JPH05258676A - Power supply device in ion source - Google Patents

Abstract

PURPOSE:To stably drive a filament current and an arc current without shortage or excess in an ion source to provide a stable ion beam and extend the life of a filament. CONSTITUTION:An initial current is preliminarily sent to a filament 1 to emit thermions. They are driven at a fixed current by an arc electrode 3 and an arc power source 7. The current Iw sent from the arc electrode 2 to the minus side of the arc power source 7 is detected by a resistance 61, and a signal is generated by a filament power source control circuit 600 so that this current is a fixed value around about 0, and the filament 1 is current-driven by a filament power source 6.

Description

Detailed Description of the Invention

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power supply device for an ion source, and more particularly to a power supply device for an ion source having an arc power supply and a filament power supply having improved control characteristics.

BACKGROUND ART As a control method of the power supply apparatus in a conventional ion source is, for example, as shown in FIG. Explaining according to this figure, the arc power supply 7 and the filament power supply 6 influence each other, but control is performed individually and independently. Arc power supply 7
Is constant current control, and the filament power supply 6 uses two types of constant current control and constant voltage control.
The magnet power source 8 is under constant current control, and the acceleration power source 9 is under constant voltage control. Considering the life of the filament 1 (tungsten) in the ion beam generator, there are the following two possible mechanisms for the filament 1 being consumed. Consumption due to passing current through the filament In this case, simply increasing the filament current
The filament wears out quickly. Consumption due to collision of ions with filament by arc discharge In this case, if the number of thermoelectrons generated from the filament decreases, arc discharge becomes difficult. Since the arc power supply is under constant current control, it tries to maintain a constant current and raises the voltage. Therefore, ions of higher energy collide with the filament, which accelerates the consumption of the filament. The amount of thermoelectrons generated from the filament is determined by the shape (diameter and length) of the filament and the magnitude of the current. Since the filament length does not change, it is determined by the filament diameter and current value. The above consumption mechanism occurs when a constant current is applied to the filament. Therefore, the diameter of the filament changes with time. As a result, the amount of thermoelectrons is changed. In either case, this change over time triggers a vicious cycle of the exhaustion mechanism and, respectively, which eventually accelerates the exhaustion. is there. However, such a conventional power supply device control method for an ion source has the following problems because each power supply is individually and independently controlled. First, when the filament power supply is controlled by constant current, the filament is consumed by the mechanism of consumption and the cross-sectional area is reduced. As a result, the current density is increased, and the consumption mechanism is further accelerated. In addition, the ion beam fluctuates as the amount of thermoelectrons fluctuates. When the filament power supply is controlled by constant voltage, the filament is consumed and the cross-sectional area is reduced by the same mechanism of consumption as in constant current. The constant voltage control does not change the current density, but the amount of thermionic emission from the filament surface decreases as the cross-sectional area decreases. As a result, the mechanism of consumption will accelerate this time. Even in this case, the ion
The beam fluctuates. In either case, the consumption mechanism generated by the current flowing through the filament triggers, and the consumption mechanism and progresses, respectively. Once such a situation is reached, they become a vicious circle and accelerate the consumption of filaments. Therefore, there were problems such as difficulty in obtaining a stable ion beam and short life of the filament. From the above, in order to extend the life of the filament, it is necessary to set the amount of thermoelectrons generated from the filament to an optimum value at which these two contradictory mechanisms intersect with each other.

DISCLOSURE OF THE INVENTION The present invention controls the amount of thermoelectrons generated from a filament in an ion source,
Stable ions by stabilizing the arc discharge
The challenge is to extend the life of the filament at the same time as obtaining the beam.

In order to solve such a problem, the present invention firstly drives the arc electrode by a constant current power source, detects the current value flowing from the negative electrode of the arc electrode, and A control circuit is provided that feeds back the filament current so that the detected value becomes a constant value centered around 0 and operates so as to supply stable thermoelectrons from the filament.

