INFLUENCE OF LOW-ENERGY ION-BOMBARDMENT ON THE PROPERTIES OF TIN FILMS DEPOSITED BY RF MAGNETRON SPUTTERING

The influence of low energy ion bombardment on the properties of TiN films deposited by r.f. (13.56 MHz) magnetron sputtering in the low pressure range has been examined. The ion bombardment is obtained by d.c. biasing of the substrates in the range from 0 to -200 V. The deposition rate decreases rapidly for low bias voltages (-10 V) and remains constant (15 nm min(-1)) for more negative bias values. The decrease of the film resistivity in the same range of bias voltages (from 0 to -10 V) is due to oxygen elimination and to a film microstructural change. The resistivity reaches a minimum value (80 mu Omega cm) and slightly increases for high negative bias voltages (-200 V) because of a small argon entrapping. The residual macrostresses sigma are compressive and reach a maximum value of -12 GPa (r.f power 200 W) for a bias voltage V-b of about -100 V. They are well correlated with the change in the lattice parameter a. The microstrain distribution e first increases with ion bombardment (from 0 to 100 eV) and then remains constant (e = 0.8%). The size D of the crystallites decreases rapidly in the bias range from 0 to -50 V but very slowly in the range from -50 to -200 V where D falls to 20 nm.