Nanochemistry, nanostructure, and electrical properties of Ta ₂O ₅ film deposited by atomic layer deposition and plasma-enhanced atomic layer deposition

Ta ₂O ₅ films were deposited by plasma-enhanced atomic layer deposition (PEALD) and thermal ALD on native oxide surface (SiO _x/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 (J _L-V), and oxide breakdown characteristics. Although high-resolution transmission electron microscopy showed structurally sharp Ta ₂O ₅/SiO _x interfaces in forming gas annealed PEALD Ta ₂O ₅/SiO _x/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 Ta ₂O ₅ films were clearly reflected in the J _L- V data. Moreover, the fixed charge density (Q _f=5 × 10 ¹¹q C/cm ^-2) was thickness invariant in PEALD Ta ₂O ₅. For similar PEALD and ALD Ta ₂O ₅ thickness in Ta ₂O ₅/SiO _x/Si stacks, the latter showed a lower D _it 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.