METHOD FOR TRANSFERRING A LAYER OF A HETEROSTURTURE

Description

Domaine technique

[0001] The invention relates to a method of transferring a layer of a heterostructure onto a receiving substrate. Etat de la technique

[0002] In the field of microelectronics, layer transfer processes are used to transfer a layer from a first substrate, called the donor substrate, to a second substrate, called the recipient substrate.

[0003] The Smart Cut™ process is thus well known for enabling the manufacture of semiconductor-on-insulator substrates, but also other composite substrates, for example piezoelectric-on-insulator substrates. This process comprises the formation of a weakening zone by implanting atomic species in the donor substrate, in order to delimit a layer of interest to be transferred, the bonding of the donor substrate to the receiving substrate, then the detachment of the donor substrate along the weakening zone, so as to transfer the layer of interest to the receiving substrate.

[0004] In some situations, it is not possible to directly transfer a layer from a donor substrate to the receiving substrate, for example due to constraints related to the transfer process. More specifically, the bonding of the donor substrate to the receiving substrate can be achieved by means of silicon oxide layers previously formed on the surface of each of the two substrates. However, to obtain the detachment of the layer of interest to be transferred, it is necessary to carry out an annealing, in a temperature range of 100°C to 600°C.When the donor substrate and the recipient substrate have different thermal expansion coefficients - which is the case, for example, between a donor substrate made of a piezoelectric material and a recipient substrate made of silicon - said annealing causes significant deformation ("bow" in English terminology) of the assembly of the two substrates, which is detrimental to the transfer insofar as it can cause breakage of the substrates.

[0005] To minimize such deformation, it is possible to form an intermediate substrate called a pseudo-donor substrate, in which the donor substrate is assembled on a temporary support substrate.

[0006] The transfer method then comprises a preliminary step of forming the donor pseudo-substrate, by bonding the donor substrate to the support substrate, a step of thinning the donor substrate, a step of implanting atomic species in the donor pseudo-substrate to delimit the layer of interest to be transferred, a step of bonding the donor pseudo-substrate to the final receiving substrate, and a step of detaching the donor pseudo-substrate along the weakening zone to transfer the layer of interest to the receiving substrate.

[0007] Application WO 2019 / 186032 in the name of the applicant describes such a method suitable for the formation of a piezoelectric-on-insulator type substrate.

[0008] One problem that arises when manufacturing such a pseudo-donor substrate is its fragility. Indeed, the substrates used in microelectronics are provided with a peripheral chamfer that avoids the presence of particularly fragile sharp angles at the edge of the substrates. Given the thinness of the thinned donor substrate, said substrate has a sloping edge and thus forms a very thin and brittle blade.

[0009] However, the debris generated by the breakage of this blade is likely to contaminate the production line and the substrates used on this line.

[0010] Document EP 2 469 709 discloses a method of manufacturing a heterostructure in which a piezoelectric substrate is ground around its perimeter, bonded to a support substrate and then thinned.

[0011] The article by Inoue et al, Edge trimming for surface activated dielectric bonded wafers, Microelectronic Engineering, vol. 167, October 18, 2016, pp. 10-16 and documents US 2012 / 126669, US 2020 / 098974, FR 2 935 535 and EP 0 854 500 describe methods for trimming bonded piezoelectric and / or semiconductor substrates, before or after bonding. The transfer of a useful layer using double substrate bonding techniques is known from FR 2 925 221, for example. Brève description de l'invention

[0012] An aim of the present invention is therefore to enable the manufacture of a heterostructure (pseudo-donor substrate) comprising a thinned donor substrate while minimizing the risk of breakage of said donor substrate and the transfer of a layer of said heterostructure onto a receiving substrate.

[0013] To this end, the invention proposes a method for transferring a layer of a heterostructure onto a receiving substrate, comprising the following successive steps: formation of the heterostructure, comprising the steps of: providing a donor substrate of a first material and a support substrate of a second material, bonding the donor substrate to the support substrate, thinning the donor substrate, so as to form said heterostructure (H) comprising the thinned donor substrate on the support substrate, -removing a peripheral portion of the donor substrate, forming a weakening zone in the thinned donor substrate so as to delimit a layer of the first material to be transferred, bonding said heterostructure to a receiving substrate, the layer of the first material to be transferred being located at the bonding interface, detaching the donor substrate along the weakening zone so as to transfer the layer of the first material to the receiving substrate.

[0014] Removing the peripheral annular portion of the donor substrate (also called "trimming"), which can be carried out before or after bonding said substrate to the support substrate, helps prevent the formation of a brittle blade.

