Method for transferring a thin film onto a supporting substrate - Patent application

Abstract

The present invention relates to a method for transferring a thin film onto a support substrate, comprising: (1) providing a bonded structure including a donor substrate and a support substrate assembled by direct bonding at their respective front surfaces along a bonding interface, the donor substrate including a buried brittle surface, and (2) applying an adiabatic breakdown treatment to the bonded structure to induce spontaneous separation along said surface accompanied by growth of microcracks in the buried brittle surface through thermal activation, the separation resulting in the transfer of the thin film from the donor substrate to the support substrate. The method is characterized in that the adiabatic breakdown treatment exhibits (1) a heating rate of more than 1°C / s between an initial temperature of at least 250°C and a level temperature of 500°C or higher, and (2) a temperature profile such that the bonded structure is subjected to a temperature gradient varying from 40°C to 120°C between a central region and a peripheral region.

Description

[Technical field]

[0001] The present invention relates to the field of microelectronics and semiconductors. In particular, the present invention relates to a method for transferring a thin film onto a support substrate based on Smart Cut™ technology, where the thin film exhibits improved roughness after separation. In particular, the transfer method can be used to manufacture SOI structures. [Background technology]

[0002] The Smart Cut™ technology is well known for producing SOI (silicon-on-insulator) structures and, more generally, for thin film transfer. This technology is based on the formation of a buried brittle surface in a donor substrate by implanting said substrate with light chemical species, which together with the front surface of the donor substrate defines the thin film to be transferred. The donor substrate and the support substrate are then joined at their respective front surfaces to form a bonded structure. The assembly is advantageously carried out by direct bonding, by molecular adhesion, i.e. without the aid of an adhesive material, so that a bonded interface is established between the two assembled substrates. The growth of microcracks in the buried brittle surface by thermal activation can result in spontaneous separation along said surface, resulting in the transfer of the thin film onto the support substrate (forming a laminated structure, for example of the SOI type). The remaining donor substrate can be reused for subsequent film transfers. After separation, a finishing treatment is usually applied to the laminated structure to restore the crystal quality and surface roughness of the transferred thin film. These treatments are known to involve oxidizing or smoothing heat treatments (under neutral or reducing atmospheres), chemical cleaning and / or etching steps, and / or chemical-mechanical polishing steps. A variety of inspection tools are available to check the overall surface of the thin film.

[0003] If the separation at the embedded brittle surface is spontaneous, significant variations in the surface roughness of the transferred thin film are observed, both in terms of high frequencies (micro-roughness) and low frequencies (rippling, localized areas of high roughness, mottle, etc.) These variations are visible and measurable when checking the thin film in the final structure, in particular by the inspection tools mentioned above.

[0004] Recall that the surface roughness of the finished thin film can be mapped using a Surfscan™ inspection tool available from KLA-Tencor (Figure 1). The level of roughness and latent patterns (mottle, dense areas, etc.) is measured or revealed by measuring the diffuse background noise ("haze"), which corresponds to the intensity of light scattered by the surface of the thin film. The haze signal ranges from 0.1 to 10 μm. -1 The spatial frequency range of the haze varies linearly with the square of the RMS surface roughness. For details of such wide-area roughness inspection and evaluation techniques, see the paper by F. Holsteyns, "Seeing through the haze," Yield Management Solutions, Spring 2004, pp50-54.

[0005] The maps in FIG. 1 show the surface roughness of two thin layers transferred from two bonded structures that were identically processed to finish. Map (A) shows a peripheral area of ​​residual roughness known as the "dense zone" (ZD), while map (B) has none. More pronounced mottling (M) is also visible in map (A). The average and maximum roughness (expressed in ppm haze) also differ between the two maps (A) and (B). FIG. 1 shows the variability in the final quality and roughness of the thin films, which is mainly due to the variability in the surface roughness (high and low frequencies) after separation. Summary of the Invention [Problem to be solved by the invention]

[0006] Therefore, in order to improve the final quality of the transferred thin films, in the case of spontaneous detachment by thermal activation, reduction of the surface roughness of these layers after transfer (independent of spatial frequency) remains important. [Means for solving the problem]

[0007] The present invention proposes a transfer method using a unique thermal breakdown process that allows for an improved surface roughness of the thin film after separation in order to achieve a superior surface quality after the finishing step of the stacked structure, which is particularly advantageous for the manufacture of SOI structures.

