NL8400091A - METHOD FOR MANUFACTURING OPTICAL ELEMENTS WITH INTERFERENCE LAYERS. - Google Patents

Description

PTT - VO 5347

Method of manufacturing optical elements with interference layers .___________

The invention relates to a method for manufacturing optical elements, in particular filters, with interference layers from dielectric layers with alternating high and low refraction on organic and inorganic substrates.

5 The manufacture of interference layers has been known since Icing.

Depending on the requirement of the end product, the individual layer thicknesses lie between λ / 4 and λ / 8 of the so-called reference wavelength for which the calculation of the system was carried out. For example, end products are group optical elements formed by sub-abstractive and additive color separation filters, cold light mirrors, heat reflection filters, color temperature changing filters, color temperature changing reflectors, dielectric narrow band filters and beam turners.

As substrate materials, transparent or translucent materials are used from the group consisting of glass, sapphire and plastic as well as metals. A material which is known under the designation CR 39 is preferably used as plastic.

Such optical elements must meet certain requirements, namely with regard to their optical properties such as absorption freedom, stability of the angular position, etc., and with regard to their mechanical-chemical properties, such as rubbing strength, bonding strength, boiling strength, resistance to temperature as well as resistance to acids, etc.

With regard to the abovementioned properties, increasing demands have been made over time, so that the use of "soft" substances such as ZnS, cryoliethenz., Which can be thermally evaporated, has been abandoned and the use of "hard" oxide layers, such as TiCl 2 and SiO 2 and 2, for the evaporation of which electron beam guns are used.

The layer materials hitherto used for interference layer systems have generally been oxydivan titanium as a high refractive layer and oxides of silicon as a low refractive layer. Vapor deposition was usually started at <1.3 x 10 Pa and at a substrate temperature between 200 and 350 ° C. The time to reach the above-mentioned pressure as well as a temperature above 250 ° C could be up to 90 minutes. Typical evaporation rates were at about 15 A / sec for SiCl 2 and at about 3 l / s for TiCl 2. Therefore, the deposition time for producing 15 layers for a reference wavelength of Xq - 400 nm could average up to 50 minutes.

In addition, due to the strongly heated substrates, there was a considerable cooling time, which could also amount to 150 minutes. For heat-sensitive substrates, such as plastic substrates, the known layer-forming system was readily not suitable. The boiling strength 10 corresponded to DIN 58196, Part 2 C 60 for smooth substrate surfaces and to DIN 58196, Part 2 C 15 for strongly curved substrates. more achieved according to MIL C 675C.

"C60" or "C15" in the provisions regarding the cooking resistance according to DIN 58196, Part 2 mean that the coating has not peeled off by itself during a cooking time of 60 minutes and 15 minutes, respectively. Thus, TiCl 2 / SiCl 2 layers on plain substrates withstood the boiling test for about 20 hours, but on highly curved substrates (hemispherical surfaces) only for about 15 minutes. However, this does not yet mean that the respective layer has also passed the adhesion strength test in accordance with MIL C 675 C.

In particular, the last-mentioned bond strength test shows that the known coating system on strongly curved substrates, such as in particular with optical lenses, cold light mirrors, etc.

After a cooking time of only 15 minutes, it no longer had any bond strength at all.

The object of the invention is therefore based on finding a method of the type described in the preamble, which can be carried out in a more economical manner, which makes it possible to obtain layers which are also resistant to boiling and with strongly curved substrate surfaces. good adhesion, and which is also suitable for coating plastics.

The object set is achieved in the method according to the invention described in the opening paragraph, that as a first layer on the substrate A 2 O 2 is applied as a layer with a low refraction, on which further layers of ZnS and Al are alternated in alternating order. ^ O ^ are applied, and the last layer is a layer of A ^ O ^ applied.

8400091.-3-

While the application of Al 2 O 3 layer as a covering or protective layer, per se, is known, the underlying layer combination is new, including the measure that the first layer on the substrate is an A 2 O 2 layer. layer is applied. It has surprisingly been found that Al 2 O 2 is very clearly an excellent adhesive which performs its action even under extreme oblique evaporation, as is the case, for example, on the rim of half-spherical glass caps. In any case, the reverse order, namely applying ZnS as the first layer, has not led to the excellent bonding strength as achieved in the present mode of operation. The high bond strength and cooking strength is very clearly accomplished by the first adhesive bonding agent acting and can have thicknesses between 10 and 300 nm, without significant changes in the bond strength and cooking strength values occurring thereby. The remaining mechanical chemical properties depend mainly on the outer Al 2 O 3 layer, which may have a thickness which is several multiples of the reference wavelength core.