[0015] According to other advantageous but optional characteristics of said method, possibly combined when technically possible: the step of removing the peripheral portion of the donor substrate is carried out before bonding the donor substrate to the support substrate; the step of removing the peripheral portion of the donor substrate is carried out after bonding the donor substrate to the support substrate; the removal of the peripheral portion of the donor substrate further comprises removing a peripheral portion of the support substrate opposite said donor substrate; the step of removing the peripheral portion of the donor substrate is carried out after at least part of the thinning of the donor substrate; the donor substrate is bonded to the support substrate by a polymer bonding layer; the peripheral portion removed from the donor substrate has a width of between 300 and 1000 µm, preferably between 300 and 500 µm from the edge of the donor substrate; the donor substrate is bonded to the support substrate by molecular adhesion;the peripheral portion removed from the donor substrate has a width of between 1 and 3 mm, preferably between 2 and 3 mm from the edge of the donor substrate; the removal of the peripheral portion comprises: placing the donor substrate on a support movable in rotation about a first axis; machining the donor substrate by an abrasive wheel rotating about a second axis parallel to the first axis, the abrasive wheel being further driven in translation along the second axis; the removal of the peripheral portion comprises: placing the donor substrate on a support movable in rotation about a first axis; machining the donor substrate by an abrasive wheel rotating about a second axis perpendicular to the first axis; the method further comprises a step of polishing the donor substrate after removal of the peripheral portion; the donor substrate comprises a piezoelectric material or a semiconductor material;the thinned donor substrate has a thickness of between 10 and 100 µm, preferably between 10 and 50 µm; the support substrate comprises silicon, glass, quartz, sapphire, a ceramic, and / or polycrystalline aluminum nitride.;

[0016] According to other advantageous but optional characteristics of said method, possibly combined when technically possible: before bonding the heterostructure to the receiving substrate, an intermediate layer is formed on the donor substrate and / or the receiving substrate; the intermediate layer comprises silicon oxide, silicon nitride, silicon oxynitride, aluminum nitride (AIN), and / or tantalum oxide (Ta 2 O 5 ), or a stack of layers formed from at least two of said materials; the receiving substrate comprises silicon, silicon, glass, quartz, sapphire, a ceramic, and / or polycrystalline aluminum nitride; the receiving substrate is a silicon substrate including a charge trapping layer comprising polycrystalline silicon, silicon carbide, amorphous silicon and / or porous silicon; the support substrate and the receiving substrate comprise materials having a difference in thermal expansion coefficient of less than or equal to 5% in absolute value;the support substrate and the receiving substrate are formed from the same material; the transferred layer has a thickness between 30 nm and 1.5 µm.; Brève description des dessins

[0017] Other characteristics and advantages of this process will emerge from the detailed description which follows, with reference to the attached drawings, in which: There figure 1A is a schematic diagram of the assembly of the donor substrate and the support substrate. The figure 1B is a schematic diagram of the assembly of the donor substrate and the support substrate, after thinning of the donor substrate. The figure 2A schematically illustrates the operation of trimming the donor substrate before bonding to the support substrate. The figure 2B is a sectional view of the periphery of the heterostructure after bonding the donor substrate cut out of the figure 2A on the support substrate. The figure 2C is a cross-sectional view of the periphery of the heterostructure after thinning of the donor substrate. The figure 3A schematically illustrates the operation of trimming the donor substrate after its bonding and thinning on the support substrate. The figure 3B is a sectional view of the periphery of the heterostructure after trimming the figure 3A . There figure 4A schematically illustrates the operation of trimming the donor substrate after its bonding to the support substrate. The figure 4B is a sectional view of the periphery of the donor substrate before its thinning and of the support substrate after the trimming of the figure 4A . There figure 4C is a sectional view of the periphery of the heterostructure after thinning of the donor substrate cut out of the figure 4B . There figure 5A schematically illustrates a first method of carrying out the clipping. The figure 5B schematically illustrates a second method of carrying out the clipping. The figure 6A is a sectional view of a heterostructure formed by a method according to one embodiment of the invention. The figure 6B is a cross-sectional view of the formation of a weakening zone in the heterostructure of the figure 6A to delimit a layer to be transferred. The figure 6C is a sectional view of the bonding of the heterostructure of the figure 6B on a receiving substrate. The figure 6D is a sectional view of the layer transferred onto the receiving substrate after detachment of the heterostructure from the figure 6C along the weakening zone. The figure 7A is a sectional view of a heterostructure formed by a method according to one embodiment of the invention. The figure 7B is a cross-sectional view of the formation of a weakening zone in the heterostructure of the figure 7A to delimit a layer to be transferred. The figure 7C is a sectional view of the bonding of the heterostructure of the figure 7B on a receiving substrate. The figure 7D is a sectional view of the layer transferred onto the receiving substrate after detachment of the heterostructure from the figure 7C along the weakening zone.

