US20110127581A1 - Heterostructure for electronic power components, optoelectronic or photovoltaic components - Google Patents

Abstract

The present invention relates to a support for the epitaxy of a layer of a material of composition Al_xIn_yGa_(1-x-y)N, where 0≦x≦1, 0≦y≦1 and x+y≦1, having successively from its base to its surface; a support substrate, a bonding layer, a monocrystalline seed layer for the epitaxial growth of the layer of material Al_xIn_yGa_(1-x-y)N. The support substrate is made of a material that presents an electrical resistivity of less than 10⁻³ohm·cm and a thermal conductivity of greater than 100 W·m⁻¹·K⁻¹. The seed layer is in a material of the composition Al_xIn_yGa_(1-x-y)N, where 0≦x≦1, 0≦y≦1 and x+y≦1. The seed and bonding layers provide a specific contact resistance that is less than or equal to 0.1 ohm·cm⁻², and the materials of the support substrate, the bonding layer and the seed layer are refractory at a temperature of greater than 750° C. or even greater than 1000° C. The invention also relates to methods for manufacturing the support.

Description

FIELD OF THE INVENTION
• The present invention relates to a support for producing a heterostructure for the manufacture of electronic power components, optoelectronic components, or photovoltaic components having a support substrate, a bonding layer, a crack-free monocrystalline layer, known as the “active layer” of a material with a composition of Al_xIn_yGa_(1-x-y)N, where 0≦x≦1, 0≦y≦1 and x+y≦1, presents a thickness of between 3 and 100 micrometers, in which or upon which the power components can be manufactured, and the methods of forming such heterostructures with or without components.
BACKGROUND OF THE INVENTION
• For the vertical or planar electronic power device (MOS components, bipolar transistors, J-FET, MISFET, Schottky or PIN diodes, thyristors), optoelectronic component (Laser, LED) and photovoltaic component (solar cells) market, it is interesting to utilize an Al_xIn_yGa_(1-x-y)N (where x is equal to or between 0 and 1, y is equal to or between 0 and 1, where x+y is less than or equal to 1) conducting substrate and preferably a bulk GaN (or “freestanding”) substrate. These substrates are, however, difficult to manufacture with current technologies and remain very expensive.
• A proposed alternative consists of a heterostructure comprising a thick active layer of Al_xIn_yGa_(1-x-y)N (preferably in doped GaN) formed on a conductive substrate. But the growth of thick layers with a good crystalline quality is still difficult with current methods if the seed substrate is not of the same material as the material epitaxied.
• The epitaxy of a thick layer of GaN (approximately 10 micrometers) on a seed substrate such as doped Si or SiC, due to the differences in the coefficient of thermal expansion (CTE) and lattice parameter between the materials, leads to the formation of defects and cracks in the layer which reduces the effectiveness of the electronic, optical or optoelectronic devices formed on this material.
• In addition, as document WO 01/95380 discloses, this epitaxy necessitates the utilization of a buffer layer—for example a layer of AlN—between the seed substrate and the GaN that presents high electric resistance. The epitaxy of a thick layer of GaN on a sapphire substrate followed by the transfer of the layer to a conductive substrate by laser detachment is an expensive process. In addition, the choice of these materials does not allow a dislocation density of less than 10⁷cm⁻²to be reached in the active layer.
• In addition, the layer thus formed presents very significant bending which necessitates long preparation steps (polishing, etc.) so that it may be bonded and transferred to a final substrate.
• In addition, the transfer of a layer of GaN from a bulk substrate by the Smart Cut™ technology does not enable the desired thicknesses to be reached in a satisfactory manner to date.
• Document US 2008/0169483 describes the formation of an epitaxy substrate comprising a seed layer of GaN transferred by the Smart Cut™ technology to a support substrate. A layer of conductive GaN is then deposited on the seed layer and then it is transferred to a thermally and electrically conductive support. This method is complex since it involves two transfers of the active layer of GaN to form the final conductive structure.
• Therefore one seeks to design a heterostructure for electronic power components, optoelectronic components or photovoltaic components and a method of manufacturing the heterostructure in view of obtaining a thick, crack-free monocrystalline layer of a material of composition Al_xIn_yGa_(1-x-y)N on a support substrate, not presenting the disadvantages of methods from the prior art.
• More precisely, the heterostructure must present the following properties:
• a thick active layer, i.e., with a thickness greater than or equal to 3 micrometers, preferably greater than 10 micrometers,
• an active layer comprising a main portion with a thickness representing between 70 and 100% of the thickness of the active layer, the main portion being weakly doped so as to enable a dispersion of the electric field over the thickness of the active layer,
• a high thermal conductivity of the heterostructure, i.e., typically greater than or equal to 100 W/m·K (also written as W·m⁻¹·K⁻¹), and
• a low dislocation density in the active layer, i.e., of less than or equal to 10⁷cm⁻².
• Thus, there is a need for a support adapted for epitaxy of the active layer in view of forming the heterostructure described above. More precisely, this epitaxy support must enable growth of the thick active layer without forming cracks and must in addition present electric properties compatible with the intended applications. Such a support is now provided by the present invention.
SUMMARY OF THE INVENTION
• The support of the present invention enables and facilitates the epitaxial growth of an active layer of a material that has a composition of Al_xIn_yGa_(1-x-y)N, where 0≦x≦1, 0≦y≦1 and x+y≦1. The heterostructure formed by growing such an active layer on the support substrate represents an embodiment of the invention as do the methods for manufacturing the support(s) and heterostructure(s).
• The support generally comprises a support substrate and a bonding layer formed on the support substrate; a monocrystalline seed layer on the bonding layer, wherein the seed layer is for the epitaxial growth of an active layer of composition Al_xIn_yGa_(1-x-y)N, where 0≦x≦1, 0≦y≦1 and x+y≦1. In a preferred embodiment of the invention, the seed layer can also be a material of the composition Al_xIn_yGa_(1-x-y)N, where 0≦x≦1, 0≦y≦1 and x+y≦1. The support substrate advantageously has an electrical resistivity of less than 10⁻³ohm·cm and a thermal conductivity of greater than 100 W·m⁻¹·K⁻¹, and provides a specific contact resistance between the seed layer and the bonding layer that is less than or equal to 0.1 ohm·cm⁻². The seed layer can be doped with a concentration of dopants of between 10¹⁷and 10²⁰cm⁻³, wherein the dopants can be n type dopants. The bonding layer is typically a material having an electrical resistivity of less than or equal to 10⁻⁴ohm·cm, and the seed layer on the support substrate has an electrical resistivity of between 10⁻³and 0.1 ohm·cm.
• The materials of the support substrate, the bonding layer and the seed layer can preferably be refractory at a temperature of greater than 750° C., or more preferably the support substrate, bonding layer and seed layer are refractory at a temperature of greater than 1000° C. The material of the support substrate is preferably refractory metal chosen from the group consisting of tungsten, molybdenum, niobium or tantalum and their binary, ternary or quaternary alloys, wherein the preferred metal alloys are TaW, MoW, MoTa, MoNb, WNb or TaNb. In a preferred embodiment, the support substrate is a TaW alloy comprising at least 45% tungsten or a MoTa alloy comprising more than 65% molybdenum.
• The material of the bonding layer can comprise polycrystalline silicon, a silicide, a refractory metal, a metal boride, zinc oxide, or indium tin oxide, wherein the silicide is preferably tungsten silicide or molybdenum silicide; the refractory metal is preferably tungsten or molybdenum; and the metal boride is preferably zirconium boride, tungsten boride, titanium boride or chromium boride.
• Another aspect of the invention relates to the heterostructure for the manufacture of electronic power components, optoelectronic components or photovoltaic components comprising a support as described herein; and an active layer epitaxially grown on the seed layer made of a material characterized by having a composition of AlxInyGa_(1-x-y)N, where 0≦x≦1, 0≦y≦1 and x+y≦1. The active layer can also have a thickness of between 3 and 100 micrometers (μm).
