IN-SITU TRANSMISSION ELECTRON-MICROSCOPY STUDY OF PLASTIC-DEFORMATIONAND STRESS-INDUCED VOIDING IN AL-CU INTERCONNECTS

Plastic deformation in submicron wide Al-1 wt %Cu interconnects was st udied in situ using a straining device in the transmission electron mi croscope, Dislocation motion occurred readily in unpassivated lines bu t was nonexistent in passivated lines due to the presence of stiff oxi de sidewalls. Instead heterogeneous void nucleation occurred on strain ing to a critical limit. The void morphology was always near hemispher ical and the nucleation always took place at the line edges. Further s tretching of the lines led to a rupture of the sidewalls away from the lines, resulting in immediate dislocation motion. Void nucleation, cr oss slip, and operation of dislocation sources at line edges were all recorded on video. It was noted that dislocations almost parallel to t he plane of the lines are rarely observed and furthermore, their movem ent is sluggish. Based on the dislocation configuration observed in th ese lines, a generalized geometrical model was arrived at in order to determine the significance of grain orientation on yield stress of pas sivated lines with columnar, bamboo grains. Frequent occurrence of twi nning within the grains indicated that plastic deformation was indeed restricted in confined metal lines. (C) 1997 American Institute of Phy sics.