POSPBL-POLY SPACER POLY BUFFERED LOCOS (A Novel Trench + Shallow Element Isolation Concept)
Original Publication Date: 1993-Oct-01
Included in the Prior Art Database: 2002-Feb-15
Sub-micron BiCMOS requires a deep trench iso- lation for the Bipolar devices in order to allow for adequate scaling opportunity, while reducing para- sitic capacitances and thereby reducing gate delay at low power operations. At the same time the CMOS portion of the circuit requires an isolation scheme, that is simple scalable as well and supports a small WetT, with minimal encroachment (.6 micron at the .5 micron BiCMOS level), while supporting > 7 volts breakdown for both N+ to N+ and P+ to P+ S/D ditlG- sions at minimum device spacing for dense SBAM's. The novel POSPBL approach achieves the above cri- terion. The trench topography needs to be sutBciently planar to prevent stringer formation at subsequent poly silicon and metallization layers, while the net stress being transmitted by the trench into the adja- cent silicon islands must be sufficiently low to pre- vent the formation of defects and Bandgap lowering in the Bipolar device structure, which would lead to gain modification as a function of trench spacing. The CMOS shallow element, while also being con- strained by topography and stress issues is saddled with the additional requirement of maintaining its actual size during subsequent processing steps.