Influence of amorphous buffer layers on the crystallinity of sputter-deposited undoped ZnO films

Undoped ZnO films were deposited by radio frequency (RF) magnetron sputtering on amorphous buffer layers such as SiOx, SiOxNy, and SiNx prepared by plasma enhanced chemical vapor deposition (PECVD) for dielectric layer in thin film transistor (TFT) application. ZnO was also deposited directly on glass and quartz substrate for comparison. It was found that continuous films were formed in the thickness up to 10 nm on all buffer layers. The crystallinity of ZnO films was improved in the order on quartz>SiOx >SiOxNy>glass>SiNx according to the investigated intensities of (0 0 2) XRD peaks. The crystallite sizes of ZnO were in the order of SiOx∼glass >SiNx. Stable XRD parameters of ZnO thin films were obtained to the thickness from 40 to 100 nm grown on SiOx insulator for TFT application. Investigation of the ZnO thin films by atomic force microscope (AFM) revealed that grain size and roughness obtained on SiNx were larger than those on SiOx and glass. Hence, both nucleation and crystallinity of sputtered ZnO thin films remarkably depended on amorphous buffer layers.