摘要
低相干扫描干涉技术是微结构特征参数无损检测的有效手段。然而对高深宽比结构底部采样点需要进行大量程垂直扫描,由此引起光强漂移导致的相干信号对比度降低,以及阶跃边缘复杂衍射作用造成的相干信号混叠是高度检测过程中的两个主要难题。采用完全噪声辅助聚合经验模态分解算法分解原始信号得到一系列特征模态函数,通过提取高频特征模态函数代替原始信号滤除低频的光强漂移分量,提高相干信号对比度。高深宽比结构边缘复杂衍射作用使该位置附近的相干信号中包含两组包络,其中异常包络由相干峰位置对应上表面的附加相干信号引起并阻碍有效包络的准确判别。通过融合从相干信号中提取的对比度及强度信息并进行二值化处理,实现对高深宽比结构上下表面的识别分类,据此选择当前采样点位置对应的包络作为有效包络并最终完成结构高度的高精度检测。以校准深度为101.77μm,线宽为10.97μm的高深宽比沟槽为检测样品,10次测量的高度均值及标准差分别为101.093μm、0.316μm。
Low-coherence scanning interferometry is an effective method used for measuring characteristic parameters of microstructures with the advantage of non-destruction.However,a large range of vertical scanning is required for the sampling points at the bottom of the high-aspect-ratio structure,which causes the offset of light intensity and reduces the contrast of coherence signals.Besides,the aliasing coherence signals induced by the complex diffraction effect appear at the step edge and two main envelopes can be extracted.All these phenomena obstruct the locating of the coherence peak and then mislead the height measurement.Algorithmic processing seems to be an effective method to solve the above problems including suppressing the component of offset and demodulating the aliasing coherence signals.Due to the central shielding effect of Mirau-type objectives,the effective signals returned from the sampling points at the bottom of the high-aspect-ratio structure can be further reduced.Combined with the consideration of the magnification in the measurement of the structure with narrow linewidth,Linnik-type objectives are selected in the interference system.In this paper,the complete ensemble empirical mode decomposition with adaptive noise is used to decompose the original signals into a series of intrinsic mode functions.This algorithm can decompose the original signals into different frequency components without prior knowledge.By extracting the intrinsic mode functions with high-frequency and then replacing the original signals,the offset with low-frequency is filtered out and the contrast of coherence signals is further improved.The complex diffraction effect at the edge of the high-aspect-ratio structure results in the coherence signals containing two sets of the envelopes,among which the abnormal envelope is induced by the additional coherence signals.These additional coherence signals correspond to the interference fringes appearing near the upper edges and extending horizontally into the air.However,their contr
作者
孙一峰
高志山
范筱昕
张佳乐
马剑秋
袁群
SUN Yifeng;GAO Zhishan;FAN Xiaoxin;ZHANG Jiale;MA Jianqiu;YUAN Qun(School of Electronic and Optical Engineering,Nanjing University of Science and Technology,Nanjing 210094,China)
出处
《光子学报》
EI
CAS
CSCD
北大核心
2022年第9期323-333,共11页
Acta Photonica Sinica
基金
国家重点研发计划(No.2019YFB2005500)
国家自然科学基金(Nos.62175107,U1931120
江苏省六大人才高峰项目(No.RJFW⁃019)
中国科学院光学系统先进制造技术重点实验室基金(No.KLOMT190201)
上海在线检测与控制技术重点实验室基金(No.ZX2021102)。
关键词
干涉测量
高度测量
高深宽比
光强漂移
相干信号混叠
Interferometry
Height measurement
High-aspect-ratio
Intensity offset
Aliasing coherence signal
