Optimization of Sputter Deposition Process for Piezoelectric AlN Ultra-Thin Films

The sputtering conditions for the deposition of the layers underneath active AlN films were analyzed for improving the quality of the active AlN, and the dependence of AlN deposition temperature on crystalline quality was investigated, where a reduced deposition temperature could reduce the process time and cost. Therefore wafers with a 25 nm bottom electrode on a 15 nm adhesion layer, a 100 nm piezoelectric AlN films and a 100 nm top electrode have been deposited using different metals (Mo, Pt and Al) as bottom electrodes, different seed layers (Ti and AlN) and were deposited in two different sputtering machines. For the Mo bottom electrode, the sputtering power has also been varied between 250W, 500W, 750W and 1000W, and the deposition rates for these powers have been determined. The thickness, resistivity, rocking curve FWHM and stress have been measured for the bottom electrodes. The stress has been analyzed for the seed layers and for the AlN and top electrode layers and the rocking curve FWHM for the AlN has been measured and studied. Three structures with a Pt bottom electrode on a Ti seed layer have been created, where the active AlN films has been deposited at 300_C, 150_C and at room temperature respectively. It was shown, that AlN layers deposited on Pt bottom electrodes showed the best crystalline quality of the metals tested and the active AlN quality showed no significant difference, whether it was deposited at 150_C or 300_C.