Partial pressure gauge assembly for process contaminant detection using photoionization and associated method

Abstract

A photo ionization sensor assembly includes a housing defining a chamber having a first end and an opposite second end, and the chamber is permeable to analyte gases and non-analyte gases. The radiation source is configured to emit photons into the chamber. First, second, and third electrodes are located in the chamber. The photons ionize the analyte gas, insufficient to ionize the non-analyte gas, and cause the photoelectrons to exit from the third electrode. The controller is configured to receive a measurement of the total pressure and electrically bias the electrodes to collect photoelectrons on the first and second electrons at a ratio dependent on the total pressure. The controller is configured to determine a ratio of photoelectrons gathered on the first and second electrodes at a total pressure, and to determine an amount of current due to ionization by correcting the measured current using the determined ratio.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of and priority to U.S. Provisional Patent Application Serial No. 63 / 332,351, filed on April 19, 2022, and entitled “PARTIAL PRESSURE GAUGE FOR PROCESS CONTAMINANT DETECTION USING PHOTOIONIZATION” The entire contents of said application are incorporated herein by reference. Technical Field

[0002] The disclosed invention relates generally to the field of pressure gauges, and in particular to a partial pressure gauge for use in fault detection on semiconductor processing tools, wherein the gauge utilizes high energy photons to selectively measure contaminants in a reduced pressure inert gas. Background Art

[0003] Modern integrated circuit (IC) manufacturing starts with high-purity semiconductor wafers, and then these wafers go through hundreds of strictly controlled process steps over a period of weeks or months. After the wafer completes these steps, it is cut into a large number of smaller tube cores. These tube cores are then packaged, and the resulting devices (such as ICs) become the core of many modern electronic device devices (find a home at the heart of). Producing high-performance semiconductor devices with high yields requires strict control of the microenvironment around the wafer. In different production steps, partially completed devices are more or less at risk of damage due to exposure to certain process pollutants. For example, trace oxygen exposure during the growth of the metal layer involved in the source or drain region of the contact transistor may increase the resistance of the layer and degrade the device time constant, thereby reducing yield. As a second example, trace hydrocarbon contaminants remaining on the surface of the wafer may degrade components of semiconductor processing tools (such as lithography optics). As a third example, precursor chemicals used in metallization for dielectric deposition may not be completely cleaned from the chamber, or may leak from the process chamber back into the transfer chamber where they will damage the transfer wafer. Therefore, it is important to monitor for these contaminants during the handling, storage, and processing steps of semiconductor wafers.

[0004] Typically, the microenvironment of the wafer is maintained to be ultra-clean and pollution-free, and although some processes are in high vacuum (i.e., less than 1e-5 Torr), many modern semiconductor processes are carried out in an inert gas flow at a much lower vacuum (1 to 100 Torr). This means that during the process steps, inert gases such as nitrogen, argon, or hydrogen are quite typically present at high levels. Measuring the total pressure indicates the level of these main species, but it does not provide an indication of acceptable trace contaminants, which may exist at a level of one millionth of the total pressure. For example, if a 1ppm level of oxygen is identified in a particular tool step, additional wafers can be processed and faulty components (such as chamber o-rings) can be replaced to prevent additional wafers from being scrapped and reduce tool downtime. Similarly, low levels of organic contaminants on the wafer surface may cause defects in pattern transfer, resulting in edge placement errors and other yield impactors. In addition to yield impacts, hydrocarbon contaminants may also leave the wafer surface, degrading the complex and expensive lithography components necessary in the latest semiconductor nodes. Replacing optics and masks damaged in this manner can be very expensive. In the competitive semiconductor manufacturing industry, it is important to control all of these yield and tool impacting factors. In addition to contamination, there are other instances when determining trace levels of species in the background gas (e.g., determining etch endpoint) is important.

[0005] Total pressure can be measured with several types of gauges. These include Bayard-Alpert type ionization gauges, capacitance manometers, and thermocouple gauges, among others. Formally, only manometers measure the true pressure of a gas, as the others provide number density estimates related to the ionization cross section, heat transport, or other properties of the gas. However, approximately speaking, the most common types of gauges measure properties of the gas related to the total pressure of the gas, rather than trace components.

[0006] This problem of measuring trace components is traditionally solved by 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 a certain probability. RGAs include mass filters that separate these ions by different mass-to-charge ratios (m / z). Correlating m / z with different gases present in the microenvironment and combining it with the ionization cross section and sensor m / z sensitivity factor can be used to estimate the partial pressure 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 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. In addition, ion bombardment and oxidation may corrode the filament material. Another issue with RGAs is that low pressure is necessary to limit the effects of ion-molecule collisions in mass analyzers and to avoid ion feedback or plasma discharges in secondary electron amplifiers. Therefore, in order to attach an RGA to many modern semiconductor tools or process steps, additional pumping is required. This increases cost, delays response time, and requires considerable space around the already crowded semiconductor reaction chamber. This is also expensive. There is still a need to measure the partial pressures of trace contaminants in these higher pressure microenvironments.

