JP4534055B2 - Ion source - Google Patents

Description

  The present invention relates to an ion source capable of widely varying a dopant doping depth with respect to a substrate.

  In mass production of semiconductor devices such as VLSI, an ion source has been proposed in which monoatomic ions and molecular ions can be switched and implanted into a substrate in order to change the dopant doping depth (Patent Document 1). .

This is a microwave ion source in which microwave power is input to turn a raw material gas into a plasma, and ions for doping are emitted. By mechanically changing the volume of a plasma chamber for generating plasma, for example, BF ₃ BF ₂ ⁺ or B ⁺ can be selected and released using the above raw material gases. The volume of the plasma chamber is changed by translating two opposing wall surfaces of the plasma chamber in the opposite direction, or by moving the movable member built in the plasma chamber in parallel or rotating.
JP 2004-152702 A

According to such a conventional technique, the volume of the plasma chamber is mechanically variable, so that not only the structure becomes complicated, but also the internal working atmosphere may be impaired by incorporating a movable member, and the microwave chamber may be damaged. Since it is an ion source, there is a problem that electron energy for plasma generation is not high and it is difficult to generate B ⁺⁺ for extreme deep doping.

  Accordingly, an object of the present invention is to switch the plasma generating means to one or both of direct current arc discharge and microwave, in view of such problems of the prior art, to electrically select the type of ions to be emitted, and to adjust the doping depth. An object of the present invention is to provide an ion source capable of widely varying the thickness.

  In order to achieve such an object, the structure of the present invention includes a plasma chamber in which a filament is incorporated and a raw material gas is introduced, and a waveguide having a rectangular cross section connected to the peripheral side surface of the plasma chamber with the long side as the axial direction of the plasma chamber. A tube and an extraction electrode attached to the ion extraction outlet of the plasma chamber opposite to the waveguide, and the plasma chamber selects one or both of DC arc discharge and microwave from the waveguide. The gist is that the source gas is turned into plasma and ions from the plasma are emitted as an ion beam from the ion extraction outlet.

  In the plasma chamber, a magnetic field that is a fraction of the electron cyclotron resonance magnetic field with respect to the microwave from the waveguide can be applied in the axial direction, and the magnetic field can be set to 10 to 30 mT.

According to the configuration of the invention, the plasma chamber can be operated as a DC discharge type ion source by selecting a DC arc discharge utilizing the thermoelectrons from the filament, and plasma generating electrons for converting the source gas into plasma. energy is several 10~100eV about arc voltage equivalent, using a source gas of BF _3, a B ⁺ mainly, ions containing B ⁺⁺ can be released as an ion beam. Further, when a microwave from the waveguide is selected, it can be operated as a microwave ion source, and the electron energy (electron temperature) is about 1 to 50 eV, which is suitable for the emission of BF ₂ ⁺ and B ⁺ . Furthermore, when both of these are selected at the same time, a high electron energy of about 150 eV at the maximum can be realized, and in particular, a large amount of B ⁺⁺ can be emitted. This is because electrons for generating plasma are accelerated not only by an arc voltage but also by a microwave electric field generated in the short side direction of the waveguide, and can be accelerated to sufficiently large electron energy as a whole.

That is, according to the present invention, by selecting one or both of direct current arc discharge and microwave, BF ₂ ⁺ for extremely shallow doping on the order of several nm to B ⁺ for extremely deep doping on the order of several hundred nm. Various ions up to ⁺ can be switched and a large amount of ions can be implanted, and the doping depth can be varied widely. Moreover, since the plasma chamber does not include a mechanical movable member, there is no possibility of causing various problems associated therewith.

