Process for transferring a thin layer onto a carrier substrate

Abstract

This invention relates to a method for transferring a thin layer onto a carrier substrate, comprising the following steps: providing a bonded structure comprising a donor substrate and the carrier substrate, the two substrates being bonded together by direct bonding along a bonding interface on their respective front sides, the donor substrate further comprising an embedded weakening plane; applying a fracture heat treatment to the bonded structure to induce spontaneous separation along the embedded weakening plane, which is related to the growth of microcracks in the embedded weakening plane through thermal activation, the separation resulting in the transfer of a thin layer from the donor substrate to the carrier substrate. Notably, the fracture heat treatment has: a temperature rise rate greater than 1°C / s between an initial temperature at least below 250°C and a holding temperature at or above 500°C; and a temperature profile to subject the bonded structure to a temperature gradient varying between 40°C and 120°C between a central region and a peripheral region.

Description

Method for transferring a thin layer to a carrier substrate This invention relates to the field of microelectronics and semiconductors. Specifically, this invention relates to a method based on Smart Cut... TM This technology is used to transfer a thin layer onto a carrier substrate, the thin layer having an improved surface roughness after separation. This transfer method is particularly useful for fabricating SOI structures. Smart Cut TM The technique is well known for fabricating SOI (silicon-on-insulator) structures, and is more commonly used for transferring thin layers. This technique is based on creating an embedded weakening plane within a donor substrate by implanting light ions into the substrate; this embedded weakening plane defines the thin layer to be transferred with the front side of the donor substrate. The donor substrate and a carrier substrate are then bonded together at their respective front sides to form a bonded structure. The bonding system is advantageously achieved through direct bonding, through molecular adhesion, i.e., without the use of adhesive materials: a bonded interface is thus established between the two bonded substrates. Thermal activation causes microcracks to grow in the embedded weakening plane, which may lead to spontaneous separation along the embedded weakening plane, causing the thin layer to transfer onto the carrier substrate (forming a stacked structure, such as SOI). The remaining portion of the donor substrate can be reused for subsequent layer transfers. After separation, the stacked structure is typically finished to restore the crystalline quality and surface roughness of the transferred thin layer. These conventional processes typically involve oxidation or smoothing thermal treatments (in an inert or reducing atmosphere), cleaning and / or chemical etching and / or chemical mechanical polishing steps. Various tools for inspecting the final structure make it possible to monitor the entire surface of the thin layer. When the separation within the embedded weakened plane is spontaneous, considerable changes in the surface roughness of the transferred thin layer are observed at both high frequencies (micro-roughness) and low frequencies (ripples, localized areas of high roughness, marbling, etc.). These changes can be specifically observed and measured using the aforementioned inspection tools when monitoring the thin layer in the final structure. It is important to remember that the surface roughness of the finished thin layer can be imaged using an image obtained with a KLA-Tencor Surfscan™ inspection tool (Figure 1). Roughness grades also include latent patterns (marbling, dense zones, etc.), which can be measured or highlighted using haze measurement methods. Haze corresponds to the intensity of light scattered by the thin layer surface. The haze signal is at 0.1 μm. -1 Up to 10 μm -1 The surface roughness varies linearly with the square of the RMS surface roughness (root mean square roughness) within the spatial frequency range. For more complete information on this technique for inspecting and evaluating the roughness of large surface areas, please refer to F. Holsteyns' article "Seeing through the haze" (Yield Management Solution, Spring 2004, pp. 50-54). The images in Figure 1 show the surface roughness of two thin layers transferred from two bonded structures and treated in exactly the same way until finishing. In image (A), a residual roughness periphery region called the "dense zone (DZ)" is observed; image (B) shows no dense zone (DZ) at all. A more pronounced marble pattern (M) is also visible in image (A). Furthermore, there are significant differences in the average and maximum roughness (expressed as "haze" in ppm) between the two images (A) and (B). Figure 1 illustrates the variation in the final quality and roughness of the thin layers, primarily due to variations in surface roughness (high and low frequencies) after separation. In cases where separation is initiated through thermal activation, it remains important to reduce the surface roughness of these layers (regardless of spatial frequency) after transfer in order to improve the final quality of the transferred thin layers. This invention proposes a transfer method that utilizes a specific fracture heat treatment to obtain a thin layer with improved surface roughness after separation, thereby achieving excellent surface quality after the finishing steps of the stacked structure. This method is particularly advantageous for the fabrication of SOI structures. This invention relates to a method for transferring a thin layer onto a carrier substrate, comprising the following steps: providing a bonding structure comprising a donor substrate and the carrier substrate, the two substrates being bonded together by direct bonding along a bonding interface on their respective front sides, the donor substrate further comprising an embedded weakening plane; applying a fracture heat