U.S. patent application number 13/367600 was filed with the patent office on 2013-08-08 for methods for making thin layers of crystalline materials.
This patent application is currently assigned to Wisconsin Alumni Research Foundation. The applicant listed for this patent is Max G. Lagally, Deborah M. Paskiewicz, Boy Tanto. Invention is credited to Max G. Lagally, Deborah M. Paskiewicz, Boy Tanto.
Application Number | 20130203236 13/367600 |
Document ID | / |
Family ID | 48792317 |
Filed Date | 2013-08-08 |
United States Patent
Application |
20130203236 |
Kind Code |
A1 |
Lagally; Max G. ; et
al. |
August 8, 2013 |
METHODS FOR MAKING THIN LAYERS OF CRYSTALLINE MATERIALS
Abstract
Methods for making growth templates for the epitaxial growth of
compound semiconductors and other materials are provided. The
growth templates are thin layers of single-crystalline materials
that are themselves grown epitaxially on a substrate that includes
a thin layer of sacrificial material. The thin layer of sacrificial
material, which creates a coherent strain in the single-crystalline
material as it is grown thereon, includes one or more suspended
sections and one or more supported sections.
Inventors: |
Lagally; Max G.; (Madison,
WI) ; Paskiewicz; Deborah M.; (Oregon, WI) ;
Tanto; Boy; (Hillsboro, OR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Lagally; Max G.
Paskiewicz; Deborah M.
Tanto; Boy |
Madison
Oregon
Hillsboro |
WI
WI
OR |
US
US
US |
|
|
Assignee: |
Wisconsin Alumni Research
Foundation
|
Family ID: |
48792317 |
Appl. No.: |
13/367600 |
Filed: |
February 7, 2012 |
Current U.S.
Class: |
438/458 ;
257/E21.568 |
Current CPC
Class: |
H01L 21/02532 20130101;
H01L 21/02664 20130101; C30B 33/08 20130101; H01L 21/02658
20130101; H01L 21/02521 20130101; H01L 21/0245 20130101; C30B 29/52
20130101; H01L 21/02439 20130101; C30B 29/16 20130101 |
Class at
Publication: |
438/458 ;
257/E21.568 |
International
Class: |
H01L 21/762 20060101
H01L021/762 |
Goverment Interests
REFERENCE TO GOVERNMENT RIGHTS
[0001] This invention was made with government support under
DE-FG02-03ER46028 awarded by Department of Energy. The government
has certain rights in the invention.
Claims
1. A method for fabricating a layer of strain-relaxed,
single-crystalline material, the method comprising: growing a layer
of coherently strained single-crystalline material over a layer of
sacrificial material, the layer of sacrificial material comprising
one or more suspended sections and one or more supported sections,
wherein the strain in the portions of single-crystalline material
grown over the one or more suspended sections is lower than the
strain in the portions of single-crystalline material grown over
the one or more supported sections; selectively removing the one or
more suspended sections of the layer of sacrificial material, such
that the portions of the single-crystalline material previously
disposed over the one or more suspended sections are elastically
relaxed; and detaching the one or more elastically relaxed portions
of the layer of single-crystalline material from the remainder of
the layer of single-crystalline material.
2. The method of claim 1, wherein the one or more suspended
sections in the layer of sacrificial material are formed over
apertures in a base substrate underlying the layer of sacrificial
material.
3. The method of claim 1, wherein the coherently strained
single-crystalline material is grown to a thickness greater than
the critical thickness for plastic relaxation for the
single-crystalline material grown on a substrate of bulk
sacrificial material.
4. The method of claim 3, wherein the detached portions of the
layer of single-crystalline material are free of misfit
dislocations.
5. The method of claim 1, wherein the layer of sacrificial material
has a plurality of suspended sections and the layer of
single-crystalline material is grown as a continuous layer over the
plurality of suspended sections.
