Effect of Process Parameters on Co-Sputtered Al(1-x)ScxN Layer's Properties: Morphology, Crystal Structure, Strain, Band Gap, and Piezoelectricity

The effect of pulse direct current (DC) reactive ion co-sputtering parameters on the morphology, crystal structure, residual stress, band gap, and piezoelectric properties of the Al(1-x)ScxN thin film deposited in large target-to-substrate distance (TSD) system has been studied using Scanning Probe Microscopy, X ray Diffractometry, Spectroscopic Ellipsometry, and profilometer, among others. The process pressure was revealed to be the key factor which essentially determines the quality of the film for such system. As low as 0.2 Pa working pressure is needed to achieve smooth nitride layer with good piezoelectric properties. High N-2/(Ar + N-2) gas ratio also was shown to result in better film properties. Residual stress in nitride film, and thereby the optical band gap can be tuned by variation of process pressure, gas ratio, and Sc fraction in the studied x range (0-0.5). The Al(1-x)ScxN film deposited at low pressure, medium N-2 gas ratio with x similar to 0.41 shows high piezoelectric coefficient, relatively low residual stress, and smooth surface. Top electrode has been applied to eliminate the interfering effect of the restraining force induced by the unexcited matrix materials around tip/sample contact for Piezoresponse Force Microscopic (PFM) measurement of piezoelectric constant of thin nitride film. We have shown by comparing the corrected d(33corr) data determined with PFM to those obtained from direct piezoelectric method that PFM using proper measurement conditions and correction can be applied as a quantitative method for study of piezoelectric properties of thin film.