Semiconductor processing equipment

Abstract

The present invention provides a semiconductor processing apparatus and method, including a process control chamber upstream of the reaction chamber. [Solution] The semiconductor processing apparatus 1 includes a reactor 21, a solid raw material container 2 that supplies vaporized solid reactants to the reactor, a process control chamber 10 positioned between the solid raw material container and the reactor, a valve 9 upstream of the process control chamber, and a control system 34 that controls the operation of the valve, at least in part, based on feedback of measured pressure within the process control chamber.

Description

Technical Field

[0001] Cross - Reference to Related Applications This application claims the priority of U.S. Provisional Patent Application No. 62 / 903,566, filed on September 20, 2019, the entire content of which is incorporated herein by reference and for all purposes.

[0002] This technical field relates to semiconductor processing equipment, and in particular, to semiconductor processing equipment including a process control chamber upstream of a reaction chamber.

Background Art

[0003] During semiconductor processing, various reactant vapors are supplied to a reaction chamber. In some applications, reactant vapors of solid starting chemical substances at ambient pressure and temperature are used. These solid starting materials can be heated and sublimated to produce reactants vaporized for reaction processes such as vapor deposition. Chemical vapor deposition (CVD) may require a continuous flow of reactant vapor to the reaction chamber, while atomic layer deposition (ALD), pulsed CVD, and their hybrids include processes that are time - divided and spatially - divided pulsed depending on the desired configuration, and may require a continuous flow or pulsed supply to the reaction chamber. Such gas - phase reactants from solid substances can also be useful in other types of chemical reactions in the semiconductor industry (e.g., etching, doping, etc.) and other types of chemical reactions in various other industries. However, due in part to the small process window between the evaporation temperature and the decomposition temperature, the low vapor pressure, and the need for a uniform dose amount for such solid reactants, there is still a continuing need for improved control over the gas - phase delivery from solid reactant sources.

Summary of the Invention

[0004] In one embodiment, a semiconductor processing apparatus is disclosed. The semiconductor processing apparatus includes a reactor and a solid material container configured to supply vaporized reactants to the reactor. The semiconductor processing apparatus may include a process control chamber between the solid material container and the reactor, which is in fluid communication with the solid material container and the reactor. A process control valve may be located upstream of the process control chamber between the solid material container and the process control chamber. The semiconductor processing apparatus may include a control system configured to control the operation of the process control valve, at least in part, based on feedback of measured pressure within the process control chamber.

[0005] In another embodiment, an apparatus for forming vaporized reactants is disclosed. The apparatus may include a solid material container located in a first thermal zone at a first temperature. The apparatus may include a process control chamber downstream of the solid material container, in fluid communication with the solid material container. The process control chamber may be located in a second thermal zone at a second temperature higher than the first temperature, and may be configured to transfer the vaporized reactants to a reactor downstream of the process control chamber. The apparatus may include a process control valve located upstream of the process control chamber and in a second thermal zone between the solid material container and the process control chamber. The control system may be configured to control the operation of the process control valve, at least in part, based on feedback of measured pressure in the process control chamber.

[0006] In another embodiment, a method for forming vaporized reactants is disclosed. The method may include vaporizing solid reactants to form reactant vapor. The method may include transferring the reactant vapor to a process control chamber. The method may include controlling the operation of a process control valve upstream of the process control chamber, at least in part, based on feedback of measured pressure within the process control chamber. The method may include transferring the reactant vapor from the process control chamber to a reaction chamber. [Brief explanation of the drawing]

[0007] Herein, these and other features, aspects, and advantages of the present invention will be described with reference to drawings of several embodiments, which are intended to be illustrative rather than limiting.

[0008] [Figure 1] Figure 1 is a schematic system diagram of a semiconductor processing apparatus according to one embodiment. [Figure 2] Figure 2 is a flowchart showing semiconductor processing methods according to various embodiments. [Modes for carrying out the invention]

[0009] Embodiments disclosed herein relate to semiconductor processing apparatus for improving the control of gas-phase delivery of solid reactants such as deposition precursors. Embodiments disclosed herein can be used in conjunction with any suitable type of semiconductor processing apparatus, including atomic layer deposition (ALD) apparatus, chemical vapor deposition (CVD) apparatus, apparatus configured for variations of such pulsed processes, metal-organic CVD (MOCVD) apparatus, physical vapor deposition (PVD) apparatus, and the like.

