WO2010092471A2

WO2010092471A2 - Method and device for coating planar substrates with chalcogens

Info

Publication number: WO2010092471A2
Application number: PCT/IB2010/000280
Authority: WO
Inventors: Jörg Baier; Immo KÖTSCHAU; Reinhard Lenz; Dieter Schmid; Robert Michael Hartung
Original assignee: Centrotherm Photovoltaics Ag
Priority date: 2009-02-16
Filing date: 2010-02-15
Publication date: 2010-08-19
Also published as: WO2010092471A3; DE102009009022A1; TW201038756A

Abstract

The invention relates to a method and a device for coating planar substrates with chalcogens in the form of thin layers. The invention is intended to provide a fast and cost-effective coating of planar substrates with chalcogens, with a controlled and safe removal of the uncondensed chalcogen and a device suitable for carrying out the method. This is achieved by forming an inlet side and outlet side gas lock (6, 7) for the oxygen-tight closure of a process chamber (5), introducing one or more substrates to be coated, said substrates being temperature-regulated to a predetermined temperature, into the process chamber (5), introducing a chalcogen vapour/carrier gas mixture into the process chamber (5) which has a transport channel (4), above the substrates, forming a flow of the chalcogen vapour/carrier gas mixture through the transport channel (4) between the inlet side and outlet side gas locks (6, 7) and forming a chalcogen layer on the substrates by means of PVD during a predetermined dwell time and removing the chalcogen vapour which has not condensed onto the substrates together with the carrier gas between the gas locks, and removal of the substrates after the predetermined process time has elapsed.

Description

Method and device for coating planar substrates with chalco- gens

The invention concerns a method and a device for coating planar substrates with chalcogens, in the form of thin films, in a process chamber.

Chalcogen layers are needed, for example, in a multi-stage process for the manufacture of thin film modules on the basis of compound semiconductors. Chalcogens include the elements sulphur, selenium, tellurium and polonium. Although oxygen is one of the chalcogens, it is^' not desirable in the manufacture of thin film modules.

In this process, in a first step, metallic precursor layers and a chalcogen layer are applied to the substrate, which can, for example, be a glass substrate with a molybdenum layer. The metallic precursor layers may contain copper (Cu) , gallium (Ga) and indium (In) and can be applied to the substrate with known technologies, for example sputtering. The subject matter of the present invention is a method and a device for applying a chalcogen layer, preferably a layer of selenium, with the aim of converting the layer stack into a semiconducting layer.

This then takes place in a second step. This is achieved by means of a post-published method (PCT/EP 2008/007466) in which the prepared substrates are heated in an oven segmented into several temperature zones, at a pressure of approximately atmospheric ambient pressure in several stages, each at a predetermined temperature, up to a final temperature of between 400⁰C and 600°C and converted into semiconducting layers while maintaining the final temperature. According to the state of the art, chalcogen coating methods have also been disclosed which take place in a vacuum. In the^¬ se methods, chalcogens are thermally vaporised in the vacuum and deposited onto the substrates.

A vacuum is normally used in order to prevent the entry of oxygen, for example, during the coating with chalcogens. In the presence of oxygen, for example, selenium would react to become a toxic compound (selenium dioxide), which would dis- rupt the further processes, for example the thermal reaction of the precursor layers into semiconducting layers.

Vacuum processes in industrial mass production usually lead to high costs. Pump and sluice times lead to greater cycle times and hence, in addition to long process times, always result in low productivity.

A method of selenium deposition from the vapour phase under a protective gas onto a flexible substrate, in which sodium and/or sulphur are simultaneously or sequentially deposited by condensation onto the continuous strip, was disclosed in DE 10 2004 024 601. The deposition equipment consists of a reactor with source zone, transport area and condensation zone, whereby an inert carrier gas dilutes the selenium, sulphur and sodium vapour and transports it from the different temperature-controlled sources for condensation on the precursor. At this point the precursor is temperature-controlled to less than 100°C, so that only condensation takes place, but no reaction of the components of the precursor with the selenium, sodium and/or sulphur vapour.

A fast and economical coating process for chalcogens, in particular for the application of thin films of chalcogens in the range of 100 nm to 10 μm on large-area substrates, and a de- vice suitable for carrying out the method, was created in pat^¬ ent application PCT/EP 2008/062061.

