FR2994615A1 - Method for planarizing epitaxial layer of structure to form photovoltaic cell in e.g. photovoltaic fields, involves removing masking layer to obtain surface of epitaxial layer whose protuberances exhibit height lower than height threshold - Google Patents

Abstract

The method involves providing a structure including an epitaxial layer (2) with a flat reference surface (3). A masking layer (9) is deposited on an exposed surface so as to cover all protuberances (5) and to form an intermediate structure (7). An exposed surface of the intermediate structure is abraded until forming an opening leveled with the masking layer. The leveled epitaxial layer is engraved until reaching the flat surface. The masking layer is removed to obtain an exposed surface of the epitaxial layer whose protuberances exhibit height lower than height threshold (6). The masking layer is deposited by physical vapor deposition or chemical vapor deposition process. An independent claim is also included for a planarization structure.

Description

The present invention relates to a planarization method of an epitaxial layer, in particular of III-V material, for applications in fields such as microelectronics, optronics or photovoltaics. The present invention relates to a planarization structure adapted to the planarization of an epitaxial layer. The layers made of III-V alloy material, such as GaN, InP, GaAs, GaInP, GalnAs, GalnAsP, InGaAs, AlAs, InAs, are conventionally produced by epitaxy using various techniques, such as MBE ( acronym for Molecular Beam Epitaxy), MOCVD (Metal Organic Chemical Vapor Deposition) or MOVPE (acronym for Metal Organic Vapor Phase Epitaxy) from support substrates made of material such as InP, GaAs, sapphire, or silicon. However, these layers or stacks of layers obtained by epitaxy have surface growth defects, and in particular defects of the protuberance or growth type. These defects can laterally reach several micrometers or even several hundred micrometers, for a few nanometers to a few tens of micrometers in height. These defects or protuberances are randomly distributed over the entire surface of the epitaxial layer. Typically, the greater the thickness of the epitaxial layer, the higher the protuberances formed. The presence of these surface defects can limit or even prevent the use of structures with layers of III-V epitaxial materials for certain applications, especially when direct bonding steps, lithography, thin film deposition or other steps for which a substantially planar surface is required. It is not possible to use chemical mechanical polishing (CMP) techniques to eliminate these defects. Indeed, it is known that to planarize surfaces by CMP, it is necessary to remove at least three times the thickness of the protuberances to be smoothed.

Thus for protuberances of the order of 10 micrometers in height, at least 30 micrometers of material should be removed from the layer. However, the epitaxial layer is thin, its thickness is in particular of the order of a few tens of micrometers, or even of a lower thickness. The CMP technique is therefore not usable on these layers, it would in particular remove much too much material.

