Process for manufacturing a composite structure comprising a thin monocrystalline layer on a supporting substrate - Patents.com

Abstract

The present invention relates to a process for manufacturing a composite structure, comprising the steps of: a) providing a donor substrate (10) made of a single-crystalline material; b) providing a support substrate (20) having a first alignment pattern (21); c) applying a heat treatment to the donor substrate (10) at a temperature that results in a surface reorganization on the faces (10a, 10b) of the substrate (10), the surface reorganization resulting in the formation of first steps (13) of nanometer amplitude parallel to a first principal axis (P1); d) assembling the donor substrate (10) and the support substrate (20), including an optical alignment better than ±0.1° between an alignment mark (12) indicating the first principal axis (P1) of the donor substrate (10) and the alignment patterns (21, 22) of the support substrate (20); and e) transferring a thin layer (100) from the donor substrate (10) to the support substrate (20).

Description

[Technical field]

[0001] The present invention relates to the field of semiconductor materials for microelectronic components, in particular to a process for manufacturing a composite structure comprising a thin monocrystalline layer, for example made of silicon carbide, placed on a support substrate and allowing precise alignment of the crystallographic axes of said layer. [Background technology]

[0002] Interest in silicon carbide (SiC) has increased significantly over the past few years due to this semiconductor material's ability to enhance energy processing capabilities. SiC is increasingly being used to manufacture innovative power devices to meet the needs of emerging sectors in electronics, particularly electric vehicles.

[0003] Power devices and integrated power systems based on single crystal silicon carbide can manage much higher power densities compared to their conventional analogues made of silicon, and can do so with smaller active zone dimensions. To further limit the dimensions of power devices in SiC, it is advantageous to fabricate vertical components rather than lateral ones. For this, the SiC structure must allow vertical electrical conduction between electrodes located on the front and rear sides of the structure.

[0004] Nevertheless, high-quality monocrystalline SiC substrates for the microelectronics industry remain expensive and difficult to supply in large sizes. It is therefore advantageous to use thin layer transfer solutions to create composite structures comprising a thin layer of monocrystalline SiC on a generally low-cost support substrate, whether this is monocrystalline or polycrystalline. One well-known thin layer transfer solution is the Smart Cut™ process, which is based on implantation of light ions and assembly by direct bonding. Such a process makes it possible to produce composite structures, for example, comprising a thin layer of monocrystalline SiC (c-SiC), which is removed from a donor substrate made of c-SiC with low defect density and assembled in direct contact or through a metal layer with a support substrate made of polycrystalline SiC (p-SiC) or a support substrate made of monocrystalline SiC. Such composite structures allow vertical electrical conduction.

[0005] Certain vertically oriented electronic components fabricated in the composite structure as described above require precise alignment with respect to the crystallographic axes of the thin layers of c-SiC to achieve high performance levels. The required accuracy is typically ±0.1°. In practice, it is necessary to be able to align elements of the electronic components (e.g., gates along their length) with the crystallographic axes (11-20) of the c-SiC layers to better than 0.1°.

[0006] Although this alignment problem has only just been discussed with respect to components produced in thin layers formed from SiC, it is potentially found in single crystal thin layers composed of other materials.

[0007] It is therefore advantageous to provide a composite structure that makes it possible to find at least one crystal axis of a thin layer in a reproducible manner, thereby creating an alignment mark that is coherent with said axis and can be used with all levels of masks required for the manufacture of vertical components.

[0008] The support and donor substrates used in the fabrication of the composite structures each have a flat spot or notch that typically indicates a crystallographic axis contained within the plane of the front surface of the substrate, within an accuracy of ±1°.

[0009] Such inaccuracies make it impossible to rely on flat spots or notches in the substrate to reproducibly define alignment marks representing the crystal axes to an accuracy of ±0.1°.

[0010] In addition to this, the inaccuracies in alignment during assembly of the substrates make it clearly impossible to rely on flat spots or notches in the support substrate to define alignment marks representing the crystal axes of the thin layers obtained by the donor substrate to form the composite structure.

[0011] To achieve precise alignment of the crystal axes, X-ray diffraction (XRD) tools must be used, which makes the manufacturing process of the composite structures very complicated. Summary of the Invention

[0012] The present invention aims to overcome all or some of the above mentioned drawbacks. The present invention relates to a process for manufacturing a composite structure comprising a thin monocrystalline layer (for example made of SiC) placed on a support substrate, said composite structure allowing precise alignment of the crystallographic axis of said thin layer.

