METHOD FOR PREPARING A COMPOSITE STRUCTURE FOR THE MANUFACTURE OF A HOMOEPITAXIAL SILICON CARBIDE LAYER, AND ASSOCIATED COMPOSITE STRUCTURE

Abstract

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

Description

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

[0001] The present invention relates to the field of semiconductor materials, in particular composite structures comprising an active layer of silicon carbide (SiC) produced by homoepitaxy on a free SiC surface. It relates in particular to a manufacturing method making it possible to limit the formation of extensive defects of the basal plane dislocation bar (bBPD) type in said layer. It also relates to a composite structure on which an active layer of excellent quality can be homoepitaxied.

[0002] TECHNOLOGICAL BACKGROUND OF THE INVENTION

[0003] Silicon carbide (SiC) is a particularly interesting material for the manufacture of power devices, radio frequencies or even devices operating at very high temperatures. To develop these devices, it is usual to grow an active layer 150 of SiC (for example of polytype 4H or 6H) on the surface of a composite structure 100 including a thin layer 10 (of monocrystalline SiC) transferred onto a support substrate 20 (advantageously of polycrystalline or monocrystalline SiC of lower quality), as illustrated in [Fig.l]. A composite structure 100 can in particular be developed by a known thin layer 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) type defects. This is a complex defect characterized by the presence of a series of basal plane dislocations (BPD), created during the epitaxy, near a discontinuity of the thin layer 10; this discontinuity can exist at the level of point defects (in particular bubble or hole), or at the level of the peripheral periphery of the transferred thin layer 10. Local polytype inclusions, formed during the epitaxy on discontinuities of the growth layer 10, are generally at the origin of the extended bBPD defects ([Fig.2]).

[0005] The bBPD defects appear when the thickness of the active layer 150 exceeds a critical thickness (typically between 5 qm and 10 qm) and their extension depends on the thermal budgets applied to the structure. For example, for a composite structure 100 comprising a thin layer 10 of SiC-4H transferred onto a substrate support 20 in polycrystalline 3C SiC, the bBPD defects are aligned along the [1 -1 0 0] direction. [Fig.3] shows three maps corresponding to the free face of an active layer 150 homoepitaxied on the thin layer 10 of a composite structure 100, (a) for an active layer 150 thickness of 10 pm, (b) for an active layer 150 thickness completed to 20 pm, (c) for an active layer 150 thickness further completed up to 30 pm. It is clear that bBPD defects (dark in color on the maps) increase in density and extension on the surface of the active layer 150, with the increase in the thickness of the active layer 150.

[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 the manufacture of an active layer of monocrystalline silicon carbide, by homoepitaxy, said method making it possible to limit the density of extended defects of the basal plane dislocation (bBPD) bar 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 provided 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) providing a composite structure comprising a growth layer in monocrystalline silicon carbide, a free face of which extends along a principal plane and arranged on a support substrate, the growth layer being delimited by a peripheral circumference 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, on the crystallographic plane, 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 having an inner border that extends at a distance and continuously along the peri-

[0016]

[0017]

[0018]

[0019]

[0020]

[0021] spherical 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 North-West-South follows a general shape of the peripheral contour, - the contour passing through the North-East-South cardinal points is saw-toothed. According to other advantageous and non-limiting characteristics 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 outline passing through the North-West-South cardinal points is circular; • the contour between the cardinal points North and East comprises 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 comprises third segments each forming an angle between 0° and -90° with the reference direction and second segments normal to the reference direction; • the trench crosses the entire growth layer in depth; • the peripheral edge of the growth layer is on average between 0.5 mm and 2 mm from the peripheral edge of the support substrate of the composite structure; • the inner edge of the trench 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 edge of the growth layer; • the trench has a width, between the inner border and an outer border, 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 made by mechanical abrasion, by laser abrasion, by wet etching or by dry etching of the growth layer and potentially of part of the support substrate. The invention also relates to a method for manufacturing an active layer of monocrystalline silicon carbide by homoepitaxy on a composite structure resulting from the aforementioned preparation method, the manufacturing method comprising: 3) epitaxial growth of the active layer on the growth layer. The invention finally relates to a composite structure comprising a growth layer of monocrystalline silicon carbide, a free face of which extends along a main plane, the growth layer being arranged on a support substrate, delimited by a peripheral circumference and presenting a crystallographic orientation such that there 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, on the crystallographic plane, 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 remotely and continuously along the peripheral periphery following a contour such that, by defining four cardinal points North, South, West, East, on the peripheral periphery, with the West-East direction corresponding to the reference direction, the contour passing through the cardinal points North-West-South follows a general shape of the peripheral periphery, and the contour passing through the cardinal points North-East-South is saw-toothed.

