Impact of negative bias on the piezoelectric properties through the incidence of abnormal oriented grains in Al0.62Sc0.38N thin films

Sputter deposited A1ScN films with an Sc content of 38 at % were investigated by X-ray diffraction and electron microscopy to study the influence of the radio frequency (RF) bias on the growth of abnormally oriented grains (AOG). Scanning electron microscopy investigations showed that the nucleation and growth of AOGs occurs with applied negative RF-bias fill 4 W (51 mW/cm(2)), while the complete loss of AOGs happens at biases larger than 6 W (76 mW/cm(2)). The lack of AOGs within the film occurs together with the loss of the preferred (0001)-texture. At high bias powers, the (0001)-texture nucleates due to the strong (111)-texture of Pt-layer, but grain orientation becomes random during growth. The change of film microstructure with higher biases is reflected in the decay of piezoelectric properties. The concentration of trapped Ar atoms into the films increased with increasing bias power. The variation of the Ar-content along the film cross-section was ascribed to RF bias instabilities.