U.S. patent application number 11/927620 was filed with the patent office on 2008-09-04 for conformable contact masking methods and apparatus utilizing in situ cathodic activation of a substrate.
This patent application is currently assigned to University of Southern California. Invention is credited to Gang Zhang.
Application Number | 20080210563 11/927620 |
Document ID | / |
Family ID | 29420490 |
Filed Date | 2008-09-04 |
United States Patent
Application |
20080210563 |
Kind Code |
A1 |
Zhang; Gang |
September 4, 2008 |
Conformable Contact Masking Methods and Apparatus Utilizing In Situ
Cathodic Activation of a Substrate
Abstract
Electroplating processes (e.g. conformable contact mask plating
and electrochemical fabrication processes) that include in situ
activation of a surface onto which a deposit will be made are
described. At least one material to be deposited has an effective
deposition voltage that is higher than an open circuit voltage, and
wherein a deposition control parameter is capable of being set to
such a value that a voltage can be controlled to a value between
the effective deposition voltage and the open circuit voltage such
that no significant deposition occurs but such that surface
activation of at least a portion of the substrate can occur. After
making electrical contact between an anode, that comprises the at
least one material, and the substrate via a plating solution,
applying a voltage or current to activate the surface without any
significant deposition occurring, and thereafter without breaking
the electrical contact, causing deposition to occur.
Inventors: |
Zhang; Gang; (Monterey Park,
CA) |
Correspondence
Address: |
MICROFABRICA INC.;ATT: DENNIS R. SMALLEY
7911 HASKELL AVENUE
VAN NUYS
CA
91406
US
|
Assignee: |
University of Southern
California
|
Family ID: |
29420490 |
Appl. No.: |
11/927620 |
Filed: |
October 29, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11692864 |
Mar 28, 2007 |
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11927620 |
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10434289 |
May 7, 2003 |
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11692864 |
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60379129 |
May 7, 2002 |
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Current U.S.
Class: |
205/118 |
Current CPC
Class: |
C25D 5/12 20130101; H05K
3/243 20130101; H01L 21/76879 20130101; H05K 3/241 20130101; C25D
5/50 20130101; C25D 5/40 20130101; C25D 5/34 20130101; C25D 5/48
20130101; C25D 5/022 20130101; H01L 21/2885 20130101; C25D 5/14
20130101; C25D 5/10 20130101; C25D 5/18 20130101 |
Class at
Publication: |
205/118 |
International
Class: |
C25D 5/02 20060101
C25D005/02 |
Goverment Interests
GOVERNMENT SUPPORT
[0002] This invention was made with Government support under Grant
Number DABT63-97-C-0051 awarded by DARPA. The Government has
certain rights.
Claims
1. An electrochemical fabrication process for producing a
three-dimensional structure from a plurality of adhered layers, the
process comprising: (A) depositing a first material onto a
substrate to form a portion of a layer and depositing at least a
second material to form another portion of the layer; and (B)
forming a plurality of layers such that each successive layer is
formed adjacent to and adhered to a previously formed layer to
produce a three-dimensional structure from a plurality of adhered
layers, wherein said forming of each successive layer comprises
depositing the first material onto the previously formed layer to
form a portion of the successive layer and depositing the second
material to form another portion of the successive layer; wherein
at least a plurality of selective depositing operations are
performed during the forming of the plurality of layers and wherein
the plurality of selective depositing operations comprise: (1)
contacting the previously formed layer and a preformed patterned
contact mask having at least one opening; (2) in the presence of a
plating solution, conducting an electric current between an anode
and the previously formed layer, which functions as a cathode,
through the at least one opening in the mask, such that a selected
one of the first or second material is deposited onto the
previously formed layer to form at least a portion of the
successive layer; and (3) separating the mask from the previously
formed layer; (A) wherein for more than one layer of the plurality
of layers, in the presence of the plating solution, applying a
current between an activation anode and the previously formed
layer, which functions as a cathode, at such a level and for such a
time that at least partial activation of a desired one of the first
or second material, forming a portion of a surface of the
previously formed layer, occurs without significant deposition of
either of the first or second materials occurring, and then without
separating the previously formed layer and the plating solution,
applying a current between a deposition anode and the previously
formed layer, which functions as a cathode, at such a level so as
to cause deposition of the desired one of the first or second
material.
2. The process of claim 1 wherein the selected one of the first or
second material and the desired one of the first or second material
are the same.
3. The process of claim 1 wherein the selected one of the first or
second material and the desired one of the first or second material
are different.
4. The process of claim 1 wherein the deposition anode comprises
the activation anode.
5. The process of claim 1 wherein the deposition anode and the
activation anode are different.
6. The process of claim 1 wherein the desired one of the first or
second material comprises nickel.
7. The process of claim 6 wherein the at least partial activation
of the at least a portion of a surface of the previously formed
layer comprises activation of a material comprising nickel.
8. An electrochemical fabrication process for producing a
three-dimensional structure from a plurality of adhered layers, the
process comprising: (A) supplying at least one material to be
deposited, wherein the at least one material has an effective
deposition voltage that is higher than an open circuit voltage, and
wherein a deposition control parameter is capable of being set to
such a value that a voltage can be controlled to a value between
the effective deposition voltage and the open circuit voltage such
that no significant deposition occurs but such that surface
activation of at least a portion of a previously formed layer can
occur; and (B) forming a plurality of layers by depositing one or
more materials which include the at least one material, wherein
each successive layer is formed adjacent to and adhered to a
previously formed layer to produce a three-dimensional structure
from a plurality of adhered layers, wherein during the formation of
at least some of the plurality of layers, making electrical contact
between an anode and the previously formed layer via a plating
solution, wherein after making electrical contact between the anode
and the previously formed layer, setting the deposition control
parameter to at least one value and for a time such that at least
the portion of the previously formed layer, comprising the at least
one material, is activated without any significant deposition
occurring and thereafter applying a current between the anode and
the previously formed layer such that deposition of the at least
one material occurs, wherein the depositing of the at least one
material or a depositing of at least one other material during
formation of more than one layer of the plurality of layers
comprises: (1) contacting or placing in proximity the previously
formed layer and a patterned preformed contact mask having at least
one opening; (2) in the presence of a plating solution, conducting
an electric current between an anode and the previously formed
layer, which functions as a cathode, through the at least one
opening in the mask, such that one of the at least one deposition
material or the other deposition material is deposited onto the
previously formed layer to form at least a portion of the
successive layer, after which the mask is removed from the
previously formed layer.
9. The process of claim 8 wherein the depositing of the at least
one material comprises a deposition of nickel.
10. The process of claim 8 wherein the deposition of the at least
one material, after activation, is to a height at least as great as
a layer thickness.
11. The process of claim 10 wherein the deposition of the at least
one material comprises a deposition of nickel.
12. The process of claim 8 wherein at least a portion of at least
one layer of the plurality of layers is formed by a
non-electroplating deposition process.
13. The process of claim 8 wherein during the formation of the more
than one layer the at least one material comprises nickel or copper
and the at least one other material comprises the other of nickel
or copper.
14. The process of claim 8 wherein the depositing one or more
materials during the forming of the plurality of layers comprises
the depositing of at least one structural material and at least one
sacrificial material.
15. The process of claim 14 wherein at least a portion of the at
least one sacrificial material is removed after formation of the
plurality of layers to reveal a three-dimensional structure
comprised of the at least one structural material.
16. The process of claim 15 wherein the deposition of the at least
one material comprises a deposition of nickel.
17. The process of claim 8 wherein different masks are used during
deposition associated with formation of at least two different
layers.
18. The process of claim 8 wherein the patterned preformed contact
mask comprises a patterned conformable material and wherein a
thickness of the conformable material is less than 100 .mu.m.
19. The process of claim 8 wherein formation of each current layer
of the plurality of layers additionally comprises removing a
portion of the at least one material deposited during formation of
the current layer such that a desired surface level for the current
layer is obtained.
