Apparatus for detecting and quantifying radical concentration in semiconductor processing systems

Abstract

An embodiment disclosed herein includes a process tool for measuring neutral radical concentration. In one embodiment, the process tool comprises a process chamber and a Neutral Radical Mass Spectroscopy (NRMS) analyzer fluidically coupled to the process chamber. In one embodiment, the NRMS analyzer comprises a first chamber fluidically coupled to the process chamber, the first chamber comprising a modulator, and a second chamber fluidically coupled to the first chamber, the second chamber being a residual gas analyzer or mass spectrometer. In one embodiment, an unobstructed line of sight passes from the process chamber to the second chamber.

Description

Technical Field

[0001] Cross - Reference to Related Applications This application claims the benefit of U.S. Provisional Application No. 63 / 196,576, filed Jun. 3, 2021 and U.S. Provisional Application No. 63 / 242,402, filed Sep. 9, 2021, the entire contents of which are incorporated herein by reference, and claims priority to U.S. Application No. 17 / 735,837, filed May 3, 2022.

[0002] Embodiments of the present disclosure relate to the field of semiconductor processing, and more particularly, to tools for implementing neutral radical mass spectrometry (NRMS) and methods of using NRMS tools.

Background Art

[0003] In semiconductor processing, radical species are often used for various processing operations in a chamber. For example, radical species such as atomic fluorine can be used in etching or chamber cleaning processes. Radical species can be formed by various processes. One process for generating radical species is using plasma. For example, a fluorine - containing gas is introduced into the chamber, and the plasma decomposes the compound into elemental fluorine. Radical species are highly chemically reactive. Chemically active free radicals generated in the plasma can diffuse to the sample surface (e.g., the wafer surface). Free radicals reduce the activation energy in chemical reactions and cause material removal. Volatile chemical reaction by - products are removed from the sample surface and the process chamber by a vacuum system.

[0004] Process control of radical species is difficult. In particular, it is currently not possible to effectively measure the concentration of radical species in the processing chamber. This is partly due to the highly reactive nature of radical species. Whenever radical species come into contact with any surface or other compound, they react. Even if the surface does not react with the radical species, the surface still acts as a site for the radicals to recombine with each other, and thus can convert those species into other useless compounds. Therefore, existing mass spectrometry tools are not capable of measuring the concentration of radical species. Without the ability to quantitatively measure the concentration of radical species, effective process control, such as closed-loop control, is not possible with existing semiconductor manufacturing tools. [Overview of the project]

[0005] Embodiments disclosed herein include a processing tool for measuring neutral radical concentrations. In one embodiment, the processing tool comprises a processing chamber and a neutral radical mass spectrometry (NRMS) analyzer fluidly coupled to the processing chamber. In one embodiment, the NRMS analyzer comprises a first chamber fluidly coupled to the processing chamber, the first chamber comprising a modulator, and a second chamber fluidly coupled to the first chamber, the second chamber comprising a residual gas analyzer or mass spectrometer. In one embodiment, an unobstructed line of sight extends from the processing chamber to the second chamber.

[0006] Embodiments disclosed herein may also include methods for processing a substrate. In one embodiment, the method includes starting a plasma in a processing chamber containing the substrate. In one embodiment, the method continues by measuring the concentration of radical species in the plasma using a neutral radical mass spectrometer (NRMS) analyzer fluidly coupled to the processing chamber. In one embodiment, the method further includes comparing the measured concentration of radical species in the plasma with a setpoint concentration of radical species and adjusting one or more plasma parameters by a controller to return the measured concentration of radical species to the setpoint concentration of radical species.

