U.S. patent application number 12/182988 was filed with the patent office on 2009-09-17 for self-ionized and inductively-coupled plasma for sputtering and resputtering.
This patent application is currently assigned to APPLIED MATERIALS, INC.. Invention is credited to Fusen CHEN, Peijun DING, John C. FORSTER, Jianming FU, Praburam GOPALRAJA, Daniel C. LUBBEN, Michael A. MILLER, Roderick C. MOSELY, Suraj RENGARAJAN, Arvind SUNDARRAJAN, Xianmin TANG, Rong TAO, Zheng XU.
Application Number | 20090233438 12/182988 |
Document ID | / |
Family ID | 50881541 |
Filed Date | 2009-09-17 |
United States Patent
Application |
20090233438 |
Kind Code |
A1 |
DING; Peijun ; et
al. |
September 17, 2009 |
SELF-IONIZED AND INDUCTIVELY-COUPLED PLASMA FOR SPUTTERING AND
RESPUTTERING
Abstract
A magnetron sputter reactor for sputtering deposition materials
such as tantalum, tantalum nitride and copper, for example, and its
method of use, in which self-ionized plasma (SIP) sputtering and
inductively coupled plasma (ICP) sputtering are promoted, either
together or alternately, in the same or different chambers. Also,
bottom coverage may be thinned or eliminated by ICP resputtering in
one chamber and SIP in another. SIP is promoted by a small
magnetron having poles of unequal magnetic strength and a high
power applied to the target during sputtering. ICP is provided by
one or more RF coils which inductively couple RF energy into a
plasma. The combined SIP-ICP layers can act as a liner or barrier
or seed or nucleation layer for hole. In addition, an RF coil may
be sputtered to provide protective material during ICP
resputtering. In another chamber an array of auxiliary magnets
positioned along sidewalls of a magnetron sputter reactor on a side
towards the wafer from the target. The magnetron preferably is a
small, strong one having a stronger outer pole of a first magnetic
polarity surrounding a weaker outer pole of a second magnetic
polarity and rotates about the central axis of the chamber. The
auxiliary magnets preferably have the first magnetic polarity to
draw the unbalanced magnetic field component toward the wafer. The
auxiliary magnets may be either permanent magnets or
electromagnets.
Inventors: |
DING; Peijun; (Saratoga,
CA) ; TAO; Rong; (San Jose, CA) ; XU;
Zheng; (Foster City, CA) ; LUBBEN; Daniel C.;
(San Jose, CA) ; RENGARAJAN; Suraj; (San Jose,
CA) ; MILLER; Michael A.; (Mountain View, CA)
; SUNDARRAJAN; Arvind; (Santa Clara, CA) ; TANG;
Xianmin; (San Jose, CA) ; FORSTER; John C.;
(San Francisco, CA) ; FU; Jianming; (Palo Alto,
CA) ; MOSELY; Roderick C.; (Pleasanton, CA) ;
CHEN; Fusen; (Sunnyvale, CA) ; GOPALRAJA;
Praburam; (San Jose, CA) |
Correspondence
Address: |
KONRAD RAYNES & VICTOR, LLP;ATTN: AMAT7828
315 S. BEVERLY DRIVE, SUITE 210
BEVERLY HILLS
CA
90212
US
|
Assignee: |
APPLIED MATERIALS, INC.
Santa Clara
CA
|
Family ID: |
50881541 |
Appl. No.: |
12/182988 |
Filed: |
July 30, 2008 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
11184615 |
Jul 19, 2005 |
|
|
|
12182988 |
|
|
|
|
10495506 |
May 12, 2004 |
|
|
|
11184615 |
|
|
|
|
09685978 |
Oct 10, 2000 |
6582569 |
|
|
10495506 |
|
|
|
|
09414614 |
Oct 8, 1999 |
6398929 |
|
|
09685978 |
|
|
|
|
10202778 |
Jul 25, 2002 |
|
|
|
10495506 |
|
|
|
|
09993543 |
Nov 14, 2001 |
6610184 |
|
|
PCT/US02/36940 |
Nov 14, 2002 |
|
|
|
10495506 |
|
|
|
|
60316137 |
Aug 30, 2001 |
|
|
|
60342608 |
Dec 21, 2001 |
|
|
|
Current U.S.
Class: |
438/627 ;
257/E21.169; 257/E21.577 |
Current CPC
Class: |
H01L 21/76843 20130101;
H01L 21/76844 20130101; C23C 14/358 20130101; H01L 21/76868
20130101; H01L 21/76862 20130101; H01L 21/76873 20130101; C23C
14/568 20130101; H01L 21/76876 20130101; H01L 2221/1089 20130101;
C23C 14/3457 20130101; H01L 21/76846 20130101; H01J 2237/3327
20130101; C23C 14/564 20130101; H01L 21/76877 20130101; C23C 14/345
20130101; H01J 37/3441 20130101; H01L 21/76865 20130101; H01L
21/2855 20130101; H01L 21/76805 20130101; H01L 21/76871 20130101;
H01J 37/321 20130101; H01L 21/76814 20130101; H01J 37/3408
20130101; C23C 14/35 20130101; H01J 37/3402 20130101; C23C 14/046
20130101 |
Class at
Publication: |
438/627 ;
257/E21.169; 257/E21.577 |
International
Class: |
H01L 21/4763 20060101
H01L021/4763 |
Claims
1-82. (canceled)
83. A method for depositing a diffusion barrier and a metal
conductive layer for metal interconnects on a wafer substrate, the
method comprising: (a) depositing a first portion of the diffusion
barrier over the surface of the wafer substrate; (b) etching
through at least part of the first portion of the diffusion barrier
at the bottoms of a plurality of vias to expose at least part of an
underlying metal layer while simultaneously depositing a second
portion of the diffusion barrier on at least field regions of the
wafer substrate; (c) depositing a third portion of the diffusion
barrier, which covers at least the bottoms of the vias; and (d)
depositing the metal conductive layer over the surface of the wafer
substrate.
84. The method of claim 83, wherein at least two successive
operations in (a) through (c) are performed in the same processing
chamber.
85. The method of claim 84, wherein the processing chamber is a
plasma physical vapor deposition (PVD) chamber.
86. The method of claim 84, wherein the processing chamber
comprises a hollow cathode magnetron.
87. The method of claim 83, further comprising a degas operation
prior to (a).
88. The method of claim 83, wherein (b) comprises depositing the
second portion of diffusion barrier elsewhere on the wafer at least
as on sidewalls of the plurality of vias.
89. The method of claim 88, wherein (b) further comprises
depositing the second portion of diffusion barrier elsewhere on the
wafer including on field regions of the wafer substrate.
90. The method of claim 83, wherein (c) comprises depositing the
third portion of diffusion barrier on field regions of the wafer
substrate.
91. The method of claim 83, wherein (a) comprises sputtering a
metal from a target having an applied DC power of greater than 10
kilowatts, without significantly biasing the wafer substrate.
92. The method of claim 83, wherein (a) comprises using physical
vapor deposition (PVD).
93. The method of claim 83, wherein at least one portion of the
diffusion barrier comprises a material selected from the group
consisting of tantalum, nitrogen-doped tantalum, tantalum nitride,
titanium nitride, and tungsten nitride.
94. The method of claim 83, wherein (b) comprises sputtering a
metal from a target having an applied DC power of between about 1
and 40 kilo Watts, while applying a bias to the wafer
substrate.
95. The method of claim 94, wherein the bias comprises RF power of
between about 10 and 5000 Watts.
96. The method of claim 94, wherein (b) further comprises passing
argon gas through the process chamber.
97. The method of claim 83, wherein (b) is performed under
conditions having an etch-to-deposition ratio of greater than 1 at
the bottoms of the vias.
98. The method of claim 83, wherein (c) comprises sputtering a
metal from a target having an applied DC power of greater than 10
kilo Watts, without significantly biasing the wafer substrate.
99. The method of claim 83, wherein (c) comprises a process
selected from the group consisting of physical vapor deposition
(PVD).
100. The method of claim 83, further comprising, after (c) but
prior to (d), etching through some of the third portion of the
diffusion barrier at the bottoms of a plurality of vias, without
etching to expose an underlying metal structure.
101. The method of claim 83, wherein (d) comprises depositing
copper containing metal over the surface of the wafer
substrate.
102. The method of claim 101, wherein the metal is a copper seed
layer.
103. The method of claim 83, wherein at least (a) and (b) are
performed in the same processing chamber.
104. The method of claim 83, wherein at least (b) and (c) are
performed in the same processing chamber.
105. The method of claim 83, wherein at least (a) through (c) are
all performed in the same processing chamber.
106. A method for depositing a diffusion barrier and a metal
conductive layer on a partially fabricated integrated circuit
containing a plurality of unlanded vias, the method comprising: (a)
depositing a first portion of the diffusion barrier on the surface
of the partially fabricated integrated circuit; (b) etching through
at least part of the first portion of the diffusion barrier at the
bottoms of a plurality of unlanded and landed vias to expose at
least part of an underlying metal layer while simultaneously
depositing a second portion of the diffusion barrier on at least
field regions of the surface of the partially fabricated integrated
circuit; (c) depositing a third portion of the diffusion barrier,
which covers at least the bottoms of the vias; and (d) depositing
the metal conductive layer over the surface of the wafer
substrate.
107. The method of claim 106, further comprising a degas operation
prior to (a).
108. The method of claim 106, wherein at least two successive
operations of (a), (b), and (c) are performed in the same
processing chamber.
109. The method of claim 108, wherein the processing chamber is a
plasma physical vapor deposition (PVD) chamber.
110. The method of claim 108, wherein the processing chamber
comprises a hollow cathode magnetron.
111. The method of claim 106, wherein (a) and/or (c) comprise a
processes selected from the group consisting of physical vapor
deposition (PVD).
112. The method of claim 106, wherein at least one portion of the
diffusion barrier comprises a material selected from the group
consisting of tantalum, nitrogen-doped tantalum, tantalum nitride,
titanium nitride, and tungsten nitride.
113. The method of claim 106, wherein (b) comprises sputtering a
metal from a target having an applied DC power of between about 1
and 40 kilo Watts, while applying a bias to the wafer
substrate.
114. The method of claim 106, wherein (d) comprises depositing
copper-containing metal over the surface partially fabricated
integrated circuit.
115. The method of claim 114, wherein the metal is a copper seed
layer.
116. The method of claim 106, wherein at least (a) and (b) are
performed in the same processing chamber.
117. The method of claim 106, wherein at least (b) and (c) are
performed in the same processing chamber.
118. The method of claim 106, wherein at least (a) through (c) are
all performed in the same processing chamber.
Description
RELATED APPLICATIONS
[0001] This application is a continuation in part application of
pending application Ser. No. 09/685,978 filed Oct. 10, 2000, a
divisional application of application Ser. No. 09/414,614 filed
Oct. 8, 1999 (issued as U.S. Pat. No. 6,398,929); and is a
continuation in part of pending application Ser. No. 10/202,778,
filed Jul. 25, 2002 (which claims priority to provisional
applications 60/316,137 filed Aug. 30, 2001, and 60/342,608 filed
Dec. 21, 2001); and is a continuation in part application of
pending application Ser. No. 09/993,543, filed Nov. 14, 2001, which
are incorporated by reference in their entireties.
FIELD OF THE INVENTION
[0002] The invention relates generally to sputtering and
resputtering. In particular, the invention relates to the sputter
deposition of material and resputtering of deposited material in
the formation of semiconductor integrated circuits.
BACKGROUND ART
[0003] Semiconductor integrated circuits typically include multiple
levels of metallization to provide electrical connections between
large numbers of active semiconductor devices. Advanced integrated
circuits, particularly those for microprocessors, may include five
or more metallization levels. In the past, aluminum has been the
favored metallization, but copper has been developed as a
metallization for advanced integrated circuits.
[0004] A typical metallization level is illustrated in the
cross-sectional view of FIG. 1. A lower-level layer 110 includes a
conductive feature 112. If the lower-level layer 110 is a
lower-level dielectric layer, such as silica or other insulating
material, the conductive feature 112 may be a lower-level copper
metallization, and the vertical portion of the upper-level
metallization is referred to as a via since it interconnects two
levels of metallization. If the lower-level layer 110 is a silicon
layer, the conductive feature 112 may a doped silicon region, and
the vertical portion of the upper-level metallization formed in a
hole is referred to as a contact because it electrically contacts
silicon. An upper-level dielectric layer 114 is deposited over the
lower-level dielectric layer 110 and the lower-level metallization
112. There are yet other shapes for the holes including lines and
trenches. Also, in dual damascene and similar interconnect
structures, as described below, the holes have a complex shape. In
some applications, the hole may not extend through the dielectric
layer. The following discussion will refer to only via holes, but
in most circumstances the discussion applies equally well to other
types of holes with only a few modifications well known in the
art.
[0005] Conventionally, the dielectric is silicon oxide formed by
plasma-enhanced chemical vapor deposition (PECVD) using
tetraethylorthosilicate (TEOS) as the precursor. However, low-k
materials of other compositions and deposition techniques are being
considered. Some of the low-k dielectrics being developed can be
characterized as silicates, such as fluorinated silicate glasses.
Hereafter, only silicate (oxide) dielectrics will be directly
described, but it is contemplated that other dielectric
compositions may be used.
[0006] A via hole is etched into the upper-level dielectric layer
114 typically using, in the case of silicate dielectrics, a
fluorine-based plasma etching process. In advanced integrated
circuits, the via holes may have widths as low as 0.18 .mu.m or
even less. The thickness of the dielectric layer 114 is usually at
least 0.7 .mu.m, and sometimes twice this, so that the aspect ratio
of the hole may be 4:1 or greater. Aspect ratios of 6.1 and greater
are being proposed. Furthermore, in most circumstances, the via
hole should have a vertical profile.
[0007] A liner layer 116 may be deposited onto the bottom and sides
of the hole and above the dielectric layer 114. The liner 116 can
perform several functions. It can act as an adhesion layer between
the dielectric and the metal since metal films tend to peel from
oxides. It can also act as a barrier against inter-diffusion
between the oxide-based dielectric and the metal. It may also act
as a seed and nucleation layer to promote the uniform adhesion and
growth and possibly low-temperature reflow for the deposition of
metal filling the hole and to nucleate the even growth of a
separate seed layer. One or more liner layers may be deposited, in
which one layer may function primarily as a barrier layer and
others may function primarily as adhesion, seed or nucleation
layers.
[0008] An interconnect layer 118 of a conductive metal such as
copper, for example, is then deposited over the liner layer 116 to
fill the hole and to cover the top of the dielectric layer 114.
Conventional aluminum metallizations are patterned into horizontal
interconnects by selective etching of the planar portion of the
metal layer 118. However, a technique for copper metallization,
called dual damascene, forms the hole in the dielectric layer 114
into two connected portions, the first being narrow vias through
the bottom portion of the dielectric and the second being wider
trenches in the surface portion which interconnect the vias. After
the metal deposition, chemical mechanical polishing (CMP) is
performed which removes the relatively soft copper exposed above
the dielectric oxide but which stops on the harder oxide. As a
result, multiple copper-filled trenches of the upper level, similar
to the conductive feature 112 of the next lower level, are isolated
from each other. The copper filled trenches act as horizontal
interconnects between the copper-filled vias. The combination of
dual damascene and CMP eliminates the need to etch copper. Several
layer structures and etching sequences have been developed for dual
damascene, and other metallization structures have similar
fabrication requirements.
[0009] Lining and filling via holes and similar high aspect-ratio
structures, such as occur in dual damascene, have presented a
continuing challenge as their aspect ratios continue to increase.
Aspect ratios of 4:1 are common and the value will further
increase. An aspect ratio as used herein is defined as the ratio of
the depth of the hole to narrowest width of the hole, usually near
its top surface. Via widths of 0.18 .mu.m are also common and the
value will further decrease. For advanced copper interconnects
formed in oxide dielectrics, the formation of the barrier layer
tends to be distinctly separate from the nucleation and seed layer.
The diffusion barrier may be formed from a bilayer of Ta/TaN, W/WN,
or Ti/TiN, or of other structures. Barrier thicknesses of 10 to 50
nm are typical. For copper interconnects, it has been found useful
to deposit one or more copper layers to fulfill the nucleation and
seed functions.
