JPS62108428A - Extraction electrode system for ion source - Google Patents

Abstract

PURPOSE:To greatly reduce the number of times of minute discharge, by making the surface of a deceleration electrode convex in the face of a third electrode whose potential is kept between those of an acceleration electrode and the deceleration electrode, to suppress an electrical current loss resulting from the divergence of a beam. CONSTITUTION:The surface of a deceleration electrode 2' is made convex in the face of a third electrode 3 to make equipotential lines concave on the upside. As a result, an electric field is directed toward a center so that a force oriented toward the center acts to positive ions in a deceleration space between the electrodes 2', 3. For that reason, the divergence of an ion beam is diminished to decrease the quantity of the ion beam which collides against the electrode 3. This results in reducing the number of times of minute discharge.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to an extraction electrode shape for an ion source, and particularly to an extraction electrode system for an ion source having an extraction electrode shape suitable for low energy, high current beam extraction.

[Background of the invention]

Generally, a high-current ion beam is extracted from a high-density plasma using an acceleration-deceleration type extraction electrode system. FIG. 1 is a diagram illustrating the configuration of a conventional ion beef 1 extraction electrode system. A slit is made in the center of the electrode system, and a slit-shaped beam is drawn out in the direction perpendicular to the plane of the paper. FIG. 1 is a sectional view thereof. The ion source extraction electrode system consists of an accelerating electrode 1 for applying a potential to the plasma 5 in the plasma chamber 1' and determining the value of beam energy, a decelerating electrode 2 to which a negative voltage is applied, and a decelerating electrode 2 at an intermediate potential between the two electrodes. 3t
Consists of Ii poles. Among these, the main function of the deceleration electrode 2 is to prevent the ion beam 4 from being removed from the residual gas in the ion source device constituting the ion source or the inner wall of the ion beam transport system (grain separator, beam deflector, etc.). This is to prevent secondary electrons generated by collision with the ion source from flowing back toward the ion source acceleration electrode. If a backflow of secondary electrons occurs, the beam 4 will diverge significantly due to its own space charge.

Taking the ion source of an ion implantation device as an example, the voltage applied to the acceleration electrode 1 is typically 40 to 120 kV, the deceleration electrode voltage is approximately -2 to -10 kV, and the potential of the third electrode is grounded. Typical examples of electrode configurations in ion implantation equipment are given in Proceedings of the 5th International Conference, Ion Implantation Equipment and Technology (Proc, of 5th International Conference).
tional Conference on IonI
plantation equipment
d Technique) + p 16y1984 (North-Holland Po
I am familiar with bl, )).

Now, in the application of ion implantation to semiconductors, in recent years 40k
Ion implantation with low energy of eV or less and large current has been actively carried out. In response to this, various ideas have been made for high current ion sources for ion implantation devices to efficiently extract low energy beads 11. In general,
Efforts have been made to efficiently extract the beam by increasing the negative voltage of the deceleration electrode and increasing the extraction electric field between the acceleration electrode 1 and the deceleration electrode 2 (details in the above-mentioned known literature).
. However, with the electrode shape shown in Fig. 1, the deceleration electrode 2
The beam divergence between the electrode 3 and the third electrode 3 becomes significant, and the
The collision of the beam with the ion beam caused a spark, causing frequent discharges between the electrodes, making it impossible to obtain a stable ion beam. especially,
A microwave ion source that generates high-density plasma by microwave discharge in a magnetic field and extracts a large current ion beam from it (the structure of the microwave ion source is based on the Japanese Patent Publication No. 57-4056).
(for details), the number of interelectrode discharges (generally referred to as glitches) was as high as several dozen times per hour. Furthermore, if the acceleration electrode voltage is kept constant at 30kV and the deceleration electrode voltage is lowered from 12kV to 130kV, the acquired beam current increases, but the number of microdischarges mentioned above also increases (-) lit 11! It was done.

[Purpose of the invention]

The purpose of the present invention is to apply a high negative voltage to a deceleration electrode to extract a high current, low energy beam.

An object of the present invention is to provide an extraction electrode system for an ion source having an extraction electrode shape that suppresses ion beam divergence between electrodes and reduces the number of microdischarges.

[Summary of the invention]

Next, we will discuss the potential distribution when a high negative voltage is applied to the deceleration electrode in the conventional lead-out electrode system, and the beam divergence effect based thereon. Is Figure 2 the conventional drawer in Figure 1? T! FIG. 3 is a diagram illustrating a potential distribution shape obtained in a polar system. In the conventional f7 ((, system.

Since the deceleration '+t pole in the shape of a katakana character is used, the equipotential line formed between electrodes 2 and 3 has an upwardly convex shape as shown in the figure. Become. On the other hand, the direction of the electric field is directed outward from the center of the electrode, as indicated by the symbol E (E) in the figure. Therefore, the positively charged ion beam is subjected to a diverging effect by the outward electric field component Ex. Since this force becomes larger as the negative voltage becomes higher, the ions will spread more when a low energy beam is extracted.

For this reason, the ion beam hits the third electrode 3, and the secondary electrons emitted from the surface of the third electrode 3 serve as sparks, causing frequent micro-discharges between the electrodes 2 and 3. The shape of such equipotential lines is determined by the shape of the electrodes. Therefore, it can be expected that the divergence effect will be reduced if the electrode shape is changed so that the equipotential lines in FIG. 2 are convex downward.

