CH713317B1 - Substrate coated with an anti-reflective coating system with hard material coating and a process for its production. - Google Patents

Abstract

The invention relates to an inorganic, transparent substrate coated with an anti-reflective coating system. This comprises a hard material coating, which is designed as an amorphous, transparent layer comprising aluminum, silicon, nitrogen and oxygen. The mole fraction of the hard material layer of oxidic aluminum is greater than that of nitridic silicon, the mole fraction of the hard material layer of oxidic aluminum is greater than that of nitridic aluminum and the mole fraction of the hard material layer of oxidic aluminum is greater than that of oxidic silicon, the mole fraction of the hard material layer of nitrogen is greater than that of oxygen. The invention also relates to a method for producing such a coated substrate.

Description

Field of invention

The invention relates generally to an inorganic, transparent substrate coated with an anti-reflective coating system which comprises an amorphous hard material coating. Another aspect of the invention relates to a method for producing a hard material coating on the inorganic, transparent substrate, preferably as part of an anti-reflective coating system.

Background of the invention

Coating systems that have anti-reflection properties are state of the art today and are used in a variety of ways, for example in the field of picture glazing, for optical components, for example lenses for cameras, and in many other fields. However, such anti-reflective coatings are not exposed to any strong mechanical stress.

The German patent application DE 10 2011 012 160 A1 describes anti-reflective coatings in which the hardness of the layer system, i.e. its resistance to mechanical stress, is improved by the fact that the coatings also include a certain proportion of aluminum in addition to silicon. A hard material layer made of Si3N4 with added aluminum is used as the high-index layer.

The German patent DE 10 2008 054 139 describes scratch protection layers made of silicon oxynitride, which, however, are not part of an anti-reflective layer system. This is also due to the relatively low refractive index of these layers, which is only between 1.9 and 1.6.

Other materials are also generally known to those skilled in the art as scratch protection or hard material layers, for example Al2O3 or Y-stabilized zirconium oxide or silicon nitride doped with carbon. However, these materials are generally only unsuitable for integration in an anti-reflective coating system, which is particularly due to their unfavorable properties, for example too high thermal expansion and / or insufficient optical properties, for example too high absorption and / or an unsuitable refractive index.

The German patent application DE 10 2014 104 798 A1 describes hard anti-reflective coatings and a method for their production and their use. The hard material coating comprises crystalline aluminum nitride with a hexagonal crystal structure, in which there is a preferred orientation of the crystals. The hard material coating also includes amorphous Si3N4 and is therefore present as a nanocomposite. The mean value of the crystallite size is approx. 20 nm. The hard material layer can also be doped with other substances, for example boron, zirconium or titanium or mixtures thereof, the aluminum content in the hard material layer always having to be more than 50% by weight and is preferably more than 70% by weight, since this is the only way to ensure the formation of a crystalline phase. The contamination of the hard material coating with oxygen should be below 10 mol%. Preferably, no more than 2 mol% of oxygen should be present. At higher oxygen contents there is the risk that the preferred direction of the crystallites in the coating, which are ultimately the cause of the good scratch resistance of the coating, is no longer guaranteed. An increased oxygen content also leads to a lowering of the refractive index of the hard material layer, which is unfavorable with regard to the performance of the anti-reflective system. In addition, the very low content of oxygen in the hard material layers has the disadvantage that in the production of a coating system that includes such a hard material coating, rinsing between the nitridic processes for the deposition of the hard material layer and the oxidic coatings for the deposition of the low refractive index layer is required Reactive gas lines are necessary. This increases the process times significantly and thus leads to increased costs.

There is consequently a need for substrates comprising anti-reflective coatings which include hard material layers with excellent scratch resistance and which can be produced inexpensively.

Object of the invention

The object of the invention is to provide an inorganic, transparent substrate coated with an anti-reflective coating system, comprising a hard material coating which reduces the weaknesses of the prior art, in particular with regard to scratch resistance and manufacturing conditions. Another object of the present invention is to provide a method for manufacturing such a substrate.

Summary of the invention

The object is achieved by the subject matter of the independent claims. Preferred embodiments can be found in the dependent claims.

The inorganic, transparent substrate coated with an anti-reflective coating system of the present invention comprises a hard material coating. This hard material coating is designed as an amorphous, transparent layer comprising aluminum, silicon, nitrogen and oxygen, the mole fraction of the hard material layer of aluminum being greater than that of silicon and the mole fraction of the hard material layer of nitrogen being greater than that of oxygen.

