Interaction Between DC Plasma and Substrates in Spatial PEALD

Plasma Enhanced Atomic Layer Deposition (PEALD) is a coating method that provides high quality thin films at relatively low substrate temperatures, allowing deposition on temperature sensitive substrates such as polymer films.  DC plasma is not compatible with conventional pulse-based ALD, particularly for deposition of dielectric films, as the plasma electrode would be coated with the dielectric.  But with spatial ALD, film deposition is limited to only the substrates, and this enables the use of a direct or indirect DC plasma for PEALD.  In this work we examine a Spatial PEALD process which operates in the pressure range of 1-2 Torr, where a stable DC diode discharge may be maintained with voltage in the range of 300-600V, and the mean free path of radicals is in the range of tens of microns.  By controlling the power, pressure, and electrode spacing, the electron and ion densities at the substrate may be modulated, along with the kinetic energy of the gas molecules.  In this work, optimization of these parameters is used to demonstrate minimal substrate interaction for PEALD of metal oxide films on oxygen-sensitive surfaces such as rare earth metallic thin films, and temperature sensitive polymers including polypropylene film.