U.S. patent application number 10/262652 was filed with the patent office on 2003-04-10 for pressure modulation method to obtain improved step coverage of seed layer.
This patent application is currently assigned to Applied Materials, Inc.. Invention is credited to Angelo, Darryl, Chin, Barry, Ding, Peiijun, Hasim, Imran, Sundarrajan, Arvind.
Application Number | 20030066747 10/262652 |
Document ID | / |
Family ID | 23749738 |
Filed Date | 2003-04-10 |
United States Patent
Application |
20030066747 |
Kind Code |
A1 |
Sundarrajan, Arvind ; et
al. |
April 10, 2003 |
Pressure modulation method to obtain improved step coverage of seed
layer
Abstract
A multi-step process for the deposition of a material into high
aspect ratio features on a substrate surface is provided. The
process involves depositing a material on the substrate at a first
pressure for a first period of time and then depositing the
material on the substrate at a second pressure for a second period
of time. Modulation of the pressure influences the ionization and
trajectory of the particles, which are ionized in a plasma
environment. The method of the invention in one aspect allows for
optimum deposition at the bottom of a high aspect ratio feature
during a high pressure step and increased deposition on the
sidewalls of the feature during at least a low pressure step.
Inventors: |
Sundarrajan, Arvind; (Santa
Clara, CA) ; Angelo, Darryl; (Sunnyvale, CA) ;
Ding, Peiijun; (San Jose, CA) ; Chin, Barry;
(Saratoga, CA) ; Hasim, Imran; (San Jose,
CA) |
Correspondence
Address: |
Patent Counsel
APPLIED MATERIALS, INC.
P.O. Box 450-A
Santa Clara
CA
95052
US
|
Assignee: |
Applied Materials, Inc.
|
Family ID: |
23749738 |
Appl. No.: |
10/262652 |
Filed: |
September 30, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10262652 |
Sep 30, 2002 |
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09440679 |
Nov 16, 1999 |
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6458251 |
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Current U.S.
Class: |
204/192.12 ;
204/192.13; 204/192.15; 204/298.06; 204/298.07; 257/E21.169;
257/E21.585 |
Current CPC
Class: |
H01L 21/76877 20130101;
H01J 2237/3327 20130101; C23C 14/358 20130101; H01J 37/32082
20130101; H01L 21/76873 20130101; H01L 21/2855 20130101; H01L
21/76843 20130101; C23C 14/046 20130101; H01J 37/3402 20130101;
C23C 14/3492 20130101 |
Class at
Publication: |
204/192.12 ;
204/192.15; 204/192.13; 204/298.06; 204/298.07 |
International
Class: |
C23C 014/32; C23C
014/00 |
Claims
1. A method for depositing material on a substrate, comprising: (a)
providing a plasma in a chamber at a first pressure; (b) sputtering
a material from a target disposed in the chamber; (c) ionizing the
sputtered material; (d) depositing sputtered material onto the
substrate at a first chamber pressure; (e) modulating the pressure
in the chamber between at least the first and a second chamber
pressure; and (f) depositing sputtered material onto the substrate
at the second chamber pressure.
2. The method of claim 1, wherein the first chamber pressure and
the second chamber pressure are maintained for a total period of
time less than about 120 seconds.
3. The method of claim 1, further comprising: (g) repeating (d),
(e) and (f) during multiple steps of deposition to form a layer on
the substrate.
4. The method of claim 1, wherein the first chamber pressure is
between about 35 mTorr and about 70 mTorr.
5. The method of claim 1, wherein the second chamber pressure is
between about 10 mTorr and about 20 mTorr.
6. The method of claim 1, wherein the first chamber pressure is
between about 35 mTorr and about 70 mTorr and the second chamber
pressure is between about 10 mTorr and about 20 mTorr.
7. The method of claim 1, wherein the first chamber pressure is
higher than the second chamber pressure.
8. The method of claim 1, wherein the material is selected from the
group of copper, tantalum, tantalum nitride, tungsten, tungsten
nitride, titanium, titanium nitride and combinations thereof.
9. A method for depositing material in a feature formed on a
substrate, comprising: (a) providing a plasma in a chamber; (b)
sputtering a material from a target disposed in the chamber; (c)
ionizing the material; and (d) depositing a material onto the
feature while modulating the chamber pressure.
10. The method of claim 9, wherein the chamber pressure is
modulated between about 10 mTorr and about 70 mTorr.
