U.S. patent application number 10/180225 was filed with the patent office on 2003-01-02 for method for achieving copper fill of high aspect ratio interconnect features.
This patent application is currently assigned to Applied Materials, Inc.. Invention is credited to Carl, Daniel A., Chen, Liang, Cheung, Robin, Chin, Barry, Ding, Peijun, Dordi, Yezdi, Hashim, Imran, Hey, Peter, Sinha, Ashok K..
Application Number | 20030000844 10/180225 |
Document ID | / |
Family ID | 24607492 |
Filed Date | 2003-01-02 |
United States Patent
Application |
20030000844 |
Kind Code |
A1 |
Carl, Daniel A. ; et
al. |
January 2, 2003 |
Method for achieving copper fill of high aspect ratio interconnect
features
Abstract
One aspect of the invention provides a consistent metal
electroplating technique to form void-less metal interconnects in
sub-micron high aspect ratio features on semiconductor substrates.
One embodiment of the invention provides a method for filling
sub-micron features on a substrate, comprising reactive precleaning
the substrate, depositing a barrier layer on the substrate using
high density plasma physical vapor deposition; depositing a seed
layer over the barrier layer using high density plasma physical
vapor deposition; and electro-chemically depositing a metal using a
highly resistive electrolyte and applying a first current density
during a first deposition period followed by a second current
density during a second period.
Inventors: |
Carl, Daniel A.;
(Pleasanton, CA) ; Chin, Barry; (Saratoga, CA)
; Chen, Liang; (Foster City, CA) ; Cheung,
Robin; (Cupertino, CA) ; Ding, Peijun; (San
Jose, CA) ; Dordi, Yezdi; (Palo Alto, CA) ;
Hashim, Imran; (San Jose, CA) ; Hey, Peter;
(Sunnyvale, CA) ; Sinha, Ashok K.; (Palo Alto,
CA) |
Correspondence
Address: |
Patent Counsel
APPLIED MATERIALS, INC.
P.O. Box 450A
Santa Clara
CA
95052
US
|
Assignee: |
Applied Materials, Inc.
|
Family ID: |
24607492 |
Appl. No.: |
10/180225 |
Filed: |
June 26, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10180225 |
Jun 26, 2002 |
|
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09650108 |
Aug 29, 2000 |
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6436267 |
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Current U.S.
Class: |
205/183 ;
204/192.1; 204/192.15; 204/192.32; 205/186; 205/205; 257/E21.175;
257/E21.585 |
Current CPC
Class: |
H01L 21/76877 20130101;
H01L 21/2885 20130101 |
Class at
Publication: |
205/183 ;
205/205; 205/186; 204/192.1; 204/192.32; 204/192.15 |
International
Class: |
C23C 014/00; C23C
014/32; C23C 028/00; C23C 028/02; C25D 005/34 |
Claims
1. A method for filling sub-micron features on a substrate,
comprising: a) reactive precleaning the substrate; b) depositing a
barrier layer on the substrate using high density plasma physical
vapor deposition; c) depositing a seed layer over the barrier layer
using high density plasma physical vapor deposition; and d)
electro-chemically depositing a metal using a highly resistive
electrolyte and applying a first current density during a first
deposition period followed by a second current density during a
second period.
2. The method of claim 1 wherein the electro-chemically deposited
metal is copper.
3. The method of claim 1 wherein the step of reactive precleaning
the substrate comprises: i) introducing a preclean gas mixture
comprising 5% hydrogen and 95% helium into the chamber; ii)
maintaining chamber pressure at about 80 mTorr; iii) providing RF
power to a coil at about 450 W at 2.0 MHz; and iv) biasing a
substrate support at about 40 W.
4. The method of claim 1 wherein the step of depositing a barrier
layer comprises: i) providing about 1 kW DC power to a target; ii)
providing RF power to a coil at about 2 kW; iii) maintaining
chamber pressure at about 20 mTorr; and iv) biasing a substrate
support at about 350 W at 13.56 MHz with about a 50% duty
cycle.
5. The method of claim 1 wherein the step of depositing a seed
layer comprises: i) providing about 1 kW DC power to a target; ii)
providing RF power to a coil at between about 2 kW and about 3 kW;
iii) maintaining chamber pressure at about 40 mTorr; and iv)
maintaining temperature at about 30.degree. C.
6. The method of claim 1 wherein the metal is electro-chemically
deposited using an electrolyte comprising CuSO.sub.4 having a molar
concentration between about 0.5M and about 1.1M.
7. The method of claim I wherein the metal is electro-chemically
deposited using an electrolyte comprising HCl at a concentration
between about 50 ppm and about 100 ppm.
8. The method of claim 1 wherein the metal is electro-chemically
deposited using an electrolyte comprising a carrier additive at a
concentration between about 12.5 ml/l and about 20 ml/l.
9. The method of claim 1 wherein the metal is electro-chemically
deposited using an electrolyte comprising H.sub.2SO.sub.4 having a
concentration between about 0 and 0.2 percent.
10. The method of claim 1 wherein the first power density is at
about 2 mA/cm.sup.2 and the first period is about 18 seconds.
11. The method of claim 1 wherein the second power density is at
about 2 mA/cm.sup.2 and the second period is about 90 seconds.
12. The method of claim 1 the step of electro-chemically depositing
a metal further comprises applying a third power density to the
substrate during a third period.
13. The method of claim 1 wherein the metal is electro-chemically
deposited by flowing the electrolyte at between 2 gpm and about 4.5
gpm.
14. The method of claim 1 wherein the step of depositing the seed
layer comprises: i) depositing a first seed layer having thickness
of about 1000 .ANG.; ii) pausing for about 60 seconds; and iii)
depositing a second seed layer having thickness of about 1000
.ANG..
15. The method of claim 14 wherein the first and second seed layers
are deposited by: i) providing about 1 kW DC power to a target; ii)
providing RF power to a coil at between about 2 kW and about 3 kW;
iii) maintaining chamber pressure at about 40 mTorr; and iv)
maintaining temperature at about 30.degree. C.
16. The method of claim 15 wherein the chamber conditions are
stabilized for about 60 seconds before the first seed layer is
deposited.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The invention generally relates to semiconductor processing.
More particularly, the invention relates to metallization of
sub-micron interconnect features on a substrate.
[0003] 2. Background of the Related Art
[0004] Copper has become a choice metal for filling sub-micron,
high aspect ratio interconnect features on substrates as circuit
densities increase for the next generation of ultra large scale
integration because copper and copper alloys have lower resistivity
than aluminum and significantly higher electromigration resistance
as compared to aluminum. These characteristics are important for
supporting the higher current densities experienced at high levels
of integration and increased device speed.
[0005] The aspect ratios for the features, i.e., the ratio for the
feature height to the feature width, increases with the higher
level of integration. Many traditional deposition processes have
difficulty filling structures or features having sub-micron width
where the aspect ratio exceeds 4:1, and particularly where the
ratio exceeds 10:1. Thus, there is a great amount of ongoing effort
being directed at the formation of void-free sub-micron features
having high aspect ratios.
[0006] Despite the desirability of using copper for semiconductor
device fabrication, choices of fabrication methods for depositing
copper into very high aspect ratio features are limited because
common chemical vapor deposition processes and physical vapor
deposition processes have provided unsatisfactory results in
forming void-free sub-micron features having high aspect ratios.
Furthermore, the vapor deposition processes can be costly. As a
result, electroplating or electrochemical deposition is becoming an
accepted method for copper metallization of interconnect features
on semiconductor devices.
[0007] Metal electroplating in general is a well known art and can
be achieved by a variety of techniques. Present designs of cells
for electroplating a metal onto a substrate are generally based on
a fountain plater configuration. In the fountain plater
configuration, the semiconductor substrate is positioned above a
cylindrical electrolyte container with the plating surface facing
an opening of the cylindrical electrolyte container. The
electrolyte is pumped to flow upwardly and contact the substrate
plating surface. The substrate is electrically biased and connected
as the cathode of the plating system, and the surfaces to be plated
are electrically connected to the cathode power source to provide
the electrical current that induces the metal ions in the plating
solution to deposit onto the exposed conductive surface of the
substrate. An anode is typically disposed in the electrolyte and
electrically biased to attract the negatively charged counterparts
of the metal ions in the electrolyte. The fountain plater is
generally adequate for electroplating large, low aspect ratio
features (i.e., larger than micrometer-sized and lower than 1:1
height to width ratio). However, a number of obstacles impair
consistent electroplating of copper onto substrates having
sub-micron high aspect ratio features.
