Method for predicting ion source failure

Abstract

A method for predicting failure of a coated filament of an El ion source includes determining a threshold value for an operating parameter of the coated filament and regulating the coated filament to operate at a stable emission current. An operating parameter is measured during operation of the coated filament at the stable emission current and comparing to the threshold operating parameter. A warning signal is generated and output to a user when the measured operating parameter is equal to or greater than the threshold value. The operating parameter is at least one of a filament drive current value, a filament drive power value, and a filament drive voltage value.

Description

METHOD FOR PREDICTING ION SOURCE FAILURECROSS REFERENCE TO RELATED APPLICATION

[0001] This application is related, and claims priority to, commonly-owned Provisional Patent Application Serial No.: 63 / 540,480, filed September 26, 2023, having the same title. The entire contents of said application is incorporated by reference as if disclosed herein in its entirety.TECHNOLOGICAL FIELD

[0002] Aspects of the following disclosure relate generally to the field of electron impact ionization sources and more specifically a method for predicting the failure of an ion source in order to prevent long process delays due to unexpected ion source failure. Other aspects of this disclosure relate generally to a method for predicting the failure of an ion source of a mass spectrometer, hot ionization gauge, or in implant tool in order to prevent long process delays due to unexpected ion source failure.BACKGROUND

[0003] Mass spectrometry is a common analytical technique used to measure the mass-to- charge ratio of ions in a sample in order to determine the chemical composition of the sample. Generally, mass spectrometry requires ionization of the sample, separating the ions according to their mass-to-charge ratio, detecting the separated ions, and displaying the results as spectra showing signal intensity of the detected ions as a function of the mass-to-charge ratio.

[0004] Hot ionization pressure gauges, e.g. of the Bayard- Alpert type, are commonly used to measure the ambient pressure in vacuum chambers, e.g. semiconductor tools. Generally, hot ionization pressure gauges require the ionization of the sample, collecting the ions, measuring the resulting ion current, correlating the measured ion current to a pressure, and generating a pressure output.

[0005] Ionizing a sample, specifically a gaseous sample, may be done using an electron bombardment ionization source, a.k.a. an electron ionization (El) ion source. The El ion sourceincludes a source of electrons, which may be a filament that is heated to a temperature at which it emits electrons. The filament that is used may be a fine wire comprised of refractory metal that may or may not be coated with a metal oxide. The filament is heated by resistive heating (i.e., running an electric current through the filament) in order to achieve electron emission. The exact temperature of the filament depends, among other things, on the work function of the emitting material. The work function is the minimum energy needed to remove an electron from the solid state of the material to a point inside of a vacuum immediately outside the surface of the material.

[0006] Current state of the art filaments for Mass Spectrometers are made of either uncoated tungsten or yttria- or thoria-coated rhenium or iridium filaments. Yttria and thoria are used as coating materials due to their low work function that greatly extends the lifetime of the filament. Iridium is a preferred material to use for the filament because it is generally unreactive in the presence of most other chemicals (e.g. oxygen). During operation, the filaments are heated to above 1500°C, which results in filament material evaporating until the filament fails. The time to filament failure depends on the environment the filament is used in and other application specific parameters. However, even when filaments are operated under identical conditions, there is considerable variance in the lifetime of these filaments.

[0007] When uncoated tungsten and rhenium filaments are used, the tungsten and rhenium, which carries the current emits the electrons. As the filament material evaporates during operation, the resistivity increases and lower heating current is needed to achieve sufficient electron emission. Consequently, the heating current gradually decreases during the lifetime of the filament. By modelling this gradual decrease, the remaining life can be approximated.

[0008] However, during use the sensor filament will be exposed to different pressures and gas compositions, which causes an increase or decrease in the filament drive current. These changes due to pressure and gas composition can be bigger than the total change of the decrease due to resistivity and overshadow it. Careful data analysis is required to determine whether a gradual decrease in drive current exists, which would indicate a high possibility of filament failure. However, such analysis is difficult to impossible.

[0009] For yttria- or thoria- coated iridium filaments (or other coatings having a low workfunction), the current is run through the iridium filament to passively heat the yttria or thoria to the temperature needed for emitting the electrons. The yttria or thoria evaporates over time, while the iridium filament remains unchanged (i.e., does not evaporate). Consequently, there is no change in resistivity and no gradual decrease in drive current can be observed. After the low workfunction coating is evaporated, the drive current needs to be increased to maintain the same electron emission because iridium has a higher work function, which causes the remaining iridium filament to fail within a very short period of time (few hours). A failure warning of at most a few hours is not sufficient to perform a filament replacement during the next maintenance cycle.

[0010] These are just some of the problems associated with the current methods used to predict El ion source failure.SUMMARY

[0011] Aspects of the present disclosure are directed to a method for predicting filament failure in an electron ionization ion source, which includes providing an electron source for a mass spectrometer or hot ionization pressure gauge including a filament comprised of a material having a first work function coated with at least one second material having a second work function that is different from the first work function. The drive current of the electron source, the drive voltage and / or the electrical power delivered to the electron source is measured during operation of the mass spectrometer or hot ionization pressure gauge and a baseline filament drive current, voltage and / or power is determined. A predetermined threshold drive current value, voltage and / or power is determined based on the baseline filament drive current, voltage and / or power. A filament failure warning is issued when the filament drive current, voltage and / or power moves past the predetermined threshold drive current, voltage and / or power, where the filament failure warning predicts a time frame in which filament failure will occur so that filament replacement may be scheduled as part of tool maintenance thereby inhibiting unpredicted downtime due to filament failure.

