Method for manufacturing a silicon layer donor structure for quantum applications

Abstract

Method (100) of manufacturing a donor structure (DonStruct) bearing a silicon layer (28SiSLay) of at least 99.92% silicon 28Si, comprising the steps of: forming (130SLay) the silicon layer (28SiSLay) on a first substrate (Si_WafSLay), thus forming a seed structure (SLay); forming (120Car) a silicon nitride layer (SiN) on a second substrate (Si_WafCar), thus forming a carrier structure (Car); forming (140SLay) a silicon oxide layer (28SiO2) on the silicon layer (28SiSLay) and / or the silicon nitride layer (SiN); assembling (160) the seed (SLay) and carrier (Car) structures, the second substrate (Si_WafCar), the silicon nitride layer, the oxide layer, the silicon layer and the first substrate being stacked in that order; and expose (170, 180) a surface of the silicon layer (28SiSLay) located opposite the second substrate (Si_WafCar), thus forming the donor structure (DonStruct).Figure to be published with the abbreviation: Fig. 3.

Description

Title of the invention: Method for manufacturing a silicon layer donor structure for quantum applications. TECHNICAL FIELD OF THE INVENTION

[0001] The invention relates to a method for forming a structure comprising a 28Si silicon layer for transferring a part of this layer to form a basic substrate for the manufacture of electronic devices whose operating principle is based on the manipulation of quantum objects, in particular qubits. TECHNOLOGICAL BACKGROUND

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

[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: 28Si, 29Si, and 30Si, 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 29Si isotopes of silicon, whose nuclear magnetic moment is not zero. It is therefore preferable to eliminate as much of the 29Si proportion as possible in the silicon used as the basis for qubit manipulation devices. The 30Si isotope should also be eliminated: although the 30Si isotope does not possess spin, it causes variations in the bond lengths between atoms and therefore in the local environment of the qubits. The homogeneity of the local environment should be maximized by minimizing the presence of the 30Si isotope so that the qubits have characteristics as similar as possible to each other.

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

[0007] However, SOI (Silicon On Insulator) substrates with a quantum-quality thin layer of the silicon isotope 28Si are not commercially available. Here, "quantum quality" refers to 28Si layers sufficiently pure to maintain electron spin coherence for durations long enough to perform qubit operations, with a 28Si purity greater than 99.92%.

[0008] There is thus a need for silicon wafers suitable for use as a substrate for the manufacture of devices for manipulating electron spin qubits, capable of maintaining the isotopic purity of 28Si layers and allowing 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 comprising a thin 28Si layer on a support, with an electrically insulating layer interposed between the 28Si layer and the support. It is advantageous for the thin layer and the electrically insulating layer (the buried "BOX" mentioned above) to be sufficiently thin to ensure good coupling with a back gate, which provides additional leverage for manipulating the location of a qubit and for forming FD-SOI (or Fully Depleted SOI) technology transistors with back-bias capability.

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

[0011] A method for manufacturing substrates suitable for FD-SOI technology, with a surface layer of isotopically pure 28Si silicon suitable for quantum applications, could be based on a layer transfer technique, which requires the formation of at least one 28Si layer on a donor substrate.This donor substrate can include, as a support, a conventional bulk silicon wafer, that is to say, one made up of different silicon isotopes and containing a proportion of impurities. However, the purity, in general and in the 28Si isotope in particular, of the 28Si layer must be maintained (i) during the manufacturing process of the donor substrate, (ii) during the transfer to a recipient substrate and (iii) during the CMOS process of manufacturing transistors on the recipient substrate.

[0012] Due to the high price and low availability of quantum-quality precursors for 28Si epitaxy, the fabrication of the donor substrate and the use of the produced 28Si thicknesses need to be optimized. Description of the invention

[0013] The applicant's objective is to provide an economical method for manufacturing a donor structure of a pure 28Si silicon isotope layer for devices used in the manipulation of quantum objects, and in particular qubits formed from electron spins.

[0014] To achieve this goal, one aspect of the invention is a method for manufacturing a donor structure capable of providing a silicon layer consisting of at least 99.92% of the 28Si isotope of silicon, the method comprising the steps of: forming the silicon layer on a first substrate, thus forming a seed structure; forming a silicon nitride layer on a second substrate, thus forming a carrier structure; forming a silicon oxide layer on at least one of the silicon layer and the silicon nitride layer; assembling the seed structure and the carrier structure, in such a way that the second substrate, the silicon nitride layer, the oxide layer, the silicon layer, and the first substrate are stacked in that order; and exposing a surface of the silicon layer located opposite the second substrate, thus forming the donor structure.

[0015] A first advantage of the process is that it can be implemented using methods known and common in the semiconductor industry and put into operation serving the manufacturing of quantum devices, which accelerates the technological maturity of the manufacturing process undertaken and reduces the necessary investments in time and equipment.

