Transition of Cu film to Cu2O film through oxygen plasma treatment

Abstract

Metal?oxide-semiconductor-based thin-film transistors have attracted increasing research attention owing to their wide bandgap and minimal leakage current. However, the prevalent n-type behavior of several oxide semiconductors prompted the exploration of p-type alternatives. Among these, Cu films are promising candidates for different fields. In this study, the effectiveness of oxygen plasma treatment for the transition of Cu films to their p-type oxide semiconductor phase, i.e., Cu2O, was demonstrated with a focus on low-temperature fabrication for future integration in flexible devices. We reported the adjustability of the oxidation depth of a Cu thin film and the effect of oxidation dynamics by controlling the bottom radio frequency power of a high-density plasma system. This novel approach enabled metal-to-semiconductor transitions and modulation of the physical properties of Cu2O thin films by inducing changes in their composition and microstrain. The oxidation dynamics, oxidation depth, crystallinity, and film surface were analyzed. Moreover, the changes in the optical bandgap were determined, with the transition of the Cu (111) phase to the Cu2O (111) phase confirmed as a function of the process time. As oxidation progressed, particles formed on the surface of the Cu2O thin film and the particle size increased. Further, the oxidized Cu thin film was determined to be Cu2O rather than CuO. Therefore, oxygen plasma treatment is expected to be a new approach to low-temperature oxidation.