| When people began to explore the application of Silicon carbide high temperature devices,they concluded that the high-temperature thermal stability of metal-semiconductor Ohmic contact decreased the reliability of SiC devices,increasing the cost of devices fabrication and reducing the working time of devices in high temperature environments.Therefore,SiC high-temperture Ohmic contact has attracted more and more people's attention.From now,although rsearchers have fabricated Ohmic contact with excellent contact properties in room temperature by selecting the Ohmic contact system and annealing process parameters,high-temperature Ohmic contact system needs to be investigated further.Centred on these problems that existed in Ni/SiC Ohmic contact,the paper proposes the bilayer metallization system?A,Ni?/SiC to solve these problems.The main research results are as follows:The research shows that these problems existed in Ni/SiC systems by experiments:rough contact surface;unevenly distribued Ohmic contact layer;the segregation of excess carbon;and the formation of Kirkendall voids at the interface.Then,to solve these problems,metal layer A should satisfy the following conditions:reducing the reaction speed,suppressing the segregation of carbon cluster by absorbing free carbon to generate the stable carbide.Besides,the thermal expand coefficient of products should match with the substrate.At last,according to the reported literatures,we design a series of experiments to study?Ta,Ni?/SiC and?W,Ni?/SiC systems.From the perspective of surface morphology and electrical characteristics,we study the Ohmic contact properties of?Ta,Ni?/SiC.The investigation shows that Ta cannot absorb free carbon in Ni/Ta/SiC system.In addition,large grains formed on the surface of Ta/Ni/SiC after annealed at 1000?C,causing the failture of wire-bonding.Therefore,heavy metal?Ta?cannot improve the Ohmic contact property of Ni/SiC.According to the same method,we study the Ohmic contact properties of?W,Ni?/Si C and conclude the final metal layers of W?30 nm?/Ni?56nm?/SiC.With the same process parameters,metal W reduces the sample surface roughgness of Ni/SiC from 31 nm to 8 nm.The specific contact resistivity of W/Ni/SiC is 3.2×10-5??cm2,which is smaller than Ni/SiC(4.2×10-4??cm2)at the same annealing process.We analyze the special roles of W in the system of W/Ni/SiC by Atomic Force Microscope?AFM?,Transmission Electron Microscope?TEM?,Raman Spectra and X-ray photoelectron spectroscopy?XPS?:W decreases the reaction velocity between Ni and SiC,reducing surface roughness of the sample;W combines with free carbon to form WC,reducing the content of carbon;the thermal coefficient of WC distributed at the interface matches with the substrate,suppressing the formation of interfacial voids.Besides,we finish successfully the wire-bonding of Au/Pt/W/Ni/SiC.The results of aging test show that the specific contact resistivity of Au/Pt/W/Ni/SiC increases from 1.3×10-4??cm2 to 1.3×10-3??cm2 after aged 1000 h in the air of 300?C.On the contrary,the specific contact resistivity of Au/Pt/Ni/SiC increases from 10-4??cm2 to 10-3??cm2 after aged 400 h at the same environment.Hence,W/Ni/SiC have solved these probles existed in Ni/SiC Ohmic contact so that it has important application value. |
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