The Limits of the Post-Growth Optimization of AlN Thin Films Grown on Si(111) via Magnetron Sputtering

Hexagonal aluminium nitride (AlN) thin films prepared by the reactive magnetron sputtering method usually undergo post-growth annealing treatment aimed at the improvement of crystalline quality as a principal step for their performance as piezoelectric transducers in micro-electro-mechanical systems. Herein, the post-growth annealing of AlN films deposited on Si(111) is investigated by Raman and Fourier transform infrared spectroscopies, X-ray diffraction, and scanning probe microscopies. The thermally treated films show a positive trend in stress relaxation via annealing up to 1200 degrees C; however, it is accompanied by a dewetting of the quasi-epitaxial layer and the formation of the cubic AlN phase. The critical role is played by the AlN/Si interface being sensitive to oxidation via interstitial oxygen in Si wafers. The piezoelectric performance of the AlN/Si system is found to be inversely proportional to the post-growth annealing temperature.