WO2015044582A1 - Method of depositing an inorganic material on a substrate, in particular a micron- or submicron-scale textured substrate - Google Patents

Abstract

The present invention concerns a method of depositing an inorganic material (3) on a micron- or submicron-scale textured substrate (1) comprising the steps of preparing a solution made from inorganic precursors and a polymeric compound, depositing said solution on the substrate, and heat treating the substrate coated with the solution at a high temperature in order to break down the polymeric compound, characterised in that the polymeric compound is thermosetting, and the method comprises, before the heat treatment step, a step of so-called controlled setting of the polymeric compound. The method can be used to produce a coating layer with perfectly uniform surface distribution and thickness, in particular in the recesses and ridges of the substrate.

Description

 METHOD FOR DEPOSITING AN INORGANIC MATERIAL ON A SUBSTRATE, IN PARTICULAR TEXTURE AT THE MICRON SCALE

 The invention relates to a method for depositing an inorganic material on a substrate, particularly a textured substrate at the micron or submicron scale.

The invention is more particularly the textured substrates, but is not limited thereto. The method of the invention can also be applied to flat substrates. The term "textured substrate" means a substrate whose thickness has through cavities depending on the thickness or not, and all geometric shapes. Textured substrates, or so-called porous sub-micron scale are used in many applications. The nature of the substrate material and the type of coating layer are dependent on the intended use. Non-exhaustive examples as applications include capacitors, electrodes, solid electrolytes, laser amplifying materials, substrates with antireflection coatings, photovoltaic cells, chemical sensors, catalysis matrices. , etc.

The substrates are for example made of ceramics, glasses, semiconductors, metals, inorganic foams, etc. The deposited coatings are very varied, such as metals, ceramics, glasses, carbon (graphene, graphite), etc.

A traditional method of depositing the abovementioned materials is liquid coating, especially according to the sol-gel method, from a solution that can be aqueous or organic. Once the solution is deposited on the substrate, it must be dried. For an aqueous or organic solution, the substrate coated with the solution is treated at high temperature (for example 400 ° C or more).

The aqueous solution comprises metal salts in aqueous solution, while the organic solution comprises alkoxides, organometallics or metal salts in organic solutions. However, the liquid deposition has limitations, especially when the depth of the pores or cavities of the textured substrate have a too large form factor. In the present description, the term "form factor" refers to the ratio between the depth and the width (depth of the cavity / width of the cavity). Note that generally in industry, the form factor is defined inversely, namely the ratio width / depth or width / height.

When the form factor in the sense of the invention (depth / width) is important (or respectively low according to the definition of the form factor in industry), this presents a major drawback. The disadvantage generated is a strong deposit inhomogeneity between the bottom of the cavities, the walls and the edges of said cavities, the edges and walls being generally devoid of coating layer. The term "cavity edges" means the junction surfaces of the cavities and the upper plane surface of the substrate.

This technique has now become a major industrial process for surface coatings, including textured substrates. Indeed, because of the capillary force, the liquid penetrates and easily fills the cavities of the textured substrates. However, during the drying step it is observed that the liquid is essentially maintained in the bottom of the cavities, while it tends to withdraw from the walls, and not wet the edges. The term "wet" means the ability of a liquid to cover or not a surface. Also, at the time of drying of the liquid solution, the resulting layer is mainly concentrated in the bottom of the cavities with an excess thickness, has a non-existent thickness or very thin and / or inhomogeneous on the walls, and may even be non-existent on the edges of the cavities.

Thus, while the use of this conventional liquid deposition technique is particularly suitable for obtaining thin and dense layers on flat substrates, on the other hand, it has many disadvantages that have not yet been solved for substrates whose face to be coated. is textured. In particular, the inventors have made tests which have shown that the traditional liquid channels do not make it possible to conformably cover the pores or trenches of a textured substrate, an accumulation of the liquid solution at the bottom of the pores being systematically present.

