Method for thin layer deposition

Translation of description of equivalent WO 2009136110 A2

METHOD FOR THIN FILM DEPOT

p0002The invention relates to the field of inorganic thin layers, in particular deposited on glass substrates. It more particularly relates to a crystallization method at least part of said thin film and certain products obtained using this method.

p0003Many thin layers are deposited onto substrates, in particular flat or slightly curved glass, to impart to the materials obtained special properties: optical properties, e.g. reflection or wavelength of radiation absorption in a domain data, particular electrical conduction properties, or properties related to the ease of cleaning or the possibility for the self to clean material. These thin layers are usually based on inorganic compounds: oxides, nitrides, or metals. Their thickness usually ranges from several nanometers to several hundred nanometers, hence the adjective "slim."

p0004It may be mentioned in particular thin layers based on titanium oxide, which has the distinction of being self-cleaning, facilitating the degradation of organic compounds under the action of ultraviolet radiation and removal of mineral dirt (dust) under the action of a water runoff.

p0005These layers have the characteristic to see some of their improved properties when they are in an at least partially crystallized. generally seeks to maximize the rate of crystallization of these layers (the mass or volume fraction of crystallized material) and the crystal grain size (or the size of the coherent diffraction domains measured by X-ray diffraction methods), or in some cases to promote a particular crystallographic form.

p0006In the case of titanium oxide, it is known that titanium oxide crystallized in the anatase form is much more efficient in terms of degradation organic compounds that amorphous titanium oxide or crystalline in the rutile or brookite form.

p0007A commonly used process on an industrial scale for the deposition of thin layers, particularly on the glass substrate, is the sputtering process assisted magnetic field process called "magnetron." In this process, a plasma is created in a high vacuum in the vicinity of a target comprising the chemical elements to be deposited. The active species of the plasma, by bombarding the target, sell said elements, which are deposited on the substrate to form the desired thin layer. This process is called "reactive" when the layer is made of a material resulting from a chemical reaction between the elements torn off from the target and the gas contained in the plasma. It is well known to deposit by magnetron reactive type process, the titanium oxide layers using a target of metallic titanium or a ceramic target of TiO_x (X <2) and a plasma gas containing oxygen. The major advantage of this method lies in the possibility of depositing on a same line a very complex multilayer stack by successively pass the substrate in different targets, generally in a single device.

p0008During the industrial implementation of the magnetron sputtering process, the substrate remains at room temperature or undergoes a moderate rise in temperature (less than 80⁰C), particularly when the substrate frame rate is high (which is usually desired for economic reasons). What may be an advantage, however, a drawback in the case of the aforementioned layers, since the low temperatures involved generally do not allow sufficient crystal growth. This is particularly the case for thin layers of low thickness and / or layers made of materials whose melting point is very high. The layers obtained according to this process are therefore predominantly or totally amorphous or nano-crystallized (the average crystal grain size being less than a few nanometers), and heat treatments are necessary to obtain the desired degree of crystallization or the desired grain size . Possible thermal treatments involve heating the substrate either during the deposition or after the deposition, magnetron output line. Most generally, temperatures of at least 200⁰C or 300⁰C are necessary. Heating the substrate in industrial magnetron lines

p0009(During deposition), however, proved difficult to implement, especially because the vacuum heat transfer, necessarily radiative nature are difficult to control and involve a high cost in the case of large substrates, several meters wide. In the case of thin glass substrates, this type of treatment often involves high risk of breakage.

p0010Heating the coated substrate after the deposition, for example by placing the substrate in an oven or an oven or by subjecting the substrate to infrared radiation from conventional heating devices such as infrared lamps, also has drawbacks because these different processes contribute to indiscriminate heating the substrate and the thin layer. Heating the substrate to temperatures above 150 ° C is likely to cause breaks in the case of large substrates (several meters wide) because it is impossible to ensure the same temperature over the entire width of the substrate. Heating substrates also slows down the whole process, because it is necessary to wait for their complete cooling before considering cutting or storage, which usually takes place by stacking the substrates on each other. A controlled cooling is also essential to avoid the generation of stresses within the glass, and therefore the possibility of breakage. Such a controlled cooling is very expensive, annealing is generally not sufficiently controlled to eliminate thermal stresses within the glass, which generates an increased number of line breaks. The annealing also has the disadvantage of making the cutting of the hardest glass, cracks having a less strong tendency to propagate linearly.

