JPH0535533B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a power supply device for an ion source used in an ion implanter, an ion microanalyzer, and other devices.

(Prior Art) A Freeman ion source that generates plasma using a tungsten filament has been known as a typical ion source. In this ion source, if the tungsten filament is spattered by ions, or if a chemically active gas is used as a discharge gas, the filament will undergo a chemical reaction, causing severe wear and tear, and the ion source will have to stop operating to replace the filament. Must. Along with this, it is also required to stop the equipment that uses the ion source, which inconveniently reduces the operating efficiency of the equipment.

Therefore, the applicants first divided the discharge chamber of the ion source into a main discharge chamber and a sub-discharge chamber using partition electrodes with pores, introduced a rare gas into the sub-discharge chamber provided with the filament, In addition, a discharge gas that generates desired ions is introduced into the main discharge chamber, and the pressure in the sub-discharge chamber is made higher than that in the main discharge chamber, causing a composite discharge between the filament, the partition electrode, and the anode in the main discharge chamber. He proposed a method that would generate ions and extend the life of the filament by doing so (Japanese Patent Laid-Open No. 189841, 1983).

(Problems to be Solved by the Invention) The above-mentioned proposal uses a relatively large constant power source of about 8KW as a power source for discharging into the sub-discharge chamber, but in reality, it is difficult to start the discharge. It was found that although a voltage of about 1KV is required for the operation, a voltage of about 40V to 100V is sufficient after the discharge occurs. Using such a large-sized constant power source as described above is unreasonable because it unnecessarily operates with excessive power, and the installation space for the power source becomes extremely large, which is inconvenient in terms of equipment.

The object of the present invention is to improve the proposed ion source so that it can be operated with a small power source.

(Means for Solving the Problems) In order to solve the above-mentioned problems, the present invention divides the discharge chamber into a main discharge chamber and a sub-discharge chamber provided with a filament by a partition wall, and separates these two chambers. A rare gas is introduced into the sub-discharge chamber through the pores of the anode electrode provided in the partition wall, and a discharge gas that generates desired ions is introduced into the main discharge chamber, so that the pressure in the sub-discharge chamber is maintained as the main discharge chamber. A first power source with a high voltage and small current and a second power source with a low voltage and large current are connected in series to the anode electrode via a resistor in order to maintain the pressure higher than the pressure in the discharge chamber, A circuit connecting both the first and second power sources was connected to the anode electrode via a diode.

(Function) A rare gas such as Ar gas is introduced into the sub-discharge chamber, and a highly chemically active discharge gas such as O ₂ gas is introduced into the main discharge chamber to make the pressure in the sub-discharge chamber lower than the pressure in the main discharge chamber. enhance Then, when electricity is applied to the filament in the sub-discharge chamber and an anode voltage is applied to the anode electrode in which the pores are formed and the main discharge chamber, thermionic electrons are supplied from the filament in the sub-discharge chamber and a plasma is generated between the filament and the anode electrode. occurs. Since the pressure in the sub-discharge chamber is high, this plasma ejects from the pores formed in the anode electrode into the main discharge chamber, and between the ejected plasma and the main discharge chamber, the discharge gas is ionized and ions are generated. The generated ions are extracted in the form of a beam from an ion beam extraction port on the side of the main discharge chamber by an extraction electrode. In this case, until plasma is generated in the sub-discharge chamber, high voltage is applied from the first and second power supplies connected in series to the anode electrode, but once plasma is generated, the voltage drops and a large current begins to flow. Generally, the first power supply becomes inactive, and a low voltage and large current is exclusively supplied to the anode electrode from the second power supply via the diode, and the discharge in the sub-discharge chamber is generated by the first and second power supplies with low power. and sustain it.

(Example) An example of the present invention will be described with reference to the attached drawings.
In FIG. 1, reference numeral 1 indicates a discharge chamber having a cylindrical interior, and 2 indicates a partition wall that divides the discharge chamber 1 into an upper main discharge chamber 3 and a lower sub-discharge chamber 4. The partition wall 2 was composed of a top plate 5 of the sub-discharge chamber 4 and ceramic plates 7, 7 with an anode electrode 6 interposed therebetween.

The main discharge chamber 3 includes a second anode electrode 9 having a float potential with a ceramic plate 8 provided on the inner surface, the partition wall 2, and a third anode electrode 10 having a cylindrical cavity.
and a third anode electrode 10.
There is a slit-shaped ion extraction port 11 with a width of 2 mm in the vertical direction and a length of 25 mm, and an ion extraction port 11 located on the opposite side.
Discharge gas introduction hole 1 for introducing discharge gas such as active gas such as AsF ₅ gas or O ₂ gas or inert gas such as _Ar gas
2 was formed.

13 is a pore formed in the anode electrode 6, and extension holes 14, 14 connected to the pore 13 are also formed in the top plate 5 and ceramic plates 7, 7, so that the main discharge chamber 3 and the sub-discharge chamber 4 communicate with each other. I decided to do so. It is preferable that the pores 13 and the extended holes 14, 14 are formed linearly in the partition wall 2, and are formed close to the ion extraction port 11.

15 is an introduction hole for rare gas such as Ar gas formed in the sub-discharge chamber 4, 16 is a filament provided in front of the extension hole 14 opened in the sub-discharge chamber 4, and 17 is a second anode electrode of the main discharge chamber 3. Small holes 18 and 19 are formed in the ceramic plate 8 in front of the ion extraction hole 14 to face the extension hole 14, and are extraction electrodes provided in front of the ion extraction port 11. Magnets 21 , 21 are provided above the main discharge chamber 3 and below the sub-discharge chamber 4 constituting the discharge chamber 1 so as to apply a magnetic field 20 substantially along the axial direction of the pores 13 of the anode electrode 6 .

