Method for manufacturing a substrate comprising an electrical charge trapping layer

Abstract

The invention relates to 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 electrically 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 deposition step of the trapping layer uses a precursor gas mixture. The mixture comprises a silicon gas, an oxygen gas, and a nitrogen gas. The nitrogen gas is ammonia or a set of molecules that form ammonia in the deposition chamber during the deposition step. (See Figure 1A for the abstract.)

Description

Title of the invention: Method for manufacturing a substrate comprising an electrical charge trapping layer. Technical field

[0001] The invention relates to the production 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 production 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, a composite substrate such as a silicon-on-insulator (SOI) or piezoelectric-on-insulator (POI) board is often used. A suitable composite substrate generally comprises a high-resistivity base substrate, for example, greater than or equal to 500 Ω·cm, on which rests a thin useful layer of a single-crystal material, separated from the base substrate by a dielectric layer. Radio frequency components, such as transistors or surface acoustic wave devices, are fabricated in and / or on the useful 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, and therefore induce an electric current, for example, an eddy current. This phenomenon, known as parasitic surface conduction (or PSC), can cause power losses through dissipation, detrimental coupling between radio frequency components, or loss of linearity in one or more radio frequency components.

[0004] To overcome these drawbacks, it is known to add to the composite substrate a layer of electrical charge trapping interposed 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 manufacturing of the radio frequency components, the trapping layer may undergo heat treatments that can induce recrystallization of the trapping layer. If this occurs, it results in a loss of effectiveness of the trapping layer in its ability to trap free charge carriers, and consequently a decrease in its resistivity. Such a heat treatment may, for example, be implemented during a substep of strengthening a bonding interface during the transfer of the useful 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 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, US patent 20210074551 proposes depositing a trapping layer of polycrystalline silicon onto a base substrate of oxidized monocrystalline silicon. More specifically, the trapping layer comprises alternating first sublayers of unintentionally doped polycrystalline silicon and second sublayers of oxygen-doped polycrystalline silicon. The first sublayers have thicknesses between 20 nm and 60 nm. The second sublayers have thicknesses between 1 nm and 2 nm. The average grain size of the second sublayers is smaller than the grain size of the first sublayers. The oxygen-doped second sublayers limit the grain growth of the first sublayers during heat treatments.

[0007] US patent 20170084478 describes a composite substrate comprising a polycrystalline silicon trapping layer with a thickness between 200 nm and 1 pm, containing between 2% and 20% carbon and / or nitrogen. The presence of carbon slows down the recrystallization kinetics of the polycrystalline silicon. However, the patent 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] US patent 20210376075, subsequent to US patent 20170084478, describes a composite substrate comprising a polycrystalline silicon trapping layer containing a nitrogen atom concentration between 10¹⁶ at.cm³ and 10²⁰ at.cm³, i.e., a proportion of nitrogen atoms relative to all atoms in the trapping layer of less than 0.2%. The 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 patent, the nitrogen allows to slow down grain growth during heat treatment. However, the solution proposed in this document is not suitable if the goal is to standardize and / or increase the amount of nitrogen in a fast and efficient industrial process. Description of the invention

[0009] The invention aims to remedy, 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 greater than or equal to 900°C. 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, equal to 1100°C for a duration greater than or equal to several minutes, for example, a duration greater than or equal to 5 minutes.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.

[0010] 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.

[0011] Some preferred but not limiting aspects of this manufacturing process are as follows.

[0012] The gas comprising silicon may consist of silane or dichlorosilane.

[0013] 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 the 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%.

[0015] The trapping layer may 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 step of depositing the trapping layer in the deposition chamber. If necessary, the oxygen-containing gas may be nitrous oxide. Following the trapping layer deposition step, to proceed to 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 may be an LPCVD deposition. If so, the LPCVD deposition may 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 from 10% to 30% oxygen atoms.

