The properties of W2N thin films deposited on Si, SiO2, and Ta2O5 by plasma-enhanced chemical vapor deposition, with and without an electron cyclotron resonance plasma formed SiO2 (ECR-SiO2) top layer are comparatively investigated. The ECR-SiO2 top layer can effectively promote the conversion of W2N to pure W while samples are annealed at high temperature. After annealing at 900 degrees C, W2N with the ECR-SiO2 top layer fully converts to W without occurrence of silicidation but that without the ECR-SiO2 top layer partially, or does not convert to W at all. The resistivity for the 900 degrees C annealed samples with the ECR-SiO2 top layer is only 1/3-1/10 of that without the ECR-SiO2 top layer. The conversion of W2N to W and enhancement of this conversion by the top ECR-SiO2 layer are discussed and explained.