Partial pressure gauge assembly and associated method for detecting process contaminants using photoionization

Abstract

A photoionization sensor assembly includes a housing defining a chamber having a first end and an opposing second end, the chamber being permeable to both analyte and nonanalyte gases. A radiation source is configured to emit photons into the chamber. First, second, and third electrodes are located within the chamber. Photons ionize the analyte gas, but not enough to ionize the nonanalyte gas, and cause photoelectrons to be emitted from the third electrode. A controller is configured to receive a measurement of total pressure and electrically bias the electrodes to collect photoelectrons on the first and second electrodes at a ratio dependent on the total pressure. The controller is configured to determine the ratio of photoelectrons collected on the first and second electrodes at the total pressure and to determine the amount of current due to ionization by correcting a measured current using the determined ratio.

Description

[0001] Cross-reference to related applications

[0002] This application claims the benefit and priority of U.S. Provisional Patent Application Serial No. 63 / 332351, filed April 19, 2022, entitled “PARTIAL PRESSURE GAUGE FOR PROCESS CONTAMINANT DETECTION USING PHOTOIONIZATION”. The entire contents of the application are incorporated herein by reference. Technical Field

[0003] The disclosed invention generally relates to the field of pressure gauges, and more specifically to a partial pressure gauge for use in fault detection on semiconductor processing tools, wherein the instrument utilizes high-energy photons to selectively measure contaminants in depressurized inert gases. Background Technology

[0004] Modern integrated circuit (IC) manufacturing begins with high-purity semiconductor wafers, which then undergo hundreds of tightly controlled process steps over periods of weeks or months. After these steps, the wafer is diced into numerous smaller dies. These dies are then packaged, and the resulting devices (e.g., ICs) become the heart of many modern electronic devices. Producing high-performance semiconductor devices in high volumes requires strict control of the microenvironment surrounding the wafer. At different stages of production, partially completed devices are at risk of damage due to exposure to certain process contaminants. For example, trace oxygen exposure during the growth of the metal layers involved in the contact transistor's source or drain regions can increase the layer's resistance and degrade the device's time constant, thus reducing yield. As a second example, trace hydrocarbon contaminants remaining on the wafer surface can degrade components of semiconductor processing tools, such as photolithography optics. As a third example, precursor chemicals used in metallization during dielectric deposition may not be completely removed from the chamber or may leak back into the transfer chamber from the process chamber, where they can damage the transferred wafer. Therefore, it is important to monitor for these contaminants during the handling, storage, and processing steps of semiconductor wafers.

[0005] Typically, the microenvironment of a wafer is maintained as ultra-clean and contaminant-free, and while some processes are conducted under high vacuum (i.e., less than 1e-5 Torr), many modern semiconductor processes are carried out under much lower vacuum (1 to 100 Torr) with inert gas streams. This means that high levels of inert gases, such as nitrogen, argon, or hydrogen, are quite typical during process steps. Measuring total pressure indicates the levels of these major species, but it does not provide an indication of acceptable trace contaminants, which may be present at levels as low as one part per million of the total pressure. For example, if 1 ppm of oxygen is identified in a particular tooling step, processing of an additional wafer can be paused, and faulty components (such as chamber O-rings) can be replaced to prevent additional wafer scrap and reduce tooling downtime. Similarly, low levels of organic contaminants on the wafer surface can lead to defects in pattern transfer, resulting in edge placement errors and other yield impactors. In addition to yield impacts, hydrocarbon contaminants can also leave the wafer surface, degrading complex and expensive lithography components necessary in the latest semiconductor nodes. Replacing optics and masks damaged in this way can be extremely expensive. In the highly competitive semiconductor manufacturing industry, controlling all these yield and tooling factors is crucial. Besides contamination, there are other instances where determining trace levels of species in the background gas (e.g., to determine the etch endpoint) is important.

[0006] Total pressure can be measured using various types of instruments. These include Bayard-Alpert ionization vacuum gauges, capacitive pressure gauges, and thermocouple vacuum gauges, among others. In form, only pressure gauges measure the true pressure of a gas, as other pressure gauges provide quantity density estimates related to ionization cross-section, heat transfer, or other properties of the gas. However, approximatingly, the most common types of instruments measure the properties of the gas related to its total pressure, rather than trace components.

[0007] The problem of measuring trace components has traditionally been addressed using a special type of "ion meter" called a residual gas analyzer (RGA, such as a mass spectrometer). Like ion meters such as Bayard-Alpert instruments, RGAs use a high-energy electron beam to convert neutral species into ions. At typical electron energies of 70 to 100 eV, all gas molecules can be ionized with some probability. RGAs include mass filters that separate these ions by different mass-to-charge ratios (m / z). Correlating the m / z with the different gases present in the microenvironment and combining it with the ionization cross section and the sensor's m / z sensitivity factor can be used to estimate the partial pressures of different contaminant molecules, even if these molecules are present at low levels (i.e., 1 ppm) in most gases. Unfortunately, the use of mass spectrometry cannot be directly applied to modern semiconductor processes operating at pressures ranging from 1 to 100 Torr. This is because low pressure (<1e-4 Torr) is necessary for the operation of most RGAs. In short, in RGAs, low pressure is necessary for the operation of the filament (cathode). At pressures >1e⁻⁴ Torr, space charge begins to shield the filament from its extraction field. Furthermore, ion bombardment and oxidation can corrode the filament material. Another issue with RGA is that the low pressure is necessary to limit the effects of ion-molecule collisions in the mass analyzer and to avoid ion feedback or plasma discharge in the secondary electron amplifier. Therefore, attaching an RGA to many modern semiconductor tools or process steps requires additional suction. This increases cost, delays response time, and requires considerable space around the already crowded semiconductor reaction chamber. It is also expensive. The partial pressure of trace contaminants in these higher-pressure microenvironments remains to be measured.