[0018] For reasons of readability of the figures, the dimensions of the different elements have not necessarily been represented to scale.

[0019] Identical reference signs from one figure to another designate identical elements or elements fulfilling the same function, which are not necessarily described in detail again. Description détaillée de modes de réalisation

[0020] THE figures 1A et 1B illustrate the problem that the invention seeks to avoid when manufacturing a heterostructure intended in particular to fulfill the function of a donor pseudo-substrate with a view to subsequent transfer of a portion of said donor pseudo-substrate onto a recipient substrate.

[0021] The formation of the heterostructure comprises bonding a donor substrate 1 of a first material and a support substrate 2 of a second material.

[0022] The first material may be a material intended to be subsequently transferred to the donor substrate but which has a difference in thermal expansion coefficient with the material of the receiving substrate preventing direct transfer, as explained in the introduction. For example, but not limited to, the first material may be a piezoelectric material, such as lithium niobate (LiNbO 3 ), lithium tantalate (LiTaO 3 ), or a semiconductor material, such as nitrurgallium (GaN), indium phosphide (InP), gallium arsenide (GaAs), ...

[0023] The second material is generally different from the first material. The function of the support substrate is to temporarily support the donor substrate until a portion of the donor substrate is transferred to the receiving substrate. The second material may advantageously be chosen to have a small difference in thermal expansion coefficient with the material of the receiving substrate, i.e., typically a difference in thermal expansion coefficient of zero or in absolute value less than 5%. For example, but in a non-limiting manner, the second material may be silicon, glass, quartz, sapphire, a ceramic, polycrystalline aluminum nitride (AIN). The choice of the second material may be made according to the material of the receiving substrate to ensure the agreement of the thermal expansion coefficients of said materials. In a preferred embodiment, the second material is identical to that of the receiving substrate.

[0024] As illustrated in the figure 1A , substrates 1 and 2 each have a peripheral chamfer C on each of their main faces. In general, the chamfer has an angle of 22 to 40° relative to the main surface of each substrate and extends over a height of the order of 200 to 300 µm in the thickness direction of the substrate and a width of the order of 200 to 300 µm in the radial direction of the substrate.

[0025] For the formation of the heterostructure, the donor substrate 1 must be thinned so as to transfer a layer 10 of thickness e onto the support substrate 2. Said thinning can be carried out by etching the donor substrate from the face opposite the bonding interface I with the support substrate 2. Particularly advantageously, the etching can be carried out in several steps, with increasing fineness. Thus, a first part of the donor substrate can be removed by coarse grinding, which makes it possible to quickly reduce the thickness of the donor substrate. Then, finer grinding can be implemented to continue to reduce the thickness of the donor substrate, but by reducing the roughness of the surface of said donor substrate.Finally, chemical mechanical polishing (CMP) can be performed to smooth the surface of the thinned donor substrate to achieve the desired roughness. As mentioned below, fine grinding may not be performed directly after rough grinding but after another step in the process.

[0026] For example, the donor substrate 1 may have a thickness of the order of a few hundred micrometers, and the thinned donor substrate 10 may have a thickness e of a few tens of micrometers, for example between 10 and 100 µm, preferably between 10 and 50 µm.

[0027] In this case, as seen on the figure 1A , the thickness e is less than the thickness of the chamfer C of the donor substrate.

[0028] Therefore, as illustrated in the figure 1B which represents the assembly of the donor substrate 1 and the support substrate 2 after the thinning of the donor substrate, the thinned donor substrate 10 has a peripheral edge 100 comprising a sharp angle at the main face opposite the bonding interface I. Such a sharp angle is likely to break during handling of the heterostructure. This breakage phenomenon, called "flaking" in English terminology, is particularly harmful because the debris from the thinned donor substrate risks contaminating the entire manufacturing line using the heterostructure.

[0029] To avoid such a phenomenon, the invention proposes removing a peripheral portion of the donor substrate, before or after bonding said donor substrate to the support substrate. Such removal will also be called "edge trimming" or "edge grinding" in this text.

[0030] Said trimming aims to remove the chamfer from the thinned or unthinned donor substrate and to form a straight edge, preferably inclined at an angle α (shown on the figure 2C ) greater than or equal to 90° relative to the main face of the support substrate to avoid any jamming of particles in the corner between the main face of the support substrate and the edge of the donor substrate. In the case of an obtuse angle (α > 90°C), however, an angle relatively close to 90° will be chosen, for example between 90 and 135°, in order to prevent the layer subsequently transferred from the donor substrate to the receiving substrate from forming a brittle blade.

