DEVICE AND METHOD FOR DETERMINING THE CONCENTRATION OF A VAPOR BY MEANS OF AN OSCILLATING BODY SENSOR

Abstract

A device and a method determines the concentration of a vapor in a volume, in particular for determining or controlling the mass flow of the vapor being conveyed through the volume by a carrier gas. The device comprises a sensor, which supplies a sensor signal that is dependent on the concentration or partial pressure of the vapor. The sensor has an oscillatory body that can be brought to oscillation, the oscillation frequency of which is influenced by a mass accumulation formed on a surface of the oscillating body by the condensed vapor. The oscillating body has a temperature control unit, by means of which the oscillating body can be brought to a temperature below the condensation temperature of the vapor. An evaluation unit determines the concentration or the partial pressure of the vapor from the temporal change of the oscillator frequency.

Claims

1. A device for determining or controlling a mass flow of a vapor being conveyed through a volume (2) by a carrier gas, wherein the volume (2) can be heated by means of a heating unit (8) to a temperature above a condensation temperature of the vapor, the device comprising a sensor (1), situated in the volume (2), which supplies a sensor signal that is dependent on a concentration or a partial pressure of the vapor, the device characterized in that the sensor (1) has an oscillatory body (17) that can be brought to oscillation, an oscillation frequency of which is influenced by a mass accumulation formed on a surface (18) of the oscillating body (17) by a condensation of the vapor, wherein the oscillating body (17) has a temperature control unit (19, 20), by means of which the oscillating body can be brought to a temperature below the condensation temperature of the vapor, wherein an evaluation unit determines the concentration or the partial pressure of the vapor from a temporal change of the oscillation frequency.

2. A method for determining or controlling a mass flow of a vapor being conveyed through a volume (2) by a carrier gas, wherein the volume (2) is heated by means of a heating unit (8) to a temperature above a condensation temperature of the vapor, using a sensor (1), situated in the volume (2), which supplies a sensor signal that is dependent on a concentration or a partial pressure of the vapor, the method characterized in that the sensor (1) has an oscillating body (17), an oscillation frequency of which is influenced by a mass accumulation formed on a surface (18) of the oscillating body (17) by a condensation of the vapor, wherein the oscillating body (17) by means of a temperature control unit (19, 20) is brought to a temperature below the condensation temperature of the vapor, and the concentration or the partial pressure of the vapor is determined from a temporal change of the oscillation frequency.

3. The device according to claim 1, wherein the temperature control unit (19, 20) is a cooling unit, by which the oscillating body (17) is cooled.

4. The device according to claim 1, wherein the oscillating body (17) is a crystal of gallium orthophosphate (GaPO.sub.4). cm 5. The device according to claim 1, further comprising a feed-in device (13) with a mass flow controller (7) for setting a mass flow of the carrier gas that is fed into a vaporizer (2, 3, 4) in which a liquid or a solid body is able to be brought into a gaseous state by an application of heat, wherein the mass flow of the carrier gas and/or a vapor production rate of the vaporizer (2, 3, 4) or a vaporization temperature is able to be changed by a controller (6), which together with the sensor (1) forms a closed control circuit.

6. The device according to claim 5, wherein the controller (6) has a first and second control circuit for controlling the vapor production rate, the first control circuit, having a high time constant, by which an average vapor production rate is controlled to a predetermined average value by variation of the a delivery rate of a material which is to be vaporized, and the second control circuit having a low time constant, by which temporary deviations of the vapor production rate from the predetermined average value are compensated by changing the vaporization temperature.

