Partial pressure gauge assembly and related method for detecting process contaminants using photoionization - Patents.com

Abstract

The photoionization sensor assembly includes a housing defining a chamber having a first end and an opposing second end and transparent to analyte and non-analyte gases. A radiation source is structured to emit photons into the chamber. A first electrode, a second electrode, and a third electrode are disposed within the chamber. The photons ionize the analyte gas but are insufficient to ionize the non-analyte gas, causing photoelectrons to be emitted from the third electrode. A controller is structured to receive a measurement of the total pressure and to electrically bias the electrodes to collect photoelectrons on the first electrode and the second electrode in a ratio that depends on the total pressure. The controller is structured to determine a ratio of photoelectrons collected on the first electrode and the second electrode at the total pressure and to determine an amount of current due to ionization by correcting the measured current using the determined ratio.

Description

[Technical field]

[0001] (CROSS REFERENCE TO RELATED APPLICATIONS) This application claims the benefit of and priority to U.S. Provisional Patent Application No. 63 / 332,351, filed April 19, 2022, and entitled "PARTIAL PRESSURE GAUGE FOR PROCESS CONTAMINANT DETECTION USING PHOTOIONIZATION," the entire contents of which are incorporated herein by reference.

[0002] The disclosed invention relates generally to the field of pressure gauges, and more particularly to a partial pressure gauge for use in fault detection in semiconductor process tools, where the instrument utilizes high energy photons to selectively measure contaminants under reduced pressure of an inert gas. [Background technology]

[0003] The manufacture of modern integrated circuits (ICs) begins with high purity semiconductor wafers, which then undergo hundreds of tightly controlled process steps over a period of weeks or months. After the wafers have completed these steps, they are cut into many small dies. These dies are then packaged and the resulting devices, such as ICs, are integrated into the heart of many modern electronic devices. The manufacture of high performance semiconductor devices with high yields requires strict control of the microenvironment surrounding the wafer. At various manufacturing steps, the partially completed devices are at risk of being more or less damaged as a result of exposure to certain process contaminants. As a first example, exposure to traces of oxygen during the growth of a metal layer responsible for contacting the source or drain regions of a transistor can increase the electrical resistance of this layer and reduce the time constant of the device, thereby reducing the yield. As a second example, traces of hydrocarbon contaminants remaining on the wafer surface can degrade components of semiconductor processing tools, such as lithography optics. As a third example, precursor chemicals used for metallization of insulator deposition may be incompletely purged from the chamber or may leak back from the process chamber into the transfer chamber, damaging the wafers being transferred. Therefore, it is important to monitor for these contaminants during handling, storage, and processing steps of semiconductor wafers.

[0004] Typically, the wafer microenvironment is kept ultra-clean from contaminants, and while some processes are at high vacuum (i.e., less than 1e-5 Torr), many modern semiconductor processes occur during inert gas flows at much lower vacuums (1-100 Torr). This means that quite typically, inert gases such as nitrogen, argon, or hydrogen are present at high levels during the process steps. Measurements of total pressure indicate the levels of these major species, but do not provide an acceptable indication of trace contaminants that may be present at parts per million levels. For example, if 1 ppm levels of oxygen are identified in a particular tool step, processing of additional wafers can be halted and defective components such as chamber O-rings can be replaced to prevent additional wafer scrap and reduce tool downtime. Similarly, small levels of organic contaminants on the wafer surface can cause pattern transfer defects, resulting in edge placement errors and other yield impacts. In addition to yield impacts, residual hydrocarbon contaminants on the wafer surface can also degrade the complex and expensive lithography components required for the latest semiconductor nodes. Replacement of optics and masks damaged in this way can be very expensive. All of these yield and tool impacts are important to control in the competitive semiconductor manufacturing industry. Besides contamination, there are other instances where it is important to determine trace levels of species in background gases, such as determining the etch end point.

[0005] Total pressure can be measured with many types of instruments. These include, among others, the Bayard-Alpert ionization gauge, capacitance manometer, and thermocouple gauge. Formally, only manometers measure the true pressure of a gas, while others provide estimates of number densities related to ionization cross section, heat transport, or other properties of the gas. However, it can be roughly said that the most common types of instruments measure properties of the gas that are related to the total pressure of the gas, not the trace constituents.

