WO2018229266A1

WO2018229266A1 - Liquid production of conformal coatings of oxide materials on microstructured or macrostructured substrates

Info

Publication number: WO2018229266A1
Application number: PCT/EP2018/065995
Authority: WO
Inventors: Nathalie POIROT
Original assignee: Universite De Tours; Centre National De La Recherche Scientifique
Priority date: 2017-06-16
Filing date: 2018-06-15
Publication date: 2018-12-20
Also published as: FR3067854A1; FR3067854B1

Abstract

The present invention relates to a three-dimensional system (1) that withstands a temperature of at least 400°C, comprising a three-dimensional substrate (2) made of a material that withstands a temperature of at least 400°C, which comprises at least one microtextured or macrotextured surface (21), and a coating (3) made of a material chosen from metals and oxides. According to the invention, the textured surface (21) has an aspect ratio of between 7 and 10, and the coating (3) is a three-dimensional conformal coating that is in the form of a film, the thickness of which is between 10 nm and 1 µm. The present invention also relates to a process for the liquid production of such a three-dimensional system (1).

Description

LIQUID REALIZATION OF CONFORMAL COATINGS OF OXIDE MATERIALS ON MICRO- OR MACRO-STRUCTURED SUBSTRATES

The present invention generally relates to the liquid embodiment of a conformal coating of oxide materials on micro- or macro-structured three-dimensional substrates, and in particular a three-dimensional electrode.

For the purposes of the present invention, the term "three-dimensional substrate" means a substrate comprising on its surface a micro- or macro-structuring (or etching, for example in the form of micro- or macro-pores, trenches, holes or studs.

For the purposes of the present invention, the term "conformal coating" means a coating which covers the entire surface of the substrate on which it is disposed and which is homogeneous, regardless of the form factor of the substrate.

For the purposes of the present invention, the term "form factor" means the ratio of the average depth of the etching of the substrate (for example the height of the pore-like cavities, the slices, the holes or the pads) over its opening (for example, the width of the pores, trenches, holes or studs).

To satisfy the need for miniaturization of energy source devices, three-dimensional integration (or "3D") is one of the most studied paths in the last ten years. For example, dielectric materials are used for capacitive components such as capacitive elements MIM (acronym for the metal / insulator / metal stack) and MEMS (acronym for "Microelectromechanical Systems"). microelectromechanical devices), which are now integrated into chips. MIM capacitive elements are used in RAMs ^[1_3] and MEMS capacitive elements have been widely developed for optical or RF switch applications (acronym for "radio frequencies" ^[4_6]) The advantages of 3D architectures are the reductions in size, the cost and the increase in performance related to the increase in the specific surface area.It is shown that 3D structuring improves the properties of these devices.Therefore, research in this area is extremely active, especially in the field of micro- batteries, micro-supercapacitors, and micro-fuel cells ^[7_10] A major breakthrough was achieved by Golodnitsky in the field of Li-ion microbatteries reaching a reversible capacity of 3.5 mA.h / cm ^{2 [ 9]} , which represents a capacity 20 to 30 times higher than that of 2D thin films In the field of RF applications, the integration of functions requires a regro more complex development of monolithic means of active and passive components.

Deposition techniques for growing thin films on 3D substrates can be classified into two categories: physical deposition or chemical deposition. Physical deposits include PVD (Physical Vapor Deposition), vacuum evaporation, molecular beam epitaxy, or cathodic sputtering. These techniques require particular conditions of deposition (high voltage, vacuum, etc.) and low deposition rates (close to 10 nm.min ^-1 ). With regard to the chemical deposits, one can mention 1 electrodeposition. by electrophoresis, the CVD (Chemical Vapor Deposition) pathway, the PCVD or PECVD pathway, and the depositing techniques such as the atomic layer deposition ALD (acronym for Atomic Layer Deposition).

The aforementioned deposition methods such as CVD, PVD or ALD have the disadvantage of being expensive, requiring the use of a clean room, a high temperature and sometimes ultra-high vacuum.

In order to overcome the aforementioned drawbacks, the applicant has developed a simple and inexpensive method of liquid deposition of conformal coatings of oxide materials on micro- or macro-structured substrates.

Liquid deposition methods for making thin films on textured substrates are known to those skilled in the art. Thus, the French patent application FR3010919 describes a method of depositing an inorganic material on a textured substrate at the micron or submicron scale. In the method of FR3010919, the inorganic material is obtained after coating on the substrate with an inorganic inorganic precursor-based solution and a polymerizable polymeric compound. The substrate thus coated is then subjected to a controlled thermosetting step, followed by a multi-phase heat treatment at different temperature ranges above 500 ° C during which the polymeric compound is decomposed. It is the controlled curing step that allows the inorganic solution to conformally deposit in thin layers in all topological depressions and depressions of the substrate.

