Field of the Invention

The present invention relates to a process for modifying a substrate. In particular, the present invention provides processes for joining and separating semiconductor layers and substrates, useful for example for forming three-dimensionally stacked "system-on-chip" devices, or for transferring optoelectronic & (photo)voltaic elements. Materials of layers may for example be chosen among the IV group materials (Si, Ge...), the III/V group materials (GaN, InGaN, InGaAs..) and the materials can be polar, non polar or semi-polar according to the application. In certain embodiments the invention provides a method facilitating the removal of intermediate substrates that may be necessary for manufacturing certain semiconductor electronic devices. The invention further provides a method for facilitating access to "front" and "back" faces of semiconductor layers, which is of general importance and, in certain embodiments the invention, may be applied to the manufacture of devices containing layers of IH-N materials.

Background to the Invention

In the field of semiconductor manufacture, it is often useful or necessary in practice to join and/or remove films and/or layers of semiconducting and/or insulating material. On the one hand it may be desired to prepare final stacked structures containing a three-dimensional design of electronic, photovoltaic and/or optoelectronic elements. On the other hand, thin films of high purity material and high crystalline quality may be appropriately handled on support substrates, and it is necessary to dispose of effective means for transferring the active substrates from initial to final support substrates. Some kinds of semiconducting materials may not be available as bulk or free-standing substrates and must be handled on support substrates, despite problems of lattice mismatch and/or thermal expansion coefficient that may arise. Methods are needed for removal of the functionalized semiconducting material layer from its support. In the area of functionalized semiconductor layers such as silicon layers for example, it is useful to have available a method enabling layer transfer. The functionalization of such semiconductor layers may involve electronic circuits, photovoltaic elements (containing, for example, a Ge seed layer, and a triple junction active layer), and/or optoelectronic elements. [Being able to expose, manipulate and bond with relative ease both "front" and "back" faces of semiconductor layers enables functional elements to be introduced when the semiconductor layer treated is on a supporting substrate which allows a certain type of functional modification, and those functional elements to be occluded and then re- exposed as later required. Thus, electronic circuits may be introduced on one face of a thin layer on an initial support substrate favourable for this functionalization step, and then the exposed and functionalized "front" surface may be bonded to an intermediate substrate. The removal of the initial substrate support enables other circuits to be prepared on the "back" face of the functionalized thin layer. The exposed ^λΛ back" face may be further transferred, for example to a support adapted to the operation of the functionalized centres created, for example for heat dissipation.

Furthermore, the group III-V materials such as InGaAs, InP or InAIAs are very useful for solar cell applications and Ill-nitride materials such as GaN, AIGaN or InGaN are of considerable interest in the semiconductor industry for use in light-emitting devices such as light-emitting diodes, laser diodes and related devices. GaN is a promising material for optoelectronic applications as well as for high frequency, high power electronic devices. It is important to be able to provide GaN or InGaN layers showing a low amount of crystal defects and a high quality surface. It is of interest in these areas of technology to dispose of methods enabling IH-V and IH-N materials to be provided on a variety of surfaces and support materials. In techniques in which the III-V material is grown by epitaxy on a substrate surface, a high crystalline quality and appropriate lattice parameters of the growth substrate are necessary to enable sufficient quality IH-V growth, restricting the choice of underlying seed support substrates for the III-V material.

In systems where it is foreseen to access the III-V layer by etching techniques, this may prove problematic and lead to degradation of the III- V material.

It is also of interest to be able to expose particular faces of IH-N substrates. In effect, it is common for polar c-plane IH-N material to have a specific atom surface termination such that one surface is terminated by the element from group III and the other surface is terminated by nitrogen atoms.

Summary of the Invention

With a view to solving the problems set out above, the present invention proposes a process for modifying a substrate (10) comprising: (a) providing an initial substrate (10) having a face (10b) for bonding and an opposing face (lOr);

(b) providing a support substrate (25); wherein either the bonding face (10b) of the initial substrate (10), or a face of the support substrate (25), is provided with an electromagnetic radiation absorbing layer (24), wherein the support substrate (25) is substantially transparent to a wavelength of electromagnetic radiation (10);

(c) performing bonding to join the bonding face (10b) of the initial substrate (10) to the support substrate (25) via the electromagnetic radiation absorbing layer (24); and (e) carrying out Irradiation of the electromagnetic radiation absorbing layer (24) through the substantially transparent support substrate (25) to induce separation of the support substrate (25).

