Method for manufacturing a donor wafer for thin-film transfer, and donor wafer

Abstract

The invention relates to a method for manufacturing a donor wafer comprising the following steps: a) supplying a donor substrate made of a single-crystal material, said donor substrate having been recycled at least once, after a transfer of a thin layer of said donor substrate onto a receiving substrate so as to form a composite structure, said composite structure comprising a surface layer formed in whole or in part by the thin layer and disposed on the receiving substrate, b) checking the quality of the composite structure by inspecting a free surface of the surface layer to detect defects present on and / or in the surface layer, said defects then being classified into a first category, considered non-critical, or into a second category, considered critical.c) the selection of the donor substrate if the density of defects classified in the second category during step b) is less than a predetermined density, d) the assembly of the donor substrate selected in step c) onto a support substrate, by bonding, to form the donor wafer. The invention also relates to a donor wafer comprising a single-crystal silicon carbide donor substrate, having a thickness between 100 μm and 300 μm, disposed on a support substrate, and characterized in that a free face of the donor substrate has fewer than 0.5 micro-hole or inclusion defects / cm². Figure to be published with the abstract: No figure.

Description

Title of the invention: Method for manufacturing a donor wafer for thin film transfer, and donor wafer. FIELD OF THE INVENTION

[0001] The present invention relates to the field of semiconductors, and in particular, to the field of donor substrates for composite structures on which microelectronic components will be fabricated. The invention concerns a method for manufacturing a donor wafer for the transfer of single-crystal thin films for the fabrication of a composite structure, said donor wafer being compatible with numerous samples of high-quality thin films.

[0002] TECHNOLOGICAL BACKGROUND OF THE INVENTION

[0003] Silicon carbide (SiC) is a material of particular interest for the manufacture of power devices, radio frequencies or devices operating at very high temperatures.

[0004] Although rapidly developing, high-quality single-crystal SiC substrates remain expensive and difficult to source in large sizes (typically 150 mm or 200 mm in diameter). Therefore, it is advantageous to use film transfer solutions to create composite structures comprising a thin single-crystal SiC layer (from a high-quality single-crystal SiC donor substrate) on a lower-cost receiving substrate, for example, polycrystalline SiC (p-SiC). A well-known thin-film transfer solution is the Smart Cut™ process, based on light ion implantation and bonding between a single-crystal SiC donor substrate (m-SiC) and a receiving substrate at a bonding interface.The implantation creates a fragile, buried plane along which a separation occurs, leading to the transfer of a thin m-SiC layer onto the receiving substrate to form the composite structure. This allows for the recovery and recycling of the remaining donor substrate, potentially enabling one or more further layer transfers. Epitaxy can then be performed on the thin layer of the composite structure, followed by the fabrication of the electronic devices.

[0005] Recycling (which notably involves grinding and polishing steps to reduce the substrate thickness and restore the geometry and surface roughness performance compatible with the subsequent bonding cycle) and reusing the donor substrate several times for layer transfer constitute a clear economic advantage of the Smart Cut™ process. After several samples, However, the donor substrate thickness becomes incompatible with the technological steps required for its recycling and / or layer transfer, due to its fragility and potential curvature. In particular, edge gripping of the substrate, performed by mechanical devices (especially during the separation step specific to the Smart Cut process), is not applicable to substrates that are too thin because the risk of breakage is very high.

[0006] Document EP1324385 proposes forming a donor wafer by assembling a donor substrate onto a support, in order to address the problems of insufficient thickness and / or curvature of a thin donor substrate. The fabrication of such a donor wafer involves technological steps (including cleaning, surface preparation, bonding, heat treatments, etc.) and requires the supply of a support, preferably chosen from low-cost substrates that are compatible with layer transfer.

[0007] For this solution to be economically viable, it is important that the quality of the donor wafer ensures several transfers of high-quality thin films into composite structures.

[0008] SUBJECT OF THE INVENTION

[0009] The present invention addresses the stated problem. The invention relates to a method for manufacturing a donor wafer allowing the extraction of several high-quality thin layers for the fabrication of composite structures.

