高准确度玻璃光学元件的CMP技术研究

依据化学机械抛光（Chemical Mechanical Polishing,CMP）加工玻璃光学元件的原理,通过对抛光运动机理的理论分析,提出了抛光垫的磨削均匀性对光学元件面形的影响,并设计了新的工艺流程.通过工艺试验,完成了高准确度玻璃光学元件的CMP加工,获得了表面质量N<0.2,Rq<0.3 nm的玻璃光学元件.     

Removal of scratch on the surface of MgO single crystal substrate in chemical mechanical polishing process

Etching and chemical mechanical polishing (CMP) experiments of the MgO single crystal substrate with an artificial scratch on its surface are respectively performed with the developed polishing slurry mainly containing 2 vol.% phosphoric acid (H₃PO₄) and 10-20 nm colloidal silica particles, through observing the variations of the scratch topography on the substrate surface in experiments process, the mechanism and effect of removing scratch during etching and polishing are studied, some evaluating indexes for effect of removing scratch are presented. Finally, chemical mechanical polishing experiments of the MgO substrates after lapped are conducted by using different kinds of polishing pads, and influences of the polishing pad hardness on removal of the scratches on the MgO substrate surface are discussed.     

无损伤超光滑LBO晶体表面抛光方法研究

传统的抛光LBO晶体的方法是选用金刚石抛光粉在沥青抛光盘上抛光。沥青盘易于变形不容易修整,金刚石粉特别硬容易损伤抛光晶体表面。抛光过程中,抛光盘和抛光粉的选择是非常重要的,直接影响到抛光效率和最终的表面质量。新的抛光LBO晶体的方法,其抛光过程是一个化学机械过程,抛光盘、抛光粉和抛光材料相互作用。选用两种抛光盘(培纶和聚氨酯盘),三种较软的抛光磨料(CeO2,Al2O3和SiO2胶体),并在LBO晶体的(001)面进行抛光实验。用原子力显微镜测量和分析了表面粗糙度。结果表明,使用聚氨酯盘和SiO2胶体能够获得无损伤超光滑的LBO晶体表面,其表面粗糙度的RMS为0.3nm。     

Effects of the ultrasonic flexural vibration on the interaction between the abrasive particles; pad and sapphire substrate during chemical mechanical polishing (CMP)

In this paper, the technique of ultrasonic flexural vibration assisted chemical mechanical polishing (UFV-CMP) was used for sapphire substrate CMP. The functions of the polishing pad, the silica abrasive particles, and the chemical additives of the slurry such as pH value regulator and dispersant during the sapphire's UFV-CMP were investigated. The results showed that the actions of the ultrasonic and silica abrasive particles were the main factors in the sapphire material removal rate (MMR) and the chemical additives were helpful to decrease the roughness of sapphire. Then the effects of the flexural vibration on the interaction between the silica abrasive particles, pad and sapphire substrate from the kinematics and dynamics were investigated to explain why the MRR of UFV-CMP was bigger than that of the traditional CMP. It indicated that such functions improved the sapphire's MRR: the increasing of the contact silica particles’ motion path lengths on the sapphire's surface, the enhancement of the contact force between the contact silica particles and the sapphire's surface, and the impaction of the suspending silica particles to the sapphire's surface.     

Synthesis, characterization of ceria-coated silica particles and their chemical mechanical polishing performance on glass substrate

Nano-sized ceria particles were coated on the silica surface by the precipitation method using ammonium cerium nitrate and urea as precipitant with poly(vinylpyrrolidone) (PVP) as assistant. The structures and compositions of ceria-coated silica particles were characterized using X-ray diffraction (XRD), field-emission scanning microscopy (FE-SEM), energy dispersive spectroscopy (EDS), transmission electron microscopy (TEM) and dynamic light scattering (DLS) measurements. The results show that nano-size ceria particles were coated uniformly around the surface of silica particles when PVP was used as assistant during coating process, while without PVP, the ceria particles were grown sparsely on the silica particle surface and many ceria particles grow up through independent nucleation in the solution. Then, the chemical mechanical polishing (CMP) behaviors of the as-prepared ceria-coated silica particles on glass substrate were investigated. The CMP test results suggest that the as-prepared ceria-coated silica particles exhibit higher removal rate than pure silica particles without deteriorating the surface quality. In addition, online coefficient of friction (COF) was conducted during the polishing process. The COF data indicate that the COF values of ceria-coated silica particles are larger than those of pure silica particles due to their surface properties.     

