DE2457474C3 - Process for the production of reflection-reducing multilayers and optical bodies produced by the process - Google Patents

Description

50

The invention relates to a method for producing reflection-reducing multilayers consisting of high-refractive and low-refractive single layers, the high-refractive layer having a content of at least 80% ZrO ₂ , to which a substance is added to achieve greater homogeneity of the layer.

From AT-PS 3 00 401 interference layers are previously known, in which for the high-index layers Tantalum oxide, zirconium oxide and neodymium oxide or a mixture of oxides can be used. Ternary Mixtures with areas for the individual components to achieve homogeneous layers are not specified. CH-PS 5 56 548 also discloses an alternative material for the high-index layers Titanium oxide and zirconium oxide. From a ternary mixture with specific areas for the individual components is nowhere mentioned.

The optical properties of solid surfaces can be improved by applying interference layers or layer systems can be changed in a targeted manner. So it is B. possible by applying certain Combinations of layers in a desired spectral range that increase or reduce reflection To achieve effects. The definition of the shi-ht structure, d. H. the layer materials and the layer thickness are extensive calculations and tests in advance.

In order to achieve optimal effects, the Calculation of class systems with computers, in particular, families of curves can be created with it, from which one can see how the optical interference effect when deviating from the ideal values changes In the book of H a ρ s and Th u η "Physics of Thin Films", 1964, pages 265 ff. The optical relationships in the production described by anti-reflective coverings made of three layers. On the basis of computationally determined curves shown how the reflection properties change if the given thicknesses of the individual layers are used are not exactly adhered to and if their refractive indices deviate from the calculated ideal value. In Fig. 25 on SvMe 268 is shown by way of example, how the reflection changes when the refractive index of the middle layer of a three-layer system varies between 1.8 and 2.6. The diagram shows that there is a refractive index for the mean Layer of about 2.1 leads to optimal system properties. Deviations lead down or up already to noticeably deteriorated system properties. Compliance with a narrow range for the However, the refractive index of a high-index layer is by no means a measure that is easy to carry out.

In the case of multiple layers, the application of highly refractive material is particularly problematic, because only a few oxides are suitable for this, if the layers are to be mechanically and chemically resistant.

In the production of multilayers there are also problems in that some of the oxides in question, e.g. B. ZrO ₂ , CeO ₂ and Ta ₂ O ^, do not precipitate as a homogeneous layer: Their refractive index changes due to relationships that have not been adequately researched to date directly to the layer level, and either increasing or decreasing. Whether one or the other is the case. can be recognized by the course of the transmission curves of the substrate that has not been vaporized and that of the substrate vaporized with an oxide layer. If the two curves touch each other at a certain wavelength for which the relationship

holds, it can be assumed that the structure of the applied layer is homogeneous. Here “n” is the refractive index of the layer, “d” the thickness of the layer and λ the light wavelength for which the above-mentioned relationship applies. If, on the other hand, the transmission of the coated substrate is above or below the transmission of the uncoated substrate, then there is an inhomogeneous layer structure.

Due to the partly unknown connections about the inhomogeneous layer structure, its cause

and the possibility of influencing the evaporation process Inhomogeneities in themselves cannot be sufficient when calculating layer systems must be taken into account. This inevitably leads to erroneous results. In addition, the Inhomogeneity conditions not reproducible with sufficient accuracy under production conditions. It has Therefore, there has been no lack of effort through all possible variants of the individual process parameters to produce homogeneous oxide layers without these efforts having been a success were.

A high-index material that is often used in the production of layer systems with an optical effect is ZrO2. This oxide fulfills all expectations with regard to freedom from absorption, hardness and chemical resistance and also has a refractive index that comes very close to the ideal value for some calculated and also in practice realizable layer systems. Unfortunately, ZrO ₂ layers are very inhomogeneous. The consequence of this is that with layer systems that contain a ZrO2 layer, the calculated optical values can by far not be adhered to.

From DE-AS 20 50 556 it is already known to reduce the inhomogeneities of the refractive index of ZrO2 by adding Ta ₂ O ^. For this purpose, between 30 and 70 percent by weight of Ta _{2 Oi are added to the ZrO 2} , that is to say a considerable proportion. Preferably, the same parts by weight of the two oxides should be used; In no case should the proportion of one of the oxides be below 20 percent by weight. Because the refractive index of Ta2Os is greater than that of ZrO ₂ . can the refractive index of such a mixture only be based on the refractive index of pure ZrO due to generally known relationships? be raised. The increase is the greater, the greater the percentage of Ta ₂ O is. In this case, however, the optical properties of the highly refractive layer are defined within a narrow framework, and the scope for varying the refractive index or for adapting to the properties of the other layers is undesirably restricted. The indicated refractive index of η - 2.05 for such a mixture is based on wishful thinking.

