Method for producing a reflection-reducing layer system

Abstract

A method for producing a reflection-reducing layer system is disclosed. In an embodiment, a method includes depositing an organic layer on the substrate, generating a nanostructure in the organic layer by a plasma etching process, applying a cover layer to the nanostructure, wherein the organic layer, the nanostructure and the cover layer together form a reflection-reducing structure, wherein the cover layer comprises an inorganic material or an organosilicon compound, and wherein the cover layer is at least 5 nm thick and performing a post-treatment after applying the cover layer, wherein a material of the organic layer is at least partially removed, decomposed or chemically converted, and wherein an effective refractive index n.sub.eff,2 of the reflection-reducing structure after the post-treatment is smaller than an effective refractive index n.sub.eff,1 of the reflection-reducing structure before the post-treatment.

Claims

1. A method for producing a reflection-reducing layer system on a substrate, the method comprising: depositing an organic layer on the substrate; generating a nanostructure in the organic layer by a plasma etching process; applying a cover layer to the nanostructure, wherein the organic layer, the nanostructure and the cover layer together form a reflection-reducing structure, wherein the cover layer comprises an inorganic material or an organosilicon compound, and wherein the cover layer is at least 5 nm thick; and performing a post-treatment after applying the cover layer, wherein a material of the organic layer is at least partially removed, decomposed or chemically converted, and wherein an effective refractive index n.sub.eff,2 of the reflection-reducing structure after the post-treatment is smaller than an effective refractive index n.sub.eff,1 of the reflection-reducing structure before the post-treatment.

2. The method according to claim 1, wherein cavities and/or porous regions are formed below the cover layer during the post-treatment.

3. The method according to claim 1, wherein the effective refractive index n.sub.eff,1 of the reflection-reducing structure before the post-treatment is 1.15<n.sub.eff,1<1.25.

4. The method according to claim 1, wherein the effective refractive index n.sub.eff,18 is of the reflection-reducing structure after the post-treatment is 1.03<n.sub.eff,2<1.23.

5. The method according to claim 1, wherein the reflection-reducing structure has a refractive index gradient after the post-treatment, and wherein the effective refractive index n.sub.eff,2 in a region of the reflection-reducing structure facing the substrate is at least regionally 1.15<n.sub.eff,2<1.23, and 1.03<n.sub.eff,2<1.1 in a region facing the cover layer at least regionally.

6. The method according to claim 1, wherein the post-treatment comprises a temperature treatment at a temperature greater than 70 C.

7. The method according to claim 6, wherein the temperature treatment is performed at a relative humidity of more than 50%.

8. The method according to claim 1, wherein the post-treatment comprises a plasma treatment, a treatment with UV radiation or a treatment by ion bombardment.

9. The method according to claim 1, wherein the reflection-reducing structure is between 150 nm and 500 nm thick.

10. The method according to claim 1, wherein the organic layer comprises a nitrogen-containing organic material having a conjugated ring-shaped structure containing at least atoms carbon, nitrogen and hydrogen.

11. The method according to claim 1, wherein the organic layer contains at least one of a heterocyclic organic compound having a purine or pyrimidine backbone, a triazine, an amine or polyaminoamide, or an amino acid or a derivative of an amino acid, having a melting point >100 C.

12. The method according to claim 11, wherein triazine is melamine.

13. The method according to claim 1, wherein the organic layer contains guanine (2-amino-6-oxo-purine), xanthine (2,6-dihydroxypurine),uracil (2,4-pyrimidinedione) or mixtures of these materials.

14. The method according to claim 1, wherein the cover layer comprises an oxide, a fluoride or a nitride.

15. The method according to claim 1, wherein the cover layer comprises SiO.sub.2, Al.sub.2O.sub.3 or MgF.sub.2.

16. The method according to claim 1, wherein the cover layer is between 15 nm and 35 nm thick.

17. The method according to claim 1, wherein the reflection-reducing structure comprises structural elements in form of elevations and depressions having an average height of more than 80 nm.

18. The method according to claim 1, wherein the reflection-reducing structure comprises structural elements in form of elevations and depressions having an average width of less than 40 nm.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention will be explained in more detail in the following using examples in connection with FIGS. 1 to 4.

