Mechanism study of sidewall damage in deep silicon etch

Abstract

The formation and etch mechanism of sidewall damage in deep silicon etch using standard Bosch process have been investigated in this work for the first time. The sidewall damage occurs at a certain depth where the sidewall is not sufficiently protected from lateral etch during long-time ion bombardment, and further, we demonstrate that the formation of sidewall damage is not only related to passivation film on the trench sidewall, but also closely relies on ion-enhanced etch mechanism. In addition, it is found that the starting depth of sidewall damage is almost inversely proportional to etch pressure and ion incidence angle, which can be attributed to a broader ion angular distribution (IAD) at higher chamber pressure. Then, a quantitative etch model based on IAD function has been also proposed to investigate the dependence of the starting depth of sidewall damage on ion incidence angle. Finally, by optimizing process parameters, high-quality etch profile without any observable sidewall damage has been successfully achieved at etch pressure of 60 mTorr.