WO2013010864A2

WO2013010864A2 - Device and method for determining the vapour pressure of a starting substance vaporized in a carrier gas stream

Info

Publication number: WO2013010864A2
Application number: PCT/EP2012/063539
Authority: WO
Inventors: Michael Long; Markus Gersdorff
Original assignee: Aixtron Se
Priority date: 2011-07-19
Filing date: 2012-07-11
Publication date: 2013-01-24
Also published as: WO2013010864A3; DE102011051931A1; TW201307606A

Abstract

The invention relates to a method for producing a vapour, transported in a carrier gas, of a solid or liquid starting substance, comprising the steps of: heating a vaporizer (8), having an inlet opening (7) and an outlet opening (9); feeding an input gas stream, comprising a carrier gas, through the inlet opening (7) into the vaporizer (8); vaporizing the solid or liquid starting substance within the vaporizer (8); transporting the vapour produced in this way together with the carrier gas as an output gas stream through the outlet opening (9); determining a first value, assigned to the mass flow of the carrier gas in the input gas stream, by means of a first sensor (2); determining a second value, influenced both by the mass flow or partial pressure of the carrier gas and by the mass flow or partial pressure of the vapour in the output gas stream, by a second sensor (10); calculating the value corresponding to the partial pressure of the vapour transported in the output gas stream by establishing a relationship between the values determined by means of the two sensors (2, 10). The invention additionally relates to a device for vaporizing a liquid or solid starting substance in a heatable vaporizer.

Description

Apparatus and method for determining the vapor pressure of a starting material vaporized in a carrier gas stream

The invention relates to a method for producing a transported in a carrier gas vapor of a solid or liquid starting material.

The invention further relates to a device for vaporizing a liquid or solid starting material in a heatable evaporator, in which an inlet gas stream of a carrier gas enters through an inlet opening, which flows through the evaporator and together with the vapor generated by evaporation of the starting material as the starting gas stream from the evaporator exits through an exit opening.

A method of the type described above or a device of the type described above is described by US 7,238,389. A carrier gas stream flows through an aerosol generator with which a powdery solid in the form of suspended particles is brought into the carrier gas stream. These aerosol particles are transported with the carrier gas stream in an evaporator. The evaporator consists of a solid state foam, which is heated to an evaporation temperature. Surface contact with the solid state foam vaporizes the suspended particles within the pores of the solid state foam. The vapor thus generated is transported out of the evaporator by the carrier gas stream through an outlet opening and brought into a process chamber in which a substrate is located, on which the vapor condenses to form a layer. For this purpose, the susceptor is cooled.

US 4,769,292, US 4,885,211 and the previously cited US 7,238,389 indicate suitable organic starting materials. These are organic niche, light-emitting substances with which in a CVD reactor OLEDs can be produced.

A solid-state evaporator is also described in DE 10 2006 026 576 AI. There, the aerosol is generated by an ultrasonic exciter by whirling up a powder.

DE 10 2007 062 977 A1 describes a method and a device for the production of process gases for vapor phase deposition, in which liquid components are metered in the liquid phase.

DE 689 20 847 T2 describes a microanemometer for detecting a gas flow, which contains individual microbridge sensors. DE 692 00 451 T2 describes a device for vaporizing and feeding a liquid with a flow control valve and an evaporation valve, which are connected to each other by a channel.

US 5,339,687 describes a mass flow meter with a heating element and a Temperatursens or, which are located in the gas stream to be measured.

EP 0 370 311 describes a method and a device for vaporizing a liquid starting material, wherein a carrier gas is passed through an evaporator. The carrier gas flow is measured. The saturated with steam, leaving the evaporator carrier gas stream is measured with a second sensor. Measured values of the two sensors are correlated to determine the partial pressure of the vapor in the outlet gas flow.

EP 2 034 047 A1 describes a liquid evaporator in which a mass flow-controlled carrier gas stream is introduced. No. 5,288,325 describes an evaporator in which a mass flow-regulated carrier gas stream is introduced into a liquid to be evaporated. The mass flow of the output current is also measured. The two measured values are related to each other.

