U.S. patent application number 13/150813 was filed with the patent office on 2012-12-06 for low-temperature methods for spontaneous material spalling.
This patent application is currently assigned to KING ABDULAZIZ CITY FOR SCIENCE AND TECHNOLOGY. Invention is credited to Stephen W. Bedell, Maha M. Khayyat, Devendra K. Sadana, Katherine L. Saenger, Norma E. Sosa Cortes.
Application Number | 20120309269 13/150813 |
Document ID | / |
Family ID | 47259733 |
Filed Date | 2012-12-06 |
United States Patent
Application |
20120309269 |
Kind Code |
A1 |
Khayyat; Maha M. ; et
al. |
December 6, 2012 |
LOW-TEMPERATURE METHODS FOR SPONTANEOUS MATERIAL SPALLING
Abstract
Method to (i) introduce additional control into a material
spalling process, thus improving both the crack initiation and
propagation, and (ii) increase the range of selectable spalling
depths are provided. In one embodiment, the method includes
providing a stressor layer on a surface of a base substrate at a
first temperature which is room temperature. Next, the base
substrate including the stressor layer is brought to a second
temperature which is less than room temperature. The base substrate
is spalled at the second temperature to form a spalled material
layer. Thereafter, the spalled material layer is returned to room
temperature, i.e., the first temperature.
Inventors: |
Khayyat; Maha M.;
(Chappaqua, NY) ; Sosa Cortes; Norma E.; (New
York, NY) ; Saenger; Katherine L.; (Ossining, NY)
; Bedell; Stephen W.; (Wappingers Falls, NY) ;
Sadana; Devendra K.; (Pleasantville, NY) |
Assignee: |
KING ABDULAZIZ CITY FOR SCIENCE AND
TECHNOLOGY
Riyadh
NY
INTERNATIONAL BUSINESS MACHINES CORPORATION
Armonk
|
Family ID: |
47259733 |
Appl. No.: |
13/150813 |
Filed: |
June 1, 2011 |
Current U.S.
Class: |
451/41 ;
451/28 |
Current CPC
Class: |
H01L 21/187
20130101 |
Class at
Publication: |
451/41 ;
451/28 |
International
Class: |
B24B 1/00 20060101
B24B001/00 |
Claims
1. A method for removing a material layer from a surface of a base
substrate, said method comprising: providing a stressor layer on a
surface of a base substrate at a first temperature which is room
temperature; bringing the base substrate including the stressor
layer to a second temperature which is less than room temperature;
spalling the base substrate at the second temperature to form a
spalled material layer; and returning the spalled material layer to
room temperature.
2. The method of claim 1, wherein said base substrate has a
fracture toughness that is lower than that of the stressor
layer.
3. The method of claim 2, wherein said base substrate comprises a
semiconductor material, a glass, or a ceramic.
4. The method of claim 3, wherein said base substrate is a
semiconductor substrate, and said semiconductor substrate is single
crystalline.
5. The method of claim 1, further comprising forming a
metal-containing adhesive layer between said stressor layer and
said base substrate.
6. The method of claim 1, wherein said stressor layer is a metal, a
polymer, a spall inducing tape layer or any combination
thereof.
7. The method of claim 1, wherein said stressor layer is a metal,
and said metal comprises Ni, Cr, Fe or W.
8. The method of claim 1, wherein said stressor layer is a spall
inducing tape layer, and said spall inducing tape layer is a
pressure sensitive tape that is flexible and stress free at said
first temperature, yet ductile and tensile at the second
temperature.
9. The method of claim 8, wherein said pressure sensitive tape
comprises at least an adhesive layer and a base layer.
10. The method of claim 1, wherein the stressor layer comprises a
two-part stressor layer including a lower part and an upper part,
said upper part comprising a spall inducing tape layer.
11. The method of claim 1, further comprising forming a handle
substrate atop said stressor layer and at said first
temperature.