6. The method of claim 5, wherein the plurality of suspended
sections of the layer of sacrificial material is formed over
apertures in a base substrate underlying the layer of sacrificial
material.
7. The method of claim 1, further comprising bonding the one or
more detached portions of the single-crystalline material to a
bonding substrate.
8. The method of claim 1, wherein detaching the one or more
elastically relaxed portions of the layer of single-crystalline
material from the remainder of the layer of single-crystalline
material comprises: contacting a surface of the one or more
elastically relaxed portions of the single-crystalline material
with a bonding substrate; applying a pressure to an opposite
surface of the one or more elastically relaxed portions of the
layer of single-crystalline material to maintain the contact
between the one or more elastically relaxed portions of the layer
of single-crystalline material and the bonding substrate; and
pulling the remainder of the layer of single-crystalline material
away from the bonding substrate, such that the elastically relaxed
portions of the layer of single-crystalline material detach from
the remainder of the layer of single-crystalline material.
9. The method of claim 8, wherein the surface of the bonding
substrate is coated with a liquid, the method further comprising
evaporating the liquid coating from the surface of the bonding
substrate.
10. The method of claim 1, further comprising growing an additional
layer of single-crystalline material on the one or more elastically
relaxed, detached portions.
11. The method of claim 10, wherein the additional layer of
single-crystalline material has the same material composition as
the material of the detached portions.
12. The method of claim 10, wherein the additional layer of
single-crystalline material has a different material composition
than the material of the detached portions.
13. The method of claim 1, wherein the single-crystalline material
is a single-crystalline semiconductor alloy.
14. The method of claim 13, wherein the semiconductor alloy is
Si.sub.1-xGe.sub.x and x is at least 0.2.
15. The method of claim 1, wherein the single-crystalline material
is a transition metal oxide.
16. The method of claim 2, wherein the layer of coherently strained
single-crystalline material is grown on a silicon-on-insulator
substrate comprising a layer of single-crystalline Si disposed over
a buried oxide layer supported on a handle wafer, and further
wherein the layer of single-crystalline Si is the sacrificial layer
and the buried oxide layer and the handle wafer together form the
base substrate.
17. The method of claim 1, wherein the layer of coherently
strained, single-crystalline material has a thickness in the range
from 10 nm to 3 .mu.m and the layer of sacrificial material has a
thickness in the range from 10 nm to 3 .mu.m.
18. The method of claim 2, wherein the layer of coherently
strained, single-crystalline material has a thickness in the range
from 10 nm to 3 .mu.m, the layer of sacrificial material has a
thickness in the range from 10 nm to 3 .mu.m and the base substrate
has a thickness of at least 100 .mu.m.
Description
BACKGROUND
[0002] Many electronic and optoelectronic devices are composed of
compound semiconductor heterostructures or
ferroelectric/multiferroic structures epitaxially grown on
single-crystalline growth substrates. Compound semiconductors
represent a large class of materials with composition ranges that
can, in principle, be varied to provide a broad range of lattice
parameters. Provided an appropriate growth substrate is available,
such materials can be grown epitaxially using standard film growth
techniques. Unfortunately, the number of available
single-crystalline growth substrates for such materials is very
limited, which has hindered the development of devices based on
compound semiconductors having tailored lattice parameters.
SUMMARY
[0003] Methods for fabricating a layer of strain-relaxed,
single-crystalline material are provided. The methods comprise
growing a layer of coherently strained single-crystalline material
over a layer of sacrificial material. The layer of sacrificial
material has one or more suspended sections and one or more
supported sections, wherein the strain in the portions of
single-crystalline material grown over the one or more suspended
sections is lower than the strain in the portions of
single-crystalline material grown over the one or more supported
sections. The one or more suspended sections in the layer of
sacrificial material can be formed over apertures in a base
substrate underlying the layer of sacrificial material. The methods
further comprise selectively removing the one or more suspended
sections of the layer of sacrificial material, such that the
portions of the single-crystalline material previously disposed
over the one or more suspended sections are elastically relaxed.
