碳化硅离子注入缺陷的形成、演化机理及其对表面润湿性的影响

Both surface wetting and heterogeneous bonding of SiC ceramic are important issues whether the SiC serves as the high-temperature structural material or as the third-generation semiconductor. The wetting and bonding are usually realized by means of strong interfacial chemical interactions due to the strong covalent bond of SiC, however, the resulting highly brittle and high-resistance reaction layer cause a negative impact on the mechanical and electrical properties of the interface. So, surface modification of SiC by ion-implantation is one of the effective strategies to solve this problem. In this project, the SiC single crystal is first implanted with Pd, Ag and Ar ions, respectively, resulting in a large number of microdefects in the crystal surface layer, which brings about the increase of surface energy, so that good wetting of Ag or Al on the SiC ceramic is achieved. On the other hand, in order to remove or reduce the microdefects, a high-temperature annealing is employed to make the implanted ions migrate to the crystal surface, as a result of the improvement of the mechanical and electrical properties of bonding interface. In this project, we focus on the formation, evolution and healing processes of surface microdefects of SiC as well as their controlling, and investigate the influence rules and mechanism of defects’ features on the surface wettability of SiC ceramic. After the foregoing investigations, the formation and evolution rules of microdefects will be illuminated, the relationship between the surface microdefect characteristics and the metal/ceramic wettability will be established, and the essential mechanism for the ion-implantation improving the metal/ceramic wettability will be clarified. This research can provide a new experimental and theoretical guidance to SiC semiconductor device, ceramic brazing and electronic packaging.

碳化硅无论作为高温结构材料还是第三代半导体，其表面润湿和异质连接均是重要问题。由于其强共价键特征，通常借助强烈的化学相互作用来实现润湿和连接，但其形成的高脆、高阻反应层对界面力学和电学性能均产生不利影响。对碳化硅进行离子注入表面改性，将是解决这一难题的有效方法之一。本研究拟对SiC单晶分别离子注入Pd\Ag\Ar，在表层形成微观缺陷，缺陷导致表面能提升，实现Ag、Al在其表面的润湿。另一方面，拟通过高温弛豫退火，驱使注入离子向表面迁移，消除或减少深层缺陷，进一步提高结合界面力学和电性能。重点研究离子注入SiC表面微观缺陷的形成、演变、消退过程和调控方法，考察分析缺陷演化对表面润湿性的影响规律和机理。经过研究，建立衬底表面缺陷特征与金属/陶瓷润湿性之间的关联性，揭示离子注入影响金属/陶瓷润湿性的本质机理。该研究可为碳化硅半导体器件、陶瓷钎焊、电子封装等领域提供新的技术思路和理论基础。

为提高SiC陶瓷与金属异质界面结合，同时结合离子注入技术的优点，本项目在SiC单晶表面进行离子注入改性。利用RBS/C、AFM、XPS、拉曼光谱、蒙特卡罗模拟等手段分析了离子注入Pd、Co、Ni、Si前后SiC单晶的表面特征，主要考察了表面极性、Pd离子注入、Si含量和合金元素添加（如Cu, Mg, Zn）对Al-Si/SiC体系的润湿和界面行为的影响，研究了Si离子注入和Al含量对Cu-Al/SiC体系润湿和界面行为的影响。同时，基于第一性原理计算，研究了氢钝化和硅重构6H-SiC (0001)表面空位缺陷的形成、稳定性及演化机制，以及SiC表面本征与掺杂点缺陷对其电子性质的影响。结果表明: 离子注入能一定程度上增加SiC衬底表面粗糙度，使SiC衬底表面产生大量的高浓度缺陷（空位和晶格畸变），并部分地转为非晶态，也增加了衬底固-气表面能。Pd离子注入能明显改善纯Si Al-(5,10,12)Si 和Al-10Si-4Cu合金对SiC的润湿性，恶化纯Al和Al-12Si-2Mg合金对SiC的润湿性，但几乎不影响Al-(20,30)Si 和Al-10Si-10Zn合金对SiC的润湿性。离子注入Si能使纯Cu对SiC陶瓷由几乎不润湿转变成优良的润湿性，且随着Al含量的增加，Cu-Al/SiC体系润湿特征由严重石墨化到非反应、低反应和高反应依次转变。硅重构表面SiC单空位缺陷的形成能小于氢钝化表面，而VSi和VC空位缺陷在不同Si-C双层中出现的几率取决于其形成能大小。空位缺陷形成能与缺失原子数平方根成正比关系，即：Ef ~ n1/2，表明6H-SiC(0001)表面多缺陷的演化遵守二维演化规律。表层和内层的本征点缺陷对二维SiC电子性质的影响接近，其中反位缺陷和碳间隙缺陷的跃迁能级更接近带隙边缘，使得VBM附近的EF上移诱导产生n型传导性。Ag掺杂缺陷的电子局域性更强，对电子性质的影响较弱，而N掺杂缺陷的跃迁能级离VBM更近，更易影响SiC电子性质。总之，通过本面上基金项目研究，一定程度上揭示了SiC表面微观缺陷的形成和演变过程，衬底表面缺陷特征、离子注入工艺与金属/SiC润湿性之间的关联性，该研究可为碳化硅半导体器件、陶瓷钎焊、电子封装等领域提供新的技术思路和理论基础。