U.S. patent application number 11/505668 was filed with the patent office on 2007-06-21 for methods for making substrates and substrates formed therefrom.
Invention is credited to Alice Boussagol, Bruce Faure, Bruno Ghyselen.
Application Number | 20070141803 11/505668 |
Document ID | / |
Family ID | 36648762 |
Filed Date | 2007-06-21 |
United States Patent
Application |
20070141803 |
Kind Code |
A1 |
Boussagol; Alice ; et
al. |
June 21, 2007 |
Methods for making substrates and substrates formed therefrom
Abstract
A method for making substrates for use in optics, electronics,
or opto-electronics. The method may include transferring a seed
layer onto a receiving support and depositing a useful layer onto
the seed layer. The thermal expansion coefficient of the receiving
support may be identical to or slightly larger than the thermal
expansion coefficient of the useful layer and the thermal expansion
coefficient of the seed layer may be substantially equal to the
thermal expansion coefficient of the receiving support.
Inventors: |
Boussagol; Alice; (Brignoud,
FR) ; Faure; Bruce; (Grenoble, FR) ; Ghyselen;
Bruno; (Seyssinet, FR) |
Correspondence
Address: |
WINSTON & STRAWN LLP;PATENT DEPARTMENT
1700 K STREET, N.W.
WASHINGTON
DC
20006
US
|
Family ID: |
36648762 |
Appl. No.: |
11/505668 |
Filed: |
August 16, 2006 |
Current U.S.
Class: |
438/455 ;
257/E21.568 |
Current CPC
Class: |
C30B 33/00 20130101;
C30B 25/18 20130101; H01L 21/76254 20130101; H01L 21/2007
20130101 |
Class at
Publication: |
438/455 |
International
Class: |
H01L 21/30 20060101
H01L021/30; H01L 21/46 20060101 H01L021/46 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 21, 2005 |
FR |
05/13045 |
Claims
1. A method for making substrates comprising: providing a donor
substrate and a receiving substrate, wherein the receiving
substrate has a thermal expansion coefficient; operably connecting
the donor substrate to the receiving substrate; forming a seed
layer on the receiving substrate, wherein the seed layer has a
surface and a thermal expansion coefficient; and epitaxy of a
useful layer on the seed layer, wherein the useful layer has a
thermal expansion coefficient; wherein the thermal expansion
coefficient of the receiving substrate is equal to or greater than
the thermal expansion coefficient of the useful layer, and wherein
the thermal expansion coefficient of the seed layer is about the
same as the thermal expansion coefficient of the receiving
substrate so that the seed layer and the receiving support expand
in substantially the same way to avoid stressing or deforming the
seed layer.
2. The method of claim 1 wherein the seed layer forms a surface
portion of the donor substrate, the method further comprising
forming a weakened area in the donor substrate beneath the seed
layer and detaching the donor substrate from the seed layer at the
weakened area so that the seed layer remains operably connected to
the receiving substrate.
3. The method of claim 2, wherein the step of forming a weakened
area comprises implanting atomic species into the donor
substrate.
4. The method of claim 1, wherein the step of operably connecting
the donor substrate to the receiving substrate includes forming a
bonding layer between the seed layer and the receiving
substrate.
5. The method of claim 4 further comprising preparing the surface
of the seed layer, wherein the preparation step is selected from at
least one of the group consisting of polishing, annealing,
sacrificial oxidation interface operations and etching.
6. The method of claim 4 further comprising providing a supporting
substrate of a material selected from the group consisting of a
semi-conductor, metal, plastic and glass, and operably connecting
the useful layer to the supporting substrate.
7. The method of claim 6 further comprising detaching the seed
layer, the useful layer and the supporting substrate from the
receiving substrate and subsequently removing the seed layer from
the useful layer and the supporting substrate.
8. The method of claim 7 wherein the step of detaching comprises
performing at least one of the operations selected from the groups
consisting of heat treatment, application of stresses, irradiation
and etching.
9. The method of claim 6, wherein the step of operably connecting
the useful layer to the supporting substrate comprises forming a
bonding layer between the useful layer and the supporting
substrate, wherein the bonding layer is selected from the group
consisting of insulating layers, organic layers, metal interfaces
and seals.
