WO2012023027A1

WO2012023027A1 - Process for condensation of chalcogen vapour and apparatus to carry out the process

Info

Publication number: WO2012023027A1
Application number: PCT/IB2011/001892
Authority: WO
Inventors: Immo KÖTSCHAU; Raphael Koch; Raimund Boger
Original assignee: Centrotherm Photovoltaics Ag
Priority date: 2010-08-17
Filing date: 2011-08-17
Publication date: 2012-02-23
Also published as: TW201219104A; DE102010034653A1

Abstract

Process for the condensation of chalcogen vapour (36) and re¬ circulation of condensed chalcogen (23) into an evaporation unit (1) having the process steps of the feeding of the chal- cogen vapour (36) in the condenser (9), of the condensing of at least part of the chalcogen vapour (36) fed into the con¬ denser (9) into liquid chalcogen (23), of the recirculation of the liquid chalcogen (23) into the evaporation unit (1) via a trap (35) formed as part of a return line (17) and of the pro- vision of a column (21) of liquid chalcogen in the trap (35), of the equalisation of pressure differentials between pres¬ sures prevailing in the condenser (9) and in the evaporation unit (1) by means of this column (21) of liquid chalcogen, of the at least partial melting of a solid chalcogen stopper (22) sealing off the trap (35), and of the control of the flow of liquid chalcogen (23) through the trap (35) by means of a melt valve (24), and apparatus to carry out this process.

Description

Process for condensation of chalcogen vapour and apparatus carry out the process

The invention concerns a process for the condensation of chalcogen vapour and recirculation of condensed chalcogen to an evaporation unit, together with an apparatus to carry out the process .

Chalcogens within the meaning of the present application refers to elements from the sixth main group of the periodic table of the elements, apart from oxygen. As seen in this way, chalcogens are partially deposited by physical deposition from the vapour phase (PVD) onto objects to be coated. For example, substrates are coated with a chalcogen by means of the PVD process. This is described, for example, in WO 2009/034131 A2. In particular, chalcogens are deposited onto substrates using the PVD process as part of the production of compound semiconductor layers.

In this type of PVD process, a chalcogen vapour is usually fed by means of a carrier gas to the object to be coated, for example a substrate, where it is partially deposited onto the surface thereof. Any chalcogen vapour not deposited is carried away, for example using suction. There is now a need to reuse the chalcogen contained in the non-deposited chalcogen vapour, which is usually mixed with carrier gas and/or other gases or vapours, for further coatings. The present invention is therefore based on the problem of providing a process which makes this possible.

This problem is solved by a process with the features of claim 1. The invention is also based on the problem of providing an ap^¬ paratus to carry out this process. This problem is solved by an apparatus with the features of claim 5.

Advantageous refinements are the subject matter of each of the dependent subclaims.

The process according to the invention provides that chalcogen vapour is fed into a condenser, at least some of the chalcogen vapour fed in is condensed in the condenser to liquid chalcogen and the liquid chalcogen is recirculated via a trap formed as part of a return line into an evaporation unit. A column of liquid chalcogen is also provided in the trap. Pressure differentials between the pressures prevailing in the condenser and in the evaporation unit are equalised by means of this column of liquid chalcogen.

The column of liquid chalcogen makes it possible, despite the pressure differentials, to recirculate liquid chalcogen out of the condenser back into the evaporation unit, in which a higher pressure usually prevails than in the condenser. This recirculation can be realised by means of the effect of gravity alone. The column of liquid chalcogen can also, economically, prevent chalcogen vapour from the evaporation unit getting into the condenser via the return line. In the present case, the column of liquid chalcogen means a cohesive volume of liquid chalcogen, which extends, at least locally, over the entire cross-section of the return line. If the cross-section of the return line is locally narrowed, for example by inserts, solid chalcogen components or anything else, then the remaining cross-section opening at this point is to be regarded as the cross-section of the return line.