The invention is therefore based on the object of _{specifying a substance for achieving greater homogeneity of a ZrO 2} layer, by means of which the refractive index of the ZrO _{2 is} not shifted upwards on one side, but rather allows the refractive index of the layer to be shifted downwards or set it to a value that corresponds to _{that of pure ZrO 2.}

The object set is achieved in the method described at the beginning according to the present invention in that the high-index layer is formed by depositing a ternary mixture of 4 to 10 percent by weight AliO), 4 to 10 percent by weight TiO? and the remainder of ZrO _{2 is} generated on the substrate in a vacuum in a reactive atmosphere.

The precipitation can take place on the basis of an evaporation process, the ternary Mixture is vaporized in a particularly advantageous manner by an electron beam% '.

While the Al2O3 and ZrÜ2 are generally based on the oxide form mentioned and these oxides evaporate, both titanium metal and TiO, TijO] or TiO _{2 can be} assumed for the precipitation of the titanium component, with the TiOj in the layer in each case is formed due to the reactive atmosphere. It goes without saying

■ 5 that the oxygen consumption of the chosen Evaporation substance is dependent for chemical reasons. The percentage composition of the The ternary mixture according to the invention also applies only to the deposited layer. The percentage

in the composition of the evaporation substance changes accordingly depending on the oxygen content of the to evaporating titanium compound or pure titanium. These relationships are common to those of ordinary skill in the art however common.

π However, it is also possible to create a plate (target) from the ternary mixture and use this atomized by means of high frequency. The use of high frequency is required when the too atomizing plate is not or only poorly electrically conductive. In the event that one "or more Components of the ternary mixture is in metal form, so that there is sufficient electrical conductivity is generated, DC voltage can also be used for the atomization.

The method according to the invention, which is primarily used for the compensation of optical lenses, in particular of Spectacle lenses, lens systems, filters, substrates that are transparent in themselves and have no optical effect such as Faucet glasses etc. can be applied, brings

jo has the following advantages: The AbOj has a lower, the TiO ₂ a higher refractive index than the ZrO ₂ . By choosing appropriate proportions of the two stabilizing oxides, the refractive index can be varied within the limits resulting from the mixing ratio, in particular towards a refractive index that is smaller than that of ZrO ₂ . This makes it possible, for example, to have an optimal anti-reflective coating on glass substrates in a system consisting of three layers

4n with a refractive index of η = 1.51, so that the homogenized layer can be optimally adapted to the other layers. Even if the change in the refractive index may appear insignificant in terms of percentage, the optical interference effects can nevertheless be considerable, as can be seen from FIG. 25 on page 268 of the book "Physics of Thin Films". Furthermore, only relatively small additions of the oxides mentioned are required for adequate stabilization, the sum of the two oxides generally not needing to exceed 12 to a maximum of 18 percent by weight. This largely preserves _{the valuable optical, mechanical and chemical properties of ZrO 2 senr.} In any case, the oxides mentioned do not worsen the mechanical and chemical properties in relation to a ZrO ₂ layer without additives. In addition, the saturation vapor pressures of all components of the ternary mixture are within a narrower range, so that

bo fractional evaporation is largely ruled out. Finally, the added oxides also do not change the absorption behavior of the ZrO ₂ . The method according to the invention is also highly reproducible with regard to the color of the remaining reflections and leads to an extremely effective anti-reflective coating on the substrates.

The suitability of A1 ₂ O3 as a component of the tertiary mixture is also surprising in this respect.

seeing when this oxide was in the »Griieiin«, 8th edition, t95O, Ropes 229 and 443 just as unsuitable addition for the stabilization of ZrÜ2 is specified.

Essentially the same success is achieved if the A ^ Oj the oxide SiOi occurs in essentially the same or a slightly smaller amount.

The invention is applicable with equal advantages to interference systems consisting of any one Number of individual layers exist. The application of the , inventive method in the production of reflective triple layers, the layers in the order low-high-low-refractive index be knocked down and being their thickness ζ. Β. λ / 4

- λ / 2 - λ / 4 is chosen. Have these layer thicknesses the particular advantage that they are made by optical layer thickness gauges during their manufacture can be grasped easily and reliably. as Material for the first layer can, for example, cerium fluoride, as Materia! for the third layer MgF be used.

In the process according to the invention, the layer is deposited from the ternary mixture

- As stated - carried out in a reactive atmosphere, which is generated as follows: After the vapor deposition of the first layer at a residual gas partial pressure of a few 10 - 'Torr, oxygen is added via a needle valve before the vaporization of the ternary mixture in such an amount that the pressure is between about 6 χ ~ 10 ⁵ and 2 · ΙΟ- ⁴ Torr. As soon as the layer of the ternary mixture has deposited, the needle valve for the oxygen supply is closed again and the subsequent layer or layers are vapor-deposited under conditions that are state-of-the-art. During the evaporation process, the substrates are expediently kept at an elevated temperature of, for example, 300.degree.

