JP2010267505A - Ion source - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve efficiency of ion beam generation and elongation of life of a hot cathode, in an ion source with the hot cathode of a concentric structure. <P>SOLUTION: The ion source 2 includes a hot cathode 10 with a hollow outer conductor 12, a hollow inner conductor 14 arranged concentrically inside the same, and an annular connection conductor 16 electrically connecting tips of both conductors 12, 14. The hot cathode 10 is inserted into a plasma generating vessel 4 along a length direction of a narrow ion extraction port 6. The ion source 2 further includes a gas supply mechanism supplying raw material gas 8 inside the inner conductor 14 of the hot cathode 10 and releasing it into the plasma generating vessel 4 from the tip of the inner conductor 14. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an ion source provided with a hot cathode having a coaxial structure in which an inner conductor is disposed in a cylindrical (hollow) outer conductor.

  A cylindrical outer conductor, a solid inner conductor that is coaxially disposed inside (not filled and hollow), and the gap between the tips of the two conductors is filled with electricity between the tips. For example, Patent Document 1 discloses an ion source having a structure in which a hot cathode having a coaxial structure provided with a connecting conductor is inserted into a plasma generation container having an elongated ion extraction port. The heating current for the hot cathode is turned back through the connection conductor and flows in the opposite direction between the outer conductor and the inner conductor.

  According to the hot cathode described in Patent Document 1, (a) the outer conductor and the inner conductor are coaxial, and the heating currents flow in opposite directions in both conductors. The generated magnetic field cancels each other, and when viewed as a whole of the hot cathode, the magnetic field generated by flowing the heating current can be kept small, so that it is easy to emit thermoelectrons, (b) the tip of the hot cathode, etc. Since the volume can be made larger than that of a known filament formed of a wire (also referred to as a rod), it is said that the cathode life can be increased.

  In the conventional ion source described above, the supply of the source gas into the plasma generation container is performed from the position on the wall surface of the plasma generation container where the tip of the hot cathode is expected. Specifically, a gas supply port for supplying a source gas into the plasma generation container is provided on the bottom surface of the plasma generation container facing the ion extraction port or on the side surface orthogonal to the bottom surface.

  In such an ion source, the source gas supplied from the gas supply port is not uniformly distributed in the plasma generation container, but is determined by the positional relationship between the gas supply port and the ion extraction port that also serves as the exhaust port. With distribution. Simply put, it has a gas distribution in which the vicinity of the gas supply port is darker than the vicinity of the ion extraction port. In addition, since the inside of the plasma generation container is generally evacuated through an ion extraction port, the ion extraction port also serves as an exhaust port as described above.

  As a result, the plasma generated by the arc discharge in the plasma generation vessel is affected by the above distribution of the source gas, and the plasma axis (axis connecting the high plasma density portion) is displaced from the ion extraction port. There exists a subject that ion beam production efficiency falls. The matter corresponding to this problem is also described in the comparative examples shown in FIGS.

  Further, it is generally known that the consumption amount of the hot cathode in the ion source is approximately inversely proportional to the gas pressure in the hot cathode portion. To put it simply, when realizing a predetermined arc current, if the gas pressure is low, the rate at which the thermoelectrons emitted from the hot cathode collide with gas molecules to generate electrons (secondary electrons) is small. In order to compensate for this, for example, it is necessary to increase the amount of thermionic electrons emitted from the hot cathode by increasing the heating temperature of the hot cathode, which increases the consumption of the hot cathode. However, in the conventional ion source described above, the position where the gas pressure is highest is in the vicinity of the gas supply port provided on the wall of the plasma generation vessel and not in the vicinity of the hot cathode. Therefore, the consumption amount of the hot cathode is increased, and consequently the life of the hot cathode is shortened.

  Accordingly, the main object of the present invention is to improve ion beam generation efficiency and extend the life of a hot cathode in an ion source including a hot cathode having a coaxial structure.

