An analysis was made of the strain-hardening behaviour of thin metallic films on substrates. Stress measurements were performed on 0.5μ-thick Cu films, on Si substrates, during thermal cycling, during room-temperature stress relaxation and after quenching. Appreciable strengthening was observed during thermal cycling. A theoretical explanation of the strengthening was based upon Peach-Koehler dislocation-interaction forces. This showed that the addition of threading dislocations to a parallel array of dislocations at the film/substrate interface could contribute greatly to the strain-hardening of thin films. The calculated strain hardening accounted for a large fraction of the observed strengthening.

Dislocation Accumulation and Strengthening in Cu Thin Films. V.Weihnacht, W.Brückner: Acta Materialia, 2001, 49[13], 2365-72