Title of Invention	PROCESS FOR DEPOSITING A THIN LAYER ON A TRANSPARENT SUBSTRATE OF THE GLASS SUBSTRATE TYPE
Abstract	This invention relates to the process for depositing a thin layer (2) on a transparent substrate (1) of the glass substrate type carried out by means of a gas phase pyrolysis technique using at least two precursors, including at least one silicon precursor and at least one nitrogen precursor characterized in that, at least one nitrogen precursor is in the form of an amine.

Full Text

-1A- TRANSPARENT SUBSTRATE PROVIDED WITH AT LEAST ONE THIN LAYER BASED ON SILICON NITRIDE OR OXYNITRIDE AND THE PROCESS FOR OBTAINING IT The invention relates to a process for depositing a ,thin layer on a transparent substrate of the glass substrate type. The present invention further 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 assemblies used either in buildings, or in vehicles, or as a plasma television screen. Another application which may be envisaged is the surface treatment of containers of the glass bottle type. Within the context of the invention, the term functional glazing assembly should be understood to mean a glazing assembly in which at least one of its constituent transparent substrates is covered with a stack of thin layers so as to give it particular properties, especially thermal, optical, electrical or mechanical properties, such as a scratch-resistant property. Thus, so-called low-emissivity thin layers exist, in particular composed of doped metal oxide, for example fluorine-doped tin oxide (F:SnO2) or tin-doped indium oxide (ITO), which may be deposited on glass using pyroslysis techniques. Once coated with a low-emissivity layer, the substrate mounted, in a, glazing assembly, in particular in a building, makes it possible to reduce emission, in the far infrared, to the outside of the room or of the vehicle interior through the said glazing assembly. Thus, by reducing the energy losses due in part to this radiation leakage, the thermal comfort is greatly improved, in particular in winter. The substrate thus covered may be mounted in a double-glazing assembly, the low-emissivity layer being turned towards the gas-filled cavity separating the two substrates, for example placed as the 3 face (the faces of a multiple-glazing assembly are conventionally - 2 - numbered starting from the outermost face with respect to the room or the vehicle interior) . The double-glazing assembly thus formed therefore has enhanced thermal insulation, with a low heat-exchange coefficient K, while maintaining the benefit of solar energy influx, with a high solar factor {i.e. the ratio of the total energy entering the room to the incident solar energy). On this subject, the reader may refer, in particular, to Patent Applications EP-0,544,577, FR-2,704,543 and EP-0,500,445 . The low-emissivity layers are generally made of good electrical conductors. This allows the glazing assemblies in motor vehicles to be equipped therewith in order thereby to make heating/de-icing glazing assemblies by providing suitable current leads, which application is described, for example, in Patent EP-0,353,140 . Thin filtering layers, called selective or anti-solar layers, also exist which, deposited on substrates mounted in a glazing assembly, make it possible to reduce the heat influx from solar radiation through the glazing assembly into the room or vehicle interior, by absorption/reflection. These may, for example, be layers of titanium nitride TiN (or titanium oxynitride) , such as those obtained using a gas-phase pyrolysis technique and described in Patent Applications EP-0,638,527 and EP-0,650, 938 . It may also be a thin (less than or equal to 3 0 nm) reflective layer of aluminium, especially obtained by condensation of a metal vapour, using CVD or the deposition technique described in International Patent Application PCT/FR-96/00362 filed on 7 March 1996 in the name of Saint-Gobain Vitrage. The invention also relates to the techniques for depositing these various layers, and more particularly to those involving a pyrolysis reaction. These techniques consist in spraying "precursors", for example of an organometallic nature, which are either in the form of a gas, or in the form of a powder, or - 3 -are liquids by themselves or else in solution in a liquid, onto the surface of the substrate which is heated to a high temperature. On coming into contact with the substrate, the said precursors decompose thereon, leaving, for example, a layer of metal, oxide, oxynitride or nitride. The advantage of pyrolysis resides in the fact that it allows direct deposition of the layers onto the glass ribbon in a line for manufacturing flat glass of the float type, continuously, and also in the fact that the pyrolysed layers have (in general) very good adhesion to the substrate. The low-emissivity or filtering layers mentioned above frequently form part of a stack of layers and are, at least on one of their faces, in contact with another layer, generally a dielectric material having an optical and/or protective role. Thus, in the aforementioned Patent Applications EP-0,544,577 and FR-2,704,543, the low-emissivity layer, for example made of F:SnO2, is surrounded by two layers of dielectric of the SiO2, SiOC or metal-oxide type, which layers have a refractive index and a thickness which are selected so as to adjust the optical appearance of the substrate, in particular