Surface morphology during anisotropic wet chemical etching of crystallinesilicon

Abstract

The rich variety of micron-scale features observed in the orientation-dependentsurface morphology of crystalline silicon during anisotropic wet chemical etching isshown to have its origin at the atomistic scale. Realistic Monte Carlo simulationsshow that the pyramidal hillocks on Si(100) are the result of local stabilization ofdistributed apex atoms by (metal) impurities from solution. In the absence of thisstabilization, shallow round pits are formed on Si(100) as a result of theanisotropy between (one layer deep) pit nucleation and (isotropic) steppropagation. It is also concluded that nosed zigzag structures at vicinal (110) arethe combined result of misaligment and the etching anisotropy, showing thatthe nucleating mechanisms of morphologically related structures such aspyramidal hillocks and nosed zigzags are not necessarily the same. Thesimulations confirm that the formation of (one layer deep) triangularand hexagonal pits on exact Si(111) and of polygonal (saw-shaped) andstraight terraces in vicinal Si(111) depends on the relative rate of [12̄1] and [1̄21̄]step propagation and on the misorientation of the surface with respect to Si(111).