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• RESEARCH OF MASKING PROPERTIES OF SILICON OXIDE FILMS FOR SILICON MEMBRANE FABRICATION BY WET ETCHING

  S.V. Malohatko, E.Y. Gusev

  2021-02-13

  Abstract ▼

  Microelectromechanical sensors of the membrane type are fabricated by surface and bulk
  micromachining. In the latter case, the membranes are obtained by deep anisotropic etching of a
  single-crystal silicon layer or substrate to a thickness of 20–50 μm. In this case, both dry and wet
  etching methods are used. The advantage of wet etching is easy control of the lateral dimensions
  of the membranes and high selectivity. High selectivity of etching can be achieved due to the
  choice of the appropriate composition of the etching solution, the material of the protective coating
  and fabrication techniques. The paper presents an experimental study of the protective properties
  of silicon oxide films obtained by thermal oxidation, plasma-chemical deposition, and combined
  coating of these films under wet etching of single-crystal silicon in a 30% aqueous solution
  of potassium hydroxide at a temperature of 80°C. The etching selectivity, residual thickness,
  roughness, and surface concentration of local defects were calculated using data of stylus
  profilometry, optical interferometry, and microscopy. It was found that the rates and selectivity of
  etching of thermal oxide and plasma chemical oxide after rapid thermal annealing are quite close
  – 6,7 nm/min, 1:338 and 7 nm/min, 1:372, respectively. The surface roughness of the oxide films
  increased more when etching the thermal oxide films, as well as the plasma oxide of composite
  coating. The root-mean-square values of the residual roughness were 1–2 nm. Local defects of the
  etched alike with a concentration of 0,1–0,2 mm-2 were found in the films. It was found that the use
  of a 1 μm plasma oxide layer in a combined coating prevents etching of the thermal oxide, but to
  avoid local defects, its thickness should be increased to 1,5–2,0 μm; an annealed film of plasma
  oxide, with a thickness of 2,0 μm, can also be considered as an effective protective coating for
  deep wet etching of silicon.

• SIMULATION AND ANALYSIS OF THE STRESS-STRAIN STATE OF A PRESSURE SENSOR’S ELASTIC MEMBRANE BASED ON “SILICON ON SAPPHIRE” STRUCTURE

  S.P. Malyukov , V. D. Mishnev

  159-167

  2025-11-10

  Abstract ▼

  High accuracy and improved performance of pressure sensors are essential to ensure safety, quality and efficiency in various industries and machinery. The use of the finite element method (FEM) in the design of pressure sensors makes it possible to improve their accuracy due to a deeper analysis of mechanical and physical processes that arise when exposed to pressure loads. The purpose of this work is to build an accurate three-dimensional model of the sensitive element of the pressure sensor and to analyze the stress-strain state of the elastic membrane under the load from 0 to 15 MPa. The main tasks of the work: research of the properties and parameters of materials used as part of the sensitive element of the pressure sensor based on the structure “silicon on sapphire”; obtaining the values of the maximum equivalent stress arising in the design of the elastic membrane of the sensitive element under the influence of a pressure load of 125% of the nominal value; distribution of radial and tangential deformations of the elastic membrane and determination of the best location of resistance strain gauges on the surface of pressure sensor’s sensitive element. As a result of the research, it was found that the materials used have good resistance to an aggressive environment, as well as the ability to work in a wide temperature range and under high pressure loads. Based on the simulation results, the value of the maximum equivalent stress was determined, the stress value does not exceed the ultimate strength of the sensitive membrane, the distribution of radial and tangential deformations on the surface of the sensitive element was obtained, which makes it possible to determine the most optimal pattern of the resistance stain gauge bridge circuit.

• MODELING THE ELECTRIC FIELD OF A SILICON N-I-P NANOSTRUCTURE

  N.М. Bogatov , V. S. Volodin , L.R. Grigoryan , М. S. Kovalenko

  123-133

  2025-11-10

  Abstract ▼

  Distribution of ionized impurities, electrons, holes determines the structure, physical properties, performance characteristics of semiconductor devices. The role of surface electron states is negative, the degree of their influence on the characteristics of the device depends on the features of the structure. Reducing the size of semiconductor devices is a modern trend in improving electronics. The influence of surface states on the properties of nanoscale objects increases with decreasing size. The object of the study is the electric field of a silicon n-i-p nanostructure. The purpose of the study is to analyze the influence of surface states on the internal electric field of a silicon n-i-p nanostructure. Research objectives: 1 – Calculate numerically, taking into account the surface states, the potential and electric field strength, the concentration of donors and acceptors in a silicon n-i-p nanostructure with a diffusion doping profile.
  2 – Determine the influence of the thickness of the n-i-p nanostructure and the density of surface states on the potential and electric field strength. 3 – Determine the composition of the space charge region of the n-i-p nanostructure with the minimized influence of surface states. The calculation method is based on the numerical solution of the Poisson equation taking into account the surface states and boundary conditions, including the condition of the general electroneutrality of the sample. As a result, the distributions of the potential and electric field strength were obtained for different values of the nanostructure thickness and the density of surface states. It is shown that charged surface states change the potential and electric field strength not only in the surface region, but also in the volume of the nanostructure. The value of the strength in the base increases with decreasing thickness, this value decreases if the density of surface states exceeds 10¹³ cm^–2. Reducing the density of surface states to 10¹² cm^–2 eliminates the surface potential barrier created by them. The space charge region consists of 5 parts: a region of positive charge created by ionized donors, a region enriched in electrons, a region depleted in charge carriers, a region enriched in holes, and a region of negative charge created by ionized acceptors

