JP2006216440A - Formation method and ion source of filament used for ion source - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an ion source of compact device constitution in which the operating time for forming plasma can be prolonged in the ion source for forming the plasma of high density, and provide a preparation method of a filament having a long service life which is used for this ion source. <P>SOLUTION: In the preparation of the filament which emits a thermal electron used for the ion source, and after the diameter of a thermal electron emitting part of filament wire materials has been enlarged by thermal metal spraying in a state that both end parts of the filament wire materials are coated, both end parts of the filament wire materials not thermally metal-sprayed are attached to a plasma forming container of the ion source as a filament retaining part. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention is an ion source that generates an ion beam, and is used for an ion implantation apparatus used for manufacturing a semiconductor provided in an LSI (Large Scale Integrated Circuit), a flat display (flat panel display, FPD), or the like. The present invention relates to a source and a method for producing a filament used in the ion source.

  In a manufacturing process of a flat panel display (FPD) using a semiconductor LSI or TFT (Thin Film Transistor) using low-temperature polysilicon (LTPS) as an active matrix element, impurities such as boron, phosphorus, arsenic, etc. Is ionized and accelerated using an electric field to generate an ion beam, and this ion beam is irradiated into a silicon crystal formed on the substrate, whereby an ion implantation process for implanting ions is performed. For this ion implantation process, an ion implantation apparatus having an ion source for generating an ion beam is used. For example, in each process of manufacturing an FPD using an ion implantation apparatus, there are a channel process, an LDD process, and a source / drain process that affect the TFT characteristics. In particular, the channel process has an accuracy for controlling the gate threshold voltage. A high ion implantation process is required.

  Such an ion implantation apparatus ionizes a source gas introduced into a chamber using accelerated electrons to create a high-density plasma state, and draws ions generated by the ion source as an ion beam. It has a mechanism, a mass separation mechanism that separates only specific ions from the extracted ion beam, and a substrate operation mechanism for irradiating the substrate to be processed with an ion beam. It can be well implanted into silicon on the substrate.

  In the ion source, for example, a filament in which a resistance conductor wire is spirally wound one to several times in a chamber into which a source gas as an impurity is introduced is provided. In this state, a voltage of 1 to 10 V is applied to the filament and heated to supply thermoelectrons into the chamber, and a voltage is applied between the chamber and the filament to cause glow discharge. Causes arc discharge to generate plasma. Ions are extracted from the generated plasma to generate an ion beam. As such an ion source that generates an ion beam while maintaining arc discharge, a Bernas ion source that is a compact device configuration that generates an ion beam with high efficiency is widely known. In addition, Freeman type ion sources and bucket type ion sources are known as ion sources.

  On the other hand, in order to increase the production capacity of FPD, it is desired that the ion implantation apparatus shortens the time required for ion implantation as compared with the conventional one. The time required for the ion implantation is the sum of the transport time for transporting the substrate by the substrate operating mechanism and the processing time for implanting ions, and in particular, in the source / drain process, a large amount of ions must be implanted. Becomes longer. For this reason, in order to shorten the processing time, it is necessary to increase the current density of the ion beam to be generated and to increase the amount of ions to be implanted in a certain time, and to increase the density of the plasma that generates the ion beam. is required. However, when trying to increase the density of plasma in the chamber, there has been a problem that the operation time (life) of the apparatus is shortened because the wall surface and filaments in the chamber are eroded by the erosion action of the plasma.

In order to solve this problem, Patent Document 1 below discloses an ion source in which an auxiliary body made of a high melting point material such as tungsten or tantalum is disposed in the vicinity of the filament, and the electric potential of the auxiliary body is made lower than the electric potential of the filament. ing. Thereby, it is said that the lifetime of the filament exposed to plasma can be extended.
Patent Document 2 below discloses an ion source in which an indirectly heated cathode made of a metal material having a high emission rate of thermoelectrons such as tungsten is provided in front of a filament.

Japanese Patent Laid-Open No. 7-272657 JP 2001-167707 A

  However, these devices greatly change the basic device configuration of the conventional Bernas ion source, and also require a new power supply. For this reason, the apparatus configuration is complicated, and a compact apparatus cannot be configured.

  Accordingly, the present invention provides an ion source with a compact apparatus configuration that can extend the operation time for plasma generation in an ion source that generates high-density plasma, and the production of a long-life filament used in the ion source. It aims to provide a method.

