U.S. patent application number 13/151358 was filed with the patent office on 2011-09-29 for method of fabricating a release substrate.
This patent application is currently assigned to S.O.I.Tec Silicon on Insulator Technologies. Invention is credited to Takeshi Akatsu, Gisele Rayssac, Olivier Rayssac, Pierre Rayssac.
Application Number | 20110233733 13/151358 |
Document ID | / |
Family ID | 34717408 |
Filed Date | 2011-09-29 |
United States Patent
Application |
20110233733 |
Kind Code |
A1 |
Rayssac; Olivier ; et
al. |
September 29, 2011 |
METHOD OF FABRICATING A RELEASE SUBSTRATE
Abstract
The invention relates to a release substrate produced from
semiconductor materials, and which includes a first substrate
release layer having a surface in contact with a connecting layer,
and a second substrate release layer having a surface in contact
with the connecting layer opposite the first substrate release
layer so that the connecting layer is located between the first
substrate release layer and second substrate release layer; and a
concentrated zone of solid nanoparticles located within the
connecting layer to maintain the bonding energy of the reversible
connection substantially constant even when the substrate is
exposed to heat treatment while also facilitating breaking of the
connecting layer by mechanical action.
Inventors: |
Rayssac; Olivier; (Grenoble,
FR) ; Rayssac; Pierre; (Clairvaux d'Aveyron, FR)
; Rayssac; Gisele; (Clairvaux d'Aveyron, FR) ;
Akatsu; Takeshi; (St. Nazaire les Eymes, FR) |
Assignee: |
S.O.I.Tec Silicon on Insulator
Technologies
|
Family ID: |
34717408 |
Appl. No.: |
13/151358 |
Filed: |
June 2, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12392888 |
Feb 25, 2009 |
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13151358 |
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11481696 |
Jul 5, 2006 |
7544265 |
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12392888 |
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PCT/IB05/00347 |
Jan 24, 2005 |
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11481696 |
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Current U.S.
Class: |
257/618 ;
257/E29.022; 977/773 |
Current CPC
Class: |
Y10S 117/915 20130101;
H01L 21/76254 20130101; H01L 21/76259 20130101 |
Class at
Publication: |
257/618 ;
977/773; 257/E29.022 |
International
Class: |
H01L 29/06 20060101
H01L029/06 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 26, 2004 |
FR |
FR 0400694 |
Claims
1. A structure comprising: a first substrate release layer having a
surface in contact with a connecting layer, and a second substrate
release layer having a surface in contact with the connecting layer
opposite the first substrate release layer so that the connecting
layer is located between the first substrate release layer and
second substrate release layer; and a concentrated zone of solid
nanoparticles located within the connecting layer to facilitate
breaking of the connecting layer by mechanical action.
2. The structure of claim 1, wherein the first and second substrate
release layers are made of semiconductor material, the connecting
layer is made of an oxide or nitride of the semiconductor material
of the substrate release layers, and the solid nanoparticles are
made of a semiconductor material that is different from the
material forming the connecting layer.
3. The structure of claim 1, wherein the connecting layer and
concentrated zone of nanoparticles are stable and do not weaken
when the structure is exposed to heat treatment, but the connecting
layer can be broken at the concentrated zone of nanoparticles by
mechanical action.
4. The structure of claim 1, wherein the connecting layer comprises
SiO.sub.2 and the nanoparticles comprise Si or Ge.
5. The structure of claim 1, wherein the connecting layer has a
bonding energy that is substantially constant even when the release
substrate is exposed to heat treatments as high as 900.degree. C.
to 1100.degree. C.
6. The structure of claim 1, wherein the nanoparticles have
diameters on the order of 1 nm to 10 nm.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional of application Ser. No.
12/392,888 filed Feb. 25, 2009, which is a continuation of
application Ser. No. 11/481,696 filed Jul. 5, 2006, now U.S. Pat.