The method is realised by creating a gas curtain at the inlet and outlet sides as an oxygen-tight closure of a transport channel in an evaporation head, introduction of an inert gas into the transport channel to displace the atmospheric oxygen, introduction of one or more substrates for coating, which have been temperature-regulated to a predefined temperature, into the transport channel of the process chamber, introduction of a chalcogen vapour/carrier gas mixture from a source into the transport channel of the evaporation head over the substrates and formation of a chalcogen layer on the substrates by means of physical vapour deposition (PVD) under a predefined pres- sure, and removal of the substrates once the predefined process time has elapsed.

In the method mentioned, only part of the chalcogen vapour condenses on the substrates. The rest of the chalcogen vapour must therefore be removed in a controlled fashion.

The invention is, then, based on the problem of specifying a method and a device for coating planar substrates with chalco- gens in the form of thin films, in particular for planar sub- strates prepared with precursor layers made of any materials, preferably of substrates made of glass, with controlled removal of the uncondensed chalcogen.

The problem on which the invention is based is solved by a me- thod in which an inlet and outlet side gas lock is formed as an oxygen-tight closure of a process chamber, introduction of one or more substrates for coating which have been temperature-regulated to a predefined temperature into the process chamber in a transport direction, introduction of a chalcogen vapour/carrier gas mixture uniformly distributed over the width of the substrates into the process chamber, which has a transport channel, above the substrates, formation of a flow of the chalcogen vapour/carrier gas mixture over the sub- strates through the transport channel between the inlet and outlet side gas locks, formation of a chalcogen layer on the substrates by means of PVD during a predetermined dwell time and removal of the excess chalcogen vapour not condensed onto the substrates, and of the carrier gas between the gas locks, and removal of the substrates from the process chamber once a predefined process time has elapsed.

An inert gas, preferably nitrogen, can be used for the gas locks and/or as carrier gas.

In one embodiment of the invention the chalcogen vapour/carrier gas mixture, after being introduced into the process chamber above the substrates, flows along the transport channel in or against the direction of transport above and along the substrates before the chalcogen vapour/carrier gas mixture is removed again.

Furthermore, the substrates are preferably moved in the transport direction during coating; the movement can occur at con- stant speed.

It is also advantageous if the substrates, before introduction into the process chamber, are temperature-regulated to a temperature of below 200°C, e.g. to a temperature of between 20°C and 100⁰C or again, room temperature.

Furthermore, the substrates can be temperature-regulated, during coating, to a temperature of under 200°C, preferably between 20⁰C and 100⁰C. The problem on which the invention is based is also solved by a device for coating planar substrates with chalcogens in the form of thin films in a process chamber which is provided with an opening for introduction and an opening for removal of the planar substrates, and also has an inlet side gas lock at the opening for introduction of the substrates and an outlet side gas lock at the opening for removing the substrates and which is' provided with transport means for the planar substrates through the process chamber, by the fact that in the wall of the process chamber opposite the transport means, between the gas locks, there is an opening for a feed of a chalcogen vapour/carrier gas mixture, and, laterally offset thereto, an opening for removing the chalcogen vapour/carrier gas mixture.

The openings for introduction and removal and the gas locks make it possible to run the device in continuous operation mode, at a pressure close to atmospheric pressure and under defined residual gas conditions, in particular excluding oxy- gen.

The transport means and the openings for introduction and removal allow the introduction of one or more substrates for coating into the process chamber, transport of the substrates through the process chamber and removal of the coated substrates from the process chamber.

The coating takes place between the openings for the feed and removal of the chalcogen vapour/carrier gas mixture. The chal- cogen vapour/carrier gas mixture is introduced into the process chamber via the opening for the feed of the chalcogen vapour/carrier gas mixture. The removal by suction via the other opening leads to a flow of the chalcogen vapour/carrier gas mixture along the process chamber. This achieves an especially uniform coating.

The transport means preferably enables a movement of the sub- strates at constant speed.

Th^'e device can be operated in such a way that the chalcogen vapour/carrier gas mixture flows in or against the transport direction .

If the transport direction of the substrates is in the direction of the flow of the chalcogen vapour/carrier gas mixture, the relative speed of the chalcogen vapour to the substrate can be reduced in relation to the flow speed of the chalcogen vapour/carrier gas mixture. This enables better deposition of the chalcogen on the substrates.

If, however, the device is operated such that the transport direction of the substrates is directed against the flow of the chalcogen vapour/carrier gas mixture along the process chamber, this can even out density fluctuations of the chalcogen vapour along the process chamber and lead to a more uniform coating.

The device is arranged such that the chalcogen vapour/carrier gas mixture flows chiefly over an area of the substrates in the process chamber. By means of PVD, a chalcogen layer forms on the substrates in the process chamber.