[0008] First, a continuous metal seed layer is essential for
conducting the current required to the surfaces to be plated by the
electroplating process. When a discontinuity is present in the
metal seed layer, the portion of the seed layer that is not
electrically connected to the bias power supply does not receive
deposition during the electroplating process. Currently practiced
physical vapor deposition methods encounters difficulty in forming
a continuous, uniform seed layer within a sub-micron high aspect
ratio feature. The seed layer tends to become discontinuous on the
sidewall surfaces and the bottom surface of the feature because of
the difficulty in depositing into the narrow (i.e.,
nanometer-sized) aperture width of the feature. The discontinuities
in the seed layer prevent proper electroplating of metal onto the
seed layer, resulting in defective devices on the processed
substrate.
[0009] Second, it has been difficult to deposit into sub-micron
high aspect ratio features without forming voids in the feature
because the horizontal electroplated metal growth tends to close
off the feature at the aperture opening before the feature has been
completely filled, resulting in a void forming within the feature.
A void formation in the feature changes the material and operating
characteristics of the interconnect feature, such as decreasing
electromigration resistance, and typically causes improper
operation and premature breakdown of the device. To reduce void
formation in a high aspect ratio feature, the upper corners at the
feature opening are typically rounded off by an etching process.
However, the additional etching step to round-off corners of
features increases the processing time for each substrate and
reduces throughput of the system. Furthermore, voids may still form
within the features during the deposition process even with rounded
corners at the feature opening.
[0010] Third, currently practiced electroplating methods have not
provided consistent electroplating results between sequentially
processed substrate in a single run. Also, the material properties
of the electroplated metal layer, such as grain size, orientation,
reflectivity and resistance, are not sufficiently uniform across
the deposited substrate surface of a single substrate when
processed with typical electroplating systems.
[0011] Therefore, there is a need for a consistent metal
electroplating technique to form void-less metal interconnects in
sub-micron high aspect ratio features on semiconductor substrates.
Particularly, there is a need for a method for preparing a
substrate prior to electroplating that overcomes the problems
presented by currently practiced seed layers used in electroplating
and reduces the formation of defective devices. There is also a
need for a method for electroplating a metal into sub-micron high
aspect ratio feature that provides consistent electroplating
results between sequentially processed substrate and uniform
material properties of the electroplated metal layer across the
deposited substrate surface on a single substrate.
SUMMARY OF THE INVENTION
[0012] One aspect of the invention provides a consistent metal
electroplating technique to form void-less metal interconnects in
sub-micron high aspect ratio features on semiconductor substrates.
Another aspect of the invention provides a method for preparing a
substrate prior to electroplating that overcomes the problems
presented by currently practiced seed layers used in electroplating
and reduces the formation of defective devices. Another aspect of
the invention provides a method for electroplating a metal into
sub-micron high aspect ratio feature that provides consistent
electroplating results between sequentially processed substrate and
uniform material properties of the electroplated metal layer across
the deposited substrate surface on a single substrate.
[0013] One embodiment of the invention provides a method for
filling sub-micron features on a substrate, comprising reactive
precleaning the substrate, depositing a barrier layer on the
substrate using high density plasma physical vapor deposition;
depositing a seed layer over the barrier layer using high density
plasma physical vapor deposition; and electrochemically depositing
a metal using a highly resistive electrolyte and applying a first
current density during a first deposition period followed by a
second current density during a second period.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] 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.
[0015] 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.
[0016] FIG. 1 is a flow chart illustrating one embodiment of a
method for forming an interconnect feature on a semiconductor
substrate according to the invention.
[0017] FIGS. 2A-E are partial cross sectional views of a substrate
illustrating one embodiment of a method for forming an interconnect
feature on a semiconductor substrate according to the
invention.
[0018] FIG. 3 is a schematic view of a processing system
incorporating one or more pre-clean chambers and one or more PVD
chambers.
[0019] FIG. 4 is a cross sectional view of a pre-clean chamber.
[0020] FIG. 5 is a cross sectional view of a PVD chamber useful for
forming the barrier layers and seed layers according to the
invention.
[0021] FIG. 6 is a schematic view of an electrochemical deposition
system or electroplating system 600.
[0022] FIG. 7 is a cross sectional view of an electroplating
process cell 640 useful for performing an electrochemical
deposition of the invention.
[0023] FIG. 8 is a partial cross sectional view of one embodiment
of a wafer holder assembly.
[0024] FIG. 9 is a schematic diagram of an electrolyte replenishing
system 620.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0025] FIG. 1 is a flow chart illustrating one embodiment of a
method for forming an interconnect feature on a semiconductor
substrate according to the invention. The method 100 for forming an
interconnect on a semiconductor substrate according to the
invention provides consistent results between sequentially
processed substrate and uniform material properties across the
deposited substrate surface on a single substrate. FIGS. 2A-E are
partial cross sectional views of a substrate illustrating one
embodiment of a method for forming an interconnect feature on a
semiconductor substrate according to the invention. Prior to
performing the metallization process according to the invention, a
substrate 210 having a dielectric layer 212 formed thereon is
patterned (e.g., lithography process) and etched to form
interconnect features 214 to be filled with metal. The dielectric
layer 212 may be etched to form interconnect features 214 having
substantially vertical sidewalls (i.e., without rounding off
corners of the interconnect features). The etching process may be
performed in an etch chamber such as the IPS Etch chamber available
from Applied Materials, Inc., of Santa Clara, Calif.
[0026] Referring to FIGS. 1 and 2A-2E, the method generally
comprises: reactively pre-cleaning the exposed surfaces 216 (step
102 and FIG. 2A), depositing a barrier layer 218 over the substrate
surface utilizing high density plasma physical vapor deposition
(HDP-PVD) techniques (step 104 and FIG. 2B), depositing a seed
layer 220 over the barrier layer 218 utilizing HDP-PVD techniques
(step 106 and FIG. 2C), and electroplating a metal layer 222 on the
seed layer utilizing a highly resistive electrolyte (step 108 and
FIG. 2D). The electroplated metal layer may be planarized, such as
by chemical mechanical polishing (CMP), to define a conductive
interconnect feature 230, as shown in FIG. 2E, and further
processing may be performed on the substrate to complete
fabrication of the integrated circuit. Although a via structure is
shown in FIGS. 2A-2E, it is understood that embodiments of the
invention are useful for forming various types of interconnect
features, such as lines, contacts, dual damascene structures and
other features.
[0027] The pre-clean process (step 102), the barrier layer
deposition process (step 104), and the seed layer process (step
106) may be performed on a processing system having pre-clean
chambers and deposition chambers. FIG. 3 is a schematic view of a
processing system incorporating one or more pre-clean chambers and
one or more PVD chambers. The processing system 300 is a two-staged
vacuum processing system defined by a mainframe or platform 302
having a plurality of modules or chamber attached thereto. An
example of a commercial embodiment of a two-staged vacuum
processing platform is the Endura.RTM. platform, available from
Applied Materials, Inc., Santa Clara, Calif., which is described in
U.S. Pat. No. 5,186,718, Tepman et al., hereby incorporated by
reference in its entirety. Other examples of processing systems
useful for the present invention include the Centura.RTM., the
Endura.RTM., the Producer.RTM. and the P5000.RTM. systems available
from Applied Materials, Inc., Santa Clara, Calif.
[0028] The processing system 300 includes vacuum load-lock chambers
305 and 310 attached to a first stage transfer chamber 315. The
load-lock chambers 305 and 310 maintain vacuum conditions within
the first stage transfer chamber 315 while substrates enter and
exit the processing system 300. A first robot 320 transfers
substrates between the load-lock chambers 305 and 310 and one or
more substrate processing chambers 325 and 330 attached to the
first stage transfer chamber 315. Processing chambers 325 and 330
can be configured to perform a number of substrate processing
operations, such as chemical vapor deposition (CVD), physical vapor
deposition (PVD), etch, pre-clean, degas, orientation and other
substrate processes. The first robot 320 also transfers substrates
to/from one or more transfer chambers 335 disposed between the
first stage transfer chamber 315 and a second stage transfer
chamber 340.
