Mechanisms of Chemical-Mechanical Polishing of SiO2 Dielectric on Integrated Circuits

One of the fundamental mechanisms of chemical-Mechanical polishing (CMP) is the mechanical interaction between the wafer and polishing pad. This interaction was simulated in experiments. The vertical displacement of the wafer with respect to the polishing pad, the fictional drag of the wafer against the pad, and the pressure of the slurry trapped between the wafer and pad were measured. These experiments were performed over a range of commercially common CMP conditions. In addition, polishing rates were measured for CMP performed under induced hydrodynamic conditions where the wafer was separated from the pad by a film of slurry.

It was found that no appreciable polishing occurred under hydrodynamic CMP conditions. Under commercial CMP conditions, it was found that the wafer contacts the polishing pad asperities as evidenced by near-zero wafer displacement and high friction coefficients (?0.4). It was also found that pad conditioning (intentional roughening) causes a suction force to develop between the wafer and pad. This suction force draws the wafer into further contact with the pad, by as much as 20 μm, and corresponds to peak slurry vacuum pressures of 12 kPa (1.7 psi).     

Estimating the mechanical properties of polyurethane-impregnated felt pads

Chemical mechanical polishing (CMP) is an essential process in semiconductor fabrication. The results of CMP process are determined with the selection of consumables and process parameters. The polishing pad transports the slurry to the interface between the polishing pad and wafer and obtains material removal planarity. The mechanical properties of the polishing pad should be studied to analyze the material removal mechanism of CMP because polishing pad deformation is directly related to material removal rate and its uniformity. Various studies have investigated the stress distribution of the CMP process by using the elastic modulus and Poisson’s ratio of the polishing pad. However, these aspects of polishing pad have not been fully elucidated. In this study, we estimated the mechanical properties of commercial polyurethane-impregnated felt pads by comparing the experimentally measured compressive deformation amounts with finite element analysis results.     

Factors influencing the dressing rate of chemical mechanical polishing pad conditioning

The primary consumables in the chemical mechanical polishing (CMP) process are the polishing pad and the slurry. Among those consumables, the polishing pad significantly influences the stability of the process and the cost of consumables (CoC). Furthermore, the small holes on the pad surface will be filled by the reactant from the CMP process, and the surface of the pad will deposit hard glazing gradually. The glazing not only reduces the ability of absorbing slurry of the pad, but it also causes scratching on the work piece. In order to maintain the stability of the CMP process and return to an ideal pad surface status, we must condition the pad according to a regular time schedule. At the same time, if we use different pad conditioning factors, the dressing rate of the CMP pad will be different. Most important of all, we have to decrease the pad material abrasion due to the pad conditioning process. In conclusion, if we can understand the influence of the dressing rate and conditioning factors effectively, it will be useful for maintaining CMP process stability, extending pad life, and reducing CoC and non-processing time.     

A study of material removal amount of sapphire wafer in application of chemical mechanical polishing with different polishing pads

The study mainly explores the fabrication mechanism for fabricating sapphire wafer substrate, by using chemical mechanical polishing (CMP) method. A slurry containing the abrasive particles of SiO₂ is used to contact with the sapphire substrate polish and to produce chemical reaction for removal of sapphire wafer substrate when CMP method is used. The study observes the changes of the removal amount of sapphire wafer substrate when the pattern-free polishing pad and hole-pattern polishing pad are used under different down forces, polishing velocities, abrasive particle sizes and slurry concentrations. Employing regression analysis theory, the study makes improvement of the equation of material removal rate (MRR) to be the material removal height per 30 minutes (MRRh), and develops a compensation parameter C_rv of the error caused by the volume concentration of slurry. The results of experimental analysis show that under a certain down force, if the polishing velocity is greater, the material removal amount will be greater. Generally speaking, the material removal amount of hole-pattern polishing pad is greater than that of pattern-free polishing pad. As to the relationship between abrasive particle size and slurry concentration, when particle size is smaller, the volume concentration of slurry will be higher, and the number of abrasives for polishing wafer will be greater. As a result, a better material removal depth can be acquired. Through the above analytical results, considerable help is offered to the polishing of sapphire wafer.     