[0008] For instruments designed to operate at higher pressures (approximately 1 Torr and above), additional challenges arise. In this pressure range, the mean free path of gas molecules is typically very short relative to the sensor size. Changes in total pressure can be detected quickly when the pressure front propagates at the speed of sound. However, determining the partial pressure of a minor species at a specific point in the chamber depends on the diffusion or transport of that substance to the instrument. Therefore, the partial pressure gauge must be located close to the region of interest; otherwise, the sensor will not be able to respond quickly enough to address many common problems in the semiconductor industry. In some cases where the gas flows at high rates, the instrument may completely miss leaks or contaminants because the contaminants are diluted as they reach the sensor, for example, mounted on a pre-pipeline. Furthermore, given the very limited space around semiconductor tools, it is important to design sensors that can communicate closely with the relevant area.

[0009] These are just some of the issues associated with total pressure gauges and conventional partial pressure gauges (such as RGAs). Summary of the Invention

[0010] This disclosure relates to a sensor instrumentation assembly that can be directly inserted into a process environment. An embodiment of the partial pressure ion meter includes an electrically fed flange, a plasma generation envelope, and a series of electrodes. The dielectric envelope supports the ions and the electron lens, and completely encloses the plasma generation envelope within the process environment.

[0011] The sensor disclosed herein utilizes a lamp composed of self-contained plasma to generate high-energy photons, instead of using a thermionic filament for ionization as typically employed in the RGA discussed above. The plasma shell contains a sample of krypton under depressurization, although it may also contain argon, xenon, or other gases. A high electric field generated between two electrodes is patterned onto the exterior of the plasma shell or otherwise located near it, coupling energy into the contained gas and thus generating plasma that emits light as the excited plasma species relax back to their low-energy states. The shell can be any dielectric material capable of being sealed and withstanding the pressure difference between the plasma and the process. For example, it can be a molded piece of alumina. However, most typically, the plasma source is a blown block. The lamp is constructed of glass. Ignoring the material containing the plasma source, a UV-transparent crystal is present on one side of the lamp. This crystal is composed of a material transparent to high-energy photons. In various embodiments, the crystal may be composed of magnesium fluoride, calcium fluoride, or lithium fluoride, or some other suitable material. Moreover, as is well known from conventional photoionization sensors designed to operate under high-pressure environments (e.g., atmospheric pressure), ionization can be selective. Generally, the photon energy of krypton discharge has an energy higher than the first ionization energy of most organic molecules, but insufficient to ionize nitrogen, argon, or hydrogen.

[0012] An embodiment of the gas sensor includes a gas housing inside a flange. The gas housing may be made of aluminum oxide. In one embodiment, the optical element comprises sapphire.

[0013] An embodiment of a sensor assembly for measuring the total pressure of a gas includes a housing defining a chamber having a first end and an opposing second end. The chamber is permeable to molecules of the gas surrounding the housing. A radiation source is configured to emit photons into the chamber. A first electrode is positioned toward the first end of the chamber, a second electrode is positioned within the chamber, and a third electrode is positioned toward the second end of the chamber. A controller communicates with at least the first and second electrodes. Photons emitted into the chamber cause photoelectrons to be emitted from the third electrode. The controller is configured to electrically bias the first, second, and third conductors such that the emitted photoelectrons are attracted toward and concentrated on the first and second electrodes at a ratio dependent on the total pressure of the gas, wherein the photoelectrons generate a current on the first and second electrodes. The controller is also configured to measure the current generated on the first and second electrodes, and to determine the total pressure of the gas based on the current generated on the first and second electrodes.

[0014] In one embodiment, the radiation source is positioned toward a first end of the chamber. In another embodiment, a second end of the chamber is at least partially open to the surrounding environment. In one embodiment, the third electrode comprises gold. In another embodiment, the radiation source is at least partially surrounded by a housing. In yet another embodiment, the ratio of the distance between the first and second electrodes to the distance between the second and third electrodes is approximately 8:1. In yet another embodiment, at least one of the first, second, and third electrodes comprises a grid.

[0015] An embodiment of a photoionization sensor assembly configured to measure an analyte gas in the presence of a non-analyte gas includes a housing defining a chamber having a first end and an opposing second end. The chamber is permeable to molecules of both the analyte and non-analyte gases surrounding the housing. A radiation source is configured to emit photons into the chamber. A first conductive electrode is positioned toward the first end of the chamber, a second conductive electrode is positioned within the chamber, and a third conductive electrode is positioned toward the second end of the chamber. A controller communicates with at least the first and second conductive electrodes. The emitted photons ionize at least some molecules of the analyte gas but are insufficient to ionize molecules of the non-analyte gas. The emitted photons further strike the third conductive electrode, causing photoelectrons to be emitted. The controller is configured to receive a measurement of the total pressure of the analyte and non-analyte gases and electrically bias the first, second, and third conductive electrodes such that photoelectrons are attracted to and concentrated on the first and second conductive electrodes at a ratio depending on the total pressure of the analyte and non-analyte gases. The controller is also configured to measure the current generated on the first and second conductive electrodes and determine the ratio of emitted photoelectrons concentrated on the first and second conductive electrodes under total pressure. The controller is further configured to determine the amount of current due to ionization of the analyte gas by subtracting the current caused by photoelectrons from the measured current using the determined ratio to correct the measured current.

[0016] In one embodiment, the current for calibration measurement further includes subtracting a portion of the current measured on the second conductive electrode from the current measured on the first conductive electrode. In one embodiment, the photoionization sensor assembly also includes a pressure gauge mounted on a flange and configured to measure total pressure and provide the measured total pressure to a controller. In one embodiment, a second end of the chamber is at least partially open to the surrounding environment. In one embodiment, a third conductive electrode comprises gold. In one embodiment, a radiation source is at least partially surrounded by a housing. In one embodiment, the radiation source is positioned at a first end of the chamber.

