Effects of outgassing on the reactive sputtering of piezoelectric AlN thin films

A series of study of the effects of outgassing on pulsed-DC reactive sputtering of highly (0002)-textured AlN thin film was conducted with systematically adjusted sputtering parameters like working pressure, atmosphere, and temperature. The film quality was evaluated by its rocking curve width and residual stress, both utilizing X-ray diffraction methods, as well as by SEM and XPS analyses. It is found that with lower outgassing all the above-mentioned sputtering parameters become less effective on both rocking curve width and residual stress. The rocking curve FWHM (Full Width at Half Maximum) measurements even exhibit apparently insensitive regions to the sputtering parameters, and accompanied threshold behaviors as well. XPS analysis reveals higher oxygen content while SEM observation shows thinner and slanter columnar structure in the AlN film when outgassing is higher upon sputtering.