The present method is suitable for the manufacture of optical elements which are optically active at wavelengths between 0.39 µm and 6 µm. It is known per se that ZnS can be used for optical elements which are optically active between 0.39 µm (the beginning of their own absorption) and 14 µm. can be used between 0.2 µm (start of self-absorption) and 7 µm. Since Al2 ° 3 tends to form cracks, the range is more limited for practical reasons. The use of "soft" ZnS interlayers now surprisingly reduces the tendency to crack to the extent that the range can be extended to about 6 µm.

In carrying out the present method, the pressure at -2 at the start of the vapor deposition step may be above 1.3 x 10 Pa, for example in the range between this value and 1.05 Pa. In addition, the coating step can be started with cold substrates, namely substrates which are at room temperature, so that a pre-heating time is not necessary. As a result, the time to evaporation onset is reduced to values below 30 minutes; this is 1/3 of the prior art value mentioned earlier in this specification, 3400091 * - 4 - with the proviso that the data of the vapor deposition device is identical. Due to the extremely high evaporation rate of ZnS, which is typically about 20 S / sec versus about 3 S / sec for TiO2, the 15 layer evaporation time can be reduced to values below about 15 minutes. This is again less than 1/3 of the prior art time mentioned earlier in this specification. Due to the extraordinarily low superstate temperature, a cooling time can also be omitted.

Therefore, the amount of material produced, at a comparable size of the vapor deposition device, increases to about three times the value per unit time, so that the manufacturing cost is considerably lower.

The present method is thereby carried out in a particularly favorable manner at substrate temperatures between 20 and 180 ° C, the method being expediently carried out at the lower end part of the temperature range. This makes it possible, unlike in the prior art, to also vaporize plastics, for example the base material CR 39.

Due to the short suction time due to the less high vacuum, the absence of a heating and cooling time and due to the higher evaporation rates, as already stated, a considerably shorter process time is achieved than in the manufacture of the usual oxide layers.

It is admittedly known to produce interference layers under extreme oblique evaporation of substrate surfaces. Thereby, as a layer material, besides ZnS MgF 2 or cryolith, it is evaporated under scattered gas, whereby ZnS can also be formed by separate evaporation of Zn and S. However, the interference layer systems thus produced do not have much of the mechanical-chemical and thermal properties of the layers produced according to the present method. On the other hand, in the manufacture of coating systems from exclusively "hard" oxide coating materials, it should be noted that with high oblique evaporation, the bond strength and the boiling strength decrease substantially to zero.

In the present method, the boiling strength, both on plain substrates and on strongly curved substrates (for example on semi-spherical substrates) was tested according to DIN 58196, Part 2 C60.

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In both cases, even after a continuous cooking test for 60 hours, no loosening of the layer took place, nor was there any reduction in the abrasion strength and in the bond strength, each determined in accordance with MIL C675 C.

The low substrate temperature makes it possible for the first time to manufacture all optical elements with thin layers, which allow an absorption of approximately 1%, also from temperature-sensitive plastics, and with properties such as hitherto only of oxide materials. knows. Exceptions to these properties are only the temperature stability, which is limited because of the plastic used as a substrate, as well as the cooking test.

A layer system manufactured according to the present method is further elucidated in figure 1 of the drawing, in which the glass substrate is indicated by "S". The layers are numbered in order of application, the layer "n" being the top or top layer. which consists of * 00 ^ a9 and 1/3, ..., n-2 and n consist of A ^ Oy while the layers 2, 4, ..., n-1 consist of ZnS.

Example I.

Gaelfilter on glass.

20 In a vapor depositor of type 1100 Q (manufacturer: Firma

Leybold-Heraeus GmbH in Hanau, Federal Republic of Germany), glass disc-shaped substrates were brought and the pressure was reduced to 10 Pa in 6 minutes. Subsequently, the substrates were cleaned in a known manner by a glow discharge. The device was then brought to a vacuum of 5 x 10 Pa in 14 minutes, after which oxygen was supplied as a sprinkling gas to a pressure of 2 x 10 Pa. Thereafter, degassing was carried out with an electron beam gun for 2 minutes until the pressure remained stable. Subsequently, the Al 2 O 3 was deposited as the first layer or as an adhesive layer at a vapor deposition rate of 13 S / sec.