Once the elastically relaxed portions are formed, they can be
detached from the remainder of the layer of single-crystalline
material.
[0004] The resulting detached portions of material can be used as
epitaxial growth templates for other materials. Therefore, in some
embodiments, the methods comprise growing an additional layer of
single-crystalline material on the one or more growth templates
provided by the detached portions of the first single-crystalline
material. The additional layer of single-crystalline material can
have the same material composition (and therefore the same lattice
constant) as the single-crystalline material of growth template or
a different material composition (and different lattice constant)
than the single-crystalline material of the growth template.
[0005] The methods are well-suited for the fabrication of growth
templates made of compound semiconductor alloys or
ferroelectric/multiferroic materials.
[0006] Other principal features and advantages of the invention
will become apparent to those skilled in the art upon review of the
following drawings, the detailed description, and the appended
claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] Illustrative embodiments of the invention will hereafter be
described with reference to the accompanying drawings, wherein like
numerals denote like elements.
[0008] FIG. 1 is a schematic diagram showing one embodiment of a
method for fabricating a substrate upon which a growth template
layer can be grown.
[0009] FIG. 2 is a schematic diagram showing another embodiment of
a method for fabricating a substrate upon which a growth template
layer can be grown.
[0010] FIG. 3 illustrates a method of forming a growth template
layer on the multilayered substrate of FIG. 1.
[0011] FIG. 4 illustrates a method for detaching the elastically
relaxed portions of a single-crystalline growth template layer from
the remainder of the layer of single-crystalline material.
[0012] FIG. 5 is a schematic diagram of a multilayered, wafer-scale
substrate that can be used to fabricate an array of growth
templates.
DETAILED DESCRIPTION
[0013] Methods for making growth templates for the epitaxial growth
of compound semiconductors, other alloys, and compounds are
provided. The growth templates are thin layers of
single-crystalline material that are themselves grown epitaxially
on a substrate that includes a thin layer of single-crystalline
sacrificial material. The thin layer of single-crystalline
crystalline sacrificial material, which creates a coherent strain
in the single-crystalline material grown thereon, includes one or
more suspended sections and one or more supported sections. After
the strained layer of single-crystalline material (i.e., the
strained growth template layer) has been grown over the layer of
sacrificial material, the one or more suspended sections of the
sacrificial material are selectively removed, whereby the portions
of the layer previously disposed over the suspended sections of the
sacrificial material undergo elastic relaxation. The resulting
elastically relaxed portions of the single-crystalline material
layer are then detached from the remaining portions of the layer to
provide one or more growth templates.
[0014] The substrates upon which the single-crystalline growth
template layers are grown can be multilayered substrates that
include a base substrate material underlying the supported sections
of the layer of sacrificial material. This base substrate material
behaves as a bulk material and restricts the ability of the
sacrificial material in the supported sections to share strain with
the single-crystalline material that is epitaxially grown thereon.
In contrast, in the absence of the underlying base substrate
material, the thin, suspended sections of the layer of sacrificial
material are better able to share strain with the overlying layer
of single-crystalline material. As a result, those portions of the
growth template layer that are grown over the suspended sections of
the layer of sacrificial material have a lower strain than the
portions of the growth template layer that are grown over the
supported sections of sacrificial material. The strain sharing
between the suspended sections of the sacrificial material and the
single-crystalline material grown thereon is advantageous because
it increases the thickness at which misfit dislocations begin to
form in the single-crystalline material. This makes it possible to
fabricate thicker growth templates relative to a fabrication scheme
in which the single-crystalline material layer is grown over a
thicker (e.g., bulk), rigid substrate with which it undergoes
little or no strain sharing.
