Microstructure And Electrical Performance Of Sputter-Deposited Hafnium Oxide (hfo2) Thin Films

Hafnium oxide (HfO2) based dielectrics have been currently considered as the possible replacements for the traditional gate-oxide (SiO2) 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, HfO2 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 HfO2 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 HfO2 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\u3c200 °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 HfO2 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