DE102017102569A1 - Layer system with a blackening layer, and method and sputtering target for producing the same - Google Patents

Abstract

Known layer systems with a substrate, with a metallic conductor layer, and with a blackening layer containing copper and oxygen as main components and which is applied on at least one side on the metallic conductor layer have a visual reflection R of less than 10%. In order to develop therefrom a layer system which allows a metallic layer to be reproducibly blackened, it is proposed according to the invention that the blackening layer contains, as the main phase, crystalline Cu (II) oxide with a volume fraction of at least 70%.

Description

The invention relates to a layer system with a substrate, with a metallic conductor layer, and with a blackening layer containing copper and oxygen as main components and which is applied on at least one side on the metallic conductor layer, wherein the layer system when viewed through the blackening layer, a visual reflection R _v of less than 10%.

In addition, the invention relates to a method for producing a blackening layer of such a layer system containing copper and oxygen as main components, comprising a process of sputtering by sputtering a copper-containing sputtering target in a deposition chamber.

Moreover, the invention relates to a sputtering target for producing a blackening layer of such a layer system containing copper and oxygen as main components, and to a method for producing a sputtering target suitable for this purpose.

In liquid crystal displays, a light-absorbing layer is applied to visible, electrically conductive, metallic structures, such as, for example, metallic conductor tracks, which reduces disruptive, metallic reflections. This coating can consist of one layer or of several layers and is also referred to below as the "blackening layer".

As a rule, the blackening layer is produced by means of sputtering. Here are atoms or compounds from a solid, the sputtering target, by bombardment with high-energy ions (usually rare gas ions) dissolved out and go into the gas phase. The gaseous phase atoms or molecules are finally deposited by condensation on a substrate located near the sputtering target, where they form a layer.

In "DC sputtering", a DC voltage is applied between the target connected to the cathode and an anode (often the plant housing). By impact ionization of inert gas atoms is formed in the evacuated gas space, a low-pressure plasma whose positively charged components are accelerated by the applied DC voltage as a permanent particle flow in the direction of the sputtering target and knocked out of the target material particles upon impact, which in turn move in the direction of the substrate and precipitate there as a layer.

The DC sputtering requires an electrically conductive target material, since otherwise the target would charge due to the permanent current of electrically charged particles and thus the DC field would be compensated. On the other hand, it is precisely this sputtering method is suitable to provide layers of particularly high quality in an economical manner, so that their use is sought. This also applies to the technologically related "MF sputtering", in which two sputtering targets are switched alternately in the kHz rhythm as the cathode and anode. Both methods mentioned, the DC sputtering and the "MF sputtering" are summarized below under the term "DC sputtering" or as "sputtering under DC discharge".

State of the art

That from the WO 2014/063954 A1 known layer system consists of at least two layers, one of which is a viewer facing antireflection layer, which consists of a dielectric material and at least one further facing away from the viewer a blackening layer. As high a absorption as possible is recommended for the blackening layer, characterized by an absorption coefficient κ (kappa) of at least 0.7 (at a wavelength of 550 nm). The thickness of the blackening layer is typically in the range of 140 to 250 nm. Effective anti-reflection of the blackening layer becomes more difficult as the thickness increases.

For the production of the layer system, a sputtering target is used, which consists of an oxidic material with oxygen deficiency, either by a reduced oxide phase of substoichiometric oxide or oxynitride based on Nb ₂ O _5-x , TiO _2-x , MoO _3-x , WO _3-x , V ₂ O _5-x (x> 0) or mixtures thereof alone, or by the reduced oxide phase is adjusted together with a metallic admixture. The blackening layer consists of an oxide or an oxo-oxynitride with substoichiometric oxygen content and is deposited using this sputtering target by DC or MF sputtering in a sputtering atmosphere containing a noble gas and a reactive gas in the form of oxygen and / or nitrogen in a proportion of not more than 10% by volume. In this case, the proportion of oxygen and nitrogen in the Material of the sputtering target of the proportion of oxygen and nitrogen in the oxide or oxynitride of the blackening layer not or by a maximum of + -20%.

Similar black coatings based on ZnO + Nb ₂ O ₅ + Mo, sputtering target compositions and methods of preparation are also known from WO 2014/166803 A1 and from the WO 2016/026590 A1 known.

The JP 2002-206166 A describes a black matrix material with the main component copper oxide, which is added as a blackening component between 10 to 45 wt .-% Ag oxide. For reducing the reflectivity, additional components may be contained in an amount of 0.1 to 5 wt%, such as oxides of metals In, Ti, Zr, Sn, Zn, Ta, W, Mo.

For the direct deposition of such multi-component layers by magnetron sputtering in a sputtering atmosphere without reactive gas cermet sputtering targets are required with a demensprechenden composition. The preparation of such sputtering targets is typically carried out using ceramic powders and metal powders by hot pressing in graphite molds under vacuum or by sintering in air. The adjustment of a homogeneous distribution of oxides and metal particles with high density in the target material proves difficult, especially when the particle sizes of the alloy components are different, segregations can easily occur. However, a uniform distribution is very important for a stable sputtering process, especially if individual phases or components are poorly conductive, as is the case with many oxides.