[0017] An embodiment of a method for measuring an analyte gas in the presence of a non-analyte gas includes configuring a photoionization sensor to include:

[0018] (1) A housing that defines a chamber having a first end and an opposing second end, wherein the chamber is permeable to molecules of the analyte gas and nonanalyte gas surrounding the housing;

[0019] (2) A radiation source configured to emit photons;

[0020] (3) The first conductive electrode is positioned at the first end of the chamber;

[0021] (4) A second conductive electrode, which is positioned in the chamber;

[0022] (5) A third conductive electrode, positioned toward the second end of the chamber; and

[0023] (6) A controller that communicates with at least the first conductive electrode and the second conductive electrode.

[0024] The method further includes emitting photons from a radiation source into a chamber to ionize at least some molecules of the analyte gas, wherein the emitted photons are insufficient to ionize molecules of the non-analyte gas. The photons emitted from the radiation source into the chamber further strike a third conductive electrode and cause photoelectrons to be emitted.

[0025] The controller is configured to receive a measurement of the total pressure of the analyte gas and the non-analyte gas, and electrically bias a first, second, and third conductive electrode such that photoelectrons are attracted toward and accumulate on the first and second conductive electrodes at a ratio dependent on the total pressure of the analyte gas and the non-analyte gas. The controller is also configured to measure the current generated on the first and second conductive electrodes and determine the ratio of emitted photoelectrons accumulated on the first and second conductive electrodes at the total pressure. The controller is further configured to determine the amount of current due to the ionization of the analyte gas by correcting the measured current using the determined ratio to remove the current caused by the photoelectrons.

[0026] In one embodiment, the current for calibration measurement further includes subtracting a portion of the current measured on the second conductive electrode from the current measured on the first conductive electrode. In another embodiment, the method further includes configuring a third conductive electrode to include gold. In yet another embodiment, the method further includes configuring a second end of the chamber to be at least partially open to the surrounding environment. In yet another embodiment, the method further includes configuring the third conductive electrode to include a grid. In another embodiment, the method further includes configuring a housing to at least partially surround the radiation source. In yet another embodiment, the method further includes positioning the radiation source at a first end of the chamber.

[0027] Embodiments of a method for measuring the total pressure of a gas include configuring a photoionization sensor assembly to include:

[0028] (1) A housing that defines a chamber comprising a first end and an opposing second end, wherein the chamber is permeable to molecules of a gas surrounding the housing;

[0029] (2) A radiation source configured to emit photons into the chamber;

[0030] (3) The first electrode is positioned at the first end of the chamber;

[0031] (4) A second electrode, which is positioned in the chamber;

[0032] (5) A third electrode, positioned toward the second end of the chamber; and

[0033] (6) A controller that communicates with at least the first electrode and the second electrode.

[0034] The method further includes striking a third electrode with emitted photons to induce the emission of photoelectrons, and configuring a controller to electrically bias the first, second, and third conductors such that the emitted photoelectrons are attracted toward and concentrated on the first and second electrodes at a ratio dependent on the total gas pressure, wherein the photoelectrons generate a current on the first and second electrodes. The controller is also configured to measure the current generated on the first and second electrodes and determine the total gas pressure based on the current generated on the first and second electrodes.

[0035] In one embodiment, the method further includes positioning the radiation source toward a first end of the chamber. In another embodiment, the method further includes configuring a second end of the chamber to be at least partially open to the surrounding environment. In another embodiment, the method further includes configuring a third electrode to comprise gold. In yet another embodiment, the method further includes configuring a housing to at least partially surround the radiation source. In yet another embodiment, the method further includes configuring at least one of the first, second, and third electrodes to include a grid.

[0036] Additional features and advantages of this disclosure are described in the following description of the drawings and detailed embodiments, and will become apparent from the following description of the drawings and detailed embodiments. Attached Figure Description

[0037] The invention, which has been briefly summarized above, can be described in more detail by referring to the embodiments, some of which are illustrated in the accompanying drawings. However, it should be noted that the drawings only illustrate typical embodiments of the invention and should therefore not be considered as limiting its scope, as the invention can allow for other equivalent embodiments. Therefore, for a further understanding of the nature and purpose of the invention, reference can be made to the following detailed description, which is taken in conjunction with the accompanying drawings, wherein:

[0038] Figure 1 The illustration schematically shows a cross-sectional view of an embodiment of a clustering tool used in semiconductor manufacturing.

[0039] Figure 2 The figure shows a cross-sectional view of an embodiment of a sensor instrument used to support semiconductor manufacturing tools.

[0040] Figure 3 The illustration shows a perspective view of an embodiment of the sensor instrument.

[0041] Figure 4 Illustration Figure 3 A cross-sectional view of an embodiment of the sensor instrument.

[0042] Figure 5 The illustration shows a perspective view of an embodiment of the sensor instrument.

[0043] Figure 6 illustrates an example of predicting total pressure using a regression model based on photoelectron current in a sensor instrument.

[0044] Figure 7 The illustration shows a perspective view of another embodiment of the sensor instrument.

[0045] Figure 8 The figure shows a cross-sectional view of another embodiment of the sensor instrument.

[0046] Figure 9 Illustration Figure 8 A perspective view of an embodiment.

[0047] Figure 10 This is an example of using a sensor to perform photoelectron current correction measurements on xylene pulses of various concentrations.

[0048] Figure 11 The diagram illustrates the effectiveness of the correction for photoelectron current. Detailed Implementation

[0049] The following discussion relates to various embodiments of the data connector assembly. It will be understood that the versions described herein are examples embodying certain inventive concepts as detailed herein. Therefore, other variations and modifications will be readily apparent to those skilled in the art. Furthermore, certain terms are used throughout this discussion to provide a suitable framework of reference with respect to the drawings. These terms (e.g., “upper,” “lower,” “forward,” “backward,” “inner,” “outer,” “front,” “rear,” “top,” “bottom,” “inner,” “outer,” “first,” “second,” etc.) are not intended to limit these concepts unless specifically indicated otherwise. The terms “approximately” or “about,” as used herein, may refer to a range of 80%–125% of the claimed or disclosed values. Regarding the drawings, they are intended to depict the prominent features of the data connector assembly and are not specifically provided to scale.

