In situ monitoring of metal surface oxidation in reactive plasma using multi-sine impedance spectroscopy

The electric field near the surface of materials exposed to plasma plays a crucial role in surface reaction processes during plasma oxidation. In this study, an in situ multi-sine impedance spectroscopy (MSIS) system was developed to simultaneously measure the impedance of a target system at multiple frequencies during plasma exposure, thereby enabling evaluation of the electric field applied to surface-modified layers. Specifically, these MSIS measurements were used to monitor the plasma oxidation of Al films. The plasma–material system was modeled as a series connection of the sheath resistance ( R sh ) and a parallel resistor–capacitor circuit representing the oxide layer ( R ox and C ox ). The circuit parameters ( R sh , R ox , and C ox ) changed as the oxide layer grew; however, temporal variations in R sh under different bias conditions were nearly identical, whereas those in R ox and C ox differed depending on the bias voltage applied to the Al film. Overall, these findings elucidate the evolution of surface modification processes driven by an electric field and demonstrate that in situ MSIS is a promising technique for analyzing surface processes in reactive plasmas. • In situ multi-sine impedance spectroscopy for plasma surface modification • Monitoring surface potential during the oxidation process in reactive plasma • Evaluating effect of electric field in the oxide layer on the surface modification