Characteristics of Sol–Gel-Derived and Crystallized HfO2 Thin Films Dependent on Sol Solution

Abstract

We investigated sol–gel-derived hafnium dioxide (HfO2) films on silicon substrates fired in air at 350, 450, 550, and 700 °C for 30 min using either formic acid (HCOOH) or nitric acid (HNO3) solutions as a catalyst. At less than 450 °C, both films are amorphous and approximately 8–10 nm thick. Crystallization into the monoclinic structure (111) was found to occur at 560 °C in the HCOOH sol. In the HNO3 sol, the crystallization into the monoclinic structures (111) and (111) occurs at 470 °C. The temperature-programmed desorption curves of the sol–gel-derived HfO2 thin films using each sol solution are separated into five distinct H2O desorption components caused by physically adsorbed H2O, chemically adsorbed OH, and/or Hf–OH bonds in the HfO2 film. On the basis of these components, a model is proposed to explain the H2O desorption mechanism. The dielectric constant (relative permittivity: εHfO2) of the sol–gel-derived HfO2 film was calculated to be 11 and the EOT was estimated to be 2.1 nm, which need to be improved. As an alternative gate insulator in advanced integrated complementary metal–oxide–semiconductor (CMOS) devices, the amorphous state of the sol–gel-derived HfO2 film is promising for both sol solutions, if H2O desorption can be accomplished and other defects eliminated.