METHOD FOR PREPARING A COMPOSITE STRUCTURE FOR THE FABRICATION OF A HOMOEPITAXIATED SILICON CARBIDE LAYER, AND ASSOCIATED COMPOSITE STRUCTURE

Abstract

The invention relates to a method for preparing a composite structure comprising the following steps: 1) the provision of a composite structure comprising a growth layer of single-crystal silicon carbide, a free face of which extends along a principal plane and is disposed on a support substrate, the growth layer being delimited by a peripheral perimeter and having a crystallographic orientation such that there exists: - an angle of disorientation between a given crystallographic plane and the free face, - a direction of disorientation, projection of an axis normal to the free face, onto the crystallographic plane, and - a reference direction, projection of the direction of disorientation onto the principal plane;2) the formation of a trench in the growth layer, the trench having an inner border extending at a distance and continuously along the peripheral perimeter, following a contour such that, by defining four cardinal points (North-South-West-East) on the peripheral perimeter, with the West-East direction corresponding to the reference direction: - the contour passing through the Northwest-South cardinal points follows a general shape of the peripheral perimeter, - the contour passing through the Northeast-South cardinal points is sawtooth. The invention also relates to a composite structure capable of being produced by the aforementioned preparation process. Figure to be published with the abstract: no figure;

Description

Title of the invention: METHOD FOR PREPARING A COMPOSITE STRUCTURE FOR THE FABRICATION OF A HOMOEPITAXIAL SILICON CARBIDE LAYER, AND ASSOCIATED COMPOSITE STRUCTURE FIELD OF INVENTION

[0001] The present invention relates to the field of semiconductor materials, particularly composite structures comprising an active silicon carbide (SiC) layer fabricated by homoepitaxy on a free SiC surface. It relates in particular to a manufacturing process for limiting the formation of extended basal plane dislocation bar (bBPD) defects in said layer. It also relates to a composite structure on which an excellent quality active layer can be homoepitaxially fabricated.

[0002] TECHNOLOGICAL BACKGROUND OF THE INVENTION

[0003] Silicon carbide (SiC) is a particularly interesting material for the fabrication of power devices, radio frequency devices, or devices operating at very high temperatures. To fabricate these devices, it is common practice to grow an active SiC layer 150 (for example, of polytype 4H or 6H) on the surface of a composite structure 100 comprising a thin layer 10 (of monocrystalline SiC) transferred onto a support substrate 20 (advantageously of polycrystalline SiC or lower-quality monocrystalline SiC), as illustrated in [Fig. 1]. A composite structure 100 can notably be fabricated using a known thin-film transfer technique such as the Smart Cut™ process.

[0004] During the homoepitaxy of the active layer 150 on a composite structure 100, the applicant observed the formation and progressive extension of basal plane dislocation bar (bBPD) defects. This is a complex defect characterized by the presence of a series of basal plane dislocations (BPDs), created during epitaxy, near a discontinuity in the thin layer 10; this discontinuity may exist at point defects (in particular bubbles or holes), or at the peripheral edge of the transferred thin layer 10. Local polytype inclusions, formed during epitaxy on discontinuities in the growth layer 10, are generally the origin of the extended bBPD defects ([Fig. 2]).

[0005] bBPD defects appear when the thickness of the active layer 150 exceeds a critical thickness (typically between 5 µm and 10 µm) and their extent depends on the thermal budgets applied to the structure. For example, for a composite structure 100 comprising a thin SiC-4H layer 10 transferred onto a substrate On a polycrystalline 3C SiC support 20, the bBPD defects are aligned along the [1-100] direction. Figure 3 shows three maps corresponding to the free face of a homoepitaxial active layer 150 on the thin layer 10 of a composite structure 100: (a) for an active layer 150 thickness of 10 µm, (b) for an active layer 150 thickness completed to 20 µm, and (c) for an active layer 150 thickness further completed to 30 µm. It is clear that bBPD defects (dark-colored on the maps) increase in density and extent on the surface of the active layer 150 with increasing active layer 150 thickness.

[0006] These defects are very critical because they can, among other things, cause the deterioration of the devices subsequently developed in the active layer 150, by a bipolar degradation mechanism.

[0007] SUBJECT OF THE INVENTION

[0008] The present invention relates to a method for preparing a composite structure, particularly suitable for manufacturing a single-crystal silicon carbide active layer by homoepitaxy, said method making it possible to limit the density of extended defects of the basal plane dislocation bar (bBPD) type in said layer. The preparation method comprises, in particular, a step of forming a peripheral trench in the growth layer of the composite structure; this trench has a particular geometry in the plane of the layer and makes it possible to form a local barrier preventing or limiting the extension of bBPD defects towards the interior of the active layer. The invention also relates to a composite structure equipped with said trench.

