Abstract: Sidewalls in a pattern of a refractory metal on a substrate are passivated during plasma etching by introducing water vapor into the etching chamber. This process obtains nearly vertical sidewalls. In one exemplified embodiment, a pattern of tungsten on a chromium etch step layer was reactive ion etched. In that embodiment, the reactive ion etching was intermittently paused. After each pause, the workpiece was warmed from below about 20.degree. C. to about room temperature. Then, water vapor was introduced into the etching chamber housing the workpiece. After the water vapor was introduced, the workpiece was cooled to below about 20.degree. C. and reactive ion etching was resumed. Alternatively, water vapor can be introduced into the etching chamber continuously during plasma etching.