Abstract: A method is used for forming a low relative permittivity dielectric film by a vacuum ultraviolet CVD. The film is a silicon organic film (e.g., SiOCH, SiC, SiCH, and SiOF films) that has a controlled relative permittivity and is formed at temperatures below 350° C. The method can control the content of carbon in the film to achieve a desired relative permittivity. A desired relative permittivity can be achieved by: {circle over (1)} controlling the type and flow rate of added gas (O2, N2O) that contains oxygen atoms; {circle over (2)} controlling the flow rate of TEOS; {circle over (3)} controlling the intensity of light emitted from the excimer lamp; {circle over (4)} elevating the temperatures of the synthetic quartz window and the gas flowing in the vacuum chamber, and controlling the distance between the synthetic quartz window and the wafer; and {circle over (5)} controlling the temperature of the wafer.