11. The method of claim 10, wherein the material is selected from
the group of copper, tantalum, tantalum nitride, tungsten, tungsten
nitride, titanium nitride and combinations thereof.
12. A method for depositing one or more layers in a feature formed
on a substrate, comprising: (a) providing a plasma in a chamber
having a target and a coil disposed therein; (b) providing a signal
to the target; (c) providing a signal to the coil; (d) depositing a
first layer onto the feature at a first chamber pressure; and (e)
depositing a second layer onto the feature at a second chamber
pressure.
13. The method of claim 12, further comprising ionizing the
material prior to (d).
14. The method of claim 12, wherein the chamber pressure during (d)
and (e) is modulated between about 10 mTorr and about 70 mTorr.
15. The method of claim 12, further comprising filling the
feature.
16. The method of claim 12, wherein the first layer and/or the
second layer comprise a material is selected from the group of
copper, tantalum, tantalum nitride, tungsten, tungsten nitride,
titanium nitride and combinations thereof.
17. A program product, which when read and executed by a computer,
comprises the steps of: (a) providing a signal to a target disposed
in the chamber; (b) providing a signal to a coil; and (c)
modulating the chamber pressure during the deposition of a material
onto a substrate.
18. The method of claim 17, wherein the chamber pressure is
modulated between about 10 mTorr and about 70 mTorr.
19. The method of claim 17, wherein the chamber pressure is
modulated between a first pressure and a second pressure lower than
the first pressure.
20. The method of claim 17, wherein modulating the chamber pressure
comprises alternating the pressure between two or more values until
a feature on a substrate is filled with material.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention provides a method to enhance step
coverage of a metal film deposited into high aspect ratio features
formed on a substrate.
[0003] 2. Background of the Related Art
[0004] Physical vapor deposition (PVD) or sputtering is a known
technique used in the manufacture of integrated circuits.
Sputtering is a method by which material on a target are displaced
to a desired surface of a substrate where they form a thin film. In
a typical PVD process the target and the substrate to be coated are
placed in a vacuum chamber which is evacuated to and maintained at
a pressure of less than about 10 milliTorr. An inert gas, such as
argon, is supplied to the vacuum chamber and a pumping system
maintains the desired gas pressure in the chamber. A glow discharge
plasma is created in the chamber by supplying a negative DC or RF
potential to a cathode (typically the target) and grounding the
chamber walls and an anode (typically the substrate). The glow
discharge plasma is created in the space between the cathode and
the anode, and is generally separated from the electrodes by a dark
space or plasma sheath. In a standard PVD chamber, a dense plasma
exists near the target. This plasma is maintained by secondary
electrons emitted from the target during the sputtering process.
Using a magnetron assembly the secondary electrons are trapped by
magnetic fields to efficiently create a plasma adjacent the target.
In this arrangement, an electric field is produced that is
substantially perpendicular to the exposed surface of the target.
Thus, positive ions from the plasma are accelerated across the dark
space onto the exposed surface of the target resulting in
sputtering of the target.
[0005] The goal in most deposition processes is to deposit a film
of uniform thickness across the surface of a substrate, while also
providing good fill of lines, interconnects, contacts, vias and
other features formed on the substrate. In some applications, a
conformal liner, barrier or seed layer may be deposited. For
example, in a copper fill process a barrier layer is deposited on a
feature formed in a substrate to prevent diffusion of copper into
the base material of the substrate. Subsequently, a conformal seed
layer is deposited over the barrier layer and copper is deposited
to fill the feature. As device geometries shrink, it has become
increasingly difficult to deposit materials conformally into small
features to form barrier and seed layers in these features.
[0006] With recent decreases in the size of semiconductor devices
and corresponding decreases in device features to less than a
quarter micron (<0.25 .mu.m) in aperture width, conventional
sputtering (i.e., PVD) has been sheared through the use of a high
density plasma (HDP) PVD process, known, for example, as ionized
metal plasma (IMP) PVD. IMP-PVD uses a coil disposed between a
sputtering target and a substrate to ionize atoms sputtered from
the target. As the ionized metal atoms approach the plasma boundary
near the substrate, the electric field caused by an applied bias on
the substrate directs the ionized metal atoms in a direction
generally perpendicular to the substrate surface. These ions are
accelerated perpendicularly towards the surface of the substrate
within the plasma sheath, improving the selective or preferential
filling of high aspect ratio features, e.g., sub-quarter micron.
