Process for the treatment of metal oxide or nitride thin films

The invention relates to a method of treating thin layers based on one or more oxides, nitrides, oxynitrides or metal oxycarbides (s), and more particularly those deposited on a transparent substrate, especially glass using a technique using the empty, directly or through other layers.

The invention also relates to the application of this process to the manufacture of glazings.

Indeed, for the manufacture of self-glazing "Functional" is usually deposited on at least one of substrates composing them a thin layer or a stack of thin layers in order to impart to said glazing optical properties, for example anti-reflective, properties in the infrared (low-emissivity) and / or electrical conductivity properties. Layers in composed of oxide and / or metal nitride are then very frequently used, for example as dielectric from either side of a low-emissive layer-type layer silver or doped metal oxide layer; or as interference layer stacks in alternating oxides or nitrides at low and high refractive indices.

This raises the problem of chemical durability and / or physical these layers or stacks of layers, problem even more crucial that the coated substrate is for use as monolithic glazing, the or the layers being directly exposed to aggressions the ambient atmosphere. Even when the substrate is intended to be part of a multiple glazing unit (double glazing, glazing laminated), the layers are subjected to aggressions due to various manipulations during manufacture the glazing.

It is known, including the publication "Ion-based methods for Optical Thin Film Deposition "(Journal of Material science; JP Martin, 21 (1986) 1-25), a technique called experimental IAD (Ion-Assisted Deposition) or assistance in filing ion beam, which allows change the thin oxide layer structure. This technique is to perform the deposition of the layer by an evaporation technique while subjecting the layer, throughout its filing, the oxygen ion bombardment or argon, which allows to increase the compactness and adhesion to the carrier substrate, a phenomenon yet not completely understood. However, this type of assisted deposition is very complex embodiment, and in fact it is not applicable to substrates of very small dimensions, saw the problems particularly in terms of convergence between on the one hand the ion beam and on the other hand the particles produced by evaporation from a source highly localized, which build the layer on the substrate.

It is also known from the patent application EP-A-0328257 an oxide layer deposition technique sputter whose purpose is to accelerate deposition rates by proceeding as follows: initially is deposited a metal layer from suitable metal target in an atmosphere inert then the metal layer is converted to a metal oxide layer by subjecting it to a source ion capable of generating a plasma oxidizing ions. Said ion source is here responsible for processing chemical oxidation, the intended use aimed primarily optical glasses and not the glass.

The invention is therefore to the development of a layer processing method based on one or more oxides, nitrides, oxynitrides or oxycarbides, for make them more resistant chemically and / or physically, overcoming treatment the aforementioned drawbacks, that is to say which can be made regardless of the size of the substrate and on an industrial scale.

The object of the invention is a diaper processing method of one or several oxides, nitrides, oxynitrides or metal oxycarbides deposited on a transparent substrate, notably of glass by a sputtering technique cathode, in particular assisted by magnetic field and preferably reactive with oxygen and / or nitrogen. The method includes effect deposition of the layer and to forward the deposit by at least one step treatment by ion beam. This step involves subjecting the layer and filed an ion beam "low energy", that is to say energy less than or equal to 500 eV when they impact on the film to be treated.

Is understood in the context of the invention the term ion beam "to low energy "as a beam whose parameters are chosen to minimize spraying of the layer formed under the impact of ion beam. This notion is of course to be considered according to the intrinsic sputtering rate for given material.

The treatment according to the invention can significantly increase the physical durability and / or chemical of these layers, which seems to be explained at once by a densification of the layers, which can result specifically by an increase in their refractive index and by a some "smoothing" the surface, layers treated according to the invention having including a lower surface roughness than standard layers deposited by sputtering. This latter feature can thus further advantageously promote a better grip and a better "Topping" of a subsequently deposited layer on the layer thus treated.

Thus, and surprisingly, the authors of the invention are achieved to the aim using a deposition technique, sputtering CRT, perfectly adapted to industrial requirements of a manufacturing mass glazing of all sizes, combining treatment there ion beam. Can be "cut" completely the step of depositing and of the treatment by ion beam. This dissociation and removes all problems in assisted deposition techniques and makes the easy method of implementation to the extent that the deposit is made by a proven industrial technology and where treatment with ion beam can be consecutively deposit in the same facility.