No. 7,544,265, which is a continuation of International Application
PCT/IB2005/000347 filed Jan. 24, 2005, the entire content of each
of which is expressly incorporated herein by reference thereto.
BACKGROUND ART
[0002] The present invention relates to a method of fabricating a
release substrate produced from semiconductor materials.
[0003] The term "release substrate" means a substrate comprising
two layers which have been associated together via a reversible
connection, the connection between the two layers being breakable,
typically by mechanical action. Thus, the action of breaking the
connection between these layers corresponds to "releasing" the
substrate.
[0004] Methods of releasing a substrate are already known. As an
example, the fabrication of release substrates by bonding two
layers is known, where the bonding conditions are defined so that
the bonding energy remains limited and for this reason, the bonding
is reversible under the effect of mechanical action.
[0005] U.S. patent application 2004/0222500 provides an example of
such release substrates. The "energy" associated with a bonded
interface, or more generally, with a releasing interface of a
release substrate, is defined as corresponding to a cohesive force
between the two layers defining that interface. That energy is
generally characterized by mechanical resistance: [0006] resistance
to separating the two layers--typically under the effect of
inserting a wedge attacking the interface, and/or [0007] resistance
to delamination (applying tension to one of the two layers defining
the interface, and measuring the tensile stress corresponding to
the onset of delamination).
[0008] In many applications, treatments (for example anneal type
heat treatments) have to be carried out on the release substrate
prior to releasing it. It is known that heat treatment tends to
increase the energy (i.e. the cohesive force) of a bonding
interface between two layers. This is shown in prior art documents
such as U.S. patent applications 2001/0016399 or 2003/0008475 or
U.S. Pat. No. 6,352,909 which disclose heat treatments either for
providing a gettering layer in the wafer or for enhancing the
quality of the bonding interface in a wafer made from bonded
substrates.
[0009] One problem which arises with such release substrates is
that any treatments (in particular heat treatments) which are to be
carried out on the release substrate prior to release may
compromise the reversible nature of the "release" bond of the
substrate, rendering release problematical. Certain heat treatments
can weaken the bond so that release occurs when not desired, while
others can actually strengthen the bond making it more difficult to
release the substrates when desired. These problems are not limited
to release substrates in which the reversible connection is
constituted by bonding. In general, applying an anneal type heat
treatment to release substrates having a reversible connection that
has been formed using any technique (bonding, and other
techniques--for example, creating a porous region, etc) risks
modifying the energy associated with the reversible connection of
the substrate so that release does not occur when desired. This is
a problem which is now solved by the present invention.
SUMMARY OF THE INVENTION
[0010] The present invention now provides for the production of
release substrates which, prior to releasing, can undergo
treatments (for example, anneal type heat treatments) without
substantially affecting the energy of the reversible connection of
the release substrate. In particular, the invention provides a
method of fabricating a release substrate of semiconductor
materials, by forming a reversible connection between two substrate
release layers by providing a connecting layer of a first material,
and providing a concentrated zone of nanoparticles of a second
material in the connecting layer to facilitate release of the
substrate release layers. With this method, the connecting layer
has a bonding energy that is substantially constant even when the
release substrate is exposed to heat treatments to facilitate the
release of the substrate release rates when desired and not at
other times.
