Study On Reflectance Difference Optical Method And Instrument For Layered Micronano Structure

With the rise of two-dimensional materials,layered micro-nano structure has become one of the current research hotspots.It features nano-scale thickness and micrometer-scale horizontal dimension that means high width / height ratio.Due to the influence of substrate,the measurement of layered micro-nano structures becomes more difficult,especially the spatial two-dimensional distribution and relative position measurement.Conventional measurement methods,such as optical microscopy and scanning probe microscopy,reflect the existence of layered micro-nano structures by the differences in material properties(materials,heights,etc.)and,hence,they are less sensitive to spatial two-dimensional distribution and relative position.However,the anisotropic distribution of the material and structure in the field of view provides a basis for applying the reflectance difference optical measuring method being of high sensitivity of anisotropy.Especially when all the materials are isotropic,the unique anisotropy is caused by the abrupt change of material properties in the sample plane,so the spatial two-dimensional distribution and the relative position of the layered micronano structure can be measured by the reflectance difference optical measuring method with high sensitivity.In this paper,the microscopic reflectance difference spectroscopy is applied to measure the layered micro-nano structures: the theory of reflectance difference spectroscopy of layered micro-nano structures is proposed;the normalincidence reflectance difference spectroscopy with microscopic resolution(M-RDS)based on one liquid crystal variable phase retarder(LCVR)is designed and developed.The experimental results show that the new instrument has a micro-scale lateral resolution for the two-dimensional spatial distribution of layered micro-nano structures,and a nano-scale thickness resolution for its thickness.The main work is summarized as follows:1.The theory of reflectance difference spectroscopy of layered micro-nano structures is proposed.Based on the electromagnetic theory,the mathematical model of layered micro-nano structures and the reflectance difference(RD)signals is established by using the effective medium approximation theory and polarization optics.The effects of the relative size of the layered micro-nano structures and the measurement spot size,and the numerical aperture of the objective lens on the measurement are investigated.2.The M-RDS based on one LCVR is designed and developed.Microscopic resolution is realized by the flexible integration of the objective lens which benefits from the normal-incidence light path.The errors introduced by mechanical rotation are avoided by using LCVR,and the method of intensity modulation and signal calculation based on the least square method is applied.3.An on-line error correction method for LCVR-based polarized optical measurement system is proposed and applied to M-RDS.It is proposed that the same component intrinsic azimuth angle setting should be used in the LCVR retardance calibration and RD signal measurement,so that the influence of device defect and assembly error on the measurement is superimposed on the retardance of LCVR,which significantly reduces the measurement error.Meanwhile,this fast LCVR calibration method effectively reduces the impact of temperature drift on the measurement.4.The modulation strategy for the uniformity of spectral noise of polarimetric optical measurement system based on LCVR is proposed and applied to M-RDS.By studying the noise transfer coefficients of the measured signal,the important influence of LCVR modulation parameter,modulation range and initial retardance,on the noise suppression effect is determined.By optimizing the modulation parameters,the uniformity of spectral noise is achevied with noise suppression effect being of well.5.Three typical layered micro-nano structures are studied by M-RDS: semiconductor layered micro-nano structure built on insulator substrate;metalelectrode layered micro-nano structure built on semiconductor substrate;organic semiconductor ultra-thin films.The experimental results show that the new instrument has a micro-scale lateral resolution for the two-dimensional spatial distribution of layered micro-nano structures,and a nano-scale thickness resolution for its thickness.