Deposition of tantalum thin films by RF sputtering with substrate bias

The effects of energetic ion bombardment on the crystallographic structure of RF sputtered tantalum thin films on different substrates, particularly aluminum and silicon, have been studied. The effect of substrate biasing on ion current and film thickness has been investigated. The study included comparison between substrate ion current of DC sputtering and RF sputtering and also was aimed at finding the process parameters, which could influence the crystallographic phase of Ta film. The characterization of Ta films is carried by RBS and x-ray diffraction techniques. A magnetron sputtering system with a matching network between the source and the RF generator has been used to carry out the experimentation. The matching network was adopted from an industrial system and equipped with a manual controller designed and built during the course of this thesis work. Tuning of the matching network allowed stable operation of the sputtering source with RF power of up to 400 W with negligible reflected power (2-3%). The results of the experiments showed a significant current of ions bombarding the substrate (up to 1 .63X1015 Ions/cm2sec) that increases with negative substrate bias voltage. Significantly higher ion current is observed with RF sputtering than with DC sputtering. With RF sputtering the ratio of ions to atoms arriving at the substrate is larger than I. Under these conditions and with higher biasing voltage (a few hundred volts) the film thickness decreases due to sputtering of the deposited film by high-energy ions. XRD results showed that biasing the substrates of aluminum and silicon to -200 V influences the deposition of tantalum films with growth of bcc crystallographic phase (a phase) while films with tetragonal phase (β phase) grow at lower biasing voltage at room temperature. This research helped to understand the process conditions for RF sputtering with substrate biasing and its influence on Ta film crystallographic phase. The desired a phase tantalum films have many applications such as in fuel cells, semiconductor industry and as a coating material, which is chemically inert and resistant to corrosion