U.S. patent number RE40,218 [Application Number 10/622,001] was granted by the patent office on 2008-04-08 for electro-chemical deposition system and method of electroplating on substrates.
Invention is credited to Uziel Landau.
United States Patent |
RE40,218 |
Landau |
April 8, 2008 |
**Please see images for:
( Certificate of Correction ) ** |
Electro-chemical deposition system and method of electroplating on
substrates
Abstract
The invention provides an apparatus and a method for achieving
reliable, consistent metal electroplating or electrochemical
deposition onto semiconductor substrates. More particularly, the
invention provides uniform and void-free deposition of metal onto
metal seeded semiconductor substrates having sub-micron, high
aspect ratio features. The invention provides an electrochemical
deposition cell comprising a substrate holder, a cathode
electrically contacting a substrate plating surface, an electrolyte
container having an electrolyte inlet, an electrolyte outlet and an
opening adapted to receive a substrate plating surface and an anode
electrically connect to an electrolyte. Preferably, a vibrator is
attached to the substrate holder to vibrate the substrate in at
least one direction, and an auxiliary electrode is disposed
adjacent the electrolyte outlet to provide uniform deposition
across the substrate surface. Preferably, a periodic reverse
current is applied during the plating period to provide a void-free
metal layer within high aspect ratio features on the substrate.
Inventors: |
Landau; Uziel (Shaker Heights,
OH) |
Family
ID: |
22171736 |
Appl.
No.: |
10/622,001 |
Filed: |
July 17, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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60082521 |
Apr 21, 1998 |
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Reissue of: |
09295678 |
Apr 21, 1999 |
06261433 |
Jul 17, 2001 |
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Current U.S.
Class: |
205/96;
204/230.7; 204/272; 204/273; 204/263; 204/261; 204/260; 204/275.1;
204/297.01; 204/297.03; 205/123; 205/128; 205/149; 205/153;
205/157; 204/230.2; 205/103 |
Current CPC
Class: |
C25D
17/001 (20130101); C25D 3/38 (20130101); C25D
7/123 (20130101) |
Current International
Class: |
C25D
5/00 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
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58-182823 |
|
Oct 1983 |
|
JP |
|
63-118093 |
|
May 1988 |
|
JP |
|
04131395 |
|
May 1992 |
|
JP |
|
04280993 |
|
Oct 1992 |
|
JP |
|
6017291 |
|
Jan 1994 |
|
JP |
|
407014811 |
|
Jan 1995 |
|
JP |
|
WO 97/12079 |
|
Apr 1997 |
|
WO |
|
WO 99/16936 |
|
Apr 1999 |
|
WO |
|
WO 99/25902 |
|
May 1999 |
|
WO |
|
WO 99/25903 |
|
May 1999 |
|
WO |
|
WO 99/25904 |
|
May 1999 |
|
WO |
|
WO 99/25905 |
|
May 1999 |
|
WO |
|
WO 99/26275 |
|
May 1999 |
|
WO |
|
WO 00/32835 |
|
Jun 2000 |
|
WO |
|
WO 02/04715 |
|
Jan 2002 |
|
WO |
|
Other References
PCT Written Opinion citing additional references for
PCT/US99/28159, dated Dec. 8, 2000. cited by examiner .
PCT International Search Report dated Feb. 7, 2000. cited by
examiner .
Kenneth E. Pitney, "Ney Contact Manual," Electrical Contacts for
Low Energy Uses, 1973, no month available. cited by examiner .
Lucio Colombo, "Wafer Back Surface Film Removal," Central R&D,
SGS-Thompson, Microelectronics, Agrate, Italy, 6 pages, no month
available. cited by examiner .
Semitool, Inc., "Metallization & Interconnect," 1998, 4 pages,
no month available. cited by examiner .
Verteq Online, "Products Overview," 1996-1998, 5 pages, no month
available. cited by examiner .
Laurell Technologies Corporation, "Two control configurations
available--see WS 400 or WS-400 Lite." Oct. 19, 1998, 6 pages.
cited by examiner .
Peter Singer, "Tantalum, Copper and Damascene: The Future of
Interconnects," Semiconductor International, Jun. 1998, pages
cover, 91-91, 94, 96 & 98. cited by examiner .
Peter Singer, "Wafer Processing," Semiconductor International,
Jun., 1998, p. 70. cited by examiner .
PCT Notification of Transmittal of International Preliminary
Examination Report dated Apr. 13, 2007 for PCT/US01/31943. cited by
other .
PCT International Search Report dated Jul. 5, 2005, for
PCT/US01/31943. cited by other .
PCT International Search Report dated Jul. 5, 2005, for
PCT/US01/20622. cited by other .
PCT Written Opinion for International Application No.
PCT/US01/20624 dated Aug. 8, 2006. cited by other.
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Primary Examiner: Bell; Bruce F.
Attorney, Agent or Firm: Patterson & Sheridan, LLP
Parent Case Text
CROSS REFERENCE TO RELATED APPLICATION
This application claims the benefit of U.S. Provisional Application
Ser. No. 60/082,521, entitled "Electroplating on Substrates," filed
on Apr. 21, 1998.
Claims
What is claimed is:
1. An apparatus for electrochemical deposition of a metal onto a
substrate having a substrate plating surface, comprising: a) a
substrate holder adapted to hold the substrate in a position
wherein the substrate plating surface is exposed to an electrolyte
in an electrolyte container; wherein the substrate holder
comprises: i) a vacuum chuck having a substrate support surface;
and ii) an elastomer ring disposed around the substrate support
surface, the elastomer ring contacting a peripheral portion of the
substrate; b) a cathode electrically contacting the substrate
plating surface; c) an electrolyte container having an electrolyte
inlet, an electrolyte outlet and an opening adapted to receive the
substrate plating surface; and d) an anode electrically connected
to the electrolyte.
2. The apparatus of claim 1 wherein the substrate holder further
comprises: iii) one or more bubble release ports having one or more
openings adjacent an edge of the substrate supporting surface.
3. An apparatus for electrochemical deposition of a metal onto a
substrate having a substrate plating surface, comprising: a) a
substrate holder adapted to hold the substrate in a position
wherein the substrate plating surface is exposed to an electrolyte
in an electrolyte container; wherein the substrate holder
comprises: i) a vacuum chuck having a substrate support surface;
and ii) a gas bladder disposed around the substrate support
surface, the gas bladder adapted to contact a peripheral portion of
the substrate; b) a cathode electrically contacting the substrate
plating surface; c) an electrolyte container having an electrolyte
inlet, an electrolyte outlet and an opening adapted to receive the
substrate plating surface; and d) an anode electrically connected
to the electrolyte.
4. An apparatus for electrochemical deposition of a metal onto a
substrate having a substrate plating surface, comprising: a) a
substrate holder adapted to hold the substrate in a position
wherein the substrate plating surface is exposed to an electrolyte
in an electrolyte container; b) a cathode electrically contacting
the substrate plating surface, wherein the cathode comprises a
cathode contact member disposed at a peripheral portion of the
substrate plating surface, the cathode contact member having a
contact surface adapted to electrically contact the substrate
surface, wherein the cathode contact member comprises a radial
array of contact pins and a resistor connected in series with each
contact pin; c) an electrolyte container having an electrolyte
inlet, an electrolyte outlet and an opening adapted to receive the
substrate plating surface; and d) an anode electrically connected
to the electrolyte.
5. The apparatus of claim 4 wherein the cathode further comprises a
sensor connected across each resistor to monitor the current
flowing through the resistor.
6. An apparatus for electrochemical deposition of a metal onto a
substrate having a substrate plating surface, comprising: a) a
substrate holder adapted to hold the substrate in a position
wherein the substrate plating surface is exposed to an electrolyte
in an electrolyte container; b) a cathode electrically contacting
the substrate plating surface; c) an electrolyte container having
an electrolyte inlet, an electrolyte outlet and an opening adapted
to receive the substrate plating surface, wherein the electrolyte
outlet is defined by a gap between a first surface on the substrate
holder extending radially outward from the substrate plating
surface and a surface of the electrolyte container; and d) an anode
electrically connected to the electrolyte.
7. The apparatus of claim 6 wherein the gap has a gap width between
about 1 mm and about 30 mm.
8. An apparatus for electrochemical deposition of a metal onto a
substrate having a substrate plating surface, comprising: a) a
substrate holder adapted to hold the substrate in a position
wherein the substrate plating surface is exposed to an electrolyte
in an electrolyte container; b) a cathode electrically contacting
the substrate plating surface; c) an electrolyte container having
an electrolyte inlet, an electrolyte outlet and an opening adapted
to receive the substrate plating surface; d) an anode electrically
connected to the electrolyte; and e) a control electrode disposed
in electrical contact with the electrolyte, the control electrode
adapted to provide an adjustable electrical power.
9. The apparatus of claim 8 wherein the control electrode is
disposed outside of the electrolyte container and in electrical
contact with an outflowing electrolyte in the electrolyte
outlet.
10. The apparatus of claim 8 wherein the control electrode
comprises an array of electrode segments.
11. An apparatus for electrochemical deposition of a metal onto a
substrate having a substrate plating surface, comprising: a) a
substrate holder adapted to hold the substrate in a position
wherein the substrate plating surface is exposed to an electrolyte
in an electrolyte container; b) a cathode electrically contacting
the substrate plating surface; c) an electrolyte container having
an electrolyte inlet, an electrolyte outlet and an opening adapted
to receive the substrate plating surface; d) an anode electrically
connected to the electrolyte; and e) a vibrator attached to the
substrate holder, the vibrator transferring a vibration to the
substrate holder.
12. The apparatus of claim 11 wherein the vibrator is adapted to
vibrate the substrate holder in one or more direction.
13. An apparatus for electrochemical deposition of a metal onto a
substrate having a substrate plating surface, comprising: a) a
substrate holder adapted to hold the substrate in a position
wherein the substrate plating surface is exposed to an electrolyte
in an electrolyte container; b) a cathode electrically contacting
the substrate plating surface; c) an electrolyte container having
an electrolyte inlet, an electrolyte outlet and an opening adapted
to receive the substrate plating surface; d) an anode electrically
connected to the electrolyte; and e) a sleeve insert disposed at a
top portion of the electrolyte container, the sleeve insert
defining the opening of the electrolyte container.
