Sensor for measuring free radicals

Abstract

A sensor device includes a quartz crystal microbalance (QCM) and a coating on at least a portion of a surface of the QCM, where the coating selectively reacts with free radicals of a target gas without reacting with stable molecules of the target gas. The QCM is configured such that the resonance of the QCM varies in response to the reaction of the free radicals of the target gas with the coating, wherein the change in the resonance frequency of the QCM is related to the amount of free radicals of the target gas that have reacted with the coating.

Description

Technical Field

[0001] The present disclosure relates to gas measurement, and more particularly to the measurement of free radicals and / or ions in a gas stream. Background Art

[0002] Many processes, such as those for forming semiconductors, photovoltaic devices, displays, etc., use one or more gases to deposit layers, etch layers, clean substrates, etc. For some processes, plasma is formed and used during the deposition, etching, cleaning, etc. processes. Traditionally, flow sensors (such as mass flow controllers) are used to detect the amount of gas flowing. However, current sensors cannot measure specific subspecies of a gas, such as only the amount of free radicals in a gas, or only the amount of ions in a gas.

[0003] In semiconductor processing, free radical species are often used in various processing operations in the chamber. For example, free radical species such as atomic fluorine can be used in etching or chamber cleaning processes. Free radical species can be formed by various processes. One process for generating free radicals is to use plasma. For example, a fluorine-containing gas is flowed into the chamber, and the plasma decomposes the compound into elemental fluorine. Free radical species are highly chemically reactive.

[0004] Process control of free radical species is difficult. In particular, it is currently impossible to effectively measure the concentration of free radical species in a processing chamber. This is due in part to the highly reactive nature of free radical species. Whenever a free radical species contacts any surface or other compound, the free radical species reacts. Even if a surface does not react with free radicals, the surface can still serve as a site for free radicals to recombine with each other, thereby converting the species into other useless compounds. Therefore, existing mass spectrometry tools cannot measure the concentration of free radical species. Without the ability to quantitatively measure the concentration of free radical species, effective process control, such as dead loop control, is not possible in existing semiconductor manufacturing tools. Summary of the invention

[0005] The following is a simplified summary of the disclosure in order to provide a basic understanding of some aspects of the disclosure. The present summary is not a comprehensive overview of the contents of the disclosure. The intent of the present summary is neither to identify the key or critical elements of the disclosure nor to delineate any scope of a particular implementation of the disclosure or any scope of the claims. The sole purpose of the present summary is to present some concepts of the disclosure in a simplified form as a prelude to a more detailed description presented later.

[0006] In one aspect of the disclosure, a sensor device includes a quartz crystal microbalance (QCM) and a coating on at least a portion of a surface of the QCM, wherein the coating selectively reacts with free radicals of a target gas and does not react with stable molecules of the target gas. The QCM is configured such that a resonant frequency of the QCM changes in response to a reaction of free radicals of the target gas with the coating, and wherein the change in the resonant frequency of the QCM is related to an amount of free radicals of the target gas that have reacted with the coating.

[0007] In one aspect of the present disclosure, a manufacturing system includes a plasma source for generating plasma, a processing chamber connected to the plasma source via one or more delivery lines, and a sensor device connected to at least one of the plasma source, the processing chamber, or the one or more delivery lines. The sensor device includes a quartz crystal microbalance (QCM) including a coating that selectively reacts with free radicals of a target gas and does not react with stable molecules of the target gas to measure the amount of free radicals of the target gas.

[0008] In one aspect of the disclosure, a method includes receiving a gas stream comprising one or more gases, the one or more gases comprising a first plurality of stable molecules of a target gas and a second plurality of free radicals of the target gas. The method also includes measuring the second plurality of free radicals of the target gas without measuring the first plurality of stable molecules of the target gas using a quartz crystal microbalance (QCM), the QCM comprising a coating on at least one surface that reacts with the second plurality of free radicals of the target gas but does not react with the first plurality of stable molecules of the target gas. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] The present disclosure is illustrated by way of example and not limitation in the figures of the accompanying drawings.

[0010] Figure 1 is a cross-sectional side view of a substrate processing system including a radical sensor according to some embodiments.

[0011] Figure 2A is a cross-sectional side view of a free radical sensor according to some embodiments.

[0012] Figure 2B According to some embodiments Figure 2A Rear view of the free radical sensor.

[0013] Figure 2C According to some embodiments Figure 2A Front view of the free radical sensor.

[0014] Figure 2DAccording to some embodiments, after adding a charged grating or grid Figure 2A Cross-sectional side view of the free radical sensor.