The chalcogen vapour which is not condensed onto the substrates is removed, together with the carrier gas, via the opening for removal from the process chamber and then via at least one exhaust gas pipe. The chalcogen can then be removed, for example by using a condensation trap and/or a filter. The waste chalcogen arising must either be disposed of or fed to a reprocessing plant.

In one development of the invention, there is a further later- ally offset opening for the feed of a chalcogen vapour/carrier gas mixture in the wall of the process chamber located opposite the transport means. In this case, the feed and removal openings are offset from each other in the direction of transport, in particular the feed and removal openings are arranged in the sequence feed, removal and feed.

In a further development of the invention, a further laterally offset opening for removal of the chalcogen vapour/carrier gas mixture is located in the wall of the process chamber located opposite the transport means. In this case, the feed and removal openings are offset from each other in the direction of transport, in particular the feed and removal openings are arranged in the sequence removal, feed and removal.

The pressure conditions in the chamber are set such that defined flows can be generated from the openings for feed of the chalcogen vapour/carrier gas mixture towards the centre of the process chamber.

The coating takes place between the openings for feed of the chalcogen vapour/carrier gas mixture. As the result of this arrangement, the area in which coating takes place can be doubled in simple fashion.

It goes without saying that the number of openings for the feed and removal of a chalcogen vapour/carrier gas mixture is not limited to two or three. For better exclusion, for example of oxygen, from the process chamber, the process chamber can be surrounded by a housing. The housing has two opposing openings and a transport channel between them, for the introduction and removal of substrates using the transport means which extends through the process chamber. The openings in the housing define a subspace of the space enclosed by the housing, the so-called transport channel .

This allows the substrates to be introduced into the transport channel at one opening of the housing, transport of the substrates through the transport channel, and therefore also through the process chamber, and finally removal of the substrates at the other opening in the housing.

Chalcogen vapour which may leak from the process chamber into the space surrounded by the housing can, for example, be removed with the aid of a separate housing suction extractor.

The housing can, for example, consist of a Plexiglas box. This enables the user to monitor the process chamber visually.

The inlet and outlet side gas locks of the process chamber can each consist of two gas curtains. An additional suction ex- tractor can also be present between the two gas curtains.

This enables the gas flows on both sides of the gas lock to be adjusted independently of each other.

An inert gas, for example nitrogen, is preferably used as protective/carrier gas.

The protective gas of the respective outer gas curtains can, for example, be drawn outwards via the suction extractor of the housing and the protective gas of the respective inner gas curtains, via the opening for suction removal of the chalcogen vapour/carrier gas mixture in the process chamber, can be drawn inwards, into the process chamber.

This guarantees separation of the atmosphere in the process chamber from the atmosphere outside the process chamber.

One embodiment of the invention includes a device which allows the substrates ^' to be temperature-regulated to a temperature of under 200⁰C, for example to a temperature of between 20⁰C and 100⁰C.

The temperature-regulating device can, for example, be real- ised by a cooling device, since the substrates are heated in the hot atmosphere in the process chamber.

Furthermore, a heating device can be provided for components which come into contact with chalcogen vapour. If chalcogen vapour should condense on these components, by selective baking out, for example during servicing, the chalcogen can vaporise again and for example be removed via the housing suction extractor.

In one development of the invention, the feed and removal openings for the chalcogen vapour/carrier gas mixture are slot- shaped openings, which are aligned perpendicularly to the direction of transport and which extend over the whole of the substrate which is in the process chamber. This has the advan- tage of a more uniform coating.

Furthermore, the wall of the process chamber above the substrates, between the slot-shaped feed and removal openings can be undulating in form. In this case, the crests of the undula- tions are aligned parallel to the slot-shaped openings, i.e. perpendicularly to the direction of transport along the transport channel.

For the feed of the chalcogen vapour/carrier gas mixture via the corresponding openings, each opening for the feed of the chalcogen vapour/carrier gas mixture can, for example, be connected to an evaporation chamber via one or more pipelines, through which the chalcogen vapour/carrier gas mixture flows.

The ends of the pipelines can be distributed along a slot- shaped opening for the feed of the chalcogen vapour/carrier gas mixture in order to obtain a uniform distribution of the chalcogen vapour/carrier gas mixture over the entire opening.

In one refinement of the invention, the pipelines which lead to a slot-shaped opening can adopt the form of the slot-shaped opening in the lower part of the pipelines. This enables an almost completely uniform distribution of the chalcogen va- pour/carrier gas mixture over the entire slot-shaped opening.

Furthermore the pipelines can be provided in the lower part with constrictions followed by expansion zones.

