Enhanced tunability of the composition in silicon oxynitride thin films by the reactive gas pulsing process

摘要

Silicon oxynitride thin films were sputter deposited by the reactive gas pulsing process. Pure silicon target was sputtered in Ar, N_2 and O_2 mixture atmosphere. Oxygen gas was periodically and solely introduced using exponential signals. In order to vary the injected O_2 quantity in the deposition chamber during one pulse at constant injection time (T_(on)), the tau mounting time τ_(mou) of the exponential signals was systematically changed for each deposition. Taking into account the real-time measurements of the discharge voltage and the I(O~*)/I(Ar~*) emission lines ratio, it is shown that the oscillations of the discharge voltage during the T_(on) and T_(off) times (injection of O_2 stopped) are attributed to the preferential adsorption of the oxygen compared to that of the nitrogen. The sputtering mode alternates from a fully nitrided mode (T_(off) time) to a mixed mode (nitrided and oxidized mode) during the T_(on) time. For the highest injected O_2 quantities, the mixed mode tends toward a fully oxidized mode due to an increase of the trapped oxygen on the target. The oxygen (nitrogen) concentration in the SiO_xN_y films similarly (inversely) varies as the oxygen is trapped. Moreover, measurements of the contamination speed of the Si target surface are connected to different behaviors of the process. At low injected O_2 quantities, the nitrided mode predominates over the oxidized one during the T_(on) time. It leads to the formation of Si_3N_(4-y)O_y-like films. Inversely, the mixed mode takes place for high injected O_2 quantities and the oxidized mode prevails against the nitrided one producing SiO_(2_x)N_x-like films.