A Study of Difference in Reflow Characteristics Between Electroplated and Sputtered Cu in a Dual-Damascene Fabrication Process for Silicon Semiconductor Devices

The difference in reflow characteristics between electroplated and sputtered Cu films during high-temperature high-pressure treatment was confirmed, and the basis for this difference was analyzed. Using test element groups containing a number of via holes, it was found that electroplated Cu films had much superior embedding characteristics compared with sputtered Cu films. This was confirmed by measurements of the stress–strain curves of these Cu films, which indicated that the strength at high temperature of the electroplated films was lower than that of sputtered films. Identification of lattice defects and analysis of the microstructure of these films were carried out by positron lifetime measurements and transmission electron microscopy, respectively. The results showed that a large quantity of vacancy clusters was present in the electroplated Cu films, and this increased to a maximum after isochronal annealing at 300°C. From the results, it was shown that Cu atoms in electroplated films with a large number of vacancy clusters diffuse rapidly at around 300°C, and this rapid diffusion contributes greatly to softening of the film and a promotion in reflow behavior. This study revealed that the reflow behavior of Cu films strongly depends on the presence of vacancy clusters within it.