[0007] Additional embodiments may include plasma processing tools. In one embodiment, the processing tool comprises a processing chamber and a neutral radical mass spectrometry (NRMS) analyzer fluidly coupled to the processing chamber. In one embodiment, the NRMS analyzer comprises a first chamber fluidly coupled to the processing chamber by an isolation gate valve, the first chamber comprising a modulator and a first pump fluidly coupled to the first chamber. In one embodiment, the NRMS analyzer further comprises a second chamber fluidly coupled to the first chamber, the second chamber comprising a residual gas analyzer or mass spectrometer, a second pump fluidly coupled to the second chamber, and an unobstructed line of sight from the processing chamber to the second chamber. [Brief explanation of the drawing]

[0008] [Figure 1] This is a schematic diagram of a processing chamber coupled to a neutral radical mass spectrometry (NRMS) analyzer according to one embodiment. [Figure 2] This is a diagram of a modulator for use in an NRMS analyzer, according to one embodiment. [Figure 3A] This is a schematic diagram of a residual gas analyzer according to one embodiment. [Figure 3B] This is a schematic diagram of a residual gas analyzer using cross-beam ionization according to one embodiment. [Figure 4] This is a diagram of a process for measuring radical concentration with low background noise according to one embodiment. [Figure 5] This is a process flow diagram illustrating the processing of a substrate in a processing chamber using closed-loop control according to one embodiment. [Figure 6] This is a block diagram of an exemplary computer system according to one embodiment of the present disclosure. [Modes for carrying out the invention]

[0009] This specification describes tools for implementing neutral radical mass spectrometry (NRMS) and methods for using NRMS tools. The following description includes numerous specific details to provide a thorough understanding of the embodiments of this disclosure. It will be apparent to those skilled in the art that embodiments of this disclosure can be practiced without these specific details. In other cases, well-known embodiments, such as integrated circuit manufacturing, are not described in detail to avoid unnecessarily obscuring the embodiments of this disclosure. Furthermore, it should be understood that the various embodiments shown in the figures are illustrative and not necessarily drawn to a specific scale.

[0010] As mentioned above, it is currently not possible to measure the concentration of radical species in processing tools such as plasma chambers. Radical species are difficult to measure partly due to their high chemical reactivity with other elements. For example, radical species can react with other gases in the process, the surface of the workpiece, the surface of the chamber, etc. Since radical species are major factors in the desired chemical reactions in the process (for example, radical fluorine is a major factor in etching operations), it is highly desirable to obtain real-time quantitative measurements of radical species concentration.

[0011] Without the ability to quantitatively measure the concentration of radical species, closed-loop control of the processing environment is not possible. Closed-loop control refers to the use of quantitative measurements as feedback signals to a controller to modify processing conditions in the ongoing process. For example, in the case of measuring radical species, the concentration of radical species can be measured, and the measured value can be compared to a setpoint value. When the measured value is below the setpoint value, processing parameters can be changed to increase the radical species generation rate and output concentration; when the measured value is above the setpoint value, processing parameters can be changed to decrease the radical species concentration. Thus, a more stable and regenerative process can be implemented.

[0012] Accordingly, embodiments disclosed herein involve the use of a neutral reaction (radical) mass spectrometry (NRMS) analyzer. The NRMS analyzer is coupled to a processing chamber, such as a plasma processing chamber. The NRMS analyzer may include a pair of vacuum chambers. The first vacuum chamber includes a modulator, and the second chamber includes a residual gas analyzer. Differential pumping allows the first vacuum chamber to be at a lower pressure than the processing chamber, and the second vacuum chamber to be at a lower pressure than the first vacuum chamber. The pressure reduction allows the molecular beam containing radicals to travel from the processing chamber to the residual gas analyzer. Furthermore, a line-of-sight path exists from the processing chamber to the residual gas analyzer. This ensures that the molecular beam does not come into contact with the surface between the plasma source and the residual gas analyzer. Thus, accurate and reproducible measurements of the radical concentration in the process chamber are made.

[0013] In one embodiment, the NRMS analyzer further includes a modulator to mitigate the presence of noise. The modulator chops the molecular beam, and when the beam is detected by the RGA, the modulator generates a square wave signal that can be processed using a lock-in amplifier. Since the frequency of the square wave signal is known, noise that is at different frequencies can be filtered out, leaving a pure signal with a high signal-to-noise ratio. Therefore, accurate and highly sensitive indicators can be used to inform a controller that allows for closed-loop control of the processing operation.

