Growth and characterization of CrAlN thin film deposited by DC reactive co-sputtering

Chromium aluminium nitride (CrAlN) thin films were grown on Si wafers by DC reactive magnetron co-sputtering technique without external heating and biasing to the substrates. The effect of N₂ gas flow rate on the structure of the as-deposited films was invested. Cr and Al metals were used as sputtering targets. The Cr and Al sputtering current were fixed at 300 mA. The sputtering gas (Ar) flow rate was fixed at 10 sccm and the reactive gas (N₂) flow rate was varied from 2 sccm to 10 sccm. The crystal structure, thickness, roughness, microstructure, surface morphology, elemental composition and hardness were characterized by glancing angle X-ray diffraction (GAXRD), atomic force microscopy (AFM), field emission scanning electron microscopy (FE-SEM), energy dispersive X-ray spectroscopy (EDS) and nanoindentation technique, respectively. The results showed that, all the as-deposited films were formed as a (Cr, Al)N solid solution. The as-deposited films exhibited a nanostructure with a crystallite size of less than 40 nm. The crystal size and lattice constant was in range of 17-33 nm and 3.998-4.165 Å, respectively. The film thickness and roughness decreased from 400 nm to 244 nm and 2.8 nm to 1.4 nm, respectively, with increasing the N₂ gas flow rate. The elemental composition of the as-deposited films varied with the N₂ gas flow rate. Cross section analysis by FE-SEM showed compact columnar and dense morphology as increasing the N₂ gas flow rate. The film hardness was in range of 14.1-60.3 GPa.