AU2016100321A4 - Glass coating - Google Patents

Abstract

A sputtering apparatus (10) and method for producing a reflective coating on a substrate includes a production chamber (14) and a sputtering station (22) located within the production chamber (14). A moving means (16) is provided for moving the 5 substrate through the sputtering station (22) in a first direction and moving the substrate through the sputtering station (22) in a second direction. A common access port (18) is provided for loading and unloading of the substrate from the production chamber (14). The substrate may be toughened glass. Hl o [] c

Description

P/00/011 Regulation 3.2 AUSTRALIA Patents Act 1990 COMPLETE SPECIFICATION INNOVATION PATENT Invention Title: Glass coating The following statement is a full description of this invention, including the best method of performing it known to us: Glass Coating Field of the invention The present invention relates to production methods and apparatus for providing a reflecting layer on a substrate. In particular, although not exclusively, the invention 5 relates to production of plate glass mirrors using sputtering technology. Additionally, the invention may relate to production methods for mirrors and mirrors produced using toughened plate glass as the substrate. Background of the invention Mirrors are currently increasing in popularity as a decorating feature. They are 10 finding use in non-traditional applications such as kitchen splashbacks and bathroom and shower walls. These applications involve more difficult environmental conditions for the mirrors such as increased heat and moisture. Production of mirrors generally involves the application of a reflective coating such as a reflective metal to a substrate, typically glass. Other coatings may include an 15 intermediate coating between the glass and the reflective metal to aid adhesion and one or more protective layers for long term durability, prevention of scratches and other accidental damage. Typically, the final layer is paint. These layers typically involve different processes and so the layers are progressively built up on the substrate as it passes along a production line having a number of separate apparatus in-line in order to 20 acquire each of the discrete layers. Since economies of scale can be achieved with production line manufacturing, commercial mirrors are commonly manufactured on a large scale. Large-scale manufacturing generally involves considerable capital expenditure and occupies a large amount of industrial real estate, and may be cost prohibitive in certain countries. Thus, importing of mirrors is typical in many countries. 25 An alternative to large scale production of mirrors is local hand production. Generally, companies need to resort to hand production for customisation of the mirror beyond the large scale production product. The difficulty with hand production is that it is typically slow. It also leads to greater exposure of the workers to toxic chemicals in comparison to the large scale production plants. 2 There are supply and toxicity problems with these customised products. One such customised product is a mirror with toughened glass for use in the non traditional applications discussed above. A large scale production mirror cannot be thermally tempered to achieve the toughened glass without destroying the layers 5 making up the mirror. Thus toughened glass mirrors are often required to be hand-made locally with the supply and toxicity problems mentioned above. Accordingly, it is an object of the present invention to provide a mirror or a production method or apparatus which overcomes or at least addresses one of the abovementioned disadvantages. An alternative object of the invention is to at least 10 provide the public with useful choice over known products, methods and apparatus. Reference to any prior art in the specification is not an acknowledgment or suggestion that this prior art forms part of the common general knowledge in any jurisdiction or that this prior art could reasonably be expected to be understood, regarded as relevant, and/or combined with other pieces of prior art by a skilled person 15 in the art. Summary of the invention In accordance with a first aspect of the present invention there is provided a sputtering apparatus for producing a reflective coating on a substrate, the apparatus including: 20 a production chamber; a sputtering station located within the production chamber; and a moving means for moving the substrate through the sputtering station in a first direction and moving the substrate through the sputtering station in a second direction; and 25 a common access port for loading and unloading of the substrate from the production chamber. The moving means is preferably a conveyor, although other arrangements are possible such as a gantry or a moveable carriage. The moving means or conveyor is 3 preferably reversible so that the first pass through the sputtering station is in a first direction and the second pass through the sputtering station is in a second direction opposite to the first direction. The moving means may be driven in opposite directions as selected by the 5 operator or automatically according to the programming of the apparatus. The conveyor could comprise two conveying devices, one for each direction of travel. The sputtering apparatus is suitably a batch processing apparatus since a new substrate cannot enter the production chamber until the existing substrate is removed. Preferably, the sputtering apparatus operates to apply a reflective layer