[0013] The present invention relates to a process for manufacturing a composite structure comprising a thin layer made of a first monocrystalline material located on a support substrate, the process comprising: a) providing a donor substrate made of a first monocrystalline material having a front surface and a back surface; b) providing a support substrate having a front surface, a back surface, an edge, and a first alignment pattern on one of said surfaces or on the edge; c) a thermal treatment step applied to at least the donor substrate in a controlled atmosphere at a temperature capable of bringing about a surface reorganization on at least one of the faces of said substrate, the surface reorganization resulting in the formation of first steps of nanometer amplitude parallel to a first principal axis; d) assembling the donor substrate and the support substrate, the optical alignment being better than ±0.1° between an alignment mark indicating a first principal axis of the donor substrate and at least one alignment pattern of the support substrate before the substrates are contacted; e) transferring the thin layer from the donor substrate to a support substrate; Includes.

[0014] According to other advantageous, non-limiting features of the present invention, taken alone or in any technically feasible combination, the first alignment pattern of the support substrate is a flat spot or a notch formed on the edge of the support substrate, and the optical alignment during the assembly step uses the first alignment pattern; the first material is silicon carbide and the temperature of the heat treatment in step c) is greater than or equal to 1500°C, preferentially greater than or equal to 1600°C; a support substrate is formed from monocrystalline silicon carbide, and a heat treatment step is also applied to the support substrate and causes a surface reorganization on at least one of the faces of said substrate, the surface reorganization causing the formation of second steps of nanometer amplitude parallel to a second principal axis; a second alignment pattern of the support substrate is formed by the second step itself, by at least one pattern defined by photolithography and etching of the front side of the support substrate starting from the second step, or by at least one pattern defined by photolithography and etching of the back side of the support substrate starting from the second step; optical alignment during the assembly step uses said second alignment pattern; the first material is gallium arsenide, and the temperature of the heat treatment in step c) is 630° C. or higher; the first material is indium phosphide, and the temperature of the heat treatment in step c) is 600° C. or higher; the alignment mark is formed by the first step itself, by at least one mark defined by photolithography and etching of the front side of the donor substrate starting from the first step, or by at least one mark defined by photolithography and etching of the back side of the donor substrate starting from the first step; The assembly step includes chemical mechanical polishing of the front side of the donor substrate and / or the front side of the support substrate before the two substrates are contacted; The assembly step includes the deposition of an intermediate layer on the front side of the donor substrate and / or on the front side of the support substrate before the two substrates are brought into contact; The manufacturing process includes, prior to the assembly step, forming a recessed weak surface in a donor substrate and defining a thin layer between said recessed weak surface and a front surface of the donor substrate; The manufacturing process includes, during a transfer step, on the one hand, forming a composite structure comprising a thin layer that is placed on a support substrate, and on the other hand, a step of separation along the embedded weak surface in order to form the remaining part of the donor substrate. [Brief description of the drawings]

[0015] Other features and advantages of the present invention will become apparent from the following detailed description of the invention, given in conjunction with the accompanying drawings. [Figure 1] 1 shows a composite structure produced according to a manufacturing process according to the present invention. [Figure 2a] 5 illustrates steps of a manufacturing process according to the present invention. [Figure 2b] 5 illustrates steps of a manufacturing process according to the present invention. [Figure 2c] 5 illustrates steps of a manufacturing process according to the present invention. [Figure 2d] 5 illustrates steps of a manufacturing process according to the present invention. [Figure 2e] 5 illustrates steps of a manufacturing process according to the present invention. [Diagram 3]4 illustrates an alternative or optional step in the manufacturing process according to the present invention. [Figure 4] 4 illustrates an alternative or optional step in the manufacturing process according to the present invention. [Diagram 5] 4 illustrates an alternative or optional step in the manufacturing process according to the present invention. [Figure 6a] 4 illustrates an alternative or optional step in the manufacturing process according to the present invention. [Figure 6b] 4 illustrates an alternative or optional step in the manufacturing process according to the present invention. [Figure 6c] 4 illustrates an alternative or optional step in the manufacturing process according to the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] In the description, the same reference numbers in the figures can be used for the same types of elements. The figures are schematic representations that are not drawn to scale for ease of reading. In particular, the thicknesses of the layers along the z-axis are not drawn to scale with respect to the lateral dimensions along the x- and y-axes, and the relative thicknesses of the layers with respect to one another are not necessarily respected in the figures.

[0017] The invention relates to a process for manufacturing a composite structure 1 comprising a thin layer 100 made of a first monocrystalline material located on a support substrate 20 (FIG. 1).

[0018] The first material may be, inter alia, silicon carbide (SiC), gallium arsenide (GaAs), indium phosphide (InP), gallium nitride (GaN), aluminum nitride (AlN), silicon germanium (SiGe), silicon (Si), germanium (Ge) or others. In the remainder of the description, "c-SiC" or "c-material" will be used generally to refer to monocrystalline silicon carbide or said material in monocrystalline form, respectively.