[0016] A second advantage of this process is that it allows obtaining a donor structure of a 28Si silicon isotope layer supported by a conventional substrate, without contamination due to the diffusion of impurities and 29Si and 30Si isotopes present in this conventional substrate during manufacturing.

[0017] A third advantage is that this process allows obtaining a donor structure suitable for refining operations, possibly including thickening of the 28Si layer under conditions that are advantageous in terms of efficiency in the use of manufacturing machines and precursor gases for 28Si compared to the initial fabrication of such a layer. Indeed, during its initial formation, the 28Si layer is formed on layers that can transmit impurities and the 29Si and 30Si isotopes of silicon to it. The layer is therefore formed at a relatively low temperature to limit its contamination by diffusion of impurities and isotopes, and is thermally activated.Once transferred onto a substrate from which it is isolated by a layer of silicon nitride (SiN), it can be thickened by higher temperature processes allowing faster growth, which allows for cost savings (i) in the use of precursor gases with a high content of silicon 28Si isotope, (ii) in the time of use of epitaxial frames used for the growth of silicon layers essentially composed of the silicon 28Si isotope, and (iii) an option which consists of growing a thin layer of thermal oxide, chemical oxide or a chemically deposited oxide after the silicon nitride deposition.

[0018] According to additional non-limiting features of the process according to the invention, considered individually or in any technically feasible combination: - the process may include a step of thickening the exposed silicon layer; - the silicon layer formation step and the silicon layer thickening step can each be carried out by epitaxial growth at a first temperature and a second temperature, respectively, the second temperature being higher than the first temperature; - the process may further include, prior to the step of forming the silicon layer on the first substrate, a step of forming a layer of a silicon-germanium alloy on the first substrate, so that the layer of a silicon-germanium alloy is interposed between the first substrate and the silicon layer, and in which the step of releasing the silicon layer may include the steps of: removing at least a part of the first substrate attached to the layer of a silicon-germanium alloy; and removing the layer of a silicon-germanium alloy, by means of a selective chemical or physico-chemical attack, separate from the step of removing at least a part of the first substrate, so as to release the silicon layer; - the layer of a silicon-germanium alloy can have a proportion of 28Si silicon isotope of at least 99.92%; - the oxide layer can be formed by oxidation of the silicon layer; - the silicon layer can have, before the oxide layer formation step, a thickness of between 20 and 110 nm;

[0019] - the process may further include the steps of: before the assembly step, form a weakening plane in the first substrate by implanting ions of a light species; and fracture the first substrate at the level of the weakening plane, after the assembly step and before the step of removing at least part of the first substrate, which remains attached to the layer of a silicon-germanium alloy.

[0020] The invention extends to a method for manufacturing a structure comprising a load-bearing substrate supporting a silicon layer consisting of at least 99.92% of the 28Si isotope of silicon, the method comprising the steps of: providing a donor structure having a structure as defined by the method for manufacturing a donor structure; providing a device structure comprising a third substrate; forming another oxide layer on at least one of the silicon layer and on one face of the device structure; forming another embrittlement plane in the silicon layer by implanting ions of a light species; assembling the donor structure and the device structure, such that the third substrate, the silicon nitride layer, the other oxide layer, the silicon layer, and the first substrate are stacked in that order;fracture the silicon layer at the other weakening plane, after the assembly step, so as to obtain a support structure with the silicon layer on the surface.

[0021] According to additional non-limiting features of the process according to the invention, considered individually or in any technically feasible combination: - After the silicon layer fracturing step, a portion of the silicon layer remaining attached to the donor structure can be refreshed so that the donor structure can be reused in the implementation of the process manufacturing a structure comprising a load-bearing substrate supporting a silicon layer consisting of at least 99.92% of the 28Si isotope of silicon; - the refreshing step may include a chemical-mechanical polishing step only or a chemical-mechanical polishing and thickening step of the silicon layer;

[0022] - the silicon layer formation step and the thickening step the portion of the silicon layer can each be produced by epitaxial growth at a first temperature and a second temperature, respectively, the second temperature being higher than the first temperature;

[0023] - before the step of forming the other oxide layer, the face of the structure of The device can be coated with a layer of silicon nitride.

[0024] A first advantage of this process is that it allows the fabrication of a structure that can serve as a support for a quantum object manipulation device exhibiting high stability.

[0025] A second advantage is that it allows the reuse and refreshing of the donor structure

[0026] The invention extends to a structure for the formation of a device suitable for quantum applications, comprising: a substrate; a silicon nitride layer on the substrate; a silicon oxide layer on the silicon nitride layer; and a silicon layer consisting of at least 99.92% of the 28Si isotope of silicon on the silicon oxide layer.

