Influence of the hard masks profiles on formation of nanometer Si scalloped fins arrays

In this work, the impact of hard masks (HMs) profiles on nanometer scalloped-fins (S-fins) by reactive ion etching (RIE) is extensively investigated. A popular spacer image transfer (SIT) process originated from conventional FinFET mass fabrication is adopted for the formation of the S-fins arrays by using a new developed time division multiplexing (TDM) etching process. It is observed that the higher spacers HMs with sharp corners result in the asymmetric S-fins. In order to explain the phenomenon and achieve the desirable S-fins profiles, a possible mechanism causing the severely asymmetric S-fins is firstly proposed. It suggests that the negative charges accumulated on the non-conducting higher spacers during the RIE process play a significant role on the formation of the asymmetric profile of S-fins. An effective approach based on the proposed scheme is demonstrated by reducing the heights of spacers HMs, which improves the simultaneity of etching processes, achieves the symmetric S-fins profiles with desirable notches and obtains three vertically stacked SiNWs arrays.