p0011Heating of the substrates takes place in the case where the glass is curved and / or toughened as a glass reheating beyond its temperature softening point (generally more than 600⁰C. or 700⁰C for a few minutes) is performed. Tempering or bending thus provides the desired result of crystallization of thin films. But it would be costly to submit to such treatment all glazing for the sole purpose of improving the crystallization of the layers. In addition, the tempered glazing can not be cut, and some stacks of thin layers do not withstand high temperatures experienced during tempering glass.

p0012To solve these problems, the Applicant has developed a method of treating at least one thin layer based on titanium oxide, and continuously deposited on a first face of a substrate, characterized in that one carries each point of said at least one thin layer at a temperature of at least 300 ° C. while maintaining a temperature less than or equal to 150⁰C at any point on the face of said substrate opposite said first face, so as to increase the crystallization rate of said thin layer in continuous and without retaining step of melting said thin layer.

p0013Possible methods include in particular the heating with infrared radiation, a plasma torch or flame.

p0014The inventors have now demonstrated that it was still possible to improve the crystallization properties of the layers based on titanium oxide perfecting this method.

p0015To this end, the invention relates to a method of obtaining a material comprising a substrate and at least one thin layer based on titanium oxide at least partially crystallized and deposited on a first face of said substrate, said method comprising the steps of: depositing at least one thin layer based on titanium oxide and subjecting said at least one thin layer based on titanium oxide to a crystallization treatment by providing an energy liable to each point said at least one thin layer based on titanium oxide at a temperature of at least 300 ° C while maintaining a temperature below or equal to 150 ° C at any point on the face of said substrate opposite said first face. In the process according to the invention, the crystallization treatment is preceded by a step of depositing, above and / or below said thin layer based on titanium oxide, an energy supplier layer, capable of absorbing the energy provided during said crystallization treatment more efficiently than said at least one titanium oxide layer and / or create an additional energy during said crystallization treatment, and to transmit at least a portion of said energy to said at least one thin layer based on titanium oxide during said crystallization treatment.

p0016The improvement to the process previously developed by the Applicant is therefore in the presence of an overcoat layer and / or sub-layer (preferably an overcoat layer) which will promote the titanium oxide crystallization through of absorption or creation of energy phenomena, and transfer the energy absorbed or created to the titanium oxide layer. The final energy given to the titanium oxide layer is greater than that provided by the single crystallization treatment. The method of the invention thus allows, for the same energy supplied during the crystallization treatment, to improve the crystallization properties, or, alternatively, to obtain crystallization properties equivalent to a crystallization treatment consumes less energy .

p0017By "layer the point" means an area of ​​the layer undergoing treatment at a given time. According to the invention, the entire layer (therefore each point) is raised to a temperature of at least 300⁰C, but each point of the layer is not necessarily treated simultaneously. The layer can be treated at the same moment as a whole, each point of the layer being simultaneously heated to a temperature of at least 300⁰C. The layer may alternatively be treated so that the various points of the layer or sets of points are successively heated to a temperature of at least 300 ° C, this second embodiment being most frequently used in the case of a continuous implementation on an industrial scale.

p0018By "deposited on a first face of said substrate" is not necessarily meant that the layer is deposited directly on the substrate. It can be, but one or more sub-layers can be interposed between the substrate and to the titanium oxide base layer, as explained in the following text. The energy supplier layer is preferably deposited over the thin layer of titanium oxide. This is in this case of an overlayer.

p0019The method according to the invention allows to make a significant energy, which favors the crystallization of the thin layer by a crystal growth mechanism around nuclei already present in the layer, being in solid phase.

p0020The method according to the invention has the advantage of heating only the thin layer (thin layer or layers in the case of a stack), without significant heating of the entire substrate. It is no longer necessary to carry out a slow, controlled cooling of the substrate prior to cutting or storage of glass. This method also allows for the integration of a heating device on the existing continuous production lines, more particularly in the space between the outlet of the deposition chamber under vacuum magnetron line and the storage device of glass by stacking. It is also possible in some cases to carry out the treatment of the invention within the vacuum deposition chamber.

