JP6664206B2 - Quadrupole mass spectrometer and residual gas analysis method - Google Patents

Description

  The present invention relates to a quadrupole mass spectrometer.

  In the quadrupole mass spectrometer, there is a problem that uncharged particles such as neutral particles pass through the quadrupole portion together with the ions and collide with the detector, whereby electrons are emitted and noise is generated.

  Conventionally, as shown in Patent Literature 1, a through-hole for allowing uncharged particles such as neutral particles to pass therethrough is formed in a portion where the central axis of a quadrupole portion of a detector passes, and a neutral hole such as neutral particles is formed. It is considered that the charged particles pass through the through-hole, and only the ions are bent toward the detector by the electric field, thereby suppressing generation of noise.

  However, in such a configuration, the electric field for directing ions to the detector is formed rotationally symmetrically with respect to the central axis of the quadrupole, so that the contour lines of the electric field near the central axis are aligned with respect to the central axis. It is close to vertical and cannot bend the ion greatly. Therefore, most of the ions pass through the through-hole on the central axis, and there is a problem that the measurement accuracy cannot be improved as expected.

JP-A-10-144254

  The present invention has been made in order to solve the above-described problems, and has been made to reduce the noise by passing uncharged particles such as neutral particles and to lead only ions to the detector more efficiently to detect them. is there.

  The quadrupole mass spectrometer according to the present invention includes an ion source for ionizing a sample, a quadrupole portion in which ions generated by the ion source enter from an inlet, pass through the inside, and exit to an outlet, and In a quadrupole mass spectrometer comprising a detector for detecting ions extracted from the outlet of the pole portion, a particle passing space is formed on a central axis passing through the inlet and outlet of the quadrupole portion, A detector is provided around the particle passage space, and an electric or magnetic field that is rotationally asymmetric with respect to the central axis is formed so that ions are directed to the detector.

  According to such a quadrupole mass spectrometer, uncharged particles such as neutral particles pass through the particle passage space, but ions pass through the particle passage space due to the rotationally asymmetric electric or magnetic field. Therefore, only ions can be more efficiently guided to the detector and detected while reducing noise due to uncharged particles such as neutral particles.

  The detector is a microchannel plate detector in which a through hole forming the particle passage space is provided at the center, and an electric field forming member that forms the electric field or magnetic field is provided separately from the detector. If it is a quadrupole mass spectrometer characterized by the fact that it is possible to form a rotationally asymmetric electric field or magnetic field by applying a voltage to an electric field forming member arranged separately from the microchannel plate detector, it is expensive It is possible to efficiently detect ions without preparing a plurality of suitable microchannel plate detectors.

  Dirt accumulates on the surface of the microchannel plate due to the adhesion of ions while the ions are being detected. Therefore, it is necessary to calibrate or replace the microchannel plate every time it is used for a predetermined period.

  A plurality of the electric field forming members are provided, and the electric field or the magnetic field can be changed by applying a voltage to any one of the electric field forming members. When the calibration of the microchannel plate is performed, the electric field or the magnetic field is changed to detect the ions of the standard sample at the portion not used as the ion detection surface of the microchannel plate, thereby making it possible to calibrate the microchannel plate. Calibration of the channel plate can be performed.

  Further, by changing the electric or magnetic field and setting a portion of the microchannel plate that is not used as the ion detection surface as a new ion detection surface, the frequency of replacing the microchannel plate can be reduced.

  A plurality of detectors are provided around the particle passing space, and a voltage is independently applied to each ion detector, and the configuration is such that the rotationally asymmetric electric or magnetic field can be formed. With a quadrupole mass spectrometer, the rotationally asymmetric electric field or magnetic field can be formed without using the electric field forming member, and since each detector is independent, calibration of the microchannel plate is performed. When replacement is necessary, calibration and replacement can be performed for each detector.

  If a quadrupole mass spectrometer is characterized in that the ion detection surface of the detector is arranged facing the quadrupole part, an electric field or a magnetic field is formed on the detector and only ions are ionized. When guided toward the detection surface for detection, it is not necessary to largely bend the ions, and it is possible to reduce ions that do not bend well due to an electric or magnetic field and do not go to the ion detection surface, so that ions can be detected efficiently. .

  If the microchannel plate is used in a state where the degree of vacuum is low and there are many ions passing through the quadrupole, the amplified electrons will exceed the output limit and the linearity of detection sensitivity will decrease, There is a possibility that the service life may be shortened due to accelerated adhesion of dirt.

