蓝宝石化学机械抛光时磨粒运动轨迹及抛光效果研究

通过化学机械抛光工艺,获得表面平整度和粗糙度优良的蓝宝石晶片,提高蓝宝石键合接触面的表面性能。采用数值分析软件对蓝宝石晶片化学机械抛光过程中磨粒的运动轨迹进行仿真,结果发现,随着晶片转速的上升,磨粒的覆盖区域增大,当晶片转速与抛光盘转速接近于1∶1时,磨粒的抛光区域覆盖整个晶面。采用控制变量实验的方法研究摆臂的运动和抛光盘的转速对抛光效果的影响,并采用AFM对抛光后的蓝宝石晶片表面形貌进行分析。结果表明,抛光盘转速对抛光效果的影响最大,而移动幅度与移动速度的影响较小。通过调整晶片转速,蓝宝石晶片抛光后达到了键合工艺所要求的表面平整度和表面粗糙度要求。     

水膜吸附夹持方式在蓝宝石抛光中的可行性研究

针对目前蓝宝石抛光加工中所使用的石蜡粘贴夹持方式和抛光抛光吸附垫吸附夹持方式在抛光质量和成本等方面所存在的问题,提出了水膜吸附夹持方式,对水膜吸附环境下,吸附表面对蓝宝石晶片的法向吸附力和切向吸附力进行了测量,并分别与抛光吸附垫对蓝宝石晶片的法向吸附力和切向吸附力进行了比较,将切向吸附力作为主要评价指标,判断在蓝宝石晶片抛光加工中使用水膜吸附夹持方式的可行性。实验结果表明:单从吸附能力的层面考虑,在蓝宝石晶片抛光加工中使用水膜吸附夹持方式是可行的;45#钢比玻璃更适合作为吸附表面材料;确定吸附表面的粗糙度时应考虑蓝宝石晶片的表面粗糙度。     

基于固结磨粒的单晶蓝宝石自旋转磨削加工方法

利用固结磨粒自旋转磨削加工方法，通过金刚石磨削和化学机械磨削实现了蓝宝石晶片的高效、高质量平坦化加工。采用不同磨粒粒径的金刚石砂轮实现了蓝宝石晶片较高的材料去除率或较好的表面质量。开发了高磨粒浓度Cr2O3砂轮，采用化学机械磨削对金刚石磨削后的蓝宝石晶片进行平坦化加工。实验结果表明，化学机械磨削能够去除金刚石磨削的表面和亚表面缺陷，最终获得表面粗糙度Ra＜1 nm、无/微损伤的蓝宝石晶片。通过理论分析单颗金刚石磨粒的磨削力，发现磨粒粒径是影响材料去除率和表面质量的主要影响因素。通过XPS分析证明了Cr2O3和蓝宝石之间的固相反应过程。     

双面研磨蓝宝石衬底面形及表面粗糙度变化过程的实验研究

双面研磨作为蓝宝石衬底加工中的一道重要工序,主要目的是去除晶片表面的线切痕,使晶片表面粗糙度均匀,同时提高晶片的面形精度,使其满足一定要求。通过开展双面研磨实验,研究蓝宝石晶片的面形精度(翘曲度Warp、弯曲度Bow及总厚度偏差TTV)和表面粗糙度Ra随材料去除厚度的变化规律。在双面研磨初始阶段,翘曲度迅速减小,弯曲度减小趋势较缓,总厚度偏差和表面粗糙度值则迅速增大;随着研磨的进行,翘曲度、总厚度偏差和表面粗糙度随材料去除厚度的增大变化不大,而弯曲度Bow则随材料去除厚度的增大而逐渐减小,达到一定程度后则趋于稳定。研究结果对优化蓝宝石晶片双面研磨加工工艺、提高蓝宝石晶片双面研磨加工精度和加工效率具有重要意义。     