The invention is based on the object to optimize a device for vaporizing an aerosol. To solve this problem, the invention specified in the claims is proposed. The device according to the invention has a first sensor arranged in the flow direction in front of the inlet opening for determining a carrier gas which enters the mass flow of the carrier gas entering the evaporator. In addition, the device has a second sensor arranged in the flow direction downstream of the outlet opening for determining a value which depends on the mass flow or the partial pressure of the carrier gas as well as the mass flow or partial pressure of the steam in the outlet gas flow. Furthermore, a computing device is provided, which sets the mass flow value of the carrier gas with the value determined by the second sensor, in order thereby to calculate the partial pressure of the vapor transported in the carrier gas and to provide a value in this respect. In the method according to the invention, the input gas stream of a carrier gas is fed through an inlet opening into an aerosol generator and then together with the starting material to be evaporated as suspended particles into the evaporator. The to be evaporated, in particular organic starting material can also be stored in the evaporator. The starting material to be evaporated is fed into the evaporator together with the carrier gas. An aerosol generator is provided with which the starting material is introduced as powder or droplets into the carrier gas stream. The carrier gas stream then flows through the aerosol generator, with the starting material as Suspended suspended particles and transported the latter into the evaporator, where the solid or liquid starting material evaporates by heating the evaporator or arranged in the evaporator evaporation body. The steam thus generated is transported away as outlet gas flow through the outlet opening. In order to determine a first value assigned to the mass flow of the carrier gas flow, an input sensor is provided as the first sensor. This can be a calorimetric mass flow meter. If an aerosol generator is provided, then the input sensor is in the flow direction in front of the aerosol generator. Downstream of the outlet opening, an output sensor is provided as the second sensor, with which an output value assigned to the output gas flow is determined. The output sensor may be a calorimetric sensor, preferably a Pirani vacuum gauge. By means of which a value dependent on the total pressure can be measured. Since the carrier gas flow flows unchanged, without supplying a further gas flow or diverting a portion of the carrier gas flow from the input sensor to the output sensor, the measured value measured by the output sensor comprises contributions of both the carrier gas mass flow and the mass flow of the vapor generated in the evaporator. Since the mass flow of the carrier gas is known, it can be used to correct the output value by relating the input mass flow value and the output value. For this purpose, a computing device is used according to the invention. If a mass flow is measured with the output sensor, the correction is made merely by subtracting the input mass flow value determined by the input sensor from the output mass flow value. With a Pirani vacuum gauge used as an output sensor, the heat output of a heated measuring wire is determined. The operation and structure of such a Pirani vacuum gauge describes the

US Pat. No. 7,322,248 B1. When using such a Pirani vacuum gauge, on the one hand the carrier gas and on the other hand the steam transported by the carrier gas contributes to the release of heat. Since the mass flow of the carrier gas as Input mass flow value is known, the contribution of the carrier gas to the total heat output of the measuring wire can be computationally compensated. For this purpose, for example, it is possible to make use of data determined in preliminary experiments, which are stored as a table or as a functional connection in the computing device. As a consequence, the contribution of the steam to the heat release can be calculated from the determined total heat output of the measuring wire of the Pirani vacuum gauge. From this value can then be determined as the initial value of the partial pressure of the vapor in the output gas stream. In the calculation, the measured value of a pressure sensor can also be taken into account, with which the total pressure in the entire system is measured. Such a pressure sensor is usually part of a pressure regulator, which cooperates with a vacuum pump to keep the total pressure in the process chamber or in the process chamber upstream of the evaporator to a certain value. The Pirani vacuum gauge can be operated in the same way as described in US Pat. No. 7,322,248 B1. The electrical circuit includes two parallel bridges whose nodes are tapped from the two inputs of a comparator or operational amplifier. The heating circuit of the Pirani vacuum gauge is supplied with power via the bridge circuit, which power is supplied by the output of the comparator or operational amplifier. This keeps the heating coil of the Pirani vacuum gauge at a constant temperature that is greater than 400 ° C. Since the temperature is in a clear relationship to the resistance of the heating coil, the increased heat output due to the heat output can be tapped directly at the output of the operational amplifier.

