Method for producing a reflection-reducing layer system and reflection-reducing layer system

Abstract

A reflection-reducing layer system is disclosed. In an embodiment, the system includes a refractive index gradient layer including an inorganic material and an organic material in a spatially varying composition, wherein the refractive index gradient layer has a refractive index which decreases in a growth direction and an organic layer arranged above the refractive index gradient layer, the organic layer having a surface including a nanostructure.

Claims

1. A reflection-reducing layer system comprising: a refractive index gradient layer comprising an inorganic material and an organic material in a spatially varying composition, wherein the refractive index gradient layer has a refractive index which decreases in a growth direction; and an organic layer arranged above the refractive index gradient layer, the organic layer having a surface comprising a nanostructure.

2. The reflection-reducing layer system according to claim 1, wherein the nanostructure has a plurality of structure elements whose heights are on average between 80 nm and 130 nm and whose spacings are on average less than 100 nm.

3. The reflection-reducing layer system according to claim 1, wherein the refractive index of the refractive index gradient layer at an interface with a substrate of the reflection-reducing layer system is matched to a refractive index of the substrate.

4. The reflection-reducing layer system according to claim 1, wherein a total thickness of the reflection-reducing layer system is between 250 nm and 450 nm.

5. The reflection-reducing layer system according to claim 1, wherein the inorganic material of the refractive index gradient layer has a refractive index n1 where 1.37n11.46, and wherein the organic material of the refractive index gradient layer has a refractive index n2>n1 where 1.6n21.9.

6. The reflection-reducing layer system according to claim 1, wherein the organic material is a UV-absorbing material.

7. The reflection-reducing layer system according to claim 1, wherein the organic layer has at least regionally an effective refractive index of between 1.05 and 1.38.

8. The reflection-reducing layer system according to claim 1, further comprising an inorganic intermediate layer arranged between the organic layer and the refractive index gradient layer.

9. The reflection-reducing layer system according to claim 1, further comprising a protective layer disposed on the nanostructure, wherein the protective layer has a thickness of between 10 nm and 50 nm.

10. The reflection-reducing layer system according to claim 1, wherein the organic layer comprises melamine.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Further advantageous configurations of the reflection-reducing layer system are evident from the above description of the method, and vice versa.

(2) Embodiments of the invention are explained in greater detail below in association with FIGS. 1 to 7.

(3) FIG. 1 shows a schematic illustration of a lensfunctioning as a substratehaving a spherical surface with an illustration of the layer thickness change for various angles of vapor incidence;

(4) FIG. 2 shows a graphical illustration of reflection spectra at positions A and B of the lens shown in FIG. 1 for a conventional interference layer system composed of 4 layers (V1) and for a single layer composed of MgF.sub.2 (V2);

(5) FIGS. 3A to 3F show a schematic illustration of one exemplary embodiment of the method for producing the reflection-reducing layer system on the basis of intermediate steps,

(6) FIG. 4 shows a graphical illustration of the profile of the effective refractive index new for a first and a second exemplary embodiment of the reflection-reducing layer system;

(7) FIG. 5 shows a graphical illustration of reflection spectra at positions A and B of the lens shown in FIG. 1 for a first exemplary embodiment of the reflection-reducing layer system;

(8) FIG. 6 shows a graphical illustration of reflection spectra at positions A and B of the lens shown in FIG. 1 for a second exemplary embodiment of the reflection-reducing layer system; and

(9) FIG. 7 shows a graphical illustration of reflection spectra for the first and second exemplary embodiments of the reflection-reducing layer system.

(10) Identical or identically acting component parts are in each case provided with the same reference signs in the figures. The illustrated component parts and the size relationships of the component parts among one another should not be regarded as true to scale.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

(11) FIG. 1 schematically illustrates a spherical lens which is intended to be provided with an antireflection layer. The spherical lens thus functions as a substrate 10 for the antireflection layer. The lens is, for example, a glass lens having a refractive index n.sub.s=1.53. If a layer is deposited by means of a directional vacuum coating process such as, for example, sputtering or vapor deposition on the curved surface of the lens, the layer has, at the location at which it grows, a thickness that is dependent on the angle of the impinging vapor. It is generally known that the following holds true for the layer thickness d as a function of the angle of vapor incidence on the lens: d()=d.sub.o*cos .