[0008] The present invention relates to a method for transferring a thin film onto a supporting substrate, the method comprising the steps of: providing a bonded structure including a donor substrate and a support substrate assembled by direct bonding at their respective front surfaces along a bonding interface, the donor substrate including a buried brittle surface; applying a thermally insulating treatment to the bonded structure to induce spontaneous detachment along the buried brittle plane accompanied by thermally activated growth of microcracks, the detachment resulting in transfer of the thin film from the donor substrate to the support substrate; Includes.

[0009] The method includes the steps of: At least a heating rate of greater than 1°C / s between an initial temperature of less than 250°C and a level temperature of at least 500°C; a temperature profile such that the bonded structure is subjected to a temperature gradient varying between 40°C and 120°C between a central region and a peripheral region; It is characterized by the following.

[0010] According to advantageous features of the invention, taken alone or in any feasible combination, the following are achieved: The transfer method includes a pre-annealing applied to the bonded structure prior to the thermal insulation treatment to achieve pre-ripening of the microcracks of the buried brittle surface. The thermal budget provided by the pre-annealing is insufficient to cause spontaneous separation. The temperature gradient is 40℃~80℃. The transfer method includes, after detachment, smoothing the front surface of the thin film by annealing at temperatures above 1000°C in a neutral or reducing atmosphere, the thermal insulation and smoothing steps being carried out in the same enclosure and equipment. A buried brittle plane is formed in a donor substrate by implanting light chemical species such as hydrogen, helium, or a combination of both. The donor substrate and / or the support substrate have an insulating layer on at least their respective front sides, which forms a buried insulating layer adjacent the bonding interface in the bonded structure. To form a stacked SOI structure, the thin film from the donor substrate is single crystal silicon and the support substrate comprises single crystal silicon.

[0011] Other features and advantages of the present invention will become apparent from the following detailed description of the invention which refers to the accompanying drawings.

[0012] Some figures are schematic and not to scale for ease of reading, in particular the layer thicknesses along the z-axis are not to scale relative to the lateral dimensions along the x- and y-axes.

[0013] The same reference numbers in the drawings or description may be used for the same type of elements. [Brief description of the drawings]

[0014] [Figure 1] FIG. 2 shows two representative surface roughness maps of two transferred thin layers from two bonded structures that were identically processed to finish using conventional methods, both maps obtained via a Surfscan™ inspection tool. [Diagram 2] FIG. 2 is a graph showing the surface roughness of the thin layer as a function of time to failure for several bonded structures (of a different type than the bonded structure shown in FIG. 1) that have been identically processed to a finish by a conventional method. [Diagram 3] 1 shows a bonding structure used in an intermediate stage of the transfer method according to the invention; [Figure 4] FIG. 2 shows the laminate structure obtained by the transfer method according to the invention, and the remainder of the donor substrate. [Diagram 5] 11A to 11C are diagrams showing an example of a temperature profile during a thermal insulation breaking process carried out in the transfer method according to the present invention. [Figure 6] FIG. 2 shows two representative surface roughness maps of two transferred thin films, a first SOI structure obtained with a conventional transfer method (left) and a second SOI structure obtained with a transfer method according to the invention (right), both maps obtained via a Surfscan™ inspection tool. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] The present invention relates to a method for transferring a thin film onto a support substrate to form a laminated structure. As mentioned in the introduction, such a laminated structure may be of the SOI type, comprising a thin silicon surface layer, an intermediate insulating layer, and a silicon support substrate. Optionally, the support substrate may comprise other functional layers, such as, for example, a charge trapping layer for SOI structures designed for radio frequency applications. However, the transfer method described here is not limited to the manufacture of SOI, but can be applied to many other laminated structures in the fields of microelectronics, microsystems and semiconductors.

[0016] The transfer method according to the invention is based on the Smart Cut™ technology. If the separation at the embedded brittle plane is spontaneous, the fracture time (i.e. the time until separation occurs during thermal fracture annealing) may vary between identically processed bonded assemblies undergoing the same annealing in the same furnace. The fracture time (TF) depends on a number of parameters related to the formation of the embedded brittle plane, the fracture annealing, the nature of the bonded structure, etc. The applicant has noticed that for similarly prepared bonded structures undergoing the same fracture annealing, the separation occurring at a short fracture time (TFc) leads to a thin layer with lower high frequency surface roughness (micro-roughness) in the final laminated structure (i.e. after transfer and finishing) than the separation occurring at a longer fracture time (TF1), as shown in FIG. 2. Furthermore, a long fracture time induces localized zones of very high roughness (called dense zones ZD) at the edge of the thin film after fracture, which is not or is rare for short fracture times. As can be seen in map (A) of FIG. 1, such dense areas degrade the quality and roughness of the thin film, even after finishing.

