EVAPORATION SOURCE FOR A CVD REACTOR

Description

field of technology

[0001] The invention relates to an arrangement for supplying a process gas for use in a CVD reactor, in particular in a MOCVD reactor. A carrier gas, for example hydrogen or nitrogen, is supplied by an inlet mass flow controller or an arrangement of several inlet mass flow controllers. The carrier gas can optionally be connected directly to a process gas supply line that leads into a gas inlet of a CVD reactor or to an inlet of a source in the form of a vaporization device. In the latter case, an outlet of the vaporization device is connected to the process gas supply line, so that vapor of a liquid or solid feedstock stored in a container of the vaporization device is conveyed with the carrier gas through the process gas supply line to the CVD reactor. The vapor pressure of the feedstock in the container can be adjusted by a temperature control device, which can be used to heat or cool the container.When using this arrangement with a MOCVD reactor, the container holds a metal-organic feedstock. Additional gas sources are provided to feed other feedstocks, particularly gaseous ones, directly into the gas inlet of the CVD reactor. This allows gases of two different chemical elements, for example, elements from groups V and III, to be introduced into the process chamber of the CVD reactor. A semiconductor layer of these elements is then deposited onto a substrate located in the process chamber and heated to a process temperature.

[0002] In a central gas supply system, sources can also be provided that supply a mass flow of a gas stored in a container, such as propane or the like, which is transported with a carrier gas to one or more CVD reactors. The concentration of the reactive gas in the carrier gas can vary. Alternatively, instead of a gas stored in a container, a source can be used in which a solid or liquid feedstock is vaporized and the vapor is conveyed by a carrier gas to one or more CVD reactors in the manner described above. Here, too, the concentration of the reactive gas in the gas stream can vary over time, particularly if containers have been changed. State of the art

[0003] EP 1 870 490 A2 describes an evaporation device with a feed line through which a carrier gas, regulated by a mass flow controller, is fed into an inlet of an evaporator. The outlet of the evaporator leads into a process gas supply line, into which another carrier gas supply line leads. A compensating gas flows through this carrier gas supply line, diluting the process gas flow coming from the evaporator. A pressure regulator is provided to adjust the mass flow of the compensating gas so that the total pressure in the source vessel and in the process gas supply line is maintained at a constant value.

[0004] It is also known from the prior art to arrange a measuring device in the process gas supply line with which the concentration or partial pressure of the vapor of the feedstock in the process gas supply line is measured. For this purpose, measuring devices are used in particular that generate a sound signal, especially an ultrasonic signal, and measure the sound transit time or speed of sound within the process gas. Since the speed of sound depends on the concentration of the feedstock in the carrier gas, the concentration or partial pressure can be determined from the measured values ​​obtained in this way. However, the measured value of this measuring arrangement also depends on the total pressure in the process gas supply line or a measuring chamber of the measuring device.

[0005] It is further desirable to feed a predetermined process gas flow into a gas inlet of a CVD reactor, and in particular to feed various predetermined process gas flows into a CVD reactor through gas inlet openings located at different points. It is also desirable to provide a central gas supply that can supply process gases with a stable concentration over time.

[0006] From EP 2 687 621 A2, it is known to keep the concentration of the feedstock constant by means of a balancing gas. From US2014 / 0299206, it is known to keep the total pressure in the process gas line constant without the use of a balancing gas by using mass flow controllers and pressure regulators. From US2010 / 02852606 A1, it is known to divide process gas among several CVD reactors. Summary of the invention

[0007] The invention is based on the objective of supplying a precisely adjustable mass flow of a starting material to a CVD reactor.

[0008] The invention further aims to provide measures by which the total pressure is kept at a constant value both in the container of the source and in the process gas supply line.

[0009] Furthermore, the invention is based on the objective of specifying a CVD reactor and a method for providing a process gas.

[0010] The problem is solved by the invention specified in the claims. The dependent claims are advantageous embodiments of the suffixed claims.

