FR2540254A1 - PROCESS FOR THE PRODUCTION OF OPTICAL ELEMENTS WITH INTERFERENTIAL LAYERS - Google Patents

Abstract

Process for the production of optical elements, and in particular of filters with interference layers formed by dielectric layers with an alternately low or high refractive index, and condensed on substrates. The deposition on the substrate comprises first a layer of Al2O3 with a low refractive index, then alternating layers of ZnS and Al2O3, and finally a layer of Al2O3. Such layers can be deposited at low temperature on flat or highly curved substrates, with lower production costs, while exhibiting the optical properties of known interference layers. (CF DRAWING IN BOPI)

Description

The present invention relates to a process for the production

  optical elements, and in particular filters, with

  ferrias consisting of dielectric layers with a

  alternatively low or high refraction on organic substrates

  nics or minerals. The production of interferential layers has been known for a long time. According to the requirements imposed on the finished product, the thickness of the various layers is between X / 4 and X / 8 of the reference wavelength, for which the system has been calculated. Finished products are, for example, optical elements of the group of subtractive or additive color separation filters, mirrors

  with cold light, heat-reflecting filters, converted filters

  color temperature sensors, reflectors color temperature converters, narrow-band dielectric filters, beam splitters Materials used as substrates are transparent or translucent materials in the glass, sapphire and plastics, or metals group Plastics used

  preferably is the material known as CR 39.

  Such optical elements must satisfy certain requirements relating to their optical properties, such as absence of absorption, stability of the edge length, etc., and to their mechanochemical properties, such as abrasion resistance, adhesion , resistance to boiling water, thermal resistance and acid resistance, etc. The requirements for the above properties have steadily increased over time, so that the use of substances

  "soft", such as Zn S, cryolite, which can be evaporated thermally

  has been abandoned in favor of "hard" layers of oxides, such as Ti O 2, Si O 2, etc., for the evaporation of which

  Electronic guns are used.

  The materials hitherto used for interferential layer systems were generally titanium oxides for the high refractive index layer and silicon oxides

  for the low refractive index layer The evaporation operation

  usually started at <1.3 x 10 Pa and at a substrate temperature between 200 and 350 ° C The time required to reach the above-mentioned pressure and a temperature greater than

  250 'C could reach 90 minutes Typical evaporation rates

  These were about 1.5 nm / s for Si O 2 and about 0.3 nm / s for Ti O 2. The evaporation time required for the production of layers for a reference wavelength X = 400 nm could

  50 minutes. As a result of the warming up of subsi-

  the cooling time was significant and could reach 150 minutes The known layer system was not suitable

  for heat-sensitive substrates, such as plastics.

  The resistance to boiling water corresponded to DIN 58196/2, C 60 for flat substrate surfaces and to DIN 58196/2, C 15 for high curvature substrates. After treatment according to DIN 58196/2, C 15, no adhesion according to MIL C 675 C is no longer obtained in the

case of substrates with strong curvature.

  In the boiling water resistance indications according to DIN 58196/2, "C 60" and "C 15" mean that the coating does not

  do not detach for a boiling time of 60 or 15 minutes.

  Thus the Ti O 2 / SiO 2 layers withstand about 20 hours of boiling test on flat substrates, but only about minutes on high-curvature substrates (surface

  This does not mean, however, that the layer

  also satisfies the adhesion test according to MIL C 675 C. The last adhesion test cited in particular shows that

  substrates with a high curvature, such as those used in particular

  bind for optical lenses, cold-light mirrors, etc., the known layer system no longer has any adhesion after

  a boiling time of only 15 minutes.

  The subject of the invention is therefore a process of the abovementioned type, of economical use, which makes it possible to obtain adherent and boiling-water resistant layers even on a surface of substrate with a strong curvature, and which is also suitable for coating. of

plastics.

  According to an essential characteristic of the invention, the deposition on the substrate comprises first a layer of A 1203 with a low refractive index, then alternating layers of Zn S and A 1203, and

last one layer of A 1203.