  The ion source according to the present invention has an ion extraction port having a dimension in the Y direction larger than the dimension in the X direction, and two anodes that are orthogonal to each other in the XY plane. An ion source comprising: a plasma generation vessel also serving as a heat cathode that emits a thermoelectron into the plasma generation vessel when a heating current is passed, wherein (a) the hot cathode is a hollow outer conductor And a hollow inner conductor disposed coaxially inside the outer conductor, and between the tip of the inner conductor and the tip of the outer conductor, and electrically between the two tips. An annular connecting conductor to be connected, and the heating current is folded through the connecting conductor, and is configured to flow in the opposite direction between the outer conductor and the inner conductor, and (b) A portion including the tip of the hot cathode The orthogonal projections on the XY plane of the central axis of the hot cathode of the portion inserted in the plasma generation vessel and located in the plasma generation vessel and the central axis along the Y direction of the ion extraction port are substantially the same. (C) Furthermore, a source gas is supplied from a portion outside the plasma generation vessel into the inner conductor of the hot cathode, and the source gas passes through the inner conductor. A gas supply means for discharging from the tip of the inner conductor into the plasma generation container is provided.

  In this ion source, the tip of the hot cathode also serves as the source gas supply port, and the source gas generates plasma from the positional relationship between the hot cathode and the ion extraction port located in the plasma generation vessel as described above. It is discharged into the container along the Y direction behind the ion extraction port and in the longitudinal direction of the ion extraction port. Therefore, a region having a relatively high gas pressure is formed behind the ion extraction port and extending along the ion extraction port.

  As a result, a plasma having a density distribution is generated in the plasma generation container, such that a region having a high plasma density is behind the ion extraction port and extends along the ion extraction port. Since the ion beam can be extracted through the ion extraction port from the plasma in which the position of the region having a high plasma density corresponds well to the ion extraction port as described above, the ion beam generation efficiency is improved.

  In addition, by releasing the source gas from the tip of the hot cathode into the plasma generation vessel, the position where the gas pressure is highest in the plasma generation vessel is near the tip of the hot cathode. The number of collisions between thermionic electrons and gas molecules increases, and it becomes easier to maintain arc discharge. As a result, it becomes possible to lower the heating temperature and arc discharge voltage of the hot cathode, thereby reducing the consumption amount of the hot cathode and extending the life of the hot cathode.

  Instead of having the connection conductor, the hot cathode is configured to electrically connect the tip of the outer conductor and the tip of the inner conductor directly, and the heating current is folded at the connection. May be.

  The inner conductor of the hot cathode may be formed of a material having a higher melting point than the outer conductor.

  A reflective electrode for reflecting electrons may be provided in the plasma generation container at a position facing the tip of the hot cathode with the ion extraction port in the Y direction.

  According to the first aspect of the present invention, the tip of the hot cathode also serves as the source gas supply port, and the portion of the hot cathode located in the plasma generation vessel and the ion extraction port have the above positional relationship. Therefore, in the plasma generation container, plasma having a density distribution is generated in which a region having a high plasma density is behind the ion extraction port and extends along the ion extraction port. Since the ion beam can be extracted through the ion extraction port from the plasma in which the position of the region having a high plasma density corresponds well to the ion extraction port as described above, the ion beam generation efficiency is improved.

  In addition, by releasing the source gas from the tip of the hot cathode into the plasma generation vessel, the position where the gas pressure is highest in the plasma generation vessel is near the tip of the hot cathode. The number of collisions between thermionic electrons and gas molecules increases, and it becomes easier to maintain arc discharge. As a result, it becomes possible to lower the heating temperature and arc discharge voltage of the hot cathode, thereby reducing the consumption amount of the hot cathode and extending the life of the hot cathode.

  Furthermore, since the inner conductor of the hot cathode is hollow, it is possible to increase the thickness of the inner conductor while suppressing an increase in mass and cross-sectional area of the inner conductor as compared to a solid case. As a result, the concentration of heat per unit surface area of the inner conductor can be suppressed, and the temperature rise of the inner conductor can be suppressed. Therefore, the life of the inner conductor and the life of the hot cathode can be extended.