12. The method of claim 1, wherein said second temperature is 77 K
or less.
13. A method for removing a material layer from a surface of a base
substrate, said method comprising: providing a stressor layer on a
surface of a base substrate at a first temperature which is room
temperature; bringing the base substrate including the stressor
layer to a second temperature of less than 206 K; spalling the base
substrate at the second temperature to form a spalled material
layer; and returning the spalled material layer to room
temperature.
14. The method of claim 13, further comprising forming a
metal-containing adhesive layer between said stressor layer and
said base substrate.
15. The method of claim 13, wherein said stressor layer is a metal,
and said metal comprises Ni, Cr, Fe or W.
16. The method of claim 13, wherein said stressor layer is a spall
inducing tape layer, and said spall inducing tape layer is a
pressure sensitive tape that is flexible and stress free at said
first temperature, yet ductile and tensile at the second
temperature.
17. The method of claim 13, further comprising forming a handle
substrate atop said stressor layer and at said first
temperature.
18. The method of claim 13, wherein the stressor layer comprises a
two-part stressor layer including a lower part and an upper part,
said upper part comprising a spall inducing tape layer.
19. A method for removing a material layer from a surface of a base
substrate, said method comprising: providing a spall inducing tape
layer on a surface of a base substrate at a first temperature which
is from 15.degree. C. to 60.degree. C.; bringing the base substrate
including the spall inducing tape layer to a second temperature
which is less than room temperature; spalling the base substrate at
the second temperature to form a spalled material layer; and
returning the spalled material layer to room temperature.
20. The method of claim 19, wherein said spall inducing tape layer
is a pressure sensitive tape that is flexible and stress free at
said first temperature, yet ductile and tensile at the second
temperature.
21. The method of claim 20, wherein said pressure sensitive tape
comprises at least an adhesive layer and a base layer.
22. The method of claim 19, further comprising forming a handle
substrate atop said spall inducing tape layer and at said first
temperature.
23. The method of claim 19, wherein spall inducing tape layer
comprises an upper part of a two-part stressor layer.
24. The method of claim 19, wherein said second temperature is 77 K
or less.
25. The method of claim 19, wherein said second temperature is less
than 206 K.
Description
BACKGROUND
[0001] The present disclosure relates to semiconductor device
manufacturing, and more particularly, to methods for controlling
the removal of a surface layer from a base substrate utilizing
low-temperature spontaneous spalling.
[0002] Devices that can be produced in thin-film form have three
clear advantages over their bulk counterparts. First, by virtue of
less material used, thin-film devices ameliorate the materials cost
associated with device production. Second, low device weight is a
definite advantage that motivates industrial-level effort for a
wide range of thin-film applications. Third, if dimensions are
small enough, devices can exhibit mechanical flexibility in their
thin-film form. Furthermore, if a device layer is removed from a
substrate that can be reused, additional fabrication cost reduction
can be achieved.
[0003] Efforts to (i) create thin-film substrates from bulk
materials (i.e., semiconductors) and (ii) form thin-film device
layers by removing device layers from the underlying bulk
substrates on which they were formed are ongoing. The controlled
surface layer removal required for such applications has been
successfully demonstrated using a process known as spalling; see
U.S. Patent Application Publication No. 2010/0311250 to Bedell et
al. Spalling includes depositing a stressor layer on a substrate,
placing an optional handle substrate on the stressor layer, and
inducing a crack and its propagation below the substrate/stressor
interface. This process, which is performed at room temperature,
removes a thin layer of the base substrate below the stressor
layer. By thin, it is meant that the layer thickness is typically
less than 100 microns, with a layer thickness of less than 50
microns being more typical.
[0004] The depth of at which the crack propagates is dictated by
the thickness of the stressor layer, the inherent tensile stress of
the stressor layer, and the fracture toughness of the base
substrate being exfoliated (spalled). However, control of the
initiation of the release layer process (crack initiation and
propagation) and uniformity in the thickness of the spalled
material are difficult to achieve utilizing prior art spalling
processes.
