FR2845517A1 - Method for making a detachable semiconductor substrate and for obtaining a semiconductor element such as for a photovoltaic cell - Google Patents

Abstract

The method comprises the steps of (i) introducing the gaseous species into the substrate (1) under conditions which allow the formation of a fragile layer by the presence of micro-cavities and/or micro-bubbles in the same layer so that a thin layer of semiconductor material is demarcated between the fragile layer and one face (2) of the substrate, (ii) performing a heat treatment of the substrate for increasing the level of fragility or brittleness of the fragile layer until the appearance of local deformations of that face (2) in the form of blisters but without generating the exfoliations of the thin layer in the course of this step or in subsequent processing, and (iii) carrying out the epitaxial growth of semiconductor material on that face (2) of the substrate in order to form at least one epitaxial layer (6) on the thin layer. The introduction of the gaseous species is by ionic implantation or an implantation by plasma immersion, in particular to both faces of the substrate. Before the heat treatment, a step is introduced of forming a thickener whose thickness is sufficiently large not to generate the exfoliations in the thin layer and at the same time sufficiently small in order to avoid a separation of the substrate at the level of the fragile layer at the time of the heat treatment. The thickener is eliminated, totally or partially, before the step of epitaxial growth. A supplementary step is introduced of implementing components in the epitaxial layer, in particular of photovoltaic components. A supplementary step is introduced of forming a protection layer on the epitaxial layer, where the protection layer is designed to protect the epitaxial layer from chemical action designed to separate the substrate at the level of the fragile layer. A semiconductor element is obtained by taking a detachable semiconductor substrate and by carrying out the detachment at the level of the fragile layer so that the separation is either total for obtaining the semiconductor element in the form of a membrane, or partial for obtaining one or more semiconductor elements forming one or more components. A supplementary step is introduced of fastening the epitaxial layer to a support before the detachment, where the detachment is by the application of constraints on traction and/or shear. The detachment is by implementing a step of introducing a supplementary gaseous species, then a step of mechanical constraint and/or a heat treatment of the fragile layer. The detachment is by a chemical action on the fragile layer, or an acoustic wave treatment of the fragile layer. The detachment is by a chemical action on the fragile layer, or an acoustic wave treatment of the fragile layer. The detachable semiconductor substrate is that which has already been detached without preliminary surface conditioning. The method can be repeated so to use up the remaining substrate.

Description

REALIZATION OF A DEMONDABLE SEMICONDUCTOR SUBSTRATE AND

  OBTAINING A SEMICONDUCTOR ELEMENT

DESCRIPTION

TECHNICAL AREA

  The present invention relates to a method for

  for producing a demountable semiconductor substrate.

  It also relates to a method for obtaining a semiconductor material element.

STATE OF THE PRIOR ART

  FR-A-2 681 472 (corresponding to US Pat. No. 5,374,564) describes a method for manufacturing thin films of semiconductor material. It discloses that the introduction of a rare gas or hydrogen into a substrate is capable of inducing, under certain conditions, the formation of microcavities or micro-bubbles at a depth close to the average depth of penetration of the implanted ions. . By bringing into contact intimately this substrate, by its implanted face, with a stiffener and the achievement of a suitable heat treatment, an interaction can take place between the micro-cavities or micro-bubbles present in the implanted zone. . This interaction can then lead to a fracture at the implanted zone of the semiconductor substrate. Two parts are then obtained: a semiconductor film adhering to the stiffener on the one hand and the rest of the initially implanted substrate on the other hand. The rest of the substrate can be recycled and reused. This method makes it possible in particular to transfer a thin layer of material onto a support substrate which may be of a different nature. It allows the manufacture of

  SOI substrates ("Silicon On Insulator").

  This method can also be applied to the manufacture of a thin film of solid material other than a semiconductor material, such as, for example, a conductive or dielectric material, crystalline or not, as disclosed in document FR-A-2. 748,850

  (corresponding to US Pat. No. 6,190,998).

  Furthermore, FR-A-2 748 851 (corresponding to US Pat. No. 6,020,252) discloses a method for including technological steps requiring the use of high temperatures, for example 9000C, between the step of initial ion implantation and the final step of separation. These intermediate steps involving heat treatments can be carried out without degrading the surface state of the planar face of the wafer and without generating the fracture at the implanted zone, which would induce the separation of the superficial thin layer. They may for example be part of the electronic component manufacturing operations. In this case, the ion implantation step, for example hydrogen, must be done in a range of appropriate doses. The final separation step can then be carried out either by heat treatment or by applying a mechanical stress to the structure or again by

  combination of these two treatments.

