U.S. patent application number 09/966869 was filed with the patent office on 2002-04-25 for coil for sputter deposition.
Invention is credited to Narasimhan, Murali, Pavate, Vikram.
Application Number | 20020047116 09/966869 |
Document ID | / |
Family ID | 23645261 |
Filed Date | 2002-04-25 |
United States Patent
Application |
20020047116 |
Kind Code |
A1 |
Pavate, Vikram ; et
al. |
April 25, 2002 |
Coil for sputter deposition
Abstract
Coils for use within high density plasma chambers are provided
that do not electrically disconnect or short circuit following
repeated depositions and that produce films having reduced in-film
defect densities. To reduce in-film defect densities, dielectric
inclusion content, porosity, grain size and surface roughness of a
coil are reduced, while the mechanical strength of the coil is
increased so as to both decrease defect generation and thermal
creep rate (e.g., to prevent electrical disconnection or short
circuiting of the coil following repeated depositions).
Inventors: |
Pavate, Vikram; (San Jose,
CA) ; Narasimhan, Murali; (San Jose, CA) |
Correspondence
Address: |
PATENT COUNSEL
APPLIED MATERIALS, INC.
Legal Affairs Department
P.O.BOX 450A
Santa Clara
CA
95052
US
|
Family ID: |
23645261 |
Appl. No.: |
09/966869 |
Filed: |
September 28, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09966869 |
Sep 28, 2001 |
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09415328 |
Oct 8, 1999 |
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6315872 |
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09415328 |
Oct 8, 1999 |
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08979192 |
Nov 26, 1997 |
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6001227 |
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09415328 |
Oct 8, 1999 |
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09272974 |
Mar 18, 1999 |
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6139701 |
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Current U.S.
Class: |
257/44 ;
204/298.06; 428/98; 438/687 |
Current CPC
Class: |
Y10T 428/24 20150115;
C23C 14/3414 20130101; H01J 37/321 20130101; H01J 37/34
20130101 |
Class at
Publication: |
257/44 ;
204/298.06; 438/687; 428/98 |
International
Class: |
H01L 021/44; C23C
014/34; B32B 007/00; B32B 005/00; H01L 029/40 |
Claims
The invention claimed is:
1. A copper coil for use in a high density plasma deposition
chamber characterized by: a hardness greater than 45 Rockwell.
2. The copper coil of claim 1 further characterized by a grain size
of less than 50 microns.
3. The copper coil of claim 1 further characterized by a surface
roughness of less than 20 micro inches.
4. The copper coil of claim 1 further characterized by more than
50% material having (200) texture and less than 3% material having
(111) texture.
5. The copper coil of claim 1 further characterized by: a grain
size of less than 50 microns; and a surface roughness of less than
20 micro inches.
6. The copper coil of claim 1 further characterized by a grain size
of less than 25 microns.
7. The copper coil of claim 1 further characterized by a surface
roughness of less than 5 micro inches.
8. The copper coil of claim 1 further characterized by: a grain
size of less than 25 microns; and a surface roughness of less than
5 micro inches.
9. The copper coil of claim 1 further characterized by a purity
level between 99.995% and 99.9999% and at least one of: an
antimony, an arsenic and a bismuth content each of less than 0.03
ppm; a hydrogen content of less than 1.0 ppm; an oxygen content of
less than 5.0 ppm; and a sulfur content of less than 1.0 ppm.
10. The copper coil of claim 1 further characterized by a purity
level of less than 99.9999% and at least one of: an antimony, an
arsenic and a bismuth content each of less than 0.03 ppm; a
hydrogen content of less than 1.0 ppm; an oxygen content of less
than 5.0 ppm; and a sulfur content of less than 1.0 ppm.
11. The copper coil of claim 1 further characterized by a purity
level between 99.995% and 99.9999% and at least one of: an
antimony, an arsenic and a bismuth content each of less than 0.03
ppm; a hydrogen content of less than 1.0 ppm; an oxygen content of
less than 1.0 ppm; and a sulfur content of less than 0.05 ppm.
12. The copper coil of claim 1 further characterized by a purity
level of less than 99.9999% and at least one of: an antimony, an
arsenic and a bismuth content each of less than 0.03 ppm; a
hydrogen content of less than 1.0 ppm; an oxygen content of less
than 1.0 ppm; and a sulfur content of less than 0.05 ppm.
13. A copper coil for use in a high density plasma deposition
chamber characterized by: a grain size of less than 50 microns.
14. The copper coil of claim 13 further characterized by a grain
size of less than 25 microns.
15. The copper coil of claim 13 further characterized by a surface
roughness of less than 20 micro inches.
16. The copper coil of claim 15 further characterized by a surface
roughness of less than 5 micro inches.
17. The copper coil of claim 14 further characterized by a surface
roughness of less than 5 micro inches.
18. The copper coil of claim 13 further characterized by a purity
level between 99.995% and 99.9999% and at least one of: an
antimony, an arsenic and a bismuth content each of less than 0.03
ppm; a carbon content of less than 5.0 ppm; a hydrogen content of
less than 1.0 ppm; an oxygen content of less than 5.0 ppm; and a
sulfur content of less than 1.0 ppm.