The purpose of the invention is therefore to propose another method of deposition of inorganic material, in particular on a textured substrate, which does not have the aforementioned drawbacks of the usual technique but which retains the advantages thereof, so as to provide a coating layer of the inorganic material which is uniformly distributed and of uniform thickness over the entire surface of the substrate, in particular for textured substrates with very large form factors, and without obstructing the texturing thereof. In the remainder of the description, the term "inorganic material" is intended to mean a material as such, or a composition of several inorganic materials. According to the invention, the method of depositing an inorganic material on a substrate, in particular on a textured substrate at the micron or submicron scale, comprises the steps of:

 preparation of a solution based on inorganic precursors and a polymerizable polymeric compound,

 depositing on the substrate said solution,

 heat treatment of the substrate coated with the solution for the polymerization and decomposition of the polymerized polymeric compound,

 characterized in that

 the polymeric compound is thermosetting, and

 the method comprises, before the heat treatment step, a so-called controlled curing step of the polymeric compound, the thermal treatment for the decomposition of the polymerized polymer compound comprises placing the substrate coated with the solution, after controlled curing of the polymeric compound, with a temperature which is at least that of decomposition of the polymeric compound.

The term "polymeric compound" means a polymer or a combination of polymerizable polymers. In the remainder of the description, the term "polymer" will be used to designate as well a single polymer as a combination of polymers, or a copolymer.

After the heat treatment, the polymeric compound, including the polymerization catalyst, if a polymerization catalyst had been added to the polymeric compound, is completely decomposed. The substrate obtained by the method of the invention is a substrate comprising a layer of inorganic material in a homogeneous deposition in surface distribution and thickness in the cavities (bottom, walls and edges) and is devoid of any polymeric compound and lacking a catalyst of polymerization.

The inorganic precursors are suitably selected with respect to the inorganic material whose substrate is to be coated at the end of the manufacturing process. They are known according to the intended application. They are inorganic or organic salts that can be mixed with additives of the complexing or surfactant type.

According to one characteristic, the heat treatment of the substrate is done at high temperature. The term high temperature heat treatment means a heat treatment greater than 180 ° C to break down and oxidize the organic fraction of the deposited solution. The organic fraction of the coated solution disappeared as a result of this treatment.

Thus, according to the invention, the inventors have demonstrated that an intermediate step of controlled curing of the polymer before the heat treatment makes it possible to obtain a final deposition layer that is homogeneously distributed in the end (after heat treatment, that is, decomposition of the organic fraction). The starting liquid solution makes it easy to coat the substrate by any known type of deposition method (such as by coating, soaking-shrinking), and then the heat treatment is necessary to break down the polymer. Nevertheless, before this heat treatment, the inventors have unexpectedly demonstrated that the polymer must be cured in a controlled manner before its decomposition made it possible to obtain the desired result, that is to say a coating by the inorganic material conforming to the surface distribution and thickness, in particular at the level of the pores or trenches of a textured substrate. This controlled hardening step also makes it possible to control the appearance of cracks.

Therefore, the inventors have unexpectedly demonstrated that the process of the application allows a very homogeneous deposition for cavities with a very large form factor, namely a deposit of constant thickness both in the bottom of the cavities and on the walls and the upper edges of the cavities, which does not provide the method of the prior art.

The liquid behavior of the solution coated by the process of the prior art is a disadvantage for a textured substrate deposit. On the contrary, the curing of the polymer before the heat treatment (evaporation and decomposition) makes it possible to overcome the liquid behavior of the coated solution. The controlled curing step is to leave the substrate coated with the liquid solution for a specified time at a temperature of at most 180 ° C, before it undergoes heat treatment.