  Document FR-A-2 809 867 discloses a process comprising a step of introducing gaseous species in a layer buried in the substrate, which will lead to the formation of micro-cavities in this layer. The buried implant zone thus weakened delimits a thin layer with one face of the substrate. The process also comprises a step of eliminating all or part of the gaseous species from the weakened zone. This evacuation of the gaseous phase makes it possible to perform subsequent treatments at high temperatures without inducing deformation of the surface (for example in the form of blisters or "blisters") or total or partial separation of the surface layer. A step of superfragmentation of the micro-cavities zone may optionally be carried out by carrying out appropriate heat treatments, by applying mechanical stresses or by combining these two types of treatments. This overfragmentation of the buried zone

  may for example facilitate the final separation between the surface layer of the substrate and the substrate.

  The step of implantation of the gaseous species is carried out in a range of adapted doses allowing on the one hand the realization of a sufficient embrittlement of the buried zone and on the other hand

  the posterior elimination of gaseous species.

  In FR-A-2 758 907 (corresponding to US Pat. No. 6,316,333), the process described makes it possible to transfer a layer of material, for example silicon, on which components could be made. The substrate comprising the processed layer is prepared so that certain areas on the surface are masked. The species introduced into this substrate by an ion implantation step are then located in the non-masked areas. The hidden areas do not receive ions. At the level of the implanted zones, a buried layer of 10 specific defects related to the introduction of gaseous species, such as micro-bubbles, micro-cavities or micro-fissures, is thus obtained. The masked areas may be chosen to protect the active areas from components susceptible to degradation as the implanted ions pass through. Typically, the dimensions of the masked areas are described of the order of 1 μm. The subsequent bonding of the substrate comprising the process layer and comprising locally implanted regions, followed by a separation treatment, which can include annealing at an average temperature (approximately 4000.degree. C.), then makes it possible to transfer the active layer of components to a surface. support substrate. Indeed, the development of the cavities and micro-cracks at the level of the implanted zones is able to cause the separation on

  full plate of the superficial layer.

  The results published by C.H. Yun et al. ("Transfer of Patterned Ion-Cut Silicon Layer", Applied Physics Letters, Vol. 73, No. 19, Nov. 1998 and "Ioncut 30 Silicon Layer Transfer with Patterned Implantation of

  hydrogen ", Electrochemical Society Proceedings, vol 99-

  3, p 125) have shown that the masked areas during the implantation step can result in squares or lines whose maximum dimensions are respectively of the order of 15 μm × 15 μm and 15 μm × 5 100. Pm. The implanted zones separating these masked patterns must be at least 5 μm. It is then possible to transfer the surface layer onto a support, from a heat treatment or by application of mechanical forces external to the structure. The authors note, however, that the reported surface layer has inhomogeneities of relief at the non-implanted areas. These inhomogeneities are all the stronger as the dimensions are large (between 10 and 15 μm). The 15 authors explain that these irregular reliefs come from the deviation of the crack in the

cleavage planes (111) of the substrate.

  Another method also allows the development of a removable substrate, capable of withstanding a high temperature treatment (about 11000C) before the final disassembly of the processed surface layer. This method is based on local implantation, made possible by the use of a mask at the time of introduction of the ions (hydrogen and / or other species such as for example rare gases). The size of the implanted regions is studied so that the subsequent heat treatments for embrittlement of the buried zone and / or required for all or part of the steps for producing the components do not induce any degradation of the surface. This constraint is related to the subsequent steps of developing components, for example microelectronic, which require a perfect surface state. Obtaining removable substrates, that is to say comprising a surface layer delimited by the surface of the substrate and by a weakened buried zone, said substrates being compatible with the implementation of steps

  technology for manufacturing components and may require high temperature treatments, is of increasing interest. Photovoltaic applications have an additional requirement which is the use of a low cost process.

  Document FR-A-2,748,850, cited above, proposes a method of weakening a substrate in a buried layer, by low dose introduction of a gaseous species (for example hydrogen). The implanted dose should be selected so that thermal annealing does not induce deformation or surface exfoliation. Depending on the mechanical forces applicable to induce separation, the embrittlement stage reached at the implanted zone may then be insufficient. It may then be interesting to increase the level of weakening of

the implanted area.