In order to increase the lifetime of the filament in order to achieve the above object, there is a method in which the plasma density is decreased by increasing the volume of the chamber. However, this method requires setting a uniform magnetic field for confining plasma and reviewing each part.
On the other hand, in order to increase the lifetime of the filament, it is possible to separate the portion for providing the thermoelectron-emitting filament and the portion for confining the generated plasma as a separate container. It will be a big change.
Under such a background, the present invention is made in order to lengthen the operation time of the ion source without changing the existing apparatus configuration.

  That is, the present invention is a method for producing a filament that emits thermoelectrons used in an ion source that generates an ion beam by supplying a gas and applying a voltage, with both end portions of the filament wire covered. After increasing the diameter of the thermoelectron emission part of the filament wire by metal spraying, both ends of the filament wire not metal sprayed are attached to the plasma generation container of the ion source as a filament holding part. A method for producing a filament to be used is provided.

  According to the present invention, in an ion source that generates an ion beam by supplying a gas and applying a voltage, a chamber including an internal space in which a gas is supplied to generate plasma, and thermoelectrons are generated in the chamber. Thermoelectrons that are emitted in the chamber with respect to the diameter of both ends of the filament that pass through a sleeve that holds the filament with respect to the chamber so that the filament protrudes into the internal space of the chamber The diameter of the emission part is a thermoelectron supply source having a filament formed thick by metal spraying, and plasma generated in the internal space by applying a voltage between the chamber and the thermoelectron supply source. An ion beam outlet provided in the chamber for extracting the ion beam. To provide a source.

In the present invention, by increasing the diameter of the thermoelectron emission portion of the filament used for thermionic emission, the conventional ion source can be used as it is, and the operating life of the apparatus can be easily extended without changing the design. .
Further, according to the present invention, since the diameter of the thermoelectron emission portion of the filament is increased by metal spraying, the thickness can be freely adjusted by the metal spraying time. Further, since metal spraying can be performed on a plurality of filament wires at a time, mass production is also possible. Further, it can be suitably used as a repair filament.

Hereinafter, the ion source of the present invention and a method for producing a filament used in the ion source will be described in detail based on preferred embodiments shown in the accompanying drawings. Fig.1 (a) is sectional drawing which shows the structure of one Embodiment of the ion source of this invention.
The ion source 10 is a Bernas ion source that generates plasma by supplying a raw material gas and discharging it, and generates an ion beam by extracting ions from the plasma. As shown in FIG. 1, the ion source 10 includes a chamber 12, a filament 14, a reflective electrode plate (repeller plate) 16, a back electrode plate 18, a sleeve 20, a source gas supply port 22, an ion beam outlet 24, and a predetermined number. The main power source includes an extraction power source 26, an arc power source 28, a filament power source 30, and a raw material gas adjustment valve 32 that apply the above voltage. The chamber 12 is housed in a decompression container of an ion implantation apparatus (not shown) and is decompressed to 10 ⁻³ to 10 ⁻⁵ (Pa) in the chamber 12.

The chamber 12 is a discharge box made of a conductive material having high temperature resistance, such as tungsten, molybdenum, tantalum, or carbon, and having a rectangular parallelepiped internal space 34.
The inner wall surface of the internal space 34 of the chamber 12 is provided with a filament 14 projecting from one end face to the internal space 34, and the other end face is provided with a reflective electrode plate 16, and the filament 14 faces the reflective electrode plate 16. Are arranged to be. The filament 14 is a heating element body in which a resistance conductor wire such as tungsten is wound spirally one to several times. The reason why the filament 14 is spirally wound is to efficiently confine the plasma by using a magnetic field generated by the current flowing through the filament 14.
The internal space 34 formed by the chamber 12 has a size of, for example, 40 mm × 40 mm × 120 mm.

  A back electrode plate 18 is provided between the filament 14 and the end surface of the inner wall surface to form a cathode plate. The filament 14 is provided with a filament power supply 30 for applying a predetermined voltage, for example, several V to several tens V between both ends of the filament 14 so as to emit thermoelectrons from the filament 14 and heated to about 2000 ° C. Thermal electrons are emitted from the filament 14 into the internal space 34. Further, an arc power source 28 is provided so as to apply an arc voltage between the negative electrode end of the filament 14 and the conductive chamber 12. An arc voltage of several tens to 100 V is applied so that the potential of the chamber 12 is higher than the potential of the filament 14. The sleeve 20 through which the filament 14 passes and the conductive chamber 12 are electrically insulated by an insulator 21.

