U.S. patent application number 10/273044 was filed with the patent office on 2004-04-15 for oxide treatment and pressure control for electrodeposition.
This patent application is currently assigned to Applied Materials, Inc.. Invention is credited to Hao, Henan, Herchen, Harald, Padhi, Deenesh, Pham, Quyen, Trinh, Son N., Webb, Timothy R..
Application Number | 20040069651 10/273044 |
Document ID | / |
Family ID | 32069289 |
Filed Date | 2004-04-15 |
United States Patent
Application |
20040069651 |
Kind Code |
A1 |
Herchen, Harald ; et
al. |
April 15, 2004 |
Oxide treatment and pressure control for electrodeposition
Abstract
Method and apparatus for electrodepositing a metal onto a
substrate. An oxide treatment process is performed on a substrate
prior to making electrical contact between a seed layer of the
substrate and a conductive contact element which provides a
current. In one embodiment, the pressure at the interface between
the seed layer and the conductive contact element is controlled to
avoid detrimentally affecting a material(s) of the substrate.
Inventors: |
Herchen, Harald; (Los Altos,
CA) ; Hao, Henan; (Fremont, CA) ; Webb,
Timothy R.; (San Mateo, CA) ; Pham, Quyen;
(Sunnyvale, CA) ; Trinh, Son N.; (Cupertino,
CA) ; Padhi, Deenesh; (Santa Clara, CA) |
Correspondence
Address: |
PATENT COUNSEL
APPLIED MATERIALS, INC.
Legal Affairs Department
P.O. BOX 450A
Santa Clara
CA
95052
US
|
Assignee: |
Applied Materials, Inc.
|
Family ID: |
32069289 |
Appl. No.: |
10/273044 |
Filed: |
October 15, 2002 |
Current U.S.
Class: |
205/205 ;
204/242 |
Current CPC
Class: |
C25D 7/123 20130101;
C25D 5/34 20130101 |
Class at
Publication: |
205/205 ;
204/242 |
International
Class: |
C25D 005/34 |
Claims
What is claimed is:
1. A method of performing electrodeposition, comprising: providing
a substrate having an oxide layer on a conductive surface thereof;
performing an oxide reduction process on the oxide layer to define
an electrical contact area; contacting the electrical contact area
with an electrically conductive contact element, wherein the
electrically conductive contact element is connected to a power
source; applying a relative pressure between the electrically
conductive contact element and the substrate less than a critical
pressure capable of detrimentally deforming at least one material
of the substrate; and electrodepositing a material on the
substrate.
2. The method of claim 1, wherein the at least one material is a
low-k dielectric.
3. The method of claim 1, wherein the relative pressure is less
than about 60 psi.
4. The method of claim 1, wherein the relative pressure is between
about 10 psi and about 60 psi.
5. The method of claim 1, wherein the relative pressure is between
about 10 psi and about 30 psi.
6. The method of claim 1, wherein the electrical contact area is an
exposed portion of a seed layer.
7. The method of claim 1, wherein performing the oxide reduction
process comprises removing at least a portion of the oxide and
leaving the conductive layer thereunder generally unaltered.
8. The method of claim 1, wherein performing the oxide reduction
process comprises applying an acid to the substrate, wherein the
acid is configured to react with the oxide layer to remove oxygen
and leave the conductive layer unaltered.
9. The method of claim 1, wherein performing the oxide treatment
process comprises chemically reducing at least a portion of the
oxide into a metal.
10. The method of claim 1, wherein performing the oxide treatment
process comprises dissolving the oxide.
11. The method of claim 1, wherein performing the oxide treatment
process comprises exposing the portion of the oxide to a
plasma.
12. The method of claim 1, wherein applying the relative pressure
comprises inflating a bladder in contact with the substrate.
13. The method of claim 1, wherein the electrically conductive
contact element is an inflatable bladder and wherein applying the
relative pressure comprises inflating the bladder.
14. The method of claim 1, further comprising performing an oxide
treatment process on the electrically conductive contact element
prior to contacting the electrical contact area with the
electrically conductive contact element.
15. A method of performing an electroplating process, comprising:
providing a substrate comprising a low-k dielectric layer, a seed
layer, and an oxide formed on the seed layer; performing an oxide
treatment process on at least a portion of the oxide to expose an
electrical contact area of the seed layer; contacting the
electrical contact area with an electrically conductive contact
element, wherein the electrically conductive contact element is
connected to a power source; applying a relative pressure between
the electrically conductive contact element and the substrate less
than a critical pressure capable of detrimentally deforming at
least one material of the substrate; and electroplating a metal on
the substrate.
16. The method of claim 15, wherein the oxide treatment process is
performed in one of a spin-rinse-dry chamber and an integrated
bevel clean chamber.
17. The method of claim 15, wherein the relative pressure is less
than about 60 psi.
18. The method of claim 15, wherein the relative pressure is
between about 10 psi and about 60 psi.
19. The method of claim 15, wherein the relative pressure is
between about 10 psi and about 30 psi.
20. The method of claim 15, wherein performing the oxide treatment
process comprises applying an acid to the substrate.
21. The method of claim 15, wherein performing the oxide treatment
process comprises chemically reducing the oxide into a metal.
22. The method of claim 15, wherein performing the oxide treatment
process comprises dissolving the oxide.
23. The method of claim 15, wherein performing the oxide treatment
process comprises exposing the portion of the oxide to a
plasma.
24. The method of claim 15, wherein applying the relative pressure
comprises inflating a bladder in contact with the substrate.
25. The method of claim 15, wherein the electrically conductive
contact element is an inflatable bladder and wherein applying the
relative pressure comprises inflating the bladder.
26. The method of claim 25, wherein the relative pressure is less
than about 60 psi.
27. The method of claim 25, wherein the relative pressure is
between about 10 psi and about 60 psi.
28. The method of claim 25, wherein the relative pressure is
between about 10 psi and about 30 psi.
29. An electroplating apparatus, comprising: an oxide removal
station; an electroplating cell defining electrolyte-containing
cavity and comprising a compliant electrical contact element
configured to apply a relative pressure onto a substrate less than
a critical pressure capable of detrimentally deforming at least one
material of the substrate; a power source connected to the
electrical contact element; and at least one robot operable to
transport substrates from the oxide removal station to the
electroplating cell.