[0027] According to additional, non-limiting features of the structure according to the invention, considered individually or in any technically feasible combination: - the structure may further comprise an oxide layer interposed between the silicon nitride layer and the silicon oxide layer; and - the silicon oxide layer can have a 28Si silicon isotope purity of at least 99.92%, for example between 99.92% and 99.995%. BRIEF DESCRIPTION OF THE FIGURES

[0028] 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:

[0029] [Fig. 1] The [Fig. 1] illustrates a manufacturing process according to a first embodiment of the invention;

[0030] [Fig.2] The [Fig.2] illustrates the continuation of the process of the [Fig.1];

[0031] [Fig.3] Fig.3 is a diagram summarizing the manufacturing process of Figure 1 and 2;

[0032] [Fig.4] Fig.4 illustrates a manufacturing process according to a second method of putting into work of the invention;

[0033] [Fig.5] The [Fig.5] illustrates a continuation of the process of the [Fig.4];

[0034] [Fig.6] Fig.6 illustrates a continuation of the process of figures 4 and 5;

[0035] [Fig.7] Fig.7 is a diagram summarizing the manufacturing process of Figure 4 at 6. DETAILED DESCRIPTION OF THE INVENTION

[0036] First embodiment

[0037] A first embodiment of the present invention is described by means of figures 1 to 3 and the associated description below.

[0038] Figures 1 and 2 illustrate steps in a manufacturing process for the structure shown in (I) of [Fig. 2]. [Fig. 3] is a diagram showing the steps in the manufacturing process illustrated in Figures 1 and 2.

[0039] Fig. 2 illustrates in (I) a DonStruct structure formed of a SiN barrier layer of silicon nitride, a 28SiO2 oxide layer, and a 28SiSLay seed layer, stacked in that order on a Si_WafCar carrier substrate, each of these elements preferably being in direct contact with the element or elements immediately adjacent to it.

[0040] The Si_WafCar carrier substrate is here made of a conventional single-crystal silicon wafer. The 28SiSLay seed layer is formed of silicon. The 28SiO2 layer is formed of a silicon oxide layer. The 28SiSLay layer and, preferably, the 28SiO2 oxide layer have a silicon 28I isotope purity of at least 99.92%, for example, between 99.92% and 99.995%. Thus, the 28SiSLay layer contains less than 800 ppm of the silicon 29I isotope.

[0041] Such a structure can be used to form quantum devices: thanks to the 28Si purity of the 28SiSLay layer, the spin coherence duration of the electrons in this layer is sufficient to perform operations on qubits associated with these electrons. Integrated into a quantum device, the 28SiSLay surface layer therefore represents a good qubit support.

[0042] Furthermore, the SiN layer and the 28SiO2 oxide layer prevent, or at least limit, the migration of impurities, and in particular of atoms of the silicon isotope 29Si, from the Si_WafCar carrier substrate to the 28SiSL layer. Without a barrier layer, the diffusion of impurities would increase the concentrations of 29Si, 30Si, or dopant elements to levels incompatible with the quality required for the proper functioning of quantum devices, leading to a reduction in coherence times and causing these devices to operate similarly to devices formed within conventional substrates for FD-SOI technology transistors.

[0043] During preliminary steps 110SLay and 110Car of the process 100 for manufacturing the DonStruct structure, a seed substrate Si_WafSLay and a carrier substrate Si_WafCar are provided. In this example, the substrates each consist of a single-crystal silicon wafer, but any other substrate conventionally used in the semiconductor industry could be employed.

[0044] Figure 1 illustrates in (A) the successive formation in this order (1) of an attack-stopping silicon-germanium alloy layer (SiGe) and (2) of the 28SiSLay seed layer on the Si_WafSLay seed substrate, during two successive steps 120SLay and 130SLay. The resulting "seed structure" is designated by SLay in the figures. The 28SiSLay seed layer can be grown, for example by epitaxy, on one face of the Si_WafSLay seed substrate, and then the silicon-germanium alloy layer (SiGe) can be grown on the 28SiSLay seed layer thus formed.

[0045] Fig. 1 illustrates in (B) the formation of the 28SiO2 layer on the Si_WafSLay seed substrate, during a 140sLay step. During the 140SLay step, the 28SiSLay seed layer is superficially oxidized over a certain thickness, to form the 28SiO2 oxide layer.

[0046] Figure 1 illustrates in (C) an implantation of light species such as hydrogen, helium, or a combination of such species in the volume of the Si_WafSLay seed substrate through the 28SiO2, 28SiSLay, and SiGe layers, to form a Frgl embrittlement plane in the Si_WafSLay seed substrate during a step 150SLay. This implantation can correspond to an implantation of hydrogen and / or helium, that is, an ion bombardment of hydrogen and / or helium of the Si_WafSLay seed substrate through the 28SiO2, 28SiSLay, and SiGe layers. In a manner known per se, and as illustrated in (C), 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.

[0047] In the preceding steps, the 28SiSLay and 28SiO2 layers, and optionally the SiGe layer, are formed so that they have silicon isotope 28 (28Si) purities between 99.920% and 99.995%. Thus, the maximum concentrations of the silicon isotope 29 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 28SiSLay seed layer. Such compositions of the 28SiSLay, SiGe, and 28SiO2 layers can be achieved using a conventional growth process. epitaxial, of silane gas of purity corresponding to that of the 28Si layers, as precursor gas of the silicon of the layers.

