In a deposited-film formation method or apparatus according to the present invention,
which comprises providing a discharge electrode in a vacuum vessel equipped with
exhaust means, supplying a hydrogen gas and a raw material gas for forming a deposited
film which contains at least an Si element, generating plasma from the material
gas by supplying high frequency electric power to the discharge electrode, and
forming a deposited film on a substrate in the vacuum vessel by plasma CVD, wherein
an auxiliary electrode is arranged in plasma in the vacuum vessel, a periodically
changing voltage is applied to the auxiliary electrode without causing a discharge
to form a deposited film, whereby it is possible to form an amorphous-silicon-based
deposited film having good quality and good uniformity over a large area at a high
rate of film formation.