7. The device according to claim 5, wherein the sensor (1), and the vaporizer (2, 3, 4) are parts of a gas supply of an organic vapor phase deposition (OVPD) coating device, which has a deposition reactor (9), in which a coolable susceptor (12) is arranged for receiving one or more substrates (11) which are to be coated, wherein through a feed line (13) an inlet gas stream of the carrier gas enters into the vaporizer (2, 3, 4), which flows through the vaporizer (2, 3, 4) and together with the vapor generated in the vaporizer (2, 3, 4) by vaporizing a starting material, exits as an outlet stream from the vaporizer (2, 3, 4) through a feeder line (14), wherein a first value corresponding to a mass flow of the inlet gas stream is determined by the mass flow controller (7) arranged in front of an inlet opening and a second value dependent on the partial pressure of the vapor is determined by the sensor (1), wherein by means of a computing unit, by correlating the first and second values, a third value is obtained corresponding to a mass flow of the vapor which is transported in the outlet stream.

8. The device according to claim 1, wherein the sensor (1) is able to be heated to temperatures above 160 C.

9. The device according to claim 1, wherein the surface (18) of the oscillating body (17) is able to be closed by means of a closure (22).

10. The device according to claim 1, wherein the sensor (1) comprises a first and second sensor of identical construction, wherein the first sensor (1) is kept at a temperature below the condensation temperature of the vapor and in particular below a temperature of the volume (2), and the second sensor (1) is kept at a temperature above the condensation temperature and in particular at the temperature of the volume (2).

11. The method according to claim 2, wherein the sensor (1) is kept at a temperature greater than 160 C.

12. The method according to claim 11, wherein the temperature of the volume (2) is greater than 200 C.

13. The method according to claim 2, wherein the sensor (1) is heated, for cleaning, to a temperature above the condensation temperature of the vapor, so that the condensate formed on the sensor surface evaporates.

14. The method according to claim 2, wherein a total pressure within the volume (2) lies in a range between 0.1 and 10 mbar, and/or a mass concentration of the vapor in carrier gas lies in a range between 0.1 and 10%.

15. (canceled)

16. The method of claim 2, wherein the sensor (1) is heated to temperatures above 160 C.

Description

[0010] An example embodiment of the invention is explained below with the aid of enclosed drawings. There are shown:

[0011] FIG. 1 diagrammatically the structure of an OLED coating device and

[0012] FIG. 2 diagrammatically the structure of a QCM sensor indicated in FIG. 1.

[0013] The coating device illustrated in FIG. 1 has a deposition reactor 9. This is a gas-tight container, in which a process chamber is situated, in which a total pressure of 0.1 to 100 mbar is able to be set. In particular, a controlled total pressure of 0.1 to 10 mbar is able to be set there. Within the deposition reactor 9 there is situated a susceptor 12, which has cooling ducts 15, through which a cooling fluid can flow, in order to keep the susceptor 12 at a defined deposition temperature. A substrate 11 which is to be coated lies on the upper side of the susceptor.

[0014] Above the susceptor 12 there is situated a shower-head-like gas inlet member 10, through which a vapor-carrier gas mixture can be introduced into the process chamber arranged between susceptor 12 and gas inlet member 10. The gas inlet member 10 is kept at a temperature which lies above the condensation temperature of the vapor, so that a gaseous starting material is brought into the process chamber and the vapor can deposit itself on the substrate 11. The condensate of the vapor forms an OLED layer.

[0015] The gas inlet member 10 is fed by means of a vapor feeder line 14 with a carrier gas-vapor mixture, which is generated in a vapor generator 2,3,4. The vapor generator 2,3,4 and the vapor feeder line 14 are kept by means of a heating unit 8 at a temperature which lies above the condensation temperature of the vapor but below the breakdown temperature of the vapor.

[0016] By means of a mass flow controller 7, a defined flow of a carrier gas, for example nitrogen, is introduced into the vaporizer 2,3,4 through a feed line 13 forming an inlet opening.

[0017] In the example embodiment, the vaporizer has an injection chamber, into which an injector 4 opens, by which a solid body which is to be vaporized or a liquid which is to be vaporized is brought as an aerosol into the injection chamber. The aerosol arrives into a hot vaporization chamber 3, where it vaporizes. The liquid or the solid body is transported from a storage container via a conveying device. The injector 4 can be part of an aerosol generator 5, by which the solid body or the liquid is fed as an aerosol into the carrier gas stream. The conveying rate of the solid or liquid starting material which is to be vaporized or respectively the mass flow of the carrier gas is predetermined by a controller 6.