However, the polymer liquid route taught by FR3010919 application is a long deposit method because it requires the polymerization of the resin used.

To this end, the applicant has developed a solution consisting in depositing, on textured substrates having a high form factor, films of oxide materials or metal that conforms, that is to say homogeneously covering the entire surface of the substrates on which they are deposited. For this purpose, inorganic precursors are dissolved in a solvent, the viscosity of which is adjusted by the addition of a soluble adjuvant, and then one or more layers of the solution are deposited on the substrate which is then subjected to a heat treatment. floor. With such a method, it is possible to obtain conformal films on high aspect ratio textured substrates.

More particularly, the present invention therefore relates to a three-dimensional system resistant to a temperature of at least 400 ° C, comprising:

A three-dimensional substrate made of a material resistant to a temperature of at least 400 ° C., said substrate comprising at least one micro- or macro-textured surface, and

A coating made of a material chosen from metals and oxides,

said system being characterized in that said textured surface (21) has a form factor of between 2 and 20, and

in that said coating is a conformal coating in the form of a film whose thickness is a controlled thickness of between 10 nm and 1 μη.

By material resistant to a temperature of at least 400 ° C is meant in the sense of the present invention, a material which is not degraded at such temperatures.

By microstructured surface substrate is meant, in the sense of the present invention, a material comprising on its surface a microstructuration (for example in the form of micropores, slices, or pads), so that this textured face is microstructured. For the purposes of the present invention, a substrate with a macrostructured surface is understood to mean a material comprising on its surface a macrostructuration (for example in the form of pores, holes, slices or blocks), so that this textured face is macrostructured.

When the coating does not comply, it can be observed, for example for a metal layer overlay on a Si substrate when producing a capacitor MIM (Insulating Metallic Metal layer) an electrical breakdown during its use.

The textured surface of the three-dimensional system according to the invention has a form factor of between 2 and 20, and preferably between 3 and 7.

As the shape factor increases, ie the cavity cavity / cavity opening ratio increases, the performance of the surface area is improved. A form factor of less than 2 has the disadvantage of not increasing the surface area of the substrate enough to observe a marked effect on the measured performance. However, an excessively high form factor, especially greater than 20, will have the disadvantage of weakening the substrate without, however, preventing liquid conforming coating.

Advantageously, the substrate may be a semiconductor material, or a ceramic, or glass, or glass-ceramic, or metal, and especially metal foam, or a composite material.

In the context of the present invention, a substrate made of nickel foam, or alumina, or of microstructured silicon will preferably be used.

Advantageously, the coating of the three-dimensional system according to the invention may be chosen from perovskite-type oxides ABO ₃ or double perovskite A ₂ BO ₄ where A is a rare earth and B is a metal, or among the oxides of Mn0 ₂ , Ru0 ₂ , Si0 ₂ , Ti0 ₂ , Zr0 ₂ , Fe ₃ O ₄ , Al ₂ O ₃ , Ce0 _{2 type} .

The three-dimensional system according to the invention opens new perspectives in 3D microsystems such as MEMS, MIM, micro-batteries, micro-supercapacitors, micro-batteries.

In particular, the three-dimensional system according to the invention can be used as an electrode (cathode or anode) for fuel cells, or as an electrode for batteries and microbatteries. Finally, the three-dimensional system according to the invention can be used as capacity or supercapacity for capacitors or supercapacitors.

The subject of the present invention is also a method for producing a liquid route, comprising the following steps:

A. Preparation and / or supply of a three-dimensional substrate of a material resistant to a temperature of at least 400 ° C, said substrate comprising at least one micro- or macro-textured surface having a form factor of between 2 and 20 ;

B. Preparation of a solution of inorganic precursors (typically metallo-organic compounds) in a solvent, constituting after mixing and stirring an organometallic matrix;

C. Adding a soluble adjuvant in said solvent in an amount such that the viscosity of said solution is at least 80 mPa.s;

D. Deposition on the substrate of one or more layers of said solution;

E. Heat treatment of the substrate thus coated with the solution comprising: a first heat treatment step at a temperature of at least 90 ° C to remove the solvent from said inorganic precursor solution; then

a second heat treatment step at a temperature of between 200 ° C. and 400 ° C. to remove the adjuvant and the organometallic matrix,

a third heat treatment step at a temperature between 400 ° C. and 800 ° C. to crystallize the coating and form the oxide film, the crystallization temperature being chosen, in this temperature range, as a function of the crystallization temperature of the final product and temperature resistance of the substrate.

