FR3071662A1 - PROCESS FOR PREPARING A STRUCTURE HAVING A TRANSFERABLE MONOCRYSTALLINE SEMICONDUCTOR MATERIAL LAYER AND STRUCTURE OBTAINED BY SUCH A METHOD - Google Patents

Abstract

A method of making a structure (100) having a layer of transferable monocrystalline semiconductor material (101), comprising the following successive steps: a) providing a support substrate (102) covered by a diffusion barrier layer (103) ), b) forming, on the diffusion barrier layer (103), a stack comprising successively, from the diffusion barrier layer (103): - a tungsten oxide release layer (104), the oxide of tungsten comprising at least 70 at% oxygen, - a layer of thermally insulating amorphous material (105), - a layer of amorphous or polycrystalline semiconductor material (101), c) heating the stack, preferably by laser scanning and, preferably, in the presence of a monocrystalline seed, so as to liquefy the layer of crystalline semiconductor material (101) and, simultaneously, so as to heat the release layer (104) to a temperature knew less than 400 ° C to partially reduce the cohesion and / or adhesion of said release layer (104), d) Cooling of the stack so as to crystallize the layer of semiconductor material (101) in monocrystalline form.

Description

METHOD FOR PREPARING A STRUCTURE HAVING A LAYER OF TRANSFERABLE SINGLE-CRYSTAL SEMICONDUCTOR MATERIAL AND STRUCTURE OBTAINED BY SUCH A METHOD

DESCRIPTION

TECHNICAL AREA AND PRIOR ART

The present invention relates to a method for preparing a structure having a layer of transferable monocrystalline semiconductor material, and to a structure obtained by such a method.

The invention also relates to a method of transferring a layer of monocrystalline semiconductor material with such a structure.

The present invention finds its application in the field of microelectronics, electromechanical microsystems, photovoltaics, low cost electronics or even in the field of biology where it may be advantageous to have layers of crystalline semiconductor material , for example, to produce mass sensors on which living organisms are deposited, such as bacteria or cells.

Conventionally, to obtain a layer of monocrystalline semiconductor material, a polycrystalline or amorphous layer is deposited on the surface of a seed substrate which is then scanned by a localized heat source, such as a laser scan, so to produce the local fusion of the layer then its solidification. The layer is (re) crystallized according to the crystalline information of the germ substrate. This crystallization technique is known under the name ZMR (“Zone Melting Recrystallization”), in the case of a polycrystalline deposited layer or ZMC (“Zone Melting Crystallization”) in the case of an amorphous deposited layer. However, in practice, the layers obtained are not of monocrystalline quality. Indeed, it is difficult to control the crystallization front and the coexistence of liquid and solid zones create an accumulation of stresses leading to the appearance of crystal defects. The layers obtained are, generally, polycrystalline with grains of large sizes distributed in a homogeneous manner.

To obtain better quality layers, the ZMR process has been improved by introducing a monocrystalline seed at the start of scanning to control the crystal orientation of the layer, starting from the seed. In the case of a silicon on insulator type substrate (SOI for “Silicon on Insulator”), the seed can be obtained by making an opening in the layer of amorphous oxide so as to make the crystalline substrate accessible. As described in document US-A-2015191847 or in the article by Kühnapfel et al. ("Towards monocrystalline silicon thin films grown on glass by liquid phase crystallization", Solar Energy Materials & Solar Cells 140, 2015, 86-91), the process can also be carried out on a non-monocrystalline substrate (like glass), the germ then being positioned on the substrate by gluing or pressing. This process can, for example, be carried out to form monocrystalline films, from ΙΟμιτι to ΙΟΟμιτι thick, on a glass substrate, on the front face of a photovoltaic cell. As glass has a low thermal conductivity, the heat provided by the laser remains confined, preserving the structure underlying the substrate. However, this method cannot be applied to CMOS type substrates or flexible substrates, for example made of polymer, since these do not withstand high temperatures (typically at temperatures above 400 ° C, or even above 200 ° VS).

It is therefore necessary to carry out the crystallization on a first support substrate, resistant to high temperatures, then to transfer the monocrystalline layer to the receiving substrate.