19. The copper coil of claim 13 further characterized by a purity
level less than 99.9999% and at least one of: an antimony, an
arsenic and a bismuth content each of less than 0.03 ppm; a carbon
content of less than 5.0 ppm; a hydrogen content of less than 1.0
ppm; an oxygen content of less than 5.0 ppm; and a sulfur content
of less than 1.0 ppm.
20. The copper coil of claim 14 further characterized by a purity
level between 99.995% and 99.9999% and at least one of: an
antimony, an arsenic and a bismuth content each of less than 0.03
ppm; a hydrogen content of less than 1.0 ppm; an oxygen content of
less than 1.0 ppm; and a sulfur content of less than 0.05 ppm.
21. The copper coil of claim 14 further characterized by a purity
level less than 99.9999% and at least one of: an antimony, an
arsenic and a bismuth content each of less than 0.03 ppm; a
hydrogen content of less than 1.0 ppm; an oxygen content of less
than 1.0 ppm; and a sulfur content of less than 0.05 ppm.
22. A copper coil for use in a high density plasma deposition
chamber characterized by a purity level between 99.995% and
99.9999% and at least one of: an antimony, an arsenic and a bismuth
content each of less than 0.03 ppm; a hydrogen content of less than
1.0 ppm; an oxygen content of less than 5.0 ppm; and a sulfur
content of less than 1.0 ppm.
23. The copper coil of claim 22 further characterized by at least
one of: an oxygen content of less than 1.0 ppm; and a sulfur
content of less than 0.05 ppm.
24. A copper coil for use in a high density plasma deposition
chamber characterized by a purity level less than 99.9999% and at
least one of: an antimony, an arsenic and a bismuth content each of
less than 0.03 ppm; a hydrogen content of less than 1.0 ppm; an
oxygen content of less than 5.0 ppm; and a sulfur content of less
than 1.0 ppm.
25. A semiconductor device formed by a method comprising the steps
of: providing a substrate; providing a copper target; providing a
copper coil between the substrate and the copper target, the copper
coil characterized by a hardness greater than 45 Rockwell; and
sputtering the copper target so as to deposit a copper film on the
substrate.
Description
[0001] This application is a division of U.S. patent application
Ser. No. 09/415,328, filed Oct. 8, 1999, titled "IMPROVED COIL FOR
SPUTTER DEPOSITION", which is a continuation-in-part of U.S. patent
application Ser. No. 08/979,192, filed No. 26, 1997, titled
"IMPROVED TARGET FOR USE IN MAGNETRON SPUTTERING OF ALUMINUM FOR
FORMING METALLIZATION FILMS HAVING LOW DEFECT DENSITIES AND METHODS
FOR MANUFACTURING AND USING SUCH TARGET", issued as U.S. Pat. No.
6,001,227 on Dec. 14, 1999, and of U.S. patent application Ser. No.
09/272,974, filed Mar. 18, 1999, titled "IMPROVED COPPER TARGET FOR
SPUTTER DEPOSITION", issued as U.S. Pat. No. 6,139,701 on Oct. 31,
2000. The entire content of each of these patent applications is
hereby incorporated by reference herein in its entirety.
FIELD OF THE INVENTION
[0002] The present invention relates generally to metal film
deposition and more particularly to an improved coil for reducing
defect generation during metal film deposition within a high
density plasma deposition chamber.
BACKGROUND OF THE INVENTION
[0003] Metal films are used widely within semiconductor integrated
circuits to make contact to and between semiconductor devices
(i.e., metal interconnects). Because of the high densities required
for modern integrated circuits, the lateral dimensions of
interconnects, as well as the lateral dimensions between
interconnects, have shrunk to such a level that a single defect can
destroy an entire wafer die by shorting a junction region or
open-circuiting a gate electrode of an essential semiconductor
device. Defect reduction within interconnect metal films,
therefore, is an ever-present goal of the semiconductor industry
that increases in importance with each generation of higher density
integrated circuits.
[0004] Interconnect metal films typically are deposited via
physical vapor deposition and more recently via high density plasma
(HDP) deposition, within a plasma chamber. In both processes, a
target of to-be-deposited material (e.g., the metal comprising the
interconnect) is sputtered through energetic ion bombardment that
dislodges atoms from the target. The dislodged atoms travel to a
substrate disposed below the target and form a metal film thereon.
The metal film is patterned to form the interconnect.
[0005] For HDP deposition, in addition to the target, a coil is
provided between the target and the substrate. The coil's primary
role is to increase the plasma density, i.e., ionization fraction,
and thereby create conditions to ionize target atoms sputtered from
the target. Ionized target particles will, under the influence of
an electric field applied between the target and the substrate,
strike the substrate substantially perpendicular to the target face
and substantially perpendicular to any feature base present on the
substrate (e.g., allowing for improved filling of vias and other
surface features). Where the coil is located internally of the
chamber, the coil itself is sputtered, and dislodged coil atoms
travel to the substrate disposed below the coil and deposit
thereon. Sputtered coil atoms predominantly coat the substrate near
its edges and, where the target atoms create a center thick film on
the wafer, enhance the overall thickness uniformity of the material
layer formed on the substrate. The material properties of an HDP
coil therefore play an important role in overall deposited film
quality.