[0010] BRIEF DESCRIPTION OF THE INVENTION

[0011] The invention relates to a method for manufacturing a donor wafer comprising the following steps:

[0012] a) the supply of a donor substrate in a monocrystalline material, said donor substrate having been recycled at least once, after a transfer of a thin layer of said donor substrate, onto a receiving substrate so as to form a composite structure, said composite structure comprising a surface layer formed in whole or in part by the thin layer and disposed on the receiving substrate,

[0013] b) quality control of the composite structure, by inspecting a free surface of the surface layer, to detect defects present on and / or in the surface layer, said defects then being classified into a first category, considered non-critical, or into a second category, considered critical,

[0014] c) the selection of the donor substrate if a density of defects classified in the second category during step b) is less than a predetermined density, d) the assembly of the donor substrate selected in step c) onto a support substrate, by bonding, to form the donor wafer.

[0015] According to other advantageous and non-limiting features of the invention, taken alone or in any technically feasible combination: in step b), the free surface inspection is carried out by a technique combining confocal microscopy in visible light and photoluminescence imaging; the free surface inspected is that of the thin layer after it has undergone finishing steps; the surface layer of the composite structure controlled in step b) comprises the thin layer from the donor substrate and a raw epitaxial layer on the thin layer and having a thickness greater than or equal to Ipm, the free surface inspected being that of the epitaxial layer; the second category of defects includes crystalline origin defects of micro-hole and / or inclusion type, and the predetermined density is 0.5 defect / cm2; The second category of defects includes wedge dislocations, screw dislocations and basal plane dislocations, and a predetermined density is defined for each of these defects. Step b) includes: i) the preliminary classification of detected defects, by similarity, based on their image by visible light microscopy, using an image recognition algorithm, fed with different kinds of defects including defects of crystalline origin, likely to be present on and / or in a transferred thin layer, ii) the final classification of defects by applying the following conditions: > if a detected defect is classified as a crystalline defect in step i) with a similarity level greater than a high level, said defect is definitively classified in the second category, > if a detected defect is classified as a crystalline defect in step i) with a similarity level between a low and a high level, a photoluminescence image of said defect is analyzed by an image recognition algorithm trained on different labeled types of defects; if the defect observed on the photoluminescence image is associated with a labeled type of defect, the detected defect is definitively classified in the second category, > in other cases, the detected defect, classified as a defect of crystalline origin in step i), is definitively classified in the first category; the donor substrate provided in step a) was recycled five times, ten times, or even fifteen times, and resulted, respectively, in five, ten, or even fifteen transferred thin layers; - the single-crystal material constituting the donor substrate is silicon carbide, gallium nitride or diamond; - the substrate supporting the donor wafer is made of silicon, silicon carbide or other, with a monocrystalline or polycrystalline structure; - step d) of assembly involves an intercalated layer, placed between the donor substrate and the support substrate; - the interlayer is formed from a semiconductor or metallic material; - the process also includes the following steps: e) the implantation of light species in the donor plate from step d), to form a fragile buried plane delimiting, with a front face of the donor substrate, a thin layer to be transferred; f) the assembly of a receiving substrate with the donor wafer implanted in step e); (g) separation along the buried fragile plane to form a composite structure comprising the post-transfer thin layer and the receiving substrate, on the one hand, and the remainder of the donor platelet, on the other hand; h) the application of thermal, mechanical and / or chemical treatment(s) to a free surface of the remainder of the donor wafer, on the donor substrate side, to form a new donor wafer.

[0016] The invention also relates to a donor wafer comprising a single-crystal silicon carbide donor substrate, having a thickness between 100qm and 300qm, arranged on a support substrate 30, and characterized in that a free face of the donor substrate 1 has less than 0.5 micro-hole or inclusion defects / cm2. BRIEF DESCRIPTION OF THE FIGURES

[0017] 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:

[0018] [Fig.1] Fig.1 presents two examples of a donor platelet manufactured according to a process in accordance with the present invention;

[0019] [Fig.2] Fig.2 presents a known manufacturing process of a composite structure from a donor substrate;

[0020] [Fig.3] Fig.3 shows steps of a process for manufacturing a donor wafer according to the present invention;

[0021] [Fig.4] Fig.4 shows steps of a process for manufacturing a composite structure from a donor wafer according to the present invention;

[0022] [Fig. 5] Figure 5 shows defects detected and classified in step b) of a process of manufacture in accordance with the invention.

[0023] Some figures are schematic representations which, for the sake of readability, are not to scale. In particular, the layer thicknesses along the z-axis are not to scale with respect to the lateral dimensions along the x and y axes.

