Grain Size Engineering Using Amorphous-Ge/Si Stack to Enhance Channel Mobility for NAND Flash Memory

We demonstrated that polycrystalline-Si (poly-Si) channel mobility could be significantly enhanced through a combined effect of grain size engineering and Ge diffusion into the poly-Si channel. By crystallizing an amorphous-Ge/Si stack via thermal annealing, grain size enlargement and Ge diffusion occur together, resulting in an increase of the channel mobility of up to lpzrptsim100%. The enhanced poly-Si channel mobility improved the program and erase speeds by 55.8% and 30.5%, respectively, with no adverse effect on retention and endurance characteristics.