[0050] An embodiment of a partial pressure gauge assembly for process contaminant detection, using a photoionization sensor instrument or instrumentation assembly (“sensor”) 100 and associated components, is configured to detect the presence of hydrocarbons in a process chamber or semiconductor manufacturing assembly 10, also referred to as a manufacturing tool or cluster tool because it houses the union of chambers. In some instances, hydrocarbon contamination occurs due to incompatible components used within the manufacturing of the cluster tool 10, system leaks, or contamination that may occur on the semiconductor wafer (“wafer”) 50 itself when it is introduced into the tool 10. Reference Figure 1 The manufacturing tool 10 includes a transfer module or transfer chamber 12 and a buffer module or buffer chamber 13, configured to house wafer processing robots 14, 15 capable of handling semiconductor wafers 50. Additional process chambers 20, 22, 24, 26, 28 may be located around the transfer module 12 and the buffer module 13. In an embodiment, one or more of the additional process chambers 20, 22, 24, 26, 28 are open to the environment of the transfer / buffer chambers 12, 13, such that the internal environment of the additional process chambers 20, 22, 24, 26, 28 is enabled to move into the environment of the transfer / buffer chambers 12, 13, and / or the environment of the transfer / buffer chambers 12, 13 is enabled to move into the internal environment of the additional process chambers 20, 22, 24, 26, 28. After the wafer is removed from cassette 30, it is moved through process chambers 20, 22, 24, 26, and 28, which may be configured to receive the wafer as part of a manufacturing step and may contain various reagents, materials, or processes used during one or more manufacturing steps. Some or all of the transfer chamber 12 and the additional process chambers 20, 22, 24, 26, and 28 are maintained at a pressure below atmospheric pressure via a vacuum system, which may be separate from or integrated with the manufacturing tool 10. The manufacturing tool 10 includes a degassing chamber 26, which is configured to receive and heat the wafer 50. Heating the wafer 50 activates volatile species present on the wafer 50, such as water and hydrocarbons, thereby removing them from the wafer by evaporation prior to the manufacturing process.

[0051] The sensor instrument 100 can be mounted at one or more locations within the manufacturing tool 10. For example... Figure 1As shown, sensor instrument 100 is installed in degassing chamber 26. A key advantage of sensor instrument 100 is its ability to detect the presence of analytes such as hydrocarbons, determine the signal associated with that analyte, and use that signal to determine the partial pressure of the analyte. This partial pressure information can then be used to determine the completion or success of the degassing process, or to detect abnormally high contamination levels that may indicate upstream problems in the process (e.g., photoresist removal, cleaning processes, etc.).

[0052] exist Figure 2-5 In an embodiment of the sensor instrument 100 shown, the sensor instrument 100 has a first end 111 located outside the process or manufacturing environment and a second end 113 located inside the process environment. The sensor is mounted on a flange 112 and a sealing element 115 (e.g., a gasket or O-ring), the flange 112 being fixed against the exterior of a process chamber (not shown), the sealing element 115 providing an hermetically tight seal. A support 114 abuts against the outward-facing surface of the flange 112, and a wall 116 is coupled from the support 114 to the opposite side of the flange 112. As shown, the wall 116 is generally cylindrical in shape and defines a space 117. The support 114 is used to support at least two source electrodes 118, each located near a radiation source 130. The source electrode 118 may include a metallized portion on the surface of the radiation source 130, a conductive strip bonded to the radiation source 130, or a conductive ring soldered to a circuit board 150 as shown here, the circuit board 150 being attached to a support 114 via a board support 151. As shown, the radiation source 130 is a lamp having a first source end 131 located outside the process environment and a second source end 133 fixed inside the housing 110. The radiation source 130 surrounds a volume filled with a gas (e.g., Kr gas); however, other embodiments may use different gases. The radiation source 130 is composed of a generally transparent material that is shatter-resistant and capable of withstanding high heat and pressure variations. In embodiments, the radiation source may be made of glass (e.g., glass). It consists of or surrounds the flange 112 and the radiation source 130. The seal 122 may be located between the flange 112 and the radiation source 130 to create an airtight seal. As shown, the seal 122 is an O-ring with a compressive force applied by the support 114 to maintain the airtight seal.

[0053] A space 117 defined by wall 116 is lined with dielectric 160 to form an ionization chamber 162, which is defined at a first end by a radiation window 163 sealed to a second source end 133 of radiation source 130. The radiation window 163 is composed of a UV-transparent crystal that allows high-energy photons to enter the ionization chamber 162 from radiation source 130. In some embodiments, the radiation window 163 may be composed of magnesium fluoride, calcium fluoride, lithium fluoride, or some other suitable material. A plurality of openings 164 extend through dielectric 160 and wall 116 to allow gas from process chamber 189 to permeate or enter the ionization chamber 162. A first electrode 170 is located in the ionization chamber 162 such that the radiation window 163 is located between the second source end 133 of radiation source 130 and the first electrode 170. Figure 4 As shown in the embodiments, the first electrode 170 includes an edge or outer edge 172, wherein one or more lateral members 174 span the width of the outer edge 172 and / or form a grid-like pattern. A plurality of openings 176 are defined between the lateral members 174 and the outer edge 172 through the first electrode 170.

[0054] Still referencing Figure 4 The second electrode 180 is spaced apart from the first electrode 170 and located away from the radiation window 163. The second electrode 180 includes an edge or outer edge 182, wherein one or more lateral members 184 extend across the width of the edge 182 and / or form a grid-like pattern. The edge 182 and the one or more lateral members 184 define a plurality of openings 186 through the second electrode 180. The third electrode 190 is spaced apart from the second electrode 180 and located between the second housing end 113 and the second electrode 180. Like the first and second electrodes 17, 180, the third electrode 190 includes an edge or outer edge 192, wherein one or more lateral members 194 extend across the width of the edge 192 and / or form a grid-like pattern. The edge 192 and the one or more lateral members 194 define a plurality of openings 196 through the third electrode 190. Electrical signals and bias voltages are transmitted through the flange 112 by means of a generally 120 ( Figure 2 The feedthrough and conductors indicated are provided to the first, second, and third electrodes 170, 180, and 190, respectively.

