Method for manufacturing an optical layer system and an optical layer system manufactured thereby - Patents.com

Abstract

The present invention comprises a plurality of layers disposed on a substrate, some of which have a high refractive index n H Another part of the layer has a low refractive index n L and a further portion of the layer has a medium refractive index n M where n H >n M ≧n L The present invention relates to a method for producing an optical layer system, in which layers with different refractive indices are arranged in an alternating stack, and to said optical layer system. The problem of defining a method by which optical layer systems can be easily realised in short process times and in large quantities with consistent quality without the need for long purging times between layer depositions is solved in that the layers of the optical layer system are deposited on a substrate from one and the same material by a selected coating process, where the material is hydrogenated amorphous silicon (a-Si:H) or hydrogenated germanium (Ge:H), and the refractive index and extinction coefficient of each layer of the layer system are adjusted by controlling the process parameters of the selected coating process.

Description

[Technical field]

[0001] The present invention relates to a method for producing an optical layer system consisting of multiple layers.

[0002] The invention also relates to an optical layer system comprising a plurality of layers produced by the method according to the invention and arranged on a substrate, some of the layers having a high refractive index n H Another part of the layer has a low refractive index n L and a further portion of the layer has a medium refractive index n M where n H >n M ≧n L and the optical layer system is arranged in a stack of alternating layers having different refractive indices.

[0003] Optical layer systems, especially optical filters, such as bandpass filters in Time of Flight (ToF) spectroscopy for face or gesture recognition or LIDAR for optical distance or speed measurement, are usually manufactured from two different optical materials for the near infrared (NIR) or infrared (IR) range, such as a-Si:H as the high refractive index material and SiO2 as the low refractive index material.

[0004] In a typical gesture recognition system, a light source shines near-infrared light on a user. An image sensor captures the emitted light reflected from the user, providing a 3D image of the user. A processing system then analyzes this 3D image to recognize the user's gestures.

[0005] Optical filters, particularly bandpass filters, are used to transmit the emitted light to an image sensor while substantially blocking ambient light. Optical filters thus serve to block ambient light. For this purpose, optical filters with a narrow passband in the near infrared wavelength range, for example 800 nm to 1100 nm, are required. Furthermore, optical filters must have a high transmission level / degree within the passband and a high blocking level or stopband outside the passband, with the transmittance of the stopband ideally approaching zero.

[0006] Conventionally, optical filters comprise two bandpass filters arranged on opposite sides of a substrate. The passbands of the bandpass filters are then matched to each other such that the passband of the bandpass filter on the back side of the substrate includes the passband of the filter on the front side of the substrate. At the same time, the passbands of the filters are matched to each other so that an anti-reflection effect is produced. Thus, the bandpass filter on the back side of the substrate blocks wavelengths outside the passband of the bandpass filter on the front side of the substrate. Each filter consists of alternating high and low refractive index layers. In general, various oxides such as titanium dioxide (TiO2), niobium pentoxide (Nb2O5), tantalum pentoxide (Ta2O5) or silicon dioxide (SiO2) are used for the high and low refractive index layers.

[0007] US Patent No. 9,945,995 discloses such an optical filter having a passband that at least partially overlaps the wavelength range of 800 nm to 1100 nm. The optical filter comprises a filter stack of alternating high and low refractive index layers of hydrogenated silicon. Each of the hydrogenated silicon layers has a refractive index greater than 3 over the wavelength range of 800 nm to 1100 nm and an extinction coefficient less than 0.0005 over the wavelength range of 800 nm to 1100 nm. The low refractive index material is a dielectric material, typically an oxide. Suitable low refractive index materials are silicon dioxide (SiO2), aluminum oxide (Al2O3), titanium dioxide (TiO2), niobium pentoxide (Nb2O5), tantalum pentoxide (Ta2O5) and mixtures thereof, i.e., mixed oxides.

[0008] Also known from US 9989684 is an optical interference filter with improved transmission in the passband of the filter, where the interference filter disclosed comprises a stack of layers, at least one layer consisting of hydrogenated amorphous silicon with a high refractive index and at least one layer consisting of one or more dielectric materials with a refractive index lower than that of the hydrogenated amorphous silicon.

