JP2019139956A - Ion source for mass spectrometer - Google Patents

Abstract

To provide a long-life and low-cost ion source for a mass spectrometer that can maintain predetermined sensitivity without providing a power source for grid heating.SOLUTION: The ion source IS for a mass spectrometer according to the present invention, which analyzes a gas component in a test body, includes a filament 4 that emits thermoelectrons when energized, and a grid 5 with a cylindrical outline that draws thermoelectrons by a potential difference with the filament 4, and the grid 5 is made of a material whose thermal conductivity at 300K is 173 W/(m K) or more.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an ion source for a mass spectrometer that analyzes a gas component in a test body.

  In a vacuum process performed in a vacuum processing apparatus such as film formation by sputtering or vapor deposition, not only the pressure in the vacuum chamber of the vacuum processing apparatus but also the composition (gas component) of the gas remaining in the vacuum chamber is large. May have an effect. In order to analyze the gas component remaining in the vacuum chamber as described above, a mass spectrometer has been widely used.

  A quadrupole type mass spectrometer will be described as an example. The mass spectrometer is composed of a sensor unit that is detachably attached to a test body such as a vacuum chamber, and a control unit that controls the sensor unit. Yes. The sensor unit is attached to the test body in the upper direction, the sensor unit is provided at the lower end and collects ions, and four cylindrical shapes provided above the ion detection unit. Are provided with a quadrupole portion (mass separation portion) in which the electrodes are arranged at predetermined intervals in the circumferential direction, and an ion source provided on the upper side of the quadrupole portion. An ion source is comprised from the grid formed by shape | molding metal mesh-shaped members in a cylinder shape, and the filament arrange | positioned around the grid (for example, refer patent document 1). In this case, molybdenum or platinum-coated molybdenum is generally used as the grid material.

  Here, in the vacuum processing apparatus of the above type, various materials and gases are used depending on the processing performed therein, and these may adhere to each component of the sensor unit as a contaminant. Here, regarding the grid of the ion source, since the temperature of the grid itself is low and the temperature distribution is not uniform, the contaminants easily adhere to the grid surface and do not adhere uniformly to the grid surface. When a negative charge is formed on the surface of the contaminant that locally adheres to the grid surface, the potential distribution of the ionization chamber inside the grid changes, and this changes the location where ions are generated. As a result, the sensitivity of the mass spectrometer is determined by the ionization efficiency of the gas components at the ion source and the efficiency of guiding ions from the ion source to the quadrupole. The problem of damaging

  As a solution to such a problem, it is proposed to remove molecules and atoms attached to the surface by heating the grid itself with its internal resistance by energizing the grid (see, for example, Patent Document 2). . However, this increases the number of parts, such as the need to provide a separate power source, resulting in high costs.

JP 2012-234776 A JP 2000-39375 A

  In view of the above points, it is an object of the present invention to provide a long-life and low-cost ion source for a mass spectrometer that can maintain a predetermined sensitivity without providing a power source for grid heating or the like. Is.

  In order to solve the above problems, an ion source for a mass spectrometer of the present invention is an ion source for a mass spectrometer that analyzes a gas component in a test body, and a filament that emits thermal electrons when energized, And a grid that draws thermoelectrons with a potential difference from the filament, and the grid is made of a material having a thermal conductivity of 300 W or more at 173 K / (m · K).

  According to the present invention, when the thermoelectrons are emitted by energizing the filament, the grid itself is also heated by the radiant heat from the filament. At this time, as a material of the grid, for example, a material such as copper, gold, silver, or platinum that has a thermal conductivity at 300 K of 173 W / (m · K) or more is used. It is higher than that of the conventional example, and is substantially equal throughout. For this reason, it is possible to make it difficult for contaminants to adhere to the surface of the grid. As a result, the ion source for the mass spectrometer of the present invention has a long lifetime and low cost that can maintain a predetermined sensitivity without providing another heating power source or the like.

  By the way, when assembling an ion source to a mass spectrometer, it is common to fix and arrange a grid in advance on a disk-shaped support base made of a conductive material. In this case, although the grid is fixed to the support base by spot welding, if the material of the grid is, for example, copper, it cannot be fixed to the support base using spot welding or the like. Therefore, in the present invention, it is preferable that the grid further includes a support body made of another conductive material different from the material, and can be fixed to the support base via the support body. According to this, if the support is a material conventionally used as a component of an ion source for a mass spectrometer such as molybdenum, after attaching the support to the grid by a known method such as caulking, Similar to the conventional example, it can be fixed to the support base using spot welding.

  Further, in the case where the grid has a cylindrical outline, if the support has a claw piece that clamps the grid from both ends in the generatrix direction, for example, the support can be separated from the support by vibration during transportation. A configuration in which the grid is securely held can be realized without incurring problems such as dropping off of the grid, which is advantageous.

