Etching Properties of DC Sputtered Al Thin Films in Silicon Micromachining

Surface morphology and etch rates of DC magnetron sputtered aluminum films on (100) Si were investigated in the scope of substrate preheat temperature and thermal annealing of Al thin film. Hillock formation in the Al film was found to be strongly dependent on the preheat temperature in the range of 100deg-300degC and less on the annealing temperature. Hillock size and density were significantly increased when aluminum was sputtered on silicon dioxide layer. Sputtered Al films were used as the etch mask for micromachining of (100) silicon and were studied as a function of etch temperature, time and the addition of ammonium peroxodisulfate (AP) into the anisotropic etchant consisting of 5%TMAH-water+1.5% dissolved silicon. The aluminium mask exhibited excellent etch selectivity, comparable to the silicon dioxide or silicon nitride etch mask