skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: Anodic processes in the chemical and electrochemical etching of Si crystals in acid-fluoride solutions: Pore formation mechanism

Abstract

The interaction of heavily doped p- and n-type Si crystals with hydrofluoric acid in the dark with and without contact with metals having greatly differing work functions (Ag and Pd) is studied. The dependences of the dissolution rates of Si crystals in HF solutions that contain oxidizing agents with different redox potentials (FeCl{sub 3}, V{sub 2}O{sub 5} and CrO{sub 3}) on the type and level of silicon doping are determined. Analysis of the experimental data suggests that valence-band holes in silicon are not directly involved in the anodic reactions of silicon oxidation and dissolution and their generation in crystals does not limit the rate of these processes. It is also shown that the character and rate of the chemical process leading to silicon dissolution in HF-containing electrolytes are determined by the interfacial potential attained at the semiconductor–electrolyte interface. The mechanism of electrochemical pore formation in silicon crystals is discussed in terms of selfconsistent cooperative reactions of nucleophilic substitution between chemisorbed fluorine anions and coordination- saturated silicon atoms in the crystal subsurface layer. A specific feature of these reactions for silicon crystals is that vacant nonbonding d{sup 2}sp{sup 3} orbitals of Si atoms, associated with sixfold degenerate states corresponding to themore » Δ valley of the conduction band, are involved in the formation of intermediate complexes. According to the suggested model, the pore-formation process spontaneously develops in local regions of the interface under the action of the interfacial potential in the adsorption layer and occurs as a result of the detachment of (SiF{sub 2}){sub n} polymer chains from the crystal. Just this process leads to the preferential propagation of pores along the <100> crystallographic directions. The thermodynamic aspects of pore nucleation and the effect of the potential drop across the interface, conduction type, and free-carrier concentration in the crystal on the pore size and structure are discussed. The concepts developed in the study can consistently account for experimental facts characterizing the etching of silicon crystals with various electrical parameters under various conditions providing the anodic polarization of crystals in HF-containing solutions.« less

Authors:
; ;  [1]
  1. Ioffe Physical–Technical Institute (Russian Federation)
Publication Date:
OSTI Identifier:
22649592
Resource Type:
Journal Article
Resource Relation:
Journal Name: Semiconductors; Journal Volume: 51; Journal Issue: 4; Other Information: Copyright (c) 2017 Pleiades Publishing, Ltd.; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; 37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; CHEMISORPTION; CHROMIUM OXIDES; CRYSTALS; DISSOLUTION; DOPED MATERIALS; ELECTROCHEMISTRY; ELECTROLYTES; ETCHING; FLUORIDES; INTERFACES; IRON CHLORIDES; LAYERS; N-TYPE CONDUCTORS; P-TYPE CONDUCTORS; REDOX POTENTIAL; SILICON; VANADIUM OXIDES

