Deep anisotropic silicon etching with the expanding thermal plasma (ETP) technique using fluorine-based chemistries was demonstrated. The ETP technique makes use of a remote high-density plasma source and it has a good control of the downstream plasma chemistry. Both a cryogenic etching process and a time-multiplexed etching process were developed. Etch rates up to 12 mu m min(-1) and selectivities higher than 300 were obtained while feature profiles were comparable to those obtained with the widely used inductively coupled plasma reactors. Therefore, this deep anisotropic silicon etching technique is an attractive alternative for the fabrication of microstructures with high-aspect-ratio features. (c) 2007 The Electrochemical Society.