EP2870278A1 - Substrate comprising a layer of silicon and/or germanium and one or a plurality of nanowires oriented perpendicular to the surface of the substrate - Google Patents

Substrate comprising a layer of silicon and/or germanium and one or a plurality of nanowires oriented perpendicular to the surface of the substrate

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Publication number
EP2870278A1
EP2870278A1 EP13744670.4A EP13744670A EP2870278A1 EP 2870278 A1 EP2870278 A1 EP 2870278A1 EP 13744670 A EP13744670 A EP 13744670A EP 2870278 A1 EP2870278 A1 EP 2870278A1
Authority
EP
European Patent Office
Prior art keywords
substrate
layer
silicon
germanium
monocrystalline
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP13744670.4A
Other languages
German (de)
French (fr)
Inventor
Elin Sondergard
Yann COHIN
Jean-Christophe Harmand
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Saint Gobain Recherche SA
Centre National de la Recherche Scientifique CNRS
Original Assignee
Saint Gobain Recherche SA
Centre National de la Recherche Scientifique CNRS
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Saint Gobain Recherche SA, Centre National de la Recherche Scientifique CNRS filed Critical Saint Gobain Recherche SA
Publication of EP2870278A1 publication Critical patent/EP2870278A1/en
Withdrawn legal-status Critical Current

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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B82—NANOTECHNOLOGY
    • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
    • B82Y10/00—Nanotechnology for information processing, storage or transmission, e.g. quantum computing or single electron logic
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B82—NANOTECHNOLOGY
    • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
    • B82Y40/00—Manufacture or treatment of nanostructures
    • C—CHEMISTRY; METALLURGY
    • C30—CRYSTAL GROWTH
    • C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
    • C30B1/00—Single-crystal growth directly from the solid state
    • C30B1/02—Single-crystal growth directly from the solid state by thermal treatment, e.g. strain annealing
    • C30B1/023—Single-crystal growth directly from the solid state by thermal treatment, e.g. strain annealing from solids with amorphous structure
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    • C30B23/00—Single-crystal growth by condensing evaporated or sublimed materials
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    • C30—CRYSTAL GROWTH
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    • C30B29/00—Single crystals or homogeneous polycrystalline material with defined structure characterised by the material or by their shape
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    • C30B29/06—Silicon
    • C—CHEMISTRY; METALLURGY
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Definitions

