Properties of reactive sputtered alumina-silica mixtures.

Standard antireflective coatings applied to hard substrates like sapphire suffer from poor abrasion resistance. Silica is used as low refractive index layer in many multilayer systems although it has a lower hardness than the substrate. In this work an attempt was made to enhance the hardness by the addition of alumina. Magnetron sputtering was used in two different ways because it delivers dense coatings with high durability. Nanoindention hardness measurements of mixed alumina-silica films are presented in comparison to haze measurements after a sand trickling test. The hardness of silica is unexpectedly lowered by the addition of small amounts of alumina. Two different stacks were coated in which the low refractive index layers were sputtered as pure material and material mixtures. The thickness loss results after an oscillation abrasion test are presented.

Origin of particles during reactive sputtering of oxides using planar and cylindrical magnetrons.

Particles generated during reactive magnetron sputtering cause defects in optical thin films, which may lead to losses in optical performance, pinholes, loss of adhesion, decreased laser-induced damage thresholds and many more negative effects. Therefore, it is important to reduce the particle contamination during the manufacturing process. In the present paper, the origin of particles during the deposition of various oxide films by midfrequency pulsed reactive magnetron sputtering was investigated. Several steps have been undertaken to decrease the particle contamination during the complete substrate handling procedure. It was found that conditioning of the vacuum chamber can help to decrease the defect level significantly. This level remains low for several hours of sputtering and increases after 100 hours of process time. Particle densities of SiO(2) films deposited with cylindrical and planar dual magnetrons at different process parameters as well as different positions underneath the target were compared. It was observed that the process power influences the particle density significantly in case of planar targets while cylindrical targets have no such strong dependence. In addition, the particle contamination caused by different cylindrical target materials was analyzed. No major differences in particle contamination of different cylindrical target types and materials were found.

Optical properties of silicon titanium oxide mixtures prepared by metallic mode reactive sputtering.

In this paper different SiO(2)-TiO(2) mixtures are prepared by metallic mode reactive sputtering. The samples were sputtered from cylindrical targets in a sputter-up configuration using an additional plasma source for oxidization. The different ratios of SiO(2) and TiO(2) in the mixtures are prepared by a target sputtering power variation. Optical film properties of the mixtures such as refractive index, which is determined by ellipsometric measurements, and optical bandgap, which is measured by photometric (transmission) measurements, are investigated. The thin-film structure is investigated by x-ray diffraction analysis and the stress of the films is presented. It is shown that the metallic mode reactive sputtering in the present configuration is applicable to continuously tune optical and mechanical properties. Finally the sputtered mixed materials are compared with other optical standard materials such as Nb(2)O(5), Ta(2)O(5), HfO(2), and Al(2)O(3).

In situ thickness determination of multilayered structures using single wavelength ellipsometry and reverse engineering.

An in situ monitoring setup and process control loop were developed and integrated into a magnetron sputtering coater equipped with a Sentech SE 401 single wavelength ellipsometer, including the engineering of software for in situ process control to enhance production accuracy. By using that software, the system allows direct monitoring of the layer thickness on a moving substrate. It is shown that it is possible to determine the complex index of refraction from the distribution of measurements depending on the layer thickness. A strategy has been developed for in situ reverse thickness engineering of the top layers to compensate measurement errors.

Measurement of the translational and rotational Brownian motion of individual particles in a rarefied gas.

We measured the free Brownian motion of individual spherical and the Brownian rotation of individual nonspherical micrometer-sized particles in rarefied gas. Measurements were done with high spatial and temporal resolution under microgravity conditions in the Bremen drop tower so that the transition from diffusive to ballistic motion could be resolved. We find that the translational and rotational diffusion can be described by the relation given by Uhlenbeck and Ornstein [Phys. Rev. 36, 823 (1930)]. Measurements of rotational Brownian motion can be used for the determination of the moments of inertia of small particles.