X-RAY-DIFFRACTION INVESTIGATION OF THE ANODIC-OXIDATION OF POROUS SILICON

A systematic study of porous silicon anodic oxidation is reported. We have studied the evolution of the lattice parameter versus oxidation l evels for p- and p(+)-type materials by using high-resolution x-ray di ffraction, which gives a determination of the strains of the porous la yer. The analysis of an asymmetric reflection enables us to measure th e lattice parameter parallel to the surface. Moreover a diffuse scatte ring, observed at the bottom of the Bragg peaks, comes from the porous structure. The study of this diffuse scattering with reciprocal space maps gives information about the pore size and shape. It is shown tha t the evolution of the lattice mismatch parameter is related to the su rface stress variations. After a review of previous works on porous si licon strains and on surface stresses of silicon we discuss the origin of the strains of as-formed and oxidized porous silicon. (C) 1996 Ame rican Institute of Physics.