  • the present invention relates to a substrate comprising a continuous or discontinuous layer of silicon and / or germanium consisting of one or more monocrystalline grains, and on this layer, one or more nanowires whose longitudinal axis is oriented perpendicularly to the surface. of the substrate.
  • the invention also relates to a method of manufacturing such a substrate.
  • Nanowires oriented perpendicular to the surface of a substrate have remarkable properties vis-à-vis the phenomena of transport and electronic or optical confinement.
  • the orthogonality of the growth of nanowires with respect to the surface of a substrate is of great interest because this feature facilitates not only their insertion in electronic devices, but also optical or optoelectronic.
  • a glass substrate comprising a crystallized silicon layer on which is deposited an insulating layer having openings serving as growth zones of the nanowires.
  • the crystallized silicon layer comprises monocrystalline grains defined by grain boundaries.
  • the vertical growth of the nanowires is made possible by the choice of a surface size to delimit the areas of growth below the surface of each monocrystalline silicon grain.
  • This document discloses that out of 28 openings, 10 are facing a grain edge. Through these 10 apertures, 8 nanowires grow vertically but with a smaller diameter than the nanowires growing in apertures not including a grain edge and 2 openings do not lead to nanowire growth.
  • the crystallized silicon layer has a thickness of between 10 and 100 nm, preferably 50 nm.
  • the monocrystalline grains have an average lateral dimension of 200 nm to about 1 ⁇ .
  • the only crystallization process of the silicon layer described in this document is laser annealing. No indication is given on the surface roughness of such a crystallized silicon layer.
  • a deviation from normal to the substrate (or surface) more or less important can be observed and attributed to various causes such as the intrinsic roughness of the substrate or an inclination of monocrystalline grains on the substrate reverberating on the growth of nanowires.
  • the present invention relates to the manufacture of vertical nanowires on various substrates which may be amorphous or have a crystalline orientation other than the orientation suitable for vertical growth, or even on substrates incompatible with the growth of nanowires, obtained by a method which is simple to use. enforce.
  • substrates which may be amorphous or have a crystalline orientation other than the orientation suitable for vertical growth, or even on substrates incompatible with the growth of nanowires, obtained by a method which is simple to use. enforce.
  • the applicants have developed a substrate:
  • the invention therefore relates to a substrate comprising on at least a portion of one of its surfaces a layer of silicon and / or germanium of thickness E consisting of one or more monocrystalline grains, all oriented so that they have planes (111) parallel to the surface of the substrate, and on this layer, one or more nanowires whose longitudinal axis is oriented perpendicular to the surface of the substrate characterized in that: the one or more monocrystalline grains of the silicon and / or germanium layer have a lateral dimension D, defined as a chord of the grain edge, on all grains strictly greater than 1 ⁇ , preferably greater than 2 ⁇ and at best greater than 5 ⁇ ,
  • the ratio D / E between the lateral dimension D and the thickness of the layer of silicon and / or germanium is greater than 25, preferably 100.
  • chord D a line segment joining two points of the outline of a grain.
  • the lateral dimension of the grains can be measured by image processing obtained by any microscopic observation mode, direct or indirect, such as scanning electron microscopy, transmission electron microscopy, backscatter electron diffraction (Electron backscatter diffraction "), Atomic force microscopy and optical microscopy.
  • this characteristic is considered to be satisfied when at least 80%, preferably at least 90%, better still at least 95% and even better 100% of the grains have at least one lateral dimension D greater than 1 ⁇ .
  • the invention relates to a substrate comprising, on at least a part of one of its surfaces, one or more monocrystalline grains of non-joined silicon and / or germanium and all oriented so that they present planes (111) parallel to the surface of the substrate, and on each grain one or more nanowires whose longitudinal axis is oriented perpendicular to the surface of the substrate.
  • non-contiguous monocrystalline grains are grains isolated from each other by a distance, preferably of at least 10 nm, the assembly thus forming a discontinuous layer.
  • the invention also relates to a method of manufacturing a substrate comprising the following steps:
  • the invention also relates to any device based on such a substrate and capable of in particular be chosen from light receiving or emitting elements such as photovoltaic solar cells, laser diodes, light emitting diodes, photocathodes or from electronic components such as bipolar transistors and metal-insulator-semiconductor (MIS) transistors. ).
  • light receiving or emitting elements such as photovoltaic solar cells, laser diodes, light emitting diodes, photocathodes or from electronic components such as bipolar transistors and metal-insulator-semiconductor (MIS) transistors.
  • a nanowire whose longitudinal axis is oriented perpendicular to the surface of the substrate corresponds to a nanowire pushing from the silicon and / or germanium layer in a direction perpendicular to the substrate.
  • the nanowires of perpendicular orientation according to the invention form an angle at very close to 90 ° with respect to the surface of the substrate.
  • the angle ⁇ may deviate from the value of 90 ° for example because of disorder, defects or stress during the growth of nanowires and monocrystalline grains.
  • At least 90%, preferably at least 95%, better 100% of perpendicular orientation nanowires have an angle ⁇ with respect to the surface of the substrate of 90 ° ⁇ 10 °, preferably 90 ° ⁇ 5 ° or better 90 ° ⁇ 2.5 °.
  • the epitaxy of the nanowires on the thin layer of silicon and / or intermediate germanium allows vertical growth of the nanowires, without contact or coalescence between them.
  • the silicon and / or germanium layer consists of one or more monocrystalline grains with high lateral extension and low roughness.
  • the monocrystalline grains are all oriented so that they have planes (111) parallel to the surface of the substrate although having extremely low thicknesses (of the order of ten nanometers). All of these characteristics contribute to obtaining excellent vertical growth of nanowires.
  • the substrate of the invention does not require an insulating layer comprising openings serving as a growth zone to obtain the vertical growth of the nanowires.
  • Another beneficial aspect of the invention lies in the fact that the advantageous properties of the silicon and / or germanium layer are obtained for thin layers.
  • nanowires to be integrated in complex devices, must be connected to a conductive electrode.
  • This electrode may therefore for example be a conductive layer deposited between the substrate and the silicon and / or germanium layer. The lower the thickness of the silicon and / or germanium layer, the less the conductivity through this layer will be obstructed and the easier it will be to connect the nanowires to the electrode.
  • the manufacturing process which comprises the formation induced by a metal-induced crystallization ("Metal Induced Lateral Crystallization") of the layer of silicon and / or germanium consisting of one or more monocrystalline grains.
  • the crystallization induced by a metal is obtained by depositing a metal layer above or below a layer of the material that it is desired to crystallize, that is to say a layer of silicon and / or or amorphous germanium.
  • the metal layer may be a layer of a metal selected from aluminum (Al), silver (Ag), gold (Au), antimony (Sb), copper (Cu), nickel ( Ni) or lead (Pb).
  • the layer of amorphous material (a-Si or a-Ge) crystallizes at a chosen temperature, sufficient and less than the temperature of the eutectic between the metal and the material to be crystallized.
  • a-Si or a-Ge amorphous material
  • Crystalline growth is achieved at the interface between the metal layer and the amorphous layer.
  • the crystals formed fit and then grow in the metal layer.
  • different stacks are obtained at the end of crystallization.
  • the metal layer When one deposits successively on the substrate, the metal layer then the amorphous layer, one obtains, after crystallization, a substrate comprising a crystalline layer covered with a metal layer. To allow the growth of the nanowires, it is necessary to eliminate this metal layer.
  • the layer of silicon and / or germanium consisting of one or more monocrystalline grains is formed below the metal layer, the latter is removed by selective etching.
  • the aluminum layer can be etched completely and selectively by using a mixture of concentrated hydrochloric acid and nitric acid.
  • the surface oxides of aluminum and / or silicon can also be etched for example with fluoridic acid (5%).
  • the amorphous layer then the metal layer When one deposits successively on the substrate, the amorphous layer then the metal layer, one obtains, after crystallization, a layer of silicon and / or germanium consisting of one or more monocrystalline grains formed above the metal layer.
  • the presence of this metal layer interposed between the substrate and the layer of silicon and / or germanium consisting of one or more monocrystalline grains is interesting because it can partially or completely provide an electrode function.
  • the substrate may therefore comprise a metal layer, preferably aluminum, interposed between said substrate and the layer of silicon and / or germanium consisting of one or more monocrystalline grains.
  • the choice of the metal used to catalyze the crystallization may give the silicon and / or germanium layer particular properties.
  • the metal layer and the layer of silicon and / or amorphous germanium can be deposited by any conventional deposition methods such as chemical and physical vapor deposition.
  • these layers are deposited by magnetic field assisted sputtering ("magnetron deposition").
  • the grains can grow until they coalesce.
  • the relative thickness of the deposited layers is a key parameter allowing or not the coalescence of the grains:
  • the layer of crystallized materials forms a discontinuous layer
  • the layer of crystallized materials forms a continuous layer
  • the layer of crystallized material forms a continuous layer further comprising prominent islands.
  • the silicon and / or germanium layer consisting of one or more monocrystalline grains may be continuous or discontinuous.
  • thickness E is understood to mean the average thickness of the monocrystalline grains constituting it.
  • the thickness of the silicon and / or germanium layer E is, in order of increasing preference, less than 50 nm, less than 40 nm, less than 30 nm, less than 20 nm, of between 5 and 15 nm.
  • the roughness of the surface of the grain (s) constituting the silicon and / or germanium layer measured by the atomic force microscopy technique is less than 5 nm, preferably less than 2 nm, and better than 1 nm. According to the invention is called "roughness", the standard deviation of the relief of the upper surface of a monocrystalline grain, taken at the scale of the grain surface.
  • the monocrystalline grains have a wafer shape whose edges are irregular.
  • the monocrystalline grains may have various forms more or less elongated.
  • the monocrystalline grain or grains of the continuous or discontinuous layer of silicon and / or germanium may have a lateral dimension D strictly greater than 1 ⁇ , preferably greater than 2 ⁇ .
  • the silicon and / or germanium layer may be n or p doped.
  • the layer of silicon and / or germanium consisting of one or more monocrystalline grains can be obtained by crystallization induced by antimony.
  • the silicon and / or germanium layer further comprises antimony atoms and can be doped with antimony.
  • an antimony layer may also be interposed between the substrate and the silicon and / or germanium layer.
  • the silicon and / or germanium layer may be p-doped.
  • the layer of silicon and / or germanium consisting of one or more monocrystalline grains is preferably obtained by crystallization induced by aluminum.
  • the silicon and / or germanium layer furthermore comprises aluminum atoms and can therefore be doped with aluminum.
  • an aluminum layer may also be interposed between the substrate and the silicon and / or germanium layer. According to the first embodiment, a continuous layer can be obtained when the grains grow until they coalesce. A discontinuous layer can also be obtained.
  • a masking step consisting in depositing a layer above the substrate and for structuring openings in this layer before the step of depositing a metal layer above above or below a layer of silicon and / or amorphous germanium. This step makes it possible to selectively deposit the metal layer and the amorphous silicon and / or germanium layer in an ordered pattern on the substrate.
  • the monocrystalline grain or grains advantageously have at least one of the following characteristics:
  • the monocrystalline grains have a lateral dimension D greater than 2 ⁇ , preferably greater than 4 ⁇ and better still greater than 5 ⁇ ,
  • the ratio D / E between the lateral dimension D and the thickness of the layer of silicon and / or germanium is in order of increasing preference greater than 50, greater than 100, greater than 200, greater than 400, greater than 500 ,
  • the monocrystalline grain or grains have at least two lateral dimensions D1 and D2 perpendicular strictly greater than 1 ⁇ , preferably greater than 2 ⁇ , and better still greater than 5 ⁇ ,
  • the ratio between the lateral dimensions D, D1 and / or D2 and the height H of the nanowires is greater than 1, preferably 2.
  • the non-contiguous monocrystalline grains may also satisfy the characteristics defined above.
  • the substrate comprises one or more monocrystalline grains of non-joined silicon and / or germanium, the assembly thus forming a discontinuous layer.
  • This discontinuous layer consisting of non-contiguous monocrystalline grains can be obtained by adjusting the deposition parameters such as the thickness ratio between the metal layer and the layer of amorphous material or by decreasing the duration of the growth phase in order to prevent the coalescence of monocrystalline grains.
  • the discontinuous layer consisting of non-contiguous monocrystalline grains can be obtained by adding, during the manufacturing process, a step of depositing a layer above the substrate and of a step of structuring apertures of controlled size in this layer before the deposition step, in the desired order, of a metal layer and a layer of silicon and / or amorphous germanium.
  • This additional step makes it possible not only to selectively deposit the metal layer and the layer of amorphous silicon and / or germanium in a predetermined pattern on the substrate, but above all, by choosing nanometric openings, it is possible to obtain in each opening the growth of one and only one monocrystalline grain.
  • the monocrystalline grains preferably have a predetermined pattern having a maximum lateral dimension of 100 nm.
  • the monocrystalline grains may have larger lateral dimensions. This advantageous variant therefore makes it possible to obtain a substrate comprising one or more monocrystalline grains in a predetermined pattern.
  • the grains preferably have a maximum lateral dimension of less than 5 ⁇ , preferably less than 2 ⁇ .
  • the silicon and / or germanium layer may further comprise metal atoms selected from aluminum, silver, gold, antimony, copper, nickel, and lead. These atoms can come from the process for preparing the silicon and / or germanium layer comprising monocrystalline grains.
  • the invention advantageously makes it possible to grow nanowires on any type of substrate.
  • These substrates have at least a part of their flat surface, a sufficiently low surface roughness and a thermal compatibility with the conditions of the manufacturing process including melting points or sufficiently high glass transition temperatures.
  • the substrates used according to the invention may be flat over the entire surface of the surface or locally on sections of the surface.
  • a substrate comprising a texturing may be used according to the invention insofar as at least a portion of one of its surfaces corresponding to the area where it is desired to grow the nanowires is plane.
  • the substrate may therefore be chosen from amorphous, inorganic or organic substrates, the solid crystalline substrates comprising an orientation incompatible with vertical growth of nanowires, in particular an orientation other than (111), or simply incompatible with the growth of the nanowires.
  • amorphous substrate that is particularly suitable according to the invention, mention may be made of glass substrates.
  • a solid crystalline substrate that is particularly suitable according to the invention, mention may be made of solid silicon substrates having in particular a crystalline orientation other than that (111), such that (001).
  • a solid crystalline substrate having an orientation other than that allowing the vertical growth of nanowires is also interesting.
  • silicon substrates having a (001) orientation are used in microelectronics for reasons of manufacturing processes.
  • this orientation does not allow vertical growth of nanowires.
  • the method of the invention therefore makes it possible to convert a surface that is not adapted to the vertical growth of the nanowires into a suitable surface, allowing the integration of vertical nanowires into microelectronics.
  • the substrate is a solid silicon substrate not comprising its planes (111) parallel to the surface of the substrate, that is to say comprising an orientation other than (111), optionally covered by a silicon oxide layer, or any other layer compatible with the crystallization process, such as a zinc oxide (ZnO) layer.
  • ZnO zinc oxide
  • fused silica and borosilicates which have a glass transition temperature higher than the necessary temperatures of the manufacturing process.
  • the substrate may further comprise one or more layers located between the substrate and the layer of silicon and / or germanium consisting of one or more monocrystalline grains. This or these layer (s) can confer multiple properties on the substrate.
  • the substrate comprises at least one conductive layer providing the function of an electrode.
  • the substrate comprises the following stack defined starting from the substrate:
  • nanowires an upper electrode.
  • the lower and upper electrodes each comprise at least one electrically conductive layer.
  • the conductive layer may comprise transparent conductive oxides (TCO), that is, materials that are both good conductors and transparent in the visible, such as tin oxide and indium (ITO) , In203, Sn02 doped with antimony or fluorine (SnO2: F) or ZnO doped with aluminum (ZnO: Al).
  • TCO transparent conductive oxides
  • ITO tin oxide and indium
  • ITO indium
  • the conductive layer may also comprise transparent conductive polymers which are organic compounds with conjugated double bonds whose conductivity can be enhanced by chemical or electrochemical doping. These conductive layers based on conductive oxides or conductive polymers are preferably deposited on thicknesses of the order of 50 to 100 nm.
  • the conductive layer may also be a metal layer, for example Ag, Al, Pd, Cu, Pd, Pt, In, Mo, Au.
  • the electroconductive metal layer may be a thin layer, called TCC ("transparent conductive coating") having, preferably, a thickness between 2 and 50 nm.
  • Nanowires are objects of high crystalline quality. Their small lateral dimension makes it possible to elastically relax the stresses and to effectively trap potential defects extended to their free surface. Nanowires typically have diameters of the order of 10 to 200 nm and heights (or lengths) ranging from a few hundred nanometers to a few microns. The composition of the nanowire can be modulated at will along and perpendicular to its axis of growth. The nanowires can therefore comprise different substructures such as radial or axial heterostructures, or else different doping.
  • a height H preferably of at least 100 nm or at least 1 ⁇
  • the nanowires are chosen from metal oxides, silicon, germanium and the semiconductors III-V and II-VI,
  • III-V semiconductors may be chosen from GaAs, GaN, GaP, GaSb, InAs, InP, InSb, InN, and from among all the ternary or quaternary alloys intermediate between these binary compounds.
  • the stage of development or growth of the nanowires can be carried out by any which crystal growth technique and in particular by chemical vapor deposition (CVD), by laser ablation, by molecular beam epitaxy, by plasma assisted deposition, by chemical means in the liquid phase.
  • CVD chemical vapor deposition
  • laser ablation by laser ablation
  • molecular beam epitaxy by plasma assisted deposition
  • plasma assisted deposition by chemical means in the liquid phase.
  • WO 2009/054804 describes for example the conditions for the growth of semiconductor nanowires III-V by a chemical vapor deposition process that can be applied according to the present invention. However, it is preferred to carry out the growth step by molecular beam epitaxy.
  • the parameters of the growth step of the nanowires are chosen to selectively grow the nanowires only on the monocrystalline grains. These parameters are in particular the flows of injected starting materials and the temperature of the substrate.
  • the nanowires can be placed on the substrate randomly or in an ordered pattern.
  • ordered patterns can be obtained by assigning a predetermined location to each nanowire.
  • the ordered patterns can also be achieved by assigning a predetermined location to multiple nanowires defining a set of nanowires. In this case, the ordered pattern is not obtained by the pattern resulting from the location of each nanowire but by the pattern resulting from the location of the different sets of nanowires.
  • the method further comprises a step of depositing a layer above the silicon and / or germanium layer and a step of structuring openings, in this layer making it possible to grow nanowires according to ordered patterns.
  • the method of manufacturing the substrate further comprises a step of depositing a layer above the substrate and a step of structuring openings, in this layer for selectively depositing the metal layer and the amorphous silicon and / or germanium layer in an ordered pattern.
  • This method also comprises a nanowire growth step on the ordered patterns of monocrystalline grains of silicon and / or germanium.
  • the pattern will be defined by the location of each nanowire or each set of nanowires.
  • the size of the openings is preferably nanometric.
  • FIGS. 1 to 5 illustrate various diagrams representing the method of manufacturing a substrate according to the invention with perspective views and sectional views:
  • FIG. 1 represents a method of manufacturing a substrate according to the first embodiment of the invention with a crystallization induced by a so-called "direct” metal
  • FIG. 2 represents a method of manufacturing a substrate according to FIG. first embodiment of the invention with crystallization induced by a so-called "inverse" metal
  • FIG. 3 represents a method of manufacturing a substrate according to the first embodiment of the invention in which a layer of silicon and / or germanium is obtained placed on the substrate in a defined pattern
  • FIG. 4 represents a method for manufacturing a substrate according to the second embodiment of the invention in which controlled growth is achieved in order to obtain non-contiguous monocrystalline grains
  • FIG. 5 represents a method of manufacturing a substrate according to the second embodiment of the invention according to which a masking step is used to obtain non-contiguous monocrystalline grains in a predetermined pattern which will allow the nanowires to grow in accordance with a ordered pattern.
  • FIG. 6 is a scanning electron microscope image and a schematic representation of said image
  • FIG. 7 represents the profile of the contrast in the light field, taken perpendicular to the plane of the substrate as a function of the depth in nanometer, of an image obtained by transmission electron microscopy on a thinned slice sample after crystallization and etching,
  • FIG. 8 corresponds to an X-ray diffraction spectrum at grazing incidence of the silicon layer after crystallization and etching
  • FIG. 9 represents an image taken under a scanning electron microscope of a nanowire.
  • the diagram of FIG. 1 represents the main steps of the method of manufacturing a substrate according to the first embodiment of the invention with a crystallization induced by a so-called "direct" metal, that is to say by a layer of silicon and / or amorphous germanium above a metal layer.
  • the process of Figure 1 comprises the following four steps.
  • the first step consists of depositing successively and in this order on a substrate 1, a metal layer 3 and a layer of silicon and / or amorphous germanium 2a.
  • the second step corresponds to the actual crystallization of the layer of silicon and / or amorphous germanium 2a. Crystallization occurs at the interface between the metal layer 3 and the amorphous layer 2a (a-Si and / or a-Ge). The formed crystals then grow in the metal layer, rejecting the metal above, which leads to the end of the crystallization step at a reverse of the stack.
  • a substrate is obtained comprising a layer of silicon and / or germanium 2c consisting of one or more monocrystalline grains formed below the metal layer 3.
  • the third step is to eliminate by selective etching the metal layer 3 to allow the growth of the nanowires.
  • the fourth step corresponds to the actual growth of the nanowires on the monocrystalline grains constituting the crystallized layer of silicon and / or germanium 2c.
  • the process described by the scheme of Figure 2 differs essentially from that of Figure 1 in that the crystallization induced by a metal is called "inverse".
  • the process of Figure 2 comprises the following three steps.
  • the first step consists in depositing successively and in this order on a substrate 1, a layer of silicon and / or amorphous germanium 2a and a metal layer 3.
  • the second step corresponding to the crystallization leads to obtaining a substrate comprising a layer of silicon and / or germanium 2c consisting of one or more monocrystalline grains formed above the metal layer 3. it is not necessary to carry out an etching step contrary to the method illustrated in FIG.
  • the third step corresponds to the proper growth of the nanowires on the monocrystalline grains constituting the crystallized layer of silicon and / or germanium 2c.
  • the diagram of FIG. 3 represents the main steps of the method of manufacturing a substrate according to the first embodiment of the invention with crystallization induced by a so-called "direct" metal in which a layer of silicon and / or of germanium according to a defined pattern.
  • This method includes the use of a mask to mask the part of the surface of the substrate on which it is not desired grow nanowire.
  • the first step consists in depositing on the substrate a layer of the masking material 5.
  • the second step is to structure openings in this layer 5.
  • these first two steps can be replaced by the use of a mask or stencil simply applied to the substrate.
  • the third step consists in depositing successively on the substrate 1 comprising the structured layer 5, a metal layer 3 and a layer of silicon and / or amorphous germanium 2a.
  • the structured layer 5 can be removed before or after the crystallization of silicon.
  • the fourth step consists of the removal of the layer 5 used for the structuring.
  • a substrate 1 is thus obtained, successively comprising a metal layer 3 and a layer of silicon and / or amorphous germanium 2a.
  • the fifth step leads to obtaining a substrate comprising a layer of silicon and / or germanium 2c consisting of one or more monocrystalline grains formed above the metal layer 3 deposited in the pattern corresponding to the opening of the structured layer.
  • the sixth step is to eliminate by selective etching the metal layer 3 to allow the growth of the nanowires.
  • the seventh step corresponds to the actual growth of the nanowires on the monocrystalline grains constituting the crystallized layer of silicon and / or germanium 2c.
  • the fourth step corresponds to the crystallization and leads to obtaining a substrate comprising a layer of silicon and / or germanium 2c consisting of one or more monocrystalline grains formed below the metal layer 3
  • the fifth step consists in eliminating the metal layer 3 by selective etching.
  • the sixth step consists of the removal of the layer used for structuring 5. This gives a substrate 1 comprising a layer of silicon and / or germanium 2c consisting of one or more monocrystalline grains deposited in the pattern corresponding to the opening of the structured layer 5.
  • the seventh step corresponds to the actual growth of the nanowires on the monocrystalline grains constituting the crystallized layer of silicon and / or germanium 2c.
  • the process illustrated in FIG. 3 makes it possible to grow the nanowires in ordered patterns.
  • the diagram of FIG. 4 represents the main steps of the process for manufacturing a substrate according to the second embodiment of the invention with a crystallization induced by a so-called "direct" metal in which controlled growth is achieved in order to obtain unconjugated monocrystalline grains.
  • the process of Figure 4 comprises the following four steps.
  • the first step consists in successively depositing on a substrate 1, a metal layer 3 and a layer of silicon and / or amorphous germanium 2a.
  • the second step corresponds to the crystallization of the layer of silicon and / or amorphous germanium 2a.
  • the crystalline growth is controlled to prevent coalescence of the grains for example by choosing to deposit a metal layer 3 thicker than the layer of silicon and / or amorphous germanium 2a.
  • a substrate is obtained comprising a layer of silicon and / or germanium 2c consisting of one or more non-contiguous monocrystalline grains formed below the metal layer 3.
  • the third step is to eliminate by selective etching the metal layer 3 to allow the growth of the nanowires.
  • the fourth step corresponds to the actual growth of the nanowires on the monocrystalline grains constituting the layer of silicon and / or germanium 2c. Thanks to adequate experimental conditions, the nanowires do not grow on the surface of the substrate which does not comprise a monocrystalline grain.
  • FIG. 5 represents the fabrication of a substrate according to the second embodiment of the invention according to which a masking step is used to obtain non-contiguous monocrystalline grains in a pattern and one or more predetermined shapes. This method differs from that of FIG. 3 in that to obtain non-contiguous monocrystalline grains, the patterns of the mask used must have sufficiently small lateral dimensions.
  • the first step consists in depositing a layer 5 on the substrate 1.
  • the second step consists in structuring openings of controlled size in this layer 5.
  • the maximum lateral dimension of the openings D 0 must preferably be less than 5 ⁇ .
  • the choice of the nature of the layer used to achieve this structuring will be depending on the conditions of the process.
  • the resins conventionally used in lithography can be mentioned as a layer. It is also possible to envisage oxide layers that could be structured by selective etching.
  • the third step consists in depositing successively on a substrate 1, a metal layer 3 and a layer of silicon and / or amorphous germanium 2a.
  • the fourth step consists in removing the layer used for structuring 5. This gives a substrate 1 successively comprising a metal layer 3 and a layer of silicon and / or amorphous germanium 2a.
  • the fifth step leads to obtaining a substrate comprising a layer of silicon and / or germanium 2c consisting of monocrystalline grains of silicon and / or non-joined germanium formed below the metal layer 3 and deposited according to the pattern corresponding to the opening of the structured layer 5.
  • the sixth step is to eliminate by selective etching the metal layer 3 to allow the growth of the nanowires.
  • the seventh step corresponds to the actual growth of the nanowires on the non-joined monocrystalline grains constituting the layer of silicon and / or germanium 2c. It is then possible to grow one or more nanowires according to the characteristics of the growth, and / or the size of the monocrystalline grains.
  • the substrate comprising on at least a portion of one of its surfaces a continuous or discontinuous layer of silicon and / or germanium consisting of one or more monocrystalline grains, all oriented so that they have plans (111). ) parallel to the surface of the substrate can allow the growth of any other object of varied shape such as layers and pads, consisting of materials that require substrates having an adequate crystalline orientation (111) for their growth by epitaxy.
  • These objects are of the same nature as the nanowires and preferably are semiconductors III-V or II-VII.
  • the invention may also relate to a substrate comprising on at least a portion of one of its surfaces a layer of silicon and / or germanium consisting of one or more monocrystalline grains, all oriented so that they have plans ( 111) parallel to the surface of the substrate, and on this layer, one or more objects of varied shape.
  • a substrate finds application in various fields such as electronics, optics or optoelectronics. Examples
  • the amorphous aluminum-silicon stack is deposited by DC magnetron sputtering onto fused silica, glass, and oxidized Si (100) substrates (250 nm surface-amorphous SiO 2 obtained by wet oxidation of Si (100) at 950 ° C). All types of substrates were previously rinsed with acetone, ethanol and deionized water.
  • a layer of 10 nm of aluminum is deposited at a power of 50 W, under an argon pressure of 1.5 ⁇ bar, at room temperature, and placed at a floating electric potential (deposition rate of 2.24 ⁇ "1). the 10 nm of amorphous silicon are deposited consecutively to aluminum, without breaking the vacuum, and a power of 20 W (all other identical operating conditions) (deposition rate of 0.46 s" 1).
  • the stacks are annealed at 400 ° C. for 15 h under a nitrogen atmosphere (2 L min -1 ).
  • the surface aluminum layer is etched wet: the substrate is immersed in a concentrated hydrochloric acid solution (37% by weight) for 15 minutes at room temperature; where appropriate, the amorphous oxide layer Al-Si-O (present at the p-Si-Al interface) may be etched with a dilute aqueous solution of hydrofluoric acid (5% by weight).
  • the morphology of the layers is analyzed by optical microscopy, scanning electron microscopy and transmission electron microscopy.
  • FIG. 6 is a scanning electron microscope image, as well as a schematic representation of said image, of an oxidized silicon substrate (001) on which a silicon layer has crystallized.
  • the thickness of the layer comprising monocrystalline grains of silicon is 10 nm.
  • the hatched parts delimit the grains and the white parts the Si0 2 .
  • Roughness at the grain surface level was measured using an atomic force microscope (AFM). By measuring this roughness on several grains, the most unfavorable roughness measured on a grain is 1, 2 nm.
  • FIG. 7 represents the profile of the contrast in a light field, taken perpendicular to the plane of the substrate as a function of the depth in nanometer, of an image obtained by transmission electron microscopy on a thinned slice sample after crystallization and etching.
  • the resulting profile is characteristic of grain crystallization with (111) planes parallel to the surface of the substrate.
  • the crystalline properties of the p-Si layer were also analyzed by grazing incidence X-ray diffraction (GIXRD: Grazing Incidence X-Ray Diffraction), due to the fineness of the layer.
  • GIXRD grazing incidence X-ray diffraction
  • the layers of p-Si have a perfect texture (111) as shown by the spectrum of figure 8. Only the families of plane ⁇ 220 ⁇ and ⁇ 422 ⁇ are observed by GIXRD: it is the signature of the texture (111 ) complete movie.
  • the nanowires are obtained by evacuating and degassing the substrate comprising the thin layer followed by a conventional nanowire growth procedure (any catalyst and any III-V material).
  • GaAs nanowires autocatalysts The growth of GaAs nanowires autocatalysts is carried out by molecular beam epitaxy (MBE) MBE in a frame 32 of Riber, under a rotation of 7 rounds min "1 and a flow equivalent to a planar Gallium growth of 2.0 ⁇ s "1 (pressure of 3.0-10 7 Torr).
  • MBE molecular beam epitaxy
  • the thin film substrates are degassed under vacuum at 450 ° C. for 1 hour.
  • the substrate is transferred to the growth chamber and is heated to 450 ° C.
  • Gallium is deposited for 60 s (amount equivalent to 19 monolayers of Ga).
  • the temperature is raised from 450 ° C to 580 ° C (growth temperature) in 10 minutes using a ramp.
  • the shutter As (in the form of As 4) and Ga are opened simultaneously, respectively providing flow 4,2- 10 "6 torr and 10 3,0- “7 Torr.
  • Arsenic pressure is linearly increased to 5,2- 10 "6 torr, 300 s. Growth is maintained under these conditions for an additional 300 s.
  • the sources of As 4 and Ga are simultaneously closed, and the sample is transferred out of the growth chamber.
  • FIG. 9 represents an image taken under a scanning electron microscope of a nanowire obtained according to the method of the invention.
  • the nanowire is vertical on the surface of a monocrystalline grain of silicon.

