JP4223866B2 - Mass spectrometer - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a mass spectrometer that analyzes sample ions generated by an ion source.
[0002]
[Prior art]
A mass spectrometer is an apparatus that causes ions generated from a sample to fly in a vacuum, separates ions having different masses in the course of flight, and records them as a spectrum. The mass spectrometer includes a magnetic mass spectrometer that performs mass dispersion of ions using a sector magnetic field, and a quadrupole mass spectrometer (QMS) that performs selection (filtering) of ions by mass using a quadrupole electrode. ), A time-of-flight mass spectrometer (TOFMS) that separates ions using a difference in flight time of ions according to mass, and the like are known.
[0003]
Among these mass spectrometers, the magnetic field type mass spectrometer and the QMS are suitable for ion sources that continuously generate ions, whereas the TOFMS is an ion that generates ions in a pulsed manner. Conforms to the source. Therefore, if an attempt is made to use a continuous ion source for TOFMS, it is necessary to devise how to use the ion source. An orthogonal acceleration time-of-flight mass spectrometer (OA-TOFMS; orthogonal acceleration TOFMS) is an example of TOFMS devised so that pulsed ions can be ejected from a continuous ion source.
[0004]
FIG. 1 shows a typical OA-TOFMS configuration. OA-TOFMS is a continuous type of electron impact (EI) ion source, chemical ionization (CI) ion source, field desorption (FD) ion source, electrospray (ESI) ion source, fast atom bombardment (FAB) ion source, etc. External ion source 1, a differential exhaust wall 10 including first and second partition walls and a vacuum pump (not shown), and a first orifice provided on the first partition wall of the differential exhaust wall 10 2, a ring lens 3 placed in the differential exhaust wall 10, a second orifice 4 provided on the second partition wall constituting the differential exhaust wall 10, and an ion guide 5. An intermediate chamber 11, a lens group 6 comprising a converging lens and a deflector, a launcher 7 comprising an ion extrusion plate and an acceleration lens (grid), a reflector 8 for reflecting ions, and an ion detector 9 Structure composing any ion optics and a measuring chamber 13 placed.
[0005]
In such a configuration, ions generated from the sample in the external ion source 1 are first introduced into the differential exhaust wall 10 through the first orifice 2. The ions to be diffused in the differential exhaust wall 10 are focused by the ring lens 3 in the differential exhaust wall 10 and introduced into the intermediate chamber 11 through the second orifice 4. The ions introduced into the intermediate chamber 11 are guided to the high-vacuum measurement chamber 13 by reducing the kinetic energy in the intermediate chamber 11 and reducing the ion beam diameter by the high frequency electric field generated from the ion guide 5. A third orifice 12 is provided in a partition wall that partitions the intermediate chamber 11 and the measurement chamber 13. The ions guided from the ion guide 5 are shaped into an ion beam having a constant round diameter by the third orifice 12 and introduced into the measurement chamber 13.
[0006]
A lens group 6 including a converging lens and a deflector and an incident beam regulating slit (not shown) are installed at the entrance of the measurement chamber 13. The ion beam that has entered the measurement chamber 13 is corrected for beam diffusion and deflection by the lens group 6, and the cross-sectional shape of the beam is adjusted by the incident beam regulating slit, and then introduced into the launcher 7. In the launcher 7, an ion reservoir in which an ion extrusion plate and a grid are arranged to face each other, and an acceleration lens arranged in a direction orthogonal to the axial direction of the ion reservoir are installed.
[0007]
As shown in FIG. 2, the ion beam first enters in parallel toward the ion reservoir 17 sandwiched between the ion extrusion plate 14, the grid 15, and the acceleration lens 16 in a low energy state of 20 to 50 eV. The ion beam 18 having a certain length moving in parallel in the ion reservoir 17 is applied with a pulsed acceleration voltage of about several kV on the ion extrusion plate 14, whereby the ion beam 18 enters the direction (X It is accelerated in the form of pulses in the direction perpendicular to the (axial direction) (Z-axis direction), becomes an ion pulse 19, and starts flying toward a reflector (not shown) provided at a position facing the ion reservoir 17.