20. An electrochemical fabrication process for producing a
three-dimensional structure from a plurality of adhered layers, the
process comprising: forming a plurality of successive layers,
wherein each successive layer is formed from the deposition of one
or more materials, and wherein each successive layer is formed
adjacent to and adhered to an immediately preceding layer, wherein
forming each of at least a portion of the plurality of successive
layers comprises: (A) contacting an immediately preceding layer and
a preformed patterned contact mask having at least one opening; (B)
in the presence of a plating solution, conducting an electric
current between an anode and the immediately preceding layer
through the at least one opening in the mask, such that a first
material is deposited onto the immediately preceding layer to form
at least a portion of a successive layer; and (C) separating the
mask from the immediately preceding layer; and wherein for one or
more of the plurality of layers, the forming of the successive
layer comprises, in the presence of the plating solution, applying
a current between an activation anode and at least a portion of the
immediately preceding layer, at such a level and for such a time
that at least partial activation of at least a portion of a surface
of the immediately preceding layer, comprising at least one of the
one or more materials, occurs without significant deposition of any
material occurring, and then without separating the immediately
preceding layer and the plating solution, applying a current
between a deposition anode and the immediately preceding layer at
such a level so as to cause deposition of the at least one of the
one or more materials.
Description
RELATED APPLICATIONS
[0001] This application is a continuation of U.S. patent
application Ser. No. 11/692,864, filed Mar. 28, 2007 which is a
continuation of U.S. patent application Ser. No. 10/434,289 filed
May 7, 2003, which claims benefit of U.S. Provisional Patent
Application No. 60/379,129, filed on May 7, 2002 which are hereby
incorporated herein by reference as if set forth in full.
FIELD OF THE INVENTION
[0003] This invention relates to the field of electrochemical
deposition and more particularly to the field of electrochemical
deposition using conformable contact masks that are formed separate
from a substrate (e.g. INSTANT MASKS.TM.) to control deposition,
such as for example in Electrochemical Fabrication (e.g. EFAB.TM.)
where such masks are used to control the selective electrochemical
deposition of one or more materials according to desired
cross-sectional configurations so as to build up three-dimensional
structures from a plurality of at least partially adhered layers of
deposited material.
BACKGROUND
[0004] A technique for forming three-dimensional structures (e.g.
parts, components, devices, and the like) from a plurality of
adhered layers was invented by Adam L. Cohen and is known as
Electrochemical Fabrication. It is being commercially pursued by
MEMGen.RTM. Corporation of Burbank, Calif. under the name EFAB.TM..
This technique was described in U.S. Pat. No. 6,027,630, issued on
Feb. 22, 2000. This electrochemical deposition technique allows the
selective deposition of a material using a unique masking technique
that involves the use of a mask that includes patterned conformable
material on a support structure that is independent of the
substrate onto which plating will occur. When desiring to perform
an electrodeposition using the mask, the conformable portion of the
mask is brought into contact with a substrate while in the presence
of a plating solution such that the contact of the conformable
portion of the mask to the substrate inhibits deposition at
selected locations. For convenience, these masks might be
generically called conformable contact masks; the masking technique
may be generically called a conformable contact mask plating
process. More specifically, in the terminology of MEMGen.RTM.
Corporation of Burbank, Calif. such masks have come to be known as
INSTANT MASKS.TM. and the process known as INSTANT MASKING.TM. or
INSTANT MASK.TM. plating. Selective depositions using conformable
contact mask plating may be used to form single layers of material
or may be used to form multi-layer structures. The teachings of the
'630 patent are hereby incorporated herein by reference as if set
forth in full herein. Since the filing of the patent application
that led to the above noted patent, various papers about
conformable contact mask plating (i.e. INSTANT MASKING) and
electrochemical fabrication have been published: [0005] 1. A.
Cohen, G. Zhang, F. Tseng, F. Mansfeld, U. Frodis and P. Will,
"EFAB: Batch production of functional, fully-dense metal parts with
micro-scale features", Proc. 9th Solid Freeform Fabrication, The
University of Texas at Austin, p 161, August 1998. [0006] 2. A.
Cohen, G. Zhang, F. Tseng, F. Mansfeld, U. Frodis and P. Will,
"EFAB: Rapid, Low-Cost Desktop Micromachining of High Aspect Ratio
True 3-D MEMS", Proc. 12th IEEE Micro Electro Mechanical Systems
Workshop, IEEE, p 244, January 1999. [0007] 3. A. Cohen, "3-D
Micromachining by Electrochemical Fabrication", Micromachine
Devices, March 1999. [0008] 4. G. Zhang, A. Cohen, U. Frodis, F.
Tseng, F. Mansfeld, and P. Will, "EFAB: Rapid Desktop Manufacturing
of True 3-D Microstructures", Proc. 2nd International Conference on
Integrated MicroNanotechnology for Space Applications, The
Aerospace Co., April 1999. [0009] 5. F. Tseng, U. Frodis, G. Zhang,
A. Cohen, F. Mansfeld, and P. Will, "EFAB: High Aspect Ratio,
Arbitrary 3-D Metal Microstructures using a Low-Cost Automated
Batch Process", 3rd International Workshop on High Aspect Ratio
MicroStructure Technology (HARMST'99), June 1999. [0010] 6. A.
Cohen, U. Frodis, F. Tseng, G. Zhang, F. Mansfeld, and P. Will,
"EFAB: Low-Cost, Automated Electrochemical Batch Fabrication of
Arbitrary 3-D Microstructures", Micromachining and Microfabrication
Process Technology, SPIE 1999 Symposium on Micromachining and
Microfabrication, September 1999. [0011] 7. F. Tseng, G. Zhang, U.
Frodis, A. Cohen, F. Mansfeld, and P. Will, "EFAB: High Aspect
Ratio, Arbitrary 3-D Metal Microstructures using a Low-Cost
Automated Batch Process", MEMS Symposium, ASME 1999 International
Mechanical Engineering Congress and Exposition, November, 1999.
[0012] 8. A. Cohen, "Electrochemical Fabrication (EFABTM)", Chapter
19 of The MEMS Handbook, edited by Mohamed Gad-El-Hak, CRC Press,
2002. [0013] 9. "Microfabrication--Rapid Prototyping's Killer
Application", pages 1-5 of the Rapid Prototyping Report, CAD/CAM
Publishing, Inc., June 1999.
[0014] The disclosures of these nine publications are hereby
incorporated herein by reference as if set forth in full
herein.
[0015] The electrochemical deposition process may be carried out in
a number of different ways as set forth in the above patent and
publications. In one form, this process involves the execution of
three separate operations during the formation of each layer of the
structure that is to be formed: [0016] 1. Selectively depositing at
least one material by electrodeposition upon one or more desired
regions of a substrate. [0017] 2. Then, blanket depositing at least
one additional material by electrodeposition so that the additional
deposit covers both the regions that were previously selectively
deposited onto, and the regions of the substrate that did not
receive any previously applied selective depositions. [0018] 3.
Finally, planarizing the materials deposited during the first and
second operations to produce a smoothed surface of a first layer of
desired thickness having at least one region containing the at
least one material and at least one region containing at least the
one additional material.
[0019] After formation of the first layer, one or more additional
layers may be formed adjacent to the immediately preceding layer
and adhered to the smoothed surface of that preceding layer. These
additional layers are formed by repeating the first through third
operations one or more times wherein the formation of each
subsequent layer treats the previously formed layers and the
initial substrate as a new and thickening substrate.
[0020] Once the formation of all layers has been completed, at
least a portion of at least one of the materials deposited is
generally removed by an etching process to expose or release the
three-dimensional structure that was intended to be formed.
