Pore formation mechanisms for the Si-HF system

Abstract

A model is presented with the potential to account for all processes of the reactive Si -liquid interface including, e.g., current oscillations, and the formation of nano-, meso, and macropores with their specific dependence on crystal orientation. The model assumes that current flow is spatially and temporally inhomogeneous -current thus flows in current "lines" occurring in current "bursts". The mean cycle time between correlated current bursts is mostly given by the kinetics of oxide dissolution and hydrogen passivation (which introduces a strong surface orientation dependence). Structure generation at the Si electrode (current oscillations in the time domain or pore formation in the space domain) under these assumptions is a self-organized process resulting from an interplay of synchronizing and desynchronizing mechanisms. Synchronizing mechanisms always couple the nucleation of a new current burst in a specific area to the history of that area, desynchronizing mechanisms may also depend on the interaction of current burst. Examples for synchronizing mechanisms are enhanced nucleation probabilities on (100) surfaces, response to local oxides from another current burst, or coupling of current bursts by space charge region effects. Desynchronisation results, e.g., from quantum wire effects, or local reduction of reactants or potential by a current line. The model accounts qualitatively for most if not all observed phenomena, gives a number of quantitative relations, and makes numerous predictions.

Self-organized pore formation and open-loop control in semiconductor etching

“…1) in diluted HF is quite complicated and exhibits two current peaks and strong currentor voltage oscillations at large current densities (for reviews see [2,3]). These oscillations have been decribed quantitatively by the Current-Burst-Model [4,5,6,7]. The IV-characteristics of the siliconhydrofluoric acid contact shows different phenomena from generation of a porous silicon layer (PSL), oxidation and electropolishing (OX) and electrochemical oscillations at higher anodic bias.…”

Morphological and optical characteristics of porous silicon produced by anodization process in HF-acetonitrile and HF-ethanol solutions

“…This argument was supported in the literature, from the chemical composition studies of PS layer, using IR spectroscopy measurements showing that the silicon surface is terminated with hydrogen, although the Si-F (6 eV) bond is much strong than Si-H bond. 7,12,14,[18][19][20][21][22][23][24] Figure 1 shows top view images of typical PS samples prepared by photoelectrochemical oxidation of n-type silicon, etching time of 60 min and current density of 11 mA cm -2 . The samples were prepared with two different solutions of HF-ethanol and HF-MeCN, for two types of Si resistivity.…”

“…PL spectra corresponding to samples prepared in each solution with the same anodization conditions, current density (56.5 mA cm -2 ), anodization time (10 min) and resistivity [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] cm, are shown in Figure 3. PL spectrum for sample produced from HF-MeCN solution presented a blue shift peak that may depend on the pore depth and diameter.…”

Electrochemical Fabrication and Characterization of Silicon Microwire Anodes for Li Ion Batteries

“…The process of oxide formation and dissolution is continuous over the etching process. 13,14 This etching modus allows obtaining wider pores (thinner walls). Without the addition of water, the oxidation process is limited, and direct dissolution of silicon is performed, preferentially at the pore tips (producing thinner pores).…”