For the design of technological process for creating device structures based on niobium and single-crystal silicon with thedesired properties, empirical and theoretical knowledge about the solid-phase interaction process in the system of a thin niobium film is required. The purpose of the research was a comprehensive study of the redistribution of components during the formation of thin niobium films on single-crystal silicon obtained by magnetron-assisted sputtering followed by vacuum annealing. The structure and phase composition were studied by X-ray phase analysis, scanning electron microscopy, and atomic force microscopy. Distribution of components along the depth was determined using the Rutherford backscattering spectrometry. The traditional experimental method for studying the process of interdiffusion of components in binary macroscopic systems is the placing of inert marks. However, the use of this method in systems containing thin films is hindered by the comparable thicknesses of the films and marks. This circumstance makes the mathematical modelling the most convenient method for the analysis of the interdiffusion process in thin-film systems. The interdiffusion model during the formation of polycrystalline niobium film – single-crystal silicon systems, developing the Darken’s theory for the limited solubility components was proposed. Grain boundary diffusion of silicon in the intergrain space of a polycrystalline niobium film was proposed. Numerical analysis of the experimental distribution of concentrations within the model established that silicon is the dominant diffusant in the studied system. The temperature dependence of the individual diffusion coefficient of silicon DSi = 3.0 10-12exp(-0.216 eV/(kT)) cm2/s in the temperature range 423–773 K was determined. The model is applicable to the description of the redistribution of components in the thin niobium film – single-crystal silicon system prior to synthesis conditions providing the chemical interaction of the metal with silicon and the formation of silicides. It illustrates the mechanism of the possible formation of silicide phases not by layer-by-layer growth at the Nb/Si grain boundary, but in its vicinity due to deep mutual diffusion of the components
Thin metal films are used in semiconductor and microelectronic devices to form ohmic and non-ohmic contacts to singlecrystal silicon. A common feature of the used Ме–Si systems is the low mutual solubility of elements and the polycrystalline nature of metal films. Solid-phase interactions during the deposition of metals on single-crystal silicon and the subsequent vacuum annealing results in the redistribution of the elements near the Me/Si interface. An important task facing the material science of solid-state electronics is to develop a mechanism of solid-phase interaction of metal thin films and single-crystal silicon. The aim of our study – was to develop a quantitative model of interdiffusion in the Ме–Si system under conditions of limited solubility of the components. The article suggests a mechanism of formation of Me–Si systems based on the diffusion and segregation of silicon near the intergrain boundaries of the metal and the limited formation of complexes during the diffusion-induced penetration of metal into silicon. The article suggests a model of reactive interdiffusion in thin metal film – single-crystal silicon systems under conditions of limited solubility of the components. Mathematical modelling was used to study the interaction of magnetron-sputtered metals Ti, W, and Nb with single-crystal silicon during isothermal vacuum annealing. The numerical analysis of experimental distributions of concentrations of Me and Si obtained by Rutherford backscattering spectroscopy allowed us to determine their individual diffusion coefficients in Me-Si systems. The model can be used for empirical studies of the redistribution of the elements of two-layer systems with limited solubility, as well as to forecast the technological conditions for the production of electronic devices.
We demonstrated the possibility of using the mathematical form of Darken's theory, applied to the description of the Kirkendall effect in binary systems, to the description of reactive interdiffusion in non-stoichiometric polycrystalline film oxide systems with limited solubility. The aim of the study was the simulation of reactive interdiffusion under vacuum annealing of a thin film system consisting of two non-stoichiometric polycrystalline titanium and cobalt oxides. The nonstoichiometric nature of the system assumes the presence of mobile components, free interstitial cobalt and titanium cations in it. Phase formation occurs as a result of reactive interdiffusion and trapping of mobile components of the system on inter-grain traps. The proposed mechanism describes the formation of complex oxide phases distributed over the depth of the system. A complex empirical research technique was used, involving Rutherford backscattering spectrometry, X-ray phase analysis and modelling methods. The values of the characteristic parameters of the process were determined by numerical analysis of the experimentally obtained distributions of the concentrations of the components within the developed model. During vacuum annealing of a thin film two-layer system of non-stoichiometric TiO2–x–Co1–уO oxides in temperature range T = 773 – 1073 К, the values of the individual diffusion coefficients of cobalt DCo = 5.1·10–8·exp(–1.0 eV/(kT) cm2/s and titanium DTi = 1.38·10–13·exp(–0.31 eV/(kT) cm2/s were determined. It was shown that for T = 1073 K, the phase formation of CoTiO3 with a rhombohedral structure occurs. The extension of the phase formation region of complex cobalt and titanium oxides increases with an increase in the vacuum annealing temperature and at 1073 K it is comparable with the total thickness of the film system. The model allows predicting the distribution of the concentrations of the components over the depth of multilayer nonstoichiometric systems in which reactive interdiffusion is possible.
