JP2006049102A - Plasma ion source for metal-containing carbon cluster manufacturing apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a plasma ion source suitable for manufacturing metal-containing carbon cluster. <P>SOLUTION: In the plasma ion source, element to be contained is made to contact with a metal electrode at a high temperature in the vacuum vessel (ion chamber) to be ionized. Thermoelectrons generated from high-temperature portions are accelerated and made to collide with neutral elements which are not ionized, in spite of contacting to increase ionization ratio. The ion chamber has an ion extraction electrode portion, in which the charged ions are extracted from the plasma produced in the ion chamber to be provided as an ion beam to a containing process portion requiring the ions. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an ion source that generates ions by converting elements into plasma. In particular, a plasma ion source suitable for application to metal-encapsulated carbon cluster production is provided. The present invention can also be applied to an ion source of an ion implantation apparatus used for manufacturing a semiconductor device.

JP-A-2-311757 R.E.Smalley, The Sciences, March / April, p.22 (1991) Journal of Plasma and Fusion Research Vol.75 No.8 pp.927-933 (August 1999) "Properties and Applications of Fullerene Plasma"

  For example, as described in Non-Patent Document 1, in 1991, Smalley et al. Confirmed the existence of an element-encapsulated carbon cluster having another element in the hollow portion of the carbon cluster.

  However, the synthesis method of Smalley et al. Was a method by laser irradiation, and it was not possible to obtain a large amount of element-encapsulated carbon clusters that could identify the element-encapsulated carbon clusters and identify the material properties.

  In recent years, attention has been paid to various usefulness of the inclusion carbon cluster, and a technique capable of producing the inclusion carbon cluster with higher yield is expected.

  Currently, element-embedded carbon clusters typically include laser evaporation, which evaporates by irradiating a powerful laser beam onto a graphite disk, arc discharge, in which arc discharge is performed using a mixed carbon rod as a raw material, gas phase Among them, it is known to be generated by a gas phase collision method in which element ions collide with carbon clusters, a plasma method (Tohoku University method), or the like.

  A method shown in Fig. 1 of Non-Patent Document 2 has been proposed as a technique for generating element-encapsulated carbon clusters by the Tohoku University plasma method. In a vacuum vessel, a carbon cluster is injected into the plasma flow of the element to be included, and the inclusion carbon cluster is generated by depositing the inclusion carbon cluster on a deposition substrate (deposition plate) arranged downstream of the plasma flow. It is.

  A conventional technology for generating element-encapsulated carbon clusters by the plasma method will be briefly described with reference to FIG.

  When the inclusion target substance is discharged from the inclusion target element discharge device (element oven 2) toward the hot plate 1 (for example, a tungsten plate) heated to about 2700 ° C., a flow 5 of the inclusion element plasma is formed by contact ionization. The An inclusion target element (for example, alkali metal) is heated and discharged at a temperature higher than the sublimation temperature of the inclusion target element in a discharge device (element oven 2).

  In this manner, the inclusion target element 9 deposited on the inner wall of the vacuum vessel 8 outside the hot plate 1 does not contribute to the generation of the inclusion target element plasma flow 5 and is wasted. Also, the inclusion target element 10 that is reflected from the hot plate 1 without being converted into plasma and deposited on the inner wall of the vacuum vessel 8 does not contribute to the generation of the flow 5 of the inclusion target element plasma.

  The plasma flow 5 moves toward the base 7. Carbon cluster molecules discharged from the carbon cluster oven 3 are mixed with the plasma flow 5 (encapsulation target element ions) in the heating cylinder 4 to generate element-encapsulated carbon clusters on the substrate 7. Since carbon cluster molecules can be supplied in large quantities to the heated cylinder 4 as required, the element encapsulation efficiency (number of element-encapsulated carbon cluster molecules / number of elements to be encapsulated sublimated from the element oven) is introduced into the heated cylinder 4 It is determined by the amount of plasma (number of inclusion target element ions).

  Thus, in order to increase the yield of the element-encapsulated carbon cluster in the element-encapsulated carbon cluster production apparatus by the plasma method, it is important to increase the plasma flow 5 (number of element ions to be included). In the experiments conducted by the inventors so far, the ionization efficiency (number of inclusion target element ions / number of inclusion target elements sublimated from the element oven) by this method was about 1% at maximum.

  A magnetic field is applied in parallel to the plasma flow (in the horizontal direction in the drawing) so that the plasma flow 5 does not diffuse into the tube wall of the vacuum vessel 8, but is omitted in FIG.

