利用复合磨粒抛光液的硅片化学机械抛光

为了提高硅片的抛光速率,利用复合磨粒抛光液对硅片进行化学机械抛光.分析了SiO2磨粒与聚苯乙烯粒子在溶液中的ζ电位及粒子间的相互作用机制,观察到SiO2磨粒吸附在聚苯乙烯及某种氨基树脂粒子表面的现象.通过向单一磨粒抛光液中加入聚合物粒子的方法获得了复合磨粒抛光液.对硅片传统化学机械抛光与利用复合磨粒抛光液的化学机械抛光进行了抛光性能研究,提出了利用复合磨粒抛光液的化学机械抛光技术的材料去除机理,并分析了抛光工艺参数对抛光速率的影响.实验结果显示,利用单一SiO2磨料抛光液对硅片进行抛光的抛光速率为180 nm/min;利用SiO2磨料与聚苯乙烯粒子或某氨基树脂粒子形成的复合磨粒抛光液对硅片进行抛光的抛光速率分别为273 nm/min和324 nm/min.结果表明,利用复合磨粒抛光液对硅片进行抛光提高了抛光速率,并可获得Ra为0.2 nm的光滑表面.     

Fabrication of a resin-bonded ultra-fine diamond abrasive polishing tool by electrophoretic co-deposition for SiC processing

A resin-bonded ultra-fine diamond abrasive polishing tool is fabricated by electrophoretic co-deposition (EPcD), and the processing performance of the tool is evaluated in this study. The dispersion stability of suspensions is characterized by a laser particle size analyzer and settlement ratio. The cathodic EPcD of composite powder is realized by adding Al³⁺ into the suspension. The sintering temperature of composite coatings is determined by differential thermal analysis/thermogravimetry. The surface morphology of the composite coating is observed under a confocal microscope. Results show that uniform, dense, and smooth coatings with diamond and resin particles distributed homogeneously are obtained from the steel substrate. A large (Φ150 mm) polishing tool with a 20 μm-thick coating is successfully prepared using the above process. A smooth mirror surface of SiC wafer with a nanoscale roughness (4.3 nm) is achieved after processing with the ultra-fine diamond abrasive polishing tool.     

Viscoelastic behavior of polishing pad: Effects on edge roll-off during silicon wafer polishing

In semiconductor device fabrication, surface flatness of silicon wafers has a significant impact on the chip yield. Hence, there is a strong demand to prevent the deterioration in surface flatness near the wafer edge due to edge roll-off during polishing. In the present study, we investigate the viscoelastic behavior of polishing pads and its effects on the uniformity of material removal distribution near the wafer edge. On the basis of the findings, we propose polishing conditions required to improve surface flatness near the wafer edge. The double-sided polishing experiments performed using silicon wafers reveal that the proposed polishing conditions effectively reduce edge roll-off.     

A phenomenological model of polishing of silicon with diamond abrasive

A phenomenological model of polishing hemispherical silicon asperities with spherical diamond abrasives is presented. Removal of the asperity material is quantitatively determined by a removal rate constant K. It is based on our molecular dynamics (MD) simulation studies considering the probability of removal of asperity atoms by an abrasive. The dependence of the removal rate constant K on the diameter and velocity of abrasives, number of asperities and abrasives per unit area, and cutting depth has been investigated. The rate constant K is found to be insensitive to the density of asperities, but linearly dependent on the density of abrasives.     

剪切增稠抛光磨料液的制备及其抛光特性

为了实现对工件的剪切增稠抛光(STP),采用机械混合与超声波分散法制备了一种Al2O3基STP磨料液,并研究了它们的抛光特性。利用应力控制流变仪考察其流变性能,通过扫描电镜和光学轮廓仪研究了单晶硅加工后表面显微组织的变化,并测量其表面粗糙度。结果表明:STP磨料液具有剪切变稀和可逆的剪切增稠特性,达到临界剪切速率后,会形成Al2O3"粒子簇";当剪切速率增大至1000s-1,储能模量,耗能模量和耗散因子都增至最大值,此时主要表现为类似固体的弹性行为,有利于形成类似"柔性固着磨具"。在STP加工单晶硅过程中,采用塑性去除的材料去除方式。随着抛光时间的延长,硅片去除速率先增大后减小;表面粗糙度不断减小并趋于稳定。实验显示,磨粒浓度不宜过高,否则会因剪切增稠效应造成黏度过大,导致流动性差而影响抛光质量。当Al2O3质量分数为23%时,抛光25min后,硅片表面粗糙度Ra由422.62nm降至2.46nm,去除速率达0.88μm/min,表明其能实现单晶硅片的高效精密抛光。     