[0026] According to other advantageous and non-limiting characteristics 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 outline passing through the North-West-South cardinal points is circular; • the contour between the cardinal points North and East comprises 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 comprises 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 rectilinear; • the first segments and / or the third segments are curved; • the crystallographic plane is the (0 0 0 1) plane and the misorientation direction is the [11-2 0] crystallographic direction; • the crystallographic plane is the (0 0 0 -1) plane and the misorientation direction is the [-1-120] crystallographic direction; • the disorientation angle is 4°. BRIEF DESCRIPTION OF THE FIGURES

[0027] Other characteristics and advantages of the invention will emerge from the detailed description of the invention which follows with reference to the appended figures in which:

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

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

[0030] [Fig.3] [Fig.3] shows 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 μm of growth, (b) after 20 μm of growth, (c) after 30 μm of growth; the dark areas correspond to extended bBPD defects (BPD network, SSF, partial dislocations); the maps were obtained on 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-processing method preparation of a composite structure in accordance with the present invention;

[0036] [Fig.5] [Fig.5] shows a diagram representing the disorientation angle, 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] shows cross-sectional diagrams of the edge of five structures composites in accordance with 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 in accordance with the invention;

[0040] [Fig. 8a]

[0041] [Fig.8b] Figures 8a and 8b show surface maps of layers active homoepitaxial growth layers on 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 tri-defects angular downstream of a trench, considering the direction of growth by steps (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 monocrystalline silicon carbide, by homoepitaxy on the growth layer 10 of said composite structure 100.

[0044] The method 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 the 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 periphery 10c, which is a major source of initial defects likely to give rise to the extended bBPD defects after epitaxy of the active layer 150.

[0045] The first step of the method corresponds to the provision of a composite structure 100 comprising a growth layer 10 made of monocrystalline silicon carbide, a free face 10a of which extends along a main plane (x,y). The growth layer 10 is arranged on a support substrate 20. The composite structure 100 is typically in the form of a circular wafer with a diameter of 100mm, 150mm, 200mm, or even more, as is usually the case in the field of semiconductors and microelectronics. 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 produced by a layer transfer technique such as the Smart Cut™ process.

[0047] In a first sub-step a), a donor substrate 1 made of monocrystalline silicon carbide and a support substrate 20 are provided ([Fig.4a]). The monocrystalline 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 subsequently be assembled, and with a thickness typically between 300 μm and 800 μm. It has a front face 1a and a rear face 1b. The surface roughness of the front face 1a is advantageously chosen to be less than 1 nm RMS, or even less than 0.5 nm RMS, measured by atomic force microscopy (AFM) on a scan of 20 μm x 20 μm. The type of doping and the resistivity of the donor substrate 1 are defined according to the application and the devices targeted. 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 (its type and level of doping) can also be chosen according to the intended application.

[0048] The second sub-step b) comprises the implantation of light species in a donor substrate 1, to form a buried fragile plane 11 delimiting, with a front face 1a of the donor substrate 1, the surface layer to be transferred 10' ([Fig.4b]). The light species are preferentially hydrogen and / or helium, and are im planted in the donor substrate 1, at a depth consistent with the thickness of the targeted growth layer 10. These light species will form, around the determined depth, microcavities distributed in a thin layer parallel to the free surface 1a of the donor substrate 1, i.e. parallel to the (x,y) plane in the figures. This thin layer is called the buried fragile plane 11 for the sake of simplification. The implantation energy of the light species is chosen so as to reach the targeted 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' having a thickness of the order of 100nm to 1500nm. The dose and the implantation energy can of course vary depending on the light 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 sub-step.

[0049] The third sub-step 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 1a ([Fig.4c]). The lateral dimensions in the main 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 has a thickness typically between approximately 50 qm and several hundred micrometers, for example between 50 qm and 650 qm, or between 100 qm and 450 qm, or between 200 qm and 350 qm.

