Growth, microstructure and electrical properties of sputter-deposited hafnium oxide (HfO 2) thin films grown using a HfO 2 ceramic target

Abstract

Hafnium oxide (HfO 2) thin films have been made by radio-frequency (rf) magnetron-sputtering onto Si(1 0 0) substrates under varying growth temperature ( T s). HfO 2 ceramic target has been employed for sputtering while varying the T s from room temperature to 500 °C during deposition. The effect of T s on the growth and microstructure of deposited HfO 2 films has been studied using grazing incidence X-ray diffraction (GIXRD), and high-resolution scanning electron microscopy (HR-SEM) coupled with energy dispersive X-ray spectrometry (EDS). The results indicate that the effect of T s is significant on the growth, surface and interface structure, morphology and chemical composition of the HfO 2 films. Structural characterization indicates that the HfO 2 films grown at T s < 200 °C are amorphous while films grown at T s > 200 °C are nanocrystalline. An amorphous-to-crystalline transition occurs at T s = 200 °C. Nanocrystalline HfO 2 films crystallized in a monoclinic structure with a (−1 1 1) orientation. An interface layer (IL) formation occurs due to reaction at the HfO 2–Si interface for HfO 2 films deposited at T s > 200 °C. The thickness of IL increases with increasing T s. EDS at the HfO 2–Si cross-section indicate that the IL is a (Hf, Si)–O compound. The electrical characterization using capacitance–voltage measurements indicate that the dielectric constant decreases from 25 to 16 with increasing T s. The current–voltage characteristics indicate that the leakage current increases significantly with increasing T s due to increased ILs.