14. An apparatus for electrochemical deposition of a metal onto a
substrate having a substrate plating surface, comprising: a) a
substrate holder adapted to hold the substrate in a position
wherein the substrate plating surface is exposed to an electrolyte
in an electrolyte container; b) a cathode electrically contacting
the substrate plating surface; c) an electrolyte container having
an electrolyte inlet, an electrolyte outlet and an opening adapted
to receive the substrate plating surface; d) an anode electrically
connected to the electrolyte; and e) a flow adjuster wedge disposed
at a top portion within the electrolyte container.
15. An apparatus for electrochemical deposition of a metal onto a
substrate having a substrate plating surface, comprising: a) a
substrate holder adapted to hold the substrate in a position
wherein the substrate plating surface is exposed to an electrolyte
in an electrolyte container; b) a cathode electrically contacting
the substrate plating surface; c) an electrolyte container having
an electrolyte inlet, an electrolyte outlet and an opening adapted
to receive the substrate plating surface; d) an anode electrically
connected to the electrolyte; and e) a gas knife to supply a gas
flow across the wafer plating surface to remove residual
electrolyte.
16. An apparatus for electrochemical deposition of a metal onto a
substrate having a substrate plating surface, comprising: a) a
substrate holder adapted to hold the substrate in a position
wherein the substrate plating surface is exposed to an electrolyte
in an electrolyte container; b) a cathode electrically contacting
the substrate plating surface; c) an electrolyte container having
an electrolyte inlet, an electrolyte outlet and an opening adapted
to receive the substrate plating surface; d) an anode electrically
connected to the electrolyte; and e) a wafer catcher disposed at a
top portion within the electrolyte container.
17. An apparatus for electrochemical deposition of a metal onto a
substrate having a substrate plating surface, comprising: a) a
substrate holder adapted to hold the substrate in a position
wherein the substrate plating surface is exposed to an electrolyte
in an electrolyte container; b) a cathode electrically contacting
the substrate plating surface; c) an electrolyte container having
an electrolyte inlet, an electrolyte outlet and an opening adapted
to receive the substrate plating surface; d) an anode electrically
connected to the electrolyte; and e) a reference electrode adapted
to monitor the cathode and the anode.
18. An apparatus for electrochemical deposition of a metal onto a
substrate having a substrate plating surface, comprising: a) a
substrate holder adapted to hold the substrate in a position
wherein the substrate plating surface is exposed to an electrolyte
in an electrolyte container; b) a cathode electrically contacting
the substrate plating surface; c) an electrolyte container having
an electrolyte inlet, an electrolyte outlet and an opening adapted
to receive the substrate plating surface; d) an anode electrically
connected to the electrolyte; and e) a rinsing solution supply
selectively connected to the electrolyte inlet.
19. An apparatus for electrochemical deposition of a metal onto a
substrate having a substrate plating surface, comprising: a) a
substrate holder adapted to hold the substrate in a position
wherein the substrate plating surface is exposed to an electrolyte
in an electrolyte container; b) a cathode electrically contacting
the substrate plating surface; c) an electrolyte container having
an electrolyte inlet, an electrolyte outlet and an opening adapted
to receive the substrate plating surface; d) an anode electrically
connected to the electrolyte; and e) gas bubble diverting vanes
disposed within the electrolyte container to divert gas bubbles
toward an electrolyte container sidewall.
20. A method for electrochemical deposition of a metal onto a
substrate, comprising: a) providing an electrochemical deposition
cell comprising: 1) a substrate holder; 2) a cathode electrically
contacting a substrate plating surface; 3) an electrolyte container
having an electrolyte inlet, an electrolyte outlet and an opening
adapted to receive a substrate plating surface; and 4) an anode
electrically connected to an electrolyte; b) applying electrical
power to the cathode and the anode; and c) flowing an electrolyte
to contact the substrate plating surface, wherein the electrolyte
flows between about 0.25 gallons per minute (gpm) to about 15
gpm.
21. A method for electrochemical deposition of a metal onto a
substrate, comprising: a) providing an electrochemical deposition
cell comprising: 1) a substrate holder; 2) a cathode electrically
contacting a substrate plating surface; 3) an electrolyte container
having an electrolyte inlet, an electrolyte outlet and an opening
adapted to receive a substrate plating surface; and 4) an anode
electrically connected to an electrolyte; b) applying electrical
power to the cathode and the anode; and c) flowing an electrolyte
to contact the substrate plating surface; wherein the step of
applying an electrical power to the cathode and the anode
comprises: 1) applying a cathodic current density between about 5
mA/cm.sup.2 and about 40 mA/cm.sup.2 for about 1 second to about
240 seconds.
22. The method of claim 21 wherein the step of applying an
electrical power to the cathode and the anode further comprises: 2)
applying a dissolution reverse current between about 5 mA/cm.sup.2
and about 80 mA/cm.sup.2 for about 0.1 seconds to about 100
seconds.
23. A method for electrochemical deposition of a metal onto a
substrate, comprising: a) providing an electrochemical deposition
cell comprising: 1) a substrate holder; 2) a cathode electrically
contacting a substrate plating surface; 3) an electrolyte container
having an electrolyte inlet, an electrolyte outlet and an opening
adapted to receive a substrate plating surface; and 4) an anode
electrically connected to an electrolyte; b) applying electrical
power to the cathode and the anode; and c) flowing an electrolyte
to contact the substrate plating surface; wherein the step of
applying an electrical power to the cathode and the anode
comprises: 1) applying a cathode current density between about 5
mA/cm.sup.2 and about 40 mA/cm.sup.2 for about 1 second to about
240 seconds; 2) applying a dissolution reverse current between
about 5 mA/cm.sup.2 and about 80 mA/cm.sup.2 for about 0.1 seconds
to about 100 seconds; 3) applying a cathodic current density
between about 5 mA/cm.sup.2 and about 40 mA/cm.sup.2 for about 1
seconds to about 240 seconds; and 4) repeating step 2 and step
3.
24. A method for electrochemical deposition of a metal onto a
substrate, comprising: a) providing an electrochemical deposition
cell comprising: 1) a substrate holder; 2) a cathode electrically
contacting a substrate plating surface; 3) an electrolyte container
having an electrolyte inlet an electrolyte outlet and an opening
adapted to receive a substrate plating surface; and 4) an anode
electrically connected to an electrolyte; b) applying electrical
power to the cathode and the anode; c) flowing an electrolyte to
contact the substrate plating surface; d) providing a control
electrode in electrical contact with an electrolyte of an
electrochemical deposition cell; and e) adjusting the electrical
power provided by the control electrode during deposition.
25. The method of claim 24 wherein the electrical power provided by
the control electrode is adjusted synchronously with a
deposition/dissolution cycle of an electrochemical deposition
process.
26. A method for electrochemical deposition of a metal onto a
substrate, comprising: a) providing an electrochemical deposition
cell comprising: 1) a substrate holder; 2) a cathode electrically
contacting a substrate plating surface; 3) an electrolyte container
having an electrolyte inlet, an electrolyte outlet and an opening
adapted to receive a substrate plating surface; and 4) an anode
electrically connected to an electrolyte; b) applying electrical
power to the cathode and the anode; c) flowing an electrolyte to
contact the substrate plating surface; and d) vibrating a component
of the electrochemical deposition cell in one or more
directions.
27. A method for electrochemical deposition of a metal onto a
substrate, comprising: a) providing an electrochemical deposition
cell comprising: 1) a substrate holder; 2) a cathode electrically
contacting a substrate plating surface; 3) an electrolyte container
having an electrolyte inlet, an electrolyte outlet and an opening
adapted to receive a substrate plating surface; and 4) an anode
electrically connected to an electrolyte; b) applying electrical
power to the cathode and the anode; c) flowing an electrolyte to
contact the substrate plating surface; and d) vibrating a component
of the electrochemical deposition cell at a vibrational frequency
between about 10 Hz and about 20,000 Hz and a vibrational amplitude
between about 0.5 micron and about 100,000 micron.
28. A method for electrochemical deposition of a metal onto a
substrate, comprising: a) providing an electrochemical deposition
cell comprising: 1) a substrate holder; 2) a cathode electrically
contacting a substrate plating surface; 3) an electrolyte container
having an electrolyte inlet, an electrolyte outlet and an opening
adapted to receive a substrate plating surface; and 4) an anode
electrically connected to an electrolyte; b) applying electrical
power to the cathode and the anode; c) flowing an electrolyte to
contact the substrate plating surface; d) rotating the substrate
holder about a central axis through the substrate.
29. An apparatus for electrochemical deposition of a metal onto a
substrate, comprising: a) a substrate holder comprising: i) a
vacuum chuck having a substrate support surface; and ii) an
elastomer ring disposed around the substrate support surface, the
elastomer ring contacting a peripheral portion of the substrate; b)
a cathode electrically contacting a substrate plating surface; c)
an electrolyte container having an electrolyte inlet, an
electrolyte outlet and an opening adapted to receive a substrate
plating surface, wherein the electrolyte outlet is defined by a gap
between a first surface extending radially outward from the
substrate plating surface and a surface of the electrolyte
container; d) an anode electrically connected to the electrolyte,
the anode comprising: i) a porous enclosure for flow of an
electrolyte therethrough; ii) a metal disposed within the
enclosure; and iii) an electrode disposed within the enclosure; e)
a control electrode in electrical contact with an electrolyte, the
control electrode adapted to provide an adjustable electrical
power; and f) a vibrator attached to the substrate holder, the
vibrator adapted to transfer a vibration in one or more directions
in the substrate holder.
.Iadd.30. An apparatus for electrochemically depositing a metal
onto a semiconductor substrate, comprising: a container having a
fluid inlet, a fluid outlet, and an open portion, the container
being configured to contain an electrochemical plating solution
therein; a substrate holder assembly configured to electrically
contact a substrate plating surface and support the plating surface
in fluid communication with the electrochemical plating solution
via the open portion; an anode in fluid communication with the
electrochemical plating solution; and a porous fluid flow
adjustment member positioned across the container between the anode
and the open portion, wherein the porous fluid flow adjustment
member comprises a ceramic member..Iaddend.
