U.S. patent application number 10/940518 was filed with the patent office on 2005-02-10 for two step method for filling holes with copper.
Invention is credited to Chiang, Tony, Chin, Barry L., Ding, Peijun.
Application Number | 20050032369 10/940518 |
Document ID | / |
Family ID | 25320241 |
Filed Date | 2005-02-10 |
United States Patent
Application |
20050032369 |
Kind Code |
A1 |
Ding, Peijun ; et
al. |
February 10, 2005 |
Two step method for filling holes with copper
Abstract
A method of filling trenches or vias on a semiconductor
workpiece surface with copper using sputtering techniques. A copper
wetting layer and a copper fill layer may both be applied by
sputtering techniques. The thin wetting layer of copper is applied
at a substrate surface temperature ranging between about 20.degree.
C. to about 250.degree. C., and subsequently the temperature of the
substrate is increased, with the application of the sputtered
copper fill layer beginning at above at least about 200.degree. C.
and continuing while the substrate temperature is increased to a
temperature as high as about 600.degree. C. Preferably the
substrate temperature during application of the sputtered fill
layer ranges between about 300.degree. C. and about 500.degree.
C.
Inventors: |
Ding, Peijun; (San Jose,
CA) ; Chiang, Tony; (Mountain View, CA) ;
Chin, Barry L.; (Saratoga, CA) |
Correspondence
Address: |
Applied Materials, Inc.
Patent/Legal Department
P.O. Box 450A
Santa Clara
CA
95052
US
|
Family ID: |
25320241 |
Appl. No.: |
10/940518 |
Filed: |
September 14, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10940518 |
Sep 14, 2004 |
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10369856 |
Feb 20, 2003 |
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6793779 |
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10369856 |
Feb 20, 2003 |
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08855059 |
May 13, 1997 |
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6605197 |
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Current U.S.
Class: |
438/687 ;
257/E21.169; 257/E21.585 |
Current CPC
Class: |
H01L 21/76877 20130101;
H01L 21/2855 20130101 |
Class at
Publication: |
438/687 |
International
Class: |
H01L 021/28 |
Claims
1. A method of filling copper into a hole formed in a dielectric
layer in a substrate, comprising the steps of: a first step
performed in a first reactor of depositing copper into said hole to
form a copper layer on walls of said hole to a thickness of no more
than 100 nm and leaving a reduced-sized hole; and a second step
performed in a second reactor which is a first sputter reactor of
sputtering copper to fill said reduce-sized hole with copper.
2. The method of claim 1, wherein said first reactor is a CVD
reactor.
3. The method of claim 1, wherein said first reactor is a second
sputter reactor.
4. The method of claim 3, wherein said first step includes RF
biasing a applying an RF bias to a platen supporting said
substrate.
5. The method of claim 4, wherein a high density plasma is produced
in said first step.
6. The method of claim 3, wherein a high density plasma is produced
in said first step.
Description
RELATED APPLICATIONS
[0001] This application is a continuation of Ser. No. 10,369,856,
filed Feb. 20, 2003, issue fee paid, which is a continuation of
Ser. No. 08/855,059, filed May 13, 1997, now issued as U.S. Pat.
No. 6,605,197.
FIELD OF THE INVENTION
[0002] The present invention pertains to the use of sputtering as a
means for filling trenches and vias with copper (and alloys
thereof). Sputtering techniques include Gamma copper ("long throw"
deposition), IMP copper (ionized metal plasma deposition), coherent
copper, and traditional (standard) copper deposition. In
particular, when the sputtering of copper is carried out under
particular process conditions, it is possible to fill feature sizes
of 0.4 micron or less having aspect ratios of 1 or greater.
BACKGROUND ART
[0003] As the feature size of semiconductor patterned metal
features has become increasingly finer, it is particularly
difficult to use the techniques known in the art to provide
multilevel metallurgy processing. In addition, future technological
requirements include a switch from the currently preferred
metallurgy of aluminum to copper, because of copper's lower
resistivity and higher electromigration resistance. The standard
reactive ion etching method frequently used for patterning a
blanket metal cannot be practiced with copper, since there are no
volatile decomposition products of copper at low temperatures (less
than about 200.degree. C.). The alternative deposition liftoff
techniques are also limited in applicability in a copper structure,
given the susceptibility of copper to corrosion by the lift-off
solvents. Therefore a damascene structure is used which requires
the filling of embedded trenches and/or vias.
