Low temperature crystallization of amorphous silicon using an excimer laser

Abstract

Low temperature processing is a prerequisite for compatible technologies involving combined a-Si and poly-silicon devices or for fabricating these devices on glass substrates. This paper describes excimer-laser-induced crystallization of thin amorphous silicon films deposited by plasma CVD (a-Si:H) and LPCVD (a-Si). The intense, pulsed UV produced by the laser is highly absorbed by the thin amorphous material, but the average temperature is compatible with low temperature processing. The process produces crystallites whose structure and electrical characteristics vary according to starting material and laser scan parameters. The crystallized films have been principally characterized using x-ray diffraction, TEM, and transport measurements. The results indicate that crystallites nucleate in the surface region and are randomly oriented. The degree of crystallization near the surface increases as the doping level and/or deposited laser energy density is increased. The crystallite size increases with a power law dependence on deposited energy, while the conductivity increases exponentially above threshold for unintentionally doped PECVD films. The magnitude of the Hall mobility of the highly crystallized samples is increased by two orders of magnitude over that of the amorphous starting material.