JPH0982274A - Quadrupole mass spectrometry device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a quadrupole mass spectrometry device allowing the mass of high-energy ions to be easily analyzed by arranging two sets of quadrupole electrodes at a pre-stage and a post-stage along the travel path of sample ions, and applying DC voltage as well as high-frequency voltage to respective quadrupole electrodes in a superposed state. SOLUTION: Two sets of quadrupole electrodes 11 and 12 are laid in series along the path of a sample ion beam 14 with the center axes of quadrupole electric field aligned. Then, the opposite electrodes of each set are wired to each other for application of the same potential thereto. Furthermore, conditions for DC voltage and high-frequency voltage applied to the quadrupole electrodes 11 at a pre-stage are determined on the basis of the second stable zone of the Mathieu's lines. Also, the conditions for each voltage applied to the quadrupole electrodes 12 at a post-stage is derived from the first stable zone of the Mathieu's lines. In addition, mass is roughly analyzed with the pre-stage quadrupole electrodes 11 and, then, analyzed with the post-stage quadrupole electrodes 12 under an enough resolution maintained, thereby providing a high resolution.

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 analysis of high-energy ions in etching semiconductor wafers 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 diagram showing the structure of a conventional quadrupole mass spectrometer. In the ion source portion indicated by reference numeral 1, sample gas molecules 2 which are sample pieces are irradiated with an electron beam 3 to be ionized, and the ions are accelerated and focused by electrodes 17 to form incident ions 4. The incident ions 4 travel in the electric field of the quadrupole electrode part 5 and have a specific mass-to-charge ratio (M /
Ions having Z: M are atomic mass units and Z is the number of charges) and acceleration energy pass through the quadrupole electrode unit 5, and specific ions 8 are detected by the ion detection unit 7 and recorded in the recorder 10. In the electric field of the quadrupole electrode part 5, four quadrupole electrodes 9 each having a cylindrical shape or an inner cross section having a hyperbolic shape are connected as shown in the drawing, and a voltage in which a direct current and a high frequency voltage are superimposed is applied to the quadrupole 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 the equations (1) and (2).

[Equation 1] Where U is a DC voltage applied to the quadrupole electrode part 5, V is a high frequency voltage applied to the quadrupole electrode part 5, m is the mass of the ion (M × 1.66 × 10 ⁻²⁷ kg), and e is the ion The amount of charge (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: the first stable region in A, the second stable region in B, and C in the Mathieu diagram shown in FIG. It was determined from the third stable region in and the 1'stable region in D. In FIG. 3, the ions 4 incident in the electric field of the quadrupole electrode portion 5 are synchronized with the high frequency voltage (V) in x and y.
While oscillating in the z direction, the initial velocity at the time of incidence is maintained in the z direction, and the z direction advances toward the ion detector 7. In the electric field of the quadrupole electrode section 5, 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 are approximately represented by the equation (3). It is known that a relationship is established.

[0005]

[Equation 2] However, h is a constant that differs depending on the conditions of the first, second, and 1 ′ stable regions. For example, in the first stable region condition, h≈
It is known that under the conditions of 3.5 and the second stable region, h≈0.7. From equation (1), a certain unit resolution M /
It can be seen that there is a minimum of n needed to obtain ΔM. Here, n is represented by the equation (4).

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

If the accelerating voltage V _i is too high, the ions pass through the electric field of the quadrupole electrode section 5 before sufficient ion discrimination is performed, and sufficient mass resolution cannot be obtained. Therefore, in order to satisfy M / ΔM ≧ 2M under the condition of the first stable region,
V _i is about 50 V or less, and V _i is 500 in the second stable region.
It has been confirmed by the inventors 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 analysis of high-energy ions of about V or more is performed, an electrode for decelerating incident ions is attached under the condition of the first or second stable region, or the quadrupole electrode itself is 500 V
It is necessary to apply a bias voltage of a certain level or higher (or equivalent to the acceleration energy of ions). However, in order to decelerate the incident ions, a plurality of deceleration electrodes must be combined, and a power source for supplying a voltage applied to the deceleration electrodes must be prepared. Further, in order to apply the bias voltage to the quadrupole electrode itself, the withstand voltage of the high frequency voltage generating circuit must be increased.