treatment to the bonding structure to induce spontaneous separation along the embedded weakening plane, which is related to the growth of microcracks in the embedded weakening plane through thermal activation, the separation causing a thin layer to transfer from the donor substrate to the carrier substrate. Notably, this method involves a fracture heat treatment with: a temperature rise rate greater than 1°C / s between an initial temperature below 250°C and a holding temperature above or equal to 500°C, and a temperature profile to subject the bonded structure to a temperature gradient varying between 40°C and 120°C between a central region and a peripheral region. According to some advantageous features of the invention, it can be implemented alone or in any feasible combination: the transfer method includes applying a pre-tempering to the bonded structure prior to the fracture heat treatment to pre-curing microcracks in the embedded weakening plane, the thermal budget provided by the pre-tempering being insufficient to cause spontaneous separation; the temperature gradient is between 40°C and 80°C; the transfer method includes, after the separation, a smoothing step on the front side of the thin layer by applying a tempering at a temperature above 1000°C in a neutral or reducing atmosphere, the fracture heat treatment and the smoothing step being performed in the same chamber and the same equipment; the embedded weakening plane is formed in the donor substrate by implanting a light element such as hydrogen or helium or a combination of both; the donor substrate and / or the carrier substrate have an insulating layer at least on their respective front sides, the insulating layer forming an embedded insulating layer in the bonded structure adjacent to the bond interface; The thin layer from the donor substrate is made of monocrystalline silicon, and the carrier substrate contains monocrystalline silicon in order to form a stacked structure of one type of SOI. This invention relates to a method for transferring a thin layer onto a carrier substrate to form a stacked structure. As described in the preamble, such a stacked structure can be, in particular, of the SOI type, comprising a silicon surface layer, an intermediate insulating layer, and a silicon carrier substrate. The carrier substrate may, as needed, include other functional layers, such as a charge-trapping layer, for example, in an SOI structure designed for radio frequency applications. However, the transfer method according to the invention is not limited to the fabrication of SOIs; it can also be applied to many other stacked structures in the fields of microelectronics, microsystems, and semiconductors. The transfer method according to the present invention is based on Smart Cut TMTechnology. When separation in the embedded weakened plane is spontaneous, the fracture time (i.e., the time when separation ends during thermal fracture tempering) can differ among multiple bonded structures treated in the same manner with the same tempering and furnace. The fracture time (FT) depends on various parameters related to the formation of the embedded weakened plane, fracture tempering, and the nature of the bonded structure. The applicant has observed that for bonded structures prepared in a similar manner and subjected to the same fracture tempering, the final stacked structure resulting from separation occurring at short fracture times (sTF) (i.e., after transfer and finishing) exhibits lower high-frequency surface roughness (micro-roughness) of the thin layer compared to those resulting from separation occurring at longer fracture times (lFT), as shown in Figure 2. Furthermore, long fracture times result in a very high roughness in localized regions at the edges of the fractured thin layer (referred to as the dense region DZ), which is hardly or not present at all with short fracture times. As shown in image (A) of Figure 1, this dense region degrades the roughness quality of the thin layer even after finishing. Therefore, the transfer method according to the present invention aims to initiate spontaneous separation in the embedded weakened plane in a desired manner (short fracture time) and repeatably (low dispersion fracture time between multiple similar bonded structures) in order to substantially improve the surface roughness of the transferred thin layer. Therefore, the transfer method first includes providing a bonding structure 100 comprising a donor substrate 1 and a carrier substrate 2, the two substrates being bonded together by direct bonding along a bonding interface 3 at their respective front sides (1a, 2a) (Fig. 3). The donor substrate 1 is preferably in wafer form with a diameter of 100 mm, 150 mm, 200 mm, 300 mm, or 450 mm and a thickness typically between 300 μm and 1 mm. It has a front side 1a and a back side 1b. The surface roughness of the front side 1a is selected to be less than 1.0 nm RMS, and even more preferably less than 0.5 nm RMS (measured by atomic force microscopy (AFM), for example, within a 20 μm × 20 μm scan range). The donor substrate 1 can be made of silicon or any other semiconductor or insulating material that may be capable of thin-layer transfer (e.g., SiC, GaN, etc.). It should also be noted that the donor substrate 1 may include one or more additional layers 12, such as an insulating layer, on at least its front side 1a. As illustrated in FIG3, after the donor substrate 1 and the carrier substrate 2 are bonded, the additional layer 12 becomes an embedded intermediate layer in the bonding structure 100. The donor substrate 1 includes an embedded weakened plane 11 that defines one of the thin layers 10 to be transferred. (e.g., Smart Cut) TMAs is known in the art, this embedded weakening plane 11 can be formed by implanting a lightweight element such as hydrogen, helium, or a combination of both. The lightweight element is implanted into the donor substrate 1 at a given depth, consistent with the target thickness of the thin layer 10. These lightweight elements will form microcavities near the given depth, distributed in the form of a thin