FR3059339A1 - PROCESS FOR FORMING SILICON DIOXIDE FILMS - Google Patents

Abstract

The invention relates to a method for forming at least one silicon dioxide film on a substrate (40) by a chemical vapor deposition technique in a deposition chamber (20), the method comprising evaporation of an organometallic precursor on one side of the substrate (40) maintained at a temperature between 200 ° C and 350 ° C, preferably between 250 ° C and 350 ° C, the organometallic precursor comprising tetraacetoxysilane.

Description

Holder (s): COMMISSIONER OF ATOMIC ENERGY AND ALTERNATIVE ENERGIES Public establishment, CHANEL PARFUMS BEAUTE.

Extension request (s)

Agent (s): BREVALEX Limited liability company.

164) PROCESS FOR FORMING SILICON DIOXIDE FILMS.

FR 3 059 339 - A1

16 /) The invention relates to a method of forming at least one silicon dioxide film on a substrate (40) by a chemical vapor deposition technique in a deposition chamber (20), the method comprising the evaporation of an organometallic precursor on one face of the substrate (40) maintained at a temperature between 200 ° C and 350 ° C, preferably between 250 ° C and 350 ° C, the organometallic precursor comprising tetraacetoxysilane.

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PROCESS FOR FORMING SILICON DIOXIDE FILMS

DESCRIPTION

TECHNICAL AREA

The present invention relates to a method of forming a film of silicon dioxide. More particularly, the invention relates to a method of forming a silicon dioxide film at a moderate temperature and having the optical properties compatible with the use of an interference filter. The interference filter can be formed on microparticles, for applications in cosmetology for example.

PRIOR ART

The formation of films by chemical vapor deposition ("CVD" or "Chemical Vapor Deposition" according to Anglo-Saxon terminology) is known to those skilled in the art. This technique based on the evaporation of a precursor on a surface of a substrate makes it possible to form films conforming to said surface.

In order to promote the reactivity of the precursors with the surface of the substrate, and above all to obtain a film having a sufficient density and / or free of impurities due to the decomposition of the precursors, it may be necessary to form said film at a relatively high temperature. high, for example greater than 450 ° C.

CVD is used in particular for the formation of silicon dioxide films in the microelectronics industry, and uses standard organometallic precursors such as TEOS (tetraethoxysilane SifOCzHsb). The temperature of formation of the films of silicon dioxide is then of the order of 450 ° C. by the technique of chemical vapor deposition assisted by plasma (“PECVD” or “Plasma Enhanced Chemical Vapor Deposition” according to Anglo-Saxon terminology ).

However, a silicon dioxide film formed by CVD with a standard precursor at a temperature below 350 ° C will be of lower optical quality.

More particularly, its density decreases, and impurities due to the decomposition of the precursors remain trapped in said film.

However, some applications require the formation of relatively pure and dense silicon dioxide films at moderate temperatures, for example below 350 ° C.

Among the applications of interest, we can cite the formation of interference filters, comprising an alternation of films of silicon dioxide and titanium dioxide, on dispersed supports such as microparticles (for example spherical). These interference filters formed on microparticles are used in particular in cosmetology. Titanium dioxide films, having the optical properties required for the formation of interference filters, are generally formed by CVD (with “TIPP” as precursor) at temperatures between 250 ° C and 350 ° C. Thus, on the industrial level in order not to penalize the production rates, it is preferable to be able to also form the films of silicon dioxide in an equivalent temperature range, and by CVD.

It may also be necessary to form films of dense silicon dioxide, free of impurities, and at low temperature (for example between 200 and 350 ° C.) for applications in microelectronics, for example after the formation of the interconnections.

Thus, an object of the present invention is to provide a method of forming a film of silicon dioxide at moderate temperatures, and having the qualities required for the formation of interference filters.

Another object of the invention is to propose a method for forming an interference filter comprising a film of silicon dioxide formed at a moderate temperature.

