U.S. patent application number 11/927361 was filed with the patent office on 2008-07-31 for method for electrochemical fabrication.
This patent application is currently assigned to University of Southern California. Invention is credited to Adam L. Cohen.
Application Number | 20080179279 11/927361 |
Document ID | / |
Family ID | 21928664 |
Filed Date | 2008-07-31 |
United States Patent
Application |
20080179279 |
Kind Code |
A1 |
Cohen; Adam L. |
July 31, 2008 |
Method for Electrochemical Fabrication
Abstract
An electroplating method that includes: a) contacting a first
substrate with a first article, which includes a substrate and a
conformable mask disposed in a pattern on the substrate; b)
electroplating a first metal from a source of metal ions onto the
first substrate in a first pattern, the first pattern corresponding
to the complement of the conformable mask pattern; and c) removing
the first article from the first substrate, is disclosed.
Electroplating articles and electroplating apparatus are also
disclosed.
Inventors: |
Cohen; Adam L.; (Rancho
Palos Verdes, CA) |
Correspondence
Address: |
MICROFABRICA INC.;ATT: DENNIS R. SMALLEY
7911 HASKELL AVENUE
VAN NUYS
CA
91406
US
|
Assignee: |
University of Southern
California
|
Family ID: |
21928664 |
Appl. No.: |
11/927361 |
Filed: |
October 29, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11622279 |
Jan 11, 2007 |
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11927361 |
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10677409 |
Oct 1, 2003 |
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11622279 |
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09493496 |
Jan 28, 2000 |
6790377 |
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10677409 |
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09055183 |
Apr 3, 1998 |
6027630 |
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09493496 |
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60043742 |
Apr 4, 1997 |
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Current U.S.
Class: |
216/33 ;
205/640 |
Current CPC
Class: |
C25D 17/06 20130101;
C25D 5/10 20130101; B81C 1/00126 20130101; B81C 2201/032 20130101;
Y10T 428/12486 20150115; C25D 5/022 20130101; C25D 5/22 20130101;
B81C 2201/0197 20130101; C25D 5/12 20130101; H05K 3/241 20130101;
B33Y 10/00 20141201; B81C 2201/0181 20130101; H01L 21/2885
20130101; C25D 1/00 20130101; B33Y 70/00 20141201; C25D 1/003
20130101; Y10T 428/239 20150115 |
Class at
Publication: |
216/33 ;
205/640 |
International
Class: |
B32B 38/00 20060101
B32B038/00; C25F 3/16 20060101 C25F003/16 |
Claims
1. A method for fabricating a multi-layer three-dimensional
structure, comprising: (i) forming a first layer, comprising: a)
providing a first mask in contact with a substrate, wherein the
mask has a first pattern of openings therein; b) depositing a first
pattern of a first material from a source of the first material
onto said substrate using the first mask to form a portion of a
first layer, wherein the first material comprises a sacrificial
material or a structural material; c) removing the first mask from
the substrate; d) depositing a second material onto the substrate,
wherein the second material comprises the other of a structural
material or a sacrificial material; (ii) building additional layers
adjacent to and adhered to previously formed layers; and (iii)
removing undesired elements of structural material from at least
the first layer via etching or electropolishing.
2. The method of claim 1 wherein the first material is a first
metal.
3. The method of claim 2 wherein the second material is a second
metal.
4. The method of claim 3 wherein the first metal is the sacrificial
material and the second metal is the structural material.
5. The method of claim 4 wherein the undesired elements of the
second metal are removed via chemical etching.
6. The method of claim 4 wherein the undesired elements of the
second metal are removed via electropolishing.
7. The method of claim 3 wherein the first metal is the structural
material and the second metal is the sacrificial material.
8. The method of claim 7 wherein the undesired elements of the
first metal are removed via chemical etching.
9. The method of claim 7 wherein the undesired elements of the
first metal are removed via electropolishing.
10. The method of claim 1 wherein the forming of the first layer
comprises removing a portion of at least one of the deposited
materials.
11. The method of claim 10 wherein the removing is performed during
a process of planarizing a surface of the first layer.
12. The method of claim 1 wherein the first material comprises a
sacrificial material and the second material comprises a structural
material, and wherein the method additionally comprises: (iii)
releasing the structural material from the sacrificial material
after formation of the multi-layer structure.
13. The method of claim 1 wherein the first material comprises a
structural material and the second material comprises a sacrificial
material, and wherein the method additionally comprises: (iii)
releasing the structural material from the sacrificial material
after formation of the multi-layer structure.
14. A method for fabricating a multi-layer three-dimensional
structure, comprising: (i) forming a first layer, comprising: a)
providing a first mask in contact with a substrate, wherein the
mask has a first pattern of openings therein; b) depositing a first
pattern of a first material from a source of the first material
onto said substrate using the first mask to form a portion of a
first layer; c) removing the first mask from the substrate; d)
providing a second mask in contact with the substrate, and/or first
material, wherein the mask has a second pattern of openings
therein; e) etching a void, having a second pattern, into the
substrate and/or the first material using the second mask; f)
removing the second mask from the substrate and/or first material;
g) depositing a second material into the void; and (ii) building
layers adjacent to and adhered to previously formed layers, wherein
at least one of first or second materials is a structural material
and removing an undesired portion of the structural material via an
etching or electropolishing operation.
15. The method of claim 14 wherein the first material is a first
metal.
16. The method of claim 15 wherein the second material is a second
metal.
17. The method of claim 16 wherein the first metal is the
sacrificial material and the second metal is the structural
material.
18. The method of claim 17 wherein the undesired elements of the
second metal are removed via chemical etching.
19. The method of claim 16 wherein the undesired elements of the
second metal are removed via electropolishing.
20. The method of claim 15 wherein the first metal is the
structural material and the second metal is the sacrificial
material.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. patent
application Ser. No. 11/622,279, filed Jan. 11, 2007 which in turn
is a continuation of U.S. patent application Ser. No. 10/677,409,
filed Oct. 1, 2003 which in turn is a continuation of U.S. patent
application Ser. No. 09/493,496, filed Jan. 28, 2000 which is a
divisional of U.S. patent application Ser. No. 09/055,183, filed
Apr. 3, 1998, now U.S. Pat. No. 6,027,630; which in turn claims
priority to U.S. Provisional Patent Application No. 60/043,742,
filed on Apr. 4, 1997. Each of these prior applications is
incorporated herein by reference as if set forth in full.
BACKGROUND OF THE INVENTION
[0002] The invention relates to forming structures by
electrochemical deposition.
[0003] Microfabrication processes (also referred to as
micromachining) are being developed and refined for eventual
application to the manufacture of complex devices including
machines and instrumentation. These processes are being directed to
the production of machines of miniaturized devices having features
in the range of a few microns and in some cases features in the
submicron range, some of which currently exist on a macroscopic
scale.
[0004] Microfabrication processes include: bulk micromachining, in
which material is removed from regions of a substrate; surface
micromachining, in which a thin conformal structural layer and one
or more sacrificial layers are deposited onto a substrate; and
LIGA, which generates 2.5-D extruded shapes by molding materials
around metals molds which were formed by the metals being
electrodeposited within openings in thick synchrotron-processed
photoresists. These processes are used to produce structures of
simple geometries (e.g., they can be defined by 1-4 different cross
sections), and are usually customized for each application.
[0005] Solid freeform fabrication, which is also referred to as
rapid prototyping, is used to manufacture macroscopic parts from
hundreds of layers by generating one layer at a time. These
processes produce features typically greater than 50-100 um in
width using layers typically greater than 50-150 um thick. These
processes typically generate a layer serially. These processes
employ structures for supporting the part being manufactured. The
support structures are often customized to the part.
SUMMARY OF THE INVENTION
[0006] In one aspect, the invention features an electroplating
method that includes: a) contacting a first substrate with a first
article, which includes a substrate and a conformable mask disposed
in a pattern on the substrate; b) electroplating a first metal from
a source of metal ions onto the first substrate in a first pattern,
the first pattern corresponding to the complement of the
conformable mask pattern; and c) removing the first article from
the first substrate.
[0007] In preferred embodiments, the method further includes
electroplating a second metal from a second metal ion source onto
the first substrate. In one embodiment, the step of electroplating
the second metal includes: a) contacting the first substrate with a
second article including a substrate and a conformable mask
disposed in a pattern on the substrate; b) electroplating a second
metal onto the first substrate in a second pattern, the second
pattern corresponding to the complement of the conformable mask
pattern of the second article; and c) removing the second article
from the first substrate. The method can further include building
additional layers.
[0008] In one embodiment, the invention features an electroplating
method that includes repeatedly contacting a substrate with a
patterned conformable mask; electroplating a first metal form a
source of ions onto the substrate in a pattern, the pattern
corresponding to the complement of the conformable mask pattern;
and removing the mask from the substrate.
[0009] In another embodiment, the invention features a method for
manufacturing an element that includes forming a multi-layer
structure by repeatedly forming layers according to the
above-described electroplating methods.
[0010] In another aspect, the invention features an electroplating
article that includes a substrate having a first major surface and
a conformable mask disposed in a pattern on the first major surface
of the substrate. The article is capable of electroplating a
pattern of metal complementary to the pattern of the conformable
mask onto an electrode when the article is placed in contact with
the electrode in the presence of a metal ion source and subjected
to an electric field.
[0011] In other aspects, the invention features an electroplating
apparatus that includes an electrolyte, which includes ions of a
first metal and ions of a second metal, an anode in contact with
the electrolyte, a cathode in contact with the electrolyte, and a
first article (e.g., the above described electroplating article) in
contact with the electrolyte.
[0012] In one embodiment, the electroplating apparatus includes a
first electroplating reservoir that includes an electrolyte, which
includes a first metal ion, disposed within the first reservoir, an
anode in contact with the electrolyte, a cathode in contact with
the electrolyte, and an article (e.g., an article described above)
in contact with the electrolyte; a second electroplating reservoir
that includes an electrolyte, which includes ions of a second
metal, disposed within the second reservoir, and an anode in
contact with the electrolyte.
[0013] In another aspect, the invention features a method for
manufacturing an electroplating article. The method includes: a)
applying a conformable mask to an article comprising a first
substrate and a patterned resist disposed on the first substrate;
b) contacting a second substrate to said conformable mask such that
the conformable mask obtains a pattern complementary to the resist
pattern; c) separating the first substrate from the conformable
mask (the conformable mask remaining adhered to the article); and
d) removing the resist.
[0014] In one embodiment, the method for manufacturing an
electroplating article includes providing a porous medium having a
first surface; b) treating said porous medium to create one or more
nonporous regions; c) applying a film to said first surface of said
porous medium; d) patterning the film to create a patterned mask;
and e) removing at least a portion of the one or more nonporous
regions.