[0048] Although the fabrication of a SiGe layer with a silicon isotope purity of between 99.920% and 99.995% is optional, such purity prevents contamination of the 28SiSLay layer with 29Si and 30Si isotopes during its formation in the epitaxial framework. It should be noted that in this case, the 28SiSiay layer 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 28SiDon and SiGe layers.

[0049] Since the 28SiO2 oxide layer is obtained by oxidizing the 28Si SLay layer, it exhibits the same 28Si purity characteristics as the latter. 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 SLay and Car structures (see below), after assembly of the two structures (see step 150, illustrated in (E) of [Fig. 1]). Naturally, it is a silicon oxide composed of oxygen and the 28Si isotope of silicon from the 28SiSLay layer. The 28SiCar layer is oxidized only to a certain thickness, strictly less than its thickness and a function of the target thickness for the 28SiO2 layer.

[0050] Furthermore, the 28SiO2 layer can also be formed by HDP-CVD type deposition (HDP-CVD for High Density Plasma CVD), which is carried out at a relatively low temperature compared to thermal oxidation, which advantageously limits the thermal budget imposed on the 28SiCar layer, and therefore limits the diffusion of other Si isotopes in the layer intended to contain the quantum object manipulation devices.

[0051] Before the 130Car oxidation step, the 28SiSLay layer should have a thickness approximately equal to the sum of the target thickness for the 28SiO2 layer and the final target thickness for the 28SiCar layer of the SLay structure. For example, thicknesses between 10 and 100 nm, preferably between 20 and 40 nm, can be used for the 28SiSLay layer immediately after the formation of the 28SiO2 layer, and between 5 and 20 nm for the 28SiO2 oxide layer. Thus, a thickness between 15 and 120 nm can be used for the surface 28SiSLay layer at the time of its deposition, before its oxidation to form the 28SiO2 oxide layer. The SiGe attack arrest layer can have a thickness between 10 and 100 nm, or preferably between 20 and 50 nm, typically 30 nm.

[0052] As a variant of the carrier structure Car, a carrier structure Car' can be formed with an oxide film Ox, such as a silicon oxide film or a silicon nitride oxide film, which can be formed by growth or deposition to a thickness of 1 to 10 nm on the silicon nitride SiN barrier layer, as illustrated in (D1) of [Fig. 1]. The carrier structure Car' can then replace the carrier structure Car in the processes described below. A first advantage of this variant is to facilitate bonding with another oxide layer in a process such as that illustrated below in (E) of [Fig. 1]. A second advantage of this variant is to reduce mechanical damage induced by the compressive stress generated by the silicon nitride SiN layer in any structure incorporating this layer. This effect is achieved by at least partial relaxation or absorption of the stress in the oxide film Ox. [Fig. 1]Figure (D) illustrates the formation of the silicon nitride SiN barrier layer on the Si_WafCar carrier substrate during a step 120Car. The resulting carrier structure is designated by Car in the figures. The SiN barrier layer can be deposited on one face of the Si_WafCar carrier substrate by conventional deposition methods, such as chemical vapor deposition (CVD), possibly plasma-enhanced chemical vapor deposition (PECVD), or atomic layer deposition (ALD). The silicon nitride layer can have a thickness between 10 and 50 nm, preferably between 20 and 30 nm. One option is to grow or deposit a SiO2 film on the Si_WafCar carrier substrate to reduce stress-induced damage.

[0053] Fig. 1 illustrates in (E) the assembly of the SLay and Car structures to obtain a Set assembly, necessary for the formation of the DonStruct structure comprising a stack of SiN, 28SiO2 and 28SiSLay layers. Following the formation of the embrittlement plane Frgl, the seed structure SLay is flipped over and the 28SiO2 layer is brought into intimate contact with the top layer of the carrier structure Car, here the SiN layer, 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 160.

[0054] Fig. 2 illustrates the steps of the process necessary to go from the state illustrated in (E) to the DonStruct structure illustrated in (I).

[0055] Figure 2 illustrates in (F) the fracture of the Si_WafSLay seed substrate at the level of the Frgl embrittlement plane obtained by ion implantation, such that a portion of the Si_WafSLay seed substrate is detached from the Car carrier structure, while a portion of the Si_WafSLay seed substrate and the SiGe and SiSLay layers remain detached. and 28SiO2 remain fixed there, during a fracture-shrinkage step 170. This fracture can be obtained 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.

[0056] An alternative to the formation of a weakening plane and the fracture of the Si_WafSLay substrate at this plane may consist of thinning the donor substrate Si_WafSLay after its assembly, for example by etching, grinding and / or chemical mechanical polishing (CMP). This thinning may be used to completely remove the seed substrate, or only partially, for example to achieve the situation illustrated in (F) of [Fig. 2].

