WO2007053016A2 - Surface and method for the manufacture of photovolataic cells using a diffusion process - Google Patents

Surface and method for the manufacture of photovolataic cells using a diffusion process Download PDF

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Publication number
WO2007053016A2
WO2007053016A2 PCT/NL2006/000556 NL2006000556W WO2007053016A2 WO 2007053016 A2 WO2007053016 A2 WO 2007053016A2 NL 2006000556 W NL2006000556 W NL 2006000556W WO 2007053016 A2 WO2007053016 A2 WO 2007053016A2
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WO
WIPO (PCT)
Prior art keywords
furnace
furnace pipe
pipe
gas
cooling
Prior art date
Application number
PCT/NL2006/000556
Other languages
French (fr)
Other versions
WO2007053016A3 (en
Inventor
Robert Wibbelink
Original Assignee
Holdingmij. Wilro B.V.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Holdingmij. Wilro B.V. filed Critical Holdingmij. Wilro B.V.
Priority to EP06824251A priority Critical patent/EP1951935A2/en
Publication of WO2007053016A2 publication Critical patent/WO2007053016A2/en
Publication of WO2007053016A3 publication Critical patent/WO2007053016A3/en

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Classifications

    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
    • H01L21/67—Apparatus specially adapted for handling semiconductor or electric solid state devices during manufacture or treatment thereof; Apparatus specially adapted for handling wafers during manufacture or treatment of semiconductor or electric solid state devices or components ; Apparatus not specifically provided for elsewhere
    • H01L21/67005—Apparatus not specifically provided for elsewhere
    • H01L21/67011—Apparatus for manufacture or treatment
    • H01L21/67098—Apparatus for thermal treatment
    • H01L21/67109—Apparatus for thermal treatment mainly by convection
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F27—FURNACES; KILNS; OVENS; RETORTS
    • F27B—FURNACES, KILNS, OVENS, OR RETORTS IN GENERAL; OPEN SINTERING OR LIKE APPARATUS
    • F27B17/00—Furnaces of a kind not covered by any preceding group
    • F27B17/0016—Chamber type furnaces
    • F27B17/0025—Especially adapted for treating semiconductor wafers
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F27—FURNACES; KILNS; OVENS; RETORTS
    • F27B—FURNACES, KILNS, OVENS, OR RETORTS IN GENERAL; OPEN SINTERING OR LIKE APPARATUS
    • F27B5/00—Muffle furnaces; Retort furnaces; Other furnaces in which the charge is held completely isolated
    • F27B5/04—Muffle furnaces; Retort furnaces; Other furnaces in which the charge is held completely isolated adapted for treating the charge in vacuum or special atmosphere
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L31/18—Processes or apparatus specially adapted for the manufacture or treatment of these devices or of parts thereof

Definitions

  • the invention relates to a furnace for adding by means of a diffusion process a material to a substrate being arranged m a furnace pipe, the material being supplied in gaseous state, such as this takes place m the manufacture of photo-voltaic solar cells.
  • a furnace of this type typically comprises a furnace pipe xn which the actual diffusion process may take place, a positioning device for positioning substrates m the furnace pipe, at least one heating element for heating the furnace, and a gas infection device for injecting gases needed for the diffusion process into the inside of the furnace pipe.
  • Such furnace is known m practice and is for example applied m semi-conductor industry wherein at temperatures above 600 °C a diffusion process takes place.
  • the substrates, for instance panels, which are used m these diffusion furnaces have a typical width of about 300 mm and the cylinder shaped furnace pipe has a typical diameter of 380 mm.
  • An object of the invention is to provide a diffusion furnace with which the cycle time for the An object of the present invention is to provide a diffusion furnace suitable for the manufacture of photo-voltaic solar cells, in particular photo-voltaic solar cells having a width larger than 300 mm.
  • Another object of the invention is to provide a diffusion furnace with which the cycle time may considerably be reduced.
  • a furnace comprising:
  • the furnace comprises a cooling device configured to cool gases in the furnace pipe.
  • the gases and substrates which are heated during the diffusion process may be cooled down within a short period after the diffusion process is finished. As a consequence, the cycle time for a batch of substrates is substantially reduced.
  • cooling device may be used in a further embodiment to control the temperature more accurately, and therewith the diffusion process within the furnace pipe.
  • the cooling device may be any cooling device capable of cooling the process gases within the furnace pipe.
  • the cooling device is configured to directly cool the process gases.
  • Such cooling device may be referred to as an internal cooling device.
  • the cooling device comprises a cool circuit configured to circulate gas, in particular process gases, from the inside of the furnace pipe through a cooling unit.
  • gas in particular process gases
  • the process gases may be pumped out of the inside of the furnace pipe to a cooling unit in which the gases are cooled.
  • the cooling unit which is preferably located outside the furnace pipe may comprise a heat exchanger unit for cooling of the gas. After cooling the process gases are reintroduced into the furnace pipe.
  • the cooling circuit comprises a pump unit for circulating the gas .
  • the pump unit may be any suitable pump for circulating the gases in the cooling circuit, for instance a centrifugal pump.
  • the furnace pipe comprises two opposite open ends, a gas outlet of the cooling circuit being arranged at a first end of the furnace pipe and a gas inlet being arranged at an opposite second end of the furnace pipe.
  • the process gases are taken out of the furnace pipe at one side of the furnace and reintroduced at the other end of the furnace pipe.
  • substantially all process gases will be taken out of the inside of the furnace pipe and cooled in the cooling unit.
  • this has the advantage that no openings have to be made in the furnace pipe to provide the cooling circuit.
  • the furnace comprises a first lid and a second lid each being configured to close an end of the furnace pipe, the cooling circuit running through the first and second lid.
  • the furnace comprises a loading part supporting the positioning device and a furnace part supporting the furnace pipe, wherein said loading part is movable with respect to said furnace for loading/unloading the positioning device in the furnace pipe, wherein a first part of the cooling circuit is arranged in said loading part and a second part of the cooling circuit is arranged in said furnace part, wherein the furnace comprises an automatic cooling circuit connection device for automatically connecting said first and second part of the cooling circuit during loading of the positioning device in the furnace pipe.
  • a first part of the cooling circuit is arranged in the loading part of the furnace and a second part of the cooling circuit is arranged in the furnace part supporting the furnace pipe, for instance in an embodiment where the cooling circuit runs through opposite ends of the furnace pipe.
  • the connection between the first and second part of the cooling circuit is automatically closed when placing the positioning device carrying a number of substrates in the furnace, in the furnace pipe .
