Effects of boron depletion on the microstructure evolution of Cu(B) alloys deposited on Ti underlayer

This study examined the effects of a Ti underlayer on the microstructure evolution of Cu(B)/Ti/SiO2 thin films upon annealing. For comparison, Cu(B)/SiO2 was annealed at temperatures ranging from 100 to 900 °C. In the case of Cu(B)/SiO2, abnormal grain growth abruptly occurred at approximately 400 °C and continued at temperature ≥ 400 °C. The growth was based on the formation of {111} twins along the 〈112〉 direction. In the case of Cu(B)/Ti/SiO2, the Ti underlayer reacts with B atoms to form titanium boride, which acts as a sink for the outdiffusion of B atoms. The redistribution of boron, as a result of the formation of titanium boride, has a significant influence on the microstructure evolution in Cu(B)/Ti/SiO2 samples at temperature ≥ 400 °C. Abnormal grain growth was observed at between 400 and 500 °C, which is believed to have been driven by strain energy minimization. At 600 °C and higher, B depletion from the grain interiors caused a relaxation of the elastic strain, resulting in normal grain growth.