The effect of this is that the chalcogen vapour/carrier gas mixture which flows through these constrictions becomes banked up and hence compressed and then is expanded again. This process is repeated. As a result, the chalcogen vapour/carrier gas mixture is distributed over the desired length and enables a homogenous coating of the substrates.

For a uniform removal by suction of the chalcogen vapour/carrier gas mixture over the entire slot-shaped opening to remove the chalcogen vapour/carrier gas mixture by suction, the exhaust gas pipes at the slot-shaped opening can adopt the form of the slot-shaped opening and be provided with constrictions followed by expansion zones.

The evaporation chamber is a chamber with at least one outlet for removal of the chalcogen vapour/carrier gas mixture, to which the pipelines are connected. The chamber can have at least one additional inlet for the supply of solid chalcogen and one entrance for the feed of a carrier gas.

The solid chalcogen melts in the heatable evaporation chamber and forms a selenium pool. The chamber can be equipped with a level sensor for metering the chalcogen quantity.

The carrier gas, which enters the chamber and preferably has already been heated, absorbs chalcogen vapour in the chamber and the chalcogen vapour/carrier gas mixture is fed via one or more pipelines to an opening for the feed of the chalcogen vapour/carrier gas mixture.

In order to control the flow rate at which the carrier gas flows into the chamber, it can be monitored by a flow meter and adjusted by a fine-control valve. It goes without saying that the control can take place automatically.

In order to prevent any backflow from an opening for the feed of the chalcogen vapour/carrier gas mixture to an evaporation chamber, an additional carrier gas feed can be provided in each pipeline between evaporation chamber and feed opening. The so-called additional process gas introduced through these additional feeds thereby generates suction which draws the chalcogen vapour/carrier gas mixture out of the chamber. In order to control the flow rate at which the additional process gas flows into a pipeline between evaporation chamber and opening for the feed of the chalcogen vapour/carrier gas mixture, each pipeline can be monitored with a flow meter and ad- justed via a fine-control valve.

An increased flow rate of the additional process gas leads to a greater flow of chalcogen vapour/carrier gas mixture in the associated pipeline between evaporation chamber and slot- shaped opening for the feed of the chalcogen vapour/carrier gas mixture.

By independently regulating the flows of additional process gas, the homogeneity of the deposition perpendicular to the direction -of transport can be further improved.

Since, as already described, not all of the chalcogen vapour is deposited on the substrates, this chalcogen vapour/carrier gas mixture has to be removed as exhaust gas via the suction extraction opening. In order to limit the loss of chalcogen, this exhaust gas can be divided by a flow volume divider. Part is then still removed as exhaust gas, referred to as residual waste gas, while the other part can for example be made available again for coating via the additional carrier gas feeds or via the carrier gas feeds of the chambers. In that case the temperature of the chalcogen vapour/carrier gas mixture which is returned should never be below the condensation temperature of the chalcogen, in order to prevent any condensation of the chalcogen in the recirculation system.

In one development of this exhaust gas recirculation system, chalcogen is removed from the residual exhaust gas and the gas recirculated for coating is enriched with chalcogen. At least one feed device can be built into the device for feeding the solid chalcogen into the evaporation chamber. A feed device may consist of a container, which may be in the form of a funnel and which provides a stock of chalcogen, a metering device, which allows a predetermined quantity to be introduced into an evaporation chamber via at least one pipeline, and a valve for each pipeline. The valves are opened during the feed of the chalcogen and otherwise remain closed, so that any escape of chalcogen vapour from the evaporation chamber into the feed device is prevented as far as possible.

In large plants for coating substrates with chalcogens, a uniform distribution in one chamber can be guaranteed by having several inlets for the supply of solid chalcogen. In that case a feed device can distribute solid chalcogen uniformly at the various inlets to a chamber, or a separate feed device can also be provided for each inlet.

A further way to prevent any escape of chalcogen vapour from an evaporation chamber into a feed device can be realised by feeding a carrier gas into the pipeline between valve and evaporation chamber. The flow rate of this carrier gas feed can, for example, be captured by means of a flow meter and adjusted via a fine-control valve.

In one embodiment of the invention, components which may come into contact with the chalcogen vapour or the chalcogen vapour/carrier gas mixture are preferably made from a material which is resistant to this mixture, e.g. graphite.

Furthermore, components which come into contact with chalcogen vapour should be heated so that any condensation of the chalcogen on these components is prevented. This avoids expensive cleaning and servicing. One way to realise this is to accommodate parts of the device in a block, for example made from graphite, and to heat this to the desired temperature using an integrated heater.

