Mass Analyzer

Abstract

A mass spectrometer capable of recovering as quickly as possible when a decrease in sensitivity occurs during the component analysis of gas introduced from a test sample Vc is provided. [Solution] An ion source (4), a mass separator (5), and a detector (6) are sequentially stored within a main pipe (31) of an envelope (3) from one end to the other. The ion source has a filament (41), a motion imparting chamber (42) that imparts a predetermined motion to thermions emitted from the filament, and an ionization chamber (43) that ionizes gas introduced from a test piece by colliding the thermions with the gas. An inner pipe (35) is inserted into a first branch pipe (32) of the envelope, with its tip protruding into the main pipe and extending to the ionization chamber. A cylindrical body (9) is provided that is detachably inserted into the ionization chamber (43), and an air hole (92) is opened in the cylindrical body to allow ventilation between the inside and outside of the cylindrical body.

Description

[Technical Field]

[0001] The present invention relates to a mass spectrometer that analyzes the components of a gas introduced from a test body in a vacuum atmosphere. [Background technology]

[0002] The present inventors have proposed a mass spectrometer of this type, as described in Patent Document 1. This spectrometer comprises an envelope having a main pipe extending in the X-axis direction and a branch pipe branching from the main pipe and extending in one direction along the Z-axis, perpendicular to the X-axis direction. A switching valve is interposed in the branch pipe, which is connected to a test object. The main pipe contains an ion source, a mass separator, and a detector, which are housed in this order from one end of the main pipe to the other end downstream in the X-axis direction. Typically, the mass separator and detector are integrated into one unit. The ion source includes a filament located at the upper end in the X-axis direction that emits thermoelectrons when energized, a motion imparting chamber located downstream of the filament in the X-axis direction that imparts a predetermined motion to the emitted thermoelectrons, and an ionization chamber located adjacent to the motion imparting chamber downstream in the X-axis direction, which ionizes gas introduced from the test object by colliding the thermoelectrons with the gas. An inner tube is inserted into the branch pipe, with its tip protruding into the main pipe and extending to the ionization chamber.

[0003] When analyzing the components of gas introduced from a test specimen in a vacuum environment, a direct current is passed through the filament, lighting it (glowing red), and emitting thermoelectrons. The thermoelectrons emitted from the filament rotate in a spiral within the motion imparting chamber and reach the ionization chamber. At the same time, gas from the test specimen is introduced directly into the ionization chamber through an inner tube and ionized, and this ionized gas is introduced into the mass separation section. The mass separation section then stably oscillates and allows only certain ions to pass through, and these ions reach the ion collector, which serves as the detection section, where the ion current flowing through the ion collector is measured. The components of the gas introduced from the test specimen are analyzed based on these measurements.

[0004] Here, the gas introduced from the test specimen may contain, for example, silicon-based gas. Analysis of the components of such gases generates insulating contaminants in the ionization chamber, which then adhere to and deposit on the inner wall surfaces defining the ionization chamber. When the inner wall surfaces become covered with insulating contaminants, this adversely affects the ionization potential of the gas, ultimately reducing the number of gas ions that reach the ion collector via the mass separation section, resulting in a decrease in sensitivity. Therefore, this type of mass spectrometer is required to be able to remove contaminants and quickly restore sensitivity, and to do so, it is necessary to be able to access the areas (or parts) where contaminants are attached with a relatively small amount of effort. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 7544895 Summary of the Invention [Problem to be solved by the invention]

[0006] In view of the above, an object of the present invention is to provide a mass spectrometer that can recover sensitivity as quickly as possible when sensitivity is reduced during analysis of the components of gas introduced from a test sample. [Means for solving the problem]