[0024] The same references on the figures may be used for elements of the same nature. DETAILED DESCRIPTION OF THE INVENTION

[0025] The invention relates to a method for manufacturing a donor wafer 10, formed of a donor substrate 1 arranged on a support substrate 30 ([Fig. 1]). The donor wafer 10 can have a diameter of 100 mm, 150 mm, 200 mm, or even more. For a diameter of 150 mm, its thickness is, for example, between 250 µm and 750 µm, with a typical value of 350 µm; for a diameter of 200 mm, its thickness can vary between 250 µm and 800 µm, with a typical value of 500 µm. The donor substrate 1 is made of a single-crystal material, which may, in particular, be silicon carbide (of polytype 6H, 4H, or 3C), gallium nitride, or diamond. The support substrate 30 is advantageously formed from a lower-cost material, of monocrystalline or polycrystalline structure; it may, for example, be silicon or silicon carbide. As will be described later, the donor substrate 1 can be in direct contact with the support substrate 30 ([Fig.l] (i)) or via an intercalated layer 50 ([Fig.l] (ii)). .

[0026] The process for manufacturing such a donor wafer 10 comprises a first step a) of supplying a donor substrate 1 made of monocrystalline material. The donor substrate 1 has been recycled at least once, i.e. it has been used for the transfer of a thin film 11 onto a receiving substrate 20, so as to form a composite structure 100.

[0027] Preferably, the thickness-to-diameter ratio of the donor substrate 1 is less than or equal to 0.2%, or even less than or equal to 0.15%. This low ratio reflects a relatively small thickness of the donor substrate 1, below which the applicant observed that it was risky to implement technological steps for layer transfer or recycling. The layer transfer steps referred to here are those involved in the well-known Smart Cut™ process. Recycling a donor substrate 1, also within the framework of the Smart Cut™ process, that is, after a thin layer 11 of said donor substrate 1 has been transferred onto a recipient substrate 20, is also known; it notably requires steps of grinding and / or polishing the edges of the donor substrate 1 to remove a non-transferred ring due to the lack of bonding between the donor substrate 1 and the recipient substrate 20. periphery. This peripheral bonding defect stems in particular from the edge drop and chamfer that characterize these substrates. The untransferred rim present on the remainder of the donor substrate after transfer extends to approximately 0.5 mm to 3 mm from the substrate edge; its thickness is identical to the thickness of the transferred thin layer 11. Recycling also includes full-plate chemical polishing, cleaning, surface preparation, and potentially heat treatment steps, in order to remove a disturbed surface layer, a residue of the buried brittle plane 2, and to reduce surface roughness, for the reuse of the recycled donor substrate as a new donor substrate 1. The target roughness is less than 0.5 nm RMS, or even on the order of 0.1 nm RMS (measured by atomic force microscopy (AFM), on typical scans of 5 x 5 sq m or more).

[0028] Figure 2 illustrates the various steps involved in a layer transfer. The donor substrate 1 undergoes implantation of light species on its front face 1a to form a buried brittle plane 2, which, together with the front face 1a, defines a thin layer 11 to be transferred (Fig. 2 (i)). As is well known, the implanted light species can, for example, be hydrogen, helium, or both. The implantation doses and energies are adjusted according to the desired thickness of the thin layer 11 to be transferred. The donor substrate 1 thus implanted is bonded to a recipient substrate 20 by molecular adhesion, i.e., without the addition of adhesive material, along a bonding interface 4 (Fig. 2 (ii)). Separation then occurs along the buried brittle plane 2 by the application of heat treatment and / or mechanical stress.This results in the formation of the composite structure 100 comprising the thin layer 11 transferred onto the receiving substrate 20, on the one hand, and the remainder 1' of the donor substrate, on the other hand ([Fig.2] (iii)). Note that an intermediate layer of an electrically conductive material (e.g., silicon or tungsten) or an insulating material (e.g., silicon oxide) can be deposited on one or both of the faces to be joined of the donor substrate 1 and the receiving substrate 20, before assembly; in such a case, the composite structure 100 comprises the intermediate layer, interposed between the thin layer 11 and the receiving substrate 20.

[0029] The composite structure 100 then undergoes finishing steps, such as heat treatments, mechanical, mechano-chemical (polishing) or chemical (etching) thinning, and / or cleaning, so as to eliminate residual light species as well as a disturbed surface layer, residue of the buried brittle plane 2, and so as to restore a high crystalline quality to the thin layer 11 and thus to form a surface layer 11” compatible with subsequent component development steps.