[0010] For example, ALD is a method for growing very uniform thin films on a substrate. In a time-divided ALD reactor, the substrate is placed in an impurity-free reaction space, and at least two different reactants (precursors, or other reactant vapors) are alternately and repeatedly injected into the reaction space in the gas phase. The reactant vapors can therefore contain one or more reactants and one or more solvents. The growth of the film forms a solid layer of atoms or molecules based on alternating surface reactions occurring on the surface of the substrate because the temperatures of the reactants and the substrate are selected so that the molecules of the alternately injected gas-phase reactants react only on the substrate with its surface layer. The reactants are injected in doses high enough to bring the surface close to saturation during each injection cycle. Thus, the process is theoretically self-regulating, independent of the concentration of the starting materials, and thereby makes it possible to achieve extremely high film uniformity and thickness accuracy of a single atomic or molecular layer. Similar results are obtained in a space-divided ALD reactor, where the substrate is moved to zones that are alternately exposed to different reactants. The reactants can contribute to the growing film (precursor) and / or perform other functions, such as oxidizing, reducing, or removing ligands from the precursor's adsorbed species to facilitate the reaction or adsorption of subsequent reactants. The ALD method can be used for growing both elemental and compound thin films. ALD can involve two or more alternative reactants that are repeated in a cycle, and different cycles can have different numbers of reactants. A true ALD reaction tends to produce fewer than a monolayer per cycle. Practical applications of the ALD principle tend to have real-world deviations from true saturation and monolayer limitations, and hybrid or deformable processes can achieve higher deposition rates while achieving some or all of the conformability and controllability advantages of ALD.

[0011] As described herein, a solid reactant source (or reactant solvent mixture) can be sublimated in a heated vessel to form reactant vapors that are delivered to a reactor or reaction chamber. However, the sublimation of solid reactant materials can be a slow process, for example, orders of magnitude slower than that of liquid reactant evaporation systems. Furthermore, the sublimation rate of solid reactant materials can vary depending on the shape of the raw material container, the surface area of ​​the solid precursor particles, the irregular shape of the solid reactant particles, and other components of the semiconductor processing system. For example, in some cases, the surface area of ​​the solid reactant particles may change during operation depending on the solid particle aggregates. The sublimation rate may change over time during operation, and the supply of vaporized reactants to the reaction chamber may also be inconsistent and variable.

[0012] In some semiconductor processing equipment, the dose of solid raw material reactants can be controlled by controlling the vapor pressure in the solid raw material container, the flow rate through the container, and the pulse time. For example, a control device such as a master flow controller (MFC) or pressure controller can be provided upstream of the solid raw material container. The control device may be located away from the heat source used to sublimate the solid reactant source, as the control device is not suitable for high-temperature environments. As mentioned above, if the sublimation rate changes, the amount of reactant delivered per pulse may change, which can reduce wafer yield and increase costs. Therefore, improvements in the supply of vaporized solid reactants to the reactor remain an ongoing need.

[0013] Figure 1 is a schematic system diagram of a semiconductor processing apparatus 1 according to various embodiments. Apparatus 1 may include a solid material container 2 configured to supply vaporized solid reactants to a reactor 21. The solid material container 2 may include a heater that causes the sublimation of solid reactant source particles into vaporized reactants. Examples of solid material containers that may be used in apparatus 1 disclosed herein include any suitable type of solid material container, including those shown and described in U.S. Patent Nos. 7,122,085 and 8,137,462, and U.S. Patent Application Publication No. 2018 / 0094350 (each in its entirety by reference and incorporated herein in its entirety for all purposes).

[0014] An inert gas source 3 can supply an inert carrier gas to a solid raw material container 2 along an inert gas line 4. In various embodiments, a gas mass flow controller (MFC) can meter the supply of gas along the inert gas line 4. An inert gas valve 6 is provided along the inert gas line 4 and can regulate the flow of inert gas to the solid raw material container 2. In some embodiments, the inert gas valve 6 may comprise an adjustable valve with multiple flow conductance settings. In other embodiments, the inert gas valve 6 may include a binary on / off valve, where the valve 6 allows or shuts off the flow of inert gas along the inert gas line 4. In the embodiment of Figure 1, the inert gas can assist in supplying and carrying reactant vapors to the reactor 21.

