【作者】 宋晓岚；

【导师】 邱冠周；

【作者基本信息】 中南大学 ， 材料学， 2008， 博士

【摘要】 随着集成电路（IC）的快速发展,对衬底材料硅单晶抛光片表面质量的要求越来越高,化学机械抛光（CMP）是目前能实现全局平面化的唯一方法。研究硅片CMP技术中浆料性质、浆料与硅片相互作用、抛光速率及硅片CMP过程机理具有重要理论指导意义和实际应用价值。本文运用胶体化学、电化学和量子化学的原理和方法,系统研究了半导体硅片CMP技术中若干重要问题。详细研究了水相体系纳米SiO₂浆料的分散稳定性能,考察了纳米SiO₂颗粒在不同pH值介质中的润湿性和稳定性,探讨了不同分散方法及加入不同种类表面活性剂对纳米SiO₂颗粒吸光度、表面Zeta电位和吸附量等的影响,并通过颗粒间相互作用能的计算,分析讨论了纳米SiO₂浆料在不同条件下的分散行为和作用机理。研究得出,纳米SiO₂颗粒的等电点(pH_IEP)约为2,在酸性介质中有较好的润湿性,在碱性介质中有较好的稳定性,其分散行为与其表面Zeta电位有很好的一致关系,随pH升高,由于增加颗粒表面Zeta电位,产生静电排斥作用使稳定性提高;机械搅拌和超声波均可有效促进纳米SiO₂浆料的分散,但保持浆料持久稳定需加入表面活性剂作为分散剂;不同种类表面活性剂的分散机理不同,非离子型Triton X-100主要通过在颗粒表面形成吸附层,产生空间位阻效应,同时可在一定程度上改变颗粒表面电Zeta电位,产生静电排斥效应而阻止颗粒聚集;阳离子型CPB和阴离子型SDBS主要由于静电排斥效应起稳定作用;加入1:1 TritonX-100/SDBS复配物则可同时增强静电排斥和空间位阻作用,能显著改善纳米SiO₂颗粒的分散能力,获得达30 d以上稳定的浆料。运用电化学实验方法,采用旋转圆盘电极,系统研究了不同掺杂类型及不同晶面半导体硅片在纳米SiO₂浆料中的腐蚀成膜特性和成膜机理,分析了硅片成膜随浆料pH值、SiO₂固含量、成膜时间和H₂O₂浓度等条件的变化规律;通过自行组装的CMP装置,进一步探讨了硅片在动态CMP过程中的电化学行为,研究了抛光压力、抛光转速、SiO₂固含量、浆料pH值以及H₂O₂浓度等因素对硅片抛光时的腐蚀电位和电流密度的影响和作用机理。结果表明:Si（100）晶面成膜速度较Si（111）晶面快,硅片成膜符合Müller模型;浆料pH值对硅片成膜和CMP时的腐蚀电位及腐蚀电流密度影响很大,pH值约为10.5时硅片表面形成的钝化膜最厚（约5.989（?））,而CMP时其腐蚀电流密度最大,说明此时腐蚀成膜和抛光去膜速率最快;浆料中加入一定浓度H₂O₂作为氧化剂能加速硅片成膜,并使CMP时的腐蚀电位升高,腐蚀电流密度增大,从而促进抛光去膜;一定程度提高抛光压力、抛光转速以及SiO₂固含量有助于硅片表面钝化膜的去除;由此获得了本实验条件下的抛光优化工艺参数如下。n（100）:40kPa,100rpm,5～10wt%SiO₂,pH10.5,1vol%H₂O₂n（111）:40kPa,200rpm,5～10wt%SiO₂,pH10.5,1vol%H₂O₂p（100）:40kPa,200rpm,5～10wt%SiO₂,pH10.5,2vol%H₂O₂p（111）:60kPa,200rpm,5～10wt%SiO₂,pH10.5,2vol%H₂O₂在CMP电化学研究基础上,考察了n（100）和n（111）型半导体单晶硅片在纳米SiO₂浆料中不同抛光压力、抛光转速、SiO₂固含量、浆料pH值、H₂O₂浓度以及抛光时间等条件下的抛光速率,分析得出硅片CMP过程机理。研究发现,抛光速率随浆料中SiO₂固含量的增加会发生材料去除饱和现象:抛光速率随抛光压力和抛光转速增加而呈次线性方式增加,说明CMP是机械和化学协同作用的过程;抛光速率随抛光时间延长逐渐减小,但变化程度趋于平稳;抛光速率随浆料pH值和H₂O₂浓度变化曲线上出现最大值,是由于化学作用和机械作用达到动态平衡;相同条件下Si（100）晶面的抛光速率远大于Si（111）晶面;认为硅片CMP是一个成膜—去除—再成膜的循环往复过程;半导体硅片CMP动态电化学与抛光速率研究结果很好的一致性,表明电化学可作为硅片CMP过程及机理探讨的可靠方法,从而为硅片CMP研究提供了新思路。应用量子化学计算方法,探讨了硅片CMP的化学作用机理。模拟Si（111）面构造出一种硅簇模型,并推测硅片CMP过程得到的硅晶面为H中止;对反应势能面上的反应物、产物、中间体和过渡态的几何构型进行了全优化,研究了硅片CMP过程的反应路径:比较了浆料中采用不同碱对硅片的CMP效果;并从热力学角度研究了水对硅片CMP的作用机理,建立了相应的团簇结构模型以描述≡Si—O—Si≡等类物质的性质,计算得出了主要反应的溶解自由能和平衡常数,为进一步开展更深入的研究奠定了理论基础。成功配制出粗抛和中抛浆料（GRACE2040）并应用于北京有研硅股半导体硅片的CMP工业生产中。结果表明:GRACE2040作为粗抛或中抛浆料,其粗抛去除速率达到北京有研硅股质量要求;粗、中抛光垫的使用寿命超过正常值（20h）;抛光硅片几何参数、表面质量参数、表面粗糙度和合格品率均超过国家及北京有研硅股质量标准。北京有研硅股认为,GRACE2040粗、中抛光液完全能满足现有抛光工艺的要求,建议采购部将其纳入合格分供方名录。更多还原

【Abstract】 With the rapid development of the integrated circuit（IC）,the requirement for high surface quality of single crystals silicon wafer keeps continuous increasing.At present,chemical mechanical polishing（CMP）is the only way that can realize global planarization.The study concerning the properties of the CMP slurry,the interactions between slurry and silicon wafer during CMP,the remove rate,and the CMP mechanism is of importance for both theoretical guide and practical application.In this paper,the several important aspects concerning the CMP process of silicon wafer have been investigated using the principles and methods of colloid chemistry,electrochemistry and quantum chemistry.The dispersion and stability properties of the nano-SiO₂ slurries in an aqueous phase has been systematically studied.The wetting and stability of the nano-SiO₂ particles in an aqueous system at different pH were investigated.The influence of dispersion method