[0015] In other aspects, the present invention is directed to the
calculation, storage and retrieval of cross section geometry of a
three dimensional object for generation of patterned masks
reflecting that geometry and for use in an electroplating method.
The data and control processes of various embodiments of the
invention can be implemented by a software application program
executed in a general purpose computing system.
[0016] The data and control processes of various embodiments of the
invention can be embodied in an electroplating method implemented
via the application program and also in an article of manufacture,
in the form of a data storage medium that stores application
program code arranged to carry out that method upon execution by a
processor.
[0017] The electroplating methods and articles allow fabrication of
devices from thin layers of materials such as, e.g., metals,
polymers, ceramics, and semiconductor materials. The electroplating
methods produce relatively homogeneous, isotropic elements (e.g.,
devices) without interlayer junctions. The electroplating methods
can be performed at low temperatures, thus allowing substrates such
as integrated circuits and silicon wafers to be used as plating
substrates.
[0018] The electroplating methods of various embodiments of the
invention can be used to fabricate devices of freeform geometry
including high aspect ratio devices, hollow devices with internal
features, devices with cantilevered and "chandelier" geometries,
and functional assemblies of interconnected, stationary or moving
parts (i.e., devices fabricated in an assembled state). The
electroplating articles, apparatus, and methods also are
particularly useful in mass production of devices.
[0019] Other features and advantages of various aspects of the
invention will be apparent from the following description of the
preferred embodiments thereof, and from the claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] FIG. 1 is view taken in cross section of an electroplating
article according to one embodiment of the invention;
[0021] FIG. 2 is a view taken in cross section of an electroplating
article according to a second embodiment of the invention;
[0022] FIGS. 3a-3d are diagrams of a first embodiment of a method
for forming an electroplating article;
[0023] FIGS. 4a-4e are diagrams of a second embodiment of a method
for forming an electroplating article;
[0024] FIGS. 5a-5e are diagrams of a third embodiment of a method
for forming an electroplating article;
[0025] FIGS. 6a-6d are diagrams of a fourth embodiment of a method
for forming an electroplating article;
[0026] FIGS. 7a-7f are diagrams of a fifth embodiment of a method
for forming an electroplating article;
[0027] FIGS. 8a-8e are diagrams of a sixth embodiment of a method
for forming an electroplating article;
[0028] FIGS. 9a-9c are diagrams of a seventh embodiment of a method
for forming an electroplating article;
[0029] FIGS. 10a-10c are diagrams of a method for forming a deposit
according to an electroplating method of an embodiment of the
invention;
[0030] FIGS. 11a-11m are diagrams of a method according to the
electroplating method of an embodiment of the invention;
[0031] FIGS. 12a-12c are diagrams of a method according to the
electroplating method of an embodiment of the invention;
[0032] FIGS. 13a-13i are diagrams of a method for fabricating an
element on an integrated circuit;
[0033] FIGS. 14a-14e are diagrams of a method for assembling
elements fabricated together;
[0034] FIGS. 15a-15b are diagrams of an element manufactured
according to the electroplating method of an embodiment of the
invention;
[0035] FIGS. 16a-16d are views taken in cross section of elements
manufactured according to one embodiment of the invention;
[0036] FIG. 17 is an electroplating apparatus according to one
embodiment of the present invention;
[0037] FIG. 18 is a view taken in cross section of a substrate in
contact with an electroplating article;
[0038] FIG. 19 is a top view of a portion of an electroplating
apparatus of an embodiment of the invention;
[0039] FIG. 20 is a top view of a portion of an electroplating
apparatus according to an embodiment of the present invention;
[0040] FIG. 21 is a top view of a portion of an electroplating
apparatus according to an embodiment of the present invention;
[0041] FIG. 22 is a view taken in cross section of an
electroplating article holder of an embodiment of the present
invention;
[0042] FIG. 23 is a view taken in cross section of an
electroplating apparatus of an embodiment of the present
invention;
[0043] FIG. 24 is a highly enlarged view taken in cross section of
a substrate in position in the electroplating apparatus of FIG.
23;
[0044] FIG. 25 is a view taken in cross section of a portion of an
electroplating apparatus of an embodiment of the invention;
[0045] FIG. 26 is a view taken in cross section of another portion
of the electroplating apparatus of FIG. 25;
[0046] FIG. 27 is a diagram of a three dimensional object (shown in
two dimensions) with cross section lines indicated;
[0047] FIG. 28 is a functional block diagram of a computing system
configured for calculation of cross sections of a three dimensional
structure and for driving an electroplating apparatus of an
embodiment of the present invention;
[0048] FIG. 29 is a flow diagram illustrating a method for
generating mask pattern files and apparatus control files;
[0049] FIG. 30 is a flow diagram illustrating a method for
manufacturing a three dimensional object;
[0050] FIG. 31 is a view taken in cross section of an
electromagnetic motor;
[0051] FIGS. 32a-32d are diagrams of an electroplating method
employing more than one article according to a third embodiment of
the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0052] The embodiments feature electroplating methods, apparatus
and articles that enable the manufacture of elements having complex
structures. The electroplating methods include selective
electroplating of layers that may include both structural materials
(e.g., metals) and support (i.e., sacrificial) materials; and
subsequent removal (e.g., by etching, melting, or electrolytically
dissolving) of the support materials. The structural material
remaining after removal of the support material defines an element
such as a microscopic or mesoscopic device. The electroplating
methods employ electroplating articles that include a patterned
conformable mask, optionally adhered to a support such as an
electrode or a porous medium.
[0053] In general, various embodiments of the invention feature
electroplating articles for use in electroplating methods. The
electroplating method occurs in an electroplating apparatus that
includes an electroplating bath filled with electrolyte, an anode,
and a cathode. The electrolyte contains metal ions and, optionally,
other additives. The anode can be part of the electroplating
article, as described below, or can be located at a distance from
the article. Throughout this application, the substrate to be
plated functions as the cathode unless otherwise specified. To
simplify the description, the materials are referred to as metals
and similar features are indicated with the same reference
numerals.
[0054] Electroplating Article
[0055] Referring to FIG. 1, electroplating article 4, of a
preferred embodiment of the invention includes a patterned
conformable mask 6 adhered to a support 8. The electroplating
article can also be only a patterned conformable mask (i.e. without
a support). The support can be a porous medium (e.g., a filter), an
anode, and combinations thereof. The article can include a
plurality of different mask patterns on a single support. The
different mask patterns can be contacted by a substrate in a
predetermined sequence to sequentially plate a plurality of metal
layers where each metal layer has a pattern corresponding to the
complement of the mask pattern contacted, to form a multi-layered
element. Referring to FIG. 2, electroplating article 4 can include
one or more edge masks 13 on the outer surface of the article, for
confining the metal being plated.
[0056] Contact between the electroplating article and the substrate
to be plated is made by pressing the patterned mask against the
substrate using a well-controlled, uniform pressure. The
appropriate masking pressure will prevent flash (i.e., the
deposition of metal in the area covered by the mask), and will
prevent distortion of the features defined by the mask. When the
electroplating article is removed from contact with the substrate,
the mask remains adhered to the support and thus remains part of
the electroplating article.
[0057] A variety of methods can be used to improve release of the
mask from the substrate to be plated so as to prevent delamination
of the mask from the support: for example, gradually peeling the
electroplating article (if flexible) off of the substrate
optionally with the aid of a dull blade; adding a
non-stick/lubricating compound to the electrolyte; coating the mask
surface with a non-stick composition (e.g., sputtered
polytetrafluoroethylene); and vibration (e.g., ultrasound).
[0058] Patterned Conformable Mask
[0059] The patterned conformable mask is sufficiently deformable
(e.g., elastically deformable) to permit conformance of the mask to
the surface of a substrate to be plated to maximize contact between
the mask and the substrate, and to minimize (preferably eliminate)
the presence of gaps between the mask and the substrate. Maximizing
contact between the mask and the substrate minimizes the potential
for flash formation. The mask is also sufficiently durable to
enable repeated use (i.e., contacting with and removing from a
substrate). The mask is sufficiently rigid and thin to prevent
distortion of the mask features (i.e., the positive and negative
features constituting the closed and open features of the mask
pattern respectively) by the masking pressure. The mask preferably
is relatively thick compared to its peak and valley roughness and
the curvature of the substrate to be plated.
[0060] The mask preferably exhibits very high volume electrical
resistivity (e.g., 10.sup.14 Ohm-cm), has a very low permeability
to ions in the electrolyte solution, and is chemically non-reactive
with the plating electrolytes at the temperatures at which the
plating operation is conducted. The mask can be hydrophilic or
hydrophobic, with hydrophilic being preferred. In the case of
hydrophobic materials, relatively higher amounts of wetting agents
can be included in the electrolyte to ensure wetting of the mask
material.
[0061] The mask preferably is capable of forming a strong bond
(e.g., a chemical or mechanical bond) to the support, such that
small (e.g., 15.times.15 .mu.m) isolated positive features are not
delaminated by the mask fabrication process, normal handling of the
mask or by removal of the mask material from the substrate to be
plated.
[0062] The patterned mask is preferably substantially planar and
smooth to enable conformance to the substrate to be plated. The
mask is capable of being patterned with negative and positive
features of varying dimensions (e.g., 10-25 um or smaller, such as
submicron), preferably with no mask residue blocking the negative
features of the mask pattern. The pattern of the mask includes
apertures (i.e., negative features) extending through the mask
thickness and defined by one or more sidewalls of the mask. The
mask features preferably have a substantially planar wall profile
and may have a slight wall angle. The wall angle may be slightly
divergent toward the substrate to be plated, i.e. the negative
features are slightly larger at the substrate than at the support.
Such wall angles may aid in separating the mask from the substrate
and may aid in facilitating re-contacting the mask to the substrate
in the presence of an existing deposit.
[0063] The mask can be compound so as to include more than one
layer of material, e.g., a relatively rigid layer (e.g., a high
aspect ratio photoresist, e.g., SU-8 commercially available from
MicroChem Corporation or synchrotron-processed
polymethylmethacrylate), and a conformable layer. Another example
of a useful rigid layer is a positive photoresist such as Clariant
AZ4620, which can be patterned by exposing it to ultraviolet light
through the patterned conformable layer.
[0064] Examples of useful masking compositions for conformable
portions of the mask include elastomers such as, e.g.,
polydimethylsiloxane (i.e., silicone rubber) commercially
available, e.g., under the trade designation Sylgard from
Dow-Corning (e.g., Sylgard 182 and 184), and under the trade
designation RMS-033 from Gelest. The masking compositions can
include other additives, e.g., photoinitiators, fillers, and
hydrogen getters.
