Intrinsic Stress in Evaporated Metal Films

Abstract

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.

Tetherless thermobiochemically actuated microgrippers

“…For a given joint length and width composed of elastically isotropic thin films, the product of residual stress and thickness of each film dictated the final flex angle of the joint. Using a KLA-Tencor Flexus FLP2904 wafer curvature thin film stress device, we first determined that 50-nm films of Cr evaporated by our equipment (thickness measured by using a quartz crystal microbalance integrated within the evaporator) directly onto silicon wafers had residual stresses of Ϸ1 GPa and that 200-250 nm of Cu had tensile residual stresses of Ϸ0.04-0.08 GPa, respectively; these values are consistent with those reported in literature (17). Taking the literature values for elastic moduli of Cr and Cu films to be 144 GPa (30) and 130 GPa (31), the model (details in SI Text) predicted a bend angle of 95°-70°for a Cr/Cu bilayer (with no polymer) composed of a range of Cu thicknesses between 200 and 250 nm, respectively (Fig.…”

“…We fabricated a stressed Cr thin film by thermal evaporation (15)(16)(17)(18) and subsequently evaporated a minimally stressed Cu film to form the bilayer. The flexing of the bimetallic joints (to close the gripper) was driven by the release of residual tensile stress within the Cr thin film, and similar bending behavior of stressed thin films has been previously observed (8,(19)(20)(21)(22)(23)(24).…”

Ion beam sputter deposited zinc telluride films

“…While more data is needed to confirm this, other work (Ref. 19) on a large number of materials has shown…”

Three-Dimensional Simulation of Intrinsic Stress Build-Up in Thin Films

“…Generally such rearrangements result in the shrinkage of the film. While the film is attached to the substrate a tensile stress develops [8].…”