WO2015110546A1

WO2015110546A1 - Method for producing a reflection-reducing layer system, and a reflection-reducing layer system

Info

Publication number: WO2015110546A1
Application number: PCT/EP2015/051278
Authority: WO
Inventors: Ulrike Schulz; Friedrich RICKELT; Stephane Bruynooghe; Diana Tonova; Thomas Koch
Original assignee: Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e.V.; Carl Zeiss Jena Gmbh
Priority date: 2014-01-23
Filing date: 2015-01-22
Publication date: 2015-07-30
Also published as: DE102014100769A1; DE102014100769B4

Abstract

The invention relates to a method for producing a reflection-reducing layer system (5) on a substrate (10), comprising the following method steps: - applying a first layer (1) to the substrate (10), - applying an inorganic second layer (2) which is evaporated at a vapour angle of incidence of greater than 60° in order to produce a porous layer structure, - applying an organic layer (3) and - producing a nanostructure (31) in said organic layer (3) by means of a plasma etching process. The invention also relates to a reflection-reducing layer system (5) that can be produced using said method.

Description

description

Process for the preparation of a reflection-reducing

Layer system and reflection-reducing layer system

The invention relates to a method for producing a reflection-reducing layer system and a

reflection-reducing layer system. This patent application claims the priority of German Patent Application 10 2014 100 769.7, the disclosure of which is hereby incorporated by reference.

For anti-reflection of surfaces, in particular of optical elements or displays, are usually

reflection-reducing interference layer systems used, which contain several alternating layers of high-refractive and low-refractive materials. As a material with a particularly low refractive index in the visible

Spectral range is often MgF ₂ with n = 1.38 used. The anti-reflection effect of conventional dielectric

Coating systems could be improved if lower refractive index materials were available. An alternative possibility for reducing the reflection of an optical element is known from the patent specification

DE 10241708 B4 known. In this method, on the surface of a plastic substrate by means of a

Plasma etching process generates a nanostructure, by which the reflection of the plastic substrate is reduced. The

Anti-reflection of an optical element by the creation of a nanostructure on its surface has the advantage that a slight reflection over a wide

Incidence angle range is achieved.

The document DE 102008018866 AI describes a

reflection-reducing interference layer system on which an organic layer is applied, which by means of a

Plasma etch process is provided with a nanostructure.

However, plasma etched nanostructures only reach a depth of 80 nm to 120 nm on most materials. Such a thickness is sufficient for plane and slightly curved surfaces to be a substrate in the visual spectral range of 400 nm to 700 nm for vertical incidence of light

reflect that the residual reflection is only about 1%.

In some cases, however, broadband antireflective coatings are required, which should work over larger light incidence angle ranges.

An improvement could be achieved if one could make a low-refractive gradient layer so thick that a significant reduction of the reflection is achieved in a broad spectral range and also for large angles of incidence. The technical realization on high-index substrates (n> 1.7) is easier than on the conventional low-refractive glasses, since even with natural materials, a layer structure can be realized in which the refractive index gradually decreases.

For the production of relatively thick layers with an effective refractive index <1.38 there are only a few technical possibilities. W. Joo, HJ Kim and JK Kim, "Broadband Antireflection Coating Covering from Visible to Near Infrared Wavelengths by Using Multilayered Nanoporous Block Copolymer Films, Langmuir 26 (7), 2010, 5110-5114, describes the production of a thick gradient layer by means of sol-gel processes

multilayer gradient layers is from the publication S.R. Kennedy, M.J. Brett, "Porous Broadband Antireflection Coating by Glancing Angle Deposition", Appl Opt. 42, 4573-4579, 2003, known. In this case, oxides or fluorides are vapor-deposited on the substrate at an oblique angle. By

Shading effects also arise here porous

Layers. For this reason, the substrate must be positioned at an angle to the direction of vapor incidence. The invention is based on the object, an improved method for producing a reflection-reducing

Specify layer system, with the various surfaces broadband and largely angle-independent can be anti-reflective, the method especially for

low refractive glasses and plastics with a refractive index n _s <1.7 should be suitable. Furthermore, an improved reflection-reducing layer system is to be specified.

