Magnet unit for magnetron sputtering apparatus

A magnet unit for a magnetron sputtering apparatus, the magnet unit being disposed above a target, provided that a side of the target that gets sputtered is defined to be a sputtering surface and that a sputtering surface side of the target is defined to be lower,

• the magnet unit comprising:
• a yoke made of magnetic material and disposed so as to lie opposite to the target;
• and a plurality of magnets disposed on a lower surface of the yoke, wherein a leakage magnetic field in which a line passing through a position where the vertical component of the leakage magnetic field becomes zero is closed in an endless manner, is caused to locally act on a lower space of the target, the lower space being positioned between a center of the target and a periphery thereof, the magnet unit being driven for rotation about the center of the target,
• wherein the yoke has:
• in a predetermined position thereof a recessed groove formed in a circumferentially elongated manner along an imaginary circle in a manner to be recessed from an upper surface of the yoke downward or penetrating the yoke;
• and an auxiliary yoke disposed in a manner to be freely engaged with, or released out of engagement with, the recessed groove.