Investigation of Optimum Deposition Conditions of Radio Frequency Reactive Magnetron Sputtering of Al0.7Sc0.3N Film with Thickness down to 20 nm

Ferroelectric aluminum scandium nitride (Al0.7Sc0.3N) has attracted increasing interest due to its high remanent polarization (P-r, >100 mu C cm(-2)) and coercive field (E-c, >5 MV cm(-1)). The four radio frequency reactive magnetron sputtering conditions (sputtering power, N-2 flow ratio, pressure, and temperature) influence the ferroelectric and material properties of 45 nm-thick Al0.7Sc0.3N deposited on the TiN/SiO2/Si substrate. Crystallinity is enhanced under the deposition conditions with higher adatom energy but deteriorates when the growth condition increases over the optimum. The well-crystallized films have (002)-preferred orientation with the in-plane compressive stress imposed by the peening effect and thermal stress. The imposed compressive stress increases the c(0)/a(0) value, where c(0) and a(0) mean the c- and a-axis lattice parameters, which eventually increases the E-c of the film. P-r increases with the c(0)/a(0) value, but other factors also influence the change. The films with high oxygen concentration show the wake-up properties due to the large percentage of domain walls and their depinning. Finally, ferroelectricity is confirmed with films down to a thickness of 20 nm. However, the thinnest film shows a higher E-c and lower P-r. These findings imply the presence of non-ferroelectric interfacial layers, which induce the depolarization effect.

Automated summary

Ferroelectric aluminum scandium nitride (Al0.7Sc0.3N) has attracted increasing interest due to its high remanent polarization and coercive field. The deposition conditions significantly affect the crystallinity and properties of the films. Compressive stress and the c(0)/a(0) value increase the E-c and P-r of the films. Films with high oxygen concentration exhibit wake-up properties. However, the thinnest film shows non-ferroelectric behavior.