The present invention proposes a process for modifying a substrate (10) comprising:

(a) providing a substrate comprising a. support substrate (25) substantially transparent to a wavelength of electromagnetic radiation; b. a layer (aa) bonded to the support substrate (25); and c. an electromagnetic radiation absorbing layer (24) in- between the support substrate and the layer (aa);

(b) carrying out irradiation of the electromagnetic radiation absorbing layer (24) through the substantially transparent support substrate (25) to induce separation of the support substrate (25).

Brief Description of Figures

Figure 1 represents a schematic view of the general process of the invention. Figure 2 represents a schematic view of an example process of the invention in which a part of initial substrate (10) is removed to form a new layer (aa).

Figures 3 and 4 represent schematic views of example processes of the invention in which, respectively, the layer (aa) is functionalized to produce a layer (aa)', and/or further layers are bonded to the layer (aa).

Figure 5 is a schematic view of an example process of the invention in which ion implantation is used as well as bonding to a final substrate.

Figure 6 is a schematic view of a further example process of the invention in which ion implantation is used as well as bonding to a final substrate. Detailed Description of the Invention

Figure 1 represents a schematic view of the general process of the invention. As shown in Figure 1, the invention combines both a bonding step

(Sl in Figure 1) and a step of irradiation (S2) of the bonded entity with electromagnetic radiation, such as visible light and/or ultraviolet radiation.

The bonding of layers may involve molecular, eutectic, hot, pressured or anodic bonding. As an example, bonding may be achieved using one or more oxide bonding layers (not shown in Figure 1), that may be added to one or both of the faces of substrates being bonded. An appropriate example of a material for an oxide bonding layer is silicon dioxide (SiCb). Silicon dioxide materials for bonding purposes may be provided in layers thermally or by chemical vapour chemical deposition techniques such as LPCVD or PECVD.

Concerning the electromagnetic radiation absorbing layer (24), the composition of this layer is chosen in such a way as to absorb electromagnetic radiation emitted by a source such as a laser at a chosen wavelength and allow the separation of bonded entity under the effect of the energy absorbed. Thus, in general, in the process for modifying a substrate (10) in the present invention, the separation of the support substrate (25) of step e) is due to chemical and/or physical changes in the electromagnetic radiation absorbing layer (24).

By "separation of the bonded entity" it is meant that the binding energy of each element forming the bonded entity is weaker after the application of the electromagnetic radiation than before. The actual detachment of the elements from each other, if this result is indeed desired, may require application of additional energy such as mechanical efforts. According to the nature of the absorbing layer, the energy absorbed will give rise to different effects, for example atomic level vibration, sublimation, specific diffusion or formation of a gas, which in itself leads to separation, as defined above, or chemical reactions. Mechanisms involving purely thermal effects as well as photochemistry can thus be behind the separation mechanism.

In the process of the present invention, the absorbing layer (24) may appropriately comprise at least one material selected from the group consisting of: Si _x Ny : H, Si3N ₄ , Si _x Ny, GaN, AIN, InN, or mixed nitrides of one or more of In, Ga and Al or poly Si, amorphous Si (H rich) or crystalline Si. In a variant, several absorbing layers (24) may be introduced and buried in the bonding layer so that several irradiations for several subsequent separations may be performed.

Laser irradiation is preferably carried out in the framework of the present invention across the support substrate (25). The latter support substrate (25) must therefore be substantially transparent to the wavelength of visible light and/or ultraviolet radiation being used to effect the separation mechanism, that is the material of the support substrate has a weak optical absorption coefficient at the wavelength used, for example less than about 10 ¹ cm ^"1 , or has a forbidden optical band which is larger than that of the material of the absorbing layer (24). The absorbing layer (24) may appropriately be a material of the type Si _x N _y :H, Si ₃ N ₄ in amorphous form, Si _x Ny, or a IH-N material deposited for example in a polycrystalline form (the latter being less expensive in an industrial context than a monocrystalline form). These materials enable irradiation to be carried out at a wavelength that remains above the absorption wavelength of typical support materials. Another appropriate possibility within the present invention is to use a HI-N material as the layer (24) absorbing electromagnetic radiation such as visible light and/or ultraviolet radiation. If a substrate such as initial substrate (10) is itself a HI-N material which is to be processed so as to introduce functionalities, the use of the same IH-N material layer as an absorbing layer (24) will preferably be carried out with the two HI-N layers (functionalized layer and sacrificial electromagnetic radiation absorbing layer) being separated by a bonding layer, such as a silicon dioxide bonding layer. Among IH-N materials which can be used as absorbing layers, one may cite GaN (with a wavelength of absorption below 360 nm in view of the forbidden band of 3.4 eV), AIN (below 198 nm in view of the forbidden band of 6.2 eV), InN (below 230 nm in view of the forbidden band at 0.7 eV). A Nd/YAG or excimer laser may be used to induce decomposition or other effects of such an electromagnetic radiation absorbing layer (24) that could lead to separation.

