【作者】 蒋建忠；

【导师】 赵永武；

【作者基本信息】 江南大学 ， 轻化工技术与工程， 2009， 博士

【摘要】 化学机械抛光（简称CMP）是机械削磨和化学腐蚀的组合技术,该工艺的基本原理是借助抛光液中磨粒的机械磨削及化学氧化剂的腐蚀作用来完成对工件表面的材料去除,并获得光洁表面。由于化学机械抛光技术（CMP）在全局平坦化方面独一无二的特点以及操作步骤少等特色,已成为目前公认的唯一的全局平坦化技术,在集成电路（IC）芯片生产线上广泛应用了十几年。但是由于CMP过程影响因素的复杂性,抛光盘特征参数和工作参数对于CMP材料去除率的敏感性和平坦化程度的影响规律仍没有被人们充分认识,抛光液中磨粒的机械作用和化学物质的化学作用的协同效应对CMP材料去除率的影响规律还需要进一步的深入研究。随着集成电路产品制造朝着高精度、高密度、高集成度方向的快速发展,CMP工艺面临严峻挑战。目前CMP技术遇到的最大挑战状是需要一个更全面的物理模型来合理解释CMP的各种结果,从理论上指导CMP加工参数的优化,建立起更为可靠的、高效的CMP过程。本论文建立了更为完善的、考虑更多因素的CMP数学模型。首先,本文根据分子动力学模拟单个磨粒切削芯片的研究结果,提出了一种基于CMP芯片表面材料非晶层吸附去除机理。并基于这种机理,结合芯片／磨粒／抛光盘三体接触当量梁的弯曲假设,充分考虑了抛光盘与芯片接触的大变形和超弹性特点,应用芯片／抛光盘大变形非线性修正赫兹接触理论建立了一种新的表征机械化学抛光过程中材料去除速率的数学模型。通过微观实验和理论计算,证实了CMP材料非晶层吸附去除机理的合理性。模型中引入了一个表征单个磨粒吸附去除芯片表面非晶层能力的比例系数κ,κ体现了化学作用和机械作用对CMP过程的综合影响。模型中建立了计算单个磨粒压入芯片的深度δ_w的新模型,新模型更加全面,包含了更加丰富的信息。接着,通过理论计算,确认了磨粒与芯片表面分子间的吸附力对CMP材料去除过程的重要影响。在此基础上,根据磨粒在CMP过程的力平衡方程式,导出一个考虑分子间作用力的磨粒压入芯片表面的深度模型。经过理论分析,找到了判断CMP材料去除模型中磨粒／芯片分子间的吸附力是否可以忽略的判断依据及临界值。然后利用这些理论结果修正了前面提出的CMP过程非晶层材料吸附去除机理,建立起考虑磨粒与芯片表面分子间的吸附力的CMP材料去除模型,并与旧的模型进行了对比。结果发现：磨粒较小时,分子间的吸附力的影响较为明显；磨粒较大时,分子间的吸附力对CMP过程的影响可以忽略不计。随后,通过深入分析CMP过程氧化剂与磨粒的化学机械协同作用机理,将CMP过程分为两个阶段：化学作用主导阶段和机械作用主导阶段。然后应用微观接触力学和颗粒粒度分布理论,对这两个阶段分别建立了表征芯片表面材料吸附去除率的数学模型,并根据这两个阶段的平衡点推出了表征芯片表面氧化膜生成速度的数学表达式。根据芯片表面氧化膜生成速度的理论计算结果,从理论上证实了CMP单分子层材料去除机理假设的正确性。最后,本文根据芯片表面分子／原子氧化去除动态平衡原理,从能量角度推导出了定量计算磨粒吸附系数k的理论公式,并定性分析了众多物理化学因素对CMP过程磨粒吸附系数k的影响规律。并利用这个公式对前面提出的CMP过程材料非晶层吸附去除模型进行了修正。修正后的得到的CMP单分子层材料吸附去除模型以表面分子／原子氧化去除动态平衡原理为基础,模型中不仅考虑了芯片、磨粒、抛光垫以及抛光工艺等参数对材料去除率的影响,而且考虑了芯片／磨粒分子间的吸附力、磨粒压入深度和抛光盘的大变形和超弹性特点的影响；创造性地引入了氧化剂浓度C₀,从而使氧化剂浓度对CMP过程材料去除速率的影响规律可以定量化计算,理论计算结果成功地解释了氧化剂浓度C₀增加到一定程度,CMP材料去除率趋于饱和,即不再增加的现象。CMP单分子层材料吸附去除模型反映出的磨粒平均直径、氧化剂浓度和抛光盘弹性模量对CMP材料去除率的影响规律与试验结果非常吻合,清晰地解释了CMP中化学机械作用的协调性。本论文通过严密的理论推导和试验验证,建立了定量描述CMP材料去除率的数学物理模型,为优化CMP工艺参数提供理论依据,为高效、环保、精确和低成本地控制CMP过程提供了一定的理论指导。更多还原

