Transparent substrate with at least one thin silicon nitride or oxynitride based layer and process for obtaining the same

The present invention relates to a transparent substrate which is provided with at least one thin layer. The main application of the invention is the manufacture of so-called functional glazing used either in buildings or in vehicles or as a plasma television screen. Another possible application is the surface treatment of containers of the-type glass bottles.

In the context of the invention, it is necessary to understand, by functional glazing, a glazing unit of which at least one of its constituent transparent substrates is covered with a stack of thin layers, in order to confer on it particular properties, in particular thermal, optical, electrical or mechanical such as an anti-scratch property.

There are thus thin layers called low-emissive, in particular composed of doped metal oxide, for example fluorinated doped tin oxide (SnO₂: F) or tin-doped indium oxide (ITO), which can be deposited on glass by pyrolysis techniques. Once coated with a low-emissive layer, the substrate mounted glazing in particular in a building reduces the far-infrared emission to the outside of the room or the passenger through said glazing. By thus reducing the energy losses due in part to this radiation leakage, thermal comfort is greatly improved, especially in winter.

The substrate thus covered can be mounted in double glazing, the low-emissive layer being turned towards the gas strip spacing the two substrates, for example arranged in face 3 (the faces of a multiple glazing are conventionally numbered starting with by the outermost face relative to the room or the cabin). The double-glazing thus formed then has a reinforced thermal insulation, with a low heat exchange coefficient K while retaining the benefit of the solar energy inputs, with a solar factor (the ratio of the total energy entering into the room). local and incident solar energy) high. On this subject, the reader may refer in particular to patent applications EP-0544 577, FR-2704 543 and EP-0500 445.

The low-emissive layers are also good electrical conductors, which allows to equip the windows for the automobile to make heating / defrosting windows by providing the appropriate power supplies, application described for example in the patent EP-0353 140.

There are also thin filtering films called selective or sunscreen which, deposited on substrates mounted glazing, reduce the heat input of solar radiation through the glazing in the room or the cabin, by absorption / reflection. It may be, for example, titanium nitride (or oxynitride) TiN layers, such as those obtained by a gas phase pyrolysis technique and described in patent applications EP-0638 527 and EP-0650 938. It may also be a thin aluminum reflective layer (less than or equal to 30 nm), in particular obtained by condensation of metal vapor, by CVD or by the deposition technique described in the international patent application PCT / FR-96/00362 filed on March 7, 1996 in the name of SAINT-GOBAIN VITRAGE.

The invention is also interested in the deposition techniques of these various layers, and more particularly to those using a pyrolysis reaction. The latter consist in projecting "precursors", for example of organo-metallic nature, either in gaseous form, or in powder form, or liquid by themselves or else in solution in a liquid, on the surface of the substrate raised to high temperature. Said precursors, on contact, decompose there leaving, for example, a layer of metal, oxide, oxynitride, or nitride. The advantage of the pyrolysis lies in the fact that it makes it possible to deposit the layers directly on the glass ribbon of a float-type flat glass production line, and also in that the layers Pyrolysis has (in general) a strong adhesion to the substrate.

The low-emission or filtering layers mentioned above are frequently part of a stack of layers, and are located on at least one of their faces, in contact with another layer, generally a dielectric material with an optical role and / or protective.

Thus, in the aforementioned patent applications EP-0544 577 and FR-2704 543, the low-emissive layer, for example in SnO₂: F, is surrounded by two layers of dielectric SiO type₂, SiOC or metal oxide, layers of refractive index and thickness selected to adjust the optical appearance of the substrate, including reflection, for example its color.

In patent application EP-0500 445 also mentioned above, the low-emissive ITO layer is surmounted by a layer of aluminum oxide in order to protect it from oxidation, and also, under certain conditions, to suppress the need to give it a reduction annealing and / or allow the bending or quenching of the substrate once coated without damaging its properties.

TiO layer₂ or the double layer TiO₂/ SiOC which overcomes the TiN filtering layer in the aforementioned patent application EP-0650 938 also serves to protect the TiN from oxidation and to improve its durability in general.

