Ion implantation of silicon at the nanometer scale

SiO2 layers (similar to 0.5 mu m thick) thermally grown on (100) Si were irradiated with 12.5 MeV Ti ions at 10(9) cm(-2) fluence, and subsequently exposed to the HF vapor, in order to selectively etch the latent tracks generated by the passage of swift ions. Nearly cylindrical nanoholes having diameters as small as 25 nm, with an average value of 54 +/- 5 nm, were generated by this procedure. The nanopatterned SiO2 layer served as a mask for selective amorphization of the underlying Si, achieved by implantation with 180 keV Ar+ ions at a fluence of 2.0x10(15) cm(-2). Dip in aqueous HF solution was then performed to selectively etch ion amorphized Si, thus transferring the nanometric pattern of the SiO2 mask to the underlying substrate. As expected, the maximum depth of amorphizazion in Si, and consequently of etching depth, decreases when the hole radius decreases below values of the order of the lateral ion straggling. The effect has been characterized and investigated by the comparison of experiments and three dimensional Monte Carlo simulations.