[0004] A typical process for producing a multilevel structure
having feature sizes in the range of 0.5 micron (.mu.m) or less
would include: blanket deposition of a dielectric material;
patterning of the dielectric material to form openings; deposition
of a conductive material onto the substrate in sufficient thickness
to fill the openings; and removal of excessive conductive material
from the substrate surface using a chemical, mechanical, or
combined chemical-mechanical polishing techniques. Currently the
conductive material is deposited using chemical vapor deposition
(CVD), evaporation, and sputtering. Chemical vapor deposition,
being completely conformal in nature, tends to create voids in the
center of the filled opening, particularly in the instance of high
aspect ratio features. Further, contaminants from the deposition
source are frequently found in the deposited conductive material.
Evaporation is successful in covering shallow features, but is
generally not practical for the filling of high aspect ratio
features. Sputtered copper, prior to the present invention, was not
considered as a technique for filling of high aspect ratio
openings, as voids typically occurred along the sidewalls of the
openings. The sputtering technique included cold (typically below
about 150.degree. C.) deposition of sputtered copper so that the
copper would adhere to the substrate surface, followed by an
annealing process (without deposition) at temperatures in excess of
about 400.degree. C., to reflow the copper and obtain filling of
the trench or via. However, such a reflow process takes hours, due
to the low bulk diffusivity of copper.
[0005] U.S. Pat. No. 5,246,885 to Braren et al., issued Sep. 21,
1993, describes the problems listed above, and proposes the use of
a laser ablation system for the filling of high aspect ratio
features. Alloys, graded layers, and pure metals are deposited by
ablating targets comprising more than one material using a beam of
energy to strike the target at a particular angle. The ablated
material is said to create a plasma composed primarily of ions of
the ablated material, where the plasma is translated with high
directionality toward a surface on which the material is to be
deposited. The preferred source of the beam of energy is a UV
laser. The heating of the deposition surface is limited to the
total energy deposited by the beam, which is said to be
minimal.
[0006] U.S. Pat. No. 5,312,509 of Rudolph Eschbach, issued May 17,
1974, discloses a manufacturing system for low temperature chemical
vapor deposition of high purity metals. In particular, a
semiconductor substrate including etched patterns is plasma
cleaned; subsequently, the substrate is coated with adhesion and
nucleation seed layers. A reactor connected to the process chamber
containing the substrate sublimes a precursor of the metal to be
deposited, which is then transported to the substrate. A reactor
heat transfer system provides selective reactor cooling and heating
above and below the precursor sublimation temperature under the
control of programmable software. The heated chuck on which the
substrate sits heats the substrate above the dissociation
temperature of the precursor, releasing the metal from the
precursor onto the substrate to nucleate the metal species onto the
seed layer on the substrate. Then the system is pumped to a lower
pressure and the substrate is advanced to the next process chamber.
This manufacturing system is recommended for the chemical vapor
deposition of pure copper at low temperatures. Although an adhesion
barrier layer (and a sputtered seed layer if required) are said to
be deposited using sputter deposition, the copper layer is applied
solely by CVD deposition, to avoid the sidewall voiding which is
said to occur if sputtering is used for the copper deposition. The
CVD copper deposition is carried out using a wafer temperature
controlled within a temperature range of 120.degree. C. to
250.degree. C. during the nucleation of the metal species upon the
substrate (with the temperature being lower at other times during
the process).
[0007] U.S. Pat. No. 5,354,712 to Ho et al., issued Oct. 11, 1994,
describes a method for forming interconnect structures for
integrated circuits. Preferably, a barrier layer of a conductive
material which forms a seed layer for metal deposition is provided
selectively on the sidewalls and bottom of interconnect trenches
defined in a dielectric layer. Subsequently, a conformal layer of
metal is selectively deposited on the barrier layer within the
interconnect trench. The metal layer comprises copper which is
deposited by chemical vapor deposition from an organo-metallic
precursor at temperatures. In particular, the layer of copper is
deposited by CVD from copper (hexafluoroacetylacetonate) trimethyl
vinylsilane compound by pyrolysis at low temperatures, between
about 120.degree. C. and 400.degree. C., onto a conductive barrier
layer of sputtered titanium nitride (TiN) which lines via holes,
providing a seed layer for selective growth of the conformal layer
of copper. The temperature of the substrate surface on which the
conductive barrier layer resides does not appear to be
specified.