In document US-A-5397713, the layer of semiconductor material is crystallized on a support substrate containing a graphite film. Graphite is a material resistant to high temperatures and having low energy cleavage planes. After crystallization, a receiving substrate is fixed on the monocrystalline layer, then by applying mechanical stress, the graphite film is broken, along the cleavage planes, releasing the receiving substrate and the monocrystalline layer from the support substrate. However, it can be difficult to produce a graphite film over a large area while controlling its crystallographic orientation and its roughness, and therefore to produce monocrystalline layers of thin thickness and of good quality.

It is also possible, as described in document US-A2012074526, to produce a layer heavily doped with volatile impurities (arsenic or antimony for example) under the layer of semiconductor material to be crystallized. When the layer of semiconductor material is crystallized by laser scanning, the doped layer is liquefied and the impurities escape from the liquid layer. During cooling, the impurities precipitate locally creating zones of crystalline defects, which weakens the structure. A receiving substrate is then bonded to the crystallized layer, and the application of mechanical stress makes it possible to separate the crystallized layer from the rest of the support substrate at the level of the weakened zone. However, in this process, two liquid phases (the layer of semiconductor material and the doped layer) are produced simultaneously under laser irradiation, which makes the structure unstable and more difficult to control, which can lead to the formation of defects within the layer of crystalline semiconductor material.

STATEMENT OF THE INVENTION

It is, therefore, an object of the present invention to provide a process for producing a structure, having a layer of transferable monocrystalline semiconductor material, easy to implement and leading to a good quality crystal structure.

The aim stated above is achieved by a process for producing a structure having a layer of transferable monocrystalline semiconductor material, comprising the following successive steps:

a) Supply of a support substrate covered by a diffusion barrier layer,

b) Formation, on the diffusion barrier layer, of a stack comprising successively, from the diffusion barrier layer:

a tungsten oxide release layer, the tungsten oxide comprising at least 70 atomic% of oxygen, a layer of a thermally insulating amorphous material, a layer of a semiconductor, amorphous or polycrystalline material,

c) Heating of the stack, preferably by laser scanning and, preferably, in the presence of a monocrystalline seed, so as to liquefy the layer of semiconductor material, and, simultaneously, so as to heat the release layer at a temperature above 400 ° C to partially reduce the cohesion and / or the adhesion of said detachment layer,

d) Cooling of the stack so as to crystallize the layer of semiconductor material, amorphous or polycrystalline, in monocrystalline form.

By crystallization is meant, here and thereafter, the recrystallization of a polycrystalline deposited layer or the crystallization of an amorphous deposited layer leading to a layer of monocrystalline semiconductor material.

By layer of monocrystalline material is meant that at least 80% of the layer is in monocrystalline form, preferably at least 90% and even more preferably at least 95%.

By transferable layer, it is meant that the layer can be detached from a first substrate (support substrate) and transferred to a second said substrate of interest (receiving substrate).

By tungsten oxide is meant an oxide of general formula WO _X (with x the stoichiometry index of the oxide, whole or not whole), such as, for example, WO ₃ and WO ₃ , ₅ . We will choose x such that x> 7/3.

The heating is carried out so as to reach, at the level of the layer of semiconductor material, a temperature higher than the melting temperature of the semi-crystalline material, that is to say, for example, at a temperature higher than 1414 ° C for silicon and at a temperature higher than 938 ° C for germanium.

The method differs from the prior art basically in that it implements a tungsten oxide layer having a particular stoichiometry.

The supply of energy necessary for the crystallization process leads to an increase in temperature at the detachment layer. During step c), the temperature of the detachment layer is locally greater than 400 ° C., and preferably greater than or equal to 500 ° C., for example from 500 ° C. to 700 ° C. It has surprisingly been demonstrated that, when a layer of tungsten oxide having at least 70 atomic% of oxygen is heated to such temperatures, defects appear in the layer, and the latter partially loses its adhesion and cohesion properties.

After the heat treatment of step c) necessary for crystallization, the tungsten oxide layer loses from 20% to 80%, preferably from 30% to 60%, even more preferably from 30% to 50%, its properties. of cohesion and / or adhesion.

