DE3941796A1 - Optical multilayer coating - with high anti-reflection, useful for glass and plastics substrates - Google Patents

Abstract

An optical multilayer coating, esp. with high anti-reflection, comprises the following layer sequence starting from the front (viewing) side of the substrate: (i) a high refractive index layer (4), pref. of TiO2 and pref. of thickness 100 Angstroms +/-10%; (ii) a low refractive index layer (5), pref. of Al2O3 and pref. of thickness 400 Angstroms +/- 5%; (iii) a high refractive index layer (6), pref. of TiO2 and pref. of thickness 1040 Angstroms +/- 2%; and (iv) a low refractive index layer (7), pref. of SiO2 and pref. of thickness 940 Angstroms +/- 2%. Also claimed is prodn. of the coating by cathodic sputtering, esp. d.c. reactive magnetron sputter deposition, or by vapour deposition, (plasma-) CVD or pyrolysis. USE/ADVANTAGE - The coating is useful as an anti-reflection coating on glass, plastics foil or other transparent material, esp. substrate of refractive index 1.5-1.6. It has high light transmission, extremely low thickness (about 30% less than prior art coatings) and recuded prodn. costs since high thickness precision for the first two layers is not required.

Description

The invention relates to a covering consisting of a optically acting layer system, for substrates, wherein the layer system in particular a high anti-reflection effect having.

There is a wide range of coating systems for Substrates, in particular for glass, the particular optical Fulfill functions. The present invention relates the genus of antireflection coatings, respectively Anti-reflective coating systems.

By the German patent application 36 29 996 is a Attachment unit for the cathode ray tube of monitors, TV sets and the like, consisting of a Glass pane, in particular a gray glass pane, a Front anti-reflection equipment and one rear absorption coating, wherein the Absorption coating metal atoms, known become.

In this German patent application is suggested that the absorption coating single layer of chrome,  built up of a chromium / nickel alloy or silicides and antistatic and grounded, as well as with a thickness is provided which the light transmission around the uncoated glass pane by about one Third lowers.

In the US Patent 38 54 796 is still a Coating proposed to reduce the To serve reflection. The coating should be for one Substrate, which is a plurality of Has layers. In the order starting at Substrate is the following arrangement in the US patent described: three groups of at least two Lambda / 4-layers, the successive layers of the first group have a refractive index that is below the refractive index of the substrate. The Layers of the second group have one increasing refractive index and the layers of the third Group have a refractive index below the Refractive index of the substrate. more details can be found in the cited US patent.

The state of the art still includes the US Patent 37 61 160th There will be a Broadband antireflection coating and substrates that coated with it are proposed. They point at least four layers for high index glass and at least six layers for low index glass on. Further details are the mentioned US-Script refer to.  

Furthermore, in US Patent 36 95 910 a Method of applying an antireflective coating described on a substrate. This coating exists from several individual layers. The procedure for the Application of the antireflection layers takes place under Vacuum, using electron beams. Further details are the aforementioned US patent refer to.

Furthermore, the prior art belongs to the US Pat. No. 3,829,197 which discloses an antireflection coating, which is designed as a multilayer system describes. This surface should be on a strong breaking substrate be attached. The shift system consists of five individual layers, which are mutually adapted, in terms of their refractive index and in Respect to their optical thickness. Through this adaptation should have a favorable antireflection curve with a broad, shallow, middle part can be achieved. Further Details of this proposal are those mentioned US Patent refer to.

The state of the art still includes the Swiss Patent 2 23 344. This document is concerned with a coating to reduce the surface reflection. The coating consists of at least three layers with different refractive indices. The reduction of Surface reflection should be according to this document by a certain selection of the refractive indices of the individual Layers are achieved.

The invention is based on the following tasks:

The invention is intended to create a condition for the Production of antireflection coatings on transparent Substrates, especially those substrates, the one Refractive index of n = about 1.5 to 1.6. simultaneously the light transmission should be high and the total thickness the coating should be as low as possible so that the Production costs can be reduced accordingly.

With the invention, a concept is to be proposed, in the large-scale DC-reactive with magnetron from Metal target can be sputtered.

The small number of layers of the layer system, the small thickness of the individual layers of the layer system, the selection of inexpensive feedstock and the Possibility of DC-reactive with magnetron from the metal target to sputter, lead to a very economic Production of the invention Anti-reflective coating system.

The task complex on which the invention is based belongs the special task to make it possible that the first and the second layer strong in their thicknesses can vary without the cheap Antireflection effect of the whole system, consisting of four layers, significantly changes.