[0008] In any case, this process suffers from the conformal
deposition of the metallic layer which tends to cause voids in the
center of the filled opening, as previously described, and from the
presence of contaminant residues from the precursor material which
remain in the deposited metallic fill.
[0009] U.S. Pat. No. 5,585,673, issued to Joshi et al. on Dec. 17,
1996, discloses refractory metal capped low resistivity metal
conductor lines and vias. In particular, the low resistivity metal
is deposited using physical vapor deposition (e.g., evaporation or
collimated sputtering), followed by chemical vapor deposition (CVD)
of a refractory metal cap. Recommended interconnect metals include
Al.sub.xCu.sub.y (wherein the sum of x and y is equal to one and
both x and y are greater than or equal to zero). The equipment
required for collimated sputtering is generally difficult to
maintain and difficult to control, since there is a constant build
up of sputtered material on the collimator over time. Collimated
sputtering is described in U.S. Pat. No. 5,478,455 to Actor et al.,
issued Dec. 26, 1995. Collimation, whether for sputtering or
evaporation, is inherently a slow deposition process, due to the
reduction in sputtered flux reaching the substrate.
[0010] It would be highly desirable to have a sputtering process
for copper deposition which uses a substantially standard
sputtering process chamber and target, while providing a complete
fill of vias and trenches.
SUMMARY OF THE INVENTION
[0011] It has been discovered that the surface diffusion
characteristics of copper over a particular temperature range
enable the complete filling of vias and trenches using sputtering
techniques previously believed incapable of achieving such
filling.
[0012] In particular, the copper fill layer may be applied in a
single step process or in a two step process. In the single step
process, for feature sizes of about 0.75 .mu.m or less, when the
aspect ratio of the feature to be filled is less than approximately
3:1, the temperature of the substrate to which the copper fill
layer is applied should range from about 200.degree. C. to about
600.degree. C. (preferably from about 200.degree. C. to about
500.degree. C.); when the aspect ratio is about 3:1 or greater, the
copper fill layer should be applied over a temperature ranging from
about 200.degree. C. to about 600.degree. C. (preferably from about
300.degree. C. to about 500.degree. C.). The deposition can be
initiated at the low end of the temperature range, with the
temperature being increased during deposition.
[0013] In the two step process, a thin, continuous wetting
(bonding) layer of copper is applied at a substrate surface
temperature of about 20.degree. C. to about 250.degree. C. The
wetting layer thickness (on the wall of the trench or via) should
be a minimum of about 5 nm, and typically may be about 10 nm to
about 30 nm, depending on feature size and aspect ratio.
Subsequently, the temperature of the substrate is increased, with
the application of fill copper beginning at about 200.degree. C. or
higher and continuing as the temperature is increased to that
appropriate for the feature size. When both the copper wetting
layer and the copper fill layer are applied in a single process
chamber, the deposition may be a continuous deposition. In such
case, process conditions are varied during the deposition, with the
copper fill layer being applied at a slower rate than the copper
wetting layer, to provide better deposition control.
[0014] When the copper wetting layer is applied in one process
chamber and the copper fill layer is applied in a second process
chamber, typically the substrate with copper wetting layer already
applied is placed on a heated support platen in the second process
chamber. For a small feature size (0.5 .mu.m or less) and an aspect
ratio of 1:1 or greater, it is better to wait until the substrate
is heated to a temperature of at least 200.degree. C. prior to
beginning application of the copper fill layer, or to begin the
fill layer deposition at a slower rate while the substrate is
heating.
[0015] The selection of a single step process or a two step process
depends on the composition and structure of the surface upon which
the copper is being deposited and the feature size of the trench or
via to be filled.
[0016] The copper sputtering technique used in the single step
process is selected from Gamma deposited copper, Coherent copper,
IMP copper, and traditional standard sputter deposition copper.
[0017] The copper deposition method used for application of the
thin, continuous, wetting layer of copper in the two step process
may be one of the sputtered copper techniques listed above or may
be chemical vapor deposition (CVD) copper or evaporation deposited
copper, depending on the feature size of the trench or via to be
filled. The deposition method used for the copper fill layer is
selected from the sputtering techniques listed above, to provide a
more contaminant-free and more rapid filling of the trench or
via.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] FIG. 1 shows a schematic of a scanning electron microscope
(SEM) cross-sectional image of a silicon oxide substrate having
trenches in its surface, with a barrier layer deposited over the
substrate surface and a Gamma-sputtered copper fill layer overlying
the barrier layer. The substrate surface temperature was
approximately 50.degree. C. at the time the copper fill layer was
applied.