As an anti-reflective coating system is understood in the context of the present invention, a coating system which the reflection in particular in the visible range of the electromagnetic spectrum, that is in the range from 380 nm to 780 nm, preferably in the range between 450 nm and 650 nm, of a substrate, so that disruptive reflections are avoided and objects which are arranged behind the substrate as seen from the viewer are more visible. Such anti-reflective coating systems are known to the person skilled in the art and, depending on the requirements and the substrate used, comprise a different sequence of high-index and low-index layers.

In the context of the present invention, a layer of a material is referred to as a layer which is applied to a substrate, in particular in the form of a so-called thin layer, with a thickness of less than 1 μm. In the context of the present invention, the terms layer and coating are used largely synonymously to denote such a layer of a material.

The oxygen content in the hard material layer is preferably more than 2 mol%, preferably more than 5 mol% and particularly preferably more than 10 mol%, with an oxygen content of 17 mol% not being exceeded.

It has been shown that with such a composition of the hard material layer, the crystallinity and, accordingly, also a preferred orientation of crystallites of AlN are no longer given. If the oxygen content remains within the stated limits, however, the coating surprisingly still has good hardness and scratch resistance, which are improved, for example, compared to other amorphous hard material layers, as described, for example, in DE 10 2011 012 160 A1.

The composition of the hard material layer can be measured with secondary ion mass spectrometry (SIMS) and layer removal by means of a cesium ion beam. It is true that an exact quantitative determination of the coating composition is not possible by means of such a method, but this method provides information about the components present in the layer and their relationship to one another. The analysis of the removed layer or surface components is usually carried out using a mass spectrometer. The layer or surface components are determined here by means of the charge to mass ratio, with the mass being able to be assigned to certain particles or ions if the qualitative surface or layer components are known.

For the layer system considered here with a hard material layer comprising nitrogen, oxygen, aluminum and silicon, the following particles in particular come into consideration: AlO with a molar mass of about 42.98 g / mol AlN with a molar mass of about 40.988 g / mol SiO2 with a molar mass of about 60.083 g / mol SiN with a molar mass of about 42.092 g / mol

The molar masses were calculated here with the average atomic weight of the corresponding elements, so that slight deviations from the value given above are possible, which, however, are familiar to the person skilled in the art and do not hinder the determination of the particles on the basis of their mass.

The particles are ionized during the material removal. However, since the charge does not affect the mass of the particle, the charge of the particle is not taken into account in the following when considering the intensity. In the representation of the intensity profiles, all particles were regarded as negative particles and plotted accordingly, regardless of whether the charge was positive or negative. The level of the signal remains unaffected by this reversal of polarity.

According to one embodiment of the invention, the hard material coating is characterized by a time-of-flight intensity sputtering time profile, determined in secondary ion mass spectrometry (hereinafter also referred to as "ToF-SIMS") and layer removal by means of a cesium ion beam, in which the The highest intensity level is that of the particle with a molar mass of about 42.98 g / mol, AlO.

The above-mentioned “ToF-SIMS” method (ToF-SIMS = “Time of Flight Secondary Ion Mass Spectrometry”) is particularly preferably used as the secondary ion mass spectrometry. In this process, the masses of the secondary ions are determined, which are released by bombarding the surface with an ion beam. The intensity-sputtering time profile is created in that the intensities of the detected secondary ions are continuously recorded while the examined sample is bombarded with the beam of primary ions, preferably cesium ions, and the surface is thereby successively removed.

The particles under consideration are those particles which are typically examined in the ToF-SIMS examination of oxides and nitrides. If the focus is therefore on the highest intensity level of a particle, the corresponding nitridic and / or oxidic particles are considered for this. In particular, the oxidic particles AIO and SiO2 as well as the nitridic particles AIN and SiN are considered and compared with one another with regard to their intensity levels.

According to yet another embodiment of the invention, the hard material layer is characterized by a time-of-flight intensity sputtering time profile, determined in secondary ion mass spectrometry and layer removal by means of a cesium ion beam, in which the second highest intensity level is that of the particle with the molar mass of is about 42.092 g / mol, SiN.

According to yet another embodiment of the invention, the hard material layer is characterized by a time-of-flight intensity sputtering time profile, determined in secondary ion mass spectrometry and layer removal by means of a cesium ion beam, in which the third highest intensity level is that of the particle with the molar mass of is about 40.998 g / mol, AlN.

The intensity levels of the individual components can be related to one another by, for example, referring the absolute intensities in each case to the particle with the highest intensity.