[0006] This problem of measuring trace constituents has traditionally been solved by using a special type of "ion gauge" called a residual gas analyzer (RGA, e.g. a type of mass spectrometer). Like ion gauges such as the Bayard-Alpert gauge, RGAs use a high-energy electron beam to convert neutral species into ions. With typical electron energies of 70-100 eV, all gas molecules can be ionized with some probability. RGAs contain mass filters to separate these ions by their different mass-to-charge ratios (m / z). By relating the m / z to the different gases present in the microenvironment, and combining it with the ionization cross-sections, and the m / z sensitivity factor of the sensor, it can be used to estimate the partial pressures of different contaminant molecules, even if they are present at low levels (i.e. 1 ppm) in the majority of gases. Unfortunately, the use of mass spectrometry cannot be directly applied to modern semiconductor processes that operate at pressures between 1-100 Torr. This is because low pressures (<1e-4 Torr) are required for the operation of most RGAs. In brief, RGAs require low pressure to operate the filament (cathode). At pressures above 1e-4 Torr, space charge begins to mask the filament from its extraction field. In addition, ion bombardment and oxidation can erode the filament material. Another problem with RGAs is that low pressure is required to limit the effects of ion-molecule collisions in the mass spectrometer and to avoid ion feedback or plasma discharge in the secondary electron amplifier. Therefore, additional pumping is required to install RGAs in many modern semiconductor tools or process steps. This increases costs, slows response times, and requires significant space around the already crowded semiconductor reactor chamber. It is also expensive. There remains a need to measure the partial pressure of trace contaminants in these high 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 gas molecules is typically very short compared to the dimensions of the sensor. Because the pressure front propagates at the speed of sound, changes in total pressure can be detected quickly. However, determining the partial pressure of a trace species at a particular point in the chamber depends on the diffusion or transport of that species to the instrument. Therefore, the partial pressure gauge must be able to be installed near the area of ​​interest, otherwise the sensor will not respond quickly enough to address many common problems in the semiconductor industry. In the specific case of fast flowing gases, the instrument may miss a leak or contaminant entirely, because the contaminant will be diluted by the time it reaches a sensor installed in the foreline, for example. Furthermore, considering that the space around the semiconductor tool is very limited, it is important to design a sensor that can communicate closely to the area of ​​concern.

[0008] These are just a few of the problems associated with traditional partial pressure gauges, such as total pressure gauges and RGAs. Summary of the Invention

[0009] The present disclosure is directed to a sensor gauge assembly that may be inserted directly into a process environment. One embodiment of a partial pressure ion gauge includes an electrical feedthrough flange, a plasma generation envelope, and a series of electrodes. A dielectric housing supports ion and electron lenses and contains the plasma generation envelope entirely inside the process environment.

[0010] Rather than using a hot cathode filament for ionization, as is typical of the RGAs described above, the sensor disclosed herein utilizes a lamp consisting of a self-contained plasma to generate high energy photons. The plasma envelope contains a sample of krypton gas at reduced pressure, but it can also contain argon, xenon, or other gases. A high electric field generated between two electrodes patterned on the outside of the plasma envelope, or otherwise placed near the envelope, couples energy to the contained gas, thereby creating a plasma that emits light as excited plasma species return to their lower energy state. The envelope can be any dielectric that is sealable and can withstand the pressure difference between the plasma and the process. For example, it can be a molded piece of alumina. However, the most typical plasma source is constructed from Pyrex® blown glass pieces. Regardless of the material that comprises the plasma source, there is a UV-transparent crystal on one side of the lamp. This crystal is constructed from 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. Also, ionization may be selective, as is known from conventional photoionization sensors designed for operation in high pressure environments (e.g., atmospheric pressure). In general, the photon energy of a krypton discharge is equal to or greater than the first ionization energy of most organic molecules, but is not sufficient to ionize nitrogen or argon or hydrogen.

[0011] An embodiment of the gas sensor includes the gas envelope inside the flange. The gas envelope may be constructed from alumina. In one embodiment, the optical element includes sapphire.

[0012] One embodiment of a sensor assembly for measuring a total pressure of a gas includes a housing defining a chamber including a first end and an opposing second end. The chamber is transparent to molecules of the gas surrounding the housing. A radiation source is structured to emit photons into the chamber. A first electrode is disposed relative to the first end of the chamber, a second electrode is disposed within the chamber, and a third electrode is disposed relative to the second end of the chamber. A controller is in communication with at least the first and second electrodes. The photons emitted into the chamber cause emission of photoelectrons from the third electrode. The controller is structured to electrically bias the first, second, and third conductors such that the emitted photoelectrons are attracted toward and collected on the first and second electrodes in a ratio that depends on the total pressure of the gas, the photoelectrons generating a current on the first and second electrodes. The controller is further structured 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.

[0013] In one embodiment, the radiation source is disposed against a first end of the chamber. In one embodiment, the second end of the chamber is at least partially open to the surrounding environment. In one embodiment, the third electrode comprises gold. In one embodiment, the radiation source is at least partially surrounded by a housing. In another embodiment, 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 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] One embodiment of a photoionization sensor assembly structured 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 transparent to molecules of the analyte gas and the non-analyte gas surrounding the housing. A radiation source is structured to emit photons into the chamber. A first conductive electrode is disposed against the first end of the chamber, a second conductive electrode is disposed within the chamber, and a third conductive electrode is disposed against the second end of the chamber. A controller is in communication with at least the first conductive electrode and the second conductive electrode. 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 the emission of photoelectrons. The controller is configured to receive measurements of the total pressure of the analyte gas and the non-analyte gas and to electrically bias the first, second and third conductive electrodes such that photoelectrons are attracted toward and collected on the first and second conductive electrodes in a ratio that depends on the total pressure of the analyte gas and the non-analyte gas. The controller is further configured to measure current generated on the first and second conductive electrodes and determine a ratio of emitted photoelectrons that are collected on the first and second conductive electrodes at the total pressure. The controller is further configured to determine an 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 one embodiment, correcting the measured current further comprises subtracting a fraction 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 further comprises a pressure gauge attached to the flange and structured to measure a total pressure and provide the measured total pressure to the controller. In one embodiment, the second end of the chamber is at least partially open to the ambient environment. In one embodiment, the third conductive electrode comprises gold. In one embodiment, the radiation source is at least partially surrounded by a housing. In one embodiment, the radiation source is disposed at the first end of the chamber.