[0014] Referring now to Figure 1, a schematic diagram of a tool 100 according to one embodiment is shown. In one embodiment, the tool 100 comprises a processing chamber 105. The processing chamber 105 may be a plasma chamber or a sub-atmospheric chamber. In one embodiment, the processing tool 105 is suitable for etching operations, deposition operations, chamber cleaning operations, plasma processing operations, or other types of operations commonly seen in semiconductor manufacturing equipment. In one embodiment, one or more substrates (e.g., wafers) (not shown) may be placed inside the processing tool 105. In one embodiment, the processing chamber 105 may be maintained at a pressure suitable for the desired operation. In certain embodiments, the pressure may be between about 1 Torr and about 200 Torr.

[0015] In one embodiment, the tool 100 may further comprise an NRMS analyzer 120 fluidly coupled to a processing chamber 105. For example, a valve 107 may be provided along a tube between the processing chamber 105 and the NRMS analyzer 120. In one embodiment, the valve 107 is of a type that allows an unobstructed line of sight 170 between the processing chamber 105 and the NRMS analyzer 120. For example, the valve 107 may be a shut-off gate valve. A shut-off gate valve may allow a binary operating state; that is, the valve 107 may be open (i.e., 1) or closed (i.e., 0). When the valve 107 is open, the line of sight 170 is unobstructed and a pure molecular beam from the processing chamber 105 can pass through and enter the NRMS analyzer 120. The use of such a valve 107 is separate from the processing chambers in which general valves are used. Generally, a needle valve would be used. However, a needle valve results in an obstruction of the line of sight 170. Therefore, when the needle valve is used, the pure molecular beam may not exit the processing chamber 105.

[0016] In one embodiment, the NRMS analyzer 120 may include a first chamber 125. The first chamber is fluidly coupled to a valve 107 by a tube. In one embodiment, an orifice 108 may be provided between the valve 107 and the first chamber 125. The orifice 108 may have a diameter of about 1 mm or less. However, it should be understood that the line of sight 170 passes through the orifice 108 without obstruction. In one embodiment, the first chamber 125 may be at a lower pressure than the processing chamber 105. For example, a turbopump 123 may provide the first chamber 125 with a desired pressure. In one embodiment, the pressure in the first chamber 125 may be between about 1 mTorr and about 100 mTorr. In a particular embodiment, the pressure in the first chamber 125 may be about 10 mTorr. A valve 124 may be provided between the first chamber 125 and the turbopump 123. The turbopump 123 can be fluidically coupled to the forepump 113.

[0017] Despite being fluidically coupled to each other, a pressure difference between the processing chamber 105 and the first chamber 125 can be maintained. This pressure difference can be maintained by the use of a small orifice 108 and a turbopump 123. That is, the turbopump 123 is not the same pump used for the processing chamber 105. Such a setup (i.e., each chamber having its own pump) is sometimes referred to herein as a differential pumping configuration. One embodiment involves the use of a multistage pump with different stages connected to two differentially pumped chambers, thus allowing for different pressures in each chamber. Radical species flow from the processing chamber 150 to the first chamber 125 along an unobstructed line of sight 170, but the lower pressure in the subsequent chamber reduces the background of the target species and thus effectively increases the signal-to-noise ratio.

[0018] In one embodiment, the first chamber 125 may be called a modulation chamber because the first chamber 125 may include a modulator 127. The modulator 127 may be a device that enables the molecular beam to be modulated. For example, the modulator 127 may include a rotating disk with an aperture at the correct position, allowing the molecular beam to pass through for a short time, while the modulator 127 blocks the molecular beam for the rest of the time. Thus, the molecular beam is switched on and off by the modulator 127.

[0019] Referring now to Figure 2, a diagram of a modulator according to one embodiment is shown. As shown, the modulator 227 comprises an aperture 228. When the modulator 227 is spun (as indicated by the arrow), the aperture 228 aligns with the orifice 208. When the aperture 228 is aligned with the orifice 208, the signal is on, and when the aperture is not aligned with the orifice 208, the signal is off. The rotation speed can be selected to give the signal a desired frequency. For example, the frequency can be selected to be between about 10 Hz and about 1000 Hz. In a particular embodiment, the frequency may be about 40 Hz. In the illustrated embodiment, a single aperture 228 is shown. However, it should be noted that multiple apertures 228 may be used to increase the signal frequency without the need to increase the rotation speed of the modulator 227.