[0021] The preferred method of performing the selective
electrodeposition involved in the first operation is by conformable
contact mask plating. In this type of plating, one or more
conformable contact (CC) masks are first formed. The CC masks
include a support structure onto which a patterned conformable
dielectric material is adhered or formed. The conformable material
for each mask is shaped in accordance with a particular
cross-section of material to be plated. At least one CC mask is
needed for each unique cross-sectional pattern that is to be
plated.
[0022] The support for a CC mask is typically a plate-like
structure formed of a metal that is to be selectively electroplated
and from which material to be plated will be dissolved. In this
typical approach, the support will act as an anode in an
electroplating process. In an alternative approach, the support may
instead be a porous or otherwise perforated material through which
deposition material will pass during an electroplating operation on
its way from a distal anode to a deposition surface. In either
approach, it is possible for CC masks to share a common support,
i.e. the patterns of conformable dielectric material for plating
multiple layers of material may be located in different areas of a
single support structure. When a single support structure contains
multiple plating patterns, the entire structure is referred to as
the CC mask while the individual plating masks may be referred to
as "submasks". In the present application such a distinction will
be made only when relevant to a specific point being made.
[0023] In preparation for performing the selective deposition of
the first operation, the conformable portion of the CC mask is
placed in registration with and pressed against a selected portion
of the substrate (or onto a previously formed layer or onto a
previously deposited portion of a layer) on which deposition is to
occur. The pressing together of the CC mask and substrate occur in
such a way that all openings, in the conformable portions of the CC
mask contain plating solution. The conformable material of the CC
mask that contacts the substrate acts as a barrier to
electrodeposition while the openings in the CC mask that are filled
with electroplating solution act as pathways for transferring
material from an anode (e.g. the CC mask support) to the
non-contacted portions of the substrate (which act as a cathode
during the plating operation) when an appropriate potential and/or
current are supplied.
[0024] An example of a CC mask and CC mask plating are shown in
FIGS. 1(a)-1(c). FIG. 1(a) shows a side view of a CC mask 8
consisting of a conformable or deformable (e.g. elastomeric)
insulator 10 patterned on an anode 12. The anode has two functions.
FIG. 1(a) also depicts a substrate 6 separated from mask 8. One is
as a supporting material for the patterned insulator 10 to maintain
its integrity and alignment since the pattern may be topologically
complex (e.g., involving isolated "islands" of insulator material).
The other function is as an anode for the electroplating operation.
CC mask plating selectively deposits material 22 onto a substrate 6
by simply pressing the insulator against the substrate then
electrodepositing material through apertures 26a and 26b in the
insulator as shown in FIG. 1(b). After deposition, the CC mask is
separated, preferably non-destructively, from the substrate 6 as
shown in FIG. 1(c). The CC mask plating process is distinct from a
"through-mask" plating process in that in a through-mask plating
process the separation of the masking material from the substrate
would occur destructively. As with through-mask plating, CC mask
plating deposits material selectively and simultaneously over the
entire layer. The plated region may consist of one or more isolated
plating regions where these isolated plating regions may belong to
a single structure that is being formed or may belong to multiple
structures that are being formed simultaneously. In CC mask plating
as individual masks are not intentionally destroyed in the removal
process, they may be usable in multiple plating operations.
[0025] Another example of a CC mask and CC mask plating is shown in
FIGS. 1(d)-1(f). FIG. 1(d) shows an anode 12' separated from a mask
8' that comprises a patterned conformable material 10' and a
support structure 20. FIG. 1(d) also depicts substrate 6 separated
from the mask 8'. FIG. 1(e) illustrates the mask 8' being brought
into contact with the substrate 6. FIG. 1(f) illustrates the
deposit 22' that results from conducting a current from the anode
12' to the substrate 6. FIG. 1(g) illustrates the deposit 22' on
substrate 6 after separation from mask 8'. In this example, an
appropriate electrolyte is located between the substrate 6 and the
anode 12' and a current of ions coming from one or both of the
solution and the anode are conducted through the opening in the
mask to the substrate where material is deposited. This type of
mask may be referred to as an anodeless INSTANT MASK.TM. (AIM) or
as an anodeless conformable contact (ACC) mask.
[0026] Unlike through-mask plating, CC mask plating allows CC masks
to be formed completely separate from the fabrication of the
substrate on which plating is to occur (e.g. separate from a
three-dimensional (3D) structure that is being formed). CC masks
may be formed in a variety of ways, for example, a
photolithographic process may be used. All masks can be generated
simultaneously, prior to structure fabrication rather than during
it. This separation makes possible a simple, low-cost, automated,
self-contained, and internally-clean "desktop factory" that can be
installed almost anywhere to fabricate 3D structures, leaving any
required clean room processes, such as photolithography to be
performed by service bureaus or the like.
[0027] An example of the electrochemical fabrication process
discussed above is illustrated in FIGS. 2(a)-2(f). These figures
show that the process involves deposition of a first material 2
which is a sacrificial material and a second material 4 which is a
structural material. The CC mask 8, in this example, includes a
patterned conformable material (e.g. an elastomeric dielectric
material) 10 and a support 12 which is made from deposition
material 2. The conformal portion of the CC mask is pressed against
substrate 6 with a plating solution 14 located within the openings
16 in the conformable material 10. An electric current, from power
supply 18, is then passed through the plating solution 14 via (a)
support 12 which doubles as an anode and (b) substrate 6 which
doubles as a cathode. FIG. 2(a), illustrates that the passing of
current causes material 2 within the plating solution and material
2 from the anode 12 to be selectively transferred to and plated on
the cathode 6. After electroplating the first deposition material 2
onto the substrate 6 using CC mask 8, the CC mask 8 is removed as
shown in FIG. 2(b). FIG. 2(c) depicts the second deposition
material 4 as having been blanket-deposited (i.e. non-selectively
deposited) over the previously deposited first deposition material
2 as well as over the other portions of the substrate 6. The
blanket deposition occurs by electroplating from an anode (not
shown), composed of the second material, through an appropriate
plating solution (not shown), and to the cathode/substrate 6. The
entire two-material layer is then planarized to achieve precise
thickness and flatness as shown in FIG. 2(d). After repetition of
this process for all layers, the multi-layer structure 20 formed of
the second material 4 (i.e. structural material) is embedded in
first material 2 (i.e. sacrificial material) as shown in FIG. 2(e).
The embedded structure is etched to yield the desired device, i.e.
structure 20, as shown in FIG. 2(f).
[0028] Various components of an exemplary manual electrochemical
fabrication system 32 are shown in FIGS. 3(a)-3(c). The system 32
consists of several subsystems 34, 36, 38, and 40. The substrate
holding subsystem 34 is depicted in the upper portions of each of
FIGS. 3(a) to 3(c) and includes several components: (1) a carrier
48, (2) a metal substrate 6 onto which the layers are deposited,
and (3) a linear slide 42 capable of moving the substrate 6 up and
down relative to the carrier 48 in response to drive force from
actuator 44. Subsystem 34 also includes an indicator 46 for
measuring differences in vertical position of the substrate which
may be used in setting or determining layer thicknesses and/or
deposition thicknesses. The subsystem 34 further includes feet 68
for carrier 48 which can be precisely mounted on subsystem 36.
[0029] The CC mask subsystem 36 shown in the lower portion of FIG.
3(a) includes several components: (1) a CC mask 8 that is actually
made up of a number of CC masks (i.e. submasks) that share a common
support/anode 12, (2) precision X-stage 54, (3) precision Y-stage
56, (4) frame 72 on which the feet 68 of subsystem 34 can mount,
and (5) a tank 58 for containing the electrolyte 16. Subsystems 34
and 36 also include appropriate electrical connections (not shown)
for connecting to an appropriate power source for driving the CC
masking process.
[0030] The blanket deposition subsystem 38 is shown in the lower
portion of FIG. 3(b) and includes several components: (1) an anode
62, (2) an electrolyte tank 64 for holding plating solution 66, and
(3) frame 74 on which the feet 68 of subsystem 34 may sit.
