ANISOTROPIC ETCHING OF DEEP TRENCH FOR SILICON MONOLITHIC MICROWAVE INTEGRATED-CIRCUIT

The anisotropic etching of deep trenches in bulk Si for isolating glob al buried collectors in Si monolithic microwave integrated circuits ha s been successfully developed with SF6/C2ClF5 gas mixtures. Using phot oresist as the etching mask, deposition of polymer thin film on the si dewalls of the trench occurred, hence inhibiting lateral etching and m ade the process anisotropic. Under optimal processing conditions, an e tching anisotropy of 0.98 and an etching selectivity of silicon to pho toresist higher than 28 were observed.