U.S. patent application number 10/419717 was filed with the patent office on 2004-02-05 for immersion bias for use in electro-chemical plating system.
Invention is credited to Dordi, Yezdi N., Hey, H. Peter W..
Application Number | 20040020780 10/419717 |
Document ID | / |
Family ID | 31188930 |
Filed Date | 2004-02-05 |
United States Patent
Application |
20040020780 |
Kind Code |
A1 |
Hey, H. Peter W. ; et
al. |
February 5, 2004 |
Immersion bias for use in electro-chemical plating system
Abstract
A method for immersing a substrate into a processing solution.
The method includes connecting a power supply between a conductive
layer on the substrate and an electrode positioned in the
processing solution, immersing the substrate into the processing
solution, and applying an electrical bias to the conductive layer
during the immersion.
Inventors: |
Hey, H. Peter W.;
(Sunnyvale, CA) ; Dordi, Yezdi N.; (Palo Alto,
CA) |
Correspondence
Address: |
Patent Counsel
Applied Materials, Inc.
P.O. Box 450A
Santa Clara
CA
95052
US
|
Family ID: |
31188930 |
Appl. No.: |
10/419717 |
Filed: |
April 21, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10419717 |
Apr 21, 2003 |
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09766060 |
Jan 18, 2001 |
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6551484 |
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Current U.S.
Class: |
205/137 ;
205/134; 257/E21.175 |
Current CPC
Class: |
H01L 21/2885 20130101;
C25D 7/123 20130101; C25D 5/18 20130101; C25D 17/001 20130101; C25D
5/605 20200801; C25D 5/003 20130101; C25D 21/00 20130101 |
Class at
Publication: |
205/137 ;
205/134 |
International
Class: |
C25D 005/00 |
Claims
1. A method for immersing a substrate into a processing solution,
comprising: connecting a power supply between a conductive layer on
the substrate and an electrode positioned in the processing
solution; immersing the substrate into the processing solution; and
applying a forward electrical bias to the conductive layer during
the immersion.
2. The method of claim 1, wherein the forward bias is a plating
bias configured to deposit metal ions in the processing solution
onto the conductive layer.
3. The method of claim 2, wherein the forward bias is a low plating
bias.
4. The method of claim 3, wherein the processing solution is an
electrochemical plating solution.
5. The method of claim 4, wherein the conductive layer is a seed
layer.
6. The method of claim 5, wherein immersing further comprises
rotating the substrate.
7. The method of claim 5, wherein immersing further comprises
tilting the substrate.
8. The method of claim 1, wherein applying the electrical bias
comprises applying a plating bias to the conductive layer
sufficient to overcome etching of the conductive layer by the
processing solution.
9. The method of claim 1, wherein the electrical bias is configured
such that the conductive layer is at a lower electrical potential
than the anode.
10. The method of claim 1, comprising continuing the application of
the electrical bias until a forward plating bias is applied to the
conductive layer.
11. A method for immersing a substrate into an electrochemical
plating solution, comprising: electrically connecting a seed layer
on the substrate with a first terminal of a power supply;
electrically connecting an anode positioned in the electrochemical
plating solution to a second terminal of a power supply; immersing
the substrate into the electrochemical plating solution; and
applying an electrical bias between the first terminal and second
terminal during the immersing.
12. The method of claim 11, wherein the electrical bias is a low
plating voltage.
13. The method of claim 11, wherein the electrical bias is
configured such that the first terminal has a lower electrical
potential than the second terminal.
14. The method of claim 11, further comprising rotating the
substrate during the immersion.
15. The method of claim 11, further comprising tilting the
substrate during the immersion.
16. The method of claim 11, further comprising rotating and tilting
the substrate during the immersion.
17. The method of claim 11, wherein the electrical bias is a
forward bias configured to prevent etching of the seed layer by the
electrochemical plating solution.
18. The method of claim 1 1, wherein the electrolyte solution has a
pH of less than about 5.
19. The method of claim 11, comprising continuing the application
of the electrical bias after the immersion until a plating bias is
applied.
20. A method for immersing a substrate into an electrochemical
plating cell, comprising: securing the substrate to an electrical
contact element; rotating the substrate; immersing the substrate
into a plating solution contained in the electrochemical plating
cell; applying an immersion bias to the substrate during the
immersing; applying a plating bias after the substrate is immersed
in the plating solution.
21. The method of claim 20, comprising tilting the substrate during
the immersion process.
22. The method of claim 21, comprising positioning the substrate
horizontally before increasing the immersion bias to the plating
bias.
23. The method of claim 20, wherein the immersion bias is a forward
bias.
24. The method of claim 23, wherein the forward bias is a low
plating bias.
25. The method of claim 20, comprising continuing the immersion
bias until the plating bias is applied.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of co-pending U.S. patent
application Ser. No. 09/766,060 filed Jan. 18, 2001, which claims
benefit of U.S. Pat. No. 6,258,220, filed Apr. 18, 1999. Each of
the aforementioned raelated patent applications are hereby
incorporated by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention generally relates to deposition of a
metal film on a substrate. More particularly, the electric
current/voltage established between an anode and a substrate seed
layer during metal film deposition on a substrate.
[0004] 2. Description of the Related Art
[0005] Electroplating, previously limited in integrated circuit
design to the fabrication of lines on circuit boards, is now used
to deposit metal film on substrates to form interconnect features,
such as vias or trenches. One feature filling method that utilizes
electroplating requires initially depositing a diffusion barrier
layer on the substrate by a process such as chemical vapor
deposition (CVD), physical vapor deposition (PVD), or an
electroless plating systems. A seed layer is deposited on the
diffusion barrier layer by CVD, PVD, or an electroless plating
systems to define a plating surface on the substrate. A metal film
is then deposited on the substrate seed layer by electroplating.
The deposited metal is planarized by another process such as
chemical mechanical polishing (CMP), to define conductive
interconnect features.
[0006] Electro-chemical plating (ECP), one embodiment of
electroplating, is performed by establishing a voltage across an
electrolyte solution between the anode and the substrate seed
layer. Both the anode and the substrate seed layer are disposed in
contact with the electrolyte solution during ECP. During normal ECP
operations, a sufficient negative voltage, known as a plating
voltage, is established between the seed layer on the substrate and
the anode to attract metal ions in the electrolyte solution to
deposit as metal film on the seed layer. The plating voltage is
typically applied when the substrate seed layer is fully immersed
in the electrolyte solution within the ECP system. A solid-state
power supply, applied under the control of a controller, is used to
apply electric voltages/currents between the anode and the seed
layer. When electroplating substrates, efforts are made to ensure
the production of a consistent electric current density across the
seed layer on the substrate during the plating process. For each
plating location on the seed layer, the metal film deposition rate
varies as a function of the electric current density at that
location. Therefore, variations in the electric current density
across the seed layer on the substrate likely result in
inconsistent plating rates and deposited metal film thickness
across that seed layer.
[0007] When an ECP system is not being used to deposit metal film
on a substrate for an extended period, such as during production
downtime, portions of the head assembly such as the electric
contacts are typically immersed in the electrolyte solution to
limit oxidation of the head assembly that results from exposure of
the electric contacts to air. Immersion of the head assembly into
the electrolyte solution also minimizes formation of crystals that
may form due to evaporation of water from the electrolyte solution
containing chemicals such as copper sulfate.
[0008] Typical solid state power supplies for electroplating
systems produce a slight or trickle current that flows from the
anode to the electric contacts through the electrolyte solution
even when the power supply is turned off. This slight or trickle
current is known as a current leak, and the extent of the current
leak is a quantified value in each solid state power supply. Though
the trickle current level is typically small, it can cause metal
ions from the electrolyte solution to deposit as metal film on the
electric contacts, and thereby alter the electric characteristics
of the electric contacts. Changes to the electrical or physical
characteristics of the electric contacts, including oxidation,
crystal formation, and deposition, adversely affect the consistency
of the electric voltage/current supplied by the power supply
through the electric contacts via the electrolyte solution to the
substrate seed layer and adversely affects the resultant uniformity
of the deposition metal film.
[0009] Therefore, there remains a need for an electrochemical
plating system that limits the current leakage from the power
supply through the electric contacts and reduces the metal film
deposition onto the electric contacts resulting from the current
leakage.
SUMMARY OF THE INVENTION
[0010] The present invention generally provides a method for
immersing a substrate into a processing solution. The method
includes connecting a power supply between a conductive layer on
the substrate and an electrode positioned in the processing
solution, immersing the substrate into the processing solution, and
applying an electrical bias to the conductive layer during the
immersion.
[0011] Embodiments of the invention further provide a method for
immersing a substrate into a processing fluid. The method includes
electrically connecting a seed layer on the substrate with a first
terminal of a power supply, electrically connecting an anode
positioned in the electrochemical plating solution to a second
terminal of a power supply, immersing the substrate into the
electrochemical plating solution, and applying an electrical bias
between the first terminal and second terminal during the
immersing.
[0012] Embodiments of the invention further provide a method for
immersing a semiconductor substrate into an electrochemical plating
cell. The method includes securing the substrate to an electrical
contact element, rotating the substrate, immersing the substrate
into a plating solution contained in the electrochemical plating
cell, applying an immersion bias to the substrate during the
immersing, and applying a plating bias after the substrate is
immersed in the plating solution.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] So that the manner in which the above recited features,
advantages and objects of the present invention are attained 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.
[0014] FIG. 1 is a cross sectional view of one embodiment of
electro-chemical plating (ECP) system;
[0015] FIG. 2 is a perspective view of another embodiment of an ECP
system;
[0016] FIG. 3 is a top schematic view of the ECP system shown in
FIG. 2;
[0017] FIG. 4 is a schematic perspective view of one embodiment of
spin-rinse-dry (SRD) module, incorporating rinsing and dissolving
fluid inlets;
[0018] FIG. 5 is a side cross sectional view of the SRD module of
FIG. 4, and shows a substrate in a processing position vertically
disposed between fluid inlets;
[0019] FIG. 6 is a cross sectional view of an embodiment of
electroplating process cell;
[0020] FIG. 7 is a partial cross sectional perspective view of an
embodiment of a cathode contact ring;
[0021] FIG. 8 is a cross sectional perspective view of the cathode
contact ring of
[0022] FIG. 7 showing an alternative embodiment of contact
pads;
[0023] FIG. 9 is a cross sectional perspective view of the cathode
contact ring of FIG. 7 showing an alternative embodiment of the
contact pads and an isolation gasket;
[0024] FIG. 10 is a cross sectional perspective view of the cathode
contact ring of FIG. 7 showing an embodiment of the isolation
gasket;
[0025] FIG. 11 is a simplified schematic diagram of the electric
circuit through each contact;
[0026] FIG. 12 is a cross sectional view of one embodiment of a
substrate assembly;
[0027] FIG. 12A is an enlarged cross sectional view of an
embodiment of the bladder area of FIG. 12;
[0028] FIG. 13 is a partial cross sectional view of one embodiment
of a substrate holder plate;
[0029] FIG. 14 is a partial cross sectional view of one embodiment
of a manifold;
[0030] FIG. 15 is a partial cross sectional view of one embodiment
of a bladder;
[0031] FIG. 16 is a schematic diagram of one embodiment of an
electrolyte solution replenishing system;
[0032] FIG. 17 is a cross sectional view of one embodiment of a
rapid thermal anneal (RTA) chamber;
[0033] FIG. 18 is a perspective view of an alternative embodiment
of a cathode contact ring;
[0034] FIG. 19 is a partial cross sectional view of an alternative
embodiment of seal to be used in a substrate holder assembly;
[0035] FIG. 20 is a cross sectional view of one embodiment of an
encapsulated anode that can be used in the process cell shown in
FIG. 6;
[0036] FIG. 21 is a cross sectional view of another embodiment of
an encapsulated anode that can be used in the process cell shown in
FIG. 6;
[0037] FIG. 22 is a cross sectional view of yet another embodiment
of an encapsulated anode that can be used in the process cell shown
in FIG. 6;
[0038] FIG. 23 is a cross sectional view of another embodiment of
an encapsulated anode that can be used in the process cell shown in
FIG. 6;
[0039] FIG. 24 is a top schematic view of a mainframe transfer
robot having a flipper robot incorporated therein;
[0040] FIG. 25 is an alternative embodiment of the substrate holder
system having a rotatable head assembly;
[0041] FIGS. 26a and 26b are cross sectional views of embodiments
of a degasser module;
[0042] FIG. 27 shows a graph of voltage as the ordinate plotted as
a function of time plotted as the abscissa for an exemplary metal
film deposition process using the substrate holder system shown in
FIG. 25; and
[0043] FIG. 28 shows one embodiment of a method that is controlled
by the controller of FIG. 3 during immersion of a substrate into
electrolyte solution.
[0044] FIG. 29 shows another embodiment of a method that is
controlled by the controller of FIG. 3 during immersion of a
substrate into electrolyte solution.
[0045] The terms "below", "above", "bottom", "top", "up", "down",
"upper", and "lower" and other positional terms used herein are
shown with respect to the embodiments in the figures and may be
varied depending on the specific relative orientation of the
processing apparatus.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0046] One aspect of this disclosure relates to multiple
embodiments of electro-chemical plating (ECP) systems, all of which
are used to deposit a metal film on a seed layer on a substrate.
