Intrinsic Stress in Evaporated Metal Films

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The sign and magnitude of the intrinsic stresses observed in evaporated metal films cannot be predicted from a priori knowledge. In an effort to correlate the observed intrinsic stress, S, with other physical parameters, S has been measured in films of fifteen different metals. The stress was measured in situ by the cantilevered substrate technique. The films were evaporated from an electron bombarded source in vacuums of 10−6 to 10−7 Torr onto glass substrates at room temperature. Under these conditions the intrinsic stress was generally found to be tensile, though exceptions were observed. The data obtained indicate that films of metals with higher melting temperatures and larger shear moduli have intrinsic stresses which approach a magnitude roughly equal to 0.01 of the shear modulus. It is suggested that such high values of stresses are generated by the annealing and constrained shrinkage of disordered material buried behind the advancing surface of the growing films. Reduction of the stress is predicted when surface rearrangements preempt the need for extensive subsequent internal annealing. This proposal is considered in the relation to the experimental observation that the intrinsic stress is small when the ratio of the (absolute) substrate and melting temperatures exceeds 1/4.