  The technology for generating element-encapsulated carbon clusters by the plasma method of the Tohoku University method is expected as a method for obtaining element-encapsulated carbon clusters with high yield, but the specific technology that can mass-produce encapsulated carbon clusters with high efficiency and high quality is Various studies are still underway. In particular, in order to enable mass production of metal-encapsulated carbon clusters using this method, it is important that the plasma flow of the encapsulated element can be generated stably and in large quantities.

  Conventionally, as a general ion source, a Bernus type using Free Electron Impact Ionization, a Freeman type, and a microwave type using high frequency power are known. As an ion source used in a semiconductor manufacturing apparatus, an apparatus that generates ions by converting a predetermined gas into plasma by the above arc discharge is often used.

  Since an ion source used in a semiconductor manufacturing apparatus is made mainly for the purpose of implanting impurities with high accuracy into a semiconductor substrate, it is not always necessary to generate a large amount of ion plasma flow. On the other hand, in order to mass-produce metal-encapsulated carbon clusters by the plasma method, it is important to be able to stably generate a large amount of plasma flow of the inclusion target element.

  The ion generation method by the contact ionization plasma method has a well-known example by the measurement use (gas chromatography). For example, as known in Patent Document 1, a technique is known in which an analyte is brought into contact with a heated solid surface for ionization. For measurement purposes, even if the ionization rate and the amount of generated ions are very small, there is no practical problem, and the prior art contact ionization plasma method is not suitable for high density ion plasma generation, which is the subject of the present invention.

  In order to produce metal-encapsulated carbon clusters with high efficiency and high yield, a high-purity and high-density stable plasma flow containing a large amount of encapsulated elements is required. However, as described in the prior art, a high-density plasma flow cannot be obtained with an ion source for a semiconductor device manufacturing apparatus and an ionization apparatus for measurement purposes. If element plasma can be generated with high purity and high density for a metal-encapsulated carbon cluster production apparatus, it can be used as an impurity implantation ion source required for an ion implantation apparatus for semiconductor device production.

  A vacuum vessel according to claim 1, a heating vessel for ejecting an ionization target element in the vacuum vessel, and an electrode for contact ionization, the electrode being a cylindrical shape, and the ionization target element being a cylindrical electrode A plasma generating apparatus characterized by having a structure in which an incident angle is not less than 0 degrees and not more than 90 degrees, and plasma is emitted from the opposite side of the cylindrical electrode. By using this means, the neutral element discharged from the element heating container contacts the electrode part heated to about 2700 ° C a plurality of times, obtains thermal energy from the electrode, emits electrons, and corrects. Ionize.

  A vacuum vessel according to claim 2, a heating vessel for ejecting an ionization target element, an electrode for contact ionization, and an auxiliary electrode in the vacuum vessel, and a magnetic field in a space in which the electrode is arranged A structure in which a positive potential is applied to the auxiliary electrode, the element to be ionized is incident from one side of the ionization electrode, contact ionization and electron impact ionization are generated simultaneously, and plasma is emitted from the opposite side of the ionization electrode A plasma generator characterized by the above. Neutral elements that have not been positively ionized by contact ionization cause electrons to undergo accelerated collisions to cause impact ionization, further improving ionization efficiency.

6. The plasma generator according to claim 5, wherein the ionization target element according to any one of claims 1, 2, 3, and 4 is an alkali metal. If the oven is heated to about 500 ° C., the contained alkali metal can be sublimated, and the present invention provides a flow of high-density and high-purity alkali metal ions. Since alkali metal sublimation is performed by heating, if it is necessary to prevent cross contamination of unnecessary metal species, a dedicated oven is used for each metal species. In order to sublimate a larger amount of alkali metal at a low temperature, an alkali metal compound such as a metal amide having a low sublimation temperature (high vapor pressure) (for example, LiNH _{2 in} the case of lithium) is preferably used.

  7. The plasma generator according to claim 6, wherein the ionization target element according to any one of claims 1, 2, 3, and 4 is B, In, As, P, and Sb. If the means of any one of Claims 1, 2, 3, and 4 is used, these ionic species used for impurity ion implantation into a semiconductor device are also introduced with boron trifluoride gas (B) or metal particles (In , As, P, Sb) can be stably generated with high ionization efficiency by sublimation in an oven. Sublimation of solid elements is performed by heating, but the heating temperature differs depending on the type of element (for example, P requires about 280 ° C and B requires about 2550 ° C), which also prevents cross contamination. It is not possible to use the same oven for sublimation. Use a dedicated oven for each element.

  An apparatus for producing a metal-encapsulated carbon cluster, comprising the plasma generator according to claim 7. By using this means, metal-encapsulated carbon clusters can be produced with high efficiency and high yield.

