U.S. patent application number 14/804031 was filed with the patent office on 2016-01-21 for apparatus and methods for micro-transfer-printing.
The applicant listed for this patent is X-Celeprint Limited. Invention is credited to Salvatore Bonafede, Christopher Bower, David Gomez, David Kneeburg, Matthew Meitl.
Application Number | 20160020131 14/804031 |
Document ID | / |
Family ID | 53794193 |
Filed Date | 2016-01-21 |
United States Patent
Application |
20160020131 |
Kind Code |
A1 |
Bower; Christopher ; et
al. |
January 21, 2016 |
APPARATUS AND METHODS FOR MICRO-TRANSFER-PRINTING
Abstract
In an aspect, a system and method for assembling a semiconductor
device on a receiving surface of a destination substrate is
disclosed. In another aspect, a system and method for assembling a
semiconductor device on a destination substrate with topographic
features is disclosed. In another aspect, a gravity-assisted
separation system and method for printing semiconductor device is
disclosed. In another aspect, various features of a transfer device
for printing semiconductor devices are disclosed.
Inventors: |
Bower; Christopher;
(Raleigh, NC) ; Meitl; Matthew; (Durham, NC)
; Gomez; David; (Durham, NC) ; Bonafede;
Salvatore; (Chapel Hill, NC) ; Kneeburg; David;
(Durham, NC) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
X-Celeprint Limited |
Cork |
|
IE |
|
|
Family ID: |
53794193 |
Appl. No.: |
14/804031 |
Filed: |
July 20, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
62027166 |
Jul 21, 2014 |
|
|
|
62026694 |
Jul 20, 2014 |
|
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|
Current U.S.
Class: |
294/213 |
Current CPC
Class: |
H01L 31/1892 20130101;
H01L 2224/83011 20130101; H01L 2224/32225 20130101; H01L 2924/1034
20130101; B41K 3/12 20130101; H01L 24/83 20130101; H01L 2224/32245
20130101; H01L 2924/10332 20130101; H01L 21/3065 20130101; H01L
21/52 20130101; H01L 21/683 20130101; H01L 2224/83001 20130101;
H01L 24/75 20130101; H01L 2221/68377 20130101; B41F 16/00 20130101;
B41F 16/006 20130101; H01L 2224/83895 20130101; H01L 2924/1032
20130101; H01L 2924/10335 20130101; H01L 2221/68318 20130101; H01L
2224/83894 20130101; H01L 2221/68368 20130101; H01L 2224/83
20130101; H01L 2224/95001 20130101; B41F 16/0073 20130101; H01L
2224/7598 20130101; H01L 2224/83013 20130101; H01L 2224/832
20130101; H01L 21/565 20130101; H01L 24/97 20130101; H01L 25/50
20130101; H01L 2221/68354 20130101; H01L 2224/83024 20130101; H01L
2224/97 20130101; H01L 2924/10328 20130101; H01L 2924/10336
20130101; H01L 23/3171 20130101; H01L 2224/75315 20130101; B41K
3/04 20130101; H01L 23/293 20130101; H01L 2924/10253 20130101; H01L
2924/10329 20130101; B41F 16/0046 20130101; H01L 21/568 20130101;
H01L 21/67103 20130101; H01L 2924/10337 20130101; H01L 21/6835
20130101; H01L 2224/97 20130101; H01L 2924/10338 20130101; B25J
15/00 20130101; H01L 2221/68381 20130101 |
International
Class: |
H01L 21/683 20060101
H01L021/683; B25J 15/00 20060101 B25J015/00 |
Claims
1. A conformable transfer device with reduced crowning, the
transfer device comprising: a bulk volume having a first surface
and a second surface, opposite the first surface, and a side
between the first surface and the second surface, wherein the bulk
area comprises a tapered surface connecting the side to the first
surface; and a plurality of printing posts disposed on the first
surface of the bulk volume for picking up printable material,
wherein the plurality of printing posts and the bulk volume are
arranged such that a force applied to the second surface of the
bulk volume is transmitted to the plurality of printing posts.
2. The device of claim 1, wherein an aspect ratio(height to width)
of each post of the plurality of posts is less than or equal to 4:1
(e.g., from 2:1 to 4:1).
3-8. (canceled)
9. The device of claim 1, wherein the plurality of printing posts
have a first Young's modulus and the base has a second Young's
modulus, greater than the first Young's modulus.
10-16. (canceled)
17. The device of claim 1, wherein a least a portion of the posts
are arranged on the first surface from 1 mm to 15 mm away from a
edge of the first surface (e.g., from 1 mm to 5 mm or 5 mm to 10
mm, 10 mm to 15 mm from the edge).
18. The device of claim 1, wherein the bulk volume has a side
surface between the first and second surfaces.
19. (canceled)
20. The devices of claim 18, wherein the side surface has a rounded
profile (e.g., convex or concave).
21. The device of claim 18, wherein the side surface has a beveled
edge forming an angle from horizontal (parallel to the first
surface) of no greater than 75.degree. (e.g., no greater than
60.degree., no greater than 45.degree., no greater than 30.degree.,
or no greater than 15.degree.).
22. A conformable transfer device comprising an elastomer (e.g.,
PDMS) slab (e.g., bulk volume) having a mesa configuration with a
surface upon which a plurality of (e.g., array of) posts are
disposed, wherein one or more of the following holds [any of (i),
(ii), and/or (iii)]: (i) the edge of the mesa has a beveled and/or
rounded edge so as to reduce distortion of the surface and allow
accurate spacing of the plurality of posts; (ii) the plurality of
posts are arranged on the surface at least 1 mm away from the edge
(e.g., from 1 mm to 5 mm or 5 mm to 20 mm from the edge); and (iii)
the mesa has a thickness no greater than 10 mm (e.g., from 1 to 5
mm).
23. The device of claim 22, wherein the edge of the mesa has a
beveled edge forming an angle from horizontal (parallel to the
surface) of no greater than 75.degree. (e.g., no greater than
60.degree., no greater than 45.degree., no greater than 30.degree.,
or no greater than 15.degree.).
24. The device of claim 22, wherein the edge of the mesa has a
rounded profile (e.g., convex or concave).
25-32. (canceled)
33. The device of claim 22, wherein the posts have a first Young's
modulus and the mesa has a second Young's modulus, greater than the
first Young's modulus.
34-41. (canceled)
42. A conformable transfer device, the transfer device comprising:
a bulk volume having a first surface and a second surface, opposite
the first surface; a mesa disposed on the bulk volume; a layer
comprising a plurality of posts (e.g., array of posts) disposed on
the mesa, opposite the bulk volume, for picking up printable
material, wherein the plurality of posts, the mesa, and the bulk
volume are arranged such that a force applied to the second surface
of the bulk volume is transmitted to the plurality of posts.
43. The device of claim 42, wherein a thickness of the mesa is
greater than a thickness of the posts.
44. The device of claim 42, wherein an aspect ratio(height to
width) of each post of the plurality of posts is less than or equal
to 4:1 (e.g., from 2:1 to 4:1).
45-47. (canceled)
48. The device of claim 42, wherein a ratio of a thickness of the
posts to a thickness of the bulk volume is from 1:1 to 1:10 (e.g.,
from 1:1 to 1:2, 1:2 to 1:4, 1:4 to 1:6, 1:6 to 1:8, or 1:8 to
1:10).
49-50. (canceled)
51. The device of claim 42, wherein the posts have a first Young's
modulus and the bulk volume has a second Young's modulus, greater
than the first Young's modulus.
52. (canceled)
53. The device of claim 51, wherein the mesa has the second Young's
modulus.
54-61. (canceled)
62. The device of claim 42, wherein the bulk volume has a side
surface between the first and second surfaces.
63. (canceled)
64. The devices of claim 62, wherein the side surface has a rounded
profile (e.g., convex or concave).
65. The device of claim 62, wherein the side surface has a beveled
edge forming an angle from horizontal (parallel to the first
surface) of no greater than 75.degree. (e.g., no greater than
60.degree., no greater than 45.degree., no greater than 30.degree.,
or no greater than 15.degree.).
66-86. (canceled)
Description
PRIORITY APPLICATIONS
[0001] This application claims priority to and the benefit of U.S.
Provisional Patent Application No. 62/026,694, filed Jul. 20, 2014,
entitled "Apparatus and Method for Micro-Transfer Printing" and
U.S. Provisional Patent Application No. 62/027,166, filed Jul. 21,
2014, entitled "Methods and Tools for Micro-Transfer Printing," the
contents of each of which is incorporated by reference herein in
its entirety.
FIELD OF THE INVENTION
[0002] The present invention relates to methods and tools for
micro-transfer-printing printable devices to destination
substrates.
BACKGROUND OF THE INVENTION
[0003] The disclosed technology relates generally to methods and
tools for micro-transfer-printing. It is often difficult to pick up
and place ultra-thin and/or small devices using this technology.
Micro transfer printing permits the selection and application of
these ultra-thin, fragile, and/or small devices without causing
damage to the devices themselves.
[0004] Micro-transfer-printing allows for deterministically
assembling and integrating arrays of micro-scale, high-performance
devices onto non-native substrates. In its simplest embodiment,
micro-transfer-printing is analogous to using a rubber stamp to
transfer liquid-based inks from an ink-pad onto paper. However, in
micro-transfer-printing the "inks" are composed of high-performance
solid-state semiconductor devices and the "paper" can be
substrates, including plastics and other semiconductors. The
micro-transfer-printing process leverages engineered elastomer
stamps coupled with high-precision motion-controlled print-heads to
selectively pick-up and print large arrays of micro-scale devices
onto non-native destination substrates.
[0005] Adhesion between the elastomer transfer device and the
printable element can be selectively tuned by varying the speed of
the print-head. This rate-dependent adhesion is a consequence of
the viscoelastic nature of the elastomer used to construct the
transfer device. When the transfer device is moved quickly away
from a bonded interface, the adhesion is large enough to "pick" the
printable elements away from their native substrates, and
conversely, when the transfer device is moved slowly away from a
bonded interface the adhesion is low enough to "let go" or "print"
the element onto a foreign surface. This process may be performed
in massively parallel operations in which the stamps can transfer,
for example, hundreds to thousands of discrete structures in a
single pick-up and print operation.
[0006] Micro transfer printing also enables parallel assembly of
high-performance semiconductor devices onto virtually any substrate
material, including glass, plastics, metals, or other
semiconductors. The substrates may be flexible, thereby permitting
the production of flexible electronic devices. Flexible substrates
may be integrated in a large number of configurations, including
configurations not possible with brittle silicon-based electronic
devices. Additionally, plastic substrates, for example, are
mechanically rugged and may be used to provide electronic devices
that are less susceptible to damage or electronic performance
degradation caused by mechanical stress. Thus, these materials may
be used to fabricate electronic devices by continuous, high-speed,
printing techniques capable of generating electronic devices over
large substrate areas at low cost (e.g., roll to roll
manufacturing).
[0007] Moreover, these micro transfer printing techniques can print
semiconductor devices at temperatures compatible with assembly on
plastic polymer substrates. In addition, semiconductor materials
may be printed onto large areas of substrates thereby enabling
continuous, high speed printing of complex integrated electrical
circuits over large substrate areas. Moreover, fully flexible
electronic devices with good electronic performance in flexed or
deformed device orientations may be provided to enable a wide range
of flexible electronic devices.
[0008] Micro-structured stamps may be used to pick up micro
devices, transport the micro devices to the destination, and print
the micro devices onto a destination substrate. The transfer device
(e.g., micro-structured stamp) can be created using various
materials. Posts on the transfer device can be generated such that
they pick up material from a pick-able object and then print the
material to the target substrate. The posts can be generated in an
array fashion and can be a range of heights depending on the size
of the printable material. Compression (in the z direction) of the
transfer device can be used to fully laminate the array of
printable objects to the posts of the transfer device.
Additionally, compression can be used to allow for a critical
velocity to be reached by increasing the distance the stamp is
moved at a set acceleration based on the equation v.sup.2=2ad.
[0009] However, compression of the transfer device poses several
issues. Among other things, there is a possibility of sagging
between posts. This sag allows for unwanted materials to be picked
up from the source substrate. As the span between adjacent posts is
increased, the risk of sag causing problems increases.
Additionally, there is a crowning effect that can be noted at the
edge of the transfer device bulk material that is caused by the
coefficient of thermal expansion (CTE) mismatch between the bulk
material and the hard plate interface (e.g., glass) as shown, for
example, in FIG. 22. Thus, there is a need for techniques that
minimize or eliminate at least these issues and increase bonding
when devices are printed.
[0010] Transfer printing with a visco-elastic stamp material
requires a high-velocity separation between stamp and source
material to "pick" chips. Typical applications use approximately 1
g of acceleration to accomplish the chip or die "pick" process
step. However, the velocity at separation occurs at small distances
(e.g., tens of microns or less) dependent on the compression of the
stamp at lamination. Thus, there is a need for greater acceleration
to create higher separation velocities at small distances that in
turn increases the adhesion between the stamp and source.
SUMMARY OF THE INVENTION
[0011] As described herein, the present disclosure provides methods
and tools for micro transfer printing. In certain embodiments, the
disclosed technology utilizes high acceleration when picking up
chips from the source wafer. Traditional methods of the "pick"
process utilize a vertical stage (with stamp attached) that moves
the stamp rapidly upward, away from the substrate. Typically,
approximately 1 g of acceleration is used to pick up devices from
the native substrate. In certain embodiments, it is advantageous to
increase the initial acceleration (5-100 g) to achieve higher
velocities during the pick process. The velocity at separation
occurs at very small travel distances that are dependent on the
compression of the stamp at lamination. Higher acceleration can
create higher separation velocities at small distances that in turn
increases the adhesion between the stamp and source. Movement of
the stamp in the downward direction, away from the source
substrate, during the "pick" process can increase the overall
acceleration by moving with gravity, and therefore can add an
additional 1 g of acceleration to the transfer.
[0012] In certain embodiments, heat-assisted
micro-transfer-printing is performed to adhesiveless surfaces and
topographic surfaces. Polymer encapsulations can be used to enhance
transfer of semiconductor devices to non-native substrates when the
polymer is designed to contract and then reflow while in contact
with the destination substrate. The polymer layer can be
subsequently removed while leaving behind the transferred device on
the non-native substrate. This also improves the ability to
micro-transfer-print to topographic surfaces.
[0013] A plasma treatment (e.g., no vacuum required) can be
performed during micro transfer printing. The plasma can be applied
to bottom surfaces of devices that are attached to an elastomer
transfer-element. This treatment of bottom surfaces can be used (i)
to provide improved bonding between the devices and destination
substrate, (ii) to clean the bottom surface of devices that have
been fabricated using epitaxial lift-off methods, and (iii) to
remove thin layers of oxides (e.g., Cu--Cu, CuSn--Cu,
Cu--Sn--Sn--Cu, Au--Au) from the bottom surface (e.g., if a
reducing gas such as forming gas, ammonia, formic acid, etc., is
added to the plasma). The treatment can be applied to the devices
while they are on the transfer device in a manner in which the
devices are un-distributed (e.g., do not fall of the stamp).
[0014] In certain embodiments, plasma treatment can be applied to
the bottom surfaces of devices that are attached to the transfer
device. The treatment can be used to improve bonding between the
devices and the destination substrate. The treatment can be used to
clean the bottom surfaces and or to remove any layers of oxides
from the bottom surfaces. If the devices have a backside metal, the
plasma can be used to remove oxides from the surface of the
metal.
[0015] In certain embodiments, if the devices have a backside
metal, the semiconductor elements are printed to a destination
substrate with mating metal pads that have been coated with a flux.
After transferring the devices, the flux can be reflowed thereby
leaving a good metal connection between the pads and the backside
metal on the devices.
[0016] A crowning effect can be noted at the edge of the transfer
device bulk material manufactured using prior art methods. The
crowning is caused by the coefficient of thermal expansion (CTE)
mismatch between the bulk material and the hard-plate interface
(e.g., glass) as shown, for example, in FIG. 22. In certain
embodiments, the disclosed technology includes transfer devices
designed to eliminate or reduce issues related to crowning. In
certain embodiments, the crown is cut with a razor so that
printable semiconductor elements are not picked up by the crown
during a print operation.