The detachment layer of tungsten oxide, after the heat treatment, has for example a bonding energy of less than 1000 mJ / m ² , and preferably less than or equal to 700 mJ / m ² and, even more preferably, less than or equal to 500 mJ / m ² .

The release layer nevertheless remains sufficiently cohesive and / or adhesive to hold the upper part of the structure (the thermally insulating amorphous layer, the layer of semiconductor material, and possibly the substrate of interest) with the lower part of the structure (the support substrate, the barrier layer).

The poor mechanical strength of the tungsten layer after the heat treatment facilitates the subsequent detachment of the monocrystalline layer from the support substrate. By applying mechanical stress to the weakened detachment layer, it is then easy to separate the upper part from the lower part of the structure,

Advantageously, the tungsten oxide comprises from 70% to 90 atomic% of oxygen, preferably from 75% to 90% and even more preferably from 80% to 90%.

Advantageously, the release layer has a thickness ranging from 2 to 100 nm, preferably from 5 nm to 50 nm, and even more preferably from 10 nm to 50 nm.

Advantageously, the tungsten oxide layer is deposited by spraying. This technique makes it possible to obtain layers of low roughness (less than 1 nm RMS), which makes it possible to interfere less with the formation of the monocrystalline layer during crystallization, but also to better control the stoichiometry of tungsten oxide.

The layer of thermally insulating amorphous material prevents the melting of the tungsten oxide layer, in particular in the case of the crystallization of a silicon layer which requires a high energy supply, while allowing sufficient energy to pass locally a temperature such that the layer loses part of its adhesion properties.

Advantageously, the layer of thermally insulating amorphous material is made of oxide, preferably of silicon oxide. The oxide layers have high melting temperatures (for example, higher than 1600 ° C. for silicon oxide) and are particularly suitable for the temperatures involved during crystallization.

Advantageously, the thermally insulating amorphous layer has a thickness ranging from 500 nm to 15 pm, preferably from 1 pm to 10 pm.

The diffusion barrier layer makes it possible to physically separate the materials from the substrate and the release layer, and to avoid the diffusion of the constituent elements of the support substrate towards the tungsten layer.

Advantageously, the diffusion barrier layer is made of metallic nitride, preferably of silicon nitride. By metallic nitride is meant a metal nitride or a metalloid nitride such as silicon.

Advantageously, the diffusion barrier layer has a thickness ranging from 5 nm to 100 nm, preferably from 5 nm to 50 nm. A thin layer will be less rough and will interfere less during crystallization. Such thicknesses are conducive to the retention of impurities liable to diffuse.

Advantageously, the support substrate is made of glass, which makes it possible to carry out the process on an industrial scale while reducing the development costs.

Advantageously, the semiconductor material is silicon or germanium.

The method according to the invention can be carried out on large surfaces. Currently, the size of monocrystalline films is limited by the diameter of the ingots (typically 200mm or 300mm in diameter, for growth of the Czochralski type). It is possible here to work with plates of several square meters (panes) and to form a monocrystalline layer of large surface.

The stack and the underlying elements are capable of supporting the thermal budget of a ZMR or ZMC type crystallization process.

The invention also relates to a structure having a layer of transferable crystalline semiconductor material successively comprising, and preferably consisting of:

- a support substrate,

- a diffusion barrier layer,

a tungsten oxide release layer, the tungsten oxide comprising at least 70 atomic% of oxygen,

- a layer of thermally insulating amorphous material,

- a layer of monocrystalline semiconductor material.

The substrate and the various preferred layers have been described above.

Advantageously, the structure successively comprises, and preferably consists of:

- a glass support substrate,

a diffusion barrier layer of oxide, preferably of SiO ₂ ,

a tungsten oxide release layer, the tungsten oxide comprising at least 70 atomic% of oxygen,

a layer of metallic nitride, preferably of silicon nitride,

- a layer of monocrystalline silicon or monocrystalline germanium.

The structure of the invention differs fundamentally from the prior art by the presence of the tungsten oxide release layer which allows the transfer of a part of the structure, and more particularly the transfer of the layer of semi-material. crystalline conductor, on a substrate of interest.

