DE102009011496A1 - Process and device for the thermal conversion of metallic precursor layers into semiconducting layers with chalcogen recovery - Google Patents

Abstract

The present invention relates to a process for the thermal conversion of metallic precursor layers on flat substrates into semiconducting layers with a chalcogen recovery and to an apparatus for carrying out the process. The invention has for its object to provide a fast and easy to implement method for the thermal conversion of metallic precursor layers on flat substrates in semiconductive layers and a suitable method for performing the device with the lowest possible primary use of chalcogens. This is achieved by heating substrates in an oven at about atmospheric pressure to a final temperature between 400 ° C and 600 ° C and converting them into semiconducting layers in an atmosphere of a mixture of at least one carrier gas and chalcogen vapor, but not in the reaction spent chalcogen vapor is made available to the process via exhaust gas recirculation.

Description

at The present invention is a method and a device for the thermal conversion of metallic precursor layers on flat substrates in semiconducting layers with a chalcogen recovery.

For a cheap and environmentally friendly energy production By converting sunlight into electrical energy becomes one Production of highly efficient solar cells if possible low material and energy consumption needed. Promising here are thin-film solar cells, in particular solar cells based on compound semiconductors such as copper-indium-gallium-selenide (CIGS).

at the invention of the underlying method for the preparation of Semiconducting layers is a multi-step process. The Metallic precursor layers can be copper (Cu), gallium (Ga) and indium (In) included. You can with known Technologies, such as sputtering, on the substrate, which a glass substrate with a molybdenum layer (Mo) can be, be applied. In a second step will be in a tempering process the metallic precursor layers in a chalcogen-containing atmosphere, preferably consisting of selenium and / or sulfur, in semiconducting layers, preferably converted to a CuInGaSe (CIGS) layer. The chalcogens take at room temperature, ie about 20 ° C, a solid Physical state and evaporate at temperatures above about 350 ° C.

such Substrates prepared with a semiconductive layer can then further processed to solar modules. Essential for Good efficiency is the most complete Implementation of the metallic precursor layers in a semiconducting Layer with the same layer thickness and as homogeneous as possible Composition over the surface of the substrate time.

To the prior art are methods for the thermal conversion of these prepared precursor layers in semiconducting layers become known, which take place in a vacuum. The problem with the vacuum processes is the long conversion time, also called process time. this leads to in industrial implementation problems, because long process times always accompanied by low productivity. A solution On the one hand, the use of many machines would be simultaneous, which would mean high investment costs, or on the other hand, the acceleration of the processes. Therefor However, the prior art provides no evidence.

Furthermore, the prior art has disclosed processes for the thermal conversion of these prepared precursor layers into semiconducting layers which proceed under atmospheric conditions and with the supply of hydrogen-containing gases, for example hydrogen selenide ( EP 0 318 315 A2 ). However, the use of toxic gases such as hydrogen selenide is problematic.

Out EP 0 662 247 B1 discloses a process for producing a chalcopyrite semiconductor on a substrate, wherein the substrate prepared with metals such as copper, indium or gallium in an inert process gas to a final temperature of at least 350 ° C at a rate of at least 10 K / Second is heated up. The final temperature is maintained for a period of 10 seconds to 1 hour in which the substrate is exposed to sulfur or selenium as a component in excess of the components copper, indium or gallium. For this purpose, a cover at a distance of less than 5 mm in the sense of an encapsulation is located above the layer structure on the substrate. The partial pressure of sulfur or selenium is above the partial pressure, which would form over a stoichiometrically exact composition of the starting components copper, indium or gallium and sulfur. However, no oven segmented into different temperature ranges suitable for a continuous process is described.

In the post-published international patent application PCT / EP 2008/007466 is an easy to implement, rapid flow method for the thermal conversion of metallic layers on any substrates in semiconducting layers, as well as an appropriate device for performing the method indicated.

Reached This is done with a process in which the at least one metallic Precursor layer prepared substrates in one in different Temperature ranges segmented oven at about atmospheric Ambient pressure in several steps, each to a predetermined Temperature up to the final temperature between 400 ° C and 600 ° C heated and while maintaining the final temperature in one Atmosphere of a mixture of a carrier gas and chalcogen vapor are converted into semiconducting layers.

