Abstract: A particle beam etching system and method are disclosed in which ion and substantially ion-free chemical radical beams are generated separately and directed onto the same portion of a semiconductor wafer to be etched, preferably perpendicular to the wafer. The beam diameters are substantially smaller than the etching area, and the wafer is moved in an x,y plane to expose the entire etching area to the beams. The redical beam is preferably supersonic, with a flux in the approximate range of 10.sup.19 -10.sup.21 particles per steradian per second, while the ion beam preferably has a density of approximately 10.sup.14 ions per cm.sup.2 per second. The progress of the etching and the location of etching end points are continuously monitored and used to control the etching rate and wafer movement, yielding etching that is both anisotropic and selective, with an accurate and uniform etch depth.