Method for manufacturing a substrate comprising an electric charge trapping layer

Abstract

The invention relates to a method for manufacturing an acceptor substrate in order to form a composite substrate, the method comprising a step of providing a base substrate, and a step of depositing, in a deposition chamber, an electric charge trapping layer in contact with the base substrate. The trapping layer comprises from 40% to 80% of silicon atoms, from 0.1% to 45% of oxygen atoms, and from 0.2% to 50% of nitrogen atoms. The step of depositing the trapping layer implements a mixture of precursor gases. The mixture comprises a gas comprising silicon, a gas comprising oxygen and a gas comprising nitrogen. The gas comprising nitrogen is ammonia or a set of molecules that form ammonia in the deposition chamber during the deposition step.

Description

Description Title: Process for manufacturing a substrate comprising an electrical charge trapping layer TECHNICAL FIELD [ooi] The invention relates to the fabrication of a receiving substrate comprising an electrical charge trapping layer, intended to receive a thin crystalline layer by a layer transfer technique, to obtain a composite substrate. The composite substrate can be useful for the fabrication of radio frequency (RF) components, i.e., those processing signals with frequencies between 20 kHz and 300 GHz, or even higher. PREVIOUS STATE OF THE ART

[0002] For radio frequency applications, composite substrates such as silicon-on-insulator (SOI) or piezoelectric-on-insulator (POI) boards are often used. A suitable composite substrate typically comprises a high-resistivity base substrate, for example, 500 G·cm or higher, upon which rests a thin, single-crystal active layer separated from the base substrate by a dielectric layer. Radio frequency components, such as transistors or surface acoustic wave (SAW) devices, are fabricated within and / or on top of this active layer.

[0003] However, in such a composite substrate, fixed charges are generally trapped in the dielectric layer. These attract free charge carriers from the base substrate, inducing a region of low resistivity near the interface between the dielectric layer and the base substrate. Thus, during operation, radio frequency components are likely to animate these free charge carriers, thereby inducing an electric current, such as an eddy current. This phenomenon, known as parasitic surface conduction (PSC), can cause power losses through dissipation, detrimental coupling between radio frequency components, or linearity losses in one or more radio frequency components.

[0004] To overcome these drawbacks, it is known to add a layer of electrical charge trapping to the composite substrate, sandwiched between the base substrate and the dielectric layer. The trapping layer is typically a polycrystalline layer. comprising grains, or crystallites, and grain boundaries, which act as traps for free charge carriers. The trapping layer is more resistive and efficient the smaller the grains and the denser the grain boundaries.

[0005] However, during the manufacturing of the composite substrate, or during the fabrication of the radio frequency components, the trapping layer may undergo heat treatments that can induce recrystallization. If this occurs, it results in a loss of effectiveness in the trapping layer's ability to trap free charge carriers, and consequently, a decrease in its resistivity. Such a heat treatment can, for example, be implemented during a substep of strengthening a bonding interface during the transfer of the active layer onto the base substrate. During this strengthening substep, the trapping layer may, for example, be subjected to a temperature between 900 °C and 1250 °C for a duration of between 10 seconds and 2 hours.It is known in particular that a polycrystalline silicon trapping layer in contact with a monocrystalline silicon base substrate is likely to recrystallize from the interface between the trapping layer and the base substrate.

[0006] Several solutions exist in the prior art to mitigate this phenomenon. For example, US20210074551 proposes depositing a trapping layer of polycrystalline silicon onto an oxidized monocrystalline silicon base substrate. More specifically, the trapping layer comprises alternating layers of unintentionally doped polycrystalline silicon and oxygen-doped polycrystalline silicon. The first sublayers have thicknesses between 20 nm and 60 nm, while the second sublayers have thicknesses between 1 nm and 2 nm. The average grain size of the second sublayers is smaller than that of the first sublayers. The oxygen-doped second sublayers limit grain growth in the first sublayers during heat treatments.

[0007] The US20170084478 document describes a composite substrate comprising a polycrystalline silicon trapping layer between 200 nm and 1 pm thick, containing between 2% and 20% carbon and / or nitrogen. The presence of carbon slows the recrystallization kinetics of the polycrystalline silicon. However, the document provides no specific information on the role of nitrogen and does not indicate the nature of the gas that enables its presence in the layer.

