【作者】 高尚；

【导师】 康仁科；

【作者基本信息】 大连理工大学 ， 机械制造及其自动化， 2013， 博士

【摘要】 电子产品对高性能、多功能、小型化和低成本的需求推动了集成电路(IC)制造技术的高速发展,特别是便携式电子产品的飞速发展对IC封装技术提出了越来越高的要求,其中,叠层三维立体封装技术由于其空间占用小,电性能稳定、成本低等优点成为未来的主要发展趋势。在封装整体厚度不变甚至减小的趋势下,要增加堆叠层数,必须对各层硅片进行背面减薄,且要求减薄硅片具有高面型精度、无表面／亚表面损伤。目前,采用金刚石砂轮的超精密磨削技术在硅片的背面减薄加工中得到广泛应用,但是,随着硅片尺寸和原始厚度的增大以及减薄厚度的减小,超精密磨削减薄技术面临着表面层损伤、弯曲/翘曲变形、加工效率等问题。因此,面向IC封装技术对超薄硅片的需求,以提高硅片表面层质量、面型精度和减薄效率为目的,本文深入研究了金刚石砂轮磨削减薄硅片的亚表面损伤特性、变形机理和崩边规律以及采用软磨料砂轮的机械化学磨削技术,对于实现硅片的高效率、低损伤、超薄化磨削加工具有重要的指导意义。论文的主要研究内容和结论如下：(1)建立了硅片旋转磨削的磨粒切削深度数学模型,推导出磨粒切削深度与磨削参数、砂轮尺寸及硅片表面径向位置的数学关系,指出磨粒切削深度随着砂轮粒径、砂轮进给速度、硅片转速和硅片表面径向距离的增大而增大,随着砂轮周长、砂轮齿宽和砂轮转速的增大而减小。采用角度截面显微观测法研究了金刚石砂轮磨削硅片的亚表面损伤深度沿硅片径向和周向的分布及光磨对磨削硅片亚表面损伤分布的影响,在此基础上,研究了磨削参数对亚表面损伤深度的影响,并基于建立的磨粒切削深度数学模型分析了相应规律的产生原因。研究表明,无光磨条件下磨削硅片的亚表面损伤深度沿周向在<110>晶向处大于<100>晶向,沿径向从中心到边缘逐渐增大；光磨条件下磨削硅片的亚表面损伤深度沿整个硅片表面几乎是均匀的,且光磨后的硅片亚表面损伤深度小于无光磨条件下磨削硅片；随着砂轮粒度的减小、转速的增大及进给速度的减小,亚表面深度明显地减小,但硅片转速对亚表面损伤深度的影响较小。(2)基于Ansys有限元软件研究了金刚石砂轮磨削减薄硅片过程中砂轮、真空吸盘与硅片间的作用力情况,揭示了硅片磨削减薄后发生变形的机理。基于圆形薄板弯曲变形理论建立了弹性小变形范围下的硅片超精密磨削减薄变形的数学模型,推导出硅片磨削减薄的变形量与亚表面损伤层深度、表面层加工应力、减薄厚度及单晶硅自身力学特性之间的数学关系,并通过试验对数学模型进行了验证。研究表明,随着硅片亚表面损伤深度的增大、减薄厚度的减小及表面层加工应力的增大,磨削减薄硅片的变形相应的增大,硅片变形的理论值与实测值基本相同。(3)通过硅片磨削减薄试验研究了崩边形状和尺寸沿硅片圆周的变化规律,在此基础上,研究了砂轮粒度、减薄厚度、磨削方式和砂轮进给速度等磨削参数等崩边尺寸的影响,并基于单晶硅的各向异性力学特性和工件旋转法磨削硅片的磨削力特征揭示了崩边规律的产生机理。结果表明,沿硅片圆周位于<100>晶向的崩边形状为等腰直角三角形,位于<110>晶向的崩边形状为矩形,但崩边尺寸沿硅片圆周不同晶向处没有明显的变化；随着砂轮粒度的减小、减薄厚度的增大及砂轮进给速度的减小,减薄硅片的崩边尺寸相应的减小,且顺磨方式减薄硅片的崩边尺寸小于逆磨方式减薄硅片。(4)针对金刚石砂轮磨削硅片的表面层损伤问题,提出采用软磨料砂轮的机械化学磨削技术。根据单晶硅的材料特性,研制了用于硅片磨削的CeO2、Fe2O3和MgO三种软磨料砂轮,并研究了软磨料砂轮的修整方法。通过检测硅片表面粗糙度、表面／亚表面损伤、砂轮修整间隔、主轴电机电流、磨削比及材料去除率等参数,研究了软磨料砂轮的磨削性能,并与同粒度金刚石砂轮的磨削性能以及化学机械抛光(CMP)的加工效果进行了对比分析。通过检测软磨料砂轮磨削硅片表面的化学成分分析了磨料、单晶硅和添加剂之间在磨削过程中发生的化学反应,建立了软磨料砂轮磨削硅片的材料去除机理模型。研究表明,软磨料砂轮磨削的硅片表面层质量远好于金刚石砂轮磨削硅片,接近于CMP的加工效果,且材料去除率高于CMP。(5)在上述研究的基础上,根据不同粒度金刚石砂轮磨削减薄硅片的材料去除率、亚表面损伤深度、崩边和变形以及软磨料砂轮机械化学磨削的特点,提出硅片一次装夹定位条件下,依次采用#600金刚石砂轮粗磨、#3000金刚石砂轮精磨和#3000MgO软磨料砂轮机械化学磨削的硅片高效低损伤磨削减薄工艺,利用该工艺获得了磨削减薄厚度为401μm的超薄硅片。更多还原

【Abstract】 The demands of high-performance, multi-function, miniaturization and low-cost for electronic products promote the rapid development of integrated circuit(IC) manufacturing technology. Especially the high-speed evolution of portable electronic products puts forward higher and higher requirements for IC packaging technology.3D stacked package technology becomes the main development direction of IC packaging technology for its advantages in lowering space occupation, elevating electrical stability, reducing costs, etc. To raise layer number of3D stacked package without enlarging the overall package thickness, the silicon wafer in each layer needs back thinning. Furthermore, the back thinned wafers are required to have high surface accuracy and free surface/subsurface damage. Although being widely used in back thinning of silicon wafers, ultra-precision grinding technology with diamond grinding wheel is facing the problems of subsurface damage, wafer warpage/bow, machining efficiency, etc with an increase in diameter and thickness of prime wafers,but a decrease in finical thinning thickness. To meet IC packaging demand for ultra-thin wafers and improve surface