DE1228489B - Process for the production of thin, in the visible wavelength range practically absorption-free oxide layers for optical purposes by vapor deposition in a vacuum - Google Patents

Description

Process for the production of thin layers in the visible wavelength range practically. absorption-free oxide layers for optical purposes by vapor deposition In the vacuum thin oxide layers are used in technology to a large extent as protective layers and used as layers for optical purposes. They serve as protective layers in addition, sensitive surfaces of bodies, e.g. B. of precision parts in precision engineering, of lenses, surface mirrors and the like, Cregen corrosion and mechanical damage to protect. In the optical industry, oxide layers are also used as high and low refractive layers for anti-reflective coatings, further for Interference filters, beam splitters, heat filters, cold light mirrors, coatings for spectacle lenses and the like used. Layer the mechanical and optical properties of such oxides depend not only on the type of oxide applied, but to a very large extent also depends on the type of application process.

The production of oxide layers by direct vapor deposition of oxidic starting substances in a vacuum and condensation of the vapors on the documents to be covered is known. For many optical purposes, this process has the disadvantage that most oxides result in absorbent layers on evaporation and condensation in a vacuum, even if oxides are actually absorption-free as starting substances. be used. Presumably this is due to the fact that the vacuum has a reducing effect on most oxides at high temperature and that - this is an average valid rule - the unsaturated oxides mostly show optical absorption. There are only a few exceptions to this: B. niobium oxide and cerium oxide can be evaporated in vacuo, resulting in absorption-free layers.

In order to circumvent these difficulties in manufacturing the oxide layers without absorption, further processes have been developed. It is known to produce absorption-free metal oxide layers by vapor deposition of absorbent layers and subsequent oxidation of the same or by cathode sputtering of the metals in question in oxygen (cf. also the work by K. H am in er, "Increase in glass reflection through metal oxide layers" in "Optics" 3 , No. 5/6, 1948, p. 495).

Another known method is the vapor deposition of the starting substances in an oxidizing atmosphere.

For the fabrication of thin oxide layers, the known methods have the disadvantage that they are time-consuming, so that Vielschidlitsysteme, z. B. interference heat filters and cold light mirrors (which often consist of 20 to 30 individual layers), are quite expensive to manufacture.

In the case of the known oxidation of absorbent layers, namely the individual layers separately (or at best only a very few individual layers together) are oxidized because the oxygen cannot be absorbed by thicker layers diffused through enough. Oxidation also works with thinner layers just very sluggishly in front of you. In the case of subsequent oxidation, the layers also change their thickness. The adherence to exact layer thickness relationships that are necessary for interference systems is indispensable is made very difficult. Another disadvantage- this well-known The process consists in the fact that there are many bodies on which the thin layers are applied should be, z. B. cemented lens systems, not on those required for the oxidation high temperatures.

The other well-known process, cathodic sputtering in oxygen, is in itself very time-consuming and also often leads to inadmissible heating the documents to be documented. Also show those produced by sputtering Layers often have stronger scattered light than those produced by vapor deposition Layers made of the same layered materials and for this reason are not everywhere applicable.

According to the best methods available so far, z. B. for the production of a cold light mirror made up of 25 individual layers of alternating high and low refractive index layers of SiO and TiO, as it is used for cinema projectors, takes about 6 to 8 hours in a vacuum vapor deposition process, if the layers should be hard and adherent and sufficiently free of absorption.

The present invention relates to a new method of manufacture thin oxide layers practically absorption-free in the visible wavelength range for optical purposes, in particular on substrates, on glass, by vapor deposition of oxidic and / or oxidizable substances in vacuo, optionally in the presence of an oxidizing one Atmosphere, which is characterized by being at the same time as the oxidic and / or oxidizable substances one or more elements and / or oxides from the Rare earth group. (including yttrium, lanthanum and cerium) evaporated will.

