Plasma generating device

A plasma generating device to treat substrates in a vacuum chamber, comprising a cathode (17,5,2,1) which at its upper surface contains the material to be treated in the form of a target (1) and comprising at least one magnetic device (10,11,12) at the back side of the target to generate in the area of the cathode surface at least one tunnel-like magnet field (15) which forms tunnel foot poles (16) on the cathode surface, whereby the tunnel-like field (15) extends at least along a part of a horizontal tunnel axis, and the magnetic device (10,11,12) includes means for displacing at least one of the tunnel foot poles (16) perpendicular to the horizontal tunnel axis, the magnetic device (10,11,12) including a fixed first magnetic pole generating device (11) and surrounding, as a closed frame, at least a second magnetic pole generating device (10) which contains said means for displacing the corresponding tunnel foot pole (16), the second magnetic pole generating device consisting of a pair of permanent magnets (13,14) which are placed on their longitudinal axes parallely pivotable to the target (1) such that in the area of the cathode surface a tunnel-like laterally modifiable magnet field is generated.