[0008] US20210376075, which postdates US20170084478, describes a composite substrate comprising a polycrystalline silicon trapping layer containing a concentration of nitrogen atoms between 10 16 at.crrr 3 and 10 20 at.crrr 3This means that the proportion of nitrogen atoms relative to all atoms in the trapping layer is less than 0.2%. Nitrogen atoms are introduced into the trapping layer by implantation. Several implantation steps are planned to attempt to uniform the nitrogen concentration. According to this document, nitrogen slows grain growth during heat treatment. However, the solution proposed in this document is not suitable if the goal is to uniform and / or increase the amount of nitrogen in a fast and efficient industrial process. DESCRIPTION OF THE INVENTION

[0009] The invention aims to overcome, at least in part, the drawbacks of the prior art, and more particularly to provide a method for manufacturing a receiving substrate for a composite substrate comprising a polycrystalline silicon trapping layer having a high density of traps for free charge carriers, even after undergoing heat treatment, for example at a temperature of 900°C or higher. The trapping layer obtained with the manufacturing method of the invention makes it possible, in particular, to guarantee a high level of RF performance in relation to a thermal budget specification that must be met for the manufacture of radio frequency components, namely 1100°C for a duration of several minutes or more, for example, 5 minutes or more.More specifically, the trapping layer is preserved during manufacturing processes requiring one or more heat treatments that may be used for the production of radio frequency components. [ooio] To this end, the object of the invention is a method for manufacturing a receiving substrate to form a composite substrate, comprising a step of supplying a base substrate, a step of deposition in a deposition chamber of an electrical charge trapping layer in contact with the base substrate. The trapping layer comprises 40% to 80% silicon atoms, 0.1% to 45% oxygen atoms, and 0.2% to 50% nitrogen atoms. The step of deposition of the trapping layer uses a mixture of precursor gases. The mixture comprises a gas containing silicon, a gas containing oxygen, and a gas containing nitrogen. The gas containing nitrogen is ammonia or a set of molecules that form ammonia in the deposition chamber during the deposition step. [ooii] Some preferred but not limiting aspects of this manufacturing process are as follows.

[0012] The gas containing silicon can be made up of silane or dichlorosilane. [ooi3] The oxygen-containing gas may be nitrous oxide. The nitrogen-containing gas may be ammonia. Nitrous oxide and / or ammonia may be introduced into the deposition chamber at flow rates relative to the total flow rate of precursor gases of between 5% and 20% and between 3% and 20%, respectively.

[0014] The relative flow rate of nitrous oxide can be between 8% and 17%. The relative flow rate of ammonia can be between 3% and 10%. [ooi5] The trapping layer can have a thickness of less than 300 nm, or less than 200 nm.

[0016] The process for manufacturing a receiving substrate to form a composite substrate may further include a step of depositing a silicon oxide layer directly after the trapping layer deposition step in the deposition chamber. If necessary, the oxygen-containing gas may be nitrous oxide. Following the trapping layer deposition step, to proceed with the silicon oxide layer deposition step, the flow rate of the silicon-containing gas may be decreased, the flow rate of the nitrogen-containing gas may be stopped, and the flow rate of nitrous oxide may be increased.

[0017] The deposition step can be an LPCVD deposition. If so, the LPCVD deposition can be carried out at a temperature between 600 °C and 800 °C.

[0018] The deposition chamber can be subjected to a pressure between 6.7 Pa and 133 Pa during the deposition stage.

[0019] The trapping layer can comprise 10% to 30% oxygen atoms.

[0020] The trapping layer can comprise 15% to 50% nitrogen atoms, preferably 20% to 40%.

[0021] The invention also relates to a method for manufacturing a composite substrate comprising a step of producing a receiving substrate by a manufacturing process according to any one of the preceding characteristics, and a step of transferring a useful layer onto the trapping layer.

[0022] The transfer step may include the provision of a silicon donor substrate which may include a bonding face free of silicon oxide and the useful layer such that the useful layer extends deep into the donor substrate from the bonding face.

