绿色环保化学机械抛光液的研究进展

原子级加工制造是实现半导体晶圆原子尺度超光滑表面的有效途径.作为大尺寸高精密功能材料的原子级表面制造的重要加工手段之一,化学机械抛光(chemical mechanical polishing,CMP)凭借化学腐蚀和机械磨削的耦合协同作用,成为实现先进材料或器件超光滑无损伤表面平坦化加工的关键技术,在航空、航天、微电子等众多领域得到了广泛应用.然而,为了实现原子层级超滑表面的制备,CMP工艺中常采用的化学腐蚀和机械磨削方法需要使用具有强烈腐蚀性和高毒性的危险化学品,对生态系统产生了不可逆转的危害.因此,本文以绿色环保高性能抛光液作为对象,对加工原子量级表面所采用的化学添加剂进行分类总结,详尽分析在CMP过程中化学添加剂对材料表面性质调制的作用机理,为在原子级尺度下改善表面性质提供可参考的依据.最后,提出了CMP抛光液在原子级加工研究中面临的挑战,并对未来抛光液发展方向作出了展望,这对原子尺度表面精度的进一步提升具有深远的现实意义.     

光学工艺 光学加工工艺与设备

TN305.2 2007054867pH值对铌酸锂晶片抛光速率及抛光表面的影响=Effectof pHon polishing velocity and glazed surface of LN wafer[刊,中]/武晓玲(河北工业大学微电子研究所.天津(300130)) ,刘玉岭…//半导体技术.? 2007 , 32(1) .?37-39采用化学机械抛光方法,自制碱性抛光液     

微尺度流道内液体表观黏性系数的分子理论

在考虑分子间作用力的基础上，讨论了各向同性壁面对微流道内非极性分子液体表观黏性系数的影响，建立了考虑壁面影响的表观黏性系数分子理论公式.研究结果显示，在靠近壁面处，壁面对表观黏性系数的影响是很大的，这取决于壁面材料和流体介质的分子间作用力.随着离开壁面距离的增加，壁面对表观黏性系数的影响衰减很快.在液态氩为流体介质的条件下，壁面影响大约可涉及到第10层氩分子，即影响深度为4 nm左右. 关键词： 微尺度流道 表观黏性系数 固壁影响 分子理论     

射流抛光中抛光液黏度对材料去除函数的影响

抛光液黏度是影响射流抛光(FJP)效果的重要因素,针对硬脆光学元件射流抛光中对抛光液黏度缺乏系统研究的现状,研究了抛光液黏度变化对材料去除函数的影响。建立射流抛光连续相、离散相模型和磨损模型,计算不同黏度下磨粒运动轨迹,分析磨料颗粒撞击速度矢量随黏度的变化规律。配置不同黏度相同质量分数的抛光液,结合BK7工件静态采斑实验研究与塑性磨损理论计算,获得不同黏度下的材料去除函数,分析黏度对去除函数的影响机制,并进一步研究由此引起的工件表面粗糙度变化。结果表明:随着抛光液黏度增大,材料去除函数的去除深度减小、去除形状及去除范围保持不变,这有利于降低工件表面粗糙度。该研究扩展了现有光学元件射流抛光材料去除理论,对实际抛光液黏度调控具有理论指导意义。     

磁性复合流体分散性及其对BK 7光学玻璃抛光性能的影响

针对BK7光学玻璃材料去除率和抛光质量不断提高的需求,提出通过减少磁性复合流体(MCF)抛光液颗粒的团聚、提高MCF分散性,配制性能优良的抛光液,提高BK7光学玻璃的MCF抛光性能.MCF中添加不同质量分数的高分子类分散剂聚乙烯醇(PVA),采用激光粒度分布仪测试MCF抛光液中颗粒的粒径分布和中位粒径,探究不同PVA浓度的抛光液对BK7光学玻璃抛光性能的影响.试验结果表明:当PVA质量分数为3%时,中位粒径达到最小值5.854μm,MCF的分散性最好,对光学玻璃的抛光性能大幅提高,当PVA质量分数为5%时,经MCF抛光10min后材料去除率达到最大值26.4×10~(-4)g/min,表面粗糙度达到最小值8.23nm.MCF中添加适量PVA能够减少抛光液颗粒的团聚,提高MCF的分散性,提升BK7光学玻璃的磁性复合流体抛光性能.     

