Atomic Layer Deposition of Lithium Phosphorus Oxynitride

An atomic layer deposition (ALD) process is successfully developed for fabricating high-quality lithium phosphorus oxynitride (LiPON) thin films for a potential use as a conformal solid-state electrolyte coating in 3D Li-ion microbattery technology. In our ALD process the challenge of simultaneously incorporating phosphorus and nitrogen in the films is overcome by using a novel nitrogen-containing phosphorus precursor, diethyl phosphoramidate, together with lithium hexamethyldisilazide as the lithium precursor. A temperature window is found around 270–310 °C, where homogeneous films are realized and the film growth is controlled in a digital manner by the number of ALD cycles at a rate of ∼0.7 Å/cycle. The process allows for a high N-to-P ratio in the films, which is beneficial for achieving the required high ionic conductivity. For a film deposited at 330 °C with a composition of Li 0.95 PO 3.00 N 0.60 according to RBS/NRA analysis, an ionic conductivity value as high as 6.6 × 10 –7 S cm –1 is measured at 25 °C.