10. The method of claim 10 further comprising burying a structure
in the second bonding layer.
11. The method of claim 1 further comprising forming the seed layer
from a material for which the thermal expansion coefficient is
(1+.epsilon.) times the thermal expansion coefficient of the
receiving substrate, and forming the useful layer from a material
for which the thermal expansion coefficient is greater than or
equal to (1.+-..epsilon.') times the thermal expansion coefficient
of the receiving substrate.
12. The method of claim 1 which further comprises forming at least
one of the seed layer and the receiving substrate from a material
selected from the group consisting of silicon, germanium, silicon
carbide, GaN, AlN and sapphire, and optionally where the chemical
composition of the seed layer and that of the receiving substrate
are identical.
13. The method of claim 1 further comprising detaching the seed
layer and the useful layer from the receiving substrate by
performing at least one of the operations selected from the group
consisting of heat treatment, application of mechanical, thermal or
electrostatic stresses, irradiation and etching.
14. The method of claim 22 further comprising performing an
operation selected from the group consisting of dry, wet, gas,
chemical and plasma etching or irradiation using a laser.
15. The method of claim 1 further comprising removing the seed
layer from the useful layer.
16. The method of claim 1 further comprising reusing the receiving
substrate to make another substrate.
17. The method of claim 1, wherein the step of forming the seed
layer comprises thinning the donor substrate after bringing the
donor substrate into contact with the receiving substrate.
18. A method for making substrates comprising: providing a donor
substrate and a receiving support; forming a seed layer from the
donor substrate; transferring the seed layer onto the receiving
support; forming a useful layer on the seed layer; wherein the
thermal expansion coefficient of the receiving support is equal to
or greater than the thermal expansion coefficient of the useful
layer, and wherein the thermal expansion coefficient of the seed
layer is about equal to the thermal expansion coefficient of the
receiving support.
19. The method of claim 18 wherein forming the seed layer comprises
inserting atomic species into the donor substrate and forming a
weakened area beneath the seed layer.
20. The method of claim 18 wherein forming a useful layer comprises
epitaxy of the useful layer on the seed layer.
21. The method of claim 18 wherein transferring the seed layer to
the receiving support comprises bonding the donor substrate to the
receiving support and detaching the seed layer and the useful layer
from the receiving support.
22. The method of claim 21 further comprising removing the seed
layer from the useful layer and transferring the useful layer onto
a supporting substrate.
23. A substrate comprising: a receiving support having a thermal
expansion coefficient; a seed layer having a thermal expansion
coefficient, wherein the seed layer is operably connected to the
receiving support; and a useful layer having a thermal expansion
coefficient, the useful layer being operably connected to the seed
layer; wherein the thermal expansion coefficient of the receiving
support is greater than or equal to the thermal expansion
coefficient of the useful layer, and wherein the thermal expansion
coefficient of the seed layer is about equal to the thermal
expansion coefficient of the receiving support so that the seed
layer and the receiving support expand in substantially the same
way to avoid stressing or deforming the seed layer.
24. The substrate of claim 23, wherein the seed layer is made of a
material for which the thermal expansion coefficient is equal to
(1+.epsilon.) times the thermal expansion coefficient of the
receiving support.
25. The substrate of claim 23 wherein the useful layer is made of a
material for which the thermal expansion coefficient is greater
than or equal to (1.+-..epsilon.') times the thermal expansion
coefficient of the receiving support.
26. The substrate of claim 23, wherein the at least one of the seed
layer and the receiving support is made of a material selected from
the group consisting of silicon, germanium, silicon carbide, GaN,
AlN and sapphire and optionally where the chemical composition of
the seed layer and that of the receiving substrate are
identical.
27. The substrate of claim 23 further comprising a supporting
substrate comprising a material selected from the group consisting
of semiconductors, plastic, glass and metal, and optionally
including a bonding layer connecting the supporting substrate and
the useful layer.
28. The substrate of claim 27 further comprising a structure buried
in the bonding layer.
29. The substrate of claim 23 further comprising a bonding layer
connecting the seed layer and the receiving support, wherein the
bonding layer is comprised of a material selected from the group
consisting of insulating layers, organic layers, metal interfaces
and sealing layers.
