Patent attributes
A low refractive index SiO2 film is provided which uses a starting material for forming an SiO2 film and has a lower refractive index than the conventional SiO2 film. A starting material gas comprising a gas containing a fluorine atom, a gas containing a silicon atom and an alkyl group having 1 to 4 carbon atoms or an alkyl group having 1 to 4 carbon atoms with a part or the whole of hydrogen atoms substituted by a fluorine atom, and a gas containing an oxygen atom is subjected to plasma CVD in a vacuum chamber 1 to form an SiO2 film on a web 2 in a plasma zone 5. The SiO2 film thus formed has, at least one low refractive index element selected from a fluorine atom, an alkyl group having 1 to 4 carbon atoms, and an alkyl group having 1 to 4 carbon atoms with a part or the whole of hydrogen atoms substituted by a fluorine atom, and the SiO2 film with the low refractive index element introduced thereinto has a lower refractive index than an SiO2 film with the low refractive index element not introduced thereinto.