On the other hand, when the voltage condition of the first stable region is applied to the quadrupole electrode 9 and mass analysis is performed, the acceleration voltage V _i is 50.
Mass analysis is possible even with ions of about 0 V or more under the condition of mass resolution M / ΔM ≧ 2M, but the mass peaks due to the first stable region appear at the same time, and the mass peaks 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. M / ΔM ≧ 2M is defined as an ion having an energy with an accelerating voltage of more than 500 V, which enables easy mass analysis of high energy ions. An object of the present invention is to provide a quadrupole mass spectrometer capable of performing mass analysis while maintaining the mass resolution of

[0010]

In the quadrupole mass spectrometer of the present invention, two sets of quadrupole electrodes are arranged along a traveling path of a sample ion at a front stage and a rear stage of the path, and the two sets of quadrupole electrodes are arranged. A quadrupole mass spectrometer provided with means for applying a DC voltage and a high frequency voltage to the electrodes, respectively, the conditions of the DC voltage and the high frequency voltage applied to the preceding quadrupole electrode of the two sets of quadrupole electrodes. Is determined from the second stable region of the Mathieu diagram derived from the Mathieu differential equation, and the conditions of the DC voltage and the high frequency voltage applied to the quadrupole electrode in the subsequent stage are the 1st 'stable state of the Mathieu diagram. It is characterized by being derived from a region.

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

Ions with a certain mass to charge ratio M / Z are 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, but this equation is a straight line passing through the origin of the (a, q) plane and the scent is determined by the ratio of U and V, and M
Determined regardless of / Z. When this U / V ratio is determined, all the different M / Z ions are lined up on this straight line. This is called a mass scan line.
Of all the ions lined up on the mass scan line, only M / Z ions lined up on the line in the stable region can pass the quadrupole electric field. If the slope of the mass scan line is changed by increasing or decreasing the U / V ratio to reduce the overlap between the stable region and the mass scan line, the M / Z range of ions that can pass through the quadrupole electric field is narrowed, and a certain Only M / Z ions of

In the quadrupole mass spectrometer, when mass analysis is performed in 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 resulting from 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 the mass spectrum of the first stable region appears. In order to clearly obtain the mass spectrum of the 1'st stable region, it becomes necessary to remove the mass spectrum of the 1st stable region, which causes a large background.

Therefore, two sets of quadrupole electrodes are used and they are arranged in series along the flow of incident ions. First, rough mass analysis is performed in the quadrupole electrode part of the preceding stage, and ions having a specific M / Z are obtained. Is injected into the quadrupole electrode section in the subsequent stage. Next, an analysis is performed with sufficient resolution by the quadrupole electrode in the latter stage. In this way, by adopting the method of limiting the ions that enter into the electric field of the quadrupole electrode portion in the subsequent stage, it is possible to achieve a significant reduction in the background caused by the first stable region and to achieve high resolution.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 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 an embodiment of the present invention. In the figure, reference numeral 11 is a front quadrupole electrode, reference numeral 12 is a rear quadrupole electrode, reference numeral 13 is a capacitor, and reference numeral 14 is an incident ion.

As shown in FIG. 1, two sets of quadrupole electrodes are provided,
This is arranged in series along the path of the ion beam. At this time, it should be noted that the central axes of the quadrupole electric fields formed by the two sets of quadrupole electrodes 11 and 12 are aligned. The above two sets of quadrupole electrodes 11 and 12 are connected as shown in FIG. With respect to each set of the quadrupole electrodes 11 and 12, the electrodes facing each other of the quadrupole electrodes are connected and the same potential is applied.

In the present embodiment, the preceding quadrupole electrode 1
The voltage under the second stable region condition is applied to No. 1, and the voltage under the first stable region condition is applied to the quadrupole electrode 12 in the subsequent stage. 1
In order to apply a voltage to the two sets of quadrupole electrodes 11 and 12 by the high frequency power source of the table, a capacitor 13 (electrostatic capacity C ₁ ) is inserted in 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. In addition to the high frequency voltage, the direct current voltage (U) is superimposed and applied to the quadrupole electrode 11 in the front stage,
The voltage is applied under the second stable region condition. The voltage application terminals of the four-terminal electrode in FIG. 1 are a, b, c, and d. As an example, the length l of the quadrupole electrode 11 in the front stage is 20 mm, and the length l of the quadrupole electrode 12 in the rear stage is about 200 mm.

In order to obtain the electrostatic capacitance (C ₁ ) of the capacitor 13 inserted in the circuit in FIG. 1, its equivalent circuit is shown in FIG. 2 (A).

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

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

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

Now, by the impedance meter 10, the quadrupole electrodes 11 and 12 of the front and rear stages used in this embodiment are used.
The electrostatic capacitance C ₃ of the quadrupole electrode 11 in the front stage was 10 pF, and the electrostatic capacitance C ₂ of the quadrupole electrode 12 in the rear stage was around 30 pF. 1st stage quadrupole electrode
The electrostatic capacity C ₄ including the cable of the power supply for supplying the DC voltage applied to 1 was about 30 pF. Equation (5) and (6)
From the formula, it becomes formula (7), so

(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 high frequency voltage condition of the second stable region can be applied to the quadrupole electrode 11 in the front stage, and the quadrupole in the rear stage. The electrode 12 may be applied with the voltage condition of the first stable region.