[0009] BRIEF DESCRIPTION OF THE INVENTION

[0010] The invention relates to a method for preparing a composite structure comprising the following steps:

[0011] 1) the provision of a composite structure comprising a growth layer in single-crystal silicon carbide, one free face of which extends along a principal plane and is disposed on a supporting substrate, the growth layer being delimited by a peripheral perimeter and having a crystallographic orientation such that there exists:

[0012] - a disorientation angle between a given crystallographic plane and the free face,

[0013] - a direction of disorientation, projection of an axis normal to the free face, onto the crystallographic plan, and

[0014] - a reference direction, projection of the direction of disorientation onto the plane main ;

[0015] 2) the formation of a trench in the growth layer, the trench exhibiting an inner border that extends at a distance and continuously along the perimeter of the perimeter-

[0016]

[0017]

[0018]

[0019]

[0020]

[0021] pherical following a contour such that, by defining four cardinal points North, South, West, East, on the peripheral perimeter, with the West-East direction corresponding to the reference direction: - the contour passing through the cardinal points Northwest-South follows a general shape of the peripheral perimeter, - the contour passing through the cardinal points North-East-South is jagged. According to other advantageous and non-limiting features of the invention, taken alone or in any technically feasible combination: • the composite structure is in the form of a generally circular plate and the contour passing through the cardinal points North-West-South is circular; • the contour between the cardinal points North and East includes first segments each forming an angle between 0° and 90° with the reference direction, and second segments normal to the reference direction; • the contour between the cardinal points East and South includes third segments each forming an angle between 0° and -90° with the reference direction and second segments normal to the reference direction; • the trench penetrates deep through the entire growth layer; • the peripheral perimeter of the growth layer is located on average between 0.5mm and 2mm from the peripheral edge of the substrate supporting the composite structure; • the inner edge of the trench is located more than 0.1mm, more than 0.5mm, more than 1mm, more than 2mm, more than 3mm, or even more than 5mm from the peripheral perimeter of the growth layer; • the trench has a width, between the inner edge and an outer edge, of between 0.1 qm and 1000qm; • the trench extends from its inner edge, at least to the peripheral perimeter, or even to a peripheral edge of the supporting substrate; • The trench is created by mechanical abrasion, laser abrasion, wet etching or dry etching of the growth layer and potentially part of the supporting substrate. The invention also relates to a method for manufacturing a single-crystal silicon carbide active layer by homoepitaxy on a composite structure obtained from the aforementioned preparation process, the manufacturing process comprising: 3) the epitaxial growth of the active layer on the growth layer. The invention also relates to a composite structure comprising a growth layer of single-crystal silicon carbide, a free face of which extends along a principal plane, the growth layer being disposed on a support substrate, delimited by a peripheral perimeter and exhibiting a crystallographic orientation such that it exists:

[0022] - a disorientation angle between a given crystallographic plane and the free face,

[0023] - a direction of disorientation, projection of an axis normal to the free face, onto the crystallographic plan, and

[0024] - a reference direction, projection of the direction of disorientation onto the plane main.

[0025] The composite structure comprising a trench in the growth layer, the trench having an inner border which extends at a distance and continuously along the peripheral perimeter following a contour such that, by defining four cardinal points North, South, West, East, on the peripheral perimeter, with the West-East direction corresponding to the reference direction, the contour passing through the North-West-South cardinal points follows a general shape of the peripheral perimeter, and the contour passing through the North-East-South cardinal points is sawtooth.

[0026] According to other advantageous and non-limiting features of the invention, taken alone or in any technically feasible combination: • the composite structure is in the form of a generally circular plate and the contour passing through the cardinal points North-West-South is circular; • the contour between the cardinal points North and East includes first segments each forming an angle between 0° and 90° with the reference direction and second segments normal to the reference direction; • the contour between the cardinal points East and South includes third segments each forming an angle between 0° and -90° with the reference direction and second segments normal to the reference direction; • the growth layer has a thickness, and the trench has a depth at least equal to said thickness; • the first segments and / or the third segments are straight; • the first segments and / or the third segments are curved; • the crystallographic plane is the (0 0 0 1) plane and the disorientation direction is the crystallographic direction [11-2 0]; • the crystallographic plane is the (0 0 0 -1) plane and the disorientation direction is the crystallographic direction [-1-120]; • The angle of disorientation is 4°. BRIEF DESCRIPTION OF THE FIGURES

[0027] Other features and advantages of the invention will become apparent from the detailed description of the invention which follows with reference to the accompanying figures in which:

[0028] [Fig.1] Fig.1 shows the section of a composite structure before and after growth of a homoepitaxial active layer;