Dry or wet etching processes are required in the manufacture of the coating systems and their implementation in complex layer constructions. In the coating industry common etching solutions based on HCl, HNO ₃ , H ₃ PO ₄ , H ₂ SO ₄ , CH ₃ COOH, H ₂ O ₂ , K ₂ SO ₃ , K ₂ SO ₄ , K ₂ S ₂ O ₅ , K ₂ HSO ₅ , KHSO ₄ and optionally also chlorine or fluorine-containing salts or compounds such as FeCl ₂ , NH ₄ F, H ₅ F ₂ N, NaHF ₂ , KHF ₂ are for example US 6,881,679 B2 . US 7,850,886 B2 and US 7,521,366 B2 known.

Cermet layer systems, however, are generally difficult to etch, as regions of metallic phase require etchants other than the oxide matrix. Plasma etching has also proved difficult. Thus, for example, in the case of combinations of an oxide and a noble metal, the oxide is predominantly etched, so that metal particles remain and can contaminate the sputtering system and subsequent substrates.

The disadvantages mentioned above avoid a generic layer system for the electrodes of a touch-sensitive screen (panel), as it is known from the US 2013/0215067 A1 is known. On a transparent, planar substrate of the panel, an electrode grid made of a metal is applied. The electrode metal is aluminum, silver, copper, molybdenum, neodymium, nickel or alloys thereof. On the electrode grid, a black matrix coating is applied, which may consist of dielectric material, metal, alloy, metal oxide, metal nitride, metal oxynitride or metal carbide. In another embodiment, a black matrix layer based on copper oxynitride is first deposited on the transparent substrate, and then an electrode layer made of pure copper. This layer system has a total reflectivity of 6% for light of a wavelength of 550 nm, as viewed in the direction of the blackening layer, this value not containing the reflection at the air-substrate interface (which is about 4%).

Technical task

In order to avoid disturbing reflections, the layer system should in principle show a high absorption and a low reflection in the visible spectral range. It has been found that known layer systems with a blackening layer of copper oxynitride as the main component do not meet these requirements reproducibly.

In addition, the conductor layer and the blackening layer should preferably be producible by DC or MF sputtering due to quality considerations and economic reasons, which requires an electrically conductive target material. The reactive sputtering of a copper target used in the prior art represents a most cost-effective solution with regard to the sputtering target, since Cu targets are also available industrially with high purities.

A disadvantage of reactive DC magnetron sputtering, however, is that it can lead to a so-called "target poisoning" by a high degree of coverage of the target with metal oxide or other metal compounds, thereby changing the properties of the deposited layers.

It is therefore an object of the invention to develop a layer system which allows a metallic layer - such as tracks, electrodes and the like, which may consist for example of Al, Ag, Cu, Mo, W, Ni, Ti and alloys thereof - To blacken by means of a thin layer so that no disturbing metallic reflections occur more.

A further object is to develop a sputtering target as well as a deposition method for such black coatings on conductor layers with the highest possible coating rate while keeping the coating properties as constant as possible. The sputtering target should preferably be usable in a reactive DC or MF sputtering process, avoiding "target poisoning".

General description of the invention

The light-absorbing layer system according to the invention

With regard to the layer system, this object is achieved on the basis of a layer system of the type mentioned above in that the blackening layer contains as the main phase crystalline Cu (II) oxide with a volume fraction of at least 70%.

The aim of the invention is to blacken with a blackening layer an underlying conductor layer for a viewer. However, it has been shown that it is unfavorable to start from layer systems in which the cover layers have a very high degree of absorption, such as, for example, blackening layers with an absorption coefficient κ (kappa) of more than 0.70 (at the wavelength 550 nm), as recommended by the above-mentioned prior art. It turns out that the cover layer shows particularly good blackening properties if it is only slightly absorbent and the absorption coefficient κ (kappa) is below 0.7, in the range from 0.4 to 0.69. This criterion is fulfilled when the blackening layer contains as main components copper and oxygen, the main phase being crystalline Cu (II) oxide, the main phase meaning that it accounts for at least 70% by volume in the layered material. The comparatively low absorption is achieved by a copper oxide-containing matrix with no or at most low metal content. The visual blackening impression for the viewer is based not only on light absorption in the blackening layer, but also on extinguishing interference between the radiation components reflected at the conductor layer and the blackening layer.

For the absorption index kappa (κ):
n * kappa = k,
with k = extinction coefficient, which in turn into the complex refractive index
N = n + i k *
is received and by means of a damping contribution by the imaginary part in the refractive index of the layer is taken into account.

The molar fraction of the main components copper and oxygen in the material of the blackening layer is at least 70 mol%. The copper fraction is present exclusively or predominantly as stoichiometric or substoichiometric copper (II) oxide (CuO); Metallic phase, copper (I) oxide and oxinitridische components may be included in minor proportions. Particularly preferred is a blackening layer in which the proportion of Cu and CuO in the blackening layer is at least 95 mol%.

The blackening layer may contain fractions of oxidic or oxinitridic material with substoichiometric oxygen content or metallic phase. A stoichiometric oxide and a stoichiometric oxynitride are characterized by having unoccupied O and N valences, respectively. Copper (II) oxide (CuO) is considered as a stoichiometric oxide in this regard.

The thickness of the blackening layer and its refractive index are preferably coordinated so that for light in the visible wavelength range extinguishing interference results between the proportion of light which is reflected on the surface of the blackening layer and the proportion of light which is reflected at the interface between blackening layer and metal layer ,

The surface of the layer system facing the viewer is formed, for example, by the blackening layer or by the substrate. The reflection on this surface depends on the refractive index. The substrate may be a dielectric solid, such as glass, plastic or transparent ceramic, which serves as a support for the conductor layer or for the blackening layer. The refractive index of such substrates is typically in the range of 1.4 to 2.0. A blackening layer with the The above main components have a relatively lower refractive index, typically in the range of 2.6 to 2.95. All the above refractive index data refer to a measuring wavelength of 550 nm.

