Controlling Residual Stress and Suppression of Anomalous Grains in Aluminum Scandium Nitride Films Grown Directly on Silicon

Deposition of Aluminum Scandium Nitride (AlScN) films directly on Silicon at high Sc alloying levels, with controlled stress, and free of anomalous grains (AOGs) is demonstrated using reactive co-sputtering. The average stress and AOG formation consider the Sc alloying range between 20.3 and 36.6 atomic % and for film thicknesses from 400 nm to 1000 nm for 27.3% and 31.7% Sc alloying. The combination of a gradient seed layer and proper process gas mixture is shown to inhibit formation of AOGs in AlScN with up to 36% Sc alloying even when grown directly on Si. It is demonstrated that the total flow can be utilized to control the average film stress across the 20-36% doping range while the process gas mixture primarily impacts the density of AOG formation in the AlScN films. Bulk acoustic wave resonators fabricated from 380 nm and 485 nm thick low stress and AOG free Al
_0.68
Sc
_0.32
N films grown directly on Si demonstrate high frequency operation of 3.6 and 4.8 GHz, high electromechanical coupling >20%, and quality factors in excess of 500. [2021-0252]