[0023] The transfer step may include molecular bonding of the donor substrate to the recipient substrate by bringing the bonding face and the silicon oxide layer into contact. This contact may be followed by heat treatment at a temperature of 900°C or higher.

[0024] The donor substrate may be provided with a donor substrate embrittlement plane delimiting the useful layer, molecular bonding may include fracturing the embrittlement plane, and the transfer step may further include smoothing the useful layer after molecular bonding by implementing heat treatment. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Other aspects, objects, advantages and features of the invention will become more apparent from the following detailed description of preferred embodiments thereof, given by way of non-limiting example, and made with reference to the accompanying drawings in which: Figures 1A to 1D are schematic cross-sectional views of a process for manufacturing a composite substrate; Figure 2A is an experimental result giving examples of oxygen and nitrogen concentrations in trapping layers obtained from different deposition conditions; Figure 2B is an experimental result comparing RF performance levels obtained after heat treatment at 900 °C with the respective trapping layers from the experiment in Figure 2A; Figures 3A to 3C are AFM maps of three trapping layers from those in the experiment in Figure 2A. DETAILED DESCRIPTION OF SPECIFIC METHODS OF IMPLEMENTATION

[0026] In the figures and throughout the description, the same reference numerals represent identical or similar elements. Furthermore, the various elements are not drawn to scale to ensure clarity in the figures. Moreover, the different embodiments and variants are not mutually exclusive and may be combined. Unless otherwise indicated, the terms "approximately," "about," and "in the order of" mean within 10%, and preferably within 5%. Furthermore, The terms "between ... and ..." and equivalents mean that the boundaries are included, unless otherwise stated.

[0027] The invention relates to a method for manufacturing a receiving substrate. The receiving substrate may be part of a composite substrate used for manufacturing radio frequency components. The receiving substrate comprises a base substrate and a trapping layer of polycrystalline silicon in physical contact with the base substrate. The base substrate may be made of silicon; optionally, it may include a thin layer of silicon oxide in contact with the trapping layer. The thin layer of silicon oxide may be native, deposited, or thermally bonded.

[0028] The trapping layer further comprises oxygen atoms and nitrogen atoms in sufficient quantities to restrain the growth of silicon grains in the trapping layer when subjected to heat treatment compared with an unintentionally doped polycrystalline silicon layer undergoing the same heat treatment.

[0029] In the absence of oxygen, a deposited polycrystalline silicon layer, possibly containing nitrogen, has a columnar grain structure in which the grains generally elongate predominantly in one direction of layer growth. However, it has been observed that adding oxygen atoms in combination with nitrogen atoms to a polycrystalline silicon layer results in grains with virtually identical dimensions in all spatial directions, typically within 20%. This increases the density of electrical charge traps and improves the layer's stability during heat treatment.

[0030] Furthermore, during the deposition of a trapping layer on polycrystalline silicon, it was found that combining a gas containing oxygen—such as nitrous oxide (N₂O)—with ammonia (NH₃) allows for the introduction of sufficient oxygen and nitrogen atoms into the trapping layer to improve the RF performance of radio frequency components fabricated in and / or on a composite substrate incorporating the trapping layer. In comparison, the amount of nitrogen introduced in the presence of nitrous oxide, without ammonia, is virtually zero, regardless of the nitrous oxide flux.

[0031] Preferably, the amount of nitrogen introduced into the trapping layer is strictly less than a concentration above which a dielectric silicon nitride forms, which can be verified experimentally. The trapping layer has a sufficient silicon concentration, greater than or equal to 40%, to form an effective quantity of silicon crystallites capable of trapping electrical charges. It However, it may locally contain regions of silicon nitride or silicon oxide, generally amorphous. When the trapping layer contains less than 45% oxygen and less than 50% nitrogen, these potential regions do not significantly impact the trapping of electrical charges. When present, they are generally nanometric in size.

