METHOD FOR PRODUCING AN OPTICAL LAYER SYSTEM, AND AN OPTICAL LAYER SYSTEM PRODUCED THEREWITH

Abstract

Method for producing an optical layer system that includes a multiplicity of layers arranged on a substrate, where part of the layers has a high refractive index n.sub.H, another part has a low refractive index n.sub.L and a further part has a middle refractive index n.sub.M, where n.sub.H>n.sub.Mn.sub.L and the layers having different refractive indices have an alternating stacked arrangement. The layers of the optical layer system are deposited onto a substrate by a selected coating method from an identical material which is hydrogenated amorphous silicon (a-Si:H) or hydrogenated germanium (Ge:H), where a refractive index and an extinction coefficient of each layer of the multiplicity of layers of the layer system are adjusted by a regulation of process parameters of the selected coating method.

Claims

1. A method for producing an optical layer system consisting of a multiplicity of layers, where the layers of the optical layer system are deposited onto a substrate by a selected coating method from an identical material which is hydrogenated amorphous silicon, a-Si:H, or hydrogenated germanium, Ge:H, and where a refractive index and an extinction coefficient of each layer of the multiplicity of layers of the layer system are adjusted by a regulation of process parameters of the selected coating method.

2. The method for producing an optical layer system as claimed in claim 1, where the identical material is a Si:H:x or Ge:H:x, where x comprises nitrogen (N.sub.2) or chlorine (Cl.sub.2).

3. The method for producing an optical layer system as claimed in claim 1, where the coating method is a sputtering process, where the sputtering process takes place either reactively by a reactive gas mixture of argon, Ar, and/or krypton, Kr, and/or helium, He, and/or xenon, Xe, and hydrogen, H, and/or nitrogen and/or chlorine, or the sputtering takes place by Ar, Kr, He and/or Xe and the layers of the layer system are hydrogenated to a-Si:H or Ge:H by a plasma source and/or ion source, or the sputtering process is carried out as a combination of reactive sputtering and of the plasma source and/or ion source used, where the refractive index and the extinction coefficient of each individual a-Si:H or Ge:H layer of the layer system are adjusted via a ratio of hydrogen to Ar, Kr, He and/or Xe.

4. The method for producing an optical layer system as claimed in claim 1, where the reactive gas mixture is argon, Ar, and nitrogen, N, or argon, Ar and oxygen, O.sub.2.

5. The method for producing an optical layer system as claimed in claim 1, where the coating method is a chemical vapor deposition process, CVD process, where the CVD process takes place either with plasma enhancement or catalytically or thermally by an evaporator unit and a plasma source, where 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 a gas flow regulation via a ratio of silane or germane and hydrogen and/or of a power of the evaporator unit and the plasma source.

6. The method for producing an optical layer system as claimed in claim 1, where the coating method is an electron beam evaporation process in conjunction with an ion source, where 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 an establishment of an absolute gas flow and/or a ratio of partial gas flows in a gas mixture of the ion source and of a power of an evaporator unit and the ion source.

7. The method for producing an optical layer system as claimed in claim 2, where the optimum process parameters for adjusting a defined refractive index and extinction coefficient of each a-Si:H or Ge:H layer of the layer system are ascertained experimentally by prior trials or simulations.

8. An optical layer system which is produced according to of the method as claimed in claim 1, comprising a multiplicity of layers arranged on a substrate, where one part of the layers has a high refractive index n.sub.H and another part of the layers has a low refractive index n.sub.L and also a further part of the layers has a middle refractive index n.sub.M, where n.sub.H>n.sub.Mn.sub.L, where the layers having different refractive indices have an alternating stacked arrangement, wherein the multiplicity of layers are formed of an identical material, where the high-, mid- and low-index layers differ only in their stoichiometry of a doping gas and where the optical properties of the high-, mid- and low-index layers are adjustable by the stoichiometry of the doping gas by a process controller.

9. The optical layer system as claimed in claim 8, wherein the layer system has two or more layers having a mid-index refractive index nMy, where y is an integer greater than zero and where n.sub.H>n.sub.M1n.sub.M2 . . . n.sub.My>n.sub.L.

10. The optical layer system as claimed in claim 8, wherein the identical material is hydrogenated amorphous silicon, a-Si:H, or hydrogenated germanium, Ge:H, and the doping gas is hydrogen, H.