[0029] The transfer chambers 335 are used to maintain ultrahigh
vacuum conditions in the second stage transfer chamber 340 while
allowing substrates to be transferred between the first stage
transfer chamber 315 and the second stage transfer chamber 340. A
second robot 345 transfers substrates between the transfer chambers
335 and a plurality of substrate processing chambers 350, 355, 360
and 365. Similar to processing chambers 325 and 330, each of the
processing chambers 350 to 365 can be configured to perform a
variety of substrate processing operations. For example, the
processing chamber 350 may be a CVD chamber configured to deposit a
dielectric film; the processing chamber 355 may be an etch chamber
configured to etch apertures or openings in a dielectric film for
forming interconnect features; the processing chamber 360 may be a
PVD chamber configured to deposit a barrier film; and the
processing chamber 365 may be a PVD chamber configured to deposit a
metal film. A plurality of processing systems/platforms may be
required to perform all of the processes required to complete
manufacturing of an integrated circuit or chip. One embodiment of
the process system includes one PVD chamber configured to deposit
barrier layers and two PVD chambers configured to deposit seed
layers.
[0030] A controller 370 may control the overall operation of the
processing system 300 and the individual processes performed in
each of the substrate processing chambers. The controller 370 may
include a microprocessor or computer (not shown) and a computer
program executed by a microprocessor or computer. Substrates are
brought to vacuum load-lock chambers 305 and 310 by a conveyor belt
or robot system (not shown) controlled by the controller. The
robots 320 and 345 are also operated by the controller to transfer
substrates between the various processing chambers of the
processing system 300. Additionally, the controller 370 may control
and/or coordinate with other components or systems connected to the
processing system 300.
[0031] An example of a processing system for preparing a substrate
for an electrochemical deposition process is the Endura.RTM.
Electra.TM. Barrier and Seed System, available from Applied
Materials, Inc., Santa Clara, Calif. Although one specific
configuration of the preparation processing system is described
below, the inventors contemplate utilizing a variety of
configurations to perform the individual processes according to the
invention.
[0032] Referring back to FIG. 1, the exposed surfaces of the
substrate is pre-cleaned in step 102 prior to deposition of the
barrier layer and seed layer onto the substrate. The processing
system 300 includes one or more pre-clean chambers. FIG. 4 is a
cross sectional view of a pre-clean chamber. Generally, the
pre-clean chamber 410 has a substrate support member 412 disposed
in a chamber enclosure 414 under a quartz dome 416. The substrate
support member 412 includes a central pedestal plate 418 disposed
within a recess 420 on a quartz insulator plate 422. The upper
surface of the central pedestal plate 418 typically extends above
the upper surface of the quartz insulator plate 422. A gap 424,
typically between about 5 mils and 15 mils, is formed between a
bottom surface of the substrate 426 and the top surface of the
quartz insulator plate 422. During processing, the substrate 426 is
placed on the central pedestal plate 18 and located thereon by
positioning pin 432. The peripheral portion of the substrate 26
extends over the quartz insulator plate 422 and overhangs the upper
edge of the quartz insulator plate 422. A beveled portion 428 of
the quartz insulator plate 422 is disposed below this overhanging
peripheral portion of the substrate 426, and a lower annular flat
surface 430 extends from the lower outer edge of the beveled
portion 428. The insulator plate 422 and the dome 416 may comprise
other dielectric materials, such as aluminum oxide and silicon
nitride, and the insulator plate 422 and the dome 416 are typically
parts of a process kit that system operators periodically replace
during routine maintenance.
[0033] The process for pre-cleaning the substrate 426 in the
pre-clean chamber 410 may involve a reactive process and/or a
sputter-etching process using the substrate 426 as the sputtering
target. Generally, the reactive pre-clean process (step 104) may be
performed on the substrate by introducing a pre-clean gas mixture
comprising hydrogen (between about 0% and about 10%) and helium
(between about 90% and about 100%) into the chamber and providing
RF power (between about 300 W and about 600 W at about 1 to 4 MHz)
to a plasma generation coil. The substrate support may be biased
between about 10 and 100 W. The chamber pressure may be maintained
between about 40 mTorr and 200 mTorr during the pre-clean process.
The reactive pre-clean process may be carried out for between about
30 seconds and 120 seconds. After the pre-clean process, the
substrate is transferred to a high density plasma physical vapor
deposition chamber for deposition of a barrier layer and a seed
layer over the surfaces of the substrate.
[0034] In one embodiment of the invention, the reactive pre-clean
process (step 104) is performed on the substrate by introducing a
pre-clean gas mixture comprising 5% hydrogen and 95% helium into
the chamber and providing RF power to a coil at about 450 W at
about 2.0 MHz. The substrate support is biased at about 40 W. The
chamber pressure is maintained at about 80 mTorr during the
pre-clean process. The reactive pre-clean process is carried out
for about 60 seconds. After the pre-clean process, the substrate is
transferred to a high density plasma physical vapor deposition
chamber for deposition of a barrier layer (step 104) and a seed
layer (step 106) over the surfaces of the substrate.
[0035] Referring back to FIG. 3, the processing system includes one
or more physical vapor deposition (PVD) chambers configured to
deposit barrier layers and one or more PVD chambers configured to
deposit seed layers. To enhance efficiency and throughput of the
system, one configuration of the processing system includes one
physical vapor deposition (PVD) chamber configured to deposit
barrier layers and two PVD chambers configured to deposit seed
layers disposed in connection to the back-end central transfer
chamber.
[0036] FIG. 5 is a cross sectional view of a PVD chamber useful for
forming the barrier layers and seed layers according to the
invention. An example of a PVD chamber is the Electra IMP.TM.
chamber, available from Applied Materials, Inc., Santa, Clara,
Calif. Although the invention is described utilizing ionized metal
plasma (IMP) chambers, the inventors contemplates utilizing other
PVD chambers, including medium and high density plasma PVD
chambers, to form the barrier layers and the seed layers according
to the invention.
[0037] Referring to FIG. 5, the PVD chamber 500 generally includes
a chamber enclosure 502, a substrate support member 504, a target
506, a shield 508 and a coil 510. The target 506 is disposed
opposite of the substrate support member 504 and is electrically
connected to a power supply 512. The shield 508 generally surrounds
the region between the target 506 and the substrate support member
504 and is typically connected to a ground connection. The coil 510
is disposed interior of the shield 508 and is connected to an RF
power supply 514. A gas inlet 516 disposed through the enclosure
502 introduces one or more processing gases into the chamber during
processing. A chamber outlet 532 is disposed through a bottom
portion of the enclosure 502 and attached to an exhaust system
which maintains desired chamber pressure during processing.
[0038] The substrate support member 504 is attached to an actuator
shaft 518 disposed through the bottom of the enclosure 502. The
actuator shaft 518 is connected to an actuator 520 which
facilitates movement of the substrate support member 504 to various
positions in the chamber. A slit valve 526 disposed on a sidewall
of the enclosure 502 facilitates transfer of substrates into and
out of the chamber. A substrate lift assembly 522 disposed relative
to the substrate support member 504 facilitates positioning of a
substrate onto and off of the substrate support member 504. The
substrate support member 504 may include temperature controls, such
as cooling fluid channels, disposed adjacent the substrate support
surface to maintain substrate temperature at a desired temperature
during processing. The substrate support member 504 may be
connected to a substrate support bias power supply 530. An example
of a substrate support member useful for depositing seed layers
according one embodiment of the invention is the LT-BESC.TM. (Low
Temperature Biasable Electrostatic Chuck) from Applied Materials,
Inc., of Santa Clara, Calif. During processing, the substrate
support member 504 positions a substrate disposed thereon to a
position below a cover ring 524 disposed on a lower portion of the
shield 508 to shield the perimeter edge of the substrate from
deposition.