Biasing of the substrate relative to plasma potential is widely
used in HDP-PVD to control the energy of ions reaching the
substrate and improve directivity. Because the ionized metal atoms
are traveling normal to the surface of the substrate, they can
deposit into the bottom of high aspect ratio features without
hitting the sidewalls of the features and forming overhangs at the
top comers of the features.
[0007] One of the problems with HDP-PVD is due to the relatively
large difference in molar mass between the target material and the
plasma gas. For example, the molar mass ratio of Copper to Argon is
about 1.59. Because of this difference, target atoms cannot be
readily ionized in the HDP-PVD chamber. In an attempt to increase
ionization of the sputtered metal particles, it has been suggested
to increase the chamber pressure, thereby increasing the plasma
density. The higher density, in turn, reduces the mean free path
between particles resulting in more collisions and increased
ionization. However, the deposition results are compromised once
the pressure reaches an upper limit.
[0008] Another problem with HDP-PVD is the inability to achieve
conformal coverage in the increasingly smaller device features.
Conformal coverage of the bottoms and sidewalls of the features is
needed to optimize subsequent processes such as electroplating.
Electroplating requires conformal barrier layers and conformal seed
layers within the device features in order to ensure uniform
filling of the feature. While conventional HDP-PVD processes
achieve good bottom coverage due to the directionality of the ions
provided by the bias on the substrate, the sidewall coverage is not
as good. This result is caused in part by the induced high
directionality of ions toward the bottoms of the features with
little directionality toward the sidewalls.
[0009] Therefore, there is a need for a metal deposition process
which provides conformal coverage in high aspect ratio
features.
SUMMARY OF THE INVENTION
[0010] The present invention generally provides a method for
depositing a generally conformal film on a substrate to form
barrier layers and/or seed layers. The method includes deposition
of a material at a first pressure followed by deposition of the
material at a second pressure. In one embodiment, the first
pressure is higher than the second pressure. The high pressure step
results in relatively more deposition of a material on a feature
bottom and the low pressure step results in relatively more
deposition of material on the sidewalls of the feature.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] So that the manner in which the above recited features,
advantages and objects of the present invention are attained and
can be understood in detail, a more particular description of the
invention, briefly summarized above, may be had by reference to the
embodiments thereof which are illustrated in the appended
drawings.
[0012] It is to be noted, however, that the appended drawings
illustrate only typical embodiments of this invention and are
therefore not to be considered limiting of its scope, for the
invention may admit to other equally effective embodiments.
[0013] FIG. 1 is a diagram of a typical processing chamber using a
coil.
[0014] FIG. 2 is a graphical representation of a first embodiment
pressure modulation curve.
[0015] FIG. 3 is a graphical representation of a second embodiment
pressure modulation curve.
[0016] FIG. 4 is a schematic representation of the angular
distribution of ions effected by low pressure.
[0017] FIG. 5 is schematic representation of the angular
distribution of ions effected by high pressure.
[0018] FIG. 6A-D illustrates the effects of pressure modulation on
deposition of a material in a feature.
[0019] FIG. 7 is a schematic diagram of the semi-conductor
substrate formed in a dielectric material.
[0020] FIG. 8 is a schematic diagram of the semi-conductor
substrate via FIG. 7 having a barrier layer formed thereon.
[0021] FIG. 9 is a schematic diagram of the semi-conductor
substrate via FIG. 8 having a seed layer formed thereon.
[0022] FIG. 10 is a schematic diagram of the semiconductor
substrate via FIG. 9 having a conducting material deposition
therein to fill the via.
[0023] FIG. 11 is a schematic diagram of the semiconductor
substrate via of FIG. 10 after planarization.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0024] The invention will be described below in reference to an
ionized metal plasma (IMP) process that can be carried out using
process equipment, such as an Endura.RTM. platform, available from
Applied Materials, Inc., located in Santa Clara, Calif. The
equipment preferably includes an integrated platform having an
HDP-PVD chamber, such as ion metal plasma (IMP) processing chamber,
known as an IMP VECTRA.TM. chamber, available from Applied Material
Inc. of Santa Clara, Calif. Although the invention is preferably
carried out in an HDP-PVD chamber, any chamber enabling the
ionization and deposition of a material on a substrate can be used
to advantage. Such chambers include electron cyclotron resonance
(ECR) chambers and hollow cathode chambers.