In the case of the deposition of the layers by cathode sputtering, the oxygen pressure is expediently in a range between ^{3 × 10 − J} and 3 × 10 × Torr.

example 1

Several spectacle lenses were located in the recipient of a vacuum vapor deposition system. After the usual known cleaning process by glowing, the spectacle lenses, which had a refractive index of η = 131, were heated to a temperature of 300 ° C., whereupon a λ / 4 layer made of cerium fluoride with a refractive index of η = 1.7 as the first layer , was evaporated. An electron beam evaporator with a crucible turret was used for vapor deposition, in the depressions of which the various vapor deposition substances were kept ready. Following the first layer - as described above - the reactive atmosphere would be set and

') The second, high-index layer was vapor-deposited, which consisted of 88 percent by weight ZrÜ2.6 percent by weight T1O2 and 6 percent by weight Al ₁ Oi. The supply of oxygen was then interrupted, and a third layer of magnesium fluoride with a refractive index of η - 1.38 was subsequently applied by vapor deposition to a thickness of λ / 4. An excellent reduction in reflections was achieved over a wide range of wavelengths, and no inhomogeneities whatsoever within the Schichlen system could be concluded on the basis of the examination criteria described at the beginning.

Example 2

The process according to Example I was repeated, but with the difference that a ternary mixture of 84 percent by weight ZrO2.8 percent by weight T1O2 and 8 percent by weight Al2O3 was evaporated under otherwise identical conditions for the deposition of the second high-index layer. In this way, products of practically equivalent quality were obtained, with only the wavelength range in which the maxima ¹ '; Reflection reduction occurred was slightly narrower. In this case, too, no inhomogeneities within the layer system could be inferred on the basis of the examination criteria described at the beginning.

The adherence to the layer thickness was based on the use of an optical layer thickness measuring device achieved. Details of such meters are well known in the art and the meters are commercially available are.

In the figure, an embodiment of the product produced by the method according to the invention is explained in more detail. The figure shows a section through a substrate with a vapor-deposited 3-layer interference system. In the figure, 10 denotes a substrate in the form of a glass plate with a refractive index η- 1.51. A first layer with a thickness of λ / 4 made of cerium fluoride with a refractive index of π = 1.7 is vapor-deposited thereon. This is followed by a high-index layer made from the ternary oxide mixture according to the invention, which has a refractive index of η- 2.1 and a thickness of λ / 2. The ternary mixture consists of 88 percent by weight ZrO2, 6 percent by weight T1O2 and 6 percent by weight \ 12Oj. A cover layer made of MgF with a refractive index of η = 138 and a thickness of λ / 4 forms the end. The layer system according to the figure was produced by the method according to Example 1. "

1 sheet of drawings

Claims (6)

Patent claims: 1. Process for the production of reflection-reducing multilayers, consisting of high refractive index and low refractive index individual layers, the high refractive index layer having a content of has at least 80% ZrO2, which is a substance is added to achieve greater homogeneity of the layer, characterized in that that the high refractive index layer by depositing a ternary mixture of 4 to 10 percent by weight AI2O3, 4 to 10 percent by weight T1O2 and the remainder ZrO2 on the substrate in the Vacuum is generated under a reactive atmosphere. 2. A method for the production of reflection-reducing triple layers according to claim 1, characterized in that characterized in that the layers are deposited in the order low-high-low refractive index are chosen, wofc-; i their thickness λ / 4 - λ / 2 - λ / 4 will. 3. The method according to claim 2, characterized in that the first layer of cerium fluoride, the second layer made of a ternary mixture of 88 percent by weight Ζ1Ό2.6 percent by weight T1O2 and 6 percent by weight Al2O3 and the third layer is built up from MgF. 4. The method according to claim 1, characterized in that the high refractive index layer is produced by depositing a mixture of 3 to 10 percent by weight SiO ₂ , 4 to 10 percent by weight TiCb and the remainder ZrC> 2 on the substrate in a vacuum under a reactive atmosphere. 5. Optical bodies, such as lenses, filters with reflection-reducing multiple layers, consisting of high-refractive and low-refractive individual layers, the high-refractive layer having a content of at least 80% ZrCb, to which a substance is added to achieve greater homogeneity of the layer. 4n shows that the high-index layer consists of a ternary mixture of 4 to 10 percent by weight Al ₂ O ₃ , 4 to 10 percent by weight TiO ₂ and the remainder ZrO ₂ . 6. Optical body according to claim 5, characterized in that the high-index layer consists of a ternary mixture of 3 to 10 percent by weight SiO ₂ , 4 to 10 TiO ₂ and the remainder ZrO ₂ .