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.