Ultra-high vacuum measurements of the internal stress of PVD titanium films as a function of thickness and its dependence on substrate temperature

Abstract

The internal stress of thin titanium films was measured during, as well as after, their deposition under ultra-high vacuum (uhv) conditions using a cantilever beam technique. Diverse measurements were made at a number of constant deposition temperatures between room temperature and 350°C. At room temperature titanium films exhibit only tensile stress over the whole thickness range. In terms of our model for the origin of internal film stress such a stress curve is characteristic of materials with a low mobility, i.e. high melting point, and indicates columnar grain growth. For deposition at substrate temperatures above about 60°C, tensile, as well as compressive stresses are found with increasing film thickness. This indicates a transition to an island growth mode due to increased metal mobility. In addition, this increased mobility at a higher temperature leads to a more pronounced recrystallization which correlates well with the larger stress changes after the film deposition. Furthermore, results of experiments are presented in which we have used 100 nm thick titanium films as substrates for the deposition of a second titanium film. Variations in the chemical or physical properties (e.g. deposition temperature or oxidation) of this titanium substrate are also reflected in the stress vs thickness curves obtained for the additional titanium films.