U.S. patent application number 13/021939 was filed with the patent office on 2011-06-30 for method of electrochemically fabricating multilayer structures having improved interlayer adhesion.
This patent application is currently assigned to University of Southern California. Invention is credited to Adam L. Cohen, Kieun Kim, Ezekiel J. J. Kruglick, Ananda H. Kumar, Michael S. Lockard, Gang Zhang.
Application Number | 20110155580 13/021939 |
Document ID | / |
Family ID | 46302038 |
Filed Date | 2011-06-30 |
United States Patent
Application |
20110155580 |
Kind Code |
A1 |
Zhang; Gang ; et
al. |
June 30, 2011 |
Method of Electrochemically Fabricating Multilayer Structures
Having Improved Interlayer Adhesion
Abstract
Multi-layer microscale or mesoscale structures are fabricated
with adhered layers (e.g. layers that are bonded together upon
deposition of successive layers to previous layers) and are then
subjected to a heat treatment operation that enhances the
interlayer adhesion significantly. The heat treatment operation is
believed to result in diffusion of material across the layer
boundaries and associated enhancement in adhesion (i.e. diffusion
bonding). Interlayer adhesion and maybe intra-layer cohesion may be
enhanced by heat treating in the presence of a reducing atmosphere
that may help remove weaker oxides from surfaces or even from
internal portions of layers.
Inventors: |
Zhang; Gang; (Monterey Park,
CA) ; Cohen; Adam L.; (Los Angeles, CA) ;
Lockard; Michael S.; (Lake Elizabeth, CA) ; Kumar;
Ananda H.; (Fremont, CA) ; Kruglick; Ezekiel J.
J.; (San Diego, CA) ; Kim; Kieun; (Pasadena,
CA) |
Assignee: |
University of Southern
California
|
Family ID: |
46302038 |
Appl. No.: |
13/021939 |
Filed: |
February 7, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12206621 |
Sep 8, 2008 |
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13021939 |
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10841382 |
May 7, 2004 |
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12206621 |
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10434289 |
May 7, 2003 |
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10841382 |
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60533946 |
Dec 31, 2003 |
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60506103 |
Sep 24, 2003 |
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60474625 |
May 29, 2003 |
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60468741 |
May 7, 2003 |
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60379129 |
May 7, 2002 |
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Current U.S.
Class: |
205/118 ;
205/224 |
Current CPC
Class: |
C25D 5/50 20130101; H01L
21/2885 20130101; C25D 5/34 20130101; C25D 5/40 20130101; H05K
3/243 20130101; C25D 1/003 20130101; C25D 5/022 20130101; C25D 5/18
20130101; C25D 5/48 20130101; C25D 5/12 20130101; H01L 21/76879
20130101; H05K 3/241 20130101; C25D 5/10 20130101; C25D 5/14
20130101 |
Class at
Publication: |
205/118 ;
205/224 |
International
Class: |
C25D 5/02 20060101
C25D005/02; C25D 5/50 20060101 C25D005/50 |
Claims
1. A fabrication process for forming a multi-layer
three-dimensional structure, comprising: (a) forming and adhering a
layer to a previously formed layer and/or to a substrate, wherein
the layer comprises a desired pattern of at least one material; and
(b) repeating the forming and adhering operation of (a) at least
once to build up a three-dimensional structure from a plurality of
adhered layers; (c) after formation of at least a plurality of
layers, subjecting the multi-layer structure to a heat treatment,
wherein a maximum effective temperature during heat treatment is
less than a recrystallization temperature of at least one metal
forming part of the structure, and wherein the heat treatment is
applied for a sufficient time and at a sufficient temperature and
in an environment that allows interlayer adhesion to be enhanced a
substantial amount, and wherein the forming and adhering of at
least one layer comprises use of an adhered mask in the selective
patterning of at least one material.
2. The process of claim 1 wherein the substantial amount comprises
at least a factor of two.
3. The process of claim 1 wherein the substantial amount comprises
at least a factor of five.
4. The process of claim 1 wherein the substantial amount
corresponds to the interlayer adhesion strength being greater than
about 50% of the yield strength of the interlayer material.
5. The process of claim 1 wherein the substantial amount
corresponds to the interlayer adhesion strength being greater than
about the yield strength of the interlayer material.
6. The process of claim 1 wherein the substantial amount
corresponds to the interlayer adhesion strength being greater than
about 50% of the ultimate tensile strength of the intra-layer
material.
7. A fabrication process for forming a multi-layer
three-dimensional structure, comprising: (a) forming and adhering a
layer to a previously formed layer and/or to a substrate, wherein
the layer comprises a desired pattern of at least one material; and
(b) repeating the forming and adhering operation of (a) at least
once to build up a three-dimensional structure from a plurality of
adhered layers; (c) after formation of at least a plurality of
layers, subjecting the multi-layer structure to a heat treatment,
wherein the heat treatment is applied to the structure for a
temperature, a time, and in an environment such that a substantial
increase in interlayer adhesion results without significantly
reducing the yield strength of the intra-layer material, and
wherein the forming and adhering of at least one layer comprises
use of an adhered mask in the selective patterning of at least one
material.
8. The process of claim 7 wherein the substantial increase
comprises at least a factor of two and the reducing is no more than
50% of the yield strength prior to heat treatment.
9. The process of claim 7 wherein the substantial amount comprises
at least a factor of five and the reducing is no more than 75% of
the yield strength prior to heat treatment.
10. The process of claim 7 wherein the substantial amount
corresponds to the interlayer adhesion strength being greater than
about 50% of the yield strength prior to heat treatment and the
yield strength after heat treatment is no less than 75% of the
yield strength prior to heat treatment.
11. The process of claim 7 wherein the substantial amount
corresponds to the interlayer adhesion strength being greater than
about the yield strength after heat treatment and the yield
strength after heat treatment being no less than 75% of its value
prior to heat treatment.
12. The process of claim 7 wherein the substantial amount
corresponds to the interlayer adhesion strength being greater than
about 50% of the ultimate tensile strength of the intra-layer
material and the ultimate tensile strength of the interlayer
material being no less than 75% of its value prior to heat
treatment.
13. A fabrication process for forming a multi-layer
three-dimensional structure, comprising: (a) forming and adhering a
layer to a previously formed layer and/or to a substrate, wherein
the layer comprises a desired pattern of at least one material; and
(b) repeating the forming and adhering operation of (a) at least
once to build up a three-dimensional structure from a plurality of
adhered layers; (c) after formation of at least a plurality of
layers, subjecting the multi-layer structure to a heat treatment,
wherein the heat treatment results in the formation of a structure
which behaves monolithically up to at least 50% of the yield
strength of the intra-layer material, and wherein the forming and
adhering of at least one layer comprises use of an adhered mask in
the selective patterning of at least one material.
14. The process of claim 13 wherein yield strength of the
intra-layer material is that of the intra-layer material prior to
heat treatment.
15. The process of claim 13 wherein yield strength of the
intra-layer material is that of the intra-layer material after heat
treatment.
16. The process of claim 13 wherein monolithic behavior exists when
stresses are at or below 50% of the yield strength of the
intra-layer material and inter-layer adhesion failure is no more
likely to occur than intra-layer cohesion failure.
17. The process of claim 13 wherein monolithic behavior exists when
stresses are at or below about 50% of the ultimate yield strength
of the intra-layer.
18. The process of claim 17 wherein yield strength of the
intra-layer material is that of the intra-layer material prior to
heat treatment.
19. The process of claim 17 wherein yield strength of the
intra-layer material is that of the intra-layer material after heat
treatment.
20. A fabrication process for forming a multi-layer
three-dimensional structure, comprising: (a) forming and adhering a
layer to a previously formed layer and/or to a substrate, wherein
the layer comprises a desired pattern of at least one material; and
(b) repeating the forming and adhering operation of (a) at least
once to build up a three-dimensional structure from a plurality of
adhered layers; (c) after formation of at least a plurality of
layers, subjecting the multi-layer structure to a heat treatment,
wherein the heat treatment results in the formation of a structure
which is no more likely to experience interlayer adhesion failure
than intra-layer cohesion failure when applied stress is at least
50% of the yield strength of the intra-layer material.
21. The process of claim 20 wherein yield strength of the
intra-layer material is that of the intra-layer material prior to
heat treatment.
22. The process of claim 20 wherein yield strength of the
intra-layer material is that of the intra-layer material after heat
treatment.
Description
RELATED APPLICATIONS
[0001] This Application is a continuation of U.S. patent
application Ser. No. 12/206,621 (Microfabrica Docket No.
P-US102-F-SC), filed on Sep. 8, 2008. The '621 continuation of U.S.
patent application Ser. No. 10/841,382 (P-US102-A-SC), filed May 7,
2004. The '382 application is a continuation-in-part of U.S. patent
application Ser. No. 10/434,289 (P-US059-A-SC), filed on May 7,
2003, and claims benefit of U.S. Provisional Patent Application
Nos. 60/533,946 (P-US078-B-MF), filed on Dec. 31, 2003; 60/506,103
(P-US078-A-SC), filed on Sep. 24, 2003; 60/474,625 (P-US051-B-MG),
filed May 29, 2003; and 60/468,741 (P-US051-A-MG), filed May 7,
2003. The '289 application claims benefit of U.S. Provisional
Patent Application No. 60/379,129 (P-US009-A-SC), filed on May 7,
2002. Each of these applications is hereby incorporated herein by
reference as if set forth in full.
FIELD OF THE INVENTION
[0002] The embodiments of various aspects of the invention relate
generally to the formation of three-dimensional structures (e.g.
meso-scale or microscale structures) using electrochemical
fabrication methods wherein heat treatment is provided to improve
interlayer adhesion.
BACKGROUND
[0003] A technique for forming three-dimensional structures (e.g.
parts, components, devices, and the like) from a plurality of
adhered layers was invented by Adam L. Cohen and is known as
Electrochemical Fabrication. It is being commercially pursued by
Microfabrica.TM. Inc. of Van Nuys, Calif. under the name EFAB.RTM..
This technique was described in U.S. Pat. No. 6,027,630, issued on
Feb. 22, 2000. This electrochemical deposition technique allows the
selective deposition of a material using a unique masking technique
that involves the use of a mask that includes patterned conformable
material on a support structure that is independent of the
substrate onto which plating will occur. When desiring to perform
an electrodeposition using the mask, the conformable portion of the
mask is brought into contact with a substrate while in the presence
of a plating solution such that the contact of the conformable
portion of the mask to the substrate inhibits deposition at
selected locations. For convenience, these masks might be
generically called conformable contact masks; the masking technique
may be generically called a conformable contact mask plating
process. More specifically, in the terminology of Microfabrica.TM.
Inc. of Van Nuys, Calif. such masks have come to be known as
INSTANT MASKS.TM. and the process known as INSTANT MASKING or
INSTANT MASK.TM. plating. Selective depositions using conformable
contact mask plating may be used to form single layers of material
or may be used to form multi-layer structures. The teachings of the
'630 patent are hereby incorporated herein by reference as if set
forth in full herein. Since the filing of the patent application
that led to the above noted patent, various papers about
conformable contact mask plating (i.e. INSTANT MASKING) and
electrochemical fabrication have been published: [0004] (1) A.
Cohen, G. Zhang, F. Tseng, F. Mansfeld, U. Frodis and P. Will,
"EFAB: Batch production of functional, fully-dense metal parts with
micro-scale features", Proc. 9th Solid Freeform Fabrication, The
University of Texas at Austin, p 161, August 1998. [0005] (2) A.