[0007] In order to solve the above problems, the mass spectrometer of the present invention, which analyzes the components of gas introduced from a test body in a vacuum atmosphere, comprises an envelope having a main pipe section extending in the X-axis direction and a branch pipe section branching from the main pipe section and extending in one direction in the Z-axis direction perpendicular to the X-axis direction, a switching valve is interposed in the branch pipe section and connected to the test body, an ion source, a mass separation section, and a detection section are stored in this order in the main pipe section from one end side to the other end side downstream in the X-axis direction, and the ion source is a filler disposed upstream in the X-axis direction that emits thermoelectrons when current is applied. thermions are positioned downstream in the X-axis direction of the filament and impart a predetermined motion to the emitted thermoelectrons; and an ionization chamber adjacent to the downstream side of the motion imparting chamber in the X-axis direction, in which gas introduced from the test piece collides with the thermoelectrons to ionize the gas. An inner tube is inserted into the branch pipe section, with its tip protruding into the main pipe section and extending into the ionization chamber. A cylindrical body is provided which is detachably inserted into the ionization chamber and covers the inner wall surface which defines the ionization chamber, and an air hole is opened in the cylindrical body to allow ventilation inside and outside the chamber.

[0008] According to the present invention, even if insulating contaminants are generated due to the gas introduced from the test sample through the inner tube during gas analysis, the contaminants will only adhere and accumulate mainly on the inner surface of the cylindrical body. Therefore, by replacing the cylindrical body itself, i.e., by removing the contaminated cylindrical body from the ionization chamber and reattaching a new or cleaned cylindrical body to the ionization chamber, the contaminants can be removed from the ionization chamber and sensitivity can be quickly restored.

[0009] In the present invention, when the motion imparting chamber and a portion of the ionization chamber are defined by the inner wall surface of a magnet unit formed by stacking multiple ring-shaped magnets in the X-axis direction, and one end of the main pipe section facing the filament is closed by a cover plate that can be opened and closed, it is preferable to provide a support that supports both free ends of the filament and a pedestal to which the support is detachably attached and that holds one end of the magnet unit in the X-axis direction, the pedestal being detachably attached at a predetermined position within the main pipe section, and the cylindrical body being fitted to the magnet unit from the downstream side in the X-axis direction. According to this, when replacing the cylindrical body, the cover plate is removed from one end of the main pipe section, and then the support including the filament is removed. This allows the magnet unit and the pedestal to be pulled out toward one end of the main pipe section, and the cylindrical body can be replaced in this state. Therefore, compared to, for example, removing the mass separation section and other components of the present invention of the mass separator from the other end of the main pipe section and then removing the branch pipe section before replacing the cylindrical body, the cylindrical body can be replaced with fewer work steps, improving workability.

[0010] In the present invention, it is preferable that the air vents are formed by a plurality of small holes opened at predetermined intervals around the entire circumference of the cylindrical body at the part of the cylindrical body facing the tip of the inner tube. When reattaching the cylindrical body to the magnet unit, it is not necessary to determine the phase of the cylindrical body relative to the inner tube, which further improves the workability of replacing the cylindrical body.

[0011] In the present invention, it is also preferable that one end face of the cylindrical body in the X-axis direction is closed by a front plate, and the other end face of the cylindrical body in the X-axis direction is closed by a rear plate, and that the front plate has a first through-hole that allows the passage of thermoelectrons from the motion imparting chamber, and the rear plate has a second through-hole that allows the passage of ionized gas to the mass separation section. This is advantageous because it allows most of the contaminants to adhere and deposit on the inner surface of the cylindrical body and minimizes the adhesion and deposition of contaminants on other parts or components. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a front view of a mass spectrometry system including a mass spectrometer according to an embodiment of the present invention. [Figure 2] FIG. 2 is an enlarged cross-sectional view of a main part of the mass spectrometer of FIG. 1. [Figure 3] FIG. 10 is a perspective view of a cylindrical body that covers the inner surface of the motion imparting chamber of the ionization chamber. [Figure 4] FIG. 2 is an enlarged cross-sectional view showing the main parts of the mass spectrometer in an exploded state. DETAILED DESCRIPTION OF THE INVENTION

[0013] Hereinafter, with reference to the drawings, an embodiment of a mass spectrometer MA of the present invention will be described, in which a test object is a vacuum chamber Vc in which a predetermined vacuum process is performed, and the components of a gas introduced from the vacuum chamber Vc in a vacuum atmosphere are analyzed. In the following, terms indicating directions such as up, down, left, and right are used based on the attitude of the mass spectrometer MA shown in Figure 1. Furthermore, directions perpendicular to each other on the floor surface are referred to as the X-axis direction and the Y-axis direction, and a direction perpendicular to the X-axis direction and the Y-axis direction is referred to as the Z-axis direction.