[0017] The transfer method according to the invention therefore aims to initiate spontaneous separation at the embedded brittle surface in an early (short time to failure) and repeatable (low variation in time to failure between multiple similar bonded structures) manner in order to substantially improve the surface roughness of the transferred thin film.

[0018] For this purpose, the transfer method first comprises the step of providing a bonded structure 100 comprising a donor substrate 1 and a support substrate 2 assembled by direct bonding at their respective front surfaces (1a, 2a) along a bonding interface 3 (Figure 3).

[0019] The donor substrate 1 is preferably in the form of a wafer with a diameter of 100 mm, 150 mm, 200 mm, 300 mm or even 450 mm and a thickness typically between 300 μm and 1 mm. The donor substrate 1 comprises a front surface 1a and a rear surface 1b. The surface roughness of the front surface 1a is selected to be less than 1.0 nm RMS, preferably even less than 0.5 nm RMS (measured by atomic force microscope (AFM), e.g., on a 20 μm×20 μm scan). The donor substrate 1 can be made of silicon or any other semiconducting or insulating material (e.g., SiC, GaN, etc.) where thin film transfer may be of interest.

[0020] It should also be noted that the donor substrate 1 may include, at least on its front surface 1a, one or more additional layers 12, such as an insulating layer, which become embedded intermediate layers in the bonded structure 100 after assembly of the donor substrate 1 and the support substrate 2, as shown in FIG.

[0021] The donor substrate 1 includes a buried brittle surface 11 that defines the thin film 10 to be transferred. As is well known for the Smart Cut™ technology, such a buried brittle surface 11 can be formed by implanting light species such as hydrogen, helium, or a combination of both. The light species are implanted at a defined depth in the donor substrate 1 that corresponds to the thickness of the target thin film 10. These light species form microcavities around the defined depth that are distributed in the thin film approximately parallel to the front surface 1a of the donor substrate 1, or parallel to the (x,y) plane in the figure. For the sake of simplicity, this thin film will be referred to as the buried brittle surface 11.

[0022] The implantation energy of the light species is selected to reach a given depth. For example, hydrogen ions are implanted with energies between 10 keV and 210 keV and a density of 5×10 16 / cm 2 ~1×10 17 / cm 2ions are implanted at a dose of 100 to 1500 nm, defining a thin film 10 with a thickness of the order of 100 to 1500 nm. It is recalled that, prior to the ion implantation step, an additional layer may be deposited on the front surface 1a of the donor substrate 1. This additional layer may, for example, consist of a material such as silicon oxide or silicon nitride. It may be retained for the next assembly step (forming all or part of the intermediate layer of the bonded structure 100) or it may be removed.

[0023] Also, the support substrate 2 is preferably in the form of a wafer with a diameter of 100 mm, 150 mm, 200 mm, 300 mm or even 450 mm and a thickness typically between 300 μm and 1 mm. The support substrate 2 comprises a front surface 2a and a rear surface 2b. The surface roughness of the front surface 2a is selected to be less than 1.0 nm RMS, preferably even less than 0.5 nm RMS (measured by AFM, for example, on a 20 μm×20 μm scan). The support substrate 2 can be made of silicon or any other semiconducting or insulating material in which thin film transfer may be of interest. In the context of the present invention, due to the assembly of the donor substrate 1 and said support substrate 2, the material constituting the support substrate 2 must be compatible with the application of temperatures of 400° C. or more to the bonded structure 100.

[0024] It should also be noted that the support substrate 2 may comprise, at least on its front surface 2a, one or more additional layers, e.g., insulating layers and / or charge trapping layers, which (or these) are embedded in the bonded structure 100 after assembly of the donor substrate 1 and the support substrate 2.

[0025] The assembly between the donor substrate 1 and the support substrate 2 is based on direct bonding by molecular adhesion. As is known per se, said bonding forms a bonding interface 3 without the need for adhesive materials, since an atomic-scale bond is established between the joining surfaces. In particular, there are several types of molecular adhesion bonds, which differ according to the respective temperature, pressure, atmospheric conditions or treatments before contacting the surfaces. We can mention bonding at room temperature with or without prior plasma activation of the surfaces to be assembled, atomic diffusion bonding (ADB), surface-activated bonding (SAB), etc.

