JPH0589790A - Freeman ion source - Google Patents

Abstract

PURPOSE:To lower the voltage of partition wall of discharging chambers, lower the energy of ions impurities in plasma in a low-arc-voltage discharging chamber, lower the sputtering efficiency, and lower the filament cosuming speed by guiding the electrons in the arc discharge from the partition wall of the discharging chambers to an arc electric source through resistors. CONSTITUTION:Low arc voltage discharging chambers 2, 2 having filaments 6, 6 are formed and at the same time there are provided partition wall 3, 3 of discharging chambers having through holes 3b, 3b in the side walls 3c, 3c and main arc chamber's partition wall 8 composing a main arc chamber 1 communicated with the discharging chambers through the through holes 3b, 3b. The partition walls 3, 3 of the discharging chambers are connected with the main arc chamber's partition wall in insulated state and the partition walls 3, 3 of the discharging chambers are connected to an arc electric source 5 through resistors 4, 4.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a Freeman ion source capable of obtaining a beam amount of an ion beam over a wide range with good controllability, and more specifically, it reduces a sputtering rate on a filament during arc discharge. As a result, the present invention relates to a Freeman ion source capable of increasing the filament renewal interval.

[0002]

2. Description of the Related Art Conventionally, as shown in FIG. 4, a Freeman ion source has a discharge chamber partition wall 51 to which a positive voltage is applied.
And a linear filament 52, which is arranged in the discharge chamber partition wall 51 in the vicinity of the ion extraction hole 51a and to which a negative voltage is applied.
And a working gas supply means 54 for supplying a working gas into the discharge chamber partition wall 51, and while applying an external magnetic field Bs parallel to the axis of the filament 52, the discharge chamber partition wall 51 and the filament 52 are separated. An arc discharge is generated by the potential difference, and a plasma is generated by the arc discharge and the working gas.

At this time, the effective range length of the electrons of the arc discharge is determined by the combined magnetic field of the rotating magnetic field due to the filament current flowing through the filament 52 and the external magnetic field Bs. The increase / decrease in length is closely related to the increase / decrease in the probability of collision between electrons and the working gas. That is, for example, when the effective range length is increased,
By increasing the collision probability, it is possible to generate high-density plasma in the vicinity of the ion extraction hole 51a of the discharge chamber partition wall 51, and it is possible to increase the beam amount of the ion beam.

As a result, in the Freeman ion source, since the filament current changes the emission amount of electrons and the strength of the synthetic magnetic field, the probability of collision between electrons and working gas can be controlled in a wide range by the filament current. Since the operation can be easily stabilized by controlling the filament current, it is widely used in the ion implantation apparatus in which wide range setting of the impurity implantation amount and uniform implantation are desired.

[0005]

However, in the above-mentioned conventional Freeman ion source, the ions having a positive charge in the plasma consume the filament 52 having a negative voltage by sputtering, so that the filament 52 is, for example, 20 to 4.
There is a problem that it needs to be updated every 0 hours. In particular, for the Freeman ion source used in the production apparatus, the update of the filament 52 causes a decrease in the operating rate due to the stop of the apparatus, so that the conventional update interval becomes a big problem, and further update is required. Increased spacing is desired.

Therefore, the consumption rate of the filament 52 is
Focusing on the fact that the sputtering voltage depends on the arc voltage, which is the potential difference between the discharge chamber partition wall 51 and the filament 52, a method of reducing the sputtering voltage by reducing the arc voltage can be considered. In this case,
Although it is possible to increase the update interval by decreasing the consumption rate of the filament 52, there is a lower limit to the arc voltage, and the reduction of the sputter rate by decreasing this arc voltage is sufficient to update the filament 52. The spacing cannot be increased sufficiently.

Therefore, it is an object of the present invention to provide a Freeman ion source capable of sufficiently increasing the renewal interval of the filament 52.

[0008]

Means for Solving the Problems Claims 1 and 2
In order to solve the above problems, the Freeman ion source of the invention of (1) is a partition wall connected to the positive electrode side of the arc power supply, and an arc discharge is generated by a potential difference between the filament connected to the negative electrode side of the arc power supply to generate plasma. It is generated and has the following features.

That is, the Freeman ion source of claim 1 is
A partition wall forms a low arc voltage discharge chamber containing a filament, and a discharge chamber partition wall having a passage hole in a side wall, and a main arc chamber partition wall forming a main arc chamber in a communicating state by the passage hole. It consists of The discharge chamber partition wall and the main arc chamber partition wall are connected in an insulated state, and the discharge chamber partition wall is connected to the arc power source through a resistor.