[0010] The deposition of the liner layer or the metallization by
conventional physical vapor deposition (PVD), also called
sputtering, is relatively fast. A DC magnetron sputtering reactor
has a target which is composed of the metal to be sputter deposited
and which is powered by a DC electrical source. The magnetron is
scanned about the back of the target and projects its magnetic
field into the portion of the reactor adjacent the target to
increase the plasma density there to thereby increase the
sputtering rate. However, conventional DC sputtering (which will be
referred to as PVD in contrast to other types of sputtering to be
introduced) predominantly sputters neutral atoms. The typical ion
densities in PVD are often less than 10.sup.9 cm.sup.-3. PVD also
tends to sputter atoms into a wide angular distribution, typically
having a cosine dependence about the target normal. Such a wide
distribution can be disadvantageous for filling a deep and narrow
via hole 122 such as that illustrated in FIG. 2, in which a barrier
layer 124 has already been deposited. The large number of off-angle
sputter particles can cause a layer 126 to preferentially deposit
around the upper corners of the hole 122 and form overhangs 128.
Large overhangs can further restrict entry into the hole 122 and
cause inadequate coverage of the sidewalls 130 and bottom 132 of
the hole 122. Also, the overhangs 128 can bridge the hole 122
before it is filled and create a void 134 in the metallization
within the hole 122. Once a void 134 has formed, it is often
difficult to reflow it out by heating the metallization to near its
melting point. Even a small void can introduce reliability
problems. If a second metallization deposition step is planned,
such as by electroplating, the bridged overhang make subsequent
deposition more difficult.
[0011] One approach to ameliorate the overhang problem is
long-throw sputtering in which the sputtering target is spaced
relatively far from the wafer or other substrate being sputter
coated. For example, the target-to-wafer spacing can be at least
50% of wafer diameter, preferably more than 90%, and more
preferably more than 140%. As a result, the off-angle portion of
the sputtering distribution is preferentially directed to the
chamber walls, but the central-angle portion remains directed
substantially to the wafer. The truncated angular distribution can
cause a higher fraction of the sputter particles to be directed
deeply into the hole 122 and reduce the extent of the overhangs
128. A similar effect can be accomplished by positioning a
collimator between the target and wafer. Because the collimator has
a large number of holes of high aspect ratio, the off-angle sputter
particles tend to strike the sidewalls of the collimator, and the
central-angle particles tend to pass through. Both long-throw
targets and collimators typically reduce the flux of sputter
particles reaching the wafer and thus tend to reduce the sputter
deposition rate. The reduction can become more pronounced as throws
are lengthened or as collimation is tightened to accommodate via
holes of increasing aspect ratios.
[0012] Also, the length that long throw sputtering may be increased
may be limited. At the few milliTorr of argon pressure often used
in PVD sputtering, there is a greater possibility of the argon
scattering the sputtered particles as the target to wafer spacing
increases. Hence, the geometric selection of the forward particles
may be decreased. A yet further problem with both long throw and
collimation is that the reduced metal flux can result in a longer
deposition period which can not only reduce throughput, but also
tends to increase the maximum temperature the wafer experiences
during sputtering. Still further, long throw sputtering can reduce
over hangs and provide good coverage in the middle and upper
portions of the sidewalls, but the lower sidewall and bottom
coverage can be less than satisfactory.
[0013] Another technique for deep hole lining and filling is
sputtering using a high-density plasma (HDP) in a sputtering
process called ionized metal plating (IMP). A typical high-density
plasma is one having an average plasma density across the plasma,
exclusive of the plasma sheaths, of at least 10.sup.11 cm.sup.-3,
and preferably at least 10.sup.12 cm.sup.-3. In IMP deposition, a
separate plasma source region is formed in a region away from the
wafer, for example, by inductively coupling RF power into a plasma
from an electrical coil wrapped around a plasma source region
between the target and the wafer. The plasma generated in this
fashion is referred to as an inductively coupled plasma (ICP). An
HDP chamber having this configuration is commercially available
from Applied Materials of Santa Clara, Calif. as the HDP PVD
Reactor. Other HDP sputter reactors are available. The higher power
ionizes not only the argon working gas, but also significantly
increases the ionization fraction of the sputtered atoms, that is,
produces metal ions. The wafer either self-charges to a negative
potential or is RF biased to control its DC potential. The metal
ions are accelerated across the plasma sheath as they approach the
negatively biased wafer. As a result, their angular distribution
becomes strongly peaked in the forward direction so that they are
drawn deeply into the via hole. Overhangs become much less of a
problem in IMP sputtering, and bottom coverage and bottom sidewall
coverage are relatively high.
[0014] IMP sputtering using a remote plasma source is usually
performed at a higher pressure such as 30 milliTorr or higher. The
higher pressures and a high-density plasma can produce a very large
number of argon ions, which are also accelerated across the plasma
sheath to the surface being sputter deposited. The argon ion energy
is often dissipated as heat directly into the film being formed.
Copper can dewet from tantalum nitride and other barrier materials
at elevated temperatures experienced in IMP, even at temperatures
as low at 50 to 75 C. Further, the argon tends to become embedded
in the developing film. IMP can deposit a copper film as
illustrated at 136 in the cross-sectional view of FIG. 3, having a
surface morphology that is rough or discontinuous. If so, such a
film may not promote hole filling, particularly when the liner is
being used as the electrode for electroplating.
[0015] Another technique for depositing metals is sustained
self-sputtering (SSS), as is described by Fu et al. in U.S. patent
application Ser. No. 08/854,008, filed May 8, 1997 and by Fu in
U.S. Pat. No. 6,183,614 B1, Ser. No. 09/373,097, filed Aug. 12,
1999, incorporated by reference in their entireties. For example,
at a sufficiently high plasma density adjacent a copper target, a
sufficiently high density of copper ions develops that the copper
ions will resputter the copper target with yield over unity. The
supply of argon working gas can then be eliminated or at least
reduced to a very low pressure while the copper plasma persists.
Aluminum is believed to be not readily susceptible to SSS. Some
other materials, such as Pd, Pt, Ag, and Au can also undergo
SSS.
[0016] Depositing copper or other metals by sustained
self-sputtering of copper has a number of advantages. The
sputtering rate in SSS tends to be high. There is a high fraction
of copper ions which can be accelerated across the plasma sheath
and toward a biased wafer, thus increasing the directionality of
the sputter flux. Chamber pressures may be made very low, often
limited by leakage of backside cooling gas, thereby reducing wafer
heating from the argon ions and decreasing scattering of the metal
particles by the argon.
[0017] Techniques and reactor structures have been developed to
promote sustained self-sputtering. It has been observed that some
sputter materials not subject to SSS because of sub-unity resputter
yields nonetheless benefit from these same techniques and
structures, presumably because of partial self-sputtering, which
results in a partial self-ionized plasma (SIP). Furthermore, it is
often advantageous to sputter copper with a low but finite argon
pressure even though SSS without any argon working gas is
achievable. Hence, SIP sputtering is the preferred terminology for
the more generic sputtering process involving a reduced or zero
pressure of working gas so that SSS is a type of SIP. SIP
sputtering has also been described by Fu et al. in U.S. Pat. No.
6,290,825 and by Chiang et al. in U.S. patent application Ser. No.
09/414,614, filed Oct. 8, 1999, both incorporated herein by
reference in their entireties.
[0018] SIP sputtering uses a variety of modifications to a fairly
conventional capacitively coupled magnetron sputter reactor to
generate a high-density plasma (HDP) adjacent to the target and to
extend the plasma and guide the metal ions toward the wafer.
Relatively high amounts of DC power are applied to the target, for
example, 20 to 40 kW for a chamber designed for 200 mm wafers.
Furthermore, the magnetron has a relatively small area so that the
target power is concentrated in the smaller area of the magnetron,
thus increasing the power density supplied to the HDP region
adjacent the magnetron. The small-area magnetron is disposed to a
side of a center of the target and is rotated about the center to
provide more uniform sputtering and deposition.
[0019] In one type of SIP sputtering, the magnetron has unbalanced
poles, usually a strong outer pole of one magnetic polarity
surrounding a weaker inner pole of the other polarity. The magnetic
field lines emanating from the stronger pole may be decomposed into
not only a conventional horizontal magnetic field adjacent the
target face but also a vertical magnetic field extending toward the
wafer. The vertical field lines extend the plasma closer toward the
wafer and also guide the metal ions toward the wafer. Furthermore,
the vertical magnetic lines close to the chamber walls act to block
the diffusion of electrons from the plasma to the grounded shields.
The reduced electron loss is particularly effective at increasing
the plasma density and extending the plasma across the processing
space.
[0020] SIP sputtering may be accomplished without the use of RF
inductive coils. The small HDP region is sufficient to ionize a
substantial fraction of metal ions, estimated to be between 10 and
25%, which effectively sputter coats into deep holes. Particularly
at the high ionization fraction, the ionized sputtered metal atoms
are attracted back to the targets and sputter yet further metal
atoms. As a result, the argon working pressure may be reduced
without the plasma collapsing. Therefore, argon heating of the
wafer is less of a problem, and there is reduced likelihood of the
metal ions colliding with argon atoms, which would both reduce the
ion density and randomize the metal ion sputtering pattern.
[0021] A further advantage of the unbalanced magnetron used in SIP
sputtering is that the magnetic field from the stronger, outer
annular pole projects far into the plasma processing area towards
the wafer. This projecting field has the advantage of supporting a
strong plasma over a larger extent of the plasma processing area
and to guide ionized sputter particles towards the wafer. Wei Wang
in U.S. patent application Ser. No. 09/612,861 filed Jul. 10, 2000
discloses the use of a coaxial electromagnetic coil wrapped around
the major portion of the plasma process region to create a magnetic
field component extending from the target to the wafer. The
magnetic coil is particularly effective in combining SIP sputtering
in a long-throw sputter reactor, that is, one having a larger
spacing between the target and the wafer because the auxiliary
magnetic field supports the plasma and further guides the ionized
sputter particles. Lai discloses in U.S. Pat. No. 5,593,551 a
smaller coil in near the target.
[0022] However, SIP sputtering could still be improved. One of its
fundamental problems is the limited number of variables available
in optimizing the magnetic field configuration. The magnetron
should be small in order to maximize the target power density, but
the target needs to be uniformly sputtered. The magnetic field
should have a strong horizontal component adjacent the target to
maximize the electron trapping there. Some component of the
magnetic field should project from the target towards the wafer to
guide the ionized sputter particles. The coaxial magnetic coil of
Wang addresses only some of these problems. The horizontally
arranged permanent magnets disclosed by Lai in U.S. Pat. No.
5,593,551 poorly address this effect.
[0023] Metal may also be deposited by chemical vapor deposition
(CVD) using metallo-organic precursors, such as Cu-HFAC-VTMS,
commercially available from Schumacher in a proprietary blend with
additional additives under the trade name CupraSelect. A thermal
CVD process may be used with this precursor, as is very well known
in the art, but plasma enhanced CVD (PECVD) is also possible. The
CVD process is capable of depositing a nearly conformal film even
in the high aspect-ratio holes. For example, a film may be
deposited by CVD as a thin seed layer, and then PVD or other
techniques may be used for final hole filling. However, CVD copper
seed layers have often been observed to be rough. The roughness can
detract from its use as a seed layer and more particularly as a
reflow layer promoting the low temperature reflow of after
deposited copper deep into hole. Also, the roughness indicates that
a relatively thick CVD copper layer of the order of 50 nm may be
needed to reliably coat a continuous seed layer. For the narrower
via holes now being considered, a CVD copper seed layer of a
certain thickness may nearly fill the hole. However, complete fills
performed by CVD can suffer from center seams, which may impact
device reliability.
[0024] Another, combination technique uses IMP sputtering to
deposit a thin copper nucleation layer, sometimes referred to as a
flash deposition, and a thicker CVD copper seed layer is deposited
on the IMP layer. However, as was illustrated in FIG. 3, the IMP
layer 136 can be rough, and the CVD layer tends to conformally
follow the roughened substrate. Hence, the CVD layer over an IMP
layer will also tend to be rough.
[0025] Electrochemical plating (ECP) is yet another copper
deposition technique that is being developed. In this method, the
wafer is immersed in a copper electrolytic bath. The wafer is
electrically biased with respect to the bath, and copper
electrochemically deposits on the wafer in a generally conformal
process. Electroless plating techniques are also available.
Electroplating and its related processes are advantageous because
they can be performed with simple equipment at atmospheric
pressure, the deposition rates are high, and the liquid processing
is consistent with the subsequent chemical mechanical
polishing.
[0026] Electroplating, however, imposes its own requirements. A
seed and adhesion layer is usually provided on top of the barrier
layer, such as of Ta/TaN, to nucleate the electroplated copper and
adhere it to the barrier material. Furthermore, the generally
insulating structure surrounding the via hole 122 requires that an
electroplating electrode be formed between the dielectric layer 114
and the via hole 122. Tantalum and other barrier materials are
typically relatively poor electrical conductors, and the usual
nitride sublayer of the barrier layer 124 which faces the via hole
122 (containing the copper electrolyte) is even less conductive for
the long transverse current paths needed in electroplating. Hence,
a good conductive seed and adhesion layer are often deposited to
facilitate the electroplating effectively filling the bottom of the
via hole.
[0027] A copper seed layer deposited over the barrier layer 124 is
typically used as the electroplating electrode. However, a
continuous, smooth, and uniform film is preferred. Otherwise, the
electroplating current will be directed only to the areas covered
with copper or be preferentially directed to areas covered with
thicker copper. Depositing the copper seed layer presents its own
difficulties. An IMP deposited seed layer provides good bottom
coverage in high aspect-ratio holes, but its sidewall coverage can
be small such that that the resulting thin films can be rough or
discontinuous. A thin CVD deposited seed can also be too rough. A
thicker CVD seed layer, or CVD copper over IMP copper, may require
an excessively thick seed layer to achieve the required continuity.
Also, the electroplating electrode primarily operates on the entire
hole sidewalls so that high sidewall coverage is desired. Long
throw provides adequate sidewall coverage, but the bottom coverage
may not be sufficient.
SUMMARIES OF ILLUSTRATIVE EMBODIMENTS
[0028] One embodiment of the present invention is directed to
sputter depositing a liner material such as tantalum or tantalum
nitride, by combining long-throw sputtering, self-ionized plasma
(SIP) sputtering, inductively-coupled plasma (ICP) resputtering,
and coil sputtering in one chamber. Long-throw sputtering is
characterized by a relatively high ratio of the target-to-substrate
distance and the substrate diameter. Long-throw SIP sputtering
promotes deep hole coating of both the ionized and neutral
deposition material components. ICP resputtering can reduce the
thickness of layer bottom coverage of deep holes to reduce contact
resistance. During ICP resputtering, ICP coil sputtering can
deposit a protective layer, particularly on areas such as adjacent
the hole openings where thinning by resputtering may not be
desired.
[0029] Another embodiment of the present invention is directed to
sputter depositing an interconnect material such as copper, by
combining long-throw sputtering, self-ionized plasma (SIP)
sputtering and SIP resputtering in one chamber. Again, long-throw
SIP sputtering promotes deep hole coating of both the ionized and
neutral copper components. SIP resputtering can redistribute the
deposition to promote good bottom corner coverage of deep
holes.
[0030] SIP tends to be promoted by low pressures of less than 5
milliTorr, preferably less than 2 milliTorr, and more preferably
less than 1 milliTorr. SIP, particularly at these low pressures,
tends to be promoted by magnetrons having relatively small areas to
thereby increase the target power density, and by magnetrons having
asymmetric magnets causing the magnetic field to penetrate farther
toward the substrate. Such a process may be used to deposit a seed
layer, promoting the nucleation or seeding of an after deposited
layer, particularly useful for forming narrow and deep vias or
contacts through a dielectric layer. A further layer may be
deposited by electrochemical plating (ECP). In another embodiment,
a further layer is be deposited by chemical vapor deposition
(CVD).
[0031] One embodiment includes an auxiliary magnet array in a
magnetron sputter reactor disposed around the chamber close to the
wafer and having a first vertical magnetic polarity. The magnets
may either be permanent magnets or an array of electromagnets
having coil axes along the central axis of the chamber.
[0032] In one embodiment, a rotatable magnetron having a strong
outer pole of the first magnetic polarity surrounds a weaker pole
of the opposite polarity. The auxiliary magnets are preferably
located in the half of the processing space near the wafer to pull
the unbalanced portion of the magnetic field from the outer pole
towards the wafer.
[0033] Resputtering in an SIP chamber may be promoted in multiple
steps in which, in one embodiment, biasing of the wafer is
increased during deposition. Alternatively, power to the target may
be decreased during deposition to redistribute deposition to the
bottom corners of vias and other holes.
