Abstract:
The disclosure relates to a process for manufacturing a composite structure, the process comprising the following steps: a) providing a donor substrate and a carrier substrate; b) forming a dielectric layer; c) forming a covering layer; d) forming a weakened zone in the donor substrate; e) joining the carrier substrate and the donor substrate via a contact surface having an outline; f) fracturing the donor substrate via the weakened zone, steps b) and e) being executed so that the outline is inscribed in the outline, and step c) being executed so that the covering layer covers the peripheral surface of the dielectric layer.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a national phase entry under 35 U.S.C. §371 of International Patent Application PCT/FR2014/050666, filed Mar. 21, 2014, designating the United States of America and published as International Patent Publication WO 2014/154978 A1 on Oct. 2, 2014, which claims the benefit under Article 8 of the Patent Cooperation Treaty and under 35 U.S.C. §119(e) to French Patent Application Serial No. 1300738, filed Mar. 29, 2013, the disclosure of each of which is hereby incorporated herein in its entirety by this reference. 
     
    
     TECHNICAL FIELD 
       [0002]    This disclosure relates to a method for manufacturing a composite structure. The disclosure also relates to a composite structure. 
       BACKGROUND 
       [0003]    A method, illustrated in  FIG. 1 , for manufacturing a composite structure comprising, from its rear face to its front face, a supporting substrate  1 , a covering layer  2 , at least one dielectric layer  3  and a useful layer  4 , and known from the prior art (see, for example, the document EP 1780794), comprises the following steps:
       a) providing a donor substrate  5  and the supporting substrate  1 ;   b) forming at least the dielectric layer  3  comprising:
           a first surface in contact with the donor substrate  5 ,   a second surface opposite to the first surface,   a peripheral surface connecting the first and second surfaces together;   
           the dielectric layer  3  has a contour Cz;   c) forming the covering layer  2  arranged so as to cover the second surface of the dielectric layer  3 ;   d) forming a weakened zone  6  in the donor substrate  5  delimiting the useful layer  4  in contact with the first surface of the dielectric layer  3 ;   e) assembling the supporting substrate  1  and the donor substrate  5 , so that the supporting substrate  1  and the covering layer  2  are in contact along a contact surface  7  having a contour Cs;   f) breaking the donor substrate  5  along the weakened zone  6 .       
 
         [0014]    Hereinafter, the assembly formed by the useful layer  4 , the dielectric layer  3  and the covering layer  2  will be designated by the term stack of layers  8 . 
         [0015]    At the end of step f), the stack of layers  8  is transferred onto the supporting substrate  1  in order to form the composite structure. 
         [0016]    As illustrated in  FIG. 2 , the composite structure has a peripheral ring  9 . 
         [0017]    This peripheral ring  9  is situated in a peripheral zone of the supporting substrate  1  and, in which, in the absence of sufficient adhesion between the supporting substrate  1  and the donor substrate  5 , the transfer of the stack of layers  8  does not take place. 
         [0018]    Thus, a step is observed at the limit separating the peripheral ring  9  from the stack of transferred layers  8 . 
         [0019]    Moreover, the flanks of the covering layer  2  and dielectric layer  3  are exposed at the step and, therefore, not protected from any chemical attacks. 
         [0020]    Consequently, the chemical attack may generate particles via delamination of the useful layer  4 . 
         [0021]    When only the dielectric layer  3  or the covering layer  2  is formed, for example, the dielectric layer  3 , this step is also observed. A creep of the useful layer  4  is generally executed so as to cover or encapsulate the dielectric layer  3  at the step. 
         [0022]    However, the applicant has found that, when there is a covering layer  2  and at least one dielectric layer  3 , the step of breaking at the edge of the substrate is atypical.  FIG. 3  thus shows the steps obtained on such a substrate after the breaking step f). 
         [0023]    When there are several intermediate layers present, the breaking step does not lead to a single step but, on the contrary, to several steps. It appears in fact that the break propagates at the periphery of the substrate, not along the weakened zone but at the interface between the dielectric layer  3  and the covering layer  2 . 
         [0024]    The main drawback of this manufacturing method is, therefore, that it leads to an atypical break at the edge of the substrate. 
         [0025]    This is, in particular, the case when the composite structure comprises, from its rear face toward its front face, a silicon substrate, a silicon dioxide layer, a silicon nitride layer, a silicon dioxide layer and a silicon layer. 
         [0026]    Moreover, the presence of several steps makes it impossible for the creep to take place by heat treatment of the useful layer  4  so as to protect the covering layer  2  and the dielectric layer  3  at the step. 
         [0027]    This is because, during heat treatment, dewetting of the useful layer  4  rather than creep is observed. 
         [0028]    One aim of the disclosure is, therefore, to propose a method for manufacturing a composite substrate that makes it possible to execute a step of creep of the useful layer  4  so as to cover the exposed surface of the covering layer  2  and of the dielectric layer  3  at the step. 
       BRIEF SUMMARY 
       [0029]    This disclosure aims to remedy the aforementioned drawbacks and relates to a method for manufacturing a composite structure comprising, from its rear face toward its front face, a supporting substrate, a covering layer, at least one dielectric layer and a useful layer, the method comprising the following steps:
       a) providing a donor substrate and the supporting substrate;   b) forming at least the dielectric layer comprising:
           a first surface in contact with the donor substrate,   a second surface opposite to the first surface,   a peripheral surface connecting the first and second surfaces together;   
           the dielectric layer has a contour;   c) forming the covering layer arranged so as to cover the second surface of the dielectric layer;   d) forming a weakened zone in the donor substrate delimiting the useful layer in contact with the first surface of the dielectric layer;   e) assembling the supporting substrate and the donor substrate, so that the supporting substrate and the covering layer are in contact along a contact surface having a contour;   f) breaking the donor substrate along the weakened zone;   the method being remarkable in that steps b) and e) are performed so that the contour of the dielectric layer fits within the contour of the contact surface, and step c) is executed so that the covering layer covers the peripheral surface of the dielectric layer.       
 