The invention also relates to a method for transferring a layer of crystalline semiconductor material from the structure as defined above, comprising the following steps:

fixing one or more receiving substrates to the layer of monocrystalline semiconductor material of the structure,

- application of mechanical stress so as to detach the tungsten oxide release layer from the layer of the diffusion barrier layer and to transfer the layer of monocrystalline semiconductor material to the receiving substrate.

Advantageously, the receiving substrate or substrates are chosen from a CMOS type substrate or a layer of polymer, for example adhesive.

The layer of semiconductor material is crystallized on the support substrate, resistant to temperatures, then it is transferred to the substrate of interest (receiving substrate). The substrate of interest can be of any type, for example flexible, made of polymer, and / or contain electronic components sensitive to temperature. If the receiving substrate (for the intended application) is smaller in size than that of the crystallized layer, then it is possible to obtain several film transfers from a single crystallization scan.

Advantageously, after the transfer of the layer of crystalline semiconductor material onto the receiving substrate, the support substrate covered with the diffusion barrier layer is reused in a process for preparing a structure having a layer of of crystalline semiconductor material such as previously defined. As the crystalline film is detached from the support substrate, it is possible to recycle and reuse this substrate, which reduces preparation costs.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be better understood on the basis of the description which follows and of the appended drawings in which:

FIG. 1 is a schematic view, in section and in profile, of a structure having a layer of transferable crystalline semiconductor material according to a first embodiment of the invention,

FIG. 2 is a schematic representation of a step in the process for preparing a structure having a layer of transferable crystalline semiconductor material according to a particular embodiment of the invention,

FIG. 3 is a schematic view, in section and in profile, of a structure having a layer of transferable crystalline semiconductor material on which a substrate of interest has been fixed according to a particular embodiment of the invention,

FIG. 4 is a schematic view, in section and in profile, of a structure having a layer of transferable crystalline semiconductor material on which several substrates of interest have been fixed according to a particular embodiment of the invention,

FIG. 5 schematically represents a step in the process for transferring a layer of crystalline semiconductor material, according to a particular embodiment of the invention,

FIG. 6 schematically represents a step in the process for transferring a layer of crystalline semiconductor material, according to a particular embodiment of the invention,

FIG. 7 schematically represents, in section and in profile, a layer of crystalline semiconductor material transferred onto a receiving substrate, according to a particular embodiment of the invention,

- Figure 8 shows schematically, in section and in profile, a layer of crystalline semiconductor material transferred to a receiving substrate, according to a particular embodiment.

The different parts shown in the figures are not necessarily shown on a uniform scale, to make the figures more readable.

The different possibilities (variants and embodiments) must be understood as not being mutually exclusive and capable of being combined with one another.

DETAILED PRESENTATION OF PARTICULAR EMBODIMENTS

Structure 100:

First of all, reference is made to FIG. 1 which represents a structure 100 having a layer of transferable crystalline semiconductor material 101. The structure 100 successively comprises:

a support substrate 102,

- a diffusion barrier layer 103,

a detachment layer 104 of tungsten oxide, the tungsten oxide comprising at least 70 atomic% of oxygen,

a layer of thermally insulating amorphous material 105,

- a layer of monocrystalline semiconductor material 101.

Support substrate 102:

The support substrate 102 is a mechanical support for producing the layer of crystalline semiconductor material 101.

The support substrate 102 advantageously has a coefficient of thermal conductivity less than 200W / m.K to limit the loss of heat in the substrate. We will use, for example, a support substrate 102 having a coefficient of thermal conductivity of the order of 150W / m.K, such as silicon or ceramic. This embodiment will be particularly advantageous in the case of the crystallization of a germanium layer.

According to a variant, a very good thermal insulator will be used, for example, a material having a coefficient of thermal conductivity of the order of 1-2

W / m.K, such as glass. This embodiment will be particularly advantageous in the case of the crystallization of a silicon layer.

Preferably, a support substrate 102 made of glass will be used because this material resists well in temperature, and makes it possible to reduce the costs of developing the process. Large surface glass substrates can be used.