[0065] Porous Medium
[0066] The porous medium has interconnected pores and is permeable
to ions and additives present in electrolyte compositions. The
porous medium can have one or more layers of varying porosity. The
porous medium preferably has a pore size considerably finer than
the minimum negative feature of the mask. The pores are preferably
uniform in open area, e.g., the open area of any 20 .mu.m square of
the medium is consistent to 1%. Particularly useful porous mediums
may be porous mediums that are useful as filters, and particularly
those that have a particle retention rating in the range of 0.3-3
.mu.m. For those porous mediums that include multiple porous
layers, each porous layer can vary in porosity and pore size, with
the porous medium in closest proximity to the substrate to be
plated exhibiting the above characteristics. The surfaces of the
porous medium that contact the mask should be sufficiently flat and
smooth to ensure that the surface of the adhered mask that contacts
the substrate to be plated is also flat and smooth.
[0067] The porous medium is chemically non-reactive with the
electrolyte solution at the operating temperature of the
electrolyte bath. Preferred porous mediums are hydrophilic. The
porous medium preferably is permeable to gas to allow venting of
gas bubbles generated during the electroplating method.
[0068] Preferably the porous medium is free from shedding (i.e.,
does not release portions of itself into surrounding fluid), and is
sufficiently durable so as to withstand multiple electroplating
operations. Examples of suitable porous medium materials include
rigid, hydrophilic, slip cast ceramic disk porous mediums
(commercially available from Coors Ceramics) and hydrophilized
membrane porous mediums made from, e.g., polypropylene
(commercially available under the trade designation GH from
Gelman), polyvinylidenefluoride (commercially available under the
trade designation Durapore from Millipore) and
polytetrafluoroethylene (commercially available under the trade
designation LCR from Millipore). Rigid porous mediums can provide
masking pressure when supported by their edges alone.
[0069] Particularly useful highly permeable, porous mediums include
relatively thin, flexible, porous membranes. Porous membranes can
be combined with a more rigid porous medium, which serves as a
backing to provide the requisite pressure for masking applications.
The porous membrane can be sandwiched between the more rigid porous
medium and the mask and the porous medium can be used to supply the
requisite masking pressure for the plating operation. The more
rigid porous medium can have a relatively more coarse (i.e.,
larger) porosity than that useful for direct contact with the mask.
Porous membranes can be integrated with the mask composition (or
transformed into a mask).
[0070] To assist handling, porous membranes can be installed in the
drumhead fixture described below, or temporarily adhered to a rigid
flat substrate (e.g., a silicone wafer, glass) with an adhesive
composition (e.g., dry film photoresist). Porous membranes can be
processed while adhered to the substrate and, after processing,
removed by dissolving the adhesive.
[0071] Masking pressure can be applied to the porous membrane by
the momentum of a stream or jet of electrolyte impinging on the
membrane from behind, optionally in combination with dense
particles incorporated into the electrolyte, and increasing the
viscosity of the electrolyte, for example, by the addition of a
polymer. Masking pressure can also be applied to the membrane by
sealing the membrane against the walls of the tank of the
electroplating system and then pressurizing the electrolyte,
causing the membrane to be pushed against the substrate to be
plated. A dummy substrate can be used when the substrate to be
plated is smaller than the porous medium to prevent the membrane
from bulging.
[0072] One example of an electroplating method that employs a
porous membrane includes pressing a relatively more rigid porous
medium against the membrane, applying current, depositing a metal
for a period, removing the current, withdrawing the rigid porous
medium from contact with the membrane, slightly displacing the
relatively more rigid porous medium in its own plane (e.g., in an
orbital or linear fashion), and repeating the cycle. Displacing the
relatively more rigid porous medium during each cycle allows a
different portion of the rigid porous medium to make contact with
the membrane. Preferably the mask/membrane separates from the
substrate to be plated while the relatively more rigid porous
medium is separated from the membrane so as to allow exchange of
fluids between the microvolume and bulk electrolyte.
[0073] Another membrane plating method includes pressing a granular
medium, tiny spheres, or rollers against the membrane using, e.g.,
a rigid screen. The tiny spheres and rollers can be rotated in a
pattern (e.g., a linear pattern using linear movement or a circular
pattern using an orbital movement) on the membrane continuously or
intermittently so as to average the local non-uniformities in pore
structure of the rollers/spheres. Preferably the amplitude of
movement is equal to (more preferably several times greater than)
the diameter of the sphere or cylinder. Preferably the
spheres/cylinders are relatively small and the membrane is
relatively thick. The spheres/cylinders can be made of the metal
being plated.
[0074] Anode
[0075] The electroplating article can consist of a patterned mask
on an anode. The anode can be soluble or insoluble, rigid or
flexible, porous or nonporous, and can include an erodable layer
(e.g., a metal layer) supported by a conductive material that does
not erode (e.g., platinized titanium). The anode can be of any
dimension including a thin flexible sheet of metal.
[0076] A soluble anode will tend to erode during use. The anode can
be "redressed" periodically by reversing the polarity of the anode
and plating metal back onto the anode through the negative features
of the mask. The excess metal is supplied by the electrolyte in
conjunction with another anode according to, e.g., through-mask
plating processes used in electronics manufacturing. For a system
in which the mask is physically supported by and attached to a
porous medium, and an anode is located directly behind the
membrane, moving the anode will prevent localized erosion of the
anode.
[0077] Forming Electroplating Articles
[0078] In general, methods for forming electroplating articles
include applying a solid mask or liquid masking composition to a
support, i.e., an anode, a porous medium and combinations thereof.
The solid mask can be patterned prior or subsequent to attachment
to the support. Liquid masking compositions can be patterned on a
non-porous substrate (e.g., inert material, or a material that can
be dissolved or melted (e.g., substrates of plastic, lacquer, or
low melting point alloy)), cured (e.g., crosslinked, polymerized,
hardened, solidified, gelled, and combinations thereof), and
attached to a support or patterned and solidified directly on the
support.
[0079] Preparation of the Support
[0080] It is preferable to planarize the surface of the support
that will receive the mask, so as to provide a smooth flat surface
for receiving the mask. When applying the mask to an anode, it is
preferable to first prepare the anode surface so as to maximize
adhesion to the mask. Examples of useful anode surface preparation
methods include chemical microetching, lapping, sandblasting, and
sintering a thin layer of powder onto the surface. A chemical
adhesion promoter (e.g., Sylgard Prime Coat) can also be used.
[0081] A variety of methods can be used to maintain or improve
adhesion of the mask to a porous medium. These methods include
melting the mask while pressing it into the porous medium resulting
in a mechanical interlocking of the mask with the porosity of the
porous medium, and applying an adhesive composition between the
mask and the porous medium. Adhesion of the mask to the porous
medium can also be enhanced by employing an adhesive that is a
meltable material (e.g., glass), which can be dry deposited (e.g.,
sputtered) onto the surface of the patterned mask. When using an
adhesive composition, it is preferable to employ methods that
confine the adhesive composition to the areas located between the
mask and the support (e.g., preventing the adhesive from bridging a
negative feature that is only a few microns wide).
[0082] Liquid masking compositions have a tendency to soak into
(i.e., uncontrollably absorb into) the pores of a porous medium. A
variety of methods can be employed to reduce "soak in" in regions
of the porous medium that are to remain porous. Examples of
suitable methods for preventing soak in include: (1) supplying
pressurized air to one side of the porous medium; (2) treating the
porous medium with a temporary filler composition that soaks in and
fills the pores and then solidifies to form a barrier to
penetration of the liquid masking composition; and (3) treating the
porous medium with a temporary filler composition that is
immiscible with and denser than the liquid masking composition. The
surface of the porous medium can be abraded after infiltrating the
pores with filler composition to expose uncoated and unfilled
surfaces allowing direct adhesion of the mask to the support. The
filler composition can be dissolved or otherwise removed from the
porous medium after the liquid masking composition has been cured
to a solid.
[0083] Examples of useful filler compositions include
acetone-soluble waxes and lacquers, soluble waxes used for
investment casting cores, water soluble salts, gels, Crystal Bond
509, soluble thermoplastics, and phase-change materials (e.g., ice,
electrorheological fluids).
[0084] Referring to FIGS. 3a-3d, one example of a method for
rendering a porous medium temporarily nonporous using a filler
composition includes: spinning a thin layer of a liquid filler
composition 132 onto a relatively flat surface 131 (e.g., a silicon
wafer) (preferably the thickness of the filler composition layer is
adjusted so as to fill the pores of the porous medium to a
predetermined height); contacting a first surface 136 of porous
medium 130 to the spun-on filler composition 132 (FIG. 3a);
allowing filler composition 132 to seep into the pores of the
porous medium to a predetermined height (FIG. 3b); solidifying the
filler composition 132; and applying (e.g., by spinning on) a
sufficient amount of liquid masking composition 134 to a second
surface 138 of the porous medium 130 opposite the first surface 136
through which filler composition 132 entered the porous medium 130.
Liquid masking composition 134 is applied so as to produce a layer
of masking composition of desired thickness on the surface of the
porous medium. The remainder of the liquid masking composition 134
can seep into the porous medium (for purposes of adhesion) only to
the surface of the solidified filler 132 (FIG. 3c). The method
further includes curing the masking composition 134; removing
solidified filler 132; etching the negative features of the mask
through the layer of porous medium 130 that is saturated with
masking composition 134 to at least a depth at which the solidified
filler 134 existed (FIG. 3d).
[0085] Other methods for preventing or limiting soak in include
restricting the volume of liquid masking composition that is
applied to the porous medium to only a fraction of the pore volume
in the porous medium causing the liquid to only partially fill the
pores. One such method includes spraying a liquid masking
composition onto the porous medium, while carefully controlling the
flow rate and speed of the spray pattern. Another method involves
spin coating the liquid masking composition onto a non-absorbing
sheet to obtain a uniform thin layer, and placing the porous medium
in contact with the spun on liquid masking composition. When the
porous medium is peeled away from the sheet or the sheet is
dissolved or melted, a thin coating of masking composition is
transferred to the porous medium (i.e., the masking composition
remains adhered to the porous medium). The liquid masking
composition can be cured prior to or subsequent to removal of the
sheet.
[0086] Another method for preventing soak in involves applying the
liquid masking composition to a porous medium while the porous
medium is spinning at high speed; the centrifugal forces spread the
masking composition into a thin layer before it has had time to
soak in excessively.