as the 10 substrate passes in the first direction through the sputtering station. In the second direction through the sputtering station, preferably, a protective layer is applied at the sputtering station. Thus, the same apparatus can be used to apply both the reflective layer as well as the protective layer. Additionally, having the substrate making multiple passes through the sputtering station means that two or more layers can be applied 15 without any increase in industrial real estate compared to the requirement for a single layer. Preferably, the reflective layer is a reflective metal such as aluminium, silver, copper, stainless steel or titanium, to name a few. Such metals are typically applied in the presence of argon gas as will be understood by those skilled in the field of ?0 sputtering technology. However, alternative gases may be used for different effects, such as colour effects in the reflective layer. The protective layer is preferably silicon nitride which provides a protective coating over the reflective metal layer. The silicon nitride is deposited in the sputtering apparatus through the use of silicon target(s) which emit particles in the presence of 25 nitrogen gas and react to create a protective layer of silicon nitride on the substrate. Where a reflective metal is first applied in the presence of argon gas, this requires a change of gas in the production chamber. Therefore, the sputtering apparatus is operable to provide argon gas for the first pass of the substrate past the sputtering station. The sputtering apparatus is also operable to evacuate the argon gas and 30 provide an alternative gas such as nitrogen into the production chamber prior to the second pass of the substrate past the sputtering station. 4 It is conceivable that a second protective layer may be applied over the first protective layer. For this purpose, the moving means may operate to move the substrate in a third pass past the sputtering station. The gas may also be changed for this pass. For example, a second protective layer may be titanium or stainless steel 5 which may be deposited by the sputtering apparatus in the presence of argon gas. As will be understood with sputtering technology, the production chamber is a vacuum chamber which includes the sputtering station. Preferably, the sputtering station is disposed in an intermediate location between the ends of the production chamber. Preferably, there are first and second holding bays located on either side of the 10 sputtering station, each holding bay being of sufficient length for receipt of the substrate, without the substrate encroaching on the sputtering station. For example, where the sputtering apparatus is equipped to deal with a substrate of plate glass, the holding bays may be equipped to accommodate a sheet of plate glass between 3.5 and 4 metres in length. The first holding bay enables the substrate to enter the production 15 chamber so that vacuum conditions can be achieved in the production chamber before the substrate passes through the sputtering station. Likewise, the second holding bay accommodates the full length of the substrate after the first pass and prior to the second pass through the sputtering station. The common access port is preferably the sole access port into the production ?0 chamber. The access port serves as a vacuum lock to maintain the vacuum conditions within the production chamber. An additional vacuum lock may be provided between the first holding bay and the sputtering station. This enables vacuum conditions to be retained within at least part of the production chamber when the first holding bay is open to the atmosphere through the access port. 25 The provision of a common access port reduces industrial real estate since the substrate is not being conveyed past the second holding bay. In a preferred form of the invention a loading bay is provided immediately adjacent to the access port to enable loading of the substrate into the production chamber. Preferably, the loading bay is in the form of a table including a reversible 30 moving means or conveyor. 5 The nature of sputtering technology may be more fully understood from the explanation accompanying figure 1. However, the details of sputtering technology will be understood by those skilled in the art. The sputtering apparatus preferably uses magnetron sputtering technology. 5 Preferably, the sputtering apparatus uses a DC planar cathode for use with the selected reflective metal target. Thus, the sputtering station preferable includes one or more cathode + target + DC power supply assemblies. Additionally, the apparatus uses a twin cathode coupled to an AC medium frequency cathode power supply for use with twin silicon targets. Thus, the sputtering station may also include one or more twin cathode + 10 twin target + AC power supply assemblies. The substrate used may include glass such as toughened glass, or alternatively plastic may be used. In accordance with a second aspect of the present invention there is provided a method of providing a reflective coating on a substrate, the method including: 15 providing a sputtering apparatus having a sputtering station; operating the sputtering apparatus to provide a reflective layer on the substrate; operating the sputtering apparatus to provide a protective layer over the reflective layer; wherein the substrate is passed in a first direction through the sputtering station 20 to apply the reflective layer and is subsequently passed in a second direction through the sputtering station to apply the protective layer; and wherein the substrate is passed through a common access port for loading and unloading into the production chamber. Preferably, the substrate is passed in one direction through the sputtering station 25 to apply the reflective layer and then reversed and passed in the opposite direction through the sputtering station to apply the protective layer. However, there may be three or more passes to apply the reflective layer before the protective layer is applied. 