The control of the speed and the control of the diaphragms (for covering the evaporator) were done by means of the oscillating quarz method. After the Al 2 O 2 layer, the first ZnS layer was evaporated at a vapor deposition rate of 10 l / s, while the Al 2 O 2 layer was kept at an elevated temperature level by a low energy supply. After closing the diaphragm for the ZnS evaporator (thermal evaporator), it was also kept at an elevated temperature level by a low energy supply gp, and the electron beam 84 00 09 1 -6-

J *. V

gun was brought back to evaporation power. * By alternating repetition of these coating processes, a total of 17 separate layers of the nature and layer thicknesses shown below were deposited.

^ 1. low Al ^ Og ^ X λ / 4 for 450 ΠΓΠ (reference wavelength) 2. low ZnS 0.45 x λ / 4 for 450 nm 3. low AlgOj 0.9 X λ / 4 for 450 ΠΓΠ 4. low ZnS 0.95 x λ / 4 for 45 0 nm 5. layer AlgOg ^ X λ / 4 for 450 nm: 10 6. layer ZnS 1 x λ / 4 for 450 nm 7. layer A1 g 0 3 1 χλ / 4 for 450 nm 8 '. layer ZnS 1 x λ / 4 for 45 0 nm 9 · layer Al £ 0 ^ 1 X λ / 4 for 450 nm 10. layer ZnS 1 x λ / 4 for 450 nm 15 11. layer A ^ Og 1 x λ / 4 for 450 nm 12. layer ZnS 1 x λ / 4 for 450 nm 13. layer AlgOg 1 X λ / 4 for 450 nm 14. layer ZnS 1 x λ / 4 for 450 nm 15. layer ^ "^ 2 ^ 3 ^ x λ / 4 for 450 nm 20 16. layer ZnS 1 X λ / 4 for 450 nm 17. layer A ^ Og 2.1 X λ / 4 for 450 nm ..

The outside temperature was set on average at about 50 ° C.

The pressure was kept constant throughout the process. After evaporation of the last (17) layer, the evaporators were turned off and after cooling after 1 minute the device was allowed to refill.

Interference layers were obtained on all substrates, which passed the above-described tests for rub resistance, bond strength and boiling strength. In addition, an absorption below 1%, a long-term stability of the angle (steep drop in the measurement curve in the transmission measurement) of 10 nm was obtained from opening the device to standstill.

Example II.

35 Yellow filter on CR 39.

Example I was repeated, with the only difference that instead of the glass substrates, substrates of the CR 39 plastic were used 840009 (-7-liF "" ···. The plastic substrates warmed during the course of the coating from room temperature to about 50 ° C. The final product perfectly complied with the optical and mechanical requirements, only the boiling test was omitted, in particular excellent rubbing and bonding strength according to MIL C 675 was obtained.

Example III.

Cold air mirror on hemispherical surface.

Substrates for cold light mirrors from glass were introduced into the vapor deposition device according to example I. This involved half 10 spheres with a diameter of 32 and 54 mm, respectively, and a central opening, as used, for example, for projector countries.

The process parameters for vacuum suction, glow discharge cleaning, and process pressure, including the entry of oxygen as a scattering gas, as well as the vapor deposition rates for the individual layers, corresponded to those in Example I. At the "elevated temperature level" for such a temperature level, from which spontaneous evaporation could be initiated, without, however, that the substances concerned could develop a vapor pressure sufficient for significant evaporation. By alternately repeating the individual coating steps, a total of 35 separate layers of the nature and layer thicknesses indicated in the table below were deposited.

The street temperature was set on average at approximately 50 ° C. The pressure was kept constant throughout the process.

After evaporation of the last (35) layer, the evaporators were turned off and after cooling after 1 minute the device was flooded.

Interference layers were obtained on all substrates, which passed the above-described tests for rub resistance, bond strength and boiling strength. This was also and in particular the case for the cold light mirrors with a diameter of 32 mm, which are particularly critical because of the small radius of curvature with regard to the cooking resistance. In addition, an absorption below 1% was obtained, as well as a long-term stability of the angular position of 10 nm from the opening of the device to the standstill.

