Electrical and morphological characteristics of amorphous LPCVD Nitrogen Doped Silicon thin films after heat treatment

This work investigated the electrical and morphological properties of nitrogen doped silicon (NIDOS) thin films. The samples are obtained by LPCVD at low temperature (465degC) by a mixture of disilane (Si₂H₆) and ammonia (NH₃). This stage of deposit is followed by a heat treatment at several temperatures and durations. The resistivity measurements showed an increase in the resistivity values with the increase in the nitrogen tenor for films annealed at temperatures lower or equals to 1000degC. However, for an annealing temperature of 1100degC, results show an improvement of films conductivity with the increase both, the annealing duration and the nitrogen tenor. The X-ray diffraction and the SEM observations showed that the film crystallinity increases with the duration annealing, and that the high nitrogen content inhibits the crystallization phenomena. The crystallization mode of NIDOS films has been determined using the Kolmogorov-Johnson-Mehl-Avrami (KJMA) model and grain size distribution study. Results show that the nucleation in NIDOS films occurs heterogeneously at the interface NIDOS/SiO₂. The crystallites reach the film surface in a one-dimensional way during a short time and continue to grow laterally (bi-dimensional crystallization). The improvement of the electrical characteristics of NIDOS films are strongly related to its morphological evolution of the amorphous to the polycrystalline phase.