[0032] The RF performance of a radio frequency component or circuit can be estimated by performing RF characterization of the composite substrate on and / or in which the component or circuit is intended to be formed. As documented in the January 2015 publication "White paper - RF SOI Characterisation" by SOITEC, the RF performance of a substrate can be characterized by measuring the second harmonic distortion (HD2). As explained in more detail in that publication, which is referenced here, a coplanar waveguide is formed on an electrically insulating layer of a receiving substrate intended to receive a useful layer to obtain the composite substrate. A 900 MHz input signal with a power of -15 dBm is applied to the coplanar waveguide.A measurement of the second harmonic (HD2) of an output signal from the input signal allows one to predict the RF performance of the component or radio frequency circuit, in particular its linearity.

[0033] Initially, a process for producing a receiving substrate 1 and a composite substrate 10 will be described in relation to figures 1A to 1D.

[0034] Figure 1A shows a basic substrate 100. This substrate has a top face and a bottom face opposite the top face, substantially parallel to the top face. The basic substrate 100 can be a silicon wafer, for example, with a diameter of 150 mm, 200 mm, or 300 mm. If applicable, the basic substrate 100 preferably has a resistivity greater than or equal to 500 G·cm, for example, between 1 kΩ·cm and 20 kΩ·cm, or even greater than or equal to 20 kΩ·cm.

[0035] Hereinafter, and for the remainder of this description, we define a three-dimensional orthogonal (X, Y, Z) direct coordinate system, where the X and Y axes form a plane parallel to the upper face of the base 100 substrate, and where the Z axis is oriented substantially orthogonally to the upper face of the base 100 substrate, from the lower face to the upper face. In the following description, the terms "vertical" and "vertically" refer to an orientation substantially parallel to the Z axis, and the terms "horizontally" and "horizontally" refer to an orientation substantially parallel to the (X, Y) plane. Furthermore, the terms "lower" and "upper" refer to an increasing positioning as one moves away from the base 100 substrate along the +Z direction. The term "lateral" refers to an orientation substantially parallel to the Z axis.

[0036] Optionally, the top surface may undergo surface preparation, which could involve one or more cleaning, polishing, and / or oxidation substeps. A polycrystalline silicon trapping layer 110 is then deposited in a deposition chamber. This can be a low-pressure chemical vapor deposition (LPCVD) process in an LPCVD deposition chamber. For this deposition, a precursor gas mixture is used. The gas mixture comprises a gas containing silicon atoms, a gas containing oxygen atoms, and a gas containing nitrogen. The oxygen-containing gas is advantageously nitrous oxide (N₂O), as is the case in this manufacturing process example. The nitrogen-containing gas is advantageously ammonia (NH₃) or a set of molecules that form ammonia in the deposition chamber during deposition.In this example, the nitrogen-containing gas is ammonia. The gas mixture may not contain any other gases. The deposition chamber may be part of an LPCVD deposition system capable of processing a large number of plates in parallel, for example, 120 plates, in order to reduce production costs.

[0037] The gas containing silicon atoms can be silane (SihL) and / or dichlorosilane (SihLCh, or DCS) and / or trichlorosilane (HChSi) and / or disilane (Si2He) and / or trisilane (SisHs). In the specific example described here, the gas containing silicon atoms is silane.

[0038] The deposition temperature is between 500 °C and 900 °C. When the gas containing silicon atoms is silane, the deposition temperature is preferably between 600 °C and 750 °C, and even more preferably between 650 °C and 700 °C. When the gas containing silicon atoms is dichlorosilane, the deposition temperature is preferably between 700 °C and 800 °C. When the gas containing silicon atoms is disilane or trisilane, the deposition temperature is preferably between 500 °C and 700 °C. During deposition, the pressure in the deposition chamber is between 0.05 Torr and 1 Torr, and preferably between 0.2 Torr and 0.5 Torr.

[0039] The thickness of the trapping layer 110, measured parallel to the Z-axis, is, for example, between 10 nm and 1.5 pm, preferably between 50 nm and 300 nm, for example between 70 nm and 200 nm. A thin trapping layer, for example less than 200 nm, or even less than 100 nm, reduces mechanical stresses and, consequently, deformations of the receiving substrate 1 and / or the composite substrate 10. In industrial applications, a thinner trapping layer 110 is advantageous for reducing manufacturing costs. Its surface roughness is less than that of a trapping layer of the same type. but thicker. In addition, a thinner trapping layer 110 allows for a reduction in the amount of material removed during a possible subsequent polishing step, for example a mechano-chemical polishing substep for surface preparation for direct bonding.

