JP2019032964A - Quadrupole type mass spectrometer and discrimination method for sensitivity reduction therefor - Google Patents

Abstract

To provide a quadrupole type mass spectrometer capable of discriminating sensitivity reduction of an ion source as speedily as possible.SOLUTION: A quadrupole type mass spectrometer MA configured to analyze a gas component in a specimen comprises: an ion source 4 which includes a filament 41 and a grid 43 and ionizes a gas; a quadrupole part 3 configured by disposing four columnar electrodes 31 at predetermined intervals in a circumferential direction; a first ion collector 2 which collects a predetermined mass number of gas ions passed through the quadrupole part 3; and a second ion collector 6 which collects gas ions generated by the ion source 4. The quadrupole type mass spectrometer is configured to measure a predetermined mass number of partial gas pressures inside of a specimen from a first ion current value flowing in the first ion collector 2, and to measure a total pressure inside of the specimen from a second ion current value flowing in the second ion collector 6. The quadrupole type mass spectrometer also comprises discrimination means which defines sensitivity within a range in which gas analysis is not influenced as reference sensitivity and, when a ratio of the first ion current value with respect to the second ion current value becomes equal to or less than a discrimination value that is set based on the reference sensitivity, discriminates that sensitivity is reduced.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a quadrupole mass spectrometer that analyzes a gas component in a test body and a determination method for determining a decrease in sensitivity thereof.

  In vacuum processing performed in a vacuum processing apparatus such as sputtering or vapor deposition, not only the pressure at the time of processing but also the gas component (residual gas component) remaining in the vacuum chamber (test body) is the film quality, etc. May have a significant impact. In order to analyze such residual gas components, a quadrupole mass spectrometer has been conventionally used.

  This type of quadrupole mass spectrometer is known from Patent Document 1, for example. This has an ion source having a filament and a grid to ionize a gas, a quadrupole portion in which four columnar electrodes are arranged at predetermined intervals in the circumferential direction, and a predetermined through which the quadrupole portion is passed. A first ion collector that collects gas ions of mass number is provided, and a gas partial pressure of a predetermined mass number in the test body can be measured from a first ion current value flowing through the first ion collector. In addition, this device further includes a second ion collector that collects ions of the gas generated by the ion source so that the total pressure in the test body can be measured from the second ion current value flowing through the second ion collector. It has become.

  Here, when analyzing the gas component remaining in the specimen using the above quadrupole mass spectrometer, molecules and atoms in the specimen adhere to the grid and become contaminated. It is known that the sensitivity decreases, and as a result, the indicated value of the gas partial pressure of a predetermined mass number to be measured gradually decreases. If the analysis of the remaining gas component is continued in such a state that the indicated value is small, this may not be detected in the case where a vacuum leak occurs in the test body, which is performed in the test body. This will greatly affect the vacuum processing.

  Therefore, it has been conventionally performed to periodically introduce a calibration gas containing a predetermined gas component into the test body and measure the calibration gas component to determine a decrease in sensitivity (for example, see Patent Document 2). . However, in this case, since it is necessary to temporarily interrupt the vacuum processing performed in the test body, there is a problem that not only mass production is impaired but also a calibration gas facility is required, resulting in high cost.

Japanese Patent No. 5669324 JP-A-9-55185

  In view of the above points, it is an object of the present invention to provide a quadrupole mass spectrometer that can determine sensitivity reduction as quickly as possible and a method for determining sensitivity reduction.

  In order to solve the above problems, a quadrupole mass spectrometer for analyzing a gas component in a test body has an ion source having a filament and a grid to ionize a gas and four columnar electrodes in a circumferential direction. A quadrupole part arranged at intervals, a first ion collector that collects gas ions having a predetermined mass number that has passed through the quadrupole part, and a second that collects gas ions generated by the ion source. A gas partial pressure of a predetermined mass number in the test body from a first ion current value flowing through the first ion collector, and a total pressure in the test body from a second ion current value flowing through the second ion collector. The reference value is a sensitivity within a predetermined range that does not affect the analysis of the gas component, and the ratio of the first ion current value to the second ion current value is set based on the reference sensitivity. Equal to or less than , Characterized in that it comprises a determination means and desensitization.