[0050] The assembly is made by direct bonding, by molecular adhesion, along a bonding interface 40. Optionally, an intermediate layer (not shown) can be formed on the front face 1a 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 the assembly; it can be chosen to be of the same nature or of a different nature from 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 assembled surfaces. Several There are several types of molecular bonding, which differ in particular in their temperature, pressure, atmosphere or treatment conditions prior to bringing the surfaces into 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 sub-step may comprise, prior to bringing the faces 1a, 20a to be assembled into contact, conventional sequences of cleaning by chemical means (for example, RCA cleaning), surface activation (for example, by oxygen or nitrogen plasma) or other surface preparations (such as cleaning by brushing), capable of promoting the quality of the bonding interface 40 (low defectivity, high adhesion energy).

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

[0054] The fourth sub-step 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 support 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 carried out 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 the propagation of a fracture along said fragile plane 11. Alternatively or jointly, a mechanical stress can be applied to the bonded assembly and in particular at the buried fragile plane 11, so as to propagate or help to propagate mechanically 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 of between 5nm and 100nm RMS. The surface layer 10' is delimited, in the (x,y) plane, by a peripheral periphery 10'c, set back from the peripheral edge 20c of the support substrate 20. As mentioned previously, this peripheral periphery 10'c may be serrated and irregular; on average, it is spaced from the peripheral edge 20c by a distance (width of the non-bonded peripheral crown) typically of between 0.5mm and 2mm.

[0056] Finally, the fifth sub-step e) of finishing comprises the application of thermal, mechanical and / or chemical treatments to the free surface 10'a of the layer su surface 10', to form the composite structure 100 provided with the growth layer 10 made of monocrystalline silicon carbide ([Fig.4e]). In particular, this sub-step e) may comprise a mechanical-chemical smoothing treatment of the free surface 10'a of the surface layer 10'. A removal for example of between 50nm and 300nm makes it possible to effectively restore the surface state of the layer, typically leading to a roughness less than or equal to 0.5nm RMS, or even less than or equal to 0.1nm RMS (AFM scan 10x10qm2 or 20x20qm2). Sub-step e) may also comprise at least one heat treatment at a temperature of between 1200°C and 1800°C. Such a 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 makes it possible to strengthen the bonding interface 40.

[0057] At this stage of the method, the growth layer 10 of the composite structure 100 has a first thickness typically between a few tens of nm and a few hundreds of nm, for example, between 50 nm and 1000 nm. The growth layer 10 is delimited by a peripheral periphery 10c having irregularities. In general, said peripheral periphery 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 will be noted that the distance between the peripheral periphery 10c and the edge 20c can vary, below 0.5 mm or above 2 mm, depending on the structures.

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

[0059] We can define a disorientation direction DD, which corresponds to the projection of the z axis normal to the free face 10a, onto the crystallographic plane PC. Finally, we define a reference direction DR, projection of the disorientation direction DD onto the main plane (x,y).

[0060] Due to the disorientation of the free face 10a relative to a crystallographic plane PC, the homoepitaxy of the active layer 150 on the thin layer 10 will take place by step growth (atomic step in the form of a Si-C bilayer, or steps of a few nanometers in height in a “step-bunching” mechanism), steps whose base plane is parallel to the crystallographic plane PC. The reference direction DR translates the growth direction of the steps in the main plane (x,y). It will appear in the second step of the method how the definition of the reference direction DR is useful.

[0061] As an example, the crystallographic plane PC may be the (0 0 0 1) plane and the misorientation direction DD is the [1 1 -2 0] crystallographic direction; the reference direction DR is then the projection of the [1 1 -2 0] crystallographic direction into 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 [-1 -1 2 0] crystallographic direction. According to still other examples, the crystallographic plane PC could be the (1 1 -2 0) plane or the (10-10) plane, with associated misorientation directions DD and reference directions DR.

[0062] The method according to the invention then comprises 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 border 130 (edge ​​of the trench 131 located on the side of the center of the composite structure 100) and may have an outer border 132 (edge ​​of the trench 131 located on the side of the peripheral edge of the composite structure 100). In the main plane (x,y), the inner border 130 extends at a distance (towards the inside of the layer 10) and continuously along the peripheral periphery 10c ([Fig.6], [Fig.7a]). Preferably, it 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 periphery 10c of the growth layer 10, in the direction of the center of the structure 100.

