Investigations On SiC Super Junction Schottky Diodes

Due to their superior physical properties,including wide bandgap,high critical electric field,high thermal conductivity and high saturation carrier velocity,silicon carbide has become a promising candidate for next-generation power semiconductor devices.Decreasing the specific on resistance is a major goal for SiC unipolar device optimization.During the past 30 years,the conducting performances of SiC unipolar power devices have been improved continually but are limited by the theoretical one dimensional unipolar limit of SiC material.Super Junction(SJ)concept is expected to be proved an effective way to break this theoretical SiC unipolar limit.The two mature Si-based SJ fabrication techniques,namely,multi-epitaxy and trench-and-epi-regrowth,cannot be directly applied to SiC material due to the processing difficulties and high costs.Therefore,this thesis proposes a novel trench-etching-and-sidewall-implant technique and carries out a systematic theoretical and experimental investigation on this novel technique.The main contributions of this thesis include:1.This thesis proposes a novel trench-etching-and-sidewall-implant technique to realize SJ concept in SiC material.The voltage rating can be increased by increasing the trench etching depth rather than increasing the multi-extaxy repeating times.The compensation dopants can be incorporated by ion implantation rather than epitaxy regrowth.This technique provides the most feasible and effective path for the initial experimental exploration of SiC SJ devices.2.This thesis carries out a comprehensive design study on SiC trench SJ devices,analyzes the impact mechanism of key structure parameter on device electrical performances and proposes a novel technique to ajust charge compensation by altering annealing temperature.By thoroughly studying the influences of key structure paramters,including P region doping concentration,mesa width,trench depth and sidewall angle,the proposed SiC trench SJ devices are theoretically shown to be capable of breaking the theoretical one dimensional unipolar limit of SiC material.Charge balance target has been achieved in our experiment,thus verifying the feasibility of the anneal-temperature-adjustment design.3.This thesis experimentally fine-tunes the etching process for SiC trench SJ devices for the first time.The influences of typical trench morphology flaws,including micro-trenches,trench corner bumps and sidewall roughness,on device reverse blocking characteristics are studied.By fine-tuning the ICP etching recipes and etching mask process,favorable 6?m-deep micro-trench-free trench profiles with aspect ratio above 2:1 are achieved.The density of corner bumps and sidewall roughness can also been well controlled.Baed on the above contributions,this thesis successfully reported the first functional SiC super junction devices,1.35kV SiC SJ Schottky diodes.The measured device specific on-resistance was 0.92m?·cm2,which successfully breaks the theoretical one dimensional unipolar limit of SiC material.This thesis sufficiently proves the feasibility and effectiveness of adopting trench-etching-and-sidewall-implantation technique to realize SJ theory in SiC power devices.Its results could provide useful references for the future development of SiC-based SJ devices towards higher voltage rating and more advanced structure.