[0019] The process first comprises step a) of providing a donor substrate 10 made of a first monocrystalline material (FIG. 2a).

[0020] The thin layer 100 of the composite structure 1 is formed starting from the donor substrate 10 upon completion of the process of the present invention, and therefore the crystallographic orientation, crystal quality and degree of doping of the donor substrate 10 are also selected to meet the required specifications of the components, e.g. vertical components, that are to be produced in the thin layer 100.

[0021] By way of example, a donor substrate 10 formed from c-SiC may have an offcut angle of less than 4.0°±0.5° relative to the <11-20> crystal axis and a lattice constant of 5 / cm 2 Less than or even 1 / cm 2 In N-doped form, the donor substrate preferentially has a resistivity between 0.015 ohm.cm and 0.030 ohm.cm, typically 1500 / cm, depending on the sensitivity of the target component to these defects. 2 A donor substrate 10 can be selected that has a low density of basal plane dislocations (BPDs) that is equal to or less than 100 nm.

[0022] Alternatively, the c-SiC donor substrate 10 may comprise an initial substrate 10' and, on the side of its front surface 10a, a surface layer 110, produced for example by epitaxy and having the necessary properties for the future thin layer 100, which will be formed starting from said surface layer 110 upon completion of the process of the invention (FIG. 3). In this case, the density of BPD-type defects in the surface layer 110 is lower than that in the initial substrate 10', preferably less than 5 / cm. 2 Less than or even 1 / cm 2 It can be assumed that it is less than

[0023] By way of further example, a donor substrate 10 formed from c-InP may have an offcut angle of 2°.

[0024] The donor substrate 10 is preferentially in the form of a circular wafer with a diameter of 100 mm or 150 mm or even 200 mm and a thickness generally between 300 and 800 microns. The donor substrate 10 has a front surface 10a, a rear surface 10b and an edge 10c forming its circular periphery. The surface roughness of the front surface 10a is advantageously chosen to be less than 1 nm Ra (average roughness) measured by atomic force microscope (AFM) on a scan of 20 microns by 20 microns.

[0025] The donor substrate 10 is typically provided with a flat spot 11 or a notch formed on its edge 10c. Generally, the flat spot 11 (or notch) marks one particular crystal axis contained in the plane (x,y) of the front surface 10a, and in the case of a substrate made of c-SiC, the crystal axis (11-20) is for example parallel to the flat spot 11. Nevertheless, the precision of this marking is low, since the flat spot 11 guarantees the orientation of the crystal axis to ±1°.

[0026] According to another option, the donor substrate 10 may be provided with one or more micrometer or millimeter patterns, which may be produced by known techniques of lithography, etching and deposition on its front side 10a or on its rear side 10b and which may indicate one particular crystallographic direction.

[0027] The process also includes a step b) of providing a support substrate 20 (FIG. 2b). The support substrate 20 may be selected from any material compatible with the microelectronic processes typically used to produce components based on a first material. Thus, the support substrate 20 may be formed from silicon, silicon carbide, gallium arsenide, indium phosphide, etc.

[0028] If the first material of the donor substrate (10) (and the thin layer (100)) is silicon carbide, the support substrate 20 is advantageously made of polycrystalline silicon carbide (p-SiC) or made of monocrystalline silicon carbide. If made of monocrystalline silicon carbide, a higher degree of defects and dislocations can be tolerated than in the case of the donor substrate 10 (and the thin layer 100 resulting therefrom). Preferentially, the support substrate 20 has a resistivity of 0.015 ohm.cm to 0.030 ohm.cm in order to meet the requirements of electrical conduction of vertical components that may be produced in the future composite structure 1.

[0029] The support substrate 20 is preferentially in the form of a circular wafer with a diameter of 100 mm or 150 mm, or even 200 mm, and a thickness generally between 300 and 800 microns. The support substrate 20 has a front surface 20a, a rear surface 20b, and an edge 20c forming its circular periphery. The surface roughness of the front surface 20a, as in the case of the donor substrate 10, is advantageously chosen to be less than 1 nm Ra.

[0030] The support substrate 20 generally comprises an alignment pattern 21 (hereinafter referred to as the first alignment pattern 21) located on one of the front and rear surfaces 20a and 20b or on the edge 20c. In Fig. 2b, the first alignment pattern 21 is a flat spot formed on the edge 20c of the support substrate 20. Alternatively, the first alignment pattern 21 may consist of a notch also formed on the edge 20c. According to yet another option, the first alignment pattern 21 may consist of one or more micrometer or millimeter patterns produced by known techniques of lithography, etching and deposition on the front surface 20a or rear surface 20b of the support substrate 20 and capable of indicating a certain direction or acting as a marker for aligning the level of a subsequent lithography mask.