[Function] In this ion source, since thermoelectrons are emitted from the filament and arc discharge is performed, a current path can be created by the movement of thermoelectrons, and each current has a more complicated path than a normal circuit. ing. Therefore, the current paths from the filament power supply and the arc power supply will also be described in detail below. Regarding the filament power supply, there are two possible routes, a current I1 flowing through the filament itself and a current I2 flowing through the filament from the arc electrode 3 due to the emission of thermoelectrons from the filament. Regarding the arc power supply, there are two possible routes, a current I4 flowing from the arc electrode 2 through the arc electrode 3 and a current I3 flowing from the arc electrode 2 through the filament. Four types of current paths are conceivable from these two power supplies, and they add or cancel each other. From the above, in the present invention, attention was paid to the apparent current Iw, which is a combination of the current I2 and the current I4. When this current Iw is a positive current, the filament current is small and thermionic emission is small. Therefore, the current I2 also becomes small. At this time, since the amount of thermoelectrons from the filament is small in the arc power supply, an attempt is made to forcibly cause arc discharge between the arc electrodes 2 and 3 by increasing the arc voltage.
Therefore, the current I4 increases. Therefore, the current Iw becomes positive because the current I4 becomes larger than the current I2. In this case, it becomes a state of the mechanism of consumption. On the contrary, when the current Iw is negative, the filament current is large and thermions are often emitted. Therefore, the current I2 also becomes large. Since the amount of thermoelectrons from the filament is sufficient, the arc voltage drops. At this time, the arc discharge becomes a state in which a large amount of current flows from the arc electrode 2 through the filament along with the movement of thermoelectrons. Therefore, the current I4 decreases, and the current I4 becomes smaller than the current I2, so that the current Iw becomes negative. In this case, it becomes a state of the mechanism of consumption. From the above, it is considered that when the current Iw is almost 0, the amount of thermoelectrons emitted from the filament with respect to the arc discharge is not excessive. Therefore, since the amount of thermoelectrons emitted from the filament is controlled in relation to the discharge state of the arc electrode, the arc discharge is stabilized and the filament drive current is controlled without excess or deficiency.