[0014] Referring to FIG. 1, Ms denotes a mass spectrometry system equipped with a mass spectrometer MA according to this embodiment. The mass spectrometry system Ms includes a stand 1 that is installed on a floor Fl (installation surface) of a clean room or the like. The stand 1 has a first framework 11 formed by assembling frames 11a into a rectangular parallelepiped shape. A second framework 12 formed by assembling frames 12a into a rectangular shape is connected to the frame 11a, which is located at the right end in the X-axis direction and on the upper side in the Z-axis direction, so as to protrude upward in the Z-axis direction. The frame 11a of the first framework 11 and the frame 12a of the second framework 12, which face the floor Fl, are each provided with casters and support legs 13a, 13b. A vacuum pump 2 is installed in the internal space of the first framework 11.

[0015] The vacuum pump 2 can be composed of, for example, a turbomolecular pump 21 mounted on a support plate 14 installed between the frames 11a, and a rotary pump 22 on its back pressure side. If the back pressure side of the turbomolecular pump 21 can be connected to a vacuum pump (not shown) installed in the vacuum chamber Vc, the rotary pump 22 can be omitted. In this case, a fore valve (not shown) is installed on the back pressure side of the turbomolecular pump 21. A first vacuum gauge Pg, such as a Pirani vacuum gauge, is attached to a connecting pipe 23 leading from the turbomolecular pump 21 to the rotary pump 22. The mass spectrometer MA of this embodiment is installed directly above the turbomolecular pump 21. In FIG. 1, 24 denotes, for example, a control box that houses devices for controlling the operation of the vacuum pump 2, and is communicatively connected to a control unit 7 (described later).

[0016] Referring also to FIG. 2, the mass spectrometer MA includes an envelope 3. The envelope 3 has a main pipe 31 extending in the X-axis direction, a branch pipe branching from the main pipe 31 and extending upward in the Z-axis direction (hereinafter referred to as the "first branch pipe 32"), and another branch pipe branching from the main pipe 31 and extending downward in the Z-axis direction (hereinafter referred to as the "second branch pipe 33") to face the mass separation section (described below). A switching valve 34 is interposed in the first branch pipe 32, and a gas inlet pipe 32a of the first branch pipe 32 extending from the switching valve 34 is connected to a predetermined position in the vacuum chamber Vc. By opening and closing the switching valve 34, gas within the vacuum chamber Vc can be selectively introduced. A second vacuum gauge Dg, such as an ionization vacuum gauge, is attached to the gas inlet pipe 32a. A sleeve member 32b is also threadedly fitted into the first branch pipe 32. A resin inner tube 35 is inserted into the first branch pipe portion 32 while being held by a sleeve member 32b, and the lower end of the inner tube 35 is connected to the side surface of a disk-shaped member 43a so as to communicate with an ionization chamber 43 (described later). The second branch pipe portion 33 is connected to a suction port (not shown) of a turbomolecular pump 21 located directly below it in the Z-axis direction.

