Interpoly Oxide Related Fast Bit Failures in the Himos ™ Flash Memory Cell

A new data retention failure of the HIMOS™ cell is shown in this paper. The characterization of the failing bit reveals several differences with usual moving bits : the floating gate charge leaks through the interpoly dielectric. Investigations on the process suggest local damage of the interpoly oxide due to exposure to the erase junction implant. The issue is caused by notching of the erase junction implant mask allowing this implant to degrade the interpoly oxide. The issue is solved by the introduction of a bottom anti reflective coating layer, preventing this notching resulting is a significant increase of the yield and the processing window.