[0020] Referring again to Figure 1, the second chamber 130 is fluidically coupled to the first chamber 125. The second chamber 130 may be a residual gas analyzer (RGA), a mass spectrometer, etc. The second chamber 130 is maintained at a pressure lower than the pressure in the first chamber 125. In one embodiment, the second chamber 130 may have a pressure between about 0.1 μTorr and about 100 μTorr. In a particular embodiment, the pressure in the second chamber 130 may be about 1 μTorr. The pressure in the second chamber 130 may be maintained by a turbopump 133. As described above, the use of separate turbopumps 133 between the first chamber 125 and the second chamber 130 is sometimes called differential exhaust.

[0021] In one embodiment, the second chamber 130 is fluidly coupled to the first chamber 125 through an orifice 109 along a tube between the two chambers. The orifice 109 can have a diameter of about 1 mm or less. Despite the small diameter, the line of sight 170 extends from the first chamber 125 to the second chamber 130. That is, the line of sight 170 is unobstructed from the processing chamber 105, through the first chamber 125, and into the second chamber 130. Thus, a molecular beam of radical species can pass from the processing chamber 105 to the second chamber 130 (i.e., the mass spectrometer or RGA) without contacting the surface. The purity of the molecular beam results in a concentration indication in the second chamber 125 that is essentially equivalent to the concentration of radicals in the processing chamber 105.

[0022] Next, referring to FIG. 3A, a schematic view of a second chamber 330 according to one embodiment is shown. The second chamber 330 can include an ion source and a mass filter. The mass filter can be adjusted to filter out all ion species except those having a particular atomic or molecular mass-to-charge ratio. As shown, the line of sight 370 extends through the RGA component of the second chamber. Although a particular RGA architecture is shown in FIG. 3A, it should be understood that any suitable RGA or mass spectrometer configuration can be used with the NRMS analyzer 120.

[0023] In a particular embodiment shown in FIG. 3A, a quadrupole mass spectrometer is shown. That is, a pair of rods 335 is shown in the cross-sectional view illustrated. The third and fourth rods 335 are outside the plane of FIG. 3A. In one embodiment, a filament 331 is provided at the first end of the RGA device. The filament 331 can be a tungsten filament or any other suitable material for generating electrons. In one embodiment, the filament 331 is held at a potential of about -70V. Electrons enter the optical path 370 through an aperture 332 through a grounded component 334 of the ion source. The electrons strike reactive species along the line of sight 370 and ionize them. Negative ion optics and extraction plate 336 focus the ionized reactive species before they enter the mass filter portion of the RGA device.

[0024] The mass filter can include a set of four rods 335. The rods 335 can be supplied with an AC voltage. For example, the AC voltage can be about 2,000V. In one embodiment, a DC voltage can be supplied via the AC voltage. Control of the DC voltage enables selection of the mass that will propagate to the sensor 337 through the four rods 335. In a particular embodiment, the DC voltage can be between about 0V and about 100V. The sensor 337 senses the number of radical species that have successfully passed through the RGA device. In one embodiment, the sensor 337 can include an electron multiplier tube to increase the sensitivity of the device. In other embodiments, the sensor 337 can include a Faraday cup.

[0025] Referring now to FIG. 3B, a cross-sectional view of an RGA device according to an additional embodiment. The RGA in FIG. 3B utilizes cross-beam ionization. As indicated by the axis, neutrals along the molecular beam 370 travel from left to right. Electrons from the filament 331 propagate in the plane of FIG. 3B. Ions resulting from the collision of electrons with neutral species then propagate downward toward the mass filter portion and the sensor 337. That is, the sensor 337 need not be along the molecular beam 370 in some embodiments.

