Ion source

An ion source includes a plasma generating chamber into which an ionization gas containing fluorine is introduced, a hot cathode provided on one side in the plasma generating chamber, an opposing reflecting electrode which is provided on other side in the plasma generating chamber and reflects electrons when a negative voltage is applied from a bias power supply to the opposing reflecting electrode, and a magnet for generating a magnetic field along a line, which connects the hot cathode and the opposing reflecting electrode, in the plasma generating chamber. The opposing reflecting electrode is formed of an aluminum containing material.

TECHNICAL FIELD

The present disclosure relates to an ion source which is employed in an ion implantation apparatus that implants aluminum ions into a target such as a silicon carbide (SiC) substrate, or the like, for example, and generates an ion beam containing the aluminum ions.

RELATED ART

An example of the ion source of this type is set forth in Patent Literature 1.

In the related-art ion source set forth in Patent Literature 1, a plate formed of the aluminum containing material (e.g., aluminum oxide) is provided in the ionization chamber apart from an electrode (cathode) and a recoil plate as the components used for the plasma generation/confinement, and the plasma being generated by ionizing a fluoride gas (e.g., silicon tetrafluoride) is caused to erode the plate formed of the aluminum containing material such that the aluminum ions are emitted into the plasma.

In the related-art ion source, the plate formed of the aluminum containing material and used exclusively to generate the aluminum ions must be provided apart from the components used for the plasma generation/confinement. Therefore, such a problem exists that the number of items is increased correspondingly and a structure becomes complicated.

SUMMARY

Exemplary embodiments of the present invention to provide an ion source that generates an ion beam containing aluminum ions, in which a reduction of the number of items and a simplification of the structure in the ion source can be attained.

An ion source for generating an ion beam containing an aluminum ion, according to an exemplary embodiment of the invention, includes:

a plasma generating chamber which is also used as an anode and generates a plasma in an interior, and into which an ionization gas containing fluorine is introduced;

a hot cathode provided on one side in the plasma generating chamber and isolated electrically from the plasma generating chamber;

an opposing reflecting electrode which is provided on other side in the plasma generating chamber to oppose to the hot cathode and is isolated electrically from the plasma generating chamber, to which a voltage that is negative in contrast to a potential of the plasma generating chamber is applied, and which reflects electrons in the plasma generating chamber and is formed of an aluminum containing material; and

a magnet which generates a magnetic field along a line connecting the hot cathode and the opposing reflecting electrode, in the plasma generating chamber.

In place of the application of the negative voltage to the opposing reflecting electrode, the opposing reflecting electrode may be set to a floating potential.

According to the exemplary embodiment of the invention, the aluminum particles such as the aluminum ions, etc. can be emitted into the plasma from the opposing reflecting electrode that has a function of reflecting the electrons in the plasma generating chamber such that the aluminum ions can be contained in the plasma. Therefore, unlike the foregoing ion source in the related art, there is no need to provide particularly the plate that is used exclusively to generate the aluminum ions. As a result, a reduction of the number of items and a simplification of the structure of the ion source can be attained.

Also, the magnet for generating the magnetic field along the line that connects the hot cathode and the opposing reflecting electrode is provided. Therefore, the electrons in the plasma generating chamber reciprocally moves between the hot cathode and the opposing reflecting electrode, so that the high-density plasma can be generated between the hot cathode and the opposing reflecting electrode. The opposing reflecting electrode is positioned at the edge portion of such high-density plasma, and the plasma is ready to move in the direction along the magnetic field and the opposing reflecting electrode is positioned at the edge portion in the easily moving direction. Therefore, the opposing reflecting electrode is exposed effectively to the high-density plasma. Accordingly, the aluminum particles such as the aluminum ions, or the like can be emitted effectively into the plasma from the opposing reflecting electrode. As a result, it is made easy to increase an amount of aluminum ions contained in the ion beam.

The above-mentioned ion source further includes:

a backside reflecting electrode which is provided at a back of an electron emitting portion of the hot cathode in the plasma generating chamber to oppose to the opposing reflecting electrode, which is isolated electrically from the plasma generating chamber, to which a voltage that is negative in contrast to the potential of the plasma generating chamber is applied, and which reflects the electrons in the plasma generating chamber and is formed of an aluminum containing material.

In place of the application of the negative voltage to the backside reflecting electrode, the backside reflecting electrode may be set to a floating potential.

