Properties of titanium and aluminum thin films deposited by collimated sputtering

Abstract

A study of the properties of titanium and aluminum films deposited by collimated sputtering is presented. The effect of square grid collimators on the film coverage and film bulk properties has been studied experimentally and theoretically using a Monte Carlo vapor transport simulation, SIMSPUD. The computer simulation is able to model the effect of collimation on the angular distributions of deposited atoms and predict the film coverage and deposition rate changes for both titanium and aluminum. In good agreement with these predictions, experimental films show that bottom coverage in trenches of aspect ratio (depth:width) 1.2 can be significantly improved from 50% to more than 80% for a titanium film, and from 35% to more than 82% for an aluminum film with a collimator of aspect ratio 2. As a further consequence of collimation, the microstructure and film properties are altered in comparison with conventional films. For example, free-standing micro-beam experiments and X-ray diffraction spectra both show a substantial increase in compressive stress in Ti films deposited using collimation. In addition, collimation slightly alters the grain orientation distribution in Ti films, although pressure has a much more important role in determining microcrystallinity. Most of these collimation effects can be explained in terms of changes in the angular distributions, deposition rates and peening.