Wafer-Scale Integration of Piezo- and Ferroelectric Al0.64Sc0.36N Thin Films by Reactive Sputtering

TL;DR

This paper demonstrates the successful wafer-scale deposition of high-quality Al0.64Sc0.36N piezoelectric thin films with uniform properties across 200 mm wafers, enabling advanced MEMS device applications.

Contribution

It introduces an optimized sputtering process for high scandium-content AlScN films with high deposition rate, low defects, and uniform piezoelectric properties across large wafers, overcoming previous growth challenges.

Findings

Achieved high-quality Al0.64Sc0.36N films with low defect density.

Demonstrated uniform piezoelectric coefficients across 200 mm wafers.

Established process conditions for stress control and high deposition rate.

Abstract

Large-area deposition of Aluminium-Scandium-Nitride (Al1-xScxN) thin films with higher Sc content (x) remains challenging due to issues such as abnormal orientation growth, stress control, and the undesired crystal phase. These anomalies across the wafer hinder the development of high scandium-content AlScN films, which are critical for microelectromechanical systems applications. In this study, we report the sputter deposition of Al0.64Sc0.36N thin films from a 300 mm Al0.64Sc0.36 alloy target on 200 mm Si(100) wafers, achieving an exceptionally high deposition rate of 8.7 {\mu}m/h with less than 1% AOGs and controllable stress tuning. Comprehensive microstructural and electrical characterizations confirm the superior growth of high-quality Al0.64Sc0.36N films with exceptional wafer-average piezoelectric coefficients (d33,f =15.62 pm/V and e31,f = -2.9 C/m2) owing to low point defects density and grain mosaicity. This was accomplished through the implementation of an optimized seed layer and a refined electrode integration strategy, along with optimal process conditions. The wafer yield and device failure rates are analysed and correlated with the average stress of the films and their stress profiles along the diameter. The resulting films show excellent uniformity in structural, compositional, and piezoelectric properties across the entire 200 mm wafer, underscoring their strong potential for next-generation MEMS applications.