[0020] The trapping layer may comprise from 15% to 50% nitrogen atoms, preference 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 supplying a silicon donor substrate which may include a bonding face devoid 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; the molecular bonding may include fracturing the embrittlement plane, and the transfer step may further include smoothing the useful layer after molecular bonding by means of a heat treatment. Brief description of the drawings

[0025] Other aspects, objectives, advantages and features of the invention will become clearer upon reading the following detailed description of preferred embodiments of this, given by way of non-limiting example, and made with reference to the attached drawings on which:

[0026] Figures IA to 1D are schematic cross-sectional views of a manufacturing process for a composite substrate;

[0027] [Fig.2A] is an experimental result giving examples of oxygen and nitrogen concentrations in trapping layers obtained from different deposition conditions;

[0028] [Fig.2B] is an experimental result comparing RF performance levels obtained after heat treatment at 900 °C with the respective trapping layers of the experiment in [Fig.2A];

[0029] Figures 3A to 3C are AFM maps of three trapping layers from among those of the experiment in [Fig.2A].

[0030] DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

[0031] 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 in order to enhance the clarity of 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 limits are inclusive, unless otherwise stated.

[0032] 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 made 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 modified silicon oxide.

[0033] The trapping layer further comprises oxygen atoms and nitrogen atoms in sufficient quantities to restrain the growth of silicon grains of the trapping layer when subjected to heat treatment compared with an unintentionally doped polycrystalline silicon layer undergoing the same heat treatment.

[0034] 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. It has been observed that the addition of oxygen atoms in combination with nitrogen atoms to a polycrystalline silicon layer allows to obtain grains having essentially 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.

[0035] Furthermore, during the deposition of a polycrystalline silicon trapping layer, it has been found that the combination of a gas containing oxygen—such as nitrous oxide (N2O)—and ammonia (NH3) allows 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 including the trapping layer. In comparison, the amount of nitrogen introduced in the presence of nitrous oxide, without ammonia, is essentially zero, regardless of the nitrous oxide flux. 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.

[0036] The RF performance of a radio frequency component or circuit can be estimated by performing an 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" published by SOITEC, the RF performance of a substrate can be characterized by a second harmonic distortion (HD2) measurement. As explained in more detail in that publication, which is introduced here by reference, 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.Measuring the second harmonic (HD2) of an output signal derived from the input signal allows us to predict the RF performance of the component or radio frequency circuit, particularly its linearity.

[0037] Initially, a method for producing a receiving substrate 1 and a composite substrate 10 will be described in relation to figures IA to 1D.

[0038] In [Fig. 1A], a basic substrate 100 is provided. The basic substrate 100 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 Ω·cm, for example between 1 kΩ·cm and 20 kΩ·cm, or even greater than or equal to 20 kΩ·cm.

[0039] Here and for the remainder of the description, we define a three-dimensional orthogonal direct frame (X, Y, Z), where the X and Y axes form a plane parallel to the upper face of the base substrate 100, where the Z-axis is oriented substantially orthogonally to the top face of the base substrate 100, from the bottom face to the top face. In the following description, the terms "vertical" and "vertically" refer to an orientation substantially parallel to the Z-axis, and the terms "horizontal" 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 substrate 100 along the +Z direction. The term "lateral" refers to an orientation substantially parallel to the Z-axis.

[0040] Optionally, the top surface is prepared, which may involve one or more cleaning and / or polishing and / or oxidation substeps. A trapping layer 110 of polycrystalline silicon is then deposited in a deposition chamber. This can be a low-pressure chemical vapor deposition (LPCVD) 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 example of a manufacturing process. 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.

[0041] The gas containing silicon atoms may be silane (SiH4) and / or dichlorosilane (SiH2Cl2, or DCS) and / or trichlorosilane (HCl3Si) and / or disilane (Si2H6) and / or trisilane (Si3H8). In the particular example described here, the gas containing silicon atoms is silane.

[0042] 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, preferably between 0.2 Torr and 0.5 Torr. 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 surface preparation polishing substep for direct bonding.

[0043] 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%.

[0044] Figure 1B is an optional step for depositing an insulating layer 120. The insulating layer 120 can be a dielectric layer, for example, of silicon nitride (SiNx) or silicon oxide (SiOx). The insulating layer 120 has, for example, a thickness measured parallel to the Z-axis of between 10 nm and 10 pm, for example, between 50 nm and 4 pm.

[0045] Advantageously, the insulating layer 120 is, as shown here, 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 and 120 themselves, are thus free of contaminating particles that may 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.

