Reactive sputtering of TiOxNy coatings by the reactive gas pulsing process: Part III: The particular case of exponential pulses

A new and original method, namely the reactive gas pulsing process (RGPP), was optimised to deposit titanium oxynitride thin films by dc reactive magnetron sputtering. Pure titanium target was sputtered in a reactive atmosphere composed of argon, nitrogen and oxygen. Argon and nitrogen gases were injected with a constant mass flow rate whereas oxygen was periodically supplied into the sputtering chamber. An exponential signal was generated to the oxygen mass flow meter with a constant pulsing period T = 45 s. During the injection time of the oxygen gas (tON time), the exponential shape was systematically modified in order to better control the amount of reactive gas introduced. Duty cycle was also changed and led to an extended alternation of the process between the nitrided and oxidised sputtering mode. Speed of poisoning of the titanium target surface by oxygen was calculated assuming real time measurements of the target potential. It was clearly shown that duty cycle and shape of the exponential signals used during oxygen injection are fundamental pulsing parameters. Both parameters must be taken into account in order to adjust and improve the monitoring of RGPP system for the deposition of titanium oxynitride coatings. Such approach prevents the full poisoning of the target surface by oxygen or nitrogen, and consequently, a wide range of oxynitride compounds can be easily reached.