The condensation of the chalcogen vapour in the condenser can take place, for example, on plates arranged in the condenser, which are tempered by passing tempered oil through them.

The chalcogen vapour can be fed into the condenser, for example, in the form of a chalcogen vapour-carrier gas mixture, using gaseous nitrogen as carrier gas.

The chalcogen vapour can be fed into the condenser by means of a gas mixture flow. For example, a flow of a chalcogen vapour- carrier gas mixture is formed, which feeds the chalcogen va- pour not deposited during the PVD process into the condenser. This type of flow can be realised by means of a suction device, in particular by means of a ventilator.

Chalcogen vapour which is not condensed in the condenser is preferably fed to a filter, which separates the chalcogen vapour from any other components of the gas mixture, for example from the carrier gas. The other gas components can then be emitted as residual gas or exhaust gas into the environment or, if necessary, be subjected to further purification steps.

The siphon, often referred to in English-speaking countries as a "trap", can in principle be a trap of any construction, for example a bottle trap, a "P-trap" or an "S-trap". Preferably, a trap is used which has at least one U-shaped pipe section, for example a P-trap or an S-trap. The cross-sectional shape of the pipe section is immaterial. Preferably, selenium vapour or sulphur vapour is used as chal- cogen vapour. Following condensation, in these cases, liquid selenium or liquid sulphur is present accordingly. Preferably, the temperature prevailing in the condenser, for example the temperature of the oil-tempered plates described above, is kept at values of between 220°C and 300°C, especially preferably at a value of 270°C. These temperature values have especially proven themselves in the condensation of selenium vapour.

Advantageously, the column of liquid chalcogen is at least partly solidified, thus forming a solid chalcogen stopper sealing off the trap. This can for example take place at the end of the process, so as to seal off the return line durably. A long period of heating to keep the column of liquid chalcogen in liquid state can thus be omitted, without the risk arising, when the process is resumed, of chalcogen vapour getting from the evaporation unit via the return line into the condenser.

Conversely, according to the invention, a solid chalcogen stopper sealing off the trap can be at least partially melted and thereby form the column of liquid chalcogen. At the start of the process, it is thus possible to ensure that liquid chalcogen can flow through the trap and so liquid chalcogen can be recirculated to the evaporation unit.

Preferably, a return line is used which is formed from a down line connecting the condenser with the trap, the trap and a connecting line connecting the trap with the evaporation unit. Temperatures prevailing in these three sections of the return line are controlled independently of each other. Especially preferably, they are regulated independently of each other. This makes it possible to control and/or regulate the tempera^¬ ture of the liquid chalcogen in said sections of the return line independently of each other, and in this way to control and/or regulate the flow characteristics of the liquid chalco- gen in these sections independently. A down line in the present sense does not necessarily run monotonically with a decline. However, one which does, or a vertical course of the down line, is preferable. In practice it has proven advantageous to keep the temperature prevailing in the down line at values of between 220 °C and 270°C, the temperature prevailing in the trap at values of between 190°C and 270°C and the temperature prevailing in the connecting line at values of between 240°C and 500°C, prefera- bly at approximately 270°C. Especially in conjunction with the use of selenium vapour as chalcogen vapour, this has proven itself, since the selenium in the down line is then semi- liquid to thin-liquid, the selenium in the connecting line is thin-liquid, and the flow of liquid selenium through the trap can be controlled or regulated by means of the temperature prevailing in the trap.

