Accuracy of channel resistance and current gain methods of L/sub eff/ extraction

In this paper, we report a physically based interpretation of the MOSFET effective channel length, L/sub eff/. L/sub eff/ of a MOSFET is usually extracted from measurements of the linear region current gain (1/K method) or the linear region resistance (resistance method) on transistors with different gate lengths. We find that the extracted L/sub eff/ of a submicron lightly doped drain/source (LDD) MOSFET is strongly influenced by diffusion of minority carriers (electrons for NMOSFETs) from the gate-controlled LDD overlap region into the inversion layer. This changes the resistance of the inversion layer at the source/drain ends and thus causes the extracted L/sub eff/ to deviate from the metallurgical channel length, L/sub met/. The impact of minority carrier diffusion is stronger for shorter channel lengths; therefore, the extracted /spl Delta/L(=L/sub gate/-L/sub eff/ where L/sub gate/ is the drawn gate length) increases with decreasing gate length. The choice of gate lengths used in L/sub eff/ extraction will, thus, influence the value for L/sub eff/. MINIMOS 2D simulations have been used to study this effect. The results have been confirmed by actual measurements on submicron LDD MOSFETs. This analysis has been used to select the best choices of L/sub gate/ and bias condition to minimize errors in the measurement of L/sub eff/.< >