[0009] To improve the performance of optical filters, for example in gesture recognition systems, it is desirable to reduce the number of layers, the total coating thickness, and the wavelength shift with the change in the angle of incidence (AOI). It is also desirable to minimize the transmission in the region of the stop band outside the pass band. Wavelength shift in the sense of the present invention means the shift of the pass band of the filter, which should be as small as possible so that there is approximately the same filter characteristic at different viewing angles of the filter. An improvement approach for this is to use a material for the high index layer that has a higher refractive index than conventional oxides have over the wavelength range of interest, as disclosed for example in US Pat. No. 9,945,995. In addition to a high refractive index, the material also needs to have a low extinction coefficient over the wavelength range of interest in order to provide a high transmission level within the pass band. However, up to now, different materials have always been used for layers with different refractive indices.

[0010] A significant drawback of using different materials for such optical filters is that they are usually deposited on the substrate in the same coating apparatus. Different coating sources and coating processes must be used, with different process gases for each coating source. This leads to lengthy purging processes when changing the coating source and therefore the process gas, making the process times very long.

[0011] Furthermore, the manufacturing process for high quality optical interference filters or optical layer systems having many different layers and layer materials is complex and time consuming.

[0012] It is therefore an object of the present invention to define a method for producing an optical layer system that does not have the disadvantages of the prior art, such as long purging times between layer depositions, etc. It is desirable for the optical layer system to be easily produced by the method, in particular for the process times to be short, so that mass production of the final product produced by the method can be achieved with consistent quality.

[0013] It is also an object of the present invention to define an optical layer system which has optimal layer properties for the field of use and which can be produced efficiently and reproducibly.

[0014] This problem is solved by a method for producing an optical layer system consisting of several layers according to independent patent claim 1.

[0015] In the method for producing an optical layer system consisting of several layers according to the invention, the layers of the optical layer system are deposited on a substrate from the same material by a selected coating process, said material being hydrogenated amorphous silicon (a-Si:H) or hydrogenated germanium (Ge:H), and the refractive index and extinction coefficient of each layer of the several layers of the layer system are adjusted by controlling the process parameters of the selected coating process.

[0016] It is particularly advantageous that in the manufacturing method according to the invention, regardless of the coating process, only a single material, namely a-Si:H:x or Ge:H:x, is deposited for the optical layer system, and the optical properties such as the refractive index and extinction coefficient of each layer are adjustable only by controlling one or more typical process parameters of the selected coating process. x can represent further process gases such as nitrogen (N2) or chlorine (Cl2). This makes the manufacturing method very simple, shorter and therefore more cost-effective than the prior art, since no purging processes between different layer materials and process gases are required.

[0017] In one embodiment of the method according to the invention, the coating process is a sputtering process, whereby the sputtering process is carried out reactively by a reactive gas mixture of argon (Ar) and / or krypton (Kr) and / or helium (He) and / or xenon (Xe) with hydrogen (H2), or the sputtering of silicon is carried out by Ar, Kr, He and / or Xe and the layers of the layer system are hydrogenated by a plasma source and / or ion source to obtain a-Si:H or Ge:H, or the sputtering process is carried out as a combination of reactive sputtering and the plasma source and / or ion source used, whereby the refractive index and extinction coefficient of the individual a-Si:H:x or Ge:H:x layers of the layer system are adjusted by the ratio of hydrogen to Ar, Kr, He and / or Xe. x stands for further layer components which may be present in one embodiment of the method but do not have to be present. This applies to all selectable coating processes.

[0018] If the sputtering technique is chosen as the coating process, there are several production variants for the production of a-Si:H or Ge:H. One of the variants is that the sputtering process is carried out reactively, i.e. a reactive gas mixture, preferably consisting of argon and hydrogen, is used. In the case of other layer compositions, such as a-Si:H:N, nitrogen or oxygen can also be used as reactive gas for the sputtering process. The use of nitrogen (N) or oxygen (O2) has the advantage that the layer stress of the deposited layer can be corrected in the direction of compressive stress due to their larger ionic or atomic radius with respect to hydrogen. As a result, the tensile stress of the a-Si:H or Ge:H layer can be reduced or corrected.

[0019] In a further variant, the sputtering process with argon and / or krypton and / or helium and / or xenon can be carried out in such a way that only a sub-nanometer thick silicon or germanium layer is deposited by sputtering, which layer is hydrogenated, nitrided, oxidized, oxynitrided or hydronitrided in a post-treatment step by an ion and / or plasma source. These two process steps are repeated iteratively until the desired layer thickness is achieved. In the post-treatment step, the substrate with the metal sputtered layer is passed through a plasma generated by a plasma and / or ion source. This source can be, for example, an ICP (inductive coupled plasma) source.