         [0041]    Thus, after the transfer step f), the stack of layers is transferred onto the supporting substrate. 
         [0042]    The stack of transferred layers comprises a central portion and a peripheral portion. 
         [0043]    The central portion of the stack comprises the useful layer, the dielectric layer and the covering layer. 
         [0044]    The peripheral portion comprises only the useful layer and the covering layer. 
         [0045]    It is then observed that a simple step is obtained. The peripheral portion corresponds to the transfer of a stack comprising a single intermediate layer. 
         [0046]    Thus, the fracture step leads to a single step at the peripheral ring. 
         [0047]    Consequently, the composite structure obtained allows creep of a useful layer, by executing a heat treatment, for example, so as to encapsulate the covering layer, in particular, at the single step. 
         [0048]    According to one embodiment, the supporting substrate comprises:
       a top surface onto which the covering layer, the dielectric layer and the useful layer are transferred;   a bottom surface opposite to the top surface;   a peripheral zone connecting the bottom surface and the top surface;       
 
         [0052]    the contour of the contact surface and the peripheral zone of the supporting substrate delimit an essentially annular surface of width L, and steps b) and e) are executed so that the contour of the dielectric layer and the peripheral zone of the supporting substrate delimit an essentially annular surface with a width of between 105% and 150%, preferably between 110% and 140%, even more preferentially between 115% and 130%, of the width L. 
         [0053]    According to one embodiment, the dielectric layer is formed in two steps, b1) and b2):
       b1) deposition of a layer of dielectric material on the donor substrate;   b2) partial removal of the layer of dielectric material so that the residual layer of dielectric material forms the dielectric layer.       
 
         [0056]    According to one embodiment, the dielectric layer comprises silicon nitride, and has a thickness of between 10 nm and 80 nm. 
         [0057]    According to one embodiment, the covering layer comprises silicon dioxide, and has a thickness greater than 80 nm. 
         [0058]    According to one embodiment, the donor substrate comprises at least one of the following materials: silicon, germanium, and silicon germanium alloy. 
         [0059]    According to one embodiment, step f) is followed by a heat treatment step intended to encapsulate the covering layer and the dielectric layer with the useful layer. 
         [0060]    According to one embodiment, the donor substrate comprises an additional layer, the additional layer being in contact with the dielectric layer, the additional layer having the same chemical composition as the covering layer. 
         [0061]    According to one embodiment, the donor substrate comprises silicon, the additional layer comprises silicon dioxide, the dielectric layer comprises silicon nitride and the covering layer comprises silicon dioxide. 
         [0062]    The disclosure also relates to a composite structure comprising, from its rear face to its front face, a supporting substrate, a covering layer, at least one dielectric layer and a useful layer, the dielectric layer having:
       a first surface in contact with the useful layer;   a second surface in contact with the covering layer;   a peripheral surface connecting the first surface and the second surface, the composite structure being remarkable in that the covering layer covers in its entirety the peripheral surface of the dielectric layer, so that the useful layer and the covering layer encapsulate the dielectric layer.       
 
