JPH05299046A - Ion source beam drawing-out method and device thereof - Google Patents

Abstract

(57) [Abstract] [Purpose] To optimize the beam extraction of an ion source that generates metal ions by vacuum arc discharge. An arc discharge is generated between an anode 2 and a cathode 3, which are provided in the vacuum enclosure 1 so as to be insulated from each other, and an arc discharge is generated, and a part of the cathode is generated. The metal plasma formed by vaporizing and ionizing the metal is introduced into the plasma chamber from the discharge region, and the grid opening 15
Extract the ion beam from. Suppressor grid 13
If the ratio of the current of the extractor grid 12 to the current of the above is less than or equal to the threshold value K determined for each element, the arc current indicating the maximum extractor current is calculated as the integrating circuit 19 and the arithmetic circuit 2.
Ion implantation is performed by controlling so as to obtain 0. [Effect] In addition to stable ion implantation, it is not necessary for the operator to have variations in implantation conditions and fine adjustment of the arc current during implantation, and the implantation efficiency can be increased to shorten the processing time.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ion source beam extraction method and apparatus for generating metal ions by vacuum arc discharge.

[0002]

Japanese Patent Laid-Open No. 63-276858 discloses an ion source for producing a large amount of metal ions by directly ionizing the metal by vacuum arc discharge. FIG. 6 shows a schematic view of a conventional example of a beam extraction device for such an ion source.

In FIG. 6, a vacuum enclosure 1 is provided with an anode 2 and a metal cathode 3 which are installed insulated from each other. The cathode 3 is in contact with a trigger electrode 6 connected to a trigger ring 5 via an insulating material 4.
A trigger discharge is generated between the trigger ring 5 and the cathode 3 by momentarily applying a high voltage between the cathode 3 and the trigger electrode 6 connected to the trigger power supply 7. Also,
Between the anode 2 and the cathode 3, an arc power source 8 is previously provided.
, A voltage is applied, and a vacuum arc discharge is generated triggered by the trigger discharge. Due to the occurrence of the vacuum arc discharge, a point called a cathode spot in which energy is concentrated appears at the tip of the cathode 3, and the substance in this portion is evaporated and ionized to generate metal plasma. The generated metal plasma passes through the anode opening 9 and the discharge region 1
From 0 to the plasma chamber 11.

The plasma chamber 11 is provided with three grids each having an opening of an extractor grid 12, a suppressor grid 13, and a ground grid 14. Normally, the extractor grid 12 and the anode 2 are held at a high voltage of several kV to several hundred kV, while the suppressor grid 13 is applied with a negative voltage. Also, the ground grid 14 is grounded,
The metal ions guided to the plasma chamber 11 are electrostatically accelerated between the grids, pass through the grid openings 15, and are processed in the processing chamber 1.
6 is pulled out. Here, the suppressor grid 13 is
It is provided to prevent free electrons existing in the processing chamber 16 from flowing back to the plasma chamber 11. Ammeters 17 and 18 are connected to the extractor grid 12 and the suppressor grid 13, respectively.

The conventional device thus constructed is
A vacuum arc discharge is generated between the cathode 3 and the anode 2 to evaporate and ionize the cathode material and accelerate between the grids to extract an ion beam. A variable parameter necessary for optimal beam extraction with a certain ion species and accelerating voltage using this ion source is the arc current that governs the plasma density. Conventionally, beam extraction is performed with a single shot, and at this time, the extractor current Iext flowing through the extractor grid 12
Suppressor current Isup flowing through the suppressor grid 13
Is measured and a large Iext is obtained within a range where Isup does not increase.
To change the arc current Iarc,
After trial and error, the proper arc current Iarc was determined.

[0006]

In the conventional method, when the ion species and the accelerating voltage are changed, there is no quantitative means for determining the optimum arc current. Since ion implantation was also performed, the ion implantation efficiency was poor and the processing time was sometimes long. Also, even if you decide the arc current once,
As the operation progressed, the cathode was consumed, the arc generation conditions changed, and it was often necessary to manually adjust the arc current.

In view of the above problems of the prior art, the main object of the present invention is to extract the beam of the ion source which can prevent the operator from varying the operating conditions and can eliminate the need for fine adjustment of the arc current during ion implantation. A method and an apparatus therefor are provided.