The support substrate 102 has a thickness of several tens of micrometers to a few millimeters. We will use, for example, a substrate having a thickness ranging from 80μιτι to 2mm, and preferably from 500μιτι to ΙΟΟΟμιτι.

The layer of monocrystalline semiconductor material 101:

The semiconductor material is silicon or germanium.

The layer of semiconductor material 101 has a thickness ranging from 10 nm to 10 μm. It could also have greater thicknesses, such as 50pm. Thicknesses less than or equal to 10 μm will be preferred, in particular for the production of MEMS.

The tungsten oxide release layer 104:

The layer 101 of crystalline semiconductor material is transferable thanks to the presence of the detachment layer 104. The detachment layer 104 is of tungsten oxide WO _X , preferably with 3 <x <4.

Tungsten oxide comprising at least 70 atomic% of oxygen. Preferably, the tungsten oxide comprises from 70% to 90 atomic% of oxygen, even more preferably from 75% to 90% and even more preferably from 80% to 90%.

Preferably, the tungsten oxide is WO ₃ . For example, it is the monoclinic or quadratic form of WO ₃ . The release layer 104 has a thickness ranging from 2 nm to 100 nm, preferably from 5 nm to 50 nm, and even more preferably from 10 nm to 50 nm.

Advantageously, the roughness of such a tungsten oxide layer is low (typically less than 1 nm RMS, preferably less than 0.5 nm).

The layer 104 of tungsten oxide is surrounded on both sides by a diffusion barrier layer 103 and by a thermally insulating amorphous layer 105.

The diffusion barrier layer 103:

The diffusion barrier layer 103 prevents contamination of the tungsten oxide layer by the chemical elements contained in the support substrate. For example, in the case of a glass support substrate, the diffusion barrier layer prevents contamination by chlorides.

The diffusion barrier layer 103 is preferably made of metallic nitride. It may be made of a metalloid nitride, such as a silicon nitride, or of a metallic nitride, such as tungsten nitride.

It has a thickness ranging from 5 nm to 100 nm, preferably from 5 nm to 50 nm.

The layer of thermally insulating amorphous material 105:

The layer of thermally insulating amorphous material 105 prevents any interference between the layer of semiconductor material 101 and the release layer 104 during crystallization. It is, for example, a layer of metal oxide. It is, for example, alumina or silicon oxide SiO ₂ .

The layer of thermally insulating amorphous material 105 has, for example, a conductivity less than 30W / m.K, preferably less than 10 and even more preferably less than 2.

The thermally insulating amorphous layer 105 has a thickness ranging from 500 nm to 15 μιτι, preferably from Ιμιτι to ΙΟμιτι, for example of the order of 5 μιτι. A sufficient thickness will be chosen to control the thermal budget applied to the detachment layer 104. This makes it possible to confine the heat supply and thus to control the phase change of the tungsten oxide. During laser scanning, the part of the tungsten oxide, ahead of the laser beam (upstream of the laser beam), cannot change phase because the heat supply is not sufficient. Thus when the beam reaches a point of the layer of semiconductor material to be crystallized, the part of the layer of underlying tungsten oxide has not yet changed phase. The phase change of tungsten oxide takes place only when it is under the laser beam.

This thermally insulating layer 105 also plays, advantageously, the role of barrier layer. It prevents contamination of the layer to be crystallized by tungsten, especially during crystallization.

For example, the structure 100 successively comprises, and preferably consists of:

a support substrate 102 made of glass,

a diffusion barrier layer 103 of oxide, preferably of S1O2,

a tungsten oxide detachment layer 104, the tungsten oxide comprising at least 70 atomic% of oxygen,

a layer of thermally insulating amorphous material 105 made of metal nitride, preferably silicon nitride,

a layer 101 of crystalline silicon or of crystalline germanium.

