Investigation of Polyimide Residue Due to Reactive Ion Etching in O 2

Cured silicone modified polyimide (PI) on packaged dice and blanket wafers were dry etched in a ambient under varying conditions in both a production reactive ion etching (RIE) tool in an integrated circuit (IC) clean room environment and in a desktop RIE tool in a laboratory environment. It has been consistently found that a thin residual grass‐like film remains on the die surface of silicone modified PI samples following RIE exposure. Scanning electron microscopy (SEM) imaging of the residual film indicates a grass‐like structure of varying density. The film density is found to be dependent on tool power and exposure time. Nonsilicone modified blanket PI film, RIE etched under similar conditions in the laboratory tool, results in clean surfaces except in the perimeter regions of the die. The production tool produces efficient PI removal leaving clean die surfaces for both silicone modified and unmodified PI films under all RIE setting conditions evaluated. X‐ray photoelectron spectroscopy (XPS) or electron spectroscopy for chemical analysis (ESCA) analysis of the die surfaces suggest the residual polyimide is due to the silicon content of the modified polyimide. Low level metal contamination, also detected on the die surfaces following the RIE exposure, is most likely due to sputtering from the bond wire and die attached platform in the case of packaged samples and from the aluminum chuck in the case of blanket samples. The environment appears to be a possible secondary source for the residual grass film.