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

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 Formula structures. This is the case when the Formula 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.

Fatal systemic fluorosis due to hydrofluoric acid burns

A patient with a 70% hydrofluoric acid burn developed systemic dissemination of fluoride ion from a 9% to 10% body surface area exposure on the lower extremities. Severe hypocalcemia and intractable ventricular arrhythmias resulted. This case is the second documented occurrence of hypocalcemia from hydrofluoric acid burns. It is the first case to document myocardial injury and systemic fluorosis from a skin burn.