[0031] For this purpose, in certain embodiments, the width of the removed peripheral portion (denoted L on the figures 2A , 3A And 4A which will be described below) is greater than or equal to the width of the chamfer of the donor substrate.

[0032] Furthermore, as explained in detail below, the width of the removed peripheral portion may depend on the method of bonding the donor substrate to the support substrate.

[0033] A first bonding method is molecular adhesion bonding, in which the donor substrate and the support substrate, possibly covered with an oxide layer, are in direct contact, the adhesion being ensured by intermolecular forces at the bonding interface, in particular of the Van der Walls type. In a manner known per se, such bonding may require preparation of the surfaces to be bonded, in particular polishing, cleaning, and / or plasma activation.

[0034] A second bonding method is bonding via a polymeric layer, as described in particular in document WO 2019 / 186032. Said polymeric layer may be formed by depositing a photopolymerizable layer on the surface of at least one of the substrates, bonding the substrates via said photopolymerizable layer, then irradiating the assembly with a light flux whose wavelength is chosen to have a low absorption coefficient with respect to one of the substrates. Thus, the light flux passes through said substrate without being absorbed and reaches the adhesive layer, thus allowing its polymerization. For example, when the donor substrate is made of a piezoelectric material, the light flux may have a wavelength of between 320 and 365 nm and be applied through the donor substrate.

[0035] In practice, the polymeric layer can be formed as follows.

[0036] A photopolymerizable adhesive layer is deposited on the surface of at least one of the substrates. The deposition can advantageously be carried out by centrifugal coating, or "spin coating" in English terminology. This technique consists of rotating the substrate on which the deposition of the photopolymerizable layer is planned on itself at a substantially constant and relatively high speed, in order to spread said photopolymerizable layer uniformly over the entire surface of the substrate by centrifugal force. For this purpose, the substrate is typically placed and held by vacuum on a rotating plate. A person skilled in the art is able to determine the operating conditions, such as the volume of adhesive deposited on the surface of the substrate, the rotation speed of the substrate, and the minimum deposition time depending on the desired thickness of the adhesive layer.The thickness of the deposited photopolymerizable adhesive layer is typically between 2 and 8 µm.

[0037] According to a non-limiting example, the photopolymerizable adhesive layer marketed under the reference “NOA 61” by the company NORLAND PRODUCTS can be used in the present invention.

[0038] The donor substrate and the support substrate are then bonded via said photopolymerizable layer to form a heterostructure. The bonding is preferably carried out at room temperature, i.e. approximately 20°C. However, it is possible to carry out the hot bonding at a temperature between 20°C and 50°C, and more preferably between 20°C and 30°C. In addition, the bonding step is advantageously carried out under vacuum, which makes it possible to desorb water from the surfaces forming the bonding interface, i.e. the surface of the adhesive layer and the surface of the handling substrate or the piezoelectric substrate.

[0039] The heterostructure is then subjected to irradiation by a light flux, in order to polymerize the adhesive layer. The light source is preferably a laser. The light radiation, or light flux, is preferably ultraviolet (UV) radiation. Depending on the composition of the adhesive layer, UV radiation with a wavelength between 320 nm and 365 nm will preferably be chosen. The irradiation is carried out by exposing the free face of the donor substrate to the incident light radiation. Thus, the light radiation penetrates into the heterostructure from the free face of the donor substrate, passes through the donor substrate, until it reaches the adhesive layer, thus causing the polymerization of said adhesive layer. The polymerization of the adhesive layer makes it possible to form a polymer layer which ensures the mechanical cohesion of the heterostructure, keeping the donor substrate and the support substrate bonded together.

[0040] The irradiation of the heterostructure gives rise to a thermal process whereby the donor substrate, crossed by the radiation, can partially absorb the energy of the radiation and heat up. Excessive heating would be likely to destabilize the structure of the donor substrate if it is piezoelectric, which could lead to a degradation of the physical and chemical properties of the piezoelectric layer. In addition, excessive heating could cause deformation of the donor substrate and the support substrate due to their difference in thermal expansion coefficient. In order to avoid excessive heating of the donor substrate, the irradiation is advantageously carried out in a pulsed manner, that is to say by exposing the heterostructure to a plurality of pulses of light rays. Each pulse is carried out for a determined irradiation time, which may be equal or different from one pulse to another.The pulses are spaced in time by a determined rest time during which the heterostructure is not exposed to light rays. A person skilled in the art is able to determine the irradiation time of each pulse, the rest time between each pulse, as well as the number of pulses to be carried out to completely polymerize the adhesive layer. Thus, for example, it will be possible to implement around ten pulses lasting 10 seconds each, separated by rest times also lasting 10 seconds each.