The combinatorial effect of lower reflection at the front of the blackening layer and partial erasure by interference with the proportion of light backscattered at the interface to the metal surface results in a particularly lower visual reflection R _v for the visible wavelength range for a viewer. A measure of this is the wavelength of 550 nm in the green spectral range, for which the sensitivity of the human eye is highest. The visual reflection of the layer system according to the invention is therefore lower than in the case of layers in which the blackening layer has a particularly high absorption capacity (with kappa> 0.7). A particularly suitable thickness of the blackening layer with respect to extinguishing interference is in the range of 30 to 55 nm.

A measure of the effectiveness of the cover is thus the overall low visual reflection R _v . This is understood to mean the normalized reflection on the eye sensitivity, which is calculated from the total reflection of the layer system. To calculate the visual reflection R _v , the measured values of a spectrometer are folded with the standardized factors of eye sensitivity and integrated or summed. These factors of eye sensitivity are specified in DIN EN 410.

As far as the reflection measurement is carried out by a transparent medium such as a glass substrate or plastic, to determine an effective visual reflection R _v , _{eff of} the layer system to subtract the reflection on the surface of this transparent medium of the total reflection. In the case of a glass substrate, this is about 4%.

In a layer system in which the metallic conductor layer is disposed between the substrate and the blackening layer and terminates the blackening layer directly against air, the visual reflection R _{v is} preferably less than 6% as measured from the blackening layer toward the substrate.

In a layer system in which the blackening layer is arranged between the substrate and the metallic conductor layer or the blackening layer is covered by a transparent cover layer, the visual reflection R _{v is} preferably less than 10% as measured by the transparent substrate or the transparent cover layer on the blackening layer.

The observer sees in this case through the substrate or the cover layer on the blackening layer, so that to determine the effective visual reflection R _v , _{eff of} the layer system, the reflection at the surface of the substrate or the cover layer is subtracted from the total reflection.

The blackening layer may contain at least one additional component, for example selected from the group of the metals Zn, Sn, In, Nb, Mo, W, Ti, Mn and oxides of these metals.

The metals mentioned are present in metallic form as a pure element, as an alloy constituent and / or as a stoichiometric or as a substoichiometric metal compound (oxides). They serve, for example, to adapt the refractive index or the etching behavior of the blackening layer.

An especially easy to produce layer system results when the metallic conductor layer contains as the main component with a mole fraction of more than 90% copper, and particularly preferably consists of copper.

The double layer of conductor layer and blackening layer contains substantially copper and can be easily structured with commercially available etchants for Cu electrodes. Suitable copper etchants are based, for example, on H ₂ O ₂ . By adding other metals or oxides, the etching rate of the conductor layer and / or blackening layer can be changed. Suitable additives are, for example: Zn, Sn, In, Nb, Mo, W, Ti, Mn, oxides and oxynitrides of these metals and mixtures or alloys thereof.

The sputtering target according to the invention

With regard to the sputtering target for producing the blackening layer of the layer system according to the invention, the abovementioned object is achieved in that it consists of a target material in which copper and copper (II) oxide make up the largest molar fraction.

The sputtering target according to the invention consists essentially (with a molar fraction of more than 70%, preferably more than 95%) of copper and of copper oxide and / or copper oxinitride. The molar proportion of copper (II) oxide is at least 70%. The copper (II) oxide is present in finely divided form as possible; the average particle size (D ₅₀ value) is less than 50 μm, with individual agglomerates also having larger dimensions, for example 200 μm.

Alone by the content of metallic copper, the target material has an oxygen deficiency compared to a stoichiometric, volloxidischen material. For this purpose, the oxidic or the oxinitridische phase may additionally contribute, if it is substoichiometric.

In the sputtering target according to the invention, the oxygen content of the blackening layer of the layer system according to the invention is already applied exactly or at least approximately. This means that fine adjustment of the layer stoichiometry can be achieved by small additions of reactive gases (in particular of oxygen) with not more than 10% by volume in the sputtering atmosphere, so that the abovementioned technological difficulties in sputtering off metal targets under a highly reactive atmosphere are avoided. In addition to oxygen, the addition of other reactive gases such as nitrogen is suitable.

The lack of oxygen of the sputtering target according to the invention results from the content of metal and possible substoichiometric oxides. This metal content is preferably in the range of 10 to 20 vol .-%, this statement based purely mathematical assumption that the oxygen content of any existing substoichiometric oxides is distributed to the most stable oxides to the full stoichiometry, so that purely mathematically a metallic phase with remains in the above-mentioned proportion.

With regard to the adaptation of the etching behavior or the refractive index of the blackening layer, the material contains one or more additional components selected from a group consisting of oxides, substoichiometric oxides or oxynitrides of Zn, Sn, In, Nb, Mo, W, Ti and Mn. These components are preferably contained in a proportion of less than 25% by volume.

The sputtering target according to the invention is electrically conductive and can therefore be processed in a DC or MF DC voltage process; it preferably exhibits a resistivity of less than 10 μΩ * cm, preferably less than 1 μΩ * cm.

