Research On Substrate Termination Structure Based On Curved Junction Extension

Generally, interdigitated layout is adopted for high voltage LDMOS which used as switching transistor to satisfy the current demand. One problem that limits the BV of the LDMOS transistor is the concentration of the electric field at the tip of source fingers with small curvature radius. In this thesis, a substrate termination structure based on curved junction extension is proposed to ameliorate curvature effect. A slightly doped P-sub, which inserted between heavily doped P-body and N-drift in the curved junction, alleviates electric field crowding at the abrupt P-body/N-drift junction, thus avoiding the premature avalanche breakdown. The fabrication of an LDMOS with the proposed substrate termination structure is compatible with the standard CMOS process. An LDMOS with substrate termination structure is promising for it can withstand high voltage without increasing the die size and manufacturing cost of the transistor. A 786 V Triple RESURF LDMOS with ultra-low specific on-resistance and an 800 V SJ LDMOS are experimentally obtained.1. substrate termination structure for Triple RESURF LDMOSIn the curved source part, substrate termination structure is adopted to reduce the electric field crowding and achieve high BV. In the straight edge part, Triple RESURF LDMOS can withstand high BV and obtain low Ron,sp according to the RESURF principle. The dopant concentration of deep N-well and P-top is analyzed to study its influence to the BV and Ron,sp of the transistor. The length of source and drain field plate, the length LP at the substrate termination region are also analyzed. The transitional region between the straight junction region and curved junction region is simulated using 3D device simulation software to study the relative position of deep N-well and P-top. Finally, a 786 V Triple RESURF LDMOS with Ron,sp of 110 m?·cm2 is experimentally obtained at a drift length of 65 μm, which validates the substrate termination structure.2. substrate termination structure for SJ LDMOSIn the curved source part of SJ LDMOS, substrate termination structure is also adopted to reduce the electric field crowding and achieve high BV. In the straight edge part, flat and uniform electric field distribution can be achieved by mutual depletion of the P/N pillars, resulting in high BV in SJ LDMOS. At the same time, heavily doped N pillar reduces the Ron,sp. The dopant concentration of the drift region is analyzed and optimized, as well as the dopant concentration, width, junction depth, and sequence of the P/N pillars. Finally, an 800 V SJ LDMOS is experimentally obtained at a drift length of 70 μm, which validates the substrate termination structure.