This aspired insensitivity of the first two relatively thin layers in terms of the cheap Anti-reflection effect of the whole system brings one Set of advantages:  

Considering the layer thicknesses of the first two layers does not need to be applied with the utmost accuracy or if you look during the Application method certain tolerance freedoms in the can afford first and second shift, it will Overall manufacturing process according to easier and cost-effective.

Overall, the overall package is the layers relatively thin. It is about 30% below comparable Layer systems of the prior art. Even the thinnest of the overall package makes the manufacturing process cheaper.

The objects of the invention are achieved in that on the substrate side facing the viewer (front) ( 2 ) in the local order from the front ( 2 ) to the viewer a first, high-refractive index material, preferably TiO ₂ , layer ( 4 ) (first layer) is arranged, followed by a second, low-refractive material, preferably Al ₂ O ₃ , having layer ( 5 ) (second layer) is arranged, subsequently a third high refractive index material, preferably TiO ₂ , having layer ( 6 ) (third Layer), a fourth low-refractive material, preferably SiO ₂ , having layer ( 7 ) (fourth layer) is arranged following.

It can be provided that the first layer ( 4 ) comprises compounds from the group: TiO ₂ , ZnS, Bi ₂ O ₃ , or mixtures of the compounds from this group.

Furthermore, it is proposed that the second layer ( 5 ) comprises oxides from the group: Al ₂ O ₃ , MgO, SiO ₂ , SiAl oxide, NiSi oxide, or mixed oxides from this group.

In addition, it can be provided that the third layer ( 6 ) comprises compounds from the group: TiO ₂ , ZnS, Bi ₂ O ₃ , or mixtures of the compounds from this group.

Finally, the fourth layer ( 7 ) may comprise compounds from the group: SiO ₂ , MgF ₂ or mixtures of the compounds from this group.

With regard to the refractive coefficients, it is proposed in a further embodiment of the invention that the first layer ( 4 ) consists of a material with a refractive index of n greater than or equal to 2.2, preferably n = 2.4, that the second layer ( 5 ) consists of a material having a refractive index of n = about 1.6, that the third layer ( 6 ) consists of a material having a refractive index of n greater than or equal to 2.2, preferably n = 2.4, that the fourth layer ( 7 ) consists of a material having a refractive index of n smaller than or equal to 1.5, preferably of n = 1.48.

With regard to the layer thicknesses, it is proposed that the first layer has a thickness of 100 angstroms +/- 10% that the second layer has a thickness of 400 Ångström +/- 5%, the third layer has a Thickness of 1040 angstroms +/- 2% has the fourth Layer has a thickness of 940 angstroms +/- 2%, such values for the respective layer thicknesses within said layer thickness tolerances  be chosen, the interdependence of each Layer thicknesses and the materials used to each other account.

In a preferred embodiment it is provided that, on the substrate side (front side) ( 2 ) facing the observer, in the local sequence from the front side ( 2 ) to the viewer, a first layer ( 4 ) with high refractive index, preferably TiO ₂ , is applied to the substrate. (first layer) is arranged, which has a thickness of 100 angstroms +/- 10%, subsequently a second low-refractive index material, preferably Al ₂ O _3, having layer (5) (second layer) is arranged, which has a thickness of 400 Ångström +/- 5%, followed by a third high refractive index material, preferably TiO ₂ , having a layer ( 6 ) (third layer) having a thickness of 1040 angstroms +/- 2%, followed by a fourth low refractive index material, preferably SiO ₂ , having layer ( 7 ) (fourth layer), which has a thickness of 940 Angstroms +/- 2%.

Of particular advantage for a cost-effective production is the proposal, after the one Sputtering method, in particular a DC-reactive sputtering from the target with magnetron for Coating is used.

It can be provided for the first and third layers that is formed by DC-reactive sputtering of the Ti target with magnetron, a layer of TiO ₂ in the presence of a Sputtergasgemisches comprising Ar and O ₂ , and that at a pressure of about 5 × 10 ^-3 mbar.

For the second layer, it is proposed that a layer of Al ₂ O _{3 be formed} in the presence of a sputtering gas mixture comprising Ar and O ₂ by DC-reactive sputtering from the Al target with magnetron, at a pressure of about 8x 10 ^-3 mbar.

For the fourth layer, it is proposed that by DC-reactive sputtering from the Si target with magnetron, a layer of SiO _{2 is formed} in the presence of a sputtering gas mixture comprising Ar and O ₂ , at a pressure of about 1.2 × 10 ^-2 mbar.

