Comparative study of pulsed laser deposited HfO_2 and Hf-aluminate films for high-k gate dielectric applications

摘要

The thermal stability and the electrical properties of HfO_2 and Hf-aluminate films prepared by the pulsed laser deposition technique have been investigated by X-ray diffraction, differential thermal analysis, capacitance-voltage correlation, leakage-current measurements and high-resolution transmission electron microscopy observation, respectively. A crystallization transformation from HfO_2 amorphous phase to poly-crystalline monoclinic structure occurs at about 500 ℃. In contrast, the amorphous structure of Hf-aluminate films remains stable at higher temperatures up to 900 ℃. Rapid thermal annealing at 1000℃ for 3 min leads to a phase separation in Hf-aluminate films. Tetragonal HfO_2(111) is predominant, and Al_2O_3 separates from Hf-aluminate and is still in the amorphous state. The dielectric constant of amorphous HfO_2 and Hf-aluminate films was determined to be about 26 and 16.6, respectively, by measuring a Pt/dielectric film/Pt capacitor structure. A very small equivalent oxide thickness (EOT) value of 0.74 nm for a 3-nm physical thickness Hf-aluminate film on a n-Si substrate with a leakage current of 0.17 A/cm~2 at 1-V gate voltage was obtained. The interface at Hf-aluminate/Si is atomically sharp, while a thick interface layer exists between the HfO_2 film and the Si substrate, which makes it difficult to obtain an EOT of less than 1 nm.