[0029] [Fig.2] Figure [Fig.2] shows an image of an extensive defect, obtained by imaging by photoluminescence, after growth of an active layer on the growth layer of a composite structure: we can see in the bottom left of the image an irregular area (the black region being the crown of the composite structure, devoid of an active layer) and the start of an extended bBPD defect;

[0030] [Fig.3] Fig.3 presents three maps of the surface of an active layer, at different stages of its growth on the thin layer of a composite structure: (a) after 1 Oum of growth, (b) after 20pm of growth, (c) after 30µm of growth; the dark areas correspond to extended bBPD defects (BPD network, SSF, partial dislocations); the maps were obtained on a SICA88 type equipment;

[0031] [Fig.4a]

[0032] [Fig.4b]

[0033] [Fig.4c]

[0034] [Fig.4d]

[0035] [Fig. 4e] Figures 4a, 4b, 4c, 4d, 4e show sub-steps of the pre-process preparation of a composite structure according to the present invention;

[0036] [Fig. 5] Figure 5 presents a diagram representing the angle of disorientation, the direction of disorientation and the reference direction, in a growth layer of a composite structure according to the invention;

[0037] [Fig. 6] [Fig. 6] presents cross-sectional diagrams of the edge of five structures composites conforming to the invention, representing five different peripheral trench options;

[0038] [Fig.7a]

[0039] [Fig. 7b] Figures 7a and 7b each show a top view of a structure composite according to the invention;

[0040] [Fig. 8a]

[0041] [Fig. 8b] Figures 8a and 8b show surface maps of layers active homoepitaxies on growth layers of test composite structures, not conforming to a composite structure according to the invention;

[0042] [Fig.9] Fig.9 presents an explanatory diagram showing the formation of sorting defects angular downstream of a trench, considering the direction of step growth (corresponding to the reference direction). DETAILED DESCRIPTION OF THE INVENTION

[0043] The present invention relates to a method for preparing a composite structure 100, particularly suitable for the manufacture of an active layer 150 in single-crystal silicon carbide, by homoepitaxy on the growth layer 10 of said composite structure 100.

[0044] The process according to the invention aims to provide an active layer 150 of improved quality by implementing a local barrier in the growth layer 10, capable of blocking the extension of bBPD defects towards the center of the active layer 150. This local barrier is defined to take into account a specificity of the composite structures 100, namely that the growth layer 10 has an irregular peripheral perimeter 10c, which is a major source of initial defects likely to give rise to extended bBPD defects after epitaxy of the active layer 150.

[0045] The first step of the process consists of providing a composite structure 100 comprising a growth layer 10 of single-crystal silicon carbide, a free face 10a of which extends along a principal plane (x,y). The growth layer 10 is disposed on a support substrate 20. The composite structure 100 is typically in the form of a circular wafer with a diameter of 100 mm, 150 mm, 200 mm, or even more, as is commonly the case in the semiconductor and microelectronics industries. The thickness of the structure 100 extends along the z-axis in the figures.

[0046] As indicated in the introduction, the composite structure 100 can be developed by a layer transfer technique such as the Smart Cut™ process.

[0047] In a first substep a), a donor substrate 1 of single-crystal silicon carbide and a support substrate 20 are provided ([Fig. 4a]). The single-crystal SiC can be of polytype 4H, 6H, or 3C. The donor substrate 1 is preferably in the form of a wafer with a diameter identical to, or very close to, that of the support substrate 20 with which it will be subsequently assembled, and a thickness typically between 300 µm and 800 µm. It has a front face la and a back face 1b. The surface roughness of the front face la is advantageously chosen to be less than 1 / 800 µm RMS, or even less than 0.5 nm RMS, measured by atomic force microscopy (AFM) on a 20 µm x 20 µm scan. The type of doping and the resistivity of the donor substrate 1 are defined according to the application and the devices intended. The support substrate 20 corresponds to the mechanical support of the future composite structure 100.It is advantageously formed from polycrystalline silicon carbide (p-SiC) or from monocrystalline SiC of lower crystalline quality. Its electrical properties (type and level of doping) can also be chosen according to the intended application.

[0048] The second substep b) comprises the implantation of light species in a donor substrate 1, to form a buried fragile plane 11 delimiting, with a front face of the donor substrate 1, the surface layer to be transferred 10' ([Fig. 4b]). The light species are preferably hydrogen and / or helium, and are im planted in the donor substrate 1, at a depth consistent with the target thickness of the growth layer 10, these lightweight species will form microcavities around the determined depth, distributed within a thin layer parallel to the free surface la of the donor substrate 1, i.e., parallel to the (x,y) plane in the figures. For simplicity, this thin layer is called the buried fragile layer 11. The implantation energy of the lightweight species is chosen to reach the target depth. For example, hydrogen ions will be implanted at an energy between 10 keV and 250 keV, and at a dose between 5E16 / cm2 and 1E17 / cm2, to delimit a surface layer 10' with a thickness on the order of 100 nm to 1500 nm. The dose and implantation energy can, of course, vary depending on the lightweight species chosen.Note that a protective layer may be deposited on the front face of the donor substrate 1, prior to the ion implantation step. This protective layer may be composed of a material such as silicon oxide or silicon nitride, for example. It may be removed prior to the next substep.

