碳化硅晶体中穿透位错缺陷的甄别及其控制机制研究

SiC power devices with higher blocking voltage, lower loss, and higher efficiency performance, bring about technological innovation for the development of power electronic. Based on outstanding performance advantages, the main development direction of power devices is aimed at SiC material. However, there are still a large number of dislocation defects in SiC single crystals, restricting SiC as a mature material for further mainstream higher power device applications (such as ultra-high voltage DC power transmission and smart grid field)..In this study, we carry out the investigation of the discrimination of threading dislocation defects in SiC single crystals and its control mechanism. In-situ observation and tracking of the formation and development of dislocation etch pits are investigated by laser confocal microscopy and scanning electron microscopy. Based on etch pit sectional view information and dislocation stress field characteristics, the corresponding relationship between the cross-section evolution process of the corrosion pit and the type of dislocation will be established with a large number of statistical results. The characteristic parameters of various types of corrosion pits are extracted and the evolution model of threading dislocation corrosion pit is established to identify various types of threading dislocation defects. Transmission electron microscopy is used to confirm the dislocation categories. Based on the anisotropy of growth rate and the nucleation mechanism of vapor phase growth system, the lateral growth of SiC crystal under physical vapor transport will be studied using patterned SiC seed and selective-area preferential nucleation growth method. The distribution and density of threading dislocations in the corresponding lateral growth regions will be investigated to conclude the control law of threading dislocation defects by the lateral growth process of SiC single crystal, which lays on a theoretical basis for the performance improvement of SiC substrates.

SiC功率器件具有高耐压、低损耗、高效率特性，给电力电子带来重要技术革新，成为下一代功率器件的主要研究方向。然而SiC衬底中高密度的位错缺陷，阻碍了其在高压大容量方面的应用（如超高压直流输送电和智能电网领域）。.本项目开展SiC晶体中穿透位错缺陷的甄别及其控制机制研究。采用激光共聚焦显微镜和扫描电镜原位观察、跟踪位错腐蚀坑的形成与发展，结合腐蚀机理与位错应力场特点，分类统计腐蚀坑截面形状及其演化过程与位错类型的对应关系，提取出腐蚀坑的特征参数，建立位错腐蚀坑演化模型，甄别出各类型的穿透位错缺陷，并借助透射电镜对位错类别进行确认。基于生长速率各向异性规律和气相生长系统成核机制，采用图形化籽晶和选择区域优先成核生长方法，研究SiC单晶的横向生长规律，统计分析相应横向生长区域穿透位错分布及密度，明确SiC晶体的横向生长过程对各类型穿透位错缺陷的控制规律，为SiC衬底和器件性能提升奠定理论基础。

SiC单晶具有优良的电学、热学和力学性能，是制备高温、高频、大功率、高压器件的理想材料，随着新能源汽车市场需求的快速爆发，为提升整车续航能力、降低重量，就需要使用SiC MOSFET的功率模块作为逆变器，提高能源转换效率。因此，对大尺寸、高质量的SiC衬底材料的需求潜力巨大。然而SiC衬底中高密度的位错缺陷，制约了SiC材料在电子器件特别是SiC高功率器件中更广泛的应用。本项目开展了SiC晶体中穿透位错缺陷的甄别及其控制机制研究。利用熔融KOH腐蚀SiC衬底观察穿透型位错，采用激光共聚焦显微镜原位观察、跟踪位错腐蚀坑的形成与发展，研究SiC单晶衬底的腐蚀规律。根据腐蚀坑的形貌演变和截面形状，共获得三种类型的腐蚀坑，结合位错理论中的应力场分析，确认了不同类别腐蚀坑对应的穿透位错类型。制作了图形化SiC籽晶，使得台面侧壁显露面为{11-20}和{1-100}非极性面，研究了图形化籽晶法横向生长规律，获得了晶向、生长温度及生长压力对横向生长速率的影响规律，腐蚀结果显示在沟槽横向生长区域相比台面垂直生长区域穿透位错密度明显降低。利用籽晶背部两种不同热导率物质的周期性分布，调制SiC籽晶表面温度场分布，达到控制驱动力场的目的，强制在预定义图形对应过饱和度区域优先成核，实现了SiC晶体生长过程中选择区域优先成核生长，腐蚀结果显示穿透位错分布与籽晶背面制作图形的排布及边界一致，横向生长区域穿透位错密度明显降低。本研究工作为国内低缺陷密度SiC单晶生长提供了理论基础，以期缩小国内在SiC单晶衬底位错缺陷研究方面与国外之间的差距。