In one refinement of the invention, the feed and removal openings for the chalcogen vapour/carrier gas mixture, and the evaporation chambers, including the connecting pipelines, are housed in an evaporation head which is inserted in a recess in the wall opposite the transport means, i.e. above the substrates .

The evaporation head preferably consists of a material which is resistant to chalcogen vapour, in particular for example of graphite.

The evaporation head can, for example, be brought to a desired temperature by means of an integrated heater.

Furthermore, a thermal decoupling of the evaporation head from the process chamber can be provided. This allows, for example, the evaporation head to stay at high temperatures, while for example the transport means can be temperature-regulated to low temperatures.

In one refinement of the invention, the evaporation head can be placed under a sealed cover with integrated cooling system. The internal space of the cover can, in one special embodiment, be flooded with a protective gas and suctioned out.

In one development of the invention, further components which come into contact with chalcogen vapour, for example the evaporation chambers and the pipelines between evaporation chamber and the opening for feeding in the chalcogen va- pour/carrier gas mixture, and also nitrogen gas feeds can be housed in the evaporation head. The housing of the nitrogen gas feeds in the evaporation head has the advantage that the nitrogen gas is already heated in the evaporation head.

One embodiment of the invention is explained with the aid of the attached drawings, which show:

Fig. 1 an overview of a device for coating substrates with chalcogens,

Fig. 2 a process chamber with inlet and outlet side gas locks,

Fig. 3 an evaporation head and

Fig. 4 a diagrammatic drawing of a feed device for sele- niurn .

Figure 1 shows an overview of a device for coating substrates, such as previously prepared glass substrates, with chalcogens. In the rest of the description, coating with selenium will be assumed. So that, for example, toxic selenium dioxide cannot be produced, the whole process must take place in a defined atmosphere, in particular excluding oxygen. For example, nitrogen can be used as protective/carrier gas.

This is guaranteed inter alia by a housing 1 which consists of a Plexiglas box, or another suitable material, and a housing suction extractor 2. The housing 1 has two opposing openings 1.1, 1.2 (see arrows) for the introduction and removal of the substrates, not shown, using a transport means 3. The openings 1.1, 1.2 in the housing 1 define a partial space of the space enclosed by the housing 1 and this is in fact a transport channel 4.

A central partial area of the transport channel 4 defines a process chamber 5. This process chamber 5 is surrounded by walls and also has two opposing openings 5.1, 5.2 (see arrows) through which the transport channel 4 passes. These openings 5.1, 5.2 allow substrates to be transported into the process chamber 5 and out again with the aid of the transport means 3 via the transport channel 4. The substrates are transported at a constant rate.

Fig. 2 shows that both openings 5.1 and 5.2 of the process chamber 5 are provided with an inlet side 6 and outlet side 7 gas lock. Each gas lock 6, 7 consists of two gas curtains made from nitrogen, which are indicated by arrows in Fig. 2. The nitrogen gas of the respective outer gas curtains is suctioned out via a housing suction extractor, while the nitrogen gas of the respective inner gas curtains is drawn inwards via a suc- tion extractor in the process chamber 5, into the process chamber 5.

The gas locks 6, 7 allow the plant to be operated in continuous operation mode, at atmospheric pressure and under defined residual gas conditions, in particular excluding oxygen.

The actual coating of the substrates takes place in the area of a recess 8, which is located in the wall of the process chamber 5 opposite the transport means 3. To this end, the evaporation head 9 shown in detail in Fig. 3 is inserted into this recess 8, cf. also Fig. 1. The evaporation head 9 is a block of graphite with milled-out sections. For further protection, so that no selenium can escape into the environment, the evaporation head 9 is placed under a sealed cover 10 (Fig. 1) with an integrated cooling system, not shown. The space between the cover 10 and the evaporation head 9 can be flooded or flushed with nitrogen and suctioned out.

A selenium vapour/ nitrogen gas mixture is introduced into the process chamber 5 via a slot-shaped opening 11 in the evaporation head 9, which is aligned perpendicularly to the transport direction of the substrates. Suction removal via a further slot-shaped opening 12, which is aligned parallel to the slot- shaped opening 11 for feeding the selenium vapour/nitrogen gas mixture and is offset with respect to this in the transport direction of the substrates leads to a flow of the selenium vapour/carrier gas mixture along the transport channel 4 in the process chamber 5. The actual coating takes place in the area of the process chamber 5 which is delimited by the two openings 11, 12. This zone is therefore also referred to as the coating zone.