.Iadd.31. An apparatus for electrochemically depositing a metal
onto a semiconductor substrate, comprising: a container having a
fluid inlet, a fluid outlet, and an open portion, the container
being configured to contain an electrochemical plating solution
therein; a substrate holder assembly configured to electrically
contact a substrate plating surface and support the plating surface
in fluid communication with the electrochemical plating solution
via the open portion, wherein the substrate holder assembly
comprises a cathode contact member and a backside substrate
engaging member configured to urge the substrate plating surface
against the cathode contact member; an anode in fluid communication
with the electrochemical plating solution; and a porous fluid flow
adjustment member positioned across the container between the anode
and the open portion..Iaddend.
.Iadd.32. The apparatus of claim 31, wherein the cathode contact
member comprises: an annular member; and at least one substrate
contact element positioned on the annular member..Iaddend.
.Iadd.33. The apparatus of claim 32, comprising an insulative
coating positioned on an outer surface of the annular
member..Iaddend.
.Iadd.34. The apparatus of claim 32, wherein the at least one
substrate contact element comprises a continuous ring configured to
electrically contact a perimeter of the plating
surface..Iaddend.
.Iadd.35. The apparatus of claim 34, comprising an O-ring seal
member positioned radially inward of the continuous
ring..Iaddend.
.Iadd.36. The apparatus of claim 32, wherein the at least one
substrate contact element comprises a plurality of substrate
contact pins radially positioned on the annular member to
electrically contact a perimeter of the plating
surface..Iaddend.
.Iadd.37. The apparatus of claim 36, comprising an annular seal
member positioned on the annular member radially inward of the
plurality of substrate contact pins, the annular seal member being
configured to sealable engage the plating surface to prevent the
electrochemical plating solution from passing
therebetween..Iaddend.
.Iadd.38. The apparatus of claim 32, comprising at least one bubble
release port positioned adjacent an edge of the annular
member..Iaddend.
.Iadd.39. The apparatus of claim 31, wherein the backside substrate
engaging member comprises an elastomer seal positioned to sealably
engage a backside perimeter of the substrate..Iaddend.
.Iadd.40. The apparatus of claim 31, wherein the backside substrate
engaging member comprises an inflatable bladder assembly positioned
to engage a backside perimeter of the substrate..Iaddend.
.Iadd.41. An apparatus for electrochemically depositing a metal
onto a semiconductor substrate, comprising: a container having a
fluid inlet, a fluid outlet, and an open portion, the container
being configured to contain an electrochemical plating solution
therein; a substrate holder assembly configured to electrically
contact a substrate plating surface and support the plating surface
in fluid communication with the electrochemical plating solution
via the open portion; an anode in fluid communication with the
electrochemical plating solution; a porous fluid flow adjustment
member positioned across the container between the anode and the
open portion; and an egress gap of between about 1 mm and about 30
mm between an outer surface of the substrate holder assembly and an
inner surface of the container, wherein the egress gap is between
about 2 mm and about 6 mm..Iaddend.
.Iadd.42. An apparatus for electrochemically depositing a metal
onto a semiconductor substrate, comprising: a container having a
fluid inlet, a fluid outlet, and an open portion, the container
being configured to contain an electrochemical plating solution
therein; a substrate holder assembly configured to electrically
contact a substrate plating surface and support the plating surface
in fluid communication with the electrochemical plating solution
via the open portion; an anode in fluid communication with the
electrochemical plating solution; a porous fluid flow adjustment
member positioned across the container between the anode and the
open portion; and at least one auxiliary electrode positioned in
fluid communication with the electrochemical plating
solution..Iaddend.
.Iadd.43. The apparatus of claim 42, wherein the at least one
auxiliary electrode comprises at least one electrode member
positioned below the substrate plating surface, the at least one
auxiliary electrode being in electrical communication with a source
of electrical power..Iaddend.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to deposition of a metal
layer onto a substrate. More particularly, the present invention
relates to an apparatus and a method for electroplating a metal
layer onto a substrate.
2. Background of the Related Art
Sub-micron multi-level metallization is one of the key technologies
for the next generation of ultra large scale integration (ULSI).
The multilevel interconnects that lie at the heart of this
technology require planarization of interconnect features formed in
high aspect ratio apertures, including contacts, vias, lines and
other features. Reliable formation of these interconnect features
is very important to the success of ULSI and to the continued
effort to increase circuit density and quality on individual
substrates and die.
As circuit densities increases, the widths of vias, contacts and
other features, as well as the dielectric materials between them,
decrease to sub-micron dimensions, whereas the thickness of the
dielectric layers remains substantially constant, with the result
that the aspect ratios for the features, i.e., their height divided
by width, increases. Many traditional deposition processes have
difficulty filling sub-micron structures where the aspect ratio
exceed 2:1, and particularly where it exceeds 4:1. Therefore, there
is a great amount of ongoing effort being directed at the formation
of void-free, sub-micron features having high aspect ratios.
Elemental aluminum (Al) and its alloys have been the traditional
metals used to form lines and plugs in semiconductor processing
because of aluminum's low electrical resistivity, its superior
adhesion to silicon dioxide (SiO.sub.2), its ease of patterning,
and the ability to obtain it in a highly pure form. However,
aluminum has a higher electrical resistivity than other more
conductive metals such as copper and silver, and aluminum also can
suffer from electromigration phenomena. Electromigration is
considered as the motion of atoms of a metal conductor in response
to the passage of high current density through it, and it is a
phenomenon that occurs in a metal circuit while the circuit is in
operation, as opposed to a failure occurring during fabrication.
Electromigration can lead to the formation of voids in the
conductor. A void may accumulate and/or grow to a size where the
immediate cross-section of the conductor is insufficient to support
the quantity of current passing through the conductor, and may also
lead to an open circuit. The area of conductor available to conduct
heat therealong likewise decreases where the void forms, increasing
the risk of conductor failure. This problem is sometimes overcome
by doping aluminum with copper and with tight texture or
crystalline structure control of the material. However,
electromigration in aluminum becomes increasingly problematic as
the current density increases.
Copper and its alloys have lower resistivity than aluminum and
higher electromigration resistance as compared to aluminum. These
characteristics are important for supporting the higher current
densities experienced at high levels of integration and increased
device speed. Copper also has good thermal conductivity and is
available in a highly pure state. Therefore, copper is becoming a
choice metal for filling sub-micron, high aspect ratio interconnect
features on semiconductor substrates.
Despite the desirability of using copper for semiconductor device
fabrication, choices of fabrication methods for depositing copper
into high aspect ratio features are limited. Precursors for CVD
deposition of copper are ill-developed and involve complex and
costly chemistry. Physical vapor deposition into such features
produces unsatisfactory results because of limitations in `step
coverage` and voids formed in the features.
As a result of these process limitations, electroplating, which had
previously been limited to the fabrication of patterns on circuit
boards, is just now emerging as a method to fill vias and contacts
on semiconductor devices. FIGS. 1A-1E illustrate a metallization
technique for forming a dual damascene interconnect in a dielectric
layer having dual damascene via and wire definition, wherein the
via has a floor exposing an underlying layer. Although a dual
damascene structure is illustrated, this method can be applied also
to metallize other interconnect features. The method generally
comprises physical vapor depositing a barrier layer over the
feature surfaces, physical vapor depositing a conductive metal seed
layer, preferably copper, over the barrier layer, and then
electroplating a conductive metal over the seed layer to fill the
structure/feature. Finally, the deposited layers and the dielectric
layers are planarized, such as by chemical mechanical polishing
(CMP), to define a conductive interconnect feature.
Referring to FIGS. 1A through 1E, a cross sectional diagram of a
layered structure 10 is shown including a dielectric layer 16
formed over an underlying layer 14 which contains electrically
conductive features 15. The underlying layer 14 may take the form
of a doped silicon substrate or it may be a first or subsequent
conducting layer formed on a substrate. The dielectric layer 16 is
formed over the underlying layer 14 in accordance with procedures
known in the art such as dielectric CVD to form a part of the
overall integrated circuit. Once deposited, the dielectric layer 16
is patterned and etched to form a dual damascene via and wire
definition, wherein the via has a floor 30 exposing a small portion
of the conducting feature 15. Etching of the dielectric layer 16
can be accomplished with various generally known dielectric etching
processes, including plasma etching.
Referring to FIG. 1A, a cross-sectional diagram of a dual damascene
via and wire definition formed in the dielectric layer 16 is shown.
The via and wire definition facilitates the deposition of a
conductive interconnect that will provide an electrical connection
with the underlying conductive feature 15. The definition provides
vias 32 having via walls 34 and a floor 30 exposing at least a
portion of the conductive feature 15, and trenches 17 having trench
walls 38.
Referring to FIG. 1B, a barrier layer 20 of tantalum or tantalum
nitride (TaN) is deposited on the via and wire definition, such
that aperture 18 remains in the via 32, by using reactive physical
vapor deposition, i.e., by sputtering a tantalum target in a
nitrogen/argon plasma. Preferably, where the aspect ratio of the
aperture is high (e.g. 4:1 or higher) with a sub-micron wide via,
the Ta/TaN is deposited in a high density plasma environment,
wherein the sputtered deposition of the Ta/TaN is ionized and drawn
perpendicularly to the substrate by a negative bias on the
substrate. The barrier layer is preferably formed of tantalum or
tantalum nitride, however other barrier layers such as titanium,
titanium nitride and combinations thereof may also be used. The
process used may be PVD, CVD, or combined CVD/PVD for texture and
film property improvement. The barrier layer limits the diffusion
of copper into the semiconductor substrate and the dielectric layer
and thereby dramatically increases the reliability of the
interconnect. It is preferred that the barrier layer has a
thickness between about 25 .ANG. and about 400 .ANG., most
preferably about 100 .ANG..
Referring to FIG. 1C, a PVD copper seed layer 21 is deposited over
the barrier layer 20. Other metals, particularly noble metals, can
also be used for the seed layer. The PVD copper seed layer 21
provides good adhesion for subsequently deposited metal layers, as
well as a conformal layer for even growth of the copper
thereover.
Referring to FIG. 1D, a copper layer 22 is electroplated over the
PVD copper seed layer 21 to completely fill the via 32 with a
copper plug 19.
