A focused ion beam of gallium was used to implant into the top layer of a bi-layer structure on a silicon wafer. The structures studied were spin-on glass/organic and electron beam deposited Si/organic. Plasma etch conditions were found which gave substantial etch rate differences between the implanted and non-implanted material. The material was then patterned by dry processing methods. The plasma etch produces a vertical wall 2.0 µm high with a rectangular profile free of debris. The variation in line width along the line is a small fraction of the line width. Or, the line width is constant along the line and is approximately equal to 0.4µm, the spot size of the focused ion beam on the wafer. The variation in line width as a function of implantation dose was determined and shown capable of yielding a reproducible line width. The results are shown to be superior to single resist exposure. Potential applications are presented.