[0012] Aspects of the present disclosure are directed to a method for predicting failure of a coated filament of an El ion source. In some embodiments, the method includes determining a threshold value for an operating parameter of the coated filament and continuously regulating thecoated filament to operate at a stable emission current. An operating parameter is measured during operation of the coated filament at the stable emission current and is compared to the threshold operating parameter. A warning signal is generated and output to a user when the measured operating parameter is equal to or greater than the threshold value. In some embodiments, a remaining life of the coated filament is estimated based on the comparison of the measured operating parameter with the threshold value and output to the user along with the warning signal. The operating parameter is at least one of a filament drive current value, a filament drive power value, and a filament drive voltage value.

[0013] In some embodiments, the method further comprises determining a baseline operating parameter, wherein the threshold value for the operating parameter is determined based on the baseline operating parameter. In some embodiments of the method, the stable emission current is maintained by: continuously measuring the emission current from the coated filament; generating an emission control signal based on the measured emission current and transmitting the emission control signal to an energy supply unit configured to supply an amount of energy to the filament; and controlling the amount of energy supplied to the coated filament via the emission control signal.

[0014] In some embodiments, the method further comprises automatically scheduling filament maintenance when the warning signal is generated. In some embodiments of the method, the coated filament comprises a metal with a first work function and a coating with a second work function that is different from the first work function. In some embodiments of the method, the first work function is less than the second work function. In some embodiments of the method, the first work function is greater than the second work function.

[0015] Some aspects of the present disclosure are directed to a method for predicting filament failure in an electron ionization ion source include programming one or more processors and data storage devices to store and execute a plurality of computer-readable instructions configured to: (1) measure a drive current, voltage and / or power of an electron source or the electrical current delivered to the electron source; (2) determine a baseline filament drive current, voltage and / or power or baseline electrical current, which is then used to determine a predetermined threshold drive current, voltage and / or power or a predetermined thresholdelectrical current; (3) monitor the drive current, voltage and / or power or electrical current delivered to the electron source during each use of the electron source; (4) issue a fdament failure warning when the value of the filament drive current, voltage and / or power or the value of the electrical current delivered to the electron source crosses the predetermined threshold drive current, voltage and / or power or the predetermined electrical current. The filament failure warning provides a three (3) to six (6) month or more window in which to schedule maintenance in order to replace the filament.

[0016] Some aspects of the present disclosure are directed to an El ion source monitoring system including an El ion source comprising a filament, an electronics unit in communication with the filament and an El ion source monitoring unit in communication with the electronics unit. In some embodiments, the electronics unit is structured to provide an amount of energy to heat the filament to give off electrons, measure an emissions current from the filament, and regulate the amount of energy provided to the filament to maintain a stable emissions current. In some embodiments, the El ion source monitoring unit is structured to receive signals from the electronics unit pertaining to at least one measured operating parameter of the filament, compare the measured operating parameter to a threshold operating parameter, and generate and output a warning signal to a user when the measured operating parameter is equal to or greater than the threshold value. In some embodiments the El ion source monitoring unit is structured to estimate a remaining filament life based on the comparison of the measured operating parameter with the threshold value, and output the estimated filament life along with the warning signal. In some embodiments, the operating parameter is at least one of a filament drive current value, a filament drive power value, and a filament drive voltage value.

[0017] In some embodiments of the system, the electronics unit maintains a stable emission current by measuring the emission current from the filament and regulating the amount of energy provided to the filament based on the measured emission current. In some embodiments, the emission current is measured continuously during use of the El ion source. In some embodiments, the emission current is measured at a specific frequency. In some embodiments, the frequency is at least once per second. In some embodiments, the frequency is at least one every 5 seconds. In some embodiments, the frequency is at least one per minute. In some embodiments of the system,the El ion source monitoring unit comprises a user input interface including a display. In some embodiments of the system, the fdament comprises a metal with a first work function and is coated with a coating with a second work function that is different from the first work function. In some embodiments of the system, the first work function is less than the second work function. In some embodiments of the system, the first work function is greater than the second work function. In some embodiments of the system, the electronics unit includes an energy source and an emission control unit in communication with the energy source. In some embodiments of the system, the El ion source is part of a mass spectrometer. In some embodiments of the system, the El ion source is part of a hot ion gauge.BRIEF DESCRIPTION OF DRAWINGS

[0018] A more particular description of the invention briefly summarized above may be had by reference to the embodiments, some of which are illustrated in the accompanying drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments. Thus, for further understanding of the nature and objects of the invention, references can be made to the following detailed description, read in connection with the drawings.

[0019] Fig. 1 schematically illustrates a cross section of an embodiment of a mass spectrometer including an El ion source comprising a filament.

[0020] Fig. 2 illustrates a side perspective embodiment of the ion source of Fig. 1.

[0021] Fig. 3 illustrates an embodiment of a hot ion gauge having an El ion source comprising a filament.

[0022] Fig. 4 graphically illustrates a prior art method for predicting ion source failure.

[0023] Fig. 5A graphically illustrates an example of filament drive current versus time when the filament has a higher work function than the material coating the filament.

[0024] Fig. 5B graphically illustrates another example of filament drive current versus time when the filament has a higher work function than the material coating the filament.

[0025] Fig. 5C graphically illustrates an example of filament drive power versus time when the filament has a higher work function than the material coating the filament.

[0026] Fig. 5D graphically illustrates another example of filament drive power versus time when the filament has a higher work function than the material coating the filament.

[0027] Fig. 5E graphically illustrates an example of filament drive voltage versus time when the filament has a higher work function than the material coating the filament.

[0028] Fig. 5F graphically illustrates another example of filament drive voltage versus time when the filament has a higher work function than the material coating the filament.

[0029] Fig. 6A graphically illustrates an example of filament drive current versus time when the filament has a lower work function than the material coating the filament.

[0030] Fig. 6B graphically illustrates another example of filament drive current versus time when the filament has a lower work function than the material coating the filament.

[0031] Fig. 6C graphically illustrates an example of filament drive power versus time when the filament has a lower work function than the material coating the filament.

[0032] Fig. 6D graphically illustrates another example of filament drive power versus time when the filament has a lower work function than the material coating the filament.

