Effects of post-treatments on ultrathin nitride/oxide stacks prepared by commercial rapid thermal CVD (RTCVD) cluster tools have been investigated. Two-step post-deposition treatments (i.e., NH3 nitridation followed by N2O annealing) were performed at different temperatures to study their effects on dielectric integrity and electrical characteristics. And found that the gate stack can be more stoichiometric, thinner equivalent oxide thickness (EOT) and significant reduction in leakage current simultaneously by increasing NH3 nitridation temperature. But it suffered from slightly transconductance (G(m)) degradation due to incorporation of excess nitrogen. In addition, due to interfacial modification, the improved G(m) can be obtained by N2O annealing. However, N2O annealing step also results in increasing EOT and degradation in gate current characteristics.