Synthesis of Lithium Phosphorus Oxynitride (LiPON) Thin Films by Li3 PO4 Anodic Evaporation in Nitrogen Plasma of a Low-Pressure Arc Discharge

Abstract

Thin amorphous films of LiPON solid electrolyte were prepared by anodic evaporation of lithium orthophosphate Li3 PO4 in an arc discharge with a self-heating hollow cathode at a nitrogen pressure of 1 Pa. Distribution of the arc current between two electrodes having an anode potential provided independent control of the evaporation rate of Li3 PO4 and the density of nitrogen plasma. Stabilization of the evaporation rate was achieved using a crucible with multi-aperture cover having floating potential. The existence of a threshold value of discharge current (40 A) has been established, which, upon reaching ionic conductivity over 10−8 S/cm, appears in the films. Probe diagnostics of discharge plasma were carried out. It has been shown that heating the films during deposition by plasma radiation to a temperature of 200◦ C is not an impediment to achieving high ionic conductivity of the films. Dense uniform films of LiPON thickness 1 µm with ionic conductivity up to 1 × 10−6 S/cm at a deposition rate of 4 nm/min are obtained.