JPS61140048A - Secondary ion mass spectrometer - Google Patents

Abstract

PURPOSE:To simultaneously analyze positive and negative secondary ions by analyzing the negative secondary ions as they are, while analyzing the positive secondary ions after converting them to negative ions, and furthermore switching these operations at a high speed. CONSTITUTION:With a switch 12 being brought into contact with a contact 13 and with an outer cylinder 21 having positive voltage being applied thereto, negative secondary ions are removed and positive secondary ions are allowed to pass through. Hereby, the positive secondary ions are converted to negative ions 10 in an ionic charge converter 17 and analyzed by a mass spectrometer 5. While, with the switch 12 brought into contact with a contact 14 and with the outer cylinder 21 having negative voltage being applied thereto, the positive secondary ions are removed and negative secondary ions are allowed to pass through. Hereby, the negative secondary ions pass through the ionic charge converter 17 as they are and enter into the mass spectrometer 5 for analysis. Moreover, switched the switch 12 at a sufficiently higher speed than a mass scanning speed of the mass spectrometer 5, both the positive and negative secondary ions can simultaneously be analyzed.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to a secondary ion mass spectrometer, which has been improved so that it can simultaneously analyze positive and negative secondary ions emitted from a sample. be.

<Prior art> A secondary ion mass spectrometer collides accelerated ions (referred to as -order ions) with a sample to be analyzed, and guides the secondary ions emitted from the sample through a mass spectrometer to determine their mass. The purpose is to identify the substance and analyze the sample. An example of the conventional method is shown in FIG. As shown in the figure, an analysis sample 3 is installed in a vacuum container 7 equipped with a vacuum pump 8, and an ion source 1 is placed above the analysis sample 3.
Further, a mass spectrometer 5 is arranged obliquely above the analysis sample 3, and this mass spectrometer 5 is connected to an amplifier 61 installed outside the vacuum container 7.

Such a secondary ion mass spectrometer is used as follows.

First, after the vacuum container 7 is sufficiently evacuated by the vacuum pump 8, the analysis sample 3 is irradiated with the accelerated ion beam 2 generated by the ion source 1. As a result, atoms on the surface of the sample 3 are sputtered and scattered away from the surface. Some of the sputtered atoms are ionized.

This is the secondary ion 4. The secondary ions 48 are guided to the mass spectrometer 5, their mass is analyzed and extracted as an electrical signal. The electrical signal is amplified and recorded by an amplifier 6, and the composition of the sample 3 is analyzed.

<Problems to be solved by the invention> Among the secondary ions 4 emitted from the sample 3, there are two types, one with a positive charge and the other with a negative charge. Since the secondary ions have different content ratios, it is necessary to simultaneously examine both positive and negative secondary ions in order to perform accurate analysis of sample 3.

However, in order to measure positively charged secondary ions and negatively charged secondary ions with the conventional secondary ion mass spectrometer described above, it is necessary to reverse the potential relationship between the sample 3 and the mass spectrometer 5. It takes time to reverse. Therefore, with conventional secondary ion mass spectrometers, it is difficult to simultaneously measure positive and negative secondary ions.

Even if negative secondary ions were measured immediately after measuring positive secondary ions, the state of the sample would have changed.
This may introduce large errors into the analysis.

The present invention eliminates these drawbacks, by analyzing negatively charged secondary ions to their extent, and positively charged secondary ions by adding electrons.
It is an object of the present invention to provide a secondary ion mass spectrometer that can convert negatively charged ions to analysis and can switch between positive and negative secondary ion analysis at high speed.