in reflection, for example its colour. In Patent Application EP-0,500,44 5, also previously mentioned, the low-emissivity layer of ITO lies under a layer of aluminium oxide so as to protect it from oxidation and also, under certain conditions, to avoid having to subject it to a reducing annealing operation and/or to allow the substrate, once coated, to be bent or toughened without adversely affecting its properties. The TiO2 layer or the TiO2/SiOC double layer which covers the TiN filtering layer in the aforementioned Patent Application EP--0 650 938 also has the function of protecting the TiN from oxidation and of improving its durability in general. - 4 - However, it is important to be able to be certain of the integrity of the stacks of thin layers. Thus, it is necessary for them to display: - the ability to withstand chemical attack. This is because it frequently happens that the transparent substrate, once coated with layers, is stored for quite a long period before being mounted in a glazing assembly. If it is not carefully packaged in a sealed, and therefore expensive manner, the layers with which it is coated may be directly exposed to a contaminated atmosphere or may be subjected to cleaning by detergents which are not well suited to removing dust therefrom, even if the substrates are subsequently joined together in a double-glazing assembly or in a laminated glazing assembly with the deposited thin layers as the 2 or 3 face, and therefore protected. Moreover, apart from this storage problem, stacks susceptible to chemical corrosion are a disincentive to the use of the substrates as "monolithic glazing assemblies" or to an arrangement of the layers as the 1 or 4 face in the case of multiple glazing assemblies, i.e. configurations in which the layers are exposed all year long to the ambient atmosphere; - the ability to resist mechanical damage. For example, the transparent substrate, once coated with layers, may be used in configurations in which it is readily exposed to damage of the scratching type. Consequently, on the one hand, the substrate no longer has a "correct" aesthetic appearance, since it is partially scratched, and, on the other hand, the durability both of the stack and of the substrate is greatly diminished, sites of mechanical weakness possibly, depending on the case, being introduced. There is therefore a continual search for stack of layerss having improved chemical and/or mechanical durability. However, these improvements must not be to the detriment of the optical properties of the assembly formed by the substrate and the stack of thin layers. - 5 - As mentioned previously, overlayers of dielectric material already exist which provide a degree of protection of the subjacent layers in the stack. In order to maintain integrity, exposed to intense or lengthy chemical corrosion, and/or to protect the possibly "weaker" subjacent layers completely, Patent Application EP-0, 712, 815. describes a thin layer based on an oxide comprising silicon and a third element, for example in the form of a halogen of the fluorine F type, which facilitates the formation of a mixed silicon/aluminium structure. This layer is particularly suitable for use as the final layer in stacks in which the functional layer is of the filtering or low-emissivity type on glazing assemblies, since it may fulfil an optical function, in particular a function of optimizing the appearance in reflection, and may guarantee a degree of constancy over time of the appearance of the glazing assemblies. However, it is not necessarily capable of resisting mechanical damage, such as scratches, since it has a hardness which is not extremely high. It is known that one type of hard thin layer most particularly designed to be durable and stable with respect to mechanical abrasion and/or chemical attack is a thin layer based on silicon nitride which may, as the case may be, contain a certain amount of impurities such as oxygen and carbon. Thus, one type of thin layer based on silicon nitride is known, this being deposited on a substrate by a gas-phase pyrolysis technique using two precursors, the silicon-containing precursor being a silane and the nitrogen-containing precursor being either inorganic, of the ammonia type, or organic, of the hydrazine type, in particular methyl-substituted hydrazine. When the deposition is carried out using nitrogen-containing precursors of the ammonia type, the temperatures are too high (greater than 700°C) to be able to be compatible, for example, with continuous - 6 - deposition on a ribbon of silica-soda-lime glass in the chamber of a float bath since, at these temperatures, these standard glasses have not yet reached their dimensional stability. As regards the nitrogen-containing precursors of the hydrazine type, these have a degree of toxicity which makes their industrial application problematic. It is also known to deposit a thin layer based on silicon nitride by the same technique as that mentioned above, in particular by using not two precursors but only one, this containing both silicon and nitrogen, of the Si (NMe2) 4_nHn type. The deposition rates which may be achieved are too low to be able to exploit the deposition process on an industrial scale. Furthermore, the synthesis of this product is relatively complex and therefore expensive, and the respective proportions of the nitrogen-containing and silicon-containing