Atomic Layer-deposited Si-nitride/SiO2 stack gate dielectrics for future high-speed DRAM with enhanced reliability

Atomic layer-deposited (ALD) Si-nitride/SiO₂ stack gate dielectrics were applied to high-performance transistors for future scaled DRAMs. The stack gate dielectrics of the peripheral pMOS transistors excellently suppress boron penetration. ALD stack gate dielectrics exhibit only slightly worse negative-bias temperature instability (NBTI) characteristics than pure gate oxide. Enhanced reliability in NBTI was achieved compared with that of plasma-nitrided gate SiO₂. Memory-cell (MC) nMOS transistors with ALD stack gate dielectrics show slightly smaller junction leakage than those with plasma-nitrided gate SiO₂ in a high-drain-voltage region, and have identical junction leakage characteristics to transistors with pure gate oxide. MCs having transistors with ALD stack gate dielectrics and those with pure gate oxide have the identical retention-time distribution. Taking the identical hole mobility for the transistors with ALD stack gate dielectrics to that for the transistors with pure gate oxide both before and after hot carrier injection (previously reported) into account, the ALD stack dielectrics are a promising candidate for the gate dielectrics of future high-speed, reliable DRAMs.