• The seed layer and the active layer are made of materials that provide a difference in lattice parameter of less than 0.005 Å. The active layer comprises a main portion in which the thickness represents between 70 and 100% of the thickness of the active layer; and in which the concentration of dopants is less than or equal to 10¹⁷cm⁻³.
• The CTE of the support substrate material is between a minimum value that is less than 0.5·10⁻⁶K⁻¹below the CTE of the material of the main portion of the active layer and a maximum value that is no more than 0.6·10⁻⁶K⁻¹above the CTE of the material of the main portion of the active layer at the temperatures used for epitaxially forming the active layer. Thus, crack-free active layers can be obtained.
• The active layer has a dislocation density of less than 10⁸cm⁻², or more preferably the active layer has a dislocation density of less than 10⁷cm⁻².
• The main portion of the active layer is inserted between a subjacent portion and a superjacent portion, and wherein the subjacent and superjacent portions each comprise a concentration of dopants greater than 10¹⁷cm⁻³that is of a different type than the active layer. The material of the main portion, the subjacent portion and the superjacent portion can be GaN. When the main portion of the active layer is inserted between a subjacent portion and a superjacent portion, the material of the main portion can be of a different Al_xIn_yGa_(1-x-y)N composition than the subjacent portion and the superjacent portion of the active layer. The thickness of the main portion can represent 100% of the thickness of the active layer, and the material of the main portion can be of doped n type GaN. The n type GaN of the main portion is preferably silicon doped GaN.
• The main portion of the active layer and the seed layer can be comprised of the same material. In a particular embodiment, the support substrate is in molybdenum, the bonding layer is tungsten, the seed layer is GaN and the active layer is GaN.
• The invention also relates to an electronic power, optoelectronic or photovoltaic component formed in or on the active layer of the heterostructure described above, and comprising at least one electrical contact on the active layer and one electrical contact on the support substrate.
• The present invention also related to the method of manufacturing a support for the epitaxy of a layer of material which comprises forming a bonding layer upon a donor substrate or a support substrate; bonding the donor substrate to the support substrate such that the bonding layer is situated at the interface of the substrates; and removing a portion of the donor substrate to leave a seed layer on the support substrate for epitaxial growth of an active layer, wherein the donor substrate, the support substrate and the bonding layer are refractory materials at a temperature greater than 750° C. The material of the support substrate is preferably a metal chosen from among tungsten, molybdenum, niobium and/or tantalum and their binary, ternary or quaternary alloys, such as TaW, MoW, MoTa, MoNb, WNb or TaNb.
• The support substrate is generally bonded to the donor substrate at the bonding layer(s) by molecular adhesion. The seed layer is a monocrystalline material layer adapted for the epitaxial growth of a material of composition Al_xIn_yGa_(1-x-y)N, where 0≦x≦1, 0≦y≦1 and x+y≦1.
• The materials of the support substrate, the seed layer and the bonding layer are chosen such that the specific contact resistance between the seed layer and the bonding layer is less than or equal to 0.1 ohm·cm⁻². The support substrate desirably has an electrical resistivity of less than 10⁻³ohm·cm⁻¹and a thermal conductivity of greater than 100 W·m⁻¹·K⁻¹. The seed layer can be doped by implantation or diffusion of a dopant species.
• The method can further comprise implanting ions into the donor substrate to form an embrittlement zone at a depth that is substantially equal to the thickness of the seed layer to be left on the support substrate after removing the portion of the donor substrate. The method can also be characterized in that the implantation step is carried out after the formation of the bonding layer on the donor substrate, such that the implantation is carried out through the bonding layer.
• The method can further comprise measuring the surface roughness of the donor substrate and support substrate; and depositing a bonding layer on the surface of either or both substrates that have a roughness greater than 1 nm for a 5 micrometer×5 micrometer surface measured by AFM and a peak valley surface topology of greater than or equal to 10 nm, wherein the bonding layer is deposited on the surfaces having a roughness greater than 1 nm for a 5 micrometer×5 micrometer surface measured by AFM and a peak valley surface topology of greater than or equal to 10 nm; and polished until a roughness of less than 1 nm and a peak valley surface topology of less than 10 nm is reached.
• The method can further comprise epitaxially growing an active layer on the seed layer to a thickness of between 3 and 100 micrometers without cracking to form a heterostructure.
• The method also comprises providing the active layer with a main portion whose thickness represents between 70 and 100% of the thickness of the active layer and whose concentration of dopants is less than or equal to 10¹⁷cm⁻³; and providing the material of the seed layer to present a lattice parameter difference with the material of the main portion of the active layer of less than 0.005 Å. The active layer is preferably a monocrystal line layer, and has a composition of Al_xIn_yGa_(1-x-y)N, where 0≦x≦1, 0≦y≦1 and x+y≦1.
• The method can further comprise choosing the material of the support substrate such that the CTE of the support substrate material is between a minimum value that is less than 0.5·10⁻⁶K⁻¹below the CTE of the material of the main portion of the active layer and a maximum value that is no more than 0.6·10⁻⁶K⁻¹above the CTE of the material of the main portion of the active layer at the temperatures used for epitaxially forming the active layer.
• The method can further comprise doping of the active layer, wherein the doping is carried out either during or after epitaxial growth by implantation or diffusion of dopant species.
BRIEF DESCRIPTION OF THE DRAWINGS
• Further features of this invention, its nature and various advantages will become more apparent upon consideration of the following detailed description, taken in conjunction with the accompanying drawings, in which like reference characters refer to like parts throughout, and in which:
• FIG. 1 illustrates a heterostructure in conformance with the invention,
• FIG. 2 schematically illustrates the formation of the seed layer in the donor substrate,
• FIG. 3 illustrates the formation of a bonding layer on the support substrate,
• FIG. 4 illustrates the assembly of the donor substrate on the support substrate before the fracture,
• FIG. 5 illustrates the structure resulting from the fracture of the donor substrate,
• FIG. 6 illustrates another example of a heterostructure in conformance with the invention,
• FIG. 7 illustrates an example of an electronic power component formed on a heterostructure in conformance with the invention.
• It is specified that, for reasons of figure readability, the relative sizes and scales of the thickness and features of the different layers have not been respected.
DETAILED DESCRIPTION OF THE INVENTION
• In the present text, “layer portion” is understood to refer to a part of a layer considered in the sense of the thickness of the layer. Thus, a layer may be constituted of several stacked portions, the sum of the thicknesses of portions being equal to the total thickness of the layer. The different portions of the active layer may be in the same material, but with different doping, or rather may be in different materials of composition Al_xIn_yGa_(1-x-y)N, where 0≦x≦1, 0≦y≦1 and x+y≦1. Thus, the active layer of a PIN diode may be designed with alternating InGaN/GaN/InGaN or doped p GaN/weakly doped GaN/doped n GaN layers. The active layer for optoelectronic or photovoltaic components may be constituted of a stack of layers in different materials of composition Al_xIn_yGa_(1-x-y)N, where 0≦x≦1, 0≦y≦1 and x+y≦1.
• In addition, “subjacent” designates a layer portion the farthest removed from the surface of the heterostructure and “superjacent” designates a layer portion closest to the surface of the heterostructure. By way of example, the active layer of a PIN diode comprises a single subjacent and superjacent layer on both sides of the main portion.