微晶玻璃试片的化学抛光研究

光学零件的凹槽、孔道等复杂结构无法进行机械抛光,只能采用化学抛光。分析了化学抛光的机理和微晶玻璃的组成,设计了化学抛光技术方案、工艺流程和操作方法。对微晶玻璃化学抛光前后的光学表面进行了测试、分析。结果表明:化学抛光去除量主要由化学抛光液的温度和抛光时间控制。采用氟化氢铵、氢氟酸与添加剂组成的化学抛光液和合适的化学抛光工艺,可以能够得到光滑、透明的表面,表面粗糙度可降低到100nm;可见光透过率81%~83%。     

高准确度玻璃光学元件的CMP技术研究

依据化学机械抛光（Chemical Mechanical Polishing,CMP）加工玻璃光学元件的原理,通过对抛光运动机理的理论分析,提出了抛光垫的磨削均匀性对光学元件面形的影响,并设计了新的工艺流程.通过工艺试验,完成了高准确度玻璃光学元件的CMP加工,获得了表面质量N<0.2,Rq<0.3 nm的玻璃光学元件.     

抛光颗粒尺度均匀性对射流去除特性的影响

基于单喷嘴射流抛光去除机理,研究了抛光颗粒尺度分布理想均匀时,颗粒直径和抛光液质量分数变化对冲击去除分布的影响。在此基础上,考虑到实际加工过程中,抛光粉颗粒不可避免地存在分布不均匀的情况,在非理想不均匀条件下,提出了一种分析颗粒尺度的材料去除特性模型,重点研究了不同颗粒尺度分布范围对材料去除特性的影响。结果表明:在理想状态下,冲击去除随着抛光颗粒直径的增大而减小,随着抛光液质量分数的增大而增大。当颗粒直径随机分布时,材料去除量将出现明显的波动,抛光液质量分数的增大使去除量波动也增加,去除量波动的大小与抛光粉颗粒的平均直径直接相关,且与理想均匀状态下的去除特性相比,颗粒分布不均匀性使得材料的去除量有所增大。     

液浮法抛光优化技术

一种新的光学元件表面抛光工艺—液浮抛光技术,采用具有剪切增稠效应的非牛顿流体作为抛光液,流体在抛光区域形成液膜,实现对工件表面高效、低损伤的加工。以材料去除量以及工件表面粗糙度作为评价指标,利用正交实验法对K9玻璃抛光过程中的四个关键影响因素:磨粒质量分数、磨头入口压强、磨头重力、剪切增稠相中分散相的质量分数进行实验分析,得到一组最优参数组合以及各主要影响因素对抛光效果的影响程度。对于工件表面粗糙度,采用极差法得出各因素对整个工件的影响程度的主次顺序为(主→次):二氧化硅质量分数、磨头重力、入口压强、磨粒质量分数,最佳参数组合为:磨粒氧化铈质量分数为14%,入口压强为0.3MPa,剪切增稠相中分散相二氧化硅质量分数为9%,磨头重力为34.3kg;对于材料去除量分布,经过90min的抛光,其平均去除量为0.2μm。     

基于非牛顿流体新型液浮法抛光技术研究

提出一种新的柔性抛光技术——液浮法抛光,通过软件仿真及实验对其进行探索性研究。针对抛光液为具有剪切增稠效应的流体,利用软件对该类液体的液浮法抛光技术模型进行流场分析,得到液浮抛光模型的流场压强、剪切力分布情况。仿真结果表明,液浮抛光技术对被加工件表面具有一定的剪切效果,可以实现对工件材料的去除。搭建实验平台,设计一组实验,其中配置以粒径12 nm的二氧化硅为溶质,分子量200的聚乙二醇为溶剂的非牛顿幂律流体作为抛光液的剪切增稠基液(其中二氧化硅质量分数为9 %),加入质量分数为18 %的氧化铈作为磨料的抛光液,对于初始粗糙度为23.97 nm的K9玻璃经过90 min的抛光,其粗糙度可达到1.023 nm,实验结果表明,该技术可用于光学元件的抛光加工。     

