Grain growth in Al-(Cu, Pd, Nb) thin films

The microstructure of 1 µm thick Al films containing 0.5 and 2%Cu (weight percent), 0.3%Pd, and 0.3%Pd-0.3%Nb were investigated by transmission electron microscopy (TEM) and energy dispersive x-ray spectroscopy (EDS) as a function of isochronal and isothermal anneals. The grain size, grain size distribution, and precipitate morphology of these films was measured from 200 to 500°C, with the activation energy for grain growth (Ea) determined for 1 h anneals at 200, 300, 400 and 500 °C. Normal grain growth was recorded for the AlCu films annealed at temperatures ≤400°C; however secondary grain growth occurred in the Al-2Cu film annealed for 1 h at 500°C, with grains as large as 16 µm in diameter observed. Grain growth in the Al-0.3Pd films resulted in strongly bi-modal grain size distributions, with the onset of significant grain growth retarded for 1 h anneals at temperatures ≤300°C. The addition of Nb to the Al-0.3Pd film resulted in monomodal grain size distributions over the entire temperature range. The role of crystallographic texture on grain growth in thin films is discussed.