[0007] Additional problems exist for instruments designed to operate at higher pressures (above about 1 Torr). In this pressure range, the mean free path of the gas molecules is typically very short relative to the size of the sensor. When the pressure front propagates at the speed of sound, changes in total pressure can be detected very quickly. However, determining the partial pressure of a minor species at a specific point in the chamber depends on the diffusion or transport of that species to the instrument. Therefore, the partial pressure gauge must be located close to the area of ​​interest; otherwise, the sensor will not respond quickly enough to solve many common problems in the semiconductor industry. In certain cases where the gas is flowing at high rates, the instrument may miss a leak or contaminant completely because the contaminant is diluted by the time it reaches the sensor mounted, for example, on the foreline. In addition, given that the space around a semiconductor tool is very limited, it is important to design sensors that can communicate closely with the area of ​​interest.

[0008] These are just some of the problems associated with total pressure gauges and conventional partial pressure gauges such as RGAs. Summary of the invention

[0009] The present disclosure relates to a sensor instrument assembly that can be directly inserted into a process environment. An embodiment of a partial pressure ion gauge includes an electrical feed-through flange, a plasma generation envelope, and a series of electrodes. The dielectric housing supports ion and electron lenses and completely contains the plasma generation envelope within the process environment.

[0010] The sensor disclosed herein utilizes a lamp consisting of a self-contained plasma to generate high-energy photons, rather than using a hot cathode filament for ionization as is typically done in the RGA discussed above. The plasma enclosure contains a sample of krypton gas under reduced pressure, although it may also contain argon, xenon, or other gases. A high electric field generated between two electrodes patterned onto the exterior of the plasma enclosure or otherwise located near the enclosure couples energy into the contained gas and thereby produces a plasma that emits light as the excited plasma species relax back to their low-energy states. The enclosure may be any dielectric that can be sealed and that can withstand the pressure differential between the plasma and the process. For example, it may be a molded piece of aluminum oxide. But most commonly, the plasma source is a piece of blown Glass construction. Regardless of the material comprising the plasma source, on one face of such a lamp, there is a UV transparent crystal. Such a crystal is composed of a material that is 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 in high pressure environments (e.g., atmospheric pressure), the ionization may be selective. In general, the photon energy of a krypton discharge has an energy above the first ionization energy of most organic molecules, but is insufficient to ionize nitrogen or argon or hydrogen.

[0011] An embodiment of the gas sensor comprises the gas housing inside the flange. The gas housing may be composed of aluminum oxide. In an embodiment, the optical element comprises sapphire.

[0012] An embodiment of a sensor assembly for measuring the total pressure of a gas includes a housing defining a chamber, the chamber including a first end and an opposite 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 in the chamber and a third electrode is positioned toward the second end of the chamber. A controller communicates with at least the first electrode and the second electrode. Photons emitted into the chamber cause photoelectrons to be ejected from the third electrode. The controller is configured to electrically bias the first conductor, the second conductor, and the third conductor so that the ejected photoelectrons are attracted toward the first electrode and the second electrode at a ratio depending on the total pressure of the gas and are gathered on the first electrode and the second electrode, wherein the photoelectrons generate a current on the first electrode and the second electrode. The controller is also configured to measure the current generated on the first electrode and the second electrode, and determine the total pressure of the gas based on the current generated on the first electrode and the second electrode.

[0013] In an embodiment, the radiation source is positioned toward the first end of the chamber. In an embodiment, the second end of the chamber is at least partially open to the surrounding environment. In an embodiment, the third electrode comprises gold. In an embodiment, the radiation source is at least partially surrounded by the housing. In another embodiment, the ratio of the distance between the first electrode and the second electrode to the distance between the second electrode and the third electrode is about 8:1. In a further embodiment, at least one of the first electrode, the second electrode, and the third electrode comprises a grid.

[0014] 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 opposite second end. The chamber is permeable to molecules of the analyte gas and the non-analyte gas 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 in the chamber, and a third conductive electrode is positioned toward the second end of the chamber. A controller communicates with at least the first conductive electrode and the second conductive electrode. The emitted photons ionize at least some molecules of the analyte gas and are insufficient to ionize molecules of the non-analyte gas. The emitted photons further strike the third conductive electrode, causing the emission of photoelectrons. The controller is configured to receive a measurement of the total pressure of the analyte gas and the non-analyte gas, and electrically bias the first conductive electrode, the second conductive electrode, and the third conductive electrode so that the photoelectrons are attracted toward and gathered on the first conductive electrode and the second conductive electrode at a ratio that depends on the total pressure of the analyte gas and the non-analyte gas. The controller is further configured to measure the current generated on the first conductive electrode and the second conductive electrode and determine the ratio of the ejected photoelectrons collected on the first conductive electrode and the second conductive electrode at the total pressure. The controller is further configured to determine the amount of current due to ionization of the analyte gas by correcting the measured current using the determined ratio to subtract the current caused by the photoelectrons from the measured current.