[0049] The third substep c) corresponds to the assembly of the support substrate 20, on the side of its front face 20a, with the implanted donor substrate 1, also on the side of its front face ([Fig. 4c]). The lateral dimensions in the principal plane (x,y) of the support substrate 20 (its diameter in particular) are the same as those of the composite structure 100. The support substrate 20 typically has a thickness between approximately 50 µm and several hundred micrometers, for example between 50 µm and 650 µm, or between 100 µm and 450 µm, or between 200 µm and 350 µm.

[0050] The assembly is performed by direct bonding, by molecular adhesion, along a bonding interface 40. Optionally, an intermediate layer (not shown) can be formed on the front face of the donor substrate 1, before or after the introduction of the light species, and in any case, before the assembly phase. This intermediate layer can be made of a dielectric, semiconductor, or metallic material (such as, for example, silicon oxide, silicon, silicon carbide, tungsten, titanium, etc.). Optionally, an intermediate layer can also be deposited on the face 20a to be assembled of the support substrate 20, prior to assembly; it can be of the same or different nature as the intermediate layer mentioned for the donor substrate 1. An intermediate layer can optionally be deposited on either of the two substrates 1, 20 to be assembled.The intermediate layer(s) is / are intended to be buried in the bonded assembly 50 after assembly, and ultimately in the composite structure 100.

[0051] Direct bonding by molecular adhesion does not require an adhesive material, because bonds are established at the atomic scale between the surfaces being joined. Several Several types of molecular adhesion bonding exist, differing in particular by their temperature, pressure, atmospheric conditions, or pre-treatments prior to surface contact. Examples include room temperature bonding with or without prior plasma activation of the surfaces to be joined, atomic diffusion bonding (ADB), surface-activated bonding (SAB), etc.

[0052] The assembly substep may include, prior to bringing the faces la,20a to be assembled into contact, conventional sequences of chemical cleaning (for example, RCA cleaning), surface activation (for example, by oxygen or nitrogen plasma) or other surface preparations (such as scrubbing), which may promote the quality of the bonding interface 40 (low defect, high adhesion energy).

[0053] It should be noted that the presence of a chamfer, at the level of the peripheral edge 20c of the support substrate 20 and the peripheral edge of the donor substrate 1, generates a non-bonded peripheral ring (not shown in [Fig.4c]), a ring into which the surface layer 10' will not be transferred.

[0054] The fourth substep d) corresponds to a separation along the buried fragile plane 11 to form an intermediate composite structure 100' comprising the surface layer 10' after transfer and the supporting substrate 20, on the one hand, and the remainder of the donor substrate 1', on the other hand ([Fig. 4d]). The separation along the buried fragile plane 11 is usually achieved by applying a heat treatment at a temperature between 800°C and 1200°C. Such a heat treatment induces the development of cavities and microcracks in the buried fragile plane 11, and their pressurization by the light species present in gaseous form, until a fracture propagates along said fragile plane 11. Alternatively or concurrently, mechanical stress can be applied to the bonded assembly and in particular to the buried fragile plane 11, so as to propagate or help to mechanically propagate the fracture leading to the separation.

[0055] The free surface 10'a of the surface layer 10' is usually rough after separation: for example, it has a roughness between 5 nm and 100 nm RMS. The surface layer 10' is delimited, in the (x,y) plane, by a peripheral boundary 10'c, set back from the peripheral edge 20c of the support substrate 20. As mentioned previously, this peripheral boundary 10'c can be serrated and irregular; on average, it is spaced from the peripheral edge 20c by a distance (width of the unbonded peripheral rim) typically between 0.5 mm and 2 mm.

[0056] Finally, the fifth substep e) of finishing comprises the application of thermal, mechanical and / or chemical treatment(s) to the free surface 10'a of the layer su surface 10', to form the composite structure 100 equipped with the growth layer 10 of single-crystal silicon carbide ([Fig. 4e]). In particular, this substep e) may include a mechano-chemical smoothing treatment of the free surface 10'a of the surface layer 10'. A removal, for example, of between 50 nm and 300 nm effectively restores the surface condition of the layer, typically leading to a roughness less than or equal to 0.5 nm RMS, or even less than or equal to 0.1 nm RMS (AFM scan 10 x 100 sq m² or 20 x 20 sq m²). Substep e) may also include at least one heat treatment at a temperature between 1200°C and 1800°C. This heat treatment is applied to remove residual light species from the surface layer 10' and to promote the rearrangement of its crystal lattice, thus forming a high-quality growth layer 10. It also strengthens the bonding interface 40.

