Atomistic effects in reactive direct current sputter deposition
The aim of this work is to gain a better understanding of the reactive sputtering process, with special emphasis on explanations from a microscopic point of view. Several steps were undertaken towards this end: An already existing deposition system was upgraded with new pressure gauges and a quadrupole mass analyzer to meet the new requirements for total and partial pressure determination. In consequence, it was possible to switch from the macroscopic parameter pressure to the average number of collisions. Thin films of zinc oxide and silver were deposited, and their properties were studied. These could be modified in two distinct ways: First, this was done by variation of the deposition conditions. This concept was applied to the deposition of zinc oxide films. A strong correlation between stress, surface roughness and texture of the films on one side and the total pressure during deposition on the other was observed. This behavior could be related to the impact of energetic oxygen atoms. In a second step, this assumption was verified by resputtering experiments, in which films were prepared on substrates facing away from the target. The difference in deposition rate between films prepared with and without a backing microscope slides decreased with increasing pressure. For sufficiently high pressure, the deposition rate of directly deposited films could be described by the Keller-Simmons relation. The films were rough with low stress and weak texture. In the low pressure range, films were smooth and exhibited high stresses and strong orientation. This pronounced texture was caused by selective etching of the growing film. The deposition rate was lower than expected from Keller-Simmons. At the same time, the resputtered atoms lead to an increased deposition rate of the indirectly deposited films. A completely different approach was used for the optimization of the conductivity of thin silver films. It could be shown that the sheet resistance of these films is strongly correlated to their texture. The necessary texture could be obtained by depositing silver on top of zinc oxide. The orientation of the silver grains was determined by the orientation of the zinc oxide grains because of a low lattice mismatch between the silver (111) and zinc oxide (0001) plane. Thus it was possible to deposit films with strongly improved conductivity. In order to make predictions of film properties possible, simulations were performed. The existing models were enhanced by including the cathode potential as a simulated parameter. The related material properties are the ionization cross sections of the gas atoms, and the secondary electron yield of the target material. Another important parameter in these simulations is the sputter yield. This property was determined for a large number of materials by TRIM calculations. Also, the dependence of the yield on ion mass and energy was examined. Finally, the model for the sputter deposition process was extended for the use of two reactive gases. Applying this model to the deposition of titanium oxy-nitrides showed that, for example, the film stoichiometry is not governed by thermodynamics only, but that kinetics have a significant impact as well.
info:eu-repo/classification/ddc/530, Zinkoxid, Schichtwachstum, Magnetronsputtern, Physik, sputter deposition, zinc oxide, modelling
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