The controlled cure step comprises at least two substrate placement phases at a temperature of at most 180 ° C, each phase corresponding to a distinct temperature (preferably at a constant temperature, or up to one maximum), and for an equal or different period of time. A temperature gradient is imposed from one phase to another. This curing step allows the solvent of the solution to evaporate and the polymer to cross-link and achieve a suitable degree of cure before the heat treatment. It is also important that the hardening is not at its maximum because during the decomposition during the heat treatment, the material shrinking at high temperature may otherwise crack.

This is why the duration and the temperature of the phases of the controlled curing step, and the number of phases, depend in particular on the composition of the solution, that is to say on the type of polymer, the nature of the other constituent elements and the nature of the substrate. The control of these parameters leads to an appropriate curing of the polymer for optimal shrinkage and then its decomposition, in order to achieve a homogeneous distribution of the inorganic coating.

Advantageously, the controlled curing step comprises at least two phases, a first phase for which the substrate coated with the polymer solution and based on the inorganic precursors is placed at a low temperature (below 80 ° C) for a predetermined period, in particular between five minutes and several hours, and a second phase for which the substrate is heated to a temperature between 80 ° C and 180 ° C, in particular constant, for a predetermined period, preferably at most one hour. According to one characteristic, the inorganic precursors are compatible with the polymeric compound so that the solution to be coated is stable and homogeneous.

The heat treatment consists in placing the substrate coated with the solution, after the controlled curing of the polymeric compound, with a temperature which is at least that of decomposition of the polymeric compound, especially at high temperature at a temperature above 180 ° C. The substrate can be placed directly at this high constant temperature without gradual increase in temperature from the temperature imposed at the curing stage. Alternatively, the substrate may be progressively heated from the curing temperature to the desired constant temperature.

Therefore, at the end of this heat treatment, the polymer as well as the polymerization catalyst when a polymerization catalyst has been added to the polymer, are completely decomposed. The substrate coated with the inorganic layer is devoid of polymer and polymerization catalyst. The heat treatment may comprise several phases with each a temperature step, the next phase having a higher temperature than the previous phase. The temperatures which correspond to the decomposition temperatures of the polymers are a function of the type of polymer. Generally, the heat treatment temperature is between 180 and 450 ° C.

Preferably, especially in the case of ceramics deposits, the method comprises an additional annealing or calcination step after the heat treatment, which consists of placing the substrate, the polymer of which has been decomposed, in an oxidizing or reducing atmosphere at a higher temperature. at the decomposition temperature of the polymer, in particular at a temperature above 500 ° C., preferably of the order of 700 ° C. (in particular for ceramics). This calcination step depends on the nature of the inorganic layer deposited. This step advantageously makes it possible to crystallize and densify the inorganic material. Advantageously, the solution ready to be coated based on inorganic precursors and on the polymeric compound is obtained by first producing a first mixture of a solvent and inorganic precursors, then adding to this first mixture the polymeric compound, and finally mixing all until a homogeneous mixture.

The term "solvent" in the remainder of the description any liquid capable of solubilizing the precursors, water, alcohol, an acid, any other organic solvent, or a combination of these elements. According to another characteristic, one or more polymerization catalysts, for example methyl ethyl ketone peroxide, and optionally one or more accelerators may be added to the solution ready to be coated, before or after addition of the polymeric compound and homogenization of said solution.

In known manner, the deposition step is non-limiting by spin coating ("spin-coating" in English), or dip-coating ("dip-coating" in English), or by spraying. Preferably, the thermosetting polymer is a particularly unsaturated polyester. Alternatively, other polymers are usable such as phenol or phenol-formaldehyde resins (known under the name Bakelite®), polyepoxides or epoxides (Araldite®), polyurethanes (PU), silicones, polyimides. The material of the textured substrate on which the organic material is deposited is able to withstand high temperatures, higher than those of the final heat treatment, depending on the applications and the product deposited. The substrate material carries a temperature, preferably at least 500 ° C or even in a range of 700 to 1300 ° C.

The method of the invention is particularly applicable to textured substrates having porosities ranging from nanometers to a few hundred micrometers.

