Nanochemistry, nanostructure, and electrical properties of Ta2O5 film deposited by atomic layer deposition and plasma-enhanced atomic layer deposition

Abstract

Ta 2 O 5 films were deposited by plasma-enhanced atomic layer deposition (PEALD) and thermal ALD on native oxide surface (SiOx∕Si). The properties of as-deposited and forming gas annealed films were examined and qualitatively compared with respect to nanostructural, nanochemical, capacitance-voltage and leakage-current–voltage (JL-V), and oxide breakdown characteristics. Although high-resolution transmission electron microscopy showed structurally sharp Ta2O5∕SiOx interfaces in forming gas annealed PEALD Ta2O5∕SiOx∕Si stacks, electron energy loss spectroscopy revealed interdiffusion of Ta and Si across this interface, the indiffusion length of Ta being higher than the outdiffusion length of Si. The consequent formation and enhancement of Ta–O–Si bond linkages in thicker Ta2O5 films were clearly reflected in the JL-V data. Moreover, the fixed charge density (Qf=5×1011qC∕cm−2) was thickness invariant in PEALD Ta2O5. For similar PEALD and ALD Ta2O5 thickness in Ta2O5∕SiOx∕Si stacks, the latter showed a lower Dit and higher defect density, results attributed to protons and hydroxyl groups, respectively, which stem from water used as an oxidant for the thermal ALD process.