and addition of surfactants on the stability of the nano-SiO₂ slurries was also investigated. The dispersion behavior and mechanism of the nano-SiO₂ at different conditions were analyzed and discussed using surface zeta-potential, absorbency and adsorption and calculated interaction energy between particles.The research results indicate that the isoelectric point(pH_IEP)of the nano-SiO₂ particles is approximately 2.In acidic media,the particles show a better wetting,while at basic media,a better stability.Their dispersion behavior correlated well with surface Zeta potential.With increasing pH,the surface Zeta potential of the particles increases,leading to a stable dispersion due to electrostatic exclusion.Mechanical stirring and ultrasonic dispersion both promote the dispersion of the particles.However, to keep the stability of the slurries it is necessary to use surfactants. Different types of surfactant show different dispersion mechanism. Non-ionic surfactant,Triton X-100,forms an adsorption layer on the particle surface,which produces pace steric hindrance effect and changes the surface Zeta potential which leads to electrostatic exclusion.Both of them contribute to the prevention of the particles aggregation.Cationic surfactant CPB and ionic surfactant SDBS stabilize the particle dispersion mainly via electrostatic exclusion effect.Using a mixture of Triton X-100/SDBS（1:1）enhances electrostatic the exclusion effect and space steric hindrance effect,significantly improves the dispersion of nano-SiO₂ particles,produces a slurry with 30 day stability,In terms of electrochemical experimental methods,the characteristics and the mechanism of corrosion film-forming on different types of semiconductor wafers and different crystal surfaces were systematically studied with a rotation disc electrode.The relationship between the film-forming and pH,the content of SiO₂,the concentration of H₂O₂ as well as the duration has been analyzed.With a self-made CMP device,the electrochemical behavior of the wafer during dynamic CMP process was further studied.The influence and mechanism of the pressure,rotation rate, the content of SiO₂,pH and concentration of H₂O₂ on the corrosion potential and electrical current density was investigated.The results indicate that the film-forming rate of the Si（100）face is higher than that of the Si（111）face.Film-forming is consistent with Miiller model.The pH of the slurry shows a significant influence on the corrosion potential and electrical current density.At pH=10.5,a highest passivation film was obtained,corresponding to a highest corrosion electrical current density, indicating that the rate of corrosion film-forming and film-removing of polishing is highest.Addition of H₂O₂ in the slurries as an oxidant accelerates film-forming and raises corrosion potential of CMP process, leading to a higher corrosion electric current and accelerating the removal of film.Increasing the pressure,rotation rate,and SiO₂ content enhances the removal of the passivation film.The optimal polishing conditions obtained via experiments are as following:n（100）:40kPa,100rpm,5～10wt%SiO₂,pH10.5,1vol%H₂O₂n（111）:40kPa,200rpm,5～10wt%SiO₂,pH10.5,1vol%H₂O₂p（100）:40kPa,200rpm,5～10wt%SiO₂,pH10.5,2vol%H₂O₂p（111）:60kPa,200rpm,5～10wt%SiO₂,pH10.5,2vol%H₂O₂Based