  • the cooling circuit connection device comprises a bellows arranged on the first part of the cooling circuit and a gripping device arranged on the second part of the cooling circuit, the gripping device being configured to automatically and sealingly grip the bellows during loading of the positioning device.
  • Such bellows and gripping device combination may advantageously be used in the automatic cooling circuit connection device as it provides an automatic and reliable connection between the two parts of the cooling circuit, whereby the bellows provide a certain flexibility to the connection.
  • the automatic connection device it may also be possible to provide a permanent connection between a first part of the cooling circuit arranged on the loading part and a second part of the cooling circuit arranged on the furnace part.
  • This permanent connection device may for instance comprise a long bellows or other device being compressible in the axial direction such as a telescopic connection element, which does not inhibit the movement of the loading part with respect to the furnace part for loading/unloading of the positioning device.
  • the cooling circuit is completely arranged in the furnace part. In such embodiment, the movement of the loading part with respect to the furnace part is not relevant for the cooling circuit and no special measures have to be taken.
  • the cooling circuit comprises at least one cooled valve.
  • valve used in the cooling circuit may be negatively influenced by the heat of the process gases.
  • the valve may comprise a valve seat which may actively be cooled by a cooling fluid which is pumped through a cooling space, for instance cooling channels in the valve seat. Any other type of valve cooling may also be used to ensure proper functioning of the valves of the cooling circuit. It may also be possible to provide one or more cooled valves in any other part of the furnace where the functioning of the valves may be negatively influenced by the heat produced in the furnace.
  • a furnace comprising: - a furnace pipe; - a positioning device for positioning one or more substrates in the furnace pipe;
  • the furnace comprises
  • heating elements for bringing and maintaining the temperature of the furnace pipe at a temperature above 300 0 C, which heating elements are each separately controllable, and
  • one or more temperature sensors for measuring the furnace temperatures for the purpose of the separately controllable heating elements .
  • the furnace pipe preferably comprises a diameter of at least 400 mm and has preferably a cylindrical shape. However, any other diameter and shape may also be used.
  • the furnace pipe is preferably made of quartz.
  • the diffusion process takes place at a sub- atmospheric pressure of preferably 500-1000 mbar.
  • the flushing of the furnace pipe, before the actual diffusion process starts takes place at about 0,1 mbar.
  • a flushing of the furnace pipe in an alternative embodiment can take place at higher sub-atmospheric pressures of about 500 mbar.
  • the furnace pipe comprises several separately controllable radial heating elements in radial direction.
  • the furnace pipe comprises several separately controllable radial heating elements in radial direction.
  • this convection process may be designed in such a way that the warm gas will preferably rise along the outer edge of the furnace pipe and will be guided downwards in vertical direction through the centre of the furnace pipe.
  • the gas descending in vertical direction flows between the substrates.
  • a convection flow directed in this way in the furnace pipe reduces the occurring temperature difference in radial direction of the furnace pipe in such a way that the diffusion process takes place in the desired way.
  • the above-indicated problem is solved in an embodiment, wherein in axial direction of the furnace pipe several separately controllable axial heating elements are arranged.
  • the axial heating elements By preferably keeping the axial heating elements at the ends of a furnace pipe at a higher temperature, and therewith creating several temperature zones, may be compensated for the extra heat loss from the furnace pipe to the environment at these ends of the furnace pipe.
  • the substrate temperature in axial direction of the furnace pipe can be maintained substantially homogeneous .
  • heat loss from the furnace pipe which is preferably insulated, through the environment may influence the desired controlled process course in the furnace pipe in a negative way.
  • cooling means are arranged at the outer side of the outer shell in order to bring and maintain this outer side at a predetermined temperature during the process.
  • these cooling means are embodied as fluid conduits which extend in the axial direction of the outer shell of the furnace pipe.
  • the gas injection device comprises one or more gas conduits in the axial direction of the furnace pipe.
  • these gas conduits are provided with openings at the side of this conduit resulting in a discharge in tangential direction of the furnace pipe.
  • the invention also relates to a method for the manufacture of- photo-voltaic solar cells, comprising steps of:
  • Figure Ia is a side view of a furnace according to an embodiment of the invention in the unloaded position
  • Figure Ib is a side view of a furnace according to an embodiment of the invention in the loaded position
  • Figure 2 is a top view of the device of figure 1
  • Figure 3 is a side view of the device from figure 1
  • Figure 4 is a view of the furnace with heating elements
  • Figure 5 is a side view of the furnace from figure 4
  • Figure 6 is a view of the furnace having heat shields
  • Figure 7 is a side view of the furnace with the therein directed convection flows
  • Figure 8 is a detail of the gas supply conduit in figure 7.
  • FIGS. Ia and Ib show a side view of the furnace according to an embodiment of the invention.
  • the furnace which is generally indicated with the reference numeral 2 is provided with a frame 4, arranged on foots 6 which are preferably adjustable in height, whereby the complete frame 4 preferably consists of two or more parts.
  • the furnace pipe 8 having a space for positioning substrates 10 is arranged within the frame 4.
  • the furnace pipe 8 is at the outer side provided with insulation material 12 surrounded by the outer shell 14.
  • the substrates, typically in the form of panels, are introduced in the furnace pipe 8 by means of a positioning device 16 comprising the lid 18.
  • the other side of the furnace pipe 8 is provided with a lid 20 where also the fittings 22 for the gas supply are located.
  • inlet openings 24 are provided for forced introduction of cooling air in the space between the furnace pipe 8 and the outer shell 14 as well as outlet openings 26 for this air.
  • cooling air any other suitable cooling gas or liquid may also be used to cool the space between the outer shell 42 and the outer surface of the furnace pipe 8.
  • the furnace 2 comprises a furnace part 42 supporting the furnace pipe 8 and a loading part 40 supporting the positioning device 16.
  • the furnace part 42 is stationary, while the loading part 40 is movable between an unloaded position
  • the positioning device 16 In the unloaded position, the positioning device 16 is placed outside the furnace pipe 8, so that panels or substrates supported by the positioning device 16 may be exchanged. In the loaded position, the positioning device 16 is moved into the furnace pipe 8, and lid 18 which is arranged on the positioning device 16 closes the respective end of the furnace pipe 8.
  • the loading part may be stationary and the furnace part may be movable between a loaded and unloaded position.
  • the positioning device 16 supporting a number of substrates 10 When the positioning device 16 supporting a number of substrates 10 is positioned in the furnace pipe 8 by moving the positioning device 16 to the loaded position the furnace pipe 8 is sealingly closed by the lids 18 and 20. Then the pressure within the furnace pipe is reduced and the furnace pipe 8 is flushed with inert gas. Thereafter the pressure within the furnace pipe is again reduced.