These objects are achieved by a method for producing a reflection-reducing layer system and a

reflection-reducing layer system solved according to the independent claims. Advantageous embodiments and modifications of the invention are the subject of the dependent claims.

In accordance with at least one embodiment of the method for producing the reflection-reducing layer system, a first layer is applied to a substrate. The first shift is preferably an inorganic layer, in particular an oxide or fluoride layer. Alternatively, the first layer may also comprise an organic material. It is also possible for the first layer to have several partial layers of different materials. The first layer is preferably applied to the substrate in a vacuum process, for example by thermal evaporation, electron beam evaporation or sputtering. The substrate may in particular be a glass substrate. In particular, the substrate may be an optical element such as a lens.

In a subsequent process step, a

inorganic second layer applied. The inorganic second layer is preferably an oxide or

Fluoride layer. The inorganic second layer is evaporated to form a porous layer structure at an oblique angle of incidence of the vapor, wherein the

Vapor incidence angle is advantageously greater than 60 °. Here, and below, the angle between a normal to the substrate and the

Main incident direction of the steam jet to understand. Such a deposition method is known per se under the name Glancing Angle Deposition (GLAD). The inorganic second layer can in particular be produced by vapor deposition at a vapor incidence angle between 60 ° and 85 °. In the application of the inorganic second layer, the substrate is advantageously positioned obliquely to the direction of the steam jet.

The vapor deposition of the inorganic second layer at an oblique angle of incidence has the advantage that already deposited material causes shading effects through which pores are formed during the growth of the layer. The inorganic second layer therefore has a porous layer structure after deposition. The in the porous

inorganic second layer generated pores

advantageously smaller than the wavelength of the radiation for which a reduction of the reflection is to be achieved, in particular smaller than the wavelengths of visible light.

In particular, the pores on the average in any direction are not greater than about 3 nm to 30 nm. The pores essentially contain air whose refractive index is smaller than that of the layer material. In this way, the porous inorganic second layer is caused to have a lower effective refractive index than a continuous layer of the material of the inorganic second layer. Here, the effective refractive index is to be understood here and below as the refractive index averaged over the porous layer whose value due to the pores is less than the refractive index of a continuous layer made of the same material. The

Inorganic second layer advantageously has one

Refractive index gradient, wherein the refractive index preferably decreases in the growth direction of the layer. This may be due to the fact that the number and / or the size of the pores in the growth direction of the layer increases. The thickness of the

Inorganic second layer is preferably between 30 nm and 200 nm. According to a preferred embodiment, the substrate is in the application of the inorganic second layer to a

advantageously perpendicular to the substrate axis of rotation

rotates. The rotation of the substrate about a perpendicular to Substrate standing axis of rotation in the oblique vapor deposition of the inorganic second layer has the advantage that no oblique to the substrate extending preferential direction arises in the porous layer structure. In particular, the inorganic second layer does not have a preferred direction running in the direction of vapor incidence. This will be beneficial

Polarization effects in the reflection-reducing

Layer system in the case of oblique porous

Structures could arise, avoided. For rotation of the substrate advantageously a suitable substrate holder is used. For example, a so-called planet substrate holder system can be used, which on the one hand enables a rotation of several substrate holders about a central axis of the coating installation, for example on a spherical cap, wherein at the same time the individual substrate holders rotate about a rotation axis perpendicular to the substrate. The planet substrate holder system thus has two different axes of rotation. In a subsequent further process step, an organic layer is applied. The application of the

Organic layer is preferably carried out as the application of the inorganic layers with a

Vacuum coating method. The organic material is advantageously an organic material in which a nanostructure can be produced by means of a plasma etching process.

The organic material preferably comprises one of the following materials: 2,2,4-triamino-1,3,5-triazine (melamine), 2,2'-methylene bis (6- (2H-benzotriazol-2-yl) -4- 1, 1, 3, 3-tetramethylbutyl) phenol (MBP), N, '- bis (3-methylphenyl) -N,' - diphenylbenzidine (TPD), N, N'-di (naphth-1-yl) -N , N'-diphenylbenzidine (NPB), N,, ',' -Tetraphenylbenzidine (TPB), Tris (4-) carbazoyl-9-ylphenyl) amine (TCTA), HMDSO, allylamine,

Allyl alcohol, villyl acetate, styrene, parylene.

