Magnetic shield member for quadrupole mass spectrometer

Abstract

A shield member for a mass sensor includes a body including an outer shield surface and an inner shield surface defining shield sides and a body portion that is positioned between the shield sides. The shield member further includes a support member configured to support at least a portion of the body and structured to enable airflow though the support member. The body of the shield member is configured to shield one or more components of a mass sensor from a magnetic field.

Description

MAGNETIC SHIELD MEMBER FOR QUADRUPOLE MASS SPECTROMETERCROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims the benefit and priority of U.S. Provisional Application SerialNo. 63 / 633,361, filed on April 12, 2024. The entire contents of said applications is hereby incorporated by reference.TECHNOLOGICAL FIELD

[0002] This disclosure relates generally to the field of mass spectrometry and more specifically an element or device for magnetic shielding of a quadrupole mass spectrometer sensor.BACKGROUND

[0003] Mass spectrometers are analyzers that are used to determine a mass-to- charge ratio of ions, which may be displayed as a plot of intensity as a function to the mass-to- charge ratio, otherwise known as a mass spectrum. One example of a mass spectrometer is a quadrupole mass spectrometer. The quadrupole mass spectrometer includes four parallel conducting rods spaced about a central axis along which ions are conducted. Adjacent rods are at an opposite radiofrequency (RF) phase such that, for a given set of RF and direct current (DC) potentials, only ions within a narrow mass-to-charge range will have a stable trajectory and reach the ion detector. Ions outside this range will collide with the rods and be neutralized prior to reaching the detector. A pump, such as a magnetic bearing pump (turbo pump), is used to maintaininterior spaces of the mass spectrometer at pressures below atmospheric pressure.

[0004] Current quadrupole mass spectrometers are being manufactured with lower profile manifolds in an effort to decrease the overall size of the unit. This decrease results in the sensor being moved closer to the turbo pump, which causes interference of the magnetic field generated by the turbo pump with certain mass ranges, such as low mass (AMU) ranges. The interference manifests in excess noise and / or reduces sensitivity of the sensor. One solution to this problem is to increase the size of the manifold, which is antithetical to the objective of size reduction. Other solutions may include the addition of shielding components, which can also increase the size of the mass spectrometer as well as the overall cost.

[0005] These are just some of the problems associated with current quadrupole mass spectrometers.BRIEF SUMMARY OF INVENTION

[0006] Aspects of the following disclosure are directed to embodiments of a mass sensor for a mass spectrometer including a magnetic bearing pump configured to generate a magnetic field. In some embodiments, the mass sensor includes an inlet configured to receive a gas sample, an ion source configured to generate ions from the gas sample, a mass analyzer configured to separate the generated ions based on mass, an ion detector configured to detect at least some of the separated ions, and a shield member. In some embodiments, the shield member includes a body including an outer shield surface and an inner shield surface that at least partially surrounds the mass analyzer. In some embodiments, the body defines at least one opening configured to facilitate air flow between the magnetic bearing pump and the shield interior. In some embodiments, the body is configured to align the mass analyzer. In some embodiments, the body is positioned between the mass analyzer and the magnetic bearing pump and is configured toshield the mass analyzer from the magnetic field generated by the magnetic bearing pump to improve sensitivity and tuneability in low mass ranges.

[0007] In some embodiments of the mass sensor, the body of the shield member at least partially surrounds the ion detector and is configured to shield the ion detector from the magnetic field generated by the magnetic bearing pump. In some embodiments of the mass sensor, the body of the shield member at least partially surrounds the ion source and is configured to shield the ion source from the magnetic field generated by the magnetic bearing pump. In some embodiments of the mass sensor, the body of the shield member is configured to align the ions source, the mass analyzer and the ion detector along a common axis. In some embodiments of the mass sensor, the body of the shield member is comprised of an alloy. In some embodiments of the mass sensor, the mass analyzer comprises a quadrupole. In some embodiments of the mass sensor, the shield member further includes a support member positioned between the body and the magnetic bearing pump. In some embodiments of the mass sensor, the support member includes a plurality of perforations to enable an air flow between the body and the magnetic bearing pump.

[0008] Aspects of the following disclosure are directed to embodiments of a method of shielding a mass sensor for a mass spectrometer that includes a magnetic bearing pump configured to generate a magnetic field. In some embodiments, the method includes structuring a shield member to include a body that includes an outer shield surface and an inner shield surface defining a shield interior and that at least partially surrounds a mass analyzer of the mass sensor. Some embodiments of the method include structuring the body of the shield member to define at least one opening that is configured to facilitate air flow between the magnetic bearing pump and the shield interior. Some embodiments of the method further include structuring the body of the shield member to align the mass analyzer. Some embodiments of the method further includepositioning the body of the shield member between the mass analyzer and the magnetic bearing pump to shield the mass analyzer from the magnetic field generated by the magnetic bearing pump and improve sensitivity and tuneability in low mass ranges.