[0017] In certain embodiments, a second material is placed between
the bulk volume and the hard-plate interface. As a result, the bulk
volume material directly above the second material is thinner than
it otherwise would be. This produces a smaller crown since there is
less material to deform and bulge to form the crown.
[0018] In some embodiments, the bezel or sidewall of the bulk
volume is such that crowning is minimized. As explained below,
certain shape sidewalls result in a transfer device with less
crowning.
[0019] In certain embodiments, multiple bulk material layers (e.g.,
viscoelastic material) are provided. The first bulk material layer
is on the hard-plate interface and typically has what would
normally be a problematic crown. A second bulk material layer is
provided on the first bulk material layer. The second bulk material
layer is thinner than the first bulk material layer. As the second
bulk material layer is thinner, it will have a smaller crown. The
posts are placed on the second bulk material layer and are
prominent relative to the crown on the second layer of bulk
material. Additionally, the posts are prominent relative to the
first bulk material layer since the thickness of the second bulk
material layer and the height of the posts combined is larger than
the crown on the first layer of bulk material.
[0020] In certain embodiments, the transfer devices has
multi-tiered posts with successively smaller cross sections on
successive tiers of posts. A micro-post is formed on a post. The
micro-post is used to physically contact the printable
semiconductor devices. The micro-post is typically shorter and
narrower than the post. The use of multi-tiered posts allows
desired aspect ratios for the posts to be maintained while still
allowing small devices to be picked up. The height gained by the
multi-tiered post can reduce the risk of crowning problems as the
height of the post is increased. Additionally, the multi-tiered
posts can reduce issues related to sagging.
[0021] When a transfer device is compressed during a pickup
operation, there is a possibility of sagging between posts. This
sag allows for unwanted materials to be picked up from the source
substrate. As the span between adjacent posts is increased, the
risk of sag causing problems increases.
[0022] Multi-tiered posts can be used to increase the height of the
posts while maintaining desired aspect ratios for the posts, thus
reducing issues related to sagging and crowning. In certain
embodiments, anti-sag features are provided between posts on the
transfer device. The anti-sag features can have an aspect ratio
such that they will not pick up devices. In this manner, the
anti-sag posts prevent the body of the bulk material in the
transfer device from contacting the source substrate, thereby
reducing issues related to sagging.
[0023] In certain embodiments, the transfer device is provided with
a rough surface between the posts. The rough surface reduces the
risk that printable semiconductor elements will be picked up if
sagging occurs because the rough surface reduces adhesion.
[0024] In one aspect, the disclosed technology includes a method
for assembling a semiconductor device on a receiving surface of a
destination substrate, the method including: providing the
semiconductor device formed on a native substrate; contacting a top
surface of the semiconductor device with a conformable transfer
device having a contact surface, wherein contact between the
contact surface and the top surface of the semiconductor device at
least temporarily binds the semiconductor device to the conformable
transfer device; separating the semiconductor device from the
native substrate such that the contact surface of the conformable
transfer device has the semiconductor device disposed thereon with
the semiconductor device released from the native substrate; prior
to contacting the semiconductor device with the receiving surface
of the destination substrate, exposing a backside surface of the
semiconductor device to a plasma (e.g., atmospheric plasma)
following separation from the native substrate; contacting the
semiconductor device disposed on the contact surface with the
receiving surface of the destination substrate; and separating the
contact surface of the conformable transfer device from the
semiconductor device, thereby assembling the semiconductor device
on the receiving surface of the destination substrate.
[0025] In certain embodiments, exposing the backside surface to
plasma improves bonding between the semiconductor device and the
receiving substrate of the destination substrate.
[0026] In certain embodiments, exposing the backside surface to
plasma cleans the backside surface of the semiconductor device.
[0027] In certain embodiments, exposing the backside surface to
plasma removes thin layers of oxides from the backside surface of
the semiconductor device.
[0028] In certain embodiments, the destination substrate is a
member selected from the group consisting of polymer, plastic,
resin, polyimide, PEN, PET, metal, metal foil, glass, a
semiconductor, and sapphire.
[0029] In certain embodiments, the destination substrate has a
transparency greater than or equal to 50%, 80%, 90%, or 95% for
visible light.
[0030] In certain embodiments, the native substrate comprises a
member selected form the group consisting of inorganic
semiconductor material, single crystalline silicon wafers, silicon
on insulator wafers, polycrystalline silicon wafers, GaAs wafers,
Si (1 1 1), InAlP, InP, GaAs, InGaAs, AlGaAs, GaSb, GaAlSb, AlSb,
InSb, InGaAlSbAs, InAlSb, and InGaP.
[0031] In certain embodiments, the plasma comprises a reducing
gas.
[0032] In certain embodiments, the method includes controlling at
least one of a duty cycle, residence time, power of the plasma, and
distance of the plasma to the semiconductor device to prevent
shearing and delamination of the semiconductor devices from the
contacting surface of the conformable transfer device.
[0033] In certain embodiments, the backside surface of the
semiconductor device comprises metal.
[0034] In certain embodiments, the metal is at least one of copper,
tin, aluminum, and a mixture thereof.
[0035] In certain embodiments, the receiving surface of the
destination substrate at least in part comprises metal.
[0036] In certain embodiments, the metal is at least one of copper,
tin, aluminum, and a mixture thereof.
[0037] In certain embodiments, conformable transfer device
comprises at least one of a visco-elastic stamp and an elastic
stamp.
[0038] In certain embodiments, the method includes, prior to
contacting the semiconductor device disposed on the contact surface
with the receiving surface of the destination substrate, separating
the conformable transfer device from the native substrate, thereby
picking up the semiconductor device from the native substrate.
[0039] In certain embodiments, separating the conformable transfer
device from the native substrate is performed with an initial
acceleration of no less than 5 g (e.g., 5-100 g).
[0040] In certain embodiments, said separating the conformable
transfer device from the native substrate comprises one or both of
the following: (i) moving the conformable transfer device away from
the native substrate; and (ii) moving the native substrate away
from the conformable transfer device.
[0041] In certain embodiments, the conformable transfer device
comprises at least one of a cylindrical post, triangular post,
rectangular post, pentagonal post, hexagonal post, heptagonal post,
and octagonal post.
[0042] In certain embodiments, the conformable transfer device
comprises a transfer device layer with a plurality of posts, each
of the posts shaped to contact an individual semiconductor device
from the native substrate, thereby assembling an array of
semiconductor devices on the receiving surface of the destination
substrate.
[0043] In certain embodiments, the conformable transfer device
comprises one or more anti-sag posts located between two adjacent
posts of the plurality of posts.
[0044] In certain embodiments, the anti-sag posts have a height
that is less than the height of one or more of the posts.
[0045] In certain embodiments, the surface of the transfer device
between each post of the plurality of posts is a roughened
surface.
[0046] In certain embodiments, a bulk volume of the transfer device
comprises a first material and the plurality of posts comprise a
second material, wherein the plurality of posts are disposed on the
bulk volume.
[0047] In certain embodiments, the method includes, after
contacting the semiconductor device disposed on the contact surface
with the receiving surface of the destination substrate, heating,
by a heating element, the polymer layer.
[0048] In certain embodiments, the method includes, after providing
the semiconductor device formed on a native substrate, etching at
least a portion of a release layer formed between the semiconductor
device and the native substrate.
[0049] In certain embodiments, the semiconductor device comprises a
unitary inorganic semiconductor structure.
[0050] In certain embodiments, the destination substrate comprises
Si.
[0051] In certain embodiments, the semiconductor device comprises
an encapsulating polymer layer.
[0052] In certain embodiments, the conformable transfer device
comprises one or more anti-sag posts of the same height as the
plurality of posts, each anti-sag post located between at least two
posts of the plurality of posts.
[0053] In certain embodiments, the semiconductor device is
assembled on the receiving surface of the destination substrate
such that a metal backside surface of the semiconductor device at
least partially contacts a flux layer on the destination
substrate.
[0054] In certain embodiments, the method includes, after
assembling the semiconductor device on the receiving surface of the
destination substrate, thermally treating the flux layer, thereby
securing the metal backside surface to the metal pad.
[0055] In certain embodiments, the semiconductor device has a
polymer layer disposed on a top surface of the semiconductor
device.
[0056] In another aspect, the disclosed technology includes a
method for assembling a semiconductor device on a receiving surface
of a destination substrate, the method including: providing the
semiconductor device formed on a native substrate with a polymer
layer disposed on a top surface of the semiconductor device;
contacting the polymer layer of the semiconductor device with a
conformable transfer device having a contact surface, wherein
contact between the contact surface and the semiconductor device at
least temporarily binds the semiconductor device to the conformable
transfer device; separating the semiconductor device from the
native substrate so that the semiconductor device is disposed on
the contact surface of the conformable transfer device and is
released from the native substrate; contacting the semiconductor
device disposed on the contact surface to the receiving surface of
the destination substrate; heating, by a heating element, the
polymer layer; and separating the contact surface of the
conformable transfer device from the semiconductor device so that
the semiconductor device is transferred onto the receiving surface,
thereby assembling the semiconductor device on the receiving
surface of the destination substrate.
[0057] In certain embodiments, the heating element is a
hotplate.
[0058] In certain embodiments, the heating element is disposed on a
side of the destination substrate opposite the semiconductor
device.
[0059] In certain embodiments, the destination substrate is
non-native to the semiconductor devices.
[0060] In certain embodiments, the method includes, after heating
the polymer layer, removing, at least in part, the polymer.
[0061] In certain embodiments, heat from the heating element
reduces a viscosity of the polymer layer and causes the polymer
layer to flow.
[0062] In certain embodiments, the polymer layer is disposed on the
top surface of the semiconductor device and one or more sides of
the semiconductor device.
[0063] In certain embodiments, the polymer layer encapsulates at
least a portion of the printable semiconductor on the native
substrate.
[0064] In certain embodiments, the receiving surface of the
destination substrate comprises a non-planar topographical
surface.
[0065] In certain embodiments, the destination substrate is a
member selected from the group consisting of polymer, plastic,
resin, polyimide, PEN, PET, metal, metal foil, glass, a
semiconductor, and sapphire.
[0066] In certain embodiments, the destination substrate has a
transparency greater than or equal to 50%, 80%, 90%, or 95% for
visible light.
[0067] In certain embodiments, the native substrate comprises a
member selected form the group consisting of inorganic
semiconductor material, single crystalline silicon wafers, silicon
on insulator wafers, polycrystalline silicon wafers, GaAs wafers,
Si (1 1 1), InAlP, InP, GaAs, InGaAs, AlGaAs, GaSb, GaAlSb, AlSb,
InSb, InGaAlSbAs, InAlSb, and InGaP.
[0068] In certain embodiments, the semiconductor device is
assembled on the receiving surface of the destination substrate
such that a metal backside surface of the semiconductor device at
least partially contacts a flux layer on the destination
substrate.
[0069] In certain embodiments, the method includes, after
assembling the semiconductor device on the receiving surface of the
destination substrate, thermally treating the flux layer, thereby
securing the metal backside surface to the metal pad.
[0070] In certain embodiments, the method includes, prior to
contacting the semiconductor device with the receiving surface of
the destination substrate, exposing a backside surface of the
semiconductor device, opposite the top surface of the semiconductor
device, to plasma following separation from the native
substrate.
[0071] In another aspect, the disclosed technology includes a
method for assembling a semiconductor device on a receiving surface
of a destination substrate, the method including: providing the
semiconductor device formed on a native substrate, the
semiconductor device comprising a metal backside surface;
contacting a top surface of the semiconductor device with a
conformable transfer device having a contact surface, wherein
contact between the contact surface and the semiconductor device at
least temporarily binds the semiconductor device to the conformable
transfer device; separating the semiconductor device from the
native substrate so that the contact surface of the conformable
transfer device has the semiconductor device disposed thereon with
the semiconductor device released from the native substrate;
contacting the semiconductor device disposed on the contact surface
with the receiving surface of the destination substrate, wherein
the receiving surface comprises a flux layer on a metal pad
disposed on the destination substrate; separating the contact
surface of the conformable transfer device from the semiconductor
device, thereby assembling the semiconductor device on the
receiving surface of the destination substrate such that the metal
backside surface of the semiconductor device at least partially
contacts the flux layer; and exposing the flux layer to heat,
thereby securing the metal backside surface to the metal pad.
[0072] In certain embodiments, thermally treating the flux layer
comprises exposing the flux layer to heat.
[0073] In certain embodiments, the flux layer is exposed to heat
using a heating element.
[0074] In certain embodiments, the heating element is a
hotplate.
[0075] In certain embodiments, the heating element is disposed on a
side of the destination substrate opposite the printable
semiconductor device.
[0076] In certain embodiments, providing the semiconductor device
formed on the native substrate comprises providing the
semiconductor device formed on the native substrate with a polymer
layer disposed on a top surface of the semiconductor device.
[0077] In certain embodiments, the destination substrate is a
member selected from the group consisting of polymer, plastic,
resin, polyimide, PEN, PET, metal, metal foil, glass, a
semiconductor, and sapphire.
[0078] In certain embodiments, the destination substrate has a
transparency greater than or equal to 50%, 80%, 90%, or 95% for
visible light.
[0079] In certain embodiments, the native substrate comprises a
member selected form the group consisting of inorganic
semiconductor material, single crystalline silicon wafers, silicon
on insulator wafers, polycrystalline silicon wafers, GaAs wafers,
Si (1 1 1), InAlP, InP, GaAs, InGaAs, AlGaAs, GaSb, GaAlSb, AlSb,
InSb, InGaAlSbAs, InAlSb, and InGaP.
[0080] In certain embodiments, providing the semiconductor device
formed on the native substrate comprises: forming the semiconductor
device on the native substrate; and encapsulating the printable
semiconductor at least in part with a polymer layer.
[0081] In certain embodiments, the semiconductor device formed on
the native substrate is encapsulated with a polymer layer.
[0082] In certain embodiments, the receiving surface of the
destination substrate comprises one or more non-planar
topographical features.
[0083] In certain embodiments, the one or more non-planar
topographic features comprise at least one member selected from the
group consisting of mesas, v-shaped channels, and trenches.
[0084] In certain embodiments, the semiconductor device has a
polymer layer disposed on a top surface of the semiconductor
device.
[0085] In certain embodiments, the method includes, after
contacting the semiconductor device disposed on the contact surface
with the receiving surface of the destination substrate, heating,
by a heating element, the polymer layer.
[0086] In certain embodiments, the method includes, following
separation from the native substrate and prior to contacting the
semiconductor device with the receiving surface of the destination
substrate, exposing to plasma a backside surface of the
semiconductor device, opposite the top surface of the semiconductor
device.
[0087] In another aspect, the disclosed technology includes a
conformable transfer device with reduced crowning, the transfer
device comprising: a bulk volume having a first surface and a
second surface, opposite the first surface, and a side between the
first surface and the second surface, wherein the bulk area
comprises a tapered surface connecting the side to the first
surface; and a plurality of printing posts disposed on the first
surface of the bulk volume for picking up printable material,
wherein the plurality of printing posts and the bulk volume are
arranged such that a force applied to the second surface of the
bulk volume is transmitted to the plurality of printing posts.
[0088] In certain embodiments, an aspect ratio (height to width) of
each post of the plurality of posts is less than or equal to 4:1
(e.g., from 2:1 to 4:1).
[0089] In certain embodiments, each post of the plurality of
printing posts comprises a contact surface on the end of the post
opposite the first surface, wherein the contact surfaces of the
plurality of posts are substantially in a same plane.
[0090] In certain embodiments, the thickness of plurality of
printing posts is from 1 micron to 100 microns (e.g., from 1 to 5
microns, 5 to 10 microns, 10 to 15 microns, 50 to 25 microns, 25 to
40 microns, 40 to 60 microns, 60 to 80 microns, or 80 to 100
microns).