on the study of electrochemistry,the polishing rates of n（100） and n（111）type single crystal silicon wafers with nano-SiO₂ slurries at different pressures,rotation rates,SiO₂ contents,pH values,H₂O₂ concentrations and durations were investigated.It is observed that increasing content of SiO₂ in the slurries results in a removal saturation. The polishing rate increases quasi-linearly with increasing pressure and rotation rate,indicting that CMP is a synergic process involving both mechanical and chemical effects.The polishing rate decreases gradually with increasing duration and finally reaches a constant value.On the other hand,a maximum of the polishing rate occurs with increasing pH and H₂O₂ concentration,indicating that a dynamic equilibration established between chemical and physical effect.Under the same conditions,the fact that the polishing rate of Si（100）face is significantly higher than that of Si（111） implies that the CMP process of the silicon wafer comprises of a cycle including forming-removal-reforming of film.The consistence between the study on the dynamic electrochemistry and the study on the remove rate in the CMP process of silicon wafer indicates that electrochemistry can be used as a reliable method to investigate the CMP process and its mechanism,thus providing a new route for the study of the CMP process.Using quantum chemistry calculation method,the mechanism of the chemical reactions involved in CMP process of the silicon wafer was discussed.A silicon cluster model simulating Si（111）surface has been established,allowing us to speculate that the silicon surface obtained in CMP is H-ended.In the simulation,the geometrical conformations of the reactants,product,intermediates and transition states in the reaction potential surfaces were optimized in order to find the reaction routes in the CMP process.The effect of CMP using different bases has been compared. The reaction mechanism of H₂O in the CMP process was studies based on thermodynamics.To simulate the properties of≡Si-O-Si≡cluster,group structure models have been constructed.With these models the dissolving free energy and equilibrium coefficient of the main reactions in this hydration system have been calculated,providing a theory foundation for further investigation.A coarse polishing and a fine polishing slurry（GRACE2040）have been formulated,which are now applied on an industrial scale in the CMP process in GRINM Semiconductor Materials Co.,Ltd,located in Beijing. As coarse polishing and fine polishing slurry,the coarse polishing removal rate of GRACE2040 completely meets the quality demand of GRINM.The life time of the coarse and intermediate polishing pads is higher than the normal values（20h）.The geometrical parameter,surface quality,surface roughness and eligibility of the polished silicon wafer are higher than the national and GRINM quality standard.According to GRINM,GRACE2040 coarse and intermediate polishing slurries completely meet the demand of the CMP process.GRINM will suggest to its purchasing department the addition of GRACE2040 to the list of qualified product.更多还原