[0033] Fig. 6E graphically illustrates an example of filament drive voltage versus time when the filament has a lower work function than the material coating the filament.

[0034] Fig. 6F graphically illustrates another example of filament drive voltage versus time when the filament has a lower work function than the material coating the filament.

[0035] Fig. 7A graphically illustrates an example of filament drive current versus time when the filament is coated with two different materials where the outermost material has a firstwork function, the second material has a second work function and the fdament has a third work function, where the first work function is less that the second work function, which is less than the third work function.

[0036] Fig. 7B graphically illustrates another example of filament drive current versus time when the filament is coated with two different materials where the outermost material has a first work function, the second material has a second work function and the filament has a third work function, where the first work function is less that the second work function, which is less than the third work function.

[0037] Fig. 7C graphically illustrates an example of filament drive power versus time when the filament is coated with two different materials where the outermost material has a first work function, the second material has a second work function and the filament has a third work function, where the first work function is less that the second work function, which is less than the third work function.

[0038] Fig. 7D graphically illustrates another example of filament drive power versus time when the filament is coated with two different materials where the outermost material has a first work function, the second material has a second work function and the filament has a third work function, where the first work function is less that the second work function, which is less than the third work function.

[0039] Fig. 7E graphically illustrates an example of filament drive voltage versus time when the filament is coated with two different materials where the outermost material has a first work function, the second material has a second work function and the filament has a third work function, where the first work function is less that the second work function, which is less than the third work function.

[0040] Fig. 7F graphically illustrates another example of filament drive voltage versus time when the filament is coated with two different materials where the outermost material has a first work function, the second material has a second work function and the filament has a third work function, where the first work function is less that the second work function, which is less than the third work function.

[0041] Fig. 8 illustrates an embodiment of a method for predicting fdament failure in an electron ionization ion source.

[0042] Fig. 9 schematically illustrates an embodiment of an El ion source monitoring system.

[0043] Fig. 10 schematically illustrates another embodiment of an El ion source monitoring system.DETAILED DESCRIPTION

[0044] The following discussion generally relates to various embodiments of a method of predicting fdament failure in an electron ionization ion source. It will be understood that the herein described versions are examples that embody certain inventive concepts as detailed herein. To that end, other variations and modifications will be readily apparent to those of sufficient skill. In addition, certain terms are used throughout this discussion in order to provide a suitable frame of reference with regard to the accompanying drawings. These terms such as “upper”, “lower”, “forward”, “rearward”, “interior”, “exterior”, “front”, “back”, “top”, “bottom”, “inner”, “outer”, “first”, “second”, and the like are not intended to limit these concepts, except where so specifically indicated. The terms “about” or “approximately” as used herein may refer to a range of 80%- 125% of the claimed or disclosed value. With regard to the drawings, their purpose is to depict salient features of the method of predicting filament failure in an electron ionization ion source and are not specifically provided to scale.

[0045] The electron ionization (El) ion source may be used in a variety of applications with various technology. In some embodiments, the electron ionization ion source may be part of a mass spectrometer or a hot ion gauge. Referring to Figs. 1 and 2, an embodiment of a mass spectrometer 100 is shown having an embodiment of an El ion source 101, which generally includes a source of electrons 102, which may be a fine wire filament. As shown, one or more supports 211a, 211b are structured to support the filament 102, an anode 105 defines or at least partially surrounds an ionization volume 106, and one or more electron repellers 107.

[0046] The thermionically emitted electrons from the filament 102 are acceleratedthrough a wall or anode 105 and into an ionization volume 106. The movement of the electrons is guided by electric fields resulting from potential differences maintained between the filament 102, the anode 105 (and perhaps other electrodes) by means of a control unit 200 or spectrometer control, as well as the geometry and locational relationships between the components. It is desirable to maintain the filament temperature and various electric potentials so that a constant electron emission current passes into the ionization volume 106. The electron repeller 107 may be included for steering the electrons. Inside the ionization volume 106, at least some of the accelerated or energetic electrons will collide with molecules of the gas sample that is in the ionization volume 106. The electrons have sufficient energy such that, upon colliding with the gas molecules, they will ionize and / or fragment the gas molecules to produce ions.

[0047] These ions are then accelerated and steered by means of other potentials established using ion optical elements 108 (that are part of the ion source) into the mass filter 109. When the ions having various mass-to-charge ratios reach the mass filter 109 they are separated either spatially or temporally. The ions are then detected by an ion detector 110 and a mass spectrum is determined from the output of the ion detector 110.

[0048] As previously mentioned, the filament 102 of the El ion source 101 has a finite useful lifetime. In order to emit sufficient numbers of electrons, the filament 102 must run at temperatures between 1500-2400°C. At these high temperatures the filament 102 and any coating that may be present on the filament 102 eventually evaporates resulting in filament failure and loss in productivity due to down time of the mass spectrometer 100 for filament 102 replacement. Moreover, the electron-emitting surface of the filament 102 may be chemically altered by the gases in the mass spectrometer system, which increases the work function of the electron-emitting surface while decreasing the electron emission efficiency of the electron-emitting surface. When no electrons or insufficient electrons are available to ionize the gas sample (due to a broken, misshapen, or chemically “poisoned” filament), then the mass spectrometer 100 no longer functions satisfactorily. Consequently, a process that is being monitored and / or controlled based on data produced by the mass spectrometer 100 would have to be stopped or else “run blind” until there is an opportunity to replace the filament 102. Replacement of the filament 102 is a time consuming and inconvenient process since the filament 102 is often located inside of a processvacuum chamber of a gas analyzer. As a result, the process vacuum chamber must be vented to replace the filament 102. Therefore, it is desirable to predict a filament failure so that a preemptive filament replacement can be scheduled. In this manner it is possible to schedule such filament replacement at the same time that the process chamber is off-line for other maintenance activities, thereby lessening the impact that the filament replacement has on the down-time of the tool.