• The present invention, according to a first aspect, relates to a support for the epitaxy of a layer of a material of composition Al_xIn_yGa_(1-x-y)N, where 0≦x≦1, 0≦y≦1 and x+y≦1, characterized in that it comprises, successively from its base to its surface; a support substrate, a bonding layer, a monocrystalline seed layer for the epitaxial growth of the layer of material Al_xIn_yGa_(1-x-y)N, and in that, the material of the support substrate presents an electrical resistivity of less than 10⁻³ohm·cm and a thermal conductivity of greater than 100 W·m⁻¹·K⁻¹, and the seed layer is in a material of composition Al_xIn_yGa_(1-x-y)N, where 0≦x≦1, 0≦y≦1 and x+y≦1, and the specific contact resistance between the seed layer and the bonding layer is less than or equal to 0.1 ohm·cm⁻², and the materials of the support substrate, the bonding layer and the seed layer are refractory at a temperature of greater than 750° C., preferably at a temperature of greater than 1000° C.
• In the present text, “refractory material” is understood to refer to a material that does not deteriorate at the epitaxy temperature of the layer of material of composition Al_xIn_yGa_(1-x-y)N (whether by melting or chemical reaction with gas components), and in which the electrical and thermal conductivity characteristics are not altered at this temperature (particularly by deterioration of the interfaces with other support layers).
• It is specified that, in the whole of the present text, the coefficient of thermal expansion is considered to be the linear coefficient of thermal expansion along a plane parallel to the surface of the layers at the epitaxy temperature of the active layer with relation to the bonding temperature. The vapor phase epitaxy temperature of the active layer of type AlGaInN is conventionally less than 1100° C. Bonding is generally carried out at ambient temperature.
• The coefficient of thermal expansion is conventionally measured by X-ray diffraction or by dilatometry.
• Electrical conductivity (or electrical resistivity) and specific contact resistance are measured by standardized methods that are well known to the person skilled in the art and detailed, for example, in the book titled “Semiconductor Material and Device Characterization” by Dieter Schöder (John Wiley & Sons). Specific contact resistance is measured, for example, by TLM (“Transmission Line Method” or “Transfer Length Method”). This method consists of depositing metal contacts with a length l and a width w, spaced apart by a distance L_iover the layer of semiconductor material with a thickness h. Resistance R_iis measured between different contacts so as to measure several resistance values for different distances L_ibetween the contacts. These values are transferred to an orthogonal mark whose axes represent the resistances R_iand the distances L_i. The slope and the zero distance point of the straight line obtained by joining the points enables the resistivity of the semiconductor material and the specific contact resistance to be respectively extracted.
• Thermal conductivity is measured by standardized methods well known to the person skilled in the art and are detailed, for example, in the treatise R-2-850 “Conductivity et diffusivité thermique des solides” (Conductivity and thermal diffusivity of solids) by Alain Degiovanni, published by Techniques de l'Ingénieur.
• Dislocation density may be measured by transmission electron microscopy or by cathodoluminescence.
• Other characteristics of the support substrate or heterostructure listed below can also be considered alone or in combination with any other characteristic(s):
• • the seed layer is doped with a concentration of dopants of between 10¹⁷and 10²⁰cm⁻³;
  • the dopants are preferably n type dopants;
  • the material of the support substrate is a refractory metal chosen from among tungsten, molybdenum, niobium and/or tantalum and their binary, ternary or quaternary alloys, such as TaW, MoW, MoTa, MoNb, WNb or TaNb;
  • advantageously, the support substrate is in TaW comprising at least 45% tungsten or in MoTa comprising more than 65% molybdenum;
  • the material of the bonding layer comprises polycrystalline silicon, silicide, preferably tungsten silicide or molybdenum silicide, tungsten, molybdenum, zinc oxide, a metal boride such as zirconium boride, tungsten boride, titanium boride or chromium boride, and/or indium tin oxide;
  • the bonding layer is preferentially in a material presenting an electrical resistivity of less than or equal to 10⁻⁴ohm·cm;
  • the seed layer presents an electrical resistivity of between 10⁻³and 10⁻¹ohm·cm; and
  • the active layer presents a dislocation density of less than 10⁸cm⁻², and preferably less than 10⁷cm⁻².
• The invention also relates to a heterostructure for the manufacture of electronic power components, optoelectronic components or photovoltaic components comprising successively from its base to its surface a support such as described above and, on the seed layer of the support, a crack-free monocrystalline layer, known as the “active layer” of a material of composition Al_xIn_yGa_(1-x-y)N, where 0≦x≦1, 0≦y≦1 and x+y≦1 present a thickness of between 3 and 100 micrometers, the seed layer presenting a difference in the lattice parameter with the material of the active layer of less than 0.005 Å and the active layer presenting a main portion in which the thickness represents between 70 and 100% of the thickness of the active layer and in which the concentration of dopants is less than or equal to 10¹⁷cm⁻³.
• In a particularly advantageous manner, the CTE of the support substrate material is between a minimum value that is less than 0.5-10⁻⁶K⁻¹below the CTE of the material of the main portion of the active layer and a maximum value that is no more than 0.6·10⁻⁶K⁻¹above the CTE of the material of the main portion of the active layer at the temperatures used for epitaxially forming the active layer. CTEs for Al_xIn_yGa_(1-x-y)N generally range from 3 to 5.6·10⁻⁶K⁻¹on average for temperatures ranging from room temperature to 1000° C. depending on the specific temperature and composition of the Al_xIn_yGa_(1-x-y)N:
• for InN (x=0, y=1), the CTE is around 3.5·10⁻⁶K⁻¹,
• for AlN (x=1, y=0), the general range is around 3 to 4·10⁻⁶K⁻¹,
• for GaN (x=y=0), the average CTE is around 5.6·10⁻⁶K⁻¹,
• for InGaN with 5-10% of indium (x=0.05 to 0.1; y=0), the average CTE is between about 5 to 5.5·10⁻⁶K⁻¹.
• Thus, the CTE of the support material can vary above about 2.5-10⁻⁶K⁻¹to below about 6.2·10⁻⁶K⁻¹.
• According to a particular embodiment of the heterostructure, the main portion of the active layer is inserted between a subjacent layer and a superjacent layer, each comprising a concentration of different type dopants greater than 10¹⁷cm⁻³. The material of the main portion and of the subjacent and superjacent portions is then preferably GaN.
• According to another embodiment of the heterostructure, the main portion of the active layer is inserted between a subjacent portion and a superjacent portion, each of these portions being constituted of a material Al_xIn_yGa_(1-x-y)N of a different composition.
• According to another embodiment of the heterostructure, the thickness of the main portion represents 100% of the thickness of the active layer and the material of the main portion is n type doped GaN, preferably silicon doped GaN.
• Preferably, the main portion of the active layer and the seed layer are constituted of the same material.
• In an example of embodiment of the heterostructure, the support substrate is in molybdenum, the bonding layer is in tungsten, the seed layer is in GaN and the active layer is in GaN.
• Another aspect of the invention relates to a method of manufacturing a support for the epitaxy of a layer of a material of composition Al_xIn_yGa_(1-x-y)N, where 0≦x≦1, 0≦y≦1 and x+y≦1, characterized in that it comprises the provision of a support substrate presenting an electrical resistivity of less than 10⁻³ohm·cm and a thermal conductivity of greater than 100 W·m⁻¹·K⁻¹, the provision of a donor substrate, the substrate comprising a monocrystalline seed layer adapted for the epitaxial growth of the layer, the formation of a bonding layer on the donor substrate and/or on the support substrate, the materials of the support substrate, the seed layer and the bonding layer are chosen to be refractory at a temperature greater than 750° C., preferably at a temperature greater than 1000° C., and chosen such that the specific contact resistance between the seed layer and the bonding layer is less than or equal to 0.1 ohm·cm⁻², bonding by molecular adhesion of the donor substrate on the support substrate, the bonding layer being situated at the interface, and thinning of the donor substrate to transfer it from the seed layer to the support substrate.
