Abstract
ZrN x O y thin films were deposited on P-type (100) Si wafers at 500°C using unbalanced magnetron sputtering. The reactive gases were nitrogen at fixed flow rate mixed with oxygen with increasing flow rates. The purpose of this study was to investigate the structure evolution due to changing oxygen flow rate and the accompanying variation of mechanical properties of the thin films. As the oxygen flow rate increased, the oxygen content of the film increased significantly. The major phases with increasing oxygen contents observed from X-ray diffraction (XRD) were in an order of ZrN, ZrN+Zr 2 ON 2 +monoclinic ZrO 2 (m-ZrO 2 ), cubic ZrO 2 with dissolving nitrogen (c-ZrO 2 (N)) and m-ZrO 2 . The characteristics of the ZrN x O y films could be categorized into three zones respectively predominated by ZrN (Zone I), ZrN+Zr 2 ON 2 +m-ZrO 2 (Zone II) and ZrO 2 (Zone III). The mechanical properties of the films including hardness and residual stress are substantially affected by the phase transition. The hardness of the thin films decreased from about 22GPa in Zone I to a lower value ranging from 12 to 17GPa in Zones II and III. The average residual stresses of the ZrN x O y films were measured by laser curvature method, and the stresses in the predominant phases were also individually measured using modified XRD sin 2 ψ method. The residual stress in ZrN (Zone I) was relieved due to increasing oxygen content or phase separation of m-ZrO 2 . High residual stress in c-ZrO 2 (Zone III) may be ascribed to the lattice distortion due to the excess N atoms. m-ZrO 2 and Zr 2 ON 2 were found to be low-stress phases, and might relieve the residual stresses of the films. The film hardness is not substantially related to the residual stress of the film. The appearance of Zr 2 ON 2 or m-ZrO 2 phases in the ZrN x O y thin films usually leads to the decrease of residual stress and hardness. On the other hand, for the high-stress phases ZrN and c-ZrO 2 (N), it is not as obvious that the increase of high-stress phases may result in high film hardness. Experimental results suggested that c-ZrO 2 may be stabilized at room temperature by the doped nitrogen. © 2011 Elsevier B.V.