With this method it is possible to create a hard and adhesive oxide layer with the lowest possible absorption due to the layer substances used in much shorter Zedt than after the known ones. Process to manufacture because with the procedure according to the invention either no post-oxidation in oxidizing atmosphere is required or, if one is necessary, this (in contrast to the well-known. shift temperature methods) within: one for a short period of time (often instantaneously). The vapor deposition can with relative high evaporation rate. The inventive method. now gives you the opportunity, not just a few oxides, to you, so far an exception, from the general rules, such as B. pure cerium oxide, low absorption. or to vaporize absorption-free, sonde.rn also other known oxides, their vaporization in a vacuum without reduction per se is not possible to use for the same purpose.

It is true that a method has become known for the production of oxide layers with a high dielectric constant for capacitors in which titanium is applied in a very thin layer to a support base, in particular made of nickel, and together with this support base at a temperature of about 1000 ° C. for about 15 minutes Wixd exposed to reduced air, so that a coherent layer of titanium dioxide forms in crystal form. However, the person skilled in the art could not find any from this publication. Information on a process for the production of thin, in the visible wavelength range practically absorption-free oxide layers for optical purposes. It was not possible to deduce from what was known how an oxidation state can be achieved or maintained by vapor deposition of the layers, which otherwise cannot be achieved without powerful, additional oxidation measures.

From another publication a method for the production of spinnerets was known, according to which chemical elements by cathode sputtering in an oxygen-containing. The atomization chamber is converted into oxides during the atomization process and these are deposited on the outside of the spinneret base, namely . in particular the oxides of silicon, titanium, zirconium, thorium, aluminum, bismuth, tantalum, chromium and rare earths. From this, too, one could not infer any teaching about how the formation of absorbent layers can be prevented during the production of oxide layers by vapor deposition.

According to further proposals of the invention, the mixing ratio between the starting substances and the admixed elements or oxides from the group of rare earths is chosen so that at least 5 % and at most 50 1 / o of all free or bound metal atoms contained in the mixture, cerium atoms or others Atoms are from the group of rare earths. The admixture of cerium and / or oxides of cerium or praseodymium and / or its oxides has proven to be particularly effective.

However, the effect of the invention is not to be understood in such a way that because a. Oxide that can be vaporized without absorption, e.g. B. cerium oxide, the starting substance is mixed in, now the total absorption just corresponds to the dilution is lower due to the added absorption-free component. Rather, it leads the admixture to it, that also the not so far not without disturbing absorption Vaporizable components of the starting substance produce a much lower condensate Absorption as previously known he, - give, d. i.e., it will appear to be their reduction avoided or achieved a desired oxidation during vapor deposition or the The rate of oxidation is significantly accelerated.

The invention is illustrated below using examples. In the visible range, hard and adhesive layers with high refraction properties that are practically completely free of absorption are obtained on glass substrates by adding a mixture consisting of an oxide of titanium, e.g. B. TiO, and an oxide of cerium, e.g. B. Co02 or Ce20., Evaporated in a molecular ratio of 1: 1 to 8: 1 in a vacuum (10-5 Torr) and deposited on the documents. This mixture evaporates in the tungsten crucible at temperatures of around 1700 to 21001 C without difficulty. It is surprising that in the visible non-absorption (i.e., according to the prevailing view, maximally saturated with oxygen) oxide layers are obtained, while the same oxide of titanium in the absence of Ce or the above-mentioned elements or their oxides results in absorbent layers under otherwise identical vapor deposition conditions . Such an absorption in the visible has so far even occurred when the starting substance consisted of pure TiO. The effect of the added cerium can possibly be explained by the fact that it promotes the formation of TiO, with ZD 2 a possible need for oxygen being covered by desorption (in particular by the water vapor that is always desorbed on the recipient wall). The method according to the invention provides absorption-free layers in the evaporation of TiO23 TiO and (with a brief post-oxidation) even of metallic titanium, regardless of whether cerium or the other mentioned elements. be admixed in metallic form or in the form of oxides.

Further exemplary embodiments are summarized in the table below. The figures given are guidelines; the person skilled in the art can easily decide from which of these values he can deviate in adaptation to any special circumstances. It is variable, as the person skilled in the art knows, e.g. B. the evaporation temperature depending on the desired evaporation rate, the latter in turn depending, among other things, on the desired refractive index of the layer. Fast vapor deposition regularly results in higher refractive index layers than slow vapor deposition. The evaporation time is of course also variable, not only with regard to the evaporation rate to be observed, but of course also with regard to the layer chic to be achieved.