SUMMARY
[0005] The present disclosure provides methods to (i) introduce
additional control into a material spalling process, thus improving
both the crack initiation and propagation, and (ii) increase the
range of selectable spalling depths. The methods of the present
disclosure are spontaneous spalling processes which are performed
below room temperature, not mechanical spalling processes which are
performed at room temperature as disclosed, for example, in U.S.
Patent Application Publication No. 2010/0311250 to Bedell et
al.
[0006] By "spontaneous," it is meant that the removal of a thin
material layer from a base substrate occurs without the need to
employ any manual means to initiate crack formation and propagation
for breaking apart the thin material layer from the base substrate.
By "room temperature," it is meant a temperature from 15.degree. C.
to 40.degree. C. By "low-temperature spalling," it is meant the
removal of a material layer from a base substrate at a temperature
below room temperature.
[0007] In one embodiment, the method of the present disclosure
includes providing a stressor layer on a surface of a base
substrate at a first temperature which is room temperature;
bringing the base substrate including the stressor layer to a
second temperature which is less than room temperature; spalling
the base substrate at the second temperature to form a spalled
material layer; and returning the spalled material layer to room
temperature.
[0008] In another embodiment, the method includes providing a
stressor layer on a surface of a base substrate at a first
temperature which is room temperature; bringing the base substrate
including the stressor layer to a second temperature of less than
206 Kelvin (K); spalling the base substrate at the second
temperature to form a spalled material layer; and returning the
spalled material layer to room temperature.
[0009] In yet another embodiment, the method includes providing a
spall inducing tape layer on a surface of a base substrate at a
first temperature which at approximately room temperature or
slightly above (e.g., from 15.degree. C. to 60.degree. C.);
bringing the base substrate including the spall inducing tape layer
to a second temperature which is less than room temperature;
spalling the base substrate at the second temperature to form a
spalled material layer; and returning the spalled material layer to
room temperature.
[0010] In yet a further embodiment, the method of the present
disclosure includes providing a two-part stressor layer on a
surface of a base substrate, wherein a lower part of the two-part
stressor layer is formed at a first temperature which at
approximately room temperature or slightly above (e.g., from
15.degree. C. to 60.degree. C.), wherein an upper part of the
two-part stressor layer comprises a spall inducing tape layer at an
auxiliary temperature which is room temperature; bringing the base
substrate including the two-part stressor layer to a second
temperature which is less than room temperature; spalling the base
substrate at the second temperature to form a spalled material
layer; and returning the spalled material layer to room
temperature.
[0011] By using one of the aforementioned methods, the effective
stress that induces material spalling is modified owing to
differential thermal expansion, crystal structure changes at the
crack front, fracture toughness value differences at
lower-than-room temperatures, to reach a stress regime necessary
for spalling-type fracture that would not be reached using the room
temperature spalling technique disclosed in U.S. Patent Application
Publication No. 2010/0311250.
[0012] One advantage of the aforementioned spalling methods of the
present disclosure is that the layer release process is spontaneous
at all stages of the process, from spall initiation through spall
completion. Another advantage of the present methods is that the
component of stressor layer stress due to thermal expansion
mismatch stress is reversible and will disappear upon warming back
to room temperature, thus providing a spalled stressor
layer/spalled film couple that is flatter at room temperature than
at the temperature at which it was spalled. Yet another advantage
of the present methods is that they widen the process window for
controlled, spontaneous spalling: base substrates including
stressor layers having thickness/stress values lower than the
threshold required for spalling at room temperature can be safely
stored at room temperature until spontaneous spalling is
deliberately introduced by a temperature reduction.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] FIG. 1 is a pictorial representation (through a cross
sectional view) illustrating a base substrate that can be employed
in one embodiment of the present disclosure.
