Surface roughness variation and microstructural evolution of Au thin films in rapid annealing by microwave and electric furnace heating

Microstructural evolution of Au thin film in post-annealing by microwave and by electric furnace heating was compared. Wave number spectra of film surface roughness were analyzed to characterize their roughness variation by annealing. Coarsening of film microstructure occurred consistently as the increase of the annealing temperature in both methods. Labyrinth-shaped morphologies consisting of bump-ridge crystals were formed by annealing, which might be originated from the fine-grained colonies existed in the as-deposited state. Through coalescence and growth of the grains within the colony, the bump-ridge crystals increased their height as the increase of annealing temperature. Eventually, microstructures and crystal morphologies became similar by both annealing methods above 800–850 °C. However, there are following differences observed in the low temperature annealing cases: 1. While a temporal variation of the film microstructure was observed in furnace annealing, microwave annealing exhibited smaller tendency of this feature. 2. Fine roughness (higher wave number range) of the films was reduced more in the temperature below 720 °C by microwave annealing than by furnace annealing. 3. Increase of bump-ridge height was pronounced more by microwave annealing between 600 and 800 °C, corresponding to the roughness increase in the lower wave number range. On the other hand, film coverage decreased. The reasons for the difference was discussed by consideration of the competition among the capillary driven surface diffusion, contribution of electro-migration and the thermodynamic equilibrium shapes of the film grain structures.