The sputtering target can be produced by hot pressing or hot isostatic pressing (HIP) of homogeneous mixtures of the corresponding powder components. In the method according to the invention for producing such a sputtering target, a powder mixture containing Cu ₂ O particles is compacted into a sintered body and sintered at a temperature below 800 ° C.

By compacting at a temperature below 800 ° C decomposition of the CuO is avoided. During the compression, the starting powder Cu ₂ 0 decomposes completely or partially into Cu and CuO, thus producing a very fine and homogeneous mixture of metal and oxide.

In view of a small grain size in the target material, a powder mixture containing Cu ₂ O particles having a particle size of less than 50 μm and Cu particles having a particle size of less than 100 μm is used.

In particular via hot isostatic pressing, it is possible to produce such high-density blocks with densities> 95% and even> 99% of the theoretical density.

With regard to the adaptation of the etching behavior or the refractive index of the blackening layer, the target material contains one or more additional components selected from a group consisting of oxides, substoichiometric oxides or oxinitrides of Zn, Sn, In, Nb, Mo, W, Ti and Mn. These components are preferably contained in a proportion of less than 25 mol%.

The production process for the blackening layer according to the invention

With regard to the method for producing the layer system with a blackening layer containing copper and oxygen as main components, the abovementioned object is achieved, on the one hand, by carrying out a process of reactive sputtering in which a target surface of a copper-containing sputtering target is deposited in a deposition chamber under controllable supply of oxygen sputtering process, depending on a degree of coverage of the target surface with oxidic compound a stable process window in a metallic area and a stable process window in an oxidic region, and wherein the process gas supply to an operating point in a process window in a transition region between the stable metallic mode and the stable oxide mode.

It is known that in DC reactive sputtering (DC sputtering and medium frequency sputtering) so-called "target poisoning" can occur. At high reactive gas flow, the degree of coverage of the target with metal oxide or oxynitrides increases, and at a first reactive gas flow, there is a sudden decrease in the cathode voltage and thus a transition from the so-called stable metallic mode (also referred to herein as "metallic region") - without or with low coverage - into a reactive mode (also referred to herein as a "reactive region") in which the target is completely covered with the metal compound. As a result of the significantly decreasing metal atomization rate, the reactive gas consumption in the sputtering process decreases and the reactive gas partial pressure increases. When the reactive gas flow decreases again, the degree of coverage of the sputtering target drops again, and in the case of a second reactive gas flow, another abrupt transition takes place from the reactive mode to the metallic mode. The atomization rate increases again, the reactive gas consumption increases and the reactive gas partial pressure decreases. The cathode voltage increases again significantly.

Since the second-mentioned transition from the reactive mode to the metallic mode is always at a lower reactive gas flow than the reverse transition, the reactive gas partial pressure as well as other measurement and process parameters which depend on the coverage of the sputtering target show a hysteresis curve with inflection points F1 in this variation of the reactive gas flow (lower) ascending branch (with decreasing reactive gas flow) and F2 in the (upper) descending branch (with increasing reactive gas flow). The region between the metallic and the reactive region is referred to here as the "transition mode". The degree of coverage in the transition area is less than 100% and the discharge tends to be unstable.

On the other hand, the highest possible deposition rate of oxygen-containing layers requires a high sputtering rate and a correspondingly high partial pressure of oxygen in the sputtering atmosphere, which in turn leads to entry of oxygen into the target material and to the above-mentioned target poisoning and the described hysteresis with altered layer properties. To achieve a high coating rate while maintaining the same as possible layer properties only in the transition region between the reactive mode and the metallic mode.

Working in the unstable transition area requires stabilization. This stabilization can take place, for example, by providing a separate control loop for the process gas supply, with the aid of which the process gas supply is set to an operating point in a process window in a transition region between the stable metallic mode and the stable oxidic mode. For the measurement of the oxygen partial pressure, a lambda probe can be used whose output voltage supplies the information about the oxygen partial pressure present. Another possibility of stabilization is to keep the oxygen supply at an empirically determined, constant value. This possibility is particularly suitable for sputtering systems in which the process stabilization in the transition region is comparatively simple; this is the case with the present sputtering system.

It has proved particularly advantageous in this case if the process window in the transition region is determined at least once for a specific sputtering process by recording a hysteresis curve of a parameter dependent on the oxide coverage of the target surface as a function of the amount of oxygen in the process gas, and a right turning point the hysteresis curve with increasing amount of oxygen, and a left turning point of the hysteresis curve are determined with decreasing amount of oxygen, where the right turning point a value F2 and the left turning point is assigned a value F1 of the process gas supply, and that the operating point for the process gas supply in the process window which is defined as the range between F1-0.08xF1 and F2 + 0.08xF2. Preferably, the process window is defined as the range between F1-0.05xF1 and F2 + 0.05xF2.

The values F1 and F2 are percentages of the oxygen in the total process gas supply; they are thus determined from a hysteresis diagram in which the parameter dependent on the oxide degree of coverage of the target surface is represented as a function of the amount of oxygen in the process gas. The measurement parameter which describes the hysteresis curve as a function of the degree of oxide coverage of the target surface is, for example, the cathode voltage of the DC or MF generator, the plasma impedance or the oxygen partial pressure in the plasma chamber. The degree of occupation can also be detected optically, in which case the measurement parameter directly reflects the oxide coverage density. The control loop for the process gas supply includes a sensor adapted to the respective measuring parameter, such as a lambda probe.

The specific sputtering process is the sputtering process used in the film deposition. It is characterized by the number, geometry and chemical composition of the sputtering target (s) and by the given sputtering parameters, with the exception of the oxygen supply, because this is to be determined by recording the hysteresis curve.

