests on top of the heated pedestal
180, such that its inside bottom surface 297 covers part of the top
pedestal surface 185. Also, in this position, the protruded portion
292 of the edge ring 290 covers part of the side, or outside edge
186 of the pedestal 180. A space 531 is then defined between the
outside bottom portion 298 of the edge ring 290 and a protruded
portion 203 of the heated liner 200. This gap 531 provides a choke
for the bottom, or backside, purge gas flow (to be described below)
and ensures uniform distribution of the purge gas about the edge of
the pedestal 180.
[0053] When the pedestal assembly 160 is in its second position
502, the edge ring 290 rests on top of the protruded portion 203 of
the heated liner 200. As such, the edge ring does not interfere
with access of the robotic transfer mechanism as it places and/or
retrieves the wafer to/from the pedestal 180.
[0054] The edge ring 290 can be made of a variety of materials such
as ceramic, quartz, aluminum and steel, among others. The exact
choice of material depends, of course, on the specific process
applications. For example, quartz can be used for TiN deposition
using TiCl.sub.4+NH.sub.3 chemistry.
[0055] The purpose of this edge ring 290 is two-fold: 1) to act as
a choke such that uniform pumping can be established for the gases
and/or by-products during processing; and 2) to prevent process
gases from entering behind the pedestal assembly 160, which may
cause undesirable deposits in the lower portions of the chamber
100.
[0056] During wafer processing, the pedestal assembly 160 is in the
first (top) position 501, such that the gap 520 between the top 295
of the edge ring 290 and the bottom 332 of the faceplate 330 is
about 0.05" (1.3 mm). A backside purge is established by flowing
argon through a liner purge inlet 505 into the gap 599 between the
liner 200 and chamber body 250 to prevent powder deposition on the
cold wall surfaces of the chamber body 250. This gap 599 is about
0.06" (1.5 mm) wide. To facilitate purge gas flow, a set of holes
595 is also provided through the shaft portion 590 of the wafer
lift ring 580 located around the pedestal shaft 560 at the bottom
opening 258. Undesirable deposition behind the pedestal 180 is
prevented by establishing a purge gas flow through these holes 595
into the chamber cavity 280, as illustrated by the arrows. As
previously mentioned, various spaces such as 520, 530, and 531 are
defined by different portions of the showerhead 330, pedestal 180,
edge ring 290, and liner 200. It is to be understood that
dimensions quoted for these spaces, like those quoted for other
components, are for illustrative purpose only. In general, the
choice of these dimensions depend on the desired results of a
specific process being performed in the chamber. For example,
spaces 530 and 531 are selected to ensure uniformity in the purge
gas distribution around the edge of the pedestal 180. The space 520
may be a variable parameter affecting uniformity or deposition rate
in the film deposition step itself. Suffice to say that one skilled
in the art of wafer processing would be able to arrive at optimal
combinations of these dimensions to achieve desirable wafer
processing results such as deposition uniformity.
[0057] FIG. 5b shows a perspective view of an alternative
embodiment of an edge ring 550, and FIGS. 5c and 5d show partial
cross-sectional views of the edge ring 550 being supported by a
horizontal surface 522 of the liner 200. FIG. 5c illustrates the
edge ring 550 with a top surface 551, a bottom surface 552, an
inside surface 556, an outside surface 557, and a protruded inside
portion 559. In this embodiment, the edge ring 550 is supported
entirely by the liner 200, i.e., the edge ring 550 does not contact
the pedestal 180 or wafer 564. A step 523 is provided on a
horizontal surface 522 of the liner 200 to keep the edge ring 550
in place. A key stop portion 554 located on the outside surface 557
of the edge ring 550 interfits with the step 523 of the liner 200
to facilitate secure mounting of the edge ring 550. Additionally,
three grooves or slots 565 are provided on the bottom surface 552
of the edge ring 550 (see FIG. 5d), and are located equidistant
from each other. Three pins 526 are press fit into corresponding
recessed holes 525 in the horizontal surface 522 of the liner 200.