STATEMENT OF THE INVENTION

The aims of the invention are at least partially achieved by a process for forming films of silicon dioxide on a substrate by a chemical vapor deposition technique in a deposition chamber, the process comprising evaporation, advantageously the flash evaporation of an organometallic precursor on one side of the substrate maintained at a temperature between 200 ° C and 350 ° C, preferably between 250 ° C and 350 ° C, the organometallic precursor comprising tetraacetoxysilane.

Flash or instant evaporation, we mean, for the organometallic precursor, an almost immediate evaporation. In other words, during flash evaporation, the organometallic precursor is forced to raise the temperature from ambient temperature to its evaporation temperature in a few milliseconds. More particularly, the organometallic precursor is at ambient temperature during its injection, and takes the temperature of the fluidized bed during its passage through the deposition enclosure. The rise in temperature thus imposed on the organometallic precursor causes its evaporation almost instantaneously.

According to one embodiment, the organometallic precursor is diluted in an organic solvent, the organic solvent advantageously comprising at least one of the solvents chosen from: an alcohol (advantageously isopropanol), an aromatic solvent (xylene, toluene), cyclohexane.

According to one embodiment, the organometallic precursor has a concentration in the organic solvent of between 0.01 mol / L and 0.03 mol / L.

According to one embodiment, the organometallic precursor is maintained at a temperature between 80 ° C and 150 ° C before being sprayed onto the face of the substrate.

According to one embodiment, the substrate comprises microparticles of a size between 100 nm and 500 μm, the micro particles advantageously being beads.

According to one embodiment, the microparticles comprise at least one of the materials chosen from: alumina, silicon carbide, titanium dioxide, silicon, mica.

According to one embodiment, the microparticles disposed on a main face of a porous support traversed over its entire thickness E by an inert gas so that the microparticles form a fluidized bed.

According to one embodiment, the support is maintained at a temperature below 200 ° C, advantageously below 150 ° C, for example 110 ° C.

According to one mode of implementation, the evaporation of the organometallic precursor is carried out according to cycles of evaporation, and in alternation with cycles of injection of oxygen into the deposition enclosure.

According to one embodiment, a purging of the deposition enclosure is carried out before each evaporation cycle and each injection cycle, so that the pressure in said enclosure is less than 30 mBar at the end of the purge.

According to one mode of implementation, at the end of each evaporation cycle and of each injection cycle, the pressure in the deposition enclosure is greater than 100 mBar and 60 mBar, respectively.

According to an embodiment, each evaporation cycle lasts from 5 seconds to 20 seconds.

According to an embodiment, between 20 and 100 evaporation and injection cycles are carried out.

The invention also relates to a method of manufacturing an interference filter comprising at least one film of silicon dioxide formed by the method of forming films of silicon dioxide on a substrate by a chemical vapor deposition technique.

According to one embodiment, at least one film of titanium dioxide is formed by CVD, advantageously at a temperature between 250 ° C and 350 ° C.

According to one embodiment, the at least one film of silicon dioxide and the at least one film of titanium dioxide are formed so that the interference filter comprises an alternation of films of titanium dioxide and films of silicon dioxide.

BRIEF DESCRIPTION OF THE DRAWINGS

Other characteristics and advantages will appear in the following description of the process for the formation of silicon dioxide films according to the invention, given by way of nonlimiting examples, with reference to the appended drawings in which:

FIG. 1 is a diagrammatic representation of a device for forming films by CVD adapted for implementing the method according to the invention,

- Figure 2 is an image by scanning electron microscopy in section (according to the thickness) of an interference filter formed on a silica bead, the interference filter comprising a stack of TiOz / SiO? / TiOz / SiO? / T1O2 , and obtained according to an embodiment of the invention,

