Novel cell transistor using retracted Si3N4-liner STI for the improvement of data retention time in gigabit density DRAM and beyond

In this paper, we propose a novel cell transistor using retracted Si₃N₄-liner STI (shallow trench isolation) for the enhanced and reliable operation of 256-Mb dynamic random access memory (DRAM) in 0.15-μm technology. As the technology of DRAM has been developed into the sub-quarter-micron regime, the control of junction leakage current at the storage node is much more important due to the increased channel doping concentration. With the decreased parasitic electric field at the STI corner using the retracted Si₃N₄-liner, the inverse narrow width effect (INWE) was significantly reduced. The channel doping concentration, hence, was lowered without degrading the subthreshold leakage characteristics and the channel doping profile was optimized from the viewpoint of the electric field at local areas in the depletion region. In addition to the optimized channel doping profile resulted in a dramatic increase in data retention time and device yield for 256-Mb DRAM. The proposed cell transistor can be extended to future high-density DRAMs in 0.13-μm technology and beyond