Plasma-assisted deposition of lithium phosphorus oxynitride films: Substrate bias effects

Lithium phosphorus oxynitride (Lipon) films have been synthesized by a plasma-assisted directed vapor deposition (PA-DVD) approach. In this approach, a hollow cathode technique was used to create an argon plasma through which was propagated an electron-beam generated Li3PO4 vapor entrained in a N2-doped helium gas jet. Without plasma assistance, amorphous, mud cracked and highly porous Li3PO4 films were formed. When plasma-assistance was used, nitrogen was incorporated creating a Lipon film whose composition, morphology, structure, and deposition rate could be manipulated by modifying the substrate bias. Films with spiral or very smooth surfaces could be made in this way. Fully amorphous films or films with locally crystallized regions in an amorphous matrix could be synthesized by varying the bias voltage. The presence of these local regions of crystallinity within a Lipon film decreased the Li-ion conductivities from the 10−7 S cm−1 to 10−10 S cm−1 range.