[0011] The connecting layer can be formed by a number of ways as
set forth in the following detailed description. The segregation
heat treatment is carried out at a temperature on the order of
900.degree. C. to 1100.degree. C. for a sufficient time to form the
nanoparticles and optionally in an inert atmosphere of nitrogen,
argon or mixtures thereof
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] Other aspects, benefits and advantages of the present
invention become clear from the following description of the
invention, made with reference to the accompanying drawings in
which:
[0013] FIG. 1 is a schematic diagram showing a release substrate
fabricated in accordance with the invention;
[0014] FIGS. 2a to 2c diagrammatically show three steps for
producing the release substrate in accordance with a first
implementation of the invention;
[0015] FIGS. 3a to 3d diagrammatically show four steps for
producing the release substrate in accordance with a second
implementation of the invention;
[0016] FIGS. 4a and 4b show the effect of a heat treatment which
can cause nanoparticle segregation and which can be used in the
invention; and
[0017] FIG. 5 is a phase diagram showing different Si, SiO and
SiO.sub.2 domains as a function of temperature, showing a
thermodynamic change which can be exploited in the context of the
invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0018] The invention thus provides a method which specifically aims
at fabricating a release substrate comprising two layers connected
through a reversible connection. This method preferably comprises
forming the reversible connection by a connecting layer obtained
from a first material, with the connecting layer further comprising
a concentrating zone of nanoparticles of a second material disposed
to facilitate release of the substrate. The first and second
materials are selected to maintain the energy associated with the
reversible connection substantially constant even when the
substrate is exposed to heat treatment to facilitate release.
Preferred but non-limiting aspects of the method of the invention
are as follows: [0019] the connecting layer is formed by carrying
out the following operations: [0020] creating an initial layer
produced from the first material; [0021] creating in the initial
layer an enriched region of an enrichment material, which may be
the second material or a precursor for the second material; [0022]
heat treating the enriched region to cause segregation of
nanoparticles within the first material; [0023] the enriched region
is produced by implanting the enrichment material into the initial
layer; [0024] production of the connecting layer involves the
following steps (without limitation to the order in which the steps
are carried out): [0025] forming an elemental layer, termed the
enriched layer, from an enrichment material which may be the second
material or a precursor for the second material; [0026] heat
treating the enriched layer to cause segregation of nanoparticles
within the first material; [0027] to form the connecting layer, a
layer termed the "first elemental layer" also formed from the first
material is formed beneath the enriched layer, the enriched layer
then corresponding to a layer termed the "second elemental layer";
[0028] the second elemental layer is produced by deposition onto
the first elemental layer; [0029] the first elemental layer is
produced by deposition onto a first substrate release layer; [0030]
the first elemental layer is produced on a first substrate release
layer by thermal oxidation; [0031] to form the connecting layer, a
layer termed the "third elemental layer" also formed from the first
material is formed on the surface of the enriched layer; [0032] the
third elemental layer is produced by deposition onto the enriched
layer; [0033] the third elemental layer is produced by thermal
oxidation of a portion of the material of the enriched layer;
[0034] the thickness of the enriched layer is gauged so that a
portion of the material of the layer can be used to form the third
elemental layer; [0035] the third elemental layer is formed on the
second release layer prior to assembling the second release layer
with the connecting layer; [0036] the third elemental layer is
produced by thermal oxidation of the second substrate release layer
prior to assembling the second release layer with the remainder of
the connecting layer; [0037] the segregation heat treatment is
carried out at a temperature of the order of 900.degree. C. to
1100.degree. C. for a sufficient time of about 25 to 95 minutes to
provide the nanoparticles and preferably in an inert atmosphere of
nitrogen, argon or mixtures thereof; [0038] the connecting layer is
created on a first of the two substrate release layers, and the
second release layer is formed on the connecting layer after the
segregation heat treatment step; [0039] the connecting layer is
created on a first of the two substrate release layers, and the
second release layer is formed on the connecting layer after
creating an enriched region in the connecting layer and before the
segregation heat treatment step; [0040] the first release layer is
formed beneath the connecting layer by means of a transfer
technique; [0041] the transfer technique is a SMART-CUT.RTM. type
technique; [0042] the second release layer is formed on the
connecting layer by means of a transfer technique; [0043] the
transfer technique is a SMART-CUT.RTM. type technique; [0044] the
first material may be SiO.sub.2; [0045] the second material may be
Si; [0046] the enrichment material may be SiO; [0047] the second
material may be Ge.
[0048] Before embarking on the detailed description of the
drawings, it should be noted that FIGS. 1, 2a to 2c, 3a to 3d are
diagrammatic representations which are not to scale, but which
illustrate the principles of the invention.
