Effects of annealing temperature on the electrical properties of ALD-grown Hf-silicate films having various Si contents

Five- ∼ 5.9-nm-thick pure HfO₂ and Hf-silicate films having different compositions (Hf₃₁Si₄O₆₅, Hf ₂₀Si₁₄O₆₆ and Hf₉Si ₂₄O₆₆) were grown on Si (100) substrates by using atomic layer deposition, and their electrical properties were examined in relation to the post-deposition annealing temperature by using capacitance-voltage measurements. In contrast to other samples, only the Hf₂₀Si ₁₄O₆₆ film exhibited a phase separation phenomenon in the direction of the film normal with increasing annealing temperature, which was confirmed by cross-sectional high-resolution transmission electron microscopy (HRTEM). In the case of the Hf-rich (Hf₃₁Si₄O ₆₅) and Si-rich (Hf₉Si₂₅O₆₆) samples, the flatband voltage was negatively shifted with increasing annealing temperature, mainly due to the growth of the interfacial oxide. However, the flatband voltage of the Hf₂₀Si₁₄O₆₆ film was positively shifted as the annealing temperature was increased up to 800 °C, probably due to the spinodal decomposition process, and returned back to its original value at 900 °C due to a mechanism similar to that observed in the other samples.