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Abstract

The present invention concerns a substrate comprising a continuous or discontinuous layer of silicon and/or germanium consisting of one or a plurality of monocrystalline grains, and on said layer, one or a plurality of nanowires of which the longitudinal axis is oriented perpendicular to the surface of the substrate. The invention also concerns a method for producing such a substrate.

Description

SUBSTRAT COMPRENANT UNE COUCHE DE SILICIUM ET/OU DE GERMANIUM ET UN OU PLUSIEURS NANOFILS D'ORIENTATION PERPENDICULAIRE A LA SURFACE  SUBSTRATE COMPRISING A SILICON AND / OR GERMANIUM LAYER AND ONE OR MORE SURFACE PERPENDICULAR ORIENTATION NANOWIRES
DU SUBSTRAT La présente invention concerne un substrat comprenant une couche continue ou discontinue de silicium et/ou de germanium constituée d'un ou plusieurs grains monocristallins, et sur cette couche, un ou plusieurs nanofils dont l'axe longitudinal est orienté perpendiculairement à la surface du substrat. L'invention concerne également un procédé de fabrication d'un tel substrat.  The present invention relates to a substrate comprising a continuous or discontinuous layer of silicon and / or germanium consisting of one or more monocrystalline grains, and on this layer, one or more nanowires whose longitudinal axis is oriented perpendicularly to the surface. of the substrate. The invention also relates to a method of manufacturing such a substrate.
Les nanofils orientés perpendiculairement à la surface d'un substrat présentent des propriétés remarquables vis-à-vis des phénomènes de transport et de confinement électronique ou optique. L'orthogonalité de la croissance de nanofils par rapport à la surface d'un substrat présente un fort intérêt car cette caractéristique facilite non seulement leur insertion dans des dispositifs électroniques, mais également optiques ou optoélectroniques.  Nanowires oriented perpendicular to the surface of a substrate have remarkable properties vis-à-vis the phenomena of transport and electronic or optical confinement. The orthogonality of the growth of nanowires with respect to the surface of a substrate is of great interest because this feature facilitates not only their insertion in electronic devices, but also optical or optoelectronic.
L'obtention d'une croissance verticale de nanofils nécessite l'utilisation de substrats présentant une orientation cristalline adéquate. La croissance des nanofils est donc en général réalisée sur des substrats cristallins massifs présentant une telle orientation.  Obtaining vertical growth of nanowires requires the use of substrates having a proper crystalline orientation. The growth of the nanowires is therefore generally carried out on massive crystalline substrates having such an orientation.
L'utilisation de ces substrats massifs présente toutefois des nombreux inconvénients notamment en termes de coût et de manque de souplesse pour intégrer des dispositifs plus complexes. Par exemple, le transfert vers des formats dépassant la dimension typique d'un monocristal commercial est difficilement réalisable. De plus, il n'est pas possible de moduler l'indice de réfraction ou la transmission lumineuse de ces substrats.  The use of these bulk substrates, however, has many drawbacks in particular in terms of cost and lack of flexibility to integrate more complex devices. For example, the transfer to formats exceeding the typical dimension of a commercial single crystal is difficult to achieve. In addition, it is not possible to modulate the refractive index or the light transmission of these substrates.
La croissance épitaxiale verticale de nanofils sur tout autre substrat présente plusieurs difficultés, notamment lorsque le substrat est cristallin mais sans présenter l'orientation cristalline adéquate pour la croissance de nanofils verticaux ou lorsque le substrat est amorphe.  The vertical epitaxial growth of nanowires on any other substrate presents several difficulties, especially when the substrate is crystalline but without having the appropriate crystalline orientation for the growth of vertical nanowires or when the substrate is amorphous.
Des essais de croissance de nanofils sur des substrats amorphes ont été réalisés. Cependant, lorsque le substrat est amorphe, les nanofils ne poussent dans aucune direction privilégiée.  Growth tests of nanowires on amorphous substrates were carried out. However, when the substrate is amorphous, the nanowires do not grow in any preferred direction.
Il a récemment été proposé dans la demande WO 2011/105397 d'utiliser un substrat en verre comprenant une couche de silicium cristallisé sur laquelle est déposée une couche isolante présentant des ouvertures servant de zones de croissance des nanofils. La couche de silicium cristallisé comprend des grains monocristallins délimités par des joints de grains. Selon ce document, la croissance verticale des nanofils est rendue possible grâce au choix d'une taille de surface pour délimiter les zones de croissance inférieure à la surface de chaque grain monocristallin de silicium. Ce document divulgue que sur 28 ouvertures, 10 sont au regard d'un bord de grain. Au travers ces 10 ouvertures, 8 nanofils poussent verticalement mais avec un diamètre plus faible que les nanofils poussant dans des ouvertures ne comprenant pas de bord de grain et 2 ouvertures ne conduisent pas à la croissance de nanofil. It has recently been proposed in the application WO 2011/105397 to use a glass substrate comprising a crystallized silicon layer on which is deposited an insulating layer having openings serving as growth zones of the nanowires. The crystallized silicon layer comprises monocrystalline grains defined by grain boundaries. According to this document, the vertical growth of the nanowires is made possible by the choice of a surface size to delimit the areas of growth below the surface of each monocrystalline silicon grain. This document discloses that out of 28 openings, 10 are facing a grain edge. Through these 10 apertures, 8 nanowires grow vertically but with a smaller diameter than the nanowires growing in apertures not including a grain edge and 2 openings do not lead to nanowire growth.
Selon ce document, la couche de silicium cristallisé a une épaisseur comprise entre 10 et 100 nm, de préférence 50 nm. Les grains monocristallins ont une dimension latérale moyenne de 200 nm à environ 1 μηη. Le seul procédé de cristallisation de la couche de silicium décrit dans ce document est le recuit laser. Aucune indication n'est donnée sur la rugosité de surface d'une telle couche de silicium cristallisé.  According to this document, the crystallized silicon layer has a thickness of between 10 and 100 nm, preferably 50 nm. The monocrystalline grains have an average lateral dimension of 200 nm to about 1 μηη. The only crystallization process of the silicon layer described in this document is laser annealing. No indication is given on the surface roughness of such a crystallized silicon layer.
De plus, parmi les nanofils verticaux, un écart à la normale au substrat (ou surface) plus au moins important peut être observé et attribué à des causes variées telles que la rugosité propre du substrat ou une inclinaison des grains monocristallins sur le substrat se répercutant sur la croissance des nanofils.  In addition, among the vertical nanowires, a deviation from normal to the substrate (or surface) more or less important can be observed and attributed to various causes such as the intrinsic roughness of the substrate or an inclination of monocrystalline grains on the substrate reverberating on the growth of nanowires.
Enfin, d'autres problèmes peuvent survenir lors de la croissance des nanofils tels que des phénomènes de coalescence ou l'apparition de macles.  Finally, other problems can arise during the growth of nanowires such as coalescence phenomena or the appearance of twins.
La présente invention concerne la fabrication de nanofils verticaux sur des substrats variés pouvant être amorphes ou présenter une orientation cristalline autre que l'orientation adéquate à la croissance verticale, ou même sur des substrats incompatibles avec la croissance des nanofils, obtenus selon un procédé simple à mettre en œuvre. A cette fin, les demandeurs ont mis au point un substrat :  The present invention relates to the manufacture of vertical nanowires on various substrates which may be amorphous or have a crystalline orientation other than the orientation suitable for vertical growth, or even on substrates incompatible with the growth of nanowires, obtained by a method which is simple to use. enforce. To this end, the applicants have developed a substrate:
- permettant une croissance verticale maîtrisée des nanofils, - allowing controlled vertical growth of nanowires,
- prévenant les problèmes liés à leur coalescence et à l'obtention d'une grande dispersion de leur géométrie,  - preventing the problems related to their coalescence and obtaining a great dispersion of their geometry,
- favorisant la prise de contact électrique sur un ensemble de nanofils.  - Favoring the electrical contact on a set of nanowires.
Selon un premier mode de réalisation, l'invention concerne donc un substrat comprenant sur au moins une partie de l'une de ses surfaces une couche de silicium et/ou de germanium d'épaisseur E constituée d'un ou plusieurs grains monocristallins, tous orientés de sorte qu'ils aient des plans (111 ) parallèles à la surface du substrat, et sur cette couche, un ou plusieurs nanofils dont l'axe longitudinal est orienté perpendiculairement à la surface du substrat caractérisé en ce que : ~ le ou les grains monocristailins de la couche de silicium et/ou de germanium présentent une dimension latérale D, définie comme une corde du bord de grain, sur tous les grains strictement supérieure à 1 μητι, de préférence supérieure à 2 μηη et au mieux supérieure à 5 μηη, According to a first embodiment, the invention therefore relates to a substrate comprising on at least a portion of one of its surfaces a layer of silicon and / or germanium of thickness E consisting of one or more monocrystalline grains, all oriented so that they have planes (111) parallel to the surface of the substrate, and on this layer, one or more nanowires whose longitudinal axis is oriented perpendicular to the surface of the substrate characterized in that: the one or more monocrystalline grains of the silicon and / or germanium layer have a lateral dimension D, defined as a chord of the grain edge, on all grains strictly greater than 1 μητι, preferably greater than 2 μηη and at best greater than 5 μηη,
- le rapport D/E entre la dimension latérale D et l'épaisseur de la couche de silicium et/ou de germanium est supérieur à 25, de préférence 100. the ratio D / E between the lateral dimension D and the thickness of the layer of silicon and / or germanium is greater than 25, preferably 100.
On appelle « corde » D, un segment de droite joignant deux points du contour d'un grain.  We call "chord" D, a line segment joining two points of the outline of a grain.
La dimension latérale des grains peut être mesurée par traitement d'images obtenues par tous modes d'observation microscopique, directs ou indirects, tels que la microscopie électronique à balayage, la microscopie électronique en transmission, la diffraction des électrons rétrodiffusés (« Electron backscatter diffraction »), la microscopie à force atomique et la microscopie optique.  The lateral dimension of the grains can be measured by image processing obtained by any microscopic observation mode, direct or indirect, such as scanning electron microscopy, transmission electron microscopy, backscatter electron diffraction (Electron backscatter diffraction "), Atomic force microscopy and optical microscopy.
Selon l'invention, on considère cette caractéristique comme satisfaite lorsqu'au moins 80%, de préférence au moins 90%, mieux au moins 95% et encore mieux 100% des grains présentent au moins une dimension latérale D supérieure à 1 μηη.  According to the invention, this characteristic is considered to be satisfied when at least 80%, preferably at least 90%, better still at least 95% and even better 100% of the grains have at least one lateral dimension D greater than 1 μηη.
Selon un deuxième mode de réalisation, l'invention concerne un substrat comprenant sur au moins une partie de l'une de ses surfaces un ou plusieurs grains monocristallins de silicium et/ou de germanium non jointifs et tous orientés de sorte qu'ils présentent des plans (111 ) parallèles à la surface du substrat, et sur chaque grain un ou plusieurs nanofils dont l'axe longitudinal est orienté perpendiculairement à la surface du substrat.  According to a second embodiment, the invention relates to a substrate comprising, on at least a part of one of its surfaces, one or more monocrystalline grains of non-joined silicon and / or germanium and all oriented so that they present planes (111) parallel to the surface of the substrate, and on each grain one or more nanowires whose longitudinal axis is oriented perpendicular to the surface of the substrate.
Selon l'invention, des grains monocristallins non jointifs sont des grains isolés les uns des autres par une distance, de préférence d'au moins 10 nm, l'ensemble formant ainsi une couche discontinue.  According to the invention, non-contiguous monocrystalline grains are grains isolated from each other by a distance, preferably of at least 10 nm, the assembly thus forming a discontinuous layer.
L'invention concerne également un procédé de fabrication d'un substrat comprenant les étapes suivantes :  The invention also relates to a method of manufacturing a substrate comprising the following steps:
- former par cristallisation induite par un métal sur au moins une partie de l'une des surfaces d'un substrat une couche de silicium et/ou de germanium d'épaisseur E constituée d'un ou plusieurs grains monocristallins tous orientés de sorte qu'ils aient des plans (111 ) parallèles à la surface du substrat,  - forming by metal-induced crystallization on at least a portion of one of the surfaces of a substrate a layer of silicon and / or germanium of thickness E consisting of one or more monocrystalline grains all oriented so that they have planes (111) parallel to the surface of the substrate,
- faire croître, de préférence par épitaxie, sur les grains monocristallins un ou plusieurs nanofils dont l'axe longitudinal est orienté perpendiculairement à la surface du substrat.  - Growing, preferably by epitaxy, on monocrystalline grains one or more nanowires whose longitudinal axis is oriented perpendicularly to the surface of the substrate.
L'invention concerne également tout dispositif basé sur un tel substrat et pouvant notamment être choisis parmi des éléments récepteurs ou émetteurs de lumière tels que les cellules solaires photovoltaïques, les diodes lasers, les diodes électroluminescentes, les photocathodes ou parmi des composants électroniques tels que les transistors bipolaires et les transistors MIS (« Metal-insulator-semiconductor »). The invention also relates to any device based on such a substrate and capable of in particular be chosen from light receiving or emitting elements such as photovoltaic solar cells, laser diodes, light emitting diodes, photocathodes or from electronic components such as bipolar transistors and metal-insulator-semiconductor (MIS) transistors. ).
Les termes « vertical », « perpendiculaire » et « orthogonal » peuvent être indifféremment utilisés. Selon l'invention, un nanofil dont l'axe longitudinal est orienté perpendiculairement à la surface du substrat correspond à un nanofil poussant à partir de la couche de silicium et/ou de germanium dans une direction perpendiculaire au substrat. Les nanofils d'orientation perpendiculaire selon l'invention forment en fait un angle a très proche de 90° par rapport à la surface du substrat. L'angle a peut s'écarter de la valeur de 90° par exemple à cause de désordre, de défauts ou de contrainte lors de la croissance des nanofils et des grains monocristallins. Avantageusement, au moins 90%, de préférence au moins 95%, mieux 100% des nanofils d'orientation perpendiculaire ont un angle a par rapport à la surface du substrat de 90°± 10°, de préférence 90°± 5° ou mieux 90°± 2,5°.  The terms "vertical", "perpendicular" and "orthogonal" may be used interchangeably. According to the invention, a nanowire whose longitudinal axis is oriented perpendicular to the surface of the substrate corresponds to a nanowire pushing from the silicon and / or germanium layer in a direction perpendicular to the substrate. The nanowires of perpendicular orientation according to the invention form an angle at very close to 90 ° with respect to the surface of the substrate. The angle α may deviate from the value of 90 ° for example because of disorder, defects or stress during the growth of nanowires and monocrystalline grains. Advantageously, at least 90%, preferably at least 95%, better 100% of perpendicular orientation nanowires have an angle α with respect to the surface of the substrate of 90 ° ± 10 °, preferably 90 ° ± 5 ° or better 90 ° ± 2.5 °.
L'épitaxie des nanofils sur la couche mince de silicium et/ou de germanium intermédiaire permet une croissance verticale des nanofils, sans contact ni coalescence entre eux.  The epitaxy of the nanowires on the thin layer of silicon and / or intermediate germanium allows vertical growth of the nanowires, without contact or coalescence between them.
La couche de silicium et/ou de germanium est constituée d'un ou plusieurs grains monocristallins présentant une extension latérale élevée et une rugosité faible. Les grains monocristallins sont tous orientés de sorte qu'ils présentent des plans (111 ) parallèles à la surface du substrat bien que présentant des épaisseurs extrêmement faibles (de l'ordre d'une dizaine de nanomètre). L'ensemble de ces caractéristiques concourent à l'obtention d'une excellente croissance verticale des nanofils. Contrairement au document WO 2011/1105397, le substrat de l'invention ne nécessite pas de couche isolante comprenant des ouvertures servant de zone de croissance pour obtenir la croissance verticale des nanofils.  The silicon and / or germanium layer consists of one or more monocrystalline grains with high lateral extension and low roughness. The monocrystalline grains are all oriented so that they have planes (111) parallel to the surface of the substrate although having extremely low thicknesses (of the order of ten nanometers). All of these characteristics contribute to obtaining excellent vertical growth of nanowires. Unlike the document WO 2011/1105397, the substrate of the invention does not require an insulating layer comprising openings serving as a growth zone to obtain the vertical growth of the nanowires.