Further, in the Freeman ion source of claim 2, the filament of the Freeman ion source of claim 1 is
It is characterized in that it has a pair of rod-shaped portions whose axial directions coincide with each other, and that the filament magnetic field between both rod-shaped portions is arranged in the direction of the passage hole.

[0011]

According to the structure of the first aspect, when plasma is generated by the arc discharge, the electrons of the arc discharge flow from the partition wall of the discharge chamber to the arc power source through the resistor. Therefore, the voltage of the discharge chamber partition wall to which the predetermined positive voltage is applied by the arc power source becomes lower than that of the main arc chamber partition wall to which the same positive voltage is applied by the arc power source. The reduction in the voltage of the discharge chamber partition wall causes the side wall of the discharge chamber partition wall to act on the filament as an intermediate electrode, thereby reducing the energy of the impurity ions in the plasma in the low arc voltage discharge chamber. As a result, the Freeman ion source can reduce the sputter rate and the consumption rate of the filament, so that the filament renewal interval can be sufficiently increased.

Further, according to the second aspect of the present invention, the electrons emitted from the filament positively move in the direction of the passage hole of the discharge chamber partition wall along the filament magnetic field between the rod-shaped portions, so that a positive voltage is applied. The collision with the side wall that is provided is prevented, and it can be efficiently moved to the main arc chamber through the passage hole.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The following will explain one embodiment of the present invention with reference to FIGS.

As shown in FIG. 1, the Freeman ion source according to the present embodiment is arranged on both sides of the main arc chamber 1 to which the external magnetic field Bs is similarly given, as well as to the main arc chamber 1 to which the external magnetic field Bs is given. And a pair of low arc voltage discharge chambers 2 and 2. The low arc voltage discharge chambers 2 and 2 are formed by discharge chamber partition walls 3 and 3 having conductivity such as tantalum, and these discharge chamber partition walls 3 and 3 have a predetermined size of several tens to several hundreds Ω. Resistor 4 having resistance value R ₁
It is connected to the positive electrode side of the arc power source 5 via.

In addition, the gas introducing hole 3 is formed in the side wall of the discharge chamber partition wall 3 located in the direction opposite to the main arc chamber 1 side.
a. 3a are formed, and these gas introduction holes 3a.
An operating gas supply means having a metal vapor generation furnace or the like (not shown) is connected to 3a. Then, the working gas supply means supplies a working gas, which is a working gas obtained by evaporating solid impurities in the metal vapor generation furnace or a gaseous impurity filled in the gas cylinder, to the low arc voltage discharge chamber 2.
It is designed to supply to 2.

On the other hand, slit-shaped passage holes 3b, 3b are formed in the side wall 3c, 3c located on the main arc chamber 1 side in the discharge chamber partition wall 3, 3. These passage holes 3
In the vicinity of b3b, for example, U made of tungsten or the like is used.
Character-shaped filament 6 ・ 6 is a low arc voltage discharge chamber 2 ・
2 are provided in each of the filaments 6 and 6
As shown in FIG. 2, is composed of a pair of rod-shaped portions 6a and 6b whose axial directions coincide with each other, and a bent portion 6c connecting these rod-shaped portions 6a and 6b. And the above-mentioned rod-shaped portion 6
The a and 6b are arranged parallel to the longitudinal direction of the passage holes 3b and 3b.

As shown in FIG. 1, the filaments 6 and 6 have the U-shaped center line of the filaments 6 and 6 parallel to the longitudinal center lines of the passage holes 3b and 3b, and the passage holes 3b and 3b. The ends of the filaments 3b and 3b and the rod-shaped portions 6a and 6b of the filaments 6 and 6 are arranged so that the distance between them is equal. Then, one rod-shaped portion 6a of the filament 6
Is connected to the negative side of the above-mentioned arc power source 5,
Both rod-shaped portions 6a and 6 generated by the filament current If
The filament magnetic field Bf between b is directed toward the passage holes 3b and 3b.

The above-mentioned main arc chamber 1 is arranged between the discharge chamber partition walls 3, 3 containing the above-mentioned filaments 6, 6. This main arc chamber 1 includes insulating partition walls 7 and 7 connected to the side walls 3c and 3c of the discharge chamber partition walls 3 and 3, and insulating partition walls 7 and 7.
It is formed by the main arc chamber partition wall 8 having conductivity provided between 7 and the positive arc side of the arc power source 5 is connected to the main arc chamber partition wall 8.