In a subsequent further method step, a nanostructure in the organic layer by a

Plasma etching process generated, for example by means of a

Plasma ion source with an argon-oxygen plasma. By means of the nanostructure, a refractive index gradient is advantageously generated in the organic material, so that the refractive index in the organic layer preferably decreases at an increasing distance from the substrate. In particular, the organic

Layer to an effective refractive index, which is less than the refractive index, which is a continuous layer of the

would have organic material.

The reflection-reducing made in this way

A layer system comprising the first layer, the porous inorganic second layer and the nanostructured organic layer is advantageously characterized in that the refractive index in the reflection-reducing layer system decreases from layer to layer starting from the substrate. The

Layer system takes advantage in particular that the porous inorganic second layer and the nanostructured organic layer each have effective refractive indices, which may advantageously be lower than the refractive indices that can be achieved with continuous layers. In this way, the reflection of the substrate can be reduced particularly effectively over a large incident angle range and a large wavelength range.

In a preferred embodiment, the substrate has a refractive index n _s and the first layer has a refractive index ni, where n _s >ni> 1.38. The substrate may, for example have a refractive index n _s <1.7. Preferably, therefore, 1.7>ni> 1.38.

According to a further advantageous embodiment, the inorganic second layer has an effective refractive index ri2 of 1.10 <ri 2 <1.45. Preferably, 1.10 <ri 2 <1.38. Such a low effective refractive index ri2 is in the

inorganic second layer due to the porous

Achieved layer structure, which is formed by the deposition at an oblique angle of incidence. The effective

The refractive index of the inorganic second layer is advantageously smaller than the refractive index of the first layer.

In a further advantageous embodiment, the organic layer has an effective refractive index n3, wherein

1.02 <n ₃ <1.40. Preferably, 1.08 <n ₃ <1.25. The effective refractive index n ₃ is advantageously even smaller than the effective refractive index ri 2 of the inorganic second layer. The particularly low effective refractive index n ₃ is achieved in the organic layer by the generation of the nanostructure by means of a plasma etching process.

In a preferred embodiment, the substrate has a refractive index n _s , the first layer has a refractive index ni, the inorganic second layer has an effective refractive index ri 2, and the organic layer has an effective refractive index n ₃ , where n _s >ni> n ₂ > n ₃ , In other words, that takes

Refractive index in the reflection-reducing layer system starting from the substrate from layer to layer. In this way it is achieved in particular that the refractive index over a

comparatively large total thickness decreases gradually and / or continuously. The reflection-reducing

Layer system, which is the first layer, the porous inorganic second layer and the nanostructured organic layer comprises, preferably has a total thickness of at least 200 nm. Due to the fact that the refractive index in the

reflection-reducing layer system over the entire thickness decreases gradually or continuously, a particularly good anti-reflection over a broad wavelength and

Angular range achieved.

The first layer and / or the inorganic second layer are according to a preferred embodiment an oxide layer or a fluoride layer. In particular, the first

Layer and / or the inorganic second layer

Silica, an alumina or magnesium fluoride

exhibit .

The nanostructure produced in the organic layer preferably has a thickness of at least 80 nm. According to a preferred embodiment, the nanostructure

Structural elements in the form of elevations, depressions

and / or pores whose average width is less than 130 nm. The structural elements of the nanostructure are thus advantageously substantially smaller than the wavelengths of visible light, so that the nanostructured layer can be described by an effective refractive index with respect to the incident radiation.

In a preferred embodiment of the method, after the formation of the nanostructure, a cover layer on the

Applied nanostructure, wherein the cover layer has a thickness of not more than 40 nm. The cover layer serves in particular to protect the nanostructured organic layer from mechanical damage. The cover layer is preferably an inorganic layer, in particular a Oxide or fluoride layer. Particularly suitable as material for the cover layer is silicon dioxide.

