Methods and devices for selective etching in a semiconductor process are shown. Chemical species generated in a reaction chamber provide both a selective etching function and concurrently form a protective coating on other regions. An electron beam provides activation to selective chemical species. In one example, reactive species are generated from a plasma source to provide an increased reactive species density. Addition of other gasses to the system can provide functions such as controlling a chemistry in a protective layer during a processing operation. In one example an electron beam array such as a carbon nanotube array is used to selectively expose a surface during a processing operation.