  If the quadrupole mass spectrometer is provided with a Faraday cup disposed on the central axis, the microchannel plate detector and the Faraday cup are provided as detectors. Faraday cups can be used in environments where there are many ions passing high through the quadrupole.

  In an environment where the sample concentration is low and there are few ions passing through the quadrupole, detection can be performed with high sensitivity using the microchannel plate detector, so the range of sample concentrations that can be analyzed is smaller than when using only the microchannel plate detector. Can be spread.

  A quadrupole mass spectrometer characterized by comprising a switching control unit that switches an ion detection method between a microchannel plate detector and a Faraday cup based on an output value from the detector. Can automatically switch the ion detection method between the microchannel plate detector and the Faraday cup, so you can monitor the sample concentration and save the trouble of manually switching the detector according to the sample concentration, and a wide range of sample concentrations The mass spectrometry can be performed with high sensitivity using a detector suitable for the sample concentration.

  Further, since a detector suitable for the sample concentration can be used, labor and cost for maintenance due to shortened life of the microchannel plate can be saved.

  When the quadrupole mass spectrometer according to the present invention is used for a method for analyzing residual gas in a vacuum chamber, the residual gas can be efficiently analyzed over a wide concentration range.

  According to the quadrupole mass spectrometer according to the present invention, uncharged particles such as neutral particles pass through the particle passage space, but ions pass through the particle passage space due to the rotationally asymmetric electric or magnetic field. Therefore, only ions can be more efficiently guided to the ion detection surface and detected while reducing noise due to uncharged particles such as neutral particles.

The figure showing the attachment state to the vacuum chamber of the quadrupole mass spectrometer concerning this embodiment. FIG. 2 is a structural diagram of a quadrupole mass spectrometer according to the same embodiment. FIG. 3 is a schematic diagram of a quadrupole unit and an ion detection unit according to the first embodiment. Sectional drawing of the ion detection part in the embodiment. The schematic diagram of the electric field formation member and the microchannel plate detector in the same embodiment. FIG. 9 is a schematic diagram of an ion detection unit according to another embodiment. FIG. 9 is a schematic diagram of an ion detection unit according to another embodiment. FIG. 9 is a schematic diagram of an ion detection unit according to another embodiment. FIG. 9 is a schematic diagram of an ion detection unit according to another embodiment.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

  The quadrupole mass spectrometer according to the present embodiment is used, for example, in a quadrupole mass spectrometer QMS which is attached to a vacuum chamber VC such as a semiconductor process chamber VC and analyzes residual gas in the chamber VC. Things.

  The quadrupole mass spectrometer QMS includes a casing 1, a sensor unit 2 housed inside the casing 1, and a data processing circuit 3.

  As shown in FIG. 1, the casing 1 is attached so that a tip end surface thereof is disposed inside the chamber VC, and a first cover 11 that accommodates the sensor unit 2, and the casing 1 is attached to the chamber VC to receive the data. A second cover for accommodating the processing circuit.

  A gas inlet 111 for introducing gas in the chamber VC into the sensor unit 2 is provided on the distal end surface of the first cover 11 arranged in the chamber VC.

  As shown in FIG. 2, the sensor unit 2 includes an ion source 21 for ionizing a sample gas introduced from the gas inlet 111 by electron collision, and ions for extracting, accelerating, and converging ions generated in the ion source 21. An extraction electrode 22, a quadrupole portion 23 for separating ions accelerated and focused by the ion extraction electrode 22 according to a charge-to-mass ratio by a high-frequency electric field generated by the four columnar electrodes, and a quadrupole portion A detection unit 24 for detecting the ions separated by 23 and outputting the current value to the data processing circuit 3. Reference numeral A denotes an ion extraction electrode for extracting ions from the quadrupole portion.

  As shown in FIG. 3, the detection unit 24 includes a first electric field forming member 24E1 and a second electric field forming member 24E2, which are curved strip-shaped conductive members to which an electric field is applied when a negative voltage is applied. A doughnut-shaped microchannel plate having a thickness of about 2 mm and a diameter of about 9 mm in which a circular through hole 241H having a diameter of about 2.5 mm is formed along a central axis C passing through an inlet and an outlet of the quadrupole portion 23. A vessel 241 and a cylindrical Faraday cup 242 arranged on the central axis C with its opening facing the quadrupole portion 23. In FIG. 3, an ion extraction electrode for extracting ions from the quadrupole portion is omitted.