For deposition of the blackening layer of the layer system according to the invention, it has proven to be advantageous if the process gas is a gas mixture of a noble gas and oxygen, wherein the proportion of oxygen in the gas mixture between 40 vol .-% and 48 vol .-%, preferably between 41 Vol .-% and 46 vol .-% is.

In this case, preference is given to using a sputtering target according to the invention, as described above. The sputtering target is sputtered in a pure DC or MF sputtering process, for example in a sputtering atmosphere of argon and a reactive gas such as oxygen or nitrogen.

The reactive DC magnetron sputtering of large area and approximately square sputtering targets or arrays of strip targets with plane areas of more than 0.5 m ² is used for example in the display industry for the production of large TFT arrays. Because of the large area, an oxygen gradient from the target edge to the target center can be established, which leads to inhomogeneities in the layer deposition. This then leads to inhomogeneous degrees of blackening of the deposited layer over the substrate.

In view of this, in an alternative process variant for producing a copper and oxygen main component blackening layer of a layer system, which is particularly suitable for producing large-scale blackening layers, provided that the sputtering target consists of a Targtwerkstoff in which copper and oxygen make up the largest mole fraction, wherein the proportion of oxygen in the target material differs by a maximum of 10% from the proportion of oxygen in the blackening layer to be produced.

Again, a sputtering target according to the invention is preferably sputtered in a pure DC or MF sputtering process. In this way, a blackening layer is produced on a substrate or on a conductor layer which has an oxygen content which corresponds to or comes very close to the oxygen content of the sputtering target. As a result, the target material can be transferred into the blackening layer as it is or unchanged with only slight oxidation.

Since the deposited layer does not differ significantly in its chemical composition from that of the target material used, local differences in the oxygen content of the process gas play a minor role. This allows a stable guidance of the sputtering process and the reproducible adjustment of the properties on large-area deposited blackening layers.

At best, a small addition of reactive gas of preferably less than 5 vol .-% of Sputtergasstroms is useful to allow fine tuning of the layer properties.

measurement methods

Coating thickness measurement

The layer thickness measurement was carried out by means of a stylus-type profilometer (Ambios Technology XP-200). For sample preparation, part of the substrate was covered with Kapton tape. The corresponding covered area was not sputtered. After removing the cover, the layer thickness at the resulting step between coated and uncoated area was determined.

The device calibration was carried out at 10 μm on the supplied standard. The measurement was repeated at 10 different sites of the sample and the mean was formed.

Absorption coefficient kappa

The absorption coefficient is a measure of the attenuation of electromagnetic radiation in matter and was determined by means of a spectrometer (Perkin Elmer Lambda900 / 950). The transmission and reflection measurements in the wavelength range 380-780 nm in 10 nm increment are determined integrally at the layers. The obtained transmission and reflection measured values were read into the software of the company Woollam M2000 and the refractive indices and absorption coefficients were calculated. For reference, the meter was calibrated to an uncoated substrate.

Reflection Rv

The reflection R _v was measured as directional reflection. Diffuse reflected light is not considered (ie no integrating sphere). The Perkin Elmer Lambda35 spectrometer was used for the measurement. Calibration takes place via a manufacturer-calibrated AI-sample of known reflection.

The visual reflection R _v is understood to be the normalized reflection on the eye sensitivity, which is calculated from the total reflection of the layer system. As far as the reflection measurement is carried out by a transparent medium such as a glass substrate, the reflection on the surface of this transparent medium is subtracted from the total reflection to determine the effective reflection R _{v, eff of} the layer system.

Determination of particle size

The particle size of the powders used was determined by means of laser diffraction and the CILAS 990 device. The sample was dispersed in distilled water and 0.1Ma% sodium pyrophosphate for 30 seconds by means of ultrasound and then measured. For evaluation the Fraunhofer method was used. The D50 value was determined based on the volume of the particles, which indicates the particle size at which 50% of the particles are smaller than this value.

Emission Spectrometric Analysis (ICP-OES)

An emission spectrometer Varian Vista-MPX and ICP expert software (Varian Inc.) were used. First of all, two calibration samples for the metals are prepared from standard solutions with known metal content (eg 1000 mg / l) in aqua regia matrix (concentrated hydrochloric acid and concentrated nitric acid, in the ratio 3: 1). The parameters of the ICP device were: Power: 1.25 kW Plasma gas: 15.0 l / min (argon) Auxiliary gas: 1.50 l / min (argon) atomizing gas pressure: 220 kPa (argon) Repeat: 20 s Stabilization time: 45 s Observation height: 10 mm Aspirate sample: 45 s Rinsing time: 10 s Pump speed: 20 rpm repetitions: 3

To measure a sample: Add 1 g +/- 0.1 g of the sample with 30 ml of nitric acid and 90 ml of hydrochloric acid, as indicated above, and place in a microwave (Fa: Anton Paar, instrument: Multivave 3000) at 800 ° C. 1200 W unlocked within 60 min. The digested sample is transferred with 50% by volume hydrochloric acid into a 100 ml flask and used for the measurement.

Determination of the density and method for determining the theoretical density

The density is determined by the so-called buoyancy method. For this purpose, a sample is weighed in air and in water and the volume is measured with a vernier caliper (accuracy 0.2 mm). The relative density in% is the measured density / theoretical density x100. The theoretical densities are taken from tables of standard works.

