KR20060131979A - An ionization gauge - Google Patents

Abstract

An ionization gauge for isolating an electron source from gas molecules includes the electron source for generating electrons, a collector electrode for collecting ions formed by the impact between the electrons and gas molecules, and an electron window which isolates the electron source from the gas molecules. The ionization gauge can have an anode which defines an anode volume and retains the electrons in a region of the anode. The ionization gauge can have a plurality of electron sources and/or collector electrodes. The collector electrode(s) can be located within the anode volume or outside the anode volume. The ionization gauge can have a mass filter for separating the ions based on mass-to-charge ratio. The ionization gauge can be a Bayard-Alpert type that measures pressure or a residual gas analyzer that determines a gas type.

Description

Ionization Gauge {AN IONIZATION GAUGE}

This application is a continuation of US Patent No. 10 / 799,446, filed Mar. 12, 2004, filed March 12, 2004, filed February 19, 2004, all of which is hereby incorporated by reference in its entirety.

Ionization gauges, more specifically Bayard-Alpert (BA) ionization gauges, are the most common nonmagnetic means of measuring very low pressures and have been available worldwide since published in US Patent No. 2,605,431 in 1952. It has been used extensively.

Common ionization gauges include electron sources, anodes and ion collector anodes. In the BA gauge, the electron source is located radially outside of the ionization space (anode volume) defined by the anode. The ion collector electrode is disposed in the anode volume. Electrons move from the electron source towards and through the anode and are eventually collected by the anode. However, in their movement, electrons collide with molecules and atoms of the gas, form air whose pressure is measured, and generate ions. Ions are attracted to the ion collector electrode by an electric field inside the anode. The pressure of the gas in the atmosphere can be calculated from the ionic and electron currents by the equation P = (1 / S) (Iion / Ielectron), where S is a constant using units of 1 / torr and is specific Gauge structure and electrical parameters.

The lifetime of a typical ionization gauge is approximately 10 years when the gauge is operated in a good environment. However, these same gauges and electrode sources (filaments) fail when operated at too high pressure or in gas types that degrade the emission characteristics of the electrode source. Examples of such filament interactions lead to reduced operating life due to the degradation of the electron emission characteristics of the oxide coating on the filament exposed to water vapor. Degradation of the oxide coating significantly reduces the number of electrons produced by the filaments, and exposure of water vapor leads to complete combustion of the tungsten filaments.

Residual gas analyzers (RGA) are ionization gauges that indicate the partial pressure of each gaseous component that can be determined to determine the type of gas present and to calculate the total gas pressure. RGAs measure the mass-to-volume ratio of ions present and convert them into signals. However, the RGA measures additional signal peaks that are completely counterfeit for the type of gas being sensed. These peaks form an important background spectrum in size in the low pressure range of extreme vacuum. This counterfeit spectrum is caused by the interaction of several atoms and / or molecules with the material of the filament, thus forming other compounds in the first non-gas state.

Provided herein is an ionization gauge having an electron source for generating electrons, a collector electrode for collecting ions formed by collision between electrodes and gas molecules and an electron window for isolating the electron source from gas molecules. The ionization gauge can define an anode volume and have an anode that accepts electrons in one region of the anode. The ionization gauge can have multiple electron sources and / or collector electrodes. The collector electrode (s) may be located within or outside the anode volume. The ionization gauge may have a mass filter for separation of ions based on mass to charge ratio. The ionization gauge may be a yard-alert type or residual gas analyzer judged to be pressure or gas type.

The accelerating electrode can be positioned between the electron source (s) and the electron window to accelerate the electrons to energy that allows electrons to pass through the electron window. The deceleration electrode may be located between the electron window and the collector electrode (s) to decelerate electrons to a desired energy distribution that allows ion composition by collisions between electrons and gas molecules. The anode defining the anode volume may be between the deceleration electrode (s) and the collector electrode (s). Multiple collector electrodes can be in the anode volume. The mass filter may be between the deceleration electrode (s) and the collector electrode (s).

The accelerating electrode is maintained at a potential with a potential difference between the electron source (s) and the accelerating electrode ranging from 100 volts to 10,000 volts. The electron window is at a potential equal to the acceleration electrode potential. The deceleration electrode is maintained at a potential such that the potential difference between the electron window and the deceleration electrode is in the range of 0 volts to 10,000 volts. The outer collector electrode may be between the electron window and the deceleration electrode to collect ions formed by collisions between electrons and gas molecules for high pressure states of very short mean free paths. The ionization gauge can include a plurality of external collector electrodes, acceleration electrodes and deceleration electrodes.