However, it is important to be able to ensure the integrity of the stacks of thin layers. So, they need:<ul id="ul0001" list-style="dash" compact="compact"><li>an ability to resist chemical aggression. Indeed, it often happens that the transparent substrate, once coated with layers, is stored for a long enough period before being mounted in glazing. If it is not carefully sealed, and therefore expensive, the layers it is coated can be exposed directly to a polluted atmosphere or cleaned by detergents poorly adapted to dust, even if the substrates are subsequently assembled in double glazing or laminated glazing, with the thin layers arranged in front 2 or 3, thus protected. Moreover, in addition to this storage problem, stacks that are susceptible to chemical corrosion are a barrier to the use of substrates as "monolithic glazings" or to an arrangement of layers in face 1 or 4 in the case of multiple glazing, it is that is to say configurations where the layers are year-round exposed to the ambient atmosphere.</li><li>an ability to withstand mechanical damage. For example, the transparent substrate, once coated with layers, can be used in configurations where it is easily exposed to scratch-like damage. As a result, on the one hand, the substrate no longer visually offers a "correct" aesthetic appearance since it is partially scratched and, on the other hand, the durability of both the stack and the substrate is greatly diminished, sources of embrittlement. mechanics which may, if necessary, be introduced.</li></ul>

We are therefore constantly looking for stacks of layers with improved chemical and / or mechanical durability. However, these improvements should not be at the expense of the optical qualities of the assembly consisting of the substrate and the thin film stack.

As previously mentioned, there already exist dielectric overcoats exerting some protection of the underlying layers in the stack. To remain intact in the face of intense or long-lasting chemical corrosion and / or to completely protect the underlying layers which may be more "fragile", patent application EP-0712,815 describes an oxide-based thin film comprising silicon. and a third element, for example in the form of a fluorine type halogen F, which facilitates the formation of a mixed structure of silicon and aluminum.

This layer is particularly suitable for use as a last layer in stacks where the functional layer is of the filtering or low-emission type on glazings, since it can fulfill an optical function including a function of optimizing the reflection aspect and guarantee a certain constancy in the time of the aspect of the glazings.

However, it is not necessarily able to withstand mechanical damage such as scratches because it has a hardness that is not extremely high.

It is known that a type of thin layer which is particularly suitable for being durable and stable to mechanical abrasion and / or chemical attack is a thin layer based on silicon nitride, which can, if appropriate contain a certain proportion of impurities such as oxygen and carbon.

It is thus known a type of silicon nitride-based thin layer deposited on a substrate by a gas phase pyrolysis technique from two precursors, the silicon precursor being a silane, the nitrogen precursor being either an ammonia-type mineral, is organic hydrazine type especially substituted by methyl.

When the deposition is carried out starting from nitrogen precursors of the ammonia type, the temperatures are too high (more than 700 ° C.) to be able for example to be compatible with a continuous deposit on a silica-soda-lime glass ribbon in the Float bath enclosure, because at these temperatures, these standard glasses have not yet reached their dimensional stability.

Nitrogen precursors of the hydrazine type have a certain toxicity which makes their industrial application difficult.

It is also known to deposit a thin layer based on silicon nitride by the same technique as mentioned above, in particular by using not two precursors, but only one which is both siliconized and nitrogen-type Si (NMe₂)_4-nH_not. The deposition rates that can be achieved are too low to be able to exploit the deposition process on an industrial scale. In addition, the synthesis of this product is relatively complex and therefore expensive, and it is no longer possible to modulate the respective proportions of (the) precursor (s) nitrogen (s) and silicon (s).

In addition, the known silicon nitride thin films have certain disadvantages:<ul id="ul0002" list-style="dash" compact="compact"><li>on the one hand, they are not necessarily sufficiently hard and have a lesser durability, especially when they are deposited under vacuum so as to be able, for example, to confer on a substrate provided with this single layer or a stack of thin layers comprising this layer an anti-scratch function.</li><li>on the other hand, especially when they are deposited by pyrolysis, they are absorbent at the wavelengths of the visible range, which is disadvantageous from an optical point of view.</li></ul>

YASUI K AND AL: "Growth of low stress SiN films containing carbon by magnetron plasma enhanced chemical vapor deposition" JOURNAL OF NON-CRYSTALLINE SOLIDS, JAN. 1991, NETHERLANDS, vol. 127, no. 1, ISSN 0022-3093, pages 1-7, XP002043906 and KANJI YASUI ET AL: "CHEMICAL VAPOR DEPOSITION OF LOW HYDROGEN CONTENT SILICON NITRIDE FILMS USING MICROWAVE-EXCITED HYDROGEN RADICALS" JAPANESE JOURNAL OF APPLIED PHYSICS, vol. 29, no. 5, May 1, 1990, pages 918-922, XP000136931 disclose glass substrates coated with a silicon nitride thin film comprising Si, N, O, C elements.