  • the furnace pipe is heated up to bring the temperature within the furnace pipe to a certain level for instance 500-550 0 C at which temperature the one or more substrates are heated for a certain time.
  • the process gases for the diffusion process are injected by the gas injection device. These gases which are used for the diffusion process are known in the art.
  • the gas is diffused into an layer of the substrate.
  • the process gases may quickly be cooled by a cooling device 100 as will be explained hereinafter.
  • the inside of the furnace pipe is emptied, i.e. the process gases are removed and the furnace pipe is flushed to remove any remaining process gases. Thereafter, the positioning device may be moved to the unloading position to remove the substrate or substrates from the positioning device 16.
  • a cooling device 100 is provided for the cooling of the process gases within the furnace pipe.
  • the cooling device 100 has a cooling circuit 101 comprising a gas outlet 102, a gas inlet 103, gas conduit 104, 105, a pump 106 for circulating the process gases and a heat exchanger unit 107 for cooling the circulating process gases.
  • the gas outlet 102 is arranged in lid 18, and the gas inlet 103 is arranged in lid 20.
  • the gas outlet 102 and the gas inlet 103 are arranged at opposite sides of the furnace pipe 8 (in the loaded position of the loading part 40) .
  • the automatic connection device 108 comprises a bellows 109 arranged at the part of the cooling circuit 101 of the loading unit 40.
  • the automatic connection device 108 further comprises a gripping device 110, which automatically grips the bellows 109, when this bellows 109 is pushed against the gripping device 110.
  • the automatic connection device 108 will automatically and sealingly close the cooling circuit 101 which will be used during the actual diffusion process, as will be explained hereinafter.
  • the process gases present in the furnace pipe 8 may be, in particular after the actual diffusion process is finished, pumped out of the inner side of the furnace pipe, where the actual diffusion process took place via the gas outlet 102 and gas conduit 104 to the cooling unit comprising the pump 106 and heat exchanger unit 107.
  • the process gases are cooled in the heat exchanger unit 107 and pumped further through the gas conduit 105 and gas inlet 103 back into the process chamber, i.e. the inner side of the furnace pipe 8.
  • the pump 106 may be any pump suitable for pumping the hot process gases, for instance a centrifugal pump.
  • the heat exchanger unit 107 may be any heat exchanger unit being capable of cooling the process gases of the diffusion process.
  • the process gases may be quickly cooled after the actual diffusion process has finished. As a result the cycle time of the furnace 2 may be considerably lowered.
  • the cooling circuit 101 may also be used to cool the process gases during the actual diffusion process. In this way the temperature within the furnace pipe 8 may be controlled more accurately.
  • An advantage of the above cooling circuit 101 is that the process gases may be directly cooled in the heat exchanger unit 107.
  • one or more valves may be provided with an active cooling system.
  • a valve seat of a valve may be provided with a cooling space through which cooling fluid may be pumped for temperature control of valve seat.
  • Any type of suitable valve cooling may be provided for one or more valves of the cooling circuit 101, or any other valve of the furnace 2 of which the functioning may be negatively influenced by the heat produced in the furnace 2.
  • Figure 2 shows the top view of the view in figure 1 and therein the loading part 40, the furnace part 42 and a source part 44 are clearly shown as well as a operating panel 46 with which the complete installation can be operated by an operator.
  • the number of substrates which is handled in one operation in the shown positioning device is for instance 16 plates with a width of 500 mm and a length of 1200 mm.
  • the complete installation is provided at the topside with a number of openings.
  • opening 47 is provided for removing heat by opening the furnace
  • opening 48 is provided for heat-removal from the furnace and opening 49 provides in the removal of gasses from the source part.
  • a number of pumps 50 are located with which the furnace pipe can be brought on sub-atmospheric pressure.
  • Figure 3 shows the side view of the device from figure 1 having the operation panel 46 arranged at man's height and the fittings for the gas supply 22 on the lid 20 of the furnace pipe 8.
  • the frame 4 consists of a number of stands 52 and a number of bars 54 for supporting the furnace pipe 8 and accessories.
  • the furnace pipe 8 is provided with a number of heating elements 60 arranged as shown in figure 4 between the furnace pipe 8 and the outer shell 14 of which preferably at least three are arranged adjacent in axial direction.
  • the outer axial heating elements 60 may be controlled in such a way that compensation is obtained for heat loss from the furnace pipe 8 to the environment such that the temperature distribution within the furnace pipe is substantially homogeneous and the substrates are heated with a substantially homogeneous temperature.
  • the furnace pipe 8 comprises several radial heating elements 60 as shown in figure 5. With these radial heating elements 60 compensation can be realized in the height direction of the shown furnace 2 for the temperature difference which comes into existence in the furnace pipe 8 resulting in convection.
  • the furnace pipe 8 is provided with two radial heating elements 60 in radial direction, as a consequence of which the number of separately controllable zones in the furnace pipe is six in the shown embodiment .
  • one temperature sensor per heating element there is provided one temperature sensor per heating element.
  • one temperature sensor 65 is arranged at an angle of about 45° with the vertical direction.
  • three heating elements are illustrated in the axial direction which each are provided with an own temperature sensor 65. For the shown preferred embodiment this results in a total of six temperature sensors.
  • the outer shell 14 is provided with cooling conduits 62 wherein preferably water is guided in axial direction to realize a constant heat loss from the furnace pipe to the environment which subsequently may be compensated by the heating elements 60.
  • the cooling conduits 62 are fixed by means of clamping plates 64 and bolts 66 on the outer shell 14. It will be clear that other constructions are possible.
  • FIG 6 shows the furnace pipe 8 having the heating elements 60 and the lids 18 and 20, wherein a number of heat shields 70 are arranged spaced from the respective lid and the space wherein the substrates are arranged. In the shown embodiment five heat shields are arranged at opposite sides of the furnace pipe 8. The heat shields 70 which are located at one side of the furnace pipe 8 are arranged at a small mutual distance. The heat shields 70 have as most important function to maintain the temperature in the furnace pipe homogeneous and to minimize the heat loss from this furnace pipe to the environment via the lids 18 and 20.
  • Figure 7 shows the furnace pipe 8 having the heating elements 60, of which in the radial direction two are separately controllable in the shown embodiment.
  • the substrate 80 and a gas supply conduit 82 with which gas can be supplied to the furnace pipe 8 for the purpose of the diffusion process are located.