[0016] One embodiment of a method for measuring an analyte gas in the presence of a non-analyte gas comprises: (1) a housing defining a chamber having a first end and an opposing second end, the chamber being permeable to molecules of an analyte gas and a non-analyte gas surrounding the housing; (2) a radiation source configured to emit photons; and (3) a first conductive electrode disposed against the first end of the chamber; (4) a second conductive electrode disposed within the chamber; and (5) a third conductive electrode disposed against the second end of the chamber; and (6) a controller in communication with at least the first conductive electrode and the second conductive electrode; The step of structuring the photoionization sensor to comprise:

[0017] The method further includes emitting photons from a radiation source into the chamber to ionize at least some molecules of the analyte gas, the emitted photons being insufficient to ionize molecules of the non-analyte gas. The photons emitted from the radiation source into the chamber further impinge on a third conductive electrode, causing the emission of photoelectrons.

[0018] The controller is configured to receive measurements of the total pressure of the analyte and non-analyte gases and to electrically bias the first, second and third conductive electrodes such that photoelectrons are attracted toward and collected on the first and second conductive electrodes in a ratio that depends on the total pressure of the analyte and non-analyte gases. The controller is further configured to measure current generated on the first and second conductive electrodes and determine a ratio of emitted photoelectrons that are collected on the first and second conductive electrodes at the total pressure. The controller is further configured to determine an amount of current due to ionization of the analyte gas by correcting the measured current using the determined ratio to remove current caused by the photoelectrons.

[0019] In one 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 one embodiment, the method further comprises structuring the third conductive electrode to comprise gold. In one embodiment, the method further comprises structuring the second end of the chamber to be at least partially open to the ambient environment. In one embodiment, the method further comprises structuring the third conductive electrode to comprise a grid. In another embodiment, the method further comprises structuring the housing to at least partially surround the radiation source. In a further embodiment, the method further comprises disposing the radiation source at the first end of the chamber.

[0020] One embodiment of a method for measuring a total pressure of a gas comprises: (1) a housing defining a chamber having a first end and an opposing second end, the chamber being permeable to molecules of a gas surrounding the housing; (2) a radiation source structured to emit photons into the chamber; (3) a first electrode disposed against the first end of the chamber; (4) a second electrode disposed within the chamber; and (5) a third electrode disposed against the second end of the chamber; and (6) a controller in communication with at least the first electrode and the second electrode; The step of structuring the photoionization sensor assembly to comprise:

[0021] The method further includes causing the emitted photons to impinge on a third electrode to emit photoelectrons, and configuring a controller to electrically bias the first conductor, the second conductor, and the third conductor such that the emitted photoelectrons are attracted toward and collected on the first and second electrodes in a ratio that is dependent on a total pressure of the gas, the photoelectrons generating currents on the first and second electrodes. The controller is further configured to measure the currents generated on the first and second electrodes and determine the total pressure of the gas based on the currents generated on the first and second electrodes.

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

[0023] Additional features and advantages of the present disclosure will be described in, and will be apparent from, the following Brief Description of the Drawings and Detailed Description. [Brief description of the drawings]

[0024] A more particular description of the present invention briefly summarized above can be understood by reference to embodiments, some of which are illustrated in the accompanying drawings. It should be noted, however, that the accompanying drawings illustrate only typical embodiments of the present invention and are therefore not to be considered limiting of the scope of the present invention, which may likewise admit of other effective embodiments. Accordingly, for a further understanding of the nature and object of the present invention, reference can be made to the following detailed description read in conjunction with the drawings.

[0025] [Figure 1] 1 illustrates a cross-sectional view of one embodiment of a cluster tool used in semiconductor manufacturing. [Diagram 2] 1 illustrates a cross-sectional view of one embodiment of a sensor gauge used to support a semiconductor manufacturing tool. [Diagram 3] 1 illustrates a perspective view of one embodiment of a sensor gauge. [Figure 4] 4 shows a cross-sectional view of the embodiment of the sensor gauge of FIG. 3. [Diagram 5] 1 illustrates a perspective view of one embodiment of a sensor gauge. [Figure 6] 1 shows an example of predicting total pressure based on a regression model of the photoelectron current in a sensor gauge. [Figure 7] 1 shows a perspective view of another embodiment of a sensor gauge. [Figure 8] 13 shows a cross-sectional view of another embodiment of a sensor gauge. [Figure 9] FIG. 9 shows a perspective view of the embodiment of FIG. [Figure 10] 13 is an example of photocurrent-corrected measurements of xylene pulses of various concentrations using the sensor. [Figure 11] The effectiveness of the correction for the photoelectron current is shown. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0026] The following description relates to various embodiments of the data connector assembly. It will be understood that the versions described herein are examples embodying certain inventive concepts detailed herein. As such, other variations and modifications will be readily apparent to those skilled in the art. In addition, certain terms are used throughout this description to provide an appropriate frame of reference with respect to the accompanying drawings. Terms such as "upper", "lower", "forward", "rear", "inner", "outer", "front", "rear", "upper", "lower", "inner", "outer", "first", "second", and the like are not intended to limit these concepts unless specifically indicated. The terms "about" or "approximately" as used herein may refer to a range of 80% to 125% of the claimed or disclosed value. With respect to the drawings, their purpose is to illustrate the salient features of the data connector assembly, and are not specifically provided to scale.

