Reactive sputtering of TiOxNy coatings by the reactive gas pulsing process. Part I: Pattern and period of pulses

Titanium oxynitride thin films were deposited by dc reactive magnetron sputtering. A metallic titanium target was sputtered in argon, nitrogen and oxygen reactive atmosphere. Argon and nitrogen gases were continuously injected into the process whereas oxygen mass flow rate was pulsed during the deposition. By means of a home made pulsing technique, the oxygen gas was introduced using various modulation patterns of the mass flow rate: rectangle, exponential, sine, isosceles triangle, mounting and descending triangles. The period T of the pulse length was systematically changed from 10 to 400 s. Similarly, kinetics and poisoning phenomena of the titanium target by nitrogen and oxygen were investigated from real time measurements of the target potential and total sputtering pressure. Such diagnostics allowed understanding the advantageous role of the reactive gas pulsing process (RGPP) to synthesize titanium oxynitride compounds. Some requirements, especially the shape of the pulses and the period length were established to alternate the process between the oxidised and nitrided sputtering mode. With suitable and reversible operating conditions, the RGPP led to deposit tuneable titanium oxynitride coatings, usually difficult to reach by conventional reactive sputtering.