The reflection-reducing method which can be produced by the method

Layer system advantageously comprises a first layer on a substrate, one of the first layer following

inorganic second layer, wherein the inorganic second layer is a porous layer, and one of the porous ones

inorganic second layer subsequent organic

Layer, wherein the organic layer has a nanostructure. The cover layer is advantageously applied to the organic layer.

Further advantageous embodiments of the reflection-reducing layer system will be apparent from the description of the

Procedure and vice versa.

The invention will be described below with reference to

Embodiments explained in more detail in connection with Figures 1 to 3.

Show it:

1A to IE an embodiment of a method for producing a reflection-reducing layer system on a substrate based on schematically illustrated

Intermediate steps,

Figure 2 is a graphical representation of the reflection R in

Dependence on the wavelength λ for a

Embodiment of the reflection-reducing layer system on a substrate, and Figure 3 is a graphical representation of the reflection R in

Dependence on the wavelength λ for another

Embodiment of the reflection-reducing layer system on a substrate.

Identical or equivalent components are each provided with the same reference numerals in the figures. The

Components shown and the proportions of the components with each other are not to be regarded as true to scale.

In the first intermediate step shown in FIG. 1A of a method for producing a reflection-reducing layer system, a first layer 1 has been applied to a substrate 10. The first layer 1 may be, for example, an inorganic layer. Preferably, the first layer 1 is an oxide or fluoride layer, which may in particular contain S 10 O ₂ , Al ₂ O ₃ or MgF ₂ . The first layer 1 may alternatively also mixtures of oxides or fluorides or multiple partial layers of different oxides and / or

Have fluorides.

The substrate 10 may in particular be a

act optical element in which the reflection of the

Surface should be reduced by applying the reflection-reducing layer. For example, the substrate 10 may be a lens or the surface of a display. The substrate 10 may comprise, for example, glass, in particular quartz glass, or a transparent plastic. Alternatively, it is also possible that the substrate 10 a

Semiconductor material such as silicon has.

In particular, the substrate 10 may be the surface of an optical or optoelectronic component. The first layer 1 is preferably by a

Vacuum coating method applied to the substrate 10. In particular, the first inorganic layer 1 can be applied to the substrate 10 by thermal evaporation, electron beam evaporation or sputtering.

The first layer 1 advantageously has a refractive index ni which is smaller than the refractive index n _{s of} the substrate 10.

Particularly preferably, n _s >ni> 1.38.

In the second shown schematically in Figure 1B

Process step, an inorganic second layer 2 has been applied to the first layer 1, wherein the

inorganic second layer 2 for producing a porous layer structure by a GLAD method under a

oblique angle of incidence was deposited. The deposition of the inorganic second layer 2 is preferably carried out by a vacuum coating method, in particular by thermal evaporation or electron beam evaporation. During vapor deposition of the inorganic second layer 2, the

Substrate surface so in relation to the

Main beam direction of the evaporation source rotated, that an angle between the normal to the substrate and the

Main incident direction of the steam jet at least 60 °, advantageously between 60 ° and 85 °.

Due to the deposition at an oblique angle of incidence, the inorganic second layer 2 has a plurality of pores 21 whose lateral extent is advantageously less than 130 nm. Because the size of the pores in the

inorganic second layer 2 is substantially smaller than the wavelength of visible light, the optical Describe function of the inorganic second layer 2 by an effective refractive index ri2, which is smaller than that

Refractive index is a continuous layer of the

Material of the inorganic second layer 2 would have. Advantageously, the effective refractive index ri2 of

inorganic second layer 2 has a value between 1.10 and 1.45, more preferably between 1.10 and 1.38.

In particular, the effective refractive index ri2 of the inorganic second layer 2 is advantageously smaller than the refractive index of the first layer 1. The inorganic second layer 2 preferably has an oxide or fluoride, for example Si0 ₂ , Al ₂ O ₃ or MgF ₂ . The thickness of the inorganic second layer 2 is preferably between 30 nm and 230 nm.

