HILLOCKS ON HALF-MICRON ALUMINUM LINES

A new regime of hillock growth has been observed in patterned Al98.5wt.%Si1.0wt.%Cu0.5wt.% films. The "surface" hillock and "side" hillock, which have been seen previously, form on patterned metal lines having linewidths greater than the larger Al alloy grain sizes (approximately 3-mu-m). None is seen on the fabricated lines having linewidths between 0.9 and 2-mu-m where long-range grain boundary diffusion cannot occur because of its bamboo structure. However, a new type of hillock, the "line hillock", occurs in structures having linewidths of 0.6-mu-m. The presence of this last type of hillock is inconsistent with the current understanding of hillock formation and may present severe restrictions on the down-sizing of ultra-large-scale integrated devices.