  According to invention of Claim 2, there exists the following further effect. That is, since the tip of the outer conductor of the hot cathode and the tip of the inner conductor are electrically directly connected without using the connecting conductor, the tip of the hot cathode is compared with the case of using the connecting conductor. The volume can be reduced. As a result, the thermal capacity of the hot cathode can be reduced, the time constant during temperature control can be reduced, and the responsiveness of temperature control can be improved.

  According to invention of Claim 3, there exists the following further effect. That is, although the temperature of the inner conductor of the hot cathode is higher than that of the outer conductor, the inner conductor is made of a material having a melting point higher than that of the outer conductor. The lifetime of the hot cathode can be further increased. In addition, the operating range of the hot cathode can be made wider.

  According to invention of Claim 4, there exists the following further effect. That is, since a reflection electrode for reflecting electrons is provided at a position facing the tip of the hot cathode with the ion extraction opening in the Y direction, the probability of collision between electrons and gas molecules is increased, and the plasma generation efficiency and thus The ion beam generation efficiency can be further improved. Furthermore, the uniformity of the plasma density distribution in the direction along the longitudinal direction of the ion extraction port, and hence the uniformity of the beam current density distribution is improved. As a result, it becomes easy to cope with, for example, an ion extraction port having a larger longitudinal dimension and extraction of an ion beam.

It is sectional drawing which shows one Embodiment of the ion source which concerns on this invention. It is sectional drawing which follows the line AA of FIG. FIG. 3 is an enlarged cross-sectional view showing a more specific example around the hot cathode shown in FIGS. 1 and 2. It is the schematic which shows an example of the simulation result of the plasma density distribution in the ion source shown in FIG.1 and FIG.2, and is in the same cross section as FIG. It is the schematic which shows an example of the simulation result of the plasma density distribution in the ion source shown in FIG.1 and FIG.2, and is in the same cross section as FIG. It is the schematic which shows an example of the simulation result of the plasma density distribution in the ion source of the comparative example which has a gas supply port in the wall surface of a plasma production container, and is in the same cross section as FIG. It is the schematic which shows an example of the simulation result of the plasma density distribution in the ion source of the comparative example which has a gas supply port in the wall surface of a plasma production container, and is in the same cross section as FIG. It is sectional drawing which shows partially the other example of the hot cathode which comprises the ion source which concerns on this invention. It is sectional drawing which shows partially another example of the hot cathode which comprises the ion source which concerns on this invention.

  FIG. 1 is a sectional view showing an embodiment of an ion source according to the present invention. 2 is a cross-sectional view taken along line AA in FIG. FIG. 3 is an enlarged cross-sectional view showing a more specific example around the hot cathode shown in FIGS. 1 and 2. This ion source 2 belongs to the category of a Bernas type ion source.

  The ion source 2 emits thermoelectrons from the hot cathode 10 into the plasma generation vessel 4 that also serves as an anode, and causes arc discharge between the hot cathode 10 and the plasma generation vessel 4 to enter the plasma generation vessel 4. The introduced source gas (including the case of vapor) 8 is ionized to generate a plasma 20, and an ion beam 32 is extracted from the plasma 20 through an ion extraction port 6 by an extraction electrode system 30.

Assuming that two directions orthogonal to each other in the XY plane are an X direction and a Y direction, the ion extraction port 6 has a shape in which the dimension W _{Y in the} Y direction is larger than the dimension W _{X in the} X direction. For example, the ion extraction port 6 has a slit shape that is long in the Y direction.

  In this embodiment, the extraction electrode system 30 is exemplified by a single electrode. However, the extraction electrode system 30 is not limited to this and may be constituted by a plurality of electrodes.

