Process for forming self-aligned source in flash cell using SiN spacer as hard mask

摘要

When FLASH cells are made in association with STI (as opposed to LOCOS) it is often the case that stringers of silicon nitride are left behind after the spacers have been formed. This problem has been eliminated by requiring that the oxide in the STI trenches remain in place at the time that the silicon nitride spacers are formed. After that, the oxide is removed in the usual manner, following which a SALICIDE process is used to form a self aligned source line. When this sequence is followed no stringers are left behind on the walls of the trench, guaranteeing the absence of any open circuits or high resistance regions in the source line.