A portion 527 of the pin 526 protrudes above the horizontal surface
522 of the liner 200 and engages the slot 565 at the bottom surface
552 of the edge ring 550. As such, the edge ring 550 is prevented
from rotating with respect to the liner 200. Optionally, mounting
screws (not shown) can also be used to secure the edge ring 550 to
the liner 200. Again, the dimensions disclosed for the pin and slot
arrangement are for illustrative purpose only, and do not represent
limitations pertaining to the practice of this invention. Suffice
to say that in the present arrangement, the edge ring 550 is heated
by thermal radiation from the pedestal 180, and expands before the
liner 200 reaches the same final temperature. This results in a
uniform expansion of the edge ring 550 with respect to its
centerline O-O'.
[0058] During wafer processing, when the pedestal 180 (shown in
phantom in FIG. 5c) is in the first position 501, the protruded
inside portion 559 of the edge ring 550 is disposed over the outer
perimeter 187 of the pedestal 180, such that the outer perimeter
187 and the outside edge 186 of the pedestal 180 are in close
proximity to and substantially surrounded by the edge ring 550.
Thus, undesirable deposition over the perimeter 187 and outer edge
186 of the pedestal 180 can be avoided. In this embodiment,
however, there is no direct physical contact between the pedestal
180 and the edge ring 550. Instead, a gap or space 568 is
maintained between the top 185 of the pedestal 180 and the bottom
553 of the protruded portion 559 of the edge ring 550. Another
space 566 is defined between the pedestal edge 186 and the inside
surface 556 of the edge ring 550.
[0059] A number of openings 555, e.g., about 30 in this particular
embodiment, are provided around the circumference of the edge ring
550 close to the bottom surface 552. These openings 555 extend
horizontally from the inside surface 556 to the outside surface 557
of the edge ring 550. Through these openings 555, a purge gas is
pumped from the space 566, into the space 567 between the outside
surface 557 of the edge ring 550 and the inside surface 524 of the
liner 200. The gap 568 acts as a choke to prevent any purge gas
from flowing towards the top 185 of the pedestal 180, which may
otherwise dilute the process gases and affect the deposition
process. Similar to the other edge ring 290 shown in FIG. 5a, the
top surface 551 of this edge ring 550 and the bottom 332 of the
showerhead 330 defines the space 520 through which process gases
and/or by-products are pumped out from the reaction zone 515 (see
FIG. 5a). The dimensions of these spaces 520, 566, 567 and 568 are
process-dependent, and are typically designed to suit the needs of
a particular process. For example, one skilled in the art would
seek to adjust these spacings to optimize or achieve desired
results such as deposition uniformity. Furthermore, this particular
configuration (the liner 200 supporting the edge ring 550) allows
the temperature of the edge ring 550 to be maintained within a
range of approximately 200-250.degree. C., and undesirable
deposition on the edge ring 550 is further minimized. Note that the
use of an edge ring, while highly desirable, is not absolutely
necessary for the practice of this invention.
[0060] Returning to FIG. 5a, during wafer deposition, TiCl.sub.4 in
a He carrier gas and NH.sub.3 in a H.sub.2 carrier gas are
introduced into the processing zone 515 via the showerhead assembly
300 and a chemical reaction between TiCl.sub.4 and NH.sub.3 takes
place at close proximity above the wafer 564 that is supported by
the heated pedestal 180. The reaction results in the deposition of
TiN film onto the wafer 564. A continuous gas flow is maintained by
the pumping system that is attached to the exhaust assembly 600
such that gases, including any volatile reaction products, are
pumped out of the processing zone 515 and other areas of the
chamber cavity 280, past the space 520 between the top 295 of the
quartz edge ring 290 and the bottom 332 of the faceplate 330,
through a slot 205 (see FIG. 2a) in the inside liner 200, into the
exhaust chamber 600 which is connected to the process chamber 100
by various vacuum adapter and connector components. While the
exhaust assembly 600 removes gases, the showerhead 330 replaces the
process gases and the purge gas is continuously flowed past the
outer edge 186 of the pedestal 180. This ensures a steady fresh
supply of process and purge gases within the chamber 100 during
wafer processing.
Heated Exhaust Assembly
[0061] FIG. 6 shows a cross-sectional view of one embodiment of the
exhaust assembly 600 and vacuum components connecting it to the
process chamber 100. These vacuum components comprise: an adapter
plate 601, a thermal insulator 602, an exhaust tubing 603, a band
heater 605, a cover 604, a 20-torr Baratron 606, and a reducer 607.
