Silicon surface contamination and near‐surface damage of the Si(100) substrate caused by reactive ion etching (RIE) of overlayer in plasma were characterized by x‐ray photoelectron spectroscopy (XPS), He‐ion channeling technique and high‐resolution transmission electron microscopy (HRTEM). XPS study indicates that a thin (<20Å thick) C,F polymeric layer was formed on the Si surface and underneath the polymer film a thin oxide layer (∼10Å) was produced due to air exposure after RIE. These films were also characterized in terms of chemical composition and bonding states. The C,F film displays six bonding states of carbon, i.e., , , , , C‒C/C‒H, and C‒Si. The variations of etchant gas composition and overetching time represent that the content of fluorine in residue film increase with increasing gas fraction and overetching time. The formation of residue film on surface were also investigated. The residue deposited on surface is thinner and contains less concentration of fluorine than the residue on Si surface. He ion scattering/channeling spectrum and cross‐sectional high resolution transmission electron micrograph showed that the damaged layer contains displaced Si of about , and about 25Å thick amorphous layer is present on the crystalline silicon substrate. In the micrograph of the 2 min overetched sample, point defect clusters or small isolated amorphized region and distorted lattice spacing were found in the near surface region of silicon within 200Å depth.