Materials characterization of ZrO2–SiO2 and HfO2–SiO2 binary oxides deposited by chemical solution deposition

Abstract

The thermal stability, microstructure, and electrical properties of xZrO2⋅(100−x)SiO2 (ZSO) and xHfO2⋅(100−x)SiO2 (HSO) (x=15%, 25%, 50%, and 75%) binary oxides were evaluated to help assess their suitability as a replacement for silicon dioxide gate dielectrics in complementary metal–oxide–semiconductor transistors. The films were prepared by chemical solution deposition using a solution prepared from a mixture of zirconium, hafnium, and silicon butoxyethoxides dissolved in butoxyethanol. The films were spun onto SiOxNy coated Si wafers and furnace annealed at temperatures from 500 to 1200 °C in oxygen for 30–60 min. The microstructure and electrical properties of ZSO and HSO films were examined as a function of the Zr/Si and Hf/Si ratio and annealing temperature. The films were characterized by x-ray diffraction, mid- and far-Fourier transform infrared (FTIR), Rutherford backscattering spectroscopy, and Auger electron spectroscopy. At ZrO2 or HfO2 concentrations ⩾50%, phase separation and crystallization of tetragonal ZrO2 or HfO2 were observed at 800 °C. At ZrO2 or HfO2 concentrations ⩽ 25%, phase separation and crystallization of tetragonal ZrO2 or HfO2 were observed at 1000 °C. As the annealing temperature increased, a progressive change in microstructure was observed in the FTIR spectra. Additionally, the FTIR spectra suggest that HfO2 is far more disruptive of the silica network than ZrO2 even at HfO2 concentrations ⩽25%. The dielectric constants of the 25%, 50%, and 75% ZSO films were measured and were observed to be less than the linear combination of ZrO2 and SiO2 dielectric constants. The dielectric constant was also observed to increase with increasing ZrO2 content. The dielectric constant was also observed to be annealing temperature dependent with larger dielectric constants observed in nonphase separated films. The Clausius–Mossoti equation and a simple capacitor model for a phase separated system were observed to fit the data with the prediction that to achieve a dielectric constant larger than 10 doping concentrations of ZrO2 would have to be greater than 70%.

Highly Dispersed Mixed Zirconia and Hafnia Nanoparticles in a Silica Matrix: First Example of a ZrO2–HfO2–SiO2 Ternary Oxide System

“…1b) are compared. The detected peaks were assigned according to the values reported in literature [15,[45][46][47] and the main vibrational bands are evidenced and labeled in Figure 1a and b. The typical vibrations of silica are well evident in the as-prepared samples as outlined by the bands at ca.…”

“…[47] There is no evidence of vibrations corresponding to Si-O-Zr or Si-O-Hf, which should occur at 980 cm -1 . [15,48] Upon calcination, the band ascribed to the Si-O-Si asymmetric stretching is shifted to a lower wavenumber, 1066 cm -1 . [18,49,50] A further band at 450 cm -1 was also detected, which has been ascribed by other authors to the vibrations of the Si-O-Si network.…”

“…As mentioned, in both film and powder samples, the possibly of heterolinkages occurring could be not be evidenced: Si-O-M stretching would in fact be expected at about 980 cm -1 . [15,48] As in the case of the binary systems, [34] despite the different sample composition and annealing, the vibrational spectroscopy outlines i) the formation of a polysiloxane network in the hybrid systems, ii) no remarkable differences between films and powders, and iii) incomplete polymerization of the methacrylate groups, likely due to steric hindrance and the limited mobility imposed by the silica matrix. The thermal heating induces a complete densification of the matrix and disappearance of the organic components.…”

“…As a consequence, since the properties of these binary systems are strongly affected by the composition, the microstructure, and the degree of mixing of the different oxide components, suitable synthetic routes ensuring the achievement of the required purity and homogeneity have to be found. Reported approaches to these binary systems include chemical solution deposition, [15] ultrahigh vacuum molecular beam epi-ZrO 2 and HfO 2 nanoparticles are homogeneously dispersed in SiO 2 matrices (supported film and bulk powders) by copolymerization of two oxozirconium and oxohafnium clusters (M 4 O 2 (OMc) 12 , M = Zr, Hf; OMc = OC(O)-C(CH 3 ) CH 2 ) with (methacryloxypropyl)trimethoxysilane (MAPTMS, (CH2 C(CH 3 )C(O)O)-(CH 2 ) 3 Si(OCH 3 ) 3 ). After calcination (at a temperature ≥800°C), a silica matrix with homogeneously distributed MO 2 nanocrystallites is obtained.…”

Diffusion and interface growth in hafnium oxide and silicate ultrathin films on Si(001)

“…During annealing at T≥1073K Hf silicate films are reported to phase separate into a crystalline HfO 2 -rich phase imbedded in an amorphous silica-rich matrix. 40 Moreover, phase separation in Hf silicates is complex and remains controversial. Some authors have argued that it can proceed by nucleation and growth, or by spinodal decomposition mechanisms dependent on composition and temperature ranges, resulting in different microstructures.…”