[0034] There are additional aspects to the present invention as
discussed below. It should therefore be understood that the
preceding is merely a brief summary of some embodiments and aspects
of the present invention. Additional embodiments and aspects of the
present invention are referenced below. It should further be
understood that numerous changes to the disclosed embodiments can
be made without departing from the spirit or scope of the
invention. The preceding summary therefore is not meant to limit
the scope of the invention. Rather, the scope of the invention is
to be determined only by the appended claims and their
equivalents.
BRIEF DESCRIPTION OF THE DRAWINGS
[0035] FIG. 1 is a cross-sectional view of a via filled with a
metallization, which also covers the top of the dielectric, as
practiced in the prior art.
[0036] FIG. 2 is a cross-sectional view of a via during its filling
with metallization, which overhangs and closes off the via
hole.
[0037] FIG. 3 is a cross-sectional view of a via having a rough
seed layer deposited by ionized metal plating.
[0038] FIG. 4 is a schematic representation of a sputtering chamber
usable with an embodiment of the invention.
[0039] FIG. 5 is a schematic representation of electrical
interconnections of various components of the sputtering chamber of
FIG. 4.
[0040] FIGS. 6-9B are cross-sectional views of a via liner and
metallization and formation process for a via liner and
metallization according to one embodiment of the invention.
[0041] FIG. 10 is a schematic cross-sectional view of a sputter
reactor including an auxiliary magnet array of the invention.
[0042] FIG. 11 is bottom plan view of the top magnetron in the
sputter reactor of FIG. 10.
[0043] FIG. 12 is an orthographic view of an embodiment of an
assembly supporting an auxiliary magnet array.
[0044] FIG. 13 is a schematic cross-sectional view of a sputter
reactor in which the auxiliary magnet array includes an array of
electromagnets.
[0045] FIGS. 14A and 14B are cross-sectional views of a via seed
layer and via seed layer formation process according to one
embodiment of the invention. --FIG. 15 is a schematic
representation of another sputtering chamber usable with the
invention.
[0046] FIG. 16 is an exploded view of a portion of FIG. 15
detailing the target, shields, isolators and target O-ring.
[0047] FIG. 17 is a graph illustrating the relationship between the
length of the floating shield and the minimum pressure for
supporting a plasma.
[0048] FIG. 18 is a cross-sectional view of via metallization
according to another embodiment of the invention.
[0049] FIGS. 19 and 20 are graphs plotting ion current flux across
the wafer for two different magnetrons and different operating
conditions.
[0050] FIG. 21 is a cross-sectional view of a via metallization
according to another embodiment of the invention.
[0051] FIG. 22 is a cross-sectional view of a via metallization
according to another embodiment of the invention.
[0052] FIG. 23 is a flow diagram of a plasma ignition sequence
which reduces heating of the wafer.
[0053] FIG. 24 is a cross-sectional view of via metallization
formed in accordance with a process according to another embodiment
of the invention.
[0054] FIG. 25 is a schematic representation of a sputtering
chamber in accordance with another embodiment of the invention.
[0055] FIG. 26 is a schematic representation of electrical
interconnections of various components of the sputtering chamber of
FIG. 25.
[0056] FIG. 27 is a schematic view of a integrated processing tool
on which the invention may be practiced.
DESCRIPTIONS OF ILLUSTRATIVE EMBODIMENTS
[0057] The distribution between sidewall and bottom coverage in a
DC magnetron sputtering reactor can be tailored to produce a metal
layer such as a liner layer having a desired profile in a hole or
via in a dielectric layer. A SIP film sputter deposited into a
high-aspect ratio via can have favorable upper sidewall coverage
and tends not to develop overhangs. Where desired, bottom coverage
may be thinned or eliminated by ICP resputtering of the bottom of
the via. In accordance with one aspect of the present invention,
the advantages of both types of sputtering can be obtained in a
reactor which combines selected aspects of both SIP and ICP plasma
generation techniques, which may be in separate steps. An example
of such a reactor is illustrated generally at 150 in FIG. 4. In
addition, upper portions of a liner layer sidewall may be protected
from resputtering by sputtering an ICP coil 151 located within the
chamber to deposit coil material onto the substrate.
[0058] The reactor 150 may also be used to sputter deposit a metal
layer such as a barrier or liner layer using both SIP and ICP
generated plasmas, preferably in combination, but alternatively,
alternately. The distribution between ionized and neutral atomic
flux in a DC magnetron sputtering reactor can be tailored to
produce a coating in a hole or via in a dielectric layer. As
previously mentioned, a SIP film sputter deposited into a
high-aspect ratio hole can have favorable upper sidewall coverage
and tends not to develop overhangs. On the other hand, an ICP
generated plasma can increase metal ionization such that a film
sputter deposited into such a hole may have good bottom and bottom
corner coverage. In accordance with yet another aspect of the
present invention, the advantages of both types of sputtering can
be obtained in a reactor, such as the reactor 150, which combines
selected aspects of both deposition techniques. In addition, coil
material may be sputtered to contribute to the deposition layer as
well, if desired.
[0059] The reactor 150 and various processes for forming liner,
barrier and other layers is described in detail in pending U.S.
application Ser. No. 10/202,778, filed Jul. 25, 2002 (attorney
docket No. 4044) and is incorporated by reference in its entirety.
As described therein, the reactor 150 of the illustrated embodiment
is a DC magnetron type reactor based on a modification of the
Endura PVD Reactor available from Applied Materials, Inc. of Santa
Clara, Calif. This reactor includes a vacuum chamber 152, usually
of metal and electrically grounded, sealed through a target
isolator 154 to a PVD target 156 having at least a surface portion
composed of the material to be sputter deposited on a wafer 158.
Although the target sputtering surface is depicted as being planar
in the drawings, it is appreciated that the target sputtering
surface or surfaces may have a variety of shapes including vaulted
and cylindrical. The wafer may be different sizes including 150,
200, 300 and 450 mm. The illustrated reactor 150 is capable of
self-ionized sputtering (SIP) in a long-throw mode. This SIP mode
may be used in one embodiment in which coverage is directed
primarily directed to the sidewalls of the hole. The SIP mode may
be used to achieve good bottom coverage also.
[0060] The reactor 150 also has an RF coil 151 which inductively
couples RF energy into the interior of the reactor. The RF energy
provided by the coil 151 ionizes a precursor gas such as argon to
maintain a plasma to resputter a deposition layer using ionized
argon to thin bottom coverage, or to ionize sputtered deposition
material to improve bottom coverage. In one embodiment, rather than
maintain the plasma at a relatively high pressure, such as 20-60
mTorr typical for high density IMP processes, the pressure is
preferably maintained at a substantially lower pressure, such as 1
mTorr for deposition of tantalum nitride or 2.5 mTorr for
deposition of tantalum, for example. However, a pressure in the
range of 0.1 to 40 mTorr may be appropriate, depending upon the
application. As a consequence, it is believed that the ionization
rate within the reactor 150 will be substantially lower than that
of the typical high density IMP process. This plasma may be used to
resputter a deposited layer or to ionize sputtered deposition
material or, or both. Still further, the coil 151 itself may be
sputtered to provide a protective coating on the wafer during
resputtering of the material deposited onto the wafer for those
areas in which thinning of the deposited material is not desired,
or to otherwise provide additional deposition material.
[0061] In one embodiment, it is believed that good upper sidewall
coverage and bottom corner coverage can be achieved in a multi-step
process in which in one step, little or no RF power is applied to
the coils. Thus, in one step, ionization of the sputtered target
deposition material would occur primarily as a result of the
self-ionization. Consequently, it is believed that good upper
sidewall coverage may be achieved. In a second step and preferably
in the same chamber, RF power may be applied to the coil 151 while
low or no power is applied to the target. In this embodiment,
little or no material would be sputtered from the target 156 while
ionization of a precursor gas would occur primarily as a result of
the RF energy inductively coupled by the coil 151. The ICP plasma
may be directed to thin or eliminate bottom coverage by etching or
resputtering to reduce barrier layer resistance at the bottom of
the hole. In addition, the coil 151 may be sputtered to deposit
protective material where thinning is not desired. In one
embodiment, the pressure may be kept relatively low such that the
plasma density is relatively low to reduce ionization of the
sputtered deposition material from the coil. As a result, sputtered
coil material can remain largely neutral so as to deposit primarily
onto upper sidewalls to protect those portions from thinning.
[0062] Since the illustrated reactor 150 is capable of self-ionized
sputtering, deposition material may be ionized not only as a result
of the plasma maintained by the RF coil 151, but also by the
sputtering of the target 156 itself. When it is desired to deposit
a layer with good bottom coverage, it is believed that the combined
SIP and ICP ionization processes provide sufficient ionized
material for good bottom and bottom corner coverage. However, it is
also believed that the lower ionization rate of the low pressure
plasma provided by the RF coil 151 allows sufficient neutral
sputtered material to remain un-ionized so as to be deposited on
the upper sidewalls. Thus, it is believed that the combined sources
of ionized deposition material can provide both good upper sidewall
coverage as well as good bottom and bottom corner coverage as
explained in greater detail below.
[0063] In an alternative embodiment, it is believed that good upper
sidewall coverage, bottom coverage and bottom corner coverage can
be achieved in a multi-step process in which in one step, little or
no RF power is applied to the coils. Thus, in one step, ionization
of the deposition material would occur primarily as a result of the
self-ionization. Consequently, it is believed that good upper
sidewall coverage may be achieved. In a second step and preferably
in the same chamber, RF power may be applied to the coil 151. In
addition, in one embodiment, the pressure may be raised
substantially such that a high density plasma may be maintained. As
a result, it is believed that good bottom and bottom corner
coverage may be achieved in the second step.
[0064] A wafer clamp 160 holds the wafer 158 on a pedestal
electrode 162. Resistive heaters, refrigerant channels, and thermal
transfer gas cavity in the pedestal 162 can be provided to allow
the temperature of the pedestal to be controlled to temperatures of
less than -40 degrees C. to thereby allow the wafer temperature to
be similarly controlled.
[0065] To achieve deeper hole coating with a partially neutral
flux, the distance between the target 156 and the wafer 158 can be
increased to operate in the long-throw mode. When used, the
target-to-substrate spacing is typically greater than half the
substrate diameter. In the illustrated embodiment it is preferably
greater than 90% wafer diameter (e.g. 190 mm spacings for a 200 mm
wafer and 290 mm for a 300 mm wafer), but spacings greater than 80%
including greater than 100% and greater than 140% of the substrate
diameter are believed appropriate also. For many applications, it
is believed that a target to wafer spacing of 50 to 1000 mm will be
appropriate. Long throw in conventional sputtering reduces the
sputtering deposition rate, but ionized sputter particles do not
suffer such a large decrease.
[0066] A darkspace shield 164 and a chamber shield 166 separated by
a second dielectric shield isolator 168 are held within the chamber
152 to protect the chamber wall 152 from the sputtered material. In
the illustrated embodiment, both the darkspace shield 164 and the
chamber shield 166 are grounded. However, in some embodiments,
shields may be floating or biased to a nonground level. The chamber
shield 166 also acts as the anode grounding plane in opposition to
the cathode target 156, thereby capacitively supporting a plasma.
If the darkspace shield is permitted to float electrically, some
electrons can deposit on the darkspace shield 164 so that a
negative charge builds up there. It is believed that the negative
potential could not only repel further electrons from being
deposited, but also confine the electrons in the main plasma area,
thus reducing the electron loss, sustaining low-pressure
sputtering, and increasing the plasma density, if desired.
[0067] The coil 151 is carried on the shield 164 by a plurality of
coil standoffs 180 which electrically insulate the coil 151 from
the supporting shield 164. In addition, the standoffs 180 have
labyrinthine passageways which permit repeated deposition of
conductive materials from the target 110 onto the coil standoffs
180 while preventing the formation of a complete conducting path of
deposited material from the coil 151 to the shield 164 which could
short the coil 151 to the shield 164 (which is typically at
ground).
[0068] To enable use of the coil as a circuit path, RF power is
passed through the vacuum chamber walls and through the shield 164
to ends of the coil 151. Vacuum feedthroughs (not shown) extend
through the vacuum chamber wall to provide RF current from a
generator preferably located outside the vacuum pressure chamber.
RF power is applied through the shield 164 to the coil 151 by
feedthrough standoffs 182 (FIG. 5), which like the coil standoffs
180, have labyrinthine passageways to prevent formation of a path
of deposited material from the coil 151 to the shield 164 which
could short the coil 151 to the shield 164.
[0069] The plasma darkspace shield 164 is generally
cylindrically-shaped. The plasma chamber shield 166 is generally
bowl-shaped and includes a generally cylindrically shaped,
vertically oriented wall 190 to which the standoffs 180 and 182 are
attached to insulatively support the coil 151.
[0070] FIG. 5 is a schematic representation of the electrical
connections of the plasma generating apparatus of the illustrated
embodiment. To attract the ions generated by the plasma, the target
156 is preferably negatively biased by a variable DC power source
200 at a DC power of 1-40 kW, for example. The source 200
negatively biases the target 156 to about -400 to -600VDC with
respect to the chamber shield 166 to ignite and maintain the
plasma. A target power of between 1 and 5 kW is typically used to
ignite the plasma while a power of greater than 10 kW is preferred
for the SIP sputtering described here. For example, a target power
of 24 kW may be used to deposit tantalum nitride by SIP sputtering
and a target power of 20 kW may be used to deposit tantalum by SIP
sputtering. During ICP resputtering the target power may be reduced
to 100-200 watts, for example to maintain plasma uniformity.
Alternatively, the target power may be maintained at a high level
if target sputtering during ICP resputtering is desired, or may be
turned off entirely, if desired.
[0071] The pedestal 162 and hence the wafer 158 may be left
electrically floating, but a negative DC self-bias may nonetheless
develop on it. Alternatively, the pedestal 162 may be negatively
biased by a source 202 at -30 v DC to negatively bias the substrate
158 to attract the ionized deposition material to the substrate.
Other embodiments may apply an RF bias to the pedestal 162 to
further control the negative DC bias that develops on it. For
example, the bias power supply 202 may be an RF power supply
operating at 13.56 MHz. It may be supplied with RF power in a range
of 10 watts to 5 kW, for example, a more preferred range being 150
to 300 W for a 200 mm wafer in SIP deposition.
[0072] One end of the coil 151 is insulatively coupled through the
shield 166 by a feedthrough standoff 182 to an RF source such as
the output of an amplifier and matching network 204. The input of
the matching network 204 is coupled to an RF generator 206, which
provides RF power at approximately 1 or 1.5 kW watts for ICP plasma
generation for this embodiment. For example, a power of 1.5 kW for
tantalum nitride deposition and a power of 1 kW for tantalum
deposition is preferred. A preferred range is 50 watts to 10 kW.
During SIP deposition, the RF power to the coil may be turned off
if desired. Alternatively, RF power may be supplied during SIP
deposition if desired.
[0073] The other end of the coil 151 is also insulatively coupled
through the shield 166 by a similar feedthrough standoff 182 to
ground, preferably through a blocking capacitor 208 which may be a
variable capacitor, to support a DC bias on the coil 151. The DC
bias on the coil 151 and hence the coil sputtering rate may be
controlled through a DC power source 209 coupled to the coil 151,
as described in U.S. Pat. No. 6,375,810. Suitable DC power ranges
for ICP plasma generation and coil sputtering include 50 watts to
10 kWatts. A preferred value is 500 watts during coil sputtering.
DC power to the coil 151 may be turned off during SIP deposition,
if desired.
[0074] The above-mentioned power levels may vary of course,
depending upon the particular application. A computer-based
controller 224 may be programmed to control the power levels,
voltages, currents and frequencies of the various sources in
accordance with the particular application.
[0075] The RF coil 151 may be positioned relatively low in the
chamber so that material sputtered from the coil has a low angle of
incidence when striking the wafer. As a consequence, coil material
may be deposited preferentially on the upper corners of the holes
so as to protect those portions of the hole when the hole bottoms
are being resputtered by the ICP plasma. In the illustrated
embodiment, it is preferred that the coil be positioned closer to
the wafer than to the target when the primary function of the coil
is to generate a plasma to resputter the wafer and to provide the
protective coating during resputtering. For many applications, it
is believed that a coil to wafer spacing of 0 to 500 mm will be
appropriate. It is appreciated however that the actual position
will vary, depending upon the particular application. In those
applications in which the primary function of the coil is to
generate a plasma to ionize deposition material, the coil may be
positioned closer to the target. Also, as set forth in greater
detail in U.S. Pat. No. 6,368,469, entitled Sputtering Coil for
Generating a Plasma, filed Jul. 10, 1996 (Attorney Docket
1390-CIP/PVD/DV) and assigned to the assignee of the present
application, an RF coil may also be positioned to improve the
uniformity of the deposited layer with sputtered coil material. In
addition, the coil may have a plurality of turns formed in a helix
or spiral or may have as few turns as a single turn to reduce
complexity and costs and facilitate cleaning.