A preferred embodiment of the invention consists in carrying out the depositing the layer sequentially, and to take at least a the steps of sequentially depositing at least one treatment step the ion beam. Advantageously, it is thus alternate systematically sequential deposition and ion beam treatment. We may choose to deposit the layer by a succession of deposits sequential, preferably from 5 to 30 nanometers, particularly 15 to 20 nanometers, when the desired final thickness is of the order of at least 30 nanometers; or of the order of 5 nanometers when the thickness desired end is less important, these deposits are sequential alternated with a treatment by ion beam. In this way, one can optimize the efficiency of the ion beam and at best densify the layer. Indeed, one can then make all possible compromises in terms especially thick deposited in each deposit and sequential adjustment of the beam, depending on the nature of the layer to its final thickness, its physical and performance mechanical properties, and according to industrial requirements. In Typically, the length of each treatment by ion beam is preferably less than 30 minutes, in particular between 1 and 10 minutes.

Furthermore, it improves the adhesion between coating and substrate if is carried out before any deposition, a pre-treatment of subjecting the bare substrate to the ion beam.

The characteristics of the ion beam are of course important. It is preferred, in the case of oxide deposition, oxynitride or oxycarbide, use a beam to least some of the ions are of an oxidizing nature, such as of ionized oxygen. But at least part of the ions can also be for example argon ion or nitrogen ionised, especially in the case of deposition of nitrides.

The energy of said beam "low energy" as already mentioned, must be low enough not to spray so too much the treated layer, while being high enough so that under the impact of the ions, the layer is actually made stronger. The value Energy is further adapted according to the thickness of the layer which is struck by the ion beam and easy to pulverize the material with which it is desired make a layer. In practice, it is preferred values ion energy at their impact on the film, which are less than or equal to 500 electron-volts, including less than or equal to 200 eV, for example between 200 and 50 ev, as of the order of 80 or 100 ev

Similarly, the ion density of the ion beam is of preferably set to be of the order of one to few milliamps per cm².

The method of the invention applies in particular to titanium oxide or tantalum layers, the layers zinc oxide or tin oxide or nitride silicon, titanium nitride.

The invention also relates to the device of implementation of this method, said device being provided at least one cathode, equipped with a suitable target and at least one source of ions as a beam gun ions or in the same sputtering chamber or in two separate enclosures. In the case of pregnant distinct, then we can choose in each of the enclosures, and pressure conditions of atmospheric composition slightly different or identical.

The substrate may be movably mounted relative to the target and barrel so as to be consecutively covered with a layer thin by sputtering of the target and then treated with the beam generated by the beam source. A plant for carrying out the invention comprises Thus, for example, an enclosure in which are arranged alternately cathodes and ion guns, so that the substrate to be treated moves linearly, successively and horizontally in front of said devices.

The invention also relates to the layers thus obtained, with a cure or greater durability, and / or larger and / or a lower density than the layers roughness deposited by sputtering single particular.

These layers can thus be used for the manufacture of glazing.

Other details and advantageous features of the invention apparent from the following description of embodiments not limiting, with the aid of Figures 1 and 2, to evaluate Performance layers obtained using the following two tests described, as well as Figures 3 and 4 which give spectroscopy mass structure of a layer treated according to the invention.

All involve the sequential deposition of a thin layer based titanium oxide, tantalum oxide, tin oxide or silicon oxide, on a clear glass substrate soda-lime dimensions of 15 x 10 cm² at using a sputtering device assisted by field magnetic and in a reactive atmosphere comprising oxygen. The target to be sprayed are respectively titanium, tantalum, tin or doped silicon, the cathode has a vertical length of 210 mm and a width of 90 mm. The glass substrate is vertically movable as fixed on carousel, thereby alternately perform the deposition by sputtering of the target and treat with beam ion the deposited layer beam generated by a gun ions disposed on an axis perpendicular to the substrate and marketed under the name of Commenwealth Mark II by the company Commenwealth Scientific. This type of gun emits in the present case an oxygen ion beam the ionic density, measured at 15 cm from the source emission is about 1.2 mA / cm². During processing, the substrate is about 14 cm away from the point beam emission.

In the following examples, is carried out, before all deposition, a pre-treatment of the substrate by subjecting the for 1 minute in the oxygen ion beam, in a energy less than or equal to 60 eV and an ion density of at least 0.7 mA / cm².