Subsystem 38 also includes appropriate electrical connections (not
shown) for connecting the anode to an appropriate power supply for
driving the blanket deposition process.
[0031] The planarization subsystem 40 is shown in the lower portion
of FIG. 3(c) and includes a lapping plate 52 and associated motion
and control systems (not shown) for planarizing the
depositions.
[0032] Another method for forming microstructures from
electroplated metals (i.e. using electrochemical fabrication
techniques) is taught in U.S. Pat. No. 5,190,637 to Henry Guckel,
entitled "Formation of Microstructures by Multiple Level Deep X-ray
Lithography with Sacrificial Metal layers. This patent teaches the
formation of metal structure utilizing mask exposures. A first
layer of a primary metal is electroplated onto an exposed plating
base to fill a void in a photoresist, the photoresist is then
removed and a secondary metal is electroplated over the first layer
and over the plating base. The exposed surface of the secondary
metal is then machined down to a height which exposes the first
metal to produce a flat uniform surface extending across the both
the primary and secondary metals. Formation of a second layer may
then begin by applying a photoresist layer over the first layer and
then repeating the process used to produce the first layer. The
process is then repeated until the entire structure is formed and
the secondary metal is removed by etching. The photoresist is
formed over the plating base or previous layer by casting and the
voids in the photoresist are formed by exposure of the photoresist
through a patterned mask via X-rays or UV radiation.
[0033] To form successful depositions it is of importance that
adequate adhesion occur between the deposited material and a
substrate. If it is desired to exploit the electrical properties of
the deposited material it may be desired that any resistivity
associated with the bonding between the substrate and the deposited
layer be as small as possible or at least of a similar order of
magnitude compared to the resistivity of the bulk deposit of
material. These requirements become even more important when
forming structures where a layer comprises a plurality of
separately deposited materials. These requirements become of even
further importance when forming structures from a plurality of
adhered layers. As adhesion failure or other failure on a single
layer may destroy the usefulness of the entire structure, even a
small chance of failure of achieving desired properties between
successive depositions within a given layer or of achieving desired
properties between depositions on successive layers may result in
an unacceptable failure rate when the total number of depositions
is considered. In electrochemical fabrication processes where
multiple materials may be deposited on any given layer and multiple
materials may be deposited in non-overlaying positions on
subsequent layers, it may be insufficient to consider a technique
that results in good adhesion between successive depositions of
like materials, or even depositions of a first material onto a
second material, but also depositions of the second material onto
the first material, and the like when more than two materials are
used. The loss associated with the formation of a multilayer
structure may not be the just the wasted time, wasted material, and
cost associated with a single layer but instead may be the wasted
time, wasted material, and cost associated with the formation of
the entire structure.
[0034] For successful plating to occur, a pretreatment process may
be applied, which includes three general steps: (1) cleaning to
remove all superficial substances such as grease and soil, (2)
descaling to remove scale and rust, and (3) immediately prior to
plating, activation to remove remaining oxides from metal surfaces.
The surface is made active by complete removal of all surface
contamination and oxides. After it is rendered active it must be
kept in this state until it is covered by the metal being
deposited.
[0035] Except for noble metals such as gold and platinum, most
metals exposed to air or water oxidize in a very short time to form
a thin oxide or passive film on their surfaces. Both copper and
nickel, two materials used in some preferred embodiments of
conformable contact mask plating and electrochemical fabrication,
are subject to this rapid oxidation. The oxide or passive film
usually acts as a barrier to bonding of electrodeposits. In
addition, a metal oxide usually has lower strength than the deposit
and the substrate. Thus, adhesion failure can occur due to the
presence of the oxide at a lower external force that would
otherwise be required. In addition, the presence of the oxide can
increase the electrical resistance between the two depositions. The
purpose of activation is to remove these oxide layers or to at
least render them as thin as possible. If the activation is
inadequate, a satisfactory bond of the deposit to the base metal
may not be obtained and electrical properties between the deposit
and the base metal may be different than that desired.
[0036] Various processes are known for activating copper and nickel
surfaces.
[0037] Though the need for surface activation is generally known in
the electroplating arts, the need for and optimization for surface
activation in conformable contact mask plating and electrochemical
fabrication processes have not been addressed in the field. Each of
the above noted publications that is explicitly directed to the use
of conformable contact masks (i.e. Instant Masks) and
electrochemical fabrication (i.e. EFAB), whether taken alone or in
combination, are silent concerning modifications that can be made
to the conformable contact mask plating and electrochemical
fabrication processes to enhance layer-to-layer bonding and other
inter-layer properties. A need exists in the electrodeposition
arts, and more particularly in the field of conformable contact
mask plating and electrochemical fabrication for production methods
that result in structures having intra-layer and inter-layer
properties that meet certain requirements.
SUMMARY OF THE INVENTION
[0038] It is an object of certain aspects of the invention to
provide an electrodeposition process is capable of producing
structures having a desired intra-layer or inter-layer property
that meets or exceeds a minimum requirement.
[0039] It is an object of certain aspects of the invention to
provide an electrodeposition process that produces enhanced
properties between depositions of material and existing
material.
[0040] It is an object of certain aspects of the invention to
provide a conformable contact mask plating process is capable of
producing structures having a desired intra-layer or inter-layer
property that meets or exceeds a minimum requirement.
[0041] It is an object of certain aspects of the invention to
provide a conformable contact mask plating that produces enhanced
properties between depositions of material and existing
material.
[0042] It is an object of certain aspects of the invention to
provide an electrochemical fabrication process is capable of
producing structures having a desired intra-layer or inter-layer
property that meets or exceeds a minimum requirement.
[0043] It is an object of certain aspects of the invention to
provide an electrochemical fabrication process that produces
enhanced properties between depositions of material and existing
material.
[0044] Other objects and advantages of various aspects of the
invention will be apparent to those of skill in the art upon review
of the teachings herein. The various aspects of the invention, set
forth explicitly herein or otherwise ascertained from the teachings
herein, may address any one of the above objects alone or in
combination, or alternatively may not address any of the objects
set forth above but instead address some other object ascertained
from the teachings herein. It is not intended that all of these
objects be addressed by any single aspect of the invention even
though that may be the case with regard to some aspects.
[0045] A first aspect of the invention provides a method for
activating a surface of a substrate onto which a metal will be
deposited by electrodeposition, including: (A) supplying a
substrate onto which one or more depositions may have occurred,
wherein the substrate has a surface to be activated prior to
occurrence of a deposition of at least one additional material; (B)
contacting a plating solution and the substrate; (C) contacting the
plating solution and an activation anode; and (D) applying a
voltage or current between the activation anode and the substrate
at a level and for a time such that at least partial activation of
at least a portion of the substrate surface occurs without
significant deposition of the at least one additional material
occurring onto the surface, and thereafter without separating the
substrate from the plating solution, applying a voltage or current
between a deposition anode and the substrate at a level and for a
time so as to cause deposition of the at least one additional
material.
[0046] A second aspect of the invention provides an electrochemical
fabrication process for producing a three-dimensional structure
from a plurality of adhered layers, the process including: (A)
depositing a first material onto the substrate to form a portion of
a layer and depositing at least a second material to form another
portion of the layer, wherein the substrate may include previously
deposited material; and (B) forming a plurality of layers such that
each successive layer is formed adjacent to and adhered to a
previously deposited layer, wherein said forming includes repeating
operation Error! Reference source not found. a plurality of times;
wherein at least a plurality of the selective depositing operations
include: (1) contacting the substrate and a patterned mask having
at least one opening; (2) in presence of a plating solution,
conducting an electric current between an anode and the substrate,
which functions as a cathode, through the at least one opening in
the mask, such that the selected one of the first or second
deposition materials is deposited onto the substrate to form at
least a portion of a layer; and (3) separating the mask from the
substrate; wherein for a plurality of layers, in the presence of a
plating solution, applying a current between an activation anode
and the substrate, which functions as a cathode, at such a level
and for such a time that at least partial activation of at least a
portion of a surface of the substrate occurs without significant
deposition of material occurring, and then without separating the
substrate and the plating solution, applying a current between a
deposition anode and the substrate which functions as a cathode, at
such a level so as to cause deposition of a desired one of the
first or second materials.
