Analysis of Si-SiO₂ Interface Using Charge Pumping Method with Various Capping Materials between Gate Stacks and Inter Layer Dielectric in NAND Flash Memory

We report the dependence of Si-SiO2 interface trap density after Fowler-Nordheim (F/N) stress on various capping materials between gate stacks and an inter layer dielectric (ILD) in a NAND Flash memory cell. The interface trap density was characterized by charge pumping method (CPM). When the capping layer is an oxide, the Nit after F/N stress is approximately 2 x 10(11) cm(-2), which ' is about 50% smaller than that with a nitride layer. We found that the oxide layer causes compressive stress whereas the nitride layer causes a relatively high tensile stress in the underlying substrate by measuring the warp change of the substrate. To correlate the interface state density and data retention. characteristics, we measured V-t shift after high-temperature baking. When an oxide capping layer is used, the retention characteristics of memory devices are greatly improved compared to the nitride capping case. These results show a good correlation between the interface characteristics and mechanical stress behaviors.