6 In this way, the same sputtering apparatus may be used to build up two or more layers on the substrate. Moreover, the same sputtering station may be used to apply two or more layers to the substrate. The sputtering station may include adjacently located cathode + target + power supply assemblies, each for a different layer. 5 Nevertheless the co-location of these assemblies in the sputtering station means a reduction in industrial real estate for the apparatus. The substrate can pass between the two holding bays on either side of the sputtering station as many times as required to achieve the appropriate number of layers on the substrate, without much increase in industrial real estate as compared to that required to produce one layer on the 10 substrate. In a preferred form of the method, the substrate is toughened glass. The second aspect of the invention may incorporate any of the preferred features described above in connection with the first aspect of the invention. In accordance with a third aspect of the present invention, there is provided a 15 method of making a sheet glass mirror, the method including: providing a sputtering apparatus having a sputtering station; operating the sputtering apparatus to provide a reflective layer on a substrate of toughened glass; operating the sputtering apparatus to provide a protective layer over the reflective 20 layer; wherein the toughened glass substrate makes a pass through the sputtering station to provide the reflective layer and a subsequent pass through the sputtering station to provide the protective coating. Preferably, the substrate is passed in a first direction through the sputtering 25 station to acquire the reflective layer and then reversed to pass in the opposite direction through the sputtering station to acquire the protective layer. The substrate may be passed through the sputtering station to build up as many layers as required. 7 It is understood that "toughened" glass (otherwise known as tempered glass) is a type of safety glass processed by controlled thermal or chemical treatments to increase its strength compared with normal glass. Such glass may accord with the appropriate Australian standard. 5 Any of the preferred features described in connection with any of the aspects above may be applied to the third aspect of the invention. Also described herein, but not claimed is a mirror including: toughened glass as the substrate; a layer of reflective material; and 10 a layer of silicon nitride over the layer of reflective material. Also described herein, but not claimed is a method of producing a mirror, the method including: applying a layer of reflective material to a substrate of toughened glass, followed by a layer of silicon nitride over the reflective material. 15 It will be understood that the invention disclosed and defined in this specification extends to all alternative combinations of two or more of the individual features mentioned or evident from the text or drawings. All of these different combinations constitute various alternative aspects of the invention. As used herein, except where the context requires otherwise, the term 20 "comprise" and variations of the term, such as "comprising", "comprises" and "comprised", are not intended to exclude further additives, components, integers or steps. Further aspects of the present invention and further embodiments of the aspects described in the preceding paragraphs will become apparent from the following 25 description, given by way of example and with reference to the accompanying drawings. 8 Brief description of the figures In order that the invention may be more fully understood, one embodiment will now be described by way of example, with reference to the figures in which: Figure 1 is a diagram illustrating the operation of a planar magnetron sputtering 5 apparatus; Figure 2 is a diagram illustrating a mirror produced according to a preferred embodiment of the present invention; and Figure 3 is a side view of the sputtering apparatus according to a preferred embodiment of the present invention; and 10 Figure 4 is a plan view of the sputtering apparatus illustrated in figure 3. Description of preferred embodiment Magnetron sputtering will now be described in connection with figure 1, although this technique will be well understood by those skilled in the art. Sputtering is a technique used to deposit thin films of a material onto the surface 15 of a surface substrate. By first creating a gaseous plasma and then accelerating the ions from this plasma into some source material ("target"), the source material is eroded by the arriving ions via energy transfer and is ejected in the form of neutral particles either individual atoms, clusters of atoms or molecules. As these neutral particles are ejected they will travel in a straight line unless they come into contact with something 20 other particles or a nearby surface. If a substrate such as plate glass is placed in the path of these ejected particles it will be coated by a thin film of the source material. A gaseous plasma is a "dynamic condition" where neutral gas atoms, ions, electrons and photons exist in a near balanced state simultaneously. An energy source (eg RF, DC, MW) is required to "feed" and thus maintain the plasma state while the 25 plasma is losing energy into its surroundings. One can create this dynamic condition by metering a gas (e.g. Ar) into a pre-pumped vacuum chamber and allowing the chamber pressure to reach a specific level and introducing a live electrode into this low pressure gas environment. 