The object of the invention is then to overcome the aforementioned drawbacks and therefore to develop a new thin layer based on nitride or silicon oxynitride having a greater hardness while being very little absorbent, and likely to be part of a stack of thin layers, especially in order to play a protective role vis-à-vis the chemical etching of the thin film stack in which it is incorporated.

Another object of the invention is to propose a novel process for depositing a silicon nitride or silicon oxynitride thin film, in particular by a gas phase pyrolysis technique, compatible with continuous deposition on a ribbon. of glass in the enclosure of a float bath and which allows to achieve high deposition rates.

To do this, the invention firstly relates to a transparent substrate of the glass substrate type coated with at least one thin layer based on nitride or silicon oxynitride. According to the invention, the thin layer comprises the elements Si, O, N, C in the following atomic percentages:<ul id="ul0003" list-style="dash" compact="compact"><li>If: from 30 to 60%, especially from 40 to 50%,</li><li>N: from 10 to 56%, especially from 20 to 56%,</li><li>O: from 1 to 40%, especially from 5 to 30%,</li><li>C: from 1 to 40%, especially from 5 to 30%.</li></ul>

Surprisingly, this thin layer has proved to be both very hard compared to other thin films based on known silicon nitride, very transparent and thus little or no absorbing at the wavelengths of the visible range: the high levels of Si and N show that we are in the presence of a predominantly silicon nitride material. By modulating the proportions between the minor constituents of the type C, O, it is possible to finely adjust the properties of the layer. Thus, by modifying the relative proportions of carbon and oxygen, the finite density and the refractive index of the thin layer can be finely adjusted, for example, so as to give it a mechanical hardness and optical properties. interesting and targeted. To play on the above relative proportions, it can possibly be done with a CO light oxidant₂for example for optical reasons. Carbon and nitrogen tend to increase the refractive index, oxygen having the opposite effect.

For example, the refractive index of the layer is greater than 1.6, especially between 1.8 and 2.0, preferably 1.85.

The layer may comprise other elements in the form of an additive such as fluorine, phosphorus or boron, preferably in an atomic percentage of between 0.1 and 5%. The layer may also be homogeneous or with a compositional gradient in its thickness.

Advantageously, the thin layer has a light absorption coefficient A_The less than 2% per 100 nanometers in geometric thickness, optical quality particularly demonstrated when the deposition of said layer is performed by a gas phase pyrolysis technique, as explained below.

The thin layer is advantageously part of a stack of thin layers, at least one of which is a functional layer with thermal properties, in particular filtering, sunscreen or low-emissivity and / or electrical properties and / or optical properties and or with photocatalytic properties such as a mirror function layer, doped metal oxide, metal nitride / oxynitride or aluminum or silicon type metal. It can also be part of a stack of anti-reflective layers, playing the role of the high index layer or "intermediate" index.

As doped metal oxide or metal nitride / oxynitride, it can be chosen tin oxide doped with fluorine SnO₂: F, tin-doped indium oxide ITO, zinc oxide doped with indium ZnO: In, fluorine ZnO: F, aluminum ZnO: Al, tin ZnO: Sn, the mixed oxide Cd₂ SnO₄, titanium nitride TiN, zirconium nitride ZrN.

According to an additional feature, the layer may be under the functional layer. It can then fulfill, in particular, the role of barrier layer for the diffusion of ions, in particular alkalis, oxygen from the glass-like substrate, or the role of nucleation layer, and / or have an optical role (adjustment of color, anti-iridescent effect, anti-glare effect). In certain screen-plasma applications, it can also act as a barrier layer for the migration of Ag ions.⁺ from the silver-based functional layers to the glass-like substrate.

According to another characteristic, the layer may be arranged on the functional layer. It can then be used, in particular as a protective layer of the functional layer with respect to the high-temperature oxidation or chemical corrosion, of the mechanical protection layer of the anti-scratch type, of the optical layer, of the layer improving the adhesion of the upper layer.

