Ag-Assisted Chemical Etching of (100) and (111) n-Type Silicon Substrates by Varying the Amount of Deposited Metal

A systematic study of silver-catalyzed etching in (100) and (111) n-type Silicon substrates is carried out by varying the amount and the morphology of electroless deposited silver clusters. Deposition rate is very fast during the first few seconds and then it levels at a lower value of one order magnitude for both oriented wafers. For small and well separated clusters the Si nanowires formed by the etching are aligned along the (100) axes, while for large and interconnected they are oriented along the normal to the surface. For the (100) Si substrate partially covered with small silver clusters the etching proceeds both in vertical and horizontal [100] directions. For larger coverage (70%) the Ag nanoparticles sink all together along the vertical direction. For the (111) Si substrate, when the Ag nanoparticles are isolated they sink in all the equivalent [100] directions with an irregular path; when the Ag nanoparticles begin to coalesce uniform domains of Si nanowires aligned along [100] directions are formed. When the silver clusters are well interconnected (70% of coverage), the etching is vertical. Silver coverage is then another experimental parameter to induce a preferred orientation of the etched Si nanowires.