Strategies for Optimal Chemical Mechanical Polishing (CMP) Slurry Design

Abstract

Chemical mechanical polishing (CMP) has become the preferred route for achieving wafer‐level global planarization in microelectronics device manufacturing. However, the micro‐ to molecular‐level mechanisms that control its performance and optimization are not well understood. In CMP, complex slurry chemistries react with the first few atomic layers on the wafer surfaces forming a chemically modified film. This film is subsequently mechanically abraded by nanosized slurry particles to achieve local and global planarity for multi‐level metalization. For optimal CMP performance, high material removal rates with minimal surface defectivity are required. This can be achieved by controlling the extent of interparticle and particle–substrate interactions, which are facilitated through the manipulation of the slurry composition, solution chemistry, as well as operational parameters. Interparticle interactions must be engineered to maintain slurry stability to minimize the number and extent of surface defects during polishing while maintaining adequate removal rates. The fundamental considerations, which are necessary for the development of high performance CMP slurries, are discussed in this article through model silica CMP systems.     

Role of interaction forces in controlling the stability and polishing performance of CMP slurries

Chemical mechanical polishing (CMP) is an essential step in metal and dielectric planarization in multilayer microelectronic device fabrication. In the CMP process it is necessary to minimize the extent of surface defect formation while maintaining good planarity and optimal material removal rates. These requirements are met through the control of chemical and mechanical interactions during the polishing process by engineering the slurry chemistry, particulate properties, and stability. In this study, the performance of surfactant-stabilized silica CMP slurries at high pH and high ionic strengths are investigated with particular emphasis on the particle-particle and particle-substrate interactions. It is shown that for the design of consistently high performing slurries, stability of abrasive particles must be achieved under the dynamic processing conditions of CMP while maintaining sufficient pad-particle-wafer interactions.     

Analysis the microscopic solid‐based wear process in the chemical mechanical planarization

Chemical mechanical planarization (CMP), being the important technique of realizing the surface planarization, has already been widely applied in the microelectronic and computer industry. The abrasive size employed in the CMP, far less than that employed in the conventional grinding and material removal during CMP, is on the order of atoms or clusters of atoms and molecules. Classical continuum mechanics cannot give a reasonable explanation about the phenomenon in the CMP. Large‐scale classical molecular dynamics simulation of tribology interaction among nanoparticles and materials surface has been carried out to investigate the physical essence of surface planarization. The results show that simultaneous impact of several abrasive particles or the repeated impact of abrasive particles leads to material failure. For individual asperity contact in the CMP, non‐obvious Archard adhesive wear or abrasive wear is observed. The contact area is not entirely dependent upon the external pressure but also closely related to the relative position because of lateral motion between the particles and the substrate. The results also justify that no single wear mechanism dominates all operating conditions; different wear mechanisms operate with their relative importance changing as the sliding conditions change. As the slurry particles slide relative to the wafer surface, the atomic groups experience three stages, namely, interlock, elastic–plastic deformation and finally slip process; the surface planarization is mainly accomplished in the last two stages. Copyright © 2011 John Wiley & Sons, Ltd.     

钨的化学机械抛光过程中TiN-W电偶的腐蚀行为(英文)

化学机械抛光 (CMP)技术是同时利用化学和机械作用来获得固体表面亚微米尺度上平整性非常有效的方法 ,从 90年代初期起已成为制备高质量镜头和镜面及集成电路制造过程中硅片表面预处理工艺中最常用的技术之一 .钨的化学机械抛光是用钨坯获得硅片球面平整度的重要工艺 .其过程实际上是先将钨沉积到硅上已有的薄粘附层 -氮化钛上 ,然后进行化学机械抛光 .当抛光阶段接近终了时 ,氮化钛和钨表面将同时暴露在化学抛光液中形成电偶对 ,并在界面上发生腐蚀行为 ,从而影响硅片的球面平整度 ,降低半导体器件的性能与可靠性 .本文通过采用电化学直流极化技术 ,分别获得钨与氮化钛在 0 .0 1mol/LKNO3溶液中或含有三种典型的研磨剂 (H2 O2 ,KIO3,Fe(NO3) 3)溶液中的极化曲线 ,同时设计了一种特殊的电解槽以测量钨和氮化钛之间相互作用的电流 ,初步研究了 patterned硅片上钨和氮化钛界面形成电偶对时的腐蚀行为 .根据所测的钨和氮化钛电位可知 ,当钨和氮化钛表面同时暴露在抛光液中时将形成电偶对 ,氮化钛成为阴极 ,钨为阳极 ,并于界面发生电化学反应 ,表面的不均匀腐蚀将造成硅片平整度的降低 .结果表明 ,当溶液中含有H2 O2 时钨和氮化钛界面的腐蚀速度最大 ,而当溶液中含有Fe(NO3) 3时的钨和氮化钛界面则几乎不发     

