JPH11339674A - Ion source - Google Patents

Abstract

PROBLEM TO BE SOLVED: To lengthen a stable operating time of an ion source, by making it unlikely to have a dielectric breakdown between both insulating materials caused by a conductive dirty film adhered to a peripheral surface exposed in a plasma generating container forming the two insulating materials for a filament. SOLUTION: In this ion source, a grid-shaped groove 34 is severally provided on the peripheral surface of each insulating material 24a inside a plasma generating container 2 forming two insulating materials 24 for a filament 8. A dirty conductive film is unlikely to be peeled off from the peripheral surfaces of both insulating materials 24a by this grid-shaped groove 34, and a small piece is peeled off when peeled off, and therefore a dielectric breakdown caused by the dirty film is unlikely to occur between both insulating materials 24a, and a stable operating time of the ion source can be lengthened.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ion source having a structure in which a filament having a shape bent back in the original direction, for example, a U-shape, is provided in a plasma generation vessel. The present invention relates to means for making it difficult for dielectric breakdown between two insulators for a filament or the like to occur due to a dirty film, and for extending the stable operation time of an ion source.

[0002]

2. Description of the Related Art An example of this type of ion source is disclosed in, for example, Japanese Patent Application Laid-Open No. 9-35648. Figure 8
This will be described with reference to FIG.

[0003] The ion source is Bernus (Bernu).
s) a type of ion source, which is also provided as a positive electrode, a plasma generating container 2 into which a gas is introduced from a gas inlet 6, and is provided in one side of the plasma generating container 2 through a wall surface thereof. And a reflecting electrode 10 provided in the other side of the plasma generation container 2 so as to face the filament 8.
And The plasma generation container 2 is made of a metal, more specifically, a high melting point metal such as molybdenum (Mo). In this example, the filament 8 is bent back into a substantially U-shape.

A long ion extraction slit 4 is provided on the wall surface of the plasma generation vessel 2 in a direction along an axis connecting the filament 8 and the reflection electrode 10. Near the outlet of the ion extraction slit 4, an extraction electrode 14 for extracting an ion beam 16 from the inside of the plasma generation container 2 (more specifically, from the plasma 12 generated therein) is provided. A magnetic field generator 18 for generating a magnetic field B in a direction along the axis is provided outside the plasma generation container 2.

The orientation of the filament 8 is shown in FIG. 8 for the sake of convenience to clarify the connection with the filament power supply 20. In practice, as shown in FIGS. It is arranged so that the surface including the filament 8 bent in a shape substantially parallel to the ion extraction slit 4.

As shown in FIG. 8, a filament power supply 20 for heating the filament 8 is connected to both ends of the filament 8. Between one end of the filament 8 and the plasma generation container 2, an arc power supply 22 for generating an arc discharge between the two is connected with the former being the negative electrode side. The output voltage of the filament power supply 20 is, for example, 3
The output voltage of the arc power supply 22 is about 100 V, for example.

In order to insulate the voltage applied to the filament 8, the filament 8 (specifically, its two legs 8 a and 8 b) penetrates the plasma generation vessel 2, and the filament 8 and the plasma generation Two generally cylindrical or cylindrical insulators 24 are provided to electrically insulate the container 2 from the container 2. In this example, as shown in FIG. 9, each insulator 24 is composed of two generally columnar or cylindrical insulators 24 a and 24 b fitted together from inside and outside with the wall of the plasma generation container 2 interposed therebetween. I have. At the center of both insulators 24a and 24b, there is provided a conductor 28 for penetrating the filament 8 and holding it. The conductor 28 is also made of a metal, more specifically, a high melting point metal such as molybdenum.

[0008] On the outer peripheral surface of each insulator 24 exposed inside the plasma generation container 2, specifically, in this example, on the outer peripheral surface of each insulator 24a inside the plasma generation container 2, the filament 8 and the plasma are provided. In order to increase the creepage distance with the generation container 2 and improve the dielectric strength between the two, a ring-shaped groove 26 is formed on the axis of the insulator 24 (that is, the filament 8).
). The dimension ratio between the peaks and valleys of the groove 26 is approximately 1: 1.

