Design optimisation for bipolar transistors on BESOI substrates

A strongly applications oriented silicon integrated circuit process is being developed using direct wafer bonding. By bonding a silicon wafer to an oxidised silicon wafer, thin SOI material suitable for bipolar circuits can be produced without the need for epitaxial growth. A highly doped layer is implanted into the active silicon wafer to form a buried collector. This wafer is then inverted prior to bonding to an oxidised handle wafer. The active wafer is then subjected to precision grinding and polishing to give a final silcon layer thickness in the range one to three microns. After formation of etched trenches which are filled with dielectric, the substrates with in situ buried collector are ready for bipolar processing