[0087] Another approach to preventing soak in involves forming a
barrier layer at or near the surface of the porous medium. After
processing, the barrier layer (and optionally, some of the porous
medium) is removed from the negative features of the mask, so as to
expose the porosity of the porous medium. Optionally, to improve
adhesion of the mask to the support, the regions of the barrier
layer that will correspond to the positive features of the mask can
be removed prior to application of the mask. The barrier layer can
be removed using various techniques including, e.g., chemical
etching, dry etching, ion milling, laser machining, and melting
(e.g., for thermoplastic based barriers). The barrier layer can
also be formed by applying another material to the surface of the
porous substrate, e.g., (1) by laminating a film of a solid
material, such as dry film photoresist onto the porous medium; (2)
by applying a liquid barrier layer, preferably of high viscosity,
using one of the techniques discussed above that restrict soak-in
volume; (3) by coating the porous medium with a thin layer of
powder and melting the powder layer so as to form a non-porous
coating; (4) by depositing a barrier film by vacuum evaporation,
sputtering, CVD, or other process; and (5) by using combinations
thereof.
[0088] In the case of a porous anode, soak in can be prevented
using a variety of methods which include, for example, (1) applying
a nonporous layer to the surface of the porous anode and, after
patterning the mask, removing the nonporous layer in the negative
areas of the mask to expose the anode; (2) sintering a
partly-compacted powder of anode material in a mold to create a
sintered anode with an outer non-porous layer, patterning the mask
from a masking material that is applied over the sintered material,
and immersing the structure in an etchant that attacks the metal of
the anode, such that the outer non-porous layer of sintered anode
material is dissolved (in the unmasked regions); (3) melting the
surface of the anode (e.g., by flame, or contact with a hot
surface), then patterning the mask and removing the melted surface
material to expose the porous anode material in unmasked regions;
and (4) temporarily filling the surface pores with a material,
e.g., metal electrodeposited onto the porous surface, then
patterning the mask and removing the temporary filler material to
expose the porous anode material in unmasked regions.
[0089] Patterning and Fabricating the Electroplating Article
[0090] A variety of methods can be used to pattern the
electroplating article. Referring to FIGS. 4a-4e, an example of a
method for forming an electroplating article is shown. The method
includes forming a micromold 140 by coating (e.g., by spinning) a
layer of resist 142 (e.g., photoresist commercially available under
the trade designation SU-8 5 from MicroChem Corp.) onto a substrate
144 (e.g., a silicon wafer) (FIG. 4a). Preferably the layer of
photoresist has a thickness a few microns greater than that of the
desired thickness of the final mask. The photoresist can be
patterned using a photomask and a light source (e.g., a UV light
source). A positive feature of the resist corresponds to a negative
feature of the mask. Optionally, the micromold can be made from a
non-stick material such as polytetrafluoroethylene or
polypropylene, and can include a pattern formed, e.g., by reactive
ion etching or excimer ablation, or micromolded from a master mold
according to processes similar to processes used in the fabrication
of compact disks.
[0091] The micromold surface including the photoresist and the
substrate can be passivated by allowing the micromold to be exposed
to vapors of, e.g.,
(tridecafluoro-1,1,2,2,-tetrahydrooctyl)-1-trichlorosilane
(commercially available from United Chemical Technologies). A
liquid masking composition 146 is then poured over the raised
pattern defined by the patterned photoresist (FIG. 4b). Support 148
is then pressed against micromold 140 (FIG. 4c). Uniform pressure
is applied such that liquid masking composition 146 is forced out
of the area 150 located between the raised portions (i.e., positive
features) of the resist pattern and the surface of support 148.
Preferably, liquid masking composition 146 is completely squeezed
out of the areas 150 corresponding to the positive features of
resist 142. The entire assembly 152 remains in this mating
relationship until the liquid masking composition has cured. For a
heat-curable masking composition, the assembly can be transferred
to an oven to cure.
[0092] In the case of a mask that has been cured in the oven, the
assembly is quickly disassembled to minimize differential thermal
contraction between support and the mold. The support and cured
mask 156 is pulled away from mold 140 such that cured mask 156
detaches from micromold 140, yet remains adhered to support 148
(FIG. 4d). Mask 156 exhibits a pattern inverse to that of micromold
140. Micromold 140 can be reused. After cure, before or after
detachment of the mask and mold, excess mask material 154
surrounding support 148 is removed as illustrated in FIG. 4e. If
necessary, micromold 140 can be cleaned to remove mask residue. One
example of a useful silicone cleaning composition is a silicone
stripper, e.g., Amtex CCR (commercially available from Amtex
Chemical Corp.).
[0093] Any residual layer of masking composition remaining in
negative features 158 of mask 156 (FIG. 4d) can be removed using
dry etching (e.g., RIE with a mixture of O2 and CF4 gas), which may
also reduce the thickness of the positive features of the mask. The
result of such removal is depicted in FIG. 4e. Uniform etching
extending to the edge of the support can be accomplished by
surrounding the support with a "dummy" substrate preferably of
similar composition, such that non-uniformities due to edge effects
are out of the area of interest.
[0094] When the mask is adhered to a porous medium, the etch may be
continued to remove any barrier layer present in the porous medium
from the negative features of the mask and may be continued until a
porous portion of the porous substrate is removed. If pores in a
porous medium have been filled or are non-existent, the pores are
re-established or established, e.g., by reactive ion etching.
[0095] Another method for forming an electroplating article is
shown in FIGS. 5a-5e. The method includes patterning a photoresist
142 onto a support 148 (i.e., the porous medium or the prepared
anode) to the approximate thickness desired for the final mask
(FIG. 5a). The areas of support 148 occupied by resist 142
correspond to negative features of the mask through which metal can
be deposited. When patterning a porous medium that includes a
barrier, the porous medium can be etched to remove the barrier
layer from those areas of the porous medium that are not covered by
resist. The method further includes applying a liquid masking
composition 146 to support 148 (FIG. 5b), and optionally vacuum
degassing the masking composition. A flat, smooth, non-stick (e.g.,
PTFE) sheet 160 is then pressed against resist 142, and liquid
masking composition 146 parallel to support 148 (FIG. 5c), and
pressure is applied to squeeze the liquid masking composition 146
out from between resist 142 and sheet 160. Masking composition 146
is then cured, sheet 160 is removed, and residual masking
composition overlaying the resist is removed (FIG. 5d), e.g., by
etching (e.g., reactive ionization etching using a mixture of O2
and CF4 gas). Resist 142 is then removed to expose areas of the
support previously occupied by the resist (FIG. 5e). When
patterning a porous medium, mask material that has seeped into the
negative features of the mask from neighboring positive features
can be removed by etching both mask and porous medium to the
required depth. If pores of the porous medium have been filled or
are non-existent, the pores can be established or
re-established.
[0096] Referring to FIGS. 6a-6d, another method for forming an
electroplating article includes applying (e.g., by spinning on) a
layer of photopatternable liquid masking composition 146, e.g.,
RMS-033 (commercially available from Gelest) in combination with a
photoinitiator (e.g., 2,2-dimethoxy-2-phenyl acetophenone
(commercially available from Polysciences, Inc.)), to support 148
(FIG. 6a). Liquid masking composition 146 can be covered with a
thin, oxygen-impermeable film (e.g., Mylar) to protect the
composition from contact with oxygen. Masking composition 146 is
then exposed to patterned light (e.g., UV light transmitted through
a photomask 162) to selectively cure the mask composition (FIG.
6b). The film is removed (FIG. 6c) and the photopatternable masking
composition is developed (e.g., by dissolving with xylene) removing
uncured masking composition 146 (FIG. 6d). If a nonporous barrier
layer exists, it is removed (e.g., by dry etching) from the
negative features of mask 156. Pores are established if necessary.
For those photopatternable masking compositions that are negative
working the porous medium can be completely saturated with masking
composition until there is a surface layer of masking composition
having the desired thickness. After photopatterning, the unexposed
masking composition material (including that in the pores) is
dissolved in the developer.
[0097] When patterning a porous medium, the porous medium can be
tinted a dark shade or coated with an antireflection composition to
reduce the amount of light scattered from the textured surface.
[0098] Referring to FIGS. 7a-7f, another method for making an
electroplating article is shown. The method includes applying a
liquid masking composition 146 (or a solid mask material) to
support 148 (FIG. 7a); curing liquid masking composition to form an
unpatterned solidified mask 156; coating unpatterned mask 156 with
either a thick resist 164 or a thin resist disposed on a thin metal
layer (not shown) (FIG. 7b); patterning resist 164 and, in the case
of a metal layer, using the patterned resist to pattern the metal
layer (e.g., by etching or lift-off) (FIGS. 7c and 7d); selectively
removing (e.g. by wet etch, dry etch, or ion mill) portions of
unpatterned mask 156 to form a patterned mask 156 using thick
resist 164 (and metal layer if present) as a mask (FIG. 7e); and in
the case where the substrate is a porous medium, preferably
removing the top layer of the porous medium to open pores; and
removing, e.g., by stripping, the remaining resist 16a (and metal
layer if used) (FIG. 7f).
[0099] Referring to FIGS. 8a-8c, a method for forming an
electroplating article is shown which includes: applying a liquid
masking composition 146 (or a solid mask material) to support 148
to the desired, thickness; curing (if liquid) the masking
composition to form solidified unpatterned mask 156 (FIG. 8a);
applying a photomask 162 over the mask 156 (FIG. 8b) where the
photomask has light apertures 166 and light barriers 168; exposing
solid mask 156 to patterned ultraviolet light through the photomask
162 (FIG. 8c), the UV light having an intensity and wavelength
suitable for ablating the mask and support material, e.g., a LTV
excimer laser beam; ablating mask 156 until support 148 is exposed
(FIG. 8c); and, when patterning a porous medium, ablating barrier
layer 170, if present (FIG. 8d) and, if necessary, the top layer of
the porous medium to open pores; and removing the photomask to form
the electroplating article 172 (FIG. 8e).
[0100] Methods similar to methods used in relief printing can also
be used to fabricate electroplating articles. One example of such a
method includes: applying a liquid masking composition to a relief
pattern, which might be produced by patterning a high aspect ratio
photoresist such as AZ4620 or SU-8; pressing the relief
pattern/masking composition structure against a support such that
the masking composition adheres to the support; and removing the
relief pattern. The formed electroplating article includes a
support having a mask patterned with the inverse pattern of the
relief pattern.
[0101] Another example of such a method includes: creating a relief
pattern on the support by etching of the support, or by applying a
durable photoresist, e.g., SU-8 of desired configuration; coating a
flat, smooth sheet with a thin, uniform layer of liquid masking
composition; stamping the support/resist against the coated sheet
(e.g., like a stamp and inkpad) to quickly mate those portions of
the liquid composition to the positive features of the
support/resist by unmating them from the smooth sheet (preferably
the support and the sheet are kept parallel); and curing the liquid
masking composition.
