Low Temperature Crystallization of Amorphous Silicon Films Using an Excimer Laser

Abstract

ABSTRACTIn an effort to enhance the electrical properties of silicon thin films, we have performed recrystallization experiments on a variety of amorphous silicon films using an excimer laser. The intense, pulsed UV produced by the laser (308nm, using XeCl gas) is highly absorbed by the amorphous material and thus provides intense localized heating in the near surface region. Two types of starting films were studied: plasma CVD a-Si:H and LPCVD a-Si. The subsequent modification produces crystallites whose structure and electrical characteristics vary due to starting material and laser scan parameters. The treated films have been characterized using Raman, x-ray diffraction, TEM, SIMS and transport measurements. The results indicate that crystallites nucleate in the surface region. The degree of crystallization near the surface increases dramatically as a function of deposited laser energy density and less so as a function of laser shot density. The hall mobility of the highly crystallized samples exhibit an increase of 2 orders of magnitude over the amorphous starting material. In the PECVD material, the rapid diffusion of hydrogen causes voids to be formed at intermediate laser energy densities and removal of film at higher energy densities. The LPCVD material withstands the high laser energies to produce well crystallized films with crystallite sizes greater then 1000Å.