p0021In an integrated industrial implementation in a magnetron line, the process is generally continuous in the sense that the substrate is scrolling, thus undergoes a linear movement in a direction X. Each point of the film is then preferably treated according to the following modes: either the heating means are fixed and can simultaneously process a set of points forming a line in a direction Y perpendicular to the X direction or the heating means are movable in the Y direction and the treated successively each point. The method of the invention can be implemented on a substrate placed horizontally as well as vertically. It can also be implemented on a substrate provided with thin layers on both faces, at least one layer of one side or each side being treated according to the invention. In case of thin layers deposited on both sides of the substrate are treated according to the invention, it is possible to treat said thin film layers of each face either simultaneously or sequentially by the same or different techniques, in particular according to the nature of treated layers is identical or separate. If the inventive treatment is performed simultaneously on both sides of the substrate is therefore well within the scope of the invention.

p0022It is not physically possible to heat the layer without heating the substrate, because the temperature rise in the layer necessarily entails, by thermal conduction mechanism, a heating zone that is closest to the substrate layer , and thus a high thermal gradient in the thickness of the substrate. Such high thermal gradients, sometimes referred to heat shock are known to systematically generate breakages in the case of soda-lime glass commonly used in the flat glass industry. These breakages, which originate from the differential thermal expansion between the different areas of the glass subjected to different temperatures occur more easily in the case of soda-lime glasses because their expansion coefficient is quite high. They are also more easily occur in the case of large-sized substrates (at least 1 m or 2 or even 3 m wide) because it is more difficult to ensure a high temperature homogeneity for large substrates.

p0023The inventors have however shown that a heat treatment by implementing a moderate and controlled heating of a limited area of ​​the substrate allowed to avoid this breakage problem, hitherto considered inevitable. It is therefore essential for the implementation of the present invention that the temperature of the face of the substrate opposite to the face carrying the thin treated layer is not greater than 150⁰C. This characteristic is obtained by choosing a heating method specially adapted to heat the thin layer and not the substrate and controlling the time or the intensity of heating and / or other parameters depending on the used heating mode, as described in more detail in the following text.

p0024A common feature to all usable heating methods according to the invention lies in the fact that they allow to generate a power by extremely high surface unit, which can not however be quantified in an absolute manner because it depends on many factors among wherein the nature and thickness of the thin layer. This high power by unit area achieves at the layer the required temperature extremely rapidly (typically in a time less than or equal to 1 second) and therefore to limit all the duration of treatment, the heat generated having only then no time to diffuse into the substrate. Each point of the thin layer is subjected to the treatment according to the invention (that is to say heated to a temperature greater than or equal to 300⁰C) for a time generally less than or equal to 1 second or 0.5 seconds. Conversely, the conventionally used infrared lamps not to achieve these high power per unit area, the processing time must be longer to achieve the desired temperatures (often several seconds), and the substrate is then necessarily focused at elevated temperatures by heat diffusion.

p0025In order to minimize the number of breaks for larger substrates (eg 6 m long and 3 m wide), is preferably maintained throughout the treatment a temperature below or equal to 100⁰C, in particular 50 ° C, at any point on the face of the substrate opposite to the face on which is deposited the thin layer.

p0026Another advantage of the invention lies in the fact that the method is subjected to the equivalent of quenching the thin film or stack of thin layers. Sometimes certain thin-film layers have their optical properties (color coordinates, light or energy transmission) changed when the glass is tempered. The method of the invention then provides a non-tempered glass (therefore not having within it a specific stress profile in tempered glass, which makes the cuttable) but substantially the same optical properties as if it had was soaked.

p0027The crystallization rate obtained by the process according to the invention is preferably greater than or equal to 10% or even 20% or 50%, especially 70% and even 90%. This crystallization rate, defined as the mass of material crystallized on the total mass of material, can be evaluated by X-ray diffraction using the Rietveld method. Due to a crystallization mechanism by growth of crystal grains from seeds or nuclei, increasing the crystallization rate is accompanied generally an increase of the size of the crystallized grains or coherent diffraction domains measured by X-ray diffraction

p0028The substrate is preferably transparent, glass, in particular silico-sodo-calcic. The substrate may be colorless or colored, eg blue, green, bronze or gray. It can also be plastic, such as polycarbonate or polymethyl methacrylate. It advantageously has at least one dimension greater than or equal to 1 m or 2 m and even 3 m. The thickness of the substrate usually varies between 0.5 mm and 19 mm, the method according to the invention being particularly advantageous for thinner substrates, the thickness of which is less than or equal to 4 mm, or 2 mm.