Ternary or quaternary nitride materials combining aluminium, gallium and indium may also be used as materials for an electromagnetic radiation absorbing layer (24), for example AIGaN or InGaN. These nitride materials are particularly useful because they seem to decompose with production of gaseous nitrogen. Their forbidden band defines a clear threshold of wavelength absorption, at which point the materials show a transition from almost complete transparency to almost complete absorption. Furthermore, their melting point is much higher than the temperature at which they decompose and they give rise to minimum collateral damage to the surrounding substrate when melting.

In order to enable the separation mechanism to operate, it is necessary that support substrate (25) be substantially transparent or has a high transmittance to the electromagnetic radiation such as ultraviolet and/or visible light in the wavelength region which will be used to irradiate the absorbing layer (24). The preferred minimum thickness of the absorbing layer (24) is 10 nm. When depositing the absorbing layer, care is taken to avoid forming layer(s) on both sides of the support substrate. Indeed an absorbing layer also formed on the back side of the support substrate may completely absorb irradiation, interfere with the absorption of the buried absorbing layer (24) and may block the separation step.

The use of sapphire (AI ₂ O ₃ ) is an appropriate choice for support substrate (25), because high transmittance is observed at wavelengths higher than 350 nm which corresponds to commonly used laser sources. Sapphire is also appropriate for shorter wavelengths. Other appropriate choices for support substrate (25) include materials made of at least one of the following species: LiTaO ₃ (substantially transparent at wavelengths higher than 270 nm), LiNbO ₃ (substantially transparent at wavelengths higher than 280 nm), MgO (substantially transparent at wavelengths higher than 200 nm), or glass. Other materials may also be suitable to obtain the separation, even if they do not exhibit the same high transmittance value as the one listed above, but may then require higher electromagnetic radiation energy, which is not desirable in an industrial environment.

It is possible in the present invention for electromagnetic radiation absorbing layer (24) to be linked to support substrate (25) via a bonding layer, such as an oxide bonding layer. However, in an advantageous embodiment, electromagnetic radiation absorbing layer (24) is in direct contact with the support substrate (25), without the intermediary of an oxide bonding layer.

In a preferred embodiment according to the invention, in the process for modifying a substrate (10) according to the invention, a part of the initial substrate is removed to form a layer (aa), after step a) and preferably before step e). An example of such a process is illustrated schematically in Figure 2, where initial substrate (10), in this example after the bonding step Sl, is partially thinned or ablated by a method such as grinding, polishing, SMART CUT®, by a laser lift off technique or etching, to give rise to modified layer (aa) derived from initial substrate (10). Further preferred in the present invention is a process for modifying a substrate including such a step of removing part of the initial substrate to form a layer (aa), and then, in a step (d), after step c) in the above- mentioned process: - functionalizing the layer (aa); and/or

- bonding further layers to the layer (aa). These two further preferred embodiments are illustrated schematically in Figures 3 and 4.

In Figure 3, (aa)' represents a functionalized layer (aa) (derived from initial substrate (10)). Functionalization in step (d), shown in a schematic illustrative example in step S3 of Figure 3 following on from steps Sl and S2 as shown in Figure 2, may include forming regions with photovoltaic, optical, optoelectronic, electronic and/or mechanical functions in or on the layer (aa). It is also to be understood that functionalization step may includes any technological step that changes the layer characteristic such as forming material layers, thin layer or sufficiently thick layer to be freestanding, or forming active layers.

In Figure 4, a further substrate (30) is bonded to the entity comprising layer (aa), electromagnetic radiation absorbing layer (24) and support substrate (25) in a step S3, following on e.g. from steps Sl and S2 as shown in Figure 2. In Figure 4, the possibility that layer (aa) may have been functionalized is indicated by the legend (aa) / (aa)'. It is also possible that support substrate (25), instead of or in addition to layer (aa), contain regions with photovoltaic, optical, optoelectronic, electronic and/or mechanical functions. Bonding may be performed to join the exposed face of layer (aa), derived from initial substrate (10), to a final substrate (30) that may also be functionalized. Bonding may, for example, be performed via a silicon dioxide bonding layer laid down by the processes discussed above. This bonding may also contain an electromagnetic radiation absorbing layer for a subsequent separation of support substrate (30) if needed.

