WO2013034404A1

WO2013034404A1 - Vacuum coating apparatus

Info

Publication number: WO2013034404A1
Application number: PCT/EP2012/065865
Authority: WO
Inventors: Frank Fuchs; Andreas Geiss; Michael Neumayer; Guido Mahnke; Harald Rost; Michael Klosch-Trageser; Tobias Bergmann
Original assignee: Schmid Vacuum Technology Gmbh
Priority date: 2011-09-05
Filing date: 2012-08-14
Publication date: 2013-03-14
Also published as: DE102011113294A1; TW201319298A

Abstract

A vacuum coating apparatus and a method for vacuum coating a substrate are disclosed, having an evacuable coating chamber (12), in which there is provided a substrate carrier (28) for holding a substrate (30) to be coated, having an electrode (24) above the substrate carrier (28), having a counter-electrode (32), and having a gas feed (22) having at least one gas outlet opening (26) for feeding process gases in the direction of the substrate (30). A distance (d) between the substrate carrier (28) and the electrode (24) can be altered. Furthermore, at least one flow guiding element is provided between the electrode (24) and the substrate carrier (28), which flow guiding element can be in the form of a frame which extends from the electrode (24) in the direction of the substrate carrier (28) (Figure 1 ).

Description

VACUUM COATING APPARATUS

[0001] The invention relates to a vacuum coating apparatus having an evacu- able coating chamber, in which there is provided a substrate carrier for holding a substrate to be coated, having an electrode above the substrate carrier, having a counter-electrode, and having a gas feed having at least one gas outlet opening for feeding process gases into the coating chamber.

[0002] Such vacuum coating apparatuses are known in principle (cf., for example, US 6,626,186 B1 ). They are used for numerous coating tasks. This may be for example a CVD (Chemical Vapour Deposition) method or a PECVD (Plasma Enhanced Chemical Vapour Deposition) method. In the case of the latter, an RF voltage is applied between the electrode and the counter-electrode, as a result of which a plasma is generated. Such methods are used for example in the production of solar cells, for instance in order to apply a nitride coating in order to passivate the surface of solar cells.

[0003] A problem with such processes is clean implementation of the process in order to apply a contaminant-free coating of constant thickness to the substrate surface, the coating being as uniform as possible. The coating result is influenced here by numerous process parameters, such as the gas composition of the reaction gases, the temperature of the substrate to be coated, the temperature within the coating chamber, the distance between the electrode and the counter-electrode, the voltage or frequency applied, the flow profile of the process gases, and further parameters.

[0004] Even though the relevant process parameters can as a rule be controlled automatically, there are processes that deviate in a variety of ways, and nonuniform coatings, which can lead to rejects. [0005] DE 10 2008 026 000 A1 discloses a vacuum coating apparatus in which a first process gas is let into the vacuum chamber over the entire width of the surface to be coated of a substrate, a second process gas is let into the vacuum chamber in the region of the narrow sides of the substrate, and process gas is extracted by suction from the narrow sides of the substrate during the coating.

[0006] However, this relates only to a vacuum-supported method with different process gases, without the coating process being supported by an electrical field between an electrode and a counter-electrode. The relevant vacuum chamber is designed for a continuous process using a coating source for instance in the form of a linear magnetron sputtering source.

[0007] In view of this, the invention is directed to the object of disclosing a vacuum coating apparatus wherein the coating process can be carried out more uniformly than in previous designs and with high stability in a manner largely free of contaminants. Furthermore, an improved vacuum coating method with use of a voltage between an electrode and a counter-electrode with a feed of process gas shall be disclosed, the method allowing implementation of the process which is uniform and stable.

[0008] This object is achieved according to the invention in the case of a vacuum coating apparatus of the type mentioned at the beginning in that a distance between the substrate carrier and the electrode located opposite is alterable.

[0009] The object of the invention is completely achieved in this way.