layer quality, surface accuracy and machining efficiency, this dissertation aims to investigate the subsurface damage characteristics, warping mechanism and edge chipping of silicon wafers in diamond grinding and the mechanical-chemical grinding(MCG) technology with soft abrasive grinding wheel. The research results provide practical guidance for realizing high-efficiency and low-damage silicon wafer thinning by ultra-precision grinding. The main research works and conclusions are as follows:(1) A mathematical model of the grain depth-of-cut in wafer rotation grinding was established and the formula of the grain depth-of-cut was derived, which correlated grain depth-of-cut with grinding parameters, dimensions of the diamond cup wheel and distance from wafer center to the sample location. As the increase in grain size, wheel feedrate, wafer speed and distance from wafer center to the sample location, the grain depth-of-cut increased, while the increase in circumference and teeth width of the diamond cup wheel, wheel speed would decrease the grain depth-of-cut. Using the angle cross-section microscopy, the subsurface damage distributions along radial and circumferential direction of silicon wafers ground by diamond grinding wheels were investigated, and the effect of spark-out process on the subsurface damage distribution was analyzed. On that basis, the effects of grinding parameters on subsurface damage depth were also studied and the reasons were analyzed based on the established mathematical model of the grain depth-of-cut. The experiment results showed that in the ground wafer without spark-out process, the subsurface damage depth in<110> crystal orientation was larger than that in<100> crystal orientation and the subsurface damage depth increased along the radical direction from the centre to the edge; but in the ground wafer with spark-out process, the subsurface damage depths in different circumferential and radial locations were almost the same. And the subsurface damage depth in ground silicon wafers with spark-out process was significantly smaller than that without spark-out process. The subsurface damage depth decreased with a decrease in grain size and wheel feedrate, and an increase in the wheel speed, but the effect of wafer speed on subsurface damage depth was less.(2) Wafer holding mechanics on a vacuum chuck and grinding-induced stress distribution during a wafer thinning process were investigated using Ansys simulation software, and the warping mechanism of silicon wafers after grinding thinning was revealed. Based on the deflection theory of the circular thin plate, a mathematical model was established for predicting the wafer warp in the wafer grinding thinning when wafer deflection was small in the elastic range. The model correlated wafer warping with subsurface damage depth, machining stresses, wafer thinning thickness and the mechanical properties of the monocrystalline silicon, and the model was verified through thinning experiments of silicon wafers.The results indicated that as the increase in subsurface damage depth and machining stresses, the wafer warping increased; while the increase in wafer thinning thickness would decrease the wafer warping. And the model also showed a good agreement with the experimental results.(3) Edge chipping profile and size distributions along circumferential direction of thinned silicon wafers in diamond grinding thinning were experimentally investigated, on that basis, the effects of grinding parameters such as grain size, wafer thinning thickness, grinding mode and wheel feedrate on edge chipping size were also studied. The study also discussed the edge chipping mechanisms based on crystal orientation and machining mechanics of a wafer in thinning. The experiment results indicated that the edge chipping profile in the <100> crystal orientation of a ground silicon wafer was almost a isosceles right triangle and that in the<110> crystal orientation similar to a rectangle, but the edge chipping size was independent on the crystal orientation and thus wafer edge location. The edge chipping size decreased with a decrease in grain size and down-feedrate, but an increase in the wafer thickness. And the edge chipping size was larger in the down-grinding mode than in the up-grinding mode. (4) Aiming at the surface layer damage of silicon wafers in diamond grinding, a mechanical-chemical grinding(MCG) technology with soft abrasive grinding wheel was proposed. Based on the material properties of single crystal silicon, the soft abrasive grinding wheels using CeO2, Fe2O23and MgO as abrasives for grinding silicon wafer were developed. The dressing method of soft abrasive grinding wheel was studied. Through measuring wafer surface roughness, surface/subsurface damage, dressing interval, spindle motor current, grinding ratio and material removal rate, and comparing with the machining effects of diamond wheel grinding and chemical mechanical polishing(CMP), the grinding performances of the soft abrasive grinding wheels were investigated. The surface component of silicon wafer ground with soft abrasive grinding wheel was inspected and the chemical reaction between abrasives, additives and single crystal silicon was analyzed. The material removal model in silicon wafer grinding with soft abrasive grinding wheel was established. The results demonstrated that the surface layer quality of silicon wafers ground by the soft abrasive grinding wheels were all much better than the diamond grinding wheel and comparable to CMP, but the material removal rate in wafer grinding with soft abrasive grinding wheels was higher than about CMP.(5) Building upon the above research on material removal rate, subsurface damage, edge chipping and wafer warping of diamond grinding and characteristics of MCG with soft abrasive grinding wheel, a novel high-efficiency and low-damage ultra precision grinding thinning process of silicon wafers by stages using#600diamond grinding wheel,#3000diamond grinding wheel and#3000MgO soft abrasive grinding wheel in one single clamping step was proposed. Using the proposed thinning process, the minimum thinning thickness of silicon wafer reached40μm.更多还原