高光效LED氮化镓衬底的无损伤机械-化学交互材料微观去除机制研究

High-luminaire-efficiency GaN-based LED has put forward a high request for the chemical mechanical polishing (CMP) quality of GaN homogeneous substrate. Due to the lack of the scientific understanding on the material microscopic removal mechanism of GaN under mechano-chemical interaction, the material removal rate is low and defect-control in global planarization is hard during CMP process of GaN. To solve this problem, we will study the mechanism of nondestructive microscopic material removal of GaN by single abrasive particle in the polishing fluid environment with atomic force microscopy and other equipment from microwear view. Firstly, material microscopic removal rules under mechanical interaction, chemical etching and mechano-chemical interaction will be investigated respectively. Then, combined with the analysis of chemical composition and lattice feature on material removal area, mechano-chemical interaction relationship, the dynamic balance mechanism of lattice damage generation and eliminatition under mechano-chemical interaction will be further studied. The nondestructive microscopic material removal mechanism of GaN via mechano-chemical interaction will be discussed. Finally, we will propose the nondestructive and high rate removing condition through optimization, and then carry out the experimental verification on CMP device. The expected results would not only enrich the basic theory on nanotribology and ultraprecision machining, but also help to provide theoretical guidance for high quality and high efficiency CMP fabrication on GaN homogeneous substrate for GaN-based LED.

高发光效率氮化镓(GaN)基LED对GaN同质衬底的化学机械抛光(CMP)质量提出了严苛要求。由于缺乏对GaN材料机械-化学交互微观去除机制的科学认识，目前GaN衬底的CMP加工存在材料去除率低、全局平坦化缺陷控制难等问题。为此，本项目拟从微观磨损角度，借助原子力显微镜等手段，独立研究单个磨粒在抛光液环境中对GaN材料的无损伤机械-化学交互微观去除机制。在探明机械作用、化学作用及机械-化学交互作用下的材料微观去除规律的基础之上，结合微区化学成分和晶格分析，深入研究去除过程中机械作用和化学作用的交互关系、交互作用下晶格损伤产生与消除的动态平衡机制，进而探讨无损伤的机械-化学交互材料微观去除机理。最后通过优化提出无损伤、高速率的材料微观去除条件，进行CMP实验验证。预期成果可丰富纳米摩擦学和超精密加工的基础理论，为高光效GaN基LED应用中GaN同质衬底的高质量、高效率CMP加工提供理论指导。

高光效GaN基LED芯片制造对GaN同质衬底的高效平坦化与缺陷控制提出了极高要求。深入理解超耐磨GaN 表面机械-化学交互微观去除机制，是研发适合于GaN衬底无损伤、高效平坦化超精密加工技术的关键。为此，本项目联结AFM实验、分子动力学仿真与TEM/XPS等分析手段，系统研究了GaN表面机械-化学交互微观材料去除与亚表面晶格损伤机理。. 主要内容、重要成果及其科学意义简述如下：（1）晶体极性与环境湿度强烈影响GaN-Al2O3界面的机械-化学反应；水分子增加显著促进机械化学反应，从而加速N极性面的材料去除；表面悬键与OH-之间的斥力是决定机械化学反应活性的原因。揭示出GaN表面无损伤的机械化学去除机制，为无损伤、高效率的超精密加工技术研发提供必要的理论基础。（2）对比研究了金刚石与Al2O3磨粒对GaN表面的机械与机械化学去除。由塑性变形与犁沟效应主导的机械去除符合Archard定律，去除率与湿度、速度无关；机械化学去除则不符合Archard定律，去除率与接触压力呈指数函数关系而与湿度正相关。结合阿伦尼乌斯化学动力学与DMT接触力学分析，发现临界活化体积与能量势垒可描述机械化学反应外部的机械活化能。揭示出机械作用与化学作用的交互关系，为深入认识GaN原子级去除机理奠定基础。（3）系统研究了速度、划擦深度、磨粒形状与尺寸等因素对表面去除与亚表面损伤的影响规律，从原子尺度揭示出去除过程中亚表层损伤的演化机制，为研发无损伤的超精密加工技术提供理论支撑。（4）表面织构可以有效降低GaN表面摩擦磨损与亚表面晶格损伤。归因于不同的位错网络，m-GaN比c-GaN表现出更低的去除率与更高的亚表面损伤。这可为极性/非极性GaN器件表面的抗摩减磨设计提供理论依据。项目执行过程中以第一或通讯作者身份在Friction、Tribol. Int.、Appl. Surf. Sci. 等知名期刊发表SCI论文10篇。