F. steps D and E being repeated until a coating having the desired total thickness is obtained, typically between 70 nm and 300 nm.

The advantages of the liquid process according to the present invention are, besides its speed, its simplicity and its low cost, its reliability linked to the high stability of the solutions. Finally, the process according to the invention does not involve vacuum and excessively high temperatures. The only requirement of this method is the control of the viscosity of the inorganic precursor solution, which is essential to obtain a good coating on macro and micro-structured 3D substrates with a high aspect ratio.

The viscosity of the inorganic precursor solution is adjusted by changing the concentration of the solution and adding an adjuvant to obtain a high viscosity, typically a viscous compound. This adjuvant must not interact with precursors inorganic solution, and therefore does not influence the final chemical composition of the deposited compound.

Advantageously, it is possible to use as an adjuvant to adjust the viscosity of the solution of inorganic precursors, a polyethylene glycol (generally designated by the acronym PEG) or a glycerol in a polar protic solvent.

As PEG, PEG 400 or PEG 2000 will preferably be used in the process according to the invention.

Advantageously, it is possible to use as inorganic precursors tetrahydrated lanthanum nitrate, nickel acetate, strontium hydroxides, barium, titanium isopropoxide.

Other advantages and features of the present invention will result from the description which follows, given by way of nonlimiting example and with reference to the appended figures:

FIGS. 1A and 1B show two SEM images of trenches with different form factors

(respectively 7 and 3) obtained after deep etching by the standard cryogenic process DRIE

(acronym for the English term "Deep Reactive Ion Etching") of a silicon substrate;

FIGS. 2A and 2B show two SEM images of trenches in a silicon substrate having a shape factor of 3 coated with a single layer of La03 obtained from a tetrahydrated lanthanum nitrate solution and nickel acetate whose viscosity is of the order of 9.8 mPa.s, Figure 2B is a detailed view of the bottom of a trench of Figure 2A;

FIGS. 3A to 3C show three SEM images of a trench of a silicon substrate, the factor of which It has a shape of 8, and is coated with a single layer of i03 obtained from a solution of tetrahydrated lanthanum nitrate, nickel acetate and PEG, the viscosity of which is of the order 39 mPa.s;

FIG. 4 shows five SEM images of a trench of a silicon substrate, whose form factor is 3 and which is coated with a single layer of La03 obtained from a solution of lanthanum nitrate. tetrahydrate, nickel acetate and

PEG whose viscosity is of the order of 85 mPa.s;

FIGS. 5A and 5B are two SEM images of trenches of a silicon substrate, whose form factor is 5.6, and which are coated with five layers of La i03 obtained from a solution of lanthanum nitrate tetrahydrate, nickel acetate and glycerol whose viscosity is of the order of 80-85 mPa.s.

FIG. 6 shows three SEM images of trenches of a silicon substrate whose shape factor is 8 and which are coated with a layer of La03 obtained from a tetrahydrated lanthanum nitrate solution. , nickel acetate and glycerol whose viscosity is of the order of 80-85 mPa.s.

FIG. 7 schematically represents a three-dimensional system according to the invention.

Figures 1 to 6 are described in more detail in the following examples, which illustrate the invention without limiting the scope.

FIG. 7 schematically shows an example of a three-dimensional system 1 according to the invention used in the examples, which comprises: a three-dimensional substrate 2 made of a material resistant to a temperature of at least 400 ° C, comprising at least one micro- or macro-textured surface 21 having a form factor of between 3 and 8, and

a conformal coating 3 of a metallic or oxide type and in the form of a film whose thickness is between 10 nm and 1 μη. EXAMPLES

Equipment for making the deposit: spinette (in English known under the name "spin-coater"): spin-coater Suss RC8 marketed by Suss Microtec;

Support products: silicon substrates;

precursors: tetra-hydrated lanthanum nitrate of Sigma Aldrich (La (NO ₃ ) ₃ , 6H ₂ O, 99.9%) and nickel acetate of Sigma Aldrich (Ni (OOCCH ₃ ) ₂ , 4H ₂ O, 99.9%) ;

methoxyethanol from Sigma Aldrich, C ₃ H ₈ O ₂ , 99.9%). This solvent is chosen for two reasons:

the first reason is the presence of alcohol groups which allow a high affinity with the metal atoms of lanthanum nitrate tetrahydrate and nickel acetate, as well as a good combination with the La ³⁺ and Ni ²⁺ atoms; this has the consequence that no precipitation is observed during the evaporation of the solvent;

the second reason is the high affinity of 2-methoxyethanol on the silicon substrate. viscosity additives: glycerol, PEG 2000

Characterization

Morphological analysis: the morphology of the deposited films is observed by scanning electron microscopy (SEM). The SEM micrographs were obtained on a Zeiss ultra plus FEG - SEM equipment at a 2kV acceleration voltage with an InLens SE detector, the working distance being about 2 to 3 mm.