[0039] To achieve conformal coverage of surfaces within high aspect
ratio features, the barrier layer according to one embodiment of
the invention may be deposited using the following processing
parameters in an ionized metal plasma physical vapor deposition
chamber. The chamber pressure during the deposition process may be
maintained at between about 5 mT to about 100 mT, preferably
between about 10 mT and about 30 mT. The target may be DC-biased at
between about 1 kW and about 3 kW with a bias voltage between about
100 V and about 300 V. The coil may be RF-biased at between about 1
kW and about 3 kW. The substrate support member may provide a
substrate bias at between about 0 W and about 500 W with a bias
voltage between about 50 V and about 300 V.
[0040] In one embodiment, a barrier layer comprising tantalum (Ta)
is deposited utilizing the following chamber operating parameters.
The target is DC-biased at about 1 kW DC power to a target. The
coil is RF-biased at about 2 kW. The chamber pressure is maintained
at about 20 mTorr. The substrate support is biased at about 350W at
about 13.56 MHz with an about 50% duty cycle. For a feature having
less than about 0.35 .mu.m opening width and >4:1 height to
width aspect ratio, the barrier layer deposition process is carried
out for about 18 seconds to deposit a barrier layer having about
150 .ANG. film thickness on the surfaces of the interconnect
feature.
[0041] A seed layer is deposited over the barrier to provide
surfaces from which the electrochemical deposition may occur.
During the electro-deposition process, the seed layer is
electrically connected to a power supply of the electroplating
system. To achieve conformal coverage of surfaces within high
aspect ratio features, the seed layer according to one embodiment
of the invention may be deposited using the following processing
parameters in an ionized metal plasma physical vapor deposition
chamber. The chamber pressure during the deposition process may be
maintained at between about 5 mT to about 100 mT, preferably
between about 30 mT and about 50 mT. The target may be DC-biased at
between about 1 kW and about 3 kW with a bias voltage between about
100 V and about 300 V. The coil may be RF-biased at between about 1
kW and about 5 kW. The substrate support member may provide a
substrate bias at between about 0 W and about 500 W with a bias
voltage between about 50 V and about 300 V.
[0042] In one embodiment of the invention, the step of depositing a
seed layer comprises: providing about 1 kW DC power to a target;
providing RF power to a coil at between about 2 kW and about 3 kW;
maintaining chamber pressure at about 40 mTorr; and maintaining
substrate support temperature at about 30 C. The substrate support
is biased at about 350 W at about 13.56 MHz with an about 50% duty
cycle. For a feature having less than about 0.35 .mu.m opening
width and >4:1 height:width aspect ratio, the seed layer
deposition process is carried out for about 50 seconds to deposit
about a barrier layer having about 2000 .ANG. film thickness.
[0043] In another embodiment of the invention, the electroplating
process may be enhanced by a two-step seed layer process. The above
described seed layer deposition is performed by depositing 1000
.ANG. of seed layer material, pausing for between about 30 seconds
and about 120 seconds, and depositing another 1000 .ANG., utilizing
similar processing parameters. Additionally, the gas input and
chamber pressure of the PVD chamber may be stabilized for about
30-120 seconds before the deposition of the seed layer. After
deposition of the seed layer on the substrate, the substrate may be
transferred to an electrochemical deposition system to complete
metallization of the interconnect features.
[0044] FIG. 6 is a schematic view of an electrochemical deposition
system or electroplating system 600. The electroplating system 600
generally comprises a loading station 610, a mainframe 614, and an
electrolyte replenishing system 620. The electroplating system
platform 600 may be enclosed in a clean environment using panels
such as plexiglass panels. Additionally, the mainframe 614 may be
separated from the loading station 610 by plexiglass panels to
separate the wet processing regions on the mainframe and the dry
regions on the loading station. Slit valves or other door
mechanisms disposed on the plexiglass panels may be utilized to
facilitate substrate transfers on the system. The mainframe 614
generally comprises a centrally located mainframe transfer robot
616, a spin-rinse-dry (SRD) station 612, and a plurality of
processing stations 618. Each processing station 618 may include
one or more processing cells 640. An electrolyte replenishing
system 620 is positioned adjacent the mainframe 614 and connected
to the process cells 640 individually to circulate electrolyte used
for the electroplating process. The electroplating system 600 also
includes a control system 622, typically comprising a programmable
microprocessor, which controls operation of all components of the
electroplating system.
[0045] The loading station 610 may include one or more wafer
cassette receiving areas 624, one or more loading station transfer
robots 628 and at least one wafer orientor 630. The number of wafer
cassette receiving areas, loading station transfer robots and wafer
orientor disposed in the loading station 610 may be configured
according to the desired throughput of the system. As shown for the
embodiment, the loading station 610 includes two wafer cassette
receiving areas 624, two loading station transfer robots 628 and
one wafer orientor 630. A wafer cassette 632 containing wafers or
substrates 634 is loaded onto the wafer cassette receiving area 624
to introduce wafers 634 into the electroplating system. The loading
station transfer robot 628 transfers wafers 634 between the wafer
cassette 632 and the wafer orientor 630. The loading station
transfer robot 628 comprises a typical transfer robot commonly
known in the art. The wafer orientor 630 positions each wafer 634
in a desired orientation to ensure that the wafer is properly
processed. The loading station transfer robot 628 also transfers
wafers 634 between the loading station 610 and the mainframe 614.
In an alternative embodiment having one or more thermal anneal
chambers 611 disposed adjacent the loading station, the loading
station transfer robot 628 also transfers wafers 634 between the
loading station 610 and the thermal anneal chambers. A detailed
description of an electroplating system having an anneal chamber is
provided in commonly assigned U.S. patent application Ser. No.
09/289,074, by Dordi et al., entitled ELECTRO-CHEMICAL DEPOSITION
SYSTEM, filed on Apr. 8, 1999, which is hereby incorporated by
reference in its entirety.
[0046] In the embodiment shown in FIG. 6, the SRD station 612 is
disposed on the mainframe 614 at a position adjacent the loading
station 610. One or more pass-through cassettes 638 may be disposed
above the SRD station 612 to facilitate wafer transfers between the
loading station 610 and the mainframe 614. Wafers may be placed on
and removed from slots in the pass-through cassettes by the loading
station transfer robot 628 and the mainframe transfer robot 616. In
one embodiment, the mainframe transfer robot 616 comprises a
plurality of individual robot arms 644 that provides independent
access of wafers in the processing stations 618, the pass-through
cassettes and the SRD station 612. One embodiment of an SRD chamber
is described in commonly assigned U.S. patent application Ser. No.
09/201,566, by Lloyd et al., entitled SPIN-RINSE-DRYING PROCESS FOR
ELECTROPLATED SEMICONDUCTOR WAFERS, filed on Nov. 30, 1998, which
is hereby incorporated by reference in its entirety.
[0047] The electroplating system 600 may include a plurality of
processing stations to accomplish the desired throughput and
efficiency requirements. As shown in FIG. 6, the electroplating
system 600 includes two processing stations 618, and each
processing station 618 includes two processing cells 640. The
mainframe transfer robot 616 serves to transfer wafers between
different stations disposed on the mainframe, including the
processing stations 618, the pass-through cassettes, and the SRD
stations 612. As shown in FIG. 6, the mainframe transfer robot 616
comprises two robot arms 642, corresponding to the number of
processing cells 640 per processing station 618. Each robot arm 642
may be operable independently of the other arm to facilitate
independent transfers of wafers in the system. Alternatively, the
robot arms 642 operate in a linked fashion such that one robot
extends as the other robot arm retracts. A flipper robot 644 is
attached as an end effector for each of the robot arms 642. Flipper
robots are generally known in the art and can be attached as end
effectors for wafer handling robots. An example of a flipper robot
is the model RR701, available from Rorze Automation, Inc., located
in Milpitas, Calif. A vacuum gripper 654 may be disposed on the end
effector to securely hold a wafer in a flipped position. The main
transfer robot 616 which has a flipper robot as the end effector is
capable of transferring substrates between different stations
disposed on the mainframe as well as flipping the substrate being
transferred to the desired surface orientation, i.e., substrate
processing surface being face-down for the electroplating process.