30. The apparatus of claim 29, wherein the oxide treatment station
comprises an acid applicator configured to apply an acid to at
least a portion of the substrate.
31. The apparatus of claim 29, wherein the oxide treatment station
comprises a plasma source.
32. The apparatus of claim 29, wherein the oxide treatment station
comprises an integrated bevel clean chamber.
33. The apparatus of claim 32, wherein the integrated bevel clean
chamber comprises an acid applicator configured to apply an acid to
at least a portion of the substrate.
34. The apparatus of claim 29, wherein the oxide treatment station
comprises a spin-rinse-dry chamber.
35. The apparatus of claim 34, wherein the spin-rinse-dry chamber
comprises an acid applicator configured to apply an acid to at
least a portion of the substrate.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention generally relates to methods and
apparatus for processing substrates in electrochemical
environments.
[0003] 2. Description of the Related Art
[0004] Metallization for sub-quarter micron sized features is a
foundational technology for present and future generations of
integrated circuit manufacturing processes. In devices such as
ultra large scale integration-type devices, i.e., devices having
integrated circuits with more than a million logic gates, the
multilevel interconnects that lie at the heart of these devices are
generally formed by filling high aspect ratio interconnect features
with a conductive material, such as copper or aluminum.
Conventionally, deposition techniques such as chemical vapor
deposition (CVD) and physical vapor deposition (PVD) have been used
to fill these interconnect features. However, as interconnect sizes
decrease and aspect ratios increase, void-free interconnect feature
fill via conventional metallization techniques becomes increasingly
difficult. As a result thereof, plating techniques, such as
electrochemical plating (ECP) and electroless plating, for example,
have emerged as viable processes for filling sub-quarter micron
sized high aspect ratio interconnect features in integrated circuit
manufacturing processes.
[0005] Metal ECP may be accomplished through a variety of methods
using a variety of metals. Copper and copper alloys are generally a
choice metal for ECP as a result of copper's high electrical
conductivity, high resistance to electromagnetic migration, good
thermal conductivity, and it's availability in a relatively pure
form. Typically, electrochemically plating copper or other metals
and alloys involves initially depositing a thin conductive seed
layer over the substrate surface to be plated. The seed layer may
be a copper alloy layer having a thickness of about 2000 .ANG., for
example, and may be deposited through PVD or other deposition
techniques. The seed layer generally blanket covers the surface of
the substrate, as well as any features formed therein. Once the
seed layer is formed, a metal layer may be plated onto/over the
seed layer through an ECP process. The ECP layer deposition process
generally includes application of an electrical bias to the seed
layer, while an electrolyte solution is flowed over the surface of
the substrate having the seed layer formed thereon. The electrical
bias applied to the seed layer attracts metal ions suspended or
dissolved in the electrolytic solution to the seed layer. In this
manner, ions are plated on the seed layer, thereby forming a metal
layer over the seed layer.
[0006] Present designs of cells for electroplating a metal on
semiconductor substrates are generally based of a fountain plater
type configuration. FIG. 1 is a cross sectional view of a
simplified typical fountain plater cell 100 incorporating contact
pins. Generally, the fountain plater cell 100 includes an
electrolyte container 120 having a top opening, a substrate holder
114 disposed above the electrolyte container 112, an anode 116
disposed at a bottom portion of the electrolyte container 112 and a
contact ring 120 contacting the substrate 122. A plurality of
grooves 124 are formed in the lower surface of the substrate holder
114. A vacuum pump (not shown) is coupled to the substrate holder
114 and communicates with the grooves 124 to create a vacuum
condition capable of securing the substrate 122 to the substrate
holder 114 during processing. The contact ring 120 comprises a
plurality of metallic or semi-metallic contact pins 126 distributed
about the peripheral portion of the substrate 122 to define a
central substrate plating surface. The plurality of contact pins
126 extend radially inwardly over a narrow perimeter portion of the
substrate 122 and contact a conductive seed layer of the substrate
122 at the tips of the contact pins 126. A power supply (not shown)
is attached to the pins 126 thereby providing an electrical bias to
the substrate 122. The substrate 122 is positioned above the
cylindrical electrolyte container 112 and electrolyte flow impinges
perpendicularly on the substrate plating surface during operation
of the cell 110.
[0007] While present day electroplating cells and techniques
generally achieve acceptable filling of features on larger scale
substrate features (i.e., features greater than 1 micron), a number
of obstacles impair consistent reliable electroplating onto
substrates having sub-micron-sized, high aspect ratio features. One
particular obstacle is oxidation accumulating on the seed layer.
Prior to immersion into the electrolytic solution of the plating
cell, an oxide layer may have formed (inadvertently or
intentionally) by exposure to an oxygen-containing environment.
Oxidation is known to act as an electrical resistor. As such, the
presence of oxidation on the seed layer can reduce the conductivity
between the seed layer and the power source (via the contact
member). Further, because the oxidation layer may be non-uniform,
the resulting plated metal may also be non-uniform. In addition,
the oxidation layer may compromise the ability of the subsequently
deposited bulk metal to adhere. Therefore, there is a need for a
method and apparatus to remove oxide layers from a seed layer prior
to making electrical contact therewith.