[0020] The third variant is a combination of the two previous ones. Reactive gases are used in the sputtering process both during the deposition of the sub-nanometer-thick layers and during the post-treatment with plasma and / or ion sources. The final stoichiometry and structure of the a-Si:H:x or Ge:H:x layer are adjusted by selecting the gas flow rates, e.g. the ratio of argon to reactive gas in the sputter source or plasma and / or ion source, the power of the sputter source or plasma and / or ion source, and the temperature of the surface / substrate to be coated. These determine the optically relevant variables such as the refractive index and extinction coefficient of each layer of the optical layer system.

[0021] The relationship between the optical properties of the high, medium and low refractive index layers and the process variables of the sputtering process is carried out experimentally prior to the layer production. The individual process steps during the deposition of the optical layer system are then based on these investigations. An important control variable during the production of a-Si:H:x or Ge:H:x layers is the ratio of hydrogen to a reactive gas, such as argon; the higher the proportion of hydrogen in the reactive gas, the lower the material density and therefore the refractive index. For the adjustment of the ratio of argon to hydrogen, values ​​from 1:2 to 5:1 are adjusted, in particular in the range of 1:3 to 4:1. The ratio of the gas mixtures is selected from one another in such a way that the refractive index can be adjusted in a range suitable for the filter, so that a refractive index as high as possible and at the same time a extinction coefficient as low as possible can be realized for the cavity of the filter to be produced. On this basis, the refractive index of the high refractive index layers of the filter stack is adjusted higher, with the associated deterioration of the extinction coefficient being accepted. Similarly, the refractive index of the low refractive index layers of the filter stack is adjusted as low as possible, with the lowest possible extinction coefficient being taken into account.

[0022] The deposition of a-Si:H:N is one example of a layer of a deposited filter stack. Layers of a-Si:H:N:Cl, a-(Si,Ge):H, a-(Si,Ge):H:N and / or a-(Si,Ge):H:N:Cl can also be produced using the method according to the invention. Further combinations of silicon or germanium hydrides and reactive gases are possible and are not limited to the aforementioned combinations.

[0023] In a further embodiment of the method according to the invention, the reactive gas mixture is argon and nitrogen N2 or argon and oxygen O2. The choice of reactive gas mixture depends on the layer composition to be deposited. This has the advantage that the layer stress can be corrected in the direction of compressive stress due to the larger ionic or atomic radius relative to hydrogen. As a result, the tensile stress of the a-Si:H or Ge:H layer can be reduced or corrected.

[0024] In another embodiment of the method according to the invention, the coating process is a chemical vapour deposition process (CVD process), the CVD process is carried out either plasma-assisted or catalytic or thermal with the aid of an evaporator unit and a plasma source, and the refractive index and extinction coefficient of each a-Si:H or Ge:H layer of the layer system are adjusted by gas flow control by the ratio of silane or germanium to hydrogen or by the power of the evaporator unit and the plasma source. Gas flow control means adjusting the absolute gas flow of silane or germanium or hydrogen, or keeping one of the gases of silane or germanium or hydrogen constant and controlling the other gas, respectively, or preparing a gas mixture of the two gases. Thus, the stoichiometry of each filter layer can be adjusted by the gas flow of silane gas or germanium gas and hydrogen and their ratio to each other in the gas mixture of the plasma source (partial gas flow), and / or by the power of the evaporator unit and / or the plasma source.

[0025] If chemical vapour deposition (CVD) is chosen as the coating process, various variants of CVD techniques such as plasma-assisted CVD (PECVD), catalytic CVD or thermal CVD can be used for the production of a-Si:H:x or Ge:H:x layers. The optical properties of the deposited a-Si:H:x or Ge:H:x layers of the layer system are adjusted by the difference in the ratio of the reactive gases to each other. In particular, the ratio of H2 to silane or germanium is adjusted by gas flow control so that the desired optical properties are obtained. Here, the relationship between the ratio of the process gases, the flow rate of the process gases, the substrate temperature, which is usually 160-200 ° C, the power of the plasma source, which is controlled either by direct current voltage or by radio frequency as required, the refractive index and the extinction coefficient are experimentally determined in advance for the various layers and the desired layer properties. These process variables are then used for the production of the optical layer system.

[0026] The coating process can also produce a-Si:H:N layers by adding nitrogen as a third reactive gas. By adding additional process gases or using germanium instead of silicon, it is also possible to produce a-Si:H:N:Cl, a-(Si,Ge):H, a-(Si,Ge):H:N, and / or a-(Si,Ge):H:N:Cl layers. Additional combinations of hydrogenated silicon or germanium with reactive gases are possible and are not limited to the above combinations.