[0057] Figure 2 illustrates in (G) the removal, during a step 180, of the residual layer Si_WafSLay_i of the seed substrate Si_WafSLay_i which remained attached to the support structure Car at the end of step 180. The purpose of this step is to release the SiGe layer from the residual layer Si_WafSLay_i. This step can be implemented by a selective attack of the silicon Etch(Si_WafSLay_i), by wet means by using, for example, a chemical solution or by dry means by using, for example, a plasma, or by a mechanochemical attack of the CMP type (Chemical Mechanical Etching in English terminology). Such an attack makes it possible to eliminate the residual Si_WafSLay_ i layer formed of silicon by using the SiGe layer as an attack stop layer, by means of a process of selective removal of silicon from the Si_WafSLay i layer 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 methods for selectively attacking silicon with respect to a silicon-germanium alloy. The silicon constituting the residual Si_WafSLay4 layer can be selectively attacked with respect to the siGe by using a KOH:H2O solution.

[0058] Figure 2 illustrates in (H) the removal, during step 190, of the SiGe layer, released following step 180. This step can be implemented by wet or dry selective etching of the silicon-germanium alloy Etch(SiGe), stopped by the 28Si layer. The chemical route can employ known chemical solutions, for example, an HF / HNO3 / H2O chemical solution with relative volume proportions of 1 / 100 / 100, to remove the SiGe layer from the 28Si layer, with a selectivity varying from 10:1 to 100:1, depending on the processing and optimization conditions. Another SiGe etching technique is a dry method based on plasma etching of silicon-germanium using fluorine- or chlorine-based chemistries to etch the SiGe film with controlled selectivity by adjusting the plasma conditions and gas mixtures. Such an etch allows the removal of the SiGe layer formed from a silicon-germanium alloy by using the 28SiSLay layer as an etch-stopping layer, employing a process of selectively removing the silicon-germanium alloy from the SiGe layer relative to the silicon forming the 28SiSLay layer. For example, see US patent documents 9,236,265 B2, US 11,875,997 B2, or WO 2006 / 027332 A1, which describe processes for the selective etching of silicon-germanium alloys relative to silicon.

[0059] Regarding the selective etch(Si_WafSLay i) etch, a selective etch of silicon with respect to the silicon-germanium alloy can be considered as an etch exhibiting a silicon etch rate at least twice as high as the silicon-germanium alloy etch rate. Conversely, regarding the selective etch(SiGe) etch, a selective etch of the silicon-germanium alloy with respect to silicon can be considered as an etch exhibiting a silicon-germanium alloy etch rate at least twice as high as the silicon etch rate.

[0060] Step 190 is distinct from step 180: step 180 consists of etching silicon selectively with respect to silicon-germanium, while step 190 consists of etching silicon-germanium selectively with respect to silicon.

[0061] Following step 190, a finishing process can be applied to the 28SiSLay seed layer obtained from the SLay seed structure. This finishing process may consist of one or more mechanical and / or chemical thinning operations on the 28SiSLay seed layer to a desired thickness and / or polishing of its accessible face, so as to improve its flatness and reduce its roughness. The finishing step may be similar to those used in the fabrication of substrates for FD-SOI technology. This finishing step may be designed so that the 28SiSLay layer can serve as a seed layer for the epitaxial growth of silicon.

[0062] Figure 2 illustrates in (G) an optional thickening step 195 of the 28SiSLay layer and the obtaining of a donor structure DonStruct. Step 195 can be implemented by epitaxial growth of a silicon layer on the 28SiSLay seed layer in the same way that the 28SiSLay seed layer was initially formed on the SiGe layer in step 130SLay, to form a silicon 28Si isotope layer having a silicon 28 isotope purity of between 99.920% and 99.995%. The 28SiSLay layer then fulfills the function of a crystal growth seed.

[0063] An important point distinguishes steps 130SLay and 195: in step 130SLay, the 28Si Lay layer is formed on the SiGe layer of silicon-germanium alloy, which separates it from the Si_WafSLay seed substrate made of conventional silicon, relatively rich in impurities and in the 29Si and 30Si isotopes of silicon. In this configuration, an excessive temperature rise would cause the impurities and the 29Si and 30Si isotopes of silicon to diffuse into the 28Si Lay layer through the SiGe layer. In contrast, during step 195, the 28SiSLay seed layer, which is grown by an additional deposition of the silicon 28Si isotope, is separated from its carrier substrate Si_Waf Car by the silicon oxide layer 28SiO2 and especially by the silicon nitride layer SiN, which is an effective barrier to the diffusion of impurities and the 29Si and 30Si isotopes contained in this carrier substrate.

[0064] This distinction allows higher epitaxial growth temperatures to be used for step 195 than for step 130SLay, and therefore to obtain better yields, with advantages regarding associated costs such as the quantities of precursor gases to be used or the time required for growth and therefore the duration of use of the epitaxial growth frames.

[0065] The silicon epitaxial growth of step 130SLay can be implemented at a first temperature between 350 and 500°C, and the silicon epitaxial growth of step 195 at a second temperature between 600 and 1000°C and higher than the first temperature.