[0008]
The ions accelerated in the vertical direction are the velocity in the X-axis direction when introduced into the measurement chamber 13, and the velocity in the Z-axis direction given by the ion extrusion plate, the grid, and the acceleration lens in the direction perpendicular thereto. Therefore, they fly not in the complete Z-axis direction but in the slightly Z-axis direction, reflected by the reflector 8, and reach the ion detector 9.
[0009]
In the process of accelerating ions, the same potential difference acts on the ions regardless of the mass of the ions. Therefore, the lighter ions have a higher speed and the heavier ions have a lower speed. As a result, a difference in ion mass appears as a difference in arrival time until it reaches the ion detector 8, and a difference in ion mass can be separated as a difference in flight time of ions.
[0010]
In this way, the ion beam generated from the continuous ion source 1 is accelerated in a pulse form by the launcher 7 including the ion extrusion plate, the grid, and the acceleration lens. It can be applied to TOFMS that is compatible with an ion source (Patent Document 1).
[0011]
[Patent Document 1]
JP 2002-117802 [Patent Document 2]
JP 2000-243343 A [Non-Patent Document 1]
Japan Society of Invention and Innovation Technical Report, 93-29191
[0012]
[Problems to be solved by the invention]
By the way, when ions of low acceleration energy of about 20 to 50 eV are irradiated to the device constituent members in the path through which ions pass, if the conductivity of the member surface is low, the ions have there. Charges are accumulated and become charged. In that case, an abnormal electric potential that was not assumed in the original ion optical system was formed in the charged part, and the electric field generated there deflected low-speed ions in a direction deviating from the original flight trajectory. This hinders ion transport to the subsequent stage.
[0013]
In fact, in order to perform differential pumping, an orifice is provided to partition the space, and a slit is provided to block a part of the ion beam path to restrict the spread of the ion beam to the subsequent stage. It was found that an abnormal phenomenon occurred in the portion where the charge of the irradiated ions was accumulated due to the charge accumulated.
[0014]
One of the biggest reasons why such a charging phenomenon occurs is that an insulating oxide film is formed on the surface of the member exposed to ion beam irradiation, and dirt on the member surface accumulates over time. The electrical resistance on the surface of the member is increased.
[0015]
In view of the above-described points, an object of the present invention is to provide a mass spectrometer capable of improving or alleviating the charging phenomenon at an orifice part or a slit part.
[0016]
[Means for Solving the Problems]
In order to achieve this object, the mass spectrometer of the present invention provides:
The portion where the ions introduced into the mass spectrometer collide with a low acceleration energy of 100 eV or less after introduction is separated from the ground potential by an electric insulating material, and a voltage can be applied. By applying a DC voltage having polarity and capable of accelerating ions more than the energy at which the sputtering effect can be obtained, ions are accelerated and collided with the portions, and the surface is sputtered with ions.
[0018]
An ion source for ionizing the sample;
An intermediate slit placed after the ion source and provided to take ions into an intermediate chamber that maintains a higher vacuum than the ion source;
An ion guide placed behind the middle slit to guide the captured ions;
A differential exhaust orifice that is placed downstream of the ion guide and takes the induced ions into a higher vacuum region;
An incident beam restricting slit that is placed downstream of the differential exhaust orifice and restricts the shape of the captured ion stream,
An ion reservoir provided after the incident beam regulating slit;
A time-of-flight spectroscopic unit that applies predetermined kinetic energy to the ions in the ion reservoir, pushes the ions in a pulse manner in a direction crossing the axial direction of the ion reservoir, and analyzes the flight time of the ions;
An ion detector that detects an ion pulse flying through the time-of-flight spectrometer,
Said intermediate slit, and said differential pumping orifice, of the incident beam restricting slit, at least one, separated from the ground potential by the electrical insulating material, as well as to apply a structure capable voltage, the polarity of the ions By applying a DC voltage having a reverse polarity, ions are accelerated and collided with the application portion, and the surface is sputtered with ions .
[0019]
The ion source is an EI ion source or a CI ion source.
[0020]
Further, an electric field shield for shielding a leakage electric field is provided after the incident beam regulating slit.
