EP3362416A1

EP3362416A1 - Method for rapid annealing of a stack of thin layers containing an indium overlay

Info

Publication number: EP3362416A1
Application number: EP16794373.7A
Authority: EP
Inventors: Antoine Diguet; Nicolas MERCADIER; Johann SKOLSKI; Matthieu ORVEN; Camille JOSEPH; Yemima BON SAINT CÖME
Original assignee: Saint Gobain Glass France SAS; Compagnie de Saint Gobain SA
Current assignee: Saint Gobain Glass France SAS
Priority date: 2015-10-16
Filing date: 2016-10-12
Publication date: 2018-08-22
Also published as: WO2017064420A1; US20180305250A1; CO2018004061A2; BR112018007675A2; KR20180066205A; AU2016338962A1; RU2018117903A3; JP2018531872A; MX2018004583A; ZA201802154B; RU2018117903A; CN108137395A; CA2999205A1; FR3042492A1; FR3042492B1

Abstract

The invention relates to a heat treatment method involving irradiating a substrate, comprising a sheet of glass coated on one of the surfaces thereof with a stack of thin layers, in an atmosphere containing oxygen (O₂), with electromagnetic radiation having a wavelength between 500 and 2000 nm, said electromagnetic radiation coming from an emission device placed opposite the stack of thin layers, a relative movement being created between said emission device and said substrate so as to heat the stack of thin layers to a temperature of at least 300°C for a brief period of less than one second, preferably less than 0.1 second. Said method is characterized in that the last layer in the stack, in contact with the atmosphere, referred to as the overlay, is a metal layer of indium or an indium alloy. The invention also relates to a substrate for implementing this method and a substrate obtainable by this method.

Description

METHOD FOR QUICKLY RELEASING A THIN FILM STACK CONTAINING AN INDIUM-BASED OVERCAST

The invention relates to the field of inorganic thin films deposited on glass or plastic substrates. In particular, it relates to a method of rapid surface annealing of thin film stacks after deposition using an overlayer that absorbs electromagnetic radiation.

Many thin mineral layers are deposited on transparent substrates, in particular flat or slightly curved glass, in order to confer on the materials obtained particular properties: optical properties, for example reflection or absorption of radiation of a range of lengths of d given wave, properties of particular electrical conduction, or properties related to the ease of cleaning or the possibility for the material to self-clean.

A method commonly used on an industrial scale for the deposition of thin layers, in particular on glass substrate, is the magnetic field assisted sputtering method, called the "magnetron" process. In this process, a plasma is created under a high vacuum near a target comprising the chemical elements to be deposited. The active species of the plasma, by bombarding the target, tear off said elements, which are deposited on the substrate forming the desired thin layer. This process is called "reactive" when the layer consists of a material resulting from a chemical reaction between the elements torn from the target and the gas contained in the plasma. The major advantage of this method lies in the possibility of depositing on the same line a very complex stack of layers by successively scrolling the substrate under different targets.

During the industrial implementation of the magnetron process, the substrate remains at ambient temperature or undergoes a moderate temperature rise (less than 80 ° C.), particularly when the running speed of the substrate is high, which is generally sought for economic reasons. This moderate temperature, which may at first sight appear to be an advantage, is a disadvantage in the case of above-mentioned layers, because the low deposition temperatures do not generally make it possible to obtain a sufficiently low resistivity. Heat treatments are then necessary to obtain the desired resistivity.

It is known to carry out local and rapid laser annealing (laser flash heating) of thin coatings deposited on flat substrates. For this, the substrate is scanned with the coating to be annealed under a laser line, or a laser line above the substrate carrying the coating (see for example WO2008 / 096089 and WO 2013/156721).

Laser annealing is used to heat thin coatings for a fraction of a second at high temperatures, on the order of several hundred degrees, while preserving the underlying substrate.

It has also been proposed to replace in such a rapid surface annealing process the laser light sources, such as laser diodes, by intense pulsed light (IPL) lamps also called flash lamps. In the international application WO 2013/026817 there is thus proposed a method of manufacturing a low-emission coating comprising a step of depositing a thin layer based on silver, then a step of rapid surface annealing of said layer in the purpose of decreasing its emissivity and increasing its conductivity. For the annealing step, the substrate coated with the silver layer is scrolled under a set of flash lamps downstream of the deposition station of the layer.

For rapid annealing to be effective, the thin film or the stack to be annealed must absorb at least a portion of the electromagnetic radiation used. To overcome insufficient absorption, it has been proposed to deposit on the stack to anneal a "temporary" thin layer having a high absorption of the radiation used. The absorbent thin layer can be removed after treatment, for example by washing, or it can be chosen to become sufficiently transparent after the heat treatment.