According to the invention, the flow of liquid chalcogen through the trap is controlled by means of a melt valve. When connected accordingly to a control circuit, it is also possible to regulate the flow of liquid chalcogen through the trap. A melt valve means an apparatus which is able to change the flow through the trap by melting or solidifying an object arranged in the trap; in solidified state, said object at least partially reduces the line cross-section of said trap. Flow changes can also be effected by changing the viscosity of the liquid chalcogen. An example of a melt valve is described in more detail in connection with the apparatus according to the invention . In one preferred embodiment of the process, the flow of liquid chalcogen through the trap is switched on and off by adjusting the temperature prevailing in the trap and hence also the tem- perature of the trap itself, in such a way that either chalcogen which is in the trap solidifies until it no longer flows, or a flow of the chalcogen through the trap is possible. If the flow through the trap is turned on, the rate of flow of the liquid chalcogen through the trap is then controlled or regulated by controlling or regulating the temperature prevailing in the down line.

The apparatus according to the invention to carry out the process has a condenser and a return line connected to the condenser to carry away liquid chalcogen out of the condenser, the return line having a trap through which the liquid chalcogen can flow, at least some of the time. The trap is provided with a first heating device, by means of which the trap can be separately heated, at least in a section. Separate heatability means that the trap can be heated separately from any other heating devices. The first heating device is part of a melt valve .

As already explained above, the trap can in principle be a trap of any type of construction, for example a bottle trap, a "P-trap" or an "S-trap". Preferably, a trap is used which has at least one U-shaped pipe section, for example a P-trap or an S-trap. The cross-sectional shape of the pipe section is immaterial .

The first heating device is preferably arranged on a horizontal section of the trap. In the case of a trap with a U-shaped pipe section, the first heating device is especially preferably arranged at a bend of the U-shaped pipe section, since ad- vantageously a column of liquid chalcogen is formed here, and the temperature and state of aggregation thereof, as the case may be, can then be influenced by means of the first heating device .

Advantageously, the first heating device is part of a melt valve, which has a cooling device alongside the first heating device. A melt valve of this type can, as was explained above, be used to control or regulate the flow of the liquid chalco- gen through the trap.

Preferably the cooling device has a hollow cylinder with a cavity arranged in a sheath of the hollow cylinder, which is suitable for a cooling medium to be flushed through. It also has an inlet opening out into the cavity, which is suitable for introducing the cooling medium into the cavity, and an outlet leading out of the cavity, which is suitable for con^¬ ducting the cooling medium out of the cavity. Preferably the hollow cylinder surrounds the trap in some sections. Independently hereof, the melt valve is preferably arranged on a horizontal section of the trap. In the case of a trap with a U-shaped pipe section, the melt valve is especially preferably arranged at a bend of the U-shaped pipe sec- tion, since advantageously a column of liquid chalcogen is formed here, and the temperature and state of aggregation thereof can then be controlled or regulated by means of the melt valves and so the flow of the liquid chalcogen through the trap can be controlled or regulated.

In practice, a first heating device has proven itself which has at least one heating unit of the first type arranged alongside the hollow cylinder in the longitudinal direction of extension of the hollow cylinder. Preferably the first heating device has at least two heating units of the first type arranged alongside the hollow cylinder in the longitudinal direction of extension of the hollow cyl- inder. The hollow cylinder is thereby arranged between these at least two heating units of the first type. As a result, inter alia, the calorific output of the melt valve and hence its switching speed can be improved. Advantageously, the heating units of the first type are provided with a thermal insulation, in order to reduce thermal emission in undesirable directions. The main aim is to prevent thermal emission to the environment of the return line. Also, the thermal insulation can reduce heating of areas of the melt valve which are freely accessible during operation, so reducing the risk of injury if these freely accessible parts are touched .

Preferably the first heating device has at least one heating unit of the second type arranged on an outer surface area of the hollow cylinder. This enables a hollow cylinder cooled down by the through-flow of the cooling medium to heat up more quickly, resulting in a shorter switching time of the melt valve. As heating unit of the second type, it is especially preferable to provide a heating unit with a calorific output per area greater than the heating units of the first type. This can further shorten the switching time.