According to the exemplary embodiment of the invention, further advantages described hereunder can be achieved. That is, the aluminum particles are emitted into the plasma not only from the opposing reflecting electrode but also the backside reflecting electrode by the erosion, the sputtering, and the like caused by the fluorine ions in the plasma. Therefore, an amount of aluminum ions contained in the ion beam can be increased by increasing an amount of aluminum particles that are emitted into the plasma.

Also, the hot cathode is provided in vicinity of the backside reflecting electrode, and thus a temperature of the backside reflecting electrode is increased by a radiant heat from the hot cathode. As a result, an improvement of a sputter ratio and an increase of a vapor pressure of the aluminum containing material can be expected, and thus an amount of aluminum particles that are emitted into the plasma can be increased. Therefore, an amount of aluminum ions contained in the ion beam can be increased from this viewpoint.

Also, in the case of this invention, the backside reflecting electrode having a function of reflecting the electrons in the plasma generating chamber is also used as the aluminum particle emitting electrode. Therefore, unlike the ion source in the related art, there is no necessity that the plate used exclusively to generate the aluminum ions should be particularly provided. As a result, a reduction of the number of items and a simplification of the structure of the ion source can be attained in contact to the case where such plate is particularly provided.

In the above-mentioned ion source, the hot cathode is an indirectly heated type hot cathode which has a cathode member which emits thermions by a heating and a filament which heats the cathode member, the cathode member being arranged in an opening portion of the plasma generating chamber, and

a wall surface containing the opening portion of the plasma generating chamber is formed of an electric insulating aluminum containing material.

The wall surface containing the opening portion of the plasma generating chamber may be formed of an aluminum containing material.

Alternatively, the wall surface formed of an aluminum containing material may be set to a floating potential or, a voltage that is negative in contrast to the potential of the plasma generating chamber may be applied to the wall surface.

According to the exemplary embodiment of the invention, further advantages described hereunder can be achieved. That is, the aluminum particles are emitted into the plasma not only from the opposing reflecting electrode but also the wall surface formed of the aluminum containing material of the plasma generating chamber by the erosion, the sputtering, and the like caused by the fluorine ions in the plasma. Therefore, an amount of aluminum ions contained in the ion beam can be increased by increasing an amount of aluminum particles that are emitted into the plasma.

Also, the hot cathode is provided in vicinity of the wall surface formed of the aluminum containing material, and thus a temperature of the wall surface formed of the aluminum containing material is increased by a radiant heat from the hot cathode. As a result, an improvement of a sputter ratio and an increase of a vapor pressure of the aluminum containing material can be expected, and thus an amount of aluminum particles that are emitted into the plasma can be increased. Therefore, an amount of aluminum ions contained in the ion beam can be increased from this viewpoint.

Also, in the case of this invention, a part of the wall surface constituting the aluminum generating chamber, i.e., the wall surface containing the opening portion, is also used as the aluminum particle emitting electrode. Therefore, unlike the ion source in the related art, there is no necessity that the plate used exclusively to generate the aluminum ions should be particularly provided. As a result, a reduction of the number of items and a simplification of the structure of the ion source can be attained in contact to the case where such plate is particularly provided.

Other features and advantages may be apparent from the following detailed description, the accompanying drawings and the claims.

DETAILED DESCRIPTION

FIG. 1is a schematic sectional view showing an embodiment of an ion source according to this invention. This ion source is the ion source that generates (extracts out) an ion beam34containing aluminum ions, and is equipped with a plasma generating chamber2that is used to generate a plasma4in an interior and also serves as an anode for an arc discharge. This plasma generating chamber2is shaped into a rectangular parallelepiped, for example, but the shape is not limited to this shape.

An ionization gas8containing fluorine is introduced into the plasma generating chamber2through a gas inlet port6. The position of the gas inlet port6is not limited to a position in the illustrate example. The reason why the ionization gas8containing fluorine is used is that, since the fluorine has a very strong chemical action and has a strong reactivity with other materials, the plasma4generated by ionizing the ionization gas8containing fluorine has a strong action to emit aluminum particles such as aluminum ions, or the like from an opposing reflecting electrode20described later.

As the ionization gas8containing fluorine, a fluoride gas such as boron fluoride (BF3), silicon tetrafluoride (SiF4), germanium fluoride (GeF4), or the like, or a gas containing fluorine (F2), for example, is employed. As the ionization gas8containing fluorine, for example, the fluoride gas itself or the fluorine itself may be employed, or their diluted gas diluted with an appropriate gas (e.g., helium gas) may be employed.

A hot cathode12is provided on one side in the plasma generating chamber2. This hot cathode12is electrically isolated from the plasma generating chamber2, and emits thermions into the plasma generating chamber2.