(2) In the figures:

(3) FIGS. 1A to 1D show an example of the method for producing a reflection-reducing layer system using schematically illustrated intermediate steps;

(4) FIG. 2 shows a graphic representation of the reflection R as a function of the wavelength in an example of a reflection-reducing layer system produced with the process before post-treatment and after post-treatment;

(5) FIG. 3 shows a graphical representation of an infrared spectrum of the reflection-reducing layer system according to the example of FIG. 2 before post-treatment and after post-treatment; and

(6) FIG. 4 shows a graphic representation of the reflection R as a function of the wavelength in another example of a reflection-reducing layer system produced with the process before post-treatment and after post-treatment.

(7) Identical or equivalent components are each provided with the same reference signs in the figures. The components shown as well as the proportions of the components among each other are not to be regarded as true to scale.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

(8) In the intermediate step of the method shown in FIG. 1A, an organic layer 2 was applied to a substrate 1. The substrate 1 may have a flat or curved surface and may comprise, for example, glass, plastic or semiconductor material. In particular, the substrate 1 can be an optical element with a surface to be coated with an anti-reflection coating. For example, substrate 1 can be a lens such as a spectacle lens or the surface of a display.

(9) The organic layer 2 is preferably about 150 nm to 500 nm thick. With a layer thickness in this range, the organic layer 2 is thick enough that a sufficiently deep nanostructure can be produced in it in a further process step.

(10) The organic layer 2 is preferably applied using a vacuum coating process. This has the advantage that the entire reflection-reducing layer system can be applied in a vacuum process. For example, a PVD or CVD process can be used to apply the organic layer 2. Alternatively, it is also possible to apply the organic layer 2 using a wet-chemical process.

(11) The organic layer 2 is formed from a material that can be at least partially removed, decomposed and/or chemically converted in a subsequent process step. Particularly suitable are nitrogen-containing organic materials with a conjugated ring-shaped structure which contain at least the atoms carbon, nitrogen and hydrogen. Examples of such materials are heterocyclic organic compounds with a purine or pyrimidine backbone, in particular also naturally occurring substances such as guanine (2-amino-6-oxo-purine), xanthine (2,6-dihydroxypurine) and uracil (2,4-pyrimidinedione) or mixtures of these materials. Other suitable materials are triazines such as melamine and other high-melting point amines or polyaminoamides, as well as amino acids and their high-melting point derivatives. The material of the organic layer 2 is in particular a material with a melting point above 100 C.

(12) In the example shown in FIG. 1A, the organic layer 2 has been applied directly to the surface of the substrate 1. Alternatively, it is also possible to apply one or more additional layers to the substrate 1 before applying the organic layer 2. The at least one further layer can already have a reflection-reducing effect on the substrate 1, which is to be enhanced with the method described here. For example, a reflection-reducing interference layer system can be applied to substrate 1 before the organic layer 2 is applied.

(13) After applying the organic layer 2, a plasma etching process is performed as shown in FIG. 1B to produce a nanostructure 4 in the organic layer 2. The nanostructure 4 is preferably generated by ion bombardment with a plasma ion source 5. For example, an argon-oxygen plasma can be used. Such a plasma etching process is known from the documents DE 10241708 B4 or DE 102008018866 A1 mentioned in the introduction and is therefore not explained in detail.

(14) Before the plasma etching process is performed, a thin initial layer (not shown) can be applied to the organic layer 2 to be structured, which preferably has a thickness of only about 2 nm. The initial layer is preferably a thin oxide layer, nitride layer or fluoride layer. This procedure is known from the publication DE 102008018866 A1.

(15) The nanostructure has a large number of structural elements in the form of elevations and depressions, whereby the elevations are advantageously at least 80 nm high and have a width of advantageously not more than 40 nm and particularly advantageously between 15 nm and 35 nm. The nanostructured organic layer 2 has an effective refractive index n.sub.eff,1, which is lower than the refractive index of the organic layer 2 before the generation of the nanostructure. Preferably, the effective refractive index n.sub.eff,1 of the nanostructured organic layer 2 is between 1.15 and 1.25.