Cohen, G. Zhang, F. Tseng, F. Mansfeld, U. Frodis and P. Will,
"EFAB: Rapid, Low-Cost Desktop Micromachining of High Aspect Ratio
True 3-D MEMS", Proc. 12th IEEE Micro Electro Mechanical Systems
Workshop, IEEE, p 244, January 1999. [0006] (3) A. Cohen, "3-D
Micromachining by Electrochemical Fabrication", Micromachine
Devices, March 1999. [0007] (4) G. Zhang, A. Cohen, U. Frodis, F.
Tseng, F. Mansfeld, and P. Will, "EFAB: Rapid Desktop Manufacturing
of True 3-D Microstructures", Proc. 2nd International Conference on
Integrated MicroNanotechnology for Space Applications, The
Aerospace Co., April 1999. [0008] (5) F. Tseng, U. Frodis, G.
Zhang, A. Cohen, F. Mansfeld, and P. Will, "EFAB: High Aspect
Ratio, Arbitrary 3-D Metal Microstructures using a Low-Cost
Automated Batch Process", 3rd International Workshop on High Aspect
Ratio MicroStructure Technology (HARMST'99), June 1999. [0009] (6)
A. Cohen, U. Frodis, F. Tseng, G. Zhang, F. Mansfeld, and P. Will,
"EFAB: Low-Cost, Automated Electrochemical Batch Fabrication of
Arbitrary 3-D Microstructures", Micromachining and Microfabrication
Process Technology, SPIE 1999 Symposium on Micromachining and
Microfabrication, September 1999. [0010] (7) F. Tseng, G. Zhang, U.
Frodis, A. Cohen, F. Mansfeld, and P. Will, "EFAB: High Aspect
Ratio, Arbitrary 3-D Metal Microstructures using a Low-Cost
Automated Batch Process", MEMS Symposium, ASME 1999 International
Mechanical Engineering Congress and Exposition, November, 1999.
[0011] (8) A. Cohen, "Electrochemical Fabrication (EFAB.TM.)",
Chapter 19 of The MEMS Handbook, edited by Mohamed Gad-El-Hak, CRC
Press, 2002. [0012] (9) "Microfabrication--Rapid Prototyping's
Killer Application", pages 1-5 of the Rapid Prototyping Report,
CAD/CAM Publishing, Inc., June 1999.
[0013] The disclosures of these nine publications are hereby
incorporated herein by reference as if set forth in full
herein.
[0014] The electrochemical deposition process may be carried out in
a number of different ways as set forth in the above patent and
publications. In one form, this process involves the execution of
three separate operations during the formation of each layer of the
structure that is to be formed: [0015] 1. Selectively depositing at
least one material by electrodeposition upon one or more desired
regions of a substrate. [0016] 2. Then, blanket depositing at least
one additional material by electrodeposition so that the additional
deposit covers both the regions that were previously selectively
deposited onto, and the regions of the substrate that did not
receive any previously applied selective depositions. [0017] 3.
Finally, planarizing the materials deposited during the first and
second operations to produce a smoothed surface of a first layer of
desired thickness having at least one region containing the at
least one material and at least one region containing at least the
one additional material.
[0018] After formation of the first layer, one or more additional
layers may be formed adjacent to the immediately preceding layer
and adhered to the smoothed surface of that preceding layer. These
additional layers are formed by repeating the first through third
operations one or more times wherein the formation of each
subsequent layer treats the previously formed layers and the
initial substrate as a new and thickening substrate.
[0019] Once the formation of all layers has been completed, at
least a portion of at least one of the materials deposited is
generally removed by an etching process to expose or release the
three-dimensional structure that was intended to be formed.
[0020] The preferred method of performing the selective
electrodeposition involved in the first operation is by conformable
contact mask plating. In this type of plating, one or more
conformable contact (CC) masks are first formed. The CC masks
include a support structure onto which a patterned conformable
dielectric material is adhered or formed. The conformable material
for each mask is shaped in accordance with a particular
cross-section of material to be plated. At least one CC mask is
needed for each unique cross-sectional pattern that is to be
plated.
[0021] The support for a CC mask is typically a plate-like
structure formed of a metal that is to be selectively electroplated
and from which material to be plated will be dissolved. In this
typical approach, the support will act as an anode in an
electroplating process. In an alternative approach, the support may
instead be a porous or otherwise perforated material through which
deposition material will pass during an electroplating operation on
its way from a distal anode to a deposition surface. In either
approach, it is possible for CC masks to share a common support,
i.e. the patterns of conformable dielectric material for plating
multiple layers of material may be located in different areas of a
single support structure. When a single support structure contains
multiple plating patterns, the entire structure is referred to as
the CC mask while the individual plating masks may be referred to
as "submasks". In the present application such a distinction will
be made only when relevant to a specific point being made.
[0022] In preparation for performing the selective deposition of
the first operation, the conformable portion of the CC mask is
placed in registration with and pressed against a selected portion
of the substrate (or onto a previously formed layer or onto a
previously deposited portion of a layer) on which deposition is to
occur. The pressing together of the CC mask and substrate occur in
such a way that all openings, in the conformable portions of the CC
mask contain plating solution. The conformable material of the CC
mask that contacts the substrate acts as a barrier to
electrodeposition while the openings in the CC mask that are filled
with electroplating solution act as pathways for transferring
material from an anode (e.g. the CC mask support) to the
non-contacted portions of the substrate (which act as a cathode
during the plating operation) when an appropriate potential and/or
current are supplied.
[0023] An example of a CC mask and CC mask plating are shown in
FIGS. 1(a)-1(c). FIG. 1(a) shows a side view of a CC mask 8
consisting of a conformable or deformable (e.g. elastomeric)
insulator 10 patterned on an anode 12. The anode has two functions.
FIG. 1(a) also depicts a substrate 6 separated from mask 8. One is
as a supporting material for the patterned insulator 10 to maintain
its integrity and alignment since the pattern may be topologically
complex (e.g., involving isolated "islands" of insulator material).
The other function is as an anode for the electroplating operation.
CC mask plating selectively deposits material 22 onto a substrate 6
by simply pressing the insulator against the substrate then
electrodepositing material through apertures 26a and 26b in the
insulator as shown in FIG. 1(b). After deposition, the CC mask is
separated, preferably non-destructively, from the substrate 6 as
shown in FIG. 1(c). The CC mask plating process is distinct from a
"through-mask" plating process in that in a through-mask plating
process the separation of the masking material from the substrate
would occur destructively. As with through-mask plating, CC mask
plating deposits material selectively and simultaneously over the
entire layer. The plated region may consist of one or more isolated
plating regions where these isolated plating regions may belong to
a single structure that is being formed or may belong to multiple
structures that are being formed simultaneously. In CC mask plating
as individual masks are not intentionally destroyed in the removal
process, they may be usable in multiple plating operations.
[0024] Another example of a CC mask and CC mask plating is shown in
FIGS. 1(d)-1(f). FIG. 1(d) shows an anode 12' separated from a mask
8' that includes a patterned conformable material 10' and a support
structure 20. FIG. 1(d) also depicts substrate 6 separated from the
mask 8'. FIG. 1(e) illustrates the mask 8' being brought into
contact with the substrate 6. FIG. 1(f) illustrates the deposit 22'
that results from conducting a current from the anode 12' to the
substrate 6. FIG. 1(g) illustrates the deposit 22' on substrate 6
after separation from mask 8'. In this example, an appropriate
electrolyte is located between the substrate 6 and the anode 12'
and a current of ions coming from one or both of the solution and
the anode are conducted through the opening in the mask to the
substrate where material is deposited. This type of mask may be
referred to as an anodeless INSTANT MASK.TM. (AIM) or as an
anodeless conformable contact (ACC) mask.
[0025] Unlike through-mask plating, CC mask plating allows CC masks
to be formed completely separate from the fabrication of the
substrate on which plating is to occur (e.g. separate from a
three-dimensional (3D) structure that is being formed). CC masks
may be formed in a variety of ways, for example, a
photolithographic process may be used. All masks can be generated
simultaneously, prior to structure fabrication rather than during
it. This separation makes possible a simple, low-cost, automated,
self-contained, and internally-clean "desktop factory" that can be
installed almost anywhere to fabricate 3D structures, leaving any
required clean room processes, such as photolithography to be
performed by service bureaus or the like.
[0026] An example of the electrochemical fabrication process
discussed above is illustrated in FIGS. 2(a)-2(f). These figures
show that the process involves deposition of a first material 2
which is a sacrificial material and a second material 4 which is a
structural material. The CC mask 8, in this example, includes a
patterned conformable material (e.g. an elastomeric dielectric
material) 10 and a support 12 which is made from deposition
material 2. The conformal portion of the CC mask is pressed against
substrate 6 with a plating solution 14 located within the openings
16 in the conformable material 10. An electric current, from power
supply 18, is then passed through the plating solution 14 via (a)
support 12 which doubles as an anode and (b) substrate 6 which
doubles as a cathode. FIG. 2(a), illustrates that the passing of
current causes material 2 within the plating solution and material
2 from the anode 12 to be selectively transferred to and plated on
the cathode 6. After electroplating the first deposition material 2
onto the substrate 6 using CC mask 8, the CC mask 8 is removed as
shown in FIG. 2(b). FIG. 2(c) depicts the second deposition
material 4 as having been blanket-deposited (i.e. non-selectively
deposited) over the previously deposited first deposition material
2 as well as over the other portions of the substrate 6. The
blanket deposition occurs by electroplating from an anode (not
shown), composed of the second material, through an appropriate
plating solution (not shown), and to the cathode/substrate 6. The
entire two-material layer is then planarized to achieve precise
thickness and flatness as shown in FIG. 2(d). After repetition of
this process for all layers, the multi-layer structure 20 formed of
the second material 4 (i.e. structural material) is embedded in
first material 2 (i.e. sacrificial material) as shown in FIG. 2(e).
The embedded structure is etched to yield the desired device, i.e.
structure 20, as shown in FIG. 2(f).
[0027] Various components of an exemplary manual electrochemical
fabrication system 32 are shown in FIGS. 3(a)-3(c). The system 32
consists of several subsystems 34, 36, 38, and 40. The substrate
holding subsystem 34 is depicted in the upper portions of each of
FIGS. 3(a) to 3(c) and includes several components: (1) a carrier
48, (2) a metal substrate 6 onto which the layers are deposited,
and (3) a linear slide 42 capable of moving the substrate 6 up and
down relative to the carrier 48 in response to drive force from
actuator 44. Subsystem 34 also includes an indicator 46 for
measuring differences in vertical position of the substrate which
may be used in setting or determining layer thicknesses and/or
deposition thicknesses. The subsystem 34 further includes feet 68
for carrier 48 which can be precisely mounted on subsystem 36.
[0028] The CC mask subsystem 36 shown in the lower portion of FIG.
3(a) includes several components: (1) a CC mask 8 that is actually
made up of a number of CC masks (i.e. submasks) that share a common
support/anode 12, (2) precision X-stage 54, (3) precision Y-stage
56, (4) frame 72 on which the feet 68 of subsystem 34 can mount,
and (5) a tank 58 for containing the electrolyte 16. Subsystems 34
and 36 also include appropriate electrical connections (not shown)
for connecting to an appropriate power source for driving the CC
masking process.
[0029] The blanket deposition subsystem 38 is shown in the lower
portion of FIG. 3(b) and includes several components: (1) an anode
62, (2) an electrolyte tank 64 for holding plating solution 66, and
(3) frame 74 on which the feet 68 of subsystem 34 may sit.
Subsystem 38 also includes appropriate electrical connections (not
shown) for connecting the anode to an appropriate power supply for
driving the blanket deposition process.