[0006] As described in parent applications, U.S. Ser. No.
08/979,192, filed Nov. 26, 1997 and U.S. Ser. No. 09/272,974, filed
Mar. 18, 1999, both aluminum target manufacturers and copper target
manufacturers conventionally focus on the purity of sputtering
targets to reduce defect densities or to otherwise affect
deposition of high quality metal films. Similar emphasis is placed
on the purity of coils employed in HDP deposition chambers (e.g.,
HDP deposition chambers typically employ a target and a coil having
similar purity levels). However, despite high purity levels for
both targets and coils, the defect densities of conventional HDP
deposited metal films remain high.
[0007] Accordingly, a need exists for a coil for use within an HDP
deposition chamber that produces metal films having reduced defect
densities.
SUMMARY OF THE INVENTION
[0008] The present inventors have discovered that in addition to
target purity, other factors are of significant importance to
defect reduction as recognized and described in parent
applications, U.S. Ser. No. 08/979,192, filed Nov. 26, 1997 and
U.S. Ser. No. 09/272,974, filed Mar. 18, 1999. These other factors
must be considered to reduce defect densities during plasma
deposition as the purity of the target alone does not assure
adequate metal film quality and high device yield.
[0009] Specifically, it has been found that in addition to target
material purity, the following target material parameters have a
direct affect on defect generation during sputter deposition of
metal films: dielectric inclusion content (e.g., target material
oxides, nitrides, etc.), porosity (e.g., non-conductive voids due
to gas trapping during target formation), grain size, surface
roughness and hardness. With respect to aluminum targets, control
of dielectric inclusions is of primary importance for controlling
aluminum film quality. Reducing the concentration of dielectric
inclusions such as Al.sub.2O.sub.3 within an aluminum target can
decrease certain as-deposited or "in-film" defect densities (e.g.,
splat densities) by up to five fold. With respect to copper
targets, increasing the hardness of a copper target is as much a
factor in defect reduction as reduced dielectric inclusion
concentration. Namely, a certain hardness range for the copper
target is required to provide the copper target with sufficient
mechanical/electrical strength to prevent localized mechanical
breakdown, and thus ejection of a relatively large, greater than a
few microns piece of target material, during plasma processing.
[0010] For HDP deposition processes, the present inventors have
discovered that defect reduction results when a coil (e.g.,
aluminum or copper) has material parameters similar to the above
described target material parameters (e.g., reduced dielectric
inclusion concentration, sufficient hardness, etc.). Also, it has
been found that thermal cycling can cause the coil to move
sufficiently to disconnect it from the terminal or feedthrough
through which it connects to its power supply or to short circuit
the coil through contact with another chamber structure such as a
shield that supports the coil. Thus, to prevent a coil from
electrically disconnecting or short circuiting following repeated
depositions (e.g., due to repeated expansion and contraction caused
by thermal cycling), the thermal creep rate and mechanical strength
of the coil must be considered. As used herein, thermal creep rate
refers to the time rate at which a material changes shape due to
prolonged stress or exposure to elevated temperatures.
[0011] To control the thermal creep rate and strength of a copper
coil, the coil's grain size preferably is reduced. For example, a
copper coil's grain size preferably is limited to below 50 microns,
and most preferably to below 25 microns. The smaller the grain
size,, the lower the thermal creep rate and the greater the
strength of the copper coil. The preferred thermal creep rate,
strength and grain size are achieved by limiting the copper coil's
purity level to a level of less than 99.9999%, preferably within
the range from 99.995% to 99.9999% (e.g., less pure than previously
believed necessary). This overall purity level range is maintained
while the concentration levels of impurities that adversely affect
a copper coil's thermal creep rate and strength are reduced (e.g.,
antimony, arsenic, bismuth, hydrogen, oxygen, sulfur, etc.). An
aluminum coil's thermal creep rate and strength primarily are
controlled by alloying (as is known in the art).
[0012] By thus controlling the dielectric inclusion content,
porosity, grain size, surface roughness, thermal creep rate and
strength of a coil, defect generation during HDP deposition may be
decreased while the risk of the coil becoming electrically
disconnected or short circuited during processing is reduced.
[0013] Other objects, features and advantages of the present
invention, as well as the structure of various embodiments of the
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
[0014] The present invention is described with reference to the
accompanying drawings. In the drawings, like reference numerals
indicate identical or functionally similar elements. Additionally,
the leftmost digit of a reference numeral identifies the drawing in
which the reference numeral first appears.
[0015] FIG. 1A is a side diagrammatic illustration, in section, of
the pertinent portions of a high density plasma sputtering chamber
configured in accordance with the present invention;
[0016] FIG. 1B is a top plan view of the coil and shield of FIG.