[0030] According to a first variant ([Fig.2] (iv)), the surface layer 11” of the composite structure 100 is made up of the thin layer 11, after the latter has undergone The finishing stages. The surface layer 11” exhibits, at its free surface 1la, a typical roughness less than or equal to 0.5 nm RMS, 0.2 nm RMS, or even 0.1 nm RMS (measured by AFM, on typical scans of 5x5 sq m² to 30x30 sq m²). The composite structure 100 can be used for component fabrication, which fabrication may include a preliminary step of epitaxial growth of an additional layer to thicken the surface layer 11” (particularly for power electronic components).

[0031] According to a second embodiment ([Fig. 2] (v)), the surface layer 11′ of the composite structure 100 comprises the thin layer 11 (having undergone all or part of the finishing steps) and an epitaxial layer 11′ raw on the thin layer 11 and having a thickness greater than or equal to 5 µm, 10 µm, or even 15 µm or 30 µm. The microelectronic components can be fabricated on and / or in the epitaxial layer 11′.

[0032] As mentioned previously, the remaining 1' of the donor substrate ([Fig.2] (iii)) is recycled to produce a new donor substrate 1 with a thickness less than the initial thickness of the donor substrate before recycling. Recycling results in the consumption of a thickness varying between 3 µm and 1 µm depending on the processes used.

[0033] Advantageously, the donor substrate 1 supplied in step a) was recycled five times, ten times, or even fifteen times, and thus gave rise, respectively, to five, ten, or even fifteen thin layers 11, each transferred onto a receiving substrate 20, to form a composite structure 100.

[0034] For example, a donor substrate 1 of diameter 150mm, supplied in step a), may have a thickness less than or equal to 300pm, 275pm, 250pm, 225pm, or even 200pm, and typically greater than or equal to 100pm, or even 150pm.

[0035] The thickness-to-diameter ratio mentioned above can help to identify recycled donor substrates 1, eligible for the manufacture of a donor wafer 10 because they are mechanically fragile and outside the specification of traditional equipment (low thickness, potentially significant curvature and deformation), and also brought to the end of classic recycling cycles (cost optimization).

[0036] The manufacturing process according to the invention then includes a step b) of quality control of the composite structure 100, by inspection of a free surface lla,ll'a of the surface layer 11”, to detect defects present on and / or in the surface layer 11”, said defects being then classified into a first category, considered non-critical, or into a second category, considered critical.

[0037] Advantageously, for materials such as SiC and GaN, the inspection of the free surface 1la, 1l'a is carried out by a technique coupling microscopy Confocal imaging in visible light (differential interference contrast - DIC) and photoluminescence imaging. Differential interference contrast (also called Nomarski) is an illumination technique that allows the detection of minute variations in a surface's topography by exploiting the interference of light waves. Photoluminescence imaging is based on local variations in the intensity of a photoluminescence (PL) signal emitted by the free surface, following excitation by an incident electromagnetic beam. In a SICA88-type instrument (Lasertech company), which will be used in the remainder of this description, the incident excitation beam has a wavelength of 313 nm, and the emitted photoluminescence signal is collected in a wavelength range from 700 nm to 1000 nm. The local variations in the intensity of the PL signal reflect modified properties of the material (stress, roughness, flatness, etc.).), corresponding to a defect. This defect may appear on the generated PL image as white or black spot(s) depending on its characteristics.

[0038] Equipment of the SICA88 type can be used to inspect, for example, bulk m-SiC substrates before or after epitaxy. The JEITA (Japan Electronics and Information Technology Industries Association) standard includes four documents relating to the zoology of defects on / in a layer produced by homoepitaxy on a 4H-SiC substrate (EDR 4712 / 100) and to non-destructive procedures for optical inspection of these defects (EDR 4712 / 200, / 300, / 400). In particular, it specifies a procedure for evaluating and referencing defects by combining optical inspection and photoluminescence imaging.

[0039] According to the second variant mentioned above, the free surface 1l'a of the surface layer 11” inspected in step b) is the free surface of the epitaxial layer 11' ([Fig.2] (v)). If the thickness of this layer 11' is sufficiently large (typically 8 µm and more), this gives it the same properties as a bulk substrate when inspected by an optical technique; thus, conventional inspection methods can be implemented for the control in step b). The defects classified in the second (critical) category then correspond mainly to threading screw dislocations (TSD), threading edge dislocations (TED), and basal plane dislocations (BPD).