[0041] The polymerized adhesive layer therefore makes it possible to bond the donor substrate and the support substrate without exposing them to a thermal budget that would be likely to deform them, which makes it possible to give the heterostructure sufficient mechanical strength for the subsequent transfer of a piezoelectric layer. The thickness of the polymerized adhesive layer is preferably between 2 and 8 µm. This thickness depends in particular on the material constituting the photopolymerizable adhesive layer deposited before bonding, the thickness of said photopolymerizable adhesive layer, and the experimental irradiation conditions.

[0042] In an alternative embodiment, in particular when neither the donor substrate nor the support substrate is sufficiently transparent to the light flux necessary to polymerize the photopolymerizable layer, a polymeric adhesive capable of polymerizing under the effect of low temperature annealing (i.e. typically less than 100°C) can be used.

[0043] This second method of bonding using a polymeric layer (whether polymerizable by irradiation or by low-temperature annealing) is particularly advantageous in the context of the present invention, because it makes it possible to reduce the width of the peripheral portion of the donor substrate, and thus to reduce the duration of the trimming operation.

[0044] Indeed, in the case of bonding by a polymer layer, the width of the peripheral portion to be removed from the donor substrate may be between 300 and 1000 µm, preferably between 300 and 500 µm from the edge of said substrate. By edge of the substrate, is meant in the present text the outermost edge of the substrate, outside the chamfered portion; in other words, the edge of the substrate defines the maximum diameter of the substrate.

[0045] In the case of molecular bonding, the width of the peripheral portion to be removed from the donor substrate may be between 1 and 3 mm, preferably between 2 and 3 mm from the edge of the donor substrate.

[0046] This difference between the trimmed width according to the two bonding methods is explained by the fact that, in the case of molecular adhesion bonding, there is a peripheral crown presenting, beyond the chamfer, a width of the order of 1 or 2 mm on which it is difficult to ensure continuous bonding between the two substrates. This requires the donor substrate to be trimmed over a width greater than or equal to this crown, so as to ensure continuous bonding over the entire surface of the substrates.

[0047] In the case of bonding by a polymer layer, the bonding is ensured continuously by the polymer layer up to the chamfer, which makes it possible to trim the donor substrate over a narrower width than in the case of bonding by molecular adhesion, this width being able to be simply slightly greater than that of the chamfer. This results in a less significant loss of the first material.

[0048] Regardless of the method of bonding the donor substrate to the support substrate, the trimming of the donor substrate can be carried out at different stages of the manufacture of the heterostructure, the width of the removed peripheral portion being chosen according to the bonding method.

[0049] In a first embodiment, illustrated in the figures 2A-2C , the trimming is carried out before bonding the donor substrate to the support substrate.

[0050] There figure 2A schematically illustrates the operation of trimming the donor substrate before bonding to the support substrate, the thick dotted line delimiting the peripheral portion removed during trimming. In this operation, it is not necessary to carry out the trimming over the entire thickness of the donor substrate. Indeed, since the donor substrate is intended to be thinned after being bonded to the support substrate, it is sufficient to carry out the trimming over a depth P greater than the thickness e of the donor substrate targeted after thinning, starting from the face of the donor substrate intended to be bonded to the support substrate. Furthermore, as explained above, the width L of the removed peripheral portion is greater than the width of the chamfer C.

[0051] There figure 2B is a sectional view of the periphery of the heterostructure after bonding of the donor substrate 1 cut out of the figure 2A on the support substrate 2. Although no bonding layer is shown in this figure, a polymeric layer as described above can be used to ensure bonding between the two substrates, as an alternative to bonding by molecular adhesion.

[0052] The portion 10 of the donor substrate resulting from the thinning is schematically delimited by a dotted line, said line representing the surface of the donor substrate after the thinning.

[0053] There figure 2C is a cross-sectional view of the periphery of the heterostructure after thinning of the donor substrate. We therefore observe that, unlike the case of the figure 1B , the edge 100 of the thinned donor substrate 10 forms a right or obtuse angle relative to the surface of the support substrate and is therefore less likely to break.

[0054] In a second embodiment, illustrated in the figures 3A-3B , the trimming is carried out after the bonding and thinning of the donor substrate on the support substrate.

[0055] There figure 3A schematically illustrates the trimming of the thinned donor substrate 10 on the support substrate 2 (the donor substrate having been previously bonded to the support substrate and then thinned to the desired thickness). Although no bonding layer is shown in this figure, a polymeric layer as described above can be used to ensure bonding between the two substrates, as an alternative to bonding by molecular adhesion.

