Anisotropic etching of deep trench for silicon monolithic microwave integrated circuit

The anisotropic etching of deep trenches in bulk Si for isolating global buried collectors in Si monolithic microwave integrated circuits has been successfully developed with SF₆/C₂ClF₅ gas mixtures. Using photoresist as the etching mask, deposition of polymer thin film on the sidewalls of the trench occurred, hence inhibiting lateral etching and made the process anisotropic. Under optimal processing conditions, an etching anisotropy of 0.98 and an etching selectivity of silicon to photoresist higher than 28 were observed.