[0047] A third aspect of the invention provides an electrochemical
fabrication process for producing a three-dimensional structure
from a plurality of adhered layers, the process including: (A)
supplying at least one material to be deposited, wherein the at
least one material has an effective deposition voltage that is
higher than an open circuit voltage, and wherein a deposition
control parameter is capable of being set to such a value that a
voltage can be controlled to a value between the effective
deposition voltage and the open circuit voltage such that no
significant deposition occurs but such that surface activation of
at least a portion of the substrate can occur; (B) forming a
plurality of layers by depositing one or more materials which
include the at least one material, wherein each successive layer is
formed adjacent to and adhered to a previously deposited layer,
wherein after making electrical contact between an anode and the
substrate via a plating solution, setting the deposition control
parameter to at least one value and for a time such that at least a
portion of the surface of the substrate is activated without any
significant deposition occurring, and thereafter without breaking
the electrical contact, applying a current between the anode and
the substrate such that deposition of the at least one material
occurs, wherein the deposition of the at least one material or a
deposition of at least one other material includes: (1) contacting
or placing in proximity a patterned mask having at least one
opening and a substrate; (2) in presence of a plating solution,
conducting an electric current between an anode and the substrate,
which functions as a cathode, through the at least one opening in
the mask, such that one of the at least one deposition material or
the other deposition material is deposited onto the substrate to
form at least a portion of a layer, after which the mask is removed
from the substrate.
[0048] A fourth aspect of the invention provides an electrochemical
fabrication process for producing a three-dimensional structure
from a plurality of adhered layers, the process including: forming
a plurality of layers, wherein each layer is formed from the
deposition of one or more materials, and wherein each successive
layer is formed adjacent to and adhered to a previously deposited
layer, wherein said forming includes: (A) contacting the substrate
and a patterned mask having at least one opening; (B) in presence
of a plating solution, conducting an electric current between an
anode and the substrate, which functions as a cathode, through the
at least one opening in the mask, such that the first deposition
material is deposited onto the substrate to form at least a portion
of a layer; and (C) separating the mask from the substrate; and
wherein for a plurality of layers, in the presence of a plating
solution, applying a current between an activation anode and the
substrate, which functions as a cathode, at such a level and for
such a time that at least partial activation of at least a portion
of the substrate surface occurs without significant deposition of
material occurring, and then without separating the substrate and
the plating solution, applying a current between a deposition anode
and the substrate, which functions as a cathode, at such a level so
as to cause deposition of a second material which may be different
from or the same as the first material.
[0049] A fifth aspect of the invention provides a method for
activating a surface of a substrate in preparation for deposition
of a first material, including: (A) supplying a substrate onto
which one or more depositions may have occurred, wherein the
substrate has a surface to be activated prior to occurrence of a
deposition of the first material; (B) contacting a patterned mask
to the substrate, wherein the patterned mask has at least one
opening; (C) in the presence of a plating solution, conducting an
electric current through the at least one opening in the patterned
mask between a deposition anode and the substrate, wherein the
substrate functions as a cathode, such that a second deposition
material is deposited onto the substrate, to form at least a
portion of a layer; and (D) applying a current between an
activation anode and the substrate through a plating solution at a
level and for a time such that at least partial activation of at
least a portion of a surface of the substrate occurs without
significant deposition of the first material occurring onto the
surface, and then without separating the substrate and the plating
solution, applying a current between a deposition anode and the
substrate at a level and for a time so as to cause deposition of
the first material, and wherein the substrate functions as a
cathode.
[0050] A sixth aspect of the invention provides an electrochemical
fabrication apparatus for producing a three-dimensional structure
from a plurality of adhered layers, the process including: (A) a
plurality of preformed masks, wherein each mask includes a
patterned conformable dielectric material that includes at least
one opening through which deposition can take place during the
formation of at least a portion of a layer, and wherein each mask
includes a support structure that supports the patterned
conformable dielectric material; (B) means for selectively
depositing at least a portion of a layer onto the substrate,
wherein the substrate may include previously deposited material;
and (C) means for forming a plurality of layers such that each
successive layer is formed adjacent to and adhered to a previously
deposited layer, wherein the means of (B) is used a plurality of
times; wherein means of (B) includes: (1) means for contacting the
substrate and the conformable material of a selected preformed
mask; (2) means for applying an electric current through a plating
solution within at least one opening in the selected mask between
an anode and the substrate, wherein the anode includes a selected
deposition material, and wherein the substrate functions as a
cathode, such that the selected deposition material is deposited
onto the substrate to form at least a portion of a layer; and (3)
means for separating the selected preformed mask from the
substrate; and (D) means for applying a current between an
activation anode and the substrate through a plating solution,
which substrate functions as a cathode, at such a level and for
such a time that at least partial activation of at least a portion
of the substrate surface occurs without significant deposition of
material occurring, and then without separating the substrate and
the plating solution, applying a current between a deposition anode
and the substrate, which substrate functions as a cathode, at such
a level so as to cause deposition onto the substrate to occur; and
(E) means for operating the means of (D) during the formation of a
plurality of layers.
[0051] Further aspects of the invention will be understood by those
of skill in the art upon reviewing the teachings herein. Other
aspects of the invention may involve combinations of the above
noted aspects of the invention and/or addition of various features
of one or more embodiments. Other aspects of the invention may
involve apparatus that can be used in implementing one or more of
the above method aspects of the invention. These other aspects of
the invention may provide various combinations of the aspects
presented above as well as provide other configurations,
structures, functional relationships, and processes that have not
been specifically set forth above.
BRIEF DESCRIPTION OF THE DRAWINGS
[0052] FIGS. 1(a)-1(c) schematically depict side views of various
stages of a CC mask plating process, while FIGS. 1(d)-(g)
schematically depict a side views of various stages of a CC mask
plating process using a different type of CC mask.
[0053] FIGS. 2(a)-2(f) schematically depict side views of various
stages of an electrochemical fabrication process as applied to the
formation of a particular structure where a sacrificial material is
selectively deposited while a structural material is blanket
deposited.
[0054] FIGS. 3(a)-3(c) schematically depict side views of various
example subassemblies that may be used in manually implementing the
electrochemical fabrication method depicted in FIGS. 2(a)-2(f).
[0055] FIGS. 4(a)-4(i) schematically depict the formation of a
first layer of a structure using adhered mask plating where the
blanket deposition of a second material overlays both the openings
between deposition locations of a first material and the first
material itself.
[0056] FIG. 5 provides an example of a failed structure due to
failed adhesion between two layers.
[0057] FIGS. 6(a) and 6(b) depict cathodic polarization curves for
a nickel substrate in a nickel sulfamate plating bath.
[0058] FIG. 7(a)-7(c) depict Ni cathode potentials before and after
various forms of activation.
[0059] FIG. 8 depicts a perspective view of a 5 layer structure
that was used in performing a contact resistance analysis for in
situ cathodically activated nickel depositions.
[0060] FIG. 9(a)-9(c) respectively illustrate the set up for (1) an
adhesive based adhesion test, (2) a solder based adhesion test, and
(3) the Ollard method of testing adhesion.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0061] FIGS. 1(a)-1(g), 2(a)-2(f), and 3(a)-3(c) illustrate various
features of one form of electrochemical fabrication that are known.