(12) In this case, d.sub.o is the layer thickness in the center of the lens (perpendicular vapor incidence). In the case of a perfect hemisphere, the layer thickness is thus 0 nm at the outermost edge; at least theoretically, no layer at all is deposited. At a point B of the lens, this point having an angle of vapor incidence of =60, the layer thickness decrease is already 50% compared with the midpoint A of the lens, on which midpoint the vapor impinges perpendicularly (=0).

(13) FIG. 2 illustrates the influence of the layer thickness decrease toward the edge of the lens for comparative examples (not according to the invention) of conventional antireflection layers. The illustration shows the reflection R as a function of the wavelength at the points A and B of the lens shown in FIG. 1 for a conventional interference layer system composed of four layers (V1) and for a single layer composed of MgF.sub.2 (V2). The graphic illustrates that, at the midpoint A of the lens, the residual reflection that can be achieved with the interference layer system V1 composed of four layers is lower than that which can be achieved with the individual layer V2. At the point B, at which the layer thickness is reduced by 50%, a lower residual reflection R and thus a better antireflection arrangement are achieved with the individual layer V2. In other words, the multilayered interference layer system has a lower tolerance to changes in the layer thickness than the individual layer. With the method according to embodiments of the invention the intention is to produce an antireflection layer which has a particularly low residual reflection both in the case of perpendicular light incidence and in the case of oblique light incidence.

(14) FIGS. 3A to 3F illustrate a first exemplary embodiment of the method for producing a reflection-reducing layer system on the basis of intermediate steps.

(15) In the exemplary embodiment of the method, the substrate 10 illustrated in FIG. 3A is provided with a reflection-reducing layer system. In the exemplary embodiment illustrated, the substrate 10 is a planar substrate. Alternatively, in the method the substrate 10 could be, in particular, a curved substrate, such as, for example, the spherical lens illustrated in FIG. 1. The substrate 10 can be, in particular, a glass or plastics substrate.

(16) In the intermediate step illustrated in FIG. 3B, a refractive index gradient layer 1 has been applied to the substrate 10 by coevaporation of an inorganic material and an organic material. The refractive index gradient layer 1 preferably contains MgF.sub.2 or SiO.sub.2 as inorganic material and melamine as organic material. Alternatively, it is possible for the preferred inorganic materials MgF.sub.2 or SiO.sub.2 to be combined with a different organic material, for example, with one of the UV-absorbing organic materials described above. Instead of MgF.sub.2, other fluorides such as AlF.sub.3, for example, or fluoride mixtures such as cryolite, for example, can be used as inorganic material, wherein these fluorides are distinguished by a particularly low refractive index of n<1.4.

(17) The coevaporation of the inorganic material and the organic material is preferably effected with ion assistance, wherein, by way of example, a plasma ion source is used to generate ions of nitrogen or some other inert gas with a maximum ion energy of approximately 45 eV to 60 eV, which impinge on the refractive index gradient layer 1 during vapor deposition.

(18) The refractive index gradient layer 1 preferably has a thickness of 70 nm to 200 nm, preferably approximately 150 nm. The concentration of the organic material is preferably not more than 95% in a region at the interface with the substrate 10. In the region at the interface with the substrate 10, the concentration of the organic material is preferably chosen in such a way that the refractive index of the refractive index gradient layer 1 is matched to the refractive index of the substrate 10 in this region. In this context, matched means, in particular, that the refractive index of the refractive index gradient layer at the interface with the substrate deviates from the refractive index of the substrate by not more than 0.1, preferably not more than 0.05.

(19) In a region at the interface facing away from the substrate 10, the concentration of the organic material is preferably less than 5%. The thickness of this region can advantageously be at least 30%, preferably at least 40%, or even at least 50%, of the total thickness of the refractive index gradient layer 1.

(20) In the method step illustrated in FIG. 3C, an inorganic intermediate layer 3 preferably containing SiO.sub.2 has been applied to the refractive index gradient layer 1. The inorganic intermediate layer preferably has a thickness of between 2 nm and 15 nm and is densified during growth preferably by ion bombardment with argon or oxygen ions.

