Silicon oxynitride thin films synthesised by the reactive gas pulsing process using rectangular pulses

Silicon oxynitride thin films were synthesised by the reactive gas pulsing process using an argon, oxygen and nitrogen gas mixture from a semiconductor Si target. Argon and nitrogen were introduced at a constant mass flow rate, whereas oxygen gas was periodically supplied using a rectangular pulsed flow rate. The O2 injection time TON (or duty cycle α) was the only varied parameter. The influences of this parameter on the discharge behaviour, on the Si target voltage, and on the resulting chemical composition of the films were investigated. The temporal evolution of the total pressure exhibits exponential shape differing from the rectangular oxygen pulse shape, due to the response time of the gas flowmeter and to the progressive oxidation of the target and the chamber walls. During the TON time, the preferential adsorption of the introduced O2 induces a decay in Si target voltage. Reversion to the nitrided mode is still possible as soon as the O2 injection is stopped. The elemental analyses assessed by secondary neutral mass spectrometry (SNMS) showed that the O/N ratio within silicon oxynitride films linearly depends on the TON time. Increasing the duty cycle α over a certain value results in an oxidised steady state formation during the TON time. This formation was observed by real time measurements of the emission lines ratio I(O*)/I(Ar*) indicative of the O2 partial pressure and confirmed by the time derivative of the target voltage. During the TOFF time, the alternation with the nitrided mode becomes impossible, leading to the specific synthesis of stoichiometric SiO2 films.