JPS6331920B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an apparatus for generating a high-velocity neutral atomic beam. This type of apparatus is used as an atomic beam source when applying a neutral atomic beam to a sample and performing mass spectrometry on secondary ions emitted from the sample, or when removing a sample surface.

Neutral atoms themselves cannot be accelerated directly, but by generating ions of the same atom separately, accelerating this ion, and utilizing the resonance charge exchange reaction between the accelerated ion and the same atom. Fast neutral atoms can be obtained. In a resonance charge exchange reaction, only charges are exchanged between an ion and a neutral atom of the same type, and the ion changes into a neutral atom without losing much of its momentum or kinetic energy. It is a reaction that is converted. When an ion beam accelerated with a voltage of several KV passes through a gas of similar atoms, the charge exchange reaction described above occurs, and a neutral atomic beam with an energy of several KeV is formed as an extension of the ion beam. However, in order to increase the conversion efficiency of the ion beam into a neutral atom beam, increasing the neutral atom density in the space where the neutral atom beam is generated, that is, increasing the gas pressure, The chances of collision between the atoms in the ions and neutral atoms in the gas increase, resulting in greater scattering of the neutral atom beam, and an increase in reactions other than the above-mentioned charge exchange reactions between ions and neutral atoms. Since the attenuation of the ion beam itself also increases, the neutral atomic beam cannot be strengthened beyond a certain level.

The present invention aims to provide a neutral atom beam generator that can improve the efficiency of converting ion beams into neutral atom beams through special measures and can obtain strong neutral atom beams with low input ion beams. It is.

The present invention provides an ion reflecting electrode in the neutral atomic beam generation space and causes the ions to reciprocate within this space, thereby increasing the chances of collision between the generated neutral atomic beam atoms and the neutral atomic gas atoms. It is characterized by obtaining a strong neutral atomic beam with low input power by increasing the chance of collision between ions and neutral atoms without causing any interference. The present invention will be explained in detail below with reference to Examples.

FIG. 1 shows an embodiment of the invention. Reference numeral 1 denotes the outer casing of the device, which is at ground potential and is connected to an exhaust pump (not shown), creating a vacuum of about 10 ^-5 Torr inside.
D4 is an ion reflecting electrode, and a neutral atom beam exit aperture A4 is opened in the center. I4 is an insulator that holds this ion-reflecting electrode within the outer casing 1. To the left of the ion reflecting electrode D4 is a neutral atom beam generating section, into which gas is introduced through the gas introduction tube g1. S is an ion source supported within the outer casing by an insulator Is, and a high voltage is applied to it. Gas is also introduced into the ion source S through the gas introduction pipe g2, and the pressure inside the ion source S is higher than that outside. An electron beam is formed within the ion source S, and ions are generated by collisions between atoms of the introduced gas and electrons. D in the space between the ion source S and the ion reflecting electrode D4
1, D2, and D3 are electrodes that form an electrostatic lens system, and D1 and D3 are at ground potential.
An appropriate voltage is applied to lens 2, and the lens system as a whole focuses the ions.
A high voltage is applied to the ion source S, and the electrode D
Since 1 is the ground potential, ions generated in the ion source S are extracted by the electrode D1, accelerated by the potential difference between the ion source S and the electrode D1, and are surrounded by the electrodes D1, D2, and D3. is made to enter the collision space. The ions entering the collision space are converged while traveling to the right, and head toward the neutral atomic beam exit aperture A4. A high voltage that is the same potential as the ion source S or slightly higher than that is applied to the ion reflecting electrode D4, and the electrode D3 of the lens system
An ion deceleration electric field is formed between the aperture A4 and the aperture A4, and ions traveling toward the aperture A4 are reflected by this electric field. For this reason, the ions that have entered the collision space repeatedly move back and forth within the same space. During this reciprocating movement of the ions, the resonance charge exchange reaction described above occurs when the ions collide with the neutral atoms of the gas in the collision space, producing high-energy neutral atoms. As mentioned above, this neutral atom has the same kinetic energy and momentum as the original ion, so a neutral atom beam that travels to the right and left is formed, and a neutral atom beam that travels to the right is formed. will be emitted to the right from aperture A4.