[0040] According to the first variant mentioned above, the surface layer 11” inspected in step b) has a small thickness ([Fig.2] (iv)). The applicant has developed a specific methodology for classifying first and second category defects on such a layer, because the methods usually implemented on bulk substrates can give error-laden classifications on thin films, particularly when the receiving substrate 20 is polycrystalline. This methodology also applies to the second variant, when the thickness of the epitaxial layer 11' is insufficient to completely screen the underlying receiving substrate 20.

[0041] The defects present on and / or in the surface layer 11 can be induced by crystalline defects initially present on and / or in the donor substrate 1, or by variations in the topology of the donor substrate 1 and the recipient substrate 20, or by particles or other surface contaminants which have not been completely eliminated, before the step of assembling the donor substrate 1 onto the recipient substrate 20. They can therefore be defects of crystalline origin, or bonding defects such as holes (local absence of surface layer 11”) or bubbles (defect at the bonding interface 4, at which the thin layer 10 is not bonded and forms a blister).

[0042] The SICA88 metrology equipment is capable of classifying detected defects based on images captured by visible light microscopy, using an image recognition algorithm. The algorithm is fed with verified images of bubbles, holes, and other defects of crystalline origin, likely to be present on and / or in a transferred thin film; it can thus learn to recognize each of these defects and calculate a level of similarity between the defect detected on the free surface 1la of the surface layer 11” and its database, taking into account criteria of size, shape, color, contrast, etc.

[0043] The control step b) therefore advantageously includes a step i) of preliminary classification of defects, by similarity, then, a step ii) of final classification of defects by application of particular conditions, set out below.

[0044] At the end of step i), each defect detected on the surface layer 11” is associated with an identified type of defect (for example, hole, bubble, or crystalline defect), with a certain level of similarity (between 0 and 1). Due to the presence of a polycrystalline support substrate 20 under the surface layer 11”, the preliminary identification performed automatically by the equipment is not sufficiently reliable to determine the quality of the composite structure 100. Indeed, this identification can be affected by the underlying grains, and the level of similarity assigned to the detected defect does not, by itself, allow one to determine whether said defect is indeed of the identified type or whether it is a “false defect”.

[0045] The control process therefore includes a step ii) of final classification of defects by application of particular conditions to defects of crystalline origin: I. if the level of similarity associated with a detected defect is greater than a high level, said defect is definitively classified in the second category (critical defect); II. If the similarity level associated with the detected defect is between a low and a high level, the PL (photoluminescence) image of said defect is analyzed by an image recognition algorithm trained on different labeled types of defects. Two cases can then arise: - if the detected fault is associated with a labeled type of fault, said fault is definitively classified in the second category (critical fault); - if the detected fault is not recognized as being a labeled type of fault, said fault is definitively classified in the first category (non-critical fault); III. Finally, if the level of similarity associated with the detected defect is lower than the low level, the said defect is also definitively classified in the first category (non-critical defect).

[0046] The PL image recognition algorithm is fed and trained with verified PL images of defects likely to be present on and / or in a surface layer 11": it can thus learn to recognize each of these defects and classify them into predefined categories (i.e., associate them with labeled defect types), taking into account criteria such as size, shape, contrast, etc. A labeled defect type therefore corresponds to a real defect, whose signature on the PL image is expressed by specific criteria (as mentioned above).

[0047] In condition (II), when the PL image associated with the analyzed defect corresponds to one of the labeled types of defects, this confirms that we are dealing with a "true defect" and the defect is thus classified in the second category; on the other hand, when the PL image does not correspond to any of the labeled types of defects and / or the PL image does not show any particular contrast (no PL signal), the defect is considered a "false defect", and falls into the first category.

[0048] The application of the aforementioned conditions to defects detected on a composite structure 100 composed of a surface layer 11” of m-SiC deposited on a receiving substrate 20 of p-SiC will now be illustrated. The low and high levels of similarity are defined at 0.3 and 0.85 respectively on a SICA88 instrument. Figure 5 illustrates defects of crystalline origin detected on and / or in the thin layer 10 and referenced in [1], [2], and [3]:

[0049] [1] DIC Image: Similarity level higher than high level => Defect classified in the second category;

[0050] [2] DIC Image: Similarity level between the high level and the low level => Defect classified in the second category because labeled defect detected on the PL image;

[0051] [3] DIC Image: Similarity level lower than low level => Secondary defect classified in the first category.

