Relationship between hardness and grain size in electrodeposited copper films

Copper films were electrodeposited under various conditions and the relationship between the hardness and grain size of the films was investigated. The Vickers hardness depended on the processing conditions. This is because the processing conditions affected the grain size. In particular, nanocrystalline Cu film with a grain size of 31 nm was obtained by optimizing the electrodeposition conditions. The hardness of the nanocrystalline film deviated from the Hall–Petch relationship because the grain size dependence of hardness is smaller for the grain sizes of <100 nm than those of >100 nm. Also, the constants Hv0 and kHv in the Hall–Petch relationship for films processed with thiourea were different from those for films processed with gelatin. The differences may not be related to texture but to superabundant vacancies generated in the process of electrodeposition.