[0049] Turning to Fig. 3, the El ion source 150 of a hot ionization gauge 151 is shown. In some embodiments, the hot ionization gauge 151 may be a Bayard- Alpert (BA) type. In some embodiments the hot ionization gauge 151 includes a filament 152, an anode 160, and a collector pin 170. In some embodiments, the filament 152 may be supported by a filament support 154. In some embodiments, one or more of the components of the hot ionization gauge 151 may be supported by a mounting flange 180. The mounting flange 180 enables the entire hot ionization gauge 151 to be installed and uninstalled very easily and quickly into a system, such as a vacuum chamber. The components of the hot ionization gauge 151, such as the filament 152, the anode 160, and the collector pin 170 are structured to be positioned inside a vacuum chamber. In some embodiments, the mounting flange 180 includes one or more pass throughs 182, which enable electrical connections between components of the hot ionization gauge, such as the filament 152 and a power source and / or control unit positioned on an opposite side or atmospheric side of the mounting flange 180.

[0050] In operation, the El ion source 150 for the hot ionization gauge 151 operates similar to that previously described for mass spectrometers. For example, the filament 152 is heated to emit electrons. The electrons are accelerated toward the anode 160 where they ionize gas molecules. The resulting ions are steered towards the collector pin 170, which is generally maintained at a negative potential relative to the anode 160. A collector detects the ions and measures the current, which is proportional to the pressure.

[0051] The following discussion focus on a method for predicting ion source failure using measurements of an operating parameter of an El ion source. In some embodiments, the operating parameter is a filament drive current, and / or a filament drive power and / or a filament drive voltage provided to the El ion source. As shown in Figs. 1-3, the filament 102 comprises a conductivematerial. In some embodiments, the conductive material includes conductive ceramic, carbide or oxide. In some embodiments, the conductive material includes rhenium, with a coating of yttria oxide (Y2O3). Electrical current is passed through the fdament 102 to resistively heat the fdament 102 and passively heat the yttria coating causing the yttria to emit electrons. The emission of electrons from the yttria results in continuous evaporation of the yttria coating while the filament drive current remains stable. When the yttria coating is almost completely evaporated, the drive current will need to increase in order to keep the emitted electron current constant because the electrons are now being emitted by the structural material of the filament 102, which has a higher work function than yttria, thus requiring a higher temperature for the same emission current density. Once the yttria is completely evaporated, all of the electrons are being emitted by the rhenium and the drive current stabilizes at a higher level until filament failure.

[0052] The difference in drive current between a state where all of the electrons are being emitted by the yttria and a state where all of the electrons are being emitted by the rhenium is significantly large and is reliably detected by the control unit 200. The control unit 200 will then notify the user (or tool) that the filament 102 is reaching the end of its lifetime and replacement should be scheduled. In an embodiment, the method provides a notification indicating that the filament 102 is close to failure and should be replaced. The method is able to predict filament failure less than one (1) month ahead of time, and up to three (3) to six (6) months or more ahead of time in order to provide ample time to schedule maintenance without significant interruption. The prediction takes into consideration the electron emission current provided by the filament 102.

[0053] Figure 4 graphically illustrates an example of a prior art method of predicting ion source failure. The drive current against the operating time for an ion source comprising a wire filament that is an electron source. As shown, the filament 102 / 152 performs at or near the stable baseline drive current L from scan 1 to scan G. After scan G, the filament’s performance begins to decline until scan H when the drive current reaches the predefined threshold filament drive current T. The filament failure warning is issued at scan H or just after scan H. The user is given from scan H to just before scan J to replace the filament 102 / 152 before filament failure occurs at scan J. In the embodiment shown, the period between scan G and scan H encompasses only about eight (8) operating hours.

[0054] Turning to Figs. 5A and 5B, the filament drive current (mA) is plotted against operating time, or operating hours, from time 0 to time N. From time 0 to time A, the filament 102 is performing normally at a baseline or average filament drive current L that is below a predefined threshold filament drive current T. In an embodiment, the predefined threshold filament drive current T may differ from the baseline drive current L by about a 5% , however in other embodiments, the predefined threshold filament drive current T may differ from the baseline drive current L by more than about 5%. Between time A and time B, in a first embodiment, the filament drive current being represented by a dotted line gradually creeps up to and beyond the predefined threshold filament drive current T. A new, higher baseline current H is established between time E and F until a filament failure at time F. Alternatively, normal filament operation is shown between time 0 and time C with a sharp spike in current shortly before time C. A new, higher baseline filament current H is established between time D and time F until a filament failure at time F. Comparing Figs. 5A and 5B, one can observe that the higher baseline filament current H may exhibit a slope that is approximately zero as shown in Fig. 5A or may exhibit a downward slope as shown in Fig. 5B. The downward slope or change in the drive current is relatively small as compared to the changes in the drive current between time A and time B and after time F.

[0055] In the first embodiment, the gradual rise in filament drive current is detected by the control unit 200 and the failure notification is generated. Accordingly, the rising drive current trend may result in the notification of filament failure. In the second embodiment, the sharp increase in the filament drive current over a short period of time is detected by the control unit 200, which triggers generation of the failure notification. In another embodiment, the failure notification is generated when the filament drive current moves above the predetermined threshold filament drive current T for a single measured time point or for a predetermined plurality of consecutive time points. In an embodiment, the predetermined plurality of consecutive time points is at least three (3) time points. Generally speaking and still referring to Figs. 5A and 5B, the user will be warned of filament failure at either time D or time E, which will provide a period of time in which to repair the filament prior to time F. In some embodiments, the period of time may be from a few weeks to a few months.

[0056] In some embodiments, the baseline filament drive current L may be determined bythe control unit 200 during one or more uses of the filament 102 / 152 or from the use of previous filaments used in the ion source or from experimentation. The predetermined settings discussed above may be determined experimentally and programmed into the control unit 200 and / or may be determined and stored by the control unit 200 by the manufacturer.