[0015] Figure 2E An equivalent circuit of a piezoelectric resonator according to some embodiments is shown.

[0016] Figure 2F An exploded view of one example of a free radical sensor included in a sensor holder is shown in accordance with some embodiments.

[0017] Figure 2G An example sensor holder for a free radical sensor is shown in accordance with some embodiments.

[0018] Figure 2H An example sensor holder for a free radical sensor is shown in accordance with some embodiments.

[0019] Figure 3 is a flow chart of one embodiment of a method for making a free radical sensor.

[0020] Figure 4 is a flow chart of one embodiment of a method of controlling a plasma source using a radical sensor. DETAILED DESCRIPTION

[0021] Embodiments of the present disclosure relate to a novel sensor that can detect molecules and / or atoms of a particular species, such as free radicals and / or ions of a particular gas. Conventional gas sensors (e.g., such as those in mass flow controllers) measure the total amount of gas and cannot distinguish molecules and / or atoms of a particular species of gas. For example, a mass flow controller can measure the total gas flow, but cannot measure the amount of any particular species of gas or the amount of a particular molecular species of a particular species of gas. The embodiments discussed herein provide a sensor device that can detect the amount and / or concentration of a particular molecular species of a particular gas. For example, the sensor device discussed in the embodiments herein can be designed to measure the amount of fluorine radicals, or the amount of hydrogen radicals, or the amount of nitrogen radicals, which have not been detectable to date without the use of expensive optical equipment such as spectrometer equipment.

[0022] Embodiments include sensor devices that use a specialized coating on the surface of a piezoelectric material that oscillates at a measurable resonant frequency. The coating acts as a filter to filter out all molecules except free radicals of a target gas species. An example of such a piezoelectric material that can be used is quartz. For example, embodiments include a quartz crystal microbalance (QCM) having such a specialized coating on one surface of the QCM. The specialized coating is designed for a specific application and is reactive only to selected molecular gas species used in those specific applications. Examples of applications for designable sensor devices include etching operations, plasma-assisted deposition processes (e.g., plasma-assisted atomic layer deposition), and the like. The coating on the piezoelectric material changes mass based on the coating's reaction to selected molecular gas species (e.g., to free radicals of a specific molecule). Changes in the coating mass cause the resonant frequency of the piezoelectric material to change. This change in resonant frequency is measurable and can be used to determine the number of molecular species that react with the coating. Therefore, the sensor device can directly measure specific molecular species of a specific gas (e.g., fluorine free radicals, hydrogen free radicals, etc.). This direct measurement of free radicals enables a plasma source to perform dead-loop control.

[0023] In an example, for a fluorine-based etch process, the etch rate can be closely related to the concentration of fluorine radicals. However, the concentration of fluorine radicals has not been directly detectable to date, so engineers would guess the concentration of fluorine radicals based on other known values, such as known plasma power, known gas flow rate, etc. By using a sensor device as described herein, the amount of fluorine radicals flowing can be directly measured, and the measurement can be used to finely control the amount of radicals output by a plasma source such as a remote plasma source (RPS).

[0024] Without the ability to quantitatively measure the concentration of free radical species, it is impossible to perform dead-loop control on the processing environment. Dead-loop control refers to using quantitative measurements as feedback signals to the controller to modify the processing conditions in the ongoing process. For example, in the case of measuring free radical species, the concentration of free radical species can be measured, and the measured value can be compared with the set value. When the measured value is lower than the set value, the processing parameters can be changed to increase the generation rate and output concentration of free radical species, or when the measured value is higher than the set value, the processing parameters can be changed to reduce the concentration of free radical species. Therefore, a more stable and reproducible process can be achieved in an embodiment. Therefore, the embodiments disclosed herein include a free radical sensor, the free radical sensor includes a piezoelectric oscillator (e.g., QCM), the surface of the piezoelectric oscillator is coated with a film, the film is reactive to the target free radical species of the target gas or molecule, but is not reactive to the stable molecules of the gas or molecule or the free radicals or stable species of other gases or molecules flowing with the target gas or molecule. The free radical sensor can be used for dead-loop control of a plasma source.