  • the furnace pipe 8 is provided with one gas conduit which is arranged at the lowest point in the furnace pipe 8. It will be clear that embodiments having several gas conduits 82 located at different positions in the furnace pipe also are possible.
  • the gas conduit 82 is provided with two rows openings 84 which each are placed at an angle of 45° with respect to the vertical direction as shown in figure 8. Other embodiments are conceivable.
  • the gas supply conduit is preferably provided with openings having small dimensions such that a counter pressure exist in order to realize an equal discharge of the gas over the total length of the furnace pipe.
  • the several zones are illustrated in which the furnace pipe 8 may be divided. These are a master zone 86 preferably at the underside of the furnace pipe 8 as shown, a correction zone 90 at the upper side of the furnace pipe 8 as shown and two transit zones 88 in the area between the master zone 86 and the correction zone 90. Further the directed convection flows are indicated in the drawing by means of arrows. The convection comes into existence as a consequence of the temperature difference within the furnace pipe 8 which is the result of the relative large diameter of the furnace pipe and the relative low temperature of the diffusion process in which temperature range convection place a relatively important role. In this convection process the warm gas will rise.
  • convection flow patterns may be created by using the radial heating elements 60.
  • the creation of these flow patterns may be supported by the presence of one or more gas conduits 82 as explained hereinabove. For this reasons the openings in the gas conduits 82 may be placed at other angles to support the desired convection flow patterns.
  • the furnace described above provides a number of features which alone or in combination increase control accuracy of the temperature making temperature control in a diffusion process in a furnace pipe having larger diameter than state of the art furnaces possible without obtaining products with a substantial lower quality.
  • the furnace is suitable for the manufacture of solar cells which are based on the alloys or methods described in US2006222558 , WO2005017978 A2 and WO2005017979 KZ, the contents of these patent applications being herein incorporated in their entirety by reference .
  • the furnace comprising one or more of the features or aspects of the invention, alone or in combination, may also be used for the manufacture of any other substrates, such as panels, in particular when temperature control/distribution within the furnace pipe during the diffusion process is of importance for the quality of the final products.

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  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • General Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • Condensed Matter Physics & Semiconductors (AREA)
  • General Physics & Mathematics (AREA)
  • Manufacturing & Machinery (AREA)
  • Computer Hardware Design (AREA)
  • Microelectronics & Electronic Packaging (AREA)
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  • Electromagnetism (AREA)
  • Chemical Vapour Deposition (AREA)
  • Furnace Details (AREA)
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  • Vaporization, Distillation, Condensation, Sublimation, And Cold Traps (AREA)

Abstract

The invention relates to a furnace (2), comprising : - a furnace pipe (8), - a positioning device (16) for positioning substrates (10) in the furnace pipe (8), - at least one heating element (60) for heating the furnace (2), - a gas injection device (82). The invention is further characterized in that the furnace comprises a cooling device (100) configured to cool gases in the furnace pipe (8).

Description

Title: Furnace and method for the manufacture of photo-voltaic solar cells using a diffusion process.
The invention relates to a furnace for adding by means of a diffusion process a material to a substrate being arranged m a furnace pipe, the material being supplied in gaseous state, such as this takes place m the manufacture of photo-voltaic solar cells. A furnace of this type typically comprises a furnace pipe xn which the actual diffusion process may take place, a positioning device for positioning substrates m the furnace pipe, at least one heating element for heating the furnace, and a gas infection device for injecting gases needed for the diffusion process into the inside of the furnace pipe.
Such furnace is known m practice and is for example applied m semi-conductor industry wherein at temperatures above 600 °C a diffusion process takes place. The substrates, for instance panels, which are used m these diffusion furnaces have a typical width of about 300 mm and the cylinder shaped furnace pipe has a typical diameter of 380 mm.
Until now such furnaces were also used for solar cells. However, it is desirable to provide solar cells having dimensions larger than the above-indicated, dimensions. Larger dimensions of the substrate also requires a larger process chamber, i.e. the space within the furnace pipe. When increasing the dimensions of such process chamber it is increasingly difficult to control the temperature within the process chamber, in particular m the relatively low temperature range in which the diffusion process for the manufacture of a photo-voltaic cell is carried out. During this process it is very important to accurately control the temperature within the process chamber. However, due to the low temperature range, typically in the range of 500-550 0C, the distribution of heat within the furnace pipe is mainly based on convection. A drawback of the known diffusion furnace is that due to the required accuracy of the temperature, the maximum dimensions of a solar panel manufactured in this way were until now limited to a maximum width of the substrate of 300 mm.
Another drawback of the known diffusion furnace is that the cooling down of the process gases and the substrates m the furnace pipe after the diffusion process has finished, takes considerable time. As a consequence, the cycle time is negatively influenced by this cooling down period.
An object of the invention is to provide a diffusion furnace with which the cycle time for the An object of the present invention is to provide a diffusion furnace suitable for the manufacture of photo-voltaic solar cells, in particular photo-voltaic solar cells having a width larger than 300 mm.
Another object of the invention is to provide a diffusion furnace with which the cycle time may considerably be reduced.
According to a first aspect of the invention, there is provided a furnace, comprising:
- a furnace pipe,
- a positioning device for positioning substrates in the furnace pipe,
- at least one heating element for heating the furnace,
- a gas injection device, characterized in that the furnace comprises a cooling device configured to cool gases in the furnace pipe. By providing a cooling device with which it is possible to cool the process gases present within the furnace pipe, the gases and substrates which are heated during the diffusion process may be cooled down within a short period after the diffusion process is finished. As a consequence, the cycle time for a batch of substrates is substantially reduced.
Furthermore, the cooling device may be used in a further embodiment to control the temperature more accurately, and therewith the diffusion process within the furnace pipe.
The cooling device may be any cooling device capable of cooling the process gases within the furnace pipe. Preferably, the cooling device is configured to directly cool the process gases. Such cooling device may be referred to as an internal cooling device.