As the hot cathode12, the directly heated type as shown in this embodiment may be employed or the indirectly heated type as shown in an embodiment described later (seeFIG. 3, or the like) may be employed.

In this embodiment, the hot cathode12is a U-shaped filament, and is electrically isolated from the plasma generating chamber2with an insulator14. In this case, a direction of the filament is shown for convenience sake to clarify the connection to a DC heating power supply16. Actually, this filament is arranged such that a plane containing the U-shaped filament is positioned in substantially parallel with an ion extracting port10described later. This is also true in another embodiment shown inFIG. 2. In this case, the filament may be shaped other than the U-shape.

The DC heating power supply16for heating the hot cathode12is connected across the hot cathode12. A DC arc power supply18is connected between one end of the hot cathode12and the plasma generating chamber2such that its positive electrode side is directed to the plasma generating chamber2. This arc power supply18applies an arc voltage VAbetween the hot cathode12and the chamber2to generate an arc discharge in such a manner that the ionization gas8introduced into the plasma generating chamber2is ionized to generate the plasma4.

The opposing reflecting electrode20is provided on the other side (the opposite side to the hot cathode12) in the plasma generating chamber2. This opposing reflecting electrode20is provided to oppose to the hot cathode12, and has a function of reflecting (in other words, repelling or repulsing. Ditto with the followings) the electrons in the plasma generating chamber2(mainly, the thermions emitted from the hot cathode12. Ditto with the followings). This opposing reflecting electrode20is isolated electrically from the plasma generating chamber2with an insulator22.

In this embodiment, a bias voltage VBthat is negative in contrast to a potential of the plasma generating chamber2is applied to the opposing reflecting electrode20from a DC bias power supply24. A magnitude of the bias voltage VBmay be decided with regard to a balance among an action of reflecting the electrons by the opposing reflecting electrode20, an action of emitting the aluminum particles such as the aluminum ions, or the like from the opposing reflecting electrode20, an action of sputtering the surface of the opposing reflecting electrode20by the ions in the plasma4, etc. From such viewpoint, it is preferable that a magnitude of the bias voltage VBshould be set to about 40 V to 150 V, for example. When the ionization gas8is the gas containing the boron fluoride (BF3), the magnitude of about 60 V to 120 V out of them is more preferable.

The opposing reflecting electrode in the publicly known ion source is formed of a refractory metal such as titanium (Ti), tantalum (Ta), molybdenum (Mo), or the like, or their alloy. But the above opposing reflecting electrode20is formed of the aluminum containing material. The aluminum containing material is an aluminum compound such as aluminum oxide (Al2O3), aluminum nitride (AlN), or the like, for example. Also, the aluminum (Al) can be employed when a temperature control is applied.

A magnet30is provided on the outside of the plasma generating chamber2. The magnet30generates a magnetic field28along a line26that connects the hot cathode12and the opposing reflecting electrode20. The magnet30is formed of an electromagnet, for example, but a permanent magnet may also be employed. A direction of the magnetic field28may be set in the opposite direction to that in the illustrated example.

Because of the foregoing presence of the opposing reflecting electrode20and the magnetic field28, the electrons in the plasma generating chamber2move reciprocally between the hot cathode12and the opposing reflecting electrode20while turning in the magnetic field28around an axis in the direction of the magnetic field28. As a result, a collision probability between the electrons and gas molecules of the ionization gas8is enhanced, then an ionization efficiency of the ionization gas8is increased, and thus a generation efficiency of the plasma4is increased. More concretely, the high-density plasma4can be generated between the hot cathode12and the opposing reflecting electrode20.

The ion extracting port10used to extract out the ions from the plasma4is provided in the wall surface of the plasma generating chamber2. In this embodiment, the ion extracting port10has a long and narrow shape in the direction along the line26. More concretely, this port10is shaped into a long slit in the direction along the line26. However, the shape of the ion extracting port10is not limited to this shape.

A extracting electrode system32is provided near the outlet of the ion extracting port10. The extracting electrode system32is used to extract out the ion beam34from the plasma generating chamber2(more concretely, from the plasma4generated there). The extracting electrode system32is constructed by a sheet of electrode in the illustrated example. But this extracting electrode system32is not limited to this, and this extracting electrode system32may be constructed by plural sheets of electrodes.