In one embodiment, the mainframe transfer robot 616 provides
independent robot motion along the X-Y-Z axes by the robot arm 642
and independent substrate flipping rotation by the flipper robot
end effector 644. By incorporating the flipper robot 644 as the end
effector, the mainframe transfer robot 616 may transfer a wafer
from a processing surface up position in the pass-through cassette
to a process surface down position in the electroplating process
cell.
[0048] FIG. 7 is a cross sectional view of an electroplating
process cell 640 useful for performing an electrochemical
deposition of the invention. The electroplating process cell 640
generally comprises a head assembly 710, a process kit 720 and an
electrolyte collector 740. Preferably, the electrolyte collector
740 is secured onto the body 742 of the mainframe 614 over an
opening 743 that defines the location for placement of the process
kit 720. The electrolyte collector 740 includes an inner wall 746,
an outer wall 748 and a bottom 747 connecting the walls. An
electrolyte outlet 749 is disposed through the bottom 747 of the
electrolyte collector 640 and connected to the electrolyte
replenishing system 620 (shown in FIG. 6) through tubes, hoses,
pipes or other fluid transfer connectors.
[0049] The head assembly 710 is mounted onto a head assembly frame
752. The head assembly frame 752 includes a mounting post 754, a
post cover 755, and a cantilever arm 756. The mounting post 754 is
mounted onto the body of the mainframe 614, and the post cover 755
covers a top portion of the mounting post 754. The process head
assembly 710 may be a rotatable head assembly having a rotational
actuator is disposed on the cantilevered arm and attached to the
head assembly to rotate the head assembly during wafer processing.
In one embodiment, the mounting post 754 provides rotational
movement (as indicated by arrow A1) with respect to a vertical axis
along the mounting post to allow rotation of the head assembly
frame 752. The cantilever arm 756 extends laterally above the
mounting post 754 and is pivotally connected to the post cover 755
at the pivot joint 759. The rotatable head assembly 710 is attached
to a mounting slide 760 disposed at the distal end of the
cantilever arm 756. The mounting slide 760 guides the vertical
motion of the head assembly 710. A head lift actuator 758 is
disposed on top of the mounting slide 760 to provide vertical
displacement of the head assembly 710.
[0050] One end of the cantilever arm 756 is connected to the shaft
753 of a cantilever arm actuator 757, such as a pneumatic cylinder
or a lead-screw actuator, mounted on the mounting post 754. The
cantilever arm actuator 757 provides pivotal movement (as indicated
by arrow A2) of the cantilever arm 756 with respect to the pivot
joint 759 between the cantilever arm 756 and the post cover 755.
When the cantilever arm actuator 757 is retracted, the cantilever
arm 756 moves the head assembly 710 away from the process kit 720
to provide the spacing required to remove and/or replace the
process kit 720 from the electroplating process cell 740. When the
cantilever arm actuator 757 is extended, the cantilever arm 756
moves the head assembly 710 toward the process kit 720 to position
the wafer in the head assembly 710 in a processing position. The
cantilever arm actuator 757 may also be used to control the entry
angle of a wafer as the wafer is lowered into contact with the
electrolyte at the beginning of the electroplating process.
[0051] The head assembly 710 may include a rotating actuator 764
slideably connected to the mounting slide 760. The shaft 768 of the
head lift actuator 758 is inserted through a lift guide 766
attached to the body of the rotating actuator 764. In one
embodiment, the shaft 768 is a lead-screw type shaft that moves the
lift guide 766 (as indicated by arrows A3) between various vertical
position. The rotating actuator 764 is connected to the wafer
holder assembly 750 through the shaft 770 and rotates the wafer
holder assembly 750 (as indicated by arrows A4). The wafer holder
assembly 750 includes a bladder assembly for holding a wafer and a
cathode contact ring for providing electrical contact to a seed
layer on a wafer.
[0052] The rotation of the wafer during the electroplating process
may enhance the deposition results. However, rotation of the head
assembly may not be necessary to achieve uniform electroplating
deposition, particularly where the uniformity of electroplating
deposition is achieved by adjusting the processing parameters, such
as the electrolyte chemistry, electrolyte flow and other
parameters.
[0053] The head assembly may also be rotated as the head assembly
is lowered to position the wafer in contact with the electrolyte in
the process cell as well as when the head assembly is raised to
remove the wafer from the electrolyte in the process cell. The head
assembly may be rotated at a high speed (i.e., >20 rpm) after
the head assembly is lifted from the process cell to enhance
removal of residual electrolyte on the head assembly.
[0054] The wafer holder assembly 750 generally comprises a wafer
holder 724 and a cathode contact ring 722. In general, the contact
ring 722 comprises an annular body having a plurality of conducting
members disposed thereon. The annular body is constructed of an
insulating material to electrically isolate the plurality of
conducting members. Together the body and conducting members form a
diametrically interior substrate seating surface which, during
processing, supports a substrate and provides a current
thereto.
[0055] FIG. 8 is a partial cross sectional view of one embodiment
of a wafer holder assembly. The wafer holder assembly 750 includes
a wafer holder 724 which secures a substrate in contact with the
contact ring 722. The contact ring 722 includes an annular body
portion 819 and a contact portion 817 extending from the body
portion 819 to provide electrical contact with a seed layer on a
substrate plating surface 824. The wafer holder 724 includes a
bladder assembly 870 having an inflatable bladder 836 attached to a
back surface of an intermediary wafer holder plate 810. In one
embodiment, a portion of the inflatable bladder 836 is sealingly
attached to the back surface 812 of the intermediary wafer holder
plate 810 using an adhesive or other bonding material. The front
surface 814 of the intermediary wafer holder plate 810 is adapted
to receive a wafer or substrate 821 to be processed, and an
elastomeric o-ring 816 is disposed in an annular groove 818 on the
front surface 814 of the intermediary wafer holder plate 810 to
contact a peripheral portion of the wafer back surface. The
elastomeric o-ring 816 provides a seal between the wafer back
surface and the front surface of the intermediary wafer holder
plate 810. The intermediary wafer holder plate 810 may include a
plurality of bores or holes 820 extending through the plate that
are in fluid communication with a vacuum port to facilitate
securing the wafer on the wafer holder using a vacuum force applied
to the backside of the wafer. The inflatable bladder does not
directly contact a wafer being processed, and thus the risk of
cutting or damaging the inflatable bladder during wafer transfers
is significantly reduced. The elastomeric O-ring 816 is preferably
coated or treated to provide a hydrophilic surface (as discussed
above for the surfaces of the cathode contact ring) for contacting
the wafer, and the elastomeric O-ring 816 is replaced as needed to
ensure proper contact and seal to the wafer.
[0056] Referring back to FIG. 7, the process kit 720 is positioned
below the wafer holder assembly 750. The process kit 720 generally
comprises a bowl 730, a container body 772, an anode assembly 774
and a filter 776. The anode assembly 774 may be disposed below the
container body 772 and attached to a lower portion of the bowl 730,
and the filter 776 is disposed between the anode assembly 774 and
the container body 772. The container body 772 may be a cylindrical
body comprised of an electrically insulative material, such as
ceramics, plastics, plexiglass (acrylic), lexane, PVC, CPVC, and
PVDF. Alternatively, the container body 772 can be made from a
metal, such as stainless steel, nickel and titanium, which is
coated with an insulating layer, such as Teflon.TM., PVDF, plastic,
rubber and other combinations of materials that do not dissolve in
the electrolyte and can be electrically insulated from the
electrodes (i.e., the anode and cathode of the electroplating
system). The container body 772 is sized and adapted to conform to
the wafer plating surface and the shape of the of a wafer being
processed through the system, typically circular or rectangular in
shape. One embodiment of the container body 772 comprises a
cylindrical ceramic tube having an inner diameter that has about
the same dimension as or slightly larger than the wafer
diameter.