Multiple embodiments of ECP systems are described in detail. A
substrate holder system including a head assembly is provided that
secures substrates during immersion of substrates into an
electrolyte solution within the ECP system. The-head assembly
includes electric contacts that controllably supply electricity to
the seed layer on the substrate to effect the electric biasing
between the anode and the seed layer. Any level of positive voltage
biasing of the seed layer relative to the anode can result in metal
film deposition on the seed layer. Biasing of the electric contacts
relative to the anode when the ECP system is not being used for
electroplating is described. The voltage biasing of the electric
contacts as described limits the depth of metal film deposition on
the electric contacts. Additionally, maintaining the electric
contacts immersed in the electrolyte solution during down-time
limits chemical crystal formations, with such chemicals as copper
sulfate, on the electric contacts. The voltage biasing can also
limit metal film deposition of varying depths on the seed
layer.
[0047] 1. ECP System and Operation
[0048] The structure and voltage biasing of electric contacts are
maintained in a pristine condition against the effects of leakage
current in an ECP system. FIG. 1 shows one embodiment of ECP system
10, such as a fountain plater, used in electroplating. The ECP
system 10 includes an electrolyte cell 12, a substrate holder
system 14, an anode 16, and a contact ring 20. The electrolyte cell
12 contains electrolyte solution, and the electrolyte cell has a
top opening 21 circumferentially defined by the contact ring 20.
The substrate holder system 14 is disposed above the electrolyte
cell and is capable of displacing the substrate to be immersed into
and out of the electrolyte solution. The substrate, held by the
substrate holder system 14, is immersed in and removed from the
electrolyte solution through the top opening of the electrolyte
cell. The substrate holder system 14 is also capable of securing
and positioning the substrate in a desired position within the
electrolyte solution during processing. The contact ring 20
comprises a plurality of metal or metal alloy electric contacts
that electrically contact the substrate seed layer. A controller
222 controls the electric voltage/current supplied by a solid-state
power supply to the electric contacts. The solid-state power supply
is electrically connected to the contacts and to the anode, and the
controller provides an electric current to the substrate when the
seed layer on the substrate is being plated. The controller 222
thereby determines the electric current/voltage established across
the electrolyte solution, from the anode to the seed layer on the
substrate. In periods when the seed layer is biased with a positive
voltage relative to the anode, metal film can deposit on the seed
layer at a rate that is a function of the voltage. A leakage or
trickle current is a known current that is provided by any specific
solid-state power supply when the power supply is turned off. The
following embodiments of ECP system illustrate how the operation of
solid-state power supplies can be operated to an ECP system in a
manner to limit any metal film deposition or chemical crystal
formations that form on the electric contacts as a result of the
leakage current. The ECP system overcomes the leakage or trickle
current produced by solid-state power supply when the power supply
is turned off.
[0049] FIG. 2 is a perspective view of one embodiment of ECP system
200. FIG. 3 is a top schematic view of the ECP system 200 of FIG.
2. Referring to both FIGS. 2 and 3, which should be viewed and
considered together, the ECP system 200 generally comprises a
loading station 210, a rapid thermal anneal (RTA) chamber 211, a
spin-rinse-dry (SRD) station 212, a mainframe 214, and an
electrolyte solution replenishing system 220. In one embodiment,
the ECP system 200 is enclosed in a clean environment using panels
such as made from PLEXIGLAS.RTM. (a registered trademark of the
Rohm and Haas Company of West Philadelphia, Pa.). The mainframe 214
generally comprises a mainframe transfer station 216 and a
plurality of processing stations 218. Each processing station 218
includes one or more process cells 240. An electrolyte solution
replenishing system 220 is positioned adjacent the ECP system 200
and connected to the process cells 240 individually to circulate
electrolyte solution used for the electroplating process.
[0050] The controller 222, whose components are shown in FIG. 3,
comprises a central processing unit (CPU) 260, memory 262, circuit
portion 265, input output interface (I/O) 279, and bus, not shown.
The controller 222 may be a general-purpose computer, a
microprocessor, a microcontroller, or any other known suitable type
of computer or controller. The CPU 260 performs the processing and
arithmetic operations for the controller 222. The controller 222
controls the processing, robotic operations, timing, and other
operations associated with the ECP system 200. The controller
controls the voltage applied to the anode 16, the seed layer on the
substrate 22, and the operation of the substrate holder assembly
450 as shown in FIG. 6.
[0051] The memory 262 includes random access memory (RAM) and read
only memory (ROM) that together store the computer programs,
operands, operators, dimensional values, system processing
temperatures and configurations, and other parameters that control
the electroplating operation. A bus (not numbered) provides for
digital information transmissions between CPU 260, circuit portion
265, memory 262, and I/O 279. The bus also connects I/O 279 to the
portions of the ECP system 200 that either receive digital
information from, or transmit digital information to, the
controller 222.
[0052] I/O 279 provides an interface to control the transmissions
of digital information between each of the components in controller
222. I/O 279 also provides an interface between the components of
the controller 222 and different portions of the ECP system 200.
Circuit portion 265 comprises all of the other user interface
devices, such as display and keyboard.
[0053] In this disclosure, the term "substrate" is intended to
describe wafers, semiconductor substrates, liquid crystal diode
(LCD) displays, or other objects that can be processed within the
ECP system 200. The substrates are generally circular or
rectangular, may be of any size, though the circular substrates
commonly have a 200 mm or 300 mm diameter, and may include notch or
flat edge indentations that assist in providing and maintaining
proper wafer orientation about its vertical axis. The loading
station 210 may include one or more substrate cassette receiving
areas 224, one or more loading station transfer robots 228 and at
least one substrate orientor 230. The number of substrate cassette
receiving areas, loading station transfer robots 228 and substrate
orientors included in the loading station 210 can be configured
according to the desired throughput of the system. As shown for one
embodiment in FIGS. 2 and 3, the loading station 210 includes two
substrate cassette receiving areas 224, two loading station
transfer robots 228 and one substrate orientor 230. A substrate
cassette 232 containing one or more substrates 234 in
vertically-spaced cassette shelves provides a location where the
substrates can be stored, removed from, or inserted in conjunction
with the ECP system. The loading station transfer robot 228
transfers substrates 234 between the substrate cassette 232 and the
substrate orientor 230. The loading station transfer robot 228
comprises a typical transfer robot commonly known in the art. The
substrate orientor 230 positions each substrate 234 in a desired
orientation to ensure that the substrate is properly processed. The
loading station transfer robot 228 also transfers substrates 234
between the loading station 210 and the SRD station 212 and between
the loading station 210 and the thermal anneal chamber 211.
[0054] FIG. 4 is a schematic perspective view of a spin-rinse-dry
(SRD) module of the present invention, incorporating rinsing and
dissolving fluid inlets. FIG. 5 is a side cross sectional view of
the SRD module of FIG. 4 and shows a substrate in a processing
position vertically disposed between fluid inlets. The SRD station
212 may include one or more SRD modules 236 and one or more
substrate pass-through cassettes 238. In one embodiment, the SRD
station 212 includes two SRD modules 236, corresponding to the
number of loading station transfer robots 228, and a substrate
pass-through cassette 238 is positioned in close proximity to each
SRD module 236. The substrate pass-through cassette 238 facilitates
substrate transfer between the loading station 210 and the
mainframe 214. The substrate pass-through cassette 238 provides
access to and from both the loading station transfer robot 228 and
a robot in the mainframe transfer station 216.
[0055] Referring to FIGS. 4 and 5, the SRD module 238 comprises a
bottom 330a and a sidewall 330b, and an upper shield 330c which
collectively define a SRD module bowl 330d, where the shield
attaches to the sidewall and assists in retaining the fluids within
the SRD module. Alternatively, a removable cover could also be
used. A pedestal 336, located in the SRD module, includes a
pedestal support 332 and a pedestal actuator 334. The pedestal 336
supports the substrate 338, shown in FIG. 5, on the pedestal upper
surface during processing. The pedestal actuator 334 rotates the
pedestal to spin the substrate and raises and lowers the pedestal
during etching, rinsing, and certain spinning of the substrate. The
substrate may be held in place on the pedestal by a plurality of
clamps 337. The clamps pivot with centrifugal force and in one
embodiment engage the substrate in the edge exclusion zone of the
substrate. The clamps engage the substrate only when the substrate
lifts off the pedestal during the processing.
[0056] The SRD module 236 is connected between the loading station
210 and the mainframe 214. The mainframe 214 generally comprises a
mainframe transfer station 216 and a plurality of processing
stations 218. Referring to FIGS. 2 and 3, the mainframe 214, as
shown, includes two processing stations 218, each processing
station 218 having two process cells 240. The mainframe transfer
station 216 includes a mainframe transfer robot 242. The mainframe
transfer robot 242 may comprise a plurality of individual robot
arms 244 that provides independent access of substrates in the
processing stations 218 and the SRD stations 212. As shown in FIG.
3, the mainframe transfer robot 242 comprises two robot arms 244,
corresponding to the number of process cells 240 per processing
station 218. Each robot arm 244 includes a robot blade or end
effector 2404 for holding a substrate during a substrate transfer.
In one embodiment, each robot arm 244 may operate independently of
the other arm to facilitate independent transfers of substrates in
the system. Alternatively, the robot arms 244 operate in a linked
fashion such that one robot extends as the other robot arm
retracts.
[0057] In one embodiment, the mainframe transfer station 216
includes a flipper robot 248 that facilitates transfer of a
substrate from a face-up position on the robot blade 2404 of the
mainframe transfer robot 242 to a face down position for a process
cell 240, such as an ECP, that requires face-down processing of
substrates. The flipper robot 248 includes a main body 250 that
provides both vertical and rotational movements with respect to a
vertical axis of the main body 250 and a flipper robot arm 252 that
provides rotational movement along a horizontal axis along the
flipper robot arm 252. In one embodiment, a vacuum suction gripper
254, disposed at the distal end of the flipper robot arm 252, holds
the substrate as the substrate is flipped and transferred by the
flipper robot 248. The flipper robot 248 positions a substrate into
the process cell 240 for face-down processing. The details of the
electroplating process cell will be discussed below.
[0058] FIG. 24 is a top schematic view of a mainframe transfer
robot incorporating a flipper robot. The mainframe transfer robot
242 as shown in FIG. 24 serves to transfer substrates between
different stations attached the mainframe station, including the
processing stations and the SRD stations. The mainframe transfer
robot 242 includes a plurality of robot arms 2402, two are shown,
and a flipper robot 2404 is attached as an end effector for each of
the robot arms 2402. Flipper robots are generally known in the art
and can be attached as end effectors for substrate handling robots,
such as model RR701, available from Rorze Automation, Inc., located
in Milpitas, Calif. The main transfer robot 242 comprising a
flipper robot as the end effector is capable of transferring
substrates between different stations attached to 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 242 provides independent robot motion
along the X-Y-Z axes by the robot arm 2402 and independent
substrate flipping rotation by the flipper robot end effector 2404.
By incorporating the flipper robot 2404 as the end effector of the
mainframe transfer robot, the substrate transfer process is
simplified because the step of passing a substrate from a mainframe
transfer robot to a flipper robot is eliminated.
[0059] FIG. 6 is a cross sectional view of one embodiment of an
electroplating process cell 400. The electroplating process cell
240 shown in FIGS. 2 and 3 may be configured as the electroplating
process cell 400 shown in FIG. 6. The process cell 400 generally
comprises a head assembly 410, a process cell 420 and an
electrolyte solution collector 440. In one embodiment, the
electrolyte solution collector 440 is secured onto the body 442 of
the mainframe 214 over an opening 443 that defines the location for
placement of the process cell 420. The electrolyte solution
collector 440 includes an inner wall 446, an outer wall 448 and a
bottom 447 connecting the walls. An electrolyte solution outlet 449
is disposed through the bottom 447 of the electrolyte solution
collector 440 and connected to the electrolyte solution
replenishing system 220 shown in FIG. 2 through tubes, hoses, pipes
or other fluid transfer connectors.
[0060] The head assembly 410 is mounted onto a head assembly frame
452. The head assembly frame 452 includes a mounting post 454 and a
cantilever arm 456. The mounting post 454 is mounted onto the body
442 of the mainframe 214, and the cantilever arm 456 extends
laterally from an upper portion of the mounting post 454. In one
embodiment, the mounting post 454 provides rotational movement with
respect to a vertical axis along the mounting post to allow
rotation of the head assembly 410. The head assembly 410 is
attached to a mounting plate 460 disposed at the distal end of the
cantilever arm 456. The lower end of the cantilever arm 456 is
connected to a cantilever arm actuator 457, such as a pneumatic
cylinder, mounted on the mounting post 454. The cantilever arm
actuator 457 provides pivotal movement of the cantilever arm 456
with respect to the joint between the cantilever arm 456 and the
mounting post 454. When the cantilever arm actuator 457 is
retracted, the cantilever arm 456 moves the head assembly 410 away
from the process cell 420 to provide the spacing required to remove
and/or replace the process cell 420 from the electroplating process
cell 400. When the cantilever arm actuator 457 is extended, the
cantilever arm 456 moves the head assembly 410 toward the process
cell 420 to position the substrate in the head assembly 410 in a
processing position.
