A study on the impact of processing parameters on low-voltage power MOSFET

Power MOSFET is the most commonly used power device due to its low gate drive power and fast switching speed compared to the existing power biplar transistor.It features a vertical structure with source and drain on opposite sides of the wafer to support higher current and voltage.The performance of power MOSFET is restricted by the internal resistance. A careful optimisation of the gate width (W G ) is required to minimise the internal resistance.Moreover, the doping concentration of N-epitaxial drift region and its thickness are chosen to obtain the desired breakdown voltage. In the device designed to support low voltage (<50 V), the doping concentration of the P-base region is comparable with the doping concentration of the N-drift region to support part of the applied voltage. The maximum doping concentration of the P-base region must be chosen to attain a threshold voltage for low voltage power MOSFET in the range of 1 - 2 V. In this study, the vital parameters in manufacturing the power VD-MOSFET,such as P-base and N-drift doping concentrations, thickness of N-drift region, and gate width are investigated. The impact of those parameters on the threshold voltage,breakdown voltage and internal on-resistance is recorded and analysed. The VD-MOSFET model used in this study is capable to withstand the breakdown voltage less than 30V. The model is simulated using 2D device and process simulation software from SILVACO; ATLAS and ATHENA. In the simulation, one parameter is varied, while the rest are kept constant.It is shown that, P-base doping concentration is significant in determining the threshold voltage.The threshold voltage is proportional to
the P-base doping concentration.On the other hand, the breakdown voltage is inversely proportional to the N-drift doping concentration.Thicker N-drift region may support higher breakdown voltage, but will increase the internal on-resistance.