Research On Gate Dielectric And Schottky Barrier Of Silicon Carbide Devices

SiC MOSFET devices and SiC SBD devices are the most widely used devices based on silicon carbide materials.However,the gate oxide layer of the MOSFET device has the problems of high leakage and low breakdown,and the Schottky contact in the SBD device has the problem of unevenness of the barrier.At present,because high-k dielectric materials such as Hf O₂,Al₂O₃,and Ti O₂ have the advantages of high dielectric constant and thermal stability,it is the key to research to improve the low breakdown electric field and high leakage of MOS capacitors.In addition,the good interface passivation characteristics of high-k dielectrics are also a way to improve the unevenness of the Schottky barrier.This paper studies and uses the atomic layer deposition(ALD)technology to deposit and grow Al₂O₃ and Hf O₂ high-k dielectric films applied to SiC MOS devices,thereby improving the high leakage current and low breakdown electric field problems of traditional Si O₂ dielectric structures.Through C-V curve parameter extraction and curve trend analysis,it is found that the flat band voltage,hysteresis voltage and interface state density of Hf O₂/Al₂O₃/Si O₂/SiC are higher than those of Hf O₂/Si O₂/Al₂O₃/SiC structure.In addition,the TEM test found that the interface uniformity of Al₂O₃/SiC is higher than that of Si O₂/SiC,and there are black carbon clusters at the Si O₂/SiC interface,indicating that Al₂O₃/SiC has good interface characteristics.After comparing Hf O₂/Al₂O₃/Si O₂/SiC and Hf O₂/Si O₂/Al₂O₃/SiC after annealing at 300°C and 400°C,it was found that the interface characteristics at 400°C were significantly degraded.Through the I-V curve,it is found that compared with Si O₂/SiC MOS capacitors,the leakage current of the high-k dielectric stack structure is reduced by 1-2 orders of magnitude,and the breakdown electric field is increased by more than three times.Especially the breakdown electric field of Hf O₂(50nm)/Si O₂(2nm)/Al₂O₃(2nm)/SiC reached 21.5MV/cm.A layer of Al₂O₃ film is grown between Ti metal and 4H-SiC to form a MIS Schottky diode.Through the electrical tests of C-V and I-V,it is found that on the one hand,there is a dipole at the contact interface between the two due to the insertion of the high-k dielectric.The generation of the layer,the dipole layer will cause a difference in the potential on both sides of the interface and thus produce a modulation of the Schottky barrier height.On the other hand,due to the good interface passivation effect of Al₂O₃ film and the TEM test shows that the insertion of high-k dielectric reduces the diffusion of Ti into SiC,thereby reducing the silicide formed by solid-state reaction,and finally improving the uniformity of Schottky interface.