On The way can be good semiconducting layers at heating rates be obtained well below 10 K / second.

According to the state of the art, it must be ensured that sufficient chalcogens are present when the final temperature is reached, so that as complete a transformation as possible of the metalli Precursor layers can be made in semiconducting layers.

This is ensured by an excess supply of chalcogens. Not consumed in the reaction, excess Chalcogen is combined with the carrier gas removed an exhaust duct of the furnace. According to the state of the art can the chalcogens from the discharged chalcogen vapor / carrier gas mixture, also called exhaust gas, filtered out and disposed of as waste.

Of the Invention is based on the object, a method and an apparatus for the thermal conversion of metallic precursor layers indicate semiconducting layers of the best possible quality, whereby the waste of chalcogenes should be significantly reduced. The smaller amounts of waste lead to a simplified Production processes and to reduce costs, because less chalcogens must be used primarily.

Reached This is done with a process in which the at least one metallic Precursor layer prepared substrates in an oven at approx. Atmospheric pressure to a final temperature between 400 ° C and heated to 600 ° C and in an atmosphere from a mixture of at least one carrier gas and chalcogen vapor be transformed into semiconducting layers, being a part of not in the reaction consumed chalcogen vapor over a Exhaust gas recirculation provided to the process again becomes.

Preferably becomes the chalcogen selenium and as carrier gas an inert Gas, such as nitrogen, used.

In In a further development of the invention, the substrates are in one furnace segmented into several temperature ranges in several steps heated to a respective predetermined temperature.

there For example, the substrates in the oven will be simultaneously and incrementally transported from segment to segment, whereby the residence time in the is identical to individual segments.

The Dwell time can be between 20 and 100 seconds, preferably between 40 and 80 seconds, preferably between 50 and 70 seconds and the Example is 60 seconds.

The Heating the substrates can be done in stages from room temperature to Example about 150 ° C, 450 ° C and 550 ° C made with the end temperature not exceeding the 550 ° C mark got to.

The Substrate can then be in at least one Step to be cooled to room temperature.

For the provision of the necessary chalcogen vapor for conversion of the metallic precursor layers in semiconducting layers, the Substrates prior to introduction into the oven already with at least a Chalkogenschicht be provided.

The Chalcogens on the substrate evaporate on thin layers of chalcogen in the oven completely and stand in the oven for the Conversion process available.

at thick chalcogen layers, the chalcogens can only partially evaporate. It can be partly a transformation of the metallic Precursor layers take place with the molten chalcogens.

The Chalcogen layers are preferred by vapor deposition of chalcogens placed on the metallic precursor layers. This can be done under atmospheric conditions in a continuous process.

One rapid evaporation of the chalcogens from the substrates can lead to density variations of the Chalcogens lead along the furnace. This can turn local to an undersupply of chalcogenes when reaching the Final temperature lead, which is locally incomplete Conversion of the metallic precursor layers into semiconducting layers can lead.

The Exhaust gas recirculation according to the invention has now in addition to the reduction of the primary use of chalcogens the positive effect the chalcogen concentration along the furnace to smooth.

One further smoothing effect and another warranty a sufficiently high concentration of chalcogen in thin Chalcogen layers on the substrates can over ensures the introduction of chalcogen vapor via a source which, however, can be used to advantage if the substrates do not have a chalcogen layer.

As a result, may alternatively or in addition to an advance Coating the substrates provided with a chalcogen layer be that chalcogen vapor from an external source of steam in the Furnace chamber initiated or in the furnace chamber of an internal Steam source is generated.

The invention can furthermore be characterized in that the metallic precursors layers are produced by sequential sputtering of copper / gallium and indium.

To For this purpose, for example, consisting of glass substrates are first provided by sputtering with a molybdenum layer, on then a second layer of copper / gallium from a compound Copper / gallium target and finally a third layer be sputtered from indium from an indium target under high vacuum. typically, the coating with molybdenum takes place in a first sputtering plant, the coating with copper / gallium and indium in a second Sputter.

Farther The heating of the substrates and the transformation of the metallic ones take place Precursor layers preferably in the absence of, for example Oxygen and hydrogen, or with the least possible Oxygen and hydrogen partial pressure.