Means for Solving the Problems> The configuration of the secondary ion mass spectrometer of the present invention that achieves the above object bombards a sample with accelerated partial ions to release secondary ions from the sample. , a secondary ion mass spectrometer in which the secondary ions are sequentially passed through an ion filter and an ion charge converter to identify and analyze the quality t-' of the mass spectrometer, the ion filter includes an inner cylinder and an outer cylinder. are arranged concentrically, and one of the inner and outer cylinders is grounded, and the other one is applied with a reversible positive or negative potential by a potential switching means, The ion charge converter has a circular thermoelectron generating filament arranged concentrically inside a cylindrical envelope, and a slightly negative voltage is applied to the filament to the cylindrical envelope. The cylindrical envelope is characterized by being filled with an electron cloud.

<Function> The potential switching means switches the voltage applied to either the inner cylinder or the outer cylinder of the ion filter to positive or negative, so that, for example, secondary ions that can pass through the ion filter are changed to positively charged ones. When the negative charged secondary ions are removed from this ion filter, the positively charged secondary ions enter the ion charge converter.

The inside of the cylindrical envelope of this ion charge converter is filled with a cloud of electrons with low kinetic energy.
The positive secondary ions that enter the envelope and enter the electron cloud capture and neutralize the electrons in the electron cloud, and further
It attaches several electrons, becomes a negative charge, flies out of the envelope, and is analyzed by a mass spectrometer.

Further, the voltage applied to either the inner cylinder or the outer cylinder of the ion filter is switched between positive and negative by means of a potential switching means, and, for example, secondary ions that can pass through this ion filter are selected as only those having a negative charge. However, when the positively charged secondary ions are removed by this ion filter, the negatively charged secondary ions enter the ion charge converter. The negatively charged secondary ions incident on the ion charge converter are electrically repelled by the electrons in the electron cloud that fills the cylindrical envelope, so that no electron capture or attachment occurs. The sample is taken out of the envelope and analyzed using a mass spectrometer.

Moreover, the potential switching means is repeatedly switched at high speed, for example, at a speed sufficiently faster than the mass sweep speed of a mass spectrometer. The analysis of secondary ions is done alternately at high speed, that is, they are analyzed at the same time as burial.

Embodiment Hereinafter, an embodiment of the present invention will be described in detail with reference to FIGS. 1 and 2. Note that the same parts as those in the prior art described above are given the same numbers and detailed explanation thereof will be omitted.

As shown in FIG. 2, in this embodiment, the secondary ions 4 emitted from the sample 3 are passed through an ion charge conversion device 91 and then passed through a mass spectrometer 51. In the device 9, the positive secondary ions are converted into negative ones, and the negative secondary ions pass through as they are.
In any case, the polarity of the secondary ions 10 when ejected from the ion charge conversion device 9 is positive 7. The ion charge conversion device 9 includes an ion filter 11 as shown in FIG.
The secondary ions pass through the ion filter 11 and the ion charge converter 17.

As shown in FIG. 1, the ion filter 11 has an inner tube 22 arranged concentrically inside an outer tube 21, and the inner tube f! ! ff22 is grounded, while the outer cylinder 21i is selectively connected to a DC power source 15 or 16 by a switch (potential switching means) 12. When the switch 12 is brought into contact with the contact 13I, a positive voltage is applied to the outer cylinder 21i by the DC power supply 15, and therefore, the positively charged ions in the secondary ions 4 have their orbits inward. While converging in the direction of #22 and passing through the ion filter, negatively charged ions diverge in the direction of the outer cylinder 21 and pass through the ion charge converter 17.
Only positively charged ions enter. Moreover, when the switch 12 is brought into contact with the contact point 14, the opposite phenomenon occurs,
Only negatively charged secondary ions pass through the ion charge converter 1.
It will be in 7.