A purely mechanical thinning technique can be envisaged although the thinning obtained has less than one micrometer or even two micrometers of precision, without reducing the number of protuberances. Thus, all initial protuberances would remain at thinning with a height of 1 to 2 micrometers. But the problem of the density of protuberances (number of protuberances brought to the surface of the epitaxial layer) can be very important: for example, direct bonding is not feasible in the case of a density greater than 1000 protuberances (of height 1 to 2 μm) for a surface with a diameter of 100 mm. Gluing 10 becomes possible for a density of less than 500. One of the aims of the invention is to overcome one or more of these disadvantages. For this purpose and according to a first aspect, the invention relates to a planarization method of an epitaxial layer comprising the steps of: a) providing a structure comprising an epitaxial layer comprising a flat reference surface and one face exposed comprises protuberances having a height greater than or equal to a threshold height with respect to the reference plane surface; b) depositing a masking layer on the exposed face so as to cover all the protuberances and to form an intermediate structure; ) Abrase the exposed surface of the intermediate structure to form an opening through the masking layer at each of the protuberances having a height greater than or equal to the threshold height, d) etching the epitaxial layer at each through aperture the masking layer until reaching the flat reference surface, and e) Remove the masking layer e so as to obtain an exposed face of the epitaxial layer whose protuberances have a height less than the threshold height. Throughout the application, the term "reference plane surface" is understood to mean a surface of the epitaxial layer predominantly present at the desired dimension. Thus, this method makes it possible to eliminate, simply and at low cost, the most troublesome protuberances on the exposed face of the epitaxial layer, that is to say the protuberances whose height is greater than or equal to a threshold height which may interfere with subsequent process steps, without altering the quality of the material, while maintaining the initial thickness or the desired dimension of the epitaxial layer. In contrast to mechanical thinning the removal of the most troublesome protuberances is complete and the density of residual protuberances is thereby reduced. It is important to note that the residual protuberances (of height less than the threshold height) can generate defects in subsequent steps, however, thanks to the invention these defects are less important (in size and density) than 10 in the case where the steps would be applied directly to the epitaxial layers, or even after mechanical thinning treatment. Preferably, the step of depositing the masking layer is obtained by a method of PVD (Physical Vapor Deposition) or CVD (Chemical Vapor Deposition) type, such as PECVD (Plasma Enhanced Chemical Vapor Deposition) or evaporation. . These deposition techniques are inexpensive and allow a good recovery of the protuberances of the epitaxial layer, including the flanks of the protuberances, whatever their shape, vertical, oblique, curved or other. Advantageously, the masking layer is deposited on a thickness less than the threshold height. This thickness is indeed sufficient to effectively hide the surface of the epitaxial layer and all the protuberances. It further limits the cost of the masking layer by the use of a small amount of material. According to one possibility, the step of abrading the exposed surface of the intermediate structure is obtained by mechanical thinning, such as by grinding (or grinding in English). For example, a grinding wheel having teeth of different grain sizes flushes the exposed face of the intermediate structure which is also maintained by suction on a support (by a chuck in English). This method provides good control over the uniformity and thickness removed to achieve the desired threshold height. Preferably, the material of the masking layer is chosen such that its mechanical hardness is similar to that of the material of the epitaxial layer so as to promote a homogeneous mechanical thinning of the exposed face of the intermediate structure. Indeed, if the hardness of the material of the masking layer is equivalent to that of the material of the protuberances, the speed of the thinning will be similar at any point on the surface, whether it consists of the masking layer and / or protuberances.

According to one possibility, the threshold height is one micrometer and preferably 0.5 micrometer. The protuberances less than 1 or even 0.5 micrometer are indeed not a problem for the rest of the process. Thus, the grinding technique allowing thinning to less than one micrometer, or even 0.5 micrometers accuracy is quite suitable for the desired threshold height. Advantageously, the step of etching the epitaxial layer is obtained by selective etching and preferably by selective anisotropic etching. The masking layer therefore remains inert to etching and the anisotropy of the etching makes it possible to etch more rapidly the planes parallel to the surface of the epitaxial layer than the perpendicular planes. Etching with different peaks of depth is avoided. The protuberances are etched to a substantially smooth surface at the depth of the reference plane surface. This favors the estimation of the etching time and the precise control of the etched thickness to reach the reference plane surface. According to one possibility, the selective etching of the epitaxial layer is carried out chemically or by dry route, such as RIE (English Reactive Ion Etching means reactive ion etching). Advantageously, the step of removing the masking layer is obtained by selective etching, dry or wet, so as not to damage the material of the epitaxial layer and maintain the flatness obtained in step d) . According to one possibility, the method comprises, after step e), a step f) of performing a chemical-mechanical polishing CMP of the exposed face 30 so as to planarize the protuberances of height less than the threshold height. According to a particular configuration, the process comprises, after step e) a step g) consisting in performing an implantation of ionic species in the epitaxial layer so as to form an embrittlement zone delimiting a thin layer and a step h) carrying out a transfer of the thin layer onto a final support substrate. Thus, when, for example, the material of the transferred thin film is GaN and the final silicon support substrate, a structure adapted for applications in various fields such as power and optoelectronics is obtained. According to another configuration, step a) consists in providing a structure comprising at least one epitaxial layer on a support substrate and in that the method comprises, after step e), a step i) consisting in bonding the exposed face on a final support substrate via at least one metal layer and a step j) of removing the support substrate.