Using X-ray phase analysis, scanning electron microscopy atomic force and magnetic force microscopy, and IR spectroscopy the properties of polycrystalline TiO2 films modified by cobalt during magnetron sputtering and subsequent pulsed photon processing in air have been investigated. It has been found that in the course of the modification, a nanocrystalline (with a grain size of ~ 50 nm) film consisting of cobalt and titanium oxides is formed. Their surface exhibits magnetic properties. In the IR reflection spectra obtained at different incident angle of beam, two of the transverse optical (TO) phonons and their corresponding longitudinal (LO) phonons above 500–600 cm–1 were observed, which identify the formation of Co3O4 in the spinel structure. The study of optical absorption indicates the predominant existence in the films of phases with direct optical transitions. The optical band gap value was 1.43 and 1. 83 eV for Co3O4 and 2.65 eV for the cubic phase of CoO.
that may be accompanied by the processes of mutual diffusion and phase formation. Controlled technological process of forming coatings with the given properties entails the necessity of forecasting the evolution of the phase composition. This in turn requires the development of algorithms and quantitative models of the processes. Reactive mutual diffusion in polycrystalline metal (oxide film systems with limited component solubility) has not been simulated before. The simulation allows selecting the annealing conditions (time and temperature) necessary for the inclusion and uniform distribution of metal in the oxide lattice. A quantitative model of the interaction in a multi-layer system metal — polycrystalline oxide of the other metal under conditions of limited solubility is developed. The model is based on the concepts of mutual diffusion of the components and the bulk reactions of the formation of complex oxides. The developed model was applied to the analysis of the process of modifying thin films of titanium oxide with transition metals. The model allowed us to perform a numerical analysis of the experimental concentrations of the component distributions in polycrystalline Co - Ti02 and Fe - Ti02 thin-film systems. The individual diffusion coefficients of the studied metals and titanium under conditions of vacuum annealing were determined. The model provides a good description of the basic systematic features of the process: the appearance of titanium in the metal film and deep penetration of Fe and Co into the film of titanium oxide. It also explains the fact that complex oxides are formed not by layer-by-layer growth at the metal-oxide interface, but throughout the entire thickness of Ti02 film. The results of analysis of the processes of interracial interaction in layered systems accompanied by the reaction mutual diffusion can be used to predict the evolution of the phase composition, as well as to control the technological processes of obtaining materials with the desired properties.
Предложена модель, развивающая теорию Даркена взаимной диффузии в бинарной системе с неограниченной растворимостью, на случай реакционной взаимодиффузии в двухслойной системе, состоящей из поликристаллических фаз оксидов двух металлов и содержащей подвижные и неподвижные компоненты в каждой из фаз. В рамках модели проведён численный анализ экспериментальных концентрационных распределений титана и кобальта в тонкоплёночной системе TiO2-x–Co1-yO, полученных методом резерфордовского обратного рассеяния, при отжиге в вакууме. Анализ выявил доминирующую роль диффузии подвижного кобальта в фазу TiO2-x по сравнению с диффузией подвижного титана в фазу Co1-yO и область локализации образования фаз сложных окси-дов в окрестности межфазной границы TiO2-x–Co1-yO. REFERENCES Chebotin V. N. Fizicheskaya khimiya tverdogo tela [Physical chemistry of a solid body]. M.: Khimiya Publ., 1982, 320 p. (in Russ.) Tretyakov Yu. D. Tverdofaznye reaktsii [Solid phase reactions]. M.: Khimiya Publ., 1978, 360 p. (in Russ.) Afonin N. N., Logacheva V. A. Interdiffusion and phase formation in the Fe–TiO2 thin-fi lm system. Semiconductors, 2017, v. 51(10), pp. 1300–1305. https://doi.org/10.1134/S1063782617100025 Afonin N. N., Logacheva V. A. Cobalt modifi cation of thin rutile fi lms magnetron-sputtered in vacuum technical. Technical Physics, 2018, v. 63(4), pp. 605–611. https://doi.org/10.1134/S1063784218040023 Kofstad P. Nonstoichiometry, diffusion, and electrical conductivity in binary metal oxides. Wiley-Interscience, 1972, 382 p. Smigelskas A. D., Kirkendall E. O. Zinc Diffusion in alpha brass. Trans. AIME, 1947, v. 171, pp. 130–142. Chambers S. A., Thevuthasan S., Farrow R. F. C., Marks R. F., Thiele J. U., Folks L., Samant M. G., Kellock A. J., Ruzycki N., Ederer D. L., Diebold U. Epita xial growth and properties of ferromagnetic co-doped TiO2 anatase. Appl. Phys. Lett., 2001, v. 79, pp. 3467–3469. https://doi.org/10.1063/1.1420434 Matsumoto Y., Murakami M., Shono T., Hasegawa T., Fukumura T., Kawasaki M., Ahmet P., Chikyow T., Koshihara S., Koinumaet H. Room-temperature ferromagnetism in transparent transition metal-doped titanium dioxide. Science, 2001, v. 291, pp. 854–856. https://doi.org/10.1126/science.1056186 Darken L. S. Diffusion, mobility and their interrelation through free energy in binary metallic systems. Trans. AMIE, 1948, v. 175, pp. 184–190. Samarsky A. A. [Theory of difference schemes]. M.: Nauka Publ., 1977, 656 с. (in Russ.) Afonin N. N., Logacheva V. A., Gerasimenko Yu. A., Dolgopolova E. A., Khoviv A. M. Interaction of cobalt and titanium with thin fi lms of their oxides during vacuum annealing // [Condensed Matter and Interphase], 2013, v. 15 (3), p. 232-237. URL: https://journals.vsu.ru/kcmf/article/view/902/984 (in Russ.)
Properties of polycrystalline TiO 2 films modified by magnetron sputtering of cobalt followed by pulsed photon-irradiation processing in air are investigated by methods of X-ray phase analysis, raster electron microscopy, atomic force microscopy, magnetic force microscopy, and IR spectroscopy. Formation of a nanocrystalline (with a grain size of ~50 nm) film consisting of cobalt and titanium oxides the surface of which exhibits magnetic properties is established in the process of modification. The IR reflectance spectra obtained at different angles of incidence in the region between 500 and 600 cm –1 reveal the presence of two bands belonging to transverse modes (TO) and two corresponding bands belonging to the longitudinal modes (LO). These bands are indicative of formation of Co 3 О 4 with spinel structure. Investigation of optical absorption suggests a predominant existence of phases characterized by direct interband transitions with energies of 1.43 and 1.83 eV for Co 3 O 4 , along with a transition with energy of 2.65 eV for cubic phase of CoO, in the films.
Purpose. A model of reactive interdiffusion in a bilayer system of polycrystalline oxides of two metals with moving and stationary components in each phase is proposed. The model develops Darken theory of interdiffusion in a binary system with unlimited solubility. Results. The model provides for the existence of an immobilized metal in two states – in the composition of the traps of its phase and in the form of the oxide of another metal trapped in the trap in the phase. The interdiffusion of the mobile component of metals into phases of neighboring oxides with subsequent capture to trap centers serves as the basis for the formation of phases of complex oxides. The formulation of the boundary-value problem of the model is considered. Conclusions. Within the framework of the model, a numerical analysis of the experimental concentration distributions of titanium and cobalt in the TiO2–x – Co1–уO thin-fi lm system obtained by the Rutherford backscattering method was performed. The analysis revealed the dominant role of the diffusion of mobile cobalt into the TiO2–x phase compared with the diffusion of mobile titanium into the Co1–уO phase and the region of localization of the formation of complex oxide phases in the vicinity of the TiO2–x–Co1–у O interface.