Advantageously, the at least one heating unit of the second type arranged on the outer surface area and the hollow cylinder are surrounded by a housing, which is suitable for pre^¬ venting contact with the heating unit of the second type or with the hollow cylinder when in operation. This housing can, for example, be a cage of corresponding form. In one variant embodiment of the apparatus, the melt valve has at least one temperature sensor, which is preferably arranged on an inner surface area of the hollow cylinder. Especially preferably, the at least one temperature sensor, which can for example consist of a thermocouple, is connected to a control or a regulation device, which is in turn connected to least some of the heating units, so that these can be regulated or controlled on the basis of the readings of the temperature sensor.

The return line is preferably formed from a down line connecting the condenser with the trap, the trap and a connecting line, which is suitable for connecting the trap with an evapo- ration unit. The down line is also provided with a second heating device, by means of which the down line can be separately heated, at least in some sections. Furthermore, the connecting line is provided with a third heating device, by means of which the connecting line can be separately heated, at least in some sections. In this way, said sections of the return line can be heated separately. As already mentioned above, it is not necessarily required that the down line runs monotonically with a decline. But this type, or a vertical course of the down line, is preferable.

The down line is advantageously designed as a downpipe, the connecting line as a connecting pipe. The cross-sectional forms of downpipe and connecting pipe are immaterial. The condenser can be connected via a filter line with a filter, which is suitable for filtering chalcogen vapours out of a gas mixture containing chalcogen vapour. Uncondensed chalcogen vapours can be filtered out with this filter, so that very little or none of the chalcogen vapours get into the atmosphere.

Preferably the condenser is connected via the return line with an evaporation unit. The liquid chalcogen can thus be fed back to the evaporation unit and reused. The evaporation unit can, for example, be formed in essence from a graphite block comprising a cavity, in which, in operation, melted chalcogen is arranged.

A ventilator can be provided to feed chalcogen vapour into the condenser, said ventilator being suitable for generating a gas flow leading into the condenser. For example, a chalcogen va^¬ pour-carrier gas mixture flow leading into the condenser can be formed by the ventilator.

The invention will next be explained in more detail on the ba^¬ sis of figures. Where expedient, elements with the same action are given the same reference numbers. The figures show:

Concept view of an embodiment of the process according to the invention and the apparatus accord^¬ ing to the invention

Schematic detail view of the apparatus from Figure

1

Enlarged detail view of the return line from Figure 2 in closed condition

Figure 4 Schematic sectional view through the melt valve

from Figures 2 and 3 Figures 1 and 2 illustrate a first embodiment of the process according to the invention and of the apparatus according to the invention. In this embodiment, the apparatus according to the invention has a condenser 9 and a return line 17 connected to the condenser 9 to carry away liquid chalcogen from the condenser 9. In the embodiment shown, as chalcogen vapour, a selenium vapour-nitrogen mixture 36 is fed into the condenser. Nitrogen here acts as a carrier gas for the selenium vapour.

The selenium vapour of the selenium vapour-nitrogen mixture 36 originates from an evaporation unit 1, in which liquid selenium 2 is arranged. Gaseous nitrogen is introduced into the evaporation unit via a nitrogen inlet 3 under overpressure and conducted over the liquid selenium 2. The nitrogen used as carrier gas hereby absorbs selenium vapour. The resulting selenium vapour-nitrogen mixture 36 is next fed via a supply line 5 to a coating head 4, shown schematically. In a coating area 6 of the coating head 4, a part of the selenium vapours contained in the selenium vapour-nitrogen mixture 36 is deposited onto a substrate 7. The substrate 7 is thereby guided past underneath the coating head 4, preferably at a constant speed, in order to achieve homogeneous coating. The majority of the selenium vapour, however, remains in the selenium va- pour-nitrogen mixture 36 and is, as shown schematically in Figure 1, fed via the feed line 8 to the condenser 9.