The invention further relates to an apparatus and a method for depositing an organic starting material as a layer on a substrate, wherein the organic starting material is brought in the form of suspended particles in a carrier gas stream, the aerosol thus generated as a mass flow of the or- ganic material is fed to an evaporator, in which the suspended particles are vaporized by supplying heat, the vapor thus generated is brought from the carrier gas stream in a process chamber, where it condenses on the surface of a substrate forming the layer. It is essential that the partial pressure of the vapor before entering the process chamber is determined by the method described above using an input sensor and an output sensor. The device may have suitable means to influence the rate of production of the vapor. To control these influencing means, the determined partial pressure of the steam can be used.

In a variant of the invention, in which the second sensor is also a calorimetric mass flow meter, it is provided that this calorimetric mass flow meter is a high-temperature mass flow meter. The mass flow meter has, as in the prior art (US 3,680,377 or DE 11 2005 002 773 T5) two spaced-apart heating elements. Each of the two heating elements is heated by means of an electric heating current. As a result, the temperature of the gas flowing past them is increased. The voltage applied to the heating elements or from the current flowing through the heating elements can be used by an evaluation circuit to determine the mass flow of the gas flowing through the cavity, for example through a pipe. In the high-temperature mass flow meter used according to the invention, two heating elements are provided which are each formed by a filament. These two filaments project freely into the cavity through which the gas flows, for example a tube. The two filaments extend essentially congruently in planes extending essentially transversely to the flow direction. The filaments may be tungsten wires, which are shaped into a helix in the manner of a filament of an incandescent lamp. The distance of the two imaginary planes, in each of which one of the two filaments extends, is less than a characteristic or the entire length of the Filament. The characteristic length may be a diameter of a surface bounded by the filament or the distance between two imaginary points of the filament. The distance is so small that the temperature increase, which is supplied to the gas locally on the first filament, is also effective on the second filament.

In addition, the invention also relates to such a high-temperature mass flow meter as such, in which each of the two heating elements is in each case formed by a filament projecting freely into the cavity. The two filaments each extend in an imaginary plane. The two virtual planes are essentially transverse to the flow direction of the gas. The two levels are parallel to each other. In the direction of flow, the filaments lie congruently one behind the other in each case in one of the planes. The diameter of the filament is preferably at most 5 μιη. In operation, the filament can be heated to a temperature of about 400 ° C. The wall of the cavity, so the tube into which the two filaments protrude, can be heated. It is heated to a temperature substantially equal to the temperature of the filament. It can also be slightly lower, for example 10 ° C lower. The temperature of the filament is adjusted so that the gases that flow through the cavity, so in particular the tube, do not disassemble by contact on the hot filament. In a preferred embodiment, the high-temperature tower mass flow meter interacts with an electronic bridge circuit. It may be a DC bridge or an AC bridge. The AC bridge is preferred because it can be used to compensate for drift effects. The high-temperature mass flow meter preferably has two tungsten filaments. These filaments are connected in parallel in the bridge circuit with resistors. The gas stream flowing past the upstream filament cools the upstream filament. This goes with a decrease in the resistance of the upstream associated filamentes. Again, the gas flowing past the upstream filament is heated and partially releases its heat to the downstream filament so that the latter warms up, with the result that the resistance of the downstream filament rises. This heat transport can be determined by comparing the currents flowing through the two filaments or the two voltages applied to the filaments. For example, if the bridge circuit in non-flowing gas in equilibrium, it is brought in a gas flow out of balance. A bridge voltage is formed, which is essentially proportional to the mass flow through the cavity or the pipe.

The invention will be explained with reference to the accompanying drawings. Show it:

1 is a block diagram of a device for depositing an organic starting material as a layer on a substrate;

FIG. 2 is a perspective view of a Pirani sensor known from the prior art; FIG.