A review on the progress towards improvement in surface integrity of Inconel 718 under high pressure and flood cooling conditions

Self-conditioning performance of polishing pad is an important characteristic to influence processing efficiency and service life in chemical mechanical polishing (CMP). The slurry can react with the pad surface, which affects its self-conditioning performance in fixed abrasive polishing process. Wear ratio of wafer material removal rate (MRR) and pad wear rate is introduced to evaluate self-conditioning performance of fixed abrasive pad (FAP). To clear the effect of chemical additive on FAP self-conditioning, wear ratio, FAP surface topography, friction coefficient, and acoustic emission signal of polishing process were investigated in fixed abrasive polishing of quartz glass with ferric nitrate, ethylenediamine (EDA), and triethanolamine (TEA) slurry, respectively. Results indicate that TEA slurry can provide excellent self-conditioning of FAP in fixed abrasive polishing of quartz glass. MRR and wear ratio maintain high levels during the whole polishing process. Friction coefficient and acoustic emission signal are more stable than that of the other two chemical additives. An appropriate amount of TEA, which is beneficial to enhance MRR and extends service life of FAP, is added in the polishing slurry to improve FAP self-conditioning in fixed abrasive polishing process.     

Numerical analysis of hydrodynamic process of circular-translational-moving polishing (CTMP)

By keeping a pad moving relative to a wafer along a circular path without rotation, we developed a polishing technique called circular-translational-moving polishing (CTMP), which permits multidirectional polishing of the work piece and thus bears the advantage of isotropic polishing and a potential increase of material removal rate (MRR) on the wafer. To illuminate the mechanisms of CTMP and determine the optimum process variables in a CTMP process, a three-dimensional hydrodynamic lubrication model for CTMP with a smooth and rigid pad under a quasi-stable state is established in a polar coordinate system. The model equations are further calculated numerically by the finite difference method. The instantaneous distribution of fluid pressure is obtained, which shows that a negative pressure exists. The reason for negative pressure in CTMP and its effect on polishing is discussed. Moreover, the nominal clearance of the fluid film, roll, and pitch angles under different working conditions are obtained in terms of the applied load, moments, and polishing velocity. The obtained numerical analysis can be used as guidance for choosing operation parameters in a practical CTMP application.     

Numerical analysis of hydrodynamic process of circular-translational-moving polishing (CTMP)

By keeping a pad moving relative to a wafer along a circular path without rotation, we developed a polishing technique called circular-translational-moving polishing (CTMP), which permits multidirectional polishing of the work piece and thus bears the advantage of isotropic polishing and a potential increase of material removal rate (MRR) on the wafer. To illuminate the mechanisms of CTMP and determine the optimum process variables in a CTMP process, a three-dimensional hydrodynamic lubrication model for CTMP with a smooth and rigid pad under a quasi-stable state is established in a polar coordinate system. The model equations are further calculated numerically by the finite difference method. The instantaneous distribution of fluid pressure is obtained, which shows that a negative pressure exists. The reason for negative pressure in CTMP and its effect on polishing is discussed. Moreover, the nominal clearance of the fluid film, roll, and pitch angles under different working conditions are obtained in terms of the applied load, moments, and polishing velocity. The obtained numerical analysis can be used as guidance for choosing operation parameters in a practical CTMP application.     

利用三维格子Boltzmann法研究化学机械抛光中压力分布

利用三维格子Boltzmann法(LSM),对化学机械抛光(CMP)的润滑过程做了数值模拟,得到了不同晶片和抛光垫转速下的压力分布,并讨论了抛光液黏度对高压涡中压力最大值的影响.数值模拟结果表明,晶片自转是产生"双涡图"的主要原因,抛光垫旋转则主要产生"单涡图",抛光垫和晶片旋转的综合作用一起影响抛光效果,其中抛光垫的转速的改变对去除率影响较大.利用格子Bohzmann法模拟润滑问题,所得结果与求解Reynolds方程的结果一致,并具有计算效率高、几何直观等特性,能实现CMP过程的三维模型,且较容易实现对多相流的模拟.     

CMP过程芯片表面氧化膜生成速度影响因素的分析

根据理论和试验分析,将机械化学抛光(CMP)过程分成两个阶段:化学作用主导阶段和机械作用主导阶段,并从机械作用角度导出CMP过程两个阶段芯片表面材料去除率的数学模型,模型全面地考虑了抛光盘特性参数(弹性模量、硬度、表面粗糙度峰的尺寸分布)、CMP工作参数(压力和抛光速度)、抛光液中磨粒的机械作用和氧化剂种类、氧化剂浓度等化学作用的影响。然后根据这两个阶段的平衡点导出定量描述芯片表面氧化膜生成速度的数学模型。详细分析机械作用因素(磨粒的浓度、磨粒的粒度分布特性)、化学作用因素(抛光液中氧化剂种类、浓度)以及磨粒/芯片/抛光盘的材料特性参数对芯片表面氧化膜生成速度的影响规律。该CMP过程芯片表面氧化膜生成速度定量模型的导出,对进一步深入研究CMP材料去除机理和更加准确地控制CMP过程,具有一定的指导作用。     

