立方碳化硅CMP过程中机械作用分子动力学仿真

为了更好地理解立方碳化硅在化学机械抛光(CMP)过程中原子层面的材料去除机理,利用分子动力学(MD)方法建立了金刚石磨粒刻划碳化硅的原子模型,仿真研究了金刚石磨粒半径、刻划深度和刻划速度对碳化硅表面形貌、晶体结构、摩擦力和原子去除率的影响规律,并与无定型二氧化硅氧化膜的机械刻划作用的仿真结果进行了对比分析.结果发现:碳化硅在机械刻划过程中局部会出现非晶态变化;刻划深度增大会导致切削力和切削温度增大,原子去除率也随之增加;刻划速度的改变会影响温度和原子去除率,而对切削力几乎无影响;磨粒半径的增加会导致切削力和温度的增加,在压入深度相同的情况下对原子去除率影响不大;碳化硅表面生成的二氧化硅膜能大幅度降低切削力,但由于其结构的影响,机械刻划作用仅使氧化膜产生明显的致密化,而不产生磨屑.     

Preparation of porous alumina abrasives and their chemical mechanical polishing behavior

Porous alumina abrasives with different pore sizes were prepared using hydrothermal synthesis method by different hydrothermal temperatures. The pore structure, pore size and pore volume of the products were characterized by transmission electron microscopy and nitrogen adsorption desorption isotherm measurement. The chemical mechanical polishing (CMP) performances of porous alumina abrasives in hard disk substrate CMP were investigated. The results show that, the polished surface average roughness (Ra) decreases when the pore diameter of porous alumina abrasive increases. By comparison with solid alumina abrasive, the prepared porous alumina abrasives give lower Ra, and the porous alumina abrasive with 8.61 nm pore diameter has higher material removal rate under the same polishing conditions.     

精细雾化抛光氮化硅陶瓷的抛光液配制参数优化

采用超声精细雾化施液抛光对氮化硅陶瓷基体进行抛光,研究了不同的pH值、磨料浓度以及氧化剂含量对氮化硅陶瓷基体抛光的材料去除率的影响,优化了pH值、磨料浓度及氧化剂含量,并与传统的化学机械抛光进行了对比。结果表明:当二氧化硅磨粒质量分数为5wt%,氧化剂含量为1wt%,pH值为8时,材料去除率MRR为108.24nm/min且表面粗糙度Ra为3.39nm。在相同的抛光参数下,传统化学机械抛光的材料去除率MRR为125nm/min,表面粗糙度Ra为2.13nm;精细雾化抛光的材料去除率及表面粗糙度与传统抛光接近,但精细雾化抛光所用抛光液用量仅为传统抛光所用抛光液用量的1/9。     

Chemical mechanical polishing (CMP) of on-axis Si-face 6H-SiC wafer for obtaining atomically flat defect-free surface

Due to its high mechanical hardness and excellent chemical inertness, SiC single-crystal wafer is extremely difficult to realize effectively removed total planarization. Owing to crystalline polarity and anisotropy, material removal rate (MRR) on Si-face (0001) of SiC wafer is significantly lower than C-face (000 $ \bar{1} $ ) for a defect-free surface. In the paper, the slurry containing hydrogen peroxide (H₂O₂), potassium hydroxide and abrasive colloidal silica, is introduced to chemical mechanical polishing (CMP) of on-axis Si-face 6H-SiC wafer, resulting in acquiring high MRR with 105 nm/h, and atomically flat defect-free surface with atomic step-terrace structure and roughness of 0.0667 nm by atomic force microscope (AFM), in order to satisfy further demands of electronic device fabrication towards substrate wafer performance. The effects of the three ingredients in the slurry towards MRR of SiC wafer, polished surface quality and coefficient of friction in polishing process are studied. Optical microscope, optical interferometry profiler and AFM are used to observe the polished surface. In addition, the CMP removal mechanism of SiC wafer and the formation of ultra-smooth surface are discussed.     

残余相和烧结温度对碳化硅陶瓷抗混酸腐蚀特性的影响

本工作主要研究了残余相和晶粒尺寸对碳化硅的抗混酸(HF-HNO₃)腐蚀特性。通过不同的烧结方法(固相烧结、液相烧结、反应烧结)制备出残余相不同的碳化硅材料。结果表明: 与液相烧结碳化硅(LPS SiC)和反应烧结碳化硅(RB SiC)相比, 固相烧结碳化硅(SSiC)具有更好的腐蚀抗性, 这是由于残余相石墨的抗腐蚀性强, 以及残余相在材料中形成不能相互联通的岛状结构。通过调节碳化硅的烧结温度, 可以影响材料中的晶粒尺寸, 研究结果发现相同烧结温度下随着残余相含量的增加, 材料腐蚀失重线性增加, 对曲线进行线性拟合, 其Y轴截距的绝对值代表不含碳的试样在该烧结温度下的腐蚀失重。研究表明随着烧结温度由2100℃升高到2160℃, 晶粒尺寸由2 μm增加到6 μm。此时其Y轴截距的绝对值分别为9.22(2100℃), 5.81(2130℃), 0.29(2160℃), 表明晶粒尺寸的增加有利于提高材料的抗腐蚀能力。     