  As shown in FIG. 4, the first electric field forming member 24E1 and the second electric field forming member 24E2 are arranged on the quadrupole of the ion detection surface 241S of the micro channel plate detector 241 so as to avoid the central axis C. On the side of the unit 23, it is arranged at a position separated by a predetermined distance from the ion detection surface 241S.

  The first electric field forming member 24E1 and the second electric field forming member 24E2 are arranged symmetrically with respect to the center axis C, and connected to the voltage sources V1 and V2 built in the second cover 12. , So that an independent voltage can be applied to each of them.

  The microchannel plate detector 241 is arranged such that the ion detection surface 241S faces the outlet of the quadrupole portion 23, and the through hole 241H is formed at the center to function as the ion detection surface 241S. Is approximately 0.5 mm, a plate-shaped anode electrode 241A for detecting secondary electrons emitted from the micro-channel plate 241P, and a donut type having the through hole 241H formed at the center. And the ceramic base 241B.

  The microchannel plate 241P is formed by bundling a large number of glass tubes formed of, for example, high-lead glass having a diameter of about 10 μm and penetrating in the thickness direction. These glass tubes extend in the thickness direction of the microchannel plate 241P. It is attached in a state inclined about 10 degrees with respect to it.

  Further, a metal electrode is deposited on the surface of the microchannel plate 241P, and a voltage source V3 built in the second cover 12 is connected to this electrode, so that the ion detection surface 241S of the microchannel plate 241P is connected. And a positive voltage can be applied to the surface on the side from which secondary electrons are emitted.

  A connection terminal for applying a negative voltage to the ion detection surface 241S of the microchannel plate 241P is provided on the ion detection surface 241S when viewed from the entrance side of the quadrupole portion 23. 23 are arranged in the shaded portions of the columnar electrodes.

  A positive voltage is applied to the anode electrode 241A by a voltage source V4 built in the second cover 12, and the anode electrode 241A is held inside the ceramic base 241B.

  The Faraday cup 242 is a conductive cup made of, for example, copper, and is arranged so that the quadrupole section 23, the microchannel plate detector 241 and the Faraday cup 242 are arranged in this order.

  The Faraday cup 242 is connected to the micro channel plate detector 241 when no voltage is applied to the micro channel plate 241P, the first electric field forming member 24E1, and the second electric field forming member 24E2 by the voltage sources V1, V2, and V3. This detects ions passing through the through hole 241H.

  The data processing circuit 3 includes an amplifier, an A / D converter, a D / A converter, a CPU, a memory, a communication port, and the like, and performs mass spectrometry based on a current value output from the sensor unit 2. If necessary, the analysis result is transmitted to a general-purpose computer or the like.

  The data processing circuit 3 functions as the voltage sources V1, V2, V3, and V4 for applying a voltage to the microchannel plate 241P, the first electric field forming member 24E1, the second electric field forming member 24E2, and the anode electrode 241A. are doing.

  In addition, the data processing circuit 3 is configured to determine whether the first electric field forming member 24E1 or the second electric field forming member 24E2 is based on a current value output from the micro channel plate detector 241 or the Faraday cup 242. It also functions as a switching controller that issues commands to the voltage sources V1, V2, V3, and V4 that apply a voltage to the plate 241P.

  The data processing circuit 3 may be a single device or a plurality of devices connected to each other by wire or wirelessly, and may use a general-purpose computer as a part thereof.

  Next, an example of the operation of the quadrupole mass spectrometer configured as described above will be described with reference to FIGS.

  Ions generated in the ion source 21 and passed through the quadrupole portion 23 travel toward the detection portion 24 along the central axis C together with uncharged particles such as neutral particles. At this time, uncharged particles such as neutral particles pass through the through holes 241H formed in the microchannel plate detector 241 due to inertial motion, and only charged ions bend their trajectories by the rotationally asymmetric electric field. And reaches the ion detection surface 241S and is detected.

  When the rotationally asymmetric electric field is formed, for example, by applying a negative voltage to the first electric field forming member 24E1, ions are detected on some of the ion detection surfaces 241S on the surface 241S1. I have.

  In such a case, when the calibration of the microchannel plate 241P becomes necessary, the voltage applied to the first electric field forming member 24E1 is released from the control unit to the voltage source V1, and the voltage source is released. A command is issued to V2 to apply a voltage to the second electric field forming member 24E2.