It is thus possible to produce a structure for a future device, comprising several epitaxial layers and adapted according to the materials used for photovoltaic applications. According to one particular arrangement, the structure comprises a stack of one or more epitaxial layers on a support substrate, preferably formed from a material chosen from binary, ternary or quaternary alloys of elements of columns III and V, such as the GaN, InP, GaAs, GaInP, GalnAs, GalnAsP, InGaAs, AlAs, InAs. According to a second aspect, the subject of the invention is a planarization structure comprising an epitaxial layer of a III-V material on a support substrate, the epitaxial layer comprising a reference plane surface and an exposed face comprising protuberances having a height less than or equal to a threshold height with respect to the reference plane surface, and a masking layer deposited on the exposed face and covering the protuberances, the masking layer having through windows at the apex of the protuberances of height equal to the threshold height. so that the top of these protuberances is exposed. This structure advantageously makes it possible to eliminate the protuberances of a threshold height determined by a selective etching of the material of the epitaxial layer. The removal of the masking layer then makes it possible to recover an epitaxial layer having protuberances below the threshold height so that it can be used in other process steps. Other aspects, objects and advantages of the present invention will appear better on reading the following description of an embodiment thereof, given by way of nonlimiting example and with reference to the accompanying drawings. The figures do not necessarily respect the scale of all the elements represented so as to improve their readability.