  Here, in a quadrupole mass spectrometer that can measure both the gas partial pressure and the total pressure of a predetermined mass number, molecules and atoms in the specimen adhere to the grid and become contaminated. When the sensitivity decreases, the indicated value of the gas partial pressure of a predetermined mass number becomes smaller faster than the indicated value of the total pressure. Focusing on this, in the present invention, the ratio of the first ion current value to the second ion current value is obtained, and a determination value set based on this ratio (for example, the reference sensitivity is experimental or empirical). It is possible to determine whether or not the sensitivity has decreased. As described above, in the present invention, the first ion current value and the second ion current that are constantly measured in order to measure the gas partial pressure and the total pressure of a predetermined mass number in the test body using the quadrupole mass spectrometer. Since it is possible to determine a decrease in sensitivity from the change in value, it is not necessary to temporarily stop the vacuum processing performed in the test body, and the sensitivity without using the calibration gas equipment used in the conventional example above. Decrease can be determined as quickly as possible.

  In the present invention, if the first ion current value is selected from the gas ions having a predetermined mass number that have passed through the quadrupole portion, the first ion current value is maximized. Sensitivity reduction can be determined as quickly as possible. On the other hand, if the sum of gas ions having a predetermined mass number that has passed through the quadrupole portion is used as the first ion current value, the vacuum atmosphere in the test body at the time of determination has the same total pressure and partial pressure. Even in such a case, an accurate determination can be made, which is advantageous.

  In order to solve the above-mentioned problem, the gas in the test body is ionized by an ion source, and gas ions having a predetermined mass number that has passed through the quadrupole portion are collected by a first ion collector. A determination method for determining a decrease in sensitivity of an ion source in a quadrupole mass spectrometer that measures a gas partial pressure from a flowing first ion current value is to capture gas ionized in a test body by a second ion collector. And a determination value in which the ratio of the first ion current value to the second ion current value flowing through the second ion collector is smaller than the reference sensitivity, with the sensitivity within a predetermined range that does not affect the analysis of the gas component as the reference sensitivity And the step of determining that the sensitivity has been reduced when it is equal to or less than the same.

The side view explaining the connection of the sensor part and control unit of the quadrupole mass spectrometer of embodiment of this invention. The figure which shows the change of the ionic current value and the total pressure which were measured with the quadrupole mass spectrometer of this embodiment. The flowchart which shows the determination method of the sensitivity fall of a quadrupole type | mold mass spectrometer.

  Hereinafter, a quadrupole mass spectrometer MA according to an embodiment of the present invention will be described with reference to the drawings. In the following description, the mounting direction of a sensor unit S (described later) with respect to a test specimen (not shown) will be described as upward.

  With reference to FIG. 1, the quadrupole mass spectrometer MA includes a sensor unit S and a control unit C. The sensor unit S has a disk-shaped support 1. The support 1 is made of a metal such as aluminum or stainless steel, and an O-ring 11 is provided on the outer peripheral edge of the upper surface. A first ion collector 2 is provided on the support 1. The first ion collector 2 is composed of a Faraday cup that collects ions of a predetermined mass number of gas atoms and gas molecules that pass through each electrode of a quadrupole portion 3 to be described later. The first ion collector 2 is connected to a connection terminal 21 erected on the support 1.

  A quadrupole part 3 is provided on the first ion collector 2. The quadrupole part 3 includes four columnar electrodes 31 (two are shown in the figure) extending in the vertical direction and arranged at predetermined intervals in the circumferential direction. The opposing electrodes 31 are electrically connected, and the opposing electrodes 31 are connected to two connection terminals 32 a and 32 b erected on the support 1. An ion source 4 is provided on the quadrupole part 3, and the ion source 4 includes a filament 41 and a grid 43. The grid 43 is configured by assembling thin metal wires in a lattice shape and in a cylindrical shape, and is connected to a connection terminal 42 a erected on the support 1. The filament 41 includes three metal support pins 44a to 44c suspended from a support frame (not shown) at a predetermined interval in the circumferential direction, and a center support pin 44a and support pins 44b and 44c on both sides. Two filament pieces 41 a and 41 b connected to each other are provided, and the entire outer periphery of the grid 43 is surrounded. In this case, the central support pin 44a serves as a filament common, the support pin 44a is connected to the connection terminal 45b provided upright on the support body 1, and the support pins 44b and 44c on both sides stand on the support body 1. The connection terminal 45a is wired.