[0015] For the purposes of this disclosure, a multilayered
substrate, as described above, can be a substrate wherein the
sacrificial material of the sacrificial layer is different from the
base substrate material (or base substrate materials). A
semiconductor-on-insulator substrate provides one such multilayered
substrate, as discussed in greater detail, below. However, a
multilayered substrate can also refer to a substrate made of a
single material, wherein the topmost layer of the material is
defined by a thin, continuous layer of the material and a lower
layer of the material is defined by a thicker layer of the same
material having one or more holes etched therein (i.e., a
non-continuous layer).
[0016] FIG. 1 is a schematic diagram showing one embodiment of a
method for fabricating a substrate upon which a single-crystalline
growth template layer can be grown. Panel (a) of FIG. 1 shows a
cross-sectional view of a multilayered substrate that can be used
as a starting material. In this case, the multilayered substrate is
a semiconductor-on-insulator substrate, such as
silicon-on-insulator (SOI), that includes an upper layer of
single-crystalline semiconductor (e.g., Si) 102, which serves as a
sacrificial layer during the fabrication of the growth template
layer. A thin buried oxide layer (e.g., SiO.sub.2) 104 is disposed
below the upper layer and a handle layer (e.g., Si) 106 is disposed
below the buried oxide layer. By way of illustration only, typical
thickness ranges for sacrificial layer 102 and oxide layer 104 are
from about 10 nm to about 3 .mu.m and from about 150 nm to about 3
.mu.m, respectively. Panels (b) and (c) in FIG. 1 show the
fabrication of unsupported sections in sacrificial layer 102. In
this step one or more holes 108 are patterned and selectively
etched through handle layer 106. For a silicon handle layer,
suitable etchants include potassium hydroxide (KOH) and
tetramethylammonium hydroxide (TMAH). During this etching step, the
sacrificial layer can be protected by a coating of etchant
resistant material 110, such as SiO.sub.2 or SiN.sub.x, deposited
on the outer surface of the substrate structure. As shown in panel
(c), once a hole has been made in handle layer 106, a second
etching step can be used to etch through buried oxide layer 104.
This leaves a portion 112 of sacrificial layer 102 over the
resulting hole 114 suspended, while the remainder of sacrificial
layer 102 remains attached to and supported by buried oxide layer
104. Panels (d) and (e) show top and bottom views, respectively, of
the resulting structure. In the top view, the location of the hole
underlying the sacrificial layer is shown in dashed lines.
[0017] FIG. 2 is a schematic diagram showing another embodiment of
a method for fabricating a substrate upon which a
single-crystalline growth template layer can be grown. In this
embodiment, the base substrate is a single-layer of material 206,
such as silicon, as shown in panel (a). As in the previous
embodiment, a hole 208 can be etched through base substrate 206,
using an appropriate etchant and etchant-resistant coating 210.
Panel (b) shows a cross-sectional side view of the structure with
the etchant-resistant coating. Panel (c) shows a top view of the
structure after coating 210 has been removed. After one or more
holes have been formed through the base substrate 206, a thin layer
of sacrificial material 202 can be transferred to the upper surface
of the base substrate such that it covers the one or more holes.
(Methods for forming, releasing and transferring thin semiconductor
layers from one substrate to another are described, for example, in
U.S. Pat. No. 7,354,809.) Panels (d)-(f) show side, top and bottom
views, respectively, of the resulting two-layered substrate
structure, including suspended section 212. Again, in the top view,
the location of the hole underlying the sacrificial layer is shown
in dashed lines.
[0018] Once the multilayered substrate has been formed, it can be
used to grow a layer of the single-crystalline material (the growth
template layer). FIG. 3 illustrates a method of forming a
single-crystalline material layer on the multilayered substrate of
FIG. 1. In this figure, a regular grid pattern is used to represent
a single-crystalline, defect-free material. Prior to the growth of
the single-crystalline material, the suspended section 112 of
sacrificial layer 102 can be strain-free. However, as the material
320 is grown epitaxially on sacrificial layer 102, a strain is
created in the sacrificial material. For example, when
Si.sub.1-xGe.sub.x alloy is grown on Si, the larger lattice
constant of the SiGe alloy creates a tensile strain in the Si and a
compressive strain in the SiGe. However, because the suspended
sections of the Si sacrificial layer are thin and unsupported,
those sections are able to share elastic strain with the SiGe layer
to a much greater extent than the supported sections of the
sacrificial layer. As a result, the SiGe grown on the suspended
section (or sections) of the sacrificial layer has less compressive
strain than the SiGe grown on the supported section (or sections).
