Residual stress improvement of platinum thin film in Au/Pt/Ti/p-GaAs ohmic contact by RF sputtering power

This work seeks to characterize residual stress and microstructure of platinum thin film in Au/Pt/Ti/p-GaAs ohmic contact. Platinum thin films are deposited on p-GaAs (1 0 0) wafer and SiO2 via patterned area on it by a RF sputtering deposition system while different deposition powers are considered. Evolution of residual stress, roughness and grain size of the films by changing the deposition power are studied. The residual stress is measured by substrate curvature method, and the microstructure of the films is considered by SEM and AFM analysis. AFM analyze shows that Pt layer roughness dramatically increases from 2.2 nm to 8.7 nm on SiO2 substrate and from 1.05 nm to 5 nm on GaAs substrate when power increases from 150 W to 300 W. Also SEM images show that grain size increases on either GaAs or SiO2 substrates and step coverage deteriorates by increasing the deposition power. Pt layer stress measurement shows that there is a minimum and suitable point at 200 W for GaAs substrate. Also it is observed that the platinum stress changes from tensile to compressive for SiO2 substrate when RF deposition power increases from 200 W to 250 W.