  The hot cathode 10 includes a hollow outer conductor 12, a hollow inner conductor 14 coaxially disposed inside the outer conductor 12, and a gap between the tip of the outer conductor 12 and the tip of the inner conductor 14. It has an annular connecting conductor 16 that is provided and electrically connects the two tip portions. Therefore, unlike the above-described conventional hot cathode, the hot cathode 10 can pass the source gas 8 through the inside (more specifically, inside the internal conductor 14) as will be described later. It can also be said that both the outer conductor 12 and the inner conductor 14 have a cylindrical shape (however, as described below, the cross section is not limited to a circle).

A heating power source 34 is connected between the outer conductor 12 and the inner conductor 14 of the hot cathode 10, and the heating current I _H supplied from the heating power source 34 is folded back through the connecting conductor 16 at the tip, The outer conductor 12 and the inner conductor 14 flow in opposite directions. By the heating current I _H , the hot cathode 10 more specifically, the outer conductor 12, the inner conductor 14 and the connection conductor 16 constituting the heat cathode 10 generate heat and emit thermoelectrons into the plasma generation container 4.

In this embodiment, the outer conductor 12 and the inner conductor 14 are respectively supported by current introduction terminals 62 and 64 provided outside the plasma generation container 4 as shown in FIG. The heating current I _H is supplied from the heating power source 34.

  In this embodiment, the heating power source 34 is an example of a DC power source, but is not limited thereto, and may be an AC power source.

  In this embodiment, the outer conductor 12 and the inner conductor 14 are both circular in cross section. However, the outer conductor 12 and the inner conductor 14 are not limited to this, and both the cross section may be oval or polygonal.

  In this embodiment, the connection conductor 16 has an annular shape. However, the connection conductor 16 is not limited to this, and the connection conductor 16 may be matched with the cross-sectional shapes of the outer conductor 12 and the inner conductor 14.

  In this embodiment, the connection conductor 16 is fitted and coupled between the distal end portion of the outer conductor 12 and the distal end portion of the inner conductor 14. The connection between the connection conductor 16 and the outer conductor 12 and the inner conductor 14 may be, for example, only a connection by fitting, or a combination of fitting and welding. When welding is used in combination, the reliability of the connection is improved.

  The outer conductor 12, the inner conductor 14, and the connecting conductor 16 are respectively high, such as molybdenum (melting point 2896K), tantalum (melting point 3290K), tungsten (melting point 3695K), rhenium (melting point 3459K), iridium (melting point 2739K). It is preferably formed of a high melting point material such as a melting point metal or an alloy containing two or more of these metals.

  The portion including the tip of the hot cathode 10 is inserted into the plasma generation container 4. In addition, referring to FIG. 2, the portion of the hot cathode 10 including the tip is the central axis 11 of the hot cathode 10 and the central axis of the ion extraction port 6 along the Y direction. 7 are orthogonally projected on the XY plane so that they are substantially aligned with each other. That is, the central axis 11 of the hot cathode 10 and the central axis 7 of the ion extraction port 6 are substantially parallel to each other, and orthogonal projections of the extended lines of the central axes 11 and 7 on the XY plane are mutually Substantially overlap. In this specification, “substantially” means that a slight deviation is allowed to such an extent that the ion source 2 can achieve the effects described later.

  The portion where the hot cathode 10 penetrates the plasma generation container 4 is insulated by an electrical insulator 44 in this embodiment. However, instead of using the electrical insulator 44, the hot cathode 10 and the plasma generation container 4 may be electrically insulated by space insulation (for example, insulation by a gap of about 1 mm or less).

  A direct current voltage is applied between the hot cathode 10 (more specifically, the inner conductor 14 in this embodiment) and the plasma generation vessel 4 to cause the arc discharge to flow an arc current. A direct-current arc power source 36 is connected with the plasma generation container 4 on the positive electrode side. Since the temperature near the tip of the hot cathode 10 is higher than the others, the arc discharge is mainly generated between the tip and the plasma generation container 4, so that the amount of consumption near the tip of the hot cathode 10 is reduced. growing.