The reflective electrode 10 has a substantially cylindrical shape in this example, and is attached to the plasma generation vessel 2 via an insulator 30 having a substantially cylindrical shape. This reflection electrode 10
Has a function of repelling electrons emitted from the filament 8, and may be set to a floating potential without being connected to anywhere as in the example shown in FIG. 8, or may be connected to the filament 8 and fixed at the filament potential. You may. Even at a floating potential, light and high mobility electrons in the plasma 12 are incident on the reflective electrode 10 far more than ions, and are charged to a negative potential. Has the effect of repelling.

If such a reflective electrode 10 is provided,
The electrons emitted from the filament 8 are reflected by the filament 8 while rotating around the magnetic field B under the action of the axial magnetic field B applied in the plasma generation container 2 and the electric field perpendicular thereto. As a result, the electrons reciprocate with the electrode 10, and as a result, the probability of collision between the electrons and the gas molecules increases, the ionization efficiency of the gas increases, and a high-density plasma 12 is generated in the plasma generation container 2. be able to.

[0011]

When the operation of the ion source is continued, a thin conductive film adheres to the portion exposed in the plasma generation vessel 2. The contaminated film is, for example, a film generated by decomposing a gas introduced into the plasma generation container 2, or a film generated by a reaction between the gas and a metal constituting the plasma generation container 2 or the like. More specifically, in order to extract a boron ion beam, boron fluoride (B
When the F ₃ ) gas is introduced, a conductive dirt film is generated in which the fluorine reacts with, for example, molybdenum constituting the plasma generating vessel 2.

Here, paying attention to the two insulators 24a on the left and right exposed in the plasma generation vessel 2, the dirt film naturally adheres also to the outer peripheral surfaces thereof. When the operating time of the ion source is prolonged and contamination proceeds, the contamination film is partially peeled off due to thermal strain or the like. When it comes off,
Normally, the film is peeled up while keeping the state of the thin film.

However, when the filament 8 bent back in the original direction is used as in this ion source, the two insulators 24a on the left and right sides have to be arranged very close to each other. For example, the gap G ₁ between the two insulators 24a (see FIG. 9) is only about 3 mm. As shown in FIG. 10, the peeled dirt film 32 is connected (bridged) between the two insulators 24a, and the insulation between the two insulators 24a may be broken.

Further, as the contamination progresses, the outer peripheral surface of each insulator 24a is at the potential of one end of the filament 8 via the conductive dirt film remaining without peeling, and the potentials are different from each other. . Since the portions having different potentials are connected by the dirt film 32 peeled off as described above, as a result, electrical insulation between both ends of the filament 8 cannot be maintained. As a result, for example, the left and right insulators 24a are electrically short-circuited through the peeled dirt film 32. Then, the filament 8 cannot be stably energized and heated, and the ion source cannot be operated stably.

Accordingly, the present invention is to reduce the occurrence of dielectric breakdown between the two insulators due to a conductive dirt film attached to the outer peripheral surface of the two insulators for the filament which is exposed in the plasma generation vessel. The main purpose is to increase the stable operation time of the source.

[0016]

The ion source according to the present invention comprises:
A lattice-shaped groove is provided on the outer peripheral surface of the two insulators exposed in the plasma generation container.

With such a structure, the dirt film adhering to the outer peripheral surface of the insulator naturally adheres also to the lattice-shaped grooves. The film attached in this groove acts as if it were a wedge. In addition, when the grooves are formed in a lattice shape (that is, vertical and horizontal grooves), the action of a wedge is stronger as compared with the conventional ring-shaped grooves (that is, only horizontal grooves) because the vertical grooves exist. Become. Therefore, the dirt film attached to the outer peripheral surface of the insulator is less likely to be peeled off.

Further, even when the dirt film is peeled off from the outer peripheral surface of the insulator, the size of the dirt film to be peeled is smaller than that of a conventional ring-shaped groove because the grooves have a lattice shape. This is because the dirt film is thinner at the lattice-shaped groove or at the corner of the groove than at the peak, and when the dirt film is peeled off, it is cut at the thinned portion. This is because a soil film having a size corresponding to the minute is easily generated, whereas a band-shaped soil film long in the circumferential direction is easily generated in the case of the conventional ring-shaped groove.