[0076] A variety of coil support standoffs and feedthrough
standoffs may be used to insulatively support the coils. Since
sputtering, particularly at the high power levels associated with
SSS, SIP and ICP, involves high voltages, dielectric isolators
typically separate the differently biased parts. As a result, it is
desired to protect such isolators from metal deposition.
[0077] The internal structure of the standoffs is preferably
labyrinthine as described in greater detail in copending
application Ser. No. 09/515,880, filed Feb. 29, 2000, entitled
"COIL AND COIL SUPPORT FOR GENERATING A PLASMA" and assigned to the
assignee of the present application. The coil 151 and those
portions of the standoffs directly exposed to the plasma are
preferably made of the same material which is being deposited.
Hence, if the material being deposited is made of tantalum, the
outer portions of the standoffs are preferably made of tantalum as
well. To facilitate adherence of the deposited material, exposed
surfaces of the metal may be treated by bead blasting which will
reduce shedding of particles from the deposited material. Besides
tantalum, the coil and target may be made from a variety of
deposition materials including copper, aluminum, and tungsten. The
labyrinth should be dimensioned to inhibit formation of a complete
conducting path from the coil to the shield. Such a conducting path
could form as conductive deposition material is deposited onto the
coil and standoffs. It should be recognized that other dimensions,
shapes and numbers of passageways of the labyrinth are possible,
depending upon the particular application. Factors affecting the
design of the labyrinth include the type of material being
deposited and the number of depositions desired before the
standoffs need to be cleaned or replaced. A suitable feedthrough
standoff may be constructed in a similar manner except that RF
power would be applied to a bolt or other conductive member
extending through the standoff.
[0078] The coil 151 may have overlapping but spaced ends. In this
arrangement, the feedthrough standoffs 182 for each end may be
stacked in a direction parallel to the plasma chamber central axis
between the vacuum chamber target 156 and the substrate holder 162,
as shown in FIG. 4. As a consequence, the RF path from one end of
the coil to the other end of the coil can similarly overlap and
thus avoid a gap over the wafer. It is believed that such an
overlapping arrangement can improve uniformity of plasma
generation, ionization and deposition as described in copending
application Ser. No. 09/039,695, filed Mar. 16, 1998 and assigned
to the assignee of the present application.
[0079] The support standoffs 180 may be distributed around the
remainder of the coil to provide suitable support. In the
illustrated embodiments the coils each have three hub members 504
distributed at 90 degree separations on the outer face of each
coil. It should be appreciated that the number and spacing of the
standoffs may be varied depending upon the particular
application.
[0080] The coil 151 of the illustrated embodiments is each made of
2 by 1/4 inch heavy duty bead blasted tantalum or copper ribbon
formed into a single turn coil. However, other highly conductive
materials and shapes may be utilized. For example, the thickness of
the coil may be reduced to 1/16 inch and the width increased to 2
inches. Also, hollow tubing may be utilized, particularly if water
cooling is desired.
[0081] The appropriate RF generators and matching circuits are
components well known to those skilled in the art. For example, an
RF generator such as the ENI Genesis series which has the
capability to frequency hunt for the best frequency match with the
matching circuit and antenna is suitable. The frequency of the
generator for generating the RF power to the coil is preferably 2
MHz but it is anticipated that the range can vary at other A.C.
frequencies such as, for example, 1 MHz to 200 MHz and non-RF
frequencies. These components may be controlled by the programmable
controller 224 as well.
[0082] Returning to FIG. 4, the lower cylindrical portion 296 of
the chamber shield 166 continues downwardly to well in back of the
top of the pedestal 162 supporting the wafer 158. The chamber
shield 166 then continues radially inwardly in a bowl portion 302
and vertically upwardly in an innermost cylindrical portion 151 to
approximately the elevation of the wafer 158 but spaced radially
outside of the pedestal 162.
[0083] The shields 164, 166 are typically composed of stainless
steel, and their inner sides may be bead blasted or otherwise
roughened to promote adhesion of the material sputter deposited on
them. At some point during prolonged sputtering, however, the
deposited material builds up to a thickness that it is more likely
to flake off, producing deleterious particles. Before this point is
reached, the shields should be cleaned or more likely replaced with
fresh shields. However, the more expensive isolators 154, 168 do
not need to be replaced in most maintenance cycles. Furthermore,
the maintenance cycle is determined by flaking of the shields, not
by electrical shorting of the isolators.
[0084] A gas source 314 supplies a sputtering working gas,
typically the chemically inactive noble gas argon, to the chamber
152 through a mass flow controller 316. The working gas can be
admitted to the top of the chamber or, as illustrated, at its
bottom, either with one or more inlet pipes penetrating apertures
through the bottom of the shield chamber shield 166 or through a
gap 318 between the chamber shield 166, the wafer clamp 160, and
the pedestal 162. A vacuum pump system 320 connected to the chamber
152 through a wide pumping port 322 maintains the chamber at a low
pressure. Although the base pressure can be held to about 10.sup.-7
Torr or even lower, the pressure of the working gas is typically
maintained at between about 1 and 1000 milliTorr in conventional
sputtering and to below about 5 milliTorr in SIP sputtering. The
computer-based controller 224 controls the reactor including the DC
target power supply 200, the bias power supply 202, and the mass
flow controller 316.
[0085] To provide efficient sputtering, a magnetron 330 is
positioned in back of the target 156. It has opposed magnets 332,
334 connected and supported by a magnetic yoke 336. The magnets
create a magnetic field adjacent the magnetron 330 within the
chamber 152. The magnetic field traps electrons and, for charge
neutrality, the ion density also increases to form a high-density
plasma region 338. The magnetron 330 is usually rotated about the
center 340 of the target 156 by a motor-driven shaft 342 to achieve
full coverage in sputtering of the target 156. To achieve a
high-density plasma 338 of sufficient ionization density to allow
sustained self-sputtering, the power density delivered to the area
adjacent the magnetron 330 can be made high. This can be achieved,
as described by Fu and Chiang in the above cited patents, by
increasing the power level delivered from the DC power supply 200
and by reducing the area of magnetron 330, for example, in the
shape of a triangle or a racetrack. A 60 degree triangular
magnetron, which is rotated with its tip approximately coincident
with the target center 340, covers only about 1/6 of the target at
any time. Coverage of 1/4 is the preferred maximum in a commercial
reactor capable of SIP sputtering.
[0086] To decrease the electron loss, the inner magnetic pole
represented by the inner magnet 332 and magnetic pole face should
have no significant apertures and be surrounded by a continuous
outer magnetic pole represented by the outer magnets 334 and pole
face. Furthermore, to guide the ionized sputter particles to the
wafer 158, the outer pole should produce a much higher magnetic
flux than the inner pole. The extending magnetic field lines trap
electrons and thus extend the plasma closer to the wafer 158. The
ratio of magnetic fluxes should be at least 150% and preferably
greater than 200%. Two embodiments of Fu's triangular magnetron
have 25 outer magnets and 6 or 10 inner magnets of the same
strength but opposite polarity. Although depicted in combination
with a planar target surface, it is appreciated that a variety of
unbalanced magnetrons may be used with a variety of target shapes
to generate self ionized plasmas. The magnets may have shapes other
than triangular including circular and other shapes.
[0087] When the argon is admitted into the chamber, the DC voltage
difference between the target 156 and the chamber shield 166
ignites the argon into a plasma, and the positively charged argon
ions are attracted to the negatively charged target 156. The ions
strike the target 156 at a substantial energy and cause target
atoms or atomic clusters to be sputtered from the target 156. Some
of the target particles strike the wafer 158 and are thereby
deposited on it, thereby forming a film of the target material. In
reactive sputtering of a metallic nitride, nitrogen is additionally
admitted into the chamber from a source 343, and it reacts with the
sputtered metallic atoms to form a metallic nitride on the wafer
158.
[0088] FIGS. 6-9b show sequential cross-sectional views of the
formation of liner layers in accordance with a one aspect of the
present invention. With reference to FIG. 6, an interlayer
dielectric 345 (e.g. silicon dioxide) is deposited over a first
metal layer (e.g., a first copper layer 347a) of an interconnect
348 (FIG. 9b). A via 349 then is etched in the interlayer
dielectric 345 to expose the first copper layer 347a. The first
metal layer may be deposited using CVD, PVD, electroplating or
other such well-known metal deposition techniques, and it is
connected, via contacts, through a dielectric layer, to devices
formed in the underlying semiconductor wafer. If the first copper
layer 347a is exposed to oxygen, such as when the wafer is moved
from an etching chamber in which the oxide overlaying the first
copper layer is etched to create apertures for creation of vias
between the first copper layer and a second to be deposited metal
layer, it can readily form an insulating/high resistance copper
oxide layer 347a' thereon. Accordingly, to reduce the resistance of
the copper interconnect 348, any copper oxide layer 347a' and any
processing residue within the via 349 may be removed.
[0089] A barrier layer 351 may be deposited (e.g., within the
sputtering chamber 152 of FIG. 4) over the interlayer dielectric
345 and over the exposed first copper layer 347a prior to removing
the copper oxide layer 347a'. The barrier layer 351, preferably
comprising tantalum, tantalum nitride, titanium nitride, tungsten
or tungsten nitride prevents subsequently deposited copper layers
from incorporating in and degrading the interlayer dielectric 345
(as previously described).
[0090] If, for example, the sputtering chamber 152 is configured
for deposition of tantalum nitride layers, a tantalum target 156 is
employed. Typically, both argon and nitrogen gas are flowed into
the sputtering chamber 152 through the gas inlet 360 (multiple
inlets, one for each gas, may be used), while a power signal is
applied to the target 156 via the DC power supply 200. Optionally,
a power signal may also be applied to the coil 151 via the first RF
power supply 206. During steady state processing, nitrogen may
react with the tantalum target 156 to form a nitride film on the
tantalum target 156 so that tantalum nitride is sputtered
therefrom. Additionally, non-nitrided tantalum atoms are also
sputtered from the target, which atoms can combine with nitrogen to
form tantalum nitride in flight or on a wafer (not shown) supported
by the pedestal 162.
[0091] In operation, a throttle valve operatively coupled to the
exhaust outlet 362 is placed in a mid-position in order to maintain
the deposition chamber 152 at a desired low vacuum level of about
1.times.10.sup.-8 torr prior to introduction of the process gas(es)
into the chamber. To commence processing within the sputtering
chamber 152, a mixture of argon and nitrogen gas is flowed into the
sputtering chamber 152 via a gas inlet 360. DC power is applied to
the tantalum target 156 via the DC power supply 200 (while the gas
mixture continues to flow into the sputtering chamber 152 via the
gas inlet 360 and is pumped therefrom via the pump 37). The DC
power applied to the target 156 causes the argon/nitrogen gas
mixture to form an SIP plasma and to generate argon and nitrogen
ions which are attracted to, and strike the target 156 causing
target material (e.g., tantalum and tantalum nitride) to be ejected
therefrom. The ejected target material travels to and deposits on
the wafer 158 supported by the pedestal 162. In accordance with the
SIP process, the plasma created by the unbalanced magnetron ionizes
a portion of the sputtered tantalum and tantalum nitride. By
adjusting the RF power signal applied to the substrate support
pedestal 162, a negative bias can be created between the substrate
support pedestal 162 and the plasma. The negative bias between the
substrate support pedestal 162 and the plasma causes tantalum ions,
tantalum nitride ions and argon ions to accelerate toward the
pedestal 162 and any wafer supported thereon. Accordingly, both
neutral and ionized tantalum nitride may be deposited on the wafer,
providing good sidewall and upper sidewall coverage in accordance
with SIP sputtering. In addition, particularly if RF power is
optionally applied to the ICP coil, the wafer may be sputter-etched
by the argon ions at the same time the tantalum nitride material
from the target 156 deposits on the wafer (i.e., simultaneous
deposition/sputter-etching).
[0092] Following deposition of the barrier layer 351, the portion
of the barrier layer 351 at the bottom of the via 349, and the
copper oxide layer 347a' (and any processing residue) thereunder,
may be sputter-etched or resputtered via an argon plasma as shown
in FIG. 7, if thinning or elimination of the bottom is desired. The
argon plasma is preferably generated in this step primarily by
applying RF power to the ICP coil. Note that during sputter-etching
within the sputtering chamber 152 (FIG. 4) in this embodiment, the
power applied to the target 156 is preferably either removed or is
reduced to a low level (e.g., 100 or 200 W) so as to inhibit or
prevent significant deposition from the target 156. A low target
power level, rather than no target power, can provide a more
uniform plasma and is presently preferred.
[0093] ICP argon ions are accelerated toward the barrier layer 351
via an electric field (e.g., the RF signal applied to the substrate
support pedestal 162 via the second RF power supply 41 of FIG. 4
which causes a negative self bias to form on the pedestal), strike
the barrier layer 351, and, due to momentum transfer, sputter the
barrier layer material from the base of the via aperture and
redistribute it along the portion of the barrier layer 351 that
coats the sidewalls of the via 349. The argon ions are attracted to
the substrate in a direction substantially perpendicular thereto.
As a result, little sputtering of the via sidewall, but substantial
sputtering of the via base, occurs. To facilitate resputtering, the
bias applied to the pedestal and the wafer may be 400 watts, for
example.
[0094] The particular values of the resputtering process parameters
may vary depending upon the particular application. Copending or
issued application Ser. Nos. 08/768,058; 09/126,890; 09/449,202;
09/846,581; 09/490,026; and 09/704,161, describe resputtering
processes and are incorporated herein by reference in their
entireties.
[0095] In accordance with another aspect of the present invention,
the ICP coil 151 may be formed of liner material such as tantalum
in the same manner as the target 156 and sputtered to deposit
tantalum nitride onto the wafer while the via bottoms are
resputtered. Because of the relatively low pressure during the
resputtering process, the ionization rate of the deposition
material sputtered from the coil 151 is relatively low. Hence, the
sputtered material deposited onto the wafer is primarily neutral
material. In addition, the coil 151 is placed relatively low in the
chamber, surrounding and adjacent to the wafer.
[0096] Consequently, the trajectory of the material sputtered from
the coil 151 tends to have a relatively small angle of incidence.
Hence, the sputtered material from the coil 151 tends to deposit in
a layer 364 on the upper surface of the wafer and around the
openings of the holes or vias in the wafer rather than deep into
the wafer holes. This deposited material from the coil 151 may be
used to provide a degree of protection from resputtering so that
the barrier layer is thinned by resputtering primarily at the
bottom of the holes rather than on the sidewalls and around the
hole openings where thinning of the barrier layer may not be
desired.
[0097] Once the barrier layer 351 has been sputter-etched from the
via base, the argon ions strike the copper oxide layer 347a', and
the oxide layer is sputtered to redistribute the copper oxide layer
material from the via base, some or all of the sputtered material
being deposited along the portion of the barrier layer 351 that
coats the sidewalls of the via 349. Copper atoms 347a'', as well,
coat the barrier layer 351 and 364 disposed on the sidewalls of the
via 349. However, because the originally deposited barrier layer
351 along with that redistributed from the via base to via sidewall
is a diffusion barrier to the copper atoms 347a'', the copper atoms
347a'' are substantially immobile within the barrier layer 351 and
are inhibited from reaching the interlayer dielectric 345. The
copper atoms 347a'' which are deposited onto the sidewall,
therefore, generally do not generate via-to-via leakage currents as
they would were they redistributed onto an uncoated sidewall.
[0098] Thereafter, a second liner layer 371 of a second material
such as tantalum may be deposited (FIG. 8) on the previous barrier
layer 351 in the same chamber 152 or a similar chamber having both
an SIP and ICP capabilities. A tantalum liner layer provides good
adhesion between the underlying tantalum nitride barrier layer and
a subsequently deposited metal interconnect layer of a conductor
such as copper. However, in some applications, it may be preferred
to deposit just a barrier layer or just a liner layer prior to a
seed layer or filling the hole.
[0099] The second liner layer 371 may be deposited in the same
manner as the first liner layer 351. That is, the tantalum liner
371 may be deposited in a first SIP step in which the plasma is
generated primarily by the target magnetron 330. However, nitrogen
is not admitted so that tantalum rather than tantalum nitride is
deposited. In accordance with SIP sputtering, good sidewall and
upper sidewall coverage may be obtained. RF power to the ICP coil
151 may be reduced or eliminated, if desired.
