Here I explain the KOH simulator software (ACES) from University of Chicago  for a chain process of DRIE followed by KOH undercut. This software is very simple yet power to understand how Si etching works and design the mask to optimize the etch speed and crystal planes .
 https://cleanroom.byu.edu/koh  Bereyhi, Mohammad J., et al. "Perimeter Modes of Nanomechanical Resonators Exhibit Quality Factors Exceeding 10 9 at Room Temperature." Physical Review X 12.2 (2022): 021036.