An original reactive sputtering method, namely the reactive gas pulsing process
(RGPP) was developed for the synthesis of titanium oxynitride thin films. Such a method
implements a metallic titanium target dc sputtered, a constant supply of argon and nitrogen
gases and a pulsing oxygen mass flow rate, which is periodically controlled vs. time.
Various period times and different patterns can be generated: rectangle, sine, isosceles
triangle, mounting or descending triangle and exponential. Real-time measurements of the
target potential as well as total sputtering pressure are recorded in order to study the
instability phenomena of the process. They are also pertinent diagnostic tools to select the
most suitable pulsing patterns required to alternate the process between the nitrided and the
oxidized sputtering modes. As a result, alternation is produced for exponential and
rectangular patterns. For the latter, the influence of the duty cycle α, defined as the ratio of
the injection time of oxygen by the pulsing period, on the behaviour of the reactive
sputtering process and optical properties of deposited films, is systematically investigated.
Finally, the added value brought by the exponential patterns is examined. It is shown that
the exponential pulse leads to significant improvements of the oxygen injection. The
purpose is to introduce the right amount of oxygen so as to poison the titanium target
surface without saturating the sputtering atmosphere by oxygen. Thus, the speed of
pollution of the target surface appears as an appropriate parameter to better understand the
beneficial effect of the exponential shape on the control of the RGPP method.
Keywords: Reactive sputtering, reactive gas pulsing process (RGPP), titanium
oxynitride, pulse shape, rectangular pulses, exponential pulses, duty cycle, process
stability, target poisoning, hysteresis, optical transmittance, sputtering yield,
deposition rate, pumping speed, target potential, nitrided sputtering mode, oxidized
sputtering modes, pulsing period, multilayer structure, target pollution speed.