The relative directions and magnitudes of the tensile and
compressive strains experienced within the single-crystalline
growth template layer and the sacrificial layer are represented by
arrows in panel (b) of FIG. 3.
[0019] Initially, the single-crystalline growth template layer may
be grown to a thickness below the critical thickness for plastic
relaxation for the same material, grown using the same growth
conditions, on a rigid bulk substrate having the same material
composition as the sacrificial layer. However, it is advantageous
to grow the layer of single-crystalline material to a
dislocation-free thickness greater than which could be achieved on
a rigid, bulk substrate, because thicker growth templates are less
delicate and easier to handle. The present methods make thicker,
defect-free growth possible in those portions of the
single-crystalline material layer grown over the suspended sections
of the sacrificial layer. As shown in panel (c) of FIG. 3, as the
thickness of the growth template layer exceeds the critical
thickness, it undergoes plastic relaxation causing misfit
dislocations 322 (shown as slanted lines in the grid) to form in
material 320 disposed above the supported sections of sacrificial
layer 102. However, the suspended sections of the sacrificial layer
will continue to share strain elastically with the overlying
single-crystalline material. This strain sharing can cause the
suspended parts of the bilayer (e.g., Si/SiGe) to expand and bow,
as shown in panel (c), but, because the bilayer is pinned by the
surrounding supported sections of the sacrificial layer, it cannot
curl. The strain sharing allows for thicker, misfit
dislocation-free growth. One advantage of this aspect of the
present methods is that it allows for the growth of defect-free
layers of even highly strained alloys (e.g., Si.sub.1-xGe.sub.x
having a high Ge content) at thicknesses that could not be achieved
via growth directly on a bulk or fully supported substrate.
[0020] In some embodiments, the composition of the
single-crystalline material and the growth parameters, including
growth temperature and deposition rate, can be controlled such that
a dislocation-free layer of the single-crystalline material is
grown to a thickness greater than its equilibrium critical
thickness through the formation of metastable layers of the
material. The thickness at which dislocations begin to form in this
metastable structure is referred to as the kinetic critical
thickness of the material.
[0021] Once the single-crystalline growth template layer 320 has
been grown to the desired thickness, the suspended section of
sacrificial layer 102 can be etched away leaving a suspended
portion 324 in growth template layer 320 disposed above a hole 326,
as shown in panel (d) of FIG. 3. In the case of a Si sacrificial
layer and a SiGe growth template layer, the etchants KOH and TMAH
will etch the Si much faster than the SiGe. Therefore, no
protective layer is needed because the etchant will take a long
time to undercut the Si supporting the supported portions of the
SiGe alloy layer. Once the suspended section of the sacrificial
layer is removed, the material that was previously located above
that section can elastically relax, adopting the lattice constant
of the bulk single-crystalline material. This relaxation may be
accompanied by expansion of the suspended portion of the
single-crystalline material, which can make that portion wrinkle or
bow further.
