The invention relates to a vacuum evaporation apparatus for solid materials.
An important goal in modern research in energy is to find methods to convert sunlight into current, having only low costs. Thin film solar cells promise to have lower costs compared with common solar cells.
These thin films can, for instance, be produced by a sputtering process or by evaporation of solid materials onto a substrate. A continuous vacuum evaporation device for metal has been described, where a substrate to be coated moves within a vacuum chamber (U.S. Pat. No. 4,880,960). A deposition material in particle form is stored in a reservoir closed on its lowermost part by a plate. A cable links the plate to a valve which closes the supply opening of a crucible heated to a temperature for evaporation of the deposition material. A control device using at least one electromagnet allows the plate to pivot and thus to open the valve. A quantity of powder falls into the crucible, then the plate and the valve are returned to closed position. A screen with a mesh having dimensions smaller than those of the deposition material particles in the crucible allows passage of the vapor only on subsequent deposition onto the substrate.
Furthermore, there is described an apparatus for coating a substrate, wherein the apparatus comprises an evaporation source and a system for distributing the evaporated material onto the substrate (DE 102 24 908 A1). The system for distributing further comprises a line source, wherein the line source and the substrate can be moved relatively to each other.
A method for depositing semiconductor layers on a substrate for evaporation in vacuum and by dosed supply of a base product in N evaporators has also been described (FR 2 456 144). The supply of the product is periodically. Each of the N evaporators is, one after another, heated up to a temperature lower than the boiling temperature of the base product and is loaded with a dose which is necessary for the continuous coating of the active portion of the evaporator and which is sufficient for a complete vaporisation during time T until the next loading.
One problem, however, which exists, when a product is evaporated, is that the evaporation can hardly be stopped within a few seconds. This is because the material has to cool off and this needs some time.
Therefore, it is an object of the present invention to solve the problem mentioned above.
The invention therefore relates to an apparatus for evaporating solid materials, for instance, selenium for coating a substrate. The solid material is brought into a first crucible via a feeding source. In this crucible the material melts at a temperature which is preferably slightly higher than its melting point. The molten material flows via a transporting device, for instance, a pipe into a second crucible, where the material evaporates at a temperature higher than its boiling point and is transported to a substrate. In order to stop the evaporation within a very short time preferably within one to two minutes, a cooling device for cooling the material beyond its melting point is arranged at the transporting device. With this cooling device the material in the transporting device can be cooled down beyond its melting point in a very short time.
The invention is shown in the figures and explained by the following description.
On top of the housing 3 a charging device 9 is arranged which has an upper part 10, a middle part 11 and a lower part 12. The middle part 11 is vacuum sealed and provides a charging valve 14. On top of the upper part 10 a removable lid 13 is arranged. This lid 13 can be removed if the upper part 10 has to be provided with solid material, for instance selenium.
However, before the upper part 10 is filled with said solid material, the valve 14 has to be closed. Then the upper part 10 is flooded with a gas, e.g. air or nitrogen, via a pipe which is not shown in
Afterwards the lid 13 is replaced and fastened and the upper part 10 is evacuated by a pump not shown in
With the charging valve 14 the quantity of solid material coming from the upper part 10 can be regulated, so that only a defined quantity of solid material passes the lower part 12, before it reaches the interior of the housing 3.
The housing 3 is connected to a pump system via a tube or pipe 15, so that a vacuum can be created in the housing 3. The pump system is not shown in
Onto the mounting flange 17 a third mounting flange 19 is arranged which holds an evaporation pipe 20 via a holding device 21 for holding the evaporation pipe 20. The evaporation pipe 20 itself has a holding device 22 by its own, which is fixed to the holding device 21 of the mounting flange 19. These two holding devices form a holder 23. Although only one holder 23 is shown in
This evaporation pipe 20 is arranged on a device 24 in which a crucible for evaporating the material is arranged, which cannot be seen in
As illustrated in
The device 24 is connected to a protrusion 30 of a device 31 for holding a crucible which is arranged inside the housing 3 via a pipe 32.
A cut B-B through the apparatus 1 according to
In
The melting crucible 43 is arranged within the device 31 for holding the crucible 43. The crucible 43 can be heated by thermal oil which is kept between two walls 44, 45 in an intermediate room 46. Instead of heating the crucible 43 by thermal oil, it can also be heated by a resistance heater or an induction coil. On top of the crucible 43 a hood 47 is provided. But when the cooling process is started, this intermediate room 46 acts as quick shut down device for cooling, as it serves as a pathway for a cooling medium, for instance water.
Another shut down device 52 for cooling is arranged also in form of pipes around the outer parts of the crucible 50. On top of the device 24 holding the crucible 50 the evaporation pipe 20 is arranged.
This evaporation pipe 20 comprises a first inner pipe 53 having the distribution system 39, showing to the side where the substrate 2 passes the apparatus 1. The inner pipe 53 is surrounded by at least one half pipe. In
In
To control the temperature in the apparatus 1, temperature measuring devices can be applied, so that the temperature of the material in the crucibles 43, 50, the pipe 49 and the interior of the pipe 20 can be controlled. The temperature can therefore be adapted to the temperature needed at every stage of the process.
