Well Extensions for trench devices

摘要

A bulge well structure for trench devices in wells of a conductivity type opposite to that of the substrate where the bottom of the trench has localized, extra doping. The additional doping into the bottom of the trench prior to device formation may be implanted while the photoresist mask for the trench formation is still in place. In one embodiment of the method, the trenches and the bulge or well extension formations at their bottoms are created before isolation regions are formed. The structure and method permit increased doping only where needed and are compatible with thin epitaxial layers and sharp transition interfaces of epitaxy with substrate for optimum latchup protection. No extra masks are required and the tight packing allowed by trench technology is not altered. Protection against soft errors and junction leakage by forming DRAM trench capacitors in a well of opposite conductivity type from the substrate may be provided.