p0029The face of the substrate opposite to the face on which the titanium oxide-based layer is deposited may be bare, or be covered by one or more thin layers. It can especially be based on titanium oxide layer, or layers of thermal features (layers or stacks of solar control or low-emissivity, particularly of the type comprising at least one silver layer) or optical (by examples antireflective layers or stacks).

p0030Based on the titanium oxide layer is preferably a titanium oxide layer (optionally doped with a metal ion, e.g., an ion of a transition metal, or nitrogen atoms, atoms, of fluorine ...).

p0031The entire surface of this layer is preferably in contact with the outside so that the titanium oxide can fully play its self-cleaning function. However, it may be advantageous to coat the titanium oxide-based layer with a thin hydrophilic layer, especially one based on silica. One advantage of the method according to the invention is that the thin layer results from the energy supplier layer after the crystallization treatment, as detailed in the following text.

p0032To further enhance the crystallization of these layers, it is possible to provide directly under the base of titanium oxide layer an underlayer having the effect of promoting crystal growth of titanium oxide, especially in anatase form . It can in particular be an underlayer in ZrO 2, as described in WO 02/40417, or a sub-promoting layer heteroepitaxial growth of titanium oxide in the anatase form, as described for example in the application WO2005 / 040058, in particular a layer of BaTiO₃ or SrTiO₃.

p0033Other sublayers may be inserted between the substrate and the titanium oxide-based layer. It can be, for example barrier layers to the migration of alkali metals, especially layers based on SiO 2, from

p0034SiOC, AI alumina₂O₃, Silicon nitride Si₃NOT₄. It can still be layers or stacks thermal functions (layers or stacks of solar control or low-emissivity, particularly of the type comprising at least one silver layer) or optical (for example antireflective layers or stacks).

p0035The thin layer of titanium oxide or energy-providing layer may be obtained by any type of process, particularly processes that generate predominantly amorphous layers or nano-crystalline, such as magnetron sputtering, the deposition process chemical vapor assisted by plasma (PECVD), the vacuum evaporation method, or the sol-gel process. However, it is preferably a "dry" layer, not containing aqueous or organic solvent, as opposed to a "wet" layer, for example obtained by the sol-gel process.

p0036The thin layer of titanium oxide base and the energy supplier layer are preferably deposited by sputtering, particularly assisted by a magnetic field (magnetron).

p0037In the case of a layer obtained by the sol-gel process, precursors in solution (sol) are deposited on the substrate, the layer obtained being then dried and annealed to remove any trace of solvent. In this case, the energy supplied by the heating then serves mainly to remove the solvent, without necessarily affecting the crystallization properties of the layer, and it is therefore be more difficult to improve these properties in a sufficiently short time not also heat the substrate.

p0038The energy supplier layer is preferably deposited in direct contact with the base of titanium oxide layer, preferably on the latter. In this way we optimize the energy transfers to the energy supplier to the layer of titanium oxide-based layer. The energy supplier layer preferably has an absorption in a domain of wavelengths between 300 and 3000 nm, preferably between 600 and 1100 nm, especially between 800 and 1100 nm. It is thus possible to use techniques implementing radiation in this area, such as YAG lasers, laser diodes or infrared lamps associated with focusing devices. Energy-providing layer absorbs this radiation, and transmitted by conduction part of the energy to the titanium oxide layer. Without energy supplier layer of titanium oxide would not be affected by this type of radiation because it has no specific absorption in this wavelength domain.

p0039The energy-providing layer can, alternatively or additionally, be capable of transmitting energy by exothermic reactions, including combustion or oxidation. Energy-providing layer may thus burn under the effect of the crystallization treatment, emitting near, and transferring to the titanium oxide layer a significant energy which contribute to improve its crystallization.

p0040Energy-providing layer can be capable of evaporating at least partially or completely during the crystallization treatment. In the case of a combustion reaction or oxidation, the layer may become at least partially gas.

p0041Energy-providing layer may still be susceptible to oxidation at least partially or completely during the crystallization treatment, and become at least partially transparent in the visible range.

p0042These providers of energy layers that evaporate or oxidize can be termed sacrificial layers in the sense that, after playing their role as purveyor of energy to the benefit of titanium oxide, they are no longer in as such (in their original form) of the final material. Alternatively, the energy supplier layer, or its reaction product during the crystallization treatment, can remain on the surface of the material after treatment. In this case, it may be necessary to remove them, for example by chemical treatment or cleaning. Different layers of natures can implement one or more of these advantageous properties.