         [0066]    The transferred stack of layers comprises a central portion and a peripheral portion. 
         [0067]    The central portion of the stack comprises the useful layer, the dielectric layer and the covering layer. 
         [0068]    The peripheral portion comprises only the useful layer and the covering layer. 
         [0069]    Thus, a simple step is observed and the peripheral portion corresponds to a stack comprising a single intermediate layer. 
         [0070]    Consequently, the composite structure obtained allows creep of the useful layer, by execution of a heat treatment, for example, so as to encapsulate the covering layer at the single step. 
         [0071]    According to one embodiment, the useful layer comprises at least one of the following materials: silicon, germanium, and silicon germanium alloy. 
         [0072]    According to one embodiment, the useful layer comprises a monocrystalline material. 
         [0073]    According to one embodiment, the covering layer comprises silicon dioxide. 
         [0074]    According to one embodiment, the dielectric layer comprises silicon nitride. 
         [0075]    According to one embodiment, the covering layer has:
       a first surface in contact with the supporting substrate,   a second surface in contact with the dielectric layer,   a peripheral surface connecting the first and second surfaces of the covering layer,   the useful layer covering the peripheral surface of the covering layer.       
 
         [0080]    According to one embodiment, the additional layer is interposed between the useful layer and the dielectric layer, the additional layer having the same chemical composition as the covering layer. 
         [0081]    According to one embodiment, the useful layer comprises monocrystalline silicon, the additional layer comprises thermal silicon dioxide, the dielectric layer comprises silicon nitride, and the covering layer comprises silicon dioxide. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0082]    Other features and advantages will emerge from the following description of embodiments of a manufacturing method according to the disclosure, given by way of non-limitative examples with reference to the accompanying drawings, in which: 
           [0083]      FIG. 1  is a schematic representation of a manufacturing method according to the techniques known from the prior art; 
           [0084]      FIG. 2  is a view of the front face of a composite structure obtained by a manufacturing method according to the known techniques of the prior art; 
           [0085]      FIG. 3  is a view in cross section of a substrate used in the manufacturing method according to the known techniques of the prior art; 
           [0086]      FIGS. 4A and 4B  are schematic representations of a first embodiment of the disclosure; 
           [0087]      FIG. 5  is a view in transverse section of a composite structure that has been obtained by a manufacturing method according to the disclosure and has undergone an encapsulation treatment; 
           [0088]      FIGS. 6A and 6B  are schematic representations of a second embodiment of the disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0089]    For the various embodiments, the same references will be used for identical elements or ones fulfilling the same function, for reasons of simplification of the description. 
         [0090]    The method illustrated in  FIGS. 4A and 4B  is a method for manufacturing a composite structure comprising, from its rear face to its front face, a supporting substrate  10 , a covering layer  20 , at least one dielectric layer  30  and a useful layer  40 , the method comprising the following steps:
       a) providing a donor substrate  50  and the supporting substrate  10 ;   b) forming at least the dielectric layer  30  comprising:
           a first surface in contact with the donor substrate,   a second surface opposite to the first surface,   a peripheral surface connecting the first and second surfaces together;   
           the dielectric layer  30  has a contour Cz;   c) forming the covering layer  20  arranged to cover the second surface of the dielectric layer  30 ;   d) forming a weakened zone  60  in the donor substrate  50  delimiting the useful layer  40  in contact with the first surface of the dielectric layer  30 ;   e) assembling the supporting substrate  10  and the donor substrate  50 , so that the supporting substrate  10  and the covering layer  20  are in contact along a contact surface  70  having a contour Cs;   f) breaking the donor substrate  50  along the weakened zone  60 .       
 