In a further method step shown schematically in FIG. 1C, an organic layer 3 is applied to the porous inorganic second layer 2. The

Organic layer is advantageous from a material

formed, which is in a subsequent

Process step by means of a plasma etching process

can be structured. The organic layer 3 is preferably applied like the two previously applied layers 1, 2 by a vacuum coating process. For example, the application of the organic layer 3 may be by a PVD or a CVD method. In particular, the production of the organic layer 3 can take place by means of thermal evaporation or by means of a plasma polymerization process.

After the application of the organic layer 3 is a

Plasma etching process performed. As shown in FIG. 1D, a nanostructure 31 is thus produced in the organic layer 3 in this way. The nanostructure 31 is preferably produced by ion bombardment by means of a plasma Ion source. In this case, for example, an argon-oxygen plasma can be used. Such a plasma etching is known per se from the document DE 10241708 B4 and is therefore not explained in detail at this point.

The nanostructure 31 advantageously has a depth of

at least 80 nm. Preferably, the depth of the

Nanostructure 31 between 80 nm and 200 nm. The nanostructure 31 may, for example, have columnar structures with an average height of 90 nm to 120 nm. By means of the nanostructure 31 is in the organic layer 3 a

Refractive index gradient generated in which the refractive index in

increasing distance from the substrate 10 decreases. The nanostructure 31 can, for example, structural elements in the form of

Have elevations, depressions and / or pores whose

Width is preferably less than 130 nm on average. The nanostructured organic layer 3 in this way preferably has an effective refractive index n ₃ , where 1.02 <n ₃ <1.40. Preferably, 1.08 <n ₃ <1.25. The

effective refractive index n _{3 of} the nanostructured organic

Layer 3 is in particular smaller than the refractive index ri 2 of the porous second inorganic layer 2. Advantageously, the refractive index decreases stepwise or continuously starting from the substrate in the layer sequence, so that n _s >ni> ri 2> nj.

In a further method step shown schematically in FIG. 1 IE, a cover layer 4 is applied to the

nanostructured organic layer 3 has been applied. The cover layer 4 preferably has a thickness of less than 30 nm. For example, the cover layer may be about 20 nm thick. Due to its small thickness forms the

Cover layer, the nanostructure in accordance with and substantially In particular, it does not level these out. The cover layer 4 may in particular be an oxide or fluoride layer, more preferably a Si0 ₂ layer. Preferably, the

Covering layer 4 with a vacuum coating method, for example by electron beam evaporation, PECVD

(Plasma Enhanced Chemical Vapor Deposition) or ALD (Atomic Layer Deposition) applied.

The reflection-reducing layer system 5 finished in this way advantageously has a total thickness of at least 200 nm. This has the advantage that the

Refractive index starting from the substrate 10 over a large

Thickness gradually and / or continuously decreases, creating a good anti-reflection effect of

reflection-reducing layer system over a wide

Wavelength and angle range is achieved.

In FIG. 2, the reflection R is dependent on the

Wavelength λ for a first embodiment of the reflection-reducing layer system for the angles of incidence 0 °, 50 ° and 60 ° shown. In the embodiment, a 70 nm-thick MgF ₂ layer was applied as the first inorganic layer 1 to a glass substrate 10 having quartz glass with a refractive index n _s = 1.47. On the first inorganic layer 1, a 65 nm-thick inorganic second layer 2 was vapor-deposited by a GLAD method at an oblique angle of incidence. The second inorganic layer is a MgF ₂ layer. On top of this was an organic layer 3 of melamine

deposited and provided by a plasma etching with a nanostructure. On the organic layer 3 of melamine was subsequently a 20 nm thick cover layer S1O ₂ , wherein a total thickness of the nanostructured melamine layer and the cover layer is 95 nm. The reflection curves shown in Figure 2 show that at incidence angles of 0 ° and 50 °, the residual reflection in the visible spectral range from 400 nm to 700 nm is consistently less than 1%, and at an angle of incidence of 60 ° still less than 2%.