Ces caractéristiques permettent de limiter, voire supprimer, les inconvénients liés à la présence de joints de grain pouvant générer toutes sortes de défauts ainsi que les inconvénients liés à l'inclinaison des grains monocristallins sur le substrat pouvant générer des écarts par rapport à la vertical des nanofils verticaux.  These characteristics make it possible to limit or even eliminate the drawbacks associated with the presence of grain boundaries that can generate all kinds of defects as well as the disadvantages associated with the inclination of monocrystalline grains on the substrate that can generate deviations from the vertical of the grains. vertical nanowires.
Un autre aspect bénéfique de l'invention repose sur le fait que les propriétés avantageuses de la couche de silicium et/ou de germanium sont obtenues pour des fines épaisseurs. Or, les nanofils, pour être intégrés dans des dispositifs complexes, doivent être connectés à une électrode conductrice. Cette électrode peut donc par exemple être une couche conductrice déposée entre le substrat et la couche de silicium et/ou de germanium. Plus l'épaisseur de la couche de silicium et/ou de germanium est faible, moins la conductivité au travers de cette couche sera gênée et plus il sera facile de connecter les nanofils à l'électrode. Another beneficial aspect of the invention lies in the fact that the advantageous properties of the silicon and / or germanium layer are obtained for thin layers. However, nanowires, to be integrated in complex devices, must be connected to a conductive electrode. This electrode may therefore for example be a conductive layer deposited between the substrate and the silicon and / or germanium layer. The lower the thickness of the silicon and / or germanium layer, the less the conductivity through this layer will be obstructed and the easier it will be to connect the nanowires to the electrode.
Une autre caractéristique particulièrement avantageuse provient du procédé de fabrication qui comprend la formation par cristallisation induite par un métal (« Métal Induced latéral Crystallization ») de la couche de silicium et/ou de germanium constituée d'un ou plusieurs grains monocristallins. La cristallisation induite par un métal est obtenue par dépôt d'une couche métallique au-dessus ou en-dessous d'une couche du matériau que l'on souhaite cristalliser, c'est-à-dire d'une couche de silicium et/ou de germanium amorphe. La couche métallique peut être une couche d'un métal choisi parmi l'aluminium (Al), l'argent (Ag), l'or (Au), l'antimoine (Sb), le cuivre (Cu), le nickel (Ni) ou le plomb (Pb).  Another particularly advantageous characteristic comes from the manufacturing process which comprises the formation induced by a metal-induced crystallization ("Metal Induced Lateral Crystallization") of the layer of silicon and / or germanium consisting of one or more monocrystalline grains. The crystallization induced by a metal is obtained by depositing a metal layer above or below a layer of the material that it is desired to crystallize, that is to say a layer of silicon and / or or amorphous germanium. The metal layer may be a layer of a metal selected from aluminum (Al), silver (Ag), gold (Au), antimony (Sb), copper (Cu), nickel ( Ni) or lead (Pb).
Au contact de la couche métallique, la couche du matériau amorphe (a-Si ou a-Ge) cristallise à une température choisie, suffisante et inférieure à la température de l'eutectique entre le métal et le matériau à cristalliser. On parle alors d'interdiffusion lors du recuit sous l'eutectique (recuit sous atmosphère inerte entre 250 et 550°C donnant les facettes (111 ) du p-Si). D'un point de vue phénoménologique, il apparaît des germes cristallins dans la couche métallique (nucléation) qui croissent spontanément et forment ainsi des grains (croissance).  In contact with the metal layer, the layer of amorphous material (a-Si or a-Ge) crystallizes at a chosen temperature, sufficient and less than the temperature of the eutectic between the metal and the material to be crystallized. We then speak of interdiffusion during annealing under the eutectic (annealing under an inert atmosphere between 250 and 550 ° C giving facets (111) of p-Si). From a phenomenological point of view, crystalline seeds appear in the metal layer (nucleation) which grow spontaneously and thus form grains (growth).
La croissance cristalline est réalisée à l'interface entre la couche métallique et la couche amorphe. Les cristaux formés s'insèrent et croissent alors dans la couche métallique. Selon le positionnement de la couche métallique par rapport à la couche amorphe, on obtient en fin de cristallisation des empilements différents.  Crystalline growth is achieved at the interface between the metal layer and the amorphous layer. The crystals formed fit and then grow in the metal layer. Depending on the positioning of the metal layer with respect to the amorphous layer, different stacks are obtained at the end of crystallization.
Lorsque l'on dépose successivement sur le substrat, la couche métallique puis la couche amorphe, on obtient, après cristallisation, un substrat comprenant une couche cristalline recouverte d'une couche métallique. Pour permettre la croissance des nanofils, il est nécessaire d'éliminer cette couche métallique. Selon un mode de réalisation du procédé de l'invention, lorsque la couche de silicium et/ou de germanium constituée d'un ou plusieurs grains monocristallins est formée en-dessous de la couche métallique, cette dernière est retirée par gravure sélective. Par exemple, dans le cas d'une cristallisation induite par de l'aluminium, la couche d'aluminium peut être gravée totalement et sélectivement par utilisation d'un mélange d'acide chlorhydrique concentré et d'acide nitrique. Enfin, les oxydes superficiels d'aluminium et/ou de silicium peuvent également être gravés par exemple à l'acide fluoridrique (5%). When one deposits successively on the substrate, the metal layer then the amorphous layer, one obtains, after crystallization, a substrate comprising a crystalline layer covered with a metal layer. To allow the growth of the nanowires, it is necessary to eliminate this metal layer. According to one embodiment of the process of the invention, when the layer of silicon and / or germanium consisting of one or more monocrystalline grains is formed below the metal layer, the latter is removed by selective etching. For example, in the case of aluminum-induced crystallization, the aluminum layer can be etched completely and selectively by using a mixture of concentrated hydrochloric acid and nitric acid. Finally, the surface oxides of aluminum and / or silicon can also be etched for example with fluoridic acid (5%).
Lorsque l'on dépose successivement sur le substrat, la couche amorphe puis la couche métallique, on obtient, après cristallisation, une couche de silicium et/ou de germanium constituée d'un ou plusieurs grains monocristallins formée au-dessus de la couche métallique. La présence de cette couche métallique intercalée entre le substrat et la couche de silicium et/ou de germanium constituée d'un ou plusieurs grains monocristallins est intéressante car elle peut assurer partiellement ou totalement une fonction d'électrode. Le substrat peut donc comprendre une couche métallique, de préférence d'aluminium, intercalée entre ledit substrat et la couche de silicium et/ou de germanium constituée d'un ou plusieurs grains monocristallins. Enfin, le choix du métal utilisé pour catalyser la cristallisation peut conférer à la couche de silicium et/ou de germanium des propriétés particulières. Par exemple, dans le cas d'une cristallisation induite par de l'aluminium, il est possible d'obtenir des grains monocristallins de silicium et/ou de germanium dopés de type p, par exemple par de l'aluminium. Pour les mêmes raisons que celles exposées ci-dessus, l'amélioration de la conductivité de la couche de silicium et/ou de germanium peut présenter un avantage déterminant.  When one deposits successively on the substrate, the amorphous layer then the metal layer, one obtains, after crystallization, a layer of silicon and / or germanium consisting of one or more monocrystalline grains formed above the metal layer. The presence of this metal layer interposed between the substrate and the layer of silicon and / or germanium consisting of one or more monocrystalline grains is interesting because it can partially or completely provide an electrode function. The substrate may therefore comprise a metal layer, preferably aluminum, interposed between said substrate and the layer of silicon and / or germanium consisting of one or more monocrystalline grains. Finally, the choice of the metal used to catalyze the crystallization may give the silicon and / or germanium layer particular properties. For example, in the case of aluminum-induced crystallization, it is possible to obtain p-type doped silicon and / or germanium monocrystalline grains, for example by aluminum. For the same reasons as those set out above, the improvement of the conductivity of the silicon and / or germanium layer may have a decisive advantage.
Le procédé d'obtention de la couche de silicium et/ou de germanium constituée d'un ou plusieurs grains monocristallins, permettant à la fois le dopage du silicium et/ou du germanium ainsi que la formation d'une couche métallique conductrice pouvant servir d'électrode facilite effectivement l'intégration de dispositifs complexes sur ce substrat.  The process for obtaining the silicon and / or germanium layer consisting of one or more monocrystalline grains, allowing both the doping of silicon and / or germanium and the formation of a conductive metal layer that can serve The electrode effectively facilitates the integration of complex devices on this substrate.
La couche métallique et la couche de silicium et/ou de germanium amorphe peuvent être déposées par tous procédés classiques de dépôt tels que les dépôts chimiques et physiques en phase vapeur. De manière avantageuse, ces couches sont déposées par pulvérisation cathodique assistée par champ magnétique (« dépôt magnétron »).  The metal layer and the layer of silicon and / or amorphous germanium can be deposited by any conventional deposition methods such as chemical and physical vapor deposition. Advantageously, these layers are deposited by magnetic field assisted sputtering ("magnetron deposition").
En choisissant des paramètres de dépôt et des conditions de recuit appropriés, les grains peuvent croître jusqu'à leur coalescence. L'épaisseur relative des couches déposées est un paramètre clé permettant ou non la coalescence des grains :  By choosing suitable deposition parameters and annealing conditions, the grains can grow until they coalesce. The relative thickness of the deposited layers is a key parameter allowing or not the coalescence of the grains:
- lorsque l'épaisseur de la couche métallique est supérieure à l'épaisseur de la couche de matériau amorphe, la couche de matériaux cristallisés forme une couche discontinue,  when the thickness of the metal layer is greater than the thickness of the layer of amorphous material, the layer of crystallized materials forms a discontinuous layer,
- lorsque l'épaisseur de la couche métallique est égale à l'épaisseur de la couche de matériau amorphe, la couche de matériaux cristallisés forme une couche continue, when the thickness of the metal layer is equal to the thickness of the layer of amorphous material, the layer of crystallized materials forms a continuous layer,
- lorsque l'épaisseur de la couche métallique est inférieure à l'épaisseur de la couche de matériau amorphe, la couche de matériau cristallisé forme une couche continue comprenant en outre des ilôts proéminents. when the thickness of the metal layer is less than the thickness of the amorphous material, the layer of crystallized material forms a continuous layer further comprising prominent islands.
La couche de silicium et/ou de germanium constituée d'un ou plusieurs grains monocristallins peut être continue ou discontinue. Lorsque la couche de silicium et/ou de germanium est discontinue, on entend par épaisseur E, l'épaisseur moyenne des grains monocristallins la constituant.  The silicon and / or germanium layer consisting of one or more monocrystalline grains may be continuous or discontinuous. When the silicon and / or germanium layer is discontinuous, thickness E is understood to mean the average thickness of the monocrystalline grains constituting it.
L'épaisseur de la couche de silicium et/ou de germanium E est, par ordre de préférence croissant, inférieure à 50 nm, inférieure à 40 nm, inférieure à 30 nm, inférieure à 20 nm, comprise entre 5 et 15 nm.  The thickness of the silicon and / or germanium layer E is, in order of increasing preference, less than 50 nm, less than 40 nm, less than 30 nm, less than 20 nm, of between 5 and 15 nm.
La rugosité de la surface du ou des grains constituant la couche de silicium et/ou de germanium mesurée par la technique de microscopie à force atomique est inférieure à 5 nm, de préférence inférieure à 2 nm, et au mieux inférieure à 1 nm. On appelle selon l'invention « rugosité », l'écart-type du relief de la surface supérieure d'un grain monocristallin, prise à l'échelle de la surface du grain.  The roughness of the surface of the grain (s) constituting the silicon and / or germanium layer measured by the atomic force microscopy technique is less than 5 nm, preferably less than 2 nm, and better than 1 nm. According to the invention is called "roughness", the standard deviation of the relief of the upper surface of a monocrystalline grain, taken at the scale of the grain surface.
Les grains monocristallins ont une forme de plaquette dont les bords sont irréguliers. Les grains monocristallins peuvent avoir des formes variées plus ou moins allongées.  The monocrystalline grains have a wafer shape whose edges are irregular. The monocrystalline grains may have various forms more or less elongated.
Le ou les grains monocristallins de la couche continue ou discontinue de silicium et/ou de germanium peuvent présenter une dimension latérale D, strictement supérieure à 1 μηη, de préférence supérieure à 2 μηη.  The monocrystalline grain or grains of the continuous or discontinuous layer of silicon and / or germanium may have a lateral dimension D strictly greater than 1 μηη, preferably greater than 2 μηη.
La couche de silicium et/ou de germanium peut être dopée n ou p.  The silicon and / or germanium layer may be n or p doped.
En particulier, la couche de silicium et/ou de germanium constituée d'un ou plusieurs grains monocristallins peut être obtenue par cristallisation induite par de l'antimoine. Dans ce cas, la couche de silicium et/ou de germanium comprend en outre des atomes d'antimoine est peut donc être dopée par de l'antimoine. Selon une variante de l'invention, une couche d'antimoine peut également être intercalée entre le substrat et la couche de silicium et/ou de germanium.  In particular, the layer of silicon and / or germanium consisting of one or more monocrystalline grains can be obtained by crystallization induced by antimony. In this case, the silicon and / or germanium layer further comprises antimony atoms and can be doped with antimony. According to a variant of the invention, an antimony layer may also be interposed between the substrate and the silicon and / or germanium layer.
Dans une variante particulièrement avantageuse, la couche de silicium et/ou de germanium peut être dopée p. En particulier, la couche de silicium et/ou de germanium constituée d'un ou plusieurs grains monocristallins est obtenue de préférence par cristallisation induite par de l'aluminium. Dans ce cas, la couche de silicium et/ou de germanium comprend en outre des atomes d'aluminium est peut donc être dopée par l'aluminium. Selon un mode de réalisation particulier, une couche d'aluminium peut également être intercalée entre le substrat et la couche de silicium et/ou de germanium. Selon le premier mode de réalisation, une couche continue peut être obtenue lorsque les grains croissent jusqu'à leur coalescence. Une couche discontinue peut également être obtenue. Il suffit d'ajouter, lors du procédé de fabrication, une étape de masquage consistant à déposer une couche au-dessus du substrat et de réaliser la structuration d'ouvertures dans cette couche avant l'étape de dépôt d'une couche métallique au-dessus ou en-dessous d'une couche de silicium et/ou de germanium amorphe. Cette étape permet de déposer sélectivement la couche métallique et la couche de silicium et/ou germanium amorphe selon un motif ordonné sur le substrat. In a particularly advantageous variant, the silicon and / or germanium layer may be p-doped. In particular, the layer of silicon and / or germanium consisting of one or more monocrystalline grains is preferably obtained by crystallization induced by aluminum. In this case, the silicon and / or germanium layer furthermore comprises aluminum atoms and can therefore be doped with aluminum. According to a particular embodiment, an aluminum layer may also be interposed between the substrate and the silicon and / or germanium layer. According to the first embodiment, a continuous layer can be obtained when the grains grow until they coalesce. A discontinuous layer can also be obtained. It suffices to add, during the manufacturing process, a masking step consisting in depositing a layer above the substrate and for structuring openings in this layer before the step of depositing a metal layer above above or below a layer of silicon and / or amorphous germanium. This step makes it possible to selectively deposit the metal layer and the amorphous silicon and / or germanium layer in an ordered pattern on the substrate.
Selon ce premier mode de réalisation, le ou les grains monocristallins présentent avantageusement au moins l'une des caractéristiques suivantes :  According to this first embodiment, the monocrystalline grain or grains advantageously have at least one of the following characteristics:
- les grains monocristallins présentent une dimension latérale D supérieure à 2 μητι, de préférence supérieure à 4 μηη et mieux supérieure à 5 μητι,  the monocrystalline grains have a lateral dimension D greater than 2 μητι, preferably greater than 4 μηη and better still greater than 5 μητι,
- le rapport D/E entre la dimension latérale D et l'épaisseur de la couche de silicium et/ou de germanium est par ordre de préférence croissant supérieur à 50, supérieur à 100, supérieur à 200, supérieur à 400, supérieur à 500,  the ratio D / E between the lateral dimension D and the thickness of the layer of silicon and / or germanium is in order of increasing preference greater than 50, greater than 100, greater than 200, greater than 400, greater than 500 ,
