超声弯曲振动辅助化学机械抛光原子级光滑蓝宝石衬底机理研究

Atomically smooth sapphire is widely used as the substrate material to manufacture semiconductor lighting devices and large-scale integrated circuits. However, its efficient polishing and mechanism research are the important scientific and technical issues to be solved urgently. The applicants have applied ultrasonic flexural vibration to sapphire CMP (UFV-CMP) in the previous research. It almost doubled the polishing efficiency and obtained atomically smooth sapphire simultaneously. Nevertheless, investigations on revealing the polishing mechanisms of UFV-CMP are still inadequate. Therefore, this project will research the effects and polishing laws of ultrasonic vibration, chemical and mechanical factors during the polishing process via the combination of experiments, numerical simulation and theoretical modeling. Their functions and inherent relationships on the formation of chemical products, the removal of material and the generation of atomically smooth surface on sapphire will be studied. Moreover, the process of material exchange and the evolution rule of crystal structure will be revealed. The removal mechanism of sapphire UFV-CMP will be clear by the interpretation of interactions among ultrasonic, mechanical, and chemical functions at the micro/nano scales. Based on cross-disciplines of tribology, mechanics, material, physics and chemistry, the dynamic process of sapphire UFV-CMP will be investigated. Moreover, a theoretical model of sapphire UFV-CMP will be constructed and provide theoretical support for revealing the polishing mechanism. This project will develop advanced theories and techniques with independent intellectual property rights for high efficiency ultra-precision polishing of hard and brittle materials including sapphire.

原子级光滑蓝宝石是大规模集成电路、半导体照明器件等的重要衬底材料，但其高效抛光及机理研究是亟待解决的重要科学和技术问题。前期研究中申请人将超声弯曲振动应用于蓝宝石衬底化学机械抛光，提高抛光效率近一倍同时得到原子级光滑表面，但对机理的研究尚不充分。鉴于此，本项目拟利用自制超声辅助抛光装置，实验研究与数值仿真、理论建模相结合，研究抛光过程中超声、化学、机械等因素对蓝宝石衬底的抛光规律和作用机制；探索其在蓝宝石表面化学产物生成、材料去除和原子级光滑表面形成方面的作用和内在联系，揭示材料表面物质交换过程和晶体结构演变规律；在微纳尺度阐明超声、化学、机械交互作用下蓝宝石衬底去除机理；在摩擦学、力学、材料学、物理、化学等学科交叉基础上，研究超声弯曲振动辅助化学机械抛光蓝宝石材料的动态过程并构建理论模型，揭示抛光机理。为蓝宝石等硬脆性材料的高效超精密抛光提供先进的具有自主知识产权的理论和技术。

原子级光滑蓝宝石是大规模集成电路、半导体照明器件等的重要衬底材料，但其高效抛光及机理研究是亟待解决的重要科学和技术问题。本项目提出了一种可同时大幅提高加工效率和质量的超声弯曲振动辅助化学机械抛光(UV-CMP)新工艺，改进了抛光设备，优化了抛光垫、抛光液、磨粒尺寸、pH值及工艺参数，得到原子级光滑蓝宝石表面。研究了超声、化学、机械等因素对蓝宝石的抛光规律和作用机制，明确超声与二氧化硅颗粒的协同作用是材料去除的主要因素。表征蓝宝石表面化学成分、元素分布和亚表面晶体结构，阐明其化学反应、物质扩散和晶体结构变化过程，表明超声波能量介入抛光后，化学反应速度更快，反应层硬度更低，机械去除率以及磨粒的有效利用率更高，且亚表面损伤和晶体缺陷减小。使用计算流体动力学(CFD)研究流速、压强、温度及气含率等物理场，以及分子动力学(MD)仿真获得原子层面上材料形貌、晶体结构、温度、切削力等变化规律，在微纳尺度阐明蓝宝石UV-CMP材料去除机理。引入超声后，抛光液以湍流形式流动，超声频率升高，流场中心区域速度有所升高，速度均布范围更广；流体压强显著增大；温度有所降低；最大气含率均布范围更广。振幅提高，流场中心区域流速明显升高；压强增大；温度升高，且中心区域温度显著高于边缘区域；最大气含率增大且均布范围更广。提高振动频率和振幅，去除蓝宝石原子所需的平均切向力和法向力降低，工件温度上升，有利于材料去除，但亚表面损伤厚度总体呈增大趋势。并建立以蓝宝石晶体为基底，反应物为表面层的原子模型，阐明固相反应对蓝宝石抛光的影响。同时考虑固-固接触和流体动力接触模式，结合两体磨损、磨料冲击、磨粒/抛光垫的弹性模量、硬度、粗糙峰尺寸和分布等特性、化学作用、超声和其他因素的影响，建立蓝宝石UV-CMP理论模型。实验研究与数值仿真、理论建模相结合，揭示抛光机理。项目研究成果为蓝宝石等硬脆性材料的高效超精密抛光提供先进的具有自主知识产权的理论和技术。