[0008] Another undesirable effect caused by the presence of an
oxide layer is the need for increased relative pressure between the
substrate and the cathode contact member. In general, it is
desirable to apply a pressure (typically greater than 300 psi)
between the substrate plating surface and the cathode contact
member sufficient to ensure good, reliable electrical contact
therebetween. Insufficient pressure can result in inadequate
contact, which may produce non-uniform plating of metal over the
seed layer. The presence of an oxide layer requires more pressure
than would be needed in the absence of an oxide layer because the
oxide layer must be penetrated to allow contact between the
underlying seed layer and the cathode contact member. However,
excessive pressure can fracture the seed layer and damage other
underlying layers. The application of such pressure may be
particularly detrimental where one of the underlying layers is a
soft and/or porous material, such as a low-k dielectric. The
effects of forcibly applying a cathode contact member to a
substrate are illustrated in FIG. 2. FIG. 2 shows a side cross
sectional view of a substrate 200 comprising a base material 202, a
low-k dielectric layer 204, a copper seed layer 206, and an oxide
layer 208. As evidenced by FIG. 2, it should be clear that the term
"substrate" as used herein refers to a base material which may have
one or more layers disposed thereon. The base material 202 may be,
for example, Si or SiO. A contact pin 210 is shown disposed on the
substrate 200. In particular, the contact pin 210 extends over the
oxide layer 208 and has been forced against the substrate 200 with
sufficient pressure to penetrate the oxide layer 208. The resulting
deformation caused by the contact pin 210 is translated to the
low-k layer 204, resulting in a nonuniform profile of the low-k
layer 204. In turn, the nonuniform profile of the low-k layer 204
can produce local non-uniformities of the subsequently
electroplated layer. In addition,
[0009] Therefore, there is a need for and apparatus and a method
for removing oxide from a substrate and uniformly depositing a
conductive material on the substrate, where the substrate includes
a material capable of being detrimentally affected by pressure
necessary to ensure good electrical contact between the substrate
and an electrical contact element.
SUMMARY OF THE INVENTION
[0010] Embodiments of the invention generally include applying an
oxide removal process to a copper seed layer prior to performing an
electrodeposition process.
[0011] One embodiment provides a method of performing
electrodeposition on a substrate having an oxide formed on a
conductive surface of the substrate. At least a portion of the
oxide is removed to define an electrical contact area. The
electrical contact area is then contacted with an electrically
conductive contact element, wherein the electrically conductive
contact element is connected to a power source. A relative pressure
is applied between the electrically conductive contact element and
the substrate. The relative pressure is less than a critical
pressure capable of detrimentally deforming at least one material
of the substrate. A material is then electrodeposited on the
substrate.
[0012] Another embodiment provides a method of performing an
electroplating process on a substrate including a low-k dielectric
layer, a seed layer, and an oxide formed on the seed layer. At
least a portion of the oxide is removed to expose an electrical
contact area of the seed layer. The electrical contact area is then
contacted with an electrically conductive contact element, wherein
the electrically conductive contact element is connected to a power
source. A relative pressure is applied between the electrically
conductive contact element and the substrate. The relative pressure
is less than a critical pressure capable of detrimentally deforming
at least one material of the substrate. A metal is then
electroplated on the substrate.
[0013] Yet another embodiment provides an electroplating apparatus
having an oxide removal station; an electroplating cell defining
electrolyte-containing cavity and including a compliant electrical
contact element configured to apply a relative pressure onto a
substrate. The relative pressure applied by the compliant
electrical contact element is less than a critical pressure capable
of detrimentally deforming at least one material of the substrate.
A power source is connected to the electrical contact element. The
electroplating apparatus further includes at least one robot
operable to transport substrates from the oxide removal station to
the electroplating cell.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] So that the manner in which the above recited features of
the present invention are attained and can be understood in detail,
a more particular description of the invention, briefly summarized
above, may be had by reference to the embodiments thereof, which
are illustrated in the appended drawings. It is to be noted,
however, that the appended drawings illustrate only typical
embodiments of this invention, and therefore, are not to be
considered limiting of its scope, for the invention may admit to
other equally effective embodiments.
[0015] FIG. 1 is a side cross sectional view of a prior art
electroplating chamber.
[0016] FIG. 2 is a side cross sectional view of a substrate having
a contact element disposed thereon and illustrating the deformation
of a low-k dielectric layer by the contact element.
[0017] FIG. 3 is a plan view of an electroplating system.
[0018] FIG. 4 is a cross sectional view of an electroplating
cell.
[0019] FIG. 4A is a partial cross sectional perspective view of one
embodiment of a cathode contact ring and a frontside bladder
assembly.
[0020] FIG. 5 is partial cross sectional perspective view of one
embodiment of a cathode contact ring having a front side
electrically conductive bladder assembly disposed thereon.
[0021] FIG. 6 is partial cross sectional perspective view of one
embodiment of a cathode contact ring having a front side
electrically conductive bladder assembly disposed thereon and
further showing a backside bladder assembly.
[0022] FIG. 7 is a simplified cross sectional view of a substrate
wherein the copper oxide layer has been removed to allow contact
between a contact element and an exposed copper layer.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0023] Embodiments of the invention generally include performing an
oxide removal process to remove oxides from a copper seed layer
prior to performing an electrodeposition process. The oxide layer
on metals is known to inhibit good electrical contact from being
made, thereby detrimentally affecting the electrodeposition
process. Accordingly, removing the oxide layer to expose the
underlying metal improves the electrical contact with a contact
element (e.g., the contact pins 419 or the bladder 504). In some
embodiments, an oxide removal process is applied to the electrical
contact member(s), which supplies current to the seed layer.
[0024] Referring to FIG. 7, a side cross-sectional view of a
substrate 700 is shown. The substrate 700 has been processed
according to the invention to remove oxide formation from the seed
layer. The substrate 700 comprises a base material 702, a low-k
dielectric layer 704 and a seed layer 706. The base material 702
may be, for example, Si or SiO. The seed layer 706 may be copper. A
contact element 710 is shown disposed on the substrate 700. In
particular, the contact element 710 extends over, and in contact
with, the oxide layer 708. In contrast to FIG. 2, the low-k layer
704 has not been deformed by application of excess pressure. This
is made possible as a result of having removed any oxide to expose
the seed layer 706, prior to bringing the substrate into contact
with a contact element 710. The absence of an oxide layer on the
seed layer 706 allows for good and reliable contact to be made
between the contact element 710 and the seed layer 706 with less
pressure than would be required had the oxide not been removed.
