Persons

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Anisotropic etching in KOH solution with electrochemical stopping is commonly used in formation of thin silicon membranes of sensitive elements in various MEMS devices. However, the data of investigating the process of electrochemical stop-etching of elements in various MEMS devices are absent. In the work the process of electrochemical stop etching in KOH solution for structures using the n-type silicon layers, formed by diffusion on the p -type silicon substrate with a smooth and relief surface, has been studied. It has been studied that when using a 2-electrode circuit with positive (relative to the solution) voltage, applied to an n-layer, for a structure with an n-layer, formed on a smooth surface, the etching stops at the pn -junction boundary and as the result, a membrane forms, uniform in thickness over the entire area of the plate. When using a 2-electrode circuit for a structure with a relief surface during etching the current density J is 70-100 times greater than in the case of a smooth surface, the etching is non-uniform across the plate and stops long before reaching the pn -junction. It has been found that for a structure with a relief surface when using a circuit with two voltage sources, with an additional negative (relative to the solution) voltage, applied to the p-substrate at U » -2.0 V, the etching stops at the pn -junction interface, and as the result, it is possible to obtain silicon membrane, fairly uniform in thickness over the entire area of the plate. The dependences of the current density J (between the n -layer of silicon and the solution) on the etching time t have been obtained for the structures with a smooth and relief surface, which makes it possible to determine the end of the etching process.

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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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Sample surface examination in atomic force microscopy is carried out using cantilevers having the form of elastic consoles with sharp needle (tip) at the free end. Quality of images obtained from atomic force microscope (AFM) heavily depends on tip sharpness degree. Silicon cantilevers made based on wet anisotropic etching are widely used in atomic force microscopy. This paper studies the dependence of the shape and size of the resulting tip on the concentration of KOH in the solution, as well as the effect of pyrogenic oxidation and oxidation in a dry oxygen atmosphere on the sharpness of the tip during the sharpening process. It was shown that when 70 % concentration is used, tips with the highest aspect ratio and maximum height are obtained. In this case, the shape of the needle is an octagonal pyramid, the lateral faces of which are formed by eight crystallographic planes from {311} and {131}. It was found that in a two-stage sharpening process, consisting of pyrogenic oxidation and oxidation in a dry oxygen atmosphere, it is possible to form sufficiently sharp probes with a tip radius of 2-5 nm and an apex angle of 14-24°. It has been established that a one-stage sharpening process based on pyrogenic oxidation provides only the production of probes with a radius of about 14 nm. Comparative tests of the manufactured probes in obtaining AFM images of a test sample of a polycrystalline silicon film with hemispherical grains (HSG-Si) were presented. Research study has revealed that such a statistical parameter as the relative increment of the surface area S is the most sensitive to probe sharpness for surfaces of the HSG-Si film type.

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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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