Characterization of radical-enhanced atomic layer deposition process based on microwave surface wave generated plasma

Abstract

A plasma-assisted atomic layer deposition system employing a microwave surfatron plasma was developed and characterized by spatially resolved Langmuir probe diagnostics and optical emission spectroscopy. The deposition process was applied on TiO2 thin films prepared on Si wafers. The surfatron is equipped with a small ring electrode serving as a source of weak radio frequency plasma helping with fast and reliable ignition of the discharge in molecular gas. Results evaluated in the pure argon plasma proved that the plasma potential and the plasma density are homogeneous in the radial direction, while a rapid decrease was observed in the axial direction. Adding up to 30% of nitrogen into the gas mixture led to less homogeneous plasma parameters in the radial direction together with the increase of the electron effective temperature. Optical emission spectra revealed many Ar I lines of neutral atoms with only a few Ar II ions’ lines. The gradual addition of nitrogen causes a systematic decrease in the Ar I line intensity. We expect that excited nitrogen molecules are produced by the inelastic collisions with electrons and by the collisional quenching of metastable Ar(4s) states. On the other hand, oxygen atom and ion lines are detected when oxygen was mixed with argon. Deposited TiO2 thin films are characterized by the anatase phase when the substrate temperature is 250 °C. The anatase phase is observed even for the substrate temperature of 200 °C; however, the microwave power delivered into the surfatrons must be lower in comparison with the prior case.