【Abstract】 Chemical mechanical polishing combines aqueous corrosion chemistry and contact mechanics to obtain material removal and planarization of wafer surface. Chemical mechanical polishing (CMP) is superior to other planarization technologies in producing excellent local and global planarization at low cost, and thus is widely adopted in IC fabrication. However, the fundamental mechanisms of material removal and the interactions of the chemical and mechanical effects are not well understood, which limits a better control and improvement of the CMP process. With the rapid development to smaller feature size, higher resolution, denser packing and multi-layer interconnects of ultra large scale integrated (ULSI) circuits, the CMP techonology now is facing a stringent challenge. The present challenge of the CMP processing is to develop physical models to explain these processes which then will lead to the development of new and more robust processes.In this study, fundamental understandings of the mechanics of material removal during CMP are established based on the modeling of wafer-pad-particle interactions. First, On the basis of the analysis of the molecular dynamics simulation of sliding contact between a single micro-particle and a smooth flat surface, a new approach for the material removal in CMP process is put forward in this paper, which deems that the amorphous material is stripped off the wafer surface to be the wear debris due to the adhesion of the abrasive particles when sliding across the wafer surface. Meanwhile, in accordance with this approach, combined with the equivalent beam bending model for a three body contact among pad/wafer/particles, a new mathematical model about the material removal rate in CMP process is developed, The model comprehensively considers the influence of most valuables in CMP process including pad properties, operational conditions and slurry characteristics. Especially, the large deformation and the super elasticity of the pad while in contact with wafer surface are involved in the model. What’s more, a new important parameter k, named adhesion coefficient, which represents the ability to remove the amorphous layer on wafer surface by a single particle, is firstly put forward in the model. It is the comprehensive parameter incorporating the mechanical effect and the chemical effect. After the validation of some teams of experimental data, it is found that the removal rates predicted by the model agree well with those experimental value under same CMP conditions.Then, through theorical calculation, the importance of the molecular adhesion force between a particle and wafer surface to CMP material removal rate is confirmed. And then, based on the force balance equation of particles embedded into the interface between the pad and wafer surface during CMP, a new model considering the molecular adhesion force of the indentation depth of a particle into wafer surface is achieved. In addition, the result of the new model is compared with the old one which did not consider the effect of the molecular adhesion force. After theorical analysis and deduction,the estimation criterions and critical value which deside whether the molecular adhesion force should be neglected or not are introduced. Utilizing these theorical results, the aftermentioned amorphous material removal model in CMP is reviced by considering the molecular adhesion force. After validation of experimental data, it is concluded that when the abrasive diameter is smaller than the critical value, the effect of molecular adhesion force on CMP material removal rate is noticeable and can not be neglected, when larger than the critical value, the effect of molecular adhesion force can be neglected.Furthermore,according to the theoretical and experimental analysis, the CMP process is divided into two phases:chemical effect dominant phase and mechanical effect dominant phase. Then, from the balance point of the two phases, a new equation, which can quantitatively describes the generation rate of oxidized layer on wafer surface in CMP is developed. The modeling of the generation rate of oxidized layer in CMP will further the research of the CMP material removal mechanism and offer a direction to control the CMP process more accurately. Based on the theorically calculating result of generation rate of oxidized layer, it is authenticated that the hypothesis of molecular scale material removal mechanism in CMP is right.Finally, on the basis of the dynamical equilibrium of oxidation and removal of wafer surface atoms/molecules, the adhesion coefficient k is deduced quantitively from the scope of energy. And then the effects of lots of physical and chemical variables on the adhesion coefficient k are analysed qualitatively. Utilizing the equation of k, the aftermentioned amorphous material removal model in CMP is reviced. The reviced model is based on the chemical-mechanical synergetic effects, and not only incorporates the mechanical effect of the slurry particles, the chemical role of the slurry, other important factors on CMP process such as wafer material properties, pad surface profiles and operating variables, but also includes the influence of molecular adhesion force between wafer surface and abrasive particle, the large deformation and super elactricity of the contact of pad and wafer surface and the identation depth of abrasive into wafer surface. Particularly, the oxidant concentration in slurry is firstly integrated in the model, which causes that the influence law of the oxidant concentration in slurry on material removal rate MRR can be calculated quantitatively. The model predictions of abrasive diameter, oxidant concentration as well as pad elasticity modulus are presented in graphical form and show good agreement with the published experimental data.In general, the optimization of the controlling parameters involved in the polishing process can be obtained through model predictions. Optimization scheme of high performance slurries and operation parameters to reduce wafer scale variation can be developed on the basis of this study. In addition, the value of the experimental and modeling efforts of current study can provide guidelines for the design of novel polishing processes and for the identification of unexplored process parameters. The reported findings in this study can also provide a fundamental understanding of the polishing mechanisms and can provide guidelines for controlling the CMP process more accurately.更多还原