The plant is operated in such a way that the selenium vapour/carrier gas mixture flows in the transport direction (Fig. 2) of the substrates.

In order to obtain a uniform coating of the substrates perpendicularly to the transport direction, the selenium vapour must be applied uniformly over the entire width of the substrate. A homogenous distribution may be crucial for further process steps .

To this end, one pipeline via which the selenium vapour/carrier gas mixture is fed to the slot-shaped opening 11 has the form of the slot-shaped opening in the lower part. The homogenous distribution is effected via a slot 13 for feeding the selenium vapour/carrier gas mixture with several consecutive constrictions and expansions in the evaporation head 9 (Fig. 3) . The slot 13 for feeding in this case runs parallel to the slot-shaped opening 11 and ends at this opening. The mixture then builds up in a constriction and can then expand again in an expansion zone. This process is repeated several times. As a result, the selenium vapour/carrier gas mixture is uniformly distributed over the entire slot-shaped opening 13.

Furthermore, the wall of the process chamber 5, between the slot-shaped opening 11 for feeding and the slot-shaped opening 12 for removing has an undulating surface with undulation crests perpendicular to the transport direction of the sub- strates. This achieves a better mixing of the chalcogen vapour/carrier gas mixture passed over the surface of the substrates .

The selenium which does not condense on the substrates in the coating zone between the slots 11, 12 is removed together with the nitrogen via the slot-shaped opening 12 for removal by suction and then via a slot 14 for removal by suction which runs parallel to the slot-shaped opening 12 for removal by suction 'and ends at this opening, out of the process chamber 5 and then carried away via an exhaust gas pipe 15 which is angled slightly downwards. The slot 12 for removal by suction and the exhaust gas pipe 15 can together be regarded as an exhaust gas pipe which adopts the form of the slot-shaped opening 12 towards the slot-shaped opening 14. The slot 12 for re- moval by suction is also provided with several constrictions and expansions. This enables uniform removal by suction of the excess selenium vapour/carrier gas mixture over the entire width . Fig. 4 shows a diagram of a feed device for selenium.

Selenium is commercially available in spherical form in solid aggregate condition. The spheres have a diameter of approx. 3 mm. The selenium spheres are poured into a funnel-shaped container 16 and stored there in readiness. The funnel-shaped container 16 has an opening at its lower end through which the selenium spheres can fall perpendicularly downwards into a metering device 17 located thereunder. The funnel-shaped con- tainer 16 is also equipped with a level meter.

The metering device 17 consists of a cylindrical housing and a pivoted part, also cylindrical, pivotably mounted centrally therein, henceforth referred to as the drum. The housing has two holes, one on the top and one on the bottom, on the same reference diameter and offset by 180° in their position. The inner pivoted part has four holes, which lie on the same reference diameter. In terms of length, the two parts are designed such that no selenium sphere can fit between them.

If the holes in the parts lie aligned on top of each other, the selenium spheres can fall into the drum. If the drum is turned by 90°, the selenium spheres can leave the drum and the housing, falling vertically downwards.

The number of selenium spheres and hence the quantity of selenium which is provided can be metered via the interval which ^■ elapses between the 90° rotations and the number of selenium spheres which fit into the hole in the drum.

Next, the selenium spheres fall through an essentially vertical pipeline 18 into a heated chamber 19, also known as the evaporation chamber. A valve 20 is built into the vertical pipeline 18, designed as a ball valve with full opening, which is only opened in the metering period. As a result, next to no vapour can escape from the heated chamber in which the selenium vapour is present into the feed device.

Another means of preventing any escape of selenium vapour from the evaporation chamber 19 into the feed device via the pipeline 18 of the metering device 17 or from the container 16 is realised by a nitrogen gas feed in the pipeline 21 between valve 20 and evaporation chamber 19. This nitrogen flow gener- ates a flow into the evaporation chamber 19 and prevents any flow in the opposite direction.

As described, the selenium spheres fall from above into the chamber 19. The chamber 19 is a simple horizontal hole or ope- ning in a block of graphite, i.e. in the evaporation head 9

(Fig. 3) and is closed off at both ends. The selenium collects in this chamber 19, which in addition to the selenium feed via the pipeline 18, also has an inlet 22 and an outlet 23. Said inlet and outlet 22, 23 are located on the upper side of the hole.

The block, i.e. the evaporation head 9, is heated together with the selenium via a heater, not shown. As a result of this heating, the selenium is firstly melted and then vaporised as the temperature rises further. In the lower part of the chamber there is then a liquid pool of selenium 24, and in the upper part selenium vapour 25.

