Microscopic mechanism of the hydrogen effect on the ductility of electroless copper

Abstract

Electroless copper deposition processes are governed by the, simultaneous reduction of copper and hydrogen. Therefore, the probability of incorporating atomic and/or molecular hydrogen into the deposits is high, making electroless copper more liable to high porosity and low ductility than electrolytic copper. Microscopic mechanism for hydrogen-related embrittlement in electroless copper deposits are discussed in detail here. Examinations of the microstructures using scanning and transmission electron microscopes revealed that small (20–300 Å) gas bubbles are incorporated uniformly throughout the films, whereas large (~ 2000 Å) bubbles are trapped at the grain boundaries. The latter bubbles were found to be the major determinant of the film ductility, while the small bubbles are believed to contribute to the hardening of the deposits. Low-temperature (150°C) post-annealing treatment, accompanied by the out-diffusion of hydrogen, improved the part of the ductility for which hydrogen embrittlement is responsible by the pressure effect. A theoretical model describing ductile fracture by the coalescence of voids was found to explain quantitatively an experimental trend for the ductility change with void volume fraction.