[0015] In an embodiment, correcting the measured current further comprises subtracting a portion of the current measured on the second conductive electrode from the current measured on the first conductive electrode. In an embodiment, the photoionization sensor assembly further comprises a pressure gauge mounted on the flange and configured to measure the total pressure and provide the measured total pressure to the controller. In an embodiment, the second end of the chamber is at least partially open to the surrounding environment. In an embodiment, the third conductive electrode comprises gold. In an embodiment, the radiation source is at least partially surrounded by the housing. In an embodiment, the radiation source is positioned at the first end of the chamber.

[0016] 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: (1) a housing defining a chamber having a first end and an opposing second end, wherein the chamber is permeable to molecules of the analyte gas and non-analyte gas surrounding the housing; (2) a radiation source configured to emit photons; (3) a first conductive electrode positioned toward a first end of the chamber; (4) a second conductive electrode positioned in the chamber; (5) a third conductive electrode positioned toward the second end of the chamber; and (6) A controller in communication with at least the first conductive electrode and the second conductive electrode.

[0017] The method also includes emitting photons from a 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. The photons emitted from the radiation source into the chamber further strike the third conductive electrode and cause emission of photoelectrons.

[0018] The controller is configured to receive a measurement of the total pressure of the analyte gas and the non-analyte gas, and electrically bias the first conductive electrode, the second conductive electrode, and the third conductive electrode so that photoelectrons are attracted toward and collected on the first conductive electrode and the second conductive electrode at a ratio that depends 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 conductive electrode and the second conductive electrode, and determine the ratio of the ejected photoelectrons collected on the first conductive electrode and the second conductive electrode at the total pressure. The controller is also configured to determine the amount of current caused by ionization of the analyte gas by correcting the measured current using the determined ratio to remove the current caused by the photoelectrons.

[0019] In an embodiment, correcting the measured current further comprises subtracting a portion of the current measured on the second conductive electrode from the current measured on the first conductive electrode. In an embodiment, the method further comprises configuring the third conductive electrode to comprise gold. In an embodiment, the method further comprises configuring the second end of the chamber to be at least partially open to the surrounding environment. In an embodiment, the method further comprises configuring the third conductive electrode to comprise a grid. In another embodiment, the method further comprises configuring the housing to at least partially surround the radiation source. In a further embodiment, the method further comprises positioning the radiation source at the first end of the chamber.

[0020] An embodiment of a method of measuring total pressure of a gas includes configuring a photoionization sensor assembly to include: (1) a housing defining a chamber including a first end and an opposing second end, wherein the chamber is permeable to molecules of a gas surrounding the housing; (2) a radiation source configured to emit photons into the chamber; (3) a first electrode positioned toward a first end of the chamber; (4) a second electrode positioned in the chamber; (5) a third electrode positioned toward the second end of the chamber; and (6) A controller that communicates with at least the first electrode and the second electrode.

[0021] The method also includes striking the third electrode with the emitted photons to cause emission of photoelectrons, and configuring the controller to electrically bias the first conductor, the second conductor, and the third conductor so that the emitted photoelectrons are attracted toward and collected on the first and second electrodes at a ratio that depends on the total pressure of the gas, wherein the photoelectrons generate 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 pressure of the gas based on the current generated on the first and second electrodes.

[0022] In an embodiment, the method further comprises positioning the radiation source towards the first end of the chamber. In an embodiment, the method further comprises configuring the second end of the chamber to be at least partially open to the surrounding environment. In an embodiment, the method further comprises configuring the third electrode to include gold. In an embodiment, the method further comprises configuring the housing to at least partially surround the radiation source. In another embodiment, the method further comprises configuring at least one of the first electrode, the second electrode, and the third electrode to include a grid.

[0023] Additional features and advantages of the present disclosure are described in and will be apparent from the following description of the drawings and detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The invention briefly summarized above may be described in more detail by reference to embodiments, some of which are illustrated in the accompanying drawings. However, it should be noted that the drawings illustrate only typical embodiments of the invention and are therefore not to be considered as limiting the scope thereof, as the invention may admit of other equally effective embodiments. Therefore, in order to further understand the nature and purpose of the present invention, reference may be made to the following detailed description read in conjunction with the accompanying drawings, in which:

[0025] Figure 1 A cross-sectional view of an embodiment of a cluster tool used in semiconductor manufacturing is schematically illustrated.

