Pulsed laser deposition CN x films and carbon plume dynamic study

Abstract

Carbon nitride films were synthesized by a KrF excimer laser ablation of a graphite target in a controlled nitrogen atmosphere. The laser fluence was set at 10, 12 and 16 J/cm². These thin films were deposited on <100> silicon substrate kept at room temperature and placed parallel to the target surface at a distance of 3 cm. The pressure of nitrogen was varied from 0.1 to 1 mbar. The deposited films were characterized with different diagnostic techniques. Scanning electron microscopy (SEM) and Atomic force microscopy (AFM) were used to study their surface morphology and to measure their surface roughness. The crystalline structure of the films was analyzed by X-ray diffraction (XRD). Film composition was investigated by Rutherford backscattering spectrometry (RBS) analysis. The bonding structures were performed by Fourier transformed infrared spectroscopy (FTIR). SEM observation indicates that CNx film present a granular structure for all pressures used. Film structure evolves from amorphous to a polycrystalline structure at 16 J/cm². This crystalline structure depends on nitrogen pressure. The carbon plume dynamics was also investigated by fast imaging. This study was performed into 0.2 and 1 mbar nitrogen pressures. The light emitted by the plasma was observed along the perpendicular to the ejection direction through a fast intensified charge-coupled device (ICCD, Princeton Instruments PI-MAX, 1024 x 256 pixels). Different regimes of expansion dynamics have been evidenced. Emission of C₂ and CN were also imaged using interference filters. The CN radical is considered to be the mainly precursor to CN_x growth.