The Task is further solved by a device that from an oven with a furnace chamber, which has an opening to the Introducing the substrates and an opening for dispensing having the substrates, with a gas lock at the opening for introducing the substrates, with a gas lock at the opening for applying the substrates, with a transport for the substrates and with an exhaust passage for removing a chalcogen vapor / carrier gas mixture consists of the furnace chamber, wherein it is further provided that the Device on the exhaust duct a flow divider and / or a recycling device that allows it or not recycled chalcogenes from the furnace chamber in the reaction. For this purpose, for example, be provided that between the flow divider and the furnace chamber disposed a return passage is.

Preferably the chalcogen selenium is used.

A Gas lock allows it with suitable gas flows, the Gas atmospheres on both sides of an opening to disconnect without the opening with solid doors to have to close.

In a development of the device, the gas flows on both sides of the gas locks independently be set.

The Gas locks of the furnace chamber can from each at least two gas curtains. There may also be additional Exhausts between the gas curtains be present.

Prefers is used as protective / carrier gas an inert gas, such as Nitrogen, used.

The opening for introducing the substrates, the opening for spreading the substrates and the gas locks allow the Device in a continuous process, at a pressure in the vicinity the atmospheric pressure and under defined residual gas conditions, especially excluding oxygen and hydrogen, too operate.

The Means of transport, the opening for introducing the substrates and the opening for discharging the substrates allow Introducing the substrates into the oven chamber, transporting the Substrates through the oven chamber and applying the substrates after the conversion of the metallic precursor layers into semiconductive layers out of the oven chamber.

In In one embodiment of the invention, the chalcogen vapor / carrier gas mixture is transferred over introduced the exhaust duct in the recycling device, in the recycling device the exhaust gas is in two adjustable by means of a flow divider Split partial exhaust streams. A first partial exhaust gas flow is the furnace chamber, preferably at the entrance of the furnace chamber, fed again.

Of the second partial exhaust gas stream, called residual exhaust gas, via a Remaining exhaust duct discharged.

The Residual exhaust gas can be filtered and then removed. Of the Waste of chalcogens must be disposed of or reprocessed be supplied.

Of the Flow divider may according to another Substituted the invention with a recycling device connected or part of a recycling device, in which the second partial exhaust gas stream (residual exhaust gas) chalcogens withdrawn and the first Partial exhaust stream are slammed so that the back into the furnace chamber recycled gas enriched with chalcogens is. The discharged residual exhaust gas has a lower Concentration of chalcogens and therefore falls even less Waste of chalcogens. At the same time, a higher Share of chalcogens used for the process exploited.

In a particular embodiment of the device is the temperature one or more of the walls in the interior of the furnace chamber, Flow divider Recycling device, exhaust channel and return channel to a temperature greater than the condensation temperature the chalcogens are set and held.

This prevents chalcogen vapor from condensing on these interior walls and stick there. This would be at a loss Chalcogen lead and a costly maintenance require.

The Temperature of the walls does not have to be the same everywhere be. It can vary in particular in the furnace chamber. The oven chamber can in several consecutive segments S1 ... Sn with different Temperatures be divided.

The Inner chamber temperatures of furnace chamber, flow divider Recycling device, exhaust channel and return channel as well as in the different segments can, for example, with Help heating and cooling systems independently be set.

In A further development of the invention is each segment of the thermally isolated from other segments. This makes possible, that adjacent segments at significantly different temperatures can be brought.

Farther can the furnace chamber total or / and each segment for be thermally insulated to the energy input for to reduce the heating of the segment.

In an embodiment of the invention consist of the walls the furnace chamber made of graphite.

The Transport in the segmented into several temperature ranges Furnace preferably allows a gradual and simultaneous transport of all in the furnace chamber located substrates to the next Segment.

by virtue of the stepwise and simultaneous transport of the substrates of Segment by segment, is the residence time of the substrates in the individual Segments identical and can be, for example, about 60 seconds.

To the better exclusion of, for example, oxygen or hydrogen from the furnace chamber, the furnace chamber can be from a housing with an opening for introducing the substrates and an opening be surrounded to dispense the substrates.

The Housing can, for example, a stainless steel cladding be.

Farther the housing can be a separate housing exhaust own and it can be a purge with a protective gas provided be.

In An embodiment of the invention has the housing a separate cooling system. This allows the radiated Dissipate heat of the furnace chamber.