To evaluate the chemical and physical durability layers treated according to the invention, they were submitted, at least in the first instance, two types of test: the test said "Taber" is the test for to assess the abrasion resistance of the layer. It is done with wheels made of abrasive powder embedded in an elastomer. The machine is manufactured by the Company Taber Instrument Corporation in the United States. It's about model 174 "Standard Abrasion Tester", the wheels are Type CS10F loaded with 500 grams. The layer is subjected to 650 rotations. We measure its abrasion to the gradual reduction its light reflection R_L at a wavelength 550 nm.

The test called "test HCl" consists of immersing the substrate coated in an aqueous solution of HCl of a concentration 1 mol / liter and heated to 100 ° C until degradation layer ; Also resulting in a reduction of R_L.

Some of the results of these tests are included in the accompanying figures.

Moreover, the surface state of the layers was analyzed by atomic force microscopy. Were evaluable and their roughness, measured by the value of the squared difference medium (called "Root Mean Square" or RMS in English) on a surface of one square micrometer and expressed in angstroms.

EXAMPLE 1

The pretreatment of the substrate is carried out using the beam at an energy of 60 eV and an ion density 0.7 mA / cm².

Is deposited by 3 sequential deposition of a 15 nm layer titanium oxide of 45 nm. Each deposit is made in following conditions:<ul><li>pressure: 0,264 Pa (2.10^-3 torr)</li><li>atmosphere: argon / oxygen 15% by volume of oxygen</li><li>Applied power: 2.4 Watts / cm²</li></ul>

Each such deposit is followed by treatment with the oxygen ion beam under the following conditions:<ul><li>ion energy at their impact on the film: 84 ev</li><li>ion density: 1.2 mA / cm²</li><li>treatment duration: 5 minutes</li></ul>

The layer obtained is densified, which results in a significant increase in its refractive index, equal to 2.45, then a layer of TiO₂ called hereinafter "standard" of the same thickness deposited in the same conditions but without treatment by ion beam an index of 2.37. It is becoming much less rough surface as the mean square deviation of the roughness is only 14 angstroms (1.4 nm), whereas the the standard layer is 35 angstroms (3.5 nanometers).

Figures 1 and 2 show the results respectively testing "Taber" and "HCl" of a layer of TiO₂standard (curves C1) and the layer according to Example 1 (C2 curves). In Figure 1, the number of abrasion towers x-axis is given, the light reflection value R_Lpercentage in the ordinate. In Figure 2, the abscissa shows the time in minutes and the ordinate the value of R_L. The figures clearly show that the layer of Example 1 is much more resistant to mechanical abrasion and attack acid as the standard layer.

EXAMPLE 2

Repeating the conditions of pretreatment, deposit and ion beam treatment of Example 1, deposited in 6 sequential alternating deposits with 6 treatments beam by a titanium oxide layer of 900 nm.

The layer thus treated is densified, its index refractive index is 2.52 instead of 2.37 for a layer "Standard" of the same thickness. Its roughness is further reduced in considerable proportions, since its square deviation average roughness is only 2.6 angstroms (0.26 nm) while a "standard" layer shows a gap of 35 Angstroms (3.5 nanometers).

EXAMPLE 3

The pretreatment of the substrate is carried out using the beam set at an energy of 45 eV and an ion density 1.4 mA / cm².

Then deposited by three sequential deposits of 5 nanometers a layer of 15 nanometers of titanium oxide, deposits alternating with 3 treatment by ion beam in the same conditions as in the preceding examples. We evaluates chemical resistance by testing by the test "HCl" in comparison with a layer of TiO₂ likewise thickness "standard", that is to say deposited by sputtering cathode without treatment by ion beam.

After 8 minutes, the "standard" layer is completely deteriorated, the value of R_L measured is that of the bare glass. the Rather, the film treated according to the invention withstands since it degrades completely that beyond 2 hours (R_L equal to 9.3% after 2 hours).

EXAMPLE 4

Is deposited in one deposit a 25 nm oxide layer tantalum. The deposit is made under the following conditions :<ul><li>pressure: 0,264 Pa (2.10^-3 torr)</li><li>atmosphere: argon / 30% oxygen by volume of oxygen</li><li>Applied power: 1.45 W / cm²</li></ul>

This deposition is followed by a beam processing of oxygen ions under the following conditions:<ul><li>ion energy at their impact on the film: 84 ev</li><li>ion density: 1.2 mA / cm²</li><li>treatment duration: 5 minutes.</li></ul>

The treated film is densified. Its standard deviation roughness average is 1.9 angstroms (0.19 nm), while that of a tantalum oxide layer of the same thickness deposited by the same method of deposit but not treated is 4.1 angstroms (0.41 nm).

