Effects of Post-Metal Annealing on Electrical Characteristics and Thermal Stability of W[sub 2]N/Ta[sub 2]O[sub 5]/Si MOS Capacitors

The thermal stability and electrical properties of W 2 N / Ta 2 O 5 / Si metal oxide semiconductor (MOS) capacitors upon post-metal annealing in H 2 or N 2 + H 2 ambient at 400-600°C for 30 min are investigated. After annealing at 400-500°C, the W 2 N gate remains intact but, due to loss of nitrogen, partly transforms to WO 3 after annealing at 600°C. The partial oxidation of W 2 N is more noticeable when annealing in H 2 ambient than in N 2 + H 2 , and also induces greatly increased resistivity. However, the capacitance-voltage (C-V) curves of the W 2 N / Ta 2 O 5 / Si MOS capacitors are similar before and after post-metal annealing. C-V hysteresis measurements showed that charges within the Ta 2 O 5 layer of the as-fabricated MOS structure are positive, and the density is 4.94 × 10 12 cm −2 . After annealing in H 2 , the charge density decreased with increasing annealing temperature, and the charge polarity became negative after annealing at 600°C. In N 2 + H 2 , the charge polarity became negative right after annealing at 400°C, and the density was below 10 12 cm −2 . For the I-V curves, the leakage current decreases with increasing annealing temperature at positive bias, and H 2 annealing results in lower leakage currents than N 2 + H 2 annealing. In contrast, the leakage currents are all similar when the samples are stressed at negative bias, regardless of the annealing temperature and ambient.