In the remainder of the description, for the sake of simplification, identical, similar or equivalent elements of the various embodiments bear the same numerical references. Figures 1 to 5 are an illustration of the block diagram of the method according to one embodiment of the invention. FIGS. 6 to 9 are a schematic illustration of steps subsequent to the method for the preparation of a structure adapted to different applications according to one embodiment of the invention. FIGS. 10 to 15 illustrate an alternative embodiment of the method and steps for preparing a photovoltaic device structure according to one embodiment of the invention. FIG. 1 (step a) illustrates a structure 1 comprising an epitaxial layer 2 on a support substrate 10. The epitaxial layer 2 consists of an alloy of elements III-V and comprises a flat surface of reference 3 at one side desired. The epitaxial layer 2 also has an exposed face 4 having epitaxial defects such as protuberances 5 which can reach a height of up to several tens of micrometers with respect to the reference plane surface 3. From a height 6 threshold of the order of 1 or 0.5 micrometer (symbolized by the dashed lines in Figure 1), these protuberances 5 become particularly troublesome for the achievement of subsequent steps, such as the deposition of thin layers or the direct bonding for example, for the preparation of structures for devices, especially when their density is important. FIG. 2 illustrates an intermediate structure 7 formed in step b) 25 by the deposition of a masking layer 9 covering the exposed face 4 of the epitaxial layer 2 and all its protuberances 5. Among the possible deposition methods, the PVD (acronym for Physical Vapor Deposition) and CVD (Chemical Vapor Deposition) such as PECVD (Plasma Enhanced Chemical Vapor Deposition) are the preferred methods because of their low cost and their ability to covering the exposed face 4 of the epitaxial layer 2, all the protuberances 5 and their flanks 8. The deposition parameters are adjusted so that the masking layer 9 formed has a relatively homogeneous thickness, especially on the topology, and less than the threshold height 6. In addition to its inertia in the etching of III-V materials, the masking layer 9 is preferably chosen from a material having the my mechanical hardness than the III-V material of the epitaxial layer 2. This provides the same vis-à-vis the mechanical thinning resistance. The mechanical hardness of III-V materials are well referenced in the prior art. For example, according to the website http://www.ioffe.ru/SVA/NSM/ 5 'accessed on 15/06/2012, for an epitaxial layer material 2 of low hardness, such as InP, InAs or InSb, the masking layer 9 is advantageously formed from amorphous Si or from polymer resins. For a material of higher hardness, such as GaAs or GaN, the suitable masking layer materials 9 are selected from 5iO 2, SiN, AlN or Ni. FIG. 3 illustrates step c) of the method of abrading the exposed surface of the intermediate structure 7 to form an opening 11 through the masking layer 9 at each of the protuberances 5 whose height is greater than or equal to at the threshold height 6. This abrasion is achieved by mechanical thinning such as by grinding. According to a possibility not shown, the grinding is obtained by means of a grinding wheel whose teeth can be of different grain sizes. The intermediate structure 7 is held on a suction support (chuck in English) of its entire surface so that it can easily control uniformity and height during thinning. The TTV (acronym for Total Thickness Variation) impacted by the rectification is less than about one micrometer and the thickness control is performed at plus or minus 0.5 micrometer. According to one possibility, the abrasion is carried out until the residual height of the intermediate structure 7 is equal to the threshold height 6. As a result, the protuberances 5 whose height is greater than the threshold height 6 are reduced. and the protuberances 5 whose height is equal to the threshold height 6 have their vertex at the surface exposed at the end abrasion. At the same time, a through opening 11 has been formed in the masking layer 9 at these protuberances 5. On the other hand, the masking layer 9 has not been opened at the level of the protuberances 5 whose height is less than at the threshold height 6. According to an arrangement that is not illustrated, the height control is carried out by means of mechanical comparators installed in the abrasion device which make it possible, during thinning, to know the residual height of the intermediate structure 7 relative to the plane reference surface 3. FIG. 4 illustrates step d) of the method which selectively and anisotropically etches the material of the protuberances 5 from the openings 11 formed in the masking layer 9. etching of the defects can be carried out chemically or by dry route (for example by RIE - Reactive Ion Etching in English) until reaching the flat reference surface 3. The etching time is measured according to the etching agent used and the etched material. For InP and GaAs-based materials, etching solutions are well known and referenced in the literature. Some examples are shown in Table 1 below. Table 1 (1) (2): Engraving agent HC1: H3P01: H2801 C, 40-HCl: 03: H C'1: HCl: H20 BHF 1-1202 :: F120 2: E1202 HNo, H2SO4 H202 :: H20 H20 .H20 .H20 .1-120 H "Material 1-1, POI GaAs SGG DC GGGS InP GSSSGGG InGaAs SGG DC S InGaAsP SG GaInP GS GaAsP GG AlGaP G AlGaAs DC DC AllnP GGG InAlAs DC DC InGaAlAs DC S 02 GS: the material allows to stop the etching, G: the material is etched, DC: the behavior is dependent on the composition of the etching agent. 15 (2) This information is extracted from a website accessed on 13/01/2012 at: tittp: //terpconnect.umd.edu/-browns/wetetch.html 'and which reports the results mentioned in several published articles, notably from the journal J. Electrochem. Soc. According to one possibility not illustrated, the GaN etching can be carried out by reactive ion etching (RIE) or by etching using an ICP RIE (Inductively Coupled Plasma Reactive Lonic Etching) plasma torch which increases the etching rate. using chlorine gases, such as BCI3 or SiCl4. (See Reactive Ion Etching of GaN using BCI3C by ML.E. Lin et al., published in Appl., Phys., Lett., 64 (7), 14 February 1994, p 887-888 and Advanced in GaN Dry Etching. Process Capabilities' by Mr De Vre et al Unaxis USA, Inc., Nextral (Available at: http://www.plasmatherm.com/ in the R & D section, technical papers - accessed on 13/08/2012) Moreover, the masking layer 9 covering the flanks 8 of the protuberances, the etching by the flanks 8 is avoided, which makes it possible to precisely control the etched thickness According to a possibility not illustrated, the etching can be continued slightly beyond of the flat surface of reference 3 without affecting the interest of the epitaxial layer 2 thus planarized.In fact, the depressions (or unevenness) formed by a slight over-etching generate defects of smaller sizes than the defects resulting from protuberances 5 in subsequent steps, such as the bonding or adhesion of a deposited layer. This can be explained by the rigidity of the backplate bonded to the planarized surface or the compliance of the deposit technique used. Moreover, because of their reduced sizes, the impact of the defects generated by the depressions is much smaller in the subsequent manufacture of devices.