[0066] The thicknesses of the 28SiO2 and SiN layers can be chosen to ensure an adequate level of barrier effect to prevent contamination of the germ layer 28SiSLay by, in particular, 29Si and 30Si from the Si_WafCar support.

[0067] Another advantage of the DonStruct donor structure, stemming from the barrier quality of the SiGe layer, is that the donor structure can be used repeatedly to transfer a portion of the thickness of its 28SiSLay layer to another substrate, while maintaining a purity of the 28SiSLay layer acceptable for quantum applications. This can be the 28SiSLay layer as initially formed on the SiGe layer, or the 28SiSLay layer as thickened following step 195.

[0068] The second embodiment, described below, illustrates a process capable of employing the donor structure DonStruct, obtained for example by means of process 100, to form a suitable support for an electronic device adapted to quantum applications.

[0069] Second embodiment

[0070] The second embodiment of the present invention is described by means of figures 4 to 7 and the associated description below.

[0071] Figures 4 and 5 illustrate steps in a process 200 for manufacturing the structure shown in [Fig. 5]. [Fig. 6] illustrates a reconditioning of the donor structure for reuse in the process steps shown in Figures 4 and 5. [Fig. 7] is a diagram showing the steps in the manufacturing process shown in Figures 4 to 6.

[0072] Figure 5 illustrates a DevStruct that forms a support for the formation of an electronic device suitable for quantum applications. This structure comprises a Si_WafDev device support on which are stacked, in this order, a silicon nitride SiN layer, a silicon oxide 28SiO2 layer, and a silicon 28SiSLayi layer, each of these elements preferably being in direct contact with the element or elements immediately adjacent to it. The Si_WafDev device support is here made of a conventional single-crystal silicon wafer. The 28SiSLayi layer, and preferably the 28SiO2 layer, each have a silicon 28Si isotope purity of at least 99.92%, for example, between 99.92% and 99.995%. This structure is obtained as illustrated in Figures 4 and 5.

[0073] During preliminary steps 210Don and 210Dev of the process 200 of manufacturing the DevStruct structure, a DonStruct structure as defined in the first embodiment and the Si_WafDev device support are provided, respectively.

[0074] Fig. 4 illustrates in (B) the application of steps 220Don and 230Don to the DonStruct structure illustrated in (A).

[0075] Step 220Don, which may be similar to step 140SLay, consists of forming a silicon oxide layer 28SiO2 on the 28SiSLay layer. As with step 140SLay, the oxidation of the 28SiSLay layer makes it possible to obtain a silicon oxide layer of 28Si isotope purity of silicon of the same level as that of the 28SiSLay layer.

[0076] Step 230Don consists of the formation of a Frgl embrittlement layer in the 28SiSLay layer by means of an implantation lmp of light species such as hydrogen, helium, or a combination of such species, in the volume of the 28SiSLay layer through the 28SiO2 layer. This implantation can correspond to an implantation of hydrogen and / or helium, that is, an ion bombardment of hydrogen and / or helium of the 28SiSLay layer. In a manner known per se, and as illustrated in (B), the implanted ions form a Frgl embrittlement plane.The type and dose of the implanted species and the implantation energy are chosen according to the type and thickness of the layers traversed, and the desired implantation depth.

[0077] Figure 4 illustrates in (C) the formation of a silicon nitride SiN layer on the Si_WafDev device support, during a 220Dev step - This layer can be formed in the same way and according to the same parameters as the silicon nitride barrier layer formed during the 120Car step.

[0078] Figure 4 illustrates in (D) the assembly of the DonStruct and DevStruct structures for to obtain an Ass assembly, necessary for the formation of the finalized DonStruct structure, the Ass assembly comprising a stack of SiN, 28SiO2 and 28SiSLay- layers

[0079] More specifically, following the formation of the embrittlement plane Frgl of step 230Don, the DonStruct structure is flipped and the 28SiO2 layer formed on the 28SiSLay layer is brought into intimate contact with the upper layer of the DevStruct structure, here the SiN layer, 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 240.

[0080] Figure 5 illustrates a 250 fracture stage of the 28SiSLay layer at the level of the Frgl embrittlement plane obtained by ion implantation, such that the donor structure DonStruct is detached from the device structure DevStruct leaving a 28SiSLay part of the 28SiSLay layer attached to it.

[0081] This fracture can be obtained 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.

[0082] At the end of step 250 of fracturing and withdrawal, the two distinct and separate structures DonStruct and DevStruct are found.

