Three-dimensional scanning of ion-implanted porous silicon

As it was recently shown, the porosity of porous Si gradually decreases und er ion implantation, until the sample completely transforms into a compact material. To determine the underlying elementary process, we measured the d egree of densification along the ion track. Different types of porous Si la yers were implanted from the side of the samples parallel to the surface by 4.0 MeV He-4(+) ions. The implanted lateral spots were scanned three-dimen sionally by Rutherford backscattering spectrometry (RBS) microprobe using 2 MeV He-4(+) ions. Results obtained for columnar and spongy type porous Si samples clearly indicate that the densification occurs most intensively in a narrow depth region around the penetration depth of the ions, i.e., it is mainly caused by ion cascades. Based on this phenomenon, production of dee ply buried narrow compact layers in porous materials seems to be accessible . (C) 1999 Elsevier Science B.V. All rights reserved.