CORRELATION OF DISPERSION STABILITY WITH SURFACTANT CONCENTRATION AND ABRASIVE PARTICLE SIZE FOR CHEMICAL MECHANICAL POLISHING (CMP) SLURRIES

The preparation of stable colloidal slurries is often difficult in industries where many chemical components are added into the slurries. A critically acclaimed example of such an industry is the chemical mechanical polishing (CMP) industry which involves polishing slurries with several chemical additives. In the present work, the stabilization of a slurry used for CMP of metals is investigated in detail. This high ionic strength slurry has been stabilized using an optimaJ combination of sodium dodecyl sulfate (anionic surfactant) and Tween 80 (nonionic surfactant). The amount of surfactant needed to impart stability has been investigated in this study for two different sizes of abrasive particles. It has been found that the amount of surfactant needed to stabilize the slurry increases as the total surface area per gram of panicles increases. Slurry stabilization has been correlated with particle size measurements. It has been found that the average panicle size of the slurry decreases as the stability of the slurry increases. Stable slurries have been found to have particle sizes close to those of the particles before agglomeration. It is proposed that the stabilized CMP slurries can lead to reduced defects in wafers by preventing agglomeration of panicles.     

Water-in-Oil Dispersion for KH2PO4 (KDP) Crystal CMP

Chemical mechanical polishing (CMP) has become an essential process in the manufacturing of advanced microelectronic devices. More recently, CMP has also been applied to the process of other advanced materials such as optical crystals and thin films. Typically, a CMP slurry is formulated as an aqueous dispersion which may contain abrasive particles, activating agent, passivating agent, surfactant, etc. Due to its sensitivity to water, hygroscopic crystals must not be processed with aqueous based slurry. In this study, a new abrasive-free system based on water-in-oil microemulsion was investigated to address this challenge. More specifically, a dispersion made of dodecanol, Triton X-100, and water was studied for its potential application in KH₂PO₄(KDP) crystal processing. In this unique polishing system, water molecules are caged into micelles so the reaction between KDP and water is controlled. As a result, the static etch rate of the substrate surface is minimized. During polishing process, the frictional action between crystal surface and pad leads to the release of reactive water molecules. The material removal is, thus, enhanced. In this paper, the techniques used to characterize such abrasive-free system were first introduced. The water-in-oil structures were characterized and confirmed by conductivity, dynamic lighting scattering and dynamic nuclear magnetic resonance (NMR) measurements. The performance of this system on the process of KDP crystals was then discussed. The static etch rate and the material removal rate in polishing process were measured under various conditions in order to elucidate the polishing mechanism. Finally, the potential application of such a novel nonaqueous polishing system in CMP beyond KDP crystals is discussed.     

Cassia obtusifolia MetE as a Cytosolic Target for Potassium Isolespedezate,a Leaf‐Opening Factor of Cassia plants: Target Exploration by a Compact Molecular‐Probe Strategy

Affinity chromatography by using ligand‐immobilized bead technology is generally the first choice for target exploration of a bioactive ligand. However, when a ligand has comparatively low affinity against its target, serious difficulties will be raised in affinity‐based target detection. We report here that the use of compact molecular probes (CMP) will be advantageous in such cases; it enables the retention of moderate affinity between the ligand and its target in contrast to immobilizing the ligand on affinity beads that will cause a serious drop in affinity to preclude target detection. In the CMP strategy, a CMP containing an azide handle is used for an initial affinity‐based labeling of target, and subsequent tagging by CuAAC with a large FLAG tag will give a tagged target protein. By using the CMP strategy, we succeeded in the identification of Cassia obtusifolia MetE as a cytosolic target protein of potassium isolespedezate ( 1 ), a moderately bioactive ligand.     