The process for producing the structure 100:

The method of producing a structure 100 having a layer of crystalline semiconductor material 101, as defined above, will now be described. The process includes the following successive steps:

supply of a support substrate 101 covered by a diffusion barrier layer 103,

formation of a stack on the diffusion layer by a stack comprising, successively, from the diffusion barrier layer 103:

a detachment layer 104 of tungsten oxide, a layer of thermally insulating amorphous material 105, a layer of semiconductor material 101, amorphous or polycrystalline,

- local supply of energy to the stack so as to heat it; the heating leads to the melting of the layer of semiconductor material 101 and at the same time to the embrittlement (reduction in the bonding energy in particular) of the detachment layer 104,

- cooling the stack so as to crystallize the layer of semiconductor material 101, which was initially in amorphous or polycrystalline form, in monocrystalline form.

The different layers of the structure, and in particular the diffusion barrier layer 103, the thermally insulating amorphous layer 105, as well as the layer of semiconductor material 101 will be produced by any conventional technique of microelectronics adapted and chosen by those skilled in the art. job. It can be, for example, chemical phase deposition (or CVD for "Chemical Vapor Deposition"), physical vapor deposition (or PVD for "Physical Vapor Deposition"), by chemical vapor deposition assisted by plasma (or PECVD for “Plasma-Enhanced Chemical Vapor Déposition”), etc.

The crystallization is preferably carried out under laser irradiation. It can be carried out for a period of approximately one minute for a local temperature on the layer of semiconductor material of 1400 ° C. or for 15 minutes for a temperature of 700 ° C.

Preferably, as shown in FIG. 2, to achieve crystallization, a monocrystalline seed can be placed in contact with the layer of semiconductor material 101. During step b), the laser scanning is carried out from the interface between the seed and the layer of semiconductor material towards the layer of semiconductor material so as to give the crystalline orientation of the seed to said layer during its crystallization. The crystallization process described in document USA-2015191847 is incorporated herein by reference.

The tungsten oxide layer 104 is preferably deposited by spraying a tungsten target using a plasma composed of a mixture of Ar and O ₂ ("reactive-PVD"), preferably at room temperature. The dioxygen will react with the pulverized tungsten and lead to the deposition of an oxidized phase, the stoichiometry of which depends on the partial pressure of oxygen. A layer obtained with such a deposition technique advantageously has a low roughness.

The tungsten oxide layer 104 is cohesive and adhesive after deposition and at room temperature.

When the tungsten oxide layer, having more than 70 atomic% of oxide, is heated above a certain temperature (for example above 400 ° C., and preferably at least 500 ° C.), defects appear in the layer, which makes it more fragile while retaining sufficient cohesion and adhesion to hold the upper layers of the structure in place. The thermal budget for crystallization is sufficient to reveal these defects. Preferably, the tungsten oxide layer is heated to a temperature below 700 ° C.

This drop in adhesion and cohesion is sufficient to allow the subsequent detachment of this layer by applying mechanical stress ("peel-off"). The detachment layer 104 remains, however, sufficiently coherent and solid to hold the crystallized layer 101, and prevent it from breaking or wrinkling (due to internal or thermal stresses).

For example, for a tungsten oxide layer 104 containing 75 atomic% of oxygen, a heat treatment at 500 ° C. leads to a bonding energy of approximately 600 mJ / m ² while the bonding energy is 1100mJ / m2 for heat treatment at 400 ° C. The bonding energy measurements were carried out using the DCB “Double Cantilever Beam” technique.

Transfer of the layer of monocrystalline semiconductor material 101 onto a substrate of interest 200:

One or more receiving substrates 200 can be fixed on the layer of crystalline semiconductor material 101 in order to be able to transfer it (FIGS. 3, 4 and 5). The receiving substrate 200 is the substrate of interest, that is to say the substrate on which it is desired to transfer, transfer the layer of crystalline semiconductor material. The receiving substrate 200 can be of any type. It can be a CMOS type substrate or a polymer layer. The polymer layer can be, for example, polyimide or polymethyl methacrylate. The receiving substrate 200 can be adhesive.

The receiving substrate 200 may have a surface similar to that of the layer of semi-crystalline material or of smaller size. Advantageously, as shown in FIGS. 4 and 5, several receiving substrates can be positioned, fixed, glued on the same crystallized layer 101. This process is particularly advantageous since several receiving substrates can be fixed on the same support substrate 102, which reduces considerably the development costs and makes the process industrializable on a large scale.