30. The substrate of claim 23, wherein the seed layer and the
useful layer has a thickness of at least 50 .mu.m.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to methods for making
substrates and substrates for use in optics, electronics or
opto-electronics and, in particular, substrates which may be used
for making solar cells, light-emitting diodes and lasers.
BACKGROUND OF THE INVENTION
[0002] In the field of substrates for optics, electronics or
opto-electronics, two main types of methods are well known for
forming a thin layer on a supporting substrate. According to a
first type of method, a thin layer taken from a donor substrate is
transferred onto a receiving supporting substrate to obtain
substrates including a thin useful layer. Useful layer is the layer
of the substrate on which electronic components such as, for
example, light-emitting diodes or other components may be made.
[0003] According to second type of method, the thin layer is
deposited on a receiving supporting substrate by a deposition
technique. This deposition technique may notably consist of epitaxy
or chemical vapor deposition. Regardless of the type of method used
for forming a useful layer on a receiving supporting substrate, in
some instances it is necessary to remove at least one portion of
the receiving support to obtain a final substrate including at
least the useful layer. Such removal of the receiving support
results in loss of materials, thereby putting a strain on the
manufacturing costs of such substrates.
[0004] In order to find a remedy to this drawback, a method for
making substrates has been devised which includes a useful thin
layer method in which the receiving supporting substrate is removed
in order to be recycled. Such a method is described in an
alternative embodiment of U.S. Pat. No. 6,794,276, which describes
a method for making substrates. This method includes a step for
transferring a seed layer on a receiving support by molecular
adhesion at a bonding interface, a step for epitaxy of a useful
layer on the seed layer and a step for applying stresses in order
to lead to removal of the assembly (i.e., removal of the seed layer
and of the useful layer from the receiving support at the bonding
interface). Seed layer is the material layer which allows
development of the epitaxied useful layer.
[0005] In U.S. Pat. No. 6,794,276, certain specifications are
required for allowing the seed layer to adapt to thermal expansions
of the receiving support and the useful layer during heat
treatments to which the substrate is subject. For this purpose, it
is recommended that the seed layer has sufficiently small
thickness, of the order of 0.5 microns, and preferably less than
1,000 .ANG.. U.S. Pat. No. 6,794,276 also mentions the fact that
the receiving support consists of a material for which the thermal
expansion coefficient is 0.7 to 3 times larger than that of the
useful layer. It is specified that the thermal expansion
coefficient is the proportionality coefficient of the change in the
length of a solid as a function of the initial length of the solid
and of its change in temperature according to the following
formula:
.DELTA.L=.alpha.L.sub.0.DELTA.T where .alpha.=thermal expansion
coefficient
[0006] In an alternative embodiment, the method taught by U.S. Pat.
No. 6,794,276 allows the receiving supporting substrate to be
reused after its removal.
[0007] It is desirable to improve the method taught by U.S. Pat.
No. 6,794,276. In particular, improvements are needed for reducing
the risk of breaking the substrate, deteriorating, cracking the
seed layer or the occurrence of a residual deflection of the final
substrate making it unusable during the various heat treatments
applied to the substrate. These improvements are now provided by
the present invention.
SUMMARY OF THE INVENTION
[0008] The invention relates to a method for making substrates for
optics, electronics, or opto-electronics which includes providing a
donor substrate and a receiving substrate, wherein the receiving
substrate has a thermal expansion coefficient; operably connecting
the donor substrate to the receiving substrate; forming a seed
layer on the receiving substrate, wherein the seed layer has a
surface and a thermal expansion coefficient; and epitaxy of a
useful layer on the seed layer, wherein the useful layer has a
thermal expansion coefficient. Advantageously, the thermal
expansion coefficient of the receiving substrate is equal to or
greater than the thermal expansion coefficient of the useful layer,
and the thermal expansion coefficient of the seed layer is about
the same as the thermal expansion coefficient of the receiving
substrate so that the seed layer and the receiving support expand
in substantially the same way to avoid stressing or deforming the
seed layer.