The gas pressure in the recipient is also variable. The person skilled in the art knows that he must keep the partial pressure of those gases which do not exert an oxidizing effect as low as possible. Therefore, with the help of suitable metering devices, it only varies the partial pressure of those gases (02, H20) which can cause this oxidation. Finally, the mixing ratios in particular are also variable, because there are no strict limits to the mixing ratios at which the effect intended according to the invention would suddenly set in. Rather, there are layers that are obtained from the starting substances alone without the addition of elements or oxides from the group of rare earths, to layers in which the added components predominate, i.e. practically layers made from the oxides of the rare earths used Earth, be won, all transitions. The properties of the layers obtained also change correspondingly, but, as already mentioned, the basic knowledge of the invention consists in the fact that the optical absorption of the specified from the evaporation and condensation. Mixtures obtained layers is much lower than would be expected from the mixing ratios alone. This is expressed by the fact that an admixture of more than 5 mol percent results in almost completely absorption-free layers in many of the examples cited, while with a simple dilution of the layers obtainable from the starting substances alone with an absorption-free rare earth oxide at a dilution of 50 % always even half of the original waste absorption, usually up to 30% of the incident light at A betTägt in the order of several percents / 4 layers, would be left.

The rule seems to apply that the process according to the invention is particularly suitable for the production of layers of such oxides whose heat of formation (related to each oxygen atom in the molecule) smaller than the image values of cerium oxide (Ce0.) Is.

In the following table are listed under a) under the numbers 1 to 8 elements or oxides of the group of rare earths (including yttrium, lantanum and cerium), which can be added to the starting substances. It is often convenient to use non-pure elements or oxides from the said group for admixture with the starting substances, because these are difficult to obtain. Rather, the commercially available rare earth mixtures (including the ytter earths) can be used without further ado, the usual percentage composition of which is given in the table. These contents given under a) are not to be confused with the molar percentages on the addition of the rare earths to the starting substances.

The table also gives examples under b) , specifically in line 1 suitable starting substances; in line 2, commercially available rare earth mixtures which are suitable for admixture or which have been tried and tested, whereby the information 1 to 8 means that any of the substance mixtures specified in section a) can be used; in line 3 useful evaporation temperatures for the substances mentioned; in line 4 suitable materials for the evaporation ships, whereby in columns 1 and 2 it is still to be distinguished whether oxides or metals are taken as starting substances according to line 1. The person skilled in the art also knows that some of the substances mentioned could be converted into vapor form just as well as by thermal evaporation by the cathode sputtering process, which is equivalent to the vacuum evaporation process with regard to many applications, and then condensed on the substrates.

Under c) of the table, three different variants (cc, fl, y) of vapor deposition in the production of layers according to the invention are given. It b # e, this confirms the per se known experience that vapor deposition at about room temperature of the carrier and the usual vacuum (variant β) can be replaced by vapor deposition in a higher vacuum, but at a higher temperature of the substrate (Variantex); likewise, a shorter vapor deposition time (variant y) requires an aftertreatment at a somewhat elevated temperature.

Section d) of the table below finally gives examples for carrying out the process, according to which the starting substances are evaporated separately.