In particular WO2010 / 142926 discloses the use of a metal Ti overlay which effectively absorbs infrared radiation and which oxidizes, in contact with the atmosphere and under the influence of heat, in ΤΊΟ2. However, titanium dioxide has several disadvantages: its refractive index is particularly high (of the order of 2.6 at a wavelength of 550 nm) and the presence of a thin layer of T1O2 in the last layer of a low-emissive stack of an insulating glazing can decrease or, conversely, undesirably increase the solar factor g of the glazing. Moreover, the presence of a layer of T1O2 on transparent conductive oxides (TCO), such as ΙΊΤΟ {indium tin oxide), serving as electrodes for photovoltaic cells or electro-optical devices, can reduce the quality of the contacts. electrical and complicate patterning (patterning) of TCO by laser abrasion or chemical etching.

Another absorbent overcoat, already used by the Applicant, is a thin SnZn alloy layer which strongly absorbs infrared radiation and oxidizes in contact with the atmosphere and under the influence of the increase in SnZnO temperature. The thickness of SnZn overlays is however limited to a few nanometers only. For larger thicknesses, sufficient oxidation of the alloy requires either too long radiation exposure times - i.e., low scroll speeds, or extremely high laser powers. In both cases this results in an undesirable increase in production costs related to the annealing step.

The present invention is based on the discovery that indium metal or an indium-based alloy can be used very efficiently as a transient overcoat for rapid annealing of thin-film stacks. This metal, although more expensive than titanium or SnZn alloy, has the advantage of oxidizing more easily than these. This oxidation facility allows the implementation of a surface annealing at much higher speeds of scrolling than for known overlays based on titanium or SnZn.

In addition, when indium is used as an alloy with tin, the oxidation results in ΙΊΤΟ, the most common transparent conductive oxide. Thus, an overcoat of indium tin alloy (InSn) deposited on an ITO layer will melt, after oxidation, with the underlying ITO layer. The structuring ability by chemical etching or laser will not be reduced.

In addition, the refractive index of indium oxide (between 1.4 - 1.5) and that of ΙΤΟ (about 1.8) are lower than that of T1O2. When metal-based overcoats are used for improve the absorbance of a low emissive stack for insulating glass, the presence of a final layer in ln ₂ 0 ₃ or an oxide of an indium alloy, such as ΙΊΤΟ, will have less negative impact on the solar factor than a final layer of ΤΊΟ ₂ .

The subject of the present invention is a thermal treatment method comprising the irradiation of a substrate comprising a transparent sheet, preferably a glass sheet, coated on one of its faces with a stack of thin layers, under an atmosphere containing oxygen (O2), with electromagnetic radiation having a wavelength between 500 and 2000 nm, said electromagnetic radiation being derived from a transmitter device placed opposite the stack of thin layers, a relative displacement being created between said emitter device and said substrate so as to bring the stack of thin layers to a temperature of at least 300 ° C for a short duration of less than one second, preferably less than 0.1 seconds, said method being characterized by the fact that the last layer of the stack, in contact with the atmosphere, called overcoat, is an indium layer or an alloy e based on indium.

The present application also relates to a substrate for the implementation of such a method. This substrate comprises a transparent sheet, preferably a glass sheet, coated on one of its faces with a stack of thin layers, the last layer, in contact with the atmosphere, called overcoat, is a layer of indium or an alloy based on indium, preferably an alloy of indium and tin (InSn).

Finally, the present application relates to a substrate that can be obtained by a process as defined above and defined in more detail below.

The term "indium-based alloy" in the present application means an alloy containing a majority of indium atoms, that is to say more than 50% of atoms relative to the totality of the metal atoms of the alloy. .

Preferably, an indium alloy containing more than 60%, in particular more than 70% and even more preferably more than 80% of indium atoms, will be used relative to all the metal atoms of the alloy. The indium overcoat or indium-based alloy is a metal layer. This term encompasses in this application the layers where all the atoms are in the zero oxidation state but also the weakly oxidized layers. Indeed, it is very difficult, if not impossible to perform a sputter deposition in the total absence of oxygen which is always present in the trace state. Moreover, the metal overcoat, when left in the open air after deposition for several hours, or even days, gradually changes in appearance, probably following oxidation on the surface. Finally, the Applicant has found that the presence of small amounts of oxygen (up to about 5 mol%) introduced into the plasma during the deposition does not affect the effectiveness of the overcoat.

The term "metal overlay" therefore encompasses in the present application overlays containing up to 10% oxygen atoms based on the total amount of metal atoms and oxygen.