[0011] The invention relates primarily and essentially to an arrangement for supplying a process gas for use in a known CVD reactor. The arrangement according to the invention can be part of a gas supply system for a CVD reactor. The arrangement has a supply line that is connected or connectable to a carrier gas source. However, several supply lines can also be provided, which can be connected to different carrier gas sources. Thus, different carrier gases can be used. The arrangement has an outlet, which, in particular, can be connected as a process gas supply line to a gas inlet device of a CVD reactor. Exemplary embodiments of the invention can include a first inlet mass flow controller for supplying a first mass flow of a carrier gas, a reactive gas, or a mixture of a carrier gas and a vapor or reactive gas.The inlet of the first input mass flow controller can be connected to a carrier gas source. An outlet of the first input mass flow controller can be connected to a feed line of an evaporation device. This can be done by means of a switching device. The evaporation device has a vessel that forms an evaporation volume. A feed material to be evaporated can be stored in the vessel. This feed material can be liquid or solid. The feed line opens into the vessel in such a way that the carrier gas flowing in through the feed line passes through the powdered or liquid feed material to become saturated with vapor of the feed material. A discharge from the evaporation device, originating from the evaporation volume, is connected to a process gas supply line to the CVD reactor.A mass flow consisting of the carrier gas and a reactive gas, for example the vaporized feedstock, flows through the process gas supply line to the CVD reactor. Additional supply lines may be provided through which other gaseous feedstocks enter the CVD reactor. In particular, it is provided that a metal-organic feedstock of an element from Group III is vaporized in the vaporization device, and a gas of an element from Group V is supplied to the CVD reactor via a separate supply line.

[0012] The inlet of the inlet mass flow controller can also be connected to a source of reactive gas. While in the previously described variant only the carrier gas flows through the inlet mass flow controller, in the second variant the reactive gas, or a mixture of the reactive gas and the carrier gas, or a vapor generated in a central vaporization device, flows through the inlet mass flow controller, particularly together with a carrier gas. The gas sources in this variant can be central gas sources connected to a central gas supply that provides one or more process gases to multiple CVD reactors.The central evaporation device can have the properties described above, wherein the central evaporation device has a larger container for receiving the starting material to be evaporated, and it can be provided that this container is continuously refilled from a storage container.

[0013] The process gas source can be a container holding a gaseous feedstock, which could be, for example, a hydride. However, the gaseous feedstock can also be any other reactive gas, including, in particular, a carbon-containing gas, a silicon-containing gas, or the like. The gas can be stored in the container in its purest form. Alternatively, the gas can be stored in the container as a gas mixture with another gas. In the latter case, the concentration of the reactive gas in the container can vary depending on the batch.