抛光垫磨损非均匀性研究

抛光垫是化学机械抛光的重要组成部分,其磨损的非均匀性对被加工工件面型精度和抛光垫修整有重要影响。基于直线摆动式抛光方式,研究了抛光过程中抛光垫与工件的相对运动,建立了抛光垫磨损模型,分析了抛光工艺参数对抛光垫磨损及均匀性的影响。研究结果表明,工件与抛光垫的转速比为1.11,正弦偏心直线摆动形式,摆动幅度系数为2,摆动频率系数在0.1~0.2之间,抛光垫表面磨损更均匀,并根据抛光垫表面磨损特性优化了抛光垫形状。优化的抛光垫具有更好的面型保持性,延长了修整间隔,为抛光工艺设计提供理论指导。     

小工具数控抛光对元件表面中频误差的匀滑研究

数控抛光已被广泛应用于光学元器件的加工制造,而抑制元件表面中频误差是加工过程中一项十分重要的内容。基于Presston方程对数控小工具抛光盘去除函数进行了建模,得到了理论化的去除函数表达式。结合去除函数,在参数化匀滑模型基础上通过建立多参数的时变理论模型,表明元件表面中频误差是随抛光过程呈指数型收敛的,其收敛效率取决于材料参数、体积去除率等抛光工艺参数。对理论模型的匀滑曲线进行了模拟分析,实现了不同工艺条件下的匀滑效率的对比。结果表明:在不同抛光盘材料的匀滑过程中,材料系数越大,其整体匀滑效率越高。同样,抛光盘体积去除率越大,对表面误差的匀滑效率也会越高。进行了一组空间周期分别为3,5,7 mm的波纹误差的匀滑实验,其结果表明,在相同的抛光参数下,具有较大空间频率的波纹匀滑效率会更高,收敛曲线下降得更快。最后对比了不同材料抛光盘匀滑效率,从实验上证实了沥青盘在波纹匀滑效率上远高于聚氨酯材料的抛光盘。     

3mm厚大口径超薄元件双面抛光工艺北大核心CSCD

基于环摆双面抛光技术,研究了3mm厚大口径超薄元件的双面抛光加工工艺。通过对双面抛光原理的分析,对转速比、抛光垫面形、抛光液等工艺参数上作了优化,并通过加工模拟进行验证。通过工件环分离器减薄技术解决了3mm厚超薄元件的装夹问题。在SYP152双面主动抛光机上进行了加工工艺实验,通过调节转速比实现3mm厚大口径超薄元件面形的高效收敛,验证了加工的可行性,并且达到了面形精度优于1.5λ(λ=632.8nm)、表面粗糙度优于1nm的技术水平。     

Nanopolishing of silicon wafers using ultrafine-dispersed diamonds

In the present study, two new methods are proposed for the polishing of silicon wafers using ultrafine-dispersed diamonds (UDDs). The first proposed polishing method uses a polishing tool with an ultrafine abrasive material made through the electrophoretic deposition of UDDs onto a brass rod. Dry polishing tests showed that the surface roughness of the silicon wafer was reduced from R_a=107 to 4 nm after polishing for 30 min. The second method uses a new polishing pad with self-generating porosity. By polishing with the new pad in combination with the polycrystalline UDD in a water suspension, it is possible to achieve the specified surface roughness of the silicon wafer much faster than when using a conventional pad made of foamed polyurethane. The tests showed that the surface roughness of the silicon wafer was reduced from R_a=107 to 2 nm after polishing for 90 min.     