In an embodiment the cooling device comprises a cool circuit configured to circulate gas, in particular process gases, from the inside of the furnace pipe through a cooling unit. By providing a cooling circuit the process gases may be pumped out of the inside of the furnace pipe to a cooling unit in which the gases are cooled. The cooling unit, which is preferably located outside the furnace pipe may comprise a heat exchanger unit for cooling of the gas. After cooling the process gases are reintroduced into the furnace pipe. In an embodiment the cooling circuit comprises a pump unit for circulating the gas . The pump unit may be any suitable pump for circulating the gases in the cooling circuit, for instance a centrifugal pump. In an embodiment the furnace pipe comprises two opposite open ends, a gas outlet of the cooling circuit being arranged at a first end of the furnace pipe and a gas inlet being arranged at an opposite second end of the furnace pipe. In this way the process gases are taken out of the furnace pipe at one side of the furnace and reintroduced at the other end of the furnace pipe. As a consequence, substantially all process gases will be taken out of the inside of the furnace pipe and cooled in the cooling unit. Furthermore, this has the advantage that no openings have to be made in the furnace pipe to provide the cooling circuit. In an embodiment the furnace comprises a first lid and a second lid each being configured to close an end of the furnace pipe, the cooling circuit running through the first and second lid. By providing a cooling circuit through the first and second lid of the furnace, a gas inlet and gas outlet may be provided at opposite ends of the furnace.
In an embodiment the furnace comprises a loading part supporting the positioning device and a furnace part supporting the furnace pipe, wherein said loading part is movable with respect to said furnace for loading/unloading the positioning device in the furnace pipe, wherein a first part of the cooling circuit is arranged in said loading part and a second part of the cooling circuit is arranged in said furnace part, wherein the furnace comprises an automatic cooling circuit connection device for automatically connecting said first and second part of the cooling circuit during loading of the positioning device in the furnace pipe.
It may be desirable that a first part of the cooling circuit is arranged in the loading part of the furnace and a second part of the cooling circuit is arranged in the furnace part supporting the furnace pipe, for instance in an embodiment where the cooling circuit runs through opposite ends of the furnace pipe. In such embodiment it is advantageous that the connection between the first and second part of the cooling circuit is automatically closed when placing the positioning device carrying a number of substrates in the furnace, in the furnace pipe . In an embodiment the cooling circuit connection device comprises a bellows arranged on the first part of the cooling circuit and a gripping device arranged on the second part of the cooling circuit, the gripping device being configured to automatically and sealingly grip the bellows during loading of the positioning device. Such bellows and gripping device combination may advantageously be used in the automatic cooling circuit connection device as it provides an automatic and reliable connection between the two parts of the cooling circuit, whereby the bellows provide a certain flexibility to the connection.
As an alternative for the automatic connection device it may also be possible to provide a permanent connection between a first part of the cooling circuit arranged on the loading part and a second part of the cooling circuit arranged on the furnace part. This permanent connection device may for instance comprise a long bellows or other device being compressible in the axial direction such as a telescopic connection element, which does not inhibit the movement of the loading part with respect to the furnace part for loading/unloading of the positioning device. In another alternative embodiment the cooling circuit is completely arranged in the furnace part. In such embodiment, the movement of the loading part with respect to the furnace part is not relevant for the cooling circuit and no special measures have to be taken. In an embodiment the cooling circuit comprises at least one cooled valve. It may be possible that the functioning of a valve used in the cooling circuit may be negatively influenced by the heat of the process gases. In such case it may be advantageous to provide active cooling of the valve. In an embodiment the valve may comprise a valve seat which may actively be cooled by a cooling fluid which is pumped through a cooling space, for instance cooling channels in the valve seat. Any other type of valve cooling may also be used to ensure proper functioning of the valves of the cooling circuit. It may also be possible to provide one or more cooled valves in any other part of the furnace where the functioning of the valves may be negatively influenced by the heat produced in the furnace.
According a second aspect of the invention, there is provided a furnace, comprising: - a furnace pipe; - a positioning device for positioning one or more substrates in the furnace pipe;
- a heating element, and
- a gas injection device, characterized that the furnace comprises
- two or more heating elements for bringing and maintaining the temperature of the furnace pipe at a temperature above 3000C, which heating elements are each separately controllable, and
- one or more temperature sensors for measuring the furnace temperatures for the purpose of the separately controllable heating elements .
By providing two or more heating elements the The furnace pipe preferably comprises a diameter of at least 400 mm and has preferably a cylindrical shape. However, any other diameter and shape may also be used. The furnace pipe is preferably made of quartz. By using a furnace pipe with a relative large diameter preferably in the range of 400-640 mm, and preferably a wall thickness of 8-10 mm, it is possible to manufacture larger photovoltaic solar cells in a furnace having a width of preferably 500 mm. Herewith an efficient manufacturing process can be obtained.
In an embodiment the diffusion process takes place at a sub- atmospheric pressure of preferably 500-1000 mbar. By contrast the flushing of the furnace pipe, before the actual diffusion process starts, takes place at about 0,1 mbar. However, a flushing of the furnace pipe in an alternative embodiment can take place at higher sub-atmospheric pressures of about 500 mbar.
It is remarked that as a consequence of a combination of a larger diameter of the furnace pipe and the lower temperature at which the diffusion process takes place, large temperature differences may occur in the furnace pipe as well in the actual direction as radial direction of the furnace pipe. Experiments have shown that even with a diameter of the furnace pipe of 450 mm a temperature difference of 20 0C may occur in radial direction of the furnace pipe, while a difference up to about 5 0C would be acceptable. Because manufacture of such solar cells takes place at a relatively low temperature of 500-550 0C, the radiation heat will not compensate potential temperature differences.
The above indicated problem is solved with an embodiment of the device, wherein the furnace pipe comprises several separately controllable radial heating elements in radial direction. By means of these separate radial heating elements in radial direction of the furnace pipe different temperature zones may be obtained, with which the temperature difference in this direction may be minimalized to at least less than 5 0C, wherein the homogeneity of the diffusion process remains within the specifications by using the occurring convection process.
In this convection process the warmer gas will rise. By controlling the heating elements, this convection process may be designed in such a way that the warm gas will preferably rise along the outer edge of the furnace pipe and will be guided downwards in vertical direction through the centre of the furnace pipe. The gas descending in vertical direction flows between the substrates. A convection flow directed in this way in the furnace pipe reduces the occurring temperature difference in radial direction of the furnace pipe in such a way that the diffusion process takes place in the desired way.
In alternative embodiments other convection flow patterns may be created during the diffusion process within the furnace pipe by using the radial heating elements. Further it is remarked that in axial direction of the furnace pipe temperature differences may occur, in particular at the ends of the furnace pipe where a larger heat transfer to the environment of the furnace pipe will occur.
The above-indicated problem is solved in an embodiment, wherein in axial direction of the furnace pipe several separately controllable axial heating elements are arranged. By preferably keeping the axial heating elements at the ends of a furnace pipe at a higher temperature, and therewith creating several temperature zones, may be compensated for the extra heat loss from the furnace pipe to the environment at these ends of the furnace pipe. By the proper selection of the temperature the substrate temperature in axial direction of the furnace pipe can be maintained substantially homogeneous .