The plasma chamber has a vertically long cylindrical shape or approximate cylindrical shape, a square cylinder with a square cross section or an approximate square shape, etc., and confines electrons for plasma generation using trochoidal motion to stably generate high-density plasma. Therefore, a magnetic field is applied in the axial direction. However, the magnetic field is preferably a fraction of the electron cyclotron resonance magnetic field for microwaves, and is preferably set to 10 to 30 mT (100 to 300 gauss). This is because it was newly found that the microwave ion source has a peak in the emission characteristics of BF ₂ ⁺ by applying a magnetic field as small as a fraction of the electron cyclotron resonance magnetic field. Also, such a magnetic field is approximately equivalent to the magnetic field applied to the plasma chamber when operated as a DC discharge ion source, and thus for all modes of operation that select DC arc discharge, microwave, or both. This is because an electromagnet for forming a magnetic field can be used in common.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  The ion source includes a plasma chamber 11, a waveguide 21 attached to the plasma chamber 11, and extraction electrodes 31, 32, and 33 (FIGS. 1 and 2).

  The plasma chamber 11 is formed in a vertically long approximate cylindrical shape. On the peripheral side surface of the plasma chamber 11, for example, a microwave MW introduction port 11 a closed via a sealing plate 15 such as a quartz plate and a vertically long ion extraction port 11 b on which the extraction electrode 31 is mounted are opposed to each other. Are open. The waveguide 21 is a waveguide having a rectangular cross section for transmitting a microwave MW from a microwave oscillator (not shown). The waveguide 21 is connected to the introduction port 11a through the flange 21a with the long side as the axial direction of the plasma chamber 11. It is connected. Therefore, the microwave MW inlet 11 a is formed in a vertically long shape that matches the waveguide 21.

  A filament 12, an electron reflector 13, and an anti-cathode 14 are incorporated in the plasma chamber 11. The electronic reflector 13 is supported by being insulated from the plasma chamber 11 through an insulating material 12 a so as to be integrated with the filament 12 incorporated in the upper portion of the plasma chamber 11. The anti-cathode 14 is insulated from the plasma chamber 11 via an insulating material 14a, and is disposed in the lower part of the plasma chamber 11 so as to face the upper filament 12 and the electron reflector 13. A pipe 16 for introducing a source gas is connected to the plasma chamber 11, and an axial magnetic field B connecting the filament 12, the electron reflector 13 and the anti-cathode 14 can be applied by an electromagnet (not shown).

  In the extraction electrodes 31, 32, 33, slits 31 a, 32 a, 33 a corresponding to the ion extraction outlet 11 b of the plasma chamber 11 are formed, respectively. The extraction electrode 31 is directly attached to the ion extraction outlet 11b, and the extraction electrodes 32 and 33 are arranged at an appropriate interval from the extraction electrode 31 through a cylindrical insulating material (not shown). However, the insulating material that supports the extraction electrodes 31, 32, 33 is integrated with the plasma chamber 11 and the extraction electrodes 31, 32, 33 together with a base flange (not shown) attached to the plasma chamber 11 on the side where the waveguide 21 is connected. Shall be sealed.

  The filament 12 in the plasma chamber 11 can be heated by an external power source (not shown). Further, a power source E1 for arc discharge is connected between the filament 12, the electron reflector 13 and the plasma chamber 11, and the plasma chamber 11 holds the ground voltage together with the extraction electrode 31 through the power source E2 at about +100 kV, for example. Has been. The anti-cathode 14 is held at the same potential as the filament 12 and the electronic reflector 13 via an external lead wire (not shown). On the other hand, the extraction electrode 32 is maintained at a ground voltage of about -1 kV, for example, via the power source E3, and the extraction electrode 33 is directly grounded.

