<title>Characterization and in-line control of UV-transparent silicon nitride films for passivation of FLASH devices</title>

Abstract

UV-transparent silicon nitride (UV-SiN) films were deposited in a plasma enhanced chemical vapor deposition (PECVD) reactor. The material and optical properties of the films were characterized for non-volatile memory devices as passivation layers. Factorial designed-of-experiments were used to study the dependence of the film properties on various process parameters. The UV-transparent SiN films are characterized by deposition rate, film uniformity, UV transmittance, film stress, refractive index, wet etch rate and hydrogen content. In this study, high quality SiN films with low compressive stress, low hydrogen content and high UV transmittance (greater than 80% for 1.5 micrometer thick film) were successfully deposited and this film has been incorporated into the passivation scheme of submicron FLASH devices. Because the absorption coefficient of silicon material is very high in the UV region, direct and accurate UV transmittance measurement for SiN by optical transmission spectrometry can only be made when SiN is deposited on quartz substrate. In this work, a simple method was used to calculate the UV-transmittance of SiN film deposited on silicon wafers from the measured extinction coefficient using a spectro-ellipsometer. This method has been further demonstrated for in-line monitoring of UV transmittance of SiN films.