[0025] Figure 1 1 is a cross-sectional view of a manufacturing system 100 for performing a plasma-based process in an embodiment. The manufacturing system may include a processing chamber 101 coupled to a plasma source 158 via one or more gas delivery lines 133. The processing chamber 101 may be, for example, a plasma etching reactor, a deposition chamber, or the like. The processing chamber may be suitable for etching operations, deposition operations, chamber cleaning operations, plasma processing operations, or any other type of operation typical of a semiconductor manufacturing facility. In one embodiment, one or more substrates (e.g., wafers) 144 may be disposed within the processing chamber 101. In one embodiment, the processing chamber 101 may be maintained at a pressure suitable for the target operation. In a particular embodiment, the pressure may be between about less than one torr and about 200 torr.

[0026] The processing chamber 101 and / or the plasma source 158 can be connected to a controller 188, which can control the plasma source 158 and / or the processing of the processing chamber 101 (e.g., by controlling set points, loading recipes, etc.). A radical sensor 135 can be connected to the gas delivery line 133 to detect the concentration of radicals in the gas or plasma delivered by the plasma source 158.

[0027] In one embodiment, the manufacturing system 100 may include a radical sensor 135 that is fluidly coupled to the processing chamber 101 and / or the gas delivery line 133. For example, a valve may be disposed along a tube between the processing chamber 101 and the radical sensor 135. In one embodiment, the valve is a valve that allows an unobstructed line of sight between the processing chamber 101 and the radical sensor 135. For example, the valve may be an isolation gate valve. The isolation gate valve may allow for a binary operating state. That is, the valve may be open (i.e., 1) or closed (i.e., 0). When the valve is open, the line of sight is unobstructed. Alternatively, another type of valve, such as a needle valve, may be used.

[0028] In an embodiment, the free radical sensor 135 includes a piezoelectric substrate in a support. The piezoelectric substrate is oscillated at a resonant frequency by applying an alternating current to the piezoelectric substrate. One or more surfaces of the piezoelectric substrate are coated with a film that is reactive to a narrow range of molecular species. Specifically, the film is composed of a material that reacts to a target molecular species of a specific target gas in the gas used in the process. In one embodiment, the free radical sensor includes a QCM having at least one coated surface coated with a film that selectively reacts with free radicals of a specific gas. The free radical sensor 135 is described in more detail below with reference to the accompanying drawings in the foregoing text.

[0029] In an embodiment, the plasma source 158 is a remote plasma source (RPS) that generates plasma at a remote location and delivers the externally generated plasma to the processing chamber 101. Alternatively, the processing chamber 101 may include an integrated plasma source (not shown) that can generate plasma within the processing chamber. In either case, the radical sensor 135 can be disposed within or connected to the processing chamber 101, rather than being disposed within or connected to the gas delivery line 133 in an embodiment.

[0030] According to some embodiments, the processing chamber 101 includes a substrate support assembly 150. The substrate support assembly 150 includes a disk 166 (e.g., may include an electrostatic chuck (ESC)). The disk 166 may perform an adsorption operation, such as vacuum adsorption, electrostatic adsorption, etc. The substrate support assembly 150 may further include a base plate, a cooling plate, and / or an insulator plate (not shown).

[0031] The processing chamber 100 includes a chamber body 102 and a lid 104, which enclose an interior volume 116. The chamber body 102 can be made of aluminum, stainless steel, or other suitable materials. The chamber body 102 generally includes a sidewall 108 and a bottom 110. An outer liner 116 can be disposed adjacent to the sidewall 108, for example, to protect the chamber body 102. The outer liner 116 can be made of a plasma or halogen-containing gas resistant material and / or coated with a plasma or halogen-containing gas material. The outer liner 116 can be made of or coated with aluminum oxide. The outer liner 116 can be made of or coated with yttrium oxide, yttrium oxide alloys, oxides of the foregoing, and the like.

[0032] An exhaust port 126 can be defined in the chamber body 102 and can couple the interior volume 106 to a pump system 128. The pump system 128 can include one or more pumps, valves, lines, manifolds, tanks, etc. for evacuating and regulating the pressure of the interior volume 106.

[0033] The lid 104 can be supported on the sidewall 108 of the chamber body 102. The lid 104 can be openable to allow access to the interior volume 106. The lid 104 can provide a seal for the processing chamber 100 when closed. A plasma source 158 can be coupled to the processing chamber 100 to provide treatment, cleaning, purge, flushing, etc. gases and / or plasma to the interior volume 106 through a gas distribution assembly 130. The gas distribution assembly 130 can be integrated with the lid 104.

