Method for producing a silicon substrate for quantum applications

Abstract

The invention relates to a method (100) for producing a structure comprising a carrier substrate (Si_WafCar) supporting a silicon layer (28SiDon) and an oxide layer (28SiO2) inserted between the silicon layer and the carrier substrate, the method comprising transferring the first silicon layer (28SiDon), formed on a layer (SiGe) of a silicon-germanium alloy on a donor structure (Don), onto the carrier substrate (Si_WafCar), then removing the substrate (Si_WafDon) from the donor structure and the silicon-germanium layer (SiGe), the silicon layer (28SiDon) consisting of at least 99.92% of silicon isotope 28Si.

Description

METHOD FOR MANUFACTURING A SILICON SUBSTRATE FOR QUANTUM APPLICATIONS TECHNICAL FIELD OF THE INVENTION

[0001] The invention relates to a method for forming a substrate comprising a silicon layer 28 If on an electrically insulating layer, this substrate is suitable for forming a basis for electronic devices whose operating principle relies on the manipulation of quantum objects, in particular qubits. TECHNOLOGICAL BACKGROUND

[0002] Silicon is recognized as a promising material for electronic devices based on manipulating electron spin, which represents their magnetic moment. Information can be stored and manipulated by acting on electron spin, rather than using their electric charge as in conventional electronics. Electron spin can also be used as a qubit support to implement quantum information theory, by exploiting superpositions of spin states with a well-defined phase. See EP 3 975 072 A1 and US 2023 / 0026518 for further information.

[0003] The duration of phase retention, and therefore of information retention, is defined by the coherence time. Long coherence times are necessary for operations on qubits to be performed or for quantum information to be stored before a read operation, during which the qubit loses its coherence and the information is lost.

[0004] Silicon has three stable isotopes: the isotopes 28 If, 29 Yes and 30 Si, which make up approximately 92.2%, 4.7%, and 3.1% of natural silicon, respectively. One of the mechanisms that causes spin state decoherence is the presence of isotopes 29 If silicon is involved, its nuclear magnetic moment is not zero. Therefore, it is preferable to eliminate as much as possible the proportion of 29 If in the silicon used as the basis for qubit manipulation devices. The isotope 30Si should also be eliminated: although the isotope 30 If it does not possess spin, it leads to variations in the bond lengths between atoms and therefore in the local environment of the qubits. It is necessary to maximize the homogeneity of the local environment by minimizing the presence of the isotope. 30 So that the qubits have characteristics as close to each other as possible.

[0005] One solution is to use silicon enriched with isotopes 28 If. Schneider et al. (E. Schneider and J. England, “Isotopically Enriched Layers for Quantum Computers Formed by 28 "Si Implantation and Layer Exchange" (ACS Appl. Mater. Interfaces 2023, 15, 21609–21617) propose a silicon isotope layer enrichment technique 28 If based on the ionic implantation of ions 28If, in an aluminum layer formed on a native oxide-free silicon substrate followed by layer exchange crystallization, a layer of 28 High purity is required on the silicon substrate. Schneider also explains that defects at the interfaces of the device layers necessitate high-quality dielectrics and / or techniques to distance the qubits from the interfaces and the noise they cause, depending on the geometry of the qubit placement, whether close to or far from the interfaces.

[0006] Spin qubit manipulation devices can be fabricated using silicon as a base and standard CMOS (Complementary Metal Oxide Semiconductor) or FD-SOI (Fully Depleted Silicon On Insulator) manufacturing processes from the semiconductor industry. FD-SOI technology, in particular, allows for precise control over the location of the qubits, away from the interfaces between the silicon and the gate dielectric or the buried oxide layer of the substrate (BOX).

[0007] However, SOI (Silicon On Insulator) type substrates possessing a thin layer of the isotope 28 Quantum-grade silicon is not commercially available. Here, "quantum quality" refers to layers of 28 If sufficiently pure to sustain the spin coherence of electrons for durations long enough to perform operations on qubits, with a purity in 28If greater than 99.92%.