In this ion source, the opposing reflecting electrode20formed of the aluminum containing material is exposed to the plasma4that is generated by ionizing the ionization gas8containing the fluorine. On account of the erosion caused by the fluorine ion, the fluorine radical, and the like in the plasma4, the sputtering caused by the ions such as the fluorine ion, and the like in the plasma4, etc., the aluminum particles such as the aluminum ions, or the like are emitted from the opposing reflecting electrode20, and the aluminum ions are contained in the plasma4. The aluminum particles emitted from the opposing reflecting electrode20may be emitted as the aluminum ions or emitted as the neutral aluminum atoms. The neutral aluminum atoms collide with the electrons in the plasma4to some extent, and are ionized into the aluminum ions. In this manner, the aluminum ions (e.g., Al+, Al2+, Al3+. Ditto with the followings) are contained in the plasma4. As a result, the ion beam34containing the concerned aluminum ions can be generated.

In this manner, according to this ion source, the aluminum particles such as the aluminum ions, and the like can be emitted into the plasma4from the opposing reflecting electrode20that has a function of reflection the electrons in the plasma generating chamber2, and the aluminum ions can be contained in the plasma4. In other words, the opposing reflecting electrode20that reflects the electrons in the plasma generating chamber2is also used for the purpose of emitting the aluminum particles. Therefore, unlike the foregoing ion source in the related art, there is no need to provide particularly the plate that is used exclusively to generate the aluminum ions. As a result, a reduction of the number of items and a simplification of the structure of the ion source can be attained.

In addition, the magnet30for generating the magnetic field28along the line26that connects the hot cathode12and the opposing reflecting electrode20is provided. Therefore, the electrons in the plasma generating chamber2moves reciprocally between the hot cathode12and the opposing reflecting electrode20, as described above. The plasma4can be generated at a high density between the hot cathode12and the opposing reflecting electrode20. The opposing reflecting electrode20is positioned at the end portion of such high-density plasma4, the plasma4is easily movable in the direction along the magnetic field28, and the opposing reflecting electrode20is positioned at the end portion in the easily movable direction. Therefore, the opposing reflecting electrode20can be exposed effectively to the high-density plasma4. Accordingly, the aluminum particles such as the aluminum ions, and the like can be emitted effectively into the plasma4from the opposing reflecting electrode20. As a result, it can be made easy that an amount of aluminum ions contained in the ion beam34is increased.

In the foregoing ion source in the related art, the plate formed of the aluminum containing material is fitted on the bottom surface of the ionization chamber. The opposing reflecting electrode20can be exposed more effectively to the plasma4than the plate located in such position in connection to the magnetic field28. Therefore, the aluminum particles such as the aluminum ions, and the like can be emitted more effectively into the plasma4. In turn, the ion beam34containing a larger amount of aluminum ions can be generated.

Normally, the unnecessary particles are stacked on the surfaces, which are exposed to the plasma4, including the surface of the opposing reflecting electrode20along with the operation of the ion source, i.e., along with the generation of the plasma4. When the opposing reflecting electrode20is observed particularly, the bias voltage VBthat is negative with respect to the plasma generating chamber2is applied to the opposing reflecting electrode20. Therefore, the opposing reflecting electrode20can achieve the action of accelerating the ions in the plasma4by the bias voltage VBto pull in them, in addition to the above action of reflecting the electrons. The particles stacked on the surface of the opposing reflecting electrode20are sputtered by the accelerated ions, and thus the surface of the opposing reflecting electrode20can be cleaned. Therefore, the action of exposing the surface itself of the opposing reflecting electrode20and emitting the aluminum particles from the surface can be maintained stably for a longer time.

In contrast, the foregoing ion source in the related art is not constructed such that the negative voltage in contrast to the ionization chamber is applied to the plate formed of the aluminum containing material (or this plate is set to a floating potential). Therefore, such an action is not expected that the particles stacked on the surface of the concerned plate are sputtered by the accelerated ions and thus the surface of the concerned plate is cleaned. As a result, a function of emitting the aluminum particles from the concerned plate is quickly lowered.

The opposing reflecting electrode20is exhausted after the aluminum particles are emitted from the opposing reflecting electrode20. Therefore, the opposing reflecting electrode20may be exchanged as occasion demands. This respect is similar to the case of the plate in the foregoing ion source in the related art.

By the way, when the aluminum ions are implanted into the target such as the silicon carbide substrate, or the like by using this ion source as the ion implantation apparatus, a mass separator that selects the aluminum ions of a necessary momentum by separating a momentum (e.g., mass) of the ion beam34may be provided between the ion source and the target, as occasion demands. This is also true of the case where the ion source in the embodiment described hereunder is employed.

Next, several other embodiments of the ion source according to this invention will be explained hereunder. Here, in the explanation of respective following embodiments, the same reference symbols are affixed to the same or equivalent portions as or to those in the embodiment explained previously (for example, the embodiment shown inFIG. 1). Mainly differences from the embodiment explained previously will be explained hereunder.

