The effect of post-process annealing on optical and electrical properties of mixed HfO2–TiO2 thin film coatings

Abstract

In this paper a comparison of electrical and optical properties of mixed hafnium-titanium oxides is described. Thin films were deposited with the use of the magnetron co-sputtering method. For further analysis (Hf 0.52 Ti 0.48)Ox and (Hf 0.29 Ti 0.71) Ox coatings, which were amorphous directly after the deposition process, were chosen,. Moreover, post-process annealing was also performed in order to compare the electrical and optical properties of amorphous and nanocrystalline thin films with the same material composition. It was found that the phase transition from amorphous to orthorhombic HfTiO 4 occurred in the case of (Hf 0.52 Ti 0.48)Ox coating at 650 °C. In turn, the phase transition to TiO 2-anatase was observed at the temperature of 600 °C in the case of (Hf 0.29 Ti 0.71)Ox thin film. The leakage current for both amorphous coatings was in the range of 10 −7-10 −8 A/cm 2. After additional annealing and phase transition, the leakage current slightly decreased for (Hf 0.29 Ti 0.71)Ox thin film, while in the case of (Hf 0.52 Ti 0.48)Ox sample the resistance switching effect was observed. The dielectric constant was equal to 24 and 25 for amorphous (Hf 0.52 Ti 0.48)Ox and (Hf 0.29 Ti 0.71)Ox films, respectively. However, after the phase transition it decreased to 15 for (Hf 0.52 Ti 0.48)Ox and increased to 51 for (Hf 0.29 Ti 0.71)Ox film. The results of optical studies showed that amorphous thin films were well transparent in a visible light range with an average transparency of ca. 85%. After the phase transition to HfTiO 4-orthorhombic and TiO 2-anatase, a slight decrease in the transparency level by 3% and a redshift of the cutoff wavelength was observed. Moreover, additional annealing caused small changes of the optical band gap energy, refractive index and extinction coefficient.

Influence of Substrates on Structure Development and Concentration of Residual Impurities in Hafnium–Titanium-Oxide Films Grown by Atomic Layer Deposition

“…This was an expected result as the monoclinic HfO 2 films (Figure d) were obtained and characterized in our experiments too. The permittivity values of as-grown Hf x Ti 1– x O y films that contained the orthorhombic phase were comparable to those of the films crystallized during the postgrowth annealing. , For instance, values of 51–55 at x = 0.30 and 30–37 at x = 0.66 were measured for our films, while the relative permittivity values, obtained in earlier studies after the postgrowth annealing of amorphous films at 500–650 °C, were 51 at x = 0.29, 51 at x = 0.30, and 40 at x = 0.64 . Corresponding values of amorphous films were 25 at x = 0.29, 31 at x = 0.30, and 25 at x = 0.64 …”

“…9,17 For instance, values of 51−55 at x = 0.30 and 30−37 at x = 0.66 were measured for our films, while the relative permittivity values, obtained in earlier studies after the postgrowth annealing of amorphous films at 500−650 °C, were 51 at x = 0.29, 17 51 at x = 0.30, 9 and 40 at x = 0.64. 9 Corresponding values of amorphous films were 25 at x = 0.29, 17 31 at x = 0.30, 9 and 25 at x = 0.64. 9 These results demonstrate that the application of seed layers leading to the in situ crystallization during the deposition allowed a considerable reduction of processing temperatures needed for producing dielectrics with high permittivity.…”

“…In previous ALD studies, amorphous Hf x Ti 1– x O y films have been obtained in x ranges of 0.30–0.85, 0.50–0.70, 0.11–0.86, and 0.20–0.66 at substrate temperatures of 300 ,, and 350 °C on Si substrates ,,, as well as on Pt films . Unfortunately, the amorphous films possess markedly lower refractive index and permittivity values than the crystalline films with the same composition. , Therefore, to improve the properties of films, postdeposition annealing has been used to crystallize the films. ,, As a result of annealing, an orthorhombic phase isomorphous with orthorhombic HfTiO 4 ( o -HfTiO 4 , a ternary compound with elemental composition equal to that of Hf x Ti 1– x O y with x = 0.5 and y = 2) has been formed in the films. , However, relatively high annealing temperatures (500–750 °C) have been needed for this purpose. ,, Thus, approaches supporting the growth of crystalline phases at lower temperatures are of marked interest.…”

“…9,16 However, relatively high annealing temperatures (500−750 °C) have been needed for this purpose. 9,16,17 Thus, approaches supporting the growth of crystalline phases at lower temperatures are of marked interest.…”

Effect of Annealing Temperature on the Microstructure and Optical Properties of Lanthanum-Doped Hafnium Oxide

“…By comparing with the standard card PDF#73-0445 of La 2 Hf 2 O 7 , it was found that the corresponding peak appeared at 600 • C. The XRD analysis shows that with the increase in temperature, the diffraction peak position of the sample obviously moves to a small angle, revealing the existence of tensile stress inside the sample. The crystallite size was calculated using the Debye-Scherrer formula [32][33][34]:…”