This invention relates to sputtering apparatus which deposits a coating on the surface of a moving flexible substrate supported on a water cooled cylindrical drum.

Sputtering techniques and apparatus are well documented. Sputtering involves the ionisation of gas whose ions are accelerated in a field to a target (cathode) where they impinge and eject atoms or molecules from the target. The introduction of a magnetic field causes the electrons to spiral as they travel to the anode increasing collisions with gas atoms and producing more ions which attack the target. The atoms or molecules from the target when freed from the target are collected on a surface above the target.

In principle USA Patent 4,166,018 describes a planar sputtering apparatus. It is inherent in the design of this apparatus that the target is substantially planar and that the sputtered particles are emitted from each side of the centre line of the target. A single closed loop erosion pattern is produced in the surface of the target. As a result the utilization of the target is not particularly high. This is disadvantageous particularly where the target material is expensive. USA patent

4,221,652 describes a device with a cylindrical target where the sputtered particles are emitted in all directions from the outer surface of the target. A magnetic system may be moved axially within the cylindrical target. This improves target utilization as compared with an arrangement which employs a static magnetic system, but still leaves substantial areas of the target unused.

The ideal disposition for the substrate to collect the sputtered particles emitted from the target is in the case of the planar sputtering apparatus a flat sheet parallel to the surface of the target and extending beyond the edges of the target; in the case of the device with a cylindrical target a cylinder positioned outside of the target and concentric with the target.

The moving flexible substrate receives heat when the sputtered particles are collected on it. This causes a temperature rise of the substrate which could cause damage to the substrate. Typically the substrate is supported from a chilled cylindrical water cooled drum. This does not provide the ideal disposition for either of the above two devices. Loss of sputtered partices occur in each case. Also the ideal place for sputtered particles to be emitted is along the centre line of- the planar apparatus where no such emission takes place.

Additionally the edges of the film would have poor uniformity: because of the increase of emission in the case of the planar apparatus and because of the low emission from the cylindrical device due to the film having to be positioned beyond the anodes mentioned in this patent. Compensation could be achieved by shielding the sputtered particles from the substrate at the edges of the substrate or reducing the width of the film. Both courses of action lead to further reduced efficiency in relation to the sputtered particles arriving at the substrate when compared with the particles leaving the target.

US Patent 4,356,073 describes an apparatus with a rotating cylindrical target where the sputtered particles are emitted from a longitudinal axis. This partly overcomes the problem with the cylindrical target above but many of the emitted particles do not arrive at the moving substrate. The number of particles arriving at the substrate can be increased by pinching the magnetic field. The intensity of bombardment of the target is such that low melting point materials will begin to melt, limiting the deposition rate of the target.

According to one aspect of the present invention, there is provided a machine for depositing atoms and

molecules on a substrate comprising a chamber, means for evacuating the chamber, and means for sputtering material onto the substrate the means for sputtering comprising an elongate target and a magnet system disposed adjacent the target, the magnet system comprising a plurality of magnets disposed to produce lines of magnetic force extending in the direction of the elongate axis of the target.

The majority of web coating machines utilise aluminium as the material to be deposited. This is vaporized from resistance heated intermetallic evaporators. For normal coating thicknesses web speeds of 10 m/s can readily be achieved. The evaporators typically 150mm long x 25 mm wide are pitched at 100 mm centres with their axes in line with the running direction of the web.

The advantages of sputtering are that as the target is colder less radiant heat is transferred to the substrate and the risk of heat damage for this reason is reduced. Due to the bombardment of the substrate with ions during the metallisation process the adhesion of the evaporant to the substrate is improved.

The quality of the deposition is excellent, being of the same quality as the target material. All non-magnetic

materials can be evaporated with this system. The system ideally lends itself to reactive sputtering so that oxides and other combinations can be deposited on the substrate.

The basic drawback is the rate of evaporation for all materials including aluminium is very low and hence its output even with a multiple source arrangement would be less than one tenth of that from a resistance heated source.

