Preparation And Study Of Tungsten Based 4H-SiC Schottky Diode

Silicon carbide（SiC）is widely used in high-temperature and high-voltage devices because of its excellent electrical properties,and has become a current research hotspot for semiconductor material.For SiC devices,the interface quality between metal and semiconductor will affect the electrical properties,and thus affect the practical application of the devices.In recent years,when studying 4H-SiC Schottky diodes,it has been found that solid-state reactions occur between the metal and SiC after high-temperature annealing,and there is barrier inhomogeneity at the contact interface,which leads to degradation of the electrical properties of the devices.Therefore,it is necessary to avoid excessive reaction at the Schottky diodes interface and improve the quality of the Schottky contact.In this thesis,several tungsten-based Schottky contact systems are proposed:W/4H-SiC,W-C alloy/4H-SiC,W/Al₂O₃/4H-SiC,and W/Ti/4H-SiC.The effects of different annealing temperatures or intercalation thicknesses on the Schottky contact characteristics are investigated.Then,the proposed alloy system and intercalation system are analyzed in comparison with the basic pure tungsten system by combining electrical tests and microstructure characterization.The important parameters of Schottky devices can be extracted by I-V and C-V tests,and the homogeneity of Schottky barriers is analyzed by I-V-T tests.Material characterization methods such as scanning electron microscopy（SEM）,transmission electron microscopy（TEM）and energy dispersive spectroscopy（EDS）are used to observe the surface and interface morphological changes of Schottky devices.In this thesis,the Schottky contact characteristics of W-C alloy/4H-SiC and W/4H-SiC are comparatively studied.The W-C alloy system has stable reverse leakage current,ideal factor closer to the ideal value,and smaller change rate of barrier height after annealing at different temperatures,where the optimal annealing temperature is 500°C.Combined with the material characterization comparison,the W-C alloy system can reduce the interfacial chemistry reaction and effectively improve the Schottky contact quality after annealing at 500°C.The breakdown voltage is increased to 1008 V for W-C alloy/4H-SiC SBD after adding field plate termination with Si O₂ as the dielectric layer.Finally,the Schottky contact properties of W/Al₂O₃/4H-SiC and W/Ti/4H-SiC were studied in this thesis,in which W/Al₂O₃（1nm）/4H-SiC exhibited better electrical properties after annealing at400°C and low surface roughness,which could form a clear and flat contact interface,so the insertion of high-k dielectric Al₂O₃ could effectively improve the W/4H-SiC potential barrier inhomogeneity problem.In contrast,W/Ti/4H-SiC undergoes elemental diffusion after high-temperature annealing,which intensifies the interfacial reaction and cannot improve the Schottky contact properties of W/4H-SiC.