[0031] In the case of a single crystal support substrate 20, the first alignment pattern 21 marks a crystal axis contained within a plane (x,y) parallel to the front surface 20a of the substrate 20 with an accuracy of ±1°, as described above for the donor substrate 10.

[0032] The process according to the invention then comprises a step c) of a thermal treatment applied to the donor substrate 10 and optionally to the support substrate 20, in a controlled atmosphere, at a temperature capable of bringing about a surface reorganization on at least one of the faces of the treated substrate. The surface reorganization gives rise to the formation of steps (step bunching) that are parallel to one another and have a nanometric amplitude, for example of the order of a few nanometers up to 500 nm.

[0033] Without being limiting, some examples of heat treatments are given below for different types of first materials.

[0034] If the first material is silicon carbide, the heat treatment of step c) is applied to the donor substrate 10 (and potentially to the support substrate 20, if the latter is also made of silicon carbide) at a temperature of 1500°C or more, preferentially 1600°C or more. The temperature is generally chosen between 1500°C and 1800°C, for example 1700°C, and the atmosphere is advantageously an inert or reducing atmosphere based on argon and / or a mixture of argon and about 2% hydrogen. Such a temperature is high enough to allow at least one compound of silicon carbide (i.e. here silicon) to be leached out.

[0035] When applied to a c-SiC substrate, such a heat treatment leads to a surface reorganization on at least one of the faces of said substrate, which results in the formation of steps that are parallel to one another and have nanometer amplitudes of a few nanometers up to the order of 500 nm.

[0036] When the first material is gallium arsenide, the temperature of the heat treatment of step c) is chosen to be equal to or higher than 630° C. under an arsine atmosphere, the leaching of arsenic resulting in the expected surface reorganization.

[0037] If the first material is indium phosphide, the temperature of the heat treatment of step c) is chosen to be equal to or higher than 600° C. in a phosphine atmosphere, in which case it is the phosphorus that tends to leach out and surface reorganizations in the form of steps can occur.

[0038] In the examples mentioned, and more generally, whatever the first material of the donor substrate 10, the application of a heat treatment of step c) under controlled atmosphere allows a surface reorganization in the form of steps and prevents (limits) the appearance of holes (etch pits).

[0039] Thus, as shown in FIG. 2c, after the heat treatment step, the donor substrate 10 has steps 13 (hereinafter referred to as first steps) on its front surface 10a and / or on its back surface 10b, all of which are parallel to a principal axis P1 (hereinafter referred to as the first principal axis), which presents a well-defined crystal axis depending on the nature of the first material.

[0040] That is, when the donor substrate 10 is formed from 4H or 6H polytype of c-SiC, the principal axis P1 is parallel to the crystal axis (1-100).

[0041] The presence of a first step 13 on the front surface 10a and / or rear surface 10b of the donor substrate 10 may constitute an alignment mark 12 indicating a principal axis P1 and, therefore, an associated crystallographic axis in the plane (x,y).

[0042] According to another option, the alignment mark 12 is formed, starting from a first step 13, on the front surface 10a of the donor substrate 10 by means of at least one mark defined by conventional techniques of photolithography and etching (FIG. 4).

[0043] According to yet another option, at least one mark is defined on the rear surface 10b of the donor substrate 10 starting from a first step 13, thus forming an alignment mark 12 on the rear surface 10b. This option is advantageous in that it avoids a local structuring of the front surface 10a of the donor substrate 10, which is favorable for subsequent assembly steps.

[0044] If the support substrate 20 is composed of a first monocrystalline material like the donor substrate 10, the heat treatment step c) may also be applied to the support substrate 20, so that a step 23 (called the second step) is created on the front surface 20a of the support substrate 20 and / or on the back surface 20b of the support substrate 20, all of which are parallel to a principal axis P2 (called the second principal axis), which represents a clearly defined crystal axis of the support substrate 20.

[0045] It should be noted that, in case the support substrate 20 consists of a monocrystalline material different from the first material, a heat treatment step c) can be applied to the support substrate 20, which differs (in terms of temperature and / or atmosphere) from the heat treatment step applied to the donor substrate 10. The conditions of step c) are then defined so as to bring about the desired surface reorganization in the support substrate 20.

[0046] As shown in FIG. 2c, the presence of a second step 23 on the front surface 20a and / or back surface 20b of the support substrate 20 may constitute a second alignment pattern 22 indicating a principal axis P2 and, consequently, an associated crystal axis in the plane (x,y).

[0047] According to another option, the second alignment pattern 22 is formed, starting from a second step 23, on the front surface 20a of the support substrate 20 by means of at least one pattern (defined by conventional techniques of photolithography and etching) (Figure 4).

[0048] According to yet another option, at least one pattern is defined on the rear surface 20b of the support substrate 20 starting from a second step 23, thus forming a second alignment pattern 22 on the rear surface 20b.