[0015] The pressure and temperature of the solid material container 2 can be controlled so that the solid reactant particles sublimate into reactant vapor. In the illustrated embodiment, an inert carrier gas from an inert gas source 3 can serve to transport or propel the reactant vapor to the reactor 21. In other embodiments, the reactant vapor may be supplied along the supply line 5 without using a separate inert carrier gas supply, based on the vapor pressure of a downstream vacuum source that draws in the heated reactant and / or vapor. By omitting a separate inert gas source and transporting the reactant vapor through the supply line 5, the costs and complexity associated with the apparatus 1 can be beneficially reduced. The reactant vapor can be supplied to the filter 8 along the reactant vapor supply line 5. A reactant gas valve 7 may be provided to meter the supply of reactant vapor from the solid material container 2 to the filter 8. The reactant gas valve 7 may comprise any suitable type of valve, such as an adjustable valve or a binary on / off valve. In the illustrated embodiment, for example, the reactant gas valve 7 may comprise a container isolation valve, such as a binary on / off valve. The filter 8 may be configured to capture and vaporize liquid droplets or solid particles present due to incomplete sublimation.

[0016] The process control chamber 10 may be positioned between the solid raw material container 2 and the reactor 21. The process control chamber 10 can measure or control the amount of reactant vapor supplied to the reactor 21 along the reactant supply line 5. The process control chamber 10 can function as an intermediate volume where reactants are collected in vapor form before being delivered to the reactor 21. Controlling the supply of reactant vapor to the reactor 21 using the process control chamber 10 can beneficially enable more precise control of the reactant vapor dose to the reactor 21.

[0017] The process control valve 9 can be located upstream of the process control chamber 10. In the illustrated embodiment, the process control 9 may be located between the filter 8 and the process control chamber 10. In other embodiments, the process control valve 9 may be located between the filter 8 and the solid raw material container 2. In some embodiments, the process control valve 9 may comprise a binary on / off valve for allowing or blocking the flow of vaporized reactants to the process control chamber 10. Beneficially, the use of a binary on / off valve for the process control valve 9 can be relatively inexpensive and durable in high-temperature environments. In other embodiments, the process control valve 9 may comprise a diaphragm valve or a proportioning valve for controlling the flow conductance of vaporized reactants to the process control chamber 10. The reactor supply valve 11 may be located downstream of the process control chamber 10, for example, between the process control chamber 10 and the reactor 21. In some embodiments, the reactor supply valve 11 may comprise a binary on / off valve or an adjustable valve for controlling the flow conductance. For example, in the illustrated embodiment, the reactor supply valve 11 may comprise a binary valve configured to operate in a high-temperature environment. In some embodiments, a piezoelectric valve can be used for the reactor supply valve 11. In various embodiments, a high-temperature proportioning valve can be used. In other embodiments, other types of valves may be suitable.

[0018] The reactant gas supply line 5 can supply reactant vapor to the intake manifold 18 of the reactor 21. The intake manifold 18 can supply reactant vapor to the reaction chamber 30 of the reactor 21. A disperser 35, such as a showerhead as shown, or a horizontal injection device in other embodiments, may include a plenum 32 that is in fluid communication with a plurality of openings 19. The reactant vapor can pass through the openings 19 and be supplied into the reaction chamber 30. The substrate support 22 may be configured, or sized and shaped to support a substrate 36, such as a wafer, in the reaction chamber 30. The dispersed reactant vapor can come into contact with the substrate and react to form a layer (e.g., a single layer) on the substrate. The disperser 35 can disperse the reactant vapor to form a uniform layer on the substrate.

[0019] The exhaust line 23 can be in fluid communication with the reaction chamber 30. The vacuum pump 24 can apply suction to the exhaust line 23 to discharge vapor and excess material from the reaction chamber 30. The reactor 21 may be equipped with any suitable type of semiconductor reactor, such as an atomic layer deposition (ALD) apparatus or a chemical vapor deposition (CVD) apparatus.