In the ion charge converter 174, the cylindrical envelope 23
A circular thermoelectron generating filament 18 is arranged concentrically inside the cylindrical envelope 231ζ, and a filament ignition power source 19 is connected to the filament 18. 18
A voltage several volts lower than 1ζ is applied. A large amount of thermoelectrons are emitted from the thermoelectron generating filament 18 heated by the power source 19, and these thermoelectrons are emitted from the filament 18.
Since the potential of the filament 18 is maintained several volts higher than that of the envelope 23, an electron cloud is formed concentrated near the center of the filament 18. When a positively charged secondary ion rushes into such an electron cloud, this ion captures the electron in the middle, neutralizes it, attaches one more electron, and creates one negative electron ion.
On the other hand, when negatively charged secondary ions enter the electron cloud, an electrical repulsion force acts to capture and capture the electrons.
No adhesion occurs, and these secondary ions fly out of the envelope 23 as they are.

The secondary ion mass spectrometer having the above configuration is used as follows. First, the switch 12 is brought into contact with the contact 13I to apply a positive voltage to the outer cylinder 21, thereby excluding negative secondary ions and allowing positive secondary ions to pass through. 7. The electron cloud filled with ion abuse transformer F - the positive secondary ions rush in, this secondary ion captures and neutralizes one electron in the middle, and generates one more. attaches electrons to form negative ions 0
is converted to

Thereafter, the negative ions 10 ejected from the ion charge converter 17 (-) are analyzed using a mass spectrometer 51.

On the other hand, when the switch 12 is brought into contact with the contact 14, the outer cylinder 21
A negative voltage of 1 is applied to exclude positive secondary ions and allow negative secondary ions to pass.

Then, these negative secondary ions pass through the ion charge converter 17 and enter the mass spectrometer 5, where they are analyzed.

Furthermore, if the switch 128 is switched from the contact 13 to the contact 14 at high speed, for example, at a speed sufficiently faster than the mass sweep speed of the mass spectrometer 5, positively and negatively charged secondary ions can be analyzed almost simultaneously. becomes. In the above embodiment, the inner cylinder 22-'fi- of the ion filter 11 was grounded, and a positive or negative potential was applied to the outer cylinder 21 in a reversible manner. The inner cylinder 22I may be grounded, and a positive or negative potential may be reversibly applied to the inner cylinder 22I.

<Effects of the Invention> As explained above in detail, the secondary ion mass spectrometer of the present invention analyzes negative secondary ions as they are, and converts positive secondary ions into negatively charged ions. If the switching is carried out at high speed, simultaneous analysis of both positive and negative ions becomes possible.

[Brief explanation of the drawing]

1 and 2 relate to one embodiment of the present invention, and FIG. 18!
! 1 is a block diagram of an ion charge conversion device, FIG. 2 is a block diagram of a secondary ion mass spectrometer, and FIG. 3 is a block diagram of a conventional secondary ion mass spectrometer. In the drawing, l is an ion source, 2 is a partial ion beam, 3 is an analysis sample,
4 is a secondary ion, 5 is a mass spectrometer, 6 is an amplifier, 7 is a vacuum container, 8 is a vacuum pump, 9 is an ion charge conversion device, 1
1 is an ion filter, 12 is a switch, 13° 14 is a switch contact, 15.16 is a DC power supply, 17 is an ion charge converter, 18 is a filament for generating thermionic electrons, 19 is a power supply for filament ignition, 20 is a DC power supply , 21 is an outer cylinder, 22 is an inner cylinder, and 23 is a cylindrical envelope. Figure 1 Figure 2

Claims (1)

[Claims] Secondary ions are bombarded with accelerated primary ions to release secondary ions from the sample, and the secondary ions are passed through an ion filter and an ion charge converter in order to identify and analyze their mass using a mass spectrometer. In the ion mass spectrometer, the ion filter has an inner cylinder and an outer cylinder arranged concentrically, and one of the inner and outer cylinders is grounded, and the other is connected to a positive or negative potential by a potential switching means. The ion charge converter has a circular thermionic generating filament concentrically disposed inside a cylindrical envelope, and a slight difference between the filament and the cylindrical envelope. A secondary ion mass spectrometer characterized in that the cylindrical envelope is filled with an electron cloud by applying a negative voltage.