ACTIVATION-ENERGY FOR OSTWALD RIPENING OF AL2CU IN AL(4 WT-PERCENT CU) THIN-FILMS USING A LATERAL DIFFUSION COUPLE

The activation energy E(a) for Ostwald ripening (coarsening) of Al2Cu(THETA phase) precipitates in Al(4 wt. % Cu) thin films was determined using a lateral diffusion couple. A 1 mum thick Al(4 wt. % Cu) blanket film was deposited on lines Of Al2Cu embedded in SiO2. With annealing at temperatures between 400 and 450-degrees-C (1.4-2.5 wt. % Cu in solution) for 1 to 80 h, THETA precipitates were dissolved in regions between 10 and 110 mum wide parallel to the Al2Cu lines. The width of this region increased as the square root of the annealing time. The E(a) was determined to be 2.5+/-0.5 eV from an Arrhenius plot. This value is much larger than both the activation energies for Cu lattice and grain-boundary diffusion in Al. Understanding the coarsening kinetics of Al2Cu is important since the reliability of Al(Cu) metallizations is strongly dependent on the microstructure.