[0014] The CVD reactor contains a susceptor, which can be heated to a process temperature and on which a substrate to be coated is located. Several substrates can be coated simultaneously in a single process chamber of the CVD reactor. For this purpose, the different process gases, along with a carrier gas, are fed into the process chamber via a gas inlet device. According to the invention, it is proposed that an inlet of a pressure regulator is connected to a second or the same carrier gas source to which the first inlet mass flow regulator is connected. The pressure regulator can supply a compensating gas, which is injected into the process gas supply line to maintain the total pressure in the process gas supply line at a constant value. The pressure regulator can also simultaneously maintain the total pressure within the vessel of the vaporization device at a constant value.According to a further aspect of the invention, it is proposed that at least one further mass flow controller be arranged in the process gas supply line between the outlet of the pressure regulator and the CVD reactor or downstream of the pressure regulator. Since the process gas mass flow passes through this mass flow controller, it is hereinafter referred to as the process gas mass flow controller. According to a further aspect of the invention, it is proposed that a device for measuring the concentration or partial pressure of the vapor of the feedstock is arranged in the process gas supply line between the outlet of the pressure regulator and the CVD reactor or downstream of the pressure regulator and upstream of the process gas mass flow controller. The pressure regulator controls the total pressure in a measuring chamber of this measuring device for measuring the concentration or partial pressure of the vapor of the feedstock.The partial pressure is kept at a constant value by generating an ultrasonic signal. The sound wave's transit time over a measuring section can be measured, ensuring the measurement is not distorted by varying total pressures. The process gas mass flow controller can be positioned between the measuring device and the CVD reactor. The process gas mass flow controller regulates the mass flow of the reactive gas entering the CVD reactor. Combining a process gas mass flow controller with a pressure regulator and a device for measuring concentration or partial pressure offers the additional advantage of allowing adjustment of the setpoint of the process gas mass flow controller and / or the inlet mass flow controller. The mass flow value supplied by the process gas mass flow controller can depend on the concentration or partial pressure of the vapor in the process gas supply line.The measures described above improve the performance of a source arrangement for a MOCVD reactor with regard to the inaccuracy of an adjustable mass flow of a feedstock. According to a further development of one or more of the aspects described above, it is possible to divide the process gas flow, which is maintained at a constant total pressure by the pressure sensor, or the mass flow determined by the measuring device with respect to its concentration or partial pressure, into several partial mass flows. For this purpose, the process gas supply line can be split into two or more gas supply lines, each containing a process gas mass flow controller. The process gas mass flows controlled by the process gas mass flow controllers can be fed into the process chamber of the CVD reactor at different points.For this purpose, the CVD reactor can have a gas inlet device with several gas inlet openings arranged at different locations. In a further development of the invention, a single pressure regulator can be used to generate several compensating gases that can be fed into the process gas supply lines of different reactor arrangements. In this arrangement, the process gas supply lines of the different CVD reactors are maintained at the same total pressure. For this purpose, the output of the pressure regulator is connected to different process gas supply lines, wherein the gas supply lines preferably open into the process gas supply line upstream of process gas mass flow controllers and / or upstream of a measuring device for measuring the concentration or partial pressure.

[0015] In the arrangement according to the invention for providing a process gas, it can in particular be provided that the total pressure in the process gas supply line is maintained or can be maintained at a predetermined value by feeding in a compensating gas flow of a carrier gas with a pressure regulator, wherein the gas flow flowing through the process gas supply line to the CVD reactor is regulated by a mass flow controller arranged downstream of the pressure regulator or the injection point of the compensating gas supplied by the pressure regulator into the process gas supply line.

[0016] With the device and method according to the invention, a process gas mass flow, generated by a central gas source or by a gas source individually assigned to each CVD reactor, can be maintained at a constant pressure. Furthermore, it is possible to maintain the concentration of the reactive gas within the carrier gas flow at a constant value, regardless of the mass flow supplied by the source. It is also possible to maintain the pressure in a plurality of vaporization vessels assigned to one or more CVD reactors at a common pressure using only one pressure regulator.

[0017] A variant of the invention relates to such a gas supply device or CVD reactor, in which a source of a gaseous feedstock, which may be a vaporized liquid, a vaporized solid, or a feedstock supplied from a gas cylinder, provides a time-varying concentration of the feedstock in a carrier gas. To provide a constant mass flow of a process gas, which has a constant partial pressure of the feedstock, even with such a source, it is proposed that the gaseous feedstock be fed into the process gas supply line via an inlet mass flow controller. A gas supply line of a pressure regulator opens into this process gas supply line, and the pressure regulator maintains the total pressure in the process gas supply line at a constant value by injecting a compensating gas.The pressure in the measuring device for measuring the concentration of a partial pressure is also kept constant by the pressure regulator. The measuring device provides a measured value, which is fed to a control device. This control device can provide a setpoint with which the input mass flow controller is operated in such a way that the process gas mass flow controller receives a gas mixture with a constant mixture. A process gas mass flow controller can be provided downstream of the measuring device.