[0057] At this stage of the process, the growth layer 10 of the composite structure 100 has an initial thickness typically ranging from a few tens of nm to a few hundred nm, for example, between 50 nm and 1000 nm. The growth layer 10 is delimited by a peripheral rim 10c exhibiting irregularities. In general, said peripheral rim 10c is located, on average, between 0.5 mm and 2 mm from the peripheral edge 20c of the support substrate 20 of the composite structure 100. It should be noted that the distance between the peripheral rim 10c and the edge 20c can vary, below 0.5 mm or above 2 mm, depending on the structure.

[0058] The growth layer 10, made of single-crystal SiC, has a crystallographic orientation such that there is a disorientation angle α between a given crystallographic plane PC and the free face 10a of the growth layer 10, or in other words, a disorientation angle α between the normal nPC to the crystallographic plane PC and the normal z (z-axis of the orthonormal coordinate system shown in the figures) to the free face 10a ([Fig. 5]). This disorientation angle α can, for example, be 4°.

[0059] A disorientation direction DD can be defined, which corresponds to the projection of the z-axis normal to the free face 10a onto the crystallographic plane PC. Finally, a reference direction DR is defined, which is the projection of the disorientation direction DD onto the principal (x,y) plane.

[0060] Due to the misorientation of the free face 10a with respect to a crystallographic plane PC, the homoepitaxy of the active layer 150 on the thin film 10 will occur through the growth of steps (atomic steps in the form of a Si-C bilayer, or steps a few nanometers high in a "step-bunching" mechanism), steps whose base plane is parallel to the crystallographic plane PC. The reference direction DR represents the direction of step growth in the principal (x,y) plane. The usefulness of defining the reference direction DR will become apparent in the second step of the process.

[0061] By way of example, the crystallographic plane PC may be the (0 0 0 1) plane and the misorientation direction DD is the crystallographic direction [1 1 -2 0]; the reference direction DR is then the projection of the crystallographic direction [1 1 -2 0] onto the principal (x,y) plane. According to another example, the crystallographic plane PC may be the (0 0 0 -1) plane and the misorientation direction DD is the crystallographic direction [-1 -1 2 0]. According to still other examples, the crystallographic plane PC could be the (1 1 -2 0) plane or even the (10 - 10) plane, with associated misorientation directions DD and reference directions DR.

[0062] The process according to the invention then includes a second step corresponding to the formation of a local barrier in the growth layer 10. This local barrier corresponds to a trench 131 made in the growth layer 10.

[0063] The trench 131 has an inner edge 130 (edge ​​of the trench 131 located on the side of the center of the composite structure 100) and may have an outer edge 132 (edge ​​of the trench 131 located on the side of the peripheral edge of the composite structure 100). In the principal plane (x,y), the inner edge 130 extends at a distance (towards the interior of the layer 10) and continuously along the peripheral perimeter 10c ([Fig. 6], [Fig. 7a]). Preferably, it is located more than 0.1 mm, more than 0.5 mm, more than 1 mm, more than 2 mm, more than 3 mm, or even more than 5 mm from the peripheral perimeter 10c of the growth layer 10, in the direction of the center of the structure 100.

[0064] When delimited by an inner border 130 and an outer border 132, the trench 131 typically has a width, in the principal plane (x,y), of between 0.1 µm and 1000 µm, for example 60 µm ([Fig. 6] (i), (ii), (iii)). Alternatively, the trench 131 may correspond to a cut-out, delimited by an inner border 130 and extending to the peripheral perimeter 10c, or even beyond, for example to the peripheral edge 20c of the supporting substrate 20 ([Fig. 6], (iv), (v)).

[0065] According to a first embodiment, this trench 131 penetrates the entire growth layer 10 ([Fig. 6] (i), (iv)). It may optionally extend into the supporting substrate 20 of the composite structure 100: the depth of the trench 131 could then be a few tens of micrometers, for example 30 µm ([Fig. 6] (ii), (v)). According to a second embodiment, the trench 131 has a depth less than the thickness of the growth layer 10, for example a few hundred nm ([Fig. 6] (iii)).

[0066] The trench 131 can be made by mechanical abrasion (sawing, honing), by laser abrasion, by wet etching or by dry etching of the growth layer 10 (and possibly of the supporting substrate 20). It can be made at different times during the manufacture of the composite structure 100.