It is impossible to indicate the actual thickness of the metal overcoat of indium or indium alloy. Indeed, indium and some indium alloys have a relatively low melting point and there is probably a phenomenon of dewetting of thin solid films, widely described in the literature especially for thin films of gold or silver. money. The indium overlay or indium-based alloy is therefore not a continuous layer of uniform thickness but consists of rounded elements having submicron dimensions. The analysis by atomic force microscopy (AFM) carried out on the overcoats, before and after heat treatment, revealed that these relief elements have a shape in "sugar loaf" (peaks of substantially parabolic shape). The Applicant has found that this characteristic shape of the surface elements of the overcoat is retained after heat treatment and therefore constitutes a marker of the substrate before heat treatment but also of the substrate obtained by the process according to the invention. The diameter of these relief elements, seen from above, is of the order of a few tens of nanometers, generally between 10 and 200 nm.

The parameter allowing to characterize most clearly and directly the quantity of deposited material seems to be the surface density of the overlay. So that this surface mass is independent of the rate oxidation, it will be expressed as the mass of all the metal atoms (indium and alloyed metals) per unit area. This surface mass does not vary in principle significantly during the rapid annealing process and is also found in principle in the final product after annealing.

This surface mass can be determined by microanalysis using an electron microprobe or a Castaing microprobe, for example a "SX Five" model microprobe from Cameca (15 kV, mode line, at 150 nA, on the elements and lines: In-La and Sn-La). If necessary, this microanalysis by electron microprobe can be coupled to a SIMS secondary ionization mass spectrometry analysis.

This surface mass can then be used to calculate what could be called an "equivalent thickness of the metal overlay", dividing it by the density of the material. A pure indium layer with a surface density of 10 g / cm ² having a theoretical density of 7.31 g / cm ³ would thus have an equivalent thickness of 13.7 nm. This equivalent thickness does not, however, take into account the increase in the actual thickness of the overlayer due to possible oxidation, partial or total.

The surface weight of the overcoat, expressed as the mass of metal atoms per unit area, is advantageously between 1 and 30 μg cm ² , preferably between 3 and 25 μg / cm ² and in particular between 4 and 15 μς / ιη ² .

The heat treatment according to the invention results in an oxidation of the surface layer and thus modifies the fraction of metal atoms in the overlay. It is important to note, however, that the heat treatment does not modify the amount of metal atoms per unit area of the overlayer and the above-mentioned weight per unit weight ranges are therefore valid for the overlayer before and after heat treatment according to invention.

Indium can be alloyed with one or more other metals. The metal or metals and their atomic proportion in the alloy must be chosen so that, after total oxidation, the absorption of the overlayer is negligible compared with the absorption of the initial alloy in the metallic state. . Nonlimiting examples of such Al, Ga, Ge, Zn, Ti, Sn, Bi, Pb, Ad, Ag, Cu and Ni alloy metals may be mentioned.

In particular, tin (Sn) will be used in a proportion of between 5 and 30%, in particular between 8 and 20% by weight. In a particularly preferred embodiment, illustrated hereinafter in the examples, the overlayer is a layer of an alloy of indium and tin (InSn), in particular an alloy containing approximately 90% of indium atoms. and 10% tin atoms.

The process according to the invention is particularly advantageous for the manufacture of glass sheets intended for the manufacture of insulating glass units. These glass sheets carry on their surface a stack of thin layers, called "low emissivity" (in English low emissivity or low e) comprising at least one metal layer reflecting the infrared radiation, preferably a silver layer, between two dielectric layers.

Such low emissivity stacks are known in the art. They may comprise a single layer of silver or several layers of silver, for example two or three layers of silver.

Glass sheets with stacks comprising a single layer of silver are marketed by the Applicant, for example under the names Planitherm ^® One.

In general, the stack of thin films subjected to rapid annealing according to the invention preferably has at least one electroconductive layer other than the overlayer in contact with the atmosphere. This electroconductive layer may be a metal layer, for example a silver layer as mentioned above, or a layer of a transparent conductive oxide.

In one embodiment of the method of the present invention, the penultimate layer of the stack of thin layers, that is to say that located directly under the indium-based overcoat in contact with the atmosphere , is a layer of indium oxide and tin (ITO). This embodiment is particularly advantageous when the overlayer is InSn alloy, because the thickness of the ITO layer formed by oxidation of the overcoat adds to that of the underlying ITO layer and therefore decreases the resistance per square (RD) of it.

In another embodiment, the thin film stack comprises a metallic functional layer, in particular based on silver, placed between two antireflection coatings each comprising at least one dielectric layer. The antireflection coating between the indium-based overcoat and the functional layer preferably comprises a silicon nitride layer, of a thickness between about 10 and 50 nm, directly in contact with the overlayer, and a layer of a metal oxide having a refractive index between 2.3 and 2.7 and preferably having a thickness of between 5 and 15 nm, directly in contact with the silicon nitride layer.