[0009] Some embodiments of the method further include structuring a support member to be positioned between the body and the magnetic bearing pump. Some embodiments of the method further include structuring the support member to define a plurality of perforations that are configured to enable an air flow between the body and the magnetic bearing pump. Some embodiments of the method further include structuring the shield member to be comprised of an alloy.

[0010] Aspects of the following disclosure are directed to embodiments of a shield member for a mass sensor. In some embodiments, the shield member includes a body including an outer shield surface and an inner shield surface that defines shield sides and a body portion that is positioned between the shield sides. In some embodiments, the shield member includes a support member that is configured to support at least a portion of the body and is structured to enable airflow though the support member. In some embodiments of the shield member, the body is configured to shield one or more components of a mass sensor from a magnetic field.

[0011] In some embodiments of the shield member, the support is configured to be positioned between a magnetic bearing pump of a mass spectrometer and the body. In some embodiments of the shield member, the support member includes a plurality of perforations. In some embodiments of the shield member, the body is coupled to the support member. In some embodiments of the shield member, the body is comprised of an alloy. In some embodiments of the shield member, the body comprises a concave shape.BRIEF DESCRIPTION OF DRAWINGS

[0012] 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.

[0013] FIG. 1 illustrates a perspective view of an embodiment of a mass spectrometer having a distance DI between a sensor and a magnetic bearing pump.

[0014] FIG. 2 schematically illustrates an embodiment of a sensor of the mass spectrometer of FIG. 1.

[0015] FIG. 3 schematically illustrates an embodiment of a quadrupole mass filter or mass analyzer of the sensor.

[0016] FIG. 4 illustrates a perspective view of an embodiment of a compact or low profile mass spectrometer having a distance D2 between a sensor and a magnetic bearing pump, which is less than DI of the embodiment of FIG. 1.

[0017] FIG. 5 schematically illustrates an embodiment of a sensor of the mass spectrometer of FIG. 4.

[0018] FIG. 6 illustrates an exploded view of an embodiment of a sensor of the mass spectrometer of FIG. 4.

[0019] FIG. 7 illustrates an assembled view of the sensor of FIG. 6.

[0020] FIG. 8 illustrates an embodiment of a shield member of the sensor of FIG.

[0021] FIG. 9 schematically illustrates another embodiment of a sensor of the mass spectrometer of FIG. 4.

[0022] FIG. 10 illustrates a perspective view of an embodiment of the shield member of the sensor of FIG. 9.

[0023] FIG. 11 illustrates a perspective view of the embodiment of the shield member of FIG. 10 separated from an embodiment of a magnetic bearing pump.

[0024] FIG. 12 illustrates a perspective view of the embodiment of the shield member of FIG. 10 coupled to an embodiment of a magnetic bearing pump.

[0025] FIG. 13 A shows a mass spectrum of a gas sample analyzed using the mass spectrometer of FIG. 1 exhibiting a peak at 2AMU.

[0026] FIG. 13B shows a mass spectrum of a gas sample analyzed using a compact mass spectrometer similar to that of FIG. 4, but without a shield member .

[0027] FIG. 13C shows another example of the mass spectrum of FIG. 13 A.

[0028] FIG. 13D shows a mass spectrum of a gas sample analyzed using a compact mass spectrometer similar to that of FIG. 4, but with a shield member according to the disclosure.DETAILED DESCRIPTION

[0029] The following discussion relates to various embodiments of a shielding device for a quadrupole mass spectrometer sensor. 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 referencewith 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 shielding device for a quadrupole mass spectrometer sensor and are not specifically provided to scale.

[0030] Figure 1 shows an example of a prior art quadrupole mass spectrometer (“mass spectrometer”) 10. As shown, the mass spectrometer 10 generally includes a manifold 12 with an inlet 14 at one end. The manifold 12 may be coupled to an electronics box or an electronic control 16 at an opposing end. The manifold 12 and the electronic control 16 are supported by a base 18. A magnetic bearing pump 20 is positioned between the base 18 and the manifold 12. The magnetic bearing pump 20 and the manifold 12 are shown as being spaced apart by a distance DI . In operation, the inlet 14 of the mass spectrometer 10 is fluidly or pneumatically coupled to a process chamber of a manufacturing or fabrication assembly in a gas-tight manner such that gases from the process chamber may enter the mass spectrometer 10 through the inlet 14 and be analyzed by the sensor 100 (FIG. 2). The magnetic bearing pump 20 acts to maintain a pressure inside at least the sensor 100 (FIG. 2) of the mass spectrometer at a pressure that is below atmospheric pressure.