SiO_2/CeO_2复合磨粒的制备及在蓝宝石晶片抛光中的应用

采用均相沉淀法制备了SiO2/CeO2复合磨料,并利用X射线衍射仪(XRD)、透射电子显微镜(TEM)、傅里叶变换红外光谱仪(FT-IR)等对样品的相组成和形貌进行了表征。将所制备的SiO2/CeO2复合磨料用于蓝宝石晶片的化学机械抛光,利用原子力显微镜检测抛光后的蓝宝石晶片表面粗糙度。结果表明:所制备的SiO2/CeO2复合磨粒呈球形,粒径在40-50nm;在相同条件下,经过复合磨料抛光后的蓝宝石晶片表面粗糙度为0.32nm,材料去除速率为16.4nm/min,而SiO2抛光后的蓝宝石晶片表面粗糙度为0.92nm,材料去除速率为20.1nm/min。实验显示,复合磨料的材料去除速率略低于单一SiO2磨料,但它获得了较好的表面质量,基本满足蓝宝石作发光二极管(LED)衬底的工艺要求。     

基于金刚石微粉的单晶蓝宝石CMP工艺研究

单晶蓝宝石具有高的机械和光学性能,已被广泛应用于光电子、通讯、国防等领域。以提高加工后单晶蓝宝石表面质量和缩短加工时间为最终目标,采用化学机械抛光的方法抛光蓝宝石,得到了一种可行有效的抛光单晶蓝宝石的加工工艺路线。试验结果表明,采用6μm金刚石磨料粗抛蓝宝石晶片1.5 h,表面粗糙度值由220.05 nm快速降到7.88 nm;然后采用3μm金刚石磨料精抛蓝宝石晶片3 h,可以获得Ra约为2.82 nm(测量区域700μm×530μm)的表面粗糙度值。此抛光工艺能满足蓝宝石衬底高效、低损伤的抛光要求。     

络合剂对蓝宝石晶片化学机械抛光的影响

利用自制的抛光液对蓝宝石晶片进行化学机械抛光,研究化学机械抛光过程中抛光压力、抛光液pH值、SiO2浓度、络合剂种类及其浓度等参数对抛光速率的影响,采用MicroNano D-5A扫描探针显微镜观察抛光前后蓝宝石晶片的表面形貌。结果表明:在抛光条件为压力7psi、转速为50 r/min、抛光液流量为60 mL/min,抛光液组成为pH值12、SiO2浓度5%、络合剂Ⅰ及其浓度为1.25%时,得到最大抛光速率为35.30 nm/min,蓝宝石晶片表面质量较好,表面粗糙度Ra达到0.1 nm。     

碳化硼研磨后蓝宝石晶体的亚表面损伤

介绍了蓝宝石材料的亚表面损伤形成机制。考虑碳化硼磨料可产生较小亚表面损伤的优点,本文基于游离磨料研磨方式,研究了不同粒度碳化硼磨料研磨后蓝宝石晶体的亚表面损伤。利用KOH化学腐蚀处理技术,对研磨后的样品进行了刻蚀;通过特定的腐蚀坑图像间接反映了蓝宝石晶体的亚表面损伤形貌特征,获得了W20、W10和W5碳化硼磨料产生的亚表面损伤深度,得到了在不同刻蚀时间下蓝宝石亚表面损伤形貌、表面粗糙度和刻蚀速率。研究结果显示:游离碳化硼磨料研磨造成的蓝宝石晶体的亚表面损伤密度相当显著,但损伤深度并不大,其随磨料粒度的增大而增大,W20、W10和W5粒度的磨料研磨后产生的亚表面损伤深度分别为7.4,4.1和2.9μm,约为磨料粒度的1/2。得到的结果表明采用碳化硼磨料研磨有利于获得低亚表面损伤的蓝宝石晶片,而采用由大到小的磨料逐次研磨可以快速获得低亚表面损伤的蓝宝石晶片。     

LED用蓝宝石衬底抛光技术进展

蓝宝石单晶衬底具有优秀的物理化学性质,作为LED的主要衬底材料,其晶片表面质量要求非常高,而加工工艺在很大程度上决定了表面质量。对蓝宝石衬底加工的各种工艺原理作简要介绍,如化学机械抛光、磁流变抛光、浮法抛光等,指出这些加工方法的优缺点、发展进程等。目前蓝宝石衬底的抛光质量已经达到:表面粗糙度0.1nm,平面度0.5μm。随着生产工艺的不断进步,数字化、全自动、绿色无污染的抛光工艺是未来蓝宝石衬底加工的发展方向。     