FIG. 5 illustrates the step e) of removing the masking layer 9 by selective etching without altering the underlying material of the epitaxial layer 2. This etching is carried out for example by selective dry etching or by means of solutions Well-known chemical such as dilute hydrofluoric acid solution for a 5iO 2 masking material, or TMAH (Tetramethylammonium hydroxide) for silicon. Thus, the protuberances 5 of the epitaxial layer 2 whose initial height was greater than or equal to the threshold height 6 have been totally eliminated, thus reducing the density of residual protuberances. The planarized exposed face 4 thus has protuberances 5 lower than the threshold height 6 in low density so as not to hinder the achievement of subsequent steps involved in the manufacture of devices. A detailed example of embodiment of the process is now described with reference to FIGS. 1 to 9. The GaN epitaxial layer 2 is deposited by MOVPE (acronym for Metal Organic Vapor Phase Epitaxy) on a sapphire support substrate 10 (FIG. step a). The layer 2 has a thickness of about ten micrometers. GaN formed is n-type because of the doping presence with a proportion of 1-3.1018 Si / cm3. GaN has a crystalline structure of wurzite type, the axis c of which is normal to the plane or to the plane plane of reference 3 of the epitaxial layer 2.

The layer 2 of GaN thus formed has on the surface steps of a height of 1 to 1.5 microns, due to epitaxial growth, and round or hexagonal growth defects, with a lateral dimension varying from a few tens of times. micrometers to 1 mm, and a height of the order of a few hundred nm. These protuberances 5 make it impossible to directly bond the layer 2. As illustrated in FIG. 2 (step b), a nickel masking layer 9 is then formed by PVD with a thickness of about 100 nm on the exposed face 4 of the GaN so as to prepare an intermediate structure 7 of which all the protuberances 5 are covered.

According to step c) of the method illustrated in FIG. 3, the grinding step is carried out on the exposed surface of the intermediate structure 7 until reaching a threshold height 6 of 0.5 micrometer above the flat surface. reference number 3 GaN. Through-openings 11 in the nickel layer 9 are thus formed at the level of the GaN protuberances 5 of a height greater than or equal to 0.5 micrometer. FIG. 4 illustrates the step d) of the method consisting in performing RIE etching of the GaN growth defects at the openings 11 in the masking layer 9. The precise conditions of the etching are described in the article Reactive Ion Etching of GaN using BCI3 C from ML.E. Lin et al. appeared in Appl. Phys. Lett. 64 (7), 14 February 1994, pp 887-888. After removing the GaN protuberances with an initial height greater than or equal to 0.5 micrometer, the nickel masking layer 9 is removed by an organic solvent solution (such as ethylene glycol dimethyl ether or dimethoxyethane DME) containing HF. (step e) - Figure 5). The exposed face 4 of the GaN layer 2 and thus planarized is then covered with a bonding layer 12 in 5iO 2 deposited on a thickness of 10 nanometers which reproduces the defects 5 without preventing the bonding (Figure 6). In the worst case, this extra thickness generates a local defect at the bonding interface. The coated layer 2 is then implanted with ionic species based on H + with an energy of 60keV and a dose of 3.5E17 H / cm 2 (Figure 7- step g)). The implantation generates a weakening zone 13 delimiting a thin layer 14 within the GaN layer. The implanted structure is then cleaned by a series of Caro / SC1 / Scrubber type cleaning steps.

