Improvement in smoothness of anisotropically etched silicon surfaces: Effects of surfactant and TMAH concentrations

We investigated the anisotropic etching properties of single-crystal silicon using tetramethyl-ammonium-hydroxide (TMAH) water solutions containing poly-oxethylene-alkyl-phenyl-ether (NC-200) as a surfactant. When the surfactant was added at 0.1% of the total volume of the etchant, the etched surface morphologies drastically changed, along with the anisotropy of the etching rate. We found that by using the surfactant at the low TMAH concentration region, a smooth mirror-like surface can be etched in both (1 0 0) and (1 1 0) orientations simultaneously. Although the addition of the surfactant reduces the etching rate, we show how this procedure can be used to improve the roughness of an etched surface without significantly increasing the overall processing time.