Abstract: A cavity band was formed in crystalline silicon by implanting of 1×10¹⁷/cm² He⁺ at an energy of 35 keV. 1×10¹⁷/cm² O⁺ ions were subsequently implanted beneath the cavity band. The He-O ions co-implanted silicon was studied using RBS/C, SRP and XTEM. The results indicate that the cavities have strong gettering effect to oxygen. After a 1000⁰C annealing, the implanted oxygen released from their original position and diffused to the cavity band, forming a nanocavity-contained oxide layer. The precipitation of oxide on the cavity walls restricts the diffusion and coalescence of the cavities. A new SIMOX structure which contains an oxidized porous layer may be formed basing on these phenomena.