[0018] In the vaporization body 3, heat is supplied to the solid material which is to be vaporized or to the liquid which is to be vaporized, in particular the generated aerosol, so that the solid body or the liquid changes its aggregation state. The starting material leaves the vaporization body 3 as vapor transported in the carrier gas through a duct 14 forming an outlet opening. It reaches the volume 2, in which a sensor element 1 is situated, which is able to determine the mass concentration or respectively the partial pressure of the vapor within the volume 2. From the carrier gas mass flow set in the mass flow controller 7, the mass flow of the vapor through the duct 14 adjoining the volume 2, therefore the outlet duct, can be determined.

[0019] The controller 6 receives as input parameter either the sensor signal of the sensor 1 or else a measurement signal, obtained from the sensor signal 1 by measured value transformation, proportional to the mass flow of the vapor.

[0020] By variation of the conveying rate of the solid body which is to be vaporized, or of the liquid which is to be vaporized, or by variation of the vaporization temperature of the material which is to be vaporized and variation of the mass flow value fed in in the mass flow controller 7, the mass flow of the vapor can be adjusted and kept temporally constant.

[0021] The sensor 1 illustrated in FIG. 2 has a housing 24. The housing 24 has an opening 21. The opening is able to be closed by means of a closure 22. The closure position is illustrated by dashed lines in FIG. 2. The base of the opening 21 is formed by an active surface 18 of a crystal of gallium orthophosphate or of a similar material. The crystal 17 is kept by means of a temperature control unit 19 at a temperature which is lower than the temperature of the volume 2. Whereas the temperature of the volume 2 lies above the condensation temperature of the vapor, therefore in particular above 350 C., the temperature of the crystal 17 and in particular the temperature of the active surface lies at a temperature which is lower than the condensation temperature of the vapor, therefore for example at 300 C. This has the result that a layer, becoming thicker over time, is deposited on the surface 18. This layer is condensed vapor.

[0022] By means of an electrical excitation device, which is not illustrated, the crystal 17 forms an oscillating circuit. The resonance frequency of this oscillating circuit is determined by the physical characteristics of the crystal 17. The resonance frequency is, however, also influenced by the mass accumulation on the active surface 18. The condensed layer forms a mass accumulation on the active surface, which leads to a damping and to a detuning of the resonance frequency. For example, the resonance frequency can decrease with an increasing layer thickness. The frequency with which the crystal 17 oscillates is therefore a measurement for the thickness of the layer which is deposited on the active surface 18. Consequently, the alteration rate of the frequency is a measurement for the vapor concentration (the partial pressure) within the volume, because the deposition rate, therefore the growth rate of the layer deposited on the active surface 18 is dependent on the vapor concentration.

[0023] The growth rate of the layer deposited on the active surface 18 is, however, also dependent on the temperature of the crystal 17 or respectively the temperature of the active surface 18. In order to guarantee as long a time of use of the sensor as possible, provision is made that the temperature of the active surface lies only slightly below the condensation temperature. For example, the temperature of the active surface 18 can be 50 C. less than the condensation temperature of the vapor. Such a high temperature results not only in a small growth rate, but also the formation of a dense or respectively compact layer. The deposited layer forms with a minimal malposition concentration, therefore a densest packing of the molecules forming the layer. This results in a low damping of the oscillating behavior of the crystal 17. A smaller growth rate suppresses, furthermore, diffusion influences which the carrier gas has on the growth rate.

[0024] The vapor consists of aromatic hydrocarbons, which as a solid body have a higher elasticity than metal or other inorganic materials.

[0025] With the method according to the invention, by means of the previously described sensor 1 the mass concentration of a vaporized organic starting material in a carrier gas can be determined selectively. N.sub.2 is used for example as carrier gas. This takes place at raised temperatures above 200 C. and at gas pressures in the range of 0.1 and 10 mbar. The proportion of the vapor in the vapor-carrier gas mixture can be 0.1 to 10%. The sensor 1 achieves a response time of less than 0.1 seconds. As part of a control circuit, a vapor feed rate can be kept temporally constant with the sensor 1.

