| Al fine lines in VLSI circuits are under a hydrostatic tension stress state and fail by a phenomenon called stress-induced-voiding. Diffusional controlled void growth mechanisms of stress-induced-voiding have been reported, but are difficult to accept because they predict slow void growth. The classical creep theory suggests an alternative mechanism: void growth controlled by power-law creep. To study the controlling void growth mechanism of metals under hydrostatic tension stresses, delayed fracture tests for steel-silver brazed joints were conducted because the stress state of the silver layer is similar to that of Al lines in ICs. Two brazing methods were used to prepare the specimens: vacuum and hydrogen brazing. Although there was a large variation in the strength of the brazed joint for both brazing processes, four of 15 specimens tested showed t{dollar}rmsb{lcub}f{rcub} >{dollar} 10 hours. The t{dollar}rmsb{lcub}f{rcub}{dollar} versus stress plot suggests that the void growth is controlled by power-law creep, or precisely, by power-law break-down. By examining the fractography of the specimens, the grain boundaries of the silver layer were parted during the delayed fracture tests. The suspected fracture mechanism is as follows: dislocations glide to the grain boundaries, then pile-up and creep, so voids grow at the grain boundaries until fracture occurs. This mechanism may be operative in stress-induced-voiding of Al lines in ICs. |