A novel polishing method for single-crystal silicon using the cavitation rotary abrasive flow

Traditional low-pressure abrasive flow polishing can produce highly smooth surfaces, but the efficiency of this method is too low for polishing of hard-brittle materials parts. This paper proposes a novel cavitation rotary abrasive flow polishing (CRAFP) method. The energy generated from the cavitation bubble collapse is used to increase the kinetic energy of the abrasive particles in the low-pressure abrasive flow and the motion randomness of the abrasive particles near the wall; thereby, the efficiency and quality of low-pressure abrasive flow polishing are improved. The CRAFP mechanism was first introduced, and then the characteristics of the CRAFP process were investigated using computational fluid dynamics (CFD)-based abrasive flow simulation. Subsequently, a single-crystal silicon wafer polishing test was carried outperformed to verify the validity of the CRAFP method. The polishing results were compared with those of the traditional low-pressure abrasive flow polishing method. After 8 h of polishing using the CRAFP method and the traditional low-pressure abrasive flow polishing method, the surface roughness of the workpiece decreased to7.87 nm and 10.53 nm, respectively. Furthermore, by starting at similar initial roughness values, the polishing time required to reduce the roughness to 12 nm was 3.5 h and 6 h, respectively. The experimental results demonstrated that CRAFP can satisfy the surface requirements of single-crystal silicon (R_a < 12 nm) and exhibit high polishing efficiency and good quality.     

抛光垫在蓝宝石衬底化学机械抛光中的应用研究

在分析化学机械抛光中常用抛光垫的材质、性能、表面结构基础上,研究了抛光垫对蓝宝石衬底抛光质量的影响规律:材质硬的抛光垫可提高衬底的平面度;材质软的抛光垫可改善衬底的表面粗糙度;表面开槽的抛光垫可提高抛光效率;表面粗糙的抛光垫可提高抛光效率;对抛光垫进行适当的修整可使抛光垫表面粗糙;用聚氨酯类抛光垫能够使得蓝宝石衬底的抛光面小于0.3nm的表面粗糙度.     

固着磨料抛光碳化硅反射镜的去除函数

进一步研究了采用固着磨料数控加工碳化硅反射镜的工艺,基于平转动加工方式的去除函数理论推导出了多丸片抛光盘的去除函数模型.根据趋近因子、曲线距离等结果对抛光盘运动偏心距及丸片间距等参数进行优化,由优化后的参数指导实验.理论模型与实验结果对比显示,理论最大去除率与实验数据的偏差为0.007 3 μm/min,偏差比例为5.58%;理论去除函数曲线与实验曲线的距离偏差Drms为0.084 9 μm,偏差比例为7.01%.在分析部分,引入填充因子来间接评价去除函数形状.实验结果很好地验证了理论模型的准确性.该模型对固着磨料磨具抛光的工艺过程具有很好的预测性,在加工碳化硅反射镜领域极大地弥补了使用散粒磨料工艺加工所带来的不足,使加工效率得以明显提升.     

Prediction of the surface roughness and material removal rate in chemical mechanical polishing of single-crystal SiC via a back-propagation neural network

Chemical mechanical polishing (CMP) is a common method for realising the global planarisation and polishing of single-crystal SiC and other semiconductor substrates. The strong oxidant hydroxyl radicals (·OH) generated by the Fenton reaction can effectively oxidise and corrode the SiC substrate, and are thus used to improve the material removal rate (MRR) and surface roughness (Ra) after polishing of SiC during CMP. Therefore, it is necessary to study the material removal mechanism in detail. Based on the modified Preston equation, the effects of the CMP process parameters on the MRR and Ra after polishing of SiC and their relationship were studied, and a prediction model of the CMP process parameters, MRR, and Ra after polishing was also established based on a back-propagation neural network. The MRR initially increased and then decreased, and the Ra after polishing initially decreased and then increased, with increasing FeSO₄ concentration, H₂O₂ concentration, and pH value. The MRR continuously increased with increasing abrasive particle size, abrasive concentration, polishing pressure, and polishing speed. However, the Ra continuously decreased with increasing abrasive particle size and abrasive concentration, increased with increasing polishing pressure, and initially decreased and then increased with increasing polishing speed. The established prediction model could accurately predict the relationship between the process parameters, MRR and Ra after polishing in CMP (relative prediction error of less than 10%), which could provide a theoretical basis for CMP of SiC.     