- le ou les grains monocristallins présentent au moins deux dimensions latérale D1 et D2 perpendiculaires strictement supérieure à 1 μητι, de préférence supérieure à 2 μητι, et mieux supérieure à 5 μητι,  the monocrystalline grain or grains have at least two lateral dimensions D1 and D2 perpendicular strictly greater than 1 μητι, preferably greater than 2 μητι, and better still greater than 5 μητι,
- le rapport entre les dimensions latérales D, D1 et/ou D2 et la hauteur H des nanofils est supérieur à 1 , de préférence 2.  the ratio between the lateral dimensions D, D1 and / or D2 and the height H of the nanowires is greater than 1, preferably 2.
Dans une variante du deuxième mode de réalisation, les grains monocristallins non jointifs peuvent également satisfaire les caractéristiques définies ci-dessus.  In a variant of the second embodiment, the non-contiguous monocrystalline grains may also satisfy the characteristics defined above.
Selon le deuxième mode de réalisation, le substrat comprend un ou plusieurs grains monocristallins de silicium et/ou de germanium non jointifs, l'ensemble formant ainsi une couche discontinue. Cette couche discontinue constituée de grains monocristallins non jointifs peut être obtenue en jouant sur les paramètres de dépôt tels que sur le rapport d'épaisseur entre la couche métallique et la couche de matériau amorphe ou en diminuant la durée de la phase de croissance afin d'empêcher la coalescence des grains monocristallins.  According to the second embodiment, the substrate comprises one or more monocrystalline grains of non-joined silicon and / or germanium, the assembly thus forming a discontinuous layer. This discontinuous layer consisting of non-contiguous monocrystalline grains can be obtained by adjusting the deposition parameters such as the thickness ratio between the metal layer and the layer of amorphous material or by decreasing the duration of the growth phase in order to prevent the coalescence of monocrystalline grains.
Selon une autre variante de ce deuxième mode de réalisation, la couche discontinue constituée de grains monocristallins non jointifs peut être obtenue par ajout, lors du procédé de fabrication, d'une étape de dépôt d'une couche au-dessus du substrat et d'une étape de structuration d'ouvertures de taille contrôlée dans cette couche avant l'étape de dépôt, dans l'ordre souhaité, d'une couche métallique et d'une couche de silicium et/ou de germanium amorphe. Cette étape additionnelle permet non seulement de déposer sélectivement la couche métallique et la couche de silicium et/ou germanium amorphe selon un motif prédéterminé sur le substrat, mais surtout, en choisissant des ouvertures nanométriques, on peut obtenir dans chaque ouverture, la croissance d'un et un seul grain monocristallin. According to another variant of this second embodiment, the discontinuous layer consisting of non-contiguous monocrystalline grains can be obtained by adding, during the manufacturing process, a step of depositing a layer above the substrate and of a step of structuring apertures of controlled size in this layer before the deposition step, in the desired order, of a metal layer and a layer of silicon and / or amorphous germanium. This additional step makes it possible not only to selectively deposit the metal layer and the layer of amorphous silicon and / or germanium in a predetermined pattern on the substrate, but above all, by choosing nanometric openings, it is possible to obtain in each opening the growth of one and only one monocrystalline grain.
Pour obtenir un substrat comprenant spécifiquement un seul nanofil par grain monocristallin, les grains monocristallins présentent de préférence un motif prédéterminé présentant une dimension latérale maximale de 100 nm.  To obtain a substrate specifically comprising a single nanowire by monocrystalline grain, the monocrystalline grains preferably have a predetermined pattern having a maximum lateral dimension of 100 nm.
Si on ne souhaite pas se limiter à un seul nanofil par grain, les grains monocristallins peuvent avoir des dimensions latérales supérieures. Cette variante avantageuse permet donc d'obtenir un substrat comprenant un ou plusieurs grains monocristallins selon un motif prédéterminé. Les grains présentent de préférence une dimension latérale maximale inférieure à 5 μητι, de préférence inférieure à 2 μηη.  If it is not desired to be limited to a single nanowire per grain, the monocrystalline grains may have larger lateral dimensions. This advantageous variant therefore makes it possible to obtain a substrate comprising one or more monocrystalline grains in a predetermined pattern. The grains preferably have a maximum lateral dimension of less than 5 μητι, preferably less than 2 μηη.
La couche de silicium et/ou de germanium peut comprendre en outre des atomes métalliques choisis parmi l'aluminium, l'argent, l'or, l'antimoine, le cuivre, le nickel, et le plomb. Ces atomes peuvent provenir du procédé de préparation de la couche de silicium et/ou de germanium comprenant des grains monocristallins.  The silicon and / or germanium layer may further comprise metal atoms selected from aluminum, silver, gold, antimony, copper, nickel, and lead. These atoms can come from the process for preparing the silicon and / or germanium layer comprising monocrystalline grains.
L'invention permet avantageusement de faire pousser des nanofils sur tout type de substrat. Ces substrats présentent au moins une partie de leur surface plane, une rugosité de surface suffisamment faible et une compatibilité thermique avec les conditions du procédé fabrication notamment des points de fusion ou des températures de transition vitreuse suffisamment hauts.  The invention advantageously makes it possible to grow nanowires on any type of substrate. These substrates have at least a part of their flat surface, a sufficiently low surface roughness and a thermal compatibility with the conditions of the manufacturing process including melting points or sufficiently high glass transition temperatures.
Les substrats utilisés selon l'invention peuvent être plan sur toute l'étendue de la surface ou localement sur des tronçons de la surface. Par exemple, un substrat comprenant une texturation peut être utilisé selon l'invention dans la mesure où au moins une partie de l'une de ses surfaces correspondant à la zone où l'on souhaite faire croître les nanofils soit plane.  The substrates used according to the invention may be flat over the entire surface of the surface or locally on sections of the surface. For example, a substrate comprising a texturing may be used according to the invention insofar as at least a portion of one of its surfaces corresponding to the area where it is desired to grow the nanowires is plane.
Le substrat peut donc être choisi parmi les substrats amorphes, minéraux ou organiques, les substrats cristallins massifs comprenant une orientation incompatible avec une croissance verticale de nanofils notamment une orientation autre que (111 ), ou bien simplement incompatibles avec la croissance des nanofils. A titre de substrat amorphe convenant tout particulièrement selon l'invention, on peut citer les substrats en verre. A titre de substrat cristallin massif convenant tout particulièrement selon l'invention, on peut citer les substrats de silicium massif présentant notamment une orientation cristalline autre que (111 ), telle que (001 ). The substrate may therefore be chosen from amorphous, inorganic or organic substrates, the solid crystalline substrates comprising an orientation incompatible with vertical growth of nanowires, in particular an orientation other than (111), or simply incompatible with the growth of the nanowires. As an amorphous substrate that is particularly suitable according to the invention, mention may be made of glass substrates. As a solid crystalline substrate that is particularly suitable according to the invention, mention may be made of solid silicon substrates having in particular a crystalline orientation other than that (111), such that (001).
La possibilité de faire pousser des nanofils sur des substrats amorphes de type verre est particulièrement intéressante. On peut obtenir à grande échelle des substrats à faible coût présentant des propriétés de transparence avantageuses.  The possibility of growing nanowires on amorphous substrates of glass type is particularly interesting. Large inexpensive substrates with advantageous transparency properties can be obtained on a large scale.
L'utilisation d'un substrat cristallin massif présentant une orientation autre que celle permettant la croissance verticale de nanofils est également intéressante. Par exemple, seuls des substrats de silicium présentant une orientation (001 ) sont utilisés en microélectronique pour des raisons de procédés de fabrication. Or, cette orientation ne permet pas une croissance verticale des nanofils. Le procédé de l'invention permet donc de convertir une surface non adaptée à la croissance verticale des nanofils en une surface adaptée, permettant l'intégration de nanofils verticaux en microélectronique.  The use of a solid crystalline substrate having an orientation other than that allowing the vertical growth of nanowires is also interesting. For example, only silicon substrates having a (001) orientation are used in microelectronics for reasons of manufacturing processes. However, this orientation does not allow vertical growth of nanowires. The method of the invention therefore makes it possible to convert a surface that is not adapted to the vertical growth of the nanowires into a suitable surface, allowing the integration of vertical nanowires into microelectronics.
Pour faire cristalliser une couche à base de silicium et/ou de germanium de sorte qu'elle présente des plans (111 ) parallèles à la surface du substrat cristallin massif présentant une orientation cristalline différente, plusieurs possibilités sont envisageables. La cristallisation induite par un métal ayant lieu à l'interface métal/matériau amorphe est envisageable. En tout état de cause, il est possible de déposer une fine couche de passivation entre le substrat et les couches métalliques ou amorphes. Selon un mode de réalisation, le substrat est un substrat de silicium massif ne comprenant pas ses plans (111 ) parallèles à la surface du substrat, c'est-à-dire comprenant une orientation autre que (111 ), éventuellement recouvert d'une couche d'oxyde de silicium, ou toute autre couche compatible avec le procédé de cristallisation, telle qu'un couche d'oxyde de zinc (ZnO).  To crystallize a silicon-based layer and / or germanium so that it has (111) planes parallel to the surface of the solid crystalline substrate having a different crystalline orientation, several possibilities are possible. The crystallization induced by a metal occurring at the metal / amorphous material interface is conceivable. In any case, it is possible to deposit a thin layer of passivation between the substrate and the metal or amorphous layers. According to one embodiment, the substrate is a solid silicon substrate not comprising its planes (111) parallel to the surface of the substrate, that is to say comprising an orientation other than (111), optionally covered by a silicon oxide layer, or any other layer compatible with the crystallization process, such as a zinc oxide (ZnO) layer.
A titre de substrat de verre présentant une bonne résistance thermique, on peut citer la silice fondue et les borosilicates qui présentent une température de transition vitreuse plus élevée que les températures nécessaires du procédé de fabrication.  As a glass substrate having a good thermal resistance, mention may be made of fused silica and borosilicates which have a glass transition temperature higher than the necessary temperatures of the manufacturing process.
Le substrat peut comprendre en outre une ou plusieurs couches situées entre le substrat et la couche de silicium et/ou de germanium constituée d'un ou plusieurs grains monocristallins. Cette ou ces couche(s) peuvent conférer des propriétés multiples au substrat. De préférence, le substrat comprend au moins une couche conductrice assurant la fonction d'électrode.  The substrate may further comprise one or more layers located between the substrate and the layer of silicon and / or germanium consisting of one or more monocrystalline grains. This or these layer (s) can confer multiple properties on the substrate. Preferably, the substrate comprises at least one conductive layer providing the function of an electrode.
Selon un mode de réalisation avantageux le substrat comprend l'empilement suivant défini en partant du substrat :  According to an advantageous embodiment, the substrate comprises the following stack defined starting from the substrate:
- une électrode inférieure,  a lower electrode,
- une couche continue ou discontinue de silicium et/ou de germanium,  a continuous or discontinuous layer of silicon and / or germanium,
- des nanofils, - une électrode supérieure. nanowires, an upper electrode.
Les électrodes inférieures et supérieures comprennent chacune au moins une couche conductrice électriquement. La couche conductrice peut comprendre des oxydes conducteurs transparents (TCO), c'est-à-dire des matériaux qui sont à la fois bon conducteurs et transparents dans le visible, tels que l'oxyde d'étain et d'indium (ITO), In203, Sn02 dopé à l'antimoine ou au fluor (Sn02 : F) ou ZnO dopé à l'aluminium (ZnO : Al). La couche conductrice peut également comprendre des polymères conducteurs transparents qui sont des composés organiques à doubles liaisons conjuguées dont la conductivité peut être améliorée par dopage chimique ou électrochimique. Ces couches conductrices à base d'oxydes conducteurs ou de polymères conducteurs sont de préférence déposées sur des épaisseurs de l'ordre de 50 à 100 nm.  The lower and upper electrodes each comprise at least one electrically conductive layer. The conductive layer may comprise transparent conductive oxides (TCO), that is, materials that are both good conductors and transparent in the visible, such as tin oxide and indium (ITO) , In203, Sn02 doped with antimony or fluorine (SnO2: F) or ZnO doped with aluminum (ZnO: Al). The conductive layer may also comprise transparent conductive polymers which are organic compounds with conjugated double bonds whose conductivity can be enhanced by chemical or electrochemical doping. These conductive layers based on conductive oxides or conductive polymers are preferably deposited on thicknesses of the order of 50 to 100 nm.
La couche conductrice peut également être une couche métallique, par exemple en Ag, Al, Pd, Cu, Pd, Pt, In, Mo, Au. La couche électroconductrice métallique peut être une couche mince, dites TCC (« Transparent conductive coating ») présentant, de préférence, une épaisseur comprise entre 2 et 50 nm.  The conductive layer may also be a metal layer, for example Ag, Al, Pd, Cu, Pd, Pt, In, Mo, Au. The electroconductive metal layer may be a thin layer, called TCC ("transparent conductive coating") having, preferably, a thickness between 2 and 50 nm.
Les nanofils semi-conducteurs sont des objets de haute qualité cristalline. Leur faible dimension latérale permet de relaxer élastiquement les contraintes et de piéger efficacement d'éventuels défauts étendus à leur surface libre. Les nanofils présentent typiquement des diamètres de l'ordre de 10 à 200 nm et des hauteurs (ou longueurs) allant de quelques centaines de nanomètres à quelques microns. La composition du nanofil peut être modulée à volonté le long de et perpendiculairement à son axe de croissance. Les nanofils peuvent donc comprendre différentes sous-structures telles que des hétérostructures dites radiales ou axiales, ou encore différent dopage.  Semiconductor nanowires are objects of high crystalline quality. Their small lateral dimension makes it possible to elastically relax the stresses and to effectively trap potential defects extended to their free surface. Nanowires typically have diameters of the order of 10 to 200 nm and heights (or lengths) ranging from a few hundred nanometers to a few microns. The composition of the nanowire can be modulated at will along and perpendicular to its axis of growth. The nanowires can therefore comprise different substructures such as radial or axial heterostructures, or else different doping.
Les nanofils pouvant être utilisés selon l'invention présentent avantageusement les caractéristiques suivantes :  The nanowires that can be used according to the invention advantageously have the following characteristics:
- un diamètre compris entre 5 et 500 nm, de préférence entre 20 et 200 nm et mieux entre 30 et 80 nm,  a diameter of between 5 and 500 nm, preferably between 20 and 200 nm and better still between 30 and 80 nm,
- une hauteur H de préférence d'au moins 100 nm ou d'au moins 1 μητι,  a height H preferably of at least 100 nm or at least 1 μητι,
- les nanofils sont choisis parmi les oxydes métalliques, le silicium, le germanium et les semi-conducteurs lll-V et ll-VI,  the nanowires are chosen from metal oxides, silicon, germanium and the semiconductors III-V and II-VI,
- les semi-conducteurs lll-V peuvent être choisis parmi GaAs, GaN, GaP, GaSb, InAs, InP, InSb, InN, et parmi tous les alliages ternaires ou quaternaires intermédiaires entre ces composés binaires.  the III-V semiconductors may be chosen from GaAs, GaN, GaP, GaSb, InAs, InP, InSb, InN, and from among all the ternary or quaternary alloys intermediate between these binary compounds.
L'étape d'élaboration ou croissance des nanofils peut être réalisée par n'importe quelle technique de croissance cristalline et en particulier par dépôt chimique en phase vapeur (CVD), par ablation laser, par épitaxie par jets moléculaires, par dépôt assisté par plasma, par voie chimique en phase liquide. The stage of development or growth of the nanowires can be carried out by any which crystal growth technique and in particular by chemical vapor deposition (CVD), by laser ablation, by molecular beam epitaxy, by plasma assisted deposition, by chemical means in the liquid phase.