[0027] To improve the layer properties, the coating process may involve a heat treatment of the layers or the entire optical layer system in a vacuum or argon atmosphere. Typical temperatures for the post-treatment step (post-treatment annealing) are between 100°C and 370°C, preferably between 200°C and 285°C, for 1 min to 60 min, advantageously 10 min.

[0028] In the thermal CVD process, a-Si:H:x or Ge:H:x layers of the optical layer system with different stoichiometry and thus different optical properties are deposited using an evaporator unit for silicon in combination with a plasma source (assist source), the plasma source being operated with a mixture of argon and hydrogen. To produce nitrides, oxides, oxynitrides or hydronitrides, the corresponding gases can also be mixed in the process. The adjustment of the refractive index and extinction coefficient of the layers of the optical layer system deposited using the thermal CVD process is carried out by adjusting the absolute gas flow rates in the respective gas mixture in the ion source and the ratio of the partial gas flow rates (silane, germanium, hydrogen, etc.) determined prior to the deposition, as well as the power of the evaporator unit and the plasma source. This adjusts the stoichiometry of each layer and thus controls the optical behavior. Usually, a temperature of 100°C to 300°C, preferably 140°C to 240°C, is aimed for the substrate temperature at which the layer deposition takes place.

[0029] In preliminary tests, the optimal process parameters for the respective geometry of the evaporator, the substrate to be coated and the plasma source are determined for depositing layers with high, low or medium refractive index. The layers of the optical layer system can then be deposited with this known data.

[0030] In another further embodiment of the method according to the invention, the coating process is an electron beam evaporation process combined with an ion source, and the refractive index and extinction coefficient of each a-Si:H:x or Ge:H:x layer of the layer system are adjusted by adjusting the absolute and / or partial gas flow rates in the gas mixture of the ion source and the power of the evaporator unit and / or the ion source. By absolute gas flow rates is meant the total gas flow rates of doping gases such as hydrogen (H2) and / or nitrogen (N2) and / or chlorine (Cl2) and / or mixtures of these doping gases. Individual doping gases can also be controlled with partial gas flow rates.

[0031] If a deposition process is selected as the coating process for depositing a-Si:H:x or Ge:H:x layers with different stoichiometry and thus different optical properties, an evaporator unit for silicon or germanium in combination with an ion source (assist source) is required, the ion source being operated with a mixture of argon and hydrogen. Corresponding gas mixtures can also be used to produce nitrides, oxides, oxynitrides or hydronitrides. The adjustment of the refractive index and extinction coefficient of each a-Si:H:x or Ge:H:x layer of the optical layer system is carried out by adjusting the absolute gas flow rates and / or the ratio of the partial gas flow rates in the respective gas mixture in the ion source as well as the power of the evaporator unit and / or the ion source. This allows the stoichiometry of each layer to be adjusted and thus the optical behavior to be controlled. Usually, a substrate temperature of 100°C to 300°C, preferably 140°C to 240°C, is aimed for.

[0032] In preliminary tests, the optimal process parameters for each deposition tool, substrate and ion source configuration are determined for high, low or medium refractive index layers, after which the layers of the optical layer system can be deposited with this known data.

[0033] In one embodiment of the method according to the invention, the optimal process parameters of the coating process selected to adjust the given / desired refractive index and extinction coefficient of each a-Si:H:x or Ge:H:x layer of the layer system are determined experimentally by prior testing or simulation.

[0034] The object of the present invention is also achieved by an optical layer system according to the invention.

[0035] In an optical layer system according to the invention produced by a method according to any one of claims 1 to 7, the layers are formed from the same material, the high, medium and low refractive index layers differ only in the stoichiometry of the doping gas, and the optical properties of the high, medium and low refractive index layers can be adjusted by process control via the stoichiometry of the doping gas.

[0036] In one variant of the optical layer system according to the invention, the layer system has an average refractive index n My where y is an integer greater than zero, and n H >n M1 ≧n M2 ≧…≧n My >n L This means that the layer system can comprise several layers with an average refractive index, with the medium refractive index layer located between the high and low refractive index layers having a different refractive index from the high and low refractive index layers, whereas the medium refractive index layers can have partially identical and / or mutually different refractive indices.

[0037] Thus, the layer system according to the invention may be formed from layers with only high or low refractive index. It is also possible for the layers of the layer system to have high, medium and low refractive indexes, or the layer system may be formed from layers with one layer with high refractive index, several layers with medium refractive index and one layer with low refractive index, with the refractive index of the medium refractive index layers being partially formed identically or differently.

[0038] The use of the same chemical elements for all layers of the optical layer system has the advantage that no changeover between different coating materials is necessary and therefore no lengthy purge processes are required between the individual layer deposition steps, and process times are significantly reduced, making mass production feasible.