Citation Formats

Ulin, V. P., Ulin, N. V., and Soldatenkov, F. Yu., E-mail: f.soldatenkov@mail.ioffe.ru. Anodic processes in the chemical and electrochemical etching of Si crystals in acid-fluoride solutions: Pore formation mechanism. United States: N. p., 2017. Web. doi:10.1134/S1063782617040212.
Ulin, V. P., Ulin, N. V., & Soldatenkov, F. Yu., E-mail: f.soldatenkov@mail.ioffe.ru. Anodic processes in the chemical and electrochemical etching of Si crystals in acid-fluoride solutions: Pore formation mechanism. United States. doi:10.1134/S1063782617040212.
Ulin, V. P., Ulin, N. V., and Soldatenkov, F. Yu., E-mail: f.soldatenkov@mail.ioffe.ru. Sat . "Anodic processes in the chemical and electrochemical etching of Si crystals in acid-fluoride solutions: Pore formation mechanism". United States. doi:10.1134/S1063782617040212.
@article{osti_22649592,
title = {Anodic processes in the chemical and electrochemical etching of Si crystals in acid-fluoride solutions: Pore formation mechanism},
author = {Ulin, V. P. and Ulin, N. V. and Soldatenkov, F. Yu., E-mail: f.soldatenkov@mail.ioffe.ru},
abstractNote = {The interaction of heavily doped p- and n-type Si crystals with hydrofluoric acid in the dark with and without contact with metals having greatly differing work functions (Ag and Pd) is studied. The dependences of the dissolution rates of Si crystals in HF solutions that contain oxidizing agents with different redox potentials (FeCl{sub 3}, V{sub 2}O{sub 5} and CrO{sub 3}) on the type and level of silicon doping are determined. Analysis of the experimental data suggests that valence-band holes in silicon are not directly involved in the anodic reactions of silicon oxidation and dissolution and their generation in crystals does not limit the rate of these processes. It is also shown that the character and rate of the chemical process leading to silicon dissolution in HF-containing electrolytes are determined by the interfacial potential attained at the semiconductor–electrolyte interface. The mechanism of electrochemical pore formation in silicon crystals is discussed in terms of selfconsistent cooperative reactions of nucleophilic substitution between chemisorbed fluorine anions and coordination- saturated silicon atoms in the crystal subsurface layer. A specific feature of these reactions for silicon crystals is that vacant nonbonding d{sup 2}sp{sup 3} orbitals of Si atoms, associated with sixfold degenerate states corresponding to the Δ valley of the conduction band, are involved in the formation of intermediate complexes. According to the suggested model, the pore-formation process spontaneously develops in local regions of the interface under the action of the interfacial potential in the adsorption layer and occurs as a result of the detachment of (SiF{sub 2}){sub n} polymer chains from the crystal. Just this process leads to the preferential propagation of pores along the <100> crystallographic directions. The thermodynamic aspects of pore nucleation and the effect of the potential drop across the interface, conduction type, and free-carrier concentration in the crystal on the pore size and structure are discussed. The concepts developed in the study can consistently account for experimental facts characterizing the etching of silicon crystals with various electrical parameters under various conditions providing the anodic polarization of crystals in HF-containing solutions.},
doi = {10.1134/S1063782617040212},
journal = {Semiconductors},
number = 4,
volume = 51,
place = {United States},
year = {Sat Apr 15 00:00:00 EDT 2017},
month = {Sat Apr 15 00:00:00 EDT 2017}
}
  • Illumination lowers the rate of porous-layer formation under galvanostatic polarization, so that the linear and parabolic kinetics found in the dark is transformed to linear kinetics. Under the effect of light, oxidation of silicon to the divalent state is the predominant reaction; this promotes formation of a more porous structure because of inhibition of the growth of macropores taking place in the dark when silicon dissolves to tetravalent compounds.
  • The maximum in the photopotential curve recorded at n-type silicon during the formation of porous surface layers is caused by the stages of this process, by the relative oxidation rates of silicon to compounds of higher and lower valency, and by the shift of the zone of the chief processes from the interface between the single crystal and the porous layer with macropores to a region of the porous layer adjacent to this zone. Illumination increases the rate of silicon oxidation to compounds of lower valency in the region of potentials where the photopotentials in the transition region are highest.more » Higher water concentrations in the electrolyte inhibit silicon dissolution involving the formation of fluorine compounds, and enhance oxidation to silicon-oxygen compounds, which has the effect that the range of potentials of photovoltaic activity increases drastically while porous-layer formation is relatively delayed.« less
  • Chemical and electrical processes developing at the semiconductor-electrolyte interface under conditions of anodic polarization were analyzed. It was shown that dense chemisorption coatings are formed on the surface of III-V crystals at voltages of pore formation onset, and a degenerate inversion layer is formed on the semiconductor side. In this case, a drop of the largest part of the applied voltage in the adsorption layer creates the prerequisites for nucleophilic substitution reactions involving chemisorbed anions and coordination-saturated atoms under the crystal surface. The mechanisms of these reactions were considered as applied to sphalerite-structured crystals. The results of experimental studies ofmore » the structures and compositions of porous layers in III-V crystals formed in various electrolytes at various polarization voltages are explained on the basis of the obtained concepts.« less
  • The 2.5V range within which the lead-acid battery operates is divided into three separate lead electrode systems. During passivation of the Pb/PbSO/sub 4/ electrode, the electrolyte in the pores of the PbSO/sub 4/ layer is alkalized, and at potentials more positive than -0.4V the Pb/PbO/PbSO/sub 4//H/sub 2/SO/sub 4/ electrode system is formed. At potentials more positive than +0.95V in the dark, following a semiconductor mechanism, PbO is oxidized first to PbO /SUB n/ , and then to ..cap alpha..-PbO/sub 2/. When ..cap alpha..-PbO/sub 2/ comes into contact with the bulk of the H/sub 2/SO/sub 4/, the PbSO/sub 4/ crystals aremore » oxidized to ..beta..PbO/sub 2/.« less
  • Possible ways for increasing the photoluminescence quantum yield of porous silicon layers have been investigated. The effect of the anodization parameters on the photoluminescence properties for porous silicon layers formed on silicon substrates with different crystallographic orientations was studied. The average diameters for silicon nanoclusters are calculated from the photoluminescence spectra of porous silicon. The influence of the substrate crystallographic orientation on the photoluminescence quantum yield of porous silicon is revealed. A model explaining the effect of the substrate orientation on the photoluminescence properties for the porous silicon layers formed by anode electrochemical etching is proposed.