  In this ion source 2, instead of providing a gas supply port in the plasma generation vessel 4 as in the conventional ion source, the source gas 8 is supplied from the portion outside the plasma generation vessel 4 into the inner conductor 14 of the hot cathode 10. The gas supply means for discharging the source gas 8 through the inner conductor 14 from the tip of the inner conductor 14 into the plasma generation container 4 is provided.

  More specifically, in this embodiment, as shown in FIG. 3, as an example of the gas supply means, it is inserted into the other end portion of the inner conductor 14 of the hot cathode 10 (that is, the end portion outside the plasma generation vessel 4). And a gas pipe 68 connected to the gas nozzle 66 and supplying the raw material gas 8 thereto.

  However, the gas supply means may be other than the embodiment shown in FIG. For example, the structure may be such that the gas nozzle 66 is close to or in contact with the other end of the internal conductor 14, or the gas pipe 68 is connected, inserted, close to or in contact with the other end of the internal conductor 14 without providing the gas nozzle 66. It may be a structure or the like.

  Since the gas nozzle 66 also becomes high temperature like the internal conductor 14, it is preferable to form the high-melting point metal or high-melting point material as described above for the internal conductor 14 and the like.

  In this embodiment, the ion source 2 further includes a first reflective electrode 40 in a portion on the opposite side of the hot cathode 10 in the plasma generation container 4, and a second portion at the root of the hot cathode 10. The reflective electrode 42 is provided. 45 and 46 are electrical insulators. Further, a magnetic field 52 in a direction along a line connecting the hot cathode 10 and the reflective electrode 40 is applied to the inside of the plasma generation container 4 by a magnet 50 provided outside thereof. However, the direction of the magnetic field 52 may be opposite to that illustrated.

  The magnetic field 52 suppresses diffusion of electrons and ions in the plasma 20 in a direction intersecting the magnetic field 52 to generate a high-density plasma 20, in other words, increase the generation efficiency of the plasma 20. Contribute to. Both the reflective electrodes 40 and 42 also reflect electrons (thermoelectrons) emitted from the hot cathode 10 and electrons in the plasma 20 to increase the collision probability between the electrons and gas molecules, so that the plasma 20 having a high density is produced. In other words, it contributes to increasing the generation efficiency of the plasma 20.

  In the ion source 2, the tip of the hot cathode 10 also serves as a supply port for the source gas 8. That is, the source gas 8 is supplied from the root of the hot cathode 10 toward the tip, and is released into the plasma generation container 4 from the tip of the hot cathode 10 (more specifically, the tip of the internal conductor 14). Since the inner conductor 14 usually has a relatively small diameter with respect to its entire length, the raw material gas 8 emitted from the tip of the inner conductor 14 often goes straight along the central axis 11 of the hot cathode 10. . Moreover, due to the positional relationship between the hot cathode 10 and the ion extraction port 6 in the portion located in the plasma generation container 4, the source gas 8 is behind the ion extraction port 6 in the plasma generation container 4. It is emitted along the Y direction which is the longitudinal direction of the ion extraction port 6. Accordingly, a region having a relatively high gas pressure is formed just behind the ion extraction port 6 and extending along the ion extraction port 6. When the supply flow rate of the source gas 8 is changed, the gas pressure in the plasma generation container 4 changes, but the gas distribution in the plasma generation container 4 does not change greatly.

  Since the region having a relatively high gas pressure is close to the electron emission portion near the tip of the hot cathode 10, the thermoelectrons emitted from the hot cathode 10 easily collide with gas molecules and continue the ionization reaction. It becomes easy to let you. As a result, a plasma 20 having a density distribution is generated in the plasma generation container 4 such that a region having a high plasma density is directly behind the ion extraction port 6 and extends relatively straight along the ion extraction port 6. . In this way, the ion beam 32 can be extracted from the plasma 20 in which the position of the region having a high plasma density corresponds well to the ion extraction port 6 through the ion extraction port 6, so that the ion beam generation efficiency is improved.

