A new technique for localized formation of SOI active regions

The oxidation of electrochemically etched porous silicon (PSi) has demonstrated success in the formation of device quality localized SOI for CMOS applications. A primary advantage with a localized SOI formation is the ability to integrate novel device structures and optoelectronics (i.e. optical switches, waveguides) with bulk silicon CMOS. The formation of PSi can be done selectively by controlling the Fermi level in areas to be etched or not etched, which is typically done by adjusting the level of doping. An alternative method is to introduce a reversible donor species such as protons or fluorine (this work) for the selective formation of islands of crystalline silicon surrounded by porous silicon. Implanted fluorine in silicon has demonstrated a donor effect upon annealing at low temperature (600degC), which is reversible as the fluorine outdiffuses during higher temperature annealing (1000degC). Crystalline silicon islands that were fabricated with this technique have a thickness of about 300 nm and are completely surrounded by oxidized porous silicon. Further study will investigate the device quality of the localized SOI structures for microelectronic and optoelectronic applications.