Growth and Characterization of Hf–Silicate/Al₂O₃ Gate Stacks Grown on Si(100) by Self-Limiting Atomic Layer Deposition

A thin film structure of a HfSi_xO_y/Al₂O₃/Si gate stack was fabricated on Si(100) by self-limiting atomic layer chemical vapor deposition (ALCVD). An atomically flat interface of Al₂O₃/silicon was observed and the impurity concentrations in the bulk film were below the XPS detection limit. Hf–silicate (HfSi_xO_y) film was deposited using tetrakis-diethylamido-hafnium [Hf(N(C₂H₅)₂)₄] and tetra-n-butyl-orthosilicate [Si(OC₄H₉)₄]. The grown Hf–silicate film showed a Si-rich composition (∼30% HfO₂), whereas an Al₂O₃ layer showed a stoichiometric composition ratio of O/Al. The electrical properties of the gate stack were characterized using capacitance–voltage (C–V) and current–voltage (I–V) measurements of the metal–oxide–metal (MIM) structure. The dielectric constant (k∼10.5) of the HfSi_xO_y/Al₂O₃ film was higher than that (k∼8.1) of an Al₂O₃ single layer of a similar thickness. Rapid thermal annealing (RTA)-treated HfSi_xO_y/Al₂O₃ films showed a positive shift in flat band voltage (V_fb), whereas as-deposited samples did not show positive shifts in V_FB. The leakage current densities (J_g) of the as-grown and the annealed HfSi_xO_y/Al₂O₃ films were both below 1×10^-7 A/cm² at a bias of -1.0 V.