The annular adapter plate 601 mates directly to the chamber body
250 around the side opening 256, and fits around the outside of an
exhaust tubing 603 which extends partly into the process chamber
100 side opening 256. A thermal insulator 602 is fitted adjacent to
the adapter 601 on the side away from the process chamber 100. This
thermal insulator 602 provides insulation between the heated
exhaust assembly 600, which is maintained at a temperature of about
150.degree. C., and the chamber body 250, which is maintained at a
temperature of about 60-65.degree. C. A band heater 605 is located
around a substantial portion of the outside wall of the exhaust
tubing 603. An annular cover 604 fits over the outside of the
insulator 602, the band heater 605 and the remaining exhaust tubing
portion 603. At the far end 613 of the exhaust tubing (away from
the process chamber 100) is a reducer 607, which has a larger
diameter opening 617 on one end to mate with the exhaust tubing
603, and a smaller diameter opening 627 at the other end to mate to
additional components of the exhaust assembly 600. A 20-torr
Baratron pressure gauge 606 is connected to the reducer 607 via a
side port. Numerous heaters are installed to maintain the exhaust
assembly 600 at a temperature of approximately 150-200.degree. C.
so as reduce undesirable deposits from coating the interior walls
of the exhaust assembly 600 and the associated vacuum components.
For example, a series of flexible heaters 625, 645, 655, 665 and
675, are installed around the outside walls of the exhaust assembly
600, a 2" manual angle valve 620, a 1" manual valve 640, cold trap
650, isolation valve 660, and throttle valve 670. Note that heating
is necessary even for the isolation valve 660 and the throttle
valve 670 which are located beyond the cold trap 650 in order to
prevent the formation of undesirable deposit inside these vacuum
components. Additionally, to minimize heat loss and to provide a
safe operating environment, heater jackets 609, 629, 619a, 619b,
619c and 619d are provided around the reducer 607, the 2" manual
angle valve 620 and various parts of the exhaust assembly 600.
[0062] The cold trap 650 is connected between the manual valve 620
and the isolation valve 660. A heater 655 is provided around the
inlet 651 of the cold trap 650 to keep the temperature in the range
of 150-200.degree. C. This prevents undesirable deposits from
forming on the interior of the inlet 651 of the cold trap 650. A
baffle plate 659 is provided close to the top 650T of the cold trap
650. A multi-loop cooling coil 656 is brazed to the bottom 650B of
the cold trap 650, and cooling water at a temperature of about
20-25.degree. C. is circulated inside the cooling coil 656. When
the exhaust gases enter the cold trap 650 through the inlet 651,
they are diverted by the baffle plate 659 to flow radially
outwards. Some of the condensibles, such as HCl and other
by-products from the TiCl.sub.4/NH.sub.3 reaction, are trapped onto
the baffle plate 659, but most are trapped onto the cooling coil
656, which offers a relatively large trapping surface area. The
remaining exhaust gases exit the cold trap 650 through an axially
located channel 658 which is connected to the outlet 652 of the
cold trap 650, and pass through the isolation valve 660 and the
throttle valve 670 before being exhausted into the exhaust line
690.
[0063] Although a chlorine-based chamber cleaning process (to be
described below) provides efficient dry cleaning of the interior of
the exhaust assembly 600, powder deposits tend to accumulate after
an extended period of wafer processing--e.g., 5000 wafers. These
deposits can readily be removed by cleaning with water or hydrogen
peroxide during periodic maintenance. The use of the heated exhaust
assembly 600 contributes to equipment uptime by facilitating
chamber maintenance and extending the time between chamber
cleanings.