In this way it is possible to further characterize coating compositions and to differentiate coatings of different compositions from one another.

According to a further embodiment of the invention, the hard material coating is therefore characterized by a ratio of the mean intensities of the particle with the molar mass of about 42.98 g / mol, AlO, to that of the particle with the molar mass of about 42.092 g / mol, SiN, between 1.6 and 2.8, preferably between 1.9 and 2.4, the mean intensities each being determined in a time-of-flight intensity sputtering time profile, determined in secondary ion mass spectrometry and layer removal by means of a cesium Ion beam.

According to yet another embodiment of the invention, the hard material layer is characterized by a ratio of the mean intensities of the particle with the molar mass of about 42.98 g / mol, AlO, to that of the particle with the molar mass of about 40.998 g / mol, AlN, between 2 to 4, preferably between 2.5 and 3.6, the mean intensities each being determined in a time-of-flight intensity sputtering time profile, determined in secondary ion mass spectrometry and layer removal by means of a cesium ion beam.

According to yet another embodiment of the invention, the hard material layer is characterized by a ratio of the mean intensities of the particle with the molar mass of about 42.98 g / mol, AlO, to that of the particle with the molar mass of about 60.083 g / mol, SiO2, between 110 and 250, the mean intensities being determined in each case in a time-of-flight intensity sputtering time profile, determined in secondary ion mass spectrometry and layer removal by means of a cesium ion beam.

In contrast, in the layers of the prior art which comprise significantly less oxygen than the layers according to embodiments of the present invention, significantly different ratios of the mean intensities are obtained. The following table compares values which were obtained for a comparative example and an exemplary embodiment according to the present invention. M (42.98 g / mol) / 2.1 0.16 M (42.092 g / mol) M (42.98 g / mol) / 3.2 0.26 M (40.988 g / mol) M (42, 98 g / mol) / 146 1370 M (60.083 g / mol)

The intensity ratios in the hard material layer according to the prior art and the hard material layer according to one embodiment of the invention thus differ significantly from one another.

In particular, it should be pointed out that the hard material layer of the embodiment according to an embodiment of the invention fulfills all three features with regard to the intensity relationships at the same time.

Although these intensity ratios do not indicate the exact quantitative compositions of the layers under consideration, they are a measure of the elements between which bonds are formed within the layers. The direct comparison thus shows that in the exemplary embodiment considered above, in contrast to the comparative example, the proportion of AlO particles increased compared to SiN and AlN, but decreased compared to SiO2. The conditions under consideration thus show that in the layers of the exemplary embodiment according to one embodiment of the invention the proportion of oxygen is significantly increased compared to the layer of the prior art under consideration.

Surprisingly, this significant increase in the oxygen content leads to an increase in the scratch resistance compared to the known amorphous layers of the prior art. This is all the more astonishing as the good scratch protection effect of the layers of the prior art can be attributed to the fact that they comprise nanocrystalline AlN with a preferred orientation of the crystallites. Such a layer structure only occurs when the oxygen content of the layers is as low as possible and is preferably less than 2 mol%.

The low refractive index layer particularly preferably comprises SiO2, for example aluminum-doped SiO2, as the coating material, the proportion of aluminum being up to 10% by weight, based on the sum of the masses of silicon and aluminum.

The low refractive index layer preferably comprises SiO2 as the main component, but can also be doped with further components, for example with boron, zirconium, titanium or mixtures thereof.

According to one embodiment of the invention, the refractive index of the low refractive index layer is in the range from 1.3 to 1.6, preferably 1.45 to 1.5, at a wavelength of 550 nm.

According to yet another embodiment of the invention, the refractive index of the hard material layer at a wavelength of 550 nm is in the range from 1.8 to 2.3, preferably 1.95 to 2.1.

The inorganic transparent substrate, on which an anti-reflective coating system can be applied according to the present invention, can be a glass, for example a borosilicate glass, an aluminosilicate glass, a soda lime glass, a synthetic quartz glass, a lithium aluminosilicate glass or a optical glass be formed. However, it is also possible for the substrate to be crystalline. For example, the substrate can comprise a single crystal for optical purposes, a sapphire, a corundum or calcium fluoride. It is also possible for the substrate to be designed as so-called sapphire glass or as a glass ceramic.

In the context of the present invention, a crystalline, in particular a monocrystalline, Al2O3-comprising, transparent, preferably colorless material is referred to as sapphire glass. It is a term used especially in the watch industry for the single-crystal, Al2O3-encompassing, transparent cover material of dials.