• RESEARCH OF TEMPERATURE AND CONCENTRATION ON ANISOTROPIC WET ETCHING OF MONOCRYSTALLINE SILICON

  S.V. Malokhatko , D.A. Bakshevnikov , Gusev E. Y. Gusev

  2021-08-11

  Abstract ▼

  The main material of most mechanical sensors is silicon. For the formation of silicon structures,
  the methods of bulk micromachining - deep etching of the substrate – are used. Anisotropic
  wet etching is traditionally used to form structures that are subject to high requirements for dimensional
  accuracy and reproducibility. In this case, an aqueous solution of alkali is used as an
  etchant. Determining the optimal mode by the concentration and temperature of the solution will
  allow you to obtain a relatively uniform, smooth surface at a high etching rate. An experimental
  study of the influence of concentration (20-40%) and temperature (60-80°C) was carried an aqueous
  KOH solution on the etching rate of monocrystalline silicon, as well as the surface morphology
  under conditions of a long etching process. The etching rates in 20%, 30%, and 40% solution
  for the selected temperature range were 0.68–2.0 μm/min, 0.77–2.4 μm/min, and 0.7–1.9 μm/min,
  respectively. The morphology of the silicon surface at a depth of 270 microns was analyzed. It was
  found that at a solution concentration of 20% KOH and 80°C, a developed surface morphology
  with a roughness of ~ 400 nm is formed; a decrease in the solution temperature makes it possible
  to obtain a more even surface with a residual roughness of ~ 340 nm. At a concentration of 30%
  KOH solution, the surface is more uniform with a roughness of ~ 100 nm; a change in temperature
  from 60 to 80 °C has almost no effect on its morphology. At a concentration of KOH solution of40% and 80°The initial relief of the etching surface is sufficiently developed ~ 340 nm, and a decrease
  in the temperature of the solution to 60°C allows it to be reduced to a state characteristic of
  the etching condition at 30% and a temperature of 80°C.

• DESIGN OF SILICON MICROPROBE FOR MINIMALLY INVASIVE NEURAL INTERFACE

  E. Y. Gusev , A.V. Saryev

  2021-08-11

  Abstract ▼

  Microprobes have become an important tool in the study of brain activity. Research and development
  in the field of invasive neurointerfaces is aimed at reducing the characteristic damage
  to the nervous tissue by reducing the diameter of the implanted probes to less than 100 μm. Such
  structures are produced by micromachining, in particular, by types of anisotropic etching. In this
  case, the size and shape of the probe are influenced by the etching conditions. The latter should betaken into account at the designing of the probe. The paper evaluates the ranges of the geometric
  parameters of a silicon microprobe taking into account the etching conditions and the number of
  electrodes. Analytical calculations were carried out for the structure of the probe, represented by
  four regions of different widths, carrying up to seven electrodes. The dependences of bottom base
  width of a trapezoidal section of the probe and the size of the mask on the thickness and width of
  the top base are received. The admissible ranges of sizes for the proposed case of the four-level
  microprobe are established; in particular, the minimum values of the width of the top base were
  17, 28, 39 and 50 microns, and the corresponding ranges of permissible values of the probe thickness
  for cases with 1 electrode – 30–58 microns, 2 and 3 electrodes – 30–51 microns, 4 and 5
  electrodes – 30–43 microns, and for the case of a probe with 6 and 7 electrodes – 30–35 microns.
  The correction value of the mask size is estimated, reflecting the effect of etching conditions on the
  probe geometry.

• IMPULSE CHARACTERISTICS OF SILICON STRUCTURES WITH N-P JUNCTION IRRADIATED BY PROTONS

  N.М. Bogatov, V.S. Volodin, L.R. Grigoryan, А.I. Kovalenko, М.S. Kovalenko

  2022-11-01

  Abstract ▼

  Currently, methods are being actively developed to create semiconductor structures with desired
  properties by irradiation with ionizing particles (radiation defect engineering). The interaction
  of radiation defects with impurities, dislocations and other structural defects causes a change in the
  properties of semiconductors and semiconductor devices. Irradiation with protons makes it possible
  to controllably create radiation defects with a distribution maximum in a pre-calculated region. The
  aim of this work is to analyze the effect of irradiation with low-energy protons on the impulse characteristics
  of silicon structures with an n+-p junction. The task is to determine the effective lifetime  of
  charge carriers in the space charge region (SCR) of the n+-p junction. The n+-p-p+-structures made
  of silicon grown by the Czochralski method, irradiated from the side of the n+-layer by a low-energy
  proton flux at sample temperatures of 300 K and 83 K were studied. To measure the impulse characteristics,
  bipolar rectangular voltage pulses with a constant amplitude of 10 mV and a frequency of
  1 MHz were used. The experimental data are explained using models of nonstationary charge carrier
  transport in inhomogeneous semiconductors and the formation of radiation defects in silicon underthe action of protons. Depth distributions of the average number of primary radiation defects are
  calculated: interstitial silicon, vacancies, divacancies created by one proton per unit length of the
  projective path. It is shown that irradiation with protons with a dose of 1015 cm2 and an energy of
  40 keV does not change the value of , but with an energy of 180 keV creates a region with an effective
  lifetime of 5.5108 s in the SCR of the n+-p junction.