[0014] FIG. 2 is a pictorial representation (through a cross
sectional view) illustrating the base substrate of FIG. 1 after
forming an optional metal-containing adhesion layer on a surface of
the base substrate.
[0015] FIG. 3 is a pictorial representation (through a cross
sectional view) illustrating the structure of FIG. 2 after forming
a stressor layer and/or spall inducing tape layer on a surface of
the optional adhesion layer.
[0016] FIG. 4 is a pictorial representation (through a cross
sectional view) illustrating the structure of FIG. 3 after forming
an optional handle substrate atop the stressor layer.
[0017] FIG. 5 is a pictorial representation (through a cross
sectional view) illustrating the structure of FIG. 4 after removing
an upper portion of the base substrate by utilizing a
low-temperature spontaneous spalling method of the present
disclosure.
DETAILED DESCRIPTION
[0018] The present disclosure, which relates to methods to (i)
introduce additional control into a material spalling process, thus
improving both the crack initiation and propagation, and (ii)
increase the range of selectable spalling depths, will now be
described in greater detail by referring to the following
discussion and drawings that accompany the present application. It
is noted that the drawings of the present application are provided
for illustrative purposes and, as such, they are not drawn to
scale.
[0019] In the following description, numerous specific details are
set forth, such as particular structures, components, materials,
dimensions, processing steps and techniques, in order to provide a
thorough understanding of the present invention. However, it will
be appreciated by one of ordinary skill in the art that the present
disclosure may be practiced with viable alternative process options
without these specific details. In other instances, well-known
structures or processing steps have not been described in detail in
order to avoid obscuring the various embodiments of the present
disclosure.
[0020] It will be understood that when an element as a layer,
region, or substrate is referred to as being "on" or "over" another
element, it can be directly on the other element or intervening
elements may also be present. In contrast, when an element is
referred to as being "directly on" or "directly over" another
element, there are no intervening elements present. It will also be
understood that when an element is referred to as being "beneath"
or "under" another element, it can be directly beneath or under the
other element, or intervening elements may be present. In contrast,
when an element is referred to as being "directly beneath" or
"directly under" another element, there are no intervening elements
present.
[0021] Reference is now made to FIGS. 1-5 which illustrate the
basic processing steps of the method of the present disclosure
which spalls, i.e., exfoliates, a material layer from a base
substrate in a controlled manner. The material layer that is
spalled is thin and may or may not include one of more devices
thereon. The term "thin" is used to denote that the material layer
that is spalled has a thickness that is typically less than 100
microns, with a thickness of less than 50 microns being more
typical.
[0022] Specifically, FIGS. 1-5 illustrate a low-temperature
spontaneous spalling method that includes providing a stressor
layer on a surface of a base substrate at a first temperature which
is at room temperature; bringing the base substrate including the
stressor layer to a second temperature which is less than room
temperature; spalling the base substrate at the second temperature
to form a spalled material layer; and returning the spalled
material layer to room temperature, e.g., the first
temperature.
[0023] Referring first to FIG. 1 there is illustrated a base
substrate 10 having an upper surface 12 that can be employed in the
present disclosure. The base substrate 10 employed in the present
disclosure may comprise a semiconductor material, a glass, a
ceramic, or any another material whose fracture toughness is less
than that of the stressor layer to be subsequently formed.
[0024] Fracture toughness is a property which describes the ability
of a material containing a crack to resist fracture. Fracture
toughness is denoted K.sub.Ic. The subscript Ic denotes mode I
crack opening under a normal tensile stress perpendicular to the
crack, and c signifies that it is a critical value. Mode I fracture
toughness is typically the most important value because spalling
mode fracture usually occurs at a location in the substrate where
mode II stress (shearing) is zero, and mode III stress (tearing) is
generally absent from the loading conditions. Fracture toughness is
a quantitative way of expressing a material's resistance to brittle
fracture when a crack is present.