9 Ever present "free electrons" will immediately be accelerated away from the negatively charged electrode (cathode). These accelerated electrons will approach the outer shell electrons of neutral gas atoms in their path and, being of a like charge, will drive these electrons off the gas atoms. This leaves the gas atom electrically 5 unbalanced since it will have more positively charged protons than negatively charged electrons. Thus it is no longer a neutral gas atom but a positively charged "ion" (e.g. Ar +). At this point the positively charged ions are accelerated into the negatively charged cathode striking the surface and "blasting" loose electrode material (diode 10 sputtering) and more free electrons by energy transfer. The additional free electrons feed the formation of ions and the continuation of the plasma. All the while, free electrons find their way back into the outer electron shells of the gas ions thereby changing them back into neutral gas atoms. Due to the laws of conservation of energy, when these electrons return to a ground state, the resultant 15 neutral gas atom gained energy and must release that same energy in the form of a photon. The release of these photons is the reason the plasma appears to be glowing. Diode sputtering however has two major problems - the deposition rate is slow and the electron bombardment of the substrate is extensive and can cause overheating and structural damage. 20 The development of magnetron sputtering deals with both of these issues simultaneously. By using magnets behind the cathode to trap the free electrons in a magnetic field directly above the target surface, these electrons are not free to bombard the substrate to the same extent as with diode sputtering. At the same time the extensive, circuitous path carved by these same electrons when trapped in the 25 magnetic field, enhances their probability of ionizing a neutral gas molecule by several orders of magnitude. This increase in available ions significantly increases the rate at which target material is eroded and subsequently deposited onto the substrate. Figures 3 and 4 illustrate a sputtering apparatus 10 including a loading table 12 and a production chamber 14. The loading table 12 includes a reversible conveyor 10 including a motor 15 to drive a chain drive (not shown). The rubber rollers 16 have sprockets (not shown) on the ends enabling them to be driven by the chain drive. The production chamber 14 includes a similar conveyor contained within the chamber. 5 The elongate production chamber 14 includes an access port 18 adjacent to the loading table 12. The access port 18 is in the form of a vacuum gate 18 to retain the vacuum conditions within the production chamber 14. The production chamber 14 also includes a first holding bay 20. The holding bay 20 is elongate and sized to accommodate a sheet of plate glass of maximum dimension 3660 mm x 1250 mm. 10 Adjacent to the first holding bay is the sputtering station 22 which will be described in further detail below. On the opposite side of the sputtering station 22 is a second holding bay 24 which is elongate and of substantially similar dimensions to the first holding bay 20. The production chamber is maintained under vacuum conditions for the 15 sputtering to occur. Typically, the vacuum conditions are in the range of 8 x 10-3 to 5 x 10-3 Pa. A vacuum pumping system 26 is comprised of various pumps operating in succession to create the desired vacuum conditions as well as valves and pipelines. From one atmosphere to 8 x 10-3 may take 6-7 minutes by the vacuum pumping system 26. 20 The sputtering apparatus 10 also includes a gas filling system 28. Once the vacuum conditions are created in the production chamber 14, the gas filling system 28 operates to introduce a gas such as argon into the production chamber. The working pressure is about 8 x 10-2 Pa. Alternatively, some reactive gases like nitrogen and oxygen can be introduced 25 into the production chamber 14. During sputtering, these reactive gases react with the particles ejected from the target. For example, where the target is titanium, TiO 2 , TiN may be produced. In the case of nitrogen with a silicon target, silicon nitride will be deposited on the substrate. In the preferred form of the sputtering apparatus, the gas filling system 28 is 30 provided with four sets of gas mass-flow controllers. Where a gas is to be changed over 11 to achieve different coating effects, the existing gas in the production chamber 14 must be pumped out and the production chamber 14 filled with the new gas. The production chamber 14 also includes a second vacuum gate 30 between the first holding bay 20 and the sputtering station 22. The reason for this will now be 5 explained. During initial use of the machine, the first vacuum gate 18 is opened and the substrate is conveyed into the production chamber 14 by the action of the conveyor of the loading table 12 and the conveyor of the production chamber 14. The first holding bay fully accommodates the substrate and the vacuum gate 18 is closed, enabling the 10 vacuum conditions to extend throughout the production chamber 14. The vacuum gate 30 is open. The substrate then passes through the sputtering station 22 so that the substrate progressively receives the first layer as it passes through the sputtering station 22. Typically, the first layer is a coating of reflective metal, preferably aluminium. The second holding bay 24 is similar, if not identical in size to the first holding bay 20. 