The inventors have surprisingly demonstrated that the method was particularly effective, even for textured substrates whose cavities have very important form factors, in particular form factors of 1 and more, in particular 2, 3, 8, or else 40 or even 80, the form factor being defined by the ratio cavity depth / width of the cavity.

Thus, the process allows for these cavities whose depth is very large relative to their width to provide an extremely homogeneous inorganic element layer deposition, both on the bottom of the cavities and on the walls and the upper edges, while the Prior art processes provide for such substrates inhomogeneous deposits with a deposit accumulation in the bottom of cavities and a lack of deposition on the walls and edges.

The applications of the method of the invention are numerous on textured surface substrates.

Non-exhaustively, the nature of substrates that can withstand temperatures of at least 400.degree. To 500.degree. degradation: ceramics (Al ₂ 0 ₃ , YSZ, etc.), metals (Ni, Fe, etc.), semiconductors (Si, etc.), some glasses (silica), or their mixtures (glass-ceramics, composites, etc. ), and their structures having porosities ranging from nanometers to a few hundred micrometers.

Non-exhaustively, there may be mentioned as applications associated with the inorganic materials to be deposited:

 supercapacities or capacitors for capacitors: TiO 2, O 2 O, RuO 2,

C0O2, NiO, ZnO and CeO2,

thermoelectricity, catalysis, deposits of insulating and electrical compounds by deposits of materials of the Ruddlesden-Popper A _{n +} 1 Bn0 ₃ n ₊ 1 type where A and B are metallic or non-metallic cations,

the cathodes for fuel cells such as perovskite type oxides (AB0 ₃ or A ₂ B0 ₄ ): ₂ - _x Sr _x NiO ₄ , La ₂ - _x Sr _x CuO ₄ , LSM, LSCF,

the anodes for NiO -YSZ, Ti-YSZ, Nb-TiO ₂ , Ni-SDC fuel cells,

 solid electrolytes for micro-batteries,

solid electrolytes for doped CeO ₂ ceramics fuel cells, of yttriated zirconia (Zr ₂ O ₃ -% Y ₂ O ₃ ),

- the piézolélectricité (dielectric materials of perovskite structure), from Lead zirconate titanate Pb (Zr _x, Ti _-x) O ₃ (PZT noted), of the doped barium titanates or non strontium (Ba-i _-x Sr _x TiO ₃ ), PZNTs (Pb (Zn _/ 3Nb _2/3 ) O ₃ ), SBT (strontium tantalate and bismuth),

other applications in catalysis by infiltration of Ruddlesden-Popper phases can be envisaged. The infiltrated materials may be Sr ₃ FeMO ₆ (M = Fe, Co, Ni), La ₂ NiO ₄ for example,

lithium cathodes of the LiMO ₂ (LiCoO ₂ , LiNiO ₂ , etc.) or LiMPO ₄ (LiMnPO ₄ , LiCoPO ₄ ) type, the CeO ₂ -Y ₂ O ₃ electrolytes, materials for lasers: yttrium and aluminum garnet of general formula Y ₃ AI ₅ 0i ₂ (YAG) doped with Nd, Er, Tr, Yb, Ho, yttrium perovskite structure and Nd-doped aluminum and noted Nd -YAP, YAB system (yttrium, aluminum, boron), Nd-doped LiYF ₄ crystals (Nd-YLF), Nd-YVO ₄ , Ce-LiSAF (LiSAF: chromium-doped lithium strontium aluminum fluoride), Ce-LiCAF (LiCAF) LiCaAIF ₆ ), U-CaF ₂ , Sm-CaF ₂ ,

anti-reflective treatments: MgF ₂ , Al ₂ O ₃ ,

 deposits of nano-alloys or hybrid nanoparticles or nanomaterials based on metals or metal oxides or nanowires of alloys or others on porous support: catalysis (Ru-Pt, Ir-Pd, Au-Cu, Au-Pt) , optical (FeRh), magnetic alloys such as FeCo, Ag-Co, Co1-xPtx for example for magnetic storage (magnetic memory),

chemical sensors with metal oxides such as In ₂ 0 ₃ , Ta ₂ 0 ₃ , CuTa ₂ 0 ₆ , La ₂ 0 ₃ , Ag ₂ 0 ....,