In FIG. 3, the reflection R is dependent on the

Wavelength λ for a second embodiment of the

reflection-reducing layer system, which differs from the first embodiment in that the substrate is a glass substrate of the type B270 with a

Refractive index n _s = 1.53, and that the first inorganic layer 1 comprises a first sub-layer, which is a 50 nm-thick Si0 ₂ layer, and a second sub-layer, which is a 40 nm thick MgF ₂ layer is formed. The porous inorganic second layer 2, the organic layer, and the cap layer 4 are formed in this embodiment as in the first embodiment. The reflection curves shown in Figure 3 show that even in this

Embodiment at the angles of incidence 0 ° and 50 ° each a residual reflection of consistently less than 1% is achieved, and even at an angle of incidence of 60 °, the residual reflection is continuously less than 2%. The invention is not limited by the description with reference to the embodiments. Rather, the includes

Invention every new feature as well as every combination of

Characteristics, which in particular any combination of features in The patent claims, even if this feature or this combination itself is not explicitly in the

Claims or embodiments is given.

Claims

claims

1. A method for producing a reflection-reducing layer system (5) on a substrate (10), comprising the method steps:

Applying a first layer (1) to the substrate (10),

- Applying a second layer (2), wherein the second layer is an inorganic layer, which is used to produce a porous layer structure under a

Vapor deposition angle greater than 60 ° is evaporated,

- Applying an organic layer (3), and

- Producing a nanostructure (31) in the organic layer (3) by a plasma etching process.

2. The method according to claim 1,

wherein the substrate has a refractive index n _s and the first layer (1) has a refractive index ni, where n _s >ni> 1.38.

3. The method according to any one of the preceding claims,

wherein the inorganic second layer (2) has a

effective refractive index ri2, where 1.10 <ri2 <1.45.

4. The method according to any one of the preceding claims,

wherein the organic layer (3) has an effective

Refractive index n ₃ , where 1.02 <n ₃ <1.40 applies.

5. Process according to claims 2, 3 and 4,

where n _s >ni> n 2> n 3. Method according to one of the preceding claims, wherein the reflection-reducing layer system (5) has a thickness of at least 200 nm.

Method according to one of the preceding claims, wherein the first layer (1) and / or the inorganic second layer (2) comprises an oxide or a fluoride.

Method according to one of the preceding claims, wherein the application of the inorganic second layer (2) by vapor deposition at a vapor incidence angle between 60 ° and 85 °.

Method according to one of the preceding claims, wherein the substrate (10) during application of the

inorganic second layer (2) is rotated about a perpendicular to the substrate (10) standing axis of rotation.

Method according to one of the preceding claims, wherein the inorganic second layer (2) has a thickness between 30 nm and 200 nm.

Method according to one of the preceding claims, wherein the nanostructure (31) has structural elements in the form of elevations, depressions and / or pores whose average width is less than 130 nm.

Method according to one of the preceding claims, wherein after the formation of the nanostructure (31), a cover layer (4) is applied to the nanostructure (31), wherein the cover layer (4) has a thickness of not more than 40 nm. Reflection-reducing layer system (5) on one

Substrate (10) comprising

a first layer (1) on the substrate (10),

- one of the first layer (1) subsequent inorganic second layer (2), wherein the inorganic second

Layer is a porous layer, and

- one of the porous inorganic second layer (2) subsequent organic layer (3), wherein the

organic layer (3) has a nanostructure (31).

A reflection-reducing layer system according to claim 13, wherein

the substrate (10) has a refractive index n _s and the first layer (1) has a refractive index ni, where n _s >ni> 1.38,

- The inorganic second layer (2) has an effective refractive index ri2 with 1.10 <ri2 <1.45, and the organic layer (3) has an effective refractive index n ₃ , wherein 1.02 <n3 <1.40 applies.

Reflection-reducing layer system according to claim 13 or 14,

wherein the inorganic second layer (2) has a thickness between 30 nm and 200 nm.

Reflection-reducing layer system according to one of

Claims 13 to 15,

wherein the inorganic second layer (2) has no preferred direction oblique to the substrate (10).

Reflection-reducing layer system according to one of

Claims 13 to 16,

wherein a cover layer (4) on the nanostructure (31) is arranged, wherein the cover layer (4) has a thickness of not more than 40 nm.