Heat treatment induced phase separation and phase transformation of ZrNxOy thin films deposited by ion plating

Nanocrystalline ZrNxOy thin films were deposited on p-type Si (100) substrates using hollow cathode discharge ion-plating (HCD-IP) and the films were annealed at 700 and 900 °C in the controlled atmosphere. The purpose of this study was to investigate the phase separation, phase transformation and the accompanying change of properties of the heat-treated ZrNxOy films deposited by ion plating. With the increase of oxygen flow rate ranging from 0 to 10 sccm, the primary phase of the as-deposited films evolved from ZrN to nearly amorphous structure and further to monoclinic ZrO2 (m-ZrO2). After heat treatment at 700 and 900 °C, phase transformation occurred in the samples deposited at 8 and 10 sccm O2, where a stoichiometric crystalline Zr2ON2 was found to derive from m-ZrO2 with dissolving nitrogen (m-ZrO2(N)). The hardness of the ZrNxOy thin films could be correlated to the fraction of Zr2ON2 + m-ZrO2. The film hardness decreased significantly as the fraction of ZrO2 + Zr2ON2 exceeded ~ 60%, which was due to phase transition by increasing oxygen flow rate or phase transformation induced by heat treatment. The phase separation of m-ZrO2 from ZrN with dissolving oxygen (ZrN(O)) may relieve the residual stress of the ZrNxOy specimens deposited at 5 and 8 sccm O2, while direct formation of m-ZrO2 increased the stress of the film deposited at 10 sccm O2. On the other hand, the phase transformation from m-ZrO2(N) to Zr2ON2 by heat treatment at both 700 and 900 °C may effectively relieve the residual stress of the ZrNxOy films.