Ceria concentration effect on chemical mechanical polishing of optical glass

It was found material removal rate (MRR) sharply increased from 250 to 675 nm/min as the concentration decreased from 1 to 0.25 wt% in optical glass chemical mechanical polishing (CMP) using ceria slurries. Scanning electron microscopy was employed to characterize the ceria abrasive used in the slurry. Atomic force microscopy results showed good surface had been got after CMP. Schematic diagrams of the CMP process were shown. Furthermore, the absorption spectra indicated a sudden change from Ce⁴⁺ to Ce³⁺ of the ceria surface when the concentration decreased, which revealed a quantum origin of the phenomenon.     

Investigation into layers formed by selective transfer CMP mechanisms with atomic force microscope

To understand mechanisms of chemical mechanical planarization (CMP), an atomic force microscope (AFM) was used to characterize polished layer surfaces formed by selective transfer after a set of polishing experiments. It is know that in the process of friction of two materials and in the presence of own lubricants, wear phenomenon itself manifests as a transfer of material from an element of a friction couple on the other, this phenomenon being characteristic to the selective transfer process. A selective transfer can be safely achieved in a friction couple, if there is a favorable energy, and in the presence of relative movement, if in the friction area is a material made by copper and the lubricant is adequate (glycerin or special lubricant). The forming selective layer on the contact surfaces makes that the friction force to be very low because of the structure formed by selective transfer. To optimize the CMP process, one needs to obtain information on the interaction between the slurry abrasive particles (with the size range of about 30–70 nm) and the polished surface. To study such interactions, we used AFM. Surface analysis of selective layer using the AFM revealed detailed surface characteristics obtained by CMP. Studying the selective layer CMP, of which the predominated one is copper (in proportion of over 85%), we found that the AFM scanning removes the surface oxide layer in different rates depending on the depth of removal and the pH of the solution. Oxide removal happens considerably faster than the copper CMP removal from the selective layer. This is in agreement with generally accepted models of copper CMP. It was found that removal mechanisms depend on the slurry chemistry, potential per cent of oxidizer, and the applied load. This presentation discusses these findings. Both load force and the friction forces acting between the AFM tip and surface during the polishing process were measured. One big advantage of using the AFM tip (of radius about 50 nm) as abrasive silica particle is that we can measure forces acting between the particle-tip and the surface being polished. Here, we report measurement of the friction force while scratching and polishing. The correlation between those forces and removal rate is discussed.     

Influence of adhesion of silica and ceria abrasive nanoparticles on Chemical-Mechanical Planarization of silica surfaces

We report on a direct measurement of adhesion between abrasive nanoparticles of irregular shape, which are used in semiconductor industry in the process of Chemical-Mechanical Planarization (CMP), and silica surface. The adhesion of ceria and silica nanoparticles to silica surface is measured in multiple chemistries of different CMP slurries using a specially developed atomic force microscopy (AFM) method. Using this method, we study the influence of adhesion on the main parameters of CMP, removal rate and defectivity, scratches. While being plausible to expect correlation between these parameters and adhesion, it has not been systematically studied as of yet. We observed direct correlation between adhesion and removal rate. Comparing the measured defectivity and adhesion, we observe the presence of some correlation between these parameters. We conclude that both adhesion and shape of abrasive particles influence defectivity, micro-scratches. Direct measurements of the adhesion between abrasive nano-particles and surface can be used in the screening of new slurries as well as various modeling related to wearing of the surfaces.     

A mathematical model for material removal and chemical-mechanical synergy in chemical-mechanical polishing at molecular scale

This paper presents a mathematical material removal model based on the chemical and mechanical synergistic effects in the chemical-mechanical polishing (CMP) process. It seems to explain the transition from a chemically dominant region to a mechanically dominant region. In addition, this model predicts the effects of most variables involved in the CMP process including the processing conditions (velocity, downpressure), pad properties (modulus, hardness and asperity sizes) and slurry characteristics (particle size, concentration and distribution). The results reveal some insights into the micro-contact and wear mechanisms of the CMP process.     

