Etching of high aspect ratio structures in Si using SF ₆/O ₂ plasma

The etching mechanism of deep (∼10 μm) submicron diameter holes with high aspect ratios (>10) using plasmas maintained in mixtures of SF ₆ and O ₂ gases was investigated. A low-pressure, high-density, inductively coupled plasma etching reactor with a planar coil was used for the etching. The influence of SF ₆-to-O ₂ gas ratio, pressure, and rf-bias voltage on the etch rate and selectivity was also analyzed using Si wafers, which were patterned with 0.35-0.5 μm diameter holes in a SiO ₂ mask. The etch rate and anisotropy were determined using the F-to-ion flux ratio and F-to-O flux ratio.