Lithium phosphorous oxynitride films synthesized by a plasma-assisted directed vapor deposition approach

A plasma-assisted directed vapor deposition approach has been explored for the synthesis of lithium phosphorous oxynitride Lipon thin films. A Li3PO4 source was first evaporated using a high voltage electron beam and the resulting vapor entrained in a nitrogen-doped supersonic helium gas jet and deposited on a substrate at ambient temperature. This approach failed to incorporate significant concentrations of nitrogen in the films. A hollow cathode technique was then used to create an argon plasma that enabled partial ionization of both the Li3PO4 vapor and nitrogen gas just above the substrate surface. The plasma-enhanced deposition process greatly increased the gas phase and surface reactivity of the system and facilitated the synthesis and high rate deposition of amorphous Lipon films with the N /P ratios between 0.39 and 1.49. Manipulation of the plasma-enhanced process conditions also enabled control of the pore morphology and significantly affected the ionic transport properties of these films. This enabled the synthesis of electrolyte films with lithium ion conductivities in the 10−7–10−8 S /m range. They appear to be well suited for thin-film battery applications. © 2008 American Vacuum Society. DOI: 10.1116/1.2823491