[0052] The final classification step ü) allows for refining the criticality of the detected defects, of the crystalline origin type. It is essentially these crystalline origin defects that will be taken into account in the following step c) of the process, to determine whether there is an advantage in selecting the donor substrate 1 (from which all or part of the surface layer 11” of the composite structure 100 originates), to produce a donor wafer 10. These crystalline origin defects generally correspond to microholes (“micropipe”) or inclusions.

[0053] Thus, in step b) of quality control of the composite structure 100, according to the first or second variant, a density of second category defects is obtained, global density (set of second category defects) or individual density for each of the types of defects falling into the second category.

[0054] The process according to the invention then includes a step c) of selecting or downgrading the donor substrate that provided the thin layer 11 to the controlled composite structure 100. The donor substrate 1 is selected to continue the process steps if an overall density of defects classified in the second category during step b) is less than a predetermined density or if the individual densities of defects classified in the second category during step b) are respectively less than predetermined densities.

[0055] By way of example, for a composite structure 100 according to the first variant, the donor substrate 1 will be selected if the overall density of second category defects detected on and / or in the surface layer 11” (for example in SiC) of the associated composite structure 100 is less than 0.5 defect / cm2, or even less than 0.1 defect / cm2.

[0056] Also by way of example, for a composite structure 100 according to the second variant, the donor substrate 1 will be selected on the basis of one or more types of defects falling into the second category, and if the individual densities of second category defects detected on the surface layer 11” of the composite structure are less than the following specifications: - the density of defects of crystalline origin (micro-holes, inclusions) falling into the second category is less than 0.5 defects / cm2, or even 0.1 defects / cm2 and / or - the TED defect density falling into the second category is less than 8000 defects / cm2, 6000 defects / cm2, 4000 defects / cm2, or even 2000 defects / cm2, and / or - the TSD defect density falling into the second category is less than 500 defects / cm2, 400 defects / cm2, 250 defects / cm2, or even 150 defects / cm2, and / or - the density of BPD defects falling into the second category is less than 3000 defects / cm2, 2500 defects / cm2, 1500 defects / cm2, or even 750 defects / cm2.

[0057] If the overall density or individual densities of second category defects, detected on and / or in the surface layer 11” of the composite structure 100, is / are greater than or equal to the predetermined density(s), the donor substrate 1 is downgraded (not selected), i.e. it will not be used in the subsequent stages of the manufacturing process according to the invention.

[0058] The process according to the invention then includes a step d) of assembling the donor substrate 1, selected in step c), onto a support substrate 30, by bonding, to form a donor wafer 10 ([Fig.3]).

[0059] The assembly advantageously takes place between the rear face 1b of the donor substrate 1 and a front face 30a of the support substrate 30, defining a bonding interface 40. Any known type of bonding can be implemented: bonding by molecular adhesion, bonding via polymer layers, bonding by thermocompression, etc.

[0060] It should be noted that several types of molecular adhesion bonding exist, which differ in particular in their temperature, pressure, atmospheric conditions, or pretreatments 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. As is known, molecular adhesion bonding requires that the surfaces to be joined have very low roughness and be free of contaminants and particles. Surface preparations (etching, chemical polishing, etc.), cleaning (ozone, RCA, etc.), and other surface activations (O2, N2 plasma, etc.) are necessary.) can be applied to the faces to be joined lb,30a in such a way as to promote the quality and energy of the bonding of the interface 40. A roughness of less than 0.5 nm RMS is preferably targeted for the rear face 1b of the donor substrate 1 and for the front face 30a of the support substrate 30. Optionally, an interlayer 50 can also be deposited on one or both of the faces lb,30a prior to assembly. The interlayer 50 is intended to be embedded in the donor wafer 10, between the donor substrate 1 and the support substrate 30 ([Fig. 1] (ii)). The bonding interface 40 may be adjacent to or within said interlayer 50. The interlayer 50 is preferably made of a semiconductor material (e.g., Si) or a metallic material (e.g., W, Ti). Its thickness can vary between a few nm and several hundred nm.

[0061] The donor substrate 1, which has already undergone one or more recycling processes, is relatively thin; the support substrate 30 is chosen so that the total thickness of the donor wafer 10 is on the order of 625 µm for a diameter of 150 mm, and on the order of 725 µm for a diameter of 200 mm. The support substrate 30 has a typical thickness between 300 µm and 450 µm.

[0062] The assembly step d) advantageously includes a heat treatment, applied to the donor wafer 10, to consolidate the bonding interface 40. For example, a donor structure 10 comprising a donor substrate 1 in m-SiC and a support substrate 30 in p-SiC can be annealed at about 1200°C for 30 min.