Once the receiving substrate 200 is fixed, mechanical stress is applied so as to detach the tungsten oxide release layer 104 from the diffusion barrier layer 103, and to transfer the layer of crystalline semiconductor material 101 to the receiver substrate 200 ( figure 6).

The process for transferring the crystallized layer 101 is ideally carried out, after crystallization, cold and mechanically, by fixing (for example by gluing) the receiving substrate 200 to the crystallized layer 101. Finishing treatments can be carried out on the crystallized layer 101 before fixing the receiving substrate 200.

By way of illustration, FIG. 7 represents a monocrystalline layer 101 transferred onto a receiving substrate 200 formed of a solid support 201, covered with several transistors 202 and metallic interconnection 203. A bonding interface 204 is present in contact with the layer monocrystalline 101. After transfer, the monocrystalline layer 101 is covered with the thermally insulating layer 105 and with part of the tungsten oxide layer 104.

The surface of the monocrystalline layer 101 can be cleaned for example with selective wet etching to remove the tungsten oxide residues and, optionally, the amorphous layer 105 (FIG. 8).

The tungsten oxide residues can be removed with any suitable solution, conventionally used in the field of microelectronics, such as for example a NH ₄ OH: H ₂ O ₂ mixture.

The support substrate 102 covered by the diffusion barrier layer 103 can be recycled, and used to produce a new structure. Selective wet etching can, if necessary, be carried out to remove the tungsten oxide residues present before a new use.

Illustrative and nonlimiting examples of a process for producing a structure having a layer of transferable crystalline semiconductor material and transfer of said layer:

Different structures 100 have been produced. In the first structure, the support substrate 102 is a 700 μm thick glass substrate sold by the company Eagle XG. On this support substrate 102 are successively deposited:

a layer 103 of SiN 50nm thick by PECVD, a layer 104 of WO _X 4nm thick by "reactive PVD", the oxide comprises approximately 78 atomic% of oxygen. The layer was produced at a ratio R of 25% with R defined by the ratio of the oxygen flow rate to the sum of the oxygen flow rate and the argon flow rate, a layer 105 of SiO2 5 μm thick by PECVD, a layer of amorphous silicon 1 μm thick by PECVD.

A monocrystalline seed is then introduced at the level of the amorphous silicon layer. A laser scan is then carried out so as to crystallize the silicon layer 101 and to degrade by introducing defects in the tungsten oxide layer 104.

During laser scanning, the temperature at the amorphous silicon layer is 1400 ° C. The tungsten oxide layer 104 protected by the thermally insulating layer 105 is at a temperature of 1200 ° C. under the laser beam. The heat diffuses in a reasonable manner in the layer of tungsten oxide 104. The layer of tungsten oxide 104 is for example at 700 ° C. before the crystallization front. In other words, the crystallization front is ahead of the phase change front of the tungsten, which avoids the formation of defects, the appearance of local detachments of the tungsten layer at the part of the non-crystallized layer. The crystallization is thus of better quality.

In the second structure, the support substrate 102 is made of silicon and has a thickness of 500 μιτι. On this support substrate 102 are successively deposited:

- a layer 103 of SiN 50nm thick by PECVD,

- A layer 104 of WO _{X 4} nm thick by "reactive PVD", the oxide comprises approximately 78 atomic% of oxygen. The layer was produced at a ratio R of 25% with R defined by the ratio of the oxygen flow rate to the sum of the oxygen flow rate and the argon flow rate,

a layer 105 of SiO ₂ more than 5 μm thick by PECVD,

- a layer of amorphous germanium Ιμιτι thick by PECVD

A monocrystalline germ of germanium is then introduced at the level of the layer of amorphous germanium. A laser scan is then carried out so as to crystallize the germanium layer 101 and to introduce defects into the tungsten oxide layer 104.

A flexible adhesive film 200 is then positioned on each structure

100 of the two examples. Mechanical peeling is carried out to separate the crystalline layer of silicon or germanium 101 from the support substrate 102. The crystalline layer

101 has been transferred to the adhesive film 200 without being broken.

