JP3346688B2 - Quadrupole mass spectrometer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a quadrupole mass spectrometer, and more particularly to a field using high energy ions, for example, mass spectrometry of high energy ions in etching of a semiconductor wafer or the like using an ion beam or discharge plasma. It relates to a suitable quadrupole mass spectrometer.

[0002]

2. Description of the Related Art FIG. 3 is an explanatory view showing the structure of a conventional quadrupole mass spectrometer. The ion source section denoted by reference numeral 1 irradiates the sample gas molecules 2, which are sample pieces, with an electron beam 3 to be ionized, and accelerates and focuses the ions by electrodes 17 to form incident ions 4. The incident ions 4 travel in the electric field of the quadrupole electrode unit 5 and have a specific mass-to-charge ratio (M /
Z: M is an atomic mass unit, Z is the number of charges) and ions having acceleration energy pass through the quadrupole electrode unit 5, and specific ions 8 are detected by the ion detection unit 7 and recorded on the recorder 10. The electric field of the quadrupole electrode unit 5 is formed by connecting four cylindrical or quadrupolar quadrupole electrodes 9 whose inner cross sections are hyperbolic as shown in FIG. An electric field is formed between the electrodes.

FIG. 4 shows a Matthew diagram. The vertical axis a and the horizontal axis q in FIG. 4 are defined by equations (1) and (2).

(Equation 1) Here, U is a DC voltage applied to the quadrupole electrode unit 5, V is a high-frequency voltage applied to the quadrupole electrode unit 5, m is the mass of the ion (M × 1.66 × 10 ⁻²⁷ kg), and e is the ion The charge amount (coulomb), r ₀ is the inner radius of the quadrupole electrode, and ω is the angular frequency.

In the conventional quadrupole mass spectrometer, the conditions of the voltage applied to the quadrupole electrode 9 are as follows: a first stable area in A, a second stable area in B, C in the Matthew diagram shown in FIG. The first stable region in D and the first stable region in D were determined. In FIG. 3, ions 4 incident into the electric field of the quadrupole electrode unit 5 synchronize with the high-frequency voltage (V) to obtain x and y.
While oscillating in the direction, the laser beam proceeds in the direction of the ion detector 7 while maintaining the initial velocity at the time of incidence in the z direction. In the electric field of the quadrupole electrode section 5, the equation (3) approximately shows between the number of vibrations n of the ion synchronized with the high frequency voltage (V) and the half width resolution M / ΔM of the mass peak of the ion. It is known that the relationship holds.

[0005]

(Equation 2) Here, h is a constant that differs individually under the conditions of the first, second, and first 'stable regions. For example, in the first stable region condition, h ≒
It is known that h ≒ 0.7 under the condition of 3.5 and the second stable region. From equation (1), a certain unit resolution M /
It can be seen that there is a minimum n required to obtain ΔM. Here, n is expressed by equation (4).

(Equation 3) However, f is the frequency of the high frequency voltage V, is ι geometrical length of the quadrupole electrodes, the V _i is the acceleration voltage of the incident ions. Usually, f is 1 to 5 MHz, and l is about 200 mm.

[0006] accelerating ions before the voltage V _i is too large, sufficient ion discrimination is performed will pass through the electric field of the quadrupole electrode portions 5, sufficient mass resolution is obtained. Therefore, in order to satisfy M / ΔM ≧ 2M under the condition of the first stable region,
V _i is less about 50 V, is V _i in the second stability region 500
The inventors have confirmed that it is necessary to be about V or less and about 3 kV or less in the first 'stable region.

[0007]

The acceleration voltage V _i is 500
When mass spectrometry of high-energy ions of about V or more is performed, an electrode for decelerating incident ions is attached under the conditions of the first or second stable region, or 500 V is applied to the quadrupole electrode itself.
It is necessary to apply a bias voltage of a degree or more (or equivalent to the acceleration energy of ions). However, in order to decelerate incident ions, a plurality of deceleration electrodes must be combined, and a power supply for supplying a voltage to be applied to the deceleration electrodes must be prepared. Further, in order to apply a bias voltage to the quadrupole electrode itself, the withstand voltage of the high-frequency voltage generating circuit must be increased.

On the other hand, if the voltage condition of the first 'stable region is applied to the quadrupole electrode 9 to mass spectrometry, the accelerating voltage V _i is 50
Even with ions of about 0 V or more, mass analysis can be performed under the condition of mass resolution M / ΔM ≧ 2M, but mass peaks due to the first stable region appear at the same time, and the mass peak based on the first stable region and the first ' There is a problem that the mass peaks based on the stable region overlap.