[0040] Preferably, the precursor gases are introduced into the deposition chamber at substantially constant respective flow rates, so that the trapping layer 110 has substantially uniform concentrations of silicon, oxygen and nitrogen atoms, for example each within 2%.

[0041] Figure 1B shows an optional step in the deposition of an insulating layer 120. The insulating layer 120 can be a dielectric layer, for example made of silicon nitride (SiN₂). x ) or silicon dioxide (SiO₂ x ). The insulating layer 120, for example, has a thickness measured parallel to the Z axis of between 10 nm and 10 pm, for example between 50 nm and 4 pm.

[0042] Advantageously, the insulating layer 120, as shown here, is made of silicon dioxide and deposited in the LPCVD deposition chamber directly after the deposition of the trapping layer 110, i.e., without re-exposing the base substrate 100 to air between the deposition of the trapping layer 110 and the deposition of the insulating layer 120. The interface between the trapping layer 110 and the insulating layer 120, and the trapping and insulating layers 110 themselves, are thus free of contaminating particles that could originate from the ambient air. One or more cleaning steps can be avoided. To achieve this objective, it is possible, for example, at the end of the trapping layer deposition step (110), to decrease the flow rate of the gas containing silicon, to interrupt the flow rate of ammonia and to increase the flow rate of nitrous oxide.Thus, it is possible to take advantage of the fact that nitrous oxide, in the absence of ammonia, does not incorporate nitrogen into a polycrystalline silicon deposit to obtain a nitrogen-free silicon oxide insulating layer 120. For example, when the silicon-containing gas is silane or dichlorosilane, the nitrous oxide flow rate can be increased to between 50 and 60 times the flow rate of the silicon-containing gas. Preferably, the insulating layer 120 is deposited at a deposition temperature between 700 °C and 850 °C, or even between 780 °C and 850 °C, in order to increase the deposition rate.

[0043] Figures 1C and 1D schematically represent a step of transferring a useful layer 210 onto the trapping layer 110. The useful layer 210 can be transferred onto the trapping layer 110 so as to be in contact with it, particularly when the step in Figure 1B is not performed. Alternatively, as shown here, the step of figure 1 B is carried out and the useful layer 210 is transferred onto the trapping layer 110 so as to be in contact with the insulating layer 120.

[0044] In Figure 1C, a donor substrate 200 is provided, comprising a bonding face and the useful layer. The useful layer 210 is delimited in depth, on one side opposite the bonding face, by a weakening plane 205 previously introduced into the donor substrate 200, for example, by implanting light atomic species such as hydrogen and / or helium. The implantation can be carried out in one or more substeps through a protective layer, for example, silicon oxide. The protective layer has advantageously been removed before the step in Figure 1C, so that the bonding face is free of silicon oxide.

[0045] Alternatively, the useful layer 210 may be a dummy portion of the donor substrate 200 intended to remain after thinning of the donor substrate 200 from a face opposite the bonding face, involving one or more lapping and / or polishing steps. The useful layer 210 may also be a layer separated from a main portion of the donor substrate 200 by a separating layer suitable for selective etching with respect to the useful layer 210.

[0046] The active layer 210 extends parallel to the bonding face, preferably over a substantial portion of the donor substrate 200. The active layer 210 extends inward from the protective layer, if present, or from the bonding face otherwise. The active layer 210 is, for example, made of a piezoelectric material, a ferroelectric material, or a semiconductor material. Here, it is made of single-crystal silicon.

[0047] The donor substrate 200 is bonded to the base substrate 100 by direct bonding. For this purpose, the bonding face is brought into contact with the insulating layer 120 when present, or with the trapping layer 110 otherwise. Several direct bonding methods known to those skilled in the art are applicable to the invention. These may include molecular bonding, for example, hydrophilic or hydrophobic bonding at room temperature, possibly after plasma or chemical activation of one or more of the faces to be joined. They may also include atomic diffusion bonding (ADB) or surface activated bonding (SAB).