- photovoltaic cells: thin layers of indium copper diselenium (CIS), cadmium telluride (CdTe), among others,

 - Insulating or conductive ceramics, glass,

the protections of porous metal substrates against corrosion by deposition of Si0 ₂ , Zr0 ₂ , Al ₂ O ₃ , Ti0 ₂ and CeO ₂ , etc.,

- the coatings of particles.

The present invention is now described with the aid of examples which are only illustrative and in no way limit the scope of the invention, and from the attached illustrations, in which:

 - Figure 1 shows a schematic sectional view of a textured substrate before the deposition process;

FIG. 2a is a sectional scanning electron microscope (SEM) view of a cavity (having a shape factor of 2) of a textured substrate coated according to the method of the prior art, usual and known sol-gel, at a magnification of 3000 of the substrate;

Figure 2b is a detail view of Figure 2a at a magnification of 30,000;

FIGS. 3a to 3e are different photos taken at SEM according to different magnifications of the substrate and illustrating different details of a cavity of a textured substrate coated according to the method of the invention and whose cavities have a form factor of 3, in particular:

 FIG. 3a: magnification of 2000 and illustrating a cavity,

FIG. 3b: magnification of 10,000 and illustrating the bottom of the cavity,

 FIG. 3c: magnification of 30,000 and illustrating a corner of the bottom of the cavity,

 FIG. 3d: magnification of 50,000 and illustrating a portion of the opposite walls of the cavity,

 FIG. 3e: magnification of 50,000 and illustrating one of the two opposite junction edges of the cavity and the upper face of the substrate,

FIG. 4 illustrates a schematic view of a textured test substrate coated with the same polymer as the substrate of FIG. 3a, without the hardening control equivalent to that of FIG. 3a;

Figure 5a illustrates a textured substrate obtained according to the method of the invention with a form factor for cavities of 8;

Figure 5b is a detail view of Figure 5a;

FIG. 6a illustrates a comparative test of a cavity of a textured substrate identical to that of FIG. 5a with the same coating which was obtained from the process of the invention without the controlled hardening step of the invention;

Figure 6b is a detail view of Figure 6a. FIG. 1 schematically illustrates a textured substrate 1 having an upper surface 10 and comprising in its thickness cavities or porosities 2 at the micron or a few tens of microns scale, or else submicron, the substrate being coated with a layer of inorganic material 3 which covers both the upper face 10, the cavities 2 and the joining edges 53 connecting the cavities 2 to the upper face 10. The form factor is for example of the order of 2 or 3 or more. The form factor of Figure 2a is 2.

The other figures correspond to snapshots taken with a scanning electron microscope (SEM) and different magnifications. The dimensions of a cavity considered in FIG. 3a is of the order of 10 μιτι wide and 30 μιτι deep, resulting in a form factor of 3. The shape factor of FIGS. 5a to 6b is 8.

Depending on the needs related to the use of the substrate, the cavities may have any type of geometric shape, be randomly distributed or not, extend linearly or sparsely. The techniques of formatting, texturing or etching are well known and will not be described here.

The invention is more particularly described with regard to textured substrates and not planar substrates. Indeed, current deposition techniques of inorganic layers for flat substrates, when applied to textured substrates, are unsatisfactory. The result obtained consists of a large deposit at the bottom of the cavity whose thickness tapers on the walls up towards the upper face of the substrate until disappearing on the joining edges. Figures 2a and 2b illustrate precisely the disadvantages of this method. FIG. 2a shows a cavity 5 inhomogeneously coated with a LaNiO ₃ layer deposited by the usual aqueous sol-gel technique. The form factors between FIGS. 2a (prior art) and 3a (invention) are substantially similar, respectively 2 and 3. It can be seen in FIG. 2a that the bottom 50 of the cavity has a layer 60 greater than the walls 51. and 52. FIG. 2b, which is a detail view of a wall 52 and the upper portion of the cavity, at the junction edge 53, shows a thin layer thickness 61 along the wall 52. , and the absence of material on the edge 53.