According to another characteristic, the thin layer is the only layer covering the substrate and advantageously performs an anti-scratch function. The geometrical thickness of the layer can be adjusted very freely over a very wide range from 5 nm to 5 μm, especially between 20 and 1000 nanometers, a fairly substantial thickness of at least 250 nm being for example preferred to accentuate the anti-aging effect. streak of the substrate provided with at least said layer, a layer of lower thickness being generally sought for another functionality (nucleation, adhesion ...).

The subject of the invention is also the process for obtaining the previously defined substrate, which method consists in depositing the silicon nitride-based thin layer by a gas phase pyrolysis technique (also known as "Chemical Vapor Deposition"). CVD) which uses at least two precursors including at least one of silicon and at least one of nitrogen. According to the process of the invention, at least one nitrogen precursor is an amine.

The choice of such a nitrogen precursor is particularly advantageous: it is of adequate reactivity insofar as it makes it possible to carry out the deposition at temperatures where the glass substrate of the standard silico-sodo-calcium substrate type has reached its optimum level. Dimensional stability, particularly in the context of a float glass production line.

In addition, the deposition rates reached are sufficiently high to be able to deposit substantial thicknesses in the floating chamber.

The silicon precursor chosen may advantageously be a silane, of the hydride and / or silicon alkyl silazane type.

The amine may be chosen from primary, secondary or tertiary amines, in particular containing alkyl radicals having from 1 to 6 carbon atoms each.

Thus, it may be ethylamine C₂H₅NH₂, methylamine CH₃NH₂, dimethylamine (CH₃)₂NH, butylamine C₄H₉NH₂, propylamine C₃H₇NH₂.

The choice of the appropriate amine for a given layer of geometric thickness and / or refractive index results from a compromise to be found between a certain number of parameters such as steric hindrance, reactivity, etc.

Preferably, the ratio by number of moles of the amount of nitrogen precursor on the amount of silicon precursor is between 5 and 30, advantageously equal to 10.

It is indeed important to control such a ratio to avoid, on the one hand, an insufficient incorporation of nitrogen and, on the other hand, any risk of nucleation in the gaseous phase and hence any risk of powder formation. This limits the risk of fouling of the device and decreases in production efficiency.

According to an additional characteristic, when it is desired to incorporate an additive, a precursor of the additive independent of the silicon precursor and the amine is chosen. It can for example be a fluorinated gas of the CF type₄ when the desired additive is fluorine F or a PO type phosphate-bearing organic gas (OCH₃)₃ or a gas of the triethylphosphite, trimethylphosphite, trimethylborite, PF type₅, PCl₃, PBr₃, PCl₅ when the desired additive is phosphorus P or boron B. These additives advantageously allow to generally increase the deposition rate.

The deposition temperature is in line with the choice of precursors, especially the amine. It is between 550 and 760 ° C. It may be preferably between 600 and 700 ° C: that is to say between the temperature where the glass in particular soda-lime-silica is dimensionally stable and the temperature that it has at its output from the enclosure of float.

Advantageously, in the variant in which the glass composition of the substrate is adapted to an electronic application, it is between 660 ° C. and 760 ° C.

According to this variant, an advantageous composition may be that described in application WO-96/11887. This, expressed in percentages by weight, is of the type:<tables id="tabl0001" num="0001"><table frame="all"><tgroup cols="2" colsep="1" rowsep="0"><colspec colnum="1" colname="col1" colwidth="78.75mm" /><colspec colnum="2" colname="col2" colwidth="78.75mm" /><tbody valign="top"><row><entry namest="col1" nameend="col1" align="left">SiO₂</entry><entry namest="col2" nameend="col2" align="right">45 - 68%</entry></row><row><entry namest="col1" nameend="col1" align="left">al₂O₃</entry><entry namest="col2" nameend="col2" align="right">0 - 20%</entry></row><row><entry namest="col1" nameend="col1" align="left">ZrO₂</entry><entry namest="col2" nameend="col2" align="right">0 - 20%</entry></row><row><entry namest="col1" nameend="col1" align="left">B₂O₃</entry><entry namest="col2" nameend="col2" align="right">0 - 20%</entry></row><row><entry namest="col1" nameend="col1" align="left">N / A₂O</entry><entry namest="col2" nameend="col2" align="right">2 - 12%</entry></row><row><entry namest="col1" nameend="col1" align="left">K₂O</entry><entry namest="col2" nameend="col2" align="right">3.5 - 9%</entry></row><row><entry namest="col1" nameend="col1" align="left">CaO</entry><entry namest="col2" nameend="col2" align="right">1 - 13%</entry></row><row rowsep="1"><entry namest="col1" nameend="col1" align="left">MgO</entry><entry namest="col2" nameend="col2" align="right">0 - 8%</entry></row></tbody></tgroup></table></tables> with:<ul id="ul0004" list-style="bullet" compact="compact"><li>SiO₂ + Al₂O₃ + ZrO₂ ≤ 70%</li><li>al₂O₃ + ZrO₂ ≥ 2%</li><li>N / A₂O + K₂O ≥ 8%</li></ul> and optionally BaO and / or SrO in the following proportions:<maths id="math0001" num=""><math display="block"><mrow><mtext>11% ≤ MgO + CaO + BaO + SrO ≤ 30%</mtext></mrow></math><img file="EP0857700B1_D0001.tif" /></maths> with a lower annealing temperature of at least 530 ° C and a coefficient α of 80 to 95.10^-7° C^-1.

