Study On SiC MOS Interface Control Mechanism And Process With Alkaline Earth Metal Layer

Silicon carbide?SiC?has become the material of choice for a new generation of high-power devices because of its excellent physical properties such as large bandgap,high thermal conductivity,high critical electric field and high saturation drift velocity.However,the commercial market promotion of SiC MOS structure devices still has two technical challenges:one is low channel mobility,the other is the threshold stability and reliability of the devices,both of which are directly related to the MOS interface quality.In order to solve these problems,the research focuses mainly on reducing the density of states at interface through the formation of the gate oxide layer and the annealing process.In this paper,an alkaline earth metal Ba is used to form an interfacial layer at the interface between SiC and SiO₂,and the interface is controlled by passivation of Barium ions to improve the interface quality.First,the physical mechanism of Ba interface layer to improve the interface characteristics is studied theoretically.Many kinds of superlattice interface models are established,such as 4H-SiC surface model,interface model without transition layer,interface model with transition layer,and interface model with transition layer in which Ba is introduced.The calculation results of the 4H-SiC surface model show that the dangling bond of the Si surface is the main cause of the interface states.The comparative study of the SiC/SiO₂ interface model without transition layer and the interface model with transition layer shows that the transition layer consisting of SiC_xO_y substances will introduce a large number of interface states in the bandgap,resulting in a decrease in the calculated value of the band gap.The calculation results for the Ba-containing interface model show that the two kinds of interface structures with Si-Ba-O or O-Ba-O bond have a significant increase in the band gap.It makes a shift of the interface traps'energy levels away from the midgap.This shift of energy is enough to push the near interface traps away from the conduction band.Among them,the improvement effect of the interface model with the O-Ba-O bonding is more pronounced,which provides a theoretical basis for the formulation of the next experimental scheme.Then,an experimental scheme for forming a Ba interface layer?Ba IL?between SiC and SiO₂ was developed.A special kind of SiC MOS capacitor with Al/SiO₂/Ba IL/SiC/Ni structure and the traditional SiO₂/SiC structure are fabricated by magnetron sputtering.At the same time,several groups of comparative experiments are set up to study the influence of annealing temperature,thickness of Ba dielectric layer and different annealing atmosphere on the interface characteristics of SiO₂/Ba IL/SiC MOS capacitor.The interface quality and electrical characteristics of the samples are tested.The results of the ellipsometric test show that the thickness of the gate oxide layer will increase after annealed in the oxygen-containing mixed atmosphere at 950°C.This is because the pre-deposited Ba diffuses on the side toward the SiO₂ and absorbs oxygen to form the oxide of Ba.On the one hand,it has a metal-enhanced oxidation effect.However,after annealed in an oxygen-containing mixed atmosphere at 500°C,there is no change in the thickness of the gate oxide layer,indicating that the annealing in Ar+O₂ at 500°C may not effectively oxidize the Ba.The XPS test,C-V test,and I-V test are conducted on the MOS capacitor to obtain the interface material composition of different samples,important parameters reflecting the interface quality and J-E characteristic curves.The results show that the Ba element exists mainly in the form of simple substance after annealed in pure Ar atmosphere.Compared to500°C,the annealing temperature of 950°C will reduce the the quantity of Ba at the interface,the gate leakage has improved slightly.The increase in the deposition thickness of the Ba layer causes the diffusion of Ba throughout the entire gate oxide layer,making the gate leakage of the device more severe.The results of the subsequent oxygen-containing mixed atmosphere annealing experiments show that the Ba is mainly present in the form of BaO₂ after annealed in an oxygen-containing mixed atmosphere,and the presence of BaO₂ reduces the types of suboxides at the interface.The experimental results show that the interface quality of samples annealed in Ar+O₂?O₂ is 5%?mixed atmosphere is better than the sample without Ba IL annealed in the same annealing conditions.The C-V hysteresis is 34.7%lower and the interface state density is reduced by54.0%.At the same time,the gate leakage characteristic of the sample with Ba IL has also improved.The critical breakdown field increased from 7 MV/cm to 8 MV/cm@1?A/cm².The annealing effect of N₂+O₂?O₂ is 5%?mixed atmosphere is more obvious than that of Ar+O₂?O₂ is 5%?mixed atmosphere.