Referring to FIG. 1E, the top portion of the structure 10, i.e.,
the exposed copper is then planarized, preferably by chemical
mechanical polishing (CMP). During the planarization process,
portions of the copper layer 22, copper seed layer 21, barrier
layer 20, and dielectric layer 16 are removed from the top surface
of the structure, leaving a fully planar surface with conductive
interconnect 39.
Metal electroplating in general is a well-known art and can be
achieved by a variety of techniques. Common designs of cells for
electroplating a metal on wafer-based substrates involve a fountain
configuration. The substrate is positioned with the plating surface
at a fixed distance above a cylindrical electrolyte container, and
the electrolyte impinges perpendicularly on the substrate plating
surface. The substrate is the cathode of the plating system, such
that ions in the plating solution deposit on the conductive exposed
surface of the substrate and the micro-sites on the substrate.
However, a number of obstacles impair consistent reliable
electroplating of copper onto substrates having a sub-micron scale,
high aspect ratio features. Generally, these obstacles involve
difficulty with providing uniform current density distribution
across the substrate plating surface, which is needed to form a
metal layer having uniform thickness. A primary obstacle is how to
get current to the substrate and how to ensure that the current is
uniformly distributed thereon.
One current method for providing power to the plating surface uses
contacts (e.g., pins, `fingers`, or springs) which contact the
substrate seed layer. The contacts touch the seed layer as close as
practically possible to the edge of the substrate, to minimize the
wasted area on the wafer due to the presence of the contacts. The
`excluded` area can no longer be used to ultimately form devices on
the substrate. However, the contact resistance of the contacts to
the seed layer may vary from contact to contact, resulting in a
non-uniform distribution of current densities across the substrate.
Also, the contact resistance at the contract to seed layer
interface may vary from substrate to substrate, resulting in
inconsistent plating distribution between different substrates
using the same equipment. Furthermore, the plating rate tends to be
higher near the region of the contacts and be lower at regions
remote from the contacts due to the resistivity of the thin seed
layer that has been deposited on the substrate. A fringing effect
of the electrical field also occurs at the edge of the substrate
due to the highly localized electrical field formed at the edge of
the plated region, causing a higher deposition rate near the edge
of the substrate.
A resistive substrate effect is usually pronounced during the
initial phase of the electroplating process and reduces the
deposition uniformity because the seed layer and the electroplated
layers on the substrate deposition surface are typically thin. The
metal plating tends to concentrate near the current feed contacts,
i.e., the plating rate is greatest adjacent the contacts, because
the current density across the substrate decreases as the distance
from the current feed contacts increases due to insufficient
conductive material on the seed layer to provide a uniform current
density across the substrate plating surface. As the deposition
film layer becomes thicker due to the plating, the resistive
substrate effect diminishes because a sufficient thickness of
deposited material becomes available across the substrate plating
surface to provide uniform current densities across the substrate.
It is desirable to reduce the resistive substrate effect during
electroplating.
Traditional fountain plater designs also provide non-uniform flow
of the electrolyte across the substrate plating surface, which
compounds the effects of the non-uniform current distribution on
the plating surface by providing non-uniform replenishment of
plating ions and where applicable, plating additives, across the
substrate, resulting in non-uniform plating. The electrolyte flow
uniformity across the substrate can be improved by rotating the
substrate at a high rate during the plating process. Such rotation
introduces complexity into the plating cell design due to the need
to furnish current across and revolving interface. However, the
plating uniformity still deteriorates at the boundaries or edges of
the substrate because of the fringing effects of the electrical
field near the edge of the substrate, the seed layer resistance and
the potentially variable contact resistance.
There is also a problem in maintaining an electroplating solution
to the system having consistent properties over the duration of a
plating cycle and/or over a run of multiple wafers being plated.
Traditional fountain plater designs generally require continual
replenishing of the metal being deposited into the electrolyte. The
metal electrolyte replenishing scheme is difficult to control and
causes build-up of co-ions in the electrolyte, resulting in
difficult to control variations in the ions concentration in the
electrolyte. Thus, the electroplating process produces inconsistent
results because of inconsistent ion concentration in the
electrolyte.
Additionally, operation of a plating cell incorporating a
non-consumable anode may cause bubble-related problems because
oxygen evolves on the anode during the electroplating process.
Bubble-related problems include plating defects caused by bubbles
that reach the substrate plating surface and prevent adequate
electrolyte contact with the plating surface. It is desirable to
eliminate or reduce bubble formation from the system and to remove
formed bubbles from the system.
Therefore, there remains a need for a reliable, consistent metal
electroplating apparatus and method to deposit uniform, high
quality metal layers on substrates to form sub-micron features.
There is also a need to form metal layers on substrates having
micron-sized, high aspect ratio features to fill the features
without voids in the features.
SUMMARY OF THE INVENTION
The invention provides an apparatus and a method for achieving
reliable, consistent metal electroplating or electrochemical
deposition onto substrates. More particularly, the invention
provides uniform and void-free deposition of metal onto substrates
having sub-micron features formed thereon and a metal seed layer
formed thereover. The invention provides an electro-chemical
deposition cell comprising a substrate holder, a cathode
electrically contacting a substrate plating surface, an electrolyte
container having an electrolyte inlet, an electrolyte outlet and an
opening adapted to receive a substrate and an anode electrically
connect to an electrolyte. The configuration and dimensions of the
deposition cell and its components are designed to provide uniform
current distribution across the substrate. The cell is equipped
with a flow-through anode and a diaphragm unit that provide a
combination of relatively uniform flow of particular-free
electrolyte in an easy to maintain configuration. Additionally, an
agitation device may be mounted to the substrate holder to vibrate
the substrate in one or more directions, ie., x, y and/or z
directions. Still further, an auxiliary electrode can be disposed
adjacent the electrolyte outlet to provide uniform deposition
across the substrate surface and to shape as necessary the
electrical field at the edge of the substrate and at the contacts.
Still further, time variable current waveforms including periodic
reverse and pulsed current can be applied during the plating period
to provide a void-free metal layer within sub-micron features on
the substrate.
BRIEF DESCRIPTION OF THE DRAWINGS
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.
It is to be noted, however, that the appended drawings illustrate
only typical embodiments of this invention and are therefore not to
be considered limiting of its scope, for the invention may admit to
other equally effective embodiments.
FIGS. 1A-1E are cross sectional views of a dual damascene
interconnect in a .Iadd.dielectric .Iaddend.layer illustrating a
metallization technique for forming such interconnect.
FIG. 2 is a partial vertical cross sectional schematic view of a
cell for electroplating a metal onto semiconductor substrates.
FIG. 2a is a partial cross sectional view of a continuous ring
cathode member in contact with a substrate on a substrate
holder.
FIG. 3 is a schematic top view of a cathode contact member
comprising a radial array of contact pins disposed about the
circumference of the substrate and the cell body showing one
arrangement of auxiliary electrodes.
FIG. 4 is a schematic diagram of the electrical circuit
representing the electroplating system through each contact pin and
resistors.
FIG. 5 is a partial vertical cross sectional schematic view of a
weir plater containing soluble copper beads enclosed between porous
diaphragms in the anode compartment.
FIGS. 6a and 6b are schematic illustrations of an embodiment of a
multi-substrate processing unit.
FIG. 7 is a horizontal cross sectional schematic view of another
embodiment of a multi-substrate batch processing unit.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
The present invention generally provides several embodiments of a
new electrochemical cell and a method of operation of the cells to
deposit high quality metal layers on substrates. The invention also
provides new electrolyte solutions which can be used to advantage
in the deposition of metals, and copper in particular, into very
small features, i.e., micron sized features and smaller. The
invention will be described below first in reference to the
hardware, then operation of the hardware and then chemistry of the
electrolyte solutions.
Electrochemical Cell Hardware
FIG. 2 is a cross sectional schematic view of a cell 40 for
electroplating a metal onto a substrate. The electroplating cell 40
generally comprises a container body 42 having an opening on the
top portion of the container body to receive and support a
substrate holder 44 thereover. The container body 42 is preferably
an annular cell comprised of an electrically insulative material,
such a plastic, plexiglass (acrylic), lexane, PVC, CPVC, and PVDF.
Alternatively, the container body can be made from a metal, such as
stainless steel, nickel or titanium which is coated with an
insulating layer, e.g., Teflon.RTM., PVDF, plastic or rubber, or
other combinations of materials which can be electrically insulated
from the electrodes (ie., the anode and the cathode) of the cell
and which do not dissolve in the electrolyte. The substrate holder
44 serves as a top cover for the container body and has a substrate
supporting surface 46 disposed on the lower surface thereof. The
container body 42 is preferably sized and adapted to conform to the
shape of the substrate 48 being processed, typically square,
rectangular or circular in shape and to the size of the plated
region thereon.
An electroplating solution inlet 50 is disposed at the bottom
portion of the container body 42. The electroplating solution is
pumped into the container body 42 by a suitable pump 51 connected
to the inlet 50 and flows upwardly inside the container body 42
toward the substrate 48 to contact the exposed substrate surface
54.
The substrate 48 is secured on the substrate supporting surface 46
of the substrate holder 44, preferably by a plurality of passages
in the surface 46 maintainable at vacuum to form a vacuum chuck
(not shown). A cathode contact member 52 is disposed on the lower
surface of the substrate holder 44 and supports a substrate over
the container. The cathode contact member 52 includes one or more
contacts which provide electrical connection between a power supply
49 and a substrate 48. The cathode contact member 52 may comprise a
continuous conductive ring or wire or a plurality of conductive
contact fingers or wires 56 (Shown in FIG. 3) in electrical contact
with the substrate plating surface 54. FIG. 3 is an exploded
perspective view of a substrate holder 44 having a cathode contact
member comprising a radial array of contact pins 56 disposed about
the circumference of the substrate. The contact pins 56 (eight
shown) extend radially inwardly over the edge of the substrate 48
and contact a conductive layer on the substrate 48 at the tips of
the contact pins 56, thereby providing good electrical contact to
the substrate plating surface 54. Also, the radial array of contact
pins present a negligible barrier to the flow of the electrolyte,
resulting in minimal electrolyte flow distrubance near the plating
surface of the substrate. Alternatively, the cathode contact member
may contact the edge of the substrate in a continuous ring or
semi-continuous ring (i.e., a segmented ring).