[0027] One embodiment of a partial pressure gauge assembly for process contaminant detection using a photoionization sensor gauge or gauge assembly ("sensor") 100 and related assemblies is configured to detect the presence of hydrocarbons in a process chamber or in a semiconductor production or manufacturing assembly 10, also referred to as a manufacturing tool or cluster tool for housing the associated chamber. In some cases, hydrocarbon contamination may occur as a result of incompatible components used in the manufacturing of the cluster tool 10, system leaks, or the contamination may be present in the semiconductor wafers ("wafers") 50 themselves when introduced to the tool 10. With reference to FIG. 1, the manufacturing tool 10 includes a transfer module or transfer chamber 12 and a buffer module or buffer chamber 13 structured to house wafer handling robots 14, 15 capable of handling the semiconductor wafers 50. Additional process chambers 20, 22, 24, 26, 28 may be positioned around the transfer module 12 and buffer module 13. In one embodiment, one or more of the additional process chambers 20, 22, 24, 26, 28 may be open to the environment of the transfer / buffer chambers 12, 13, thereby allowing the internal environment of the additional process chambers 20, 22, 24, 26, 28 to move to the environment of the transfer / buffer chambers 12, 13 and / or allowing the environment of the transfer / buffer chambers 12, 13 to move to the internal environment of the additional process chambers 20, 22, 24, 26, 28. After the wafer is removed from the cassette 30, it moves through the process chambers 20, 22, 24, 26, 28, which may be structured to accept a 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 sub-atmospheric pressure via a vacuum system, which may be separate from or integral to the manufacturing tool 10. A degassing chamber 26 is included in the manufacturing tool 10 and is configured to receive and heat a wafer 50.Heating the wafer 50 activates volatile species present on the wafer 50, such as water and hydrocarbons, so that they are removed from the wafer by evaporation before the manufacturing process proceeds.

[0028] The sensor gauge 100 may be installed in one or more locations within the manufacturing tool 10. As shown in FIG. 1, the sensor gauge 100 is installed within the degassing chamber 26. A primary advantage of the sensor gauge 100 is that it can detect the presence of an analyte, such as a hydrocarbon, determine a 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 an upstream problem in the process (e.g., photoresist removal, cleaning process, etc.).

[0029] In the embodiment of the sensor gauge 100 shown in Figures 2-5, the sensor gauge 100 has a first end 111 disposed outside a process or manufacturing environment and a second end 113 disposed inside the process environment. The sensor is attached to a flange 112 that fastens against the outside of a process chamber (not shown) and a sealing element 115 (e.g., a gasket or O-ring) that forms an airtight seal. A support 114 seats against an outer opposing surface of the flange 112 and a wall 116 is coupled from the support 114 to the opposing surface of the flange 112. As shown, the wall 116 is generally cylindrical in shape and defines a space 117. The support 114 serves to support at least two source electrodes 118, each disposed proximate to a radiation source 130. The source electrodes 118 may include metallization on a surface of the radiation source 130, conductive tape adhered to the radiation source 130, or, as shown here, conductive rings soldered to a circuit board 150 that is attached to the support 114 by a board support 151. As shown, the radiation source 130 is a lamp having a first source end 131 disposed outside the process environment and a second source end 133 secured inside the housing 110. The radiation source 130 encloses a volume filled with a gas, such as Kr gas, although other embodiments may use different gases. The radiation source 130 is constructed of a substantially transparent material that is shatter-resistant and capable of withstanding high heat and pressure fluctuations. In one embodiment, the radiation source may be constructed of or surrounded by glass, such as Pyrex®. A seal 122 may be disposed between the flange 112 and the radiation source 130 to form an airtight seal. As shown, this seal 122 is an O-ring, and a compressive force is applied by the support 114 to maintain the airtight seal.

[0030] The space 117 defined by the walls 116 is lined with a dielectric 160 to form an ionization chamber 162 bounded at a first end by a radiation window 163 that is sealed to the second source end 133 of the radiation source 130. The radiation window 163 is constructed of a UV-transparent crystal that allows high energy photons to pass from the radiation source 130 to the ionization chamber 162. In some embodiments, the radiation window 163 may be constructed of magnesium fluoride, calcium fluoride, lithium fluoride, or some other suitable material. A plurality of openings 164 traverse the dielectric 160 and the walls 116 to allow gas from the process chamber 189 to pass through or enter the ionization chamber 162. A first electrode 170 is disposed within the ionization chamber 162 such that the radiation window 163 is located between the second source end 133 of the radiation source 130 and the first electrode 170. 4, the first electrode 170 includes a rim or outer rim 172 having one or more cross-members 174 spanning the width of the outer rim 172 and / or forming a grid-like pattern. A plurality of openings 176 are defined between the cross-members 174 and the outer rim 172 across the first electrode 170.

