The events associated with fractures along interfaces between copper thin films and glass substrates were investigated by X-ray diffraction and transmission electron microscopy (TEM). In the as-bonded films the Bragg diffraction lines were shifted and broadened (relative to pure strain-free copper) due to residual in-plane tensile strains arising from the differences in thermal contraction between the copper and the substrates; TEM studies of these films in cross-section showed that the residual stresses had been relieved somewhat by dislocation densities as high as 1010 lines/cm2 in Cu/SiO2 films.

The passage of a crack along the Cu/glass interfaces led to a significant reduction in the line shift and a slight reduction in the line broadening. Thus dislocations generated by the fracture events ‘plastically relaxed’ the residual stresses present in the as-bonded Cu by superposing a compressive component onto the pre-existing in-plane tensile strains. This dislocation generation was confirmed by TEM studies. In addition, it was found that the greater the strength of an interface, the greater was the reduction in mean strain due to the fracture; this is consistent with a larger crack-tip plastic zone and the generation of greater numbers of dislocations in the Cu films by fracture along interfaces of higher toughness (i.e. bond strength).