[0061] The head assembly 410 generally comprises a substrate holder
assembly 450 and a substrate assembly actuator 458. The substrate
assembly actuator 458 is mounted onto the mounting plate 460, and
includes a head assembly shaft 462 extending downwardly through the
mounting plate 460. The lower end of the head assembly shaft 462 is
connected to the substrate holder assembly 450 to position the
substrate holder assembly 450 in a processing position and in a
substrate loading position.
[0062] The substrate holder assembly 450 comprises an electric
contact 466. FIG. 7 is a cross sectional view of one embodiment of
a electric contact 466. In general, the electric contact 466
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.
[0063] Referring now to FIG. 7 in detail, one embodiment of
electric contact 466 generally comprises a plurality of conducting
members 765 at least partially disposed within an annular
insulative body 770. The insulative body 770 is shown having a
flange 762 and a downward sloping shoulder portion 764 leading to a
substrate seating surface 768 located below the flange 762. The
flange 762 and the substrate seating surface 768 lie in offset and
substantially parallel planes. Thus, the flange 762 may be
understood to define a first plane while the substrate seating
surface 768 defines a second plane parallel to the first plane
wherein the shoulder 764 is disposed between the two planes.
However, electric contact design shown in FIG. 7 is intended to be
merely illustrative. In another embodiment, the shoulder portion
764 may be of a steeper angle including a substantially vertical
angle so as to be substantially normal to both the flange 762 and
the substrate seating surface 768. Alternatively, the electric
contact 466 may be substantially planar thereby eliminating the
shoulder portion 764. However, for reasons described below, one
embodiment comprises the shoulder portion 764 shown in FIG. 6 or
some variation thereof.
[0064] The conducting members 765 are defined by a plurality of
outer electric contact pads 780 annularly disposed on the flange
762, a plurality of inner electric contact pads 772 disposed on a
portion of the substrate seating surface 768, and a plurality of
embedded conducting connectors 776 which link the pads 772, 780 to
one another. The conducting members 765 are isolated from one
another by the insulative body 770. The insulative body may be made
of a plastic such as polyvinylidenefluoride (PVDF), perfluoroalkoxy
resin (PFA), TEFLON.RTM. (a registered trademark of the E.I. duPont
de Nemours and Company) and TEFZEL.RTM. (a registered trademark of
the E.I. duPont de Nemours and Company) or any other insulating
material such as Alumina (Al.sub.2O.sub.3) or other ceramics. The
outer contact pads 780 are electrically coupled to the power supply
to deliver current and voltage to the inner contact pads 772 via
the connectors 776 during processing. In turn, the inner contact
pads 772 supply the current and voltage to a substrate by
maintaining contact around a peripheral portion of the substrate.
Thus, in operation the conducting members 765 act as discrete
current paths electrically connected to a substrate.
[0065] Low resistivity, and conversely high conductivity, are
directly related to good plating. To ensure low resistivity, the
conducting members 765 may be made of such exemplary materials as
copper (Cu), platinum (Pt), tantalum (Ta), titanium (Ti), gold
(Au), silver (Ag), stainless steel or other conducting materials.
Low resistivity and low contact resistance may also be achieved by
coating the conducting members 765 with a conducting material.
Thus, the conducting members 765 may, for example, be made of
copper, that has a resistivity of approximately 2.times.10.sup.-8
.OMEGA..multidot.m, coated with platinum that has a resistivity of
approximately 10.6.times.10.sup.-8 .OMEGA..multidot.m. Coatings
such as tantalum nitride (TaN), titanium nitride (TiN), rhodium
(Rh), Au, Cu, or Ag on a conductive base materials such as
stainless steel, molybdenum (Mo), Cu, and Ti are also possible.
Further, since the contact pads 772, 780 are typically separate
units bonded to the conducting connectors 776, the contact pads
772, 780 may comprise one material, such as Cu, and the conducting
members 765 another, such as stainless steel. Either or both of the
pads 772, 180 and conducting connectors 776 may be coated with a
conducting material. Additionally, because plating repeatability
may be adversely affected by oxidation that acts as an insulator,
the inner contact pads 772 comprise a material resistant to
oxidation such as Pt, Ag, or Au.
[0066] In addition to being a function of the contact material, the
total resistance of each circuit is dependent on the geometry, or
shape, of the inner contact inner contact pads 772 and the force
supplied by the contact ring 466. These factors define a
constriction resistance, RCR, at the interface of the inner contact
pads 772 and the substrate seating surface 768 due to asperities
between the two surfaces. Generally, as the applied force is
increased the apparent area is also increased. The apparent area
is, in turn, inversely related to R.sub.CR so that an increase in
the apparent area results in a decreased R.sub.CR. Thus, to
minimize overall resistance it is desired to maximize force. The
maximum force applied in operation is limited by the yield strength
of a substrate which may be damaged under excessive force and
resulting pressure. However, because pressure is related to both
force and area, the maximum sustainable force is also dependent on
the geometry of the inner contact pads 772. Thus, while the contact
pads 772 may have a flat upper surface as in FIG. 7, other shapes
may be used to advantage. For example, two shapes are shown in
FIGS. 8 and 9. FIG. 8 shows a knife-edge contact pad and FIG. 9
shows a hemispherical contact pad. A person skilled in the art will
readily recognize other shapes which may be used to advantage. A
more complete discussion of the relation between contact geometry,
force, and resistance is given in Ney Contact Manual, by Kenneth E.
Pitney, The J. M. Ney Company, 1973, which is hereby incorporated
by reference in its entirety.
[0067] The number of connectors 776 may be varied depending on the
particular number of desired contact pads 772, shown in FIG. 7. For
a 200 mm substrate, at least twenty-four connectors 776 are spaced
equally over 360.degree. in one embodiment. However, as the number
of connectors reaches a critical level, the compliance of the
substrate relative to the contact ring 466 is adversely affected.
Therefore, while more than twenty-four connectors 776 may be used,
contact uniformity may eventually diminish depending on the
topography of the contact pads 772 and the substrate stiffness.
Similarly, while less than twenty-four connectors 776 may be used,
current flow is increasingly restricted and localized, leading to
poor plating results. Since the dimensions of the process cell can
be configured to suit a particular application. For example, the
dimensions would be changed to compensate between a 200 and a 300
mm substrate.
[0068] As shown in FIG. 10, the substrate seating surface 768
comprises an isolation gasket 782. The isolation gasket is disposed
on the insulative body 770 and extends diametrically interior to
the inner contact pads 772 to define the inner diameter of the
contact ring 466. The isolation gasket 782 extends slightly above
the inner contact pads 772, e.g., a few mils, and may in one
embodiment comprise an elastomer such as VITON.RTM. (a registered
trademark of the E.I. duPont de Nemours and Company of Wilmington,
Del.), TEFLON.RTM. (a registered trademark of the E.I. duPont de
Nemours and Company of Wilmington, Del.), buna rubber and/or the
like. Where the insulative body 770 also comprises an elastomer the
isolation gasket 782 may be of the same material. In the latter
embodiment, the isolation gasket 782 and the insulative body 770
may be monolithic, i.e., formed as a single piece. However, the
isolation gasket 782 is formed separate from the insulative body
770 so that it may be easily removed for replacement or
cleaning.
[0069] While FIG. 10 shows one embodiment of the isolation gasket
782 wherein the isolation gasket is seated entirely on the
insulative body 770, FIGS. 8 and 9 show an alternative embodiment.
In the latter embodiment, the insulative body 770 is partially
machined away to expose the upper surface of the connecting member
776 and the isolation gasket 782 is disposed thereon. Thus, the
isolation gasket 782 contacts a portion of the connecting member
776. This design requires less material to be used for the inner
contact pads 772 that may be advantageous where material costs are
significant such as when the inner contact pads 772 include
gold.
[0070] During processing, the isolation gasket 782 maintains
contact with a peripheral portion of the substrate plating surface
and is compressed to provide a seal between the remaining electric
contact 466 and the substrate. The seal prevents the electrolyte
solution from contacting the edge and backside of the substrate. As
noted above, maintaining a clean, pristine, contact surface is
necessary to achieving high plating repeatability. Previous contact
ring designs did not provide consistent plating results because
contact surface topography varied over time. The contact ring
limits, or substantially minimizes, deposits which would otherwise
accumulate on the inner contact pads 772 and change their
characteristics thereby producing highly repeatable, consistent,
and uniform plating across the substrate plating surface.
[0071] FIG. 11 is a simplified schematic diagram representing a
possible configuration of the electric circuit for the contact ring
466. To provide a uniform current distribution between the
conducting members 765, an external resistor 700 is connected in
series with each of the conducting members 765. The resistance
value of the external resistor 700, represented as R.sub.EXT, is
greater than the resistance of any other component of the circuit.
As shown in FIG. 11, the electric circuit through each conducting
member 765 is represented by the resistance of each of the
components connected in series with the power supply 702. R.sub.E
represents the resistance of the electrolyte solution, which is
typically dependent on the distance between the anode and the
cathode contact ring and the chemical composition of the
electrolyte solution. Thus, R.sub.A represents the resistance of
the electrolyte solution adjacent the substrate plating surface
754. R.sub.S represents the resistance of the substrate plating
surface 754, and R.sub.C represents the resistance of the cathode
conducting members 765 plus the constriction resistance resulting
at the interface between the inner contact pads 772 and the
substrate plating layer 754. Generally, the resistance value of the
external resistor (R.sub.EXT) is at least as much as .SIGMA.R,
where .SIGMA.R equals the sum of R.sub.E, R.sub.A, R.sub.S and
R.sub.C. The resistance value of the external resistor (R.sub.EXT)
is greater than .SIGMA.R such that .SIGMA.R is negligible and the
resistance of each series circuit approximates R.sub.EXT.
[0072] Typically, one power supply is connected to all of the outer
contact pads 780 of the electric contact 466, resulting in parallel
circuits through the inner contact pads 772. However, as the inner
contact pad-to-substrate interface resistance varies with each
inner contact pad 772, more current will flow, and thus more
plating will occur, at the site of lowest resistance. However, by
placing an external resistor in series with each conducting member
765, the value or quantity of electric current passed through each
conducting member 765 becomes controlled mainly by the value of the
external resistor. As a result, the variations in the electrical
properties between each of the inner contact pads 772 do not affect
the current distribution on the substrate. The uniform current
density applied across the plating surface contributes to a uniform
plating thickness of the metal film deposited on the seed layer on
the substrate. The external resistors also provide a uniform
current distribution between different substrates of a
process-sequence.
[0073] Although the contact ring 466 is designed to resist deposit
buildup on the inner contact pads 772, over multiple substrate
plating cycles the substrate-pad interface resistance may increase,
eventually reaching an unacceptable value. An electronic
sensor/alarm 704 can be connected across the external resistor 700
to monitor the voltage/current across the external resistor to
address this problem. If the voltage/current across the external
resistor 700 falls outside of a preset operating range that is
indicative of a high substrate-pad resistance, the sensor/alarm 704
triggers corrective measures such as shutting down the plating
process until the problems are corrected by an operator.
Alternatively, a separate power supply can be connected to each
conducting member 765 and can be separately controlled and
monitored to provide a uniform current distribution across the
substrate. A very smart system (VSS) may also be used to modulate
the current flow. The VSS typically comprises a processing unit and
any combination of devices known in the industry used to supply
and/or control current such as variable resistors, separate power
supplies, etc. As the physiochemical, and hence electrical,
properties of the inner contact pads 772 change over time, the VSS
processes and analyzes data feedback. The data is compared to
pre-established setpoints and the VSS then makes appropriate
current and voltage alterations to ensure uniform deposition.
[0074] FIG. 18 is a perspective view of an alternative embodiment
of a cathode contact ring. The cathode contact ring 1800 as shown
in FIG. 18 comprises a conductive metal or a metal alloy, such as
stainless steel, copper, silver, gold, platinum, titanium,
tantalum, and other conductive materials, or a combination of
conductive materials, such as stainless steel coated with platinum.
The cathode contact ring 1800 includes an upper mounting portion
1810 adapted for mounting the cathode contact ring onto the
substrate holder assembly and a lower substrate receiving portion
1820 adapted for receiving a substrate therein. The substrate
receiving portion 1820 includes an annular substrate seating
surface 1822 having a plurality of contact pads or bumps 1824
disposed thereon and evenly spaced apart. When a substrate is
positioned on the substrate seating surface 1822, the contact pads
1824 physically contact a peripheral region of the substrate to
provide electric contact to the electroplating seed layer on the
substrate deposition surface. The contact pads 1824 are coated with
a noble metal, such as platinum or gold, that is resistant to
oxidation.
[0075] The exposed surfaces of the cathode contact ring, except the
surfaces of the contact pads that come in contact with the
substrate, are treated to provide hydrophilic surfaces or coated
with a material that exhibits hydrophilic properties. Hydrophilic
materials and hydrophilic surface treatments are known in the art.
