A plasma excitation device is described for use in depositing a film on a substrate from a plasma formed by distributed electron cyclotron resonance. The device comprises a microwave antenna having anend from which microwaves are emitted, a magnet disposed in the region of the said antenna end and defining therewith an electron cyclotron resonance region in which a plasma can be generated, and agas entry element having an outlet for a film precursor gas or a plasma gas. The outlet is arranged to direct gas towards a film deposition area situated beyond the magnet, as considered from the microwave antenna.