Modeling and experimental research on a removal mechanism during chemical mechanical polishing at the molecular scale

In order to understand the fundamentals of the chemical mechanical polishing(CMP) material removal mechanism,the indentation depth of a slurry particle into a wafer surface is determined using the in situ nanomechan-ical testing system tribo-indenter by Hysitron.It was found that the removal mechanism in CMP is most probably a molecular scale removal theory.Furthermore,a comprehensive mathematical model was modified and used to pinpoint the effects of wafer/pad relative velocity,which has not been modele...     

基于分子量级的化学机械抛光理论与实验研究

为了理解CMP材料去除机理,本文采用原位纳米压痕仪研究了单个磨粒和芯片的接触状态。结果表面,CMP材料去除机理更应该采用原子/分子材料去除机理描述。此外,本文建立的修正数学模型定性预测了氧化剂浓度和磨粒/芯片相对速度对材料去除速率影响的基本规律,与发表的实验结果相吻合。实验结果与讨论对进一步加原子/分子深材料去除机理提供了一定的理论意义。     

Effect of mechanical process parameters on friction behavior and material removal during sapphire chemical mechanical polishing

The effect of mechanical process parameters such as down force and rotation speed on friction behavior and material removal rate (MRR) was investigated during chemical mechanical polishing (CMP) of sapphire substrate. It was found that the increase in both rotation speed and down force can enhance the MRR and friction force almost linearly depends on the down force and rotation speed. The coefficient of friction (COF) decreases with increasing rotation speed under a fixed down force but keeps constant regardless of variation in down force under a fixed rotation speed. Moreover, the relationship between friction force and MRR was obtained. MRR was proportional to friction force with increasing down force whereas converse proportional to that with increasing the rotation speed. In addition, MRR data are fitted to the Preston equation in the sapphire CMP.     

Effects of process parameter variations on the removal rate in chemical mechanical polishing of 4H-SiC

The effects of temperature, slurry pH, applied pressure, and polishing rotation rate on the material removal rate during chemical mechanical polishing (CMP) of 4H-silicon carbide wafers using colloidal silica slurry and polyurethane/polyester fiber polishing pads have been studied. Measured removal rates varied from around 100 Å/hr to nearly 2500 Å/hr depending on the values of the various parameters. The amount of material removed was determined by measuring the wafer mass before and after polishing. Variations in temperature and slurry pH did not produce significant changes in the measured removal rates. Higher polishing pressures resulted in increased material removal rates from 200 to 500 Å/hr but also produced excessive polishing pad damage. Variations in pad rotational speeds produced the largest changes in material removal rates, from around 200 to around 2000 Å/hr for rotational speeds between 60 and 180 rpm, but the variations were non-linear and somewhat inconsistent. This CMP formula is shown to consistently produce damage free surfaces but the optimum removal rate is slow.     

SiLK dielectric planarization by chemical mechanical polishing

As the feature size of integrated circuits is driven to smaller dimensions the importance of the inter- and intralayer isolator capacitance in future metallization schemes becomes more pronounced. Organic polymers with low dielectric constants are one class of material choice for the replacement of SiO₂. However, their successful integration into functional circuits requires new fabrication procedures. The embedded dielectric scheme offers an evolutionary path for their successful integration into a subtractive etched, aluminum-based integrated circuit. This scheme can effectively lower the total capacitance while minimally changing the rest of the metallization fabrication process. However, the non-conformal deposition of spin-on polymers requires an effective planarization process. Therefore, this paper focuses on the planarization capability of a chemical mechanical polishing process (CMP) using SiLK resin as the interlayer dielectric material. The experimental results demonstrate the high planarization capability of the CMP process using a commercially available slurry. The post-CMP degree of planarization is greater than 95% for all feature dimensions and this planarity can be achieved rapidly. SiLK dielectric coatings are therefore considered as a promising candidate to replace SiO₂ in existing Al/W-based technologies.     

