Strain-Induced Grain Growth during Rapid Thermal Cycling of Aluminum Interconnects
Robert R. Keller, Roy H. Geiss, Nicholas Barbosa, Andrew J. Slifka, David T. Read
We demonstrate by use of automated electron backscatter diffraction (EBSD) the rapid growth of grains in non-passivated, sputtered Al-1Si interconnects during 200 Hz thermal cycling induced by alternating electric current. Mean grain diameters were observed to increase by more than 70 % after an accumulated cycling time of less than six minutes over a temperature range of 200 degrees C, which corresponded to a total strain range of 4 x 10-3. Plasticity in growing grains primarily took the form of topography formation at the free surface and grain rotation, while consumed grains tended to retain relatively high dislocation content. Grain growth was characterized by means of pairwise comparisons in EBSD pattern quality across moving boundaries. Out of 92 cases where a grain was observed to grow into its neighbor, 61 cases indicated that the growing grain had a higher average pattern quality factor than that of the consumed grain, at the 95 % confidence level. The results are consistent with a strain induced boundary migration mechanism, wherein stored plastic strain energy differences from grain to grain drive growth, some of which was observed after only 10 seconds of cycling.