Two series of thin zirconium nitride coatings samples were prepared by balanced magnetron sputtering under different bias voltage conditions (-50 V and -100 V respectively). The composition was varied by changing the nitrogen pressure in the N2-Ar-gas mixture from 40 to 50 at.% nitrogen.. This chemical composition was examined after deposition by EPMA. The layer thickness varies from 3.8 to 5.8 mm.
Main attention was paid to microstructural characterization by X-ray diffraction.
In all coatings the cubic ZrN-phase was detected. In addition in samples prepared at -100 V bias the hexagonal Zr phase was found.
For coatings prepared at -50 V bias potential a <111>- texture for the ZrN phase. These ZrN <111>-texture was less pronounced for layers prepared at higher bias voltage. In addition a very strong <002>-texture for the pure zirconium was found for samples prepared at -100 V bias voltage.
The grain size and the microstrains were calculated using the pseudo-VOIGT-method described by LANGFORD [1]. All coatings exhibit very fine grained microstructure. Using additional tilting experiments no significant dependence of the grain size on the inclination of the lattice planes with respect to the surface was found.
The state of stress was characterized by X-ray diffraction method using a Psi-goniometer and a calculation method described by WINHOLTZ and COHEN [2]. The stresses in all layers are found to be compressive and of a very high level ranging from -7 to -12 GPa. The main difference between coatings prepared at -50 V and -100 V bias voltage is the different value of the shear stresses. These stresses are found to be nearly zero in the high and significant increased in the low voltage regime. In the usual BRAGG-BRENTANO-geometry also high stresses perpendicular to the surface were detected. To get a more realistic view on the stress distribution in the layers, depth profiling was carried out using a method described by SCHUBERT et. al. [3]. Starting with a low compressive stress state near the surface - about -2.5 GPa - the stress increases rapidly with increasing penetration depth. This typical behaviour was found for all coatings.
1. Langford, J. I.: Accuracy in Powder Diffraction, NBS
Special Publication 567, Washington 1980, 255
2. Winholtz, R. A., Cohen, J. B.: Aust. J. Phys. 41 (1988),
189
3. Schubert, A., K„mpfe, B., Auerswald E., Michel B.:
Proceedings Europ„ische Eigenspannungstagung,
Frankfurt 1992