[0102] Referring to FIGS. 9a-9c, a method for forming an
electroplating article is shown in which a surface layer of porous
medium 148 is saturated with a liquid masking composition to the
thickness of the desired mask. Liquid masking composition is
solidified producing a matrix 174 of solid mask 156 and porous
medium 148. Matrix 174 is then patterned, e.g., by etching or
ablating selected areas of the matrix to a depth at least equal to
the depth of the matrix "layer", to form electroplating article
176. Alternately, the method can include saturating the entire
porous medium with liquid masking composition, pattern curing the
liquid masking composition, and removing the uncured masking
composition.
[0103] Other methods of forming electroplating articles include,
e.g., applying masking composition selectively to a support by such
processes as screen printing, stencil printing and inkjet printing;
and for porous mediums, melting a surface layer of the porous
medium and forming negative features in the surface of the porous
medium by etching/ablating through the melted layer to expose the
pores of the porous medium and generate a relief pattern. The
methods for forming electroplating articles can also include
etching the negative features (i.e., windows) of the mask pattern
to increase the amount of relief on the electroplating article. In
the case of a porous medium and a printed silicone mask, etching
can be conducted by an oxygen plasma.
[0104] The Electroplating Method
[0105] In general, select embodiments of the invention features
electroplating methods that include contacting a substrate to be
plated with an electroplating article; selectively electroplating a
first metal, e.g., a support or sacrificial metal; and
electroplating a second metal, e.g., a structural metal. The step
of electroplating a second metal can include selectively
electroplating the second metal using an electroplating article or
blanket depositing the second metal. The electroplating method can
be used to plate a single layer of metal or the method can be
repeated such that additional metal is plated onto previously
plated metal layers producing a multi-layered structure. After a
predetermined number of layer(s) have been plated, at least a
portion of the support metal can be removed, e.g., by etching. The
structural metal that remains defines a microscopic or mesoscopic
device.
[0106] The method can also employ two electroplating articles to
plate a single layer of one metal. Referring to FIGS. 10a-10c, a
first metal is plated in a first pattern 230 (FIG. 10a), the same
metal is then plated in second pattern 232 (FIG. 10b), to form
plated metal layer 234 (FIG. 10c). Second pattern 232 may overlap
first pattern 230.
[0107] One example of an electroplating method of an embodiment of
the invention is shown in FIGS. 11a-11m. The method includes
contacting a substrate to be plated 2 (FIG. 11a) with first article
4a, which includes mask 6 and support 8 (FIG. 11b), in the presence
of a first metal ion source (i.e., electrolyte and anode 10);
depositing a first metal 12 (FIGS. 11b and 11c), e.g., a
sacrificial metal; contacting substrate 2 with a second article
14a, which includes mask 16 and a support 18, depositing a second
metal 20, e.g., a structural metal, in the presence of a second
metal ion source (i.e., electrolyte and anode 22) (FIG. 11d;
optionally planarizing the layer; and repeating this method using
differently patterned electroplating articles 4b, 4c, 14b, 14c
(FIGS. 11e-11k) to produce multi-layered structure 24 (FIG. 111),
which, after etching all of sacrificial metal 12, becomes element
26 (FIG. 11m). The second article can include a mask that has
oversized positive features such that the surface area of one or
more positive features of the mask extends beyond the corresponding
surface area of the first plated metal.
[0108] The element formed during the electroplating method can
remain attached to the substrate or can be removed from the
substrate. One method for removing the element includes plating a
first layer of support material onto the substrate such that
etching removes the source of attachment of the element to the
substrate.
[0109] Another electroplating method is depicted in FIGS. 12a-12c.
The electroplating method includes: contacting a substrate to be
plated 2 with an electroplating article (not shown); selectively
depositing a first metal 12 (i.e., either the structural or the
support metal) (FIG. 12a); blanket depositing a second metal 20
(FIG. 12b), and mechanically planarizing the deposited layer to
achieve a flat, smooth layer 28 of precise thickness (FIG. 12c).
The planarized surface can be rinsed to remove abrasive particles
present on the surface. Preferably the support metal is selectively
plated and the structural metal is blanket deposited.
[0110] Examples of useful planarization methods include mechanical
(e.g., diamond lapping and silicon carbide lapping),
chemical-mechanical, and non-mechanical (e.g., electrical discharge
machining), planarization processes. Diamond lapping is a
particularly preferred planarization process. Diamond lapping can
be performed using a single grade of diamond abrasive, e.g., about
1-6 micron, or diamond abrasives of various grades. Lapping with
different grades of abrasive can be performed using separate
lapping plates, or in different regions of a single plate. For
example, a coarse diamond abrasive can be applied to the outer
region of a spinning circular lapping plate, and a fine diamond
abrasive can be applied to the inner region. A removable circular
wall can be provided between the inner and outer regions to
increase segregation. The layer to be planarized first contacts the
outer region of the plate, is then optionally rinsed to remove
coarse abrasive, and then is moved to the inner region of the
plate. The planarized surface can then be rinsed using a solution,
e.g., water-based or electrolyte-based solution, to remove both
abrasive and abraded particles from the planarized layer. The
abrasive slurry preferably is easily removable, e.g.,
water-soluble. Layer thickness, planarity and smoothness can be
monitored, e.g., using an optical encoder, wear resistant stops,
and by mating the layer under a known pressure with a precision
flat metal plate and measuring the resistance across the
plate-layer junction. Thickness of the plated metal can also be
measured by, for example, contacting the plated metal with a mask
having a pattern that is complementary to the plated metal pattern
and measuring the displacement.
[0111] One example of a preferred planarization process includes
allowing the work piece, i.e., the substrate having the layer to be
planarized, to rotate within a "conditioning ring" on the lapping
plate. Lapping can also be performed by moving a workpiece around
the surface of a lapping plate using the X/Y motion stages of the
electroplating apparatus without rotating or releasing the
workpiece. In this way, the tangential motion of the plate with
respect to the substrate rotates through 360 degrees. The timing of
slurry delivery may be synchronized to the motion of the substrate
such that the slurry is delivered to the plate. Movement of the
workpiece can occur in paths other than circular including a path
having a sinusoidal orbit of the form r=r0+AsinB.theta..
[0112] The substrate to be plated can include a conductive surface
or a nonconductive surface provided with a conductive layer. The
substrate to be plated can be planar or nonplanar. The substrate to
be plated can also be a previously electroplated or deposited metal
or a layer that includes at least one metal.
[0113] The electroplating method can be performed, e.g., on an
integrated circuit. One example of an electroplating method
performed on an integrated circuit is shown in FIGS. 13a-13i. To
permit electrical contact during plating, the aluminum pads can be
connected to conductors that terminate at distant contact pads,
which can be temporarily tied together by a bus. Referring to FIGS.
13a-13i, the electroplating method of this embodiment includes:
spin coating a layer of polyimide 34 onto thin copper disk 36;
adhering copper disk 36 to bottom surface of silicon wafer 38 with
the polyimide coated surface of the copper disk contacting the
bottom surface of the wafer (FIG. 13b), which includes aluminum pad
40, narrow conductor 42, contact pad 41, and passivation layer 44
(FIGS. 13a and 13b); partially sawing through wafer 38 to assist
separation of the die after processing; spin coating photosensitive
polyimide 35 on the top surface of wafer 38 to protect aluminum
pads 40 and 41 during subsequent etching and to fill saw line 46;
patterning polyimide to expose pads 40 to be plated and pads 41 for
electrical contact (FIG. 13c); degreasing wafer; immersing the
structure in zincate plating solution; applying photoresist and
patterning to create a bus; joining contact pads 41 by sputtering
of copper to form a bus 48 (FIG. 13d) that is in contact with pads
41 for the electroplating method; patterning resist 35 over bus 48
to prevent nickel from depositing on bus 48; plating enough nickel
50 (FIG. 13e) on aluminum pad 40 to allow planarization; removing
the resist 35; making electrical contact with the plated metal;
sputtering a planar base 51 and plating a sufficient amount of
copper 52 over the entire wafer surface to allow planarization;
planarizing surface to expose nickel 50 (FIG. 13g); electroplating
the layers of the microstructure (FIG. 13h); etching copper 51 and
52 including bus 48 and copper disk 36; and stripping polyimide 34
thereby defining microstructure device 54 attached to wafer 38
(i.e., the integrated circuit) (FIG. 13i).
[0114] The electroplating methods can employ cyclic plating to
improve uniformity of the deposited metal layer. Cyclic plating
includes very briefly interrupting the current applied to the
electrode in synchronization with removing the mask from the
substrate to be plated, which simultaneously replenishes the
electrolyte additives, vents any gases, and discharges particulates
and broken-down additives from the microvolume defined by the
support, the substrate to be plated, and the mask. Current is then
re-applied in synchronization with contacting, i.e., remating, the
mask with the substrate. This method can be repeated until the
desired thickness of metal has been deposited. The walls of the
mask can be given a slight taper or draft (i.e., negative features
defined by the mask are slightly larger on the side of the mask
contacting the substrate), to facilitate repeated contact of a mask
with a substrate in the presence of a deposit of incomplete
thickness.
[0115] Uniformity of the plated metal layer can be improved by
controlling current density and adjusting current density on a
feature-by-feature basis by controlling the local thickness, and
optionally the local porosity, of the support of the electroplating
article. Uniform plating can also be achieved by using an insoluble
anode as a support, where the insoluble anode has a thin layer of a
soluble coating located thereon that has a thickness calculated to
provide the desired thickness of plated metal on the substrate.
Once the finite amount of ions in the volume of electrolyte within
the area defined by the mask (including ions created from any
soluble coating that was initially part of the anode) are consumed
plating ceases and the coating and the substrate are plated. As
long as the initial coating on the insoluble anode is uniform in
thickness, the plated metal will be uniform in thickness.
[0116] Hydrogen bubble formation can also be minimized by employing
a low current density to increase current efficiency; decreasing
temperature and/or pressurizing the electrolyte in bulk to increase
the solubility of hydrogen in the electrolyte; employing a mask
material that is impermeable to the electrolyte but gas permeable
(e.g., a hydrophobic microporous material); performing the
electroplating method under vacuum so that gas bubbles are pulled
out of the mask features; employing antipitting agents (e.g., SNAP
for nickel sulfamate electrolytes) to minimize the formation of
pits by reducing the attachment of the gas bubbles to the
substrate; increasing the masking pressure, which can locally
increase electrolyte pressure due to reduced microvolume, which
will establish large pressures on the electrolyte in localized
areas keeping hydrogen in solution; and incorporating hydrogen
gettering agent into the mask material (e.g., by mixing a fine
powder into the liquid masking composition).