Phase analysis and determination of the phase fraction

The samples pulverized by means of agate mortars were introduced into the sample carrier while avoiding formation of textures and were measured in transmission using a Stadi P X-ray powder diffractometer from Stoe & Cie. The Linear Position Sensitive Detector (LPSD) with a range of 6.60 ° is used and measured in the measuring range 2 theta (3.000 ° to 79.990 °) with a step size of 0.010 °. The measurement time is 240 seconds in increments of 0.55 ° (20 sec / step), the entire measurement takes 6.47 hours. It works with Cu-K-a-1 radiation (= 1.54056 angstroms). The generator used operates with a voltage of 40 kV and a current of 30 mA. Adjustment and calibration of the diffractometer is done with the NIST standard Si (640 d).

The volume fractions of the respective phases were determined as follows: The X-ray diffraction diagrams were evaluated with the aid of the Quantitative Phase Analysis: Rietveld SiroQuant®, Version V4.0 program and from the line intensities the relative proportions of the phases were determined and then, using the theoretical densities on Vol. -% converted.

Conversion of mass fractions into percent by volume

• m mass; V-volume
• Density, theo. = Mass / volume
• Volume% = mass _n / density _n / (mass ₁ / density ₁ + mass _n / density _n )

list of figures

• 1 eine schematische Darstellung des erfindungsgemäßen Schichtsystems in einer Ausführungsform mit einer Schwärzungsschicht zwischen einem Substrat und einer Leiterschicht in einem Querschnitt,
• 2 eine Ausführungsform des erfindungsgemäßen Schichtsystems mit einer Leiterschicht zwischen einer Schwärzungsschicht und einem Substrat in schematischer Darstellung,
• 3 ein Diagramm zur Erläuterung der Hysterese der Kathodenspannung beim reaktiven Gleichspannungssputtern,
• 4 den spektralen Verlauf der Reflexion des Schichtsystems Glas / Schwärzungsschicht 1 / Leiterschicht,
• 5 den spektralen Verlauf der Reflexion des Schichtsystems Glas / Schwärzungsschicht 2 / Leiterschicht,
• Figur 6 Röntgenbeugungsdiagramme der Schwärzungsschicht 1 und der Schwärzungsschicht 2 der in den 4 und 5 erläuterten Schichtsysteme,

The invention will be explained in more detail with reference to a patent drawing and an embodiment. In detail shows:

• 1 a schematic representation of the layer system according to the invention in an embodiment with a blackening layer between a substrate and a conductor layer in a cross section,
• 2 an embodiment of the layer system according to the invention with a conductor layer between a blackening layer and a substrate in a schematic representation,
• 3 a diagram for explaining the hysteresis of the cathode voltage in the reactive DC voltage sputtering,
• 4 the spectral course of the reflection of the layer system glass / blackening layer 1 / conductor layer,
• 5 the spectral course of the reflection of the layer system glass / blackening layer 2 / conductor layer,
• FIG. 6 shows X-ray diffraction patterns of the blackening layer 1 and the blackening layer 2 of FIG 4 and 5 explained layer systems,

1 schematically shows a layer system consisting of two layers A, B. 1 according to the invention. The first layer is a blackening layer A sputtered on a transparent glass plate S, on which in turn a conductor layer L is applied. The blackening layer A is made of copper and copper oxide. The conductor layer L; It is made of pure copper. The shift system 1 is for a viewer looking 2 from the glass plate S opaque and at the same time almost black; the blackening layer A covers the conductor layer L and thereby prevents metallic reflections.

2 schematically shows a layer system 21 with alternative layer structure. The conductor layer L is sputtered on a transparent glass plate S, and on the conductor layer L, a blackening layer A. The conductor layer L is made of copper. The blackening layer A is made of copper and copper oxide. Also the shift system 21 works for a viewer with a view 2 opaque from the glass plate S and almost black at the same time; the blackening layer A also hides the conductor layer L and thereby prevents unwanted metallic reflections.

Several such layer systems 1 ; 21 were generated and their properties measured. The respective compositions and properties are listed in Table 1.

Production of sputtering targets

Starting from powder mixtures corresponding to the components listed in Table 1 (in% by volume), planar, round sputtering targets with a diameter of 75 mm were produced by hot pressing. For this purpose, powder components of purity 3N5 and an average particle size of less than 100 microns (copper) or with an average particle size of less than 50 microns (copper (I) oxide) were mixed on a roller block.

Hot isostatic pressing can be used to produce high-density blocks with densities> 95% and even> 99% of theoretical density. The output component Cu ₂ 0 disintegrates during compression wholly or partly in Cu and CuO and thus produces a very fine and homogeneous mixture of metal and oxide. The sintering temperature is set to a maximum of 790 ° C during compression in order to avoid thermal decomposition of CuO.

Production of layer systems

These sputtering targets were deposited on glass substrates by DC sputtering in a sputtering atmosphere of argon and oxygen. In a series of experiments, the blackening of a 400 nm thick Cu layer was investigated by sputtering different blackening layers.

For this purpose, a first layer (blackening layer A) was deposited on the glass substrate S from a copper target with partially reactive sputtering. Subsequently, and without interrupting the vacuum, the metallic copper layer L was sputtered thereon from the same copper target. The thickness of the blackening layer A was optimized in each case by a few experiments with the aim of obtaining the lowest possible visual reflection. Corresponding layer thicknesses were in the range of 36.5 to 53 nm.

