微分干涉差共焦显微膜层微结构缺陷探测系统

Detection system of multilayer coating microstructure defects based on differential interference contrast confocal microscopy

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。

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.