A level sensor, not shown, is provided to regulate the level in the chamber 19. The level sensor sends a signal to the described metering device, if there is too little selenium in the chamber 19. The process described then begins, so that selenium falls into the chamber. Once a sufficient level is rea- ched, the level sensor stops the metering process by means of a signal.

The selenium vapour which has formed in the chamber must now be passed On to the substrate. It is now necessary to guarantee that the selenium vapour can neither cool down nor condense. The vapour is transported via a carrier gas. Nitrogen is used as carrier gas. This must firstly be heated to the same temperature as that prevailing in the chamber. The nitro- gen gets into the chamber 19 containing the selenium vapour through the inlet 22. There the selenium vapour is absorbed and carried as selenium vapour/nitrogen mixture through the outlet 23 of the chamber 19 in the direction of the substrate. The pipeline between chamber and slot-shaped opening 13 for the feed must also be heated in order to prevent any condensation of selenium, which would entail expensive maintenance work.

In order to realise this preheating of the nitrogen gas, the heating of the evaporation chamber and of the transport channels more easily, everything is accommodated in the graphite evaporation head 9. The entire evaporation head 9 is heated. The nitrogen gas is passed through a meander, not shown, in the evaporation head 9. The gas is thereby heated to the tem- perature of the evaporation head 9.

In addition, the flow of the nitrogen gas mixed with selenium vapour is guided via a further nitrogen gas feed 26, located in the pipeline between evaporation chamber and slot-shaped opening 11 for the feed 11. The inflow of this gas, known as additional process gas, generates slight suction, which draws the gas mixture out of the chamber 19. The flow via the nitrogen gas feed for the additional process gas can be measured by a flow meter and adjusted via a fine-control valve. In order to control the flow rate of the nitrogen feed for the additional process gas 26, the nitrogen feed into the pipeline 21 and the nitrogen feed into the evaporation chamber 22, the- se are each equipped with a flow meter and a fine-control valve. This allows the corresponding flows to be measured and then adjusted.

In the above embodiment, selenium stands for the other chalco- gens, apart from oxygen.

List of reference numbers

1 Housing

1.1 Opening

1.2 Opening

2 Housing suction extractor

3 Transport means

4 Transport channel

5 Process chamber

5.1 Opening

5.2 Opening

6 Inlet side gas lock

7 Outlet side gas lock

8 Recess

9 Evaporation head

10 Cover

11 Slot-shaped opening for feed

12 Slot-shaped opening for removal by suction

13 Slot for feed

14 Slot for removal by suction

15 Exhaust gas pipe

16 Container

17 Metering device

18 Pipeline

19 Chamber

20 Valve

21 Nitrogen gas feed into the pipeline

22 Inlet

23 Outlet

24 Selenium pool

25 Selenium vapour

26 Nitrogen gas feed for the additional process gas

Claims

1. Method for coating planar substrates with chalcogens, in the form of thin films, in a process chamber, c h a r a c t e r i s e d b y :

- formation of an inlet and outlet side gas lock (6, 7) for the oxygen-tight closure of the process chamber (5),

- introduction of one or more substrates for coating which have been temperature-regulated to a predefined temperature in a transport direction into the process chamber (5) , introduction of a uniformly across the width of the substrates distributed chalcogen vapour/carrier gas mixture above the substrates into the process chamber (5) having a transport channel (4)

- formation of a flow of the chalcogen vapour/carrier gas mixture over the substrates through the transport channel (4) between the inlet and outlet side gas locks (6, I)₁

- formation of a chalcogen layer on the substrates by means of PVD during a predetermined dwell time in the process chamber (5) and

- removal of the excess chalcogen vapour not condensed onto the substrates, and of the carrier gas between the gas locks (6, 7), and removal of the substrates from the process chamber (5) once a predetermined dwell time has elapsed.

2. Method according to claim 1, c h a r a c t e r i s e d i n t h a t after being introduced into the process chamber (5), the chalcogen vapour/carrier gas mixture flows along the trans- port channel (4) above the substrates in the direction of transport and is then removed again

3. Method according to claim 1, c h a r a c t e r i s e d i n t h a t after being introduced into the process chamber (5), the chalcogen vapour/carrier gas mixture flows along the transport channel (4) above the substrates counter to the direction of transport and is then removed again.

4. Method according to one of claims 1 to 3, c h a r a c t e r i s e d i n t h a t before being introduced into the process chamber (5), the substrates are temperature-regulated to a temperature of under 200⁰C, preferably room temperature.

