Role of plasma properties in controlling crystallinity and phase in oxide films grown by plasma-enhanced atomic layer epitaxy

Abstract

Plasma-enhanced atomic layer epitaxy (PEALE) is a cyclic atomic layer deposition process that incorporates plasma-generated species into one of the cycle substeps to achieve layer-by-layer crystalline growth. The addition of plasma generally provides unique gas phase chemistries and a substantially reduced growth temperature compared to thermal approaches. Indeed, when properly configured, PEALE systems can deliver high-quality crystalline films with structural characteristics that rival those grown by conventional thermal equilibrium growth processes such as molecular beam epitaxy or metalorganic chemical vapor deposition. However, the inclusion of plasma also adds a complex array of reaction pathways that can be challenging to understand and control. This work focuses on the use of plasma diagnostics to inform the choice of process conditions for PEALE. Optical emission and vacuum ultraviolet emission spectroscopy, as well as spatially resolved Langmuir probe measurements, are employed to characterize an inductively coupled plasma source used for the growth of epitaxial TiO2 and Ga2O3 films on sapphire. Under plasma conditions with large concentrations of atomic oxygen and significant ion energy (30–50 eV), highly crystalline TiO2 and Ga2O3 films were grown, indicating that both reactive neutral chemistry and ion energy are important in these processes.