Precursor Chemistry of Lithium Phosphorus Oxynitride Film for Metalorganic Chemical Vapor Deposition

Abstract

In this study, precursor chemistry of lithium phosphorus oxynitride (LiPON) film is investigated for metalorganic chemical vapor deposition (MOCVD). As a solid-electrolyte, LiPON film is widely used for all solid state thin film batteries. All solid state thin film batteries can provide as much power as conventional coin batteries, but is small enough to be used to provide power to semiconductor-related chips. The battery is safer, thinner and has faster charge and discharge current rate than conventional liquid batteries. It offers the prospect of supplying micro systems with long lasting, environmentally friendly and sustainable electrical power. In general, a sputtering method is applied to deposit LiPON film. LiPON film deposited by sputtering methods has some problems such as the generation of pin-holes, poor coverage and low deposition rates. These problems lead to higher cost and inferior properties of all solid state thin film batteries. In order to overcome these problems, we investigated the possibility of LiPON film deposited by MOCVD. A variety of Li precursors such as lithium tert-butoxide (LiOtBu), lithium hexamethyldisilazide (LiHMDS) and 2,2,6,6-tetramethyl-3,5-heptanedionato lithium (LiTMHD) shown in the table on the left below, were used in our experiments. Regarding P precursor, tris(dimethylamino)phosphine (TDMAP) was used in our experiments. We found the appropriate Li and P precursor chemistry for depositing LiPON films. In addition, as shown in the figure on the right below, it was confirmed that N atom concentration in all LiPON films is precisely controlled due to NH3 and O2 gas chemistry. In summary, we concluded that NH3 and O2 gas chemistry, and the combination of LiOtBu as Li precursor and TDMAP as P precursor, are critical factors for depositing LiPON film using MOCVD. Figure 1