Via hole process for GaAs monolithic microwave integrated circuit using two-step dry etching

A fast, reproducible, and reliable via hole dry etching process for GaAs monolithic microwave integrated circuit (MMIC) fabrication is described. The etching process consists of two steps. During the first etching step, BCl3/Cl2/Ar gas mixture is used to achieve a high etch rate and small lateral etching. In the second etching step, CCl2F2 gas is used to achieve a selective etching of the GaAs substrate with respect to the front side metal layer, which is 500 Å thick chromium. Via holes are formed from the back side of a 100 μm thick GaAs substrate and are electroplated with gold (∼20 μm thick). The resulting via hole profile and surface morphology are satisfactory for reproducible and reliable MMIC via groundings.