The Investigation And Optimization Of High-Voltage Power MOSFET Cell

This thesis mainly research of high-voltage Power MOSFET cell structure. Based on the cell structure parameters, a high breakdown voltage, low specific on-resistance, low specific gate-drain capacitance semi-super junction cell device is designed.Firstly, this thesis describes the principles of super junction and semi-super junction. The super junction devices can break the "silicon limits" theory, which make the relationship between resistance and breakdown voltage not only power of 2.5. Under the same voltage, on-resistance of super junction and semi-super junction is less than normal VDMOS devices. Compared with super junction devices, semi-super junction devices inherit the merits and reduce difficulty of process flow. Furthermore, semi-super junction devices improve the reverse recovery characteristics.Different from normal VDMOS devices, breakdown voltage of semi-super junction are beard by super junction structure and N type Bottom Assist Layer. It is well known that switching performance of power devices is determined by the gate-drain capacitance. In order to optimize the gate-drain capacitance, the doping concentration of P column and N column can be improved except for optimize gate oxide thickness. However, the study found that decrease of gate-drain capacitance will lead to increase of on-resistance.Through a great quantity of simulation, epitaxial layer thickness, doping concentration of epitaxial layer, length of gate, gate oxide thickness, mask window of boron ion implantation are selected. In addition, semi-super junction MOSFET devices are charge compensation devices. The balance of P column and N column is very important. If the charge balance is slightly worse, breakdown voltage will be dropped quickly. So this thesis makes a detailed study on super junction process flow. Three super junction process flows are used in common manufacturing process, just as multi-step epitaxial technique, multi-step ion implantation technique and trench etching and epitaxial filling technique. But compared with the third technique, the first two techniques are complex and high cost, the wavy and untidy edge of P column affects charge balance. It is easier to achieve charge balance by the third technique.Through trench etching and epitaxial filling technique, doping concentration and the depth and width of P column are selected. To ensure the equal width of P column and N column, charge balance can be achieved by setting same doping concentration. Then doping concentration of P column and N column will be selected through specific gate-drain capacitance and specific on-resistance product. Which can optimize specific gate-drain capacitance and specific on-resistance.Finally, a semi-super junction cell structure with breakdown voltage of 1023V, specific on-resistance of 43.31 mΩ·cm2, specific gate-drain capacitance of 0.29pF/cm2 is designed. Under the same epitaxial layer conditions, the breakdown voltage is increased by 107.1% compared with normal VDMOS structure, specific on-resistance is decreased by 19.0% and specific gate-drain capacitance is reduced by 99.5%. This can highlight the superiority of semi-super junction structure in this thesis and provide theoretical guidance for the practical production.