The high frequency voltage and the DC voltage in the second and first 'stable regions can be supplied from a common voltage generating circuit. A direct current voltage is superimposed on the high frequency voltage and applied to the terminal abcd. FIG. 2B is an explanatory diagram of a DC voltage dividing circuit. According to the voltage divider circuit of FIG. 2 (B), U '= (R / (R + R')) * U-U '= (R / (R + R')) * (-U) DC voltage U, U ' The partial pressure ratio is a = 2.
8 and U _ab / U _cd = 2.8 / 0.03 with a = 0.03 in the 1'st stable region. Therefore, 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 in which the two quadrupole electrodes are combined is as follows.

A sample gas is introduced into the ion source, and sample ions 14 are made incident on the two sets of quadrupole electrodes 11 and 12. As described above, the DC voltage (U) and the high frequency voltage (V) are superposedly applied between the quadrupole electrodes, and the quadrupole electrode 11 in the preceding stage is applied.
A quadrupole electric field in the second stable region is formed therebetween, and a quadrupole electric field in the first stable region is formed between the quadrupole electrodes 12 in the subsequent stage. When the ions 14 generated in the ion source are incident along the central axes of the quadrupole electrodes 11 and 12 (in the z-axis direction), the electric fields generated in the quadrupole electrodes 11 and 12 while advancing in the z direction 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 x and y axes. It vibrates with a large amplitude and can pass through the quadrupole electrodes 11 and 12.

Ions having other M / Z increase in amplitude in the quadrupole electrode 11 or 12, and
Alternatively, it is caught by 12 or passes through the gap between the quadrupole electrodes 11 and 12 and does not reach the ion detection part. Ions roughly discriminated in the electric field between the quadrupole electrodes 11 in the second stable region in the former stage are mass analyzed with a resolution of M / ΔM ≧ 2M by the electric field between the quadrupole electrodes 12 in the first 'stable region in the latter 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.

5 to 7 show typical spectrum waveform data when the first, second, and 1'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 = 10V. 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 = 400V. FIG. 7 is a mass spectrum of the first stable region, which is an example in which the sample is air and the ion acceleration voltage V _i = 1000V.

When the quadrupole electric field in the second stable region and the quadrupole electric field in the 1'st 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 cause of the peak baseline rising on the low mass side is
This is because the spectrum based on the stable region has appeared. Therefore, when the quadrupole electric field in the second stable region and the quadrupole electric field in the 1'stabilized region are combined with each other for the same sample gas as in this embodiment, the first stable region is obtained as shown in FIG. 8B. It is possible to cut the rise of the baseline based on it, and obtain a clear mass spectrum.

[0029]

INDUSTRIAL APPLICABILITY The quadrupole mass spectrometer of the present invention can obtain a mass spectrum having a mass peak with unit resolution M / ΔM ≧ 2M for ions having an energy of more than 500 eV with a simple device configuration. Therefore, it is possible to easily perform mass analysis of high-energy ions, which has been difficult with a conventional quadrupole mass spectrometer, and it can be used for a plasma process monitor, discrimination of ions emitted from an ion gun, and the like.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a quadrupole electrode section of a quadrupole mass spectrometer according to an 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 the 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, (a)
Shows before improvement, and (b) shows after improvement.

[Explanation of symbols]

 1 ion source 2 sample piece (sample gas molecule) 3 electron beam 4,14 incident ion 5 quadrupole electrode section 6,6 voltage application terminal 7 ion detection section 8 specific ion 9 quadrupole electrode 10 recorder 11 quadrupole electrode in the previous stage 12 Secondary quadrupole electrode 13 Capacitor

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tetsuya Abe 801-1 Mukaiyama, Naka-machi, Naka-gun, Ibaraki Prefecture 801-1 Inside the Naka Institute, Hara Institute of Japan (72) Yoshio Murakami 801-1 Mukaiyama, Naka-machi, Naka-gun, Ibaraki Prefecture Nakahara Laboratory, Hara Institute of Japan

Claims (3)

[Claims] 1. A means for applying a DC voltage and a high-frequency voltage to the two sets of quadrupole electrodes in a superimposed manner, wherein two sets of quadrupole electrodes are arranged in a front stage and a rear stage of the route along the traveling path of sample ions. A quadrupole mass spectrometer equipped with the quadrupole electrode, wherein the DC voltage and the high-frequency voltage applied to the preceding quadrupole electrode of the two sets of quadrupole electrodes are the second condition of the Mathieu 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 quadrupole electrode in the subsequent stage are derived from the 1'stable region of the Mathieu diagram. Mass spectrometer. 2. The ratio M of the atomic mass unit M and the half-value width ΔM of the mass peak due to the atomic mass unit is M even when the acceleration energy of the ions incident on the electric field formed by the two sets of quadrupole electrodes is 500 eV or more. The quadrupole mass spectrometer according to claim 1, wherein / ΔM is 2M or more. 3. The quadrupole mass spectrometer according to claim 1, wherein the high frequency and the DC voltage in the second and first 'stable regions can be supplied from a common voltage generating circuit.