Mechanical properties of ultra-thin HfO₂ films studied by nano scratches tests

10-nm-thick atomic layer deposited HfO₂ films were characterized in terms of wear resistance and indentation hardness to investigate the thermal annealing induced impacts on mechanical properties. The wear resistance of ultra-thin films at low loads was characterized using nano-scratch tests with an atomic force microscope. The depth of the nano-scratches decreases with increasing annealing temperature, indicating that the hardness of the annealed films increases with the annealing temperatures. Surface nanoindentation was also performed to confirm the nanoscratch test results. The hardness variation of the annealed films is due to the generation of HfSi_xO_y induced by the thermal annealing. X-ray photoelectron spectroscopy measurements proved that the hardness of formed HfSi_xO_y with increasing annealing temperatures. The existence of HfSi_xO_y broadens the interface, and causes the increase of the interfacial layer thickness. As a result, the surface hardness increases with the increasing HfSi _xO_y induced by the thermal annealing.