[0091] In certain embodiments, the thickness of the bulk volume is
from 0.5 mm to 5 mm (e.g., from 0.5 to 1 mm, 1 to 2 mm, 2 to 3 mm,
3 to 4 mm, or 4 to 5 mm).
[0092] In certain embodiments, the ratio of the thickness of the
plurality of printing posts and the thickness of the bulk volume is
from 1:1 to 1:10 (e.g., from 1:1 to 1:2, 1:2 to 1:4, 1:4 to 1:6,
1:6 to 1:8, or 1:8 to 1:10).
[0093] In certain embodiments, the bulk volume has a Young's
modulus from 1 GPa to 10 GPa (e.g., from 1 to 4 GPa, 4 to 7 GPa, 7
to 10 GPa).
[0094] In certain embodiments, the plurality of printing posts have
a Young's modulus from 1 MPa to 10 MPa (e.g., from 1 to 4 MPa, 4 to
7 MPa, 7 to 10 MPa).
[0095] In certain embodiments, the plurality of printing posts have
a first Young's modulus and the base has a second Young's modulus,
greater than the first Young's modulus.
[0096] In certain embodiments, the bulk volume comprises a polymer
having a coefficient of thermal expansion less than or equal to
14.5 ppm.
[0097] In certain embodiments, the plurality of printing posts
occupy an area selected from 10 cm.sup.2to 260 cm.sup.2 (e.g., from
10 cm.sup.2to 40 cm.sup.2, 40 cm.sup.2to 80 cm.sup.2, 120
cm.sup.2to 160 cm.sup.2, 160 cm.sup.2to 200 cm.sup.2, 200 cm.sup.2
to 240 cm.sup.2, or 240 cm.sup.2 to 260 cm.sup.2).
[0098] In certain embodiments, each printing post of the plurality
of printing posts has at least one of a width, length, and height
from 50 nanometers to 10 micrometers (e.g., 50 nm to 100 nm, 100 nm
to 200 nm, 200 nm to 400 nm, 400 nm to 600 nm, 600 nm to 800 nm,
800 nm to 1 micron, 1 micron to 5 microns, or 5 microns to 10
microns).
[0099] In certain embodiments, the plurality of printing posts are
formed in a continuous, unitary layer.
[0100] In certain embodiments, the plurality of printing posts
comprises a polymer.
[0101] In certain embodiments, the bulk volume is
Polydimethylsiloxane (PDMS).
[0102] In certain embodiments, the bulk volume and the plurality of
printing posts are formed from a single material.
[0103] In certain embodiments, a least a portion of the posts are
arranged on the first surface from 1 mm to 15 mm away from a edge
of the first surface (e.g., from 1 mm to 5 mm or 5 mm to 10 mm, 10
mm to 15 mm from the edge).
[0104] In certain embodiments, the bulk volume has a side surface
between the first and second surfaces.
[0105] In certain embodiments, the side surface has a beveled
and/or rounded edge.
[0106] In certain embodiments, the side surface has a rounded
profile (e.g., convex or concave).
[0107] In certain embodiments, the side surface has a beveled edge
forming an angle from horizontal (parallel to the first surface) of
no greater than 75.degree. (e.g., no greater than 60.degree., no
greater than 45.degree., no greater than 30.degree., or no greater
than 15.degree.).
[0108] In another aspect, the disclosed technology includes a
conformable transfer device comprising an elastomer (e.g., PDMS)
slab (e.g., bulk volume) having a mesa configuration with a surface
upon which a plurality of (e.g., array of) posts are disposed,
wherein one or more of the following holds [any of (i), (ii),
and/or (iii)]: (i) the edge of the mesa has a beveled and/or
rounded edge so as to reduce distortion of the surface and allow
accurate spacing of the plurality of posts; (ii) the plurality of
posts are arranged on the surface at least 1 mm away from the edge
(e.g., from 1 mm to 5 mm or 5 mm to 20 mm from the edge); and (iii)
the mesa has a thickness no greater than 10 mm (e.g., from 1 to 5
mm).
[0109] In certain embodiments, the edge of the mesa has a beveled
edge forming an angle from horizontal (parallel to the surface) of
no greater than 75.degree. (e.g., no greater than 60.degree., no
greater than 45.degree., no greater than 30.degree., or no greater
than 15.degree.).
[0110] In certain embodiments, the edge of the mesa has a rounded
profile (e.g., convex or concave).
[0111] In certain embodiments, the device includes a substrate
(e.g., glass) upon which the elastomer slab is disposed.
[0112] In certain embodiments, an aspect ratio (height to width) of
each post of the plurality of posts is less than or equal to 4:1
(e.g., from 2:1 to 4:1).
[0113] In certain embodiments, each post of the plurality of
printing posts comprises a contact surface on the end of the post
opposite the first surface, wherein the contact surfaces of the
plurality of posts are substantially in a same plane.
[0114] In certain embodiments, the thickness of the posts is from 1
micron to 100 microns (e.g., from 1 to 5 microns, 5 to 10 microns,
10 to 15 microns, 50 to 25 microns, 25 to 40 microns, 40 to 60
microns, 60 to 80 microns, or 80 to 100 microns).
[0115] In certain embodiments, the thickness of the mesa is from
0.5 mm to 5 mm (e.g., from 0.5 to 1 mm, 1 to 2 mm, 2 to 3 mm, 3 to
4 mm, or 4 to 5 mm).
[0116] In certain embodiments, the ratio of the thickness of the
plurality of posts to the thickness of the mesa is from 1:1 to 1:10
(e.g., from 1:1 to 1:2, 1:2 to 1:4, 1:4 to 1:6, 1:6 to 1:8, or 1:8
to 1:10).
[0117] In certain embodiments, the mesa has a Young's modulus from
1 GPa to 10 GPa (e.g., from 1 to 4 GPa, 4 to 7 GPa, 7 to 10
GPa).
[0118] In certain embodiments, the posts have a Young's modulus
from 1 MPa to 10 MPa (e.g., from 1 to 4 MPa, 4 to 7 MPa, 7 to 10
MPa).
[0119] In certain embodiments, the posts have a first Young's
modulus and the mesa has a second Young's modulus, greater than the
first Young's modulus.
[0120] In certain embodiments, the posts have a Young's modulus
from 1 MPa to 5 MPa.
[0121] In certain embodiments, the mesa comprises a polymer having
a coefficient of thermal expansion less than or equal to 14.5
ppm.
[0122] In certain embodiments, the posts occupy an area selected
from 10 cm.sup.2 to 260 cm.sup.2 (e.g., from 10 cm.sup.2 to 40
cm.sup.2, 40 cm.sup.2 to 80 cm.sup.2, 120 cm.sup.2 to 160 cm.sup.2,
160 cm.sup.2 to 200 cm.sup.2, 200 cm.sup.2 to 240 cm.sup.2, or 240
cm.sup.2 to 260 cm.sup.2).
[0123] In certain embodiments, each post of the posts has at least
one of a width, length, and height from 50 nanometers to 10
micrometers (e.g., 50 nm to 100 nm, 100 nm to 200 nm, 200 nm to 400
nm, 400 nm to 600 nm, 600 nm to 800 nm, 800 nm to 1 micron, 1
micron to 5 microns, or 5 microns to 10 microns).
[0124] In certain embodiments, the posts are formed in a
continuous, unitary layer.
[0125] In certain embodiments, the posts comprises a polymer.
[0126] In certain embodiments, the mesa is Polydimethylsiloxane
(PDMS).
[0127] In certain embodiments, the mesa and the posts are formed
from a single material.
[0128] In another aspect, the disclosed technology includes a
conformable transfer device, the transfer device including: a bulk
volume having a first surface and a second surface, opposite the
first surface; a mesa disposed on the bulk volume; a layer
comprising a plurality of posts (e.g., array of posts) disposed on
the mesa, opposite the bulk volume, for picking up printable
material, wherein the plurality of posts, the mesa, and the bulk
volume are arranged such that a force applied to the second surface
of the bulk volume is transmitted to the plurality of posts.
[0129] In certain embodiments, a thickness of the mesa is greater
than a thickness of the posts.
[0130] In certain embodiments, an aspect ratio (height to width) of
each post of the plurality of posts is less than or equal to 4:1
(e.g., from 2:1 to 4:1).
[0131] In certain embodiments, each post of the plurality of
printing posts comprises a contact surface on the end of the post
opposite the first surface, wherein the contact surfaces of the
plurality of posts are substantially in a same plane.
[0132] In certain embodiments, the thickness of the posts is from 1
micron to 100 microns (e.g., from 1 to 5 microns, 5 to 10 microns,
10 to 15 microns, 50 to 25 microns, 25 to 40 microns, 40 to 60
microns, 60 to 80 microns, or 80 to 100 microns).
[0133] In certain embodiments, a thickness of the bulk volume is
from 0.5 mm to 5 mm (e.g., from 0.5 to 1 mm, 1 to 2 mm, 2 to 3 mm,
3 to 4 mm, or 4 to 5 mm).
[0134] In certain embodiments, a ratio of a thickness of the posts
to a thickness of the bulk volume is from 1:1 to 1:10 (e.g., from
1:1 to 1:2, 1:2 to 1:4, 1:4 to 1:6, 1:6 to 1:8, or 1:8 to
1:10).
[0135] In certain embodiments, the bulk volume has a Young's
modulus from 1 GPa to 10 GPa (e.g., from 1 to 4 GPa, 4 to 7 GPa, 7
to 10 GPa).
[0136] In certain embodiments, the posts have a Young's modulus
from 1 MPa to 10 MPa (e.g., from 1 to 4 MPa, 4 to 7 MPa, 7 to 10
MPa).
[0137] In certain embodiments, the posts have a first Young's
modulus and the bulk volume has a second Young's modulus, greater
than the first Young's modulus.
[0138] In certain embodiments, the mesa has the first Young's
modulus.
[0139] In certain embodiments, the mesa has the second Young's
modulus.
[0140] In certain embodiments, the bulk volume comprises a polymer
having a coefficient of thermal expansion less than or equal to
14.5 ppm.
[0141] In certain embodiments, the posts occupy an area selected
from 10 cm.sup.2 to 260 cm.sup.2 (e.g., from 10 cm.sup.2 to 40
cm.sup.2, 40 cm.sup.2 to 80 cm.sup.2, 120 cm.sup.2 to 160 cm.sup.2,
160 cm.sup.2 to 200 cm.sup.2, 200 cm.sup.2 to 240 cm.sup.2, or 240
cm.sup.2 to 260 cm.sup.2).
[0142] In certain embodiments, each post of the plurality of posts
has at least one of a width, length, and height from 50 nanometers
to 10 micrometers (e.g., 50 nm to 100 nm, 100 nm to 200 nm, 200 nm
to 400 nm, 400 nm to 600 nm, 600 nm to 800 nm, 800 nm to 1 micron,
1 micron to 5 microns, or 5 microns to 10 microns).
[0143] In certain embodiments, the posts are formed in a
continuous, unitary layer.
[0144] In certain embodiments, the posts comprise a polymer.
[0145] In certain embodiments, the bulk volume is
Polydimethylsiloxane (PDMS).
[0146] In certain embodiments, the bulk volume and the posts are
formed from a single material.
[0147] In certain embodiments, a least a portion of the posts are
arranged on the first surface from 1 mm to 15 mm away from a edge
of the first surface (e.g., from 1 mm to 5 mm or 5 mm to 10 mm, 10
mm to 15 mm from the edge).
[0148] In certain embodiments, the bulk volume has a side surface
between the first and second surfaces.
[0149] In certain embodiments, the side surface has a beveled
and/or rounded edge.
[0150] In certain embodiments, the side surface has a rounded
profile (e.g., convex or concave).
[0151] In certain embodiments, the side surface has a beveled edge
forming an angle from horizontal (parallel to the first surface) of
no greater than 75.degree. (e.g., no greater than 60.degree., no
greater than 45.degree., no greater than 30.degree., or no greater
than 15.degree.).
[0152] In another aspect, the disclosed technology includes a
method of modifying a conformable transfer device to reduce
crowning, the method comprising providing a transfer device
comprising: a bulk volume having a first surface and a second
surface, opposite the first surface, and one or more sides between
the first surface and the second surface; a plurality of printing
posts disposed on the first surface of the bulk volume for picking
up printable material, wherein the plurality of printing posts and
the bulk volume are arranged such that a force applied to the
second surface of the bulk volume is transmitted to the plurality
of printing posts; and cutting an edge of the first surface of the
bulk substrate at an non-zero angle with respect to the first
surface, thereby reducing crowning at the edge.
[0153] In certain embodiments, an aspect ratio (height to width) of
each post of the plurality of posts is less than or equal to 4:1
(e.g., from 2:1 to 4:1).
[0154] In certain embodiments, each post of the plurality of
printing posts comprises a contact surface on the end of the post
opposite the first surface, wherein the contact surfaces of the
plurality of posts are substantially in a same plane.
[0155] In certain embodiments, a thickness of plurality of printing
posts is from 1 micron to 100 microns (e.g., from 1 to 5 microns, 5
to 10 microns, 10 to 15 microns, 50 to 25 microns, 25 to 40
microns, 40 to 60 microns, 60 to 80 microns, or 80 to 100
microns).
[0156] In certain embodiments, a thickness of the bulk volume is
from 0.5 mm to 5 mm (e.g., from 0.5 to 1 mm, 1 to 2 mm, 2 to 3 mm,
3 to 4 mm, or 4 to 5 mm).
[0157] In certain embodiments, a ratio of a thickness of the
plurality of printing posts and a thickness of the bulk volume is
from 1:1 to 1:10 (e.g., from 1:1 to 1:2, 1:2 to 1:4, 1:4 to 1:6,
1:6 to 1:8, or 1:8 to 1:10).
[0158] In certain embodiments, the bulk volume has a Young's
modulus from 1 GPa to 10 GPa (e.g., from 1 to 4 GPa, 4 to 7 GPa, 7
to 10 GPa).
[0159] In certain embodiments, the plurality of printing posts have
a Young's modulus from 1 MPa to 10 MPa (e.g., from 1 to 4 MPa, 4 to
7 MPa, 7 to 10 MPa).
[0160] In certain embodiments, the plurality of printing posts have
a first Young's modulus and the bulk volume has a second Young's
modulus, greater than the first Young's modulus.
[0161] In certain embodiments, the bulk volume comprises a polymer
having a coefficient of thermal expansion less than or equal to
14.5 ppm.
[0162] In certain embodiments, the plurality of printing posts
occupy an area selected from 10 cm.sup.2to 260 cm.sup.2 (e.g., from
10 cm.sup.2to 40 cm.sup.2, 40 cm.sup.2to 80 cm.sup.2, 120
cm.sup.2to 160 cm.sup.2, 160 cm.sup.2to 200 cm.sup.2, 200 cm.sup.2
to 240 cm.sup.2, or 240 cm.sup.2 to 260 cm.sup.2).
[0163] In certain embodiments, each printing post of the plurality
of printing posts has at least one of a width, length, and height
from 50 nanometers to 10 micrometers (e.g., 50 nm to 100 nm, 100 nm
to 200 nm, 200 nm to 400 nm, 400 nm to 600 nm, 600 nm to 800 nm,
800 nm to 1 micron, 1 micron to 5 microns, or 5 microns to 10
microns).
[0164] In certain embodiments, the plurality of printing posts are
formed in a continuous, unitary layer.
[0165] In certain embodiments, the plurality of printing posts
comprises a polymer.
[0166] In certain embodiments, the bulk volume is
Polydimethylsiloxane (PDMS).
[0167] In certain embodiments, the bulk volume and the plurality of
printing posts are formed from a single material.
[0168] In certain embodiments, a least a portion of the posts are
arranged on the first surface from 1 mm to 15 mm away from a edge
of the first surface (e.g., from 1 mm to 5 mm or 5 mm to 10 mm, 10
mm to 15 mm from the edge).
[0169] In certain embodiments, the bulk volume has a side surface
between the first and second surfaces.
[0170] In certain embodiments, the side surface has a beveled
and/or rounded edge.