The sputtering parameters for the deposition of the blackening layer were chosen as follows: Dynamic coating: the speed was chosen differently depending on the layer thickness, Cathode: PK 500 (488mm × 88mm), Power: P = 2.15 kW (5 W / cm ² ), sputtering pressure: about 3 × 10 ^-3 mbar Substrate temperature: 20 ° C / unheated Ar-Flow: 200 sccm Target oxygen flow between 140 and 170 sccm (constant in each deposition process)

The oxygen flux was varied to achieve different oxygen levels in the blackening layer A. The setpoint of the oxygen flow was kept constant in each deposition process. The target value was determined empirically. This is because reactive reactive DC sputtering of the metallic copper target, depending on the oxygen supply, results in the formation of a stable metallic region, a stable reactive region, and an unstable transition region, with the oxygen supply operating point placed in the unstable transition region.

3 shows the hysteresis curve of the reactive Cu sputtering process in the form of a diagram with the voltage applied to the sputtering target cathode voltage S1 (in volts) as a function of the oxygen supply F _O2 (as% of the total process gas supply). Starting from the metallic region "Me", as the oxygen supply F _{O2 increases,} the degree of coverage of the target with Cu oxide increases, which is reflected in a decrease in the cathode voltage "S1". This decrease is initially slow and the course of the cathode voltage is flat; at a certain oxygen supply, however, the course is much steeper, which is the transition in the reactive region "Re" marked, in which the target is finally completely covered with the metal compound. With decreasing oxygen supply F _O2 , the coverage of the sputtering target decreases again and the cathode voltage S1 increases slowly at first, and faster at another specific oxygen supply F _O2 , marking the transition from the reactive region "Re" to the metallic region "Me". The area between metallic area "Me" and reactive area "Re" is referred to as "transition area" in which the degree of coverage is less than 100% and the discharge tends to be unstable. The hysteresis curve shows in the transition area thus a turning point F1 in the lower, ascending branch (with decreasing oxygen supply) and a turning point F2 in the upper, descending branch (with increasing oxygen supply). The inflection points F1 and F2 are each assigned a specific value of the oxygen supply F.

In favor of the highest possible deposition rate and setting the correct stoichiometry (absorptance) of the blackening layer with layer properties that are as constant as possible, the setpoint for the oxygen supply is placed in the transition region, more precisely in a process window, the inflection points F1 and F2 and a small range beyond so that the overall process window covers the range between F1-0.08 _X F1 and F2 + 0.08xF2. This process window is in 3 symbolized by the bar "Ü". The process window "Ü" in the transition area is determined once for each specific sputtering process. Any change in the configuration, however, requires a changed position of the hysteresis curve and a new determination of the respective process window.

For the specific sputtering process (in the embodiment) with the hysteresis curve In the diagram of 3 (Cathode voltage as a function of the proportion of the oxygen supply normalized to the total process gas supply) a turning point F1 at 42.4% and a turning point F2 at 44%. Accordingly, the range F1-0.08 _X F1 and F2 + 0.08xF2 extends between 39% by volume and 47.5% by volume, which corresponds to a process window for oxygen supply between 130 and 180 sccm. The desired value for the oxygen supply is preferably set to the average value within this process window, which is about 155 sccm, or a normalized to the entire process gas supply oxygen content of 43.5% and kept constant at this value.

By varying the layer thickness and the oxygen content of the CuO _x layer, different blackening layers were formed in a layer system according to 1 generated. Table 1 shows the deposited layer systems as well as the achieved visual reflection measured by the glass substrate S. It still contains about 4% reflection from the first glass surface. For layer systems according to 2 in which the blackening layers A are deposited directly on the Cu conductor layer L, comparable results are obtained but with about 4% lower values for the visual reflection. Table 1 blackening Test series A (O ₂ flow = 150 sccm) Series B (O ₂ flow = 160sccm) Layer thickness (nm) Visual reflection (%) Visual reflection (%) 36.5 7.36 7.24 40 7.45 7.78 45 10.94 10.1 53 15.92 15.88

The layer systems of test series A and B are characterized by a blackening layer which has an absorption coefficient kappa in the range from 0.4 to 0.69 at a wavelength of 550 nm.

4 shows for the layer systems of the test series A the course of the reflection R in [%] over the wavelength range λ in [nm] of about 380 nm to 780 nm. The reflection curves show at a wavelength around 550 nm in each case a minium. The lowest reflection value of 7.36% is achieved by the layer system with a blackening layer with the thickness of 36.5 nm. In order to determine the effective reflection R _v , _{eff of} the double-layer system, the reflection of about 4% at the surface of the glass substrate must be subtracted from the total reflection become. After subtracting this reflection component, an effective visual reflection R _{v, eff} of about 3.4% results.

5 shows for the layer systems of the test series B the course of the reflection R in [%] over the wavelength range λ in [nm] of about 380 nm to 780 nm. The reflection curves also show here at a wavelength around 550 nm in each case a minium. The lowest reflection value of 7.24% is achieved here as well by the layer system with a blackening layer with the thickness of 36.5 nm. This results in an effective visual reflection R _v , _eff of about 3.2% after subtracting the reflection at the surface of the surface glass substrate.