[0026] The assembly process may include conventional chemical cleaning sequences (e.g. RCA cleaning), surface activation (e.g. oxygen or nitrogen plasma) or other surface treatments (such as cleaning by scrubbing) that can improve the quality of the bonding interface 3 (low defects, strong adhesion energy) before contacting the front surfaces 1a, 2a to be assembled.

[0027] Once the bonded structure 100 has been formed, the transfer method according to the invention involves applying a thermal breakdown treatment to induce spontaneous detachment along the buried brittle plane 11. The detachment results in the transfer of the thin film 10 from the donor substrate 1 to the support substrate 2, forming a laminated structure 110 (FIG. 4). A remainder 1′ of the donor substrate is also obtained.

[0028] The thermal break process according to the present invention is unique in that it is characterized by a very rapid heat-up rate and a temperature profile designed to heat the center of the bonded structure 100 relative to its periphery.

[0029] Essentially, the heat up rate of the adiabatic process is greater than 1° C. / sec, at least between an initial temperature below 250° C. and a level temperature of 500° C. or greater.

[0030] To achieve rapid heating rates, it is advantageous to use rapid annealing equipment, widely used in the semiconductor and microelectronics fields, such as furnaces known as RTA ("rapid thermal annealing") or RTP ("rapid thermal processing") furnaces. Heating in this type of equipment is provided by infrared lamps whose power is adjustable to adjust the temperature of different zones to the structure being processed.

[0031] In an RTA or RTP machine, the initial temperature when the bonded structure 100 is introduced into the furnace chamber is typically room temperature, and the heating rate can be rapid, typically on the order of 1° C. / sec to about 200° C. to 250° C. However, the rate of heating up to 250° C. is not critical, since ripening of microcavities and microcracks in the embedded brittle surface 11 is generally slow at temperatures below 250° C.

[0032] From at least 250° C., the method according to the invention provides a rapid ramp-up speed (>1° C. / sec) up to a level temperature of 500° C. or higher. The level temperature is typically 500° C.-600° C., especially when the donor substrate 1 is made of silicon. Above 250° C., the kinetics of microcrack growth in the buried brittle plane 11 becomes significant.

[0033] Further, the thermal insulation treatment is defined such that the bonded structure 100 is subjected to a temperature gradient varying from 40°C to 120°C between the central region C and the peripheral region P. The central region C refers to a region including the center of the bonded structure 100 in the (x, y) plane parallel to the bonded interface 3 (FIG. 3). The radius (in the (x, y) plane) of the central region C is typically 1% to 50% of the radius of the bonded structure 100. The peripheral region P is a region surrounding the central region C and including the edge of the bonded structure 100.

[0034] It should be noted that a rapid heat-up rate to 250° C. may be advantageous to help establish and maintain a thermal gradient between 250° C. and the level temperature in the subsequent adiabatic processing sequence.

[0035] Preferably, the thermal gradient between the central region C and the peripheral region P is between 40°C and 80°C.

[0036] An example of the temperature profile observed by the bonded structure 100 during the thermal breakdown process is shown in FIG. 5. As the set point curves show, the initial temperature is room temperature and the level temperature is 600° C. Three monitoring pyrometers T1, T2, T3 located at different points on the bonded structure 100 make it possible to observe the temperature rise and temperature gradient experienced by said structure. Pyrometer T1 is placed in the center and pyrometers T2, T3 are placed at the periphery (20 mm from the edge of the bonded assembly 100). It should be noted that the pyrometers used give reliable measurements only from 250° C. to 300° C. The heating is adjusted in separate zones of the furnace facing the bonded structure 100 to establish a temperature gradient of about 50° C. between the central area C (see the temperature curve of pyrometer T1) and the peripheral area P (see the temperature curves of pyrometers T2, T3).

[0037] The temperature gradient applied to the bonded structure 100 induces localized overheating in the central region C during the thermal breakdown process, which results in greater ripening of the microcracks of the embedded brittle plane 11 in this region compared to the peripheral regions P. The greater ripening of the microcracks in the central region C acts as fracture initiators during the rapid heating up approaching the level temperature.

[0038] This provides the advantage of propagation of the separation wave from the center to the edge of the bonded structure 100, which significantly limits the amplitude of mottle M or other fracture waves (roughness and low frequency ripples) on the surface of the transferred thin film 10. Another advantage is that separation occurs early, with a shorter fracture time than conventional fracture times for similar bonded structures subjected to conventional fracture annealing. Early fracture ensures low micro-roughness (high spatial frequency) and few, if any, localized regions of high roughness (also known as dense zones ZD).