[0008]

SUMMARY OF THE INVENTION According to the present invention, the above object is to generate an arc discharge between an anode and a cathode in a vacuum enclosure to vaporize and ionize a portion of the cathode. In a beam extraction method of an ion source that forms a metal plasma, guides the metal plasma from a discharge region to a plasma chamber, and extracts an ion beam, a threshold value K (suppressor current / extractor current) determined for each element and not more than a maximum value. A method for extracting a beam from an ion source, characterized in that the arc current is controlled so as to obtain an extractor current of the ion source, or an anode that is insulated from each other in the discharge region of the vacuum enclosure. Beam extraction of an ion source that has an extractor grid, a suppressor grid, and a ground grid in the plasma chamber. In a combination, the measured extractor current value and suppressor current value and the threshold value determined for each element based on the K (suppressor current / extractor current)
This is achieved by providing a beam extraction device for an ion source, which is characterized in that an integration circuit and an arithmetic circuit for calculating and controlling an arc current that provides the following maximum extractor current are provided.

[0009]

According to the present invention, the vacuum enclosure has an anode and a cathode which are installed separately from each other. The cathode generates an arc discharge between itself and the anode triggered by a discharge generated between the cathode and a trigger electrode connected to a power source, thereby vaporizing and ionizing a part of the cathode to form a metal plasma. The generated plasma passes through the anode opening, is guided from the discharge region to the plasma chamber, is accelerated by the acceleration grid, and the ion beam is extracted. At this time, there are appropriate plasma densities with respect to the acceleration voltage, the grid spacing, the diameter of the grid openings, and the ion species, and the arc current is changed in order to adjust them. In order to obtain the optimum arc current, an ammeter is installed to monitor the current of each grid that performs ion beam extraction, and an integrating circuit is incorporated in this to determine the currents Iext and Isup for each shot. Further, an arithmetic circuit is connected to the integrating circuit, the arc current Iarc is gradually changed to extract the beam,
The arc current Iarc that maximizes Iext can be calculated within the range of Isup / Iext ≦ K (K is determined by the element), and a feedback circuit for controlling the operation is provided.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of the present invention will now be described in detail with reference to the accompanying drawings.

FIG. 1 is a schematic view showing a beam extraction device of an ion source to which the present invention is applied. The same parts as those of the conventional example are designated by the same reference numerals and detailed description thereof will be omitted. An integrating circuit 19 is connected to the ammeters 17 and 18 connected to the extractor grid 12 and the suppressor grid 13, respectively, and the integrating circuit 19 measures the current Iext.Isup for each shot. Integrating circuit 19
An arithmetic circuit 20 is further connected to the.

When the ion beam is extracted while the arc current Iarc is increased, the plasma density in the plasma chamber 11 also increases. At this time, the plasma boundary surface of the grid opening 15 from which the ion beam is extracted is shown in FIG.
As shown in (c), it changes from concave to convex. Figure 2 (a)
2C shows the case where the arc current Iarc is small, FIG. 2B shows the case where the arc current Iarc is proper, and FIG. 2C shows the case where the arc current Iarc is large.

As shown by the arrows in FIG. 2, since the ion beam is extracted almost perpendicularly to the plasma boundary surface, if the plasma boundary surface is extremely uneven, the ion beam will pass through the grid opening 15. Instead, they collide with the suppressor grid 13 and the suppressor current Isup increases. It is considered that as the number of extracted ion beams increases, the number of ion beams colliding with the suppressor grid 13 also increases. Therefore, the current Iext of the extractor grid 12 and the current I of the suppressor grid 13 which represent the ion beam current.
Proper operation is possible by measuring sup and selecting the arc current Iarc so that this ratio Isup / Iext becomes a constant value K or less.

An example of measurement data is shown in FIG. This figure shows changes in the suppressor current Isup when the arc current Iarc at 70 kV is changed. When the arc current Iarc is 140 A or more, the suppressor current Isup is shown.
Is increasing rapidly. Here, no increase in suppressor current Isup is observed when the arc current Iarc is too small.

