Reactive Gas Pulsing Process for Oxynitride Thin Films

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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.