[0056] The thick dotted line delimits the peripheral portion removed during trimming. In this operation, the trimming is carried out over a depth P at least equal to the thickness of the thinned donor substrate 10. Preferably, the trimming extends at least partly into the thickness of the support substrate 2. Indeed, even if the surface of the support substrate has a roughness resulting from the trimming operation, this is not detrimental insofar as this surface is not intended to be bonded to the receiving substrate during the subsequent use of the heterostructure as a pseudo-donor substrate. Furthermore, as explained above, the width L of the removed peripheral portion is greater than the width of the chamfer C.

[0057] Optionally, the trimming can be carried out while the donor substrate has only been partially thinned. Thus, for example, the donor substrate can undergo a first thinning step by rough grinding, then the trimming step and a second thinning step by fine grinding or chemical-mechanical polishing, making it possible to reduce the roughness of the surface of the thinned donor substrate. This particular order of steps makes it possible to carry out the trimming while the donor substrate is still thick enough to avoid the risk of being damaged, in particular to avoid the risk of loss of cohesion of said donor substrate during the trimming. For example, in the case of a piezoelectric donor substrate, it is advantageous to maintain a thickness of 60 µm after the rough grinding in order to carry out the trimming, then to carry out the fine grinding until a thickness of the order of 10 to 20 µm is reached.

[0058] There figure 3B is a cross-sectional view of the periphery of the heterostructure after thinning of the donor substrate. We therefore observe that, unlike the case of the figure 1B , the edge 100 of the thinned donor substrate 10 forms a right (or obtuse) angle with the surface of the support substrate and is therefore less likely to break.

[0059] In a third embodiment, illustrated in the figures 4A-4C , the trimming is carried out between the bonding and the thinning of the donor substrate on the support substrate.

[0060] There figure 4A schematically illustrates the operation of trimming the donor substrate after its bonding to the support substrate, but before the thinning of said donor substrate (the donor substrate having been previously bonded to the support substrate and then thinned to the desired thickness). Although no bonding layer is shown in this figure, a polymeric layer as described above can be used to ensure bonding between the two substrates, as an alternative to bonding by molecular adhesion.

[0061] The thick dotted line demarcates the peripheral portion removed during trimming. Unlike the method of producing figures 2A-2B , the trimming is carried out over the entire thickness of the donor substrate 1. Preferably, the trimming also extends at least partly into the thickness of the support substrate 2. Indeed, even if the surface of the support substrate has a roughness resulting from the trimming operation, this is not detrimental insofar as this surface is not intended to be bonded to the receiving substrate during the subsequent use of the heterostructure as a pseudo-donor substrate. Furthermore, as explained above, the width L of the removed peripheral portion is greater than the width of the chamfer C.

[0062] There figure 4B is a sectional view of the periphery of the donor substrate before its thinning and of the support substrate after the trimming of the figure 4A .

[0063] There figure 4C is a cross-sectional view of the periphery of the heterostructure after thinning of the donor substrate. We therefore observe that, unlike the case of the figure 1B , the edge 100 of the thinned donor substrate 10 forms a right (or obtuse) angle with the surface of the support substrate and is therefore less likely to break.

[0064] There are different techniques for performing clipping.

[0065] According to a first embodiment, illustrated in the figure 5A , the substrate or assembly of substrates intended to be trimmed is positioned on a support S driven in rotation about the axis X1 of revolution of the substrate or assembly of substrates. A cutting tool T, such as an abrasive wheel, for example a diamond wheel, is driven in rotation about an axis X2 parallel to the axis X1 and is brought opposite the peripheral portion to be removed. Said tool is gradually moved towards the substrate or assembly of substrates in a direction parallel to the axis X1 (represented by the arrow), in order to gradually grind the material of the substrate or assembly of substrates that it encounters.

[0066] According to a second embodiment, illustrated in the figure 5B , the substrate or assembly of substrates intended to be trimmed is positioned on a support S rotated about the axis X1 of revolution of the substrate or assembly of substrates. A cutting tool T, such as an abrasive wheel, is rotated about an axis Y1 perpendicular to the axis X1 and is brought opposite the peripheral portion to be removed. Said tool is gradually moved towards the substrate or assembly of substrates in a direction parallel to the axis X1, in order to gradually grind the material of the substrate or assembly of substrates that it encounters. Optionally, depending on the width of the peripheral portion to be removed, the tool T may also be moved in a direction parallel to the axis Y1 in order to gradually grind the material of the substrate or assembly of substrates that it encounters in the radial direction.

[0067] Regardless of the method used, trimming has the effect of locally hardening the material ground by the tool, so that the surface exposed at the end of trimming may have a certain roughness or defects. It may then be advantageous to carry out polishing, for example chemical-mechanical polishing (CMP) to remove the hardened area and improve the surface condition of the donor substrate, in order to avoid bonding defects during subsequent transfer to a receiving substrate.