[0055] Return to Figure 2The space between the first and second electrodes 170, 180 is larger than the space between the second and third electrodes 180, 190 because the manufacturing system 10 operates at a low total pressure. When the pressure is low, there is a need to generate more ions to improve sensitivity. In an embodiment, the ratio of the space between the first and second electrodes 170, 180 to the space between the second and third electrodes 180, 190 is 8:1. This means that a larger space is needed between the first and second electrodes 170, 180 to allow sufficient gas particles to enter the ionization chamber 162 for sufficient photoionization to occur. In embodiments used in higher pressure environments, the distance between the first and second electrodes 170, 180 can be shortened, making the ratio less than 8:1. Although several embodiments show a second electrode 180 located between the first and third electrodes 170, 190, other embodiments may not have a second electrode 180 located entirely between the first and third electrodes 170, 190.

[0056] The first, second, and third electrodes 170, 180, and 190 are conductive and may be made of steel and coated with gold. Compared to materials like stainless steel, the work function of the gold plating does not undergo a significant change when exposed to oxygen. Electrodes 170, 180, and 190 are arranged in an ionization chamber 162 such that one or more of their transverse members 174, 184, and 194 shield each other. Figure 3-5 As shown, each of electrodes 170, 180, and 190 has two lateral members 174, 184, and 194. These lateral members minimize the surface area of ​​electrodes 170, 180, and 190 to reduce background noise. In other embodiments, one or more electrodes 170, 180, and 190 may have more than two lateral members.

[0057] Now refer to Figure 2-5 The operation of the sensor section of the sensor instrument 100 is discussed. The control electronics 80 or controller is schematically displayed. Figure 5The control electronics 80 are typically housed together in a housing coupled to the sensor flange 112, although they can be positioned remotely from the sensor instrument 100 and connected to it via cables. In instances where the sensor instrument 100 is positioned, for example in environments where the temperature is too high for the control electronics 80 to survive, it would be advantageous to position the control electronics 80 in a remote location. In embodiments, the control electronics 80 may include a power supply for the radiation source 130, measurement circuitry for the current of interest, a bias supply, a data processor, a communication unit, etc. The sensor instrument 100 uses photoionization to detect the presence of an analyte in the process gas that has entered the ionization chamber 162 from the process chamber 189. The radiation source 130 (in this case, a lamp) is activated using a source electrode 118 to ignite the plasma 140 within the radiation source 130. The plasma 140 emits photons that pass through the radiation window 163 and enter the ionization chamber 162. The radiation source 130 (and therefore the plasma 140) can be adjusted or controlled using a photodiode and / or a camera to measure fluctuations in the light emitted by the plasma 140. The radiation source 130 can be fine-tuned accordingly to eliminate such fluctuations. At least some of the photons have wavelengths capable of ionizing molecules of the analyte gas, such as hydrocarbon molecules, in the ionization chamber 162. When photons collide with molecules of the analyte gas, they have sufficient energy to produce ions from the analyte gas molecules by ejecting electrons.

[0058] First, second, and third electrodes 170, 180, and 190 are biased to prescribe the flow of one or more charged particles in ionization volume 162. In this example, first electrode 170 and second electrode 180 are held virtually ground by a current-to-voltage converter (I to V), and third electrode 190 acts as a cathode held at a negative potential (typically between -80V and -300V) relative to ground. Photons are emitted by radiation source 130 and travel in parallel through radiation window 163 into ionization volume 162, where they collide with analyte gas molecules. In this embodiment, radiation source 130 is positioned towards the end of ionization volume 162. Depending on the location of ionization, sensor geometry, bias voltage, and / or background gas pressure, each collision has a probability that causes electrons to be ejected from analyte gas molecules, generating positive ions that move toward the cathode / third electrode 190, while simultaneously causing ejected electrons to move toward either first electrode 170 or second electrode 180. Some photons have wavelengths short enough to effectively ionize most organic molecules, but their energy is insufficient to ionize the background gas that may be present in the ionization chamber 162, typically nitrogen, argon, or hydrogen.

[0059] The electron flow that accumulates at the first electrode 170 and the second electrode 180 passes through the feedthrough 120 (see...). Figure 2 The current is transmitted to control electronics 80, where it is converted into voltage, amplified, and digitized. The presence of an electron flow, as detected by controller 80, is an indication that the analyte gas may be present in process chamber 189. In addition to this electron flow generated by the photoionization of analyte gas molecules, another source of electron flow can be measured by sensor instrument 100. For example, photons with sufficient energy to ionize hydrocarbons have more energy than those sufficient to eject electrons from most conductors (photoelectrons). Photoelectrons generated at the surface of third electrode 190 are accelerated and focused toward first and second electrodes 170, 180 by an electric field established by the bias of third electrode 190, thereby generating a baseline current on these electrodes and contributing any noise and drift present in this photoelectron current to the measurement signal of interest. If these photoelectron currents were constant, they could be subtracted precisely from the signal, but they are typically not constant. Therefore, reducing noise and drift in the photoelectron current improves the ability of sensor instrument 100 to measure hydrocarbons. One way to reduce absolute noise and drift is to reduce the photoelectron current overall. This can be achieved by reducing the area of ​​the third electrode 190 exposed to UV photons. By reducing the exposed area of ​​the third electrode, or the third electrode 190, which acts as a photoelectron source, the photoelectron current and the absolute noise on that current can be reduced. An embodiment of the sensor instrument 100 shown in the figure has a third electrode 190 comprising two gold wires with a diameter of 0.75 mm, stretched across the diameter of the third electrode to provide the required electric field while minimizing the photoelectron generation area as far as possible in practice.