[0008] There is therefore a need for silicon wafers suitable for use as substrates in the fabrication of devices for manipulating electron spin qubits, capable of maintaining the isotopic purity of the layers of 28 If and to allow the manipulation of qubits at chosen locations, compatible with the type of device envisaged.

[0009] More specifically, there is a need for SOI-type substrates with a thin layer of 28 If, on a support, an electrically insulating layer is interposed between the layer of 28 If and the support. It is advantageous that the thin film and the electrically insulating layer (the buried "BOX" mentioned above) are thin enough to be able to form FD-SOI technology transistors or Fully Depleted SOI in English terminology.

[0010] Furthermore, considering that quantum applications require working at very low temperatures, for example below 3 K or on the order of 10 mK, while employing control electronics physically as close as possible to the supports of the manipulated quantum quantities, the integration on the same substrate of FD-SOI transistors and quantum quantity manipulation devices is advantageous: the FD-SOI transistors can have a low threshold voltage and operate by limiting the energy dissipation in their support, thus limiting the heating problems of these quantum quantity manipulation devices.

[0011] A manufacturing process for substrates suitable for FD-SOI technology, with a silicon surface layer 28 If isotopically pure and suitable for quantum applications, it is based on a layer transfer technique that requires the formation of two layers of 28If: one on a donor substrate and the other on a recipient substrate. These two substrates are usually made of conventional bulk silicon wafers, that is, wafers made of different silicon isotopes and containing a proportion of impurities. In the final structure, the layer 28 If the donor substrate constitutes the surface layer of silicon 28 Si and rests on a Box layer, itself separated from a solid silicon wafer of the receiving substrate by the layer of 28 If formed on it. The layer of 28 If the receiving substrate acts as a barrier to the diffusion of impurities and different isotopes from the bulk silicon wafer to the surface layer of 28 Yes, and therefore allows for maintaining the purity and quantum properties of this surface layer. French patent application FR2314256 describes such a manufacturing process.

[0012] As described above, the fabrication of substrates suitable for FD-SOI technology with a silicon surface layer 28 If isotopically pure and configured for quantum applications requires the use of 28 Si epitaxially grown on bulk Si platelets, both for a donor substrate and for a recipient substrate. The purity of the surface layer of 28 If it must be maintained (i) during the SOI manufacturing process: fabrication of the composite substrate comprising a bulk silicon support, a surface layer of 28 Yes, and a BOX layer insulating the layer 28If the bulk substrate and (ii) during the CMOS transistor fabrication process in the composite substrate. The diffusion of impurities and different silicon isotopes from the bulk silicon substrate depends on several factors: isotope and contaminant concentration, physical parameters of the SOI such as the thickness of the surface layer of 28 Yes, from the BOX, and the thickness of 28Si on which the BOX rests, and of course the thermal budget of the SOI and CMOS processes.

[0013] Consequently, to maintain the desired level of purity, known manufacturing processes for the composite substrate require thick epitaxial layers of 28 Yes, on the order of several hundred nanometers, typically 400 nm or more, for both the donor substrate and the recipient substrate.

[0014] However, the use of thick epitaxy implies a degradation of the surface quality of the resulting layers, for example, greater roughness and crystalline defects, which are key parameters to minimize in order to obtain SOI wafers with a layer of 28 If superficial, high-quality. Adjusting the epitaxial process to achieve the desired quality will involve a lower thermal budget with a longer duration, which will reduce the throughput of the epitaxial tool and the additional consumption of silane. 28 If, or other precursors necessary for the growth of the layers of 28 Yes. Due to the high price and low availability of quantum-quality precursors for epitaxy of 28 Yes, optimizing SOI manufacturing by reducing the required thickness of the layers of 28 Whether for the donor substrate and / or the recipient substrate is of great interest.

[0015] The applicant's objective is to provide a manufacturing process for a semiconductor support suitable for forming a basis for obtaining devices for manipulating quantum objects, and in particular qubits formed from electron spins.