1A;
[0017] FIG. 1C is a close-up view of the feedthroughs and coil of
FIG. 1B;
[0018] FIG. 1D is a close-up view of the feedthroughs of FIG. 1B
electrically disconnected from a conventional coil;
[0019] FIG. 1E is a close-up view of a cup and pin that couple the
coil and shield of FIG. 1B;
[0020] FIG. 1F is a close-up view of a conventional coil short
circuited to the shield of FIG. 1B; and
[0021] FIG. 2 is a graph of thermal creep rate versus applied
stress for a 99.99% pure copper coil at 600.degree. C. and at
700.degree. C., and for a 99.9999% pure copper coil at 600.degree.
C. and 700.degree. C.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0022] FIG. 1A is a side diagrammatic illustration, in section, of
the pertinent portions of a conventional high density plasma (HDP)
sputtering chamber 100 configured in accordance with the present
invention. The sputtering chamber 100 contains a coil 102 which is
operatively coupled to a first RF power supply 104 via one or more
feedthroughs 105. The coil 102 may comprise a plurality of coils, a
single turn coil as shown in FIG. 1A, a single turn material strip,
or any other similar configuration. The coil 102 is positioned
along the inner surface of the sputtering chamber 100, between a
sputtering target 106 and a substrate pedestal 108. Both the coil
102 and the target 106 are formed from the to-be-deposited material
(e.g., copper, aluminum, etc.).
[0023] The substrate pedestal 108 is positioned in the lower
portion of the sputtering chamber 100 and typically comprises a
pedestal heater (not shown) for elevating the temperature of a
semiconductor wafer or other substrate supported by the substrate
pedestal 108 during processing within the sputtering chamber 100.
The sputtering target 106 is mounted to a water cooled adapter 110
in the upper portion of the sputtering chamber 100 so as to face
the substrate receiving surface of the substrate pedestal 108. A
cooling system 112 is coupled to the adapter 110 and delivers
cooling fluid (e.g., water) thereto.
[0024] The sputtering chamber 100 generally includes a vacuum
chamber enclosure wall 114 having at least one gas inlet 116
coupled to a gas source 118 and having an exhaust outlet 120
coupled to an exhaust pump 122 (e.g., a cryopump or a cryoturbo
pump). The gas source 118 typically comprises a plurality of
processing gas sources 118a, 118b such as a source of argon, helium
and/or nitrogen. Other processing gases may be employed if
desired.
[0025] A removable shield 124 that surrounds the coil 102, the
target 106 and the substrate pedestal 108 is provided within the
sputtering chamber 100. The shield 124 may be removed for cleaning
during chamber maintenance, and the adapter 110 is coupled to the
shield 124 (as shown). The shield 124 also supports the coil 102
via a plurality of cups 126a-e attached to, but electrically
isolated from the shield 124, and via a plurality of pins 128a-e
coupled to both the cups 126a-e and the coil 102. The coil 102 is
supported by resting the coil 102 on the pins 128a-e which are
coupled to the cups 126a-e. Any other known methods for supporting
the coil 102 may be similarly employed. The cups 126a-e and the
pins 128a-e comprise the same material as the coil 102 and the
target 106 (e.g., copper or aluminum) and are electrically
insulated from the shield 124 via a plurality of insulating regions
129a-e (e.g., a plurality of ceramic regions). The structure of the
cups 126a-e, the pins 128a-e and the insulating regions 129a-e are
described further below with reference to FIGS. 1B-1F. The
sputtering chamber 100 also includes a plurality of bake-out lamps
130 located between the shield 124 and the chamber enclosure wall
114, for baking-out the sputtering chamber 100 as is known in the
art.
[0026] The sputtering target 106 and the substrate pedestal 108 are
electrically isolated from the shield 124. The shield 124 may be
grounded so that a negative voltage (with respect to grounded
shield 124) may be applied to the sputtering target 106 via a first
DC power supply 132 coupled between the target 106 and ground, or
may be floated or biased via a second DC power supply 133 coupled
to the shield 124. Additionally, a negative bias may be applied to
the substrate pedestal 108 via a second RF power supply 134 coupled
between the pedestal 108 and ground. A controller 136 is
operatively coupled to the first RF power supply 104, the first DC
power supply 132, the second DC power supply 133, the second RF
power supply 134, the gas source 118 and the exhaust pump 122.
[0027] To perform deposition within the sputtering chamber 100, a
substrate 138 (e.g., a semiconductor wafer, a flat panel display,
etc.) is loaded into the sputtering chamber 100, is placed on the
substrate pedestal 108 and is securely held thereto via a clamp
ring 140. An inert gas such as argon then is flowed from the gas
source 118 into the high density plasma sputtering chamber 100 and
the first DC power supply 132 biases the sputtering target 106
negatively with respect to the substrate pedestal 108 and the
shield 124. In response to the negative bias, argon gas atoms
ionize and form a plasma within the high density plasma sputtering
chamber 100. An RF bias preferably is applied to the coil 102 via
the first RF power supply 104 to increase the density of ionized
argon gas atoms within the plasma and to ionize target atoms
sputtered from the target 106 (as described below).