[0019] FIG. 2 shows a schematic of an SEM cross-sectional image of
the same copper-filled trench composite structure as that shown in
FIG. 1, but where the substrate surface temperature was
approximately 170.degree. C. at the time the copper fill layer was
Gamma sputtered.
[0020] FIG. 3 shows a schematic of an SEM cross-sectional image of
the same copper-filled trench composite structure as that shown in
FIGS. 1 and 2, but where the substrate surface temperature was
approximately 325.degree. C. at the time the copper fill layer was
applied.
[0021] FIG. 4A shows a schematic of a scanning electron microscope
(SEM) cross-sectional image of a silicon oxide substrate having
trenches in its surface, with a barrier layer of tantalum deposited
over the oxide surface, a wetting layer of aluminum deposited over
the tantalum surface, a second wetting layer of IMP copper
deposited over the aluminum wetting layer, and a copper fill layer
of Gamma sputtered copper deposited over the wetting layer of IMP
copper. The IMP copper was deposited with the substrate surface at
about 250.degree. C. and the Gamma copper was deposited with the
substrate surface at about 325.degree. C. The feature size for the
trench is approximately 0.75 .mu.m wide and 1.5 .mu.m deep.
[0022] FIG. 4B shows a schematic of a scanning electron microscope
(SEM) cross-sectional image of the same structure as that described
above, except that the feature size for the trench is approximately
0.5 .mu.m wide and 1.5 .mu.m deep. The IMP copper wetting layer was
deposited with the substrate surface at approximately 300.degree.
C. and the Gamma copper fill layer was deposited with the substrate
surface at about 325.degree. C.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0023] The present disclosure pertains to a method of filling
semiconductor structure trenches and vias with sputtered copper,
wherein the surface diffusion characteristics of copper over a
particular temperature range enable the complete filling of vias
and trenches using sputtering techniques previously believed
incapable of achieving such filling.
[0024] I. Definitions
[0025] As a preface to the detailed description, it should be noted
that, as used in this specification and the appended claims, the
singular forms "a", "an", and "the" include plural referents,
unless the context clearly dictates otherwise. Thus, for example,
the term "a semiconductor" includes a variety of different
materials which are known to have the behavioral characteristics of
a semiconductor, reference to a "plasma" includes a gas or gas
reactants activated by an RF or DC glow discharge, and reference to
"copper" includes alloys thereof.
[0026] Specific terminology of particular importance to the
description of the present invention is defined below.
[0027] The term "aspect ratio" refers to the ratio of the height
dimension to the width dimension of particular openings into which
an electrical contact is to be placed. For example, a via opening
which typically extends in a tubular form through multiple layers
has a height and a diameter, and the aspect ratio would be the
height of the tubular divided by the diameter. The aspect ratio of
a trench would be the height of the trench divided by the minimal
width of the trench at its base.
[0028] The term "coherent copper" refers to copper which is applied
using a collimated deposition technique.
[0029] The term "completely filled" refers to the characteristic of
the copper-filled feature, wherein there is essentially no void
space present in the copper-filled feature.
[0030] The term "copper" refers to copper and alloys thereof,
wherein the copper content of the alloy is at least 80 atomic %.
The alloy may comprise more than two elemental components.
[0031] The term "feature" refers to contacts, vias, trenches, and
other structures which make up the topography of the substrate
surface.
[0032] The term "Gamma" or ".gamma. sputtered copper" or "Gamma
copper" refers to non-collimated magnetron sputtered copper which
is sputtered at low process chamber (gas) pressures, with improved
directionality of the depositing atoms. The improved directionality
is achieved by increasing the distance between the target cathode
and the workpiece surface (the throw) and by reducing the process
gas pressure during sputtering. Typically the distance between the
substrate and the target is about the diameter of the substrate or
greater; and, preferably, the process gas pressure is sufficiently
low that the mean free path for collision within the process gas is
greater than the distance between the target and the substrate.
[0033] The term "ion-deposition sputtered" and the term "ion metal
plasma (IMP) refer to sputter deposition, preferably magnetron
sputter deposition (where a magnet array is placed behind the
target). A high density, inductively coupled RF plasma is
positioned between the sputtering cathode and the substrate support
electrode, whereby at least a portion of the sputtered emission is
in the form of ions at the time it reaches the substrate
surface.
