U.S. patent application number 10/696207 was filed with the patent office on 2005-05-05 for distributing forces for electrodeposition.
Invention is credited to Gallina, Mark J..
Application Number | 20050092614 10/696207 |
Document ID | / |
Family ID | 34550080 |
Filed Date | 2005-05-05 |
United States Patent
Application |
20050092614 |
Kind Code |
A1 |
Gallina, Mark J. |
May 5, 2005 |
Distributing forces for electrodeposition
Abstract
The force required to seal a surface of an object for
electrodeposition may be controlled. For example, the object may
rest on a support that carries the majority of the force required
for surface sealing. Further, pads mounted on the ends of flexible
beams may exert a variable force to establish electrical contact
with the object that may be controlled. By controlling the forces
exerted on an object damage to the object's surface may be
minimized or eliminated.
Inventors: |
Gallina, Mark J.;
(Hillsboro, OR) |
Correspondence
Address: |
TROP PRUNER & HU, PC
8554 KATY FREEWAY
SUITE 100
HOUSTON
TX
77024
US
|
Family ID: |
34550080 |
Appl. No.: |
10/696207 |
Filed: |
October 29, 2003 |
Current U.S.
Class: |
205/157 ;
204/288.3 |
Current CPC
Class: |
C25D 17/001 20130101;
C25D 17/06 20130101 |
Class at
Publication: |
205/157 ;
204/288.3 |
International
Class: |
C25D 017/10 |
Claims
What is claimed is:
1. A device comprising: more than one spring electrical contact to
contact a first surface of an object, said first surface of said
object to have a material electrodeposited thereon; and a base to
directly support said first surface of said object without being
directly connected to said spring electrical contacts, said base to
distribute the force to seal a second surface of said object.
2. The device of claim 1 including a soft, acid resistant material
disposed on said base.
3. The device of claim 1 wherein said base is spaced inward from
said contacts.
4. The device of claim 1 wherein said spring electrical contacts
are connected to a frame.
5. The device of claim 4 wherein said spring electrical contacts
are resilient beams that terminate with tips.
6. The device of claim 5 wherein said object has an outer edge,
said base to distribute a force at said object outer edge and said
tips to contact said object inward from said base.
7. The device of claim 4 wherein said base and said frame are
annular.
8. The device of claim 4 wherein said frame and said beams are
coated with an acid-resistant material.
9. The device of claim 1 wherein said base substantially
continuously contacts said surface.
10. The device of claim 1 wherein said spring electrical contacts
independently deflect while electrical contact is made with said
object.
11. A system comprising: a frame having spring electrical contacts
to electrically contact a first surface of an object to enable
electrodeposition on said object first surface; a base to directly
support said object, said base and said frame not directly
connected; and a sealing ring to seal a second surface of said
object to prepare for electrodeposition.
12. The system of claim 11 including a plating cell to house said
object for electroplating.
13. The system of claim 12 including an electrode.
14. The system of claim 13 including a power supply.
15. The system of claim 14 including a thrust plate and a seal
plate.
16. The system of claim 11 wherein said base is annular defining an
annular aperture.
17. The system of claim 11 wherein said base is to distribute the
force required to seal said second surface of said object.
18. The system of claim 11 wherein said object is a wafer and a
metal or metal alloy is to be deposited on said first surface.
19. The system of claim 11 wherein said object is a wafer and
copper or an alloy including copper is to be deposited on said
first surface.
20. The system of claim 11 wherein said spring electrical contacts
apply a variable force less than the force that if applied would
exceed the mechanical strength of said object.
21. A method comprising: sealing a second side of an object to
prepare said object for electrodeposition; directly physically
supporting said object on a first side to enable said sealing; and
electrically contacting said first side of said object with spring
electrical contacts to facilitate electrodeposition, said
electrical spring contacts and said support not in direct
contact.
22. The method of claim 21 including distributing the force to seal
said second side of said object about the periphery of said
object.
23. The method of claim 21 including applying a variable force with
said spring electrical contacts to facilitate
electrodeposition.
24. The method of claim 23 including determining the length and the
maximum displacement of said spring electrical contacts.
25. The method of claim 21 including distributing the force to seal
said second side of said object without exceeding the strength of
said object first side.