[0046] Figures IC 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 [Fig. 1B] is not performed. Alternatively, as shown here, the step in [Fig. 1B] is performed and the useful layer 210 is transferred onto the trapping layer 110 so as to be in contact with the insulating layer 120.

[0047] In [Fig. IC], a donor substrate 200 is provided, comprising a bonding face and the useful layer. The useful layer 210 is delimited in depth, on a 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 [Fig. IC], so that the bonding face is free of silicon oxide.

[0048] Alternatively, the useful layer 210 may be a dummy portion of the donor substrate 200 intended to be a remaining portion of the donor substrate 200 after thinning of the donor substrate 200 from a face of the donor substrate 200 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 being selectively etched with respect to the useful layer 210.

[0049] The useful layer 210 extends parallel to the bonding face, preferably over a substantial portion of the donor substrate 200. The useful layer 210 extends inward from the protective layer, if present, or from the bonding face otherwise. The useful 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.

[0050] The donor substrate 200 is assembled 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 brought into contact. They may also include bonding by atomic diffusion (or ADB, for "Atomic Diffusion Bonding"). in English), or even a surface activated bonding (or SAB, for "Surface Activated Bonding" in English).

[0051] Preferably, when the insulating layer 120 is present and the useful layer 210 is made of silicon, the bonding face is free of silicon oxide.

[0052] In [Fig. 1D], a composite substrate 10 is obtained, comprising the trapping layer 110. The donor substrate 200 is fractured at the level of the weakening plane 205 so as to separate the useful layer 210 from a sacrificial portion of the donor substrate 200. The fracture is conventionally initiated by an energy input in the form of heat treatment and / or mechanical action. Thus, the useful layer 210 is transferred onto the base substrate 100 and onto the trapping layer 110.

[0053] After separation of the useful layer 210, a finishing step comprising one or more of the prior art finishing treatments can 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 closing, a bonding interface resulting from the 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.

[0054] With reference to Figures 2A, 2B, 3A, 3B, and 3C, results of experiments obtained by a process as described in relation to [Fig. 1A] and possibly 1B, implementing different LPCVD deposition conditions of the trapping layer 110, will now be described. For these experiments, a flow of each precursor gas i constituting the precursor gas mixture is introduced into the LPCVD deposition chamber at an absolute flow rate d, 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 dr>i, equal to the absolute flow rate d of precursor gas i divided by the sum of the absolute flow rates of all the precursor gases.

[0055] For the experiments in Figures 2A, 2B, 3A, 3B, and 3C, the precursor gas mixture consists of silane (SiH4), nitrous oxide (N2O), and ammonia (NH3). Thus, the relative flow rates of silane, nitrous oxide, and ammonia are given by the following respective formulas:

[0056] . rfSiHA d$itf

[0057] , _ rJf2O dsiH+dyp+dyH,

[0058] >____

[0059] For these experiments, the deposition temperature is between 600 and 750 °C. The pressure is maintained in a range between 0.1 and 0.5 Torr. The trapping layers 110 have thicknesses of approximately 200 nm + / - 50 nm. The base substrate 100 has a resistivity of approximately 8000 Ohm.cm.

[0060] In [Fig. 2A], oxygen and nitrogen concentrations are given as atomic percentages in trapping layers 110, as a function of different relative flow rates of nitrous oxide (abscissa axis) and different relative flow rates of ammonia (ordinate 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 second for nitrogen. Thus, for example, experimental point P6(10%, 20%) corresponds to a trapping layer 110 comprising an oxygen atom concentration of 10% relative to the total number of atoms in the trapping layer 110, and a nitrogen atom concentration of 20% relative to 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 an atomic concentration of 20% implies that the atomic concentration is at least between 18% and 22%.

[0061] Surprisingly, by comparing experimental points P2 to P5, it was found 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 allows for effective nitrogen introduction into the trapping layer 110 (experimental point P1).

[0062] In [Fig. 2B], power measurements of the second harmonic (HD2, y-axis in dBm) obtained with trapping layers 110 corresponding to experimental points P1 to P8 of [Fig. 2A] are shown. 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 substep of strengthening a bonding interface during the transfer of the useful layer 210. The experimental heat treatment is carried out at a temperature of 900 °C for a duration of 120 minutes.