3 shows a further embodiment in a representation according to FIG. 1;

4 shows a perspective view of a high-temperature mass flow meter which is inserted into the steam line 12; a DC bridge circuit for determining the mass flow of the gas through the steam line 12; 6 schematically shows the temperature profile through a gas flowing past a filament in the flow direction,

7 schematically shows the temperature profile of the gas flowing past two successive filaments in the direction of flow and an AC bridge circuit for determining the mass flow of the gas through a cavity, in particular the steam line 12 from a gas source, not shown, with a valve, not shown, in which it can be hydrogen, nitrogen or a noble gas, fed into a carrier gas line 1. In the carrier gas line 1 is a mass flow meter 2, which operates on a calorimetric measuring principle and which supplies an input mass flow value Sl to a computing device 20 which corresponds to the mass flow of the instantaneously flowing through the mass flow meter 2 carrier gas. With a carrier gas line 3, the carrier gas, which is known in terms of its mass flow, is fed to an aerosol generator 4. The aerosol generator 4 may comprise a brush wheel with which powder particles are rubbed off by a powder pressed into a solid, which particles are brought into the carrier gas stream, which further transports the powder particles as suspended particles, as described, for example, by US Pat. No. 5,820,678. As an aerosol generator 4 but also a screw conveyor can be used, as described for example by US 7,501,152 B2. Also usable is an aerosol generator according to DE 10 2006 026 576 A1, with which a powder stored in a storage container 5 is fluidized. It is essential that the aerosol generator flows through the carrier gas. By an aerosol line 6, the suspended particles are brought through an inlet opening 7 in an evaporator 8. In the evaporator 8 may be a solid state foam, as described for example in US 2009/0039175 AI. This solid-state foam is suitably heated to an evaporation temperature so that the suspended particles passing into contact with the surface of the evaporation body evaporate. But it is also possible that the suspended particles are heated by contactless heating. Preferably, however, the suspended particles enter the tortuous pore cavities of the solid-state foam in order to absorb heat there by surface contact with the webs formed by the open-pore foam body. Preferably, such an evaporator 8 is used, in which the heat transfer surfaces of the evaporation body can be heated or cooled quickly, so as to influence the evaporation rate by a short-term change in temperature. The partial pressure of the vapor leaving the evaporation chamber 8 through the outlet opening 9 in the starting gas stream depends on the evaporation rate. The exit from the outlet opening 9 output gas stream is fed through a steam line, which is heated by a heater 13, a CVD reactor.

The reactor housing 14 of the CVD reactor is gas-tight and includes a gas inlet member 15 in the form of a shower head. The gas outlet surface of the gas inlet member 15, which points downwards in a vertical direction, has a multiplicity of gas outlet openings arranged in a sieve-like manner, through which the outlet gas flow is introduced into a process chamber 16 arranged below the gas inlet member 15.

The bottom of the process chamber 16 is formed by a susceptor 18, which is cooled and on which a substrate 17 is located. By means of a vacuum pump 19, the total pressure within the process chamber 16 and within the evaporation chamber of the evaporator 8 can be adjusted. It can be regulated in a pressure range of 0.1 to 100 mbar. For this purpose, a pressure sensor 24 is provided.

Preferably, in the process chamber, a glass substrate is coated with a light-emitting layer of an organic material. On the substrate layer sequences are deposited, as described in US 7,238,389, US 4,769,292 or US 4,885,211. For the deposition of such OLEDs at room temperature or up to 300 or 400 ° C solid organic starting materials are used. These are evaporated in the evaporation chamber 8 at temperatures between 300 and 400 ° C.

In a first exemplary embodiment (FIG. 1 and FIG. 2), a Pirani sensor 10, which supplies a sensor signal S2, is inserted in a recess 11 of the steam line 12, which may be formed by a blind flange, as the output sensor. This sensor signal S2 is also fed to the computing device 20.

In a second embodiment (Figure 3 to Figure 7) is in the

Steam line 12, the sensor portion of a Hochtemperaturmassenflussmes- sers 26. With the high-temperature mass flow meter 26, the mass flow through the steam line 12 can be determined. This sensor signal is also fed to the computing device 20. The output sensor 10 supplies a sensor signal S2, which is a value for the heat output of a measuring wire, which is heated to more than 400 ° C. The heat output depends on the total pressure of the gas within the cavity 11 and the steam line 12 from. The total pressure is controlled by the vacuum pump 19 and is thus known. Also known is the mass flow of the carrier gas through the steam line, since this corresponds to the mass flow through the mass flow meter 2. It is therefore possible to deduct the contribution of the carrier gas from the total heat output of the helix 21 in the pirani sensor 10 to the gas. As a result, the contribution to heat dissipation remains of the steam carried in the carrier gas. From this value, the partial pressure of the vapor in the outlet gas flow, ie in the steam line 12, can then be calculated.

