is provided to a back bias generator such as the generator 26 of fig1 in the system of fig3 two target plates are respectively connected and disposed onto two target holders which are fixed to both inner ends of the chamber 210 so as to make the target plates face each other a pair of permanent magnets are accommodated in the target holders so as to create a magnetic field therebetween substantially perpendicular to the surface of the target plates the wafer 200 is disposed closely to the magnetic field which will define a plasma region so as to preferably face it the electrons emitted from the both target plates by applying the voltage are confined between the target plates because of the magnetic field to promote the ionization of the inert gas so as to form a plasma region the positive ions of the inert gas existing in the plasma region are accelerated toward the target plates the bombardment of the target plates by the accelerated particles of the inert gas and ions thereof causes atoms of the material forming the plates to be emitted the wafer 200 on which the thin film is to be disposed is placed around the plasma region so that the bombardment of these high energy particles and ions against the thin film plane is avoided because of effective confinement of the plasma region by the magnetic field the back bias rf power supply causes an effective dc u2018 back bias u2019 between the wafer 200 and the chamber 210 this bias is negative so it repels the low.