[0018] It can therefore be provided that in a gas flow of a gaseous feedstock or a mixture of a gaseous feedstock and a carrier gas, regulated by an inlet mass flow controller and where the partial pressure of the feedstock is subject to temporal fluctuations, a dilution gas flow of a carrier gas, regulated by a pressure controller, is fed downstream of the inlet mass flow controller, and these two gas flows are fed into a measuring device for measuring the partial pressure or concentration of the feedstock, wherein the total pressure within the measuring cell of the measuring device is kept constant by a pressure controller which additionally feeds a compensating gas flow into the measuring cell, and the mass flow of the feedstock is varied by a control device such that the concentration or partial pressure of the feedstock in the measuring cell fluctuates only within narrow limits.The process gas mass flow regulator located downstream of the measuring point keeps the sum of the mass flow of the feedstock and the dilution gas flow constant, resulting in a change in the dilution gas flow via the pressure regulator. Brief description of the drawings

[0019] The invention will now be explained in more detail using exemplary embodiments. The figures shown are: Fig. 1 schematically shows a source arrangement for providing a vaporized organometallic starting material, Fig. 2 schematically shows a representation according to Figure 1 However, a second embodiment in which a pressure regulator 8 is connected via several gas supply lines 12, 12', 12" to various process gas supply lines 9, 9', 9" of a total of three reactor arrangements, and Fig. 3 schematically represents a representation according to Figure 1, in which a process gas supply line 9 is split into two process gas supply lines 9', 9" through which a process gas flows to different gas inlet openings 15, 15' of a gas inlet device of a CVD reactor 1 by means of process gas mass flow controllers 13, 13', Fig. 4 a further embodiment of the invention in which a reactive gas is taken from a gas container in which a concentration of a reactive gas is contained that depends on the respective batch, Fig. 5 a further embodiment in which a central gas source with a vaporization source feeds several CVD reactors, Fig. 6 a further embodiment of the invention in which a CVD reactor is fed by a plurality of gas sources in which the same total pressure is maintained in the vaporization vessel in each case. Description of the embodiments, Fig.Fig. 7 Another embodiment in which a vapor of a reactive gas from a central vaporization source 19 is used, Fig. 8 Another embodiment in which two process gas mass flow controllers 13, 13' are connected in parallel to each other, and Fig. 9 Another embodiment in which two process gas mass flow controllers 13, 13' are connected in parallel to each other.

[0020] The in the Figures 1 to 3 The source arrangements shown in Figures 5 and 6 each have at least one source for providing vapor of a solid or liquid starting material 3, which is stored in a container 4 of an evaporation device 2, 2', 2". The evaporation device 2, 2', 2" has an inlet through which a carrier gas can flow into the container 4. The carrier gas, for example hydrogen, nitrogen, or a noble gas, becomes saturated with the vapor of the starting material and leaves the container 4 through a vent.

[0021] The inlet and outlet of the container 4 are connected to a switching device 5 which has several valves that can be switched in such a way that a carrier gas flow supplied by an arrangement of one or more inlet mass flow controllers 10, 11 (hereinafter referred to as carrier gas mass flow controller) either flows through the container 4 or past the container 4.

[0022] In the exemplary embodiment, the arrangement for providing a carrier gas mass flow consists of two mass flow controllers 10 and 11, which have different flow ranges. Mass flow controller 11 can, for example, have a larger flow range than mass flow controller 10. The carrier gas supply line 6 is connected to both mass flow controllers 10 and 11, with a shut-off valve arranged in the supply line to mass flow controller 11.

[0023] The source arrangement is used to provide a metal-organic feedstock for a CVD reactor 1, 1', 1" in which one or more substrates 17 rest on a heated susceptor 16 forming the bottom of a process chamber 18.

[0024] The exemplary embodiments each feature at least one CVD reactor 1, 1', 1" . In the one described in the Figure 1 In the illustrated embodiment, a process gas supply line 9, into which the vapor of the feedstock conveyed by the carrier gas from the evaporation device 2 is fed, leads into a gas inlet opening 15 of a CVD reactor 1.