[0100] Following deposition of the tantalum liner layer 371, the
portion of the liner layer 371 at the bottom of the via 349 (and
any processing residue) thereunder, may be sputter-etched or
resputtered via an argon plasma in the same manner as the bottom of
the liner layer 351, as shown in FIG. 9a, if thinning or
elimination of the bottom is desired. The argon plasma is
preferably generated in this step primarily by applying RF power to
the ICP coil. Again, note that during sputter-etching within the
sputtering chamber 152 (FIG. 4), the power applied to the target
156 is preferably either removed or is reduced to a low level
(e.g., 500 W) so as to inhibit or prevent significant deposition
from the target 156 during thinning or elimination of the bottom
coverage of the second liner layer 371. In addition, the coil 151
is preferably sputtered to deposit liner material 374 while the
argon plasma resputters the layer bottom to protect the liner
sidewalls and upper portions from being thinned substantially
during the bottom portion resputtering.
[0101] In the above described embodiment, SIP deposition of target
material on the sidewalls of the vias occurs primarily in one step
and ICP resputtering of the via bottoms and ICP deposition of coil
151 material occurs primarily in a subsequently step. It is
appreciated that deposition of both target material and coil
material on the sidewalls of the via 349 can occur simultaneously,
if desired. It is further appreciated that ICP sputter-etching of
the deposited material at the bottom of the via 349 can occur
simultaneously with the deposition of target and coil material on
the sidewalls, if desired. Simultaneous deposition/sputter-etching
may be performed with the chamber 152 of FIG. 4 by adjusting the
power signals applied to the coil 151, the target 156 and the
pedestal 162. Because the coil 151 can be used to maintain the
plasma, the plasma can sputter a wafer with a low relative bias on
the wafer (less than that needed to sustain the plasma). Once the
sputtering threshold has been reached, for a particular wafer bias
the ratio of the RF power applied to the wire coil 151 ("RF coil
power") as compared to the DC power applied to the target 156 ("DC
target power") affects the relationship between sputter-etching and
deposition. For instance, the higher the RF:DC power ratio the more
sputter-etching will occur due to increased ionization and
subsequent increased ion bombardment flux to the wafer. Increasing
the wafer bias (e.g., increasing the RF power supplied to the
support pedestal 162) will increase the energy of the incoming ions
which will increase the sputtering yield and the etch rate. For
example, increasing the voltage level of the RF signal applied to
the pedestal 162 increases the energy of the ions incident on the
wafer, while increasing the duty cycle of the RF signal applied to
the pedestal 162 increases the number of incident ions.
[0102] Therefore, both the voltage level and the duty cycle of the
wafer bias can be adjusted to control sputtering rate. In addition,
keeping the DC target power low will decrease the amount of barrier
material available for deposition. A DC target power of zero will
result in sputter-etching only. A low DC target power coupled with
a high RF coil power and wafer bias can result in simultaneous via
sidewall deposition and via bottom sputtering. Accordingly, the
process may be tailored for the material and geometries in
question. For a typical 3:1 aspect ratio via on a 200 mm wafer,
using tantalum or tantalum nitride as the barrier material, a DC
target power of 500 W to 1 kW, at an RF coil power of 2 to 3 kW or
greater, with a wafer bias of 250 W to 400 W or greater applied
continuously (e.g., 100% duty cycle) can result in barrier
deposition on the wafer sidewalls and removal of material from the
via bottom. The lower the DC target power, the less material will
be deposited on the sidewalls. The higher the DC target power, the
more RF coil power and/or wafer bias power is needed to sputter the
bottom of the via. A 2 kW RF coil power level on the coil 151 and a
250 W RF wafer power level with 100% duty cycle on the pedestal
162, for example may be used for simultaneous
deposition/sputter-etching. It may be desirable to initially (e.g.,
for several seconds or more depending on the particular
geometries/materials in question) apply no wafer bias during
simultaneous deposition/sputter-etching to allow sufficient via
sidewall coverage to prevent contamination of the sidewalls by
material sputter-etched from the via bottom.
[0103] For instance, initially applying no wafer bias during
simultaneous deposition/sputter-etching of the via 349 can
facilitate formation of an initial barrier layer on the sidewalls
of the interlayer dielectric 345 that inhibits sputtered copper
atoms from contaminating the interlayer dielectric 345 during the
remainder of the deposition/sputter-etching operation.
Alternatively, deposition/sputter-etching may be performed
"sequentially" within the same chamber or by depositing the barrier
layer 351 within a first processing chamber and by sputter-etching
the barrier layer 351 and copper oxide layer 347a' within a
separate, second processing chamber (e.g., a sputter-etching
chamber such as Applied Materials' Preclean II chamber).
[0104] Following deposition of the second liner layer 371 and
thinning of the bottom coverage, a second metal layer 347b is
deposited (FIG. 9b) to form the copper interconnect 348. The second
copper layer 347b may deposited either as a coating or as a copper
plug 347b' as shown in FIG. 9b over the second liner layer 371 and
over the portion of the first copper layer 347a exposed at the base
of each via. The copper layer 347b may include a copper seed layer.
Because the first and second copper layers 347a, 347b are in direct
contact, rather than in contact through the barrier layer 351 or
the second liner layer 371, the resistance of the copper
interconnect 348 can be lower as can via-to-via leakage currents as
well. However, it is appreciated that in some applications, it may
be desired to leave a coating of the liner layer or the barrier
layer or both at the bottom of the via.
[0105] If the interconnect is formed of a different conductor metal
than the liner layer or layers, the interconnect layer may be
deposited in a sputter chamber having a target of the different
conductor metal. The sputter chamber may be an SIP type or an ICP
type. However, at present deposition of a copper seed layer is
preferred in a chamber of the type described below in connection
with FIG. 10. The metal interconnect may be deposited by other
methods in other types of chambers and apparatus including CVD and
electrochemical plating.
[0106] A copper seed layer may be deposited by another plasma
sputtering reactor 410 as illustrated in the schematic
cross-section view of FIG. 10. The reactor 410 and various
processes for forming seed and other layers is described in
copending application Ser. No. 09/993,543, filed Nov. 14, 2001
(attorney docket No. 6265) which is incorporated herein by
reference in its entirety. As described therein, a vacuum chamber
412 includes generally cylindrical sidewalls 414, which are
electrically grounded. Typically, unillustrated grounded
replaceable shields are located inside the sidewalls 414 to protect
them from being sputter coated, but they act as chamber sidewalls
except for holding a vacuum. A sputtering target 416 composed of
the metal to be sputtered is sealed to the chamber 412 through an
electrical isolator 418. A pedestal electrode 422 supports a wafer
424 to be sputter coated in parallel opposition to the target 416.
A processing space is defined between the target 416 and the wafer
424 inside of the shields.
[0107] A sputtering working gas, preferably argon, is metered into
the chamber from a gas supply 426 through a mass flow controller
428. An unillustrated vacuum pumping system maintains the interior
of the chamber 412 at a very low base pressure of typically
10.sup.-8 Torr or less. During plasma ignition, the argon pressure
is supplied in an amount producing a chamber pressure of
approximately 5 millitorr, but as will be explained later the
pressure is thereafter decreased. A DC power supply 434 negatively
biases the target 416 to approximately -600VDC causing the argon
working gas to be excited into a plasma containing electrons and
positive argon ions. The positive argon ions are attracted to the
negatively biased target 416 and sputter metal atoms from the
target.
[0108] The invention is particularly useful with SIP sputtering in
which a small nested magnetron 436 is supported on an unillustrated
back plate behind the target 416. The chamber 412 and target 416
are generally circularly symmetric about a central axis 438. The
SIP magnetron 436 includes an inner magnet pole 440 of a first
vertical magnetic polarity and a surrounding outer magnet pole 442
of the opposed second vertical magnetic polarity. Both poles are
supported by and magnetically coupled through a magnetic yoke 444.
The yoke 444 is fixed to a rotation arm 446 supported on a rotation
shaft 448 extending along the central axis 4438. A motor 450
connected to the shaft 448 causes the magnetron 436 to rotate about
the central axis 438.
[0109] In an unbalanced magnetron, the outer pole 442 has a total
magnetic flux integrated over its area that is larger than that
produced by the inner pole 440, preferably having a ratio of the
magnetic intensities of at least 150%. The opposed magnetic poles
440, 442 create a magnetic field inside the chamber 412 that is
generally semi-toroidal with strong components parallel and close
to the face of the target 416 to create a high-density plasma there
to thereby increase the sputtering rate and increase the ionization
fraction of the sputtered metal atoms. Because the outer pole 442
is magnetically stronger than the inner pole 440, a fraction of the
magnetic field from the outer pole 442 projects far towards the
pedestal 422 before it loops back to behind the outer pole 442 to
complete the magnetic circuit.
[0110] An RF power supply 454, for example, having a frequency of
13.56 MHz is connected to the pedestal electrode 422 to create a
negative self-bias on the wafer 424. The bias attracts the
positively charged metal atoms across the sheath of the adjacent
plasma, thereby coating the sides and bottoms of high aspect-ratio
holes in the wafer, such as, inter-level vias.
[0111] In SIP sputtering, the magnetron is small and has a high
magnetic strength and a high amount of DC power is applied to the
target so that the plasma density rises to above 10.sup.10
cm.sup.-3 near the target 416. In the presence of this plasma
density, a large number of sputtered atoms are ionized into
positively charged metal ions. The metal ion density is high enough
that a large number of them are attracted back to the target to
sputter yet further metal ions. As a result, the metal ions can at
least partially replace the argon ions as the effective working
species in the sputtering process. That is, the argon pressure can
be reduced. The reduced pressure has the advantage of reducing
scattering and deionization of the metal ions. For copper
sputtering, under some conditions it is possible in the process
called sustained self-sputtering (SSS) to completely eliminate the
argon working gas once the plasma has been ignited. For aluminum or
tungsten sputtering, SSS is not possible, but the argon pressure
can be substantially reduced from the pressures used in
conventional sputtering, for example, to less than 1 milliTorr.
[0112] In one embodiment of the invention, an auxiliary array 460
of permanent magnets 462 is positioned around the chamber sidewalls
414 and is generally positioned in the half of the processing space
towards the wafer 424. In this embodiment, the auxiliary magnets
462 have the same first vertical magnetic polarity as the outer
pole 442 of the nested magnetron 436 so as to draw down the
unbalanced portion of the magnetic field from the outer pole 442.
In the embodiment described in detail below, there are eight
permanent magnets, but any number of four or more distributed
around the central axis 438 would provide similarly good results.
It is possible to place the auxiliary magnets 462 inside the
chamber sidewalls 414 but preferably outside the thin sidewall
shield to increase their effective strength in the processing
region. However, placement outside the sidewalls 414 is preferred
for overall processing results.
[0113] The auxiliary magnet array is generally symmetrically
disposed about the central axis 438 to produce a circularly
symmetric magnetic field. On the other hand, the nested magnetron
436 has a magnetic field distribution is asymmetrically disposed
about the central axis 438 although, when it is averaged over the
rotation time, it becomes symmetric. There are many forms of the
nested magnetron 436. The simplest though less preferred form has a
button center pole 440 surround by an circularly annular outer pole
442 such that its field is symmetric about an axis displaced from
the chamber axis 438 and the nested magnetron axis is rotated about
the chamber axis 438. The preferred nested magnetron has a
triangular shape, illustrated in the bottom plan view of FIG. 11,
with an apex near the central axis 438 and a base near the
periphery of the target 416. This shape is particularly
advantageous because the time average of the magnetic field is more
uniform than for a circular nested magnetron.
[0114] The effective magnetic field at a particular instant of time
during the rotation cycle is shown by the dotted lines of FIG. 10.
A semi-toroidal field B.sub.M provides a strong horizontal
component close to and parallel to the face of the target 416,
thereby increasing the density of the plasma, the rate of
sputtering, and the ionization fraction of sputtered particles. An
auxiliary field B.sub.A1, B.sub.A2 is the sum of the field from the
auxiliary magnet array 460 and from the unbalanced portion of the
field of the nested magnetron 436. On the side of the chamber away
from the nested magnetron 436, the component B.sub.A1 from the
unbalanced portion of the field of the nested magnetron 436
predominates, and it does not extend far towards the wafer 424.
However, near the chamber sidewall 414 on the side of the nested
magnetron 436, the auxiliary magnet 462 is strongly coupled to the
outer magnet pole 442, resulting in a magnetic field component
B.sub.A2 that projects far towards the wafer 424. Out of the plane
of the illustration, the magnetic field component is an combination
of the two components B.sub.A1, B.sub.A2.
[0115] This structure effects the result that a strong vertical
magnetic field is produced near to and along a substantial length
of the chamber sidewall 414 in a region beneath the nested
magnetron 436 sweeping about it because of the alignment of the
magnetic polarities of the auxiliary magnets 442 and the strong
outer magnetic poles 442. As a result, there is a strong vertical
magnetic field on the exterior side of the chamber 412 adjacent the
area of the target 416 being most strongly sputtered. This
projecting field is effective for both extending the region of the
plasma and for guiding the ionized particles to the wafer 424.
[0116] The auxiliary magnet array 460 may be implemented by the use
of two semi-circular magnet carriers 470, one of which is
illustrated orthographically in FIG. 12. Each carrier 470 includes
four recesses 472 facing its interior and sized to receive a
respective magnet assembly 474 including one magnet 462. The magnet
assembly 474 includes an arc-shaped upper clamp member 476 and a
lower clamp member 478, which capture the cylindrically shaped
magnet 462 into recesses when two screws 480 tighten the two clamp
members 476, 478 together. The carriers 470 and clamp members 476,
478 may be formed of non-magnetic material such as aluminum. The
lower clamp member 478 has a length to fit into the recess 472 but
the upper clamp member 476 has end portions extending beyond the
recess 472 and through which are drilled two through holes 482. Two
screws 484 pass through respective through holes to allow the
screws 484 to be fixed in tapped holes 486 in the magnet carrier
470, thereby fixing the magnet 462 in position on the magnet
carrier 470. Two so assembled semi-circular magnet carrier 470 are
placed in a ring around the chamber wall 414 and fixed to it by
conventional fastening means. This structure places the magnets 462
directly adjacent the exterior of the chamber wall 414.
[0117] The solenoidal magnetic field created inside the
electromagnetic coil of Wei Wang is substantially more uniform
across the diameter of the reactor chamber than is the peripheral
dipole magnetic field created by an annular array of permanent
magnets. However, it is possible to create a similarly shaped
dipole field by replacing the permanent magnets 462 with, as
illustrated in the cross-sectional view of FIG. 13, an annular
array of electromagnetic coils 490 arranged around the periphery of
the chamber wall. The coils 490 are typically wrapped as helices
about respective axes parallel to the central axis 438 and are
electrically powered to produce nearly identical magnetic dipole
fields inside the chamber. Such a design has the advantage of
allowing the quick adjustment of the auxiliary magnetic field
strength and even the polarity of the field.
[0118] This invention has been applied to SIP sputtering of copper.
While a conventional SIP reactor sputters a copper film having a
non-uniformity of 9% determined by sheet resistance measurements,
it is believed that the auxiliary magnetron can be optimized to
produce a non-uniformity of only 1% in some embodiments. The
improvement in uniformity may be accompanied by a reduced
deposition rate in some applications, for the deposition of thin
copper seed layers in deep holes, which may be desirable for
improved process control in some applications.
[0119] Although the invention has been described for use in an SIP
sputter reactor, the auxiliary permanent magnet array can be
advantageously applied to other target and power configurations
such as the annularly vaulted target of the SIP.sup.+ reactor of
U.S. Pat. No. 6,251,242, the hollow cathode target of U.S. Pat. No.
6,179,973 or "Ionized Physical-vapor deposition Using a
Hollow-cathode Magnetron Source for Advanced Metallization" by
Klawuhn et al, J. Vac. Sci Technology, July/August 2000, the
inductively coupled IMP reactor of U.S. Pat. No. 6,045,547 or a
self ion sputtering (SIS) system which controls ion flux to a
substrate using an ion reflector as described, for example, in "Cu
Dual Damascene Process for 0.13 micrometer Technology Generation
using Self Ion Sputtering (SIS) with Ion Reflector" by Wada et al.,
IEEE, 2000. Other magnetron configurations may be used, such as
balanced magnetrons and stationary ones. Further, the polarity of
the auxiliary magnets may be parallel or anti-parallel to the
magnetic polarity of the outer pole of the top magnetron. Other
materials may be sputtered including Al, Ta, Ti, Co, W etc. and the
nitrides of several of these which are refractory metals.
