Microstructure and electrical performance of sputter-deposited hafnium oxide thin films

Hafnium oxide (HfO2) based dielectrics have been currently considered as the possible replacements for the traditional gate-oxide (SiO 2) of the complementary metal-oxide semiconductor (CMOS) devices. The high dielectric constant, wide band gap, and thermal stability in contact with Si make HfO2 a potential material for application in CMOS devices. The performance of HfO2 as a gate oxide material, however, depends on its quality and interface structure with Si. In this work, HfO 2 thin films have been deposited by rf sputtering onto Si(100) substrates under varying growth temperatures (Ts). The objective of the work is to understand the growth and microstructure of sputter-deposited HfO 2 films and optimize the conditions to produce high-quality materials. A HfO2 ceramic target has been employed for sputtering while varying the substrate temperature, Ts, from 25°C to 500°C. The effect of growth temperature on the microstructure of the deposited HfO 2 films has been studied using grazing incidence x-ray diffraction (GIXRD), X-ray photoelectron spectroscopy (XPS) and high-resolution scanning electron microscopy (HR-SEM). The results indicate that the HfO2 films grown at Ts<200°C are amorphous. An amorphous-to-crystalline transition occurs at Ts = 200°C. Nanocrystalline HfO2 films crystallized in a monoclinic structure with a particle size of ∼20 nm. Cross-sectional HRSEM and capacitance analyses of metal-oxide-semiconductor capacitors indicate the presence of an interfacial layer between HfO 2 and Si that increases in thickness as the substrate temperature increases. Energy dispersive spectroscopy (EDS) shows that the interfacial layer is composed of HfSiO and has a dielectric constant much lower than 25. In contrast, dielectric constants as high as 25 were obtained from HfO2 films grown at room temperature.