[0025] In the Figure 2In the illustrated embodiment, three separate process gas supply lines 9, 9', 9", each containing vapor of the feedstock conveyed by the carrier gas from an evaporation device 2, 2', 2", each lead into a gas inlet opening 15 of a CVD reactor 1, 1', 1". Here, a single pressure regulator 8 with a discharge split into several gas supply lines 12, 12', 12" is connected to several source arrangements of different CVD reactors 1, 1', 1".

[0026] In the Figure 3In the illustrated embodiment, a process gas supply line 9, into which the vapor of the feedstock conveyed from the evaporation device 2 by the carrier gas is fed, splits into two process gas supply lines 9', 9". Each of these process gas supply lines 9', 9" contains a process gas mass flow controller 13, 13'. The mass flow controlled by the two process gas mass flow controllers 13, 13' opens into two different gas inlet openings 15, 15' of the same CVD reactor 1. Two separately controlled process gas flows are generated, which are fed into a process chamber 18 of a CVD reactor at different points.

[0027] The exemplary embodiments show a pressure regulator 8. The pressure regulator 8 is connected to a carrier gas supply line 7. The carrier gas supply line 7 can be connected to the same carrier gas source as the carrier gas supply line 6. However, it is also possible to connect the carrier gas supply line 7 to a different carrier gas source. The carrier gas flow fed into the pressure regulator 8 passes through the pressure regulator 8, which is designed to maintain a constant pressure in a gas supply line 12, 12', 12" connected to the outlet of the pressure regulator 8. For this purpose, the pressure regulator 8 has a control loop. The pressure regulator 8 also maintains a constant total pressure in the vessels 4 of the evaporation devices 2, 2', 2". The gas supply lines 12, 12', 12" open into the process gas supply lines 9, 9', 9" downstream of the vessel 4.

[0028] The exemplary embodiments further show optional measuring devices 14, 14', 14" with which the concentration or partial pressure of the starting material in the carrier gas can be determined. In particular, a device known as an epison can be used as the measuring device. With this measuring device, a measured value is obtained by measuring the time of flight of sound, which depends on the concentration or partial pressure of the starting material and also on the total pressure in a measuring chamber of the measuring device. The compensating gas flow generated by the pressure regulator 8 is fed upstream of the measuring device 14, 14', 14" into the process gas supply line 9, 9', 9" in each case. This maintains the total pressure within the measuring chamber of the measuring device 14, 14', 14" at a constant value.

[0029] Each of the process gas supply lines 9, 9', 9" is equipped with a process gas mass flow controller 13, 13', 13", which regulates the mass flow of the process gas fed into the respective CVD reactor 1, 1', 1" via the process gas supply line 9, 9', 9". As a result of this design, the respective mass flow controller 13, 13', 13" regulates the mass flow of a mixture consisting of a carrier gas and the vapor of a feedstock, where the partial pressure of the feedstock is known. Any necessary setpoint correction of the process gas mass flow controller's setpoint can be performed using the value measured by the measuring device 14, 14', 14".

[0030] In the Figure 4In the illustrated embodiment, the source 19 for supplying a reactive gas conveyed in a carrier gas has a container 20, for example a gas cylinder, in which a pure reactive gas, for example a hydride of an element of group V or group IV, is stored. However, the gas cylinder can also contain another gas, for example propane. It can be provided, in particular, that a diluted reactive gas is already stored in the container 20, for example a mixture between a reactive gas and a carrier gas, for example hydrogen or nitrogen. A mass flow controller 10, which in this case is an input mass flow controller, provides a predetermined mass flow of the reactive gas or the gas mixture. Parallel to the input mass flow controller 10 is a mass flow controller 11 with a larger value range, which can be selectively activated.

[0031] A pressure regulator 8 introduces a compensating gas flow into the existing gas flow such that the total pressure within the measuring device 14 is maintained at a constant value. The concentration of the process gas in the process gas supply line 9 can be determined in the measuring device 14. A control unit 21, via the inlet mass flow controller 19, maintains the concentration of the reactive gas in the process gas flow through the process gas supply line 9 at a constant value.