Instead of the provision of the above bias power supply24, the opposing reflecting electrode20may be connected to the hot cathode12and may be fixed at the cathode potential, like the embodiment shown inFIG. 2. More concretely, the opposing reflecting electrode20may be connected to (a) connection portion a between the negative electrode of the heating power supply16and one end of the hot cathode12, like the example shown inFIG. 2, or (b) a connection portion b between the positive electrode of the heating power supply16and the other end of the hot cathode12(i.e., the negative electrode of the arc power supply18). In either case, the negative voltage that is negative in contrast to the potential of the plasma generating chamber2can be applied to the opposing reflecting electrode20. Concretely, in the case of (a), the negative voltage of a magnitude of VA+VHcan be applied and, in the case of (b), the negative voltage of a magnitude of VAcan be applied. Where VAdenotes an arc voltage as the output voltage of the arc power supply18, and VHdenotes the output voltage of the heating power supply16. A magnitude of the arc voltage VAis set to about 40 V to 120 V, for example, and a magnitude of the output voltage VHis set to about 2 V to 4 V, for example.

In the case of (a), the heating power supply16and the arc power supply18are also used as the DC power supply that applies the negative voltage to the opposing reflecting electrode20. In the case of (b), the arc power supply18is also used as the DC power supply that applies the negative voltage to the opposing reflecting electrode20. The AC power supply may be employed as the heating power supply16. In such case, the above (b) may be employed.

In the case of this embodiment, the negative voltage that is negative in contrast to the potential of the plasma generating chamber2can be applied to the opposing reflecting electrode20. Therefore, the almost similar advantages of the opposing reflecting electrode20to the case in the embodiment shown inFIG. 1can be achieved.

In place of the application of the negative voltage to the opposing reflecting electrode20, the opposing reflecting electrode20may not be connected electrically to any portion and may be set to a floating potential. Even when the opposing reflecting electrode20is set to a floating potential, the electrons whose mass is lighter than the ions in the plasma4and whose mobility is higher that such ions are incident on the opposing reflecting electrode20in an amount that is greater than the ions. Therefore, the opposing reflecting electrode20is charged negatively, and the similar action to the case where the negative voltage is applied to the opposing reflecting electrode20can be achieved. That is, the substantially similar advantages of the opposing reflecting electrode20to those in the case of the embodiments shown inFIG. 1andFIG. 2can be achieved.

Here, (a) the bias power supply24is provided like the embodiment shown inFIG. 1, (b) the opposing reflecting electrode20is connected to the hot cathode12like the embodiment shown inFIG. 2, and (c) the opposing reflecting electrode20is not connected to any portion and is set to a floating potential are compared mutually. In the case of (a), the bias voltage VBcan be chosen freely, and therefore the optimum voltage for the aluminum ion generation, and the like can be applied easily to the opposing reflecting electrode20. In the case of (b), the arc power supply18, etc. are also used as the power supply that is used to apply the negative voltage to the opposing reflecting electrode20. Therefore, the power supply used exclusively for the opposing reflecting electrode20is not needed, and thus a configuration of the power supply can be simplified. Also, a potential of the opposing reflecting electrode20can be fixed. In the case of (c), the power supply used exclusively for the opposing reflecting electrode20is not needed, and thus a configuration of the power supply can be simplified. It is possible to say that the similar situation is true of other embodiments described later.

As described later, the indirectly heated type may be employed as the hot cathode12. An example is shown inFIG. 3.

The hot cathode12has a cathode member36for emitting the thermions when heated, and a filament38for heating the cathode member36. A concrete structure that the cathode member36and the filament38are arranged in the plasma generating chamber2is shown inFIG. 3in a simplified mode. The publicly known structure as set forth in Japanese Patent No. 3758667, for example, may be employed. This is similarly applied to the embodiments shown inFIG. 5toFIG. 7.

A DC heating power supply40for heating the filament38is connected to the filament38. ADC bombard power supply42is connected between the filament38and the cathode member36to direct its positive electrode side to the cathode member36. This bombard power supply42accelerates the thermions emitted from the filament38toward the cathode member36and heats the cathode member36by utilizing the impact of the thermions. The above-mentioned arc power supply18is connected between the cathode member36and the plasma generating chamber2.