If the uncoated substrate is in the form of glass, it is preferably a chemically or thermally toughened glass.

According to a further preferred embodiment of the invention, the substrate has a coefficient of linear thermal expansion α20-300 in the range from 7 * 10 <-6> to 10 * 10 <-6> K <-1>.

In the context of the present invention, the linear thermal expansion coefficient α20-300 is given in the range from 20 ° C to 300 ° C, unless stated otherwise. The terms α and α20-300 are used as synonyms in the context of this invention, unless expressly stated otherwise. The specified value is the nominal mean thermal coefficient of linear expansion according to ISO 7991, which is determined in static measurements.

According to a further preferred embodiment of the invention, the hard material layer comprises carbon. It has been shown that such a carbon content is particularly advantageous for the formation of a hard, scratch-resistant layer. The inventors assume that this is due to the formation of very small amounts of hard and thus scratch-resistant carbides, for example SiC, in the layer. The proportion of carbon in a hard material layer according to one embodiment of the invention can be seen, for example, in a time-of-flight sputtering time profile, determined in secondary ion mass spectrometry and layer removal by means of a cesium ion beam, as particles with a molar mass of about 26.018 g / mol, CN.

According to one embodiment of the invention, the hard material coating is characterized by a ratio of the mean intensities of the particle with the molar mass of about 42.98 g / mol, AlO, to that of the particle with the molar mass of about 26.018 g / mol, CN, between 110 and 215, preferably between 140 and 175, the mean intensities each being determined in a time-of-flight intensity sputtering time profile, determined in secondary ion mass spectrometry and layer removal by means of a cesium ion beam.

According to a further embodiment of the invention, the inorganic, transparent substrate comprising an anti-reflective coating system has a reflectance in the wavelength range from 450 nm to 650 nm of at most 2%.

According to embodiments of the present invention, the substrate is designed in such a way that this low degree of reflection is not only present immediately after the coating, but also after a mechanical load, as is the case, for example, in tests that are standardly used in the watch industry. Such a test is, for example, the so-called Bayer test.

In this test, the surface of the test body, for example a substrate provided with an anti-reflective coating system, is loaded for a predetermined time with precisely specified sand under predetermined conditions and then the surface of the test body is examined for damage. The exact conditions for such tests are specified, for example, in DIN 52348 and ASTM F735-11. With regard to the inorganic, transparent substrate under consideration, comprising an anti-reflective coating system according to embodiments of the invention, this test is carried out with different types of sand: On the one hand, new sand containing aluminum oxide is used, Furthermore, already aged sand comprising aluminum oxide with an average age is used, Finally, previously damaged sand containing aluminum oxide is also used.

In order to increase the reproducibility of the results, preconditioned sand is preferably used.

As a rule, stress tests with 8000 stress cycles are carried out.

Another test for specifying the hardness of the layers is the so-called sand trickle test.

The exact conditions for such tests are specified, for example, in DIN 52348 and ASTM F735-11.

According to one embodiment of the invention, the anti-reflective coating system comprises four layers.

According to a further embodiment of the invention, the anti-reflective coating system comprises five layers. This embodiment is particularly preferred when the substrate comprises a material with a relatively high refractive index. In this case the first layer is preferably a layer with a low refractive index, for example silicon dioxide.

Another aspect of the present invention relates to a method for producing a hard material coating on an inorganic, transparent substrate. The hard material coating is preferably designed as part of an anti-reflective coating system, particularly preferably as a high-index layer of the anti-reflective coating system. The hard material coating is designed as an amorphous, transparent layer comprising aluminum, silicon, nitrogen and oxygen, the mole fraction of nitrogen in the hard material layer being greater than that of oxygen and the mole fraction of nitrogen in the hard material layer being greater than that of oxygen. The procedure consists of the following steps: Providing a target comprising aluminum and silicon. The mole fraction of aluminum in the target is greater than the mole fraction of silicon in the target. Introducing a substrate, preferably an inorganic, transparent substrate, into a reactor. The reactor can in particular comprise a system for the physical deposition of layers and can be designed, for example, as a sputtering system, for example as a sputtering system for reactive and / or partially reactive magnetron sputtering. Evacuate the reactor to a final pressure of less than 5 * 10 <-6> mbar. Providing a reactive gas comprising nitrogen and oxygen. The molar nitrogen content of the reactive gas is greater than the molar oxygen content. Deposition of a hard material layer by reactive sputtering on at least one surface of the substrate.