[0083] The DevStruct device structure described above is, following step 250, provided with a 28SisLay i silicon layer derived from the 28SiSLay layer and having substantially the same proportion of silicon 28Si isotope and the same quantum properties as the latter. Immediately after the fracturing step, the free surface of the 28SisLay i layer is irregular and rough, and requires the application of a finishing step 260Dev to the 28SisLay i layer. This finishing process may consist of one or more mechanical and / or chemical thinning operations on the 28SiSLay seed layer to a desired thickness and / or polishing of its free face to improve its flatness and reduce its roughness. The finishing step may be similar to those used in the manufacture of substrates for FD-SOI technology and / or the finishing step following step 190.This finishing step can be planned in such a way that the 28SiSLay i layer can serve as a substrate for device formation. quantum, incorporating for example FD-SOI technology transistors. After the 260Dev step, the 28Sis Lay-i layer can have a thickness between 4 nm and 50 nm, preferably between 5 nm and 20 nm. The finishing 260Dev step can be implemented by chemical-mechanical polishing (CMP).

[0084] Following step 250, the donor structure DonStruct is provided with a 28SiSLay-2 silicon layer, which corresponds to the 28SiSLay layer from which the 28SiSLay 1 silicon layer was removed by fracturing at the Frgl embrittlement plane. For reasons similar to those mentioned for the 28SiSLay 1 layer, a finishing treatment can be applied to the 28SiSLay-n layer during a step 260Don, so as to obtain a surface sufficiently flat and smooth for the DonStruct structure to be directly reused in step 210Don of the process 200 (Alt1 alternative) or for the 28SiSLay 1 layer to be used again as a crystal seed for epitaxial silicon growth (Alt2 alternative).

[0085] In the first alternative Altl, the respective thicknesses of the 28SiSLay, 28SiSLay 1 and 28SiSLay 2 layers can be such that it is conceivable to reuse the flattened and smoothed donor structure DonStruct in step 210Don of process 200. This is the case when the remaining thickness of the 28SiSLay 2 layer, illustrated in (B) of [Fig.5], is sufficient to consider the formation of the oxide layer and the embrittlement plane of steps 220Don and 230Don, then the fracturing of step 250, to obtain a new 28SiSLay 1 layer of sufficient thickness to form a quantum device, taking into account the finishing step 260Dev.

[0086] In a second alternative Alt2, if it is estimated that the remaining thickness of the 28SiSLay 2 layer is insufficient to implement the process 200 as described so far, the 28SiSLay 2 layer can be thickened so as to reform a 28SiSLay layer during a step 270Don, and then the donor structure DonStruct can be reused in step 210Don of process 200. In step 270Don, the 28SiSLay 2 layer acts as a crystal seed for epitaxial growth of the 28SiSLay- layer during a process similar to that of step 195 of the first embodiment. In particular, the epitaxial growth for reforming the 28SiSLay- layer can take place at a higher temperature than the initial formation of this layer during step 130SLay-

[0087] A finishing step 280Don similar to step 260Don can be applied to the layer 28SiSLay obtained by thickening the layer 28SiSLay-2, before the implementation of steps 220Don and 230Don.

[0088] This process 200 allows for high efficiency in the resources needed to obtain structures suitable for hosting quantum devices, in terms of gas precursors and usage time of thin film deposition or growth equipment.

[0089] In the processes described above, the so-called "SiN" layers have been presented as being formed of silicon nitride. An alternative would be for one, the other, or both of these layers to comprise a silicon oxynitride layer in addition to the silicon nitride layer. In these cases, the silicon nitride layer is preferably interposed between the silicon oxynitride layer and the substrate concerned, i.e., the carrier substrate Si_WafCar or the device support Si_WafDev. The silicon oxynitride layer may contain nitrogen in a nitrogen / oxygen concentration ratio greater than or equal to 0.01, 0.05, or 0.1.

[0090] 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

Demands

1. A process (100) for manufacturing a donor structure (DonStruct) capable of providing a silicon layer (28SiSLay) consisting of at least 99.92% of the 28Si isotope of silicon, the process comprising the steps of: - forming (130SLay) the silicon layer (28SiSLay) on a first substrate (Si_WafSLay), thus forming a seed structure (SLay); - forming (120Car) a silicon nitride (SiN) layer on a second substrate (Si_WafCar), thus forming a carrier structure (Car); - forming (140SLay) a silicon oxide (28SiO2) layer on at least one of the silicon layer (28SiSLay) and the silicon nitride (SiN) layer; - assemble (160) the seed structure (SLay) and the carrier structure (Car), in such a way that the second substrate (Si_WafCar), the silicon nitride layer (SiN), the oxide layer (28SiO2), the silicon layer (28SiSLay), and the first substrate (Si_WafSLay) are stacked in this order;and - expose (170, 180) a surface of the silicon layer (28SiSLay) located opposite the second substrate (Si_WafCar), thus forming the donor structure (DonStruct).;

2. The method according to claim 1, comprising a step (195, 270Don) of thickening (200) the released silicon layer (28SiSLay).

3. The method according to claim 2, wherein the step (130SLay) of forming the silicon layer (28SiSLay) and the step (270Don) of thickening the portion (28SiLay_2) of the silicon layer are each carried out by epitaxial growth at a first temperature and a second temperature, respectively, the second temperature being higher than the first temperature.