When the indirectly heated hot cathode12is provided, the bias voltage VBmay be applied to the opposing reflecting electrode20or the opposing reflecting electrode20may be connected to the hot cathode12and may be fixed at the cathode potential. More concretely, the opposing reflecting electrode20may be connected to (a) a connection portion c between the negative electrode of the heating power supply40and one end of the filament38, (b) a connection portion d between the positive electrode of the heating power supply40and the other end of the filament38, and (c) a connection portion e between the cathode member36and the arc power supply18(i.e., the negative electrode of the arc power supply18), as indicated with a chain double-dashed line inFIG. 3. In either case, the negative voltage that is negative in contrast to the potential of the plasma generating chamber2can be applied to the opposing reflecting electrode20. Concretely, the negative voltage of a magnitude of VA+VD+VFcan be applied in the case of (a), the negative voltage of a magnitude of VA+VDcan be applied in the case of (b), and the negative voltage of a magnitude of VAcan be applied in the case of (c). Where VAdenotes the above arc voltage, VDdenotes the output voltage of the bombard power supply42, and VFdenotes the output voltage of the heating power supply40. A magnitude of the arc voltage VAis set to about 40 V to 120 V as described above, for example, a magnitude of the output voltage VFis set to about 2 V to 4 V, for example, and a magnitude of the output voltage VDis set to about 300 V to 600 V, for example.

In the case of (a), the arc power supply18, the bombard power supply42, and the heating power supply40are also used as the DC power supply that applied the negative voltage to the opposing reflecting electrode20. In the case of (b), the arc power supply18and the bombard power supply42are also used as the DC power supply that applied the negative voltage to the opposing reflecting electrode20. In the case of (c), the arc power supply18is also used as the DC power supply that applied the negative voltage to the opposing reflecting electrode20. An AC power supply may also be employed as the heating power supply40. In such case, the above case of (b) or (c) may be employed.

Meanwhile, as set forth in Japanese Patent No. 3797160, for example, some ion sources are equipped with the reflecting electrode (backside reflecting electrode) on the hot cathode side, in addition to the opposing reflecting electrode20. In this case, as described above, both reflecting electrodes in the publicly known ion source are formed of not the aluminum containing material but a refractory metal or its alloy. An embodiment of an embodiment in which a backside reflecting electrode corresponding to the backside reflecting electrode is further provided is shown inFIG. 4.

In the ion source of this embodiment, a backside reflecting electrode44equipped with a function of reflecting the electrons in the plasma generating chamber2is further provided at the back of the electron emitting portion of the hot cathode12in the plasma generating chamber2. This backside reflecting electrode44is provided to oppose to the opposing reflecting electrode20, and is isolated electrically from the plasma generating chamber2. The negative voltage that is negative in contrast to the potential of the plasma generating chamber2is applied to the backside reflecting electrode44(or the backside reflecting electrode44is set to a floating potential, as described above). This backside reflecting electrode44is formed of the aluminum containing material, as described above.

As the means for supporting the backside reflecting electrode44in the plasma generating chamber2while isolating electrically from the plasma generating chamber2, the publicly known means can be employed. In this embodiment, the backside reflecting electrode44is supported by an insulator48, which is also used as a current introducing terminal, as an example, but the supporting means is not limited to this. In an embodiment shown inFIG. 5, an illustration of the supporting means of the backside reflecting electrode44is omitted.

The electron emitting portion of the hot cathode12denotes the portion, which emits particularly many thermions, of the hot cathode12. Concretely, the electron emitting portion corresponds to a top end portion of the hot cathode12(a top end portion on the inside of the plasma generating chamber2). In the case of the indirectly heated type hot cathode12, the electron emitting portion corresponds to a top end portion of the cathode member36(a top end portion on the inside of the plasma generating chamber2).

In this embodiment, the backside reflecting electrode44has a hole46through which the hot cathode12(more concretely, its leg portion) passes while keeping electric insulation. A clearance of about 3 mm, for example, is provided between the hot cathode12and the backside reflecting electrode44. Therefore, it is possible to say that the backside reflecting electrode44is provided in vicinity of the hot cathode12.

In this event, (a) the bias voltage VBthat is negative in contrast to the potential of the plasma generating chamber2may be applied to the backside reflecting electrode44from the bias power supply24while using the bias power supply24commonly as the opposing reflecting electrode20, like the example shown inFIG. 4, or (b) the bias voltage that is negative in contrast to the potential of the plasma generating chamber2may be applied to the backside reflecting electrode44from the DC bias power supply that is different from the bias power supply24, or (c) the voltage that is negative in contrast to the potential of the plasma generating chamber2may be applied to the backside reflecting electrode44by connecting the backside reflecting electrode44to the connection portion a or b, like the case of the opposing reflecting electrode20shown inFIG. 2.

