Semiconductor processing device

Abstract

To provide a semiconductor processing device that includes a process control chamber upstream of a reaction chamber.SOLUTION: A semiconductor processing device 1 includes: a reactor 21; a first thermal zone 13 that has a solid source vessel 2 supplying a vaporized solid reactant to the reactor; and a second thermal zone 14 having a process control chamber 10. The process control chamber 10 is disposed between the solid source vessel and the reactor, a process control valve 9 being included upstream of the process control chamber. A control system 34 controls operation of the process control valve based at least in part on feedback of measured pressure in the process control chamber, the pressure being monitored and transmitted by a pressure transducer 12.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims priority to U.S. Provisional Patent Application No. 62 / 903,566, filed September 20, 2019, the entire contents of which are incorporated herein by reference in their entirety and for all purposes.

[0002] The technical field relates to semiconductor processing equipment, and in particular to semiconductor processing equipment that includes a process control chamber upstream of a reaction chamber. [Background technology]

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

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

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

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

[0007] These and other features, aspects, and advantages of the present invention will now be described with reference to drawings of several embodiments that are intended to illustrate, but not limit, the invention.

[0008] [Figure 1] FIG. 1 is a schematic system diagram of a semiconductor processing apparatus according to one embodiment. [Diagram 2] FIG. 2 is a flow chart illustrating a semiconductor processing method, in accordance with various embodiments. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

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

[0010] For example, ALD is a method for growing very uniform thin films on a substrate. In a time-resolved 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 thus include vapors that contain one or more reactants and one or more solvents. The growth of the film is based on alternating surface reactions occurring on the surface of the substrate to form a solid layer of atoms or molecules, because the reactants and the temperature of the substrate are selected such that the molecules of the alternately injected gas-phase reactants react with the surface layer only on the substrate. The reactants are injected at a dose high enough that the surface approaches saturation during each injection cycle. The process is therefore independent of the concentration of the starting materials and is theoretically self-regulating, thereby making it possible to achieve extremely high film uniformity and thickness precision of single atomic or molecular layers. Similar results are obtained in a space-resolved ALD reactor, where the substrate is moved to zones alternately exposed to different reactants. Reactants can contribute to the growing film (precursors) and / or perform other functions such as oxidizing, reducing, or removing ligands from adsorbed species of precursors to facilitate reaction or adsorption of subsequent reactants. ALD methods can be used for the growth of both elemental and compound thin films. ALD can involve two or more reactants alternated in cycles, and different cycles can have different numbers of reactants. True ALD reactions tend to produce less than a monolayer per cycle. Practical applications of ALD principles tend to have real-world deviations from the true saturation and monolayer limitations, and hybrid or variant processes can obtain higher deposition rates while achieving some or all of the conformal and control benefits of ALD.

[0011] As described herein, a solid reactant source (or reactant solvent mixture) can be sublimated in a heated vessel to form a reactant vapor that is delivered to a reactor or reaction chamber. However, sublimation of solid reactant material can be a slow process, e.g., orders of magnitude slower than liquid reactant evaporation systems. Furthermore, the sublimation rate of solid reactant material can vary depending on source vessel geometry, surface area of ​​solid precursor particles, irregularly shaped solid reactant particles, and other components of the semiconductor processing system. For example, in some cases, the surface area of ​​solid reactant particles can change during operation depending on solid particle agglomeration. Sublimation rates can change over time during operation, and the supply of vaporized reactants to the reaction chamber can also be inconsistent and variable.

[0012] In some semiconductor processing equipment, the solid source reactant dose can be controlled by controlling the vapor pressure in the solid source vessel, the flow rate through the solid source vessel, 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 source vessel. The control device may be remote from the heat source used to sublimate the solid reactant source because the control device is not compatible with 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. Thus, there is still a continuing need for improved supply of vaporized solid reactant to the reactor.

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

[0014] An inert gas source 3 can supply an inert carrier gas along an inert gas line 4 to the solid source vessel 2. 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 can be provided along the inert gas line 4 to regulate the flow of inert gas to the solid source vessel 2. The inert gas valve 6 can comprise an adjustable valve having multiple flow conductance settings in some embodiments. In other embodiments, the inert gas valve 6 can include a binary on-off valve, where the valve 6 allows or blocks the flow of inert gas along the inert gas line 4. In the embodiment of FIG. 1, the inert gas can help supply and carry the reactant vapor to the reactor 21.