[0032] Container 20 can be equipped with a central gas supply.

[0033] The one in Figure 4 The source designated with 20 can also be formed by a source arrangement as described in the Figures 1 to 3 has been described, namely by an evaporation device 2, with a container 4 in which a solid or liquid starting material 3 to be evaporated is located. Such a device is shown in the Figure 7 A carrier gas is fed into container 4 in the manner described above by means of at least one carrier gas mass flow controller 10, 11, so that a mixture of the vapor of the feedstock and the carrier gas flows through the inlet mass flow controller 10, 11, whereby the concentration of the vapor of the feedstock in the carrier gas can vary. Container 4 is part of a central vaporization source 19, which supplies a continuous vapor stream conveyed by a carrier gas to a plurality of local gas supply units 26. The contents of container 4 can be continuously replenished from another container 27.

[0034] The Figure 7Figure 26 shows two such local gas supply units 26, each for supplying gas to a CVD reactor 1. Switching valves 24 are provided, allowing the reactive feedstock, which in this case is a mixture of a carrier gas and a vapor, to be fed into the inlet mass flow controller 10, 11. The switching valve 24 allows either a carrier gas or the reactive gas to be fed into the inlet mass flow controller 10. The carrier gas is fed in to purge the piping of the local gas supply unit 26. Each gas supply unit 26 has a control device 21, which allows the mass flow of the reactive gas to be adjusted so that the concentration of the feedstock at the measuring cell of the measuring device 14 is kept at a constant value.

[0035] The Figure 5 shows a further embodiment as a variant to the one in the Figure 3In the illustrated embodiment, the mass flow of the process gas splits into several partial flows, each of which is directed to different CVD reactors 1, 1', 1" and each process gas supply line 9, 9', 9" leading to a CVD reactor 1, 1', 1" is assigned an individual process gas mass flow controller 13, 13', 13".

[0036] The one in Figure 6The illustrated embodiment shows a CVD reactor connected to several different sources of a solid or liquid feedstock, for example, a metal-organic compound. Each source is associated with a measuring device 14, 14', 14" for measuring the respective concentration of the feedstock in the process gas supply line 9, 9', 9". The process gas flow through each of the process gas supply lines 9, 9', 9" can be controlled by a process gas mass flow controller 13, 13', 13". The process gas mass flows enter a gas inlet of the CVD reactor, and the process gases can exit from various gas inlet openings of the gas inlet.

[0037] The Figure 8Figure 1 shows another variant of the several previously described embodiments. A reactive gas, a mixture of a reactive gas with a carrier gas, or a mixture of steam with a carrier gas is fed into the process gas supply line 9 in the manner described above. Here, too, a control device 21 can be provided, which controls an input mass flow controller by specifying a setpoint to the mass flow controller 10, 11. A first process gas mass flow controller 13 is provided, which supplies a mass flow of a process gas that is continuously fed into the CVD reactor 1. A switching valve 22 allows process gas supplied by a second process gas mass flow controller 13' to be selectively fed into the CVD reactor 1 or into an exhaust line 23.With such a device, the mass flow fed into the CVD reactor 1 can be changed in a very short time because the total mass flow of the process gas flowing through the mass flow controller 13, 13' remains constant. This does not disrupt the operation of the controller 21.

[0038] A similar device shows the Figure 9However, here the second process gas mass flow controller 13' is directly connected to an exhaust line 23, so that the mass flow through the mass flow controller 13' does not enter the CVD reactor 1, but only the mass flow through the first process gas mass flow controller 13. The mass flow of the process gas through the process gas mass flow controller 13 can be varied by means of a control device 25. Simultaneously, the process gas mass flow through the second process gas mass flow controller 13' into the exhaust line 23 is also changed. The change in the two process gas mass flows is such that the sum of the process gas mass flows flowing through the process gas mass flow controllers 13 and 13' remains constant. This allows layers to be deposited on substrates in the CVD reactor 1, the layer properties of which change with the layer thickness. By adjusting the parameters in the Figures 8 and 9In the illustrated embodiments, if the total flow of the process gas is kept constant, the controller 21 is not disturbed.