蓝宝石衬底基片工艺质量检测指标及方法的研究进展

根据蓝宝石衬底基片国家标准和国际质量保证体系标准,结合目前蓝宝石衬底基片生产和科研的实际情况,阐述了目前蓝宝石衬底基片生长、掏棒切片、研磨抛光和清洗加工过程中的质量检测指标、检测方法,以及检测设备.指出了蓝宝石衬底基片检测技术的研究对衬底基片生产的重要性.总结了蓝宝石衬底基片检测技术的现状,半导体材料GaN衬底用蓝宝石单晶的纯度要达到99.999％以上,位错密度在102/cm2范围内,晶片切片厚度偏差不超过20μm,表面粗糙度要达到Ra0.3nm水平.指出了现有检测技术的不足和今后的发展趋势,对蓝宝石衬底检测技术的进一步发展具有引导性的作用.     

利用图像处理技术评价硅片表面清洗率

介绍了一种基于Matlab图像处理工具箱技术的评价硅片表面污染颗粒激光清洗率的新方法。借助Matlab图像处理工具箱,对清洗前后硅片表面光学显微镜照片进行处理,编写硅片表面激光干法清洗率的评价程序,统计清洗前后硅片表面评价区域的污染颗粒个数,对清洗效果进行定量评价。研究结果证明,利用此方法统计的颗粒数准确度达97.6%,得到的激光清洗率准确度达99.2%。结果表明,借助图像处理技术评定清洗效果是一种高效、快速、准确的新方法。     

激光清洗硅片表面Al2O3颗粒的试验和理论分析

以KrF准分子激光器为激光源,对目前工业上常用的硅片研磨抛光液的主要成分Al₂O₃颗粒进行激光清洗的试验和理论分析。建立一维热传导模型,利用有限元分析软件MSC.MarC模拟硅片表面的温度随激光作用时间和能量密度的分布。通过理论计算,量化了颗粒所受到的清洗力以及其与硅片表面之间的粘附力,理论预测出1 μm Al₂O₃颗粒的激光清洗阈值为60 mJ/cm²。在理论分析的指导下,利用248 nm、30 ns的KrF准分子激光进行单因素试验,研究激光能量密度、脉冲个数、激光束入射角度对激光干法清洗效率的影响,并且实验验证了清洗模型以及场增强效应对激光清洗结果的影响。     

A THRESHOLD MODEL FOR LASER CLEANING OF LARGER SILICON WAFERS

High cleaning quality for silicon wafers without damage is a challenge in laser cleaning technologies. Laser cleaning of Al₂O₃ micro-particles, which are the main contaminants of silicon wafer lapping and polishing solutions used in industry, from silicon wafers was studied for determining laser energy for high efficient particle removal while not causing damage to the wafers. As the cleaning force is generated from laser-energy absorption and conduction of the wafer, heat-conduction model on silicon wafer was developed during laser irradiation using a finer finite element method, from which cleaning force exerting on the particles greater than the adhesion force between the particle and the substrate, but less than the wafer damage energy of laser input was determined. Calculations of the laser energy threshold values for both particle cleaning and wafer damage were conducted for silicon wafers of 200 mm in diameter and 0.2 mm in thickness, and they were found to be about 60 mJ/cm² and 320 mJ/cm², respectively. The laser energy threshold model was finally verified experimentally using a KrF Excimer laser and found to be in good agreement with the experimental data. With the cleaning parameters from the model, the cleaning efficiency of as high as 98% has been achieved.     

Development of binder-free CMG abrasive pellet and finishing performance on mono-crystal sapphire

Chemo-mechanical-grinding (CMG) is a fixed abrasive process by integrating chemical reaction and mechanical grinding for sapphire wafer finishing, and shows advantages in surface integrity, geometric controllability and waste disposal. However, the material removal rate (MRR) obtained by the traditional CMG wheel is not high enough to meet the requirement from the mass production of sapphire wafers. As a potential solution, a new CMG wheel with extremely high abrasive concentration has been proposed. This paper targets on developing of binder-free abrasive pellets (BAP) with 100 wt% abrasive as well as investigating the performance of BAP in sapphire wafer finishing. The results of CMG experiment reveal that the MRR and surface roughness (Ra) of sapphire wafer finished by BAP constructed CMG wheel are able to reach 1.311 μm/h and 0.993 nm respectively. The characterization by Raman microscope indicates that the finished sapphire wafer also owns excellent subsurface integrity.     