[0026] Referring again to Figure 1, signal 180 is provided from the NRMS analyzer 120 to the computer 185. As shown in the figure, signal 180 is a modulated signal (e.g., a square wave). The modulated signal 180 is provided as a result of the modulator 127. As will be described in more detail below, the modulated signal 180 may be used in conjunction with signal processing operations to provide a high signal-to-noise ratio. In one embodiment, the computer 185 may be any computing device capable of receiving the modulated signal 180 as input. In such an embodiment, the computer 185 may analyze the modulated signal 180 to determine the concentration of radical species in the processing chamber 105. In a particular embodiment, the computer 185 may be a controller. When the radical concentration is far from a desired setpoint, the controller may be configured to change one or more processing parameters of the processing chamber 105 (e.g., gas flow rate, voltage, frequency, or any other controllable parameter) to bring the radical concentration back to the desired setpoint. In this way, the NRMS analyzer 120 enables closed-loop control of the processing environment.

[0027] Referring next to Figure 4, a process flow of a method for processing a signal acquired by an NRMS analyzer 120 according to one embodiment is shown. As shown, a signal 452 is generated by a high-gain electron multiplier tube 451 at the end of a second chamber 430 (e.g., an RGA or mass spectrometer). As shown, signal 452 is a modulated signal (e.g., a square wave). Since the modulation frequency of modulator 127 is known, the modulator signal 454 can be fed to a lock-in amplifier 453. The lock-in amplifier essentially filters out all signals that are not at the modulation frequency, leaving a high signal-to-noise ratio signal. A fast Fourier transform (FFT) is then taken to give magnitude and phase, which can be fed to a digitizer 455. The resulting signal is then fed to a computer 456. The computer 456 can be used as a controller to give closed-loop control of the processing operation in the processing chamber. In one embodiment, the square wave signal from the RGA and the control signal from the modulator may first be digitized, and the digital information may then be processed to numerically obtain FFT values ​​for magnitude and phase, thereby replacing the hardware of the lock-in detector with software employing a Fourier transform algorithm.

[0028] It should be understood that closed-loop control refers to the use of quantitative measurements as feedback signals to a controller to modify processing conditions in an ongoing process. For example, in the case of measuring radical species, the concentration of radical species may be measured, and the measured value may be compared to a setpoint value. When the measured value is below the setpoint value, processing parameters may be changed to increase the radical species generation rate and output concentration; when the measured value is above the setpoint value, processing parameters may be changed to decrease the radical species concentration. Thus, a more stable and regenerative process can be implemented.

[0029] Referring now to Figure 5, a process flow diagram is shown illustrating a process 590 for processing a substrate in a processing chamber using closed-loop control according to one embodiment. In one embodiment, the processing chamber may be used for any process that utilizes radical species. In some embodiments, process 590 is an etching operation, a deposition operation, a chamber cleaning operation, a plasma processing operation, or other types of operation commonly seen in semiconductor manufacturing equipment. In certain embodiments, process 590 is a process that utilizes radical species to implement the process. For example, radical fluorine may be used in an etching or chamber cleaning process.

[0030] In one embodiment, process 590 may begin with operation 591, which includes forming radical species in a processing chamber. In one embodiment, radical species may be formed by a plasma process. A controller may be used to control the plasma source, source gas flow rate, pressure, etc., to give a desired radical species concentration. In a particular embodiment, the radical species is atomic fluorine.

[0031] In one embodiment, process 590 may continue with operation 592, which includes measuring the radical species concentration in the processing chamber. In one embodiment, the radical species concentration may be detected by an NRMS analyzer. For example, the NRMS analyzer may be fluidically coupled to the processing chamber. The NRMS analyzer may be substantially similar to the NRMS analyzer 120 described in more detail above. For example, the NRMS analyzer may comprise a first chamber for modulation and a second chamber for mass spectrometry (e.g., a quadrupole mass spectrometer). The NRMS analyzer may be coupled to the processing chamber by a shut-off gate valve. When operation 591 is implemented, the shut-off gate valve is opened. The molecular beam is then allowed to propagate from the processing chamber to the second chamber in an unhindered manner. The NRMS analyzer may provide a controller with a measure of the radical species concentration. For example, in some embodiments, a process similar to the process shown in Figure 4 may be used.