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

[0065] According to a first variant, this trench 131 passes in depth through the entire growth layer 10 ([Fig.6] (i), (iv)). It may possibly extend into the support substrate 20 of the composite structure 100: the depth of the trench 131 may then be a few tens of micrometers, for example 30 μm ([Fig.6] (ii), (v)). According to a second variant, 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, lapping), by laser abrasion, by wet etching or by dry etching of the growth layer 10 (and possibly of the support substrate 20). It can be made at different times during the manufacture of the composite structure 100.

[0067] The trench 131 may be formed in the composite structure 100 at the end of the sub- step e) of finishing previously described. Alternatively, it can be formed in the intermediate composite structure 100', before carrying out the sub-step e) of finishing. 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 1a, during the sub-step a) or after the sub-step b) of implantation. Formed in the donor substrate 1, to a depth greater than or equal to the thickness of the surface layer 10' which will 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 composite structure 100 obtained.

[0068] According to the present invention, the inner edge 130 of the trench 131 has, in the main plane (x,y), a particular and asymmetrical contour. To describe this contour, it is appropriate to define four cardinal points (North, South, West, East), arranged on the peripheral periphery 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 a reference point to define the characteristics of the contour of the inner edge 130 in the main plane (x,y).

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

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

[0071] This particular asymmetrical contour was determined from observations, made by the applicant, regarding the asymmetric propagation of the extended bBPD defects from the irregularity formed by a trench. In a first test, a circular trench 121 along the entire peripheral periphery 10c of the thin layer 10 was produced: [Fig.8a] (i) shows a surface mapping after a homoepitaxy of 10 μm thickness, [Fig.8a] (ii) shows a mapping of the same structure after an additional epitaxy of 10 μm (i.e. an active layer thickness 150 of 20 μm). A strong extension of the bBPD defects is observed, in the North-East-South portion of the layer, from the inner edge of the trench 121, while the North-West-South portion of the layer appears much less impacted.

[0072] In a second test, three circular 121' trenches, defining three circles inscribed in the periphery 10c of the thin layer 10, were carried out: [Fig.8b] (i) shows a surface mapping after a homoepitaxy of 100m thickness, [Fig.8b] (ii) shows a mapping of the same structure after an additional epitaxy of 100m (i.e. an active layer thickness 150 of 20pm). We observe an extension of the bBPD defects, from the inner edge of the trench 121', towards the inside of the three circles, more important in their respective eastern half-portions; while the extension of the bBPD defects, from the outer edge of the trench 121', towards the outside of the three circles, is more important in their respective western half-portions.

[0073] An 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) are formed during homoepitaxy. Considering a given step growth direction (translated by the reference direction DR in the main plane (x,y)), 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', while the extended bBPD defects can propagate easily 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 so that the inner edge 130 of the trench 131 (oriented towards the center of the growth layer 10) comprises triangular defects T (generated during homoepitaxy) capable of forming an effective local barrier to block the propagation of the bBPD defects towards said center. This barrier makes it possible to block not only the potential extended defects which would start from the trench 131, but also those initiated by the irregular peripheral periphery 10c of the growth layer 10.

[0075] This objective is achieved in particular by carrying out the aforementioned asymmetrical 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 perimeter 10c (for example, circular) and the East side contour 130NES, passing through the North-East-South cardinal points, is saw-toothed.

[0076] Preferably, the contour 130NES, between the cardinal points North and East, 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]). In addition, the contour 130NES, between the cardinal points East and South, comprises third segments S3 each forming an angle y 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 rectilinear or curved. When the segments are curved, the angles [3 and y 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 possibly also be curved.

[0078] Following the preparation method described, a method for manufacturing an active layer 150 made of monocrystalline 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 5 μm, 10 μm, or even 30 μm.

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

[0080] The physical discontinuity constituted by trench 131 induces locally disturbed epitaxial growth, with triangular defects mainly arranged on the inner edge 130 of trench 131 (oriented towards the center of growth layer 10): this forms a “wall” which allows the blocking of the sliding of BPD dislocations towards the center of the epitaxially grown active layer 150.