[0060] Furthermore, the photoelectron current generated for a given photon flux and energy distribution depends on the work function of the irradiated surface. If this work function is not constant, the generated current will not be constant, even if all other variables (photon flux, area, temperature) are fixed. The work function of the conductive surface can be affected by water or oxygen, or other highly electronegative chemicals that may be present in certain wafer etching environments. For example, when a wafer can be transferred from an oxygen-rich environment to an oxygen-free environment, these effects on the signal current are relevant to the monitoring of hydrocarbon contaminants in certain semiconductor processes. The residual effects on the background photoelectron current may mask small hydrocarbon signals of interest. Figure 11This illustration shows the effect and one way to overcome it in the sensor instrument 100. Here, a square-wave pulse of 10 ppm isobutylene is injected into the nitrogen balance from 29300 seconds to 30200 seconds, while maintaining a constant total pressure. Before and after the pulse, the sensor instrument 100 is exposed to pure nitrogen, but during the pulse, the oxygen concentration, except for isobutylene, increases from zero to 1%. When comparing the signals before and after the pulse on the first and second electrodes 170, 180, a baseline shift is discernible. This baseline shift is due to a reduction in photoelectron generation that occurs during the sample pulse and continues after the sample pulse (because the sensor 100 is exposed to oxygen). The baseline recovers only very slowly afterward. This effect is attributed to the work function of the surface of the (primarily) third electrode 190. To obtain a stable baseline relative to the pulse that can measure hydrocarbons, the photoelectron portion of the signal measured on the second electrode 180 can be subtracted from the signal measured on the first electrode 170. When this portion is selected correctly, it removes the photoelectron effect from the data, such as... Figure 11 The “correction signal” is shown in the figure.

[0061] The distribution of these photoelectrons on the first and second electrodes 170, 180 is a fairly complex function of the pressure at which the sensor 100 is operating. Figure 6a shows the photoelectron currents measured on the first and second electrodes 170, 180 as a function of the pressure in nitrogen gas with the third electrode 190 biased at -80V. The shape of these curves is due to the pressure-dependent scattering of photoelectrons from the background gas. Subtracting the correct portion of the second electrode signal from the first electrode signal to obtain the “corrected” signal can be read from a plot of the pressure of interest, such as this. Once these two curves are determined for a specific electrode geometry, the pressure in the sensor 100 can be determined from these two electrode signals during a process in which the presence of hydrocarbon signals is not expected, such as before heating during wafer degassing. As an illustration, a regression model for the pressure was created for the two electrode signals in the training dataset depicted in Figure 6a. A standard machine learning algorithm based on kernel ridge regression was used to develop a model that predicts pressure based on the two currents. This model was then applied... Figure 6b The two sensor currents in the separate test dataset shown in 6b are not used to train the model. A “predicted pressure” was found for a set of random current measurements. This predicted pressure is shown on the second y-axis. An example is shown with dashed lines, where two currents measured at ~195 Torr are used to predict the pressure at ~198 Torr. In this way, sensor 100 can be used not only to measure the partial pressure of hydrocarbons but also the total pressure in the system, even when the dominant species cannot be ionized by UV photons.

[0062] Of course, if the goal is to optimize the measurement of total pressure rather than the measurement of species ionized by UV photons, it is not necessary to attempt to minimize the photoelectron generation region as is done in the disclosed sensor 100. Moreover, it may be desirable to use a light source in which the energy is sufficient to generate photoelectrons from the third electrode or cathode, but the energy is too low to ionize hydrocarbons or other gaseous species.

[0063] The calculation of the "correction signal" and "predicted pressure" can be performed by the onboard processor in the control electronics 80 or by a remote computer.

[0064] Another approach to reducing these photoelectron effects is to stabilize photoelectron generation to counteract changes in the work function. Since the presence of oxygen and / or water on some conductive surfaces has a stronger effect on their work function than on others, careful selection of the third electrode surface material can be helpful. Gold is less susceptible to this effect than stainless steel; therefore, the third electrode 190 of the sensor 100 described herein has a gold surface. This has been achieved in various ways; for example, gold wire and gold-plated stainless steel parts. The first and second electrodes 170, 180 could also be gold-plated, but these surfaces are less critical because the typical bias in the sensor helps prevent photoelectron currents from being generated on these surfaces and accumulating elsewhere.

[0065] refer to Figure 7 Another embodiment of the sensor instrument 200 is shown. This embodiment is identical to the embodiments described above, except for the addition of an overall total pressure gauge 260. In this embodiment, the sensor instrument 200 includes a sensor portion 210 and a pressure gauge portion 260. The sensor portion 210 includes a first end 211 and a second end 213. A flange 212 or other surface is provided, configured to attach to a portion of a process chamber or other support. A support 214 is located on one side of the flange 212 and is configured to support one or more electrodes (not shown) located near a radiation source 230. The one or more electrodes are not shown, but may be similar to other embodiments of electrodes discussed previously. Similar to the embodiments discussed above, a wall is coupled relative to the support 214 to the opposite side of the flange 212 and defines a space. Figure 7 As shown and as described in other embodiments, the radiation source 230 is a lamp. The radiation source 230 has a first source end 231 located externally and a second source end fixed internally. One or more feedthroughs 220 may be connected to or communicate with a power supply device or controller 80. As shown, the radiation source 230 surrounds a volume filled with a gas (e.g., Kr gas); however, other embodiments may use different gases. The radiation source 230 is composed of a generally transparent material that is shatter-resistant and capable of withstanding high heat and pressure variations. In embodiments, the radiation source 230 is made of glass (e.g., glass). )composition.