(16) In a further method step which is shown in FIG. 1C, a cover layer 3 is applied to the nanostructured organic layer 2. The cover layer 3 is preferably an inorganic layer, in particular an oxide, nitride or fluoride layer such as silicon oxide, aluminum oxide, silicon nitride or magnesium fluoride. Alternatively, the cover layer 3 can contain an organosilicon compound, such as a plasma polymer. A particularly suitable material for the cover layer is SiO.sub.2.

(17) The coating 3 is advantageously no thicker than 50 nm. The thickness of the cover layer 3 is preferably between 5 nm and 35 nm, especially between 15 nm and 35 nm. The thin cover layer 3 covers the nanostructure of the organic layer 2 advantageously conformally, i.e., it reproduces the elevations and depressions of the organic layer 2. Together with the organic layer 2 which has the nanostructure 4, the cover layer 3 forms a reflection-reducing structure 6.

(18) In a further process step, which is shown in FIG. 1D, the previously produced reflection-reducing structure 6 comprising the nanostructured organic layer 2 and the cover layer 3 is post-treated. The post-treatment is, for example, a temperature treatment, which is preferably carried out at a temperature of T70 C. Preferably, the temperature treatment is carried out at a high relative humidity r.sub.h50%.

(19) A preferred form of post-treatment is the application of an oxygen-containing plasma from an ion source 5, as previously used for the etching step of the organic layer 2. The treatment can then take place in the same vacuum process immediately after the deposition of the cover layer 3.

(20) The post-treatment causes the material of the organic layer 2 to be at least partially removed, decomposed and/or converted. In particular, it is possible that at least part of the organic material of organic layer 2 is decomposed into gaseous components, in particular NH.sub.3, which escape from the layer system. The gaseous components may escape in particular through the thin cover layer 3. Due to the fact that the cover layer 3 has only a very small thickness and is applied to the nanostructured organic layer 2, the cover layer 3 can have at least a low porosity, which allows gaseous components to escape from the organic layer 2.

(21) During post-treatment, cavities and/or porous areas 2a can form, especially below the cover layer 3. However, it can also be achieved that the material of the organic layer 2 changes overall. A change of the material of the organic layer 2 shows up in particular in a change of the IR spectra.

(22) The cover layer 3 of inorganic material or the organosilicon compound is advantageously unaffected by the post-treatment, so that its properties, in particular its shape and thickness, do not essentially change during the post-treatment.

(23) The post-treatment has the advantage that the effective refractive index of the reflection-reducing structure 6 is further reduced. The effective refractive index n.sub.eff,2 of the reflection-reducing structure 6 after post-treatment is lower than the effective refractive index n.sub.eff,1 before post-treatment. The effective refractive index n.sub.eff,2 of the reflection-reducing structure 6 after post-treatment is preferably between 1.03 and 1.23. The particularly low effective refractive index after post-treatment has the advantage that the reflection-reducing effect is further increased.

(24) It is also possible that the organic component is more strongly decomposed and/or removed towards the surface of the reflection-reducing structure 6 and thus a refractive index gradient is formed or strengthened. At the tips of the nanostructure is then significantly more low refractive cover layer material located and in the lower area of the nanostructure is more higher refractive organic material located. In this case, the effective refractive index n.sub.eff,2 decreases in the direction from the substrate 1 to the surface. Preferably the effective refractive index n.sub.eff,2 in a region of the reflection-reducing structure facing the substrate 1 is at least regionally 1.15<n.sub.eff,2<1.23, and in a region facing the cover layer 3 is at least regionally 1.03<n.sub.eff,2<1.1. A particularly good reflection-reducing effect is achieved by the refractive index gradient produced in this way.

(25) In addition, the reflection-reducing layer system produced in this way has the advantage that the optical properties do not change significantly in a humid, warm climate. Thus, the reflection-reducing coating is characterized by improved climate stability.