[0039] In one preferred variant of the optical layer system according to the invention, the identical material is hydrogenated amorphous silicon (a-Si:H) or hydrogenated germanium (Ge:H) and the doping gas is hydrogen (H2).

[0040] Hydrogenated amorphous silicon has the distinct advantage that its refractive index can be tuned over a wide range depending on the stoichiometry of the hydrogen incorporated. The use of hydrogenated silicon (Si:H) for high-index layers in optical filters has been described by Lairson et al. in a paper entitled "Reduzierte Winkelverschiebungs-Infrarot-Bandpassfilterbeschichtungen" (Proceedings of the SPIE, 2007, Vol. 6545, S. 65451C-1-65451C-5) and by Gibbons et al. in a paper entitled "Entwicklung und Implementierung eines hydrierten a-Si-reaktiven Sputter-Abscheidungsprozesses" (Proceedings of the Annual Technical Conference, Society of Vacuum Coaters, 2007, Vol. 50, S. 327-330).

[0041] In one preferred variant of the optical layer system according to the invention, the optical layer system is configured as a bandpass filter.

[0042] Preferably, the bandpass filter, which is made up of a sequence of high, medium and / or low refractive index layers, has a refractive index of n H = 3.35 to 3.8, extinction coefficient k < 0.001, and the refractive index n M = 3.0 to 3.6, k < 0.001, and the low refractive index layer has a refractive index n L = 2.5 to 3.3, k < 0.001.

[0043] In another preferred variant, the bandpass filter consisting of a sequence of high, medium and / or low refractive index layers has a refractive index n H=3.6 to 3.8, extinction coefficient k<0.0001, and the medium refractive index layer has a refractive index n M = 3.2 to 3.3, k < 0.0001, and the low refractive index layer has a refractive index n L = 3.0 to 3.1, k < 0.0001.

[0044] If the optical layer system according to the invention is configured as a bandpass filter, this optical bandpass filter preferably has a refractive index n M or n L At least two medium or low refractive index cavity layers having a refractive index n L or n H and at least five layer stacks formed of alternating low and high refractive index layers having the same refractive index.

[0045] Each high, medium or low refractive index layer forms a cavity in the bandpass filter, i.e. an area where constructive interference of the incident radiation occurs, resulting in high transmission of the optical filter. Depending on the number of cavities formed in the optical filter, the transmission and the passband width of the filter can be precisely adjusted. By selecting the refractive index in combination with the layer thickness of the cavity, the wavelength shift of the passband of the optical bandpass filter can be reduced. This means that the characteristics of the filter are almost the same even for different angles of incidence of the incident radiation.

[0046] In addition to the cavity, there are layer stacks in the layer system that act as mirror layers and form the so-called stop band of the filter. The more layer stacks there are in an optical bandpass filter of a corresponding thickness, the more the incident radiation in this area is reduced by destructive interference.

[0047] In a further variant of the optical layer system, the optical layer system comprises, in addition to the high-index layer made of a-Si:H:x or a-Ge-H:x and the low-index layer made of a-Si:H:x or a-Ge-H:x, a further layer made of Si3N4 or SiO2. Such a layer system has the advantage that the range of possible refractive indices is extended, especially for the low index, in the case of SiO2, which has a refractive index of 1.4 to 1.47 in the wavelength range above 800 nm. In the case of Si3N4, which is a material with a medium refractive index compared to a-Si:H and SiO2, it is possible to adjust the optical parameters of the filter more precisely, since Si3N4 has a refractive index of 2 to 2.1 in the wavelength range above 800 nm.

[0048] In one variation of the optical layer system, the optical layer system is formed as a rugate filter, in which a refractive index gradient can be formed across multiple layers, which refractive index gradient can be adjusted for each of the multiple layers by process control via the stoichiometry of one or more doping gases.

[0049] By this process, this preferred variant forms so-called quasi-rugate filters in the individual mirror systems, where mirror system in the sense of the invention means an interference filter structure consisting of high, medium and / or low refractive index layers and the formed cavities. Rugate filters are dielectric mirrors that selectively reflect certain wavelength ranges of light. This effect is achieved by a periodic, continuous or quasi-discrete change in refractive index depending on the thickness of the mirror. Certain wavelength components of light cannot propagate in the rugate filter and are reflected. A particular challenge here is to achieve a continuous or quasi-discrete refractive index profile. This is adjusted by the chemical composition of the filter layers depending on the layer thickness. This can be achieved by continuously changing the gas composition during the deposition process of the individual filter layers, whereby the stoichiometry of the doping gas in the deposited filter material is adjusted by dynamic process control, resulting in different refractive indices.