26. The method of claim 21 including depositing a conductive
material on said object first side.
27. The method of claim 26 including depositing a metal or metal
alloy on said object first side.
28. The method of claim 21 including displacing adjacent spring
electrical contacts with respect to said object first side.
29. The method of claim 21 including initially contacting said
object with said spring electrical contacts, said initial contact
having little or no associated force.
30. The method of claim 21 including electrically contacting said
first side of said object without exceeding the strength of said
object first side.
Description
BACKGROUND
[0001] The present invention relates generally to electrodeposition
and particularly to electrodeposition onto silicon wafers or other
objects.
[0002] With large scale circuit integration comes a need for
smaller features and increased circuit density. As component
density increases, the surface space available to connect the
components decreases. One solution to this "wiring" problem is to
layer insulating materials and conductive materials. Generally, the
conductive layers are connected by conductive vias or plugs formed
through the insulating material.
[0003] The metal and insulating material used to interconnect
device components may determine the overall device performance. For
example, interconnect resistance (R) and capacitance (C), the RC
constant, may be an indicator of circuit speed. For example, a high
RC constant may indicate a slow circuit signal. Interconnecting
components with metals having low resistivity may lower the RC
value. Further, separating interconnects with a dielectric having a
low dielectric constant may reduce capacitance, which would also
lower the RC value. Thus, when resistivity and capacitance are both
reduced, device performance may increase.
[0004] Aluminum and aluminum alloys have enjoyed widespread use to
interconnect components in integrated circuits. However, aluminum
may limit the speed of some circuits. Further, aluminum may be
difficult to deposit in vias having small depth to width or aspect
ratios. In contrast, copper has a lower resistance than aluminum,
hence it is a better conductor. Thus, copper layered with a low
capacitance dielectric may be well suited for smaller, faster
integrated circuits. Copper use in integrated circuits however, is
not without its own unique challenges. For example, copper is not
easily patterned or etched. Thus, copper deposition in vias and/or
trenches that have been etched in a dielectric is one way to form
copper interconnects and plugs.
[0005] Copper may be deposited on a wafer via chemical vapor
deposition (CVD), plasma enhanced CVD, sputtering, and
electrodeposition such as electroplating. Electroplating generally
takes place at lower temperatures and at a lower cost than other
deposition techniques. Further, electroplating is a favored
deposition technique when using dielectrics having low dielectric
constant.
[0006] To deposit a metal on a wafer via electrodeposition, the
back surface of the wafer is sealed off and electrical contact is
made with the front surface of the wafer. Sealing the back of the
wafer off and establishing electrical contact with front of the
wafer may require considerable force to be exerted on the wafer. As
such, soft materials such as low dielectric insulators may be
susceptible to damage.
[0007] Accordingly, there is a need for a way to deposit a
conductive material without causing significant damage to the
object that the conductive material is to be deposited on.
BRIEF DESCRIPTION OF THE DRAWING
[0008] FIG. 1 is a cross section of a simplified system for
electrodeposition;
[0009] FIG. 2 is a bottom-up view of a portion of the system of
FIG. 1 according to some embodiments of the present invention;
[0010] FIG. 3 is a cross section of the portion of the system of
FIG. 2;
[0011] FIG. 4 is a cross section of an alternate embodiment of a
portion of the system of FIG. 1;
[0012] FIG. 5 is a partial cross section of the portion of FIG. 3
before electrical contact is made with an object to be
electroplated;
[0013] FIG. 6 is a partial cross section of the portion of FIG. 3
when initial contact is made with the object to be electroplated;
and
[0014] FIG. 7 is a partial cross section of the portion of FIG. 3
when electrical contact for deposition is made with the object to
be electroplated.
DETAILED DESCRIPTION
[0015] Referring to FIG. 1, an exemplary plating cell or system 10
for electrodeposition is shown in simplified form. Generally, a
metal, metal alloy or other conductive material may be deposited on
an object 12 while the object 12 is immersed in the plating cell
10. For example, in some embodiments, the object 12 may be a wafer.
Thus, copper, gold, lead, nickel or alloys thereof may be deposited
on the wafer 12 using system 10. The system 10 may include a
container 14, an anode 16, a seal assembly 18, a frame 20, a base
22 and a power supply 24.