• According to other characteristics of the method, considered alone or in combination:
• • the seed layer is formed in the donor substrate by ionic implantation so as to create in the donor substrate an embrittlement zone at a depth substantially equal to the thickness of the seed layer;
  • the implantation step is carried out after the formation of the bonding layer on the donor substrate, the implantation being carried out through the bonding layer;
  • the method comprises doping of the seed layer, the doping being carried out by implantation or diffusion of dopant species;
  • when the roughness of the donor substrate or support substrate is less than 1 nm for a 5 micrometer×5 micrometer surface measured by AFM and presents a peak valley surface topology of less than 10 nm, the bonding layer is only deposited on the other substrate;
  • when the roughness of the support substrate is greater than or equal to 1 nm for a 5 micrometer×5 micrometer surface measured by AFM and presents a peak valley surface topology greater than or equal to 10 nm, the bonding layer is deposited and polished until a roughness of less than 1 nm and a peak valley surface topology of less than 10 nm is reached.
• Another aspect of the invention lastly relates to a method of manufacturing a heterostructure comprising a monocrystalline layer known as the “active layer” and a material of composition Al_xIn_yGa_(1-x-y)N, where 0≦x≦1, 0≦y≦1 and x+y≦1, characterized in that the method comprises:
• the formation according to the method described previously of the support for the epitaxy of the layer of Al_xIn_yGa_(1-x-y)N, and
• after the formation of the support, a step of growth by epitaxy of the active layer on the seed layer, without cracking, until a thickness of between 3 and 100 micrometers is obtained.
• The active layer presenting a main portion whose thickness represents between 70 and 100% of the thickness of the active layer and whose concentration of dopants is less than or equal to 10¹⁷cm⁻³and the material of the seed layer being chosen to present a lattice parameter difference with the material of the main portion of the active layer of less than 0.005 Å.
• In a particularly advantageous manner, the material of the support substrate is chosen such that its CTE is between a minimum value that is less than 0.5·10⁻⁶K⁻¹below the CTE of the material of the main portion of the active layer and a maximum value that is no more than 0.6·10⁻⁶K⁻¹above the CTE of the material of the main portion of the active layer at the temperatures used for epiaxially forming the active layer. The method advantageously comprises doping of the active layer, the doping being carried out for the epitaxy step or, after epitaxy, by implantation or diffusion of dopant species.
• Preferably, the material of the support substrate is a metal chosen from among tungsten, molybdenum, niobium and/or tantalum and their binary, ternary or quaternary alloys, such as TaW, MoW, MoTa, MoNb, WNb or TaNb.
• Non-limiting examples of the different aspects and embodiments of the invention will now be described in reference to the figures.
• With reference toFIG. 1, theheterostructure1 proposed in the present invention comprises anactive layer4 of a material of composition Al_xIn_yGa_(1-x-y)N, where 0≦x≦1, 0≦y≦1 and x+y≦1.
• Thislayer4 is called active since it is the layer in or on which the electronic power components such as MOS, J-FET, MISFET, Schottky diodes or even thyristors; or LED components, lasers, solar cells are intended to be formed.
• The thickness of theactive layer4 is between 3 and 100 micrometers, and preferably on the order of 10 micrometers.
• Theactive layer4 is bonded onto asupport substrate10 through abonding layer2 whose properties will be detailed below.
• Theactive layer4 is formed by epitaxy on aseed layer3 that may be the same material as that of the active layer or a different material.
• The manufacturing method of such aheterostructure1, which will be described in detail later, mainly comprises the following steps:
• the provision of thesupport substrate10;
• the provision of a donor substrate comprising aseed layer3 adapted for the epitaxy of theactive layer4;
• the transfer of theseed layer3 to thesupport substrate10, thebonding layer2 mentioned above being formed at the interface; and
• the growth by epitaxy of theactive layer4 on theseed layer3.
• The assembly of thesupport substrate10, thebonding layer2 and theseed layer3, which constitutes a support for the epitaxy of theactive layer4 allowing the heterostructure illustrated inFIG. 1 to be formed, presents a total electrical resistivity of less than or equal to that of the bulk GaN comprising a dopant concentration of 10¹⁸cm⁻³, i.e. a total electrical resistivity of less than or equal to 10⁻²ohm·cm and preferentially a thermal conductivity on the order of magnitude as that of the GaN, i.e. greater than or equal to 100 W·m⁻¹·K⁻¹so as to propose an alternative to the utilization of a bulk GaN substrate, that is difficult to find on the market and is expensive.
• Thus, heterostructure1 such as defined above presents a sufficient vertical electrical conductivity for the intended applications such as the operation of Schottky diodes.
• In addition, thematerials constituting heterostructure1 and the manufacturing methods are chosen such that the heterostructure may resist epitaxy temperatures of the active layer without deteriorating the materials or their electrical and thermal properties and thus enable operation of devices equivalent to devices formed from a bulk III/N material.
• Features of the support substrate according to various embodiments of the present invention will now be described.
• Thesupport substrate10 is in a material presenting an electrical resistivity of less than 10−3 ohm·cm and a thermal conductivity of greater than 100 W·m⁻¹·K⁻¹.
• The material of thesupport substrate10 is also “refractory,” i.e., it presents thermal stability at active layer formation temperatures.
• It presents a coefficient of thermal expansion close to that of the material ofactive layer4 at epitaxy temperature as defined herein to prevent stressing of the epitaxied layer during the heating preceding growth and during cooling of the heterostructure after epitaxy.
• For example, the epitaxy temperature in vapor phase by MOCVD, HVPE of the GaN and the AlN to date is around 1000° C.-1100° C., and around 800° C. for InGaN and Al_xIn_yGa_(1-x-y)N.
• In fact, if the coefficient of thermal expansion of thesupport substrate10 is less than (respectively, greater than) that of theseed layer3, theseed layer3 will be in compression (respectively, in tension) at the epitaxy temperature.
• Such being the case, this constraint in tension or in compression may be harmful to the quality of the epitaxy.
• In addition, if theepitaxied layer4 is relaxed during the epitaxy and its coefficient of thermal expansion is greater than (respectively, less than) that of thesupport substrate10, it will be in tension (respectively, in compression) during cooling.
• Beyond a threshold thickness, the constraints in tension as in compression are likely to relax by the formation of cracks or crystalline defects in the epitaxied layer, which reduces the efficacy of the devices formed from this layer.
• The sufficiently “close” character of the coefficient of thermal expansion of the support substrate with relation to that of the active layer is determined as a function of the predominant material chosen for the active layer, i.e., the material of the main portion where appropriate.
• Thus, for example, for anactive layer4 in GaN (whose coefficient of thermal expansion is on the order of 5.6·10⁻⁶K⁻¹), thesupport substrate10 may present a coefficient of thermal expansion of between 5.1·10⁻⁶and 6.1·10⁻⁶K⁻¹at the epitaxy temperature of the active layer.
• In general, it is considered that the coefficients of thermal expansion of the active layer (noted CTE active layer) and of the support substrate (noted CTE support) must be linked by the following relationship:
• CTE active layer: 0.5·10⁻⁶K⁻¹≦CTE support≦CTE active layer+0.6·10⁻⁶K⁻¹
• Thesupport substrate10 is metal-based and is preferably chosen from among tungsten (W), molybdenum (Mo), niobium (Nb) and/or tantalum (Ta) and their binary, ternary or quaternary alloys, such as TaW, MoW, MoTa, MoNb, WNb or TaNb.
• In particular, the TaW alloy comprising at least 45% tungsten (preferably 75%) is likely to present a coefficient of thermal expansion in accordance with that of GaN while possessing good thermal and electrical conductivity properties.
• The MoTa alloy comprising more than 65% molybdenum is also suitable.
• The characteristics of some materials are found in Table 1 herein, for indicative purposes.