For coating can also be known methods be used, for example proposed that a per se known vapor deposition is used for coating that a per se known chemical vapor deposition (CVD) method for Coating is used, that is a known per se Plasma-assisted Chemical Vapor Deposition (CVD) method is used for coating or that a per se known pyrolysis method for Coating is used.

The invention achieves the following advantages:

The tasks described above are solved. It should be mentioned that it is through the invention has been made possible that the first and the second layer can vary greatly in their thickness without getting the favorable antireflection effect of the overall system, consisting of four layers, significantly changes.  

Overall, the overall package is the layers relatively thin. It is about 30% below comparable Layer systems of the prior art. Even the thinnest of the overall package makes the manufacturing process cheaper.

Further details of the invention, the task and the advantages achieved are the following description to take an embodiment of the invention.

This embodiment is based on two figures explained.

Fig. 1 shows a layer system.

FIG. 2 shows the refection curve in percent over wavelengths in nm.

The substrate 1 can be made of glass or of a plastic film or of another transparent material. The front side 2 of the substrate is the side of the substrate facing the viewer. The layer applied to the front side of the substrate is referred to as the "first" layer 4 . The "second" layer 5 , the "third" layer 6 , the "fourth" layer 7 follow in the direction of the viewer. With the arrow 3 , the viewing direction of the viewer is symbolized.

The following is a description of a layer system in which the reflection on the surface of a polyester film facing the viewer was measured in the visible wavelength range of the light. The measurement results are shown graphically with reference to the curve 8 in FIG. 2.

In describing the layer system, the reference numerals of the description of Fig. 1 are used.

The shift system is structured as follows:
Substrate: polyester film, thickness 32 microns, refractive index n = 1.6
"first" layer ( 4 ) Material: TiO ₂ , thickness 100 Angstroms Refractive index n = 2.4
"second" layer ( 5 ) Material: Al ₂ O ₃ , thickness 400 Angstroms Refractive index n = 1.6
"third" layer ( 6 ) Material: TiO ₂ , thickness 1040 Angstrom Refractive index n = 2.4
"fourth" layer ( 7 ) Material: SiO ₂ , thickness 940 Angstroms Refractive index n = 1.48

For this layer system, the reflection became as above shown on the surface of the polyester film in Percent, for a wavelength range from 360 nm to 730 nm.

The following are the measurement results for the reflection in a table specific wavelengths faced:  

Wavelength (nm) Reflection (%) 730 0.82 690 0.22 650 0.2 620 0,152 590 0.18 560 0.24 540 0.252 520 0.244 500 0.208 480 0.168 460 0.168 440 0.42 430 0.74 410 1.92 400 2.96 390 4.36 380 4.56 360 4.56

As shown, the results of the measurements are graphically represented as a curve in FIG . On the abscissa 9 of the coordinate system in Fig. 2, the wavelengths are entered in nm. On the ordinate 10 of the coordinate system, the percentages for the reflection are entered.

From the curve is clearly visible that the reflection in the core wavelength range of visible light especially between 450 and 700 nm, extraordinary is low. It is well below 1%. This is the desired high antireflection effect in surprising clearly achieved.

The shift system with which the above commented Reflection values were obtained after the following have been prepared described method:

It was sputtered with magnetron and that in a reactive gas atmosphere, consisting of a gas mixture of Ar and O₂.
Target material: Ti, Al, Si.
Process pressure level:
during sputtering from the Ti target: 5 × 10 ^-3 mbar
during sputtering from the Al target: 8 × 10 ^-3 mbar
during sputtering from the Si target: 1.2 × 10 ^-2 mbar
It was sputtered stoichiometrically (fully oxidic).

List of items

1 substrate, glass, foil
2 front side
3 arrow, line of sight
4 "first" layer
5 "second" layer
6 "third" layer
7 "fourth" layer
8 curve
9 abscissa
10 ordinates

Claims (16)

