Proton Isolation for GaAs Integrated Circuits

Significant improvement in the electrical isolation of closely spaced GaAs integrated circuit (IC) devices has been achieved with proton implantation. Isolation voltages have been increased by a factor of four in comparison to a selective implant process. In addition, the tendency of negatively based ohmic contacts to reduce the current flow in neighboring MESFET´s (backgating) has been reduced by at least a factor of three. The GaAs IC compatible process includes implantation of protons through the SiO ₂ field oxide layer and a three-layered dielectric- Au mask which is definable to 3-µm linewidths and is easily removed. High temperature storage tests have demonstrated that proton isolation, with lifetimes on the order of 10 ⁵ h at 290° C, is not a lifetime limiting component in a GaAs IC process.