[0025] In one embodiment, the contact element 710 is a compliant
member, such as the bladder 504. As defined herein, "compliant"
means sufficiently flexible or compressible to allow the compliant
member to deform and follow the contours of the mating surface
(i.e., the substrate 700), with the difference in pressure needed
for high and low points of the mating surface being a relatively
small percentage (for example, between about 10% and about 20%) of
the average applied pressure, or pressure applied at a point at an
intermediate height. In another embodiment, the contact element is
relatively non-compliant (e.g., contact pins 419 described below
with reference to FIGS. 4 and 4A), but a pressure control mechanism
(e.g., the bladder assembly 430 described below with reference to
FIGS. 5 and 6) is provided to avoid application of excessive
pressure. Regardless of the particular embodiment, the electrical
contact apparatus of the present invention provide a degree of
control over the relative pressure between a substrate and
electrical contact. Preferably, the pressure at the interface
between the substrate and electrical contact (referred to herein as
"contact pressure") is less than a critical pressure, defined
herein as a minimum pressure at which one or more of the materials
(typically the weakest material) formed on the substrate are
detrimentally affected (e.g., cracked). Stated another way, the
contact pressure is a pressure which most closely approaches, but
does not exceed, the maximum stress or yield strength of the
weakest material on the substrate. For example, the critical
pressure at which low-k cracks has been measured at between 800 and
3000 psi, depending on the type of low-k. Therefore, in one
embodiment for low-k applications, a contact pressure is between
about 40 and about 400 psi, and preferably at about 150 psi for the
most delicate present-day low k material. In a another embodiment,
the contact pressure is less than about 60 psi. In still another
embodiment, the contact pressure is less than 30 psi. In still
another embodiment, the contact pressure is less than 10 psi.
[0026] Following are a variety of embodiments for removing oxide
from a copper seed layer and for providing a current to the copper
seed layer in a pressure controlled manner. It should be
understood, however, that the following embodiments are merely
illustrative, and other embodiments are equally within the scope
and spirit of the invention.
[0027] The System
[0028] FIG. 3 is a plan view of an electrochemical deposition
system. The electrochemical deposition system 300 generally
comprises a loading station 310, a pair of pre-/post-process
chambers 311 and 312, a mainframe 314, and an electrolyte
replenishing system 320. In one embodiment, the chambers 311 and
312 include any combination of thermal anneal chambers,
spin-rinse-dry (SRD) stations and integrated bevel clean (IBC)
chambers. For purposes of illustration, embodiment described herein
refer to the chamber 311 is a thermal anneal chamber and the
chamber 312 is a SRD chamber. Each of the foregoing chambers is
available from Applied Materials, Inc. of Santa Clara, Calif. The
electrochemical deposition system 300 also includes a control
system 322, typically comprising a programmable microprocessor.
Preferably, the electrochemical deposition system 300 is enclosed
in a clean environment using panels such as Plexiglas panels.
[0029] The mainframe 314 generally comprises a mainframe transfer
station 316 and a plurality of processing stations 318. Each
processing station 318 includes one or more electrochemical
processing cells 340.
[0030] The loading station 310 preferably includes one or more
substrate cassette receiving areas 324, one or more loading station
transfer robots 328 and at least one substrate orienter 330. A
substrate cassette 332 containing substrates 334 is loaded onto the
substrate cassette receiving area 324 to introduce substrates 334
into the electrochemical deposition system 300. The SRD station 312
includes one or more SRD modules 336 and one or more substrate
pass-through cassettes 338. The substrate pass-through cassette 338
provides access to and from both the loading station transfer robot
328 and a robot 317 in the mainframe transfer station 316.
[0031] An electrolyte replenishing system 320 is positioned
adjacent the electrochemical deposition system 300 and connected to
the process cells 340 individually to circulate electrolyte used
for the electroplating process. Illustratively, the electrolyte
replenishing system 320 includes a main electrolyte tank 360, a
plurality of source tanks 362, and a plurality of filter tanks 364.
The main electrolyte tank 360 is the source of electrolyte for each
of the cells 340. The chemical composition of the electrolyte
contained in the main electrolyte tank 360 is maintained using
chemicals provided from the source tanks 362. The filter tanks 364
are configured to filter the electrolyte in the main electrolyte
tank 360 prior to being distributed to the various cells 340.
[0032] In one embodiment, a cleaning process is performed to remove
oxide from a surface of a substrate prior to electroplating a
conductive material onto the substrate. Preferably, the oxide
cleaning process is performed within the system 300 in order to
minimize the possibility of reoxidation while transferring the
substrates to the process cells 340. Relatedly, the substrate
transfer time between the oxide cleaning facility and the process
cell 340, in which the electrodeposition is to be performed, is
preferably minimized. In one embodiment, one or more of the
pre/post process chambers 311 and 312 are configured for performing
an oxide cleaning process. In a particular embodiment, the chambers
311,312 are integrated bevel clean chambers, rapid thermal anneal
chambers and/or spin-rinse-dry chambers.
[0033] Generally, the process cells 340 are any type of cells
adapted for electrodepositing a metal onto a substrate. As such, it
is contemplated that the process cells 340 may be, for example,
configured for face up or face down electroplating. Further,
electrical contact between a substrate and a contact element (e.g.,
contact element 710) may be made on a front side of a substrate, a
backside of a substrate, or both. For brevity, preferred
embodiments will be described only with reference to a face down
fountain plater cell in which front side electrical contact is
made. However, persons skilled in the art will recognize that any
other electric deposition techniques/apparatus requiring physical
contact between an electrical element and a substrate may be used
to advantage.