[0048] Preferably, when the insulating layer 120 is present and the useful layer 210 is silicon, the bonding face is free of silicon oxide.

[0049] In Figure 1D, a composite substrate 10 is obtained, comprising the trapping layer 110. The donor substrate 200 is fractured at the weakening plane 205 to separate the useful layer 210 from a sacrificial portion of the donor substrate 200. The fracture is typically initiated by the application of energy in the form of heat treatment and / or mechanical action. The useful layer 210 is thus transferred to the base substrate 100 and to the trapping layer 110.

[0050] After separation of the useful layer 210, a finishing step comprising one or more of the prior art finishing treatments may be applied to the useful layer 210 and / or the trapping layer 110 and / or the insulating layer 120. The finishing step may, for example, include a substep for reinforcing, or even sealing, a bonding interface resulting from direct bonding. The finishing step may also include a substep for thinning the useful layer 210 involving sacrificial oxidation, followed by smoothing the useful layer 210 by heat treatment under a neutral gas, for example, argon.

[0051] In connection with Figures 2A, 2B, 3A, 3B, and 3C, we will now describe the results of experiments obtained using a process as described in connection with Figure 1A and possibly 1B, implementing different LPCVD deposition conditions for the trapping layer 110. For these experiments, a flow rate of each precursor gas i constituting the precursor gas mixture is introduced into the LPCVD deposition chamber at an absolute flow rate dj, generally measured in standard cubic centimeters per minute (sccm). Each precursor gas i is then associated with a flow rate relative to the total flow rate of the precursor gases d r , equal to the absolute flow rate dj of precursor gas i, divided by the sum of the absolute flow rates of all precursor gases.

[0052] For the experiments in Figures 2A, 2B, 3A, 3B, and 3C, the precursor gas mixture consists of silane (SihL), nitrous oxide (N2O), and ammonia (NH3). The relative flow rates of silane, nitrous oxide, and ammonia are given by the following respective formulas: J > d SiH4-r,SiH4j 1 j 1 j aSiH4"T a N2O "T a NH3 ,, _ dNH 3 ar,NH3— aSiH4"T a N2O "T a NH3

[0053] For these experiments, the deposition temperature is between 600 °C and 750 °C. The pressure is maintained in a range between 0.1 and 0.5 Torr. The layers The trapping layers 110 have thicknesses of approximately 200 nm + / -50 nm. The basic substrate 100 has a resistivity approximately equal to 8000 Ohm.cm.

[0054] Figure 2A shows the concentrations of oxygen and nitrogen as atomic percentages in trapping layers 110, as a function of different relative flow rates of nitrous oxide (x-axis) and different relative flow rates of ammonia (y-axis), in the LPCVD deposition chamber. The oxygen and nitrogen concentrations obtained are given in parentheses for different experimental points P1 to P8, first for oxygen, and then for nitrogen. Thus, for example, experimental point P6 (10%, 20%) corresponds to a trapping layer 110 with an oxygen concentration of 10% of the total number of atoms in the trapping layer 110, and a nitrogen concentration of 20% of the total number of atoms in the trapping layer 110.Atomic concentrations are measured here using energy-dispersive X-ray spectroscopy (EDS) coupled with transmission electron microscopy (TEM). The measurement uncertainty of the atomic concentrations given as percentages is between 1 and 2 percentage points. Thus, a measurement result of 20% atomic concentration implies that the atomic concentration is at least between 18% and 22%.

[0055] Surprisingly, a comparison of experimental points P2 to P5 revealed that nitrous oxide does not incorporate nitrogen into the trapping layer 110, regardless of the relative flow rate of nitrous oxide compared to the silane flow rate. In contrast, ammonia effectively introduces nitrogen into the trapping layer 110 (experimental point P1).

[0056] Figure 2B shows power measurements of the second harmonic (HD2, y-axis in dBm) obtained with trapping layers 110 corresponding to experimental points P1 to P8 in Figure 2A. The measurement method is identical to that described in the publication "White paper - RF SOI Characterisation" of January 2015. The HD2 measurements were performed after an experimental heat treatment, representative of a sub-step of strengthening a bonding interface during the transfer of the useful layer 210. The experimental heat treatment was carried out at a temperature of 900 °C for a duration of 120 minutes.