[0034] Examples of process gases that may be used in the process chamber 100 include halogen-containing gases, such as F2, C2F6, SF6, SiCl4, HBr, NF3, CF4, CHF3, CH2F3, Cl2, and SiF4. Other reactive gases may include O2 or N2O. Non-reactive gases may be used for flushing or as carrier gases, such as N2, He, Ar, etc. The gas distribution assembly 130 (e.g., a showerhead) may include a plurality of holes 132 located on a downstream surface of the gas distribution assembly 130. The holes 132 may direct a gas flow to a surface of the substrate 144. In some embodiments, the gas distribution assembly may include a nozzle (not shown) that extends through a retainer in the cover 104. A seal may be formed between the nozzle and the cover 104. The gas distribution assembly 130 may be made of and / or coated with a ceramic material such as silicon carbide, yttrium oxide, etc. to provide resistance to the process conditions of the process chamber 100.

[0035] The substrate support assembly 150 is disposed in the interior volume 106 of the processing chamber 100 below the gas distribution assembly 130. The substrate support assembly 150 holds the substrate 144 during processing. An inner liner (not shown) may be coated on the perimeter of the substrate support assembly 148. The inner liner 118 may share features (e.g., manufacturing materials, functions, etc.) with the outer liner 116.

[0036] The substrate support assembly 150 may include a support base 152, an insulator plate, a base plate, a cooling plate, and a disk 166. The disk 166 may include an electrode 536 for providing one or more functions. The electrode 536 may include an adsorption electrode (e.g., for securing the substrate 144 to the upper surface of the disk 166), a heating electrode, an RF electrode for plasma control, and the like.

[0037] The protective ring 146 may be disposed on a portion of the disk 166 at the outer periphery of the disk 166. The disk 166 may be coated with a protective layer (not shown). The protective layer 136 may be a ceramic such as Y2O3 (yttria or yttrium oxide), Y4Al2O9 (YAM), Al2O3 (aluminum oxide), Y3Al5O 12 (YAG), YAlO3 (YAP), quartz, SiC (silicon carbide), Si3N4 (silicon nitride), Sialon, AlN (aluminum nitride), AlON (aluminum oxynitride), TiO2 (titanium dioxide), ZrO2 (zirconium oxide), TiC (titanium carbide), ZrC (zirconium carbide), TiN (titanium nitride), TiCN (titanium carbon nitride), Y2O3 stabilized ZrO2 (YSZ), etc. The protective layer can be a ceramic composite, such as YAG, yttria-zirconium oxide solid solution, silicon carbide-silicon nitride solid solution, etc. distributed in an alumina matrix. The protective layer can be sapphire or MgAlON.

[0038] The disk 166 may also include a plurality of gas channels, such as grooves, terraces, and other features that may be formed in the upper surface of the disk 166. The gas channels may be fluidly coupled to the gas source 105. The gas from the gas source 105 may be used as a heat transfer or backside gas, may be used to control one or more lift pins of the disk 166, etc. Multiple gas sources (not shown) may be utilized. The gas channels may provide a gas flow path for a backside gas, such as He, through holes drilled in the disk 166. The backside gas may be provided to the gas channels under a controlled pressure to enhance heat transfer between the disk 166 and the substrate 144.

[0039] The disk 166 may include one or more clamping electrodes. The clamping electrodes may be controlled by a chuck power supply 182. The clamping electrodes may also be coupled to one or more RF power supplies via matching circuits for maintaining a plasma formed by process gas and / or other gases within the processing chamber 100. The RF power supplies may be capable of generating RF signals with a frequency from about 50 kilohertz (kHz) to about 3 gigahertz (GHz) and a power of up to about 10,000 watts. The heating electrodes of the disk 166 may be coupled to a heater power supply 178.

[0040] The controller 188 may control one or more parameters and / or set points of the plasma source 158 and / or the processing chamber 101. The system controller 188 may be and / or include a computing device such as a personal computer, a server computer, a programmable logic controller (PLC), a microcontroller, etc. The system controller 188 may include one or more processing devices, which may be general-purpose processing devices, such as microprocessors, central processing units, etc. More specifically, the processing device may be a complex instruction set computing (CISC) microprocessor, a reduced instruction set computing (RISC) microprocessor, a very long instruction word (VLIW) microprocessor, or a processor that implements other instruction sets or a processor that implements a combination of instruction sets. The processing device may also be one or more special-purpose processing devices, such as an application specific integrated circuit (ASIC), a field programmable gate array (FPGA), a digital signal processor (DSP), a network processor, etc. The system controller 188 may include data storage devices (e.g., one or more disk drives and / or solid-state drives), main memory, static memory, network interfaces, and / or other components. The system controller 188 may execute instructions to perform any one or more of the methods and / or embodiments described herein. The instructions may be stored on a computer-readable storage medium, which may include main memory, static memory, secondary memory, and / or a processing device (during execution of the instructions). In an embodiment, execution of the instructions by the system controller 188 causes the system controller to perform Figure 4 For example, the system controller 188 may receive measurements from the free radical sensor 135 indicating the concentration of free radicals of a particular species in the received or generated plasma, and may adjust one or more properties or settings (e.g., such as plasma power) of the plasma source 158 in response to the measured free radical concentration. The system controller 188 may also be configured to allow a human operator to input and display data, operating commands, etc.

