High-Rate Anisotropic Etching of Silicon by Remote Microwave Plasma in Sulfur-Hexafluoride

Microwave plasma is used to study the effects of metal catalysts and substrate temperature on the etching of single-crystalline silicon wafers. Silicon etching without undercut has been achieved at elevated substrate temperatures without the use of ion bombardment of SF₆ plasma with copper mask. The use of copper mask not only increases the silicon etch rate compared to that using photoresist mask but also leads to a vertical etching profile when the substrate temperature is around 335°C. The increase in etch rate is consistent with the increase of the concentration of atomic fluorine measured by optical emission spectroscopy. The anisotropic etching is found to be caused by the deposition on the sidewalls of etched holes with thin films containing mainly Cu_xS and some CuF_y as confirmed by EDAX analysis.