Influence of thickness on the material characteristics of reactively sputtered W2N layer and electrical properties of W/W2N/SiO2/Si capacitors

The material characteristics of W2N layer and electrical properties of W/W2N/SiO2/Si metal–oxide–semiconductor (MOS) capacitors with different W2N thickness upon annealing in N2 + H2 ambient at 500 °C for 20 min are investigated. The nitrogen concentration of W2N for the W/W2N stack with thin W2N layer (≤10 nm) is lower than that for the W/W2N stack with thick W2N layer (≥15 nm). In addition, the crystallinity of W2N in the W/W2N (15 nm) stack is better than that in the W/W2N (10 nm) stack. For all capacitors, the oxide charges decrease significantly after annealing and the amount of oxide charges is independent of the W2N thickness. However, the work function (Φm) of the W/W2N (≤10 nm) stack (∼4.6 eV) is smaller than that of W/W2N (15 nm) stack (∼5.0 eV). The Φm of W/W2N (15 nm) stack is close to that of W2N single layer. After annealing, the Φm of W/W2N (15 nm) stack and W2N single layer decrease, especially for the W2N single layer. But for the W/W2N (≤10 nm) stack, the Φm increases after annealing.