[0171] In certain embodiments, the side surface has a rounded
profile (e.g., convex or concave).
[0172] In certain embodiments, the side surface has a beveled edge
forming an angle from horizontal (parallel to the first surface) of
no greater than 75.degree. (e.g., no greater than 60.degree., no
greater than 45.degree., no greater than 30.degree., or no greater
than 15.degree.).
[0173] In another aspect, the disclosed technology includes a
conformable transfer device, the transfer device including: a bulk
volume having a first surface and a second surface, opposite the
first surface; and a plurality of posts disposed on the first
surface of the bulk volume for picking up printable material,
wherein each posts comprises a base section and a top section,
wherein the top section has a cross-sectional area smaller than
that of the base section (e.g., less than 50%, 30%, 25%, 10% of the
cross-sectional area of the base section).
[0174] In certain embodiments, each of the plurality of posts
comprises a contact surface on the end of the post opposite the
first surface, wherein the contact surfaces of the plurality of
posts are substantially in a same plane.
[0175] In certain embodiments, a thickness of posts ranges from 1
micron to 100 microns (e.g., from 1 to 5 microns, 5 to 10 microns,
10 to 15 microns, 50 to 25 microns, 25 to 40 microns, 40 to 60
microns, 60 to 80 microns, or 80 to 100 microns).
[0176] In certain embodiments, a thickness of the bulk volume is
from 0.5 mm to 5 mm (e.g., from 0.5 to 1 mm, 1 to 2 mm, 2 to 3 mm,
3 to 4 mm, or 4 to 5 mm).
[0177] In certain embodiments, a ratio of a thickness of the posts
to a thickness of the bulk volume is from 1:1 to 1:10 (e.g., from
1:1 to 1:2, 1:2 to 1:4, 1:4 to 1:6, 1:6 to 1:8, or 1:8 to
1:10).
[0178] In certain embodiments, the bulk volume has a Young's
modulus from 1 GPa to 10 GPa (e.g., from 1 to 4 GPa, 4 to 7 GPa, 7
to 10 GPa).
[0179] In certain embodiments, the posts have a Young's modulus
from 1 MPa to 10 MPa (e.g., from 1 to 4 MPa, 4 to 7 MPa, 7 to 10
MPa).
[0180] In certain embodiments, the posts have a first Young's
modulus and a base has a second Young's modulus, greater than the
first Young's modulus.
[0181] In certain embodiments, the bulk volume comprises a polymer
having a coefficient of thermal expansion less than or equal to
14.5 ppm.
[0182] In certain embodiments, the posts occupy an area selected
from 10 cm.sup.2 to 260 cm.sup.2 (e.g., from 10 cm.sup.2 to 40
cm.sup.2, 40 cm.sup.2 to 80 cm.sup.2, 120 cm.sup.2 to 160 cm.sup.2,
160 cm.sup.2 to 200 cm.sup.2, 200 cm.sup.2 to 240 cm.sup.2, or 240
cm.sup.2 to 260 cm.sup.2).
[0183] In certain embodiments, each post of the plurality of posts
has at least one of a width, length, and height from 50 nanometers
to 10 micrometers (e.g., 50 nm to 100 nm, 100 nm to 200 nm, 200 nm
to 400 nm, 400 nm to 600 nm, 600 nm to 800 nm, 800 nm to 1 micron,
1 micron to 5 microns, or 5 microns to 10 microns).
[0184] In certain embodiments, the posts are formed in a
continuous, unitary layer.
[0185] In certain embodiments, the posts comprise a polymer.
[0186] In certain embodiments, the bulk volume is
Polydimethylsiloxane (PDMS).
[0187] In certain embodiments, the bulk volume and the posts are
formed from a single material.
[0188] In certain embodiments, an aspect ratio (height to width) of
each post of the plurality of posts is less than or equal to 4:1
(e.g., from 2:1 to 4:1).
[0189] In certain embodiments, the bulk volume has a side surface
between the first and second surfaces.
[0190] In certain embodiments, the side surface has a beveled
and/or rounded edge.
[0191] In certain embodiments, the side surface has a rounded
profile (e.g., convex or concave).
[0192] In certain embodiments, the side surface has a beveled edge
forming an angle from horizontal (parallel to the first surface) of
no greater than 75.degree. (e.g., no greater than 60.degree., no
greater than 45.degree., no greater than 30.degree., or no greater
than 15.degree.).
[0193] In certain embodiments, a least a portion of the posts are
arranged on the first surface from 1 mm to 15 mm away from a edge
of the first surface (e.g., from 1 mm to 5 mm or 5 mm to 10 mm, 10
mm to 15 mm from the edge).
[0194] In another aspect, the disclosed technology includes a
conformable transfer device, the transfer device including: a bulk
volume having a first surface and a second surface, opposite the
first surface; a plurality of printing posts disposed on the first
surface of the bulk volume for picking up printable material; a
plurality of anti-sag posts disposed on the first surface of the
bulk volume for preventing the first surface of the bulk volume
from sagging and inadvertently picking up printable material when
printable material is picked up by the plurality of printing posts,
wherein the plurality of printing posts and the bulk volume are
arranged such that a force applied to the second surface of the
bulk volume is transmitted to the plurality of printing posts.
[0195] In certain embodiments, the plurality of printing posts and
the plurality of anti-sag posts are disposed on a connecting layer
positioned between the plurality of printing posts and the
plurality of anti-sag posts.
[0196] In certain embodiments, the connecting layer comprises a
thin metal layer.
[0197] In certain embodiments, each of the plurality of posts
comprises a contact surface on the end of the post opposite the
first surface, wherein the contact surfaces of the plurality of
posts are substantially in a same plane.
[0198] In certain embodiments, a thickness of the printing posts is
from 1 micron to 100 microns (e.g., from 1 to 5 microns, 5 to 10
microns, 10 to 15 microns, 50 to 25 microns, 25 to 40 microns, 40
to 60 microns, 60 to 80 microns, or 80 to 100 microns).
[0199] In certain embodiments, a thickness of the bulk volume is
from 0.5 mm to 5 mm (e.g., from 0.5 to 1 mm, 1 to 2 mm, 2 to 3 mm,
3 to 4 mm, or 4 to 5 mm).
[0200] In certain embodiments, a ratio of a thickness of the
printing posts to a thickness of the bulk volume is from 1:1 to
1:10 (e.g., from 1:1 to 1:2, 1:2 to 1:4, 1:4 to 1:6, 1:6 to 1:8, or
1:8 to 1:10).
[0201] In certain embodiments, the bulk volume has a Young's
modulus from 1 GPa to 10 GPa (e.g., from 1 to 4 GPa, 4 to 7 GPa, 7
to 10 GPa).
[0202] In certain embodiments, the printing posts have a Young's
modulus from 1 MPa to 10 MPa (e.g., from 1 to 4 MPa, 4 to 7 MPa, 7
to 10 MPa).
[0203] In certain embodiments, the printing posts have a first
Young's modulus and the bulk volume has a second Young's modulus,
greater than the first Young's modulus.
[0204] In certain embodiments, the bulk volume comprises a polymer
having a coefficient of thermal expansion less than or equal to
14.5 ppm.
[0205] In certain embodiments, the printing posts occupy an area
selected from 10 cm.sup.2 to 260 cm.sup.2 (e.g., from 10 cm.sup.2
to 40 cm.sup.2, 40 cm.sup.2 to 80 cm.sup.2, 120 cm.sup.2 to 160
cm.sup.2, 160 cm.sup.2 to 200 cm.sup.2, 200 cm.sup.2 to 240
cm.sup.2, or 240 cm.sup.2 to 260 cm.sup.2).
[0206] In certain embodiments, each of the printing posts has at
least one of a width, length, and height from 50 nanometers to 10
micrometers (e.g., 50 nm to 100 nm, 100 nm to 200 nm, 200 nm to 400
nm, 400 nm to 600 nm, 600 nm to 800 nm, 800 nm to 1 micron, 1
micron to 5 microns, or 5 microns to 10 microns).
[0207] In certain embodiments, the printing posts are formed in a
continuous, unitary layer.
[0208] In certain embodiments, the printing posts comprise a
polymer.
[0209] In certain embodiments, the bulk volume is
Polydimethylsiloxane (PDMS).
[0210] In certain embodiments, the bulk volume and the printing
posts are formed from a single material.
[0211] In certain embodiments, the anti-sag posts are interspersed
between the printing posts.
[0212] In certain embodiments, the plurality of anti-sag posts have
a greater modulus than the printing posts.
[0213] In certain embodiments, an aspect ratio (height to width) of
each post of the posts is less than or equal to 4:1 (e.g., from 2:1
to 4:1).
[0214] In certain embodiments, a least a portion of the posts are
arranged on the first surface from 1 mm to 15 mm away from a edge
of the first surface (e.g., from 1 mm to 5 mm or 5 mm to 10 mm, 10
mm to 15 mm from the edge).
[0215] In certain embodiments, the bulk volume has a side surface
between the first and second surfaces.
[0216] In certain embodiments, the side surfaces has a beveled
and/or rounded edge.
[0217] In certain embodiments, the side surface has a rounded
profile (e.g., convex or concave).
[0218] In certain embodiments, the side surface has a beveled edge
forming an angle from horizontal (parallel to the first surface) of
no greater than 75.degree. (e.g., no greater than 60.degree., no
greater than 45.degree., no greater than 30.degree., or no greater
than 15.degree.).
[0219] In another aspect, the disclosed technology includes a
conformable transfer device, the transfer device including: a bulk
volume having a first surface and a second surface, opposite the
first surface; and a plurality of posts disposed on the first
surface of the bulk volume for picking up printable material,
wherein the plurality of posts and the bulk volume are arranged
such that a force applied to the second surface of the bulk volume
is transmitted to the plurality of posts, wherein a portion of the
area of the first surface unoccupied by the plurality of posts
comprises a roughened area (e.g., thereby anti-sagging).
[0220] In certain embodiments, the roughened area comprises a
plurality of features, each feature having a width less than the
width of each post and a height less than the height of each
post.
[0221] In certain embodiments, the roughened area is located on the
first surface between the posts.
[0222] In certain embodiments, the roughened area comprises a
patterned array of features.
[0223] In certain embodiments, the roughened area comprises a
random array of features.
[0224] In certain embodiments, each of the plurality of posts
comprises a contact surface on the end of the post opposite the
first surface, wherein the contact surfaces of the plurality of
posts are substantially in a same plane.
[0225] In certain embodiments, a thickness of posts is from 1
micron to 100 microns (e.g., from 1 to 5 microns, 5 to 10 microns,
10 to 15 microns, 50 to 25 microns, 25 to 40 microns, 40 to 60
microns, 60 to 80 microns, or 80 to 100 microns).
[0226] In certain embodiments, a thickness of the bulk volume is
from 0.5 mm to 5 mm microns (e.g., from 0.5 to 1 mm, 1 to 2 mm, 2
to 3 mm, 3 to 4 mm, or 4 to 5 mm).
[0227] In certain embodiments, a ratio of a thickness of the posts
and a thickness of the bulk volume is from 1:1 to 1:10 (e.g., from
1:1 to 1:2, 1:2 to 1:4, 1:4 to 1:6, 1:6 to 1:8, or 1:8 to
1:10).
[0228] In certain embodiments, the bulk volume has a Young's
modulus from 1 GPa to 10 GPa (e.g., from 1 to 4 GPa, 4 to 7 GPa, 7
to 10 GPa).
[0229] In certain embodiments, the posts have a Young's modulus
from 1 MPa to 10 MPa (e.g., from 1 to 4 MPa, 4 to 7 MPa, 7 to 10
MPa).
[0230] In certain embodiments, the posts have a first Young's
modulus and the bulk volume has a second Young's modulus, greater
than the first Young's modulus.
[0231] In certain embodiments, the bulk volume comprises a polymer
having a coefficient of thermal expansion less than or equal to
14.5 ppm.
[0232] In certain embodiments, the posts occupy an area selected
from 10 cm.sup.2 to 260 cm.sup.2 (e.g., from 10 cm.sup.2 to 40
cm.sup.2, 40 cm.sup.2 to 80 cm.sup.2, 120 cm.sup.2 to 160 cm.sup.2,
160 cm.sup.2 to 200 cm.sup.2, 200 cm.sup.2 to 240 cm.sup.2, or 240
cm.sup.2 to 260 cm.sup.2).
[0233] In certain embodiments, each of the posts has at least one
of a width, length, and height from 50 nanometers to 10
micrometers.
[0234] In certain embodiments, the posts are formed in a
continuous, unitary layer.
[0235] In certain embodiments, the posts comprise a polymer.
[0236] In certain embodiments, the bulk volume is PDMS.
[0237] In certain embodiments, the bulk volume and the posts are
formed from a single material.
[0238] In certain embodiments, the conformable transfer device is a
visco-elastomeric stamp.
[0239] In certain embodiments, the conformable transfer device is
an elastomeric stamp.
[0240] In certain embodiments, the elastomer stamp is made of
Polydimethylsiloxane (PDMS).
[0241] In certain embodiments, an aspect ratio (height to width) of
each post of the posts is less than or equal to 4:1 (e.g., from 2:1
to 4:1).
[0242] In certain embodiments, the posts are arranged on the first
surface from 1 mm to 15 mm away from a edge of the first surface
(e.g., from 1 mm to 5 mm or 5 mm to 10 mm, 10 mm to 15 mm from the
edge).
[0243] In certain embodiments, the bulk volume has a side surface
between the first and second surfaces.
[0244] In certain embodiments, the side surfaces has a beveled
and/or rounded edge.
[0245] In certain embodiments, the side surface has a rounded
profile (e.g., convex or concave).
[0246] In certain embodiments, the side surface has a beveled edge
forming an angle from horizontal (parallel to the first surface) of
no greater than 75.degree. (e.g., no greater than 60.degree., no
greater than 45.degree., no greater than 30.degree., or no greater
than 15.degree.).
[0247] In another aspect, the disclosed technology includes a
conformable transfer device, the transfer device including: a base
comprising a first material; a sub-base comprising a second
material and disposed on the base (e.g., wherein the sub-base has a
smaller cross-sectional area than the base); a bulk volume
comprising a material different from the base and the sub-base and
disposed at least partly on the sub-base (e.g., and also at least
partly at the base), wherein a thickness of a portion of the bulk
volume that is disposed on the sub-base is less than a thickness of
the sub-base; and a plurality of posts disposed on the bulk volume,
opposite and above the sub-base, for picking up printable material,
wherein the plurality of posts, the base, the sub-base, and the
bulk volume are arranged such that a force applied to a surface of
the base opposite the sub-base is transmitted to the plurality of
posts.
[0248] In certain embodiments, the first material comprises
glass.
[0249] In certain embodiments, the first and second materials are
the same.
[0250] In certain embodiments, the bulk volume and the plurality of
posts are formed from a single material.
[0251] In certain embodiments, the bulk volume comprises a
polymer.
[0252] In certain embodiments, the first material is
transparent.
[0253] In certain embodiments, the second material is
transparent.
[0254] In certain embodiments, each of the plurality of posts
comprises a contact surface on the end of the post opposite the
bulk volume, wherein the contact surfaces of the plurality of posts
are substantially in a same plane.
[0255] In certain embodiments, a thickness of the posts is from 1
micron to 100 microns (e.g., from 1 to 5 microns, 5 to 10 microns,
10 to 15 microns, 50 to 25 microns, 25 to 40 microns, 40 to 60
microns, 60 to 80 microns, or 80 to 100 microns).
[0256] In certain embodiments, a thickness of the bulk volume is
from 0.5 mm to 5 mm (e.g., from 0.5 to 1 mm, 1 to 2 mm, 2 to 3 mm,
3 to 4 mm, or 4 to 5 mm).
[0257] In certain embodiments, a ratio of a thickness of the posts
to a thickness of the bulk volume is from 1:1 to 1:10 (e.g., from
1:1 to 1:2, 1:2 to 1:4, 1:4 to 1:6, 1:6 to 1:8, or 1:8 to
1:10).
