Defects introduced into electroplated Cu films during room-temperature recrystallization probed by a monoenergetic positron beam

Abstract

Positron annihilation was used to probe vacancy-type defects in electroplated Cu films deposited on $\mathrm{Ta}∕{\mathrm{SiO}}_2∕\mathrm{Si}$ . Doppler broadening spectra of the annihilation radiation were measured for the Cu films during grain growth at room temperature (i.e., self-annealing). The line-shape parameter $S$ increased during self-annealing, and the observed time dependence of $S$ was well described by the Johnson-Mehl-Avrami-Kolmogorov kinetics. After self-annealing, the values of $S$ were found to be larger than the $S$ value for annealed pure Cu, suggesting that the positrons annihilated from the trapped state by vacancy-type defects in grains. From a comparison with the results of previous isochronal annealing experiments, the major species of defects introduced during self-annealing was found to be vacancy clusters. The size of these defects increased, but their concentration decreased, with increasing film thickness. In thicker Cu films, an enhanced flow of atoms and subsequent rapid grain growth cause such defect behavior.