  According to the process described in document FR-A-2 809 867, mentioned above, the introduction of a controlled dose makes it possible at the same time to weaken the buried zone and then to evacuate the gas, in order to limit a pressure effect during a rise in temperature. There is therefore no deformation or exfoliation of the surface during high technological steps.

  temperatures. This technique requires rigorous control of dose and dose homogeneity of implanted species. It may be interesting to relax the technological constraints relating to a narrow window of implantation parameters.

  Document FR-A-2 758 907, cited above, proposes a local introduction of gaseous species after making the components in the surface layer of the substrate. The introduction of these species leads to the formation of a discontinuous buried layer of micro-cavities capable of generating the fracture after joining the processed substrate on a support substrate. The substrate is thus weakened after the completion of the different technological steps of manufacturing the components. The accessible size of the zones to be masked (which correspond to the active zones of the components) can be limiting according to the targeted applications. For example, for component sizes of several tens of μm to several hundred μm, this technique is difficult to implement. In addition, depending on the component manufacturing technology used, the thickness of the active layer, i.e., having the components, may be up to several μm (for example, about 50 μm for the silicon photovoltaic cells). . The introduction of the gaseous species at a deep depth while effectively protecting the zones by masking can then be difficult, particularly because of the equipment required (specific implants, accelerators) as well as costly, for example for

photovoltaic applications.

  A removable substrate may also be made according to the method described above and using a mask at the time of introduction of the ions. This method implements an intermediate stage of pre-implantation masking which will allow, by lateral confinement of the buried micro-cracks, to greatly limit the appearance of deformations in the form of blisters on the surface of the substrate. The surface state of the substrate is then perfectly compatible with different steps of producing components, for example microelectronic. On the other hand, this method can have the disadvantage of a high cost, especially in application fields such as photovoltaics.

EXPOSURE OF THE INVENTION

  The present invention has been conceived in order to reduce costs, but with the aim of obtaining a processed surface layer which can be separated or detached from its surface.

  substrate without breakage or deterioration of the structure.

  The subject of the invention is therefore a method for producing a demountable semiconductor substrate, comprising the following steps: introduction of gaseous species into the substrate according to conditions enabling the formation of a layer weakened by the presence in this layer micro-cavities and / or microbubbles, a thin layer of semiconductor material being thus delimited between the embrittled layer and a face of the substrate, - thermal treatment of the substrate to increase the level of embrittlement of the weakened layer, this heat treatment being conducted until the appearance of local deformations of said substrate face in the form of blisters but without generating exfoliations of the thin layer during this step and during the rest of the process, epitaxial semiconductor material on

  said substrate face for providing at least one epitaxial layer on said thin layer.

  The introduction of gaseous species can be carried out by ion implantation or implantation by

plasma immersion.

  Before the step of heat treatment of the substrate, a step may be provided for forming a thickener whose thickness is sufficiently large not to generate exfoliations in the thin layer and sufficiently small to prevent separation of the substrate. at the level of the embrittled layer 30 during the heat treatment step of the embrittled layer. The thickener can then be removed totally or partially before the epitaxial step. It may be provided an additional step of subjecting the epitaxial layer to at least one step of producing components. It may be a step of producing photovoltaic components. It may also be provided an additional step of forming a protective layer 10 on the epitaxial layer, this protective layer being intended to protect the epitaxial layer with a chemical etching intended for the separation of the substrate

at the level of the weakened layer.

  The subject of the invention is also a method 15 for obtaining a semiconductor material element, characterized in that it comprises the following steps: providing a demountable semiconductor substrate obtained by the method for producing a substrate demountable semiconductor as described above, - disassembly of the demountable semiconductor substrate by detachment of this substrate at the level of the embrittled layer, the detachment being either total to provide a semiconductor material element forming a membrane and consisting of the thin layer of semiconductor material and the epitaxial layer, either partial to provide one or more semiconductor material elements forming one or more components and consisting of a portion of the thin layer of semiconductor material and the epitaxial layer. It can also be provided an additional step of fixing the epitaxial layer on

  a support before the disassembly step.

  The detachment may result from the application of tensile stress and / or shear stress. It may result from the implementation of a step of introducing additional gaseous species into the embrittled layer, then a step of mechanical stress and / or heat treatment of the weakened layer. He can too

  result from the application of an opening constraint at the level of the weakened layer. It can still result from a chemical attack of the weakened layer. It may still result from a combination of these methods.