Chamber Cleaning Process
[0064] As with most processing equipment, periodic chamber cleaning
is necessary to ensure cleanliness of the processed wafers. An
in-situ chlorine-based thermal cleaning process has been developed
for this purpose. When TiN deposition is accomplished using
TiCl.sub.4 and NH.sub.3, a TiN film deposit is formed on the
chamber interior (as opposed to a powder deposit of adduct ammonia
salt), as long as the wall temperature is kept at around
150-250.degree. C. This film can be effectively removed (etched) by
the use of an in-situ thermal chlorine process. This thermal
cleaning process is described in a commonly assigned U.S. patent
application Ser. No. 09/163,711, filed on Sep. 30, 1998 by Vasudev
et al., and is hereby incorporated by reference. Chlorine gas is
introduced into the chamber 100 via the same flow path as for
TiCl.sub.4 inside the showerhead assembly 300. Typical process
conditions include a chlorine flow rate in the range of 500 sccm, a
pressure in the range of 10-20 torr, and a temperature range of
600-700.degree. C. for the heater 180, and 150-250.degree. C. for
the interior walls of chamber 100. Of course, the process
parameters may be adjusted to suit specific needs, depending on the
actual cleaning process conditions employed. In addition to thermal
cleaning, it is anticipated that the chamber 100 can also be
adapted for use with other cleaning techniques such a plasma-based
or remote microwave chlorine processes. For example, adaptation for
plasma-based cleaning processes would require a modification of the
chamber lid 310 to accommodate RF biasing, as well as to allow for
electrical isolation from ground. To ignite a cleaning plasma, RF
power would be applied between the showerhead assembly 300 and the
chamber body 250 and liner 200 (ground). The hardware modifications
necessary to implement plasma cleaning are described below in the
section on plasma generation.
Post-Deposition Anneal
[0065] After TiN film deposition, an annealing step can be used to
improve the film properties. Film annealing is performed by thermal
annealing the wafer at a relatively high temperature, e.g.,
750.degree. C., which is readily attainable using the existing
heated pedestal 180. Annealing reduces traces of chlorine in the
TiN film, which may otherwise result in undesirably high film
resistivity. Alternatively, plasma annealing may also be used, in
which case, the showerhead 330 acts as a top RF electrode while the
pedestal 180 serves as a bottom ground electrode. The hardware
modifications necessary for plasma annealing are described
below.
Plasma Generation
[0066] Although the existing chamber 100 described above is
suitable only for non-plasma application, the chamber can readily
be modified for plasma-enhanced applications such as deposition,
cleaning or annealing. For thermal deposition process, the entire
lid assembly (i.e., cooling plate assembly 400, lid/gas box 310 and
showerhead 330) is coupled to the grounded chamber body 250 and
liner 200. In plasma applications, however, RF power is applied to
the showerhead 330. Electrical isolation is therefore required
between the showerhead 330 and the chamber body 250. FIG. 7a
illustrates one embodiment of a modified configuration for plasma
application. For example, the RF lids used for existing CVD
chambers, such as CVD Ti, W, Al and dielectric chamber lids
(configured for plasma application) are suitable for adaptation to
the high temperature CVD chamber of the present invention. As shown
in FIG. 7a, both the showerhead 330 and the gas box 710 are
electrically insulated from the chamber lid 720 by a ceramic
isolator 780. The chamber lid 720 and the chamber body 250 remain
at ground. FIG. 7b shows an RF module 750, which supplies RF power
to the showerhead 330. The RF module 750 can either be chamber
installed or remotely installed, and provides RF power to the
showerhead 330 through a RF connecting rod 752, a RF plunger
connector 754 and a RF strap connector 756. Several delrin
insulators 770 insulate these RF connectors 752, 754 and 756 from
the chamber body 250 and the chamber lid 720. During deposition,
process gases enter the process chamber 100 via separate gas inlets
711 and 712 of the gas box 710, which is connected to the dual-gas
showerhead 330. To prevent electrical breakdown of process gases
inside the gas delivery lines, a voltage gradient assembly 790 is
installed over the gas box 710 around the gas inlets 711 and 712.
Detailed description of this voltage gradient assembly 790 is
provided in a commonly-assigned U.S. Pat. No. 5,362,526 entitled
"Plasma-Enhanced CVD Process Using TEOS for Depositing Silicon
Oxide", filed on Jan. 23, 1991. This patent is herein incorporated
by reference.
[0067] It should be emphasized that there is no inherent limitation
restricting the use of this high temperature chamber to TiN film
deposition. In general, other CVD film deposition can also be
performed using this high temperature chamber. Furthermore, it is
possible to extend the use of this chamber to facilitate other
process applications. The dual-gas showerhead arrangement will be
useful in any application where there is a need to separately
introduce processing gases without premixing, and the heated liner
may also find applications in various etch and deposition processes
where deposition of by-products of the process are reduced by
heating chamber surfaces.
[0068] Although a preferred embodiment which incorporates the
teachings of the present invention has been shown and described in
detail, those skilled in the art can readily devise many other
varied embodiments that still incorporate these teachings.
* * * * *