[0025] When the base substrate 10 comprises a semiconductor
material, the semiconductor material may include, but is not
limited to, Si, Ge, SiGe, SiGeC, SiC, Ge alloys, GaSb, GaP, GaAs,
InAs, InP, and all other III-V or II-VI compound semiconductors. In
some embodiments, the base substrate 10 is a bulk semiconductor
material. In other embodiments, the base substrate 10 may comprise
a layered semiconductor material such as, for example, a
semiconductor-on-insulator or a semiconductor on a polymeric
substrate. Illustrated examples of semiconductor-on-insulator
substrates that can be employed as base substrate 10 include
silicon-on-insulators and silicon-germanium-on-insulators.
[0026] When the base substrate 10 comprises a semiconductor
material, the semiconductor material can be doped, undoped or
contain doped regions and undoped regions.
[0027] In one embodiment, the semiconductor material that can be
employed as the base substrate 10 can be single crystalline (i.e.,
a material in which the crystal lattice of the entire sample is
continuous and unbroken to the edges of the sample, with no grain
boundaries). In another embodiment, the semiconductor material that
can be employed as the base substrate 10 can be a polycrystalline
(i.e., a material that is composed of many crystallites of varying
size and orientation; the variation in direction can be random
(called random texture) or directed, possibly due to growth and
processing conditions). It is noted that when the semiconductor
material is a polycrystalline material the spalling process of the
present disclosure spalls certain grains, while leaving certain
grains unspalled. As such, spalling of polycrystalline
semiconductor material using the low-temperature spalling process
of the present disclosure may produce a non-continuous spalled
material layer. In yet another embodiment of the present
disclosure, the semiconductor material that can be employed as the
base substrate 10 can be amorphous (i.e., a non-crystalline
material that lacks the long-range order characteristic of a
crystal). Typically, the semiconductor material that can be
employed as the base substrate 10 is a single crystalline
material.
[0028] When the base substrate 10 comprises a glass, the glass can
be an SiO.sub.2-based glass which may be undoped or doped with an
appropriate dopant. Examples of doped SiO.sub.2-based glasses that
can be employed as the base substrate 10 include undoped silicate
glass, borosilicate glass, phosphosilicate glass, fluorosilicate
glass, and borophosphosilicate glass.
[0029] When the base substrate 10 comprises a ceramic, the ceramic
is any inorganic, non-metallic solid such as, for example, an oxide
including, but not limited to, alumina, beryllia, ceria and
zirconia, a non-oxide including, but not limited to, a carbide, a
boride, a nitride or a silicide; or composites that include
combinations of oxides and non-oxides.
[0030] In some embodiments of the present disclosure, one or more
devices including, but not limited to, transistors, capacitors,
diodes, BiCMOS, resistors, etc. can be processed on and/or within
the upper surface 12 of the base substrate 10 utilizing techniques
well known to those skilled in the art. The upper portion of the
base substrate that includes the one or more devices can be removed
utilizing the spalling methods of the present disclosure.
[0031] In some embodiments of the present disclosure, the upper
surface 12 of the base substrate 10 can be cleaned prior to further
processing to remove surface oxides and/or other contaminants
therefrom. In one embodiment of the present disclosure, the base
substrate 10 is cleaned by applying to the base substrate 10 a
solvent such as, for example, acetone and isopropanol, which is
capable of removing contaminates and/or surface oxides from the
upper surface 12 of the base substrate 10.
[0032] Referring now to FIG. 2, there is illustrated the base
substrate 10 of FIG. 1 after forming an optional metal-containing
adhesion layer 14 on upper surface 12. The optional
metal-containing adhesion layer 14 is employed in embodiments in
which the stressor layer to be subsequently formed has poor
adhesion to upper surface 12 of base substrate 10. Typically, the
metal-containing adhesion layer 14 is employed when a stressor
layer comprised of a metal is employed.