[0034] FIG. 4 is a partial vertical cross sectional schematic view
of an exemplary fountain plater cell 340 for electroplating a metal
onto a substrate. The cell 340 is merely illustrative for purposes
of describing the present invention. Other cell designs may
incorporate and use to advantage the present invention. The
electroplating cell 340 generally comprises a container body 402
having an opening on the top portion thereof. The container body
402 is preferably made of an electrically insulative material such
as a plastic which does not break down in the presence of plating
solutions. The container body 402 is preferably sized and shaped
cylindrically in order to accommodate a generally circular
substrate at one end thereof. However, other shapes can be used as
well. As shown in FIG. 4, an electroplating solution inlet 404 is
disposed at the bottom portion of the container body 402. A
suitable pump 406 is connected to the inlet 404 to
supply/recirculate the electroplating solution (or electrolyte)
into the container body 402 during processing. In one aspect, an
anode 408 is disposed in the container body 402 to provide a metal
source in the electrolyte. The container body 402 includes an
egress gap 410 bounded at an upper limit by a shoulder 412 of a
cathode contact ring 414 and leading to an annular weir 416. The
weir 416 has an upper surface at substantially the same level (or
slightly above) a seating surface 417 of a plurality of conducting
pins 419 of the cathode contact ring 414. The weir 416 is
positioned to ensure that a substrate plating surface 420 of a
substrate 421 is in contact with the electrolyte when the
electrolyte is flowing out of the electrolyte egress gap 410 and
over the weir 416. Alternatively, the upper surface of the weir 416
is positioned slightly lower than the seating surface 417 such that
the plating surface 420 is positioned just above the electrolyte
when the electrolyte overflows the weir 416, and the electrolyte
contacts the substrate plating surface 420 through meniscus
properties (i.e., capillary force).
[0035] The cathode contact ring 414 is shown disposed at an upper
portion of the container body 402. A power supply 422 is connected
to a flange 424 to provide power to the pins 419 which define the
diameter of the substrate plating surface 420. The shoulder 412 is
sloped so that the upper substrate seating surface of the pins 419
is located below the weir 416 or are at least positionable at a
position where the substrate plating surface 420 will be in contact
with electrolyte as electrolyte flows over the weir 416.
Additionally, the shoulder 412 facilitates centering the substrate
421 relative to the conducting pins 419.
[0036] The contact pins 419 generally comprise a low resistivity,
and conversely high conductivity, material resistant to oxidation.
In some cases, materials which oxidize to a few monolayers are
acceptable, so long as electrons can tunnel through the monolayers.
In one embodiment the contact pins 419 comprise a noble metal,
e.g., platinum (Pt), ruthenium (Ru), iridium (Ir), rhodium (Rh),
and/or palladium (Pd). The contact pins 419 may be solid or coated
with the desired conductive material. Other conducting materials
which may be used (but may be less desirable, due to their
susceptibility to oxidation, for example) include copper (Cu),
tantalum (Ta), titanium (Ti), molybdenum (Mo), silver (Ag) and gold
(Au).
[0037] A mounting plate 432 having an annular flange 434 is seated
on an upper rim of the container body 402. The mounting plate 432
(which may be substantially disc-shaped) has a centrally disposed
vacuum port 441 formed therein. The vacuum port 441 is preferably
attached to a vacuum/pressure pumping system 459 (shown in FIG. 4)
adapted to selectively supply a pressure or create a vacuum at a
backside of the substrate 421. The pumping system 459 comprises a
pump 445, a cross-over valve 447, and a vacuum ejector 449
(commonly known as a Venturi). One vacuum ejector that may be used
to advantage in the present invention is available from SMC
Pneumatics, Inc., of Indianapolis, Ind. The pump 445 may be a
commercially available compressed gas source and is coupled to one
end of a hose 451, the other end of the hose 451 being coupled to
the vacuum port 441. The hose 451 is split into a pressure line 453
and a vacuum line 455 having the vacuum ejector 449 disposed
therein. Fluid flow is controlled by the cross-over valve 447 which
selectively switches communication with the pump 445 between the
pressure line 453 and the vacuum line 455. Preferably, the
cross-over valve has an OFF setting whereby fluid is restricted
from flowing in either direction through hose 451. A shut-off valve
461 disposed in hose 451 prevents fluid from flowing from pressure
line 455 upstream through the vacuum ejector 449. The desired
direction of fluid flow is indicated by arrows.
[0038] As shown in FIG. 4A, an inflatable bladder assembly 430 is
disposed on the mounting plate 432 at an upper end of the container
body 402 above the cathode contact ring 414. The inflatable bladder
assembly 430 comprises a bladder 436 disposed on a lower surface of
the mounting plate 432 is thus located opposite and adjacent to the
pins 419 with the substrate 421 interposed therebetween.
Illustratively, the bladder 436 is partially disposed within an
annular recess 440 formed within the mounting plate 432. The
bladder 436 is secured by a manifold 446. The manifold 446
comprises a mounting rail 452 disposed between an inner shoulder
448 and an outer shoulder 450. The mounting rail 452 is adapted to
be at least partially inserted into an annular mounting channel 443
of the mounting plate 432. A plurality of fluid outlets 454 formed
in the manifold 446 provide communication between the bladder 436
and inlets 442 formed in the mounting plate 432. Seals 437, such as
O-rings, are disposed in the annular manifold channel 443 in
alignment with the inlet 442 and outlet 454 and secured by the
mounting plate 432 to ensure an airtight seal. Conventional
fasteners (not shown) such as screws may be used to secure the
manifold 446 to the mounting plate 432 via cooperating threaded
bores (not shown) formed in the manifold 446 and the mounting plate
432.
[0039] In FIG. 4A, lip seals 456 are shown disposed on the inner
shoulder 448 and the outer shoulder 450. A portion of the bladder
436 is compressed against the walls of the annular recess 440 by
the manifold 446 which has a width slightly less (e.g. a few
millimeters) than the annular recess 440. Thus, the manifold 446,
the bladder 436, and the annular recess 440 cooperate to form a
fluid-tight seal. To prevent fluid loss, the bladder 436 is
preferably comprised of some fluid impervious material such as
silicon rubber or any comparable elastomer which is chemically
inert with respect to the electrolyte and exhibits reliable
elasticity. Where needed a compliant covering may be disposed over
the bladder 436 and secured by means of an adhesive or thermal
bonding. The covering may comprise an elastomer such as Viton.TM.,
buna rubber or the like, which may be reinforced by Kevlar.TM., for
example. In one embodiment, the covering and the bladder 436
comprise the same material. The covering has particular application
where the bladder 436 is liable to rupturing. Alternatively, the
bladder 436 thickness may simply be increased during its
manufacturing to reduce the likelihood of puncture.
[0040] The precise number of inlets 442 and outlets 454 may be
varied according to the particular application without deviating
from the present invention. For example, while FIG. 4 shows two
inlets with corresponding outlets, an alternative embodiment could
employ a single fluid inlet to the bladder 436.