[0034] The term "IMP sputtered copper" or "IMP copper" refers to a
copper deposition which was sputtered using the IMP sputter
deposition process.
[0035] The term "reactive ion deposition" or "reactive ion metal
plasma (IMP)" refers to ion-deposition sputtering wherein a
reactive gas is supplied during the sputtering to react with the
ionized material being sputtered, producing an ion-deposition
sputtered compound containing the reactive gas element.
[0036] The term "SEM" refers to a scanning electron microscope.
[0037] The term "standard copper deposition" refers to copper
deposited using traditional sputtering techniques.
[0038] The term "traditional sputtering" refers to a method of
forming a film layer on a substrate wherein a target is sputtered
and the material sputtered from the target passes between the
target and the substrate to form a film layer on the substrate, and
no means is provided to ionize a substantial portion of the target
material sputtered from the target before it reaches the substrate.
One apparatus configured to provide traditional sputtering is
disclosed in U.S. Pat. No. 5,320,728, the disclosure of which is
incorporated herein by reference. In such a traditional sputtering
configuration, the percentage of target material which is ionized
is less than 10%, more typically less than 1%, of that sputtered
from the target.
[0039] II. An Apparatus for Practicing the Invention
[0040] A process system in which the method of the present
invention may be carried out is the Applied Materials, Inc. (Santa
Clara, Calif.) Endura.RTM. Integrated Processing System. The system
is shown and described in U.S. Pat. Nos. 5,186,718 and 5,236,868,
the disclosures of which are incorporated by reference.
[0041] The sputtering processes referenced herein are generally
known in the art. Gamma sputtering is described in detail in U.S.
Pat. No. 5,516,403, and by S. M. Rossnagel and J. Hopwood in their
paper titled "Thin, high atomic weight refractory film deposition
for diffusion barrier, adhesion layer, and seed layer applications"
J. Vac. Sci. Technol. B 14(3), May/June 1996. The IMP sputtering
process is presented by S. M. Rossnagel and J. Hopwood in "Metal
ion deposition from ionized mangetron sputtering discharge, J. Vac.
Sci. Technol. B, Vol. 12, No. 1 (January/February 1994). Coherent
sputtering and traditional sputtering are well known in the
art.
[0042] III. The Structure of the Copper Filled Trench or Via
[0043] We have been able to create a completely filled trench or
via having a feature size of about 0.4 .mu.m and an aspect ratio of
greater than 1:1 (up to about 3:1 presently). The trench or via may
be filled using any of the sputtering techniques described above,
including standard traditional sputtering. The present method is
expected to provide a complete fill for smaller feature sizes, but
these have yet to be evaluated. The copper-filled trench or via
exhibits excellent sidewall wetting with a void-free fill, when
filled in accordance with the method disclosed herein.
[0044] Although the background art cited reported that trenches and
vias could not be completely filled using sputtering techniques, we
discovered that by controlling the surface diffusion
characteristics of copper over a particular temperature range, we
could enable the complete filling of vias and trenches using such
sputtering techniques.
[0045] Depending on the dielectric material used in contact with
the copper, it may be necessary to use a barrier layer between the
copper and the dielectric material. For example, it is well known
in the art that it is necessary to use a barrier layer between
silicon oxide and copper. We have determined that when the trench
or via surface is silicon oxide, a barrier layer selected from
tantalum, tantalum nitride, tantalum-silicon nitride, titanium
nitride, titanium-silicon nitride, tungsten nitride and
tungsten-silicon nitride prevents diffusion of copper into the
silicon oxide while permitting a complete copper fill of the small
feature sizes described herein, using the method described herein.
In cases where it is difficult for copper to adhere to a barrier
layer, a wetting layer may be used over the surface of such a
barrier layer. For example, and not by way of limitation, we have
discovered that aluminum and titanium provide excellent wetting
layers in contact with either a copper wetting layer or a copper
fill layer.
[0046] Although a barrier layer or a wetting layer (when present)
affects the ability of the copper to flow into and fill a trench or
via, the control of the copper deposition temperature has the
greatest effect on obtaining a completely filled feature. The
effect of the barrier layer surface or the barrier layer with
overlying wetting layer surface is believed to be a second order
effect, whereas the copper deposition temperature has a first order
effect.
