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

Abstract

Electrochemical etching of semiconductors, apart from many technical applications, provides an interesting experimental setup for self-organized structure formation capable e.g. of regular, diameter-modulated, and branching pores. The underlying dynamical processes governing current transfer and structure formation are described by the CurrentBurst-Model: all dissolution processes are assumed to occur inhomogeneously in time and space as a Current Burst (CB); the properties and interactions between CB's are described by a number of material-and chemistry-dependent ingredients, like passivation and aging of surfaces in different crystallographic orientations, giving a qualitative understanding of resulting pore morphologies. These morphologies cannot be influenced only by the current, by chemical, material and other etching conditions, but also by an open-loop control, triggering the time scale given by the oxide dissolution time. With this method, under conditions where only branching pores occur, the additional signal hinders side pore formation resulting in regular pores with modulated diameter.

Uniform and Nonuniform Nucleation of Pores during the Anodization of Si, Ge, and III-V Semiconductors

“…Among the first porous domains were the ones observed in anodically etched GaP and described in detail by Erne et al 19 The present paper reports other distinct domain types observed in Ge, GaAs, and InP. No domain formation had been observed in Si until the recent discovery of the rather exotic "fractal" pores 22 which form clear surface domains. The aim of this paper is to discuss the etching conditions, the mechanism of domain formation, and the most common and uncommon features by comparing different types of domains.…”

On the origin of dissimilar pore evolution on patterned and unpatterned (100) n-type silicon

“…Due to a locally enhanced field around sharp structures, originally small pores closely neighboring to a prestructured nucleus can be bundled and pressed together into the predefined site and thus a larger pore forms. This can be understood as a phase separation mechanism of pores, as addressed in CBM [19,24] : due to the strengthened interactions (induced by localized field enhancement) between local CBs, the prestructured nuclei gather much more electric-field lines (and thus CBs) and attract the highest current density while rendering the other parts (outside the nuclei) totally inert. Note that in this work all anodizations were performed without any mask (i.e.…”

“…Electric-field effect as well as current-burst-model (CBM) was employed to interpret the underlying mechanism. electrochemistry, surface morphology, patterned and unpatterned specimen, physical and chemical factor, I-V (current-voltage) curveConcerning porous silicon (PS) formation, numerous work with respect to SCR (space charge region) effects [1][2][3][4][5][6] , electrochemical oxidation [7,8] , hydrogen passivation or incorporation [9,10] , breakdown mechanism [11,12] , diffusion-limited random walk [13,14] , surface instabilities [15][16][17] , current bursts [18,19] , geometry relativity [20,21] , solvent effects [22] , etc. [23][24][25] , has been advanced.…”

Pattern Formation during Anodic Etching of Semiconductors

“…31 where an amplitude modulation of the pore etching current with a frequency of around 33 mHz showed a large effect whereas other frequencies did not noticeably change the pore geometry Generally, given the non-linear nature of the CB model, one might expect that superimposed periodic external disturbances at frequencies that scale with the internal (CB) frequencies of the system might produce strong non-linear effects.…”