Search

Search Results

• 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.

• 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.