JPH0423372B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a gas phase ion source suitable for use in an ion beam device such as an ion beam lithography device, and particularly to a gas phase ion source suitable for use in an ion beam device such as an ion beam lithography device. This provides a gas phase ion source that can be used.

[Prior Art] Recently, ion beam devices using gas phase ion sources have been developed.

This gas phase ion source is an ion source that supplies, for example, helium gas to an emitter tip formed with a sharp tip, and ionizes helium gas molecules by ionizing them using a strong electric field.

In such an ion source, in order to apply a high voltage to the emitter and increase the beam current, it is necessary to cool the emitter to about 4 mm.
Therefore, a structure as shown in FIG. 2 has been developed.

In Figure 2, 1 is the outer wall of the ion source whose interior is kept in a high vacuum, 2 is a tank filled with a refrigerant, such as liquid helium 3, and the edge of the opening 4 formed at the top of the outer wall 1 of the ion source is made of stainless steel. It is supported in a thermally insulated state through bellows 5 made of aluminum. Reference numeral 6 denotes an electrically insulating material having high thermal conductivity, such as sapphire, which is fixed to the bottom of the tank 2, and an emitter 8 having a sharp tip is held in the center of the bottom of the sapphire via a holder 7. There is. Reference numeral 9 denotes an extraction electrode disposed opposite to the emitter 8, and an ion passage hole 9a is formed in the center thereof. is supported by Reference numeral 11 denotes a pipe for introducing, for example, helium gas into the vicinity of the emitter 8. 12 is a supply pipe for supplying liquid helium into the tank 2, and 13 is a discharge pipe for discharging the helium gas vaporized within the tank 2 to the outside. Reference numeral 14 denotes a lid for closing the opening 4, and is made of a heat insulating material.

By doing so, the emitter 8 is electrically insulated by the sapphire 6 from the ion source outer wall 1 and the tank 2 which are at ground potential, and at the same time is cooled through the sapphire. Therefore, this Emitsuta 8
Helium gas is emittered from the pipe 11 while applying a constant accelerating voltage of several hundred KV from an accelerating power source not shown, and applying an extraction voltage of about several tens of KV between the emitter 8 and the extraction electrode 9. When supplied nearby, helium gas molecules adhere to the tip of the emitter 8, and the attached gas molecules are ionized by the strong electric field between the emitter and the extraction electrode. Ions generated by this ionization are extracted by an extraction voltage and simultaneously accelerated toward an anode (not shown) by an accelerating voltage.

[Problems to be Solved by the Invention] By using saphire as described above, it is possible to cool the emitter, which is maintained at a high voltage, while the emitter is electrically insulated from the earth potential tank. However, since the saphire is interposed between the tank and the emitter, the cooling efficiency is poor, it takes time to cool the emitter to the liquid helium temperature, and a temperature gradient occurs. is also unavoidable.

SUMMARY OF THE INVENTION The present invention has been made in view of this problem, and it is an object of the present invention to provide a gas phase ion source that can efficiently cool an emitter with a simple configuration.

[Means for Solving the Problems] In order to achieve the above object, the present invention includes an emitter to which a high voltage is applied, a tank filled with a refrigerant inside to cool the emitter, and a tank facing the emitter. an extraction electrode arranged and to which an extraction voltage is applied between the emitter and the emitter; a means for supplying ionized gas to the emitter and its surrounding area;
In a gas phase ion source, the bottom of the tank is formed of a conductive material and has a length equal to or longer than the dielectric strength distance of the refrigerant corresponding to the high voltage applied to the emitter. The bottom of the tank is insulated from the surroundings by configuring a part of the tank with an electrical insulator having The feature is that the emitter is fixed through a holder.

Hereinafter, embodiments of the present invention will be explained in detail based on the drawings.

[Embodiment] FIG. 1 is a schematic configuration diagram showing an embodiment of the present invention, and the same reference numerals as in FIG. 2 indicate the same components.

That is, in this embodiment, the tanks 2 are numbered 2a and 2b.
The tanks 2a and 2b are divided into two in the vertical direction as shown in FIG. The holder 7 holding the emitter 8 is directly fixed to the bottom of the tank 2b which is electrically insulated.