A sputtering process is referred to as partially reactive if less reactive gas is used during the process than is necessary to achieve a stoichiometric layer. The stoichiometry is then, for example, only fully achieved through a downstream process step, e.g. a separate oxygen source.

According to a further embodiment of the invention, the process gas comprises argon.

According to yet another embodiment of the invention, the molar nitrogen content of the reactive gas is greater than twice the molar oxygen content, preferably greater than four times the molar oxygen content.

Description of the drawings

In the following, the invention is explained in more detail by way of example with the aid of drawings.

1 shows, in a schematic representation that is not true to scale, a transparent, inorganic substrate 1 which comprises an anti-reflective coating system 2. This anti-reflective coating system 2 comprises a hard material coating comprising aluminum, silicon, nitrogen and oxygen, the mole fraction of aluminum in the hard material layer being greater than that of silicon and the mole fraction of nitrogen in the hard material layer being greater than that of oxygen. This is applied to a surface of the substrate. In general, however, without being limited to the example shown, it is also possible that part or the entire surface of the substrate is covered with such a coating system or that, for example, two sides of the substrate, for example opposite sides, are covered with such an anti-reflective coating. Coating system 2 are coated.

Figure 2 shows a time-of-flight intensity sputter time profile. The intensity of the signal in standardized units is plotted logarithmically on the y-axis, and the sputtering time in seconds is plotted on the x-axis. The sample examined with secondary ion mass spectrometry is ablated from the surface so that the components of the layer deposited last are detected at low sputtering times and the substrate material is only removed at high sputtering times.

The units are here generally standardized in such a way that they are related to a signal assumed to be constant, for example to the aluminum signal, provided that the substrate comprises Al2O3 as a main component, such as a sapphire substrate.

In the present case, in FIG. 2, a substrate on which a coating system comprising 5 layers has been deposited has been examined. The layer deposited last is designed as a low refractive index layer and comprises SiO2 as the main component. This is also shown in the sputter time profile shown here, in which the particle to be identified as SiO2 has the highest intensities.

Under this layer, a high-index hard material layer according to one embodiment of the invention is applied. At the interface between the low-refractive-index layer and the high-refractive-index hard material layer, there is an increase in the AlO signal. These are interface effects, which can be attributed, for example, to preparative effects during sample production or also during the deposition of the coating. These peaks are not taken into account when considering the intensity levels of the individual particles.

It turns out that in the highly refractive hard material layer examined here, according to one embodiment of the invention, the signal of the AIO particle is the strongest signal, that is to say has the highest intensity level. The particle with the second highest intensity level is SiN, followed by AIN as the particle with the third highest intensity level. SiO2 is detected with a lower intensity.

The material was removed by means of a cesium ion beam.

It is also noteworthy that the hard material layer according to an embodiment of the invention, the intensity-sputtering time profile of which is shown in FIG. 2, has a proportion of BO.

According to a particularly preferred embodiment, the hard material coating is characterized by a ratio of the mean intensities of the particle with the molar mass of about 42.98 g / mol, AlO, to that of the particle with the molar mass of about 42.092 g / mol, SiN, between 1.6 and 2.8, preferably between 1.9 and 2.4, the mean intensities each being determined in a time-of-flight intensity sputtering time profile, determined in secondary ion mass spectrometry and layer removal by means of a cesium ion beam .

According to yet another embodiment of the invention, the hard material layer is further characterized by a ratio of the mean intensities of the particle with the molar mass of about 42.98 g / mol, AlO, to that of the particle with the molar mass of about 40.998 g / mol, AlN, between 2 to 4, preferably between 2.5 and 3.6, the mean intensities each being determined in a time-of-flight intensity sputtering time profile, determined in secondary ion mass spectrometry and layer removal by means of a cesium ion beam.

According to yet another embodiment of the invention, the hard material layer is also characterized by a ratio of the mean intensities of the particle with the molar mass of about 42.98 g / mol, AlO, to that of the particle with the molar mass of about 60.083 g / mol, SiO2, between 110 to 250, the mean intensities being determined in each case in a time-of-flight intensity sputtering time profile, determined in secondary ion mass spectrometry and layer removal by means of a cesium ion beam.

In particular, all three of the aforementioned relationships can also be present simultaneously on a hard layer according to an embodiment of the invention. But it is also possible that only one of these relationships is implemented.