  While the deposition of a layer of A 1203 as a cover or protection layer is known, the underlying combination of layers is novel, including the characteristic of the deposition of a layer of A 1203 as a protective or protective layer.

  layer of Ai 203 first on the substrate It is amazing to

  tater that A 1203 is obviously an excellent bonding agent,

  which acts even in the case of evaporation under a very strong inclination

  example, on the edge of hemispherical glass caps

  The reverse order, that is to say the deposition of Zn S as the first layer, did not give the excellent adhesion obtained with the procedure according to the invention. It is obvious that the adhesion and the resistance with high boiling water are produced by the first

  layer of A 1203, which acts as a coupling agent and can

  have a thickness between 10 and 300 nm without appreciable fluctuations in the values of adhesion and water resistance

  The other mechanochemical properties depend essentially on

  of the outer layer of A 1203, the thickness of which

  reach a multiple of the reference wavelength.

  The process according to the invention is suitable for the production of

  optically acting optical elements at wavelengths between 0.39 and 6 pm It is known to use Zn S for optically acting optical elements between 0.39 pm (onset of self absorption) and 14> m Ai 203 is usable between 0.2 pm (start of the own absorption) and 7 pm The range is narrower for practical reasons, since Ai 203 however has a tendency to crack The use of "soft" intermediate layers of Zn S surprisingly reduces the tendency to crack at the point of

  allow an extension of the range up to about 6 pm.

  For the implementation of the process according to the invention, the pressure at the beginning of the evaporation can be greater than 1.3 × 10 5 Pa, and

  for example between this last value and 1.05 Pa.

  In addition, deposition may start with cold substrates,

  that is to say at room temperature, so that a time of pre-

  heating is useless The time elapsing until the beginning of the evaluation

  poration falls below 30 minutes, one-third of the value previously indicated for the prior art, assuming identical characteristics of the evaporation device The possible evaporation value of Zn S, extremely high and typically about 2.0 nm / s against about 0.3 nm / s for Ti O 2, can reduce

  the evaporation time of 15 layers at a lower value

  than about 15 minutes A cooling time is also

  unnecessary because of the extremely low temperature of the substrate.

  For a comparable size of the evaporation device, the number of charges per unit of time is thus substantially tripled, so

  that the production costs are much lower.

  The process according to the invention is advantageously used

  at a substrate temperature of between 20 and 180 OC, and

  at the lower end of the Controllable Temperature Range.

  to the prior art, it is thus possible to deposit by evapo-

  rationing of layers on plastics such as

CR 39.

  The low pumping time resulting from the lower vacuum, the suppression of a heating and cooling time, and the higher evaporation rates ensure, as previously indicated, a much shorter treatment time than the production.

conventional oxide layers.

  It is certainly known to produce interferential layers by evaporation at very high inclination on substrate surfaces In addition to Zn S, Mg F 2 or cryolite is deposited under dispersive gas; Zn S can also be produced by separate evaporation of Zn and S The interferential layer systems thus produced, however, do not have by far the mechanochemical and thermal properties of the layers produced according to the invention. It should also be noted that in the case of the production of systems

  layers exclusively from "hard" oxide materials, the adhesion

  resistance and resistance to boiling water tend to

  towards zero in case of evaporation under very steep inclination.

254 G 254

  In the case of the process according to the invention, the resistance to boiling water on flat substrates and on substrates with a high curvature

  (hemispherical for example) has been studied according to DIN 58196/2, C 60.

  In both cases and even after 60 hours of the boiling water resistance test, there is no evidence of layer separation and no decrease in abrasion resistance and adhesion, each determined by MIL C 675 C. The low temperature of the substrate allows for the first time

  to produce all the optical elements with thin layers,

  absorbing about 1% more, even on thermosensitive plastics and with properties only known for oxidized materials so far. The only exceptions are thermal stability, limited by a plastic substrate,

and the boiling test.