[0017] The ion source 4, mass separator 5, and detector 6 are housed in this order within the main pipe 31, from the left side in the X-axis direction toward its right end downstream in the X-axis direction (from left to right in FIG. 1( a)). A hermetic seal 71a is attached to the right end of the main pipe 31 to seal the interior. A control unit 7 is connected via the hermetic seal 71a. A cover plate 31a is detachably attached to the opening at the left end in the X-axis direction of the main pipe 31 using a bolt B1 as a fastening means, thereby closing the interior of the main pipe 31. Although not specifically shown or described, for example, a heat insulating material is provided on the outer surface of the cover plate 31a, and appropriate heat insulating materials are also provided on the outer surface of the main pipe 31, etc. Providing a heat insulating structure such as a reflector or a heat-reflective surface structure on the inner surface of the main pipe 31, etc., can contribute to miniaturization. The ion source 4 has a filament 41 that is disposed at the left end in the X-axis direction and emits thermoelectrons when energized, a motion imparting chamber 42 that is located downstream of the filament 41 in the X-axis direction and imparts a predetermined motion to the thermoelectrons emitted from the filament 41, and an ionization chamber 43 that is located downstream of the motion imparting chamber 42 in the X-axis direction and ionizes gas introduced from the vacuum chamber Vc by colliding the thermoelectrons with the gas.

[0018] A first chamber 431, which is a portion of the ionization chamber 43 downstream in the X-axis direction, is defined by a countersunk hole formed in a disk-shaped member 43a that is fixed within the main pipe section 31 and has a predetermined plate thickness. A communication hole 43b, which is smaller in diameter than the countersunk hole that connects the ionization chamber 43 to the mass separation section 5, is formed in the downstream surface of the disk-shaped member 43a in the X-axis direction. A downstream portion of a magnet unit 42a, which is composed of multiple stacked ring-shaped magnets, is fitted into a relatively large-diameter hole located upstream in the X-axis direction. The inner space of the magnet unit 42a is divided into two chambers, front and rear, in the X-axis direction by a partition plate 42c with through-holes 42b that allow electrons to pass through. The rear space defines a second chamber 432, which is the remaining portion of the ionization chamber 43 upstream in the X-axis direction. The front space constitutes a motion imparting chamber 42 that imparts motion to thermions emitted from the filament 41 so that the thermoelectrons rotate helically. A plurality of first support columns 44 are erected at intervals in the circumferential direction on the surface of the disk-shaped member 43a on the upstream side in the X axis direction, and a base plate 45 constituting a base portion is detachably attached to the upper ends of the first support columns 44 in the X axis direction with bolts B2. In this case, the base plate 45 also serves to hold the other end of the magnet unit 42a. A plurality of second support columns 46 are erected on the surface of the base plate 45 on the upstream side in the X axis direction.

[0019] A base plate 41a serving as a support for the filament 41 is detachably attached to the second support column 46 by bolts B3 serving as fastening means. In this case, a countersunk hole 31b is formed in the downstream surface of the cover plate 31a in the X-axis direction. When the cover plate 31a is attached, a portion of a support pin 41b (described later) is housed in the countersunk hole 31b. The ion source 4 is positioned in the main pipe 31 so that the bolts B3 fastening the base plate 41a can be easily accessed when the cover plate 31a is removed. A plurality of through-holes (not shown) are formed in predetermined positions in the base plate 41a. One end of a support pin 41b, bent in a U-shape and serving as a support, extending in the X-axis direction, is inserted into each through-hole in an electrically insulated manner. The free ends of the filament 41, bent in a convex shape toward the downstream side in the X-axis direction, are connected to one end of a pair of support pins 41b extending downstream in the X-axis direction. The filament 41 is made of a base metal made of iridium, the surface of which is coated with yttrium oxide by plating, and is bent in a convex (V-shape) at the center. The shape of the filament 41 is not limited to this, and any shape such as a straight line or an arc can be used.

[0020] The other end of support pin 41b extending in the X-axis direction is configured to be freely retractable and engage with rigid conductive tube 71b, which is installed within main tubular portion 31 so as to extend over substantially its entire length. Although not specifically shown or described, the other end of conductive tube 71b is wired to a terminal (not shown) of hermetic seal 71a, to which wiring from control unit 7 is connected. Mass separator 5, located downstream in the X-axis direction of ionization chamber 43 via multiple focus electrodes 8 each having communication holes 81, is a so-called quadrupole type mass separator. It includes four cylindrical electrodes 51 elongated in the X-axis direction and arranged at 90-degree intervals in the circumferential direction. Opposing electrodes 51 are fixed within main tubular portion 31 and electrically connected to each other. Ion collector 6, serving as a detector and located downstream in the X-axis direction of mass separator 5, is configured as a Faraday cup that collects ions of gas atoms or gas molecules of a predetermined mass number that reach mass separator 5 after passing through each electrode 51 of mass separator 5. It should be noted that components of the mass spectrometer MA, such as the mass separation unit 5, the detection unit 6, and the focus electrode 8, can be well-known components, and therefore detailed description thereof will be omitted here.

