This paper reports a comprehensive study on the influence of nitrogen incorporation on high-k (HK) device performance and reliability. Two approaches including dielectric nitrogen annealing and interfacial layer (IL) nitrogen annealing are investigated. It is found the HK nitrogen annealing is a better solution for the trade-off between mobility and inversion oxide thickness than IL annealing. The positive bias temperature instability characteristic is improved by HK annealing. However, the HK nitrogen annealing lowers the barrier of dielectric and thus results in an abnormally high leakage current.