WO2013034411A2

WO2013034411A2 - Vacuum coating apparatus

Info

Publication number: WO2013034411A2
Application number: PCT/EP2012/065908
Authority: WO
Inventors: Andreas Geiss; Guido Mahnke; Harald Rost; Michael Klosch-Trageser
Original assignee: Schmid Vacuum Technology Gmbh
Priority date: 2011-09-05
Filing date: 2012-08-14
Publication date: 2013-03-14
Also published as: WO2013034411A3; TW201327618A; DE102011113293A1

Abstract

A vacuum coating apparatus is disclosed having an evacuable coating chamber (12), wherein there is provided a substrate carrier (28) for holding a substrate (30) to be coated, having an electrode (24) above the substrate (30) to be coated, and having a counter- electrode (32) wherein the substrate carrier (28) is held on a plate (32) which preferably consists of graphite and which is connected as the counter-electrode.

Description

VACUUM COATING APPARATUS

[0001] The invention relates to a vacuum coating apparatus having an evacuable coating chamber, in which there is provided a substrate carrier for holding a substrate to be coated, having an electrode above the substrate carrier and having a counter-electrode.

[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, said 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 and frequency applied, the flow profile of the process gases, and further parameters.

[0004] Against this background, the invention is based on the object of improving a vacuum coating apparatus of the type mentioned at the beginning in such a way that the coating process can be carried out as uniformly as possible and with high stability. Furthermore, an improved vacuum coating method with use of a voltage between an electrode and a counter-electrode with a feed of process gas is intended to be specified, said method allowing implementation of the process which is as uniform and stable as possible. [0005] 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 the substrate carrier is held on a plate which is connected as the counter-electrode and preferably consists of graphite.

[0006] The object of the invention is completely achieved in this way.

[0007] Whereas in conventional vacuum coating apparatuses a substrate to be coated, for instance a wafer, rests directly on a substrate carrier made of carbon fibre (CFC), which is connected as a counter-electrode, the substrate carrier is held according to the invention on a plate which is connected as the counter-electrode. Thus, the substrate is held in a more homogeneous field, since the electrical field extends as far as the plate. In this way, a more homogeneous coating result can be achieved.

[0008] In a preferred development of the invention, the plate consists of graphite. Graphite is a much better heat conductor than a metal substrate carrier, and thus contributes to homogeneous temperature distribution and thus to an improved coating.

[0009] On account of its weight and the large surface area, the plate is preferably composed of a plurality of individual plates.

[0010] In a preferred configuration of the invention, the plate is heated. In particular when the plate consists of graphite, a particularly homogeneous temperature distribution is achieved on account of the good heat conductivity, and as a result a more homogeneous coating result can be achieved.

[0011] Whereas in conventional installations the substrate carrier is indirectly heated, the plate, on which the substrate carrier is held, can be heated throughout. As a result, a much more uniform temperature is ensured.

[0012] For heating, a plurality of heating elements, for instance in the form of resistance heating elements, are preferably arranged beneath the plate. The heating elements are preferably distributed as uniformly as possible over the entire surface of the plate in order to achieve a particularly homogeneous temperature distribution. Each heating element can be actuated or regulated individually.

[0013] A plurality of gas outlet bores, which are preferably distributed as uniformly as possible over the entire surface of the electrode, preferably pass through the electrode.

[0014] In a further preferred configuration of the invention, a flow guiding element, preferably in the form of a frame, is provided on the electrode, said flow guiding element extending in the direction of the substrate carrier.

[0015] On account of these measures, a uniform flow of the process gases in the direction of the substrate is supported, as a result of which the coating result is improved.

[0016] According to a further configuration of the invention, the distance between the electrode and the substrate carrier is alterable.

[0017] Whereas in conventional vacuum coating methods this distance is fixedly specified, 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 configured more uniformly and coating processes that deviate can be stabilized by adapting the distance between the electrode and the counter-electrode.

[0018] In this way, an improved implementation of the process, optionally with automatic control of the distance between the electrode and the counter-electrode, can be achieved. [0019] The distance between the electrode and the substrate carrier can preferably be set here such that a gap of about 2 to 20 mm, preferably about 2 to 5 mm, remains between a flow guiding element and the substrate carrier.

[0020] The vacuum coating apparatus according to the invention operates preferably in batch mode.

[0021] For the purpose of a high throughput, a vacuum coating installation can be coupled to a plurality of coating apparatuses having a common charging cell, wherein at least one of the coating apparatuses can be decoupled from the operation of the remaining coating apparatuses for maintenance purposes as a maintenance cell, wherein the capacity of the remaining coating apparatuses is designed such that the nominal capacity of the vacuum coating installation is achieved without the maintenance cell.

[0022] In this way, maintenance work can be carried out in the maintenance cell during an ongoing coating process, without the installation having to be shut down. In this way, an uptime of about 97 % on average can be achieved.

[0023] It is possible to operate all coating apparatuses belonging to the vacuum coating installation during normal operation simultaneously at reduced capacity while achieving the nominal throughput capacity.

[0024] Alternatively, a selected one of all the coating aparatuses may intentionally be put out of order to be idle while the remaining coating aparatuses are operated at higher throughput capacity to maintain the total nominal throughput capacity.

