Lateral Autodoping Suppression by Selective Epitaxy Capping and Its Application in High Speed BiCMOS

fabrication. Other advanced technique like trench isolation may be considered. Trench isolation is, however, involved and expensive. A simple solution is to apply the recently reported selective epi growth (SEG)4-6). Fig.2 illustrates the process sequence. Single crystal silicon is selectively grown inside oxide windows. The highly doped buried layer is now capped. In addition, the oxide protects the off-buried layer region from the arsenic contamination. Subsequently, the oxide mask is removed and an epitaxy layer of desired doping is deposited. Lateral autodoping can be reduced by 2-3 orders of magnitude while maintaining a low arsenic buried layer sheet