Other electrochemical fabrication techniques are set forth in the
'630 patent referenced above, in the various previously
incorporated publications, in various other patents and patent
applications incorporated herein by reference, still others may be
derived from combinations of various approaches described in these
publications, patents, and applications, or are otherwise known or
ascertainable by those of skill in the art from the teachings set
forth herein. All of these techniques may be combined with those of
the various embodiments of various aspects of the invention to
yield enhanced embodiments. Still other embodiments be may derived
from combinations of the various embodiments explicitly set forth
herein.
[0062] FIGS. 4(a)-4(i) illustrate various stages in the formation
of a single layer of a multi-layer fabrication process where a
second metal is deposited on a first metal as well as in openings
in the first metal where its deposition forms part of the layer. In
FIG. 4(a), a side view of a substrate 82 is shown, onto which
patternable photoresist 84 is cast as shown in FIG. 4(b). In FIG.
4(c), a pattern of resist is shown that results from the curing,
exposing, and developing of the resist. The patterning of the
photoresist 84 results in openings or apertures 92(a)-92(c)
extending from a surface 86 of the photoresist through the
thickness of the photoresist to surface 88 of the substrate 82. In
FIG. 4(d), a metal 94 (e.g. nickel) is shown as having been
electroplated into the openings 92(a)-92(c). In FIG. 4(e), the
photoresist has been removed (i.e. chemically stripped) from the
substrate to expose regions of the substrate 82 which are not
covered with the first metal 94. In FIG. 4(f), a second metal 96
(e.g., silver) is shown as having been blanket electroplated over
the entire exposed portions of the substrate 82 (which is
conductive) and over the first metal 94 (which is also conductive).
FIG. 4(g) depicts the completed first layer of the structure which
has resulted from the planarization of the first and second metals
down to a height that exposes the first metal and sets a thickness
for the first layer. In FIG. 4(h) the result of repeating the
process steps shown in FIGS. 4(b)-4(g) several times to form a
multi-layer structure are shown where each layer consists of two
materials. For most applications, one of these materials is removed
as shown in FIG. 4(i) to yield a desired 3-D structure 98 (e.g.
component or device).
[0063] A basic standard plating configuration (i.e. non-CC mask
plating configuration) includes an anode and a cathode which are
immersed in a plating bath. The distance between the anode and
cathode is at least 1 mm. A power source provides a pre-set current
passing through the plating cell so that the anode metal usually
dissolves into the plating bath and the metal ions in the plating
bath are reduced at the cathode to become a metallic deposit.
Depending on various parameters, including the composition of the
plating bath, the plating bath is usually operated at a constant
temperature some wherein the range of between 20-60.degree. C. The
plating bath is agitated mechanically or by compressed air to
ensure that fresh plating solution is delivered to the cathode and
that the products of the electrochemical reactions are removed from
the electrodes into the bulk solution.
[0064] Through-mask plating is a selective plating process since
the substrate (cathode) is patterned by a thin non-conductive
material (e.g. a patterned photoresist). Otherwise, its plating
configuration is the same as that of standard plating process as
outlined above. As such, through-mask plating, for the purposes
herein, may be considered a selective form of standard plating.
[0065] CC mask plating is different from normal and through-mask
plating in several aspects. In one form of CC mask plating, the
plating bath is trapped in a closed volume defined by the
substrate, the side walls of the conformable material, and the
anode. Examples of such closed volumes 26a and 26b are depicted in
FIG. 1(b). Another form of CC mask plating may involve the use of a
porous support and a distal anode. In this alternative form of CC
mask plating, the barrier presented by the support portion of the
CC mask, though allowing at least some ion exchange, may present a
sufficient hindrance to the exchange of some components of the
plating solution that the solution in the deposition region may
still be considered to be substantially isolated from the bulk
solution. This trapping results in little or no mass exchange
between the volume of solution in the plating region and the bulk
solution and as such no or little fresh solution with proper
additives can be supplied into the microspace and no or little
reaction products can be removed.
[0066] A preferred form of CC mask plating involves closed volumes
where at least one of the dimensions of at least one of the plating
volumes is on the order of tens of microns (e.g. 20 to 100 .mu.m)
or less. As such, this form of CC mask plating may be considered to
be a microbath plating process (i.e. micro-CC mask plating).
[0067] In micro-CC mask plating, the preferred separation between
the anode and cathode is presently between about 20 .mu.m and about
100 .mu.m, and more preferably between about 40 and 80 .mu.m. As
such, regardless of the size of the area being deposited, these
preferred embodiments may be considered to be micro-CC mask plating
processes. Of course thinner separation distances (e.g. 10 .mu.m or
less) and thicker separation distances (300 .mu.m or more) are
possible. Due to this close spacing between anode and cathode,
deposition processes at the cathode and dissolution processes at
the anode, unlike standard plating, are highly interacting.
[0068] Agitating the plating bath, as is common with standard
plating processes, though possible, is not necessarily desirable in
electrochemical fabrication due potentially to the high interaction
between anode and cathode processes and due to the believed
enhanced risk of shorting when agitation is used. Shorting refers
to a portion of the deposition height bridging the space between
the cathode and the anode prior to the lapse of the desired
deposition time, in which case the current is directed almost
solely through deposited conductive material as opposed to flowing
primarily through the plating bath as intended such that the
continuing of deposition is inhibited.
[0069] Using a pyrophosphate bath at high temperature (i.e. above
around 43.degree. C. to 45.degree. C.), though recommended in the
standard plating processes, is not desirable in the current form of
micro-CC mask plating due to the higher rate of attack at the
interface between the CC mask support and the conformable material
and the associated shortening of CC mask life.
[0070] CC mask plating has its own characteristics and the
conventional wisdom associated with standard plating processes may
be more of a hindrance than a help in developing commercially
viable CC mask plating processes and systems.
[0071] Successful deposits in most electrodeposition processes must
not only have desired thicknesses of appropriate uniformity, they
must also demonstrate reasonable adhesion to the substrate on which
they were deposited. In some forms of CC mask plating (e.g.
electrochemical fabrication) these deposits must also show
reasonable bulk properties (i.e. intra-deposit characteristics),
and reasonable inter-deposit characteristics (e.g. reasonable
adhesion between successive deposits, and reasonably small contact
resistance between deposits). These reasonable inter-deposit
characteristics in electrochemical fabrication where a single
structural material and a single sacrificial material are being
used may involve four unique situations: (1) characteristics
between structural material being deposited and previously
deposited structural material, (2) characteristics between
sacrificial material being deposited and previously deposited
sacrificial material (3) characteristics between structural
material being deposited and previously deposited sacrificial
material, and (4) characteristics between sacrificial material
being deposited and previously deposited structural material. In
other forms of conformable mask plating or electrochemical
fabrication where no sacrificial material is used, the possible
situations may be reduced to the first one listed above. On the
other hand, in other forms of CC mask plating or electrochemical
fabrication, if more than one structural material is used or more
than one sacrificial material is used, the classification of
potential situations may be more complex.
[0072] Of the possible situations that may arise, characteristics
involving structural material to structural material contact is the
most critical in that the characteristics must not only be
appropriate to allow production of the structure but they must also
meet any use requirements to which the structure will be placed. Of
course if the structure will remain adhered to the original
substrate when the structure is put to use, the contact
characteristics between the structure and the original substrate
may also be of elevated importance.
[0073] As noted above, in some preferred embodiments of
electrochemical fabrication, the materials to be plated are nickel
and copper. In some preferred embodiments of CC mask plating and
electrochemical fabrication, before performing the first plating
operation in association with a given layer the deposits from the
previous layer are planarized by lapping. Ultrasonic cleaning may
also be used.
