Magnetron Sputter Deposition of Low-Stress Cubic Boron Nitride Films using Ar-N2-CH4 Gas Mixtures
S. Ulrich, J. Ye, M. Stüber, C. Ziebert, Forschungszentrum Karlsruhe, Germany
The 36th International Conference on Metallurgical
Coatings and Thin Films,
Vortrag, Carbon and Nitride Materials:
Synthesis-Structure-Property Relationships, Boron Nitride and Carbon Nitride
and Group-III (
Cubic boron nitride (c-BN) films produced by PVD and plasma-assisted CVD techniques typically exhibit undesired high compressive stresses. One of the effective and feasible methods to reduce stress and hence improve film adhesion has been a controlled addition of a third element into the film during deposition. In the present study, BN films were grown on to silicon substrates using reactive magnetron sputtering with a hexagonal BN target. An auxiliary flow of methane was mixed into argon and nitrogen as the working gas. The deposition was conducted at various methane flow rates at 400°C substrate temperature, 0.3 Pa total working pressure, and -250 V substrate bias. The structure and mechanical characteristics of the deposited films were then examined in dependence of the methane flow rate. With increasing methane flow rate from 0 to approx. 1.0 sccm, the fraction of the cubic BN phase in the deposited films decreased gradually down to approx. 70%, whereas the film stress was reduced much rapidly and almost linearly in relation to the methane flow rate. At 1.0 sccm methane, the stress became approx. 3 times reduced. Owing to the significantly decreased film stress, adherent, micrometer thick, c-BN dominant films can be allowed to form on silicon substrate. The microstructure and mechanical properties of the films will be illustrated through FTIR, SEM, AFM, nanoindentaion and so on.