[0057] An upper portion of the container body 772 extends radially
outwardly to form an annular weir 778. The weir 778 extends over
the inner wall 746 of the electrolyte collector 740 and allows the
electrolyte to flow into the electrolyte collector 740. The upper
surface of the weir 778 may be disposed at the same level or higher
than the contact surface of the cathode contact ring 722 during
processing to ensure electrolyte contact to the wafer plating
surface. In one embodiment, the upper surface of the weir 778
includes an inner annular flat portion 780, a middle inclined
portion 782 and an outer declined portion 784. When a wafer is
positioned in the processing position, the wafer plating surface is
positioned in the cylindrical opening of the container body 772,
and a gap for electrolyte flow is formed between the lower surface
of the cathode contact ring 722 and the upper surface of the weir
778. The lower surface of the cathode contact ring 722 may be
disposed above the inner flat portion 780 and the middle inclined
portion of the weir 778. The outer declined portion 784 is sloped
downwardly to facilitate flow of the electrolyte into the
electrolyte collector 740.
[0058] A lower portion of the container body 772 extends radially
outwardly to form a lower annular flange 786 for securing the
container body 772 to a flange 741 on the body 742 of the mainframe
614. The outer dimension (i.e., circumference) of the annular
flange 786 is smaller than the dimensions of the opening 743 on the
body 742 of the mainframe 614 and the inner circumference of the
electrolyte collector 740 to allow removal and replacement of the
process kit 720 from the electroplating process cell 640. In one
embodiment, a plurality of bolts 788 are fixedly disposed on the
annular flange 786 and extend downwardly through matching bolt
holes 789 on the body 742 of the mainframe 614, and a plurality of
removable fastener nuts 790 secure the process kit 720 onto the
body 742 of the mainframe 614. The nuts/bolts combination
facilitates fast and easy removal and replacement of the components
of the process kit 720 during maintenance.
[0059] The bowl 730 is secured onto the annular flange 786 of the
container body 772 radially inwardly of the flange 741 of the body
742 of the mainframe 614. The bowl 730 generally comprises a
cylindrical portion 732 and a bottom portion 734. An upper annular
flange 736 extends radially outwardly from the top of the
cylindrical portion 732. The upper annular flange 736 includes a
plurality of holes 737 that matches the number of bolts 738
extending from the lower annular flange 786 of the container body
772. To secure the upper annular flange 736 of the bowl 730 and the
lower annular flange 786 of the container body 772, the bolts 738
are inserted through the holes 737, and fastener nuts 739 are
fastened onto the bolts 738. A seal 787, such as an elastomer
O-ring, is disposed between container body 772 and the bowl 730
radially inwardly from the bolts 788 to prevent leaks from the
process kit 720. The outer dimension (i.e., circumference) of the
upper annular flange 736 is smaller than the inner dimensions of
the flange 741 of the body 742 on the main frame 614 to facilitate
installation or removal of the bowl 730 from the container body
772.
[0060] The filter 776 may be attached to and completely covers the
lower opening of the container body 772 (or the upper opening of
the bowl 730). The filter 776 may keep contaminate particles from
reaching the substrate plating surface. The filter 776 may also be
utilized to provide a desired electrolyte flow pattern to the
substrate plating surface to enhance plating results.
[0061] An anode assembly 774 is disposed below the filter 776 in
the bowl 730 and may be removably secured to the bowl 730. The
anode assembly 774 comprises a consumable anode that serves as a
metal source in the electrolyte. Alternatively, the anode assembly
774 comprises a non-consumable anode, and the metal to be
electroplated is supplied within the electrolyte from the
electrolyte replenishing system 620. As shown in FIG. 7, the anode
assembly 774 includes a metal source 796, an anode enclosure 794,
and a filter membrane 778. The filter membrane 778 may comprise a
hydrophilic membrane which filters byproducts (e.g., anode sludge)
from the dissolution of the metal source 796 and other undesired
particles. The metal source 796 may comprise a soluble metal plate,
such as high purity copper plate for electrochemical deposition of
copper. Alternatively, the metal source 776 may comprise metal
particles enclosed in a porous anode enclosure or a perforated
metal sheet.
[0062] One or more anode electrode contacts 798 are inserted
through the anode enclosure 794 to provide electrical connection to
the metal source 796 from a power supply. The anode electrode
contact 798 may be made from a conductive material that is
insoluble in the electrolyte, such as titanium, platinum and
platinum-coated stainless steel. The anode electrode contact 798
extends through the bowl 730 and is connected to an electrical
power supply. In one embodiment, the anode electrical contact 798
includes a threaded portion 797 for a fastener nut 799 to secure
the anode electrical contact 798 to the bowl 730, and a seal, such
as an elastomer washer, may be disposed between the fastener nut
799 and the bowl 730 to prevent leaks from the process kit 720.
[0063] The anode enclosure 794 includes an electrolyte inlet 791
which is connected to an electrolyte supply line 702 through the
bottom portion 734 of the bowl 730. The anode enclosure 794 also
includes an electrolyte outlet 792 which is connected to the
electrolyte replenishing system 620. The electrolyte inlet/outlet
of the anode assembly facilitates metal dissolution from the
soluble metal of the metal source 796.
[0064] The process bowl 730 includes an electrolyte inlet 704 which
may be releasably connected to an electrolyte supply line 702. The
electrolyte supply line 702 provides the main electrolyte flow into
the electroplating cell for facilitating the electrochemical
deposition. The electrolyte inlet 704 and the electrolyte supply
line 702 may be connected by a releasable connector that
facilitates easy removal and replacement of the process kit 720.
When the process kit 720 needs maintenance, the electrolyte is
drained from the process kit 720, and the electrolyte flow in the
electrolyte supply line is discontinued and drained. The connector
for the electrolyte supply line is released from the electrolyte
inlet 704, and the electrical connection to the anode assembly 774
is also disconnected. The head assembly 710 is raised or rotated to
provide clearance for removal of the process kit 720. The process
kit 720 is then removed from the mainframe 614, and a new or
reconditioned process kit is replaced into the mainframe 614.
[0065] Alternatively, the bowl 730 along with the anode and the
filter may be removed from the container body 772 for maintenance.
In this case, the nuts securing the bowl 730 and the container body
772 and the nuts securing the anode assembly 774 to the bowl 730
are removed to facilitate removal of the bowl 730 and the anode
assembly 774. New or reconditioned anode assembly may be placed and
secured to the bowl 730, and the bowl 730 may be re-secured onto
the container body 772.
[0066] FIG. 9 is a schematic diagram of an electrolyte replenishing
system 620. The electrolyte replenishing system 620 provides the
electrolyte to the electroplating process cells for the
electroplating process. The electrolyte replenishing system 620
generally comprises a main electrolyte tank 902, a dosing module
903, a filtration module 905, a chemical analyzer module 916, and
an electrolyte waste disposal system 922 connected to the analyzing
module 916 by an electrolyte waste drain 920. One or more
controllers control the composition of the electrolyte in the main
tank 902 and the operation of the electrolyte replenishing system
620. The controllers are independently operable but integrated with
the control system 622 of the electroplating system platform
600.
[0067] The main electrolyte tank 902 provides a reservoir for
electrolyte and includes an electrolyte supply line 912 that is
connected to each of the electroplating process cells through one
or more fluid pumps 908 and valves 907. A heat exchanger 924 or a
heater/chiller disposed in thermal connection with the main tank
902 controls the temperature of the electrolyte stored in the main
tank 902. The heat exchanger 924 is connected to and operated by
the controller 910.
[0068] The dosing module 903 is connected to the main tank 902 by a
supply line and includes a plurality of source tanks 906, or feed
bottles, a plurality of valves 909, and a controller 911. The
source tanks 906 contain the chemicals needed for composing the
electrolyte and typically include a deionized water source tank and
copper sulfate (CuSO.sub.4) source tank for composing the
electrolyte. Other source tanks 906 may contain hydrogen sulfate
(H.sub.2SO.sub.4), hydrogen chloride (HCI) and various additives
such as glycol. Each source tank is preferably color coded and
fitted with a unique mating outlet connector adapted to connect to
a matching inlet connector in the dosing module. By color coding
the source tanks and fitting the source tanks with unique
connectors, errors caused by human operators when exchanging or
replacing the source tanks are significantly reduced.