[0025] FIG. 1 is a schematic cross-sectional view of an IMP chamber
100 that can be used to advantage with the present invention. The
chamber 100 includes sidewalls 101, lid 102, and bottom 103. A
target 104 comprising the material to be sputtered is disposed in
the chamber 100 on the lid 102. A substrate support member 112 is
movably disposed in the chamber 100 and provides an upper support
surface 105 for supporting a substrate 110. The support member 112
is mounted on a stem connected to a lift motor 114 that raises and
lowers the substrate support 112 between a lowered
loading/unloading position and a raised processing position. An
opening 108 in the chamber 100 provides access for a robot (not
shown) to deliver and retrieve substrates 110 to and from the
chamber while the substrate support member is in the lowered
loading/unloading position. A lift plate 116 connected to a lift
motor 118 is mounted in the chamber 100 and raises and lowers pins
120 mounted in the substrate support. The pins 120 raise and lower
the substrate 110 to and from the upper surface 105 of the
substrate support member 112. A shield 124 is disposed in the
chamber to shield the chamber walls from the sputtered material. A
coil 122 is preferably mounted to the shield via supports 126
between the substrate support member 112 and the target 105 and
provides electromagnetic fields in the chamber to assist in
generating and maintaining a plasma between the target 104 and
substrate 110. The electromagnetic fields produced by the coil 122
effect a high density plasma which ionizes the sputtered target
material. The ionized material is then directed toward the
substrate 110 and deposited thereon. The supports 126 electrically
insulate the coil 122 from the shield 124 and the chamber 100. A
clamp ring 128 is mounted between the coil 122 and the substrate
support 112 and shields an outer edge and backside of the substrate
110 from sputtered materials when the substrate 110 is raised into
a processing position to engage the lower portion of the clamp ring
128.
[0026] Three power supplies are used in the chamber 100. A first
power supply 130 delivers either RF or DC power to the target 104
to cause the processing gas to form a plasma. Magnets 106 disposed
behind the lid 102 form a magnetic field at the target surface,
which trap electrons and increase the density of the plasma
adjacent to the target 104 in order to increase the sputtering
efficiency. A second power source 132, preferably a RF power
source, supplies electrical power typically in the megahertz range
to the coil 122. A third power source 134, preferably a RF or a DC
power source, biases the substrate support member 112 with respect
to the plasma and provides directional attraction of the ionized
sputtered material toward the substrate 110.
[0027] One or more plasma gases are supplied to the chamber 100
through a gas inlet 136 from gas sources 138, 140 as metered by
respective mass flow controllers 142, 144. One or more vacuum pumps
146 are connected to the chamber 100 at an exhaust port 148 to
exhaust the chamber 100 and maintain the desired pressure in the
chamber 100. Preferably the vacuum pump 146 is a cryopump or any
pump capable of sustaining an acceptable low pressure.
[0028] A microprocessor/controller 149 controls the functions of
the power supplies, lift motors, mass flow controllers for gas
injection, vacuum pump, and other associated chamber components and
functions. The microprocessor/controller 149 executes a machine
readable program product stored in a memory in order to perform the
steps of the invention. In the preferred embodiment the memory is a
hard disk drive, and the microprocessor/controller 149 can include
analog and digital input/output boards, interface boards and
stepper motor controller boards. Optical and/or magnetic sensors
are generally used to move and determine the position of movable
mechanical assemblies.
[0029] In operation, a robot delivers a substrate 110 to the
chamber 100 through the opening 108. The pins 120 are extended
upward to lift the substrate 110 from the robot. The robot then
retracts from the chamber 100 and the opening 108 is sealed. The
pins 120 lower the substrate 110 to the upper support surface 105
of the substrate support member 112. The substrate support member
112 raises the substrate 110 to engage the clamp ring 128. One or
more plasma gases are then introduced into the chamber 100 to
stabilize the chamber 100 at a process pressure. A plasma is
generated between the target 104 and the substrate support member
112 with power from the first power source 130. The second power
source 132 delivers power to the coil 122 to densify the plasma and
ionize the flux of sputtered target material from the target 104 to
form ions. The ions are accelerated toward the substrate 110, which
is biased by the third power source 134. After deposition, the
substrate support member 112 is lowered, the pins 120 are raised to
lift the substrate 110, the robot enters the chamber 100 to
retrieve the substrate 110, and if desired, delivers another
substrate for processing.