FIG. 3 is a graphic representation of reflectivity curves (given in "%" along the vertical axis), as a function of the wavelength (given in "nm" along the horizontal axis) of a layer of SiO2 formed on a silicon substrate, more particularly, the curves A and B, represent, respectively, the theoretical reflectivities of a layer of SiO2 according to polarizations s and p, and according to an incidence at 45 ° with respect to normal, and the curves A ′ and B ′ represent, respectively, the reflectivities of a layer of SiO 2, obtained according to the present invention, according to polarizations s and p, and according to an incidence at 45 ° relative to normal,

- Figure 4 is a graphic representation of the reflectivity curve (given in "%" along the vertical axis), as a function of the wavelength (given in "nm" along the horizontal axis) of a filter interference formed according to the present invention, more particularly the interference filter is formed on silica beads which comprise, successively and from the surface of the silica beads, a film of titanium dioxide of 97 nm, a film of silicon dioxide of 135 nm, a film of titanium dioxide of 86 nm, and a film of silicon dioxide of 60 nm.

DETAILED PRESENTATION OF PARTICULAR EMBODIMENTS

For the different modes of implementation, the same references will be used for identical elements or ensuring the same function, for the sake of simplification of the description.

The invention described in detail below implements a process for forming films of silicon dioxide. More particularly, the films of silicon dioxide are formed by CVD and in a range of moderate temperatures, namely between 200 ° C. and 350 ° C. Also, in order to give these films of silicon dioxide the quality required for the formation of interference filters, taking into account their formation temperature, an organometallic precursor comprising tetraacetoxysilane (hereinafter Si (OAc) 4) is used during the formation of said films.

In Figure 1, we can see a chemical vapor deposition device 10 adapted for the implementation of the invention.

The present invention includes forming films of silicon dioxide by CVD on a substrate.

By substrate is meant both a solid substrate and microparticles.

The solid substrate may be a substrate comprising a semiconductor, insulating, or metallic material.

The solid substrate may include microelectronic, and / or optical devices.

We limit the rest of the description to the formation of films on microparticles, knowing that a person skilled in the art, with his general knowledge, can adapt the method according to the invention to large, massive substrates.

The microparticles can comprise at least one of the materials chosen from: alumina, silicon carbide, titanium dioxide, silicon, silica of mica type.

The microparticles 40 can have a size of between 100 nm and

500 pm.

The microparticles 40 can advantageously be beads.

By microparticle size is meant the largest of the dimensions of said microparticles. Furthermore, within the meaning of the invention, all the microparticles 40 of the same batch do not necessarily have the same size. Also, when considering a batch of microparticles having a given size, it is clear that said size is an average size.

During the formation of the silicon dioxide film, the microparticles 40 can form a fluidized bed.

By fluidized bed is meant a set of microparticles suspended by an ascending gas stream. In this regard, a person skilled in the art can consult the document [1] cited at the end of the description.

In order to implement the process for forming silicon dioxide films, the microparticles are placed in a deposition enclosure 20, extending along an axis XX ′, of the chemical vapor deposition device 10.

The deposition enclosure 20 comprises in its lower part B a support 30 on which the microparticles 40 rest.

The support 30 comprises two main faces 31 and 32 parallel to each other (and perpendicular to the axis XX ').

The support 30 is advantageously porous so that a gas can pass through it over its entire thickness E. The thickness E of the support 30 is the shortest distance between the main faces 31 and 32. The support 30 may comprise at least one materials chosen from: aluminum, stainless steel type.

Thus, as soon as microparticles 40 are arranged on the support 30, and that the latter is traversed by a gas over its entire thickness E, said microparticles are set in motion and a fluidized bed is created. For example, the gas allowing the implementation of the fluidized bed enters the deposit enclosure 20 through a first inlet 51. This configuration is therefore particularly advantageous, since it is desired to form a film over the entire surface of each microparticles. In fact, as soon as the microparticles form a fluidized bed, their entire surface is exposed to a reactive gas capable of being present in the deposition enclosure 20. More particularly, statistically, each surface portion of each of the microparticles forming the bed fluidized is exposed to the reactive gas in an equivalent way (in terms of duration and quantity of reactive gas), so that the film formation is homogeneous on each of the microparticles and between the microparticles.

