Diffusivity of Cu in amorphous (a-) Ta2 O5 is increased by low temperature annealing above 350 °C but the increase is suppressed by adding SiO2 to Ta2 O5. To clarify the reasons, we investigated the structural difference between a-Ta2 O5 and a-SiO2-Ta2 O5. The results show that the low temperature annealing does not cause polycrystallization of Ta2 O5 but purges weakly bonded oxygen atoms from the bulk and decreases the film density. Adding SiO2 to Ta2 O 5 is shown to increase the coordination number of Ta-O, which results in the improved thermal stability.
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