[0067] The trench 131 can be formed in the composite structure 100 at the end of the sub- finishing substep e) described previously. Alternatively, it can be formed in the intermediate composite structure 100' before performing finishing substep e). Finally, according to another alternative, the trench 131 can be made in the donor substrate 1, on the side of its face to be assembled, during substep a) or after implantation substep b). Formed in the donor substrate 1, to a depth greater than or equal to the thickness of the surface layer 10' to be transferred, the trench 131 will be "transferred" into the surface layer 10' of the intermediate composite structure 100' and, consequently, into the growth layer 10 of the resulting composite structure 100.

[0068] According to the present invention, the inner edge 130 of the trench 131 has a particular and asymmetrical contour in the principal plane (x,y). To describe this contour, four cardinal points (North, South, West, East) are defined, arranged on the peripheral perimeter 10c, with the West-East direction corresponding to the reference direction DR, as illustrated in [Fig. 7a]. These cardinal points N, S, W, E will serve as reference points to define the characteristics of the contour of the inner edge 130 in the principal plane (x,y).

[0069] Thus oriented, the growth layer 10 of the composite structure 100 is provided with a trench 131 with an inner border 130 whose western contour 130NW, passing through the cardinal points Northwest-South, follows a general shape of the peripheral perimeter 10c. For example, in the case of a composite structure 100 in the form of a generally circular plate, the peripheral perimeter has a general circular shape: the western contour 130NW is therefore circular. In Figures 7a and 7b, which illustrate a composite structure in the form of a circular plate with a flat section (to the South), the western contour 130NW follows the general shape of the peripheral perimeter 10c, namely, circular in one part and flat in another part.

[0070] The contour on the East side 130NES, passing through the Northeast-South cardinal points, is, for its part, sawtooth.

[0071] This particular asymmetric contour was determined from observations made by the applicant regarding the asymmetric propagation of extended bBPD defects from the irregularity formed by a trench. In a first test, a circular trench 121 was created along the entire peripheral perimeter 10c of the thin layer 10: [Fig. 8a] (i) shows a surface map after homoepitaxy of 100 m thickness, [Fig. 8a] (ii) shows a map of the same structure after an additional epitaxy of 100 m (i.e., an active layer thickness 150 of 200 m). A strong extension of the bBPD defects is observed in the Northeast-South portion of the layer, from the inner edge of trench 121, while the Northwest-South portion of the layer appears much less affected.

[0072] In a second test, three circular trenches 121', defining three circles Inscribed within the perimeter 10c of the thin layer 10, the following were carried out: [Fig. 8b] (i) shows a surface map after a homoepitaxy of 10m thickness, [Fig. 8b] (ii) shows a map of the same structure after an additional epitaxy of 100m (i.e., an active layer thickness 150 of 20pm). An extension of the bBPD defects is observed, from the inner edge of trench 121', towards the interior of the three circles, more pronounced in their respective eastern halves; while the extension of the bBPD defects, from the outer edge of trench 121', towards the exterior of the three circles, is more pronounced in their respective western halves.

[0073] One explanation put forward by the applicant is that a trench 121,121' formed in the growth layer 10 is an irregularity at which triangular defects T (stacking faults and inclusions of the 3C-SiC type or other) form during homoepitaxy. Considering a given step growth direction (translated by the reference direction DR in the principal (x,y) plane), the triangular defects T will form downstream of the trench 121,121'. It is assumed that these triangular defects T provide an effective barrier to the propagation of bBPD defects downstream of the trench 121,121', whereas extended bBPD defects can easily propagate upstream of the trench 121,121', where the triangular defects T are absent, as illustrated in [Fig. 9].

[0074] Thus, the invention aims to form a trench 131, the contour of which is defined such that the inner edge 130 of the trench 131 (oriented towards the center of the growth layer 10) has triangular defects T (generated during homoepitaxy) capable of forming an effective local barrier to block the propagation of bBPD defects towards said center. This barrier makes it possible to block not only potential extended defects that would start from the trench 131, but also those initiated by the irregular peripheral perimeter 10c of the growth layer 10.

[0075] This objective is achieved in particular by carrying out the aforementioned asymmetric contour illustrated in [Fig.7a], in which the West side contour 130NOS, passing through the North-West-South cardinal points, follows the general shape of the peripheral contour 10c (for example, circular) and whose East side contour 130NES, passing through the North-East-South cardinal points, is sawtooth.

[0076] Preferably, the contour 130NES, between the North and East cardinal points, comprises first segments S1, each forming an angle [3] between 0° and 90° with the reference direction DR, and second segments S2 normal to the reference direction DR ([Fig. 7b]). Furthermore, the contour 130NES, between the East and South cardinal points, comprises third segments S3, each forming an angle [3] between 0° and -90° with the reference direction DR, and second segments S2 normal to the reference direction DR.