Farther In the housing, a sensor for detecting the presence a gas and / or a gas concentration, for example a Oxygen sensor and / or a H2Se sensor attached.

Of the Oxygen sensor allows an undesirable - penetration of oxygen in the space between housing and furnace chamber determine.

Of the H2Se sensor is used as a safety measure to prevent the emergence of Determine selenium in good time and the operator accordingly to warn.

A Device according to the invention is intended below will be explained on an exemplary embodiment. Show

1 a schematic longitudinal sectional view of the device, and

2 a section of the device, namely a gas lock, as used in the embodiment.

In 1 is a furnace chamber 1 with an exhaust duct 7 shown. At this exhaust channel 7 are a flow divider 2 and a recycling device 3 arranged, wherein the flow divider 2 and the recycling device 3 are united in an assembly. From the flow divider 2 out leads a return channel 8th back to the oven chamber 1 , at the beginning of the return channel 8th back into the oven chamber 1 empties. To the recycling device 3 closes a residual exhaust duct 9 on, through which the residual exhaust gas is removed. The oven chamber 1 is equipped with an input-side and an output-side gas lock 4 Mistake.

Inside the oven chamber 1 is a transport device 10 arranged, which comprises a plurality of successively arranged transport rollers. The transport device 10 serves to transport the substrates 11 through the oven chamber 1 , The oven chamber 1 is divided into a plurality of successively arranged segments which are independently temperature-controlled and thermally insulated from each other. For reasons of clarity, however, the separate presentation of the individual segments was dispensed with and the oven chamber 1 was shortened compared to a real device, which is indicated by dashed chamber walls in the middle part.

When Shielding gas / carrier gas is carried out in a device Example process using nitrogen.

2 shows an embodiment of the gas locks 4 , The multi-level gas curtains consist of two adjacent inlets 5 for nitrogen curtains with each of the top and bottom opposing gas streams, whereby a small overpressure is generated centrally in the lock area, and from a suction, which arranged by top and bottom between the two nitrogen curtains outlets 6 is realized. This arrangement makes it possible to independently adjust the gas flows on both sides of the gas curtain.

By The gas curtains will allow substrates through the furnace in a continuous process, at atmospheric pressure and under defined residual gas conditions, in particular with exclusion of oxygen, to transport.

The walls of the oven chamber 1 consist of graphite and are surrounded by a stainless steel sheath, not shown, which has a separate suction and a purge with nitrogen.

Farther can be different temperatures along the oven chamber with the help of heating and / or cooling systems.

The substrates prepared with a copper / gallium, indium and selenium layer 11 be with the help of the transport device 10 through the entrance-side gas lock 4 through into the oven chamber 1 brought in. There are the substrates 11 gradually along the oven chamber 1 transported from segment to segment and finally at the end of the furnace chamber 1 through the exit-side gas lock 4 executed again.

The Dwell time in each segment is in one in the device Example process performed 60 seconds.

At the beginning of the oven chamber 1 Selenium starts on the substrate 11 to melt and then evaporates completely with thin chalcogen layers. The selenium vapor mixes with the nitrogen to form a selenium vapor / carrier gas mixture. This mixture is controlled by controlling the gas flows inside the furnace through the furnace chamber 1 through the substrates in the system 11 away to the exhaust duct 7 transported to the furnace. There is no transport in the reverse direction.

at thick chalcogen layers, the chalcogens can only partially evaporate. It can be partly a transformation of the metallic Precursor layers take place with the molten chalcogens.

The control of the gas flow is made possible by the gas flows on both sides of the gas locks 4 and in the exhaust duct 7 are independently adjustable. The speed of the gas flow in the furnace chamber 1 from the entrance to the kiln to the exhaust duct 7 must be aware of the transport speed of the substrates 11 Be tuned so that upon reaching the reaction temperature selenium is present in excess to convert the metallic precursor layers in a CIGS layer.

Unused selenium will pass through the exhaust channel 7 dissipated. According to the invention, the exhaust duct leads 7 the selenium vapor / carrier gas mixture to the flow divider 2 to.

In the flow divider 2 the exhaust gas is divided into two adjustable partial exhaust gas streams.