[0033] The optional metal-containing adhesion layer 14 employed in
the present disclosure includes any metal adhesion material such
as, but not limited to, Ti/W, Ti, Cr, Ni or any combination
thereof. The optional metal-containing adhesion layer 14 may
comprise a single layer or it may include a multilayered structure
comprising at least two layers of different metal adhesion
materials.
[0034] The metal-containing adhesion layer 14 that can be
optionally formed on the upper surface 12 of base substrate 12 is
formed at room temperature (15.degree. C.-40.degree. C.) or above.
In one embodiment, the optional metal-containing adhesion layer 14
is formed at a temperature which is from 20.degree. C. to
180.degree. C. In another embodiment, the optional metal-containing
adhesion layer 14 is formed at a temperature which is from
20.degree. C. to 60.degree. C.
[0035] The metal-containing adhesion layer 14, which may be
optionally employed, can be formed utilizing deposition techniques
that are well known to those skilled in the art. For example, the
optional metal-containing adhesion layer 14 can be formed by
sputtering, chemical vapor deposition, plasma enhanced chemical
vapor deposition, chemical solution deposition, physical vapor
deposition, and plating. When sputter deposition is employed, the
sputter deposition process may further include an in-situ sputter
clean process before the deposition.
[0036] When employed, the optional metal-containing adhesion layer
14 typically has a thickness of from 5 nm to 200 nm, with a
thickness of from 100 nm to 150 nm being more typical. Other
thicknesses for the optional metal-containing adhesion layer 14
that are below and/or above the aforementioned thickness ranges can
also be employed in the present disclosure.
[0037] Referring now to FIG. 3, there is illustrated the structure
of FIG. 2 after forming a stressor layer 16 on an upper surface of
the optional metal-containing adhesion layer 14. In some
embodiments in which the optional metal-containing adhesion layer
14 is not present, the stressor layer 16 is formed directly on the
upper surface 12 of base substrate 10; this particular embodiment
is not shown in the drawings, but can readily be deduced from the
drawings illustrated in the present application.
[0038] The stressor layer 16 employed in the present disclosure
includes any material that is under tensile stress on base
substrate 10 at the spalling temperature. Illustrative examples of
such materials that are under tensile stress when applied atop the
base substrate 10 include, but are not limited to, a metal, a
polymer, such as a spall inducing tape layer, or any combination
thereof. The stressor layer 16 may comprise a single stressor
layer, or a multilayered stressor structure including at least two
layers of different stressor material can be employed.
[0039] In one embodiment, the stressor layer 16 is a metal, and the
metal is formed on an upper surface of the optional
metal-containing adhesion layer 14. In another embodiment, the
stressor layer 16 is a spall inducing tape, and the spall inducing
tape is applied directly to the upper surface 12 of the base
substrate 10. In another embodiment, for example, the stressor
layer 16 may comprise a two-part stressor layer including a lower
part and an upper part. The upper part of the two-part stressor
layer can be comprised of a spall inducing tape layer.
[0040] When a metal is employed as the stressor layer 16, the metal
can include, for example, Ni, Cr, Fe or W. Alloys of these metals
can also be employed. In one embodiment, the stressor layer 16
includes at least one layer consisting of Ni.
[0041] When a polymer is employed as the stressor layer 16, the
polymer is a large macromolecule composed of repeating structural
units. These subunits are typically connected by covalent chemical
bonds. Illustrative examples of polymers that can be employed as
the stressor layer 16 include, but are not limited to, polyimides
polyesters, polyolefins, polyacrylates, polyurethane, polyvinyl
acetate, and polyvinyl chloride.