[0028] Because argon ions have a positive charge, argon ions within
the plasma are attracted to the negatively biased sputtering target
106 and strike the sputtering target 106 with sufficient energy to
sputter target atoms from the target 106. The RF power applied to
the coil 102 increases the ionization of the argon atoms, and, in
combination with the coupling of the coil power to the region of
argon and sputtered target atoms, results in ionization of at least
a substantial portion of the sputtered target atoms. The ionized,
sputtered target atoms travel to and deposit on the substrate 138
so as to form over time a continuous target material film 142
thereon. Because the sputtered target atoms are ionized by the coil
102, the target atoms strike the substrate 138 with increased
directionality under the influence of the electric field applied
between the target 106 and the substrate pedestal 108 (e.g., by the
first DC power supply 132). The second RF power supply 134 may be
employed to apply a negative bias to the substrate pedestal 108
relative to both the sputtering target 106 and to shield 124 to
further attract sputtered target atoms to the substrate 138 during
deposition.
[0029] In addition to target atoms, coil atoms are sputtered from
the coil 102 during deposition and deposit on the substrate 138.
Because of the coil's proximity to the wafer's edge the sputtered
coil atoms predominantly coat the substrate 138 near its edges and,
where the flat target atoms tend to deposit a center thick layer,
result in overall uniformity of the thickness of the film 142
deposited on the substrate 138. Following deposition, the flow of
gas to the high density plasma sputtering chamber 100 is halted,
all biases (e.g., target, pedestal and coil) are terminated, and
the substrate 138 is removed from the high density plasma
sputtering chamber 100.
[0030] Ideally, the film 142 deposited on the substrate 138 is
highly uniform and defect free. However, as described in parent
applications U.S. Ser. No. 08/979,192, filed Nov. 26, 1997 and U.S.
Ser. No. 09/272,974, filed Mar. 18, 1999, a substantial number of
blobs or splats of target material (i.e., splat defects or splats)
appear within films formed by sputter deposition when a
conventional sputtering target is employed. High density plasma
deposited films exhibit similar splat defects when conventional
coils and/or conventional sputtering targets are employed.
[0031] Splat defects are believed to result from arc-induced
localized heating of a target or a coil that melts and liberates a
portion of the target/coil material. The liberated target/coil
material travels to the substrate 138, splatters thereon, cools and
reforms, due to surface tension, as a splat defect in the deposited
film 142. Splats are very large (e.g., 500 .mu.m) in relation to
typical metal line widths (e.g., less than 1 .mu.m) and affect
device yield by shorting over two or more metal lines. It is
believed that up to 50% of the in-film defects produced in current
interconnect metallization schemes are induced, splat-type
defects.
[0032] The present inventors have discovered that the following
target/coil material parameters have a direct affect on splat
generation:
[0033] 1. the number of dielectric inclusions such as target/coil
material oxides (e.g., Al.sub.2O.sub.3 for aluminum targets and
coils, CuO for copper targets and coils, etc.);
[0034] 2. the porosity of the target/coil material (e.g., the
number of non-conductive voids due to gas trapping during target or
coil formation);
[0035] 3. the grain size of the target/coil material;
[0036] 4. the surface roughness of the target/coil; and
[0037] 5. the mechanical strength or hardness of the
target/coil.
[0038] As described in parent application, U.S. Ser. No.
08/979,192, filed Nov. 26, 1997, with regard to aluminum targets,
control of the number of dielectric inclusions is of primary
importance for reducing splat formation (e.g., all other causes
create a minimal number of splats as compared to those caused by
dielectric inclusions). During HDP deposition of aluminum, control
of the number of dielectric inclusions within an aluminum coil is
of primary importance for reducing splat formation due to the coil.
Other aluminum target and aluminum coil manufacturing parameters
may be controlled less stringently without undue risk of
significantly increased splat formation.
[0039] As described in parent application, U.S. Ser. No.
09/272,974, filed Mar. 18, 1999, in contrast to the mechanical
properties of aluminum targets, the mechanical properties (e.g.,
mechanical strength/hardness, grain size, and surface roughness) of
copper targets play a very significant role (in addition to
dielectric inclusions) in splat formation. Mechanical properties
have been found to play a similar role in splat formation with
regard to copper coils used during HDP deposition of copper.
[0040] Accordingly, to reduce arc-induced splat formation during
plasma processing within an HDP deposition chamber, any target
(e.g., aluminum, copper, etc.) and any coil employed preferably
have the following properties: a reduced number of dielectric
inclusions, non-porosity (e.g., few voids and little entrapped
gas), and good mechanical properties (e.g., high strength or
hardness, small grain size and little surface roughness). The
significance each factor plays in splat formation, however, depends
on the target/coil material in question.