The use of a Pirani sensor to determine the vapor pressure of the vapor of the vaporized organic starting material is particularly advantageous when rapidly heatable evaporation body are used, since the reaction times of such an output sensor are very small.

FIG. 2 shows an example of a sensor head of a Pirani sensor as described in US Pat. No. 7,322,248 B1. The sensor head has a helix 21 made of tungsten, which is suspended approximately along the edges of a rectangle or a trapezoid, not shown in the drawing, and which is heated to temperatures above 400 ° C. The coil 21 is held in position by two supporting arms 22 acting on two adjacent rectangular edges. In the evaluation circuit may be a double bridge circuit, as described in the publication described above. The operating temperature of the coil 21 is about 50 ° C higher than the evaporation temperature or the temperature within the vapor line 12. The terminal contacts 23 may be made of Constantan. About the resistance, which results from the quotient of the current passing through the coil 21 and that at the Wendel 21 voltage is calculable, the temperature can be determined. The power that can be determined from the product of current and voltage can be used to calculate the heat flow. In the exemplary embodiment illustrated in FIGS. 3 to 5, a high-temperature mass flow meter 26 is used as the second sensor.

Such a mass flow meter is also an object of the invention. The mass flow meter has a base, which is screwed into an opening of the steam line 12. The steam line 12 forms a cavity through which a gas flows. This hollow space has an inlet opening 12 'and an outlet opening 12 "The flow direction defined by the position of the inlet opening 12' and the bearings of the outlet opening 12" is crossed by two imaginary planes substantially transversely to the flow direction. In each of the two imaginary levels there is a filament 27, 28 made of a tungsten wire. The wire is coiled. It can be a double helix, as they are known from conventional incandescent filaments in incandescent lamps. Each of the two filaments 27, 28 has a U-shape. The two mutually parallel filaments 27, 28 are held by carriers 29. The ends of the tungsten filaments 27, 28 are connected to terminal contacts 23 made of Constantan.

In the current direction, the two filaments 27, 28 are substantially congruent one behind the other. The two filaments 27, 28 have a substantially constant distance from each other. The spacing of the two filaments 27, 28 is substantially less than the length of each of the two filaments 27, 28 and also substantially less than a characteristic diameter of a surface framed or partially framed by one of the filaments 27, 28. FIG. 3 schematically describes the structure of a device for depositing an organic starting material as a layer on a substrate. With regard to the design and arrangement of the aerosol generator 4, the mass flow meter 2, the evaporator 8, the CVD reactor housing 14 and the pressure sensor 24 and the vacuum pump 19, reference is made to the explanation of Figure 1 reference.

Unlike the embodiment shown in Figure 1 is here in the steam line 12, a high-temperature mass flow meter 26, as has been previously described. The mass flow meter has two filaments 27, 28, which are located one behind the other in the flow direction in the steam line 12. Unlike the prior art, no bypass is required here, through which a gas flow to be measured is branched off. The two filaments 27, 28 are connected to the computing device 20, in which an evaluation device is also integrated, with which the voltage applied to the two filaments 27, 28 or the currents flowing through the two filaments 27, 28 can be measured.

The evaluation circuit can be designed as a bridge circuit, as shown in FIG. The filaments may have a thickness which is less than or equal to 5 μιτι. The filaments can be operated at temperatures above 400 ° C or below 650 ° C. With such an arrangement pressures of 0.001 to 0.5 mbar can be measured via a DC bridge. Preferably, pressure differences are determined in a range between 0.001 and 0.1 mbar.

FIG. 6 shows the temperature profile in the region of a single filament 27, 28 in the flow direction f. The curve s shows the temperature profile when the flow V is equal to zero. At a gas flow V through the Steam line 12 shifts the temperature curve in the flow direction. It is represented by d.