[0031] 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 a rim or outer rim 182 having one or more cross members 184 that span the width of the rim 182 and / or form a grid-like pattern. The rim 182 and the one or more cross members 184 define a plurality of openings 186 across the second electrode 180. The third electrode 190 is spaced apart from the second electrode 180 and is disposed between the second housing end 113 and the second electrode 180. Similar to the first electrode 17 and the second electrode 180, the third electrode 190 includes a rim or outer rim 192 having one or more cross members 194 that span the width of the rim 192 and / or form a grid-like pattern. The rim 192 and the one or more cross members 194 define a plurality of openings 196 across the third electrode 190. Electrical signals and bias voltages are supplied through flange 112 to first electrode 170, second electrode 180, and third electrode 190 by feedthroughs and conductors generally indicated by 120 (FIG. 2).

[0032] Returning to FIG. 2, since the manufacturing system 10 operates at a low total pressure, the space between the first electrode 170 and the second electrode 180 is larger than the space between the second electrode 180 and the third electrode 190. At lower pressures, more ions need to be generated to increase sensitivity. In one embodiment, the ratio of the space between the first electrode 170 and the second electrode 180 to the space between the second electrode 180 and the third electrode 190 is 8:1. This means that a larger space between the first electrode 170 and the second electrode 180 is needed to allow enough 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 electrode 170 and the second electrode 180 can be reduced so that the ratio is less than 8:1. Some of the embodiments show the second electrode 180 being disposed between the first electrode 170 and the third electrode 190, while other embodiments may not have the second electrode 180 being disposed completely between the first electrode 170 and the third electrode 190.

[0033] The first electrode 170, the second electrode 180, and the third electrode 190 are conductive and may be constructed of steel and coated with gold plating. The gold plating does not significantly change the work function when exposed to oxygen, as compared to the work function of materials such as stainless steel. The electrodes 170, 180, 190 are positioned in the ionization chamber 162 such that their one or more cross members 174, 184, 194 shadow each other. As shown in Figures 3-5, each of the electrodes 170, 180, 190 has two cross members 174, 184, 194. The cross members allow the surface area of ​​the electrodes 170, 180, 190 to be minimized to reduce background noise. In other embodiments, one or more of the electrodes 170, 180, 190 have more than two cross members.

[0034] The operation of the sensor portion of the sensor gauge 100 will now be described with reference to Figures 2-5. The control electronics 80 or controller is shown diagrammatically in Figure 5 and is in communication with the sensor gauge 100. The control electronics 80 are typically grouped together in a box that couples to the sensor flange 112, but they may be located remotely from the sensor gauge 100 and connected to the sensor gauge 100 by a cable. Locating the control electronics 80 remotely is advantageous, for example, when the sensor gauge 100 is located in an environment where the temperature is too high for the control electronics 80 to be present. In one embodiment, the control electronics 80 may include a power supply for the radiation source 130, measurement circuitry for the current of interest, a bias voltage source, a data processor, communication means, etc. The sensor gauge 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 the source electrode 118 to ignite a plasma 140 in the radiation source 130. The plasma 140 emits photons through the radiation window 163 into the ionization chamber 162. The radiation source 130 (and thus the plasma 140) can be adjusted or controlled using a photodiode and / or a camera to measure variations in the light emitted by the plasma 140. The radiation source 130 can be fine-tuned accordingly to remove such variations. At least some of the photons are of a wavelength capable of ionizing the molecules of the analyte gas in the ionization chamber 162, e.g., molecules of a hydrocarbon gas. When the photons collide with the molecules of the analyte gas, they have sufficient energy to generate ions from the molecules of the analyte gas by releasing electrons.

[0035] The first electrode 170, the second electrode 180, and the third electrode 190 are biased to direct one or more flows of charged particles in the ionization volume 162. In one example, the first electrode 170 and the second electrode 180 are held at virtual ground through a current-to-voltage amplifier (I-to-V), and the third electrode 190 acts as a cathode held at some negative potential with respect to ground, typically between −80V and −300V. Photons are emitted by the radiation source 130 and travel through the radiation window 163 into the ionization volume 162 where they collide with the analyte gas molecules. In one embodiment, the radiation source 130 is positioned against an end of the ionization volume 162. Each collision has some probability of causing the ejection of electrons from the analyte gas molecules that generate positive ions that move towards the cathode / third electrode 190, while the ejected electrons move towards the first electrode 170 or the second electrode 180, depending on where the ionization occurs, the geometry of the sensor, the bias voltage, and / or the pressure of the background gas. Although some of the photons have wavelengths short enough to efficiently ionize most organic molecules, the photons do not have enough energy to ionize background gases, typically nitrogen or argon or hydrogen, that may be present in the ionization chamber 162.

[0036] The electron current collected at the first electrode 170 and the second electrode 180 is conveyed by the feedthrough 120 (see FIG. 2) to the control electronics 80 where the current is converted to a voltage, amplified and digitized. The presence of the electron current detected by the controller 80 indicates that the analyte gas may be present in the process chamber 189. In addition to this electron current generated by the photoionization of the analyte gas molecules, other sources of electron current can also be measured by the sensor gauge 100. For example, photons with enough energy to ionize hydrocarbons have more than enough energy (photoelectrons) to eject electrons from most conductors. Photoelectrons generated at the surface of the third electrode 190 are accelerated and collected towards the first electrode 170 and the second electrode 180 by the electric field established by the bias of the third electrode 190, causing a baseline current on these electrodes, and all of the noise and drift present in this photoelectron current contributes to the measured signal of interest. If these photoelectron currents were constant, it would be enough to subtract them from the signal, but they are generally not constant. Thus, reducing both the noise and drift of the photoelectron current improves the ability of the sensor gauge 100 to measure hydrocarbons. One way to reduce the absolute noise and drift is to reduce the photoelectron current as a whole. This can be done 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 acting as a photoelectron source, the photoelectron current and the absolute noise associated with this current can be reduced. The embodiment of the sensor gauge 100 shown in the drawings has a third electrode 190 with a diameter of 0.75 mm and two gold wires stretched across the diameter of the third electrode, providing the required electric field while minimizing the photoelectron generation area as much as is deemed practical.

