Detection system of multilayer coating microstructure defects based on differential interference contrast confocal microscopy
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摘要:多层膜极紫外光刻掩模"白板"缺陷是制约下一代光刻技术发展的瓶颈之一，为提高对掩模"白板"上的膜层微结构缺陷的分辨能力，提出了一种微分干涉差共焦显微探测系统方案。基于标量衍射理论，计算了系统横向和轴向分辨率。利用MATLAB建模仿真，在数值孔径为0.65、工作波长为405 nm时，分析比较了微分干涉差共焦显微系统、传统显微系统和共焦显微系统的分辨率。结果表明微分干涉差共焦显微系统具有230 nm的横向分辨率和25 nm轴向台阶高度差的分辨能力（对应划痕等缺陷形式）。此外，仿真和分析了实际应用中探测器尺寸、样品轴向偏移等的影响，模拟分析了膜层微结构缺陷的探测，结果表明本系统可以探测200 nm宽、10 nm高的微结构缺陷，较另外两种系统有更好的探测能力。Abstract:Defects in the multilayer extreme ultraviolet lithography(EUV) mask "whiteboard" have become an important issue to restrict the development of next-generation lithography. A detection system based on differential interference contrast(DIC) confocal microscopy is proposed in order to improve the ability of distinguishing the microstructure defects on the lithography mask "whiteboard". Based on the scalar diffraction theory, the lateral and axial resolution of the system are calculated. In the condition that numerical aperture of 0.65 and working wavelength of 405 nm, resolutions of DIC confocal microscopy, traditional microscopy and the confocal microscopy system are compared and analyzed using MATLAB. The results show that the DIC confocal microscopy has the ability of lateral resolution of 230 nm and resolution of axial step height difference of 25 nm(corresponding to defects such as scratches). In addition, the effect of factors such as the size of detector and the axial deviation of the sample are also simulated and analyzed. The experimental results show that the proposed system can detect multilayer coating microstructure defects with a width of 200 nm and a height of 10 nm, which has better detection ability than the other two systems.
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图 3共焦和DIC共焦系统归一化光强分布曲线
Figure 3.Uniformization intensity curves of confocal and DIC confocal system
图 63种系统的横向归一化光强分布曲线对比
Figure 6.Comparison of uniformization lateral intensity distribution curves of 3 systems
图 8(a) 探测器直径分别为2.5 μm, 1.67 μm, 1 μm时共焦系统的轴向光强响应曲线; (b)探测器直径为2.5 μm, 1 μm, 0.5 μm时的DIC共焦系统的台阶光强响应曲线
Figure 8.(a)Intensity curves of confocal system with detector diameter of 2.5 μm, 1.67 μm, 1 μm; (b)Intensity curves of DIC confocal systems with detector diameter of 2.5 μm, 1 μm, 0.5 μm
图 9不同轴向偏移时DIC共焦系统的台阶响应
Figure 9.Stair response curves of DIC confocal system under differentz-axial offsets
表 1共焦和DIC共焦系统仿真值与理论值拟合结果
Table 1.Comparison between simulation and theoretical result of two systems
系统名称 横向分布相关系数 轴向分布相关系数 共焦系统 1 0.997 0 DIC共焦系统 1 0.996 3 
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表 23个系统横向分辨率比较
Table 2.Comparison of lateral resolutions among the 3 systems
(μm) 系统名称 半高全宽(FWHM) 传统显微镜 0.32 共焦系统 0.23 DIC共焦系统 0.23 下载:
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表 3共焦系统与DIC共焦系统镜面反射拟合结果
Table 3.Specular reflection fitting result of confocal and DIC confocal system
系统名称 相关系数R 共焦系统 0.997 2 DIC共焦系统 0.996 8 下载:
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样品轴向偏移/μm 相关系数R -0.3 0.998 5 -0.15 0.999 1 0 0.999 3 0.15 0.999 1 0.3 0.998 7 下载:
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表 5不同尺寸缺陷对应的归一化探测光强
Table 5.Uniformization intensity of micro-defects with different sizes
z/nm d/nm 200 240 280 -20 1.141 0 1.254 2 1.280 5 -10 1.066 8 1.125 0 1.138 1 0 1.000 0 1.000 0 1.000 0 10 0.942 2 0.880 0 0.867 6 20 0.895 0 0.766 5 0.742 5 下载:
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