Another advantageous composition, derived from the application FR97 / 00498 is, always in percentages by weight, of the type: <tables id="tabl0002" num="0002"><table frame="all"><tgroup cols="2" colsep="1" rowsep="0"><colspec colnum="1" colname="col1" colwidth="78.75mm" /><colspec colnum="2" colname="col2" colwidth="78.75mm" /><tbody valign="top"><row><entry namest="col1" nameend="col1" align="left">SiO₂</entry><entry namest="col2" nameend="col2" align="left">55 - 65%, preferably 55-60%</entry></row><row><entry namest="col1" nameend="col1" align="left">al₂O₃</entry><entry namest="col2" nameend="col2" align="left">0 - 5%</entry></row><row><entry namest="col1" nameend="col1" align="left">ZrO₂</entry><entry namest="col2" nameend="col2" align="left">5 - 10%</entry></row><row><entry namest="col1" nameend="col1" align="left">B₂O₃</entry><entry namest="col2" nameend="col2" align="left">0 - 3%</entry></row><row><entry namest="col1" nameend="col1" align="left">N / A₂O</entry><entry namest="col2" nameend="col2" align="left">2 - 6%</entry></row><row><entry namest="col1" nameend="col1" align="left">K₂O</entry><entry namest="col2" nameend="col2" align="left">5 - 9%</entry></row><row><entry namest="col1" nameend="col1" align="left">MgO</entry><entry namest="col2" nameend="col2" align="left">0 - 6%, preferably 1-6%</entry></row><row><entry namest="col1" nameend="col1" align="left">CaO</entry><entry namest="col2" nameend="col2" align="left">3 - 11%, preferably 7-11%</entry></row><row><entry namest="col1" nameend="col1" align="left">SrO</entry><entry namest="col2" nameend="col2" align="left">4 - 12%</entry></row><row rowsep="1"><entry namest="col1" nameend="col1" align="left">BaO</entry><entry namest="col2" nameend="col2" align="left">0 - 2%</entry></row></tbody></tgroup></table></tables> with:<ul id="ul0005" list-style="bullet" compact="compact"><li>N / A₂O + K₂O ≥ 10%</li><li>MgO + CaO + SrO + BaO&gt; 11%, preferably&gt; 15%</li></ul> and a lower annealing temperature of at least 600 ° C. (Another variant consists, keeping the proportions of the other constituents unchanged, to choose a level of Al₂O₃ from 5 to 10% and a ZrO rate₂ from 0 to 5%).

It is recalled that the so-called lower temperature of annealing ("strain point") is the temperature that a glass presents when it reaches a viscosity η equal to 10^14.5 poise.

It is thus preferable to deposit the layer with a substantially inert or reducing atmosphere, for example in a mixture N₂/ H₂ without or almost without oxygen continuously on a float glass ribbon, in the float chamber and / or in a box for controlling the inert atmosphere, without oxygen, to deposit it further downstream of the float line, to temperatures possibly a little lower.

