JPH09320516A - Quadrupole spectrometer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make a quadrupole spectrometer less affected by the projection of an ion current, reduce the rate of deterioration of a detector, and enhance the reliability of mass spectrometry. SOLUTION: A quadrupole spectrometer, in which an ion current from an ion source 3 is passed through a quadrupole mass filter 4 and detected by a detector 5, has a control means 7 for controlling the flow of the ion current into the detector 5 by changing bias potential with respect to the detector 5. If the ion current does not project during mass spectrometry, the potential of the detector 5 is lowered by the control means 7 relative to the potential of the ion source 3 and that of the quadrupole mass filter 4, and the ion current is introduced into the detector 5 and measured; if the ion current projects, the potential of the detector 5 is heightened by the control means 7 relative to the potential of the ion source 3 and that of the quadrupole mass filter 4, and control is performed to prevent the ion current from flowing into the detector 5 so as to prevent a strong ion current from flowing into the detector to prevent deterioration of the detector and saturation of an amplifier.

Description

Detailed Description of the Invention

[0001]

The present invention relates to a quadrupole mass spectrometer used for analyzing mass spectra and the like.

[0002]

2. Description of the Related Art It is generally known as mass spectrometry that an ionized sample is separated and detected in accordance with a mass / charge ratio, thereby measuring a mass spectrum. Then, qualitative analysis of the sample can be performed from the peak position of the mass spectrum, and quantitative analysis can be performed from the peak intensity. As a means for separating and detecting the ionized sample in accordance with the mass / charge ratio, a quadrupole type is known. FIG. 8 is a schematic configuration diagram for explaining a conventional quadrupole mass spectrometer. In FIG. 8, the conventional quadrupole mass spectrometer comprises a quadrupole 41 with four electrodes. Among the electrodes of the quadrupole 41, a pair of electrodes facing each other is applied to each of which a positive and negative DC voltage U and a high frequency voltage V'are superposed, and applied to the ion source 31.
The ion current 33 generated in step 3 is accelerated and led to the electrode gap,
Only the ions passing between the electrodes are detected by the detector 57. Ions passing through the electrode of the quadrupole 41 have a ratio m / z of the mass m to the number of charges z in proportion to the high frequency voltage V ', so that V / changes while keeping U / V' constant. By doing so, the ions for each mass are detected.

[0003]

In a semiconductor manufacturing apparatus, gas analysis in a vacuum chamber may be performed in order to control gas components for quality control of film formation and the like. When the gas analysis in the vacuum chamber is performed using the conventional quadrupole mass spectrometer, the ion current derived from the ion source such as the vacuum chamber may project. There is a problem that such a protrusion of the ion current deteriorates the detector and affects the measurement of the mass spectrum. For example, in a semiconductor manufacturing apparatus such as a sputtering apparatus, a process gas such as argon gas is introduced into a vacuum chamber. When a specific gas such as argon gas is thus introduced, the amount of the specific gas component introduced in the vacuum chamber is larger than that of the other gas components, so that the ion current corresponding to the mass number of the specific gas is It becomes significantly stronger than the ion currents of other mass numbers.

The strong ion current has a problem of accelerating the deterioration of the detector such as the secondary electron multiplier. Also,
In general, the detection signal from the detector is amplified by an amplifier in the detection circuit. FIG. 9 shows the amplifier output of the ion current with respect to the mass number. The amplifier outputs an ion current according to the mass number. However, when a large current flows from the detector to the amplifier, the amplifier causes a saturation phenomenon and outputs a constant value regardless of the magnitude of the ion current, as in the saturation region indicated by A in FIG. Then, after the detection current from the detector decreases, the amplifier needs a predetermined time to return from the saturated state to the normal state.
Therefore, for example, as shown by B in FIG. 9, an unstable portion occurs in a part of the mass spectrum, which causes a problem in the reliability of the measurement of the mass spectrum.

Therefore, the present invention solves the above-mentioned problems of the conventional quadrupole mass spectrometer, and provides a quadrupole mass spectrometer which is hardly affected by the protrusion of ion current. It is intended to reduce the deterioration of the detector of the meter and to enhance the reliability of mass spectrum measurement by the quadrupole mass spectrometer.

