A semiconductor wafer having a main surface is provided. A first etch resistant mask is provided on the main surface. A first reactive ion etching step that forms a first group of trenches using the first etch resistant mask is performed. Each of the trenches in the first group is covered with a second etch resistant mask after performing the first reactive ion etching step. A second reactive ion etching step that forms a second group of trenches using one or both of the first etch resistant mask and the second etch resistant mask is performed. The trenches in the second group are laterally offset from the trenches in the first group. The first and second reactive ion etching processes are performed such that a depth of the trenches of the first group is substantially equal to a depth of the trenches in the second group.