[0120] The auxiliary magnet array thus provides additional control
of the magnetic field useful in magnetron sputtering. However, to
achieve deeper hole coating with a partially neutral flux, it is
desirable to increase the distance between the target 416 and the
wafer 424, that is, to operate in the long-throw mode. As discussed
above in connection with the chamber of FIG. 4, in long-throw, the
target-to-substrate spacing is typically greater than half the
substrate diameter. When used in SIP copper seed deposition, it is
preferably greater than 140% wafer diameter (e.g. 290 mm spacing)
for a 200 mm wafer and greater than 130% (e.g. 400 mm spacing) for
a 300 mm wafer, but spacings greater than 80% including greater
than 90% and greater than 100% of the substrate diameter are
believed appropriate also. For many applications, it is believed
that a target to wafer spacing of 50 to 1000 mm will be
appropriate. Long throw in conventional sputtering reduces the
sputtering deposition rate, but ionized sputter particles do not
suffer such a large decrease.
[0121] One embodiment of a structure which can be produced by the
chamber of FIG. 4 and the chamber of FIG. 10 is a via illustrated
in cross-section in FIG. 14a. A seed copper layer 492 is deposited
by the chamber of FIG. 10 in the via hole 494 over the liner layers
formed in the chamber of FIG. 4, which may include one or more
barrier and liner layers such as the aforementioned TaN barrier
351, 364 and Ta liner layers 371, 374 under conditions promoting
SIP and ICP. The SIP copper layer 492 may be deposited, for
example, to a blanket thickness of 50 to 300 nm or more preferably
of 80 to 200 nm. The SIP copper seed layer 492 preferably has a
thickness in the range of 2 to 20 nm on the via sidewalls, more
preferably 7 to 15 nm. In view of the narrow holes, the a sidewall
thickness in excess of 50 nm may not be optimal for some
applications. The quality of the film can in some applications be
improved by decreasing the pedestal temperature to less than 0
degrees C. and preferably to less than -40 degrees C. In such
applications quick SIP deposition is advantageous.
[0122] If, for example, the sputtering chamber 410 is configured
for deposition of copper layers, a copper target 416 is employed.
In operation, a throttle valve operatively coupled to the chamber
exhaust outlet is placed in a mid-position in order to maintain the
deposition chamber 410 at a desired low vacuum level of about
1.times.10.sup.-8 torr prior to introduction of the process gas(es)
into the chamber. To commence processing within the sputtering
chamber 410, argon gas is flowed into the sputtering chamber 410
via a gas inlet 428. For deposition of copper seed in a long throw
SIP chamber, a very low pressure is preferred, such as 0-2 mTorr.
In the illustrated embodiment, a pressure of 0.2 mTorr is suitable.
DC power is applied to the copper target 416 via the DC power
supply 434 (while the gas mixture continues to flow into the
sputtering chamber 410 via the gas inlet 360 and is pumped
therefrom via a suitable pump). The power applied to the target 416
may range for a copper target in a range of 20-60 kWatts for a 200
mm wafer. In one example, the power supply 434 can apply 38 kWatts
to the copper target 416 at a voltage of -600VDC. For larger wafers
such as 300 mm wafers, it is anticipated that larger values such as
56 kWatts may be appropriate. Other values may also be used,
depending upon the particular application.
[0123] The DC power applied to the target 416 causes the argon to
form an SIP plasma and to generate argon ions which are attracted
to, and strike the target 416 causing target material (e.g.,
copper) to be ejected therefrom. The ejected target material
travels to and deposits on the wafer 424 supported by the pedestal
422. In accordance with the SIP process, the plasma created by the
unbalanced magnetron ionizes a portion of the sputtered copper. By
adjusting the RF power signal applied to the substrate support
pedestal 422, a negative bias can be created between the substrate
support pedestal 422 and the plasma.
[0124] The power applied to the pedestal 422 may range for copper
seed deposition in a range of 0-1200 watts. In one example, the RF
power supply 454 can apply 300 watts to the pedestal 422 for a 200
mm wafer. For larger wafers such as 300 mm wafers, it is
anticipated that larger values may be appropriate. Other values may
also be used, depending upon the particular application.
[0125] The negative bias between the substrate support pedestal 422
and the plasma causes copper ions and argon ions to accelerate
toward the pedestal 422 and any wafer supported thereon.
Accordingly, both neutral and ionized copper may be deposited on
the wafer, providing good bottom, sidewall and upper sidewall
coverage in accordance with SIP sputtering. In addition, the wafer
may be sputter-etched by the argon ions at the same time the copper
material from the target 416 deposits on the wafer (i.e.,
simultaneous deposition/sputter-etching).
[0126] Following or during deposition of the seed layer 492, the
portion of the seed layer 492 at the bottom 496 of the via 494 may
be sputter-etched or resputtered via an argon plasma as shown in
FIG. 14B, if redistribution of the bottom is desired. The bottom
496 may be redistributed to increase coverage thickness of the
bottom corner areas 498 of the copper seed layer as shown in FIG.
14B. In many applications, it is preferred that the copper seed
layer bottom 496 not be completely removed to provide adequate seed
layer coverage throughout the via.
[0127] The argon plasma is preferably generated in this
resputtering step as SIP plasma by applying power to the target and
to the pedestal. SIP argon ions are accelerated toward the seed
layer 492 via an electric field (e.g., the RF signal applied to the
substrate support pedestal 422 via the second RF power supply 454
of FIG. 10 which causes a negative self bias to form on the
pedestal), strike the seed layer 492, and, due to momentum
transfer, sputter the seed layer material from the base of the via
aperture and redistribute it along the portion 498 of the seed
layer 492 that coats the bottom corners of the via 349.
[0128] The argon ions are attracted to the substrate in a direction
substantially perpendicular thereto. As a result, little sputtering
of the via sidewall, but substantial sputtering of the via base,
occurs. Note that during resputtering of the copper seed layer
within the sputtering chamber 410 (FIG. 10) in this embodiment, the
power applied to the pedestal 422 may be increased to a higher
value, such as 600-1200 watts, or 900 watts, for example, to
facilitate redistribution of the copper seed layer bottom. Thus, in
this example, the pedestal power is raised from a level below 600
watts (e.g. 300 watts) to a level greater than 600 watts (e.g. 900
watts) to enhance the redistribution effect of the
resputtering.
[0129] In another example, the power applied to the target 416 may
be reduced to a lower value, such as below 30 kWatts or 28 kWatts,
for example, so as to inhibit deposition from the target 416 to
facilitate redistribution of the copper seed layer bottom. A low
target power level, rather than no target power, can provide a more
uniform plasma and is presently preferred in those embodiments in
which target power is reduced for seed layer bottom redistribution.
Thus, in this example the target power is lowered from a level
above 30000 (e.g. 38 kwatts) to a level lower than 30000 watts,
(e.g. 28 kWatts) to enhance resputtering.
[0130] In yet another example, the resputtering of the copper seed
layer bottom may be performed simultaneously throughout the copper
seed layer deposition such that the target and pedestal power
levels may be maintained relatively constant (such as 38 kWatts and
300 watts, respectively) during the seed layer deposition. In other
embodiments, target power reductions may be alternated or combined
with pedestal power increases to facilitate seed layer bottom
redistribution.
[0131] The particular values of the resputtering process parameters
may vary depending upon the particular application. Copending or
issued application Ser. Nos. 08/768,058; 09/126,890; 09/449,202;
09/846,581; 09/490,026; and 09/704,161, describe resputtering
processes and are incorporated herein by reference in their
entireties.
[0132] The SIP copper seed layer 492 has good bottom and sidewall
coverage and enhanced bottom corner coverage. After the copper seed
layer 492 is deposited, the hole is filled with a copper layer 18,
as in FIG. 1, preferably by electro-chemical plating using the seed
layer 492 as one of the electroplating electrodes. Alternatively,
the smooth structure of the SIP copper seed layer 492 also promotes
reflow or higher-temperature deposition of copper by standard
sputtering or physical vapor deposition (PVD).
[0133] The chambers of FIGS. 4 and 10 utilize both ionized and
neutral atomic flux. As described in U.S. Pat. No. 6,398,929
(attorney docket No. 3920) which is incorporated herein by
reference in its entirety, the distribution between ionized and
neutral atomic flux in a DC magnetron sputtering reactor can be
tailored to produce an advantageous layer in a hole in a dielectric
layer. Such a layer can be used either by itself or in combination
with a copper seed layer deposited by chemical vapor deposition
(CVD) over a sputtered copper nucleation layer. A copper liner
layer is particularly useful as a thin seed layer for electroplated
copper.
[0134] The DC magnetron sputtering reactors of the prior art have
been directed to either conventional, working gas sputtering or to
sustained self-sputtering. The two approaches emphasize different
types of sputtering. It is, on the other hand, preferred that the
reactor for the copper liner combine various aspects of the prior
art to control the distribution between ionized copper atoms and
neutrals. An example of such a reactor 550 is illustrated in the
schematic cross-sectional view of FIG. 15. The reactors of FIGS. 4,
10 and 13 may utilize these aspects of the reactor of FIG. 15 which
is also based on a modification of the Endura PVD Reactor available
from Applied Materials, Inc. of Santa Clara, Calif. The reactor 550
includes a vacuum chamber 552, usually of metal and electrically
grounded, sealed through a target isolator 554 to a PVD target 556
having at least a surface portion composed of the material, in this
case copper or a copper alloy, to be sputter deposited on a wafer
558. The alloying element is typically present to less than 5 wt %,
and essentially pure copper may be used if adequate barriers are
otherwise formed. A wafer clamp 560 holds the wafer 558 on a
pedestal electrode 562. Unillustrated resistive heaters,
refrigerant channels, and thermal transfer gas cavity in the
pedestal 562 allow the temperature of the pedestal to be controlled
to temperatures of less than -40 degrees C. to thereby allow the
wafer temperature to be similarly controlled.
[0135] A floating shield 564 and a grounded shield 566 separated by
a second dielectric shield isolator 568 are held within the chamber
552 to protect the chamber wall 552 from the sputtered material.
The grounded shield 566 also acts as the anode grounding plane in
opposition to the cathode target 556, thereby capacitively
supporting a plasma. Some electrons deposit on the floating shield
564 so that a negative charge builds up there. The negative
potential not only repels further electrons from being deposited,
but also confines the electrons in the main plasma area, thus
reducing the electron loss, sustaining low-pressure sputtering, and
increasing the plasma density.
[0136] Details of the target and shields are illustrated in the
exploded cross-sectional view of FIG. 16. The target 556 includes
an aluminum or titanium backing plate 570 to which is soldered or
diffusion bonded a copper target portion 572. A flange 573 of the
backing plate 570 rests on and is vacuum sealed through a polymeric
target O-ring 574 to the target isolator 554, which is preferably
composed of a ceramic such as alumina. The target isolator 554
rests on and is vacuum sealed through an adaptor O-ring 575 to the
chamber 552, which in fact may be an aluminum adaptor sealed to the
main chamber body. A metal clamp ring 576 has on its inner radial
side an upwardly extending annular rim 577. Unillustrated bolts fix
the metal clamp ring 576 to an inwardly extending ledge 578 of the
chamber 552 and capture a flange 579 of the grounded shield 566.
Thereby, the grounded shield 566 is mechanically and electrically
connected to the grounded chamber 552.
[0137] The shield isolator 568 freely rests on the clamp ring 576
and may be machined from a ceramic material such as alumina. It is
compact but has a relatively large height of approximately 165 mm
compared to a smaller width to provide strength during the
temperature cycling of the reactor. The lower portion of the shield
isolator 568 has an inner annular recess fitting outside of the rim
577 of the clamp ring 576. The rim 577 not only acts to center
inner diameter of the shield isolator 568 with respect to the clamp
ring 576 but also acts as a barrier against any particles generated
at the sliding surface 580 between the ceramic shield isolator 568
and the metal ring clamp 576 from reaching the main processing
area.
[0138] A flange 581 of the floating shield 564 freely rests on the
shield isolator 568 and has a tab or rim 582 on its outside
extending downwardly into an annular recess formed at the upper
outer corner of the shield isolator 568. Thereby, the tab 582
centers the floating shield 564 with respect to the target 556 at
the outer diameter of the shield isolator 568. The shield tab 582
is separated from the shield isolator 568 by a narrow gap which is
sufficiently small to align the plasma dark spaces but sufficiently
large to prevent jamming of the shield isolator 568, and the
floating shield 581 rests on the shield isolator 568 in a sliding
contact area 583 inside and above the tab 582.
[0139] A narrow channel 584 is formed between a head 585 of the
floating shield 564 and the target 556. It has a width of about 2
mm to act as a plasma dark space. The narrow channel 584 continues
in a path extending even more radially inward than illustrated past
a downwardly projecting ridge 586 of the backing plate flange 574
to an upper back gap 584a between the shield head 585 and the
target isolator 554. The structure of these elements and their
properties are similar to those disclosed by Tang et al., in U.S.
patent application Ser. No. 09/191,253, filed Oct. 30, 1998. The
upper back gap 584a has a width of about 1.5 mm at room
temperature. When the shield elements are temperature cycled, they
tend to deform. The upper back gap 584a, having a smaller width
than the narrow channel 584 next to the target 556, is sufficient
to maintain a plasma dark space in the narrow channel 584. The back
gap 584a continues downwardly into a lower back gap 584b between
the shield isolator 568 and the ring clamp 576 on the inside and
the chamber body 552 on the outside. The lower back gap 584b serves
as a cavity to collect ceramic particles generated at the sliding
surfaces 580, 583 between the ceramic shield isolator 568 and the
clamp ring 576 and the floating shield 564. The shield isolator 568
additionally includes a shallow recess 583a on its upper inner
corner to collect ceramic particles from the sliding surface 583 on
its radially inward side.
[0140] The floating shield 564 includes a downwardly extending,
wide upper cylindrical portion 588 extending downwardly from the
flange 581 and connected on its lower end to a narrower lower
cylindrical portion 590 through a transition portion 592.
Similarly, the grounded shield 566 has an wider upper cylindrical
portion 594 outside of and thus wider than the upper cylindrical
portion 588 of the floating shield 564. The grounded upper
cylindrical portion 594 is connected on its upper end to the
grounded shield flange 580 and on its lower end to a narrowed lower
cylindrical portion 596 through a transition portion 598 that
approximately extends radially of the chamber. The grounded lower
cylindrical portion 596 fits outside of and is thus wider than the
floating lower cylindrical portion 590; but it is smaller than the
floating upper cylindrical portion 564 by a radial separation of
about 3 mm. The two transition portions 592, 598 are both
vertically and horizontally offset. A labyrinthine narrow channel
600 is thereby formed between the floating and grounded shields
564, 566 with the offset between the grounded lower cylindrical
portion 596 and floating upper cylindrical portion 564 assuring no
direct line of sight between the two vertical channel portions. A
purpose of the channel 600 is to electrically isolate the two
shields 564, 566 while protecting the clamp ring 576 and the shield
isolator 568 from copper deposition.
[0141] The lower portion of the channel 600 between the lower
cylindrical portions 590, 596 of the shields 564, 566 has an aspect
ratio of 4:1 or greater, preferably 8:1 or greater. The lower
portion of the channel 600 has an exemplary width of 0.25 cm and
length of 2.5 cm, with preferred ranges being 0.25 to 0.3 cm and 2
to 3 cm. Thereby, any copper ions and scattered copper atoms
penetrating the channel 600 are likely to have to bounce several
times from the shields and at least stopped by the upper grounded
cylindrical portion 594 before they can find their way further
toward the clamp ring 576 and the shield isolator 568. Any one
bounce is likely to result in the ion being absorbed by the shield.
The two adjacent 90 degrees turns or bends in the channel 600
between the two transition portions 592, 598 further isolate the
shield isolator 568 from the copper plasma. A similar but reduced
effect could be achieved with 60 degrees bends or even 45 degrees
bends but the more effective 90 degrees bends are easier to form in
the shield material. The 90 degrees turns are much more effective
because they increase the probability that copper particles coming
from any direction will have at least one high angle hit and
thereby lose most their energy to be stopped by the upper grounded
cylindrical portion 594. The 90 degrees turns also shadow the clamp
ring 576 and shield isolator 568 from being directly irradiated by
copper particles. It has been found that copper preferentially
deposits on the horizontal surface at the bottom of the floating
transition portion 592 and on the vertical upper grounded
cylindrical portion 594, both at the end of one of the 90 degrees
turns. Also, the convolute channel 600 collects ceramic particles
generated from the shield isolator 568 during processing on the
horizontal transition portion 598 of the grounded shield 566. It is
likely that such collected particles are pasted by copper also
collected there.
