Impact of Film Stress and Film Thickness Process Control on GaAs-TiAu Metal Adhesion

Abstract

The fabrication of GaAs-based optoelectronic ridge-waveguide devices requires deposition of a topside-contact metallization for proper device operation. Fabrication delays occurring during the processing of TiAu-contact pads have been linked to poor adhesion and metal blister formation, factors that negatively affect the final device yield. In this study, we examined sputter-deposited Ti and Au films to determine the impact of film-thickness process control and film stress as measured by wafer bow. We theorized that competing stress relaxation forces between the Ti and Au films would produce a post-deposition change in wafer bow, which affects the Au film, setting the stage for blister creation. We now report the development of a reduced-stress sputter-deposited TiAu-contact metallization and demonstrate the utility of the modified process with fabrication of blister-free ridge-waveguide devices with high device yield.