[0030] The planarization subsystem 40 is shown in the lower portion
of FIG. 3(c) and includes a lapping plate 52 and associated motion
and control systems (not shown) for planarizing the
depositions.
[0031] In addition to teaching the use of CC masks for
electrodeposition purposes, the '630 patent also teaches that the
CC masks may be placed against a substrate with the polarity of the
voltage reversed and material may thereby be selectively removed
from the substrate. It indicates that such removal processes can be
used to selectively etch, engrave, and polish a substrate, e.g., a
plaque.
[0032] The '630 patent further indicates that the electroplating
methods and articles disclosed therein allow fabrication of devices
from thin layers of materials such as, e.g., metals, polymers,
ceramics, and semiconductor materials. It further indicates that
although the electroplating embodiments described therein have been
described 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 therein, or in separate processes that occur
throughout the electroplating method. It indicates that 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. It also indicates that
multiple support materials (i.e. sacrificial materials) can be
included in the electroplated element allowing selective removal of
the support materials.
[0033] Another method for forming microstructures from
electroplated metals (i.e. using electrochemical fabrication
techniques) is taught in U.S. Pat. No. 5,190,637 to Henry Guckel,
entitled "Formation of Microstructures by Multiple Level Deep X-ray
Lithography with Sacrificial Metal layers". This patent teaches the
formation of metal structure utilizing mask exposures. A first
layer of a primary metal is electroplated onto an exposed plating
base to fill a void in a photoresist, the photoresist is then
removed and a secondary metal is electroplated over the first layer
and over the plating base. The exposed surface of the secondary
metal is then machined down to a height which exposes the first
metal to produce a flat uniform surface extending across the both
the primary and secondary metals. Formation of a second layer may
then begin by applying a photoresist layer over the first layer and
then repeating the process used to produce the first layer. The
process is then repeated until the entire structure is formed and
the secondary metal is removed by etching. The photoresist is
formed over the plating base or previous layer by casting and the
voids in the photoresist are formed by exposure of the photoresist
through a patterned mask via X-rays or UV radiation.
[0034] Another method of forming multilayer microstructures is
taught in U.S. Pat. No. 6,332,568 to Todd Christenson, entitled
"Wafer Scale Micromachine Assembly Method". This patent describes a
method for fusing together, using diffusion bonding, micromachine
subassemblies which are separately fabricated. A first and second
micromachine subassembly are fabricated on a first and second
substrate, respectively. The substrates are positioned so that the
upper surfaces of the two micromachine subassemblies face each
other and are aligned so that the desired assembly results from
their fusion. The upper surfaces are then brought into contact, and
the assembly is subjected to conditions suited to the desired
diffusion bonding.
[0035] The formation of a micromechanical resonator was described
by Wan-Thai Hsu, Seungbae Lee, and Clark T. C. Nguyen in a paper
entitled "In Situ Localized Annealing for Contamination Resistance
and Enhanced Stability in Nickel Micromechanical Resonators"
published in "Digest of Technical Papers, 10th International
Conference on Solid-State Sensors and Actuators", Sendai Japan,
Jun. 7-10, 1999, pp. 932-935. This paper describes a technique in
which a micromechanical resonator is operated at large amplitudes
while in situ localized annealing occurs at temperatures exceeding
880.degree. C. Such annealing is shown to be an effective method
for both removal of surface contaminants and for possible
"redistribution" of the structural material towards substantially
higher quality factor Q and greatly enhanced drift stability. The
technique not only provides insight identifying contamination as a
dominant mechanism for Q-degradation in nickel-plated
micromechanical resonators exposed to uncontrolled environments,
but also offers a convenient method for restoring a contaminated
device to its original high-Q (Q=14,172) characteristics. This
paper further describes a process for producing a nickel
microresonator on which testing may be performed. The process
begins with a silicon substrate on which 2 microns of oxide was
grown. Next 300 angstroms of titanium and 2700 angstroms of gold
were evaporated and then patterned to form interconnects. Next 1.8
microns of aluminum was evaporated and then vias were patterned
into the aluminum to expose the underlying gold. Next, nickel
plating was used to create deposits that filled the vias and was
timed such that a planarized nickel aluminum surface was achieved
in the regions of the vias. Next a 200 angstrom deposit of nickel
was evaporated over the entire surface. This evaporated deposit
served as a seed layer and as the beginning of structural layer
processing. A photoresist mold was then formed over the evaporated
nickel and then 3 microns of nickel was plated into mold. The mold
and seed layer were then removed and thereafter the aluminum was
removed. The paper provides an SEM image of the resonator as well
as a schematic of the electrical set up for testing.
[0036] A need exists in the art for improving adhesion between the
layers of a multilayer structure when those layers are not formed
separate from one another but are formed in intimate contact with
one another and already adhered to one another prior to heat
treatment.
SUMMARY OF THE DISCLOSURE
[0037] It is an object of at least one aspect of the invention to
provide an electrochemical fabrication technique that yields
improved properties of fabricated structures.
[0038] It is an object of at least one aspect of the invention to
provide an electrochemical fabrication technique that yields
improved interlayer adhesion.
[0039] It is an object of at least one aspect of the invention to
provide a heat treated structure having significantly improved
interlayer adhesion while not significantly reducing the yield
strength of the intra-layer material.
[0040] It is an object of at least one aspect of the invention to
reduce the presence of metallic oxides that may be located along
the interfaces between successively deposited layers or portions of
layers.
[0041] It is an object of at least one aspect of the invention to
provide a heat treated structure having improved properties where
the structure remains protected by a sacrificial material until it
is time for use.
[0042] Other objects and advantages of various aspects of the
invention will be apparent to those of skill in the art upon review
of the teachings herein. The various aspects of the invention, set
forth explicitly herein or otherwise ascertained from the teachings
herein, may address any one of the above objects alone or in
combination, or alternatively they may not address any of the
objects set forth above but instead address some other object of
the invention which may be ascertained from the teachings herein.
It is not intended that all of these objects be addressed by any
single aspect of the invention even though that may be the case
with regard to some aspects.
[0043] In a first aspect of the invention, a fabrication process
for forming a multi-layer three-dimensional structure, includes:
(a) forming and adhering a layer of material to a previously formed
layer and/or to a substrate, wherein the layer includes a desired
pattern of at least one material; and (b) repeating the forming and
adhering operation of (a) at least twice to build up a
three-dimensional structure from a plurality of adhered layers,
wherein the desired patterning on at least two layers is different;
(c) after formation of at least a plurality of layers, subjecting
the multi-layer structure to a heat treatment; wherein the
structure includes at least one metal, and wherein formation of the
desired pattern for at least one layer includes use of an adhered
mask.
[0044] In a second aspect of the invention, a fabrication process
for forming a multi-layer three-dimensional structure, includes:
forming a patterned deposit of at least one first material on to a
substrate or previously deposited material such that at least one
void exists around or within the patterned deposit of the at least
first material; depositing at least one second material into at
least a portion of the at least one void; (c) trimming the deposit
of at least on of the at least one first material or the at least
one second material to a desired level; (d) repeating the forming
and adhering operations of (a)-(c) a plurality of times to build up
a three-dimensional structure from a plurality of adhered layers;
(e) after formation of at least a plurality of layers, subjecting
the multi-layer structure to heat treatment, wherein at least one
deposited material includes a metal, and wherein the forming of the
patterned deposit for at least one layer includes use of an adhered
mask.
[0045] In a third aspect of the invention, a fabrication process
for forming a multi-layer three-dimensional structure, includes:
(a) forming and adhering a layer to a previously formed layer
and/or to a substrate; and (b) repeating the forming and adhering
operation of (a) at least once to build up a three-dimensional
structure from a plurality of adhered layers, wherein at least a
plurality of the layers each include at least two deposited
materials; (c) after formation of at least a plurality of layers
and while at least two materials remain in contact adhered to one
another, subjecting the multi-layer structure to a heat treatment;
wherein the structure includes at least one metal.
[0046] In a fourth aspect of the invention, a fabrication process
for forming a multi-layer three-dimensional structure, includes:
(a) forming and adhering a layer to a previously formed layer
and/or to a substrate; and (b) repeating the forming and adhering
operation of (a) at least once to build up a three-dimensional
structure from a plurality of adhered layers, wherein the forming
of at least a plurality of layers includes removing at least some
deposited material in a planarization operation; (c) after
formation of at least a plurality of layers, subjecting the
multi-layer structure to a heat treatment; wherein the structure
includes at least one metal, and wherein the forming and adhering
of at least one layer includes use of an adhered mask in the
selective patterning of at least one material.
[0047] In a fifth aspect of the invention, a fabrication process
for forming a multi-layer three-dimensional structure, includes:
(a) forming and adhering a layer to a previously formed layer
and/or to a substrate, wherein the layer includes a desired pattern
of at least one material; and (b) repeating the forming and
adhering operation of (a) at least once to build up a
three-dimensional structure from a plurality of adhered layers,
wherein the desired patterning of at least one material deposited
on a subsequent layer adheres directly to the desired patterning of
at least one material deposited on a preceding layer; (c) after
formation of at least a plurality of layers, subjecting the
multi-layer structure to a heat treatment; wherein the structure
includes at least one metal, and wherein the forming and adhering
of at least one layer includes use of an adhered mask in the
selective patterning of at least one material.
[0048] In a sixth aspect of the invention, a fabrication process
for forming a multi-layer three-dimensional structure, includes:
(a) forming and adhering a layer to a previously formed layer
and/or to a substrate, wherein the layer includes a desired pattern
of at least one material; and (b) repeating the forming and
adhering operation of (a) at least once to build up a
three-dimensional structure from a plurality of adhered layers; (c)
after formation of at least a plurality of layers, subjecting the
multi-layer structure to a heat treatment, wherein the structure is
heated in a manner such that any local temperature variations
within the structure do not directly result from localized
differences in electrical conductivity of the structural material;
wherein the structure includes at least one metal, and wherein the
forming and adhering of at least one layer includes use of an
adhered mask in the selective patterning of at least one
material.
[0049] In a seventh aspect of the invention, a fabrication process
for forming a multi-layer three-dimensional structure, includes:
(a) forming and adhering a layer to a previously formed layer
and/or to a substrate, wherein the layer includes a desired pattern
of at least one material; and (b) repeating the forming and
adhering operation of (a) at least once to build up a
three-dimensional structure from a plurality of adhered layers; (c)
after formation of at least a plurality of layers, subjecting the
multi-layer structure to a heat treatment such that substantially
all portions of the structure are heated to a substantially uniform
temperature; wherein the structure includes at least one metal.
[0050] In an eighth aspect of the invention, a fabrication process
for forming a multi-layer three-dimensional structure, includes:
(a) forming and adhering a layer to a previously formed layer
and/or to a substrate, wherein the layer includes a desired pattern
of at least one material; and (b) repeating the forming and
adhering operation of (a) at least once to build up a
three-dimensional structure from a plurality of adhered layers; (c)
after formation of at least a plurality of layers, subjecting the
multi-layer structure to a heat treatment, wherein a maximum
temperature during heat treatment is less than a recrystallization
temperature of at least one metal forming part of the structure,
and wherein the forming and adhering of at least one layer includes
use of an adhered mask in the selective patterning of at least one
material.
