An intermediate semiconductor structure in fabrication includes a silicon semiconductor substrate, a hard mask of silicon nitride (SiN) over the substrate and a sacrificial layer of polysilicon or amorphous silicon over the hard mask. The sacrificial layer is patterned into sidewall spacers, each of the sidewall spacers having vertically tapered inner and outer sidewalls providing a rough triangular shape. The rough triangular sidewall spacers are used as a temporary hard mask to pattern the SiN hard mask.