[0037] Furthermore, the photoelectron current generated for a given photon flux and energy profile depends on the work function of the illuminated surface. If this work function is not constant, the current generated will not be constant even if all other variables (photon flux, area, temperature) are fixed and given. The work function of a conductive surface can be affected by the presence of water or oxygen or other highly electronegative chemicals, such as may be present in certain wafer etch environments. These effects on the signal current are relevant, for example, for monitoring hydrocarbon contaminants in certain semiconductor processes where the wafer may be transferred from an oxygen-containing environment to an oxygen-free environment. Residual effects on the background photoelectron current may mask small hydrocarbon signals of interest. Figure 11 illustrates this effect in this sensor gauge 100 and one way to overcome it. Here, a rectangular pulse of 10 ppm isobutylene is injected into the nitrogen balance from 29300 seconds to 30200 seconds while keeping the total pressure constant. Before and after the pulse, the sensor gauge 100 was exposed to pure nitrogen, but during the pulse, in addition to the isobutylene, the oxygen concentration was increased from zero to 1%. Comparing the signals before and after the pulse for the first electrode 170 and the second electrode 180, a shift in the baseline can be identified. This baseline shift is due to a decrease in photoelectron generation that occurs during and continues after the sample pulse as the sensor 100 is exposed to oxygen. The baseline then recovers, albeit very slowly. This effect is due (mainly) to the work function of the surface of the third electrode 190. To obtain a stable baseline for the hydrocarbon pulse that can be measured, a fraction of the photoelectrons of the signal measured at the second electrode 180 can be subtracted from the signal measured at the first electrode 170. When this fraction is chosen correctly, the effect of the photoelectrons is removed from the data, as shown in "corrected signal" in FIG. 11.

[0038] The distribution of these photoelectrons on the first electrode 170 and the second electrode 180 is a fairly complex function of the pressure at which the sensor 100 is operating. FIG. 6a shows the photoelectron current measured at the first electrode 170 and the second electrode 180 as a function of pressure in nitrogen with a bias of −80V on the third electrode 190. The shape of these curves is due to the pressure-dependent scattering of the photoelectrons from the background gas. The exact percentage of the second electrode signal to subtract from the first electrode signal to derive a “corrected” signal can be read from such a plot for the pressure of interest. 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 the process where no hydrocarbon signal is expected to be present, for example, before turning on the heating in a wafer degassing process. As an example, a regression model of pressure was created for the two electrode signals in the training set of data shown in FIG. 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 to two sensor currents from another test data set shown in FIG. 6b, which was not used to train the model. For a random set of current measurements, a "predicted pressure" was determined. This predicted pressure is displayed on the second y-axis. An example is shown by the dotted line, where two currents measured at about 195 Torr were used to predict a pressure of about 198 Torr. Thus, sensor 100 can be used to measure not only hydrocarbon partial pressures, but also the total pressure in a system, even when the dominant species cannot be ionized by UV photons.

[0039] Of course, if one is optimizing for total pressure measurements rather than measurements of species ionized by UV photons, it is not necessary to try to minimize the photoelectron generation area, as is done in the disclosed sensor 100. It may also be desirable to use a light source where the energy is sufficient to generate photoelectrons from the third electrode or cathode, but where the energy is too low to ionize hydrocarbons or other gas species.

[0040] The calculations of the "correction signal" and "predicted pressure" may be performed by an on-board processor within the control electronics 80, or by a remote computer.

[0041] Another way to reduce these photoelectron effects is to stabilize the photoelectron generation against changes in work function. The work functions of some conductive surfaces are more strongly affected by the presence of oxygen and / or water on them than others, so careful selection of the material of the third electrode surface can help. Gold is less affected by this 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, with gold wire and gold-plated stainless steel parts. The first electrode 170 and second electrode 180 can also be gold-plated, but these surfaces are less critical, since the typical bias of the sensor helps to prevent photoelectron current from being generated on these surfaces and collected elsewhere.

[0042] Referring to FIG. 7, another embodiment of the sensor gauge 200 is shown. This embodiment is the same as the one above, except for the addition of an integrated total pressure gauge 260. In this embodiment, the sensor gauge 200 comprises a sensor portion 210 and a pressure gauge portion 260. The sensor portion 210 comprises a first end 211 and a second end 213. A flange 212 or other surface configured to be attached to a portion of a process chamber or other support is provided. A support 214 is disposed on one side of the flange 212 and is structured to support one or more electrodes (not shown) disposed proximate to the radiation source 230. The one or more electrodes are not shown, but may be similar to other embodiments of electrodes previously described. As in the previously described embodiment, a wall is coupled to the opposite side of the flange 212 relative to the support 214 to define a space. As shown in FIG. 7 and described in other embodiments, the radiation source 230 is a lamp. The radiation source 230 has a first source end 231 disposed on the outside and a second source end fixed on the inside. One or more feedthroughs 220 may be connected to or in communication with a power source or controller 80. As shown, the radiation source 230 encloses a volume filled with a gas, such as Kr gas, although other embodiments may use different gases. The radiation source 230 is constructed from a substantially transparent material that is shatter resistant and capable of withstanding high heat and pressure fluctuations. In one embodiment, the radiation source 230 is constructed from a glass, such as Pyrex®.

