Evolution of sputtered HfO₂ thin films upon annealing

We investigated the evolution of the physical and electrical properties of HfO₂ thin films deposited by the reactive DC magnetron sputtering method on the (100) silicon substrate upon annealing. The HfO₂ thin films deposited at room temperature were amorphous, while the films after annealing were poly crystalline. The crystallization temperature of the HfO₂ thin films was dependent on the annealing methods (RTF or Furnace) and ambient (nitrogen or oxygen). The microstructures of HfO₂ thin gate oxides of T_ox <15 A thick were analyzed by HRTEM, XPS and XRD. We also focused on the interfacial layer between HfO₂ thin films and silicon substrates. Due to its high oxygen diffusivity, any annealing led to oxygen diffusion rapidly through the HfO₂ films. The EOT increased upon annealing due to the increased SiO₂-containing layer. The HfO₂ thin films deposited at room temperature have the undesirable interfacial states due to the surface damage by sputtering. We found that the HfO₂ thin films <15 A thick were optimized by RTP or furnace annealing.