Focused ion beam process for removal of copper

Focused ion beam technology (FIB) utilizes an apparatus that focuses an ion beam from an ion source through a lens and irradiates the beam onto a sample. In the fabrication of integrated circuits, FIB is frequently used to mill away (etch) material by irradiating an ion beam of relatively high current onto the substrate. The focused ion beam can be directed to a very small point on a semiconductor device and then scanned, raster fashion, over a surface where material is to be removed. As an ion impinges on the semiconductor device surface, its momentum is transferred, resulting in the removal of one or more surface atoms according to a process called sputtering. By selecting a raster pattern of a given overall shape, for example a horizontal raster pattern, a correspondingly shaped area of surface material can be removed. Often several successive layers of a semiconductor device are removed in a given area in order to reach and possibly sever an underlying layer. A process for milling copper metal from a substrate having an exposed copper surface includes absorbing a halogen gas onto the exposed copper surface to generate reaction products of copper and the halogen gas; removing unreacted halogen gas from the surface; and directing a focused ion beam onto the surface to selectively remove a portion of the surface comprising the reaction products.