[0021] The control unit 7 includes a housing 71, which incorporates a control unit including a computer, memory, sequencer, and the like, although these are not specifically shown or described. The control unit performs various controls, such as operating the power supply and processing the ion current value measured by the ammeter and displaying it on a display (not shown). The housing 71 also incorporates devices such as a filament lighting power supply that applies a DC current to the filament 41 to light it, a DC+RF power supply that applies a DC voltage and a radio frequency voltage between the pair of electrodes 51 of the electrically coupled mass separator 5, and an ammeter that measures the ion current value collected by the ion collector 6 and flowing to ground, and these devices are appropriately wired and connected via terminals of the hermetic seal 71a. Since a known device can be used as the control unit 7, further description will be omitted.

[0022] When analyzing gas in a vacuum chamber Vc using the mass spectrometry system Ms, the gas inlet pipe 32a is connected to the vacuum chamber Vc, and the switching valve 34 is closed while the vacuum chamber Vc is evacuated and the vacuum pump 2 is operated. Although not specifically shown or described, on-off valves are provided between the connecting pipe 23 and the second branch pipe 33 and the turbomolecular pump 21. First, the rotary pump 22 is operated with each on-off valve closed. When the pressure indicated by the Pirani vacuum gauge Pg reaches a predetermined value, the turbomolecular pump 21 is operated. When the pressure indicated by the electronic vacuum gauge Dg reaches the predetermined value, the system is ready to begin gas analysis. To start gas analysis, a power supply within the control unit 7 applies a direct current to the filament 41, lighting it (turning it red hot) and emitting thermoelectrons. The thermoelectrons emitted from the filament 41 are rotated in a spiral shape so as to extend their residence time within the motion imparting chamber 42, and pass through the through-hole 42b in the partition plate 42c to reach the ionization chamber 43. At the same time, the switching valve 34 is opened, and the gas within the vacuum chamber Vc is introduced directly into the ionization chamber 43 via the inner tube 35 within the second branch pipe section 33. This causes the introduced gas to be ionized.

[0023] Next, a predetermined voltage, a superimposed DC and AC voltage, is applied to the four electrodes 51 of the mass separator 5 by the DC+RF power supply of the control unit 7. As a result, the difference between the central electric field of the mass separator 5 and the voltage applied to the filament 41 causes ions of the gas ionized in the ionization chamber 43 to be drawn into the mass separator 5 through the communication holes 81 of the focus electrode 8. At this time, the focus electrode 8 is maintained at a lower potential than the filament 41, thereby converging the ions heading toward the mass separator 5. As ions pass through the mass separator 5, they oscillate as they pass, and depending on the AC voltage and frequency, only certain ions oscillate stably and pass through, reaching the ion collector 6. The ion current flowing through the ion collector 6 is measured by an ammeter provided in the control unit 7, and the ion current value at that time is output to the control unit of the control unit 7.

[0024] A spectrum is obtained by linearly varying the AC voltage while maintaining a constant ratio of the DC voltage to the AC voltage, and the components of the gas introduced from the vacuum chamber Vc are analyzed from the ion current value. In this case, an indication value calculated from the ion current value for a specific gas component can be displayed on a display (not shown) provided in the control unit 7. The gas introduced from the vacuum chamber Vc through the inner tube 35 may contain, for example, a silicon-based gas. Analysis of the components of such gas generates insulating contaminants in the ionization chamber 43. If these generated contaminants adhere to and accumulate on the inner walls of the disk-shaped member 43a and magnet unit 42a that define the ionization chamber 43, covering them with insulating contaminants, the number of gas ions reaching the ion collector 6 via the mass separation unit 5 decreases, resulting in a decrease in sensitivity. Therefore, a configuration is required that allows for the removal of contaminants to quickly restore sensitivity.