[0258] In certain embodiments, the bulk volume has a Young's
modulus from 1 GPa to 10 GPa (e.g., from 1 to 4 GPa, 4 to 7 GPa, 7
to 10 GPa).
[0259] In certain embodiments, the posts have a Young's modulus
from 1 MPa to 10 MPa (e.g., from 1 to 4 MPa, 4 to 7 MPa, 7 to 10
MPa).
[0260] In certain embodiments, the posts have a first Young's
modulus and the base has a second Young's modulus, greater than the
first Young's modulus.
[0261] In certain embodiments, the bulk volume comprises a polymer
having a coefficient of thermal expansion less than or equal to
14.5 ppm.
[0262] In certain embodiments, the posts occupy an area selected
from 10 cm.sup.2 to 260 cm.sup.2 (e.g., from 10 cm.sup.2 to 40
cm.sup.2, 40 cm.sup.2 to 80 cm.sup.2, 120 cm.sup.2 to 160 cm.sup.2,
160 cm.sup.2 to 200 cm.sup.2, 200 cm.sup.2 to 240 cm.sup.2, or 240
cm.sup.2 to 260 cm.sup.2).
[0263] In certain embodiments, each post of the plurality of posts
has at least one of a width, length, and height from 50 nanometers
to 10 micrometers (e.g., 50 nm to 100 nm, 100 nm to 200 nm, 200 nm
to 400 nm, 400 nm to 600 nm, 600 nm to 800 nm, 800 nm to 1 micron,
1 micron to 5 microns, or 5 microns to 10 microns).
[0264] In certain embodiments, the posts are formed in a
continuous, unitary layer.
[0265] In certain embodiments, the posts comprise a polymer.
[0266] In certain embodiments, the bulk volume is
Polydimethylsiloxane (PDMS).
[0267] In certain embodiments, the bulk volume has a greater
modulus than the posts.
[0268] In certain embodiments, an aspect ratio (height to width) of
each post of the posts is less than or equal to 4:1 (e.g., from 2:1
to 4:1).
[0269] In certain embodiments, a least a portion of the posts are
arranged on the first surface from 1 mm to 15 mm away from a edge
of the first surface (e.g., from 1 mm to 5 mm or 5 mm to 10 mm, 10
mm to 15 mm from the edge).
[0270] In certain embodiments, the bulk volume has a side surface
between the first and second surfaces.
[0271] In certain embodiments, the side surface has a beveled
and/or rounded edge.
[0272] In certain embodiments, the side surface has a rounded
profile (e.g., convex or concave).
[0273] In certain embodiments, the side surface has a beveled edge
forming an angle from horizontal (parallel to the first surface) of
no greater than 75.degree. (e.g., no greater than 60.degree., no
greater than 45.degree., no greater than 30.degree., or no greater
than 15.degree.).
[0274] In another aspect, the disclosed technology includes a
conformable transfer device, the transfer device including: a bulk
volume having a first surface and a second surface, opposite the
first surface, wherein the bulk volume has a first composition; a
plurality of posts disposed on the first surface of the bulk volume
for picking up printable material, wherein the plurality of posts,
and the bulk volume are arranged so that a force applied to the
second surface of the base by the base is transmitted to the
plurality of posts, wherein at least a part of (e.g., all of each
post or a top portion of each post) each post has a second
composition different from the first composition.
[0275] In certain embodiments, at least a part of each post has the
second composition.
[0276] In certain embodiments, a bottom portion of each post
closest to the bulk volume has the second composition.
[0277] In certain embodiments, the first composition comprises a
polymer.
[0278] In certain embodiments, the second composition comprises a
polymer.
[0279] In certain embodiments, the first composition comprises a
hardener.
[0280] In certain embodiments, the second composition comprises a
hardener.
[0281] In certain embodiments, the base is glass.
[0282] In certain embodiments, each post of the plurality of posts
comprises a contact surface on the end of the post opposite the
first surface, wherein the contact surfaces of the plurality of
posts are in substantially a same plane.
[0283] In certain embodiments, a thickness of the posts is from 1
micron to 100 microns (e.g., from 1 to 5 microns, 5 to 10 microns,
10 to 15 microns, 50 to 25 microns, 25 to 40 microns, 40 to 60
microns, 60 to 80 microns, or 80 to 100 microns).
[0284] In certain embodiments, a thickness of the bulk volume is
from 0.5 mm to 5 mm (e.g., from 0.5 to 1 mm, 1 to 2 mm, 2 to 3 mm,
3 to 4 mm, or 4 to 5 mm).
[0285] In certain embodiments, a ratio of a thickness of the posts
and a thickness of the bulk volume is from 1:1 to 1:10 (e.g., from
1:1 to 1:2, 1:2 to 1:4, 1:4 to 1:6, 1:6 to 1:8, or 1:8 to
1:10).
[0286] In certain embodiments, the bulk volume has a Young's
modulus from 1 GPa to 10 GPa (e.g., from 1 to 4 GPa, 4 to 7 GPa, 7
to 10 GPa).
[0287] In certain embodiments, the posts have a Young's modulus
from 1 MPa to 10 MPa (e.g., from 1 to 4 MPa, 4 to 7 MPa, 7 to 10
MPa).
[0288] In certain embodiments, the posts have a first Young's
modulus and the base has a second Young's modulus, greater than the
first Young's modulus.
[0289] In certain embodiments, the bulk volume comprises a polymer
having a coefficient of thermal expansion less than or equal to
14.5 ppm.
[0290] In certain embodiments, the posts occupy an area selected
from 10 cm.sup.2 to 260 cm.sup.2 (e.g., from 10 cm.sup.2 to 40
cm.sup.2, 40 cm.sup.2 to 80 cm.sup.2, 120 cm.sup.2 to 160 cm.sup.2,
160 cm.sup.2 to 200 cm.sup.2, 200 cm.sup.2 to 240 cm.sup.2, or 240
cm.sup.2 to 260 cm.sup.2).
[0291] In certain embodiments, each post of the plurality of posts
has at least one of a width, length, and height from 50 nanometers
to 10 micrometers (e.g., 50 nm to 100 nm, 100 nm to 200 nm, 200 nm
to 400 nm, 400 nm to 600 nm, 600 nm to 800 nm, 800 nm to 1 micron,
1 micron to 5 microns, or 5 microns to 10 microns).
[0292] In certain embodiments, the posts are formed in a
continuous, unitary layer. In certain embodiments, an aspect ratio
(height to width) of each post of the plurality of posts is less
than or equal to 4:1 (e.g., from 2:1 to 4:1).
[0293] In certain embodiments, a least a portion of the posts are
arranged on the first surface from 1 mm to 15 mm away from a edge
of the first surface (e.g., from 1 mm to 5 mm or 5 mm to 10 mm, 10
mm to 15 mm from the edge).
[0294] In certain embodiments, the bulk volume has a side surface
between the first and second surfaces.
[0295] In certain embodiments, the side surface has a beveled
and/or rounded edge.
[0296] In certain embodiments, the side surface has a rounded
profile (e.g., convex or concave).
[0297] In certain embodiments, the side surface has a beveled edge
forming an angle from horizontal (parallel to the first surface) of
no greater than 75.degree. (e.g., no greater than 60.degree., no
greater than 45.degree., no greater than 30.degree., or no greater
than 15.degree.).
BRIEF DESCRIPTION OF THE FIGURES
[0298] The foregoing and other objects, aspects, features, and
advantages of the present disclosure will become more apparent and
better understood by referring to the following description taken
in conjunction with the accompanying drawings.
[0299] FIGS. 1A through 1C are illustrations of heat-assisted
micro-transfer-printing with photoresist encapsulation.
[0300] FIGS. 2A and 2B are illustrations of heat-assisted printing
of semiconductor elements onto a destination, non-native substrate
having topographic features.
[0301] FIG. 3A is an SEM image of example semiconductor elements
printed on a non-native substrate.
[0302] FIG. 3B is an SEM image of example semiconductor elements
printed on a non-native substrate having topographic features.
[0303] FIG. 4 is an example diagram illustrating the application of
plasma to a contact surface of the semiconductor elements.
[0304] FIG. 5A is an example diagram illustrating the application
of plasma to the contact surface of the semiconductor elements.
[0305] FIG. 5B is an illustration of metal-to-metal joining of the
semiconductor devices to the destination substrate after applying
plasma to the contact surface of the semiconductor elements.
[0306] FIG. 6 is an example diagram illustrating application of
plasma to the contact surface of the semiconductor devices.
[0307] FIGS. 7A through 7D are examples of shapes of outputs of the
plasma source.
[0308] FIG. 8A through 8C are illustrations printing semiconductor
elements to a destination substrate with a flux layer thereon.
[0309] FIGS. 9A through 9C illustrate a typical method of picking
up semiconductor elements.
[0310] FIGS. 10A and 10B illustrate an example of gravity-assisted
separation of the semiconductor elements from the native
substrate.
[0311] FIGS. 11A and 11B are diagrams illustrating another example
of gravity-assisted separation of the semiconductor elements from
the native substrate.
[0312] FIG. 12 is a diagram of an example transfer device with an
array of posts.
[0313] FIGS. 13A and 13B are illustrations of a typical transfer
device and sag occurring during compression.
[0314] FIGS. 14A and 14B are illustrations of a multi-tiered
stamp.
[0315] FIG. 15 is an illustration of a multi-tiered stamp.
[0316] FIG. 16 is an illustration of a casting for forming a
transfer device with multi-layer posts.
[0317] FIGS. 17A through 17C are SEM images of multi-layer posts
configured in an array.
[0318] FIGS. 18 and 19 are diagrams of examples of the anti-sag
features.
[0319] FIGS. 20A and 20B are diagrams that illustrate roughened
areas incorporated on the transfer device between posts.
[0320] FIGS. 21A and 21B are illustrations of example composite
transfer devices.
[0321] FIG. 22 is an illustration of crowning at the edge of the
bulk material (e.g., PDMS layer) of a stamp.
[0322] FIG. 23 is an illustration of crowning occurring on a piece
of elastomer.
[0323] FIG. 24 is an illustration of an example transfer device
with significant crowning.
[0324] FIG. 25 is an illustration of an example transfer device
made with multiple components to reduce crowning.
[0325] FIG. 26 is an illustration of an example transfer device
with reduced crowning.
[0326] FIG. 27 is an illustration of an example transfer device
with reduced crowning.
[0327] FIGS. 28A and 28B are illustrations of an example transfer
device with a mesa and an array of posts on the mesa.
[0328] FIG. 29 is an illustration of an example transfer device
with reduced crowning.
[0329] FIGS. 30A through 30B are illustrations of a method of
reducing the crowning on a transfer device.
[0330] FIGS. 31A through 31G illustration example sidewall profiles
for use with a transfer device.
[0331] FIG. 32 is a plot of the crowning height from the top
surface of the elastomer as a function of the lateral position
coordinate on the top surface of the elastomer sidewall for each of
the sidewall profiles shown in FIGS. 31A through 31G.
[0332] FIG. 33 is a plot of the crown height produced during
formation of transfer devices with the sidewall profiles shown in
FIGS. 31A through 31G.
[0333] The features and advantages of the present disclosure will
become more apparent from the detailed description set forth below
when taken in conjunction with the drawings, in which like
reference characters identify corresponding elements throughout. In
the drawings, like reference numbers generally indicate identical,
functionally similar, and/or structurally similar elements.
DETAILED DESCRIPTION OF THE INVENTION
[0334] As used herein the expression "semiconductor element" and
"semiconductor structure" are used synonymously and broadly refer
to a semiconductor material, structure, device, or component of a
device. Semiconductor elements include high-quality single
crystalline and polycrystalline semiconductors, semiconductor
materials fabricated via high-temperature processing, doped
semiconductor materials, organic and inorganic semiconductors, and
composite semiconductor materials and structures having one or more
additional semiconductor components or non-semiconductor
components, such as dielectric layers or materials or conducting
layers or materials. Semiconductor elements include semiconductor
devices and device components including, but not limited to,
transistors, photovoltaics including solar cells, diodes,
light-emitting diodes, lasers, p-n junctions, photodiodes,
integrated circuits, and sensors. In addition, semiconductor
element can refer to a part or portion that forms a functional
semiconductor device or product.
[0335] "Semiconductor" refers to any material that is a material
that is an insulator at a very low temperature, but which has an
appreciable electrical conductivity at temperatures of about 300
Kelvin. The electrical characteristics of a semiconductor can be
modified by the addition of impurities or dopants and controlled by
the use of electrical fields. In the present description, use of
the term semiconductor is intended to be consistent with use of
this term in the art of microelectronics and electronic devices.
Semiconductors useful in the present invention can include
elemental semiconductors, such as silicon, germanium and diamond,
and compound semiconductors, for example group IV compound
semiconductors such as SiC and SiGe, group III-V semiconductors
such as AlSb, AlAs, Aln, AlP, BN, GaSb, GaAs, GaN, GaP, InSb, InAs,
InN, and InP, group III-V ternary semiconductors alloys such as
Al.sub.xGal-.sub.xAs, group II-VI semiconductors such as CsSe, CdS,
CdTe, ZnO, ZnSe, ZnS, and ZnTe, group I-VII semiconductors CuCl,
group IV-VI semiconductors such as PbS, PbTe and SnS, layer
semiconductors such as PbI.sub.2, MoS.sub.2 and GaSe, oxide
semiconductors such as CuO and Cu.sub.2O. The term semiconductor
includes intrinsic semiconductors and extrinsic semiconductors that
are doped with one or more selected materials, including
semiconductor having p-type doping materials and n-type doping
materials, to provide beneficial electronic properties useful for a
given application or device. The term semiconductor includes
composite materials comprising a mixture of semiconductors or
dopants. Specific semiconductor materials useful for in some
applications of the present invention include, but are not limited
to, Si, Ge, SiC, AlP, AlAs, AlSb, GaN, GaP, GaAs, GaSb, InP, InAs,
GaSb, InP, InAs, InSb, ZnO, ZnSe, ZnTe, CdS, CdSe, ZnSe, ZnTe, CdS,
CdSe, CdTe, HgS, PbS, PbSe, PbTe, AlGaAs, AlInAs, AlInP, GaAsP,
GaInAs, GaInP, AlGaAsSb, AlGaInP, and GaInAsP. Porous silicon
semiconductor materials are useful for applications of the present
invention in the field of sensors and light-emitting materials,
such as light-emitting diodes (LEDs) and solid-state lasers.
Impurities of semiconductor materials are atoms, elements, ions or
molecules other than the semiconductor material(s) themselves or
any dopants provided in the semiconductor material. Impurities are
undesirable materials present in semiconductor materials that can
negatively impact the electronic properties of semiconductor
materials, and include but are not limited to oxygen, carbon, and
metals including heavy metals. Heavy-metal impurities include, but
are not limited to, the group of elements between copper and lead
on the periodic table, calcium, sodium, and all ions, compounds
and/or complexes thereof.
[0336] "Substrate" refers to a structure or material on which, or
in which, a process is (or has been) conducted, such as patterning,
assembly or integration of semiconductor elements. Substrates
include, but are not limited to: (i) a structure upon which
semiconductor elements are fabricated, deposited, transferred or
supported (also referred to as a native substrate); (ii) a device
substrate, for example an electronic device substrate; (iii) a
donor substrate having elements, such as semiconductor elements,
for subsequent transfer, assembly or integration; and (iv) a target
substrate for receiving printable structures, such as semiconductor
elements. A donor substrate can be, but is not necessarily, a
native substrate.
[0337] "Destination substrate" as used herein refers to the target
substrate (also referred to as a non-native substrate) for
receiving printable structures, such as semiconductor elements.
Examples of display substrate materials include polymer, plastic,
resin, polyimide, polyethylene naphthalate, polyethylene
terephthalate, metal, metal foil, glass, flexible glass, a
semiconductor, and sapphire.
[0338] Printable" relates to materials, structures, device
components, or integrated functional devices that are capable of
transfer, assembly, patterning, organizing, or integrating onto or
into substrates without exposure of the substrate to high
temperatures (e.g. at temperatures less than or equal to about 400,
200, or 150 degrees Celsius). In one embodiment of the present
invention, printable materials, elements, device components, or
devices are capable of transfer, assembly, patterning, organizing
or integrating onto or into substrates via solution printing,
micro-transfer printing, or dry transfer contact printing.