[0010] Whereas in conventional vacuum coating methods the distance between the electrode and the counter-electrode is fixedly specified, in the vacuum coating method according to the invention, the distance between the substrate carrier, on which the substrate is held, and the electrode can be altered. By altering the distance between the substrate carrier or counter-electrode and the electrode, the coating process can be adjusted to different conditions. Altered conditions can be taken into account during numerous coating cycles and coating processes that deviate over time can be stabilized by adapting the distance between the electrode and the counter-electrode.

[0011] The vacuum coating apparatus according to the invention operates preferably in batch mode. It may be for instance a PECVD method or a CVD method.

[0012] In a development of the invention, there is provided a lifting device, by means of which the substrate carrier is movable.

[0013] Although it would also be possible in principle to make the electrode vertically adjustable, in the case of adjustment of the substrate carrier by means of a lifting device, an advantageous embodiment is achieved in particular when the vacuum coating apparatus is configured with two planes arranged one above the other, between which the substrate carrier can in any case be moved by a lifting device, in order in this way to be able to achieve better throughput in a batch installation. Preferably, in this case the upper plane is used for coating, while the lower plane serves as a buffer for fully coated substrates and allows increased throughput in conjunction with a suitable handling device.

[0014] In an advantageous development of the invention, the distance between the electrode and the substrate carrier is automatically adjustable, preferably settable by means of a controller depending on at least one coating parameter.

[0015] In this way, an improved implementation of the process with automatic control of the distance between the counter-electrode and the electrode can be achieved.

[0016] The object of the invention is also achieved by a method for vacuum coating a substrate with application of a voltage between an electrode located opposite the substrate and a counter-electrode, with a feed of process gas into the coating chamber, wherein a distance between the electrode and the counter-electrode is set, preferably automatically controlled depending on at least one process parameter. [0017] As already mentioned above, such a method allows more uniform implementation of the process with particularly high quality.

[0018] In an advantageous development of this method, the process gas is fed here via a multiplicity of gas outlet openings in the electrode and is directed by at least one flow guiding element in the direction of the substrate, suction extraction preferably taking place in the bottom region of the coating chamber.

[0019] As a result, a particularly uniform feed of the process gases from above in the direction of the substrate is allowed, with the result that particularly uniform coating results can be achieved

[0020] According to an alternative embodiment of the invention, the object is achieved in the case of a vacuum coating apparatus of the type mentioned at the beginning in that at least one flow guiding element extends between the electrode and the substrate carrier.

[0021] In this way, particularly homogeneous and uniform coating of the substrate is supported. On account of the use of the flow guiding element between the electrode and the substrate carrier, the process gases fed from above can be directed particularly uniformly in the direction of the substrate. A lateral escape of the process gases, before they have passed over the substrate surface, is prevented or minimized in this way.

[0022] In a preferred development of the invention, the flow guiding element is in the form of a frame which extends from the electrode in the direction of the substrate carrier.

[0023] Here, the at least one gas outlet opening is preferably arranged within a chamber enclosed by the flow guiding element. [0024] Further preferably, a plurality of gas outlet openings are provided in the electrode.

[0025] On account of this measure, a particularly uniform, extensive feed of process gases from above in the direction of the substrate is ensured, and this leads to a particularly high coating quality.

[0026] In a further advantageous configuration of the invention, the flow guiding element is arranged and dimensioned such that a gap of at most 20 mm, preferably of at most 10 mm, further preferably of at most 6 mm remains between the substrate carrier and the flow guiding element.

[0027] In a further preferred configuration of the invention, the flow guiding element is arranged and dimensioned such that a gap of about 2 to 20 mm, preferably of about 2 to 7 mm, particularly preferably of about 2 to 5 mm remains between the substrate carrier and the flow guiding element.

[0028] It has been shown that, with such dimensioning of the gap, particularly good coating results are achievable.

[0029] In particular in conjunction with automatic setting of the distance between the substrate carrier and the electrode, the remaining gap can be set in the specified range of between 2 and 20 mm such that optimized implementation of the process can be achieved.

[0030] In a further preferred configuration of the invention, the substrate carrier is held on a plate, preferably on a graphite plate, which is connected as the counter- electrode.