[0016] The container 14 may be any container for use in
electrodeposition. As shown in FIG. 1, the container 14 is box-like
having sides 26 and a bottom 28, although embodiments of the
present invention are not limited in this respect. The container 14
may also include a top (not shown). When in use, the container 14
may be filled with an electrolytic solution 32. In some
embodiments, ions in the electrolyte 32 facilitate electroplating.
Further, in some embodiments the anode 16 may add ions to the
electrolytic solution 32. For example, the anode 16 may be disposed
in the electrolyte 32 within container 14. Thus, when a voltage
potential is applied to the anode 16 and the object 12 to be
plated, ions may be released into the electrolyte 32 via an
oxidation reaction. Generally, the anode 16 is a metal or
combination of metals and may be a single piece or segmented,
although embodiments are not limited in this respect.
[0017] The seal assembly 18 may also be disposed in the container
14. In some embodiments, the seal assembly 18 may include a thrust
plate and/or a seal plate (not individually shown) having a
flexible seal material or mechanism such as a sealing ring 30. In
some embodiments, the sealing ring 30 may be positioned to contact
the backside 36 of the wafer 12 to create a watertight seal to
prevent deposition and/or contamination on the wafer backside 36.
For example, a force may be applied by the seal assembly 18 (force
producing mechanism not shown) to the backside 36 of the wafer 12
while the base 22 supports the wafer 12 at the front side 36,
holding the wafer 12 stationary. Thus, when the sealing force is
applied, a watertight seal is create by the sealing ring 30. As
such, conductive material is not deposited on the wafer backside
36.
[0018] During electrodeposition, the frame 20 and base 22 may
oppose the seal assembly 18 to contact the front side 34 of the
wafer 12. Generally, current is supplied to the wafer 12 through
the frame 20. In contrast, there is no electrical connection
between the base 22 and the wafer 12. Thus, the base 22 may serve
as a support for the wafer 12 during surface sealing and/or
electrodeposition.
[0019] The power supply 24 may connect the frame 20 and the anode
16. Generally, the power supply 24 delivers a positive voltage to
the anode 16 and a negative voltage to the frame 20. In this way,
when the wafer 12 and anode 16 are disposed in the electrolyte 32
an electric circuit may be completed from the wafer 12 to the anode
16.
[0020] When system 10 is in use, a conductive material such as
copper may be deposited on the front side 34 of the wafer 12,
although embodiments of the invention are not limited with respect
to the conductive material or a wafer. Generally, to deposit a
metal on a wafer 12 via electroplating, the wafer 12 front side 34
is pre-coated with a seed layer (not shown). For example, if copper
is to be deposited, a seed layer of copper may be deposited over a
barrier layer by physical vapor deposition (PVD) or high density
plasma PVD although embodiments are not so limited. Further, the
backside 36 of the wafer 12 may be sealed off to prevent deposition
on other than the front side 34. The wafer 12, backside seal
assembly 18, frame 20 and base 22, or portions thereof may be
immersed in the electrolytic solution 32 including ions of the
metal (e.g., Cu.sup.2+) to be deposited.
[0021] While in solution 32, the wafer 12 front side 34 may be
electrically connected to the power supply 24 via the frame 20. The
anode 16 may also be electrically connected to the supply 24. Thus,
when an electric potential is applied, metal ions from the
electrolytic solution 32 may be reduced at the wafer 12 front side
34 to deposit the conductive material, although embodiments are not
limited in this respect. Further, oxidation at the anode 16 may
replenish the supply of metal ions in the electrolyte 32. Thus, in
some embodiments, the system 10 may be utilized to deposit copper
in vias and/or trenches on a wafer 12 front side 34 to form plugs
and interconnects respectively. Overfill of the conductive material
during electrodeposition may be removed by chemical mechanical
polishing (CMP) or any other suitable removal technique.
[0022] Referring to FIGS. 2 and 3, details of the frame 20 and base
22 are shown. With respect to FIG. 2, the frame 20 and base 22 are
devoid of a coating 48 to better illustrate the frame 20 and base
22 in this view. Further, although not shown, the frame 20 and base
22 may be independently attached to a robot. In this way, in some
embodiments the frame 20 and base 22 are not connected, which may
enable independent movement.