layer, generally parallel to the front surface 1a of the donor substrate 1, i.e., parallel to the plane (x, y) in the diagram. For simplicity, this thin layer is referred to as the embedded weakening plane 11. The implantation energy of the light element is selected to reach a given depth. For example, with energies between 10 keV and 210 keV, 5E16 / cm 2 and 1E17 / cm 2 Hydrogen ions are implanted at doses between 100 nm and 1500 nm to define a thin layer 10 with a thickness on the order of 100 nm to 1500 nm. It should be remembered that an additional layer may be deposited on the front side 1a of the donor substrate 1 prior to the ion implantation step. This additional layer may be made of a material such as silicon oxide or silicon nitride. It may be retained for the next bonding step (and form all or part of the intermediate layer of the bonded structure 100), or it may be removed. The carrier substrate 2 preferably has a diameter of 100 mm, 150 mm, 200 mm, 300 mm, or 450 mm and a wafer form with a thickness typically between 300 μm and 1 mm. It has a front side 2a and a back side 2b. The surface roughness of the front side 2a is selected to be less than 1.0 nm RMS, or even more preferably less than 0.5 nm RMS (measured by AFM, e.g., within a 20 μm × 20 μm scan range). The carrier substrate 2 can be made of silicon or any other semiconductor or insulating material that can be transferred in thin layers. In the context of this invention, the materials forming the carrier substrate 2 should be compatible with temperatures applied to the bonding structure 100 formed by the bonding of the donor substrate 1 and the carrier substrate 2 at or above 400°C. It should also be noted that the carrier substrate 2 may include one or more additional layers, such as an insulating layer and / or a charge-trapping layer, at least on its front side 2a. After the donor substrate 1 and the carrier substrate 2 are bonded, this (or these) additional layers are embedded in the bonding structure 100. The bonding between the donor substrate 1 and the carrier substrate 2 is based on direct bonding via molecular attachment. It is well known that this type of bonding does not require an adhesive material because the bonding occurs at the atomic level between the bonding surfaces, forming a bonding interface 3. Several types of molecular attachment bonding exist, each differing in terms of isotemperature, pressure, atmospheric conditions, or processing before bringing the surfaces into contact. Room temperature bonding (regardless of whether the surfaces to be bonded are pre-activated by plasma), atomic diffusion bonding (ADB), and surface activated bonding (SAB) are worth mentioning. Before bringing the front surfaces 1a and 2a to be bonded into contact, the bonding steps may include chemical cleaning (e.g., RCA cleaning) and surface activation (e.g., with the aid of oxygen or nitrogen plasma) or other surface preparation (such as washing) in a known sequence, which may promote the quality of the bonding interface 3 (low defect density, high adhesion energy). A bonded structure 100 is formed, and according to the transfer method of the present invention, it is conceivable to apply a fracture heat treatment to it to induce spontaneous separation along the embedded weakening plane 11. This separation causes the thin layer 10 to transfer from the donor substrate 1 to the carrier substrate 2 to form a stacked structure 110 (FIG. 4). In addition, the remaining portion 1' of the donor substrate is obtained. The fracture heat treatment according to the present invention is characterized by having a very rapid rate of temperature rise and a temperature profile that is set to overheat the center of the bonded structure 100 compared to the periphery. Basically, the temperature rise rate of this fracture heat treatment is greater than 1°C / s, at least between an initial temperature below 250°C and a holding temperature above or equal to 500°C. To achieve rapid temperature rise, it is advantageous to use rapid tempering equipment, such as furnaces called RTA (Rapid Thermal Tempering) or RTP (Rapid Thermal Processing), which are widely used in the semiconductor and microelectronics fields. Heating in this type of equipment is achieved using infrared lamps with adjustable power to adjust the temperature of each zone according to the structure being processed. In RTA or RTP equipment, when the bonding structure 100 is introduced into the furnace chamber, its initial temperature is typically ambient temperature. The temperature rise rate is also rapid, typically increasing at a rate of 1°C / s to approximately 200°C–250°C. However, due to the curing of microcavities and microcracks embedded in the weakening plane 11, temperatures below 250°C are generally slow, so the temperature rise rate to 250°C is not critical. Starting at least from 250°C, the method according to the invention provides a rapid heating rate (>1°C / s) up to a holding temperature greater than or equal to 500°C. The holding temperature is typically between 500°C and 600°C, particularly when the donor substrate 1 is made of silicon. Above 250°C, the growth rate of microcracks in the embedded weakened plane 11 is significant. The fracture heat treatment is further defined as subjecting the bonded structure 100 to a temperature gradient varying between 40°C and 120°C between a central region C and a peripheral region P. The central region C is understood to be the area encompassing the center of the bonded structure 100, located in a (x,y) plane parallel to the bond interface 3 (Figure 3). The radius of the central region C (in the (x,y) plane) is typically between 1% and 50% of the radius of the bonded structure 100. The peripheral region P is the area surrounding the central region C and encompassing the edge of the bonded structure 100. It should be noted that a rapid temperature rise to 250°C may help establish and maintain a thermal gradient between 250°C and the holding temperature in the subsequent fracture heat treatment sequence. Ideally, the thermal gradient between the central region C and the surrounding