Fine grinding of silicon wafers: effects of chuck shape on grinding marks

Silicon wafers are used for production of most microchips. Various processes are needed to transfer a silicon ingot into wafers. With continuing shrinkage of feature sizes of microchips, more stringent requirement is imposed on wafer flatness. Fine grinding of silicon wafers is a patented technology to produce super flat wafers at a low cost. Six papers on fine grinding were previously published in this journal. The first paper discussed its uniqueness and special requirements. The second one presented the results of a designed experimental investigation. The third and fourth papers presented the mathematical models for the chuck shape and the grinding marks, respectively. The fifth paper developed a mathematical model for the wafer shape and the sixth paper studied machine configurations for spindle angle adjustments. This paper is a follow up of the above-mentioned work. A mathematical model to predict the depth of grinding marks for any chuck shape will be first developed. With the developed model, effects of the chuck shape (as well as the wheel radius) on the depth of grinding marks will be studied. Finally, results of pilot experiments to verify the model will be discussed.     

Origin,modeling and suppression of grinding marks in ultra precision grinding of silicon wafers

A phenomenon commonly encountered in grinding of silicon wafers is the grinding marks, which are difficult to remove by subsequent polishing process, and have been a great obstacle to the manufacture of silicon wafers with higher flatness. In this paper, the grinding marks formation mechanism was clarified, a grinding marks formation model and an angular wavelength model were developed, and a grinding marks suppression method was proposed. A series of grinding experiments were carried out to verify the developed models and investigate the effect of the wafer rotational speed, the wheel rotational speed, the infeed rate, the axial run out of the cup wheel and the spark out time. The results show that: (1) grinding marks are waviness generated on silicon wafers caused by non-uniform material removal circumferentially due to the axial run out of the cup wheel; (2) grinding marks present multiple angular wavelengths characteristics; (3) the angular wavelength of grinding marks is a one-variable function of the rotational speed ratio of the wheel to the wafer; and (4) grinding marks could be suppressed significantly by properly selecting the rotational speed ratio.     

Fine grinding of silicon wafers: designed experiments

Silicon wafers are the most widely used substrates for semiconductors. The falling price of silicon wafers has created tremendous pressure to develop cost-effective processes to manufacture silicon wafers. Fine grinding possesses great potential to reduce the overall cost for manufacturing silicon wafers. The uniqueness and the special requirements of fine grinding have been discussed in a paper published earlier in this journal. As a follow-up, this paper presents the results of a designed experimental investigation into fine grinding of silicon wafers. In this investigation, a three-variable two-level full factorial design is employed to reveal the main effects as well as the interaction effects of three process parameters (wheel rotational speed, chuck rotational speed and feed-rate). The process outputs studied include grinding force, spindle motor current, cycle time, surface roughness and grinding marks.     

大尺寸硅片自旋转磨削运动分析及仿真

本文利用数学矩阵方法,建立大尺寸硅片自旋转磨削运动的理论模型,研究了砂轮半径、硅片和砂轮旋转速度、旋转方向等因素的选择及各因素对磨削轨迹的影响,同时还研究了磨粒合成运动速度的变化规律。研究结果表明,随着砂轮半径的增大,磨削轨迹的曲率减小,选用较小直径砂轮将更有利硅片表面质量的提高。当转速比i大于零,随着i值的增大,磨削轨迹的曲率逐渐减小。在转速比i小于零的情形,当转速比i=-2时,磨削轨迹曲率为0,磨削轨迹的形状接近一条直线。磨粒合成运动速度随砂轮转速和硅片转速的增大而增大。     

Fine grinding of silicon wafers: a mathematical model for the wafer shape

Over 90% of semiconductors are built on silicon wafers. The fine grinding process has great potential to produce very flat wafers at a low cost. Four papers on fine grinding have been previously published by the authors. The first paper discussed its uniqueness and special requirements. The second one presented the results of a designed experimental investigation. The third and fourth papers presented mathematical models for the chuck shape and the grinding marks, respectively. As a follow up, this paper develops a mathematical model for the wafer shape. After the model is described, its practical applications in wafer manufacturing are discussed.     