By reactive gas, we mean a gas adapted to react chemically with the surface of the microparticles and thus form a film, the nature of the reactive gas will be discussed later in the description. Furthermore, we note that the reactive gas first crosses the support 30, over its entire thickness E, before reaching the fluidized bed formed by the microparticles 40.

Furthermore, the chemical vapor deposition device 10 comprises two thermal regulation systems 60 and 61 (for heating and cooling), disposed respectively in the lower part B and the upper part H of the deposition enclosure 20. This arrangement makes it possible to heat the lower parts B and upper H of the deposition enclosure 20 in a differentiated manner. More particularly, the fluidized bed of microparticles suspended in the volume of the deposition enclosure 20 can be heated to a higher temperature. higher than the support 30. More particularly, the support 30 can be maintained, by the thermal regulation system 60, at a temperature below the reaction or decomposition temperature of the reactive gases which are liable to pass through it, thus avoiding clogging of said support 30.

For example, the temperature of the fluidized bed formed by the microparticles 40, near or in the upper part H of the deposition enclosure, can be between 200 ° C and 350 ° C, advantageously between 250 ° C and 350 ° C .

The temperature of the support 30 can be between 100 ° C and 150 ° C.

The process for forming silicon dioxide films comprises the evaporation of an organometallic precursor in the deposit enclosure 20. By spraying in the deposit enclosure 20, it is understood that the organometallic precursor is introduced into the enclosure deposit 20 in the form of a finely divided solution. Furthermore, the evaporation of the organometallic precursor takes place on the surface of the microparticles.

It is understood that the organometallic precursor is a reactive gas.

Furthermore, the organometallic precursor is introduced into the deposition enclosure through a second inlet 52.

According to the invention, the organometallic precursor is tetraacetoxysilane. This chemical compound is particularly advantageous since it decomposes from 175 ° C., and therefore makes it possible to form films of silicon dioxide on the surface of the microparticles, the microparticles advantageously being in the form of a fluidized bed.

It is understood, without it being necessary to specify it, that tetraacetoxysilane reacts with an oxidizing chemical species to form a film of silicon dioxide by CVD. The oxidizing species can for example be dioxygen, ozone, water vapor.

The surface of the microparticles forming the fluidized bed is then advantageously maintained at a temperature between 200 ° C and 350 ° C, preferably between 250 ° C and 350 ° C.

Advantageously, the tetraacetoxysilane, before being injected into the deposition enclosure, can be diluted in an organic solvent.

The organic solvent can advantageously comprise at least one of the solvents chosen from: isopropanol, cyclohexane, an aromatic solvent (for example toluene, xylene).

The inventors have also demonstrated that the solvating power of isopropanol makes it possible to obtain excellent adhesion of tetraacetoxysilane to the surface of the microparticles 40, thus promoting the reactivity of said precursor with the surface of the microparticles 40.

After dilution, the concentration of tetraacetoxysilane can be between 0.01 mol / L and 0.15 mol / L.

Still advantageously, before being injected into the deposition enclosure, the tetraacetoxysilane can be maintained at a temperature between 80 ° C. and 150 ° C., for example 100 ° C.

The process for forming silicon dioxide films according to the invention can also comprise the injection of dioxygen into the deposition enclosure 20.

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The oxygen can be injected into the enclosure at room temperature. In other words, the temperature of the oxygen, as soon as it is in the enclosure, is imposed by the temperature inside said enclosure.

The dioxygen is intended to react with tetraacetoxysilane to form a film of silicon dioxide on the surface of the microparticles 40.