BRIEF DESCRIPTION OF THE DRAWINGS

  The invention will be better understood and others

  advantages and particularities will appear on reading the description which follows, given as a

  non-limiting example, accompanied by the accompanying drawings, in which: FIG. 1 is a cross-sectional view of an ion-implanted semiconductor substrate for forming an embrittled buried layer according to the invention; FIG. 2 is a cross-sectional view of the semiconductor substrate of FIG. 1 having undergone a heat treatment making it possible to increase the level of embrittlement of the embrittled buried layer, according to the invention; FIG. 3 is a cross-sectional view of the semiconductor substrate of FIG. 2 after the epitaxy of a layer of semiconductor material on the entire implanted surface of the substrate, according to the invention; FIG. 4 is a cross-sectional view of the semiconductor substrate of FIG. 2 after the epitaxy of a layer of semiconductor material on a portion of the implanted face of the substrate according to the invention; FIG. 5 is a cross-sectional view of the semiconductor substrate of FIG. 3 after production of components in the epitaxial layer, according to the invention; Figure 6 is a cross-sectional view of the semiconductor substrate of Figure 5 after attachment of the epitaxial layer on a support, according to the invention; FIG. 7 is a cross-sectional view of the semiconductor substrate attached to its support, as shown in FIG. 6, in the course of

  the separation step, according to the invention.

  EXPOSURE OF PARTICULAR RESTORATION MODES

  The method according to the invention applies in particular to the field of photovoltaic applications.

  It allows the production of a substrate (in particular silicum) having a buried embrittled layer, which can undergo the different epitaxial growth and cell development steps, specific to the target photovoltaic application, and then allow the final separation. between the superficial layer

processed and the rest of the substrate.

  This process is based on the implantation of gaseous species such as hydrogen ions and / or rare gases, capable of creating, around the maximum concentration depth, a zone weakened by microcavities, "platelets" and / or micro-bubbles A heat treatment is used to increase the level of embrittlement of the embrittled layer 10. This thermal treatment will be called thereafter the embrittlement heat treatment Under certain conditions, this embrittlement heat treatment imposed on the substrate implanted result in the formation of cavities and / or micro-cracks in the weakened buried zone resulting in the appearance of blisters or bubbles or

  "blisters" on the surface of the substrate.

  According to the process of the invention, the implantation conditions (the main parameters of which are energy, dose and temperature) as well as the parameters of the embrittlement heat treatment and the various subsequent optional steps for preparing the substrate ( heat treatments, layer deposits, etc.) must be chosen according to the nature of the substrate (nature of the material, crystalline orientation, etc.), so that no exfoliation of the surface layer occurs. By exfoliation is meant a partial detachment of the thin layer at the weakened zone. In the same way, during the technological steps specific to the intended application, for example, during a step of epitaxial growth of the silicon layer necessary for the realization of

  solar cells, no exfoliation will be generated.

  After all or part of the realization of the 5 photovoltaic components, and respecting certain

  implemented subsequently, the treated surface layer (about 50 pim) can be separated from the initial substrate by cracking at the weakened zone by the micro-cavities 10 and / or micro-cracks.

  The process begins with the creation of a weakened buried layer that will allow, after the completion of technological steps, the separation between a surface layer and the rest of the substrate. It is based on the introduction into the substrate of gaseous species such as hydrogen and / or other rare gases (helium, etc.) by a technique allowing a controlled localization of the species at depth (for example ion implantation). implantation by plasma immersion ...). Such an implantation makes it possible to form a weakened buried zone typically composed of micro-cavities, "1platelets" and / or microbulles .This disturbed buried zone delimits with the

  surface of the substrate a surface layer.

  In order to increase the level of

  embrittlement of the implanted zone, optional steps of preparation of the substrate comprising, for example, a heat treatment and / or a thickening deposit may be performed on the substrate 30 before the embrittlement heat treatment.

  Indeed, under thermal activation, the micro-cavities and / or "platelets", generated during implantation for example of hydrogen ions, will follow a growth law. Thus, if the implanted dose is sufficient, the cumulative effect of increasing the size of the cavities and / or micro-cracks and the gas pressure in them is the appearance of local deformations of the layer.

  superficial in the form of blisters.

  The characteristics (morphology, size, density) of these micro-cracks and / or cavities reflect

  the weakened state of the implanted area.

  According to a variant of the embrittlement treatment, it is possible to deposit an oxide on the surface of the implanted substrate before any heat treatment. It will play a mechanical role of thickener that allows micro-cracks to develop laterally in larger dimensions, under the effect of adequate thermal annealing. Microcrack characteristics favorable to greater embrittlement can be obtained by

the addition of this deposited layer.