[0041] A fluid source 438 is fluidly coupled to the bladder 436 via
the inlets 442 and the outlets 454. In the illustrative embodiment,
quick-disconnect hoses 444 couple the fluid source 438 to the
inlets 442. In operation, the fluid source 438 supplies a fluid,
i.e., a gas or liquid, to the bladder 436 allowing the bladder 436
to be inflated to varying degrees.
[0042] Persons skilled in the art will readily appreciate other
arrangements which do not depart from the spirit and scope of the
present invention. For example, where the fluid source 438 is a gas
supply it may be coupled to hose 451 thereby eliminating the need
for a separate compressed gas supply, i.e., pump 445. Further, a
separate gas supply and vacuum pump may supply the backside
pressure and vacuum conditions. While it is preferable to allow 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, an arrangement such as the one described
above including a vacuum ejector and a cross-over valve is
preferred.
[0043] Those skilled in the art will readily recognize other
embodiments which are contemplated by the present invention. For
example, while FIG. 4A shows a preferred bladder 436 having a
surface area sufficient to cover a relatively small perimeter
portion of the substrate backside at a diameter substantially equal
to the contact pins 419, the bladder assembly 430 may be
geometrically varied. Thus, the bladder assembly 430 may be
constructed using more fluid impervious material to cover an
increased surface area of the substrate 421.
[0044] The operation of the bladder assembly 430 will be described
in detail below.
[0045] In another embodiment, the contact element which provides
electrical current to a seed layer from a power source is a
compliant element, adapted to mitigate the possibility of the
forming soft/fragile underlayers formed on a substrate. In one
embodiment, the compliant element is an inflatable electrically
conductive contact element. FIGS. 5 and 5A show a cross-sectional
view of one embodiment of an inflatable electrically conductive
contact element assembly 500. For brevity and simplicity, identical
components previously described will be referenced by like
numerals.
[0046] The electrically conductive bladder assembly 500 is shown
disposed on an annular contact ring 502. The electrically
conductive bladder assembly 500 comprises a electrically conductive
bladder 504. In one embodiment, the electrically conductive bladder
504 is a continuous annular ring. In one aspect, the use of a
continuous ring provides a continuous current conductivity
interface about a periphery of a substrate 421. However, in another
embodiment, the electrically conductive bladder 504 may comprise a
plurality of discrete inflatable contact elements. In any case, the
bladder 504 is preferably disposed in an exclusion area of the
substrate 421 to avoid rendering an unacceptably large portion of
the substrate seed layer unusable. In one embodiment, the exclusion
area of a 200 mm substrate is between about 1 mm and about 3 mm
wide.
[0047] The electrically conductive bladder 504 is disposed in an
annular recess 506 formed in the annular contact ring 504. One or
more inlets 508 are formed in the contact ring 504 and lead into a
relatively enlarged annular mounting channel 510. The electrically
conductive bladder 504 is secured within the annular recess 506 by
a retaining member 514. The retaining member 514, in turn, may be
secured to the annular contact ring my fasteners, such as screws
(not shown). Illustratively, a plurality of O-rings 507 (one shown)
may be disposed in the mounting channel 510 between each inlet 508
and the retaining member 514. At least one outlet 512 is formed in
the retaining member 514 in order to fluidly couple the inlets 508
with the electrically conductive bladder 504. Each inlet 508 is
fluidly coupled to a fluid channel 516 formed in the contact ring
504. The fluid channel 516, in turn, is fluidly coupled to a fluid
source 518 via a fluid supply line 520. Accordingly, the fluid
source 518 is coupled to the bladder 504 via the fluid channel(s)
516, inlet(s) 508 and outlet(s) 512 to supply a fluid, i.e., a gas
or liquid, to the bladder 504 allowing the bladder 504 to be
inflated to varying degrees. In this manner, the relative pressure
between the bladder 504 and a substrate 421 can be controlled by
inflating the bladder 504.
[0048] To prevent fluid loss, the bladder 504 is preferably
comprised of some fluid impervious material such as silicon rubber
or any comparable elastomer which is chemically inert with respect
to the electrolyte and exhibits reliable elasticity. In one
embodiment, a compliant covering may be disposed over the bladder
504 and secured by means of an adhesive or thermal bonding. The
covering may comprise an elastomer such as Viton.TM., buna rubber
or the like, which may be reinforced by Kevlar.TM., for example. In
one embodiment, the covering and the bladder 504 comprise the same
material. The covering has particular application where the bladder
504 is liable to rupturing. Alternatively, the bladder 504
thickness may simply be increased during its manufacturing to
reduce the likelihood of puncture.
[0049] In any case, the bladder 504 is electrically conductive and
is connected to a power supply 422 capable of providing a current
to the bladder 504. In one embodiment, the bladder 504 is made
electrically conductive by disposing a conductive covering over the
bladder 504. For example, a metal strip may be wrapped around the
outer surface of the bladder 504. In another embodiment,
electrically conductive material may be embedded within the bladder
504, thereby "metallizing" the bladder 504.
[0050] The conductive portion of the bladder 504 preferably
comprises a low resistivity, high conductivity, material resistant
to oxidation. For example, in one embodiment the bladder 504
comprises a noble metal, e.g., platinum (Pt), ruthenium (Ru),
iridium (Ir), rhodium (Rh), and/or palladium (Pd). Other conducting
materials which may be used include copper (Cu), tantalum (Ta),
titanium (Ti), molybdenum (Mo), beryllium (Be), silver (Ag) and
gold (Au). In some embodiments, the bladder 504 may be solid or
coated with the desired conductive material. Persons skilled in the
art will recognize other embodiments.
[0051] In another embodiment, the front side electrically
conductive bladder 504 is used in combination with the backside
bladder assembly 430 described above with reference to FIG. 4. One
such embodiment shown in FIG. 6. The provision of a bladder on
either side of a substrate allows for additional pressure control.
Further, the bladder 436 disposed on the backside of a substrate
may mitigate generation of particulate (i.e., by relative friction
between the mounting plate 432 and the substrate 420).
[0052] It should be understood that the metallized bladder 504 is
merely one embodiment providing a compliant contact element.