By doing so, the emitter can be held in the tank portion that is insulated from the ion source outer wall 1. Therefore, the emitter 8 (holder 7) is cooled directly with liquid helium without being cooled via saphire as in the conventional case, so that the emitter can be cooled to the liquid helium temperature.

By the way, since the tank 2b is electrically connected to the ion source outer wall 1 via the liquid helium 3, it is necessary to prevent dielectric breakdown due to this.
Therefore, by selecting the height of the insulator 15 to a length that allows the liquid helium to withstand the high voltage (acceleration voltage) applied to the emitter 8, dielectric breakdown due to the liquid helium is prevented. Here, the dielectric strength of liquid helium is about 20 KV/mm, so if the accelerating voltage is 100 KV, the insulation of liquid helium against the accelerating voltage (100 KV) can be maintained by making the length of the insulator 15 5 mm or more.

At this time, it goes without saying that when selecting the length and shape of the insulator, consideration must be given to the creeping distance so as to prevent dielectric breakdown due to creeping discharge of the insulator.

Further, the above description is an example of the present invention, and many modifications can be made in implementing the present invention. For example, in the above embodiment, the insulator 15 for insulating the tank is provided in the middle of the tank, but the present invention is not limited to this. A bellows may be interposed between the insulator and the outer wall), and a tank may be attached to the other end of the insulator.
However, in this case, the entire tank is kept at a high voltage, so there is a risk that it will be more likely to discharge. On this point, if the structure is as shown in Figure 1, only a limited part of the tank will be kept at high voltage.
That worry will go away.

Further, as shown in FIG. 3, the entire side wall of the tank 2 is formed of an insulator 15, and a bottom plate 16 made of a material with high thermal conductivity such as copper is fixed to the lower end of the insulator. The emitter 8 may be attached to the lower surface via the holder 7.

In addition, although the tank is electrically insulated from the outer wall of the ion source using an insulator, electrical insulating materials with high thermal conductivity such as sapphire or alumina may be used, but the invention is not limited to this. You may do so.

[Effects] As detailed above, according to the present invention, the bottom of the tank is generally formed of a conductive member having good thermal conductivity, and the bottom of the tank containing the refrigerant is provided with a conductive material in the optical axis direction. By fixing the emitter through a conductive holder whose vertical surface is larger than that of the emitter and insulating this tank from the surroundings, the cooling efficiency of the emitter is improved, and the emitter can be brought down to liquid helium temperature in a short time. It can be cooled to 100%, and no temperature gradient occurs.

Further, in the present invention, the bottom of the tank is surrounded by an electric insulator having a length equal to or longer than the dielectric strength distance of the refrigerant corresponding to the high voltage applied to the emitter. Since the tank is insulated from the tank, dielectric breakdown caused by the refrigerant filled in the tank can be prevented. As a result, the insulation of the refrigerant against the high voltage applied to the emitter is maintained.

[Brief explanation of drawings]

FIG. 1 is a schematic structural diagram showing one embodiment of the present invention, FIG. 2 is a diagram for explaining a conventional example, and FIG. 3 is a schematic structural diagram showing another embodiment of the present invention. 1: Ion source outer wall, 2: Tank, 3: Liquid helium, 4: Opening, 5: Bellows, 6: Saffire, 7: Holder, 8: Emitter, 9: Extraction electrode,
9a: Ion passage hole, 10: Support cylinder, 11: Pipe, 12: Supply pipe, 13: Discharge pipe, 1
4: Lid body, 15: Insulator.

Claims (1)

[Claims] 1. An emitter to which a high voltage is applied; a tank filled with refrigerant to cool the emitter;
An extraction electrode arranged opposite to the emitter and to which an extraction voltage is applied between the emitter and the emitter, a means for supplying ionized gas to the emitter and its surrounding area, and a vacuum container housing these members. In the gas phase ion source, the bottom of the tank is formed of a conductive member, and the tank is formed by an electrical insulator having a length equal to or longer than the dielectric strength distance of the refrigerant corresponding to the high voltage applied to the emitter. The bottom of the tank is insulated from the surroundings by forming a part of the tank, and the emitter is fixed to the bottom of the tank via a conductive holder whose surface perpendicular to the optical axis direction is larger than that of the emitter. A gas phase ion source featuring: