【作者】 刘海军；

【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， 2016， 博士

【摘要】 在集成电路芯片制造中,为增加产能和降低成本,大尺寸硅片应用越来越广；同时为了提高芯片性能与封装密度,发展三维封装技术要求对大尺寸硅片进行减薄加工。减薄过程中产生的残余应力导致硅片产生翘曲变形,将会增加硅片在传输和后续加工中的碎片率。硅片的翘曲变形是评价硅片加工质量的重要技术指标,也是分析硅片加工残余应力、优化减薄工艺的重要依据。但是,由于减薄硅片刚度较低,变形测量中极易受到外力的影响,特别是重力的影响,目前消除重力影响的硅片面形测量方法存在局限性；此外,由于磨削减薄硅片呈现大变形特征,现有根据变形计算残余应力的方法存在较大误差。因此,本文研究了消除重力影响的减薄硅片的翘曲变形测量方法,开发了硅片变形测量装置,进而分析了磨削减薄硅片残余应力与变形的关系,主要研究内容与结论如下：(1)提出了减薄硅片翘曲变形的测量方法。测量过程中硅片由三点支撑并保持静止,利用二维工作台,采用非接触位移传感器对硅片表面轮廓进行扫描测量,通过计算分离重力附加变形的方法以及通过将硅片浸入重液消除重力影响的方法获得硅片的实际变形。(2)研究了分离重力附加变形的计算方法。分析了三点支撑方式下支撑点位置对硅片重力附加变形的影响,提出了确定硅片与支撑点位置的方法；建立了硅片重力附加变形的有限元模型,并通过硅片反转法对模型进行了验证；建立了利用有限元模型计算重力附加变形,并从测量的硅片表面轮廓中分离重力附加变形得到硅片的实际变形的方法。(3)研究了消除重力影响的液浸法。将三点支撑的硅片浸没于密度稍小于硅的重液中,利用液体浮力消除绝大部分重力对硅片变形的影响,结合计算法分离残余重力附加变形得到硅片实际变形。通过对比不同溶液的密度与安全性,确定了适用于液浸法的两种溶液。通过分析激光在不同介质传播时的折射以及液面波动对测量结果的影响,研究了测量数据的修正方法,提出了消除液面波动影响的措施,通过在空气和重液中对标准样件的对比测量,确定了测量数据的修正系数。(4)开发了减薄硅片变形测量装置与控制系统。采用激光三角位移传感器与花岗岩气浮导轨二维运动平台搭建了测量装置；采用“PC机+控制卡”的方式开发了开放式的控制系统,采用Matlab与VC++联合编程的方法编写了运动控制、数据处理及图像显示软件。对测量装置的几何精度和测量传感器精度的综合分析结果表明,所研制的测量装置测量硅片变形的不确定度为士1.7μm,并与商用激光干涉仪测量标准样件面形的结果进行了对比验证。(5)分析了磨削减薄硅片残余应力与变形之间的关系。利用有限元方法,考虑各向异性建立了硅片残余应力与变形之间的数学模型,可根据硅片变形求解残余应力。分析了硅片残余应力对重力附加变形的影响。当硅片残余应力小于变形分叉临界值时,硅片实际变形与重力附加变形符合线性叠加关系,可以采用反转法测量硅片面形,但残余应力会引入较大的测量误差,可通过计算法予以修正；当硅片残余应力超过变形分叉临界值时,硅片实际变形与重力附加变形不再符合线性叠加关系,适合采用液浸法进行测量。更多还原

【Abstract】 Large silicon wafers are widely used to increase productivity and reduce cost in the manufacturing of integrated circuits. Besides, three dimensional packages are adopted to increase packaging density and enhance the chip performance, which require thinned silicon wafers. Residual stress is induced on the wafer surface during thinning processes and would lead to wafer deformation. Wafers with large deformation tend to break easily during machining and transmission processes, leading to yield loss. The wafer deformation measurement plays an important role to assess the machining quality of wafers. Also, the wafer deformation could be used to analyze the residual stress and improve the processing technique. However, the precise measurement of the deformation of thinned silicon wafers is significantly affected by external forces (especially gravity) due to their low rigidity. There exist limits for current measurement methods which are used to cancel gravitational effect. Besides, the stress-deformation relations of the ground wafers are in the nonlinear range and there exist large errors when the existing equations are used to calculate the residual stress by the wafer deformation. In this dissertation, measurement methods which are used to cancel gravitational effect were proposed and a measurement apparatus was developed. Also the stress-deformation relationship was analyzed for ground silicon wafers. The main research works and conclusions are as follows:(1) Deformation measurement methods were proposed aiming for thinned silicon wafers. The silicon wafer is static and supported by three points during the measuring process. A non-contact displacement sensor mounted on a two dimensional motion stage was selected to scan the surface profile of the wafer. To cancel gravitational effect during the measurement process, the method to compute and separate gravity-induced deflection (GID) according to the supporting positions was proposed. Also the method in wich the wafer is immersed in a liquid to cancel gravitational effect was proposed.(2) The computing method to separate the GID was studied. The effect of support location on the GID of the wafer supported by three points was analyzed. The methods to acquire the positions of the supports and the wafer were proposed. The FEM model of the wafer was created and verified using the inverting method by measuring a double-sided polished wafer. The GID could be computed using the FEM model according to the actual locations of the supports. Then the true wafer shape could be obtained by subtracting the GID from the measured wafer profile.(3) The liquid immersion method to cancel the gravitational effect was studied. The wafer is immersed in the liquid of which the density is slightly smaller than that of silicon. The buoyancy force on the wafer cancels out most of the effect of gravity. The residual effect of gravity is further removed by subtracting the residual deflection calculated using the computing method from the measured result. The suitable liquids were selected through the comparison of density and safety of different liquids. The correction method for the measurement data was studied through analyzing the transismission of the laser light in different media. The measure to eliminate the effect of the fluctuation of liquid level was proposed. The correction factor was determined by comparing the measurement results of standard specimen in air and in the liquid.(4) A measurement apparatus and its control system were developed. Laser triangulation sensor and two dimensional motion stage based on air-bearing granitic guides were adopted to build the apparatus. The open control system was developed based on PC and motion control card. The motion control, data processing and image display software was developed using the Matlab and VC++ softwares. The combined uncertainty for the wafer deformation measurement is ±1.7 μm through the analysis of the geometric accuracy of the developed apparatus and the linear accuracy of the laser sensor. It was verified by the surface profile meausurement result of a standard specimen by a commercial interferometer.(5) The relationship between the residual stress and the deformation of the ground silicon wafers was analyzed. The mathematical model between the wafer deformation and the residual stress was established using the FEM model which includes the effect of the anisotropy of monocrystalline silicon. The residual stress could be calculated by the wafer deformation. Besides, the effects of the residual stress on GID were researched. When the residual stress is smaller than the critical value, the wafer deformation and the GID could be superposed on each other. However, the effect of residual stress would lead to errors when the inverting method is used. The computing method could be adopted to correct the result. When the residual stress is larger than the critical value, the wafer bifurcates. The wafer deformation and the GID could not be superposed on each other. The liquid immersion method could be used to measure the wafer deformation.更多还原