[0049] It should be noted that the heat treatment can favor the appearance of steps 13, 23 on one or the other of the faces of the substrate 10, 20 to which it is applied. In particular, c-SiC of the 4H polytype is polar and can have either the Si-face or the C-face as the front face. That is, taking into account the different energy levels of these two faces, the surface reorganization of the Si-face will generate, under certain annealing conditions, many more steps of larger amplitude than the reorganization of the C-face.

[0050] The process then comprises a step d) of assembling the donor substrate 10 and the support substrate 20 via their respective front faces 10a, 20a. This step comprises an intimate contact of the two substrates 10, 20 to carry out a direct bonding by molecular adhesion. As is known per se, such bonding requires that the surfaces to be assembled are pre-cleaned to remove contaminants (particles, organics, etc.) and potentially activated to favour chemical surface terminations favourable for the propagation of the bonding wave and for a good strength of the bonding interface.

[0051] According to the invention, before the substrates 10, 20 are brought into contact, an optical alignment of better than ±0.1° is performed between the alignment mark 12 indicating the first principal axis P1 of the donor substrate 10 and at least one alignment pattern 21, 22 of the support substrate 20. The alignment between the alignment mark 12 and the alignment patterns 21, 22 targets an accuracy of better than ±0.1° or even better than ±0.05°.

[0052] The purpose of this alignment is to ensure that the first principal axis P1 (corresponding to one particular crystal axis of the donor substrate 10 and therefore of the thin layer 100 obtained therefrom) is accurately marked by the first alignment pattern 21 or the second alignment pattern 22 of the support substrate 20.

[0053] It is recalled that it is likewise possible to perform optical alignment between marks or patterns located on the front surfaces 10a, 20a, rear surfaces 10b, 20b or edges 10c, 20c of the donor substrate 10 and the support substrate 20.

[0054] According to a first variant, the optical alignment, whatever it may be, is performed between the alignment mark 12 and the first alignment pattern 21 of the support substrate 20 (FIG. 2d). In such a case, it is not necessary for the support substrate 20 to be subjected to a heat treatment step c), since the second alignment pattern 22 based on the second step 23 is not used. The first variant is advantageously used when the support substrate 20 comprises an amorphous or polycrystalline material, for example p-SiC.

[0055] According to a second variant, the optical alignment is carried out between the alignment mark 12, whatever it may be, and the second alignment pattern 22, whatever it may be, of the support substrate 20 (FIG. 5). In such a case, a heat treatment of step c) has been applied to the support substrate 20 in order to generate the second step 23 necessary to form the second alignment pattern 22. This second variant is advantageously used when the support substrate 20 comprises a monocrystalline material, for example c-SiC. The second variant is also preferred when the future composite structure 1 is intended for the generation of vertical components. Indeed, for these components it is advantageous to directly assemble the respective semiconducting surfaces (for example made from c-SiC) of the substrates 10, 20 (for example via a hydrophobic direct bond), although it should be noted that a misalignment of more than 0.2° between the crystal axes contained in the plane (x,y) of the donor substrate 10 and the crystal axes contained in the plane (x,y) of the support substrate 20 increases the resistivity of the assembly interface, which is detrimental to the vertical electrical conduction of the components. It is therefore advantageous to be able to align the crystal axes of the two substrates 10, 20 to within ±0.1° during assembly, as provided by the process according to the invention.

[0056] Step d) of assembling the substrates 10, 20 may include a surface treatment of one or the other of the front surfaces 10a, 20a of the donor substrate 10 and the support substrate 20 to make them smooth before contacting them. Indeed, the presence of a step 13 at least on the front surface 10a of the donor substrate 10 may affect the quality of the direct bond. The principles described below with respect to the donor substrate 10 apply in an analogous manner when a second step 23 is present on the front surface of the support substrate 20.

[0057] Thus, chemical mechanical polishing of the front surface 10a of the donor substrate 10 may for example be performed before optical alignment and contacting of the two substrates 10, 20. Since polishing results in the disappearance of the first step 13, it is necessary that the alignment marks 12 of the donor substrate 10 (or the second alignment patterns 22 of the support substrate 20) have been formed from the step 13 before said polishing. Alternatively, even if the first step 13 is removed on the front surface 10a, the steps 13 present on the back surface 10b of the donor substrate 10 may be used directly to generate the alignment marks 12 or for optical alignment.