SiC/BN层状陶瓷耐损伤性能

采用压痕法在SiC/BN层状陶瓷试样的表面引入不同尺寸的表面裂纹,利用三点弯曲测量含裂纹试样的极限断裂应力,研究了不同尺寸的表面裂纹对层状陶瓷断裂强度的影响;根据压痕载荷-强度实验结果,测定层状陶瓷的阻力曲线,并与单相SiC陶瓷对比。结果表明,层状陶瓷的压痕强度对压痕裂纹深度的变化不敏感,阻力曲线呈上升型;而单相SiC陶瓷的压痕强度随压痕裂纹深度的增加急剧下降,阻力曲线呈平稳型,说明层状陶瓷具有优异的耐损伤性能和升值R-曲线行为。分析认为,裂纹在弱界面处发生偏折是层状陶瓷具有优良耐损伤性能和升值R-曲线行为的主要原因。这为陶瓷材料在含有一定的制备和加工缺陷以及承受冲击、磨损等接触损伤的条件下保持高强度提供了可能。     

半固着磨具特性对其磨耗和工件材料去除的影响

为获得先进陶瓷材料的高效、高精度加工,通过采用新研制的半固着磨具来实现一种半固着磨粒加工技术．制作了以SiC为磨料的不同粒度和磨料浓度的半固着磨具（SFAT）,讨论分析了磨料粒度和磨料浓度对半固着磨具特性（剪切强度和表面硬度等）的影响．采用所制作的半固着磨具加工单晶硅片,研究半固着磨具的磨耗率和工件材料去除率．初步实验结果表明,磨料粒度#1000和磨料质量分数为65％的半固着磨具的磨具磨耗率最小且工件材料去除率最大．实验结果有助于指导半固着磨具制作．     

光学元件聚氨酯抛光特性研究

本文研究了应用于平面光学元件的快速抛光技术,从材料去除率、元件面形和表面粗糙度出发,对快速抛光技术应用于平面大口径元件的加工效果进行了探讨。研究了在快速抛光技术中压力和主轴转速对材料去除率的影响,验证了Preston公式在快速抛光中的适用性,快速抛光技术的去除效率可达10μm/h;其次,研究了聚氨酯抛光元件面形的精度,对于330mm×330mm元件可达～1.0λ（λ=632.8nm）;最后,对快速抛光系统中抛光粉颗粒大小及形态随使用时间的变化进行了观测,并测量了使用300目和500目抛光粉时快速抛光元件表面粗糙度以及其随抛光粉使用时间的变化。     

Analysis of particles in magnetorheological polishing fluid for finishing of ferromagnetic cylindrical workpiece

Magnetorheological honing process is developed for nanofinishing of internal surfaces of ferromagnetic and non-ferromagnetic cylindrical objects. The process makes use of smart fluid called magnetorheological (MR) polishing fluid for finishing which has a property to become stiff in the existence of magnetic field. The smart MR polishing fluid is made with the ingredients of carbonyl iron (CI) particles, abrasive particles, and base fluid. Direct current given to the electromagnet coil engenders magnetic field on finishing tool surface. Magnetic force acts on magnetic CI particles which further exert the repulsive force on nonmagnetic silicon carbide (SiC) abrasive particles and performs finishing when tool rotates as well as reciprocates inside the cylindrical workpiece. The CI and SiC particles present in MR polishing fluid are magnetically simulated and analyzed using finite element (FE) analysis. The distribution of magnetic flux density and magnitude of magnetic force acting on CI particles are analyzed through FE analysis. It is found that the CI particles which are available adjacent to the active abrasives are major responsible for indenting the active abrasive particles into workpiece surface. Also, the effect of finishing tool surface areas and particles size on the strength of chains of CI particles in MR polishing fluid have been analyzed.     