Advantageously, the injection (evaporation) of the tetraacetoxysilane can be carried out according to cycles of evaporation, and in alternation with cycles of injection of dioxygen into the deposit enclosure 20. In other words, the injection of the tetraacetoxysilane and the injection of dioxygen are performed over different time periods, and without overlap (in other words distinct). We are talking about pulsed CVD.

Pulsed CVD allows better control of the decomposition of species, therefore better control of the deposition kinetics, and therefore the deposition rates. This is all the more important when the thicknesses deposited are very small.

We speak of evaporation cycles when it comes to the injection of tetraacetoxysilane, and injection cycles when it comes to the injection of dioxygen.

The dioxygen injected during the injection cycles can be mixed with an inert gas, for example nitrogen. In this case, the proportion of nitrogen relative to the oxygen can be between 30% and 60%, for example 50%.

Still advantageously, a purge of the deposition enclosure 20 is carried out before each evaporation cycle and each injection cycle, so that the pressure in said enclosure is less than 30 mBar at the end of the purge. The purge can be carried out by a pumping system connected to the deposit enclosure 20.

At the end of each evaporation cycle, the pressure in the deposition enclosure 20 can be greater than 100 mBar.

At the end of each injection cycle, the pressure in the deposition chamber 20 can be greater than 60 mBar.

Evaporation cycles can last from 5 seconds to 20 seconds.

Advantageously, 20 to 100 evaporation and injection cycles can be performed.

Thus, although formed at relatively low temperatures (below 350 ° C), the silicon dioxide films have a density as well as optical properties comparable to those of the same film formed at higher temperature with a standard organometallic precursor. FIG. 3 also compares the optical properties (reflectivity) of a layer of S1O2 93 nm thick formed on a plane silicon substrate according to the inventive method, with the theoretical reflectivity of a film of S1O2 of the same thickness also formed on a planar silicon substrate. It is thus observed in FIG. 3 that the film formed according to the inventive method has optical properties very close to what is theoretically expected.

Thus, the process for forming a film of silicon dioxide on the microparticles can comprise the following steps:

the introduction of the microparticles into the deposition enclosure, more particularly on the support 30;

- The formation of the fluidized bed by passage of an ascending gas stream through the support 30;

- Heating the area of the enclosure occupied by the fluidized bed at a temperature between 200 ° C and 350 ° C, and heating the support 30 to a temperature below 200 ° C, advantageously below 110 ° C;

- the pluvisation of tetraacetoxysilane

- the injection of oxygen.

The process for forming silicon dioxide films can advantageously be implemented for the formation of interference filters.

The interference filter may include a stack of a film of silicon dioxide and a film of titanium dioxide.

The titanium oxide film is advantageously formed by CVD with TTIP (titanium tetraisopropoxide) as a precursor, for example diluted in toluene or isopropanol at a concentration of 0.3 mol / L.

The conditions for the formation of the silicon dioxide film according to the invention can be transposed to the formation of the titanium dioxide film.

The films of silicon dioxide and of titanium dioxide are advantageously formed in the same chemical vapor deposition device 10.

The formation of the interference filter is not limited to a stack of a film of titanium dioxide (TiC> 2) and a film of silicon dioxide (S1O2).

The interference filter can comprise a stack of 3 films according to the TiOz / SiOz / TiOz sequence.

The interference filter can comprise a stack of 4 films according to the TiOz / SiOz / TiOz / SiOz sequence.

The design of the interference filter (number of films and their thickness) is part of the general knowledge of those skilled in the art.

The interference filter is advantageously formed on microparticles, for example beads 100 micrometers in diameter.

The inventors have thus formed interference filters on balls of 100 micrometers in diameter comprising a stack of 5 films (FIG. 2).

The stack of the 5 films comprises, in order, a 72 nm titanium dioxide film, a 50 nm silicon dioxide film, a 150 nm titanium dioxide film, a 72 nm silicon dioxide film nm, a 72 nm film of titanium dioxide.