[0050] In a further variant of the optical layer system, the optical layer system is formed as an optical interference filter.

[0051] Advantageously, the optical interference filter has a transmission range of 420 nm to 2800 nm, preferably 800 nm to 1100 nm. The passband width is advantageously 10 to 50 nm at 50% transmission. The edge steepness at 10% to 90% transmission is advantageously 8 to 20 nm. The transmission of the stopband is advantageously less than 1% transmission, advantageously less than 0.1% transmission, but better still less than 0.01% transmission, in the range 400 to 910 nm and in the range 970 to 1100 nm.

[0052] These wavelength ranges of the passbands and stopbands are determined by the thicknesses of the individual layers of the filter: in particular, the width of the passbands is adjusted by the number of cavities and their refractive indices and their layer thicknesses.

[0053] The final design of the optical filter depends on the requirements dictated by the subsequent application, for example in a sensor. Here, certain requirements are imposed on the passband and the stopband. These target values ​​allow the layer stack sequence to be determined from the layers of the optical layer system using an optical model. Thus, the thicknesses of the individual layers, the number, arrangement and thicknesses of the mirror layers and cavities determine the optical behavior of the filter.

[0054] The near infrared range from 800 to 1100 nm is particularly important for filter applications in sensors that can measure distances using time-of-flight and generate three-dimensional image information, which plays a key role in modern future technologies such as LIDAR (Light detection and ranging) for autonomous driving and human-machine interaction, for example during gesture and face recognition by mobile end devices.

[0055] The present invention will be described in more detail below with reference to exemplary embodiments. [Brief description of the drawings]

[0056] [Figure 1] FIG. 2 shows an embodiment of an optical layer system according to the invention as an optical interference filter with four different filter examples (ad). [Diagram 2] FIG. 2 shows exemplary transmission bands of the interference filter according to the invention of FIG. [Diagram 3] FIG. 2 is a schematic diagram of a sputtering process for producing an optical layer system according to the invention. [Figure 4] FIG. 2 shows an example application of the optical layer system according to the invention as a TOF sensor for face recognition.

[0057] FIG. 1 shows an embodiment of the optical layer system according to the invention as an optical interference filter. The optical interference filter is deposited on a substrate 1. The deposition can be carried out, for example, by means of a sputtering process, a CVD process or an evaporation process (eBeam). An interference filter usually consists of several layers with different refractive indices and extinction coefficients. The several layers form a layer stack, whereby cavities and mirror systems are arranged alternately. The mirror system on the other hand consists or is stacked of different mirror layers, usually alternating high, low and / or medium refractive index layers. The optical thickness of the cavity corresponds to λ / 4 and the thickness of the mirror layers to λ / 2.

[0058] Figure 1a) shows an example of a filter with two cavities 3 and a mirror system 2 made of a-Si:H. The two cavities 3 have the same refractive index n1, e.g. n1=3.1, and the mirror system 2 has two different refractive indices 21, 22, e.g. n1=3.1 and n2=3.6.

[0059] Figure 1b) shows an example of a filter with two cavities 3 and a mirror system 2 made of a-Si:H. The two cavities 3 have different refractive indices n1 31 and n2 32, e.g. n1 = 3.1 and n2 = 3.6. The mirror layers 21, 22 of the mirror system likewise have different refractive indices, e.g. n1 = 3.1 and n2 = 3.6.

[0060] Figure 1c) shows an example of a filter with three cavities 3 and a mirror system 2 made of a-Si:H. The three cavities 3 have different refractive indices n1 31, n2 32 and n3 33, e.g. n1 = 3.6, n2 = 3.2 and n3 = 3.1. The mirror layers 21, 22 of the mirror system likewise have different refractive indices, e.g. n1 = 3.1 and n2 = 3.6.

[0061] Fig. 1d) shows an example of a filter with three cavities 3 and a mirror system 2 made of a-Si:H. The three cavities 3 have different refractive indices n1 31, n2 32 and n3 33, e.g. n1 = 3.6, n2 = 3.2 and n3 = 3.1. The mirror layers 21, 22, 23 of the mirror system likewise have different refractive indices, e.g. n1 = 3.6, n2 = 3.2 and n3 = 3.1.

[0062] Figure 2 shows an exemplary transmission band of the interference filter according to the invention of figure 1. Due to the exclusive use of a-Si:H, the filter effective refractive index is higher than when using a lower refractive index material such as SiO2. The shift of the transmission band is inversely proportional to the effective refractive index. In other words, the higher the effective refractive index, the smaller the shift of the transmission band.

