ELASTIC AND VISCOELASTIC ANALYSIS OF STRESS IN THIN-FILMS

The occurrence of stress in thin films has led to serious considerations of stability problems in the semiconductor industry. It may cause mechanical failure of films, such as adhesion reduction or contact peel-off, or variations in electrical properties. The existence of stress will also alter electromigration behavior for thin metal lines. The elastic stress in a multilayered structure due to thermal processing is calculated by use of the principle of mechanics balance. It is found that the variation of thickness in one film will not affect the magnitude of stress in another film. The shearing and peeling stress at the edge of a patterned structure, which is responsible for the peeling of a film at the edge, is then modeled and discussed in detail. Finally, the relaxation of stress by viscous motion of SiO2 is analyzed based on Maxwell's viscoelastic model.