This article describes the evaluation of post-etch residue removal after descumming BCB (Benzocyclobutene). BCB is widely used in the electronics industry due to its low tangent loss at the high frequency (tan d = 10(-3) at 10 GHz). The BCB film is descummed by brief exposure to plasma after curing. The descumming process is necessary to remove the residue that remains after the developing process. O-2/CF4, in which the ratio of O-2 to CF4 is 80:20, has been used as etching gas. It is critical to have the low contact resistance between BCB and Cu in the BCB/Cu interconnecting structure. We have tried a few chemicals to make the surface clean for the low contact resistance and found that the EKC chemical is very effective to clean via surface. (C) 2003 Elsevier Science B.V. All rights reserved.