Mosfet channel length: extraction and interpretation

Abstract

This paper focuses on MOSFET channel length: its definition extraction and physical interpretation. After a brief review of the objectives of channel length extraction and previous extraction methods the principle and the algorithm of the latest "shift and ratio" (S&R) method are described. The S&R method allows the channel mobility to be an arbitrary function of gate voltage and at the same time provides a way to determine the threshold voltage of shortchannel devices independent of their parasitic resistances. Accurate and consistent results are obtained from nMOSFET and pMOSFET data down to 0.05 //m channel length. By applying the S&R method to model generated currentvoltage (IV) curves it is shown that the extracted channel length should be interpreted in terms of the injection points where the MOSFET current spreads from the surface layer into the bulk sourcedrain region. This implies significant degradation of shortchannel effects (SCE's) if the lateral sourcedrain doping gradient is not abrupt enough. Several remaining issues including errors due to channellengthdependent mobilities difficulties with lightlydoped drain (LDD) MOSFET's and interpretation of capacitancevoltage (CV) extracted channel lengths are discussed in Section VIII. © 2000 IEEE.