A study on surface grinding of 300 mm silicon wafers

Most of today's IC chips are made from 200 mm or 150 mm silicon wafers. It is estimated that the transition from 200 mm to 300 mm wafers will bring a die cost saving of 30–40%. To meet their customers' needs, silicon wafer manufacturers are actively searching for cost-effective ways to manufacture 300 mm wafers with high quality. This paper presents the results of a study on surface grinding of 300 mm silicon wafers. In this study, a three-factor two-level full factorial design is employed to reveal the main effects as well as the interaction effects of three process parameters (wheel rotational speed, chuck rotational speed and feedrate). The process outputs studied include spindle motor current, surface roughness, grinding marks and depth of subsurface cracks.     

Fine grinding of silicon wafers: a mathematical model for the chuck shape

Fine grinding of silicon wafers is a patented technology to manufacture super flat semiconductor wafers cost-effectively. Two papers on fine grinding were previously published in this journal, one discussed its uniqueness and special requirements, and the other presented the results of a designed experimental investigation. As a follow up, this paper presents a study aiming at overcoming one of the technical barriers that have hindered the widespread application of this technology, namely, the difficulty and uncertainty in chuck preparation. Although the chuck shape is critically important in fine grinding, there are no standard procedures for its preparation. Furthermore, the information on the relation between the set-up parameters and the resulting chuck shape is not readily available. In this paper, a mathematical model for the chuck shape is first developed. Then the model is used to predict the relations between the chuck shape and the set-up parameters. Finally, the results of the pilot experiments to verify the model are discussed.     

JS1100大型自动控制砂轮回转试验机

本文介绍了大型自动控制砂轮回转试验机的设计研制，通过设计体式砂轮卡盘及新结构防护罩，采用交流变频、计算机控制技术，研制出了新一代性能优良的大型回转试验机，具有自动化程度离，操作维护简便，数字化显示主轴转速，节能等优点。     

cBN砂轮在低速磨削中的应用

cBN砂轮在高速设备上使用非常广泛,但在老式低速磨床上采用cBN砂轮的非常少。我们在这方面做了大胆的尝试,就是在老式磨床上不做任何改进,直接更换相同直径的陶瓷cBN砂轮,通过更换皮带轮改变传动比,把砂轮速度从51.4 m/s提升到64.8 m/s,增大冷却液流量、压力,确定冷却液冲刷位置,改变切削的进给量,使cBN砂轮的一个修整频次内寿命大幅提升。最后证明陶瓷cBN砂轮在低速磨床中一样可以替代刚玉砂轮,并且不需要大的改造投资,可以获得非常好的综合经济效益。     

基于有限差分模型的磨削弧区流场动压力数值分析

磨削弧区动压力对通过磨削区磨削液的有效流量、润滑和冷却作用有重要影响。本研究基于流体动压理论,建立了磨削弧区的动压力分布数学模型,将微分方程简化至近似泊松方程形式后,采用有限差分法将连续方程离散化,得出了磨削区动压力的数值解,并提出了迭代优化算法,提高了计算效率。将砂轮特性参数纳入数学模型之中,可根据砂轮材质、砂轮与工件间隙、砂轮转速等参数预报磨削弧区的磨削液动压力分布。在此理论模型基础上,进行了验证实验,证明模型的科学性。结果表明:通过输入砂轮各项参数,该模型可以快速、准确地预报动压力的分布,为磨削加工提供参考。      

A new in-feed centerless grinding technique using a surface grinder

This paper deals with the development of an alternative centerless grinding technique, i.e., in-feed centerless grinding based on a surface grinder. In this new method, a compact centerless grinding unit, composed of an ultrasonic elliptic-vibration shoe, a blade and their respective holders, is installed onto the worktable of a surface grinder, and the in-feed centerless grinding operation is performed as a rotating grinding wheel is fed in downward to the cylindrical workpiece held on the shoe and the blade. During grinding, the rotational speed of the workpiece is controlled by the ultrasonic elliptic-vibration of the shoe that is produced by bonding a piezoelectric ceramic device (PZT) on a metal elastic body (stainless steel, SUS304). A simulation method is proposed for clarifying the workpiece rounding process and predicting the workpiece roundness in this new centerless grinding, and the effects of process parameters such as the eccentric angle, the wheel feed rate, the stock removal and the workpiece rotational speed on the workpiece roundness were investigated by simulation followed by experimental confirmation. The obtained results indicate that: (1) the optimum eccentric angle is around 6°; (2) higher machining accuracy can be obtained under a lower grinding wheel feed rate, larger stock removal and faster workpiece rotational speed; (3) the workpiece roundness was improved from an initial value of 19.90 μm to a final one of 0.90 μm after grinding under the optimal grinding conditions.     