[0074] A copper surface usually contains a layer of oxide film
after being lapped, rinsed and exposed to air before plating. For
example, when a clean copper surface is exposed to air or water, a
thin layer of Cu.sub.2O film quickly forms. With time, the oxide
thickness may reach up to 40-50 .ANG. in thickness in air at room
temperature but it can be readily removed by dipping in 5%
H.sub.2SO.sub.4 for a few seconds. After acid dipping and a quick,
thorough rinse, the copper containing substrate can be immediately
put into the plating tank. In this way, oxide formation can be
minimized. The active state of a copper surface can be maintained
in a nickel sulfamate bath (i.e. a preferred bath for plating
nickel in the electrochemical fabrication process) and a copper
pyrophosphate bath (i.e. a preferred bath for plating copper in the
electrochemical fabrication process) since the nickel bath is a
weak acid solution (pH.about.4.0) and the copper bath contains the
copper complexing agent pyrophosphate.
[0075] Nickel normally passivates in air, water, and plating baths
to form a passive oxide film on its surface. Nickel coatings can
not be successfully plated with good adhesion on to passive nickel
surfaces. An activated surface can readily become passive again if
it is allowed to dry or is exposed to oxygen-containing solutions.
The problem with nickel is to activate its surface and to keep it
active until plating has started. In electrochemical fabrication,
good adhesion between nickel layers is very important since layered
microstructures can fall apart even if poor adhesion occurs only at
one layer. FIG. 5 shows a failed chain that was produced by
electrochemical fabrication (i.e. EFAB) in which two layers
separated in region 82 at one horizontal link due to improper
activation.
[0076] Various nickel activation processes are known. A simple mild
activation method is chemical acid dipping in a 20-25% by volume
HCl solution or a 15% by volume H.sub.2SO.sub.4 where nickel oxide
(NiO) can be dissolved into nickel ions and water. Despite its
instability in acids, NiO may still break down at a very low rate.
By these simple methods, adequate activation may be obtained on
some nickel surfaces but not on all.
[0077] For faster treatment, concentrated acids such as HNO.sub.3
or HF can be used, e.g., HNO.sub.3:H.sub.2O or HF:H.sub.2O with 1:1
ratios by volume. Unfortunately, these acids also dissolve the
nickel metal at a faster rate as well.
[0078] Electrochemical activation is more successful for ensuring
good adhesion between the deposit (e.g. nickel) and the substrate
(e.g. nickel). There are three basic types: (1) anodic treatment,
(2) cathodic treatment, and (3) a combination of anodic and
cathodic treatment. Well-known and generally practiced methods for
producing adherent nickel electrodeposits on nickel and nickel
alloys are described in detail in ASTM Standards B558 and B343. In
the anodic treatment, nickel is used as an anode immersed in an
acid solution, e.g., H.sub.2SO.sub.4. The oxide film and a small
amount of nickel are dissolved by an external anodic current. In
the cathodic treatment, nickel is used as a cathode immersed in HCl
or H.sub.2SO.sub.4. An applied cathodic current reduces the oxide
to the metal. No base metal is etched using this method. Usually
this method is recommended when the nickel surface has not been
severely passivated. The combined anodic and cathodic treatment,
which generally employs an anodic treatment followed by a cathodic
treatment, has two variations. In one variation the process is
carried out in an acid solution, while in the other the process is
performed in a combined nickel activation-plating bath.
Furthermore, the second process involves deposition of a nickel
deposit on the nickel surface after the anodic treatment.
[0079] In certain preferred embodiments of electrochemical
fabrication, each layer is actually a composite of copper and
nickel. A preferred treatment should generally not cause
significantly different etching rates for copper and for nickel.
Otherwise, the flatness of a layer may suffer or even the
dimensions of a deposited layer within the plane of deposition if a
selective deposit were performed in association with a given layer
prior to performing the activation process.
[0080] A combined anodic and cathodic treatment recommended by ASTM
B343 was evaluated for electrochemical fabrication. In the
treatment procedure the surface is first etched at a current
density of 20 mA/cm.sup.2 for 10 minutes (i.e. the substrate on
which further deposition will occur is treated as the anode) then
passivated (e.g. an oxide film is formed) by use of a high anodic
current density of 200 mA/cm.sup.2 for 2 minutes (this high current
density results in passivation as opposed to significant
dissolution), and finally made cathodic for 2 or 3 seconds at 200
mA/cm.sup.2. The recommended treatment solution was 16.6%
H.sub.2SO.sub.4 by volume. Unfortunately, after this treatment, a
significant differential in etching rate was noticed between the
copper and nickel composite layer. Although it produced excellent
adhesion, this treatment does not appear to be suitable for a
multilayer electrochemical fabrication process that uses both
nickel and copper.
[0081] To minimize differential etching, a cathodic treatment has
an advantage since it reduces the oxide, but does not attack the
base metal. Cathodic treatments alone have not been previously
proposed for use in electrochemical fabrication and standard
cathodic activation treatments are not carried out in the same bath
as is used for plating. In these standard processes, after cathodic
activation, the substrate needs to be rinsed and is then
transferred into the plating bath. During this period, a thin oxide
film forms. If handled efficiently, the oxide may not have
sufficient thickness to interfere significantly with adhesion but
this handling and the extent of oxide formation may still remain an
uncontrolled variable. Additionally, depending on the time between
immersion into the plating bath and the beginning of plating,
further thickening of the oxide may occur. However, an ideal
cathodic treatment, and the treatment proposed herein, would be one
which could be carried out within the plating bath. Furthermore in
the most preferred approach, plating can be carried out immediately
after activation (i.e. in-situ cathodic activation) by switching
the cathodic current to the desired plating value, thereby avoiding
the formation of an oxide between the cathodic activation treatment
and the plating.
[0082] Many deposits can be obtained at a potential of the cathode
that is slightly lower than its stable open-circuit potential
because the deposition process has a fairly small activation
overvoltage which can usually be neglected. In these metal plating
baths, in-situ cathodic activation is impossible since deposits
form even when only small currents pass through the cathode.
[0083] However, for nickel the activation overvoltage is large. The
nickel deposit can not be obtained unless the potential of the
cathode is at least -200 mV beyond its stable open-circuit
potential. This feature is useful since either the oxide or H.sup.+
is reduced in this no-deposit region by the applied cathodic
current. Also, the H.sub.2 formed as the result of the reduction of
H.sup.+ can reduce the oxide since H.sub.2 is a reducing agent.
[0084] Experiments were performed to determine the deposition
overvoltage of nickel on copper and of nickel on nickel (the same
result was obtained for both substrates) in the sulfamate bath. A
complete cathodic polarization curve is shown in FIG. 6(a) while
the portion 112 of FIG. 6(a) is shown in FIG. 6(b). The test
samples were copper or nickel disks with an exposed area of 1.27
cm.sup.2. The polarization curve has a distinct change 84 at about
-0.68 V (vs. SCE). No nickel deposit could be seen before this
potential by visually checking the copper disk, however at more
negative potentials the nickel deposition occurred. This
no-deposition region is about 420 mV wide which also means that
nickel deposition does not occur if the cathodic current density is
less than 90 .mu.A/cm.sup.2.
[0085] If we use a current density of 50 .mu.A/cm.sup.2 for the
reduction of nickel oxide in the sulfamate bath and assume that the
NiO reduction efficiency is 100%, we arrive at a reduction rate of
NiO of about 1030 .ANG./hr or 17 .ANG./min. Theoretically, if the
oxide thickness is of the order of .about.50 .ANG., application of
a cathodic current density of 50 .mu.A/cm.sup.2 for several minutes
should reduce the NiO completely.
[0086] Experiments were performed to evaluate the effect of such
cathodic treatment, open circuit plating bath potentials of nickel
samples before and after the in-situ cathodic treatment were
measured in a 5% Na.sub.2SO.sub.3 solution at room temperature.