Metals which are suitable as starting substances and the temperatures at which they can be vaporized from coal boats are listed in section d); Metals and oxides suitable for evaporation from molybdenum ships are also given. a) 1. Cerium mischmetal. about 50 % Ce, 20 1 / o Nd, 5 % Pr, 25 % La + other rare earths; 2. ceria: 99.9 1 / o CeO .; 3. Cerite oxide: about 50 % Ce023, 20% La20., 5 % Pr203, 20% Nd203, 5 % other oxides; 4. Lanthanum oxide: 99.4% La20; 5. Neodymium Oxide: about 90 % Nd.O., 8 % Pr6011, 2% SM203; 6. Praseodymium oxide: about 97 % Pr, 01 "0.2% Nd203, 0.25 1 / o Ce02, balance La20"; 7. Samarium oxide: about 95% Sin203, 2% Pr2031 1 %, Nd203; 8. Didymoxide: about 40% Nd20.31 10 % Pr20 ", 13 Vo La20 .. remainder other oxides. b) Starting substance Si or SiO Ti or TiO oSn Cu Cr or Fe the Si + Si02 or Ti + Ti02 the Cr + Cr203 Mn or Ni Co or Si02 sn02 or Cr203 Fe0 To mix in 1 to 8 1 to 8 1 to 8 1 1 to 8 1 2 to 8 2 to 8 2 to 8 Evaporation temperature, 'C about 1450 1700 1350 1500 1300 1050 1500 1600 1800 Shuttle material ...... for metal for metal Mo Mo W Mo WWW mixtures: C mixtures: C for oxide for oxide mixed. Mole mixed-. W. C) variant a 1 fl 1 7 Evaporation time per A / 4 layer in minutes .......... 2 2 <1 Temperature of the support, 1 C ...................... 300 30 < 200 Pressure (02 + HO), mm Hg ....................... 1-15-5 1-10-4 <5 - 10-5 Post-treatment ................................ none no tempering, 300 ° C, air d) Separate evaporation of the starting substance and the elements or oxides to be added from the group of rare earths (including yttrium, lanthanum and cerium) from C boats: Zr (2100- C), Th (2400 ' C), V (2050 'Q; from Mo-Schiffehen: Pb (8000 C), In (600') C), 11 (650 'C), ZnO (9001 C), CdO (9001 C), Bi (800' C), Mo03 ( are 5 to 50 mole percent to implement the method, a device according to the invention shown in the drawing 1: Cerit- and yttrium earths (Q 14001 of W-boat blending amount of Cerit- and yttrium earths; 700 C), where, 3 (700 'Q... means the recipient, which can be evacuated to a pressure of about 10-4 mm Hg or better via a line 2 with valve 3 by means of a vacuum pump This crucible consists of one of the substances listed in the table for the evaporation boat. 5 is the holding device for the crucible, 6 the holding device for the be, -dampfende glass plate or lens 7. 8 and 9 are the power supplies for the electrical heating coil 10, which the. Crucible 4 surrounds. 11 and 12 illustrate the vacuum tight electrical feedthroughs.

The entire arrangement is built on a base plate 13 . The vacuum-tight seal between the bell of the recipient and the base plate is made by the seal 14.

For some embodiments of the inlet of oxygen or 'Waseerdampf or atmospheric air into the container is required. The gas supply line 15, which can be shut off by means of a valve 16, serves this purpose.

To carry out the method according to the invention according to section d) of the table, two separate parts are required in the vapor deposition system. The second crucible can be arranged in the same way as the crucible 4 in recipients and provided with its own power supply lines. The following is the implementation of the method according to section d) of the table. explained using a special example: In the vacuum evaporation system described above, a first boat becomes. Thorium evaporates from carbon at a temperature of about 2100 ° C and the resulting vapors are deposited on the lens 7. (Since the crucible is made of carbon, it can be heated by direct passage of current without the use of a heating coil surrounding it.) At the same time, a second crucible, which is arranged in the same recipient and which is made of tungsten, becomes an element or an oxide from the group of rare earths, e.g. B. the cerium mischmetal mentioned under a) 1 of the table, brought to evaporation, the vapors of which are reflected on the lens at the same time as the thorium vapors. This creates a mixed layer, which is, however, under the influence of the elements from the group of rare earths. The presence of oxidizing gases immediately changes into a completely absorption-free oxide layer, & ie consists partly of thorium oxide, partly of the oxides of the rare earths used. The oxidizing gas, e.g. B. water vapor, is admitted via line 15 by means of the valve 16 up to a pressure in the recipient of about 2 - 10-4 mni Hg. The amount of materials in the two evaporation boats is measured so that the proportion of vapors, au & the oxides of rare earths in the vapor space is 5 to 10 mole percent. It has not yet been clarified exactly what the effect of the method according to the invention is based on, whether possibly on a catalytic effect of the pure or in the form of an oxide admixed metal from the group of rare earths (including yttrium, lanthanum and cerium) or perhaps on the formation of special ones Compounds or intermediate products in the evaporation material or in the resulting layer. For technical application, however, it is important to realize that this process can be used to significantly shorten the times required for vapor deposition of known oxide layers if it is important to achieve low-absorption oxide layers.

