Influence of nitrogen content in W N _x on its thermal stability and electrical property as a gate electrode

The effects of nitrogen concentration on the thermal stability and electric properties of the W Nx film as the gate electrode are investigated. W Nx is deposited by using reactive radio frequency sputtering, and films with composition of W N0.6, W N0.8, and W N1.5 are obtained at 10, 25, and 40% of N2 partial flow ratio, respectively. The crystal structure of the W N0.6 film indicates that this film is a mixture of W+ W2 N, while W N0.8 and W N1.5 films both show the W2 N phase. After annealing in N2 + H2 (N2 H2 =9:1) ambient at 500°C, the surface of the W N0.6 film reveals only the W-O bonding but no W-N bonding. In addition, oxygen diffuses from Si O2 into W N0.6 and leads to the formation of a mixing layer. Subsequently, flatband voltage (VFB) of the metal oxide semiconductor capacitor shifts positively after annealing at 500°C. After annealing at 500°C, W N0.8 and W N1.5 films exhibit better resistance to oxidation than the W N0.6 film, regardless of the surface of the W Nx film or the interface between W Nx and Si O2. Resistivity of all W Nx films increases after annealing and also increases with increasing nitrogen content in the W Nx films. However, neither the nitrogen content in the W Nx nor the postmetal annealing affect the leakage current of W Nx Si O2 Si capacitors at both positive and negative biases.