  For a given substrate, the implantation parameters, the heat treatment of embrittlement as well as the conditioning parameters of the substrate (heat treatments, deposition of layers acting as thickeners, etc.) dictate the size and density of blisters on the surface of the substrate. i.e. also the size and density of microcracks and / or cavities underlying them,

contained in the implanted area.

  The level of embrittlement of the substrate can thus be parameterized according to the implantation conditions and the characteristics of the subsequent treatments. Thus for a given substrate, it is necessary to choose the implantation conditions (energy, dose, temperature) so that: - the realization of an adequate embrittlement treatment effectively leads to the obtaining of micro-fissures of great dimension, which can generate blisters on the surface of the substrate. However, this treatment should under no circumstances generate

  exfoliations of the superficial layer.

  any subsequent treatment, linked to the technological steps specific to the intended application, for example epitaxy in the 7000 C 11000 C range,

  does not induce local exfoliation of the layer.

  The process according to the invention combines implantation conditions and embrittlement treatments which make it possible to avoid local exfoliation of the surface layer before and after the various technological steps relating to

the intended application.

  The set of implantation conditions and treatments to increase the embrittlement

  must make it possible to obtain a substrate comprising micro-fissures localized in the implanted zone, giving rise to the appearance of blisters on its surface.

  These micro-cracks are randomly distributed in the buried embrittlement plane and their size follows a Gaussian distribution law. This state of embrittlement is such that any additional treatment imposed on the substrate, especially the high temperature treatments, does not induce local exfoliation of the surface layer 5 delimited by the implanted zone and the surface of the substrate, for example at the one or more micro-cracks. It is important to note that the morphology, size and density of the micro-cracks and cavities present in the embrittled layer may be variable depending on the subsequent treatments imposed on the weakened substrate. The high thermal budgets for which the reconstruction of the material constituting the substrate is significant have a significant influence on the morphological change of the microcracks formed after implantation, followed by an embrittlement treatment requiring a low thermal budget. After high thermal budgets, these micro-cracks and / or cavities evolve towards stable polyhedral forms. In particular, a polyhedral reconstruction of the crack edges is noted. Their sizes and densities also depend strongly on the thermal budget imposed on the weakened substrate. It may be noted that the embrittlement stage may also comprise a heat treatment at high temperature, so as to transform the micro-cracks and / or cavities present in the implanted zone into stable objects (evacuation of all or part of the gaseous species and at least partial reconstruction of the crack edges). This is to avoid any exfoliation phenomenon during the technological steps of epitaxy and / or realization

of component.

  At this stage, and to enable the development of photovoltaic components, for example, the epitaxial growth of a thick silicon layer (up to about 50 μm) can be performed on the cloned substrate. The "soft" relief of blisters on the surface (typically of a diameter ranging from a few pm to a few tens of im, and whose maximum deformation can reach a few hundred nanometers) makes it possible to obtain thick layers of monocrystalline silicon by epitaxy. of good quality

for the intended application.

  Various stages of development of photovoltaic type components can then be performed. The rest of the process corresponds to the

  final separation between the surface layer and the initial substrate. This separation will be at the level of the weakened buried zone.

  This step can be performed by applying a tensile, shear or mixed mode stress involving traction

  and shear, to the weakened zone.

  According to a first embodiment, the processed surface layer may be separated from its source substrate, thereby generating a self-supporting membrane. This membrane may be separated on the entire surface of the substrate or locally at a component or a set of components, by applying an opening constraint to

level of the weakened area.

  According to a second embodiment, a low-cost support substrate may be bonded via an adhesive layer (polymer, resin, ceramic, metal or other ...) to the silicon process layer. The separation, for example by applying tensile and / or shear stresses and / or in a mixed mode to the bonded structure, can then be effected at the level of the zone

buried fragile.

  The initial substrate is then obtained on the one hand, peeled off from a thin layer (this layer being the zone delimited by the implanted zone and the surface of the initial substrate), and the support on the other hand, comprising the membrane. semiconductor material (e.g.

silicon) processed.

  According to a variant of the process and to facilitate the final separation of the membrane of the initial substrate, a chemical etching may be carried out. A solution of the SECCO type has the property of attacking silicon and more preferentially the areas of silicon which are constrained and / or which have undergone plastic deformation and / or disturbed by the presence of inclusions, structures or other morphological transformations. Thus, the embrittled zone comprising micro-cracks and / or cavities whose lateral size may vary from a few tens of nanometers to a few tens of μm, will be a zone

  privileged attack of the SECCO solution. In this way, it is possible to initiate a separation of the processed surface layer of the initial substrate by progressive localized consumption by the chemical solution of the buried embrittled zone. According to this variant of the separation step, it will be necessary to deposit a protective layer, in particular on the processed upper face of the substrate, so as to avoid degradation of the cells and / or components produced.