As described above, according to the present invention, the conductive dirt film is less likely to be peeled from the outer peripheral surfaces of the two insulators for the filament, and if it is peeled, it is peeled with a small size. This makes it difficult for insulation breakdown to occur during the operation, and the stable operation time of the ion source can be extended.

[0020]

FIG. 1 is a sectional view showing an example of an ion source according to the present invention as viewed from an ion beam extraction direction. FIG. 2 is an enlarged view showing the periphery of a filament insulator in FIG. 8 and 9 are denoted by the same reference numerals, and differences from the conventional example will be mainly described below.

In this embodiment, each of the two insulators 24 for the filament 8 is formed on the outer peripheral surface of the two insulators 24 exposed in the plasma generation vessel 2, specifically, in this embodiment, each insulator 24 is formed. On the outer peripheral surface of each insulator 24a inside the plasma generating container 2 is provided a vertical and horizontal lattice-like groove 34, respectively.

The width of the lattice-shaped groove 34 is, for example, 0.2 m.
For example, the depth is set to about 0.3 mm. If the width of the groove is too large, the above-mentioned dirt film adhering thereto becomes large and easily peeled off. Therefore, it is preferable to make the width as narrow as possible. For example, the thickness is preferably 0.5 mm or less.

The vertical and horizontal dimensions of each section surrounded by the lattice-shaped groove 34, that is, each mountain portion 35 (see FIG. 2) influences the size of the dirt film to be peeled off. preferably below the aforementioned dimensions of the gap G ₁ was between. In this example, as an example, the size of the mountain portion 35 is set to 2
mm square.

With such a structure, the above-described conductive dirt film adhering to the outer peripheral surface of the insulator 24a naturally adheres to the inside of the lattice-shaped groove 34. The film adhered in the groove 34 acts as if it were a wedge. Moreover, when the grooves 34 are formed in a lattice shape (that is, vertical and horizontal grooves), compared with the conventional ring-shaped groove 26 (that is, only the horizontal grooves), since the vertical grooves are present, an action like a wedge is provided. Becomes stronger. Therefore, the dirt film attached to the outer peripheral surface of the insulator 24a is less likely to be peeled off.

Further, even when the dirt film is peeled off from the outer peripheral surface of the insulator 24a, since the grooves 34 are formed in a lattice shape,
As compared with the conventional ring-shaped groove 26, the size of the soiled film to be peeled is smaller. This is because the dirt film is thinner at the lattice-shaped groove 34 or at the corners of the groove 34 than at the peak 35, and when the dirt film comes off, it is cut at the thinned portion. Is more likely to form a dirt film equivalent to one section, that is, a size equivalent to a mountain portion 35, whereas the conventional ring-shaped groove 26 has an insulator 24.
This is because a long strip-shaped dirt film is likely to be generated in the circumferential direction of a.

As described above, according to this ion source, the conductive dirt film is less likely to be peeled off from the outer peripheral surfaces of the two insulators 24a for the filament 8, and if it is peeled, it is peeled with a small size. Both insulators 24
The dielectric breakdown between “a” is less likely to occur, and the stable operation time of the ion source can be extended.

The lattice-shaped grooves 34 need not necessarily be perpendicular to each other in the vertical and horizontal directions as in the examples shown in FIGS. 1 and 2. For example, as shown in FIGS. It may be crossed. Further, a configuration in which a lateral groove passing through the intersection point is further added to the groove 34 in FIG. 4 may be used.

Each insulator 24 does not necessarily need to be composed of two insulators 24a and 24b as in the above example. For example, it may be composed of a columnar or cylindrical insulator integrated inside and outside. In this case, the above-described lattice-shaped groove 34 is provided on the outer peripheral surface exposed in the plasma generation vessel 2. good.

The inner insulator 24a may be divided into two cylindrical insulators 241a and 242a as shown in FIG. 5, for example. The above-described lattice-shaped groove 34 may be provided on the outer peripheral surface of the outer insulator 241a exposed inside.