FIG. 7 shows the same conditions. Now, however, two densely adjacent filaments are arranged one behind the other in the direction of flow f. The curves di and d _{2 represent} the temperature profiles of a heated filament 27, 28, respectively, if no second filament were arranged in the vicinity. The curve denoted by s represents the temperature distribution, which results when two heated filaments 27, 28 are arranged one behind the other and through the flow channel 12, a gas stream V flows. It can be seen that the temperature of the downstream filament 28 is slightly greater than the temperature of the upstream filament 27 (indicated by o in Figure 7). With the bridge circuit shown in Figure 5, a value can be obtained that represents the mass flow through the flow channel 12.

The mass flow meter 2 provides the mass flow of the carrier gas. From the difference of the mass flows determined by the mass flow meter 10 and the mass flow meter 2, the mass flow of the vaporized organic material can be determined.

FIG. 8 shows a bridge circuit in which, unlike the bridge circuit shown in FIG. 5, no direct current flows but an alternating current flows through the filaments 27, 28. The filaments are also indicated here as resistors Ri and R ₂ in the diagram. Resistors in the order of about 10 Ω R ₃ and R4 are connected in parallel as a bridge to the two resistors of the filaments Ri and R ₂ . The nodes of both resistors are connected to the inputs of an operational amplifier. The current flowing through the upstream filament with resistor Ri heats the upstream filament. The current flowing through the downstream filament with the resistor R ₂ heats the downstream filament. It turns each one belonging to the corresponding temperature resistance. The bridge circuit can be adjusted so that the bridge is in equilibrium with non-flowing gas, so the bridge voltage is zero. A stream of gas flowing through the tube transports heat from the upstream filament to the downstream filament, with the result that both filaments are cooled to different extents. The resulting difference in resistance results in a bridge voltage that is proportional to the mass transport through the tube.

With the very high sensitivity of the AC bridge, changes of 0.5 ppm in the bridge impedance can be measured. The bridge voltages here are typically at values of about 6 mV. The AC signal is converted via a low-pass filter into a DC output signal. By using an AC bridge, not only drift effects but also errors due to the noise are compensated.

All disclosed features are essential to the invention. The disclosure content of the associated / attached priority documents (copy of the prior application) is hereby also incorporated in full in the disclosure of the application, also for the purpose of including features of these documents in claims of the present application. The subclaims characterize in their optional sibling version independent inventive development of the prior art, in particular to make on the basis of these claims divisional applications. LIST OF REFERENCE NUMBERS

1 carrier gas line 26 Hochtemperaturmassenfluss-

2 mass flow meter

3 carrier gas line 27 filament

4 aerosol generator 28 filament

5 reservoir 29 carrier

6 Aerosol line Sl Input mass flow values

7 inlet opening S2 sensor signal

8 evaporator V gas flow

9 outlet opening d flow direction

10 Pirani sensor di temperature profile

11 Blind flange / cavity d ₂ Temperature profile

12 steam line f flow direction

12 'entrance Ri resistance

12 "outlet Ra resistance

13 heating Rs resistance

14 CVD reactor housing R4 resistor

15 gas inlet (shower head)

16 process chamber

17 substrate

18 susceptor

19 vacuum pump

20 computing device

21 helix

22 support arms

23 connection contacts

24 pressure sensor

Claims

EXPECTATIONS

1. Method for producing a transported in a carrier gas

Vapor of a solid or liquid starting material comprising the steps: feeding a carrier gas stream into an aerosol generator (6) through a carrier gas power (3);

Generating an aerosol in the aerosol generator (6);

Transporting the aerosol into a vaporizer using the carrier gas stream;

Heating the evaporator (8);

Evaporation of the solid or liquid starting material within the evaporator (8);

Transporting the steam generated in this way together with the carrier gas as a starting gas stream through the outlet opening (9);

Determining a first value assigned to the mass flow of the carrier gas in the carrier gas line (3) by means of a first sensor (2);

Determining a second value influenced by both the mass flow or partial pressure of the carrier gas and the mass flow or partial pressure of the vapor in the output gas stream using a second sensor (10);

Calculating a value corresponding to the partial pressure of the vapor transported in the output gas stream by relating the values determined by the two sensors (2, 10).