The reflective electrode plate 16 is a reflective plate that is provided in the internal space 34 so as to face the filament 14 and reflects the thermal electrons moving toward the reflective electrode plate 16. The reflective electrode plate 16 and the chamber 12 are electrically insulated by an insulator 21. The reflective electrode plate 16 is connected to the negative electrode of the filament power supply 30. The back electrode plate 18 in the direction opposite to the direction of the reflective electrode plate 16 with respect to the filament 14 is connected to the cathode of the filament 14 so that the back electrode plate 18 and the reflective electrode plate 16 have the same potential. Composed.
On the other hand, on the outside of the chamber 12, N-pole and S-pole electromagnets 36 are formed so that a magnetic field is formed along the arrangement direction (X direction in FIG. 1) of the back electrode plate 18, the filament 14, and the reflective electrode plate 16. , 38 are provided.
A source gas supply port 22 is provided on the inner wall surface of the internal space 34 and is connected to a gas supply source (not shown) via a supply pipe 42, and supply of the source gas is adjusted via a source gas adjustment valve 32. It has become so.

  In such an internal space 34 of the chamber 12, arc discharge is started by the electrons emitted from the filament 14 and the arc voltage applied between the chamber 12 and the filament 14, and the plasma is excited. The electrons in the plasma reach the reflecting electrode plate 16 while moving toward the reflecting electrode plate 16 while causing a spiral motion by the action of the magnetic fields of the electromagnets 36 and 38, and are reflected by the reflecting electrode plate 16 to be reflected by the back electrode plate. Head to 18. Further, the electrons are reflected from the back electrode plate 18. Thus, the electrons moving in the internal space 34 further collide with the source gas molecules, the gas molecules are positively ionized to generate plasma, and the generated plasma is held in the entire internal space 34. In this state, ions are extracted from the slit-shaped ion beam outlet 24 provided on the side wall of the chamber 12 by the extraction voltage applied to the extraction electrode 40, and an ion beam is generated. Here, the extraction electrode 40 is provided with an extraction power supply 26 so that a predetermined potential is generated between the extraction electrode 40 and the chamber 12, and the extraction electrode 40 is set to have a low potential when viewed from the chamber 12.

  In such an ion source 10, the filament 14 penetrates the sleeve 20 that holds the filament with respect to the chamber 12 so that the filament protrudes into the internal space 34 of the chamber 12, as shown in FIG. The diameter of the thermoelectron emission portion 14a exposed to the internal space 34 in the chamber 12 is thicker than that of the filament end portions 14b by metal spraying.

  The thermionic emission portion 14a of the filament 14 has a negative potential, and as described above, electrons move between the reflective electrode plate 16 and the back electrode 18 to generate plasma having positive ions. The thermoelectron emitting portion 14a of the filament having the potential of is easily eroded by the collision of positive ions. For this reason, only the thermoelectron emission portion 14a exposed to the internal space 34 in the chamber 12 is subjected to metal spraying to increase the diameter of the other portions to increase the life time of the filament.

The diameter of the filament both ends 14b covered with the sleeve 20 and the back electrode 18 of the filament 14 is 2 mm, for example, whereas the diameter of the thermionic emission portion 14a is 2.5 to 3.5 mm. preferable. At this time, if the diameter of the thermoelectron emission portion 14a is thicker than 2 mm, a large amount of electric power is required to emit sufficient thermoelectrons for plasma generation, and in some cases, it is necessary to strengthen the power source.
Accordingly, the life is extended by the increase in the diameter of the thermoelectron emission portion 14a of the filament 14.
On the other hand, the reason why the diameter of the portion other than the filament end portions 14b is not increased does not affect the lifetime of the filament 14 even if the diameter of this portion is increased, and is further provided on the back electrode plate 16. This is because it is impossible to pass through the through-hole through which the filament 14 passes and the sleeve 20 having a diameter determined so as to be in close contact with the filament 14 without a gap.
Thus, by increasing only the diameter of the thermoelectron emission portion 14a of the filament 14, the lifetime of the filament can be extended without changing the device configuration of the conventional Bernas ion source.