[0025] 3 and 4, in this embodiment, the cylindrical body 9 is detachably inserted into the ionization chamber 43. Specifically, the portion of the cylindrical body 9 located upstream in the X-axis direction is fitted into the second chamber 432 of the ionization chamber 43 from the downstream side in the X-axis direction, partially covering the inner wall surface of the magnet unit 42a. Furthermore, a protruding portion 91 of the cylindrical body 9 protruding upstream in the X-axis direction from the magnet unit 42a is inserted into a countersunk hole in the disk-shaped member 43a that defines the first chamber 431 of the ionization chamber 43, covering substantially the entire inner surface. The protruding portion 91, which faces the tip of the inner tube 35, has an air hole 92 that allows ventilation between the inside and outside of the protruding portion 91. The cylindrical body 9 may be made of any material, for example, a processed sheet metal, as long as it has the same potential as the ionization chamber 43 during gas component analysis. Furthermore, the cylindrical body 9 is sized to obtain a contact pressure that ensures stable conduction throughout its lifespan, and an equivalent potential is guaranteed. The vent holes 92 are composed of multiple small holes opened at predetermined intervals around the entire circumference of the protruding portion 91. Both end surfaces of the cylindrical body 9 in the X-axis direction are closed by a front plate 93 and a rear plate 94. The front plate 93 has a first through hole 93a that allows electrons to pass from the motion imparting chamber 42, and the rear plate 94 has a second through hole 94a that allows ionized gas to pass through the communication hole 81 of the focus electrode 8 to the mass separation unit 5. The front plate 93 and the rear plate 94 do not need to be fixed to the periphery of the front and rear openings of the cylindrical body 9 along their entire circumference. Conversely, if the front plate 93 and the rear plate 94 are partially fixed, the cylindrical body 9 becomes easier to deform, which is advantageous, for example, as it improves the workability when fitting it into the second chamber 432 or pulling it out from the second chamber 432.

[0026] As described above, even if insulating contaminants are generated due to the gas introduced from the vacuum chamber Vc through the inner tube 35 during gas component analysis, the contaminants mainly adhere to and accumulate on the inner surface of the cylindrical body 9. Since both ends of the cylindrical body 9 in the X-axis direction are blocked by the front plate 93 and rear plate 94, respectively, most of the contaminants adhere to and accumulate on the inner surface of the cylindrical body 9, minimizing adhesion and accumulation of contaminants on other parts or components. Therefore, simply replacing the cylindrical body 9 itself removes the contaminants from the ionization chamber 43 and quickly restores sensitivity. Referring to FIG. 4 , the bolt B1 is released to remove the cover plate 31a from one end of the main pipe 31 in the X-axis direction. Next, the bolt B3 is released, allowing the support 41a including the filament 41 to be pulled out toward one end in the X-axis direction. The bolt B2 is released, allowing the magnet unit 42a including the base plate 45 to be pulled out toward one end in the X-axis direction. The cylindrical body 9 can be replaced with the magnet unit 42a while it is removed from the main pipe 31. This allows the cylindrical body 9 to be replaced with fewer steps, improving workability. Furthermore, when reassembling the cylindrical body 9 to the magnet unit 42a, because the air vents 92 are composed of a plurality of small holes opened at predetermined intervals around the entire circumference of the protruding portion 91, there is no need to determine the phase of the cylindrical body 9 relative to the inner pipe 35, further improving workability in replacing the cylindrical body 9.

