Persons

Active research of the GeSbTe material (GST225) is connected with the possibility of creating multi-level non-volatile elements for high-speed integrated optical functional circuits. The principle of multi-level recording in these devices is based on the formation of regions in GeSbTe thin films with partial crystallization and significantly different optical properties. To predict the parameters of the effect that initiates phase transformations and reliably ensure a reversible transition between a set of logical states, it is necessary to have reliable information about the optical characteristics of GeSbTe thin films in states with different degrees of crystallization and the conditions for their production. Thereby, the purpose of this research was to determine the influence of phase state GeSbTe films on the extinction coefficient ( k ) and refractive index ( n ) and study changes in the values of optical band gap depending on the annealing temperature have been considered. The obtained samples of GeSbTe thin films were examined using atomic force microscopy, X-ray phase analysis, and energy dispersion X-ray phase analysis, and energy-dispersive microanalysis to determine the film thickness, morphology, phase state, and composition of the films. The ellipsometry method was used to obtain the spectra of ellipsometric angles ψ and Δ (the amplitude and phase components of light wave) and the parameters n and k were determined. The influence of layer and mathematical models on the calculation dispersion of optical parameters of GeSbTe films, have been considered. It was found a significant increase in the values of n and k on the wavelength of 1550 nm when annealing above 200 °C has been found. It has been shown that in the amorphous state, GeSbTe thin films have an optical band gap equal to 0,71 eV, and in the crystalline = 0,47 eV. It was determined that the dependences of the refractive index, extinction coefficient, and optical band gap on the degree of crystallization of GeSbTe thin films are close to linear.

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Plasma-enhanced CVD silicon nitride films SiN obtained from the gases of SiH and NH are widely used in microelectronics, micro- and nanoelectromechanical systems. For many applications, the residual mechanical stresses and composition of films are important characteristics. The properties of SiN films (in particular mechanical stresses and composition) significantly depend on deposition conditions: the reacting gases ratio, gas mixture composition, power and frequency of plasma generator, temperature and pressure at deposition. Despite the large amount of research, the obtained data on dependence of the properties and composition of SiN films on the deposition conditions are not sufficiently complete. In the present work, the influence of the reacting gases ratio on the mechanical stresses and composition has been studied for the PECVD silicon nitride films SiN , obtained from a gaseous mixture of SiH and NH using a low-frequency plasma. It was found that for PECVD SiN films with increasing of the reacting gases ratio (SiH to NH) from 0,016 to 0,25 the compressive mechanical stress decreases by 31%, the stoichiometric coefficient decreases from 1,40 to 1,20, the refractive index increases from 1,91 to 2,08, the concentration of N-H bonds decreases 7,4 times, the concentration of Si-H bonds increases 8,7 times and the concentration of hydrogen atoms decreases by 1,5 times. The obtained dependences can be used for controlled production of SiN films with specified characteristics: residual mechanical stresses, refractive index, stoichiometric coefficient and concentration of hydrogen-containing bonds.

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One way to obtain perfect nitride structures for microelectronics is to use the atomic layer epitaxy growth method. The paper considers the influence on the growth dynamics and uniformity of the distribution of the deposited gallium nitride (GaN) layer of such process parameters as the pressure in the reactor, the flow rate of the trimethylgallium precursor and the substrate temperature in the deposition zone (growth temperature). The experiments were carried out in the original reactor in which the flow of gases to the surface of the substrates was carried out horizontally, the growth temperature in different experiments was in the range of 450-540 °C, pressure was varied from 4·10 Pa (400 mbar) up to 5·10 Pa (50 mbar), flow trimethylgallium ranged from 3 to 120 ml/min. The thickness of the layers is determined on a spectral ellipsometer. Obtained samples were studied by atomic-layer microscopy. Conditions of carrying the process for obtaining a uniform thickness of epitaxial layers of GaN on sapphire substrates have been researched.

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An algorithm of the relief analysis for the purpose of calculating the mechanical stresses in selected direction on a wafer in the form of a program package Matlab has been designed and implemented. The method provides the possibility of measurement at each point of the sample that delivers a visual picture of the data to obtain the distribution of mechanical stresses on the wafer surface. Using this technique the measurement of mechanical stresses in the film of plasma chemical silicon nitride has been conducted. The analysis in the environment of the device-technological simulation TCAD has been performed.

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