p0043Energy-providing layer may for example be titanium metal. Titanium metal absorbs in the area of ​​wavelengths in the visible and near infrared area in which its oxide is transparent. In addition, part of the metal titanium will evaporate during the heat treatment, the other part oxidizes to become titanium oxide. The titanium metal layer therefore disappears during the crystallization treatment, and the final product no longer comprises absorbent titanium overcoat. The titanium layer is preferably deposited by cathodic magnetron sputtering (magnetron sputtering) using a titanium target in an argon atmosphere.

p0044The energy supplier layer can also be made of carbon, especially graphite type and / or diamond. The carbon absorbs infrared radiation, and as a result of the crystallization treatment, especially when implementing a flame or a plasma torch, the carbon will undergo a combustion reaction. The energy released by this exothermic reaction will help to promote the crystallization of titanium oxide. The graphite layer is preferably deposited by cathodic magnetron sputtering (magnetron sputtering) using a graphite target in an argon atmosphere. Other possible methods include depositing by ion source, chemical vapor deposition, plasma enhanced (PECVD).

p0045Energy-providing layer may also be made of silicon, optionally alloyed with aluminum. Silicon has a strong absorption in the wavelength range from visible to near infrared. Under the effect of the crystallization treatment, especially when implementing a laser emitting in the infrared, the silicon will also oxidize, giving rise to a layer of silica, possibly comprising aluminum. This oxidation is exothermic and will therefore generate an energy part of which serve to promote the crystallization of titanium oxide. The layer of silica obtained is hydrophilic and may contribute, if its thickness is low (less than 5 nm, or less than 2 nm), to improve properties of photoinduced hydrophilicity of titanium oxide, and consequently its self-cleaning and anti-fouling properties. The silicon may be doped with aluminum in particular at contents of between 5 and 10 wt%. The presence of aluminum indeed improves the chemical stability of the layer. In addition, the sputter deposition of such layers is facilitated, because aluminum contributes to increasing the electron conductivity of the silicon target.

p0046The energy supplier layer may also be made of titanium or silicon carbide. These layers exhibit strong absorption in the visible and near-infrared domain for which titanium oxide is transparent. Under the effect of the crystallization treatment, these layers will oxidize to titania respectively (and thus be integrated with the underlying titanium oxide layer, creating an extra thickness), or silicon oxide, which has the above advantages. The energy supplier layer has a thickness advantageously comprised between 1 and 100 nm, especially between 1 and 20 nm.

p0047For simplicity, the crystallization treatment is preferably under air and / or at atmospheric pressure. Some treatments are however compatible with the vacuum, and it may be advantageous to carry out crystallization treatment within the vacuum deposition chamber.

p0048Different heating means make it possible to implement the crystallization treatment, allowing the generation of power by a very high surface unit. heating the parameters such as the power of the heating or heating time means are adapted on a case by case basis by the skilled person depending on various parameters such as the nature of the heating process, the thickness of the layer , the size and thickness of the substrates to be treated etc.

p0049The crystallization treatment may be performed using infrared radiation. To minimize heat gain to the substrate, the wavelength of the radiation chosen is preferably not included in the part of the infrared radiation absorbed by the substrate. For the above reasons, the radiation must be characterized by a high power per unit area. For this reason, heating the thin layer is preferably formed using a laser emitting infrared radiation. Infrared lamp systems associated with a focusing device (e.g., a cylindrical lens) to achieve high power per unit area can also be used. One can use a laser emitting radiation whose wavelength is between 5 and 15 micrometers, for example a CO 2 laser emitting radiation whose wavelength is 10.6 micrometers. The advantage is that titanium oxide absorbs in this field of wavelengths. However, it is preferable to use a laser emitting radiation whose wavelength is between 0.5 and 3 micrometers. then is preferably chosen an energy supplier layer having a high absorption in this field of wavelengths, such as titanium, carbon as graphite, silicon, optionally doped with aluminum, or silicon carbide or titanium. A YAG laser (aluminum garnet and yttrium Y2AI15O2) doped with neodymium, emitting, in continuous or pulsed mode, a radiation of about 1 micrometer wavelength, has proved particularly suitable, especially when the substrate does not absorb in this field of wavelengths, which is the case with clear glasses, the content by weight of iron oxide is 0.1% or less. It is also possible to employ diode lasers whose emission wavelength is around 800 nm.

p0050The use of excimer lasers, emitting radiation in the ultraviolet range, is also possible for layers absorbing such radiation.

