Effect of nitrogen flow ratio on the microstructure evolution and nanoindented mechanical property of the Ta-Si-N thin films

The relations among the process, microstructure, and nanomechanical properties of cosputtered Ta-Si-N thin films have been investigated. The microstructure evolution and varied hardness and elastic modulus property of Ta-Si-N were influenced by nitrogen flow ratios [FN₂% = FN₂/(Far + FN₂) × 100%] during cosputtering together with phase formation and the composition of films. The microstructure of Ta-Si-N formed at a low 2-10 FN₂% was an amorphous-like phase with nanocrystalline grains embedded in an amorphous matrix, while polycrystalline Ta-Si-N was obtained at a high 20-30 FN₂%. The cubic TaN phase or (Ta_1-x, Si_x)N solid solution is much easier to form polycrystallites than noncubic Ta₅Si₃, Ta₂Si, and Ta₂N phases from grazing incidence x-ray diffractometry results. Amorphous-like Ta-Si-N films had much higher nanohardness, stiffness, elastic recovery percentage, and a closer boundary compared to polycrystalline films. A maximum nanohardness of 15.2 GPa was obtained at 3 FN₂%. An increased hardness of polycrystalline films at 20-30 FN₂% is attributed to the higher amount of the hard TaN phase.