The evaporation unit 1 and the coating head can, as a variation from the illustration in Figure 1, be in the form of a single unit. For example, a homogenous graphite block can be provided, in which both the evaporation unit and the coating head are arranged. Further details hereof and of the coating head per se are described in German patent application number 10 2009 009 022. The selenium vapour-nitrogen mixture 36 is fed in, in the present embodiment, by means of a ventilator 14 which forms a flow of the selenium vapour-nitrogen gas mixture into the con- denser 9. To this end, the ventilator 14 generates an underpressure in the feed line 8. Oil-tempered plates 10 which are kept at a temperature of around 270 °C are arranged in the condenser 9. The selenium vapour contained in the selenium vapour-nitrogen mixture 36, at least most of it, condenses on these plates, collects in a hopper 11 and is fed back from there via a return line 17, indicated by a broken line in Figure 1, into the evaporation unit 1. Uncondensed selenium vapour is introduced via a filter line 13, together with the carrier gas nitrogen, into a filter 12 where it is separated from the nitrogen. The remaining nitrogen, together with any further gas components, gets into the atmosphere via the suction line 15 and the exhaust gas line 16 or is fed to a further exhaust gas treatment facility. Figure 2 illustrates, in an enlarged partial view, details of the return line 17. As can be seen from Figure 2, the return line has a trap 35, which in this case is designed as an S- trap. Figure 2 also shows that the return line 17 is formed from a down line connecting the condenser 9 to the trap 35, said down line in this case being designed as a downpipe 18, the trap 35 itself, and a connecting line designed as a connecting pipe 20.

The trap 35 has a U-shaped pipe section 19. A column 21 of liquid selenium is provided in this U-shaped pipe section 19, by means of which pressure differentials between the condenser 9 and the evaporation unit 1 are equalised. This equalisation of pressure differentials is shown in Figure 2 in that the column 21 of liquid selenium is higher on the left in the U- shaped pipe section 19 than on the right. In the evaporation unit 1, therefore, as expected, a higher pressure prevails than in the condenser 9. If condensed, liquid selenium now gets from the condenser into the return line 17, the height of the column 21 of liquid selenium on both sides rises until the liquid selenium on the right side can overcome the trap 35 and gets into the connecting line 20, from where it reaches the evaporation unit 1. A melt valve 24 is arranged at the bend of the U-shaped pipe sections 19 in Figure 2. By altering the temperature of the selenium in this area, this valve controls its flow through the trap 35. If the liquid selenium is cooled down, its viscosity rises and the flow is reduced. Conversely, the flow can be increased by heating. In an extreme case, any selenium present in the U-shaped section 19 solidifies or melts and in this way the flow through the trap 35 can be either completely stopped or initiated. Thus the flow of selenium through the return line 17 can be turned on or off by means of the melt valve 24. This is explained in more detail below on the basis of the detail view from Figure 3.

Figure 3 shows a solid selenium stopper 22 arranged in the U- shaped pipe section 19. This may have been formed, for exam- pie, after the end of the process or in connection with a process interruption, in order to close off the return line 17. Figure 3 illustrates the conditions after a renewed start of operation of the apparatus. In the condenser 9, selenium vapour has already been condensed, so that there is liquid se- lenium in the downpipe 18. In the U-shaped pipe section 19, the solid selenium stopper 22 is subsequently melted by means of the melt valve, at least until a column of liquid selenium forms and liquid selenium 23 can pass through the U-shaped pipe section 19. The melt valve 24 represents a first heating device, by means of which the trap 35 can be separately heated .

As can be seen in Figure 3, the downpipe 18 is provided with a second heating device 39 and the connecting pipe 20 with a third heating device 40. These are designed in such a way that the downpipe 18 as well as the connecting pipe 20 can be separately heated. As a result, the flow characteristics, in particular the flow rate, of the liquid selenium in the downpipe 18 or the connecting pipe 20 can be controlled independently of each other. In the view in Figure 2, for greater clarity, the second and the third heating devices are not shown.