[0049] FIG. 1 shows a release substrate 10 fabricated in accordance
with the invention. The release substrate comprises: [0050] two
layers 11a, 11b which correspond to two layers which can be
detached. These two layers are termed below "substrate release
layers". The layers may be formed from a semiconductor material
such as silicon; [0051] a connecting layer 12 which acts as a
reversible connection between the layers 11a, 11b for the release
substrate 10. The connecting layer 12 is produced from a "first
material", for example a material such as SiO.sub.2; [0052] solid
particles 13 should also be noted at the core of the connecting
layer 12, which particles correspond to nanoparticles, as shall be
seen. The solid nanoparticles 13 are organized into a zone of
concentration within the first material which facilitates release
of the substrate 10 at the connecting layer 12; [0053] the
nanoparticles 13 are produced from a "second material" which
differs from the "first material" mentioned above. As an example,
it may be a semiconductor material such as Si or Ge when the first
material is SiO.sub.2.
[0054] It should be emphasized that the term "nanoparticles" as
used here means solid particles of very small size--on the order of
a few nanometers (nm) to a few tens of nanometers. In one
application of the invention, the diameter of the nanoparticles is
typically of the order of 1 nm to 10 nm. The "zone of
concentration" of the nanoparticles corresponds to a zone in which
the majority of nanoparticles are concentrated.
[0055] It should be pointed out that in general, it is possible to
produce the release layers 11a, 11b from any semiconductor
material. In the same manner, the layer 12 and the nanoparticles 13
can be produced from a material that differs from those mentioned
above. In any event, the material of the nanoparticles 13 ("second
material") is different from the material of the connecting layer
12 ("first material"). The two materials are selected to ensure
that the mechanical properties of the connecting layer 12 are
stable when the substrate 10 undergoes a heat treatment prior to
detaching (this aspect is described in more detail below).
[0056] The connecting layer 12 is formed: [0057] by creating a
layer, termed the initial layer, in the first material, which forms
the basis for the connecting layer 12 (SiO.sub.2 in the present
example); [0058] the initial layer may be created directly on the
layer 11b, for example by deposition or thermal oxidation; [0059]
by forming a region 120 termed the enriched region in the thickness
of the initial layer; [0060] to this end, a region comprising a
material termed the enrichment material is formed in the thickness
of the layer 12; [0061] the material may be the second material
mentioned above corresponding to the nanoparticle material, or a
precursor for the second material. The term "precursor" for the
second material means a material that can produce the second
material after a suitable heat treatment, such as a semiconductor
oxide. In the case in which the second material is Si, the
precursor is typically SiO or SiO.sub.2; [0062] by carrying out a
heat treatment on the enriched region 120 (or 122 as can be seen in
the second implementation of the invention) to cause nanoparticles
of the second material to segregate within the layer 12 based on
the first material; [0063] at the end of this heat treatment, the
second release layer 11a may be formed, covering the connecting
layer 12, to finalize fabrication of the release substrate 10.
[0064] In all of the implementations of the invention, the layer
11a may also be formed after creating the enriched region 120 but
before heat treating the enriched region 120 to cause nanoparticle
segregation therein. It should be pointed out that the segregation
process is described in more detail below, more particularly with
reference to FIGS. 4a, 4b and 5.
[0065] FIGS. 2a to 2c show the principal steps employed in the
invention in accordance with a first implementation. FIG. 2a shows
the formation of an initial layer of SiO.sub.2 on a layer 11b of
silicon, for example by deposition of SiO.sub.2 or thermal
oxidation of Si.
[0066] FIG. 2b shows one manner of enriching the initial layer. In
this implementation, enrichment is achieved by implantation I into
the initial layer covering the layer 11b. The implanted species
corresponds to the second material mentioned above, or to a
precursor for the second material. Thus, for example, it may be
silicon or germanium. At the end of the implantation, the implanted
species (silicon atoms, for example) are distributed in a
substantially regular manner and aggregated to a greater or lesser
extent within the thickness of the initial layer of SiO.sub.2.