Further, it is remarked that heat loss from the furnace pipe which is preferably insulated, through the environment may influence the desired controlled process course in the furnace pipe in a negative way.
The above-indicated problem is solved with an embodiment, wherein cooling means are arranged at the outer side of the outer shell in order to bring and maintain this outer side at a predetermined temperature during the process. Preferably, these cooling means are embodied as fluid conduits which extend in the axial direction of the outer shell of the furnace pipe.
By means of these cooling means a constant heat loss from the furnace pipe to the environment is realized, making compensation of this loss by means of the separately controllable heating elements possible. In this way a more constant temperature within the furnace pipe is realized. The control behaviour of the heating elements is therewith improved. Subsequently, it is remarked that for the purpose of the diffusion process in the furnace pipe gas injection will take place. By gas injection the flow pattern in the furnace pipe is influenced, with which further temperature differences in the furnace pipe may be introduced. The above-indicated problem is solved with an embodiment, wherein the gas injection device comprises one or more gas conduits in the axial direction of the furnace pipe. Preferably these gas conduits are provided with openings at the side of this conduit resulting in a discharge in tangential direction of the furnace pipe. In the preferred embodiment uses made of one gas conduit which is placed in the lowest point of the furnace pipe in vertical direction with openings at the side of this conduit by which the directed convection flow is further supported and directed to flow from this lowest points along the side walls of the furnace pipe in tangential direction to the highest point. Herewith temperature difference within the furnace pipe are further reduced.
The invention also relates to a method for the manufacture of- photo-voltaic solar cells, comprising steps of:
- loading a substrate in a furnace pipe; - reducing pressure in the furnace pipe;
- flushing the furnace pipe with inert gas and again reducing the pressure;
- heating up the furnace pipe with the substrate;
- heating the substrate to a temperature of about 500-5500C; - injecting process gas;
- diffusing the gas in the applied layer of the substrate;
- emptying and flushing the furnace pipe; and
- unloading the substrate.
The invention will now be elucidated at the hand of a number of examples, whereby reference is made to the appended drawing in which: Figure Ia is a side view of a furnace according to an embodiment of the invention in the unloaded position,
Figure Ib is a side view of a furnace according to an embodiment of the invention in the loaded position, Figure 2 is a top view of the device of figure 1,
Figure 3 is a side view of the device from figure 1, Figure 4 is a view of the furnace with heating elements, Figure 5 is a side view of the furnace from figure 4, Figure 6 is a view of the furnace having heat shields, Figure 7 is a side view of the furnace with the therein directed convection flows, and
Figure 8 is a detail of the gas supply conduit in figure 7.
Figures Ia and Ib show a side view of the furnace according to an embodiment of the invention. The furnace which is generally indicated with the reference numeral 2 is provided with a frame 4, arranged on foots 6 which are preferably adjustable in height, whereby the complete frame 4 preferably consists of two or more parts. The furnace pipe 8 having a space for positioning substrates 10 is arranged within the frame 4. The furnace pipe 8 is at the outer side provided with insulation material 12 surrounded by the outer shell 14. The substrates, typically in the form of panels, are introduced in the furnace pipe 8 by means of a positioning device 16 comprising the lid 18. The other side of the furnace pipe 8 is provided with a lid 20 where also the fittings 22 for the gas supply are located. At the circumference of the outer shell 14 inlet openings 24 are provided for forced introduction of cooling air in the space between the furnace pipe 8 and the outer shell 14 as well as outlet openings 26 for this air. Instead of cooling air any other suitable cooling gas or liquid may also be used to cool the space between the outer shell 42 and the outer surface of the furnace pipe 8.
The furnace 2 comprises a furnace part 42 supporting the furnace pipe 8 and a loading part 40 supporting the positioning device 16. In the shown embodiment the furnace part 42 is stationary, while the loading part 40 is movable between an unloaded position
(figure Ia) and a loaded position (figure Ib) . In the unloaded position, the positioning device 16 is placed outside the furnace pipe 8, so that panels or substrates supported by the positioning device 16 may be exchanged. In the loaded position, the positioning device 16 is moved into the furnace pipe 8, and lid 18 which is arranged on the positioning device 16 closes the respective end of the furnace pipe 8. In an alternative embodiment the loading part may be stationary and the furnace part may be movable between a loaded and unloaded position.
When the positioning device 16 supporting a number of substrates 10 is positioned in the furnace pipe 8 by moving the positioning device 16 to the loaded position the furnace pipe 8 is sealingly closed by the lids 18 and 20. Then the pressure within the furnace pipe is reduced and the furnace pipe 8 is flushed with inert gas. Thereafter the pressure within the furnace pipe is again reduced.
After the pressure has been reduced to a predetermined pressure, the furnace pipe is heated up to bring the temperature within the furnace pipe to a certain level for instance 500-5500C at which temperature the one or more substrates are heated for a certain time. During this time or thereafter the process gases for the diffusion process are injected by the gas injection device. These gases which are used for the diffusion process are known in the art. Then the gas is diffused into an layer of the substrate. After the diffusion process has finished, the process gases may quickly be cooled by a cooling device 100 as will be explained hereinafter. Then the inside of the furnace pipe is emptied, i.e. the process gases are removed and the furnace pipe is flushed to remove any remaining process gases. Thereafter, the positioning device may be moved to the unloading position to remove the substrate or substrates from the positioning device 16.
A cooling device 100 is provided for the cooling of the process gases within the furnace pipe. The cooling device 100 has a cooling circuit 101 comprising a gas outlet 102, a gas inlet 103, gas conduit 104, 105, a pump 106 for circulating the process gases and a heat exchanger unit 107 for cooling the circulating process gases. The gas outlet 102 is arranged in lid 18, and the gas inlet 103 is arranged in lid 20. Thus, the gas outlet 102 and the gas inlet 103 are arranged at opposite sides of the furnace pipe 8 (in the loaded position of the loading part 40) . This has the advantage that the process gases will be circulated through the inside of the furnace pipe 8 from one end to the other end, and also that no openings need to be provided in the furnace pipe 8 for the provision of the cooling circuit 101. As is clear from figures Ia and Ib, a part of the cooling circuit 101 is arranged within the loading part 40, and a part of the cooling circuit 101 is arranged within the furnace part 42. As the loading part 40 is movable with respect to the furnace part 42 between at least the unloaded position and the loaded position, the cooling circuit 101 is designed to allow for such movement. In the embodiment shown in figures Ia and Ib, an automatic connection device 108 is provided with which, when moving the loading part 40 from the unloaded position to the loaded position, automatically a sealing connection between both parts of the cooling circuit 101 is obtained.