[0041] FIG. 2A to FIG. 2D An embodiment of a sensor for detecting free radicals of a target gas species according to an embodiment of the present disclosure is shown. Figure 2Ais a cross-sectional side view of a free radical sensor according to some embodiments. Figure 2B According to some embodiments Figure 2A Rear view of the free radical sensor. Figure 2C According to some embodiments Figure 2A Front view of the free radical sensor.

[0042] In an embodiment, the free radical sensor comprises a QCM sensor base. A piece of solid material of any shape can generally oscillate at a certain resonant frequency. By increasing the mass of the vibrating unit, it generally results in a decrease in the resonant frequency of the solid material. This is the basic principle of QCM.

[0043] The QCM sensor base may comprise a thin plate of quartz crystal oscillating in a thickness-shear mode, as such a QCM sensor base has a high sensitivity to mass changes across the crystal. The piezoelectric properties of quartz crystal allow the crystal to be driven to oscillate and its resonant frequency to be measured by simple electrical means. In an embodiment, the quartz crystal is precisely cut at certain angles relative to its crystallographic axis. In an embodiment, the quartz crystal is an AT-cut quartz crystal.

[0044] like FIG. 2A to FIG. 2C As shown, the free radical sensor 200 includes a quartz crystal base 215, which may have a flat face and a convex face. The flat face may be the front face, while the convex face may be the back face. The flat face may be covered by a front electrode 230. The convex face may be covered by a rear electrode, which includes a rear electrode edge 225 connected to a rear electrode center 220 via one or more electrode bridges 227. This configuration enables an alternating current to be applied to and / or read from the electrode without compromising the ability of the quartz body 215 to oscillate freely. The sensing surface of the QCM may be the central region of the front surface (e.g., the central region of the front electrode 230). In an embodiment, the sensing surface of the QCM is coated with a film 235 that is sensitive to reactions with specific molecular species of the target gas species. The composition of the film 235 may depend on the application in which the free radical sensor 200 will be used.

[0045] In some embodiments, the film 235 is composed of a material that reacts with free radical molecular species of the target gas, but does not react with stable molecular species of the target gas. For example, the material may react with fluorine free radicals, but may not react with stable molecules containing fluorine (e.g., F2, C2F6, SF6, NF3, CHF3, CH2F3, etc.). The material may also not react with other molecules that may be included in the gas flow, whether the other molecules are free radicals or stable molecular species. For example, the material may react with fluorine free radicals, but may not react with carbon free radicals, nitrogen free radicals, hydrogen free radicals, etc. Alternatively, the material may react only with hydrogen free radicals, or may react only with carbon free radicals, or may react only with some other free radicals.

[0046] In one embodiment where the radical sensor is tuned to detect fluorine radicals, the film or coating 235 includes silicon dioxide (SiO2), tungsten or tungsten oxide (e.g., tungsten (III) oxide or W2O3) and / or an organic material (e.g., photoresist). In one embodiment where the radical sensor is tuned to detect fluorine radicals, the film or coating 235 includes a transition metal that can selectively react with fluorine radicals. In one embodiment where the radical sensor is tuned to detect hydrogen radicals, the film or coating 235 includes a polymer of carbon and hydrogen. An example of a polymer that can be used is polymethyl methacrylate (PMMA). In one embodiment where the radical sensor is tuned to detect nitrogen radicals, the film or coating 235 includes a fluorinated polymer. In an embodiment, the target radical reacts with the film 235 to form a gas that consumes some portion of the film 235. The consumption of some portion of the film 235 reduces the number of molecules in the film 235 and thereby reduces the overall mass of the film. This reduction in mass can be detected by the QCM sensor on which the film 235 has been formed.

[0047] In some embodiments, the reaction of the target radical species with the film 235 generates a solid byproduct. The solid byproduct adheres to the film 235, thereby increasing the mass of the film 235. This increase in mass can be detected by the QCM sensor on which the film 235 has been formed.