[0026] Figure 2 A cross-sectional view of an embodiment of a sensor instrument for supporting a semiconductor manufacturing tool is illustrated.

[0027] Figure 3 A perspective view of an embodiment of a sensor meter is illustrated.

[0028] Figure 4 Graphics Figure 3 A cross-sectional view of an embodiment of a sensor instrument.

[0029] Figure 5 A perspective view of an embodiment of a sensor meter is illustrated.

[0030] FIG. 6 illustrates an example of predicting total pressure based on a regression model of photoelectron current in a sensor meter.

[0031] Figure 7 A perspective view of another embodiment of a sensor meter is shown.

[0032] Figure 8 A cross-sectional view of another embodiment of a sensor instrument is shown.

[0033] Fig. 9 Graphics Figure 8 A perspective view of an embodiment of the present invention.

[0034] Fig.10 An example of using the sensor to perform photoelectron current correction measurements of xylene pulses of various concentrations.

[0035] Fig.11 Plotting the effectiveness of the correction for the photoelectron current. DETAILED DESCRIPTION

[0036] The following discussion relates to various embodiments of the data connector assembly. It will be understood that the versions described herein are examples that embody certain inventive concepts as described in detail herein. To this end, other variations and modifications will be readily apparent to those skilled in the art. In addition, certain terms are used throughout this discussion in order to provide a suitable reference frame with respect to the accompanying drawings. These terms (such as "upper", "lower", "forward", "backward", "inside", "outside", "front", "rear", "top", "bottom", "inside", "outside", "first", "second", etc.) are not intended to limit these concepts unless specifically indicated as such. The terms "approximately" or "approximately" as used herein may refer to a range of 80%-125% of the value claimed or disclosed. With respect to the drawings, their purpose is to depict the salient features of the data connector assembly and are not particularly provided to scale.

[0037] An embodiment of a partial pressure gauge assembly for process contaminant detection using a photoionization sensor meter or meter assembly ("sensor") 100 and associated components is configured to detect the presence of hydrocarbons in a process chamber or semiconductor production or manufacturing assembly 10, which assembly 10 is also referred to as a manufacturing tool or cluster tool because of the combination of chambers it houses. In some instances, hydrocarbon contamination occurs due to incompatible components used within the fabrication of cluster tool 10, system leaks, or contamination may occur on the semiconductor wafer ("wafer") 50 itself when the semiconductor wafer ("wafer") 50 is introduced into 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, which are configured to accommodate wafer handling robots 14, 15 capable of handling semiconductor wafers 50. Additional process chambers 20, 22, 24, 26, 28 can 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 can be open to the environment of the transfer / buffer chambers 12, 13, so 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 the cassette 30, it is moved through process chambers 20, 22, 24, 26, 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. The transfer chamber 12 and some or all of the additional process chambers 20, 22, 24, 26, 28 are maintained at a pressure below atmospheric pressure via a vacuum system, which may be separate from the manufacturing tool 10 or may be integrated with the manufacturing tool 10. A degas chamber 26 is included in the manufacturing tool 10 and 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 before the manufacturing process is performed.

[0038] The sensor instrument 100 may be installed at one or more locations in the manufacturing tool 10. Figure 1 As shown in FIG, a sensor meter 100 is installed in a degassing chamber 26. A key advantage of the sensor meter 100 is that it is able to detect the presence of an analyte such as hydrocarbons, determine a signal associated with the 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, which can indicate upstream problems in the process (e.g., photoresist removal, cleaning process, etc.).

[0039] exist Figure 2-5In the embodiment of the sensor meter 100 shown in FIG. 1 , the sensor meter 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 that is fixed against the exterior of a process chamber (not shown) and a sealing element 115 (e.g., a gasket or o-ring) that creates a gas-tight seal. A support 114 abuts against an outwardly facing surface of the flange 112, and a wall 116 is coupled from the support 114 to an 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 of which is located near a radiation source 130. The source electrode 118 may include a metallization on the surface of the radiation source 130, a conductive tape bonded to the radiation source 130, or a conductive ring soldered to a circuit board 150 as shown here, which is attached to the 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), although other embodiments may use different gases. The radiation source 130 is composed of a generally transparent material that is shatter-resistant and can tolerate high heat and pressure changes. In an embodiment, the radiation source can be made of glass (e.g., ) is composed of or surrounded by a flange 112. A seal 122 can 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 having a compressive force applied by the support 114 to maintain an airtight seal.

