JPS5956400A - Neutral atomic beam generator - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an apparatus for generating a high-speed neutral atomic beam. This type of apparatus applies a neutral atomic beam to a sample and performs mass spectrometry, etc. on secondary ions emitted from the sample. It is used as an atomic beam source when the sample surface is to be removed.

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, the neutral atom density in the space where the neutral atom beam is generated is increased, that is, the gas pressure is increased. The chances of collision between the atoms in the neutral atom gas and the atoms in the gas increase, and the scattering of the neutral atom beam increases, resulting in an increase in reactions other than the above-mentioned charge exchange reactions between the neutral ions and the neutral atoms. Since this also increases the attenuation of the ion beam itself, it is not possible to strengthen the neutral atomic beam beyond the extent that it is possible.

The present invention aims to provide a neutral atom beam generator that can increase the efficiency of converting an ion beam into a neutral atom beam by special means and can obtain a strong neutral atom beam with a low input ion beam. It is.

The present invention provides an ion reflecting electrode in a neutral atomic beam generation space and causes ions to reciprocate within this space.
strong neutral atoms at low inputs by increasing the chances of collisions between ions and neutral atoms without increasing the chances of collisions between atoms of the generated neutral atom beam and atoms of the neutral atom gas It is characterized by obtaining a beam. The present invention will be explained in detail below with reference to Examples.

FIG. 1 shows an embodiment of the invention. 1 is the outer casing of the device, which is at ground potential, and is connected to an exhaust pump (not shown), and the inside is 1.
The vacuum is about 0' Torr. D4 is an ion reflecting electrode with a neutral atom beam exit aperture A4 in the center.
is open. Step 4 is to attach this ion-reflecting electrode to the outer casing.
It is an insulator that holds it inside. The left side of the ion reflecting electrode D4 is a neutral atom beam generating section, into which gas is introduced through a gas introduction tube gl. S is an ion source and an insulator Is
It is supported within the outer casing by a high voltage. 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,
Ions are generated by collisions between atoms of the introduced gas and electrons. Ion source S and ion reflecting electrode D4
In the space between DI, D2. D3 is an electrode forming an electrostatic lens system, DI and D3 are at ground potential, and an appropriate voltage is applied to D2 in the center, so that the lens system as a whole focuses ions. Since a high voltage is applied to the ion source S and the electrode D1 is at ground potential, ions generated in the ion source S are transferred to the electrode DI.
, and accelerated by the potential difference between the ion source S and the electrode D2, the ion source S and the electrode D2. It is made to enter the collision space surrounded by D3. The ions that have entered the collision space are converged while traveling to the right and head toward the neutral atom 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 an ion deceleration electric field is formed between the ion reflecting electrode D4 and the lens system electrode D3, and the ion is directed toward the aperture A4. The ions that have proceeded 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 motion of the ions, collisions with the ions occur. As mentioned above, these neutral atoms have the same kinetic energy and momentum as the original ions, so a neutral atomic beam is eventually formed that travels to the right and left.
The neutral atomic beam traveling to the right will be emitted to the right from the aperture A4.

Now let the reaction cross section of the resonance charge exchange reaction be σ, the neutral atom density of the gas in the collision space be n, and the intensity of the ion beam be Ni.
, If the intensity of the neutral atom beam is Nn, then the intensity of the neutral atom beam when an ion passes through the collision space once is Nn
1 is Nn1=n・σ・Ni1− ・・・・・・・・・・・・
...It is expressed as (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 make the intensity Nnl of the neutral atom beam a dog, it is necessary to increase n if Nil is constant, but if n is made too large, the high-energy neutral atoms generated will be scattered by collisions as described above. Furthermore, the ion beam is attenuated by reactions other than the resonance charge exchange reaction between ions and neutral atoms, and the intensity of the neutral atom beam is reduced. In the present invention, n is set to such an extent that reactions other than resonance charge exchange reactions can be ignored. Therefore, considering the ion's second collision space passage due to the ion's reciprocating motion, the neutral atom beam intensity Nn2 generated at that time is N n 2 = na (Ni1 - Nnl ) ---
−=・Given by (2). - N n within 0 on the right side of the equation
Subtracting 1 indicates that the ion beam intensity decreases by the amount that a portion of the ion beam changes to a neutral atomic beam. In the same manner, the neutral atomic beam becomes stronger when the ions pass through the collision space for the second time. In the figure, the intensity N of the neutral atom beam emitted from the neutral atom beam exit aperture A4 to the right is the above Nnl...NnK.
. . , only the odd-numbered ones are used, and the effective neutral atomic beam conversion efficiency 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 M1 is stretched over the aperture of the electrode D1 facing the ion source S.
A wire mesh λ Mt is also stretched over the aperture facing 4, and these wire meshes are connected to the ion source S.
and electrode D1 and between electrode D3. This is provided to prevent the ion acceleration and ion reflection electric fields between D4 from entering the collision space between D1 and D3. Also, a wire mesh MJ 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). There is no way to prevent this.

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 detailed description thereof will be omitted, and only points that are different from the embodiment shown in FIG. 1 will be described. In this embodiment, a collision chamber C is provided separately from the space surrounded by the lenses DI and 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 reflection electrode D4 and returned to the exit aperture of the ion source S.9 They are again accelerated to the right and sent to the electrode D4. and the ion 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, D'l, D2. D3
. . . Electrode constituting the lens system, D4 . . . Ion reflecting electrode, gl2g2 . . . Gas introduction tube. Agent Patent Attorney Hirosuke 9-

Claims (1)

[Claims] An electrode that accelerates the 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 that generates an ion neutralization reaction between both electrodes.