  A focus electrode 5 is provided between the ion source 4 and the quadrupole part 3 to efficiently focus ions traveling toward the quadrupole part 3. The focus electrode 5 is made of a metal plate having a central opening, and the support pin 44a and the focus electrode 5 are connected by a wiring W so that the potential of the filament 41 and the potential of the focus electrode 5 are equal. A plate-like second ion collector 6 is provided above the ion source 4 so as to face the first ion collector 2 across the grid 43. The second ion collector 6 is connected to a connection terminal 61 provided vertically through the support 1.

  On the other hand, the control unit C includes a housing F (indicated by a one-dot chain line in FIG. 1), and the housing F incorporates a control unit C1 including a computer, a memory, a sequencer, and the like. The control unit C1 performs overall control of operation of each power source described later, switching of a switching element in a power supply circuit (not shown), determination of sensitivity decrease by executing a flowchart described later, notification of sensitivity decrease described later, and the like. For this reason, the control part C1 is corresponded to the determination means in a claim. Also, in the housing F, there are a filament lighting power source E1 that turns on the filament 41 by passing a direct current through the filament 41, and a grid power source E2 that applies a higher potential to the grid 43 than the filament 41. Built in. The positive output from the power supply E1 is connected to a connection terminal 45a that is electrically connected to the support pins 44b and 44c on both sides, and the positive output from the power supply E2 is connected to the connection terminal 42a for the grid. The side is grounded.

  In the housing F, a DC + RF power source E3 for applying a DC voltage and a high frequency voltage to the electrodes 31 and 31 that are electrically coupled to each other is built in, and the output of the DC + RF power source E3 is connected to the electrodes 31 and 31, respectively. ing. In addition, a power supply E4 that applies a potential to the filament 41 in order to create a predetermined potential difference between the filament 41 and the grid 43 is built in the housing F, and a positive output from the power supply E4 is supplied from the power supply E2. The negative output from the power supply E4 is connected to the negative output from the power supply E1. In this case, the output from the minus side is connected to the wiring from the connection terminal 45b that is electrically connected to the support pin 44a that is the filament common. Further, in the housing F, an ammeter 22 connected to the first ion collector 2 for measuring a first ion current value flowing through the first ion collector 2 and a second ion collector 6 connected to the first ion collector 2 An ammeter 62 for measuring the second ion current value flowing through the two ion collector 6 is attached. In the following, an example of use of the quadrupole mass spectrometer MA will be described by taking, as an example, a case where a test body (not shown) is a vacuum chamber in which a film forming process is performed and a gas component remaining in the vacuum chamber is analyzed. .

  After mounting the sensor unit S at a predetermined position in the vacuum chamber, the vacuum chamber is evacuated. When the vacuum chamber is evacuated to a predetermined pressure, measurement of gas partial pressure and total pressure by the quadrupole mass spectrometer MA is started. The filament 41 is energized by the power source E1, and thermionic electrons are emitted from the filament 41. Then, a positive voltage is applied to the grid 43 by the power source E2, and the emitted thermoelectrons are drawn. At this time, gas ions are generated from gas atoms and molecules around the filament colliding with the thermal electrons. The gas ions are converged by the focus electrode 5 and drawn into the quadrupole part 3 while being accelerated by an acceleration voltage corresponding to the potential difference between the grid 43 and the quadrupole part 3. When a predetermined voltage in which direct current and alternating current are superimposed is applied to the electrodes 31 and 31 of the quadrupole portion 3 by the power source E3, the gas ions reach the first ion collector 2 for each mass-to-charge ratio. The first ion current value flowing through the first ion collector 2 is measured by the ammeter 22. On the other hand, part of the gas ions generated in the ion source 4 reaches the second ion collector 6, and the second ion current value flowing through the second ion collector 6 is measured by the ammeter 62. The first ion current value and the second ion current value are input to the control unit C1, and the control unit C1 generates a gas partial pressure of a predetermined mass number from the first ion current value to the total value from the second ion current value. The pressure is calculated respectively.

  By the way, when the gas component remaining in the test body is analyzed using the quadrupole mass spectrometer MA, molecules and atoms in the test body adhere to the grid 43 and become contaminated. Sensitivity decreases. Therefore, it is necessary to configure the quadrupole mass spectrometer MA so that the gas component can be analyzed with high accuracy by determining the sensitivity decrease as quickly as possible. When the sensitivity is lowered, for example, replacement or cleaning of the ion source 4 is performed, but since a known method can be applied to this, detailed description is omitted here.