precursor or precursors can no longer be varied. In addition, the known thin layers based on silicon nitride have certain drawbacks: - on the one hand, they are not necessarily sufficiently hard and are less durable, in particular when they are vacuum-deposited in order to be able, for example, to endow a substrate provided with this single layer, or with a stack of thin layers comprising this layer, with a scratch-resistance function; and - on the other hand, in particular when they are deposited by pyrolysis, they are absorbent at wavelengths in the visible range, this being deleterious from an optical standpoint. The object of the invention is thus to remedy the aforementioned drawbacks and therefore to develop a novel thin layer based on silicon nitride or oxynitride having a greater hardness while being very much less absorbent, and capable of forming part of a stack of thin layers, in particular so as to fulfil therein a protective function with respect to chemical attack of the stack of thin layers in which it is incorporated. - 7 -Another object of the invention is to provide a novel process for depositing a thin layer based on silicon nitride or oxynitride, in particular using a gas-phase pyrolysis technique which is compatible with continuous deposition on a ribbon of glass in the chamber of a float bath and which allows high deposition rates to be achieved. To do this, the subject of the invention is first of all a transparent substrate of the glass substrate type, covered with at least one thin layer based on silicon nitride or oxynitride. According to the invention, the thin layer contains the elements Si, 0, N, C in the following atomic percentages: - Si: from 30 to 60%, in particular from 40 to 50%, - N: from 10 to 56%, in particular from 20 to 56%, - O: from 1 to 40%, in particular from 5 to 30%, - C: from 1 to 40%, in particular from 5 to 30%. Surprisingly, this thin layer has turned out to be both very hard, compared to the other known thin layers based on silicon nitride, and very transparent and therefore has a low or zero absorbence at the wavelengths in the visible range: the high Si and N contents show that what is involved is a material which mostly consists of silicon nitride. By varying the proportions between the minor constituents, of the C, O type, the properties of the layer may be finely adjusted. Thus, by varying the relative proportions of carbon and oxygen, it is possible both, for example, to "fine tune" the density and the refractive index of the thin layer so as to endow it with a mechanical hardness and with optical properties which are very useful and desirable. In order to vary the aforementioned relative proportions, this may possibly be accomplished using a gentle oxidizing agent of the CO2 type, for example for optical reasons. This is because carbon and nitrogen - 8 - have a tendency to increase the refractive index, oxygen having more the opposite effect. For example, the refractive index of the layer is greater than 1.6, in particular between 1.8 and 2.0, preferably 1.85. The layer may contain 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 have a composition gradient through its thickness. Advantageously, the thin layer has a light absorption coefficient AL of less than 2% for a geometrical thickness of 100 nanometres, which optical quality is particularly demonstrated when the said layer is deposited using a gas-phase pyrolysis technique, as explained below. The thin layer advantageously forms part of a stack of thin layers, at least one layer of which is a functional layer having thermal, in particular filtering, solar-protection or low-emissivity properties and/or electrical properties and/or optical properties and/or photocatalytic properties, such as a layer having a mirror function, of the type consisting of a doped metal oxide, of a metal nitride/oxynitride or of a metal of the aluminium or silicon type. It may also form part of a stack of antireflection layers, acting as the high-index or "intermediate"-index layer. It is possible to choose, as the doped metal oxide or the metal nitride/oxynitride, fluorine-doped tin oxide F:SnO2, tin-doped indium oxide ITO, indium-doped zinc oxide In:ZnO, fluorine-doped zinc oxide F:ZnO, aluminium-doped zinc oxide Al:ZnO, tin-doped zinc oxide Sn:ZnO, the mixed oxide Cd2Sn04, titanium nitride TiN or zirconium nitride ZrN. According to an additional characteristic, the layer may be under the functional layer. It may then fulfil, in particular, the role of a barrier layer to the diffusion of ions, especially of alkali metals, and of oxygen from the glass-type substrate, or else the - 9 - role of a nucleation layer, and/or have an optical role (adjustment of the colour, anti-iridescence effect, antireflection effect). In some applications of the plasma-screen type, it may also fulfil the role of a barrier layer to the migration of Ag+ ions from the silver-based functional layers into the glass-type substrate. According to another characteristic, the layer may be located on the functional layer. It may then serve, in particular, as a layer for protecting the functional layer from high-temperature oxidation or from chemical corrosion, as a mechanical protection layer of the scratch-resistant type, a layer having an optical role or a layer improving the adhesion of the upper layer. According to another characteristic, the thin layer is the only layer