With the planar sputtering device described in USA Patent 4,166,018, the lines of evaporation are transverse to the running direction of the web. The evaporation rates of planar sputtering devices are very much less than that from the resistance heated evaporators mentioned above. By turning the lines of evaporation through 90° for the planar magnetron source the rate of evaporation and hence deposit on the substrate is greatly enhanced.

According to another aspect of the present invention, there is provided a machine for depositing atoms and molecules on a substrate comprising an elongate flexible web of material comprising a chamber, means for evacuating the chamber, a curved rotatable surface for supporting the flexible web, means for sputtering

material onto the web, the means for sputtering comprising a target having a curved surface which is substantially concentric to the curved surface, and one or more magnets associated with the target.

In a preferred embodiment of the invention means are provided for moving the or each magnet to move the magnetic field produced in order to promote uniform deposition and equalize erosion of the target. Where the substrate support surface is rotatable the means for moving are operative to move the magnets substantially in the direction of the rotational axis of the rotatable surface. Where the surface is curved it forms part of a rotatable cylindrical drum which may be cooled. The or each magnet for the curved target is also curved and disposed concentrically with the target with its magnetic field lines substantially coaxial with the axis of rotation of the curved surface.

In order that the invention may be more clearly understood one embodiment thereof will now be described, by way of example, with reference to the accompanying drawings, in which:-

Figure 1 shows a diagrammatic cross-sectional view of a web winding machine fitted with a sputtering apparatus,

Figure 2 is a diagrammatic perspective view of a target forming part of the sputtering apparatus for Figure 1,

Figure 3 is a partial diagrammatic cross sectional view of magnets forming part of the sputtering apparatus of Figure 1,

Figure 4 is a partial diagrammatic cross sectional view of the sputtering apparatus and the curved rotating surface of Figure 1.

Figure 5 diagrammatically shows a plan view of a conventional erosion pattern produced on a target,

Figure 5a diagrammatically shows a partial plan view of a magnet system for producing the pattern of Figure 5,

Figure 5b shows a section along the line A-A of Figure 5,

Figure 6 shows a view corresponding to that of Figure 5 but showing an erosion pattern produced by a magnet system in accordance with the invention,

Figure 6a shows a plan view of part of the magnet

system for producing the pattern of Figure 6, and

Figure 6b shows a section along the line B-B of Figure 6.

Referring to Figure 1, the web winding machine fitted with the sputtering apparatus comprises a web guidance system and a sputtering apparatus disposed in a vacuum chamber 1. The vacuum chamber is of substantially circular cross-section and ports 2A and 2B are disposed in the wall of the chamber. A vacuum pumping system (not shown) is connected to the port 2A to enable the vacuum chamber to be evacuated. Port 2B is connected to an inert gas supply system (also not shown) . The web guidance system comprises a chilled rotating drum 3, a supply reel 4, and a take-up reel 5. In operation, a web 6 to be coated is unwound from the supply reel, passes over the drum 3 and is rewound onto the take up reel 5. The drum 3 is cooled- by a mixture of water and ethylene glycol, the operational temperature usually being in the range -5 to -30°C. The coolant circuit which passes through the axle upon which the drum turns is conventional and is therefore not shown in great detail.

The sputtering apparatus indicated generally by the reference numeral 8, comprises a metal enclosure 9 of generally U-shaped cross section which is closed at the

ends. A target 10 of the material to be sputtered is clamped by clamps 11 to the top ends of the enclosure 9. This now forms the closed box of the sputtering apparatus. Magnets 13, are disposed in the closed box. An *0* ring seal 14 is disposed between the enclosure 9 and the target 10. Anodes 15 are disposed between the target 10 and drum 3 adjacent the drum. A DC power supply 16 is connected through the wall of the chamber 1. The negative side is connected to the enclosure 9 which is in good contact with target 10. The positive side is connected to the anodes 15. This provides the potential difference between the anodes 15 and the cathode (target 10) . Water coolant is passed through the closed box of the sputtering apparatus 8 via coolant lines 17 which also pass through the wall of the chamber.

