JP3024233B2 - Ion beam extraction electrode system - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ion beam extraction electrode system device for alleviating space charge and suppressing ion beam divergence in an ion beam extraction and transport system.

[0002]

2. Description of the Related Art An electrode system for extracting an ion beam from a positive ion source will be described with reference to the drawings. FIG. 13 shows a basic configuration of a three-electrode system. Is extracted as an ion beam by a plasma electrode 1, an extraction electrode 2, and a ground electrode 3 arranged at the outlet of the ion source, accelerated, and guided to an ion beam transport unit. A bias potential is applied to the plasma electrode 1 and the extraction electrode 2 by a power source 4 and a power source 5 of the illustrated polarity, and the plasma electrode potential Vp, the extraction electrode potential Ve, the ground electrode potential Vg, and the potential between the respective electrodes are simply shown. It becomes like FIG. The vertical axis in the figure indicates the potential, and the horizontal axis indicates the position. The extraction electrode 2 is biased to a negative potential with respect to the ground electrode 3, thereby preventing back-flow of electrons generated downstream of the ground electrode 3 to the ion source side.

FIG. 15 shows a basic configuration diagram of a four-electrode system. Compared with a three-electrode system, the plasma electrodes 1 and
An acceleration electrode 4 is disposed between the extraction electrode 2 and the ground electrode 3 in addition to the extraction electrode 2 and the ground electrode 3. The sum potential Vp of the power sources 5 and 6 is applied to the plasma electrode 1, the positive potential Ve lower than the plasma electrode 1 by the potential of the power source 5 is applied to the extraction electrode 2, and the acceleration electrode 4 is shown in FIG. A negative bias potential is applied by the polar power supply 7 to extract and accelerate the ion beam. Each electrode and the potential between the electrodes are as shown in FIG.

Although the divergence of the ion beam obtained from the ion source is suppressed by the action of the electrostatic lens in the above-mentioned extraction electrode system, the ion beam downstream of the ground electrode 3 is provided.
In the beam transport section, the ion beam tends to diverge due to the space charge effect of the ion beam itself. This tendency increases as the current density of the ion beam increases and as the degree of vacuum in the transport section increases.

In order to reduce the space charge effect, there is a method of intentionally flowing a beam neutralizing gas into the ion beam transport section, and inserting a neutralizer into the transport section. Has been adopted.

However, the above gas inflow method inevitably deteriorates the degree of vacuum in the ion beam path, and a high voltage is applied to a small distance (gap) in the extraction portion and the acceleration portion of the ion beam. It induces a discharge or breakdown between the gaps, which also creates new impurity ions. Also, in the method of inserting a neutralizer described above, in the case of providing a thermal filament for electron emission in the transport portion, generation of sputtered particles due to collision of a beam with the thermal filament, evaporation due to heating of the filament, etc. The ion beam profile is deteriorated due to the formation of impurities based on nitrogen and the ratio of neutralization becomes larger in the vicinity of the filament. Similarly, the introduction of the gas causes problems of impurity formation and deterioration of the ion beam profile.

[0007]

SUMMARY OF THE INVENTION The present invention relates to an ion beam extraction electrode system capable of suppressing generation of impurities and deformation of an ion beam profile, relaxing space charges, and suppressing ion beam divergence. The purpose is to provide.

[0008]

According to the present invention, there is provided an ion beam extraction electrode system, comprising: a ground electrode made of a thermionic emission material; a heating control means for the ground electrode; and a bias potential variably applied to the ground electrode. Means.

[0009]

With the heating of the ground electrode, the electrode itself, which is indispensable in the extraction electrode system, emits electrons for neutralizing the ion beam due to the potential of the ion beam. Since it is neutralized, the beam is neutralized without newly forming impurities and without deforming the ion beam profile, thereby alleviating the space charge and diverging the ion beam. Suppress. By controlling the ground electrode temperature and the bias potential by the heating control means and the bias potential variable applying means, the amount of electron emission from the ground electrode can be adjusted to an appropriate value.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to FIGS. FIG. 1 shows a configuration diagram of an ion beam extraction electrode system in a three-electrode system. An ion beam is provided from a plasma generation chamber of an ion source at a plasma electrode 1, an extraction electrode 2, and an extraction electrode 2 disposed at an outlet of the ion source. And it is pulled out by the ground electrode 3 configured to have an electron emission function,
Accelerated and transported. A bias potential is applied to the plasma electrode 1 and the extraction electrode 2 by the power sources 4 and 5. The ground electrode 3 is made of, for example, a material similar to a normal thermoelectron emission filament material, tungsten, tantalum, molybdenum, tungsten containing thorium, lanthanum hexafluoride, or the like, so that it can be heated by the flow of a heating current to emit thermoelectrons. Although the shape and the heating mode of the electrode 3 will be described later, the figure shows, for example, a slit type electrode cross section, and a bias potential is applied to the electrode 3 by a variable voltage source 6 which is a bias potential variable applying means. You. FIG. 2 shows the plasma electrode potential Vp, the extraction electrode potential Ve, the ground electrode potential Vg, and the potential between the electrodes. The vertical axis in the figure indicates the potential, and the horizontal axis indicates the position. By adjusting the variable voltage source 6, the potential of the ground electrode 3 can be controlled to any polarity and magnitude with respect to the ground potential.