[0057] In some embodiments, the filament failure may be determined by measuring the filament drive power. Figures 5C and 5D graphically illustrate the filament drive power delivered to electron source, in this case the filament 102 / 152, over time. As can be seen upon comparison of Fig. 5C to Fig. 5A and Fig. 5D to Fig. 5B, the electric power trend in Fig. 5C is similar to the drive current trend in Fig. 5A and the electric power trend in Fig. 5D is similar to the drive current trend of Fig. 5B. The term “power” as used herein refers to the product of a current and a voltage. Referring to Figs. 5C and 5D, from time 0 to time A, the filament 102 / 152 is performing normally at a baseline or average filament drive power BP that is below a predefined threshold filament drive power P. In some embodiments, the predefined threshold filament drive power P may differ from the baseline drive power BP by about a 5%, however in other embodiments, the predefined threshold filament drive power P may differ from the baseline drive power BP by more than about 5%. Between time A and time B, in a first embodiment, the filament drive power being represented by a dotted line gradually creeps up to and beyond the predefined threshold filament drive power P. A new, higher baseline power HP is established between time E and F until a filament failure at time F. Alternatively, normal filament operation is shown between time 0 and time C with a sharp spike in drive power shortly before time C. A new, higher baseline filament drive power HP is established between time D and time F until a filament failure at time F. Comparing Figs. 5C and 5D, one can observe that the higher baseline filament power HP may exhibit a slope that is approximately zero as shown in Fig. 5C or may exhibit a downward slope as shown in Fig. 5D. The downward slope or change in the drive power is relatively small as compared to the changes in the drive power between time A and time B and after time F.

[0058] In some embodiments, filament failure may be determined by measuring filament drive voltage. Figures 5E and 5F graphically illustrate the filament drive voltage delivered to electron source, in this case the filament 102 / 152, over time. As can be seen upon comparison of Fig. 5E to Figs. 5 A and 5C and Fig. 5F to Figs. 5B and 5D, the filament drive voltage trend in Fig.5E is similar to the drive current trend in Fig. 5A and the electric power trend in Fig. 5C. In addition, the filament drive voltage trend of Fig. 5F is similar to the drive current trend in Fig. 5B and the electric power trend in Fig. 5D. Referring to Figs. 5E and 5F, from time 0 to time A, the filament 102 / 152 is performing normally at a baseline or average filament drive voltage BV that is below a predefined threshold filament drive voltage V. In some embodiments, the predefined threshold filament drive voltage V may differ from the baseline drive voltage BV by about a 5%, however in other embodiments, the predefined threshold filament drive voltage V may differ from the baseline drive voltage BV by more than about 5%. Between time A and time B, in a first embodiment, the filament drive voltage being represented by a dotted line gradually creeps up to and beyond the predefined threshold filament drive voltage V. A new, higher baseline voltage HV is established between time E and F until a filament failure at time F. Alternatively, normal filament operation is shown between time 0 and time C with a sharp spike in drive voltage shortly before time C. A new, higher baseline filament drive voltage HV is established between time D and time F until a filament failure at time F. Comparing Figs. 5E and 5F, one can observe that the higher baseline filament voltage HV may exhibit a slope that is approximately zero as shown in Fig. 5E or may exhibit a downward slope as shown in Fig. 5F. The downward slope or change in the filament drive voltage is relatively small as compared to the changes in the drive voltage between time A and time B and after time F.

[0059] In figures 5A-5F, the times are referred to in the abstract as reference time points A, B, C, D, E, and F. However, it may not be the case that each of the time points references corresponds to the same actual time in each of the plots. For example, time A in Fig. 5A may correspond to a real time that is different from the real time corresponding to A in Fig. 5C.

[0060] The embodiments discussed above and shown in the corresponding figures pertain to a rhenium filament coated with a material having a lower work function than the filament material, such as yttria, however in other embodiments the filament 102 / 152 may be coated with a material having a higher work function than the filament material. The embodiments of Figs. 6A-6F illustrate drive current, drive power or drive voltage of a filament 102 / 152 coated with a material having a higher work function than the filament material potted against operating time in hours.

[0061] Referring to Figs. 6A and 6B, the filament drive current (mA) is plotted against operating time or operating hours. As shown, a base line L or average drive current is determined similarly as in Figs. 5A and 5B and plotted as is a predefined threshold filament drive current T, which may differ from the base line drive current L by about 5%, or which may differ by more than about 5%. As shown in Figs. 6A and 6B, between time 0 and time A', the filament drive current remains above or at the base line filament drive current L. However, as the filament coating is evaporated, more and more of the electrons are being emitted from the filament 102 / 152 material (comprised of a material having a lower work function than the coating material) itself and fewer electrons are being emitted from the coating, which results in a decreasing drive current. Between time A' and B', the filament drive current is shown to gradually decrease to the predefined threshold filament drive current T. Accordingly, between time E' and F', a lower base line drive current K is established until filament failure occurs at time F1. In other words, the user is given time period E'-F' to replace the filament 102 / 152 before it fails. Alternatively, the filament drive current may sharply decrease to the predefined threshold filament drive current as is seen between times B' and C. At time C or just after time C, the filament failure notification is generated. Accordingly, between times D' and F1, a lower base line drive current K is established until filament failure at time F'. In other words, the user is given time period D'-F' to replace the filament 102 / 152 before it fails. Comparing Figs. 6A and 6B, one can observe that the lower baseline filament current K may exhibit a slope that is approximately zero as shown in Fig. 6A or may exhibit a downward slope as shown in Fig. 6B. The downward slope or change in the drive current is relatively small as compared to the as compared to the changes in the drive current between time A' and time B' and after time F'.