[0025] In this way, maintenance work can be carried out in the maintenance cell during the ongoing coating process, without the installation having to be shut down. In this way, an uptime of about 97 % on average can be achieved.

[0026] The object of the invention is also achieved by a method for vacuum coating a substrate with application of a voltage between an electrode and a counter- electrode, with a feed of process gas, wherein the substrate is arranged on a substrate carrier between the electrode and a plate which preferably consists of graphite and which is connected as the counter-electrode.

[0027] As already mentioned above, such a method allows more uniform implementation of the process with particularly high quality.

[0028] 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.

[0029] 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.

[0030] 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.

[0031] 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).

[0032] In Figure 1 , a vacuum coating apparatus according to the invention is designated overall by the number 10.

[0033] 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.

[0034] 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.

[0035] 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.

[0036] 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, said 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.

[0037] 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.

[0038] 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.

[0039] 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.

[0040] 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, said 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.

[0041] 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.

[0042] 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.

[0043] The graphite plate 32, which is connected as the counter-electrode, serves to homogenize the electrical field. 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.

[0044] 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.

[0045] 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 ex- traded from the lower plane 40, with the door 50 open, via the handling device 54, as is indicated by the arrow 58.

[0046] 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.

[0047] The installation preferably operates in a cyclical manner in batch mode.

[0048] 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.

[0049] Each coating cell P1 , P2, P3 and the maintenance cell M is formed by a vacuum coating apparatus 10 in the above-described manner.

[0050] 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.

[0051] 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.

[0052] 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.

[0053] 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.

[0054] 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.

[0055] In a different configuration, all cells P1 to P4 and M may be used simultaneously for production at reduced capacity. For maintenance, one of the cells M is decoupled from the remaining cells P1 to P4 which then operate at higher capacity close to their maximum capacity, to thereby achive nominal total output capacity while one cell M undergoes maintenance.

Claims

1 . 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 said substrate (30) to be coated, and having a counter-electrode (32), characterized in that the substrate carrier (28) is held on a plate (32) which is connected as the counter-electrode.

2. The vacuum coating apparatus of claim 1 , characterized in that the plate (32) consists of graphite.

3. The vacuum coating apparatus of claim 1 or 2, characterized in that the plate (32) is composed of a plurality of individual plates.

4. The vacuum coating apparatus of any of the preceding claims, characterized in that the plate (32) is heated.

5. The vacuum coating apparatus of claim 4, characterized in that a plurality of heating elements (34) are arranged beneath the plate (32).

6. The vacuum coating apparatus of claim 5, characterized in that the heating elements (34) are arranged in a manner distributed as uniformly as possible underneath the surface of the plate (32), wherein the heating elements (34) can preferably be regulated individually.

7. The vacuum coating apparatus of any of the preceding claims, characterized in that a plurality of gas outlet bores (26) for feeding process gases pass through the electrode (24).

8. The vacuum coating apparatus of any of the preceding claims, characterized in that a flow guiding element (70), preferably in the form of a frame, is provided on the electrode (24), said flow guiding element (70) extending in the direction of the substrate carrier (28).

9. The vacuum coating apparatus of any of the preceding claims, characterized in that the distance (d) between the substrate carrier (28) and the electrode (24) is alterable during a coating process, preferably such that a gap of about 2 to 15 millimetres, preferably of about 3 to 7 millimetres, particularly preferably of about 4 to 5 millimetres, remains between the substrate carrier (28) and a flow guiding element (70) that extends from the electrode (24).

10. A vacuum coating installation having a plurality of coating apparatuses (10), in particular according to one of the preceding claims, which are coupled to a common charging cell (82), wherein at least one of the coating apparatuses (10) can be decoupled from the operation of the remaining coating apparatuses (10) for maintenance purposes as a maintenance cell (M), wherein the capacity of the remaining coating apparatuses (10) is designed such that the nominal capacity of the vacuum coating installation is achieved without the maintenance cell (M).

1 1 . A method of vacuum coating a substrate (30) comprising the application of a voltage between an electrode (24) and a counter-electrode (32), further comprising a feed of process gas, wherein the substrate (30) is arranged on a substrate carrier (28) between the electrode (24) and a plate (32) which preferably consists of graphite and which is connected as the counter-electrode.

12. The method of claim 1 1 , 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).

13. A method of vacuum coating a substrate (30) comprising providing a vacuum coating installation having a plurality of coating apparatuses (10), in particular according to one of the preceding claims, wherein each coating apparatus (10) is of identical configuration and is coupled to a common charging cell (82), wherein one of the coating apparatuses (10) is decoupled from the operation of the remaining coating apparatuses (10) for maintenance purposes as a maintenance cell (M), wherein the vacuum coating installation has a certain nominal throughput capacity, and wherein the vacuum coating installation is operated without a selected one of said coating apparatuses (10) at nominal throughput capacity, while said selected one of said remaining coating apparatuses (10) is decoupled from the operation of the remaining coating apparatuses (10) for maintenance purposes.

14. The method of claim 13, wherein each coating apparatus (10) of said plurality of coating apparatuses (10) is operated simultaneously at a capacity lower than its nominal troughput capacity during normal operation, and for maintenance purposes a selected one of said coating apparatuses (10) is decoupled from the remaining appartuses (10), while the remaining coating apparatuses (10) are operated at a higher capacity than during normal operation, perferably close to their maximum throughput capacity.