Under-layer behavior study of low resistance Ta/TaN_x barrier film

This study finds that the resistivity of Ta/TaN_x films depends on both the Ar re-sputtering amount and the N₂ flow of under-layer TaN_x deposition. As the Ar re-sputtering amount of under-layer TaN_x films increases, the resistivity of Ta/TaN_x bi-layers decreases because Ar re-sputtering can provide a driving force to make the upper Ta metal phase transformation from a high-resistivity β-phase to a low-resisitivty α-phase. On the other hand, increasing the N₂ flow of under-layer TaN_x deposition also makes the Ta resistivity trend down. The behavior is because increasing the N₂ flow can lower the energy barrier of phase transformation from β-phase Ta to α-phase Ta. A proposed model is provided to describe the effect of the Ar re-sputtering amount and the N₂ flow of under-layer TaN_x deposition on the phase transformation of upper Ta metals.