Persons skilled in the art will recognize a variety of other
compliant contact elements suitable for electrodeposition
processes. For example, the contact pins 419 shown in FIG. 4 may be
made compliant. In one embodiment, the contact pins 419 are
manufactured to be flexible members, much like a leaf spring. In
this way, the radially extended contact pins 419 may be deflected
from a plane in which the pins reside in the absence of an applied
force. The degree of deflection may be controlled according to the
amount of applied pressure and the flexibility of the pins.
[0053] The operation of the bladder assembly 500 will be described
below.
[0054] System Operation: Oxide Cleaning Processes and Pressure
Control
[0055] The present invention contemplates a variety of oxide
cleaning and/or treatment techniques. In one embodiment, substrates
are remotely cleaned (remove oxides formed on a seed layer of the
substrates) and then transferred to the system 300. The substrates
may be introduced to the loading station 310 and then transferred
to one of the various process cells 340 by operation of the robots
of the system 300. In another embodiment, the oxide cleaning
process is performed within the system 300. That is, substrates are
transferred to an integrated cleaning station (described above) and
subsequently to one of the various process cells 340. In yet
another embodiment, the process cells 340 are adapted to perform in
situ cleaning. The latter embodiment minimizes the possibility of
reoxidation during substrate transfer because the cleaning and
electrodeposition are performed in the same chamber.
[0056] In general, the oxide cleaning process performed prior to
electrodeposition may be any of a variety of processes, including
known and unknown processes. One method of removing oxide is by the
application of an acid to dissolve oxides formed on a seed layer.
Illustrative acids which may used to dissolve oxides are shown in
Table I.
1 TABLE I Chemical Composition Concentration(s) Sulfuric acid in
deionized 0.1 to 6% by wt water (DI) HF in DI 0.1 to 6% by wt HCl
in DI 0.1 to 6% by wt HCl and NH.sub.4OH in DI 0.1 to 6% by wt for
HCl, and 0.1 to 2% for NH.sub.4OH HOCH.sub.2COOH (Glycolic 1 to 30%
by wt acid) in DI
[0057] In one aspect, acids may allow selective removal the oxide
from the seed layer to avoid undesirably diminishing the available
seed material. Other techniques capable of achieving selectivity
between the oxide and the underlying metal may also be used to
advantage.
[0058] In another embodiment, a reducing agent is used to reduce
the oxide. That is, the oxide is exposed to hydrogen, thereby
allowing the oxygen in the oxide to combine with the hydrogen,
resulting in water. The water evaporates or can be boiled away to
leave the exposed metal seed layer. In one embodiment, the reducing
agent may be an acid which provides a source of hydrogen atoms or
hydrogen ions. Illustrative reducing agents and their respective
concentrations are provided below in Table II. The advantage of
using the reduction process is that the oxide layer that forms over
the seed layer reacts with a portion of the seed layer, and
therefore, assuming that a copper seed layer is implemented, for
example, then the oxide layer includes some copper from the seed
layer therein. This copper generally forms a copper oxide layer. As
such, when the copper oxide layer is removed, a portion of the seed
layer is also removed in conventional oxide removal processes.
However, when the reduction process of the invention is
implemented, the chemical reaction utilized is configured to remove
the oxygen component of the oxide, while leaving the cupper
component of the oxide layer. As such, the copper content or
thickness of the seed layer is generally unchanged or unaltered
2TABLE II Chemical Composition Concentration(s) UV activated H2 gas
3 to 100% H2 in Ar or other relatively inert gas, such as N2 Plasma
activated H2 gas 3 to 100% H2 in Ar or other relatively inert gas,
such as N2 Carboxyl Acid 1 to 30% by weight Formic Acid 1 to 30% by
weight Aldehydes (e.g., acetaldehyde 10 to 100% by weight or
propionaldehyde) Alcohols (e.g., methanol, 10 to 100% by weight
ethanol)
[0059] In one embodiment, hydrogen ions in a liquid acid react with
cupric oxide on the surface of the seed layer to reduce the copper
oxide back to copper, while creating H.sub.2O as part of the
reaction. Copper reacting in this manner is dissolved into the
acid, since there is a charge transfer. The reaction is described
by the following equation:
CuO+2H.sup.+Cu.sup.2+(aq)+H.sub.2O (Equation 1)
[0060] Embodiments further provide for the application of an acid
followed by a degassed deionized water rinse. Use of a deionized
rinse flushes the dissolved oxygen from the substrate surface,
thereby reducing the possibility for re-oxidation of the metal
layer prior to making contact. In one embodiment, an oxidation
removal step and a deionized rinse are performed in a
spin-rinse-dry chamber (e.g., one of chambers 311 and 312 of FIG.
3).
[0061] In another embodiment, oxidation removal is performed in the
presence of a plasma. For example, a hydrogen plasma may be
generated and allowed to interact with the oxidized surface of a
substrate having a copper seed layer. The resulting reaction is
described by the following equation:
CuO+2H.sup.++2e.sup.-Cu(s)+H.sub.2O (Equation 2)
[0062] Note that according to this reaction oxidized copper (CuO)
reacts with hydrogen ions to produce solid copper. In one aspect,
an advantage achieved by plasma cleaning in this manner is
minimizing the amount of copper removed from the substrate,
including the copper that was initially in oxidized state. This
result is particularly advantageous for thin seed layers since last
of the seed copper is removed. In a particular embodiment the
hydrogen plasma process is performed in an anneal chamber.
Accordingly, it is contemplated that an anneal chamber, e.g.,
chamber 311 or 312, is equipped with a plasma source capable of
generating a plasma from a hydrogen-containing gas, such as forming
gas. In one embodiment, the hydrogen containing gas is about 96%
nitrogen and about 4% hydrogen.
[0063] When performing oxide removal processes it may be desirable
to remove only that portion of the oxide necessary to make
electrical contact with a contact element (e.g., the bladder 504).