Novel automatic electrochemical–mechanical polishing (ECMP) of metals for scanning electron microscopy

A low-stress automated polishing device was developed for preparing titanium and nickel alloys for scanning electron microscopy imaging. The system used pulsed electrochemical reactions within an alkaline electrolyte to generate a thin passivation layer on the surface of the sample, which was removed by the mechanical vibration of the system. The passivation layer development and removal were documented for Ti–6Al–4V and IN718 samples subjected to varying electrical potential cycles and polishing times. Results indicated that the applied cyclic potentials removed material faster than typical removal techniques. In addition, electron back scatter diffraction data showed a decrease in subsurface damage using the developed electrochemical–mechanical process compared to standard mechanical polishing techniques.     

A nano-scale mirror-like surface of Ti–6Al–4V attained by chemical mechanical polishing

Metal Ti and its alloys have been widely utilized in the fields of aviation, medical science, and micro-electromechanical systems, for its excellent specific strength, resistance to corrosion, and biological compatibility. As the application of Ti moves to the micro or nano scale, however, traditional methods of planarization have shown their short slabs.Thus, we introduce the method of chemical mechanical polishing(CMP) to provide a new way for the nano-scale planarization method of Ti alloys. We obtain a mirror-like surface, whose flatness is of nano-scale, via the CMP method. We test the basic mechanical behavior of Ti–6Al–4V(Ti64) in the CMP process, and optimize the composition of CMP slurry.Furthermore, the possible reactions that may take place in the CMP process have been studied by electrochemical methods combined with x-ray photoelectron spectroscopy(XPS). An equivalent circuit has been built to interpret the dynamic of oxidation. Finally, a model has been established to explain the synergy of chemical and mechanical effects in the CMP of Ti–6Al–4V.     

Effect of additives for higher removal rate in lithium niobate chemical mechanical planarization

High roughness and a greater number of defects were created by lithium niobate (LN; LiNbO₃) processes such as traditional grinding and mechanical polishing (MP), should be decreased for manufacturing LN device. Therefore, an alternative process for gaining defect-free and smooth surface is needed. Chemical mechanical planarization (CMP) is suitable method in the LN process because it uses a combination approach consisting of chemical and mechanical effects. First of all, we investigated the LN CMP process using commercial slurry by changing various process conditions such as down pressure and relative velocity. However, the LN CMP process time using commercial slurry was long to gain a smooth surface because of lower material removal rate (MRR). So, to improve the material removal rate (MRR), the effects of additives such as oxidizer (hydrogen peroxide; H₂O₂) and complexing agent (citric acid; C₆H₈O₇) in a potassium hydroxide (KOH) based slurry, were investigated. The manufactured slurry consisting of H₂O₂-citric acid in the KOH based slurry shows that the MRR of the H₂O₂ at 2 wt% and the citric acid at 0.06 M was higher than the MRR for other conditions.     

微型激光扩束镜高质量表面加工工艺的研究

研究了微型激光扩束镜准超光滑表面的加工工艺。分析了机床速度、压力、抛光粉、工作温度、抛光模等对高质量表面的影响。选定了一系列的工艺参数,大幅度地提高了产品的合格率。     

基于压力补偿原理的抛光面形快速收敛技术

 为解决强激光系统中大口径光学元件抛光面形精度收敛困难的问题,提出了一种基于压力补偿原理的抛光面形快速收敛技术。利用独特的抛光垫修整技术,将抛光垫表面修整成特定形状,使工件与抛光垫的接触面产生不均匀的压力分布,并结合精确的抛光转速控制,以加快工件面形精度的收敛速度。实验结果表明,将抛光垫修整成微凸面形,可以有效避免抛光中元件过早塌边问题,能将大口径平面元件的初抛时间从数天缩短到6 h以内,元件面形精度提高到1个波长左右。     

Ultrasonic flexural vibration assisted chemical mechanical polishing for sapphire substrate

