JPH07122230A - Secondary ion mass-spectrometer - Google Patents

Abstract

PURPOSE:To perform the separation of mass-spectrum of secondary ions with the mass numbers close to one another, by leading out a DC voltage and a high frequency AC voltage from the second stable region which gives a stable solution of Mathieu equation, and thereby enhancing the resolution. CONSTITUTION:The insides of an analyzer tube 2 and a quadripolar mass separator 4 are evacuated by a vacuum pump 8, wherein the separator 4 consists of a quadripolar electrode having the second stable region as the electric field conditions. A high speed atomic beam or ion beam 9 is emitted by a beam source 1 and bombards a specimen. Secondary ions 10 are emitted from this specimen bombarded, and they are discriminated by the mass separator 4, and only ion having a specific mass is selected and put into a secondary electron multiplier tube 5. There the ion is converted into an electron, emitted upon passing an amplifier 6, and recorded by a recorder 7. In this manner, secondary ions 10 are separated by masses and subjected to analysis.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a secondary ion mass spectrometer, and particularly to a sample substance by irradiating a sample with a primary beam composed of a high-speed particle beam and separating and identifying secondary ions emitted from the sample. It relates to a secondary ion mass spectrometer for measuring the mass of a.

[0002]

2. Description of the Related Art It has long been known that a mass spectrometer utilizing electric field conditions of a quadrupole electrode is used for mass spectrometry of ions (for example, Fujinaga et al., "Mass filter", Vacuum 11 vol. 4). No. (1968), pp. 1-8). Also, the results of studies on the analysis of the stability of the ion orbit under the electric field condition of the quadrupole electrode have been announced (Hiroki et al., "Ion Orbit Analysis in Quadrupole Mass Spectrometer (I)", Vacuum 3).
Volume 5, No. 12 (1992), pp. 8-16).

Details of a quadrupole mass separator for discriminating secondary ions are shown in FIG. Reference numeral 11 in the figure is a quadrupole electrode,
Reference numeral 12 is a power source for applying DC and high-frequency AC voltage, and 13 is a secondary ion having a specific mass that passes through the quadrupole electric field. Reference numeral 5 is a secondary electron multiplier, and the amount of incident ions is converted into a current and detected. Quadrupole electrode 11 of mass separation unit
Is an assembly of four metal columns whose outer circumferences are convex hyperbolas (or arcs), which are accurately assembled in parallel with each other using insulating spacers so that the convex hyperbolas (or arcs) face each other. It has a structure where a so-called quadrupole electric field can be created in the space surrounded by four metal columns.

The basis of ion discrimination of the quadrupole electrode 11 is 4
The voltage applied to the quadrupole electrode 11 of the book is to cause the ions to move according to Matthew's equation of motion.
By connecting as shown in Fig. 2 and creating an electric field in which the alternating current and direct current are superposed in the space surrounded by the quadrupole electrodes, the ions incident along the central axis have the strength of the alternating current and direct current electric field, Frequency, ion mass-to-charge ratio m / e, and other conditions are met, the quadrupole electric field is not diverged, and vibrations occur in the x and y directions while proceeding in the z direction to reach the ion detector. . Except for ions satisfying the specific condition, excessive vibration is generated in the process of vibrating in the x and y directions, and the ions collide with the quadrupole electrode and are removed.

The movement of ions in a quadrupole field is described by the Mathieu equation:

[Equation 1]

Here, a and q are as follows.

[Equation 2] However, e: electron charge, U: DC voltage, V: AC voltage, m: ion mass, r ₀ : electric field radius, ω: angular frequency The solution of the Mathieu equation is that the ions have a constant amplitude for an infinite time. It is divided into a stable solution that follows a stabilized orbit that does not exceed it and an unstable solution whose amplitude increases infinitely with time. Whether the solution of the Mathieu equation is stable depends on a
The relationship of q can be determined by the Mathieu diagram shown on the (a, q) plane. The Matthew diagram is shown in FIG.
The stable region is indicated by reference numeral I, the second stable region is indicated by reference numeral II, and the third stable region is indicated by reference numeral III. An enlarged view of the first stable region is shown in FIG. 3 (B), and an enlarged view of the second stable region is shown in FIG. 3 (C).