A model for wafer scale variation of removal rate in chemical mechanical polishing based on elastic pad deformation

It is well known that within wafer non-uniformity (WIWNU), due to the variation in material, removal rate (MRR) in the whole wafer plays an important role in determining the quality of a wafer planarized by CMP. Various material removal models also suggest that the MRR is strongly influenced by the interface pressure. In the present work, an analytical expression for pressure distribution at the wafer and pad interface is developed. It is observed that depending on the wafer curvature and polishing conditions, the interface pressure may exhibit significant variation. The analytical model predictions are first verified against finite element method (FEM) simulations. The predicted analytical pressure profiles are then utilized in Preston's equation to estimate the MRR, and these MRR predictions are also compared to experimental observations. The analytical results suggest, that for a specified wafer curvature there exists a certain polishing condition (and vice versa) that will enable holding the WIWNU within a specified tolerance band. The proposed model facilitates the design space exploration for such optimal polishing conditions.     

化学机械抛光中的硅片夹持技术

目前半导体制造技术已经进入0.1 3μm时代,化学机械抛光(CMP)已经成为IC制造中不可缺少的技术.本文描述了下一代IC对大尺寸硅片(≥300mm)局部和全局平坦化精度的要求,介绍了目前工业发达国家在化学机械抛光加工中硅片夹持技术方面的研究现状,分析了当前硅片夹持技术中存在的问题,并指出了未来大尺寸硅片超精密平坦化加工中夹持与定位技术的发展趋势.     

Effect of organic acids on copper chemical mechanical polishing

In chemical mechanical polishing (CMP) of Cu, organic acids are often used as additives of slurries. This paper studied the effects of citric acid, oxalic acid, glycolic acid and glycine on Cu CMP performance. Our experiments explored the difference of these organic acids in surface reactions with Cu. The results showed that organic acids could chelate the passive film of Cu, and oxalic acid would further form precipitates with copper ions to change the chemical and mechanical action during CMP. Potential-pH diagrams, electrochemical polarization and impedance analyses were used to examine the behaviors of Cu in various organic acid slurries. The results indicated that the proposed equivalent circuits from impedance analysis for Cu CMP system could provide a good index to surface roughness. Furthermore, we also discussed the effects of used organic acids on reducing particle contamination after Cu CMP by measuring the difference of isoelectric points between Cu and α-Al₂O₃. The result showed that the addition of organic acid could efficiently decrease particle contamination.     

液体喷射抛光技术研究

液体喷射抛光(FJP)技术是近几年提出的一种新型光学抛光工艺,本文简介了这种抛光技术的原理,介绍了我们的研究结果,其中包括在抛光机理方面提出抛光液中磨料粒子的径向流动对工件产生的径向磨削剪切作用是材料去除的关键;建立了较完善的描述FJP过程的数学模型;提出了获得较理想工作函数的方法;得到了求解时间驻留函数的一种算法;另外还研究了不同FJP溶液及一些工艺参数对样品表面粗糙度的影响、被抛光材料特性对材料去除率及表面粗糙度的影响等.结合这些研究建立了一套非球面数控液体喷射抛光没备和相关工艺,并利用其对实际非球面做了数控抛光实验,最后得到其截面的误差优于0.15靘PV,表面粗糙度Ra达到2.25nm,实验结果表明此技术可用于非球面的数控抛光.     

Experimental investigation on mechanisms of silicon chemical mechanical polishing

In this research, we conducted a series of experiments to investigate the mechanisms of chemical mechanical polishing (CMP) of silicon. Experimental approaches include tribological tests of frictional and lubricating behavior, chemical analysis, and surface characterization. Specifically, the effects of pH in slurry, surface roughness of wafers, and nano-particle size on removal rate were studied. A transmission electron microscope (TEM), a scanning electron microscope (SEM), and x-ray characterization tools were used to study the change of surface structure and chemistry. Experimental results indicate that the removal rate and planarization are dominated by the surface chemistry.     

A model for wafer scale variation of material removal rate in chemical mechanical polishing based on viscoelastic pad deformation

