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

Abstract

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.