[0032] In one embodiment, process 590 may continue with operation 593, which includes comparing the measured radical species concentration to the setpoint concentration. When the measured radical species concentration is substantially equal to the setpoint concentration, as indicated by branch 594, the control parameters are maintained and the process continues. Branch 594 may continue by returning to operation 592 to make additional measurements, or the process may terminate as indicated by branch 595. When the measured radical species concentration is substantially above or below the setpoint concentration, branch 596 is taken. Based on branch 596, the controller may adjust one or more of the processing parameters to bring the radical species concentration back towards the setpoint concentration, as indicated by box 597. The process may then continue by returning to operation 592, making additional measurements of the radical species concentration, which are compared to the setpoint in operation 593.

[0033] In some embodiments, process 590 may be used as part of a machine learning (ML) and / or artificial intelligence (AI) algorithm used to control the processing of one or more substrates in a processing tool and / or the processing of substrates in multiple different processing chambers. For example, a controller may use the ML or AI process to return the radical species concentration to a setpoint. Furthermore, the data collected by process 590 may be stored for use as training or learning data for the ML or AI algorithm.

[0034] Figure 5 shows a schematic representation of a machine in an exemplary form of computer system 500, in which a set of instructions can be executed to cause the machine to perform one or more of the methodologies described herein. In alternative embodiments, the machine may be connected to (e.g., networked with) other machines in a local area network (LAN), intranet, extranet, or internet. The machine may operate as a server machine or a client machine in a client-server network environment, or as a peer machine in a peer-to-peer (or distributed) network environment. The machine may be a personal computer (PC), tablet PC, set-top box (STB), personal digital assistant (PDA), cellular telephone, web appliance, server, network router, switch or bridge, or any machine capable of executing a set of instructions (sequential or otherwise) specifying the actions to be taken by that machine. Furthermore, although only a single machine is shown, the term “machine” shall also be interpreted to include any set of machines (e.g., computers) that individually or collectively execute a set of instructions (or sets of instructions) to perform one or more of the methodologies described herein.

[0035] An exemplary computer system 500 includes a processor 502 communicating with each other via a bus 530, main memory 504 (e.g., read-only memory (ROM), flash memory, dynamic random access memory (DRAM) such as synchronous DRAM (SDRAM) or Rambus DRAM (RDRAM), static memory 506 (e.g., flash memory, static random access memory (SRAM), MRAM), and secondary memory 518 (e.g., a data storage device).

[0036] The processor 502 represents one or more general-purpose processing devices, such as a microprocessor or a central processing unit. More specifically, the processor 502 may be a composite instruction set computing (CISC) microprocessor, a reduced instruction set computing (RISC) microprocessor, a very long instruction word (VLIW) microprocessor, a processor implementing another instruction set, or a processor implementing a combination of instruction sets. The processor 502 may also be one or more dedicated processing devices, such as an application-specific integrated circuit (ASIC), a field-programmable gate array (FPGA), a digital signal processor (DSP), or a network processor. The processor 502 is configured to execute processing logic 526 for performing the operations described herein.

[0037] The computer system 500 may further include a network interface device 508. The computer system 500 may also include a video display unit 510 (e.g., a liquid crystal display (LCD), a light-emitting diode display (LED), or a cathode ray tube (CRT)), an alphanumeric input device 512 (e.g., a keyboard), a cursor control device 514 (e.g., a mouse), and a signal generation device 516 (e.g., a speaker).

[0038] The secondary memory 518 may include a machine-accessible storage medium (or more specifically, a computer-readable storage medium) 532 storing one or more sets of instructions (e.g., software 522) that embody one or more of the methodologies or functions described herein. The software 522 may also reside entirely or at least partially in the main memory 504 and / or the processor 502 while the computer system 500 is executing the software 522, the main memory 504 and the processor 502 also constitute the machine-readable storage medium. The software 522 may further be transmitted or received over the network 520 via the network interface device 508.

