Threshold-voltage analysis of short- and narrow-channel MOSFET's by three-dimensional computer simulation

In small size MOSFET's, short- and narrow-channel effects simultaneously occur. There is a mutual dependency between these effects when the source-to-substrate bias increases or the channel stopper impurity dose under the field oxide surrounding the active region becomes dominant. A three-dimensional numerical program, based on the finite difference method, has been developed to analyze the threshold-voltage changes due to the small size effect. A sufficient convergence rate with acceptable memory size is obtained from optimum node discretization and an initial solution guess with sophisticated boundary conditions. The simulation results are compared with experimental data obtained from actual devices. Good agreement has been obtained on the threshold-voltage change with the channel width, taking into account an accurate QSSprofile. Some numerical and graphical outputs of the device simulator explain the mechanism of small size effects.