  A layer system produced according to the invention is shown in Figure 1, on which the glass substrate is designated by "S" The layers are numbered in the order of their dep 8 t, the layer "n" being the layer The layers 1, 3 n-2 and N are in A 1203, while the layers 2, 4 n-1 are in Zn S. Example 1: "Yellow filter on glass" A typical evaporation plant 1100 Q (manufacturer Leybold-Heraeus Company GmbH, Hanau, Federal Republic of Germany) is charged with disc-shaped glass substrates, then a pressure of Pa is established by pumping in 6 minutes The substrates are then cleaned in a known manner by a corona The vacuum is then made in 14 minutes in the installation, to a pressure of 5 x 10-3 Pa, then oxygen is admitted as a dispersive gas up to a pressure of 2 x 10 Pa A 1203 is then degassed for 2 minutes by an electron gun, until the pressure remains stable Al, 23 is then evaporated to form the first layer or the bonding agent, at a speed of 1.3 nm / s The speed regulation and the control of the diaphragms (for covering the vaporizers) are done by the oscillating quartz method After the layer of A 1203, the first layer of Zn S is deposited at a rate of 1, Onn Vs, while A 1203 is maintained at a higher temperature level by one.

  low energy input After closing the diaphragm

  Zn S (thermal vaporizer), the Zn S is also maintained at a higher temperature level by a low energy input and the evaporation power of the electron gun is increased again The following 17 layers are deposited in total over there

  alternating repetition of these deposition processes.

  1 layer of A 1203 2 layer of Zn S 3 layer of 4 layer of layer A 12 6 layer of 7 layer of 8 layer of 9 layer of layer of 11 layer of 12 layer of 13 layer of 14 layer of layer of 16 layer of 17 layer of

A 12 03

Zn S Zn S

A 12 03

Zn S

A 1203

Zn S

A 12 03

Zn S

A 1203

Zn S

A 12 03

Zn S

A 12 03

  The temperature 0.45 0.9 0.95 2.1 average 1 e 2.1 average x X / 4 for 450 nm x% / 4 for 450 nm x> / 4 for 450 nm x% / 4 for 450 nm x% / 4 for 450 nm x X / 4 for 450 nm x X / 4 for 450 nm x> / 4 for 450 nm x% / 4 for 450 nm x X / 4 for 450 nm x> / 4 for 450 nm x X / 4 for 450 nm x% / 4 for 450 nm x X / 4 for 450 nm x% / 4 for 450 nm x% / 4 for 450 nm

x> / 4 for 450 nm.

  of the substrate s'ab (reference wavelength)

bed at 50 C approximately.

  The pressure is kept constant throughout the duration of the

  process After the dep 6 t of the last layer (17 th), the vapors

  risers are cut then, after cooling in 1 minute,

the installation is flooded.

  Interferential layers are obtained on all the substrates satisfying all the previously described tests of resistance to abrasion, adhesion and resistance to boiling water. In addition, an absorption of less than 1% and a long-term stability of the position are obtained. the edge of 10 nm (fast decay of the transmission measurement curve, between opening and stopping

of the installation.

  Example 2: "Yellow filter on CR 39" Example 1 is repeated with the only difference that the glass substrates are replaced by plastic substrates CR 39 During the deposition of the layers, the plastic substrates s' warm up from room temperature to 50 OC

  The finished product perfectly meets the optimum requirements

  mechanical issues; only the boiling test is omitted. In particular, excellent resistance to abrasion and adhesion is obtained according to MIL C 675 C. Example 3: "Mirror with cold light on a hemispherical surface" The evaporation plant according to US Pat. example 1 is responsible for

  substrates for glass cold-light mirrors

  spheres having a diameter of 32 or 54 mm and a central opening,

  of the type used for example for projector lamps.

  The process parameters are identical to those of Example 1 for the evacuation, the corona cleaning, the working pressure including the admission of oxygen as a dispersive gas and the speed

  evaporation of the various layers The "higher level of temperature

  "allows the start of spontaneous evaporation, without the substances under consideration being able to develop a

  sufficient vapor for significant evaporation The following 35 layers

  are deposited by alternating repetition of the various operations

deposit.

  The average temperature of the substrate is approximately 50 ° C.

  The pressure is kept constant throughout the duration of the pro-

  After the deposit of the last layer (35 th), the vaporizers

  are cut off and then, after cooling down in one minute, the

the installation is drowned.

  interferential layers are obtained on all the substrates

  satisfying the previously described tests of resistance to abrasion

  its adhesion and resistance to boiling water.

  especially for cold-light mirrors with a diameter of 32 mm, whose resistance to boiling

  especially critical because of the short radius of

  In addition, an absorption of less than 1% and a long-term stability of the opening and the rear 1 layer 2 layer 3 layer 4 layer 6 layer 7 layer

8.