FIG. 1 is a diagram showing an embodiment of the present invention. First, the configuration will be described. The ion source is composed of a filament 1 housed in a vacuum chamber 4 having an ionized gas inlet (not shown) and an arc electrode 2 surrounding the filament 1.
Is provided. This arc electrode 2 is usually called a Wenelton electrode. An arc electrode 3 is arranged so as to face the arc electrode 2. The arc electrode 3 has an aperture 31 with a narrowed inlet and a plasma boundary cup 32 serving as an ion outlet at the same potential. Further extraction electrode 41
Are provided at the positions shown. The vicinity of the arc electrode 1 is excited by the magnet coil 5 from the outside of the vacuum chamber 4 to excite the ionized gas inside. The magnet coil 5 is driven by a magnet power source 8 at a constant current. The acceleration power supply 9 is connected between the arc electrode 3 and the extraction electrode 41 and driven at a constant voltage. An arc power source 7 is connected between the arc electrode 2 and the arc electrode 3 and is driven at a constant current. The current Iw flowing out from the arc electrode 2 is detected by the resistor 61 and sent to the filament power supply control circuit 600. The internal connection diagram of the filament power supply control circuit 600 has the configuration shown in FIG. The current Iw is detected as a voltage value by the resistor 61,
Connected between input terminals 631,632. The input terminal 632 is connected to the + input terminal of the operational amplifier 640. Operational amplifier 640
Constitutes a buffer amplifier circuit, the output of which is sent to the-input terminal of the next operational amplifier 650 via the resistor 641. A resistor 65 is placed between the output terminal and the − input terminal of this operational amplifier 650.
1 is connected to form an inverting amplifier circuit. Then, the output terminal of the operational amplifier 650 is connected to the + input terminal of the operational amplifier 660 via the resistor 663. Operational amplifier
The − input terminal of 660 is fed back by resistors 661 and 662 to form a non-inverting amplifier circuit, and the end of resistor 662 is a negative value reference set by variable resistor 664 and constant voltage diode 665. Voltage is injected. The output of the operational amplifier 660 is sent to the-input terminal of the operational amplifier 670 via the resistor 671. A resistor 672 and a capacitor 673 are connected between the − input terminal and the output terminal of the operational amplifier 670 and are fed back to form an inverting amplifier circuit. And operational amplifier 670
+ Input terminal of the power supply voltage Vcc is resistor 677 and variable resistor
A voltage is applied by being divided by 675 and a resistor 676. A diode 674 for protection at the time of polarity reversal is connected between the-input terminal and the GND terminal of the operational amplifier 670.
Then, the output of the operational amplifier 670 is sent to the + input terminal of the operational amplifier 680. The operational amplifier 680 constitutes a buffer amplifier circuit, the output terminal of which is connected via the diode 683 to the output terminal 69.
Connected to 0. In addition, the power supply voltage Vcc is applied to the output terminal 690.
The voltage divided by the variable resistor 682 is supplied via the diode 684. In the filament power supply control circuit 600 configured as described above, when the voltage between the input terminals 631 and 632 is almost 0, a predetermined output voltage value is generated between the output terminals 690 and 691, and when the input changes from 0, the change occurs. A voltage proportional to that amount is generated. The output voltage of the filament power supply control circuit 600 is supplied to the filament power supply 6 and is controlled by a current proportional to the voltage to supply power to the filament 1. In the ion beam generator configured as described above, first, the starting voltage corresponding to the setting of the variable resistor 682 in the filament power supply control circuit 600 appears at the output terminal 690, and the filament power supply 6 corresponds to this voltage.
Sends a starting current to the filament 1. Although not shown, the starting voltage set by the variable resistor 682 is cut off once the ion source is started. Then, the arc power source 7 connected between the arc electrodes 2 and 3 drives at a constant current to generate a plasma arc in the vacuum chamber 4. At this time, the current Iw flowing out from the arc electrode 3
In response to this, the filament power supply control circuit 600 operates, and in response to this, the filament power supply 6 is current driven. Therefore, although the amount of thermoelectrons in the filament 1 affects the arc state, the arc state is detected by the current Iw flowing out from the arc electrode 3, and this current is controlled to be a constant value centered at about 0. The thermoelectron amount of the filament 1 can be stably generated without excess or deficiency. Generally, in the ion source, the ambient temperature, the degree of vacuum,
If the conditions such as the supply amount of the introduced gas, the current flowing through the excitation magnet coil 5 and the current flowing through the arc electrode are kept constant, the largest factor that changes the state of arc discharge is
The amount of thermoelectrons generated from the filament is supplied as described above, so that a stable ion beam can be obtained from the ion source.

As described above, according to the present invention, in the power supply device for an ion source, a constant current is first passed through the arc electrode, the current Iw flowing out from the arc electrode is detected, and the current is centered at about 0. Since the filament current is controlled to have a constant value, the filament current is controlled so that the arc state is stable. Therefore, by supplying the amount of thermoelectrons of this filament without excess or deficiency, a stable ion beam can be obtained, and at the same time, the life of the filament can be significantly extended.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of a power supply device in an ion source according to the present invention.

FIG. 2 is a diagram showing an embodiment of a filament power supply control circuit.

FIG. 3 is a diagram showing an example of a power supply device in a conventional ion source.

[Explanation of symbols]

 1 ... Filament 2 ... 2nd arc electrode 3 ... 1st arc electrode 4 ... Vacuum chamber 5 ... Magnet coil 6 ... Filament power supply 7 ... Arc power supply 8 ... Magnet power supply 9 ... Acceleration power supply 41 ... Extraction electrode 32 ... Plasma boundary Cup 31 ... Aperture 600 ... Filament power supply control circuit

Claims (1)

[Claims] 1. An ion source comprising at least a linear filament, a pair of arc electrodes and a magnet coil, and a phylammet power supply for driving the filament,
The current flowing out from the arc power source for driving the pair of arc electrodes at a constant current, the magnet power source for driving the magnet coil and the acceleration power source, and the negative side electrode of the pair of arc electrodes is detected, and the current is almost zero. A power supply device for an ion source, comprising a filament power supply control circuit for controlling the filament power supply so that the filament power supply has a constant center value.