JPH0720068A - Surface analyzing method using ion beam - Google Patents

Abstract

PURPOSE:To perform highly accurate analysis by using <3>He as a gaseous starting material for generating ions. CONSTITUTION:A shield box 1 is composed of a ceiling, side faces, and floor and covers a rectangular high-voltage terminal 2 supported on the floor of the box 1 by a plurality of insulating supports 11. The floor of the box 1 and the lower surface of the terminal 2 is separated from each other by an insulating distance at which the floor can withstand the high voltage applied across the terminal. A high-voltage power source 12 is provided between the floor of the box 1 and the terminal 2. An ion source 5 is incorporated in the terminal 2 and connected to the entrance of a particle accelerator 3 provided between the terminal 2 and box 1 through a beam pipeline 9. By using such a constitution, plasma is generated by introducing a gaseous starting material <3>He to the ion source 5 and a positive voltage is applied across the ion source 5. Generated ions are accelerated by means of the accelerator 3 and converged through convergent lenses 15a and 15b. After purifying a separated <3>He<2+> ion beam by means of an electromagnet 16 for mass separation, the ion beam is introduced to an analyzing chamber 19 and made incident an a sample 30 on a material holder 20.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to an ion beam surface analysis method.

[0002]

2. Description of the Related Art FIG. 1 is a schematic plan view of a commonly used ion beam surface analyzer.

In FIG. 1, a shielding box 1 is composed of a ceiling, side surfaces, and a floor, and covers a substantially rectangular high-voltage terminal 2 supported on the floor by a plurality of insulating columns 11. The floor surface of the shielding box 1 and the lower surface of the high voltage terminal 2 are separated by an insulation distance having a sufficient withstand voltage against the high voltage applied to the high voltage terminal 2. A high voltage power supply 12 is installed between the floor surface of the shielding box 1 and the lower surface of the high voltage terminal 2.

An ion source 5 is provided inside the high voltage terminal 2.
Is connected via a beam pipe 9 to the inlet (high voltage side) of the accelerating pipe 3 arranged between the high voltage terminal 2 and the shielding box 1. The accelerating tube 3 is provided with a plurality of metal rings F, and a resistor R is provided between them.
With high voltage terminal 2 and shield box 1
And an equipotential surface is formed on each surface of the metal ring F to maintain a high voltage. The exit (ground potential side) of the accelerating tube 3 is connected to the beam pipe 14a outside the shielding box 1, which is further connected with converging lenses 15a and 15b for converging the ion beam, and then the beam pipe 14b. The focusing lenses 15a and 15b share the focusing in the x-axis direction and the y-axis direction, respectively, with the z-axis being the traveling direction of the ion beam. Further, the beam pipe 14b is connected to the mass separation electromagnet 16, which is further connected to the analysis beam pipe 17 and then to the analysis chamber 19.

Inside the analysis beam pipe 17, a pair of diaphragms 18a and 18b each having an aperture are provided at a predetermined distance.

A sample holder 20 is provided at the center of the analysis chamber 19, and the sample 30 is used as the analysis chamber 1.
It is attached to the sample holder 20 from the atmosphere side by the sample transport mechanism 21 provided in the No. 9.

A particle detector 23 for detecting particles scattered from the sample surface is provided in the analysis chamber 19, and a signal cable 24 taken out from the particle detector 23 is passed through a vacuum introduction terminal on the side wall of the vacuum chamber 19. It is connected to a data processing system (not shown) on the atmosphere side.

Further, a vacuum pump 22 for exhausting the inside of the system including the analysis chamber 19 is connected to the side wall of the chamber 19.

A generally used ion beam analyzer is constructed as described above, and its operation will be described below.

