EVAPORATOR BOAT CONTROL SYSTEM, PVD MACHINE AND METHOD OF OPERATING THE PVD MACHINE

Abstract

The invention relates to a system for controlling evaporator boats, having a fixture (16) for receiving a plurality of evaporator boats (14), an energy source (18) for providing energy for heating each of the evaporator boats (14), a supply wire drive (24) for each of the evaporator boats (14), at least one camera (32) adapted for capturing an image of at least one of a plurality of evaporator boats (14) mounted in the fixture (16), and a control (26), the control (26) having an image analyzation module (36) and being adapted for providing a control signal for the supply wire drive (24) and a control signal for the energy source (18), the control signals depending at least in part from an output of the image analyzation module (36). The invention further relates to a PVD machine and to a method of operating the machine.

Claims

1. A system for controlling evaporator boats, the system comprising: a fixture for receiving a plurality of evaporator boats; an energy source for providing energy for heating each of the plurality of evaporator boats; a supply wire drive for each of the plurality of evaporator boats; at least one camera adapted for capturing an image of at least one of the plurality of evaporator boats mounted in the fixture; and a controller having an image analyzation module, the controller being configured to: provide a first control signal for the supply wire drive; and provide a second control signal for the energy source, the first control signal and the second control signal depending at least in part from an output of the image analyzation module.

2. The system of claim 1, wherein the at least one camera captures the image of a plurality of the plurality of evaporator boats.

3. The system of claim 1, further comprising: a light filter.

4. The system of claim 1, wherein the controller is further configured to provide a third control signal for a transport speed of a substrate to be deposited.

5. A PVD machine comprising: a web supply, a system for controlling evaporator boats as claimed in claim 1, and a process chamber in which at least the fixture for the evaporator boats (14), the supply wire drive, and an area for depositing the web supply are arranged.

6. The machine of claim 5, wherein the at least one camera is arranged outside and/or inside the process chamber.

7. The machine of claim 5, wherein the controller uses a closed control loop.

8. The machine of claim 5, further comprising a surface inspection system for inspecting a surface of a web downstream of a deposition area, and the controller is further configured to receive an output signal of the surface inspection system.

9. The machine of claim 5, further comprising a screen for displaying a visualization of at least one parameter relevant for the control of the evaporator boats, the at least one parameter being at least one of a shape of a pool of molten material and a temperature of the molten material.

10. The machine of claim 9, wherein the visualization has color enhancements to highlight process problems.

11. A method of operating a PVD machine as claimed in claim 5, wherein the second control signal for the energy source controls at least one of a power, a current and a voltage supplied to a respective evaporator boat and depends from the output of the image analyzation module.

12. The method of claim 11, wherein the controller is further configured to provide a third control signal for a transport speed of a substrate to be deposited, the third control signal depending at least in part from the output of the image analyzation module.

13. The method of claim 11, wherein the first control signal for the supply wire drive controls a speed with which a supply wire is advanced towards respective evaporator boats.

14. The method of claim 11, wherein the image analyzation module is configured to analyze at least one parameter of a set of parameters, the set of parameters including: a shape of a pool of molten material or evaporator boat, a size of the pool of molten material, a temperature of the molten material and/or evaporator boat, and an aspect ratio of the pool of molten material.

15. The method of claim 11, wherein the controller takes into account information on an age of a respective evaporator boat.

16. The method of claim 11, wherein the controller uses different sets of target parameters for the plurality of evaporator boats for different evaporator materials, different evaporator boat dimensions, and/or different deposition requirements.

Description

[0024] The invention will now be described with reference to an embodiment which is shown in the enclosed drawings. In the drawings:

[0025] FIGS. 1a and 1b are schematic views of a PVD machine according to the invention;

[0026] FIG. 2 is a schematic view of a fixture for evaporator boats as used in the machine of FIGS. 1a and 1b;

[0027] FIG. 3 is a schematic view of a visualization of a pool of molten material on an evaporator boat;

[0028] FIGS. 4a and 4b are examples of images captured from an evaporator boat via the camera of the PVD machine, with the pool of molten material having the desired shape;

[0029] FIGS. 5a and 5b are examples of images captured from an evaporator boat via the camera of the PVD machine, with the pool of molten material being too large;

[0030] FIG. 6 is a schematic representation of the pool of molten material on an evaporator boat, with the pool being too small;

[0031] FIG. 7 is a schematic representation of the pool of molten material on an evaporator boat, with the pool being too large;

[0032] FIG. 8 is a schematic representation of the pool of molten material on an evaporator boat, with the pool having the desired size;

[0033] FIG. 9 is a schematic representation of a pool of molten material on a new evaporator boat;

[0034] FIG. 10 is a schematic representation of a pool of molten material caused by a de-centered wire supply;

[0035] FIG. 11 is a schematic representation of an evaporator boat having a contact issue; and

[0036] FIGS. 12a and 12b are a schematic representation of an analyzation of the pool of molten material regarding defects.