As illustrated in FIG. 8, the GaN face coated with the SiO 2 bonding layer 12 is then glued by direct bonding to a silicon final support substrate 15 having been previously cleaned in the same steps. The defects resulting from the residual protuberances 5 are very thin compared to the scale of the gluing so that they are not illustrated in the diagrams for the sake of clarity. Heat treatment leads to the fracture at the embrittlement zone 13 so that a thin film 14 or GaN film with a thickness of the order of 480 nm is transferred onto the final Si substrate 15 (FIG. step h)). According to one possibility not illustrated, light polishing and / or annealing at high temperature (in the range of 800 ° C to 1000 ° C) can then be applied to eliminate any defects in the fractured surface. The residual protuberances, of height less than the threshold height and in low density, may possibly generate gluing and transfer defects, but the invention makes it possible to make the gluing and the transfer possible on the majority of the GaN surface while limiting the size and density of the defects. This gives a final structure 16 composed of GaN / 5iO 2 / Si that can be used for various applications, particularly in areas such as power or optoelectronics. A second exemplary embodiment is now described in detail with reference to FIGS. 10 to 15 for the preparation of a structure 17 adapted to the formation of a photovoltaic cell. The support substrate 10 is, for example, of n-type solid GaAs (doped with silicon in a range of 1-2E18 Si / cm 3). It is placed in an epitaxy reactor type MOCVD (Metal Organic Chemical Vapor Deposition). A stack of layers 2 of III-V materials is epitaxially grown on its surface, the stack consists of layers 2 of the following materials: layer of (A1) GaInP 2a (pn junction for a sub-cell 1 in English csubcell 1 ') / Ga (ln) As layer 2b (pn junction for subcell 2) / GalnAs 2c layer (pn junction for subcell 3) (Figure 10, step a). With reference to FIG. 11 (step b), a 5iO 2 masking layer 9 is deposited by PECVD to a thickness of 200 nm so that all the asperities of the exposed face 4 of the GalnAs layer 2c are covered. The SiO 2 layer is then densified by annealing at 500 ° C for 2h. With reference to FIG. 12 (step c), the abrasion is achieved by grinding (first coarse and then finishing) to a threshold height 6 of 1 micrometer above the plane reference surface 3 of FIG. the layer of GalnAs 2c. Thus, the protuberances 5 of initial height greater than 1 micrometer are decreased to a height of 1 micrometer, and the masking layer 9 of SiO 2 is open at these protuberances 5.

In addition, the protuberances 5 of initial height equal to 1 micrometer are not decreased, against the layer 9 of SiO 2 is also open at these protuberances 5. The protuberances 5 of initial height less than 1 micrometer are not decreased and the layer 9 of SiO 2 completely covers them.

With reference to FIG. 13 (step d)), the etching of the protuberances 5 of the GalnAs 2c layer is carried out by selective etching under the following conditions: H 3 PO 4: H 2 O 2: H 2 O in the proportions 1: 1: 38. The etching rate of GalnAs is -0.10 micrometre / minute. The etching is therefore carried out for 20 minutes so as to completely etch the protuberances 5 whose initial height was greater than or equal to 1 micrometer. The duration of the etching may vary according to the proportions of reagents used. The SiO 2 layer 9 is then removed by selective wet etching in a 10% dilute HF solution for 10 min.

The exposed face of the GalnAs 2c layer is thus planarized: all the protuberances 5 of initial height greater than or equal to 1 micrometer have been entirely eliminated and the residual protuberances have a height of less than 1 micrometer and a reduced density so that limit their impact when carrying out subsequent steps.

After cleaning with a solution of (NH4) 2S for 40 minutes and then rinsing and drying the resulting structure, a metallic deposit is then made on the surface of the planarized GalnAs 2c layer, so as to form the next stack 18: Ti 50nm / Pt 200nm / Au 1 micrometer. The same deposit is made on a final silicon support substrate after cleaning with a 1% dilute HF solution for 1 minute. The two surfaces covered with the stack 18 of Ti / Pt / Au are then glued by thermo-compression at 250 ° C. under a pressure of 30KN applied for 30 minutes (step i - FIG. 14). On the scale of the bonding, the extra thicknesses are minute and are not represented at layers 18. The residual protuberances 5 having a thickness less than the total thickness of the deposited stack and a low density, the bonding is obtained without macroscopic defect (observable by acoustic microscopy for example). Finally, according to step j) (FIG. 15), the initial GaAs support substrate 10 is removed by chemical etching in a phosphoric acid solution H 3 PO 4: H 2 O 2: H 2 O to expose the (A1) GaInP 2a layer and to release the junction of the sub-cell 1. The final structure 17 obtained corresponds to a photovoltaic cell concentration type "inverted metamorphic multijunction" on which it remains to achieve the front and rear face contacts. Thus, the present invention proposes a planarization process protuberances 5 present on the surface of epitaxial layers 2, in particular III-V material, which is simple to implement, applicable to many materials, and inexpensive. This method makes it possible to obtain exposed faces that are sufficiently flat to be easily used later in device manufacturing steps such as gluing, lithography or film deposition. It goes without saying that the invention is not limited to the embodiment described above by way of example but that it includes all the technical equivalents and variants of the means described as well as their combinations.