[0041] For instance, aluminum target/coil material typically
comprises an aluminum alloy such as AlCu (typically less than 0.5%
Cu) that when manufactured with prior art methodologies, has
sufficient mechanical strength and small enough grain size to
prevent significant splat formation due to arc-induced mechanical
failure and surface-roughness-induced field-enhanced emission.
However, aluminum's primary dielectric inclusion (Al.sub.2O.sub.3)
is highly resistive and charges easily when exposed to a plasma
environment. Therefore, splat formation due to dielectric breakdown
and secondary electron heating is common in aluminum targets/coils.
Accordingly, decreasing dielectric inclusion content (rather than
improving mechanical properties) within an aluminum target/coil is
the primary mechanism for reducing splat formation during aluminum
film formation.
[0042] With respect to reducing splat formation during copper film
deposition, improving the mechanical properties of a copper
target/coil is as important as decreasing dielectric inclusion
content. Because copper target/coil material is highly pure copper
and not an alloy (i.e., it is not purposefully alloyed with a
second material), the hardness of the copper target/coil material
is dictated by the intrinsic hardness of copper and any impurities
within the copper.
[0043] Copper is naturally a soft metal, and copper target/coil
material becomes softer as the purity level of the material
increases. Additionally, the grain size of the copper target/coil
material increases with increasing purity. Accordingly, the present
inventors have discovered that above a certain purity level, splat
formation during copper film deposition actually increases (due to
arc-induced mechanical failure and surface-roughness-induced
field-enhanced emission) with increasing levels of copper
target/coil material purity.
[0044] Further, the main dielectric inclusion within copper (e.g.,
CuO), is not as highly resistive as Al.sub.2O.sub.3. CuO,
therefore, is less susceptible to charging at the inclusion to
metal interface region, dielectric breakdown and secondary electron
heating than is Al.sub.2O.sub.3, and splat formation due to
dielectric inclusions is less pronounced for copper targets/coils.
Nonetheless, splat formation can occur during use of copper
targets/coils due to CuO induced charging at a CuO inclusion to
metal interface region, dielectric breakdown and secondary electron
heating and control of dielectric inclusion content within copper
target/coil material remains important to reduce these effects.
[0045] With regard to the coil 102, in addition to the above
described properties (e.g., reduced dielectric inclusion content,
porosity, material grain size, surface roughness, etc.), thermal
creep rate of the coil 102 also must be considered. Specifically,
the coil 102 should be provided with sufficient mechanical strength
to reduce the thermal creep rate of the coil 102 to a value that
prevents electrical disconnection of the coil 102 from the
feedthroughs 105 or electrical shorting of the coil 102 due to
contact with the shield 124 following repeated depositions within
the chamber 100 as described with reference to FIGS. 1B-1F.
[0046] FIG. 1B is a top plan view of the coil 102 coupled to the
shield 124 via the cups 126a-e and the pins 128a-e. The cups 126a-e
and the pins 128a-e are electrically isolated from the shield 124
via the insulating regions 129a-e. The first RF power supply 104 is
coupled to the coil 102 via a first feedthrough 105a and via a
second feedthrough 105b as shown. A close-up of the connection
between the feedthroughs 105a, 105b and the coil 102 is shown in
FIG. 1C, and a close-up of the connection between the coil 102 and
the shield 124 (via the cup 126a, the pin 128b and the insulating
region 129a) is shown in FIG. 1E.
[0047] If a conventional coil 102' is employed within the
deposition chamber 100, following repeated depositions within the
chamber 100, the coil 102' may disconnect from either the first
feedthrough 105a or the second feedthrough 105b as shown in FIG.
1D. The coil 102' also may be short circuited through contact with
the shield 124 as shown in FIG. 1F. Electrical disconnection of the
coil 102' from either feedthrough 105a, 105b occurs due to thermal
creep induced movement of the coil away from the feedthroughs 105a,
105b that is driven by the thermal cycling of the coil 102' that
accompanies repeated depositions. Thermal creep induced movement of
the coil 102' toward the shield 124 similarly causes short
circuiting of the coil 102'. However, by reducing the thermal creep
rate of the inventive coil 102 (as described below) thermal creep
induced movement of the coil 102 away from the feedthroughs 105a,
105b and toward the shield 124 is significantly reduced so that
electrical disconnection and short circuiting of the coil 102 do
not occur and the coil 102 primarily maintains the position shown
in FIG. 1C and FIG. 1E.
[0048] As previously described, aluminum targets/coils typically
are formed from a 0.5% copper/99.5% aluminum alloy that has
sufficient mechanical strength and a small enough grain size to
prevent significant mechanically induced splat formation. Likewise,
the thermal creep rate of alloyed aluminum coils typically is low
enough to prevent electrical disconnection of an aluminum coil from
the feedthroughs 105 or electrical shorting of the aluminum coil
due to contact with the shield 124 following repeated HDP
depositions. Accordingly, the main concern with aluminum coils is
defect generation; and the preferred aluminum coil material is the
same as the preferred aluminum target material described in parent
application, U.S. Ser. No. 08/979,192, filed Nov. 26, 1997.