In one embodiment according to the process of the present invention, the initial substrate (10) may be a bulk free-standing substrate. In one embodiment, the initial substrate (10) may comprise a surface layer (12) having a face (10b) for bonding to the support substrate (25), and an underlying support substrate (11) acting as a template on which surface layer (12) has been deposited. The initial substrate (10) may also comprise a surface layer (12), an intermediate layer and an underlying support substrate (11). In such systems, with or without an intermediate layer, the surface layer (12) and bulk substrate (10) from which layer (aa) is formed may appropriately comprise at least one of the group selected from: GaN, InGaN, SiC, Si, Si(OOO), Si(IIl), GaAs, ZnO, crystalline AIN, AIGaN, InGaAs, InP, Ge, InAIAs. The layer (aa) may also be formed in a semiconductor material for example from the IV group materials (such as Si, Ge), the III/V group materials (polar or non polar or semi-polar materials such as GaN, InGaN, InGaAs).

The initial substrate (10) to be used in the process of the present invention may appropriately contain an underlying support substrate (11) chosen for a reasonable dilatation coefficient match and/or lattice parameter match between the support and the surface layer (12) comprising sapphire (AI ₂ O ₃ ), LiTaO ₃ , LiNbO ₃ , MgO, Si, SiC or a metal alloy containing one or more of Cr, Ni, Mo and W. Such materials may also be used in the final substrate (30), in embodiments where there is such a final substrate.

In the case where the initial substrate (10) comprises a surface layer (12) grown on an underlying support substrate (11), it is preferable to ensure a reasonable lattice match between initial seed support substrate (11) and the surface layer (12), from which the layer (aa) in which functionalities are to be introduced, is formed. As an example, where the surface layer (12) is a IH-N material, appropriate initial seed support materials may for example include: sapphire (AI ₂ O ₃ ), SiC, Si(IIl), GaAs, ZnO, crystalline AIN.

In a preferred process embodiment according to the present invention, in the framework of a process including thinning of initial substrate (10) to produce layer (aa), epitaxy as a step of functionalization may be carried out on layer (aa), for example to obtain a sufficient thickness of material for the layer then produced to become a free standing substrate. In a further preferred embodiment, ion implantation is performed in said initial substrate (10), prior to bonding to the support substrate (25) via the radiation absorbing layer (24) in step (c), so as to provide a plane of weakness defining an upper region of said substrate (10), and removing the upper region by splitting at the plane of weakness. Thus, in a first preferred embodiment of the process according to the present invention, as is shown schematically in Figure 5, a IH-N material layer is withdrawn from an initial donor substrate using Smart Cut® technology. Namely, the HI-N material (12 in Figure 5) may be initially present on a bulk donor substrate (11 in Figure 4). In an example of this, as shown in Figure 1, a IH-N material is shown which may be GaN grown by epitaxy on a "template" such as sapphire. An alternative embodiment would be to use a IH-N material attached to a support substrate via an intermediate bonding layer-such an arrangement may be referred to as GaNOS (GaN bonded On Sapphire). Ion implantation is carried out (step Sl in Figure 5), and then bonding (step S2 in Figure 5) is performed to a second substrate, linking the IH-N surface (12) through a bonding material layer (23) to an electromagnetic radiation absorbing layer (24) on a support substrate (25). The bonding may also be performed without the bonding material layer (23), directly between the support substrate, the absorbing layer (24) and the IH-N material layer (12). Splitting (step S3 in Figure 5) at the plane of weakness generated by ion implantation may then be achieved. In a manner known to the skilled in the art, implantation of hydrogen ions, co- implantation of hydrogen and helium ions, and more generally implantation of light ions, may be performed. A generally appropriate implantation dose of hydrogen ions for GaN lies between 1 x 10 ¹⁷ and 6 x 10 ¹⁷ atoms / cm ² , with an implantation energy range of 10 to 210 keV. Implantation may generally be performed at a temperature lying between 20 and 400 ⁰ C, preferably between 50 and 150 ⁰ C. The skilled person knows how to adjust the implantation so as to obtain a depth of the plane of weakness of between 50 and 1000 nm, and the temperature and duration of the heating process used to induce separation and splitting about the plane of weakness are known to varying according to implantation conditions, and in particular the implantation ion dose. In step S4 in Figure 5, the surface exposed by splitting about the plane of weakness is bonded to a final substrate (30), in this case chosen to comprise a final support substrate (31) and a bonding layer (33). Subsequently, in step S5 in Figure 5, the entity thus obtained, containing elements from each of the initial, second and third substrates, is subjected to electromagnetic radiation, directed through transparent support substrate (25), the radiation having a wavelength chosen so as to be absorbed by electromagnetic radiation absorbing layer (24) and to lead to the separation of substrate (25).

