JPH0533447U - Freeman type ion source - Google Patents

Abstract

(57) [Summary] [Purpose] To suppress changes in the characteristics of ion beams due to filament consumption. A thermoelectron emission filament 4 is provided near the ion extraction hole 2 of the arc chamber 1, and a magnetic field adjusting filament 7 is arranged in parallel with the filament 4. As the filament 4 is consumed by spattering,
Although the filament current is reduced, a current is passed through the magnetic field adjusting filament to compensate for the reduction in the rotating magnetic field strength caused by the current in the filament 4. It is possible to suppress the change in the plasma generation state in the vicinity of the ion extraction hole due to the change in the rotating magnetic field strength and to extract the ion beam having a constant characteristic.

Description

[Detailed description of the device]

[0001]

[Industrial application]

 The present invention relates to a Freeman type ion source capable of suppressing changes in characteristics of plasma and ion beams due to consumption of filaments.

[0002]

[Prior Art]

 FIG. 2 is a cross-sectional view of an essential part showing an example of a conventional Freeman-type ion source. An ion extraction hole (slit) 2, an ion substance source vapor, and a gas inlet 3 are formed in a side wall of an arc chamber 1. A linear thermionic emission filament 4 made of tungsten, tantalum wire, etc. is attached to the end wall of the arc chamber 1 using an insulating member 5, and is close to the ion extraction hole 2 deviated from the center of the arc chamber 1. The filament 4 is connected to a power source (not shown) via the current introducing terminal 6.

The filament 4 is biased to a negative potential with respect to the arc chamber 1 serving as an anode, and an external magnetic field of 20 to 100 Gauss acts from the outside of the arc chamber 1 in parallel with the filament 4. In a predetermined vacuum atmosphere, a filament current of 150 to 200 A is supplied to the filament 4 and an ion material source gas is supplied from the gas inlet 3. An arc discharge is generated between the filament 4 and the arc chamber 1, and a plasma of an ionic substance is generated in the arc chamber 1. After plasma generation, the filament current is controlled so that the arc current becomes constant. A rotating magnetic field is generated around the filament 4 by the filament current, and a high density plasma is generated near the ion extraction hole 2 by the combined magnetic field of this magnetic field and the filament 4 and the normal external magnetic field, and the electrostatic extraction method is used. Thus, the ion beam is extracted from the ion extraction hole 2.

Such a Freeman type ion source generally has good ion beam stability, a wide variable range of the ion beam amount, a plate-like ion beam can be easily extracted, and maintenance is also easy. It has the advantage of being used in a high-current ion implanter.

[0005]

[Problems to be solved by the device]

 However, the filament 4 is worn away by spatter and the like as the ion source is operated. When the filament 4 is consumed, the resistance value increases, and the filament temperature for the required thermionic emission can be maintained at a smaller filament current. With the consumption of the filament, the filament current is initially about 150 A, for example. From 50 to 60 A, it changes to a sufficient state. Such a change in the filament current causes a change in the rotating magnetic field strength, which changes the characteristics of the generated plasma, and thus the extracted ion beam. In the ion implanter, due to such a phenomenon that the characteristics change, operating parameters below the ion source for obtaining the optimum ion beam are changed, making it difficult to completely automate the device.

It is an object of the present invention to provide a Freeman type ion source capable of suppressing changes in plasma and ion beam characteristics due to filament consumption.

[0007]

[Means for Solving the Problems]

 The present invention is characterized in that, in the Freeman type ion source, a magnetic field adjusting filament is arranged in parallel near the thermionic emission filament.

[0008]

[Action]

 When the current decreases as the thermionic emission filament is consumed, a current is passed through the magnetic field adjustment filament to keep the strength of the rotating magnetic field around the filament constant. Changes in the characteristics of the plasma, and thus the characteristics of the ion beam extracted from the ion source, are suppressed.

[0009]

Embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a cross-sectional view of an essential part of one embodiment, and the same reference numerals as those in FIG. 2 indicate the same parts. A linear magnetic field adjusting filament 7 also made of tungsten, tantalum, or the like is provided in parallel near the thermionic emission filament 4 in parallel with the filament 4, and the filament 7 is connected to the end of the arc chamber 1. It is insulated and attached to the portion by an insulating member 8. Filament currents are supplied to the thermionic emission filament 4 and the magnetic field adjusting filament 7 from independent power sources (not shown) through the current introducing terminals 6 and 9, respectively. The thermionic emission filament 4 is biased to a negative potential with respect to the arc chamber 1, and the magnetic field adjusting filament 7 is set to the same potential as the arc chamber 1.

A filament current is supplied to the thermionic emission filament 4 as in the case of the conventional Freeman type ion source. When the filament 4 is consumed by the operation of the ion source, the filament current decreases. Although the rotating magnetic field strength decreases due to the decrease in this current, a current in the same direction as the thermionic emission filament 4 is caused to flow through the magnetic field adjusting filament 7, and the rotating magnetic field of this current causes the current in the thermionic emission filament 4 to change. It compensates the decrease of the rotating magnetic field strength and keeps the strength of the rotating magnetic field around both filaments constant.

In the above embodiment, one filament 7 for magnetic field adjustment is arranged in parallel with the filament 4 for thermoelectron emission, but a plurality of filaments for magnetic field adjustment are provided around the thermoelectron emission filament. They may be dispersed and arranged as appropriate.

[0012]

[Effect of the device]

 Since the present invention is configured as described above, the strength of the rotating magnetic field can be maintained constant even when the thermionic emission filament is exhausted, so that the plasma in the vicinity of the ion extraction hole in the arc chamber is maintained. It is possible to suppress the change in the generation state, and it is possible to extract an ion beam having a constant characteristic. Further, since the rotating magnetic field adjusting filament has the same potential as the anode of the arc chamber, the filament is hardly consumed by sputtering. Therefore, in the ion implanter, complete automation of operating parameters can be achieved.

[Brief description of drawings]

FIG. 1 is a sectional view of an essential part of an embodiment of the present invention.

FIG. 2 is a cross-sectional view of a main part of an example of a conventional Freeman type ion source.

[Explanation of symbols]

 1 Arc chamber 2 Ion extraction hole 3 Gas inlet 4 Thermionic emission filament 5, 8 Insulation member 6, 9 Current introduction terminal 7 Magnetic field adjustment filament

Claims (1)

[Scope of utility model registration request] 1. A Freeman-type ion source comprising a filament for magnetic field adjustment arranged in parallel in the vicinity of a filament for emitting thermoelectrons.