[0039] It is considered advantageous if the elements described above are arranged in the following sequence in the direction of flow of the carrier gas: The vaporization device 2, 2', 2" is arranged upstream of the gas supply line inlet 12, 12', 12" of the pressure regulator 8. The measuring device 14 is arranged downstream of the pressure regulator 8, or rather, the gas supply line inlet 12, 12', 12" of the pressure regulator 8. The at least one process gas mass flow controller 13, 13', 13" is arranged downstream of the measuring device 14.

[0040] It is further considered advantageous that several source arrangements, each comprising a bubbler-designed evaporation device 2, 2', 2", are connected in parallel, with a common pressure regulator 8 being used to maintain a constant pressure in the bubbler's vessel 4. Different gas streams can be provided to feed process gases into different process chambers 18. List of reference symbols

[0041] 1 CVD reactor 15' Gas inlet opening 1' CVD reactor 16 Susceptor 1" CVD reactor 17 substrate 2 Evaporation device 18 Trial Chamber 2' Evaporation device 19 central evaporation source 2'' Evaporation device 20 container 3 Starting material 21 Control device 4 container 22 valve 5 switching device 23 Exhaust pipe 6 Carrier gas supply 24 valve 7 Carrier gas supply 25 Control unit 8 Pressure regulator 26 local gas supply facility 9 Process gas supply 9' Process gas supply 27 container 9" Process gas supply 10 Input mass flow controller 11 Input mass flow controller 12 Gas supply line 12' Gas supply line 12'' Gas supply line 13 Process gas mass flow controller 13' Process gas mass flow controller 13'' Process gas mass flow controller 14 Measuring device 14' Measuring device 14'' Measuring device 15 Gas inlet opening

Claims

1. Assembly for providing a process gas for use in a CVD reactor (1, 1', 1"), with a gas source (2-5, 19, 20) having an input mass flow controller (10, 11) for providing a mass flow of a gas-phase starting material transported with a carrier gas, which is conveyed through a process gas feed line (9, 9', 9") to the CVD reactor (1, 1', 1"), wherein a pressure measuring apparatus having a pressure regulator (8) for measuring the total pressure, and a measuring apparatus (14, 14', 14") for measuring the concentration or the partial pressure of the starting material in the carrier gas are arranged in the process gas feed line (9, 9', 9"), with a closed loop control device (21) with which the concentration or the partial pressure of the starting material is kept at a constant value in the process gas feed line (9, 9', 9"), and with a carrier gas feed line (7) for feeding a balance gas into the process gas feed line (9, 9', 9"), wherein a process gas mass flow controller (13, 13', 13") is arranged downstream of the measuring apparatus (14, 14', 14"), and the closed loop control device (21) is configured to regulate the mass flow of the starting material flowing into the CVD reactor with the process gas mass flow controller (13, 13', 13") while the total pressure is kept at a constant value with the pressure regulator (8), characterized in that the pressure regulator (8) delivers the balance gas (9), wherein the measuring apparatus (14, 14', 14") is located between an outlet of the pressure regulator and the process gas mass flow controller (13, 13', 13").

2. Assembly according to Claim 1, characterized in that a vapour source (19) provides a vapour that is transported in a carrier gas.

3. Assembly according to Claim 1, characterized in that the reactive gas conveyed through the process gas feed line (9, 9', 9") flows through the inlet mass flow controller (10, 11), and the gas source is a vapour source (19) which constitutes a container storing the reactive gas.