• TABLE 1
  Material Characteristics

  	CTE at ambient	CTE at	Thermal	Electrical
  	temperature	1000° C.	conductivity	resistivity
  	(10−6K−1)	(10−6K−1)	(W/m · K)	(microohm · cm)

  Mo metal	4.8	5.6-6.0	140	5
  W metal	4.5	5.1	165	5
  Ta metal	6.3	7.0	54	13
  Nb metal	7.3	8.3	54	15
  GaN	3.5	5.6	150

• Thesupport substrate10 is obtained, for example, by sintering (for the W for example) or by hot pressing.
• Depending on the nature of the material of thesupport substrate10 and the epitaxy temperature of the active layer4 (for a material of the AlInGaN type, this varies between 800 and 1100° C.), evaporation or diffusion of the support substrate may be produced, with the effect of contaminating the active layer.
• In this case, one may encapsulate thesupport substrate10 by a protective layer (not represented) in view of the application of thermal budgets of active layer growth. For example, a layer of silicon nitride or aluminum nitride may be deposited on the rear face and the lateral faces of the support substrate by a CVD or PVD deposition (respectively “Chemical Vapor Deposition” and “Phase Vapor Deposition”).
• Features of the seed layer according to various embodiments of the present invention will now be described.
• Themonocrystalline seed layer3 is in a material Al_xIn_yGa_(1-x-y)N, where 0≦x≦1, 0≦y≦1 and x+y≦1 and is electrically conductive. The layer is obtained by transfer to thesupport substrate10 from adonor substrate30, which may be bulk or rather formed of several layers (for example, a layer of GaN deposited on a sapphire support).
• The material of the seed layer is refractory, i.e., it does not deteriorate during epitaxy of the active layer.
• Theseed layer3 transfer method is obtained by a step of bonding thedonor substrate30 by molecular adhesion on thesupport substrate10 followed by a step of thinning thedonor substrate30 to obtain theseed layer3. This thinning may be carried out by any technique adapted to the materials utilized and whose implementation is well known to the person skilled in the art, such as chemical mechanical polishing CMP, grinding, laser irradiation at the interface between two layers constituting the donor substrate or preferably a SMART CUT™ type method. A detailed description of this method may, for example, be found in patent EP 05 33 551 or in the book “Silicon-On-Insulator Technology Materials to VLSI”, by Jean-Pierre Colinge, 2nd edition, published by Kluwer Academic Publishers, pages 50 and 51.
• Schematically, with reference toFIG. 2, theseed layer3 is defined in thedonor substrate30 by carrying out an implantation of ionic species (for example, hydrogen) in which the implantation peak of the species has a depth substantially equal to the desired thickness for theseed layer3. The zone with the maximum implanted species concentration constitutes anembrittlement zone31 that may be fractured by the application, for example, of an adapted thermal budget.
• The thickness of the seed layer is preferentially between 100 nm and 500 nm.
• The material chosen for theseed layer3 preferably presents a lattice parameter adapted to the epitaxial growth of theactive layer4.
• preferably a material presenting a difference in lattice parameter with the material of theactive layer4 of less than 0.005 Å is chosen.
• For example, one may thus carry out an epitaxy of InGaN at 1.4% In on a seed layer of GaN, or rather an epitaxy of AlGaN at 6.5% Al on a seed layer of GaN.
• According to another example, for epitaxy of an active layer of GaN of a thickness of between 3 and 100 micrometers, one may remove a seed layer from a bulk substrate of GaN.
• Preferably, theseed layer3 is removed from the N polarity face of thedonor substrate30 such that the layer bonded to thesupport substrate10 presents an exposed face of Ga polarity, from which the resumption of epitaxy is easier with current techniques.
• Nevertheless, one may also remove the seed layer from the Ga polarity face of the donor substrate so as to carry out epitaxy on the N polarity face of the seed layer or carry out a double transfer so as to obtain an exposed face of the seed layer of Ga polarity.
• Ideally, the material of theseed layer3 is the same as that of the epitaxied active layer4 (this is then homoepitaxy).
• It then presents the same crystalline structure and, provided that the support substrate does not lead to constraints in the seed layer, there is no lattice parameter difference between the material of the seed layer and that of the active layer, which prevents the formation of new defects in the epitaxied crystal.
• Homoepitaxy (active layer of GaN epitaxied on a seed layer of GaN) thus enables the lowest possible dislocation density to be obtained in the active layer.
• In the case of homoepitaxy, the seed layer may be distinguished from the active layer by a difference in resistivity of these two layers when the active layer and the seed layer present different doping. In the absence of doping, it is sometimes possible to distinguish the interface between the two layers by TEM (Transmission Electron Microscopy).
• In addition, theseed layer3 advantageously presents an electrical resistivity of between 10⁻³and 0.1 ohm·cm.
• This resistivity is preferably the lowest possible resistivity, approximately 10⁻³ohm·cm, in order to facilitate making ohmic contact with the support substrate, which corresponds to a concentration of dopants of between 10¹⁷and 10²⁰cm⁻³.
• The material of theseed layer3 and its level of doping are chosen so as to prevent constituting an electrical conduction barrier between the active layer and the support substrate of the final heterostructure.
• The desired dopant may already be present in the layer removed from the donor or doping may be carried out by diffusion or implantation of dopant species before epitaxy of theactive layer4, depending on the desired device. Preferably, this n type doping (for example by silicon) is easier to carry out, especially as it facilitates making electrical contact with thebonding layer2.
• In addition, theseed layer3 is sufficiently thin (between 100 nm and 500 nm, for example) so that the effect of its coefficient of thermal expansion is negligible compared to that of thesupport substrate10 and that of theactive layer4.
• Features of the active layer according to various embodiment of the present invention will now be described. To respond to the conductivity criterion ofheterostructure1 and to be able to support a large electric field (i.e., on the order of 10⁶V·cm⁻¹), the epitaxiedactive layer4 of Al_xIn_yGa_(1-x-y)N comprises dopants with a concentration of less than or equal to 10¹⁷cm⁻³, in order to disperse as much as possible the electric potential drop over the entire thickness of the layer.
• Doping is obtained, for example by incorporating silicon, which leads to n type doping.
• Doping may be carried out during growth of theactive layer4.
• Thanks to the choice of the material of theseed layer3, the dislocation density in the active layer is less than 10⁸cm⁻², preferably less than 10⁷cm⁻².
• In addition, a wise choice of thesupport substrate10, such as stated above, enables a thickactive layer4, free from cracks, to be obtained over a thickness of between 3 and 100 micrometers, preferably between 3 and 20 micrometers, further preferably approximately 10 micrometers.
• By way of information, it is specified that the term crack in the present invention is differentiated from dislocation in that the crack in a film of crystalline material corresponds to a crystalline cleavage that extends more or less deeply in the thickness of the film, i.e., a separation of the material into two parts, which creates, on both sides of the cleavage, two free surfaces in contact with air, while the film comprising a dislocation remains continuous.
