The production capabilities for optical multilayer coatings were improved significantly in the last decade. So called "shift free" coatings have become a standard in the coating production. Direct optical monitoring plays a key role to improve the layer thickness accuracy and takes advantage of error compensation effects. For the production of DWDM filters direct monitoring was introduced in the last decade. Continuous measurement is applied on relatively small substrate areas. (Ø < 200 mm). The paper reports substantial progress which has been achieved for coating systems with large area substrate holders (up to Ø 1050 mm). The stationary light spot of a single wavelength optical monitor is far out of centre of the rotating substrate holder. Intermittent monitoring on a substrate or a witness is applied. This technique enables rapid prototyping with tight specifications and high yields in large area batch coaters. Application results of challenging optical multilayer systems are demonstrating clearly the potential of this powerful monitoring technique. The monitoring capability was investigated for a lot of different layer systems such as dielectric mirrors, anti-reflection coatings, sophisticated edge filters, polarizer coatings, beam splitters and multiple cavity band-pass filters. Strong coincidence of theory with experiment was achieved with PIAD and magnetron sputtering. Reproducibility experiments have clearly shown the benefits of this monitoring technique.
The requirements to produce high performance coatings increase dramatically when moving from 248 nm to 193 nm. The quality of DUV thin film components is mainly determined by the optical properties of the applied layer materials. The reduction of losses due to scattering and absorption of dielectric materials is essential for excellent properties of the coating results. The most common oxide and fluoride materials SiO2, Al2O3, MgF2 and LaF3 have been investigated and optimized. Plasma ion assisted deposition was applied for the deposition of the oxide materials, using improved coating equipment such as the modified APSpro (advanced plasma source). The paper reports the results of DUV coatings using plasma ion assisted deposition for the oxide materials. Single layers of silica and alumina and multilayer systems with both materials were investigated. In addition, MgF2 and LaF3, conventionally coated at very high temperatures, have been performed to demonstrate the improved capabilities of the optimized SYRUSpro DUV for DUV applications with all the new features.
Plasma-IAD with the APS (advanced plasma source) has been introduced into the market in 1992. Up to now this technique is used worldwide in almost 100 coating systems. A large number of different layer systems has been investigated in R&D and applied in production. For ophthalmic applications plasma-IAD with the APS is used for antireflection systems as well as for wear resistant coatings onto organic substrates. New processes which combine the AR coating and the hardcoating on ophthalmic lenses have been successfully introduced into mass production. Plasma-IAD is also used for laser protection coatings onto plastic substrates. The ability for the production of shift free multilayer coatings is utilized in manufacture for many applications such as steep edge filters for color separation, rugate filters for laser protection, narrow-bandpass filters in the NIR region for wavelength multiplexing in the field of fiber optic communication or for radiometers in the UV-B region. A review of the development of some important APS based coating processes and applications shows the flexibility of plasma-IAD with the APS. Actual evaluations of the optical constants of Ta2O5 layers deposited with APS assistance show a low extinction coefficient and a stable refractive index. New results of the performance, temperature behavior and long term stability of some interference filters confirm high packing density and low absorption of the films produced with plasma-IAD. The result of a reproducibility experiment demonstrates high process stability and high monitoring accuracy.
To protect the soft surface of organic CR 39 ophthalmic lenses we
built up a parallel plate reactor and developed a Plasma Enhanced
Chemical Vapor Deposition (PECVD) process for Si02 protection films.
Beside high transmission in the VIS-range we obtained refractive
indices between n=1.46 and n=l.49 depending on the process parameters
at layer- thicknesses of 2,5 jnn to 5 jmt. Deposition rates up to 30 A/s
and thickness uniformities of 10 % were achieved. The mechanical
properties of these layers were tested with different methodes and
gave better results compared with other technologies like ion-assisted
deposition or lacquering.
The residual reflectance colors of broadband antireflection coatings for ophthalmic optics have been investigated as a function of
statistical production errors, lateral thickness changes and incidence
angle of light. The goal was to design coatings with good production
stability, low lateral color variation even over steeply curved lens
surfaces and low angular color shift. The investigations show that the
final design can only be a compromise between the different requirements.
Using a parallel plate reactor we optimized a PECVD process and
coated Si02-films on CR 39 lenses with layer-thicknesses of 2,5 trn to
5 I_tIn. Besides high transmittance in the VIS-range we obtained
refractive indices between n=1.46 and n=1.49 depending on the process
parameters. We achieved deposition rates up to 30 A/s and thickness
uniformities of 10 %. The abrasion resistance of these layers were
tested with different inethodes and gave better results compared with
techniques like lAD or lacquering.
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