The cathode contact member 52 provides electrical current to the
substrate plating surface 54 to enable the electroplating process
and therefore is preferably comprised of a metallic or
semi-metallic conductor. The contact member 52 may also include a
non-plating or insulative coating to prevent plating on surfaces
that are exposed to the electrolyte on the contact member. Plating
on the cathode contact member may change the current and potential
distributions adjacent to the contact member and is likely to lead
to defects on the wafer. The non-plating or insulation coating
material can comprise of a polymeric coating, such as Teflon.RTM.,
PVDF, PVC, rubber or an appropriate elastomer. Alternatively, the
contact member may be made of a metal that resists being coated by
copper, such as tantalum (Ta), tantalum nitride (TaN), titanium
nitride (TiN), titanium (Ti), or aluminum. The coating material
prevents plating onto the contact and ensures predictable
conduction characteristics through the contact to the surface of
the substrate. If the contact members are made of metals that are
stable in the chemical environment of the cell but may be coated
with copper throughout the plating process, such as platinum, gold,
and/or their alloys, the contact member is preferably protected by
an insulative sheet, an elastomer gasket or coating. The contacts
preferably provide low contact resistance to the substrate surface
or are coated, particularly in the contact region with a material
that provides low contact resistance to the substrate surface.
Examples include copper or platinum. Plating on the contact region
of the cathode contact member 52 may change the physical and
chemical characteristics of the conductor and may eventually
deteriorate the contact performance, resulting in plating
variations or defects. Hence, the contact region is preferably
insulated from the electrolyte by a surrounding insulating ring,
sleeve, gasket or coating disposed on the contact member outside
the region where the contact physically contacts the substrate.
Examples of such coatings include PVDF, PVC, Teflon.RTM., rubbers
or other appropriate elastomer. If the contact member becomes
plated, an anodic current may be passed through the contacts
periodically for a brief time to deplate the contact member. The
cathode for this rejuvenation process may be either the regular
anode (reverse biased) or the auxiliary electrodes described
later.
Typically, one power supply is connected to all of the contact pins
of the cathode contact member, resulting in parallel circuits
through the contact pins. As the pin-to-substrate interface
resistance varies, between pin locations, 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
contact pin, the value or quantity of electrical current passed
through each contact pin becomes controlled mainly by the value of
the external resistor, because the overall resistance of each
contact pin-substrate contact plus the control resistor branch of
the power supply to substrate circuit is substantially equal to
that of the control resistor. As a result, the variations in the
electrical properties between each contact pin do not affect the
current distribution on the substrate, and a uniform current
density results across the plating surface which contributes to
uniform plating thickness. To provide, a uniform current
distribution between each of the contact pins 56 of the radial
array configuration of cathode contact member 52, both during the
plating cycle on a single substrate and between substrates in a
plating run of multiple substrates, an external resistor 58 is
connected in series with each contact pin 56. FIG. 4 is a schematic
diagram of the electrical circuit representing the electroplating
system through each contact pin of the cathode contact member 52
and the external resistor 58 connected in series with each contact
pin 56. Preferably, the resistance value of the external resistor
(RE.sub.EXT) 58 is greater than the resistance of any other
resistive component of the circuit. As shown in FIG. 4, the
electrical circuit through each contact pin 56 is represented by
the resistance of each of the components connected in series with
the power supply. R.sub.E represents the resistance of the
electrolyte, which is typically dependent on the distance between
the anode and the cathode and the composition of the electrolyte
solution. R.sub.A represents the resistance of the electrolyte
adjacent the substrate plating surface within the double layer and
the boundary layer. R.sub.S represents the resistance of the
substrate plating surface, and R.sub.C represents the resistance of
the cathode contacts 56. Preferably, the resistance value of the
external resistor (R.sub.EXT) is greater than the total of R.sub.E,
R.sub.A, R.sub.S and R.sub.C, e.g., >1 .OMEGA. and preferably
>5 .OMEGA.. The external resistor 58 also provides a uniform
current distribution between different substrates of a
process-sequence.
As each substrate is plated, and over multiple substrate plating
cycles, the contact-pin-substrate interface resistance still may
vary, eventually reaching an unacceptable value. An electronic
sensor/alarm 60 can be connected across the external resistor 58 to
monitor the voltage/current across the external resistor to address
this problem. If the voltage/current across any external resistor
58 falls outside of a preset operating range that is indicative of
a high pin-substrate resistance, the sensor/alarm 60 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 contact pin and can
be separately controlled and monitored to provide a uniform current
distribution across the substrate.
An alternative to the contact pin arrangement is a cathode contact
member 52 comprising a continuous ring that contacts the peripheral
edge of the substrate. FIG. 2a is a partial cross sectional view of
a continuous ring cathode member 53 in contact with a substrate 48
disposed in a substrate holder 44. The continuous ring cathode
member 52 maximizes the cathode contact with the substrate plating
surface 54 and minimizes the current distribution non-uniformity by
eliminating the problems of individual contact pins.
Referring again to FIG. 2, the backside of the wafer must be sealed
to prevent the migration of plating or electrolyte solution to the
backside of the substrate. In one embodiment, where the substrate
is held on by a vacuum chuck in the substrate holder and the
substrate must be loaded against the cathode contact member 52, an
elastomer (e.g., silicone rubber) ring 62 is disposed partially
within the substrate holder 44 to seal the backside of the
substrate 48 from the electroplating solution and to enhance
loading of the substrate 48 against the cathode contact member 52.
The elastomer ring 62 shown in FIG. 2 is a wedge-shaped ring,
although other shapes can also be used effectively. The resiliency
of the elastomer ring, when compressed by the substrate, forces the
substrate into good electrical contact with the cathode contact
member 52 and provides a good seal for the backside of the
substrate 48.
Optionally, the substrate holder 44 may include a gas inflated
bladder 64 disposed adjacent the elastomer ring 62 to enhance the
seal created by the elastomer ring 62 and improve the electrical
contact between the cathode contact member 52 and the substrate
plating surface 54. The gas inflated bladder 64 is disposed in an
annular cavity adjacent the elastomer ring 62 and can be inflated
by a gas to exert pressure on the elastomer ring 62 and urge the
substrate to exert pressure on the elastomer ring 62 and urge the
substrate into contact with the contact member 52. To relieve the
contact pressure between the elastomer ring 62 and the backside of
the substrate 48, a relief valve deflates the gas inflated bladder
64 to allow the elastomer ring 62 to retract into the substrate
holder 44.
The substrate holder 44 is positioned above the container body 42
so that the substrate plating surface 54 of a substrate faces the
opening of the container body 42. The substrate holder 44 is
disposed on an outer ring 66 that is connected to the top portion
of container body 42. An insulating O-ring 68 is disposed between
the substrate holder 44 and an outer ring shoulder 66. Preferably,
the substrate holder 44 includes a beveled lower portion 70 that
corresponds to a beveled upper edge 72 of the container body 42
which together form at least a partial circumferential outlet 74,
from about 1 mm to about 30 mm, between the substrate holder 44 and
the container body 42 for electrolyte flow therethrough. The outlet
74 preferably extends around the perimeter of the container body
and cover, but it may alternatively be segmented as shown in FIG. 3
to provide electrolyte egress corresponding to the spaces adjacent
the segmented auxiliary electrodes 84. The width of the outlet can
be adjusted by raising or lowering the substrate holder 44 relative
to the upper surface of the container body to accommodate different
plating process requirements. Preferably, the width of the outlet
is between about 2 mm and about 6 mm. The outlet 74 preferably has
a narrow and sloped egress to enhance the outward flow of
electrolyte and to minimize stagnant circulation .Iadd.corners
.Iaddend.where bubble entrapment can occur. As shown in FIG. 2, the
outlet 74 provides electrolyte egress at about a 45.degree.
downward slope. The electrolyte egress outlet 74 continues through
a space 76 between the inner surface of the outer ring shoulder 66
and the outer surface of the container body 42. Then the
electrolyte flows through one or more outlets 78 connected to a
pump (not shown) and recirculates through the electroplating cell
40 through inlet 50.
A ring or sleeve insert 80 disposed in the upper portion of the
container body 42 can be used to precisely define the plating area
of the substrate. The insert 80 is modularly changeable to adapt an
electroplating cell for various substrate sizes, including 200 mm
and 300 mm sizes, and shapes, including circular, rectangular,
square, etc. The size and the shape of the container body 42 are
preferably changed correspondingly for each size and shape of
substrate to approximate the size and shape of the substrate. The
insert 80 also insulates and protects the edge of the substrate 48
from non-uniform plating by limiting the current flow to the
circumference of the plating surface, thereby reducing the fringing
effects encountered when the cell size is larger than the plating
surface.
As plating occurs on the substrate, ions in solution plate
(deposit) from the solution onto the substrate. To provide
additional plating material, ions must diffuse through a diffusion
boundary layer adjacent the plating surface. Typically, in the
prior art, replenishment is provided through hydrodynamic means by
the flow of solution past the substrate and by substrate rotation.
However, hydrodynamic replenishment schemes still provide
inadequate replenishment because of the no slip condition at the
boundary layer where the electrolyte immediately adjacent the
plating surface has zero velocity and is stagnant. To address these
limitation and increase replenishment, a vibrational agitation
member 82 is provided to control the mass transport rates (boundary
layer thickness) at the surface of the substrate. The vibrational
agitation member 82 is preferably mounted to the substrate holder
44 to vibrate the substrate 48. The vibrational agitation member 82
usually comprises a motor or a vibrational transducer that moves
the substrate holder 44 back and forth on one or more axes at a
frequency from about 10 Hz to about 20,000 Hz. The amplitude of the
vibration is preferably between about 0.5 micron and about 100,000
micron. The vibrational agitation member 82 may also provide
additional vibration in a second direction that is parallel to the
substrate plating surface 54, such as vibrating the substrate in
the x-y directions, or in a direction orthogonal to the substrate
plating surface 54, such as in the x-z directions. Alternatively,
the vibrational agitation member 82 may vibrate the substrate in
multiple directions, such as the x-y-z directions.
