Kinetics of Al grain growth, Al2Cu precipitation, and dissolution in blanket thin films and fine lines

Abstract

The apparent activation energy Ea for Al grain growth, Al2Cu (Θ-phase) precipitation, and Al2Cu dissolution were determined by ramped resistance measurements for both Al(Cu) blanket films and patterned lines. The Ea’s measured for the initial stages of grain growth in 0.5-, 1-, and 2-μm-thick Al(4 wt % Cu), Al(2 wt % Cu), and Al films ranged from 1.19 to 1.46 eV. The Ea’s for grain growth were higher for 0.6–0.9-μm-wide Al(Cu) lines than for blanket Al(Cu) films 1.89–3.1 eV, and the temperature of the peak transformation rate occurred at a much higher temperature, 310–400 vs 90–155 °C. This is due to the geometric constraints in patterned lines. The Ea’s for Al2Cu precipitation in Al(4 wt % Cu) and Al(2 wt % Cu) films varied from 0.86 to 1.25 eV. For 0.6-μm-wide Al(4 wt % Cu) lines, the Ea for Al2Cu precipitation was 1.7 eV. The Ea’s for Al2Cu dissolution increased with decreasing Cu content from 1.62–1.74 eV to 2.23–2.30 eV with Al(4 wt % Cu) and Al(2 wt % Cu) films, respectively. The temperature of the peak reaction rate Tp for Al2Cu dissolution increased markedly with increasing film thickness at constant ramp rates. These results demonstrate that the microstructure and Cu distribution in Al(Cu) interconnections on microelectronic chips vary as a function of feature size. This implies that blanket film data is not necessarily applicable to patterned features.