[0063] FIG. 3 shows a schematic diagram of a sputtering process for producing an optical layer system according to the invention.

[0064] During sputter deposition, energetic particles are directed at the silicon target 7, where these particles have sufficient energy to knock silicon atoms out of the target 7 and transport them under the influence of a magnetic or electric field to the surface of the substrate 1 for coating. The sputtering gas can be, for example, argon (Ar) from an argon source. Alternatively, other inert gases that can be ionized, such as, for example, xenon, can be used as the sputtering gas.

[0065] In a further manufacturing variant, a plasma source and / or an ion source 10 is used to adjust the reactive gas content 6 in the non-reactive or only partially reactive sputtered layer. In order to adjust the desired stoichiometry, the sputtered layer is subsequently treated with a plasma source and / or an ion source 10, respectively, after deposition of the sub-nanometer thick layer.

[0066] To produce hydrogenated amorphous silicon, hydrogen is supplied to the process chamber through a gas inlet during the sputter deposition process. The gas amounts of sputtering gas and hydrogen, or another doping gas if required, can be adjusted by dynamic flow controllers. This allows the stoichiometry of the doping gas desired for the production of low, medium and high index layers to be adjusted and controlled to ensure that identical optical properties are produced as gas flow rates vary among the low, medium and high index layers. Process parameters such as substrate temperature, target bias voltage (-V), process chamber pressure and total flow rate can similarly affect and control the incorporation of hydrogen into the silicon.

[0067] The layer materials thus produced are deposited on a substrate in a sequence and layer thicknesses that are pre-determined by means of an optical model in order to meet the optical requirements, for example of an optical filter. Precise knowledge of the correlation between the optical properties (refractive index and extinction coefficient) of the individual layers and the process parameters is an important prerequisite to be able to make correct predictions, for example of the properties of an optical filter, using the model that is used in advance for the simulation of the optical layer system to be produced. The process parameters (process pressure, gas flow rates, gas ratios, power of the sputtering source / plasma source and / or ion source, temperature) are precisely adjusted for each layer of high, low or medium refractive index, so that reproducible layer properties are obtained.

[0068] The method according to the invention makes it unnecessary to switch between different sputtering materials, e.g. niobium pentoxide and silicon dioxide, or to introduce different doping gases, e.g. oxygen and hydrogen, for layers with different refractive indices. It also makes long purging times in the process chamber unnecessary, which increases productivity and improves layer properties. This is especially important when large volumes of the final product to be produced are required.

[0069] FIG. 4 shows an example of the application of the optical layer system according to the invention as a TOF sensor for face recognition. The TOF sensor consists of a light source 11, which is usually a laser. This light source emits light 15, which is reflected by a three-dimensional object 14. The reflected light 16 is detected by a photodetector 12. It is advantageous if an optical filter 13 in the form of a band-pass filter is arranged in front of the photodetector 12. This filter ensures that only radiation of the wavelength emitted by the light source is detected and processed. For the filter 13 to function optimally, it must have a high transmission within the passband and a very low transmission outside the passband. It is also important that the filter has a large tolerance with regard to wavelength shifts for different angles of incidence of the light. These requirements must be incorporated into the design of the filter. [Explanation of symbols]

[0070] 1 Base material 2. Mirror layer 21 First mirror layer having refractive index n1 22 second mirror layer having refractive index n2 23 third mirror layer having refractive index n3 3 Cavity 31 First cavity having refractive index n1 32 A second cavity having a refractive index n2 33 A third cavity having a refractive index n3 4. Sputtering gas 5. Sputtered particles 6 Reactive Gases 7. Sputtering Targets 8 Base material 9. Coating 10 Plasma and / or ion source 11 Light source 12 Photodetector 13 Optical Filters 14 Three-dimensional objects 15 Emitted source light 16 Reflected source light

Claims

1. 1. A method for producing an optical layer system consisting of several layers, the layers of said optical layer system being deposited on a substrate from the same material by a selected coating process, said material being hydrogenated amorphous silicon a-Si:H or hydrogenated germanium Ge:H, and the refractive index and extinction coefficient of each layer of said several layers of the layer system being adjusted by controlling the process parameters of the selected coating process.

