Effects of annealing on the microstructure and electrical properties of TaN-Cu nanocomposite thin films

TaN-Cu nanocomposite thin films used as materials for thin-film resistors (TFR) were prepared by magnetron dc reactive co-sputtering. With the introduction of N₂ gas flow into the Ar/N₂ plasma, different phases of β-Ta, Ta₂N, TaN, and Cu can be observed, resulting in different electrical properties of TaN-Cu thin films. After deposition, rapid thermal processing (RTP) was applied to anneal the thin films at 400 °C for 2, 4, 8 min in Ar ambient, causing the nucleation and growth of Cu nanoparticles. It was found that the resistivity and TCR changed after various annealing time due to the counteractions among the quantum effect caused by the nanosized Cu particles, the amorphous matrix, and loosened TaN matrix after Cu precipitation. The most obvious increase in the resistivity was found when annealing for 4 min, and the most decrease in TCR occurred after 4 min annealing. In general, a suitable combination of annealing time, Cu at.%, and N₂ flow rate is required to reach near-zero TCR value. Longer annealing time requires less Cu at.% to reach zero-TCR point.