[0057] These measurement results highlight that the combination of nitrogen and oxygen atoms in the trapping layer 110 (experimental points P6 to P8) allows us to reach a second harmonic power strictly lower than the second harmonic powers obtained in the absence of oxygen (point experimental point P1) or in the absence of nitrogen (experimental points P2 to P5). As an example, the power of the second harmonic obtained for point P6 is 151.0 times lower than that obtained for experimental point P1 (a difference of -21.79 dBm) and 4.9 times lower than that obtained for experimental point P3 (a difference of -6.9 dBm). Again, as an example, the power of the second harmonic obtained for point P7 is 113.0 times lower than that obtained for experimental point P1 (a difference of -20.53 dBm) and 3.7 times lower than that obtained for experimental point P3 (a difference of -5.64 dBm). For example, it has been observed that a relative flow rate of nitrous oxide d r ,N2O between 5% and 20%, in combination with a relative ammonia flow rate of rWith an NH3 concentration between 3% and 20%, it is possible to introduce, during deposition, an oxygen concentration and a nitrogen concentration in the trapping layer 110 that are greater than or equal to, respectively, the effective oxygen concentration and the effective nitrogen concentration of the trapping layer 110. This allows for a reduction in the power of the second harmonic compared to the prior art after heat treatment at 900 °C. The effective oxygen concentration is 0.1%, preferably 7%, or even 10%. The effective nitrogen concentration is 0.2%, preferably 20%. It is possible that the oxygen and / or nitrogen atoms are concentrated mainly at the grain boundaries of the trapping layer 110 and that the silicon nanocrystals are essentially devoid of oxygen and / or nitrogen.

[0058] Advantageously, the relative flow rate of nitrous oxide d rN2O is between 8% and 17%. Advantageously, relative ammonia flow rate r NH3 between 3% and 10%. It is preferable to combine these two advantageous ranges. In Figure 2A, the combination of these two advantageous ranges, enclosing the experimental points P6 and P7, is represented by a rectangle of dashed lines.

[0059] Morphological results help explain the RF performance obtained. Some of these results are shown in Table 1. The first column indicates the number of the analyzed experimental point from among those in Figure 2A. The second column gives the average grain size in nm, measured in a plane parallel to the (X, Y) plane, following the experimental heat treatment. The third and fourth columns show the roughness measurements of the trapping layer 110 before the experimental heat treatment, obtained using an atomic force microscope on a 1 µm square area of ​​the trapping layer 110. The third column gives the root mean square (RMS) roughness in nm. The fourth column gives the peak-to-valley (PV) roughness height in nm.Figures 3A, 3B and 3C are maps obtained using an atomic force microscope. trapping layers corresponding respectively to experimental points P1, P4 and P7, during the roughness measurements of the third and fourth columns of Table 1. Table 1

[0060] After the deposition of trapping layer 110, the surface roughness of trapping layer 110 containing oxygen and nitrogen atoms (experimental point P7) is lower than the surface roughness of trapping layers lacking oxygen (experimental point P1) or nitrogen (experimental point P4). This indicates that incorporating a combination of oxygen and nitrogen atoms reduces grain size. This is confirmed by measurements of the grain size of trapping layers 110 after the experimental heat treatment (first column).

[0061] To estimate the grain size of a trapping layer 110, one can, for example, count the number of grains within an electron microscopy image or an AFM map containing a significant number of grains (e.g., 1000 or more), calculate the average grain area by dividing the image or map area by the total number of grains, and calculate the diameter of a circle with the same area as the average grain area. A more precise measurement of grain size is possible using X-ray diffractometer (XRD).

[0062] Specific embodiments have just been described. Various variations and modifications will be apparent to those skilled in the art. For example, it is possible to use precursor gases that allow the incorporation of more than one atom of interest per molecule, chosen from silicon, nitrogen, or oxygen. In this case, those skilled in the art can adjust the relative flow rates of the precursor gases to obtain nitrogen and oxygen concentrations greater than or equal to their respective effective concentrations of nitrogen and oxygen.