The system from the ion source 5 to the analysis chamber 19 is evacuated by a vacuum pump 22 and maintained in a vacuum state. Although not shown, a vacuum pump may be separately provided on the upstream side so as to exhaust gas. In this case, a vacuum valve is provided on the way to hermetically seal the analysis chamber 19 side and the upstream side. It may be possible to shut off. A material gas for ion generation is introduced into the ion source 5 from a cylinder (not shown) through a tube. Similarly, when the output of a power supply for plasma generation (not shown) is applied to the ion source 5, the material gas introduced into the ion source 5 becomes plasma. Further, when a positive voltage is applied to the ion source 5, ions are extracted from the plasma and enter the accelerating tube 3 through the beam pipe 9. The ions that have entered the accelerating tube 3 are accelerated by the high voltage power supply 12 with energy that is the product of the voltage applied to the high voltage terminal 2 and the valence of the ions, and then are converged by the converging lenses 15a and 15b. The mass separation electromagnet 16 is reached. The ions are deflected in the vacuum pipe in the mass separation electromagnet 16 according to the magnetic field formed by the electromagnet 16, the valence of the ions, and the Lorentz force generated by the ion velocity due to the acceleration voltage. Impurities are removed by a separation slit (not shown) attached on the downstream side of, and only desired ions pass through this and enter the analysis beam pipe 17. After the ion beam entering the analysis beam pipe 17 is restricted to a divergence angle geometrically determined by the distance between the pair of diaphragms 18a and 18b provided in the analysis beam pipe 17 and the aperture width of those apertures, , Reaches the analysis chamber 19 and enters the sample 30 attached to the sample holder 20. As described above, the inside of the analysis chamber 19 is evacuated by the vacuum pump 22 and maintained at a vacuum of a pressure sufficient for surface analysis. Part of ions 31 (hereinafter, referred to as probe ions) incident on the sample 30 are scattered on the surface of the sample 30 and part 3 of scattered particles (probe ions and particles neutralized by the probe ions) 3
2 is incident on the particle detector 23. As a result, the signal generated by the particle detector 23 is taken out to the atmosphere side via the signal cable 24, inputted to a data processing system (not shown), and displayed as various spectra such as an energy spectrum.

Next, regarding the surface analysis by the above-mentioned general ion beam surface analyzer, as an example, Rutherford backscattering (RBS; Ratherford Back)
The analysis using Scattering will be explained.

A part of the probe ions 31 incident on the sample 30 mounted on the sample holder 20 is part of the sample 3.
It is elastically collided with atoms on the surface of 0 (and atoms near the surface of the sample) and scattered in all directions, but a part of them is scattered backward (with the flight direction of the probe ions being the front). Almost all of the scattered particles are elastically scattered,
Momentum and kinetic energy are preserved before and after a collision. Therefore, if the mass and valence of the probe ions, the accelerating voltage, and the mass of the sample 30 are known, the energy of the flying particles backscattered at a certain angle is based on the assumption that the momentum and the kinetic energy are conserved. It can be calculated and obtained. That is, the ratio of the energy of scattered particles to the energy of incident particles is called a K factor, and is uniquely determined by the type of probe ion 31, the type of sample, and the position (scattering angle) of the particle detector 23. If the acceleration energy and the mass of the flying particles are known, the material of the sample 30 can be identified by measuring the energy of the particles scattered in a certain angular range.

FIG. 2 shows a typical energy spectrum of Rutherford backscattering <W. K. Chu, J. W. Mayer, M.M. A. Nicolette, "Backscatter Spectroscopy," Academic Press, New York, 19
Quoted from 1978 >>. In FIG. 2, the horizontal axis represents energy, and the vertical axis represents the number of particles backscattered and counted by the particle detector 23. The sample is Au (gold), Ag (silver), Cu (copper) S
It is implanted into an i (silicon) substrate, the probe ions are ⁴ He ⁺ , the acceleration energy is 2.8 MeV, and the position (scattering angle) of the particle detector 23 is 170 °. In addition, A
The ordinates of u, Ag, and Cu are quintupled.

A for this probe ion ⁴ He ⁺
The K factors of u, Ag, and Cu are about 0.92,
0.86 and 0.78, and when the incident energies are multiplied by the respective K factors, the energies of He particles scattered on the surfaces of Au, Ag and Cu and incident on the particle detector 23 are 2.58 MeV and 2. The energy positions of the respective peaks detected in the energy spectrum of FIG. 2 are almost the same as the energy values calculated by the above calculation. By the way, the K factor of Si is 0.57, and the peak energy in the calculation is 1.6 Me.
V, which is also in agreement with the energy spectrum of FIG. Note that the energy spectrum by Rutherford backscattering appears as a peak at the maximum energy position determined by the mass of the sample element, or a steep step. The latter is formed by the fact that when the sample is in the substrate or the sample is thick, the energy lost particles in the substrate or in the sample are also scattered, resulting in a continuous spectrum into the low energy region.

Atoms having a smaller mass number than the sample to be analyzed are used as probe ions, and H or He is generally used. Although ⁴ He ⁺ is also used in the example of FIG. 2 described above, higher analysis accuracy may be required depending on the purpose of analysis and sample. In that case, the acceleration energy is doubled by ^changing the probe ion ⁴ He ⁺ to ⁴ He ²⁺ , that is, by setting the valence of the ion to 2, so that the acceleration energy is doubled. The scale of the spectrum should be doubled, the spectrum width of the element to be analyzed should be widened, and the element in the sample should be easily identified.

