Thermal stability, microstructure, and electrical properties of atomic layer deposited Hf₆Ta₂O₁₇ gate dielectrics

Abstract

The intent of this work is to investigate thermal stability, microstructure, and electrical properties of thin Hf₆Ta₂O₁₇ high-k gate dielectrics. X-ray diffraction and transmission electron microscopy analysis reveal that an as-deposited Hf₆Ta₂O₁₇ film is amorphous with a ∼1-nm interfacial layer. After a 1000 °C anneal, the film is a mixture of orthorhombic-Hf₆Ta₂O₁₇ and monoclinic HfO₂ with a thicker interfacial layer. Uniform Hf and Ta Auger depth profiles are observed for as deposited and annealed films. Secondary ion mass spectrometry (SIMS) analysis shows Hf and Ta profiles are unchanged following the 1000 °C anneal, indicating good thermal stability. There is, however, a clear indication of Si up-diffusion into Hf₆Ta₂O₁₇, particularly after annealing at 1000 °C. No Hf or Ta is found in the Si substrate. Well-behaved capacitance-voltage curves and low leakage current characteristics were obtained for Mo/ Hf₆Ta₂O₁₇ capacitors for as-deposited and 1000 °C annealed films. A flatband voltage (V_fb) shift towards negative voltage is observed for the annealed film when compared to the as-deposited film, indicating the presence of more positive charge, or less negative charge. Furthermore, capacitance-voltage stress measurements were performed to study charge trapping behaviors. A smaller V_fb shift is observed for as deposited (<10 mV) versus the 1000 °C annealed (30-40 mV) Hf₆Ta₂O₁₇, indicating more charge trapping after the high temperature anneal.