Combining X-Ray Diffraction and Substrate Deflection Analysis to Understand Internal Stress in Electroless Copper Films

Abstract

ABSTRACTElectroless copper films are usually the first conducting layer on the insulating substrates of printed circuit boards. For this and other emerging applications, the internal stress of the copper layer is an important consideration both for film adhesion and film-substrate interaction. We have combined stress/strain analysis based on X-ray diffraction, which is sensitive to the strain of the copper crystallites, with a conventionally used technique that analyses the bending of the substrate (Deposit Stress Analyzer). Both techniques were implemented in such a way that the stress could be monitored continuously during the deposition of the films from the electroless plating bath as well as afterwards. These tests were carried out for three chemical formulations and the results from both techniques agree qualitatively. For one bath, the substrate bending method detects a 60 nm region of local stress at the film-surface interface.