Relationship Between Structure and Electromigration Characteristics of Pure Aluminum Films

Aluminum films were deposited from a high purity aluminum source by the self-ion assisted technique onto oxidized silicon wafers with TiN sub-layers. The ions were accelerated toward the substrate by potentials of 0, 3 and 6 kV. The films were patterned into strips 670 μm long and 8 μm wide using photo-lithographic procedures and wet etching. Average drift velocities were measured in the films tested under electromigration conditions. Electromigration activation energy was obtained for the films. It was found that electromigration activation energy increased with the acceleration potential. The strength of the (111) fiber texture, however, decreased with the acceleration potential. Therefore, the weaker textures resulted in higher electromigration activation energies. These results can be explained in terms of grain boundary structure, which controls electromigration behavior. By using orientation imaging microscopy to characterize the structures, it was shown that the weaker textured specimens contained a high fraction of low angle and low diffusivity grain boundaries.

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