Still by way of example, an interference filter formed on silica balls, and comprising, successively and from the surface of the silica ball, a film of titanium dioxide of 97 nm, a film of silicon dioxide of 135 nm, a film of titanium dioxide of 86 nm, and a film of silicon dioxide of 60 nm, will show a red color.

The method of forming silicon dioxide films according to the present invention is not limited to the formation of interference filters for cosmetology. In fact, this process for forming silicon dioxide films is advantageously implemented for the functionalization of powders used in 3D printing, in the photovoltaic field, for the production of electrodes which can be activated in the visible (for discharge plasmas at dielectric barrier), or in the field of air treatment.

REFERENCES [1] C. Vahlas et al., “Fluidization, Spouting, and Meta l-Orga nie CVD of Platinum Group Metals on Powders, Chem. Vap. Deposition, Volume 8, Issue 4, July, 2002, pages 127-144.

Claims (15)

1. Method for forming at least one silicon dioxide film on a substrate (40) by a chemical vapor deposition technique in a deposition chamber (20), the method comprising the evaporation of an organometallic precursor on a face of the substrate (40) maintained at a temperature between 200 ° C and 350 ° C, preferably between 250 ° C and 350 ° C, the organometallic precursor comprising tetraacetoxysilane. 2. Method according to claim 1, in which the organometallic precursor is diluted in an organic solvent, the organic solvent advantageously comprising at least one of the solvent chosen from: an alcohol, an aromatic solvent (xylene, toluene), cyclohexane 3. The method of claim 2, wherein the organometallic precursor has a concentration in the organic solvent of between 0.01 mol / L and 0.15 mol / L. 4. Method according to one of claims 1 to 3, wherein the organometallic precursor is maintained at a temperature between 80 ° C and 150 ° C before being sprayed on the face of the substrate (40). 5. Method according to one of claims 1 to 4, wherein the substrate (40) comprises microparticles (40) of a size between 100 nm and 500 pm, the microparticles (40) advantageously being beads. 6. Method according to claim 5, in which the microparticles (40) comprise at least one of the materials chosen from: alumina, silicon carbide, titanium dioxide, silicon, mica. 7. The method of claim 5 or 6, wherein the microparticles (40) disposed on a main face (32) of a porous support (30) traversed over its entire thickness E by an inert gas so that the microparticles (40 ) form a fluidized bed. 8. The method of claim 7, wherein the support is maintained at a temperature below 200 ° C, preferably below 150 ° C, for example 110 ° C. 9. Method according to one of claims 1 to 8, in which the evaporation of the organometallic precursor is carried out according to evaporation cycles, and in alternation with cycles of injection of oxygen in the deposition enclosure (20) . 10. The method of claim 9, wherein a purge of the deposition enclosure (20) is carried out before each evaporation cycle and each injection cycle, so that the pressure in said enclosure is less than 30 mBar at the outcome of the purge. 11. The method of claim 10, wherein at the end of each evaporation cycle and each injection cycle, the pressure in the deposition chamber (20) is greater than 100 mBar and 60 mBar, respectively. 12. Method according to one of claims 9 to 11, wherein each evaporation cycle lasts from 5 seconds to 20 seconds and / or between 20 and 100 evaporation and injection cycles are executed. 13. A method of manufacturing an interference filter comprising at least one film of silicon dioxide formed according to one of claims 1 to 12. 14. The manufacturing method according to claim 13, wherein at least one film of titanium dioxide is formed by CVD, advantageously at a temperature between 250 ° C and 350 ° C. 5 15. The manufacturing method according to claim 14, wherein the at least one film of silicon dioxide and the at least one film of titanium dioxide are formed so that the interference filter comprises alternating films of titanium dioxide. and silicon dioxide films. S.61187 1/4 2/4 3/4 0 f ^ l ————— I ————— 1 ———-— Γ ————— j— 200 400 600 800 1000 1200 1400