[0016] To achieve this goal, one aspect of the invention is a method for manufacturing a structure comprising a carrier substrate supporting a silicon layer, with an oxide layer interposed between the carrier substrate and the silicon layer, the method comprising the steps of forming a layer of a silicon-germanium alloy on a donor substrate; forming a first silicon layer on the silicon-germanium alloy layer, thus forming a donor structure; forming an oxide layer on at least one of the first silicon layer and a carrier structure comprising the carrier substrate; assembling the donor structure and the carrier structure, such that the carrier substrate, the oxide layer, the first silicon layer, the silicon-germanium alloy layer and the donor substrate are stacked in that order; removing at least a portion of the donor substrate attached to the silicon-germanium alloy layer;and remove the layer of a silicon-germanium alloy, in which the first silicon layer consists of at least 99.92% isotope; 28 If it's silicon.

[0017] A first advantage of the process is that it can be implemented by methods known and common in the field of the semiconductor industry and put to use in the manufacture of quantum devices, which accelerates the technological maturity of the manufacturing process undertaken and reduces the necessary investments in time and equipment.

[0018] A second advantage of this process is that it allows for savings (i) in the use of precursor gases with a high content of the silicon 28Si isotope and (ii) in the usage time of the epitaxial frames used for the growth of silicon layers essentially composed of the isotope 28 If it's silicon. Indeed, a layer of silicon of an isotope 28It can be formed relatively finely, without having to take into account isotope contamination 29 Yes and 30 If silicon and impurities from a support substrate, contamination due to the diffusion of species caused by a thermal oxidation treatment.

[0019] According to additional, non-limiting characteristics of the support according to the invention, considered individually or in any technically feasible combination:

[0020] - the process may further include a step of forming a second layer of silicon on the carrier substrate before the step of forming the oxide layer;

[0021] - the second silicon layer can be made up of at least 99.92% isotope 28 If silicon;

[0022] - the oxide layer can be formed by oxidation of at least one of the first silicon layer and the second silicon layer;

[0023] - the oxide layer can be formed by oxidation of the first silicon layer;

[0024] - the first silicon layer can have a thickness of between 20 and 110 nm before the oxide layer formation stage;

[0025] - at least one of the first silicon layer and the second silicon layer can be formed by epitaxial growth;

[0026] - the layer of a silicon-germanium alloy may have a proportion of isotopes 28 If it is silicon of at least 99.92%;

[0027] - the layer of a silicon-germanium alloy can be formed by epitaxial growth;

[0028] - the layer of a silicon-germanium alloy can have a thickness between 20 and 100 m, preferably between 30 and 70 nm;

[0029] - the layer of a silicon-germanium alloy can have a germanium content of between 15% and 30%;

[0030] - the oxide layer can have a thickness between 10 and 50 nm;

[0031] - the second silicon layer can have a thickness greater than 200 nm, preferably between 200 nm and 500 nm;

[0032] - at least one of the donor substrate and the carrier substrate can be formed from a single-crystal silicon wafer; and

[0033] - the process may further include the steps of: before the assembly step, forming a weakening plane in the donor substrate by implanting ions of a light species; and fracturing the donor substrate at the level of the weakening plane, after the assembly step and before the step of removing at least a part of the donor substrate, which remains attached to the layer of a silicon-germanium alloy.

[0034] The structure obtained by the above process is suitable for the formation of a quantum device, and comprises: a carrier substrate; a first isotope layer 28 Silicon dioxide; a layer of silicon oxide; a second layer of isotope 28 If silicon is used, the structure being formed by the substrate, the first isotope layer 28 If silicon, the first layer is silicon oxide, and the second layer is isotope 28 If silicon, stacked in this order, in which the first isotope layer 28 If silicon and the second isotope layer 28 If silicon is made up of at least 99.92% of isotopes 28 If silicon. Preferably, the silicon oxide layer has a proportion of isotope 28 If it's silicon of at least 99.92%.

[0035] A primary advantage of the structure is to provide an adequate basis for the development of quantum devices by employing technologies already well mastered in the field of semiconductors.