During these tests, in-situ cathodic treatment was performed in the
5% Na.sub.2SO.sub.3 solution as it was believed that the actual
solution used would have little impact on the treatment process
(i.e. the results obtained are believed to be similar to those that
would be obtained by activating in the plating solution. If the
oxide is at least partially removed (i.e. the surface is at least
partially activated), the potentials before and after the treatment
should be different. Since an activated nickel surface is easily
repassivated in oxygen-containing solutions, in order to obtain a
true nickel potential after the in-situ cathodic treatment, the
Na.sub.2SO.sub.3 (a reducing agent) solution was employed to
minimize the oxygen content in the solution to form an
almost-oxygen-free environment (since Na.sub.2SO.sub.3 consumes
oxygen). Currents were applied and potentials were measured using
an EG&G 273 Potentiostat/Galvanostat. A saturated calomel
electrode (SCE) was used as a reference electrode. The applied
activation current density was 50 .mu.A/cm.sup.2. Nickel disks
(purity: 99.9+% from Goodfellow) with an exposed area of 1.27
cm.sup.2 were polished with SiC sandpaper (grit 600), degreased in
acetone, dipped in 5% H.sub.2SO.sub.4 for 1 min, washed with Di
water in between, and finally dried with compressed air. The
specimens were then placed in air for at least 1 hour to form an
oxide film on the nickel surface at room temperature. The oxide
films formed rapidly (i.e. within a few seconds) in air at room
temperature, however the initial rapid oxidation of nickel quickly
decreased after several minutes as the oxide films formed. The
experimental oxidation time assured that there were oxide films of
similar thickness on each specimen.
[0087] The results of the potential measurements are shown in FIG.
7(a). The stable potential of the untreated nickel sample was -560
mV (vs. SCE), which was more positive than that of the samples with
in-situ cathodic treatment. This means that the surface was
activated by the in situ cathodic treatment since the more negative
the potential, the more active the surface. Preferably the
treatment time should be enough to finish nickel surface
activation, which depends on the oxide thickness. The experimental
results confirmed that the more treatment time, the more negative
the stable nickel potential after the treatment, which indicates
that the degree of the cathodic reduction of the oxide became
greater with treatment time. The stable potential (.about.-0.710 V
vs. SCE) of the sample after the 2 min treatment was very close to
that (.about.-0.730 V vs. SCE) of the sample after the 4 min
treatment. As such an activation time of 2 minutes may be
sufficient for some purposes but increased activation time may
still provide some enhancement though with significantly
diminishing returns versus the time spent.
[0088] The contact resistance between layers was measured for a
5-layer microstructure produced by the electrochemical fabrication
process using a four-point probe method. The structure measured is
depicted in FIG. 8. Before plating each nickel layer, the base
surface was activated by an in-situ cathodic activation at 50
.mu.A/cm.sup.2 for 5 min. The measured total resistance for this
microstructure was 201 .mu..OMEGA.. Neglecting any contribution to
total resistance from the interfaces between layers, the resistance
for this bulk microstructure can be calculated. For the pure nickel
a resistivity of 7.2 .mu..OMEGA.-cm is known, which in turn yields
a total anticipated resistance for the nickel structure (of the
configuration tested) to be 195.3 .mu..OMEGA.. Comparing this to
the measured resistance and assuming any difference is the result
of the summed contact resistance for each layer, then the contact
resistance for each layer is only 1.14 .mu..OMEGA.. Since the
contact resistance represents the resistance of the oxide film at
the interface, this small contact resistance means that only very
little oxide was present. Since the actual resistivity of the
interlayer portions of the nickel deposit from the sulfamate bath
could be greater than that of the pure nickel, the actual contact
resistance could be even less.
[0089] Experiments were run using other activation processes with
the results being shown in FIGS. 7(b) and 7(c). The other
activation processes included acid dipping, and use of two
commercial activation products known as Original C-12 (from Puma
Chemical of Warne, N.C.) and Multiprep 506 (from MacDermid, Inc. of
Waterbury, Conn.). The potentials of the nickel samples after acid
dipping (acid activation) in 20% HCl and in 20% H.sub.2SO.sub.4 by
volume were measured in a 5% Na.sub.2SO.sub.3 solution at room
temperature. The results are shown in FIG. 7(b). In the Original
C-12 activator solution, the nickel surface can be activated either
by simple immersion or by applying a voltage of 2V between the
cathode (which is the nickel sample) and an anode for 30 to 60
seconds. The measured stable potentials in a 5% Na.sub.2SO.sub.3
solution at room temperature for a selected time for each treatment
method are shown in FIG. 7(c). The Multiprep 506 solution was used
to activate a nickel surface by dipping the surface into the
solution at 55.5.degree. C. for 2.5 minutes. The measured stable
potential after the treatment in a 5% Na.sub.2SO.sub.3 solution at
room temperature is shown in FIG. 7(c).
[0090] As can be seen from these figures the in situ cathodic
activation process yielded larger negative voltages and thus higher
levels of activation. The stable nickel potentials in the
Na.sub.2SO.sub.3 solution after the acid treatment, the Original
C-12 treatment, and the Multiprep 506 treatment were more negative
than that of the untreated sample, but more positive than that of
the in-situ cathodically treated sample. Although the measured
potentials do not reveal the extent of adhesion of the deposit
resulting from the different treatment methods, the most active
nickel surface was obtained by the in-situ cathodic treatment since
the treated samples had the most negative potential undergoing both
the 2 minute and 4 minute treatments among all tested activation
methods.
[0091] Adhesion tests were performed with measurements being
obtained from three different methods: an adhesion method which is
schematically depicted in FIG. 9(a), a soldering method which is
schematically depicted in FIG. 9(b), and the Ollard method which is
schematically depicted in FIG. 9(c) where measurements were made
using an Instron Model 4204 universal testing instrument (Instron
Corporation of Canton, Mass.) using a crosshead speed of 5
mm/minute. Adhesion tests showed that samples that under went in
situ cathodic activation resulted in improved adhesion strength
compared to samples where deposition occurred without any
activation process. In a total of seven tests, under specific
conditions, using in situ cathodic activation, five strengths were
measured to be between about 32-40 MPa with one measurement at
about 23 MPa and a final measurement at about 47 MPa. Four tests
where no activation process was used yielded three strengths
between about 14-20 MPa and one strength at about 2 MPa.
[0092] It is clear from these results that the in situ cathodic
activation process provides a very active surface with enhanced
adhesion between the substrate and the deposit. It is anticipated
that the in situ cathodic activation process can be combined with
other standard or commercial methods so that even better coating
adhesion may be realized. Furthermore it is believed that post
formation heat treatment may be used to greatly improving the
adhesion strength of metallic deposits.
[0093] Various other embodiments of the present invention exist.
Some of these embodiments may be based on a combination of the
teachings herein with various teachings incorporated herein by
reference. Some embodiments may not use any blanket deposition
process and/or they may not use a planarization process. Some
embodiments may involve the selective deposition of a plurality of
different materials on a single layer or on different layers. Some
embodiments may use blanket depositions processes that are not
electrodeposition processes. Some embodiments may use selective
deposition processes on some layers that are not conformable
contact masking processes and are not even electrodeposition
processes. Some embodiments may use nickel as a structural material
while other embodiments may use different materials such as gold,
silver, or any other electrodepositable materials that can be
separated from the copper and/or some other sacrificial material.
Some embodiments may use copper as the structural material with or
without a sacrificial material. Some embodiments may remove a
sacrificial material while other embodiments may not. In some
embodiments the anode may be different from the conformable contact
mask support and the support may be a porous structure or other
perforated structure. Some embodiments may use multiple conformable
contact masks with different patterns so as to deposit different
selective patterns of material on different layers and/or on
different portions of a single layer. In some embodiments, the
depth of deposition will be enhanced by pulling the conformable
contact mask away from the substrate as deposition is occurring in
a manner that allows the seal between the conformable portion of
the CC mask and the substrate to shift from the face of the
conformal material to the inside edges of the conformable
material.
[0094] In view of the teachings herein, many further embodiments,
alternatives in design and uses of the instant invention will be
apparent to those of skill in the art. As such it is not intended
that the invention be limited to the particular illustrative
embodiments, alternatives, and uses described above but instead
that it be solely limited by the claims presented hereafter.
* * * * *