It is well known that within-wafer nonuniformity (WIWNU) due to the variation in material removal rate (MRR) in chemical mechanical polishing (CMP) significantly affects the yield of good dies. The process control for a batch CMP operation is further complicated by wafer-to-wafer nonuniformity (WTWNU) caused by MRR decay when a number of wafers are polished with the same unconditioned pad. Accordingly, the present work focuses on modeling the WIWNU and WTWNU in CMP processes. Various material removal models suggest that the MRR is strongly influenced by the interface pressure. It is also well known that the viscoelastic properties of the pad play an important role in CMP. In the present work, an analytical expression for pressure distribution (and its associated MRR) at the wafer-pad interface for a viscoelastic pad is developed. It is observed that under constant load, which is typical during main polishing in CMP, the spatial distribution of the interface pressure profile may change with time from edge-slow to edge-fast, depending on the combination of wafer curvature, down pressure, and pad properties. For constant displacement operations, the pressure profile retains its edge-slow or edge-fast characteristics over time. The analytical model predictions of MRR based on viscoelastic pad properties also correlate very well to existing experimental observations of MRR decay when an unconditioned pad is used to polish a number of wafers. Based on these observations, it may be conjectured that the viscoelastic material properties of the pad play a primary role in causing the observed MRR decay. The analytical results obtained in the present work can also provide an estimation of evolution of thickness removal distribution over the entire wafer. This may be used for determining the optimum thickness of the overburden material and its polishing time, and for effective control of CMP processes.     

Material removal rate in chemical-mechanical polishing of wafers based on particle trajectories

Distribution forms of abrasives in the chemical mechanical polishing (CMP) process are analyzed based on experimental results.Then the relationships between the wafer,the abrasive and the polishing pad are analyzed based on kinematics and contact mechanics.According to the track length of abrasives on the wafer surface,the relationships between the material removal rate and the polishing velocity are obtained.The analysis results are in accord with the experimental results.The conclusion provides a theoretical guide for further understanding the material removal mechanism of wafers in CMP.     

基于磨粒运动轨迹的硅片化学机械抛光材料去率研究

硅片化学机械抛光（CMP）是机械作用与化学作用相结合的技术,硅片表面的化学反应层主要是由抛光液中磨料的机械作用去除,磨粒对硅片表面的摩擦和划擦对硅片表面材料的去除起着重要作用。磨粒在硅片表面上的划痕长度直接影响硅片表面的材料去除率。本文首先在实验结果的基础上分析了硅片CMP过程中磨粒的分布形式,然后根据运动学和接触力学理论,分析了硅片、磨粒及抛光垫三者之间的运动关系,根据磨粒在硅片表面上的运动轨迹长度,得出了材料去除率与抛光速度之间的关系,该分析结果与实验结果一致,研究结果可为进一步理解硅片CMP的材料去除机理提供理论指导。     

精密数控抛光碳化硅表面去除特性研究

计算机数控精密机械抛光技术是制造高精度、高质量光学元件表面的主要技术之一。然而,对于碳化硅材料表面去除特性方面的研究却相对较少。在航天航空领域中,陶瓷类材料碳化硅的应用较为广泛。针对计算机数控精密机械抛光技术,根据一系列的抛光实验,研究并总结出碳化硅材料表面的去除机理。基于选择不同等级的四种变量参数:抛光磨头转速、抛光压力、磨头补偿量和抛光头角度,分析碳化硅材料表面的去除趋势。采用Taguchi方法可以有效优化实验设计参数、减少实验整体次数。结果表明:文中总结出对应的抛光参数组合和材料表面的去除特性,确保加工出高质量表面的碳化硅材料。     

光学石英基片CMP表面粗糙度的研究

In order to achieve a high-quality quartz glass substrate and to improve the performance of Ti O2 antireflection coating,chemical mechanical polishing(CMP) method was used.During CMP process,some process parameters including pressure,polishing head speed,platen speed,slurry flow rate,polishing time,and slurry temperature were optimized to obtain lower quartz surface roughness.According to the experiment results,when pressure was 0.75 psi,polishing head speed was 65 rpm,platen speed was 60 rpm,slurry flow rate 150 m L/min,slurry temperature 20°C,and polishing time was 60 s,the material removal rate(MRR) was 56.8 nm/min and the surface roughness(Ra) was 1.93 °(the scanned area was 1010 m2/.These results were suitable for the industrial production requirements.     