[0036] A second advantage of the structure is that it guarantees the reliability of the devices obtained thanks to the presence of a bilayer of 28 Yes and of 28 SiO2 acts as a barrier to undesirable elements contained in the substrate, such as isotopes 29 Yes and 30 If silicon, or even carbon, oxygen, or nitrogen atoms. It would indeed be difficult and extremely expensive to produce silicon substrates made purely of the isotope 28 If silicon. The available substrates are therefore made of natural silicon, containing at least the three isotopes 28 If, 29 if and 30 If silicon, as well as impurities such as carbon, oxygen, and nitrogen. BRIEF DESCRIPTION OF THE FIGURES

[0037] Other features and advantages of the invention will become apparent from the detailed description of the invention which follows with reference to the accompanying figures in which:

[0038] Laillustre un process de fabrication selon un premier mode de mise en mise en œuvre de l'invention;

[0039] Laillustre the continuation of the process of the ;

[0040] This is a diagram summarizing the manufacturing process of figures 1 and 2;

[0041] This illustrates a manufacturing process according to a second embodiment of the invention; and

[0042] This is a diagram summarizing the manufacturing process of the. DETAILED DESCRIPTION OF THE INVENTION

[0043] First method of implementation

[0044] A first embodiment of the present invention is described by means of figures 1 to 3 and the associated description below.

[0045] Figures 1 and 2 illustrate steps in a manufacturing process for the structure shown in (H). A diagram showing the steps of the manufacturing process illustrated in Figures 1 and 2 is also included.

[0046] Laillustre en (H) a Strct structure formed from a 28Si barrier layer Car , a 28SiO2 oxide layer, and a 28Si surface layer Don , stacked in this order on a Si_Waf carrier substrate Car , each of these elements preferably being in direct contact with the element or elements immediately adjacent to it.

[0047] The Si_Waf carrier substrate Car The 28Si barrier layer is made of a conventional single-crystal silicon wafer. Car and the surface layer 28Si Don are made of silicon. The 28SiO2 layer is made of a silicon oxide layer. The 28Si layers Car 28SiDon and 28SiO2 in particular exhibit isotope purity 28 If the silicon is at least 99.92% pure, for example, between 99.92% and 99.995%. Thus, the 28Si silicon layers Car and 28Si Don contain less than 800 ppm of isotope 29 If it's silicon.

[0048] Such a structure can be used to form quantum devices on its surface, thanks to the characteristics of the 28Si surface layer Don : thanks to its purity in 28 Yes, the spin coherence duration of the electrons in this shell is sufficient to perform operations on qubits associated with these electrons. Integrated into a quantum device, the surface 28Si shell Don Therefore, it represents a good support for qubits.

[0049] In addition, the 28Si barrier layer Car and the 28SiO2 oxide layer prevents, or at least limits, the migration of impurities, and in particular atoms of the isotope 29If silicon from the substrate supports Si_Waf Car down to the surface layer 28Si Don Without a barrier layer, the diffusion of impurities would increase concentrations of 29 If, 30 If dopants or elements are present at levels incompatible with the quality required for the proper functioning of quantum devices, this leads to a reduction in coherence times and causes these devices to function similarly to devices formed within conventional substrates for FD-SOI technology transistors.

[0050] During preliminary stages 110 Don and 110 Car of process 100 for manufacturing the Strct structure, a Si_Waf donor substrate Don and a Si_Waf carrier substrate Carare provided. In this example, the substrates are each made of a single-crystal silicon wafer, but any other substrate conventionally used in the semiconductor industry could be used.

[0051] Figure (A) illustrates the successive formation in this order (1) of an attack-stopping silicon-germanium alloy layer (SiGe) and (2) of the surface layer 28Si Don on the donor substrate Si_Waf Don , during two successive stages 120 Don and 130 Don The resulting structure, known as the "donor structure," is designated Don in the figures. The surface layer 28Si can be grown, for example by epitaxy. Don on one face of the Si_Waf donor substrate Don , then the layer of a silicon-germanium alloy SiGe on the surface layer 28Si Don thus formed.

[0052] Laillustre en (B) the formation of the 28Si barrier layerCar and the 28SiO2 layer on the Si_Waf support substrate Car , during two successive stages 120 Car and 130Car, respectively. The resulting "load-bearing structure" is designated by Car in the figures. The 28Si barrier layer can be grown, for example by epitaxy. Car on one face of the Si_Waf substrate Car during stage 120 Car During stage 130 Car , the 28Si barrier layer Car is superficially oxidized over a certain thickness, so as to form the 28SiO2 oxide layer.