It has often proven convenient to use the mixtures to be evaporated to produce in a previous melting process by adding a mixture, e.g. B. off Ti, TiO 2 and cerium oxide (or cerium itself), melted in a vacuum and solidified Product is shredded and used as a starting material for later evaporation thinner Serves the purpose. In some cases, however, it has proven to be practical, i.e. to produce mixtures to be evaporated in a previous sublimation process, z. B. a mixture of Si and Ce02 powder in a vacuum sublime, rt, the sublimation product crushed and used as the starting material for the vapor deposition of thin layers. In order to carry out this procedure, attention is drawn to the fact that some of the Products obtained by sublimation are strongly pyro-phoric and self-ignite tend and therefore handled with caution and preferably only in small quantities Need to become. For example, this has been observed with a mixture of SiO and ceria, which was used to produce absorption-free silicon oxide layers (SiO alone with layer thicknesses such as those required for interference systems are highly absorbent Layers).

Occasionally it is advantageous to evaporate the mixtures under simultaneous heating of the substrate. In itself, this is vapor deposition already known of thin layers with simultaneous heating of the documents.

When carrying out the procedure, as mentioned, there is often one Oxidation of the condensate takes place, with the required oxygen also in one usual # it evaporation vacuum (10-4 Torr or better) evacuated evaporation equipment frequently is available in sufficient quantities in the residual gas atmosphere. Probably As already mentioned, the required oxygen comes from that of the walls of the Evaporation system desorbed water vapor.

An artificial enrichment of the residual gas atmosphere with oxygen is, as has been shown, often appropriate, but the vacuum and the vapor deposition rate can be kept higher than with the known methods of this type and still hard and adhesive layers with the lowest possible absorption easily achieved will.

In some cases, the complete oxidation of the layers does not take place until after the vapor deposition on the carrier, as soon as an oxidizing gas mixture (air) is let into the vapor deposition system. This subsequent oxidation - subsequent oxidation of layers is known as such - takes place when the application of the layers according to the method of the invention was carried out at very high speed, so that, for. B. an opaque and metallic shining layer after the vapor deposition at the moment of flooding, the installation with atmospheric air and possibly under the additional effect of a moderate temperature increase due to the previous vapor deposition instantly turns into a completely transparent, absorption-free oxide layer. Even layer substances that would otherwise only be available through the use of high temperatures. and long tempering times, oxidize easily and quickly if an element of the rare earths or their oxides is added to the evaporation materials.

Claims (2)

Claims: 1. Process for the production of thin, in the visible wavelength region practically absorption-free oxide layers for optical purposes "especially on substrates on glass, by vapor deposition of oxidic and / or oxidizable substances in a vacuum, optionally in the presence of an oxidizing atmosphere, d a d g e urch - indicates that simultaneously with the oxide and / or oxidizable substances, one or more elements and / or oxides from the group of rare earth (including yttrium, lanthanum and cerium) are vapor-deposited.. 2. The method according to claim 1, characterized in that the starting substances are evaporated as a mixture. 3. The method according to claim 1, characterized in that the starting substances are evaporated separately. 4. The method according to claim 1 to 3, characterized in that the ratio between the starting substances is chosen so that the proportion of free or bound rare earth atoms is at least 5 and at most 50 mol percent. 5. The method according to claim 1 to 4, characterized in that cerium and / or cerium oxide are used as rare, iie-earth components. 6. The method according to claim 1 to 4, characterized in that prascodyni and / or praseodymium oxide are used as the rare earth component. 7. The method according to claim 1 to 6, characterized. that silicon and / or silicon oxide are used as oxidic and / or oxidizable substances. 8. The method according to claim 1 to 6, characterized in that titanium and / or titanium oxide are used as oxidic and / or oxidizable substances. 9. The method according to claim 1 to 6, characterized in that tin # and / or zinc oxide are used as oxidic and / or oxidizable substances. Considered publications: German Patent Specifications Nos. 845 883, 883 546, 892 024, 900489.