[0077] The first segments S1 and / or the third segments S3 may be straight or curved. When the segments are curved, the angles θ and θ are defined between the reference direction and the segment passing through the starting and ending points of each curved segment. Note that the second segments S2 could also potentially be curved.

[0078] Following the preparation process described, a manufacturing process for an active layer 150 in single-crystal silicon carbide can be implemented, by carrying out a third step corresponding to the epitaxial growth of the active layer 150 on the growth layer 10 of the composite structure 100, provided with its trench 131. The active layer 150 has a second thickness, typically greater than or equal to 5pm, 10pm, or even 30pm.

[0079] This epitaxial growth of silicon carbide is carried out in the classic temperature range, namely between 1500°C and 1900°C.

[0080] The physical discontinuity that constitutes the trench 131 induces locally disturbed epitaxial growth, with triangular defects mostly arranged on the inner border 130 of the trench 131 (oriented towards the center of the growth layer 10): this forms a "wall" which allows the blocking of the sliding of the BPD dislocations towards the center of the active epitaxial layer 150.

[0081] The disruption of epitaxial growth related to trench 131 remains local, however, and the rest of the active layer 150 grows according to the crystalline structure of the growth layer 10.

[0082] The invention also relates to the composite structure 100 comprising the growth layer 10, disposed on the support substrate 20, and the trench 131 formed in said growth layer 10. As mentioned previously with reference to the method of preparing the composite structure 100, the growth layer 10 is delimited by a peripheral boundary 10c and has a crystallographic orientation such that:

[0083] - a disorientation angle α between a given crystallographic plane PC and its face free 10a, - a direction of disorientation DD, projection of an axis (z) normal to the free face, onto the crystallographic plane PC, and - a reference direction DR, projection of the disorientation direction DD onto the principal plane (x,y).

[0084] The inner edge 130 of the trench 131 extends at a distance (towards the center of the layer) and continuously along the peripheral perimeter 10c, following a particular contour such that, by defining four cardinal points (North, South, West, East) on said peripheral perimeter 10c, with the West-East direction corresponding to the reference direction DR, the contour 130NOs passing through the North-West-South cardinal points follows the general shape of the peripheral perimeter 10c (for example, circular), and the contour 130nes passing through the North-East-South cardinal points is sawtooth ([Fig.7a]).

[0085] In other words, the geometry of the inner border 130 contour is defined such that, knowing the reference direction DR, triangular defects T form predominantly on said inner border 130 (oriented towards the center of the growth layer 10) during epitaxial growth. This makes it possible to block bBPD defects initiated by the peripheral perimeter 10c of the growth layer 10 or by the trench 131 itself.

[0086] Advantageously, the contour between the North and East cardinal points comprises first segments S1 each forming an angle [3] between 0° and 90° with the reference direction DR and second segments S2 normal to the reference direction DR; furthermore, the contour between the East and South cardinal points comprises third segments S3 each forming an angle [3] between 0° and -90° with the reference direction DR and second segments S2 normal to the reference direction DR ([Fig.7b]).

[0087] The invention also relates to the composite structure 100 provided with the active layer 150 raw by homoepitaxy on the growth layer 10, and whose trench 131 allows obtaining an excellent quality of active layer 150, because it is free from or very weakly impacted by a propagation of extended defects bBPD in the central region of the structure (region inside the contour of the trench 131).

[0088] Of course, the invention is not limited to the embodiments and examples described, and alternative embodiments can be made without departing from the scope of the invention as defined by the claims.

Claims

Demands

1. Method for preparing a composite structure (100) comprising the following steps: 1) supplying a composite structure (100) comprising a growth layer (10) of single-crystal silicon carbide having a free face (10a) extending along a principal plane (x,y) and disposed on a support substrate (20), the growth layer (10) being delimited by a peripheral perimeter (10c) and having a crystallographic orientation such that there exists: - a disorientation angle (a) between a given crystallographic plane (PC) and the free face (10a), - a disorientation direction (DD), projection of an axis (z) normal to the free face (10a), onto the crystallographic plane (PC), and - a reference direction (DR), projection of the disorientation direction (DD) onto the principal plane (x,y);2) the formation of a trench (131) in the growth layer (10), the trench (131) having an inner border (130) which extends at a distance and continuously along the peripheral perimeter (10c) following a contour such that, by defining four cardinal points (North-South-West-East) on the peripheral perimeter (10c), with the West-East direction corresponding to the reference direction (DR): - the contour (130NOS) passing through the North-West-South cardinal points follows a general shape of the peripheral perimeter (10c), - the contour (130NES) passing through the North-East-South cardinal points is sawtooth.;

2. A preparation method according to the preceding claim, wherein the composite structure (100) is in the form of a circular plate and the contour (130NOS) passing through the North-West-South cardinal points is circular.