5. Method according to one of the preceding claims, c h a r a c t e r i s e d i n t h a t the substrates are temperature-regulated during coating to a temperature of under 200⁰C, preferably between 20⁰C and 100⁰C.

6. Device for coating planar substrates with chalcogens, in the form of thin films, in a process chamber which is provided with an opening for introduction of the substrates and with an opening for removal of the substrates and which comprises an inlet side gas lock at the opening for introduction of the substrates and an outlet side gas lock at the opening for removal of the substrates, and which is provided with a transport means for the planar substrates through the process chamber, c h a r a c t e r i s e d i n t h a t in the wall of the process chamber (5) opposite the trans- port means, between the gas locks (6, 7) there is an open- ing (11) for feeding in a chalcogen vapour/carrier gas mixture and laterally offset thereto an opening (12) for removal of the chalcogen vapour/carrier gas mixture.

7. Device according to claim 6, c h a r a c t e r i s e d i n t h a t a further opening, laterally offset with respect to the other two openings (11, 12), is present in the wall opposite the transport means for feeding in a chalcogen vapour/carrier gas mixture, while the openings are arranged ^Ύ in the sequence feed, removal and feed along the process chamber ( 5) .

8. Device according to claim 6 or 7, c h a r a c t e r i s e d i n t h a t a housing (1) surrounds the process chamber (5) and is pro- vided with two opposing openings (1.1, 1.2) and a transport channel (4) between them, which extends through the process chamber ( 5 ) .

9. Device according to claim 8, c h a r a c t e r i s e d i n t h a t the housing (1) has a suction extractor.

10. Device according to one of claims 6 to 9, c h a r a c t e r i s e d i n t h a t the gas locks (6, 7) each consist of at least two gas curtains .

11. Device according to claim 10, c h a r a c t e r i s e d i n t h a t there is a suction extractor between the gas curtains of the gas locks (6, 7) .

12. Device according to one of claims 6 to 11, c h a r a c t e r i s e d i n t h a t the device provides a temperature regulation device for temperature-regulating the substrates to a temperature un- der 200⁰C.

13. Device according to one of claims 6 to 12, c h a r a c t e r i s e d i n t h a t the openings (11, 12) are slot-shaped openings which are aligned perpendicularly to the transport direction and which each extend over the entire width of the substrates located in the process chamber (5) .

14. Device according to claim 13, c h a r a c t e r i s e d i n t h a t the wall of the process chamber (5) above the substrates between the slot-shaped openings (11) for feeding and the slot-shaped opening (12) for removal has an undulating surface with undulation crests perpendicular to the direction of transport of the substrates.

15. Device according to one of claims 6 to 14, c h a r a c t e r i s e d i n t h a t each opening for feeding in a chalcogen vapour/carrier gas mixture is connected via at least one pipeline with an evaporation chamber (19) .

16. Device according to claim 15, c h a r a c t e r i s e d i n t h a t the pipelines which lead to a slot-shaped opening (11; 12) adopt the form of the slot-shaped opening (11; 12) in the lower part and are provided with constrictions followed by expansion zones.

17. Device according to claim 15 or 16, c h a r a c t e r i s e d i n t h a t the evaporation chambers (19) are each connected with at least one feed device, consisting of a container (16) and a metering device (17), via pipelines with valves (20) .

18. Device according to one of claims 15 to 17, c h a r a c t e r i s e d i n t h a t between the evaporation chambers (19) and the respective opening (11) for feeding in the chalcogen vapour/carrier gas mixture, an additional carrier gas feed (26) is present .

19. Device according to claim 18, c h a r a c t e r i s e d i n t h a t a flow volume divider is connected with the opening (12) for removal by suction of the chalcogen vapour/carrier gas mixture, while one outlet of the flow volume divider is connected with the additional carrier gas feed (26) .

20. Device according to one of claims 6 to 19, c h a r a c t e r i s e d i n t h a t the openings (11, 12) for feeding and removal of the chalcogen vapour/carrier gas mixture, and the evaporation chambers (19) including the connecting pipelines are accommodated in an evaporation head (9) which is inserted in a recess (8) in the wall of the process chamber (5) opposite the transport means .

21. Device according to claim 20, c h a r a c t e r i s e d i n t h a t the evaporation head (9) is provided with a heater

22. Device according to claims 20 and 21, c h a r a c t e r i s e d i n t h a t the^' evaporation head (9) is placed under a sealed cover^'

(10) with integrated cooling system.

23. Device according to claim 22, c h a r a c t e r i s e d i n t h a t the space between the cover (10) and the evaporation head

(9) can be flooded with a protective gas and suctioned out