Here, according to the experiments by the present inventors, the first ion current of specific gas ions such as H ₂ , H ₂ O, O ₂ , Ar, CO ₂ , and N ₂ + CO when the grid 43 has been contaminated. When the value and the change of the second ion current value are measured, as shown in FIG. 2, the second ion current value becomes smaller earlier than the first ion current value. This is because the incident area of the gas ions of the first ion collector 2 is smaller than the incident area of the second ion collector 6, and the generation location of the gas ions in the ion source 4 changes due to the contamination of the grid 43. It is considered that the amount of ions reaching the first ion collector 2 is reduced before the amount of ions reaching the second ion collector 6.

  Therefore, in the present embodiment, the sensitivity within a predetermined range that does not affect the analysis of the gas component is set as the reference sensitivity, the ratio of the first ion current value to the second ion current value is obtained, and this ratio is set based on the reference sensitivity. When the value is equal to or lower than the determination value, it is determined that the sensitivity is lowered. In this case, the reference sensitivity is arbitrarily set according to the quadrupole mass spectrometer MA, and the determination value is obtained by, for example, multiplying the reference sensitivity by a coefficient obtained experimentally or empirically. . Further, the determination means for determining the sensitivity decrease is incorporated as a program in the control unit C1, and the sensitivity decrease determination is executed at a constant cycle or an arbitrarily set cycle. Hereinafter, with reference to FIG. 3, a determination procedure of sensitivity reduction by the control unit C <b> 1 as a determination unit will be specifically described.

If the determination of the sensitivity decrease is started while the gas partial pressure and the total pressure in the test body are being measured, the process proceeds to STEP 1 and a gas ion having a predetermined mass number to be determined for the sensitivity decrease is selected. As the determination target, for example, the one having the maximum first ion current value is automatically selected. However, according to the processing performed in the vacuum chamber with respect to the control unit C1, H _A specific gas ion such as ₂ , H ₂ O, O ₂ , Ar, CO ₂ , or N ₂ + CO may be appropriately selected and set.

When the gas ion to be determined is selected, the process proceeds to STEP 2 to determine whether or not the total pressure in the test body is equal to or higher than a predetermined pressure (for example, 1 × 10 ⁻⁵ Pa). If it is lower, the process proceeds to STEP 3 and the sensitivity reduction determination is terminated. This is because if the total pressure is lower than the predetermined pressure, the value of the first ion current that normally flows through the first ion collector 2 is low, and this may not be able to accurately determine a decrease in sensitivity. In such a case, the control unit C1 may notify that the decrease in sensitivity cannot be determined via a not-illustrated notification unit such as a liquid crystal display or a speaker. When this notification is received, the ion source 4 is replaced or cleaned.

On the other hand, when the total pressure in the test body becomes equal to or higher than the predetermined pressure, the process proceeds to STEP 4 to determine whether or not a predetermined standby time t has elapsed from the start of measurement of the gas partial pressure and the total pressure, There When elapsed, the process proceeds to STEP5, the measurement data of the first ion current value I ₁ and the second ion current value I ₂ is obtained. In this case, for example, the control unit C1 obtains an average value of both the first and second ion current values per unit time, and uses the first ion current value I ₁ and the second ion current value as measurement data. and so as to obtain as I _2. In addition, in order to more accurately determine the sensitivity reduction, the measurement data is acquired a plurality of times with a predetermined standby time, an average value of the measurement data acquired a plurality of times is obtained, and the obtained value is obtained as the measurement data. it may be used as the first ion current value I ₁ and the second ion current value I ₂ as.