[0023] In some embodiments, the frame 20 may be circular and may
include a circular inner portion 42 that defines an aperture.
However, the frame 20 may be any shape such as a square, rectangle,
pentagon, octagon and the like. One or more flexible or spring-like
beams 38 may be connected to and extend from the frame inner
portion 42. For example, the individual spring-like beams 38 may
have a first end 44 and a second end 46. The beam 38 may be joined
to the frame 20 at the first end 44 to project inwardly from the
frame inner portion 42. Further, the second end 44 may terminate
with a contact point or pad 40. The points 40 may be configured to
minimize localized areas of high pressure on the front side 34 of
the wafer 12. As shown in FIG. 2, there are eight beams 38, each
associated with a contact pad 40. However, embodiments are not
limited with respect to the number of beams 38.
[0024] The contacts 40 and beams 38 may provide electrical contact
to the wafer 12. For example, the frame 20, beams 38 and pads 40
may be a conductive metal such as stainless steel as one example,
although embodiments are not so limited. However, the frame 20 and
beams 38 may be coated with a soft, chemically resistant material
48 such as KALREZ of Dupont Dow Elastomers as one example. In some
embodiments, the beams 38 may be independently coated to preserve
resiliency. Generally, only a portion of each contact pad 40 is
coated with the material 48. For example, the surface 50 of the
points 40 lack the coating 48. In this way, the surface 50 may
electrically contact the wafer 12. The coating 48 on the pads 40
may be continuous with the coating 48 on the beams 38 in some
embodiments of the present invention. Thus, there are many ways to
coat the frame 20, beams 38 and pads 40 and embodiments of the
present invention are not limited in this respect.
[0025] Still referring to FIGS. 2 and 3, the base 22 may also be
annular having an inner portion 52 that defines an annular
aperture. However, like the frame 20, the base 22 may be any shape
and the inner portion 52 may define an aperture of complementary
shape. Further, in some embodiments, the base inner portion 52 may
be serpentine, have "V's", or the like. The shape of the base 22
and/or inner portion 52 may complement the shape of the wafer 12
and/or the frame 20 although embodiments of the invention are not
so limited.
[0026] The wafer 12 may be uniformly seated on the base inner
portion 52. For example, the base 22 may be a strong metal such as
stainless steel or titanium, as a few examples. Further, the base
22 may be coated with the material 48. Referring to FIG. 3, in some
embodiments, the wafer 12 may be seated on the material 48 that
covers the top surface 56 of the base inner portion 52. However, as
shown in FIG. 4, the base inner portion 52 may be bent toward the
wafer 12. As such, the wafer 12 may be seated on or be supported by
the material 48 that covers the end portion 54 of the base inner
portion 52.
[0027] The region of the base inner portion 52 (e.g., coated
surface 56 or end portion 54) that supports the wafer 12 may
substantially continuously contact the wafer front side 34 to
uniformly seat the wafer 12 thereon. That is, in some embodiments
the support region may make continuous contact with the periphery
of the wafer 12. Alternately, in other embodiments continuous
contact with the wafer 12 may be interrupted. For example, the base
22 may have elevated surfaces that contact the wafer 12 at is
periphery. Either way, the force required for sealing may be
distributed about the periphery of the wafer 12 by the base inner
portion 52. In those embodiments including interrupted contact, it
is preferable to have the maximal amount of base 22 surface area
(coated or uncoated) contacting the wafer 12. In this way, the
force required for sealing may be distributed about the wafer 12
periphery without creating localized areas of high pressure that
could damage the wafer 12.
[0028] Damage to the wafer 12 front side 34 may be reduced or
eliminated by controlling the amount of force each contact pad 40
places on the wafer 12 front side 34. Controlling the amount of
force may be influenced by beam 38 design. For example, each beam
38 may be spring-like or flexible and may independently deflect
relative to the wafer 12 front side 34. That is, each beam 38 may
approximate a cantilevered beam with an end load. Thus, the force
supported on the beam 38 end or pad 40 may be calculated according
to equation 1. 1 F " = - 3 dEI L 3 ( Equation 1 )
[0029] where F" (FIG. 7) is the supported force, d is the
displacement of the contact 40, E is the Modulus of Elasticity, I
is the Moment of inertia of a cross-sectional area, and L is the
length of the beam 38. Thus, when working with materials with low
mechanical strength the beams 38 and/or pads 40 may be designed to
deliver a force that will enable electrical contact for deposition
yet not exceed the mechanical strength of the front side 34,
including a front side 34 having one or more films disposed
thereon.