covering the substrate and advantageously fulfils a scratch-resistance function. The geometrical thickness of the layer may be very freely adjusted within a very wide range of 5 nm to 5 µm, in particular between 2 0 and 10 0 0 nanometres, quite a substantial thickness of at least 250 nm being, for example, preferred in order to accentuate the scratch-resistance effect of the substrate provided with at least the said layer, a layer having a smaller thickness being generally desired for another functionality (nucleation, adhesion, etc.). The subject of the invention is also the process for obtaining the above-defined substrate, which process consists in depositing the thin layer based on silicon nitride by means of a gas-phase pyrolysis technique (also called CVD) or using at least two precursors, including at least one silicon precursor and at least one nitrogen precursor. According to the process of the invention, at least one nitrogen precursor is an amine. The choice of such a nitrogen-containing precursor is particularly advantageous: it has sufficient reactivity insofar as it makes it possible - 10 -to carry out the deposition at temperatures at which the glass substrate of the standard silica-soda-lime substrate type has fully achieved its dimensional stability, in particular in the context of a float-glass production line. In addition, the deposition rates achieved are sufficiently high to be able to deposit substantial thicknesses in the float chamber. The silicon-containing precursor chosen may advantageously be a silane, of the silicon hydride and/or alkyl type, or a silazane. The amine may be chosen from primary, secondary or tertiary amines, in particular those with alkyl radicals having from 1 to 6 carbon atoms each. Thus, it may be ethylamine C2H5NH2, methylamine CH3NH2, dimethylamine (CH3)2NH, butylamine C4H9NH2 or propylamine C3H7NH2. The choice of suitable amine for a layer having a given geometrical thickness and/or a given refractive index results from a compromise to be found between a certain number of parameters such as steric hindrance, reactivity, etc. Preferably, the ratio, in terms of number of moles, of the amount of nitrogen precursor to the amount of silicon-containing precursor is between 5 and 30, and advantageously is equal to 10. It is in fact important to control such a ratio in order to avoid, on the one hand, insufficient incorporation of nitrogen and, on the other hand, any risk of nucleation in the gas phase and consequently any risk of forming powder. The risks of clogging up the device and reductions in production efficiency are thus limited. According to an additional characteristic, when it is desired to incorporate ah additive, a precursor of the additive independent of the silicon-containing precursor and the amine precursor is chosen. It may, for example, be a fluorinated gas of the CF4 type when the desired additive is fluorine F or an organic - 11 - phosphate carrier gas of the PO(OCH3)3 type or a gas of the triethylphosphite, trimethylphosphite, trimethyl-borite, PF5, PC13/ PBr3 or PCl5 type when the desired additive is phosphorus P or boron B. Advantageously, these additives generally allow the deposition rate to be increased. The deposition temperature is appropriate to the choice of precursors, in particular the amine. Preferably, it is between 550 and 760°C. It may preferably be between 600 and 700°C, i.e. between the temperature at which the glass, in particular silica-soda- lime glass, is dimensionally stable and the temperature that it has on exiting the float chamber. Advantageously, in the variant in which the glass composition of the substrate is suitable for an electronic application, it is between 660° and 760°C. According to this variant, an advantageous composition may be that described in Application WO 96/11887. This composition, expressed in percentages by weight, is of the type: SiO2 45 - 68% A12O3 0 - 20% ZrO2 0 - 20% B2O3 0 - 20% Na2O 2 - 12% K2O 3.5 - 9% CaO 1 - 13% MgO 0 - 8 % with: o SiO2 + A12O3 + ZrO2 = 70% o A12O3 + ZrO2 =2% o Na2O + K2O = 8% and optionally BaO and/or SrO in the following proportions: 11% = MgO + CaO + BaO + SrO = 30% with a lower annealing temperature of at least 53 0 °C and an a coefficient of 80 to 95 x 10-7/°C. - 12 - Another advantageous composition, drawn from Application FR 97/00498, is, still in percentages by weight, of the type: SiO2 55 - 65%, preferably 55 - 60% A12O3 0-5% ZrO2 5 - 10% B2O3 0-3% Na2O 2-6% K2O 5-9% MgO 0 - 6%, preferably 1-6% CaO 3 - 11%, preferably 7 - 11% SrO 4 - 12% BaO 0-2% with: o Na2O + K2O = 10% o MgO + CaO + SrO + BaO > 11%, preferably > 15% and a lower annealing temperature of at least 600°C. (Another variant consists in choosing an A12O3 content of 5 to 10% and a ZrO2 content of 0 to 5%, keeping the proportions of the other constituents unchanged). It will be recalled that the so-called lower annealing ("strain-point") temperature is the temperature that a glass has when it reaches a viscosity r\ equal to 10 ' poise. It is thus preferable to deposit the layer in an essentially inert or reducing atmosphere, for example an N2/H2 mixture containing no or almost no oxygen, continuously on a ribbon of float glass, in the float chamber and/or in a box for control of the oxygen-free inert atmosphere, in order to deposit it further downstream of the float line, possibly at slightly lower temperatures. The invention