  Other solutions for etching the semiconductor material at the embrittled area can also be used provided the process parts of the substrate are effectively protected. We can notably mention the TMAH, the KOH if the

  semiconductor material is silicon.

  According to a variant of the method, this step consisting of a localized attack at the weakened zone can be carried out before the production of the components (for example photovoltaic cells). Thus, it will not be necessary to take precautions to protect the processed face

weakened substrate.

  This preferred chemical etching technique can be used alone to totally separate the processed membrane from its initial substrate, in order to obtain a self-supporting layer or for the purpose of reporting this

  membrane on an economical mechanical support.

  According to one variant, this etching technique can be used in conjunction with a mechanical separation technique by application of external forces such as, for example, traction. In this case, the chemical attack will have the advantage of initiating and locating the crack at the weakened buried zone and

  thus to facilitate the final dissociation.

  According to one variant, the substrate may be subjected to acoustic wave treatments

(ultrasound, nanovibration, ...).

  According to a variant of the process, it is possible to carry out a treatment intended to diffuse gaseous species, for example hydrogen, through the front face or the rear face of the processed substrate. The techniques used can be, for example, plasma hydrogenation, or other methods of introducing gaseous species by diffusion. This step may make it possible to increase the level of embrittlement of the buried zone of micro-cracks and / or micro-cavities. The species introduced into the material are preferentially trapped at the level of

the area of micro-cracks.

  The final separation can then be carried out by a suitable heat treatment and / or by application of an adequate mechanical stress and / or by a treatment comprising at the same time a treatment

  thermal and mechanical treatment.

  The initial substrate peeled with a surface layer can then be recycled for

  realization of another substrate to be weakened.

  FIG. 1 is a cross-sectional view of a semiconductor substrate 1, in this example it is a silicon substrate, which will be subjected to the method of the invention, according to a first example of implementation. The main face 2 of the silicon substrate 1 is covered with a layer of silicon oxide 3. An ion implantation of hydrogen, represented symbolically by arrows in FIG. 1, is carried out in the substrate 1 through the layer The implantation beam 10 has an energy of 210 keV and a dose of 6.1016H * / cm 2. It causes the formation of a weakened buried layer 4 comprising microbubbles and

micro-cavities.

  Annealing at 550WC for 30 minutes is performed on this substrate to increase the level of embrittlement of the implanted area. Indeed, under thermal activation, the cavities induced by implantation follow a growth law to form micro-fissures and / or cavities of larger size which causes the appearance of blisters 5 to

  the surface of the substrate as shown in Figure 2.

  The oxidized surface of the substrate is then deoxidized, and then a technological step of silicon epitaxy in the liquid phase or in the vapor phase is carried out. Figure 3 shows the presence of a layer

  epitaxial 6 on the main face 2 of the substrate 1.

  The thickness of the epitaxial layer 6 may be 50 μm. Liquid phase epitaxy can be made at a temperature of about 9500C for 2 hours. The vapor phase epitaxy can be made around

11000C for 1 hour.

  According to a second example of implementation

  of the invention, the ion implantation of hydrogen is carried out for an energy of 76 keV and a dose of 6.10'6H + / cm 2 through a layer of silicon oxide of 400 nm covering a silicon substrate. A PECVD deposit is then performed to obtain an additional silicon oxide layer 3 μm thick.

  This substrate can then undergo an embrittlement treatment such as annealing at an increasing temperature from 4000.degree. C. to 11000.degree. C., the temperature rise occurring for example at 30.degree. C./min and the treatment time at 11000.degree. . This treatment has the effect of growing the cavities and / or micro-cracks in the implanted area 15 and then stabilize these cavities and / or micro-cracks at high temperature so that it does not change the the surface condition of the substrate during removal of the oxide thick layer or during

  subsequent technological steps.

  The oxidized surface of the substrate is then deoxidized, prior to a technological step of epitaxy in liquid phase or silicon vapor,

  a thickness of between 20 μm and 50 μm.

