Origin of Stress Memorization Mechanism in Strained-Si nMOSFETs Using a Low-Cost Stress-Memorization Technique

Implementation of strained-Si MOSFETs with optimum low-cost stress-memorization technique for a 40-nm technology CMOS process was demonstrated. Devices fabricated on (1 0 0) substrate with 〈1 0 0〉channel orientation provide additional 8% current drivability improvement for strained-Si nMOSFETs without any degradation of pMOSFETs performance. The stress-memorization technique (SMT) mechanism was experimentally verified by studying the impact of layout geometry (length of source/drain LS/D and polyspacing) on the device performance. In the SMT devices with L S/D down to 0.11 μm and polyspace reduced to 120 nm, no obvious current improvement and more performance degradation are observed compared with control device (only strained contact etch-stop layer), indicating that the benefit of the SMT is substantially eliminated and showing that the SMT-induced stress is mainly originated from the source/drain region in our case.