The invention thus makes it possible to manufacture filtering solar control glazings, with stacks of the type:<ul id="ul0006" list-style="dash" compact="compact"><li>glass / TiN and / or ZrN / layer according to the invention / SiOC and / or SiO₂, said layer according to the invention making it possible to have a much stronger interface between the TiN layer and / or the ZrN layer on the one hand, and the SiOC layer and / or the SiO layer₂, on the other hand. It also makes it possible to have an effective protection of TiN and / or ZrN against the possible risk of surface oxidation either on an industrial line after the deposition of the SiOC layer and / or SiO₂, or off-line industrial for example when the substrate provided with the stack of layers, once cut, undergo heat treatments like bending / quenching or annealing. Advantageously, the layer has a geometrical thickness of between 10 and 50 nanometers, the thin layer according to the invention has a geometrical thickness of between 5 and 20 nanometers, and the overlayer in SiOC and / or SiO₂ a geometrical thickness of between 30 and 100 nanometers.</li><li>or the type:    glass / Al / thin layer according to the invention,</li></ul> the reflective layer of aluminum being either thin (less than or equal to 30 nm) or thicker when the mirror function is sought, such as that described in the aforementioned international patent application PCT / FR-96/00362, the thin layer according to the invention having both a protective role vis-à-vis the oxidation and an anti-scratch function.

The invention also makes it possible to produce glazing whose essential function is to be anti-scratch, that is to say glazing such as floor slabs, glass furniture where the glass substrate is only coated with the glass. Si-based thin film₃NOT₄ according to the invention optionally associated with an anti-iridescence layer.

This advantageously protects the glass from any degradation. The thin layer according to the invention can also be associated with low-emission layers with stacks of the type:    glass / SiOC / SnO₂: F or ITO / thin layer according to the invention.

In these stacks, the SiOC underlayer can of course be replaced by other metal oxides, such as those described in the patent application EP-0677 493.

The thin layer according to the invention also makes it possible to manufacture any type of functional glazing provided with a stack of thin layers which are of high durability and which are capable of being soaked and / or curved when the substrate used is a glass substrate.

The invention also makes it possible to produce glazings for which an anti-soiling function is desired, with stacks of the type:    Glass / thin layer according to the invention / TiO₂

In these stacks, the thin film according to the invention essentially acts as a barrier layer for alkalis migrating from the glass to the titanium oxide layer TiO₂, the photocatalytic effect of the latter being thus increased. In addition, if the thickness of the layer according to the invention is adapted so that it is in interferential interaction, it also has the role of being an anti-iridescence layer.

Titanium oxide TiO₂ can be in the form of predominantly crystallized particles of anatase type, as described in the patent application WO 97/10188.

However, it may also be in the form of an at least partially crystallized film, such as that described in patent application WO 97/10186.

The invention finally allows the manufacture of emissive screens type flat screens such as plasma screens. The thin layer according to the invention can then play different roles depending on the nature of the chemical composition of the substrate on which it is deposited, and / or the destination (front or back side) of the same substrate in the screen and therefore, the nature of the functional layers that surmount it, such as electrodes, phosphors (photophores), essential elements for the operation of the screen.

Thus, in the case where the glass substrate is of the "alkali-blocked" type, that is to say of composition substantially devoid of diffusing species of the alkaline type, the thin layer according to the invention very effectively fulfills the essential role. barrier layer to the migration of diffusing species from the top coatings to the substrate, in particular the silver-based electrode.

Similarly, in the case where the composition of the glass substrate comprises alkalis, it also acts as a barrier layer to their migration.

The invention also applies to the surface treatment of containers of the glass bottle or flask type, the hard layer according to the invention reinforcing said containers for example vis-à-vis the manipulations likely to deteriorate and this regardless of the relative thickness inhomogeneity of said layer observed. The deposition of the hard layer according to the invention can thus be carried out on the outer wall of the containers by reinforcing it mechanically in particular against shocks but also on the inner wall of the containers in order, for example, to prevent the release of elements. from the substrate.

Other advantageous details and characteristics will emerge below from the description of nonlimiting exemplary embodiments with the aid of FIGS. 1 and 2 appended hereto. For the sake of clarity, these figures do not respect the proportions concerning the relative thicknesses of the different materials.

In all the following examples, the deposition of all the thin layers is carried out in the floating chamber.

<u>EXAMPLE 1</u>:

FIG. 1 represents a substrate 1 of clear silico-soda-lime glass 3 millimeters thick, for example that marketed under the trademark PLANILUX by the company SAINT-GOBAIN VITRAGE, coated with the thin layer based on silicon nitride 2 developed by the invention.