thus allow manufacture of filtering solar-control glazing assemblies with stacks of the type: glass/TiN and/or ZrN/layer according to the invention/SiOC and/or SiO2, the said layer according to the invention making it possible to have a much stronger interface between, on - 13 -the one hand, the TiN layer and/or the ZrN layer and, on the other hand, the SiOC layer and/or the SiO2 layer. It also makes it possible to provide any effective protection of the TiN and/or ZrN from the risk of surface oxidation either on the industrial line after deposition of the SiOC and/or SiO2 layer, or off the industrial line, for example when the substrate provided with the stack of layers, once it has been cut up, undergoes heat treatments of the bending/toughening or annealing type. Advantageously, the layer has a geometrical thickness of between 10 and 5 0 nanometres, the thin layer according to the invention has a geometrical thickness of between 5 and 2 0 nanometres and the SiOC and/or SiO2 overlayer has a geometrical thickness of between 3 0 and 100 nanometres; or else of the type: glass/Al/thin layer according to the invention, the aluminium reflective layer either having a small thickness (less than or equal to 30 nm) or having a greater thickness when the mirror function is desired, such as that described in the aforementioned International Patent Application PCT/FR-96/00362, the thin layer according to the invention having both a role as oxidation-protection agent and a scratch resistance function. The invention also makes it possible to produce glazing assemblies whose essential functionality is that of being scratch-resistant, i.e. glazing assemblies such as floor slabs and glass furniture in which the glass substrate is only coated with the thin layer based on Si3N4 according to the invention, optionally combined with an anti-iridescence layer. Advantageously the glass is thus protected from any degradation. The thin layer according to the invention may also be combined with low-emissivity layers using stacks of the type: - glass/SiOC/F:SnO2 or ITO/thin layer according to the invention. - 14 - In these stacks, the SiOC sublayer may obviously be replaced by other metal oxides, such as those described in Patent Application EP-0,677,493 . The thin layer according to the invention likewise makes it possible to manufacture any type of functional glazing assembly provided with a stack of thin layers, which has high durability and is capable of being toughened and/or bent when the substrate used is a glass substrate. The invention furthermore makes it possible to produce glazing assemblies for which an anti-fouling function is desired, using stacks of the type: -. glass/thin layer according to the invention/Ti02 In these stacks, the thin layer according to the invention essentially has the role of acting as a barrier layer to the alkali metals migrating from the glass into the layer based on titanium oxide TiO2, the photocatalytic effect of the latter thus being enhanced. In addition, if the thickness of the layer according to the invention is suitable for it to undergo interferential interaction, it also acts as an anti-iridescence layer. The titanium oxide TiO2 may be mostly in the form of crystallized particles of the anatase type, as described in 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. Finally, the invention allows manufacture of emissive screens of the flat-screen type, such as plasma screens. The thin layer according to the invention may then fulfil different functions depending on the nature of the chemical composition of the substrate on which it is deposited, and/or on the location (front or rear face) of this same substrate in the screen and therefore on the nature of the functional layers which are on top of it, such as the electrodes and the luminophores (photophores), 15 components which are essential for the operation of the screen. Thus, in the case in which the glass substrate is of the "blocked alkali" type, i.e. having a composition substantially free of diffusing species of the alkaline type, the thin layer according to the invention very effectively fulfils the essential role of barrier layer to the migration of species diffusing from the upper coatings towards the substrate, in particular from the silver-based electrode. Likewise, in the case in which the composition of the glass substrate contains alkali metals, it also fulfils the role of barrier layer to their migration. The invention also applies to the surface treatment of glass-bottle type containers or flasks, the hard layer according to the invention strengthening the said containers, for example with respect to handling operations likely to damage them, whatever the observed relative thickness inhomogeneity of the said layer. The deposition of the hard layer according to the invention may thus be carried out on the external wall of the containers, by mechanically strengthening it, in particular protecting it from impact, but also on the internal wall of the containers so as, for example, to prevent components from leaking out of the substrate. Other details and advantageous characteristics will emerge below from the description of non-limiting illustrative embodiments with the aid of the appended Figures 1 and 2. For the sake of clarity, these figures do not respect the proportions with regard to the relative thicknesses of the various materials. In all