15 The second holding bay 24 fully accommodates the substrate once it has passed through the sputtering station 22. At this point, the argon gas which exists in the production chamber 14 may be evacuated and an alternative gas such as nitrogen pumped into the production chamber 14. The conveyor in the production chamber 14 is stationary during the changeover of gas. The conveyor then reverses, passing the ?0 substrate a second time through the sputtering station 22 in the opposite direction so that a second layer e.g. silicon nitride is progressively applied to the substrate as it passes through the sputtering station. The substrate is then received in the first holding bay 20. At this point, the substrate is then ready for ejection from the production chamber through the access port 18. Alternatively, the substrate may pass again 25 through the sputtering station to receive a third layer on the substrate. Successive layers are also possible. It will also be understood that plural layers of aluminium may be applied before the one or more subsequent protective layers. Thus, the substrate passes through the sputtering station as many times as required to build up the desired layers, with 30 changes of gas required depending on the layer to be deposited. 12 Once the substrate is ready for ejection from the first holding bay 20, the second vacuum gate 30 is closed. Once closed, the first vacuum gate 18 can be opened to eject the substrate from the production chamber 14. Thus, the presence of the second vacuum gate 30 maintains the vacuum conditions in at least a part of the production 5 chamber 14. The completed mirror is received on the loading table 12 for dispatch. It will be understood that the only access into the production chamber 14 is through the access port 18. The sputtering station 22 contains three cathode + power supply + target assemblies. These are not shown in detail but will be understood by those skilled in the 10 art. The first two assemblies include a planar cathode for which there is provided a DC power supply. The DC planar cathode is operated in conjunction with a planar target. Suitable targets include aluminium, nickel chromium, stainless steel, titanium and other metals. There are two such DC planar cathode + power supply arrangements arranged side by side in the sputtering station 22. For example, a first DC planar cathode + power 15 supply arrangement 32 may be set up for an aluminium target. A second DC planar cathode + power supply arrangement 34 may be set up for a titanium target. The sputtering station 22 also includes a twin cathode + medium frequency cathode power supply arrangement 36. In such an arrangement, there are twin cathodes to which AC current is alternately applied. Such a twin arrangement is used ?0 minimise contamination of the target material. The twin cathode arrangement is used for the silicon targets. The silicon targets are used in the presence of nitrogen gas to create a layer of silicon nitride as a protective layer on the substrate. Silicon nitride is a relatively inert material which provides protection for the aluminium layer. It is currently understood that an outer layer of silicon nitride may be all that is 25 required to create sufficient protection over the reflective layer. Thus the silicon nitride layer may be the outer layer of the finished mirror. A third pass (or subsequent to the second pass) through the sputtering station 22 may use the titanium target in the presence of argon gas to create a layer of titanium on the substrate. This third protective layer is currently considered optional, although 30 further trials are underway. 13 It will be understood that the co-location of the cathode + power supply arrangements 32, 34, 36 in the sputtering station 22 increases the overall functionality of the apparatus 10. This means that only two holding bays 20, 24 are required either side of the sputtering station to achieve different sputtered layers onto the substrate. 5 Many different layers may be applied to the substrate, without increasing the overall length of the apparatus 10. The power supply for the DC planar cathode is constant DC power source. The input capacity is 60 KVA for each source. The apparatus 10 includes a process controller to fully automate the process, 10 except for loading and unloading. The fully automatic control can ensure repeatability of the coating process. The controller also allows for manual adjustment and commissioning. The working status of the apparatus 10 is shown on a touch screen (not shown) where instructions can be input and the procedure monitored. 15 The thickness of the substrate may be between 3 mm to 10 mm. Typically, the cycle time is from 10-15 minutes per cycle. The apparatus 10 is water cooled as illustrated schematically in figure 1. Figure 2 illustrates schematically the finished mirror from the sputtering apparatus 10. The mirror 40 includes planar substrate 42 of toughened glass. Applied to 20 the substrate 42 are one or more layers 44 of aluminium which form a complete coating over the substrate 42. Over the aluminium layer(s) are one or more layers 46 of silicon nitride, typically Si 3

