Chemical composition and properties of MoAl thin films deposited by sputtering from MoAl compound targets

Molybdenum-based thin films are widely used as back-contact layers in solar cells, as interconnect material or diffusion barriers in microelectronics, or as gate and source/drain lines in thin film transistor liquid crystal displays. Within this work, the sputter behavior of three different molybdenum-aluminum compound targets with Al contents of 24, 37, and 49 at. % manufactured by cold gas spraying as well as the chemical composition, the microstructure, and the properties of the deposited thin films have been investigated. The increase in the Al content in the targets results in an increasing deposition rate of the films. The fine-columnar films are characterized by the formation of a body-centered cubic solid solution resulting in an electrical resistivity increasing from 100 μΩ cm for 10 at. % Al to more than 200 μΩ cm for 30 at. % Al. Monte Carlo simulations of sputtering and gas phase transport indicate that the observed large deviations of the chemical compositions of the films with respect to the target are mainly caused by aluminum losses due to gas phase scattering.