[0015] The pressure and temperature of the solid source vessel 2 may be controlled such that the solid reactant particles are sublimated into reactant vapor. In the illustrated embodiment, an inert carrier gas from an inert gas source 3 may serve to carry or propel the reactant vapor to the reactor 21. In other embodiments, the reactant vapor may be supplied along the supply line 5 without the use of a separate inert carrier gas supply, based on the vapor pressure of the heated reactant and / or downstream vacuum source drawing the vapor. Omitting a separate inert gas source and conveying the reactant vapor through the supply line 5 may beneficially reduce the cost and complexity associated with the apparatus 1. The reactant vapor may 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 the reactant vapor from the solid source vessel 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 vessel isolation valve, such as, for example, a binary on-off valve. Filter 8 may be configured to capture and vaporize liquid droplets or solid particles present due to incomplete sublimation.

[0016] A process control chamber 10 may be disposed between the solid source container 2 and the reactor 21. The process control chamber 10 may meter or control the amount of reactant vapor provided to the reactor 21 along the reactant supply line 5. The process control chamber 10 may function as an intermediate volume where the reactant is collected in vapor form before being delivered to the reactor 21. Using the process control chamber 10 to control the supply of the reactant vapor to the reactor 21 may beneficially allow for more precise control of the reactant vapor dose to the reactor 21.

[0017] The process control valve 9 may 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 source container 2. In some embodiments, the process control valve 9 may comprise a binary on-off valve that allows or blocks the flow of the vaporized reactant to the process control chamber 10. Advantageously, the use of a binary on-off valve for the process control valve 9 may be relatively inexpensive and durable for use in high temperature environments. In other embodiments, the process control valve 9 may comprise a diaphragm valve or a proportioning valve to control the flow conductance of the vaporized reactant to the process control chamber 10. The reactor feed valve 11 may be located downstream of the process control chamber 10, for example, between the process control chamber 10 and the reactor 21. The reactor feed valve 11 may comprise a binary on-off valve or an adjustable valve to control the flow conductance in some embodiments. For example, in the illustrated embodiment, reactor feed valve 11 may comprise a binary valve configured to operate in a high temperature environment. In some embodiments, a piezoelectric valve may be used for reactor feed valve 11. In various embodiments, a high temperature proportioning valve may be used. In other embodiments, other types of valves may be suitable.

[0018] The reactant gas supply line 5 can supply reactant vapor to an inlet manifold 18 of the reactor 21. The inlet manifold 18 can supply reactant vapor to a reaction chamber 30 of the reactor 21. A distribution device 35, such as a showerhead as shown, or a horizontal injector in other embodiments, can include a plenum 32 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 can 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 contact and react with the substrate to form a layer (e.g., a monolayer, etc.) on the substrate. The distribution device 35 can distribute the reactant vapor to form a uniform layer on the substrate.

[0019] Exhaust line 23 may be in fluid communication with reaction chamber 30. Vacuum pump 24 may apply suction to exhaust line 23 to evacuate vapors and excess materials from reaction chamber 30. Reactor 21 may comprise any suitable type of semiconductor reactor, such as an atomic layer deposition (ALD) apparatus, a chemical vapor deposition (CVD) apparatus, or the like.

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

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

[0022] As shown in FIG. 1, the apparatus 1 may include a first thermal zone 13 maintained at a first temperature, and a second thermal zone 14 maintained at a second temperature. In various embodiments, the second temperature of the second thermal zone 14 may be higher than the first temperature of the first thermal zone 13 to minimize the risk of condensation of the intact solid reactants. 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., in the range of 10° C. to 40° C., or in the range of 20° C. to 30° C. In various embodiments, one or more of the solid source vessel 2, the inert gas source 3, the inert gas valve 6, and the reactant gas valve 7 may be disposed within the first thermal zone 13. The first thermal zone may be maintained at a temperature high enough to sublimate the solid reactant particles into vaporized reactants, but not so high as to cause thermal decomposition of the reactants. The second thermal zone 14 can include one or more of 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 thermal zone 14. The pressure transducer 12 can be located within the second thermal zone 14, such as inside the process control chamber 10.