One company providing a hydrophilic surface treatment is Millipore
Corporation, located in Bedford, Mass. The hydrophilic surface
significantly reduces beading of the electrolyte solution on the
surfaces of the cathode contact ring and promotes smooth dripping
of the electrolyte solution from the cathode contact ring after the
cathode contact ring is removed from the electroplating bath or
electrolyte solution. By providing hydrophilic surfaces on the
cathode contact ring that facilitate run-off of the electrolyte
solution, plating defects caused by residual electrolyte solution
on the cathode contact ring are significantly reduced. The
inventors also contemplate application of this hydrophilic
treatment or coating in other embodiments of cathode contact rings
to reduce residual electrolyte solution beading on the cathode
contact ring and the plating defects on a subsequently processed
substrate that may result therefrom.
[0076] Referring to FIGS. 12 and 12A, the substrate holder assembly
464 is positioned above the electric contact 466 and comprises a
bladder assembly 470 that provides pressure to the backside of a
substrate and ensures electric contact between the substrate
plating surface and the electric contact 466. The inflatable
bladder assembly 470 is disposed on a substrate holder plate 832. A
bladder 836 disposed on a lower surface of the substrate holder
plate 832 is thus located opposite and adjacent to the contacts on
the electric contact 466 with the substrate 821 interposed
therebetween. A fluid source 838 supplies a fluid, i.e., a gas or
liquid, to the bladder 836 allowing the bladder 836 to be inflated
to varying degrees.
[0077] Referring now to FIGS. 12, 12A, and 13, the details of the
bladder assembly 470 will be discussed. The substrate holder plate
832 is shown as substantially disc-shaped having an annular recess
840 formed on a lower surface and a centrally disposed vacuum port
841. One or more inlets 842 are formed in the substrate holder
plate 832 and lead into the relatively enlarged annular mounting
channel 843 and the annular recess 840. Quick-disconnect hoses 844
couple the fluid source 838 to the inlets 842 to provide a fluid
thereto. The vacuum port 841 is attached to a vacuum/pressure
pumping system 859 adapted to selectively supply a pressure or
create a vacuum at a backside of the substrate 821. The pumping
system 859, shown in FIG. 12, comprises a pump 845, a cross-over
valve 847, and a vacuum ejector 849 commonly known as a venturi.
One vacuum ejector that may be used is available from SMC
Pneumatics, Inc., of Indianapolis, Ind. The pump 845 may be a
commercially available compressed gas source and is coupled to one
end of a hose 851, the other end of the hose 851 being coupled to
the vacuum port 841. The hose 851 is split into a pressure line 853
and a vacuum line 855 having the vacuum ejector 849 disposed
therein. Fluid flow is controlled by the cross-over valve 847 which
selectively switches communication with the pump 845 between the
pressure line 853 and the vacuum line 855. The cross-over valve has
an OFF setting whereby fluid is restricted from flowing in either
direction through hose 851. A shut-off valve 861 disposed in hose
851 prevents fluid from flowing from pressure line 855 upstream
through the vacuum ejector 849. The desired direction of fluid flow
is indicated by arrows.
[0078] Where the fluid source 838 is a gas supply it may be coupled
to hose 851 thereby eliminating the need for a separate compressed
gas supply, i.e., pump 845. Further, a separate gas supply and
vacuum pump may supply the backside pressure and vacuum conditions.
While one embodiment allows for both a backside pressure as well as
a backside vacuum, a simplified embodiment may comprise a pump
capable of supplying only a backside vacuum. However, as will be
explained below, deposition uniformity may be improved where a
backside pressure is provided during processing. Therefore, a
vacuum ejector and a cross-over valve may be included.
[0079] Referring now to FIGS. 12A and 14, a substantially circular
ring-shaped manifold 846 is disposed in the annular recess 840. The
manifold 846 comprises a mounting rail 852 disposed between an
inner shoulder 848 and an outer shoulder 850. The mounting rail 852
is adapted to be at least partially inserted into the annular
mounting channel 843. A plurality of fluid outlets 854 formed in
the manifold 846 provide communication between the inlets 842 and
the bladder 836. Seals 837, such as O-rings, are disposed in the
annular manifold channel 843 in alignment with the inlet 842 and
outlet 854 and secured by the substrate holder plate 832 to ensure
an airtight seal. Conventional fasteners such as screws may be used
to secure the manifold 846 to the substrate holder plate 832 via
cooperating threaded bores formed in the manifold 846 and the
substrate holder plate 832.
[0080] Referring now to FIG. 15, the bladder 836 is shown, in
section, as an elongated substantially semi-tubular piece of
material having annular lip seals 856, or nodules, at each edge. In
FIG. 12A, the lip seals 856 are shown disposed on the inner
shoulder 848 and the outer shoulder 850. A portion of the bladder
836 is compressed against the walls of the annular recess 840 by
the manifold 846 which has a width slightly less, e.g., a few
millimeters, than the annular recess 840. Thus, the manifold 846,
the bladder 836, and the annular recess 840 cooperate to form a
fluid-tight seal. To prevent fluid loss, the bladder 836 includes
(is formed entirely from or is coated with) some fluid impervious
material such as silicon rubber or any comparable elastomer which
is chemically inert with respect to the electrolyte solution and
exhibits reliable elasticity. Where needed a compliant covering 857
may be disposed over the bladder 836, as shown in FIG. 15, and
secured by means of an adhesive or thermal bonding. The covering
857 preferably comprises an elastomer such as VITON.RTM., buna
rubber or the like, which may be reinforced by KEVLAR.RTM. (a
registered trademark of the E.I. duPont de Nemours and Company of
Wilmington, Del.), for example. In one embodiment, the covering 857
and the bladder 836 comprise the same material. The covering 857
has particular application where the bladder 836 is liable to
rupturing. Alternatively, the bladder 836 thickness may simply be
increased during its manufacturing to reduce the likelihood of
puncture. The exposed surface of the bladder 836, if uncovered, and
the exposed surface of the covering 857 my be coated or treated to
provide a hydrophilic surface. This coating promotes dripping and
removal of the residual electrolyte solution after the head
assembly is lifted above the process cell.
[0081] The precise number of inlets 842 and outlets 854 may be
varied according to the particular application. For example, while
FIG. 12 shows two inlets with corresponding outlets, an alternative
embodiment could employ a single fluid inlet that supplies fluid to
the bladder 836.
[0082] In operation, the substrate 821 is introduced into the
container body 802 by securing it to the lower side of the
substrate holder plate 832. This is accomplished by engaging the
pumping system 159 to evacuate the space between the substrate 821
and the substrate holder plate 832 via port 841 thereby creating a
vacuum condition. The bladder 836 is then inflated by supplying a
fluid such as air or water from the fluid source 838 to the inlets
842. The fluid is delivered into the bladder 836 via the manifold
outlets 854, thereby pressing the substrate 821 uniformly against
the contacts of the electric contact 466. The electroplating
process is then carried out. Electrolyte solution is then pumped
into the process cell 420 toward the substrate 821 to contact the
exposed substrate plating surface 820. The power supply provides a
negative bias to the substrate plating surface 820 via the electric
contact 466. As the electrolyte solution is flowed across the
substrate plating surface 820, ions in the electrolytic solution
are attracted to the surface 820 and deposit on the surface 820 to
form the desired film.
[0083] Because of its flexibility, the bladder 836 deforms to
accommodate the asperities of the substrate backside and contacts
of the electric contact 466 thereby mitigating misalignment with
the conducting electric contact 466. The compliant bladder 836
prevents the electrolyte solution from contaminating the backside
of the substrate 821 by establishing a fluid tight seal at a
portion close to the perimeter of a backside of the substrate 821.
Once inflated, a uniform pressure is delivered downward toward the
electric contact 466 to achieve substantially equal force at all
points where the substrate 821 and electric contact 466 interface.
The force can be varied as a function of the pressure supplied by
the fluid source 838. Further, the effectiveness of the bladder
assembly 470 is not dependent on the configuration of the electric
contact 466. For example, while FIG. 12 shows a pin configuration
having a plurality of discrete contact points, the electric contact
466 may also be a continuous surface.
[0084] Because the force delivered to the substrate 821 by the
bladder 836 is variable, adjustments can be made to the current
flow supplied by the contact ring 466. As described above, an oxide
layer may form on the electric contact 466 and act to restrict
current flow. However, increasing the pressure of the bladder 836
may counteract the current flow restriction due to oxidation. As
the pressure is increased, the malleable oxide layer is compromised
and superior contact between the electric contact 466 and the
substrate 821 results. The effectiveness of the bladder 836 in this
capacity may be further improved by altering the geometry of the
electric contact 466. For example, a knife-edge geometry is likely
to penetrate the oxide layer more easily than a dull rounded edge
or flat edge.
[0085] Additionally, the fluid tight seal provided by the inflated
bladder 836 allows the pump 845 to maintain a backside vacuum or
pressure either selectively or continuously, before, during, and
after processing. Generally, however, the pump 845 is run to
maintain a vacuum only during the transfer of substrates to and
from the electroplating process cell 400 because it has been found
that the bladder 836 is capable of maintaining the backside vacuum
condition during processing without continuous pumping. Thus, while
inflating the bladder 836, as described above, the backside vacuum
condition is simultaneously relieved by disengaging the pumping
system 859, e.g., by selecting an off position on the cross-over
valve 847. Disengaging the pumping system 859 may be abrupt or
comprise a gradual process whereby the vacuum condition is ramped
down. Ramping allows for a controlled exchange between the
inflating bladder 836 and the simultaneously decreasing backside
vacuum condition. This exchange may be controlled manually or by
computer.
[0086] As described above, continuous backside vacuum pumping while
the bladder 836 is inflated is not needed and may actually cause
the substrate 820 to buckle or warp leading to undesirable
deposition results. It may be desirable to provide a backside
pressure to the substrate 820 in order to cause a "bowing" effect
of the substrate to be processed. Bowing of the substrate may
results in superior deposition on the substrate since portions,
such as the periphery, of the substrate are displaced by the bowing
nearer to the anode than other portions. The bowing may make the
metal film deposition more uniform if portions of the seed layer
having a lesser current density are displaced closer to the anode
to make the electric current density more uniform across the
substrate. Thus, pumping system 859 is capable of selectively
providing a vacuum or pressure condition to the substrate backside.
For a 200 mm substrate, for example, a backside pressure up to 5
psi is selected to bow the substrate. The degree of bowing is
variable according to the pressure supplied by pumping system 859.
Because substrates typically exhibit some measure of pliability, a
backside pressure causes the substrate to bow or assume a convex
shape relative to the upward flow of the electrolyte solution.
[0087] Those skilled in the art will readily recognize other
embodiments. For example, while FIG. 12A shows a bladder 836 having
a surface area sufficient to cover a relatively small perimeter
portion of the substrate backside at a diameter substantially equal
to the electric contact 466. The geometric configuration of the
bladder assembly 470 can be varied. Thus, the bladder assembly may
be constructed using more fluid impervious material to cover an
increased surface area of the substrate 821.
[0088] FIG. 19 is a partial cross sectional view of an alternative
embodiment of a substrate holder assembly. The alternative
substrate holder assembly 1900 comprises a bladder assembly 470, as
described above, having the inflatable bladder 836 attached to the
back surface of an intermediary substrate holder plate 1910. A
portion of the inflatable bladder 836 is sealingly attached to the
back surface 1912 of the intermediary substrate holder plate 1910
using an adhesive or other bonding material. The front surface 1914
of the intermediary substrate holder plate 1910 is adapted to
receive a substrate 821 to be processed. An elastomeric o-ring 1916
is disposed in an annular groove 1918 on the front surface 1914 of
the intermediary substrate holder plate 1910 to contact a
peripheral portion of the substrate back surface. The elastomeric
o-ring 1916 provides a seal between the substrate back surface and
the front surface of the intermediary substrate holder plate. The
intermediary substrate holder plate includes a plurality of bores
or holes 1920 extending through the plate that are in fluid
communication with the vacuum port 841. The plurality of holds 1920
facilitate securing the substrate on the substrate holder plate
using a vacuum force applied to the backside of the substrate.
According to this alternative embodiment of the substrate holder
assembly, the inflatable bladder does not directly contact a
substrate being processed, and thus the risk of cutting or damaging
the inflatable bladder during substrate transfers is significantly
reduced. The elastomeric O-ring 1916 may be coated or treated to
provide a hydrophilic surface for contacting the substrate. The
elastomeric O-ring 1916 is replaced as needed to ensure proper
contact and seal to the substrate.
[0089] FIG. 25 is an alternative embodiment of the substrate holder
system 14 having a rotatable head assembly 2410. In one embodiment,
a rotational actuator is disposed on the cantilevered arm and
attached to the head assembly to rotate the head assembly during
substrate processing. The rotatable head assembly 2410 is mounted
onto a head assembly frame 2452. The alternative embodiment of head
assembly frame 2452 and the rotatable head assembly 2410 are
mounted onto the mainframe similarly to the head assembly frame 452
and head assembly 410 as shown in FIG. 6 and described above. The
head assembly frame 2452 includes a mounting post 2454, a post
cover 2455, and a cantilever arm 2456. The mounting post 2454 is
mounted onto the body of the mainframe 214, and the post cover 2455
covers a top portion of the mounting post 2454. In one embodiment,
the mounting post 454 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 2452. The cantilever
arm 2456 extends laterally from an upper portion of the mounting
post 2454 and is pivotally connected to the post cover 2455 at the
pivot joint 2459. The rotatable head assembly 2410 is attached to a
mounting slide 2460 disposed at the distal end of the cantilever
arm 2456. The mounting slide 2460 guides the vertical motion of the
head assembly 2410. A head lift actuator 2458 is disposed on top of
the mounting slide 2460 to provide vertical displacement of the
head assembly 2410.
