A 680 V LDMOS on a thin SOI with an improved field oxide structure and dual field plate

Abstract

A 680 V LDMOS on a thin SOI with an improved field oxide (FOX) and dual field plate was studied experimentally. The FOX structure was formed by an “oxidation-etch-oxidation" process, which took much less time to form, and had a low protrusion profile. A polysilicon field plate extended to the FOX and a long metal field plate was used to improve the specific on-resistance. An optimized drift region implant for linear-gradient doping was adopted to achieve a uniform lateral electric field. Using a SimBond SOI wafer with a 1.5 μm top silicon and a 3 μm buried oxide layer, CMOS compatible SOI LDMOS processes are designed and implemented successfully. The off-state breakdown voltage reached 680 V, and the specific on-resistance was 8.2 Ω·mm2.