JPH0617097U - Plasma electrode reflector mounting structure - Google Patents

Abstract

(57) [Abstract] [Purpose] In an ion source that uses metal vapor as an ion beam, a reflector is provided along the inside of the chamber. This is because it reflects the radiation. Conventionally, a reflector that is fixed to the plasma electrode has a bolt screwed into the female screw hole of the electrode mounting plate from the through hole of the reflector. Since the bolt has a higher temperature than the female screw hole and undergoes larger thermal expansion, seizure is more likely to occur. The purpose is to prevent burn-in. [Structure] A hole is formed in the electrode mounting plate, and the head of the bolt is fixed to the hole. Insert the reflector hole through the male thread of the bolt,
Secure the reflector by screwing the nut into the male screw hole. No seizure occurs because the nut expands more than the bolt.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to a structure for fixing a reflector of an ion source to a plasma electrode. The ion source introduces a gas into the inside and excites it into plasma by arc discharge between the filament and the chamber, high frequency plasma discharge, microwave discharge, etc., and the ion beam is generated by the action of the electric field of the extraction electrode. It is something that is pulled out to the outside. Those that are gases at room temperature do not need to be so hot.

However, in recent years, ion beams such as metals that are solid at room temperature have been required. Si, Al, Cr, P and the like. Ion beams may be formed by plasmaizing these compounds that are gases. However, in this case, a large amount of unnecessary ions are generated, so mass separation must be performed. In order to omit the mass separation mechanism, a solid simple substance must be used as a raw material from the beginning. The solid raw material is heated to a high temperature to form vapor, which is then introduced into the ion source to form plasma. Heat confinement is important in such ion sources.

A permanent magnet is provided on the outer wall of the chamber. This is to form a cusp magnetic field and confine the plasma inside the chamber. The outer wall of the chamber is cooled by flowing water so that the permanent magnets are not demagnetized. Therefore, the temperature of the wall surface of the chamber is low. Therefore, in the case of an ion source that requires a high temperature, a member that reflects radiant heat may be provided along the inner wall of the chamber. This is a stack of several thin plates of Mo, Ta or W. It is called a radiation shield, a reflector, or a reflector. Here, a reflector is used. The present invention relates to a novel structure for fixing a reflector to a plasma electrode.

[0004]

[Prior art]

 FIG. 5 shows a simplified cross section of the ion source. The ion source chamber 1 is a space that can be evacuated. It consists of a cylindrical part and a lid plate part at the end. A plurality of filaments 8 are provided through the cover plate portion. This is an electron emitting filament at cathode potential and a reflector heating filament at anodic potential. Chamber 1 is at anodic potential. The electron emitting filament itself is energized to generate thermoelectrons. This is attracted to the electric field of the chamber 1 and accelerated. The accelerated electrons collide with the introduced gas molecules and become ionized. This is the excitation of plasma by arc discharge. Besides that, there are various means of excitation. Although the ion source chamber by arc discharge is shown here, the present invention can also be applied to ion sources having other excitation methods.

A permanent magnet 9 is provided along the outer wall of the chamber 1. This forms a cusp magnetic field to confine the plasma 10 in the center of the inside. A plasma electrode 4 having a plurality of ion through holes is provided on the outlet side. Outside this, a negative electrode and a ground electrode having holes at the same position are further provided, but they are not shown because they are irrelevant to the present invention. When the metal vapor or the like is used as the ion beam, the reflectors 6, 7, 11 are provided along the inner surface of the chamber wall. These are made by stacking a plurality of thin plates of Ta, Mo, W and the like. This is called dimple processing, and small projections are formed on the plate. This is because the plates do not come into surface contact with each other, increasing the probability of reflection of radiation and reducing the loss due to conduction. The greater the number, the higher the reflectance.

The reflector is provided so as to surround a space where plasma exists. A disk-shaped end reflector 11 is provided near the filament. A side reflector 7 is provided along the inner circumference of the chamber 1. Further, a plasma electrode reflector 6 is provided just inside the plasma electrode 4. This reflector is a plate with a wide opening in the center. The central part serves as an ion outlet.

