In this letter, fluorinated silicon oxide (FxSiOy) films were deposited in the electron cyclotron resonance (ECR) chemical vapor deposition system with SiH4, O2, and CF4 as the reaction gases. The CF4, in contrast to SiF4 or FSi(OC2H5)3 used in other reports, is an indirect fluorinating source. The fluorinating mechanism is similar to that of the etching of oxide by fluorocarbon plasma, therefore, the thermal stability of the incorporated fluorine must strongly depend on the deposition temperature. It is found that the thermal stability and moisture resistance are greatly improved by increasing the deposition temperature. However, the higher deposition temperature also results in a higher compressed stress and dielectric constant. Besides, to get the moisture resistance, the deposition temperature must be above 300 °C. On the other hand, ECR‐SiO2 (without fluorination), even deposited at room temperature, is shown to have a good water resistance. Therefore, by choosing deposition temperature for FxSiOy to have enough thermal tolerance and capping with ECR‐SiO2, the moisture resistor is suggested for the inter metal dielectric applications.