单晶SiC激光表面改性复合磨削加工去除机理及加工工艺研究

Single crystal SiC has attracted much attention as the third generation semiconductor material. However, because of its high hardness and brittleness, the process of the single crystal SiC is difficult and the processing cycle is long, which directly limits the application and promotion of the corresponding devices. Grinding has the characteristics of high efficiency, simple technology and wide application. With the development and application of precision/ultra-precision grinding equipment and technology, many scholars hope to achieve high-efficiency and low-damage processing of single crystal SiC by means of precision/ultra-precision grinding. However, there are a series of problems in grinding process, such as grinding wheel wear, passivation and sub-surface damage. These problems can hardly be solved by improving the processing parameters. Therefore, the industrial application of grinding process in single crystal SiC processing is seriously restricted. The laser surface modification technology is used to form a modified layer with periodic micro/nano structures on the surface of SiC wafer. SiC surface modified layer can be quickly removed by grinding technology. The micro/nano structures can effectively reduce the contact time between abrasive and workpiece, reduce the cumulative damage behavior. The strength and hardness of the modified layer micro/nano structures are lower than that of the matrix, which reduce the grinding difficulty of the surface of the material and the wear of the grinding wheel.

单晶SiC作为第三代半导体材料吸引了大量关注，但是硬度高脆性大，使得该材料加工难度大，加工周期长，直接限制了相应器件的应用推广。磨削加工具有效率高、工艺简单以及适用范围广等特点，随着精密超精密磨削加工设备及技术的发展和应用，国内外很多学者希望通过精密超精密磨削加工手段实现单晶SiC材料的高效低损伤加工。但是，磨削加工过程中存在砂轮磨损及钝化以及亚表面损伤严重等一系列问题，这些问题很难通过改善加工参数的方式彻底解决，因此磨削加工工艺在单晶SiC加工领域的工业应用受到严重制约。本课题采用激光扫描方法，在SiC晶圆表面生成具有微纳结构的改性层，结合磨削加工技术快速去除SiC表面改性层材料。该表面微纳结构可有效减少磨粒与工件接触时间，降低加工区域损伤累积行为。而且改性层微纳结构区域强度及硬度低于基体，从而降低材料表面磨削加工难度，改善砂轮磨损现象。

作为第三代宽带隙半导体，单晶SiC具有临界击穿电场高、抗辐射能力强、载流子饱和迁移速度快等一系列优点。但是SiC材料硬度高、脆性大，金刚石线锯切割后的SiC晶圆表面质量很差，亚表面损伤层非常严重。加工过程中材料去除率较低，加工周期长。通过改善工件材料表面可加工性的方式来降低该材料的加工难度，将有效提高单晶SiC精密超精密磨削加工工艺。本课题利用分子动力学手段研究了单晶SiC改性层在磨粒刻划作用下微观去除机制，验证了高频脉冲激光表面改性辅助磨削加工的可行性。结合聚焦离子束分析及激光拉曼光谱分析等手段，分析改性层微纳结构区域及附近基体区域的物相分布状态，给出材料表面激光辐照影响区物相分布形式，得到了磨粒刻划过程中塑性变形机制、切屑分离机制、磨粒磨损形式及磨损量变化规律。针对高频脉冲激光诱导单晶SiC表面周期性微纳结构及改性层可加工性进行研究。分析了不同脉冲数量作用下表面条纹结构演变过程，找到激光光斑重叠率与表面改性层三维几何形貌的对应关系。分析了改性层三维几何形貌对切屑分离机制及加工表面形貌的影响。结合纳米刻划手段分析了SiC改性层摩擦磨损形式及可加工特性。分析重复加工及加工参数对材料去除过程的影响规律。给出了高频脉冲激光辅助粗糙表面改性的去除机制。分析了磨粒动态刻划过程中的磨粒磨损形式及表面形貌演变规律，给出了加工表面质量及演变规律。本课题通过高频脉冲激光实现单晶SiC表面改性，对改性表面材料去除机制、亚表面损伤形式以及材料可加工性进行了系统分析，分析了高频脉冲激光辐照条件下应变率效应、磨粒旋转运动与晶体各向异性影响机制及激光辐照热效应的影响机制。重点分析了改性层材料的去除机理，对后续指导激光表面改性复合加工工艺的深入研究提供理论指导，对推动SiC材料磨削加工工艺具有重要的应用价值。