The layer thickness of the individual layers of the anti-reflective coating system was in the example considered here, starting from the substrate, for the first (low refractive index) layer approx. 10 nm, for the second, high refractive index layer (hard material layer) approx. 30 nm, for the third, again low-refractive-index layer approx. 14 nm, for the fourth layer approx. 132 and the fifth layer approx. 88 nm. However, it is evident to the person skilled in the art that such layer thicknesses are only exemplary and result from the requirements placed on the optical properties . Deviations from the values given here are therefore possible.

In comparison, FIG. 3 shows a representation of an inorganic transparent substrate comprising an anti-reflective coating according to the prior art. The intensity of the signal is again plotted in standardized units on the y-axis on a logarithmic scale, and the sputtering time in seconds is plotted on the x-axis. Again, the top layer of the anti-reflective coating system can be found with short sputtering times, while with long sputtering times the particles that arise when the substrate is ablated are applied with high sputtering times from approx. 720 seconds. The intensity curve for AIO shows oscillations that may result from the sputtering process in terms of process technology, but could also have measurement-related causes.

The hard material layer, which is present at sputtering times from approx. 280 sec, shows that of the SiN particle as the most intense signal, then that of AIN and only in third place that of AIO. The intensity of the SiO2 signal is particularly low. In comparison to hard material layers according to embodiments of the present invention, the following differences result: The highest intensity level in the time-of-flight intensity sputter time profile is now not that of AIO, but of SiN, The second highest intensity level is that of AIN, not SiN, The third highest intensity level is that of AIO, not that of AIN.

Furthermore, the intensity ratios have changed. For example, the ratio of AlO to SiN is approx. 0.16, that of AlO to AlN approx. 0.26 and that of AlO to SiO2 approx. 1370. These ratios were calculated based on the mean intensity level of the sputtering time profiles.

4 shows an illustration of a time-of-flight intensity sputtering time profile for a substrate according to an embodiment of the invention. Again, the intensity is plotted in standardized units on the y-axis, and the sputtering time in seconds on the x-axis. In addition to the intensities for AIO and SiO2, the intensity of the signal CN is also considered. It turns out that the hard material layer according to one embodiment of the invention has a carbon content, which can be detected here in the form of the particle CN. This small but significant proportion of carbon in the hard material layer contributes to an improvement in the scratch resistance, for example through the formation of SiC compounds. The proportion of carbon in a hard material layer according to one embodiment of the invention is thus visible, for example, in a time-of-flight sputter time profile, determined in secondary ion mass spectrometry and layer removal by means of a cesium ion beam, as particles with a molar mass of about 26.018 g / mol, CN.

According to one embodiment of the invention, the hard material coating is characterized by a ratio of the mean intensities of the particle with the molar mass of about 42.98 g / mol, AlO, to that of the particle with the molar mass of about 26.018 g / mol, CN, between 110 and 215, preferably between 140 and 175, the mean intensities each being determined in a time-of-flight intensity sputtering time profile, determined in secondary ion mass spectrometry and layer removal by means of a cesium ion beam.

Fig. 5 shows an XRD diagram. The counting rate of the signal is plotted on the y-axis and the 2-theta angle on the x-axis. The crystalline reflex is clearly recognizable here, which is obtained with a hard material coating as part of an anti-reflex coating system for a transparent substrate of the prior art. It is a reflection of the crystalline AlN phase. This contrasts with two X-ray diagrams for a hard material layer according to an embodiment of the invention. These do not show any crystalline reflex, neither in the spectrum considered here nor at other angles. They are therefore X-ray amorphous.

6 shows a comparison of reflection spectra of different anti-reflective coating systems before and after a stress test. The reflection in% is plotted on the y-axis and the wavelength in nm is plotted on the x-axis. The reflection curve 3 of an uncoated sapphire substrate is also listed as a comparison.

Reflection curve 4 shows the reflection of an anti-reflective coating system on a sapphire substrate according to the prior art before the stress test, and reflection curve 5 shows the reflection of the same substrate after the test. The deterioration, i.e. increase in reflection, which can be attributed to the at least partial destruction and removal of the coating system, is clearly recognizable.

In comparison, the reflection curves 6 and 7 are plotted, each showing the reflection of a coated substrate according to an embodiment of the invention, with reflection curve 6 showing the reflection before mechanical loading, and reflection curve 7 showing the reflection curve after mechanical loading.