[0053] In the previous steps, the 28Si layers are formed Don 28Si Car and optionally SiGe, so that they exhibit silicon isotope 28 purities 28Si between 99.920% and 99.995%. Thus, the maximum concentrations of the silicon-29 isotope in these layers are, at least initially, between 800 and 50 ppm, concentrations low enough to allow the fabrication of quantum devices based on electron spin on the surface 28Si layer Don Such compositions of the 28Si layers Don 28Si Car and SiGe can be achieved by using, in a conventional epitaxial growth process, silane gas of a purity corresponding to that of the layers in 28 Yes, as a precursor gas of silicon in the layers.

[0054] Even though manufacturing a SiGe layer with a silicon isotope-28 purity between 99.920% and 99.995% is only optional, such purity helps avoid isotope contamination. 29 Yes and 30 Si layer 28Si Donin the epitaxial matrix during its formation. In this case, the 28Si layer Don is relaxed, and the quantum confinement of a quantum device formed on this layer must be ensured by a vertical electrostatic field. Preferably, the same epitaxial framework is used for the successive formation of the two 28Si layers Don and SiGe.

[0055] The 28SiO2 oxide layer is obtained here by the oxidation of the 28Si layer Car it exhibits the same characteristics of purity in 28 If that's the case. This oxidation operation can be carried out conventionally by applying a heat treatment under an oxygen atmosphere. The 28SiO2 layer is preferentially formed by thermal oxidation to ensure a good interface quality between the 28SiO2 layer and each of the 28Si layers. Don and 28Si Car, after assembly of the two substrates (see step 150, illustrated in (D) of the diagram). Naturally, it is a silicon oxide formed from oxygen and the isotope 28 Si of the silicon of the 28Si layer Car The 28Si layer Car is oxidized only over a certain thickness, strictly less than its thickness and depending on the thickness targeted for the 28SiO2 layer.

[0056] Furthermore, the 28SiO2 layer can also be formed by HDP-CVD deposition (HDP-CVD for High Density Plasma CVD), which is carried out at a relatively low temperature compared to thermal oxidation, thus advantageously limiting the thermal budget imposed on the 28Si layer. Car , and thereby limit the diffusion of other Si isotopes in the layer intended to contain the quantum object manipulation devices.

[0057] The thicknesses of the 28SiO2 and 28Si layers Carcan be chosen in such a way as to guarantee an adequate level of barrier effect to prevent contamination of the surface layer 28Si Don by, in particular, the 29 If, while limiting the thickness of the 28SiO2 layer, for example for applications based on FD-SOI technology which requires a thin 28SiO2 layer, the inventors were able to determine, through computer simulation, sets of thicknesses for the 28Si layers. Don , 28SiO2 and 28Si Car , allowing us to guarantee a certain level of purity of the 28Si layer Don while advantageously minimizing the thickness of the 28Si layer Car for a given thickness of the 28SiO2 layer, chosen for its compatibility with conventional FD-SOI technology processes.

[0058] Table Tab1 shows such thickness sets for two purity levels, at 99.9% and 99.99% of 28 If for the 28Si layer DonThe numerical simulations were calculated considering the 28Si layer Car has a purity level of 99.99% 28 Yes. These calculations take into account, in particular, a thermal budget corresponding to that of the realization of the Strct structure and the conventional fabrication of an FD-SOI transistor, which is the highest thermal budget experienced by the layers, including the fabrication steps of CMOS transistors and qubit devices formed in the 28Si layer. Don 28Si thickness Don (after finishing) Thickness of 28SiO2 Thickness of 28Si Car for a 28Si layer Don 99.9% purity, 28mm thick Car for a 28Si layer Don 99.99% purity 16 nm 50 nm 30 nm 250 nm 16 nm 20 nm 200 nm 420 nm