[0142] Returning to the large view of FIG. 15, the lower
cylindrical portion 596 of the grounded shield 566 continues
downwardly to well in back of the top of the pedestal 562
supporting the wafer 558. The grounded shield 566 then continues
radially inwardly in a bowl portion 602 and vertically upwardly in
an innermost cylindrical portion 604 to approximately the elevation
of the wafer 558 but spaced radially outside of the pedestal
562.
[0143] The shields 564, 566 are typically composed of stainless
steel, and their inner sides may be bead blasted or otherwise
roughened to promote adhesion of the copper sputter deposited on
them. At some point during prolonged sputtering, however, the
copper builds up to a thickness that it is likely to flake off,
producing deleterious particles. Before this point is reached, the
shields should be cleaned or more likely replaced with fresh
shields. However, the more expensive isolators 554, 568 do not need
to be replaced in most maintenance cycles. Furthermore, the
maintenance cycle is determined by flaking of the shields, not by
electrical shorting of the isolators.
[0144] As mentioned, the floating shield 564 accumulates some
electron charge and builds up a negative potential. Thereby, it
repels further electron loss to the floating shield 564 and thus
confines the plasma nearer the target 556. Ding et al. have
disclosed a similar effect with a somewhat similar structure in
U.S. Pat. No. 5,736,021. However, the floating shield 564 of FIG.
16 has its lower cylindrical portion 590 extending much further
away from the target 556 than does the corresponding part of Ding
et al., thereby confining the plasma over a larger volume. However,
the floating shield 564 electrically shields the grounded shield
566 from the target 556 so that is should not extend too far away
from the target 556. If it is too long, it becomes difficult to
strike the plasma; but, if it is too short, electron loss is
increased so that the plasma cannot be sustained at lower pressure
and the plasma density falls. An optimum length has been found at
which the bottom tip 606 of the floating shield 566, as shown in
FIG. 16, is separated 6 cm from the face of the target 556 with a
total axial length of the floating shield 566 being 7.6 cm. Three
different floating shields have been tested for the minimum
pressure at which copper sputtering is maintained. The results are
shown in FIG. 17 for 1 kW and 18 kW of target power. The abscissa
is expressed in terms of total shield length, the separation
between shield tip 606 and target 556 being 1.6 cm less. A
preferred range for the separation is 5 to 7 cm, and that for the
length is 6.6 to 8.6 cm. Extending the shield length to 10 cm
reduces the minimum pressure somewhat but increases the difficulty
of striking the plasma.
[0145] Referring again to FIG. 15, a selectable DC power supply 610
negatively biases the target 556 to about -400 to -600VDC with
respect to the grounded shield 566 to ignite and maintain the
plasma. A target power of between 1 and 5 kW is typically used to
ignite the plasma while a power of greater than 10 kW is preferred
for the SIP sputtering described here. Conventionally, the pedestal
562 and hence the wafer 558 are left electrically floating, but a
negative DC self-bias nonetheless develops on it. On the other
hand, some designs use a controllable power supply 612 to apply a
DC or RF bias to the pedestal 562 to further control the negative
DC bias that develops on it. In the tested configuration, the bias
power supply 612 is an RF power supply operating at 13.56 MHz. It
may be supplied with up to 600 W of RF power, a preferred range
being 350 to 550 W for a 200 mm wafer.
[0146] A gas source 614 supplies a sputtering working gas,
typically the chemically inactive noble gas argon, to the chamber
552 through a mass flow controller 616. The working gas can be
admitted to the top of the chamber or, as illustrated, at its
bottom, either with one or more inlet pipes penetrating apertures
through the bottom of the shield grounded shield 566 or through a
gap 618 between the grounded shield 566, the wafer clamp 560, and
the pedestal 562. A vacuum pump system 620 connected to the chamber
552 through a wide pumping port 622 maintains the chamber at a low
pressure. Although the base pressure can be held to about 10.sup.-7
Torr or even lower, the pressure of the working gas is typically
maintained at between about 1 and 1000 milliTorr in conventional
sputtering and to below about 5 milliTorr in SIP sputtering. A
computer-based controller 624 controls the reactor including the DC
target power supply 610, the bias power supply 612, and the mass
flow controller 616.
[0147] To provide efficient sputtering, a magnetron 630 is
positioned in back of the target 556. It has opposed magnets 632,
634 connected and supported by a magnetic yoke 636. The magnets
create a magnetic field adjacent the magnetron 630 within the
chamber 552. The magnetic field traps electrons and, for charge
neutrality, the ion density also increases to form a high-density
plasma region 638. The magnetron 630 is usually rotated about the
center 640 of the target 556 by a motor-driven shaft 642 to achieve
full coverage in sputtering of the target 556. To achieve a
high-density plasma 638 of sufficient ionization density to allow
sustained self-sputtering of copper, the power density delivered to
the area adjacent the magnetron 630 must be made high. This can be
achieved, as described by Fu in the above cited patents, by
increasing the power level delivered from the DC power supply 610
and by reducing the area of magnetron 630, for example, in the
shape of a triangle or a racetrack. A 60 triangular magnetron,
which is rotated with its tip approximately coincident with the
target center 640, covers only about 1/6 of the target at any time.
Coverage of 1/4 is the preferred maximum in a commercial reactor
capable of SIP sputtering.
[0148] To decrease the electron loss, the inner magnetic pole
represented by the inner magnet 632 and unillustrated magnetic pole
face should have no significant apertures and be surrounded by a
continuous outer magnetic pole represented by the outer magnets 634
and unillustrated pole face. Furthermore, to guide the ionized
sputter particles to the wafer 558, the outer pole should produce a
much higher magnetic flux than the inner pole. The extending
magnetic field lines trap electrons and thus extend the plasma
closer to the wafer 558. The ratio of magnetic fluxes should be at
least 150% and preferably greater than 200%. Two embodiments of
Fu's triangular magnetron have 25 outer magnets and 6 or 10 inner
magnets of the same strength but opposite polarity.
[0149] When the argon is admitted into the chamber, the DC voltage
difference between the target 556 and the grounded shield 566
ignites the argon into a plasma, and the positively charged argon
ions are attracted to the negatively charged target 556. The ions
strike the target 556 at a substantial energy and cause target
atoms or atomic clusters to be sputtered from the target 556. Some
of the target particles strike the wafer 558 and are thereby
deposited on it, thereby forming a film of the target material. In
reactive sputtering of a metallic nitride, nitrogen is additionally
admitted into the chamber, and it reacts with the sputtered
metallic atoms to form a metallic nitride on the wafer 558.
[0150] The illustrated chamber is capable of self-ionized
sputtering of copper including sustained self-sputtering. In this
case, after the plasma has been ignited, the supply of argon may be
cut off in the case of SSS, and the copper ions have sufficiently
high density to resputter the copper target with a yield of greater
than unity. Alternatively, some argon may continue to be supplied,
but at a reduced flow rate and chamber pressure and perhaps with
insufficient target power density to support pure sustained
self-sputtering but nonetheless with a significant but reduced
fraction of self-sputtering. If the argon pressure is increased to
significantly above 5 milliTorr, the argon will remove energy from
the copper ions, thus decreasing the self-sputtering. The wafer
bias attracts the ionized fraction of the copper particle deep into
the hole.
[0151] However, to achieve deeper hole coating with a partially
neutral flux, it is desirable to increase the distance between the
target 556 and the wafer 558, that is, to operate in the long-throw
mode. In long-throw, the target-to-substrate spacing is typically
greater than half the substrate diameter. When used, it is
preferably greater than 90% wafer diameter, but spacings greater
than 80% including 100% and 140% of the substrate diameter are
believed appropriate also. The throws mentioned in the examples of
the embodiment are referenced to 200 mm wafers. Long throw in
conventional sputtering reduces the sputtering deposition rate, but
ionized sputter particles do not suffer such a large decrease.
[0152] The controlled division between conventional (argon-based)
sputtering and sustained self-sputtering (SSS) allows the control
of the distribution between neutral and ionized sputter particles.
Such control is particularly advantageous for the sputter
deposition of a copper seed layer in a high aspect-ratio via hole.
The control of the ionization fraction of sputtered atoms is
referred to as self-ionized plasma (SIP) sputtering.
[0153] One embodiment of a structure produced by the invention is a
via illustrated in cross-section in FIG. 18. A seed copper layer
650 is deposited in the via hole 22 over the barrier layer 24
using, for example, the long-throw sputter reactor of FIG. 15 and
under conditions promoting SIP. The SIP copper layer 650 may be
deposited, for example, to a blanket thickness of 50 to 300 nm or
more preferably of 80 to 200 nm. The SIP copper seed layer 650
preferably has a thickness in the range of 2 to 20 nm on the via
sidewalls, more preferably 7 to 15 nm. In view of the narrow holes,
the sidewall thickness should not exceed 50 nm. The quality of the
film is improved by decreasing the pedestal temperature to less
than 0 degrees C. and preferably to less than -40 degrees C. so
that the coolness afforded by the quick SIP deposition becomes
important.
[0154] The SIP copper seed layer 650 has good bottom coverage and
enhanced sidewall coverage. It has been experimentally observed to
be much smoother than either IMP or CVD copper deposited directly
over the barrier layer 24. After the copper seed layer 650 is
deposited, the hole is filled with a copper layer 118, as in FIG.
1, preferably by electrochemical plating using the seed layer 650
as one of the electroplating electrodes. However, the smooth
structure of the SIP copper seed layer 650 also promotes reflow or
higher-temperature deposition of copper by standard sputtering or
physical vapor deposition (PVD).
[0155] Several experiments were performed in SIP depositing such a
seed layer into a 0.20 .mu.m-wide via hole in 1.2 .mu.m of oxide.
With a target-to-substrate spacing of 290 mm, a chamber pressure of
less than 0.1 milliTorr (indicating SSS mode) and 14 kW of DC power
applied to the target with a 601 triangular magnetron, a deposition
producing 0.2 .mu.m of blanket thickness of the copper on top of
the oxide produces 18 nm on the via bottom and about 12 nm on the
via sidewalls. Deposition times of 30 s and less are typical. When
the target power is increased to 18 kW, the bottom coverage
increases to 37 nm without a significant change in sidewall
thickness. The higher bottom coverage at higher power indicates a
higher ionization fraction. For both cases, the deposited copper
film is observed to be much smoother than seen for IMP or CVD
copper.
[0156] The SIP deposition is relatively fast, between 0.5 to 1.0
.mu.m/min in comparison to an IMP deposition rate of no more than
0.2 .mu.m/min. The fast deposition rate results in a short
deposition period and, in combination with the absence of argon ion
heating, significantly reduces the thermal budget. It is believed
that the low-temperature SIP deposition results in a very smooth
copper seed layer.
[0157] A 290 mm throw was used with the standard triangular
magnetron of Fu utilizing ten inner magnets and twenty-five outer
ones. The ion current flux was measured as a function of radius
from the target center under various conditions. The results are
plotted in the graph of FIG. 19. Curve 660 is measured for 16 kW of
target power and 0 milliTorr of chamber pressure. Curves 662, 664,
664 are measured for 18 kW of target power and chamber pressures of
0, 0.2, and 1 milliTorr respectively. These currents correspond to
an ion density of between 10.sup.11 and 10.sup.12 cm.sup.-3, as
compared to less than 10.sup.9 cm.sup.-3 with a conventional
magnetron and sputter reactor. The zero-pressure conditions were
also used to measure the copper ionization fraction. The spatial
dependences are approximately the same with the ionization fraction
varying between about 10% and 20% with a direct dependence on the
DC target power. The relatively low ionization fraction demonstrate
that SIP without long throw would has a large fraction of neutral
copper flux which would have the unfavorable deep filling
characteristics of conventional PVD. Results indicate that
operation at higher power is preferred for better step coverage due
to the increased ionization.
[0158] The tests were then repeated with the number of inner
magnets in the Fu magnetron being reduced to six. That is, the
second magnetron had improved uniformity in the magnetic flux,
which promotes a uniform sputtered ion flux toward the wafer. The
results are plotted in FIG. 20. Curve 668 displays the ion current
flux for 12 kW of target power and 0 milliTorr pressure; curve 670,
for 18 kW. Curves for 14 kW and 16 kW are intermediate. Thus, the
modified magnetron produces a more uniform ion current across the
wafer, which is again dependent on the target power with higher
power being preferred.
[0159] The relatively low ionization fractions of 10% to 20%
indicate a substantial flux of neutral copper compared to the 90%
to 100% fraction of IMP. While wafer bias can guide the copper ions
deep into the holes, long throw accomplishes much the same for the
copper neutrals.
[0160] A series of tests were used to determine the combined
effects of throw and chamber pressure upon the distribution of
sputter particles. At zero chamber pressure, a throw of 140 mm
produces a distribution of about 45 degrees; a throw of 190 mm,
about 35 degrees; and, a throw of 290 mm, about 25 degrees. The
pressure was varied for a throw of 190 mm. The central distribution
remains about the same for 0, 0.5 and 1 milliTorr. However, the
low-level tails are pushed out almost 101 for the highest pressure,
indicative of the scattering of some particles. These results
indicate that acceptable results are obtained below 5 milliTorr,
but a preferred range is less than 2 milliTorr, a more preferred
range is less than 1 milliTorr, and a most preferred range is 0.2
milliTorr and less. Also, as expected, the distribution is best for
the long throws.
[0161] A SIP film deposited into a high-aspect ratio hole has
favorable upper sidewall coverage and tends not to develop
overhangs. On the other hand, an IMP film deposited into such a
hole has better bottom and bottom corner coverage, but the sidewall
film tends to have poor coverage and be rough. The advantages of
both types of sputtering can be combined by using a two-step copper
seed sputter deposition. In a first step, copper is deposited in an
IMP reactor producing a high-density plasma, for example, by the
use of RF inductive source power. Exemplary deposition conditions
are 20 to 60 millitorr of pressure, 1 to 3 kW of RF coil power, 1
to 2 kW of DC target power, and 150 W of bias power. The first step
provides good though rough bottom and bottom sidewall coverage. In
a second and preferably subsequent step, copper is deposited in an
SIP reactor of the sort described above producing a lesser degree
of copper ionization. Exemplary deposition conditions are 1 Torr
pressure, 18 to 24 kW of DC target power and 500 W of bias power.
The second step provides good smooth upper sidewall coverage and
further smoothes out the already deposited IMP layer. The blanket
deposition thicknesses for the two steps preferably range from 50
to 100 nm for the IMP deposition and 100 to 200 nm for the SIP
layer. Blanket thicknesses may be a ratio of 30:70 to 70:30.
Alternatively, the SIP layer can be deposited before the IMP layer.
After the copper seed layer is sputter deposited by the two-step
process, the remainder of the hole is filled, for example, by
electroplating.
[0162] The SIP sidewall coverage may become a problem for very
narrow, high-aspect ratio vias. Technology for 0.13 .mu.m vias and
smaller is being developed. Below about 100 nm of blanket
thickness, the sidewall coverage may become discontinuous. As shown
in the cross-sectional view of FIG. 21, the unfavorable geometry
may cause a SIP copper film 680 to be formed as a discontinuous
films including voids or other imperfections 682 on the via
sidewall 30. The imperfection 682 may be an absence of copper or
such a thin layer of copper that it cannot act locally as an
electroplating cathode. Nonetheless, the SIP copper film 680 is
smooth apart from the imperfections 682 and well nucleated. In
these challenging geometries, it is then advantageous to deposit a
copper CVD seed layer 684 over the SIP copper nucleation film 680.
Since it is deposited by chemical vapor deposition, it is generally
conformal and is well nucleated by the SIP copper film 680. The CVD
seed layer 684 patches the imperfections 682 and presents a
continuous, non-rough seed layer for the later copper
electroplating to complete the filling of the hole 22. The CVD
layer may be deposited in a CVD chamber designed for copper
deposition, such as the CuxZ chamber available from Applied
Materials using the previously described thermal process.
[0163] Experiments were performed in which 20 nm of CVD copper was
deposited on alternatively a SIP copper nucleation layer and an IMP
nucleation layer. The combination with SIP produced a relatively
smooth CVD seed layer while the combination with IMP produced a
much rougher surface in the CVD layer to the point of
discontinuity.
[0164] The CVD layer 684 may be deposited to a thickness, for
example, in the range of 5 to 20 nm. The remainder of the hole may
then be filled with copper by other methods. The very smooth seed
layer produced by CVD copper on top of the nucleation layer of SIP
copper provides for efficient hole filling of copper by
electroplating or conventional PVD techniques in the narrow vias
being developed. In particular for electroplating, the smooth
copper nucleation and seed layer provides a continuous and nearly
uniform electrode for powering the electroplating process.
