A New Failure Mechanism of MLC NOR Flash Memory Caused by Aggravated Drain Disturb Due to Co-Salicidation Process

We report a new failure mode of multi-level cell (MLC) NOR flash memory induced by anomalously increased drain disturb. The aggravated disturb, occurring in ppm level, is shown to be caused by an abnormal lateral encroachment of cobalt silicide on the drain side of the NOR flash cell. The failure mode, which becomes more critical as the NOR flash cell scales down, can be alleviated by optimizing the thickness of cobalt salicidation and controlling the defect density induced by spacer etch and ion implantation on the drain side.