[0020] In the embodiment shown in Figure 1, the pressure transducer 12 can monitor the pressure in the process control chamber 10. A feedback circuit can electrically connect the pressure transducer 12 to the process control valve 9. The control system 34 can control the operation of various components of the apparatus 1. The control system 34 may include processing electronics configured to control the operation of one or more of the valves 6, 7, 9, 11, the pressure transducer 12, the process control chamber 10, the reactor 21 (and its various components), and the vacuum pump 24. In some embodiments, one or more valves (such as valve 7) can be manually controlled for switching or recharging the solid material 2. Although illustrated as a single structure in Figure 1, it should be understood that the control system 34 may include multiple controllers or subsystems having processors, memory devices, and other electronic components that control the operation of various components of the apparatus 1. As used herein, the term “control system” includes any combination of individual controller devices and processing electronics that may be integrated with or connected to other devices (such as valves and sensors). Therefore, in some embodiments, the control system 34 may include a central controller that controls the operation of multiple (or all) system components. In some embodiments, the control system 34 may comprise multiple distributed controllers that control the operation of one or more system components. The control sequence may be hardwired or programmed within the control system 34.

[0021] As described above, controlling the sublimation of the solid reactant source for delivery to the reactor 21 can be difficult. Fortunately, the embodiment in Figure 1 may include feedback control of the measured pressure in the process control chamber 10 to control the concentration or dose of vaporized reactant supplied to the process control chamber 10. For example, the process control valve 9 can be operated by the control system 34 to open or close based on the measured pressure in the process control chamber 10.

[0022] As shown in Figure 1, the apparatus 1 may include a first heat zone 13 maintained at a first temperature and a second heat zone 14 maintained at a second temperature. In various embodiments, the second temperature of the second heat zone 14 may be higher than the first temperature of the first heat zone 13 in order to minimize the risk of spontaneous solid reactant condensation. In various embodiments, for example, the second temperature may be higher than the first temperature by a temperature difference in the range of 5°C to 45°C, 10°C to 40°C, or 20°C to 30°C. In various embodiments, one or more of the solid raw material container 2, inert gas source 3, inert gas valve 6, and reactant gas valve 7 may be located within the first heat zone 13. The first heat zone can be maintained at a temperature high enough to sublimate solid reactant particles into vaporized reactants, but not high enough to cause thermal decomposition of the reactants. The second heat zone 14 may include one or more of the following: a filter 8, a process control valve 9, a process control chamber 10, a pressure transducer 12, and a reactor supply valve 11, along with supply lines connecting components within the second heat zone 14. The pressure transducer 12 may be located within the second heat zone 14, for example, inside the process control chamber 10.

[0023] If the heat zones 13 and 14 are separated, a heater jacket can be provided on the portion of the supply line 5 between the zones to maintain the line at a temperature higher than that of the first heat zone 13. By placing the filter 8 within the heated second heat zone 14, the capture and vaporization of liquid droplets or solid particles that may be delivered through the filter 8 can be beneficially improved.

[0024] In the illustrated embodiment, the electronic components of the process control valve 9, reactor supply valve, pressure transducer 12, and / or control system 34 may be manufactured to withstand high-temperature processing. For example, the process control valve 9 may be a high-temperature diaphragm valve with a high response speed, such as an ALD or DH series valve from Swagelok, Solon, Ohio. Similarly, the pressure transducer 12 may include a high-temperature sensor, such as a capacitive manometer pressure transducer. Some components or wiring of the control system 34 may also be configured to operate in a high-temperature environment.

[0025] During operation, the pressure transducer 12 can monitor the pressure in the process control chamber 10 and transmit the measured pressure to the control system 34. In embodiments where the valve 9 is a binary on / off valve, based on the measured pressure, the control system 34 can send commands to the control valve 9 to open or close the valve 9. For example, in various embodiments, the closed-loop control system can control the opening and / or closing (e.g., valve timing, frequency, etc.) of the valve 9 based on feedback of the pressure of the process control valve 9 measured by the pressure transducer 12. In various embodiments, for example, a proportional-integral-derivative (PID) controller can be used to control the operation of the control valve 9. In some embodiments, the control system 34 can determine the time the control valve 9 is open in order to achieve or maintain a desired process control chamber setpoint pressure provided to the PID or other controller. Furthermore, the reactor supply valve 11 may be programmed to have a pulse time selected to generate a desired dose of reactant vapor to the reaction chamber 30, at least partially based on the setpoint pressure of the process control chamber 10, for example, the pressure of the reactant vapor in the process control chamber 10. The flow rate of reactant vapor into the reaction chamber 30 can be determined at least in part based on the pressure in the process control chamber (e.g., approximately the same as the pressure setpoint) and the pulse time of the reactor supply valve 11. The amount of solid material consumed in the solid material container 2 can be estimated based on the flow rate. In various embodiments, the pulse time of the reactor supply valve 11 can be adjusted to take into account the consumption of solid material in container 2. The control system 34 can automatically adjust the replenishment time of the process control chamber 10 if the sublimation rate of the reactant changes. Beneficially, controlling the supply of reactant vapor to the process control chamber 10 via metering based on the measured pressure in the chamber 10 can improve wafer yield and deposition uniformity. In other embodiments, the control system 34 can adjust the flow conductance by sending commands to the control valve 9 to increase or decrease the flow rate of reactant vapor through the valve 9 along a plurality of flow conductance values.