2. The method according to claim 1 or in particular according thereto, characterized in that a Pirani vacuum meter is used as the second sensor (10) and/or a calorimetric mass flow meter is used as the first sensor (2).

3. Method according to one or more of the preceding claims or in particular according thereto, characterized in that in order to determine the partial pressure of the steam, a correction value is subtracted from the value supplied by the second sensor (10) or from a value derived from this value, which is derived from the The value determined by the first sensor (2) is obtained, for the determination of which data determined in particular in preliminary tests are used.

4. Method according to one or more of the preceding claims or in particular according thereto, characterized in that the aerosol is a

Solid aerosol is.

5. Device for evaporating a liquid or solid starting material in a heatable evaporator (8), into which an input gas stream of a carrier gas enters through an inlet opening (7).

Flows through the evaporator (8) and, together with a steam generated by evaporation of the starting material, emerges as an output gas stream from the evaporator (8) through an outlet opening (9), with an outlet opening in front of the inlet opening in the flow direction

(7) arranged first sensor (2) for determining a first value assigned to the mass flow of the input gas stream, a second sensor (10) arranged in the flow direction after the outlet opening (9) for determining both the mass flow or partial pressure of the carrier gas and the mass flow respectively Second value dependent on the partial pressure of the steam, and a computing device (20) which is determined by the relationship

Setting the two values provides a value corresponding to the partial pressure of the vapor transported in the output gas stream, characterized by a value downstream of the inlet opening (2) in the flow direction and the evaporator

(8) upstream aerosol generator (4), the is flowed through by the carrier gas stream.

Device according to claim 5 or in particular according thereto, characterized in that the input sensor (2) and/or the output sensor (10) is a calorimetric sensor, in particular the output sensor (10) being a Pirani vacuum meter and the input sensor (2) being a measuring device. mustard flow meter.

Device according to one or more of claims 5 or 6 or

in particular afterwards, characterized in that the aerosol generator (4) pulverizes a solid and brings the powder particles into the carrier gas stream.

Device according to one or more of claims 5 to 7 or in particular according thereto, characterized in that the output sensor (10) is a high-temperature mass flow meter which has two heating elements which can each be heated by an electrical current, each of the two heating elements being freely inserted into one of the Exit openings

(9) filament (27, 28) projecting downstream in the flow direction (12) is formed, the filaments (27, 28) lying in imaginary planes extending essentially transversely to the flow direction.

Device according to one or more of claims 5 to 8 or in particular according thereto, characterized in that the two filaments (27, 28) lie in the imaginary planes running parallel to one another in such a way that they are essentially congruent one behind the other in the direction of flow.

10. Device according to one or more of claims 5 to 9 or in particular according thereto, characterized in that the length of the filaments te (27, 28) is significantly larger than the essentially constant distance between the two filaments (27, 28) from one another.

11. Device according to one or more of claims 5 to 10 or in particular according thereto, characterized in that the filaments (27, 28) are formed from a helical wire and / or that the filaments (27, 28) each have the shape at least in some areas have a U.

12. High-temperature mass flow meter, with a cavity (12) through which a gas can flow in one direction of flow, with two heating elements (27, 28) spaced apart from one another in the direction of flow, each of which can be heated by means of an electrical heating current to the temperature of the gas flowing past them to increase the gas, and with an electronic evaluation circuit (20) in order to calculate a mass flow through the cavity (12) from the values of the voltage applied to the respective heating element (27, 28) or the current flowing through the respective heating element (27, 28). to determine the flowing gas, characterized in that each of the two heating elements (27, 28) is formed by a filament projecting freely into the cavity (12), the two filaments (27, 28) being in virtual, essentially transverse to the direction of flow extending levels.

13. High-temperature mass flow meter according to claim 12 or in particular according thereto, characterized in that the two filaments (27, 28) in

Lie essentially congruently one behind the other in the direction of flow and/or are formed by a helical wire and/or each have the shape of a U at least in some areas. High-temperature mass flow meter according to claims 12 to 13 or in particular according thereto, characterized in that the distance between the two imaginary planes in which the filaments (27, 28) extend is less than the entire length of the filaments (27, 28) or a characteristic length for example, the maximum distance between two sections of a filament (27, 28).