  The plasma density distribution described above will be further described using simulation results.

  4 and 5, the density distribution of the plasma 20 in the plasma generation container 4 of this ion source is represented by several equal density lines 22. As shown in FIG. 5, the axis 24 of the plasma 20 (the axis connecting the high plasma density portions) is substantially parallel to the central axis 7 along the Y direction of the ion extraction port 6, and both axes 24, 7 The orthogonal projections on the XY plane substantially overlap each other, and a region having a high plasma density is formed extending just behind the ion extraction port 6 and relatively straight along the longitudinal direction of the ion extraction port 6. You can see that. Further, as shown in FIG. 4, it can be seen that the region having the high plasma density is formed near the ion extraction port 6.

  Thus, in this ion source 2, the ion beam 32 can be extracted through the ion extraction port 6 from the plasma 20 in which the position of the region having a high plasma density corresponds well to the ion extraction port 6, so that the ion beam generation efficiency is increased. Will improve.

  In other words, even with the same arc current (that is, the output current of the arc power supply 36 at the time of arc discharge), the plasma 20 spreads thinly over a wide area in the plasma generation vessel 4 or the area where the plasma density is high is the ion extraction port. The ion beam 32 is more efficiently emitted from the plasma 20 by being localized along the ion extraction port 6 in the vicinity of the ion extraction port 6 as in the examples shown in FIGS. It can be pulled out.

  As a result, for example, it becomes easy to increase the beam current of the ion beam 32. Alternatively, instead of increasing the beam current of the ion beam 32, the heating temperature of the hot cathode 10 can be lowered, the consumption amount of the hot cathode 10 can be kept small, and the life of the hot cathode 10 can be extended.

  For comparison, the result of simulating the plasma density distribution in the ion source 2a having a structure in which the gas supply port 28 is provided on the wall surface of the plasma generation vessel 4 and the source gas 8 is introduced into the plasma generation vessel 4 therefrom is shown in FIG. As shown in FIG. Both figures correspond to FIGS. 4 and 5, respectively.

  In the ion source 2a of this comparative example, since the hot cathode 10 is not used for introducing the raw material gas 8, a lid 19 is provided in the distal end portion of the internal conductor. Except for the means for introducing the raw material gas 8, it has substantially the same structure as the ion source 2 of the above embodiment.

  6 and 7, the density distribution of the plasma 20 in the plasma generation container 4 of the ion source 2a is represented by some equal density lines 22. FIG. As shown in FIG. 7, the axis 24 of the plasma 20 is shifted from the central axis 7 of the ion extraction port 6. In this ion source 2 a, the supply direction of the source gas 8 from the gas supply port 28 and the ion extraction port 6 are in a twisted positional relationship, and the gas supply port 28 and the plasma generation container 4 opposed thereto are in a twisted positional relationship. Since the distance to the wall surface is relatively short, the raw material gas 8 supplied from the gas supply port 28 is reflected by the opposing wall surface, becomes turbulent in the vicinity thereof, and the gas pressure becomes equivalently high, that is, the gas supply It is considered that a region having a high gas pressure is formed in the vicinity of the opposite side of the mouth 28, and the plasma 20 also has a high density in that region.

  Since the ion beam 32 is extracted from the plasma 20 through the ion extraction port 6, if such a shift occurs, it becomes difficult to extract ions in a region having a high plasma density, so that the ion beam generation efficiency decreases. . This has been described above as a problem of the conventional ion source.