  By devising the contact ionization electrode structure according to the present invention, the ionization efficiency of the inclusion target element can be increased, and the metal-encapsulated carbon cluster can be produced with high efficiency and high yield (for example, claims 1, 2, 3, 4, 5, 7).

  According to the sixth aspect of the present invention, since high-density and high-purity ion plasma can be continuously generated, it can also be used as an impurity-implanted ion source for a semiconductor manufacturing apparatus.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. Although an alkali metal will be described as an example, the operation principle is the same for other elements and molecules.

  FIG. 2 is a cross-sectional view of an essential part for explaining the principle of operation of a plasma ion source according to one embodiment of the present invention. For this purpose, a high-temperature cylindrical contact ionization electrode 11 (for example, a coil-shaped or ribbon-shaped tungsten filament) and an ion extraction electrode 13 for extracting ions from the generated plasma to the outside are shown. In order not to complicate the figure, a vacuum vessel that blocks these electrode portions from the outside air is omitted.

Alkali metal element gas ejected by raising the temperature of the element oven 12 is applied to the inner wall of the cylindrical contact ionization electrode 11 heated to about 2700 ° C. by applying a current of about 20 A at an applied voltage of 10 V, and an incident angle of 0 ° to 90 °. Collide with: Electrons in the outermost shell of the alkali metal element that has received thermal energy from the electrode 11 flow into the electrode 11, and the remaining alkali metal element is positively charged to become alkali ions (M ⁺ ), and the flow of the alkali ion plasma. 15 is generated.

  Since alkali metal can be contact ionized only slightly in one collision, it is necessary to increase the ionization efficiency by colliding with the inner wall of the cylindrical contact ionization electrode 11 many times. In the experiments by the inventors, in the case of sodium (Na), if the temperature of the coiled tungsten filament is set to about 2700 ° C. and the filament coil length is set to about 10 times the inner diameter in FIG. As a result of multiple collisions, the ionization efficiency is several times that of the method of making a single collision with the hot plate 1 of FIG.

  Alkali ions and free electrons coexist in the high-density plasma flow 15 thus obtained. If this plasma flow is used as the plasma flow 5 in FIG. 1, alkali ions several times the conventional amount can be introduced into the heating cylinder 4, so that an alkali metal-encapsulating carbon cluster can be produced with high efficiency and high yield.

  By applying a negative potential to the ion extraction electrode 13 with respect to the contact ionization electrode 11, it can be used as an ion source that can repel electrons to the contact ionization electrode 11 side and extract only metal ions. Application to is considered.

  Although the method for obtaining a high-density plasma flow only by contact ionization has been described with reference to FIG. 2, a technique for increasing ionization efficiency by accelerating electrons and colliding with a neutral alkali metal element that could not be contact ionized will be described below. To do.

  3A has a structure in which an auxiliary electrode 16 (for example, a tungsten thin wire) is arranged at the center of the contact ionization electrode 11 of FIG. 2 and a magnetic field 17 is applied parallel to the auxiliary electrode 16 (in the horizontal direction in the drawing). . A positive voltage (for example, 100 V) is applied to the auxiliary electrode 16 with respect to the contact ionization electrode 11. The thermoelectrons jumping out from the contact ionization electrode 11 try to fly toward the auxiliary electrode 16. However, in a space formed between the auxiliary electrode 16 and the contact ionization electrode 11 by receiving a Lorentz force by a magnetic field 17 applied at right angles to the traveling direction, electrons around the auxiliary electrode 16 with the magnetic field direction as an axis. Continues the orbital motion while turning. When the strength of the magnetic field is set so that the electrons cannot reach the auxiliary electrode 16 immediately, electrons that have obtained high kinetic energy from the potential applied to the auxiliary electrode 16 are in the middle of rotational movement with neutral elements that could not be contact ionized. In several collisions, neutral alkali metal elements are ionized. This is shown in FIG. 3b. Some of the rotating electrons are shown to make the figure easier to see. Although not shown in the drawing, such impact ionization due to rotating electrons occurs throughout the space where the electrons formed between the contact ionization electrode 11 and the auxiliary electrode 16 exist. By adopting a method of using both contact ionization and impact ionization in FIG. 3, the inventors were able to further increase the ionization efficiency of the alkali metal element as compared with the method in FIG.

  Modified examples of the plasma generator using both contact ionization and impact ionization are shown in FIGS. 4, 5, and 6.

