Improvement of sidewall roughness in deep silicon etching

摘要

The recently developed High Aspect Ratio Si Etch (HARSE) process is widely used for applications requiring silicon structures with high aspect ratios. This process relies on the alternation of sidewall passivation and silicon etching phases and enables the obtainment of high silicon etch rates and highly anisotropic profiles. This paper reports an innovative approach to improve the sidewall roughness through a multiple-step HARSE process using an ICP system. Unlike the standard HARSE process, the etching conditions for this new process are gradually altered in order to reinforce the silicon etch efficiency as a function of the silicon depth previously etched. Trenches with aspect ratios as high as 40 can be achieved. The sidewall roughness along the entire etching depth is less than 8 nm rms. In comparison with the standard HARSE process in which ripples appear on the trenches sidewall, the sidewall roughness is improved by a factor of 4.