The process according to the invention is preferably carried out under conditions such that the step of rapid thermal treatment by irradiation results in a reduction in the square resistance and / or emissivity of the thin film stack from minus 15%, preferably at least 20%. This reduction of course includes that resulting from the contribution of the oxidized overcoat to the conductivity of the total stack.

According to a preferred embodiment, the electromagnetic radiation is laser radiation, in other words the emitting device is a laser, preferably a laser emitting a focused laser beam at the plane of the overlay, in the form of a laser line irradiating simultaneously all or part of the width of the substrate, preferably the entire width of the substrate.

The laser radiation is preferably generated by modules comprising one or more laser sources as well as optical shaping and redirection.

The laser sources are typically laser diodes or fiber lasers, including fiber, diode or disk lasers. The laser diodes make it possible to economically achieve high power densities with respect to the electric power supply, for a small space requirement. The size of the fiber lasers is even smaller, and the linear power obtained can be even higher, but at a higher cost. Fiber lasers are lasers in which the locus of laser light generation is spatially offset from its delivery location, the laser light being delivered by means of at least one optical fiber. In the case of a disk laser, the laser light is generated in a resonant cavity in which is located the emitter medium which is in the form of a disk, for example a thin disk (about 0.1 mm thick) in Yb: YAG. The light thus generated is coupled in at least one optical fiber directed towards the place of treatment. Fiber or disk lasers are preferably pumped optically by means of laser diodes.

The radiation from the laser sources is preferably continuous. The wavelength of the laser radiation is preferably in a range from 900 to 1100 nm, in particular from 950 to 1050 nm.

In the case of a disk laser, the wavelength is, for example, 1030 nm (emission wavelength for a Yb: YAG laser). For a fiber laser, the wavelength is typically 1070 nm.

In the case of non-fiber lasers, the shaping and redirecting optics preferably comprise lenses and mirrors, and are used as means for positioning, homogenization and focusing of the radiation.

The positioning means are intended to arrange the radiation emitted by the laser sources along a line. They preferably include mirrors.

The aim of the homogenization means is to superpose the spatial profiles of the laser sources in order to obtain a homogeneous linear power along the line. The homogenization means preferably comprise lenses enabling the incident beams to be separated into secondary beams and the recombination of said secondary beams into a homogeneous line.

The means for focusing the radiation make it possible to focus the radiation on the stack of thin layers to be treated, and more particularly on the absorbent overlayer, in the form of a line of desired length and width. The focusing means preferably comprise a focusing mirror or a converging lens. In the case of fiber lasers, the shaping optics are preferably grouped in the form of an optical head positioned at the output of the optical fiber or each optical fiber.

The optical shaping of said optical heads preferably comprise lenses, mirrors and prisms and are used as means of transformation, homogenization and focusing of the radiation.

The transformation means comprise mirrors and / or prisms and serve to transform the circular beam, obtained at the output of the optical fiber, into a non-circular, anisotropic, line-shaped beam. For this, the transformation means increase the quality of the beam along one of its axes (fast axis, or axis of the width I of the laser line) and reduce the quality of the beam according to the other (slow axis, or axis of the length L of the laser line).

The homogenization means superimpose the spatial profiles of the laser sources in order to obtain a homogeneous linear power along the line. The homogenization means preferably comprise lenses enabling the incident beams to be separated into secondary beams and the recombination of said secondary beams into a homogeneous line.

Finally, the means for focusing the radiation make it possible to focus the radiation at the level of the working plane, that is to say in the plane of the thin-film stack to be treated, in the form of a line of length and of desired width. The focusing means preferably comprise a focusing mirror or a converging lens.

When only one laser line is used, the length of the line is advantageously equal to the width of the substrate. This length is typically at least 1 m, especially at least 2 m and in particular at least 3 m. It is also possible to use several lines, disjointed or not, but arranged so as to treat the entire width of the substrate. In this case, the length of each laser line is preferably at least 10 cm, preferably at least 20 cm, in particular in a range from 30 to 100 cm, preferably from 30 to 75 cm, in particular from 30 to 60 cm.

The term "length" of the line means the largest dimension of the line, measured at the surface of the stack of thin layers, and by "width" the dimension in a second direction perpendicular to the first. As is usual in the field of lasers, the width (w) of the line corresponds to the distance, in this second direction, between the beam axis where the intensity of the radiation is maximum and the point where the Radiation intensity is equal to 1 / e ² times the maximum intensity.