2. The same material is a-Si:H:x or Ge:H:x, where x is nitrogen (N ２ ) or chlorine (Cl ２ 2. A method for producing the optical layer system of claim 1, comprising the steps of:

3. 2. Method for producing an optical layer system according to claim 1, wherein the coating process is a sputtering process, which is carried out reactively by a reactive gas mixture of argon Ar and / or krypton Kr and / or helium He and / or xenon Xe with hydrogen H and / or nitrogen and / or chlorine, or the sputtering is carried out by Ar, Kr, He and / or Xe and the layers of the layer system are hydrogenated by a plasma and / or ion source to obtain a-Si:H or Ge:H, or the sputtering process is carried out as a combination of reactive sputtering with the plasma and / or ion source used, wherein the refractive index and the extinction coefficient of the individual a-Si:H or Ge:H layers of the layer system are adjusted by the ratio of hydrogen to Ar, Kr, He and / or Xe.

4. The reactive gas mixture is argon Ar and nitrogen N, or argon Ar and oxygen O ２ 2. The method for producing an optical layer system according to claim 1,

5. 2. Method for producing an optical layer system according to claim 1, wherein the coating process is a chemical vapor deposition process, i.e. a CVD process, which is performed either plasma-assisted or catalytic or thermal using an evaporator unit and a plasma source, and the refractive index and the extinction coefficient of each a-Si:H:x or Ge:H:x layer of the layer system are adjusted by gas flow control via the ratio of silane or germanium to hydrogen and / or the power of the evaporator unit and the plasma source.

6. 2. Method for producing an optical layer system according to claim 1, wherein the coating process is an electron beam evaporation process combined with an ion source, and the refractive index and the extinction coefficient of each a-Si:H:x or Ge:H:x layer of the layer system are adjusted by adjusting the absolute and / or partial gas flow rates in the gas mixture of the ion source and the power of an evaporator unit and of the ion source.

7. Method for producing an optical layer system according to any one of claims 2 to 6, wherein the optimum process parameters for adjusting the predefined refractive index and extinction coefficient of each a-Si:H or Ge:H layer of the layer system are determined experimentally by preliminary tests or simulations.

8. An optical layer system comprising a plurality of layers produced by the method according to any one of claims 1 to 7 and arranged on a substrate, some of the layers having a high refractive index n Ｈ Another portion of the layer has a low refractive index n Ｌ and a further portion of the layer has a medium refractive index n Ｍ where n Ｈ >n Ｍ ≧n Ｌ 1. An optical layer system in which the layers having different refractive indices are arranged in an alternating stack, characterized in that the layers are made of the same material, the high, medium and low refractive index layers differ only in the stoichiometry of a doping gas, and the optical properties of the high, medium and low refractive index layers are adjustable by process control via the stoichiometry of the doping gas.

9. The layer system has an average refractive index n Ｍｙ where y is an integer greater than zero, and n Ｈ >n Ｍ１ ≧n Ｍ２ ≧…≧n Ｍｙ >n Ｌ 9. The optical layer system according to claim 8, wherein:

10. 10. Optical layer system according to claim 8 or 9, characterized in that said identical material is hydrogenated amorphous silicon a-Si:H or hydrogenated germanium Ge:H and said doping gas is hydrogen H.

11. 11. The optical layer system according to claim 8, wherein the optical layer system is configured as a bandpass filter.

12. The bandpass filter is composed of a layer sequence of high, medium and / or low refractive index layers, and in the wavelength range from 800 nm to 1100 nm, the high refractive index layer made of a-Si:H has a refractive index n Ｈ = 3.35 to 3.8, extinction coefficient k < 0.001, and the medium refractive index layer has a refractive index n Ｍ = 3.0 to 3.6, k < 0.001, and the low refractive index layer has a refractive index n Ｌ 12. The optical layer system according to claim 11, characterized in that: k=2.5-3.3, k<0.

001.

13. The bandpass filter is composed of a layer sequence of high, medium and / or low refractive index layers, and in the wavelength range of 900 nm to 980 nm, the high refractive index layer made of a-Si:H has a refractive index n Ｈ = 3.6 to 3.8, extinction coefficient k < 0.0001, and the medium refractive index layer has a refractive index n Ｍ = 3.2 to 3.3, k < 0.0001, and the low refractive index layer has a refractive index n Ｌ 11. The optical layer system of claim 10, wherein k=3.0-3.1, k<0.0001.

14. 11. The optical layer system according to claim 8, wherein the optical layer system is formed as a rugate filter, and wherein a refractive index gradient can be formed across the layers, the refractive index gradient being adjustable for each of the layers of the optical layer system by the process control via the stoichiometry of the doping gas.

15. 11. The optical layer system according to claim 8, wherein the optical layer system is configured as an optical interference filter.

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