[0026] As the sensor according to the invention can be cleaned automatically and in situ by heating the active surface 18 to a temperature above the condensation temperature, a preferred variant of the invention has two or more such sensors 1, which can be used optionally for controlling. The sensor which is used for controlling is cooled to a temperature below the condensation temperature of the vapor via the feed line/discharge line 20 with a cooling fluid, which is fed into the cooling ducts 15 of the temperature control unit. The sensor frequency is supplied to the controller 6 via electric lines 23. The opening 21 is opened.

[0027] A sensor 1 which is not used for controlling is not cooled. Its active surface 18 has a temperature which lies above the condensation temperature of the vapor, so that a layer which is formed there can vaporize or so that no layer grows there. The opening 21 can, however, also be closed with the closure 22.

[0028] The controller 6 provides two variables. With a first variable, the delivery rate of a material which is to be vaporized, in particular of a powder which is to be vaporized, is set. For example, this can take place by controlling the rotation speed of a worm conveyor, by which a powder is conveyed to an aerosol generator, by which it is brought into a gas stream which is directed to vaporizer surfaces. With a second variable, the temperature of the vaporizer surfaces is set. Certain amounts of the powder which is to be vaporized can adhere to the vaporization surfaces and thus form a reservoir. By means of this reservoir, through variation of the vaporization temperature, the vapor production rate can be varied in the short term. The long-term variation of the vapor production rate takes place by controlling the conveying rate with which the material which is to be vaporized is brought into the vaporizer.

[0029] The controller 6 therefore comprises two control circuits. With the first control circuit, which has a high time constant, the delivery rate of the material which is to be vaporized is controlled. The delivery rate is set so that an average vapor production rate is kept to a predetermined nominal value. With the second control circuit, the vaporization temperature is altered. The second control circuit has a low time constant compared to the time constant of the first control circuit. With this second control circuit, temporary deviations of the vapor production rate can be reacted to by altering the vaporization temperature. For example, by lowering the vaporization temperature, the vaporization capacity can be reduced. Hereby, a storage mass can collect in the vaporizer. By raising the vaporization temperature, this storage mass can be vaporized, in order to react to a temporary lowering of the delivery rate.

[0030] A control method which is used here, or respectively a control device which is to be used, are described by DE 10 2011 051 261 A1, DE 10 2011 051 260 A1 and DE 10 2011 051 931 A1, which belong to the subject of the disclosure of this application.

[0031] The above statements serve to explain the inventions encompassed by the application as a whole, which further develop the prior art at least through the following feature combinations respectively independently, namely:

[0032] A device, which is characterized in that the sensor 1 has an oscillating body 17 able to be brought to oscillation, the oscillation frequency of which is influenced by a mass accumulation formed on a surface 18 of the oscillating body 17 by the condensed vapor, wherein the oscillating body 17 has a temperature control unit 19, 20, by which it is able to be brought to a temperature below the condensation temperature of the vapor, wherein an evaluation unit determines the concentration or respectively the partial pressure from the temporal change of the oscillator frequency.

[0033] A method, which is characterized in that the sensor 1 has an oscillating oscillation body 17, the oscillation frequency of which is influenced by a mass accumulation formed on a surface 18 of the oscillating body 17 by the condensed vapor, wherein the oscillating body 17 is brought by means of a temperature control unit 19, 20 to a temperature below the condensation temperature of the vapor and the concentration or respectively the partial pressure is determined from the temporal change of the oscillator frequency.

[0034] A device or a method which are characterized in that the temperature control unit 19, 20 is a cooling unit, by which the oscillating body 17 is cooled.

[0035] A device or a method, which are characterized in that the oscillating body 17 is a crystal of gallium orthophosphate (GaPO.sub.4).