Specifically, for aluminum deposition within the HDP deposition
chamber 100, the coil 102 preferably has one or more of the
characteristics listed in TABLE 1, and most preferably in TABLE 2.
All other aluminum material characteristics described in parent
application, U.S. Ser. No. 08/979,192, filed Nov. 26, 1997, may be
employed for the coil 102, and the coil 102 may be manufactured as
described therein or by any other known techniques.
1 TABLE 1 PROPERTY PREFERRED RANGE Dielectric Inclusion Content,
less than about 5000 where such inclusions have inclusions per gram
of coil widths of 0.3 micron or more material Hydrogen content less
than about 0.5 ppm Carbon content less than about 10 ppm Oxygen
content less than about 10 ppm Nitrogen content less than about 10
ppm Metal grain size less than about 100 micron (200) textured
material greater than 50% (111) textured material less than about
3% Hardness greater than about 50 (Rockwell scale) Surface
roughness less than about 20 microinches Alloy strengthening addend
greater than about 0.5% Cu by weight Alloy precipitate size about 5
microns or less Other impurities less than about 10 ppm
[0049]
2 TABLE 2 PROPERTY PREFERRED RANGE Dielectric Inclusion Content,
less than about 5000 where such inclusions have inclusions per gram
of coil widths of 0.1 micron or more material Hydrogen content less
than about 0.075 ppm Carbon content less than about 5 ppm Oxygen
content less than about 10 ppm Nitrogen content less than about 7
ppm Metal grain size between about 75 micron and 90 micron (200)
textured material greater than 75% (111) textured material less
than about 1% Hardness greater than about 50 (Rockwell scale)
Surface roughness less than about 16 microinches Alloy
strengthening addend about 0.5% Cu by weight Alloy precipitate size
less than about 4 microns Other impurities less than about 5
ppm
[0050] Unlike aluminum coils, copper coils are much more
susceptible to electrical disconnection and/or short circuiting
because copper is naturally a soft metal and thus has a larger
thermal creep rate. Accordingly, as the purity level of a copper
coil increases, the likelihood of thermal creep induced electrical
disconnection and/or short circuiting increases.
[0051] FIG. 2 is a graph of thermal creep rate versus applied
stress for a 99.99% pure copper coil at 600.degree. C. (first curve
200) and at 700.degree. C. (second curve 202), and for a 99.9999%
pure copper coil at 600.degree. C. (third curve 204) and at
700.degree. C. (fourth curve 206). With reference to FIG. 2, for a
given applied stress level, the thermal creep rate generally
increases with copper coil purity (e.g., thermal creep rate may be
reduced by reducing copper coil purity) because the mechanical
strength of the coil decreases as copper purity increases.
[0052] Accordingly, to reduce splat formation and thermal creep
during copper film deposition, a copper coil is provided having
both increased mechanical strength (e.g., hardness) and decreased
inclusion content. Specifically, a copper coil is provided having a
hardness value greater than about 45 Rockwell as the present
inventors have discovered that copper coils having hardnesses
greater than about 45 Rockwell produce far fewer splats than softer
copper coils and do not electrically disconnect or short circuit
following repeated depositions.
[0053] To control hardness, the grain size of a copper coil
preferably is decreased. Grain size is decreased (and hardness
increased) preferably by limiting copper coil material purity to a
level of less than 99.9999%, preferably within a range between
99.995% to 99.9999% copper. This purity range is significantly less
than the purity level of many commercially available copper coils,
and is in stark contrast to the industry trend of using higher and
higher purity copper coils. Copper coils having purity levels in
the range between 99.995% and 99.9999% can have hardnesses greater
than 45 Rockwell if properly manufactured (e.g., employing the
manufacturing methods described in parent application U.S. Ser. No.
09/272,974, filed Mar. 18, 1999).
[0054] TABLES 3 and 4 contain preferred and most preferred,
respectively, copper coil material parameter ranges for reducing
splat formation and thermal creep during plasma processing,
although a purity level of less than 99.9999% copper is
specifically contemplated by the inventors.
3 TABLE 3 Purity level 99.995% to 99.9999% Antimony content Less
than about 0.03 ppm Arsenic content Less than about 0.03 ppm
Bismuth content Less than about 0.03 ppm Carbon content Less than
about 5.0 ppm Hydrogen content Less than about 1.0 ppm Oxygen
content Less than about 5.0 ppm Nitrogen content Less than about
1.0 ppm Sulfur content Less than about 1.0 ppm Metal grain size
Less than about 50 micron (200) textured material Greater than 50%
(111) textured material Less than about 3% Hardness Greater than 45
(Rockwell scale) Surface roughness Less than about 20 micro-inches
Other Impurities Less than about 10 ppm
[0055]
4 TABLE 4 Purity level 99.995% to 99.9999% Antimony content Less
than about 0.03 ppm Arsenic content Less than about 0.03 ppm
Bismuth content Less than about 0.03 ppm Carbon content Less than
about 1.0 ppm Hydrogen content Less than about 1.0 ppm Oxygen
content Less than about 1.0 ppm Nitrogen content Less than about
1.0 ppm Sulfur content Less than about 0.05 ppm Metal grain size
Less than about 25 micron (200) textured material Greater than 50%
(111) textured material Less than about 3% Hardness Greater than 45
(Rockwell scale) Surface roughness Less than about 5.0 micro-inches
Other Impurities Less than about 10 ppm
[0056] A copper coil hardness greater than 45 Rockwell provides
adequate localized material strength and immunity against
mechanical fracturing to reduce splat formation during copper film
deposition and a small enough thermal creep rate to prevent
electrical disconnection and short circuiting of the copper coil
following repeated depositions. This hardness range preferably is
achieved by limiting grain size to less than about 50 microns
(TABLE 3) and preferably to less than about 25 microns (TABLE 4).