[0069] The deionized water source tank preferably also provides
deionized water to the system for cleaning the system during
maintenance. The valves 909 associated with each source tank 906
regulate the flow of chemicals to the main tank 902 and may be any
of numerous commercially available valves such as butterfly valves,
throttle valves and the like. Activation of the valves 909 is
accomplished by the controller 911 which is preferably connected to
the system control 622 to receive signals therefrom.
[0070] The electrolyte filtration module 905 includes a plurality
of filter tanks 904. An electrolyte return line 914 is connected
between each of the process cells and one or more filter tanks 904.
The filter tanks 904 remove the undesired contents in the used
electrolyte before returning the electrolyte to the main tank 902
for re-use. The main tank 902 is also connected to the filter tanks
904 to facilitate re-circulation and filtration of the electrolyte
in the main tank 902. By re-circulating the electrolyte from the
main tank 902 through the filter tanks 904, the undesired contents
in the electrolyte are continuously removed by the filter tanks 904
to maintain a consistent level of purity. Additionally,
re-circulating the electrolyte between the main tank 902 and the
filtration module 905 allows the various chemicals in the
electrolyte to be thoroughly mixed.
[0071] The electrolyte replenishing system 620 also includes a
chemical analyzer module 916 that provides real-time chemical
analysis of the chemical composition of the electrolyte. The
analyzer module 916 is fluidly coupled to the main tank 902 by a
sample line 913 and to the waste disposal system 922 by an outlet
line 921. The analyzer module 916 generally comprises at least one
analyzer and a controller to operate the analyzer. The number of
analyzers required for a particular processing tool depends on the
composition of the electrolyte. For example, while a first analyzer
may be used to monitor the concentrations of organic substances, a
second analyzer is needed for inorganic chemicals. In the specific
embodiment shown in FIG. 9, the chemical analyzer module 916
comprises an auto titration analyzer 915 and a cyclic voltametric
stripper (CVS) 917. Both analyzers are commercially available from
various suppliers. An auto titration analyzer which may be used to
advantage is available from Parker Systems and a cyclic voltametric
stripper is available from ECI. The auto titration analyzer 915
determines the concentrations of inorganic substances such as
copper chloride and acid. The CVS 917 determines the concentrations
of organic substances such as the various additives which may be
used in the electrolyte and by-products resulting from the
processing which are returned to the main tank 902 from the process
cells.
[0072] The analyzer module shown FIG. 9 is merely illustrative. In
another embodiment, each analyzer may be coupled to the main
electrolyte tank by a separate supply line and be operated by
separate controllers. Persons skilled in the art will recognize
other embodiments.
[0073] In operation, a sample of electrolyte is flowed to the
analyzer module 916 via the sample line 913. Although the sample
may be taken periodically, preferably a continuous flow of
electrolyte is maintained to the analyzer module 916. A portion of
the sample is delivered to the auto titration analyzer 915 and a
portion is delivered to the CVS 917 for the appropriate analysis.
The controller 919 initiates command signals to operate the
analyzers 915, 917 in order to generate data. The information from
the chemical analyzers 915, 917 is then communicated to the control
system 622. The control system 622 processes the information and
transmits signals which include user-defined chemical dosage
parameters to the dosing controller 911. The received information
is used to provide real-time adjustments to the source chemical
replenishment rates by operating one or more of the valves 909
thereby maintaining a desired, and preferably constant, chemical
composition of the electrolyte throughout the electroplating
process. The waste electrolyte from the analyzer module is then
flowed to the waste disposal system 922 via the outlet line
921.
[0074] Although a preferred embodiment utilizes real-time
monitoring and adjustments of the electrolyte, various alternatives
may be employed according to the present invention. For example,
the dosing module 903 may be controlled manually by an operator
observing the output values provided by the chemical analyzer
module 916. The system software may allow for both an automatic
real-time adjustment mode as well as an operator (manual) mode.
Further, although multiple controllers are shown in FIG. 9, a
single controller may be used to operate various components of the
system such as the chemical analyzer module 916, the dosing module
903, and the heat exchanger 924. Other embodiments will be apparent
to those skilled in the art.
[0075] The electrolyte replenishing system 620 also includes an
electrolyte waste drain 920 connected to an electrolyte waste
disposal system 922 for safe disposal of used electrolytes,
chemicals and other fluids used in the electroplating system. The
electroplating cells may include a direct line connection to the
electrolyte waste drain 920 or the electrolyte waste disposal
system 922 to drain the electroplating cells without returning the
electrolyte through the electrolyte replenishing system 620. The
electrolyte replenishing system 620 may also includes a bleed off
connection to bleed off excess electrolyte to the electrolyte waste
drain 920.
[0076] The electrolyte replenishing system 220 may also include one
or more degasser modules 930 adapted to remove undesirable gases
from the electrolyte. The degasser module generally comprises a
membrane that separates gases from the fluid passing through the
degasser module and a vacuum system for removing the released
gases. The degasser modules 930 may be placed in line on the
electrolyte supply line 912 adjacent to the process cells 640. The
degasser modules 930 may be positioned as close as possible to the
process cells 640 so that most of the gases from the electrolyte
replenishing system are removed by the degasser modules before the
electrolyte enters the process cells. In one embodiment, each
degasser module 930 includes two outlets to supply degassed
electrolyte to the two process cells 640 of each processing station
618. Alternatively, a degasser module 930 is provided for each
process cell. The degasser modules can be placed at many other
alternative positions. For example, the degasser module can be
placed at other positions in the electrolyte replenishing system,
such as along with the filter section or in a closed-loop system
with the main tank or with the processing cell. As another example,
one degasser module is placed in line with the electrolyte supply
line 912 to provide degassed electrolyte to all of the process
cells 640 of the electrochemical deposition system. Additionally, a
separate degasser module is positioned in-line or in a closed-loop
with the deionized water supply line and is dedicated for removing
oxygen from the deionized water source. Because deionized water is
used to rinse the processed substrates, free oxygen gases are
preferable removed from the deionized water before reaching the SRD
modules so that the electroplated copper is less likely to become
oxidized by the rinsing process. Degasser modules are well known in
the art and commercial embodiments are generally available and
adaptable for use in a variety of applications. Commercially
available degasser modules are available from Millipore
Corporation, located in Bedford, Mass.
[0077] Although not shown in FIG. 9, the electrolyte replenishing
system 620 may include a number of other components. For example,
the electrolyte replenishing system 620 preferably also includes
one or more additional tanks for storage of chemicals for a wafer
cleaning system, such as the SRD station. Double-contained piping
for hazardous material connections may also be employed to provide
safe transport of the chemicals throughout the system. Optionally,
the electrolyte replenishing system 620 includes connections to
additional or external electrolyte processing system to provide
additional electrolyte supplies to the electroplating system.
[0078] Referring back to FIG. 6, the electroplating system platform
600 includes a control system 622 that controls the functions of
each component of the platform. The control system 222 may be
mounted above the mainframe 614 and comprises a programmable
microprocessor. The programmable microprocessor is typically
programmed using a software designed specifically for controlling
all components of the electroplating system platform 600. The
control system 622 also provides electrical power to the components
of the system and includes a control panel that allows an operator
to monitor and operate the electroplating system platform 600. The
control panel may be a stand-alone module that is connected to the
control system 622 through a cable and provides easy access to an
operator. Generally, the control system 622 coordinates the
operations of the loading station 610, the SRD station 612, the
mainframe 614 and the processing stations 618. Additionally, the
control system 622 coordinates with the controller of the
electrolyte replenishing system 620 to provide the electrolyte for
the electroplating process.