When a coating process is started, the upper part 10 of the charging device 9 is filled with the material used for coating the substrate 2. If the material is selenium, it preferably has the form of granules.
By opening the charging valve 14, the material gets into the storage container 41 without breaking the vacuum. The charging valve 14 will be closed and the material will be transported by the feeder 48 to the pipe 42, to then eventually fall into the crucible 43. In this crucible 43 the material is molten, the crucible 43 having a temperature which is higher than the melting point of the solid material. In the case of selenium the temperature only has to be slightly higher than its melting point of 221° C.
The quantity of material falling into the crucible 43 can be controlled by the feeder 48, which can be run automatically, so that a variation of the filling amplitude in the crucibles 43, 50 is kept at a minimum. In the housing 3 as well as in the charging device 9 having the lid 13 on top of it, there is a stable vacuum throughout the whole process.
When the heating process is started thermal oil runs through the shut down devices 46, 51 and 52. The thermal oil thus acts as a heating medium. The material in the crucibles 43, 50 and in the pipe 49 hence is heated by that thermal oil.
Once the material got into the crucible 43 it is molten, so that it can pass the pipe 49 and can get into the crucible 50. In this crucible 50 the temperature is much higher in order to convert the liquid material 64 into its gaseous form, i.e. vapor. This vapor rises into the interior 56 of the evaporation pipe 20 and leaves said pipe 20 via the linear distribution system 39. The vapor then moves in the direction of the substrate 2 in order to generate a layer of that material as the substrate 2 passes the apparatus 1. The heater arranged at the inner pipe 53 hinders the vapor to condense at the surface of the inner pipe 53 or in the holes of the distribution system 39.
When the process is stopped the heaters are shut off and the quick shut down devices 51, 52 for cooling are switched on, so that the cooling media, e.g. water, thermal oil, gas, runs through these shut down devices 46, 51, 52 for cooling in order to cool the material down. For a quick cooling of the molten material 64 in the crucible 50, it is important that the crucible 50 does not comprise too much molten material 64. Thus the volume of the crucible 50 is kept quite small compared to the volume of the crucible 43.
It is important to cool the material in the crucibles 43, 50 down to a temperature which lays beyond the melting point. After the material is cooled down, the cooling media is removed from the shut down devices 51, 52 so that the shut down devices 51, 52 can be filled with air again, having a heat capacity which is much lower compared to that of the cooling media.
Cleaning the apparatus is also effortless, because the evaporation pipe 20 can be easily removed by removing the flange 19. After this, the flanges 16, 17 can be removed so that the housing 3 is open to two sides.
Therefore, maintenance of the apparatus 1 is also easy because all devices comprise clutches for quick coupling. Therefore, the device 9 can also be exchanged easily. After having cleaned the apparatus 1 a new process can be started using a new and different material for the coating process.
The charging device 9 can comprise a star feeder with for instance four segments. One of those segments is arranged just above the valve 14, the segment comprising no material.
The charging procedure is started by closing the valve 14 and venting the upper part 10. The lid 13 is then removed from the device 9 and the upper part 10 is charged with the solid material. Thereafter the lid 13 is replaced and the upper part 10 is evacuated by a pump not shown in
By turning the star feeder the material falls through the opening of the valve 14 so that it can get into the crucible 43 via the storage container 41. Afterwards the valve 14 is closed again.
The charging device 9 can also comprise a cup charger having at least one cup. This at least one cup can be canted like a crucible.
After the device 9 is closed by the lid 13, the valve 14 is closed and the upper part 10 is vented. The lid 13 is removed again and the at least one cup is filled with a material. The lid is put on top of the device 9 again and the valve 14 is opened after that the device 9 has been evacuated. Then the at least one cup is canted and the material falls through the opening of the valve 14 into the storage container 41 of the housing 3. From there it runs through the pipe 42 to finally reach the crucible 43.
The device 9 can furthermore comprise a container charger having a rotary hoisting-gear and a hoisting-gear with a charger basket.
When the charging process is started, the valve 14 is closed and the device 9 is vented. The device 9 is then lifted and pivoted to a side. The charging basket is lowered, so that the basket can be changed by a basket filled with material. The basket is then pulled into the device 9 by the hoisting-gear. The device 9 is pivoted over the valve 14 and then put upon the valve 14. The device is then evacuated and the valve opened, so that the material can get into the crucible 43.
In this embodiment the material can be selenium having the form of granules.
As shown in
Again the liquid material 70, 65, for example selenium, in the two crucibles 50, 43 has approximately the same altitude due to the circumstance that the quantity of the solid material can be controlled automatically via a computer by the valve 14, not shown in
Instead of the quick shut down devices 46, 51, 52 it is possible to arrange a screen above the crucible 50 to prevent the vapor from leaving the evaporation pipe 20. However, especially in the case when selenium is used as a material, it is hard to prevent selenium from passing the screen because of its high vapor pressure. Such an arrangement would have to be very complex in its construction. Therefore, the shut down devices 46, 51, 52 are preferred.
The present application claims priority from to commonly owned and assigned application No. 60/950,778, Attorney Docket No. APPL-026/00US, entitled Vacuum Evaporation Apparatus for Solid Materials, which is incorporated herein by reference.
Number | Date | Country | |
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60950778 | Jul 2007 | US |