[0039] The improvement in roughness achieved by implementing the transfer method according to the invention is shown in Figure 6. The first map shows the surface roughness of a thin film transferred to a first SOI structure obtained using a conventional transfer method (including finishing steps), and the presence of mottle and breaking waves on the surface is evident. The second map shows a second SOI structure 110 obtained using the transfer method according to the invention (including finishing steps). The SOI structure 110 is free of mottle M or other dense areas ZD.

[0040] The transfer method according to the invention also enables high speed adiabatic processes to be achieved, thanks to the very short duration of these processes.

[0041] In an advantageous embodiment of the transfer method, a pre-annealing is applied to the bonded structure 100 before the fracture insulation process in order to achieve pre-ripening of the microcavities and microcracks of the buried brittle surface 11. However, the thermal budget provided by the pre-annealing remains insufficient to cause spontaneous separation. Typically, the thermal budget for pre-ripening targets 25% to 75% of the thermal budget for fracture resulting in spontaneous separation. In the case of a silicon donor substrate, the pre-annealing temperature is preferably set at about 350 ° C.

[0042] The pre-annealing can be carried out in conventional horizontal or vertical furnaces or in RTA or RTP furnaces. It is important that the pre-aging is carried out as uniformly as possible within the buried brittle surface 11, regardless of the area of ​​the plate (center or periphery).

[0043] Pre-maturation of the microcracks of the buried brittle surface 11 can further improve the surface roughness of the thin film 10 after separation by reducing the gap in the maturity of the microcracks present at the time of separation initiated by the thermal gradient (applied during the thermal breakdown process). To act as a fracture initiator, it is essential to establish a significant temperature gradient between the central region C and the peripheral region P, which can induce a significant difference in the maturity of the microcracks during the rapid heating up. If the microcracks in the peripheral region of the buried brittle surface 11 are not sufficiently matured when the fracture wave propagates, it is not preferred because mottle-type defects will be generated. Therefore, for very high thermal gradients applied in the thermal breakdown process (e.g., more than 50°C, or even more than 80°C), it is advantageous to perform a maturation pre-annealing, which brings the entire buried brittle surface 11 to a level of maturity compatible with fracture propagation without generating mottle.

[0044] The transfer method according to the invention may also include a step of smoothing the front surface 10a of the thin film 10 after separation.

[0045] This step eliminates the surface roughness caused by the fracture of the embedded brittle plane 11 and restores the crystalline quality of the transferred thin film. The resulting laminated structure 110 after separation is typically removed from the furnace where the thermal insulation was performed and is thermally, chemically and / or mechanochemically treated in conventional finishing steps.

[0046] Advantageously, the smoothing step of the transfer method herein comprises applying an annealing at a temperature above 1000° C. in a neutral or reducing atmosphere immediately after the thermal insulation breaking process, without removing the laminated structure 110 from the furnace enclosure in which it was broken and without further cooling down to ambient temperature. The laminated structure 110 and the remaining part 1′ of the donor substrate remain separate but close to each other, thus providing a perfectly controlled “local” atmosphere facing the broken surface. Essentially such a local atmosphere is formed by the injected gas and is completely non-oxidizing, so that the surface of the thin film 10 can be smoothed very effectively (i.e. at a lower temperature than a surface uniformly and lightly covered with native oxide) without any oxidation.

[0047] Therefore, the smoothing step is preferably carried out in the same furnace and closed vessel as the separation step, and the temperature is raised to the range of 1000° C. to 1200° C. The atmosphere in the furnace chamber is neutral or reducing (preferably Ar, H 2 , Ar / H 2 ).

[0048] At this stage (unlike the fracture stage), ensure that the temperature experienced by the laminate structure 110 is uniform and homogenous across its surface, since temperature gradients between the center and edges are detrimental at this stage.

[0049] The in situ sequence of the thermal break and smoothing steps in the same furnace enclosure, without temperature drop and without return to the outside atmosphere, is particularly advantageous since it ensures extremely low contamination of the surface of the transferred thin film 10, a complete absence of native oxides and, consequently, an extremely high smoothing efficiency. It also benefits from reduced roughness after detachment due to early fracture initiation.

[0050] RTA and RTP furnaces are perfectly suited for this type of sequence, which requires rapid ramping (breakdown adiabatic treatment) and heating up (smoothing phase). This process sequence is advantageous from the productivity point of view.

[0051] EXEMPLARY EMBODIMENTS In particular, the transfer method can be used to fabricate FDSOI (fully depleted SOI) structures, ie structures with a thin surface film and a thin buried insulating layer.