金刚石砂轮精密修整工艺研究

金刚石砂轮机械磨削是砂轮整形的传统方式。砂轮旋转速度以及工具砂轮的进给量是金刚石砂轮机械精密整形的主要工艺参数。通过在超硬材料砂轮整形机床上的大量实验和砂轮磨削力的分析,得到了金属结合剂和树脂结合剂金刚石砂轮精密整形的比较理想的工艺参数;确定了工具砂轮的线速度应在11 m/s左右,工具砂轮轴转速在1 050～1 800 r/min;金刚石砂轮轴转速设定在400～1 000r/min,金刚石砂轮的线速度为2.6～10.5 m/s。同时,分析比较了机械修锐和喷砂修锐的效果。     

面向绿色制造的快速点磨削磨削液供给参数计算

高速／超高速磨削条件下,砂轮边缘的高速空气带会阻碍磨削液注入磨削区。空气带压力与砂轮速度的平方成正比。快速点磨削是一种新型高速／超高速磨削技术,接触区很小,实际磨削功率低,冷却及散热效果好。在分析了高速／超高速磨削砂轮周围旋转空气带动压力及速度分布特点的基础上,根据热力学原理及快速点磨削特点,分析并建立了磨削液的供给流量和供液速度的理论模型。在此基础上,建立了面向绿色制造的快速点磨削的磨削液喷嘴直径及供液压力的工程计算公式。     

5G覆铜板叠层复合材料高效切磨工艺试验研究

为解决5G覆铜板叠层复合材料板材现有的冲压剪切工艺毛刺飞边严重的问题,提出采用烧结金刚石开槽薄片砂轮切磨工艺替代剪切工艺的方法,在分析设计开槽砂轮结构参数的基础上,研制相应的烧结金刚石开槽薄片砂轮,试验研究不同工艺参数对切磨过程上下表面覆铜层加工毛刺的影响规律和磨削区温度的变化规律。试验结果表明:单位Z向磨削力随磨削速度的增大而增大,随进给速度的增大而减小,随砂轮切入角度的增大先增大后减小;且毛刺飞边高度的变化趋势与单位Z向磨削力的变化趋势相反。磨削温度随磨削速度和进给速度的增大而升高,随砂轮切入角度的增大先升高后降低。切磨5G覆铜板的最优参数组合是磨削速度为34.56 m/s,进给速度为1 200 mm/min,砂轮切入角度为22.0°,在此参数下加工既能保证毛刺飞边高度小于300 μm,又能兼顾较低的磨削区温度。      

Influence of different grinding wheel and dressing roller specifications on grinding wheel wear

A targeted adjustment of the dressing results and the methodological influence of the dressing process on the non-stationary wear of a grinding wheel after dressing increases the productivity and the reproducibility of grinding processes. Despite the great economic importance of grinding processes with vitrified corundum grinding wheels and the great relevance of the dressing process for the application behavior of these grinding wheels, quantitative models are missing for the purposeful design of the dressing process. In previous studies, a dressing model was successfully developed which predicts the dressing force in the dressing process as well as the workpiece roughness and the grinding wheel wear behavior in a grinding process for a specific grinding wheel and form roller specification. However, a transferability of this model to other grinding wheel and form roller specifications is not possible because the influence of the grain size and the hardness of the grinding wheel as well as the dressing tool topography on the grinding wheel wear and thus on parameters of the dressing model are not known. The objective of this work was to extend the model to additional grinding wheel and form roller specifications to ensure a broad applicability of the model.     