The average width of a laser line is preferably at least 35 μm, especially in a range from 40 to 100 μm, in particular from 40 to 70 μm. Throughout this text we mean by "average" the arithmetic mean. Over the entire length of the line, the distribution of widths is narrow in order to limit as much as possible any heterogeneity of treatment. Thus, the difference between the largest width and the smallest width is preferably at most 10% of the average width value. This figure is preferably at most 5%.

The formatting and redirection optics, in particular the positioning means, can be adjusted manually or using actuators to adjust their positioning remotely. These actuators, typically motors or piezoelectric shims, can be manually controlled and / or adjusted automatically. In the latter case, the actuators will preferably be connected to detectors as well as to a feedback loop.

At least a portion of the laser modules, or all of them, is preferably arranged in a sealed box, advantageously cooled, in particular ventilated, in order to ensure their thermal stability.

Laser modules are preferably mounted on a rigid structure, called "bridge", based on metal elements, typically aluminum. The structure preferably does not include a marble slab. The bridge is preferably positioned parallel to the conveying means so that the focal plane of the laser line remains parallel to the surface of the substrate to be treated. Preferably, the bridge comprises at least four feet, the height of which can be individually adjusted to ensure parallel positioning under all circumstances. The adjustment can be provided by motors located at each foot, either manually or automatically, in relation to a distance sensor. The height of the bridge can be adapted (manually or automatically) to take into account the thickness of the substrate to be treated, and thus ensure that the plane of the substrate coincides with the focal plane of the laser line.

The linear power of the laser line is advantageously at least 300 W / cm, preferably at least 400 W / cm, in particular at least 500 W / cm. It is even advantageously at least 600 W / cm, especially 800 W / cm or 1000 W / cm. The linear power is measured at the focusing plane of the laser line, that is to say at the plane of the thin-film stack, also called the work plane of the installation.

It can be measured by placing a power detector along the line, for example a power-meter calorimetric, such as in particular the power meter Beam Finder S / N 2000716 Cohérent Inc. The power is advantageously distributed in a manner homogeneous along the entire length of the laser line. Preferably, the difference between the highest power and the lowest power is less than 10% of the average power.

The energy density supplied to the stack of thin layers by the laser device is preferably between 20 J / cm ² and 500 J / cm ² , in particular between 50 J / cm ² and 400 J / cm ² .

According to another preferred embodiment, the device emitting electromagnetic radiation is an intense pulsed light (IPL) lamp, hereinafter referred to as a flash lamp.

Such flash lamps are generally in the form of glass or quartz tubes sealed and filled with a rare gas, provided with electrodes at their ends. Under the effect of a short-term electrical pulse, obtained by discharging a capacitor, the gas ionizes and produces a particularly intense incoherent light. The emission spectrum generally comprises at least two emission lines; it is preferably a continuous spectrum having a maximum emission in the near ultraviolet.

The lamp is preferably a xenon lamp. It can also be a lamp with argon, helium or krypton. The emission spectrum preferably comprises several lines, especially at wavelengths ranging from 160 to 1000 nm. The duration of each light pulse is preferably in a range from 0.05 to 20 milliseconds, in particular from 0.1 to 5 milliseconds. The repetition rate is preferably in a range from 0.1 to 5 Hz, in particular from 0.2 to 2 Hz.

The radiation may be from several lamps arranged side by side, for example 5 to 20 lamps, or 8 to 15 lamps, so as to simultaneously treat a wider area. In this case, all lamps can emit flashes simultaneously.

The lamp is preferably arranged transversely to the longer sides of the substrate. The lamp has a length preferably of at least 1 m in particular 2 m and even 3 m so as to be able to process large substrates.

The capacitor is typically charged at a voltage of 500 V to 500 kV. The current density is preferably at least 4000 A / cm ² . The total energy density emitted by the flash lamps, relative to the surface of the treated stack, is preferably between 1 and 100 J / cm ² , in particular between 1 and 30 J / cm ² , or even between 5 and 20 J / cm ² .

The high power densities and densities make it possible to heat the thin film stack very quickly at high temperatures.

During the process according to the invention each point of the stack is preferably heated to a temperature of at least 300 ° C., in particular 350 ° C. or even 400 ° C., and even 500 ° C. or 600 ° C. The maximum temperature is normally reached when the point of the stack considered passes under the radiation device, for example under the laser line or under the flash lamp. At a given moment, only the points of the surface of the stack located under the radiation device, for example under the laser line, and in its immediate vicinity are normally at a temperature of at least 300 ° C. For laser line distances greater than 2 mm, especially 5 mm, including downstream of the laser line, the stack temperature is normally at most 50 ° C, and even at 40 ° C or above. 30 ° C.