This grain size range is achieved via selection of the purity range
of 99.995% to 99.9999%.
[0057] Minimizing oxygen incorporation with the copper coil
material is very important for reducing metal oxide dielectric
inclusions such as CuO. Further, limiting nitrogen and carbon
content, while less important, reduces metal nitride and metal
carbide inclusions, respectively.
[0058] Impurities that adversely affect mechanical properties of a
copper coil include antimony, arsenic, bismuth, hydrogen and
sulfur. Antimony, arsenic, bismuth and sulfur reduce copper coil
hardness through interactions at copper grain boundaries. Sulfur,
for instance, readily forms CuS at copper grain boundaries which
renders a copper coil brittle and susceptible to arc-induced
mechanical failure. Accordingly, reducing antimony, arsenic,
bismuth and sulfur content increases copper coil mechanical
strength, and can reduce splat formation.
[0059] Hydrogen is highly mobile in copper and embrittles copper by
combining with copper oxide to form water (H.sub.2O). Additionally,
trapped hydrogen forms voids during casting of the copper coil.
Reducing hydrogen content, therefore, reduces splat formation by
reducing arc-induced mechanical failure and field-enhanced emission
due to gas trapping.
[0060] Other common impurities within copper coil material include
metallic impurities such as aluminum, iron, magnesium, silver and
zinc. These metallic impurities usually are the highest
concentration impurities and thus are the primary factors
controlling grain size and hardness of the copper coil. Therefore,
one or more of the metallic impurities should be present in the
range of approximately 100 to 5000 ppm to maintain the purity level
of the copper coil material within the range of 99.995% to
99.9999%.
[0061] Metal working techniques such as forging, rolling and
deforming alter the texture and hardness of the copper coil. As
known in the art, post-work metal texturing of at least 50% (200)
texture and less than 3% (111) texture enhances uniformity of
physical vapor deposition and is preferred.
[0062] Finally, providing a copper coil with smooth surfaces (e.g.,
less than 20 micro inches, more preferably less than 5 micro
inches) reduces the number of sharp protrusions on the coil's
surfaces so as to reduce field-enhanced emission induced splat
formation during copper film deposition. The smoothed surfaces
should be ultrasonically cleaned prior to use to reduce
arc-inducing surface contaminants that can otherwise permanently
roughen the smoothed surface (e.g., via arcing during burn-in).
[0063] With reference to FIG. 1, deposition of a copper film having
a substantially reduced in-film defect (e.g., splat) density is
performed by:
[0064] 1. providing a copper coil 102 and a copper target 106
having one or more properties in accordance with TABLE 3 and/or
TABLE 4;
[0065] 2. placing the substrate 138 on the pedestal 108;
[0066] 3. biasing the target 106 relative to the shield 124 and
pedestal 108;
[0067] 4. applying RF power to the coil 102;
[0068] 5. introducing argon into the shielded region of the chamber
100 so as to produce a plasma therein; and
[0069] 6. maintaining the plasma until the desired thickness for
the copper film is formed on the substrate 138.
[0070] Preferably about 1-3 kW of power is applied to the target
106 and 1-3 kW of power is applied to the coil 102 (most preferably
2 kW) during copper deposition. A similar process may be performed
for the deposition of an aluminum film having a substantially
reduced in-film defect density, if an aluminum coil and an aluminum
target having one or more properties in accordance with TABLE 1
and/or TABLE 2 are employed.
[0071] Primarily because the copper coil 102 and the copper target
106 are harder than conventional copper coils and targets and have
fewer dielectric inclusions, copper films deposited using the
copper coil 102 and the copper target 106 have significantly fewer
in-film defects than copper films deposited via conventional copper
coils and targets. Further, the cost of depositing copper films is
reduced as the copper coil 102 and the copper target 106 are less
expensive to manufacture than the ultra-high purity copper coils
and targets typically employed.
[0072] 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, limiting the purity range of copper coil material is the
preferred method for increasing copper coil strength and reducing
thermal creep rate. However, it may be possible to alloy a copper
coil having a purity level higher than 99.9999% while still
maintaining adequate copper coil hardness and small grain size.
Further, various manufacturing methods may be employed to achieve
one or more of the desired ranges set forth in TABLES 1-4.
[0073] 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.
* * * * *