A slit-shaped ion extraction hole 8a is formed on the upper surface wall of the main arc chamber partition wall 8 and an extraction electrode 9 to which a negative voltage is applied is formed above the ion extraction hole 8a. The ground electrode 10 that serves as a deceleration electrode is arranged in this order. The extraction electrode 9 and the ground electrode 10 are respectively formed with an extraction electrode hole 9a and a ground electrode hole 10a, and the extraction electrode 9 collects positively-charged impurity ions from the main arc chamber 1 that generated plasma. The extracted ion beam 11 is passed through the extraction electrode hole 9a and the ground electrode hole 10a.

The operation of the Freeman ion source in the above structure will be described.

First, from the arc power source 5 to both filaments 6
When the filament current If is passed through 6, the filament 6
・ 6 will start to generate heat. At this time, a positive voltage is applied to the main arc chamber partition wall 8 and the discharge chamber partition wall 3 by the arc power source 5, while the filaments 6
Is applied with a negative voltage by the arc power supply 5.
Therefore, the heated filaments 6 and 6 emit electrons due to the potential difference between the main arc chamber partition wall 8 and the discharge chamber partition wall 3 to generate arc discharge.

After that, the working gas passes through the gas introduction holes 3a, 3a of the discharge chamber partition wall 3, 3 and the low arc voltage discharge chamber 2.2.
When the gas particles of the working gas collide with the electrons, plasma consisting of impurity ions and electrons is generated.

By the above arc discharge, the filament 6
Some of the electrons emitted from 6 move toward the discharge chamber partition walls 3 and 3 to which a positive voltage is applied by the arc power source 5, and pass through the discharge chamber partition walls 3 and 3 and the resistors 4 and 4. It will flow to. At this time, the amount of electrons flowing from the discharge chamber partition wall 3/3 to the arc power source 5 is determined by the resistance value R ₁ of the resistors 4 4 and the resistance value Rp _{1 of the} plasma. septum 3-3, by a current I ₁ generated by the electron flow between the two resistance values R _1, Rp ₁ described above, negative voltage and the main arc chamber filament 6.6 1
It has an intermediate voltage (Va-R ₁ × I ₁ ) lower than the arc voltage Va, which is the potential difference from the positive voltage of V.

In the discharge chamber partition walls 3 and 3 having the above intermediate voltage, the side walls 3c and 3c work as intermediate electrodes for the filaments 6 and 6, and the arc voltage is, for example, 1/2 to 1 / A potential difference of about 3 is formed in the low arc voltage discharge chamber 2.2. The gas pressure in the low arc voltage discharge chamber 2.2 is only because the low arc voltage discharge chamber 2.2 and the main arc chamber 1 are communicated with each other through the passage holes 3b and 3b. Is higher than the gas pressure of. Therefore, the arc discharge in the low arc voltage discharge chamber 2.2 is maintained even at the intermediate voltage due to the high gas pressure.

As a result, the sputtering rate of impurity ions in the plasma generated in the low arc voltage discharge chamber 2.2 is
Since the filaments 6 and 6 are sputtered with energy corresponding to the potential difference between the side walls 3c and 3c and the filaments 6 and 6, the sputtering rate of impurity ions having energy corresponding to the arc voltage is reduced. become. The reduction of the sputtering rate is due to the filament 6
The wear rate of 6 will be reduced, and the renewal interval of the filaments 6 will be increased.

On the other hand, from the arc power source 5 to the filament 6
When a filament current If is passed through 6, the filament 6
A filament magnetic field Bf is formed around 6 as shown in FIGS. 2 and 3. The filament magnetic fields Bf have the same magnetic field directions in the central portions of the parallel rod-shaped portions 6a and 6b, and are in a mutually reinforcing state in the passage holes 3b and 3b direction of the discharge chamber partition walls 3 and 3.

Therefore, as shown in FIG. 1, the electrons emitted from the filaments 6, 6 move positively along the filament magnetic field Bf in the direction of the through holes 3b, 3b of the discharge chamber partition walls 3, 3. And the side wall 3c with a positive voltage
The collision with 3c is prevented, and it is efficiently introduced into the main arc chamber 1 through the passage holes 3b and 3b.

