OBSERVATION OF SILICON ETCH PIT FORMATION IN QUIESCENT CONCENTRATED AQUEOUS HF SOLUTIONS

A new type of etch pit has been found in p-type Czochralski-grown crys talline silicon after long-time immersion in quiescent concentrated aq ueous HF solutions. These etch pits of 80-300 mum diameter, which may be characterized by a center hillock surrounded by porous material, sh ow the four-fold and three-fold symmetry of [100] and [111] oriented s ilicon, respectively. A formation mechanism is proposed, based on the presence of local p-n junctions due to oxygen related (thermal) donor formation. Ambient illumination is suggested to drive the electrochemi cal (anodic) dissolution process.