[0009] In another embodiment, the method for making substrates
includes providing a donor substrate and a receiving support;
forming a seed layer from the donor substrate; transferring the
seed layer onto the receiving support; and forming a useful layer
on the seed layer. Again, the thermal expansion coefficient of the
receiving support is equal to or greater than the thermal expansion
coefficient of the useful layer, and the thermal expansion
coefficient of the seed layer is about equal to the thermal
expansion coefficient of the receiving support so that the seed
layer and the receiving support expand in substantially the same
way to avoid stressing or deforming the seed layer.
[0010] Thus, during subsequent heat treatments which the structure
will undergo, the seed layer and the receiving support may
substantially expand in the same way. The receiving support may
expand slightly less than the seed layer so that the seed layer may
be placed under slight compression avoiding any deterioration of
the seed layer.
[0011] In a preferred embodiment, the seed layer may consist of a
material for which the thermal expansion coefficient is equal to
(1+.epsilon.) times that of the receiving support, with .epsilon.
of the order of 0.2, and preferably .epsilon. equals 0.1. Further,
the useful layer may consist of a material for which the thermal
expansion coefficient may be larger than or equal to
(1.+-..epsilon.') times that of the receiving support, with a
typical value of 0.2 for .epsilon.'. The seed layer and/or the
receiving support may be made of, for example, silicon, germanium,
silicon carbide, GaN or sapphire. Moreover, the chemical
composition of the seed layer, advantageously, may be identical to
that of the receiving support.
[0012] A composite substrate may be created using the method
described herein. The composite substrate may be used for optics,
electronics, or opto-electronics, The substrate may have at least
one seed layer on a receiving support, and an epitaxied useful
layer on the seed layer. The thermal expansion coefficient of the
receiving support may be identical to or slightly larger than the
thermal expansion coefficient of the useful layer, and the thermal
expansion coefficient of the seed layer may be substantially equal
to the thermal expansion coefficient of the receiving support so
that the seed layer and the receiving support-expand in
substantially the same way to avoid stressing or deforming the seed
layer.
[0013] Other advantages and features will become better apparent
from the description which follows of several alternative
embodiments, given as non-limiting examples, of the method for
making substrates according to the invention as well as of the
substrate obtained by the method.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] The present invention can be better understood by reference
to the following drawings, wherein like references numerals
represent like elements. The drawings are merely exemplary to
illustrate certain features that may be used singularly or in
combination with other features and the present invention should
not be limited to the embodiments shown.
[0015] FIG. 1 is a schematic illustration of the steps of an
exemplary embodiment of a method for making a substrate; and
[0016] FIG. 2 is a schematic illustration of the steps of an
alternative exemplary embodiment of a method for making a
substrate.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0017] With reference to FIG. 1, the method according to the
invention includes a step for implanting atomic species at a
determined depth in a donor substrate 1 in order to form a weakened
area 2. In step 100, the donor substrate may be boned upon or
otherwise adhered onto a receiving substrate 3 by any appropriate
means known in the art.
[0018] As referred to below, bonding may mean intimate contact of
the donor substrate 1 with the receiving substrate 3 in order to
join the donor substrate 1 and the receiving substrate 3 by
molecular adhesion. Bonding may be obtained according to various
methods such as, for example, (1) having a surface of the donor
substrate 1 come into direct contact with a surface of the
receiving substrate; (2) forming a bonding layer in order to make a
connecting layer on the surface of the donor substrate 1, forming a
bonding layer in order to make a second connecting layer on the
surface of the receiving supporting substrate 3 and having the
surfaces of the respective connecting layers of the donor substrate
1 and the donor substrate 3 come into contact with each other; and
(3) forming a bonding layer on only one of both substrates.
[0019] In one embodiment, the bonding layer may consist of, for
example, an insulating layer or a dielectric layer. In such an
embodiment, the donor substrate 1 may be bonded onto the receiving
substrate 3 by means of a bonding layer 4 deposited on the surface
of the donor substrate and/or the receiving substrate 3. In
addition, an annealing step may be applied at this stage for
strengthening the bonding interface between the bonding layer 4 and
the surface of the donor substrate 1 and/or the receiving substrate
3. Nonetheless, bonding may be achieved according to any of the
methods known to one skilled in the art.