[0063] Thus, for example, if the precursor gas mixture consists of disilane (Si2He), nitrous oxide (N2O) and ammonia (NH3), in order to maintain the same ratio Due to the proportionality between the species, it is necessary to divide by two the absolute flow rate of disilane compared to that which would have been chosen for silane, since disilane incorporates twice as many silicon atoms in the trapping layer 110 as silane.

Claims

DEMANDS 1. A method for manufacturing a receiving substrate (1) to form a composite substrate (10), comprising: o a step of supplying a base substrate (100), o a step of depositing in a deposition chamber an electrical charge trapping layer (110) in contact with the base substrate (100), the trapping layer comprising: • 40% to 80% silicon atoms, • from 0.1% to 45% oxygen atoms, and • from 0.2% to 50% nitrogen atoms, the trapping layer deposition step employing a precursor gas mixture, the mixture comprising a gas including silicon, a gas including oxygen and a gas including nitrogen, characterized in that the gas including nitrogen is ammonia or a set of molecules forming ammonia in the deposition chamber during the deposition step.

2. A manufacturing process according to claim 1, wherein the gas comprising silicon consists of silane or dichlorosilane.

3. A manufacturing process according to claim 2, wherein the oxygen-containing gas is nitrous oxide, the nitrogen-containing gas is ammonia, and wherein nitrous oxide and ammonia are introduced into the deposition chamber at flow rates relative to the total flow rate of precursor gases of between 5% and 20% and between 3% and 20%, respectively.

4. A manufacturing process according to claim 3, wherein the relative flow rate of nitrous oxide is between 8% and 17%, and the relative flow rate of ammonia is between 3% and 10%.

5. A manufacturing method according to any one of claims 1 to 4, wherein the trapping layer has a thickness of less than 200 nm.

6. A manufacturing method according to any one of claims 1 to 5, further comprising a step of depositing a layer of silicon oxide (120) directly after the step of depositing the trapping layer (110) in the deposition chamber.

7. A manufacturing process according to claim 6, wherein the oxygen-containing gas is nitrous oxide, and wherein, after the trapping layer deposition step (110), a flow rate of the silicon-containing gas is decreased, a flow rate of the nitrogen-containing gas is stopped, and a flow rate of nitrous oxide is increased to proceed with the silicon oxide layer deposition step.

8. A manufacturing method according to any one of the preceding claims, wherein the deposition step is an LPCVD deposition.

9. Manufacturing process according to claim 8, wherein the LPCVD deposition is carried out at a temperature between 600 °C and 800 °C.

10. Manufacturing method according to claims 8 or 9, wherein the deposition chamber is subjected to a pressure between 6.7 Pa and 133 Pa during the deposition step.

11. A manufacturing process according to any one of the preceding claims, wherein the trapping layer comprises from 10% to 30% oxygen atoms.

12. A manufacturing process according to any one of the preceding claims, wherein the trapping layer comprises from 15% to 50% nitrogen atoms, preferably 20% to 40%.

13. Method for manufacturing a composite substrate (10) comprising: o a step of producing a receiving substrate (1) by a manufacturing process according to any one of claims 1 to 12, o a step of transferring a useful layer (210) onto the trapping layer (110).

14. A manufacturing process according to claim 13, wherein the receiving substrate (1) is obtained by a manufacturing process of a receiving substrate (1) according to claims 6 or 7, and wherein the transfer step comprises: o supplying a donor substrate (200) of silicon comprising a bonding face devoid of silicon oxide and the useful layer (210) such that the useful layer (210) extends deep into the donor substrate (200) from the bonding face, o molecular bonding of the donor substrate (200) to the receiving substrate (1) by bringing the bonding face and the silicon oxide layer (120) into contact, followed by heat treatment at a temperature greater than or equal to 900°C.

15. A manufacturing method according to claim 14, wherein the donor substrate (200) is provided with a weakening plane (205) of the donor substrate (200) delimiting the useful layer (210), the molecular bonding comprises a fracture of the weakening plane (205), and the transfer step also includes a smoothing of the useful layer (210) subsequent to molecular bonding by implementing a heat treatment.

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