V. A. Logacheva

Growth of niobium oxide films on single-crystal silicon

Abstract200-nm-thick niobium films grown on single-crystal silicon wafers by magnetron sputtering have been oxidized by annealing in flowing oxygen. X-ray diffraction examination revealed the metal-like phase Nb6O in the as-deposited films. Annealing in flowing oxygen for 1 h led to the formation of tetragonal NbO2 at 570 K and hexagonal Nb2O5 at temperatures above 770 K. The grain size and surface roughness of the films were evaluated using atomic force microscopy.

Effect of vacuum annealing on the phase composition of In/SnO/Si, In/SnO2/Si, and Sn/In2O3/Si heterostructures

The chemical interaction between indium and thin SnO and SnO2 films and between tin and thin In2O3 films during vacuum annealing was studied. The metallic films were deposited onto single-crystal silicon substrates by magnetron sputtering, the SnO and SnO2 films were produced by heat-treating the Sn film in flowing oxygen at 673 and 873 K, respectively, and the In2O3 film was produced by heat-treating the In film at 573 K. The results indicate that annealing of the In/SnO/Si and In/SnO2/Si heterostructures in vacuum (residual pressure of 0.33 × 10−2 Pa) at 773 K gives rise to the reduction of Sn and oxidation of In, whereas annealing of Sn/In2O3/Si causes partial tin substitution for indium in the cubic indium oxide lattice.

Phase composition and electrical conductivity of indium tungstate films produced from bilayer structures

Indium tungstate films have been synthesized via oxidation of indium and tungsten layers deposited on crystalline silicon and fused quartz substrates by magnetron sputtering. The structure and electrical properties of the films have been analyzed in relation to the oxidation procedure, which is shown to have a strong effect on the phase composition of the films. The dc conductivity of the films exhibits inverse Arrhenius behavior.

Lead titanate ferroelectric films on single-crystal silicon

This paper reports on the results of investigations into the phase transformations observed in Pb/Ti/Si and Ti/Pb/Si thin-film heterostructures upon layer-by-layer magnetron sputtering of lead and titanium onto a single-crystal silicon substrate and subsequent annealing in an oxygen atmosphere. It is shown that the dielectric properties of lead titanate films depend on the order of sputtering of lead and titanium metal layers onto the surface of single-crystal silicon. The ferroelectric properties are revealed in 3000-nm-thick lead titanate films prepared by two-stage annealing of the Pb/Ti/Si thin-film heterostructure (with the upper lead layer) at T1=473 K and T2=973 K for 10 min. These films are characterized by the coercive field Ec=4.8 kV/cm and the spontaneous polarization Ps=16.8 µC/cm2. The lead titanate films produced by annealing of the Ti/Pb/Si thin-film heterostructure (with the upper titanium layer) do not possess ferroelectric properties but exhibit properties of a conventional dielectric.

Growth and structure of PbWO4 films

Lead tungstate films have been grown on silicon by magnetron sputtering followed by heat treatment at various temperatures. The thermal oxidation of metal-oxide (Pb/WO3/Si and W/PbO2/Si) and metal-metal (Pb/W/Si) bilayer systems at temperatures above 870 K yields films that are dominated by monoclinic PbWO4 and contain WO3, also monoclinic. The optimal configuration for PbWO4 synthesis is Pb/WO3/Si because, even during lead deposition onto tungsten oxide, we observe the formation of lead tungstate, PbWO4, and subsequent heat treatment increases the percentage of this phase in the film.

Phase Composition and Optical Properties of Thin Films Based on Lanthanum and Tungsten Oxides

We have studied the phase composition and optical properties of 150-to 500-nm-thick films based on lanthanum and tungsten oxides, produced by magnetron sputtering followed by heat treatment at 773 K in vacuum and flowing oxygen. The oxide films have been found to have high transmission in the range 250 to 900 nm and an absorption band between 190 and 250 nm. Analysis of their absorption edge indicates that its complex structure is due to the presence of several phases. The energies of direct transitions evaluated from the spectra of the films coincide with the band gaps of the phases present in the films.

Component Redistribution during Nb and In/Nb Film Growth on Single-Crystal Silicon

The component redistribution during the growth of Nb and In/Nb films on single-crystal silicon has been studied by Rutherford backscattering spectroscopy and X-ray diffraction. The results indicate that magnetron sputtering of indium onto niobium films gives rise to mass transfer across the Nb/Si interface and to niobium and silicon heterodiffusion, accompanied by chemical reactions and the formation of silicides. The likely reason for this is the generation of defects during the magnetron sputtering of indium.

Preparation of thin lead stannate layers on single-crystal silicon

Thin films containing lead stannates were prepared on single-crystal silicon substrates by annealing Sn/Pb/Si and Pb/Sn/Si structures produced by magnetron sputtering with the use of solid Sn targets and solid or liquid (self-sputtering) Pb targets. The structures were annealed in flowing oxygen for 10 min at temperatures in the range 520–1120 K. The phase composition of the films is found to strongly depend on the Pb deposition procedure, the sequence of layers in the as-grown heterostructure, and thermal oxidation conditions.

Thermal oxidation of Ti and pb thin films deposited on single-crystal silicon

Thin Pb–Ti–O films on single-crystal Si were prepared by magnetron sputtering followed by thermal oxidation of Pb/Ti/Si and Ti/Pb/Si structures. Oxidation of Pb/Ti bilayers was found to yield lead oxides, which then react with Ti to form lead titanate. Ti/Pb bilayers on Si could be converted into stoichiometric lead titanate, through titanium and lead oxides, by oxidation between 870 and 1070 K. Some of the films exhibited ferroelectric properties.

Interdiffusion and phase formation in the Fe–TiO 2 thin-film system

The interaction of magnetron-sputtered metal iron with titanium-oxide films upon isothermal vacuum annealing is studied by X-ray phase analysis, secondary-ion mass spectrometry, atomic-force microscopy, and mathematical simulation. A mechanism for the formation of complex oxides at grain boundaries is suggested. The mechanism is based on the reaction diffusion of metal iron into titanium oxide. A quantitative model of reaction interdiffusion in two-layer polycrystalline metal–oxide film systems with limited component solubility is developed. From numerical analysis of the experimental distributions of the metal concentrations in the Fe–TiO2 film system, the individual diffusion coefficients are determined. It is found that, under the conditions of vacuum annealing at 1073 K, the diffusion coefficients of iron and titanium are 8.0 × 10–13 and 3.0 × 10–15 cm2 s–1, respectively.