[0022] FIG. 4 illustrates a method for detaching the elastically
relaxed portions of the single-crystalline growth template layer
from the remainder of the single-crystalline material layer. In
this method, the structure, including the multilayered substrate
and the growth template layer are flipped such that the underside
of the suspended portion of the growth template layer is exposed
through the etched hole in the substrate and the opposite side is
placed in contact with a new host substrate 430 or "bonding
substrate", as shown in panel (a). Host substrate 430 may be coated
with a liquid film, such as a water or organic solvent film, 432 in
order to increase the adhesion between the growth template material
and the bonding substrate. Detachment can be achieved by inserting
a shaft 434 through the hole such that it applies pressure to the
elastically relaxed portion of the growth template layer and forces
the elastically relaxed portion of that layer into contact with the
underlying bonding substrate. While this pressure is maintained,
the layer of growth template material is pulled away from the
bonding substrate causing the elastically relaxed portion 324 of
that layer to detach from the remainder (i.e., the supported
portion) of the layer, as shown in panel (b) of FIG. 4. Heating the
bonding substrate causes the liquid coating to evaporate and
strengthens the bond between the detached portion of the
single-crystalline material and the bonding substrate, as shown in
panel (c). This can be accomplished by slowly increasing the heat
from room temperature to the desired annealing temperature in an
oven or on a hot plate.
[0023] Once the detached portion of the single-crystalline growth
template layer is bonded to the new bonding substrate, it is ready
for use as a growth template for the epitaxial growth of a lattice
matched or a lattice mismatched (strained) material. For example,
the growth template can be used to epitaxially grow more of the
same material or can be used to grow a different material. If a
different material is grown, that material may have the same
lattice constant or, more likely, a different lattice constant than
the material of the growth template. In the latter case, the
newly-grown material may be grown with a tensile or a compressive
strain, depending on the relative lattice mismatch. Epitaxial
growth techniques that can be employed include chemical vapor
deposition, molecular beam epitaxy, and liquid phase epitaxy.
[0024] FIGS. 1-4 illustrate the fabrication of a single, detached,
elastically relaxed growth template comprising a single-crystalline
material. However, the methods can also be used to fabricate arrays
of growth templates simply by using a multilayered base substrate
having a plurality of suspended sections in the sacrificial layer.
By growing a continuous layer of single-crystalline material over
the plurality of suspended sections, removing the plurality of
suspended sections from the layer of sacrificial material, and
detaching the resulting plurality of elastically relaxed portions
of single-crystalline material from the layer of single-crystalline
material, arrays of growth templates can be made. FIG. 5 is a
schematic diagram of a multilayered substrate that can be used to
fabricate an array of growth templates. Panel (a) is a
cross-sectional view of the substrate showing a sacrificial layer
502 that includes a plurality of suspended sections 512.
Sacrificial layer 502 is disposed over a base substrate layer 506
through which a plurality of holes 508 has been etched. The holes
in the base substrate material can be formed in a variety of shapes
and sizes. Panels (b) and (c) in FIG. 5 show the bottom views of an
array of hexagonal holes and an array of square holes,
respectively. The elastically relaxed growth templates made from
these substrates would be laid out in the same array pattern and
have similar sizes and shapes as the holes. Arrays such as these
can be made over large areas, including wafer-scale areas. Thus,
the arrays can cover areas of at least 20 mm.sup.2, at least 50
mm.sup.2, at least 100 mm.sup.2, at least 200 mm.sup.2, at least
300 mm.sup.2, or greater.
[0025] The present methods can be used to fabricate epitaxial
growth templates from a variety of materials, including alloys
comprising semiconductor elements, alloys comprising metal oxides,
ceramic alloys, and compounds, such as metal oxides. Semiconductor
alloys that can be used as epitaxial growth templates include
binary, ternary, and quaternary semiconductor alloys. Examples of
these include Group IV-IV, Group III-V, and Group II-VI
semiconductor alloys. Specific examples of these include
Si.sub.1-xGe.sub.x (0<x<1), In.sub.xGa.sub.1-xP,
In.sub.xGa.sub.1-xAs, and In.sub.xAl.sub.1-xAs (0<x<1). The
composition of the semiconductor alloy to be used as an
epitaxial-growth template can be tailored to provide a desired
lattice constant. Because the present methods allow for misfit
dislocation-free growth to thicknesses greater than the critical
thickness for plastic relaxation on bulk or rigid substrates,
growth templates comprising highly strained alloys can be
fabricated. For example growth templates of Si.sub.1-xGe.sub.x can
be fabricated with x values of at least 0.4, at least 0.5, at least
0.6, or at least 0.8.