Le document WO 2009/054804 décrit par exemple les conditions pour la croissance de nanofils de semi-conducteurs lll-V par un procédé de dépôt chimique en phase vapeur pouvant s'appliquer selon la présente invention. Toutefois, on préfère réaliser l'étape de croissance par épitaxie par jets moléculaires. Les paramètres de l'étape de croissance des nanofils sont choisis pour faire croître sélectivement les nanofils uniquement sur les grains monocristallins. Ces paramètres sont notamment les flux des matériaux de départ injectés et la température du substrat.  WO 2009/054804 describes for example the conditions for the growth of semiconductor nanowires III-V by a chemical vapor deposition process that can be applied according to the present invention. However, it is preferred to carry out the growth step by molecular beam epitaxy. The parameters of the growth step of the nanowires are chosen to selectively grow the nanowires only on the monocrystalline grains. These parameters are in particular the flows of injected starting materials and the temperature of the substrate.
Les nanofils peuvent être placés sur le substrat de manière aléatoire ou selon un motif ordonné. Pour obtenir de motifs ordonnés plusieurs alternatives sont envisageables. Les motifs ordonnés peuvent être obtenus en attribuant un emplacement prédéterminé à chaque nanofil. Les motifs ordonnés peuvent également être obtenus en attribuant un emplacement prédéterminé à plusieurs nanofils définissant un ensemble de nanofils. Le motif ordonné est dans ce cas non pas obtenu par le motif résultant de l'emplacement de chaque nanofil mais par le motif résultant de l'emplacement des différents ensembles de nanofils.  The nanowires can be placed on the substrate randomly or in an ordered pattern. To obtain ordered patterns, several alternatives are possible. The ordered patterns can be obtained by assigning a predetermined location to each nanowire. The ordered patterns can also be achieved by assigning a predetermined location to multiple nanowires defining a set of nanowires. In this case, the ordered pattern is not obtained by the pattern resulting from the location of each nanowire but by the pattern resulting from the location of the different sets of nanowires.
Selon une alternative avantageuse, le procédé comporte en outre une étape de dépôt d'une couche au-dessus de la couche de silicium et/ou de germanium et une étape de structuration d'ouvertures, dans cette couche permettant de faire croître des nanofils selon des motifs ordonnés.  According to an advantageous alternative, the method further comprises a step of depositing a layer above the silicon and / or germanium layer and a step of structuring openings, in this layer making it possible to grow nanowires according to ordered patterns.
Selon un autre mode de réalisation avantageux, le procédé de fabrication du substrat comporte en outre une étape de dépôt d'une couche au-dessus du substrat et une étape de structuration d'ouvertures, dans cette couche permettant de déposer sélectivement la couche métallique et la couche de silicium et/ou germanium amorphe selon un motif ordonné. Ce procédé comporte également une étape de croissance de nanofils sur les motifs ordonnés de grains monocristallins de silicium et/ou de germanium.  According to another advantageous embodiment, the method of manufacturing the substrate further comprises a step of depositing a layer above the substrate and a step of structuring openings, in this layer for selectively depositing the metal layer and the amorphous silicon and / or germanium layer in an ordered pattern. This method also comprises a nanowire growth step on the ordered patterns of monocrystalline grains of silicon and / or germanium.
Selon la taille des ouvertures, le motif sera défini par l'emplacement de chaque nanofil ou de chacun des ensembles de nanofils. Pour obtenir des motifs définis par l'emplacement de chaque nanofil, la taille des ouvertures est de préférence nanométrique.  Depending on the size of the openings, the pattern will be defined by the location of each nanowire or each set of nanowires. To obtain patterns defined by the location of each nanowire, the size of the openings is preferably nanometric.
Les caractéristiques et avantages de l'invention apparaîtront dans la description de plusieurs modes de réalisation qui va suivre, faite en se référant aux dessins annexés dans lesquels les figures 1 à 5 illustrent différents schémas représentant le procédé de fabrication d'un substrat selon le l'invention avec des vues en perspective et des vues en coupe : The features and advantages of the invention will become apparent from the description of several embodiments which follows, with reference to the accompanying drawings, in which FIGS. 1 to 5 illustrate various diagrams representing the method of manufacturing a substrate according to the invention with perspective views and sectional views:
- la figure 1 représente un procédé de fabrication d'un substrat selon le premier mode de réalisation de l'invention avec une cristallisation induite par un métal dite « directe », - la figure 2 représente un procédé de fabrication d'un substrat selon le premier mode de réalisation de l'invention avec une cristallisation induite par un métal dite « inverse », FIG. 1 represents a method of manufacturing a substrate according to the first embodiment of the invention with a crystallization induced by a so-called "direct" metal; FIG. 2 represents a method of manufacturing a substrate according to FIG. first embodiment of the invention with crystallization induced by a so-called "inverse" metal,
- la figure 3 représente un procédé de fabrication d'un substrat selon le premier mode de réalisation de l'invention dans lequel on obtient une couche de silicium et/ou de germanium placé sur le substrat selon un motif défini, FIG. 3 represents a method of manufacturing a substrate according to the first embodiment of the invention in which a layer of silicon and / or germanium is obtained placed on the substrate in a defined pattern,
- la figure 4 représente un procédé de fabrication d'un substrat selon le deuxième mode de réalisation de l'invention dans lequel on réalise une croissance contrôlée afin d'obtenir des grains monocristallins non jointifs, FIG. 4 represents a method for manufacturing a substrate according to the second embodiment of the invention in which controlled growth is achieved in order to obtain non-contiguous monocrystalline grains,
- la figure 5 représente un procédé de fabrication d'un substrat selon le deuxième mode de réalisation de l'invention selon lequel on utilise une étape de masquage pour obtenir des grains monocristallins non jointifs selon un motif prédéterminé qui permettra la croissance des nanofils selon un motif ordonné.  FIG. 5 represents a method of manufacturing a substrate according to the second embodiment of the invention according to which a masking step is used to obtain non-contiguous monocrystalline grains in a predetermined pattern which will allow the nanowires to grow in accordance with a ordered pattern.
Pour la clarté du dessin, les épaisseurs relatives des différentes couches et éléments sur les figures n'ont pas été respectées.  For the sake of clarity, the relative thicknesses of the different layers and elements in the figures have not been respected.
Enfin, les figures 6 à 8 représentent :  Finally, Figures 6 to 8 show:
- la figure 6 est une image prise au microscope électronique à balayage ainsi qu'une représentation schématique calquée de ladite image, FIG. 6 is a scanning electron microscope image and a schematic representation of said image,
- la figure 7 représente le profil du contraste en champ clair, pris perpendiculairement au plan du substrat en fonction de la profondeur en nanomètre, d'une image obtenue par microscopie électronique en transmission sur un échantillon en tranche amincie après cristallisation et gravure,  FIG. 7 represents the profile of the contrast in the light field, taken perpendicular to the plane of the substrate as a function of the depth in nanometer, of an image obtained by transmission electron microscopy on a thinned slice sample after crystallization and etching,
- la figure 8 correspond à un spectre de diffraction des rayons X en incidence rasante de la couche de silicium après cristallisation et gravure,  FIG. 8 corresponds to an X-ray diffraction spectrum at grazing incidence of the silicon layer after crystallization and etching,
- la figure 9 représente une image prise au microscope électronique à balayage d'un nanofil.  FIG. 9 represents an image taken under a scanning electron microscope of a nanowire.
Le schéma de la figure 1 représente les principales étapes du procédé de fabrication d'un substrat selon le premier mode de réalisation de l'invention avec une cristallisation induite par un métal dite « directe », c'est-à-dire par dépôt d'une couche de silicium et/ou de germanium amorphe au-dessus d'une couche métallique. Le procédé de la figure 1 comprend les quatre étapes suivantes. La première étape consiste à déposer successivement et dans cet ordre sur un substrat 1 , une couche métallique 3 et une couche de silicium et/ou de germanium amorphe 2a. The diagram of FIG. 1 represents the main steps of the method of manufacturing a substrate according to the first embodiment of the invention with a crystallization induced by a so-called "direct" metal, that is to say by a layer of silicon and / or amorphous germanium above a metal layer. The process of Figure 1 comprises the following four steps. The first step consists of depositing successively and in this order on a substrate 1, a metal layer 3 and a layer of silicon and / or amorphous germanium 2a.
La deuxième étape correspond à la cristallisation proprement dite de la couche de silicium et/ou de germanium amorphe 2a. La cristallisation se produit à l'interface entre la couche métallique 3 et la couche amorphe 2a (a-Si et/ou a-Ge). Les cristaux formés croissent alors dans la couche métallique, rejetant le métal au-dessus, ce qui conduit à la fin de l'étape de cristallisation à un inversement de l'empilement. On obtient un substrat comprenant une couche de silicium et/ou de germanium 2c constituée d'un ou plusieurs grains monocristallins formée en-dessous de la couche métallique 3.  The second step corresponds to the actual crystallization of the layer of silicon and / or amorphous germanium 2a. Crystallization occurs at the interface between the metal layer 3 and the amorphous layer 2a (a-Si and / or a-Ge). The formed crystals then grow in the metal layer, rejecting the metal above, which leads to the end of the crystallization step at a reverse of the stack. A substrate is obtained comprising a layer of silicon and / or germanium 2c consisting of one or more monocrystalline grains formed below the metal layer 3.
La troisième étape consiste à éliminer par gravure sélective la couche métallique 3 afin de permettre la croissance des nanofils.  The third step is to eliminate by selective etching the metal layer 3 to allow the growth of the nanowires.
La quatrième étape correspond à la croissance proprement dite des nanofils sur les grains monocristallins constituant la couche cristallisée de silicium et/ou de germanium 2c.  The fourth step corresponds to the actual growth of the nanowires on the monocrystalline grains constituting the crystallized layer of silicon and / or germanium 2c.
Le procédé décrit par le schéma de la figure 2 diffère essentiellement de celui de la figure 1 en ce que la cristallisation induite par un métal est dite « inverse ». Le procédé de la figure 2 comprend les trois étapes suivantes.  The process described by the scheme of Figure 2 differs essentially from that of Figure 1 in that the crystallization induced by a metal is called "inverse". The process of Figure 2 comprises the following three steps.
La première étape consiste donc à déposer successivement et dans cet ordre sur un substrat 1 , une couche de silicium et/ou de germanium amorphe 2a et une couche métallique 3.  The first step consists in depositing successively and in this order on a substrate 1, a layer of silicon and / or amorphous germanium 2a and a metal layer 3.
La deuxième étape correspondant à la cristallisation conduit à l'obtention d'un substrat comprenant une couche de silicium et/ou de germanium 2c constituée d'un ou plusieurs grains monocristallins formée au-dessus de la couche métallique 3. Il n'est donc pas nécessaire de réaliser d'étape de gravure contrairement au procédé illustré par la figure 1.  The second step corresponding to the crystallization leads to obtaining a substrate comprising a layer of silicon and / or germanium 2c consisting of one or more monocrystalline grains formed above the metal layer 3. it is not necessary to carry out an etching step contrary to the method illustrated in FIG.
La troisième étape correspond à la croissance proprement des nanofils sur les grains monocristallins constituant la couche cristallisée de silicium et/ou de germanium 2c.  The third step corresponds to the proper growth of the nanowires on the monocrystalline grains constituting the crystallized layer of silicon and / or germanium 2c.
Le schéma de la figure 3 représente les principales étapes du procédé de fabrication d'un substrat selon le premier mode de réalisation de l'invention avec une cristallisation induite par un métal dite « directe » dans lequel on obtient une couche de silicium et/ou de germanium selon un motif défini. Ce procédé comprend l'utilisation d'un cache pour masquer la partie de la surface du substrat sur laquelle on ne souhaite pas faire croître de nanofil. The diagram of FIG. 3 represents the main steps of the method of manufacturing a substrate according to the first embodiment of the invention with crystallization induced by a so-called "direct" metal in which a layer of silicon and / or of germanium according to a defined pattern. This method includes the use of a mask to mask the part of the surface of the substrate on which it is not desired grow nanowire.
La première étape consiste à déposer sur le substrat une couche du matériau de masquage 5.  The first step consists in depositing on the substrate a layer of the masking material 5.
La deuxième étape consiste à structurer des ouvertures dans cette couche 5.  The second step is to structure openings in this layer 5.
Le choix de la nature de la couche utilisée pour réaliser cette structuration sera fonction des conditions du procédé. On peut citer à titre de couche les résines traditionnellement utilisées pour la lithographie. On peut également envisager des couches d'oxydes qui pourraient être structurées par gravures sélective. Enfin, selon un autre mode de réalisation, ces deux premières étapes peuvent être remplacées par l'utilisation d'un masque ou pochoir simplement appliqué sur le substrat.  The choice of the nature of the layer used to carry out this structuring will depend on the conditions of the process. The resins conventionally used for lithography can be mentioned as a layer. It is also possible to envisage oxide layers that could be structured by selective etching. Finally, according to another embodiment, these first two steps can be replaced by the use of a mask or stencil simply applied to the substrate.
La troisième étape consiste à déposer successivement sur le substrat 1 comprenant la couche structurée 5, une couche métallique 3 et une couche de silicium et/ou de germanium amorphe 2a.  The third step consists in depositing successively on the substrate 1 comprising the structured layer 5, a metal layer 3 and a layer of silicon and / or amorphous germanium 2a.
A partir de cette étape deux alternatives sont envisageables, la couche structurée 5 peut être supprimée avant ou après la cristallisation du silicium.  From this step two alternatives are conceivable, the structured layer 5 can be removed before or after the crystallization of silicon.
Selon la première alternative, la quatrième étape consiste en la suppression de la couche 5 utilisée pour la structuration. On obtient alors un substrat 1 comprenant successivement une couche métallique 3 et une couche de silicium et/ou de germanium amorphe 2a. La cinquième étape conduit à l'obtention d'un substrat comprenant une couche de silicium et/ou de germanium 2c constituée d'un ou plusieurs grains monocristallins formée au-dessus de la couche métallique 3 déposé selon le motif correspondant à l'ouverture de la couche structurée. La sixième étape consiste à éliminer par gravure sélective la couche métallique 3 afin de permettre la croissance des nanofils. La septième étape correspond à la croissance proprement dite des nanofils sur les grains monocristallins constituant la couche cristallisée de silicium et/ou de germanium 2c.  According to the first alternative, the fourth step consists of the removal of the layer 5 used for the structuring. A substrate 1 is thus obtained, successively comprising a metal layer 3 and a layer of silicon and / or amorphous germanium 2a. The fifth step leads to obtaining a substrate comprising a layer of silicon and / or germanium 2c consisting of one or more monocrystalline grains formed above the metal layer 3 deposited in the pattern corresponding to the opening of the structured layer. The sixth step is to eliminate by selective etching the metal layer 3 to allow the growth of the nanowires. The seventh step corresponds to the actual growth of the nanowires on the monocrystalline grains constituting the crystallized layer of silicon and / or germanium 2c.
Selon la deuxième alternative, la quatrième étape correspond à la cristallisation et conduit à l'obtention d'un substrat comprenant une couche de silicium et/ou de germanium 2c constituée d'un ou plusieurs grains monocristallins formée au-dessous de la couche métallique 3. La cinquième étape consiste à éliminer par gravure sélective la couche métallique 3. La sixième étape consiste en la suppression de la couche utilisée pour la structuration 5. On obtient alors un substrat 1 comprenant une couche de silicium et/ou de germanium 2c constituée d'un ou plusieurs grains monocristallins déposé selon le motif correspondant à l'ouverture de la couche structurée 5. La septième étape correspond à la croissance proprement dite des nanofils sur les grains monocristallins constituant la couche cristallisée de silicium et/ou de germanium 2c. According to the second alternative, the fourth step corresponds to the crystallization and leads to obtaining a substrate comprising a layer of silicon and / or germanium 2c consisting of one or more monocrystalline grains formed below the metal layer 3 The fifth step consists in eliminating the metal layer 3 by selective etching. The sixth step consists of the removal of the layer used for structuring 5. This gives a substrate 1 comprising a layer of silicon and / or germanium 2c consisting of one or more monocrystalline grains deposited in the pattern corresponding to the opening of the structured layer 5. The seventh step corresponds to the actual growth of the nanowires on the monocrystalline grains constituting the crystallized layer of silicon and / or germanium 2c.
