Position and pressure effects in rf magnetron reactive sputter deposition of piezoelectric zinc oxide

Abstract

c-axis oriented thin films of piezoelectric ZnO have been deposited on room-temperature substrates by rf magnetron sputtering of zinc in a reactive ambient of 100% oxygen over a pressure range from 5-70 mTorr. Below 10 mTorr the film structure, orientation, and physical properties depend on the position of the substrates with respect to the target. This is attributed primarily to resputtering of the film in the region of the target erosion area by high-energy neutral oxygen. At higher pressures where the mean free path inhibits such effects, the film structure and properties are uniform. At 700-W sputtering power, the optimum pressure lies between 20-30 mTorr leading to highly oriented ZnO over a large area of plasma with a dielectric constant of 11, conductivity at 300° C=2× 10^-10 Ω^-1cm^-1, and Rayleigh wave velocity=2600 m/s. The films are characterized using optical transmittance, electrical conductivity, dielectric constant and SAW, and acoustic microscope measurements.