To form a low dielectric constant, a low etching rate, the insulating layer having the properties of high insulation. Process for supplying a gas containing a predetermined element into the processing chamber accommodating the substrate; A step of supplying a carbon-containing gas into the processing chamber accommodating the substrate; A step of supplying a nitrogen-containing gas into the processing chamber accommodating the substrate; Predetermined by the cycle to perform at the same time ratio (非) it performed a predetermined number of times, and a step of forming a xanthan nitride film on the substrate; and a step of supplying an oxygen-containing gas into the processing chamber accommodating the substrate element-containing gas, the carbon-containing gas, said nitrogen containing gas and the step of supplying a gas from the oxygen-containing gas, wherein in said predetermined element-containing gas, the carbon-containing gas, said nitrogen containing gas and the oxygen-containing gas a gas other than a gas in a ratio (非) fed into the treatment chamber and, in the process for supplying the oxygen-containing gas, the oxidation by the oxygen-containing gas in the layer formed on the substrate up to that point where the unsaturated under a condition, a method for manufacturing a semiconductor device to oxidize the layer is provided.