[0090] The lower end of the cantilever arm 2456 is connected to the
shaft 2453 of a cantilever arm actuator 2457, such as a pneumatic
cylinder or a lead-screw actuator, mounted on the mounting post
2454. The cantilever arm actuator 2457 provides pivotal movement,
as indicated by arrow A2, of the cantilever arm 2456 with respect
to the pivot joint 2459 between the cantilever arm 2456 and the
post cover 2454. When the cantilever arm actuator 2457 is
retracted, the cantilever arm 2456 moves the head assembly 2410
away from the process cell 420. The movement of the head assembly
2410 provide the spacing required to remove and/or replace the
process cell 420 from the electroplating process cell 240. When the
cantilever arm actuator 2457 is extended, the cantilever arm 2456
moves the head assembly 2410 toward the process cell 420 to
position the substrate in the head assembly 2410 in a processing
position.
[0091] The rotatable head assembly 2410 includes a rotating
actuator 2464 slideably connected to the mounting slide 2460. The
shaft 2468 of the head lift actuator 2458 is inserted through a
lift guide 2466 attached to the body of the rotating actuator 2464.
In an embodiment, the shaft 2468 is a lead-screw type shaft that
moves the lift guide, as indicated by arrows A3, between various
vertical positions. The rotating actuator 2464 is connected to the
substrate holder assembly 2450 through the shaft 2470 and rotates
the substrate holder assembly 2450, as indicated by arrows A4. The
substrate holder assembly 2450 includes a bladder assembly, such as
the embodiments described above with respect to FIGS. 12-15 and 19,
and a cathode contact ring, such as the embodiments described above
with respect to FIGS. 7-10 and 18.
[0092] The rotation of the substrate during the electroplating
process generally enhances the deposition results. In one
embodiment, the head assembly is rotated between about 2 rpm and
about 200 rpm, preferably between about 20 and 40 rpm, when the
substrate is immersed in the electrolyte solution, during the
electroplating process. The substrate holder assembly 2472 can be
rotated to impart rotation to the substrate as the substrate holder
system 14 lowers the seed layer on the substrate into contact with
the electrolyte solution in the process cell. The head assembly is
raised to remove the seed layer on the substrate from the
electrolyte solution in the process cell. The head assembly is
preferably rotated at a high speed, i.e., between about 100 and
2500 rpm, after the head assembly is lifted from the process cell
to enhance removal of residual electrolyte solution from the head
assembly by centrifugel force.
[0093] In one embodiment, the uniformity of the deposited film has
been improved within about 2%, i.e., maximum deviation of deposited
film thickness is at about 2% of the average film thickness, while
standard electroplating processes typically achieves uniformity at
best within about 5.5%. However, rotation of the head assembly is
not necessary to achieve uniform electroplating deposition in some
instances, particularly where the uniformity of electroplating
deposition is achieved by adjusting the processing parameters, such
as the chemicals in the electrolyte solution, electrolyte solution
flow and other parameters.
[0094] Referring back to FIG. 6, a cross sectional view of an
electroplating process cell 400, the substrate holder assembly 450
is positioned above the process cell 420. The process cell 420
generally comprises a bowl 430, a container body 472, an anode
assembly 474 and a filter 476. In one embodiment, the anode
assembly 474 is disposed below the container body 472 and attached
to a lower portion of the container body 472, and the filter 476 is
disposed between the anode assembly 474 and the container body 472.
The container body 472 is preferably a cylindrical body comprised
of an electrically insulative material, such as ceramics, plastics,
PLEXIGLAS.RTM. (acrylic), lexane, PVC, CPVC, and PVDF.
Alternatively, the container body 472 can be made from a coated
metal, such as stainless steel, nickel and titanium. The coated
metal is coated with an insulating layer such as TEFLON.RTM. (a
trademark of the E. I. duPont de Nemoirs Company of Wilmington,
Del.), PVDF, plastic, rubber and other combinations of materials
that do not dissolve in the electrolyte solution. The insulating
layer can be electrically insulated from the electrodes, i.e., the
anode and cathode of the ECP system. The container body 472 is
sized and adapted to conform to the substrate plating surface and
the shape of the of a substrate being processed through the system,
typically circular or rectangular in shape. One embodiment of the
container body 472 comprises a cylindrical ceramic tube having an
inner diameter that has about the same dimension as or slightly
larger than the substrate diameter. Rotational movement typically
required in typical ECP systems is not required to achieve uniform
plating results when the size of the container body conforms to
about the size of the substrate plating surface.
[0095] An upper portion of the container body 472 extends radially
outwardly to form an annular weir 478. The weir 478 extends over
the inner wall 446 of the electrolyte solution collector 440 and
allows the electrolyte solution to flow into the electrolyte
solution collector 440. The upper surface of the weir 478 matches
the lower surface of the electric contact 466. The upper surface of
the weir 478 includes an inner annular flat portion 480, a middle
inclined portion 482 and an outer declined portion 484. When a
substrate is positioned in the processing position, the substrate
plating surface is positioned above the cylindrical opening of the
container body 472. A gap for electrolyte solution flow is formed
between the lower surface of the electric contact 466 and the upper
surface of the weir 478. The lower surface of the electric contact
466 is disposed above the inner flat portion 480 and the middle
inclined portion of the weir 478. The outer declined portion 484 is
sloped downwardly to facilitate flow of the electrolyte solution
into the electrolyte solution collector 440.
[0096] A lower portion of the container body 472 extends radially
outwardly to form a lower annular flange 486 for securing the
container body 472 to the bowl 430. The outer dimension, i.e.,
circumference, of the annular flange 486 is smaller than the
dimensions of the opening 444 and the inner circumference of the
electrolyte solution collector 440. The smaller dimension of the
annular flange to allow removal and replacement of the process cell
420 from the electroplating process cell 400. In one embodiment,
multiple bolts 488 are fixedly disposed on the annular flange 486
and extend downwardly through matching bolt holes on the bowl 430.
A plurality of removable fastener nuts 490 secure the process cell
420 onto the bowl 430. A seal 487, such as an elastomer O-ring, is
disposed between container body 472 and the bowl 430 radially
inwardly from the bolts 488 to prevent leaks from the process cell
420. The nuts/bolts combination facilitates fast and easy removal
and replacement of the components of the process cell 420 during
maintenance.
[0097] In one embodiment, the filter 476 is attached to and
completely covers the lower opening of the container body 472, and
the anode assembly 474 is disposed below the filter 476. A spacer
492 is disposed between the filter 476 and the anode assembly 474.
In an embodiment, the filter 476, the spacer 492, and the anode
assembly 474 are fastened to a lower surface of the container body
472 using removable fasteners, such as screws and/or bolts.
Alternatively, the filter 476, the spacer 492, and the anode
assembly 474 are removably secured to the bowl 430.
[0098] The anode assembly 474 in one embodiment comprises a
consumable anode that serves as a metal source in the electrolyte
solution. Alternatively, the anode assembly 474 comprises a
non-consumable anode, and the metal to be electroplated is supplied
within the electrolyte solution from the electrolyte solution
replenishing system 220. As shown in FIG. 6, the anode assembly 474
is a self-enclosed module having a porous anode enclosure 494 that
may be made of the same metal as the metal to be electroplated,
such as copper. Alternatively, the anode enclosure 494 is made of
porous materials, such as ceramics or polymeric membranes. A
soluble metal 496, such as high purity copper for electro-chemical
plating of copper, is disposed within the anode enclosure 494. The
soluble metal 496 preferably comprises metal particles, wires or a
perforated sheet. The porous anode enclosure 494 also acts as a
filter that keeps the particulates generated by the dissolving
metal within the anode enclosure 494. As compared to a
non-consumable anode, the consumable, i.e., soluble, anode provides
gas-generation-free electrolyte solution and minimizes the need to
constantly replenish the metal in the electrolyte solution.
[0099] An anode electrode contact 498 is inserted through the anode
enclosure 494 to provide electrical connection to the soluble metal
496 from a power supply. In one embodiment, the anode electrode
contact 498 is made from a conductive material that is insoluble in
the electrolyte solution, such as titanium, platinum and
platinum-coated stainless steel. The anode electrode contact 498
extends through the bowl 430 and is connected to an electric power
supply. Preferably, the anode electric contact 498 includes a
threaded portion 497 for a fastener nut 499 to secure the anode
electric contact 498 to the bowl 430, and a seal 495 such as a
elastomer washer, is disposed between the fastener nut 499 and the
bowl 430 to prevent leaks from the process cell 420.
[0100] The bowl 430 generally comprises a cylindrical portion 502
and a bottom portion 504. An upper annular flange 506 extends
radially outwardly from the top of the cylindrical portion 502. The
upper annular flange 506 includes a plurality of holes 508 that
matches the number of bolts 488 from the lower annular flange 486
of the container body 472. Bolts 488 are inserted through the holes
508, and the fastener nuts 490 are fastened onto the bolts 488 that
secure the upper annular flange 506 of the bowl 430 to the lower
annular flange 486 of the container body 472. In one embodiment,
the outer dimension, i.e., circumference, of the upper annular
flange 506 is about the same as the outer dimension, i.e.,
circumference, of the lower annular flange 486. Preferably, the
lower surface of the upper annular flange 506 of the bowl 430 rests
on a support flange of the mainframe 214 when the process cell 420
is positioned on the mainframe 214.
[0101] The inner circumference of the cylindrical portion 502
accommodates the anode assembly 474 and the filter 476. Preferably,
the outer dimensions of the filter 476 and the anode assembly 474
are slightly smaller than the inner dimension of the cylindrical
portion 502. These relative dimensions force a substantial portion
of the electrolyte solution to flow through the anode assembly 474
first before flowing through the filter 476. The bottom portion 504
of the bowl 430 includes an electrolyte solution inlet 510 that
connects to an electrolyte solution supply line from the
electrolyte solution replenishing system 220. In one embodiment,
the anode assembly 474 is disposed about a middle portion of the
cylindrical portion 502 of the bowl 430. The anode assembly 474 is
configured to provide a gap for electrolyte solution flow between
the anode assembly 474 and the electrolyte solution inlet 510 on
the bottom portion 504.
[0102] The electrolyte solution inlet 510 and the electrolyte
solution supply line are connected by a releasable connector that
facilitates easy removal and replacement of the process cell 420.
When the process cell 420 needs maintenance, the electrolyte
solution is drained from the process cell 420, and the electrolyte
solution flow in the electrolyte solution supply line is
discontinued and drained. The connector for the electrolyte
solution supply line is released from the electrolyte solution
inlet 510, and the electric connection to the anode assembly 474 is
also disconnected. The head assembly 410 is raised or rotated to
provide clearance for removal of the process cell 420. The process
cell 420 is then removed from the mainframe 214, and a new or
reconditioned process cell is replaced into the mainframe 214.
[0103] Alternatively, the bowl 430 can be secured onto the support
flange of the mainframe 214, and the container body 472 along with
the anode and the filter are removed for maintenance. In this case,
the nuts securing the anode assembly 474 and the container body 472
to the bowl 430 are removed to facilitate removal of the anode
assembly 474 and the container body 472. New or reconditioned anode
assembly 474 and container body 472 are then replaced into the
mainframe 214 and secured to the bowl 430.
[0104] FIG. 20 is a cross sectional view of one embodiment of an
encapsulated anode. The encapsulated anode 2000 includes a
permeable anode enclosure that filters or traps "anode sludge" or
particulates generated as the metal is dissolved from the anode
plate 2004. As shown in FIG. 20, the anode plate 2004 comprises a
solid piece of copper. In one embodiment, the anode plate 2004 is a
high purity, oxygen free copper, enclosed in a hydrophilic anode
encapsulation membrane 2002. The anode plate 2004 is secured and
supported by a plurality of electric contacts or feed-throughs 2006
that extend through the bottom of the bowl 430. The electric
contacts or feed-throughs 2006 extend through the anode
encapsulation membrane 2002 into the bottom surface of the anode
plate 2004. The flow of the electrolyte solution, as indicated by
the arrow A, from the electrolyte solution inlet 510 disposed at
the bottom of the bowl 430 through the gap between the anode and
the bowl sidewall. The electrolyte solution also flows through the
anode encapsulation membrane 2002 by permeation into and out of the
gap between the anode encapsulation membrane and the anode plate,
as indicated by the arrow B. In one embodiment, the anode
encapsulation membrane 2002 comprises a hydrophilic porous
membrane, such as a modified polyvinyllidene fluoride membrane,
having porosity between about 60% and 80%, more preferably about
70%, and pore sizes between about 0.025 .mu.m and about 1 .mu.m,
more preferably between about 0.1 .mu.m and about 0.2 .mu.m. One
example of a hydrophilic porous membrane is the Durapore
Hydrophilic Membrane, available from Millipore Corporation, located
in Bedford, Mass. As the electrolyte solution flows through the
encapsulation membrane, anode sludge and particulates generated by
the dissolving anode are filtered or trapped by the encapsulation
membrane. Thus, the encapsulation membranes improve the purity of
the electrolyte solution during the electroplating process, and
defect formations on the substrate during the electroplating
process caused by anode sludge and contaminant particulates are
significantly reduced.