9. 10. 11. 12. 13. 14. 15. 16. 17.

18.

19. 20. 21. 22.

23.

24. 25. 26. 27.

28.

29. 30. 31. 32.

33.

  layer layer layer layer layer layer layer layer layer layer layer layer layer layer layer layer layer layer 1203 Zn S 1203 Zn S 1203 Zn S 1203 Zn S 1203 Zn S A 1203 Zn S A 1203 Zn S A 1203 Zn S A 1203 Zn S A 1203 A Zn S A 1203 Zn S A 1203 Zn S A 1203 Zn S Zn S 1203 At 1203 of Zn S of A 1203 of Zn S of A 1203 of Zn S of A 1203 of Zn S of A 1203 ie of the position of the edge of 10 nm between

t of the installation.

  2.27 x A / 4 for 400 nm 1.80 x "" 1.67 x "" 1.21 x "" 1.85 x "" 1.63 x "" 1.81 x 1.62 x 1, 60 x 1.78 x 1.65 x 1.59 x 1.44 x 1.63 x 1.32 x 1.43 x 1.40 x 1.34 x 1.40 x 1.32 x 1.40 x 1.46 x 1.28 x 1.12 x 1.13 x 1.14 x 1, 14 x 1.08 x 1.06 x 0.91 x 1.08 x 1.26 x 1.05 x Il x I he 11 f He t, 11 He

11 I 1

  If it is not possible to use it, it is necessary to use it, if it is not possible

2540254-

  34 layer of Zn S 0.55 x X / 4 for 400 nm layer of A 1203 1.06 x "Example 4:" Anti-reflective layers "The evaporation plant according to Example 1 is loaded by various substrates of 50 x 50 x 2 mm made of the following materials: glass (BK 7) polycarbonate ("Makrolon" by BAYER)

CR 39.

  The process parameters are identical to those of Example 1, with the exception of the absence of oxygen and control of the diaphragms

by a photometric measurement.

  The next seven layers are deposited; it is amazing

  note that it is possible to produce anti-reflective coatings

  made, still having excellent mechanical and chemical resistance, although the refractive index of the two constituents is

greater than that of the substrate.

  1 layer of A 1203 1 xt / 4 for 913 nm 2 layers of Zn S 1 x> / 4 for 127 nm 3 layers of A 1203 1 x X / 4 for 556 nm 4 layers of Zn S 1 x> / 4 for 264 nm layer of A 1203 1 x X / 4 for 242 nm 6 layer of Zn S 1 x> / 4 for 619 nm 7 layer of A 1203 1 x> / 4 for 616 nm The reflection properties are shown in FIG. with the reflection values in ordinate It is a good broadband anti-reflective treatment, between about 460 and 640 nm, which can even

  be qualified as very good for plastic substrates.

  Of course, various modifications may be made by those skilled in the art to the principle and to the devices which have just been described as non-limiting examples,

  without departing from the scope of the invention.

Claims (4)

claims   Process for the production of optical elements, and in particular filters with interferential layers consisting of dielectric layers with alternately low or high refractive index on organic or inorganic substrates, said method being characterized in that the deposition on the substrate comprises first a layer of A 1203 low refractive index, then alternating layers of Zn S and A 1203, and lastly a layer of A 12 03   Process according to claim 1, characterized by depositing the first layer at a substrate temperature of between 20 and 50 ° C. 3 Method according to claim 1, characterized in that the dep 6 t   is carried out by a method of evaporation under a pressure of between 1.3 x 10 and 1.05 Pa.   4 Process according to claim 3, characterized by an evaporation rate of between 1.0 and 1.5 nm / s for Al 203 and between 1.0 and 3.0 nm / s for Zn S.   Use of the process according to claims 1 to 4 for the   filter production of the subtractive separation filter group   color additive, cold-light mirrors, thermal filters   reflective, color temperature converter filters, color temperature converter reflector, narrow band dielectric filters, beam splitters, in connection   with substrates of the group glass, sapphire, plastic.