[0026] The control system 34 according to various embodiments can also automatically account for changes in the sublimation rate over time. For solid precursors, the sublimation rate may depend at least in part on the geometric shape of the feed container 2. For example, a mass of solid material may be disposed in a region of part of the container 2, while the interior volume of the feed container 2 can change as the solid precursor is consumed such that in other regions of the container 2 the solid material can be empty, and the exposed surface area of the solid material can also change. Changes in the volume of the feed container 2 and the exposed surface area of the solid precursor can change the sublimation rate and may affect the reactant content of the gas delivered to the reactor. Advantageously, the setpoint pressure for the control valve 9 can be set to a level lower than the vapor pressure of the solid feedstock and can be selected to automatically correct for changes in the sublimation rate. For example, if the sublimation rate decreases, the valve 9 can automatically correct by remaining open for a longer period of time to reach the control pressure setpoint. Advantageously, therefore, by using closed-loop feedback control for the control valve 9, the user can automatically correct for changes in the sublimation rate without continuously monitoring and correcting for the changes in the sublimation rate.

[0027] Thus, a feedback circuit having the process control valve 9, the pressure transducer 12, and the control system 34 can accurately control the pressure in the process control chamber 10 to provide an efficient and effective dosage or delivery of the gaseous reactant from the solid reactant source. By utilizing components of the high-temperature compatible valve 9, the pressure transducer 12, and / or the control system 34, the overall size of the system can also be reduced and closed-loop feedback control can be provided for accurately supplying the vaporized reactant to the reactor 21.

[0028] Figure 2 is a flowchart of a semiconductor processing method 40 according to various embodiments. Method 40 begins in block 41, in which solid reactant (e.g., deposition precursor) fine particles are vaporized into reactant vapor through a sublimation process. For example, the particles of the solid reactant can be placed in a solid raw material container and heated to a temperature higher than the sublimation temperature. In some embodiments, an inert carrier gas can be provided to help deliver the reactant vapor to the reactor. In other embodiments, a separate inert carrier gas may not be used. In various embodiments, the solid raw material container may be placed in a first heat zone which includes one or more heaters configured to maintain a first temperature in the first heat zone above the sublimation temperature of the reactant material. In various embodiments, for example, a higher temperature for the first heat zone may increase the utilization of the solid precursor. The temperature of the first heat zone may be sufficiently high (e.g., above the sublimation temperature) to prevent re-solidification of the vaporized precursor.

[0029] Moving to block 42, the reactant vapor can be transferred to the process control chamber. For example, a valve (such as the reactant valve 7) can be controllably opened and closed to deliver the reactant vapor from the raw material 2 to the reactant gas line. As described above, in various embodiments, the reactant valve 7 may be equipped with an on / off valve. In some embodiments, the reactant vapor may pass through a heated filter that captures solid particles or droplets and ensures that the delivered reactant is in the gas phase. The process control chamber may function as an intermediate metering volume where the vaporized reactant is collected before being delivered to the reaction chamber of the reactor.

[0030] In block 43, the operation of the process control valve located upstream of the process control chamber can be controlled by the control system. In various embodiments, the process control valve can be adjusted (e.g., to be shut on or off, or adjusted to a set flow conductance) at least in part based on the measured pressure in the process control chamber. A pressure transducer can be used to monitor the pressure in the process control chamber, as described herein. The control system can control the entry of reactant vapors into the process control chamber via the process control valve by utilizing an appropriate control method (such as closed-loop control by pressure setpoint of a PID controller). In various embodiments, one or more of the process control chamber 10, filter 8, process control valve 9, and pressure transducer 12 may be located in a second thermal zone which may be set to a higher temperature compared to the first thermal zone.