region P should be between 40°C and 80°C. Figure 5 illustrates an example of the temperature profiles of the bond structure 100 during this fracture heat treatment. The initial temperature is ambient temperature, and the holding temperature is 600°C, as shown in the setpoint profile. Three control pyrometers, T1, T2, and T3, are located at different points on the bond structure 100 to allow observation of the temperature increase and the gradient experienced by the bond structure: pyrometer T1 is located at the center, and pyrometers T2 and T3 are located at the periphery (20 mm from the edge of the bond structure 100). It should be noted that the control pyrometers used can only provide reliable measurements in the range of 250°C–300°C. Heating is adjusted according to the bond structure 100 in different zones of the furnace to establish a temperature gradient of approximately 50°C between the central zone C (see the temperature profile of pyrometer T1) and the peripheral zone P (see the temperature profiles of pyrometers T2 and T3). The temperature gradient applied to the bonded structure 100 during the spalling heat treatment induces localized overheating in the central region C, which, compared to the peripheral region P, results in the microcracks of the embedded weakening plane 11 becoming more mature in the central region C. Near the holding temperature, the higher maturity of the microcracks in the central region C acts as a fracture initiation factor during the rapid temperature rise. This provides the bonded structure 100 with the advantage of transmitting the separation wave from the center to the edges, which greatly limits the marble-like patterns M or other fracture waves (low-frequency ripples and roughness) on the surface of the thin layer 10 after transfer. Another advantage stems from the fact that separation appears to occur earlier, with a shorter fracture time here than that of similar bonded structures subjected to conventional fracture tempering. Early fracture ensures low micro-roughness (high spatial frequency) and few or no high-roughness local areas (also known as dense regions DZ). Figure 6 illustrates the improvement in surface roughness provided by using the transfer method according to the present invention. The first image shows the surface roughness of the transferred thin layer in a first SOI structure obtained using a conventional transfer method (including a finishing step): note the marble pattern and fracture wave present on the surface. The second image shows a second SOI structure 110 obtained by the transfer method according to the present invention (including a finishing step). This SOI structure 110 does not have the marble pattern M or other dense areas DZ. The transfer method according to the invention also enables high-rate fracture heat treatment because the fracture heat treatment period is very short. In an advantageous embodiment of the transfer method, a pre-tempering is applied to the bond structure 100 prior to actual processing to pre-curing microcavities and microcracks in the embedded weakening plane 11. However, the thermal budget provided by this pre-tempering is still insufficient to cause spontaneous separation. Typically, this pre-curing thermal budget is targeted to be between 25% and 75% of the fracture thermal budget leading to spontaneous separation. In the case of silicon donor substrates, the pre-tempering temperature is preferably limited to about 350°C. The pre-tempering can be performed in a conventional, horizontal or vertical furnace or in an RTA or RTP furnace. It is important that the pre-maturation occurs as uniformly as possible within the embedded weakening plane 11, regardless of the wafer region (center or periphery). Pre-curing of microcracks embedded in the weakened plane 11 can further improve the surface roughness of the separated thin layer 10 by reducing the difference in curing degree of microcracks at the moment of separation when the thermal gradient (applied during fracture heat treatment) begins. Specifically, to achieve fracture initiation, it is necessary to establish a significant temperature gradient between the central region C and the peripheral region P; however, this gradient may lead to large differences in the curing degree of microcracks during rapid temperature rise. If the curing degree of microcracks in the embedded weakened plane 11 in the peripheral region is too low at the moment of fracture wave propagation, marble-like defects will occur, which is therefore unfavorable. Therefore, pre-tempering is advantageous when a very high thermal gradient (e.g., above 50°C, or even above 80°C) is applied during the fracture heat treatment, which will give the entire embedded weakened plane 11 a curing degree compatible with fracture propagation without producing marble patterns. The transfer method according to the present invention may further include a smoothing step on the front side 10a of the thin layer 10 after separation. These steps are performed to eliminate surface roughness associated with fractures in the embedded weakened plane 11 and to restore the crystalline quality of the transferred thin layer. The resulting stacked structure 110 is typically removed from a furnace that has undergone fracture heat treatment for heat treatment, chemical and / or mechanochemical treatment in a conventional finishing step. Advantageously, the smoothing step of the transfer method here involves applying tempering directly after the fracture heat treatment at a temperature above 1000°C in an inert or reducing atmosphere, without removing the stacked structure 110 from the furnace chamber where the fracture treatment has been performed, or even without cooling back to ambient temperature. Since the stacked structure 110 and the remaining portion 1' of the donor substrate, although separated, remain opposite each other, a "local" atmosphere with perfect control over the fracture surface can be advantageous. This local atmosphere is primarily formed for the implantation gas and is completely non-oxidizing: therefore, the surface of the thin layer 10 is completely free of oxidation and can be smoothed very effectively, i.e., compared to when the surface is covered with a small amount of primary oxide at lower temperatures. Therefore, by increasing the temperature to a range of 1000°C – 1200°C, this smoothing step is preferably carried out in the same chamber and furnace as the separation step. The atmosphere in the furnace chamber is inert or reducing (preferably Ar, H₂). 