Each point of the stack is brought to the maximum temperature of the heat treatment for a time advantageously in a range from 0.05 to 10 milliseconds, in particular from 0.1 to 5 milliseconds, or from 0.1 to 2 milliseconds. In the case of treatment with By means of a laser line, this time is fixed both by the width of the laser line and by the relative speed of displacement between the substrate and the laser line. In the case of a flash lamp treatment, this duration corresponds to the duration of the flash.

The flash lamp device can be installed inside the vacuum deposition system or outside in a controlled atmosphere or in ambient air.

The laser radiation is partly reflected by the stack to be processed and partly transmitted through the substrate. For safety reasons, it is preferable to have in the path of these reflected and / or transmitted radiation means for stopping the radiation. This will typically metal housings cooled by fluid circulation, including water. In order to prevent the reflected radiation from damaging the laser modules, the propagation axis of the or each laser line forms an angle that is preferentially non-zero with the normal to the substrate, typically an angle of between 5 and 20 °.

When the substrate is moving, in particular in translation, it can be set in motion by any mechanical conveying means, for example using strips, rollers, trays in translation. The conveying means preferably comprises a rigid frame and a plurality of rollers. The pitch of the rollers is advantageously in a range from 50 to 300 mm. The rollers preferably comprise metal rings, typically made of steel, covered with plastic bandages. The rollers are preferably mounted on low-clearance bearings, typically three rolls per step. In order to ensure perfect flatness of the conveying plane, the positioning of each of the rollers is advantageously adjustable. The rollers are preferably driven by means of pinions or chains, preferably tangential chains, driven by at least one motor.

The speed of the relative displacement movement between the substrate and each radiation source is advantageously at least 2 m / min or 4 m / min, in particular 5 m / min and even 6 m / min or 7 m / min, or 8 m / min and even 9 m / min or 10 m / min. According to some embodiments, in particular when the radiation absorption by the stack is high or when the stack can be deposited with high deposition rates, the speed of the relative displacement movement between the substrate and the source of the radiation is at least 12 m / min or 15 m / min, especially 20 m / min and even 25 or 30 m / min. In order to ensure a treatment that is as homogeneous as possible, the speed of the relative displacement movement between the substrate and each radiation source varies during the treatment by at most 10% in relative, in particular 2% and even 1% relative to at its nominal value.

Preferably, the radiation source is fixed, and the substrate is in motion, so that the relative displacement velocities will correspond to the running speed of the substrate.

Another advantage of using a metal indium overlay or an indium alloy resides in the excellent optical homogeneity of the treated substrates.

When dealing with large substrates carrying stacks of thin layers, by scrolling rapidly under a laser line, we often note an optical defect called "lineage". The lineage corresponds to a lack of homogeneity of treatment. When the laser line under which the substrate bearing the layer to be annealed is not perfectly smooth, for example when its thickness or its linear power is not strictly the same all along the laser line, it is forms visible defects as lines parallel to the running direction (longitudinal lineage). There is also a transversal lineage (perpendicular to the scroll direction) that is due to irregularities of scroll speed.

As will be shown hereinafter in the examples, the lineage of annealed substrates according to the invention is less pronounced than that observed with absorbent overcoats of metallic Ti or SnZn.

As indicated above, the subject of the present invention is also a substrate that can be obtained by the process according to the invention. This substrate has, as the last layer of the stack of thin layers, a layer of indium oxide or mixed oxide of indium and another metal. This layer is both very thin and has a characteristic surface relief formed by parabolic peaks ("sugar loaf").

This surface relief is in particular very different from that of a layer of ITO deposited by sputtering magnetron cathode which presents generally a mean square deviation (R _a ) less than 1 nm, or even less than 0.5 nm, and which lacks such characteristic elements.

FIG. 3 shows an atomic force microscopy image of the surface of an oxide overcoat oxidized to ITO (indium tin oxide) after heat treatment. There are rounded grains juxtaposed. The roughness profile of this surface, shown in Figure 4, shows that each of these grains corresponds to a peak having a substantially parabolic shape.

In one embodiment, the substrate obtained by the process according to the invention comprises an unhardened glass sheet coated on one of its faces with a stack of thin layers comprising a thin layer of silver between two thin dielectric layers, the last layer of the stack of thin layers, in contact with the atmosphere, being a layer of indium oxide or indium tin oxide (ITO) with a weight per unit area, expressed as the mass of metal atoms per unit area, comprised between 1 and 30 μg / cm ² , preferably between 3 and 25 μg / cm ² .

The layer of indium oxide or indium tin oxide (ITO) has a surface relief with a mean square deviation (Ra) (determined by atomic force microscopy (AFM) on a surface of 1 μιτι ² ) between 1 and 5 nm, the majority of relief elements having a shape in "sugar loaf".