[0020] In step 200, a seed layer 5 may be detached from the donor
substrate 1 at the weakened area 2. Thereafter, in step 300 a
useful layer 6 may be deposited on the surface of the seed layer 5.
In one preferred embodiment, the useful layer 6 may be obtained by
epitaxy, which is well known to one skilled in the art, according
to step 300. The step 200 for implanting atomic species and for
detaching the seed layer 5 corresponds to a SMART-CUT.RTM. method,
a general description of which is found in the publication
Silicon-On-Insulator Technology: Materials to VLSI, 2nd Edition of
Jean-Pierre Colinge, Kluwer Academic Publishers, p. 50 and 51.
Those skilled in the art will appreciate that detachment of the
seed layer 5 and of the donor substrate 1 may be achieved by an
operation such as, for example, heat treatment, application of
mechanical stresses, chemical etching, or a combination of at least
two of these operations.
[0021] The seed layer 5 may consist of a material for which the
thermal expansion coefficient is equal to (1+.epsilon.) times that
of the receiving support 3, with .epsilon. of the order of 0.2, and
preferably .epsilon. equals 0.1. It will however be observed that
thermal expansion may vary with temperature, with the deposition
technique, with the defects present inside the layers and also with
the measurement techniques. Thus, when the structure is undergoing
heat treatments (e.g., during detachment of the seed layer 5 and
the useful layer 6 of the receiving substrate 3) the seed layer 5
and the receiving support 3 will substantially expand in the same
way. The receiving support 3 will expand slightly less than the
seed layer 5 so that the latter may be placed under slight
compression, thereby avoiding deterioration of the seed layer
5.
[0022] The useful layer 6 may consist of a material which has a
thermal expansion coefficient which is larger than or equal to
(1.+-..epsilon.') times that of the receiving support 3, with the
value of .epsilon.' between 0 and 0.8 and, preferably, between 0.2
and 0.3. Expansions of the different layers 5, 6 and the receiving
support 3 of the same order of magnitude during heat treatments may
be obtained because of the closeness of the thermal expansion
coefficients of the useful layer 6, the seed layer 5 and the
receiving support 3. In this way, any risk of deterioration of the
substrate or occurrence of a residual deflection of the final
substrate may be avoided.
[0023] The seed layer 5 and/or the receiving support 3 may comprise
a material such as, for example, silicon (e.g., {111} silicon),
germanium, polycrystalline or monocrystalline silicon carbide, GaN,
polycrystalline or monocrystalline AlN, and sapphire. Further, the
chemical composition of the seed layer 5 may be identical with that
of the receiving support 3.
[0024] Between the steps for detaching 200 and for depositing 300
the useful layer, the method may also include steps for preparing
the surface of the seed layer 5. These preparation steps may
include, for example, polishing, annealing, smooth annealing
operations (e.g., under hydrogen), annealing operations for
strengthening the bond, sacrificial oxidization interface
operations (i.e., for oxidizing and then removing the oxidized
material), etching operations, etc.
[0025] Step 400 may lead to detachment at the bonding layer 4 of
the assembly, consisting of the seed layer 5 and the useful layer
6, from the receiving support 3. If a self-supported substrate is
desired, the assembly formed by the seed layer 5 and the useful
layer 6 may only be able to be detached from the receiving support
3 if the thickness of the assembly is greater than or equal to 50
.mu.m.
[0026] In order to perform the detachment, different techniques may
be used. For example, detachment may be accomplished by application
of mechanical, thermal, electrostatic stresses; application of any
type of etching (wet, dry, gas, etching, plasma etching, etc.)
and/or application of any type of etching by irradiation such as
laser irradiation (e.g., by chemical etchings at the bonding layer
4), or the like. The receiving substrate 3, which may either be
destroyed or recycled in order to reuse it during the making of a
new substrate, may then be obtained on the one hand, and a
structure consisting of the seed layer 5 and the useful layer 6 may
be obtained on the other hand. It will be appreciated that for
performing the detachment of the assembly (consisting of the seed
layer 5 and the useful layer 6) from the receiving support 3 at the
bonding layer 4, chemical etching may advantageously be used if the
receiving substrate 3 is intended to be destroyed. On the other
hand, if the receiving substrate 3 is intended to be recycled for
reuse, mechanical stress or chemical etching of the bonding layer 4
may preferably be used, which provides full detachment of substrate
3. The seed layer may then be removed by any appropriate means
known to those skilled in the art.
