Channeling effects during focused-ion-beam micromachining of copper

The rapid introduction of copper metallization for semiconductor devices ha s prompted increased research into focused-ion-beam micromachining of coppe r. Studies with the aim of increasing the material removal rate of Cu by fo cused-ion-beam micromachining have been complicated by variable micromachin ing behavior apparently resulting from differing Cu film morphologies produ ced by the various Cu deposition procedures. This work examined the microma chining behavior of thin copper films produced by physical-vapor deposition (PVD) and electroplating, as well as single-crystal copper samples. PVD co pper films were found to be preferentially textured along (111), with a col umnar grain structure. Channeling effects within this type of grain structu re provide a geometric enhancement of the material removal rate of 30% when the sample normal is tilted 12 degrees from the incident ion beam, regardl ess of sample rotation. Single-crystal (111) copper was found to exhibit si milar material removal rate enhancement (averaged over 360 degrees rotation ) when tilted 12 degrees, verifying that the etching enhancement observed i n the PVD films is directly related to their (111) texture. Compared to the PVD film, electroplated (EP) copper thin films contained a significantly m ore random grain orientation. Consequently, the EP films did not exhibit an y appreciable variation in material removal rate beyond the expected cosine dependence when tilted with respect to the incident Ga+ beam normal. Micro machining of the electroplated films, which have larger randomly oriented g rains, results in grain decoration due to preferential etching producing se vere micromachining-induced topography. (C) 2000 American Vacuum Society. [ S0734-2101(00)15904-4].