Claims (15)

1. Method for preparing a structure (100) having a transferable layer of monocrystalline semiconductor material (101), comprising the following successive steps: a) Supply of a support substrate (102) covered by a diffusion barrier layer (103), b) Formation, on the diffusion barrier layer (103), of a stack comprising successively, from the diffusion barrier layer (103): - a tungsten oxide release layer (104), the tungsten oxide comprising at least 70 atomic% of oxygen, - a layer of a thermally insulating amorphous material (105), - a layer of a semiconductor material (101), amorphous or polycrystalline, c) Heating the stack, preferably by laser scanning and, preferably, in the presence of a monocrystalline seed, so as to liquefy the layer of crystalline semiconductor material (101) and, simultaneously, so as to heat the detachment layer (104) at a temperature above 400 ° C to partially decrease the cohesion and / or adhesion of said detachment layer (104), d) Cooling of the stack so as to crystallize the layer of semiconductor material, amorphous or polycrystalline, in monocrystalline form. 2. Method according to claim 1, characterized in that the tungsten oxide comprises from 70% to 90 atomic% of oxygen, preferably from 75% to 90% and even more preferably from 80% to 90%. 3. Method according to one of claims 1 and 2, characterized in that the release layer (104) has a thickness ranging from 2 to 100 nm, preferably from 5 nm to 50 nm, and even more preferably from 10 nm to 50 nm. 4. Method according to any one of claims 1 to 3, characterized in that the tungsten oxide layer (104) is deposited by spraying. 5. Method according to any one of claims 1 to 4, characterized in that the layer of thermally insulating amorphous material (105) is of oxide, preferably of silicon oxide. 6. Method according to any one of the preceding claims, characterized in that the thermally insulating amorphous layer (105) has a thickness ranging from 500 nm to 15 pm, preferably from lpm to 10 pm. 7. Method according to any one of the preceding claims, characterized in that the diffusion barrier layer (103) is made of metallic nitride, preferably of silicon nitride. 8. Method according to any one of the preceding claims, characterized in that the diffusion barrier layer (103) has a thickness ranging from 5 nm to 100 nm, preferably from 5 nm to 50 nm. 9. Method according to any one of the preceding claims, characterized in that the support substrate (102) is made of glass. 10. Method according to any one of the preceding claims, characterized in that the semiconductor material is silicon or germanium. 11. Structure (100) having a layer of transferable crystalline semiconductor material (101), obtained according to the method defined in any one of claims 1 to 10, successively comprising, and preferably consisting of: - a support substrate (102), - a diffusion barrier layer (103), - a tungsten oxide release layer (104), the tungsten oxide comprising at least 70 atomic% of oxygen, - a layer of thermally insulating amorphous material (105), - A layer of monocrystalline semiconductor material (101). 12. Structure according to claim 11, characterized in that the structure (100) successively comprises, and preferably consists of: - a support substrate (102) made of glass, a diffusion barrier layer (103) of oxide, preferably of SiO ₂ , - a tungsten oxide release layer (104), the tungsten oxide comprising at least 70 atomic% of oxygen, a layer (105) of metallic nitride, preferably of silicon nitride, - A layer (101) of monocrystalline silicon or of monocrystalline germanium. 13. Method for transferring a layer of crystalline semiconductor material (101) from the structure (100) as defined in any one of claims 11 and 12, comprising the following steps: fixing one or more receiving substrates (200) to the layer of crystalline semiconductor material (101) of the structure (100), - application of mechanical stress so as to detach the tungsten oxide release layer (104) from the layer of the diffusion barrier layer (103) and to transfer the layer of crystalline semiconductor material (101) to the receiving substrate (200). 14. Method according to claim 13, characterized in that the receiving substrate (s) (200) are chosen from a CMOS type substrate or a polymer layer, for example adhesive. 15. Transfer method according to one of claims 13 and 14, characterized in that, after the transfer of the layer of crystalline semiconductor material (101) on the receiving substrate (200), the support substrate (102) covered of the diffusion barrier layer (103) is reused in a process for preparing a structure (100) having a layer of transferable crystalline semiconductor material (101) as defined in one of claims 1 to 10 .