8400091 /, *

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-8- 1. layer Al 2.2 7 x 4 for 400 nm 2. laaf - Zn5 1.80 x - * 3. layer A1 2 9 3 * "" * 4. layer Zn S 1, 21 x - · 5 5. layer Al2 ° 3 1 * 85 * '' 6. layer ZnS 1.63 x_ '' - "7. layer Al ^ O ^ l, * 8 1x" "* 8. layer 2nS 1.62 x" '' 9. layer AljOg 1.60 x 11 "*" 10 10. layer ZnS 1.78 x '' '' 11. layer A ^ 2 ^ 3 1.65 x 12. layer ZnS 1.59 x 13. layer A ^ 2 ^ 3 l, 44x 14. low ZnS 1.63.x '' '' 15 15. low Al ^ l, 52x '' '' 16. low ZnS 1.43 x '' '' 17. low AljOg 1.40 x '' '' 18. Layer ZnS 1.34 x '*' "19. Layer AlgOg 1.40 x" '20 20. Layer ZnS 1.32 x ""' '21. Layer A1203 1.40 x '' 22. layer ZnS 1.46 x '' 23. _ layer AljOg 1.2S x '' 24. la: g ZnS 1.12 x '' '' '25 25. layer AlgOg 1.13 x' ' 26.Layer ZnS 1.14 x '' 27.Layer Al2 ° 3 1 '14 x' '28.Layer ZnS 1.08x' '29.Layer AljOg 1.06 x' '30 30'. Layer ZnS 0, 91-x 31.low 'AlgOg 1.08 x' '32.'low ZnS 1.26 x * * 33.laaf ·· A1203 1.05 x * * 34.low - ZnS 0.55 x * * 35 35 low Al ^ 1.06 x '* 8400091. -9- w · -—--.

Example IV.

Anti-reflex layers.

Different plate-shaped substrates with dimensions of 50 mm x 50 mm x 2 mm 5 and made of the following materials were introduced into the evaporation device according to example I:

Glass (BK7)

Polycarbonate ("Makrolon" from Bayer) CR 39.

The process parameters were similar to those of Example 1, except that no oxygen was introduced and the diaphragm control was by photometer measurement.

A total of seven layers were vapor deposited according to the table below, it was surprising that, although both components had refractive indices greater than that of the substrate, flawless anti-reflective layers could be formed which additionally provided excellent mechanical and chemical resistance.

1. layer A12C> 3 lx λ / 4 for 913 nm 20 2. layer ZnS 1 x λ / 4 for 127 nm 3. layer Al2 ° 3 1 x λ / 4 for 556 nm 4. layer ZnS 1 x λ / 4 for 264 nm 5. layer A ^ O ^ 1 x ^ 4 for 242 nm 6. layer ZnS 1 x λ / 4 for 619 nm 25 7. layer Al203 1 x λ / 4 for 616 nm

The reflective properties are shown graphically in Figure 2, with the reflectia values in percent on the ordinate. This concerns a good broad-band reflection between approximately 460 and 640 nm, which can even be regarded as very good for artificial staff substrates.

8 * 00091

Claims (5)

1. Method for manufacturing optical elements, in particular filters, with dielectric interference layers. layers with alternating low and high refraction on organic and inorganic substrates, characterized in that as the first layer on the substrate 5 a "*" s ^ aa <? is applied with a low refraction, on which further layers of ZnS and Al 2 O 3 are applied in alternating order, and the last layer is a layer of A 2 O 3. A method according to claim 1, characterized in that the first layer is applied at a sustrate temperature of 20-180 ° C. Process according to claim 1, characterized in that the coating is carried out by a vapor deposition process at pressures between 1.3 x 10 and 1.05 Pa. Method according to claim 3, characterized in that at a vapor deposition rate of between 10 and 15 lb / sec. and the ZnS at a vapor deposition rate between 10 and 30 lb / sec. is evaporated. 5. Use of the methods according to claims 1-4 in the manufacture of filters from the group formed by subtractive and additive color separation filters, cold light mirrors, heat reflection filters, filters for changing the color temperature, reflectors for changing the color temperature, dielectric narrow-band filters and beam latches in combination with substrates from the group formed by glass, sapphire and plastic. 8400091