The frequency of the vibration can be synchronized to the plating
cycles (discussed in detail below) to tailor-fit the mass transport
rates to the deposition process needs. Conventional electroplating
systems cannot incorporate this feature because high frequency
interruptions or reversals cannot be made in pumped induced
electrolyte flow due to the fluid's inertia in conventional
electroplating systems. The vibration also enhances removal of
residual plating and rinse solution from the substrate surface
after completion of the plating cycle.
The substrate holder 44 can also be rotated, either fully or
partially, in addition to the vibrational agitation to further
enhance uniform plating thickness. A rotational actuator (not
shown) can be attached to the substrate holder 44 and spin, or
partially rotate in an oscillatory manner, the substrate holder
about a central axis through the center of the substrate holder.
The rotational movement of the plating surface against the
electrolyte enhances the exposure of fresh electrolyte across the
plating surface to improve deposition uniformity.
Another advantage of vibrating the substrate 48 is that the
vibration exposes the vias and trenches to fresh electroplating
solutions. As the solution adjacent to the substrate becomes
depleted of the deposition metal, the reciprocation of the
substrate replenishes the areas adjacent to the vias and trenches
with fresh electroplating solution preferably having a high
concentration of copper or other deposition metal. This is achieved
by translating the mouth of the trench or the via on a substrate
plating surface to a region of the solution that has not been
facing the trench or via and is therefore less depleted of the
reactant. An alternative to vibrating the substrate holder 44 and
the substrate 48 is vibrating the electrolyte. A vibrational
transducer (not shown) can be placed within the container body to
directly agitate the electrolyte, or the vibrational transducer can
be placed outside of the container body and indirectly agitate the
electrolyte by vibrating the container body. The vibrational
agitation member 82 also helps to eliminate bubble related defects
by encouraging bubbles to move from the plating surface 54 and be
evacuated from the cell 40.
Gas bubbles may be trapped with the substrate installation into the
cell, carried by the electrolyte flow through the system, or
generated by the electrochemical reaction at the anode or the
cathode. The gas bubbles are preferably exhausted from the cell to
prevent defects in the plating process. A plurality of gas
diverting vanes may be disposed above the anode to divert evolved
gases toward the sidewall of the electrolyte container. Generally,
gas bubbles will move to a higher elevation because of their lower
specific gravity, and the gas bubbles flows along with the
electrolyte that flows generally upward and outward with respect to
the substrate. The vibration is applied to the electrolyte or the
substrate support member detaches the bubbles from the substrate
surface and enhances the movement of the gas bubbles out of the
cell. Preferably, a plurality of gas release ports 81 (as shown in
FIG. 5) are disposed adjacent the periphery of the substrate
support surface 46 through the substrate holder 44 to evacuate gas
bubbles from the cell. The gas release ports 81 are positioned at
an upward angle to allow gas bubble release from the cell 40 while
preventing electrolyte egress through the gas release slots. A
number of optional measures are available to prevent electrolyte
squirting out of the gas release ports 81. First, the gas release
ports can be positioned higher than the static head of the
electrolyte. Second, the gas release ports can be treated to be
hydrophobic, for example, by a Teflon.RTM. tube insert. Third, a
counter gas pressure sufficient to prevent solution egress can be
externally applied through the exit of the gas release ports.
Lastly, the gas release ports can be capped with a small reservoir
sufficient in volume to capture the gas bubbles.
In addition to the anode electrode and the cathode electrode, an
auxiliary electrode can be disposed in contact with the electrolyte
to change the shape of the electrical field over the substrate
plating surface. An auxiliary electrode 84 is preferably disposed
outside the container body to control the deposition thickness,
current density and potential distribution in the electroplating
cell to achieve the desired electroplating results on the
substrate. As shown in FIG. 2, the auxiliary electrode 84 is
disposed within the outer ring 66 adjacent the inner surface of the
outer ring 66. Alternatively, the auxiliary electrode 84 can be
disposed within the container body at the top portion of the
container body as shown in FIG. 2a. The auxiliary electrode 84 is
preferably mounted outside the container body because copper
deposits may build up on the auxiliary electrode when it is
cathodically polarized, or the deposited copper may dissolve,
releasing particulates when the auxiliary electrode is anodically
polarized. With the auxiliary electrode 84 placed within the
container body 42, the non-adhering deposits may flake off or the
dissolving particulate matter may get in solution and contact the
substrate plating surface 54 and cause damage or defects on the
substrate. By placing the auxiliary electrode 84 outside the
container body 42, non-adhering deposition material flows with the
outflowing electrolyte to the recirculating pump. The outflowing
electrolyte is filtered, and the non-adhering deposits are removed
from the system. Furthermore, because the flow rate of the
electrolyte is relatively high outside of the container body 42 (as
compared to the flow rate near the substrate plating surface 54),
non-adhering deposits are less likely to occur on the auxiliary
electrode 84. Another advantage of placing the auxiliary electrode
outside of the container body is that periodic maintenance can be
easily performed by replacing another modular auxiliary electrode
unit onto the electroplating cell. Placement of the auxiliary
electrodes inside the container body, however, may provide a higher
degree of control and resulting higher uniformity of
deposition.
The auxiliary electrode 84 may comprise a ring, a series of
concentric rings, a series of segmented rings, or an array of
spaced electrodes to match a corresponding array of cathode contact
pins 56. The auxiliary electrode 84 may be positioned on the same
plane as the substrate plating surface 54 or on varying planes to
tailor fit the current and potential distribution on the substrate
48. Alternatively, a plurality of concentric ring auxiliary
electrodes can be configured to activate at different potentials or
to activate potentials in sequence according to the desired
process. FIG. 3 shows a configuration of an auxiliary electrode 84
comprising an array of segmented electrodes matching an array of
cathode contact pins 56 to overcome the effect of discrete contacts
that tend to localize the deposition thickness near the region of
the contact. The auxiliary electrode 84 shapes the electric field
by equalizing the localization effects of the discrete contacts.
The auxiliary electrode 84 also can be used to eliminates the
adverse effects of the initially resistive substrate on the
deposition thickness distribution by varying the current/potential
according to the deposition time and thickness. The
current/potential auxiliary electrode 84 may be dynamically
adjusted from a high current level during an initial stage of
electroplating to a gradually decreasing current/potential as the
electroplating process continues. The auxiliary electrode may be
turned off before the end of the electroplating process, and can be
programmed to match various process requirements. The use of the
auxiliary electrode eliminates the need for physical,
non-adjustable cell hardware to abate the initial resistive
substrate effect. Also, the auxiliary electrode can be synchronized
with the reverse plating cycles to further tailor fit the desired
deposition properties.
Alternatively, the auxiliary electrode comprises a segmented
resistive material having multiple contact points such that the
voltage of the auxiliary electrode varies at different distances
from the contact points. This configuration provides corresponding
variations of potential for a discrete cathode contacting member
configuration. Another variation of the auxiliary electrode
provides a variable width electrode that corresponds to a
configuration of discrete cathode contacting pins so that an
effective higher voltage (and current) is provided at the substrate
contacting points of the cathode contact member while an effective
lower voltage (and current) is provided in the region between the
substrate/cathode contacting points. Because the effective voltage
provided by the variable width auxiliary electrode decreases as the
distance increases between the auxiliary electrode and the edge of
the substrate, the variable width auxiliary electrode provides a
closer distance between the auxiliary electrode and the edge of the
substrate where the cathode contact member are located.
Preferably, a consumable anode 90 is disposed in the container body
42 to provide a metal source in the electrolyte. As shown in FIG.
2, a completely self-enclosed modular, soluble copper anode 90 is
disposed about the middle portion of the container body 42. The
modular anode comprises metal particles 92 or metal wires, or a
perforated or a solid metal sheet, such as high purity copper,
encased in a porous enclosure 94. In one embodiment, the enclosure
94 comprises a porous material such as a ceramic or a polymeric
member within which the metal particles 92 are encased. An anode
electrode contact 96 is inserted into the enclosure 94 in
electrical contact with the metal particles 92. The anode electrode
contact 96 can be made from an insoluble conducive material, such
as titanium, platinum, platinum-coated stainless steel, and
connected to a power supply 49 to provide electrical power to the
anode. The porous sheet of the enclosure 94 acts as a filter that
provides particle-free electrolyte to the substrate plating surface
54 because the filter keeps the particulates generated by the
dissolving metal within the encased anode. The soluble copper anode
90 also provides gas generation-free electrolyte into the solution
unlike the process using a gas-evolving insoluble anode and
minimizes the need to constantly replenish the copper electrolyte.
The metal particles 92 can be in the shape of pellets or wires or a
perforated plate encased in or confined within electrode 96. These
shapes offer high surface area as well as a passage for the
electrolyte flow. The high surface area of the metal particles
minimizes anode polarization and oxidative side reactions,
including oxygen coevolution, and leads to a moderate current
density for copper plating during the substrate anodic dissolution
stage of the periodic reverse plating cycle (discussed in more
detail below). If it is desirable to have a smaller surface area
exposed to the electrolyte due to excess additive decomposition on
the anode, it may be desirable to cover the downward facing side
(facing towards the flow) of the perforated plate sheet or wires
with an insulating material.
Preferably, the anode 90 is a modular unit that can be replaced
easily to minimize interruptions and to allow easy maintenance.
Preferably, the anode 90 is positioned a distance greater than one
(1) inch, and more preferably, greater than 4 inches, away from the
substrate plating surface 54 (for a 200 mm substrate) to assure
that the effects of level variations in the anode copper caused by
anode dissolution, particulate fluidization and assembly tolerances
become negligible once the electrolyte flow reaches the substrate
surface.
FIG. 5 is a partial vertical cross sectional schematic view of an
alternative embodiment of an electro-chemical deposition cell of
the invention. The embodiment as shown is a weir plater 100
comprising similar components as the electroplating cell 40
described above. However, the container body include an upper
annular weir 43 that has an upper surface at substantially the same
level as the plating surface such that the plating surface is
completely in contact with the electrolyte even when the
electrolyte is barely flowing out of the electrolyte egress gap 74
and over the weir 43. Alternatively, the upper surface of the weir
43 is positioned slightly lower than the plating surface such that
the substrate plating surface is positioned just above the
electrolyte when the electrolyte overflows the weir 43, and the
electrolyte attaches to the substrate plating surface through
meniscus properties (i.e., capillary force). Also, the auxiliary
electrode may need to be repositioned closer to the electrolyte
egress to ensure contact with the electrolyte to be effective.