2. Ar / H 2). Unlike the fracture step, this step ensures that the temperature of the stacked structure 110 is consistent and uniform across the entire surface. In this step, a temperature gradient between the center and the edges is detrimental. When in-situ ( ) are performed sequentially in the same furnace chamber During the fracture heat treatment and smoothing steps in situ, the temperature does not drop back or return to the outside atmosphere, which is particularly advantageous because it ensures extremely low contamination on the surface of the thin layer 10 after transfer, with no native oxides at all, resulting in a very high smoothing effect. This also helps to reduce the roughness after separation, since fracture is expected to occur. RTA or RTP type furnaces are well-suited for this step sequence, as they offer the ability to rapidly heat up (fracture heat treatment) and increase to high temperatures (smoothing steps). This step sequencing is an advantage in terms of productivity. Exemplary implementation: A transfer method is performed to produce an FDSOI (fully depleted SOI) structure, namely a thin surface layer with a small thickness and a thin embedded insulating layer with a small thickness. The donor substrate 1 is a single-crystal silicon wafer with a diameter of 300 mm, and includes a silicon oxide insulating layer 12 with a thickness of 35 nm on its front side 1a. The buried weakening plane 11 is established by applying energies of 35 keV and 25 keV respectively, and 1... e 16 / cm 2 and 1 e 16 / cm 2 It is formed by the combined implantation of helium and hydrogen ions at specific doses. The carrier substrate 2 is a single-crystal silicon wafer with a diameter of 300 mm. Then, conventional surface preparation (cleaning operation, plasma activation) of the two substrates 1 and 2 is performed to prepare for bonding through molecular attachment. The bonding system is achieved by making the front surfaces 1a and 2a of the donor substrate 1 and the carrier substrate 2 in direct contact, making it possible to obtain a bonded structure 100. The bond structure 100 is introduced into an RTP furnace for fracture heat treatment in the following sequence: 1. The chamber is placed under vacuum. 2. Nitrogen gas is used. 2. Filling: 20 s 3. Temperature rises from ambient temperature to 270°C: 15 s 4. Stabilizes at 270°C: 20 s 5. Temperature rises from 270°C to 600°C: 4°C / s 6. Tempering at 600°C: 120 s 7. Temperature drops (from 600°C to 300°C): 60 s 8. Temperature drops (from 300°C to ambient temperature): 450 s. Adjust the heating zone of the RTP furnace to apply a temperature gradient of approximately 50°C between the center and peripheral regions P of the bonded structure 100. Localized overheating in the central region C acts as a fracture initiation factor, and premature separation occurs during the fracture heat treatment, typically at the end of the heating process (step 5 in the above sequence). Compared to the SOI structure obtained from the bonded structure processed by conventional methods, the surface 10a of the thin layer 10 after transfer according to the present invention is of improved quality because it has little or no marble pattern M or dense area DZ. The micro-roughness ("haze") of the surface of the smoothed thin layer 10 is also lower than that obtained by conventional methods. Of course, the present invention is not limited to the embodiments described in this specification, and variations thereof may be implemented without departing from the scope of the present invention as defined in the claims. 1: Donor substrate 1': Remaining part 1a, 2a, 10a: Front side 1b, 2b: Back side 2: Carrier substrate 3: Bonding interface 10: Thin layer 11: Embedded weakening plane 12: Extra layer 100: Bonding structure C: Central area DZ: Dense area M: Marble pattern P: Peripheral area Referring to the accompanying drawings, other features and advantages of the invention will become apparent from the following detailed description, in which: Figure 1 illustrates two images representing the surface roughness of two transferred thin layers, according to a conventional method, from two bonded structures that have been treated in the same manner up to finishing; these two images are rendered using Surfscan. TM The inspection tool was used to obtain the following: Figure 2 shows a graph of the surface roughness of the thin layer as a function of fracture time, according to a conventional method, for multiple bond structures (different from the bond structure mentioned with reference to Figure 1) and treated in the same manner until finishing; Figure 3 shows a bond structure as an intermediate step in the transfer process according to the present invention; Figure 4 shows a stacked structure and the remainder of the donor substrate obtained by the transfer method according to the present invention; Figure 5 shows an example of a temperature curve during a fracture heat treatment performed according to the transfer method according to the present invention; Figure 6 shows two images representing the surface roughness of two transferred thin layers of the first (left) and second (right) SOI structures, the first obtained by a conventional transfer method and the second by the transfer method according to the present invention; both images were obtained using Surfscan. TM The inspection tools were obtained. Some diagrams are presented in a simplified, schematic manner and are not drawn to scale for clarity. In particular, the layer thickness along the z-axis is not proportional to the lateral dimensions along the x- and y-axis. In diagrams and descriptions, the same symbols may be used for elements of the same nature.