The automatic connection device 108 comprises a bellows 109 arranged at the part of the cooling circuit 101 of the loading unit 40. The automatic connection device 108 further comprises a gripping device 110, which automatically grips the bellows 109, when this bellows 109 is pushed against the gripping device 110. Thus at the end of the moving of the positioning device 16 to the loaded position as shown in figure Ib, the automatic connection device 108 will automatically and sealingly close the cooling circuit 101 which will be used during the actual diffusion process, as will be explained hereinafter.
The process gases present in the furnace pipe 8 may be, in particular after the actual diffusion process is finished, pumped out of the inner side of the furnace pipe, where the actual diffusion process took place via the gas outlet 102 and gas conduit 104 to the cooling unit comprising the pump 106 and heat exchanger unit 107. The process gases are cooled in the heat exchanger unit 107 and pumped further through the gas conduit 105 and gas inlet 103 back into the process chamber, i.e. the inner side of the furnace pipe 8.
The pump 106 may be any pump suitable for pumping the hot process gases, for instance a centrifugal pump. Furthermore, the heat exchanger unit 107 may be any heat exchanger unit being capable of cooling the process gases of the diffusion process.
By providing such cooling device 100 the process gases may be quickly cooled after the actual diffusion process has finished. As a result the cycle time of the furnace 2 may be considerably lowered.
In a possible embodiment the cooling circuit 101 may also be used to cool the process gases during the actual diffusion process. In this way the temperature within the furnace pipe 8 may be controlled more accurately. An advantage of the above cooling circuit 101 is that the process gases may be directly cooled in the heat exchanger unit 107.
It may be possible that the functioning of one or more valves being provided in the cooling circuit 101 may be negatively influenced by the heat of the process gases the circulating through the cooling circuit 101. In order to minimize the chance on malfunctioning of these valves, one or more valves may be provided with an active cooling system. For instance a valve seat of a valve may be provided with a cooling space through which cooling fluid may be pumped for temperature control of valve seat. Any type of suitable valve cooling may be provided for one or more valves of the cooling circuit 101, or any other valve of the furnace 2 of which the functioning may be negatively influenced by the heat produced in the furnace 2. Figure 2 shows the top view of the view in figure 1 and therein the loading part 40, the furnace part 42 and a source part 44 are clearly shown as well as a operating panel 46 with which the complete installation can be operated by an operator. The number of substrates which is handled in one operation in the shown positioning device is for instance 16 plates with a width of 500 mm and a length of 1200 mm. The complete installation is provided at the topside with a number of openings. At the loading part opening 47 is provided for removing heat by opening the furnace, opening 48 is provided for heat-removal from the furnace and opening 49 provides in the removal of gasses from the source part. In the source part 44 a number of pumps 50 are located with which the furnace pipe can be brought on sub-atmospheric pressure.
Figure 3 shows the side view of the device from figure 1 having the operation panel 46 arranged at man's height and the fittings for the gas supply 22 on the lid 20 of the furnace pipe 8. The frame 4 consists of a number of stands 52 and a number of bars 54 for supporting the furnace pipe 8 and accessories.
The furnace pipe 8 is provided with a number of heating elements 60 arranged as shown in figure 4 between the furnace pipe 8 and the outer shell 14 of which preferably at least three are arranged adjacent in axial direction. As a result the outer axial heating elements 60 may be controlled in such a way that compensation is obtained for heat loss from the furnace pipe 8 to the environment such that the temperature distribution within the furnace pipe is substantially homogeneous and the substrates are heated with a substantially homogeneous temperature.
In radial direction the furnace pipe 8 comprises several radial heating elements 60 as shown in figure 5. With these radial heating elements 60 compensation can be realized in the height direction of the shown furnace 2 for the temperature difference which comes into existence in the furnace pipe 8 resulting in convection. Preferably the furnace pipe 8 is provided with two radial heating elements 60 in radial direction, as a consequence of which the number of separately controllable zones in the furnace pipe is six in the shown embodiment .
In the shown embodiment there is provided one temperature sensor per heating element. In figure 5 one temperature sensor 65 is arranged at an angle of about 45° with the vertical direction. In figure 4 three heating elements are illustrated in the axial direction which each are provided with an own temperature sensor 65. For the shown preferred embodiment this results in a total of six temperature sensors. The outer shell 14 is provided with cooling conduits 62 wherein preferably water is guided in axial direction to realize a constant heat loss from the furnace pipe to the environment which subsequently may be compensated by the heating elements 60. The cooling conduits 62 are fixed by means of clamping plates 64 and bolts 66 on the outer shell 14. It will be clear that other constructions are possible. Figure 6 shows the furnace pipe 8 having the heating elements 60 and the lids 18 and 20, wherein a number of heat shields 70 are arranged spaced from the respective lid and the space wherein the substrates are arranged. In the shown embodiment five heat shields are arranged at opposite sides of the furnace pipe 8. The heat shields 70 which are located at one side of the furnace pipe 8 are arranged at a small mutual distance. The heat shields 70 have as most important function to maintain the temperature in the furnace pipe homogeneous and to minimize the heat loss from this furnace pipe to the environment via the lids 18 and 20. Figure 7 shows the furnace pipe 8 having the heating elements 60, of which in the radial direction two are separately controllable in the shown embodiment. In the furnace pipe the substrate 80 and a gas supply conduit 82 with which gas can be supplied to the furnace pipe 8 for the purpose of the diffusion process are located. In the shown embodiment of the device the furnace pipe 8 is provided with one gas conduit which is arranged at the lowest point in the furnace pipe 8. It will be clear that embodiments having several gas conduits 82 located at different positions in the furnace pipe also are possible. The gas conduit 82 is provided with two rows openings 84 which each are placed at an angle of 45° with respect to the vertical direction as shown in figure 8. Other embodiments are conceivable. The gas supply conduit is preferably provided with openings having small dimensions such that a counter pressure exist in order to realize an equal discharge of the gas over the total length of the furnace pipe. Furthermore, in figure 7 the several zones are illustrated in which the furnace pipe 8 may be divided. These are a master zone 86 preferably at the underside of the furnace pipe 8 as shown, a correction zone 90 at the upper side of the furnace pipe 8 as shown and two transit zones 88 in the area between the master zone 86 and the correction zone 90. Further the directed convection flows are indicated in the drawing by means of arrows. The convection comes into existence as a consequence of the temperature difference within the furnace pipe 8 which is the result of the relative large diameter of the furnace pipe and the relative low temperature of the diffusion process in which temperature range convection place a relatively important role. In this convection process the warm gas will rise. These convection flows are directed in the furnace pipe 8 as shown in such a way that the rising gas flows along the outer wall of the furnace pipe 8 from the underside in the master zone 82 in tangential direction to the correction zone 90. From the correction zone 90 the gas flows downwards between the substrates 80 and back to the master zone 86. By means of the experimentally determined location of the openings 84 and the gas conduit 82 this corrected convection is supported, with which also a good distribution of the gaseous material in the furnace pipe 8 is realized.