A flow adjuster 110 comprising a variable thickness conical profile
porous barrier can be disposed in the container body between the
anode and the substrate to enhance flow uniformity across the
substrate plating surface. Preferably, the flow adjuster 110
comprises a porous material such as a ceramic or a polymer which is
used to provide a selected variation in electrolyte flow at
discrete locations across the face of the substrate. FIG. 5
illustrates the electrolyte flow between the porous barrier and the
substrate plating surface along arrows A. The flow adjuster 110 is
increasingly thinner toward the center of the structure, and thus
of the wafer, which results in a greater flow of electrolyte
through this region and to the center of the substrate to equalize
the electrolyte flow rate across the substrate plating surface.
Without the flow adjuster, the electrolyte flow is increased from
the central portion to the edge portion because the electrolyte
egress is located near the edge portion. Also, the cone-shaped flow
adjuster 110 tapers away from the substrate surface, extending
furthest away from the substrate surface at the edge of the
substrate. Preferably, the cone-shaped tapering and the increasing
thickness of the flow adjuster are optimized according to the
required electrolyte flow rate and the size of the substrate
plating surface to provide a uniform electrolyte flow rate across
the substrate plating surface. A similar effect can be achieved
with a perforated plate. The size and spacings of the perforations
may be adjusted to produce the desired flow distribution.
A broken substrate catcher (not shown) can be placed within the
container body to catch broken substrate pieces. Preferably, the
broken substrate catcher comprises a mesh, a porous plate or
membrane. The porous wedge or the perforated plate described above
may also serve for this purpose.
A refining electrode (not shown) can be placed in the sump (not
shown) for pre-electrolysis of the electrolyte and for removal of
metal and other chemical deposit buildup in the sump. The refining
electrode can be continuously activated or periodically activated
according to the needs of the system. The refining electrode when
made of copper and polarized anodically can be used to replenish
copper in the bath. This external electrode can thus be used to
precisely adjust the copper concentration in the bath.
A reference electrode (not shown) can be employed to determine
precisely the polarization of the anode, the cathode and the
auxiliary electrode.
Once the electroplating process is completed, the electrolyte can
be drained from the container body to an electrolyte reservoir or
sump, and a gas knife can be incorporated to remove the film of
electrolyte remaining on the substrate plating surface. The gas
knife comprises a gas inlet, such as a retractable tube or an
extension air tube connected to a hollow anode electrode, which
supplies a gas stream or a gas/liquid dispersion that pushes the
electrolyte off the substrate surface. The gas can also be supplied
through the gap between the substrate holder 44 and the container
body 42 to blow on the substrate surface.
A deionized water rinse system (not shown) can also be incorporated
into the electroplating system to rinse the substrate free of
electrolyte. A supply of deionized water or other rinsing solutions
can be connected to the inlet 50 and selectively accessed through a
inlet valve. After the electrolyte has been drained from the
container body, the deionized water or other rinsing solution can
be pumped into the system through inlet 50 and circulated through
the container body to rinse the substrate surface. While the
processed substrate is being rinsed, the cathode and anode power
supply is preferably inactivated in the cell. The deionized water
fills the cell and flows across the surface of the substrate to
rinse the remaining electrolyte off the surface. The vibrational
member may be activated to enhance rinsing of the plated surface. A
number of separate deionized water tanks can be utilized
sequentially to increase the degree of purity of the rinse water.
To utilize more than one rinsing solution supply, a rinsing cycle
is preferably completed and the rinsing solution completely drained
from the cell before the next rinsing solution is introduced into
the cell for the next rinsing cycle. The used deionized water rinse
can also be purified by plating out the metal traces acquired
during the rinse cycle by the rinsing solution or by circulating
the used deionized water through an ion exchange system.
FIG. 6a and 6b are schematic illustrations of an embodiment of a
multi-substrate processing unit. A plurality of substrates 48 are
mounted on a substrate holder 200, and a matching plurality of
container bodies 202 are positioned to receive the substrate
plating surfaces. The container bodies preferably share a common
electrolyte reservoir 204. However, each individual electroplating
cell 202 preferably comprises individual electroplating system
controls to ensure proper processing of individual substrates.
FIG. 7 is a horizontal cross sectional schematic view of another
embodiment of a multi-substrate batch processing unit 208. The
electrolyte container body 210 as shown in FIG. 7 is a hexagonal
drum, but any polygonal drum can be utilized as long as each face
of the polygon is large enough to mount a substrate 48 thereon. A
cathode contact member 212 is also mounted on each face of the
polygon to provide electrical current to the substrate plating
surface 54. An anode 214 preferably comprises a concentric
polygonal drum rotatably mounted within the container body 210.
Alternatively, the anode 214 may comprises a cylindrical body
mounted concentrically within the container body 210. The container
body 210 can also be a cylindrical body having multiple substrate
cavities to receive substrates. Also, a number of substrates can be
mounted on each face of the polygon.
A plurality of auxiliary electrodes 216 can be placed in the cell
at the corners of the polygon. Alternatively, ring shaped or
segmented ring auxiliary electrodes 218 can be placed around each
substrate 48 to match the cathode contact members 212 similarly to
the arrangement of the auxiliary electrodes shown in FIG. 3.
Preferably, the auxiliary electrodes dynamically adjust to
compensate current distribution over the substrate by gradually
decreasing the current of the auxiliary electrodes as the resistive
substrate effect tapers off after the initial deposition period. A
porous separator/filter (not shown) can be placed between the anode
and the cathode to trap particulates.
A vibrational agitation member (not shown) can be connected to the
container body to vibrate the substrates. However, substrate
vibration may be unnecessary when the polygonal anode drum is
rotated sufficient fast, preferably between about 5 revolutions per
minute (RPM) and about 100 RPM, to provide a high degree of
agitation to the electrolyte. The rotating polygonal anode also
provides a pulsed or transient electrical power (voltage/current
combination) due to the varying distance between the active anode
surfaces and the substrate because of the rotation. Because the
anode is polygonal in shape, as the anode rotates, the distance
between cathode and the anode varies from a maximum when the anode
polygon faces are aligned with the cathode polygon faces in
parallel planes and a minimum when the anode polygon corners are
aligned with the centers of the cathode polygon faces. As the
distance between the anode and the cathode varies, the electrical
current between the anode and the cathode varies
correspondingly.
Another variation provides a horizontally positioned polygonal
drum. The container body is rotated around the horizontal axis to
position one polygon face on top to allow loading and unloading of
a substrate while the other substrates are still being
processed.
Yet another variation provides the substrates to be mounted on the
outer surfaces of the inner polygon drum which now is the cathode,
and the container body becomes the anode. This configuration allows
the cathode drum to be lifted from the electrolyte for easy loading
and unloading of the substrates.
Operating Conditions
In one embodiment of the invention, a periodic reverse potential
and/or current pulse or an intermittent pulse current is delivered
to the substrate to control the mass transfer boundary layer
thickness and the grain size of the deposited material. The
periodic reverse and pulse current/potential also enhances deposit
thickness uniformity. The process conditions for both the
deposition stage and the dissolution stage can be adjusted to
provide the desired deposit profile, usually a uniform, flat
surface. In general, plating/deposition is accomplished with a
relatively low current density for a relatively long interval
because low current density promotes deposition uniformity, and
dissolution is accomplished with a relatively high current density
for a relatively short interval because high current density leads
to highly non-uniform distribution that preferentially shaves or
dissolves deposited peaks.
For a .Iadd.pre-determined .Iaddend.grain size, a current pulse
comprising a higher negative current density for a short time
(between about 50 mA/cm.sup.2 and about 180 mA/cm.sup.2 for about
0.1 to 100 ms) is applied to nucleate an initial layer of copper
deposits followed by a constant current density applied for a long
interval (between about 5 mA/cm.sup.2 and about 80 mA/cm.sup.2 for
up to a few minutes) to continue deposition. The length of the
deposition interval can be adjusted according to the deposition
rate to achieve the desired deposition thickness over the substrate
surface.
To completely fill high aspect ratio trenches, vias or other
interconnect features, a current reversal or dissolution interval
may be applied to achieve some dissolution of the deposited metal.
The dissolution interval is preferably applied at a current density
much higher than the current density of the deposition current but
for a short time interval to ensure a net deposit. The dissolution
interval can be applied once or periodically during a deposition
process to achieve the desired results. The deposition interval can
be divided into a number of short intervals followed by a
corresponding number of even shorter dissolution intervals to
completely fill high aspect ratio interconnect features. Then, a
constant deposition current density is applied to achieve a uniform
deposition thickness across the field. Typically, a deposition
cycle comprises a deposition current density of between about 5
mA/cm.sup.2 and about 40 mA/cm.sup.2 followed by a dissolution
current density between about 5 mA/cm.sup.2 and about 80
mA/cm.sup.2. The deposition cycle is repeated to achieve complete,
void-free filling of high aspect ratio features, and optionally, a
final application of the deposition current density is applied to
form a uniform field deposition thickness across the substrate
plating surface. Alternatively, the current reversal/dissolution
cycle can be achieved by providing a constant reverse voltage
instead of a constant reverse current density.
Because the resistive substrate effect is dominant during the
beginning of the plating cycle, a relatively low current density,
preferably about 5 mA/cm.sup.2, is applied during the initial
plating. The low current density provides very conformal plating
substantially uniformly over the plating surface, and the current
density is gradually increased as the deposition thickness
increases. Also, no current reversal for dissolution is applied
during the initial stage of the plating process so that the metal
seed layer is not at risk of being dissolved. However, if a current
reversal is introduced for striking or nucleation purposes, the
reverse current density is applied at a low magnitude to ensure
that no appreciable metal seed layer is dissolved.
Optionally, a relaxation interval between the deposition interval
and the dissolution interval allows recovery of depleted
concentration profiles and also provides improved deposition
properties. For example, a relaxation interval where no
current/voltage is applied between the deposition interval and the
dissolution interval, allows the electrolyte to return to optimal
conditions for the processes.
