Effects of scandium addition on electrical resistivity and formation of thermal hillocks in aluminum thin films

This study investigates the effects of doping aluminum (Al) films with minor amounts of scandium (Sc) on the electrical resistivity and the formation of thermal hillocks. The pure Al and Al-Sc films, prepared via sputtering deposition, before and after isochronal annealing are examined using a scanning electron microscope and a transmission electron microscope. In-situ thermal stress analyses of the films are also carried out. The grain size of the as-deposited films is reduced by addition of Sc. Moreover, the Sc can immobilize the grain boundaries, retarding grain growth and re-crystallization of the films during annealing. Although the as-deposited Al-Sc films show higher resistivity than that of a pure Al film, the former is significantly decreased after annealing at 300 °C. The hillock density dramatically reduces with increasing the Sc concentration in the films. Average size of the hillocks in Al-Sc films clearly increases when the temperature is elevated.