Process engineering to reduce self-aligned contact failure by reducing process-driven thermal stress on tungsten-dual poly gate stacks in sub-60Â nm DRAM devices

► Self-aligned contact (SAC) failures issues in W-dual poly metal gate of DRAM. ► Asymmetrical relief of W stress may create torque resulting in gate leaning. ► Stress induced by transformation of the amorphous WNx barrier and side of the gate. ► Decreased SAC failure and improved reliability by reducing the NH3 pre-purge time.