[0067] The structure shown in FIG. 2b then undergoes segregation
heat treatment. In this implementation, as in the other
implementations of the invention, the segregation heat treatment
may be carried out at a temperature on the order of 900.degree. C.
to 1100.degree. C. It should be recalled that the segregation heat
treatment is explained in more detail below. At the end of the
segregation heat treatment, a structure such as that shown
diagrammatically in FIG. 2c is obtained. The segregation heat
treatment causes segregation of the implanted species (for example
silicon), forming the nanoparticles. After covering the structure
with a second release layer 11a (for example by deposition of the
desired material or by bonding the layer thereto), a release
substrate of the type shown in FIG. 1 is obtained.
[0068] FIGS. 3a to 3d show steps in accordance with a second
implementation of the invention. In this implementation, the
connecting layer is formed by producing successive different
elemental layers in the substrate release layer 11b. It should be
noted that in a variation, it is possible to provide just one
"elemental layer" (in this case, the single elemental layer is the
layer 122--see below).
[0069] In this second implementation, the elemental layers (or the
elemental layer 122 in the case in which only a single elemental
layer is used) form the connecting layer of the substrate on the
release layer 11b. In this implementation, as in all of the
implementations of the invention, the other release layer 11a is
then assembled with the connecting layer--for example by
transferring the layer 11a to the connecting layer, by bonding. It
should, however, be pointed out that, in all of the implementations
of the invention, it is also possible to form the second release
layer directly on the connecting layer (by deposition, or by any
other known technique for producing the layer).
[0070] FIG. 3a shows the formation of a first elemental layer 121.
The layer 121 may be formed directly onto the layer 11b, for
example by thermal oxidation, or by other means (for example
deposition). The first elemental layer is produced from the first
material defined above, namely SiO.sub.2 in the present
example.
[0071] FIG. 3b shows the formation of a second elemental layer 122,
by covering the first elemental layer 121. This second elemental
layer 122 is produced from the enrichment material mentioned above,
namely the second material (Si or Ge, for example), or a precursor
for the second material. The layer 122 thus corresponds to the
enriched region of the connecting layer. The second elemental layer
122 can be deposited on the layer 121, if desired. A third
elemental layer 123 is then formed on the surface of the layer 122,
which third elemental layer is produced from the same material as
the first elemental layer 121. The third elemental layer can be
produced by deposition onto the second elemental layer. It should
be pointed out that other methods for associating the layer 123
with the layer 122 can also be envisaged (thermal oxidation,
bonding, etc). In the case in which the layer 123 is produced on
the layer 122 using a technique such as thermal oxidation, which
involves consumption of part of the material of the subjacent layer
122 (consumption of part of the Si of layer 122 to form the
SiO.sub.2 of layer 123), the thickness of the layer 122 will have
been gauged so that its thickness is sufficient to provide the
material necessary to carry out the technique for producing the
layer 123.
[0072] By the successive formation of the three elemental layers
121, 122, 123, a layer 12 is thus created in which the layer 122
corresponds to the enriched region. Heat treatment is then carried
out to cause segregation in the enriched region, as was the case
for the first implementation described above. This forms a
structure as shown in FIG. 3d, in which the connecting layer 12
comprises a zone for concentrating nanoparticles 13 of the second
material, following the segregation heat treatment.
[0073] It should be pointed out that in this second implementation
of the invention, it is possible to dispense with the first
elemental layer 121 and/or the third elemental layer 123. Overall,
then, in the second implementation, it is possible to produce
several structural configurations, depending on the number of
elemental layers in the connecting layer (1, 2 or 3 elemental
layers).
