Impact from JFET Region Doping on Characteristics of Power MOSFETs

With a fixed breakdown voltage of the power MOSFET, the on-state resistance is always optimized by introducing a heavy doping concentration into the JFET region. This heavy doping concentration can be accomplished by ion implantation and following corresponding thermal steps. The implanted atoms distribute in a related range of depth. This phenomenon will make compensation of the p-type impurities in base regions. Thus the threshold voltage and blocking capability of the device will be different from the intended targets. In this paper, analytical and simulation study are made to analyze the impact from JFET region doping on the characteristics of power MOSFETs. Process parameters like implantation dosage and drive-in temperature are the key factors which have important influence on the final device characteristics. With fixed drive-in temperature and time, bigger implantation dosage will lead a bigger compensation of the p-type atoms in base regions. Then the threshold voltage and the breakdown voltage will be smaller. With a fixed implantation dosage, the higher drive-in temperature will make the atoms diffuse deeper. If the junction depth of the JFET region doping exceeds the junction depth of the base regions, the breakdown voltage will decrease obviously. So the process parameters for JFET region doping should be adjusted carefully.