Dear Kim

As Andrea suggested you can use HNA for making the circular grooves. In wet
etchants, it is not possible to etches circular masking shapes (or other shapes)
with vertical sidewalls due to crystallographic limitation of silicon. If the
sidewalls is not a issue, you can use surfactant (NC-200, PEG, Triton-X-100)
added 25 TMAH in order to etch any shapes of masking pattern with negligible
undercutting at the rounded and sharp corners, curved and <100> edges.
Recently some studies of TMAH+surfactant have been published  for the
fabrication of new shapes of structures. Some of the references are given below: