Miakonkikh, Andrew V

Miakonkikh A., Kuzmenko V., Efremov A., Rudenko K.

Rudenko K.V., Efremov A.M., Kuzmenko V.O., Miakonkikh A.V.

The influence of the initial mixture composition, gas pressure and input power on electro-physical parameters and density of fluorine atoms in SF6 + Ar + He plasma produced in an inductive-type reactor at 2 MHz was investigated. The combination of plasma diagnostics by Langmuir probes and optical emission spectroscopy allowed one to determine behaviors of electrons- and ions-related plasma characteristics vs. variable operating parameters as well as to suggest mechanisms responsible for corresponding effects. In particular, it was shown that the substitution of argon by helium at constant SF6 content in a feed gas affects the electron temperature, densities of charged species and plasma electronegativity through changes in both total ionization rate and electron energy losses during their interactions with dominant neutral particles. It was found that input power produces the maximum effect on the F atom density (by ~ 9 times at w = 800–1250 W) while the influence of the Ar/He ratio and gas pressure (especially at p < 15 mtorr) appears to be much weaker. Such situation is caused by opposite trends of electron temperature and electron density that results in rather small changes in the effective frequency of SFx + e → SFx-1 + F + e reaction family. It was found that fluxes of both fluorine atoms (ГF) and positive ions (Г+) follow changes in their densities, and the minimum ГF/Г+ value in He-rich plasmas corresponds to low pressures and input powers. For citation: Miakonkikh A.V., Kuzmenko V.O., Efremov A.M., Rudenko K.V. Plasma parameters and fluorine atom density in SF6 + Ar + He gas mixture: effects of Ar/He mixing ratio, pressure and input power. ChemChemTech [Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol.]. 2025. V. 68. N 3. P. 42-49. DOI: 10.6060/ivkkt.20256803.7130.

Miakonkikh A., Chesnokov Y., Gaidukasov R., Kuzmenko V.

The article presents the electrophysical characteristics of tantalum nitride films deposited by the ALD method. For the studies, the films were deposited on crystal silicon wafers with a surface orientation of 100. To enable measurements of the electrical resistance, the films were also deposited on thermally oxidized silicon wafers with an oxide thickness of 300 nm. Preliminary estimates of the spectral dependences of the refractive index and absorption coefficient of the films were performed by spectral ellipsometry. The specific electrical resistance was determined by the four-probe method at several points on the wafer. The study of the homogeneity of deposition was carried out by the method of spectral ellipsometry. Additionally, ellipsometric models are proposed that allow one to estimate the specific resistance and optical characteristics of the films, both during in situ growth and for a film tens of nanometers thick.

Rudenko M.K., Miakonkikh A.V., Rudenko K.V.

One promising approach to increase the capacity density of integral microcapacitors, microsupercapacitors, and microbatteries is three-dimensional structure design, where electrodes are exposed in three dimensions instead of conventional in-plane electrodes. Such structures include nanowires, nanotubes, nanopillars, nanoholes, nanosheets, and nanowalls. In this work, a cryogenic silicon etching process suitable for fabrication of structures with high electrode area is proposed. A numeric model of this process is experimentally calibrated and used for pillar array structure sidewall area optimization. The use of adaptive Runge–Kutta–Fehlberg time integrator allows to achieve almost linear overall computation complexity as a function of simulated etching time, despite the linear increase in conductance computation complexity with depth. A rule for choosing optimal geometric structure parameters under technological constraints is formulated. An optimized trefoil-like structure is proposed, resulting in a total 5.5% increase in sidewall area with respect to the hexagonal array of circular pillars, resulting in 20.33 sidewall area per unit chip area for 30 min long etch or 31.80 for 60 min long etch.

Fetisenkova K., Melnikov A., Kuzmenko V., Miakonkikh A., Rogozhin A., Tatarintsev A., Glaz O., Kiselevsky V.

The selectivity of the reactive ion etching of silicon using a negative electron resist AR-N 7520 mask was investigated. The selectivity dependencies on the fraction of SF6 in the feeding gas and bias voltage were obtained. To understand the kinetics of passivation film formation and etching, the type and concentration of neutral particles were evaluated and identified using plasma optical emission spectroscopy. Electron temperature and electron density were measured by the Langmuir probe method to interpret the optical emission spectroscopy data. A high etching selectivity of 8.0 ± 1.8 was obtained for the etching process. The optimum electron beam exposure dose for defining the mask was 8200 pC/m at 30 keV.

Kuzmenko V., Melnikov A., Isaev A., Miakonkikh A.

The possibilities of optimization of the two-step atomic layer etching process for HfO2 in conventional plasma etching tools were studied. The surface modification step was realized in Ar/CF4/H2 plasma, and the reaction between the modified layer and the surface was activated by Ar ion bombardment from the plasma in the second step. Investigation of the effects of activation step duration, DC bias during activation, and Ar plasma density was carried out. The mechanism of the etching process has been shown to involve fluorination of oxide during the modification step and subsequent removal of fluorine-containing particles at the activation step. An increase in parasitic sputtering rate and lower process saturation with the growth of DC bias during activation was demonstrated. The advantage of the ALE process in lower surface roughness over the conventional etching process was shown. Similar etching characteristics of HfO2 and ZrO2 suggest a similarity in the etching process for the mixed hafnium-zirconium oxide material.

Miakonkikh A., Kuzmenko V.

This article discusses a method for forming black silicon using plasma etching at a sample temperature range from −20 °C to +20 °C in a mixture of oxygen and sulfur hexafluoride. The surface morphology of the resulting structures, the autocorrelation function of surface features, and reflectivity were studied depending on the process parameters—the composition of the plasma mixture, temperature and other discharge parameters (radical concentrations). The relationship between these parameters and the concentrations of oxygen and fluorine radicals in plasma is shown. A novel approach has been studied to reduce the reflectance using conformal bilayer dielectric coatings deposited by atomic layer deposition. The reflectivity of the resulting black silicon was studied in a wide spectral range from 400 to 900 nm. As a result of the research, technologies for creating black silicon on silicon wafers with a diameter of 200 mm have been proposed, and the structure formation process takes no more than 5 min. The resulting structures are an example of the self-formation of nanostructures due to anisotropic etching in a gas discharge plasma. This material has high mechanical, chemical and thermal stability and can be used as an antireflective coating, in structures requiring a developed surface—photovoltaics, supercapacitors, catalysts, and antibacterial surfaces.

Permiakova O., Pankratov S., Isaev A., Miakonkikh A., Chesnokov Y., Lomov A., Rogozhin A.

Memristive structures are among the most promising options to be components of neuromorphic devices. However, the formation of HfO2-based devices in crossbar arrays requires considerable time since electroforming is a single stochastic operation. In this study, we investigate how Ar+ plasma immersion ion implantation (PI) affects the Pt/HfO2 (4 nm)/HfOXNY (3 nm)/TaN electroforming voltage. The advantage of PI is the simultaneous and uniform processing of the entire wafer. It is thought that Ar+ implantation causes defects to the oxide matrix, with the majority of the oxygen anions being shifted in the direction of the TaN electrode. We demonstrate that it is feasible to reduce the electroforming voltages from 7.1 V to values less than 3 V by carefully selecting the implantation energy. A considerable decrease in the electroforming voltage was achievable at an implantation energy that provided the dispersion of recoils over the whole thickness of the oxide without significantly affecting the HfOXNY/TaN interface. At the same time, Ar+ PI at higher and lower energies did not produce the same significant decrease in the electroforming voltage. It is also possible to obtain self-compliance of current in the structure during electroforming after PI with energy less than 2 keV.

Antonov V.A., Tikhonenko F.V., Popov V.P., Miakonkikh A.V., Rudenko K.V., Sverdlov V.A.

The silicon-on-sapphire (SOS) pseudo-MOSFETs with high-k buried hafnium dioxide interlayer (IL) were investigated after the hydrogen induced Si and HfO2 layer transfer on c-sapphire wafers and annealing at 600-1100 °C. HRTEM, GIXRD and Raman measurements were used to reveal the hafnia phases for furnace and rapid thermal annealings (FA and RTA).

Budarin A.S., Skvortsov L.A., Kuznetsov E.V., Silantyev I.V., Miakonkikh A.V., Pavlov A.Y., Galiev R.R., Davlyatshina A.R., Avramchuk A.V., Khabibullin R.A.

Permyakova O.O., Rogozhin A.E., Myagonkikh A.V., Rudenko K.V.

The mechanism of resistive switching in Pt/HfO2(8 nm)/HfOXNY(4 nm)/TiN structures, in which there are two resistive switching modes: bipolar resistive switching and complementary resistive switching. We demonstrate that resistive switching without external current compliance is possible. It is shown experimentally that the conductivity in the low-resistance state corresponds to the space-charge-limited current. A qualitative model is proposed that describes the transition from bipolar resistive switching to complementary resistive switching using Schottky barrier modulation at the metal-insulator interface. Based on this model, an explanation is given for the degradation of the low-resistance state during endurance measurements.

Gaidukasov R.A., Miakonkikh A.V.

This article discusses model and model-free approaches to solve problems of spectral ellipsometry as applied to microelectronic problems related to measuring the thicknesses and optical parameters of thin layers of dielectrics, metals, and semiconductors. Model approaches are based on the use of a priori information about the form of the Cauchy, Drude, Drude–Lorentz, and Tauc–Lorentz dispersion relation. Model-free approaches can use any smooth multiparameter functional relationship that can describe a smooth spectral curve. We can also use machine learning (ML) to implement a model-free approach, which is suited for determining the thickness of multilayer structures and their optical characteristics and can significantly increase the speed of data processing.

Miakonkikh A.V., Kuzmenko V.O., Efremov A.M., Rudenko K.V.

The electrophysical parameters of the plasma and the kinetics of plasma-chemical processes in a CF4 + H2 + Ar mixture while varying the CF4/H2 ratio are studied. When using diagnostic methods and plasma modeling together, it is found that replacing tetrafluoromethane with hydrogen (a) leads to a decrease in the plasma density and an increase in electronegativity; and (b) it causes a disproportionately sharp drop in the concentration of fluorine atoms. The reason for the latter effect is the increase in the frequency of the death of atoms in reactions of the CHFx + F → CFx + HF type initiated by heterogeneous recombination via the CFx + H → CHFx mechanism. The simultaneous increase in the concentration of polymer-forming CHxFy (x + y < 3) radicals indicates an increase in the polymerization load of the plasma on the surfaces in contact with it.

Polyakov A.Y., Vasilev A.A., Kochkova A., Schemerov I., Yakimov E.B., Miakonkikh A., Chernykh A.V., Lagov P., Pavlov Y.S., Doroshkevich A.S., Isaev R.S., Romanov A.A., Alexanyan L.A., Matros N., Azarov A., et. al.

Double polymorph γ/β-Ga2O3 structures remain crystalline upon unprecedentedly high crystal disorder levels where other semiconductors lose their long-range symmetry and, eventually, become amorphous. However, it is unclear if this radiation...

Popov V.P., Antonov V.A., Volodin V.A., Miakonkikh A.V., Rudenko K.V., Skuratov V.A.

The results are presented on changes in the parameters of pseudo-MOS transistors based on silicon-on-sapphire (SOS) mesastructures upon irradiation with swift heavy ions (SHIs) of Xe $${}^{+26}$$ (150 MeV) and Bi $${}^{+51}$$ (670 MeV) to a fluence of $$2\,\times\,10^{11}$$ cm $${}^{-2}$$ , indicating the accumulation of mechanical stresses and charges in the intermediate ferroelectric (Fe) layers of HfO $${}_{2}$$ films (HO) with a thickness of 20 nm and Hf $${}_{0.5}$$ Zr $${}_{0.5}$$ O $${}_{2}$$ (HZO) laminated with inserts of Al $${}_{2}$$ O $${}_{3}$$ monolayers (HA, HZA) or without them. SOS heterostructures are formed by direct bonding and hydrogen transfer of a silicon film (500 nm) with HA and HZA nanolayers pre-applied by plasma-stimulated atomic layer deposition onto sapphire. Electrophysical parameters are determined from the drain current—gate voltage characteristics ( $$I_{\textrm{ds}}$$ – $$V_{\textrm{g}})$$ of pseudo-MOS transistors with tungsten drain/source electrodes (100 nm) deposited by magnetron sputtering on SOS mesastructures through a lithographic mask. Comparison of the characteristics with Raman scattering analysis showed the correspondence of the mechanical compressive stresses introduced by SHI irradiation in silicon with the ratios of the Xe and Bi track volumes in the HA ferroelectric and sapphire.

Zhang X., Zhu J., Cheng J., Zhang R., Xia J., Guo R., Wang H., Xu Y.

Miakonkikh A., Kuzmenko V., Efremov A., Rudenko K.

Xu X., Luo Z., Sun H., Xu Y., Gao L., Yu Z.

Polyakov A.Y., Schemerov I.V., Vasilev A.A., Romanov A.A., Lagov P.B., Miakonkikh A.V., Chernykh A.V., Romanteeva E.P., Chernykh S.V., Rabinovich O.I., Pearton S.J.

The electrical properties and deep trap spectra of semi-insulating Ga2O3(Fe) implanted with Si ions and subsequently annealed at 1000 °C were investigated. A significant discrepancy was observed between the measured shallow donor concentration profile and the profile predicted by Stopping Power and Range of Ions in Matter simulations, indicating substantial compensation. Deep level transient spectroscopy revealed the presence of deep acceptors at Ec −0.5 eV with a concentration of ∼10¹⁷ cm−³, insufficient to fully account for the observed compensation. Photocapacitance spectroscopy identified additional deep acceptors with optical ionization thresholds near 2 and 2.8–3.1 eV, tentatively attributed to gallium vacancy-related defects. However, the combined concentration of these deep acceptors still fell short of explaining the observed donor deactivation, suggesting the formation of electrically neutral Si-vacancy complexes. Furthermore, the properties of Ga2O3 (Fe) implanted with Si and subjected to hydrogen plasma treatment at 330 °C were also examined. This material exhibited high resistivity with the Fermi level pinned near Ec –0.3 eV, similar to common radiation defects in proton-implanted Ga2O3. A prominent deep center near Ec −0.6 eV, consistent with the known E1 electron trap attributed to Si-H complexes, was also observed. These results highlight the challenges associated with Si implantation and activation in Ga2O3 and suggest that hydrogen plasma treatment, while effective for Ga-implanted Ga2O3 is less suitable for Si-implanted material due to the formation of compensating Si-H complexes.

Pearton S.J., Ren F., Polyakov A.Y., Yakimov E.B., Chernyak L., Haque A.

Gallium oxide (Ga2O3) exists in different polymorphic forms, including the trigonal (α), monoclinic (β), cubic (γ), and orthorhombic (κ) phases, each exhibiting distinct structural and electronic properties. Among these, β-Ga2O3 is the most thermodynamically stable and widely studied for high-power electronics applications due to its ability to be grown as high-quality bulk crystals. However, metastable phases such as α-, γ-, and κ-Ga2O3 offer unique properties, including wider bandgap or strong polarization and ferroelectric characteristics, making them attractive for specialized applications. This paper summarizes the radiation hardness of these polymorphs by analyzing the reported changes in minority carrier diffusion length (LD) and carrier removal rates under various irradiation conditions, including protons, neutrons, alpha particles, and gamma rays. β-Ga2O3 demonstrates high radiation tolerance with LD reductions correlated to the introduction of electron traps (E2*, E3, and E4) and gallium–oxygen vacancy complexes (VGa–VO). α-Ga2O3 exhibits slightly better radiation hardness similar to κ-Ga2O3, which also shows minimal LD changes postirradiation, likely due to suppressed defect migration. γ-Ga2O3 is the least thermodynamically stable, but surprisingly is not susceptible to radiation-induced damage, and is stabilized under Ga-deficient conditions. The study highlights the role of polymorph-specific defect dynamics, doping concentrations, and nonuniform electrical properties in determining radiation hardness. We also discuss the effect of radiation exposure on the use of NiO/Ga2O3 heterojunction rectifiers that provide superior electrical performance relative to Schottky rectifiers. The presence of NiO does change some aspects of the response to radiation. Alloying with Al2O3 further modulates the bandgap of Ga2O3 and defect behavior, offering potentially tunable radiation tolerance. These findings provide critical insights into the radiation response of Ga2O3 polymorphs, with implications for their use in aerospace and radiation-hardened power electronics. Future research should focus on direct comparisons of polymorphs under identical irradiation conditions, defect identification, and annealing strategies to enhance radiation tolerance.

Alessi A., Lin J., Safarov V.I., Drouhin H.-., Romero Vega L., Cavani O., Grasset R., Jaffrès H., Konczykowski M.

Yang R., Wei H., Tang G., Cao B., Chen K.

Lithium niobate (LiNbO3) has remarkable ferroelectric properties, and its unique crystal structure allows it to undergo significant spontaneous polarization. Lithium niobate plays an important role in the fields of electro-optic modulation, sensing and acoustics due to its excellent electro-optic and piezoelectric properties. Thin-film LiNbO3 (TFLN) has attracted much attention due to its unique physical properties, stable properties and easy processing. This review introduces several main preparation methods for TFLN, including chemical vapor deposition (CVD), molecular beam epitaxy (MBE), pulsed laser deposition (PLD), magnetron sputtering and Smartcut technology. The development of TFLN devices, especially the recent research on sensors, memories, optical waveguides and EO modulators, is introduced. With the continuous advancement of manufacturing technology and integration technology, TFLN devices are expected to occupy a more important position in future photonic integrated circuits.

Shi Z., Gao X., Xie M., Xie T., Li Z., Zhao H., Wang Y., Gao X.

Luo T., Chen X., Yang Z., Chen W., Huang C., Luo H., Pei Y., Lu X., Wang G., Chen Z.

Orthorhombic ε-Ga2O3 is the second most stable phase of the Ga2O3 family, which is usually grown on hexagonal substrates by hetero-epitaxy. Due to the mismatch of rotational symmetry between the ε-Ga2O3 film and the substrate, the hetero-epitaxy of ε-Ga2O3 is accompanied by the problem of rotation domains, which brings a high density of defects in the film. This paper focuses on the epitaxial lateral overgrowth (ELO) of ε-Ga2O3 by metal–organic chemical vapor deposition (MOCVD). Based on the investigation of nucleation temperature, mask period and direction, the optimal conditions for the ELO growth of ε-Ga2O3 via MOCVD are established. It is found that both the thermal diffusion capability of Ga adatoms and the growth rate anisotropy of ε-Ga2O3 play important roles during the ELO of ε-Ga2O3. A high growth temperature and a short mask period can suppress the nucleation of irregular ε-Ga2O3 grains and improve the crystal quality. Further comparison of different designs of ELO masks revealed that the striped ELO masks predominantly promote the quasi-single-domain growth of ε-Ga2O3. Notably, for samples with striped ELO windows along the sapphire $$\left\langle {11\overline{2}0} \right\rangle$$ , rotation domains are effectively suppressed and the ratio of 0°, + 120°, and − 120° domains increases from 1.01:1:1 to 2.6:1:1.

Asteriti A., Verzellesi G., Sozzi G., Baraldi A., Mazzolini P., Moumen A., Parisini A., Pavesi M., Bosi M., Mosca R., Seravalli L., Fornari R.

The “photo‐gain effect” amplifying the DC photocurrent of κ‐Ga2O3 UV‐C photoresistors is analyzed by means of 2D numerical simulations and linked to the capture of photogenerated holes by deep donor levels, probably associated with oxygen vacancies. The resulting ionization of the deep donors leads to an increase in the electron density, hence to enhanced conductivity under illumination.

Koishybayeva Z., Konusov F., Pavlov S., Sidelev D., Nassyrbayev A., Gadyrov R., Tarbokov V., Polisadova E., Akilbekov A.

Cristoloveanu S., Nowak E., Barbot J., Grenouillet L., Radu I.

Gavdush A.A., Zhelnov V.A., Dolganov K.B., Bogutskii A.A., Garnov S.V., Burdanova M.G., Ponomarev D.S., Shi Q., Zaytsev K.I., Komandin G.A.

Vanadium dioxide ( $$\hbox {VO}_2$$ ) is a favorable material platform of modern optoelectronics, since it manifests the reversible temperature-induced insulator-metal transition (IMT) with an abrupt and rapid changes in the conductivity and optical properties. It makes possible applications of such a phase-change material in the ultra-fast optoelectronics and terahertz (THz) technology. Despite the considerable interest to this material, data on its broadband electrodynamic response in different states are still missing in the literature. This hampers the design and implementation of the $$\hbox {VO}_2$$ -based devices. In this paper, we combine the Fourier-transform infrared (FTIR) spectroscopy, THz pulsed spectroscopy (TPS), and four-contact probe method to study the $$\hbox {VO}_2$$ films prepared by magnetron sputtering on a c-cut sapphire substrate. Considering different temperatures of a substrate and pressures of atmosphere, we reconstruct complex dielectric permittivity of $$\hbox {VO}_2$$ film in the frequency range of 0.2–150 THz, along with its static conductivity. The dielectric response is modeled using Lorentz and Drude kernels, which make possible splitting contributions from vibrational modes and free charge carriers to the total dynamic conductivity. By studying $$\hbox {VO}_2$$ at different substrate temperatures and atmosphere pressures, we show that IMT appears to be pressure-dependent, which we attribute to the different thermostatic conditions of a sample. Finally, we estimate somewhat optimal thickness and temperature of the $$\hbox {VO}_2$$ film in metallic phase for the THz optoelectronic applications. Our finding should be useful for further developments of the $$\hbox {VO}_2$$ -based devices and technologies.

Brey L., Fertig H.A.

Nos J., Iséni S., Kogelschatz M., Cunge G., Lefaucheux P., Dussart R., Tillocher T., Despiau-Pujo É.

Ultraviolet (UV) absorption spectroscopy is used to monitor the CF radical density in CF4 inductively coupled plasma (ICP) plasmas as a function of the substrate temperature. The CF density decreases dramatically when the wafer temperature is reduced from 20 to −130 °C by applying identical plasma conditions, demonstrating that the CF surface sticking coefficient increases as the surface temperature is reduced. This suggests that CF4 plasma could be used to form sidewall passivation layers and perform anisotropic etching at cryogenic temperature, which is impossible at room temperature. Subsequently, a cyclical Bosch type etching process of silicon was evaluated at −100 °C using CF4 plasma to passivate the trench sidewalls. Anisotropic etch profiles were obtained with an etch rate of 4.4 μm/min. Compared to a typical Bosch process using highly polymerizing c-C4F8 plasma, chamber wall contamination could be significantly reduced, alleviating a major issue of this cyclic process. Furthermore, CF4 has a 28% lower global warming potential than c-C4F8.

Shibanov D.R., Lopaev D.V., Maslakov K.I., Konnikova M.R., Rakhimov A.T.

Xu J., Refino A.D., Delvallée A., Seibert S., Schwalb C., Hansen P.E., Foldyna M., Siaudinyte L., Hamdana G., Wasisto H.S., Kottmeier J., Dietzel A., Weimann T., Prüssing J.K., Bracht H., et. al.

The pursuit of sculpting materials at increasingly smaller and deeper scales remains a persistent subject in the field of micro- and nanofabrication. Anisotropic deep-reactive ion etching of silicon at cryogenic temperatures (cryo-DRIE) was investigated for fabricating arrays of vertically aligned Si nanowires (NWs) of a large range of dimensions from micrometers down to 30 nm in diameter, combined with commonly used wafer-scale lithography techniques based on optical, electron-beam, nanoimprint, and nanosphere/colloidal masking. Large selectivity of ∼100 to 120 and almost 700 was found with resists and chromium hard masks, respectively. This remarkable selectivity enables the successful transfer of patterned geometries while preserving spatial resolution to a significant extent. Depending on the requirements by applications, various shapes, profiles, and aspect ratios were achieved by varying process parameters synchronously or asynchronously. High aspect ratios of up to 100 comparable to the best result by metal-assisted wet-chemical etching and sub-μm trenches by DRIE were obtained with NW diameter of 200 nm, at an etch rate of ∼4 μm/min without being collapsed. At the same time, low surface roughness values were maintained on the NW top, sidewall, and bottom surface of ∼0.3, ∼13, and ∼2 nm, respectively, as well as high pattern fidelity and integrity, which were measured using angle-resolved Fourier microscopy, combined atomic force, and scanning electron microscopy on selected NWs. This work establishes the foundation in the controllable development of Si nanoarchitectures, especially at sub-100 nm structures, for energy-harvesting and storage, damage-free optoelectronics, quantum, photovoltaics, and biomedical devices.

Zhu X., Pan A., Shokouhi B., Cui B.

Fabrication of high aspect ratio silicon nanopillars is challenging for various applications. A cryogenic silicon etching process using SF6 and O2 plasma is investigated to create silicon nanopillars with 10 μm height and tens of nanometers apex. In the process, fluorine radicals react with silicon atoms, releasing volatile SiFx byproducts and then oxygen atoms interact with SiFx and deposit a SiOxFy film acting as an inhibitor. By adjusting the O2 concentration and the forward radio frequency power, this process modifies the formation of the SiOxFy passivation film and adjusts the bombardment of ions onto the inhibitor, resulting in the desired positive taper angles of silicon pillars. Two etching steps, with higher and lower O2 concentrations, are consecutively combined to create a sharp apex and a wide base. The results demonstrate the high etching rate and controllability of cryogenic etching to obtain high aspect ratio silicon pillars with desired profiles.

Zhu X., Wang Z., Zhu C., Shen J., Shokouhi B., Ekinci H., Cui B.

Inductively coupled plasma etching of silicon nanostructures for metalens applications using a continuous, multi-step C4F8/SF6 plasma was investigated to achieve high aspect ratio (HAR) features down to tens of nanometers with smooth sidewalls. In the process, the ion bombardment and the free radical transport significantly change among HAR nanostructures as the etching progresses, posing challenges to profile control. With a fixed gas ratio, a change in the profile angle occurs at a depth of approximately 400 nm, transitioning from a positive taper to a negative one. Additionally, a wave-like pillar profile is produced when using three separate (i.e., plasma turned off after each step) etching processes with varying gas ratios. To optimize passivation and etching, we adopt a three-step C4F8/SF6 plasma etching process with varying gas ratios at different etching depths. By keeping the plasma on after each step, the continuous, three-step process provides more flexibility for tuning the etching of HAR nanostructures with smooth and vertical profiles. Metalens nanostructures with 71 nm diameter and 1 μm height were created using the appropriate gas ratio. The feature size variation is less than 10 nm. This proposed continuous, multi-step process improves the controllability of silicon etching in C4F8/SF6 plasma, facilitating the nanofabrication of silicon metalens and other nanodevices.

Refino A.D., Eldona C., Hernandha R.F., Adhitama E., Sumboja A., Peiner E., Wasisto H.S.

AbstractMiniaturization of modern microelectronics to accommodate the development of portable and smart devices requires independent energy storage that is compact, lightweight, reliable, and integrable on-chip. Three-dimensional lithium-ion microbatteries are considered as promising candidates to fill the role, owing to their high energy and power density. Combined with silicon as a high-capacity anode material, the performance of the microbatteries can be further enhanced. In this review, the latest developments in three-dimensional silicon-based lithium-ion microbatteries are discussed in terms of material compatibility, cell designs, fabrication methods, and performance in various applications. We highlight the relation between device architecture and performance as well as comparison between different fabrication technologies. Finally, we suggest possible future studies based on the current development status to provide a research direction towards further improved three-dimensional silicon-based lithium-ion microbatteries.

Lomonte E., Stappers M., Krämer L., Pernice W.H., Lenzini F.

AbstractEfficient fiber-to-chip couplers for multi-port access to photonic integrated circuits are paramount for a broad class of applications, ranging, e.g., from telecommunication to photonic computing and quantum technologies. Grating-based approaches are often desirable for providing out-of-plane access to the photonic circuits. However, on photonic platforms characterized by a refractive index ≃ 2 at telecom wavelength, such as silicon nitride or thin-film lithium niobate, the limited scattering strength has thus far hindered the achievement of coupling efficiencies comparable to the ones attainable in silicon photonics. Here we present a flexible strategy for the realization of highly efficient grating couplers on such low-index photonic platforms. To simultaneously reach a high scattering efficiency and a near-unitary modal overlap with optical fibers, we make use of self-imaging gratings designed with a negative diffraction angle. To ensure high directionality of the diffracted light, we take advantage of a metal back-reflector patterned underneath the grating structure by cryogenic deep reactive ion etching of the silicon handle. Using silicon nitride as a testbed material, we experimentally demonstrate coupling efficiency up to − 0.55 dB in the telecom C-band with high chip-scale device yield.

Gaidukasov R.A., Miakonkikh A.V.

This article discusses model and model-free approaches to solve problems of spectral ellipsometry as applied to microelectronic problems related to measuring the thicknesses and optical parameters of thin layers of dielectrics, metals, and semiconductors. Model approaches are based on the use of a priori information about the form of the Cauchy, Drude, Drude–Lorentz, and Tauc–Lorentz dispersion relation. Model-free approaches can use any smooth multiparameter functional relationship that can describe a smooth spectral curve. We can also use machine learning (ML) to implement a model-free approach, which is suited for determining the thickness of multilayer structures and their optical characteristics and can significantly increase the speed of data processing.

Miakonkikh A.V., Kuzmenko V.O., Efremov A.M., Rudenko K.V.

The electrophysical parameters of the plasma and the kinetics of plasma-chemical processes in a CF4 + H2 + Ar mixture while varying the CF4/H2 ratio are studied. When using diagnostic methods and plasma modeling together, it is found that replacing tetrafluoromethane with hydrogen (a) leads to a decrease in the plasma density and an increase in electronegativity; and (b) it causes a disproportionately sharp drop in the concentration of fluorine atoms. The reason for the latter effect is the increase in the frequency of the death of atoms in reactions of the CHFx + F → CFx + HF type initiated by heterogeneous recombination via the CFx + H → CHFx mechanism. The simultaneous increase in the concentration of polymer-forming CHxFy (x + y < 3) radicals indicates an increase in the polymerization load of the plasma on the surfaces in contact with it.

Vinuesa G., García H., Poblador S., González M.B., Campabadal F., Castán H., Dueñas S.

In this letter, we study the impact of the temperature on the resistive switching effect of TiN/Ti/HfO2/W metal–insulator-metal devices. An analysis of the conduction mechanisms is made, with the low resistance state being ruled by nearest neighbor hopping, while the conduction in the high resistance state is dominated by Schottky emission. Taking into account the filamentary mechanism behind the resistive switching effect, a thorough analysis of the Schottky emission allows for the calculation of the gap between conductive filament tip and metal electrode in the high resistance state. We report an increase of this gap when temperature lowers below a certain value. Moreover, the mentioned gap adopts values of integer multiples of the the mean distance between traps obtained by the hopping model.

Pan J., He H., Dan Y., Lin Y., Yang S., Li M., Li T.

Hsiao S., Britun N., Nguyen T., Sekine M., Hori M.

Chouprik A., Savelyeva E., Korostylev E., Kondratyuk E., Zarubin S., Sizykh N., Zhuk M., Zenkevich A., Markeev A.M., Kondratev O., Yakunin S.

The nanosecond speed of information writing and reading is recognized as one of the main advantages of next-generation non-volatile ferroelectric memory based on hafnium oxide thin films. However, the kinetics of polarization switching in this material have a complex nature, and despite the high speed of internal switching, the real speed can deteriorate significantly due to various external reasons. In this work, we reveal that the domain structure and the dielectric layer formed at the electrode interface contribute significantly to the polarization switching speed of 10 nm thick Hf0.5Zr0.5O2 (HZO) film. The mechanism of speed degradation is related to the generation of charged defects in the film which accompany the formation of the interfacial dielectric layer during oxidization of the electrode. Such defects are pinning centers that prevent domain propagation upon polarization switching. To clarify this issue, we fabricate two types of similar W/HZO/TiN capacitor structures, differing only in the thickness of the electrode interlayer, and compare their ferroelectric (including local ferroelectric), dielectric, structural (including microstructural), chemical, and morphological properties, which are comprehensively investigated using several advanced techniques, in particular, hard X-ray photoelectron spectroscopy, high-resolution transmission electron microscopy, energy dispersive X-ray spectroscopy, X-ray diffraction, and electron beam induced current technique.

Kim Y., Kang H., Ha H., Choi M., Jeon M., Cho S.M., Chae H.

AbstractThe plasma atomic layer etching (ALE) process for Ru was developed with surface fluorination and ion bombardment. We employed two methods for surface fluorination: (i) fluorocarbon deposition using CHF3 or C4F8 plasmas and (ii) chemisorption and diffusion with CF4 plasma. C4F8 plasma generated a more fluorine rich fluorocarbon layer on the Ru surface compared with CHF3 plasma, and a higher etch per cycle (EPC) of 1.5 nm/cycle was achieved with C4F8 plasma, in contrast to the 0.6 nm/cycle achieved with CHF3 plasma. Moreover, chemisorption and diffusion with CF4 plasma yielded an EPC of 1.2 nm/cycle. The ALE process using CHF3 plasma shows the lowest fluorine residue and lowest surface roughness compared with the ALE process using C4F8 and CF4 plasmas.

Chouprik A., Mikheev V., Korostylev E., Kozodaev M., Zarubin S., Vinnik D., Gudkova S., Negrov D.

The development of the new generation of non-volatile high-density ferroelectric memory requires the utilization of ultrathin ferroelectric films. The most promising candidates are polycrystalline-doped HfO2 films because of their perfect compatibility with silicon technology and excellent ferroelectric properties. However, the remanent polarization of HfO2 films is known to degrade when their thickness is reduced to a few nanometers. One of the reasons for this phenomenon is the wake-up effect, which is more pronounced in the thinner the film. For the ultrathin HfO2 films, it can be so long-lasting that degradation occurs even before the wake-up procedure is completed. In this work, an approach to suppress the wake-up in ultrathin Hf0.5Zr0.5O2 films is elucidated. By engineering internal built-in fields in an as-prepared structure, a stable ferroelectricity without a wake-up effect is induced in 4.5 nm thick Hf0.5Zr0.5O2 film. By analysis of the functional characteristics of ferroelectric structures with a different pattern of internal built-in fields and their comparison with the results of in situ piezoresponse force microscopy and synchrotron X-ray micro-diffraction, the important role of built-in fields in ferroelectricity of ultrathin Hf0.5Zr0.5O2 films as well as the origin of stable ferroelectric properties is revealed.

Fetisenkova K.A., Rogozhin A.E.

The application of the structure and principles of the human brain opens up great opportunities for creating artificial systems based on silicon technology. The energy efficiency and performance of a biosimilar architecture can be significantly higher compared to the traditional von Neumann architecture. This paper presents an overview of the most promising artificial neural network (ANN) and spiking neural network (SNN) architectures for biosimilar systems, called neuromorphic systems. Devices for biosimilar systems, such as memristors and ferroelectric transistors, are considered for use as artificial synapses that determine the possibility of creating various architectures of neuromorphic systems; methods and rules for training structures to work correctly when mimicking biological learning rules, such as long-term synaptic plasticity. Problems hindering the implementation of biosimilar systems and examples of architectures that have been practically implemented are discussed.