As such, in the case of using an acid as a reducing agent or
dissolving agent, application of the acid may be restricted to
electrical contact area on a substrate (typically on a perimeter of
the substrate). To this end, acid may be applied by a brush or
swab. In one embodiment, the acid applicator is located in an
integrated bevel clean (IBC) chamber a spin-rinse-dry (SRD)
chamber, such as one of the chambers 311, 312 described above with
reference to FIG. 3. Illustratively, applicators 313 (two shown)
are shown disposed in the pre/post processing chamber 312. The
applicators 313 may be pivot mounted or fixed in place and may
comprise a brush, nozzle or other fluid applicator disposed at one
end. Preferably, the applicators 313 are configured to apply a
fluid with minimal splashing, in order to avoid affecting areas of
a substrate which do not require treatment and to conserve the
fluid being applied. A fluid feed (not shown) may be coupled to the
applicators 313 to replenish oxide treatment fluid as needed.
[0064] In one embodiment, the oxide cleaning techniques described
herein can be applied to the electrical contact element, e.g., the
contact pins 419 and the electrically conductive bladder 504. Using
this approach would allow less expensive materials to be used for
the electrical contact element (i.e., materials relatively less
resistant to oxidation). In one embodiment, the contact elements
are cleaned using electrolyte fluid in the container body 402 (FIG.
4), which may have the appropriate oxide treatment chemistry as
described herein.
[0065] Following the oxide removal process (on the substrate and,
in some embodiments, on the electrical contact element), the
substrate may be brought into contact with the contact element in
order to supply a current to the exposed seed layer. Where the
contact assembly of FIG. 4 is used, a substrate 421 is introduced
into the container body 402 by securing it to the lower side of the
mounting plate 432. This is accomplished by engaging the pumping
system 459 to evacuate the space between the substrate 421 and the
mounting plate 432 via port 441 thereby creating a vacuum
condition. The bladder 436 is then inflated by supplying a fluid
such as air or water from the fluid source 438 to the inlets 442.
The fluid is delivered into the bladder 436 via the manifold
outlets 454, thereby pressing the substrate 421 uniformly against
the contact pins 419. An electrolyte is then pumped into the cell
340 by the pump 406 and flows upwardly inside the container body
402 toward the substrate 421 to contact the exposed substrate
plating surface 420. The power supply 422 provides a negative bias
to the substrate plating surface 420 via the contact pins. As the
electrolyte is flowed across the substrate plating surface 420,
ions in the electrolytic solution are attracted to the surface 420.
The ions then deposit on the surface 420 to form the desired
film.
[0066] Because of its flexibility, the bladder 436 deforms to
accommodate the asperities of the substrate backside and contact
pins 419 thereby mitigating misalignment with the conducting pins
419. The compliant bladder 436 prevents the electrolyte from
contaminating the backside of the substrate 421 by establishing a
fluid tight seal at a perimeter portion of a backside of the
substrate 421. Once inflated, a uniform pressure is delivered
downward toward the pins 419 to achieve substantially equal force
at all points where the substrate 421 and pins 419 interface. The
force can be varied as a function of the pressure supplied by the
fluid source 438. Further, the effectiveness of the bladder
assembly 430 is not dependent on the configuration of the cathode
contact ring 414. For example, while FIG. 4 shows a pin
configuration having a plurality of discrete contact points (i.e.,
the surfaces 417 of the pins 419), the cathode contact ring 414 may
also be a continuous surface.
[0067] Additionally, the fluid tight seal provided by the inflated
bladder 436 allows the pump 445 to maintain a backside vacuum or
pressure either selectively or continuously, before, during, and
after processing. Generally, however, the pump 445 is run to
maintain a vacuum only during the transfer of substrates to and
from the electroplating cell 340 because it has been found that the
bladder 436 is capable of maintaining the backside vacuum condition
during processing without continuous pumping. Thus, while inflating
the bladder 436, as described above, the backside vacuum condition
is simultaneously relieved by disengaging the pumping system 459,
e.g., by selecting an OFF position on the cross-over valve 447.
Disengaging the pumping system 459 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 436 and the simultaneously decreasing backside vacuum
condition. This exchange may be controlled manually or by
computer.
[0068] The operation using the bladder assembly 500 according to
the embodiments of FIG. 5 or FIG. 5 may be similarly performed.
Accordingly, a detailed description of the operation is not
necessary. Briefly, the conductive side of the substrate 421 (i.e.,
the surface having the seed layer disposed thereon) is disposed on
the bladder 504. The fluid source 518 is activated to inflate the
bladder 504 to a desired degree. In the embodiment of FIG. 6, the
bladder 436 may be similarly inflated by the fluid source 438.
Operation of the power supply 422 establishes a potential drop
between the anode 408 and the electrically conductive bladder 504
to initiate electroplating of a metal onto the substrate 421.
[0069] In one aspect, the oxide removal processes provided herein
reduce the electrical contact resistance between the contact
element and the seed layer. Accordingly, good, reliable electrical
contact between the contact element and the seed layer may be
achieved with relatively less pressure, as compared to techniques
in which oxide removal is not performed. As a consequence, the
integrity of the underlying low-k layer is protected and the
possibility of cracking of the seed layer is lessened or
eliminated. Further, the compliant electrical contacts (e.g., the
bladder assemblies) provided herein provide a convenient apparatus
and method for controlling the relative pressure between a
substrate and an electrical contact element. When oxide removal
techniques are combined with pressure control techniques, uniform
plating results can be achieved.
EXAMPLE
[0070] FIG. 8 shows the results of resistance contact measurements
with respect to pressure for two contact elements, Pin A and Pin B.
The units on both the horizontal and vertical axes are arbitrary.
The contact resistance was measured for each pin without an oxide
treatment process and with an oxide treatment process. The
substrates used had seed layers 400 Angstroms thick and were
treated with an oxide cleaning liquid comprising 1% H.sub.2SO.sub.4
by weight, in DI water. The process time was about 10 seconds of
application with the 1% acid, followed by a DI rinse. The
substrates were then exposed to air for 20 minutes before the
contact resistance measurement was made.
[0071] While the foregoing is directed to embodiments of the
present invention, other and further embodiments of the invention
may be devised without departing from the basic scope thereof, and
the scope thereof is determined by the claims that follow.
* * * * *