Now let σ be the reaction cross section of the resonance charge exchange reaction, n be the neutral atom density of the gas in the collision space, Ni be the intensity of the ion beam, and Nn be the intensity of the neutral atom beam. The intensity Nn1 of the neutral atomic beam when it passes through is expressed as Nn1=n・σ・Ni1 (1). Here, the subscript number means the first pass. Conventionally, the ion reflecting electrode D4 was not provided and the ions passed through the collision space only once, so the intensity of the resulting neutral atom beam was given by the above equation (1). In this case, in order to increase the intensity Nn1 of the neutral atom beam, it is necessary to increase n if Ni1 is constant, but if n is made too large, as mentioned above, the high-energy neutral atoms generated will be affected by collisions. As a result, the ion beam is scattered and the attenuation of the ion beam due to reactions other than the resonance charge exchange reaction between ions and neutral atoms increases, and the intensity of the neutral atom beam decreases. In the present invention, n is set to such an extent that reactions other than resonance charge exchange reactions can be ignored. Therefore, if we consider the ion's second collision through space during its reciprocating motion, the neutral atomic beam intensity Nn2 generated at that time is given by Nn2 = nσ (Ni1 - Nn1) (2). The reason why Nn1 is subtracted in the right-hand side () of the above equation represents that the ion beam intensity decreases by the amount that a portion of the ion beam changes to a neutral atomic beam. Similarly, the neutral atomic beam intensity NnK at the K-th collision space passage of ions is NnK=nσ(Ni1− _K−1 〓 ^j=1 Nnj) (3). In the figure, neutral atomic beam exit aperture A4
The intensity N of the neutral atomic beam emitted to the right from is the sum of only the odd-numbered beams among the above Nn1...NnK... N= _∞ 〓 ^j=1 Nn2j−1=Ni1/2, which is effective neutrality The conversion efficiency of the atomic beam is 50%.

In FIG. 1, a wire mesh M1 is stretched over the aperture of the electrode D1 facing the ion source S, and a wire mesh M2 is stretched over the aperture of the electrode D3 facing the electrode D4. The wire mesh is provided to shield ion acceleration and ion reflection electric fields between the ion source S and the electrode D1 and between the electrodes D3 and D4 from entering the collision space between D1 and D3, respectively. Also, a wire mesh M3 is stretched on the right side of the ion-reflecting electrode D4, but this is because a high voltage is applied to the ion-reflecting electrode, so the electric field due to this voltage extends to the space inside the device on the right side (not shown). This is to prevent

FIG. 2 shows another embodiment of the invention. In this figure as well, parts corresponding to those in FIG. 1 are designated by the same reference numerals, and a description of each part will be omitted, and only points that are different from the embodiment of FIG. 1 will be described. In this embodiment, a collision chamber C is provided separately from the space surrounded by the lenses D1 to D3 of the lens system, and gas is introduced into the collision chamber C. The ion beam extracted from the ion source S and accelerated between S and the electrode D1 is transferred to the electrode D1.
The ions are focused into the collision chamber C by a lens system consisting of lenses 1 to D3, and the ions that have passed through the collision chamber C are reflected by the reflective electrode D4 and return to the exit aperture of the ion source S, where they are accelerated to the right again and the ions collide with the electrode D4. It goes back and forth between source S. This configuration has the advantage that the exhaust loss of the gas introduced into the collision chamber C is small, and a sufficient neutral atomic beam can be obtained with the introduction of a very small amount of gas.

The device of the present invention has the above-mentioned configuration, and since the ion beam reciprocates within the collision space, almost all of the ion beam takes part in the resonance charge exchange reaction and is converted into a neutral atomic beam with high efficiency, while the generated neutral atomic beam Because it passes through the collision space only once at most, there is almost no scattering due to collisions with other atoms, making it possible to obtain a sufficiently strong neutral atomic beam even with a low-power ion source. .

[Brief explanation of drawings]

1 and 2 are longitudinal sectional side views of different embodiments of the present invention. 1...Outer casing, S...Ion source, D1, D2, D
3... Electrode constituting the lens system, D4... Ion reflecting electrode, g1, g2... Gas introduction tube.

Claims (1)

[Claims] 1 An electrode that accelerates ions generated in the ion source and an electrode that reflects the accelerated ions are provided, and the ions are caused to reciprocate between the two electrodes, and a neutral atomic gas is introduced between the two electrodes. A neutral atom beam generator was introduced to cause an ion neutralization reaction between both electrodes.