[0031] Whereas in conventional vacuum coating apparatuses the substrate carrier is itself normally connected as the counter-electrode, in this way homogenization of the electrical field between the substrate and the electrode is achieved on account of the use of the plate. It is not the substrate itself that acts as the counter-electrode but rather the plate, which is preferably configured as a graphite plate. In this way, the substrate is enclosed in a more homogeneous field between the plate, which has been shifted further downwards, and the electrode. Particular advantages arise when the plate is configured as a graphite plate, since graphite is a particularly good heat conductor, and this contributes to a uniform temperature distribution.

[0032] In a further preferred configuration of the invention, the plate, or the graphite plate, is heated.

[0033] As a result, particularly uniform heating can be achieved, in particular when the plate is embodied as a graphite plate. Whereas in conventional installations the substrate carrier is heated, the plate, on which the substrate carrier is held, can be heated throughout. As a result, a much more uniform temperature is ensured. In spite of the short cycle times for coating, rapid homogenization of the temperature at the substrate is achieved in this way on account of the graphite plate which is heated throughout.

[0034] In this way, particularly homogeneous and uniform coating is supported.

[0035] It goes without saying that the abovementioned features and those still to be explained below can be used not only in the combination given in each case, but also in other combinations or on their own, without departing from the scope of the invention.

[0036] Further features and advantages of the invention can be gathered from the following description of preferred exemplary embodiments with reference to the drawing, in which:

Figure 1 shows a cross section through a vacuum coating apparatus according to the invention in a highly simplified, schematic illustration; and Figures 2a) to 2c) show a schematic illustration of a vacuum coating installation having three coating cells, one service cell and one loading cell, which are arranged in a pentagonal manner around a central distribution cell, wherein different types of use are illustrated in a) to c).

[0037] In Figure 1 , a vacuum coating apparatus according to the invention is designated overall by reference numeral 10.

[0038] The vacuum coating apparatus 10 has a coating chamber 12, which is surrounded in an air-tight manner by a bottom 16, walls 18 and a top 14. The coating chamber 12 has an upper plane 38 and a lower plane 40 under the latter. A substrate carrier 28 can be held both in the upper plane 38 and in the lower plane 40. The substrate carrier 28 can be introduced into the upper plane 38 and extracted from the latter via an associated door 48 in the wall 18 by means of a handling device 52. For holding in the upper plane, use is made here of associated rollers 36, which can be actuated from outside the coating chamber 12 by means of vacuum bushings and which can be lowered in the wall 18 by axial movement.

[0039] In the lower plane, too, there are provided transport rollers 46, which serve to hold a substrate carrier 28, which can in turn, with the door 50 open, be introduced into and extracted from the lower plane 40 of the coating chamber 12 by means of an associated handling device 54.

[0040] A substrate carrier 28 located in the coating chamber 12 rests, with the transport rollers 36 retracted into the wall 18, on a plate 32 which consists preferably of graphite and can be moved in the vertical direction with the aid of a lifting device 42. The lifting device 42 comprises a lifting drive 64, it being possible for this to be, for example, an electric cylinder, with the aid of which a piston can be displaced in a controlled manner in the vertical direction.

[0041] The plate 32 consisting of graphite is heatable, for which purpose a plurality of heating elements 34, for example resistance heating elements, are provided on its underside, the heating elements 34 being arranged in manner distributed uniformly over the entire undersurface of the plate 32. According to Figure 1 , a planar substrate 30 is held on the substrate carrier 28, which planar substrate 30 can be coated in the coating apparatus 10. The plate 32 is connected as a counter-electrode.

[0042] Above the substrate 30, an associated flat electrode 24 is arranged at a distance d from the substrate carrier 28. A multiplicity of gas outlet openings 26 pass through the electrode 24, said gas outlet openings 26 extending in a manner distributed in the form of a grid over the entire surface of the electrode 24. The gas outlet openings 26 serve to feed process gas for a vacuum coating process, it being possible for said process gas to be fed from outside the coating chamber 12 via a connected gas feed 22.

[0043] Between the plate 32 and the electrode 24, a voltage is applied (not illustrated), it being possible for this to be an RF voltage if a PECVD process under vacuum is intended to be carried out in the coating chamber.