[0048] In some embodiments, the reaction of the target radical species with the membrane 235 is an absorption process, wherein the membrane 235 absorbs the target radical species. The absorption of the radical species results in an increase in the mass of the membrane 235. Once the membrane 235 is saturated with the target radical species and / or between process runs, a purge or cleaning process may be performed to desorb the radical species from the membrane 235. In one example, a QCM with a PMMA coating may be used to detect fluorine radicals. The PMMA may absorb fluorine radicals, and the mass change of the membrane caused by the absorption of fluorine radicals may be detected by a change in the resonant frequency of the QCM. The fluorine radicals may then be desorbed by flowing another gas, such as argon, through the radical sensor 200.

[0049] In one embodiment, the film 235 has a thickness of about 1-100 microns. In one embodiment, the film 235 has a thickness of about 30-40 microns. Other thicknesses, such as 10, 20, 30, 40, 50, 60, 70, 80 or 90 microns, can also be used for the film 235.

[0050] The QCM sensor base, including crystal 215 and electrodes 220, 225, 230, measures the area mass density (mass per unit area) of material uniformly covering the sensitive area on the sensing crystal. For heavy loads on crystal 215, its accuracy depends on knowledge of the shear mode acoustic impedance value of the deposited material. Larger crystals do not have higher sensitivity. The QCM is not a weighing device because it does not require gravity. It can be used in zero gravity space. In an embodiment, the thickness reading tests t f The density of the membrane can be calculated by using f Derived from the area mass density value, which is equal to t f ρ f . Entering an incorrect density value will result in an erroneous thickness reading. In embodiments, the areal mass density measurement is an absolute value. In embodiments, no calibration is required for a properly designed QCM. Temperature changes, stress, gas adsorption and desorption, surface reactions, etc. can all give erroneous signals.

[0051] QCM can be based on Eq. The mass on the sensing surface of the QCM is measured as, where m / A is the mass per unit area, p is the density of the material on the sensing surface of the QCM, t is the thickness, and n is a constant (≧0), where for a linear dependence, n is equal to 1. In an embodiment, the sensitivity of the QCM can be reduced to greater than 1 x 10 -9 g / cm 2 For density ρ = 2.7 g / cm 3 The thickness of a material such as aluminum, the QCM sensitivity is equivalent to The thickness variation expressed as mass per unit area or area mass density is more appropriate at the subatomic size.

[0052] Piezoelectric resonators can be represented by simple equivalent circuits for electrical analysis, such as Figure 2E The mechanical behavior of a quartz crystal resonator (e.g., QCM) can be represented by an electrical equivalent model as shown in the figure. This is the so-called Butterworth van Dyke (BVD) electrical model of a quartz crystal resonator. In the moving arm (upper branch) of the BVD model, it consists of three components that determine the series resonant frequency of the quartz crystal plate. R a corresponds to the energy dissipated due to the mechanical coupling between the crystal and its support. For QCM applications, the additional mass loading on the crystal surface also causes R a Increase. a Corresponds to the mass displaced during the oscillation. For QCM applications, the total mass includes the mass of the crystal, electrodes, and deposited thin film materials. C aCorresponds to the energy stored in the oscillator, which is related to the elastic properties of the quartz, electrodes and deposited materials. The parasitic capacitance C0 represents the total static capacitance of the crystal electrodes, support and connecting cables.

[0053] Figure 2D According to some embodiments, a charged grating or grid is added Figure 2A Cross-sectional side view of the free radical sensor. FIG. 2A to FIG. 2C The free radical sensor 200 shown in the embodiment measures all free radicals, regardless of charge. In some embodiments, it may be advantageous to measure only neutral free radicals or only free radicals with a specific charge. In order to measure only neutral free radicals of a specific molecular species, a charged grating or grid 252 may be arranged in front of the front surface of the free radical sensor 200. The charged grating or grid 252 may include a stack of a net (e.g., a wire mesh) with a specific charge. In one embodiment, as shown in the figure, the first grating or grid is positively charged, the second grating or grid may be grounded, and the third grating or grid may be negatively charged. The positively charged grid or grating may repel positively charged molecules or ions, and the negatively charged grid or grating may repel negatively charged molecules or ions. As a result, the only molecule that reaches the film 235 may be a neutral molecule. Among the neutral molecules that reach the film 235, only free radicals of a specific gas species may actually react with the film 235.