[0040] The space 117 defined by the wall 116 is lined with a dielectric 160 to form an ionization chamber 162, which is defined at a first end by a radiation window 163 sealed to the second source end 133 of the radiation source 130. The radiation window 163 is composed of a UV transparent crystal that allows high energy photons to pass from the radiation source 130 into the ionization chamber 162. In some embodiments, the radiation window 163 can be composed of magnesium fluoride, calcium fluoride, lithium fluoride, or some other suitable material. A plurality of openings 164 pass through the dielectric 160 and the wall 116 to allow gas from the process chamber 189 to penetrate or enter the ionization chamber 162. The first electrode 170 is located in the ionization chamber 162 so that the radiation window 163 is located between the second source end 133 of the radiation source 130 and the first electrode 170. As shown in FIG. Figure 4 In the embodiment shown in FIG. 1 , the first electrode 170 includes an edge or outer edge 172, wherein one or more cross members 174 span the width of the outer edge 172 and / or form a grid-like pattern. A plurality of openings 176 are defined through the first electrode 170 between the cross members 174 and the outer edge 172.

[0041] Still reference Figure 4 , the second electrode 180 is spaced apart from the first electrode 170 and away from the radiation window 163. The second electrode 180 includes an edge or outer edge 182, wherein one or more cross members 184 span the width of the edge 182 and / or form a grid-like pattern. The edge 182 and the one or more cross 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 is located between the second housing end 113 and the second electrode 180. As with the first and second electrodes 17, 180, the third electrode 190 includes an edge or outer edge 192, wherein one or more cross members 194 span the width of the edge 192 and / or form a grid-like pattern. The edge 192 and the one or more cross 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 plurality of cross members 194 that are generally formed by 120 ( Figure 2 ) are provided to the first, second and third electrodes 170, 180, 190.

[0042] Return to Figure 2 , the 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 between the first and second electrodes 170, 180 is needed to enable enough gas particles to enter the ionization chamber 162 for sufficient photoionization to occur. In embodiments for higher pressure environments, the distance between the first and second electrodes 170, 180 can be shortened so that the ratio is less than 8:1. Although several embodiments in the 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 completely between the first and third electrodes 170, 190.

[0043] The first, second and third electrodes 170, 180, 190 are conductive and may be composed of steel and coated with gold. The gold does not experience a significant change in work function when exposed to oxygen compared to the work function of materials such as stainless steel. The electrodes 170, 180, 190 are arranged in the ionization chamber 162 such that their one or more cross members 174, 184, 194 shield each other. Figure 3-5As shown in , each of the electrodes 170, 180, 190 has two cross members 174, 184, 194. The cross members enable the surface area of ​​the electrodes 170, 180, 190 to be minimized in order to reduce background noise. In other embodiments, one or more electrodes 170, 180, 190 have more than two cross members.

[0044] Now refer to Figure 2-5 The operation of the sensor portion of the sensor meter 100 is discussed. The control electronics 80 or controller is schematically shown in FIG. Figure 5 , and communicates with the sensor meter 100. The control electronics 80 are typically gathered together in a box coupled to the sensor flange 112, although they can be located remotely from the sensor meter 100 and connected to the sensor meter 100 by cables. In instances where the sensor meter 100 is located, for example, in an environment where the temperature is too high for the control electronics 80 to survive, it would be advantageous to locate the control electronics 80 in a remote location. In an embodiment, the control electronics 80 may include a power supply for the radiation source 130, a measurement circuit for the current of interest, a bias supply, a data processor, a communication section, etc. . . . The sensor meter 100 uses photoionization to detect the presence of an analyte in a 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 a plasma 140 within the radiation source 130. The plasma 140 emits photons through the radiation window 163 and into 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 a wavelength that is capable of ionizing molecules of an analyte gas, such as molecules of a hydrocarbon gas, in the ionization chamber 162. When the photons collide with molecules of the analyte gas, they have sufficient energy to create ions from the analyte gas molecules by ejecting electrons.

[0045] The first, second and third electrodes 170, 180, 190 are biased to dictate the flow of one or more charged particles in the ionization volume 162. In an example, the first electrode 170 and the second electrode 180 are held at a virtual ground by a current to voltage conversion amplifier (I to V), and the third electrode 190 acts as a cathode held at some negative potential (typically between -80V and -300V) relative to ground. Photons are emitted by the radiation source 130 and travel through the radiation window 163 into the ionization volume 162 where they collide with analyte gas molecules. In an embodiment, the radiation source 130 is positioned toward the end of the ionization volume 162. Depending on the location where ionization occurs, the geometry of the sensor, the bias voltage, and / or the pressure of the background gas, each collision has a certain probability of causing an electron to be ejected from the analyte gas molecule, thereby generating a positive ion that moves toward the cathode / third electrode 190, while the ejected electron moves toward the first electrode 170 or the second electrode 180. Some of the photons have wavelengths short enough to effectively ionize most organic molecules, but the photons are not energetic enough to ionize background gases that may be present in the ionization chamber 162, typically nitrogen or argon or hydrogen.

