Deposition of ZnO thin films by the ultrasonic spray pyrolysis technique

This paper describes the design of an ultrasonic spray pyrolysis system and the determination of the optimal conditions for deposition of ZnO thin films. The film is desired to have strong piezoactivity, high resistivity, and good thickness uniformity. Zinc acetate is the source solution for the ZnO film on top of a SiO₂/Si wafer. Controlled experiments show that the zinc acetate solution of 0.05 mol% doped with 30 at.% of LiCl can provide good ZnO films at the substrate temperature of 420°C. The optimal substrate rotation rate and nozzle tilting angle are also determined to improve the uniformity of the film. ZnO thin films deposited with these conditions show good c-axis orientation, and a resistivity higher than 10⁷ω·cm after annealing in oxygen, and good thickness uniformity across a 4″ substrate wafer. Properties of the ZnO film developed in this study are comparable to those obtained with conventional techniques.