Measurement of viscosity: the viscosity is controlled by the Brookfield viscometer (LVD-III) with a flat cone.

Preparation of inorganic precursor solutions

The preparation of the solutions consists in dissolving the precursors in the solvent in stoichiometric proportions. For this, proceed as follows:

• Lanthanum nitrate is dissolved under constant stirring in the solvent preheated to 100 ° C to evaporate the residual water;

• by continuous heating at 80-90 ° C, the solution becomes clear;

• Then add an equimolar amount of nickel acetate to the previous solution;

After 30 minutes of stirring, a homogeneous solution is obtained which constitutes an organometallic matrix;

If necessary (for examples 3 and 4 according to the invention only), the glycerol is added or PEG just before depositing the solution on the substrate.

Preparation of substrates

Silicon substrates are textured using standard cryogenic etching. Figure 1 shows two SEM images of trenches with 2 form factors (respectively 7 for Figure 1A and 3 for Figure 1B) obtained after deep etching by DRIE.

Before depositing the i03 films on substrates that have been textured, they are cleaned using the RCA (Radio Corporation of America) method after a first cleaning solution of hydrofluoric acid to remove the residues. chemical etching. The substrates are introduced for 10 min into a mixture of H ₂ O, H ₂ O ₂ and NH ₄ OH with a volume ratio of 5: 1: 1 and heated to a temperature of about 75-80 ° C.

Director of the films of The i03

The i03 films are formed on the textured and cleaned substrates as follows:

one or more layers of 150 μl of one of the inorganic precursor solutions as obtained previously is deposited by centrifugation (spin coating) on a textured silicon substrate and cleaned, using the spinette (or spin-coater) Spinl50 from SPS-Europe at 3000 rpm for 30 s; then the substrate thus coated is subjected to a heat treatment stepped in three steps: a first drying step on a heating plate at 90 ° C. for 2 minutes, to remove the solvent from the solution;

a second pyrolysis step at 375 ° C. for 3 minutes to eliminate the organometallic matrix

(previously formed when mixing the precursors with the solvent) and the adjuvant;

a third calcination step at 700 ° C. in a preheated oven for a period of 20 minutes; this treatment is similar to a rapid thermal treatment treatment, conventionally designated by the acronym RTA (for "Rapid Thermal Annealing") to crystallize the coating and form a dense film of perovskite La i03; the whole process must be repeated as many times as the desired number of layers.

EXAMPLE 1 (COMPARATIVE) A film of a single layer of i03 was made on a textured substrate whose form factor was 3, as indicated above, from a solution of hydrated lanthanum nitrate and nickel acetate (0.5 M concentration of LaNiOs). This solution without PEG and glycerol has a viscosity of about 9.8 mPa.s. FIGS. 2A and 2B show that the trenches of the textured substrate are coated with a dense film of i03 having many defects such as cracks, uncovered oxide parts, trench product build-up and filaments (particularly visible in Figure 2B which is a detailed view of the bottom of a trench of Figure 2A). In addition, the thickness is not homogeneous from the bottom to the top of the trench. EXAMPLE 2 (COMPARATIVE)

A film of a single layer of i03 is made on a textured substrate whose shape factor is 8, as indicated above, from a solution of hydrated lanthanum nitrate and nickel acetate (concentration 0.3 M LaNiO3) and PEG. This solution containing PEG has a viscosity of about 39 mPas.

Fig. 3A shows an SEM image of an entire trench, while Figs. 3B and 3C are detailed views of this trench, located respectively at the top (Fig. 3B) and bottom of the trench (Fig. 3C).

Figures 3A and 3C show cracks in the bottom of the trench, while Figures 3A and 3B show that the trench walls are non-uniformly coated with filament formation. The middle of the trenches is not coated. EXAMPLE 3 (ACCORDING TO THE INVENTION)

A single layer film of i03 was made on a textured substrate whose form factor was 3, as indicated above, from a solution comprising 1 ml of hydrated lanthanum nitrate and sodium acetate. nickel (concentration at 0.6 M) and 1 ml of PEG. This solution containing PEG has a viscosity of about 85 mPa.s.