While the reflection curves 4 and 6 for the coated substrates before mechanical loading are essentially the same and thus comparably low reflection values are also obtained, it can be seen that the increase in reflection after mechanical loading has occurred for the substrate, which is an anti-reflection - Coating system comprising a hard material layer according to one embodiment of the invention, in particular is significantly lower in the range of higher wavelengths than in the anti-reflective coating system according to the prior art.

This is also evidenced by the light microscope recordings of mechanically stressed substrates, which are shown in FIG. 7.

The two samples shown above each relate to coated substrates comprising anti-reflective coating systems of the prior art. The mechanically stressed substrates can be seen on the left in five-fold magnification, on the right in twenty-fold magnification. The lowermost sample comprises an anti-reflective coating system according to one embodiment of the invention.

It is clearly visible that the damage in the anti-reflective coating system according to one embodiment of the present invention has less damage (in the picture on the left as dark spots, in the picture on the right as light spots) than the coatings of the prior art Technique (damage can be seen as light areas). The significantly lower damage is shown macroscopically in an antireflective effect that is still good despite mechanical stress.

From a metrological point of view, this improvement in mechanical stability can be described both by specifying the photopic reflectivity (which is weighted with the sensitivity of the human eye during daytime or photopic viewing), with the mean reflection in the visible spectral range and via a change in the color locus .

In the anti-reflective coating system comprising a hard material layer according to one embodiment of the invention, the photopic reflectivity is only 0.2% higher after mechanical stress, in contrast to a 0.5% increase according to the prior art. In the embodiment considered here, the mean reflection also only deteriorates by 0.2% after mechanical loading, again in contrast to 0.5% for the systems of the prior art.

The color locus stability is even better in the embodiment of the invention considered here: there is no longer any significant change in the color locus in the x, y, CIE color space. In particular, according to one embodiment of the invention, the color locus change Δxy after a Bayer test with 8000 abrasion cycles with worn Al2O3 sand rounded off by at least 16000 previous abrasion cycles is in the range from 0 to 0.1, preferably in the range from 0 to 0.07, particularly preferably in the range from 0 to 0.05. Such changes in the color location Δxy are visually imperceptible or at most barely perceptible. The size of the color location change Δxy denotes the distance between the color location before the Bayer test and the color location after the Bayer test in the xy plane of the xy CIE color space.

If fresh or only slightly worn sand is used, there are somewhat higher color locus shifts, which, however, are still significantly lower than in known AR systems. The above information with rounded sand that was previously used for a long time (i.e. sand after at least 16,000 cycles) is preferred, as the result here depends less on the condition of the abrasive medium and is therefore easier to compare.

List of reference symbols

1 substrate 2 anti-reflective coating system 3 reflection curve of the uncoated substrate 4 reflection curve of the unloaded anti-reflective coating system of the prior art 5 reflection curve of the mechanically stressed anti-reflective coating system of the prior art 6 reflection curve of the unloaded anti-reflective Coating system according to an embodiment of the invention 7 Reflection curve of the mechanically stressed anti-reflective coating system according to an embodiment of the invention

Claims (21)