  FIG. 4 shows a structure in which the diameter of the coil-like or ribbon-like tungsten filament that is the contact ionization electrode 11 of FIG. 3 is reduced and the auxiliary electrode 16 (for example, a cylindrical tungsten plate) is arranged outside the contact ionization electrode 11. The neutral alkali metal element jumping out of the element oven is contact ionized on the inner and outer peripheral surfaces of the contact ionization electrode 11 and collides with rotating electrons in the space formed between the auxiliary electrode outside the contact ionization electrode 11 and ionization. To do. In order to make the drawing easier to see, the element oven 12 and the ion extraction electrode 13 are omitted. Further, 100 V is applied between the contact ionization electrode 11 and the auxiliary electrode 16 in the same manner as described in the explanation of FIG. 3, but it is omitted in the figure.

  The structure in which the diameter of the contact ionization electrode 11 in FIG. 4 is inclined in the length direction is shown in FIGS. In FIG. 5, the diameter of the contact ionization electrode 11 on the side from which the neutral element jumps is reduced, the diameter of the contact ionization electrode 11 on the side from which the plasma flow comes out is increased, and the auxiliary electrode 16 surrounding it is also inclined in parallel. Is given. In FIG. 6, the outer peripheral diameter of the cylindrical auxiliary electrode 16 of FIG. 5 is constant. There are cases where attention is paid to the structure of FIG. In order to realize the impact ionization efficiently by making the maximum use of the space between the auxiliary electrode 16 and the contact ionization electrode 11, the magnetic field 17 corresponds to the gradient in the length direction of the diameter of the contact ionization electrode 11. It is necessary to change the intensity. According to a known design technique, the magnetic field strength can be changed by changing the winding density of the electromagnetic coil that generates the magnetic field in accordance with the change in the length direction of the diameter of the contact ionization electrode 11.

  While specific embodiments of the present invention have been described in detail, it will be apparent to those skilled in the art that the above embodiments can be further improved, altered, and modified. All such improvements, changes and modifications are considered to be included in the present invention within the scope of the technical idea of the present invention or claims.

The conceptual diagram which shows the manufacturing apparatus of the conventional metal inclusion fullerene by a plasma method. The conceptual diagram of the plasma generator by embodiment of this invention. Conceptual diagram of plasma generator with combined contact ionization and impact ionization Illustration of impact ionization of neutral elements Conceptual diagram of modified example 1 of contact ionization and impact ionization combined plasma generator Conceptual diagram of modified example 2 of contact ionization and impact ionization plasma generator Conceptual diagram of modification 3 of the contact ionization / impact ionization combined plasma generator

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Heating plate for element inclusion plasma generation 2 Heating oven for inclusion target element 3 Carbon cluster heating oven 4 Heating cylinder
5 Flow of inclusion target element plasma
6 Carbon cluster molecules
7 Substrate
8 Vacuum container
9 Inclusion target element attached to the vacuum vessel after coming off the hot plate 10 Inclusion target element adhering to the vacuum vessel without being converted into plasma by colliding with the hot plate
11 Contact ionization electrode 12 Encapsulation target element heating oven 13 Ion extraction electrode 14 Encapsulation target neutral element flow 15 Encapsulation target element plasma flow 16 Auxiliary electrode
17 Magnetic field
18 Rotating electron 19 Incident angle

Claims (7)

A vacuum vessel, a heating vessel for ejecting an ionization target element in the vacuum vessel, and an electrode for contact ionization, the electrode being a cylinder, the ionization target element being incident on one side of the cylindrical electrode at an incident angle of 0 The plasma generator has a structure that emits plasma from the opposite side of the cylindrical electrode by being incident at an angle of not less than 90 degrees and not more than 90 degrees A vacuum vessel, a heating vessel for ejecting an ionization target element in the vacuum vessel, a contact ionization electrode, and an auxiliary electrode, applying a magnetic field to the space in which the electrode is arranged, and applying a positive potential to the auxiliary electrode A plasma generator having a structure in which an ionization target element is incident from one side of an ionization electrode, contact ionization and electron impact ionization are simultaneously generated, and plasma is emitted from the opposite side of the ionization electrode. 3. The plasma generating apparatus according to claim 2, wherein an electrode for contact ionization is disposed so as to enclose an auxiliary electrode for applying a potential for accelerating electrons to collide with an element. 3. The plasma generating apparatus according to claim 2, wherein the electrode for contact ionization is wrapped and arranged with an auxiliary electrode for applying a potential for accelerating electrons to collide with an element. 5. The plasma generating apparatus according to claim 1, wherein the ionization target element is an alkali metal. 5. The plasma generating apparatus according to claim 1, wherein the ionization target element is B, In, As, or P. An apparatus for producing a metal-encapsulated carbon cluster comprising the plasma generator according to any one of claims 1, 2, 3, 4, and 5.

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