[0058] Furthermore, prior to optical alignment and contacting, the assembly step d) may comprise depositing an intermediate layer on the front surface 10a of the donor substrate 10 and / or on the front surface 20a of the support substrate 20. The intermediate layer may be an insulating layer or a conductive layer, for example a metal layer, depending on the type of components to be produced in the composite structure 1 at the end of the process according to the invention. The insulating layer may comprise a material selected from silicon oxide, silicon nitride, etc., and the conductive layer may comprise a material selected from tungsten (W), tungsten silicide (WSi2), titanium (Ti), nickel (Ni), silicon carbonitride (for example SiCNx with x=10%), etc. To facilitate the direct bonding of the substrates 10, 20, the intermediate layer may be smoothed, for example by chemical mechanical polishing. Thus, the steps 13, 23 of the front surfaces 10a, 20a of the donor substrate 10 and the support substrate 20 are encapsulated and do not interfere with the assembly.

[0059] During the assembly step d), the contacting of the substrates 10, 20 may be performed in ambient or controlled atmosphere, for example under inert gas and / or under vacuum, and at a controlled temperature, for example between 20°C and 300°C.

[0060] In a manner known per se, the contacting of the substrates 10, 20 involves the propagation of a bonding wave, which leads to the formation of a bonding interface 30, resulting in a bonded assembly 1' (Figure 2d).

[0061] The manufacturing process according to the invention finally comprises a step e) of transferring the thin layer 100 from the donor substrate 10 onto the support substrate 20 (FIG. 2e).

[0062] According to a first embodiment, the transfer of the thin layer 100 is performed by thinning the back surface 10b of the donor substrate 10 to the desired thickness of the thin layer 100. Such thinning may for example use conventional techniques of grinding, wet or dry chemical etching and / or chemical mechanical polishing, alternating with cleaning sequences. One (or more) heat treatment(s) may be applied to strengthen the bonding interface or otherwise improve the crystallographic and / or surface quality of the thin layer 100.

[0063] According to a second embodiment, the transfer of the thin layer 10 is carried out by the Smart Cut™ process. In this case, the manufacturing process according to the invention comprises, prior to the assembly step, a step of forming a buried weak surface 15 in the donor substrate 10 to define a thin layer 100 between said buried weak surface 15 and the front surface 10a of the donor substrate 10 (FIG. 6a).

[0064] Advantageously, a step of ion implantation of optical species is carried out in the donor substrate 10 to a predefined depth. The implanted optical species are preferentially hydrogen, helium or these two species simultaneously implanted. These optical species form microcavities distributed in a thin layer parallel to the free surface of the donor substrate 10, i.e. parallel to the plane (x,y) of FIG. 6a, near the predefined depth. This thin layer is called buried weak surface 15 for simplicity. The energy of the implantation of the optical species is chosen to reach a predefined depth in the donor substrate 10, said depth corresponding to the target thickness of the thin layer 10 after transfer. For example, hydrogen ions are implanted with an energy of 10 keV to 250 keV (or up to 500 keV) and a density of 50 keV to define a thin layer 10 of the order of 100 to 1500 nm. E 16 / cm 2 ~1 E 17 / cm 2 is injected at a dose of

[0065] It should be noted that prior to the ion implantation step, a protective layer can be deposited on the front surface 10a of the donor substrate 10. This protective layer may consist of a material such as silicon oxide or silicon nitride.

[0066] Furthermore, in the second embodiment, the aforementioned assembly step d) is then carried out (FIG. 6b). A transfer step e) then consists in forming, on the one hand, a composite structure 1 comprising the thin layer 100 located on the support substrate 20, and, on the other hand, a separation along the buried plane of weakness 15 in order to form the remaining part 10″ of the donor substrate.

[0067] The separation can be caused by applying a heat treatment, typically for a few minutes to a few hours, at a temperature between 200° C. and 1000° C., in particular between 800° C. and 1000° C. for a first material made of c-SiC, or between 200° C. and 300° C. for a first material made of c-GaAs, or about 300° C. for a first material made of c-InP. During said heat treatment, the microcavities present in the buried weak surface 15 follow a growth kinetics until a breakdown wave is spontaneously initiated, which propagates over the entire extent of the buried weak surface 15, resulting in a separation between the composite structure 1 and the remaining part 10″ of the donor substrate 10.

[0068] Alternatively, separation may be induced by the application of localized stress or by a combination of thermal treatment and mechanical stress.

[0069] After detachment, the free surface of the thin layer 10 typically exhibits a roughness of 3-6 nm Ra (AFM-20 micron x 20 micron scan). The aim of the subsequent generation of components is to have a roughness of less than 1 nm Ra.

[0070] Thus, after the transfer step e), the manufacturing process may include finishing steps applied to the composite structure 1. These finishing steps are aimed in particular at improving the roughness of the free surface of the thin layer 100 (the front surface 1a of the composite structure 1).

[0071] The finishing step may in particular make use of known techniques of chemical mechanical polishing applied to the front surface 1a and may also include a heat treatment aimed at strengthening the bonding interface 30 or at improving the crystallographic and / or surface quality of the thin layer 100.