<u>EXAMPLE 5</u>

pretreatment of the substrate is carried out using the beam at an energy of 45 eV and an ion density 1.4 mA / cm² for 1 minute.

Is deposited by three sequential deposition of 23 nm each a final layer of 30 nm of tin oxide SnO₂<ul><li>pressure: 0.2 Pa (1.5x10^-3 torr)</li><li>atmosphere: argon / 69% oxygen by volume of oxygen</li><li>Applied power: 0.9 Watts / cm²</li></ul>

Each deposit is followed by treatment with beam of oxygen ions under the following conditions:<ul><li>ion energy at their impact on the film: 84 ev</li><li>ion density: 1.9 mA / cm²</li><li>processing time: 3 minutes</li></ul>

The resulting layer is cured in a very significant way, which results in particular durability Exceptional chemical. It was thus submitted one hand this layer, and secondly a layer of SnO₂ "Standard" 30 nm deposited in one step by spray but without treatment by ion beam "HCl test". Layer "Standard" degrades completely after 30 minutes, while the layer of the invention presents yet No significant degradation of traces at 48 hours.

It was noted that tin oxide layer, known to have a high sputtering rate, had the sudden tendency to re-atomising, since after three deposits of 23 nm, a layer of only 30 nm is finally obtained. It was confirmed that there for an ion beam as well energy (84 ev), limited re-atomising effect or not of the treated layer depends on the material in question. A Limited re-atomising has no disadvantageous consequences notable, except possibly in terms of the cost of commodity here reasonable cost for the oxide tin.

EXAMPLE 6

Is carried out a pre-treatment of the substrate as to Example 5.

is then deposited by radio frequency in one After 30 nm of silicon oxide SiO₂ boron doped (some percent) under the following conditions:<ul><li>pressure: 0.2 Pa (1.5x10^-3 torr)</li><li>atmosphere: argon / oxygen about 30% by volume oxygen</li><li>Applied power: 2.6 Watts / cm².</li></ul>

The deposition is followed by a treatment by the beam of oxygen ions under the following conditions:<ul><li>ion energy at their impact on the film: 60 ev</li><li>ion density: 2.2 mA / cm²</li><li>treatment duration: 5 minutes.</li></ul>

It is observed that the thus treated layer is more durable, particularly in terms of resistance to chemical aggressions, and particularly alkali resistance.

EXAMPLE 7

Is carried out a pre-treatment of the substrate as to Example 6.

Is deposited by two sequential deposition of 20 nm each a layer of 40 nm of silicon oxide SiO₂ boron doped as before, by radio-frequency.

Each of the two deposits followed by treatment with beam of oxygen ions in the same conditions as Example 6.

Again, the durability of the layer was substantially improved.

The measurements were carried out by mass spectrometry by SIMS apparatus (abbreviation for Secondary Ion Mass Spectroscopy) on the one hand a layer of SiO₂ doped "standard" bore 40 nm deposited in once without treatment to Figure 4, second layer of Example 7 Figure 3.

In these Figures 3 and 4 are represented on the abscissa the thicknesses of the layers in question in microns. Ordinate, in known manner, displaying the intensities secondary ion expressed in counts / second of measures.

On each of them, displaying the said areas "Si" thus corresponding to the silicon content in the oxide. We seen very clearly in FIG 3 that the curve "If" this some weakening in the middle of the thickness of the layer which reflects the presence of a kind of "interface" between the layers deposited in each of the two deposits sequential.

In contrast, in Figure 4, any slackening in this Gender is detectable.

It is proof that the deposited layers and treated according to the invention are modified structurally and keep track of treatment they suffered at least superficially in the interface area between sequential deposition (curves match aluminum "Al" and tungsten "W" simply means that these impurities are present in the chambers of spray. They disappear of course if other deposits devices were used).

In conclusion, the method according to the invention improve markedly the durability of a thin layer based on one or more oxides, nitrides, oxynitrides or oxicarbides metal (s) without imposing constraints that would not conceivable application for mass production of large substrates. This hardening is due to a densification phenomenon in the thickness of the layer, optionally combined with a surface modification thereof, in particular a applanissement.

Furthermore, the method has great flexibility implementation, as can be optimized independently or not, the treatment by ion beam by dissociating it from the deposition operation in itself.