The present invention has been made in view of the above-mentioned circumstances, and an ion having an acceleration voltage exceeding 500 V and having an energy exceeding 500 V can be easily subjected to mass analysis of high-energy ions by M / ΔM ≧ 2M It is an object of the present invention to provide a quadrupole mass spectrometer capable of mass spectrometry while maintaining the mass resolution.

[0010]

According to the quadrupole mass spectrometer of the present invention, two sets of quadrupole electrodes are arranged before and after the sample ion traveling path along the traveling path of the sample ions. What is claimed is: 1. A quadrupole mass spectrometer comprising: means for superimposing and applying a DC voltage and a high-frequency voltage to electrodes, respectively, wherein the DC voltage and the high-frequency voltage are applied to a preceding one of the two sets of quadrupole electrodes. Is determined from the second stable region of the Matthew diagram derived from the Matthew differential equation, and the conditions of the DC voltage and the high-frequency voltage applied to the subsequent quadrupole electrode are determined by the first'stable of the Matthew diagram. It is characterized by being derived from an area.

According to the present invention, two sets of quadrupole electrodes are arranged in series in accordance with the central axis of incident ions, and a voltage condition of the second stable region is given to the set of quadrupole electrodes in the former stage on the ion source side, while The (second-stage) quadrupole electrode is subjected to mass spectrometry by applying a voltage condition in the first 'stable region. This allows
Ions having an energy exceeding 500 eV can be subjected to mass spectrometry while maintaining a unit resolution M / ΔM ≧ 2M or more.

An ion having a certain mass-to-charge ratio M / Z is represented by r
_When the values of ₀ , ω, U, and V are determined, one point is determined on the (a, q) plane. From equations (1) and (2), a / (2q) = U
/ V is given, this equation is a straight line passing through the origin of the (a, q) plane and the odor is determined by the ratio of U to V,
It is determined independently of / Z. Given this U / V ratio, all the different M / Z ions will be on this line. This is called a mass scan line.
Of all the ions arranged on the mass scanning line, only M / Z ions arranged on the line in the stable region can pass through the quadrupole electric field. By increasing or decreasing the ratio of U / V to change the slope of the mass scan line and reducing the overlap between the stable region and the mass scan line, the range of the M / Z of ions that can pass through the quadrupole electric field becomes narrow, and Only the ions of M / Z can pass through.

In a quadrupole mass spectrometer, when mass spectrometry is performed using the first stable region, the mass scanning line also passes through the first stable region. Therefore, when obtaining the mass spectrum of the first 'stable region, the mass spectrum due to the first stable region is obtained at the same time. That is, a state in which the mass spectrum of the first stable region overlaps with the mass spectrum of the first stable region appears. In order to clearly obtain the mass spectrum of the first 'stable region, it is necessary to remove the mass spectrum of the first stable region, which is a cause of a large background.

Therefore, two sets of quadrupole electrodes are arranged in series along the flow of incident ions. First, mass spectrometry is performed coarsely at the quadrupole electrode section at the preceding stage, and ions having a specific M / Z are obtained. Into the quadrupole electrode section at the subsequent stage. Next, analysis is performed with sufficient resolution by the quadrupole electrode at the subsequent stage. In this way, by adopting a method of restricting the ions that enter the electric field of the subsequent quadrupole electrode portion, the background caused by the first stable region can be greatly reduced and the resolution can be increased.

[0015]

An embodiment of the present invention will be described below with reference to the accompanying drawings. In the drawings, the same reference numerals indicate the same or corresponding parts.

FIG. 1 is an explanatory view of a quadrupole electrode section of a quadrupole mass spectrometer according to one embodiment of the present invention. In the figure, reference numeral 11 denotes a first-stage quadrupole electrode, 12 denotes a second-stage quadrupole electrode, 13 denotes a capacitor, and 14 denotes incident ions.

As shown in FIG. 1, two sets of quadrupole electrodes are provided,
These are arranged in series along the path of the ion beam. At this time, it should be noted that the center axes of the quadrupole electric fields formed by the two sets of quadrupole electrodes 11 and 12 are matched. The two sets of quadrupole electrodes 11 and 12 are connected as shown in FIG. For each set of quadrupole electrodes 11 and 12, the opposing electrodes of the quadrupole electrodes are connected and the same potential is applied.