The shield may define the shielded volume such that a potential independent of the shield does not disturb the charge distribution within the shielded volume. The shield is at least partially open to allow delivery of gas molecules to the shielded volume. The shielded volume houses the electron source (s), collector electrode (s) and electron window. The shield is maintained at a reference potential, where the reference potential can be a ground potential.

The foregoing and other objects, features, and advantages of the present invention will become apparent from the following more detailed description of the preferred embodiments of the present invention, wherein like reference numerals refer to like elements throughout the different figures of the accompanying drawings in which: FIG. do. The drawings do not necessarily need to be scaled, and may highlight areas of interest in describing the principles of the invention.

1 is a schematic diagram of a generalized ionization gauge of the present invention;

FIG. 2A is a detailed schematic diagram of the non-nude type ionization gauge of FIG. 1; FIG.

FIG. 2B is a detailed schematic diagram of another embodiment of FIG. 2A;

3 is a schematic representation of a generalized mass spectrometer of the present invention.

Description of the preferred embodiments of the present invention is as follows.

As shown in FIG. 1, generally one ionization gauge 100 of the present invention has an insulation chamber 110 and a measurement chamber 120. The insulation chamber includes at least one electron source 140 and at least one acceleration electrode 150. The measurement chamber 120 includes at least one deceleration electrode 170, an anode 180 and at least one collector electrode 190. The two chambers 110, 120 are insulative material 130 which prevents molecules and atoms of gas from entering the isolation chamber 110 and degrading the electron source 140 (s) within the measurement chamber 120. Separated by. Insulating material 130 has an electronic window 160 that allows electrons to be transferred from insulating chamber 110 to measurement chamber 120. Although ionization gauge 100 is shown with anode 180 and collector electrode 190, these configurations are not necessary in all embodiments of the present invention as described below. In one embodiment, the ionization gauge 100 is a Bejar-Alpert type gauge.

2A illustrates a particular non-nude ionization gauge 200 embodying the present invention. While a non-nude type gauge is shown, it should be understood that a nude ionization gauge can be embodied using the principles of the present invention. The ionization gauge 200 has a configuration similar to the ionization gauge 100 (FIG. 1) described above having the following adducts. The ionization gauge 200 is housed in a tube 205 that opens at one end 225 to introduce molecules and atoms of gas into the measurement chamber 120 through the shield 220. Shield 220 and tube 205 form a shielding volume. At least one optional external collector electrode 210 is added for high pressure measurements of very short average free stroke.

FIG. 2B shows another embodiment of the invention shown in FIG. 2A. A plurality of collect electrodes 190 ′ is located within anode volume 185. The plurality of collector electrodes 190 ′ effectively inhibits electrons approaching anode support posts (not shown), thus preventing premature collection of electrons on these posts. Thus, the electron path length is significantly increased compared to that of conventional gauges of the same size. Increasing the path length of the electrons is very desirable to increase the path length of the electrons inside the anode volume 185 since this portion of the path length increases the ratio of generated ions, and thus proportionally increases the gauge sensitivity. Do. Many collector electrodes are described in US Pat. No. 6,025,723; 6,046,456; And 6,198,105, the entire contents of which are incorporated herein by reference.

In operation, molecules and atoms of the gas enter the measurement chamber 120 through the partially open shield 220. The shield 220 prevents potentials unrelated to the shield 220 from disturbing the charge distribution inside the measurement chamber 120. Shield 220 is maintained at a reference potential. In one embodiment, the reference potential is ground potential.

The electron source (s) (eg, filaments) 140 generate electrons (represented by the electron beam 208) inside the insulating chamber 110. These electrons are used to ionize gas molecules in the measurement chamber 120. The geometry of the filament 140 can be a linear ribbon, linear wire, straight ribbon, curved ribbon, straight wire, U-shaped wire, or any other shape known in the art. In one embodiment, filament 140 uses a current from an emission regulator (not shown) to resistively heat the incandescent lamp. Thermoelectrically, or in another way, the emitted electrons are accelerated by the acceleration electrodes 150 to energy that allows the electrons to be transferred through the electron window 160. Acceleration electrodes 150 operate at a potential where the potential difference between the electron source and the acceleration electrodes ranges from 100 volts to 10,000 volts, depending on the size, thickness and type of material used for the electron window. In one embodiment, the acceleration electrodes 150 are maintained at a potential difference from the electron source (s) on the order of 1,000 volts. The electronic window was published in January 1956, J.R. It may be made of aluminum as described in Young, "Penetration of Electrons and Ions," Journal of Applied Physics, all of which is incorporated herein by reference.