The perspective view which shows typically the sensor part of the quadrupole-type mass spectrometer of embodiment of this invention. The partial exploded perspective view explaining a grid. The graph which shows the result of the experiment which confirms the effect of invention.

  Hereinafter, an embodiment of an ion source for a mass spectrometer of the present invention will be described with reference to the drawings, taking a quadrupole mass spectrometer as an example. In the following description, it is assumed that a sensor unit Su described later is mounted on a test body (not shown) in the posture shown in FIG.

  Referring to FIG. 1, Su is a sensor unit of a quadrupole mass spectrometer in which the ion source according to the present embodiment is assembled, and its operation is controlled by a control unit (not shown). . Since a known control unit can be used, further explanation is omitted. The sensor unit Su has a disk-like support (not shown) made of a metal such as aluminum or stainless steel and provided with an O-ring on the outer peripheral edge of the upper surface thereof, and the ion collector 1 is disposed above the support. It is assembled. The ion collector 1 includes, for example, a Faraday cup that collects ions of a predetermined mass number of gas atoms and gas molecules that pass through electrodes 21 to 24 of the quadrupole portion 2 described later. A quadrupole part 2 is assembled above the ion collector 1. The quadrupole part 2 is composed of four columnar electrodes 21 to 24 that extend in the up-down direction and are arranged at intervals of 90 degrees in the circumferential direction. In this case, the opposing electrodes 21, 23 and 22, 24 are electrically connected to each other.

  A focus electrode 3 is assembled above the quadrupole part 2 and is always held at a lower potential than the grid 5 described later to suppress diffusion of ions incident on the quadrupole part 2. Yes. The ion source IS of this embodiment is assembled above the focus electrode 3. The ion source IS includes a filament 4 that emits thermoelectrons when energized, and a grid 5 that draws thermoelectrons by a potential difference from the filament 4. The filament 4 is formed, for example, by coating the surface of a base metal made of iridium with yttrium oxide by plating, and is formed in an arc shape so as to surround about half of the outer periphery of the grid 5. In this case, the filament 4 is supported by three metal support pins 42 erected at predetermined intervals in the circumferential direction on the disk-shaped first support base 41 and assembled in this state.

  As shown in FIG. 2, the grid 5 is formed by assembling a material having a thermal conductivity at 300 K of 173 W / (m · K) or more, for example, a thin metal wire such as gold, silver, copper, or platinum in a lattice shape. It is formed into a cylindrical shape. For example, a so-called punching metal made of copper and sheet can be formed into a cylindrical shape. The grid 5 having a cylindrical outline is inserted and held in a support body 6 having a cylindrical outline.

  The support 6 is formed by cylindrically forming ring-shaped frame portions 61 and 61 positioned at both ends in the vertical direction of the grid 5, support columns 62 connecting the frame portions 61 and 61, and a metal mesh material into a cylindrical shape. After that, the frame portions 61 and 61 and the cylindrical portion 63 fixed to the support column portion 62 are formed. Further, the claw pieces 64 project from the frame portions 61 and 61 so as to be in phase with each other in the vertical direction (in the present embodiment, two shifted by 180 degrees). In this case, the support 6 can be made of, for example, molybdenum as in the conventional ion source. And after inserting the grid 5 in the cylinder part 63 of the support body 6, the grid 5 is clamped by the said nail | claw piece 64 from the up-and-down (bus line) direction both ends by the said nail | claw piece 64, and it supports The body 6 is electrically connected. Then, in this state, the disc-shaped second support base 65 is fixed by spot welding or the like via the claw piece 64 positioned on the lower side, and assembled in this state.

  When the sensor unit Su is mounted at a predetermined position of a test body such as a vacuum chamber and the gas partial pressure is measured, the filament 4 is energized and the thermoelectrons are emitted from the filament 4. In this case, the grid 5 itself is also heated by the radiant heat from the filament 4. At this time, as a material of the grid 5, for example, a material having a thermal conductivity of 300 K or more such as copper, gold, silver, or platinum is 173 W / (m · K) or more. It is higher than that of the conventional example made of the above material, and is substantially equal throughout.

  Next, by applying a positive voltage to the grid 5 and drawing the emitted thermoelectrons, gas ions are generated from gas atoms and molecules around the filament 4 colliding with the thermoelectrons. The gas ions are converged by the focus electrode 3 and drawn into the quadrupole part 2 while being accelerated by an acceleration voltage corresponding to the potential difference between the grid 5 and the quadrupole part 2. When a predetermined voltage in which direct current and alternating current are superimposed is applied to the electrodes 21 to 24 of the quadrupole part 2, the gas ions reach the ion collector 1 for each mass-to-charge ratio, and the ion collector 1 is The flowing ion current value is measured by an ammeter not shown. Thereby, the gas partial pressure of a predetermined mass number in the test body is calculated from the ion current value.