[0027] Thereafter, the useful layer 6 may be transferred onto a
final supporting substrate 7. The final support 7 may be made of a
material such as, for example, semi-conducting or semi-conductive
materials (e.g., silicon, germanium, etc.), metals (e.g., copper),
plastic materials and glasses. Since the resultant structure no
longer undergoes any heat treatment, the final supporting substrate
7 may be made with any material which has a thermal expansion
coefficient and/or a lattice parameter different from those of the
useful layer 6.
[0028] In a preferred embodiment, the useful layer 6 may be
transferred onto the final supporting substrate 7 by bonding. The
bond may be obtained by applying a bonding layer 8 on one of the
surfaces of the useful layer 6 and/or the final supporting
substrate 7. Similar to selecting the final substrate 7, the
bonding techniques applied in this step are not limited by
temperature resistance, contaminations, the thermal expansion
coefficient and/or the lattice parameter of the useful layer 6.
[0029] The layer 8 used may comprise, for example, organic layers
(e.g., insulating layers of the SiO.sub.2, Si.sub.3N.sub.4, or
polyimides), conductive metal interfaces and seals (e.g., palladium
silicide Pd.sub.2Si, tungsten silicide WSi.sub.2, SiAu, or PdIn).
The conductive interfaces may then provide the contact on the rear
face of the layer.
[0030] Moreover, structures may be buried in this bonding layer 8
so that a rear junction contact of a triple junction may thereby be
made for producing solar cells. In one embodiment, the buried
structure may consist of a triple junction based on amorphous
silicon of the n-i-p type. This buried structure may have a lower
layer (i.e., a rear contact layer) consisting of metallization,
such as silver (Ag) or aluminium (Al), on which a conducting
transparent oxide may be deposited. The rear contact layer, on the
one hand, may provide an electrical contact with which the triple
junction solar cell may be connected and a rear mirror, on the
other hand, allowing reflection of light which has not been
absorbed by the solar cell. The latter may consist of three
amorphous silicon layers (of type n, i and p, respectively)
successively deposited on the rear contact layer. It will be
appreciated by those skilled in that art that when making LEDs,
mirrors may also be buried in the bonding layer 8.
[0031] In an alternative embodiment (not illustrated in FIG. 1),
the useful layer 6 and the seed layer 5 may be transferred onto the
final supporting substrate 7 with or without the bonding layer 8
prior to removing the seed layer 5.
[0032] Referring now to FIG. 2, atomic species may be implanted in
the same way as previously discussed--at a determined depth of a
donor substrate 1--in order to form a weakened area 2. The donor
substrate 1 in step 100 may then be adhered on a receiving
substrate 3 by any appropriate means. In step 200, a seed layer 5
may be detached from the donor substrate 1 at the weakened area 2.
Thereafter, in step 300, a useful layer 6 may be deposited on the
surface of the seed layer 5. Detachment of the seed layer 5 and the
donor substrate 1 may be achieved by an operation such as, for
example, heat treatment, application of mechanical stresses and
chemical etching, or a combination of at least two of these
operations.
[0033] In another alternative embodiment, the seed layer 5 may
originate from the thinning of the donor substrate (for example
according to a BESOI type method) before depositing the useful
layer 6. The final supporting substrate 7 may then be transferred
onto the useful layer 6 by means of a bonding layer 8. Stresses may
be applied in order detach the structure, which may consist of the
seed layer 5, the useful layer 6, the bonding layer 8 and the final
supporting substrate 7, from the receiving support 3 at the bonding
layer 4. A receiving substrate 3, ready to be recycled, may be
obtained on the one hand and a structure consisting of the seed
layer 5, the useful layer 6, the bonding layer 8 and the final
supporting substrate 7 may be obtained on the other hand. The seed
layer 5 may then be removed by any appropriate means in order to
obtain the final substrate.