[0081] The disturbance of the epitaxial growth linked to the trench 131 nevertheless remains local 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, arranged on the support substrate 20, and the trench 131 formed in said growth layer 10. As mentioned previously with reference to the method for preparing the composite structure 100, the growth layer 10 is delimited by a peripheral periphery 10c and has a crystallographic orientation such that there exists:

[0083] - a misorientation angle a 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 main 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 periphery 10c, following a particular contour such that, by defining four cardinal points (North, South, West, East) on said peripheral periphery 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 contour 10c (for example, circular), and the contour 130nes passing through the cardinal points North-East-South is saw-toothed ([Fig.7a]).

[0085] In other words, the geometry of the contour of the inner edge 130 is defined so that, knowing the reference direction DR, triangular defects T are formed mainly on said inner edge 130 (oriented towards the center of the growth layer 10), during epitaxial growth. This makes it possible to block the bBPD defects initiated by the peripheral periphery 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; in addition, the contour between the East and South cardinal points comprises third segments S3 each forming an angle y 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 grown by homoepitaxy on the growth layer 10, and whose trench 131 makes it possible to obtain an excellent quality of active layer 150, since it is devoid of or very weakly impacted by a propagation of extended bBPD defects 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 variant embodiments may be made without departing from the scope of the invention as defined by the claims.

Claims

Claims

1. A method for preparing a composite structure (100) comprising the following steps: 1) providing a composite structure (100) comprising a growth layer (10) made of monocrystalline silicon carbide, a free face (10a) of which extends along a main plane (x,y) and arranged on a support substrate (20), the growth layer (10) being delimited by a peripheral periphery (10c) and having a crystallographic orientation such that there exists: - a misorientation angle (a) between a given crystallographic plane (PC) and the free face (10a), - a misorientation 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 misorientation direction (DD) onto the main plane (x,y);2) forming a trench (131) in the growth layer (10), the trench (131) having an inner border (130) which extends remotely and continuously along the peripheral periphery (10c) following a contour such that, by defining four cardinal points (North-South-West-East) on the peripheral periphery (10c), with the West-East direction corresponding to the reference direction (DR): - the contour (130NOS) passing through the cardinal points North-West-South follows a general shape of the peripheral periphery (10c), - the contour (130NES) passing through the cardinal points North-East-South is saw-toothed.;

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

3. Preparation method according to one of the preceding claims, in which: - the contour between the North and East cardinal points comprises first segments (SI) each forming an angle (|3) 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 (y) between 0° and -90° with the reference direction (DR) and second segments (S2) normal to the reference direction (DR).

4. Preparation method according to one of the preceding claims, in which the trench (131) passes in depth through the entire growth layer (10).

5. Preparation method according to one of the preceding claims, in which the peripheral periphery (10c) of the growth layer (10) 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).

6. Preparation method according to one of the preceding claims, in which the inner edge (130) of the trench (131) 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 periphery (10c) of the growth layer (10).

7. Preparation method according to one of the preceding claims, in which the trench has a width, between the inner border (130) and an outer border (132), of between 0.1 μm and 1000 μm.

8. Preparation method according to one of claims 1 to 6, in which the trench (131) extends from its inner edge (130), at least to the peripheral periphery (10c), or even to a peripheral edge (20c) of the support substrate (20).

9. Preparation method according to one of the preceding claims, in which the trench (131) is produced by mechanical abrasion, by laser abrasion, by wet etching or by dry etching of the growth layer (10) and potentially of a part of the support substrate (20).

10. Method for manufacturing an active layer (150) of monocrystalline silicon carbide by homoepitaxy on a composite structure (100) resulting from the preparation method according to one of the preceding claims, the manufacturing method 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 monocrystalline silicon carbide, a free face (10a) of which extends along a main plane (x,y), the growth layer (10) being arranged on a support substrate (20), delimited by a peripheral periphery (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 periphery (10c) following a contour such that, by defining four cardinal points (North-South-West-East) on the peripheral periphery (10c), with the West-East direction corresponding to the reference direction (DR), the contour (130NOS) passing through the cardinal points North-West-South follows a general shape of the peripheral periphery (10c), and the contour (130NES) passing through the cardinal points North-East-South is saw-toothed.

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 cardinal points North-West-South is circular.

13. Composite structure (100) according to one of claims 11 and 12, in which: - the contour between the North and East cardinal points comprises first segments (SI) each forming an angle (|3) 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 (y) 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, in which 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, in which the first segments (SI) and / or the third segments (S3) are rectilinear.

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

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

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

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

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