[0062] Referring to Figs. 6C and 6D, the filament drive power is plotted against operating time or operating hours. As shown, a base line drive power BP or average drive current is determined similarly as in Figs. 5A and 5B and plotted as is a predefined threshold filament drive power P, which may differ from the base line drive power BP by about 5%, or which may differ by more than about 5%. As shown in Figs. 6C and 6D, between time 0 and time A', the filament drive power remains above or at the base line filament drive power BP. However, as the filament coating is evaporated, more and more of the electrons are being emitted from the filament 102 / 152 material (comprised of a material having a lower work function than the coating material) itselfand fewer electrons are being emitted from the coating, which results in a decreasing drive power. Between time A1and B1, the filament drive current is shown to gradually decrease to the predefined threshold filament drive power P. Accordingly, between time E' and F', a lower base line drive power KP is established until filament failure occurs at time F1. In other words, the user is given time period E'-F' to replace the filament 102 / 152 before it fails. Alternatively, the filament drive power may sharply decrease to the predefined threshold filament drive power as is seen between times B' and C. At time C or just after time C, the filament failure notification is generated. Accordingly, between times D1and F1, a lower base line drive power KP is established until filament failure at time F'. In other words, the user is given time period D’-F1to replace the filament 102 / 152 before it fails. Comparing Figs. 6C and 6D, one can observe that the lower baseline filament drive power KP may exhibit a slope that is approximately zero as shown in Fig. 6C or may exhibit a downward slope as shown in Fig. 6D. The downward slope or change in the drive power is relatively small as compared to the as compared to the changes in the drive power between time A1and time B1and after time F1.

[0063] Referring to Figs. 6E and 6F, the filament drive voltage is plotted against operating time or operating hours. As shown, a base line voltage BV or average drive current is determined similarly as in Figs. 5E and 5F and plotted as is a predefined threshold filament drive voltage V, which may differ from the base line drive voltage BV by about 5%, or which may differ by more than about 5%. As shown in Figs. 6E and 6F, between time 0 and time A1, the filament drive voltage remains above or at the base line filament drive voltage BV. However, as the filament coating is evaporated, more and more of the electrons are being emitted from the filament 102 / 152 material (comprised of a material having a lower work function than the coating material) itself and fewer electrons are being emitted from the coating, which results in a decreasing drive voltage. Between time A' and B', the filament drive voltage is shown to gradually decrease to the predefined threshold filament drive voltage V. Accordingly, between time E' and F', a lower base line drive voltage KV is established until filament failure occurs at time F'. In other words, the user is given time period E'-F' to replace the filament 102 / 152 before it fails. Alternatively, the filament drive current may sharply decrease to the predefined threshold filament drive voltage as is seen between times B' and C. At time C or just after time C, the filament failure notification is generated. Accordingly, between times D1and F1, a lower base line drive voltage KV is established untilfilament failure at time F'. In other words, the user is given time period D'-F1to replace the filament 102 / 152 before it fails. Comparing Figs. 6A and 6B, one can observe that the lower baseline filament voltage KV may exhibit a slope that is approximately zero as shown in Fig. 6E or may exhibit a downward slope as shown in Fig. 6F. The downward slope or change in the drive voltage is relatively small as compared to the as compared to the changes in the drive voltage between time A' and time B' and after time F'.

[0064] In figures 6A-6F, the times are referred to in the abstract as reference time points A', B', C', D', E', and F'. However, it may not be the case that each of the time points references corresponds to the same actual time in each of the plots. For example, time A' in Fig. 6A may correspond to a real time that is different from the real time corresponding to A' in Fig. 6C.

[0065] In still another embodiment shown in Figs. 7A and 7B, coatings of more than one material may be applied to the filament 102 / 152 such that the drive current will oscillate several times between two levels or baseline values, L and K, over the time period 0-N until filament failure at time F". The oscillations are used to predict the remaining life of the filament 102 / 152 where each oscillation represents a certain percentage decrease depending on the materials used to coat the filament 102 / 152. Here, the first (outermost) coating is of a material having a low work function. The second coating has a higher work function and the filament 102 / 152 itself has the highest work function of the three (3) materials. In an embodiment, the two coating may be repeated as often as desired. In another embodiment, the filament 102 / 152 may not have the highest work function as compared to the materials used to coat the filament 102 / 152. Referring to Figs. 7A and 7B, the functions oscillate three times before filament failure at time F". Accordingly, the predefined threshold filament drive current T may be crossed at times A", B", C", D" and E". These three (3) oscillations correspond to the three (3) materials used with filament failure occurring at F". Comparing Figs. 7A and 7B, one can observe that the higher baseline filament current H may exhibit a slope that is approximately zero as shown in Fig. 7A or may exhibit a downward slope as shown in Fig. 7B. The downward slope or change in the drive current is relatively small as compared to the as compared to the changes in the drive current between time A" and time B", between times C" and D" and after time F".

[0066] Similar to the embodiments of Figs. 5C-5F and 6C-6F, plotting the drive power ordrive voltage against operating time for the same filament 102 / 152 as in Figs. 7A and 7B will result in similar graphs as those of 7A and 7B. Referring to Figs. 7C and 7D, a filament drive power is plotted against operating time. Similar to Figs. 7A and 7B, the functions oscillate three times before filament failure at time F". Accordingly, the predefined threshold filament drive power P may be crossed at times A'1, B", C", D" and E". These three (3) oscillations correspond to the three (3) materials used with filament failure occurring at F". Comparing Figs. 7C and 7D, one can observe that the higher baseline filament power HP may exhibit a slope that is approximately zero between E" and F" as shown in Fig. 7C or may exhibit a downward slope as shown in Fig. 7D. The downward slope or change in the drive power is relatively small as compared to the changes in the drive power between time A" and time B", between times C" and D" and after time F".