[0165] In the filling of a via or other hole having a very
high-aspect ratio, it may be advantageous to dispense with the
electroplating and instead, as illustrated in the cross-sectional
view of FIG. 22, deposit a sufficiently thick CVD copper layer 688
over the SIP copper nucleation layer 680 to completely fill the
via. An advantage of CVD filling is that it eliminates the need for
a separate electroplating step. Also, electroplating requires fluid
flows which may be difficult to control at hole widths below 0.13
.mu.m.
[0166] An advantage of the copper bilayer of this embodiment of the
invention is that it allows the copper deposition to be performed
with a relatively low thermal budget. Tantalum tends to dewet from
oxide at higher thermal budgets. IMP has many of the same coverage
advantages for deep hole filling, but IMP tends to operate at a
much higher temperature because it produces a high flux of
energetic argon ions which dissipate their energy in the layer
being deposited. Further, IMP invariably implants some argon into
the deposited film. On the contrary, the relatively thin SIP layer
is deposited at a relatively high rate and the SIP process is not
inherently hot because of the absence of argon. Also, the SIP
deposition rates are much faster than with IMP so that any hot
deposition is that much shorter, by up to a factor of a half.
[0167] The thermal budget is also reduced by a cool ignition of the
SIP plasma. A cool plasma ignition and processing sequence is
illustrated in the flow diagram of FIG. 23. After the wafer has
been inserted through the load lock valve into the sputter reactor,
the load lock valve is closed, and in step 690 gas pressures are
equilibrated. The argon chamber pressure is raised to that used for
ignition, typically between 2 and about 5 to 10 milliTorr, and the
argon backside cooling gas is supplied to the back of the wafer at
a backside pressure of about 5 to 10 Torr. In step 692, the argon
is ignited with a low level of target power, typically in the range
of 1 to 5 kW. After the plasma has been detected to ignite, in step
694, the chamber pressure is quickly ramped down, for example over
3 s, with the target power held at the low level. If sustained
self-sputtering is planned, the chamber argon supply is turned off,
but the plasma continues in the SSS mode. For self-ionized plasma
sputtering, the argon supply is reduced. The backside cooling gas
continues to be supplied. Once the argon pressure has been reduced,
in step 696, the target power is quickly ramped up to the intended
sputtering level, for example, 10 to 24 kW or greater for a 200 mm
wafer, chosen for the SIP or SSS sputtering. It is possible to
combine the steps 694, 696 by concurrently reducing pressure and
ramping up the power. In step 698, the target continues to be
powered at the chosen level for a length of time necessary to
sputter deposit the chosen thickness of material. This ignition
sequence is cooler than using the intended sputtering power level
for ignition. The higher argon pressure facilitates ignition but
would deleteriously affect the sputtered neutrals if continued at
the higher power levels desired for sputter deposition. At the
lower ignition power, very little copper is deposited due to the
low deposition rate at the reduced power. Also, the pedestal
cooling keep the wafer chilled through the ignition process.
[0168] Many of the features of the apparatus and process of the
invention can be applied to sputtering not involving long
throw.
[0169] Although the invention is particularly useful at the present
time for copper inter-level metallization and barrier and liner
deposition, the different aspects of the invention may be applied
to sputtering other materials and for other purposes.
[0170] As described in copending application Ser. No. 10/202,778,
filed Jul. 25, 2002 (attorney docket No. 4044), which is
incorporated herein by reference in its entirety, the interconnect
layer or layers may also be deposited in a sputter chamber similar
to the chamber 152 (FIG. 4) which generates both SIP and ICP
plasmas. If deposited in a chamber such as the chamber 152, the
target 156 would be formed of the deposition material, such as
copper, for example. In addition, the ICP coil 151 may be formed of
the same deposition material as well, particularly if coil
sputtering is desired for some or all of the interconnect metal
deposition.
[0171] As previously mentioned, the illustrated chamber 152 is
capable of self-ionized sputtering of copper including sustained
self-sputtering. In this case, after the plasma has been ignited,
the supply of argon may be cut off in the case of SSS, and the
copper ions have sufficiently high density to resputter the copper
target with a yield of greater than unity. Alternatively, some
argon may continue to be supplied, but at a reduced flow rate and
chamber pressure and perhaps with insufficient target power density
to support pure sustained self-sputtering but nonetheless with a
significant but reduced fraction of self-sputtering. If the argon
pressure is increased to significantly above 5 millitorr, the argon
will remove energy from the copper ions, thus decreasing the
self-sputtering. The wafer bias attracts the ionized fraction of
the copper particle deep into the hole.
[0172] However, to achieve deeper hole coating with a partially
neutral flux, it is desirable to increase the distance between the
target 156 and the wafer 158, that is, to operate in the long-throw
mode as discussed above. The controlled division among self-ionized
plasma (SIP) sputtering, inductively coupled plasma (ICP)
sputtering and sustained self-sputtering (SSS) allows the control
of the distribution between neutral and ionized sputter particles.
Such control is particularly advantageous for the sputter
deposition of a copper seed layer in a high aspect-ratio via hole.
The control of the ionization fraction of sputtered is achieved by
mixing self-ionized plasma (SIP) sputtering and inductively coupled
plasma (ICP) sputtering.
[0173] One embodiment of a structure in accordance with the present
invention is a via illustrated in cross-section in FIG. 24. A
copper seed layer 700 is deposited in a via hole 702 over the liner
layer 704 (which may include one or more barrier and liner layers
such as the aforementioned TaN barrier and Ta liner layers) using,
for example, a long-throw sputter reactor of the type shown in FIG.
4 and under conditions promoting combined SIP and ICP and/or
alternating SIP and ICP. Here the reactor would have a target which
includes the copper or other seed layer deposition material. The
SIP-ICP copper layer 700 may be deposited, for example, to a
blanket thickness of 50 to 300 nm or more preferably of 80 to 200
nm. The SIP-ICP copper seed layer 700 preferably has a thickness in
the range of 2 to 20 nm on the via sidewalls, more preferably 7 to
15 nm. In view of the narrow holes, the sidewall thickness should
not exceed 50 nm. The quality of the film is improved by decreasing
the pedestal temperature to less than 0 degrees C. and preferably
to less than -40 degrees C. so that the coolness afforded by the
quick SIP deposition becomes important.
[0174] It is believed that the SIP-ICP copper seed layer 700 will
have good bottom coverage and enhanced sidewall coverage. As
explained in greater detail below, the copper seed layer 700 may be
resputtered either in a separate step or during the initial
deposition to redistribute the copper deposition material to
increase coverage at the inside bottom corners of the via while
usually leaving a thinner coverage in the central portion of the
via bottom. After the copper seed layer 700 is deposited (and
redistributed, if desired), the hole may be filled with a copper
layer similar to the copper layer 347b' of FIG. 14b, preferably by
electro-chemical plating using the seed layer 700 as one of the
electroplating electrodes. However, the smooth structure of the
SIP-ICP copper seed layer 700 also promotes reflow or
higher-temperature deposition of copper by standard sputtering or
physical vapor deposition (PVD).
[0175] In one embodiment, an SIP-ICP layer may be formed in a
process which combines selected aspects of both SIP and ICP
deposition techniques in one step, referred to herein generally as
an SIP-ICP step. In addition, a reactor 715 in accordance with an
alternative embodiment has a second coil 716 in addition to the
coil 151 as shown in FIG. 25. In the same manner as the coil 151,
one end of the coil 716 is insulatively coupled through a darkspace
shield 164' by a feedthrough standoff 182 to the output of an
amplifier and matching network 717 (FIG. 26). The input of the
matching network 717 is coupled to an RF generator 718. The other
end of the coil 716 is insulatively coupled through the shield 164'
by a feedthrough standoff 182 to ground, via a blocking capacitor
719, to provide a DC bias on the coil 716. The DC bias may be
controlled by a separate DC source 721.
[0176] In an ICP or combined SIP-ICP step, RF energy is applied to
one or both of the RF coils 151 and 716 at 1-3 kW and a frequency
of 2 Mhz, for example. The coils 151 and 716 when powered,
inductively couple RF energy into the interior of the reactor. The
RF energy provided by the coils ionizes a precursor gas such as
argon to maintain a plasma to ionize sputtered deposition material.
However, rather than maintain the plasma at a relatively high
pressure, such as 20-60 mTorr typical for high density IMP
processes, the pressure is preferably maintained at a substantially
lower pressure, such as 2 mTorr, for example. As a consequence, it
is believed that the ionization rate within the reactor 150 will be
substantially lower than that of the typical high density IMP
process.
[0177] Furthermore as discussed above, the illustrated reactor 150
is also capable of self-ionized sputtering in a long-throw mode. As
a consequence, deposition material may be ionized not only as a
result of the low pressure plasma maintained by the RF coil or
coils, but also by the plasma self-generated by the DC magnetron
sputtering of the target. It is believed that the combined SIP and
ICP ionization processes can provide sufficient ionized material
for good bottom and bottom corner coverage. However, it is also
believed that the lower ionization rate of the low pressure plasma
provided by the RF coils 151 and 716 allows sufficient neutral
sputtered material to remain un-ionized so as to be deposited on
the upper sidewalls by the long-throw capability of the reactor.
Thus, it is believed that the combined SIP and ICP sources of
ionized deposition material can provide both good upper sidewall
coverage as well as good bottom and bottom corner coverage. In
another embodiment, the power to the coils 151 and 716 may be
alternated such that in one step, the power to the upper coil 726
is eliminated or reduced relative to the power applied to the lower
coil 151. In this step, the center of the inductively coupled
plasma is shifted away from the target and closer to the substrate.
Such an arrangement may reduce interaction between the self ionized
plasma generated adjacent the target, and the inductively coupled
plasma maintained by one or more of the coils. As a consequence, a
higher proportion of neutral sputtered material might be
maintained.
[0178] In a second step, the power may be reversed such that the
power to the lower coil 151 is eliminated or reduced relative to
the power applied to the upper coil 716. In this step, the center
of the inductively coupled plasma may be shifted toward the target
and away from the substrate. Such an arrangement may increase the
proportion of ionized sputtered material.
[0179] In another embodiment, the layer may be formed in two or
more steps in which in one step, referred to herein generally as an
SIP step, little or no RF power is applied to either coil. In
addition, the pressure would be maintained at a relatively low
level, preferably below 5 mTorr, and more preferably below 2 mTorr
such as at 1 mTorr, for example. Furthermore, the power applied to
the target would be relatively high such as in the range of 18-24
kW DC, for example. A bias may also be applied to the substrate
support at a power level of 500 watts for example. Under these
conditions, it is believed that ionization of the deposition
material would occur primarily as a result of (SIP) self-ionization
plasma. Combined with the long-throw mode arrangement of the
reactor, it is believed that good upper sidewall coverage may be
achieved with low overhang. The portion of the layer deposited in
this initial step may be in the range of 1000-2000 angstroms, for
example.
[0180] In a second step, referred to generally herein as an ICP
step, and preferably in the same chamber, RF power may be applied
to one or both of the coils 151 and 716. In addition, in one
embodiment, the pressure may be raised substantially such that a
high density plasma may be maintained. For example, the pressure
may be raised to 20-60 mTorr, the RF power to the coil raised to a
range of 1-3 kW, the DC power to the target reduced to 1-2 kW and
the bias to the substrate support reduced to 150 watts. Under these
conditions, it is believed the ionization of the deposition
material would occur primarily as a result of high-density ICP. As
a result, good bottom and bottom corner coverage may be achieved in
the second step. Power may be applied to both coils simultaneously
or alternating, as described above.
[0181] After the copper seed layer is sputter deposited by a
process combining SIP and ICP, the remainder of the hole may be
filled by the same or another process. For example, the remainder
of the hole may be filled by electroplating or CVD.
[0182] It should be appreciated that the order of the SIP and ICP
steps may be reversed and that some RF power may be applied to one
or more coils in the SIP step and that some self-ionization may be
induced in the ICP step. In addition, sustained self sputtering
(SSS) may be induced in one or more steps. Hence, process
parameters including pressure, power and target-wafer distance may
be varied, depending upon the particular application, to achieve
the desired results.
[0183] As previously mentioned in the coils 151 and 516 may be
operated independently or together. In one embodiment, the coils
may be operated together in which the RF signal applied to one coil
is phase shifted with respect to the other RF signal applied to the
other coil so as to generate a helicon wave. For example, the RF
signals may be phase shifted by a fraction of a wavelength as
described in U.S. Pat. No. 6,264,812.
[0184] One embodiment of present invention includes an integrated
process preferably practiced on an integrated multi-chamber tool,
such as the Endura 5500 platform schematically illustrated in plan
view in FIG. 27. The platform is functionally described by Tepman
et al. in U.S. Pat. No. 5,186,718.
[0185] Wafers which have been already etched with via holes or
other structure in a dielectric layer are loaded into and out of
the system through two independently operated load lock chambers
732, 734 configured to transfer wafers into and out of the system
from wafer cassettes loaded into the respective load lock chambers.
After a wafer cassette has been loaded into a load lock chamber
732, 734, the chamber is pumped to a moderately low pressure, for
example, in the range of 10.sup.-3 to 10.sup.-4 Torr, and a slit
valve between that load lock chamber and a first wafer transfer
chamber 736 is opened. The pressure of the first wafer transfer
chamber 736 is thereafter maintained at that low pressure.
[0186] A first robot 738 located in the first transfer chamber 736
transfer the wafer from the cassette to one of two
degassing/orienting chambers 740, 742, and then to a first plasma
pre-clean chamber 744, in which a hydrogen or argon plasma cleans
the surface of the wafer. If a CVD barrier layer is being
deposited, the first robot 738 then passes the wafer to a CVD
barrier chamber 746. After the CVD barrier layer is deposited, the
robot 738 passes the wafer into a pass through chamber 748, from
whence a second robot 750 transfers it to a second transfer chamber
752. Slit valves separate the chambers 744, 746, 748 from the first
transfer chamber 736 so as to isolate processing and pressure
levels.
[0187] The second robot 750 selectively transfers wafers to and
from reaction chambers arranged around the periphery. A first IMP
sputter chamber 754 may be dedicated to the deposition of copper.
An SIP sputter chamber 756 similar to the chamber 410 described
above is dedicated to the deposition of an SIP copper seed or
nucleation layer. This chamber combines SIP for bottom and sidewall
coverage and resputtering for improved bottom corner coverage in
either a one step or a multi-step process as discussed above. Also,
at least part of the barrier layer, of, for example, Ta/TaN is
being deposited by SIP sputtering and coil sputtering and ICP
resputtering, and therefore an SIP-ICP sputter chamber 760 is
dedicated to a sputtering a refractory metal, possibly in a
reactive nitrogen plasma. The same SIP-ICP chamber 760 may be used
for depositing the refractory metal and its nitride. A CVD chamber
758 is dedicated to the deposition of a copper nucleation, seed or
liner layer or to complete the filling of the hole or both. Each of
the chambers 754, 756, 758, 760 is selectively opened to the second
transfer chambers 752 by slit valves. It is possible to use a
different configuration. For example, an IMP chamber 754 may be
replaced by a second CVD copper chamber, particularly if CVD is
used to complete the hole filling.
[0188] After the low-pressure processing, the second robot 750
transfers the wafer to an intermediately placed thermal chamber
762, which may be a cool down chamber if the preceding processing
was hot or may be a rapid thermal processing (RTP) chamber is
annealing of the metallization is required. After thermal
treatment, the first robot 738 withdraws the wafer and transfers it
back to a cassette in one of the load lock chambers 732, 734. Of
course, other configurations are possible with which the invention
can be practiced depending on the steps of the integrated
process.
[0189] The entire system is controlled by a computer-based
controller 770 operating over a control bus 772 to be in
communication with sub-controllers associated with each of the
chambers. Process recipes are read into the controller 770 by
recordable media 774, such as magnetic floppy disks or CD-ROMs,
insertable into the controller 770, or over a communication link
776.
[0190] Many of the features of the apparatus and process of the
invention can be applied to sputtering not involving long throw.
Although the invention is particularly useful at the present time
for tantalum and tantalum nitride liner layer deposition and copper
inter-level metallization, the different aspects of the invention
may be applied to sputtering other materials and for other
purposes. Provisional application No. 60/316,137 filed Aug. 30,
2001 is directed to sputtering and resputtering techniques and is
incorporated herein by reference.
[0191] It will, of course, be understood that modifications of the
present invention, in its various aspects, will be apparent to
those skilled in the art, some being apparent only after study,
others being matters of routine mechanical and process design.
Other embodiments are also possible, their specific designs
depending upon the particular application. As such, the scope of
the invention should not be limited by the particular embodiments
herein described but should be defined only by the appended claims
and equivalents thereof.
* * * * *