[0043] The tube 250 pneumatically couples the atmosphere to a pressure gauge 260, in the atmosphere in which the sensor gauge 200 is located. The pressure gauge 260 is selected to measure the range of pressures in which the sensor is intended to operate. The inclusion of the pressure gauge 260 with the sensor gauge 200 allows for savings on flanges in the process system being monitored. The pressure in the ionization chamber, measured by the pressure gauge 260, can also be used to perform the photoelectron correction described above. By measuring the pressure and photoelectron current on the second electrode, and knowing how the ratio of the photoelectron currents measured on the first and second electrodes depends on pressure, the photoelectron contribution to the current measured on the first electrode can be removed, leaving a corrected analyte signal. The pressure measurements are reported to the control electronics 80, where they can be used, recorded, and / or communicated to the user of the sensor. The walls have an interior space lined with a dielectric to define an ionization space similar to the previously described embodiment. Three electrodes (not shown) are located in the ionization space. A first electrode (not shown) is disposed proximate to a radiation window (not shown), followed by a second electrode (not shown) and a third electrode (not shown) spaced apart from one another such that the second electrode (not shown) is disposed between the first electrode (not shown) and the third electrode (not shown). The electrodes (not shown) are configured similarly to the first electrode 170, the second electrode 180, and the third electrode 190 previously described. One or more openings (not shown) may be defined in the walls and dielectric to allow gas from the process chamber to enter the ionization chamber (not shown). Detection of analytes and pressure determination proceed in a similar manner as described in the previous embodiment.

[0044] 8 and 9, another embodiment of the sensor gauge 300 is shown and described herein. This embodiment of the sensor gauge 300 positions the radiation source 330 entirely inside the process chamber 389 so that the sensor gauge 300 can be positioned adjacent to the wafer 50 being processed or any other part of the manufacturing assembly 10. The sensor gauge 300 has a multi-pin vacuum feedthrough assembly 310 with a first side 311 positioned outside the process or manufacturing environment and a second side 313 positioned inside the process environment. The multi-pin vacuum feedthrough assembly 310 has a flange 312 that fastens against the outside 388 of the process chamber 389 and a sealing element 315 that forms an airtight seal. A support 314 is positioned inside the multi-pin vacuum feedthrough assembly 310. A housing wall 316 extends away from the flange 312 and has a generally cylindrical shape that defines a space. The support 314 serves to support at least two electrodes 320, each positioned adjacent to the radiation source 330. As shown, the radiation source 330 is again a lamp. The radiation source 330 comprises a first source end 331 and a second source end 333 that is fixed within the housing 316 on the process side of the flange 312. The radiation source 330 encloses a volume that is filled with a gas, such as Kr gas, although other embodiments may use different gases. The radiation source 330 is constructed from a substantially transparent material that is shatter-resistant and can withstand high heat and pressure fluctuations. In one embodiment, the radiation source is constructed from or surrounded by glass, such as Pyrex®. In one embodiment, the housing wall 316 at least partially surrounds the radiation source 330 and acts as a sleeve that encapsulates the electrodes that drive the radiation source 330. The housing wall 316 is ideally made from Teflon® or other similar fluoropolymers as a reasonable choice for vacuum and process compatibility, as well as high breakdown voltage. This dielectric barrier serves to prevent discharges from the source electrodes that may occur at some sensor operating pressures and pressure transients that may be experienced during use. In other embodiments, the radiation source 330 is generally potted except for the radiation window 363 .

[0045] The space defined by the walls 316 is lined with a dielectric 360 to form an ionization space or ionization chamber 362 bounded 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 traverse the dielectric 360 and the walls 316 to allow gas from the process chamber to enter the ionization chamber 362. The opposite end of the ionization chamber 362 is also open to the process chamber 389, similar to the previously described sensor gauge 100, 200 embodiments. A first electrode 370 is disposed within the ionization chamber 362 such that the radiation window 363 is disposed between the second source end 333 of the radiation source 330 and the first electrode 370. In the illustrated embodiment, a second electrode 380 is disposed within the ionization space 362 spaced apart from the first electrode 370 such that the first electrode 370 is generally disposed between the radiation window 363 and the second electrode 380. The third electrode 390 is positioned against the opposite end of the ionization chamber 362, away from the second electrode 380. The first electrode 370, the second electrode 380, and the third electrode 390 may be positioned and structured similarly to other previously described embodiments. In the embodiment shown in FIG. 9, the third electrode 390 is specifically shown defining a series of circular openings 396 across the third electrode 390, but the third electrode 390 may be configured similarly to the previously described embodiments for reasons previously explained. Detection of the analyte gas molecules and determination of pressure proceeds similarly to that described in the previous embodiments. Electrical connections from the sensor to the control electronics 80 are made via pins of the feedthrough assembly 310.