[0066] Tube 250 aerodynamically couples the sensor instrument 200, which is mounted therein, to pressure gauge 260. Pressure gauge 260 is selected to measure pressure within the sensor's expected operating range. Including pressure gauge 260 with sensor instrument 200 saves flanges on the monitored process system. The pressure inside the ionization chamber, measured by pressure gauge 260, can also be used for the aforementioned photoelectron correction. Understanding how the pressure and photoelectron current measurements on the second electrode, and how the ratio of the photoelectron currents measured on the first and second electrodes depends on pressure, allows the removal of the contribution of photoelectrons to the current measured on the first electrode, leaving a corrected analyte signal. Pressure measurements are reported to control electronics 80, where they are used, recorded, and / or transmitted to the sensor user. The wall has an internal space lined with a dielectric to define an ionization space similar to the embodiments discussed earlier. Three electrodes (not shown) are located in the ionization space. The first electrode (not shown) is located near the radiation window (not shown), followed by the second and third electrodes (not shown), and spaced apart from each other such that the second electrode (not shown) is located between the first and third electrodes (not shown). Electrodes (not shown) are configured in a manner similar to the first, second, and third electrodes 170, 180, 190 discussed previously. One or more openings (not shown) may be defined in the walls and dielectric to allow gas to enter the ionization chamber (not shown) from the process chamber. Analyte detection and pressure determination are performed in a manner similar to that described in the foregoing embodiments.

[0067] refer to Figure 8 and Figure 9Another embodiment of the sensor instrument 300 is shown and will now be described. This embodiment of the sensor instrument 300 positions the radiation source 330 entirely within the process chamber 389, allowing the sensor instrument 300 to be positioned close to the wafer 50 being processed or any other part of the manufacturing assembly 10. The sensor instrument 300 has a multi-pin vacuum feedthrough assembly 310, which includes a first side 311 located outside the process or manufacturing environment and a second side 313 located inside the process environment. The multi-pin vacuum feedthrough assembly 310 has a flange 312 fixed against the outer side 388 of the process chamber 389 and a sealing element 315 that creates a hermetically tight seal. A support member 314 is located inside the multi-pin vacuum feedthrough assembly 310. A housing wall 316 extends in a direction away from the flange 312 and includes a generally cylindrical shape defining a space. The support member 314 is used to support at least two electrodes 320, each located near the radiation source 330. As shown, the radiation source 330 is also a lamp. The radiation source 330 includes a first source end 331 and a second source end 333, the second source end 333 being fixed within the housing 316 on the process side of the flange 312. The radiation source 330 surrounds a volume filled with a gas (e.g., Kr gas); however, other embodiments may use different gases. The radiation source 330 is composed of a generally transparent material that is shatter-resistant and capable of withstanding high heat and pressure variations. In embodiments, the radiation source is made of glass (e.g., glass). The housing wall 316 is composed of or surrounded by glass. In an embodiment, the housing wall 316 serves as a sleeve that at least partially surrounds the radiation source 330 and encapsulates the electrodes driving the radiation source 330. Ideally, the housing wall 316 is made of... It is made of other similar fluoropolymers as a reasonable choice for vacuum and process compatibility and high breakdown voltage. This dielectric barrier is used to prevent source electrode discharge that may occur under certain sensor operating pressures and transient pressures that may be experienced during use. In other embodiments, the radiation source 330 is typically encapsulated, except for the radiation window 363.

[0068] The space defined by wall 316 is lined with dielectric 360 to form an ionization space or ionization chamber 362, which is defined at a first end by a radiation window 363 sealed to a second source end 333 of radiation source 330. Multiple openings can pass through dielectric 360 and wall 316 to allow gas to enter the ionization chamber 362 from the process chamber. The opposite end of the ionization chamber 362 also opens to process chamber 389, as in the aforementioned embodiments of sensor instruments 100, 200. A first electrode 370 is located in the ionization chamber 362 such that the radiation window 363 is located between the second source end 333 of radiation source 330 and the first electrode 370. In the illustrated embodiment, a second electrode 380 is located in the ionization space 362, spaced apart from the first electrode 370, such that the first electrode 370 is generally located between the radiation window 363 and the second electrode 380. The third electrode 390 is positioned away from the second electrode 380 and toward the opposite end of the ionization chamber 362. The first, second, and third electrodes 370, 380, and 390 are positioned similarly to other embodiments discussed previously, and may also be constructed in a manner similar to other embodiments discussed previously. Figure 9 In the illustrated embodiment, the third electrode 390 is specifically shown and defines a series of circular openings 396 through it; however, for reasons previously explained, the third electrode 390 may be configured as in the previously described embodiments. Detection of the analyte gas molecules and determination of the pressure are performed in a manner similar to that described in the foregoing embodiments. The electrical connection from the sensor to the control electronics 80 is made via pins in the feedthrough assembly 310.

[0069] While the invention has been specifically shown and described with reference to certain exemplary embodiments, those skilled in the art will understand that various changes in detail may be made herein without departing from the spirit and scope of the invention as supported by the written description and drawings. For example, the disclosed methods and components can be used to determine the analyte quantity density or other properties of a sample in a sensor chamber. Furthermore, while exemplary embodiments are described with reference to a number of elements, it will be understood that exemplary embodiments may be practiced using fewer or more elements.

Claims

1. A sensor assembly for measuring the total pressure of a gas, comprising: a housing defining a chamber comprising a first end and an opposite second end, wherein the chamber is permeable to molecules of the gas surrounding the housing; a radiation source configured to emit photons into the chamber; a first electrode positioned towards the first end of the chamber; a second electrode positioned in the chamber; a third electrode positioned towards the second end of the chamber; and a controller in communication with at least the first and second electrodes, wherein the photons emitted into the chamber cause photoelectrons to be ejected from the third electrode; wherein the controller is configured to: electrically bias the first, second, and third electrodes such that the ejected photoelectrons are attracted towards and collect on the first and second electrodes at a rate dependent on the total pressure of the gas, wherein the photoelectrons generate a current on the first and second electrodes, measure the current generated on the first and second electrodes, and determine the total pressure of the gas based on the current generated on the first and second electrodes. the radiation source is positioned towards the first end of the chamber.