[0067] Referring to Figs. 7E and 7F, a filament drive voltage is plotted against operating time. Similar to Figs. 7A-7D, the functions oscillate three times before filament failure at time F". Accordingly, the predefined threshold filament drive voltage V may be crossed at times A", B", C", D" and E". These three (3) oscillations correspond to the three (3) materials used with filament failure occurring at F". Comparing Figs. 7C and 7D, one can observe that the higher baseline filament voltage HV may exhibit a slope that is approximately zero between E" and F" as shown in Fig. 7E or may exhibit a downward slope as shown in Fig. 7F. The downward slope or change in the filament drive voltage is relatively small as compared to the changes in the filament drive voltage between time A" and time B", between times C" and D" and after time F".

[0068] In figures 7A-7F, the times are referred to in the abstract as reference time points A", B", C", D", E", and F". However, it may not be the case that each of the time points references corresponds to the same actual time in each of the plots. For example, time A" in Fig. 7A may correspond to a real time that is different from a real time corresponding to A" in Fig. 7C.

[0069] In some embodiments, the control unit 200 is a remote unit that receives signals transmitted from a device using an El ion source, such as a mass spectrometer or a hot ionization gauge, and performs the disclosed method to predict filament failure. In some embodiments, the control unit 200 includes one or more processors and data storage units structured to store a plurality of computer-readable instructions and execute stored instructions for implementing thedisclosed method of predicting filament failure in an electron ionization ion source in a mass spectrometer. A user interface / display may be part of the control unit 200 and structured to receive input from a user and output / display information relating to the disclosed method.

[0070] Embodiments of a method 700 for predicting filament failure in an El ion source will now be described with reference to Figs. 8-10. In a first step 702 an El electron source 810 is provided that includes a filament comprised of a material having a first work function coated with at least one second material having a second work function that is different from the first work function. The drive current and / or drive power and / or drive voltage of the filament is measured at step 704 during operation of the ion source and a baseline filament drive current, and / or a baseline filament drive power, and / or a baseline filament voltage is determined. In some embodiments, the electron source is electrically coupled to a current and voltage supply 812 and an emission control unit 816. In some embodiments, the current and voltage supply 812 supplies all voltages and currents 814 to the El ion source 810. In some embodiments, a continuous measurement of emission current 818 is taken from the El ion source 810 by the emission control unit 816. In some embodiments, the emission current is measured at a specific time frequency. In some embodiments, the time frequency is at least once per second. In some embodiments, the time frequency is at least one every 5 seconds. In some embodiments, the time frequency is at least one per minute. In some embodiments, the emission control unit 816 generates an emission control signal 820 in response to the emissions current measurement 818 and transmits said emission control signal 820 to the current and voltage supply 812. In some embodiments, the current and voltage supply 812 is regulated by the emission control signal 820 in order to regulate the drive current in order to achieve a stable emission current. In some embodiments, the current and voltage supply 812 and the emission control unit are part of an electronics unit 815. In some embodiments, the electronics unit 815 includes one or more memory units 817 and one or more processing units 819, such as an analogue circuit, a microcontroller, a digital signal processor (DSP), a field programmable gate array (FPGA), which may be configured to communicate with the El ion source monitoring unit 822 to determine whether conditions for generating a filament failure warning are met. In some embodiments, the electronics unit 815 may include a housing that at least partially surrounds and contains the current and voltage supply 812 and the emission control unit 816. In some embodiments, the electronics unit may further comprise one or moreprocessors and pressure sensors that are configured to obtain additional information from the El ion source 810.

[0071] A predetermined threshold drive current value and / or drive power and / or drive voltage is determined at step 706 based on the corresponding measured baseline filament drive current and / or filament baseline drive power and / or filament baseline drive voltage. In some embodiments, one or more signals are transmitted by the electronics unit 815 to an El ion source monitoring unit 822 pertaining to information received and / or derived by the El ion source 810, the current and voltage supply 812 and / or the emission control unit 816. In some embodiments, the information includes a pressure, mass spectrum, filament drive current, filament drive power and / or filament drive voltage. In some embodiments, the El ion source monitoring unit 822 includes a user interface that outputs information to a user and accepts user input. In some embodiments, the drive current value and / or drive power and / or drive voltage is determined by the El ion source monitoring unit 822 experimentally and stored in the El ion source monitoring unit 822. In some embodiments, a plurality of experimental runs are conducted with one or more filaments until filament failure. In some embodiments, information is obtained by the electronics unit 815 during the plurality of experimental runs and transmitted to the El ion source monitoring unit 822, which in turn uses said information to determine the threshold drive current value and / or drive power and / or drive voltage.

[0072] At step 708, a filament failure warning is issued when the filament drive current moves past the predetermined threshold drive current. In some embodiments, the filament failure warning is generated and output by the El ion source monitoring unit 822 to the user. In some embodiments, the filament warning comprises at least one of a visual, audio, or electronic output. In some embodiments, the El ion source monitoring unit 822 generates a status file for the El ion source and saves any filament failure warning signal to the status file. In some embodiments, the user may program or otherwise set up the El ion source monitoring unit 822 to output saved filament failure warning signals at certain days / times. The filament failure warning, at step 710, predicts a time frame in which filament failure will occur so that filament replacement may be scheduled as part of tool maintenance thereby inhibiting unpredicted downtime due to filament failure. In some embodiments, the El ion source monitoring unit 822 estimates the amount of timeremaining before filament failure and outputs said estimate to the user along with the filament failure warning. In some embodiments, the El ion source monitoring unit 822 automatically schedules filament maintenance after generating the warning signal.

[0073] In some embodiments, the predicted time frame between the filament failure warning and the actual failure of the filament is based on the material comprising the filament, the operating parameters and the operating environment. For example, in the embodiment of Figs. 6A and 6B, the average period length of the drive current oscillation could be used as an in-situ method for predicting the time between the issuance of the filament failure warning and the failure of the filament. In some embodiments, the disclosed method provides a time frame of up to about six (6) months or more between the issuance of the filament failure warning and actual filament failure.

[0074] This detailed description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal language of the claims.