Incidentally, the conductive dirt film may adhere to the reflection electrode 10 provided in the plasma generation container 2 and peel off. In that case, the conventional reflective electrode 1
Since the outer peripheral surface of No. 0 is a smooth curved surface as shown in FIG. 9, the dirt film is relatively large and easily peels off. In addition, the outer peripheral surface of the reflection electrode 10 and the plasma generation vessel 2
Often configured very close to the wall of
The gap G ₂ between the _two (see FIGS. 9 and 10) is usually only about 3 mm. Therefore, in the related art, as shown in FIG. 11, for example, the peeled dirt film 32 connects the reflective electrode 10 and the plasma generation container 2, and the insulation between them may be broken. In this case, the potential of the reflective electrode 10 cannot be maintained normally, so that the reflective electrode 10 does not perform the above-described electron reflection function, the density of the plasma 12 decreases, and the amount of the extracted ion beam 16 decreases. For example, only a beam current of about 30% of a normal state can be obtained. Therefore, the ion source cannot be operated stably.

In order to solve this problem, a grid-like groove 36 similar to the above-described grid-like groove 34 is provided on the outer peripheral surface of the reflective electrode 10 as shown in FIG. preferable.

The vertical and horizontal dimensions of each section surrounded by the lattice-shaped groove 36, ie, each mountain portion 37, are determined by the lattice-shaped groove 34.
For the same reason as in the case of, preferably below the dimensions of the gap G ₂ between the reflective electrode 10 and the plasma generating chamber 2.

The above-described lattice-shaped groove 3 is formed in the reflection electrode 10.
If the conductive dirt film 6 is provided, the conductive dirt film is less likely to be peeled off from the outer peripheral surface of the reflective electrode 10 for the same reason as in the case of the lattice-shaped groove 34, and if it is peeled off, it is peeled with a small dimension. Dielectric breakdown between the reflective electrode 10 and the plasma generation container 2 due to the film is less likely to occur, and for this reason, the stable operation time of the ion source can be extended.

As shown in FIGS. 6 and 7, for example, a boron-containing plate 38 may be provided in the plasma generation vessel 2 so as to cross the filament 8. The boron-containing plate 38 is attached to the plasma generation vessel 2 and has the same potential as that. The boron-containing plate 38 has two holes 40, and the holes 40
Penetrate through a gap G ₃ (see FIG. 7) for electrical insulation. This boron-containing plate is made of, for example, boron nitride (B
N) A plate.

The reason for providing such a boron-containing plate 38 is as follows. That is, for example, a gas containing boron (B), phosphorus (P), or arsenic (As) is introduced into the plasma generation container 2 to inject impurities into a semiconductor, and a plasma 12 thereof is generated to generate boron, phosphorus or When extracting the ion beam 16 containing arsenic, it is generally more difficult to extract more boron ions than when extracting phosphorus ions or arsenic ions. This is generally true regardless of the type of ion source. On the other hand, when the boron-containing plate 38 as described above is provided, arc discharge between the plate 38 and the filament 8 and the plasma 12
By sputtering the boron-containing plate 38 with the ions therein, the boron ions jump out of the boron-containing plate 38 and the plasma 12 contains a large amount of boron ions, so that a large amount of boron ions can be extracted.

However, the above-mentioned conductive dirt film may adhere to the surface of the boron-containing plate 38 and come off. In this case, if the surface of the boron-containing plate 38 is a smooth flat surface, the dirt film tends to peel off with a relatively large size. The peeled dirt film forms, for example, a gap G at the hole 40.
_{When 3} is connected, the insulation between the filament 8 and the boron-containing plate 38 and thus the plasma generating vessel 2 at the same potential is broken. In such a case, an arc discharge for generating the plasma 12 cannot be normally generated in the plasma generation container 2, so that the ion source cannot be operated stably.

In order to solve this problem, for example, as shown in FIGS. 6 and 7, two opposing surfaces 38a and 38b of the boron-containing plate 38 are also formed in the same manner as the lattice-shaped grooves 34. It is preferable to provide a lattice-shaped groove 42.