[0047] FIGS. 1-3 show a schematic depicting an SEM cross-sectional
view of a silicon oxide substrate having copper-filled trenches in
its surface, where the trenches are lined with a tantalum nitride
barrier layer (which was deposited using the Gamma sputtering
technique) prior to application of the copper fill layer.
[0048] FIGS. 4A and 4B show a schematic depicting a SEM
cross-sectional view of a silicon oxide substrate having
copper-filled trenches in its surface, where the trenches are lined
with a Gamma-sputtered tantalum barrier layer which is overlaid
with a Gamma-sputtered aluminum wetting layer, followed by an IMP
sputtered second wetting layer of copper, and filled with
Gamma-sputtered copper.
[0049] One skilled in the art can envision a number of
possibilities ranging from a direct application of the sputtered
copper fill layer over an underlying dielectric substrate; to
application of a copper wetting layer over the substrate, followed
by the sputtered copper fill layer; to various combinations of
barrier layers and wetting layers used with either a copper wetting
layer and/or a sputtered copper fill layer.
[0050] IV. The Method of Application of Sputtered Copper Fill
[0051] When the underlying substrate in contact with copper is
susceptible to diffusion by copper, the sputtered copper fill is
preferably applied over a barrier layer, perhaps with a wetting
layer overlaying the barrier layer. Silicon oxide is commonly used
as a dielectric in semiconductor structures, and silicon oxide is
subject to diffusion by copper. With this in mind, the preferred
embodiments described herein are with reference to a silicon oxide
substrate having an overlying barrier layer. However, it is
understood that should a dielectric substrate be used which is not
subject to diffusion by copper, such a barrier layer would not be
necessary. A barrier layer or a wetting layer (or both) applied
over a silicon oxide surface may be applied by any technique known
in the art, including CVD and evaporation, since the major
drawbacks previously mentioned with regard to these application
techniques is minimized when the underlying layer is a sufficiently
thin layer.
[0052] The preferred embodiments described herein were produced in
an IMP process chamber capable of processing a 200 mm-diameter
silicon wafer. The substrate was a silicon wafer having a silicon
oxide surface patterned with trenches and vias in the surface of
the silicon oxide.
[0053] IMP sputtering was carried out using a copper target cathode
having a 13.37 inch (33.96 cm) diameter, and DC power was applied
to this cathode over a range from about 1 kW to about 5 kW. The
substrate was placed a distance of about 5.5 inches (14 cm) from
the copper target cathode. Typically a substrate bias voltage
ranging from 0 to about -100 V AC was applied to the substrate or
the support platen under the substrate to create a bias which
attracts ions from the plasma to the substrate. The AC bias power
ranged from 0 W to about 500 W, and the frequency was typically
from 350 kHz to 13.56 MHz. A high density, inductively coupled RF
plasma was generated in the region between the target cathode and
the substrate by applying RF power to a coil (having from 1 to 3
turns) over a range from about 400 kHz to about 13.56 MHz
(preferably about 2 MHz), at a wattage ranging from about 0.5 kW to
about 5 kW (preferably about 1 kW to about 3 kW). The atmosphere in
the process vessel was argon, the flow rate of the argon ranged
from about 6 sccm to about 140 sccm, and the process vessel
pressure ranged from about 5 mT to about 60 mT.
[0054] Gamma sputtering was carried out using the following
conditions: The DC power to the target ranged from about 1 kW to
about 18 kW. The spacing between the target and the substrate
ranged between about 150 mm and about 500 mm, with or without a
chimney between the target and the substrate. (A chimney is a
cylinder or plurality of concentric cylinders placed between the
substrate and the target to block the center of the substrate from
the edge of the target and the edge of the substrate from the
center of the target, to increase deposition uniformity.) There was
no bias applied to the substrate. The atmosphere in the process
vessel was argon and the pressure ranged from about 0.1 mT to about
5 mT. The lower the pressure, the better the bottom coverage.
[0055] Coherent sputtering was carried out using the following
conditions: The DC power to the target ranged from about 1 kW to
about 22 kW. The collimator aspect ratio ranged from about 0.5:1 to
about 2:1 (with 1:1 being preferred). The spacing between the
target and the substrate ranged from about 90 mm to about 120 mm.
There was no bias applied to the substrate. The atmosphere in the
process vessel was argon and the pressure ranged from about 0.1 mT
to about 5 mT.