It should be noted that the white halo visible in FIGS. 2a and 2b at the junction edge 53 corresponds to the typical and known phenomenon of the absence of deposition of inorganic material. In fact, when the inorganic material is correctly deposited, the conductive material makes it possible to evacuate the electrons scanned on the surface of the substrate by the scanning electron microscope, thus generating no electron deflection, whereas in the Absence of the conductive coating, the material of the substrate accumulates the electrons on its surface and becomes "luminous" by deviation of the electrons to the electronic observation.

The aim of the deposition process of the invention is therefore to coat a micron-sized or submicron-textured substrate of an inorganic material in a layer uniformly distributed in thickness and surface area, in particular in the bottom 50 of the cavities, on the walls 51 and 52 and on the edges 53 (Figure 1).

The substrate is in the embodiment of the method and with reference to FIGS. 3a to 3e, a porous silicon wafer coated with LaNiO ₃ . Figures 3a to 3e illustrate the result of the method of the invention, showing that the inorganic material 3 is distributed homogeneously in thickness and covering all surfaces. The bottom 50 (FIGS. 3a and 3b) and the walls 51 and 52 (FIGS. 3a and 3d) of a cavity are covered with an equivalent thickness 30 and 31 respectively of material, as well as the joining edges 53 in a thickness 32 just as similar (Figure 3e). The upper face 10 of the substrate (FIG. 3e) is also homogeneously covered with a thickness 33.

According to the invention, the method comprises the steps of

 preparation of a solution based on inorganic precursors and a polymerizable and thermosetting polymeric compound,

 deposition on the substrate of said solution,

 controlled curing of the polymeric compound at a temperature of less than or equal to 180 ° C,

 high temperature heat treatment of the substrate coated with the solution for the decomposition of the polymeric compound (including for the decomposition of its polymerization catalyst when a polymerization catalyst has been added to the polymer),

 and preferably annealing the substrate at a temperature greater than that of the heat treatment so as to crystallize the inorganic material.

According to the invention, the step of controlled curing of the polymer comprises at least two distinct phases for submitting the substrate at a temperature of at most 180 ° C. and at a time determined for each of the phases, a temperature gradient being imposed on the substrate. one phase to another. In the exemplary LaNiO ₃ organic material deposition on an etched silicon substrate (FIGS. 3a to 3e), the compounds are as follows:

 the solvent of the liquid solution is methoxyethanol,

 the inorganic precursors are lanthanum nitrates and nickel acetates,

the methoxyethanol is mixed with the lanthanum nitrates and nickel acetates, to provide a concentration which may vary between 0.005 mol.l ^-1 to 0.6 mol.l ^-1 ,

 to this mixture is added the polymeric compound which is a polymer resin made of a mixture of styrene and polyester between 60 and 99 percent by weight. According to the invention, it is important not to mix the polymeric resin with the precursors immediately. The solvent is first mixed with the inorganic precursors to obtain a first mixture which must be miscible in the necessary proportions with the polymer resin. Then, in this first mixture, the polymer resin is added and mixed until a stable and homogeneous solution is obtained.

With regard to the compounds used in the abovementioned example, the solution is added after homogenization and directly preceding the deposition, a polymerization catalyst, in this case methyl ethyl ketone peroxide.

The solution is then deposited on the substrate, for example by spin-coating.