Модификация кобальтом тонких пленок рутила при магнетронном распылении и вакуумном отжиге
Using X-ray phase analysis, atomic force microscopy, and secondary ion mass-spectrometry, the phase formation and component distribution in a Co–TiO2 film system have been investigated during magnetron sputtering of the metal on the oxide and subsequent vacuum annealing. It has been found that cobalt diffuses deep into titanium oxide to form complex oxides CoTi2O5 and CoTiO3. A mechanism behind their formation at grain boundaries throughout the thickness of the TiO2 film is suggested. It assumes the reactive diffusion of cobalt along grain boundaries in the oxide. A quantitative model of reactive interdiffusion in a bilayer polycrystalline metal–oxide film system with limited solubility of components has been developed. The individual diffusion coefficients of cobalt and titanium have been determined in the temperature interval 923–1073 K.
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.
Методами рентгенофазового анализа, вторично-ионной масс-спектрометрии, атомно-силовой микроскопии и математического моделирования исследовано взаимодействие магнетронным способом распыленного металлического железа с пленками оксида титана в процессе изотермического вакуумного отжига. Предложен механизм формирования сложных оксидов на границах зерен, основанный на реакционной диффузии металла Fe в оксид титана. Разработана количественная модель реакционной взаимодиффузии в двухслойных поликристаллических пленочных системах металл-оксид с ограниченной растворимостью компонентов. Численным анализом экспериментальных концентрационных распределений металлов в пленочной системе Fe-TiO2 определены значения индивидуальных коэффициентов диффузии: железа 8.0·10-13 см2/с и титана 3.0·10-15 см2/с в условиях вакуумного отжига при 1073 K. DOI: 10.21883/FTP.2017.10.45012.8531
The doping of TiO2 fi lms with various metals, including Fe, allows measuring the TiO2 band gap, which makes it possible to use the compounds for photovoltaic applications. The discussed research was aimed at studying the formation of complex oxides by IR spectroscopy on the surface and inside Fe-TiO2 fi lms. The fi lms were prepared by magnetron sputtering of iron on titanium oxide, followed by annealing in a diffractometer vacuum chamber at P = 1.33·10-2 Pa, vacuum reduction annealing at P = 10-4 Pa, and thermooxidation in fl owing oxygen at atmospheric pressure. The fi lms were deposited on single-crystal silicon substrates with a Pt sublayer. Fe magnetron sputtering was conducted in a modernized vacuum unit UVN-1: the discharge was excited in 13.3·10-2 Pa high-purity argon. The discharge voltage was 420 V. A metal iron target with an impurity level lower than 0.01 at.% was used as a cathode. The sputtering rate was 7.2 nm/s. The thickness of the iron fi lm was determined by the time of spluttering and was 120 nm. The phase composition of Fe-TiO2 fi lms was studied by X-ray powder diffraction using ARL X’TRA diffractometer. The refl ectance-absorption (RAS) and total internal refl ection (ATR) spectra of the fi lms were measured with the help of the Vertex-70 infrared Fourier spectrometer by Brooker (Germany). The refl ectance-absorption spectra were measured with a mirror refl ection attachment with a 13-83° variable incidence angle. ATR spectra were measured with a single-pass Platinum-ATR with a diamond prism. Films obtained under different annealing regimes were heterophase and contained: TiO2 in the rutile structure, two iron oxides – Fe3O4 and Fe2O3, and phases of complex oxides based on titanium and iron oxides: FeTiO3 (ilmenite) and Fe2TiO4 (ulvospinels). The research demonstrated that the shift in the characteristic vibrations of the Ti-O bond toward lower frequencies can be explained by the presence of Fe+3cations in the TiO2 crystal structure. It was established that the absorption bands caused by the deformation vibrations of the Fe-OH bond can only be observed in ATR spectra and are shifted toward higher frequencies (1.045 cm-1) compared to individual iron oxides, which indicates the formation of complex oxides in the Fe-TiO2 fi lms. The shift of the characteristic vibrations of Ti-O bond toward the lower frequencies during the modifi cation of rutile by iron is caused by distortions in the symmetry of the Ti+4 coordination environment and indicates the presence of Fe+3 cations in the crystal structure.