[0044] During a coating process, the process gas, as indicated by the arrows 74, issues uniformly downwards in the direction of the substrate 30. In order to avoid a lateral escape of the process gas and to ensure uniform access of the process gas to the substrate surface, a flow guiding element 70 is provided. This is a circumferentially closed frame which is fastened to the underside of the electrode 24 and extends downwards to just above the substrate carrier 28.

[0045] Between the lower end of the flow guiding element or frame 70 and the substrate carrier 28 there remains a gap s, which is preferably in the range of about 2 to 20 mm, in particular 2 to 5 mm, and is preferably variable with the aid of the lifting device 42 depending on at least one process parameter. To this end, the lifting device 42 is controlled via a central controller 60, as is indicated via a control line 66. A sensor 62 is illustrated purely schematically in the coating chamber 12, the sensor 62 being coupled to the central controller 60 via a line 68. This can be, for example, a temperature sensor, a pressure sensor, a sensor for sensing a particular gas partial pressure, etc. It goes without saying that the sensor 28 is merely indicated in a purely schematic manner and can be configured as any desired sensor, and that it is possible to provide a number of different sensors which are connected to the controller 60. In any case, the distance d between the substrate carrier 28 and the electrode 24 or the gap s between the lower end of the flow guiding element or frame 70 and the substrate carrier 28 can be set in dependence on one of the process parameters with the aid of the controller 60, in order to ensure optimized implementation of the process.

[0046] The coating chamber 12 can be evacuated with the aid of a vacuum pump 20. The vacuum pump 20 has a multiplicity of suction openings 21 , which are preferably arranged in a uniformly distributed manner in the bottom region of the coating chamber 12.

[0047] By way of the flow guiding element or the frame 70, very uniform access of the process gases fed via the electrode 24 to the surface of the substrate 30 is ensured.

[0048] The graphite plate 32, which is connected as the counter-electrode, serves to homogenize the electrical field, since it is easier to make contact with the graphite plate 32 than with the substrate carrier. Furthermore, graphite is a very good heat conductor, which ensures a uniform temperature distribution over the entire surface. A particularly uniform temperature distribution thus arises over the entire graphite plate 32 and thus also over the substrate carrier 28 and ultimately the substrate 30, and this leads to a correspondingly homogeneous coating result.

[0049] On account of the division of the coating chamber 12 into an upper plane 38 and a lower plane 40, a particularly fast throughput can be ensured in combination with associated handling devices and associated loading and distribution devices.

[0050] When a coating process in the upper region 38 of the coating chamber 12 is at an end, the substrate carrier 28, having the substrate 30 located thereon, can be moved into the lower plane 40 by means of the lifting device 42. With the doors 48 or 50 open, a new substrate carrier having a substrate to be coated can then be introduced by means of the handling device 52, as is indicated by the arrow 56. At the same time, the substrate carrier 28, having the fully coated substrate 30 located thereon, can be extracted from the lower plane 40, with the door 50 open, via the handling device 54, as is indicated by the arrow 58.

[0051] It goes without saying that, instead of two separate doors 48, 50 as per Figure 1 , it is also possible to provide a common, continuous door or port.

[0052] The installation preferably operates in a cyclical manner in batch mode.

[0053] Figure 2 illustrates the basic structure of a vacuum coating installation which is designated overall by the number 80. The vacuum coating installation 80 according to Figure 2a) comprises three coating cells P1 , P2, P3 and an identically constructed service cell M, and also a loading cell 82, said cells being arranged on the outside around a distribution cell 84 which has the form of a regular pentagon. The coating cells P1 , P2, P3 and the maintenance cell M can each be coupled to the distribution cell 84 via an associated port or door.

[0054] Each coating cell P1 , P2, P3 and the maintenance cell M is formed by a vacuum coating apparatus 10 in the above-described manner.