[0030] Referring to FIGS. 3 and 4, beams 38 may vary in design, as
determined by the calculated force. For example, in some
embodiments beams 38 may be a reduced thickness as compared to
frame 20. Further, beams 38 may be straight, bent, curved or any
other configuration. As shown in FIG. 3, the beams 38 may be
relatively long. As such, the pads 40 may contact the wafer 12
inward of the base 22. For example, the wafer 12 may have a given
diameter "D". In some embodiments, the contacts 40 may touch the
wafer 12 at a diameter that is about D-1.5 millimeters (mm) and the
base 22 may touch the wafer 12 at a diameter of about D-0.9 mm.
Thus, opposing pads 40 are closer to each other than opposing
portion of the base 22. Nevertheless, the front side 34 to be
deposited upon is within the openings defined by the base 22 and
the contacts 40.
[0031] As shown in FIG. 4, in some embodiments the length of the
beams 38 may be relatively short. As such, the distance between
opposing base inner portions 52 is less than the distance between
opposing pads 40. However, the distance between opposing base inner
portions 52 should still define an area that will permit deposition
on all desired surfaces of the wafer 12.
[0032] Referring to FIG. 5, when in use, the wafer 12 may initially
rest only on the base 22. For example, the wafer 12 may rest on the
surface 56 or end 54 (FIG. 4) of the base inner portion 52. As
such, front side 34 of the wafer 12 may be exposed. The frame 20
may be in a plane generally parallel to the plane of the base 22
without contacting the wafer 12. As such, there may be a gap "g"
between the wafer front side 34 and the contact pads 40.
[0033] In some embodiments, the surface seal may be established
before the contact points 40 make electrical contact with the wafer
12. For example, the seal material 30 may contact the backside 36
of the wafer 12 via the seal assembly 18. A force "F" may be
applied to the backside 36 of the wafer 12, which is held
stationary by the base 22. A resultant counterforce "F'" may be
applied to the front side 34 of the wafer 12 by the base 22. The
pressure on the front of the wafer 12 is distributed over the
interface between the wafer 12 and the base 22. Thus, damage to the
front side 34 of the wafer 12 is minimized or eliminated during
sealing.
[0034] Referring to FIG. 6, reducing the gap "g" enables initial
contact between wafer front side 34 and the contact pads 40. There
is little, if any force associated with initial contact between the
wafer 12 and pad 40. To enable initial wafer 12 and pad 40 contact,
the frame 20 may be independently moved toward the base 22.
Alternately, the base 22, wafer 12 and seal assembly 18 may be
moved toward the contacts 40, stopping with initial contact between
the wafer 12 and contact pads 40. In yet other embodiments, both
the frame 20 and base 22 may be moved independently toward each
other until initial contact between the points 40 and wafer front
side 34 is made without substantial force.
[0035] Referring to FIG. 7, electrical contact for
electrodeposition may be made by continuing to move the frame 20
and/or base 22 as described above. However, as electrical contact
is made, the wafer 12 and contact pads 40 may press against each
other to deflect the beams 38 downward a distance "d" relative to
the wafer front side 34. Because the beams 38 and/or pads 40 have
been designed to exert a calculated or predicted force on the wafer
front side 34, damage to the wafer 12 front side 34 is minimal if
at all. In other words, the force F" exerted by the contacts 40 for
the displacement of a particular beam 38 may be predicted such that
the mechanical strength of the wafer 12 and/or films disposed
thereon is not exceeded.
[0036] While the present invention has been described with respect
to a limited number of embodiments, those skilled in the art,
having the benefit of this disclosure, will appreciate numerous
modifications and variations therefrom. It is intended that the
appended claims cover all such modifications and variations as fall
within the true spirit and scope of this present invention.
* * * * *