SiC对烧结堇青石材料性能的影响

以高岭土、滑石和工业氧化铝为矿物原料烧结制备了堇青石陶瓷,通过X射线衍射仪、扫描电镜、万能材料试验机和热膨胀仪等测试手段,研究了添加不同含量SiC对烧结堇青石陶瓷相组成和性能的影响,并比较了添加不同颗粒尺寸的SiC对烧结陶瓷强度的影响。试验表明,随着SiC添加量的增加,堇青石陶瓷的弯曲强度、致密度和热膨胀系数逐渐增大。当添加SiC的质量分数为5%、粒径为5.0μm时,烧结堇青石陶瓷的强度较未添加时增大了41.9%,而热膨胀系数的增幅不大。     

新型功能陶瓷高效研磨半固着磨具(英文)

为提高功能陶瓷游离磨料研磨效率,减少大颗粒杂质侵入造成的表面损伤,提出了一种高效研磨用的新型半固着磨具(SFAT).分析了SFAT的基本工作机理及其制作过程.通过对典型的功能陶瓷工件硅片的研磨实验,分析了SFAT研磨过程中工件表面质量、加工效率、材料去除形式,以及工艺参数对加工过程的影响.实验结果表明,采用#1000 SiC磨料制作的SFAT研磨后的硅片表面粗糙度在10 min内,从215 nm提高到了30 nm.定义了单位材料去除量内表面粗糙度下降值,作为评价工件精加工表面质量改善效率的指标.实验中,利用SFAT研磨硅片的单位材料去除量内表面粗糙度下降值是相似条件下游离磨料研磨的2倍,这表明利用SFAT加工能够迅速改善工件的表面质量,能够获得比游离磨料加工更高的精加工效率.     

无压烧结合成纯Ti3SiC2及其晶体生长机理

在1400℃,用Ti,Si,C,Al,NaCl原料,氩气保护下无压烧结合成出纯净的、层状的Ti3SiC2陶瓷。用X射线衍射、扫描电子显微镜,透射电子显微镜对Ti3SiC2陶瓷的物相、表面形貌、微观结构进行表征。对合成出的Ti3SiC2陶瓷的微观形貌进行观察,发现Ti3SiC2晶体中有规整的六方形状的层状晶体,提出了Ti3SiC2晶体的自由生长的机理。Ti3SiC2晶体的生长机理由二维成核理论控制,台阶状晶体生长的形貌表明(002)晶面的生长要经过两个独立的过程。添加NaCl,有助于生成高纯度的层状Ti3SiC2陶瓷。     

旋转超声磨削Si3 N4陶瓷用金刚石磨具磨损行为研究

热压烧结Si₃N₄陶瓷材料常应用于航天飞行器中关键耐高温零部件,但由于高硬度和低断裂韧性,其加工效率和加工表面质量难以满足制造需求。为了提高热压烧结Si₃N₄陶瓷旋转超声磨削加工质量,减小由于金刚石磨具磨损带来的加工误差,开展了磨具磨损行为研究。基于热压烧结Si₃N₄陶瓷旋转超声磨削加工实验,分析了金刚石磨具磨损形式;基于回归分析建立了金刚石磨具磨损量数学模型,揭示了加工参数及磨具参数与金刚石磨具磨损量间映射关系;并研究了磨损形式与磨具磨损量及加工表面粗糙度影响规律。结果表明：磨粒磨耗是旋转超声磨削Si₃N₄陶瓷用金刚石磨具最主要磨损形式,比例超过50%;主轴转速和磨粒粒度对磨具磨损量影响最为显著;且磨损量较小时,加工表面粗糙度值反而增加。以上研究可为提高旋转超声磨削Si₃N₄陶瓷加工精度和加工质量提供指导。     

Removal rate model for magnetorheological finishing of glass

Magnetorheological finishing (MRF) is a deterministic subaperture polishing process. The process uses a magnetorheological (MR) fluid that consists of micrometer-sized, spherical, magnetic carbonyl iron (CI) particles, nonmagnetic polishing abrasives, water, and stabilizers. Material removal occurs when the CI and nonmagnetic polishing abrasives shear material off the surface being polished. We introduce a new MRF material removal rate model for glass. This model contains terms for the near surface mechanical properties of glass, drag force, polishing abrasive size and concentration, chemical durability of the glass, MR fluid pH, and the glass composition. We introduce quantitative chemical predictors for the first time, to the best of our knowledge, into an MRF removal rate model. We validate individual terms in our model separately and then combine all of the terms to show the whole MRF material removal model compared with experimental data. All of our experimental data were obtained using nanodiamond MR fluids and a set of six optical glasses.     

Lapping assisted dissolved wafer process of silicon for MEMS structures

Dissolved wafer process (DWP) is being extensively used to fabricate complex micro-electro-mechanical system (MEMS) structures. Etching non-uniformity, increased surface roughness and duration of DWP is often influence MEMS devices yields. This paper presents a modified DWP involving lapping and polishing followed by chemical etching of silicon to release MEMS based structure. The lapping experiments are performed using silicon-carbide (SiC) and alumina (Al₂O₃) abrasive. The polishing of the silicon samples is also done. The lapped and polished surfaces are compared with etched silicon surfaces in KOH and EDP solutions. The lapping-polishing process is found to be 2.5 (Al₂O₃)–3 (SiC) times faster than a standard etching processes based on KOH and EDP solutions. The average roughness (R_a) of the lapped–polished silicon surfaces are found to be 19.2 and 32.9 nm corresponding to SiC and Al₂O₃ abrasive respectively. The R_a value of EDP and KOH etched silicon surfaces are found to be 16.2 and 238.3 nm respectively. Based on the lapping—polishing results, SiC based lapping followed by polishing of silicon surface can be used as an alternate of etching of silicon during DWP. In this paper, a two-step DWP, involving lapping-polishing followed by EDP chemical etching of silicon, is used to fabricate suspended comb-type microaccelerometer structure.     