使用优化的固着磨料磨盘全口径加工碳化硅反射镜

为提高碳化硅非球面反射镜的加工质量,对加工中涉及的固着磨料工艺去除函数进行了研究。在早期的实验中测试了圆形丸片的去除函数,引入填充因子的概念来评价实验所获得的去除函数,定量获得了丸片结构与填充因子之间的关系。为了提高填充因子和磨盘的加工特性,根据圆形丸片的实验结果优化了磨头的结构并基于Matlab软件模拟了新型磨头的去除函数。在全口径范围考察了磨头工作的稳定性,并在相同加工参数条件下完成了固着磨料和散粒磨料的加工实验。为了对理论模拟和实验结果进行比较,引入结构相似度指数的概念来评价全口径反射镜去除量模拟结果与实验结果之间的相似程度。结果显示,实验得到的结构相似度指数达到了0.425 7,证明优化后的固着磨料磨头在大口径碳化硅反射镜加工方面极有应用前景。     

化学机械抛光过程中护环对硅片表面接触压强分布和宏观轮廓的影响

为了获得单晶硅片化学机械抛光过程中护环对接触压强分布的影响规律,根据有护环化学机械抛光实际出发,建立了抛光过程的接触力学模型和边界条件,利用有限元的方法对有护环抛光接触状态接触压强分布进行了计算和分析,并利用抛光实验对计算获得结果进行了验证;获得了硅片与抛光垫间的接触表面压强分布形态,以及护环几何参数对压强分布的影响规律;结果表明护环抛光接触压强的分布也存在不均匀性,而且在硅片外径邻域内接触压强最大,这些也能导致被加工硅片产生平面度误差和塌边,选择合理地护环几何参量和负载比,可以改善接触压强场分布的均匀性。     

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.     

Preparation of silane modified SiO2 abrasive particles and their Chemical Mechanical Polishing (CMP) performances

Surface modified SiO₂ particles in an aqueous environment with γ-aminopropyl triethoxysilane (APTS)/methyl trimethoxysilane (MTMOS) are introduced as abrasive in the slurry. The modified silica particles are characterized by Particle Size/Zeta Potential Analysis, Fourier Transform Infrared Spectroscopy (FTIR), Thermal Gravimetric Analysis (TGA) and Differential Scanning Calorimetry (DSC). In addition, the enhancement of polishing rate owning to the modified silicon particles in silicon wafer Chemical Mechanical Polishing (CMP) is observed.     

Highly efficient chemical mechanical polishing method for SiC substrates using enhanced slurry containing bubbles of ozone gas

In this study, a highly efficient method for chemical mechanical polishing (CMP) of silicon carbide (SiC) substrates using enhanced slurry was proposed and developed. The enhanced slurry contains bubbles of ozone gas generated by ozone gas generator in pure water mixed with a conventional commercially available slurry. Therefore, the enhanced slurry has an oxidizing effect on the Si-face of SiC substrates. To confirm the effectiveness of bubbles enclosing ozone gas, both nano-indentation test and X-ray photoelectron spectroscopy (XPS) analysis were conducted. As a result, the hardness decrease of the Si-face of the SiC substrate was confirmed through the nano-indentation test, and the generation of reaction products was confirmed on Si-face of SiC substrate in the XPS analysis. According to a series of experimental results of our proposed highly efficient CMP method for SiC substrates, the removal rate can be increased when the enhanced slurry was applied, comparing with that for the not only conventional commercially available slurry but also commercially available dedicated slurry.     

The crystallographic change in sub-surface layer of the silicon single crystal polished by chemical mechanical polishing

The effect of the contact nominal pressure on the surface roughness and sub-surface deformation in chemical mechanical polishing (CMP) process has been investigated. The experimental results show that a better surface quality can be obtained at the lower pressure, and the thickness of sub-surface deformation layer increases with the increase of the pressure. In CMP process, polishing not only introduces amorphous transformation but also brings a silicon oxide layer with a thickness of 2–3 nm on the top surface. The atomic structure of the material inside the damage layer changes with the normal pressure. Under a higher pressure (125 kPa), there are a few crystal grain packets surrounded by the amorphous region in which the lattice is distorted, and a narrow heavy amorphous deformation band appears on the deformation region side of the interface. Under a lower pressure, however, an amorphous layer can only be observed.     

