This study investigates molybdenum deposited by atomic layer deposition (ALD) as a potential gate metallization for flash memory devices. Polycrystalline (110)-oriented, with low-resistivity (∼16 μω cm) ALD Mo films were deposited on SiO2 and Al2O3 using hydrogen reduction of Mo-oxychloride precursor. On SiO2, an effective work function (EWF) of 4.75 ± 0.1 eV was obtained for as-deposited samples, and its value increased up to 4.9 ± 0.05 eV upon annealing at 600 °C, whereas on Al2O3, a stable EWF value of 5.05 ± 0.05 eV was observed. The EWF variation is correlated with changes in the composition and chemical bonding at the metal/dielectric interface. The latter were investigated by energy dispersive x-ray spectroscopy and electron energy loss spectroscopy performed using scanning transmission electron microscopy and x-ray photoelectron spectroscopy. This analysis revealed that the presence of Mo oxide at the Al2O3/Mo interface stabilizes the EWF, and the EWF increase on SiO2 is attributed to Si enrichment at the SiO2/Mo interface upon annealing. A theoretical model is suggested to explain the chemical bonding difference on SiO2 and Al2O3, based on the Mo-precursor reactions with the surface groups of the dielectric. This study emphasizes the importance of the precursor/substrate reactions in determining the compositional and, therefore, electrical properties of the metal/dielectric interface, and demonstrates that ALD Mo deposited directly on SiO2 and Al2O3 is a promising candidate for gate metallization of flash devices due to its high EWF.
|Journal of Vacuum Science and Technology A: Vacuum, Surfaces and Films
|Published - 1 Jul 2021