[0023] If the thermal zones 13, 14 are separated, a heater jacket can be provided in the portion of the feed line 5 between the zones to maintain the line at or above the temperature of the first thermal zone 13. Locating a filter 8 within the heated second thermal zone 14 can beneficially enhance the capture and vaporization of liquid droplets or solid particulates that may be delivered through the filter 8.

[0024] In the illustrated embodiment, the process control valve 9, reactor feed valve, pressure transducer 12, and / or electronic components of the control system 34 may be fabricated to accommodate high temperature processing. For example, the process control valve 9 may comprise a high temperature diaphragm valve having a high response speed, such as an ALD or DH series valve manufactured by Swagelok Corporation of Solon, Ohio. Similarly, the pressure transducer 12 may include a high temperature compatible 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 of the process control chamber 10 and communicate the measured pressure to the control system 34. In embodiments in which the valve 9 comprises a binary on-off valve, the control system 34 can send commands to the control valve 9 to open or close the valve 9 based on the measured pressure. For example, in various embodiments, a 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, a proportional integral derivative (PID) controller can be used, for example, to control the operation of the control valve 9. In some embodiments, the control system 34 can determine the time that the control valve 9 is open to achieve or maintain a desired process control chamber set point pressure that is provided to a PID or other controller. Additionally, the reactor supply valve 11 can be programmed to have a pulse time selected to generate a desired dose of reactant vapor to the reaction chamber 30 based at least in part on the set point pressure of the process control chamber 10, e.g., the pressure of the reactant vapor in the process control chamber 10. The flow rate of reactant vapor to the reaction chamber 30 can be determined based at least in part on the pressure of the process control chamber (e.g., approximately equal to the pressure set point) and the pulse time of the reactor supply valve 11. The amount of solid source consumed in the solid source 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 solid source consumption in the container 2. The control system 34 can automatically adjust the refill time of the process control chamber 10 if the reactant sublimation rate changes. Beneficially, controlling the supply to the process control chamber 10 via metering of reactant vapor based on the measured pressure in the chamber 10 can improve wafer yield and deposition uniformity. In other embodiments, the control system 34 can send instructions to the control valve 9 to adjust the flow conductance 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 take into account changes in the sublimation rate over time. For solid precursors, the sublimation rate may depend at least in part on the geometry of the source vessel 2. For example, the interior volume of the source vessel 2 can change as the solid precursor is consumed, and the exposed surface area of ​​the solid material can also change, such that a mass of solid material may be placed in some areas of the vessel 2 while other areas of the vessel 2 may be empty of solid material. Changes in the volume of the source vessel 2 and the exposed solid precursor surface area can change the sublimation rate and affect the reactant content of the gas delivered to the reactor. Beneficially, the setpoint pressure for the control valve 9 can be set at a level lower than the vapor pressure of the solid source and selected to automatically compensate for changes in the sublimation rate. For example, if the sublimation rate decreases, the valve 9 can automatically compensate by remaining open for a longer period of time to reach the control pressure setpoint. Beneficially, the use of closed-loop feedback control for the control valve 9 can therefore automatically compensate for changes in the sublimation rate without the user having to continually monitor and compensate for changes in the sublimation rate.

[0027] Thus, the feedback circuit with process control valve 9, pressure transducer 12, and control system 34 can precisely control the pressure in process control chamber 10 to provide efficient and effective dose metering or delivery of vapor phase reactant from the solid reactant source. Utilizing the high temperature compatible valve 9, pressure transducer 12, and / or control system 34 components can also reduce the overall size of the system and provide closed loop feedback control to precisely deliver vaporized reactant to reactor 21.