the following accompaning examples, the deposition of all thin layers is carried out in the float chamber. EXAMPLE 1: Figure 1 shows a clear silica-soda-lime glass substrate 1 having a thickness of 3 millimetres, for example that sold under the trademark PLANILUX by the company Saint-Gobain Vitrage, covered with the thin - 16 -layer 2 based on silicon nitride developed according to the invention. The thin layer 2 based on silicon nitride is obtained by means of a gas-phase pyrolysis technique using silane SiH4/ which is the silicon-containing precursor, and ethylamine C2H5NH2, which is the nitrogen-containing 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 approximately 10. This parameter is advantageous in that it optimizes the deposition of each of the constituents of the layer. This is because it has been observed that it must not be: - too high, otherwise there may be a risk of nucleation in the gas phase and therefore a risk of forming a powder; or - too low, otherwise there may be insufficient incorporation of nitrogen into the layer. A range of ratios from 5 to 30 proves to be quite satisfactory when it is desired to deposit a layer having a thickness of from 5 0 to 300 nm using a silane and ethylamine. The deposition was carried out on the substrate 1 heated 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 6 0 nm per minute. The layer 2 obtained as shown in Figure 1 has a thickness of approximately 3 50 nanometres and a refractive index of about 1.85. Microprobe analysis indicates that the layer 2 contains, 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 adjust the amounts of the various components incorporated, in particular that of carbon, by varying various parameters, such as the - 17 - temperature at which the deposition is carried out, the use of an amine other than ethylamine, or of a mixture of amines or of ammonia added to ethylamine as the nitrogen precursor. The various amines which have suitable reactivity are as follows: methylamine CH3NH2, dimethylamine (CH3)2NH, butylamine C4H9NH2 and propylamine C3H7NH2. Satisfactory temperatures for depositing the layer 2 according to the invention lie within a range of from 550 to 700°C. The spectrophotometric characteristics of such a layer are given in the table below, in which TL, RL and AL represent, respectively, the values of the light transmission, the light reflection and the light absorption in percentages: TL RL AL Layer 2 84 13 3 these values being measured using the D65 illuminant, at almost normal incidence. It is observed that the layer according to the invention has a very low light absorption and that it is free of any haze. {It will be recalled that the haze is the ratio of the diffuse transmission to the light transmission at a wavelength equal to 550 nm}. A test was carried out on the substrate 1 covered with the single layer 2 according to the invention which enabled the mechanical strength of the said layer to be determined. This test is carried out using grinding wheels made from an abrasive powder embedded in an elastomer. The machine is manufactured by the company Taber Instrument Corporation. It is a standard Abrasion Tester model 174 and the grinding wheels are of the CSIOF type and loaded with 500 grams. The covered substrate 1 is subjected locally to 5 0 rotations and then, using an optical microscope, the number of scratches on four squares of side equal to 1 inch, i.e. 2.54 cm, is counted. After having counted them, the average R of the number of scratches per - 18 - square is calculated. Finally, the Taber score Ts is calculated from the formula: Ts = -0.18R + 10. For a layer 2 according to the invention, having a geometrical thickness of 3 00 nanometres, this score is equal to 9.3. This value denotes very little damage and therefore is indicative of very good scratch resistance of the layer according to the invention. By way of comparative example, it may be noted that a layer of fluorine-doped tin oxide F:SnO2 having a geometrical thickness of 34 0 nanometres, known as being the "hardest" layer deposited using a gas-phase pyrolysis technique, has, as a result of the test, a Taber score Ts equal to 9.1. It may therefore be clearly seen that the layer based on silicon nitride according to the invention is a layer which intrinsically has very good resistance to mechanical abrasion and is, from an optical standpoint, very satisfactory since it is highly transparent and has a very low absorbance at wavelengths in the visible range. EXAMPLE 2: Figure 2 shows a glazing assembly of the solar-protection type, having a stack of thin layers, in which the layer 2 according to the invention has been incorporated. The clear silica-soda-lime glass substrate 1 having a thickness of 6 millimetres is covered with three successive layers: - a first layer 3 of TiN having a thickness of 2 3 nm, obtained by gas-phase pyrolysis using titanium tetrachloride TiCl4 and methylamine CH3NH2, as described in Patent Application EP-0,638,527; - a second layer 2 according to the invention having a thickness of approximately 10 nanometres and a refractive index equal to 1.85, deposited under the same conditions as Example 1; and - a third layer 4 of silicon oxycarbide SiOC having a thickness of 6 5 nm and a refractive index - 19 - equal to 1.65, also obtained by gas-phase pyrolysis using silane and ethylene as described in Patent Application EP-0,518,755, the