[0051] In a ninth aspect of the invention, a fabrication process
for forming a multi-layer three-dimensional structure, includes:
(a) forming and adhering a layer to a previously formed layer
and/or to a substrate, wherein the layer includes a desired pattern
of at least one material; and (b) repeating the forming and
adhering operation of (a) at least once to build up a
three-dimensional structure from a plurality of adhered layers,
wherein at least a plurality of the layers each include at least
one structural material and at least one sacrificial material; (c)
separating the sacrificial material from the structure to release
the structure; and (d) after formation of at least a plurality of
layers but prior to release, subjecting the multi-layer structure
to a heat treatment; wherein the structure includes at least one
metal, and wherein the forming and adhering of at least one layer
includes use of an adhered mask in the selective patterning of at
least one material.
[0052] In a tenth aspect of the invention, a fabrication process
for forming a multi-layer three-dimensional structure, includes:
(a) forming and adhering a layer to a previously formed layer
and/or to a substrate, wherein the layer includes a desired pattern
of at least one material; and (b) repeating the forming and
adhering operation of (a) at least once to build up a
three-dimensional structure from a plurality of adhered layers,
wherein at least a plurality of the layers each include at least
one structural material and at least one sacrificial material, and
wherein the desired patterning on at least two layers is different;
(c) separating the sacrificial material from the structure to
release the structure; and (d) after release, subjecting the
multi-layer structure to a heat treatment; wherein the structure
includes at least one metal, and wherein the forming and adhering
of at least one layer includes use of an adhered mask in the
selective patterning of at least one material
[0053] In an eleventh aspect of the invention, a fabrication
process for forming a multi-layer three-dimensional structure,
includes: (a) forming and adhering a layer to a previously formed
layer and/or to a substrate, wherein the layer includes a desired
pattern of at least one material; and (b) repeating the forming and
adhering operation of (a) at least once to build up a
three-dimensional structure from a plurality of adhered layers; (c)
subjecting the multi-layer structure to a heat treatment while the
structure is located in a selected atmosphere including an inert
gas, wherein the structure includes at least one metal.
[0054] In a twelfth aspect of the invention, a fabrication process
for forming a multi-layer three-dimensional structure, includes:
(a) forming and adhering a layer to a previously formed layer
and/or to a substrate, wherein the layer includes a desired pattern
of at least one material; and (b) repeating the forming and
adhering operation of (a) at least once to build up a
three-dimensional structure from a plurality of adhered layers; (c)
subjecting the multi-layer structure to a heat treatment while the
structure is located in a selected atmosphere including a reducing
gas, wherein the structure includes at least one metal.
[0055] In a thirteenth aspect of the invention, a fabrication
process for forming a multi-layer three-dimensional structure,
includes: (a) forming and adhering a layer to a previously formed
layer and/or to a substrate, wherein the layer includes a desired
pattern of at least one material; and (b) repeating the forming and
adhering operation of (a) at least once to build up a
three-dimensional structure from a plurality of adhered layers,
wherein at least a plurality of the layers each include at least
one structural material and at least one sacrificial material, and
wherein the desired patterning on at least two layers is different;
(c) separating the sacrificial material from the structure to
release the structure; (d) after release, subjecting the
multi-layer structure to a heat treatment; (e) after the heat
treatment, applying a second sacrificial material to the structure.
wherein the structure includes at least one metal.
[0056] In a fourteenth aspect of the invention, a fabrication
process for forming a multi-layer three-dimensional structure,
includes: (a) forming and adhering a layer of material to a
previously formed layer and/or to a substrate, wherein the layer
includes a desired pattern of at least one material; and (b)
repeating the forming and adhering operation of (a) at least twice
to build up a three-dimensional structure from a plurality of
adhered layers; (c) after formation of at least a plurality of
layers, subjecting the multi-layer structure to a heat treatment;
and (d) releasing the structure from the substrate, wherein the
structure includes at least one metal, and wherein the forming and
adhering of at least one layer includes use of an adhered mask in
the selective patterning of at least one material.
[0057] In a fifteenth aspect of the invention, a fabrication
process for forming a multi-layer three-dimensional structure,
includes: A fabrication process for forming a multiple multi-layer
three-dimensional structures, including: (a) forming and adhering a
layer of material to a previously formed layer and/or to a
substrate, wherein the layer includes a desired pattern of at least
one material; and (b) repeating the forming and adhering operation
of (a) at least twice to build up a plurality of three-dimensional
structures from a plurality of adhered layers; (c) after formation
of at least a plurality of layers, subjecting the multi-layer
structure to a heat treatment; and (d) dicing the plurality of
structures from one another, wherein the structure includes at
least one metal.
[0058] In a sixteenth aspect of the invention, a fabrication
process for forming a multi-layer three-dimensional structure,
includes: (a) forming and adhering a layer to a previously formed
layer and/or to a substrate, wherein the layer includes a desired
pattern of at least one material; and (b) repeating the forming and
adhering operation of (a) at least once to build up a
three-dimensional structure from a plurality of adhered layers; (c)
after formation of at least a plurality of layers, subjecting the
multi-layer structure to a heat treatment, wherein a maximum
effective temperature during heat treatment is less than a
recrystallization temperature of at least one metal forming part of
the structure, and wherein the heat treatment is applied for a
sufficient time and at a sufficient temperature and in an
environment that allows interlayer adhesion to be enhanced a
substantial amount, and wherein the forming and adhering of at
least one layer includes use of an adhered mask in the selective
patterning of at least one material.
[0059] In a seventeenth aspect of the invention, a fabrication
process for forming a multi-layer three-dimensional structure,
includes: (a) forming and adhering a layer to a previously formed
layer and/or to a substrate, wherein the layer includes a desired
pattern of at least one material; and (b) repeating the forming and
adhering operation of (a) at least once to build up a
three-dimensional structure from a plurality of adhered layers; (c)
after formation of at least a plurality of layers, subjecting the
multi-layer structure to a heat treatment, wherein the heat
treatment is applied to the structure for a temperature, a time,
and in an environment such that a substantial increase in
interlayer adhesion results without significantly reducing the
yield strength of the intra-layer material, and wherein the forming
and adhering of at least one layer includes use of an adhered mask
in the selective patterning of at least one material.
[0060] In an eighteenth aspect of the invention, a fabrication
process for forming a multi-layer three-dimensional structure,
includes: (a) forming and adhering a layer to a previously formed
layer and/or to a substrate, wherein the layer includes a desired
pattern of at least one material; and (b) repeating the forming and
adhering operation of (a) at least once to build up a
three-dimensional structure from a plurality of adhered layers; (c)
after formation of at least a plurality of layers, subjecting the
multi-layer structure to a heat treatment, wherein the heat
treatment results in the formation of a structure which behaves
monolithically up to at least 50% of the yield strength of the
intra-layer material, and wherein the forming and adhering of at
least one layer includes use of an adhered mask in the selective
patterning of at least one material.
[0061] In a nineteenth aspect of the invention, a fabrication
process for forming a multi-layer three-dimensional structure,
includes: (a) forming and adhering a layer to a previously formed
layer and/or to a substrate, wherein the layer includes a desired
pattern of at least one material; and (b) repeating the forming and
adhering operation of (a) at least once to build up a
three-dimensional structure from a plurality of adhered layers; (c)
after formation of at least a plurality of layers, subjecting the
multi-layer structure to a heat treatment, wherein the heat
treatment results in the formation of a structure which is no more
likely to experience interlayer adhesion failure than intra-layer
cohesion failure when applied stress is at least 50% of the yield
strength of the intra-layer material.
[0062] Further aspects of the invention will be understood by those
of skill in the art upon reviewing the teachings herein. Other
aspects of the invention may involve combinations of the above
noted aspects of the invention and/or addition of various features
of one or more embodiments. Other aspects of the invention may
involve apparatus that are configured to implement one or more of
the above process aspects of the invention. These other aspects of
the invention may provide various combinations of the aspects
presented above as well as provide other configurations,
structures, functional relationships, and processes that have not
been specifically set forth above but which are ascertainable from
the teachings herein.
BRIEF DESCRIPTION OF THE DRAWINGS
[0063] FIGS. 1(a)-1(c) schematically depict side views of various
stages of a CC mask plating process, while FIGS. 1(d)-(g)
schematically depict a side views of various stages of a CC mask
plating process using a different type of CC mask.
[0064] FIGS. 2(a)-2(f) schematically depict side views of various
stages of an electrochemical fabrication process as applied to the
formation of a particular structure where a sacrificial material is
selectively deposited while a structural material is blanket
deposited.
[0065] FIGS. 3(a)-3(c) schematically depict side views of various
example subassemblies that may be used in manually implementing the
electrochemical fabrication method depicted in FIGS. 2(a)-2(f).
[0066] FIGS. 4(a)-4(i) schematically depict the formation of a
first layer of a structure using adhered mask plating where the
blanket deposition of a second material overlays both the openings
between deposition locations of a first material and the first
material itself.
[0067] FIG. 5 schematically depicts a heating system in which
multiple structures have been placed for heat treatment (e.g.
diffusion bonding) in accordance with various embodiments of the
invention.
[0068] FIG. 6 depicts a block diagram of a first embodiment of the
invention where a multilayer three-dimensional structure is formed
and then heat treated such that, for example, interlayer adhesion
is improved.
[0069] FIG. 7 depicts a block diagram of a second embodiment of the
invention where the formation of a multilayer three-dimensional
structure includes an operation to planarize deposited layers of
material and wherein the structure is subjected to heat treatment
after formation.
[0070] FIG. 8 depicts a block diagram of a third embodiment of the
invention wherein the formation of a multi-layer structure includes
adhered subsequently patterned layers of material directly to
immediately preceding patterned layers of material and wherein the
structure is subjected to heat treatment after formation.
[0071] FIG. 9 depicts a block diagram of a fourth embodiment of the
invention wherein the formation of a multi-layer structure includes
the deposition of a plurality of materials during the formation of
each layer and wherein the structure is subjected to heat treatment
after formation.
[0072] FIG. 10 depicts a flowchart of a fifth embodiment of the
invention which may be considered an expanded version of the fourth
embodiment wherein one of the materials is a sacrificial material
and may be removed either before or after heat treatment.
[0073] FIG. 11 depicts a block diagram of a sixth embodiment of the
invention where a structure is separated from a sacrificial
material for heat treatment but is at least in part encapsulated
with a sacrificial material after heat treatment until it is ready
to use or is put to use at which time the sacrificial material may
be removed.
[0074] FIG. 12 depicts a flowchart of a seventh embodiment of the
invention wherein the structure may or may not be released from a
substrate prior to heat treatment.
[0075] FIG. 13 depicts a flow chart of an eighth embodiment of the
invention wherein multiple multi-layer structures are formed which
may be partially or completed diced from one another prior to heat
treatment.
[0076] FIG. 14 depicts a block diagram of a ninth embodiment of the
invention where the structure is heat treated, after formation, at
a temperature that is less than a recrystallization temperature of
at least one of the structural materials from which the structure
is formed.
[0077] FIG. 15 depicts a block diagram of a tenth embodiment of the
invention where the structure is heat treated after formation at a
temperature that significantly enhances interlayer adhesion but
does not significantly decrease the yield strength of the
intra-layer material.
[0078] FIG. 16 depicts a block diagram of an eleventh embodiment of
the invention where the structure is heat treated at a temperature
and time such that the multi-layer structure behaves monolithically
up to at least 50% of the yield strength of the intra-layer
material forming the structure.
[0079] FIG. 17 depicts a block diagram of an twelfth embodiment of
the invention where the structure is heat treated at a temperature
and time such that the multi-layer structure behaves monolithically
up to at least 50% of the ultimate tensile strength of the
intra-layer material forming the structure.
[0080] FIG. 18 depicts a block diagram of a thirteenth embodiment
of the invention where the structure is heat treated in an
atmosphere that is inert or that includes a reducing agent.
