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A Low-cost Optical Inspection System for Rapid Measurement of Surface Roughness of Polycrystalline Silicone Fabricated by Frontside and Backside Excimer Laser Crystallization
C.C. Kuo and Y.R. Chen

Excimer laser crystallization (ELC) is the most commonly employed technology for fabricating low temperature polycrystalline silicon (LTPS). Investigations on the surface roughness of polycrystalline silicon (poly-Si) thin films become an important issue because the surface roughness of poly-Si thin films is widely believed to be related to its electrical characteristics. A low-cost optical measurement system for rapid surface roughness measurement of poly-Si thin films fabricated by frontside ELC and backside ELC is developed in this study. It is found that the incident angle of 20° is a good candidate for measuring the surface roughness of poly-Si thin films. The surface roughness, y, of poly-Si thin films can be determined rapidly from the average value of the reflected total power, x, measured by the optical system developed using the trend equation of y = -0.9369x+1.0267. The maximum measurement error rate of the optical measurement system developed is less than 6.21%. The savings in measurement time of the surface roughness of poly-Si thin films is up to 83%. Backside ELC is recommended for batch production of low-temperature polycrystalline silicon thin-film transistors due to lower surface roughness of poly-Si films and higher laser beam utilization efficiency.

Keywords: Surface roughness, optical measurement, polycrystalline silicon, excimer laser crystallization (ELC)

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