Modulated self-assembly of metal–organic frameworks

Exercising fine control over the synthesis of metal–organic frameworks (MOFs) is key to ensuring reproducibility of physical properties such as crystallinity, particle size, morphology, porosity, defectivity, and surface chemistry. The principle of modulated self-assembly – incorporation of modulator molecules into synthetic mixtures – has emerged as the primary means to this end. This perspective article will detail the development of modulated synthesis, focusing primarily on coordination modulation, from a technique initially intended to cap the growth of MOF crystals to one that is now used regularly to enhance crystallinity, control particle size, induce defectivity and select specific phases. The various mechanistic driving forces will be discussed, as well as the influence of modulation on physical properties and how this can facilitate potential applications. Modulation is also increasingly being used to exert kinetic control over self-assembly; examples of phase selection and the development of new protocols to induce this will be provided. Finally, the application of modulated self-assembly to alternative materials will be discussed, and future perspectives on the area given.

This Perspective gives an overview of the modulated self-assembly of MOFs – incorporating additives and alternative precursors into syntheses – focusing on its varying influences on crystallization mechanisms, physical properties, and applications.     

Stabilization of gamma alumina slurry for chemical-mechanical polishing of copper

Stabilization of gamma-alumina suspension for chemical-mechanical polishing (CMP) of copper was investigated. Citric acid and poly(acrylic acid) (PAA) (M(w)=5000) were used as dispersant. The stability of suspension was evaluated from the changes in viscosity, particle size and zeta potential. It appears that metastable gamma-alumina mainly due to its high specific surface area and to the presence of aluminol groups on its surface is progressively transformed to bayerite (beta-Al(OH)(3)) by hydration procedure. Citric acid molecules were adsorbed onto gamma-alumina surface effectively and exhibited the excellent hydration inhibition effect. Although citrate-alumina surface complexes give barrier to the flocculation, the repulsion potential is based mainly on the electrostatic repulsion, thereby steric hindrance caused by the adsorption of these small molecules is very weak. The electrosteric repulsion, which provides more effective dispersion stability than electrostatic repulsion force, can be expected by using polyelectrolyte such as PAA; however, adsorbed layers of PAA onto solid/liquid interface are loosely formed. Therefore, a large amount of PAA was required to inhibit the surface hydration of gamma-alumina suspension, thereby the excess addition of PAA decreased the electrosteric repulsion and re-bridging of the dispersant between particles caused an increase in suspension viscosity. Therefore, synergistic effect can be expected in mixed dispersant system of citric acid and PAA, since small citric acid molecules are adsorbed faster than PAA, inhibiting the progress of surface hydration, and then adsorbed PAA layers exhibit the effective electrosteric repulsion interaction between particles with a small amount compared with PAA alone. It was revealed that the gamma-alumina slurry dispersed by mixed dispersant exhibited the improved removal rate of Cu layer by CMP polishing test.     

计算机硬盘基片CMP中表面膜特性的分析研究

目前,普遍采用化学机械抛光(Chemical-mechanical polishing,CMP)技术对计算机硬盘基片(盘片)表面进行原子级平整。CMP加工中,盘片表面膜及其特性对CMP过程及CMP性能具有关键作用。本文分别采用俄歇能谱(AES)、X射线光电子能谱(XPS)、扫描电镜(SEM)、纳米硬度计、电化学极化法等分析手段对盘片表面物理、化学及机械特性进行了研究,发现盘片CMP后表面发生了氧化,氧化膜在盘片的表层,厚度在纳米量级,氧化产物为Ni(OH)₂;氧化膜为较软的、疏松的、粗糙的多孔结构;氧化膜的存在加快了盘片表面的腐蚀磨损。结合盘片CMP试验结果,推测盘片的CMP机理为盘片表面氧化生成机械强度较低的Ni(OH)₂氧化膜及随后氧化膜的机械和化学去除,二者的不断循环实现表面的全局平面化。     

The planarity of heteroatom analogues of benzene: Energy component analysis and the planarization of hexasilabenzene

