JP3422196B2 - Ion source - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ion source used in an ion implantation apparatus for implanting impurities into a semiconductor wafer.

[0002]

2. Description of the Related Art FIG. 4 is a cross-sectional view showing a main part of a conventional ion source used in an ion implantation apparatus, 1 is an ion generation chamber, 2 is a wall of the ion generation chamber 1, 3 is a gas inlet, 4 is a filament, 5 is an insulating support, 6 is a filament lot, and 7 is a slit. The chamber wall 2 of the ion generation chamber 1 is made of a conductor such as stainless steel and is set to the ground potential.
The filament 4 is made of a metal such as tungsten formed into a rod shape or a coil shape, and is fixed to the chamber wall 2 of the ion generation chamber 1 via an insulating support 5 and electrically insulated from the chamber wall 2. ing.

The above-mentioned ion source is used in a state where it is incorporated in an ion implantation apparatus set to a predetermined vacuum degree,
Ions are generated by the following mechanism. That is, when the ion generation gas is introduced into the ion generation chamber 1 through the gas introduction port 3 and a voltage is applied to the filament 4 through the filament lot 6, the filament 4 is heated and thermoelectrons are emitted. Here, if the filament 4 is set to a positive potential relative to the chamber wall 2 of the ion generation chamber 1, the thermoelectrons emitted from the filament 4 are accelerated in the direction of the chamber wall 2 and, at the same time, shown in the figure. In response to the force of the applied magnetic field, a circular motion is performed in the ion generation chamber 1 to collide with the gas molecules for ion generation and ionize them to generate ions. The generated ions are extracted to the outside through the slit 7 by an ion extraction electrode (not shown).

[0004]

As described above, the ions generated in the ion generation chamber 1 are extracted to the outside through the slit 7, but the decomposition that occurs when the ion generation gas is ionized by the collision with thermoelectrons. The product remains in the ion generation chamber 1 and adheres to the chamber wall 2 and the surface of the insulating support 5. The residual products in the ion generation chamber 1 are generated by the decomposition of the ion generation gas as described above, and also by thermionic sputtering of the chamber wall 2 of the ion generation chamber 1 or the slit material. Products and the like, which are generally conductive. The amount of residual products increases as the operating time of the ion source increases, so that the surface of the insulating support 5 becomes conductive, and the insulation between the filament 4 and the chamber wall 2 of the ion generating chamber 1 is increased. Is reduced. As a result, the potential between the filament 4 and the chamber wall 2 cannot be maintained, and the thermoelectron emission efficiency decreases, and further, the filament 4 passes through the surface of the insulating support 5 and leaks to the chamber wall 2. A current starts to flow, and the ion generation efficiency is lowered by these factors. Therefore, when using the ion implanter, it is necessary to disassemble the ion source and remove the residual product adhering to the surface of the insulating support 5 every predetermined operating period.

However, in recent years, there are increasing cases in which a large amount of ions are required to be generated due to the demand from the device manufacturing side, and in response to these demands, the flow rate of the ion generating gas is increased or a large current is supplied to the filament. When flushed, the amount of residual product will increase accordingly. Therefore, it is necessary to frequently perform the work of removing the residual product, which causes a problem that the operating rate of the ion source is lowered and the maintenance cost is increased.

The insulating support 5 shown in FIG. 4 comprises a columnar insulating material having a through hole at the center thereof, and the filament 4 is inserted into the ion generating chamber 1 through the through hole. Therefore, the insulation between them is maintained, but since the surface area of the insulating support 5 that separates the filament 4 from the chamber wall 2 is small, the insulation is likely to be deteriorated due to the adhesion of residual products, and the removal work must be performed frequently. I won't. In order to prevent deterioration of insulation due to adhesion of residual products, a method of providing a gap between the filament 4 and the chamber wall 2 of the ion generation chamber 1 without using an insulating support is also used.
According to this method, the insulation can be maintained, but there is a problem that the ion generation gas introduced into the ion generation chamber 1 leaks from the gap and the gas flow rate must be increased so as to compensate for this leak.

