Microstructural changes in confined submicrometer aluminum films

Abstract

The stress effect on microstructure evolution in submicrometer Al dots in confinement has been studied by transmission electron microscopy. Direct observation of grain growth and void formation in the dots, unconfined as well as confined by sputtered quartz, was investigated. In the as-deposited state, most of the grains were larger than the film thickness of 300 Å, indicating that the grains have grown during the Al deposition and/or the quartz deposition. Voids were only found in the confined samples. Grain growth was retarded in the confined samples upon a stepwise annealing from room temperature to 400°C, yet secondary grain growth occurred at temperatures above 500°C. For the unconfined samples, abnormal grain growth occurred at 200°C. The retardation of grain growth in the confined sample was attributed to the lack of stress gradient and vacancy sources and the hinderance of dislocation motion. The mechanism of secondary grain growth in the confined samples was observed to be the coalesence of adjacent grains.