However, actually, even if ⁴ He ²⁺ is used, the analysis accuracy is not improved. That is, in FIG. 3, ⁴ He ²⁺ is used for the probe ion of Rutherford backscattering,
It is an energy spectrum about sample Au (gold) obtained as an accelerating voltage of 200 kV. Although the surface peak of Au appears at the energy of 400 keV, the spectrum is distorted and difficult to discriminate, and the analysis accuracy is not improved despite the use of ⁴ He ²⁺ .

The result contrary to this expectation is probe ion ⁴
It is understood that it is due to H ₂ ⁺ coexisting with He ²⁺ . That is, H ₂ gas may remain in the ion source 5, and when ⁴ He gas is ionized to ⁴ He ²⁺ ,
_{The 2} gases are also ionized to H ₂ ⁺ . This H ₂ ⁺ and ⁴ He
^Since there is almost no difference in [ion mass / ion valence] from ^2+, it cannot be separated by the mass separation electromagnet 16 having a normal separation ability, and when ⁴ He ²⁺ enters the sample. H ₂ ⁺
Is also injected at the same time. The incident H ₂ ⁺ is dissociated on the sample surface and appears in the backscattering spectrum as two H atoms each having an energy half that of the acceleration energy.

In the normal ion source 5, since the H ₂ ⁺ ion generation efficiency is higher than that of the ⁴ He ²⁺ ion generation, even if the amount of H ₂ gas remaining in the ion source 5 is very small. , H ₂ coexisting in ⁴ the He ²⁺ beam after mass separation ⁺
Can be of similar proportions, and in some cases many times higher.

When H ₂ ⁺ coexists in Rutherford backscattering using ⁴ He ²⁺ as a probe ion, the spectra of the backscattering of H atoms overlap and the analysis becomes complicated. This causes an increase in the shape of the spectrum and causes a distortion in the shape of the spectrum, which lowers the accuracy of analysis, making it difficult to identify the sample.

Therefore, in order to improve the analysis accuracy, ⁴ He
⁺ And H ₂ ⁺ and is separating is desired, and this is,
The mass separation electromagnet 16 is large, the radius of curvature of the trajectory of the ion beam is large, and the bending angle is large. Further, the opening width of the separation slit on the downstream side of the mass separation electromagnet 16 is narrow, and the mass separation electromagnet 16 is also used. This is possible by increasing the distance from the electromagnet 16. However, such a method inevitably increases the size of the apparatus and increases the manufacturing cost.

[0021]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and an object thereof is to provide an ion beam surface analysis method with high analysis accuracy without increasing the size of the apparatus. And

[0022]

The above object is to analyze the surface of a sample by injecting an ion beam accelerated from an ion source into the sample in a vacuum container and analyzing the energy spectrum of particles scattered from the sample. The ion beam surface analysis method according to claim 1, wherein ³ He is introduced as a material gas into the ion source.

The above object is also achieved by the ion beam surface analysis method according to claim 1, which utilizes Rutherford backscattering.

[0024]

By introducing ³ He as a material gas into the ion source in the ion beam surface analysis, it is possible to perform surface analysis with high analysis accuracy without being affected by the H ₂ gas remaining in the ion source.

[0025]

EXAMPLES The present invention will be specifically described below with reference to examples. In this example, in order to compare and contrast with the result (FIG. 3) of the ion beam surface analysis by Rutherford backscattering in which the probe ion was ⁴ He ²⁺ as shown in the conventional example, the general example shown in FIG. An ion beam surface analyzer is used, but ³ He is used as a material gas for the ion source 5.
Was introduced, and otherwise the analysis was performed under the same conditions and procedures as in the conventional example of FIG. That is, the material gas ³ He is introduced into the ion source 5, and the output of the power source for plasma generation is fed into the ion source 5 to generate plasma.
A positive voltage is applied to extract ions, the ions are accelerated by the accelerating tube 3, then converged by the converging lenses 15a and 15b, and the ³ He ²⁺ ion beam separated by the mass separation electromagnet 16 is separated by the separation slit. After being purified, it was introduced into the analysis chamber 19 and was made incident on the sample 30 on the sample holder 20. The sample is also Au (gold), and the acceleration voltage is 200 kV.

FIG. 4 is an energy spectrum by Rutherford backscattering using ³ He gas for ion generation in this embodiment, and as described above, the conventional example ( ⁴
The only gas used is different from He gas).