Figure 4 shows a schematic sectional view through the melt valve from Figures 2 and 3. As can be seen, the melt valve 24 has a hollow cylinder 28 with a sheath 31. A cavity 37 through which a cooling medium can be flushed is arranged in the sheath 31. Any cooling medium can be used here, for example an aerosol, water, oil or nitrogen. An inlet 29 is provided in order to introduce a cooling medium into the cavity 28. The melt valve 24 also has an outlet 30, by means of which the cooling medium can be passed out of the cavity 28. The hollow cylinder is arranged about a section 25 of the U-shaped pipe section 19. As a result, the section 25 and selenium therein can be cooled by the cooling medium flushing through the cavity 28.

The melt valve 24 also has heating units of the first type 26a, 26b, which are arranged in the longitudinal direction of extension of the hollow cylinder 28 alongside the hollow cylinder 28. The hollow cylinder 28 is arranged between these heating units of the first type 26a, 26b. A heating unit of the second type 32 is also provided, which is arranged on an outer surface area 31a of the hollow cylinder 28 and has a higher calorific output per area than the heating units of the first type 26a, 26b. As a result, a sheath 31 previously cooled down by the cooling medium can be heated up comparatively rapidly. The heating units of the first type 26a, 26b, together with the heating unit of the second type 32, form a first heating device 26a, 26b, 32 with which the trap 35 can be separately heated.

The heating units of the second type 26a, 26b are provided with thermal insulation 27. This reduces undesired thermal emission to the environment. At the same time, it serves as protection against contact. As protection against any unintentional contact with the heating unit of the second type 32 or with the hollow cylinder 28, the heating unit of the second type 32 and the hollow cylinder 28 are surrounded by a housing 33. The housing 33 acts as protection against unintentional contact with the heating unit of the second type 32 and, to^¬ gether with the thermal insulation 27, with the hollow cylin^¬ der 28.

A temperature sensor 34, which can, for example, consist of a thermocouple, is arranged on an inner surface area 31b of the hollow cylinder 28. Like the heating units of the first 26a, 26b and second type 32 and valves 42, 43 at inlet 29 and out- let 30, this temperature sensor is connected with a control or regulation device 38 shown schematically in Figure 3. As a re^¬ sult, the heating, units of the first type 26a, 26b and second type 32 and the valves 42, 43 at inlet 29 and outlet 30 can be controlled and/or regulated on the basis of the readings of the temperature sensor 34. List of reference numbers

1 evaporation unit

2 liquid selenium

3 nitrogen inlet

4 coating head

5 supply line

6 coating area

7 substrate

8 feed line

9 condenser

10 oil-tempered plate

11 hopper

12 filter

13 filter line

14 ventilator

15 suction line

16 exhaust gas line

17 return line

18 downpipe

19 U-shaped pipe section

20 connecting pipe

21 column of liquid selenium

22 solid selenium stopper

23 liquid selenium

24 melt valve

25 section of the U-shaped pipe section

26a heating unit of the first type

26b heating unit of the first type

27 thermal insulation

28 hollow cylinder

29 inlet

30 outlet sheath of the hollow cylindera outer surface area of the hollow cylinderb inner surface area of the hollow cylinder heating unit of the second type

housing

temperature sensor

trap

selenium vapour-nitrogen mixture

cavity

control/regulating device

second heating device

third heating device

valve

Claims

Process for condensation of chalcogen vapour (36) and recirculation of condensed chalcogen (23) into an evaporation unit (1) having the following process steps:

- the chalcogen vapour (36) is fed into a condenser (9),

- at least part of the chalcogen vapour (36) fed into the condenser (9) is condensed in the condenser (9) into liquid chalcogen (23),

- the liquid chalcogen (23) is recirculated to the evaporation unit (1) via a trap (35) formed as part of a return line ( 17 ) ,

- a column (21) of liquid chalcogen is provided in the trap (35) and pressure differentials between the pressures prevailing in the condenser (9) and in the evaporation unit (1) are equalised by means of this column (21) of liquid chalcogen,

- at least part of a solid chalcogen stopper (22) sealing the trap (35) is melted, thereby forming the column (21) of liquid chalcogen,

- the flow of liquid chalcogen (23) through the trap (35) is controlled by means of a melt valve (24) .

