Silicon oxynitride thin films by plasma-enhanced atomic layer deposition using a hydrogen-free metal-organic silicon precursor and N2 plasma

Abstract

We investigated the growth mechanism of SiOxNy films deposited via plasma-enhanced atomic layer deposition at low temperatures (100–300 °C) using a tetraisocyanate silane (Si(NCO)4) precursor and N2 plasma. By using tetraisocyanate silane, which does not contain hydrogen, we were able to deposit SiOxNy with notably less hydrogen, around 3–5%, compared to using silicon precursors that contain hydrogen. Additionally, the precursor ligands, including oxygen, react with surface amine groups (-NH2) to form Si–N–O bonds. Therefore, by understanding the adsorption mechanism of the precursor and controlling the temperature that can affect the bond formation, we can successfully produce SiOxNy films without any oxidizing source. We utilized density functional theory to explore the adsorption mechanism during the deposition of SiOxNy films and proposed a possible adsorption pathway of the precursors and by-products on the surface. We also employed various characterization techniques, such as spectroscopic ellipsometry, X-ray photoelectron spectroscopy, X-ray reflectometry, secondary ion mass spectroscopy, and current-electric field and capacitance-voltage analyses to establish correlations between the composition and dielectric properties of the thin films. Increasing the deposition temperature results in an increased presence of stronger and more stable Si–N bonds compared to Si–O and O–N bonds. As a result, the dielectric constant of the SiOxNy film increased from 5.8 to 7.4, while the leakage current density decreased from 1.52 × 10−8 A/cm2 to 8.56 × 10−10 A/cm2. Additionally, the counterclockwise hysteresis decreased from 0.16 V to 0.07 V as the amount of hydrogen in the SiOxNy film decreased. This can be interpreted as a reduction in hydrogen impurities, which act as charge trapping sites within the film, leading to a decrease in hysteresis with increasing temperature.