Effect of thermal annealing and oxygen partial pressure on the swelling of HfO₂/SiO₂/Si metal-oxide-semiconductor structure grown by rf sputtering: A synchrotron x-ray reflectivity study

As-grown and rapid thermal annealed thin HfO₂ films, deposited on Si(100) substrate by reactive rf sputtering at various partial pressures of O₂ and Ar, are studied by synchrotron x-ray reflectivity. The growth of interfacial layer (IL) of SiO₂ is more or less linear with the decrease in oxygen partial pressure (⁠$pO2$⁠) in the O₂/Ar mixture. The thickest oxide is found to be grown at the minimum oxygen partial pressure (⁠$pO2$⁠). It is observed that the IL swells upon annealing at higher temperature, and swelling is maximum for the sample grown in minimum $pO2$⁠. The surface roughness and thickness of the HfO₂ films decrease upon annealing indicating a denser film. The HfO₂/Si interface roughness is also decreased upon annealing. Therefore, lower annealing temperature and higher $pO2$ is to be set to reduce the IL thickness and for higher dielectric constant and larger oxide capacitance. High frequency capacitance-voltage (C–V) measurement on the devices, annealed at higher temperature, further shows the necessity for optimization of $pO2$ during the deposition of HfO₂ film to minimize the fixed oxide charge density of metal-oxide-semiconductor devices.