1. covering, consisting of an optically acting layer system, for substrates, wherein the layer system in particular has a high antireflection effect, characterized in that on the viewer facing the substrate side (front) ( 2 ) in the local order from the front ( 2 ) to Viewers a first substrate, high-refractive material, preferably TiO ₂ , having layer ( 4 ) (first layer) is arranged, subsequently a second, low-refractive material, preferably Al ₂ O ₃ , having layer ( 5 ) (second layer) is arranged , Subsequently, a third high refractive index material, preferably TiO ₂ , having layer ( 6 ) (third layer) is arranged, subsequently a fourth low-refractive material, preferably SiO ₂ , having layer ( 7 ) (fourth layer) is arranged. 2. Covering according to claim 1, characterized in that the first layer ( 4 ) comprises compounds from the group: TiO ₂ , ZnS, Bi ₂ O ₃ , or mixtures of the compounds from this group. 3. Covering according to claim 1 and / or 2, characterized in that the second layer ( 5 ) comprises oxides from the group: Al ₂ O ₃ , MgO, SiO ₂ , SiAl oxide, NiSi oxide, or mixed oxides from this group , 4. Covering according to one or more of the preceding claims, characterized in that the third layer ( 6 ) comprises compounds from the group: TiO ₂ , ZnS, Bi ₂ O ₃ , or mixtures of the compounds from this group. 5. Covering according to one or more of the preceding claims, characterized in that the fourth layer ( 7 ) comprises compounds from the group: SiO ₂ , MgF ₂ or mixtures of the compounds from this group. 6. covering according to one or more of the preceding claims, characterized in that the first layer ( 4 ) consists of a material having a refractive index of n greater than or equal to 2.2, preferably n = 2.4, that the second layer ( 5 ) consists of a material having a refractive index of n = about 1.6, that the third layer ( 6 ) consists of a material having a refractive index of n greater than or equal to 2.2, preferably n = 2.4, that the fourth layer ( 7 ) is made of a material having a refractive index n of less than or equal to 1.5, preferably of n = 1.48. 7. covering after one or more of the preceding Claims, characterized in that the first layer has a thickness of 100 Angstroms +/- 10%, that the second layer has a thickness of 400 angstroms +/- 5% that the third layer has a thickness of 1040 Angstrom +/- 2% shows that the fourth layer has a Thickness of 940 Angstroms +/- 2% has such values for the respective layer thicknesses within the mentioned Layer thickness tolerances are chosen, which are the Interdependence of the individual layer thicknesses and the consider used materials to each other. 8. covering, consisting of an optically acting layer system, for substrates, wherein the layer system in particular has a high antireflection effect, characterized in that on the viewer facing substrate side (front) ( 2 ) in the local order from the front ( 2 ) for The viewer is arranged a first, high refractive index material, preferably TiO ₂ , layer ( 4 ) (first layer) having a thickness of 100 angstroms +/- 10%, followed by a second, low refractive index material, preferably Al ₂ O. ₃ , comprising the layer ( 5 ) (second layer) having a thickness of 400 Angstroms +/- 5%, followed by a third high refractive index material, preferably TiO ₂ , comprising the layer ( 6 ) (third layer) a thickness of 1040 angstroms +/- 2%, followed by a fourth low refractive index material, preferably SiO ₂ , having layer ( 7 ) (fourth layer) ordered, which has a thickness of 940 Angstroms +/- 2%. 9. A process for the production of a coating after a or more of the preceding claims, characterized characterized in that a sputtering method, in particular a DC-reactive sputtering from the target Magnetron is used for coating. 10. The method according to one or more of the preceding claims, characterized in that is formed by DC-reactive sputtering from the Ti target with magnetron, a layer of TiO ₂ in the presence of a sputtering gas mixture comprising Ar and O ₂ , in a Pressure of about 5 × 10 ^-3 mbar. 11. The method according to one or more of the preceding claims, characterized in that by DC-reactive sputtering from the Al target with magnetron, a layer of Al ₂ O ₃ in the presence of a Sputtergasgemisches comprising Ar and O _{2 is} formed, namely at a pressure of about 8 × 10 ^-3 mbar. 12. The method according to one or more of the preceding claims, characterized in that is formed by DC-reactive sputtering from the Si target with magnetron, a layer of SiO ₂ in the presence of a sputtering gas mixture comprising Ar and O ₂ , in a Pressure of about 1.2 × 10 ^-2 mbar. 13. A process for the production of a coating after a or more of the preceding claims, characterized characterized in that a known per se Vapor deposition method is used for coating.   14. A process for the production of a coating after a or more of the preceding claims, characterized characterized in that a per se known chemical vapor Deposition (CVD) method used for coating becomes. 15. A process for the production of a coating after a or more of the preceding claims, characterized characterized in that a known per se Plasma-assisted Chemical Vapor Deposition (CVD) method is used for coating. 16. A process for the production of a coating after a or more of the preceding claims, characterized characterized in that a known per se Pyrolysis process is used for coating.