Edge Encroachments and Suppressions of Tunnel Oxide in Flash Memory Cells

The edge encroachments of tunnel oxide are experimentally found to degrade the sub-70-nm Flash cells from hydrogen-assisted gap-fill high-density-plasma chemical vapor deposition. Abnormal oxide regrowths further aggravate in subsequent thermal densification. Minimizations of the edge recesses in the corner rounding processes of shallow trench isolation are demonstrated to prevent the undesirable oxide growths from moisture penetrations. The less hydrogen content in liner oxidation plays a major role to suppress the edge encroachments. The improved oxide reliability is verified by the injected charge density and the charge to breakdown in L/S = 70/70-nm finger-type capacitors. The better programming speed and 10k cycles' endurance are confirmed in W/L = 70/70-nm memory array.