Micro-morphology of single crystalline silicon surfaces during anisotropic wet chemical etching in KOH: velocity source forests

Abstract

For silicon etched in KOH the micro-morphology of any surface, no matter the crystallographic orientation, is defined by some sort of persistent corrugations. As a matter of principle, the occurrence of these corrugations is incompatible with the classical kinematic wave theory for the evolution of crystal shapes. Either the re-entrant or the protruding edges or vertices are stabilized by some mechanism that is not accounted for in the microscopic etch rate function, i.e. are velocity sources. Exact Si{1 1 1} surfaces are dominated by etch pits caused by edge dislocations corresponding to oxygen-induced stacking faults. Exact Si{1 0 0} surfaces are dominated by circular indentations, probably owing to fast etching of accumulations of point defects. On exact and vicinal Si{1 0 0}, also pyramidal protrusions are found, which, we hypothesize, are formed and stabilized by silicate particles adhering to the surface. Exact and vicinal Si{1 1 0} surfaces are dominated by a zigzag pattern at low KOH concentration and a hillock pattern at high KOH concentration, which, we hypothesize, are also the result of the presence of silicate particles, created during etching, on the surface. Vicinal Si{1 0 0} and Si{1 1 1} surfaces, finally, are dominated by step bunching patterns, probably owing to time-dependent impurity adsorption.