In alternative embodiments other convection flow patterns may be created by using the radial heating elements 60. The creation of these flow patterns may be supported by the presence of one or more gas conduits 82 as explained hereinabove. For this reasons the openings in the gas conduits 82 may be placed at other angles to support the desired convection flow patterns.
The furnace described above provides a number of features which alone or in combination increase control accuracy of the temperature making temperature control in a diffusion process in a furnace pipe having larger diameter than state of the art furnaces possible without obtaining products with a substantial lower quality. In particular the furnace is suitable for the manufacture of solar cells which are based on the alloys or methods described in US2006222558 , WO2005017978 A2 and WO2005017979 KZ, the contents of these patent applications being herein incorporated in their entirety by reference .
However, the furnace comprising one or more of the features or aspects of the invention, alone or in combination, may also be used for the manufacture of any other substrates, such as panels, in particular when temperature control/distribution within the furnace pipe during the diffusion process is of importance for the quality of the final products.
The present invention is in no way limited to the above described embodiments; the requested rights, within the scope of which numerous modifications are conceivable, are determined by the following claims .

Claims

1. Furnace, comprising:
- a furnace pipe,
- a positioning device for positioning substrates in the furnace pipe, - at least one heating element for heating the furnace,
- a gas injection device, characterized in that the furnace comprises a cooling device configured to cool gases in the furnace pipe.
2. Furnace according to claim 1, wherein the cooling device comprises a cool circuit configured to circulate gas from the inside of the furnace pipe through a cooling unit.
3. Furnace according to claim 2, wherein the cooling circuit comprises a pump unit for circulating the gas.
4. Furnace according to any of the claims 2-3, wherein the cooling circuit comprises a heat exchanger unit.
5. Furnace according to any of the claims 2-4, wherein said furnace pipe comprises two opposite open ends, a gas outlet of the cooling circuit being arranged at a first end of the furnace pipe and a gas inlet being arranged at an opposite second end of the furnace pipe.
6. Furnace according to any of the claims 2-5, wherein the furnace comprises a loading part supporting the positioning device and a furnace part supporting the furnace pipe, wherein said loading part is movable with respect to said furnace for loading/unloading the positioning device in the furnace pipe, wherein a first part of the cooling circuit is arranged in said loading part and a second part of the cooling circuit is arranged in said furnace part, wherein the furnace comprises a cooling circuit connection device for automatically connecting said first and second part of the cooling circuit during loading of the positioning device in the furnace pipe.
7. Furnace according to claim 6, wherein the cooling circuit connection device comprises a bellows arranged on the first part of the cooling circuit and a gripping device arranged on the second part of the cooling circuit, the gripping device being configured to automatically sealingly grip the bellows during loading of the positioning device.
8. Furnace according to any of the claims 2-7, wherein said cooling circuit comprises at least one cooled valve.
9. Furnace, comprising: a furnace pipe; a positioning device for positioning one or more substrates in the furnace pipe; - a heating element, and a gas injection device, characterized that the furnace comprises
- two or more heating elements for bringing and maintaining the temperature of the furnace pipe at a temperature above 3000C, which heating elements are each separately controllable, and
- one or more temperature sensors for measuring the furnace temperatures for the purpose of the separately controllable heating elements .
10. Furnace according to any of the claims 1-9, wherein the furnace pipe comprises a diameter of at least 400 mm.
11. Furnace according to any of he claims 1-10, wherein the furnace pipe comprises in radial direction several separately controllable radial heating elements.
12. Furnace according to any of the claims 1-11, wherein the furnace pipe comprises in axial direction a number of separately controllable axial heating elements .
13. Furnace according to any of the claims 1-12, wherein the furnace pipe is a quartz pipe.
14. Furnace according to any of the claims 1-13, wherein in a forced way cooling gas is blown in the space between the furnace pipe and the outer shell.
15. Furnace according to one or more of the claims 1-5, wherein cooling means are arranged at the outer side of the outer shell to realize a constant heat loss.
16. Furnace according to claim 5, wherein the cooling means comprise fluid conduits which extend in the axial direction of the outer shell of the furnace pipe.
17. Furnace according to any of the claims 1-16, wherein the gas injection device comprises one or more gas conduits in the axial direction of the furnace pipe.
18. Furnace according to claim 17, wherein the gas conduits are provided with openings at the side resulting in a discharge in the tangential direction of the furnace pipe to support the desired air flow in the furnace pipe.
19. Method for the manufacture of photo-voltaic solar cells, comprising the steps:
- loading a substrate in a furnace pipe; - reducing pressure in the furnace pipe;
- flushing the furnace pipe with inert gas and again reducing the pressure;
- heating up the furnace pipe with the substrate;
- heating the substrate to a temperature of about 500-5500C; - injecting process gas;
- diffusing the gas in the applied layer of the substrate;
- emptying and flushing the furnace pipe; and
- unloading the substrate.
20. Method according to claim 19, whereby the heating of the substrate takes place by means of several separately controllable radial heating elements in radial direction of the furnace pipe.
21. Method according to claim 18 or 19, whereby the heating of the substrate takes place by means of several separately controllable axial heating elements in axial direction of the furnace pipe.
21. Method according to any of the claims 19-21, wherein gas within the furnace pipe is cooled at least during diffusing of the gas.
22. Method according to any of the claim 19-22, wherein the gas within the furnace pipe is cooled after the diffusion process by using a internal cooling device.
22. Method according to any of the claims 19-21 using the furnace of any of the claims 1-21.
PCT/NL2006/000556 2005-11-07 2006-11-07 Surface and method for the manufacture of photovolataic cells using a diffusion process WO2007053016A2 (en)

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NL1030360A NL1030360C2 (en) 2005-11-07 2005-11-07 Furnace and method for the production of photovoltaic solar cells using a diffusion process.
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