[0030] A method according to the invention provides a multi-step
pressure modulation method which can be performed in chamber 100 to
obtain improved step coverage of seed and barrier layers in high
aspect ratio features and in particular where aspect ratios are
>4:1. The method of the invention can also be used to fill
features formed on a substrate. The process generally involves
depositing a material on the substrate at a first pressure for a
first period of time and then depositing material on the substrate
at a second pressure for a second period of time. Modulation of the
chamber pressure influences the ionization of the sputtered
material and the travel direction of the material that is ionized
in a plasma environment.
[0031] In one embodiment, the chamber pressure is varied between an
upper limit pressure and a lower limit pressure. FIG. 2 is a
graphical representation of a pressure modulation curve 200 having
a period T.sub.1. The pressure modulation curve 200 is preferably
oscillated between an upper limit pressure 202 and a lower limit
pressure 204, thereby resulting in a pressure differential
.DELTA.P.sub.1. For deposition of a liner, barrier or seed layer,
the upper pressure 202 is preferably between about 35 mTorr and 70
mTorr, the lower pressure is preferably between about 10 mTorr and
20 mTorr. Thus, .DELTA.P.sub.1 may be between about 15 mTorr and 60
mTorr. The upper limit 202 and the lower limit 204 have
independently variable time durations t.sub.1 and t.sub.2,
respectfully. While t.sub.1 and t.sub.2 vary substantially with
particular values for other process parameters including pressure
and power, the sum of t.sub.1 and t.sub.2 is preferably less than
about 120 seconds for deposition of liner, barrier or seed layers.
Additionally, t.sub.1, t.sub.2 may be adjusted to compensate for
differences in the deposition rate which may result with changes in
chamber pressure. For example, a lower deposition rate during
t.sub.1, as compared to t.sub.2, can be compensated for by setting
t.sub.1 to be greater than t.sub.2.
[0032] The curve 200 is merely illustrative and whether the
modulation sequence is initiated at a lower pressure and then
elevated to a higher pressure or vice versa is not limiting of the
invention. Further, it is understood that the pressure modulation
curve 200 may comprise only a single period T.sub.1 for each cycle.
Thus, for example, a process recipe may allow deposition of a film
on a substrate at the upper limit pressure 202 for a period of time
and stabilize the chamber pressure at the lower limit pressure 204
for the duration of the deposition cycle. Preferably, other process
parameters such as substrate temperature, target power, etc., are
held constant or are adjusted according to recipes known in the
art. Regarding the target power, some level of power is applied to
the target 104 through the deposition cycle in order to provide
constant sputtering and deposition.
[0033] FIG. 3 illustrates another embodiment of the invention
wherein the chamber pressure is varied between more than two
pressures. For example, FIG. 3 shows a pressure modulation curve
213 having an upper pressure 212, a lower pressure 214 and an
intermediate pressure 216. The pressure difference between the
upper limit 212 and the lower limit 214 results in .DELTA.P.sub.2
which may be any quantity as determined by a particular application
and is preferably between about 15 mTorr and about 60 mTorr for
deposition of a liner, barrier or seed layer. Therefore, in
operation the chamber pressure is initially stabilized at the upper
limit pressure 212 for a period of time. Subsequently, the chamber
pressure is lowered to the intermediate pressure 216 for a period
of time. Finally, the chamber pressure is lowered to the lower
limit pressure 214 for a period of time. The total period of the
curve 213 is T.sub.2. Each of the pressures 212, 214 and 216 may be
maintained for a desired period of time as determined by a
particular application and may be repeated during a single
processing cycle at a desired frequency. As in the previous
embodiment, power is continually provided to the target 104 to
ensure sputtering therefrom throughout the deposition cycle.
[0034] The pressure modulation of the invention may be accomplished
either by varying the inlet flow of gas from gas sources and/or
varying the outlet flow of gas to the vacuum pump downstream from
the chamber. For example, with regard to process modulation curve
200 in FIG. 2, a flow rate maintained during t.sub.1 can be
decreased while the exhaust from the chamber is maintained constant
to achieve the lower limit pressure during t.sub.2. It is therefore
possible to establish a programmable sequence for various modes of
pressure modulation during the deposition process. By modulating
the pressure, good sidewall and bottom coverage can be obtained.
For example, a first pressure provides a relatively higher
deposition rate on the bottom of the feature as compared to a
second pressure, lower than the first pressure, that provides a
relatively higher deposition rate on the sidewalls of the
feature.