[0046] Although the present invention has been particularly shown and described with reference to certain exemplary embodiments, it will be understood by those skilled in the art that various changes in details may be made therein without departing from the spirit and scope of the invention, which may be supported by the written description and drawings. For example, the disclosed methods and assemblies may be used to determine the number density or other properties of an analyte of a sample in a sensor chamber. Furthermore, when an exemplary embodiment is described with reference to a certain number of elements, it will be understood that the exemplary embodiment may be implemented utilizing either fewer or more than a certain number of elements.

Claims

1. 1. A sensor assembly for measuring a total pressure of a gas, comprising: a housing defining a chamber having a first end and an opposing second end, the chamber being permeable to molecules of the gas surrounding the housing; a radiation source configured to emit photons into the chamber; a first electrode disposed against the first end of the chamber; a second electrode disposed within the chamber; a third electrode disposed against the second end of the chamber; and a controller in communication with at least the first electrode and the second electrode; Equipped with the photons emitted into the chamber cause emission of photoelectrons from the third electrode; The controller: electrically biasing the first conductor, the second conductor and the third conductor such that the emitted photoelectrons are attracted towards and collected on the first electrode and the second electrode at a rate that depends on the total pressure of the gas, the photoelectrons generating a current on the first electrode and the second electrode; measuring the current generated on the first electrode and the second electrode; determining the total pressure of the gas based on the current generated on the first electrode and the second electrode; The sensor assembly is configured as follows:

2. The sensor assembly of claim 1 , wherein the radiation source is disposed relative to the first end of the chamber.

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

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

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

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

8. 1. 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, the chamber being permeable to molecules of the analyte gas and the non-analyte gas surrounding the housing; a radiation source configured to emit photons into the chamber; a first conductive electrode disposed against the first end of the chamber; a second conductive electrode disposed within the chamber; a third conductive electrode disposed against the second end of the chamber; and a controller in communication with at least the first conductive electrode and the second conductive electrode; Equipped with the emitted photons ionize at least some molecules of the analyte gas, but the emitted photons are insufficient to ionize molecules of the non-analyte gas; the emitted photons impinge on the third conductive electrode to emit photoelectrons; The controller: 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 such that the photoelectrons are attracted toward and collected on the first conductive electrode and the second conductive electrode in a ratio that depends on the total pressure of the analyte gas and the non-analyte gas; measuring the current generated on the first conductive electrode and the second conductive electrode; determining a ratio of the emitted photoelectrons that are collected on the first conductive electrode and the second conductive electrode at the total pressure; determining an amount of current due to ionization of the analyte gas by correcting the measured current using the determined ratio and subtracting the current caused by the photoelectrons from the measured current; The photoionization sensor assembly is configured as follows:

9. 9. The photoionization sensor of claim 8, wherein the 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.

10. The photoionization sensor of claim 8 , further comprising a pressure gauge attached to the flange and configured to measure a 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 surrounding 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 surrounded by the housing.

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

15. 1. A method for measuring 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, the chamber being permeable to molecules of the analyte gas and the non-analyte gas surrounding the housing; a radiation source configured to emit photons; a first conductive electrode disposed against the first end of the chamber; a second conductive electrode disposed within the chamber; a third conductive electrode disposed against the second end of the chamber; and a controller in communication with at least the first conductive electrode and the second conductive electrode; Structuring the photoionization sensor to comprise: emitting photons from the radiation source into the chamber to ionize at least some of the molecules of the analyte gas, the emitted photons being 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; 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 such that the photoelectrons are attracted toward and collected on the first conductive electrode and the second conductive electrode in a ratio that depends on the total pressure of the analyte gas and the non-analyte gas; measuring the current generated on the first conductive electrode and the second conductive electrode; determining a ratio of the emitted photoelectrons that are collected on the first conductive electrode and the second conductive electrode at the total pressure; determining an amount of current due to ionization of the analyte gas by correcting the measured current using the determined ratio to remove current caused by the photoelectrons; structuring the controller so that A method comprising:

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

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

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

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

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

21. 1. A method for measuring a total pressure of a gas, comprising the steps of: a housing defining a chamber having a first end and an opposing second end, the chamber being permeable to molecules of the gas surrounding the housing; a radiation source configured to emit photons into the chamber; a first electrode disposed against the first end of the chamber; a second electrode disposed within the chamber; a third electrode disposed against the second end of the chamber; and a controller in communication with at least the first electrode and the second electrode; Structuring the photoionization sensor assembly to comprise: impacting the emitted photons on the third electrode to emit photoelectrons; electrically biasing the first conductor, the second conductor and the third conductor such that the emitted photoelectrons are attracted towards and collected on the first electrode and the second electrode at a rate that depends on the total pressure of the gas, the photoelectrons generating a current on the first electrode and the second electrode; measuring the current generated on the first electrode and the second electrode; determining the total pressure of the gas based on the current generated on the first electrode and the second electrode; configuring the controller so that A method comprising:

22. 22. The method of claim 21, further comprising disposing the radiation source relative to the first end of the chamber.

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

24. 22. The method of claim 21 further comprising structuring the third electrode to comprise gold.

25. 22. The method of claim 21, further comprising structuring the housing to at least partially enclose the radiation source.

26. 22. The method of claim 21, further comprising structuring at least one of the first electrode, the second electrode, and the third electrode to include a grid.

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