摘要
干涉测试是一种高精度的表面形貌无损测量方法。通常情况下,单色光干涉测试以激光作为光源,采用缩小成像方案测量表面面形。宽带光干涉测试能够有效避免单色光干涉测试时的2π相位模糊问题,常与显微成像技术相结合,测量阶跃型结构的表面微观形貌。当阶跃型结构样品的横向尺寸较大时,宽带光显微测试需要采用拼接手段,降低了测量效率。本文提出了一种缩小成像的宽带光干涉仪,该仪器可用于大尺寸阶跃型表面的形貌测量,其工作波段为480~750 nm,采用1 inch探测器形成了47.60 mm×35.76 mm的测量视场。系统组成包括照明准直镜、干涉腔和成像镜。照明准直镜采用科勒照明方案,可以提供数值孔径NA=0.015、视场直径Φ=59.6 mm的均匀照明物方视场;干涉腔集合了Mirau型等光程干涉与Fizeau型无中心遮拦的优势,由倾斜1.5°的分光平板和倾斜3°的参考平板组成;成像镜与准直镜形成双远心成像光路,成像放大率为0.25×,在宽谱段范围内的畸变校正达到0.24%。采用构建完成的宽带光干涉仪测试了USAF1951分辨率板,系统分辨率可达14 lp/mm;测试了校准高度分别为7.805μm和46.554μm的台阶板,对阶跃型结构测量的高度偏差优于0.4%。
Objective Morphological inspection is a significant step in the manufacturing process of precision machinery,integrated circuits,micro-optical devices,etc.Typical representatives are internal combustion engine fuel injectors,etched patterns on semiconductor silicon wafers,and micro-gratings.The presence of step-type structures on the surface of these components achieves certain special functions,which place nanometer-level requirements on the high measurement resolution of surface 3D morphology.Interferometric testing is a high-precision non-destructive measurement method for surface 3D morphology,which is combined with microscopic imaging technology to achieve microscopic morphology measurements.Depending on the magnification of the microscope,the lateral resolution varies from a few microns to hundreds of nanometers,and the field-of-view covers~0.1 mm×0.1 mm to~10 mm×10 mm.When the size of the part to be measured is large,the three-dimensional morphology measurement should be completed using stitching test.For some larger size parts to be measured,the lateral scale of the step-type structure is often larger,and the lateral resolution requirement of the measurement is reduced,which is no longer limited to the microscopic imaging method,and the reduced imaging scheme can be used to achieve direct measurement in a large field-of-view range.The goal of this study is to design and build a broadband optical interferometer with a large field-of-view to meet the inspection needs of large-size and step-type structure samples.Methods For the detection needs of special samples,this study selects a 1 inch detector and sets an imaging magnification target of 0.25×.According to this setting,we determine the field-of-view,numerical aperture,system focal length,and other system parameters of the entire system.After comprehensive consideration of the system's interferometric needs,this study uses the Köhler illumination system,double telecentric imaging structure,and sets a double flat tilted form of interference,which retains the characteristics of the Mirau-type structure with an equal light range and achieves a similar unobstructed effect as the Fizeau structure[Fig.1(c)].Subsequently,we select the appropriate initial structure using Zemax for the system design.After the system is built,the resolution plate and standard stage are selected for test verification and evaluation of the system.Results and Discussions The large-field broadband optical interferometer designed and built in this study operates in the 480‒750 nm band and uses a 1 inch detector to form a measurement field-of-view of 47.60 mm×35.76 mm.This system consists of an illumination collimator,an interferometric cavity,and an imaging lens.The illumination collimator adopts the Köhler illumination,providing a uniform illumination object field-of-view with NA=0.015 andΦ=59.6 mm;the interferometer cavity retains the advantages of the Mirau-type equal-range interference and the Fizeau-type no-center-obstruction feature,and consists of a spectroscopic plate tilted at 1.5°and a reference plate tilted at 3°(Fig.2);the imaging lens and collimator form a double telecentric imaging optical path with an imaging magnification of 0.25×,and the aberration correction reaches 0.24%in the wide spectral range(Fig.8).The completed broadband optical interferometer was used to test the USAF1951 resolution plate with a system resolution of up to 14 lp/mm(Fig.12),and step plates with calibration heights of 7.805μm and 46.554μm were tested with the results of 7.833μm and 46.552μm,respectively.The height deviation for the step-type structure measurement was better than 0.4%(Figs.13‒14).Conclusions To address the problem that the existing interferometric inspection system is difficult to meet the efficient measurement of three-dimensional morphology of large-size step-type structures,this study begins with the basic optical path selection,then determines the optical structure form of double telecentric and Köhler illumination,and adopts a new interferometric cavity structure form that retains the advantages of the Mirau-type equal-range interference and the Fizeau-type no-center-obstruction feature.After designing the system using Zemax,the broadband optical interferometer system with a large field-of-view was obtained.The interferometer works in the wavelength range of 480‒750 nm and uses a 1 inch detector to achieve an imaging magnification of 0.25×,a measurement field-of-view of 47.60 mm×35.76 mm,and an aberration correction of 0.24%over a wide spectral range.The completed broadband optical interferometer was used to test the USAF1951 resolution plate,consisting of two step plates whose calibration heights were 7.805μm and 46.554μm.The test results show that the system’s measurement resolution can up to 14 lp/mm,and the height deviation of the step-type structure measurement is better than 0.4%.This broadband optical interferometer can achieve both larger field-of-view measurement and step-type structure measurements while retaining very high vertical resolution.It avoids the problem of low measurement efficiency caused by stitching when using the traditional interferometer to detect large-size step-type structure samples,which has a greater application prospect in the precision measurement of precision machinery,integrated circuits,and micro-optical devices.
作者
周行
王书敏
徐舒成
马剑秋
雷李华
高志山
袁群
Zhou Xing;Wang Shumin;Xu Shucheng;Ma Jianqiu;Lei Lihua;Gao Zhishan;Yuan Qun(School of Electronic and Optical Engineering,Nanjing University of Science and Technology,Nanjing 210094,Jiangsu,China;Shanghai Institute of Metrology and Testing Technology,Shanghai 201203,China)
出处
《中国激光》
EI
CAS
CSCD
北大核心
2023年第18期241-249,共9页
Chinese Journal of Lasers
基金
国家重点研发计划(2019YFB2005500)
国家自然科学基金(62175107,U1931120)
江苏省六大人才高峰项目(RJFW-019)
中国科学院光学系统先进制造技术重点实验室基金(KLOMT190201)
上海在线检测与控制技术重点实验室基金(ZX2021102)。
关键词
测量
形貌干涉测量
宽带光
大视场
光学设计
measurement
morphological interferometry
broadband light
large field-of-view
optical design