The following examples show the absorption efficiency of a laser radiation of an indium-based metal overlay, in comparison with a metal titanium overlay (Example 1) and a metal SnZn overlay ( Examples 2 and 3).

Example 1

A thin film of ITO with a thickness of about 23 nm is deposited on a Planilux glass sheet with a thickness of 2 mm by magnetron sputtering from a ceramic target.

On two sets of samples of this sheet of glass are then deposited respectively the following metal overlays:

a 4 nm layer of titanium (comparative example) and an InSn layer (90/10) (example according to the invention) having an equivalent thickness of approximately 5 nm.

Before heat treatment both sets of samples have a square resistance (RD) of about 400 Ohm / a and a light absorbance of about 20%.

The two series of samples are subjected to laser annealing by means of a diode laser emitting laser radiation in the form of a focused line at the coating to be annealed:

- radiation wavelength: 915 + 980 nm

- linear power: 49 W / mm

- width of the line at the focal plane level: 45 μιτι

- length of the line: 30 cm

The samples are run at different speeds under this laser device, then the absorbance of the visible light is measured and the percentage of the RD value is reduced in relation to the initial value.

The results are summarized in Table 1 below

Table 1

It can be seen that the gains in conductivity obtained with the InSn overlay according to the invention are greater than those obtained with the titanium overlay according to the state of the art. The conductivity gain obtained for a sample according to the invention at a speed of 6 m / min is thus more high (65%) than that obtained at a speed of only 3 m / min for a sample with an overcoat of titanium (62%).

These results show that a titanium overlay, oxidizing to T1O2, can advantageously be replaced by an InSn overcoat which gives, after oxidation, ITO.

The samples according to the invention thus have a single layer of ITO and are advantageously free of a high-index surc2 overlayer which can adversely modify the solar factor of a glazing unit.

Example 2

All the tests are carried out on a glazing formed by a sheet of Planiclear® glass bearing on one of its faces a low emissive stack consisting of the following successive layers:

If ₃ N ₄ (30 nm)

T1O2 (12 nm)

ZnO (4 nm)

Ti (0.4 nm)

Ag (13.5 nm)

ZnO (4 nm)

Ti0 ₂ (24 nm)

Planiclear (4 mm)

Four samples are prepared which differ by the magnetron sputter absorbent overcoat prior to laser treatment.

Sample 1 (comparative): 2 nm of ΤΊΟ2

Sample 2 (comparative): 3 nm Sn _x Zn _(i-x) (x = 0.35)

Sample 3 (according to the invention): 2.8 nm InSn

Sample 4 (according to the invention): 8.4 nm InSn

The four samples were subjected to a heat treatment by a laser line with a linear power of 25 W / mm (wavelength 915 nm and 980 nm, width of the line at the focal plane 45 μηη, length of the line 30 cm). Table 2 below shows the running speeds of the substrates, visible absorption before and after laser treatment and square resistance before and after laser treatment.

Table 2

It is found that the four samples have, after heat treatment, absorption and resistance values per square approximately equivalent. For sample 4 carrying an InSn absorbent layer of 8.4 nm, however, these results could be obtained with a processing speed three times greater than that used for the SnZn absorbent layer of the state of the art (sample 2 ).

Moreover, it is clearly seen in the last column of the table that the "lineage" of the samples treated according to the invention is significantly less visible than that of the comparative samples.

The visibility of the lineage is evaluated by an operator with the naked eye according to the following notation system:

- score 1 is awarded when no inhomogeneity is perceptible to the eye,

- score 2 is awarded when localized inhomogeneities, limited to certain areas of the sample, are perceptible to the eye under intense diffuse illumination (> 800 lux),

- score 3 is awarded when localized inhomogeneities limited to certain areas of the sample are perceptible to the eye under standard illumination (<500 lux) and Note 4 is assigned when inhomogeneities throughout the entire surface of the sample are perceptible to the eye under standard illumination (<500 lux). Example 3

Two series of Planitherm samples are prepared which differ in the absorbing overlayer used:

Series 1 (according to the invention): InSn 8.4 nm

Series 2 (comparative): SnZn 5 nm

The light absorption of the two sets of samples before laser treatment is about 35%.

The samples of each series are subjected to a heat treatment, at different running speeds, under a laser line having the same characteristics as in Example 2.

FIG. 1 shows the evolution of the visible light absorption (in%) of the samples after laser treatment as a function of the running speed of the substrate.