[0046] The electron current collected at the first electrode 170 and the second electrode 180 passes through the feedthrough 120 (see Figure 2) is transmitted to the control electronics 80, where the current is converted to a voltage, amplified and digitized. The presence of an electron flow as detected by the controller 80 is an indication that an analyte gas may be present in the process chamber 189. In addition to this electron flow generated by the photoionization of the analyte gas molecules, another source of electron flow can also be measured by the sensor meter 100. For example, photons with energy sufficient to ionize hydrocarbons have more energy than the energy sufficient to eject electrons from most conductors (photoelectrons). The photoelectrons generated at the surface of the third electrode 190 are accelerated and focused toward the first and second electrodes 170, 180 by the electric field established by the third electrode 190 bias, thereby generating a baseline current on these electrodes and contributing any noise and drift present on the photoelectron current to the measurement signal of interest. If these photoelectron currents are constant, they can just be subtracted from the signal, but they are usually not constant. Therefore, reducing the noise and drift on the photoelectron current improves the ability of the sensor meter 100 to measure hydrocarbons. One way to reduce absolute noise and drift is to reduce the photoelectron current overall. This can be done by reducing the area of ​​the third electrode 190 that is exposed to UV photons. By reducing the exposed area of ​​the third electrode or third electrode 190 that acts as a photoelectron source, the photoelectron current and the absolute noise on the current can be reduced. The embodiment of the sensor instrument 100 shown in the figure has a third electrode 190 that includes two gold wires with a diameter of 0.75 mm and stretched across the third electrode diameter to provide the required electric field while reducing the photoelectron generation area as far as possible (as farasfoundpractical).

[0047] Furthermore, the photoelectron current generated for a given photon flux and energy distribution depends on the work function of the illuminated surface. If this work function is not constant, the current generated will not be constant, even given that 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 such as may be present in some wafer etch environments. These effects on the signal current are relevant to the monitoring of hydrocarbon contaminants in certain semiconductor processes, for example when a wafer may be transferred from an oxygen environment to an oxygen-free environment. The residual effect on the background photoelectron current may mask the small hydrocarbon signal of interest. Fig.11This effect and one way of overcoming it in the sensor meter 100 is illustrated. Here, a square wave pulse of 10 ppm isobutylene is injected into a nitrogen balance from 29,300 seconds to 30,200 seconds while keeping the total pressure constant. Before and after the pulse, the sensor meter 100 is exposed to pure nitrogen, but during the pulse, in addition to the isobutylene, the oxygen concentration is increased from zero to 1%. When comparing the signals before and after the pulse on the first and second electrodes 170, 180, a shift in the baseline is discernible. This shift in the baseline is due to a reduction in photoelectron production 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 afterwards. This effect is attributed to the work function of the (primarily) third electrode 190 surface. In order to obtain a stable baseline relative to which the hydrocarbon pulse can be measured, the photoelectron portion of the signal measured at the second electrode 180 can be subtracted from the signal measured at the first electrode 170. When this portion is chosen correctly, it removes the photoelectron effect from the data, as shown in FIG. Fig.11 The “correction signal” is shown in the figure.

[0048] The distribution of these photoelectrons across 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 current measured across the first and second electrodes 170, 180 as a function of pressure in nitrogen with the third electrode 190 biased at -80V. The shape of these curves is due to the pressure-dependent scattering of the photoelectrons from the background gas. The correct portion of the second electrode signal is subtracted from the first electrode signal to obtain a "corrected" signal, which can be read from a plot of the pressure of interest such as this one. Once these two curves are determined for a particular electrode geometry, the pressure in the sensor 100 can be determined from the two electrode signals during a period of time in which a hydrocarbon signal is not expected to be present, such as prior to heating during wafer degassing. As an illustration, in the training data set depicted in Figure 6a, a regression model for pressure was created for the two electrode signals. A standard machine learning algorithm based on kernel ridge regression was used to develop a model for predicting pressure based on the two currents. This model was then applied to Figure 6b Two sensor currents in a separate test data set shown in . This data in 6b was not used to train the model. For a random set of current measurements, a "predicted pressure" was found. This predicted pressure is shown on the second y-axis. An example is shown with the dashed line where two currents measured at ~195 Torr are used to predict a pressure of ~198 Torr. In this way, sensor 100 can be used to measure not only hydrocarbon partial pressures, but also the total pressure in the system, even when the dominant species cannot be ionized by UV photons.

[0049] Of course, if one were to optimize for total pressure measurement rather than measurement of species ionized by UV photons, one would not need to attempt to minimize the photoelectron generation region as is done in the disclosed sensor 100. Furthermore, one may also wish to use a light source in which the energy is sufficient to generate photoelectrons from the third electrode or cathode, but in which the energy is too low to ionize hydrocarbons or other gaseous species.

