Etch Channel Formation during Anodic Dissolution of N-Type Silicon in Aqueous Hydrofluoric Acid

Abstract

Anodic dissolution of n+‐, n‐, and n−‐type silicon in 5% aqueous hydrofluoric acid at moderate current densities results in the formation of etch channels which propagate in crystal‐oriented directions in the monocrystal. Density and depth of the channels are a function of the applied voltage, the donor concentration, and the exposure time of the electrolyte under anodic bias conditions. It is assumed that the channel formation originates at spots with a lower breakdown voltage of the depletion layer which exists on the surface of the crystal under reverse bias conditions. Channel formation in epitaxial n layers can occur during preferential electrochemical etching of the n+ substrate of n+n− structures. This is the case when the n+ to n− interface profile is not abrupt and when defects in the epitaxial layer are present. Some methods of restricting the influence of channels occurring during device processing are mentioned.

Pore formation mechanisms for the Si-HF system

“…Despite intensive research triggered by the finding that nanoporous Si shows strong luminescence [6,7], neither the intricacies of the IV -characteristic nor the processes responsible for the formation of pores, including their rather peculiar dependence on crystal orientation, are well understood. Whereas mechanisms for some aspects of pore formation have been proposed [8][9][10][11][12][13][14][15][16], they are generally restricted to one kind of pores and possess very little predictive power. This paper attempts for the first time to give a coherent theory for all phenomena encountered at the Si -liquid interface subjected to current flow, including all aspects of pore formation and seemingly unrelated issues as, e.g., the current or voltage oscillations.…”

Self-Adjusting Electrochemical Etching Technique for Producing Nanoporous Silicon Membrane

“…The quantity of holes in electrode surface and the diffusion of fluoride ion will control the mechanism of pore formation. The passivation of pore wall can be boosted by electric field supplied during the pore formation [12,14,49]. In this experimental setup, three types of silicon substrate are used, namely, undoped (>80 Ωcm), n-type (resistivity 0-100 Ωcm) and p-type (resistivity 0-100 Ωcm).…”

“…Recently, the creation of the smallest pore size has been explored to suit various applications. There are various methods that can be explored to vary the pore formation in terms of size and structure of pore silicon [11][12][13][14][15][16][17]. The self-adjusting method can create the smallest pore by controlling and manipulating certain parameters during electrochemical etching process, which are current density [18][19][20], HF concentration [21], time, silicon orientation [22], doping level [23][24][25], lighting and electrolyte mixture [25].…”

Dynamic observation of electrochemical etching in silicon

“…In p-type silicon, the etching process leaves an interconnected network of filaments with typical dimensions 3-5 nm (Cullis and Canham 1991, Smith and Collins 1992, Ross et al 1995a). In n-type silicon, the pores can range in size from nanometers to microns and tend to grow in well defined crystallographic directions with a variable degree of branching (Theunissen 1972, Chuang et al 1989, Smith and Collins 1992, Lehmann 1990, 1993, Searson et al 1992.…”