The vertical and horizontal dimensions of each section surrounded by the lattice-shaped groove 42, that is, each mountain portion 43 (see FIG. 7), are the same as those in the case of the lattice-shaped groove 34. preferably the to the following dimensions of the gap G _3.

If the lattice-shaped grooves 42 as described above are provided in the boron-containing plate 38, the surface 38a, 3
8b, the conductive dirt film is hardly peeled off, and when it is peeled off, it is peeled off with a small size, so that dielectric breakdown between the filament 8 and the boron-containing plate 38 due to the dirt film hardly occurs. The stable operation time can be extended.

[0040]

Since the present invention is configured as described above, it has the following effects.

According to the first aspect of the present invention, the conductive dirt film is less likely to be peeled from the outer peripheral surface of the two insulators for the filament which are exposed in the plasma generation container. Since the film is peeled off, dielectric breakdown between the insulators due to the dirt film is less likely to occur, and the stable operation time of the ion source can be extended.

According to the second aspect of the present invention, even when the above-described reflective electrode is further provided in the plasma generation container, the conductive dirt film is hardly peeled off from the outer peripheral surface of the reflective electrode. When the film is peeled, the film is peeled in a small size, so that dielectric breakdown between the reflection electrode and the plasma generation container due to the dirt film is less likely to occur, and for this reason, the stable operation time of the ion source can be extended.

According to the third aspect of the present invention, even when the above-mentioned boron-containing plate is further provided in the plasma generation container, the conductive dirt film is hardly peeled off from the surface of the boron-containing plate, In addition, when the film is peeled, the film is peeled in a small size, so that the dielectric breakdown between the filament and the boron-containing plate due to the dirt film hardly occurs. For this reason, the stable operation time of the ion source can be prolonged.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an example of an ion source according to the present invention as viewed from an ion beam extraction direction side.

FIG. 2 is an enlarged view showing a periphery of a filament insulator in FIG. 1;

FIG. 3 is a view showing another example of a lattice-shaped groove provided on the outer peripheral surface of an insulator for a filament.

FIG. 4 is a view showing still another example of a lattice-shaped groove provided on the outer peripheral surface of a filament insulator.

FIG. 5 is a sectional view showing an example of an insulator having a divided structure for a filament.

FIG. 6 is a cross-sectional view partially showing another example of the ion source according to the present invention when viewed from an ion beam extraction direction side.

FIG. 7 is a sectional view taken along the line CC of FIG. 6;

FIG. 8 is a cross-sectional view showing an example of a conventional ion source viewed from the side.

FIG. 9 is an enlarged cross-sectional view of the periphery of a plasma generation container of the ion source of FIG. 8 as viewed from the ion beam extraction direction.

FIG. 10 is a sectional view taken along the line AA in FIG. 9;

FIG. 11 is a sectional view taken along line BB in FIG. 9;

[Explanation of symbols]

 Reference Signs List 2 Plasma generation container 8 Filament 10 Reflecting electrode 24, 24a, 24b Insulator 34, 36, 42 Grid-shaped groove 38 Boron-containing plate

Claims (3)

[Claims] 1. A plasma generating container which also serves as an anode and into which gas is introduced, and a filament which is provided in one side of the plasma generating container and penetrates its wall surface and is bent back in the original direction. And two insulators provided at a portion where the filament penetrates the wall surface of the plasma generation container and electrically insulating the filament and the plasma generation container from each other. An ion source, wherein lattice-shaped grooves are provided on the outer peripheral surface exposed in the container. 2. A plasma processing apparatus further comprising: a reflection electrode provided on the other side of the plasma generation vessel and maintained at a filament potential or a floating potential, and a grid-like groove provided on an outer peripheral surface of the reflection electrode. The ion source according to claim 1. 3. The plasma generation vessel is provided so as to cross the filament, wherein the two holes are penetrated by the filament with a gap therebetween,
3. The ion source according to claim 1, further comprising a boron-containing plate having the same potential as that of the plasma generation vessel, wherein two opposing surfaces of the boron-containing plate are provided with lattice-shaped grooves, respectively.