Titanium oxide thin film growth by magnetron sputtering: Total energy flux and its relationship with the phase constitution

Abstract

The total energy flux transferred to the substrate in sputter deposition experiments was varied in a broad range by modifying systematically the working conditions. A titanium target was sputtered in reactive atmosphere either in DC Magnetron Sputtering (DCMS) or in the High-Power Impulse Magnetron Sputtering (HiPIMS) mode. Unbalanced (UB) and balanced (B) cathodes were utilized and the time-averaged power delivered to the plasma was set to either 400 or 800W. The total energy flux was measured in situ thanks to a heat flux sensor located at the substrate position. First, the energy flux exhibits a hysteresis when the oxygen inlet is increased and then decreased. In a second step, the normalized energy flux (φnorm) was calculated by taking into account the number of Ti atoms deposited per time unit and the discharge regimes were compared accordingly. Regardless of the sputtering method, the film phase constitution evolves from pure anatase to rutile rich anatase/rutile phase mixtures as φnorm is increased. φnorm is the highest for UB-HiPIMS configuration. A surprising result is that the energy flux related to the B-DCMS discharge at 800W is higher than the one measured for the UB-DCMS, at the same power. The enhanced plasma confinement for the balanced cathode promotes the heating of the target surface. The contribution of the IR photon flux emitted by the hot surface to the total energy flux is significantly increased. From this result, it appears that this contribution should be taken into account when discussing thin film final features.