[0026] Metal oxides, including transition metal oxides,
ferroelectric-oxides and multiferroic alloys are other classes of
materials for which growth templates can be made using the present
methods. Included among these are metal oxides having a perovskite
structure. Specific examples of metal oxides that can be fabricated
as growth templates include SrTiO.sub.3 (STO), LaTiO.sub.3,
PbZr.sub.1-xTi.sub.xO.sub.3 (PZT), BaTiO.sub.3 (BTO),
Ba.sub.1-xSr.sub.xTiO.sub.3 (BST), LiNbO.sub.3, KTaO.sub.3 and
La.sub.0.7Sr.sub.0.3MnO.sub.3 (LSMO).
[0027] The thickness of the growth template layers grown according
to the present methods will depend on the lattice mismatch between
the growth template material and the sacrificial material, as well
as on the thickness of the suspended sections of the sacrificial
layer upon which they are grown and the rate of growth and growth
conditions. By way of illustration only, in some embodiments, the
growth template layers are grown to a thickness of at least 10 nm.
This includes growth template layers grown to a thickness of at
least 40 nm, at least 100 nm and at least 1 .mu.m.
[0028] Depending on the lattice constant differences between the
growth template material and the sacrificial material, dislocations
may begin to appear at higher thicknesses of the growth template
material. Therefore, by selecting appropriate material compositions
for the growth template layer and the sacrificial layer, the
present methods can be used to provide device layers for
applications where relatively large thicknesses are desirable,
including optical, photonic, and thermoelectric applications.
[0029] The material used as a sacrificial layer during the
production of the growth template layers can be any material upon
which the growth template layers can be grown epitaxially and that
can be selectively removed from the structure once the growth
template layer has been grown to the desired thickness. For
example, Si can be used as the sacrificial layer for a SiGe alloy
growth template. GaAs can be used as the sacrificial layer for an
InGaP or InGaAs alloy growth template. SrTiO.sub.3 can be used as
the sacrificial layer for a PZT or BST growth template
[0030] The sacrificial layer should be sufficiently thin, at least
in the suspended sections, to allow it to strain share with the
overlying single-crystalline material. Thus, in some embodiments
the sacrificial layer has a thickness of no greater than about 5
.mu.m. This includes embodiments in which the sacrificial layer has
a thickness of no greater than about 3 .mu.m. For example, the
thickness of the suspended sections of the sacrificial layer can be
in the range from about 10 nm to about 3 .mu.m.
[0031] The material used as a base substrate material during the
production of the growth templates can be any material upon which
the layer of sacrificial material can be grown or to which the
layer of sacrificial material can be bonded. Typically, the base
material is substantially thicker than the sacrificial layer having
a thickness of, for example 100 .mu.m or greater (e.g., 200 to 1000
.mu.m).
[0032] The word "illustrative" is used herein to mean serving as an
example, instance, or illustration. Any aspect or design described
herein as "illustrative" is not necessarily to be construed as
preferred or advantageous over other aspects or designs. Further,
for the purposes of this disclosure and unless otherwise specified,
"a" or "an" means "one or more". Still further, the use of "and" or
"or" is intended to include "and/or" unless specifically indicated
otherwise.
[0033] The foregoing description of illustrative embodiments of the
invention has been presented for purposes of illustration and of
description. It is not intended to be exhaustive or to limit the
invention to the precise form disclosed, and modifications and
variations are possible in light of the above teachings or may be
acquired from practice of the invention. The embodiments were
chosen and described in order to explain the principles of the
invention and as practical applications of the invention to enable
one skilled in the art to utilize the invention in various
embodiments and with various modifications as suited to the
particular use contemplated. It is intended that the scope of the
invention be defined by the claims appended hereto and their
equivalents.
* * * * *