Work function tuning of plasma-enhanced atomic layer deposited WC_xN_y electrodes for metal/oxide/semiconductor devices

摘要

One of the main challenges facing the integration of metals as gate electrodes in advanced MOS devices is control over the Fermi level position at the metal/dielectric interface. In this study, we demonstrate the ability to tune the effective work function (EWF) of W-based electrodes by process modifications of the atomic layer deposited (ALD) films. Tungsten carbo-nitrides (WC_xN_y) films were deposited via plasma-enhanced and/or thermal ALD processes using organometallic precursors. The process modifications enabled us to control the stoichiometry of the WC_xN_y films. Deposition in hydrogen plasma (without nitrogen based reactant) resulted in a stoichiometry of WC_(0.4) with primarily W-C chemical bonding, as determined by x-ray photoelectron spectroscopy. These films yielded a relatively low EWF of 4.2 ± 0.1 eV. The introduction of nitrogen based reactant to the plasma or the thermal ALD deposition resulted in a stoichiometry of WC_(0.1)N_(0.6-0.8) with predominantly W-N chemical bonding. These films produced a high EWF of 4.7 ± 0.1 eV.