A semiconductor structure and a related method for fabrication thereof include an isolation region located within an isolation trench within a semiconductor substrate. The isolation region comprises; (1) a lower lying dielectric plug layer recessed within the isolation trench; (2) a U shaped dielectric liner layer located upon the lower lying dielectric plug layer and partially filling the recess; and (3) an upper lying dielectric plug layer located upon the U shaped dielectric liner layer and completely filling the recess. The isolation region provides for sidewall coverage of the isolation trench, thus eliminating some types of leakage paths.