It can be seen that at low speed (less than 10 m / minute) the light absorption of the samples of the two series is approximately equivalent (approximately 5 - 10%). As the speed of travel increases, the difference in absorption between the two series increases: the samples according to the invention retain a relatively low absorption (less than 10%) even at high scrolling speed (30%). m / min), whereas for samples using SnZn overlay, the absorption increases strongly with the rate of treatment.

FIG. 2 shows the evolution of the conductivity gain after heat treatment as a function of the running speed of the substrate. The conductivity gain is defined as the difference between the initial R & D (before heat treatment) and the final R & D (after heat treatment) relative to the initial R & D.

Gain (%) = (Rainfall - Rafinal) / Rainitiale

It can be seen that at low speed, up to about 15 meters per minute, the gain in conductivity is approximately equivalent for the two sets of samples, of the order of 20%. On the other hand at a speed of 30 meters per minute scroll, the conductivity gain after heat treatment is twice as large for the samples carrying an InSn overlay according to the invention than those carrying a comparative overlay SnZn.

Claims

1. A thermal treatment process comprising irradiating a substrate comprising a transparent sheet, preferably a glass sheet, coated on one of its faces with a stack of thin layers under an atmosphere containing oxygen (O ₂ ) with electromagnetic radiation having a wavelength between 500 and 2000 nm, said electromagnetic radiation being derived from a transmitting device placed opposite the stack of thin layers, a relative displacement being created between said transmitting device and said substrate so as to bring the stack of thin layers to a temperature of at least 300 ° C for a short duration of less than one second, preferably less than 0.1 seconds,

said method being characterized in that the last layer of the stack, in contact with the atmosphere, called overcoat, is a metal layer of indium or an indium-based alloy.

2. Method according to claim 1, characterized in that the surface weight of the overcoat, expressed as the mass of metal atoms per unit area, is between 1 and 30 μg / cm ² , preferably between 3 and 25 pg / cm ² .

3. Method according to one of the preceding claims, characterized in that the overlayer is a layer of an indium-based alloy containing more than 70% indium atoms, preferably more than 80% of indium. Indium atoms referred to all the metal atoms of the alloy.

4. Method according to one of the preceding claims, characterized in that the overlayer is a layer of an alloy of indium and tin (InSn), in particular an alloy containing about 90% of indium atoms and 10% tin atoms.

5. Method according to any one of the preceding claims, characterized in that the stack of thin layers has at least one electroconductive layer other than the overlayer in contact with the atmosphere, this electroconductive layer being a metal layer or a layer of a transparent conductive oxide.

6. Method according to claim 5, characterized in that the stack of thin layers is a low-emissivity stack comprising at least one metal layer reflecting infrared radiation, preferably a silver layer, between two dielectric layers.

7. Method according to any one of the preceding claims, characterized in that the penultimate layer of the stack of thin layers, located directly under the overlay in contact with the atmosphere, is a layer of indium and tin (ITO).

8. Method according to one of claims 5 to 7, characterized in that the heat treatment causes a reduction of the resistance per square and / or the emissivity of the stack of thin layers by at least 15%, preferably at least 20%.

9. Method according to any one of the preceding claims, characterized in that the electromagnetic radiation is laser radiation.

10. Method according to the preceding claim, characterized in that the wavelength of the laser radiation is between 900 and

1100 nm, preferably between 950 and 1050 nm.

1 1. Method according to claim 10, characterized in that the laser radiation is a focused laser beam at the plane of the overlay in the form of a laser line simultaneously radiating all or part of the width of the substrate, preferably the entire width of the substrate.

12. Method according to any one of claims 1 to 8, characterized in that the device emitting electromagnetic radiation is a flash lamp.

13. Substrate for carrying out a process according to any one of the preceding claims, comprising a transparent sheet, preferably a glass sheet, coated on one of its faces. a stack of thin layers, characterized in that the last layer of the stack, in contact with the atmosphere, called overcoat (overcoat), is an indium layer or an indium-based alloy preferably an alloy of indium and tin (InSn).

14. Substrate obtainable by a method according to any one of claims 1 to 12, comprising an unhardened glass sheet coated on one of its faces with a thin film stack comprising a thin layer of silver between two thin dielectric layers, characterized in that the last layer of the stack of thin layers, in contact with the atmosphere, is a layer of indium oxide or indium tin oxide (ITO ) with a mass per unit area, expressed as the mass of metal atoms per unit area, of between 1 and 30 μg / cm ² , preferably between 3 and 25 μς / αη ² .

15. Substrate according to claim 14, characterized in that the indium oxide or indium tin oxide (ITO) layer has a surface relief with a mean square deviation (Ra), determined by atomic force microscopy (AFM), between 1 and 5 nm, the majority of relief elements having a parabolic peak shape.