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 SiO<sub>2</sub>, Al<sub>2</sub>O<sub>3</sub>, MgF<sub>2</sub> and LaF<sub>3</sub> 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, MgF<sub>2</sub> and LaF<sub>3</sub>, conventionally coated at very high temperatures, have been performed to demonstrate the improved capabilities of the optimized SYRUS<i>pro</i> DUV for DUV applications with all the new features.
Plasma-IAD with the APS has been applied for a large number of different layer systems in production an ind R and D. The ability for the production of shift free multilayer coatings for the visible and NIR spectral range is utilized in manufacture for many applications such as steep edge filters for color separation, rugate filters for laser protection and narrow-bandpass filters for wavelength division multiplexing. An overview was given. Shift free narrowband filters for the UV-B region were published in 1996. The paper reports the result of UV coatings using plasma ion assisted deposition. Tantala/silica and hafnia/silica combinations have been used for multilayer coatings in the UV-A and UV-B spectral range. Single layers of silica and alumina and multilayer systems with both materials were investigated in the UV-B and UV-C region. The coatings were characterized by obtained transmittance and reflectance curves as well as absorption and scattering measurements. The temperature stability results are compared with coatings in the visible and NIR spectral range published.
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 Ta<SUB>2</SUB>O<SUB>5</SUB> 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.
In many applications in the field of optical coatings low dimensions and low weight of the substrates are of increasing importance. Organic substrate materials or thin glass substrates are used in many cases. Due to the low mechanical stability, these substrates are very sensitive against bending caused by the stress of the coatings. The stress of optical coatings deposited with plasma-IAD with the APS (advanced plasma source) was investigated. Based on the bending radius of coated thin glass substrates stress values were evaluated. It was found, that film stress can be influenced significantly with the deposition parameters and the use of the coating starting materials. The results of single layer coatings of various dielectric materials and completed multilayer systems are given.
Ion assisted deposition (IAD) is a well known technique to improve the properties of thermally evaporated thin films. A wide range of materials and completed layer systems have already been investigated. Because of the low total ion current and the small beam size of the commercial available ion sources, the useful substrate area is strongly limited. With a newly developed advanced plasma source (APS) we have overcome these problems. A total ion current of up to 5 A with excellent uniformity over a large area substrate holder (approximately equals 1 m<SUP>2</SUP>) has been achieved. The plasma source is installed in conventional box coating system. Besides plasma-IAD the APS is also useful for plasma-CVD processes like plasma polymerization. The principle of operation of the plasma assisted processes with the APS is described. Results of dielectric materials and completed layer systems like shift free edge filters and AR-coatings are presented. In particular, in case of organic substrate materials, the advantages of the APS are outstanding. Scratch resistant layers in combination with AR- coatings and hydrophobic surface layers onto organic substrates are successfully introduced in production.
Ion assisted deposition (lAD) is a well known technique to iniproye the properties of thin films. A wide range of materials and conipleted layer systems have already been investigated by many laboratories.
One disadvantage of this technology is the small useful substrate
area compared to conventional thermal evaporation. This is due to the
limited ion beam size of the available ion sources. Therefore we have
developed a new plasma source which is able to irradiate a substrate
holder of 800 mm diameter with high plasma current density.
The principle of operation and some details of the plasma source
are described. The experiments were done in a conventional coating system.
The plasma source has been operated at up to 90 V discharge voltage
and up to 80 A discharge current. Up to now we have deposited some
single layers with dielectric materials. For TiO2 we have achieved
an refractive index of 2.55 at 550 nm.