In the X-ray diffraction diagrams of 6 the measured diffraction intensity I (in rel. unit) is plotted against the diffraction angle 2theta. The sputtered layers of test series A and B show only slight texture differences; are almost congruent, except that the diffraction intensities in the B series are slightly lower. All reflections can be assigned to the crystalline phase Cu (II) O (tenorite). Since the main reflection for Cu ₂ 0 (cuprite) at 2Theta is ~ 36.4 degrees and thus in the right flank of the main reflection for CuO, it can not be ruled out that Cu ₂ O phase is also present in low concentration. However, other reflexes of Cuprit are not detectable; also no reflexes that would indicate metallic copper. Any phase components of Cu ₂ O phase and Cu phase are thus unmeasurable small. This shows that the microstructure - within the detection limit in the blackening layers of test series A and B - is completely formed from ZnO and the volume fraction of CuO is therefore 100%.

In the layer systems of test series A and B, the blackening layer is in contact with a transparent substrate. In the case of the layer system according to the invention, however, the blackening layer can also be in contact with a fluid medium with a refractive index n <2, such as, for example, air, nitrogen or a liquid. Depending on the refractive index of the medium, which is in direct contact with the blackening layer, slightly different reflection values then result than when measuring against a glass substrate. The lower the refractive index of the fluid medium, the higher the resulting effective reflection. Here it may be advantageous to deposit a low-refractive dielectric layer on the side of the blackening layer facing the observer, for example a conventional antireflection layer.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• WO 2014/063954 A1 [0008]
• WO 2014/166803 A1 [0010]
• WO 2016/026590 A1 [0010]
• JP 2002206166 A [0011]
• US 6881679 B2 [0013]
• US 7850886 B2 [0013]
• US 7521366 B2 [0013]
• US 2013/0215067 Al [0015]

Claims (15)

Layer system comprising a substrate, with a metallic conductor layer, and with a blackening layer containing copper and oxygen as main components, and which is applied on at least one side of the metallic conductor layer, wherein the layer system when viewed through the blackening layer, a visual reflection R _v of less than 10%, characterized in that the blackening layer contains as the main phase crystalline Cu (II) oxide with a volume fraction of at least 70%. Layer system after Claim 1 , characterized in that the proportion of CuO in the blackening layer is at least 95% by volume. Layer system after Claim 1 or 2 , characterized in that the blackening layer has a thickness in the range of 30 to 55 nm, and at a wavelength of 550 nm has an absorption coefficient kappa in the range between 0.4 and 0.69. Layer system according to one of the preceding claims, characterized in that the metallic conductor layer between the substrate and the blackening layer is arranged and - measured from the blackening layer in the direction of the substrate - a visual reflection R _v of less than 6%. Layer system according to one of Claims 1 to 3 , Characterized in that the blackening between the substrate and the metallic conductor layer is arranged, and - as measured from the substrate toward the blackening - a visual reflectance R _v of less than 10% by weight. Layer system according to one of the preceding claims, characterized in that the metallic conductor layer contains as the main component with a molar fraction of more than 90% copper. A method for producing a blackening layer of a coating system containing copper and oxygen as a main component according to one of Claims 1 to 7 comprising a process of reactive sputtering by sputtering a copper-containing sputtering target in a deposition chamber with controllable supply of an oxygen-containing process gas, the sputtering process depending on a degree of coverage of the target surface with oxidic compound a stable process window in a metallic region and a stable process window in an oxidic region, and wherein the process gas supply is set to an operating point in a process window in a transition region between the stable metallic mode and the stable oxide mode. Method according to Claim 7 characterized in that the process window in the transition region is determined for a specific sputtering process by recording a hysteresis curve of a parameter dependent on the oxide occupancy level of the target surface as a function of the amount of oxygen in the process gas, and a right turn of the hysteresis curve as the amount of oxygen increases; a left inflection point of the hysteresis curve are determined with decreasing amount of oxygen, wherein the value of F1 and the left inflection point, a value F1 of the process gas supply are assigned to the right inflection point, and that the operating point for the process gas supply is in the process window, which is defined as the Range between F1-0.08xF1 and F2 + 0.08xF2. Method according to Claim 7 or 8th , characterized in that the operating point for the process gas supply lies in the process window, which is defined as the range between F1-0.05xF1 and F2 + 0.05xF2 Method according to one of Claims 7 to 9 , characterized in that the process gas is a gas mixture of a noble gas and oxygen, wherein the proportion of oxygen in the gas mixture between 40 vol .-% and 48 vol .-%, preferably between 41 and 46 vol .-%. A method for producing a blackening layer of a coating system containing copper and oxygen as a main component according to one of Claims 1 to 6 comprising a process of sputtering by sputtering a copper-containing sputtering target in a deposition chamber, characterized in that the sputtering target consists of a target material in which copper and oxygen make up the largest mole fraction, whereby the proportion of oxygen in the target material is maximally 10% differs from the proportion of oxygen in the blackening layer to be produced. Sputtering target for producing a blackening layer of copper and oxygen as a main component of a layer system according to one of Claims 1 to 6 , characterized in that it consists of a Targetwerkstoff in which copper and copper oxide make up the largest molar fraction. Sputtering target after Claim 12 , characterized in that the Targtwerkstoff copper and copper (II) oxide in a proportion of at least 70 mol%, wherein the mole fraction of copper (II) oxide is at least 10%. Method for producing a sputtering target according to one of Claims 12 or 13 , characterized in that a powder mixture containing Cu ₂ O particles is compacted into a sintered body and sintered at a temperature below 800 ° C. Method according to Claim 14 in that a powder mixture is used which contains powder mixture Cu ₂ O particles with a particle size of less than 50 μm and Cu particles with a particle size of less than 100 μm.

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