Silicon micromachining and its impact on materials and device properties: plasma etching damage issues

Silicon micromachining is, at the present time, the tool of choice for the fabrication of microelectromechanical systems (MEMS) and, in general, miniature devices. Silicon micromachining techniques include some of the basic processing steps of IC technology especially plasma etching for the fabrication of submicron structures. However, inherent to plasma etching are damage effects to Si that can negatively influence the MEMS device performance. In this study we have explored the effects of conventional reactive ion etching (RIE) and magnetically enhanced RIE (MERIE) on the properties of Si exposed to fluorocarbon based oxide etch chemistries. By using combinations of spectroscopic ellipsometry (SE), secondary ion mass spectrometry (SIMS), and Schottky diode current-voltage-temperature (IVT) measurements, we show that damage in the form of thin layers of residual polymer and heavily damaged silicon can be induced by plasma exposure on the Si surface. SE and IVT measurements have shown that the thickness of the heavy damage layer decreases with magnetic field. This layer is proposed to comprise amorphous Si and voids and the density of the latter increases with the magnetic field. The polymer residue layer, detected by both SE and SIMS on the plasma-exposed Si surface, is observed to be thinner the higher the magnetic field.