On the other hand, when ion implantation is carried out for the purpose of surface modification of metals and ceramics, a large amount (10 ¹⁷ ions /
(cm ² or more) ion implantation is required. Therefore, it is desirable that the extracted ion beam current is as large as possible so that the processing time can be shortened. In general, when the arc current Iarc is increased to increase the plasma density, the extractor current Iext is increased.
Also increases. FIG. 4 shows an example of measurement. Therefore, Isup
It is optimal to perform the injection by selecting the arc current Iarc that maximizes the extractor current Iext under the restriction of / Iext ≤K.

Since the ion source of the present invention directly ionizes the metal by vacuum arc discharge, the valences of the generated ions are not the same but show a distribution peculiar to the ion species. IG Brown, B. Fineberg, JE Galvin, Multiply
Stripped Ion Generation in the
Metal Vapor Vacuum Ark, Berkeley,
California, July 1987; Lawrence Berkeley Laboratory Report LBL-21999 Rev.UC-34C.
1 (IGBrown, B.Feinberg, and JEGalvin, Multiply
stripped ion generation in the metal vapor vacuum
arc, Berkeley, California, September 1987; Lawren
ce Berkeley Laboratory Report LBL-21999 Rev.UC-34
Table 1 shows the ionic valences for the main metal elements described in the literature by C.1).

[0017]

[Table 1]

When the ion valences are distributed, optimal conditions cannot be taken for all the ions, and it is considered that ions in an inappropriate state collide with the suppressor grid and the value of Isup / Iext also increases. FIG. 5 shows a graph obtained by arranging the variations in the ionic valence of each element by the standard deviation of the valence distribution and measuring the value of K (Isup / Iext at the time of proper extraction) under proper extraction conditions. As is clear from FIG. 5, the value of Isup / Iext increases as the variation in the ionic valence increases. The K value for each element is shown in the right column of Table 1.

According to the invention shown in FIG. 1, the arc current I
The beam is extracted by gradually changing the arc, and Isup
The arc current Iarc that maximizes Iext within the range of / Iext ≦ K (K is a constant determined by the element) is calculated by the arithmetic circuit 20.
And is fed back to the arc power supply 8. By doing so, it becomes possible to perform optimum operation.

[0020]

As described above, according to the present invention, the extractor current Iext and the suppressor current Isup are measured, and the arc current Iarc is controlled so that the maximum Iext is obtained under the condition of Isup / Iext ≦ K. This makes it possible to perform stable injection processing, eliminate the need for operator's variation in injection conditions and fine adjustment of the arc current during injection, and increase the injection efficiency to shorten the processing time.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing the configuration of the present invention.

2 (a) to (c) are conceptual diagrams of ion beam extraction at a plasma boundary surface of a grid opening portion due to a change in arc current.

FIG. 3 is a diagram showing an example of measurement of an arc current Iarc and a suppressor current Isup.

FIG. 4 is a diagram showing an example of measurement of arc current Iarc and extractor current Iext for each element.

FIG. 5 is a graph showing the relationship between the standard deviation σ of variations in ion valence by element and Isup / Iext.

FIG. 6 is a schematic diagram showing a conventional ion source.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Vacuum enclosure 2 Anode 3 Cathode 4 Insulating material 5 Triggering 6 Trigger electrode 7 Trigger power supply 8 Arc power supply 9 Anode opening 10 Discharge area 11 Plasma chamber 12 Extractor grid 13 Suppressor grid 14 Ground grid 15 Grid opening 16 Processing chamber 17 ・ 18 Ammeter 19 Integrator circuit 20 Operation circuit

Claims (2)

[Claims] 1. An arc discharge is generated between an anode and a cathode in a vacuum enclosure to vaporize and ionize a part of the cathode to form a metal plasma, and the metal plasma is discharged from a discharge region into a plasma chamber. In the beam extraction method of the ion source for extracting the ion beam, the arc current is controlled so that the maximum extractor current is below the threshold value K (suppressor current / extractor current) determined for each element. A method for extracting a beam from an ion source, which comprises performing implantation. 2. An ion source having an anode and a cathode that are installed insulated from each other in a discharge region of a vacuum enclosure, and an extractor grid, a suppressor grid, and a ground grid provided in a plasma chamber. In the beam extraction device of, an arc with a maximum extractor current below a threshold value K (suppressor current / extractor current) determined for each element based on the measured extractor current value and suppressor current value. A beam extraction device for an ion source, comprising an integration circuit and an arithmetic circuit for calculating and controlling an electric current.