[0021]
The voltage applied to at least one of the intermediate slit, the differential exhaust orifice, and the incident beam restricting slit has a polarity opposite to the polarity of ions, and the ions are applied when colliding with the voltage application portion. is characterized in that said DC voltage that can accelerate so that the above 80 eV.
[0022]
Also, at least one of the intermediate slit, the differential exhaust orifice, and the incident beam restriction slit is heated in the vicinity of at least one of the intermediate slit, the differential exhaust orifice, and the incident beam restriction slit. A heating mechanism is provided.
[0023]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings. FIG. 3 is a diagram showing an embodiment of a mass spectrometer according to the present invention. In order to simplify the drawing, the three members of the external ion source 1, the differential exhaust wall 10, and the intermediate chamber 11 shown in FIG. Further, the intermediate slit 22 corresponds to the second orifice 4 in FIG. 1, and the differential exhaust orifice 23 corresponds to the third orifice 12 in FIG. An EI ion source or a CI ion source is used as the external ion source.
[0024]
This embodiment is different from the conventional example of FIG. 1 in that the incident is provided inside the intermediate slit 22, the differential exhaust orifice 23, and the orthogonal acceleration time-of-flight mass analyzer (time-of-flight spectrometer) 26. That is, the beam restricting slit 24 is provided via an electric insulating member. Conventionally, the intermediate slit 22, the differential exhaust orifice 23, and the incident beam restriction slit 24 provided in the orthogonal acceleration time-of-flight mass analyzer 26 have been set to the ground potential. However, in the present embodiment, the intermediate slit 22, the differential exhaust orifice 23, and the incident beam restriction slit 24 provided in the orthogonal acceleration time-of-flight mass analyzer 26 are each grounded by an electrically insulating member. The predetermined voltage is supplied from a power source (not shown).
[0025]
Although not shown for simplicity, a conductive slit member having a ground potential is provided between the incident beam restriction slit 24 and the ion reservoir 25 to shield the leakage electric field from the incident beam restriction slit 24. Also good.
[0026]
The operation of this embodiment will be described. The ions that are generated and transported by the ion generator / transport section 21 and are incident on the ion reservoir 25 inside the orthogonal acceleration time-of-flight mass analyzer 26 form an ion beam 29 as a whole. This ion beam 29 reaches a final ion reservoir 25 with the total amount being gradually reduced by collision of some of the ions with some barriers in the middle. Here, the barrier portion includes the intermediate slit 22, the differential exhaust orifice 23, and the incident beam restricting slit 24.
[0027]
The intermediate slit 22 is installed as an element on the ion optics for ion transport, and functions as an end face formation of an action field of the lens system and a front and rear electric field shield. If the size of the contour portion of the ion beam 29 is larger than the size of the opening portion of the intermediate slit 23, the portion collides with the intermediate slit 22 and the progress is stopped.
[0028]
The differential exhaust orifice 23 is provided in order to maintain the vacuum degree difference between the ion generation / transport unit 21 and the orthogonal acceleration time-of-flight mass analyzer 26. Usually, this member has pores arranged on the ion optical axis so as to provide exhaust resistance. For this reason, when the size of the contour portion of the ion beam 29 is larger than the size of the pores of the differential exhaust orifice 23, the portion collides with the member of the differential exhaust orifice 23 and the progress is stopped.
[0029]
The incident beam restriction slit 24 is installed to restrict ions guided to the ion reservoir 25 to a predetermined incident condition. On the upstream side of the incident beam restricting slit, the ion beam 29 has an excessive spread. Therefore, the width of the ion beam 29 incident on the ion reservoir 25 is limited by the incident beam restriction slit 24 to be equal to or smaller than the opening width of the incident beam restriction slit 24. As a result, ions that have failed to pass through the opening of the incident beam restricting slit 24 collide with this member and can stop traveling.
[0030]
By the way, most of the charges of the ions that have stopped colliding with the above-described three members, the intermediate slit 22, the differential exhaust orifice 23, and the incident beam restricting slit 24, move to the surface of the colliding member. become. If the three of the intermediate slit 22, the differential exhaust orifice 23, and the incident beam restricting slit 24 maintain the original highly conductive state, the charges transferred from the ions flow to the electrode power supply circuit (not shown). These three members can maintain the ground potential. However, if an insulating oxide film is formed on the surface of the member or if dirt on the surface of the member accumulates over time, the electrical resistance of the member surface increases, and the charge of ions accumulates, causing a charging phenomenon. appear.