In this embodiment, the first-stage quadrupole electrode 1
1, a voltage under the second stable region condition is applied, and a voltage under the first 'stable region condition is applied to the quadrupole electrode 12 at the subsequent stage. 1
In order to apply a voltage to the two sets of quadrupole electrodes 11 and 12 by the two high-frequency power supplies, a capacitor 13 (capacitance C ₁ ) is inserted into the application circuit as shown in FIG. The high-frequency voltage (V) applied to 12 is distributed and applied to the quadrupole electrode 11 in the preceding stage. A DC voltage (U) is superimposed and applied to the quadrupole electrode 11 in the preceding stage in addition to the high-frequency voltage,
A voltage is applied under the second stable region condition. Note that the voltage application terminals of the four-terminal electrode in FIG. 1 are a, b, c, and d. As an example, the length 1 of the first-stage quadrupole electrode 11 is 20 mm, and the length 1 of the second-stage quadrupole electrode 12 is about 200 mm.

FIG. 2A shows an equivalent circuit for obtaining the capacitance (C ₁ ) of the capacitor 13 inserted in the circuit in FIG.

(Equation 4) In FIG. 2, the relationship between the high-frequency voltage Vcd between _cd and the high-frequency voltage Vab between _ab can be expressed by equation (5).

In the second stable region in B in the Matthew diagram of FIG. 4, a has a value of about 2.8 and q has a value of about 3.0, and in the first stable region of D, a has a value of 0. , Q is 7.
It has a value around 55. From the equation (2), the high frequency voltage is proportional to q.

(Equation 5) Therefore, the ratio of the high-frequency voltage applied to the first and second quadrupole electrodes 11 and 12 can be expressed by equation (6).

The first and second quadrupole electrodes 11 and 12 used in the present embodiment are measured by an impedance meter 10.
The capacitance C ₃ of the quadrupole electrode 11 at the front stage was 10 pF, and the capacitance C ₂ of the quadrupole electrode 12 at the rear stage was around 30 pF. First quadrupole electrode 1
The capacitance C ₄ including a power supply cable for supplying a DC voltage to be applied to 1 was about 30 pF. Equation (5) and (6)
Equation (7) is obtained from the equation,

(Equation 6) _{C 2 = 30pF, C 3 =} 10pF, when by substituting C ₄ = 30 pF seek C _1, obtained with C ₁ = 53pF.

That is, in FIG. 1, if the capacitance of the capacitor 13 introduced into the circuit is 53 pF, the condition of the high frequency voltage in the second stable region can be applied to the quadrupole electrode 11 in the former stage, and the quadrupole electrode in the latter stage can be applied. A voltage condition in the first 'stable region can be applied to the electrode 12.

The high-frequency voltage and the DC voltage in the second and first 'stable regions can be supplied from a common voltage generating circuit. The terminal abcd is applied with a DC voltage superimposed on a high-frequency voltage. FIG. 2B is a diagram illustrating a DC voltage dividing circuit. According to the voltage dividing circuit of FIG. 2B, U '= (R / (R + R')) * U-U '= (R / (R + R')) * (-U) The partial pressure ratio is a = 2.
8, U _ab / U _cd = 2.8 / 0.03, where a = 0.03 in the first 'stable region, so that the partial pressure ratio is set to 100 or more. That is, R and R 'are selected so that U / U'≥100.

The operation of the quadrupole mass spectrometer combining the two quadrupole electrodes is as follows.

A sample gas is introduced into an ion source, and sample ions 14 are made incident on two sets of quadrupole electrodes 11 and 12. As described above, the DC voltage (U) and the high-frequency voltage (V) are superimposed and applied between the quadrupole electrodes.
A quadrupole electric field in the second stable region is formed therebetween, and a quadrupolar electric field in the first stable region is formed between the quadrupole electrodes 12 at the subsequent stage. When the ions 14 generated in the ion source are incident along the central axis (referred to as the z-axis direction) of the quadrupole electrodes 11 and 12, an electric field generated in the quadrupole electrodes 11 and 12 while traveling in the z direction causes It receives forces in the x-axis direction and the y-axis direction. Under certain conditions of voltage (U, V), distance between quadrupole electrodes (2r ₀ ), and frequency (f) of high-frequency voltage, only ions having a specific M / Z are limited in both the x and y axes. It vibrates with the same amplitude and can pass through the quadrupole electrodes 11 and 12.

The other ions having M / Z increase in amplitude in the quadrupole electrode 11 or 12, and
Alternatively, the ions are trapped by the probe 12 or pass through the gap between the quadrupole electrodes 11 and 12 and do not reach the ion detection unit. Ions roughly discriminated in the electric field between the quadrupole electrodes 11 in the second stage stable region in the former stage are subjected to mass analysis with a resolution of M / ΔM ≧ 2M by the electric field between the quadrupole electrodes 12 in the first stage stable region in the subsequent stage. . Ions that have passed through the electric field between the quadrupole electrodes 11 and 12 are detected by the ion detector 7 such as an ion collector, and a signal proportional to the ion current is recorded by the recorder 10 as a mass spectrum.