[0054] In one embodiment, to measure the amount of positively and / or negatively charged free radicals, a pair of free radical sensors may be used. The first free radical sensor may include a charged grating or grid, while the second free radical sensor may not include a charged grating or grid. All free radicals of the target gas species may be detected by the second free radical sensor, and only neutral free radicals of the target gas species may be detected by the first free radical sensor. The difference between the measurements of the two free radical sensors may then be calculated to determine the amount of free radicals detected by the second free radical sensor that is attributable to charged free radicals. The grating may be modified to filter out only positively charged molecules / ions or only negatively charged molecules. Thus, by combining two or more free radical sensors, each having a different grating configuration (e.g., one sensor does not include any grating), the amount of positively charged free radicals may be detected, the amount of negatively charged free radicals may be detected, and / or the amount of neutral free radicals may be detected.

[0055] Figure 2F An expanded view of an example of a free radical sensor included in a sensor holder is shown. As shown, the cover is a quartz crystal (e.g., having FIG. 2A to FIG. 2DThe form shown, with a coating that is only reactive to specific free radical species on the sensing surface) is pressed against the spring contact. The hole exposes the sensing surface, which includes the coating. Many other different configurations of sensor holders can also be used, such as Figure 2G and Figure 2H shown.

[0056] Figure 3 300 is a flow chart of one embodiment of a method 300 for manufacturing a free radical sensor. At block 305 of method 300, a coating is formed on a sensing surface of a QCM or other piezoelectric substrate. The coating may be composed of a material that selectively reacts with free radicals of a target gas species, but does not react with stable molecules of a specific gas species, and does not react with stable molecules or free radicals of other gas species to be used with the target gas species. The sensing surface may be coated by first placing a hard mask or a soft mask on the surface of the QCM or other piezoelectric substrate. The exposed areas of the surface of the QCM or other piezoelectric substrate may then be coated, and the mask may be removed. Alternatively, the coating may be formed on the entire surface, and then a portion of the coating may be selectively removed (e.g., by forming a hard mask or a soft mask on the unremoved portion of the coating, then etching the exposed portion of the coating, and finally removing the mask). At block 310, the free radical sensor is then placed in a sensor holder, such as any of those discussed above.

[0057] Figure 4 4 is a flow chart of one embodiment of a method 400 for controlling a plasma source using a free radical sensor. At block 405 of method 400, a manufacturing system flows a plasma using a first plasma source setting. The plasma can be generated by a remote plasma source (e.g., a plasma source outside a processing chamber) or a local plasma source (e.g., a plasma source inside a processing chamber). At block 410, a free radical sensor (e.g., as described above) is used to detect the concentration / amount of free radicals in the plasma. Free radicals of a target gas species can react with a coating on the free radical sensor, resulting in a change in mass on a sensing surface of the free radical sensor. The density and / or mass of the coating may be known, and changes in the mass of the coating may be detected based on changes in the resonant frequency of an oscillating piezoelectric material (e.g., a QCM) of the free radical sensor. Such changes in mass and knowledge of the mass of the material constituting the coating can be used to determine the number of free radicals that react with the coating, thereby determining the concentration and / or amount of free radicals in the gas stream.

[0058] At block 415, processing logic compares the detected concentration / amount of free radicals of the target gas species to a target concentration / amount of free radicals for the plasma. At block 420, processing logic determines whether the detected concentration / amount of free radicals of the target gas species varies from the target concentration / amount by more than a threshold amount (e.g., if the difference between the target concentration and the detected concentration exceeds a difference threshold). If the difference exceeds the difference threshold, the method continues to block 425 and adjusts one or more settings of the plasma source. For example, the plasma power may be increased to increase the amount of free radicals included in the plasma, or the plasma power may be decreased to reduce the amount of free radicals included in the plasma. If the difference is less than the difference threshold, the method may end.

[0059] Unless otherwise specifically stated, terms such as “first,” “second,” “third,” “fourth,” etc. used herein are marks used to distinguish different elements and may not have sequential meanings according to their numerical names.

[0060] The examples described herein also relate to an apparatus for performing the methods described herein. The apparatus may be specially constructed for performing the methods described herein, or it may comprise a dedicated system selectively configured to perform the methods described herein.

[0061] As used herein, the terms "over," "below," "between," "disposed on," "supporting," and "on" refer to the relative position of one material layer or component with respect to other layers or components. For example, a layer disposed over, over, or under another layer may be in direct contact with the other layer or may have one or more intervening layers. Additionally, a layer disposed between two layers may be in direct contact with the two layers or may have one or more intervening layers. Likewise, unless expressly stated otherwise, a feature disposed between two features may be in direct contact with the adjacent feature or may have one or more intervening layers.