(21) In the further method step illustrated in FIG. 3D, an organic layer 2 has been applied above the refractive index gradient layer 1 and the intermediate layer 3. The production of the organic layer 2, like the production of the refractive index gradient layer 1, is preferably effected by ion assisted vapor deposition by means of a plasma ion source which generates ions of nitrogen or some other inert gas having a maximum ion energy of approximately 45 eV to 60 eV. The organic layer 2 is preferably applied with a thickness of between 250 nm and 450 nm. The material of the organic layer 2 is preferably melamine.

(22) In the intermediate step of the method as illustrated in FIG. 3E, a nanostructure 12 has been produced in the organic layer 2 by means of a plasma etching process, wherein the nanostructure is formed by a multiplicity of structure elements in the form of elevations and depressions. The heights of the structure elements (peak-to-valley) are preferably on average between 80 nm and 130 nm, and their spacings (peak-to-peak) are preferably not more than 100 nm. In the plasma etching process, the surface of the substrate 10 is bombarded with ions by means of a plasma ion source, for example, in order to produce the nanostructure 12. Such a plasma etching process is known per se from the documents DE 10241708 B4 or DE 102008018866 A1 cited in the introductory part of the description and will therefore not be explained in any greater detail.

(23) Before carrying out the plasma etching process, it is possible to apply a thin initial layer (not illustrated) to the surface to be structured, which preferably has a thickness of only approximately 2 nm. The initial layer is preferably a thin oxide layer, nitride layer or fluoride layer. This procedure is known per se from the document DE 102008018866 A1.

(24) The nanostructure produces a refractive index gradient in the organic layer 2 which decreases in a direction pointing from the substrate 10 to the surface. The average effective refractive index of the nanostructure 12 is preferably less than 1.2. A region having a thickness of at least 100 nm and having a refractive index of less than 1.15 preferably arises at the surface.

(25) The refractive index gradient layer 1 is thus succeeded by a second refractive index gradient layer, which is formed by the nanostructure 12 in the former layer 2 and in which the refractive index decreases to an even lower value. Preferably, the refractive index decreases in the entire reflection-reducing layer sequence in the direction from the substrate 10 toward the surface. In this way, an overall very thick refractive index gradient layer is produced which brings about a particularly good antireflection arrangement over a large angular range and wavelength range. In particular, it has been found that the reflection-reducing layer sequence produced by the method brings about a very good antireflection arrangement right into the edge regions of the substrate even in the case of curved substrates since the antireflection layer produced by the method is comparatively tolerant toward changes in the layer thickness.

(26) In one advantageous configuration of the method, as illustrated in FIG. 3F, a protective layer 4 is applied to the nanostructure 12. The protective layer 4 preferably has a thickness of 10 nm to 50 nm, with preference less than 30 nm, and can be an SiO.sub.2 layer, for example. The protective layer 4 serves, in particular, for protecting the nanostructure 12 consisting of the organic material of the organic layer 2 against external influences, in particular against mechanical damage.

(27) In one exemplary embodiment of the method, a reflection-reducing layer sequence was produced, the sequence of the method corresponding to FIGS. 3A to 3F. In this case, a plastics lens 10 composed of a polycarbonate (Makrolon) was provided with the reflection-reducing layer sequence. A refractive index gradient layer 1 having a thickness of 300 nm was applied to the plastics substrate 10 by coevaporation of the organic UV absorber methyl-2-cyano-3(4-hydroxyphenyl)acrylate (obtainable under the designation SEMAsorb 20163) and MgF.sub.2.

(28) The refractive index was matched by the mixture of the materials having the refractive indices 1.7 @ 500 nm (SEMAsorb 20163) and 1.38 (MgF.sub.2) such that the effective refractive index is 1.55 in a region at the substrate and decreases gradually to 1.38 in a region at the surface. The proportion of the organic material is approximately 60% at the substrate 10 and less than 5% within the last 20 nm at the surface of the refractive index gradient layer 10. Overall, the proportion of the organic material in the refractive index gradient layer 10 is approximately 40%.

(29) Firstly an approximately 5 nm thick inorganic intermediate layer 3 composed of SiO.sub.2 for adhesion promotion and then a 250 nm thick organic layer 2 composed of melamine were subsequently applied by vapor deposition in the same vacuum process. During the vapor deposition of the SiO.sub.2 layer 3, argon and oxygen ions were accelerated in the direction of the growing SiO.sub.2 layer 3 with the aid of a plasma ion source, wherein the ion source was operated with Ar and O.sub.2 flow rates of in each case 10 sccm and ion energies of between 60 eV and 120 eV were generated.