Preferably, the vibration frequency, the pulse and/or periodic
reverse plating, the auxiliary electrode current/voltage and the
electrolyte flow are all synchronized for optimal deposition
properties. One example of synchronization is to provide vibration
only during the deposition interval so that the boundary diffusion
layer is minimized during deposition and to eliminate vibration
during the dissolution interval so that the dissolution proceeds
under mass transport control.
To improve adhesion of the metal to the seed layer during plating,
a very short, high current density strike is applied at the
beginning of the plating cycle. To minimize bubble related defects,
the strike must be short, and the current density must not exceed
values at which hydrogen evolves. This current density, preferably
between about 100 mA/cm.sup.2 to about 1000 mA/cm.sup.2,
corresponds to an overpotential not exceeding -0.34 V (cathodic)
versus for the reference electrode. A separate striking process
using a different electrolyte may be required for adhesion of the
metal plating material. Separate striking can be accomplished in a
separate cell with different electrolytes or in the same cell by
introducing and evacuating different electrolytes. The electrolytes
used for separate striking is typically more dilute in metal
concentration and may even be a cyanide based formulation.
The metal seed layer is susceptible to dissolution in the
electrolyte by the exchange current density of the electrolyte
(about 1 mA/cm.sup.2 for copper). For example, 1500 .ANG. of copper
can be dissolved in about 6 minutes in an electrolyte with no
current applied. To minimize the risk of the seed layer being
dissolved in the electrolyte, a voltage is applied to the substrate
before the substrate is introduced to the electrolyte.
Alternatively, the current is applied instantaneously as the
substrate comes in contact with the electrolyte. When a deposition
current is applied to the substrate plating surface, the metal seed
layer is protected from dissolution in the electrolyte because the
deposition current dominates over the equilibrium exchange current
density of the electrolyte.
The invention also provides for in situ electroplanarization during
periodic reverse plating. Preferably, both deposition and
dissolution steps are incorporated during a single pulse or a
sequence of rapid pulses such that at the end of the process the
trenches, vias and other interconnect features are completely
filled and planarized. The electrochemical planarization step
comprises applying a high current density during dissolution. For
example, a dissolution reverse current density of about 300
mA/cm.sup.2 is applied for about 45 seconds as an electrochemical
planarization step that leads to a substantially flat surface with
just a residual dimple of about 0.03 .mu.m. This electrochemical
planarization substantially reduces the need for chemical
mechanical polishing (CMP) and may even eliminate the need for CMP
in some applications.
Chemistry
An electrolyte having a high copper concentration (.Iadd.e.g.,
.Iaddend.>0.5M and preferably between 0.8M to 1.2M) is
beneficial to overcome mass transport limitations that are
encountered with plating of sub-micron features. In particular,
because sub-micron features with high aspect ratios typical allow
only minimal or no electrolyte flow therein, the ionic transport
relies solely on diffusion to deposit metal into these small
features. A high copper concentration preferably about 0.8M or
greater, in the electrolyte enhances the diffusion process and
eliminates the mass transport limitations because the diffusion
flux is proportional in magnitude to the bulk electrolyte
concentration. A preferred metal concentration is between about 0.8
and about 1.2 M. Generally, the higher the metal concentration the
better; however, one must be careful not to approach the solubility
limit where the metal salt will precipitate.
The conventional copper plating electrolyte includes a high
sulfuric acid concentration (about 1 M) to provide high
conductivity to the electrolyte. The high conductivity is necessary
to reduce the non-uniformity in the deposit thickness caused by the
cell configuration of conventional copper electroplating cells.
However, the present invention (including the cell configuration)
provides a more uniform current distribution. In this situation a
high acid concentration is detrimental to deposition uniformity
because the resistive substrate effects are amplified by a highly
conductive electrolyte. Furthermore, the dissolution step during
periodic reverse cycle requires a relatively low electrolyte
conductivity because a highly conductive electrolyte may promote
non-uniformity as a result of the high reverse current density.
Also, the presence of a supporting electrolyte, e.g. acid or base,
will lower the ionic mass transport rates, which, as explained
above, are essential for good quality plating. Also, a lower
sulfuric acid concentration provides a higher copper sulfate
concentration due to elimination of the common ion effect.
Furthermore, particularly for the soluble copper anode, a lower
acidic concentration minimizes harmful corrosion and material
stability problems. Thus, the invention contemplates an
electroplating solution having no acid or very low acid
concentrations. Preferably, the sulfuric acid concentration is in
the range of 0 (absence) to about 0.2M. Additionally, a pure or
relatively pure copper anode can be used in this arrangement.
In addition to copper sulfate, the invention contemplates copper
salts other than copper sulfate such as copper gluconate and copper
sulfamate that offer high solubility and other benefits, as well as
salts such as copper nitrate, copper phosphate, copper chloride and
the like.
The invention also contemplates the addition of acids other than
sulfuric acid into the electrolyte to provide for better
complexation and/or solubility for the copper ions and the copper
metal which results in improved deposition properties. These
compounds include anthranilic acid, acetic acid, citric acid,
lactic acid, sulfamic acid, ascorbic acid, glycolic acid, oxalic
acid, benzenedisulfonic acid, tartaric acid and/or malic acid.
The invention also contemplates additives to produce asymmetrical
anodic transfer coefficient (.alpha.) and cathodic transfer
coefficient (.beta.) to enhance filling of the high aspect ratio
features during reverse plating cycle.
Ultra pure water can be introduced to the substrate plating surface
to ensure complete wetting of the substrate plating surface which
enhances the electroplating process into the small features. Steam
can also be used to pre-wet the substrate plating surface.
Surfactants improve wetting by reducing surface tension of the
solution. Surfactants contemplated by the present invention
include: sodium xylene sulfonate, polyethers (polyethylene oxide),
carbowax, sodium benzoate, ADMA8 amine, Adogen, Alamine, Amaizo,
Brij, Crodesta, Dapral, Darnyl, didodecylmethyl propane sultaine,
Dowex, Empol, Ethomeen, Ethomid, Enordet, Generol, Grilloten,
Heloxy, hexadecyltrimethylammonium bromide, Hyamine, Hysoft,
Igepal, Neodol, Octadecylbenzyl propane sultaine, Olcyl betaine,
Peganate, Pluronic, Polystep, Span Surfynol, Tamol, Tergitol,
Triton, Trilon, Trylox, Unithox, Varonic, Varamide, Zonyl,
Benzylmethyl propane sultaine, alkyl or aryl betaine, alkyl or aryl
sultaine.
Levellers improve deposition thickness uniformity. Brighteners
improves the the reflectivity of the deposition surface by
enhancing uniformity of the crystalline structure. Grain refiners
produce smaller grains to be deposited. Levellers, brighteners and
grain refiners can be specially formulated and optimized for the
low acid, high copper electrolyte provided by the invention. In
optimizing these compounds for use with the invention, the effects
of the periodic reverse current need to also be considered.
Levellers, brighteners and grain refiners contemplated by the
present invention include:
inorganic minor components from: Salts of Se, As, In, Ga, Bi, Sb,
TI, or Te; and/or
organic minor components selected from (singly or in combination):
acetyl-coenzyme, aminothiols; acrylamine; azo dyes; alkane thiols,
Alloxazine; 2-Aminopyrimidine; 2-Amino-1,3,4, thiadiazole; Amino
methyl thiadiazole; 2-Aminothiadiazole; 3-amino 1,2,4, triazole;
benzal acetone, Benzopurpurin; benzophnon, Behzotriazole,
hydroxylbenzotriazole, Betizyldene acetone, Benzoic acid, Benzoil
acetic acid ethyl ester, Boric acid, cacodylic acid, Corcumin
Pyonin Y; Carminic Acid; Cinamic aldehyde, cocobetaine or decyl
betaine, cetyl betaine, cysteine; DETAPAC;
2',7'-dichlorofluorescein; dextrose, dicarboxilic amino acids;
dipeptide diaminoacid (camsine=beta alanyl hystadine),
5-p-dimethylamine benzyldene Rhodamine,
5(p-Dimethylamino-benzylidene)-2-thio barbituric, dithizone,
4-(p-Ethoxyphnylazo)-m-phenylendi-amine, ethoxilated tetramethyl
decynediol, ethoxilated quarternary amonium salts, ethyl benzoil
acetate, ethoxylated beta-naphtol, EDTA, Evan Blue; di ethylene
triamine penta acetic acid or salts, diethylenetriamine
pentacetate, penta sodium salt, glucamine, glycerol compounds,
di-glycine, d-glucamine, triglycine, glycogen, gluter aldehyde,
glutamic acid, its salts and esters (MSG), sodium glucoheptonate,
hydroxylbenzotriazole, hydroxysuccinimide, hydantoin,
4-(8-Hydroxy-5-quinolylazo)-1-naphtalenesulfonic acid,
p-(p-hydroxyphenylazo) benzene sulfonic, insulin,
hydroxybenzaldehyde, imidazoline; lignosulfonates; methionine;
mercaptobenzi-imidazoles; Martius Yellow;
2-methyl-1-p-tolyltriazene,
3-(p-Nitrophenyl)-1-(p-phenylazophnyl)triazene;
4-(p-Nitrophenylazo) resorcinol, 4-(p-Nitrophenylazo)-1-naphthol,
OCBA-orthochloro benzaldehyde, Phenyl propiolic acid,
polyoxyethylene alcohols, quarternary amonium ethoxilated alcohols,
and their fullyacid esters, polyethyleneimine, phosphalipides,
sulfasalicilic acid, linear alkyl sulfonate, sulfacetamide,
Solochrome cyanin; sugars; sorbitol, sodium glucoheptonate, sodium
glycerophosphate, sodium mercaptobenzotriazole, tetrahydropyranyl
amides, thiocarboxylic amides, thiocarbonyl-di-imidazole;
thiocarbamid, thiohydantoin; thionine acetate, thiosalicilic acid,
2-thiolhistadine, thionine, thiodicarb, thioglycolic acid,
thiodiglycols, thiodiglycolic acid, thiodipropionic acid,
thioglycerol, dithiobenzoic acid, tetrabutylamonium, thiosulfone,
thiosulfonic acid, thionicotineamide, thionyl chloride or bromide;
thiourea; TIPA; tolyltriazole, triethanolamine; tri-benzylamine;
4,5,6, triaminopyrimidine; xylene cyanole.
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. The
scope of the invention is determined by the claims which
follow.
* * * * *