Continuous deep reactive ion etching of tapered via holes for three-dimensional integration

A continuous SF6/O2 plasma process at room temperature has been used to etch tapered through-silicon vias using a DRIE-ICP tool. These features (10–100 µm in diameter) are aimed for applications in 3D integration and MEMS packaging. The effects of various process parameters such as O2 flow rate, platen bias, pressure and substrate temperature on the via profile (depth, slope angle and aspect ratio) development are investigated. The etching mechanism was also studied and x-ray photoelectron spectroscopy (XPS) analysis reveals a SiOx passivation layer of the order of ∼2 nm on the via sidewall and a substantial temperature dependence. Both tapering and anisotropy of etching depend on this passivation layer formation. Finally, suitable tapered vias with an aspect ratio of ∼5 and a slope angle of ∼83° are obtained by properly balancing the etching regimes. In this condition, a maximum etch rate of 7 µm min−1 is achieved