The electrons must have a controlled electron energy to the desired level so that ionization is allowed after the electrons are delivered through the electron window 160. Ionization occurs on higher or lower energy spreads than the nominal design energy, as described in Saul Dushman, Scientific Foundations of Vacuum Technique, 1962. Ionic composition generally occurs at electron energy on the order of 150 electron volts relative to nitrogen. Thus, the energy of the electrons is modified by the slowing electrodes 170 which allow ionization. The reduction electrodes 170 operate at a potential in which the potential difference between the electron window and the reduction electrodes ranges from 100 volts to 10,000 volts depending on the size, thickness and type of electron window and the incident electron energy required by the type of pressure measurement. . For example, as shown in FIGS. 2A and 2B, the reduction electrodes 170 are maintained at a potential that reduces electron energy such that they reach the anode grid 180 using energy of about 150 electron volts.

Anode grid 180 defines anode volume 185 and is charged to positive 180 volts with respect to ground. The anode grid 180 may be of a design such as made of a wire mesh or allowing electrons to enter and exit the anode grid 180. Most of the electrons do not attack the anode grid 180 directly, but pass through the anode grid 180 and move to the anode volume 185 where they generate ions through electron collision ionization. Electrons that do not attack the anode grid 180 or ionize any molecules pass through the anode volume 15 into the region between the anode grid 180 and the tube 205. Due to the electric field generated between the tube 205 and the anode grid 180, there are electrons that decelerate and re-accelerate back towards the grid 180. The electrons continue to cycle in this manner until they are collected by the anode grid 180 or lost on another surface. Multiple passes of electrons increase the ionization efficiency of the current compared to single pass structures.

Once generated by electron bombardment ionization, the ions tend to stay inside the anode grid 180. Ions formed inside anode volume 185 are (a) anode grid 180 at positive potential with respect to ground and (b) collector at potential near ground potential (ie, negative with respect to anode potential). The direction is set by the electric field generated by the potential difference between the electrode (s). The electric field directs the ions to the collector electrode (s) 190 where they are collected to provide the ionic current used to determine the pressure of the gas. In some embodiments, the high pressure is measured using an outer collector electrode 210 very close to the window for capture of ions formed very close to the window, not inside the anode, due to a short average free stroke at high pressure. Can be.

3 shows a residual gas analyzer (RGA) 300 embodying the present invention. The above-described RGA 300 and ionization gauges 100, 200 may include an anode grid 180 and collector electrodes 190, 190 ′ of FIGS. 1, 2A and 2B with a mass filter 310 and an ion detector 320. Are essentially the same except that they are replaced by

In operation, molecules and atoms of gas enter the measurement chamber 120. The electron source (s) 140 (eg, filaments) generate electrons inside the insulating chamber 110. Thermoelectronically emitted electrons (or electrons generated from a radioactive source or the like through field emission, photoelectron emission, plasma emission) are accelerated electrodes to energy that allows electrons to be transferred through the electron window 160. Accelerated by 150. Electrons are used to ionize gas molecules and atoms in the measurement chamber 120.

The electrons should have a controlled level of energy that is acceptable for the ionization that occurs after the electrons are transferred through the electron wed 160. The energy of the electrons is modified by the slowing electrodes 170 which are allowed for ionization.

Ions enter the mass filter 310 to separate the ions based on their mass to charge ratio (m / z). The mass filter 310 allows the selected ions to move to the ion detector 320. This mass filter 310 filters the ions based on their mass to charge ratio. Only ions that match the mass filter parameters are passed through the mass filter 310 at a given time. The ion detector 320 counts the ions and generates a signal proportional to the total number of ions at each given time as described above. This signal is recorded in a data system (not shown) which outputs the type of gas present.

While the invention has been shown and described in part with respect to preferred embodiments thereof, those skilled in the art will recognize that the invention is without departing from the scope of the invention as defined by the following claims. It will be appreciated that can be modified.