[0072] Whichever embodiment is selected, at the end of the transfer step e), the alignment mark 12 of the donor substrate 10 is either absent from the composite structure 1 (in particular if the alignment mark is located on the back surface 10b of the donor substrate 10) or is invisible or degraded (in particular if the alignment mark is located on the front surface 10a or on the edge 10c of the donor substrate 10).

[0073] It is therefore possible to rely on the alignment patterns 21, 22 of the support substrate 20 used for the optical alignment of the assembly step d) to align the components to a particular crystal axis of the thin layer 100 or in the thin layer 100, while producing the components therein. This alignment pattern indicates with a high degree of accuracy (±0.1°) the orientation of a particular crystal axis of the thin layer 100.

[0074] example: According to a non-limiting example, the donor substrate 10 provided in step a) of the manufacturing process is a wafer made of c-SiC of 4H polytype, with an orientation of 4.0°±0.5° relative to the <11-20> axis, with a diameter of 150 mm and a thickness of 350 μm. The front surface 10a of the donor substrate 10 is of C (carbon) type, while the rear surface 10b of the donor substrate 10 is of Si (silicon) type. The donor substrate 10 may comprise a flat spot 11 formed at its edge 10c and presenting within ±1° a crystallographic direction (1-100) contained in the plane (x,y) of the front surface 10a of said substrate 10.

[0075] The support substrate 20 provided in step b) of the manufacturing process is a wafer made of c-SiC of 4H polytype, with an orientation of 4.0°±0.5° relative to the <11-20> axis, with a diameter of 150 mm and a thickness of 350 μm. The support substrate 20 is provided with a flat spot 21 formed on its edge 20c, which indicates a crystallographic direction (1-100) contained in the plane (x,y) of the front surface 20a of said substrate 20. The front surface 20a is of Si type and the back surface 20b is of C type.

[0076] A conventional cleaning sequence is performed on the substrate 10, 20 prior to the thermal treatment step c).

[0077] Then, a heat treatment at 1700° C. under argon or in combination with 2% hydrogen under argon is applied to the two substrates 10, 20, resulting in the appearance of a first step 13 on the faces 10a, 10b of the donor substrate 10 and a second step 23 on the faces 20a, 20b of the support substrate 20. Considering the different energies required by the Si-type and C-type faces for surface reorganization, the first step 13 of the donor substrate 10 has a larger amplitude on the back surface 10b (Si-face) of the donor substrate 10 than on the front surface 10a (C-face) of the donor substrate 10, and the second step 23 of the support substrate 20 has a larger amplitude on the front surface 20a (Si-face) of the support substrate 20 than on the back surface (C-face) of the support substrate 20. Since the donor substrate 10 and the support substrate 20 are of the same type and have the same crystal orientation, the first principal axis P1 and the second principal axis P2, which are parallel to the first step 13 and the second step 23, respectively, correspond to the same crystal axis (1-100).

[0078] Starting from a first step 13 on the rear surface 10b of the donor substrate 10, an alignment mark 12 is defined on said rear surface 10b. Starting from a second step 23 on the front surface 20a of the support substrate 20, a second alignment pattern 22 is defined on the rear surface 20b of said substrate 20. It is to be recalled that the mark 12 and the second pattern 22 are formed so as to precisely indicate the directions of the first main axis (P1) and the second main axis (P2), respectively. The mark 12 and the second pattern 22 may each consist of two alignment crosses located at the border of the associated substrates.

[0079] Hydrogen ions enter the donor substrate 10 at a front surface 10a with an energy of 60 keV and E 16H+ / cm 2 Optionally, the donor substrate 10 may be provided with a protective layer on its front surface 10a through which the ions are implanted. A buried weak surface 15 is created in the donor substrate 10 to a depth of about 500 nm.

[0080] The assembly step d) comprises chemical mechanical polishing of the front surface 10a, 20a of the substrate 10, 20 in order to remove the pits 13, 23 produced during step c) and to restore a good surface finish and a roughness of less than 0.2 nm rms suitable for quality assembly. It is noted that the aforementioned protective layer, if present, is removed prior to polishing.

[0081] The substrates 10, 20 are then introduced into a bonding machine equipped with an alignment module that allows optical alignment better than ±0.1°. The alignment mark 12 on the rear surface 10b of the donor substrate 10 and the second alignment pattern 22 on the rear surface 20b of the support substrate 20 are used for this optical alignment between the substrates. Thus, the crystal axes (1-100) of the two substrates 10, 20 can be aligned better than ±0.1°. In other words, after assembly, the crystal axis (1-100) of the donor substrate 10 can be offset by up to 0.1° with respect to the crystal axis (1-100) of the support substrate 20.

