Grazing irradiation of porous silicon by 500 keV He ions

Different types of porous Si layers of several mu m thickness were irradiated at a glancing angle of 86 degrees by 500 keV He ions. Due to the bombardment, a surface layer corresponding to a thickness equivalent to similar to 0.12 mu m in compact Si underwent strong modifications. These processes were studied by thermal nitridation of irradiated and non-irradiated samples in N-15 ambient followed by depth profiling of the N-15 content by means of the N-15(p,alpha gamma)C-12 reaction. After irradiation with different fluences up to 48 mC/cm(2), the irradiated layer of the spongy type samples of 60, 68, and 78% porosity completely densified, preventing the penetration of the N. In columnar samples of 59, 77 and 88% porosity the N penetration remains high even for the highest irradiation dose. Results extracted from the measured N profiles of both columnar and spongy structures will be discussed. (C) 1998 Elsevier Science Ltd. All rights reserved.