[0059] Table 1

[0060] Before the oxidation step 130 Car , the 28Si layer Carmust have a thickness approximately equal to the sum of the target thickness for the 28SiO2 layer and the final target thickness for the 28Si layer Car of the Strct. structure

[0061] For example, we can consider the thicknesses typically used in FD-SOI type technologies, which are between 10 and 60 nm, preferably between 10 and 25 nm for the active layer (after finishing step 190, see below), which here corresponds to the 28Si surface layer Don and between 10 and 50 nm for the 28SiO2 oxide layer, often around 20 nm thick. Thus, a thickness of between 20 and 110 nm can be expected for the surface 28Si layer. Don , during its deposition, before its oxidation to form the 28SiO2 oxide layer. For the 28Si layer Car , we can consider a thickness greater than 200 nm, for example between 200 and 500 nm.

[0062] The SiGe attack arrest layer can have a thickness of between 20 and 100 nm, or preferably between 30 and 70 nm, typically 50 nm, and have a germanium content of between 15% and 30%.

[0063] Figure (C) illustrates an Imp implantation of light species such as hydrogen, helium, or a combination of such species in the volume of the donor substrate Si_Waf Don through the 28Si layers Don and SiGe, so as to form a Frgl embrittlement plane in the donor substrate Si_WafDon, during a step 140 Don This implantation can correspond to a hydrogen and / or helium implantation, that is, an ion bombardment of hydrogen and / or helium on the donor substrate Si_Waf Don through the 28Si layers Donand SiGe. In a manner known per se, and as illustrated in (B), the implanted ions form a Frgl embrittlement plane. The nature and dose of the implanted species and the implantation energy are chosen according to the nature and thickness of the layers traversed, and the desired implantation depth.

[0064] Laillustre en (D) the assembly of the Don and Car structures, necessary for the formation of the Struct structure comprising a stack of 28Si layers Car , 28SiO2 and 28Si Don Following the formation of the embrittlement plane Frgl, the donor structure Don is inverted and the surface layer 28Si Don is brought into intimate contact with the 28SiO2 layer of the Car support structure and is assembled there, for example by molecular bonding or any other assembly technique by direct contact of surfaces of elements to be assembled, during a step 150.

[0065] Laillustre en (E) la fracture du substrat donor Si_Waf Don at the level of the Frgl embrittlement plane obtained by ion implantation, so that a part Si_Waf Don_2 of the donor substrate Si_Waf Don is detached from the load-bearing structure. Because while a part Si_Waf Don_1 of the donor substrate Si_Waf Don and the SiGe and 28Si layers Don They remain fixed there during a fracture and shrinkage step 160. This fracture can be achieved by heat treatment, possibly assisted by mechanical stress to initiate the fracture, according to conventional layer transfer techniques well known in the field of microelectronics, such as the so-called "Smart Cut" process. Following the assembly and fracture of the donor substrate, a heat treatment can be applied to consolidate the assembly and repair the assembled layers.

[0066] An alternative to the formation of a weakening plane and the fracture of the Si_Waf substrate Don at this level may consist of a thinning of the donor substrate Si_Waf Don after its assembly, for example by etching, grinding and / or chemical mechanical polishing (CMP). This thinning can be used to completely remove the donor substrate, or only partially, for example to achieve the situation illustrated in (E) of the.

[0067] Laillustre shows the steps in the process necessary to go from the state illustrated in (E) to the Strct structure illustrated in (H).

[0068] Laillustre en (F) the elimination, during step 170, of the residual layer Si_Waf Don_1 of the donor substrate Si_Waf Don which remained fixed to the support structure. Because at the end of step 160. This step can be implemented by selective etching of silicon. Etch(Si_WafDon-1 ), by wet method using, for example, a chemical solution, or by dry method using, for example, a plasma, or by a mechanochemical etching of the CMP type (Chemical Mechanical Polishing). Such an etching makes it possible to remove the residual Si_Waf layer Don_1 formed from silicon using the SiGe layer as a etching stop layer, by means of a selective silicon removal process from the Si_Waf layer Don_1 compared to the silicon-germanium alloy forming the SiGe layer. For example, one can refer to US patent documents 8,389,416 B2, US 9,984,890 B2 or US 10,934,485 B2, which describe processes for selectively attacking silicon compared to a silicon-germanium alloy.