(30) The vapor deposition of the organic layer 2 composed of melamine was effected with ion assistance by an inert gas and with a maximum ion energy of 60 eV, with addition of Ar at a flow rate of up to 10 sccm. Afterward, with a suitable ion source which generates ions having an average energy of 80 eV (40 eV to 160 eV), a nanostructure 12 was etched into the melamine layer 2. The nanostructure 12 in the organic layer 2 produced in this way has structure elements having heights of at least 80 nm and a maximum of 140 nm depending on etching time and ion energy. Finally, a 20 nm thick protective layer 4 composed of SiO.sub.2 was applied. The average effective refractive index of the nanostructured organic layer 2 including the protective layer 4 is in the range of 1.05 to 1.15.

(31) The profile of the effective refractive index n.sub.eff as a function of a spatial coordinate zproceeding from the substrateof the first exemplary embodiment of the reflection-reducing layer system produced in this way is illustrated in FIG. 4 (curve S1) in comparison with a second exemplary embodiment (curve S2), which is explained below. The dashed lines mark a range of expedient refractive index profiles which can be realized by the method.

(32) FIG. 5 illustrates the reflection R as a function of the wavelength A for the first exemplary embodiment of the reflection-reducing layer system, such as occurs at positions A and B of the curved lens in accordance with FIG. 1. The reflection-reducing layer system has a total layer thickness of 370 nm in the central region of the curved lens and attains an average residual reflection of <0.4% in the spectral range of 400 nm to 700 nm. In the edge region of the lens where the angle of vapor incidence is up to 60 and the layer thickness has decreased to 50%, an average residual reflection of <1% is attained.

(33) In a second exemplary embodiment, a lens composed of a cycloolefin polymer (Zeonex) was used as the substrate 10. A refractive index gradient layer 1 having a gradually decreasing refractive index and a thickness of 250 nm was applied by coevaporation of melamine and MgF.sub.2. The proportion of melamine is approximately 25% in the region at the interface with the substrate and is less than 5% within the last 50 nm at the surface of the refractive index gradient layer 1. A 300 nm thick melamine layer 2 was subsequently applied by vapor deposition in the same process. Afterward, with a suitable ion source which generates ions having an average energy of 80 eV (40 eV to 160 eV), a nanostructure 12 was etched into the melamine layer 2. The nanostructure 12 in the organic layer 2 produced in this way has structure elements whose spacings are on average not more than 100 nm. Finally, a 25 nm thick protective layer 4 composed of SiO.sub.2 was applied by vapor deposition. The SiO.sub.2 preferably deposits on the crests of the structures in the directional process, such that the filling factor and the shape of the nanostructure 12 change slightly. The thickness of the nanostructured organic layer 2 including the protective layer 4 is at least 100 nm and a maximum of 130 nm.

(34) FIG. 6 illustrates the reflection R as a function of the wavelength for the second exemplary embodiment of the reflection-reducing layer system, such as occurs at positions A and B of the curved lens in accordance with FIG. 1. The reflection-reducing layer system has a total layer thickness of 360 nm in the central region of the curved lens and attains an average residual reflection of 0.5% in the spectral range of 400 nm to 700 nm. In the edge region of the lens where the angle of vapor incidence is up to 600 and the layer thickness has decreased to 50%, an average residual reflection of <1% is attained.

(35) FIG. 7 shows, for both exemplary embodiments S1 and S2, the reflection R as a function of the wavelength in a larger wavelength range of 400 nm to 1200 nm.

(36) The reflection spectra illustrated in FIGS. 5 to 7 make it clear that the antireflection layer produced by the method described herein has a particularly low residual reflection even at positions on curved substrates at which reduced layer thicknesses occur on account of an increased angle of vapor incidence during the coating process. Furthermore, the antireflection layer produced by the method is also advantageous for planar substrates if the intention is to achieve a particularly low residual reflection at large angles of light incidence, for example, at angles of incidence of up to 80, and/or over a large wavelength range, for example, of 400 nm to 1200 nm.

(37) The invention is not restricted by the description on the basis of the exemplary embodiments. Rather, the invention encompasses any novel feature and also any combination of features, which in particular includes any combination of features in the patent claims, even if this feature or this combination itself is not explicitly specified in the patent claims or exemplary embodiments.