A Study of the Post-hydrogenation Passivation Mechanism of Crystallized Poly-Si Films
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A Study of the Post-hydrogenation Passivation Mechanism of Crystallized Poly-Si Films Chong Luo1, Juan Li1, He Li1,2, Zhiguo Meng1, Chunya Wu1, Qian Huang1, Xu Shengzhi1, Hoi Sing Kwok2 and Shaozhen Xiong1♥ 1 Institute of Photo-Electronics, Nankai University, Tianjin 300071, P. R. China 2 Department of Electronic and Computer Engineering, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong, P. R. China ABSTRACT The roles of hydrogen plasma radicals on passivation of several kinds of crystallized poly-Si thin films were investigated using optical emission spectroscopy (OES) combined with Hall mobility, Raman spectra, and absorption coefficient spectra. It was found that different kinds of hydrogen plasma radicals are responsible for passivation of dissimilar poly-Si crystallized by different method. Radicals HĮ with lower energy are mainly responsible for passivating the poly-Si crystallized by solid phase crystallization (SPC) whose crystallization precursor was made by plasma enhanced chemical vapor deposition (PECVD). Higher energy radicals H* are more effective in passivating defects left over by Ni in poly-Si crystallized by Metal Induced Crystallization (MIC). The highest energy radicals Hȕ and HȖ are needed to passivate the defects in poly-Si crystallized by SPC but whose precursor was made by low pressure CVD (LPCVD). INTRODUCTION Poly-crystalline silicon (poly-Si) thin films prepared on glass substrates at temperatures below 600ć are used for large area electronic devices, because they cost less than mono-crystalline silicon, and have higher mobility and greater stability than amorphous silicon. They attract scientific interest because of their application in flat panel displays and solar cells. However, crystallized poly-Si films have more defects at grain boundaries [1] or intra-grains [2], which severely affect the performances and stabilities of the poly-Si devices. Hydrogen plasma treatment is one of the most effective methods to passivate the defects. Generally, hydrogen in silicon thin films is not only attracted to any strained regions but it also self-traps and removes dangling bonds. However, hydrogen plasmas etch Si atoms and bombard the surface of poly-Si, thereby producing some new defects [3]. As we know there are four radicals in H-plasma. Are all of the radicals playing the same role in passivation? In this work, we study the effect of hydrogen plasma radicals on passivation and analyze the relationship between H-plasma radicals and their specific role in different kinds of poly-Si films. We measured and compared the in-situ OES of the hydrogen plasma during passivation, and characterized the corresponding electrical and optical properties of passivated poly-Si thin films to check the passivation effect. Connecting the relation between each radical in OES and the passivation effect monitored by the electrical and optical properties of poly-Si, it was found that different hydrogen plasma radicals play different roles in passivating different kinds of poly-Si
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