A method for fabrication of microscopic structures that uses a beam process, such as beam-induced decomposition of a precursor, to deposit a mask in a precise pattern and then a selective, plasma beam is applied, comprising the steps of first creating a protective mask upon surface portions of a substrate using a beam process such as an electron beam, focused ion beam (FIB), or laser process, and secondly etching unmasked substrate portions using a selective plasma beam etch process. Optionally, a third step comprising the removal of the protective mask may be performed with a second, materially oppositely selective plasma beam process.