The conditions under which an ion passes through a quadrupole electric field are
Based on the stable region of the Matthew diagram. For an ion having a certain mass, when the r ₀ , ω, U, and V values are determined, one point is set on the (a, q) plane. The relation of a / 2q = U / V is given from the equation (2), but this equation is a straight line that passes through the origin of the (a, q) plane and the slope is determined by the ratio of U and V, regardless of the mass number. Set to. When this U / V ratio is determined, all ions with different masses will line up on this straight line. This is called mass scan line 14. Of the ions lined up on the mass scan line 14, only ions of mass lined up on the line in the stable region can pass through the quadrupole field. Therefore, by changing the gradient (U / V) of the mass scan line 14 to reduce the portion (Δm) overlapping with the stable region of the mass scan line, only the ions 13 of a certain specific mass pass through the quadrupole electric field. Can be made.

[0008]

Heretofore, electric field conditions based on the first stable region have been used exclusively because the AC and DC voltages do not have to be very high. However, as shown in FIG. 3 (B), since the shape of the first stable region is extremely wide downward, when the mass scan line becomes 14 ′, Δm becomes Δm ′, and the detection width Δm becomes sharp. It is easy to grow. Therefore, the DC voltage U
If the AC voltage V fluctuates even a little, Δm fluctuates greatly. In order to obtain stable resolution, it is necessary to stabilize the power source of DC voltage or AC voltage, but there is a limit to that. Therefore, the conventional quadrupole mass spectrometer using the first stable region as an electric field condition has a problem that the resolution is low and secondary ion mass spectra having close mass numbers cannot be separated.

The present invention has been made in view of the problems of the prior art, and provides a secondary ion mass spectrometer having high resolution and capable of separating mass spectra of secondary ions having close mass numbers. The purpose is to do.

A secondary ion mass spectrometer of the present invention irradiates a sample with a high-speed particle beam generation source provided in a vacuum chamber and a primary beam composed of the high-speed particle beam generated from the generation source. Means, a means for separating and identifying secondary ions emitted from the sample by a quadrupole electrode, and a means for applying a DC voltage and a high-frequency AC voltage for separating and identifying the secondary ions to the quadrupole electrode. The DC voltage and the high-frequency AC voltage provide a stable solution of the Mathieu equation.
It is characterized in that it is derived from the stable region.

[0010]

The DC voltage (U) and the high frequency AC voltage (V) applied to the quadrupole electrode are selected from the second stable region that gives a stable solution of the Mathieu equation. By comparison, it is possible to dramatically increase the resolution. Therefore, it becomes possible to separate the mass spectra of secondary ions having close mass numbers.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 is an illustration of a secondary ion mass spectrometer. In the figure, reference numeral 1 is a beam source for emitting a fast atom beam or an ion beam, 2 is an analysis tube, 3 is a sample, 4 is a quadrupole mass separator, 5 is a secondary electron multiplier, 6 is an amplifier, and 7 is an amplifier.
Is a recorder, 8 is a vacuum pump, 9 is a fast atom beam or ion beam, and 10 is a secondary ion. Code 12
DC voltage (U) and high frequency voltage (V) to the quadrupole electrode
Is a power source for applying.

The operation of this device is as follows. The inside of the analysis tube 2 and the inside of the quadrupole mass separator 4 are sufficiently exhausted by the vacuum pump 8. A high-speed atomic beam or ion beam 9 is emitted from the beam source 1 to impact the sample. Secondary ions 10 are emitted from the sample bombarded by the beam 9, and are discriminated by the quadrupole mass separator 4 composed of a quadrupole electrode having a second stable region as an electric field condition, and only ions of a specific mass are emitted. It is selected and enters the secondary electron multiplier 5. Here, the ions are converted into electrons, output through the amplifier 6 and recorded in the recorder 7. In this way, the secondary ions 10 are separated by mass and analyzed.

The quadrupole electrode 11 is composed of a ceramic member such as silicon nitride whose electrode surface is metallized. Therefore, since the dimensional accuracy is high and the coefficient of thermal expansion is small, the dimensional accuracy can be kept high even if the temperature rises.

Further, the power source 12 compares the DC voltage U and the high frequency voltage V derived from the conventional first stable region,
The voltages U and V derived from the second stable region, which is several times higher, can be supplied. Further, the voltages of the first stable region and the second stable region can be switched and supplied. Therefore, the first stable region and the second stable region can be switched and used according to the measurement target and purpose.

In the present embodiment, the DC voltage U and the AC voltage V, which are the electric field conditions in the second stable region, are applied from the power source 12 to the electric field conditions constituted by the four quadrupole electrodes. As a result, ions move in the z direction while vibrating in the x and y directions in the quadrupole electric field, and only ions having a specific mass can be detected and recorded in the recorder 7 as a mass spectrum.