[0105] FIG. 21 is a cross sectional view of another embodiment of
an encapsulated anode. The anode plate 2004 is secured and
supported on the electric feed-throughs 2006. A top encapsulation
membrane 2008 and a bottom encapsulation membrane 2010, disposed
respectively above and below the anode plate 2004, are attached to
a membrane support ring 2012 that is disposed around the anode
plate 2004. The top and bottom encapsulation membranes 2008, 2010
comprise a material from the list above. The membrane support ring
2012 comprises a relatively rigid material as compared to the
encapsulation membrane, such as plastic or other polymers. A bypass
fluid inlet 2014 is disposed through the bottom of the bowl 430 and
through the bottom encapsulation membrane 2010 to introduce
electrolyte solution into the gap between the encapsulation
membranes and the anode plate. A bypass outlet 2016 is connected to
the membrane support ring 2012 and extends through the bowl 430 to
facilitate flow of excess electrolyte solution with the anode
sludge or generated particulates out of the encapsulated anode into
a waste drain, not shown.
[0106] In one embodiment, the flow of the electrolyte solution
within the bypass fluid inlet 2014 and the main electrolyte
solution inlet 510 are individually controlled by flow control
valves 2020, 2022. The individual flow control valves 2020, 2022
are respectively placed along the fluid lines connected to the
inlets. The fluid pressure in the bypass fluid inlet 2014 is
maintained at a higher pressure than the pressure in the main
electrolyte solution inlet 510. The flow of the electrolyte
solution inside the bowl 430 from the main electrolyte solution
inlet 510 is indicated by arrows A, and the flow of the electrolyte
solution inside the encapsulated anode 2000 is indicated by the
arrows B. A portion of the electrolyte solution introduced into the
encapsulated anode flows out of the encapsulated anode through the
bypass outlet 2016. By providing a dedicated bypass electrolyte
solution supply into the encapsulated anode, the anode sludge or
particulates generated from the dissolving anode is continually
removed from the anode, thereby improving the purity of the
electrolyte solution during the electroplating process.
[0107] FIG. 22 is a cross sectional view of yet another embodiment
of an encapsulated anode. This embodiment of an encapsulated anode
2000 includes an anode plate 2004, a plurality of electric
feed-throughs 2006, a top encapsulation membrane 2008, a bottom
encapsulation membrane 2010, a membrane support ring 2012, and a
bypass outlet 2016. The anode plate 2004 is secured and supported
on the plurality of electric feed-throughs 2006. The top and a
bottom encapsulation membrane 2008, 2010 are attached to a membrane
support ring 2012. The bypass outlet 2016 is connected to the
membrane support ring 2012 and extends through the bowl 430. This
embodiment of an encapsulated anode preferably comprises materials
as described above for the previous-described embodiments of an
encapsulated anode. The bottom encapsulation membrane 2010 includes
one or more openings 2024 disposed substantially above the main
electrolyte solution inlet 510. Each opening 2024 is adapted to
receive flow of electrolyte solution from the main electrolyte
solution inlet 510 and is preferably about the same size as the
internal circumference of the main electrolyte solution inlet 510.
The flow of the electrolyte solution from the main electrolyte
solution inlet 510, indicated by the arrow A, and the flow of the
electrolyte solution within the encapsulated anode, indicated by
the arrow B. A portion of the electrolyte solution flows out of the
encapsulated anode through the bypass outlet 2016, carrying a
portion of the anode sludge and particulates generated from anode
dissolution.
[0108] FIG. 23 is a cross sectional view of another embodiment of
an encapsulated anode. This embodiment of an encapsulated anode
2000 includes an anode plate 2002, a plurality of electric
feed-throughs 2006, a top encapsulation membrane 2008, a bottom
encapsulation membrane 2010, a membrane support ring 2012, and a
bypass fluid inlet 2014. The anode plate 2002 is secured and
supported on a plurality of electric feed-throughs 2006. The top
and bottom encapsulation membranes 2008, 2010 are attached to a
membrane support ring 2012. A bypass fluid inlet 2014 is disposed
through the bottom of the bowl 430 and through the bottom
encapsulation membrane 2010 to introduce electrolyte solution into
the gap between the encapsulation membranes and the anode plate.
This embodiment of an encapsulated anode comprises materials as
described above for the above-described embodiments of an
encapsulated anode. In one embodiment, the flow of the electrolyte
solution through the bypass fluid inlet 2014 and the main
electrolyte solution inlet 510 are individually controlled by
control valves 2020, 2022, respectively. The flow of the
electrolyte solution from the main electrolyte solution inlet 510
is indicated by the arrows A while the flow of the electrolyte
solution through the encapsulated anode is indicated by arrows B.
For this embodiment, the anode sludge and particulates generated by
the dissolving anode plate are filtered and trapped by the
encapsulation membranes as the electrolyte solution passes through
the membrane.
[0109] FIG. 16 is a schematic diagram of an electrolyte solution
replenishing system 220. The electrolyte solution replenishing
system 220 provides the electrolyte solution to the electroplating
process cells for the electroplating process. The electrolyte
solution replenishing system 220 generally comprises a main
electrolyte solution tank 602, a dosing module 603, a filtration
module 605, a chemical analyzer module 616, and an electrolyte
solution waste disposal system 622. The electrolyte solution waste
disposal system 622 is connected to the analyzing module 616 by an
electrolyte solution waste drain 620. One or more controllers
control the chemical composition of the electrolyte solution in the
main tank 602 and the related operation of the electrolyte solution
replenishing system 220. In one embodiment, the controllers are
independently operable but integrated with the controller 222 of
the ECP system 200.
[0110] The main electrolyte solution tank 602 provides a reservoir
for electrolyte solution and includes an electrolyte solution
supply line 612 that is connected to each of the electroplating
process cells through one or more fluid pumps 608 and valves 607. A
heat exchanger 624 or a heater/chiller disposed in thermal
connection with the main tank 602 controls the temperature of the
electrolyte solution stored in the main tank 602. The heat
exchanger 624 is connected to and operated by the controller
610.
[0111] The dosing module 603 is connected to the main tank 602 by a
supply line and includes a plurality of source tanks 606, or feed
bottles, a plurality of valves 609, and a controller 611. The
source tanks 606 contain the chemicals needed for composing the
electrolyte solution and typically include a deionized water source
tank and copper sulfate (CuS0.sub.4) source tank for composing the
electrolyte solution. Other source tanks 606 may contain hydrogen
sulfate (H.sub.2SO.sub.4), hydrogen chloride (HCl) and various
additives such as glycol. Each source tank may be 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.
[0112] The deionized water source tank preferably also provides
deionized water to the system for cleaning the system during
maintenance. The valves 609 associated with each source tank 606
regulate the flow of chemicals to the main tank 602 and may be any
of numerous commercially available valves such as butterfly valves,
throttle valves and the like. Activation of the valves 609 is
accomplished by the controller 611 which may be connected to the
controller 222 to receive signals therefrom.
[0113] The electrolyte solution filtration module 605 includes a
plurality of filter tanks 604. An electrolyte solution return line
614 is connected between each of the process cells and one or more
filter tanks 604. The filter tanks 604 remove the undesired
contents in the used electrolyte solution before returning the
electrolyte solution to the main tank 602 for re-use. The main tank
602 is also connected to the filter tanks 604 to facilitate
re-circulation and filtration of the electrolyte solution in the
main tank 602. By re-circulating the electrolyte solution from the
main tank 602 through the filter tanks 604, the undesired contents
in the electrolyte solution are continuously removed by the filter
tanks 604 to maintain a consistent level of purity. Additionally,
re-circulating the electrolyte solution between the main tank 602
and the filtration module 605 allows the various chemicals in the
electrolyte solution to be thoroughly mixed.
[0114] The electrolyte solution replenishing system 220 also
includes a chemical analyzer module 616 that provides real-time
chemical analysis of the chemical composition of the electrolyte
solution. The analyzer module 616 is fluidly coupled to the main
tank 602 by a sample line 613 and to the waste disposal system 622
by an outlet line 621. The analyzer module 616 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 solution. 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.
16 the chemical analyzer module 616 comprises an auto titration
analyzer 615 and a cyclic voltametric stripper (CVS) 617. 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 615 determines the
concentrations of inorganic substances such as copper chloride and
acid. The CVS 617 determines the concentrations of organic
substances such as the various additives which may be used in the
electrolyte solution and by-products resulting from the processing
which are returned to the main tank 602 from the process cells.
[0115] The analyzer module shown FIG. 16 is merely illustrative. In
another embodiment each analyzer may be coupled to the main
electrolyte solution tank by a separate supply line and be operated
by separate controllers. Persons skilled in the art will recognize
other embodiments.
[0116] In operation, a sample of electrolyte solution is flowed to
the analyzer module 616 via the sample line 613. Although the
sample may be taken periodically, preferably a continuous flow of
electrolyte solution is maintained to the analyzer module 616. A
portion of the sample is delivered to the auto titration analyzer
615 and a portion is delivered to the CVS 617 for the appropriate
analysis. The controller 619 initiates command signals to operate
the analyzers 615, 617 in order to generate data. The information
from the chemical analyzers 615, 617 is then communicated to the
controller 222. The controller 222 processes the information and
transmits signals that include user-defined chemical dosage
parameters to the dosing controller 611. The received information
is used to provide real-time adjustments to the source chemical
replenishment rates by operating one or more of the valves 609. The
received information thereby maintains a desired, and preferably
constant, chemical composition of the electrolyte solution
throughout the electroplating process. The waste electrolyte
solution from the analyzer module is then flowed to the waste
disposal system 622 via the outlet line 621.
[0117] Although one embodiment utilizes real-time monitoring and
adjustments of the electrolyte solution, various alternatives may
be employed. For example, the dosing module 603 may be controlled
manually by an operator observing the output values provided by the
chemical analyzer module 616. In one embodiment, the system
software allows for both an automatic real-time adjustment mode as
well as an operator, manual, mode. Further, although multiple
controllers are shown in FIG. 16, a single controller may be used
to operate various components of the system such as the chemical
analyzer module 616, the dosing module 603, and,the heat exchanger
624. Other embodiments will be apparent to those skilled in the
art.
[0118] The electrolyte solution replenishing system 220 also
includes an electrolyte solution waste drain 620 connected to an
electrolyte solution waste disposal system 622 for safe disposal of
used electrolyte solutions, chemicals and other fluids used in the
ECP system. In one embodiment, the electroplating cells include a
direct line connection to the electrolyte solution waste drain 620,
or the electrolyte solution waste disposal system 622. The
electrolyte solution waste drain 620 drains the electroplating
cells without returning the electrolyte solution through the
electrolyte solution replenishing system 220. The electrolyte
solution replenishing system 220 preferably also includes a bleed
off connection to bleed off excess electrolyte solution to the
electrolyte solution waste drain 620.
[0119] In one embodiment, the electrolyte solution replenishing
system 220 also includes one or more degasser modules 630 adapted
to remove undesirable gases from the electrolyte solution. 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 630
are preferably placed in line on the electrolyte solution supply
line 612 adjacent to the process cells 240. The degasser modules
630 are preferably positioned as close as possible to the process
cells 240 so most of the gases from the electrolyte solution
replenishing system are removed by the degasser modules before the
electrolyte solution enters the process cells. In one embodiment,
each degasser module 630 includes two outlets to supply degassed
electrolyte solution to the two process cells 240 of each
processing station 218. Alternatively, a degasser module 630 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 solution
replenishing system, such as along with the filter section or in a
closed-loop system with the main tank or with the process cell. As
another example, one degasser module is placed in line with the
electrolyte solution supply line 612 to provide degassed
electrolyte solution to all of the process cells 240 of the
electrochemical plating 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. A commercially available degasser
module is available from Millipore Corporation, located in Bedford,
Mass.
[0120] One embodiment of the degasser module 630, as shown in FIG.
26a, includes a hydrophobic membrane 632 having a fluid, i.e.,
electrolyte solution, passage 634 on one side of the membrane 632.
A vacuum system 636 disposed on the opposite side of the membrane.
The enclosure 638 of the degasser module includes an inlet 640 and
one or more outlets 642. As the electrolyte solution passes through
the degasser module 630, the gases and other micro-bubbles in the
electrolyte solution are separated from the electrolyte solution
through the hydrophobic membrane and removed by the vacuum system.
Another embodiment of the degasser module 630', as shown in FIG.
26b, includes a tube of hydrophobic membrane 632' and a vacuum
system 636 disposed around the tube of hydrophobic membrane 632'.
The electrolyte solution is introduced inside the tube of
hydrophobic membrane, and as the electrolyte solution passes
through the fluid passage 634 in the tube. The hydrophobic membrane
separates gases and other micro-bubbles in the electrolyte
solution, and a tube that is connected to the vacuum system 636
removes the separated gasses. More complex designs of degasser
modules are contemplated, including designs having serpentine paths
of the electrolyte solution across the membrane and other
multi-sectioned designs of degasser modules.
[0121] Although not shown in FIG. 16, the electrolyte solution
replenishing system 220 may include a number of other components.