[0063] By implementing steps b) and c) of the process, it is possible to select recycled donor substrates 1 of sufficient quality to justify the implementation of manufacturing steps for a donor wafer 10. Several thin layers 11 will then be taken from the donor substrate 1, which forms part of this donor wafer 10, for the fabrication of additional composite structures 100. The probability of high quality for these structures 100 is particularly high, given the selection carried out in step c) of the process. The applicant has found that quality control of the recycled donor substrate 1 by direct inspection of the free surface of said substrate 1 does not provide sufficiently reliable selection criteria to predict the quality of the surface layer 11' of a composite structure 100 fabricated from said substrate 1.However, it showed that quality control of the surface layer 11” of a composite structure 100 (according to the first or second variant), developed from the donor substrate 1, made it possible to efficiently select or downgrade the donor substrate 1, before undertaking relatively costly manufacturing steps of a donor wafer 10.

[0064] When the donor wafer 10 is produced, the steps e) to g) below are carried out, on the one hand, to take a thin layer 11 from said wafer 10 and transfer it into a new composite structure 100, and on the other hand, to recycle the remainder 10' of the donor wafer into a new donor wafer 10:

[0065] e) Implantation of light species in the donor plate 1 from step d), to form a fragile buried plane 2 delimiting, with a front face of the donor substrate 1, a thin layer 11 to be transferred ([Fig.4] (i));

[0066] f) Assembly by molecular adhesion of a recipient substrate 20 with the donor plate 10 implanted in step e), along a bonding interface 4 ([Fig.4] (ii)); note that one and / or the other of the assembled faces may include an intermediate layer to facilitate bonding or promote vertical electrical or thermal conduction.

[0067] g) Separation along the buried fragile plane 2 to form a composite structure 100 comprising the thin layer 11 after transfer and the receiving substrate 20, on the one hand, and the remainder 10' of the donor platelet, on the other hand ([Fig.4] (iii));

[0068] h) Application of thermal, mechanical and / or chemical treatment(s) to a free surface 10'a of the remainder 10' of the donor wafer, on the side of the donor substrate 1, to form a new donor wafer 10. Recycling the remainder 10' of the donor wafer requires the same type of steps as those stated for recycling the donor substrate 1, namely grinding and / or polishing of the edges to remove the untransferred crown, full plate mechano-chemical polishing (removal typically between 3qm and 8qm), cleaning and / or other surface preparations, in order to remove a disturbed surface layer, residue of the buried brittle plane 2, and to reduce the surface roughness, for the reuse of the donor wafer 10. The target roughness is less than 0.5 nm RMS, or even on the order of 0.1 nm RMS.

[0069] Of course, thermal, mechanical and / or chemical treatments can also be applied to the free surface of the transferred thin layer 11, in order to continue the classic and already mentioned manufacturing steps of the composite structure 100 and the electronic components.

[0070] The donor wafer 10 can be used for the collection of a thin layer 11 and then be recycled more than 10 times, 20 times, 30 times, 50 times, or even 70 times, which makes it possible to maximize the use of the high-quality monocrystalline material of the donor substrate 1 which forms part of the donor wafer 10.

[0071] The invention relates in particular to a donor wafer 10 comprising a donor substrate 1 made of single-crystal silicon carbide, having a thickness of between 100 µm and 300 µm, disposed on a support substrate 30, and characterized in that a free face of the donor substrate 1 has fewer than 0.5 micro-hole or inclusion defects (crystalline defects). According to the invention, these defects are detected by inspecting the surface layer 11” of a composite structure 100, said surface layer 11” being obtained by thin-film transfer from the donor substrate 1, before the latter has been selected for the fabrication of the donor wafer 10.

[0072] Of course, the invention is not limited to the embodiments and examples described, and alternative embodiments may be made without departing from the scope of the invention as defined by the claims.

Claims

Demands

1. A method for manufacturing a donor wafer (10) comprising the following steps: a) supplying a donor substrate (1) of a single-crystal material, said donor substrate (1) having been recycled at least once, after transferring a thin layer (11) of said donor substrate (1) onto a receiving substrate (20) so as to form a composite structure (100), said composite structure (100) comprising a surface layer (11”) formed in whole or in part by the thin layer (11) and disposed on the receiving substrate (20), b) checking the quality of the composite structure (100) by inspecting a free surface (1la, 1l'a) of the surface layer (11”) to detect defects present on and / or in the surface layer (11”), said defects being then classified into a first category, considered non-critical, or into a second category, considered critical,c) selection of the donor substrate (1) if a density of defects classified in the second category during step b) is less than a predetermined density, d) assembly of the donor substrate (1) selected in step c) onto a support substrate (30), by bonding, to form the donor wafer (10).