Le procédé illustré sur la figure 3 permet bien la croissance des nanofils selon des motifs ordonnés.  The process illustrated in FIG. 3 makes it possible to grow the nanowires in ordered patterns.
Le schéma de la figure 4 représente les principales étapes du procédé de fabrication d'un substrat selon le deuxième mode de réalisation de l'invention avec une cristallisation induite par un métal dite « directe » dans lequel on réalise une croissance contrôlée afin d'obtenir des grains monocristallins non jointifs. Le procédé de la figure 4 comprend les quatre étapes suivantes.  The diagram of FIG. 4 represents the main steps of the process for manufacturing a substrate according to the second embodiment of the invention with a crystallization induced by a so-called "direct" metal in which controlled growth is achieved in order to obtain unconjugated monocrystalline grains. The process of Figure 4 comprises the following four steps.
La première étape consiste à déposer successivement sur un substrat 1 , une couche métallique 3 et une couche de silicium et/ou de germanium amorphe 2a.  The first step consists in successively depositing on a substrate 1, a metal layer 3 and a layer of silicon and / or amorphous germanium 2a.
La deuxième étape correspond à la cristallisation de la couche de silicium et/ou de germanium amorphe 2a. La croissance cristalline est contrôlée pour éviter la coalescence des grains par exemple en choisissant de déposer une couche métallique 3 plus épaisse que la couche de silicium et/ou de germanium amorphe 2a. A la fin de la cristallisation, on obtient un substrat comprenant une couche de silicium et/ou de germanium 2c constituée d'un ou plusieurs grains monocristallins non jointifs formés en-dessous de la couche métallique 3.  The second step corresponds to the crystallization of the layer of silicon and / or amorphous germanium 2a. The crystalline growth is controlled to prevent coalescence of the grains for example by choosing to deposit a metal layer 3 thicker than the layer of silicon and / or amorphous germanium 2a. At the end of the crystallization, a substrate is obtained comprising a layer of silicon and / or germanium 2c consisting of one or more non-contiguous monocrystalline grains formed below the metal layer 3.
La troisième étape consiste à éliminer par gravure sélective la couche métallique 3 afin de permettre la croissance des nanofils.  The third step is to eliminate by selective etching the metal layer 3 to allow the growth of the nanowires.
La quatrième étape correspond à la croissance proprement dite des nanofils sur les grains monocristallins constituant la couche de silicium et/ou de germanium 2c. Grâce à des conditions expérimentales adéquates, les nanofils ne poussent pas sur la surface du substrat ne comprenant pas de grain monocristallin.  The fourth step corresponds to the actual growth of the nanowires on the monocrystalline grains constituting the layer of silicon and / or germanium 2c. Thanks to adequate experimental conditions, the nanowires do not grow on the surface of the substrate which does not comprise a monocrystalline grain.
Le schéma de la figure 5 représente la fabrication d'un substrat selon le deuxième mode de réalisation de l'invention selon lequel on utilise une étape de masquage pour obtenir des grains monocristallins non jointifs selon un motif et une ou des formes prédéterminés. Ce procédé diffère de celui de la figure 3 en ce que pour obtenir des grains monocristallins non jointifs, les motifs du masque utilisé doivent avoir des dimensions latérales suffisamment faibles.  The diagram of FIG. 5 represents the fabrication of a substrate according to the second embodiment of the invention according to which a masking step is used to obtain non-contiguous monocrystalline grains in a pattern and one or more predetermined shapes. This method differs from that of FIG. 3 in that to obtain non-contiguous monocrystalline grains, the patterns of the mask used must have sufficiently small lateral dimensions.
La première étape consiste à déposer sur le substrat 1 , une couche 5.  The first step consists in depositing a layer 5 on the substrate 1.
La deuxième étape consiste à structurer des ouvertures de taille contrôlée dans cette couche 5. Pour obtenir la croissance d'un seul grain monocristallin par ouverture, la dimension latérale maximale des ouvertures D0 doit être de préférence inférieure à 5 μηη. The second step consists in structuring openings of controlled size in this layer 5. In order to obtain the growth of a single monocrystalline grain per opening, the maximum lateral dimension of the openings D 0 must preferably be less than 5 μηη.
Le choix de la nature de la couche utilisée pour réaliser cette structuration sera fonction des conditions du procédé. On peut citer à titre de couche les résines traditionnellement utilisées en lithographie. On peut également envisager des couches d'oxydes qui pourraient être structurées par gravures sélective. The choice of the nature of the layer used to achieve this structuring will be depending on the conditions of the process. The resins conventionally used in lithography can be mentioned as a layer. It is also possible to envisage oxide layers that could be structured by selective etching.
La troisième étape consiste à déposer successivement sur un substrat 1 , une couche métallique 3 et une couche de silicium et/ou de germanium amorphe 2a.  The third step consists in depositing successively on a substrate 1, a metal layer 3 and a layer of silicon and / or amorphous germanium 2a.
La quatrième étape consiste en la suppression de la couche utilisée pour la structuration 5. On obtient alors un substrat 1 comprenant successivement une couche métallique 3 et une couche de silicium et/ou de germanium amorphe 2a.  The fourth step consists in removing the layer used for structuring 5. This gives a substrate 1 successively comprising a metal layer 3 and a layer of silicon and / or amorphous germanium 2a.
La cinquième étape conduit à l'obtention d'un substrat comprenant une couche de silicium et/ou de germanium 2c constituée de grains monocristallins de silicium et/ou de germanium non jointifs formée au-dessous de la couche métallique 3 et déposé selon le motif correspondant à l'ouverture de la couche structurée 5.  The fifth step leads to obtaining a substrate comprising a layer of silicon and / or germanium 2c consisting of monocrystalline grains of silicon and / or non-joined germanium formed below the metal layer 3 and deposited according to the pattern corresponding to the opening of the structured layer 5.
La sixième étape consiste à éliminer par gravure sélective la couche métallique 3 afin de permettre la croissance des nanofils.  The sixth step is to eliminate by selective etching the metal layer 3 to allow the growth of the nanowires.
La septième étape correspond à la croissance proprement dite des nanofils sur les grains monocristallins non jointifs constituant la couche de silicium et/ou de germanium 2c. Il est alors possible de faire croître un ou plusieurs nanofils en fonction des caractéristiques de la croissance, et/ou de la taille des grains monocristallins.  The seventh step corresponds to the actual growth of the nanowires on the non-joined monocrystalline grains constituting the layer of silicon and / or germanium 2c. It is then possible to grow one or more nanowires according to the characteristics of the growth, and / or the size of the monocrystalline grains.
Enfin, le substrat comprenant sur au moins une partie de l'une de ses surfaces une couche continue ou discontinue de silicium et/ou de germanium constituée d'un ou plusieurs grains monocristallins, tous orientés de sorte qu'ils aient des plans (111 ) parallèles à la surface du substrat peut permettre la croissance de tout autre objet de forme variée tel que des couches et des plots, constitué de matériaux qui nécessitent des substrats présentant une orientation cristalline adéquate (111 ) pour leur croissance par épitaxie. Ces objets sont de même nature que les nanofils et de préférence sont des semiconducteurs lll-V ou ll-VII. L'invention peut concerner également un substrat comprenant sur au moins une partie de l'une de ses surfaces une couche de silicium et/ou de germanium constituée d'un ou plusieurs grains monocristallins, tous orientés de sorte qu'ils aient des plans (111 ) parallèles à la surface du substrat, et sur cette couche, un ou plusieurs objets de forme variée. Un tel substrat trouve application dans différents domaines tels l'électronique, l'optique ou l'optoélectronique. Exemples Finally, the substrate comprising on at least a portion of one of its surfaces a continuous or discontinuous layer of silicon and / or germanium consisting of one or more monocrystalline grains, all oriented so that they have plans (111). ) parallel to the surface of the substrate can allow the growth of any other object of varied shape such as layers and pads, consisting of materials that require substrates having an adequate crystalline orientation (111) for their growth by epitaxy. These objects are of the same nature as the nanowires and preferably are semiconductors III-V or II-VII. The invention may also relate to a substrate comprising on at least a portion of one of its surfaces a layer of silicon and / or germanium consisting of one or more monocrystalline grains, all oriented so that they have plans ( 111) parallel to the surface of the substrate, and on this layer, one or more objects of varied shape. Such a substrate finds application in various fields such as electronics, optics or optoelectronics. Examples
I. Couches minces de p-Si (111) I. Thin layers of p-Si (111)
1. Elaboration 1. Elaboration
L'empilement aluminum-silicium amorphe est déposé par pulvérisation magnétron en courant continu sur de la silice fondue, du verre, et des substrats de Si (100) oxydés (250 nm de Si02 amorphe en surface, obtenus par oxydation humide de substrats de Si (100) à 950 °C). Tous les types de substrats ont préalablement été rincés à l'acétone, à l'éthanol et à l'eau déionisée. Une couche de 10 nm d'aluminium est déposée à une puissance de 50 W, sous une pression d'argon de 1 ,5 μbar, à température ambiante, et placé à un potentiel électrique flottant (vitesse de dépôt de 2,24 Â s"1). Les 10 nm de silicium amorphe sont déposés consécutivement à l'aluminium, sans rupture du vide, et à une puissance de 20 W (toutes autres conditions opératoires identiques) (vitesse de dépôt de 0.46 Â s"1). The amorphous aluminum-silicon stack is deposited by DC magnetron sputtering onto fused silica, glass, and oxidized Si (100) substrates (250 nm surface-amorphous SiO 2 obtained by wet oxidation of Si (100) at 950 ° C). All types of substrates were previously rinsed with acetone, ethanol and deionized water. A layer of 10 nm of aluminum is deposited at a power of 50 W, under an argon pressure of 1.5 μbar, at room temperature, and placed at a floating electric potential (deposition rate of 2.24 Å "1). the 10 nm of amorphous silicon are deposited consecutively to aluminum, without breaking the vacuum, and a power of 20 W (all other identical operating conditions) (deposition rate of 0.46 s" 1).
Les empilements sont recuits à 400 °C pendant 15 h, sous atmosphère d'azote (2L min"1). The stacks are annealed at 400 ° C. for 15 h under a nitrogen atmosphere (2 L min -1 ).
La couche d'aluminium superficielle est gravée par voie humide : le substrat est plongé dans une solution d'acide chlorhydrique concentré (37% en masse) pendant 15 minutes à température ambiante ; le cas échéant, la couche d'oxyde amorphe AI-Si-0 (présente à l'interface p-Si-AI) peut être gravée par une solution aqueuse diluée d'acide fluorhydrique (5% en masse). 2. Caractérisation  The surface aluminum layer is etched wet: the substrate is immersed in a concentrated hydrochloric acid solution (37% by weight) for 15 minutes at room temperature; where appropriate, the amorphous oxide layer Al-Si-O (present at the p-Si-Al interface) may be etched with a dilute aqueous solution of hydrofluoric acid (5% by weight). 2. Characterization
La morphologie des couches est analysée par microscopie optique, par microscopie électronique à balayage et par microscopie électronique en transmission.  The morphology of the layers is analyzed by optical microscopy, scanning electron microscopy and transmission electron microscopy.
La figure 6 est une image prise au microscope électronique à balayage, ainsi qu'une représentation schématique calquée de ladite image, d'un substrat de silicium (001 ) oxydé sur lequel une couche de silicium a cristallisé. L'épaisseur de la couche comprenant des grains monocristallins de silicium est de 10 nm. Les parties hachurées délimitent les grains et les parties blanches le Si02. Par soucis de clarté, il a été représenté sur l'image modélisée une dimension latérale D ainsi que deux dimensions latérales D1 et D2 orthogonales. Tous les grains monocristallins ont au moins une dimension latérale D supérieure à 2 μητι, plus précisément de l'ordre de 5 μηη. FIG. 6 is a scanning electron microscope image, as well as a schematic representation of said image, of an oxidized silicon substrate (001) on which a silicon layer has crystallized. The thickness of the layer comprising monocrystalline grains of silicon is 10 nm. The hatched parts delimit the grains and the white parts the Si0 2 . For the sake of clarity, there is shown on the modeled image a lateral dimension D and two orthogonal lateral dimensions D1 and D2. All monocrystalline grains have at least one lateral dimension D greater than 2 μητι, more precisely of the order of 5 μηη.
La rugosité à l'échelle de la surface du grain a été mesurée à l'aide d'un microscope à force atomique (AFM). En mesurant cette rugosité sur plusieurs grains, la rugosité la plus défavorable mesurée sur un grain est de 1 ,2 nm.  Roughness at the grain surface level was measured using an atomic force microscope (AFM). By measuring this roughness on several grains, the most unfavorable roughness measured on a grain is 1, 2 nm.
La figure 7 représente le profil du contraste en champ clair, pris perpendiculairement au plan du substrat en fonction de la profondeur en nanomètre, d'une image obtenue par microscopie électronique en transmission sur un échantillon en tranche amincie après cristallisation et gravure. Le profil obtenu est caractéristique d'une cristallisation des grains avec des plans (111 ) parallèles à la surface du substrat.  FIG. 7 represents the profile of the contrast in a light field, taken perpendicular to the plane of the substrate as a function of the depth in nanometer, of an image obtained by transmission electron microscopy on a thinned slice sample after crystallization and etching. The resulting profile is characteristic of grain crystallization with (111) planes parallel to the surface of the substrate.
Les propriétés cristallines de la couche de p-Si ont également été analysées par diffraction des rayons X en incidence rasante (GIXRD : Grazing Incidence X-Ray Diffraction), en raison de la finesse de la couche. Les couches de p-Si présentent une texture (111 ) parfaite comme le montre le spectre de la figure 8. Seuls les familles de plan {220} et {422} sont observées par GIXRD : c'est la signature de la texture (111 ) complète du film.  The crystalline properties of the p-Si layer were also analyzed by grazing incidence X-ray diffraction (GIXRD: Grazing Incidence X-Ray Diffraction), due to the fineness of the layer. The layers of p-Si have a perfect texture (111) as shown by the spectrum of figure 8. Only the families of plane {220} and {422} are observed by GIXRD: it is the signature of the texture (111 ) complete movie.
II. Croissance de nanofils de GaAs autocatalysés par épitaxie par jet moléculaire II. Growth of autocatalyzed GaAs nanowires by molecular beam epitaxy
Les nanofils sont obtenus par mise sous vide et dégazage du substrat comprenant la couche mince suivie par une procédure classique de croissance des nanofils (tout catalyseur et tout matériau lll-V). The nanowires are obtained by evacuating and degassing the substrate comprising the thin layer followed by a conventional nanowire growth procedure (any catalyst and any III-V material).
La croissance des nanofils de GaAs autocatalysés est effectuée par épitaxie par jets moléculaires (EJM) dans un bâti MBE 32 de Riber, sous une rotation de 7 tours min"1 et un flux de Gallium équivalent à une croissance planaire de 2,0 Â s"1 (pression de 3,0- 10"7 Torr). The growth of GaAs nanowires autocatalysts is carried out by molecular beam epitaxy (MBE) MBE in a frame 32 of Riber, under a rotation of 7 rounds min "1 and a flow equivalent to a planar Gallium growth of 2.0 Å s "1 (pressure of 3.0-10 7 Torr).
Avant toute croissance, les substrats couches minces sont dégazés sous vide à 450 °C pendant 1 h.  Before any growth, the thin film substrates are degassed under vacuum at 450 ° C. for 1 hour.
Le substrat est transféré dans la chambre de croissance, et est porté à 450 °C. Le gallium est déposé pendant 60 s (quantité équivalente à 19 monocouches de Ga). La température est portée de 450 °C à 580 °C (température de croissance) en 10 minutes à l'aide d'une rampe.  The substrate is transferred to the growth chamber and is heated to 450 ° C. Gallium is deposited for 60 s (amount equivalent to 19 monolayers of Ga). The temperature is raised from 450 ° C to 580 ° C (growth temperature) in 10 minutes using a ramp.
Après stabilisation de la température, les obturateur (« shutters ») d'As (sous forme d'As4) et de Ga sont ouverts simultanément, donnant respectivement des flux de 4,2- 10"6 Torr et 3,0- 10"7 Torr. La pression d'arsenic est linéairement portée à 5,2- 10"6 Torr en 300 s. La croissance est maintenue dans ces conditions pendant 300 s supplémentaires. Au terme de cette durée, les sources d'As4 et de Ga sont simultanément obturées, et l'échantillon est transféré hors de la chambre de croissance. After temperature stabilization, the shutter ( "shutters") As (in the form of As 4) and Ga are opened simultaneously, respectively providing flow 4,2- 10 "6 torr and 10 3,0- "7 Torr. Arsenic pressure is linearly increased to 5,2- 10 "6 torr, 300 s. Growth is maintained under these conditions for an additional 300 s. At the end of this period, the sources of As 4 and Ga are simultaneously closed, and the sample is transferred out of the growth chamber.
La figure 9 représente une image prise au microscope électronique à balayage d'un nanofil obtenu selon le procédé de l'invention. Le nanofil est vertical sur la surface d'un grain monocristallin de silicium.  FIG. 9 represents an image taken under a scanning electron microscope of a nanowire obtained according to the method of the invention. The nanowire is vertical on the surface of a monocrystalline grain of silicon.