EXAMPLES
[0034] Two particular but non-limiting exemplary embodiments of a
resultant substrate will be described hereafter with reference to
FIG. 2. The substrates are intended for making solar cells (Example
1) and light-emitting diodes (Example 2). It should be noted,
however, that the examples are not intended to be limiting as to
the fields of application of the invention.
Example 1
[0035] According to this example, a weakened area 2 may be made by
implanting atomic species at a determined depth in the donor
substrate 1 which may be made of, for example, germanium (Ge). The
receiving substrate 3, which may also be made of Ge, may be bonded
to the donor substrate 1 by means of a bonding layer 4. The bonding
layer 4, preferably made of nitride or oxide, may be formed on the
face of at least one of the donor 1 or receiving 3 substrates.
[0036] As shown in step 200, a seed layer 5 of Ge may be detached
from the donor substrate 1 at the weakened area 2 using the
SMART-CUT.RTM. method as described herein. The seed layer 5 of Ge
may have a thermal expansion coefficient (which is also noted as
CTE) which varies from 4.6 to 6.67 10.sup.-6 for temperatures
ranging from 25.degree. C. to 600.degree. C. Detachment of the seed
layer 5 and the donor substrate 1 may be achieved by an operation
such as, for example, heat treatment, application of mechanical
stresses and chemical etching, or a combination of at least two of
these operations.
[0037] As illustrated in step 300, a useful gallium arsenide layer
6 may then be deposited on the surface of the seed layer 5. The CTE
of AsGa may be from 5.00 to 7.4 10.sup.-6 for temperatures ranging
from 25.degree. C. to 600.degree. C. Different layers, such as, for
example, InP, AsGa, GaInP, InGaAs, InGaAlP, or InGaAsN epitaxied
layers, may be successively deposited by epitaxy on the deposit of
the AsGa layer in order to form an epitaxial stack for making
junctions (e.g., triple junctions, quadruple junctions, etc.). It
will be appreciated that the useful layer 6 may have a crystalline
quality at least equal to the crystalline quality which may be
obtained by epitaxy on a massive Ge substrate.
[0038] The useful layer 6 and the seed layer 5 may then be
transferred onto a final supporting substrate 7. It will be noted
that the final support 7 may also be contacted with the epitaxial
stack if the latter is made beforehand. The final support 7 may be
made of a material such as, for example, semi-conductors (e.g.,
silicon, germanium), plastic materials and glasses. Transfer of the
useful layer 6 and the seed layer 5 onto the final supporting
substrate 7 may be performed by bonding. The bond may be performed
using a bonding layer 8 made of, for example, insulating layers
(e.g., SiO.sub.2, Si.sub.3N.sub.4, etc.), organic layers (e.g.,
polyimides), metal layers (e.g., palladium silicide Pd.sub.2Si and
tungsten silicide WSi.sub.2), and seals (e.g., SiAu, PdIn,
etc.)
[0039] The final supporting substrate 7, the seed layer 5 and the
useful layer 6 may then be detached by any appropriate means, for
example, at the bonding layer 4 from the receiving support 3. The
receiving support 3 may thereafter be recycled advantageously. This
detachment may be obtained by applying stresses at the bonding
interface such as, for example, mechanical stresses, thermal
stresses, electrostatic stresses and stresses from laser
irradiation. Thereafter, the seed layer may be removed in order to
obtain the final substrate
[0040] While the foregoing description and drawings represent the
preferred embodiments of the present invention, it will be
understood that various additions, modifications and substitutions
may be made therein without departing from the spirit and scope of
the present invention as defined in the accompanying claims. In
particular, it will be clear to those skilled in the art that the
present invention may be embodied in other specific forms,
structures, arrangements, proportions, and with other elements,
materials, and components, without departing from the spirit or
essential characteristics thereof. One skilled in the art will
appreciate that the invention may be used with many modifications
of structure, arrangement, proportions, materials, and components
and otherwise, used in the practice of the invention, which are
particularly adapted to specific environments and operative
requirements without departing from the principles of the present
invention. The presently disclosed embodiments are therefore to be
considered in all respects as illustrative and not restrictive, the
scope of the invention being indicated by the appended claims, and
not limited to the foregoing description.
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