Magnetron sputtering of precision optical coatings enabled by process stability of rotatable cathodes

Cylindrical rotatable cathodes deliver huge material amounts under stable conditions as needed for interference coatings. Sub-stoichiometric targets and plasma oxidation produce low absorbance and virtually no drift of refractive index associated with changeless material uniformity

Recent developments in precision optical coatings prepared by cylindrical magnetron sputtering

Cylindrical targets give the opportunity to improve the process stability of magnetron sputtering processes although reactive deposition might be a challenge. Sputtering from metal doped oxide targets in connection with a plasma source unlocks the full potential: the process can be driven in well-known mid-frequency mode and the plasma source ensures fully stoichiometric films with low loss. During the last years different developments for oxide cylindrical targets were done. The suitable composition has to be found regarding e.g. the density and an arc-free process as familiar for planar targets. In the tube geometry new manufacturing methods are required that ensure these properties. In the present paper we show some examples of the high refractive index materials tantalum oxide: single film characterization as well as realized complex precision optical filters. The results are accompanied by performance measurements in terms of uniformity over 200 mm glass wavers as well as carrier to carrier and batch to batch. These were measured by the position of a quarter-wave stack's edge

Deposition of abrasion resistant single films and antireflective coatings on sapphire

A series of different oxide and nitride antireflective coatings as well as single films on sapphire substrates have been deposited by magnetron sputtering. The layer stacks consist of 5–7 individual layers with a total thickness of around 300nm. Both high-index materials and low-index material were analyzed. The mechanical stability was investigated by means of optical haze increase during falling sand (“sand trickling test”) and by thickness loss during oscillating abrasionin a sand bath (tightened “Bayer test”). The dependence of the abrasion tests results on mechanical film properties, i.e. the nanoindentor hardness, was analyzed. No clear correlation of the Bayertest results and the sand trickling test results was found, which indicates that the abrasion mechanisms are different. A nitride basedantireflective coating with excellent properties from both tests has been produced

Numerical optimization of baffles for sputtering optical precision filters

The optimization of the coating uniformity of precision optical filters generally is a critical and time consuming procedure. The present paper demonstrates this optimization procedure on a new optical precision sputter coater "Enhanced Optical Sputtering System (EOSS)" at Fraunhofer IST. The coater concept is based on dual cylindrical sputtering sources and a rotating turn-table as sample-holder. For compensating non-uniformity introduced by the particle flux profile and the radially dependent track speed on the turntable, baffle elements have to be designed and inserted beneath the substrates. For that purpose the distribution of the particle flow from the cylindrical magnetron as well as the resulting thickness profile for different shaper designs is simulated using Direct Simulation Monte Carlo (DSMC) transport simulation. For comparison, experimentally obtained film thickness profiles are evaluated by spectrophotometry and ellipsometry. The simulation model is used for optimization of the baffle geometry as well as investigation on the role of long term drifts caused by target erosion and mechanical tolerances

Simulation assisted deposition of optical filters onto 3D substrates by magnetron-sputtering

The direct deposition of optical filters onto curved 3D substrates such as convex lenses is beneficial for fabricating optical devices with a minimized number of components and internal reflections. However, in order to account for spectral shifts resulting from a variation in the angle of incidence across the surface, the film thickness profile of the filter has to be carefully adapted to the surface curvature. For e. g. convex lenses, this would imply an increasing film thickness from the center towards the edge, while the natural deposition profile on such substrates in sputter deposition processes has the opposite shape. The deposition task is realized on a dual-cylindrical magnetron-sputtering compartment equipped with a sub-rotating substrate holder on a rotating turntable and specialized uniformity masks. A multi-scale simulation and optimization approach determines the shape of the uniformity masks: First, 3D Particle-in-Cell Monte Carlo (PIC-MC) simulations result in the relative erosion profile on the cylindrical sputter targets. Subsequently, the transport of sputtered material through the coater geometry is modelled via the Direct Simulation Monte Carlo (DSMC) method. Finally, a fast algorithm projects the deposition flux onto the moving and rotating substrate for arbitrary angles of the turntable rotation. The optimization scheme has been successfully validated for a band pass filter onto a spherical lens and is currently being applied on aspherical lenses. Further extension of the coupled simulation framework towards different coater and 3D substrate geometries is ongoing

Numerical shaper optimization for sputtered optical precision filters

A novel optimization procedure for optical precision sputter coaters with respect to the f ilm homogeneity is demonstrated. For a coater concept based on dual cylindrical sputtering sources and a rotating turn-table as sample-holder, the inherent radial decay of the film thickness must be compensated by shaper elements. For that purpose, a simulation model of the particle flux within such a coater is set up and validated against experimental data. Subsequently, the shaper design is optimized according to the modeled metal flux profile. The resulting film thickness deviations are minimized down to ±0.35%

Modeling of Cellular Systems: Application in Stem Cell Research and Computational Disease Modeling

The large-scale development of high-throughput sequencing technologies has allowed the generation of reliable omics data at different regulatory levels. Integrative computational models enable the disentangling of a complex interplay between these interconnected levels of regulation by interpreting these large quantities of biomedical information in a systematic way. In the context of human diseases, network modeling of complex gene-gene interactions has been successfully used for understanding disease-related dysregulations and for predicting novel drug targets to revert the diseased phenotype. Furthermore, these computational network models have emerged as a promising tool to dissect the mechanisms of developmental processes such as cellular differentiation, transdifferentiation, and reprogramming. In this chapter, we provide an overview of recent advances in the field of computational modeling of cellular systems and known limitations. A particular attention is paid to highlight the impact of computational modeling on our understanding of stem cell biology and the complex multifactorial nature of human diseases and their treatment