For example, the electrolyte solution replenishing system 220 may
also include one or more additional tanks for storage of chemicals
for a substrate 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 solution replenishing
system 220 includes connections to additional or external
electrolyte solution processing system to provide additional
electrolyte solution supplies to the ECP system.
[0122] FIG. 17 is a cross sectional view of one embodiment of rapid
thermal anneal (RTA) chamber. The RTA chamber 211 is preferably
connected to the loading station 210, and substrates are
transferred into and out of the RTA chamber 211 by the loading
station transfer robot 228. The ECP system, as shown in FIGS. 2 and
3, comprises two RTA chambers 211 disposed on opposing sides of the
loading station 210, corresponding to the symmetric design of the
loading station 210. RTA chambers are generally well known in the
art, and RTA chambers are typically utilized in substrate
processing systems to enhance the properties of the deposited
materials. A variety of RTA chamber designs, including hot plate
designs and heat lamp designs, may be used to enhance the
electroplating results. One RTA chamber is the WxZ chamber
available from Applied materials, Inc., located in Santa Clara,
Calif. Although this disclosure is described using a hot plate RTA
chamber, other types of RTA chambers may be used as well.
[0123] Referring back to FIG. 2, the ECP system 200 includes a
controller 222 that controls the functions of each component of the
platform. In one embodiment, the controller 222 is mounted above
the mainframe 214, and the controller comprises a programmable
microprocessor. The programmable microprocessor is typically
programmed using a software designed specifically for controlling
all components of the ECP system 200. The controller 222 also
provides electric power to the components of the system and
includes a control panel 223 that allows an operator to monitor and
operate the ECP system 200. The control panel 223, as shown in FIG.
2, is a stand-alone module that is connected to the controller 222
through a cable and provides easy access to an operator. Generally,
the controller 222 coordinates the operations of the loading
station 210, the RTA chamber 211, the SRD station 212, the
mainframe 214 and the processing stations 218. Additionally, the
controller 222 coordinates with the controller of the electrolyte
solution replenishing system 220 to provide the electrolyte
solution for the electroplating process.
[0124] The following is a description of one embodiment of a
substrate electroplating process sequence through the
electroplating system platform 200 as shown in FIG. 2. A substrate
cassette containing a plurality of substrates is loaded into the
substrate cassette receiving areas 224 in the loading station 210
of the electroplating system platform 200. A loading station
transfer robot 228 picks up a substrate from a substrate slot in
the substrate cassette and places the substrate in the substrate
orientor 230. The substrate orientor 230 determines and orients the
substrate to a desired orientation for processing through the
system. The loading station transfer robot 228 then transfers the
oriented substrate from the substrate orientor 230 and positions
the substrate in one of the substrate slots in the substrate
pass-through cassette 238 in the SRD station 212. The mainframe
transfer robot 242 picks up the substrate from the substrate
pass-through cassette 238 and positions the substrate for transfer
by the flipper robot 248. The flipper robot 248 rotates its robot
blade below the substrate and picks up substrate from mainframe
transfer robot blade. The vacuum suction gripper on the flipper
robot blade secures the substrate on the flipper robot blade, and
the flipper robot flips the substrate from a face up position to a
face down position. The flipper robot 248 rotates and positions the
substrate face down in the substrate holder assembly 450. The
substrate is positioned below the substrate holder plate 464 but
above the cathode contact ring 466. The flipper robot 248 then
releases the substrate to position the substrate into the cathode
contact ring 466. The substrate holder plate 464 moves toward the
substrate and the vacuum chuck secures the substrate on the
substrate holder plate 464. The bladder assembly 470 on the
substrate holder assembly 450 exerts pressure against the substrate
backside to ensure electric contact between the substrate plating
surface and the cathode contact ring 466.
[0125] To limit deposition of metal film on the electric contacts,
a negative bias is applied by the power supply 702 (shown in FIG.
11) under the control of the controller 222. The head assembly 452
is lowered to a processing position above the process cell 420. The
negative bias voltage can then be applied to the electric contacts.
The duration at which the negative bias voltage is applied to the
electric contacts is shorter than a duration that would dry the
electrolyte solution to form chemical (.e.g., copper sulfate)
crystals on the electric contacts. As such, the duration at which
the negative bias voltage may be applied to the electric contacts
before immersion of the electric contacts and the substrate into
the electrolyte solution is dependent on such factors as the
particular chemical make-up of the electrolyte solution, and the
drying conditions that the electric contacts are exposed to prior
to immersion. During the immersion of the electric contacts into
the electrolyte solution, however, a slight negative (depating) or
neutral bias voltage is applied between the anode and the seed
layer to ensure that the metal ions do not deposit on the electric
contacts, maintaining the electric contacts in a pristine
condition. The level of the slight negative or neutral bias voltage
is selected to be insufficient to cause considerable deplating of
the seed layer, or deposited metal film, on the substrate. At this
position the substrate is below the upper plane of the weir 478 and
contacts the electrolyte solution contained in the process cell
420. The power supply is activated to supply electric power, i.e.,
voltage and current, to the cathode and the anode to enable the
electroplating process. The electrolyte solution is typically
continually pumped into the process cell during the electroplating
process. The electric power supplied to the cathode and the anode
and the flow of the electrolyte solution are controlled by the
controller 222 to achieve the desired electroplating results. In
one embodiment, the head assembly is rotated as the head assembly
is lowered and also during the electroplating process.
[0126] After the electroplating process is completed, the head
assembly 410 raises the substrate holder assembly and removes the
substrate from the electrolyte solution. During removal of the
substrate from the electrolyte solution, a slight negative
(deplating) or neutral voltage is applied between the anode and the
electric contacts to limit metal film deposition on the electric
contacts. The level of the slight negative or neutral voltage is
insufficient to cause deplating of the seed layer on the substrate.
The exact level of the slight negative or neutral voltage is
dependent upon the chemical make-up of the electrolyte solution. In
one embodiment, the head assembly is spun for a period of time at a
sufficient angular velocity such as between about 50 to about 3000
RPM, to enhance removal of residual electrolyte solution from the
substrate and the substrate holder assembly. The vacuum chuck and
the bladder assembly of the substrate holder assembly then release
the substrate from the substrate holder plate. The substrate holder
assembly is raised to allow the flipper robot blade to pick up the
processed substrate from the cathode contact ring. The flipper
robot rotates the flipper robot blade above the backside of the
processed substrate in the cathode contact ring and picks up the
substrate using the vacuum suction gripper on the flipper robot
blade. The flipper robot rotates the flipper robot blade with the
substrate out of the substrate holder assembly, flips the substrate
from a face-down position to a face-up position, and positions the
substrate on the mainframe transfer robot blade. The mainframe
transfer robot then transfers and positions the processed substrate
above the SRD module 236. The SRD substrate support lifts the
substrate, and the mainframe transfer robot blade retracts away
from the SRD module 236. The substrate 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 substrate is then
positioned for transfer out of the SRD module. The loading station
transfer robot 228 picks up the substrate from the SRD module 236
and transfers the processed substrate into the RTA chamber 211 for
an anneal treatment process to enhance the properties of the
deposited materials. The annealed substrate is then transferred out
of the RTA chamber 211 by the loading station robot 228 and placed
back into the substrate cassette for removal from the ECP system.
The above-described sequence can be carried out for a plurality of
substrates substantially simultaneously in the ECP system 200.
Also, the ECP system can be adapted to provide multi-stack
substrate processing.
[0127] 2. Voltage Levels Between the Anode and the Seed Laver
[0128] The above describes an ECP system that is used to
electroplate substrates. One concern during electroplating is to
make the depth of metal film deposited across the substrate seed
layer uniform. Metal film deposition can occur on the seed layer
during the time that the substrate is being immersed in, or is
being removed from the electrolyte solution. Most of the metal film
deposition occurs when the seed layer on the substrate is fully
immersed in the electrolyte solution. To ensure the uniformity of
metal film deposition rate across the substrate seed layer, it is
important to ensure that the electric current density applied to
the seed layer is uniform across the face of the substrate. One
aspect of the. ECP system that increases the uniformity of electric
current density applied to the substrate seed layer is ensuring
that each one of the plurality of electric contacts remains
consistently pristine. A method of modulating the power supply is
described herein so that the, electric contacts are maintained in a
pristine state substantially free of metal film deposition,
oxidation, or the chemical crystals that can occur when the power
supply is off. Additionally, the modulation of the power supply
enhances uniform deposition of the metal film on the seed
layer.
[0129] The controller 222 controls the level of voltage/current
applied between the anode and the seed layer on the substrate that
is produced by a power supply. For plating consideration, the
voltage level of the seed layer is considered relative to the anode
through the electrolyte solution. FIG. 27 shows one embodiment of
plating process depicted by a graph 2700 with voltage plotted as
the ordinate 2702 versus time plotted as the abscissa 2704 during
the plating process. Any voltage level above the level of the
abscissa 2704 indicates a positive voltage of the substrate seed
layer relative to the anode, i.e., an anodic seed layer and a
cathodic anode. Any voltage level below the abscissa 2704 indicates
a negative voltage level of the seed layer relative to the anode,
i.e., a cathodic substrate seed layer and an anodic anode. A
reverse bias voltage exists where the voltage of the substrate seed
layer is greater than the voltage level of the anode. Therefore, a
reverse bias voltage represents a reverse polarity between the
anode and the seed layer as compared to the polarity of a plating
voltage. During etching portions of the plating process, greater
reverse bias typically results in a greater etch rate of the
substrate seed layer.
[0130] Reference character 2720 represents one plating voltage
cycle for a given substrate within an electrolyte cell during the
plating process. Each plating voltage cycle 2720 includes a reverse
bias voltage, also known as a metal film etch portion 2708,
indicated as 2708a or 2708b, and a plating voltage, i.e., metal
film deposition, portion 2714. The plating voltage portion 2714
represents the voltage level when a plating voltage is applied
between the anode and the substrate seed layer. During the plating
voltage portion 2714, the metal ions in the electrolyte solution
are deposited on the substrate seed layer to form a metal film. The
duration of the plating voltage portion is a function of the
chemical make-up of the electrolyte solution, the metal being used
in the ECP process, the desired thickness of the metal film
deposited on the seed layer, and other such factors. The duration
of the plating voltage portion may range from about 10 seconds to
several minutes or more depending upon the chemical make-up of the
electrolyte solution, i.e., the recipe used during the ECP process.
The voltage level of the plating voltage portion 2714 may range
from a fraction of a volt to 10 or more volts.
[0131] The reverse bias voltage 2708 is applied as the substrate is
being immersed into, or withdrawn from, the electrolyte solution.
The reverse bias voltage also exists between plating cycles such as
when there is a temporary production downtime. Such downtime exists
when no more substrates are being processed in the ECP system for
some prescribed duration, .e.g., five minutes or longer. During
such ECP system downtime, it is common to immerse the substrate
holder assembly, including.the electric contacts, in the
electrolyte solution contained in the electrolyte cell. Such
immersion of the electric contacts limit evaporation of the
electrolyte solution on the electric contacts that would otherwise
form as chemical, .e.g., copper sulfate, crystals. Voltage level
2708a represents that portion of the reverse bias voltage that is
applied during a metal film etch plating voltage cycle 2720 when
substrates are being immersed into, or removed from, the
electrolyte solution. Such reverse bias voltage, e.g., metal film
etch, portions of the cycle are applied typically for a relatively
brief duration of time, typically less than 30 seconds. During the
time that the reverse bias voltage portion 2708 of each cycle is
being applied: a) a first substrate is removed from the
electroplating cell, b) a robot removes the first substrate from
the substrate holder assembly, c) a robot inserts a second
substrate into the substrate holder assembly, and d) the substrate
holder system 14 immerses the second substrate into the
electroplating process cell. It is common for each substrate to
undergo multiple plating cycles intermixed with multiple etching or
cleaning cycles ECP processing. The voltage level of the reverse
bias voltage 2708a may vary as a function of the dimensions of the
electrolyte cell, the composition of the electrolyte solution, the
metal film, and the seed layer, etc. The substrate seed layer is
typically biased anodically relative to the anode by, e.g., about a
fraction of a volt to about 4 volts during when voltage level 2708a
is applied.
[0132] The reverse bias voltage portion 2708b is applied between
the anode and the seed layer for an extended duration when
substrates are not being processed. Such lack of processing down
time may extend from a fraction of a minute to a day or more when
no substrates are being plated. In this disclosure, the term "down
time" is applied to these extended periods no substrates are being
processed by the ECP system. To provide a consistent electric
current density across the face of the substrate during metal film
deposition on the substrate, it is important to ensure that the
electric contacts are pristine. In this disclosure, the term
"pristine" means that the electric contacts are substantially free
of electroplated metal deposits and/or dried chemical crystals
during ECP processing. During extended down-time periods when no
substrate is in the substrate holder, the substrate holder assembly
is positioned so all of the electric contacts are immersed in the
electrolyte solution. This immersion during down time limits an
oxidation reaction that results when the electric contacts are
exposed to the oxygen present in the atmosphere. The voltage level
that has to be applied to the anode and the seed layer during the
reverse bias portion 2708b is a function of the dimensions of the
electrolyte cell, the chemical composition of the electrolyte
solution and/or the seed layer, etc. However, a typical voltage
level of the reverse bias portion 2708b for copper electroplating
has the contact elements biased anodically relative to the anode by
about a fraction of a volt to about 4 volts.