[0028] FIG. 2 is a flow chart illustrating a semiconductor processing method 40 according to various embodiments. The method 40 begins at block 41, in which solid reactant (e.g., deposition precursor) particles are vaporized into a reactant vapor through a sublimation process. For example, the solid reactant particles can be placed in a solid source 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 source container may be disposed in a first thermal zone that includes one or more heaters configured to maintain a first temperature of the first thermal zone above the sublimation temperature of the reactant material. In various embodiments, for example, a higher temperature for the first thermal zone may increase utilization of the solid precursor. The temperature of the first thermal zone may be made sufficiently high (e.g., higher than the sublimation temperature) to prevent resolidification of the vaporized precursor.

[0029] Moving to block 42, the reactant vapor can be transferred to a process control chamber. For example, a valve (such as reactant valve 7) can be controllably opened and closed to deliver the reactant vapor from feedstock 2 to the reactant gas line. As discussed above, in various embodiments, reactant valve 7 can comprise an open and close valve. In some embodiments, the reactant vapor can be passed through a heated filter that traps solid particles or droplets and ensures that the delivered reactant is in the gas phase. The process control chamber can 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, operation of a process control valve located upstream of the process control chamber may be controlled by a control system. In various embodiments, for example, the process control valve may be adjusted (e.g., shut on or off or adjusted to a set flow conductance) based at least in part on the measured pressure of the process control chamber. As described herein, a pressure transducer may be used to monitor the pressure in the process control chamber. The control system may utilize an appropriate control method (such as closed loop control with a pressure set point of a PID controller) to control the ingress of reactant vapor into the process control chamber via the process control valve. 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 that may be set at a higher temperature compared to the first thermal zone.

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

[0032] Although described in detail above by way of illustrations and examples for purposes of clarity 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 present invention to the specific embodiments and examples described herein, but rather encompass all modifications and alternatives that fall within the true scope and spirit of the disclosed embodiments. Moreover, not all of the features, aspects and advantages described herein above are necessarily required to practice the present embodiment.

Claims

1. A semiconductor processing device comprising: A reactor; and a solid source vessel configured to supply vaporized reactant to the reactor; a process control chamber between the solid source vessel and the reactor, the process control chamber being in fluid communication with the solid source vessel and the reactor; a process control valve between the solid source vessel and the process control chamber, the process control valve being upstream of the process control chamber; a control system configured to control operation of the process control valve based at least in part on feedback of the measured pressure in the process control chamber.

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

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

4. The apparatus of claim 1 , wherein the process control valve comprises an on-off binary valve.

5. 10. The apparatus of claim 1, further comprising a first thermal zone at a first temperature and a second thermal zone at a second temperature higher than the first temperature, the solid source container being disposed in the first thermal zone and the process control valve and the process control chamber being disposed in the second thermal zone.

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

7. 10. The apparatus of claim 1, further comprising a filter between the solid source container and the process control chamber.

8. 10. The apparatus of claim 1, further comprising a reactor feed valve between the process control chamber and the reactor, the reactor feed valve configured to pulse the vaporized reactant into the reactor.

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

10. 1. An apparatus for forming a vaporized reactant, comprising: a solid source container disposed within a first thermal zone at a first temperature; a process control chamber downstream of the solid source vessel and in fluid communication with the solid source vessel, the process control chamber being disposed within a second thermal zone at a second temperature, higher than the first temperature, and configured to transport the vaporized reactant to a reactor downstream of the process control chamber; a process control valve disposed in the second thermal zone between the solid source vessel and the process control chamber and upstream of the process control chamber; a control system configured to control operation of the process control valve based at least in part on feedback of the measured pressure in the process control chamber.

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

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

13. The apparatus of claim 10 , wherein the process control valve comprises an on-off binary valve.

14. 11. The apparatus of claim 10, further comprising a filter between the solid source container and the process control chamber.

15. 11. The apparatus of claim 10, further comprising: a reactor downstream of a process control volume; and a reactor feed valve between the process control chamber and the reactor, the reactor feed valve configured to pulse the vaporized reactant into the reactor.

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

17. 1. A method of forming a vaporized reactant, comprising: vaporizing a solid reactant to form a reactant vapor; transporting the reactant vapor to a process control chamber; controlling operation of a process control valve upstream of the process control chamber based at least in part on feedback of the measured pressure within the process control chamber; and transporting the reactant vapor from the process control chamber to a reaction chamber.

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

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

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

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