There are various nonplanar heteroatom analogues of benzene—cyclic 6π electron systems—and among them, hexasilabenzene (Si₆H₆) is well known as a typical example. To determine the factors that control their planarity, quantum chemical calculations and an energy component analysis were performed. The results show that the energy components mainly controlling the planarity of benzene and hexasilabenzene are different. For hexasilabenzene, electron repulsion energy was found to be significantly important for the planarity. The application of the pseudo Jahn–Teller effect and the Carter–Goddard–Malrieu–Trinquier model for the interpretation of the planarity of the benzene analogues was also investigated. Furthermore, based on the quantitative results, it was revealed that the planarization of hexasilabenzene is realized by introducing substituents with π-accepting ability, such as the boryl group, that bring about a reduction of the π-electron repulsion on the silicon skeleton. © 2018 Wiley Periodicals, Inc.     

Interactions between particles with an undulated contact line at a fluid interface: capillary multipoles of arbitrary order

A colloidal particle adsorbed at a fluid interface could have an undulated, or irregular contact line in the presence of surface roughness and/or chemical inhomogeneity. The contact-line undulations produce distortions in the surrounding liquid interface, whose overlap engenders capillary interaction between the particles. The convex and concave local deviations of the meniscus shape from planarity can be formally treated as positive and negative "capillary charges," which form "capillary multipoles." Here, we derive theoretical expressions for the interaction between two capillary multipoles of arbitrary order. Depending on the angle of mutual orientation, the interaction energy could exhibit a minimum, or it could represent a monotonic attraction. For undulation amplitudes larger than 5 nm, the interaction energy is typically much greater than the thermal energy kT. As a consequence, a monolayer from capillary multipoles exhibits considerable shear elasticity, and such monolayer is expected to behave as a two-dimensional elastic solid. These theoretical results could be helpful for the understanding of phenomena related to aggregation and ordering of particles adsorbed at a fluid interface, and for the interpretation of rheological properties of particulate monolayers. Related research fields are the particle-stabilized (Pickering) emulsions and the two-dimensional self-assembly of microscopic particles.     

Formation mechanism of nonspherical gold nanoparticles during seeding growth: roles of anion adsorption and reduction rate

A small section of nonspherical particles can be observed in the further growth of spherical gold colloids exposed to a mixture of NH2OH and HAuCl4. The concentration ratio of [NH2OH]:[HAuCl4] is critical for the formation of nonspherical particles as higher ratios produce lower yields and smaller of such particles. These concentrations also affect the reaction kinetics; the reaction rate increases with [NH2OH], while independent of [HAuCl4], which we believe is due to the specific adsorption of AuCl4- onto gold surface. These nonspherical particles come from the preferential growth of {111} facets as indicated by their TEM images and electron diffraction patterns. We propose this preferential growth is ascribed to the preferential adsorption of AuCl4- on {111} facets, and some competition which determines the yield of nonspherical particles exists between the AuCl4- adsorption and the AuCl4- reduction, faster reduction counteracting the effect of this preferential adsorption and thus suppressing nonspherical particle. This result probably provides some guidance to develop a shape-controlled synthesis of gold particles without any additives.     

Colloid aspects of chemical-mechanical planarization

The essential parts of interconnects for silicon based logic and memory devices consist of metal wiring (e.g. copper), a barrier metal (Ta, TaN), and of insulation (SiO2, low-k polymer). The deposition of the conducting metal cannot be confined to trenches, resulting in additional coverage of Cu and Ta/TaN on the surface of the dielectrics, yielding an electrically conducting continuous but an uneven surface. The surplus metal must be removed until a perfectly flat surface consisting of electrically isolated metal lines is achieved with no imperfections. This task is accomplished by the chemical-mechanical planarization (CMP) process, in which the wafer is polished with a slurry containing abrasives of finely dispersed particles in submicrometer to nanometer size. The slurries also contain dissolved chemicals to modify the surfaces to be planarized. Eventually the final product must be cleared of any adhered particles and debris left after polishing is completed. Obviously the entire process deals with materials and interactions which are the focal subjects of colloid and surface science, such as the natures of abrasive particles and their stability in the slurry, the properties of various surfaces and their modifications, adhesion and detachment of the particles and different methods for the characterization of constituents, as well as elucidation of the relevant interfacial phenomena. This review endeavors to describe the colloid approach to optimize the materials and processes in order to achieve desirable polish rates and final surfaces with no imperfections. Specifically, the effects of the composition, size, shape, and charge of abrasive particles on the polish process and the quality of planarized wafers is described in detail. Furthermore, the interactions of metal surfaces with oxidizing, chelating, and other species which affect the dissolution and surface modification of metal (copper) surfaces are illustrated and related to the planarization process. Finally, using the packed column technique the adhesion phenomena of abrasives on metals and oxides is evaluated on suitable model systems, that contain the same additives in the slurries as in the actual planarization process. A close correlation is established in all cases between the attachment and detachment results with experimentally determined polish rates.     