Localized corrosion effects and modifications of acidic and alkaline slurries on copper chemical mechanical polishing

This study demonstrates the CMP performance can be enhanced by modifying the corrosion effects of acidic and alkaline slurries on copper. A corrosion test-cell with a polishing platform is connected with the potentiostat to investigate the corrosion behaviors of copper CMP in various alumina slurries. Experiments show that the slurry needs to be maintained in acidic pH<4.56 or alkaline pH>9.05 surroundings and thus better dispersion of alumina particles and less residual contaminant on copper surface can be obtained. The surface defects after copper CMP using acidic and alkaline slurries are described by pitting corrosion mechanisms, and these mechanisms can be regarded as a basis to modify their corrosion effects. Experimental results indicate that it is necessary to modify the dissolution of HNO₃ and oxidization of NH₄OH for copper CMP slurries. Consequently, the slurries of 5 wt.% HNO₃ by adding 0.1 wt.% BTA or 5 wt.% KNO₃ by adding 1 wt.% NH₄OH achieve good CMP performance for copper with higher CMP efficiency factor (CMPEF), 1460 and 486, and lower surface roughness (R_q), 4.019 and 3.971 nm, respectively. It is found that AFM micrographs can support the effectiveness of corrosion modifications for copper CMP in various slurry chemistries.     

Generation and removal of pits during chemical mechanical polishing process for MgO single crystal substrate

Magnesium oxide (MgO) single crystal is an important substrate for high temperature superconductor, ferroelectric and photoelectric applications. The function and reliability of these devices are directly affected by the quality of polished MgO surface because any defect on the substrate, such as pit or scratch, may be propagated onto device level. In this paper, chemical mechanical polishing (CMP) experiments were conducted on MgO (1 0 0) substrate using slurry mainly comprised of 1-hydroxy ethylidene-11-diphosphonic acid (HEDP) and silica or ceria particles. Through monitoring the variations of the pits topography on substrate surface, generation and removal mechanism of the pits were investigated. The experimental results indicate that the pits were first generated by an indentation or scratch caused by particles in the slurry. If the rate of chemical etching in the defect area is higher than the material removal rate, the pits will grow. If chemical reaction in the defect area is slower than the material removal rate, the pits will become smaller and eventually disappear. Consequently, these findings may provide insight into strategies for minimizing pits during CMP process.     

Modeling the effects of cohesive energy for single particle on the material removal in chemical mechanical polishing at atomic scale

This paper proposes a novel mathematical model for chemical mechanical polishing (CMP) based on interface solid physical and chemical theory in addition to energy equilibrium knowledge. And the effects of oxidation concentration and particle size on the material removal in CMP are investigated. It is shown that the mechanical energy and removal cohesive energy couple with the particle size, and being a cause of the non-linear size-removal rate relation. Furthermore, it also shows a nonlinear dependence of removal rate on removal cohesive energy. The model predictions are in good qualitative agreement with the published experimental data. The current study provides an important starting point for delineating the micro-removal mechanism in the CMP process at atomic scale.     

Modeling the effects of oxidizer, complexing agent and inhibitor on material removal for copper chemical mechanical polishing

The paper presents a novel mathematical model that systematically describes the role of oxidizer, complexing agent and inhibitor on the material removal in chemical mechanical polishing (CMP) of copper. The physical basis of the model is the steady-state oxidation reaction and etched removal in additional to mechanical removal. It is shown that the complexing agent concentration-removal relation follows a trend similar to that observed from the effects of oxidizer on Cu removal in CMP. In addition, the removal rate and the coupled effects of the chemical additives are determined from a close-form equation, making use of the concepts of chemical-mechanical equilibrium and chemical kinetics. The model prediction trends show qualitatively good agreement with the published experimental data. The governing equation of copper removal reveals some insights into the polishing process in addition to its underlying theoretical foundation.