  When a negative voltage is applied to the second electric field forming member 24E2, the electric field is changed, and ions are guided to the surface 241S2 not used as the ion detection surface 241S.

  In this way, the same standard sample is detected on each of the surface 241S1 used as the ion detection surface 241S and the surface 241S2 not used for ion detection, and the current values are compared to obtain the ion detection surface 241S. Calibrate the surface 241S1 that has been used.

  In addition, even when the surface 241S1 used as the ion detection surface 241S is contaminated by use, the electric field is changed as described above, and ions are guided to the surface 241S2 not used for ion detection. The surface 241S2, which has not been used as, can be used as a new ion detection surface.

  When an electric field is applied to the first electric field forming member 24E1 or the second electric field forming member 24E2 and ions are detected by the micro channel plate detector 241, the ions are detected by the micro channel plate detector 241 and the data processing is performed. When the current value A1 output to the circuit exceeds a predetermined value, the control unit issues a command to the voltage source V1 or V2 and V3, and the first electric field forming member 24E1 or the second electric field forming member 24E2. And the voltage applied to the microchannel plate 241P is released.

  As a result, the electric field formed so that the ions are directed to the ion detection surface 241S disappears, and the ions pass through the through hole 241H. The ions passing through the through hole 241H are detected by the Faraday cup 242 disposed behind the through hole 241H.

  On the other hand, when the current value A2 detected by the Faraday cup 242 and sent to the data processing circuit falls below a predetermined value, the control unit controls the voltage source V1 or V2 and V3 to generate the first electric field. A command is issued to apply a voltage to the member 24E1 or the second electric field forming member 24E2 and the microchannel plate 241P.

As a result, an electric field is formed so that the ions are directed to the ion detection surface 241S, and the ions are directed to the ion detection surface 241S by this electric field and are detected by the microchannel plate detector 241.

  The current value A1 detected by the microchannel plate detector 241 and output to the data processing circuit, and the current value A2 detected by the Faraday cup 242 and sent to the data processing circuit may be measured by a single instrument. good.

  According to the quadrupole mass spectrometer QMS of the present embodiment configured as described above, uncharged particles such as neutral particles pass through the through holes 241 </ b> H which are the particle passing spaces formed in the microchannel plate detector 241. Although the ions pass through, the ions receive a force on the central axis in a direction perpendicular to the central axis by the rotationally asymmetric electric field formed by the first electric field forming member 24E1 or the second electric field forming member 24E2. This can bias the ions, prevent the ions from passing through the through-hole 241H, and increase the number of ions reaching a specific ion detection surface, thereby reducing noise due to uncharged particles such as neutral particles. However, only ions can be more efficiently guided to the ion detection surface 241S and detected.

  Since a voltage can be applied to the first electric field forming member 24E1 or the second electric field forming member 24E2 to form the rotationally asymmetric electric field, ions can be efficiently prepared without preparing a plurality of expensive microchannel plates 241P. Can be detected.

  The first electric field forming member 24E1 and the second electric field forming member 24E2 are arranged on opposite sides with respect to the center axis C so that the electric field can be changed by applying an independent voltage to each. For example, as shown in FIG. 4, when a part of the surface 241S1 of the microchannel plate 241P is used, when the surface 241S1 is calibrated, as shown in FIG. Calibration can be performed using the opposite part 241S2.

  The ion detection surface 241S of the microchannel plate detector 241 is disposed facing the quadrupole portion 23 side, and the angle at which ions are bent toward the detection surface 241S can be reduced. The ions extracted from the outlet of the above can be efficiently detected.

  Possibility that ions extracted from the exit of the quadrupole portion 23 reach the portion of the quadrupole portion 23 which is shaded by the cylindrical electrode when viewed from the entrance side of the quadrupole portion 23. Is considered to be relatively low.

  Therefore, in this embodiment, when the connection terminal for applying a voltage to the microchannel plate 241P is viewed from the entrance side of the quadrupole portion 23 of the ion detection surface 241S, the quadrupole portion is formed. Since the connection terminals are arranged in the shaded portions of the 23 cylindrical electrodes, the ions are more efficiently detected as compared with the case where the connection terminals are arranged in places other than the shaded portions of the columnar electrodes. be able to.

  Since the detection unit 24 includes the microchannel plate detector 241 and the Faraday cup 242 disposed on the central axis C, ions having a high sample concentration and passing through the quadrupole unit 23 In many environments, a Faraday cup 242 can be used. In an environment where the concentration of the sample is low and the amount of ions passing through the quadrupole portion 23 is small, the ions can be detected with high sensitivity by the microchannel plate detector 241, so that the range of the residual gas concentration that can be analyzed can be expanded.