2. The sensor assembly of claim 1, wherein, the second end of the chamber is at least partially open to the ambient environment.

3. The sensor assembly of claim 1, wherein, the third electrode comprises gold.

4. The sensor assembly of claim 1, wherein, the radiation source is at least partially surrounded by the housing.

5. The sensor assembly of claim 1, wherein, a ratio of a distance between the first and second electrodes to a distance between the second and third electrodes is 8:

1.

6. The sensor assembly of claim 1, wherein, at least one of the first, second, and third electrodes comprises a grid.

7. The sensor assembly of claim 1, wherein, 8. A photoionization sensor assembly configured to measure an analyte gas in the presence of a non-analyte gas, comprising: a housing defining a chamber having a first end and an opposite second end, wherein the chamber is permeable to molecules of the analyte gas and non-analyte gas surrounding the housing; a radiation source configured to emit photons into the chamber; a first conductive electrode positioned towards the first end of the chamber; a second conductive electrode positioned in the chamber; a third conductive electrode positioned towards the second end of the chamber; and a controller in communication with at least the first and second conductive electrodes, wherein the emitted photons ionize at least some molecules of the analyte gas, wherein the emitted photons are insufficient to ionize molecules of the non-analyte gas, wherein the emitted photons impinge on the third conductive electrode causing ejection of photoelectrons, wherein the controller is configured to: receive a measurement of the total pressure of the analyte gas and the non-analyte gas, electrically bias the first, second, and third conductive electrodes such that the photoelectrons are attracted towards and collect on the first and second conductive electrodes at a rate dependent on the total pressure of the analyte gas and the non-analyte gas, measure the current generated on the first and second conductive electrodes, determine the total pressure of the analyte gas based on the current generated on the first and second conductive electrodes. ​ determining a ratio of emitted photoelectrons that collect on the first and second conductive electrodes at the total pressure, and determining an amount of current due to ionization of the analyte gas by using the determined ratio to correct the measured current to remove current caused by the photoelectrons.

9. The photoionization sensor of claim 8, wherein, The correction of the measured current further includes subtracting a portion of the current measured on the second conductive electrode from the current measured on the first conductive electrode.

10. The photoionization sensor of claim 8, further comprising a pressure gauge mounted on the flange and configured to measure total pressure and provide the measured total pressure to the controller.

11. The photoionization sensor of claim 8, wherein, The second end of the chamber is at least partially open to the ambient environment.

12. The photoionization sensor of claim 8, wherein, The third conductive electrode comprises gold.

13. The photoionization sensor of claim 8, wherein, The radiation source is at least partially enclosed by the housing.

14. The photoionization sensor of claim 8, further comprising positioning the radiation source at the first end of the chamber.

15. A method for measuring an analyte gas in the presence of a non-analyte gas, comprising: configuring a photoionization sensor to include: a housing defining a chamber having a first end and an opposite second end, wherein the chamber is permeable to molecules of the analyte gas and non-analyte gas surrounding the housing; a radiation source configured to emit photons; a first conductive electrode positioned toward the first end of the chamber; a second conductive electrode positioned in the chamber; a third conductive electrode positioned toward the second end of the chamber; and a controller in communication with at least the first and second conductive electrodes, emitting photons from the radiation source into the chamber to ionize at least some molecules of the analyte gas, wherein the emitted photons are insufficient to ionize molecules of the non-analyte gas; emitting photons from the radiation source into the chamber to impinge on the third conductive electrode and cause emission of photoelectrons, wherein the controller: receives a measurement of a total pressure of the analyte gas and the non-analyte gas, electrically biases the first, second, and third conductive electrodes such that the photoelectrons are attracted toward and collect on the first and second conductive electrodes in a ratio dependent on the total pressure of the analyte gas and the non-analyte gas, measures a current generated on the first and second conductive electrodes, determines a ratio of emitted photoelectrons that collect on the first and second conductive electrodes at the total pressure, and determines an amount of current due to ionization of the analyte gas by using the determined ratio to correct the measured current to remove current caused by the photoelectrons.

16. The method of claim 15, further comprising configuring the third conductive electrode to include gold.

17. The method of claim 15, further comprising configuring the second end of the chamber to be at least partially open to the ambient environment.

18. The method of claim 15, further comprising configuring the third conductive electrode to include a grid.

19. The method of claim 15, further comprising configuring the housing to at least partially surround the radiation source.

20. The method of claim 15, further comprising positioning the radiation source at a first end of the chamber.

21. A method of measuring a total pressure of a gas, comprising: configuring a photoionization sensor assembly to include, a housing defining a chamber including a first end and an opposite second end, wherein the chamber is permeable to molecules of the gas surrounding the housing; a radiation source configured to emit photons into the chamber; a first electrode positioned toward the first end of the chamber; a second electrode positioned in the chamber; a third electrode positioned toward the second end of the chamber; and a controller in communication with at least the first electrode and the second electrode; impinging the third electrode with the emitted photons to cause ejection of photoelectrons; and wherein the controller: electrically biases the first, second, and third electrodes such that the ejected photoelectrons are attracted toward and collect on the first and second electrodes at a rate dependent on the total pressure of the gas, wherein the photoelectrons generate a current on the first and second electrodes, measures the current generated on the first and second electrodes, and determines the total pressure of the gas based on the current generated on the first and second electrodes.

22. The method of claim 21, further comprising positioning the radiation source toward the first end of the chamber.

23. The method of claim 21, further comprising configuring the second end of the chamber to be at least partially open to an ambient environment.

24. The method of claim 21, further comprising configuring the third electrode to include gold.

25. The method of claim 21, further comprising configuring the housing to at least partially surround the radiation source.

26. The method of claim 21, further comprising configuring at least one of the first, second, and third electrodes to include a grid. ​

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