Alternately, instead of the application of the negative voltage to the backside reflecting electrode44, the backside reflecting electrode44may not be connected to any portion and may be set at a floating potential. Even when the backside reflecting electrode44is set to a floating potential, the electrons whose mass is lighter than the ions in the plasma4and whose mobility is higher that such ions are incident on the backside reflecting electrode44in an amount that is greater than the ions, like the case of the opposing reflecting electrode20that is set at a floating potential. Therefore, the backside reflecting electrode44is charged negatively, and the similar action to the case where the negative voltage is applied to the backside reflecting electrode44can be achieved.

That is, like the case of the opposing reflecting electrode20, the backside reflecting electrode44can perform an action of reflecting the electrons in the plasma generating chamber2.

In addition, the backside reflecting electrode44is exposed to the plasma4, which is generated by ionizing the ionization gas8containing the fluorine, during the operation of the ion source. In addition, the backside reflecting electrode44is formed of the aluminum containing material. Therefore, according to the similar action to that described with respect to the opposing reflecting electrode20, i.e., on account of the erosion caused by the fluorine ion, the fluorine radical, and the like in the plasma4, the sputtering caused by the ions such as the fluorine ion, and the like in the plasma4, etc., the aluminum particles are emitted from the backside reflecting electrode44into the plasma4. In other words, areas of the aluminum containing material, which undergo the erosion or the sputtering by the fluorine ions, etc. in the plasma4, can be increased rather than the case where only the opposing reflecting electrode20is formed of the aluminum containing material. As a result, an amount of aluminum ions contained in the ion beam34, i.e., an amount of aluminum ion beam, can be increased by increasing an amount of aluminum particles that are emitted into the plasma4.

Also, the hot cathode12is provided in vicinity of the backside reflecting electrode44, as described above, and a temperature of the backside reflecting electrode44is increased by a radiant heat from the hot cathode12. As a result, an improvement of a sputter ratio and an increase of a vapor pressure of the aluminum containing material can be expected, and thus an amount of aluminum particles that are emitted into the plasma4can be increased. Therefore, an amount of aluminum ions contained in the ion beam34can be increased from this viewpoint.

In short, the reason why an improvement of a sputter ratio of the backside reflecting electrode44can be expected when heated to a high temperature is that a lattice vibration the aluminum atoms and other atoms of the aluminum containing material constituting the backside reflecting electrode44becomes active when heated to a high temperature, and thus a chemical bond between these atoms is easily cut and the aluminum particles are ready to run out.

Also, the reason why an increase of a vapor pressure of the aluminum containing material can be expected when heated to a high temperature is that, when the backside reflecting electrode44is heated to a high temperature, the aluminum particles are easily emitted from the aluminum containing material into the atmosphere (i.e., the vacuum atmosphere in the plasma generating chamber2) along with the similar phenomenon that is produced in an increase of a vapor pressure. Therefore, although the aluminum particle being emitted from the aluminum containing material constituting the backside reflecting electrode44along with the above action is not strictly defined as a vapor, such event is mentioned as an increase of a vapor pressure like the case of vapor.

Also, in the case of the embodiment, the backside reflecting electrode44equipped with a function of reflecting the electrons in the plasma generating chamber2is also used as the aluminum particle emitting electrode. Therefore, unlike the ion source in the related art, there is no need that the plate used exclusively to generate the aluminum ions should be particularly provided. As a result, a reduction of the number of items and a simplification of the structure of the ion source can be attained in contrast to the case where such plate is particularly provided.

Such an embodiment is shown inFIG. 5that the above the backside reflecting electrode44is provided in addition to the opposing reflecting electrode20and also the hot cathode12is the indirectly heated type.

This hot cathode12has an almost similar structure to that of the hot cathode12shown inFIG. 3. But the cathode member36is arranged in the plasma generating chamber2in this embodiment. Also, the backside reflecting electrode44that is electrically isolated from the plasma generating chamber2is provided at the back of the electron emitting portion of the hot cathode12(i.e., as described above, the top end portion of the cathode member36) to oppose to the opposing reflecting electrode20(seeFIG. 4, etc.). In other words, it is possible to say that the backside reflecting electrode44is provided at the side back of the top end portion of the cathode member36. This provision is contained in the term “back” in this specification.

In this embodiment, the backside reflecting electrode44has the hole46through which the cathode member36passes while keeping electric insulation. A clearance of about 3 mm, for example, is provided between the cathode member36and the backside reflecting electrode44. Therefore, it is possible to say that the backside reflecting electrode44is provided in vicinity of the hot cathode12, more concretely, the cathode member36.