  According to a third example of implementation of the invention, the implantation of hydrogen is carried out by plasma immersion for an energy of 76 keV and a dose of 6.1016H + / cm 2 through a silicon oxide layer of 400. nm covering a silicon substrate. A PECVD deposit is then made to obtain an additional silicon oxide layer 3 μm thick. This substrate can then undergo an embrittlement treatment such as annealing at an increasing temperature starting from 400.degree. C. to 11000.degree. C., the temperature rise being, for example, 3 OC / min. The oxidized surface of the substrate is then partially deoxidized. The oxide is for example removed on the central part of the substrate but remains on a crown at the edge of the substrate, with a width that may range from a few hundreds of μm to a few mm. A step of liquid phase epitaxy to obtain an epitaxial layer with a thickness of between 20 μm and

pm is then performed.

  FIG. 4 illustrates this third exemplary implementation of the invention. It shows a silicon substrate comprising a buried layer

  embrittled 14, an oxide layer 13 remaining in a ring on the substrate 11 and an epitaxial layer 16 deposited on the portion of the face 2 of the substrate not covered with oxide. It can be seen that on the ring 13 20 the epitaxial recovery was not made.

  According to a fourth example of implementation of the invention, the ion implantation of hydrogen is carried out for an energy of 210 keV and a dose of 7.1016 H + / cm 2 through a layer of silicon oxide of 200 nm covering a silicon substrate. A deposit by PECVD is then performed to obtain an additional layer of silicon oxide

10 μm thick.

  This substrate may then undergo a brittleness annealing at 4500C for 14 hours, followed by

climb at 30C / min to 11000C.

  The oxidized surface of the substrate is then partially deoxidized. The oxide is for example removed on the central part of the substrate but remains on a crown at the edge of the substrate, with a width that can range from a few hundred phm to a few mm. A silicon phase epitaxy step to obtain an epitaxial layer of thickness between

and 50 pm is then performed.

  After this step, the substrate comprises a central portion on which the epitaxial uptake of

  monocrystalline silicon was possible due to deoxidation prior to epitaxy. The substrate also comprises, on its peripheral part, the silicon oxide ring on which the resumption of epitaxy has been carried out in polycrystalline form.

  According to a fifth example of implementation of the invention, the implantation of hydrogen by plasma immersion is carried out for an energy of 76 keV and a dose of 6.1016H + / cm 2 through a silicon oxide layer of 400 nm covering a double-sided polished silicon substrate. The implantation is performed on the two main faces of the substrate. A PECVD oxide deposit of 3 μm is made on this double-sided implanted substrate. This substrate is then subjected to an embrittlement treatment such as annealing at an increasing temperature starting from 400.degree. C. to 11000.degree. C., the temperature rise occurring for example at C / min. The oxidized surfaces of the substrate are then partially deoxidized. In particular, the oxide is removed on a central part of the two

  faces of the substrate but remains on a crown edge of a width that can go from hundreds of jim to a few mm. A liquid phase epitaxy step of thickness between 20 wm and 50 pm is then performed on both sides of the substrate.

  After this step, the substrate comprises a central portion on which the epitaxial recovery has been possible due to the deoxidation prior to epitaxy. The substrate comprises, on the peripheral portion of its faces, the deposited PECVD oxide ring on which the resumption of epitaxy has not been possible. Whatever the implementation of the invention, technological steps for producing components, for example photovoltaic, can be implemented. FIG. 5 shows components 7 made in the epitaxial layer 6 of the substrate represented in FIG. 3. If epitaxy has been carried out on the two main faces of the substrate, components can then be made in both

epitaxial layers.

  The substrate thus treated is then secured by means of a ceramic adhesive 8, for example on a mechanical support 9 such as a ceramic, glass or mullite substrate, as shown in FIG. 6. The insertion in the region of the weakened layer 4 of a suitable tool comprising, for example, a beveled blade will then make it possible to cut at the level of the implanted buried zone, thus separating the processed layer 6 from its initial substrate 1, and leaving it secured to the support substrate 9 The initial substrate 1 can then be recycled again.

substrate to be weakened.

  The processed substrate of the second embodiment of the invention may be secured by means of a polymer adhesive to a mechanical support such as a plastic substrate. Immersion of the bonded structure in a solution, for example of SECCOQ, causes the preferential attack of the polycrystalline silicon, the oxide ring and the embrittled buried zone, which can initiate the separation between the process layer of its initial substrate. The separation can take place entirely according to this chemical route or else be assisted by the application of a mechanical stress or else be relayed by a purely mechanical opening way implementing tension and / or shear stresses. as indicated by the arrows F in FIGS. 6 and 7. The initial substrate can then be

  recycled into new substrate to weaken.