[0037] In FIGS. 1a and 1b, the essential components of a PVD machine are shown. It comprises a process drum 10 or free span rollers 40 around which a substrate 12 in the form of a web is guided. Substrate 12 can be a thin plastic foil which is used for packaging food.

[0038] Details of the way in which substrate 12 is provided and guided (such as a supply reel, guiding rollers, a take-up reel, etc.) are not shown here as they are not relevant for understanding the invention.

[0039] For providing a deposition material to be deposited on substrate 12, a plurality of evaporator boats 14 is provided in the vicinity of process drum 10. Evaporator boats 14 are arranged in a fixture 16 so as to form a row of adjacent evaporator boats, the row being arranged in parallel with the axis of rotation of process drum 10 so that the entirety of the evaporator boats 14 extends over the entire width of substrate 12.

[0040] In the FIG. 2 configuration, evaporator boats are shown in a staggered arrangement relative to one another. Other arrangements are possible, e.g. arranging the evaporator boats in line.

[0041] Fixture 16 is adapted for supplying electric energy from an energy source 18 (schematically depicted in FIGS. 1a and 1b) to evaporator boats 14. The amount of energy supplied to evaporator boats 14 can be controlled separately for each evaporator boat 14.

[0042] Depending on the width of substrate 12, up to 60 evaporator boats 14 can be arranged adjacent each other in fixture 16.

[0043] The deposition material is supplied to each of the evaporator boats 14 in the form of a supply wire 20 which is stored on a supply reel 22. For each of the evaporator boats 14, a supply wire drive 24 is provided which control the speed with which supply wire 20 is advanced towards the respective evaporator boat 14.

[0044] Drive 24 is here implemented in the form of a stepper motor.

[0045] A control 26 is provided for controlling various functions of the PVD machine.

[0046] Control 26 controls the amount of energy provided to each of the evaporator boats 14. Further, control 26 controls the speed of drive 24.

[0047] Also connected to control 26 is a surface inspection system 28 which inspects the surface of substrate 12 downstream of process drum 10. Surface defects of the substrate provided with the deposition material as well as other quality issues can be detected by surface inspection system.

[0048] A process chamber 30 is formed which allows establishing a vacuum in the area in which the deposition material is deposited on substrate 12.

[0049] At least one camera 32 is provided for capturing an image of at least one of the evaporator boats 14. The term “camera” here designates each and every device which is able convert optical information within the viewing area of the device into electronic information.

[0050] It is possible to use one camera 32 for each of the evaporator boats 14. In order to reduce the number of necessary cameras 32, it however is preferred to use cameras 32 which each cover a plurality of evaporator boats 14. As an example, each of the cameras 32 can capture the images of six evaporator boats 14.

[0051] Cameras 32 are arranged outside of process chamber 30. A viewing window 34 is provided in a wall of process chamber 30 so as to allow the cameras to capture the images of the evaporator boats 14.

[0052] The images captured by cameras 32 (infrared and light emission) are supplied to control 26, in particular to an image analyzation module 36 which is part of control 26.

[0053] In order to facilitate image analyzation, a light filter (not shown) or a light source may be provided for the camera to increase the contrast between the surface of the pool of molten material and the surface of the evaporator boat 14. The filter facilitates detection of the pool of molten material on the evaporator boats 14.

[0054] Image analyzation module 36 is adapted for analysing the information provided by cameras 32, in particular as regards the shape of a pool of molten deposition material on each of the evaporator boats 14. The shape of the pool of molten deposition material on the evaporator boats 14 is the most relevant parameter for controlling the evaporator boats 14, in particular as regards the amount of deposition material supplied in the form of supply wire 20, and as regards the temperature of the evaporator boats 14 established by means of the amount of energy supplied from energy source 18.

[0055] Part of image analyzation module 36 is a database in which information on target pool shapes is stored. The target pool shapes can be considered as the optimum shape of the pool of molten material for the specific deposition characteristics required and also for different ages of evaporator boats 14 as the optimum shape of the pool changes when a new evaporator boat 14 is compared with an old, almost consumed evaporator boat 14.

[0056] Information on the age of the evaporator boats 14 can be obtained by the determination of the aspect ratio for the individual evaporator boats 14.