p0051For simplicity of increased implementation, the lasers used in the context of the invention may be fibers, which means that the laser radiation is injected into an optical fiber and delivered near the surface to be treated by a focusing head. The laser can also be fiber, in that the amplification medium is itself an optical fiber.

p0052Lasers that can radiate a small area (typically of the order of a fraction of a mm² some hundreds of mm²), It is necessary to treat the entire surface, to provide a movement system laser beam in the plane of the substrate or a system forming a line laser beam irradiating simultaneously the whole width of the substrate, and in which the latter comes scroll.

p0053The crystallization treatment may also be made by thermal spray techniques including a technique of projection by plasma torch (plasma spray).

p0054A plasma is an ionized gas generally obtained by subjecting a gas called "plasma" to a stimulus such as a strong direct or alternating electric field (eg electric arc). Under the action of this excitation, electrons are torn from atoms of the gas and expenses thus created migrate towards the electrode of opposite charge. These charges then excite other atoms of the gas by collision, creating avalanche effect a homogeneous or microfilament discharge or an arc. Plasmas can be "hot" (the gas is fully ionized and the plasma temperature is of the order of 10⁶⁰C), or "thermal" (the gas is almost completely ionized and the plasma temperature is of the order of 10^4oC, if such electric arcs). Plasmas contain many active species, that is to say capable of interacting with the material, including ions, electrons or free radicals. In the case of a plasma torch, a gas is blown through an electric arc, and the formed thermal plasma is blown toward the substrate to be treated. The plasma torch is commonly used to deposit thin layers on various substrates by adding to the plasma precursor in powder form.

p0055In the context of the invention, the plasma torch is preferably associated with an automatic movement system located perpendicularly to the traveling direction of the coated substrate and allowing the processing of the entire surface with subsequent return of the torch above the substrate.

p0056The blown gas is preferably nitrogen, air or argon, preferably comprising a hydrogen content by volume of between 5 and 50%, especially between 15 and 30%.

p0057The crystallization treatment may also be achieved by subjecting the thin layer to the action of at least one flame. The flame treatment is preferably conducted on a flame treatment bench located perpendicularly to the running direction of the substrate. The length of the flame treatment device is preferably at least equal to the width of the coated substrate, which allow an easy treatment in a displacement without requiring system. The gas used may be a mixture of an oxidizing gas, in particular selected from air, oxygen or mixtures thereof, and a fuel gas, in particular selected from natural gas, propane, butane, or the acetylene or hydrogen, or mixtures thereof. Oxygen is preferred as the oxidizing gas, in particular in combination with natural gas (methane) or propane, first because it allows to reach higher temperatures and therefore to shorten the treatment and to avoid the heating the substrate, and also because it avoids the creation of nitrogen oxides NO_x. To achieve the desired temperatures at the thin layer, the coated substrate is generally positioned within the visible flame, in particular at the hottest region of the flame, a portion of the visible flame then extending around the treated area.

p0058The flame treatment is a widely used technique for the treatment of the polymer surface to improve their wettability and facilitate their coating with paints. In the use made of it, the principle is to subject the surface to the action of radicals created by combustion, without wearing said high temperature surface. Patent application US 2006/128563 discloses the use of this technique to activate titanium oxide layer surfaces to improve their hydrophilicity. The treatments described, quite similar to those on the polymer substrates are to scroll a substrate at or slightly below (a few centimeters) from the tip of the visible flame. This type of treatment, which aims to create hydroxyl groups on the titanium oxide surface, however, is not suitable for bearing the thin layer of titanium oxide at temperatures above 200⁰C and to increase the titanium oxide crystallization rate, because the temperatures at the tip of the visible flame is insufficient.

p0059The flame treatment is preferred when one does not wish to implement mechanical displacement device above the substrate. The treatment by infrared radiation can in turn be implemented within the deposition device of the magnetron vacuum line. It is also advantageous when one does not wish to consume large quantities of gas. All possible combinations between different types of providers of energy layers and different crystallization processes are possible. According to a preferred embodiment of the invention, the energy supplier layer is titanium, and the crystallization treatment is performed using an infrared radiation, in particular using a laser emitting a radiation between 0.5 and 3 micrometers, for example a YAG laser or a laser diode. According to another preferred embodiment, the energy supplier layer is made of graphite and the crystallization treatment is carried out by flame treatment.