In a process such as shown schematically in Figure 5, epitaxial growth (not shown in Figure 5) may be performed on thin layer (12f) so as to produce a substrate of sufficient thickness (for example, greater than 100 microns) to enable it to be freestanding, before fracturing about the plane of weakness. Epitaxial growth may thus be performed before step S2, where a second substrate is bonded via surface layer (12f) to the initial substrate. In this case, the thermal treatment due to epitaxial growth has to be less than the heating process to induce the splitting at the plane of weakness. Epitaxial growth may also be performed on the exposed layer after step S3 of separation at the plane of weakness, or after step S5 of separation by irradiation absorption. Also, and not shown in Figure 5, functionalization may be formed in region (12f), corresponding to layer (aa), so as to form regions with photovoltaic, optical, optoelectronic, electronic and/or mechanical functions therein or thereon.

In a final step S6 of the exemplary process of Figure 5, the bonding layer (23), which previously linked the HI-N material layer (12f) with the absorbing layer (24), may be removed. If the bonding layer (23) is comprised of silicon dioxide, this layer may appropriately be removed by dry etching or mechanical polishing associated with chemical etching, for example using a dilute aqueous solution (10% by volume) of hydrofluoric acid (HF). III-N materials such as IH-N materials grown on a template such as sapphire, showing a c-plane wurtzite structure, have a gallium and a nitrogen face. The upper face is usually the gallium face, while the bottom surface (adjacent to the growth substrate), the initial donor support substrate (1) is a nitrogen face. With a process according to the above-described first preferred embodiment of the invention as applied to III-N materials, a double transfer is carried out in order to expose in the final product the gallium face, i.e. the same which was initially exposed in the initial product. It is consequently possible to begin epitaxy again at this stage on the III-N material with limiting the risk of dislocations and cracks, with respect to the situation where epitaxy was attempted starting from the nitrogen face. In the present invention, wafers of any particular diameter may be manipulated, without any specific limitation.

In an advantageous embodiment, in the process according to the invention, after step (e), epitaxy or further functionalization may be carried out on the bonding face (10b) of the initial substrate (10) liberated by the irradiation of electromagnetic radiation absorbing layer (24) in step

(e).

In a second preferred embodiment according to the present invention, the structure that can be used in the process of the invention is obtained by ion implantation in a substrate such as bulk GaN, followed by epitaxy of a HI-N material such as InGaN in such a way as to not exceed the energy input required to split the substrate along the plane of weakness generated by ion implantation, followed by bonding the GaN/InGaN material to an absorbing layer on an intermediary substrate and then carrying out fracture along the plane of weakness (analogous to step S3 in Figure 5). It is also possible to perform implantation after the epitaxy of the InGaN layer and before covering by a protection layer, so that epitaxy thermal budget is not limited. In order to ensure successful fracture about the plane of weakness, it is preferable to first bond the implanted HI-N material to an intermediate support, as shown in step S2 of Figure 5 in relation to the second embodiment, which rigidifies and strengthens the stacked entity. The present second embodiment is of interest in order to be able to continue epitaxy with InGaN, this being of interest in LED applications for example.

As an example, a layer of InGaN may be grown by epitaxy on a GaNOS substrate and then ion implantation may be carried out in the InGaN. The exposed upper face in the InGaN layer, which has gallium polarity, is bonded to an intermediate substrate having a bonding layer (23) and an absorbing layer (24). After splitting at the zone of weakness created by ion implantation, the structure consisting of the sacrificial intermediate support, the UV and/or visible light absorbing layer, the bonding layer and the InGaN layer, can be bonded to a final support substrate (see step S4 of Figure 5), which may for example be a sapphire substrate. Separation can then be carried out using irradiation via the support substrate (25) of the intermediate substrate, and a InGaNOS substrate is obtained with the required polarity on the upper face in order to begin proceed with further epitaxy.