Claims (46)

As an ionization gauge, An electron source for generating electrons; A collector electrode for collecting ions formed by collision between the electrons and gas molecules; And An electron window separating the electron source from the gas molecules Ionization gauge comprising a. The method of claim 1, An acceleration electrode between the electron source and the electron window for accelerating the electrons with energy that allows the electrons to pass through the electron window; And A deceleration electrode between the electron window and the collector electrode for decelerating the electrons An ionization gauge, characterized in that it further comprises. The method of claim 2, And said acceleration electrode comprises a plurality of acceleration electrodes. The method of claim 2, And said deceleration electrode comprises a plurality of deceleration electrodes. The method of claim 2, The ionization gauge further comprising an anode defining an anode volume, the anode surrounding the collector electrode. The method of claim 5, And the collector electrode comprises a plurality of collector electrodes. The method of claim 2, And a mass filter between the deceleration electrode and the collector electrode. The method of claim 2, And the acceleration electrode is maintained at a potential such that the potential difference between the electron source and the acceleration electrode is in the range of 100 volts to 10,000 volts. The method of claim 2, And the deceleration electrode is maintained at a potential such that the potential difference between the electron window and the deceleration electrode is in the range of 0 volts to 10,000 volts. The method of claim 2, And an external collector electrode between the electron window and the deceleration electrode. The method of claim 10, And the outer collector electrode comprises a plurality of outer collector electrodes. The method of claim 1, And the ionization gauge further comprises a shield defining a shielded volume, the shield being at least partially open to deliver the gas molecules to the shielded volume. The method of claim 12, And said shielded volume contains said electron source, said collector electrode and said electron window. The method of claim 12, And the shield is maintained at a reference potential. The method of claim 14, And said reference potential is a ground potential. The method of claim 1, And said gauge is a pressure gauge. The method of claim 1, The gauge is characterized in that the Bayard-Alpert type (Bayard-Alpert type). The method of claim 1, The gauge is characterized in that the residual gas analyzer (residual gas analyzer). The method of claim 1, The ionization gauge further comprising an anode defining an anode volume, the anode volume receiving electrons in a region of the anode. The method of claim 19, And the collector electrode is inside the anode volume. The method of claim 20, And the collector electrode comprises a plurality of collector electrodes inside the anode volume. The method of claim 19, And the collector electrode is outside the anode volume. The method of claim 22, And said collector electrode comprises a plurality of collector electrodes outside said anode volume. The method of claim 1, And a mass filter for separating ions based on a mass-to-charge ratio. The method of claim 1, And said electron source comprises a plurality of electron sources for generating electrons. A method of measuring gas pressure from gas molecules and atoms, Generating electrons in the electron source; Delivering the electrons through an electron window that isolates the electron sources from the gas molecules; And Collecting ions generated by the collision between the electrons and the gas molecules and atoms on a collector electrode Gas pressure measurement method comprising a. The method of claim 26, Generating the electrons comprises using a plurality of electron sources to generate the electrons. The method of claim 26, Delivering the electrons comprises using an accelerating electrode that accelerates the electrons with energy causing the electrons to pass through the electron window. The method of claim 28, And using the acceleration electrode comprises using a plurality of acceleration electrodes to accelerate the electrons with energy that allows the electrons to pass through the electron window. The method of claim 28, And the acceleration electrode is maintained at a potential such that the potential difference between the electron source and the acceleration electrode is in the range of 100 volts to 10,000 volts. The method of claim 26, Collecting the ions comprises decelerating the electrons using a deceleration electrode. The method of claim 31, wherein The step of using the deceleration electrode comprises using a plurality of deceleration electrodes to decelerate the electrons. The method of claim 31, wherein And the deceleration electrode is maintained at a potential such that the potential difference between the electron window and the deceleration electrode is in the range of 0 volts to 10,000 volts. The method of claim 31, wherein Collecting ions on an outer collector electrode between the electron window and the deceleration electrode. The method of claim 26, The method of measuring gas pressure further comprises stabilizing sensitivity using a shield defining a shielded volume, The shield is at least partially open to allow transfer of the gas molecules and atoms to the shielded volume such that potentials unrelated to the shield do not disturb the charge distribution inside the shielded volume. Gas pressure measurement method. 36. The method of claim 35 wherein Said shielded volume containing said electron source, said collector electrode and said electron window. 36. The method of claim 35 wherein And said shield is maintained at a reference potential. The method of claim 37, And said reference potential is a ground potential. The method of claim 26, And said collected ions are used to measure pressure. The method of claim 26, The collected ions are used to determine the gas type gas pressure measurement method. The method of claim 26, And said collector electrode is within an anode volume defined by an anode. The method of claim 41, wherein And said collector electrode comprises a plurality of collector electrodes in said anode volume. The method of claim 26, And the collector electrode is outside the anode volume defined by the anode. The method of claim 43, And said collector electrode comprises a plurality of collector electrodes outside said anode volume. The method of claim 26, And separating the ions using a mass filter based on a mass-to-charge ratio. As an ionization gauge, Means for generating electrons; Means for collecting ions formed by collisions between electrons and gas molecules from an electron source; And Means for separating means for generating electrons from the gas molecules.

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