[0031] The manifold 12 at least partially surrounds components of the sensor 100 as shown schematically in FIG. 2. The sensor 100 generally includes an ion source 22 positioned near the inlet 14 and that is structured to generate ions from the gas molecules entering the inlet 14 from the process chamber. The generated ions then move through the mass analyzer 24, suchas a quadrupole mass analyzer 25 (FIG. 3), where ions with the desired mass-to-charge ration pass on to an ion detector 26, while the other ions are neutralized by the mass analyzer 24. The ion detector 26 is in electrical communication with a data collector 75, such a computer, which receives transmissions from the ion detector 26 and generates a mass spectrum based on said transmissions. The magnetic bearing pump 20 is fluidly or pneumatically coupled to the sensor 100 in order to maintain the sensor interior 102 at a pressure that is below atmospheric pressure.

[0032] In some embodiments, the mass analyzer 24 includes a mass filter configured as a quadrupole 25, such as that shown in FIG. 3. In some embodiments, the quadrupole 25 is configured with four (4) rods or poles 25a, 25b, 25c, 25d, which are arranged to be symmetrical along X, Y and Z axes. The poles are coupled to an electrical source such that the applied potentials for each pole may be adjusted according to the desired mass-to charge of the ions to be detected. The ions with the desired mass-to-charge ratio are directed generally in direction Q through a longitudinal space 27 between the poles 25a, 25b, 25c, 25d from a first end to a second end towards the detector 26.

[0033] Turning to FIGS. 4-7, a more compact embodiment of the mass spectrometer 50 is shown. This embodiment of the mass spectrometer 50 generally includes the same or similar elements as the embodiment shown in FIG. 1. For example, the mass spectrometer 50 includes a manifold 52 with an inlet 54 at one end. The manifold 52 is coupled to an electronics box or an electronic control 56 at an opposing end. The manifold 52 and the electronic control 56 are supported by a base 58. A magnetic bearing pump 60 is positioned between the base 58 and the manifold 52. The magnetic bearing pump 60 and the manifold 52 are spaced apart by a distance D2. As can be observed, the distance DI in the mass spectrometer 10 of Fig. 1 is larger than the distance D2 in the mass spectrometer 50 shown in Fig. 2. In some embodiments, DI and D2 aremeasured from a center line Q of the sensor 100 to the top of the magnetic bearing 60. Tn some embodiments, DI is at least twice as large as D2. In some embodiments, DI is about 74mm and D2 is about 23.6mm. In some embodiments, the magnetic interference becomes negligible between 45~50mm. The smaller distance D2 results in a more compact or lower profile mass spectrometer 50. In operation, the inlet 54 of the mass spectrometer 50 is similarly fluidly or pneumatically coupled to a process chamber of a manufacturing or fabrication assembly in a gastight manner such that gases from the process chamber may enter the mass spectrometer 50 through the inlet 54 into the sensor 110. The process gases enter the inlet and enter an ion source 62 defining an ionization volume where the process gases are bombarded by electrons, which remove outer shell electrons from gas molecules to generate ions. The generated ions then move through a mass analyzer 64, where ions with the desired mass-to-charge ratio pass on to the ion detector 66, while the other ions are neutralized by the mass analyzer 64. The ion detector 66 is in electrical communication with a data collector 75, such a computer. The data collector 75 receives transmissions from the ion detector 66 and generates a mass spectrum based on said transmissions. The magnetic bearing pump 60 is pneumatically coupled to the sensor 10 in a gas tight manner and is configured to maintain a pressure inside 112 the sensor 110 that is below atmospheric pressure.

[0034] The low-profile configuration of the embodiment of the mass spectrometer 50 shown in FIG. 3 advantageously enables installation of the mass spectrometer 50 in a smaller space relative to other mass spectrometers. Accordingly, the overall footprint of a fabrication assembly may be reduced. However, the smaller distance D2 positions the manifold 52 in close proximity to the magnetic bearing pump 60 as compared to the typical mass spectrometer as shown, for example, in FIG. 1. This close proximity results in signal interference due to themagnetic field generated by the pump 20. As a result of the signal interference, the mass spectrometer has a decreased sensitivity in the low mass (AMU) ranges. Accordingly, a quadrupole 25 (FIG. 3) would not operate properly in this compact configuration.