The fixing structure of this is shown in FIG. An enlarged cross-sectional view of only the fixed portion is shown in the figure. The cooling flange 2 is fixed to the flange at the end of the chamber 1 via an insulator 12. An electrode mounting plate 3 is fixed to the cooling flange 2 with bolts (not shown). The central portion of the electrode mounting plate 3 is a porous plasma electrode. This is, for example, a Mo plate with many holes processed. The plasma electrode reflector 6 is fixed by the bolt 5. Several through holes 13 are drilled along the periphery of the reflector 6. Further, female screw holes 14 are bored in corresponding positions of the electrode mounting plate 3.

The bolt 5 is passed through the through hole 13 from the reflector 6 side, and is further screwed into the female screw hole 14 of the electrode mounting plate 3. As mentioned above, since the reflector is dimple-processed, the plates do not adhere to each other even if they are pressed with bolts. For the electrode plate and the bolt, stainless steel, molybdenum, tantalum, carbon, etc. are used depending on the operating temperature. This is a simple fixed format. This type of fixing is always used when fixing a thin plate to a surface. But this still has its drawbacks.

[0009]

[Problems to be solved by the device]

 The flange 2 to which the electrode mounting plate is fixed is cooled. It is exposed to the outside and must be cooled for safety. It must also be cooled to protect the seal material such as the O-ring. On the other hand, however, the central space where plasma exists is in a high heat state. Regarding the temperature distribution of the bolt 5 fixing the reflector 6 and the female screw hole 14, the head of the bolt near the plasma becomes hot. This heat is transmitted and the legs of the bolt become hot. It expands because it is hot.

However, since the female screw hole 14 of the electrode mounting plate 3 is mounted on the electrode mounting plate 3, the temperature is lower. Therefore, the female screw hole 14 does not expand so much. Since the bolt 5 therein expands and the female screw hole 14 does not expand so much, the thermal stress becomes excessive. It may cause burn-in. Even if the bolt is stuck in the female screw hole 14 and returned to low temperature, it cannot be rotated and cannot be removed. In order to avoid this, it is an object of the present invention to provide a reflector mounting structure in which the bolt does not burn.

[0011]

In the reflector mounting structure of the present invention, a hole is formed in an electrode mounting plate, and a bolt head is fixed to the hole so that a male screw portion of the bolt penetrates a through hole of the reflector. , The nut is screwed on the opposite side of the reflector to the male screw part of the bolt to fix the reflector. The head of the bolt and the hole of the electrode mounting plate are permanently fixed by, for example, caulking. Insert the reflector into the male thread of the bolt and tighten the nut to fix the reflector.

[0012]

[Action]

 The male screw part of the bolt and the nut are screwed together, and the nut holds down the reflector. It is the male thread of the bolt and the nut that make contact with the plasma. This part is strongly ignited by the heat of the filament and the heat of discharge. On the other hand, the bolt head is fixed to the hole of the electrode mounting plate. It is not necessary to remove the bolts to replace and repair the electrodes, just remove the nut.

Advantageously, this construction tends to heat the nut and the bolt to cool from the electrode mounting plate. The nut expands more and exceeds that of the bolt. Since the nut is on the outside and the bolt is on the inside, such thermal expansion tends to separate the inner and outer members more. As a result, there is no possibility of burn-in caused by heating. The electrode plate can be easily removed at the time of repair or replacement.

[0014]

【Example】

 FIG. 1 is a partial sectional view of an ion source showing an embodiment of the present invention. FIG. 2 is an enlarged cross-sectional view of only the reflector connecting portion by the bolt. A cooling flange 2 is fixed to the end of the ion source chamber 1 via an insulator 12. This is an O-ring, square ring, etc. Since it is an insulator, it fulfills the two functions of electrical insulation and vacuum sealing. A permanent magnet 9 is provided on the outer periphery of the chamber 1 to form a magnetic field for plasma confinement. The side reflector 7 is simply fitted inside the chamber 1.