[0035] The effects of pressure modulation on the angular
distribution of ions may be understood with reference to FIGS. 4
and 5 which show a cross-section of a via 250 formed in a substrate
251 having sidewalls 252 and a bottom 254. At a low limit pressure,
the angular distribution 256 of incoming ions 258, shown here as Cu
ions, results in a greater deposition rate on sidewalls 252 of the
via 250 to form a layer 255 thereon as shown in FIG. 4. The angular
distribution 256 results because of a decrease in the proportion of
ionized sputtered atoms. At lower chamber pressures, the plasma
density is decreased, thereby resulting in fewer collisions between
the sputtered atoms and the plasma constituents and hence, less
ionization of the sputtered atoms. Since the unionized atoms are
unaffected by the bias on the substrate, the angular distribution
256 approaches a cosine distribution producing a relatively higher
rate of deposition on the sidewalls 252.
[0036] During an upper limit pressure the angular distribution 262
of incoming ions 264 is altered to effect a greater deposition rate
at the bottom 254 of the via 250, thereby producing a layer 257 on
the bottom 254, as shown in FIG. 5. The angular distribution 262 is
a result of the increased ionization associated with a relatively
higher chamber pressure. Thus, the bias on the substrate directs
the ions more normal to the surface of the substrate.
[0037] FIGS. 6A-D show a cross-section of a via 250 having
sidewalls 252 and a bottom 254 and illustrate the progressive
deposition of a material 270 on a substrate 251 over time using
pressure modulation according to the invention. FIGS. 6A-D are
representative of deposition on sidewalls 252 and a bottom 254
during two periods of a curve which oscillates between two pressure
limits (such as in FIG. 2) due to the chamber pressure modulation.
The pressure modulation effects variable rates of deposition on the
sidewalls 252 and at the bottom 254. Initially, a relatively high
pressure results in the angular distribution 262 shown in FIG. 5,
causing the material 270 to be deposited on the bottom 254 of the
via 250 as shown in FIG. 6A. Subsequently, a relatively low
pressure results in the angular distribution 256 shown in FIG. 4
causing the material 270 to be deposited on the sidewalls 252 of
the via 250 as shown in FIG. 6B. FIG. 6C illustrates the increasing
film thickness on the bottom 254 during the subsequent high
pressure period. The pressure modulation can be repeated at a
desired frequency and with the desired time durations at the higher
and lower pressure until a conformal layer 259 of a desired
thickness is reached as shown in FIG. 6D.
[0038] Accordingly, during a relatively higher chamber pressure the
percentage of deposition on the bottom 254 of the via 250 is
higher, while during a relatively lower chamber pressure the
percentage of deposition on the sidewalls 252 is higher. Thus, by
modulating the chamber pressure to vary the angular distribution of
ions, the incremental deposition to form thin sub-layers of the
final layer thickness may be controlled, thereby resulting in
conformal step coverage and void-free deposition.
[0039] The invention has utility in any physical vapor deposition
process wherein conformal step coverage or uniform filling is
needed in the deposition of tungsten (W), titanium (Ti), titanium
nitride (TiN), aluminum (Al), copper (Cu) and other materials. One
of the essential steps in metallization of copper, for example, is
the deposition of a barrier layer and seed layer to a specified
thickness on the sidewalls and bottoms of device features, e.g.,
such as vias, trenches, contacts, etc. A minimal thickness of the
barrier layer and seed layer is desired for filling the structures
by electroplating, for example. The deposition of a barrier layer
and a seed layer in a via as steps of a copper metallization scheme
is shown in FIGS. 7-11.
[0040] FIG. 7 is a cross-sectional view of a substrate 160
comprising a silicon base 168, a conducting layer 170, and a
dielectric layer 172. A via 162 defined by a bottom 164 and side-
walls 166 are formed in the dielectric layer 172. Initially, the
substrate 160 is preferably subjected to a cleaning process such as
argon bombardment and/or reactive pre-cleaning in a pre-cleaning
chamber wherein native oxides or other contaminants on the surface
are removed.
[0041] Subsequently, the substrate 160 is moved into an IMP chamber
where a barrier layer 174 is conformally deposited over the bottom
164 and sidewalls 166 of the substrate 160, as shown in FIG. 8, to
prevent a subsequently deposited seed layer and fill material from
diffusing into the underlying dielectric layer 172. The barrier
layer 174 is preferably tantalum, tantalum nitride, tungsten,
tungsten nitride, titanium nitride or combinations thereof. The
target 104 comprises the desired barrier layer material (or at
least a portion thereof) to be deposited onto the substrate 160.