N

4 , forming a complete coating over the layer(s) 44. The foregoing describes only one embodiment of the present invention and modifications may be made thereto without departing from the scope of the invention. 25 14

Claims (7)

1. A sputtering apparatus for producing a reflective coating on a substrate, the apparatus including: a production chamber; 5 a sputtering station located within the production chamber; and a moving means for moving the substrate through the sputtering station in a first direction and moving the substrate through the sputtering station in a second direction; and a common access port for loading and unloading of the substrate from the 10 production chamber.

2. A method of providing a reflective coating on a substrate, the method including: providing a sputtering apparatus having a sputtering station; operating the sputtering apparatus to provide a reflective layer on the substrate; 15 operating the sputtering apparatus to provide a protective layer over the reflective layer; wherein the substrate is passed in a first direction through the sputtering station to apply the reflective layer and is subsequently passed in a second direction through the sputtering station to apply the protective layer; and 20 wherein the substrate is passed through a common access port for loading and unloading into the production chamber.

3. The apparatus as claimed in claim 1 or the method as claimed in claim 2 wherein the common access port is the sole access port into the production chamber for the substrate. 25

4. The apparatus or method as claimed in any one of the preceding claims wherein the common access port serves as a vacuum lock to maintain the vacuum conditions 15 within the production chamber and there are first and second holding bays on either side of the sputtering station and an additional vacuum lock is provided between the first holding bay and the sputtering station.

5. The method as claimed in claim 2 wherein the first and second directions are 5 opposite.

6. The method as claimed in claim 2 wherein the substrate is toughened glass.

7. A method of making a sheet glass mirror, the method including: providing a sputtering apparatus having a sputtering station; operating the sputtering apparatus to provide a reflective layer on a substrate of 10 toughened glass; operating the sputtering apparatus to provide a protective layer over the reflective layer; wherein the toughened glass substrate makes a pass through the sputtering station to provide the reflective layer and a subsequent pass through the sputtering 15 station to provide the protective coating. 16