[0035] Referring to FIGS. 5-7, the sensor 110 further includes a shield device or shield member 120. As shown schematically in FIG. 5, the shield member 120 is positioned inside of the manifold 52 and surrounds a portion of the sensor 110. Figures 5-7 show an embodiment of the sensor 110 where the shield member 120 surrounds and aligns the mass analyzer 64. In some embodiments, the shield member 120 may also surround at least a portion of the ion detector 66. In some embodiments, the shield member 120 aligns the ions source 62, and the mass analyzer 64 along a common axis. In some embodiments, the shield member 120 aligns the ion source 62, the mass analyzer 64, and the ion detector 66 along a common axis. As shown in the embodiments of FIGS. 6 and 8, the shield member 120 comprises a body 121 that, in some embodiments is generally hollow and includes an outer shield surface 123 and an inner shield surface 125 that at surrounds a portion of, or at least partially defines the sensor interior 112 (FIG. 5). One or more openings 122, 124, 126 may be defined in the body 121 that are structured: as a pass through for electrical connections; to accept a fastener 129 (122); to facilitate air flow between the pump 60 and the sensor 100 (124 / 126); and / or to enable access to specific sensor components. The shield member 120 may be coupled to the manifold 52 and / or to structural components of the sensor 110 and / or to a sensor flange 130 as shown in FIGS. 6 and 7. As shown, the shield member 120 is generally positioned between the magnetic bearing pump 60 and one or more sensor components, such as the mass analyzer 64 and configured to shield components of the sensor 100 from the magnetic field generated by the pump 20. As a result, the shield member 120 improves sensitivity in the low mass (AMU) ranges, which enables use of a quadrupole 25 (FIG. 3) in the compactconfiguration shown in FIG. 4.

[0036] Turning to FIGS. 9-12, another embodiment of a sensor 210 is shown that comprises a shielding element 220. In some embodiments, the shielding element 220 comprises a shielding member 230 positioned between the magnetic bearing pump 60 and one or more sensor components, such as the mass analyzer 64. The shield member 230 may be coupled to or otherwise supported by a support member 250 that is structured to couple to a portion of the magnetic bearing pump 60 or a to a conduit connecting the magnetic bearing pump 60 with the sensor 210. The coupling of the support member 250 may be accomplished, at least in part, by one or more support couplers 252 positioned on the support member 250 or formed as part of the support member 250. The support member 250 may comprise a plurality of perforations 254 to enable an air flow through the support member 250 and between the sensor 210 and the pump 60. Other embodiments of the shield member 120 previously discussed may so include a support member 250 as just described. As shown, the shielding member 230 generally comprises a body 232. In some embodiments, the body 232 comprises a concave shape with and outer shield surface 231, an inner shield surface 233, sides 235 and a body portion 234 positioned between the sides 235. In an embodiment, the outer shield surface 231 is coupled to or in contact with the support member 250 at or around the plate portion 234, and the sides 235 are structured to extend away from the support member 250 and may partially surround one or more components of the sensor, such as the mass analyzer 64.

[0037] The shield member s 120, 220 are comprised of a material with high magnetic permeability. In an embodiment, the shield member s 120, 220 are comprised of an alloy with at least 77% nickel, such as Mu-metal. The shield member s 120, 220 act to shield the sensor 110, 210 or at least certain components of the sensor 110, 210 from the magnetic field generatedby the magnetic bearing pump 60. This shielding effect enables a quadrupole 25 (FIG. 3) to be used as the mass analyzer 64 or mass fdter. The shield member 120, 220 further results in an improved tuneability as well as increased sensitivity of the low-profde mass spectrometer 50 in low mass ranges (AMU). As was discussed above, the low-profile mass spectrometer 50 is configured with the magnetic bearing pump 60 positioned at a closer distance D2 (FIG. 4) to mass sensor 110, 210 as compared to the distance DI of a typical mass spectrometer as shown in FIG. 1. Therefore, a sensor 10 without the shielding element 120, 220 is less sensitive / accurate in the low mass range due to interference of the magnetic field generated by the pump 60. This decrease in sensitivity / accuracy is best seen in FIGS. 13A-D.

[0038] Referring to FIGS. 13A and 13C, an exemplary mass spectrum generated by a mass spectrometer similar to the mass spectrometer 10 of FIG. 1 is shown with a distinct peak at 2 AMU. In comparison, FIG. 13B shows an example of a mass spectrum generated by a compact mass spectrometer, similar to that shown in FIG. 4, but which does not have a shield member 120, 220. The sample used in this example would be expected to result in a distinct peak at 4AMU. Instead, the mass spectrum in FIG. 13B exhibits a double peak, which is indicative of a decreased sensitivity of the mass spectrometer. In contrast, FIG. 13D shows a mass spectrum of the same sample as FIG. 13B measured in a compact mass spectrometer similar to that shown in FIG. 4, which includes a shield member 120, 220. The resulting mass spectrum shows the expected distinct peak at 4 AMU and exhibits a similar peak shape as the larger mass spectrometer shown in FIG. 1 having a larger distance DI between the sensor and the pump. Accordingly, the disclosed shield member 120, 220 enables the low profile configuration of the mass spectrometer 50 to be maintained without interfering with the performance.

