Study of the effects of a stepped doping profile in short-channel MOSFETs

The performance of a stepped doping profile for improving the short-channel behavior of a submicrometer MOSFET has been analyzed in detail by using a quasi-two-dimensional (quasi-2-D) MOSFET simulator including inversion-layer quantization coupled with a one-electron Monte Carlo simulation. Several second-order effects, such as mobility degradation both by bulk-impurity and interface traps, carrier-velocity saturation, and channel-length modulation, have been included in the simulator. Very good agreement between experimental and simulated results is obtained for short-channel transistors. It has been shown that including a low-doped zone of convenient thickness next to the interface over a high doping substrate improves both the electron mobility and the threshold voltage of the device, while avoiding short-channel effects. The use of simulation has allowed us to study certain kinds of devices without needing to make them.