[0063] These measurement results demonstrate that the combination of nitrogen and oxygen atoms in the trapping layer 110 (experimental points P6 to P8) makes it possible to achieve 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 (dr>N2O) between 5% and 20%, in combination with a relative flow rate of ammonia (dr>NH3) between 3% and 20%, allows for the introduction, during deposition, of 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 results in a reduction of the second harmonic power 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 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.

[0064] Advantageously, the relative flow rate of nitrous oxide drN2O is between 8% and 17%. Advantageously, the relative flow rate of ammonia drNH3 is between 3% and 10%. It is preferable to combine these two advantageous ranges. In [Fig. 2A], the combination of these two advantageous ranges, enclosing experimental points P6 and P7, is represented by a rectangle of dashed lines.

[0065] Morphological results help explain the RF performance obtained. Some of these results are shown in Table 1. The first column shows the number of the experimental point analyzed from among those in [Fig. 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 give the roughness measurement results of the trapping layer 110 before the experimental heat treatment, obtained using an atomic force microscope on a square area of ​​the trapping layer 110, 1 pm on each side. 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 at . atomic force microscope of the trapping layers corresponding respectively to experimental points PI, P4 and P7, during the roughness measurements of the third and fourth columns of Table 1. Experimental Point Grain Size (nm) Roughness (nm RMS) Roughness (nm PV) PI 50 5.44 44.6 P4 5 to 10 5.05 38.1 P7 2 2.28 20.7 Table 1

[0066] After the deposition of the trapping layer 110, the surface roughness of the trapping layer 110 containing oxygen and nitrogen atoms (experimental point P7) is thus lower than the surface roughness of the trapping layers lacking oxygen (experimental point PI) or nitrogen (experimental point P4). This indicates that the incorporation of a combination of oxygen and nitrogen atoms reduces the grain size. This is confirmed by the grain size measurements of the trapping layers 110 after the experimental heat treatment (first column).

[0067] To estimate the grain size of a trapping layer 110, it is possible, for example, to 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), to calculate the average grain area by dividing the area of ​​the image or map by the total number of grains, and to calculate the diameter of a circle having the same area as the average grain area. It is possible to measure the grain size more precisely by X-ray diffractometry (or XRD).

[0068] 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, it is within the grasp of those skilled in the art to adapt the relative flow rates of the precursor gases to obtain a nitrogen concentration and an oxygen concentration greater than or equal to the respective effective concentrations of nitrogen and oxygen.

[0069] Thus, for example, if the precursor gas mixture consists of disilane (Si2H6), nitrous oxide (N2O) and ammonia (NH3), in order to maintain the same proportionality ratio between the species, it is necessary to halve 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: • a step of supplying a base substrate (100), • a step of depositing an electrical charge trapping layer (110) in a deposition chamber in contact with the base substrate (100), the trapping layer comprising: • 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 employing a precursor gas mixture, the mixture comprising a silicon gas, an oxygen gas, and a nitrogen gas, characterized in that the nitrogen gas is ammonia or a set of molecules forming ammonia in the deposition chamber during the step of deposit.

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-comprising gas is nitrous oxide, the nitrogen-comprising gas is ammonia, and wherein the nitrous oxide and ammonia are introduced into the deposition chamber at flow rates relative to the total flow rate of the 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 silicon oxide layer (120) directly after the step of depositing the trapping layer (110) in the deposition chamber.

7. A manufacturing method 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. A manufacturing method according to claim 8, wherein the LPCVD deposition is carried out at a temperature between 600 °C and 800 °C

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

14. A manufacturing method according to claim 13, wherein the receiving substrate (1) is obtained by a manufacturing method of a receiving substrate (1) according to claims 6 or 7, and wherein the transfer step comprises: • supplying a silicon donor substrate (200) 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, • a molecular bonding of the donor substrate (200) on the recipient substrate (1) by bringing the bonding face and the silicon oxide layer (120) into contact, followed by a 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 includes a fracture of the weakening plane (205), and the transfer step further includes smoothing the useful layer (210) after the molecular bonding implementing a heat treatment.

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