Research Of Superiunction Power MOSFETs

Power semiconductor devices are widely used in electricity, energy source, consumer electronics, aerospace and other fields, and they are given more and more attention in recent years with the rise of new energy sources and energy saving industry. For high voltage power devices, the contradiction between breakdown voltage and on-resistance always exists, and there is a limit called "silicon limit". The "Superjunction(SJ)" breaks the silicon limit; it turns the relationship between on-resistance and breakdown voltage from the traditional2.5times into a linear relationship, and this greatly reduces the devices’on-resistance.In this thesis, the superjunction VDMOS and superjunction LDMOS are included. VDMOS, as a discrete device, is widely used due to excellent performance, simple process and so on. LDMOS, owing to its flexibility in being easily integrated into standard low-voltage CMOS processes, is broadly applied in Smart power IC. The600/700V series of superjunction power devices have a wide range of applications in the power adapter and other fields.The contents of this thesis include:(1) A600V-class SJ-VDMOS is proposed. Some key points, related problems and solutions encountered in the design are also presented. Three patterns of superjunction structure, the strip, square and lattice, are compared, and it is found that square pattern has the strongest capacity of charge compensation. The sidewall of the deep trench is not ideally vertical, and the trench slope will lead to charge imbalance, resulting in lower breakdown voltage; and it is noted that the positive slope case and negative slope case have a different impact on the breakdown voltage:this phenomenon is analyzed. The solution of the trench slope is also proposed in this thesis. The device is successfully fabricated, and the test result shows that the breakdown voltage is643V and specific on-resistance3.6Ω*mm2, which is similar to the performance of the Siemens’s first CoolMOS. (2) A700V-class SJ-LDMOS is proposed. Taking the process variation into account, N-well dose should be selected basing on the trade-off between on-resistance and process tolerance. The source fingertip in the layout design which is the crucial point to obtain high breakdown voltage and low on-resistance is also discussed in this thesis; the small radius is the cause of this fingertip effect. A buffer region is created to alleviate the breakdown at the source fingertip. Finally, detailed comparisons between this device and Double RESURF device are done with simulation tools, indicating that this structure greatly enhances the current capacity and will not impact the other performance parameters, such as SOA.