High precision chemical mechanical polishing of highly-boron-doped Si wafer used for epitaxial substrate

The surface waviness with concentric circular pattern is generated on highly-boron-doped Si wafer by chemical–mechanical polishing (CMP) with amine system polishing slurry. To investigate the generation mechanism of the waviness, the mechanical and chemical characteristics were clarified using the silicon crystal samples with various boron concentration level ranging from 2.9 × 10¹⁷ cm⁻³ to 1.3 × 10²⁰ cm⁻³. The conventional silicon substrate used as epitaxial wafer has boron concentration of about 2.5 × 10¹⁸ cm⁻³, a region at which the radical change of etching rate is induced with amine system chemical reagent. The mechanical micro-hardness of highly-boron-doped Si is 30% higher than that of lightly-doped Si. It is found that SiB bond in crystal lattice is firmed up and stabilized for mechanical stress and chemical reaction. To cancel the difference in CMP rate based on boron concentration deviation, increasing the mechanical action in CMP was proposed and performed. The precision CMP was performed using the harder polishing pad and a smooth surface without waviness was obtained.     

A study on the stress and nonuniformity of the wafer surface for the chemical-mechanical polishing process

In this paper, a two-dimensional axisymmetric quasic-static model for the chemical-mechanical polishing process (CMP) was established. Based on the principle of minimum total potential energy, a finite element model for CMP was thus established. In this model, the four-layer structures including the wafer carrier, the carrier film, the wafer and the pad are involved. The von Mises stress distributions on the wafer surface were analysed, and the effects of characteristics of the pad and the carrier film and the load of the carrier on the von Mises stress and nonuniformity on the wafer surface were investigated. The findings indicate that the profile of the von Mises stress distributions correlates with the removal rate profile. The elastic modulus and thickness of pad and carrier load would significantly affect the von Mises stress and nonuniformity, but those of the film did not affect very much.     

集成电路制造中的固结磨料化学机械抛光技术研究

经过对传统化学机械抛光技术的研究与分析，指出了目前ULSI制造中使用的传统化学机械抛光技术的缺点，通过对固结磨料化学机械抛光中的抛光垫结构、抛光机原理及抛光液的分析，得出了固结磨料化学饥械抛光技术的优点，同时还对硅片固结磨料化学机械抛光的缺陷进行了研究。     

Chemical boundary lubrication in chemical–mechanical planarization

Chemical–mechanical planarization (CMP) is a synergistic tribological process. It occurs between a polymeric polishing pad, a solid body to be made smooth, between which is a chemical slurry containing nanoparticles of abrasive materials. CMP functions similar to chemical boundary lubrication of mechanical systems, except that the objective of the CMP is to remove materials in a controlled manner. In this article, the lubricating behaviors of CMP are reviewed.     

Effect of conditioner load on the polishing pad surface during chemical mechanical planarization process

During the Chemical mechanical planarization (CMP), the pad conditioning process can affect the pad surface characteristics. Among many CMP process parameters, the improper applied load on the conditioner arm may have adverse effects on the polyurethane pad. In this work, we evaluated the pad surface properties under the various conditioner arm applied during pad conditioning process. The conditioning pads were evaluated for surface topography, surface roughness parameters such as Rt and Rvk and Material removal rate (MRR) and within-wafer non-uniformity after wafer polishing. We observed that, the pad asperities were collapsed in the direction of conditioner rotation and blocks the pad pores applied conditioner load. The Rvk value and MRR were founded to be in relation with 4 > 1 > 7 kgF conditioner load. Hence, this study shows that, 4 kgF applied load by conditioner is most suitable for the pad conditioning during CMP.