The thin layer based on silicon nitride 2 is obtained by a gas phase pyrolysis technique from SiH silane₄, which is the silicon precursor, and ethylamine C₂H₅NH₂which is the nitrogen precursor.

The precursor flow rates are chosen such that the volume ratio of the amount of ethylamine to the amount of silane is equal to about 10. This parameter is advantageous in that it optimizes the contribution of each of the constituents of the layer. . Indeed, it has been observed that it must not be:<ul id="ul0007" list-style="dash" compact="compact"><li>too high otherwise there may be a risk of nucleation in the gas phase and therefore a risk of powder formation.</li><li>too low otherwise there may be insufficient incorporation of nitrogen into the layer.</li></ul>

A ratio range of 5 to 30 is quite satisfactory when it is desired to deposit a layer 50 to 300 nm thick from a silane and ethylamine.

The deposition was carried out on the substrate 1 brought to a temperature of between 600 and 650 ° C., at atmospheric pressure.

Under these conditions, the growth rate of the layer 2 according to the invention reached 60 nm per minute.

The layer 2 obtained as shown in FIG. 1 has a thickness of approximately 350 nanometers and a refractive index of the order of 1.85.

Microprobe analysis indicates that the layer 2 comprises, in atomic percentages, 32.7% of silicon, 30.6% of nitrogen, 21.1% of carbon and 15.6% of oxygen.

The deposition technique according to the invention makes it possible to modulate the quantities of the various elements incorporated, in particular that of the carbon, by varying parameters such as the temperature at which the deposition is carried out, the use of another amine than ethylamine. or a mixture of amines or ammonia added to ethylamine as a nitrogen precursor.

The different amines that have adequate reactivity are as follows: methylamine CH₃NH₂, dimethylamine (CH₃)₂NH, butylamine C₄H₉NH₂ and propylamine C₃H₇NH₂. The temperatures satisfactory for the deposition of the layer 2 according to the invention are in a range of 550 to 700 ° C.

The spectrophotometric characteristics of such a layer are summarized in the table below, in which T_The, R_The, AT_The respectively represent the values ​​of light transmission, light reflection and light absorption in percentage: <tables id="tabl0003" num="0003"><table frame="all"><tgroup cols="4" colsep="1" rowsep="1"><colspec colnum="1" colname="col1" colwidth="39.37mm" /><colspec colnum="2" colname="col2" colwidth="39.37mm" /><colspec colnum="3" colname="col3" colwidth="39.37mm" /><colspec colnum="4" colname="col4" colwidth="39.37mm" /><thead valign="top"><row><entry namest="col1" nameend="col1" /><entry namest="col2" nameend="col2" align="center">T_The</entry><entry namest="col3" nameend="col3" align="center">R_The</entry><entry namest="col4" nameend="col4" align="center">AT_The</entry></row></thead><tbody valign="top"><row rowsep="1"><entry namest="col1" nameend="col1" align="center">Layer 2</entry><entry namest="col2" nameend="col2" align="center">84</entry><entry namest="col3" nameend="col3" align="center">13</entry><entry namest="col4" nameend="col4" align="center">3</entry></row></tbody></tgroup></table></tables> these values ​​being measured from the illuminant D₆₅., near normal incidence.

It is found that the layer according to the invention has a very low light absorption and that it is free of blur. (It is recalled that the blur is the ratio of the diffuse transmission on the light transmission at a wavelength equal to 550 nm).

On the substrate 1 covered with the only layer 2 according to the invention has been carried out a test that evaluates the mechanical strength of said layer. This test is performed using grinding wheels made of abrasive powder embedded in an elastomer. The machine is manufactured by the company TABER INSTRUMENT CORPORATION This is the model 174 "standard Abrasion Tester", the wheels are type CSIOF loaded 500 grams. Substrate 1, covered locally, is subjected to 50 rotations and then, using an optical microscope, a count of the stripes is made on four squares with a side equal to 1 inch. that is 2.54 cm. After making this count, we calculate the average R of the number of stripes per square. Finally, we calculate the "Taber score" T_S according to the formula:<maths id="math0002" num=""><math display="block"><mrow><msub><mrow><mtext>T</mtext></mrow><mrow><mtext>S</mtext></mrow></msub><mtext> = -0.18 R + 10</mtext></mrow></math><img file="EP0857700B1_D0002.tif" /></maths> For a layer 2 according to the invention of 300 nanometers in geometrical thickness, this "score" is equal to 9.3. This value denotes a slight deterioration and therefore reveals a very good resistance of the layer according to the invention to the scratch.

