A method for forming a silicon-containing insulation film on a substrate
by plasma polymerization includes: introducing a reaction gas comprising
(i) a source gas comprising a silicon-containing hydrocarbon cyclic
compound containing at least one vinyl group (Si-vinyl compound), and
(ii) an additive gas, into a reaction chamber where a substrate is
placed; and applying radio-frequency power to the gas to cause plasma
polymerization, thereby depositing an insulation film on the substrate.