  In addition, since the ion detection method can be automatically switched between the microchannel plate detector 241 and the Faraday cup 242 according to the sample concentration, the trouble of monitoring the concentration of the residual gas and manually switching the detection method can be eliminated. Mass spectrometry can be performed with high sensitivity by a detection method suitable for the sample concentration over a wide concentration range.

  In addition, since a detection method suitable for the sample concentration can be used, labor and cost for maintenance due to a shortened life of the microchannel plate 241P can be reduced.

  Note that the present invention is not limited to the above embodiment.

  For example, the particle passage space may be formed other than at the center of the ion detection surface, or the particle passage space may be formed outside the ion detection surface.

  The detection unit is not limited to the one that detects positively charged ions, and may be configured to detect negatively charged ions by inverting the voltage applied to the electric field forming member or the ion detection surface.

  The electric field forming member is not limited to a curved strip-shaped member, but may be a rod-shaped member or a column-shaped member. The length and size may be any.

  Further, the plurality of electric field forming members need not all have the same shape, and a plurality of electric field forming members having different shapes, lengths, and sizes may be combined.

  Further, the number of the electric field forming members is not limited to two, and for example, one or three or more electric field forming members may be provided as shown in FIGS. 7, 8 and 9, and are arranged symmetrically with respect to the central axis. It is not necessary. The intervals at which these are arranged may or may not be equal.

  The detectors 241 are, for example, as shown in FIG. 5, a plurality of microchannel plate detectors 241 provided on the central axis so as to avoid the particle passage space 24V. The voltage may be independently applied to the container 241 to form the rotationally asymmetric electric field.

  What is formed by the electric field forming member or the voltage applied to the detector is preferably a rotationally asymmetric electric field, but may be a rotationally asymmetric magnetic field.

  The shape of the ion detection surface is not limited to a circle, but may be a rectangle, another polygon, or an irregular shape.

  The detector is not limited to a microchannel plate detector, but may be a pipe-type channel-type secondary electron multiplier, a secondary electron multiplier using discontinuous dynodes, or the like.

  In addition, the present invention can be variously modified without departing from the spirit thereof.

Quadrupole mass spectrometer QMS
Ion source ・ ・ ・ 21
Quadrupole part ・ ・ ・ 23
Detector ・ ・ ・ 241
Central axis: C
Particle passing space: 24V
Ion detection surface 241S
Through hole ・ ・ ・ 241H
Electric field forming member 24E
Faraday cup 242
Vacuum chamber ・ ・ ・ VC

Claims (6)

An ion source for ionizing a sample, a quadrupole section in which ions generated by the ion source enter from an inlet, pass through the inside, and exit to an exit, and detection for detecting ions extracted from an exit of the quadrupole section. In a quadrupole mass spectrometer equipped with a
A particle passing space is formed on a central axis passing through the entrance and the exit of the quadrupole portion, a detector is provided around the particle passing space, and ions are directed to the detector. An electric or magnetic field is formed that is rotationally asymmetric with respect to
The quadrupole mass spectrometer further comprises a plurality of electric field forming members for forming the electric field or the magnetic field,
A quadrupole mass spectrometer, wherein the electric field or the magnetic field is changed by applying a voltage to any of the plurality of electric field forming members to change the ion detection surface of the detector.   2. The detector according to claim 1, wherein the detector is a microchannel plate detector in which a through-hole forming a particle passage space is provided at the center, and the electric field forming member is provided separately from the detector. The quadrupole mass spectrometer as described.   2. The device according to claim 1, wherein a plurality of detectors are provided around the particle passage space, and a voltage is independently applied to each ion detector to form the rotationally asymmetric electric or magnetic field. Quadrupole mass spectrometer.   4. The quadrupole mass spectrometer according to claim 1, further comprising a Faraday cup arranged on the central axis. As the detector, a microchannel plate detector provided with a through-hole forming a particle passing space at the center and a Faraday cup disposed on the central axis,
On the basis of the output value from the detector, quadrupole mass spectrometer according to claim 1, further comprising a switching control unit for switching the ion detection method between the Faraday cup and the microchannel plate detector.   A residual gas analysis method for analyzing residual gas in a vacuum chamber using the quadrupole mass spectrometer according to claim 1.