  As described above, according to the ion source IS of the present embodiment, the temperature of the grid 5 itself at the time of measuring the gas partial pressure is relatively high and substantially uniform throughout the grid 5. It is possible to make it difficult for contaminants to adhere to the surface of the surface. As a result, it is possible to maintain a predetermined sensitivity without providing a separate heating power source or the like and have a long life and low cost. Moreover, if the structure which hold | maintains the grid 5 with the support body 6 as mentioned above is employ | adopted, it can fix to the disk-shaped 2nd support stand 65 (support stand) by spot welding, and the grid 5 is the By being clamped from both ends in the busbar direction, for example, there is no inconvenience that the grid 5 is dropped from the support 6 due to vibration during conveyance.

  Next, in order to confirm the effect of the present invention, the following experiment was performed using a mass spectrometer having the sensor unit Su of the above embodiment. That is, as the grid 5 of the ion source IS to be mounted on the mass spectrometer, a copper punching metal formed into a cylindrical shape is used and inserted into a molybdenum support 6. What was joined to the support stand 65 by spot welding was prepared (invention product). As a comparative experiment, a support made of molybdenum without a claw piece was used as a grid (conventional product). In this experiment, the mass spectrometer is operated in a pressure range under a constant pressure with a certain amount of gas introduced, and a metal piece coated with an organic substance as a contamination source is disposed in the vicinity of the grid 5. In this state, the gas partial pressure was measured. In this case, when the filament 4 is lit, the temperature of the metal piece also rises due to radiant heat, and contamination of the grid 5 is promoted by evaporation of organic matter. And sensitivity fluctuation was acquired by evaluating the relative sensitivity from the sensitivity immediately after a test start with an invention product and a conventional product, respectively, The result is shown in FIG.

  According to this, it can be seen that, under the same conditions, the relative sensitivity of the conventional product is reduced to about 0.01% in about 15 minutes. On the other hand, it was confirmed that the product of the invention remained at a drop of about 60%, and it was confirmed that a much higher relative sensitivity than that of the conventional product could be maintained.

  The embodiment of the present invention has been described above, but the present invention is not limited to the above-described embodiment, and can be appropriately modified without departing from the scope of the technical idea of the present invention. In the above embodiment, the case where the grid 5 has a cylindrical outline has been described as an example. However, the present invention is not limited to this, and the present invention is applied to any conventional grid having other forms. be able to. Moreover, in the said embodiment, the thing provided with the frame parts 61 and 61, the support | pillar part 62, the cylinder part 63, and the nail | claw piece 64 is taken as an example as the support body 6 when the grid 5 has a cylindrical outline. As described above, if it can be fixed to the second support 65 by spot welding or the like so as to be assembled as a part to the sensor unit Su of the mass spectrometer, and it is not damaged even if it is subjected to vibration during transportation, for example, It is not limited.

  For example, as the cylindrical portion 63 of the support 6 of the above embodiment, a metal mesh material formed into a cylindrical shape is used. However, it may allow the movement of thermoelectrons when the filament 4 is lit. However, the present invention is not limited to this, and a punching metal or the like can be used, and a claw piece 64 or the like is provided on a molybdenum grid used in the current mass spectrometer as the support 6. It can also be configured.

  In the above-described embodiment, the support 6 is described as an example having the claw pieces 64 for sandwiching the grid 5 made of copper or the like from both ends. However, for example, damage during transportation is prevented only by the cylindrical portion 63. If possible, this may be omitted, or on the other hand, for example, the support column and the claw piece may be formed integrally. Furthermore, the method for fixing the grid 5 to the support 6 is not limited to the above-described caulking. Further, although the example in which the grid 5 is sandwiched from both ends in the vertical (busbar) direction by the claw pieces 64 after the grid 5 is inserted has been described as an example, for example, a support is provided only at one end in the busbar direction of the grid. May be.

  Su ... sensor unit of quadrupole mass spectrometer, IS ... ion source, 1 ... ion collector, 2 ... quadrupole part, 4 ... filament, 5 ... grid, 6 ... support, 64 ... claw piece, 65 ... Second support base (support base).

Claims (3)

An ion source for a mass spectrometer that analyzes a gas component in a test body, comprising a filament that emits thermoelectrons when energized, and a grid that draws thermoelectrons with a potential difference from the filament,
The grid is made of a material having a thermal conductivity of 173 W / (m · K) or more at 300 K, and is an ion source for a mass spectrometer.   2. The mass spectrometer according to claim 1, wherein the grid further includes a support made of another conductive material different from the material, and can be fixed to a support base via the support. Ion source. The ion source for a mass spectrometer according to claim 2, wherein the grid has a cylindrical outline.
The ion source for a mass spectrometer, wherein the support has a claw piece for clamping the grid from both ends in the generatrix direction.

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