[0117] Examples of useful etching compositions for selectively
stripping copper from nickel structures include: solutions of
ammonium hydroxide and copper sulfate, solutions of ammonium
hydroxide and sodium chlorite, with ammonium hydroxide-copper
sulfate solution being preferred for etching structures attached to
CMOS devices, and Enstripe C38 commercially available from Enthone
OMI. Etching can also be performed in the presence of vibrations,
e.g., ultrasound applied to the etchant or the substrate that was
plated, pressurized jets of etchant contacting the metal to be
etched, and surfactant. Flash present on the structural metal,
e.g., in the form of thin projections extending from the surface of
the structural metal, can be removed, e.g., by acid etching or
electropolishing.
[0118] The electroplating methods can be used to manufacture
elements having complex microstructure and close tolerances between
parts. One example of a method for manufacturing elements having
parts that fit with close tolerances, e.g., gaps between the parts
are between about 1-5 um, involves electroplating the parts of the
device in an unassembled, preferably pre-aligned, state. Once
manufactured, the individual parts can be moved into operational
relation with each other. Referring to FIGS. 14a-14e, a method of
manufacturing device 188 including gear 190 and shaft 192 having
retaining clips 200 includes the electroplating methods disclosed
above. Assembly fixture 194 is plated in a pre-aligned location
with gear 190 (FIG. 14a). Chuck 196 (e.g., electromagnetic or
vacuum) secures the assembly fixture pieces 194 as support material
198 is etched (FIG. 14b). During etching gear 190 may fall into
contact with shaft 192. Chuck 196 is then lowered, causing assembly
fixture 194 to press gear 190 over retaining clips 200 on shaft 192
and into final position, as shown in FIG. 14c. Chuck 196 is then
raised removing assembly fixture 194 from the completed device 188,
as shown in FIGS. 14d and 14e.
[0119] The electroplating method can also be used to manufacture
elements in which at least a portion of the support metal (i.e.
normally sacrificial metal) is enclosed within the structural
material such that the enclosed sacrificial metal is not etched
away during the removal process and thus becomes part of the
structure of the element. Referring to FIGS. 15a and 15b, a cross
section of a plated element 236 (FIG. 15b) is shown in which
support metal 238 remains encapsulated within structural metal 240
after the portion of support metal 238 that is accessible by
etchant (FIG. 15a) is removed.
[0120] The electroplating processes can also be used to manufacture
tooling for molding (e.g., injection molding, metal injection
molding, reaction injection molding, thermoforming, blow molding,
and die casting). Mold inserts can be manufactured by orienting
mold inserts so that the ejection axis of the part is parallel to
the stacking axis of the layers and the parting surface of the part
to be molded is the last layer deposited. The electroplating
methods can be used to form parts (i.e. elements) that include
undercuts as shown in FIG. 16a, to form parts without draft as
shown in FIG. 16b, and to form molds without undercuts and with
draft by depositing layers of structural material where each
subsequently plated layer of structural metal lies entirely within
the boundary of the previously deposited layer (e.g., layers
801-805) of structural metal, as shown in FIG. 16c. The object
produced by the mold of FIG. 16c is shown in FIG. 16d. The mold of
16c can optionally be produced without the use of a support (i.e.
sacrificial) material. Referring to FIG. 16c, layer 801 is
deposited before layer 802, and so on.
[0121] Electroplating Apparatus
[0122] The electroplating method can be performed in a variety of
electroplating apparatus. One particularly useful apparatus for
carrying out an electroplating method is shown in the side view of
FIG. 17. Apparatus 56 includes two baths 58, 60 (e.g., a nickel
plating bath and a copper plating bath), and an inspection station
62. Each bath 58, 60 is constructed to be capable of electroplating
a different metal. Each bath 58, 60 includes an electrolyte, an
anode 59, 61, and an electroplating article 4, 14. As shown,
apparatus 56 accommodates a single substrate to be plated 2. The
apparatus can be constructed to accommodate multiple substrates to
be plated and multiple electroplating articles. Each article 4, 14
includes at least one patterned conformable mask 6,16 and is
capable of depositing a pattern of metal.
[0123] The mechanical and electrochemical control of the
electroplating apparatus can be controlled by computers to
implement the electroplating method. Substrate to be plated 2 is
transported by precision motion stages 64x, 64y, 64z, equipped with
DC servo motors, stepper motors or combinations thereof, and
precision encoders, between plating baths 58, 60 and rinsing
station 66. Substrate 2 suspended on chuck 68 enters first bath 58,
positions itself over mask 6, contacts mask 6, and undergoes
plating. After a predetermined thickness of metal has been plated
onto substrate 2, substrate 2 is removed from bath 58, rinsed and
transferred to second plating bath 60 where it contacts a second
mask 16, undergoes plating to a predetermined thickness (preferably
the same thickness of the first deposited metal), is rinsed, and is
returned to first bath 58. Inspection station 62, including a
high-resolution video microscope system with PC frame grabber, can
be used in conjunction with control software to automatically
record images of the deposited layers to a hard disk. Preferably
apparatus 56 is enclosed in a sealed chamber and equipped with a
vacuum system to degas the mask.
[0124] Useful mechanisms for applying controlled, uniform pressure
to the substrate include applying a fluid pressure (e.g., through a
pneumatic or hydraulic cylinder). One particularly preferred method
for applying uniform pressure across a circular substrate includes
applying pressure at the center of the substrate through a ball
joint (e.g., a ball sandwiched between the cylinder or extension
thereof and the substrate, possibly retained by a countersink in
each). The ball allows the substrate to tilt as needed to conform
to the mask surface and to find an equilibrium position within
which pressure is uniformly distributed. The substrate can be held
against the ball by surrounding the substrate with a tight-fitting
flexible tube that is anchored at one end to the moving member.
[0125] A very stiff, precision mechanical slide (e.g., a mechanical
slide that incorporates crossed roller bearings) can be used to
provide repeatable positioning of the mated substrate. The stages
that move in the plane of the deposited layer, X/Y stages, can be
fixed in location by clamps (e.g., an electromagnetic brake).
[0126] The device (e.g., the chuck) that carries the substrate to
be plated can include a sliding insulating tube that moves into
position as metal layers are added to the substrate. Referring to
FIGS. 17 and 18, sliding insulating tube 67 is shown in cross
section in contact with edge mask 244 on support 14 and surrounding
substrate 2 and plated metal layers 250.
[0127] The electroplating apparatus can be modified to include a
device capable of directing a spray of electrolyte into the volume
defined by the negative features of the article just prior to
contacting the article to the substrate to be plated.
[0128] The electroplating apparatus can include a filtration system
to control particulate contamination within the apparatus. After
the electroplating articles and substrate(s) are loaded into the
electroplating apparatus, the apparatus can execute a self-cleaning
cycle that includes pressurized rising, ultrasonic agitation, and
filtration. The air within the apparatus can be cleaned by a
filtration system, e.g., a HEPA filtration system. The air and
electrolyte filtration processes can operate continuously
throughout the electroplating method. The electrolyte filtration
system can be incorporated into a heating and pumping system to
continuously circulate and warm the electrolyte to maintain
homogeneous concentration and constant temperature.
[0129] The thickness of the plated metal and plated metal layer can
be controlled, e.g., by measuring the deposition rates of the
metals and plating for a predetermined period; monitoring the
integrated current, with adjustments for plating efficiency,
normalizing for calculated mask area and calculating plating
thickness; and through closed loop thickness control. The closed
loop system includes inputting an estimate, based upon measured
metal plating rates, into the software that controls the
electroplating method; plating a first metal to less than the
desired thickness, pressing the substrate against a second
electroplating article, such that the mask of the electroplating
article contacts the first plated metal; forcing the substrate to
move away from the support by an amount equal to the thickness of
the plated layer; reading the thickness of the first plated metal
using a high resolution (e.g., 0.1 um) encoder, linked to the
substrate chuck; inputting this data into the software to update
the stored rate value for the first metal; plating the remaining
thickness of the first metal layer. This process and its complement
for measuring the plating thickness of the second plated metal can
be repeated every few layers as a calibration.
[0130] The position and orientation of the mask of the
electroplating article with respect to the substrate and motion
axes of the electroplating apparatus (described below) can be
determined by an alignment procedure that uses reserved areas on
the substrate to be plated and at least two distantly separated
masks, each bearing an alignment pattern. To align the mask to the
substrate, a thin layer of metal is plated onto the alignment
pattern of the substrate, the rotational and translational
misalignment of the mask with respect to the substrate is measured,
e.g., using a video microscope, and corrections. Alignment accuracy
can be verified by stripping the plated patterns and re-plating new
patterns. Alignment can be repeated throughout the electroplating
method as necessary.
[0131] Another example of a useful alignment method employs a
vernier pattern in which a pattern of fine lines having a first
pitch is deposited over a second pattern of lines having a
different pitch. The pitch spacing of the deposited pattern
compared to the existing pattern provides an indication of the
alignment error.
[0132] Referring to FIG. 19, a portion of another electroplating
apparatus 66 that includes bath 68 containing ions of a first
metal, e.g., a nickel plating bath, bath 70 containing ions of a
second metal, e.g., a copper plating bath, and multiple
electroplating articles 72a-f and 74a-e, is shown. Each substrate
to be plated (2a-2e) enters the apparatus 66 at the left end 76 of
bath 68, contacts article 72a, becomes plated with a first metal in
the pattern of the mask of article 72a, transfers to bath 70 after
rinse (not shown), contacts article 74a, becomes plated with a
second metal in the pattern of the mask on article 74a, transfers
to article 72b after rinse (not shown), in bath 68 and so on. As
depicted, substrate 2a has received deposits of the first metal and
the second metal for the first three layers of the microstructure
and the first metal portion of the fourth layer. Substrate 2b is
one layer behind substrate 2a; substrate 2c is two layers behind
substrate 2a, etc.
[0133] For elements (e.g., devices) that require dozens or hundreds
of deposited layers, the electroplating system can be arranged in
an annular design in which the electroplating articles are arranged
in rings and in which the individual electroplating articles are
replaced after having contacted each of the substrates to be
plated. One example of an apparatus for mass-producing
electroplated structures is shown in FIG. 20. Apparatus 78 is
designed to process 24 eight-inch diameter substrates 2. Apparatus
78 is concentric in design and includes an outer ring 80, and a
middle ring 82 and a central disk 85. Outer ring 80 includes
electrolyte bath 84 and electroplating articles (not shown) for
selectively plating a first metal. Middle ring 82 includes an
electrolyte bath 86 for blanket-plating a second metal. As opposed
to blanket plating, middle ring 82 can include electroplating
articles for selectively plating the second metal. Rotating lapping
plate 85 (if required), for planarizing the plated metal layers, is
located at the center of apparatus 78. All processes (first metal
selective plating, second metal blanket or selective plating and,
optionally, planarization) occur during a single cycle, but on
different substrates 2. At the end of the cycle, the substrates
undergoing plating move in the pattern shown, in part, by arrows.
