弱钝化薄膜设计及碱性下铝低压力平坦化材料高效去除机制

High-k metal gate (HKMG) technology which adopts a replacement metal gate (RMG) approach has been implemented in mass production of the semiconductor devices at 14 nm nodes. As the key integral component of the RMG, the Al metal has become the main materials stream of integrated circuits industry to define the metal gate structures. Currently, chemical mechanical planarization (CMP) is the most powerful technique for surface global planarization to achieve high surface quality at atomic level. Due to the fragile materials and thin Al films in the RMG structure, it is of urgent priority for Al CMP technique to simultaneously achieve a high material removal rate (MRR) and a damage-free surface at low polishing pressure. Additionally, the traditional acid Al CMP process could cause severe damage to the machine with high cost. .This project proposes a novel planarization process at low pressure with alkaline slurries, which combines the effects of mixed-inhibitors, lubrication and mechanical abrasion. Three main approaches are proposed to realize this novel Al CMP process. Firstly, weak inhibitory films is created by the usage of mixed-inhibitors in the alkaline slurries to compensate the low polishing pressure, which is applied to achieve a high removal rate of Al CMP at low down pressure. In addition, the MRR is enhanced by the usage of alkaline slurry comprising the mixed-abrasives because of the high hardness of Al2O3 and the promoting rate of oxygen incorporation by CeO2. Finally, one major defect as micro-scratch is developed to be eliminated by the adding of lubrications. .Understanding of the fundamental Al material removal mechanism could offer insights into the control and optimization of the CMP processes. The physical and chemical property of the weak inhibitory films are characterized. The inhibitory mechanism of mix-inhibitors on Al surface in alkaline slurry is investigated at static and dynamic conditions by a series of experiments, such as potentiodynamic polarization curve measurements, electrochemical impedance spectroscopy and open circuit potential, using the in-situ electrochemical CMP apparatus which is made at home. Furthermore, the formation of the chemical thin layer on Al surface by the synergetic effects of inhibitory and lubrication is studied, and its evolution behavior in the wear process is revealed by the experiment of a single abrasive particle on aluminum surface at variable lubrication conditions. In addition, the micro-contact mechanism between an abrasive particle and Al surface with the consideration of chemical layer is clarified, and the material removal mechanism of Al CMP at low down pressure is proposed. Finally, an optimization model for material removal rate in Al CMP process based on neural network (BP) and genetic algorithm (GA) is established, in which the typical data are obtained from the orthogonal experimental design. .The complement of this project is expected to provide essential fundamentals and technical supports to Al CMP, which will also be benefit for the machining of products such as optical glass and hard disk that require extremely high surface quality.

针对14nm节点及以下极大规模集成电路(VLSIC)对铝化学机械抛光(CMP)提出的新挑战以及传统酸性铝CMP技术存在的问题，以弱钝化、润滑和混合磨料协同作用为研究思路，设计具有弱机械强度和高致密性特点的弱钝化薄膜，匹配低压力抛光，借助碱性条件和混合磨料提高低压力下的材料去除，采用润滑的方法减少划入损伤，提出碱性下铝低压力高效无损伤平坦化加工新工艺。重点研究钝化薄膜物理化学特性，探索复合缓蚀在铝 CMP中的钝化机理、复合缓蚀与润滑协同作用下的薄膜形成机制及其磨损中的演变行为，阐述Ce电子转移和高硬度磨料对材料去除的促进机制，澄清缓蚀/润滑薄膜作用下单个磨粒与铝表面的微观接触状态，并建立其物理/数学模型，揭示低压力下铝CMP材料的高效去除机制。构建遗传算法改进神经网络的工艺模型，优化铝CMP工艺参数，旨在获得高效与低损伤的铝低压力超精密抛光工艺，以期满足下一代VLSIC制造对铝平坦化的要求。

针对14nm节点及以下极大规模集成电路(VLSIC)对铝化学机械抛光(CMP)提出的新挑战以及传统酸性铝CMP技术存在的问题，本项目以弱缓蚀、络合和润滑协同作用为研究思路，设计了具有弱机械强度和高致密性特点的弱钝化薄膜，匹配了低压力抛光，借助于碱性条件和络合作用提高了低压力下的材料去除率，采用了羧甲基壳聚糖（CMCS）润滑的方法减少划入损伤，提出了碱性下对铝低压力高效无损伤的环保型平坦化加工的新工艺。表征了甘氨酸、TAZ、BTA、壳寡糖（COS）等钝化薄膜的物理化学特性，探索了COS-H2O2络合氧化协同作用在抛光中的作用机制、复合缓蚀与润滑协同作用下的薄膜形成机理及其磨损中的演变行为，借助于TriboIndenter纳米划痕仪\UMT研究了CMCS-H2O2缓蚀/润滑薄膜作用下单个颗粒与铝表面的微观接触状态，基于接触力学及化学反应动力学建立了其物理/数学模型，揭示了低压力下铝CMP材料的高效去除机制。采用正交实验优化了铝CMP工艺参数，获得了高效与无损伤的铝低压力超精密抛光工艺。同时，将本项目提出的铝CMP的动态原位电化学测试与加工方法推广到了氮化镓硬脆晶片的超精密抛光中，对第三代半导体材料的超精密加工具有重要的借鉴意义。