[0339] "Printable semiconductor elements" of the present invention
comprise semiconductor structures that can be assembled or
integrated onto substrate surfaces, for example by using dry
transfer contact printing, micro-transfer printing, or solution
printing methods. In one embodiment, printable semiconductor
elements of the present invention are unitary single crystalline,
polycrystalline or microcrystalline inorganic semiconductor
structures. In the context of this description, a unitary structure
is a monolithic element having features that are mechanically
connected. Semiconductor elements of the present invention can be
undoped or doped, can have a selected spatial distribution of
dopants, or can be doped with a plurality of different dopant
materials, including p- and n-type dopants. The present invention
includes microstructured printable semiconductor elements having at
least one cross-sectional dimension greater than or equal to about
1 micron and nanostructured printable semiconductor elements having
at least one cross-sectional dimension less than or equal to about
1 micron. Printable semiconductor elements useful in many
applications comprise elements derived from "top down" processing
of high-purity bulk materials, such as high-purity crystalline
semiconductor wafers generated using conventional high-temperature
processing techniques. In one embodiment, printable semiconductor
elements of the present invention comprise composite structures
having a semiconductor operationally connected to at least one
additional device component or structure, such as a conducting
layer, dielectric layer, electrode, additional semiconductor
structure, or any combination of these. In one embodiment,
printable semiconductor elements of the present invention comprise
stretchable semiconductor elements or heterogeneous semiconductor
elements.
[0340] "Plastic" refers to any synthetic or naturally occurring
material or combination of materials that can be molded or shaped,
generally when heated, and hardened into a desired shape. Exemplary
plastics useful in the devices and methods of the present invention
include, but are not limited to, polymers, resins and cellulose
derivatives. In the present description, the term plastic is
intended to include composite plastic materials comprising one or
more plastics with one or more additives, such as structural
enhancers, fillers, fibers, plasticizers, stabilizers or additives
which can provide desired chemical or physical properties.
[0341] "Dielectric" and "dielectric material" are used synonymously
in the present description and refer to a substance that is highly
resistant to flow of electric current and can be polarized by an
applied electric field. Useful dielectric materials include, but
are not limited to, SiO.sub.2, Ta.sub.2O.sub.5, TiO.sub.2,
ZrO.sub.2, Y.sub.2O.sub.3, SiN.sub.4, STO, BST, PLZT, PMN, and
PZT.
[0342] "Polymer" refers to a molecule comprising a plurality of
repeating chemical groups, typically referred to as monomers.
Polymers are often characterized by high molecular masses. Polymers
useable in the present invention can be organic polymers or
inorganic polymers and can be in amorphous, semi-amorphous,
crystalline or partially crystalline states. Polymers can comprise
monomers having the same chemical composition or can comprise a
plurality of monomers having different chemical compositions, such
as a copolymer. Cross-linked polymers having linked monomer chains
are particularly useful for some applications of the present
invention. Polymers useable in the methods, devices and device
components of the present invention include, but are not limited
to, plastics, elastomers, thermoplastic elastomers, elastoplastics,
thermostats, thermoplastics and acrylates. Exemplary polymers
include, but are not limited to, acetal polymers, biodegradable
polymers, cellulosic polymers, fluoropolymers, nylons,
polyacrylonitrile polymers, polyamide-imide polymers, polyimides,
polyarylates, polybenzimidazole, polybutylene, polycarbonate,
polyesters, polyetherimide, polyethylene, polyethylene copolymers
and modified polyethylenes, polyketones, poly(methyl methacrylate,
polymethylpentene, polyphenylene oxides and polyphenylene sulfides,
polyphthalamide, polypropylene, polyurethanes, styrenic resins,
sulphone based resins, vinyl-based resins or any combinations of
these.
[0343] "Micro-transfer printing" as used herein refers to systems,
methods, and techniques for the deterministic assembly of micro-
and nano-materials, devices, and semiconductor elements into
spatially organized, functional arrangements with two-dimensional
and three-dimensional layouts. It is often difficult to pick up and
place ultra-thin or small devices, however, micro-transfer printing
permits the selection and application of these ultra-thin, fragile,
or small devices, such as micro-LEDs, without causing damage to the
devices themselves.
[0344] Microstructured stamps (e.g., elastomeric, electrostatic
stamps, or hybrid elastomeric/electrostatic stamps) can be used to
pick up micro devices, transport the micro devices to a destination
substrate, and print the micro devices onto the destination
substrate. In some embodiments, surface adhesion forces are used to
control the selection and printing of these devices onto the
destination substrate. This process can be performed massively in
parallel. The stamps can be designed to transfer a single device or
hundreds to thousands of discrete structures in a single
pick-up-and-print operation. For a discussion of micro-transfer
printing generally, see U.S. Pat. Nos. 7,622,367 and 8,506,867,
each of which is hereby incorporated by reference in its
entirety.
Heat-Assisted Micro-Transfer-Printing to Adhesiveless Surfaces and
Topographic Surfaces
[0345] FIGS. 1A though 1C are illustrations of heat-assisted
micro-transfer-printing. The transfer device 102 (e.g., conformable
transfer device, such as an elastomer or visco-elastomer stamp
(e.g., polydimethylsiloxane (PDMS) stamp)) includes an array of
posts 114 for (i) picking up printable semiconductor elements 104
from a native substrate 108 (e.g., native to the printable
semiconductor elements 104 and used to fabricate the printable
semiconductor elements 104) and (ii) transferring the printable
semiconductor elements 104 to a non-native, destination substrate
110. In certain embodiments, the printable semiconductor elements
104 are encapsulated in a polymer layer 106 (e.g., photoresist)
before they are picked up.
[0346] In certain embodiments, the printable semiconductor elements
104 are fabricated on, or from, a bulk semiconductor substrate. In
such embodiments, the non-native, destination substrate 110 is made
of either (i) a non-semiconductor and/or non-metallic material
(e.g., with conductive interconnectivity fabricated thereon) or
(ii) one or more semiconductor material of different types from the
destination substrate. Examples of non-native substrate 110
include, but not limited to, glass, sapphire, plastics, metals
and/or other semiconductors. Examples of native substrate 108
include, but not limited to, inorganic semiconductor material such
as single crystalline silicon wafers, silicon on insulator wafers,
polycrystalline silicon wafers, GaAs wafers, Si (1 1 1), InAlP,
InP, GaAs, InGaAs, AlGaAs, GaSb, GaAlSb, AlSb, InSb, InGaAlSbAs,
InAlSb, and InGaP.
[0347] FIG. 1A illustrates the transfer device 102 after having
picked up the printable semiconductor elements 104 from the native
substrate 108, but before depositing the printable semiconductor
elements 104 on the destination substrate 110. In certain
embodiments, the printable semiconductor elements 104 are
fabricated on the native substrate 108 and then coated with the
polymer layer 106 prior to the transfer device 102 picking up the
printable semiconductor elements 104 from the native substrate 108.
In certain embodiments, the polymer 106 is on a top surface and
sides of the printable semiconductor element 104. In certain
embodiments, the polymer 106 is co-planar with the bottom of the
printable semiconductor element 104 such that both the polymer 106
and the bottom of the printable semiconductor element 104 contact
the destination substrate 110 during printing as shown in FIG.
1B.
[0348] In certain embodiments, prior to the printable semiconductor
elements 104 being picked up from the native substrate 108, the
polymer layer 106 serves as an anchor or tether for the printable
semiconductor element 104 in that the layer 106 encapsulates the
printable semiconductor elements 104 to maintain the printable
semiconductor element 104 on the native substrate 108. Example
details of anchoring are described in U.S. patent application Ser.
No. 14/743,988, filed Jun. 18, 2015 and entitled Systems and
Methods for Controlling Release of Transferable Semiconductor
Structures, which is incorporated by reference herein in its
entirety. In certain embodiments, the polymer layer 106 is a
photoresist.
[0349] FIG. 1B illustrates the transfer device 102 transferring the
printable semiconductor elements 104 to the destination substrate
110. During the transfer (e.g., printing process), the polymer
layer 106, in certain embodiments, is situated between the transfer
device 102 and the printable semiconductor elements 104 and serves
as the interface for separation between the transfer device 102 and
the destination substrate 110 when the printable semiconductor
elements 104 are picked up by the transfer device 102. In certain
embodiments, the polymer layers 106 increase adhesion to the
transfer device 102 during the pick-up of the printable
semiconductor elements 104 by the transfer device 102. In certain
embodiments, subsequent to the separation of the transfer device
102 from the destination substrate 110, the polymer layer 106 is
subsequently removed thereby leaving behind the transferred
printable semiconductor elements 104 on the destination substrate
110.
[0350] In certain embodiments, the transfer device 102 places the
printable semiconductor elements 104 and polymer layers 106 on the
surface of the destination substrate 110 and remains in that
placement position for a pre-defined time to allow the polymer
layer 106 to flow, thereby separating from, or having a reduced
adhesion with, the transfer device 102. After contacting the
polymer 106 and the bottom of the printable semiconductor element
104 to the destination substrate 110, the polymer 106 can be heated
(directly or indirectly). For example, in certain embodiments, a
hot plate 112 is used to heat the destination substrate 110. The
hot plate 112, in certain embodiments, is in direct thermal contact
with the destination substrate 110. The destination substrate 110
may be heated to an equilibrium temperature prior to the printable
semiconductor elements 104 being transferred to the substrate 110.
This equilibrium temperature, for example, may be sufficient to
cause the polymer layer 106 to reflow (e.g., heat from the heating
element reduces the viscosity of the polymer layer 106 or causes
the polymer layer 106 to flow during said contact) thereby reducing
the adhesion forces between the transfer device 102 and the polymer
layer 106. In certain embodiments, a non-contact thermal source is
employed from a source that does not make direct physical contact
with the destination substrate 110.
[0351] In certain embodiments, heating the polymer 106 facilitates
printing. When a printable semiconductor element 104 is embedded in
polymer 106 as shown in FIGS. 1A and 1B and the polymer 206 is
heated, the polymer can flow, thereby facilitating printing (i.e.,
release of the printable semiconductor element 104 from the
transfer device 102). In certain embodiments, heat also causes the
transfer device 102 itself (e.g., a viscoelastic transfer device,
such as PDMS transfer device) to expand more than the chip (due to
CTE), thereby leading to shear forces between the printable
semiconductor element 104 and the transfer device 102 that
facilitate printing.
[0352] FIG. 1C illustrates a micro-transfer-printed semiconductor
elements 104 on a destination, non-native substrate 110 after the
polymer layers 106 have been removed. For example, after printing,
plasma ashing may be performed to remove the polymer layers 106,
thereby leaving behind the semiconductor elements 104 printed on
the destination substrate 110.
[0353] In certain embodiments, the destination substrate 110
includes topographic features 202 on the surface 204 of the
destination substrate 110 to contact with the printable
semiconductor elements 104 and the polymer layers 106. FIGS. 2A and
2B illustrate a heat-assisted micro-transfer transfer device 102
for printing semiconductor elements 104 onto a surface 204 of a
destination, non-native substrate 110 having topographic features
202. In certain embodiments, the topographic features are grooves,
v-shaped channels, trenches, mesas, or canals. The topographic
features may have varying depths and varying cross-sectional areas.
FIG. 2A shows the transfer device 102 placing the printable
semiconductor elements 104 with polymer layers 106 on the
topographic features 202 of the destination substrate 110. FIG. 2B
shows the printable semiconductor elements 104 situated on the
topographic features 202 of the destination substrate 110 after the
polymer layers 106 has been removed as explained in relation to
FIGS. 1A through 1C above. In certain embodiments, it is difficult
to print to topographic surfaces 202 because less surface area on
the bottom of the printable semiconductor elements 104 contacts the
destination substrate 110 due to the topographic surface 202. The
use of the polymer layer 106 as described herein is beneficial
when, among other things, printing to destination substrates 110
with topographic surfaces 202, as it reduces adhesion between the
transfer devices and the polymer layer itself. Thus, the
semiconductor elements 104 can be printed even though less of the
surface of the destination substrate 110 contacts the semiconductor
elements 104 during printing.
[0354] FIG. 3A is an SEM image of example semiconductor devices 304
printed on a non-native substrate 310. In the example, the devices
304 are InP devices fabricated from an InP substrate. The
non-native substrate 310 is made of Si. In certain embodiments, a
removal layer made of, for example, InGaAs, is employed between the
InP device 304 and the InP bulk substrate to allow, or assist, in
the separation of the device 304 from the native substrate.
[0355] FIG. 3B is a SEM image of an example semiconductor device
304 printed on a non-native substrate 310 with topographic features
302. As shown, an InP device 304 is printed on the surface of a Si
destination substrate 310. In this example, the topographic
features 302 include U-shaped channels formed on the surface of the
destination substrate 310.
Plasma Treatment During Micro-Transfer-Printing
[0356] FIG. 4 is an example diagram illustrating plasma 402 being
applied to the contact surface 404 of the semiconductor elements
104 to be printed to the destination substrate 110. In certain
embodiments, plasma 402 is applied to the contact surface 404 of
the semiconductor elements 104 to be printed to the destination
substrate 110 while the semiconductor elements 104 are on the
transfer device 102. For example, plasma 402 can be applied to
bottom surfaces 404 of devices that are attached to an elastomer
transfer device 102.
[0357] The plasma 402 treats the contact surface 404 of the
semiconductor elements 104 to improve bonding between the
semiconductor elements 104 and the destination substrate 110. In
certain embodiments, the plasma 402 is used to clean the bottom
surface 404 of devices that have been fabricated using some method
of epitaxial lift-off. For example, the plasma 402 cleans the
contact surface 404 of semiconductor elements 104 of an oxide layer
formed at the contact surface 404. Removal of thin layers of oxides
from the contact surfaces 404 can be improved by adding a reducing
gas (forming gas, ammonia, formic acid, etc.) to the plasma 402.
Semiconductor elements 104 that have been fabricated using certain
methods of epitaxial lift-off, for example, may form oxide layers
at surfaces that are exposed to an oxidizer (such as air). The
plasma 402 is of sufficient temperature to remove the thin layer of
oxides from the contact surface of the printable semiconductor
element 104 with the destination substrate 110. In certain
embodiments, a reducing gas (e.g., forming gas, ammonia, formic
acid, etc.) is added into the plasma.
[0358] The plasma 402 can be applied to the semiconductor elements
104 in a manner in which the semiconductor elements 104 on the
transfer device 102 are un-distributed (i.e., do not fall off the
stamp) while the treatment is performed. Specifically, the plasma
402 is applied to the populated transfer device 102 in a manner to
not cause a given printable semiconductor element 104 to fall off
the transfer device 102. For example, in certain embodiments in
which the transfer device 102 has a high coefficient of thermal
expansion (CTE), the temperature of the transfer device 102 is
maintained below a level that would cause shearing and delamination
of the semiconductor elements 104 from the transfer device 102. In
this instance, once the semiconductor elements 104 are on the
transfer device 102, an uncontrolled release is undesired. Any
heating of the stamp causes the transfer device 102 to effectively
grow (e.g., expand). In some instances, the transfer device 102
grows more than the printable semiconductor element 104. This can
leading to shear forces between the printable semiconductor element
104 and the transfer device 102 that causes the semiconductor
elements 104 "drop" off the transfer device 102. However, in this
instance, when the plasma 402 is applied to the populated transfer
device 102, the shear forces and release of the printable
semiconductor element 104 is undesired. A number of techniques can
be used to maintain the temperature of the transfer device 102
below a level that would cause shearing and delamination of the
semiconductor elements 104 from the transfer device 102. In certain
embodiments, the duty cycle of the plasma output, the residence
time (e.g., scan speeds of 0.5 to 5 mm/sec, 0.5 to 1 mm/sec, 1 to 2
mm/sec, 2 to 5 mm/sec), the power of the plasma 402 (e.g., 25-150
Watts or 80-100 Watts), and the distance (e.g., 0.5 to 5 mm, 0.5 to
1 mm, 1 to 2 mm, 2 to 5 mm) between the plasma 402 to the backside
surface of the semiconductor elements 104 can be modulated to
maintain the temperature of the transfer device 102 below the
desired level (e.g., below 50, 75, or 100 degrees centigrade; e.g.,
below 50 degrees centigrade with short peaks above 100 degrees
centigrade). For example, in certain embodiments, the power of the
plasma is 80 to 100 Watts, the distance to the chip is 0.5 to 1 mm
(e.g., 1 mm), and the scan speed is 0.5 to 1 mm/sec. This maintains
the stamp at a desired temperature, such as below 50 degrees C.
with short peaks above 100 degrees C. In certain embodiments, room
temperature plasma 402 is used to keep the temperature of the
transfer device 102 low enough to avoid this type of failure mode
(chips falling from the chip).