[0006]

SUMMARY OF THE INVENTION The present invention is a quadrupole mass spectrometer in which an ion current from an ion source is detected by a detector through a quadrupole mass filter by changing the bias potential for the detector. A control means for controlling the inflow of the ion current into the analyzer is provided, which makes it less susceptible to the protrusion of the ion current and reduces the deterioration of the detector of the quadrupole mass spectrometer. It is intended to improve the reliability of mass spectrum measurement by a quadrupole mass spectrometer.
In the present invention, the bias potential for the detector is the relative potential of the detector with respect to the ion source and the quadrupole mass filter. The control means of the present invention has a function of changing this bias potential, and by this function, the potential of the detector is made relatively low with respect to the potentials of the ion source and the quadrupole mass filter. Is introduced into the detector, and conversely, the potential of the detector is made higher than the potentials of the ion source and the quadrupole mass filter to prevent the ion current from being introduced into the detector.

In measuring the mass spectrum by the quadrupole mass spectrometer of the present invention, when there is no protrusion of the ion current, the control means controls the potential of the detector with respect to the potential of the ion source or the quadrupole mass filter. When the ion current is measured by introducing it into the detector while making it relatively low, and if the ion current is prominent, the control means sets the potential of the detector to the potential of the ion source or quadrupole mass filter. On the other hand, it is controlled to be relatively high so that the ion current does not flow into the detector. This prevents a strong ion current from flowing into the detector, preventing detector degradation and amplifier saturation.

The first embodiment of the present invention comprises a high sensitivity detector and a low sensitivity detector having different detection sensitivities, and the control means controls the bias potentials of both detectors. With this, the protrusion range of the ion current is obtained by prescan in which the low-sensitivity detector is used to perform scanning over the entire mass number range, and the high-sensitivity detector is used to exclude the ion current protrusion range in the mass number range. The mass spectrum is measured by scanning. In the second embodiment of the present invention, the high-sensitivity detector is arranged offset with respect to the axis connecting the ion source and the quadrupole mass filter, thereby preventing the inflow of a protruding ion current. To do. A third embodiment of the present invention provides:
An electrode is provided in the vicinity of the detector, and the inflow of an ionic current into the detector is controlled by controlling the potential of this electrode by the control means.

[0009]

Embodiments of the present invention will be described below in detail with reference to the drawings. An example of the configuration of the embodiment of the present invention will be described with reference to the schematic block diagram and the schematic configuration diagram of one embodiment of the quadrupole mass spectrometer of the present invention shown in FIGS. 1 and 2, a quadrupole mass spectrometer 1 includes an ion source 3, a quadrupole mass filter 4, a detector 5, a detection circuit 6, and a control circuit 7, and the configuration excluding the control circuit 7 is an ordinary one. It has the same configuration as the quadrupole mass spectrometer. The ion source 3 includes the measurement target 2 to the sample 2
3 is introduced and the sample 23 is ionized by excitation with the electron beam from the filament 32. The sample 23 is, for example, a gas contained in the vacuum chamber 21 included in the semiconductor manufacturing apparatus. A large amount of process gas 22 such as argon gas may be introduced into the vacuum chamber 21 of the sputtering apparatus during the processing step.

The quadrupole mass filter 4 is an electrode of a quadrupole 41 in which four cylindrical or hyperbolic rods made of stainless steel, molybdenum or the like are arranged in a balanced manner. A voltage in which a positive and negative DC voltage U and a high frequency voltage V ′ having a frequency f (MHz) are superimposed is applied. In FIG. 2, the voltage source 42 applies a voltage obtained by superimposing the DC voltage U and the high frequency voltage V ′ to the quadrupole 41.
When the distance between the electrode surface and the central axis is r (cm), the ions generated by the ion source 3 are accelerated and guided to the electrode gap, and U
When / V 'is made slightly smaller than 0.168, only ions satisfying m / z = (1 / 7.22) · (V ′ / f ² · r ² ) pass through the electrode gap. Note that m
Is mass and z is the number of charges. Therefore, by keeping V / V ′ constant and continuously changing V ′, ions for each mass are guided to the detector 5 and act as a mass filter. The detector 5 detects the ions that have passed through the quadrupole mass filter 4 and sends a detection signal to the detection circuit 6.