[0081] FIG. 19 depicts a block diagram of a fourteenth embodiment
of the invention where the structure is heat treated such that all
portions of the structure reach a substantially uniform
temperature.
[0082] FIG. 20 depicts a block diagram of a fifteenth embodiment of
the invention where the structure is heat treated such that local
temperature differences do not directly result from localized
differences in electrical conductivity (i.e. from ohmic heating
from carrying an electric current).
[0083] FIG. 21 depicts a flowchart of a sixteenth embodiment where
the structure is partially formed, released from sacrificial
material, then heat treated, and then completed with or without
refilling of sacrificial material and with or without further heat
treating.
[0084] FIGS. 22(a)-22(c) depict various views of the CAD design of
a helical spring-type contact element.
[0085] FIG. 22(d) depicts a number of helical spring-type contact
elements of FIGS. 22(a)-22(c) which are to be formed together in an
array.
[0086] FIG. 22(e) depicts an SEM image of the microstructures of
FIG. 22(d) created using an electrochemical fabrication
process.
[0087] FIG. 23 depicts a substrate containing a plurality of
devices similar to those shown in FIG. 22(b) which have been heat
treated and wherein one of the devices has been subjected to a
tensional force that has stretched the structure beyond the elastic
limits of the material wherein the structure behaved monolithically
(i.e. adhesion at the layer boundary did not fail).
DETAILED DESCRIPTION
[0088] FIGS. 1(a)-1(g), 2(a)-2(f), and 3(a)-3(c) illustrate various
features of one form of electrochemical fabrication that are known.
Other electrochemical fabrication techniques are set forth in the
'630 patent referenced above (and in pending U.S. patent
application Ser. No. 09/493,496 which a divisional of the
application that lead to the '630 patent and is hereby incorporated
herein by reference), in the various previously incorporated
publications, in various other patents and patent applications
incorporated herein by reference, still others may be derived from
combinations of various approaches described in these publications,
patents, and applications, or are otherwise known or ascertainable
by those of skill in the art from the teachings set forth herein.
All of these techniques may be combined with those of the various
embodiments of various aspects of the invention explicitly set
forth herein to yield enhanced embodiments. Still other embodiments
may be derived from combinations of the various embodiments
explicitly set forth herein.
[0089] FIGS. 4(a)-4(i) illustrate various stages in the formation
of a single layer of a multi-layer fabrication process where a
second metal is deposited on a first metal as well as in openings
in the first metal where its deposition forms part of the layer. In
FIG. 4(a), a side view of a substrate 82 is shown, onto which
patternable photoresist 84 is cast as shown in FIG. 4(b). In FIG.
4(c), a pattern of resist is shown that results from the curing,
exposing, and developing of the resist. The patterning of the
photoresist 84 results in openings or apertures 92(a)-92(c)
extending from a surface 86 of the photoresist through the
thickness of the photoresist to surface 88 of the substrate 82. In
FIG. 4(d), a metal 94 (e.g. nickel) is shown as having been
electroplated into the openings 92(a)-92(c). In FIG. 4(e), the
photoresist has been removed (i.e. chemically stripped) from the
substrate to expose regions of the substrate 82 which are not
covered with the first metal 94. In FIG. 4(f), a second metal 96
(e.g., silver) is shown as having been blanket electroplated over
the entire exposed portions of the substrate 82 (which is
conductive) and over the first metal 94 (which is also conductive).
FIG. 4(g) depicts the completed first layer of the structure which
has resulted from the planarization of the first and second metals
down to a height that exposes the first metal and sets a thickness
for the first layer. In FIG. 4(h) the result of repeating the
process steps shown in FIGS. 4(b)-4(g) several times to form a
multi-layer structure are shown where each layer consists of two
materials. For most applications, one of these materials is removed
as shown in FIG. 4(i) to yield a desired 3-D structure 98 (e.g.
component or device).
[0090] The various embodiments, alternatives, and techniques
disclosed herein may be used in combination with electrochemical
fabrication techniques that use different types of patterning masks
and masking techniques. For example, conformable contact masks and
masking operations may be used, proximity masks and masking
operations may be used (i.e. operations that use masks that at
least partially selectively shield a substrate by their proximity
to the substrate even if contact is not made), non-conformable
masks and masking operations may be used (i.e. masks and operations
based on masks whose contact surfaces are not significantly
conformable), and adhered masks and masking operations may be used
(masks and operations that use masks that are adhered to a
substrate onto which selective deposition or etching is to occur as
opposed to only being contacted to it).
[0091] In still other embodiments, shielded conductive probes may
be used as a form of direct writing of patterned deposits. An
example of such an approach is found in U.S. Pat. No. 5,641,391 to
Hunter et al., entitled "Three Dimensional Microfabrication By
Localized Electrodeposition and Etching" which is hereby
incorporated herein by reference. In still other embodiments
multiple probes may be used simultaneously or multi-cell masks may
be used that allow selective cell-by-cell deposition or etching.
Such masks and their use are described in U.S. patent application
Ser. No. 10/677,498, filed on Oct. 1, 2003, and entitled "Selective
Electrochemical Deposition Methods Using Pyrophosphate Copper
Plating Baths Containing Ammonium Salts, Citrate Salts and/or
Selenium Oxide". This patent and application are incorporated
herein by reference as if set forth in full herein.
[0092] Various embodiments of various aspects of the invention are
directed to formation of three-dimensional structures from
materials some of which are to be electrodeposited or electroless
deposited. Some of these structures may be formed from a plurality
of layers of one or more deposited materials (e.g. 3 or more
layers, more preferably five or more layers, and most preferably
ten or more layers). In some embodiments structures having features
positioned with micron level precision (e.g. less than 5 microns,
preferably less than 1 micron and more preferably less than about
0.5 microns) and minimum features size on the order of microns or
tens of microns (e.g. less than 20 microns, preferably less than 10
microns, and more preferably less than about 1 micron). In other
embodiments structures with less precise feature placement and/or
larger minimum features may be formed. In still other embodiments,
higher precision and smaller minimum feature sizes may be
desirable.
[0093] Various embodiments disclosed herein or portions of those
embodiments may be supplemented by the above incorporated and known
techniques by adding to them (for the formation of any given
structure) processes that involve the selective etching of
deposited material and the filling of created voids with additional
materials. Various other embodiments of various aspects of the
invention, may depart from the selective deposition of materials
entirely, and use blanket electrodeposition operations to deposit
materials and selective etching operations to pattern those
materials by creating voids that can be filled in using blanket
deposition operations. Various other embodiments may cause
deposition of material to deviate from a strict layer-by-layer
build up process. In a strict layer-by-layer build up process each
layer is complete formed prior to beginning formation of a
subsequent layer, e.g. an n.sup.th layer is completely formed prior
to beginning deposition operations for forming a portion of an
(n+1).sup.th layer. In these alternative processes, formation of an
(n+1).sup.th layer begins prior to completing the formation of an
n.sup.th layer. All of these techniques are considered generalized
layer-by-layer formation processes and they are used to produce
multilayer structures where successively formed layers are adhered
to previously formed adjacent layers. Such teachings are further
described in U.S. patent application Ser. No. 10/434,519, filed May
7, 2003 by Smalley, and entitled "Methods of and Apparatus for
Electrochemically Fabricating Structures Via Interlaced Layers or
Via Selective Etching and Filling of Voids". This patent
application is hereby incorporated herein by reference as if set
forth in full.
[0094] Other embodiments may use other forms of depositing
material. For example, in some embodiments deposition of material
may occur via chemical or physical vapor deposition (e.g.
evaporation or sputtering), spreading, spraying, or the like. In
some embodiments spray metal coating processes may be used to
obtain blanket or selective depositions. Spray metal coating
techniques for forming three dimensional structures and
particularly microstructures are described in U.S. patent
application Ser. No. 10/697,597, filed on Oct. 29, 2003 by Lockard
et al., and entitled "EFAB Methods and Apparatus Including Spray
Metal or Powder Coating Processes". This patent application is
hereby incorporated herein by reference. In some embodiments the
heat treating operations may be used in conjunction with porous
structural materials to improve adhesion between the individual
particles and/or to aid in infiltrating a filler material into the
pores of the structural material.
[0095] In still other embodiments heat treatment that improves
interlayer adhesion may be combined with other post layer formation
operations. For example packaging or hermetic sealing operations
may be performed in conjunction with heat treatment operations.
Hermetic sealing of packaging structures that surround components
or other devices is described in U.S. patent application Ser. No.
10/434,103, filed on May 7, 2003, by Cohen et al, and entitled
"Electrochemically Fabricated Hermetically Sealed Microstructures
and Methods of and Apparatus for Producing Such Structures". This
patent application is hereby incorporated herein by reference in
its entirety.
[0096] FIG. 5 schematically depicts a heating system in which
multiple structures have been placed for heat treatment (e.g.
diffusion bonding) according to various embodiments of the
invention. The system contains a heating chamber 102 which includes
resistive heating elements 104 and 106 and temperature sensing
device 108. The heating chamber may be selectively filled with any
of a number of gases as indicated by elements 112, 114, and 116.
Alternatively the chamber may be evacuated using a vacuum pump 118.
Filling with gas may occur after evacuation or result from a
purging process that uses the gas via one or more outlets located
on the chamber. One or more structures (for example structures 122,
124, or 126) may be placed in the chamber on support 128.
Controller 132 may then be operated to evacuate the chamber or fill
it with an appropriate gas and then it may supply power to heating
coils 104 and 106 to raise the temperature within the chamber at a
controlled rate and to a controlled final temperature after which
the temperature may be lowered in a controlled manner or the system
may simply be shut off and the temperature allowed to lower as a
result of heat dissipation from the chamber. Temperature sensor 108
may be used by the controller in a feedback loop to ensure
appropriate operation occurs. The controller 132 may be a
programmable device with an appropriate control panel and display
panel. In other heating systems multiple temperature sensors may be
used and heat may be applied to the sample in other ways. For
example, inductive coupling may be used to heat the samples burning
of a fuel source may be used to supply heat via convection,
conduction and/or radiative effects. Heating elements may be
located below, beside, and/or above the structures to be heated.
The chamber may also include a fan or other elements for enhancing
flow of gas within the chamber. In some embodiments direct
application of current applied to the sample or samples may be
used. This latter approach would seem particularly viable when the
structure remains embedded in a conductive sacrificial material but
it may also have application when structures are released and of a
design that would allow reasonably uniform current flow through all
portions of the structure or where heat conduction via the
structure itself may allow reasonable heat transfer and
temperatures to be obtained.
[0097] FIG. 6 depicts a block diagram of a first embodiment of the
invention where a multilayer three-dimensional structure is formed
and then heat treated such that, for example, interlayer adhesion
is improved. Element 152 of FIG. 6 calls for the formation of a
multi-layer structure from a plurality of adhered layers. This
formation process may involve one of the electrochemical
fabrication processes discussed above, one of the fabrication
processes incorporated herein by reference or some other
fabrication process that results in layers being formed on
previously formed layers and adhered thereto. After formation of
the structure the process moves forward to element 154 which calls
for the supplying of a heat treatment to the structure such that
interlayer adhesion, for example, is enhanced. The heat treatment
may be applied by a heating system such as that illustrated in FIG.
5, or it may be applied in a different manner. The heat treatment
is applied at a temperature and for a time that results in a
desired increase in interlayer adhesion.