超大规模集成电路制造中硅片化学机械抛光技术分析

目前半导体制造技术已经跨入0.13μm 和300mm时代,化学机械抛光(CMP)技术在ULSI制造中得到了快速发展,已经成为特征尺寸0.35μm以下IC制造不可缺少的技术。CMP是唯一能够实现硅片局部和全局平坦化的方法,但CMP的材料去除机理至今还没有完全理解、CMP系统过程变量和技术等方面的许多问题还没有完全弄清楚。本文着重介绍了化学机械抛光材料去除机理以及影响硅片表面材料去除率和抛光质量的因素。     

Size effect of nanoparticles in chemical mechanical polishing - a transient model

When a workpiece to be polished is placed on the carrier of a polishing machine, it is pressed down to the polishing pad. Large abrasives make contact between the pad and the workpiece before the smaller ones. The larger abrasives are pressed into the pad and indented into the workpiece. These particles are the active abrasives and participate in material removal. The abrasives with a size less than the gap between the pad and the workpiece move freely in the valleys/voids of the pad and are inactive. As the gap decreases during the polishing process, smaller abrasives trapped between the pad and the workpiece become active in polishing. Thus, the process of chemical-mechanical polishing is dynamic, while all previous modeling is static. This paper establishes a dynamic model for the abrasives. The modeling considers the transient motion of the workpiece/particle/pad in the vertical direction and the change of the roughness of the workpiece. A study of the transient motion shows an increasing number of active particles and a changing polishing rate in the first 2 min. It also demonstrates that the viscoelastic properties of the pad and the workpiece surface roughness are important factors in determining the polishing rate. This paper also shows that when the average particle size is smaller than an optimum size, the polishing rate increases with increasing particle size for the same particle density or same wt% abrasives. Yet, if the average particle size is larger than the optimum size, the polishing rate decreases with increasing particle size.     

在铜CMP过程中降低抛光压力与磨料的机械作用

Chemical mechanical planarization(CMP) is a critical process in deep sub-micron integrated circuit manufacturing. This study aims to improve the planarization capability of slurry, while minimizing the mechanical action of the pressure and silica abrasive. Through conducting a series of single-factor experiments, the appropriate pressure and the optimum abrasive concentration for the alkaline slurry were confirmed. However, the reduced mechanical action may bring about a decline of the polishing rate, and further resulting in the decrease of throughput.Therefore, we take an approach to compensating for the loss of mechanical action by optimizing the composition of the slurry to enhance the chemical action in the CMP process. So 0.5 wt% abrasive concentration of alkaline slurry for copper polishing was developed, it can achieve planarization efficiently and obtain a wafer surface with no corrosion defect at a reduced pressure of 1.0 psi. The results presented here will contribute to the development of a “softer gentler polishing” technique in the future.     

Aluminum-germanium-copper multilevel damascene process usinglow-temperature reflow sputtering and chemical mechanical polishing

A low-temperature multilevel aluminum-germanium-copper (Al-Ge-Cu) damascene technology was developed using reflow sputtering and chemical mechanical polishing (CMP). The maximum processing temperature for the fabrication of multilevel interconnections could be reduced to 420°C using Al-1%Ge-0.5%Cu, whereas the conventional reflow temperature was not less than 500°C. No degradation due to reflow heat cycles was observed in terms of Al-Ge-Cu wiring resistance. Electromigration test results indicated that the mean time to failure (MTTF) of Al-1%Ge-0.5%Cu was longer than 10 years at the operating condition, which was equivalent to that of Al-1%Si-0.5%Cu. The Al-1%Ge-0.5%Cu triple-level interconnection was fabricated using reflow sputtering to fill vias and wiring trenches and subsequent CMP for Al-Ge-Cu films     

Damageless Cu chemical mechanical polishing for porous SiOC/Cu interconnects

Both chemical and mechanical damages to porous SiOC film should be minimized in the Cu-CMP (chemical mechanical polishing) process for the 32-45 nm node Cu interconnect process. This paper first discusses chemical damage that occurs during direct CMP on a porous SiOC film. We found that the k-value increase after direct CMP was caused by the surfactants added to the cleaning chemicals to suppress watermark generation on the hydrophobic SiOC film surface. The surfactants assisted water molecule diffusion into the pores by improving the wettability of the film surface. N₂ annealing after direct CMP removed moisture inside the pores and restored the k-value increase. Second, the paper discusses low-pressure electro-CMP (e-CMP) technology that we developed to reduce mechanical stress on the porous SiOC film. A high removal rate and good planarization performance were obtained by optimizing the cathode area of the electro-cell and carbon material of the e-CMP pad.