As a comparative example, it may be noted that a tin oxide doped tin oxide layer₂: F of 340 nanometers in geometric thickness, known as the "hardest" layer deposited by a pyrolysis technique in the gas phase, following the test a "Taber score" T_S equal to 9.1.

It can therefore clearly be seen that the layer based on silicon nitride according to the invention is a layer which, intrinsically, has a very good resistance to mechanical abrasion and is from a very satisfactory optical point of view since it is very transparent and very not very absorbing at the wavelengths of the visible range.

<u>EXAMPLE 2</u>

FIG. 2 represents a glazing type glazing comprising a stack of thin layers in which layer 2 according to the invention has been incorporated.

The substrate 1 of clear silico-soda-lime glass 6 millimeters thick is covered with three layers successively:<ul id="ul0008" list-style="dash" compact="compact"><li>a first 23 nm thick TiN layer 3 obtained by gas phase pyrolysis from titanium tetrachloride TiCl 3₄ and methylamine CH₃NH₂ as described in patent application EP-0638 527.</li><li>a second layer 2 according to the invention of thickness approximately equal to 10 nanometers and refractive index equal to 1.85, deposited under the same conditions as Example 1.</li><li>a third SiOC silicon oxycarbide layer 4 having a thickness of 65 nm. refractive index equal to 1.65, also obtained by gas phase pyrolysis from silane and ethylene as described in patent application EP-0518 755, the layer essentially in the form of oxidation oxidizing at the outlet float, and more particularly in the lehr.</li></ul>

So we have a stack of type:    glass / TiN / Si₃NOT₄ / SiOC.

<u>EXAMPLE 3</u>:

This comparative example was made using a stack:    glass / TiN / SiOC. where the two TiN and SiOC layers have the same characteristics as those defined above and are obtained under the same deposition conditions.

It can be seen that the layer 2 according to the invention, even of a small thickness, creates a very solid interface between the first layer 3 of TiN and the overlayer 4 of SiOC.

In addition, the layer 2 according to the invention effectively protects the TiN from the possible risk of surface oxidation on the industrial line after deposition of the SiOC overlay 4. If necessary, it isolates the TiN when the substrate once cut, undergoes subsequent heat treatment of the bending / quenching or annealing type.

Similarly, after measuring the spectrophotometric values, in particular the light transmission T_The for each of the two stacks of Examples 2 and 3, as well as the solar factor F_Sit is found that the selectivity corresponding to the difference T_The-F_S is much better in the case of the "tri-layer" of Example 2 with the layer 2 according to the invention interposed between the two TiN and SiOC layers since its value is 10%. In the case of the "bi-layer" of Example 3, it is less than 7%.

It should be noted finally that if in the two previous configurations, the silicon nitride-based layer according to the invention is homogeneous in its thickness, it is also possible to predict a certain inhomogeneity in the composition in its thickness, especially in order to modulate the thickness of the refractive index and allow optimum optical and / or chemical compatibility with the layer above and / or below such as, for example, a layer enriched in Si₃NOT₄ on the TiN side and a SiON-enriched SiON layer in a sunscreen using the same layers as in Example 2. This "gradient" layer can be obtained from the same pyrolysis deposition technique in the gas phase but using a nozzle capable of creating chemical gradients such as that described in the patent application FR-2,736,632.

In conclusion, the invention has developed a new layer based on silicon nitride, particularly able to withstand mechanical abrasion and very satisfactory from an optical point of view since it is not very absorbent, which is not the case of Si-based layers₃NOT₄ known.

Very advantageously, the layer according to the invention can be deposited by pyrolysis in the gas phase at high deposition rates using a nitrogen precursor that can be used industrially without prohibitive additional cost.

The nitrogen precursor used is also of adequate reactivity because it makes it possible to reach deposition temperatures, from which it is possible without major difficulty to make three-layer in-line stacks on the float glass ribbon, for example in order to produce an anti-solar glazing with the functional TiN layer and the last SiOC layer, the layer according to the invention being advantageously incorporated in the conventional "bi-layer" stack to give a more solid interface and to isolate the functional layer of the oxidation after the SiOC overlay has been deposited, and this, without disrupting production on an industrial line, or even during thermal treatments of the off-line industrial substrate.