[0075] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting. As used herein, the singular forms “a,” “an,” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprise” (and any form of comprise, such as “comprises” and “comprising”), “have” (and any form of have, such as “has” and “having”), “include” (and any form of include, such as “includes” and “including”), and “contain” (and any form of contain, such as “contains” and “containing”) are open-ended linking verbs. As a result, a method or device that “comprises,” “has,” “includes,” or “contains” one or more steps or elements possesses those one or more steps or elements, but is not limited to possessing only those one or more steps or elements. Likewise, a step of a method or an element of a device that“comprises,” “has,” “includes,” or “contains” one or more features possesses those one or more features, but is not limited to possessing only those one or more features. Furthermore, a device or structure that is configured in a certain way is configured in at least that way, but may also be configured in ways that are not listed.

[0076] The corresponding structures, materials, acts, and equivalents of all means or step plus function elements in the claims below, if any, are intended to include any structure, material, or act for performing the function in combination with other claimed elements as specifically claimed. The description set forth herein has been presented for purposes of illustration and description, and is not intended to be exhaustive or limited to the form disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the disclosure. The embodiment was chosen and described in order to best explain the principles of one or more aspects set forth herein and the practical application, and to enable others of ordinary skill in the art to understand one or more aspects as described herein for various embodiments with various modifications as are suited to the particular use contemplated and in accordance with the following appended claims. Additional embodiments include any one of the embodiments described above and described in any and all exhibits and other materials submitted herewith, where one or more of its components, functionalities or structures is interchanged with, replaced by or augmented by one or more of the components, functionalities or structures of a different embodiment described above.

Claims

CLAIMS1. A method for predicting failure of a coated filament of an El ion source, comprising: determining a threshold value for an operating parameter of the coated filament regulating the coated filament to operate at a stable emission current; measuring an operating parameter during operation of the coated filament at the stable emission current; comparing the measured operating parameter to the threshold operating parameter; generate and output a warning signal to a user when the measured operating parameter is equal to or greater than the threshold value; outputting the warning signal, wherein the operating parameter is at least one of a filament drive current value, a filament drive power value, and a filament drive voltage value.

2. The method of claim 1, further comprising: estimating a remaining life of the coated filament based on the comparison of the measured operating parameter with the threshold value; and outputting the estimated life of the coated filament along with the warning signal.

3. The method of claim 1, further comprising determining a baseline operating parameter, wherein the threshold value for the operating parameter is determined based on the baseline operating parameter.

4. The method of claim 1, wherein the stable emission current is maintained by: continuously measuring the emission current from the coated filament; generating an emission control signal based on the measured emission current and transmitting the emission control signal to an energy supply unit configured to supply an amount of energy to the filament; controlling the amount of energy supplied to the coated filament via the emission control signal.

5. The method of claim 1, further comprising automatically scheduling filament maintenance when the warning signal is generated.

6. The method of claim 1, wherein the coated filament comprises a conductive material with a first work function and at least one coating with a second work function that is different from the first work function.

7. The method of claim 6, wherein the first work function is less than the second work function.

8. The method of claim 6, wherein the first work function is greater than the second work function.

9. The method of claim 1, wherein the coated filament comprises a conductive material with a first work function and at least two coatings, each with a different work function from each other and from the first work function, wherein the first work function is greater than at least one of the work functions of the at least two coatings.

10. The method of claim 1, wherein the coated filament comprises a conductive material with a first work function and at least two coatings, each with a different work function from each other and from the first work function, wherein the first work function is smaller than at least one of the work functions of the at least two coatings.

11. The method of claim 10, wherein the first work function is greater than at least one of the work functions of the at least two coatings and smaller than at least one of the work functions of the at least two coatings.

12. An El ion source monitoring system comprising: an El ion source comprising a filament; an electronics unit in communication with the filament and configured to,provide an amount of energy to heat the filament to produce an emission current, measure said emission current from the filament, and regulate the amount of energy provided to the filament to maintain a stable emission current; an El ion source monitoring unit in communication with the electronics unit and configured to, receive signals from the electronics unit pertaining to at least one measured operating parameter of the filament, compare the measured operating parameter to a threshold operating parameter, generate and output a warning signal to a user when the measured operating parameter is equal to or greater than the threshold value, output the warning signal, wherein the operating parameter is at least one of a filament drive current value, a filament drive power value, and a filament drive voltage value.

13. The system of claim 12, wherein the electronics unit: estimates a remaining life based on the comparison of the measured operating parameter with the threshold value; and outputs the estimated filament life along with the warning signal.

14. The system of claim 12, wherein the electronics unit maintains a stable emission current by: continuously measuring the emission current from the filament; and regulating the amount of energy provided to the filament based on the measured emission current.

15. The system of claim 12, wherein the El ion source monitoring unit comprises a user input interface including a display.

16. The system of claim 12, wherein the filament comprises a conductive material with a first work function and is coated with a coating with a second work function that is different from the first work function.

17. The system of claim 12, wherein the first work function is less than the second work function.

18. The system of claim 12, wherein the first work function is greater than the second work function.

19. The method of claim 12, wherein the coated filament comprises a conductive material with a first work function and at least two coatings, each with a different work function from each other and from the first work function, wherein the first work function is greater than at least one of the work functions of the at least two coatings.

20. The method of claim 12, wherein the coated filament comprises a conductive material with a first work function and at least two coatings, each with a different work function from each other and from the first work function, wherein the first work function is smaller than at least one of the work functions of the at least two coatings.

21. The method of claim 20, wherein the first work function is greater than at least one of the work functions of the at least two coatings and smaller than at least one of the work functions of the at least two coatings.

22. The system of claim 12, wherein the electronics unit includes an energy source and an emission control unit in communication with the energy source.

23. The system of claim 12, wherein the El ion source is part of a mass spectrometer.

24. The system of claim 12, wherein the El ion source is part of a hot ion gauge.

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