[0098] FIG. 7 depicts a block diagram of a second embodiment of the
invention where the formation of a multilayer three-dimensional
structure includes an operation to planarize deposited layers of
material and wherein the structure is subjected to heat treatment
after formation. Element 162 of FIG. 7 calls for the formation of a
three-dimensional structure which includes a plurality of adhered
layers. The formation process will include the depositing of at
least one material onto a substrate or previously formed layer such
that at least a portion of the layer is formed. Then at least a
portion of the deposited material is removed to obtain a planarized
surface that may form an outward facing portion of the structure or
alternatively it may form a surface onto which additional material
may be adhered. Planarization may occur for example by lapping,
polishing, chemical mechanical polishing, milling, diamond fly
cutting, or the like. After the depositing and removing of material
to form a first layer or portion of a layer the depositing and
removing steps are repeated to form additional layers of the
structure which are adhered together. After the formation of the
structure is complete, the process moves forward to element 164
which calls for the heat treating of the structure such that
interlayer adhesion is enhanced.
[0099] FIG. 8 depicts a block diagram of a third embodiment of the
invention wherein the formation of a multi-layer structure includes
subsequently patterned layers of material that are adhered directly
to immediately preceding patterned layers of material and wherein
the structure is subjected to heat treatment after formation.
Element 172 of FIG. 8 calls for the formation of a
three-dimensional structure from a plurality of adhered layers. The
first operation involves the forming of a first layer from a
deposit of at least one material where the material has a patterned
configuration. The material may be deposited in a patterned manner
or it may be deposited in a blanket fashion where patterning occurs
after deposition. The formation of the first layer may include the
deposition of a second material or further materials, it may also
include removal operations for the purpose of patterning or the
purpose of planarization, and/or it may also include other
operations such as cleaning operations, activation operations,
process monitoring operations, and the like. After the first layer
is formed, a second layer is formed from the deposit of at least
one material which has a patterned configuration. The patterned
material deposited to form the second layer adheres, at least in
part, directly to the patterned configuration of material forming
the first layer. In other words, there is no unpatterned
intervening material that separates the first and second layers. In
the formation of the structure a third operation involves the
repeating the second operation as necessary to build up the
structure from the plurality of layers. During the repetition
"second" is replaced by "n.sup.th" and "first" is replaced by
"(n-1).sup.th" where n is increment from 3 to N, where N is the
number of the last layer to be formed. After formation of the
structure is complete, the process moves forward to element 174
which calls for a heat treatment of the structure such that
interlayer adhesion is enhanced.
[0100] FIG. 9 depicts a block diagram of a fourth embodiment of the
invention wherein the formation of a multi-layer structure includes
the deposition of a plurality of materials during the formation of
each layer and wherein the structure is subjected to heat treatment
after formation. Element 182 calls for the formation of a
multi-layer structure where the layers are adhered to adjacent
layers and wherein each layer includes at least two deposited
materials. Each of the materials may be structural material or
alternatively at least one of the materials may be a structural
material and at least one of the other materials may be a
sacrificial material. After the structure is formed the process
moves forward to element 184 which calls for heat treating the
structure such that interlayer adhesion is enhanced.
[0101] FIG. 10 depicts a flowchart of a fifth embodiment of the
invention which may be considered an expanded version of the fourth
embodiment where one of the materials is a sacrificial material and
may be removed either before or after heat treatment. The process
of FIG. 10 begins with element 192 which calls for the formation of
a multi-layer three-dimensional structure wherein adjacent layers
are adhered to one another and where the structure includes at
least one structural material and where at least one or more layers
includes a sacrificial material.
[0102] After the structure is formed, the process moves forward to
element 194 which makes an inquiry as to whether the sacrificial
material is to be released from the structural material prior to
heat treatment. If the answer is "yes", the process moves forward
to element 196 which calls for the release of the structure from
the sacrificial material, for example, via a chemical etching
operation or the like. After which the process moves forward to
element 200 which calls for heat treating the structure such that
interlayer adhesion is enhanced. If the answer to the inquiry of
element 194 is "no", the process moves forward to element 200 which
calls for the heat treating of the structure such that interlayer
adhesion is enhanced and thereafter the process moves forward to
element 202 which calls for the release of the structure from the
sacrificial material. In some embodiments, it may be desirable to
release the structure from the sacrificial material prior to heat
treating as the presence of the sacrificial material during heat
treating may cause undesired alloying between a sacrificial
material and a structural material or it may cause creation of
undesired inter-metallic compounds at the interface between the two
materials. However, in other embodiments alloying and/or formation
of inter-metallic compounds may give desirable benefits. It may
also be desirable to cause the release prior to heat treatment
since some structural materials and sacrificial materials may have
significantly different coefficients of thermal expansion that
could result in undesirable stresses being introduced into the
structure during heat treating if the sacrificial material were
present and if the heat treating temperature is high. In other
embodiments it may be desirable to have the sacrificial material
present at the time of heat treatment of the structure, as the
sacrificial material may form a mold that will help hold the
structural material in its proper position during treatment.
[0103] FIG. 11 depicts a block diagram of a sixth embodiment of the
invention where a structure is separated from a sacrificial
material before heat treatment but is at least in part encapsulated
with a sacrificial material after heat treatment until it is ready
to use or is put to use at which time the sacrificial material may
be removed. The process of FIG. 11 begins with element 212 which
calls for the formation of a multi-layer 3-dimensional structure
where adjacent layers are adhered to one another. After the
structure is formed, the process moves forward to element 214 which
calls for the release of the structure from at least one
sacrificial material. Thereafter the process moves forward to
element 216 which calls for the heat treating of the structure such
that interlayer adhesion is enhanced. After heat treatment is
completed the process moves forward to element 218 which calls for
the applying of a sacrificial material to the structure. This
sacrificial material may be the same as a sacrificial material used
during the formation of the structure, or it may be a different
sacrificial material. For example, if the structural material is
nickel, this sacrificial material may be copper. Alternatively it
may be a photoresist material, a photopolymer, or some other
material that may be applied to the structure in a liquid state and
then separated form the structure via chemical dissolution,
melting, or the like. This applied sacrificial material may be
useful in protecting a delicate microstructure during a handling,
shipping, mounting or during other processes to which the fragile
structure may be subject. After the sacrificial material is applied
the process moves forward to element 220 which calls for the
mounting or otherwise locating of the structure into a working
position after which the process moves forward to element 222 which
calls for the release of the structure from the applied sacrificial
material.
[0104] In some alternative embodiments the sacrificial material
that is applied after heat treatment may remain in place during use
of the microstructure. For example such retention of the
sacrificial material may be useful in an RF application where the
sacrificial material may be a dielectric that helps support
portions of coaxial structures and the like. In other embodiments,
more than one sacrificial material may be used during formation of
the structure, at least one of the materials may be removed prior
to heat treatment and at least one of the materials may remain
during heat treatment, a portion of the remaining sacrificial
material may interact with the structural material during heat
treatment for a beneficial purpose, and then after heat treatment
at least a portion of this retained sacrificial material may be
removed. Alternatively, the sacrificial material may be removed
prior to heat treatment and another material added prior to heat
treatment, heat treatment may occur with this extra-material in
place, and then after heat treatment the added material may be
retained in whole or in part, or it may be removed in its
entirety.
[0105] FIG. 12 depicts a flowchart of a seventh embodiment of the
invention wherein the structure may or may not be released from a
substrate prior to heat treatment. In this embodiment it is
recognized that it may be desirable to release a structure from its
substrate prior to performing a heat treatment operation. This may
be desirable, for example, when the structure is formed from a
material which has a significantly different coefficient of thermal
expansion from that of the substrate material. After heat treatment
the structure could then be attached to a different substrate or
even potentially reattached to the initial substrate.
[0106] The process of this embodiment begins with element 232 which
calls for the formation of a multi-layer three-dimensional
structure that has layers adhered to one another. After formation
of the structure the process moves forward to element 234 which
inquires as to whether the structure should be released from the
substrate prior to heat treatment. If the answer is "yes", the
process moves forward to element 236 which calls for the release of
the structure from the substrate. This release may occur, for
example, via a meltable or dissolvable release layer that is
located between the substrate and the structure. Alternatively, it
may occur by machining away the substrate and/or etching and/or
planarizing away the substrate or a remaining portion of the
substrate. After release of the structure from the substrate, the
process moves forward to element 238 which calls for the heat
treating of the structure such that interlayer adhesion is
enhanced. If the inquiry in element 234 produced a negative
response, the process would simply move forward from element 234 to
the heat treating operation of element 238.
[0107] FIG. 13 depicts a flowchart of an eighth embodiment of the
invention wherein multiple multi-layer structures are formed which
may be partially or completed diced from one another prior to heat
treatment. The process of this embodiment begins with element 242
which calls for the formation of multiple multi-layer structures.
After formation of the multi-layer structures, the process moves
forward to element 244 which inquires as to whether partial or
complete dicing of individual structures should occur prior to heat
treatment. In some circumstances it may be desirable to partially
or completely cut through sacrificial material that may be located
between adjacent die (i.e. individual structures or sets of
structures) prior to heat treatment so that stress build ups that
might result from differentials in coefficients of thermal
expansion cannot propagate from relatively small individual die
regions across die boundaries to distal regions where they may
reach magnitudes that are capable of causing undesired distortions,
delaminations, and the like.
[0108] If inquiry 244 produces a "yes" response, the process moves
forward to element 246 which calls for the dicing of the multiple
structures. Thereafter the process moves forward to block 248 which
calls for the heat treatment of the structures such that interlayer
adhesion is enhanced. After the operation of element 248, the
process may move forward to element 252 which will be discussed
shortly.
[0109] If inquiry 244 produces a "no" response, the process moves
forward to element 250 which calls for the heat treating of the
structures such that interlayer adhesion is enhanced and thereafter
the process moves forward to element 252 which calls for the dicing
of the structures. As noted above, from element 248 the process may
also move forward to element 252 if dicing of element 246 was
incomplete and if a supplemental dicing is beneficial to complete
the separation process.
[0110] FIG. 14 depicts a block diagram of a ninth embodiment of the
invention where the structure is heat treated, after formation, at
a temperature that is less than a recrystallization temperature of
at least one of the structural materials from which the structure
is formed. The process for this embodiment starts with element 262
which calls for the formation of a multi-layer structure where
adjacent layers are adhered to each other. After formation of the
structure, the process moves forward to element 264 which calls for
heat treating the structure using a temperature that is below the
re-crystallization temperature of the structural material but is
also sufficiently high and applied for a sufficient time such that
enhanced interlayer adhesion results.
[0111] This embodiment can be illustrated with some experimental
results. In one set of experiments, adhesion tests were performed
on electrodeposited samples of nickel that were formed on a nickel
substrate. Adhesion tests were also performed on similarly prepared
samples that underwent a heat treatment at about 450.degree. C. for
5 to 9 hours. Prior to performing the electroplating of the nickel,
for all samples, the surface of the nickel substrate was treated
using an activator known as C-12 Activator from Puma Chemical of
Warne, N.C. The activation process followed the recommendations of
the manufacturer. The three samples that did not undergo heat
treatment showed adhesion failures at about 44, 53, and 68 MPa.
Three samples that underwent heat treatment showed adhesion
failures at about 153, 215, and 280 MPa. In other words, in this
experiment, adhesion improved by a factor of about 2.2 to a factor
of about 6.4 with the average being about a factor of 4.0.
[0112] In another experiment, numerous helical structures like
those shown in FIG. 22(a)-22(e) were formed. FIGS. 22(a)-22(c)
depict various views of the CAD design of a helical spring-type
contact element. In this design the thickness of each layer is 8
microns, the width of which helical element is 80 microns, the
diameter of the overall helical element (excluding the base
element) is 200 microns, and the overall height is 160 microns.