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.     

蓝宝石衬底研磨加工中研磨盘材质的影响

采用W14、W3.5的B4C磨粒对蓝宝石衬底进行粗研磨和精密研磨的试验研究.对比分析铸铁、合成铜和合成锡盘粗研磨蓝宝石衬底的表面粗糙度和研磨表面均匀性,试验结果表明,铸铁研磨盘获得的蓝宝石衬底宏观表面均匀性和平面度均优于合成铜盘和合成锡盘,经铸铁研磨盘加工后的蓝宝石衬底面型峰谷值误差小于5 μm、中心线平均表面粗糙度Ra<0.82 μm.精密研磨试验结果表明,采用合成铜盘和W3.5B4C磨粒有效地改善了蓝宝石衬底表面的均匀性,获得了Ra<20 nm、面型峰谷值误差小于1.6 μm的均匀表面,为蓝宝石的超精密研磨奠定了良好的基础.     

磨粒粒径对蓝宝石研磨均匀性影响的试验研究

通过蓝宝石衬底的单面研磨试验研究,分析了W14和W3.5的B₄C磨粒研磨后蓝宝石表面的微观形貌和宏观形貌,W14的B₄C磨粒加工后蓝宝石表面微观裂纹密集且交错分布,体现了以滚轧和挤压为主的材料脆性去除作用,相同条件下,W3.5的B₄C磨粒加工的蓝宝石表面划痕均匀,表面无微观裂纹,实现了以切削为主的材料延性去除形式。测试分析结果表明：磨粒粒径的选择对蓝宝石的研磨表面状态具有重要影响,其选择准则除考虑要达到的粗糙度等级之外,还必须同时考虑与研磨盘的嵌入作用及其对加工表面状态的影响;W3.5的B₄C磨粒研磨加工后的蓝宝石表面宏观和微观均匀性良好,表面粗糙度、平面度等符合抛光前道工序的要求。     

Abrasive removal depth for polishing a sapphire wafer by a cross-patterned polishing pad with different abrasive particle sizes

The paper establishes a new theoretical model for abrasive removal depth for polishing a sapphire wafer using chemical mechanical polishing with a polishing pad that has a cross pattern. The theoretical model uses binary image pixel division to calculate the pixel polishing times. An abrasive contact model for single-pixel multiple abrasive particles, to estimate the contact force between a single abrasive particle and the wafer, is then established. When the contact force is calculated, it is possible to calculate the abrasive depth of a single abrasive particle on the surface of the sapphire wafer. Using this theoretical model, carring a numerical simulation with a slurry of the same concentration, but with different abrasive particle diameters, determines the removal volume and average abrasive removal depth at each pixel position and the surface condition of the wafer. The simulation result is also compared with experimental data, in order to verify that the new model is feasible.     

LED蓝宝石衬底抛光表面原子台阶形貌及其周期性研究

LED蓝宝石衬底的表面质量会极大影响到后续外延质量,进而影响到LED器件性能。蓝宝石研磨片经Al2O3磨粒粗抛液、SiO2磨粒精抛液下进行化学机械抛光(CMP),最终表面经原子力显微镜(AFM)所测表面粗糙度达到0.101nm,获得亚纳米级粗糙度超光滑表面,并呈现出原子台阶形貌。同时,通过使用Zygo表面形貌仪、AFM观察蓝宝石从研磨片经Al2O3粗抛液、SiO2精抛液抛光后的表面变化,阐述蓝宝石表面原子台阶形貌的形成原因,提出蓝宝石原子级超光滑表面形成的CMP去除机理。通过控制蓝宝石抛光中的工艺条件,获得a-a型、a-b型两种不同周期规律性的台阶形貌表面,并探讨不同周期规律性台阶形貌的形成机理。