Melting point depression of Al clusters generated during the early stages of film growth: Nanocalorimetry measurements

This work investigates the thermodynamic properties of small structures of Al using an ultrasensitive thin-film differential scanning calorimeter. Al thin films were deposited onto a Si3N4 surface via thermal evaporation over a range of thicknesses from 6 to 50 Å. The Al films were discontinuous and formed nanometer-sized clusters. Calorimetry measurements demonstrated that the melting point of the clusters is lower than the value for bulk Al. We show that the melting point of the clusters is size dependent, decreasing by as much as 140 °C for 2 nm clusters. The results have relevance in several key areas for Al metallization in micro-electronics including the early stages of film growth and texture formation, the Al reflow process, and the dimensional stability of high aspect ratio Al lines.