1. An inorganic, transparent substrate coated with an anti-reflective coating system, comprising a hard material coating which is in the form of an amorphous, transparent layer comprising aluminum, silicon, nitrogen and oxygen, wherein - the molar proportion of oxidic aluminum in the hard material layer is greater than that of nitridic silicon, - The molar proportion of oxidic aluminum in the hard material layer is greater than that of nitridic aluminum and The mole fraction of oxidic aluminum in the hard material layer is greater than that of oxidic silicon, the mole fraction of nitrogen being greater than that of oxygen. 2. The substrate according to claim 1, wherein the oxygen content in the hard material layer is more than 2 mol%. 3. Substrate according to one of claims 1 or 2, wherein the hard material layer is characterized by a time-of-flight intensity sputtering time profile, determined in secondary ion mass spectrometry and layer removal by means of a cesium ion beam, in which the highest intensity level is that of the particle with the molar Mass of about 42.98 g / mol, AlO. 4. Substrate according to one of claims 1 to 3, wherein the hard material layer is characterized by a time-of-flight intensity sputtering time profile, determined in secondary ion mass spectrometry and layer removal by means of a cesium ion beam, in which the second highest intensity level is that of the particle with the molar Mass of about 42.092 g / mol, SiN. 5. Substrate according to one of claims 1 to 4, wherein the hard material layer is characterized by a time-of-flight intensity sputtering time profile, determined in secondary ion mass spectrometry and layer removal by means of a cesium ion beam, in which the third highest intensity level is that of the particle with the molar Mass of about 40.998 g / mol, AlN. 6. Substrate according to one of claims 1 to 5, wherein the hard material coating is characterized by a ratio of the mean intensities of the particle with the molar mass of about 42.98 g / mol, AlO, to that of the particle with the molar mass of about 42.092 g / mol, SiN, between 1.6 and 2.8, preferably between 1.9 and 2.4, the mean intensities each being determined in a time-of-flight intensity sputtering time profile, determined in secondary ion mass spectrometry and by means of layer removal a cesium ion beam. 7. Substrate according to one of claims 1 to 6, wherein the hard material layer is characterized by a ratio of the mean intensities of the particle with the molar mass of about 42.98 g / mol, AlO, to that of the particle with the molar mass of about 40.998 g / mol, AlN, between 2 to 4, preferably between 2.5 and 3.6, the mean intensities each being determined in a time-of-flight intensity sputtering time profile, determined in secondary ion mass spectrometry and layer removal by means of a cesium ion beam . 8. Substrate according to one of claims 1 to 7, wherein the hard material layer is characterized by a ratio of the mean intensities of the particle with the molar mass of about 42.98 g / mol, AlO, to that of the particle with the molar mass of about 60.083 g / mol, SiO2, between 110 to 250, the mean intensities being determined in each case in a time-of-flight intensity sputtering time profile, determined in secondary ion mass spectrometry and layer removal by means of a cesium ion beam. 9. Substrate according to one of Claims 1 to 8, the anti-reflective coating system comprising SiO2 as the low-refractive-index coating material. 10. The substrate according to claim 9, wherein the refractive index of the low-refractive-index layer at a wavelength of 550 nm is in the range from 1.3 to 1.6, preferably 1.45 to 1.5. 11. Substrate according to one of claims 1 to 10, the refractive index of the hard material layer at a wavelength of 550 nm in the range from 1.8 to 2.3, preferably 1.95 to 2.1. 12. Substrate according to one of claims 1 to 11, wherein the substrate as a glass, for example a borosilicate glass, an aluminosilicate glass, a soda-lime glass, a synthetic quartz glass, a lithium aluminosilicate glass or an optical glass, or crystalline, for example comprising a single crystal for optical purposes, or a sapphire or corundum or as so-called sapphire glass or as a glass ceramic. 13. The substrate of claim 12, wherein the glass is chemically or thermally toughened glass. 14. Substrate according to one of claims 1 to 13, wherein the substrate has a linear thermal expansion coefficient α20-300 in the range from 7 * 10 <-6> to 10 * 10 <-6> K <-1>. 15. Substrate according to one of claims 1 to 14, wherein the hard material layer is characterized by a ratio of the mean intensities of the particle with the molar mass of about 42.98 g / mol, AlO, to that of the particle with the molar mass of about 26.018 g / mol, CN, between 110 and 215, preferably between 140 and 175, the mean intensities each being determined in a time-of-flight intensity sputtering time profile, determined in secondary ion mass spectrometry and layer removal by means of a cesium ion beam. 16. Substrate according to one of claims 1 to 15, having a reflectance of at most 2% in the wavelength range from 450 nm to 650 nm. 17. Substrate according to one of claims 1 to 16, wherein the anti-reflective coating system comprises four layers. 18. Substrate according to one of claims 1 to 16, wherein the anti-reflective coating system comprises five layers. 19. A method for producing an inorganic, transparent substrate coated with an anti-reflective coating system, wherein the hard material coating is designed as an amorphous, transparent layer comprising aluminum, silicon, nitrogen and oxygen and wherein the molar proportion of oxidic aluminum in the hard material layer is greater than that nitridic silicon, is greater than that of nitridic aluminum and is greater than that of oxidic silicon, the mole fraction of nitrogen being greater than that of oxygen, comprising the following steps: - Provision of a target comprising aluminum and silicon, the mole fraction of aluminum in the target being greater than the mole fraction of silicon in the target, - Feeding a substrate into a reactor, - Evacuation of the reactor to a final pressure of less than 5 * 10 <-6> mbar, - Provision of a reactive gas comprising nitrogen and oxygen, the molar content of nitrogen in the reactive gas being greater than the molar content of oxygen, - Deposition of a hard material layer by reactive sputtering on at least one surface of the substrate. 20. The method according to claim 19, wherein the reactive gas comprises argon as a further component. 21. The method according to claim 19 or 20, wherein the molar content of nitrogen in the reactive gas is greater than twice the molar content of oxygen, preferably greater than four times the molar content of oxygen.