Eight layers have been deposited after having completed all of the
cycles in the system and arriving back at the starting point. Prior
to the first substrate arriving back at the first plating article,
the first plating article can be replaced by a new plating article.
Likewise after the other plating articles have contacted each of
the substrates they can be replaced, and substrates 2 can continue
around apparatus 78, receiving as many layers as are required for
the device being made. Rinsing stations are not shown but can be
located in the spaces between the plating articles. It is
anticipated that such an apparatus would permit the simultaneous
manufacture of about 2.5 million devices, each 500 microns square
by 200 microns tall, in an 8-hour period.
[0134] The electroplating apparatus can also include a single bath
containing ions of at least two metals (e.g., a Watts bath with
added copper sulphate). A method for selectively depositing two
metals from a common plating bath of their ions is described in H.
Yahalom and O. Zadok, "Formation of Compositionally Modulated
Alloys by Electrodeposition," J. Material Sci., Vol. 22, p. 494
(1987). The plating bath includes at least two electroplating
articles, each of which is dedicated to plating one of the metals.
The articles can include a single mask pattern or multiple mask
patterns in a side-by-side arrangement on the surface of the
support. In the case of an article having multiple mask patterns,
the substrate can contact the different mask patterns in a
predetermined sequence, alternating with the mask pattern(s) on the
second article, to build a three dimensional structure. Referring
to FIG. 21, an electroplating apparatus 88 that includes a single
bath 90 containing ions of two metals, e.g., nickel and copper
ions, articles for plating the first metal 92, articles for plating
the second metal 94, and substrates 2a-e, is shown.
[0135] Each substrate 2a-2e enters apparatus 88 at the left end 96
of bath 90, contacts electroplating article 92a becomes plated with
the first metal in the pattern of the mask of electroplating
article 92a, transfers to and contacts article 94a, becomes plated
with the second metal in the pattern of the mask on electroplating
article 94a, transfers to electroplating article 92b, and so on. As
depicted, substrate 2a has received deposits of the first metal and
the second metal for the first three layers of the microstructure
and the first metal portion of the fourth layer. Substrate 2b is
one layer behind substrate 2a, substrate 2c is two layers behind
substrate 2a, and so on.
[0136] A variety of methods can be used to improve the copper
deposition rate in a common bath electroplating system including,
e.g., pulsing the plating current, increasing temperature (e.g.,
laser enhanced plating), pumping electrolyte through the support of
the electroplating article, ultrasonic vibration, and increasing
the copper content in the vicinity of the copper disk. One method
for locally increasing the concentration of copper includes
galvanostatic dissolution of the copper anode while plating onto a
dummy substrate. By applying a current pulse at a density of, e.g.,
about 20-50 mA/cm2, both nickel and copper are deposited onto the
dummy substrate until sufficient copper to form a layer (about 1-2
um thick) is generated in the electrolyte located between the anode
and the substrate. At this point the dummy substrate is substituted
with the real substrate and the anode is replaced with a nickel
anode. Copper is then deposited potentiostatically.
[0137] Another method for locally increasing the concentration of
copper includes employing an electroplating article holder 98 as
shown in FIG. 22. The volume of electroplating article holder 98
contains copper rich electrolyte and is defined by side walls 100
of a cylinder, a porous support 102 having a conformable mask 104,
and anode 106 (e.g., an insoluble platinized titanium anode).
Electroplating article holder 98 includes inlet and outlet ports
for transferring electrolyte (not shown). This electroplating
article holder can be immersed within a nickel-plating bath,
optionally separated by a barrier through which the substrate can
intermittently pass.
[0138] In general when there is a risk of spontaneous deposition
onto a substrate while not in contact with an electroplating
article, the substrate preferably is biased at a more positive
potential than that at which copper reduction would occur until the
substrate has contacted the copper-electroplating article and
current has been applied. Similarly, when current is removed, the
substrate preferably is again biased until the substrate is removed
from the electrolyte or applied to another article and current is
again applied.
[0139] Another electroplating apparatus is shown in FIG. 23.
Apparatus 260 includes baths 262, 264 (e.g., a nickel plating bath
and a copper plating bath), by an inspection station 266, and
lapping station 268. Each bath 262, 264 is constructed to be
capable of electroplating a different metal. Each bath 262, 264
includes an electrolyte and an anode 270, 272. Bath 264 also
includes an electroplating article 274 for selectively depositing a
first metal. Bath 262 is used for blanket depositing a second
metal. Bath 262 includes a mask 276 for insulating the sides of the
structure (i.e. including the element) being fabricated on
substrate 2 to prevent metal from plating on the sides of either
the substrate or the structure. Referring to FIG. 24, a portion of
electroplating apparatus 260 in which substrate 2 is positioned
within electroplating bath 262 and is insulated, in part, by mask
276 is shown. Substrate 2 includes a selectively deposited layer
278 and a blanket deposited layer 280.
[0140] Referring to FIG. 25, an example of an electroplating
apparatus that includes an electroplating article that includes a
porous membrane is shown. Electroplating article 108, which is in
contact with substrate to be plated 2, includes a relatively more
rigid porous medium 110 having a relatively more coarse porosity,
and relatively thinner, flexible porous membrane 112 having a
relatively more fine porosity, and patterned mask 114 adhered to
membrane 112. Patterned mask 114 is in contact with substrate 2 and
anode 116 is disposed beyond porous medium 110. A metal deposit 118
is formed in the opening (i.e., within a negative feature) defined
by mask 114.
[0141] Referring to FIG. 26, another example of an electroplating
apparatus 120 that employs a porous membrane 112 is shown. Porous
membrane 112 is mounted as a drumhead on drum frame 122 in a way
that allows for handing and processing, maintenance of position of
the membrane 112 with respect to the substrate, and allows pressure
to be exerted on porous membrane 112 through rigid porous medium
110 contacting porous membrane 112. Porous membrane 112 is clamped
between concentric O-rings 124, and pulled taut over a rigid porous
medium, or, as shown, a cylindrical, hollow "barrel" 126 by
tightening screws 128. If a barrel is used, rigid porous medium 110
is placed within barrel 126 so as to make contact with one side of
membrane 112. Plating substrate 2 contacts the other side of porous
membrane 112. An intermediate compliant material (not shown) e.g.,
an open pore foam, may be disposed between porous membrane 112 and
rigid porous medium 110 to provide a more uniform contact pressure
between the mask and plating substrate 2.
[0142] Automated Processing
[0143] Various embodiments of the invention also feature a method
for generating mask patterns of very thin cross section for a three
dimensional structure and a method for automated electroplating
that includes contacting electroplating articles having the
generated mask patterns in a predetermined sequence to form the
three dimensional structure.
[0144] One such embodiment employs an automatic mask minimization
algorithm for optimizing the number of masks for a given geometry.
Application of the method to a valve like device 602, shown in FIG.
27, can be described with reference to perforated lines A-D which
indicate cross sections of the device 602. Cross-sections B and C
are identical and cross sections A and D are identical. A single
mask can be used for cross sections B and C and another mask can be
used for cross sections A and D. The algorithm compares the newly
calculated cross sections for use with a given metal with the
previously calculated cross sections for the same device or
possibly those used to make other devices. A new mask is generated
if the difference between the two cross sections exceeds some
predetermined (e.g., user specified) tolerance. This allows the
number of masks to be minimized, allowing a greater number of
layers to be produced from fewer electroplating articles. The
program also generates an apparatus control file which directs the
software that controls the electroplating apparatus such that masks
are selected in a predetermined sequence corresponding to mask
location within the electroplating apparatus and the layer being
plated. The system can also export a layout file representing the
first cross section of the part to be fabricated, allowing pad
design for CMOS interfacing using a standard layout editor. The
system can also display calculated cross sections to the user to
allow error checking.
[0145] FIG. 28 is a functional block diagram of an exemplary
computing system for calculation of cross sections of a three
dimensional structure in accordance with an embodiment of the
present invention. As shown in FIG. 28, system 610 may include a
processor 612, a memory 614 (e.g., a random access memory (RAM),
and a program memory (for example, a writable read-only memory
(ROM) such as a flash ROM)), input devices 616, and output devices
618. Processor 612 includes a central processing unit (CPU) that
forms part of a general-purpose computer, such as a PC, Macintosh,
or workstation. Memory 614 stores program code for execution by
processor 612 including operating system code and application
program code, and generally represents a magnetic hard drive or
other storage device in combination with a random access memory
accessed by processor 612. As one example, memory 614 could be
realized in part by a storage drive contacting removable storage
media carrying the application program code. Input devices 616
include input media for entry of user input, such as a keyboard,
mouse, and the like. Output devices 618 include display devices
including a view screen that provides graphic output, e.g., a CRT
or flat panel monitor, a printer (e.g., a desk top printer, an
inkjet printer, a laser printer, a photoplotter, and the like), the
electroplating apparatus, a linotronic printer and the like.
[0146] FIG. 29 is a flow diagram illustrating a method for
generating mask geometries and machine control parameters for
fabrication of a three dimensional structure. When the user starts
the application program, as indicated by reference numeral 620,
processor 612 receives and processes input corresponding to the
three dimensional geometry of a structure to be cross sectioned
from input devices 616 as indicated by block 622. Processor 612
determines the extents in layer plane of the entire geometry of the
three-dimensional structure as indicated by block 623. Processor
612 sets M, the number of layers (including one or more cross
sections), equal to 1 and generates cross sections for the M.sup.th
layer, as indicated by block 624. Processor 612 reads inputs
relevant to each mask geometry including, e.g., scaling of the
three dimensional geometry, layer thickness, mask dimensions,
number of copies and spacing, and tolerance for mask minimization,
as indicated by block 625. Processor 612 creates the geometry of
mask corresponding to the M.sup.th layer, as indicated by block
626, writes the geometry of the cross section(s) to a mask pattern
file, indicated by blocks 628 and 630, and writes mask
identification numbers for the M.sup.th layer to a machine control
file, as indicated by blocks 628 and 632. Memory 614 stores mask
pattern in the mask pattern file, as indicated at block 630. Memory
614 stores location information in machine control file, as
indicated at block 632. Processor 612 queries if additional layers
are needed to complete the geometry of the three-dimensional
structure, as indicated at block 634.
[0147] If so, processor 612 increments N by 1 and compares the
geometry of mask for M.sup.th layer with that of mask for M-Nth
layer, as indicated at block 642. If processor 612 calculates that
the geometry of the M.sup.th layer has been compared to the
geometry of each previous mask and no geometry matches have
occurred (i.e. a "no" answer to the inquiry of 654), then processor
612 creates a geometry of the mask for the M.sup.th layer, as
indicated at block 656. Processor 612 then writes the geometry for
the M.sup.th layer to the mask pattern file (as indicated by block
658), sends an output to the mask pattern file, as indicated by
block 660, and writes mask identification number for the M.sup.th
layer to the machine control file (as indicated by blocks 650 and
652).
