A silicon-containing insulation film is formed on a substrate by plasma
reaction using a reaction gas including (i) a source gas comprising a
silicon-containing hydrocarbon compound containing multiple
cross-linkable groups, (ii) a cross-linking gas, and (iii) an inert gas,
into a reaction chamber where a substrate is placed. The insulation film
is then exposed to electron beam radiation, thereby increasing mechanical
strength of the film without substantial alternation of its dielectric
constant.