FIGS. 5 to 7 show typical spectrum waveform data when the first, second and first 'stable regions are used. FIG. 5 is a mass spectrum of the first stable region,
This is an example in which the sample is methane gas and the ion acceleration voltage V _i = 10 V. FIG. 6 is a mass spectrum of the second stable region,
This is an example in which the sample is methane gas and the ion acceleration voltage V _i = 400 V. FIG. 7 is a mass spectrum of the first 'stable region, in which the sample is air and the ion acceleration voltage V _i = 1000 V.

When the quadrupole electric field of the second stable region and the quadrupole electric field of the first stable region are used in combination as in this embodiment, the mass spectrum is improved as follows. FIG. 8A is a mass spectrum of the first 'stable region. The reason why the peak baseline increases at the low mass side is as follows.
This is because a spectrum based on the stable region has appeared. Therefore, when the quadrupole electric field in the second stable region and the quadrupolar electric field in the first stable region are combined as in the present embodiment for the same sample gas, as shown in FIG. The rise of the baseline can be cut off, and a clear mass spectrum can be obtained.

[0029]

According to the quadrupole mass spectrometer of the present invention, a mass spectrum having a mass peak of unit resolution M / ΔM ≧ 2M can be obtained for ions having an energy exceeding 500 eV with a simple device configuration. Therefore, mass analysis of high-energy ions, which has been difficult with a conventional quadrupole mass spectrometer, can be easily performed, and can be used for plasma process monitoring, discrimination of ions emitted from an ion gun, and the like.

[Brief description of the drawings]

FIG. 1 is an explanatory view of a quadrupole electrode section of a quadrupole mass spectrometer according to one embodiment of the present invention.

2A is an equivalent circuit diagram of a capacitor portion in FIG. 1, and FIG. 2B is a circuit diagram of a DC voltage dividing circuit.

FIG. 3 is an explanatory diagram of a configuration of a conventional quadrupole mass spectrometer.

FIG. 4 is an explanatory diagram of a stable region in a Matthew diagram.

FIG. 5 is a diagram showing an example of a spectrum waveform.

FIG. 6 is a diagram showing an example of a spectrum waveform.

FIG. 7 is a diagram showing an example of a spectrum waveform.

FIG. 8 is a diagram showing an example of a spectrum waveform, and FIG.
Shows before improvement and (b) shows after improvement.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Ion source 2 Sample piece (sample gas molecule) 3 Electron beam 4, 14 Incident ion 5 Quadrupole electrode part 6, 6 Voltage application terminal 7 Ion detection part 8 Specific ion 9 Quadrupole electrode 10 Recorder 11 Previous quadrupole electrode 12 Post-stage quadrupole electrode 13 Capacitor

Continuing from the front page (72) Inventor Tetsuya Abe 801-1 Mukayama, Naka-machi, Naka-gun, Ibaraki Japan (72) Inventor Yoshio Murakami 801-1 Mukoyama, Naka-machi, Naka-gun, Naka-gun, Japan Ibaraki Japan In the laboratory (56) References JP-A-5-36376 (JP, A) JP-A-59-60856 (JP, A) JP-A-5-89826 (JP, A) JP-A-4-149952 (JP, A) (58) Fields surveyed (Int. Cl. ⁷ , DB name) H01J 49/42 G01N 27/62

Claims (3)

(57) [Claims] 1. A means for superposing and applying a DC voltage and a high-frequency voltage to the two sets of quadrupole electrodes, respectively, wherein two sets of quadrupole electrodes are arranged before and after the path along which the sample ions travel. A quadrupole mass spectrometer provided, wherein the condition of the DC voltage and the high-frequency voltage applied to the preceding quadrupole electrode of the two sets of quadrupole electrodes is the second in a Matthew diagram derived from Mathieu's differential equation. The quadrupole is determined from the stable region, and the conditions of the DC voltage and the high-frequency voltage applied to the subsequent quadrupole electrode are derived from the first 'stable region of the Matthew diagram. Mass spectrometer. 2. Even if the acceleration energy of ions incident on an electric field formed by the two sets of quadrupole electrodes is 500 eV or more, the ratio M between the atomic mass unit M and the half width ΔM of the mass peak by the atomic mass unit M The quadrupole mass spectrometer according to claim 1, wherein / M is obtained at least 2M. 3. The quadrupole mass spectrometer according to claim 1, wherein the high-frequency and DC voltages in the second and first 'stable regions can be supplied from a common voltage generation circuit.