High pressure high temperature steam oxidation poly buffer LOCOS (HP-HTPBL) field isolation process for reduced encroachment and low stress

The characterization of High Pressure-High Temperature Poly Buffer LOCOS (HP-HTPBL) isolation for 0.2 µ m design rules Non Volatile Memories is presented. Reduced bird's beak and improved charge to breakdown ( Q bd ) are obtained by combining High Pressure (25 atmospheres) 1100° C steam oxidation and 30° C/min ramp-up and 12° C/min ramp-down temperature rates. The fast temperature ramp-up inhibits the crystallization of the amorphous silicon (a-Si) buffer layer into large grain and limits the grain boundaries oxygen diffusion during the field oxidation process. Low warpage variations are obtained on 200 mm diameter wafers by the reduction of the cumulative oxidation induced stress.