layer essentially in silicon-containing form oxidizing on leaving the float, and more particularly in the lehr. The stack is therefore of the type: glass/TiN/Si3N4/Si0C. EXAMPLE 3: This comparative example was produced using a stack consisting of: glass/TiN/SiOC, in which the two layers, of TiN and SiOC, have the same characteristics as those defined above and are obtained under the same deposition conditions. It is observed that the layer 2 according to the invention, even with a small thickness, creates a very strong interface between the first layer 3 of TiN and the overlayer 4 of SiOC. In addition, the layer 2 according to the invention provides effective protection of the TiN from any risk of surface oxidation on the industrial line after deposition of the SiOC overlayer 4. Where appropriate, it isolates the TiN when the substrate, once cut up, undergoes subsequent heat treatments of the bending/toughening or annealing type. Likewise, after having measured the spectro-photometric values, in particular the light transmission TL for each of the two stacks in Examples 2 and 3, as well as the solar factor Fs, it is observed that the selectivity corresponding to the difference TL - Fs is much better in the case of the three-layer stack of Example 2 with the layer 2 according to the invention sandwiched between the two TiN and SiOC layers, since its value is 10%. In the case of the two-layer stack of Example 3, it is less than 7%. Finally, it should be noted that if, in the two configurations above, the layer based on silicon nitride according to the invention is homogeneous over its thickness, it is also clearly possible to provide a - 20 -certain compositional inhomogeneity over its thickness, in particular so as to vary the refractive index and allow optimum optical and/or chemical compatibility with the layer on top and/or underneath, such as, for example, a layer enriched in Si3N4 on the TiN side and a layer enriched in SiON on the SiOC side in a solar-protection glazing assembly using the same layers as in Example 2. This "gradient" layer may be obtained by means of the same gas-phase pyrolysis deposition technique, but using a nozzle capable of creating chemical gradients, such as that described in Patent Application FR-2,736,632. In conclusion, the invention has resulted in a novel layer based on silicon nitride, which is particularly able to withstand mechanical abrasion and is highly satisfactory from an optical standpoint since it has a very low absorbance, this not being the case with known Si3N4-based layers. Highly advantageously, the layer according to the invention may be deposited by gas-phase pyrolysis at high deposition rates using a nitrogen-containing precursor which can be used on an industrial scale without incurring a prohibitive cost burden. The nitrogen-containing precursor used furthermore has a suitable reactivity since it makes it possible to reach deposition temperatures at which it is possible, without any major difficulty, to produce three-layer stacks in line on the ribbon of float glass, for example so as to produce an anti-solar glazing assembly with the TiN functional layer and the last SiOC layer, the layer according to the invention advantageously being incorporated in the conventional two-stack layer in order to give a stronger interface and to isolate the functional layer from oxidation after deposition of the SiOC overlayer, without disrupting production on the industrial line, or else during heat treatments on the substrate off the industrial line. - 21 -WE CLAIM: 1 . Process for depositing a thin layer (2) on a transparent substrate least one nitrogen precursor is in the form of an amine .such as herein described. 2. Process as claimed in claim 1, wherein the silicon precursor is a silane, of the silicon hydride and/or alkyl type, or a silazane. 3. Process as claimed in claim 1 or 2, wherein the amine is a primary, secondary or tertiary amine, in particular one with alkyl radicals having from 1 to 6 carbon atoms each. 4. Process as claimed in claim 3, wherein the amine is ethylamine C2H5NH2 ,methylamine CH3NH2, dimethylamine (CH3)2 NH, butylamine C4H9NH2 or propylamine C3H7NH2 5. Process as claimed in one of claims 1 to 4, wherein the ratio, in terms of number of moles, of the amount of nitrogen precursor(s) to the amount of silicon precursor (2) is between 5 and 30, and preferably 10. 193277 - 22 - 6. Process as claimed in one of claims 1 to 5, wherein the precursor of the additive is independent of the silicon and nitrogen precursors and is, in particular, a fluorinated gas of the CF4 type when the additive is fluorine F, and an organic phosphate carrier gas of the PC(OCH3)3type or a gas of the triethylphosphite, trimethylphosphite, trimethylborite, PCl3 or PF5, PBr3 or PCl5 type when the additive is phosphorus P or boron B. 7. Process as claimed in one of claims 1 to 6, wherein the deposition temperature is chosen to be between 550 and 760° C and is advantageously between 660° C and 760° C- 8. Process as claimed in one of claims 1 to 7, wherein the deposition of the said thin layer is carried out in an essentially inert or hydrogen-containing atmosphere, containing no oxygen, continuously on a ribbon of float glass, in the float chamber and/or in a box for control of the inert or reducing atmosphere. MRS I BANERJEE OF H V WILLIAMS & CO APPLICANTS' AGENT Dated this 2nd day of February 1998