Surface roughness and material removal in fluid jet polishing

Based on experiments, the dependence of material removal and surface roughness on the characteristics of abrasive particles, on the workpiece, and on other process parameters such as working pressure and incidence angle in fluid jet polishing (FJP) technology were investigated. Experimental results show a volume removal rate that is approximately proportional to the square root of the Young's modulus (E) and inversely proportional to the square of the Knoop hardness (Hk) of glass. Similarly, surface roughness is also determined in FJP by elastic stiffness E and plastic parameter Hk. The influence of the incidence angle on surface roughness and material removal were studied, and a linear dependence of material removal on the working pressure was obtained. Further, it was found that an optical-quality surface can be achieved by use of Cerox 1650 abrasive particles in FJP and can satisfy the requirements of modern optical manufacturing.     

Surface polishing of 6H-SiC substrates

The surface polishing for silicon carbide （SIC） substrates was investigated and results were presented for mechanical polishing （MP） and chemo-mechanical polishing （CMP）. High quality surfaces were obtained after CMP with colloidal silica. The removal mechanism of scratches in MP and detailed physical and chemical process during CMP were analyzed. The effects of MP and CMP on the surface roughness were assessed by optical microscopy （OM）, atomic force microscopy （AFM） and step profilometry. KOH etching and high resolution X-ray diffractometry （H RXRD） were applied to evaluate the subsurface damage of 6H-SiC substrates.     

陶瓷/树脂/纤维超混杂复合材料的界面控制

以具有不同表面状态的泡沫SiC陶瓷为基本骨架,以改性酚醛树脂为基体,加入短切高硅氧玻璃纤维制备了陶瓷/纤维/树脂超混杂复合材料,研究了界面控制对超混杂复合材料界面粘结强度的影响.结果表明,对于泡沫SiC陶瓷骨架,在表面生长多孔过渡层或表面堆积SiC颗粒等方法可提高树脂陶瓷之间界面的粘结强度.通过良好的界面控制,可显著提高复合材料的弯曲强度和弯曲模量,模量的提高比强度的提高幅度更大.偶联剂处理使高硅氧纤维与树脂基体的粘结强度增加,从而提高复合材料的弯曲强度.     

固结磨料化学机械研抛K9玻璃的材料去除机理

采用失重法对固结磨料研抛K9玻璃材料去除过程中的机械与化学作用进行了分离,采用显微硬度方法分析了研抛液对K9玻璃工件表层硬度的影响.研究结果表明:研抛液能与K9玻璃发生化学反应并在其表面形成一层较基质材料软的变质层,变质层厚度随浸泡时间的延长而增加；单纯研抛液的化学作用对K9玻璃的材料去除作用有限,固结磨料研抛垫对K9玻璃的机械去除作用主要以脆性去除为主,化学与机械的交互作用是K9玻璃影响材料去除的主要方式:当研抛盘转速为200r/min时,化学作用与机械作用达到平衡,交互作用最为强烈,材料去除率达到最大值.     

Ti诱导反应熔体无压浸渗法制备(W,Ti)C/Fe复合材料

研究了一种Ti诱导反应熔体无压浸渗制备复合材料的方法: 通过凝胶注模成型工艺, 以蔗糖为造孔剂制备了多孔Ti-WC陶瓷骨架预制体, 真空状态下, 在1370℃以Fe-Cr-C合金熔体无压浸渗该预制体, 经过原位反应制备了(W,Ti)C/Fe复合材料。利用SEM-EDS、 XRD对复合材料的组织结构、 元素组成及相组成进行了测试和分析。采用旋转圆盘式摩擦试验机以SiC砂浆为磨料研究了(W,Ti)C/Fe复合材料的耐磨性。结果表明: 在浸渗过程中骨架中的Ti元素的溶解析出与C元素的原位反应促进了浸渗过程的进行, 在1370℃保温1 h, 金属液即渗透整个多孔骨架, 并且在浸渗过程中仍然维持着骨架的形状, 浸渗过程中Ti-C-WC原位反应生成具有芯-壳结构的中间富Ti、 边缘富W的(W,Ti)C增强相。摩擦磨损实验结果表明, (W,Ti)C/Fe复合材料具有优异的抗磨粒磨损性能, 其耐磨性优于工业用耐磨铸铁。