[0074] FIGS. 4a and 4b originate from an article by M. Zacharias et
al, published in Applied Physics Letters, 80 (4), 2002, p 661. More
particularly, these figures show the state of the layer
corresponding to the connecting layer prior to segregation heat
treatment (enriched region 120 of FIG. 4a) and after the treatment
(region of the finished connecting layer 12 which comprises the
nanoparticle concentration zone, in FIG. 4b). The scales are shown
in the bottom right hand corners of the two figures.
[0075] FIG. 4a thus shows an enriched region 120 composed of
SiO.sub.2 enriched with silicon atoms. This enriched region 120
may, for example, have been formed as follows: [0076] by implanting
silicon into an initial layer of SiO.sub.2 (first implementation of
the invention); or [0077] by forming an elemental layer which
corresponds to the region 120 (second implementation of the
invention).
[0078] In all cases, a silicon-enriched layer with the following
mean composition is formed within the thickness of a layer of
SiO.sub.2: Si.sub.(1-x)O.sub.x, in which X is in the range 0 to
0.68. This figure shows that the SiO is diffused into the mass of
the layer 120.
[0079] FIG. 4b shows the same region of the section after a
segregation anneal at 1100.degree. C. for a period of one hour in a
neutral nitrogen atmosphere. This figure shows that the SiO is no
longer present in the diffused state. In contrast, the magnified
section of this figure highlights discrete solid aggregates which
are separated from each other. The aggregates correspond to solid
silicon nanoparticles in the SiO.sub.2, which corresponds to the
base material for the connecting layer 12 ("first material"). These
solid nanoparticles precipitate out of the solid solution/mixed
solid phase of Si or SiO and SiO.sub.2 as explained in more detail
below. The solid nanoparticles constitute discrete points of
weakness which allow good local detachment at the layer 12. In
contrast, the configuration after segregation is extremely stable
as regards heat treatments which may be carried out before
detaching the layer 12 (and more generally a substrate 10
comprising the layer 12).
[0080] The segregation heat treatment preferably uses the following
segregation equation:
SiO x .fwdarw. x 2 SiO 2 + ( 1 - x 2 ) Si . ##EQU00001##
[0081] In the case in which x=1, this equation corresponds to
segregation of SiO into SiO.sub.2 and Si.
[0082] As explained with reference to FIG. 5, subsequent heat
treatments do not affect the general configuration of the solid
nanoparticle concentration zone in the "first material" of the
connecting layer 12. FIG. 5 shows a phase diagram indicating stable
domains for various silicon compounds. FIG. 5 shows, as a function
of temperature (up the ordinate), the stability domains of the
solid phases of Si, SiO and SiO.sub.2 (the abscissa shows the
percentage of oxygen in the Si). It can be seen that below a
temperature Ts, termed the segregation temperature, the solid
phases of Si, SiO and SiO.sub.2 can co-exist without segregation.
In the case of silicon, the segregation temperature is slightly
below 1100.degree. C.
[0083] Beyond this temperature Ts, the Si and SiO.sub.2 phases
separate by segregation. SiO does not have a stable state beyond
this temperature. The invention astutely exploits these properties.
This is achieved during segregation heat treatment, illustrated by
the changes between points A and C in FIG. 5: [0084] the starting
point for the segregation heat treatment corresponds to point A.
The point corresponds to a state at ambient temperature at which an
enriched region 120, which can be produced from silicon-enriched
SiO.sub.2, has been formed; [0085] the temperature is then raised
to a temperature B which corresponds to segregation heat treatment.
This temperature increase causes the Si or SiO present in the
SiO.sub.2 to segregate from the SiO.sub.2. During the heat
treatment, the temperature is increased to the segregation
temperature Ts; [0086] once the temperature Ts is reached (point
C), segregation between the Si or SiO on the one hand and the
SiO.sub.2 on the other hand is complete and the Si or SiO which was
present in the diffused state in the SiO.sub.2 is aggregated into
solid Si nanoparticles.