Referring to Figure 2 a perspective view of the target 10 is shown. As can be seen, this forms part of a cylinder and is concentric to the outer cylindrical surface of the drum 3. The gap between drum 3 and target 10 is therefore substantially constant across the surface of the target. Referring to Figure 3 a diagrammatic view of the main magnetic field is shown. The magnets also form part of a cylinder and are themselves concentric to the target so that the gap between the magnets and the target is substantially constant over the surface of the magnets. The magnets are arranged in a line, with their

magnetic field lines 12 coaxial with the axis of the cylinder. As can be seen each magnet is in the form of a horizontally disposed E-shape with the arms thereof pointing upwards. The outer arms are north poles and the inner arms are south poles.

Referring additionally to Figure 4, a partial side elevational view of the sputtering apparatus and chilled rotating drum 3 in cross-section is shown. The magnets are mounted on a support 20 which in turn is slidably mounted on slides 21. The slides 21 slide in chambers 23 which are connected at opposite ends respectively of the closed box to a pressure fluid supply via respective supply pipes 22. By supplying fluid alternately to the chambers 23, the magnets are made to oscillate in the closed box. The rate of oscillation can be preprogrammed.

Oscillation of the magnetic field gives a uniform ^• controllable deposit at the moving web. In addition the target wear is evened out and utilisation of up to 70% of the target is possible.

Figure 5 shows a plan view of a target 28 showing a conventional erosion pattern 29 comprising a substantially oval groove produced during sputtering on the surface of that target. Figure 5a shows a plan view

of the magnet system disposed beneath the target which, in operation, leads to the Figure 5 pattern 29. Figure 5b shows a cross-sectional view along the line A-A through both the target and the magnet system. The magnet system in plan view see (Figure 5a) has an elongate shape with a substantially straight central portion 30 and two substantially semi-circular end portions 31. In cross section (see Figure 5b) , the magnet is U-shaped, one arm of the U forming an inner south-pole (S) and the other arm of the U an outer north pole (N) . The web upon which material sputtered from the target is deposited is shown above the target diagrammatically at W. The magnetic system produces magnetic lines of force 32 which extend parallel to the direction of movement of the web over the surface of the target 28. This erosion pattern 29 leaves relatively large areas of the target untouched. This relatively low target utilization is disadvantageous particularly where the target material is expensive as is often the case.

Figures 6, 6a and 6b are views of a target and magnet system according to the invention which correspond to Figure 5, 5a and 5b. In this arrangement the target erosion pattern comprises a series of seven substantially oval grooves 39 arranged side by side along the target 38. These oval are produced during sputtering by seven respective magnets 40. One of these magnets is shown in

plan view in Figure 6a and in cross-sectional view, along the line B-B of Figure 6, in Figure 6b. As can be seen from Figure 6b, each magnet 40 is E-shaped in cross-section lying on its back so that the arms of the E are upright. The middle arm of the E is the south pole (S) and outer arms are north pole (N) . In plan view, referring to Figure 6a, the magnet comprises an outer oval north pole (N) surrounding an inner solid oval south pole (S) . The web W passes over the target in the direction of the longitudinal axis of the magnets 40. In contrast to the arrangement of Figure 6, however, the magnetic lines of forces produced by the magnets 40 extend transversely to the direction of movement of the web and parallel to the axis of rotation of the curved surface of the support for the web.

This arrangement leads to much higher target utilization than with the arrangement of Figure 5. With the arrangement of Figure 6 target utilization higher than 70% can be achieved. Although the arrangement has been described for use in metallizing a web passing over a curved surface, it can also be advantageously used in other metallizing configurations.

Evaporation from the target takes place uniformly over a larger area which reduces the risk of melting the target with intense local evaporation rates. The web can

be run faster for a given required deposit thickness or the target can be run cooler to enable better evaporation characteristics. As vaporisation is over a large area and less intense, control of deposit on the moving web is more easily controllable. For a given evaporation rate, the sputtering apparatus occupies less room. The drum size is therefore also reduced resulting in a reduction in the overall size of the coating machine. Where the surface of the target is curved and concentric to the substrate the collection rate of molecules and atoms curving at the substrate is increased.

It will be appreciated that the above embodiment has been described by way of example only and that many variations are possible without departing from the scope of the invention. For example other magnetic orientations of the magnets for the target than that shown may be employed.