In the case of ⁴ the He ²⁺ ions obtained from ⁴ He (Figure 3), ³ cases of ³ the He ²⁺ ions obtained from He (Figure 4), Au both at the energy 400keV
Although the surface peak of ³ He ^{2+ in} this example is
The appearance is clearer when is the probe ion. The clear difference, whereas spectrum coexist H ₂ ⁺ is in the case of ⁴ the He ²⁺ is distorted superimposed, ³ the He
^It is considered that H ₂ ⁺ does not coexist in the ₂ ⁺ ion beam.

To confirm this, another system was used to measure the mass spectral data using ³ He gas. An ion beam obtained by using the material gas ³ He was accelerated and converged to be guided to a 90 ° mass separation electromagnet, and a current value obtained by a Faraday cup installed behind the mass separation electromagnet was measured. FIG. 5 shows the resulting mass spectrum, but as expected, ³ He ²⁺ and H ₂ ⁺ are clearly separated because of different [ion mass / ion valence]. A thick arrow is attached to ³ He ²⁺ . H ₂ ⁺ → H ⁺ indicates a change in ions. The mass spectrum shown in FIG. 5 was obtained as follows. As the ion source 5 in FIG. 1, a duopigatron type is used, which is a cathode electrode, a nozzle type intermediate electrode, which are arranged in a line as is known,
It is composed of an anode electrode and a reflection electrode, the intermediate electrode and the reflection electrode have the same potential, and a DC arc voltage is applied between the cathode electrode and the anode electrode. The material gas ³ He introduced by the arc discharge generated by this Becomes plasma. This applied voltage is Varc = 119V in FIG. 5, and the current flowing between the cathode electrode and the anode electrode is Iarc = 5A.

An ion extraction electrode is provided on the downstream side of the reflection electrode, and when a voltage is applied to the ion extraction electrode, ions are generated from the plasma through the expansion space and the emission hole formed in the reflection electrode. The voltage applied to the ion extraction electrode at this time is V _EXT = 2 in FIG.
It is 0 kV.

Further, the mass spelltor of FIG. 5 continuously changes the magnitude of the current to the coil wound around the 90 ° mass separation electromagnet, and continuously changes the strength of the generated magnetic field. As a result, ions of different [mass / charge = (M / e)] are sequentially guided to the Faraday cup, and the magnetic field strength is taken as the horizontal axis, and the beam current (μA ) Is the vertical axis.

That is, FIG. 5 confirms that even if H ₂ gas remains in the ion source 5, H ₂ ⁺ does not coexist in the ion beam of ³ He ²⁺ incident on the sample 30. Therefore, it is proved that the ion beam surface analysis method of the present invention using ³ He as a material gas has high analysis accuracy.

Although the Rutherford backscattering analysis has been taken up as an example for explaining the method of the present invention, the method of the present invention is also effective for other ion beam surface analysis methods such as ion scattering analysis.

[0033]

As described above, when performing ion beam surface analysis, ³ H is used as the material gas for ion generation.
By using e, it is possible to perform analysis with high analysis accuracy.

[Brief description of drawings]

FIG. 1 is a schematic plan view of a general ion beam surface analyzer.

FIG. 2 is a typical energy spectrum of Rutherford backscattering by a conventional method.

[3] introduced ⁴ He as the material gas into the ion source, ⁴
2 is an energy spectrum of Rutherford backscattering by a conventional method in which He ²⁺ ions are incident on gold.

[Figure 4] introduced ³ He as the material gas to the ion source, ³
2 is an energy spectrum of Rutherford backscattering by the method of the present invention in which He ²⁺ ions are incident on gold.

FIG. 5 is a mass spectrum of an ion beam obtained by introducing ³ He as a material gas into an ion source according to a current value measured by a Faraday cup after mass separation.

[Explanation of symbols]

 3 Accelerator Tube 5 Ion Source 15a Converging Lens 15b Converging Lens 16 Electromagnet for Mass Separation 19 Analysis Chamber 23 Particle Detector 30 Sample 31 Probe Ion 32 Scattering Particle

Claims (2)

[Claims] 1. An ion beam surface analysis method in which an ion beam accelerated from an ion source is incident on a sample in a vacuum container, and the surface of the sample is analyzed by the energy spectrum of particles scattered from the sample. An ion beam surface analysis method, characterized in that ³ He is introduced into the source as a material gas. 2. The ion beam surface analysis method according to claim 1, which utilizes Rutherford backscattering.