This application is a U.S. national phase application under 35 U.S.C. § 371 of International Application No. PCT/GB2018/052748, filed Sep. 27, 2018, which claims priority to U.K. Application No. 1715779.3 filed Sep. 29, 2017, the complete disclosure of which is incorporated herein by reference.

BACKGROUND

Ceramic based clear barrier coatings are useful for a number of applications including packaging of oxygen or moisture sensitive foodstuffs, encapsulation of gas or moisture sensitive components in electronics, and a variety of other functional applications requiring barrier properties. These coatings can be applied to flexible substrates using roll to roll processing.

A number of methods for producing barrier coatings are known, for example, High Speed Physical Vapour Deposition (PVD). This method is relatively high speed and low cost, but can produce relatively poor barriers. Improved barrier properties can be achieved through a number of known techniques including reactive sputtering, Chemical Vapour Deposition and Atomic Layer Deposition. However all of these techniques are lower speed and therefore higher cost, particularly when used in roll to roll processing.

Plasma Enhanced Chemical Vapour Deposition (PECVD) is also a known technique for producing barrier coatings. However in PECVD the deposition rate is limited as the coating will only be deposited in a generated plasma zone. Increasing the amount of precursor materials applied has an effect of quenching the plasma which stops the deposition of the coating. Therefore, although high quality barrier coatings can be produced with this technique, it is a lower speed technique which results in low line speed when the technique is used in roll to roll processing.

Magnetron plasma reaction devices with multiple individual racetracks (magnetically confined regions of higher plasma density), powered from a single power source have been used to increase line speed. However, there are a number of disadvantages associated with such an arrangement. Specifically, it can be very difficult to ensure that the racetracks are stable and equally energised. Any differences and variance in the gas pressures in the vicinity of racetracks can result in uneven powering of individual racetracks causing local variation in applied power with effects on the uniformity of material produced and the ultimate long term viability of any such process. Such an arrangement therefore requires very high engineering tolerances and tight control and consistency of the magnets and process pressures when multiple individual racetracks are generated from a single power source.

SUMMARY

According to a first aspect of the invention there is provided an apparatus according to claim1.

Thus the apparatus according to the first aspect provides a single magnetron with multiple straight racetrack zones which are joined together in an alternating fashion to together form a continuous snaking or serpentine shape, where the substrate can be processed, coated or cured which increases the amount of substrate that can be treated in a given time, thus speeding up the processing, coating or curing time overall. The serpentine racetrack can for example comprise at least four generally parallel, straight regions and at least four end or turning regions which combine to define one continuous closed loop racetrack with a single path.

Advantages of the first aspect are that it only requires a single power source, and the engineering tolerances required are reduced compared to multiple racetrack systems because small variance in magnet strength, electric field strength and process pressure around the drum have a reduced effect on the racetrack powering level. Thus all areas of the racetrack are energised to substantially the same level, particularly the straight portions of the racetrack. This means that the spatial processing, coating or curing applied to the substrate is more consistent.

Substantially parallel can mean an angle of ≥0° but <45°, ≥0° but <25° or ≥0° but <10° between the elongate magnets.

The magnet array can comprise:a first elongate magnet having a first polarity;a second elongate magnet, positioned adjacent and substantially parallel to the first elongate magnet, having a second polarity opposite to the first polarity, such that the first and second elongate magnets define a first straight magnetic flux portion between them;a third elongate magnet having a first end and a second end, the third magnet being positioned adjacent and substantially parallel to the second elongate magnet, having the first polarity, such that the second and third elongate magnets define a second straight magnetic flux portion between them, the second straight magnetic flux portion being connected to the first straight magnetic flux portion by a first curved magnetic flux portion which extends around the first end of the second elongate magnet; anda fourth elongate magnet positioned adjacent and substantially parallel to the third elongate magnet, the fourth elongate magnet having a first end and a second end, the first end being adjacent to the second end of the third elongate magnet, the fourth elongate magnet having the second polarity, such that the third and fourth elongate magnets define a third straight magnetic flux portion between them, the third straight magnetic flux portion being connected to the second straight magnetic flux portion by a second curved magnetic flux portion which extends around the first end of the third elongate magnet.

One or each elongate magnet can be formed from a plurality of individual sub-magnets, all having the same orientation and polarity.

The array of elongate magnets can have a first end region, this being the end region which is closest to a first end of each of the elongate magnets, and a second end region, this being the end region which is closest to an opposite, second end of each of the elongate magnets.

The longitudinal centre of the first elongate magnet can be aligned with the longitudinal centre of the third elongate magnet. The longitudinal centre of the second elongate magnet can be aligned with the longitudinal centre of the fourth elongate magnet. The longitudinal centres of the first and third elongate magnets can be offset with respect to the longitudinal centres of the second and fourth elongate magnets.

Having an offset arrangement of the elongate magnets enables the elongate magnets to contribute to defining a serpentine or snaking racetrack.