[0062] The above description is intended to be illustrative rather than restrictive. Although specific illustrative examples and implementations are mentioned when describing the contents of the present disclosure, it will be appreciated that the contents of the present disclosure are not limited to the described examples and implementations. The scope of the present disclosure should be determined by reference to the following claims and the full scope of equivalents to which the claims are entitled.

Claims

1. A sensor device, comprising: Quartz crystal microbalance (QCM); as well as a coating on at least a portion of a surface of the QCM, wherein the coating selectively reacts with free radicals of a target gas but does not react with stable molecules of the target gas; wherein the QCM is configured such that a resonant frequency of the QCM changes in response to a reaction of the free radicals of the target gas with the coating, and wherein the change in the resonant frequency of the QCM is related to an amount of the free radicals of the target gas that have reacted with the coating. 2 . The sensor device of claim 1 , wherein the coating comprises a material that reacts with the free radicals of the target gas to form gaseous byproducts and reduce a thickness of the coating.

3. The sensor device of claim 2, wherein the target gas comprises hydrogen, and wherein the material comprises a polymer of carbon and hydrogen.

4. The sensor device of claim 3, wherein the material comprises polymethyl methacrylate (PMMA).

5. The sensor device of claim 2, wherein the target gas comprises fluorine, and wherein the material comprises silicon dioxide (SiO2), tungsten, or an oxide of tungsten.

6. The sensor device of claim 5, wherein the material comprises tungsten (III) oxide (W2O3).

7. The sensor device of claim 2, wherein the target gas comprises nitrogen, and wherein the material comprises a fluorinated polymer.

8. The sensor device of claim 1, wherein the coating comprises a material that reacts with the free radicals of the target gas to form solid byproducts and increase the thickness of the coating.

9. The sensor device of claim 1, wherein the coating includes a material that absorbs the free radicals of the target gas to increase the mass of the coating.

10. The sensor device of claim 9, wherein the radicals of the target gas are desorbed from the material in response to a second gas being applied to the sensor device.

11. The sensor device of claim 1, wherein the target gas is a component of a gas flow comprising a plurality of gases, and wherein the coating does not react with free radicals of any gas in the plurality of gases other than the free radicals of the target gas.

12. The sensor device of claim 1, wherein the coating has a thickness of 1-100 microns.

13. The sensor device of claim 1, wherein the surface of the QCM including the coating corresponds to a front electrode of the QCM.

14. The sensor device of claim 1, further comprising: A charged grid is placed on the coating, wherein the charged grid repels ions of the target gas so that only neutral radicals of the target gas reach the coating.

15. A manufacturing system comprising: a plasma source for generating plasma; a processing chamber connected to the plasma source via one or more delivery lines; as well as A sensor device connected to at least one of the plasma source, the processing chamber, or the one or more delivery lines, wherein the sensor device includes a quartz crystal microbalance (QCM) including a coating that selectively reacts with free radicals of a target gas and does not react with stable molecules of the target gas to measure an amount of the free radicals of the target gas.

16. The manufacturing system of claim 15, wherein the QCM is configured such that a resonant frequency of the QCM changes in response to a reaction of the free radicals of the target gas with the coating, and wherein the change in the resonant frequency of the QCM is related to an amount of the free radicals of the target gas that have reacted with the coating.

17. The manufacturing system of claim 15, further comprising: A controller is connected to the sensor device and the plasma source, wherein the controller adjusts one or more parameters of the plasma source in response to the amount of radicals of the target gas detected by the sensor device.

18. The manufacturing system of claim 17, wherein the controller increases plasma power in response to a determination that the amount of radicals of the target gas is below a target threshold.

19. A method comprising: receiving a gas stream comprising one or more gases, the one or more gases comprising a first plurality of stable molecules of a target gas and a second plurality of free radicals of the target gas; as well as The second plurality of free radicals of the target gas is measured without measuring the first plurality of stable molecules of the target gas using a quartz crystal microbalance (QCM), the quartz crystal microbalance (QCM) including a coating on at least one surface that reacts with the second plurality of free radicals of the target gas but does not react with the first plurality of stable molecules of the target gas.

20. The method of claim 19, wherein the one or more gases comprise a plasma output by a remote plasma source, the method further comprising: One or more parameters of the remote plasma source are adjusted to adjust a concentration of free radicals of the target gas in response to measuring the second plurality of free radicals of the target gas.

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