Influence of substrate properties on the growth of titanium films. Part I

Abstract

The internal stress of thin titanium films deposited on different substrates was measured during, as well as after, their deposition under UHV-conditions using a cantilever beam technique. The substrate films used were produced by reactive evaporation of titanium (0.075 nm s −1) at different water partial pressures at 130°C substrate temperature. Owing to the simultaneous supply of water and titanium during the deposition of the substrate titanium film its growth mode is changed from island growth (clean titanium film) to layer by layer growth. The main part of this paper presents results of experiments in which these H 2O/Ti-films, with varying amounts of water incorporated, were used as substrates for the deposition of a clean titanium film. The primary interest in these experiments was to study the influence of the chemical composition of the substrate film on the growth of the clean titanium film. At low water: titanium impact ratio during deposition of the substrate titanium layer, the growth of the clean titanium film is a continuation of the growth of the substrate layer. As soon as the water content of the substrate titanium film exceeds only a few percent the resulting stress curve indicates renewed nucleation for the clean titanium film on the substrate surface. The results of this paper further demonstrate that during the initial growth stage an additional tensile stress contribution built up at the substrate/titanium interface originates from an interaction of the arriving titanium atoms with oxygen species on the substrate surfaces. Once the continuous titanium film is formed, hydrogen diffusing from the substrate film into the growing titanium film give rise to a compressive stress contribution, which correlates with the amount of mobile hydrogen incorporated in the substrate film during its deposition. This compressive stress contribution is superimposed on the compressive stress normally built up in mobile films (i.e. island growth) owing to the lattice expansion mechanism proposed in our stress model. Water dosing of previously evaporated films, produces the changes in the stress versus thickness curve of the clean titanium film expected from the interpretations given above.