[0052] The donor substrate 1 is a single crystal silicon wafer of 300 mm diameter, containing a 35 nm thick insulating layer 12 of silicon oxide on its front side 1a. Helium and hydrogen ions are bombarded with ions of 1×10 at energies of 35 keV and 25 keV, respectively. 16 / cm 2 and x10 16 / cm 2 A buried brittle surface 11 is formed by co-implanting 11 at a dose of 0.1 to 0.5 μm.

[0053] The support substrate 2 is a single crystal silicon wafer having a diameter of 300 mm.

[0054] The two substrates 1, 2 are then subjected to conventional surface treatment (cleaning, plasma activation) with a view to molecular adhesive bonding.

[0055] The bonded structure 100 is fabricated by assembly based on direct contact between the front surface 1 a of the donor substrate and the front surface 2 a of the support substrate 2 .

[0056] The bonded structure 100 is introduced into an RTP furnace for thermal break processing and subjected to the following sequence: 1. Creating a vacuum in a closed container; 2. Nitrogen N 2 Filling time: 20 seconds; 3. Ambient to 270℃: 15 seconds; 4. Stabilization at 270℃: 20 seconds; 5. Heating from 270℃ to 600℃: 4℃ / sec; 6. Annealing at 600℃ level: 120 seconds; 7. Temperature drop (from 600°C to 300°C): 60 seconds; and 8. Temperature drop (from 300℃ to room temperature): 450 seconds Process it with.

[0057] The heating zone of the RTP furnace is adjusted to apply a temperature gradient of about 50° C. between the center of the bonded structure 100 and the peripheral region P. Localized overheating in the central region C acts as a fracture initiator, causing premature separation during the adiabatic fracture process, typically at the end of the heat-up (step 5 in the sequence above).

[0058] The surface quality 10a of the transferred thin film 10 is improved compared to the SOI structure obtained from the bonded structure processed by the conventional method, since it has no or almost no mottle M or dense zones ZD. Also, the level of micro-roughness ("haze") of the surface of the thin film 10 after smoothing is lower than the level of roughness obtained by the conventional method.

[0059] Naturally, the invention is not limited to the described embodiments, and variants can be added thereto without departing from the scope of the invention as defined by the claims.

Claims

1. A method for transferring a thin film (10) onto a support substrate (2), said method comprising the steps of: providing a bonded structure (100) comprising a donor substrate (1) and said support substrate (2) assembled by direct bonding at their respective front surfaces (1 a, 2 a) along a bonding interface (3), said donor substrate (1) comprising a buried brittle surface (11); applying a thermal breakdown treatment to the bonded structure (100) to induce spontaneous separation along the buried brittle plane (11) associated with the growth of microcracks in the buried brittle plane (11) through thermal activation, the separation resulting in the transfer of the thin film (10) from the donor substrate (1) to the support substrate (2); Including, The thermal insulation breaking treatment is a heating rate of greater than 1°C / sec between an initial temperature of at least 250°C and a level temperature of at least 500°C; a temperature profile such that the bonded structure (100) is subjected to a temperature gradient varying from 40°C to 120°C between a central region and a peripheral region; A transfer method comprising the steps of:

2. 2. The method of claim 1, further comprising the step of applying pre-annealing to the bonded structure (100) before the thermal insulation breaking treatment to achieve pre-ripening of the microcracks in the buried brittle plane (11), wherein the heat budget provided by the pre-annealing is insufficient to cause spontaneous separation.

3. 2. The transfer method according to claim 1, wherein the temperature gradient is from 40°C to 80°C.

4. 2. The method of claim 1, further comprising the step of smoothing the front surface (10a) of the thin film (10) after separation by annealing it at a temperature above 1000°C in a neutral or reducing atmosphere, wherein the thermal insulation and smoothing steps are carried out in the same sealed container and equipment.

5. 2. The transfer method according to claim 1, characterized in that the buried brittle plane (11) is formed in the donor substrate (1) by implanting light chemical species such as hydrogen, helium or a combination of these two species.

6. 2. The transfer method according to claim 1, characterized in that the donor substrate (1) and / or the support substrate (2) have an insulating layer at least on their respective front sides (1a, 2a), which forms a buried insulating layer adjacent to the bonding interface (3) in the bonding structure (100).

7. 2. The transfer method of claim 1, wherein the thin film (10) from the donor substrate (1) is made of monocrystalline silicon and the support substrate (2) comprises monocrystalline silicon, to form a stacked SOI structure (110).

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