4. Assembly according to Claim 1, characterized in that a carrier gas flow provided by the inlet mass flow controller (10, 11) flows through an evaporation container (2) of an evaporation apparatus (2, 2', 2"), and the vapour generated in the evaporation apparatus (2, 2', 2") is transported in the process gas feed line (9, 9', 9") by the carrier gas.

5. Assembly according to Claim 1, characterized in that an output of the only one pressure regulator (8) is connected via a plurality of gas feed lines (12, 12', 12"), each with a process gas feed line (9, 9', 9"), each of which is assigned to a different CVD reactor (1, 1', 1").

6. Assembly according to any one of the preceding claims, characterized in that the process gas flow flowing through the process gas feed line (9) and maintained at a predetermined total pressure by the pressure regulator (8), is divided into a plurality of sub-flows.

7. Assembly according to any one of the preceding claims, characterized in that two process gas mass flow controllers (13, 13') are connected in parallel, and the process gas flow is fed into a process chamber (18) of the CVD reactor (1) or into process chambers (18) of different CVD reactors (1, 1', 1") through two different gas inlet openings (15, 15'), each being controlled according to the mass flow.

8. Assembly according to any one of the preceding claims, characterized in that an output of the only one pressure regulator (8) is connected by each of a plurality of gas feed lines (12, 12', 12") to a different gas source (19; 2-5), with which various reactive gases are provided, which are connected to one or more CVD reactors (1, 1', 1") via process gas feed lines (9, 9', 9").

9. Assembly according to any one of the preceding claims, characterized in that the closed loop control device (21) specifies a setpoint for the inlet mass flow controller (11) in order to maintain the concentration or the partial pressure of the starting material at a constant value in the process gas feed line (9, 9', 9").

10. CVD reactor assembly with at least one carrier gas source and one CVD reactor (1, 1', 1"), characterized by an assembly for providing a process gas which is fed into the CVD reactor (1, 1', 1") according to any one of the preceding claims.

11. Method for providing a process gas, in particular in an assembly according to any one of Claims 1 to 9, wherein the concentration or the partial pressure of the starting material and the total pressure is measured in the process gas feed line (9, 9', 9") using a pressure measuring apparatus and a measuring apparatus (14, 14', 14"), the mass flow of the starting material flowing into the CVD reactor (1, 1', 1") is kept at a constant value, and a balance gas is fed into the process gas feed line (9, 9', 9"), wherein due to the infeed of the balance gas the total pressure in the process gas feed line (9, 9', 9") is kept at a constant value, and the mass flow of the starting material flowing into the CVD reactor (1, 1', 1") is kept at a constant value with a process gas mass flow controller (13, 13', 13") arranged downstream of the measuring apparatus (14, 14', 14"), characterized in that the pressure regulator (8) delivers the balance gas, wherein the measuring apparatus (14, 14', 14") is located between an outlet of the pressure regulator and the process gas mass flow controller (13, 13', 13").

12. Method according to Claim 11, characterized in that the concentration or the partial pressure of the starting material is measured in the process gas feed line (9, 9', 9") with a measuring apparatus (14, 14', 14"), and the setpoint of the process gas mass flow controller is corrected in particular with a measured value obtained in this way, and / or the concentration or the partial pressure is kept at a constant value with the measured value obtained in this way.

13. Method according to Claim 11 or 12, characterized in that the mass flow of a carrier gas flowing out of an outlet of the pressure regulator (8) is divided into a plurality of mass flows, each of which discharges into a different process gas feed line (9, 9', 9"), through each of which a process gas mass flow flows from an evaporation apparatus (2, 2', 2") to a CVD reactor (1, 1', 1") .

14. Method according to Claim 11, 12, or 13, characterized in that the process gas mass flow provided by the source (19; 2-5) is divided into a plurality of partial flows, each of which is controlled by a process gas mass flow controller (13, 13' ), flows in regulated manner through various gas inlet openings (15, 15') into a process chamber (18) of the CVD reactor (1, 1', 1"), or flows into various CVD reactors (1, 1', 1").