Effect of thermal annealing and oxygen partial pressure on the swelling of HfO_2/SiO_2/Si metal-oxide-semiconductor structure grown by rf sputtering: A synchrotron x-ray reflectivity study

摘要

As-grown and rapid thermal annealed thin HfO_2 films, deposited on Si(100) substrate by reactive rf sputtering at various partial pressures of O_2 and Ar, are studied by synchrotron x-ray reflectivity. The growth of interfacial layer (IL) of SiO_2 is more or less linear with the decrease in oxygen partial pressure (po_2) in the O_2/Ar mixture. The thickest oxide is found to be grown at the minimum oxygen partial pressure (po_2). It is observed that the IL swells upon annealing at higher temperature, and swelling is maximum for the sample grown in minimum po_2 . The surface roughness and thickness of the HfO_2 films decrease upon annealing indicating a denser film. The HfO_2/Si interface roughness is also decreased upon annealing. Therefore, lower annealing temperature and higher po_2 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 po_2 during the deposition of HfO_2 film to minimize the fixed oxide charge density of metal-oxide-semiconductor devices.