Abstract: In this invention is described a process for controlling the etching of side wall spacers to a prescribed width. A gaseous mixture of an inert gas, CF.sub.4 and CHF.sub.3 in a prescribed ratio, under pressure and with a plasma is flowed within a RIE chamber. A magnetic field in parallel with the surface of the wafer being etched is used to control the oxide/silicon selectivity. The shape and width of the side wall spacers are controlled by controlling the selectivity. Uniformity of the shape of side wall spacers over the surface of a wafer is also produced by the magnetic field which induces a higher etch rate at the edge of the wafer where the oxide coating is the thickest.