[0042] When a spall inducing tape layer is employed as the stressor
layer 16, the spall inducing tape layer includes any pressure
sensitive tape that is flexible, soft, and stress free at the first
temperature used to form the tape, yet strong, ductile and tensile
at the second temperature used during removal of the upper portion
of the base substrate. By "pressure sensitive tape," it is meant an
adhesive tape that will stick with application of pressure, without
the need for solvent, heat, or water for activation. Tensile stress
in the tape at the second temperature is primarily due to thermal
expansion mismatch between the base substrate 10 (with a lower
thermal coefficient of expansion) and the tape (with a higher
thermal expansion coefficient).
[0043] Typically, the pressure sensitive tape that is employed in
the present disclosure as stressor layer 16 includes at least an
adhesive layer and a base layer. Materials for the adhesive layer
and the base layer of the pressure sensitive tape include polymeric
materials such as, for example, acrylics, polyesters, olefins, and
vinyls, with or without suitable plasticizers. Plasticizers are
additives that can increase the plasticity of the polymeric
material to which they are added.
[0044] In one embodiment, the stressor layer 16 employed in the
present disclosure is formed at a first temperature which is at
room temperature (15.degree. C.-40.degree. C.). In another
embodiment, when a tape layer is employed, the tape layer can be
formed at a first temperature which is from 15.degree. C. to
60.degree. C.
[0045] When the stressor layer 16 is a metal or polymer, the
stressor layer 16 can be formed utilizing deposition techniques
that are well known to those skilled in the art including, for
example, dip coating, spin-coating, brush coating, sputtering,
chemical vapor deposition, plasma enhanced chemical vapor
deposition, chemical solution deposition, physical vapor
deposition, and plating.
[0046] When the stressor layer 16 is a spall inducing tape layer,
the tape layer can be applied by hand or by mechanical means to the
structure. The spall inducing tape can be formed utilizing
techniques well known in the art or they can be commercially
purchased from any well known adhesive tape manufacturer. Some
examples of spall inducing tapes that can be used in the present
disclosure as stressor layer 16 include, for example, Nitto Denko
3193MS thermal release tape, Kapton KPT-1, and Diversified
Biotech's CLEAR-170 (acrylic adhesive, vinyl base).
[0047] In one embodiment, a two-part stressor layer can be formed
on a surface of a base substrate, wherein a lower part of the
two-part stressor layer is formed at a first temperature which is
at room temperature or slight above (e.g., from 15.degree. C. to
60.degree. C.), wherein an upper part of the two-part stressor
layer comprises a spall inducing tape layer at an auxiliary
temperature which is at room temperature. Next, the base substrate
including the two-part stressor layer is brought to a second
temperature which is less than room temperature. The base substrate
10 is then spalled at the second temperature to form a spalled
material layer. The spalled material layer is then returned to room
temperature.
[0048] If the stressor layer 16 is of a metallic nature, it
typically has a thickness of from 3 .mu.m to 50 .mu.m, with a
thickness of from 4 .mu.m to 7 .mu.m being more typical. Other
thicknesses for the stressor layer 16 that are below and/or above
the aforementioned thickness ranges can also be employed in the
present disclosure.
[0049] If the stressor layer 16 is of a polymeric nature, it
typically has a thickness of from 10 .mu.m to 200 .mu.m, with a
thickness of from 50 .mu.m to 100 .mu.m being more typical. Other
thicknesses for the stressor layer 16 that are below and/or above
the aforementioned thickness ranges can also be employed in the
present disclosure.
[0050] Referring to FIG. 4, there is illustrated the structure of
FIG. 3 after forming an optional handle substrate 18 atop the
stressor layer 16. The optional handle substrate 18 employed in the
present disclosure comprises any flexible material which has a
minimum radius of curvature of less than 30 cm. Illustrative
examples of flexible materials that can be employed as the optional
handle substrate 18 include a metal foil or a polyimide foil.
[0051] The optional handle substrate 18 can be used to provide
better fracture control and more versatility in handling the
spalled portion of the base substrate 10. Moreover, the optional
handle substrate 18 can be used to guide the crack propagation
during the spontaneous spalling process of the present
disclosure.