[0069] Figure (G) illustrates the removal, during step 180, of the SiGe layer released following step 170. This step can be implemented by selective etching of the silicon-germanium alloy Etch(SiGe), either wet, for example, using a chemical solution, or dry, for example, using a plasma, or by chemical mechanical polishing (CMP). Such a polishing process removes the SiGe layer formed from a silicon-germanium alloy using the 28Si layer. Don as an etching stop layer, using a selective etching process of the silicon-germanium alloy of the SiGe layer compared to the silicon forming the 28Si layer Don For example, one can refer to patent documents US 9,236,265 B2, US 11,875,997 B2 or WO 2006 / 027332 A1, which describe processes for selectively etching silicon-germanium alloys with respect to silicon.

[0070] Regarding selective etching (Si_Waf) Don-1 ), it can be considered a selective etching of silicon with respect to the silicon-germanium alloy when the etching speed of the silicon is at least twice as high as the etching speed of the silicon-germanium alloy. Conversely, regarding the selective etching Etch(SiGe), it can be considered a selective etching of the silicon-germanium alloy with respect to silicon when the etching speed of the silicon-germanium alloy is at least twice as high as the etching speed of silicon. Thus, the selective etching Etch(Si_Waf Don-1 ) and Etch(SiGe) are distinct from each other.

[0071] Laillustre en (H) un step 190 de fini de la couche superficie 28Si Donderived from the donor structure Don. This finishing step consists of one or more mechanical and / or chemical attacks to thin the surface layer 28Si Don to a desired thickness and polishing of its accessible face. The finishing step can be similar to those used in the fabrication of substrates for FD-SOI technology. At the end of this step, the Strct structure illustrated by the is obtained.

[0072] A significant advantage of the 100 process is the thickness of the isotope silicon layer 28 If it is to be formed on the donor substrate Si_Waf Don is significantly reduced compared to existing processes, potentially limited to a thickness of 200 nm or less. This value can be compared, for example, to the 300 to 600 nm required for the isotope silicon layer. 28If the donor substrate of the process described in patent application FR 2314256. In this process, the oxide layer is obtained by oxidation of the isotope layer 28 If silicon is formed on a donor substrate, this oxidation, obtained by heating the layer, causes isotope diffusion. 29 Yes and 30 If there are impurities from the layer's support, the latter does not require a high thickness to guarantee purity. 28 If on the side of its face opposite its support. In this application, the 28Si layer Don is not subject to oxidation for the formation of the 28SiO2 oxide layer and therefore does not require such a large thickness.

[0073] Second method of implementation

[0074] A second embodiment of the present invention is described by means of figures 4 and 5 and the associated description below.

[0075] The second embodiment represents a second process 200 which is a variant of process 100 of the first embodiment. In process 100, the 28SiO2 oxide layer is formed on the 28SiCar layer, optionally by oxidation of the latter during step 130. Car In process 200, the 28SiO2 oxide layer is formed on the 28Si layer Don , possibly by oxidation of the latter; during a step 135 Don which can be implemented in the same way as step 130 Car of process 100, step 135 Don replacing step 130 Car .

[0076] Apart from this point, processes 100 and 200 are identical, with the Set structure being obtained by the assembly of the Don and Car structures during step 150, as illustrated in Figures 4 and 5, and the subsequent steps being the same. Of course, during step 150, it is the 28SiO2 layer, formed on the 28Si layer, that is formed. Don, which is in direct contact with the 28Si layer Car .

[0077] Another variant could involve applying both steps 130Car and 135Don. In this case, the two layers 28SiCar and 28SiDon are covered with a layer of 28SiO2 oxide. The assembly in step 150 then occurs through intimate contact of the two 28SiO2 layers.

[0078] Of course, in the event of the formation of oxide layers by oxidation of one, the other or both of the 28SiCar and 28SiDon layers, their respective thicknesses can be adjusted to take into account the reduction in thickness of the silicon layer concerned.

[0079] The invention is not limited to the embodiments described above and variations thereof may be made without departing from the scope of the invention as defined by the claims.