[0039] Although the machine-accessible storage medium 532 is shown to be a single medium in exemplary embodiments, the term “machine-readable storage medium” shall be construed to include a single or multiple mediums that store one or more sets of instructions (e.g., a centralized or distributed database, and / or associated caches and servers). The term “machine-readable storage medium” shall also be construed to include any medium capable of storing or encoding a set of instructions for machine execution, causing a machine to perform one or more of the methodologies of this disclosure. The term “machine-readable storage medium” shall therefore be construed to include, but are not limited to, solid memory and optical and magnetic media.

[0040] According to one embodiment of the present disclosure, a machine-accessible storage medium stores instructions that cause a data processing system to perform a closed-loop control method of radical concentration in a processing operation using an NRMS analyzer.

[0041] Therefore, a method for measuring gas concentration has been disclosed.

Claims

1. Processing chamber and A neutral radical mass spectrometry (NRMS) analyzer is fluidically coupled to the processing chamber and configured to measure the concentration of radical species in the plasma started in the processing chamber. A controller that receives signals from the NRMS analyzer, A processing tool comprising the NRMS analyzer, A first chamber fluidly coupled to the processing chamber by a shut-off gate valve, wherein the first chamber is equipped with a modulator, A second chamber is fluidly coupled to the first chamber, the second chamber being a quadrupole mass spectrometer, the quadrupole mass spectrometer being configured to produce cross-beam ionization, and an unobstructed line of sight passing linearly from the processing chamber through the first chamber to the second chamber. Equipped with, The aforementioned controller, The measured concentration of the radical species in the plasma is compared with the setpoint concentration of the radical species. To return the measured concentration of the radical species to the setpoint concentration of the radical species, one or more plasma parameters are adjusted. It is configured to perform, A processing tool in which one or more plasma parameters are adjusted using parameters selected from voltage or frequency.

2. The processing tool according to claim 1, wherein the first chamber is configured to have a first pressure lower than the pressure of the processing chamber, and the second chamber is configured to have a second pressure lower than the first pressure.

3. The processing tool according to claim 2, wherein differential exhaust is used to produce the first pressure and the second pressure.

4. The processing tool according to claim 2, wherein the first pressure is between approximately 1 mTorr and approximately 100 mTorr, and the second pressure is between approximately 0.1 μTorr and approximately 100 μTorr.

5. The processing tool according to claim 1, wherein the modulator is a disk having one or more apertures, and the disk is configured to rotate to produce a desired modulation frequency.

6. The processing tool according to claim 5, wherein the modulation frequency is between approximately 10 Hz and approximately 1000 Hz.

7. The processing tool according to claim 1, wherein the second chamber further comprises a sensor.

8. The processing tool according to claim 7, wherein the sensor is an electron multiplier tube or a Faraday cup.

9. A method for processing a substrate, Starting the plasma in a processing chamber containing a substrate, The concentration of radical species in the plasma is measured using a neutral radical mass spectrometry (NRMS) analyzer fluidly coupled to the processing chamber, The measured concentration of the radical species in the plasma is compared with the setpoint concentration of the radical species. To return the measured concentration of the radical species to the setpoint concentration of the radical species, one or more plasma parameters are adjusted by the controller. Includes, The aforementioned neutral radical mass spectrometry (NRMS) analyzer, A first chamber fluidly coupled to the processing chamber by a shut-off gate valve, wherein the first chamber is equipped with a modulator, A second chamber is fluidly coupled to the first chamber, wherein the second chamber is a quadrupole mass spectrometer, and the quadrupole mass spectrometer is configured to produce cross-beam ionization, and an unobstructed line of sight runs linearly from the processing chamber through the first chamber to the second chamber, Equipped with, A method for adjusting one or more plasma parameters, which is performed using a parameter selected from voltage or frequency.

10. The method according to claim 9, wherein a signal sensed and modulated by a sensor provided in the second chamber is supplied to a lock-in amplifier to reduce noise.

11. The first pump is fluidly coupled to the first chamber. The processing tool according to claim 1, wherein a second pump is fluidly coupled to the second chamber.

12. The processing tool according to claim 1, wherein the NRMS analyzer is configured to provide closed-loop control of the concentration of the radical species in the processing chamber.

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