Near the plasma electrode is another reflector 6. A deceleration electrode and a ground electrode are provided outside the plasma electrode, but they are omitted here. The plasma electrode reflector 6 is fixed by a bolt 15 having no enlarged diameter portion at its tip. A part of the bolt 15 is a male screw portion 16. The head does not have a diametrical expansion and has a smooth circumferential surface. Insert the head of the bolt into the hole 17 of the electrode mounting plate from the direction of the reflector. Since the hole is smaller, it is necessary to hit the bolt to insert it. In this way, the male screw portion 16 has a structure projecting to the side where the reflector is provided. Insert the reflector through hole 13 into the male thread 16 of the bolt. Further, the nut 18 is screwed into the male screw portion 16 to fix the reflector. When the nut is tightened, the reflector 6 is pressed against the electrode mounting plate 3, and since the dimple processing is performed as described above, a gap remains between the reflector and between the reflector and the electrode mounting plate. This is to prevent the heat conduction and reflect the radiation by making the reflectors point-to-contact with each other.

In such a fixed structure, when the inside of the chamber is strongly heated, the internal space surrounded by the reflector becomes extremely high in temperature. Since the electrode mounting plate 3 is fixedly connected to the cooling flange 2, the head of the bolt 15 has a relatively low temperature, and the leg portion having the male screw is also cooled by this. Since the nut is located at the tip of the bolt closest to the plasma space, the temperature becomes extremely high. Therefore, the nut thermally expands more than the male screw portion of the bolt. This is because both temperatures are different. Then, the gap between the nut and the male thread tends to open wider. The higher the temperature, the wider the voids. Therefore, the bolt and nut will not seize even if the high temperature condition is maintained for a long time, or if the high temperature condition is repeatedly applied. This is because the relationship between the inner and outer members exposed to high heat is reversed.

[0017]

[Effect of device]

 The present invention is characterized by the structure of attaching the reflector on the plasma electrode side to the electrode. The head of the bolt is fixed to the electrode, and the male screw portion is projected to the outside. Insert the reflector through-hole into this male screw part, and screw the nut into the male screw part to fix the reflector. Since the nut is heated most strongly, this causes the largest thermal expansion and the gap between the nut and the bolt expands. Therefore, seizure does not occur between the nut and the bolt at high temperature. Therefore, replacement of the reflector, replacement of the electrodes, and repair do not cause any problems. It has a simple structure, but its practical meaning is not small.

In this example, the head of the bolt is smooth and does not have a diameter-expanded portion, but it may instead have a diameter-expansion head. In this case, it is advisable to make a hole in the electrode so that the expanded head can pass through, and then bolt the bolt. Further, the shape may be such that the diameter of the head is smaller than that of the male screw. In this case, the insertion into the electrode plate is easier.

[Brief description of drawings]

FIG. 1 is a sectional view showing a plasma electrode reflector mounting structure according to an embodiment of the present invention.

FIG. 2 is an enlarged sectional view of FIG.

FIG. 3 is a cross-sectional view showing a plasma electrode reflector mounting structure according to a conventional example.

FIG. 4 is a cross-sectional view showing a plasma electrode reflector mounting structure according to a conventional example.

FIG. 5 is a sectional view showing an example of an ion source.

[Explanation of symbols]

 1 Chamber 2 Cooling Flange 3 Electrode Mounting Plate 4 Plasma Electrode 5 Bolt 6 Plasma Electrode Reflector 7 Side Reflector 8 Filament 9 Permanent Magnet 10 Plasma 11 Edge Reflector 12 Insulator 13 Through Hole 14 Female Threaded Hole 15 Bolt 16 Male Threaded Part 17 Hole 18 nut

Claims (1)

[Scope of utility model registration request] 1. A chamber capable of being evacuated to a vacuum to turn a gas or a metal vapor introduced therein into a plasma by electric discharge, a discharge mechanism for causing an electric discharge inside the chamber, and a plasma electrode provided at an outlet of the ion source chamber. When,
In an ion source including a reflector for reflecting radiant heat provided along the inner wall of the chamber, a hole is bored in the plasma electrode to fix the reflector on the plasma electrode side to the plasma electrode, and a male screw portion is provided inside the chamber. The head of the bolt is fixed to the hole of the plasma electrode so that it faces toward Plasma electrode reflector mounting structure characterized by being pressed.