The detector of the present invention shown in FIG. 2 comprises a low-sensitivity detector 51 and a high-sensitivity detector 52, and the low-sensitivity detector 51 is arranged on the central axis of the quadrupole mass filter 4 for high-sensitivity detection. The device 52 is arranged offset from the central axis. The low-sensitivity detector 51 is a detector having a low ion current detection sensitivity, and its detection output is large enough not to saturate the amplifier even with a large inflow of a large ion current. Bias power sources 53 and 54 are connected to each of the low-sensitivity detector 51 and the high-sensitivity detector 52 to adjust the relative potential with respect to the ion source 3 and the quadrupole mass filter 4. The control circuit 7 adjusts this bias potential. The bias potential controls the introduction of the ion current to the detector 5. The timing of adjusting the bias potential of the control circuit 7 is
It can be adjusted according to the output of the detection circuit 6, and the bias potential can be adjusted according to the protruding ion current during the scanning of the mass number due to the change in V ′.

In the configuration example shown in FIG. 2, the bias power sources 53 and 54 adjust the potential of the detector 5 (low-sensitivity detector 51, high-sensitivity detector 52).
Alternatively, a bias power source may be connected to the quadrupole mass filter 4 to adjust the bias potential of the detector 5 with respect to the ion source 3 and the quadrupole mass filter 4.

Next, the operation of the quadrupole mass spectrometer of the present invention will be described with reference to the flow chart of FIG. 3, the operation diagram of FIG.
This will be described with reference to the ion current amplifier output diagram of FIG. In addition,
The operation diagram of FIG. 4 shows the configuration example shown in FIG. While changing the high frequency voltage V ′ applied to the quadrupole mass filter 4, the mass number of the ions passing through the quadrupole mass filter 4 is changed, and the passing ion current is detected by the low sensitivity detector 51. FIG. 5A shows an outline of the output characteristic of the low sensitivity detector 51. Low sensitivity detector 51
Has a small output signal value with respect to the input ion current, the output signal does not saturate the amplifier. Therefore, by prescanning the analysis range using this low-sensitivity detector 51, the outline of the mass spectrum can be obtained.

FIGS. 4A and 4B show a low sensitivity detector 51.
7 shows an example of applying a bias potential in the scanning of the ion current by. FIG. 4A is an example in which a negative potential is applied to the low sensitivity detector 51 by the bias power supply 53, and FIG. 4B is a low sensitivity detector 5 by the bias power supply 53.
In this example, a negative potential is applied to 1 and a positive potential is applied to the high sensitivity detector 52 by the bias power supply 54. By applying this bias potential, the ion current that has passed through the quadrupole mass filter 4 can be guided only to the low sensitivity detector 51 without flowing into the high sensitivity detector 52 (step S1). From the mass spectrum obtained by the prescan in step S1, the range of the mass number where the ion current is projected and the amplifier is saturated, and the range of the high frequency voltage V ′ corresponding to the mass number are obtained. In FIG. 5, the range in which this amplifier is saturated is shown by the range of mass numbers sandwiched by the broken lines a and b (step S2).

Next, the high-sensitivity detector 52 is used instead of the low-sensitivity detector 51, and the high-frequency voltage V'applied to the quadrupole mass filter 4 is changed while the quadrupole is being used as in step S1. Scanning is performed by changing the mass number of ions passing through the mass filter 4 (step S3). In the scanning by the high-sensitivity detector 52, the bias potential is controlled so that the ion current does not flow into the high-sensitivity detector 52 in the saturation range obtained in step S2, and the ion current of the high-sensitivity detector 52 is controlled only in the non-saturation range. Detect (step S
4, 5, 6). FIG. 5B shows an output characteristic diagram of the high-sensitivity detector 52. In the mass number range in which the output of the high-sensitivity detector 52 is saturated, a bias is applied so that the ionic current does not flow into the high-sensitivity detector 52. By controlling the potential, deterioration of the high sensitivity detector 52 can be prevented, saturation of the amplifier can be prevented, and the reliability of the detection output can be improved. FIG. 4C is an example of applying a bias potential in the scanning of the ionic current by the high sensitivity detector 52. By applying a negative potential to the high sensitivity detector 52 by the bias power supply 54, the ionic current is highly sensitive. It is introduced into the detector 52.

