冰粒型固结磨具抛光超薄锗单晶片的基础研究

Ultra-thin germanium single-crystal wafer is the substrate material of space solar cell. Polishing process is the key factor which affects the yield and surface quality of the wafer. Traditional polishing methods can not effectively solve the problems, such as unstable quality, deformation of work piece,high fragmention rate,etc.High quality polishing ultra-thin germanium wafers with ice bonded abrasive tools is put forward in this research project. In order to make the abrasives uniformly distributed, the law of forming and three-dimensional distribution of ice particles which contain abrasives is probed. The rule of heat generation and transfer is to be researched, so as to set up temperature field model and study the processing parameters which influence the temperature field. The rule of the stress, strain and deformation of the wafer under pressure and temperature field should also be explored. In terms of cryotribology, the mechanism of ice bonded abrasive CMP and the formation mechanism of subsurface damage of germanium single-crystal wafer are to be researched. The aim of the research is to effectively control the thawing rate of the ice bonded abrasive tools and the surface shape of wafer, and decrease the fragmentation rate of the wafer dramatically. And the wafer which has super smooth surface and low(or no) subsurface damage can be yielded.The research can also provide new theory and technology for the processing of other ultra-thin hard brittle material.

超薄锗单晶片是空间太阳电池的衬底材料，抛光工艺是影响锗单晶片成品率和表面质量的关键因素，传统锗单晶抛光中存在抛光质量不稳定、工件变形大、碎片率高等难题。本项目创新性地提出采用冰粒型固结磨具实现超薄锗单晶片的高品质加工。探索含磨料冰粒的成形机理及冰结磨具中磨粒的三维分布规律，实现磨料的均匀分布；研究冰粒型固结磨具抛光过程中热量的产生与转移的规律，建立加工区域的温度场模型，探索工艺参数对温度场的影响规律；研究压力/温度场作用下工件的应力、应变与变形规律；从低温摩擦学的角度，探索冰粒型固结磨具CMP抛光锗单晶片的材料去除机理；研究冰粒型固结磨具抛光锗单晶片的亚表面损伤形成机理。实现冰粒型固结磨具融化速度的有效控制、工件材料的均匀去除及工件面形的有效控制，显著降低碎片率，得到低（无）亚表面损伤的超光滑锗单晶抛光片。为其它超薄硬脆晶体的超精密加工提供新思路和理论指导。

超薄锗单晶片是空间太阳电池的衬底材料，抛光工艺是影响锗单晶片成品率和表面质量的关键因素，传统锗单晶抛光中存在抛光质量不稳定、工件变形大、碎片率高等难题。本项目针对上述加工难题提出采用冰粒型固结磨具实现超薄锗单晶片的高品质加工。本课题通过理论和试验研究，获得冰粒型固结磨具制备技术；建立冰粒型固结磨具CMP抛光温度场和应力场模型，弄清多场耦合作用下工件的应力及变形规律；弄清冰粒型固结磨具抛光锗单晶片的材料去除机理及亚表面损伤形成机理；实现工件材料的均匀去除及工件面形的有效控制，显著降低碎片率，得到低（无）亚表面损伤的超光滑锗单晶抛光片；为我国超薄硬脆材料的光整加工提供新思路和理论指导。课题按期完成了各项研究目标，取得了以下主要成果：.1. 弄清了含磨料冰粒的成形机理及冰结磨具中磨粒的三维分布规律，实现了磨料的均匀分布，获得了冰粒型固结磨具的制备技术。.2. 建立了冰粒型固结磨具抛光温度场有限元分析模型，探索了工艺参数（压力、主轴转速、偏心距和环境温度等）对抛光区域温度场的影响规律。研究了冰粒型固结磨具的温度场分布、抛光工艺参数与其融化速度的内在关系，实现了冰粒型固结磨具融化速度的有效控制，为合理选择抛光环境温度和加工工艺参数提供了理论依据。.3. 揭示了压力/温度场作用下工件的应力与变形规律。研究发现承载器厚度增大，应力分布趋于均匀，该方法适用于小尺寸的锗片抛光；通过实验探究了升温速率对晶片变形的影响规律，研究发现升温速率越快，晶片变形越为明显，同时晶片越厚、直径越小，越不容易发生变形。.4. 从低温摩擦学的角度，阐明了冰粒型固结磨具抛光锗单晶片的材料去除机理。工件在低温抛光过程中，表面形成了软质腐蚀层，材料的去除是机械去除与化学作用耦合的结果。.5. 弄清了冰粒型固结磨具抛光锗单晶片的亚表面损伤形成机理。低温加工环境有利于减少裂纹的产生并减小亚表面裂纹深度，从而采用冰粒型固结磨具抛光对传统抛光亚表面的损伤具有抑制能力，可以进一步提高工件表面与亚表面质量。