FIG. 3 is a diagram illustrating the 'M model of the present invention. That is, in the present invention, the deceleration electrode 2' having a convex deceleration electrode surface facing the third electrode 3 is used, and the equipotential line shape is improved so as to be concave downward. In the present invention, since the direction of the electric field is toward the center, positive ions are subjected to a force acting in the direction of the center axis in the deceleration space between the electrodes 2' and 3. As a result, the number of beam 11 failures is reduced, the amount of ion beams hitting the electrode 3 is reduced, and the number of minute discharges can be reduced.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to FIG. In this example, a microwave ion source that generates high-density plasma by microwave discharge in a magnetic field and extracts an ion beam from the plasma was used as the ion source. This ion source injects microwaves generated by a magnetron 6 into a plasma chamber 5 using waveguides 7a and 7b. 10.11 is an insulator,
The coil 8 is for applying a magnetic field to the plasma chamber 5. As the acceleration electrode, a stainless steel electrode with a slit of 2 sides wide and 40rrln in length was used as the deceleration electrode 2'.
A stainless steel electrode with a width of 8 m and a length of 4.5 nn was used as the third electrode, and a stainless steel electrode with a width of 10 nn, a length of 45 m, and a thickness of 1.0 m was used as the third electrode.

The potential of the third electrode was set to the ground potential in this example.

BFA gas was introduced as a discharge gas, and an ion beam 4 containing boron (B) was extracted, which was mass-separated by a mass separator to select and obtain a B beam. In the conventional electrode configuration shown in FIG. 1, when the B beam was extracted at 30 V, for example, a current value of 3 mA after mass separation was obtained. However, the number of microdischarges reached several dozen times per hour.

On the other hand, with the electrode configuration shown in FIG. 4, even when a voltage of 30 kV was applied to the acceleration electrode and -30 kV to the deceleration electrode, a B current of 4 to 5 mA was stably obtained.

The number of microdischarges at this time was reduced to 1 to 2 times per hour.

FIG. 5 is a diagram illustrating another embodiment based on the present invention. In this example, in order to improve the equipotential line shape, the third
The electrode 3' has a concave shape relative to the deceleration electrode. In this case, since the equipotential line penetrates deeper into the 3' electrode, beam divergence in the deceleration space was strongly suppressed. The number of microdischarges also decreased to almost 0 times/hour. In Figure 5,
As the convex part of the deceleration electrode, place the chevron-shaped part 2# on the electrode 2'.
It has a split structure that can be attached to the electrode, reducing the ease of electrode processing. In order to efficiently introduce the equipotential line into the third electric potential t@3', the slit width dimensions of each electrode in the figure are selected so that d≦W holds. Also, according to experiments, one effect of the present invention is that the voltage of the deceleration electrode is 12k.
Effective above V. Especially when the deceleration electric field becomes high - 10k
When applying a voltage of V or more, there was a significant effect. Furthermore, even if the chevron-shaped portion 2' in FIG. 5 was removed, the number of minute discharges was significantly improved compared to the conventional example shown in FIG.

Next, in another embodiment shown in FIG. 4, from the viewpoint of increasing the efficiency of magnetic field generation by the coil, an accelerating electrode made of magnetic iron was used to construct an extraction electrode system. In this case, the amount of magnetic flux leaking into the space between the electrodes 2 and 3 was reduced, and the number of microdischarges was also reduced.

This is because changes in the beam trajectory due to the magnetic field in the space are reduced.

In this example, the third electrode was set to the ground potential, but it is clear that the effects of the present invention can be obtained even if the potential of this electrode is an intermediate value between the acceleration electrode potential and the deceleration electrode potential. It is.

〔Effect of the invention〕

According to the present invention, when extracting a low-energy, high-current beam from an ion source, current loss due to beam divergence can be suppressed and the number of minute discharges can be drastically reduced, which has a remarkable effect on stable beam extraction.

In particular, the present invention is suitable for an ion source for an ion implanter that requires long-term beam stability, and its effects in practical use are extremely large.

[Brief explanation of drawings]

FIG. 1 is an electrode system cross-sectional view explaining the shape and configuration of a conventional extraction electrode system for an ion source, FIG. 2 is a diagram explaining the potential distribution in the conventional extraction electrode system, and FIG. FIG. 4 is a diagram for explaining the shape of the electrode system, FIG. 4 is a diagram for explaining one embodiment based on the present invention, and FIG. 5 is a diagram for explaining another extraction electrode shape based on the present invention. 1... Acceleration electrode, 1'... Plasma chamber, 2, 2'
... Deceleration electrode, 2'... Chevron-shaped part attached to the deceleration electrode, 3, 3'... Third electrode, 4... Ion beam, 5... Plasma, 6... Magnetron ,7a,
7b...Waveguide, 8...Coil, 9...Gas introduction pipe, 10゜th /II - 2nd eye 3rd port I:x Fig. 4

Claims (1)

[Claims] 1. In an ion source that extracts an ion beam from plasma using an extraction electrode system, an acceleration electrode for applying a positive potential to the plasma, a deceleration electrode to which a negative high voltage is applied, and An ion source drawer in which the deceleration electrode surface facing the third electrode has a convex shape in the direction of the third electrode, of the extraction electrode consisting of a third electrode maintained at an intermediate potential between the acceleration electrode and the deceleration electrode. Electrode system. 2. Among the extraction electrodes described in claim 1, the third
An extraction electrode system for an ion source in which the third electrode surface facing the deceleration electrode has a concave shape. 3. The ion source uses microwave discharge in a magnetic field,
Claim 1, which is a microwave ion source that extracts an ion beam from high-density plasma, and whose accelerating electrode is made of a magnetic material (for example, iron, nickel, cobalt, ferrite, etc.) Extraction electrode system for ion source.