Annealing of Cu(B)/Ti/SiO 2 in vacuum has been carried out to investigate the effects of Ti underlayer on microstructure in Cu(B)/Ti/SiO 2 structures. For comparison, Cu(B)/Ti/SiO 2 structures was also annealed in vacuum. Three different temperature dependence of Cu growth can be seen in Cu(B)/Ti/SiO 2 ; B precipitates- pinned grain growth, abnormal grain growth, normal grain growth. The Ti underlayer having a strong affinity for B atoms reacts with the out-diffused B to the Ti surface and forms titanium boride at the Cu-Ti interface. The formation of titanium boride acts as a sink for the out-diffusion of B atoms. The depletion of boron in grain boundaries of Cu films, as results of the rapid diffusion of B along the grain boundaries and the insufficient segregation of B to the grain boundaries, induces grain boundaries to migrate and causes the abnormal grain growth. The increased bulk diffusion coefficient of B within Cu grains can be responsible for the normal grain growth occurring in the annealed Cu(B)/Ti/SiO 2 at600 ? C . In contrast, the Cu/SiO 2 structures show only the abnormal growth of grains and their sizes increasing as the temperature increases above 400 ? C .