[0359] FIG. 5A is an example diagram illustrating plasma 402 being
applied to the contact surface 404 of the semiconductor elements
104 to be printed to the destination substrate 110. In certain
embodiments, the semiconductor elements 104 have a backside metal
504, the plasma 402 can be used to remove oxides from the surface
of the metal 504. This improves metal-to-metal joining of the
backside metal 504 on the semiconductor elements 104 to the metal
506 on the destination substrate 110 as shown in FIG. 5B. Examples
of metal-to-metal materials for the metal 504 on the devices and
the metal 506 on the destination substrate 110 include, but are not
limited to, Cu--Cu, CuSn--Cu, Cu--Sn--Sn--Cu, and Au--Au.
[0360] FIG. 6 is an example photomicrograph illustrating the
application of plasma 402 to the contact surface of the
semiconductor devices.
[0361] FIGS. 7A though 7D are examples output shapes of the plasma
source. The shapes of the plasma outputs are shown as, but not
limited to, a point source, a beam source, a narrow circular
source, and a wide source.
[0362] FIG. 8A through 8C are illustrations of printing
semiconductor elements 104 having a metal layer-metal connection
808 on a destination substrate 110. In certain embodiments,
semiconductor elements 104 have a backside metal 802. The
semiconductor elements 104 can be printed to a destination
substrate 110 with mating metal pads 808 that have been coated with
a flux 806 before printing the semiconductor elements 104. The flux
806 can coat only the metal pads 808, the entire surface of the
destination substrate 110 with the metal pads 808 thereon, or a
portion (including the metal pads 808) of the destination substrate
110 with the metal pads 808 thereon.
[0363] FIG. 8A is an illustration of a transfer device 102 with
semiconductor elements 104 having a metal layer 802 disposed on the
bottom of the semiconductor elements 104. FIG. 8B is an
illustration of semiconductor elements 104 printed to a destination
substrate 110. The semiconductor elements 104 are printed onto
metal pads 808 with flux 806 thereon. The flux layer 806 is
employed between the metal layer 802 of the semiconductor elements
104 and the metal pads 808 on the destination substrate 110. The
removal of the flux reduces metal oxides on the metal pads 808,
thereby leading to good joining or bonding between metals. In
certain embodiments, the flux 806 is a resin. In certain
embodiments, the flux 806 is a no-clean flux or water-soluble flux.
For example, in certain embodiments, the flux 806 can be removed
using water (e.g., a heated water rinse).
[0364] In certain embodiments, the flux is an adhesive layer that
contains reducing agents for removal of oxides. After the
semiconductor elements 104 are printed, the flux 806 can be
reflowed thereby creating a good metal connection between metal
pads 808 on the destination substrate 110 and the backside metal
802 of the semiconductor elements 104.
[0365] A heating chamber or heating environment can be used to
thermally treat the printable semiconductor element 104 and the
destination substrate 110. The treatment causes the flux layer 804
to re-flow thereby allowing the metal layer 802 to contact the
metal contact pads 808 as shown in FIG. 8C.
Micro-Transfer-Printing with High Acceleration During Device
Pickup
[0366] FIGS. 9A through 9C illustrate a typical method of picking
up semiconductor elements 104. As shown in FIG. 9A, the devices 904
are formed on their native substrate 108. In this example, the
transfer device 102 is brought into contact with the semiconductor
elements 104 as shown in FIG. 9B. The transfer device is then moved
away (in an upward direction 902) from the source substrate 108,
thereby temporarily adhering the semiconductor elements 104 to the
transfer device 102 as shown in FIG. 9C.
[0367] The methods described in relation to FIGS. 10A-B and FIGS.
11A-B can be used to increase (e.g., by 1 or more g) the initial
acceleration (e.g., to 5 to 100 g), thereby achieving higher
velocities during the pick up process. The velocity at separation
occurs at very small travel distances (e.g., tens of microns or
less) dependent on the compression of the transfer device 102 at
lamination. Higher acceleration can create higher separation
velocities at small distances that in turn increases the adhesion
between the stamp and the source.
[0368] In certain embodiments, such as the transfer printing of an
elastic stamp material, the transfer device 102 employs
high-velocity separation between transfer device 102 and the source
of the printable elements (e.g., semiconductor elements 104 and
native substrate 108). It was found that higher acceleration can
create higher separation velocities over a smaller distance and
thus can increase the adhesion between the transfer device 102 and
the printable element (e.g., the printable semiconductor element
104). To employ gravity to assist in the separation, in certain
embodiments, the source substrate 108 is configured to move in a
downward direction to provide an additional 1 g of acceleration
during the separation process.
[0369] In certain embodiments, the transfer device 102 is
configured to accelerate the source of the printable elements
(e.g., the semiconductor elements 104 and native substrate 108)
with an initial acceleration between 5 and 100 g. The initial
acceleration allows the transfer device 102 to achieve a higher
velocity of the semiconductor elements 104 when being picked up by
the transfer device 102. The adhesion between a given transfer
device 102 and a given printable element (e.g., the semiconductor
elements 104) varies according to the speed of the separation
between the transfer device 102 and the native substrate 108 due to
the viscoelastic nature of the transfer device. To this end, when
the transfer device 102 and the printable semiconductor element 104
are moved away at a sufficient speed, the adhesion at the bond
interface between the transfer device 102 and the printable
semiconductor element 104 is sufficiently large to "pick up" the
printable element (e.g., printable semiconductor element 104) away
from its native substrate 108. Conversely, when the transfer device
102 is moved at a slower speed, the adhesion at the bond interface
between the transfer device 102 and the printable semiconductor
element 104 is low enough to "let go" or "print" the printable
semiconductor element 104 onto the non-native, destination
substrate 110.
[0370] In certain embodiments, the separate occurs over a travel
distance of (tens of microns or less). The separation distance may
be a function of the compression of the transfer device 102 at
lamination. In certain embodiments, the transfer device 102 employs
a vertical stage that moves the source (e.g., the printable
semiconductor element 104 and the native substrate 108) in the
pick-up process.
[0371] FIGS. 10A and 10B illustrate an example of gravity-assisted
separation of the semiconductor elements 104 from the native
substrate 108. In this example, the transfer device 102 is brought
into contact with the semiconductor elements 104 as shown in FIG.
10A either by moving the transfer device 102, moving the substrate
108, or a combination thereof. In this example, the arrangement and
method utilize gravity to assist with picking up the semiconductor
elements 104 from the native substrate 108. As shown, the native
substrate 108 is configured to move in a downward direction 1002
during the separation. To this end, a higher acceleration is
provided to the printable semiconductor element 104 (e.g., due to
moving with gravity) that is attached to the transfer device 102
during the pick-up operation as shown in FIG. 10B.
[0372] FIGS. 11A and 11B illustrate another example of
gravity-assisted separation of the printable semiconductor element
104 from the native substrate 108. As shown, the transfer device
102 is oriented below the source substrate 108 and the
semiconductor elements 104 are located on the bottom of the source
substrate 108 as shown in FIG. 11A. This can be accomplished by
forming the devices on the bottom of the substrate 108 or flipping
the substrate 108 with the semiconductor elements 104 thereon after
the semiconductor elements 104 are formed. The transfer device 102
is moved in a downward direction 1102 during the separation,
thereby picking up the semiconductor elements 104 so that they are
on the posts of the transfer device 102 as shown in FIG. 11B.
Again, a higher acceleration is provided to assist with picking up
the printable semiconductor element 104 (e.g., due to moving with
gravity).
[0373] In certain embodiments, the method shown in FIGS. 10A and
10B and the method shown in FIG. 11A and 11B are combined such that
both the source substrate 108 and the transfer device 102 are moved
away from each other (in a vertical direction). In such
embodiments, the separation acceleration is applied to both the
source of the printable elements (e.g., the semiconductor elements
104 and the native substrate 108) and the transfer device 102.
Transfer Devices Designed to Prevent Accidental Pick Up of Elements
Due to Sag
[0374] FIG. 12 is a diagram of an example transfer device 102 with
posts 1202 (e.g., an array of posts 1202). Typically, each post
1202 is arranged to contact a given printable semiconductor element
104 to be picked up by the transfer device 102. The posts 1202 may
have varying ranges of heights that depend, for example, on the
size of the source (e.g., the printable material such as the
printable semiconductor element 104) to be picked up by the
transfer device 102. In certain embodiments, the posts 1202 include
a cylindrical post, triangular post, rectangular post, pentagonal
post, hexagonal post, heptagonal post, and octagonal post.
[0375] In certain embodiments, during the pick-up of the printable
semiconductor element 104 from the native substrate 108, the
transfer device 102 compresses the transfer device 102 against the
source (e.g., the printable semiconductor element 104 and the
native substrate 108). The compression (e.g., in the z-direction),
in certain embodiments, allows the lamination of the array of posts
1202 onto the printable elements on the source substrate. In
addition, the compression allows for the critical velocity (for
pick-up to occur) to be reached within a smaller clearance between
the transfer device 102 and the printable semiconductor elements
104. To this end, the transfer device 102 may apply a smaller
initial acceleration. In certain embodiments, the transfer device
102 sags during compression in the pickup phase of the print cycle.
The sag may cause inadvertent pickup of semiconductor elements
104.
[0376] FIG. 13A illustrates a transfer device 1302 (e.g., the same
as or similar to the transfer device shown in FIG. 12) and FIG. 13B
illustrates sag 1304 occurring during compression of the transfer
device 1302 (e.g., during pickup). This sag 1304 causes unwanted
materials to be picked up from the source substrate. The array of
printable semiconductor devices (not shown) on the native substrate
1306 may be denser than the posts 1308 on the transfer device 1302
such that during an individual transfer (e.g., a single pick up and
print) printable devices are intentionally left on the native
substrate 1306. However, if the sag 1304 is large enough, the sag
1304 can contact the printable semiconductor devices resulting in
unintentional pick-up of these devices. A variety of solutions for
reducing (or eliminating) the likelihood of unintentional pick-up
of devices due to sag are disclosed herein, including transfer
devices with multi-tiered posts, anti-sag posts, or both.
Transfer Devices with Multi-Tiered Posts
[0377] FIGS. 14A and 14B illustrate an example multi-tiered post
1400. In certain embodiments, a multi-tiered post can be used to
eliminate (or reduce) the problems with sag described above in
relation to FIGS. 13A and 13B. As shown in FIG. 14B compared to
FIG. 13B, even if the transfer device in FIG. 14B experiences the
same amount of sag 1404 as the transfer device in FIG. 13B (sag
1304), the sag 1404 of the transfer device shown in FIG. 14B will
not pick up semiconductor devices due to the multi-tiered structure
increasing the overall height of the post while maintaining the
appropriate aspect ratio for the portion of the post (e.g.,
micro-post) that will interface with the printable device.
[0378] As shown in FIG. 14A, in certain embodiments, each post 1422
includes a base post 1412 and a micro-post 1410. The base post 1412
is wider than the micro-post 1410. In certain embodiments, the
desired aspect ratio for each base post 1412 and each micro-post
1410 is less than 4:1 (e.g., between 4:1 and 2:1). For example, a
base post 1412 can have a 20-micron width and 80-micron height and
the micro-post 1410 can have a 5-micron width and a 20-micron
height. Thus, the resulting multi-layer post has a 20-micron width
and 100-micron height that is capable of picking up 5-micron
devices. The base post 1412 can have, for example, a width of 5,
10, 15, 201, 25, 30, or 40 microns and a height of 10, 15, 20, 25,
30, 40, 50, 60, 70, 80, 90, 100, 110, 120, 130, 140, 150, or 160
microns. The micro-post 1410 can have, for example, a width of 1,
2, 3, 4, 5, 10, or 15 microns and a height of 2, 4, 6, 8, 10, 15,
20, 25, 30, 40, 50, or 60 microns.
[0379] FIG. 15 is an illustration of a transfer device 1500 with
multi-tiered posts 1522. In this example, the micro-post 1510 is
made of a viscoelastic material with a lower Young's modulus than
the post 1512 and bulk area 1502 which are both made from the same
viscoelastic material (i.e., having a higher Young's modulus than
the micro-post). Utilizing a lower Young's modulus in the
micro-posts 1510 allows printable device pick up to be tuned
accordingly. The micro post 1510 (or posts if this techniques is
applied to a transfer device without multi-tiered posts) can be
tuned to pick up printable devices while the bulk volume 1502 has a
higher Young's modulus, reducing the likelihood that the bulk area
1502 unintentionally picks up printable devices during a print
operation. In certain embodiments, the entire post 1522 is formed
of a viscoelastic material with a lower Young's modulus than the
bulk area 1502.
[0380] FIG. 16 is an illustration of a casting for a multi-tiered
transfer device (e.g., transfer device 1400 or 1500). In certain
embodiments, multi-layer posts 1602 (i.e., including micro-post
1610 and post 1612) are generated using a multiple tiered master
1604 with multiple layers 1614, 1606, 1608. These layers can have
different thicknesses and can be of different materials. The base
1614 is the layer on which the master is fabricated. In certain
embodiments, the base 1614 is a silicon wafer. The layers 1606 and
1608, in certain embodiments, are polymer layers (e.g.,
photo-imageable polymer materials) and can be formed using
spin-coating and photolithography techniques. The multi-tiered
master 1604 can be used to form transfer devices, such as those
shown in FIGS. 14A-14B and FIG. 15, with micro-posts for picking up
smaller printable objects while maintaining aspect ratios
comparable to a standard-sized base post.
[0381] In certain embodiments, the post 1602 includes a base post
1612 and a micro-post 1610. The base post 1612 is wider than the
micro-post 1610. The base post 1612 allows the micro-post 1610 to
have smaller cross-sectional area for contacting small printable
devices, while allowing the transfer device to maintain a given
post aspect ratio. In other embodiments, each base post 1612
includes an array of micro-posts 1610 thereon.
[0382] In certain embodiments, the transfer device is comprised of
a single sheet of glass and a bulk volume of polymer. The transfer
device is casted against a standard silicon wafer with either an
image-able material covering the silicon allowing for a pattern to
be generated. The silicon wafer is referred to as the master.
[0383] In certain embodiments, the glass transfer device and
silicon master are advantageously configured such that the CTE
variation between the two materials are minimized, or eliminated,
during, for example, the cure step which is performed at elevated
temperatures. The CTE matching allows the amount of pull back at
the edge of the transfer device 102 to be decreased, thereby
reducing the amount of crowning that can form at the edge of the
bulk region, as well as decrease the any kind of through-out issues
noted from post to post. In certain embodiments, a room temperature
cure is employed to minimize the pullback at the edge of the
transfer device. In certain embodiments, the transfer device 102 is
formed of a composite structure as explained below. A second
material, for example, can be employed below a thin layer of the
polymer layer (e.g., to reduce crowning).
[0384] An example of multi-tiered posts is shown in FIGS. 17A-17C.