• According to a preferred embodiment,active layer4 is made of GaN.
• According to a particular embodiment illustrated inFIG. 6,active layer4 is composed of a plurality of portions of layers, that is, by going from the bonding layer to the free surface of the active layer: aportion4aof doped n type GaN, amain portion4b, whose thickness is greater than or equal to 70% of the total thickness of the active layer, of weakly doped GaN (i.e. with a concentration of less than or equal to 10¹⁷cm⁻³) and aportion4cof doped p type GaN, or conversely.
• According to another example, theactive layer4 of a PIN diode is constituted of amain portion4bof GaN, asubjacent portion4aof InGaN and asuperjacent portion4cof InGaN.
• As is well known to the person skilled in the art, these dopings enable the desired electrical contacts to be obtained, for example in view of producing a PIN diode.
• Preferably, doping of the active layer is carried out during epitaxy, with a precursor gas such as silane for n type doping to silicon, or a precursor such as Bis Cyclopentadienyl Magnesium (Cp2Mg) (C₅H₅.2.Mg) for p type doping to magnesium.
• Alternately, doping may be obtained by implantation (for example silicon for n type doping, or magnesium for p type doping) or yet, for the superjacent portion, by diffusion of species in the portion (for example silicon for n type doping, magnesium for p type doping).
• Features of the bonding layer according to various embodiments of the present invention will now be described.
• The bonding layer is made in one or more materials chosen such that the bonding energy between the support substrate and the implanted donor substrate is greater than the fracture thermal budget.
• Competition between the fracture at theembrittlement zone31 and the separation ofsubstrates10,30 at the bonding interface, which leads to a partial, poor-quality fracture of the embrittlement zone, is thus avoided.
• In particular, the bonding layer is in a refractory material that does not deteriorate at the epitaxy temperature of the active layer.
• In addition, the material ofbonding layer2 and its thickness are chosen so as to minimize the electric potential drop at the bonding.
• Generally, the thickness ofbonding layer2 is thus less than or equal to 1 μm.
• This thickness may be greater depending on the roughness of the substrate on which it is formed that it is necessary to smooth for effective bonding; In this case, the electric potential drop will be minimized by the choice of a material presenting a lower electrical resistivity.
• Preferably,bonding layer2 is electrically and thermally conductive, and the material composing the layer preferably presents an electrical resistivity of less than or equal to 10⁻⁴ohm·cm.
• However, considering that its thickness is much less than that of the support substrate, the influence of electrical and thermal conductivities of the material constituting the layer remains limited.
• It is therefore possible to choose for this layer other materials than metals.
• Thebonding layer2 in addition enables low electrical contact resistance between one of its faces and the active layer on the one hand, and between its other face and the support substrate on the other hand.
• It is particularly desirable that the specific contact resistance betweenbonding layer2 andseed layer3 is less than or equal to 0.1 ohm·cm⁻²in order to maintain good vertical electrical conductivity despite an interface presenting a semiconductor material.
• To do this, the materials frombonding layer2 andseed layer3 are chosen such that their output energy, i.e., minimum energy, measured in electron-volts, necessary to detach an electron from the Fermi level of a material until a point situated at infinity outside the material, is in the same order of magnitude.
• A material pair satisfying this requirement is for example GaN/W, the output energy of the n type doped GaN being approximately 4.1 eV while that of the W is approximately 4.55 eV. Another pair considered may be GaN/ZrB₂(the output energy of ZrB₂is approximately 3.94 eV).
• A layer of titanium may also promote adhesion and making contact between the material of the seed layer in III/N material and the bonding layer, since it participates in lowering the height of the conduction barrier at the interface (the output energy of Ti is approximately 4.33 eV).
• A layer of titanium with a thickness of 10 nm deposited on the material ofseed layer3 or the material ofbonding layer2 before assembly is sufficient to obtain the anticipated effect.
• Thermal annealing of the two materials also enables the specific contact resistance to be improved by better interconnection of the materials at the interface.
• The bonding layer is deposited ondonor substrate30 before implantation and/or onsupport substrate10. The act of carrying out implantation in the donor substrate after deposition of the bonding layer prevents the risk of a fracture at the implanted zone due to thermal budget produced by the deposition.
• When layers of bonding material are deposited on both the donor substrate and the support substrate,bonding layer2 is constituted of the whole of these two layers.
• It is noted that when the roughness of one of the substrates (i.e., of the donor substrate or of the support substrate) is less than 1 nm for a 5 micrometer×5 micrometer surface measured by atomic force microscopy (AFM) and when it presents a peak valley surface topology of less than 10 nm measured by optical profilometry with a Wyko type apparatus, the bonding layer only has to be deposited on the other substrate. It is observed that the measured roughness is generally similar for a surface ranging from 1 micrometer×1 micrometer to 10 micrometers×10 micrometers.
• Polycrystalline silicon (p-Si) is a material of choice that adheres well to the GaN, which enables planarization of the surface of the metallic support substrate and which is easy to polish.
• A surface roughness before bonding of at the most a few angstroms RMS may thus be reached.
• To minimize the possible diffusion of silicon to theepitaxied layer4, a diffusion barrier (not represented) may be provided, for example between the seed layer and the bonding layer. For example, this diffusion barrier may be a film of AlN of a few nanometers of thickness.
• In the case of diffusion of silicon in vapor phase during epitaxy from the lateral walls of the layer to the outside of the structure, a layer forming a diffusion barrier of the lateral zones not covered by the p-Si layer may be provided.
• Alternately, one may also form thebonding layer2 by depositing a metal (for example tungsten or molybdenum), a metal oxide such as zinc oxide, a silicide formed ex-situ (for example SiW₂or SiMo) or a metal boride (such as Titanium Boride TiB₂, chromium boride CrB₂, zirconium boride ZrB₂, or tungsten boride WB, WB₂) on thedonor substrate30 before implantation and/or on thesupport substrate10.
• In a variation, it is possible to deposit a metal on thedonor substrate30 or thesupport substrate10 and to deposit a silicide or a boride on the other substrate; thebonding layer2 will then be constituted of the combination of this metal with the silicide or the boride.
• Another possibility consists of making thebonding layer2 in indium tin oxide (ITO).
• As the indium tin oxide is thermally unstable, it is preferably encapsulated before carrying out epitaxy of theactive layer4.
• Table 2 provides properties of some of the materials that are suitable forbonding layer2.
• The characteristic indicated in line L1 is the melting point (expressed in ° C.); the characteristic of line L2 is thermal conductivity (in W·m⁻¹·K⁻¹); that of line L3 is the electrical resistivity (in ohm·cm) and that of line L4 is the coefficient of thermal expansion (in 10⁻⁶K⁻¹).

