A rectangular planar magnetron with a moveable magnet assembly is known from U.S. Pat. No. 4,444,643, esp. FIGS. 10 and 11 thereof, in which the magnetic assembly is translated laterally and parallel to the major axis of the target. Further, DE-A-27 07 144 proposes a magnet assembly which is swept over a rectangular target along a linear path. As explained in U.S. Pat. No. 4,714,536, these known magnet and target assemblies do not provide a substrate with a satisfactorily uniform sputtered coat nor do they provide a satisfactorily uniform erosion of the target. U.S. Pat. No. 4,714,536 proposes that the magnet assembly is moved with a non-repetitive epicycloidal motion combined with a translational motion over the target, i.e. the magnet array performs a non-repetitive small epicycloidal motion distributed over the area of the target. The plasma race-track of this device is not elongated.
A further magnet assembly is known from U.S. 5,188,717 for use with a circular target. The principle is explained in this document that even erosion of the target can be obtained when the dwell time of the magnetic flux remains equal over each unit area of the target. The proposed solution is a specific shape to the magnet assembly, i.e. like a kidney bean, and a combined rotary and translational motion of the magnet assembly. No indication is given of how to adapt this technique to rectangular targets. The kidney bean shape does not produce an elongated plasma race-track and is not suitable for rectangular targets.
U.S. Pat. No. 5,382,344 describes a magnet assembly which produces electron paths in a plurality of race-tracks. The race-tracks are moved linearly and perpendicularly to the longest axis of the target with an oscillatory motion. The target erosion of such a device still shows preferential grooves where the magnetic flux resides for longer time per unit area than in other areas (dwell times).
In one embodiment EP-A-416 241 describes a target in the shape of a ring, whereby the target is more closely fitted to the shape of the stationary race-track. In a second embodiment a magnet array is described which may be moved in an oscillating motion limited by the cathode tray. The motion is produced by a pin on a rotating cam, the pin being journalled in the base of the magnet array. The motion produced is not described.
U.S. Pat. No. 5,328,585 discloses a linear planar magnetron sputtering apparatus with a reciprocating magnet array. The reciprocating motion can be simultaneously lateral and longitudinal with respect to the cathode target. The drive mechanism for moving the magnet array is complex and large in size and requires separate guides for each of the motions. This results in a complex universal joint in one of the drives. The two drives from these motors take up a lot of space and both penetrate the vacuum chamber increasing the complexity of seals between the vacuum chamber and atmosphere and with the cooling circuit. The magnet array is in air which limits cooling of the target. Further, the target is provided with a dark space shield outside the target area as well as strips of titanium material on either side of the silicon target. The motion of the magnet array takes the race-track outside the main target area. By sputtering beyond the target area it is possible to locate the dwell times of the motion of the magnet array outside the target area. Instead of forming grooves in the target the dwell times outside the target result in the race-track either sputtering from the titanium strips or the race-track being extinguished if the motion is so large that the magnet array overlaps the dark space shields. During sputtering, material from the target may be deposited onto the shields resulting in a layer of insulation which can break down locally causing arcing. Alternatively, if the dark space shields are moved further away, titanium is sputtered onto the substrate as a contaminant of the silicon oxide coating.
It is the object of the present invention to provide a moveable magnet array for a sputtering magnetron which is simple in construction, reliable and provides a variety of motions which may be advantageous for planar targets, particularly rectangular targets.
Further, it is an object of the present invention to provide a simple drive mechanism for a planar magnetron and a simple and efficient cooling circuit.
It is a further object of the present invention to provide a magnet assembly which provides a high utilisation of the material of the target at least in a central region thereof.