[0148] If not, processor 612 queries whether M-N is greater than or
equal to 1 as indicated at block 654.
[0149] If so, processor 612 increments N by 1 and compares the
geometry of mask for Mth layer with that of mask for M-Nth layer,
as indicated at block 642. If processor 612 calculates that the
geometry of the Mth layer has been compared to the geometry of each
previous mask and no geometry matches, then processor 612 creates a
geometry of the mask for the Mth layer, as indicated at block 656.
Processor 612 then writes the geometry for the Mth layer to the
mask pattern file (as indicated by block 658), sends an output to
mask pattern file, as indicated by block 660, and writes mask
identification number for the Mth layer to the machine control file
(as indicated by blocks 650 and 652).
[0150] Processor 612 queries whether additional layers are required
to be made of the three dimensional object (as indicated by block
634).
[0151] If so, processor 612 increments M by 1 and continues the
process again.
[0152] If not, the process ends.
[0153] FIG. 30 is a flow diagram illustrating a method for
electroplating a metal onto a substrate using patterned masks that
represent a cross sectional slice of a three dimensional object.
When the user starts the application program, as indicated by
reference numeral 720, processor 612 signals the electroplating
apparatus to perform machine initialization and sets M, the number
of layers plated equal to zero, as indicated at block 722.
Processor 612 increments M by 1 (as indicated by block 724), sets P
(i.e., the number of different metals to be plated) equal to 1 and
optionally biases the substrate to prevent spontaneous deposition
of the metal (as indicated by block 726). Processor 612 reads
machine control file (indicated by block 730) to obtain control
information about the layer that is to be plated, and reads mask
location file (indicated by block 732) to obtain information about
the location of the mask pattern to be plated. Processor 612
directs the electroplating apparatus to align the substrate to be
plated with the mask for material P of layer M and to contact the
substrate to the mask (indicated by block 728). Processor 612
optionally measures layer thickness, if necessary, as indicated by
block 734. Processor 612 receives input that the substrate is in
contact with the mask and turns off substrate bias (if turned on),
as indicated by block 736. Processor 612 instructs apparatus to
deposit material P for layer M, as indicated by block 738.
Processor 612 receives input that the cross-section has been
deposited and applies a bias to the structure, if required, as
indicated by block 740. Processor 612 instructs apparatus to remove
the substrate from contact with the mask (as indicated at block
742), and to planarize layer M to predetermined thickness (if
necessary), as indicated at block 744. Processor queries whether P
is less than the number of metals of layer M, as indicated by block
746.
[0154] If so, processor 612 increments P by 1 (as indicated by
block 748), and drives the electroplating apparatus to align the
substrate with a mask corresponding to the new value for P (i.e.,
the P metal of layer M), as indicated by block 728. Processor 612
drives electroplating apparatus to contact the substrate with the
mask (as indicated by block 748), and the above process is repeated
until P is equal to the number of metals on layer M.
[0155] Turning back to block 746, if P is not less than the number
of materials on layer M, processor 612 queries whether M is the
final layer (as indicated by block 750).
[0156] If so, processor 612 ends the electroplating process as
indicated by numeral 752.
[0157] If not, processor 612 increments M by 1 as indicated by
block 724, and processor 612 drives the electroplating process
until the final layer has been plated.
[0158] The data processes and control processes of various
embodiments of the invention can be implemented in digital
electronic circuitry, or in computer hardware, firmware, software,
or in combinations thereof. The data processes and control
processes of various embodiments of the invention can be
implemented in a computer program product tangibly embodied in a
machine-readable storage device for execution by a programmable
processor; and method steps of various embodiments of the invention
can be performed by a programmable processor executing a program of
instructions to perform functions of those embodiments of the
invention by operating on input data and generating output. The
data processes and control processes of various embodiments of the
invention can advantageously be implemented in one or more computer
programs that are executable on a programmable system including at
least one programmable processor coupled to receive data and
instructions from, and to transmit data and instructions to, a data
storage system, at least one input device, and at least one output
device. Each computer program can be implemented in a high-level
procedural or object-oriented programming language, or in assembly
or machine language if desired; and in any case, the language can
be a compiled or interpreted language. Suitable processors include,
by way of example, both general and special purpose
microprocessors. Generally, a processor will receive instructions
and data from a read-only memory and/or a random access memory.
Storage devices suitable for tangibly embodying computer program
instructions and data include all forms of non-volatile memory,
including by way of example semiconductor memory devices, such as
EPROM, EEPROM, and flash memory devices; magnetic disks such as
internal hard disks and removable disks; magneto-optical disks; and
CD-ROM disks. Any of the foregoing can be supplemented by, or
incorporated in, ASICs (application-specific integrated
circuits).
[0159] To provide for interaction with a user, the data processes
and control processes of various embodiments of the invention can
be implemented on a computer system having a display device such as
a monitor or LCD screen for displaying information to the user and
a keyboard and a pointing device such as a mouse or a trackball by
which the user can provide input to the computer system. The
computer system can be programmed to provide a graphical user
interface through which computer programs interact with users.
[0160] Other embodiments are possible. Although the above
description is directed to planar substrates, the substrate could
be non-planar. In such embodiments, the electroplating article can
be sufficiently flexible to conform to the shape of the substrate
surface, or shaped to match the surface. For example, the
electroplating article could be wrapped around a cylindrical
substrate. Masking pressure can be applied to nonplanar substrates
through a powdered medium that conforms to the mask.
[0161] In addition, although the electroplating embodiments have
been described above with respect to the use of two metals, a
variety of materials, e.g., polymers, ceramics and semiconductor
materials, and any number of metals can be deposited either by the
electroplating methods described above, or in separate processes
that occur throughout the electroplating method. A thin plating
base can be deposited, e.g., by sputtering, over a deposit that is
insufficiently conductive (e.g., an insulating layer) so as to
enable subsequent electroplating. Multiple support materials (i.e.
sacrificial materials) can be included in the electroplated element
allowing selective removal of the support materials.
[0162] The electroplating methods of various embodiments of the
invention can be used in combination with other processes.
Referring to FIG. 31, for example, electromagnetic motor 178
including armature windings 180 connected to an integrated circuit
at aluminum pads on substrate 182, can be formed by interrupting
the electroplating method and etching a portion of the support
metal (e.g., using a patterned resist) to produce cavity 184 (i.e.,
the rotor core of the motor) defined by structural metal 186
serving as an etch stop. Cavity 184 is then filled with a magnetic
powder (e.g., Ne--Fe--B), which is subsequently sintered and
magnetized. If necessary, metal is sputtered onto the sintered
magnetic powder to establish a plating base and the electroplating
method can be resumed. Such cavities can be filled with solids,
fluids or evacuated to form a vacuum.
[0163] Where multiple metals are to be deposited, the metals can be
selectively deposited on the substrate by masking only the
substrate. By only masking the substrate, the metal being
selectively plated onto the substrate is also deposited onto the
previously deposited metals. After each of the metals for a given
layer has been deposited the layer is planarized to the desired
thickness. Alternatively, the mask can cover all of the previously
deposited metals. In this alternative, the mask can also be stepped
in thickness to accommodate the topography of a partially plated
substrate.
[0164] Another embodiment of the electroplating method involves
manufacturing a structure well defined in shape and position
according to the following method: preparing a piece of rigid, high
strength material with an interconnected porosity (e.g.,
partly-sintered ceramic); shaping one surface of this piece such
that it has the inverse (in the mold making sense) shape to that of
the desired deposit; positioning the piece so that its surface lies
opposite the substrate to be plated, at the desired position of the
final deposit surface, and placing an anode on the other side of
it; plating metal onto the substrate while moving the piece
(continuously or periodically) with sufficient force and in such a
way that its surface still remains matched to that of the desired
deposit (for a planar surface, move it within the plane, for a
cylindrical surface, move it axially, etc.) (The movement can be a
vibration sufficiently large to shear and remove any portion of the
deposit that extends into the pores of the piece); continuing
plating until the entire volume between the substrate and the piece
is filled with the deposit, at which point the deposit will have
molded itself to the shape of the piece. The piece can be disposed
of, or periodically reconditioned by chemically flushing the piece
with fluid, dissolving the clogging material or placing the clogged
surface in contact with an anode and deplating it onto a substrate
in an electrolyte.
[0165] Referring to FIGS. 32a-32d, another embodiment of an
electroplating article is shown. Electroplating article 200
includes a mask adhered to and coextensive with a patterned, rigid
substrate (e.g., polymethylmethacrylate). During the electroplating
method a deposit is formed in the window(s) (i.e., negative mask
features) of the article. More specifically, substrate 204 is
contacted with a first patterned electroplating article 200, as
shown in FIG. 32a; a first metal deposit 206 is formed in a shape
defined by the pattern 202 in first electroplating article 200,
first article 200 is then removed (FIG. 32b); substrate 204 is then
contacted in alignment with a second patterned electroplating
article 208 (FIG. 32c), deposit 210 is formed, and second article
208 is removed (FIG. 32d). The plated metal is then planarized and
the method repeated until an element of sufficient thickness and
dimension has been achieved. The electroplating articles can
include a region 210 of overlapping plated metal, which will have a
corresponding greater thickness. The overlapping region can be
planarized to create a planar layer of deposited metal. Masking
pressure can be applied by pressing an anode or porous medium
against the electroplating article. The mask can be made stiffer by
increasing its thickness.
[0166] Although the electroplating methods have been described with
respect to contacting a cathode with an article and plating onto a
cathode, it is contemplated that the electroplating article can be
placed in contact with a substrate functioning as an anode such
that metal is selectively removed from the anode in a pattern
corresponding to the pattern on the electroplating article. Such a
process can be employed to selectively etch, engrave, and polish a
substrate, e.g., a plaque.
[0167] An electroplating method includes forming a layer, the
forming of the layer includes: a) contacting a substrate with a
first article, the first article includes a support and a
conformable mask disposed in a pattern on the support; b)
electroplating a first metal from a source of metal ions onto the
substrate in a first pattern, the first pattern corresponding to
the complement of the conformable mask pattern; and c) removing the
first article from the substrate. The method may further involve
one or more of (1) selectively depositing or non-selectively
depositing one or more additional materials to complete formation
of the layer, (2) planarizing deposited material after each
deposition or after all depositions for a layer, and/or (3) forming
layers adjacent previously formed layers to build up a structure
from a plurality of adhered layers. Electroplating articles and
electroplating apparatus are also disclosed.
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