Investigation of Metallized Source/Drain Extension for High-Performance Strained NMOSFETs

Extrinsic source/drain series resistance (R-SD) is becoming inevitably dominant in state-of-the-art CMOS technologies as the intrinsic device resistance continues to scale with channel length dictated by the Moore's Law. As a result, advanced scaling techniques to achieve a lower intrinsic device resistance become less effective, particularly for NMOSFETs. With an attempt to better understand R-SD impacts and identify the next key technology enabler, high-performance strained NMOSFETs featuring metallized (NiSi) source/drain extension (M-SDE) are investigated due to its cost-effective process and good short-channel scalability. The spacing between metallized extension and gate electrode edge is shown to play a very important role in RSD reduction and can significantly affect the electrical characteristics of M-SDE NMOSFETs. Tradeoff between R-SD reduction and device integrity like junction leakage and reliability is found when the extension-to-gate edge spacing is modulated. On the other hand, by optimizing the NiSi-to-gate edge spacing, M-SDE NMOSFETs exhibit a higher ON-current (ION) and a higher strain sensitivity while maintaining comparable drain-induced barrier lowering, subthreshold swing, I-OFF, and hot-carrier reliability as compared with the conventional SDE devices.