The barrier layer 174 is preferably deposited to a thickness of
about 100 .ANG. to about 450 .ANG.. The substrate support member
112 is heated to a temperature of between about 100.degree. C. and
150.degree. C. A plasma gas is then introduced into the chamber 100
to stabilize the chamber pressure at a first pressure. A
medium/high density plasma is struck and maintained by supplying RF
power between about 1 kW and about 5 kW to the coil 122. A signal
is supplied to the target of about 1 kW and about 4 kW. The
resulting negative bias attracts the plasma ions to the target 104
and causes sputtering of the target 104. The sputtered target
material is then ionized through collisions with the plasma
constituents. A 13.56 MHz signal of between about 0 kW and about
500 kW is applied to the substrate 160 in order to attract the
ionized target material to the substrate 160. The pressure is
modulated between the first pressure of between about 40 mTorr and
a second pressure of between about 15 mTorr. The first higher
pressure is selected to contribute to deposition at the bottom 164
while the second lower pressure is selected to contribute to the
sidewalls 166. The modulation may be multi-stepped to form the
deposition on the bottom and sidewalls in small increments of film
thickness so as to improve the step coverage and uniformity of the
substrate layer. Further, the upper and lower pressures may each be
maintained for periods of time between about 25-30 seconds and 15
seconds, respectively.
[0042] The sequence of the pressure modulation is variable. Thus,
the modulation sequence may be initiated at the low pressure and
then increased to the higher pressure or, alternatively, the
sequence may be initiated at the high pressure and then decreased
to the low pressure. However, to avoid the formation of overhangs
on the upper comers of the features which can prevent deposition at
the bottom of the feature it is preferred that deposition is
performed at the higher pressure first and then at the lower
pressure. Accordingly, the deposition rate at the bottom of the
features is initially higher during the higher pressure step.
Subsequently, during the lower chamber pressure, the deposition
rate on the sidewalls is relatively higher.
[0043] Following deposition of the barrier layer 174, as shown in
FIG. 9, a seed layer 176 is preferably deposited in the via 162
according to the pressure modulation of the present invention to
provide a conformal film which facilitates subsequent filling of
the via with a conducting material. In one embodiment, the seed
layer 176 comprises copper which is deposited to a thickness of
about 100 .ANG. to about 450 .ANG.. A plasma is struck and
maintained to cause sputtering of the target 104 in a manner
similar to the described above with regard to deposition of the
barrier layer. Thus, a plasma gas is then introduced into the
chamber 100 to stabilize the chamber pressure at between about 20
mTorr and 60 mTorr. A target bias of about 1 kW to about 5 kW and a
coil RF power of about 1 kW to about 5 kW are delivered to the
target 104 and coil 122, respectively. A 13.56 MHz bias of about
0-450 W is applied to the substrate 160. Deposition of the seed
layer is performed while modulating the pressure between about 45
mTorr and about 15 mTorr.
[0044] Preferably, the barrier layer 174 and seed layer 176 are
deposited as a continuous process without moving the substrate 160
into an ambient environment between deposition steps, thereby
providing good adhesion between the barrier layer 174 and the seed
layer 176. In addition, good film texture of the seed layer 176
results. Thus, the substrate 160 is preferably transferred under
vacuum conditions to another IMP chamber for seed layer
deposition.
[0045] After depositing a barrier layer and a seed layer, the via
162 is filled with a conductive material 180 as shown in FIG. 10.
The conductive material 180 shown is copper and may be deposited
according to methods known in the art such as electroplating,
chemical vapor deposition and PVD, including the pressure
modulation method of the invention. In the case of electroplating,
the substrate is preferably placed in a process cell and exposed to
an electrolytic solution. A power source is coupled to the
conducting seed layer in order to attract ions from the solution.
The ions deposit on the seed layer and fill the via 162 as shown in
FIG. 10. After the via 162 is filled, the substrate 160 is
transferred to a chemical mechanical polishing system or etching
system, where the excess material is removed from the substrate 160
and the via 162 is planarized as shown in FIG. 11.
[0046] While the foregoing is directed to the preferred embodiment
of the present invention, other and further embodiments of the
invention may be devised without departing from the basic scope
thereof, and the scope thereof is determined by the claims that
follow.
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