A study of self-aligned contact etch of NOR flash

The self-aligned contact (SAC) scheme has been imperative for NOR flash memory technology with the aggressively scaled drain space. The challenges mainly come from its high aspect ratio and the multiple issues to solve such as nitride loss loading between hole and trench, bottom profile and narrow process window. In this course, we investigated two integration schemes, the traditional SAC scheme is to simultaneously form the hole and the trench, followed by tungsten gap-fill, the reversed SAC scheme, is to only form the hole first, followed by nitride deposition. In both schemes, we examined the impact of various etch parameters on the high aspect ratio SAC etch process, including temperature, power, chemistry ratio and pulsing function. Finally we demonstrated the SAC could be successfully fabricated without any side effect.