• TABLE 2
  Bonding Layer Materials

  	p-Si	MoSi2	TaSi2	WSi2	NbSi2
  L1	1412	1870	2499	2320	2160
  L2	130	58.9
  L3	1.0 · 10−4	2.2 · 10−5	8.5 · 10−6	3.0 · 10−5	5.0 · 10−5
  L4		8.12		8.8-9.54

  		ZrB2	WBx	TiB2	CrB2
  	L1	3060	2385	2980	1850-2100
  	L2	58		64	20-32
  	L3	9.2 · 10−6	4.0 · 10−6	1.6-2.8 · 10−5	2.1 · 10−5
  	L4

• A non-limiting example of a first preferred embodiment comprising a bonding layer in p-Si will now be described below:
• First thedonor substrate30 is prepared by the following steps (seeFIG. 2):
• • Preparation of the N polarity face of abulk substrate30 of GaN: this step involves known planarization and polishing techniques.
  • CVD or PVD deposition on the face oflayer21 of p-Si with a thickness of 100 to 500 nm.
  • Implantation in thedonor substrate30 of ionic species (of hydrogen, for example) throughlayer21 of p-Si. The depth of implantation determines the thickness of theseed layer3 of GaN. For indicative purposes, the implantation energy is between 80 and 180 keV and the dose is between 2 and 4.10¹⁷at/cm².
  • Polishing by CMP (Chemical Mechanical Polishing) oflayer21 to reach a roughness compatible with bonding. Typically, the roughness before bonding must be on the order of a few angstroms RMS.
• Second, with reference toFIG. 3, thesupport substrate10 is prepared, that is in a TaW alloy containing 75% tungsten.
• This preparation comprises the deposition on thesupport substrate10 of alayer22 of p-Si with a thickness of a few hundred nanometers.
• The thickness of thelayer22 is adapted as a function of the morphology of the surface of thesupport substrate10, such that the planarization by CMP of the layer of p-Si enables a surface roughness of a few angstroms RMS to be reached.
• Then a chemical treatment prior to adhesion of the twolayers21,22 of p-Si is carried out by hydrophilic or hydrophobic bonding.
• For this purpose, the surfaces are cleaned to remove contaminants and an oxidizing or deoxidizing treatment is possibly performed on the surfaces by plasma activation, drying and exposure to atmospheres containing ozone (for oxidation). The surfaces to be bonded may also be preheated up to a temperature of approximately 200° C.
• With reference toFIG. 4, the surfaces of the twolayers21,22 of p-Si are placed in contact; therefore abonding layer2 of p-Si with a total thickness of 100 nm to 1 micrometer is formed.
• Optionally, bonding is consolidated by a thermal treatment applied from ambient temperature to approximately 200° C. with a duration of a few minutes to 2 hours. Then the fracture thermal budget is applied with a temperature ramp of between ambient temperature and approximately 600° C.
• The structure illustrated inFIG. 5 is then obtained.
• The damaged material on the fractured surface is removed (i.e., the surface of seed layer3) to reach a roughness of a few angstroms to a few nanometers RMS, adapted for a resumption of epitaxy.
• Theheterostructure1 illustrated inFIG. 1 is obtained by growing theactive layer4 onseed layer3, on the desired thickness.
• The residue of thedonor substrate30 may also be recycled by removing, by ion beam etching or chemical etching, the p-Si on the non-fractured face.
• A non-limiting example of a second preferred embodiment having a bonding layer in WSi₂is described below:
• First the donor substrate is prepared, which includes the following steps shown inFIG. 2.
• Initially the surface is prepared by planarization and polishing of the N polarity face of abulk substrate30 of GaN. A deposition is then carried out on the face oflayer21 of WSi₂silicide to a thickness of 100 to 500 nm. Annealing of the layers is implemented to form ohmic contact between the GaN and adjacent material layer(s). This annealing is carried out at a temperature of between 600 and 1200° C. for a few minutes under neutral atmosphere comprising NH₃and has the effect of reducing the contact resistance. Implantation of ionic species, such as hydrogen, throughlayer21 of WSi₂in thedonor substrate30 to a depth determining the thickness of theseed layer3 of GaN is conducted, where the implantation energy is typically between 80 and 180 keV. The WSi₂is polished by CMP to reach a roughness compatible with bonding (i.e., a few angstroms RMS).
• A second sequence of steps comprises, preparing thesupport substrate10 in TaW comprising 75% tungsten. For this purpose (seeFIG. 3), alayer22 of WSi₂with a thickness of a few hundred nanometers is deposited on thesubstrate10.
• As stated above, the thickness of thelayer22 of WSi₂is adapted as a function of the morphology of the surface of thesupport substrate10 such that the planarization by CMP of thelayer22 of WSi₂enables a surface roughness of a few angstroms RMS to be reached.
• If necessary, annealing to form ohmic contact with the TaW is carried out. The conditions of this annealing are a temperature of between 600 and 1200° C., a duration of a few minutes and a neutral atmosphere.
• Planarization by CMP of the surface of the WSi₂is then carried out. Then a chemical treatment prior to adhesion of the two layers of WSi₂is carried out by hydrophilic or hydrophobic bonding.
• For this purpose, the surfaces are cleaned to remove contaminants and an oxidizing or deoxidizing treatment is possibly performed on the surfaces by plasma activation, drying and exposure to atmospheres containing ozone (for oxidation). The surfaces to be bonded may also be preheated up to a temperature of approximately 200° C.
• The surfaces of the twolayers21,22 of WSi₂are then placed in contact; therefore abonding layer2 of WSi₂with a total thickness of 100 nm to 1 micrometer is formed.
• Optionally, bonding is consolidated by a thermal treatment applied from ambient temperature to approximately 200° C. with a duration of a few minutes to 2 hours.
• Then the fracture thermal budget is applied with a temperature ramp of between ambient temperature and approximately 600° C.
• The damaged material on the fractured surface is removed (i.e., the surface of seed layer) by dry etching (e.g., reactive ion etching (RIE)) or chemical mechanical polishing (CMP) to reach a roughness of a few angstroms to a few nanometers RMS, adapted for a resumption of epitaxy.
• Theheterostructure1 illustrated inFIG. 1 is obtained by growing theactive layer4 onseed layer3, on the desired thickness.
• The residue of the donor substrate may also be recycled by removing, by dry etching for example by RIE or wet etching (i.e., chemical etching), the WSi₂on the non-fractured face.
• A non-limiting example of a third preferred embodiment is described below:
• • First thedonor substrate30 is prepared by the following steps (seeFIG. 2):
  • Preparation of the N polarity face of abulk substrate30 of GaN: this step involves known planarization and polishing techniques.
  • CVD or PVD deposition on the face oflayer21 of W with a thickness of 100 to 500 nm.
  • Implantation in thedonor substrate30 of ionic species (of hydrogen, for example) throughlayer21 of W. The depth of implantation determines the thickness of theseed layer3 of GaN. For indicative purposes, the implantation energy is between 80 and 180 keV and the dose is between 2 and 4.10¹⁷at/cm2.
  • Polishing by CMP (Chemical Mechanical Polishing) oflayer21 to reach a roughness compatible with bonding.
    Typically, the roughness before bonding must be on the order of some angstroms RMS.
• Second, with reference toFIG. 3, thesupport substrate10 is prepared, which is of molybdenum.
• This preparation comprises the deposition on thesupport substrate10 of alayer22 of W with a thickness of a few hundred nanometers.
• The thickness of thelayer22 is adapted as a function of the morphology of the surface of thesupport substrate10, such that the planarization by CMP of the layer of W enables a surface roughness of a few angstroms RMS to be reached.
• Then the two surfaces oflayers21 and22 of W are placed in contact for bonding by molecular adhesion, thus abonding layer2 of W with a total thickness of 100 nm to 1 micrometer is formed.
• Optionally, bonding is consolidated by a thermal treatment applied from ambient temperature to approximately 200° C. with a duration of a few minutes to 2 hours. Then the fracture thermal budget is applied with a temperature ramp of between ambient temperature and approximately 600° C.
• The structure illustrated inFIG. 5 is then obtained.
• The damaged material on the fractured surface is removed (i.e., the surface of seed layer3) to reach a roughness of a few angstroms to a few nanometers RMS, adapted for a resumption of epitaxy.
• Theheterostructure1 illustrated inFIG. 1 is obtained by growing theactive layer4 of GaN onseed layer3, on the desired thickness.
• Components Based on the Heterostructure
• Theheterostructure1 described above can then be used to form electronic power components, optoelectronic components or photovoltaic components in or on theactive layer4.
• In particular, the components that can be based on said heterostructure comprise electronic power components such as MOS components, bipolar transistors, J-FET, MISFET, Schottky or PIN diodes, thyristors; optoelectronic components (e.g. Laser, LED) and photovoltaic components (solar cells).
• To that end, at least one contact may be formed on theactive layer4 of the heterostructure (which represents the “front side” of the component), and at least one contact may be formed on thesupport substrate10 of the heterostructure (which represents the “back side” of the component).
• In the case of optoelectronic components, the active layer may be relatively thin, i.e. up to 6 micrometers.
• In the case of photovoltaic or optoelectronic components, the contact formed on the active layer may be transparent or semitransparent in order to allow the transmission of the appropriate wavelength.
• The skilled person is able to define an appropriate material for the contact so as to meet this requirement.
• A non-limiting example of an electronic power component is described below:
• FIG. 7 illustrates a vertical transistor with a vertical gate (also called a “trench gate MOSFET”) made fromheterostructure1 obtained thanks to the present invention.
• On the rear face ofsupport substrate10, a metallic layer100 (for example, of aluminum) may be deposited to form a drain ohmic contact. However, the conductivity of the support substrate of the invention is chosen so as to not inevitably necessitate such a contact layer.
• Theactive layer4 of the heterostructure successively comprises asubjacent portion4aof doped n-GaN, a main portion of doped p+GaN with magnesium, and twosuperjacent regions4cof doped n+GaN for source contacts withlayers200 that are, for example, in an aluminum/titanium alloy.
• The tworegions4care deposited on both sides of a trench to form the vertical gate.
• The gate trench is covered with alayer300 of a dielectric substance (such as SiO₂or SiN) and the trench is filled withpolycrystalline silicon400.
• It is to be understood that some or all of the above described features and steps can be combined in different ways, and other variations and modifications will be apparent to those of ordinary skill in the art. It is intended that all of these embodiments, examples, variations and modifications thereon are meant to be encompassed within the spirit and scope of the present invention as set forth in the following claims. In particular, the invention may be implemented with other choices of materials, according to the criteria stated above.