[0050] The calculation of the "corrected signal" and the "predicted pressure" may be performed by an onboard processor in the control electronics 80 or by a remote computer.

[0051] Another way to reduce these photoelectron effects is to stabilize the generation of photoelectrons against work function changes. Since the presence of oxygen and / or water on some conductive surfaces has a stronger effect on their work function than other conductive surfaces, careful selection of the third electrode surface material can help. Gold is less susceptible to this effect than stainless steel, so the third electrode 190 of the sensor 100 described herein has a gold surface. This has been achieved in different ways; for example, gold wire and gold-plated stainless steel parts. The first and second electrodes 170, 180 can also be gold-plated, but these surfaces are not as important because the typical bias in the sensor helps prevent photoelectron currents from being generated on these surfaces and collecting elsewhere.

[0052] refer to Figure 7 , another embodiment of the sensor instrument 200 is shown. This embodiment is the same as the above-described embodiment except that an integral total pressure gauge 260 is added. 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 that is configured to be attached 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 the radiation source 230. The one or more electrodes are not shown, but may be similar to other embodiments of the electrodes discussed previously. Similar to the previously discussed embodiments, a wall is coupled to an opposite side of the flange 212 relative to the support 214 and defines a space. As Figure 7 As shown in and as described in other embodiments, the radiation source 230 is a lamp. The radiation source 230 has a first source end 231 located on the outside and a second source end fixed on the inside. One or more feedthroughs 220 can 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 can tolerate high heat and pressure changes. In an embodiment, the radiation source 230 is composed of glass (e.g., )composition.

[0053] Tube 250 pneumatically couples the atmosphere in which the sensor instrument 200 is mounted to a pressure gauge 260. The pressure gauge 260 is selected to measure pressure in the expected operating range of the sensor. Including the pressure gauge 260 with the sensor instrument 200 can save flanges on the monitored process system. The pressure inside the ionization chamber is measured by the pressure gauge 260 and can also be used to perform the above-mentioned photoelectron correction. The measurement of the pressure and the photoelectron current on the second electrode and the knowledge of how the ratio of the photoelectron current measured on the first and second electrodes depends on the pressure allow the contribution of the photoelectrons to the current measured on the first electrode to be removed, leaving a corrected analyte signal. The pressure measurements are reported to the control electronics 80, where they are used, recorded and / or transmitted to the user of the sensor. The wall has an internal space lined with a dielectric to define an ionization space similar to the embodiments discussed previously. 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 are spaced from each other so that the second electrode (not shown) is located between the first electrode (not shown) and the third electrode (not shown). The 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 enable gas to enter the ionization chamber (not shown) from the process chamber. Detection of the analyte and determination of pressure are performed in a manner similar to that described in the previous embodiments.

[0054] refer to Figure 8 and Fig. 9, another 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 completely within the process chamber 389, so that the sensor instrument 300 can be positioned in close proximity 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 outside 388 of the process chamber 389 and a sealing element 315 that creates a gas-tight seal. A support 314 is located inside the multi-pin vacuum feedthrough assembly 310. The housing wall 316 extends in a direction away from the flange 312 and includes a generally cylindrical shape that defines a space. The support 314 is used to support at least two electrodes 320, each of which is 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, which is 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), although other embodiments may use different gases. The radiation source 330 is composed of a generally transparent material that is shatter-resistant and can tolerate high heat and pressure changes. In an embodiment, the radiation source is composed of glass (e.g., ) or is 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 that drive the radiation source 330. The housing wall 316 is ideally composed of or other similar fluoropolymers as a reasonable choice for vacuum and process compatibility and high breakdown voltage. The dielectric barrier is used to prevent source electrode discharge that may occur at some sensor operating pressures and transient pressures that may be experienced in use. In other embodiments, except for the radiation window 363, the radiation source 330 is generally encapsulated.

[0055] The space defined by the wall 316 is lined with a 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 the second source end 333 of the radiation source 330. A plurality of openings may be passed through the dielectric 360 and the wall 316 to enable gas to enter the ionization chamber 362 from the process chamber. The opposite end of the ionization chamber 362 is also open to the process chamber 389, as in the previous embodiments of the sensor instrument 100, 200. The 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 the radiation source 330 and the first electrode 370. In the illustrated embodiment, the 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, 390 are positioned similarly to the other embodiments previously discussed and may also be constructed in a manner similar to the other embodiments previously discussed. Fig. 9 In the embodiment shown in , the third electrode 390 is specifically shown and defines a series of circular openings 396 through the third electrode 390, however, for the reasons explained previously, the third electrode 390 can be configured as in the previously described embodiments. Detection of analyte gas molecules and pressure determination are performed in a manner similar to that described in the previous embodiments. Electrical connections from the sensor to the control electronics 80 are made via pins in the feedthrough assembly 310.