3. A preparation method according to any one of the preceding claims, wherein: - the contour between the North and East cardinal points comprises first segments (S1) each forming an angle (S3) between 0° and 90° with the reference direction (DR) and second segments (S2) normal to the reference direction (DR), and - the contour between the East and South cardinal points comprises third segments (S3) each forming an angle (S3) between 0° and -90° with the reference direction (DR) and second segments (S2) normal to the reference direction (DR).

4. A preparation method according to any one of the preceding claims, wherein the trench (131) penetrates deep through the entire growth layer (10).

5. A preparation method according to any one of the preceding claims, wherein the peripheral perimeter (10c) of the growth layer (10) is located on average between 0.5mm and 2mm from the peripheral edge (20c) of the support substrate (20) of the composite structure (100).

6. A preparation method according to any one of the preceding claims, wherein the inner edge (130) of the trench (131) is located more than 0.1mm, more than 0.5mm, more than 1mm, more than 2mm, more than 3mm, or even more than 5mm from the peripheral perimeter (10c) of the growth layer (10).

7. A preparation method according to any one of the preceding claims, wherein the trench has a width, between the inner edge (130) and an outer edge (132), of between 0.10m and 1000m.

8. A preparation method according to any one of claims 1 to 6, wherein the trench (131) extends from its inner edge (130), at least to the peripheral perimeter (10c), or even to a peripheral edge (20c) of the supporting substrate (20).

9. A preparation method according to any one of the preceding claims, wherein the trench (131) is made by mechanical abrasion, laser abrasion, wet etching or dry etching of the growth layer (10) and potentially of a part of the supporting substrate (20).

10. Method of manufacturing an active layer (150) of single-crystal silicon carbide by homoepitaxy on a composite structure (100) obtained from the preparation process according to any one of the preceding claims, the manufacturing process comprising: 3) the epitaxial growth of the active layer (150) on the growth layer (10).

11. Composite structure (100) comprising a growth layer (10) of single-crystal silicon carbide, of which a free face (10a) extends along a principal plane (x,y), the growth layer (10) being disposed on a support substrate (20), delimited by a peripheral perimeter (10c) and having a crystallographic orientation such that there exists: - a disorientation angle (a) between a given crystallographic plane (PC) and the free face (10a), - a disorientation direction (DD), projection of an axis (z) normal to the free face (10a), onto the crystallographic plane (PC), and - a reference direction (DR), projection of the disorientation direction (DD) onto the principal plane (x,y), the composite structure (100) comprising a trench (131) in the growth layer (10), the trench (131) having an inner border (130) which extends at a distance and continuously along the peripheral boundary (10c) following a contour such that, by defining four cardinal points (North-South-West-East) on the peripheral boundary (10c), with the West-East direction corresponding to the reference direction (DR), the contour (130NOS) passing through the North-West-South cardinal points follows a general shape of the peripheral boundary (10c), and the contour (130NES) passing through the North-East-South cardinal points is sawtooth.

12. Composite structure (100) according to the preceding claim, in the form of a circular plate and in which the contour (130NOS) passing through the North-West-South cardinal points is circular.

13. Composite structure (100) according to any one of claims 11 and 12, wherein: - the contour between the North and East cardinal points comprises first segments (S1) each forming an angle (S3) between 0° and 90° with the reference direction (DR) and second segments (S2) normal to the reference direction (DR), and - the contour between the East and South cardinal points comprises third segments (S3) each forming an angle (S3) between 0° and -90° with the reference direction (DR) and second segments (S2) normal to the reference direction (DR).

14. Composite structure (100) according to the preceding claim, wherein the growth layer (10) has a thickness, and the trench (131) has a depth at least equal to said thickness.

15. Composite structure (100) according to one of the two preceding claims, wherein the first segments (SI) and / or the third segments (S3) are straight.

16. Composite structure (100) according to any one of claims 13 and 14, wherein the first segments (SI) and / or the third segments (S3) are curved.

17. Composite structure (100) according to any one of claims 11 to 16, wherein the crystallographic plane (PC) is the plane (0 0 0 1) and the disorientation direction (DD) is the crystallographic direction [11-2 0],

18. Composite structure (100) according to any one of claims 11 to 16, wherein the crystallographic plane (PC) is the plane (0 0 0 -1) and the disorientation direction (DD) is the crystallographic direction [-1-1 2 0],

19. Composite structure (100) according to any one of claims 11 to 18, wherein the angle of disorientation (a) is 4°.

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