11. The optical layer system as claimed in claim 1, wherein the optical layer system is formed as a bandpass filter.

12. The optical layer system as claimed in claim 11, wherein the bandpass filter consists of a layer sequence of high-, mid- and/or low-index layers, where a high-index layer of a-Si:H has a refractive index n.sub.H=3.35 to 3.8 and an extinction coefficient k<0.001, a mid-index layer has a refractive index n.sub.M=3.0 to 3.6 with k<0.001 and a low-index layer has a refractive index n.sub.L=2.5 to 3.3 with k<0.001 for a wavelength range from 800 nm to 1100 nm.

13. The optical layer system as claimed in claim 10, wherein the bandpass filter consists of a layer sequence of high-, mid- and/or low-index layers, where a high-index layer of a-Si:H has a refractive index n.sub.1=3.6 to 3.8 and an extinction coefficient k<0.0001, a mid-index layer has a refractive index n.sub.M=3.2 to 3.3 with k<0.0001 and a low-index layer has a refractive index n.sub.L=3.0 to 3.1 with k<0.0001 for a wavelength range from 900 nm to 980 nm.

14. The optical layer system as claimed in claim 1, wherein the optical layer system is formed as a Rugate filter, where via the multiplicity of layers a refractive index gradient can be formed which is adjustable by the stoichiometry of the doping gas via the process controller for each layer of the multiplicity of layers of the optical layer system.

15. The optical layer system as claimed in claim 8, wherein the optical layer system is formed as an optical interference filter.

Description

IN THE ASSOCIATED DRAWINGS

[0055] FIG. 1 shows an embodiment of the optical layer system of the invention as an optical interference filter, with 4 different filter examples (a-d);

[0056] FIG. 2 shows an illustrative transmission range of the interference filter of the invention from FIG. 1;

[0057] FIG. 3 shows a schematic representation of a sputter process for producing the optical layer system of the invention;

[0058] FIG. 4 shows a use example of the optical layer system of the invention as a ToF sensor for facial recognition.

[0059] FIG. 1 shows an embodiment of the optical layer system of the invention as an optical interference filter. The optical interference filter is deposited on a substrate 1. The deposition may take place, for example, by means of a sputter process, a CVD process or an evaporation process (e-beam). The interference filter consists in general of a multiplicity of layers which have different refractive indices and also extinction coefficients. The multiplicity of layers form layer stacks, with cavities and mirror systems alternating. The mirror systems are constructed in turn of different mirror layers, or stacked, and in general there is an alternation of high-, low- and/or mid-index layers. The optical thickness of a cavity corresponds to /4, that of the mirror layers to /2.

[0060] FIG. 1a) shows a filter example with two cavities 3 and mirror systems 2 of a-Si:H. The two cavities 3 have an identical refractive index n.sub.1, e.g., n.sub.1=3.1, and the mirror systems 2 have two different refractive indices 21, 22, e.g., n.sub.1=3.1 and n.sub.2=3.6.

[0061] FIG. 1b) shows a filter example having two cavities 3 and mirror systems 2 of a-Si:H. The two cavities 3 have different refractive indices n.sub.1 31 and n.sub.2 32, e.g., n.sub.1=3.1 and n.sub.1=3.6. The mirror layers 21, 22 of the mirror systems likewise have different refractive indices, e.g., n.sub.1=3.1 and n.sub.2=3.6.

[0062] FIG. 1c) shows a filter example having three cavities 3 and mirror systems 2 of a-Si:H. The three cavities 3 have different refractive indices n.sub.1 31, n.sub.2 32 and n.sub.3 33, e.g., n.sub.1=3.6, n.sub.2=3.2 and n.sub.3=3.1. The mirror layers 21, 22 of the mirror systems likewise have identical refractive indices, e.g., n.sub.1=3.1 and n.sub.2=3.6.

[0063] FIG. 1d) shows a filter example having three cavities 3 and mirror systems 2 of a-Si:H. The three cavities 3 have different refractive indices n.sub.1 31, n.sub.2 32 and n.sub.3 33, e.g., n.sub.1=3.6, n.sub.2=3.2 and n.sub.3=3.1. The mirror layers 21, 22, 23 of the mirror systems likewise have different refractive indices, e.g., n.sub.1=3.6, n.sub.2=3.2 and n.sub.3=3.1.