FIG. 22(d) depicts a number of helical spring-type contact elements
of FIGS. 22(a)-22(c) which are to be formed together in an array.
FIG. 22(e) depicts an SEM image of the microstructures of FIG.
22(d) created using an electrochemical fabrication process.
[0113] Some elements of an array like that of FIG. 22(e) were
subjected to a tensile pulling test to determine the viability of
interlayer adhesion. Some samples that were pulled underwent a heat
treatment while others did not. Four of the un-heat treated samples
(each initially 160 microns in height were pulled and each
experienced interlayer adhesion failure at between 100 and 300
microns of extension. Heat treated samples that were pulled and
were extended to a height of more than 2 millimeters and no
delamination was observed. The heat treatment for these samples
included raising the samples to a temperature of 500.degree. C. at
a rate of less than or equal to about 3.degree. C. per minute and
then holding the 500.degree. C. temperature for 15 minutes and then
cooling down the samples at a rate of less than or equal to about
10.degree. C. per minute. This heat treating process was performed
with the structure in a forming gas which included about 5% H2 and
about 95% N2.
[0114] FIG. 23 illustrates numerous un-pulled heat treated
structures such as structures 372 and 374 along with one pulled
structure 376 which illustrates that the structure was pulled
beyond the elastic limit of the material (i.e. into the plastic
deformation region) and that the adhesion strength was greater than
the yield strength of the structure (i.e. the stress and associated
strain at which elastic deformation gives way to plastic
deformation). Not only did these heat treated samples yield a
significant improvement in interlayer adhesion, it is also believed
that a significant decrease in interlayer electrical resistance
occurred. In these experiments, heat treatment of the samples was
performed after release of the nickel structures from a copper
sacrificial material.
[0115] It is believed that a dwell temperature (Td), i.e. a maximum
temperature of heating, of between 250.degree. C. and 350.degree.
C. could be used to achieve significant improvements in interlayer
adhesion particularly if the dwell time is appropriately increased.
It is also believed that heat treating at somewhat lower
temperatures, e.g. 150.degree. C. to 200.degree. C. may also
produce useful results. However, when working with nickel
structures it is believed a dwell temperature in the range of
350.degree. C. to 550.degree. C., or somewhat higher, would allow a
more timely obtainment of desired improvement in interlayer
adhesion. It is believed that in some embodiments the dwell time
(i.e. a time at the maximum temperature) of less than 5 minutes
could be used to achieve acceptable results. While in other
embodiments a dwell time in the range of 5 minutes to 60 minutes or
even longer may be necessary or preferable. Lower dwell
temperatures and longer dwell times may be particularly beneficial
when a portion of the structure or the substrate on which it is
attached is susceptible to heat damage. It is believed that those
of skill in the art can perform experiments to determine acceptable
dwell temperatures and dwell times as well as determining
reasonable heating and cooling rates. For example, heating rates in
some embodiments may be set in the range of 3.degree. C. to
10.degree. C. per minute or even higher.
[0116] Though in the present embodiment the maximum heat treating
temperature (i.e. dwell temperature) is intended to be below the
re-crystallization temperature of the structural material, it is
believed that in some embodiments heat treating temperatures may
exceed the re-crystallization temperatures.
[0117] For example, in some embodiments a preferred structural
material might be nickel whereas in other embodiments preferred
structural material might be copper. As nickel has a melting
temperature of about 1455.degree. C. and as the re-crystallization
temperature of nickel is believed to be about 1/2 of the absolute
melting temperature (i.e. about 590.degree. C.) it is preferred to
keep the heat treatment temperature below this 590.degree. C.
level. As the melting temperature of copper is about 1083.degree.
C. and as it is believed that the re-crystallization temperature of
copper is about 1/3 of the absolute melting temperature (i.e. about
200.degree. C.) preferred heat treating operations for copper
structures may use maximum temperatures below this 200.degree. C.
value. In other embodiments, however, where other structural
materials are used, or where nickel or copper alloys (e.g. nickel
phosphor or nickel cobalt), or nickel or copper with different
levels of impurities are used, different re-crystallization
temperatures may exist and thus different maximum preferred heat
treatment temperatures may exist. It is also understood that
different deposition processes and/or metal working processes may
yield different recrystallization temperatures for a given material
and as such, different preferred ranges of heat treating
temperatures may exist.
[0118] In applications where the structures, or components, formed
are desired to be harder and less ductile, then heat treating below
the re-crystallization temperature is preferred. However, in other
applications where the structures or components are desired to be
softer and/or more ductile, heat treating at a temperature above
the re-crystallization temperature may be more preferred. Without
limiting the scope of the applicants` invention, it is believed
that the increase in adhesion strength and possible increase in
intra-layer cohesion may result from a phenomenon known as
diffusion bonding which results in the transport of atoms across
boundaries regions. It is also possible that another mechanism is,
at least in part, responsible for the improvement in adhesion
strength. This other mechanism may involve the reduction of
metallic oxides that may exist at the interface between layers or
at other locations within a structure.
[0119] In some alternative embodiments, it may be possible to heat
treat a structure to improve interlayer adhesion and then after
release and heat treatment, it may be possible to deposit a
relatively uniform coating of material over the surface of the
structures (e.g. by electroplating or the like) to improve the
hardness and yield strength of the combined structures.
[0120] In other alternatives to the present embodiment, the forming
gas may include H.sub.2 in the range of about 1% to 10% or even
higher. In still other embodiments the atmosphere may be
substantially pure H.sub.2, while in other embodiments other
reducing gases or agents may be usable. In still other embodiments
the atmosphere may be an inert gas such as N.sub.2 or Ar. In still
further embodiments the structures may be heat treated in a vacuum.
When a gas is present during heat treatment, that gas may be held
at a pressure below one atmosphere, at substantially one
atmosphere, or at some elevated pressure. During heat treatment,
gas may be present in a stagnant mode or it may be made to flow
around the structure or structures (this may be implemented in the
form of a fan that directs the gas around the chamber or in the
form of a continuous flushing of gas through the chamber. In some
embodiments, it may be desirable to locate a second structural
material between adjacent layers of the first structural material.
This intermediate material may have a melting temperature or a
recrystallization temperature below that of the structural material
and may be used to enhance diffusion bonding.
[0121] In some embodiments more than one structural material may
exist in the structure or component, depending on the function of
each material (e.g. to give strength, enhanced conductivity, or
dielectric properties), it may be desirable to perform the heat
treatment or diffusion bonding at a temperature which is below the
lower of the two or more re-crystallization temperatures or below
some intermediate re-crystallization temperature, or below the
highest of the re-crystallization temperatures.
[0122] In some alternatives to the present embodiment, various
techniques may be combined with the techniques explicitly presented
herein. For example, it may be acceptable or desirable to perform
the heat treatment operation with the sacrificial material still in
place. In still other alternatives, heat treatment or diffusion
bonding may be practiced on a partially released structure (i.e. a
structure or component where some sacrificial material still
remains). In some embodiments separate structures may be
deliberately decoupled by introducing gaps between them so as to
eliminate or minimize the propagation of stresses associated with
differing coefficients of thermal expansion. In still other
alternative embodiments, during heat treatment compressive,
mechanical forces may be applied along a direction which is
perpendicular to the plane of the layers.
[0123] In still other alternative embodiments heat treatment may be
performed with the structure immersed in a liquid or in an
environment where gas pressure or hydro-static pressure is greater
than 10 to 50 PSI. In still other alternative embodiments heat
treatment may be performed prior to the completion of formation of
a structure. For example, it may be performed on a layer by layer
basis or periodically after the formation of a desired number of
layers.
[0124] FIG. 15 depicts a block diagram of a tenth embodiment of the
invention where the structure is heat treated after formation at a
temperature that significantly enhances interlayer adhesion but
does not significantly decrease the yield strength of the
intra-layer material. This embodiment starts with element 272 which
calls for formation of a multi-layer structure with layers that are
adhered to one another. After formation of the structure this
embodiment, proceeds to element 274 which calls for a heat
treatment of the structure using a temperature and time that
significantly enhances the interlayer adhesion but does not
significantly decrease the yield strength of the intra-layer
material.
[0125] FIG. 16 depicts a block diagram of an eleventh embodiment of
the invention. As with the other embodiments discussed so far, this
embodiment starts with the formation of a multi-layer 3-dimensional
structure where adjacent layers are adhered to one another. After
formation of the structure, the structure is heat treated using a
temperature and time such that the structure behaves monolithically
up to at least 50% of the yield strength of the intra-layer
material. In other words, interlayer adhesion does not fail at
tension levels that are below 50% of the yield strength (i.e. the
strength at which elastic deformation gives rise to plastic
deformation). In some alternatives, the monolithic behavior extends
through the full elastic deformation region while in even further
embodiments it may extend substantially into the plastic
deformation region.
[0126] FIG. 17 depicts a block diagram of an eleventh embodiment of
the invention. This embodiment begins with element 292 which calls
for a formation of a multi-layer structure where adjacent layers
are adhered to one another. After formation of the structure, the
process proceeds to element 294 which calls for heat treating the
structure using a temperature and time such that a structure
behaves monolithically up to at least 50% of the ultimate tensile
strength of the intra-layer material. In other words, interlayer
adhesion doesn't fail until tensional forces cause stress and
strain in the interlayer region to exceed 50% of the ultimate
tensile strength of the material forming the intra-layer portions
of the structure. Ultimate tensile strength refers to the tensile
stress, per unit of original surface area, at which a body will
fracture, or continue to deform under a decreasing load. When
intra-layer tensile strength or yield strength is referred to
herein, applicants mean the tensile strength or yield strength,
respectively, that a sample would have when it is formed as the
material is formed that make up the layers without the existence of
inter-layer boundaries.
[0127] FIG. 18 depicts a block diagram of a thirteenth embodiment
of the invention. In this embodiment of the invention the process
begins with the formation of a multi-layer structure where adjacent
layers are adhered to one another. After formation, the process
moves forward to element 304 which calls for the heat treatment of
the structure within an atmosphere that is either inert or contains
a reducing agent. Inert atmospheres include such gaseous material
as nitrogen (N.sub.2), argon (Ar), neon (Ne), and krypton (Kr), and
the like. Reducing agents include hydrogen gas (H.sub.2), and the
like, as well as gas mixtures that contain these agents such as
forming gases. In some alternative embodiments, it may be possible
to perform heat treatments in gases or under sprays of materials,
for example, that are not inert or offer reducing properties but
instead are chemically reactive with the structural material or
materials that make up the structures. Such materials may include,
for example, carbon containing compounds that may interact with the
surfaces of the structures to yield new structural characteristics
for the devices.
[0128] FIG. 19 depicts a block diagram of a fourteenth embodiment
of the invention where the structure is heat treated such that all
portions of the structure reach a substantially uniform
temperature. In this embodiment the process begins with element 312
which calls for the formation of a multi-layer structure with
adjacent layers that are adhered to one another. After formation,
the process proceeds to element 314 which calls for heat treatment
of a structure using a substantially uniform temperature. In other
words, using a temperature that has substantially the same value in
all portions of a structure. In these embodiments, for the
temperature to be considered substantially uniform, the temperature
variation throughout all regions of interest in a structure, during
heat treatment, is preferably less than about 25.degree. C., more
preferably less than about 15.degree. C., and most preferably less
than about 5.degree. C. Alternatively, the temperature variation
across a structure is preferably less than about 10% of the target
temperature in .degree. C., more preferably less than about 5% and
even more preferably less than about 1%. At dwell temperature, the
temperature of the structure is preferably controlled within less
than about 10% of the target dwell temperature in .degree. C., more
preferably within 5%, and even more preferably within 1%.