铜在甲胺介质铁氰化钾化学-机械抛光液中的电化学行为

二甲氧基苯胺;铜在甲胺介质铁氰化钾化学-机械抛光液中的电化学行为     

Efficient synthesis of asymmetric particles by sol-gel process

This paper presents a novel and facile method of synthesizing polymer/silica particles with controlled asymmetric morphologies. Our approach is based on the sol–gel process in which cross-linked polystyrene particles (CPS) are adopted as templates and 3-mercaptopropyltriethoxysilane is used as a single silica source. The reaction process causes silane oligomer to preferentially grow on the local surface of CPS, giving rise to polystyrene/thiol-functionalized silica composite particles with a tunable shape. It is found that the morphologies of particles can be easily tailored by changing the ratio of ethanol/water in the reaction medium. In addition, the amount of cross-linker used during the polymerization also plays a key role in the formation of various complex-shaped particles. Controlled geometries of these organic/inorganic composite particles will allow a broad range of potential applications, such as photonic crystals, Pickering emulsifier, sensors, and so on.     

Organic‐Stabilizer‐Free Polyol Synthesis of Silver Nanowires for Electrode Applications

The polyol reduction of a Ag precursor in the presence of an organic stabilizer, such as poly(vinylpyrrolidone), is a widely used method for the production of Ag nanowires (NWs). However, organic capping molecules introduce insulating layers around each NW. Herein we demonstrate that Ag NWs can be produced in high yield without any organic stabilizers simply by introducing trace amounts of NaCl and Fe(NO₃)₃ during low‐temperature polyol synthesis. The heterogeneous nucleation and growth of Ag NWs on initially formed AgCl particles, combined with oxidative etching of unwanted Ag nanoparticles, resulted in the selective formation of long NWs with an average length of about 40 μm in the absence of a capping or stabilizing effect provided by surface‐adsorbing molecules. These organic‐stabilizer‐free Ag NWs were directly used for the fabrication of high‐performance transparent or stretchable electrodes without a complicated process for the removal of capping molecules from the NW surface.     

氧化铝-g-聚丙烯酰胺复合磨粒的制备及表征

为提高α-Al₂O₃磨粒在水基介质中的分散稳定性，采用接枝聚合方法制备了Al₂O₃-g-聚丙烯酰胺复合粒子。采用FTIR、XPS、TOF-SIMS、激光粒度仪、SEM、沉降试验等对氧化铝复合粒子结构及分散性能等进行了表征。结果表明，聚丙烯酰胺以化学键形式接枝到Al₂O₃粒子表面，形成聚丙烯酰胺为壳，Al₂O₃为核的复合磨粒;接枝改性后的Al₂O₃粒子分散性明显提高，并且其分散性与Al₂O₃表面接枝量密切相关。     

修饰离子聚合度对膜-颗粒体系静电自组装的影响

采用不同聚合度的季铵阳离子聚合物作为修饰离子,对纳米Pt颗粒的合成及其在全氟磺酸膜(Ｎａｆｉｏｎ)上的静电自组装行为进行了研究,结合Ｎａｆｉｏｎ膜电导率的变化对膜-颗粒自组装机理进行了分析。结果表明:自组装过程中Ｎａｆｉｏｎ膜电导率的下降总是比Pt组装量的上升先达到平衡,表明膜-颗粒体系(MPS)的静电自组装是一个先由大量的小阳离子占据空位,然后由离子修饰的大颗粒(纳米Pt)取代的过程；改变修饰离子的聚合度同时会引起组装液中游离修饰离子的数目的变化,从而对电导率的衰减速度和组装第二阶段的脱附-组装平衡造成影响,因此随着修饰离子聚合度的增加,导电率达到平衡的时间增加,组装量达到平衡的时间减少。