FIGS. 6 and 7 show another example of the structure of the detector and an example of applying the bias potential. The configuration example of FIGS.
As the detector 5, only the high-sensitivity detector 56 is arranged, and the electrode 55 for drawing in the ion current is arranged.
In the configuration example of FIG. 6, the high sensitivity detector 56 is arranged on the central axis of the mass mass filter 4, and the electrode 55 is arranged offset from the central axis. In the prescan and the scanning within the mass number range in which the ion current does not project, the ion current is directly introduced into the high-sensitivity detector 50 and detected as shown in FIG. When scanning the range, as shown in FIG.
A negative bias potential is applied to the electrode 55 to draw an ionic current into the electrode 55 and prevent the ionic current from flowing into the high-sensitivity detector 56.

Further, in the configuration example of FIG. 7, the high sensitivity detector 5
6 is arranged offset from the central axis of the mass mass filter 4. In the pre-scanning and the scanning within the range of the mass number where the ion current does not protrude, as shown in FIG. 7A, the bias power source 58 applies a negative bias potential to the high-sensitivity detector 56, and the bias power source 57 applies the electrode 55. When a positive bias potential is applied to the high-sensitivity detector 56 to detect the ion current and the mass number range in which the ion current is projected is scanned, the bias current as shown in FIG. A positive bias potential is applied to the high-sensitivity detector 56 by the power source 58, and a negative bias potential is applied to the electrode 55 by the bias power source 57 to draw an ion current into the electrode 55, so that the ion current to the high-sensitivity detector 56 is Prevent inflow. In addition, in the configuration of FIG. 7, the electrode 55 may be arranged on the central axis of the mass mass filter 4 or may be arranged at a position offset from the central axis.

[0018]

As described above, according to the present invention,
It is possible to provide a quadrupole mass spectrometer that is not easily affected by the protrusion of ion current, reduce the deterioration of the detector of the quadrupole mass spectrometer, and measure the mass spectrum of the quadrupole mass spectrometer. The reliability can be increased.

[Brief description of drawings]

FIG. 1 is a schematic block diagram illustrating an embodiment of a quadrupole mass spectrometer of the present invention.

FIG. 2 is a schematic configuration diagram illustrating an embodiment of a quadrupole mass spectrometer of the present invention.

FIG. 3 is a flow chart for explaining the operation of the quadrupole mass spectrometer of the present invention.

FIG. 4 is an operation diagram for explaining the operation of the quadrupole mass spectrometer of the present invention.

FIG. 5 is an amplifier output diagram of ion current by the quadrupole mass spectrometer of the present invention.

FIG. 6 is another configuration example of the detector of the quadrupole mass spectrometer of the present invention and an application example of a bias potential.

FIG. 7 is another configuration example of the detector of the quadrupole mass spectrometer of the present invention and an application example of a bias potential.

FIG. 8 is a schematic configuration diagram for explaining a conventional quadrupole mass spectrometer.

FIG. 9 is an amplifier output diagram of ion current with respect to mass number by a conventional quadrupole mass spectrometer.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Quadrupole mass spectrometer, 2 ... Measuring object, 3, 31 ... Ion source, 4 ... Quadrupole mass filter, 5 ... Detector, 6 ... Detection circuit, 7 ... Control circuit, 23 ... Sample, 41 ... Quadrupole, 42
... voltage source, 51 ... low-sensitivity detector, 52, 56 ... high-sensitivity detector, 53, 54, 57, 58 ... bias power supply, 55 ...
electrode.

Claims (1)

[Claims] 1. A quadrupole mass spectrometer in which an ion current from an ion source is detected by a detector through a quadrupole mass filter, the bias potential for the detector is changed,
A quadrupole mass spectrometer, comprising a control means for controlling the flow of an ion current into a detector.