[0129] FIG. 20 depicts a block diagram of a fifteenth embodiment of
the invention where the structure is heat treated such that local
temperature differences do not directly result from localized
differences in electrical conductivity (e.g. do not result from
variations in ohmic heating at different locations within a
structure). In this embodiment of the invention, the process begins
with the formation of the multi-layer structure where adjacent
layers are adhered to one another. After formation, the process
moves forward to element 324 which calls for the heat treatment of
the structure in a manner such that local temperature differences
do not directly result from localized differences in electrical
conductivity of the structural material. In this embodiment heating
of the structure preferably occurs by convective, conductive or
radiative application of heat to the surface of the structure. In
some alternative embodiments, heating may occur by passing a
current through the devices but temperature variations across
different regions of a structure that result from ohmic heating are
preferably less than about 25.degree. C., more preferably less than
about 15.degree. C., and most preferably less than about 5.degree.
C.
[0130] FIG. 21 depicts a flowchart of a sixteenth embodiment where
the structure is partially formed, released from sacrificial
material, then heat treated, and then completed with or without
refilling of sacrificial material and with or without further heat
treating. In this embodiment of the invention, the process begins
with formation of a portion of a multi-layer structure. After the
portion of the multi-layer structure is formed, the process moves
forward to element 334 which calls for the release of the
multi-layer structure from at least one sacrificial material that
was used during its formation of the portion of the structure.
After removal of the sacrificial material, the process moves
forward to element 336 which calls for heat treating the structure,
for example, to enhance interlayer adhesion or to enhance adhesion
to other elements which may be added to the structure. After heat
treatment the process moves forward to element 338 which inquires
as to whether replacement of the sacrificial material is necessary
in order to complete formation of the structure. If the answer is
"no" the process proceeds to element 340 which calls for completing
formation of the structure after which the process moves forward to
element 342 which inquires as to whether additional heat treating
is to be performed, if the answer is "no" the process moves forward
to element 344 and ends. If the answer to the inquiry of element
342 is "yes", the process moves forward to element 346 which calls
for the performance of further heat treating and then moves forward
to element 344 and ends.
[0131] If the answer to the inquiry of element 338 was "yes", the
process moves forward to element 352 which calls for the deposition
of sacrificial material and the potential planarization of that
material in preparation for forming additional layers of the
structure. From element 352, the process moves forward to element
354 which calls for the completion of the formation of the
structure. After the structure is completed, the process moves
forward to element 356 which inquires as to whether or not the
sacrificial material is to be removed prior to any further heat
treatment. If the answer is "yes", the process moves forward to
element 358 which calls for the release of the completed structure
from the sacrificial material after which the process moves to
element 342 (which was discussed above) and either moves
immediately to the end of the process at element 344 or proceeds to
the heating treating called for by element 346 and then ends at
element 344.
[0132] If the answer to the inquiry of element 356 is "no" the
process moves forward to element 360 which calls for the
performance of additional heat treatment after which the process
moves forward to element 362 which calls for the release of the
completed structure from the sacrificial material. Thereafter, the
process moves on to element 344 and ends. This embodiment
represents one of many possible combinations of the previously
discussed embodiments and is intended to be an example of how such
combinations may be made. Alternative embodiments may allow more
than two releases of the partially formed structures and more than
two heat treatments.
[0133] A seventeenth embodiment of the invention provides a low
temperature process for heat treating a structure that has been
electrochemically fabricated (e.g. a nickel structure). The process
leads to improved interlayer adhesion with less loss of mechanical
strength than that which may result from higher temperature
processing. The primary operations of the process include: [0134]
1. Clean all released structures (i.e. structures which have been
separated from the sacrificial material used during their
formation) to remove organics and oxides by using a solvent and
dilute acid rinses [0135] 2. Place the structures in an
environmental chamber that provides for controlled temperature and
atmosphere surrounding the structures. [0136] 3. Replace the
chamber atmosphere with forming gas (e.g. having 5% hydrogen and
95% nitrogen). [0137] 4. Close all openings to the chamber and
maintain a positive pressure of forming gas inside the chamber.
[0138] 5. Ramp the temperature in the chamber from room temperature
to 250.degree. C. at a ramp rate of 10 degrees/minute. Monitor
actual chamber temperature so that it does not exceed the current
setpoint temperature by more than about 5.degree. C. during at each
time interval and particularly during the dwell period at maximum
temperature. Keep a flow of forming gas going into the chamber
throughout the ramp up and dwell periods [0139] 6. Hold the
temperature the dwell temperature (i.e. maximum temperature) for 30
minutes (i.e. a dwell time) [0140] 7. Once dwell time ends, step
down chamber temperature to room temperature by allowing chamber to
cool naturally and while continuing the flow of forming gas for the
first 30 minutes of cool down period. After 30 minutes, the
temperature should be below 200.degree. C. and the forming gas flow
may be shut off. [0141] 8. Allow cooling to continue for another 30
minutes at which point the temperature should be around 160.degree.
C. or less. [0142] 9. At this point, open chamber door and allow
for convection cooling with the room air. Allow cooling to continue
for another 30 minutes. After this time, the temperature should be
below 100.degree. C. [0143] 10. Remove the structures from the
chamber and cool the wafer or individual dies (if already diced) on
chill plate by placing the sample on a metal and allowing the
temperatures to equalize.
[0144] Experiments were performed using the process of embodiment
seventeen. These experiments used a nickel structural material and
produced significantly improved interlayer adhesion and less
overall loss of strength of the heated structures (when compared to
structures treated at higher temperatures). Inter-layer bonding was
enhanced so that interlayer adhesion did not fail during the
elastic compressions of the structures and higher overall strength
was retained (i.e. higher force needed to yield a given
deflection). Various alternatives to the seventeenth embodiment are
possible. For example, a lower dwell temperature may be possible
(e.g. 200, 150, or even 100 degrees C.); longer or shorter ramp up
times and associated rates are possible, variations in the cool
down process are possible, use of different gas environments during
heating or cool down are possible (nitrogen only, hydrogen only,
other ratios of nitrogen and hydrogen, use of inert gases such as
argon, and the like); heat treatment before or after dicing; heat
treatment before or after release; heat treatment before or after
substrate swapping, and the like. It will be within the abilities
of those of skill in art to perform basic experiments and to
determine appropriate or even optimal parameters for heat treating
various build and sacrificial materials.
[0145] Those of skill in the art will understand how to combine the
various previously presented embodiments to form more elaborate
and/or alternative embodiments. The combined embodiments may take a
single aspect from two embodiments and combine them into a single
embodiment or they may take various aspects from more than two
embodiments and combine them.
[0146] It will be understood by those of skill in the art or will
be readily ascertainable by them that various additional operations
may be added to the processes set forth herein. For example,
between performances of the various deposition operations,
performance of any etching operations, and performance of various
planarization operations cleaning operations, activation
operations, and the like may be desirable.
[0147] The patent applications and patents set forth below are
hereby incorporated by reference herein as if set forth in full.
The teachings in these incorporated applications can be combined
with the teachings of the instant application in many ways: For
example, enhanced methods of producing structures may be derived
from some combinations of teachings, enhanced structures may be
obtainable, enhanced apparatus may be derived, and the like.
TABLE-US-00001 US Pat App No, Filing Date US App Pub No, Pub Date
Inventor, Title 10/677,556 - Oct. 1, 2003 Cohen, "Monolithic
Structures Including Alignment and/or Retention Fixtures for
Accepting Components" XX/XX,XXX - Apr. 21, 2004 Cohen, "Methods of
Reducing Interlayer (Docket P-US084-A-MF) Discontinuities in
Electrochemically Fabricated Three- Dimensional Structures"
XX/XXX,XXX - May 7, 2004 Lockard, "Methods for Electrochemically
Fabricating (Docket P-US099-A-MF) Structures Using Adhered Masks,
Incorporating Dielectric Sheets, and/or Seed layers That Are
Partially Removed Via Planarization" 10/271,574 - Oct. 15, 2002
Cohen, "Methods of and Apparatus for Making High 2003-0127336A -
Jul. 10, 2003 Aspect Ratio Microelectromechanical Structures"
10/697,597 - Dec. 20, 2002 Lockard, "EFAB Methods and Apparatus
Including Spray Metal or Powder Coating Processes" 10/677,498 -
Oct. 1, 2003 Cohen, "Multi-cell Masks and Methods and Apparatus for
Using Such Masks To Form Three-Dimensional Structures" 10/724,513 -
Nov. 26, 2003 Cohen, "Non-Conformable Masks and Methods and
Apparatus for Forming Three-Dimensional Structures" 10/607,931 -
Jun. 27, 2003 Brown, "Miniature RF and Microwave Components and
Methods for Fabricating Such Components" 10/387,958 - Mar. 13, 2003
Cohen, "Electrochemical Fabrication Method and 2003-022168A - Dec.
4, 2003 Application for Producing Three-Dimensional Structures
Having Improved Surface Finish" 10/434,494 - May 7, 2003 Zhang,
"Methods and Apparatus for Monitoring 2004-0000489A - Jan. 1, 2004
Deposition Quality During Conformable Contact Mask Plating
Operations" 10/434,289 - May 7, 2003 Zhang, "Conformable Contact
Masking Methods and 20040065555A - Apr. 8, 2004 Apparatus Utilizing
In Situ Cathodic Activation of a Substrate" 10/434,294 - May 7,
2003 Zhang, "Electrochemical Fabrication Methods With 2004-0065550A
- Apr. 8, 2004 Enhanced Post Deposition Processing Enhanced Post
Deposition Processing" 10/434,295 - May 7, 2003 Cohen, "Method of
and Apparatus for Forming Three- 2004-0004001A - Jan. 8, 2004
Dimensional Structures Integral With Semiconductor Based Circuitry"
10/434,315 - May 7, 2003 Bang, "Methods of and Apparatus for
Molding 2003-0234179 A - Dec. 25, 2003 Structures Using Sacrificial
Metal Patterns" XX/XXX,XXX - May 7, 2004 Thompson,
"Electrochemically Fabricated Structures (Docket P-US104-A-MF)
Having Dielectric or Active Bases and Methods of and Apparatus for
Producing Such Structures" 10/724,515 - Nov. 26, 2003 Cohen,
"Method for Electrochemically Forming Structures Including
Non-Parallel Mating of Contact Masks and Substrates" XX/XXX,XXX -
May 7, 2004 Cohen, "Multi-step Release Method for (Docket
P-US105-A-MF) Electrochemically Fabricated Structures" 60/533,947 -
Dec. 31, 2003 Kumar, "Probe Arrays and Method for Making"
[0148] Various other embodiments exist. Some of these embodiments
may be based on a combination of the teachings herein with various
teachings incorporated herein by reference. Some embodiments may
not use any blanket deposition process and/or they may not use a
planarization process. Some embodiments may use selective or
blanket depositions processes that are not electrodeposition
processes. Some embodiments may use one or more structural
materials (e.g. nickel, gold, copper, silver, or the like). Some
processes may use one or more sacrificial materials (e.g. copper,
silver, tin, zinc, or the like). Some embodiments may remove a
sacrificial material while other embodiments may not.
[0149] In view of the teachings herein, many further embodiments,
alternatives in design and uses are possible and will be apparent
to those of skill in the art. As such, it is not intended that the
invention be limited to the particular illustrative embodiments,
alternatives, and uses described above but instead that it be
solely limited by the claims presented hereafter.
* * * * *