An analytical model of the material removal rate between elastic and elastic-plastic deformation for a polishing process

This paper develops an analytical model for the material removal rate during specimen polishing. The model is based on the micro-contact elastic mechanics, micro-contact elastic-plastic mechanics and abrasive wear theory. The micro-contact elastic mechanics between the pad-specimen surfaces used the Greenwood and Williamson elastic model. The micro-contact elastic-plastic mechanics between specimen and particle, as well as the micro-contact elastic mechanics between particle and pad, are also analyzed. The cross-sectional area of the worn groove in the specimen is considered as trapezoidal area. A close-form solution of material removal rate from the specimen surface is the function of average diameter of slurry particles, pressure, the specimen/pad sliding velocity, Equivalent Young’s modulus, RMS roughness of the pad, and volume concentration of the slurry particle.     

Investigation on the polishing of aspheric surfaces with a doughnut-shaped magnetic compound fluid (MCF) tool using an industrial robot

Aspheric elements have become essential optical surfaces for modifying optical systems due to their abilities to enhance the imaging quality. In this work, a novel method employing a doughnut-shaped magnetic compound fluid (MCF) polishing tool, and an industrial robot was proposed for polishing aspheric surfaces. Firstly, investigations on the MCF tool, including the formation process and geometry, were conducted to form an appropriate polishing tool. The distribution of abrasive particles was observed using SEM and EDX mapping. Thereafter, a conic workpiece constructed from 6061-aluminum alloy was selected as the workpiece, which was used to discover the effects of the parameters on the polishing ability of aspheric surfaces. Finally, a polishing experiment was conducted with an aspheric element under the optimized conditions. The obtained results are shown as follows. (1) A relatively regular MCF tool was obtained when the eccentricity (r), amount of MCF slurry supplied (V), revolution speed of the MCF carrier and magnet (n_c and n_m, respectively) were given at appropriate values. (2) Abrasive particles entrapped in or attached to the clusters were observed abundantly on the MCF tool sample. (3) The surface profile of the conic workpiece after 60 min of polishing indicated that material was removed evenly, and an annular polishing area was attained. Meanwhile, a higher material removal rate and better surface roughness were achieved with a smaller working gap (h) and larger volume of the MCF slurry supplied (V). (4) The roughness (Ra) of the aspheric surface decreased from 49.81 to 10.77 nm after 60 min of polishing. The shape retention obtained a Pearson correlation coefficient (Pcc) of 0.9981, which demonstrated that this novel method is appropriate for polishing aspheric elements.     

Modeling the effects of abrasive size, surface oxidizer concentration and binding energy on chemical mechanical polishing at molecular scale

No conclusive results have been proposed for the influence of the abrasive particle size on the material removal during the chemical mechanical polishing (CMP). In this paper, a mathematical model as a function of abrasive size and surface oxidizer concentration is presented for CMP. The model is proposed on the basis of the molecular-scale removal theory, probability statistics and micro contact mechanics. The influence in relation to the binding energy of the reacted molecules to the substrate is incorporated into the analysis so as to clarify the disputes on the variable experimental trends on particle size. The predicted results show that the removal rate increases sub-linearly with the abrasive particle size and oxidizer concentration. The model predictions are presented in graphical form and show good agreement with the published experimental data. Furthermore, variations of material removal rate with pressure, pad/wafer relative velocity, and wafer surface hardness, as well as pad characteristics are addressed. Results and analysis may lead further understanding of the microscopic material removal mechanism from molecular-scale perspective.     

SiC单晶片切割力建模与自适应控制

Si C单晶因优良的物理和机械性能而大量用于大功率器件和IC行业。但由于材料的高硬度和高脆性,使其加工过程变得很困难。为此,分析了Si C单晶片切割过程,建立切割过程模型,通过F检验法进行系统阶次辨识,采用遗忘因子递推最小二乘算法在线估计模型参数,建立进给量与切割力的差分方程,设计基于最小方差自校正的切割力控制器,并进行实验验证。结果表明:控制器能够很好的跟踪不同信号,具有良好的鲁棒性,提高了Si C单晶片的加工效率和表面质量。