Phase tailoring of Ta thin films by highly ionized pulsed magnetron sputtering

Abstract

Ta thin films were grown on Si substrates at different inclination angles with respect to the sputter source using high power impulse magnetron sputtering (HIPIMS), an ionized physical vapor deposition technique. The ionization allowed for better control of the energy and directionality of the sputtered species, and consequently for improved properties of the deposited films. Depositions were made on Si substrates with the native oxide intact. The structure of the as deposited films was investigated using X-ray diffraction, while a four-point probe setup was used to measure the resistivity. A substrate bias process-window for growth of bcc-Ta was observed. However, the process-window position changed with changing inclination angles of the substrate. The formation of this low-resistivity bcc-phase could be understood in light of the high ion flux from the HIPIMS discharge.

An introduction to thin film processing using high-power impulse magnetron sputtering

“…108,109 The abundance of Ta + ions in the deposition flux during the HiPIMS deposition of Ta films implies a more efficient momentum transfer to the growing surface. 12,92 This is in contrast to the growth by DCMS, where the majority of the ions in the deposition flux consists of the much lighter Ar + ions. 19 HiPIMS thus provides tools for better influencing the internal stresses of the growing Ta films and accordingly the possibility to deposit a-Ta films at room temperature (Fig.…”

“…One example is the control of the phase composition in Ta films. 12 In this case, tailoring of the phase formation is achieved by controlling the magnitude of the internal stresses. 12 This process is particularly efficient in HiPIMS discharges owing to the degree of ionization of the Ta vapor of up to 70%.…”

“…12 In this case, tailoring of the phase formation is achieved by controlling the magnitude of the internal stresses. 12 This process is particularly efficient in HiPIMS discharges owing to the degree of ionization of the Ta vapor of up to 70%. 5 Ta forms both a low resistivity bodycentered cubic crystal structure (also known as the a phase) at elevated temperatures and a metastable high resistivity tetragonal phase (b-Ta) at room temperatures.…”

“…7). 12 In HiPIMS discharges, part of the ions moves along off-normal, with respect to the target, directions 49 (see Section II D). This anomalous ion transport results in differences in the flux, the energy, and the composition of the deposited and bombarding species as functions of the deposition angle.…”

“…7 The high degree of ionization of the sputtered species has been shown to lead to the growth of smooth and dense elemental films 8 as well as reactively deposited compound films 9,10 and enable control over their phase composition, 11 microstructure, 12 as well as mechanical 13 and optical 9,11 properties. It has also been reported to be beneficial in terms of improving film adhesion, 14 enabling deposition of uniform films on complex-shaped substrates, 15,16 and having a decreased deposition temperature.…”