Chemistry: electrical and wave energy – Apparatus – Coating – forming or etching by sputtering
Reexamination Certificate
2000-07-06
2001-11-27
Nguyen, Nam (Department: 1753)
Chemistry: electrical and wave energy
Apparatus
Coating, forming or etching by sputtering
C204S192120
Reexamination Certificate
active
06322679
ABSTRACT:
The present invention relates to an improved planar magnetron with a magnet assembly suitable for sputtering or reactive sputtering of materials from a cathode target onto a substrate as well as a method of operating the magnetron.
TECHNICAL BACKGROUND
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.
SUMMARY OF THE INVENTION
The present invention provides a planar magnetron including a surface for mounting a planar substantially polygonal target having a substantially central target area for sputtering onto a substrate, the magnetron comprising: an array of magnets defining a closed loop magnetic field for generating an elongated plasma race-track above the target, means for establishing cyclical, relative, substantially translational movement between the race-track and the surface, the substantially translational movement being substantially parallel to the surface, the trace of the substantially translational movement being a two-dimensional figure and the periphery of the race-track lying substantially within the substantially central target area during each cycle, the establishing means being adapted to provide a substantially uniform erosion of the target at least within the substantially central target area. The figure is preferably generally hypotrochoidal or epitrochoidal in form. The target is preferably substantially rectangular. The present invention also provides a planar magnetron having at least a surface for mounting a planar target comprising: an array of magnets defining a closed loop magnetic field for generating a plasma race-track above the target, means for establishing repetitive, relative, substantially translational movement between the race-track and the surface, the substantially translational movement being parallel to the surface and being in the form of a two-dimensional figure, the figure being generally epitrochoidal or hypotrochoidal in form.
In the magnetrons in accordance with the present invention described above the magnet array may be an array of permanent magnets or an electromagnet or electromagnets which move to create the race-track movement defined above. Alternatively, an array of stationary electromagnets may be used and the movement of the race-track may be produced by varying the magnitude and relative phases of the currents among the electromagnets of the array.
The present invention also includes a method of operating a planar magnetron having at least a surface for mounting a planar target and an array of magnets defining a closed loop magnetic field, comprising the steps of:
generating a plasma race-track above the target; and
moving the plasma race-track relative to the surface, the movement being repetitive, substantially translational and parallel to the surface and the trace of the movement being a two-dimensional figure having a generally hypotrochoidal or epitrochoidal form.
The present invention also provides a method of operating planar magnetron including a surface for mounting a planar substantially polygonal target having a substantially central target area for sputtering onto a substrate, and an array of magnets defining a closed loop magnetic field for generating an elongated plasma race-track above the target, comprising the steps of: establishing cyclical, relative, substantially translational movement between the race-track and the surface, the substantially translational movement being substantially parallel to the surface, the trace of the movement being a two-dimensional figure and the periphery of the race-track lying substantially within the substantially central ta
Cnockaert Dirk
De Bosscher Wilmert
Cantelmo Gregg
Musgrove Jack V.
Nguyen Nam
Sinvaco N.V.
Skjerven Morrill & MacPherson LLP
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