A first partial exhaust gas flow is via the return channel 8th returned and at the beginning of the furnace chamber 1 returned to the process. At the same time, the recycling device 3 the second partial exhaust gas stream withdrawn part of the chalcogenide contained therein and enriches the first partial exhaust gas stream therewith.

The remaining part of the second partial exhaust gas stream, called residual exhaust gas, contains only a small amount of chalcogenide. This residual exhaust gas is via the Restabgaskanal 9 filtered discharged. The waste from chalcogen must be disposed of or reprocessed.

These Feedback causes a reduction of the loss on selenium, whereby less selenium is used primarily.

1

furnace chamber

2

Flow divider

3

recycling device

4

gas lock

5

inlet

6

outlet

7

exhaust duct

8th

Return passage

9

Residual exhaust duct

10

transport means

11

substratum

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited patent literature

• - EP 0318315 A2 [0006]
• EP 0662247 B1 [0007]
• - EP 2008/007466 [0008]

Claims (14)

Process for the thermal conversion of metallic precursor layers on a substrate ( 11 ) in semiconducting layers, wherein the substrates prepared with at least one metallic precursor layer ( 11 ) are heated in an oven at about atmospheric pressure to a final temperature between 400 ° C and 600 ° C and converted into semiconducting layers in an atmosphere of a mixture of at least one carrier gas and chalcogen vapor, characterized in that at least a portion of the not in the Reaction consuming chalcogen vapor is provided by an exhaust gas recirculation process again. Method according to claim 1, characterized in that the substrates ( 11 ) are heated in a multi-temperature segmented oven in several steps to a respective predetermined temperature. Method according to claim 2, characterized in that the substrates ( 11 ) are transported simultaneously and step by step from segment to segment, whereby the residence time in the individual segments is identical. Method according to claim 3, characterized that the residence time in each segment is between 20 and 100 seconds, preferably between 40 and 80 seconds, preferably between 50 and 70 seconds. Method according to one of claims 1 to 4, characterized in that the substrates ( 11 ) are provided with at least one chalcogen layer before being introduced into the furnace. Method according to one of claims 1 to 5, characterized in that chalcogen vapor from an external steam source into the furnace chamber ( 1 ) or in the oven chamber ( 1 ) is generated by an internal steam source. Device for thermal conversion of metallic precursor layers on substrates ( 11 ) in semiconducting layers, comprising a furnace chamber ( 1 ) with an opening for introducing the substrates ( 11 ) and with an opening for discharging the substrates ( 11 ), each with a gas lock ( 4 ) at the opening for insertion and at the opening for discharging the substrates ( 11 ), as well as with a transport device ( 10 ) for the substrates ( 11 ) and an exhaust duct ( 7 ) for removing exhaust gases from the furnace chamber ( 1 ), characterized in that at the exhaust duct ( 7 ) a flow divider ( 2 ) for dividing the exhaust gas flow into two partial exhaust gas streams and a return channel ( 8th ) for returning a first partial exhaust gas stream into the furnace chamber ( 1 ) are arranged. Device according to claim 7, characterized in that the return channel ( 8th ) at the beginning of the furnace chamber ( 1 ) in the oven chamber ( 1 ) opens. Apparatus according to claim 7 or 8, characterized in that the flow divider ( 2 ) with a recycling device ( 3 ) or part of a recycling device ( 3 ) is in which the second partial exhaust gas stream (residual exhaust gas) withdrawn chalcogenes and the first partial exhaust gas stream are slammed, so that the back into the furnace chamber ( 1 ) recirculated gas is enriched with chalcogens. Device according to one of claims 7 to 9, characterized in that at least one inner wall of furnace chamber ( 1 ) and / or exhaust duct ( 7 ) and / or flow divider ( 2 ) and / or recycling device ( 3 ) or / and return channel ( 8th ) is temperature controlled. Device according to one of claims 7 to 10, characterized in that the furnace chamber ( 1 ) is divided into several successive, independently temperature-controlled segments. Device according to claim 11, characterized in that that each segment is thermally insulated from the other segments is. Device according to one of claims 7 to 12, characterized in that the furnace chamber ( 1 ) in total or / and each segment is thermally insulated on its own. Device according to one of claims 7 to 13, characterized in that in the furnace chamber ( 1 ) a sensor for detecting the presence of a gas and / or a gas concentration is arranged.