[0039] In an embodiment, the shield member 120, 220 may include a coating onone or more surfaces to improve the shielding characteristics. In another embodiment, the shield member 120, 220 may be the coating itself, and may be applied on or around sensor components to provide shielding from the magnetic field generated by the pump 60. A sensor 110, 210 comprising the shielding element 120, 220 may be

[0040] While the present invention has been particularly shown and described with reference to certain exemplary embodiments, it will be understood by one skilled in the art that various changes in detail may be effected therein without departing from the spirit and scope of the invention that can be supported by the written description and drawings. Further, where exemplary embodiments are described with reference to a certain number of elements, it will be understood that the exemplary embodiments can be practiced utilizing either less than or more than the certain number of elements.

Claims

CLAIMS1. A mass sensor for a mass spectrometer including a magnetic bearing pump configured to generate a magnetic field, comprising: an inlet configured to receive a gas sample; an ion source configured to generate ions from the gas sample; a mass analyzer configured to separate the generated ions based on mass; an ion detector configured to detect at least some of the separated ions; and a shield member comprising body including an outer shield surface and an inner shield surface that at least partially surrounds the mass analyzer, wherein the body defines at least one opening configured to facilitate air flow between the magnetic bearing pump and the shield interior, wherein the body is configured to align the mass analyzer, and wherein the body is positioned between the mass analyzer and the magnetic bearing pump and configured to shield the mass analyzer from the magnetic field generated by the magnetic bearing pump to improve sensitivity and tuneability in low mass ranges.

2. The mass sensor of claim 1 , wherein the body of the shield member at least partially surrounds the ion detector and is configured to shield the ion detector from the magnetic field generated by the magnetic bearing pump.

3. The mass sensor of claim 2, wherein the body of the shield member at least partially surrounds the ion source and is configured to shield the ion source from the magnetic field generated by the magnetic bearing pump.

4. The mass sensor of claim 1, wherein the body of the shield member is configured to align the ions source, the mass analyzer and the ion detector along a common axis.

5. The mass sensor of claim 1 , wherein the body of the shield member is comprised of an alloy.

6. The mass sensor of claim 1 , wherein the mass analyzer comprises a quadrupole.

7. The mass sensor of claim 1, where the shield member further comprises a support member positioned between the body and the magnetic bearing pump.

8. The mass sensor of claim 7, wherein the support member comprises a plurality of perforations to enable an air flow between the body and the magnetic bearing pump.

9. A method of shielding a mass sensor for a mass spectrometer that includes a magnetic bearing pump configured to generate a magnetic field, comprising: structuring a shield member to comprise a body that includes an outer shield surface and an inner shield surface defining a shield interior and that at least partially surrounds a mass analyzer of the mass sensor; structuring the body of the shield member to define at least one opening configured to facilitate air flow between the magnetic bearing pump and the shield interior, structuring the body of the shield member to align the mass analyzer; and positioning the body of the shield member between the mass analyzer and the magnetic bearing pump to shield the mass analyzer from the magnetic field generated by the magnetic bearing pump and improve sensitivity and tuneability in low mass ranges.

10. The method of claim 9, further comprising structuring a support member to be positioned between the body and the magnetic bearing pump.

11. The method of claim 10, further comprising structuring the support member to define a plurality of perforations configured to enable an air flow between the body and the magnetic bearing pump.

12. The method of claim 9, further comprising structuring the shield member to be comprised of an alloy.

13. A shield member for a mass sensor, comprising: a body comprising an outer shield surface and an inner shield surface defining shield sides and a body portion positioned between the shield sides; and a support member configured to support at least a portion of the body and structured to enable airflow though the support member, wherein the body is configured to shield one or more components of a mass sensor from a magnetic field.

14. The shield member of claim 13, wherein the support is configured to be positioned between a magnetic bearing pump of a mass spectrometer and the body.

15. The shield member of claim 13, wherein the support member comprises a plurality of perforations.

16. The shield member of claim 13, wherein the body is coupled to the support member.

17. The shield member of claim 13, wherein the body is comprised of an alloy.

18. The shield member of claim 13, wherein the body comprises a concave shape.

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