[0056] Standard sputtering was carried out using the following
conditions: The DC power to the target ranged from about 1 kW to
about 18 kW. The spacing between the target and the substrate
ranged from about 40 mm to about 60 mm. There was no bias applied
to the substrate. The atmosphere in the process vessel was argon
and the pressure ranged from about 0.1 mT to about 5 mT.
EXAMPLE ONE
[0057] FIGS. 1-3 show a schematic of a cross-sectional SEM (100,
200, and 300, respectively) of a silicon oxide substrate (110, 210,
and 310, respectively) having copper-filled trenches (111, 211, and
311, respectively) in its surface. A barrier layer (112, 212, and
312, respectively) of TaN.sub.x, where x ranged between 0 and 1,
was deposited on the surface of the silicon oxide substrate to a
thickness of about 50 nm (the thickness of the TaN.sub.x on the
sidewall of the trenches ranged from about 15 to about 30 nm). The
copper fill layer was gamma sputtered to a surface layer thickness
of about 1.2 .mu.m. The trench (feature) size in all cases was 0.5
.mu.m wide and 0.5 .mu.m deep.
[0058] In FIG. 1, the copper fill was gamma sputtered (to provide
better bottom coverage) at a substrate temperature of about
50.degree. C. (100.degree. C. heater temperature) The sputtered
copper layer 116a in the area of the trenches 111 formed distinct
mounds which did not flow well, leaving voids 118 in the fill. In
addition there were distinct breaks between the copper layer 116a
in the area of the trenches 111 and the copper layer 116b in
surrounding areas, further indicating that the copper did not flow
sufficiently well to enable the complete filling of trenches
111.
[0059] In FIG. 2, the gamma sputtered copper was applied at a
substrate temperature of about 170.degree. C. (220.degree. C.
heater temperature). The sputtered copper layer 216 (a and b)
flowed better, but a few minor voids 218 were present in the trench
fill, indicating that optimum copper flow had not yet been
attained. The definition between the copper layer 216a overlying
the trenches and the copper layer 216b in the area surrounding the
trenches was less, indicating that the sputtered copper was flowing
better than it had at 50.degree. C. (as illustrated by FIG. 1).
[0060] In FIG. 3, the gamma sputtered copper was applied at a
substrate temperature of about 325.degree. C. (375.degree. C.
heater temperature) The sputtered copper layer 316 (a and b) flowed
very well, with no voids observed in the trench fill, indicating
that satisfactory, if not optimum copper flow had been attained.
The definition between the copper fill 316a overlying the trenches
and the copper layer 316b in the area surrounding the trenches was
minimal, indicating that the sputtered copper was flowing
adequately to enable complete trench filling.
[0061] In all three of the preferred embodiments described above,
the sputtered copper fill did not separate from the side wall of
the trench. This is in contrast with previous sputtering techniques
where the copper was initially deposited cold, at a substrate
temperature of less than about 150.degree. C., followed by a reflow
process step (without additional copper deposition) at a
temperature in excess of 400.degree. C. Typically, the cold
deposition followed by a reflow process step resulted in separation
of the fill from the trench wall (i.e. voiding).
EXAMPLE TWO
[0062] FIGS. 4A and 4B show a schematic of a cross-sectional SEM
(400 and 430, respectively) of a silicon oxide substrate (410 and
431, respectively) having copper-filled trenches (411, and 433,
respectively) in its surface. A barrier layer (412 and 432,
respectively) of Gamma-sputtered tantalum was deposited to a
substrate surface thickness of about 80 nm (a sidewall thickness
ranging from about 20 nm to about 40 nm) over the silicon oxide
substrate. (Had a tantalum nitride barrier layer been used, the
preferred method of application would have been reactive IMP
sputtering in the presence of nitrogen). A wetting layer (414 and
434, respectively) of Gamma-sputtered aluminum, was deposited to a
substrate surface thickness of about 100 nm (a sidewall thickness
ranging from about 10 nm to about 30 nm) over the tantalum barrier
layer. This was followed by a second wetting layer of IMP-sputtered
copper (416 and 436, respectively), which was applied to a
substrate surface thickness of about 180 nm (a sidewall thickness
ranging from about 35 nm to about 50 nm), at a substrate
temperature of about 250.degree. C. The copper fill layer was IMP
sputtered to a substrate surface thickness of about 1 .mu.m. The
trench (feature) size in FIG. 4A was about 0.67 .mu.m wide and 1.2
.mu.m deep. The trench size in FIG. 4B was about 0.4 .mu.m wide and
1.2 .mu.m deep.