  The processed substrate of the third embodiment of the invention may be secured by means of a polymer adhesive to a mechanical support such as a plastic substrate. The bonded structure can then be immersed in an HF bath. This has the consequence of attacking the peripheral oxide layer present on the weakened processed substrate. Thus, the application of the constraint during the insertion of a blade is better located at the weakened zone. This leads to the separation between the process layer and its initial substrate. The initial substrate can then be recycled to a new substrate

to weaken.

  The processed substrate of the fourth mode of implementation of the invention can be secured by means of a polymer adhesive to a mechanical support such as a plastic substrate. The immersion of the bonded structure in a solution, for example of SECCOC, causes the preferential attack of the polycrystalline silicon, the oxide ring and the embrittled buried zone, which can initiate the separation between the process layer of its initial substrate. The separation can take place entirely according to this chemical route or else be assisted by the application of a mechanical stress or else be relayed by a purely mechanical opening way implementing tension and / or shear stresses. as indicated by the arrows F in FIGS. 6 and 7. The initial substrate may then be recycled to a new substrate to be weakened. The processed substrate of the fifth embodiment of the invention may be secured by means of a polymer adhesive to a mechanical support such as a plastic substrate. The bonded structure is then immersed in an HF bath. This has as consequences

  to attack the peripheral oxide layer present on each of the faces of the weakened substrate processed.

  The application of the constraint during the insertion of a blade will be better located at the level of the weakened zone. This stress will be successively or jointly applied in the region of the weakened layer of one and the other face of the substrate. This leads to the separation between the processed layers and the initial substrate. The initial substrate can then be recycled to a new substrate to be weakened.

Claims (15)

  1. A method of producing a demountable semiconductor substrate, comprising the following steps: introduction of gaseous species into the substrate (1) according to conditions allowing the constitution of a weakened layer (4) by the presence in this layer of micro-cavities and / or microbubbles, a thin layer of semiconductor material being thus delimited between the weakened layer (4) and a face (2) of the substrate, thermal treatment of the substrate to increase the level of embrittlement of the layer Embrittled (4), this heat treatment being conducted until the appearance of local deformations of said face (2) of the substrate (1) in the form of blisters but without generating exfoliations of the thin layer during this step and in the further course of the process, - epitaxial semiconductor material (6) on said substrate side to provide at least one   epitaxially layer on said thin layer.   2. Method according to claim 1, characterized in that the introduction of gaseous species is carried out by ion implantation or implantation. by plasma immersion.   3. Method according to claim 2, characterized in that the introduction of gaseous species being carried out by implantation by plasma immersion,   the process is applied on two sides of the substrate.   4. Method according to claim 1, characterized in that, before the step of heat treatment of the substrate, there is provided a step of forming a thickener whose thickness is sufficiently large not to generate exfoliations in the thin layer and small enough to avoid the separation of the substrate at the weakened layer during the heat treatment step of the substrate. 5. Method according to claim 4, characterized in that the thickener is eliminated   totally or partially before the epitaxial step.   6. Method according to claim 1, characterized in that there is provided an additional step of submitting the epitaxial layer to   at least one step of producing components (7).   7. Method according to claim 6, characterized in that said step of producing components (7) is a step of realizing photovoltaic components.   8. Process according to any one of   preceding claims, characterized in that there is provided an additional step of forming a   protection layer on the epitaxial layer, this protective layer being intended to protect the epitaxial layer with a chemical etching intended for the separation of the substrate at the level of the weakened layer. 9. Process for obtaining a semiconductor material element, characterized in that it comprises the following steps: providing a demountable semiconductor substrate obtained by the process according to any one of the following: Claims 1 to 8,   disassembly of the demountable semiconductor substrate by detachment of this substrate at the level of the embrittled layer, the separation being either total to provide a semiconductor material element forming a membrane and consisting of the thin layer of semiconductor material and the epitaxial layer, or only partially for providing one or more semiconductor material elements forming one or more components and consisting of a portion of the thin layer of semiconductor material and the epitaxial layer. 10. Method according to claim 9, characterized in that there is provided an additional step of fixing the epitaxial layer on   a support before the disassembly step.   11. The method of claim 9, characterized in that the detachment results from the application of a tensile stress and / or a shear stress.   12. Method according to claim 9, characterized in that the detachment results from the implementation of a step of introducing additional gaseous species into the embrittled layer, then a step of mechanical stress and / or treatment thermal weakened layer.   Method according to claim 9, characterized in that the detachment results from the application of an opening constraint at the level of the weakened layer.   Method according to claim 9, characterized in that the detachment results from a   chemical attack of the weakened layer.   15. The method of claim 9, characterized in that the detachment results from an acoustic wave treatment of the embrittled layer.