Claims

REVENDICATIONS
1. Substrat comprenant sur au moins une partie de l'une de ses surfaces une couche de silicium et/ou de germanium d'épaisseur E constituée d'un ou plusieurs grains monocristallins, tous orientés de sorte qu'ils aient des plans (111 ) parallèles à la surface du substrat, et sur cette couche, un ou plusieurs nanofils dont l'axe longitudinal est orienté perpendiculairement à la surface du substrat caractérisé en ce que : A substrate comprising on at least a portion of one of its surfaces a layer of silicon and / or germanium of thickness E consisting of one or more monocrystalline grains, all oriented so that they have planes (111). parallel to the surface of the substrate, and on this layer, one or more nanowires whose longitudinal axis is oriented perpendicular to the surface of the substrate, characterized in that:
- le ou les grains rnonocristaHins de la couche de silicium et/ou de germanium présentent une dimension latérale D, définie comme une corde du bord de grain, sur tous les grains strictement supérieure à 1 μηη et  the monocrystalline grain (s) of the silicon and / or germanium layer have a lateral dimension D, defined as a grain edge chord, on all grains strictly greater than 1 μηη and
- le rapport D/E entre la dimension latérale D et l'épaisseur de la couche de silicium et/ou de germanium est supérieur à 25, de préférence 100.  the ratio D / E between the lateral dimension D and the thickness of the layer of silicon and / or germanium is greater than 25, preferably 100.
2. Substrat comprenant sur au moins une partie de l'une de ses surfaces un ou plusieurs grains monocristallins de silicium et/ou de germanium non jointifs et tous orientés de sorte qu'ils présentent des plans (111 ) parallèles à la surface du substrat, et sur chaque grain un ou plusieurs nanofils dont l'axe longitudinal est orienté perpendiculairement à la surface du substrat.  2. Substrate comprising on at least a portion of one of its surfaces one or more monocrystalline grains of silicon and / or germanium not joined and all oriented so that they have planes (111) parallel to the surface of the substrate , and on each grain one or more nanowires whose longitudinal axis is oriented perpendicular to the surface of the substrate.
3. Substrat selon la revendication 2 caractérisé en ce que les grains monocristallins de silicium et/ou de germanium non jointifs sont isolés les uns des autres par une distance d'au moins 10 nm, l'ensemble formant ainsi une couche discontinue.  3. Substrate according to claim 2 characterized in that the monocrystalline grains of silicon and / or germanium non-joined are isolated from each other by a distance of at least 10 nm, the assembly thus forming a discontinuous layer.
4. Substrat selon la revendication 2 ou 3 caractérisé en ce qu'il comprend un seul nanofil par grain monocristallin.  4. Substrate according to claim 2 or 3 characterized in that it comprises a single nanowire monocrystalline grain.
5. Substrat selon l'une quelconque des revendications 2 à 4 caractérisé en ce que les grains monocristallins présentent un motif prédéterminé présentant une dimension latérale maximale de 100 nm.  5. Substrate according to any one of claims 2 to 4 characterized in that the monocrystalline grains have a predetermined pattern having a maximum lateral dimension of 100 nm.
6. Substrat selon l'une quelconque des revendications 1 , 3 à 5 caractérisé en ce que l'épaisseur de la couche de silicium et/ou de germanium E est inférieure à 50 nm, de préférence comprise entre 5 et 15 nm.  6. Substrate according to any one of claims 1, 3 to 5 characterized in that the thickness of the silicon layer and / or germanium E is less than 50 nm, preferably between 5 and 15 nm.
7. Substrat selon l'une quelconque des revendications précédentes caractérisé en ce que la rugosité de la surface du ou des grains monocristallin(s) mesurée par la technique de microscopie à force atomique est inférieure à 5 nm, de préférence inférieure à 2 nm et au mieux inférieure à 1 nm, à l'échelle de la surface du grain.  7. Substrate according to any one of the preceding claims, characterized in that the roughness of the surface of the monocrystalline grain (s) measured by the atomic force microscopy technique is less than 5 nm, preferably less than 2 nm and at best less than 1 nm, on the scale of the grain surface.
8. Substrat selon l'une quelconque des revendications 1 à 4 et 6 à 7 caractérisé en ce que la dimension latérale D est supérieure à 2 μηη, de préférence supérieure à 5 μηη. 8. Substrate according to any one of claims 1 to 4 and 6 to 7 characterized in that the lateral dimension D is greater than 2 μηη, preferably greater than 5 μηη.
9. Substrat selon l'une quelconque des revendications 1 à 4 et 6 à 8 caractérisé en ce que le ou les grains monocristallins présentent deux dimensions latérales D-ι et D2 perpendiculaires strictement supérieures à 1 μηη, de préférence supérieures à 2 μηη, et mieux supérieures à 5 μηη. 9. Substrate according to any one of claims 1 to 4 and 6 to 8 characterized in that the monocrystalline grain or grains have two lateral dimensions D-ι and D 2 perpendicular strictly greater than 1 μηη, preferably greater than 2 μηη, and better than 5 μηη.
10. Substrat selon l'une quelconque des revendications précédentes caractérisé en ce que le ou les grains monocristallins de silicium et/ou de germanium sont dopés p ou n.  10. Substrate according to any one of the preceding claims characterized in that the monocrystalline grain or grains of silicon and / or germanium are doped p or n.
11. Substrat selon la revendication 10 caractérisé en ce que les grains monocristallins de silicium et/ou de germanium sont dopés par de l'aluminium.  11. Substrate according to claim 10 characterized in that the monocrystalline grains of silicon and / or germanium are doped with aluminum.
12. Substrat selon l'une quelconque des revendications précédentes caractérisé en ce qu'une couche métallique, de préférence d'aluminium, est intercalée entre le substrat et les grains monocristallins de silicium et/ou de germanium.  12. Substrate according to any one of the preceding claims characterized in that a metal layer, preferably aluminum, is interposed between the substrate and monocrystalline grains of silicon and / or germanium.
13. Substrat selon l'une quelconque des revendications précédentes caractérisé en ce que le substrat est choisi parmi les substrats amorphes, les substrats cristallins massifs comprenant une orientation autre que (111 ).  13. Substrate according to any one of the preceding claims characterized in that the substrate is selected from amorphous substrates, massive crystalline substrates comprising an orientation other than (111).
14. Substrat selon la revendication 13 caractérisé en ce que le substrat amorphe est un substrat en verre.  14. Substrate according to claim 13 characterized in that the amorphous substrate is a glass substrate.
15. Substrat selon la revendication 13 caractérisé en ce que le substrat est un substrat de silicium massif comprenant une orientation autre que (111 ) recouvert éventuellement d'une couche d'oxyde de silicium.  15. Substrate according to claim 13 characterized in that the substrate is a solid silicon substrate comprising an orientation other than (111) optionally covered with a silicon oxide layer.
16. Substrat selon l'une quelconque des revendications précédentes caractérisé en ce que les nanofils peuvent être choisis parmi les semi-conducteurs lll-V tels que GaAs, Substrate according to any one of the preceding claims, characterized in that the nanowires may be chosen from III-V semiconductors such as GaAs,
GaN, GaP, GaSb, InAs, InP, InSb, InN et parmi tous les alliages ternaires ou quaternaires intermédiaires entre ces composés binaires. GaN, GaP, GaSb, InAs, InP, InSb, InN and among all the ternary or quaternary alloys intermediate between these binary compounds.
17. Substrat selon l'une quelconque des revendications précédentes caractérisé en ce que le substrat comprend en outre une ou plusieurs couches situées entre le substrat et la couche de silicium et/ou de germanium constituée d'un ou plusieurs grains monocristallins.  17. Substrate according to any one of the preceding claims, characterized in that the substrate further comprises one or more layers located between the substrate and the layer of silicon and / or germanium consisting of one or more monocrystalline grains.
18. Substrat selon l'une quelconque des revendications précédentes caractérisé en ce que le substrat comprend l'empilement suivant défini en partant du substrat :  18. Substrate according to any one of the preceding claims, characterized in that the substrate comprises the following stack defined starting from the substrate:
- une électrode inférieure, a lower electrode,
- une couche continue ou discontinue de silicium et/ou de germanium,  a continuous or discontinuous layer of silicon and / or germanium,
- des nanofils,  nanowires,
- une électrode supérieure.  an upper electrode.
19. Substrat selon l'une quelconque des revendications précédentes caractérisé en ce que les nanofils sont placés sur le substrat de manière aléatoire. Substrate according to any one of the preceding claims, characterized in that the nanowires are placed on the substrate in a random manner.
20. Substrat selon l'une quelconque des revendications 1 à 18 caractérisé en ce que les nanofils sont placés sur le substrat selon un motif ordonné.  20. Substrate according to any one of claims 1 to 18 characterized in that the nanowires are placed on the substrate in an ordered pattern.
21. Procédé de fabrication d'un substrat comprenant les étapes suivantes :  A method of manufacturing a substrate comprising the steps of:
- former par cristallisation induite par un métal sur au moins une partie de l'une des surfaces d'un substrat une couche de silicium et/ou de germanium constituée d'un ou plusieurs grains monocristallins tous orientés de sorte qu'ils aient des plans (111 ) parallèles à la surface du substrat, - forming by metal-induced crystallization on at least a portion of one of the surfaces of a substrate a layer of silicon and / or germanium consisting of one or more monocrystalline grains all oriented so that they have plans (111) parallel to the surface of the substrate,
- faire croître sur le ou les grains monocristallins un ou plusieurs nanofils dont l'axe longitudinal est orienté perpendiculairement à la surface du substrat. - Growing on the monocrystalline grain or grains one or more nanowires whose longitudinal axis is oriented perpendicularly to the surface of the substrate.
22. Procédé de fabrication d'un substrat selon la revendication 21 caractérisé en ce que le ou les grains monocristallins de silicium et/ou de germanium formés sur la surface d'un substrat sont non jointifs.  22. A method of manufacturing a substrate according to claim 21 characterized in that the monocrystalline grain or grains of silicon and / or germanium formed on the surface of a substrate are non-contiguous.
23. Procédé de fabrication d'un substrat selon l'une quelconque des revendications 21 à 22 caractérisé en ce que la cristallisation induite par un métal est obtenue par dépôt d'une couche métallique au-dessus ou en-dessous d'une couche de silicium et/ou de germanium amorphe.  23. A method of manufacturing a substrate according to any one of claims 21 to 22 characterized in that the crystallization induced by a metal is obtained by depositing a metal layer above or below a layer of silicon and / or amorphous germanium.
24. Procédé de fabrication d'un substrat selon l'une quelconque des revendications 21 à 23 caractérisé en ce que lorsque la couche de silicium et/ou de germanium constituée d'un ou plusieurs grains monocristallins est formée en-dessous de la couche métallique, cette couche métallique est retirée par gravure sélective.  24. A method of manufacturing a substrate according to any one of claims 21 to 23 characterized in that when the silicon layer and / or germanium consisting of one or more monocrystalline grains is formed below the metal layer this metal layer is removed by selective etching.
25. Procédé de fabrication d'un substrat selon l'une quelconque des revendications 21 à 24 caractérisé en ce que la couche de silicium et/ou de germanium constituée d'un ou plusieurs grains monocristallins est formée au-dessus de la couche métallique.  25. A method of manufacturing a substrate according to any one of claims 21 to 24 characterized in that the silicon layer and / or germanium consisting of one or more monocrystalline grains is formed above the metal layer.
26. Procédé de fabrication d'un substrat selon l'une quelconque des revendications 26. A method of manufacturing a substrate according to any one of the claims
21 à 25 caractérisé en ce qu'il comporte en outre une étape de dépôt d'une couche au- dessus de la couche de silicium et/ou de germanium et une étape de structuration d'ouvertures dans cette couche permettant de faire croître des nanofils selon des motifs ordonnés. 21 to 25 characterized in that it further comprises a step of depositing a layer above the layer of silicon and / or germanium and a step of structuring openings in this layer for growing nanowires according to orderly motives.
27. Procédé de fabrication d'un substrat selon l'une quelconque des revendications 27. A method of manufacturing a substrate according to any one of the claims
21 à 26 caractérisé en ce qu'il comporte en outre une étape de dépôt d'une couche au- dessus du substrat et une étape de structuration d'ouvertures dans cette couche permettant de déposer sélectivement la couche métallique et la couche de silicium et/ou germanium amorphe selon un motif prédéterminé. 21 to 26 characterized in that it further comprises a step of depositing a layer above the substrate and a step of structuring openings in this layer for selectively depositing the metal layer and the silicon layer and / or amorphous germanium according to a predetermined pattern.
EP13744670.4A 2012-07-03 2013-07-02 Substrate comprising a layer of silicon and/or germanium and one or a plurality of nanowires oriented perpendicular to the surface of the substrate Withdrawn EP2870278A1 (en)

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FR1256374A FR2992980B1 (en) 2012-07-03 2012-07-03 SUBSTRATE COMPRISING A SILICON AND / OR GERMANIUM LAYER AND ONE OR MORE PERPENDICULAR ORIENTATION NANOWILS ON THE SURFACE OF THE SUBSTRATE
PCT/FR2013/051552 WO2014006319A1 (en) 2012-07-03 2013-07-02 Substrate comprising a layer of silicon and/or germanium and one or a plurality of nanowires oriented perpendicular to the surface of the substrate

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US20070224788A1 (en) * 2006-03-23 2007-09-27 Board Of Trustees Of The University Of Arkansas Fabrication of large grain polycrystalline silicon film by nano aluminum-induced crystallization of amorphous silicon

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EP2541625A1 (en) * 2010-02-25 2013-01-02 National University Corporation Hokkaido University Semiconductor device and method for manufacturing semiconductor device
KR101050467B1 (en) * 2010-04-14 2011-07-20 삼성모바일디스플레이주식회사 Polysilicon film, the method for fabrication thereof, thin film transistor with the polysilicon film and organic light emitting display device with the thin film transistor

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US20070224788A1 (en) * 2006-03-23 2007-09-27 Board Of Trustees Of The University Of Arkansas Fabrication of large grain polycrystalline silicon film by nano aluminum-induced crystallization of amorphous silicon

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WO2014006320A2 (en) 2014-01-09
FR2992980A1 (en) 2014-01-10

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