[0063] With reference to FIG. 4A, the thin, second wetting layer of
IMP-sputtered copper layer 416 was sputtered over the aluminum
wetting layer 414 at a substrate temperature of about 250.degree.
C. The substrate was subsequently transferred to a second process
chamber (which did not have the IMP ionization coil), for Gamma
sputtering of the copper fill layer. The substrate temperature was
raised to about 325.degree. C. for application of the
Gamma-sputtered copper layer 422 (a and b). The surface thickness
of the Gamma-sputtered copper layer 422 (a and b) applied was about
1 .mu.m, as previously mentioned. The Gamma-sputtered copper 418
traveled nicely over the surface of the IMP-sputtered copper layer
416, down toward the pool 420 of Gamma-sputtered copper in the
bottom of the trench 411. The slope from the upper surface 422b of
the copper layer toward the lower surface 422a of the copper layer
overlying trenches 411 was gradual, indicating good flow of the
copper into the trenches 411.
[0064] With reference to FIG. 4B, the thin, second wetting layer of
IMP-sputtered copper layer 436 was sputtered over the aluminum
wetting layer 434 at a substrate temperature of about 250.degree.
C. The substrate was subsequently transferred to a second process
chamber for Gamma sputtering of the copper fill layer. The
substrate temperature was raised to about 325.degree. C. for
application of the Gamma-sputtered copper layer 442 (a and b). The
thickness of the Gamma-sputtered copper layer 442 (a and b) applied
was about 1 .mu.m. The Gamma-sputtered copper 438 traveled nicely
over the surface of the IMP-sputtered copper layer 436, down toward
the pool 440 of Gamma-sputtered copper in the bottom of the trench
433. The slope from the upper surface 442b of copper layer 442
toward the lower surface 442a of copper layer 442 overlying
trenches 433 was gradual, indicating good flow of the copper into
the trenches.
[0065] In both of the above-described experiments, the
Gamma-sputtered copper would be expected to completely fill the
trenches to a height at least as high as the upper substrate
surface barrier and wetting layers if a thicker layer of copper
were applied.
[0066] Although the barrier layer applied in this example was
tantalum, we have also tried tantalum nitride and titanium nitride,
and found these materials to work well. One skilled in the art can
choose from known barrier layers. Although the wetting layer
applied in this Example was aluminum, applicants have also used
titanium and found that titanium works well as a wetting layer.
Additional wetting layers are known in the art.
[0067] The selection of a particular barrier layer or a barrier
layer combined with a wetting layer determines the need for
deposition of a thin (ranging between about 20 nm and about 100 nm)
wetting layer of copper prior to application of the sputtered
copper fill layer. When the sputtered copper fill tends to dewet
from the barrier layer easily, then either a single wetting layer
such as aluminum or copper, or a dual wetting layer such as a layer
of aluminum overlaid by a layer of copper may be needed. For
example, when a tantalum barrier layer is used in combination with
an overlying aluminum wetting layer, it is possible to
Gamma-sputter a copper fill layer directly over the aluminum layer
at a temperature of about 375.degree. C. When a tantalum barrier
layer alone is used, the direct application of a Gamma-sputtered
copper fill layer at 375.degree. C. provides marginal fill
characteristics. When a tantalum nitride barrier layer is used, a
thin wetting layer of copper can be used to prevent subsequent
dewetting of a Gamma-sputtered fill from the trench sidewalls.
[0068] On the basis of empirical data, the preferable substrate
temperature for application of the thin wetting layer of copper
ranges between about 25.degree. C. and about 250.degree. C. The
copper wetting layer can be applied using the following techniques:
IMP copper, CVD copper, Gamma-sputtered copper, Coherent copper, or
traditionally sputtered copper. The preferable substrate
temperature for sputtering of the copper fill layer ranges between
about 200.degree. C. and 600.degree. C., with a range between about
300.degree. C. and 500.degree. C. being even more preferred. The
sputtered copper fill layer can be applied using the following
techniques: Gamma-sputtered copper, IMP copper, Coherent copper and
traditionally sputtered copper.
[0069] The above described preferred embodiments are not intended
to limit the scope of the present invention, as one skilled in the
art can, in view of the present disclosure expand such embodiments
to correspond with the subject matter of the invention claimed
below.
* * * * *