SiC晶片原子级超光滑表面磁流变化学复合抛光加工研究

Atomically ultra-smooth (Ra≤0.3nm) and defect-free silicon carbide (SiC) substrates are required for producing high-quality epitaxial films and gate-oxide interfaces in device fabrication. Aiming at high precision, high efficiency and controllability in polishing of ultra-smooth surface at atomic scale, the magnetorheological-chemical polishing (MRCP) method is proposed based on the synergistic effect of chemical reaction and flexible mechanical removal, which combines the characteristics of flexible, high efficiency and controllability of magnetorheological finishing (MRF) with the characteristics of low damage and high precision of chemical mechanical polishing (CMP). Previous experimental results have confirmed high precision and high efficiency of the MRCP method. MRCP fluids will be prepared using the abrasives and magnetic particles with submicron and even nano scale based on the solid-state reaction principle of SiC surface. Nano scratch experiments and polishing experiments of single crystalline SiC wafer will be conducted to investigate the micromechanical behavior of SiC and the coupling mechanism of chemical reaction and mechanical removal in the effect of submicron-/nano- sized abrasives. Then the trap effect and the behavior control mechanism of submicron/nano scale abrasives in the polishing pad based on the cluster MR effect and the polishing pressure of SiC wafer will be researched thoroughly, and the synergistic effect mechanisms of chemical reaction and flexible removal of the MR polishing pad will be studied. Finally, the atomically removal mechanism and planarization mechanism of SiC surface will be revealed. It is expected to achieve a quantitative control of machining process and obtain stably an atomically ultra-smooth planarization surface of single crystal SiC substrate with high precision and high efficiency. The achievements of the project will be of benefit to the development of the 3rd-generation semiconductor industry.

SiC晶片作为光电子微电子器件衬底材料，为满足外延膜生长其表面需达到原子级表面精度(Ra≤0.3nm)。以原子级超光滑表面抛光的高精度、高效率、可控性为目标，结合集群磁流变抛光的柔性化、高效率、可控性和化学机械抛光的低损伤、高精度等特性提出集群磁流变化学复合抛光方法，前期实验结果证实了该方法可行有效。根据SiC表面固相反应原理，选用亚微米/纳米级的磨粒和磁性粒子制备磁流变化学抛光液，利用纳米划痕试验和抛光试验研究单晶SiC在亚微米/纳米磨粒作用下的微观力学行为、化学反应和机械去除的耦合作用机制；研究集群磁流变效应柔性抛光垫的磨粒容没效应、抛光压力和微量去除机理，结合抛光工艺试验研究SiC表面的化学反应与磁流变抛光柔性机械去除的协同作用机理、原子尺度材料去除过程及SiC晶片原子级超光滑表面形成机理，达到对加工过程材料微量塑性去除控制，实现SiC晶片的稳定高效、高精度的原子级超光滑表面加工。

SiC晶体是极具前途的第三代半导体材料，其抛光表面要求表面粗糙度Ra≤0.3nm才能满足外延膜生长的要求。针对SiC硬度高、脆性大、化学稳定性强、难以有效加工等问题，项目提出基于芬顿反应的SiC原子级超光滑表面集群磁流变化学复合抛光方法，进行了全面系统的研究。深入研究了基于芬顿反应的SiC表面固相反应原理，检测并研究了芬顿反应过程中Fe2+和·OH浓度对SiC表面化学反应及抛光效果的影响，系统研究了不同铁基催化剂的催化效果，采用SiC表面浸泡腐蚀、表面滴定腐蚀实验、XPS能谱分析、纳米压痕和划痕实验、抛光效果评定等方法全面评估了SiC的化学反应效果，优化了适宜单晶SiC抛光的磁流变化学抛光液。通过纳米压痕和纳米划痕实验研究了单晶SiC表面及其化学反应层的硬度、临界附着力和脆塑性转变机制，利用化学反应层的纳米力学特征评估了化学反应速度、化学反应层厚度和材料去除特性，在此基础上，设计多因素实验定量化研究了机械、化学及其交互作用在磁流变化学复合抛光中的贡献，发现磨料和磁流变抛光垫引起的机械去除占据主导地位(63.41-91.42%)，远远大于由于化学作用引起的材料去除。根据磁性粒子的磁化理论，建模计算了单点磁流变效应微磨头中磁性粒子之间的磁场作用力和对工件表面的接触压力，建立了单点磁流变微磨头的抛光压力计算模型，基于Preston方程结合被加工材料属性建立了材料去除模型，进而建立了磁极阵列的集群磁流变抛光的材料去除数学模型，通过实验和抛光力检测验证了材料去除模型，并实验研究了磁流变柔性抛光垫的磨粒“容没”效应，揭示了磁流变柔性抛光垫的材料去除特性。提出并研制了动态磁场磁流变平坦化抛光装置，实现了磁流变抛光垫的自我更新和整形。在此基础上对单晶SiC进行了系统的磁流变化学复合抛光试验研究，根据优化的工艺试验参数，在120min内就获得了单晶SiC原子级表面精度(Ra0.164nm)，材料去除率达到17.2mg/h。项目为半导体材料的超精密抛光加工提供技术和理论支持。