[0027] Although the above describes an embodiment of the present invention, various modifications are possible without departing from the scope of the technical concept of the present invention. In the above embodiment, the motion imparting chamber 42 is defined by a magnet unit 42a. However, the present invention is not limited to this. The motion imparting chamber can also be configured using a cylindrical grid, as in the above conventional example. The number of filaments 41 used is not limited to one, but can be two or more. Furthermore, the mass separation unit 5 is described as being of a quadrupole type. However, the present invention is not limited to this. Other types, such as an ion trap type or a magnetic field type, can also be used.

[0028] In the above embodiment, the vent hole 92 formed in the protruding portion 91 is described as being composed of multiple small holes. However, this is not limited thereto and may be composed of a single opening. In such a case, although not specifically illustrated, by providing, for example, an engaging hole or an engaging protrusion engaging with the engaging hole at a predetermined position on the disk-shaped member 43a defining the first chamber 431, and providing the other on the rear plate 9, the cylindrical body 9 can be easily positioned relative to the inner tube 35. Furthermore, the smaller opening area compared to a configuration using multiple small holes advantageously limits the area where contaminants adhere and accumulate to the inner surface of the cylindrical body 9. Furthermore, in the above embodiment, the cylindrical body 9 is removed from the magnet unit 42a after removal and then replaced. However, this is not limited thereto. When the magnet unit 42a is removed, the protruding portion 91 of the cylindrical body 9 fits into the countersunk hole of the disk-shaped member 43a. The cylindrical body 9 may be replaced in this state. [Explanation of symbols]

[0029] MA...mass spectrometer, Vc...vacuum chamber (test specimen), 3...envelope, 31...main pipe section, 32...first branch pipe section, 33...second branch pipe section, 34...switching valve, 35...inner pipe, 4...ion source, 41...filament, 42...motion imparting chamber, 42a...magnet unit, 43...ionization chamber, 45...base plate (component of base section), 46...second support column (component of base section), 5...mass separation section, 6...ion collector (detection section), 7...control unit, 9...cylindrical body, 92...vent hole.

Claims

1. A mass spectrometer for analyzing components of a gas introduced from a test body in a vacuum atmosphere, an envelope having a main pipe portion extending in the X-axis direction and a branch pipe portion branching from the main pipe portion and extending in one direction in the Z-axis direction perpendicular to the X-axis direction, a switching valve being interposed in the branch pipe portion and connected to the test piece; an ion source, a mass separator, and a detector are stored in this order within the main pipe section, from one end to the other end downstream in the X-axis direction; the ion source has a filament located upstream in the X-axis direction and emitting thermoelectrons when energized; a motion imparting chamber located downstream of the filament in the X-axis direction and imparting a predetermined motion to the emitted thermoelectrons; and an ionization chamber located adjacent to the motion imparting chamber downstream in the X-axis direction and in which gas introduced from a test piece collides with the thermoelectrons to ionize the gas; and an inner tube is inserted into the branch pipe section, with its tip protruding into the main pipe section and extending into the ionization chamber; a cylindrical body that is detachably inserted into the ionization chamber and covers the inner wall surface that defines the ionization chamber, and an air hole is opened in the cylindrical body to allow ventilation between the inside and outside of the cylindrical body; a mass spectrometer comprising: a main tube portion having a first end that faces a filament and a second end that faces a second end of the filament; a support body that supports both free ends of the filament; and a base portion to which the support body is detachably attached and which holds the first end of the magnet unit in the X-axis direction; the base portion is detachably attached at a predetermined position within the main tube portion; and the cylindrical body is fitted into the magnet unit from the downstream side in the X-axis direction.

2. 2. A mass spectrometer according to claim 1, wherein said vent hole is comprised of a plurality of small holes opened at predetermined intervals around the entire circumference of said cylindrical body at a portion facing the tip of said inner tube.

3. 3. The mass spectrometer according to claim 1, wherein one end face of the cylindrical body in the X-axis direction is closed by a front plate and the other end face of the cylindrical body in the X-axis direction is closed by a rear plate, and wherein the front plate is provided with a first through-hole that allows the passage of thermoelectrons from the motion imparting chamber, and the rear plate is provided with a second through-hole that allows the passage of ionized gas to the mass separation section.

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