Characterization of thin porous silicon films formed on n+/p silicon junctions by spectroscopic ellipsometry

S. Strehlke, S. Bastide, O. Polgar, M. Fried, H. Lévy-Clément

Research output: Contribution to journalArticle

15 Citations (Scopus)

Abstract

Optical and structural properties of thin porous silicon (PS) layers electrochemically formed in the outermost part of 0.3 μm thin n+ emitters of commercial p/n+ silicon shallow junctions were studied by spectroscopic ellipsometry (SE). The SE data were evaluated with a multiparameter fitting procedure based on the Bruggeman effective medium approximation by using a mixture of fine-grain polycrystalline Si and voids. The fit results show that the thicknesses of PS films grown at a constant current density of 50 mA/cm2 in 30% hydrofluoric acid (HF) with etching times of 1.5 and 3.5 s are 54 and 105 nm, respectively. When the formation time is less than 2.5 s, the porosity is a constant 60% throughout the entire PS layer. A porosity gradient occurs across the layer for formation times greater than 2.5 s, resulting in a layer of up to 85% porosity near the surface after 3.5 s. This increasing porosity is due to chemical dissolution by the HF electrolyte, occurring as a simultaneous reaction to the electrochemical PS formation. All the PS layers grow at a rate of 32 ± 3 nm s-1, which is independent of the PS formation time and is not affected by the phosphorus doping gradient in the emitter. The calculated number of elementary charges, z, needed to dissolve one Si atom from the bulk is 3.3. Comparison of the SE fit with total reflectance measurements confirms the validity of the SE modeling. PS layer thicknesses were measured independently of the SE experiments by combining secondary ion mass spectroscopy measurements and surface profiling.

Original languageEnglish
Pages (from-to)636-641
Number of pages6
JournalJournal of the Electrochemical Society
Volume147
Issue number2
DOIs
Publication statusPublished - Feb 2000

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silicon junctions
Spectroscopic ellipsometry
Porous silicon
Silicon
silicon films
porous silicon
ellipsometry
Porosity
Hydrofluoric Acid
porosity
Hydrofluoric acid
hydrofluoric acid
emitters
gradients
Reflectometers
Phosphorus
Electrolytes
phosphorus
Structural properties
voids

ASJC Scopus subject areas

  • Electrochemistry
  • Surfaces, Coatings and Films
  • Surfaces and Interfaces

Cite this

Characterization of thin porous silicon films formed on n+/p silicon junctions by spectroscopic ellipsometry. / Strehlke, S.; Bastide, S.; Polgar, O.; Fried, M.; Lévy-Clément, H.

In: Journal of the Electrochemical Society, Vol. 147, No. 2, 02.2000, p. 636-641.

Research output: Contribution to journalArticle

Strehlke, S. ; Bastide, S. ; Polgar, O. ; Fried, M. ; Lévy-Clément, H. / Characterization of thin porous silicon films formed on n+/p silicon junctions by spectroscopic ellipsometry. In: Journal of the Electrochemical Society. 2000 ; Vol. 147, No. 2. pp. 636-641.
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