         [0101]    Steps b) and e) are executed so that the contour Cz of the dielectric layer  30  fits within the contour Cs of the contact surface  70 , and step c) is executed so that the covering layer  20  covers the peripheral surface of the dielectric layer  30 . 
         [0102]    Prior to the implementation of the manufacturing method according to the disclosure, a step for determining the contour Cs of the contact surface can be executed. 
         [0103]    This determination step is particularly advantageous when it is a question of implementing the method for manufacturing a plurality of composite structures. 
         [0104]    This is because, in the context of the manufacture of a plurality of composite structures, a plurality of donor substrates  50  and a plurality of supporting substrates  10  are chosen so that the contour Cs of the contact surface is substantially equivalent (or even identical) from one composite structure to another. 
         [0105]    The donor substrates  50  in the plurality of donor substrates  50  are then chosen so as to have substantially equivalent or even equal geometric characteristics. 
         [0106]    The supporting substrates  10  of the plurality of supporting substrates  10  are then chosen so as to have substantially equivalent or even equal geometric characteristics. 
         [0107]    Geometric characteristics of a substrate means, non-limitatively, its thickness at any point on its surface, its variation in thickness and its shape. 
         [0108]    Thus, it suffices to determine the contour Cs for manufacturing a structure and to apply the result to the manufacture of a plurality of composite structures. 
         [0109]    The determination of the contour Cs may comprise the following steps:
       assembling a supporting substrate  10  and a donor substrate  50 ;   use of a scanning acoustic microscope in order to obtain an image of the contour Cs of the contact surface  70 .       
 
         [0112]    Another solution would be, in implementing the method for manufacturing a composite structure, to omit the formation of the dielectric layer  30  and to measure, at all points on the edge of the supporting substrate, the width of the peripheral ring. 
         [0113]    The appearance of the peripheral ring on the composite structure is delimited by the edge of the supporting substrate and the contour Cs of the contact surface  70 . Determination of the contour Cs is then direct. 
         [0114]    For example, the applicant has found that the manufacture of a composite structure comprising a covering layer  20  leads to the formation of a peripheral ring with a width of 0.8 mm. 
         [0115]    Particularly advantageously, the supporting substrate  10  comprises:
       a top surface onto which the covering layer  20 , the dielectric layer  30  and the useful layer  40  are transferred;   a bottom surface opposite to the top surface;   a peripheral zone connecting the bottom surface and the top surface;       
 
         [0119]    the contour Cs of the contact surface  70  and the peripheral zone of the supporting substrate  10  delimiting an essentially annular surface of width L, and steps b) and e) are executed so that the contour Cz of the dielectric layer  30  and the peripheral zone of the supporting substrate  10  delimit an essentially annular surface with a width of between 105% and 150%, preferably between 110% and 140%, even more preferentially between 115% and 130%, of the width L. 
         [0120]    Thus, in the context of a method for manufacturing a plurality of composite structures, the plurality of donor substrates  50  and the plurality of supporting substrates  10  may have a certain dispersion of their geometrical characteristics. 
         [0121]    The donor substrate  10  provided at step a) may comprise one of the materials chosen from: silicon, silicon germanium, and germanium. 
         [0122]    The supporting substrate  30  provided at step a) may consist of any of the materials normally used in the microelectronic, optical, optoelectronic and photovoltaic industries. 
         [0123]    In particular, the supporting substrate  10  comprises at least one material selected from the following group of materials: silicon, silicon carbide, silicon germanium, glass, a ceramic and a metal alloy. 
         [0124]    At least one dielectric layer  30  is formed on the donor substrate. 
         [0125]    A covering layer  20  is formed so as to cover the dielectric layer  30 . 
         [0126]    The formation of the covering layer  20  and of the dielectric layer  30  will be detailed below during the description of various embodiments. 
         [0127]    Next, a step d) of forming a weakened zone  60  in the donor substrate  50  is executed. 
         [0128]    The weakened zone  60  delimits, in the donor substrate  50 , a useful layer  40 , the useful layer being in contact with the dielectric layer  30 . 
         [0129]    The useful layer  40  is intended to be transferred onto the supporting substrate  10 . 
         [0130]    The weakened zone  60  may be created by the implantation of atomic species in the donor substrate  50 . 
         [0131]    Atomic species means atomic, molecular or ionic species. 
         [0132]    The species introduced may comprise at least one of the following species: hydrogen and helium. 
         [0133]    The hydrogen may be introduced with an energy of between 10 and 210 keV and a dose of between 7×10 15  and 1×10 17  at/cm 2 . 
         [0134]    The assembly step e) may be a molecular bonding step. 
         [0135]    The breaking step f) may advantageously be a thermal annealing executed at a temperature of between 300° C. and 600° C. 
         [0136]    At the end of step f), the composite structure is obtained. 
         [0137]    The composite structure comprises, from its front face to its rear face, the useful layer  40 , the dielectric layer  30 , the covering layer  20  and the supporting substrate  10 . 
       First Embodiment 
       [0138]    The first embodiment is illustrated in  FIGS. 4A and 4B . 
         [0139]    Formation of the Dielectric Layer  30   
         [0140]    The dielectric layer  30  may be formed in two steps:
       b1) formation of a layer of dielectric material of the donor substrate  10 ;   b2) partial removal of the layer of dielectric material so that the residual layer of dielectric material forms the dielectric layer  20 .       
 