Therefore, it has been attempted to prevent deterioration of insulation due to adhesion of residual products by devising the shape of the insulating support 5. 5 (a) and 5 (b) are cross-sectional views showing the structure of a conventionally proposed insulating support. This figure is an enlarged view of a portion corresponding to the area A shown in FIG.
It shows a state in which the filament 4 is fixed to the chamber wall 2 of the ion generating chamber 1 via the insulating support 5. Further, the dotted line shown in the figure represents the region where the residual product is attached. Unevenness is formed on the surface of the insulating support 5 shown in FIG. 5 (a), which increases the effective surface area and increases the surface resistance of the insulating support on which residual products adhere. Therefore, it is possible to delay the progress of insulation deterioration as compared with the insulating support 5 shown in FIG. However, since the amount of the residual product adhering to the surface is not different from the conventional one, a sufficient effect cannot be obtained, and furthermore, there is a problem that the uneven processing of the surface of the insulating support becomes complicated. Therefore, as shown in FIG. 5 (b), it has been proposed to widen the diameter of the end portion of the insulating support 5 to form an eaves shape (Japanese Patent Laid-Open No. 2-312141).
Issue). According to the above configuration, since the thermoelectrons emitted from the filament 4 cannot reach the chamber wall portion that is behind the eaves, this region is not sputtered, and therefore, the thermoelectrons are generated in the chamber wall 2. It is possible to prevent the deterioration of insulation due to the residual formation generated by sputtering. However, it is not possible to prevent the decomposition products of the ion-forming gas from entering the shade portion of the eaves by diffusion, and as a result, as shown in the figure, the residual product penetrates into the shade portion of the eaves. Then, they adhere to each other, and the insulation lowering progresses.

Therefore, an object of the present invention is to maintain the insulation between the filament and the chamber wall of the ion generating chamber with a simple structure.

[0009]

Means for Solving the Problems To solve the above-mentioned problems, an ion generating chamber and a filament electrically inserted into the ion generating chamber and a chamber wall of the ion generating chamber via an insulating support are provided. In an ion source that decomposes gas introduced into the ion generating chamber by applying voltage to the filament to generate ions, the insulating support has a through hole through which the filament penetrates, An opening having a diameter larger than that of the through hole is formed at an end of the insulating support, and a hollow portion having a diameter larger than the opening is formed inside the insulating support so as to be connected to the opening. An ion source characterized by the above, or the above-mentioned ion source characterized in that the insulating support is composed of an individual piece divided through the center of the through hole.

In the above structure, the filament is inserted into the ion generating chamber through the through hole provided in the insulating support.
Then, the residual product generated in the ion generation chamber enters the inside of the insulating support by diffusion through the gap between the opening formed at the end of the insulating support and the filament. Since the diameter of the opening can be narrowed by adjusting the diameter of the opening, it is possible to suppress the amount of the residual product penetrating into the inside of the insulating support to a slight amount. Further, a hollow portion is provided inside the insulating support so as to be connected to the opening, so that the hollow portion becomes a shade for a small amount of residual product that has entered and the adhesion to the inner wall thereof. Will be hindered. That is, the inner wall of the hollow portion can maintain the insulation for a long time. In the conventional example described with reference to FIG. 5 (b), the eaves provided on the insulating support 5 are also shaded to prevent the intrusion of the residual product. Since there is only a small gap between the opening and the filament, the amount of residual product that enters can be reduced as compared with the conventional structure.

[0011]

1 is a cross-sectional view of an ion source showing an embodiment of the present invention, and those having the same functions as those in FIG. 4 are designated by the same reference numerals. The chamber wall 2 of the ion generation chamber 1 is made of a conductor such as stainless steel and is set to the ground potential.
The filament 4 is made of a metal such as tungsten formed into a rod shape or a coil shape, and is fixed to the chamber wall 2 of the ion generation chamber 1 via an insulating support 5 and electrically insulated from the chamber wall 2. ing. The ion source is used by being incorporated inside an ion implanter set to a predetermined vacuum degree, and ions are generated by a mechanism similar to that described in the section of the prior art.

