New polarization scanning ellipsometry for dynamic characterization in LC cell

• Main Authors: Huan-HsuLin, 林桓旭
• Other Authors: Yu-Lung Lo
• Format: Others
• Language: en_US
• Published: 2013
• Online Access: http://ndltd.ncl.edu.tw/handle/56269259698143510526

碩士 === 國立成功大學 === 機械工程學系碩博士班 === 101 === A dynamic polarization scanning ellipsometry based on the Mueller matrix formulation and Stokes polarimetry is proposed for dynamically extracting the effective ellipsometric parameters of anisotropic material. The effective ellipsometric parameters (Ѱp’p’, Ѱp’s’, Ѱs’p’, Δp’p’, Δp’s’, and Δs’p’) describe the amplitude ratio and phase difference of two orthogonal waves in any arbitrary coordinate system with a scanning angle θ relative to the X-Y coordinate frame. The dynamic polarization scanning ellipsometry is composed of a linear polarization scanner and a polarization state analyzer. In a linear polarization scanner, an EO modulator is modulated to scan the linear polarization states of incident light with orientations in the range of 0˚ ~ 180˚. In a polarization state analyzer, two EO modulators are implemented for dynamically extracting the Stokes vectors. As a result, characteristic of a twisted nematic liquid crystal cell modulated by an AC voltage is verified by a dynamic polarization scanning ellipsometry. The dynamic variations in twist angle and tilt angle of a twisted nematic liquid crystal cell are successfully extracted by a genetic algorithm (GA) in curve fitting. Thus, without dynamically scanning the mechanical stage in the incident angle or the sample in a traditional ellipsometry or dynamically scanning spectrum in a spectroscopic ellipsometry, the frequency response in the new dynamic polarization scanning ellipsometry can be easily improved. Besides, this new system can also extract the Mueller matrix of the sample as long as the scattering effect of the sample is small enough to be ignored. It is noted that 200000 groups of Stokes parameters per second can be extracted by using the new polarization state analyzer if 200MS/s DAQ card is used. As compared to the commercial PSA from a famous company (Hinds Instruments) with only extracting 100 groups of Stokes parameters per second, the performance of number groups of Stokes parameters per second is greatly improved. Importantly, the use of EO modulators will not only improve the angular resolution, but will also eliminate mechanical vibration from a rotation mechanical stage; thereby improving the accuracy of the measurement results. In addition, this new dynamic polarization scanning ellipsometry can also provide high-speed measurement to characterize the physical properties of the anisotropic sample. For example, if 200MS/s DAQ card is used, 1000 groups of physical parameters per second can be extracted by using this new dynamic polarization scanning ellipsometry. Finally, the applications of the new dynamic polarization scanning ellipsometry in semiconductor/LCD industries can be explored in an in-line monitoring on thin-film growth on substrate and optical properties on LCD panel.