Nitrogen and oxygen transport and reactions during plasma nitridation of zirconium thin films

Zirconium nitride (ZrN) is a refractory material with good mechanical and t hermal properties. It is therefore a good candidate for hard surface treatm ent at high temperature. In this work, we report the growth and characteriz ation of ZrN by plasma assisted thermal nitridation of zirconium films in a NH3 atmosphere. The process was monitored by in situ monochromatic ellipso metry and the nitrides grown were profiled and analyzed by Auger electron s pectroscopy. By using temperatures in the 700-800 degrees C range, the mate rial obtained is quite close to ZrN, but, depending on experimental conditi ons, residual oxygen (impurities) can be easily incorporated by reaction wi th zirconium. The analysis of the ellipsometric data has shown that the nit ridation did not occur by simple growth of nitride on zirconium. Auger prof iles confirmed the presence of an oxidized zirconium layer localized betwee n the nitrided surface and the remaining metal. This oxidation was observed to occur preferentially during temperature ramping, that is, in the low te mperature regime. At high temperature, nitridation is dominant and the inco rporated oxygen is exchanged with nitrogen. Oxygen is then partly rejected by diffusion out of the film through the ZrN surface layer and partly by di ffusion in the deep zirconium sublayer. By using these observations, a new model of growth with a layered ZrN/ZrOx/Zr film was used to describe in sit u ellipsometric data. By comparing the pure thermal and the plasma treatmen ts, the advantages of the plasma assisted treatment become clearly: complet e nitridation of the zirconium layer was achieved and the oxygen amounts in the film were substantially reduced. (C) 2000 American Institute of Physic s. [S0021-8979(00)04401-7].