Проведен сравнительный анализ оптических спектров отражения-поглощения (RAS) и нарушенного полного внутреннего отражения (ATR) пленочной системы Fe-TiO2, полученной методом реактивного магнетронного распыления с последующим отжигом в вакууме и при атмосферном давлении в потоке кислорода. Показано, что смещение характеристических колебаний связи Ti–O в сторону меньших частот связано с присутствием в кристаллической структуре TiO2 катионов Fe+3. Установлено, что полосы поглощения, обусловленные деформационными колебаниями связи Fe-OH, наблюдаются только в спектрах ATR и смещены в сторону больших частот по сравнению с индивидуальными оксидами железа, что свидетельствует об образовании сложных оксидов в пленочной системе Fe-TiO2. Результаты исследований получены на оборудовании Центра коллективного пользования научным оборудованием ВГУ.
The redistribution of components in the niobium-silicon system during magnetron-assisted sputtering of niobium, vacuum annealing, and high-temperature proton irradiation is studied. It is established that, during magnetron-assisted sputtering followed by vacuum annealing, silicon penetrates through the metal film to the outer boundary of the film. Under high-temperature proton irradiation, the suppression of the diffusion of niobium into silicon is observed. This effect is attributed to the high concentration of radiation vacancies in the region of the Nb/Si interphase boundary.
Rutherford back-scattering, powder X-ray diffraction, and mathematical simulation were used to study heterodiffusion of components during formation of two-layer metallic thin-film (∼300 nm) Nb, In-Nb, and Sn-Nb systems on silicon single crystals. In terms of the Darken’s model for description of the Kirkendall effect, it follows that, during magnetron sputtering, niobium penetrates into silicon with an individual chemical diffusion coefficient of D Nb→Si =1 × 10 −15 cm 2 /s. Sputtering of a second metal (Sn or In) onto a niobium film stimulates the mass transfer of components through the Nb/Si interface and increases D Nb→Si by a factor of 3 to 40, respectively.
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.
Secondary ion mass spectrometry and numerical simulation are used to investigate phosphorus diffusion and segregation in the SiO2-Si(111) system during the thermal oxidation of phosphorus-ion-implanted silicon layers in dry and humid oxygen between 950 and 1150°C. The results demonstrate that the segregation coefficient of phosphorus in SiO2 and Si depends not only on the oxidation temperature and environment but also on the oxidation time, which is interpreted in terms of the variation in the interfacial density of intrinsic point defects as a result of implantation-damage annealing. A model for the reaction segregation of impurities in the SiO2-Si system is used to evaluate the equilibrium segregation coefficient of phosphorus as a function of temperature: = m s * in dry O2 and = 4.2 × 102exp(−0.22 eV/(kT)) in humid O2.
A model of the diffusion-segregation redistribution of phosphorus in an SiO 2 /Si system during thermal oxidation of highly doped silicon layers is developed taking into account the formation of a peak of surface impurity concentration at the interface. The formation of this surface concentration peak is attributed to a change in the free energy of the impurity atoms near the silicon surface. This process is simulated by a diffusion-segregation equation. It is shown that the developed diffusion-segregation model is quite adequate for describing the phosphorus redistribution occurring during the oxidation of uniformly doped silicon layers. For the oxidation of implanted silicon layers, it was found that the segregation coefficient of the phosphorus at the SiO 2 /Si interface is not constant but depends on time in the same way as the efficiency of transient enhanced diffusion in silicon. This phenomenon is explained by the reactivity of the impurity segregation during the thermal oxidation of silicon, when excess point defects in the implanted silicon layer affect both the oxidation process and the capture of impurity atoms by the growing silicon dioxide.