The five SEM images in Figure 4 show that the trench walls are uniformly covered with a dense coating without filaments or cracks. The bottom of a trench is covered with a thickness of i03 close to 45 nm. EXAMPLE 4 (ACCORDING TO THE INVENTION)

A film of an i03 layer is made on a textured substrate whose shape factor is 3 and 7, as indicated above, from a solution comprising 1 ml of hydrated lanthanum nitrate and acetate. nickel (concentration at 0.6 M) and 1 ml of glycerol - containing glycerol solution has a viscosity of about 80 mPa.s.

Figures 5A and 5B show that the trench walls are uniformly coated with porous coating (porosity due to decomposition of glycerol).

The textured silicon substrate is well coated with a homogeneous deposition of i03 with a thickness close to 200 nm. The edges are very well covered without varying the thickness.

The set of tests is summarized in Table 1 below: Table 1

EXAMPLE 5 (ACCORDING TO THE INVENTION)

A film of an i03 layer is made on a textured substrate whose shape factor is 8, as indicated below. above, from a solution comprising 1 mL of hydrated lanthanum nitrate and nickel acetate (0.6 M concentration) and 1 mL of glycerol-containing glycerol solution has a viscosity of about 80 mPa.s.

Figure 6 shows that the trench walls are uniformly coated with a porous coating (porosity due to the decomposition of glycerol).

The textured silicon substrate is coated with a homogeneous deposition of La03 with a thickness close to 70 nm. Edges are very well covered without cracking or uncovered areas

The set of tests is summarized in Table 2 below:

Table 2

Concentration Additive Viscosity Factor Number Quality Figure of the de (mPa. S) shape of the

solution viscosity layers coating

of

precursors

(Mol / L)

0.6 glycerol 80 8 1 good 6

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Claims

A three-dimensional system (1) resistant to a temperature of at least 400 ° C, comprising:

A three-dimensional substrate (2) of a material resistant to a temperature of at least 400 ° C, said substrate (2) having at least one micro- or macro-textured surface (21), and

A coating (3) made of a material chosen from metals and oxides,

said three-dimensional system (1) being characterized in that said textured surface (21) has a form factor of between 2 and 20, and

in that said coating (3) is a conformal coating in the form of a film whose thickness is between 10 nm and 1 μη.

A three-dimensional system (1) according to claim 1, wherein said substrate (2) is of a semiconductor material, or a ceramic, or glass, or glass-ceramic, or metal, or a composite material.

3. three-dimensional system (1) according to claims 1 or 2, wherein said substrate (2) is made of nickel foam, or alumina, or microstructured silicon.

4. three-dimensional system (1) according to any one of claims 1 to 3, wherein said coating (3) of an oxide selected from the perovskite-like oxides ABO ₃ or double perovskite A2BO ₄ where A is a rare earth and B a metal, or among the oxides of the MnO 2, RuC 2, SiO 2, Fe 3 O ₄ , TiO 2, ZrC 2, Al ₂ O ₃ , CeO _{2 type} .

5. Use of said three-dimensional system (1) as defined in any one of claims 1 to 4 as an electrode for fuel cells.

6. Use of said three-dimensional system (1) as defined in any one of claims 1 to 4 as an electrode for batteries and micro-batteries.

7. Use of said three-dimensional system (1) as defined in any one of claims 1 to 4, as capacitance or supercapacity for capacitors or supercapacitors.

8. Method of realization by liquid route, comprising the following steps:

A. preparing and / or providing a three-dimensional substrate (2) of a material resistant to a temperature of at least 400 ° C, said substrate (2) having at least one micro- or macro-textured surface (21) having a form factor of between 2 and 20;

B. Preparation of a solution of inorganic precursors in a solvent, constituting after mixing and stirring an organometallic matrix;

D. Deposition on the substrate of one or more layers of said solution;

E. Heat treatment of the substrate (2) thus coated with the solution comprising

a first heat treatment step at a temperature of at least 90 ° C to eliminate of said solution of inorganic precursors the solvent; then

a second heat treatment step at a temperature of between 200 ° C. and 400 ° C. to remove the adjuvant and the organometallic matrix;

a third heat treatment step at a temperature between 400 ° C and 800 ° C to crystallize the coating and form the oxide film;

F. steps D and E being repeated until a coating having the desired total thickness is obtained.

The process of claim 8 wherein the adjuvant is polyethylene glycol or glycerol in a protic polar solvent.

10. The method of claim 9, wherein the inorganic precursors are selected from tetra-hydrated lanthanum nitrate, nickel acetate, strontium hydroxides, barium, titanium isopropoxide.