[0079] The following is a description of a typical wafer
electroplating process sequence through the electroplating system
platform 600 as shown in FIG. 6. A wafer cassette containing a
plurality of wafers is loaded into the wafer cassette receiving
areas 624 in the loading station 610 of the electroplating system
platform 600. A loading station transfer robot 628 picks up a wafer
from a wafer slot in the wafer cassette and places the wafer in the
wafer orientor 630. The wafer orientor 630 determines and orients
the wafer to a desired orientation for processing through the
system. The loading station transfer robot 628 then transfers the
oriented wafer from the wafer orientor 630 and positions the wafer
in one of the wafer slots in the wafer pass-through cassette 638 in
the SRD station 612. The mainframe transfer robot 642 picks up the
wafer from the wafer pass-through cassette 638 and positions the
wafer for transfer by the flipper robot 648. The flipper robot 648
rotates its robot blade below the wafer and picks up wafer from
mainframe transfer robot blade. The vacuum suction gripper on the
flipper robot blade secures the wafer on the flipper robot blade,
and the flipper robot flips the wafer from a face up position to a
face down position. The flipper robot 648 rotates and positions the
wafer face down in the wafer holder assembly 750. The wafer is
positioned below the wafer holder 764 but above the cathode contact
ring 766. The flipper robot 648 then releases the wafer to position
the wafer into the cathode contact ring 766. The wafer holder 764
moves toward the wafer and the vacuum chuck secures the wafer on
the wafer holder 764. The bladder assembly 770 on the wafer holder
assembly 750 exerts pressure against the wafer backside to ensure
electrical contact between the wafer plating surface and the
cathode contact ring 766.
[0080] The head assembly 752 is lowered to a processing position
above the process kit 720. At this position the wafer is below the
upper plane of the weir 778 and contacts the electrolyte contained
in the process kit 720. The power supply is activated to supply
electrical power (i.e., voltage and current) to the cathode and the
anode to enable the electroplating process. The electrolyte is
typically continually pumped into the process kit during the
electroplating process. The electrical power supplied to the
cathode and the anode and the flow of the electrolyte are
controlled by the control system 622 to achieve the desired
electroplating results. The head assembly may be rotated as the
head assembly is lowered into contact with the electrolyte.
[0081] In one embodiment of the invention, the electroplating
process may be performed utilizing an electroplating cell
containing a highly resistive electrolyte. For copper
metallization, the electrolyte may comprise CuSO.sub.4 having a
molar concentration between about 0.5M and about 1.1M, HCl at a
concentration between about 10 ppm and about 1000 ppm, a carrier
additive at a concentration between about 5 ml/l and about 40 ml/l,
H.sub.2SO4 having a concentration less than about 0.4 percent. The
metallization or filling of the feature is accomplished by applying
a first power density to the plating surface (i.e., seed layer) at
about 1 mA/cm.sup.2 to 10 mA/cm.sup.2 for about 10 seconds to about
30 seconds followed by a second power density at about 10
mA/cm.sup.2 and about 80 mA/cm.sup.2 for about 60 seconds to about
120 seconds. The electrolyte is flowed at between 2 gpm and about
4.5 gpm during the electroplating process. No substrate rotation is
required to achieve uniform deposition results.
[0082] After the electroplating process is completed, the head
assembly 710 raises the wafer holder assembly and removes the wafer
from the electrolyte. The head assembly may be rotated for a period
of time to enhance removal of residual electrolyte from the wafer
holder assembly. The vacuum chuck and the bladder assembly of the
wafer holder then release the wafer from the wafer holder, and the
wafer holder is raised to allow the flipper robot blade to pick up
the processed wafer from the cathode contact ring. The flipper
robot rotates the flipper robot blade above the backside of the
processed wafer in the cathode contact ring and picks up the wafer
using the vacuum suction gripper on the flipper robot blade. The
flipper robot rotates the flipper robot blade with the wafer out of
the wafer holder assembly, flips the wafer from a face-down
position to a face-up position, and positions the wafer on the
mainframe transfer robot blade. The mainframe transfer robot then
transfers and positions the processed wafer above the SRD module
636. The SRD wafer support lifts the wafer, and the mainframe
transfer robot blade retracts away from the SRD module 636. The
wafer is cleaned in the SRD module using deionized water or a
combination of deionized water and a cleaning fluid as described in
detail above. The wafer is then positioned for transfer out of the
SRD module. The loading station transfer robot 628 picks up the
wafer from the SRD module 636 and transfers the processed wafer
into the wafer cassette. Alternatively, the processed wafer may be
transferred into the RTA chamber 611 for an anneal treatment
process to enhance the properties of the deposited materials. The
annealed wafer is then transferred out of the RTA chamber 611 by
the loading station robot 628 and placed back into the wafer
cassette for removal from the electroplating system. The
above-described sequence can be carried out for a plurality of
wafers substantially simultaneously in the electroplating system
platform 600 of the present invention.
EXAMPLE
[0083] The present invention provides a method for filling
sub-micron features on a substrate comprising reactive pre-cleaning
the substrate; depositing a barrier layer on the substrate using
high density plasma physical vapor deposition; depositing a seed
layer over the barrier layer using high density plasma physical
vapor deposition; and electro-chemically depositing a metal using a
highly resistive electrolyte and applying a first current density
during a first deposition period followed by a second current
density during a second period. The steps of depositing the barrier
layer and depositing the seed layer are performed in a high density
plasma chamber, and the electroplating process is performed in an
electroplating cell.
[0084] To begin the pre-clean process, a substrate having
sub-micron, high aspect ratio interconnect features is transferred
into a pre-clean chamber. A pre-clean gas mixture comprising about
5% hydrogen and about 95% helium is introduced into the chamber,
and the chamber pressure is maintained at about 80 mTorr. The RF
power provided to the coil is at about 450 W at 2.0 MHz, and the
substrate support is biased at about 40 W. The reactive pre-clean
process is carried out for about 60 seconds.
[0085] The substrate is transferred into an HDP-PVD chamber
configured to deposit a barrier layer, such as a tantalum barrier
layer. A process gas for the plasma sputtering process, such as
argon, is flowed into the chamber, and the chamber pressure is
maintained at about 20 mTorr. The target is biased at about 1 kW
DC, and the coil of the HDP-PVD chamber is biased with an RF power
at about 2 kW. The substrate support is biased at about 350 W at
13.56 MHz with about a 50% duty cycle. For a feature having less
than about 0.35 .mu.m opening width and >4:1 height:width aspect
ratio, the barrier layer deposition process is carried out for
about 18 seconds to deposit a barrier layer having about 150 .ANG.
film thickness on the surfaces of the interconnect feature.
[0086] The substrate is then transferred into another HDP-PVD
chamber configured to deposit a seed layer, such as a copper seed
layer. A process gas for the plasma sputtering process, such as
argon, is flowed into the chamber, and the chamber pressure is
maintained at about 40 mTorr. The chamber conditions are stabilized
for about 60 seconds. To begin deposition, the target is biased at
about 1 kW DC, and the coil of the HDP-PVD chamber is biased with
an RF power at about 3 kW. The substrate support is biased at about
350 W at 13.56 MHz with about a 50% duty cycle. The temperature of
the substrate support is maintained at about 30.degree. C. For a
feature having less than about 0.35 .mu.m opening width and >4:1
height:width aspect ratio, the seed layer deposition process is
carried out for about 25 seconds to deposit a seed layer having
about 1000 .ANG. film thickness on the surfaces of the interconnect
feature over the barrier layer. The deposition is paused for about
60 seconds with the bias power temporarily discontinued to the
target and the coil. Deposition is resumed after the 60 seconds
cooldown period. The seed layer deposition process is continued for
about 25 additional seconds to deposit another layer of seed layer
having about 1000 .ANG. film thickness.
[0087] The substrate is then transferred to an electrochemical
deposition system, and the interconnect features on the substrate
are filled using an electrochemical deposition or electroplating
cell containing a highly resistive electrolyte. For copper
metallization, the electrolyte comprises CuSO.sub.4 having a molar
concentration between about 0.5M and about 1.1M, HCl at a
concentration between about 50 ppm and about 100 ppm, a carrier
additive at a concentration between about 12.5 ml/l and about 20
ml/l, H.sub.2SO.sub.4 having a concentration less than about 0.2
percent. The metallization or filling of the feature is
accomplished by applying a first power density to the plating
surface (i.e., seed layer) at about 2 mA/cm.sup.2 for about 18
seconds followed by a second power density at about 40 mA/cm.sup.2
for about 90 seconds. The electrolyte is flowed at between 2 gpm
and about 4.5 gpm during the electroplating process. No substrate
rotation is required to achieve uniform deposition results.
[0088] 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.
* * * * *