[0068] The heterostructure thus formed is used as a pseudo-donor substrate to transfer a portion of the donor substrate onto a receiving substrate. Due to its edge forming a right or obtuse angle with respect to the surface of the support substrate, the thinned donor substrate is much less brittle and can be conveniently handled for carrying out the transfer process.

[0069] We will now describe, with reference to Figures 6A-6E and 7A-7E, two embodiments of a method for transferring a layer of said heterostructure onto a receiving substrate.

[0070] The receiving substrate may be selected based on the electrical and / or thermal properties of the final structure comprising the transferred layer and the receiving substrate. For example, the receiving substrate may comprise silicon, silicon, glass, quartz, sapphire, a ceramic, and / or polycrystalline aluminum nitride. In certain embodiments, particularly relating to substrates for radiofrequency applications, the receiving substrate may be a silicon substrate comprising a charge trapping layer, for example a polycrystalline silicon layer, or optionally silicon carbide, amorphous silicon and / or porous silicon.

[0071] Particularly advantageously, the support substrate and the receiving substrate may be made of materials having a difference in thermal expansion coefficient of less than or equal to 5% in absolute value, so as to allow balancing of the stresses on either side of the thinned donor substrate during the transfer process, thus avoiding deformation of said thinned donor substrate. Preferably, the support substrate and the receiving substrate may be formed from the same material.

[0072] In reference to the figure 6A , a heterostructure H is provided comprising a thinned donor substrate 10 trimmed according to any one of the embodiments described above, and a support substrate 2, said substrates being bonded by molecular adhesion. To simplify the figures, the trimmed portion of the donor substrate and, where appropriate, of the support substrate, has not been shown. The width of said trimmed portion is typically between 1 and 3 mm, preferably between 2 and 3 mm from the edge of the donor substrate.

[0073] In reference to the figure 6B , atomic species, such as hydrogen and / or helium, are implanted in the thinned donor substrate 10 in order to form a weakening zone 12 which delimits a layer 11 of the first material.

[0074] In reference to the figure 6C , the heterostructure (on the side of the layer 11 to be transferred) is bonded to the receiving substrate 3. In certain embodiments, an intermediate layer 13 is formed on the heterostructure and / or the receiving substrate. Said intermediate layer may have the function of improving the strength of the bonding and / or contributing to the electrical and / or thermal properties of the final structure. For example, the intermediate layer may comprise silicon oxide, silicon nitride, silicon oxynitride, aluminum nitride (AIN), or tantalum oxide (Ta 2 O 5 ), or even a stack of at least two of these materials. In other embodiments, the intermediate layer is dispensed with to carry out direct bonding between the heterostructure and the receiving substrate.

[0075] Optionally, a heat treatment is implemented to increase the bonding energy.

[0076] In reference to the figure 6D , the thinned donor substrate 10 is detached along the weakening zone 12, so as to transfer the layer 11 of the first material onto the receiving substrate.

[0077] In reference to the figure 7A , a heterostructure H is provided comprising a thinned donor substrate 10 trimmed according to any one of the embodiments described above, and a support substrate 2, said substrates being bonded by a polymeric layer 4. To simplify the figures, the trimmed portion of the donor substrate and, where appropriate, of the support substrate, has not been shown. The width of said trimmed portion is typically between 300 and 1000 µm, preferably between 300 and 500 µm from the edge of the donor substrate.

[0078] In reference to the figure 7B , atomic species, such as hydrogen and / or helium, are implanted in the thinned donor substrate 10 in order to form a weakening zone 12 which delimits a layer 11 of the first material.

[0079] In reference to the figure 7C , the heterostructure (on the side of the layer 11 to be transferred) is bonded to the receiving substrate 3. Although no intermediate layer is illustrated between the heterostructure and the receiving substrate, an intermediate layer as described with reference to the figure 6C can be formed at the interface.

[0080] Optionally, a heat treatment is implemented to increase the bonding energy. Said heat treatment is advantageously carried out at a temperature below 300°C so as not to degrade the polymer layer.

[0081] In reference to the figure 7D, the thinned donor substrate 10 is detached along the weakening zone 12, so as to transfer the layer 11 of the first material onto the receiving substrate 3.

[0082] By one of these transfer methods, it is possible in particular to form a piezoelectric-on-insulator type structure, successively comprising a thin piezoelectric layer having a thickness of the order of a few micrometers, a silicon oxide layer, a charge trapping layer and a silicon substrate.