The electrons transferred to the main arc chamber 1 are
Along with the electrons, the low arc voltage discharge chamber 2.2 to the passage hole 3b
Colliding with the gas particles of the working gas that has moved through 3b, plasma is also generated in this main arc chamber 1. Then, the impurity ions having a positive charge in the plasma are attracted to the extraction electrode 9 to which a negative voltage is applied, and the ion extraction hole 8 of the main arc chamber partition wall 8 is drawn.
The ion beam 11 is emitted from a.

As described above, the Freeman ion source of this embodiment has the low arc voltage discharge chamber 2.2 having the filaments 6 and the main arc chamber 1, and when plasma is generated by arc discharge. The side wall 3 of the discharge chamber partition wall 3
By using c.3c as the intermediate electrode, the potential difference between the low arc voltage discharge chambers 2.2 is made lower than the potential difference between the arc voltages, and the energy of the impurity ions in the plasma in the low arc voltage discharge chambers 2.2 is reduced. It is like this. As a result, this Freeman ion source is
By the intermediate voltage of c · 3c, the sputter rate can be reduced and the consumption rate of the filaments 6.6 can be reduced, so that the renewal interval of the filaments 6.6 can be sufficiently increased.

Although the Freeman ion source in this embodiment has two low arc voltage discharge chambers 2.2,
The present invention is not limited to this, and one or three or more low arc voltage discharge chambers 2 may be provided.

[0031]

As described above, the Freeman ion source of the invention of claim 1 causes arc discharge by the potential difference between the partition wall connected to the positive side of the arc power source and the filament connected to the negative side of the arc power source. The partition wall forms a low arc voltage discharge chamber containing a filament and is connected to the discharge chamber partition wall having a through hole on the side wall and the through hole. And a main arc chamber partition wall forming a main arc chamber, the discharge chamber partition wall and the main arc chamber partition wall are connected in an insulating state, the discharge chamber partition wall to the arc power supply through a resistor. It is a connected configuration.

As a result, the electrons of the arc discharge flow from the discharge chamber partition wall to the arc power source through the resistor, so that the voltage of the discharge chamber partition wall drops and the energy of the impurity ions in the plasma in the low arc voltage discharge chamber increases. Therefore, the sputter rate to the filament can be reduced to reduce the consumption rate of the filament, and as a result, the renewal interval of the filament can be sufficiently increased.

Further, in the Freeman ion source of the invention of claim 2, the filament of claim 1 has a pair of rod-shaped portions whose axial center directions coincide with each other, and the filament magnetic field between both rod-shaped portions is in the passage hole direction. It is the structure arranged as follows.

With this, in addition to the effect of the first aspect, the electrons emitted from the filament positively move in the direction of the passage hole of the discharge chamber partition wall along the filament magnetic field between the rod-shaped portions, so that a positive voltage is applied. With this, it is possible to prevent the collision with the side wall having the structure, and to efficiently move the side wall to the main arc chamber through the passage hole.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing a state of partition walls of a Freeman ion source of the present invention.

FIG. 2 is an explanatory diagram showing a state of a magnetic field generated around a filament.

FIG. 3 is an explanatory diagram showing a state in which electrons move along a filament magnetic field.

FIG. 4 illustrates a conventional example and is a schematic configuration diagram of a Freeman ion source.

[Explanation of symbols]

 1 main arc chamber 2 low arc voltage discharge chamber 3 discharge chamber partition wall 3a gas introduction hole 3b passage hole 3c side wall 4 resistor 5 arc power supply 6 filament 6a rod-shaped portion 6b rod-shaped portion 7 insulating partition wall 8 main arc chamber partition wall 8a ion extraction hole 9 Extraction electrode 10 Ground electrode 11 Ion beam Bf Filament magnetic field Bs External magnetic field

Claims (2)

[Claims] 1. A partition wall connected to the positive electrode side of an arc power supply,
In a Freeman ion source for generating plasma by generating an arc discharge by a potential difference with a filament connected to the negative electrode side of an arc power source, the partition wall forms a low arc voltage discharge chamber accommodating the filament, and a passage hole It comprises a discharge chamber partition wall having a side wall and a main arc chamber partition wall forming a main arc chamber that is in communication with the passage hole, and the discharge chamber partition wall and the main arc chamber partition wall are in an insulating state. The Freeman ion source is characterized in that the discharge chamber partition is connected to the arc power source through a resistor. 2. The filament has a pair of rod-shaped portions whose axial directions coincide with each other, and is arranged such that the filament magnetic field between the rod-shaped portions is in the passage hole direction. Freeman ion source described.