Optical Properties of the SiO x ( x < 2) Thin Films Obtained by Hydrogen Plasma Processing of Thermal Silicon Dioxide
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Optical Properties of the SiOx (x < 2) Thin Films Obtained by Hydrogen Plasma Processing of Thermal Silicon Dioxide V. N. Kruchinina, *, T. V. Perevalova, b, V. Sh. Alieva, d, R. M. Kh. Iskhakzaia, E. V. Spesivtseva, V. A. Gritsenkoa, b, and V. A. Pustovarovc a Rzhanov
Institute of Semiconductor Physics, Siberian Branch, Russian Academy of Sciences, Novosibirsk, 630090 Russia b Novosibirsk State University, Novosibirsk, 630090 Russia c Ural Federal University, Yekaterinburg, 620002 Russia d Novosibirsk State Technical University, Novosibirsk, 630073 Russia *e-mail: [email protected] Received January 23, 2020; revised April 15, 2020; accepted June 23, 2020
Abstract—The optical properties and composition of thermal silicon oxide thin films processed in a hydrogen electron cyclotron resonance plasma have been studied by ellipsometry, quantum-chemical modeling, and photoluminescence spectroscopy. It has been found that the plasma processing of the films leads to their oxygen depletion and the formation of nonstoichiometric oxide SiOx < 2. The parameter x of the obtained SiOx films has been determined by comparing the experimental spectral dependence of the refractive index with the dependence obtained theoretically using the ab initio calculation. It is shown that an increase in the time of processing of thermal dioxide SiO2 in a hydrogen plasma leads to an increase in the refractive index of the film, as well as in the degree of its oxygen depletion. The dependence of the parameter x of the investigated films on the hydrogen plasma processing time is plotted. Keywords: silicon oxide, ellipsometry, photoluminescence, quantum-chemical modeling DOI: 10.1134/S0030400X20100173
INTRODUCTION At present, the next-generation nonvolatile memory based on memristors is being rapidly developed [1, 2]. In addition, a memristor is a key element for neuromorphic applications. The operation principle of a memristor is switching of an active dielectric medium in metal–dielectric–metal structures between the high- and low-resistance states. A memristor is capable of storing data without energy consumption at 85°С for 10 years [3]. At present, various nonstoichiometric oxides, including HfOx, ZrOx, TaOx, AlOx, NbOx, SiNx, and SiOx, are considered to be candidates for use as active media [1]. The advantage of SiOx over other dielectrics is its compatibility with modern silicon technology. Amorphous silicon oxide is a basic dielectric of modern silicon devices; in particular, it serves as a tunnel dielectric in flash memory elements [1, 4]. The benefit of SiOx is that the variation in the parameter x (0 < x < 2) allows one to measure the band gap Eg of a dielectric in a wide range from 1.6 eV (amorphous Si [5]) to 8.0 eV (amorphous SiO2 [6]). In addition, the photoluminescent properties of SiOx make it possible to use it as a radiation source [7].
By now, many techniques for fabricating the SiOx (x < 2) thin films have been developed [8, 9]. A method that can be used for preparing nonstoichiometric oxides is
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