[0087] Furthermore, subsequent heat treatments do not modify the
nanoparticle configuration, as the segregation reaction is not
reversible.
[0088] The solid nanoparticles precipitate out of the solid (mixed
phase) solution formed by the Si or SiO and the SiO.sub.2 in the
enriched layer when the temperature Ts is reached. Precipitation of
these solid nanoparticles form a two phases region in the
connecting layer 12 that is stable with regards to subsequent heat
treatments. The segregation of the solid nanoparticles 13
introduces discrete points of weakness to the connecting layer 12.
The introduction of discrete points of weakness forms a breakable
connection that facilitates release of the substrates typically by
mechanical action.
[0089] Thus, a release substrate fabricated using the technique has
a substantially constant energy between its release layers,
regardless of the heat treatments which such a substrate undergoes
prior to releasing, but may be broken by mechanical action. The
implementations of the invention offer a number of possibilities:
[0090] the possibility of carrying out surface treatments (e.g.,
planarization, etc) on the various layers prior to bonding those
layers; [0091] the possibility of carrying out the segregation heat
treatment at different stages of the method: [0092] immediately
after forming the enriched layer (it should be recalled that in the
context of the second implementation, this enriched layer
corresponds to the elemental layer 122); [0093] after the
connecting layer has been finalized and prior to forming the
release layer 11a on the connecting layer (for example after
implanting enrichment material in the first implementation, or
after forming the ensemble of elemental layers in the second
implementation); [0094] after forming the release layer 11a on the
connecting layer; (it is possible to split the segregation heat
treatment into several heat treatment steps carried out at several
of the stages mentioned above--any combination of modes of
implementing the segregation heat treatment steps is possible);
[0095] the possibility of cleaning the surface of the exposed
layers between each step; [0096] the possibility of implementing
different types of techniques to form release layers 11a and 11b of
the desired thickness: [0097] transfer methods--in particular of
the SMART-CUT.RTM. type employing one or more weakening
implantation steps using one or more species, bonding and
detachment at the implanted zone; [0098] in this respect, the layer
11b can be formed: [0099] prior to forming the connecting layer
(and the layer 11b can be formed on a temporary stiffener if its
thickness does not allow it to be treated without a support means);
[0100] or after forming the connecting layer, by transfer onto the
lower face (that facing the bottom of the figures) of the
connecting layer of a substrate weakened by implantation in which
the thin layer bonded to the connecting layer will correspond to
the layer 11b b after detachment of the substrate at the implanted
zone; [0101] the layer 11a which is then formed on the connecting
layer can itself be formed by bonding a substrate weakened by
implantation onto an intermediate structure composed of the layer
11b and the connecting layer, then detachment of the substrate at
the implanted zone to leave on the intermediate structure only the
portion of the implanted substrate corresponding to the layer 11a;
[0102] BESOI type methods employing bonding and removal of material
from the back face (which can be carried out to form the layer 11a
on the already formed connecting layer); [0103] the possibility of
using different materials to produce the first elemental layer 121
and/or the third elemental layer 123 (in the context of the second
implementation): not only SiO.sub.2, but also materials such as
Si.sub.3N.sub.4 can be employed.
[0104] The skilled artisan of course recognizes that the
SMART-CUT.RTM. technique is well known layer transfer technique
that is published in various documents including the article by A.
J. Auberton-Herve et al entitled "Why Can SMART-CUT.RTM. Change the
Future of Microelectronics?", International Journal of High Speed
Electronics and Systems, Vol. 10, no. 1, 2000, pages 131-146.
Generally, this layer transfer technique comprises implantation of
ions in a source substrate to form a weakened zone followed by
bonding of the source substrate to a substrate that is to receive
the layer, followed by detachment of the layer from the source
substrate at the weakened zone to transfer it to the receiving
substrate.
[0105] Also, the term "deposition" as used herein can include
epitaxial growth of a semiconductor material or CVD or other layer
deposition processes.
* * * * *