Modified Gate Re-Oxidation Technology for High-Performance Embedded Dynamic RAM by Self-Adjusted Gate Bird's Beak

Abstract

The modified gate re-oxidation is described, which is a very effective simple method of improving the memory retention characteristics of embedded dynamic random access memory (DRAM). This new method forms a gate bird's beak through furnace oxidation after the formation of a silicon nitride gate spacer. The amount of gate bird's beak formed by this method is self-adjusted according to the gate width of each transistor. Large gate bird's beaks are formed selectively for narrow gate transistors. Therefore, gate-induced drain leakage (GIDL) current is suppressed for DRAM cell transistors, without any negative influence on high-speed random logic transistors. The modified gate re-oxidation sample has much better hot carrier reliability than the conventional gate re-oxidation sample. There is almost no difference in the dielectric reliability of gate oxide between the modified sample and the conventional sample. Consequently, this new process realizes the ideal embedded DRAM that has both a highly reliable memory region and a high-speed logic region.