The magnet array can further comprise one or more turning magnets. Each turning magnet can be arranged to encourage the racetrack to bend around an end region of an elongate magnet, which will be referred to as a ‘target elongate magnet’. One or each turning magnet can have an opposite polarity with respect to its target elongate magnet and the same polarity as the pair of adjacent elongate magnets between which the target magnet is situated, these adjacent magnets being referred to as ‘common elongate magnets’.

Thus the turning magnets can be used to more accurately direct the path of the racetrack to form curved sections which join the straight racetrack sections together into a serpentine shape.

Each turning magnet can be located at one end of a common elongate magnet, wherein the turning magnets each have a different orientation from the orientation of the elongate magnets. Some or all of the turning magnets can be elongate and orientated so as to be substantially perpendicular to the elongate magnets.

First and third turning magnets can be located at a first end of the first and third elongate magnets respectively and second and fourth turning magnets can be located at a second end of the second and fourth elongate magnets, wherein the second end is opposite to the first end, and wherein the turning magnets have an orientation that is substantially perpendicular (i.e. oriented at an angle >45°) to the longitudinal axis of the elongate magnets.

This arrangement of the magnet array can affect the turning of the racetrack at the curved sections more effectively and limits energy bleed in these areas.

The centre of each turning magnet can be aligned with the longitudinal axis of each corresponding elongate magnet.

Such an arrangement can provide an optimum racetrack turn, which can reduce energy bleed.

One end of each of the turning magnets can be aligned with the longitudinal axis of each corresponding elongate magnet.

The first turning magnet can be in contact with the third turning magnet and the second turning magnet can be in contact with the fourth turning magnet. This can result in a closed magnetic field.

The elongate magnets and turning magnets of the magnet array can be arranged into a staggered or zigzag formation. This can result in a closed magnetic field.

A turning magnet may be located at one end of each of the elongate magnets, wherein the turning magnets are oriented at 45° to the elongate magnets and are located at alternate ends of each of the elongate magnets. This can result in a closed magnetic field.

The magnet array can comprise additional guiding magnets spaced from the ends of the elongate magnets. This can result in a closed magnetic field.

The guiding magnets can be oriented at substantially 90° to the turning magnets.

The substrate can be flexible and the apparatus can further comprise a support such as a rotatable drum that is arranged to move in order to transport the flexible substrate.

Alternatively, the apparatus can comprise a planar magnetron sputtering reaction plate arranged adjacent and parallel with respect to the race track. Thus, in some embodiments the serpentine racetracks have application for magnetron sputtering. A conventional racetrack for magnetron sputtering is a simple loop or oval. This has limitations as it limits the maximum depth of target or reaction plate from which material can be deposited in order to achieve maximum target utilisation. This combined with the need to cool the reaction plate and magnets means that deposition rate onto the substrate is limited and simply increasing the power is not always an advantage as this can cause overheating and even melting of the reaction plate in extreme cases. Practically it is power density (Kw/m2 of reaction plate) rather than total power that needs to be considered. Very high power densities can be problematic due to cooling problems. This combined with a largely finite area for a magnetron of given width means ultimate deposition rate is limited. The present inventors have identified that these issues can be addressed with serpentine racetracks. In view of the fact that the length of a serpentine racetrack can be much longer than a conventional racetrack, much deeper and therefore larger magnetron targets for a given width can therefore be utilised as the serpentine racetrack can be designed such that it snakes around the target enabling high target utilisation of even very large targets. Thus, higher deposition powers can be utilised as although overall power is higher, the power density at any given part of the racetrack can be less or comparable to a conventional racetrack. Therefore by using the serpentine racetrack the overall power and thus deposition rate can be increased but power density can be kept to a level that enables sufficient cooling to be achieved subject to correct geometrical considerations (i.e. so that the substrate interacts with the part of the magnetron from which deposition is being achieved). For substrate coating a similar approach can also be used on cylindrical magnetrons so that more of the surface can be utilised for coating at any time.

According to a second aspect of the invention there is provided an apparatus according to claim14.

According to a third aspect of the invention there is provided a method according to claim15.

Thus the invention of the second and third aspects enables barrier layers to be manufactured in a roll to roll process by building up the barrier in multiple repeating steps, thereby increasing line speed as the barrier layer can be applied to multiple locations simultaneously.

Another advantage of the second and third aspects is that plasma quench is reduced compared with a standard PECVD process as the majority of the reaction occurs on the surface of the substrate rather than within the plasma and because each curing station introduces only a small amount of precursor to the substrate at a time.

The second and third aspects of the invention may be used advantageously in combination with the first aspect of the invention as the serpentine racetrack can be used to provide a continuous racetrack around the drum, which provides more sites available for location the curing stations of the second and third aspects. In addition, using one serpentine racetrack around the drum ensures that the plasma is more evenly energised so that each curing station cures or processes the substrate to the same or similar degree as each other curing station which makes the process more controllable and accurate.