[0082] The two substrates, which are aligned relative to each other, are then heated under an inert atmosphere (Ar or N) and vacuum (<1 E- Assembly is carried out by contacting at a temperature of 150° C. (0.8 Pa).

[0083] The transfer step e) is carried out by applying an annealing at 950° C. for 30 minutes, i.e. a spontaneous separation along the buried weak planes results in the composite structure 1 and the remaining part 10″ of the donor substrate.

[0084] The second alignment pattern 22 present on the rear surface 20b of the support substrate 20 (which is also the rear surface of the composite structure 1) accurately indicates the orientation of the crystal axis (1-100) of the thin layer 100 within ±0.1° (or better) and can be easily used during the production of the components of said layer 100 of the composite structure 1.

[0085] Of course, the invention is not limited to the embodiments and examples described, and alternative embodiments may be introduced into the invention without departing from the scope of the invention as defined by the claims.

Claims

1. A process for manufacturing a composite structure (1) comprising a thin layer (100) made of a first monocrystalline material located on a support substrate (20), comprising: a) providing a donor substrate (10) made of said first monocrystalline material having a front surface (10a) and a back surface (10b); b) providing a support substrate (20) having a front surface (20a), a back surface (20b), an edge (20c) and a first alignment pattern (21) on one of said surfaces or on said edge; a step c) of a thermal treatment applied to at least said donor substrate (10) in a controlled atmosphere at a temperature capable of bringing about a surface reorganization on at least one of said faces (10a, 10b) of said substrate (10), said surface reorganization resulting in the formation of first steps (13) of nanometer amplitude parallel to a first principal axis (P1); a step d) of assembling the donor substrate (10) and the support substrate (20) including an optical alignment of better than ±0.1° between an alignment mark (12) indicating the first principal axis (P1) of the donor substrate (10) and at least one alignment pattern (21, 22) of the support substrate (20) before the substrates (10, 20) are brought into contact; e) transferring a thin layer (100) from said donor substrate (10) to said support substrate (20); The manufacturing process includes:

2. the first alignment pattern (21) of the support substrate (20) is a flat spot or a notch formed on its edge (20c); said optical alignment during said assembly step using said first alignment pattern (21); The manufacturing process of claim 1.

3. 3. Manufacturing process according to claim 1 or 2, wherein said first monocrystalline material is silicon carbide and the temperature of the heat treatment of step c) is greater than or equal to 1500°C, preferentially greater than or equal to 1600°C.

4. the support substrate (20) is formed from single crystal silicon carbide; said step c) is also applied to said support substrate (20) and brings about a surface reorganization on at least one of said faces (20a, 20b) of said substrate, said surface reorganization causing the formation of second steps (23) of nanometer amplitude parallel to a second principal axis (P2); a second alignment pattern (22) of the support substrate (20) is formed by the second step (23) itself, by at least one pattern defined by photolithography and etching of the front surface (20a) of the support substrate (20) starting from the second step (23), or by at least one pattern defined by photolithography and etching of the back surface (20b) of the support substrate (20) starting from the second step (23), said optical alignment during said assembly step using said second alignment pattern (22); The manufacturing process of claim 3.

5. 3. The manufacturing process according to claim 1 or 2, wherein the first monocrystalline material is gallium arsenide and the temperature of the heat treatment in step c) is 630° C. or higher.

6. 3. The manufacturing process according to claim 1 or 2, wherein the first monocrystalline material is indium phosphide and the temperature of the heat treatment in step c) is 600° C. or higher.

7. The manufacturing process according to any one of claims 1 to 6, wherein the alignment mark (12) is formed by the first step (13) itself, by at least one mark defined by photolithography and etching of the front side (10a) of the donor substrate (10) starting from the first step (13), or by at least one mark defined by photolithography and etching of the back side (10b) of the donor substrate (10) starting from the first step (13).

8. The manufacturing process according to any one of claims 1 to 7, wherein the assembly step comprises chemical-mechanical polishing of the front surface (10a) of the donor substrate (10) and / or the front surface (20a) of the support substrate (20) before the two substrates (10, 20) are brought into contact.

9. The manufacturing process according to any one of claims 1 to 8, wherein the assembly step comprises the deposition of an intermediate layer on the front surface (10a) of the donor substrate (10) and / or on the front surface (20a) of the support substrate (20) before the two substrates (10, 20) are brought into contact.

10. - forming a recessed weak surface (15) in said donor substrate (10) and defining said thin layer (100) between said recessed weak surface (15) and said front surface (10a) of said donor substrate (10) prior to said assembly step; During said step e), on the one hand, a composite structure (1) is formed comprising a thin layer (100) located on said support substrate (20), and on the other hand, a separation along said buried weak surface (15) in order to form the remaining part (10'') of the donor substrate; The manufacturing process according to any one of claims 1 to 9, comprising:

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