[0055] In the present case, the same coating process is carried out in all of the coating cells P1 , P2, P3. On account of the parallel operation of the coating cells P1 , P2, P3, an increased throughput is ensured. The capacity of the coating cells P1 , P2, P3 is designed such that three coating cells suffice to ensure the nominal throughput. The maintenance cell M has an identical structure to the coating cells P1 , P2, P3 and thus serves as reserve capacity. This means that the coating process operates at nominal throughput, while at the same time maintenance work, for example cleaning work and the like, can be carried out in one cell, in the maintenance cell M, without the nominal throughput being impaired. [0056] Figure 2b) shows a different state of the vacuum coating installation 80', in which the cell P3 previously used as a coating cell in the process as per Figure 2a) is now used as the maintenance cell M, and in which the previous maintenance cell M is now operated as the coating cell P3 in the process.

[0057] Thus, the same number of coating modules are available as before, while at the same time a different one of the modules is now used for maintenance, as is indicated at M.

[0058] Figure 2c) shows a further state of the vacuum coating installation 80", in which the cell previously used as the coating cell P2 as per Figure 2b), is now used as the maintenance cell M, while the previous maintenance cell is used as the coating cell P2.

[0059] Thus, the nominal throughput of the entire vacuum coating installation can always be achieved, while one of the cells is always offline for maintenance purposes. Overall, an uptime of about 97% can be ensured with such a design.

Claims

A vacuum coating apparatus comprising an evacuable coating chamber (12), wherein a substrate carrier (28) is provided for holding a substrate (30) to be coated, further comprising an electrode (24) arranged above the substrate carrier (28), further comprising a counter-electrode (32), and further comprising a gas feed (22) having at least one gas outlet opening (26) for feeding process gases into the coating chamber (12), characterized in that a distance (d) between said substrate carrier (28) and said electrode (24) is alterable.

The vacuum coating apparatus of claim 1 , characterized in that there is provided a lifting device (42), by means of which the substrate carrier (28) is movable.

The vacuum coating apparatus of claim 1 or 2, characterized in that the distance (d) between the electrode (24) and the substrate carrier (28) is automatically adjustable, preferably settable by means of a controller (60) depending on at least one coating parameter.

The vacuum coating apparatus of any of the preceding claims, characterized in that at least one flow guiding element (70) extends between the electrode (24) and the substrate carrier (28).

The vacuum coating apparatus of claim 4, characterized in that the flow guiding element (70) is in the form of a frame which extends from the electrode (24) in the direction of the substrate carrier (28).

The vacuum coating apparatus of claim 4 or 5, characterized in that the at least one gas outlet opening (26) is arranged within a chamber (72) enclosed by the flow guiding element (70).

7. The vacuum coating apparatus of claim 6, characterized in that a plurality of gas outlet openings (26) are provided in the electrode (24).

8. The vacuum coating apparatus of any of the preceding claims, characterized in that the flow guiding element (70) is arranged and dimensioned such that a gap (s) of at most 20 millimetres, preferably of at most 10 millimetres, further preferably of at most 6 millimetres remains between the substrate carrier (28) and the flow guiding element (70).

9. The vacuum coating apparatus of claim 8, characterized in that the flow guiding element (70) is arranged and dimensioned such that a gap (s) of about 2 to 20 millimetres, preferably of about 2 to 7 millimetres, particularly preferably of about 2 to 5 millimetres remains between the substrate carrier (28) and the flow guiding element (70).

10. The vacuum coating apparatus of any of the preceding claims, characterized in that the substrate carrier (28) is held on a plate (32), preferably on a graphite plate, which is connected as the counter-electrode.

1 1 . The vacuum coating apparatus of claim 10, characterized in that the plate (32) is heated.

12. A method of vacuum coating a substrate (30) with application of a voltage between an electrode (24) located opposite the substrate (30) and a counter-electrode (32), with a feed of process gas from above, wherein a distance (d) between the electrode (24) and the counter-electrode (32) is altered, preferably depending on at least one process parameter.

13. The method of claim 12, wherein the process gas is fed via a multiplicity of gas outlet openings (26) in the electrode (24) and is directed by at least one flow guiding element (70) in the direction of the substrate (30), suction extraction preferably taking place in the bottom region of the coating chamber (12).