In order to compare the simulated and the experimental TiO2 layer morphologies, the layer thickness profile in the system as well as the angle and energy distributions of particles arriving at different places on the substrate were first determined at the Fraunhofer IST. These angular distributions were passed on to the »NASCAM« software [Lucas2010] to be used as an input variable in modeling layer growth by the kinetic Monte Carlo method (kMC). In addition, a cross-section of the experimental layers was analyzed with the aid of a scanning electron microscope (SEM). The opposite figure shows that the simulation corresponds well with the experiment and that layer morphology on the substrate may vary depending on position.
In order to compare the layer stoichiometries of the simulation and the experiment – that is, the relative quantities of titanium and oxygen atoms – flow simulations (DSMC) were carried out for selected O2 flow rates (2, 4, 6 and 8 sccm). Growth layer simulations (kMC) were also carried out over a wide range of flow rates. The layer stoichiometry was then determined and in addition layers made experimentally were investigated by Rutherford backscattering spectometry (RBS). The graph shows that there is good agreement between the results of all three methods.
Simulation expertise at the Fraunhofer IST
The parallelized simulation environment developed at the Fraunhofer IST has been optimized for thermal evaporation, magnetron sputtering and CVD processes in the low-pressure range. It enables the description of process kinetics in realistic 3D reactor geometries. Connecting up to additional simulation methods for layer growth means that intrinsic coating properties such as density, structure and optical properties can be predicted.
[Lucas2010] S. Lucas, P. Moskovkin, Thin Solid Films 513 (2010) 5355-5361.