VIA HOLE PROCESS FOR GAAS MONOLITHIC MICROWAVE INTEGRATED-CIRCUIT USING 2-STEP DRY ETCHING

Abstract

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 angstrom thick chromium. Via holes are formed from the back side of a 100 mum thick GaAs substrate and are electroplated with gold (approximately 20 mum thick). The resulting via hole profile and surface morphology are satisfactory for reproducible and reliable MMIC via groundings.