Rapid crystallization of amorphous silicon utilizing a VHF plasma annealing at atmospheric pressure

¹ Department of Physics and Functional Materials Science, The Graduate School of Science and Technology, Saitama University, 255 Shimo-Okubo, Sakura, Saitama 338-8570, Japan
² The Institute of Physics and Chemical Research, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan
³ Horiba Co. Ltd, Higashi Kanda, Chiyoda, Tokyo 101-0031, Japan

Corresponding author: shirai@fms.saitama-u.ac.jp

Received: 20 July 2006
Revised: 31 October 2006
Accepted: 1 December 2006
Published online: 24 January 2007

Abstract

The rapid crystallization of amorphous silicon utilizing a very-high-frequency (VHF) inductive coupling thermal microplasma jet of argon is demonstrated. Highly crystallized Si films were synthesized by adjusting the translational velocity of the substrate stage and flow rate of argon. The H concentration in the crystallized Si films decreased from 10²¹ cm⁻³ to 10¹⁹ cm⁻³ with no marked increases in oxygen and nitrogen impurity concentrations and defect density. The thin-film transistors of a 40-nm-thick crystallized a-Si film showed a field-effect mobility of 30–55 cm²/V s with a threshold voltage of 3–5 V. P-i-n thin-film solar cells were also fabricated for 1.5-μm-thick crystallized a-Si films, which showed an efficiency of 5.5% and filled factor of 0.52. The crystallization proceeded with time constants of 10 ms, which was of 4–6 orders of magnitude lower than the conventional laser-crystallization of a-Si. The crystallization process is discussed in terms of the viscous flow of Si-network, due to the rapid local heating and melting of a-Si.