trenches having different profiles are formed in a material , such as a semiconductor substrate , by forming a resist pattern having windows with at least two different widths . an etchant , such as fluorine , is implanted into portions of the semiconductor using an ion implantation technique . a tilt angle and an azimuth angle of the ion beam are chosen such that the fluorine ions cannot pass through narrower resist windows but can pass through wider resist windows to impinge on the underlying semiconductor substrate . the semiconductor substrate is then subjected to an anisotropic etching process . accordingly , the substrate regions exposed between the narrow - width resist windows are etched to produce trenches having highly vertical profiles . the substrate regions exposed by the wide - width resist windows , including the regions having implanted etchant ions , are preferentially etched to produce trenches having tapered profiles .