(26) FIG. 2 shows the reflection R as a function of the wavelength for a reflection reducing layer system produced according to an example of the method. In this example, a glass substrate of type B270 with a refractive index n.sub.S=1.53 was used. In a first step, a dielectric interference layer system with eight alternating TiO.sub.2 layers and SiO.sub.2 layers was deposited on the glass substrate by evaporation. The interference layer system in this example consists starting from the substrate of the layer sequence 10 nm TiO.sub.2/50 nm SiO.sub.2/28 nm TiO.sub.2/23 nm SiO.sub.2/138 nm TiO.sub.2/22 nm SiO.sub.2/22 nm TiO.sub.2/100 nm SiO.sub.2. A 200 nm thick organic layer of uracil was deposited on the interference layer system by evaporation. In the organic uracil layer, a plasma etching process was subsequently used to produce a nanostructure with structural elements about 120 nm high. In a further step, a 30 nm thick SiO.sub.2 layer was applied to the nanostructure as a cover layer. The effective refractive index of the reflection-reducing structure made up of the organic layer and the top layer is about n.sub.eff,1=1.22.

(27) In a further step, the layer system produced in this way was post-treated to complete the reflection-reducing layer system. In the example, a plasma treatment was carried out for post-treatment. Post-treatment was carried out in a microwave plasma system for 10 minutes in an O.sub.2 plasma with a power of 400 W and a pressure of 3*10.sup.2 mbar.

(28) The dashed line in FIG. 2 shows the reflection before post-treatment and the solid line shows the reflection after post-treatment. It can be seen that the residual reflection, especially in the spectral range between 400 nm and 1000 nm, is further reduced by the post-treatment. The nanostructured organic layer has an effective refractive index of only n.sub.eff,2=1.15 after post-treatment. It has also been found that the optical properties of the reflection-reducing layer system produced in this way do not change during storage for a period of 48 hours in a humid, warm climate (85% relative humidity, T=80 C.) or at a very high temperature (T=110 C.).

(29) FIG. 3 shows measured FTIR spectra of the reflection-reducing layer system according to the example given in FIG. 2 before and after plasma post-treatment. The absorption A (in arbitrary units) is shown as a function of the wavenumber. The infrared spectrum before post-treatment (dashed line) shows clear signals of the organic material (in particular the NH band) together with the pronounced signal of the SiO.sub.2 component (SiO band). In contrast, the infrared spectrum of the reflection-reducing structure post-treated in microwave plasma (solid line) hardly shows bands of the organic component.

(30) FIG. 4 shows the reflection R as a function of the wavelength for a reflection-reducing layer system that was produced according to another example of the method. In this example, a plastic substrate made of Zeonex with a refractive index n.sub.S=1.53 was used. In a first step, a first nanostructure with a depth of 100 nm and an effective refractive index of n=1.35 has been produced in the plastic substrate by a first plasma etching process.

(31) A 220 nm thick organic layer of xanthine was deposited by vapor deposition onto the first nanostructure produced in the plastic substrate. A second plasma etching process was subsequently used to produce a second nanostructure in the organic xanthine layer, which has structural elements with a height of about 120 nm. In a further step, a 20 nm thick SiO.sub.2 layer was applied as a cover layer to the second nanostructure. The effective refractive index of the second nanostructure with the cover layer is about n.sub.eff,1=1.18.

(32) In a further step, the layer system produced in this way was post-treated to complete the reflection-reducing layer system. In the example, a plasma treatment was carried out for post-treatment. The post-treatment was carried out directly in the coating plant (type Leybold SyrusPro with the plasma ion source type APS). The plasma treatment was carried out with a mixture consisting of 35% argon and 65% oxygen, a maximum ion energy of 100 eV (bias voltage 100 V) for 10 minutes at a pressure of 3*10.sup.4 mbar.

(33) The dashed line in FIG. 3 shows the reflection before post-treatment and the solid line shows the reflection after post-treatment. It can be seen that the residual reflection, especially in the spectral range between about 400 nm and about 800 nm, is further reduced by the post-treatment. The anti-reflection structure has an effective refractive index of only n.sub.eff,2=1.13 after post-treatment. It has also been found that the optical properties of the reflection-reducing layer system produced in this way do not change further during storage for a period of 48 hours in a humid, warm climate (85% relative humidity, T=50 C.) or at a very high temperature (T=100 C.).

(34) The invention is not limited by the description based on the examples. Rather, the invention includes any new feature and any combination of features, which in particular includes any combination of features in the claims, even if that feature or combination itself is not explicitly stated in the claims or examples.