[0057] During operation of the PVD machine, image analyzation module 36 analyses the shape of the pool of molten material on each of the evaporator boats 14 (for example by means of a suitable recognition software) and compares it with a target shape. Depending from the difference between the actual shape and the target shape, control 26 controls stepper motor 24 to appropriately supply deposition material to the respective evaporator boat 14, and controls energy source 18 to appropriately set the temperature of the evaporator boat 14. Controlling energy source 18 can involve changing the power, the voltage and/or the current supplied to the evaporator boats 14.

[0058] New evaporator boats 14 can be determined via aspect ratio detection.

[0059] The overall aim of control 26 is to achieve the optimum pool shape and optimum boat coverage.

[0060] Additionally, control 26 can visualize the determined shape of the pool of molten material on a screen for inspection by an operator. Visualization can in particular not only involve displaying the actual image captured by cameras 32 (see the image on the left in FIG. 3), but also involve depiction of a contrast-optimized image (see the image on the right side in FIG. 3).

[0061] For an optimum control, a close loop defect control is established which also takes into account information provided by surface inspection system 28.

[0062] Examples of images captured with one of the cameras 32 are shown in FIGS. 4a to 5b.

[0063] In FIGS. 4a and 4b, the pool shape and size are as desired. Supply voltage and power are balanced for the wire feed rate and the boat age.

[0064] In FIGS. 5a and 5b, the size of the pool is too large. The evaporator boat is too cold so that the supply power/voltage should be increased to increase the temperature, or the wire feed rate should be decreased.

[0065] In FIGS. 6 to 8, schematic examples of different pools of molten material on an evaporator boat are shown. With reference numeral R, a virtual reference frame is symbolized which can be used by the image analyzation module 36 for determining the size of the pool. Depending from the analysis of the captured image, the control controls the heating power supplied to the evaporator boats.

[0066] In FIG. 6, the pool of molten material M is too small. This is because the temperature of the evaporator boat is too high so that the evaporation rate is too high. The control is to decrease the heating power supplied to the evaporator boat.

[0067] In FIG. 7, the pool of molten material M is too large. This is because the temperature of the evaporator boat is too low so that the evaporation rate is too low. The control is to increase the heating power supplied to the evaporator boat.

[0068] In FIG. 8, the pool of molten material M has a desired size. This is because there is an equilibrium between boat temperature, supplied heating power and metal wire feeding.

[0069] After starting a deposition process, the control monitors any change of the shape of the pool of molten material M. Should the size of the pool increase from the desired condition (like in FIG. 8) increase (towards the size shown in FIG. 7), the evaporation rate is lower than it should be. Accordingly, the control will either decrease the wire feed rate or increase the power supplied to the evaporator boat, in order to prevent defects on the final product and damage to the web barrier.

[0070] The comparison between the different shapes of the pool at the start of the deposition process can take into account the evolvement over a time period.

[0071] FIG. 8 is a schematic representation of a pool of molten material during standard production. Depending upon the evaporator boat used and other factors, the pool covers different areas of the surface of the evaporator boat.

[0072] Suitable pool shapes are stored in a database so that they are available for the machine control.

[0073] If different types of processes are to be carried out, the image analyzation module 36 can control the pool so as to assume a different shape/size.

[0074] The image analyzation module 36 allows identifying potential issues and also other parameters, as will be explained with reference to FIGS. 9 to 11.

[0075] In FIG. 9, a pool of molten material can be seen which is characteristic for a new evaporator boat. It can be determined on the basis of the aspect ratio of the pool of molten material. The length of the pool is more than 5 times the width.

[0076] In FIG. 10, the entire pool is offset. This is the result of the supply wire being out of center. The control can determine this issue and indicate a warning or some other note on a control display, making an operator understand that there is a problem which should be fixed.

[0077] In FIG. 11, the light emission of the evaporator boat 14 is schematically shown, with the upper left corner emitting significantly more light than the rest of the evaporator boat 14. This indicates a problem with the electric contact from the fixture 16 to the evaporator boat, in particular a high electric resistance so that heat is generated at the point of contact.

[0078] The excessive heat can be shown on a display with an augmented reality visualization so that an operator very quickly understands the nature of the problem.

[0079] In FIGS. 12a and 12b, another example of evaluation of potential issues on the evaporator boat 14 is shown. Here, pin holes P or other defects of the pool of molten material M are monitored and possible changes over the time period are evaluated. This allows a detection of pool state and pool time trend and can influence the control of an ongoing deposition process.