[0064] FIG. 2 shows an illustrative transmission range of the interference filter of the invention from FIG. 1. As a result of the exclusive use of a-Si:H, the effective refractive index of the filter is higher than when using a material of low refractive index, such as SiO2, for example. The shift in the transmission band is inversely proportional to the effective refractive index. In other words, a high effective refractive index results in a smaller shift in the transmission band.

[0065] FIG. 3 shows the schematic representation of a sputter process for producing the optical layer system of the invention.

[0066] In the course of the sputter deposition, energetic particles are directed onto a silicon target 7, with these particles having sufficient energy to sputter out silicon atoms from the target 7 and, under the influence of a magnetic or electrical field, to transfer them to the surface of the substrate 1, which is thereby coated. The sputter gas may be, for example, argon (Ar) from an argon source. The sputter gas used may alternatively comprise other inert gases that can be ionized as well, such as xenon, for example.

[0067] A further production variant entails the use of a plasma source and/or ion source 10 for establishing the reactive gas content 6 within the non-reactively or only part-reactively sputtered layer. Following the deposition of a lamina of subnanometer thickness, the sputtered layer is retrospectively treated by means of the plasma source and/or ion source 10 in each case, in order to establish the desired stoichiometry.

[0068] In order to produce hydrogenated amorphous silicon, hydrogen is admitted to the process chamber via a gas inlet during the sputter deposition process. Dynamic flow regulators make it possible to adjust the gas quantity of sputter gas and hydrogen or, if desired, of the other doping gases. Accordingly it is possible to adjust and regulate the desired stoichiometry of the doping gases for the production of low-, mid- and high-index layers, in order to ensure the development of identical optical properties during a gas flow change between the low-, mid- and high-index layers. By means of the process parameters such as the substrate temperature, the target bias voltage (V), the process chamber pressure, the total flow rate, etc., it is likewise possible to influence and regulate the incorporation of hydrogen into the silicon.

[0069] The layer materials thus generated are deposited on the substrate in a layer thickness and sequence determined beforehand by means of optical models, in order to meet the optical requirements, for an optical filter, for example. The precise knowledge of the dependency relationships between the optical properties (refractive index and extinction coefficient) of the individual layers and the process parameters is an important prerequisite for being able to make correct predictions for the properties, of an optical filter, for example, with previously used models for the simulation of an optical layer system to be produced. For each high-, low- or mid-index layer, the process parameters (process pressure, gas flow, gas ratio, powers of the sputter source/plasma source and/or ion source, temperature) are adjusted exactly and so reproducible layer properties can be attained.

[0070] The method of the invention does away with switching between different sputter materials, such as niobium pentoxide or silicon dioxide, for example, or the admission of different doping gases, such as oxygen or hydrogen, for example, for the layers having different refractive indices. This also does away with long purge times in the process chamber, allowing the productivity to be boosted and the layer properties to be improved. This is especially of interest when the end products produced are needed in large quantity.

[0071] FIG. 4 shows a use example of the optical layer of the invention as a ToF sensor for facial recognition. The ToF sensor consists of a light source 11, typically a laser. This 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 for an optical filter 13 in the form of a bandpass filter to be arranged in front of the photodetector 12. This filter ensures that only radiation having a wavelength which is emitted by the light source is detected and processed. For the optical functionality of the filter 13, it must have a high transmission in the pass band and a very low transmission outside the pass band. It is important, moreover, that the filter has a high tolerance in relation to the wavelength shift at different incident angles of the light. These requirements must form part of the filter design process.

Method for Producing an Optical Layer System, and an Optical Layer System Produced Therewith

LIST OF REFERENCE SYMBOLS

[0072] 1 substrate [0073] 2 mirror layer [0074] 21 first mirror layer with refractive index n.sub.1 [0075] 22 second mirror layer with refractive index n.sub.2 [0076] 23 third mirror layer with refractive index n.sub.3 [0077] 3 cavity [0078] 31 first cavity with refractive index n.sub.1 [0079] 32 second cavity with refractive index n.sub.2 [0080] 32 third cavity with refractive index n.sub.3 [0081] 4 sputter gas [0082] sputtered particles [0083] 6 reactive gas [0084] 7 sputter target [0085] 8 substrate [0086] 9 coating [0087] plasma source and/or ion source [0088] 11 light source [0089] 12 photodetector [0090] 13 optical filter [0091] 14 three-dimensional object [0092] 15 emitted light of the light source [0093] 16 reflected light of the light source