The enlarged view shown in FIG. 1 shows a state in which the filament 4 is fixed to the chamber wall 2 of the ion generating chamber 1 via the insulating support 5. Further, the dotted line shown in the figure shows the region where the residual product is attached to the insulating support 5 and the chamber wall 2 of the ion generating chamber 1. As shown in the figure, a through hole 51 is formed in the insulating support 5 through its center, and the filament 4 is inserted into the ion generating chamber 1 through the through hole 51. An opening 52 having a diameter larger than that of the through hole 51 is formed at the end of the insulating support 5, and the opening 52 is formed inside the insulating support 5.
A hollow portion 53 having a diameter larger than that of the opening 52 is formed adjacent to. Residual products generated along with the generation of ions in the ion generation chamber 1 adhere to the outer surface of the insulating support 5 and the side surface of the opening 52, and further, the filament 4 and the opening.
It also penetrates into the inside of the insulating support 5 through the gap between 52. However, by setting the diameter of the opening 52 to be a value slightly larger than the diameter of the through hole 51, the above-mentioned gap can be narrowed, and as a result, the residual product that enters the inside of the insulating support 5 through the gap. The amount of can be suppressed. And
The small amount of the residual product that has entered is further suppressed by the hollow portion 53 provided adjacent to the opening 52 as a shadow and adhering to the inner wall thereof. Therefore, as shown by the dotted line in the figure, the amount of the residual product adhering to the inner wall of the hollow portion 53 is significantly smaller than in the conventional case, and the insulation is retained by the inner wall of the hollow portion 53. Become.

2 (a) and 2 (b) show a method of processing the insulating support 5 used in this embodiment. First, the same figure (a)
As shown in (1), alumina powder is molded into a stepped columnar shape using a mold, and a through hole 51 for inserting a filament is formed through the center thereof. Then, the diameter of the through hole 51 at the end of the columnar insulator thus formed is slightly widened to form the opening 52. Further, the threaded portion 54 is formed by performing die processing on the outer peripheral portion of the cylindrical insulator. Then, the columnar insulating material is divided into two through the center of the through hole 51 at the position shown by the alternate long and short dash line in the figure. Then, as shown in FIG. 7B, the hollow portion 53 is formed by grooving the region adjacent to the opening 52 for each of the divided pieces.
To form. FIG. 3 (a) is a perspective view showing the divided individual pieces of the insulating support formed as described above. When the insulating support is attached to an ion source, as shown in FIG. 3 (b). To
The divided pieces are used in the assembled state. By dividing the insulating support into two, the hollow portion 53 can be easily processed, and the cleaning operation for removing a slight amount of the residual product adhering to the inner wall of the hollow portion 53 can be facilitated. Further, since the insulating support 5 can be fixed to the chamber wall 2 of the ion generating chamber 1 by the screw portion 54, the insulating support 5 can be easily attached to the chamber wall 2 and the airtightness of the ion generating chamber can be maintained. It will also be easy.

[0014]

As described above, according to the present invention, the insulation between the ion generating chamber and the filament can be maintained for a long period of time due to the shape of the insulating support, so that the life of the ion source can be made longer than in the conventional case. This is useful for simplifying the maintenance work of the ion implanter and improving the reliability.

[Brief description of drawings]

FIG. 1 is a sectional view of an ion source showing an embodiment of the present invention.

FIG. 2 is a sectional view showing a method for processing an insulating support.

FIG. 3 is a perspective view showing an insulating support.

FIG. 4 is a sectional view showing a conventional ion source.

FIG. 5 is a cross-sectional view showing the structure of a conventional insulating support.

[Explanation of symbols]

1 Ion generation chamber 7 Slit 2 Room wall 51 Through hole 3 Gas inlet 52 Opening 4 filament 53 hollow part 5 Insulation support 54 Thread 6 filament lot

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Claims (2)

(57) [Claims] 1. An ion generation chamber and a filament electrically inserted between the ion generation chamber and a chamber wall of the ion generation chamber via an insulating support, and a voltage is applied to the filament. In the ion source for decomposing the gas introduced into the ion generating chamber to generate ions, the insulating support is formed with a through hole through which the filament penetrates, and the insulating support is provided with a through hole at an end thereof. An ion source, wherein an opening having a diameter larger than that of the hole and a hollow portion having a diameter larger than that of the opening are formed inside the insulating support so as to be connected to the opening. 2. The ion source according to claim 1, wherein the insulating support is composed of individual pieces divided through the center of the through hole.