基于像差补偿的近红外显微干涉硅通孔测量

Measurement of through silicon via by near-infrared micro interferometry based on aberration compensation

为了实现深宽比大于6∶1的硅通孔的形貌测量,提出了一种基于像差补偿的近红外显微干涉检测方法。该方法采用近红外宽带光作为光源,能够穿透硅通孔,检测系统中内置变形镜自适应像差补偿模块,主动补偿硅通孔引入的调制像差。在检测硅通孔三维形貌时,依据COMSOL Multiphysics有限元仿真软件得到的三维硅通孔高深宽比结构对探测光的调制像差规律,指导设置需变形镜补偿的像差种类和量值,用基于频域的评价函数指标阈值,判定硅通孔底部图像的聚焦状态,获得待测硅通孔清晰的底部图像,本质上提升探测光的重聚焦能力。在此基础上,使用垂直扫描干涉法得到待测硅通孔的深度与其三维形貌分布。实验测量了直径为10μm、深度为65μm、深宽比为6.5∶1和直径为10μm、深度为103μm、深宽比为10.3∶1的硅通孔深孔,并与高精度SEM的测量结果对比,深度测量的相对误差为1%。与白光显微干涉测量结果对比表明,本文所提出的方法可以获得清晰的高深宽比硅通孔的底部图像,有效增强底部的宽谱干涉信号和对比度,能够准确测量更高深宽比硅通孔的三维形貌。

Through silicon via(TSV)technology refers to the silicon micro-hole processing technology used to achieve vertical conduction and interconnection between chips.The three-dimensional(3D)morphology of TSV samples is commonly measured using destructive scanning electron microscope(SEM)profile imaging technology.In addition,white light interference technology has the advantage of non-destructive measurement;however,it is difficult to probe the light reaching the bottom of TSV samples with an aspect ratio higher than 6:1,and the topography is also distorted.To address this problem,a near-infrared micro-interference detection method based on aberration compensation is proposed in this paper.The method uses near-infrared broadband light as the probe light source,which can penetrate through the TSV.Moreover,an adaptive aberration compensation module in the form of a deformable mirror is introduced into the detection system to compensate for the modulation aberration that is synchronously generated by the TSV.The first step of detecting the TSV 3D topography is to set the type and quantity of the aberration that needs to be compensated by the deformable mirror.This is obtained using the finite element simulation software COMSOL Multiphysics based on the aberration modulation law for a 3D TSV high aspect ratio structure under the probe light.Subsequently,the evaluation function index threshold based on the frequency domain is used to estimate the focus state of the TSV bottom image.Furthermore,the refocusing ability of the probe light is essentially improved and a clear bottom image of the tested TSV is obtained.On this basis,the depth value of the tested TSV and its 3D topography distribution is calculated using vertical scanning interferometry.Finally,two types of TSV samples with a diameter of 10μm and depth of 65μm(aspect ratio 6.5),and diameter of 10μm and depth of 103μm(aspect ratio 10.3),are measured using the proposed method.The results show that the relative error of depth measurement is 1%compared with that of the high-precision SEM measurement results.Moreover,the proposed method can obtain a clear image of the TSV bottom with a high aspect ratio,and can also effectively enhance the wide spectrum interference signal and fringe contrast at the bottom compared with white light microscopic interference.Therefore,the proposed method can be used to precisely measure the 3D topography of TSVs with a higher aspect ratio.