FIGS. 3 and 4 show a configuration diagram and a potential diagram of a four-electrode system in which an accelerating electrode is added to the above-mentioned three-electrode system.
A bias potential Vp is applied to the plasma electrode 1 by the power sources 5 and 6, a positive bias potential Ve is applied to the extraction electrode 2 by the power source 6, and the acceleration electrode 4 is biased to a negative potential Va by the power source 7. The ground electrode 3 is configured to have an electron emission function in the same manner as in the above-described three-electrode system, and as shown in FIG. The polarity and magnitude of the bias potential Vg can be controlled.

FIGS. 5 to 12 show embodiments of the shape of the ground electrode and the form of Joule heating in FIGS. 1 and 3. FIG. FIG. 5 to FIG. 7 show the above-mentioned ground electrode 3 in which the opening for passing the ion beam is hole-shaped.
FIG. 5 shows the case of a single hole, and a hole-like ion beam.
The end of the ground electrode 3 in which the system passage opening 9 is formed is connected to a heating power source 11 serving as heating control means via an electrode holding / terminal portion 10.
The electrodes 3 are heated by Joule heating by applying a current to the electrodes 3 to emit thermoelectrons. By controlling the heating power supply 11, the heating current of the ground electrode 3 can be adjusted, and the heating temperature and electron emission amount of the electrode can be adjusted.
FIG. 6 shows a case in which the ground electrode 3 has a multi-hole type single electrode structure having a plurality of hole-shaped openings 9, and the electrode 3 is connected to a heating power supply 11 via an electrode holding / terminal portion 10. You. FIG. 7 is also a multi-hole type, but the ground electrode 3 is divided into three electrodes 3a, 3b and 3c.
Each divided electrode is electrically connected in series via an electrode holding / terminal portion 10 and connected to a heating power supply 11.

FIGS. 8 to 11 show the case where the ion beam passage opening 9 is of a slit type, and FIG.
Are formed so as to form a slit and a single slit between the two rod-shaped electrodes 3d and 3e. The two rod-shaped electrodes 3d and 3e are connected in parallel at the electrode holding / terminal section 10 and connected to the heating power supply 11. FIG. 9 shows a case of a single slit type as well, but two rod-shaped electrodes 3 d and 3 e are connected in series by an electrode holding / terminal section 10 and supplied with power from a heating power supply 11. FIG. 10 shows a case of a multi-slit type having two slits, and three rod-shaped electrodes 3d, 3e,
3f is connected in parallel via an electrode holding / terminal unit 10 and is supplied with power from a heating power supply 11. FIG. 11 relates to a unit having two slits, and three bar-shaped electrodes 3d to 3f are connected in series. The case where the power is connected and the power is supplied from the heating power supply 11 is shown.

FIG. 12 shows a structure in which the ground electrode 3 is configured as a mesh electrode. Both ends of the mesh 31 are connected to a heating power supply 11 via an electrode holding / terminal section 10. Although the above embodiment has been described with respect to the case where the ground electrode is heated by Joule, a laser source may be used to heat the vicinity of the ion beam opening of the ground electrode with a laser. According to such laser heating, for a heating required portion having a complicated shape,
Appropriate heating can be performed without heating other portions.

In each of the above-described heating modes, the specifications of the heating source include the material of the electrode, the length of the electrode, the same cross-sectional area, the current-carrying connection method,
It is determined according to the heating temperature and the like.

In the above embodiment, when the ground electrode 3 is heated, thermoelectrons are emitted and extracted from the ground electrode 3 by the potential of the ion beam. The maximum value of the extracted thermoelectron quantity can be obtained from the Richardson-Dashman equation in a simple electrode system model. In the region of the thermoelectron amount that does not reach this maximum value, the emission amount is limited by the space charge limiting current value. With the emission and extraction of thermoelectrons from the ground electrode 3, the ion beam is
Neutralization is performed from the process of passing through the beam opening 9. If the beam collides with the ground electrode 3 when passing through the ion beam, sputter particles as impurities are generated. This is not due to the ground electrode 3 having a thermoelectron emission function, but to thermionic electrons. This occurs even in the ground electrode which is indispensable to the beam extraction electrode system having no emission function, and the amount of impurity evaporation accompanying the increase in the temperature of the ground electrode due to the provision of the thermionic emission function is small. Therefore, the ion beam can be neutralized without newly forming impurities. The neutralization of the ion beam is performed from the process of passing through the ground electrode.
No deformation or deterioration of the memory profile.

