化学溶液沉积在单晶硅基底上外延生长立方结构AlN薄膜的界面结构控制及其导热性能研究

The high symmetry of cubic AlN crystals will reduce the phonon scattering greatly, leading to a higher thermal conductivity. At present, the preparation of metastable cubic AlN thin films on silicon substrate is still in the exploratory stage, and the factors affecting the thermal conductivity are not clear. The research proposal seeks to prepare the cubic AlN epi-films on Si (100) substrates by the Chemical Solution Deposition method. In order to optimize the interface structure, the MgO buffer layer were pre deposited on the silicon substrate achieving as texture transfer and atoms diffusion barrier. The valuable scientific information and deep mechanistic understanding are collected including the investigation of the influence of heat treatment on the evolution characteristics of precursor salts and the nitride product, the investigation of the process of AlN films epitaxial growth and the phase evolution，as will as the surface and interface structure in this process, the investigation of the influence mechanisms of oxygen atom on the epitaxial growth and thermal conductivity of cubic AlN film, the investigation of the influence of MgO seed layer density and MgO film thickness on the orientation of AlN films and the effect as an atom diffusion barrier. So as to reveal the orientation growth mechanism of AlN epitaxial films, and clarify the intrinsic relationship between the precursor salt properties, the heat treatment process and the orientation growth of AlN grains. Finally, the influence mechanism of micro orientation on the thermal conductivity of AlN thin films was obtained by the characterization of macroscopic and microscopic structure.

立方结构 AlN薄膜的高度对称性会极大的降低声子的散射，导致更高的热导率。目前单晶硅基底上亚稳态立方AlN薄膜的制备还处于探索阶段，影响薄膜热导率的因素也不确定。本项目提出采用低成本、溶液成分可控性强的化学溶液沉积法在单晶硅基底上制备立方结构的AlN外延薄膜，通过MgO过渡层结构的设计实现基底织构的传递和阻隔元素扩散的目的。项目主要研究热处理工艺对前驱盐体系的热分解特性和氮化产物成分演变的影响;研究AlN薄膜在厚度方向上的外延生长过程及该过程中成分和相的演变以及薄膜的表面、界面结构；研究氧对AlN薄膜的外延生长和导热性能的影响；研究MgO种子层密度和MgO薄膜的厚度对AlN薄膜取向的影响以及对原子扩散的阻隔作用。从而揭示AlN外延膜的取向生长机制，阐明前驱盐性质、热处理工艺及AlN晶粒的外延生长间的内在联系。结合宏观及微观取向结构的表征，获得AlN薄膜的微取向对热导率的影响规律。

立方结构 AlN的高度对称性会极大的降低声子的散射，导致更高的热导率。目前单晶硅基底上亚稳态立方AlN薄膜的制备还处于探索阶段，影响薄膜热导率的因素也不确定。本项目以尿素、双氰胺和三聚氰胺为氮源获得稳定的前驱溶液，采用该溶液制备了AlN纳米粉体，并且采用化学溶液沉积法在不同单晶基底上制备了立方AlN薄膜。对所制备材料的特性进行表征，结合工艺参数对性能的影响规律，对其生长机理进行阐述。.采用尿素为氮源在900℃获得纳米AlN粉体，前驱盐形成了尿素为配体的络合物，通过对尿素和铝盐含量的调控可以获得不同尺寸的球状颗粒；随着氮源含量的增加粉体的禁带宽度呈现线性增加趋势；采用双氰胺为氮源在900℃制备AlN纳米粉体，前驱盐混合后在温度驱动下分解、反应，AlN的获得是Al2O3被CxHyNz类产物氮化的结果。三聚氰胺与铝盐形成特殊络合产物，该络合物在1000℃直接获得AlN单晶，没有中间产物生成。 .三种氮源获得AlN粉体的机理与其热分解特性直接相关。反应产物都存在明显的残余碳，其中尿素为氮源制备粉体中非晶碳含量达到20%；抗水解性能显示采用尿素制备粉体的抗水解性能优于市场产品；氰胺类氮源制备粉体的光学带隙都出现先增加后降低的趋势，三聚氰胺制备粉体的光学带隙更接近AlN理论数据，与单晶粉体的获得有直接关系。.采用快速热处理的方法在700℃不同单晶基底(MgO(001)、Al2O3(0001)、Al2O3(10-10)，Si(001))上获得立方AlN相的多晶薄膜。单层薄膜厚度在50nm左右，薄膜外表层存在残余碳，随着膜层深度的增加逐渐出现立方AlN相，基底取向没有显示出对薄膜生长的影响。高温热处理时，硅单晶基底检测到SiC的强烈衍射峰，没有检测到SiO2的衍射峰，分析认为是前驱盐分解产物中高的非晶碳含量相关。采用激光导热法对有膜层和没有膜层的硅单晶样品进行热扩散系数的测试，硅单晶的热扩散系数为71.75 mm2/s，而涂覆薄膜样品的热扩散系数为75.16 mm2/s，薄膜对整个样品的导热性能有明显的贡献。薄膜热导率的表征以及生长机理相关研究在进展中。