Study Of Preparation And Thermal Stability Of Ohmic Contact On 4H-SiC

Silicon carbide(Si C) is one of the key materials of the third generation semiconductors. Its value should be improved in the harsh environment of high temperature due to the performance advantages of Si C. In this paper, semi-insulating(SI) and the conductive 4H-Si C substrates are base material, photolithography process is used to pattern electrodes, and contact layer(s) is(are) deposited on the Si(0001) face of 4H-Si C by a magnetron sputtering method. The effect of the annealing methods on the contact properties on the semi-insulating 4H-Si C substrate and the effect of different annealing temperatures on the long-term thermal stability on the conductive 4H-Si C substrate were investigated, respectively.It is difficult to form ohmic contact Ni/4H-Si C by conventional rapid thermal annealing(RTA) on semi-insulating 4H-Si C substrate. However, the ohmic contact is formed for the first time by UV pulsed laser annealing(LSA), and specific contact resistance is 1.97×10-3Ω×cm2. A class 20 nm-thick 3C-Si C transition layer, which is near the side of 4H-Si C of the metal/Si C interface, is observed by high-resolution transmission electron microscopy(HRTEM) after LSA. The transition layer reduces interfacial contact barrier, enhances thermionic emission probability, and plays a key role on the formation of a semi-insulating Si C ohmic contacts.The Pt/Si/Ta/Ti electrode multilayer scheme is considered as a conductive 4H-Si C ohmic contact, and the performance of the contact is studied through different RTA temperatures. When the annealing temperatures are below 800°C, the contact isrectifying properties. Ohmic contact is formed in the range of 800 ~ 1000°C. As the annealing temperature increases, the specific contact resistance(ρc) is reduced. The lowest ρc is 8.2×10-6 Ω×cm2 at 1000°C. When the annealing temperature is further increased, it reverts to rectifying behavior exceeding 1050°C. The long-term thermal stability is evaluated by aging the annealed contact at 600°C in air. The 1000 ° C annealed the contact is the best performance initially. However, the ohmic property disappears, and it have the shortest life of the thermal stability after 48 hrs in aging experiment. 900°C RTA annealed sample is still kept ohmic behavior after 24 hrs aging in air at 600°C. The thermal stability is improved. Especially, the as-deposited contact property changes from the Schottky to ohmic after aging 24 hrs with specific contact resistance of 9.36×10-6 Ω×cm2, and shows stable ρcof 8.4×10-5 Ω×cm2 for more than 576 hrs. It shows the best thermal stability property. Cross-sectional morphology and elemental analysis of metal contact layer showed that the RTA temperatures have duality on the ohmic contact formation and degradation. On the one hand, with the increase of annealing temperature, the reaction between Ti and Si C is promoted, which conductive to the formation of low specific contact resistance ohmic contact. On the other hand, higher annealing temperature makes Ta and Ti diffuse to form alloy dendrite. The homogenization time through Ta diffusion is thereby decreased. When the Ta layer becomes loose, its function of oxygen diffusion barrier is partially disappeared and lead to rapid degradation of the ohmic contact.