p0060The method according to the invention is particularly advantageous because when a substrate containing alkali metal ions (e.g. a glass of the silica-soda-lime type) is carried at an elevated temperature, said ions tend to diffuse into the oxide layer titanium diminishing significantly or even annulling its photocatalytic properties. For this reason, it is common to interpose between the thin titanium oxide layer and the substrate layer a barrier to the migration of alkali metal, as taught in application EP-A-850 204, or to increase the thickness of the titanium oxide layer so that at least the outermost surface of the layer is not contaminated, as taught in application EP-a-966 409. in the case of the method according to the invention, the substrate n is almost not heated and the migration of alkali metals is therefore virtually zero. The method of the invention thus allows to obtain glass substrates silico-sodo-calcic directly coated with a thin titanium oxide layer (for example of the order of 10 nanometers thick) and having nevertheless a very high photocatalytic activity. The invention is illustrated with examples of non-limiting embodiments that follow.

p0061A soda-lime glass substrate obtained by the float process and then cut so that its size is 3 m to 6 m width length is coated in a known manner by magnetron sputtering of a silica layer of 20 nm thick and then a thin layer of titanium oxide of 10 nm thickness.

p0062The comparative example C1 does not include energy supplier layer. Examples of the invention are however coated with an overcoat layer of Ti of 5 nm thick. The titanium layer is preferably deposited by cathodic magnetron sputtering (magnetron sputtering) using a titanium target in an argon atmosphere.

p0063Between the output of the magnetron line and the storage device, inserting a device comprising a laser diode emitting radiation at 808 nm wavelength focused on the overcoat layer of Ti, along a line corresponding to the width of the substrate.

p0064All examples except Example C2 undergo this treatment for crystallization. The glass substrate temperature during processing shall not exceed 50⁰C as measured by pyrométhe at the side of the substrate opposite the surface bearing the coating of thin layers.

p0065Table 1 below indicates the photocatalytic activity of the layers before treatment and after treatment. Each test is characterized by the thickness of the titanium overcoat and the processing speed. Processing speed, directly connected to the heating layer, expressed in meters per minute: it corresponds to the glass of the running speed in the longitudinal direction.

p0066The photocatalytic activity is a measure of stearic acid degradation rate. The measurement of the photocatalytic activity is performed as follows: cutting out samples of 5x5 cm²Wash the samples for 45 minutes under UV irradiation and under oxygen scanning, - measurement of the infrared spectrum by FTIR for wavenumbers between 4000 and 400cm^"1To form a reference spectrum, deposition of stearic acid: 60 microliters of a solution stéahque acid dissolved in an amount of 5 g / L in ethanol is deposited by spin coating on the sample, measurement of the infrared spectrum by FTIR measurement of the area of ​​the CH bonds of elongation bands₂CH₃ between 3000 and 2700 cm^"1, Exposure to UVA radiation type: the power received by the sample, about 35 W / m² to simulate exterior exposure is controlled by a photocell in the range of wavelength 315-400nm, followed by the photodegradation of stearic acid layer after successive exposures of 30 min., then 30 min. then 1 hour by measuring the CH bonds of the stretching bands of area₂CH₃ between 3000 and 2700 cm^"1. The photocatalytic activity is defined by the slope, expressed in cm^"1. min^"1From right representing the area of ​​the CH bonds of stretching bands₂CH₃ between 3000 and 2700 cm^"1For a duration between 0 and 2 hours.

p0067Table 1

p0068<img id="imgf000020_0001" he="54" wi="137" file="imgf000020_0001.tif" img-format="tif" img-content="table" orientation="portrait" inline="no" />

p0069Comparative example C1 has no energy supplier layer. The photocatalytic activity is low, but not zero, which probably reflects a slight crystallization during processing. Crystallization is slight because titanium oxide is transparent to the wavelength used and thus absorbs no energy. Comparative Example C2 was coated with a layer of titanium metal but suffered no crystallization treatment. The presence of the titanium surface greatly degrades the photocatalytic activity, which is not measurable. Examples 1 to 4 according to the invention show that the use of an energy supplier layer greatly improves the photocatalytic activity. This result is due to the fact that titanium absorbs the laser radiation and transmits this energy to the titanium oxide which can then reorder and crystallize. In addition, titanium is evaporated and / or largely oxide, since the light transmission after processing is almost as high as before deposition of the overcoat. Lower running speeds under the laser result in higher photocatalytic activities, due to heating of the more intense layer.