[0036] A device or a method, which are characterized in that by means of a feed-in device 7 a carrier gas is fed into a vaporizer 2,3,4, into which a liquid or a solid body is brought into a gaseous state by application of heat, wherein the flow rate of the carrier gas and/or the vapor production rate of the vaporizer 2,3,4 is able to be changed by a controller 6, which together with the sensor 1 forms a closed control circuit.

[0037] A device or a method, which are characterized in that the controller 6 has two control circuits for controlling the vapor production rate: A first control circuit, having a high time constant, by which an average vapor production rate is controlled to a predetermined average value by variation of the delivery rate of the material which is to be vaporized, and a second control circuit having a low time constant, by which temporary deviations of the current vapor production rate from the average value are compensated by changing the vaporization temperature.

[0038] A device or a method, which are characterized in that the sensor 1, the vaporizer 2,3,4 are parts of a gas supply of an OVPD coating device, which has a deposition reactor 9, into which a coolable susceptor 12 is arranged for receiving one or more substrates 11 which are to be coated, wherein through a feed line 13 an inlet gas stream of a carrier gas enters into the vaporizer 2,3,4, which flows through the vaporizer 2,3,4 and together with the vapor generated in the vaporizer 2,3,4 by vaporizing a starting material, exits as outlet stream from the vaporizer 2,3,4 through a feeder line 14, wherein the mass flow of the inlet stream is determined by a sensor element 7 arranged in front of the inlet opening and with the sensor 1 a value dependent on the partial pressure of the vapor, wherein by means of a computing unit, by correlating the two values, a value is obtained corresponding to the mass flow of the vapor which is transported in the outlet stream.

[0039] A device or a method, which are characterized in that the sensor 1 is able to be heated to temperatures up to 450 C.

[0040] A device or a method, which are characterized in that the surface 18 is able to be closed by means of a closure 22.

[0041] A device or a method, which are characterized in that two sensors 1 of identical construction are used, wherein respectively one sensor 1 is kept at a temperature below the condensation temperature of the vapor and in particular below the temperature of the volume 2, and the respectively other sensor 1 is kept at a temperature above the condensation temperature and in particular at the temperature of the volume 2.

[0042] A device or a method, which is characterized in that the sensor 1 is kept at a temperature of greater than 160 C., preferably greater than 180 C. and particularly preferably at a temperature of 50 C. below the temperature of the volume 2, and/or that the temperature of the volume 2 is greater than 200 C., greater than 350 C. and in particular less than 450 C.

[0043] A device or a method, which are characterized in that the sensor 1 is heated, for cleaning, to a temperature above the condensation temperature of the vapor, so that the condensate formed on the sensor surface evaporates.

[0044] A device or a method, which are characterized in that the total pressure within the volume 2 lies in the range between 0.1 and 10 mbar, and/or that the mass concentration of the vapor in the carrier gas lies in the range between 0.1 and 10%.

[0045] All disclosed features are (in themselves, but also in combination with one another) essential to the invention. The disclosure content of the associated/enclosed priority documents (copy of the prior application) is herewith also included in full into the disclosure of the application, also for the purpose of including features of these documents into claims of the present application. The subclaims characterize with their features independent inventive further developments of the prior art, in particular in order to carry out divisional applications on the basis of these claims.

LIST OF REFERENCE NUMBERS

[0046] 1 sensor [0047] 2 volume [0048] 3 vaporization body [0049] 4 injector [0050] 5 aerosol generator [0051] 6 controller [0052] 7 mass flow regulator, -controller [0053] 8 heating unit [0054] 9 deposition reactor [0055] 10 gas inlet member [0056] 11 substrate [0057] 12 susceptor [0058] 13 feed line [0059] 14 vapor feeder line [0060] 15 cooling duct [0061] 16 gas outlet opening [0062] 17 crystal [0063] 18 surface [0064] 19 temperature control unit [0065] 20 feed line/discharge line [0066] 21 opening [0067] 22 closure [0068] 23 line [0069] 24 housing