A method for forming fine grooves including forming a first silicon-nitride layer on a substrate, forming a first poly-silicon layer on the first silicon-nitride layer, forming a second silicon-nitride layer on the first poly-silicon layer, patterning the second silicon-nitride layer, etching the first poly-silicon layer using the patterned second silicon-nitride layer as a mask, forming at least one patterned oxidized portion of the first poly-silicon layer by oxidizing the substrate, first silicon-nitride layer, etched first poly-silicon layer, and patterned second silicon-nitride layer, removing the patterned second silicon-nitride layer and etched first poly-silicon layer such that the first silicon-nitride layer and at least one patterned oxidized portion of the first poly-silicon layer remain on the substrate, and forming a plurality of fine grooves over the substrate by plasma etching the first silicon-nitride layer using the at least one patterned oxidized portion of the first poly-silicon layer as a mask.