As shown in FIG. 3C, since the shape of the second stable region is vertically long and narrow and its width is very narrow, the value of the detection width Δm hardly changes regardless of the value of U / V. . Therefore, it is easy to keep the detection width Δm constant even if the DC voltage U or the AC voltage V changes. When the second stable region is used as the electric field condition, Δm can be stably made extremely small compared with the case where the first stable region is used, and the resolution can be easily and dramatically increased. .

FIG. 4 shows D ₂ ⁺ and He ⁺ when the first stable region is applied and when the second stable region is applied to the quadrupole electrode.
3 shows a mass spectrum for a sample having a mass number of about 4, which is mixed. When the first stable region is applied, a broad mass spectrum peak appears as shown in FIG.
The peaks of ₂ ⁺ and He ⁺ are overlapped and cannot be separated. On the other hand, when the second stable region is applied, as shown in FIG.
As shown in (B), the peak width of the mass spectrum becomes very small, the mass spectrum can be separated at the second digit after the decimal point, and D ₂ ⁺ and He ⁺ can be distinguished.

Similar high mass resolutions are applicable for other mass ranges. For example, if the second mass is around 28
Using high mass resolution based on the stability region, N
₂ ⁺ (mass number 28.0062), Co ⁺ (mass number 27.9)
949), C ₂ H ₄ ⁺ (mass number 28.0312), Si
^It is possible to separate and identify ions with a close mass, such as ⁺ (mass number 27.9769). In this way, it is possible to easily analyze a sample that generates secondary ions having close mass numbers and obtain output data containing a lot of information. That is, the DC voltage U and the high-frequency voltage V in the second stable region are about several times larger than those in the first stable region, but the resolution (detection width) Δm can be reduced to about 0.01 AMU.

[0020]

The secondary ion mass spectrometer according to the present invention comprises:
Secondary ions are emitted from the sample using a fast atom beam or ion beam, and the secondary ions can be discriminated by the electric field condition of the second stable region of the Mathieu equation of the quadrupole electrode so that they can be detected and analyzed. is there. Therefore, a mass spectrum with high resolution can be obtained. Therefore, it is possible to easily analyze a sample having a complicated composition having a mass number close to that in the related art, and it is possible to obtain data including a lot of information. In particular, by using an electrically neutral fast atom beam, secondary ions can be efficiently emitted without causing the problem of charge accumulation in the insulator sample.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing a device configuration of a secondary ion mass spectrometer according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram of a quadrupole mass separator.

FIG. 3 is an explanatory diagram of the Matthew diagram, showing (A) a quadrant, (B) a partially enlarged view of a first stable region, and (C) a second diagram.
The elements on larger scale of a stable area.

FIG. 4 is an explanatory diagram of a mass spectrum of an analysis result,
(A) shows the case where the first stable region is applied, and (B) shows the second
The case where the stable region is applied is shown.

[Explanation of symbols]

 1 Beam Source 2 Analytical Tube 3 Sample 4 Quadrupole Mass Separator 5 Secondary Electron Multiplier Tube 6 Amplifier 7 Recorder 8 High Vacuum Exhaust Device 9 Fast Atom Beam or Ion Beam 10 Secondary Ion 11 Quadrupole Electrode 12 DC and AC voltage application power supply 13 Specific mass ion 14 Mass scan line 15 First stable region 16 Second stable region

Claims (5)

[Claims] 1. A high-speed particle beam generation source provided in a vacuum chamber, means for irradiating a sample with a primary beam composed of a high-speed particle beam generated from the generation source, and quadruple secondary ions emitted from the sample. And a means for applying a DC voltage and a high-frequency AC voltage for separating and identifying the secondary ions to the quadrupole electrode, wherein the DC voltage and the high-frequency AC voltage are stable solutions of the Mathieu equation. A secondary ion mass spectrometer characterized in that it is derived from a second stable region that gives 2. The secondary ion mass spectrometer according to claim 1, wherein the fast particle beam is a fast atom beam. 3. The secondary ion mass spectrometer according to claim 1, wherein the fast particle beam is an ion beam. 4. The secondary ion mass spectrometer according to claim 1, wherein the quadrupole electrode is composed of a ceramic member whose electrode surface is metallized. 5. The apparatus further comprises means for switching the DC voltage and the high frequency AC voltage applied to the quadrupole electrode to a first stable region that gives a stable solution of the Mathieu equation. The secondary ion mass spectrometer according to claim 1.