The dynamic competition between stress generation and relaxation mechanisms during coalescence of Volmer-Weber thin films

Real-time measurements of stress evolution during the deposition of Volmer- Weber thin films reveal a complex interplay between mechanisms for stress g eneration and stress relaxation. We observed a generic stress evolution fro m compressive to tensile, then back to compressive stress as the film thick ened, in amorphous and polycrystalline Ge and Si, as well as in polycrystal line Ag, Al, and Ti. Direct measurements of stress relaxation during growth interrupts demonstrate that the generic behavior occurs even in the absenc e of stress relaxation. When relaxation did occur, the mechanism depended s ensitively on whether the film was continuous or discontinuous, on the proc ess conditions, and on the film/substrate interfacial strength. For Ag film s, interfacial shear dominated the early relaxation behavior, whereas this mechanism was negligible in Al films due to the much stronger bonding at th e Al/SiO2 interface. For amorphous Ge, selective relaxation of tensile stre ss was observed only at elevated temperatures, consistent with surface-diff usion-based mechanisms. In all the films studied here, stress relaxation wa s suppressed after the films became continuous. (C) 2001 American Institute of Physics.