Claims

1. A method for transferring a thin layer (10) onto a carrier substrate (2), comprising the steps of: providing a bonded structure (100) comprising a donor substrate (1) and the carrier substrate (2), the two substrates being joined by direct bonding along a bonded interface (3) at their respective front faces (1a, 2a), the donor substrate (1) comprising an embedded weakening plane (11); applying a fracture heat treatment to the bonded structure (100) to induce spontaneous separation along the embedded weakening plane (11), which relates to the growth of microcracks in the embedded weakening plane (11) through thermal activation, the separation resulting in the transfer of a thin layer (10) from the donor substrate (1) onto the carrier substrate (2), the method being characterized in that the fracture heat treatment has: At least between an initial temperature below 250°C and a holding temperature above or equal to 500°C, a temperature rise rate greater than 1°C / s and a temperature profile are used to subject the bonded structure (100) to a temperature gradient varying between 40°C and 120°C between a central region and a peripheral region.

2. The method of claim 1, which includes applying a pre-temper to the bonded structure (100) prior to the fracture heat treatment to pre-curing microcracks in the embedded weakened plane (11), the heat budget provided by the pre-temper being insufficient to cause spontaneous separation.

3. The method of claim 1 or 2, wherein the temperature gradient is between 40°C and 80°C.

4. The method of claim 1, which includes, after the separation, a smoothing step on the front side (10a) of the thin layer (10) by applying a tempering at a temperature above 1000°C in a neutral or reducing atmosphere, wherein the fracture heat treatment and the smoothing step are performed in the same chamber and the same equipment.

5. The method of claim 1, wherein the embedded weakening plane (11) is formed in the donor substrate (1) by implanting a light element such as hydrogen or helium or a combination of the two elements.

6. The method of claim 1, wherein the donor substrate (1) and / or the carrier substrate (2) have an insulating layer on at least their respective front surfaces (1a, 2a), the insulating layer forming an embedded insulating layer in the bonding structure (100) adjacent to the bonding interface (3).

7. The method of claim 1, wherein the thin layer (10) from the donor substrate (1) is made of monocrystalline silicon and the carrier substrate (2) contains monocrystalline silicon in order to form a stacked structure (110) of one type of SOI.

Images