FIG. 2 shows the electrical wiring in the embodiment shown in the first diagram.
an auxiliary discharge power supply that provides a potential for discharge within the
23 is a main discharge power source that provides the third anode electrode 10 with a potential for discharge in the main discharge chamber 3; 24 is a filament power source for generating heat in the filament 16;
Reference numeral 25 denotes an extraction power source that applies a potential for ion extraction to the extraction electrodes 18 and 19, and 27 denotes a deceleration power source. Further, 26 is a Faraday cup provided 30 cm away from the ion extraction port 11 in order to measure the ion current of the beam-shaped ions extracted from the ion extraction port 11.

The sub-discharge power source 22 has a resistor 2 on the anode electrode 6.
A circuit 2 that connects a first power source 22a of high voltage and small current and a second power source 22b of low voltage and large current in series via 8, and further connects both first and second power sources 22a and 22b.
9 was connected to the anode electrode 6 via a diode 30. For example, the first power source 22a
A power source of 1KV, 0.5A is used, and a power source of 160V, 5A, for example, is used for the second power source 22b.

The operation of the above configuration is as follows.

First, Ar gas is poured from the inlet 15 so that the degree of vacuum in the sub-discharge chamber 4 is 1 to 0.1 Torr.
AsF ₅ gas is flowed through the discharge gas inlet 12 so that the degree of vacuum in the main discharge chamber 3 is 10 ^-2 to ^{10 -3} Torr.
The degree of vacuum outside the discharge chamber 1 was set to 10 ^-4 to ^{10 -5} Torr. Next, when each power source 22, 23, 24, 25 is activated, electrons are supplied from the filament 16 and discharged between this and the anode electrode 6, resulting in Ar
Gas plasma is generated. The filament 16
The wire was constructed by fixing a 2% thorium-containing tungsten wire with a diameter of 0.6 mm to an insulating base 32 via a stainless steel connector 31.

Specifically, this discharge is a sub-discharge that occurs on the inner surface of the pores 13 of the anode electrode 6, and the plasma is generated in the pores 13 and the extension holes 14 due to the pressure difference between the main discharge chamber 3 and the sub-discharge chamber 4. When the gas flows into the main discharge chamber 3, a main discharge is induced between this and the third anode electrode 10, and a plasma of AsF ₅ gas is generated. The plasma flowing into the main discharge chamber 3 from the sub-discharge chamber 4 plays the role of a filament to generate a main discharge, but if it relies only on the pressure difference between the main and sub-discharge chambers 3 and 4, it will diffuse and dilute within the main discharge chamber 3. , since much of the AsF ₅ gas cannot be ionized, the magnets 21 and 2
1 was provided to generate a magnetic field 20 in the direction of the pores 13, along which the plasma generated by the sub-discharge was ejected into the main discharge chamber 3 along the optical axis, ionizing much of the AsF ₅ gas. Ionized As ions, etc. are extracted from the ion extraction port 1 by extraction electrodes 18 and 19.
It is pulled out in a beam shape from 1.

The sub-discharge power supply 22 receives the total voltage from the first and second power supplies 22a and 22b connected in series to the anode electrode 6 until discharge occurs in the sub-discharge chamber 4.
1160V is applied, but after the discharge occurs, the voltage decreases and the current consumption increases, so the low voltage second power supply 22 of 160V is supplied via the circuit 29 and the diode 30 rather than from the first power supply 22a with the resistor 28 interposed.
A large current flows from b to the anode electrode 6, and the discharge in the sub-discharge chamber 4 is maintained.

In the above embodiment, a current of 20.5 A is supplied to the filament 16 from its power source 24, and a current of 3.0 A is supplied to the anode electrode 6 during sub-discharge, and a current of 3.0 A is supplied to the filament 16 from the power source 24.
When a current of 1.1A is supplied to each of
It was 40mA/ ^cm2 .

(Effects of the Invention) As described above, the present invention provides a sub-discharge chamber in which a rare gas plasma is formed, and a main discharge chamber which has a lower pressure than the sub-discharge chamber and into which the plasma is introduced through the pores. In the ion source, the power supply to the anode electrode that causes discharge in the sub-discharge chamber is connected in series with a high voltage, small current power source and a low voltage, large current power source through a resistor. Since the circuit connecting the power supply is connected to the anode electrode via a diode, there is no need to prepare a large power supply with high voltage and large current, and two small power supplies are sufficient, requiring less installation space. This method has advantages such as being able to downsize the entire ion source, eliminating the waste of installing excessive power, and being economical.

[Brief explanation of the drawing]

FIG. 1 is a half-cut perspective view of an embodiment of the present invention, and FIG. 2 is a wiring diagram of what is shown in FIG. 1... Discharge chamber, 2... Partition wall, 3... Main discharge chamber,
4...Sub-discharge chamber, 6...Anode electrode, 13...
Pore, 16...Filament, 22...Sub-discharge power supply, 22a...First power supply, 22b...Second power supply, 28...Resistor, 29...Circuit, 30...Diode.

Claims (1)

[Claims] 1 The discharge chamber is divided by a partition wall into a main discharge chamber and a sub-discharge chamber provided with a filament, and these two chambers are communicated through the pores of an anode electrode provided in the partition wall, and a rare gas is supplied to the sub-discharge chamber. is introduced into the main discharge chamber, and a discharge gas is introduced into the main discharge chamber to maintain the pressure in the sub-discharge chamber higher than the pressure in the main discharge chamber. A first power source with a high voltage and small current and a second power source with a low voltage and large current are connected in series through a resistor,
A power supply device for an ion source, characterized in that a circuit connecting both first and second power supplies is connected to the anode electrode via a diode.