COMPARISON OF MEASUREMENT TECHNIQUES FOR GATE SHORTENING IN SUBMICROMETER METAL-OXIDE-SEMICONDUCTOR FIELD-EFFECT TRANSISTORS

In this paper, various methods of evaluating the electrical channel le ngth change (or gate shortening) as a result of applied gate voltage i n sub-micrometer metal oxide semiconductor field effect transistors (M OSFETs) are investigated and the method best suited for such short cha nnel length devices is reported. Studies were performed on n-channel t ransistors (n-MOSFETs) fabricated using X-ray and optical lithography and having channel lengths in the range of 0.4 to 4 mum and 1.5 to 10 mum respectively. The effective channel lengths were extracted from th e current-voltage (I-V) measurements. The measurements were made for d ifferent low and high sets of gate voltages. In comparing various meth ods it was found that the method due to Terada and Muta, and Chern et al. gave accurate results consistently for short channel MOSFETs, wher eas the Whitfield method gave accurate results only for larger channel length MOSFETs. The accuracy of the Whitfield method is sensitive to applied gate voltage during I-V measurements. The Peng and Afromowitz method is unsuitable for finding the effective channel length of sub-m icrometer MOSFETs especially if the MOSFETs have high values of extern al resistance.