[0031] Moving to block 44, the vaporized reactants in the process control chamber can be transferred to the reactor. In various embodiments, a reactor supply valve downstream of the process control chamber can be activated to supply the vaporized reactants to the reaction chamber. In various embodiments, for example, the reactor supply valve may be configured to pulse the vaporized reactants into the reactor. The pulsing of the reactor supply valve can be controlled by a control system according to a process recipe for deposition, which may be hardwired or programmed within the control system.

[0032] While details have been provided in detail by illustrations and examples for the purpose of clarification and understanding, it will be apparent to those skilled in the art that certain changes and modifications can be implemented. Therefore, the description and examples should not be construed as limiting the scope of the invention to the specific embodiments and examples described herein, but rather encompass all modifications and substitutes that possess the true scope and spirit of the disclosed embodiments. Furthermore, not all of the features, aspects and advantages described herein are necessarily required to implement these embodiments.

Claims

1. A semiconductor processing apparatus, Reactor and A solid raw material container configured to supply vaporized reactants to the reactor, Between the solid raw material container and the reactor, a process control chamber is provided that is in fluid communication between the solid raw material container and the reactor. A process control valve upstream of the process control chamber, between the solid raw material container and the process control chamber, A semiconductor processing apparatus comprising: a control system configured to control the operation of a process control valve, at least in part, based on feedback of the measured pressure in the process control chamber.

2. The apparatus according to claim 1, further comprising a pressure transducer configured to measure the pressure in the process control chamber.

3. The apparatus according to claim 1, wherein the control system comprises a proportional-integral-derivative (PID) controller.

4. The apparatus according to claim 1, wherein the process control valve comprises an on / off binary valve.

5. The apparatus according to claim 1, further comprising a first heat zone at a first temperature and a second heat zone at a second temperature higher than the first temperature, wherein the solid raw material container is located in the first heat zone and the process control valve and the process control chamber are located in the second heat zone.

6. The apparatus according to claim 5, wherein the second temperature is higher than the first temperature by an amount in the range of 5°C to 45°C.

7. The apparatus according to claim 1, further comprising a filter between the solid raw material container and the process control chamber.

8. The apparatus according to claim 1, further comprising a reactor supply valve between the process control chamber and the reactor, wherein the reactor supply valve is configured to pulse the vaporized reactant to the reactor.

9. The apparatus according to claim 1, wherein the reactor comprises a reaction chamber and a dispersion device for dispersing the vaporized reactant within the reaction chamber.

10. An apparatus for forming vaporized reactants, A solid raw material container placed in the first heat zone at the first temperature, A process control chamber located downstream of the solid raw material container, which is in fluid communication with the solid raw material container, wherein the process control chamber is located in a second heat zone at a second temperature higher than the first temperature, and is configured to transfer the vaporized reactant to a reactor downstream of the process control chamber. A process control valve is located upstream of the process control chamber, within the second heat zone between the solid raw material container and the process control chamber, An apparatus comprising: a control system configured to control the operation of a process control valve, at least in part, based on feedback of the measured pressure in the process control chamber.

11. The apparatus according to claim 10, further comprising a pressure transducer configured to measure the pressure in the process control chamber.

12. The apparatus according to claim 10, wherein the control system comprises a proportional-integral-derivative (PID) controller.

13. The apparatus according to claim 10, wherein the process control valve comprises an on / off binary valve.

14. The apparatus according to claim 10, further comprising a filter between the solid raw material container and the process control chamber.

15. The apparatus according to claim 10, further comprising a reactor downstream of a process control volume, and a reactor supply valve between the process control chamber and the reactor, wherein the reactor supply valve is configured to pulse the vaporized reactant to the reactor.

16. The apparatus according to claim 15, wherein the reactor comprises a reaction chamber and a dispersion device for dispersing the vaporized reactant within the reaction chamber.

17. A method for forming vaporized reactants, The process involves vaporizing solid reactants to form reactant vapors, Transferring the reaction material vapor to the process control chamber, Controlling the operation of the process control valve upstream of the process control chamber, at least partially based on feedback of the measured pressure within the process control chamber, A method comprising transferring the reactant vapor from the process control chamber to the reaction chamber.

18. The method according to claim 17, further comprising measuring the pressure in the process control chamber with a pressure transducer.

19. The method according to claim 17, wherein controlling the operation of the process control valve includes using a proportional-integral-derivative (PID) controller.

20. The method according to claim 17, wherein controlling the operation of the process control valve includes controlling the period of time during which the process control valve is open.

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