For producing the filament 14, first, a filament wire 15, for example, a tungsten filament wire is prepared. The filament wire 15 has a diameter of 2 mm, for example.
Next, as shown in FIG. 2, both end portions of the filament wire material including the portions covered with the sleeve 20 and the back electrode 18 of the filament wire material 15 are covered with the cover member 48 as the clamp portions 46, and the metal sprayed vacuum vessel 50 is covered. Install in.
In this state, the thermal electron emission part of the filament wire is uniformly metal sprayed to uniformly increase the diameter.
In the metal spraying, for example, the same metal material as the filament wire is sprayed by plasma metal spraying or the like. In addition to plasma metal spraying, known methods such as arc spraying, gas flame spraying, and ultra high-speed flame spraying can be used.

The reason why the both ends of the filament wire 15 are covered with the cover member 48 as the clamp portions 46 and the diameter of this portion is not increased is that, as described above, the sleeve 20 has a diameter so as to be in close contact with the filament wire without gaps. Because it is. Accordingly, the filament 14 has a step at the boundary between the thermoelectron emission portion 14a having a large diameter and the end portions 14b. Therefore, at the time of metal spraying, it is necessary to prevent a gap from being formed between the end portions of the filament wire and the cover member.
Further, when the tip position of the sleeve 20 does not coincide with the boundary between the thermoelectron emission portion 14a and the both end portions 14b, the portion of the filament 14 having a small diameter is exposed to the internal space 34, and this portion is intensively worn out. Can not extend the life.

  The filament 14 whose diameter of the thermionic emission portion 14a is increased in this way is penetrated through the holes of the back electrode 18 and the sleeve 20 using a predetermined device, and is not a metal sprayed metal at a predetermined position in the chamber 12. Both end portions of the wire are attached as filament holding portions.

As in the present invention, only the diameter of the thermoelectron emission portion of the filament used for thermionic emission is increased by metal spraying, so that the conventional ion source can be used as it is, and the operation of the apparatus can be easily performed without changing the design. Life can be extended. In particular, when the shape of the filament is a spiral, it is difficult to bend the filament having a large diameter, for example, about 2 mm into a spiral.
Moreover, the diameter of the thermoelectron emission part of a filament can be adjusted with the spraying time of metal spraying. Further, since metal spraying can be performed on a plurality of filament wires at a time, mass production is also possible. Further, it can be suitably used as a repair filament.

  As described above, the ion source of the present invention and the method for producing the filament used in the ion source have been described in detail. However, the present invention is not limited to the above embodiment, and various improvements and modifications can be made without departing from the gist of the present invention. Of course, you may do it.

(A) is sectional drawing which shows the apparatus structure of one Embodiment of the ion source of this invention, (b) is a figure which shows the shape of the filament used for the ion source shown to (a). It is a figure explaining the preparation method of the filament used for an ion source.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Ion source 12 Chamber 14 Filament 15 Filament wire 16 Reflective electrode plate 18 Back electrode plate 20 Sleeve 21 Insulator 22 Source gas supply port 24 Ion beam extraction port 26 Extraction power source 28 Arc power source 30 Filament power source 32 Source gas adjustment valve 34 Internal space 36 , 38 Electromagnet 40 Extraction electrode 42 Supply pipe 46 Clamp part 48 Cover member

Claims (2)

A method for producing a filament that emits thermoelectrons used in an ion source that generates an ion beam by supplying a gas and applying a voltage,
After the both ends of the filament wire are covered, the diameter of the thermoelectron emission portion of the filament wire is increased by metal spraying, and then the both ends of the filament wire that has not been metal sprayed are used as the filament holder for the plasma generation container of the ion source. A method for producing a filament for use in an ion source, wherein In an ion source that generates an ion beam by supplying a gas and applying a voltage,
A chamber with an internal space in which a gas is supplied to generate plasma;
A filament that emits thermoelectrons in the chamber, the diameter of both ends of the filament penetrating through a sleeve that holds the filament with respect to the chamber so that the filament protrudes into the internal space of the chamber. A thermoelectron supply source including a filament in which a diameter of a thermoelectron emission portion exposed in the chamber is formed thick by metal spraying;
And an ion beam outlet provided in the chamber for extracting an ion beam from plasma generated in the internal space by applying a voltage between the chamber and the thermoelectron supply source. Ion source.

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