THERMAL CYCLING FATIGUE AND DEFORMATION MECHANISM IN ALUMINUM-ALLOY THIN-FILMS ON SILICON

Thermal cycling was performed between room temperature and 723 K in a sputter deposited thin film of Al-l mol % Si alloy on a silicon substr ate. After given numbers of cycling, residual stress was determined at room temperature by measuring the film curvature using a laser deflec tion apparatus. Residual stress was found to increase with increasing the cycle number up to the 4th cycle, followed by a continuous decreas e by further cycling. Based on the microstructure observation, the ini tial increase of residual stress was caused by the increase of lattice dislocations and their tangling. The following decrease of residual s tress was caused by crack formation and delamination. Stress relaxatio n experiments were also performed during isothermal annealing at vario us temperatures. Analysis of the relaxation curves indicates three tem perature regions representing different deformation mechanisms. The bo undaries between the neighboring regions were found to agree with the boundaries in a deformation mechanism map calculated for an Al thin fi lm. Based on the obtained knowledge of the deformation mechanisms, the origin of the microstructure changes and the structural failure by th ermal cycling are discussed.