The sapphire substrates are polished by traditional chemical mechanical polishing (CMP) and ultrasonic flexural vibration (UFV) assisted CMP (UFV-CMP) respectively with different pressures. UFV-CMP combines the functions of traditional CMP and ultrasonic machining (USM) and has special characteristics, which is that ultrasonic vibrations of the rotating polishing head are in both horizontal and vertical directions. The material removal rates (MRRs) and the polished surface morphology of CMP and UFV-CMP are compared. The MRR of UFV-CMP is two times larger than that of traditional CMP. The surface roughness (root mean square, RMS) of the polished sapphire substrate of UFV-CMP is 0.83 Å measured by the atomic force microscopy (AFM), which is much better than 2.12 Å obtained using the traditional CMP. And the surface flatness of UFV-CMP is 0.12 μm, which is also better than 0.23 μm of the traditional CMP. The results show that UFV-CMP is able to improve the MRR and finished surface quality of the sapphire substrates greatly. The material removal and surface polishing mechanisms of sapphire in UFV-CMP are discussed too.     

Planarization process of single crystalline silicon asperity under abrasive rolling effect studied by molecular dynamics simulation

In the chemical mechanical polishing (CMP) process, the complex behaviors of abrasive particles play important roles in the planarization of wafer surface. Particles embedded in the pad remove materials by ploughing, while particles immersed in the slurry by rolling across the wafer surface. In this paper, processes of the particle rolling across a silicon surface with an asperity under various down forces and external driving forces were studied using molecular dynamics (MD) simulation method. The simulations clarified the asperity shape evolution during the rolling process and analyzed the energy changes of the simulation system and the interaction forces acted on the silica particle. It was shown that both the down force and the driving force had important influences on the amount of the material removed. With relatively small down forces and driving forces applied on the particle, the material removal occurred mainly in the front end of the asperity; when the down forces and driving forces were large enough, e.g., 100?nN, the material removal could take place at the whole top part of the asperity. The analysis of energy changes and interaction forces provided favorable explanations to the simulation results.     

化学机械抛光中纳米颗粒的作用分析

化学机械抛光（chemical mechanical polishing, CMP）是用于获取原子级平面度的有效手 段.目前，CMP的抛光液通常使用纳米级颗粒来加速切除和优化抛光质量.这类流体的流变性 能必须考虑微极性效应的影响.对考虑微极性效应的运动方程的求解，有助于了解CMP的作用 机理.数值模拟表明，微极性将提高抛光液的等效黏度从而在一定程度上提高其承载能力， 加速材料去除.这在低节距或低转速下尤为明显，体现出其具有尺寸依赖性.通过改变抛光液 中粒子的微极性，用实验研究了微极性效应对CMP中材料去除速率的影响，证明了分析的合 理性. 关键词： 化学机械抛光 微极流体 抛光液 流变特性 材料去除速率     

平转动运动方式下环形抛光盘的去除函数研究

为保证加工精度和提高抛光效率,推导了盘式动压抛光所用的环形抛光盘在平转动运动方式下的去除函数。在平转动运动方式下,与应用最为广泛的圆形抛光盘相比较,环形抛光盘的最大趋近因子提高了10.25%,更加趋近脉冲函数的特性,减少光学元件表面的中高频误差。给定初始面形误差,以相同的参数采用脉冲迭代法计算驻留时间和残留误差,经过50次迭代,仿真加工结果表明,环形抛光盘相比于圆形抛光盘的表面残留误差降低了3.65%,提高了抛光去除效率。     

Damascene Array Structure of Phase Change Memory Fabricated with Chemical Mechanical Polishing Method

A damascene structure of phase change memory （PCM） is fabricated successfully with the chemical mechanical polishing （CMP） method, and the CMP of Ge2Sb2Te5 （GST） and Ti films is investigated. The polished surface of wafer is analysed by scanning electron microscopy （SEM） and an energy dispersive spectrometer （EDS）. The measurements show that the damascene device structure of phase change memory is achieved by the CMP process. After the top electrode is deposited, dc sweeping test on PCM reveals that the phase change can be observed. The threshold current of array cells varies between 0.90mA and 1.15mA.