Claims (12)

REVENDICATIONS1. A planarization method of an epitaxial layer (2) comprising the steps of: a) providing a structure (1) comprising an epitaxial layer (2) having a planar reference surface (3) and an exposed face (4) comprising protuberances (5) having a height greater than or equal to a threshold height (6) with respect to the reference plane surface (3), b) depositing a masking layer (9) on the exposed face (4) so as to cover all the protuberances (5) and form an intermediate structure (7), (c) abrade the exposed surface of the intermediate structure (7) to form an opening (11) passing through the masking layer (9) at the level of each of the protuberances (5) having a height greater than or equal to the threshold height (6), d) engraving the epitaxial layer (2) at each opening (11) passing through the masking layer (9) until it reaches the reference flat surface (3), and e) Remove the layer for masking (9) so as to obtain an exposed face (4) of the epitaxial layer (2) whose protuberances (5) have a height less than the threshold height (6). 2. Method according to claim 1, characterized in that the step of depositing the masking layer (9) is obtained by a method 25 of PVD or CVD type. 3. Method according to one of claims 1 to 2, characterized in that the masking layer (9) is deposited on a thickness less than the threshold height (6). 30 4. Method according to one of claims 1 to 3, characterized in that the step of abrading the exposed surface of the intermediate structure (7) is obtained by mechanical thinning, such as by grinding. 35 5. Method according to one of claims 1 to 4, characterized in that the material of the masking layer (9) is selected such that its mechanical hardness is similar to that of the material of the epitaxial layer (2). 6. Method according to one of claims 1 to 5, characterized in that the threshold height (6) is 1 micrometer and preferably 0.5 micrometer. 7. Method according to one of claims 1 to 6, characterized in that the step of etching the epitaxial layer (2) is obtained by selective etching and preferably by selective anisotropic etching. 8. Method according to one of claims 1 to 7, characterized in that the step of removing the masking layer (9) is obtained by selective etching dry or wet. 9. Method according to one of claims 1 to 8, characterized in that the method comprises, after step e) a step g) of performing an implantation of ionic species in the epitaxial layer (2) so as to Forming an embrittlement zone (13) delimiting a thin layer (14) and a step h) of transferring the thin layer (14) to a final support substrate (15). 10. Method according to one of claims 1 to 8, characterized in that step a) consists in providing a structure (1) comprising at least one epitaxial layer (2) on a support substrate (10) and in that that the method comprises, after step e) a step i) of bonding the exposed face (4) to a final support substrate (15) via at least one metal layer and a step ) comprising removing the support substrate (10). 11. Method according to one of claims 1 to 10, characterized in that the structure (1) comprises a stack (18) of one or more epitaxial layers (2) on a support substrate (10), preferably formed in 35 a material selected from binary, ternary, or quaternary alloys of elements of columns III and V, such as GaN, InP, GaAs, GaInP, GalnAs, GalnAsP, InGaAs, AlAs or InAs. 12. Planarization structure comprising an epitaxial layer (2) of a III-V material on a support substrate (10), the epitaxial layer (2) having a reference surface (3) and an exposed face (4) 5 comprising protuberances (5) having a height less than or equal to a threshold height (6) with respect to the reference plane surface (3), and a masking layer (9) deposited on the exposed face (4) and covering the protuberances (5), the masking layer (9) having apertures (11) passing through the top of the protuberances (5) of height equal to the threshold height (6) so that the apex of these protuberances (5) is exposed .