         [0143]    Step b1) may be a technique of vapor deposition, low-pressure vapor deposition or plasma-assisted vapor deposition on the donor substrate  50 . It may also be a heat treatment technique in a chosen atmosphere (nitriding, oxidation, etc.). 
         [0144]    The thickness of the layer of dielectric material may be between 10 nm and 80 nm, for example, 50 nm. 
         [0145]    Step b1) is then followed by a step b2), which comprises a partial removal of the layer of dielectric material. The partial removal is executed so that the remaining or residual portion of the layer of dielectric material constitutes the dielectric layer  30 . 
         [0146]    In other words, the partial removal of the layer of dielectric material is executed on a peripheral surface of the donor substrate  50  delimited by the edge of the donor substrate  50  and the contour Cz. 
         [0147]    Thus, the residual portion of the layer of dielectric material forms the dielectric layer  30 . 
         [0148]    The peripheral surface of the donor substrate  50  may have the form of an annular surface. 
         [0149]    Step b2) may advantageously be executed by a chemical etching solution. 
         [0150]    Particularly advantageously, a plurality of dielectric layers  30  may be formed successively. For example, one dielectric layer  30  comprising silicon nitride and another dielectric layer  30  comprising silicon dioxide may be formed successively. 
         [0151]    In the case of a dielectric layer  30  comprising silicon nitride (Si 3 N 4 ), the chemical etching solution may be a solution of phosphoric acid (H 3 PO 4 ) heated to a temperature greater than 50° C. 
         [0152]    The chemical etching solution may be distributed by a nozzle on the edge of the donor substrate  50  in rotation, so as to etch the dielectric layer  30  only on the peripheral surface of the donor substrate  50  delimited by the edge of the donor substrate  10  and the contour Cz. 
         [0153]    Formation of the Covering Layer  20   
         [0154]    The covering layer  20  may be formed by a vapor deposition, low-pressure vapor deposition or plasma-assisted vapor deposition technique. 
         [0155]    The covering layer covers the second surface and the peripheral surface of the dielectric layer  30  in their entirety. 
         [0156]    The covering layer  20  may comprise a material, different from the materials of the dielectric layer  30 , selected from the following materials: silicon oxide, silicon nitride or oxynitride, aluminium nitride, aluminium oxide, polycrystalline silicon and amorphous silicon. 
         [0157]    Particularly advantageously, the covering layer  20  comprises silicon oxide and its thickness is greater than 80 nm, for example, 100 nm. 
         [0158]    At the end of step f), the composite structure is obtained. 
         [0159]    The composite structure comprises, from its rear face to its front face, a supporting substrate  10 , a covering layer  20 , at least one dielectric layer  30  and a useful layer  40 , the dielectric layer  30  having:
       a first surface in contact with the useful layer  40 ;   a second surface in contact with the covering layer  20 ;   a peripheral surface connecting the first surface and the second surface,       
 