Then, the essential step of controlled curing of the polymer comprising, for the compounds in question, two distinct phases for submitting the substrate at a temperature of at most 180 ° C. and at a time determined for each of the phases, a temperature gradient being imposed from one phase to another:

 phase 1: the substrate coated with the solution is left at a low and constant temperature, typically between 20 ° C. and 80 ° C., depending on the proportions of the polymerizable mixture and on the presence or absence of an accelerator, for the time necessary to obtain hardness (for example between 5 minutes and 4 hours), then

 phase 2: it is heated to a temperature always not exceeding 180 ° C, for example at a temperature between 80 ° C and 180 ° C, especially from a few minutes to one hour to advance the crosslinking of the polymer. At the end of the controlled cure step, the polymer mixed with the inorganic precursors became solid with minimal shrinkage. The phenomenon of constriction of a material is called "withdrawal" because of an evolution of its state or a reduction of its porosity or a partial loss of material.

The thus coated substrate is then heat-treated at a temperature of at least 180 ° C in order to evaporate the solvent and precompose the polymer, for example by placing it in an oven or on a hot plate. One or more intermediate temperature stages can be imposed to ensure a pre-decomposition of the polymer and its final decomposition. For example, a first temperature level at 180 ° C from 5 to 20 minutes will be imposed, then a last level between 375 ° C and 400 ° C between 1 and 20 minutes. The exposure time, the temperature and the number of decomposition temperature treatment phases can vary considerably depending on the type of polymer. These parameters are thus controlled to obtain the decomposition of the polymer. The polymerist will know how to define these parameters.

The substrate thus obtained comprises the inorganic coating layer and is completely free of the polymer (and polymerization catalyst) which has made it possible to distribute the solution in a homogeneous manner.

Depending on the nature of the substrate and the inorganic layer, it is possible to carry out an additional heating step at a temperature much higher than the previous temperature of heat treatment, preferably greater than 500 ° C., and in particular of the order of 700 ° C. C, for a duration that can be between 1 and 30 minutes. This step crystallizes the ceramic material for example, or the "annealing" of a metal film under a reducing atmosphere. Annealing means a heat treatment that improves the quality of the deposited film.

A similar example can be achieved with Ba _{0 6} Sr-. ₄ TiO ₃ , strontium doped barium titanate (BST). The solvent remains methoxyethanol, while the inorganic precursors are barium hydroxides, strontium hydroxides, titanium isopropoxide and diethanolamine. The thermosetting polymer is identical as are the process steps. The inventors have surprisingly demonstrated that the controlled hardening step played an important role in the expected result. Thus, FIG. 4 shows a schematic view of a comparative test substrate with a deposition of organic material having undergone a usual hardening before thermal decomposition, this material being of identical composition to that initially deposited for the substrate of FIG. 3a. In this comparative example, the test substrate coated with the polymer was left for one hour at room temperature to then directly undergo the heat treatment for decomposition of the polymer. This substrate has therefore not undergone controlled hardening within the meaning of the invention. FIG. 4 shows, after curing and before decomposition of the polymer, slight depressions 7 in the polymer at each pore due to shrinkage due to greater hardening at the pore level. However, this will lead to inhomogeneity of distribution of the inorganic layer after thermal treatment of the substrate, that is to say after the decomposition of the polymer.

In contrast, for the substrate of FIG. 3a coated with LaNiO ₃ according to the process of the invention, the polymer deposited solution underwent controlled hardening in a first phase for which the polymer remained at a temperature of 40.degree. hour, then a second phase during which it was heated at 180 ° C for ten minutes. The final result of Figure 3a (after decomposition of the polymer at 375 ° C for 10 minutes) shows a homogeneous distribution of the inorganic material. FIG. 5a shows a deposit according to the invention carried out on a form factor substrate equal to 8. The controlled hardening step corresponds to that of the substrate of FIG. 3a. There is also a homogeneous deposit at the bottom, on the edges and on the edges of the pores. Figure 5b shows a detailed view of this homogeneous deposit.