As the neutralization of the ion beam progresses, the potential of the beam decreases. Even in such a state, the ground electrode 3, that is, the opening 9 of the ground electrode 3 is very close to the beam, so that electrons are emitted (the space charge limiting current is inversely proportional to the square of the distance). In the state where the neutralization has progressed, a beam plasma is formed on the beam. The potential in this state is thermionic, ion beam
Caused by the collision of
It is determined by the generation of plasma composed of secondary electrons and low-velocity ions and the extinction on the wall. Therefore, the ground electrode 3
Is biased to an appropriate potential, the amount of electron emission can be adjusted. However, when electrons with a large energy are emitted, the potential of the beam plasma rises and tends to diverge. Therefore, it is desirable that the potential of the ground electrode 3 is not so different from the potential of the beam potential. , The amount of emitted electrons and the energy of the emitted electrons are
The temperature of the ground electrode 3 and the same bias potential Vg are
1. Since it can be properly adjusted by controlling the variable voltage sources 6 and 8, the space charge of the ion beam can be reduced and the beam can be adjusted.
It is possible to appropriately suppress the divergence of the system.

Although the above embodiment has been described with reference to a three- and four-electrode system, the present invention relates to a two-electrode system, that is, a system in which an ion beam extraction electrode system is constituted by a plasma electrode and a ground electrode. The present invention may be applied or applied to the ion beam extraction electrode system of the negative ion source by changing the polarity of the bias potential to each electrode.

[0019]

As described above, according to the present invention, electrons for beam neutralization are emitted and extracted from the ground electrode heated by the potential of the ion beam. Since the beam is formed from the time when the beam passes through the opening of the ground electrode, the beam can be neutralized without forming impurities, and the beam can be formed without deforming the beam profile.
The entire system can be uniformly neutralized. Since the amount of electrons emitted from the ground electrode and the energy of the electrons can be adjusted by controlling the heating temperature of the ground electrode and the bias potential, the relaxation of the space charge of the ion beam and the suppression of the divergence of the beam are appropriately performed. be able to.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an embodiment of the present invention for a three-electrode system.

FIG. 2 is a potential diagram of a three-electrode system.

FIG. 3 is a configuration diagram of an embodiment of the present invention for a four-electrode system.

FIG. 4 is a potential diagram of a four-electrode system.

FIG. 5 is a diagram showing the shape and heating connection of a single-hole ground electrode.

FIG. 6 is a diagram showing a shape and a heating connection diagram of a multi-hole ground electrode.

FIG. 7 is another shape and heating connection diagram of the multi-hole ground electrode.

FIG. 8 is a diagram showing a shape and a heating connection diagram of a single slit ground electrode.

FIG. 9 is another shape and heating connection diagram of the single slit ground electrode.

FIG. 10 is a diagram showing a shape and a heating connection diagram of a multi-slit ground electrode.

FIG. 11 is another shape and heating connection diagram of the multi-slit ground electrode.

FIG. 12 is a diagram showing a shape and a heating connection diagram of a mesh ground electrode.

FIG. 13 is a configuration diagram of a conventional three-electrode system.

FIG. 14 is a potential diagram of a conventional three-electrode system.

FIG. 15 is a configuration diagram of a conventional four-electrode system.

FIG. 16 is a potential diagram of a conventional four-electrode system.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Plasma electrode 2 Extraction electrode 3 Ground electrode having a thermoelectron emission function 4 Power supply 5 Power supply 6 Variable voltage source

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Shuichi Fujiwara 47, Umezu Takaunecho, Ukyo-ku, Kyoto-shi, Kyoto Inside (72) Inventor Takatoshi Yamashita 47, Umezu-Takaunecho, Ukyo-ku, Kyoto, Kyoto Nissin Electric Inside (72) Inventor Koji Matsunaga 47, Umezu Takaune-cho, Ukyo-ku, Kyoto-shi, Nissin Electric Co., Ltd. (56) References JP-A-2-54850 (JP, A) JP-A-2-239559 (JP) , A) Japanese Patent Application Laid-Open No. 2-162638 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01J 27/00-27/26 H01J 37/08

Claims (1)

(57) [Claims] 1. An electrode system for extracting an ion beam from an ion source, comprising: a ground electrode made of a thermionic emission material;
An ion beam extraction electrode system comprising: a heating control unit for the ground electrode; and a bias potential variable application unit for the ground electrode.