2. A method for manufacturing a donor wafer (10) according to the preceding claim, wherein, in step b), the inspection of the free surface (1la, 1l'a) is carried out by a technique combining confocal microscopy in visible light and photoluminescence imaging.

3. Method of manufacturing a donor wafer (10) according to any one of claims 1 and 2, wherein the inspected free surface (lia) is that of the thin film (11) after it has undergone finishing steps.

4. A method for manufacturing a donor wafer (10) according to any one of claims 1 and 2, wherein the surface layer (11”) of the composite structure (100) controlled in step b) comprises the thin layer (11) from the donor substrate (1) and an epitaxial layer (11') raw on the thin layer (11) and having a thickness greater than or equal to 1 inn, the free surface (11'a) inspected being that of the epitaxial layer (11').

5. A method for manufacturing a donor wafer (10) according to any one of claims 1 to 4, wherein the second category of defects includes crystalline defects of the micro-hole and / or inclusion type, and the predetermined density is 0.5 defects / cm2.

6. A method for manufacturing a donor wafer (10) according to claim 4, wherein the second category of defects includes wedge dislocations, screw dislocations and basal plane dislocations, and a predetermined density is defined for each of these defects.

7. A method for manufacturing a donor wafer (10) according to claim 5, wherein step b) comprises: i) the preliminary classification of detected defects, by similarity, based on their image by visible light microscopy, using an image recognition algorithm, fed with different kinds of defects, including crystalline defects, that may be present on and / or in a transferred thin film, ii) the final classification of defects by applying the following conditions: > if a detected defect is classified as a crystalline defect in step i) with a similarity level greater than a high level, said defect is definitively classified in the second category, > if a detected defect is classified as a crystalline defect in step i) with a similarity level between a low level and a high level,A photoluminescence image of said defect is analyzed by an image recognition algorithm trained on different labeled types of defects; if the defect observed in the photoluminescence image is associated with a labeled type of defect, the detected defect is definitively classified in the second category; in other cases, the detected defect, classified as a defect of crystalline origin in step i), is definitively classified in the first category.

8. A method for manufacturing a donor wafer (10) according to any one of claims 1 to 7, wherein the donor substrate (1) supplied in step a) has been recycled five times, ten times, or even fifteen times, and has given rise, respectively, to five, ten, or even fifteen transferred thin films.

9. A method for manufacturing a donor wafer (10) according to any one of claims 1 to 8, wherein the single-crystal material constituting the donor substrate (1) is silicon carbide, gallium nitride or diamond.

10. A method for manufacturing a donor wafer (10) according to any one of claims 1 to 9, wherein the support substrate (30) of the donor wafer (10) is made of silicon, silicon carbide or other, of monocrystalline or polycrystalline structure.

11. A method for manufacturing a donor wafer (10) according to any one of claims 1 to 10, wherein the assembly step d) involves an interlayer layer (50), disposed between the donor substrate (1) and the support substrate (30).

12. Method of manufacturing a donor wafer (10) according to claim 11, wherein the interlayer (50) is formed of a semiconductor or metallic material.

13. A method for manufacturing a donor wafer (10) according to any one of claims 1 to 112, further comprising the following steps: e) the implantation of light species in the donor wafer (1) from step d), to form a buried brittle plane (2) delimiting, with a front face (1a) of the donor substrate (1), a thin layer (11) to be transferred; f) the assembly of a receiving substrate (20) with the donor wafer (10) implanted in step e); g) the separation along the buried brittle plane (2) to form a composite structure (100) comprising the thin layer (11) after transfer and the receiving substrate (20), on the one hand, and the remainder (10') of the donor wafer, on the other hand; h) the application of thermal, mechanical and / or chemical treatment(s) to a free surface (10'a) of the remainder (10') of the donor wafer, on the side of the donor substrate (1), to form a new donor wafer (10).

14. Donor wafer (10) produced by a manufacturing process according to any one of the preceding claims, comprising a donor substrate (1) of single-crystal silicon carbide, having a thickness of between 100qm and 300qm, disposed on a support substrate (30), and characterized in that a free face of the donor substrate (1) has less than 0.5 microhole or inclusion defects / cm2.

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