Process according to claim 1,

c h a r a c t e r i s e d i n t h a t

an element from the group of sulphur vapour and selenium vapour is used as chalcogen vapour, preferably selenium vapour .

Process 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 column (21) of liquid chalcogen at least partially solidifies and in this way a solid chalcogen stopper (22) sealing off the trap is formed.

4. Process 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

a return line (17) is used which is formed from a down line (18) connecting the condenser (9) to the trap (35), the trap (35), and a connecting line (20) linking the trap (35) with the evaporation unit (1) and that the temperatures prevailing in these three sections (18, 35, 20) of the return line (17) are controlled, preferably regulated, independently of each other.

5. Apparatus for carrying out the process according to one of the preceding claims with

- a condenser (9) and

- a return line (17) connected to the condenser (9) to carry away liquid chalcogen from the condenser (9),

- wherein the return line (17) has a trap (35) through which the liquid chalcogen can flow, at least for a time,

- wherein the trap (35) is provided with a first heating device (26a, 26b, 32), by means of which the trap (35) can, at least in a section, be heated separately,

- and wherein this first heating device (26a, 26b, 32) is part of a melt valve (24) .

6. Apparatus according to claim 5,

c h a r a c t e r i s e d b y

a trap (35) with at least one U-shaped pipe section (19) .

7. Apparatus according to one of claims 5 to 6,

c h a r a c t e r i s e d i n t h a t

the first heating unit (26, 32) is part of a melt valve (24) which has a cooling device (28, 37, 29, 30) alongside the first heating device (26, 32).

8. Apparatus according to claim 7,

c h a r a c t e r i s e d i n t h a t

the cooling device (28, 37, 29, 30) has the following components :

- a hollow cylinder (28) with a cavity (37) arranged in a sheath (31) of the hollow cylinder (28) which is suitable for a cooling medium to be flushed through,

- an inlet (29) opening into the cavity (37) which is suitable for carrying the cooling medium into the cavity (37) ,

- an outlet (30) leading out of the cavity (37) which is suitable for carrying the cooling medium out of the cavity (37) .

9. Apparatus according to claim 8,

c h a r a c t e r i s e d i n t h a t

the first heating device (26a, 26b, 32) has at least one heating unit (26a, 26b) of the first type arranged in the longitudinal direction of extension of the hollow cylinder (28) alongside the hollow cylinder (28).

10. Apparatus according to claim 9,

c h a r a c t e r i s e d i n t h a t

the heating units of the first type (26a, 26b) are provided with a thermal insulation (27) in order to reduce thermal emission in undesired directions.

11. Apparatus according to one of claims 8 to 10,

c h a r a c t e r i s e d i n t h a t

the first heating device (26a, 26b, 32) has at least one heating unit of the second type (32) arranged on an outer surface area (31a) of the hollow cylinder (28) .

12. Apparatus according to one of claims 8 to 11,

c h a r a c t e r i s e d i n t h a t

the melt valve (24) has at least one temperature sensor (34), which is preferably arranged on an inner surface area (31b) of the hollow cylinder (28) .

13. Apparatus according to one of claims 5 to 12,

c h a r a c t e r i s e d i n t h a t

- the return line (17) is formed from a down line (18) connecting the condenser (9) with the trap (35), the trap (35) and a connecting line (20), which is suitable for connecting the trap (35) with an evaporation unit (1),

- the down line (18) is provided with a second heating device (39) by means of which the down line (18) can be separately heated, at least in some sections, and

- the connecting line (20) is provided with a third heating device (40) by means of which the connecting line (20) can be separately heated, at least in some sections.