In contrast to the invention, FIG. 6a shows a pore identical to that of FIG. 5a (of form factor equal to 8), the substrate coated with LaNiO ₃ having, however, not undergone any pre-hardening phase or controlled curing before thermal decomposition of the polymer. Indeed, the substrate coated with the polymer solution was put directly in the oven for heat treatment, that is to say to decompose said polymer, at a temperature of 375 ° C for 10 minutes. The result of FIG. 6a shows a deposit of LaNiO ₃ of considerable thickness towards the bottom of the pore, an inhomogeneous deposit on the walls and an absence of material on the edges.

Therefore, the method of the invention with a controlled polymer curing step provides a homogeneous spread of the inorganic layer over the entire surface of the substrate and at an equivalent thickness, including homogeneously in the bottom and the walls of the cavities, and the joining edges with the upper flat part. The process of the invention allows homogeneous deposition of the inorganic layer for high form factor substrates. The tests illustrated with reference to the figures relate to form factors of 2, 3 and 8. The inventors have made additional tests with even larger form factors, in particular 40 and even 80, providing homogeneity as well. unexpectedly in surface distribution and in thickness. Of course, the method is also suitable for form factors of less than 1.

Claims

1. Process for depositing an inorganic material (3) on a substrate (1) comprising the steps of:  preparation of a solution based on inorganic precursors and a polymerizable polymeric compound,  deposition on the substrate of said solution,  heat treatment of the substrate coated with the solution for the decomposition of the polymerized polymeric compound, characterized in that  the polymeric compound is thermosetting, and  the process comprises, before the heat treatment step, a controlled curing step of the polymeric compound, this controlled curing step comprising at least two distinct phases for submitting the substrate at a temperature of at most 180 ° C. and according to a predetermined duration for each of the phases, a temperature gradient being imposed from one phase to another,  the thermal treatment for the decomposition of the polymerized polymeric compound comprises placing the substrate coated with the solution, after controlled curing of the polymeric compound, at a temperature which is at least that of decomposition of the polymeric compound. 2. Method according to claim 1, characterized in that the controlled curing step comprises at least two phases, a first phase for which the substrate coated with the solution is placed at a temperature below 80 ° C for a predetermined period, especially between 5 minutes and several hours, and a second phase for which the substrate is heated to a temperature between 80 and 180 ° C for a fixed period, preferably at most one hour.  3. Method according to any one of the preceding claims, characterized in that the heat treatment comprises several phases each with a temperature step, the next phase having a higher temperature than the previous phase. 4. Method according to any one of the preceding claims, characterized in that it comprises an additional step after the heat treatment of placing the substrate whose polymer has been decomposed, at a temperature above the decomposition temperature of the polymer, in particular at a temperature above 500 ° C, preferably of the order of 700 ° C.  5. Method according to any one of the preceding claims, characterized in that the solution ready to be coated based on inorganic precursors and the polymeric compound is obtained by first producing a first mixture of a solvent and inorganic precursors, then adding to this first mixture the polymeric compound, and finally mixing the mixture until a homogeneous mixture.  6. Method according to any one of the preceding claims, characterized in that one or more polymerization catalysts, and optionally one or more accelerators, are added to the ready-to-coat solution, after addition of the polymeric compound and homogenization of said solution. 7. Process according to any one of the preceding claims, characterized in that the thermosetting polymeric compound is chosen from polyesters, polyesterphenols or phenol-formaldehyde resins, polyepoxides or epoxides, polyurethanes, silicones and polyimides. 8. Method according to any one of the preceding claims, characterized in that it is applied to a substrate which is textured having porosities ranging from nanometers to a few hundred micrometers. 9. Method according to any one of the preceding claims, characterized in that it is applied to a substrate which is textured whose cavities have a form factor of 1 and more, in particular 2, 3, 8, or even 40, or even 80, the form factor being defined by the ratio cavity depth / width of the cavity.