Research on interfacial defect clarification of silicon carbide semiconductor device oxide film using first-principle calculation analysis

近年来，有报道称用4H-SiC(0001)面(Si面)作衬底的沟槽MOS-FET沟道侧壁材料(11-20)面(A面)具有较高的沟道迁移率。为了研究非晶态SiO_2(a-SiO_2)层与A面碳化硅衬底之间的高沟道迁移率的原因，我们用计算机模拟建立了a-SiO_2/4H-SiC(11-20)原子界面结构模型，并对界面的原子结构和电子结构进行了估算。经过加热和淬火处理后，生成了界面粗糙的理论A面模型。在硅面模型中，出现在禁带中的一些缺陷能级在A面模型中并没有产生。特别是在硅面模型中，由于缺陷的能级正好位于碳化硅的导带下方，因此，由于缺陷的能级恰好位于碳化硅的导带之下，因此在硅层中产生的缺陷能级大大降低了沟道的迁移率。另一方面，在A-Face模型中，由于Si-C键位于碳化硅表面，缺陷的变形容易减小。因此，缺陷能级没有出现在A面模型的带隙中。结果表明，A面碳化硅界面高迁移率的原因是缺乏这一缺陷水平。

Recent years, it is reported that a high channel mobility is obtained in (11-20) face (A-face) of SiC which is used as trench sidewall of trench-gate MOS- FETs which uses 4H-SiC(0001) face (Si-face) for the substrate. To examine the reason for a high channel mobility at the interface between the amorphous SiO_2 (a-SiO_2) layers and the A-face SiC substrate, we generated the a-SiO_2/4H-SiC(11-20) atomic interfacial structure model with the computer simulation and evaluated the atomic and the electronic structure of the interface. The theoretical A-face model with rough interface was generated after the heating and quenching process. Some of the defect levels appeared in the bandgap in the Si-face model were not generated in A-face model. Especially, in Si-face model, the defect level, which is originated in the expanding Si-C bond, generated with Si in the SiC layer decreases the channel mobility very much because the defect has energy level just below the conduction band of SiC. On the other hand, in A-face model, it is considered that the distortion of the defect is reduced easily because Si-C bond is on the surface of the SiC layer. Therefore, the defect level did not appear in the bandgap in A-face model. It is suggested that the cause of high mobility on A-face SiC interface is a lack of this defect level.