When a magnetic field B of several tens of mT is applied in the axial direction of the plasma chamber 11, the filament 12 is heated, the arc discharge power source E 1 is operated, and, for example, a BF ₃ source gas is introduced into the plasma chamber 11 through the pipe 16. The source gas can be converted into plasma using the thermoelectrons from the filament 12 to generate a direct current arc discharge in the plasma chamber 11, and a stable high-density plasma P can be generated in the plasma chamber 11. At this time, the thermoelectrons are held while being reversed between the electron reflector 13 and the anti-cathode 14, and therefore the plasma chamber 11 operates as a so-called Bernas type DC discharge ion source. Ions from the plasma P pass through an acceleration electric field between the extraction electrodes 31 and 32 and a deceleration electric field between the extraction electrodes 32 and 33, and slits 31 a, 32 a and 33 a of the ion extraction outlet 11 b and extraction electrodes 31, 32 and 33. And is emitted to the outside as an ion beam Ib. However, ions of this time, B ⁺ is mostly a small amount of B ^++.

On the other hand, when the heating of the filament 12 is stopped, the arc discharge power source E1 is stopped, and the microwave oscillator connected to the waveguide 21 is operated, the source gas in the plasma chamber 11 is transferred to the micro-wave from the waveguide 21. The source gas can be turned into plasma by introducing the wave MW, and the plasma chamber 11 can be operated as a microwave ion source. That is, the ion beam Ib mainly composed of BF ₂ ⁺ and B ⁺ can be extracted through the ion extraction outlet 11b and the slits 31a, 32a and 33a of the extraction electrodes 31, 32 and 33. However, if the magnetic field B applied in the axial direction of the plasma chamber 11 is set appropriately at this time, the amount of BF ₂ ⁺ emitted can be particularly increased. Microwave ion source, by applying a magnetic field B = 10~30mT a fraction of corresponding electron cyclotron resonance magnetic field Bo = 87.5 mT for 2.45GHz microwave MW, release is BF ₂ ⁺ ion beam Ib This is because a prominent peak is produced in (Fig. 3).

Further, when the filament 12 is heated to activate the arc discharge power source E1 and the microwave oscillator is also activated, the plasma chamber 11 is an ion that uses both the DC discharge ion source and the microwave ion source. Acts as a source and can release large amounts of mainly B ⁺⁺ ions. Electrons for plasma generation in the plasma chamber 11 are accelerated by the introduction of the microwave MW in addition to the trochoidal motion caused by the arc voltage and the magnetic field B, and acquire sufficient kinetic energy to release B ^++. Because it can. That is, the ion beam Ib at this time can be remarkably increased as compared with a case where it is simply operated as a DC discharge ion source.

  In the above description, the plasma chamber 11 may be configured as a DC discharge ion source of another type such as a Freeman type or a PIG type instead of the Bernas type. However, the magnetic field B applied in the axial direction of the plasma chamber 11 includes a magnetic field B = 10 to 30 mT when operating as a microwave ion source, and can be realized by using a common electromagnet for all operating modes. preferable.

In the present invention, as the source gas, various materials other than BF ₃ can be used depending on the type of dopant required.

Whole structure exploded perspective view Overall configuration vertical section explanatory diagram Operation explanatory diagram

Explanation of symbols

P ... Plasma B ... Magnetic field MW ... Microwave Ib ... Ion beam 11 ... Plasma chamber 11b ... Ion extraction outlet 12 ... Filament 21 ... Waveguide 31, 32, 33 ... Extraction electrode

Patent Applicant School Corporation Kanazawa Institute of Technology
Attorney Tadaaki Matsuda, Attorney

Claims (3)

  A plasma chamber in which a filament is incorporated and a source gas is introduced, a waveguide having a rectangular cross section connected to the peripheral side surface of the plasma chamber with the long side being the axial direction of the plasma chamber, and opposite to the waveguide An extraction electrode attached to the ion extraction outlet of the plasma chamber, and the plasma chamber selects one or both of direct current arc discharge and microwave from the waveguide to convert the source gas into plasma, and plasma From the ion extraction outlet as an ion beam.   2. The ion source according to claim 1, wherein a magnetic field that is a fraction of an electron cyclotron resonance magnetic field with respect to microwaves from the waveguide is applied to the plasma chamber in an axial direction. 3. The ion source according to claim 2, wherein the magnetic field is set to 10 to 30 mT.

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