Research on Orthogonal Polarization Mirau Interferometry for Nanometer-scale Surface Profilometry

• Main Authors: Abraham Mario Tapilouw, 馬力歐
• Other Authors: Liang-Chia Chen
• Format: Others
• Language: en_US
• Published: 2013
• Online Access: http://ndltd.ncl.edu.tw/handle/nm5b7c

博士 === 國立臺北科技大學 === 自動化科技研究所 === 101 === White light interferometry (WLI) is a measurement technique with long measurement range and high measurement accuracy. The technique employs light with broadband spectrum. Accuracy of the surface profile reconstruction is determined by the contrast of the interferogram and coherence length of the light source. In this research, a new type of Mirau interferometer is developed. The developed Mirau separates light to the reference and object arm with an orthogonal polarization. Two kinds of novel optical thin film coating employed to achieve the research objective i.e. silver nanorod arrays (NRA) and reflective-type waveplate. Silver NRA is employed as the beam splitter and the reference arm of the orthogonal polarization Mirau. Meanwhile the reflective-type waveplate is employed in the reference arm of the interferometer to rotate the polarization of the reference light to be orthogonal to the object light. This enables control of the light intensity ratio between the arms by changing the polarization orientation of the incident light using a polarizer. Another polarizer is configured before the camera to enable interference between object and reference light. The experimental results show the feasibility of the polarization separation technique and the effectiveness of each polarization separator component. Standard samples such as calibrated flat mirror, standard step height, and PCB bumps are employed to measure the accuracy of the developed prototype. The consistency of the measurement results are compared with conventional WLI system as well as a point laser confocal measurement system as reference. The measurement results agree with the measurement results from the reference instruments and the repeatability of the measurement can reach down to 5 nm. The interferogram contrast obtained from the orthogonal polarization Mirau is proven to be superior to the conventional WLI for the surface with low-reflectivity. The feasibility of the technique is tested by measuring surface profile of industrial samples such as PCB boards and color filter of LCD.