         [0163]    the covering layer  20  covers in its entirety the peripheral surface of the dielectric layer  30 , so that the useful layer  40  and the covering layer  20  encapsulate the dielectric layer  30 . 
         [0164]    Thus, after the transfer step, the dielectric layer  30  of contour Cz is situated vertically in line with a central surface  80 , of contour Cp, of the supporting substrate  10 . 
         [0165]    Thus, the surface delimited by the contour Cs of the contact surface  70  and the contour Cp of the central surface  80  is opposite a stack of layers comprising only the useful layer  40  and the covering layer  20 . 
         [0166]    Moreover, the central surface  80  of the supporting substrate  10  is facing a stack of layers comprising the useful layer  40 , the dielectric layer  30  and the covering layer  20 . 
         [0167]    Thus, a single step is observed at the edge of the substrate. 
         [0168]    Consequently, the observation of a single step makes it possible to encapsulate the covering layer  20  and the dielectric layer  30  with the useful layer  40 . The encapsulation is executed by a heat treatment, without observing any dewetting of the useful layer  40  as illustrated in  FIG. 5 . 
         [0169]    In this regard, a person skilled in the art will find a technical description of encapsulation of an insulation layer by the useful layer  40  in the published application FR 2852143 A1 (E. NEYRET) 11 Sep. 2005 (Nov. 10, 2005) page 10 lines 3-28. 
         [0170]    In a particular configuration of this first embodiment, the covering layer  20  is made from polycrystalline silicon or amorphous silicon, and its thickness is between a few nm and a few thousand nm, such as, for example, 2000 nm. The dielectric layer  30  is made from silicon oxide, and the useful layer  40  is made from silicon. Thus, a composite silicon-on-insulator structure having a buried layer of polycrystalline silicon or amorphous silicon under the insulating layer is formed. This type of composite structure is particularly suitable for manufacturing semiconductor devices finding applications in the radio-frequency field. 
       Second Embodiment 
       [0171]    The second embodiment, illustrated in  FIGS. 6A and 6B , differs from the first embodiment in that the donor substrate  50  comprises an additional layer  90 , the additional layer  90  being in contact with the dielectric layer  30 , the additional layer  90  having the same chemical composition as the covering layer  20 . 
         [0172]    For example, the additional layer  90  and the covering layer  20  comprise silicon oxide. 
         [0173]    The additional layer  90  is formed directly on the donor substrate  50 , before the dielectric layer  30 . 
         [0174]    The additional layer  90  may comprise a material, different from the materials of the dielectric layer  30 , selected from the following materials: silicon oxide, silicon nitride or oxynitride, aluminium nitride, aluminium oxide, polycrystalline silicon and amorphous silicon. 
         [0175]    Advantageously, the additional layer  90  is made from silicon oxide and its thickness is between 2 nm and 20 nm, for example, 7 nm. 
         [0176]    When the donor substrate  50  is made from silicon, the additional layer  90  of silicon oxide may be obtained by thermal oxidation of this donor substrate and, therefore, form an additional layer  90  of thermal silicon dioxide. 
         [0177]    At the end of step f), the composite structure is obtained. 
         [0178]    The composite structure comprises, from its front face to its rear face, a useful layer  40 , an additional layer  90 , a dielectric layer  30 , a covering layer  20  and a supporting substrate  10 . 
         [0179]    Thus, after the transfer step, the dielectric layer  30  of contour Cz is situated vertically in line with a central surface  80  of contour Cp of the supporting substrate  10 . 
         [0180]    Thus, the surface delimited by the contour Cs of the contact surface  70  and the contour Cp of the central surface  80  is opposite a stack of layers comprising only the useful layer  40 , the additional layer  90  and the covering layer  20 . 
         [0181]    Moreover, the central surface  80  of the supporting substrate  10  is opposite a stack of layers comprising the useful layer  40 , the dielectric layer  30  and the covering layer  20 . 
         [0182]    The covering layer  20  and the additional layer  90  having the same chemical composition, their stack is then associated with a single layer of dielectric material. 
         [0183]    Thus, a single step is observed at the edge of the substrate. 
         [0184]    Consequently, the observation of a single step makes it possible to encapsulate the covering layer  20 , the dielectric layer  30  and the additional layer  90  with the useful layer  40 . The encapsulation is executed by heat treatment, without observing any dewetting of the useful layer  40 . 
         [0185]    The additional layer  90  advantageously comprises silicon dioxide. Thus, a composite structure commonly referred to as SOI ONO (silicon-on-silicon dioxide, on silicon nitride and on silicon dioxide) is formed. 
         [0186]    Thus, the disclosure is advantageously implemented for producing composite SOI ONO substrates or for producing SOI substrates for radio-frequency applications.