[0133] When the substrate is being prepared to be immersed into the
electrolyte solution after the extended reverse bias voltage
portion 2708b, the substrate seed layer continues to be reverse
biased by having positive voltage 2708, relative to the anode as a
time extension of the reverse bias voltage portion 2708b during the
immersion. This reverse bias 2708b during immersion serves a
similar function as the reverse bias voltage of 2708a. The
substrate holder assembly then immerses the seed layer into the
electrolyte solution until the seed layer is fully immersed in the
electrolyte solution. A closed electric circuit is created between
the anode and the seed layer as the substrate is being immersed.
The electric current is a function of the voltage between the anode
and the seed layer and the amount that the seed layer that has been
immersed. The reverse-bias voltage 2708b is maintained until the
substrate has been fully immersed into the electrolyte solution at
2710, then the anode and the seed layer are switched to a normal
bias voltage as shown by 2714.
[0134] The substrate generally is immersed in a horizontal
orientation into the electrolyte solution with the seed layer
facing down. In certain embodiments, the substrate may be tilted
from horizontal within the substrate holder assembly during
immersion. Such tilting provides for removal of air or air bubbles
that may otherwise be trapped within the electrolyte solution
underneath portions of the substrate holder assembly and/or
substrate, during the immersion process. Closely following the full
immersion of the substrate seed layer, the voltage between the
anode and the seed layer is changed from a positive (reverse bias)
voltage to a negative (normal bias) voltage. The negative normal
bias voltage of the anode relative to the seed layer, via the
electrolyte solution, is sufficient to cause metal ions in the
electrolyte solution to deposit metal film on the seed layer. Such
a negative normal bias voltage of the anode relative to the seed
layer is known as "plating voltage". The plating voltage typically
follows a plating recipe that is a function of the chemicals in the
electrolyte solution, the dimensions of the substrate and the
anode, etc.
[0135] The reverse bias voltage 2708a limits metal ions being
deposited as metal film on the substrate seed layer. During the
immersion of the substrate into the electrolyte solution, the
reverse bias voltage 2708a is applied to limit certain portions of
the seed layer from being coated more heavily by metal film than
other seed layer portions. Such irregular coating may result from,
e.g., irregular electrolyte solution flow about the substrate seed
layer during immersion of and/or removal of the substrate at an
angle from horizontal. As such, the reverse bias voltage 2708a
limits uneven metal film deposition on the seed layer that may
result during the immersion and/or removal of the substrate from
the electrolyte solution. Alternatively, the voltage of the anode
may be set equal to the voltage of the seed layer to limit both
excessive deposition or etching of the metal film on the seed
layer. If neither a plating voltage nor a deplating voltage is
applied to the substrate seed layer, while little deposition to the
seed layer occurs, little etching occurs. The duration from when
the first portion of the seed layer is immersed to when the
substrate is fully immersed is quite rapid, usually under three
seconds, during which time a slight reverse bias is applied.
[0136] When the voltage of the seed layer is greater than the
voltage of the anode, the ions in the electrolyte solution are not
attracted to the seed layer in sufficient quantities to effect
plating. However, certain embodiments of electrolyte solution has a
low pH, i.e., acidic, as these embodiments contain a considerable
amount of hydrochloric acid. Since such an electrolyte solution
itself is acidic, it will slightly etch (deplate) the seed layer
and/or the metal film metal if no voltage is applied between the
anode and the substrate. Thus, it might also make sense to apply a
very low plating voltage during substrate immersion.
[0137] The metal film deposition process is a function of the bias
voltage applied between the anode and the seed layer on the
substrate. As positively charged copper ions are deposited to form
the metal film on the negatively charged substrate seed layer by
the plating voltage, the copper ions from the depletion regions are
depleted. However, an atom-level electronic exchange, associated
with the chemical reaction of the anode in the electrolyte solution
current, drives copper atoms contained in the anode into the
electrolyte solution from the anode. Thus, the anode in many
embodiments includes a solid piece of copper. The plating voltage
portion 2714 can actually be a series of prescribed voltage levels
with the voltage levels and the durations selected as a function of
the composition of the electrolyte solution. The voltage levels and
durations depend on such factors as the electrolyte solution being
used, the distance between the anode and the seed layer, the
dimension of the electrolyte cell and the substrate, and the
desired metal film deposition thickness. Alternatively, the plating
voltage portion 2714 can be arranged as a series of plating
voltages alternating with a series of etching voltages. The etching
voltages can be applied, e.g., to keep openings or "throats" of
features formed in the substrate seed layer open so the features
can be more completely filled during the plating voltages.
[0138] The chemical reaction embodiments that may occur in the
embodiment of ECP system shown in FIGS. 1 or 6 may be characterized
by whether a positive bias is applied between the anode and the
seed layer to effect plating metal film on the substrate, or
whether a negative bias is applied between the anode and the seed
layer to effect deplating metal film on the substrate. If a
sufficient positive bias is applied so the voltage of the seed
layer is below the voltage of the anode to effect plating on the
substrate the following exemplary chemical reactions occur:
[0139] The anode chemical reaction is:
2H.sub.2O.fwdarw.O.sub.2+4H.sup.++4e-
[0140] The cathode (seed layer) chemical reaction is:
Cu.sup.+++2e-.fwdarw.Cu
[0141] If a sufficient negative bias is applied so the voltage of
the seed layer exceeds the voltage of the anode by a sufficient
level to effect deplating copper from the seed layer, the following
exemplary chemical reactions occur:
[0142] The anode chemical reaction is:
Cu.fwdarw.Cu.sup.+++2e-
[0143] The cathode (seed layer) chemical reaction is:
Cu.sup.+++2e-.fwdarw.Cu
[0144] The voltage of the electrolyte solution adjacent the
substrate seed layer is relatively small, e.g., about 1 volt. The
copper ions therefore arrive at the seed layer surface primarily by
diffusion within the electrolyte solution. The voltage level of the
seed layer controls the rate at which the copper ions deposit on
the substrate seed layer to form a metal film. Higher voltages
established between the anode and the substrate seed layer force
more ions into the electrolyte solution as a result of increasing
the chemical reaction between the anode and the seed layer. The
higher voltage levels result in a higher deposition rate of metal
ions onto the substrate seed layer since a higher concentration of
copper is contained in the electrolyte solution due to the
increased chemical reaction between the anode and the electrolyte
solution.
[0145] Increasing the voltage level between the anode and the seed
layer affects the deposition rate of the seed layer only up to the
level of the diffusion limit, at which level all of the diffused
ions are converted into copper ions. Above the diffusion limit, a
further increase in the voltage between the anode and the seed
layer breaks the bonds of the water in the electrolyte solution and
does not improve the deposition rate of the metal film on the seed
layer.
[0146] FIGS. 28 and 29, show one embodiment of method 2800
performed by the controller 222 that controls the electric
current/voltage applied from the anode to the seed layer, in which
a substrate is immersed into the electrolyte solution contained in
the electrolyte cell during each voltage cycle 2720. Method 2800
includes a relatively brief reverse bias voltage portion 2708a
being applied between the anode and the substrate seed layer. The
method 2800 is discussed in relation with the voltage cycle shown
in FIG. 27. Method 2800 starts with block 2802 in which the
substrate holder assembly, that holds the substrate in a position
such that the substrate is removed from the electrolyte solution
contained within the electrolyte cell, starts spinning the
substrate in at an angular velocity of less than about 100 RPM
(commonly under 30 RPM) preparation of the substrate being immersed
in the electrolyte solution. The spinning is performed only on
those substrate holder systems that are configured to spin the
substrate such as, e.g., the embodiment shown in FIG. 25. Certain
substrate holder systems, such as shown in the embodiment of FIG.
1, are not configured to rotate the substrate. Such spinning
occurs, in certain embodiments, within the neutral voltage period
2706. The period 2706 may be applied for a prescribed period after
each plating voltage portion 2714 that is sufficient to remove the
liquid from the surface of the substrate by centrifugal action.
[0147] Method 2800 continues to block 2804 in which the controller
applies the reverse bias voltage portion, 2708a as shown in FIG.
27, between the anode and the seed layer. The voltage level of the
seed layer equals, or is more positive than, the voltage level of
the anode during the reverse bias voltage portion 2708a. As such,
the seed layer is actually slightly anodic relative to the anode
during the reverse bias voltage. The positive voltage level of the
anode relative to the seed layer is of an insufficient voltage, and
applied for an insufficient duration, to cause considerable etching
of the seed layer and/or the metal film deposited on the seed
layer. When the seed layer on the substrate does not contact the
electrolyte solution in the electrolyte cell, an open circuit
exists since no medium is carrying electric current between the
anode and the seed layer. Any voltage differences between the anode
and the seed layer does not result in an associated current flow as
long as the substrate seed layer is removed from the electrolyte
solution since no current path exists between the anode and the
seed layer.
[0148] The method 2800 continues to block 2806 in which the
substrate holder system immerses the substrate seed layer into the
electrolyte solution. As soon as any portion of the seed layer is
immersed in the electrolyte solution, a closed circuit is formed
between the anode and those portions of the seed layer that are
immersed. The immersion process is performed quickly in one
embodiment to limit any undesired, or uneven etching that may occur
on the substrate as the reverse bias voltage portion 2708a is
applied between the anode and the seed layer. Such limiting of the
deposition during immersion is desired since portions of the
substrate may not be immersed early during the immersion process.
For example, certain embodiments of substrate holder systems
immerse the substrate in the electrolyte solution in a tilted
position wherein the substrate is angled from horizontal. In these
embodiments of substrate holder systems, peripheral parts of the
tilted seed layer on the substrate are immersed before other seed
layer parts. The reverse bias applied between the anode and the
seed layer limits the plating that occurs on the seed layer during
the immersion process. The method 2800 continues to block 2808
after full immersion, in which the plating voltage portion 2714 is
applied between the anode and the seed layer. Since the seed layer
is immersed in the electrolyte solution, a closed circuit is formed
between the anode and the seed layer. The substrate seed layer is
thereby cathodic relative to the anode. The deposition rate of
metal film on the seed layer on the substrate is a function of the
current density applied to the seed layer. The current density on
the seed layer is a function of the current flow between the anode
to the seed layer. The current from the anode to the seed layer, in
turn, is a function of the voltage between the anode and the seed
layer. Therefore, the controller 222 can control the deposition
rate of a metal film on the seed layer by controlling the voltage
level applied by a power supply between the anode and the seed
layer. During block 2808, the seed layer on the substrate is
processed, i.e., electroplated, at which time a metal film is
deposited on the substrate.
[0149] The method 2800 continues to block 2814 in which the
substrate held in the electrolyte cell by the substrate holder
system 14 completes the metal film deposition using plating voltage
between the anode and the seed layer, such as the plating voltage
portion 2714 shown in FIG. 27. The method 2800 continues to block
2816 in which the controller applies reverse bias voltage 2708A
between the anode and the seed layer. The duration of the reverse
bias voltage in block 2816 is envisioned to be sufficient for a
first substrate to be removed from the electrolyte solution, for a
second substrate to be positioned within the substrate holder
assembly, and for the second substrate to be immersed into the
electrolyte solution. The method 2800 then continues to block 2818
in which the substrate is removed from the process cell. During the
removal of the substrate from the process cell, the reverse bias
voltage will be sufficient to limit excessive deposits forming on
either the substrate seed layer, or the electric contact within the
substrate holder assembly. The duration in which the substrate and
the electric contacts are completely removed from the electrolyte
solution within the process cell is relatively brief to limit the
electrolyte solution drying on the face of the seed layer on the
substrate or on the electric contacts. Such limiting of the
electrolyte solution drying on the electric contacts also limits a
crystalline coating containing copper sulfate from forming on the
electric contacts that would alter the electric properties of the
electric contacts.
[0150] The method 2800 then continues to decision block 2820 in
which the controller determines if there is another substrate that
is ready to be processed. If the answer to decision block 2820 is
no, then the method 2800 continues to block 2822. In block 2822,
the controller 222 performs a loop with decision block 2910, in
which controller waits and applies the reverse bias voltage 2708b
until the next substrate is ready to be inserted within the
substrate holder assembly into the electrolyte solution. As the
reverse bias voltage 2708b is applied, the substrate holder system
holds the electric contacts in an immersed position in the
electrolyte solution. Immersing the electric contacts into the
electrolyte solution during down time limits the exposure of the
electric contacts to air, and thereby limits the oxidation of the
electric contacts. Additionally, immersing the electric contacts
into the electrolyte solution during down time limits the
evaporation of the electrolyte solution onto the surface of the
electric contacts. The evaporation of the water in the electrolyte
solution on the electric contacts would result in the coating of
the electric contacts with the copper sulfate in the electrolyte
solution. During the immersion of the electric contacts into the
electrolyte solution, the application of the reverse bias voltage
2708b is also sufficient to limit the deposition of copper from the
electrolyte solution onto the electric contacts.
[0151] If the answer to decision block 2820 is yes, then the method
2800 loops back to block 2801. Method 2800 loops continuously to
perform the waveform described relative to FIG. 27 on successive
substrates. The user can input information to the controller 222 if
it is desired to discontinue the method 2800 at any point.
[0152] 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.
* * * * *