Quartz crystal microbalance study of precursor diffusion during molecular layer deposition using cyclic azasilane, maleic anhydride, and water

The authors report the detailed growth characterization of a molecular layer deposition chemistry that utilizes a cyclic azasilane, maleic anhydride, and water in a sequential reaction sequence. They observe a three stage growth for this chemistry during which the growth rate per cycle (GPC) is initially small and increases to large steady state values. Using a quartz crystal microbalance, they observe significant diffusion of maleic anhydride and cyclic azasilane into the film that causes the large GPC. They also observe that longer purge times between precursor exposures result in a smaller GPC and an increased number of cycles required to reach steady state and large GPCs. At higher substrate temperatures, growth is suppressed due to precursor desorption. Furthermore, after long inert gas purging after film growth, significant film mass loss occurs accompanied by a loss of porosity indicated by the lack of film absorption of maleic anhydride and cyclic azasilane precursors after restarting growth. They conclude that growth using this specific chemistry is largely dominated by precursor absorption and diffusion within the film, resulting in CVD-like reactions, rather than sequential, self-limiting surface reactions. Published by the AVS.