The Role of H-Plasma in Aluminum Induced Crystallization of Amorphous Silicon
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The Role of H-Plasma in Aluminum Induced Crystallization of Amorphous Silicon Chong Luo1, Juan Li1, He Li1,2, Zhiguo Meng1, Qian Huang1, Shengzhi Xu1, Hoi Sing Kwok2, ♣ Shaozhen Xiong1♣ 1.Institute of Photo-Electronics, Nankai University, The Tianjin Key Laboratory for Photo-Electronic Thin Film Devices and Technology, Tianjin 300071, PR 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 A technique to improve and accelerate aluminum induced crystallization (AIC) by hydrogen plasma is proposed in this paper. Raman spectroscopy and Secondary Ion Mass Spectrometry of crystallized poly-Si thin films show that hydrogen plasma radicals reduce the crystallization time of AIC. This technique shortens the annealing time from 10 hours to 4 hours and increases the Hall mobility from 22.1 cm2/V·s to 42.5 cm2/V·s. The possible mechanism of AIC assisted by hydrogen radicals will also be discussed. 1. INTRODUCTION Poly-Si thin films prepared on glass substrate at temperatures lower than 600ć are of scientific interest because of their application in flat panel displays [1], solar cells [2]. However, each preparation technique for poly-Si thin films, such as Solid Phase Crystallization (SPC) and Rapid Thermal Annealing˄RTA), Laser Crystallization ˄LA˅ and Metal-induced Crystallization (MIC), has restrictive factors. For example, SPC and RTA high temperatures which sometimes exceed the glass substrate limit and Laser Crystallization needs expensive equipment. In contrast, MIC using Al as the inducing metal (called AIC) is a promising method because of its low cost and relatively short annealing time [3]. Furthermore, AIC can yield large grain size [4] and the high preferential (100) orientation [5] p-doped [6] material useful as high quality seed layer for solar cells. However, AIC still would profit from shortening its relatively long annealing time of about ten or more hours at low temperatures (around 450ć) [7]. Furthermore, poly-Si thin films crystallized by any crystallization method always contain many defects resulted from grain boundaries [7] or intra-grains [8], which severely affect the performances and stabilities of the devices made by such poly-Si thin films. Hydrogen Plasma Treatment is one of the most common methods to deal with these problems because of its low cost and simple technique [9]. In this paper, AIC in hydrogen plasma surroundings is being proposed. This technique combines the crystallization and passivation into one process, which not only reduces the annealing time but also passivates the defects in the material 2. EXPERIMENT At first, 1000 Å a-Si was deposited by low pressure chemical vapor deposition (LPCVD) on ♣
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Eagle 2000 Corning glass. This was followed by a less than 10-nm SiO2 separation layer and a 1000Å thick evaporated Al film. The glass/a-Si/SiO2/Al stack was put into a chamber which is normally used for plasma enhance
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