Achievement of top rounding in shallow trench etch

摘要

A process for forming a shallow trench having steep sidewalls near its bottom and sloping sidewalls at the top is described. The process is in 3 stages. The first stage involves methane trifluoride, carbon tetrafluoride, argon, and oxygen. The second stage involves methane trifluoride and methane monofluoride, while the third stage involves hydrogen bromide, chlorine, and helium/oxygen. If the ratio of the various components at each stage is carefully controlled along with other variables such as discharge power, pressure, and duration, the trench profile described above is obtained with a minimum of deposited polymer material on the sidewalls.