FIGS. 17A-17C are SEM images of multi-layer posts 1702 configured
in an array. The posts 1702 may be made of PDMS or other
viscoelastic materials. In some embodiments, the posts 1702 and the
bulk volume 1702 are formed of the same material. In other
embodiments, the micro-posts 1710 can be formed of a material with
a lower Young's modulus than the base posts 1712 and the bulk
volume 1702. In other embodiments, the micro-posts 1710 and the
base posts 1712 can be formed of a material with a lower Young's
modulus than the bulk volume 1702. Embodiments including
multi-material multi-tiered posts can be accomplished, for example,
by selective deposition of the materials into the cast shown in
FIG. 16. For example, material can be screen printed into the
micro-post 1610 regions of the cast followed by injection molding
of the higher Young's modulus material on top (e.g., in the base
post 1612) and bulk volume area 1702.
[0385] In certain embodiments, multi-tiered posts are also used to
solve issues related to crowning on the bulk volume as described
below. The use of the multi-tier as explained above allows the
multi-tiered post to be taller (e.g., taller than the crown on the
bulk volume) while still maintaining the appropriate aspect
ratio(s) and enabling the transfer of small devices (e.g., due to
the small contact surface area of the micro-post).
Transfer Devices with Anti-Sag Features
[0386] Examples of the anti-sag features 1802 are illustrated in
FIGS. 18 and 19. In certain embodiments, to minimize or prevent
sagging of the transfer device 102 between the posts (e.g., posts
1202 as shown in FIG. 12), the transfer device 102 includes
anti-sag features 1802. The anti-sag features 1802 prevent the bulk
volume from sagging during the compression of the transfer device
102, thereby preventing the inadvertent pick-up of unintended or
unwanted material (e.g., semiconductor elements 104 not selected
for pick-up or debris located at the surface of the native
substrate 108) from the surface of the native substrate 108. The
anti-sag features 1802 thus operate to improve the selectivity of
the transfer device 102.
[0387] As shown in FIG. 18, the transfer device 102 includes one or
more anti-sag features 1802 that can contact anti-sag regions on
the surface of the source substrate 108 between printable regions
during a pick up operation. Posts 1806 will pick up printable
devices during a pick up operation. Regions 1808 of the stamp
contact no posts 1806 or anti-sag posts 1802. These regions 1808
correspond to locations on the source substrate where printable
devices are located (or where previously located if they have
already been picked up. The compressibility and/or size of the
anti-sag features 1802 are insufficient to pick-up the printable
objects (e.g., the printable semiconductor element 104) and prevent
the bulk volume of the transfer device 102 from sagging and
touching the printable substrate.
[0388] The anti-sag features 1802 are disposed in the anti-sag
regions between regions 1808 and regions with posts 1806. In
certain embodiments, the anti-sag features 1802 have a lower
aggregate cross-section area of contact than the array of pickup
post 1806 of the transfer device 102.
[0389] The anti-sag features 1802 may be of any size or shape. In
certain embodiments, the anti-sag features 1802 are of the same
height as the posts 1806. In certain embodiments, the anti-sag
features are taller than the posts 1806. The anti-sag features may
be shaped, for example, as a cylindrical post, triangular post,
rectangular post, pentagonal post, hexagonal post, heptagonal post,
and octagonal post.
[0390] FIG. 19 is a diagram of an example transfer device 102 that
includes anti-sag features 1802 to contact printable regions on the
source (e.g., the semiconductor elements 104 and the native
substrate 108). The anti-sag posts 1802 in FIG. 19 in the same
location as those shown in FIG. 18 as well as the regions 1808.
Thus, some of the anti-sag posts 1802 will contact locations on the
native substrate where printable objects are located or were
previously located. In certain embodiments, the anti-sag features
1802 are small enough that they have no pick-up capability. In
certain embodiments, the anti-sag features 1802 have a
compressibility insufficient to have pick-up capability.
Transfer devices with Roughened Areas between Posts
[0391] In certain embodiments, to minimize or prevent the
inadvertent pickup of printable material or undesired material from
the source, the transfer device 102 includes a roughened field in
the area located between the transfer device posts 114.
[0392] FIGS. 20A and 20B are diagrams that illustrate example
roughened areas 2002 incorporated on the transfer device 102. A
roughened field 2002 is added to the area of the transfer device
102 in between the transfer device posts 104. This roughened area
2002 will help to prevent pick of printable material if there is
sag between the process posts 104. The area 2002 can be comprised
of small features that may be placed in a specific pattern array or
a random pattern array. In certain embodiments, the roughened field
2002 includes features that are smaller than the transfer device
posts 104. For example, in certain embodiments, the roughened
features may include cylindrical structures, prisms structures,
concave structures, and frusto-conical structures. In certain
embodiments, the roughened fields 2002 are placed in a uniform or
regular patterned array. In other embodiments, the roughened fields
2002 are placed in a random patterned array.
Composite Transfer Devices
[0393] FIG. 21A illustrates a composite transfer device 2100 and
FIG. 21B illustrates a composite transfer device 2150. Composite
transfer devices (e.g., 2100 and 2150) can be constructed using
different visco-elastic materials in various portions of the
transfer device. For example, PDMS has a tunable Young's modulus
tuned by controlling the cure temperature or by changing the amount
of curing agent in the resin. The polymer formation could include
several different materials used together or it could include a
different ratio of polymer and hardener. Further, materials A &
B can have different crosslink densities.
[0394] In certain embodiments, the transfer device 2100 is made of
a composite material in which a second polymer formation is
employed in the posts 2104 to improve the adhesion between a given
transfer device 2100 and a printable element (e.g., printable
semiconductor element 104). Further, a different polymer formation
for the bulk transfer device allows for less adhesion in the event
sag occurs between posts, thereby allowing sag while not picking up
printable objects. For example, visco-eleastic polymers or
visco-elastic elastomers may be used in either the post 2104 or the
bulk volume 2102. The posts 2104, in certain embodiments, have a
lower Young's modulus compared to the bulk volume 2012.
[0395] In certain embodiments, the post 2104 includes a base 2106
that has a higher Young's modulus than the post 2104. The base 2106
may have the same Young's modulus as the bulk area 2102 as shown in
FIG. 21B.
[0396] Typically, a transfer device is composed of a single sheet
of glass and a bulk volume of polymer. The transfer device is cast
against a standard silicon wafer with an imageable material (e.g.,
patterned photoresist or other photo-imageable polymers such as SU8
or BCB) covering the silicon allowing for a master pattern to be
generated. Both the glass and the polymer can be optimized so that
the CTE variation between the two can be reduced or eliminated
during the cure step at elevated temperatures. This decreases the
amount of pull back at the edge of the transfer device which
reduces the amount of crowning noted at the edge of the bulk region
and decreases differences from post to post. A room temperature
cure can also minimize the pullback at the edge of the transfer
device.
Transfer Devices with Reduced Crown
[0397] FIG. 22 is an illustration of crowning 2202 at the edge 2204
of the bulk volume 2206 (e.g., PDMS layer) of a transfer device.
The bulk volume 2206 (e.g., PDMS layer in this example) may take on
various shapes and forms. In certain embodiments, the bulk volume
2206 is cylindrical, triangular, rectangular, pentagonal,
hexagonal, heptagonal, or octagonal in shape. The crowning 2202 may
be caused by a mismatch in the coefficients of thermal expansion
(CTE) between the bulk volume 2206 and the hard-plate interface
2208 (e.g., glass in this example).
[0398] FIG. 23 is an illustration of crowning 2202 occurring on the
bulk volume 2206 (e.g., visco-elastic material). FIG. 23 is a
cross-sectional view of half of the bulk volume 2206 of a transfer
device. For the purposes of this illustration, the posts are
omitted. In certain embodiments, as the bulk volume 2206 cools on
the hard-plate interface 2208 (e.g., glass substrate), the bulk
volume 2206 distorts. This is particularly prevalent towards the
edges (e.g., edge 2204) of the bulk volume 2206. The distortion can
cause a crown 2202 to form on the top of the elastomer 2206 as
shown in FIGS. 22 and 23. The crowning 2202 creates a problem
because it can itself unintentionally pick up devices during the
transfer process.
[0399] As shown in FIG. 24, the crowning 2202 can be taller than
the posts 2402. Additionally, the distortion occurs in the x and y
direction as well (i.e., lateral distortion). As such, it is
undesirable to have the posts positioned on the area of the bulk
volume 2206 where the lateral distortion will occur as the spacing
of the posts 2402 may change when the distortion occurs (i.e., the
spacing of the posts must be known and controlled to ensure that
printing occurs properly). A typical distance "d" that the post
array would be positioned away from the edge of the bulk volume
2206 to avoid lateral distortions is 5 to 20 millimeters.
Transfer Devices With a Composite Structure
[0400] FIG. 25 is an illustration of an example transfer device
2500 with a composite structure. Typically, the transfer device
2500 is comprised of a single sheet of glass 2208 (other materials
may be used for the hard-plate interface 2208 besides glass) and a
bulk volume of viscoelastic material (e.g., PDMS). In certain
embodiments, an additional material layer 2514 is added between the
glass plate 2208 and the visco-elastic material 2506 to allow for a
thin layer 2518 of visco-elastic material 2506 to be formed on top
of the additional layer 2514. The thin layer 2518, for example, may
enable the transfer device 2500 to be fabricated with less crowning
at the edges as there is less material at the edge to form the
crown.
[0401] The second material 2514, in certain embodiments, is
permanently bonded to the first material 2208. The second material
2514 may be transparent, thereby allowing for a clearer image to be
viewed through the transfer device 2500. The second material 2514
allows the use of a thinner bulk material, thereby allowing the
transfer device 2500 to employ less compression to fully laminate
the printable area.
[0402] In certain embodiments, a glass disc is used as the second
material 2514 between the hard-plate interface 2208 (e.g., glass)
and the transfer device bulk volume 2506. The second material 2514
can be any size or shape. In certain embodiments, the array of
micro-posts 2520 are disposed over the area of the second material
2514.
[0403] FIGS. 26 and 27 are illustrations of example transfer
devices formed of a composite structure with reduced crowning.
Reducing the volume (thickness) of the elastomer below the posts
leads to smaller distortion regions (crown and lateral). FIG. 26 is
a cross section view of half of a transfer device. As compared to
FIG. 23, the transfer device in FIG. 26 has less crowning due to
the use of the second material 2514 as explained above. As shown in
FIG. 27, the crown 2702 is smaller than the crown shown in FIG. 24
and is smaller than the posts 2720 of the transfer device 2700. In
this example, the distance "d" can be reduced to 1 to 5
millimeters. Additionally, the lateral distortion is less.
Transfer Device Mesa Around the Array of Posts
[0404] FIGS. 28A and 28B are illustrations of an example transfer
device mesa 2806 with an array of posts 2804 formed thereon. Due to
the smaller post sizes needed to pick up small printable objects,
the height of the transfer device post is decreased in order to
adhere to desired post aspect ratios. As explained above, if the
length of the post (e.g., 1202) is too large relative to its width,
the post will bend during compression (e.g., when picking up a
device). However, crowning on the edge of the transfer device may
cause devices to be picked up unintentionally if the length of the
post relative to its width is such that it does not bend
appropriately during compression (e.g., a desired post aspect
ratio). A mesa 2806 has been developed around the transfer device
array 2804 that allows for a smaller portion of the transfer device
to be exposed to the wafer surface. The mesa material can allow for
a large step between the array 2804 and the bulk layer 2808. In
certain embodiments, the thickness of the mesa 2806 is greater than
the height of crowning on the bulk material 2808. This eliminates
(or significantly reduces) the risk that the crowning on the bulk
material 2808 will unintentionally pick up devices during the
transfer process. Additionally, in certain embodiments, the
thickness of the mesa 2806 is less than the thickness of the bulk
material 2808. As such, the crowning on the mesa 2806 (if any) is
smaller than that of the crowning on the bulk material 2808.
[0405] The mesa 2806 can be any shape, as long as it encompasses
the entire transfer device array 2804. The transfer device mesa
2806 may be fabricated on a bulk volume of polymer 2808 which
itself is on a single sheet of glass 2802.
[0406] FIG. 29 is an illustration of an example transfer device
2900 with reduced crowning 2920. A mesa 2806 is positioned
around/below the posts 2804. The thickness of the mesa 2806 is less
than the thickness of the bulk volume 2808 (e.g., due to the
thickness of the mesa 2806 and the height of the posts 2804). As
such, the crowning 2920 on the mesa 2806 (if any) is smaller than
that of the crowning 2930 on the bulk material 2808. The thickness
of the mesa 2806 is such that the posts 2804 are prominent over
both the crowning 2920 on the mesa 2806 and the crowning 2930 on
the bulk volume 2808. Thus, the risk of accidentally picking up
devices by the crowning 2920 and 2930 is reduced or eliminated.
Transfer Devices with the Crown At Least Partially Removed
[0407] To reduce the crowning effect, the edges 1504 may be
partially removed to produce an angled edge. FIGS. 30A and 30B are
illustrations of a method of reducing the crowning 2202 on the bulk
material 2206 as shown from a side/cross-sectional view of the
transfer device. Angling cuts 3002 can be made to the edge 2204 of
the transfer device to reduce the amount of crowning (e.g., that is
formed when transfer devices are cast and as the PDMS pulls towards
the center of the transfer device material). The cuts 3002 may be
made using a razor 3004. These cuts 3002 may be made around the
edge 2204 of the transfer device at regular intervals to
significantly reduce the amount of crowning 2202 present. In
certain embodiments, this reduces or eliminates the chance that the
bulk material 2206 of the stamp will touch down at the edge of the
transfer device before the array is fully laminated.
Transfer Device Sidewall Shapes
[0408] In certain embodiments, the shape of the elastomer sidewall
may be used to control the distortions around the edge of the
stamp. Finite element modeling was performed to understand how the
shape of the elastomer sidewall affects the distortions around the
edge of the stamp. In the example described below, a 1 mm thick, 20
mm broad slab of PDMS on 3 mm of glass, in plane strain was used.
The CTE of the glass was 7 ppm/K and the CTE of PDMS was 300 ppm/K.
The delta T was 333 K (cure temp) to 295K (lab temp). The bevel
(i.e., sidewall) of the PDMS slab was varied. A transfer device
with each of the following bevels/sidewalls was tested: 15-degree
bevel, 30-degree bevel, 45-degree bevel, 60-degree bevel, 75-degree
bevel, round bevel, elongated round bezel, and the square bevel as
shown in FIGS. 31A through 31G.
[0409] FIG. 32 is a plot of the crowning height from the top
surface of the elastomer as a function of the lateral position
coordinate on the top surface of the elastomer sidewall as for each
of the sidewall profiles shown in FIGS. 31A through 31G. FIG. 33 is
a plot of the crown height produced during formation of transfer
devices with the sidewall profiles shown in FIGS. 31A through
31G.
[0410] This analysis illustrated sidewall shapes that result in
reduced crowning. As shown in FIGS. 32 and 33, the 15-degree bevel,
30-degree bevel, 45-degree bevel, 60-degree bevel, 75-degree bevel,
round bevel, and elongated round bezel all had less crown than the
square bevel.
[0411] In certain embodiments, features of different transfer
devices discussed above are combined into a single transfer device.
For example, a transfer device may include one or more anti-crown
features, one or more sag pickup reduction features, etc.
Furthermore, methods disclosed herein may be combined into a single
method. For example, a method may include plasma treating the
semiconductor elements and heat-assisted printing.
[0412] Having described various embodiments of the disclose
technology, it will now become apparent to one of skill in the art
that other embodiments incorporating the concepts may be used. It
is felt, therefore, that these embodiments should not be limited to
the disclosed embodiments, but rather should be limited only by the
spirit and scope of the following claims.
[0413] Throughout the description, where apparatus and systems are
described as having, including, or comprising specific components,
or where processes and methods are described as having, including,
or comprising specific steps, it is contemplated that,
additionally, there are apparatus, and systems of the disclosed
technology that consist essentially of, or consist 10 of, the
recited components, and that there are processes and methods
according to the disclosed technology that consist essentially of,
or consist of, the recited processing steps.
[0414] It should be understood that the order of steps or order for
performing certain action is immaterial so long as the disclosed
technology remains operable. Moreover, two or more steps or actions
may be conducted simultaneously.
* * * * *