In some advantageous embodiments of the present invention, as mentioned previously, bonding between the initial substrate (10) and the second substrate (25) may be carried out using one or more silicon oxide bonding layers.

In an advantageous embodiment, rather than the electromagnetic radiation absorbing layer being a fully distinct layer extending across the length and breadth of the stacked entity being prepared (such that the cross-section throughout is as shown in the attached Figures), one or more of the bonding layer(s), such as oxide bonding layer(s), may contain at least one embedded region of electromagnetic radiation absorbing material comprising Si _x N _y/ Si _x Ny : H, SΪ ₃ N ₄ , GaN, AIN, InN, or mixed nitrides of one or more of In, Ga and Al.

In a third advantageous example embodiment according to the present invention, represented schematically in Figure 6, an InGaN layer is transferred using a process of molecular bonding and released by irradiation of an electromagnetic radiation absorbing layer according to the invention. An initial substrate is provided in which a layer of InGaN (12t) to be transferred is formed by epitaxy on a template showing a seed layer of GaN (12s) grown by epitaxy on, as an example, a sapphire support substrate (11). This is shown as step Sl in Figure 6, where the InGaN layer on GaN is together represented as layer (12), and the underlying support substrate (11) is sapphire. In an appropriate approach for performing the invention, the thickness of the layer of InGaN will be approximately 100 nm and the amount of indium will be of the order of 5 to 15%. The dislocation density in the layer will preferably be below 5xlO ⁸ /cm ² . GaN grown by epitaxy on a c-plane sapphire is a polar material and the upper free face is a gallium (Ga) face. This polarity is conserved by the InGaN which is grown thereupon.

In subsequent step S2, an oxide bonding layer (SiC^, layer (13) in the Figure) is laid down on the InGaN layer by a LPOJD technique. An appropriate thickness will be about 300 nm.

In subsequent step S3, implantation by ions such as hydrogen and/or helium can be carried out through the oxide layer (13) and through the InGaN, in order to create a zone of weakness at a depth of about 500 nm, the zone of weakness being situated in the GaN seed layer. A dose of the order of 4 x 10 ¹⁷ atoms/cm ² is appropriate for such an implantation.

In subsequent step S4, an intermediate substrate comprising, in order, a support substrate such as sapphire (25), an absorbant layer (24) such as Si _x Ny laid down by a PECVD technique with a thickness of about 100 nm, and a silicon dioxide bonding layer (23) having a thickness of about 500 nm, is provided. Molecular bonding is used to link the initial and intermediate substrate entities via the oxide bonding layers (13 and 23) which are brought into contact.

Heat treatment then enables, in step (S5), fracture of the entity created, removing the initial underlying initial support substrate (11) and a part of the GaN seed layer. Etching techniques known to the skilled person are then used to remove the residual GaN (between steps S5 and S6, and not shown in Figure 6), and this exposes the face of the InGaN layer (12t or aa) having N polarity. In subsequent step S6, a layer of Si _x Ny is laid down by a PECVD technique to a thickness of approximately 50 nm. This further electromagnetic radiation absorbing layer and/or adhesion layer is represented as layer (34) in Figure 6. A silicon dioxide bonding layer is then laid down by an LPCVD or PECVD technique with a thickness of approximately 500 nm to 3μm (step S7- the silicon dioxide layer is represented as 33). After preparation of the surfaces for bonding (planarization, CMP, brushing, and optionally plasma activation), the structure obtained in step S7 is put into contact with the final support substrate of sapphire, labelled (31) (step S8). Bonding reinforcement thermal treatment may be carried out, involving heating at 300 to 950 ⁰ C during several hours.

Subsequently, in step S9, electromagnetic radiation absorbing layer (24) may be irradiated, for instance by sweeping a laser beam at the surface of the substrate, at a wave length of 193 nm in order to induce decomposition and separation of the intermediate support (25 in combination with 24), possibly with the addition of mechanical energy.

Subsequent removal of possible absorbing layer residue (24) and of the oxide bonding layers (13 + 23), for example by dry etching or mechanical polishing associated with contact with diluted hydrofluoric acid, then enables the InGaN surface (12t or aa) having Ga polarity to be exposed. This may be then used as a basis for further epitaxy of InGaN and/or other active layers. The absorbing layer (34) may be used as a separation layer for separation of the support substrate (31) in a subsequent use of the final entity if needed.