     

单晶硅同质互抛实验研究

以材料的去除率和表面粗糙度为评价指标设计对比实验,验证了硬脆材料互抛抛光的可行性,得到了抛光盘转速对硬脆材料互抛的影响趋势和大小。实验结果表明：当抛光压力为48 265 Pa（7 psi）、抛光盘转速为70 r/min时,自配抛光液互抛的材料去除率为672.1 nm/min,表面粗糙度为4.9 nm,与传统化学机械抛光方式的抛光效果相近,验证了硬脆材料同质互抛方式是完全可行的;互抛抛光液中可不添加磨料,这改进了传统抛光液的成分;采用抛光液互抛时,材料去除率随着抛光盘转速的增大呈现先增大后减小的趋势,硅片的表面粗糙度随着抛光盘转速的增大呈先减小后增大的趋势。     

叶序结构抛光垫表面的抛光液流场分析

为了解决在化学机械抛光过程中抛光接触区域内抛光液的分布均匀性问题,基于生物学的叶序理论,设计葵花籽粒结构的仿生抛光垫,建市化学机械抛光抛光液流场的运动方程和边界条件,利用流体力学软件(Fluent)对抛光液的流动状态进行仿真,并获得叶序参数对抛光液流动状态的影响规律.结果表明:抛光液在基于葵花籽粒的仿生抛光垫的流动是均匀的,抛光液沿着逆时针和顺时针叶列斜线沟槽流动,有利于流体向四周发散.     

A micro-contact and wear model for chemical–mechanical polishing of silicon wafers

A micro-contact and wear model for chemical–mechanical polishing (CMP) of silicon wafers is presented in this paper. The model is developed on the basis of elastic–plastic micro-contact mechanics and abrasive wear theory. The synergetic effects of mechanical and chemical actions are formulated into the model. A close-form equation of material removal rate from the wafer surface is derived relating to the material, geometric, chemical and operating parameters in a CMP process. The model is evaluated by comparing the theoretical removal rates with those experimentally determined. Good agreement is obtained for both chemically active and inactive polishing processes. The model reveals some insights into the micro-contact and wear mechanisms of the CMP process. It suggests that the removal rate is sensitive to the particle concentration in the slurry, more sensitive to the applied load and operating speed and most sensitive to the surface hardness and slurry particle size. The model may be used to study the effects of different materials, geometry, slurry chemistry and operating conditions on CMP processes.     

Analysis of Feature-Scale Wear in Chemical Mechanical Polishing: Modeling and Experiments

An asperity-scale wear model was developed to predict feature-scale wear in chemical–mechanical polishing (CMP), and was compared to the measured evolution of a lithographically patterned feature during full-scale CMP tests. To conduct this study, a lithographic technique was used to pattern a set of raised square features into a Cu-coated silicon wafer. Two-dimensional contact profilometry was used to measure the topography of an isolated feature on each wafer both before polishing and at various intervals throughout the polishing process. In the wear modeling formulation, a pad deflection-based contact mechanics model was developed and combined with a particle-based wear model to predict the wear evolution of the sample during CMP. The predicted wear of the sample feature was found to agree well to experimental results.     

Evaluation of environmental impacts during chemical mechanical polishing (CMP) for sustainable manufacturing

Reducing energy consumption has become a critical issue in manufacturing. The semiconductor industry in particular is confronted with environmental regulations on pollution associated with electric energy, chemical, and ultrapure water (UPW) consumptions. This paper presents the results of an evaluation of the environmental impacts during chemical mechanical polishing (CMP), a key process for planarization of dielectrics and metal films in ultra-large-scale integrated circuits. The steps in the CMP process are idling, conditioning, wetting, wafer loading/unloading, head dropping, polishing, and rinsing. The electric energy, CMP slurry, and UPW consumptions associated with the process and their impacts on global warming are evaluated from an environmental standpoint. The estimates of electric energy, slurry, and UPW consumptions as well as the associated greenhouse gas emissions presented in this paper will provide a technical aid for reducing the environmental burden associated with electricity consumption during the CMP process.     

Pad surface and coefficient of friction correlation analysis during friction between felt pad and single-crystal silicon

In wafer polishing pad surface plays a crucial role in the polishing process. With the increase of friction time between pad and wafer, the pad becomes flattened or glazed with particles clogging the pores of the pad and forming a layer of slurry residue and wafer particles, leading to changes of COF, material removal rates and higher defects on the wafer surface. Thus, this study aims to determine the correlation between pad surface deformation, slurry adhesive rate and Coefficient of friction (COF) during friction between felt pad and single -crystal silicon, to analyze the relationship between pad condition and COF. The real-time COF between felt pad and single-crystal silicon wafer are tested which are sorted in groups depending on various loads and oscillation frequencies and surfaces of felt pads measuring by Scanning electron microscope (SEM) are compared. The correlation between pad surface deformation and abrasive adhesion and COF is evaluated through analyzing the experiment results.