[0056] Although the present invention has been specifically shown and described with reference to certain exemplary embodiments, it will be appreciated by those skilled in the art that various changes in detail may be made herein without departing from the spirit and scope of the present invention as supported by this written description and the accompanying drawings. For example, the disclosed methods and assemblies may be used to determine the analyte number density or other properties of a sample in a sensor chamber. In addition, where exemplary embodiments are described with reference to a certain number of elements, it will be appreciated that exemplary embodiments may be practiced using less than or more than a certain number of elements.

Claims

1. A sensor assembly for measuring the total pressure of a gas, comprising: a housing defining a chamber including a first end and an opposing 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; as well as a controller in communication with at least the first electrode and the second electrode, wherein said photons emitted into said chamber cause photoelectrons to be ejected from said third electrode; The controller is configured to: electrically biasing the first, second, and third conductors so that emitted photoelectrons are attracted toward and collected on the first and second electrodes at a ratio that depends on the total pressure of the gas, wherein the photoelectrons generate a current on the first and second electrodes, measuring the current generated at the first electrode and the second electrode, and The total pressure of the gas is determined based on the current generated at the first electrode and the second electrode.

2. The sensor assembly according to claim 1, wherein: The radiation source is positioned toward the first end of the chamber.

3. The sensor assembly according to claim 1, wherein: The second end of the chamber is at least partially open to the surrounding environment.

4. The sensor assembly according to claim 1, wherein: The third electrode includes gold.

5. The sensor assembly according to claim 1, wherein: The radiation source is at least partially surrounded by the housing.

6. The sensor assembly according to claim 1, wherein: A ratio of a distance between the first electrode and the second electrode to a distance between the second electrode and the third electrode is approximately 8:

1.

7. The sensor assembly according to claim 1, wherein: At least one of the first electrode, the second electrode, and the third electrode includes a grid.

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 opposing 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 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; as well as a controller in communication with at least the first conductive electrode and the second conductive electrode, 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 strike the third conductive electrode, causing the emission of photoelectrons, The controller is configured to: receiving a measurement of the total pressure of the analyte gas and the non-analyte gas, electrically biasing the first conductive electrode, the second conductive electrode, and the third conductive electrode so that the photoelectrons are attracted toward and accumulated on the first conductive electrode and the second conductive electrode at a ratio that depends on the total pressure of the analyte gas and the non-analyte gas, measuring a current generated at the first conductive electrode and the second conductive electrode, determining a ratio of ejected photoelectrons collected on the first conductive electrode and the second conductive electrode at the total pressure, and The amount of current due to ionization of the analyte gas is determined by correcting the measured current using the determined ratio to subtract the current due to the photoelectrons from the measured current.

9. The photoionization sensor according to claim 8, wherein: 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 the total pressure and provide the measured total pressure to the controller.

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

12. The photoionization sensor according to claim 8, wherein: The third conductive electrode includes gold.

13. The photoionization sensor according to claim 8, wherein: The radiation source is at least partially surrounded 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: The photoionization sensor is constructed to include: a housing defining a chamber having a first end and an opposing 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 conductive electrode and the second conductive electrode, 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 strike the third conductive electrode and cause the emission of photoelectrons, The controller is constructed as follows: receiving a measurement of the total pressure of the analyte gas and the non-analyte gas, electrically biasing the first conductive electrode, the second conductive electrode, and the third conductive electrode so that the photoelectrons are attracted toward and accumulated on the first conductive electrode and the second conductive electrode at a ratio that depends on the total pressure of the analyte gas and the non-analyte gas, measuring a current generated at the first conductive electrode and the second conductive electrode, determining a ratio of ejected photoelectrons collected on the first conductive electrode and the second conductive electrode at the total pressure, and The amount of current due to ionization of the analyte gas is determined by correcting the measured current using the determined ratio to remove the current due to the photoelectrons.

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

17. The method of claim 15, further comprising configuring the second end of the chamber to be at least partially open to an 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 for measuring the total pressure of a gas, comprising: The photoionization sensor assembly is constructed to include, a housing defining a chamber including a first end and an opposing 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; as well as a controller in communication with at least the first electrode and the second electrode; striking the third electrode with the emitted photons to cause emission of photoelectrons; and configuring the controller to: electrically biasing the first conductor, the second conductor, and the third conductor so that emitted photoelectrons are attracted toward and collected on the first electrode and the second electrode at a ratio that depends on the total pressure of the gas, wherein the photoelectrons generate current on the first electrode and the second electrode, measuring the current generated at the first electrode and the second electrode, and A total pressure of the gas is determined based on the current generated at the first electrode and the second electrode.

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.

Images