Documents:

00168-cal-1998-abstract.pdf

00168-cal-1998-claims.pdf

00168-cal-1998-correspondence-1.pdf

00168-cal-1998-correspondence.pdf

00168-cal-1998-description(complete).pdf

00168-cal-1998-drawings.pdf

00168-cal-1998-form-1.pdf

00168-cal-1998-form-2.pdf

00168-cal-1998-form-4.pdf

00168-cal-1998-form-6.pdf

00168-cal-1998-g.p.a.pdf

00168-cal-1998-others.pdf

00168-cal-1998-priority document.pdf

168-CAL-1998-FORM 27-1.1.pdf

168-CAL-1998-FORM 27.pdf

168-CAL-1998-FORM-27.pdf

168-cal-1998-granted-abstract.pdf

168-cal-1998-granted-acceptance publication.pdf

168-cal-1998-granted-claims.pdf

168-cal-1998-granted-correspondence.pdf

168-cal-1998-granted-description (complete).pdf

168-cal-1998-granted-drawings.pdf

168-cal-1998-granted-examination report.pdf

168-cal-1998-granted-form 1.pdf

168-cal-1998-granted-form 2.pdf

168-cal-1998-granted-form 3.pdf

168-cal-1998-granted-form 5.pdf

168-cal-1998-granted-gpa.pdf

168-cal-1998-granted-letter patent.pdf

168-cal-1998-granted-priority document.pdf

168-cal-1998-granted-reply to examination report.pdf

168-cal-1998-granted-specification.pdf

168-cal-1998-granted-translated copy of priority document.pdf