大尺寸硅片自旋转磨削的试验研究

利用基于自旋转磨削原理的硅片超精密磨床,通过试验研究了砂轮粒度、砂轮转速、工件转速及砂轮进给速度等主要因素对材料去除率、砂轮主轴电机电流以及磨削后硅片表面粗糙度的影响关系。研究结果表明,增大砂轮轴向进给速度和减小工件转速,采用粗粒度砂轮有利于提高磨削硅片的材料去除率,砂轮轴向进给速度对材料去除率的影响最为显著;适当增大砂轮转速,减小砂轮轴向进给速度,采用细粒度砂轮可以减小磨削表面粗糙度;在其它条件一定的情况下,砂轮速度超过一定值会导致材料去除率减小,主轴电机电流急剧增大,表面粗糙度变差;采用比#2000粒度更细的砂轮磨削时,材料去除率减小,硅片表面粗糙度没有明显改善。     

Experimental study on grinding force and grinding temperature of Aermet 100 steel in surface grinding

This paper investigates grinding force and grinding temperature of ultra-high strength steel Aermet 100 in conventional surface grinding using a single alumina wheel, a white alumina wheel and a cubic boron nitride wheel. First, mathematical models of grinding force and grinding temperature for three wheels were established. Then, the role of chip formation force and friction force in grinding force was investigated and thermal distribution in contact zone between workpiece and wheel was analyzed based on the mathematical model. The experimental result indicated that the minimum grinding force and the maximum grinding force ratio under the same grinding parameters can be achieved when using a CBN wheel and a single alumina wheel, respectively. When the phenomenon of large grinding force and high grinding temperature appeared, the workpiece material would adhere locally to the single alumina wheel. Grinding temperature was in a high state under the effect of two main aspects: poor thermal properties of grinding wheel and low coolant efficiency. The predicted value of grinding force and grinding temperature were compared with those experimentally obtained and the results show a reasonable agreement.     

Experimental simulation of the efficiency of high speed grinding wheel cleaning

The grinding of certain materials such as ductile material which are hard to grind implies particular conditions of work. Maintaining the cutting ability of the wheel is necessary and wheel cleaning is one of these conditions. In this paper, the parameters which are influential in maintaining a clean wheel are identified. A cleaning criterion is proposed to estimate the efficiency of the cleaning process. Using an experimental setup, the significant of the influence of the nozzle position, the flow rate and pressure, the boundary layer of air around the rotating wheel and the particle rate contained in the fluid are assessed. It is observed too that the fluid temperature has no significant effect. Lastly, the best method to clean a wheel when high speed grinding is discussed.     

金刚石砂轮磨削钛合金时的磨削力研究

为解决金刚石砂轮磨削钛合金时材料弹性模量低、弹性形变大等问题,从理论上对砂轮的受力状态进行分析。基于切屑分离准则和材料摩擦属性,构建钛合金磨削时的受力模型,并对单颗磨粒的受力状态进行有限元仿真。设计钛合金磨削加工试验,研究工艺参数变化对砂轮磨削力的影响规律。结果表明:砂轮磨削速度增加,磨削力逐渐降低;当进给速度和磨削深度增加时,磨削力增加。当磨削工艺参数改变时,砂轮的切向和法向磨削力的变化趋势大致相同,切向和法向磨削力的比值为0.29～0.37。且磨削力的理论值和试验值的变化趋势基本一致,二者相对误差的平均值在5%以内,验证了磨削力理论模型的正确性。      

Fine grinding of silicon wafers

Silicon wafers are used for the production of most microchips. Various processes are needed to transfer a silicon crystal ingot into wafers. As one of such processes, surface grinding of silicon wafers has attracted attention among various investigators and a limited number of articles can be found in the literature. However, no published articles are available regarding fine grinding of silicon wafers. In this paper, the uniqueness and the special requirements of the silicon wafer fine grinding process are introduced first. Then some experimental results on the fine grinding of silicon wafers are presented and discussed. Tests on different grinding wheels demonstrate the importance of choosing the correct wheel and an illustration of the proper selection of process parameters is included. Also discussed are the effects of the nozzle position and the flow rate of the grinding coolant.