  Returning to the description of the ion source 2 of this embodiment, in the ion source 2, the source gas 8 is discharged from the tip of the hot cathode 10 into the plasma generation container 4, whereby the gas pressure in the plasma generation container 4 is reduced. The highest region is near the tip of the hot cathode 10. Therefore, compared with the case where the source gas 8 is supplied from a position different from the tip of the hot cathode 10, for example, compared with the ion source 2 a shown in FIGS. 6 and 7, it is emitted from the tip of the hot cathode 10. Since the number of collisions between thermionic electrons and gas molecules increases, the ratio of generating electrons (secondary electrons) increases, and it becomes easier to maintain the discharge. As a result, even if the heating temperature of the hot cathode 10 and the arc discharge voltage between the hot cathode 10 and the plasma generation vessel 4 (that is, the output voltage of the arc power supply 36 during arc discharge) are reduced, the required arc discharge is achieved. It becomes possible to maintain.

  By reducing the heating temperature of the hot cathode 10, the consumption amount of the hot cathode 10 is reduced, so that the life of the hot cathode 10 can be extended.

  By reducing the arc discharge voltage, the sputtering of the hot cathode 10 received from the plasma 20 can be reduced, so that the consumption amount of the hot cathode 10 is reduced and the life of the hot cathode 10 can be extended. In addition, by operating at a low arc discharge voltage, the yield of molecular ions and cluster ions having a low ionization voltage or dissociation voltage can be increased. That is, the ratio of molecular ions and cluster ions contained in the ion beam 32 can be increased.

  Moreover, in the ion source 2 of this embodiment, since the inner conductor 14 of the hot cathode 10 is hollow, it is possible to prevent the inner conductor 14 from increasing in mass and cross-sectional area as compared with a solid case. The thickness (for example, outer diameter) of the conductor 14 can be increased. As a result, the concentration of heat per unit surface area of the inner conductor 14 can be suppressed, and the temperature rise of the inner conductor 14 can be suppressed. Therefore, the life of the internal conductor 14 and thus the life of the hot cathode 10 can be extended.

  More specifically, if the outer diameter of the inner conductor 14 is smaller than the inner diameter of the outer conductor 12, the temperature of the inner conductor 14 is necessarily higher than the temperature of the outer conductor 12, but the outer diameter of the inner conductor 14 is increased. Thus, for example, the temperature of the inner conductor 14 can be made closer to the temperature of the outer conductor 12 by bringing it closer to the inner diameter of the outer conductor 12.

The hot cathode 10, for example, as shown in FIGS. 8 and 9, instead of having the connection conductor 16, the front end portion of the outer conductor 12 and the front end portion of the inner conductor 14 are electrically directly connected, The connecting portion 18 may be configured so that the heating current I _H is folded.

  More specifically, in the hot cathode 10 shown in FIG. 8, the front end portion of the outer conductor 12 is squeezed inward so as to contact the front end portion of the inner conductor 14 and both the front end portions are electrically connected to each other. The connecting portion 18 is formed.

  In the hot cathode 10 shown in FIG. 9, the front end portion of the inner conductor 14 is spread outward, so that the front end portion of the inner conductor 14 is brought into contact with the front end portion of the outer conductor 12 to electrically connect the front end portions to each other. Is forming.

  The connection of the tip portions of the two conductors 12 and 14 in the connection portion 18 may be only a connection by fitting, or may be used in combination with welding. Use of welding together improves connection reliability.

  From the viewpoint of responsiveness of temperature control of the hot cathode 10, when comparing the hot cathodes 10 shown in FIGS. 3, 8, and 9, in the hot cathode 10 shown in FIGS. 3 and the tip of the internal conductor 14 are electrically connected directly without using a connecting conductor, so that the tip of the hot cathode 10 is compared with the hot cathode 10 of FIG. The volume can be reduced. As a result, the heat capacity of the hot cathode 10 can be reduced, the time constant during temperature control can be reduced, and the temperature control response can be improved.

