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

• Published in: Jpn J Appl Phys 2010-12, Vol.49 (12), p.121502-121502-8
• Main Authors: Shimizu, Hirofumi, Nemoto, Daiki, Ikeda, Masanori, Nishide, Toshikazu
• Format: Article
• Language: English
• ISSN: 0021-4922; 1347-4065
• DOI: 10.1143/JJAP.49.121502

We investigated sol--gel-derived hafnium dioxide (HfO 2 ) films on silicon substrates fired in air at 350, 450, 550, and 700 \circ C for 30 min using either formic acid (HCOOH) or nitric acid (HNO 3 ) solutions as a catalyst. At less than 450 \circ C, both films are amorphous and approximately 8--10 nm thick. Crystallization into the monoclinic structure ($\bar{1}11$) was found to occur at 560 \circ C in the HCOOH sol. In the HNO 3 sol, the crystallization into the monoclinic structures ($\bar{1}11$) and (111) occurs at 470 \circ C. The temperature-programmed desorption curves of the sol--gel-derived HfO 2 thin films using each sol solution are separated into five distinct H 2 O desorption components caused by physically adsorbed H 2 O, chemically adsorbed OH, and/or Hf--OH bonds in the HfO 2 film. On the basis of these components, a model is proposed to explain the H 2 O desorption mechanism. The dielectric constant (relative permittivity: $\varepsilon_{\text{HfO2}}$) of the sol--gel-derived HfO 2 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 HfO 2 film is promising for both sol solutions, if H 2 O desorption can be accomplished and other defects eliminated.