Claims

1. Method for transferring a layer from a heterostructure (H) to a receiver substrate (3), comprising the following steps in succession: - providing a donor substrate (1) of a first material and a carrier substrate (2) of a second material, - bonding the donor substrate (1) to the carrier substrate (2), - thinning the donor substrate (1), so as to form said heterostructure (H) comprising the thinned donor substrate (10) on the carrier substrate (2), - removing a peripheral portion from the donor substrate (1, 10), - forming a weakened region (12) in the thinned donor substrate (10) so as to delimit a layer (11) of the first material to be transferred, - bonding said heterostructure (H) to a receiver substrate (3), the layer (11) of the first material to be transferred being located at the bonding interface, - detaching the donor substrate (10) along the weakened region (12) so as to transfer the layer (11) of the first material to the receiver substrate (3).

2. Method according to Claim 1, wherein the step of removing the peripheral portion from the donor substrate (1) is carried out before the bonding of the donor substrate (1) to the carrier substrate (2).

3. Method according to Claim 1, wherein the step of removing the peripheral portion from the donor substrate (1) is carried out after the bonding of the donor substrate to the carrier substrate.

4. Method according to Claim 3, wherein the removal of the peripheral portion from the donor substrate further comprises removing a peripheral portion from the carrier substrate (2) facing said donor substrate (1).

5. Method according to one of Claims 3 and 4, wherein the step of removing the peripheral portion from the donor substrate (1) is carried out after the donor substrate has been at least partly thinned.

6. Method according to one of Claims 1 to 5, wherein the donor substrate (1, 10) is bonded to the carrier substrate (2) via a polymeric bonding layer (4).

7. Method according to Claim 6, wherein the width of the peripheral portion removed from the donor substrate (1, 10) is between 300 and 1000 µm, preferably between 300 and 500 µm from the edge of the donor substrate.

8. Method according to one of Claims 1 to 5, wherein the donor substrate (1, 10) is bonded to the carrier substrate (2) via molecular adhesion.

9. Method according to Claim 8, wherein the width of the peripheral portion removed from the donor substrate is between 1 and 3 mm, preferably between 2 and 3 mm from the edge of the donor substrate.

10. Method according to one of Claims 1 to 9, wherein the removal of the peripheral portion comprises: - placing the donor substrate (1, 10) on a carrier that is rotatably movable about a first axis (X1); - machining the donor substrate using an abrasive wheel rotating about a second axis (X2) parallel to the first axis (X1), the abrasive wheel further being driven in translation along the second axis (X2).

11. Method according to one of Claims 1 to 9, wherein the removal of the peripheral portion comprises: - placing the donor substrate (1, 10) on a carrier that is rotatably movable about a first axis (X1); - machining the donor substrate using an abrasive wheel rotating about a second axis (Y1) perpendicular to the first axis (X1).

12. Method according to one of Claims 1 to 11, further comprising a step of polishing the donor substrate (1, 10) after the removal of the peripheral portion.

13. Method according to one of Claims 1 to 12, wherein the donor substrate (1, 10) comprises a piezoelectric material or a semiconductor material.

14. Method according to one of Claims 1 to 13, wherein the thickness of the thinned donor substrate (10) is between 10 and 100 µm, preferably between 10 and 50 µm.

15. Method according to one of Claims 1 to 13, wherein the carrier substrate (2) comprises silicon, glass, quartz, sapphire, a ceramic, and / or polycrystalline aluminium nitride.

16. Method according to any one of Claims 1 to 15, wherein, before the bonding of the heterostructure (H) to the receiver substrate (3), an intermediate layer is formed on the donor substrate (10) and / or the receiver substrate (3).

17. Method according to Claim 16, wherein the intermediate layer comprises silicon oxide, silicon nitride, silicon oxynitride, aluminium nitride, AIN, and / or tantalum oxide Ta2O5, or a stack of layers formed of at least two of said materials.

18. Method according to any one of Claims 1 to 17, wherein the receiver substrate comprises silicon, silicon, glass, quartz, sapphire, a ceramic, and / or polycrystalline aluminium nitride.

19. Method according to Claim 18, wherein the receiver substrate is a silicon substrate including a charge-trapping layer comprising polycrystalline silicon, silicon carbide, amorphous silicon and / or porous silicon.

20. Method according to one of Claims 1 to 19, wherein the carrier substrate (2) and the receiver substrate (3) comprise materials exhibiting a difference in coefficient of thermal expansion smaller than or equal to 5% in terms of absolute value.

21. Method according to Claim 20, wherein the carrier substrate (2) and the receiver substrate (3) are formed of the same material.

22. Method according to one of Claims 1 to 21, wherein the thickness of the transferred layer (11) is between 30 nm and 1.5 µm.