Nano-structuring of silicon surface layers and nano-void formation by hydrogen plasma treatments

We summarize our recent results about nanostructuring of thin surface and sub-surface layers of Czochralski (Cz) silicon wafers by hydrogen plasma treatments. Standard Cz Si wafers were treated by a RF hydrogen plasma at about 250°C for 1 or 2 hours and subsequently annealed up to 2 hours at various temperatures up to 600°C in air. The surface/sub-surface Cz Si layers were studied by scanning electron microscopy (SEM), Raman spectroscopy and photoluminescence. On mechanically beveled samples by SEM the sub-surface wafer regions are investigated up to a depth of about 200 nm. Close to the surface, the treated wafers exhibit structures with the typical dimensions significantly below 100 nm. In deeper wafer regions, the structures become steadily larger (dimensions of a few 100 nm). By Raman spectroscopy, the samples were studied with regard to the formation of H ₂-molecules. The H₂-molecules are most probably located in sub-surface layers, but not directly at the surface, i.e. as nearly free H₂-molecules in nano-voids or platelets (Raman shift 4150 cm^-1). After annealing at 600°C in air, the nanostructured silicon exhibits a broad luminescence in the visible spectral range, which can be attributed to the evolution of the chemical structures and dimensions of Si based nano-clusters