When the measurement data is acquired in STEP 5, the process proceeds to STEP 6, and the ratio (I ₁ / I ₂ ) of the first ion current value I _{1 to} the second ion current value I ₂ is obtained, and then the process proceeds to STEP 7. , It is determined whether or not the ratio (I ₁ / I ₂ ) is larger than the determination value. In this case, the determination value is arbitrarily set to determine the sensitivity reduction. For example, the sensitivity within a predetermined range that does not affect the gas analysis is set as the reference sensitivity, and this reference sensitivity is determined experimentally or experimentally. A value obtained by multiplying the obtained coefficient (for example, 1/10 of the reference sensitivity) is preset in the control unit C1. When the ratio (I ₁ / I ₂ ) is larger than the determination value, the process proceeds to STEP 8 and the determination of the sensitivity decrease is terminated assuming that the sensitivity is normal. On the other hand, if the ratio (I ₁ / I ₂ ) is equal to or less than the determination value, the process proceeds to STEP 9, where it is determined that the sensitivity has decreased, and this is notified in the same manner as in STEP 3. In such a case, for example, since the ion source 4 is contaminated, it is necessary to replace or clean it.

  According to the above embodiment, the first ion current value and the second ion that are always measured to measure the gas partial pressure and the total pressure of a predetermined mass number in the test body using the quadrupole mass spectrometer MA. Since it is possible to determine a decrease in sensitivity from the change with the current value, it is not necessary to temporarily stop the vacuum processing being performed in the test body, and without requiring the calibration gas equipment etc. used in the conventional example, Sensitivity reduction can be determined as quickly as possible.

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 ratio of the first ion current value to the second ion current value (I ₁ / I ₂ ) is compared with the determination value, but the total pressure (TP) in the test body calculated from the second ion current value ) May be determined by comparing the ratio (I ₁ / TP) of the first ion current value to the determination value.

  In the above embodiment, as the first ion current value for determining the decrease in sensitivity, the one having the maximum first ion current value is selected, but when the gas component in the test body is known, the determination target is Gas ions may be set in advance before the start of determination, and measurement data of the first ion current value may be acquired. Moreover, if the sum total of the gas ion of the predetermined mass number which passed the quadrupole part 3 is used as a 1st ion current value, the vacuum atmosphere in the test body at the time of determination will have the same total pressure and partial pressure Even in such a case, an accurate determination can be made, which is advantageous.

  Moreover, although the said embodiment demonstrated what provided the 2nd ion collector 6 above the ion source 4, it is not limited to this. For example, a second ion collector for measuring the total pressure is provided on the support, an ion source is provided above the second ion collector, and a quadrupole part is further provided above the ion source. In addition, a first ion collector for measuring partial pressure may be provided.

  MA ... quadrupole mass spectrometer, 2 ... first ion collector, 3 ... quadrupole part, 31 ... electrode, 4 ... ion source, 41 ... filament, 43 ... grid, 6 ... second ion collector, C1 ... Control unit (determination means).

Claims (4)

A quadrupole mass spectrometer for analyzing gas components in a test body,
An ion source having a filament and a grid for ionizing a gas, a quadrupole part in which four columnar electrodes are arranged at predetermined intervals in the circumferential direction, and a gas having a predetermined mass number that has passed through the quadrupole part A first ion collector that collects ions and a second ion collector that collects gas ions generated by the ion source, and a predetermined mass number in the specimen is determined from a first ion current value flowing through the first ion collector. In the configuration configured to measure the gas partial pressure and measure the total pressure in the test body from the second ion current value flowing through the second ion collector,
Sensitivity decreases when the sensitivity within a predetermined range that does not affect the analysis of the gas component is set as the reference sensitivity, and the ratio of the first ion current value to the second ion current value is equal to or less than the determination value set based on the reference sensitivity. A quadrupole mass spectrometer characterized by comprising determination means for determining   2. The quadruple according to claim 1, wherein the first ion current value is selected from among gas ions having a predetermined mass number that have passed through the quadrupole portion, the one having the maximum first ion current value. Polar mass spectrometer.   2. The quadrupole mass spectrometer according to claim 1, wherein a sum of gas ions having a predetermined mass number that has passed through the quadrupole portion is used as the first ion current value. The gas in the test body is ionized by the ion source, and gas ions having a predetermined mass number that has passed through the quadrupole portion are collected by the first ion collector. At this time, the gas partial pressure is determined from the first ion current value flowing through the ion collector In a determination method for determining a decrease in sensitivity of an ion source in a quadrupole mass spectrometer that measures
Collecting a gas ionized in the test body by a second ion collector;
The sensitivity within a predetermined range that does not affect the analysis of the gas component is set as the reference sensitivity, and the ratio of the first ion current value to the second ion current value flowing through the second ion collector is compared with a determination value that is smaller than the reference sensitivity. And a step of determining that the sensitivity has been reduced.

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