Claims (25)

1. A support for the epitaxial growth of a layer of a material, which comprises:

a support substrate that includes a bonding layer;

a monocrystalline seed layer on the bonding layer made of a material and having properties sufficient to facilitate epitaxial growth of an active layer of Al_xIn_yGa_(1-x-y)N, where 0≦x≦1, 0≦y≦1 and x+y≦1;

wherein the seed layer and bonding layer comprise materials that provide a specific contact resistance therebetween that is less than or equal to 0.1 ohm·cm⁻², and the support substrate, the bonding layer and the seed layer each comprises a material that is refractory at a temperature of greater than 750° C.

2. The support ofclaim 1, wherein the support substrate has an electrical resistivity of less than 10⁻³ohm·cm and a thermal conductivity of greater than 100 W·m⁻¹·K⁻¹.

3. The support ofclaim 1, wherein the support substrate comprises a refractory metal selected from the group consisting of tungsten, molybdenum, niobium or tantalum and their binary, ternary or quaternary alloys.

4. The support ofclaim 3, wherein the metal alloys are TaW, MoW, MoTa, MoNb, WNb or TaNb.

5. The support ofclaim 4 wherein the metal allow is TaW comprising at least 45% tungsten or MoTa comprising more than 65% molybdenum.

6. The support ofclaim 1, wherein the bonding layer comprises a material comprising polycrystalline silicon, a silicide, a refractory metal, a metal boride, zinc oxide, or indium tin oxide.

7. The support ofclaim 1, wherein the bonding layer comprises a material having an electrical resistivity of less than or equal to 10⁻⁴ohm·cm.

8. The support ofclaim 1, wherein the seed layer has an electrical resistivity of between 10⁻³and 0.1 ohm·cm.

9. A heterostructure for the manufacture of electronic power components, optoelectronic components or photovoltaic components comprising:

the support ofclaim 1, wherein the material of seed layer is Al_xIn_yGa_(1-x-y)N, where 0≦x≦1, 0≦y≦1 and x+y≦1;

an active layer expitaxially grown on the seed layer is crack-free and is made of a material having a composition of Al_xIn_yGa_(1-x-y)N, where 0≦x≦1, 0≦y≦1 and x+y≦1, with a thickness of between 3 and 100 micrometers and a dislocation density of less than 10⁸cm⁻².

10. The heterostructure ofclaim 9, wherein the seed layer and active layer comprise materials that provide a difference in lattice parameter of less than 0.005 Å, and the active layer comprises a main portion in which the thickness represents between 70 and 100% of the thickness of the active layer and in which the concentration of dopants is less than or equal to 10¹⁷cm⁻³.

11. The heterostructure ofclaim 9, wherein the support substrate comprises a material that provides a CTE that is between a minimum value that is less than 0.5·10⁻⁶K⁻¹below the CTE of the material of the main portion of the active layer and a maximum value that is no more than 0.6·10⁻⁶K⁻¹above the CTE of the material of the main portion of the active layer at the temperatures used for epiaxially forming the active layer.

12. The heterostructure ofclaim 9, wherein the main portion of the active layer is inserted between a subjacent portion and a superjacent portion, and wherein the subjacent and superjacent portions each comprise a concentration of dopants greater than 10¹⁷cm⁻³, wherein the main portion, the subjacent portion and the superjacent comprises GaN and the dopant of the superjacent portion is different from the dopant of the subjacent layer.

13. The heterostructure ofclaim 9, wherein the main portion of the active layer is inserted between a subjacent portion and a superjacent portion, and wherein the material of the main portion is of a different Al_xIn_yGa_(1-x-y)N composition than the subjacent portion and the superjacent portion of the active layer, and the composition of the subjacent portion is different from the composition of the superjacent portion.

14. The heterostructure ofclaim 9, wherein the thickness of the main portion represents 100% of the thickness of the active layer and that the material of the main portion is of doped n type GaN, or wherein the support substrate comprises molybdenum, the bonding layer is tungsten, the seed layer is GaN.

15. An electronic power, optoelectronic or photovoltaic component formed in or on the active layer of a heterostructure accordingclaim 1, and comprising at least one electrical contact on the active layer and at least one electrical contact on the support substrate

16. A method of manufacturing a support for the epitaxy of a layer of material which comprises:

forming a bonding layer upon one of a donor substrate or a support substrate, or on both;

bonding the donor substrate to the support substrate such that the bonding layer is situated between the donor substrate and the support substrate at an interface; and

removing a portion of the donor substrate to leave a seed layer on the support substrate for epitaxial growth of an active layer, wherein the donor substrate, the support substrate and the bonding layer are refractory materials having a temperature greater than 750° C. or greater than 1000° C. and chosen to provide a specific contact resistance between the seed layer and the bonding layer that is less than or equal to 0.1 ohm·cm⁻².

17. The method ofclaim 16, wherein the support substrate has an electrical resistivity of less than 10⁻³ohm·cm⁻¹and a thermal conductivity of greater than 100 W·m⁻¹·K⁻¹.

18. The method ofclaim 16, wherein the seed layer comprises a monocrystalline material layer adapted for the epitaxial growth of a material of composition Al_xIn_yGa_(1-x-y)N, where 0≦x≦1, 0≦y≦1 and x+y≦1

19. The method ofclaim 16, which further comprises implanting ions into the donor substrate to form an embrittlement zone at a depth that is substantially equal to the thickness of the seed layer to be left on the support substrate after removing the portion of the donor substrate.

20. The method according toclaim 19, wherein the implanting is carried out after the formation of the bonding layer on the donor substrate, and through the bonding layer.

21. The method ofclaim 16, which further comprises:

measuring the surface roughness of the donor substrate and support substrate; and

depositing a bonding layer on the surface of either or both substrates that have a roughness greater than 1 nm for a 5 micrometer×5 micrometer surface measured by AFM and a peak valley surface topology of greater than or equal to 10 nm.

22. The method ofclaim 16, which further comprises epitaxially growing an active layer on the seed layer to a thickness of between 3 and 100 micrometers without cracking to form a heterostructure.

23. The method ofclaim 22, which further comprises providing the active layer with a main portion whose thickness represents between 70 and 100% of the thickness of the active layer and whose concentration of dopants is less than or equal to 10¹⁷cm⁻³.

24. The method ofclaim 22, wherein the active layer is a monocrystalline layer, and has a composition of Al_xIn_yGa_(1-x-y)N, where 0≦x≦1, 0≦y≦1 and x+y≦1.

25. The method ofclaim 22, which further comprises choosing the material of the support substrate such that the coefficient of thermal expansion (CTE) of the support substrate material is between a minimum value that is less than 0.5·10⁻⁶K⁻¹below the CTE of the material of the main portion of the active layer and a maximum value that is no more than 0.6·10⁻⁶K⁻¹above the CTE of the material of the main portion of the active layer at the temperatures used for epiaxially forming the active layer.

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