Vacancy-type defects in electroplated Cu films probed by using a monoenergetic positron beam

Abstract

Positron annihilation was used to probe vacancy-type defects in electroplated Cu films. Doppler broadening spectra of the annihilation radiation for Cu films deposited on samples with a $\mathrm{Ta}\text{(20\hspace{0.05em}}{\mathrm{nm)/SiO}}_2\text{(100\hspace{0.05em}}\mathrm{nm)/Si}$ structure were measured with a monoenergetic positron beam. For an as-deposited Cu film, the line-shape parameter S measured 20 days after deposition was larger than that measured 1 day after deposition. The observed increase in the value of S was attributed to grain growth at room temperature and the corresponding increase in the fraction of positrons trapped by vacancy clusters in the grains. In isochronal annealing experiments, the value of S for an electroplated Cu film increased for annealing below 200 °C, suggesting agglomeration of vacancy-type defects (vacancy clusters). A decrease in the S value was observed for annealing above 300 °C, and this was attributed mainly to the decrease in the concentration of vacancy clusters. The annealing stages of the defects in electroplated Cu were found to agree with those for irradiated pure Cu.