Realization of complex three-dimensional free-standing structures on silicon substrates using controllable underetching in a deep reactive ion etching

We report the realization of three-dimensional free-standing structures with high complexity on silicon substrates without using surface micromachining. The etching is feasible using the reactive ion etching method in which three gases are used in a two-step etching process. The passivation step is carried out by means of hydrogen, oxygen and sulfur-hexafluoride (SF 6 ) while the etching step uses SF 6 in a low-density capacitive-coupled radio frequency reactor. The overall etching process can be adjusted to arrive at three-dimensional structures with desired underetchings. The formation of partially and fully suspended structures is reported. Multi-level floated structures have been realized using this method.