[0052] The optional handle substrate 18 of the present disclosure
is typically, but not necessarily, formed at a first temperature
which is at room temperature (15.degree. C.-40.degree. C.).
[0053] The optional handle substrate 18 can be formed utilizing
deposition techniques that are well known to those skilled in the
art including, for example, dip coating, spin-coating, brush
coating, sputtering, chemical vapor deposition, plasma enhanced
chemical vapor deposition, chemical solution deposition, physical
vapor deposition, and plating.
[0054] The optional handle substrate 18 typical has a thickness of
from 1 .mu.m to few mm, with a thickness of from 70 .mu.m to 120
.mu.m being more typical. Other thicknesses for the optional handle
substrate 18 that are below and/or above the aforementioned
thickness ranges can also be employed in the present
disclosure.
[0055] Referring to FIG. 5, there is illustrated the structure of
FIG. 4 after removing an upper portion 10'' of the base substrate
10 by spontaneous spalling. In FIG. 5, reference numeral 10'
denotes the remaining base substrate 10 that is not spalled, while
reference numeral 10'' denotes the spalled portion of the base
substrate which can include one or more device thereon.
[0056] The spontaneous spalling process includes crack formation
and propagation which are initiated at a second temperature that is
less than room temperature. In one embodiment, the spontaneous
spalling occurs at a second temperature of 77 K or less. In another
embodiment, the spontaneous spalling occurs at a second temperature
of less than 206 K. In yet further embodiment, the second
temperature, e.g., the spontaneous spalling temperature, is from
175 K to 130 K.
[0057] Within the second temperature range mentioned above, a crack
begins to initiate and propagate spontaneously beneath the upper
surface 12 of the base substrate 10.
[0058] The second temperature used in the present disclosure for
spalling can be achieved by cooling the structure shown in FIG. 4
down below room temperature utilizing any cooling means. For
example, cooling can be achieved by placing the structure in a
liquid nitrogen bath, a liquid helium bath, an ice bath, a dry ice
bath, a supercritical fluid bath, or any cryogenic environment
liquid or gas.
[0059] The spalled material layer 10'' that is removed from the
base substrate 10 by the spontaneous spalling process mentioned
above typically has a thickness of from 1000 nm to tens of .mu.m,
with a thickness of from 5 .mu.m to 50 .mu.m being more typical.
The thickness of the spalled material layer 10'' correlates to the
depth of crack initiation and propagation.
[0060] After the spalling process, the spalled material layer 10''
is returned to the first temperature (i.e., room temperature). This
can be performed by allowing the spalled material layer 10'' to
slowly cool up to the first temperature by allowing the same to
stand at room temperature. Alternatively, the spalled material
layer 10'' can be heated up to room temperature utilizing any
heating means.
[0061] In some embodiments of the present disclosure, the optional
handle substrate 18, the stressor layer 16 and the optional
metal-containing adhesion layer 14 can be removed from the spalled
material layer 10''. When the optional handle substrate 18,
stressor layer 16 and the optional metal-containing adhesion layer
14 are removed from the spalled material layer 10'', the removal of
those layers can be achieved utilizing conventional techniques well
known to those skilled in the art. For example, and in one
embodiment, aqua regia (HNO.sub.3/HCl) can be used for removing the
optional handle substrate 18, the stressor layer 16 and the
optional metal-containing adhesion layer 14 from the spalled
material layer 10''.
[0062] The present disclosure can be used in fabricating various
types of thin-film devices including, but not limited to,
semiconductor devices, and photovoltaic devices.
[0063] While the present disclosure has been particularly shown and
described with respect to preferred embodiments thereof, it will be
understood by those skilled in the art that the foregoing and other
changes in forms and details may be made without departing from the
spirit and scope of the present disclosure. It is therefore
intended that the present disclosure not be limited to the exact
forms and details described and illustrated, but fall within the
scope of the appended claims.
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