4. The method according to any one of claims 1 to 3, further comprising, prior to the step (130SLay) of forming the silicon layer (28SiSLay) on the first substrate (Si_WafSLay), a step (120SLay) of forming a layer (SiGe) of a silicon-germanium alloy on the first substrate (Si_WafSLay), such that the layer (SiGe) of a silicon-germanium alloy is interposed between the first substrate (Si_WafSLay) and the silicon layer (28SiSLay), and wherein the step (170, 180) of removing the silicon layer (28SiSLay) comprises the steps of: - removing (180) at least a portion (Si_WafSLay_i) of the first substrate attached to the layer (SiGe) of a silicon-germanium alloy; and - removing (190) the layer (SiGe) of a silicon-germanium alloy, by means of a selective chemical or physicochemical etch (Etch(SiGe)), distinct from the step of removing (180) at least a portion (Si_WafSLay_i) of the first substrate, so as to expose the silicon layer (28SiSLay)-

5. The method according to claim 4, wherein the (SiGe) layer of a silicon-germanium alloy has a silicon 28Si isotope proportion of at least 99.92%.

6. The process according to any one of claims 1 to 5, wherein the oxide layer (28SiO2) is formed by oxidation of the silicon layer (28SiSLay)-

7. The method according to any one of claim 6, wherein the silicon layer (28SiDon) has, before the step (140SLay) of formation of the oxide layer (28SiO2), a thickness of between 20 and 110 nm.

8. The method according to any one of claims 1 to 7 in their connection with claim 4, further comprising the steps of: - before the assembly step (150), forming (140Don) a weakening plane (Fgrl) in the first substrate (Si_WafDon) by implanting ions of a light species; and - fracturing (160) the first substrate (Si_WafDon) at the level of the weakening plane (Frgl), after the assembly step (150) and before the step (170) removing at least a part (Si_WafDon_i) of the first substrate, remaining attached to the layer (SiGe) of a silicon-germanium alloy.

9. A method for manufacturing a structure (DevStruct) comprising a carrier substrate (Si_WafCar) supporting a silicon layer (28SiDon) consisting of at least 99.92% of the 28Si isotope of silicon, the method comprising the steps of: - provide (210Don) a donor structure (DonStruct) having a structure as defined by the process of claim 1; - provide (210Car, 220Dev) a device structure (DevStruct) comprising a third substrate (Si_WafDev); - form (220Don) another oxide layer on at least one of the silicon layer (28SiSLay) and one face of the device structure (DevStruct); - form (230Don) another embrittlement plane (Fgrl) in the silicon layer (28SiSLay) for the implantation of ions of a light species; - assemble (240) the donor structure (DonStruct) and the device structure (DevStruct), in such a way that the third substrate (Si_WafDev), the silicon nitride layer (SiN), the other oxide layer (28SiO2), the silicon layer (28SiSLay), and the first substrate (Si_WafSLay) are stacked in this order;- fracture (250) the silicon layer (28SiSLay) at the other embrittlement plane (Frgl), after the assembly step (240), so as to obtain a support structure with the silicon layer (28SiSLay) on the surface.;

10. The process according to claim 9, wherein, after the step (250) of fracturing the silicon layer (28SiSLay), a portion (28Si sLay 2) of the silicon layer (28SiSLay) remaining attached to the donor structure (DonStruct) is refreshed (260Don, 270Don, 280Don) so that the donor structure (DonStruct) is reused in the implementation of the process according to claim 9.

11. The process according to claim 10, the refreshing step (260Don, 270Don, 280Don) comprising a chemical-mechanical polishing step only or a chemical-mechanical polishing and silicon layer thickening step (28SiSLay)-

12. The process according to claim 11, the step (130SLay) of forming the silicon layer (28SiSLay) and the step (270Don) of thickening the portion (28SiLay 2) of the silicon layer being each carried out by epitaxial growth at a first temperature and a second temperature, respectively, the second temperature being higher than the first temperature.

13. The method according to any one of claims 11 to 14, wherein, before step (220Don) of forming the other oxide layer, the face of the device structure (DevStruct) is covered with a layer (SiN) of silicon nitride.

14. Structure (DonStruct, DevStruct) for the formation of a device suitable for quantum applications, comprising: - a substrate (Si_WafCar, Si_WafDev); - a silicon nitride (SiN) layer on the substrate (Si_WafCar); - a silicon oxide (28SiO2) layer on the silicon nitride (SiN) layer; and - a silicon (28SiSLay) layer consisting of at least 99.92% of the 28Si isotope of silicon on the silicon oxide layer.

15. Structure according to claim 14, further comprising an oxide (Ox) layer interposed between the silicon nitride (SiN) layer and the silicon oxide (28SiO2) layer.

16. Donor structure (DonStruct) according to claim 14 or 15, wherein the silicon oxide (28SiO2) layer has a silicon 28Si isotope purity of at least 99.92%, for example between 99.92% and 99.995%.