Claims

Method (100) for manufacturing a structure comprising a load-bearing substrate (Si_Waf Car supporting a silicon layer (28Si Don ), an oxide layer (28SiO2) being interposed between the carrier substrate (Si_Waf Car ) and the silicon layer (28Si Don ), the process comprising the steps of: - forming (120 Don ) a layer (SiGe) of a silicon-germanium alloy on a donor substrate (Si_Waf Don ) ;- form (130 Don ) a first layer of silicon (28Si Don ) on the (SiGe) layer of a silicon-germanium alloy, thus forming a donor (Don) structure; - to form (120 Car ) a second layer of silicon (28Si Car ) on the supporting substrate (Si_Waf Car )- former (130 Car ; 135 Don ) a layer of oxide (28SiO2) on at least one of the first silicon layer (28Si Don ) and the second silicon layer (28Si Car) of a supporting structure (Car) comprising the supporting substrate (Si_Waf Car ) and the second silicon layer (28SiCar); - assemble (150) the donor structure (Don) and the carrier structure (Car), in such a way that the carrier substrate (Si_Waf Car ), the second silicon layer (28Si Car ), the oxide layer (28SiO2), the first silicon layer (28Si Don ), the (SiGe) layer of a silicon-germanium alloy and the donor substrate (Si_Waf Don ) are stacked in this order; - eliminate (170) at least one part (Si_Waf Don_1 ) of the donor substrate attached to the (SiGe) layer of a silicon-germanium alloy (Etch(Si_Waf Don_1 )) ; and- eliminate (180) the (SiGe) layer of a silicon-germanium alloy (Etch(SiGe)), in which the first silicon layer (28Si Don ) and the second silicon layer (28Si Car ) are each made up of at least 99.92% isotope 28 If it's silicon.

2. The process according to claim 1, wherein the oxide layer (28SiO2) is formed by oxidation of at least one of the first silicon layer (28Si Don ) and the second silicon layer (28Si Car ).

3. The process according to claim 1, wherein the oxide layer (28SiO2) is formed by oxidation of the first silicon layer (28Si Don ). The method according to any one of claims 1 to 3, wherein the first silicon layer (28Si Don ) presents, before step (130 Car ) of formation of the oxide layer (28SiO2), a thickness between 20 and 110 nm.

5. The method according to claim 1 or 3, wherein at least one of the first silicon layer (28Si) Don ) and the second silicon layer (28Si Car ), is formed by epitaxial growth.

6. The method according to any one of claims 1 to 5, wherein the (SiGe) layer of a silicon-germanium alloy has an isotope proportion 28 If it's silicon of at least 99.92%.

7. The method according to any one of claims 1 to 6, wherein the (SiGe) layer of a silicon-germanium alloy is formed by epitaxial growth. The method according to any one of claims 1 to 7, wherein the (SiGe) layer of a silicon-germanium alloy has a thickness of between 20 and 100 m, preferably between 30 and 70 nm. The method according to any one of claims 1 to 8, wherein the (SiGe) layer of a silicon-germanium alloy has a germanium content of between 15% and 30%. The method according to any one of claims 1 to 9, wherein the oxide layer (28SiO2) has a thickness between 10 and 50 nm. The method according to any one of claims 1 to 10, wherein the second silicon layer (28Si Car ) has a thickness greater than 200 nm, preferably between 200 nm and 500 nm. The method according to any one of claims 1 to 11, wherein at least one of the donor substrates (Si_Waf Don ) and the supporting substrate (Si_Waf Car ) is made of a single-crystal silicon wafer.

13. The method according to any one of claims 1 to 12, further comprising the steps of: - before the assembly step (150), forming (140 Don ) a weakening plane (Fgrl) in the donor substrate (Si_Waf Don ) by implanting ions of a light species; and- fracture (160) the donor substrate (Si_Waf Don ) at the level of the weakening plane (Frgl), after the assembly step (150) and before the step (170) of removing at least one part (Si_Waf Don_1) of the donor substrate, which remained attached to the (SiGe) layer of a silicon-germanium alloy.

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