  In any of the above-described hot cathodes 10, the inner conductor 14 may be formed of a material having a melting point higher than that of the outer conductor 12. For example, the outer conductor 12 may be formed of tantalum and the inner conductor 14 may be formed of tungsten. As described above, since the temperature of the inner conductor 14 is always higher than that of the outer conductor 12, the inner conductor 14 is made of a material having a melting point higher than that of the outer conductor 12, thereby increasing the heat resistance of the inner conductor 14. As a result, the life of the internal conductor 14 and thus the life of the hot cathode 10 can be extended. In addition, the operating range of the hot cathode 10 can be made wider.

  Although it is not essential to provide the reflective electrodes 40 and 42, if they are provided, the generation efficiency of the plasma 20 can be increased as described above.

  In particular, if a reflective electrode 40 is provided opposite the tip of the hot cathode 10 with the ion extraction port 6 in the Y direction, electrons (thermoelectrons) emitted from the hot cathode 10 and electrons in the plasma 20 are heated. It is reflected at the facing portion of the cathode 10 to increase the collision probability between the electrons and gas molecules, and the plasma generation efficiency, and thus the ion beam generation efficiency, can be further improved. Furthermore, in the Y direction, since the reflective electrode 40 exists at a position facing the tip of the hot cathode 10 with the ion extraction port 6 in between, the plasma density in the direction along the longitudinal direction of the ion extraction port 6 (that is, the Y direction). Uniformity of distribution and hence uniformity of beam current density distribution is improved. As a result, for example, it becomes easy to cope with extraction of the ion extraction port 6 and the ion beam 32 having a larger longitudinal dimension.

  Each of the reflective electrodes 40 and 42 may be connected to a floating potential without being connected anywhere, or connected to one end (for example, the minus end, in this embodiment, the internal conductor 14) of the hot cathode 10 to be a hot cathode potential. Anyway. Even at a floating potential, light and high-mobility electrons in the plasma 20 are incident on the reflective electrodes 40 and 42 much more than ions, and the reflective electrodes 40 and 42 are charged to a negative potential, respectively. It has the effect of reflecting.

2 ion source 4 plasma generation vessel 6 ion extraction port 8 source gas 10 hot cathode 12 outer conductor 14 inner conductor 16 connection conductor 18 connection portion 20 plasma 32 ion beam 66 gas nozzle I _H heating current

JP 2006-54108 A (paragraphs 0020-0023, FIGS. 1 and 2)

Claims (4)

When two directions orthogonal to each other in the XY plane are defined as an X direction and a Y direction, the plasma generation container has an ion extraction port whose dimension in the Y direction is larger than the dimension in the X direction and also serves as an anode; An ion source comprising a hot cathode through which a heating current is passed to emit thermoelectrons into the plasma generation vessel;
(A) The hot cathode includes a hollow outer conductor, a hollow inner conductor disposed coaxially inside the outer conductor, and a tip between the inner conductor and the outer conductor. An annular connecting conductor that is electrically connected between both ends, and the heating current is turned back through the connecting conductor, and the outer conductor and the inner conductor are opposite to each other. Is configured to flow
(B) The portion including the tip portion of the hot cathode is inserted into the plasma generation vessel, and is along the central axis of the hot cathode of the portion located in the plasma generation vessel and the Y direction of the ion extraction port. The orthogonal projections of the central axis on the XY plane are inserted so that they are substantially aligned with each other.
(C) Furthermore, a raw material gas is supplied from a portion outside the plasma generation vessel into the internal conductor of the hot cathode, and the raw material gas is discharged from the tip of the internal conductor into the plasma generation vessel through the internal conductor. An ion source comprising gas supply means for causing the ion source to flow.   Instead of having the connection conductor, the hot cathode is configured to electrically connect the tip of the outer conductor and the tip of the inner conductor directly, and the heating current is folded at the connection. The ion source according to claim 1.   The ion source according to claim 1, wherein the inner conductor of the hot cathode is formed of a material having a higher melting point than the outer conductor.   The reflective electrode which reflects an electron is provided in the said plasma production container in the position which opposes the front-end | tip of the said hot cathode in the said Y direction in the said ion extraction opening | mouth. Ion source.

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