A semiconductor structure. The structure includes (a) a semiconductor substrate; (b) a hard mask layer on top of the semiconductor substrate; and (c) a hard mask layer opening in the hard mask layer. The semiconductor substrate is exposed to the atmosphere through the hard mask layer opening. The hard mask layer opening comprises a top portion and a bottom portion, wherein the bottom portion is disposed between the top portion and the semiconductor substrate. The bottom portion has a greater lateral width than the top portion.