[0031]
Since the ion beam 29 is in a low energy state of about 20 to 50 eV, if even a slight charging phenomenon occurs in the three of the intermediate slit 22, the differential exhaust orifice 23, and the incident beam restriction slit 24, the ion beam 29 The ions are easily deflected and ions are not smoothly introduced into the ion reservoir 25.
[0032]
At that time, if the ions collide with members such as the intermediate slit 22, the differential exhaust orifice 23, the incident beam restriction slit 24, etc., from the power source (not shown), the ions have a polarity opposite to that of the ions, and the ions are 80 eV. If a DC voltage that can be accelerated as described above is applied, ions will violently collide with the intermediate slit 22, the differential exhaust orifice 23, and the incident beam restricting slit 24 with an incident energy of 80 eV or more.
[0033]
FIG. 4 shows a graph published in Chapter 6 and FIG. 6.5.3 of Toru Kanmochi, “Vacuum Technology Handbook” (1990, published by Nikkan Kogyo Shimbun). According to this, when the incident ion energy is 2 hundred and several dozen eV or more, the sputtering effect can be seen when the ions collide.
[0034]
Therefore, if a DC voltage having a polarity opposite to that of ions is applied to the intermediate slit 22, the differential exhaust orifice 23, and the incident beam restricting slit 24 from a power source (not shown), an ion beam is generated. When it is added to the original low energy of about 20 to 50 eV and becomes an incident ion energy of more than two hundred tens eV, it collides with the intermediate slit 22, the differential exhaust orifice 23, and the incident beam restriction slit 24 These surfaces will be sputtered. As a result of the experiment, the effect of sputtering was recognized even from about 80 eV.
[0035]
When the insulating oxide film formed on the surface of the member and dirt on the surface of the member are removed by this sputtering effect, the charging phenomenon of the intermediate slit 22, the differential exhaust orifice 23, and the incident beam regulating slit 24 is It can be improved or alleviated. As a result, the charge of the colliding ions flows to the electrode power supply circuit (not shown) without being charged, and there is no deflection phenomenon of the ion beam due to charging, so that stable ion transport can be performed.
[0036]
As described above, in the time-of-flight mass spectrometer, in addition to the measurement mode, the intermediate slit 22, the differential exhaust orifice 23, and the incident beam restriction slit 24 have a polarity opposite to the polarity of ions, and are 80 eV or more. A mode that applies a DC voltage that can accelerate ions is provided, and when charging occurs, it is possible to switch to that mode without disassembling and cleaning the time-of-flight mass spectrometer. It becomes possible to do.
[0037]
At this time, ions used for sputtering are not necessarily sample ions. For example, ions of an inert gas such as helium ions, argon ions, and nitrogen gas ions, or ions of an active gas such as oxygen gas are used. Use it.
[0038]
The present invention can be modified. For example, in FIG. 3, all of the intermediate slit 22, the differential exhaust orifice 23, and the incident beam restriction slit 24 are separated from a grounded potential by an electrical insulating member, and a predetermined voltage is supplied by a power source (not shown). The electrode structure is configured such that at least one of the intermediate slit, the differential exhaust orifice, and the incident beam restricting slit is separated from the ground potential by an electrical insulating material, and a voltage can be applied. May be given.
[0039]
For example, FIG. 5 shows an example in which only the differential exhaust orifice 23 is separated from the ground potential by an electrical insulating material and is provided with an electrode structure capable of applying a voltage. Even if the electrical insulation member is separated from the grounded potential and a predetermined voltage is supplied by a power source (not shown), even if it is performed on the differential exhaust orifice 23 where charging is most likely to occur, The effect is great.
[0040]
Further, a heating mechanism is further provided in the vicinity of at least one of the intermediate slit 22, the differential exhaust orifice 23, the incident beam restricting slit 24, or the like, and the baking effect is used in combination with the sputtering effect. Thus, the work of removing contaminants adhering to the member surface may be supported.
[0041]
In addition, as described above, a method in which a portion where ions collide with low acceleration energy is separated from a ground potential by an electrical insulating material and a voltage can be applied is obtained by using a low acceleration energy of 100 eV or less and an analysis unit. The present invention can be similarly applied to a quadrupole type mass spectrometer or the like in which ions are incident on.
[0042]
【The invention's effect】
As a result of the present invention, it has become possible to provide a mass spectrometer capable of improving or mitigating the charging phenomenon at the orifice part and the slit part.
[Brief description of the drawings]
FIG. 1 is a diagram showing a conventional time-of-flight mass spectrometer.
FIG. 2 is a diagram showing a conventional time-of-flight mass spectrometer.
FIG. 3 is a diagram showing an embodiment of the present invention.
FIG. 4 is a correlation diagram between incident ion energy and the effect it provides.
FIG. 5 is a diagram showing another embodiment of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... External ion source, 2 ... 1st orifice, 3 ... Ring lens, 4 ... 2nd orifice, 5 ... Ion guide, 6 ... Lens group, 7 ... Launcher, 8 ... reflector, 9 ... ion detector, 10 ... differential exhaust wall, 11 ... intermediate chamber, 12 ... third orifice, 13 ... measurement chamber, 14 ... Ion extrusion plate, 15 ... Grid, 16 ... Acceleration lens, 17 ... Ion reservoir, 18 ... Ion beam, 19 ... Ion pulse, 21 ... Ion generation / transport section , 22 ... intermediate slit, 23 ... differential exhaust orifice, 24 ... incident beam restriction slit, 25 ... ion reservoir, 26 ... orthogonal acceleration time-of-flight mass spectrometer (time-of-flight spectroscopy) Part), 27... Ion-extruded electrode, 28. Ion exit grid 29 ... ion beam.

Claims (6)

The portion where the ions introduced into the mass spectrometer collide with a low acceleration energy of 100 eV or less after introduction is separated from the ground potential by an electric insulating material, and a voltage can be applied. A mass spectrometer characterized in that, by applying a DC voltage that has polarity and can accelerate ions more than the energy at which a sputtering effect can be obtained, ions are accelerated and collided with the portions, and the surface is sputtered with ions. . An ion source for ionizing the sample;
An intermediate slit placed after the ion source and provided to take ions into an intermediate chamber that maintains a higher vacuum than the ion source;
An ion guide placed behind the middle slit to guide the captured ions;
A differential exhaust orifice that is placed downstream of the ion guide and takes the induced ions into a higher vacuum region;
An incident beam restricting slit that is placed downstream of the differential exhaust orifice and restricts the shape of the captured ion stream,
An ion reservoir provided after the incident beam regulating slit;
A time-of-flight spectroscopic unit that applies predetermined kinetic energy to the ions in the ion reservoir, pushes the ions in a pulse manner in a direction crossing the axial direction of the ion reservoir, and analyzes the flight time of the ions;
An ion detector that detects an ion pulse flying through the time-of-flight spectrometer,
At least one of the intermediate slit, the differential exhaust orifice, and the incident beam restricting slit is separated from the ground potential by an electrical insulating material, and a voltage can be applied. A mass spectrometer characterized in that, by applying a DC voltage having a reverse polarity, ions are accelerated and collided with the applied portion, and the surface is sputtered with ions. The mass spectrometer according to claim 2 , wherein the ion source is an EI ion source or a CI ion source. It said incident beam restriction downstream of the slit, the mass spectrometer according to claim 2 or 3, wherein the provision of the electric field shield that shields the leakage electric field. The voltage applied to at least one of the intermediate slit, the differential exhaust orifice, and the incident beam restricting slit has a polarity opposite to the polarity of the ions. mass spectrometer according to claim 2, 3 or 4, wherein, characterized in that said DC voltage that can be accelerated so that the above. A heating mechanism that heats at least one of the intermediate slit, the differential exhaust orifice, and the incident beam restriction slit in the vicinity of at least one of the intermediate slit, the differential exhaust orifice, and the incident beam restriction slit. characterized in that the provided claims 2, 3, 4 or 5 mass spectrometer according.

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