In this embodiment, the negative voltage that is negative in contrast to the potential of the plasma generating chamber2may be applied to the backside reflecting electrode44like the case of the embodiment shown inFIG. 4, or the backside reflecting electrode44may not be connected electrically to any portion and may be set at a floating potential. When the negative voltage is to be applied, (a) the negative bias voltage VBmay be applied from the bias power supply24, (b) the negative bias voltage may be applied from the DC bias power supply different from the bias power supply24, or (c) the backside reflecting electrode44may be connected to the connection portion e, d, or c, like the case of the embodiment shown inFIG. 3. Indeed, there is no necessity that, when the backside reflecting electrode44fulfills the similar action to that explained in the embodiment inFIG. 4, the negative voltage that is large enough to contain the output voltage VDshould be applied to the backside reflecting electrode44. Therefore, when the backside reflecting electrode44is connected to the connection portion e and the arc voltage VAis applied thereto, the bias voltage has sufficient amplitude.

In the case of this embodiment, the almost similar advantages of the backside reflecting electrode44to those explained in the embodiment inFIG. 4can be attained. That is, in addition to the action of reflecting the electrons in the plasma generating chamber2, an amount of aluminum ions contained in the ion beam34(seeFIG. 4) can be increased by increasing an amount of aluminum particles being emitted into the plasma4. Such an event is similar to the above that, because the hot cathode12is located in the neighborhood, a temperature of the backside reflecting electrode44is increased and thus an amount of aluminum particles emitted into the plasma4is increased. Also, the backside reflecting electrode44is also used as the electrode that is used to emit the aluminum particles. As a result, a reduction of the number of items and a simplification of the structure of the ion source can be attained.

In an embodiment shown inFIG. 6, the cathode member36of the hot cathode12is arranged in an opening portion3of the plasma generating chamber2. A wall surface2acontaining the opening portion3(more concretely, one side surface containing the opening portion3) of the plasma generating chamber2is composed of the electric insulating aluminum containing material. The electric insulating aluminum containing material is the aluminum compound such as aluminum oxide (Al2O3), aluminum nitride (AlN), or the like, for example.

The wall surface2acomposed of the aluminum containing material is electrically isolative, and thus is set at a floating potential. Like the case of the backside reflecting electrode44at the floating potential described above, the electrons whose mass is lighter than the ions in the plasma4and whose mobility is higher that such ions are incident on the wall surface2ain an amount that is greater than the ions. Therefore, the wall surface2ais charged negatively.

Accordingly, like the case of the backside reflecting electrode44, this wall surface2acan also attain the action of reflecting the electrons in the plasma generating chamber2. In addition to this, such an advantage can be attained that an amount of aluminum ions contained in the ion beam34is increased by increasing an amount of aluminum particles being emitted into the plasma4. This advantage will be explained together with an embodiment shown inFIG. 7.

In an embodiment shown inFIG. 7, the wall surface2acontaining the opening portion3of the plasma generating chamber2is formed of the aluminum containing material, and is electrically isolated from the other wall surface of the plasma generating chamber2with intervention of an insulator50. In this embodiment, the aluminum containing material may be electric isolative or conductive.

Like the case of the backside reflecting electrode44in the embodiment shown inFIG. 5, the negative voltage that is negative in contrast to the potential of the plasma generating chamber2may be applied to the wall surface2abeing composed of the aluminum containing material, or the wall surface2amay not be connected electrically to any portion and may be set at a floating potential. When the negative voltage is to be applied, (a) the negative bias voltage VBmay be applied from the bias power supply24, (b) the negative bias voltage may be applied from the DC bias power supply different from the bias power supply24, or (c) the wall surface2amay be connected to the connection portion e, d, or c. For example, the wall surface2amay be connected to the connection portion e for the similar reason.

When the wall surface2ais set at a floating potential, the wall surface2acan be charged negatively by the same action as that in the case of the wall surface2ain the embodiment shown inFIG. 6. Therefore, the same advantages as those in the case where the negative voltage is applied to the wall surface2acan be attained.

In other words, like the case of the backside reflecting electrode44, or the like, the wall surface2aperforms the action of reflecting the electrons in the plasma generating chamber2.

Further, in the case of both embodiments shown inFIG. 6andFIG. 7, the wall surface2acomposed of the aluminum containing material is exposed to the plasma4, which is generated by ionizing the ionization gas8containing the fluorine, during the operation of the ion source. Therefore, according to the similar action to that described with respect to the opposing reflecting electrode20and the backside reflecting electrode44, i.e., on account of the erosion caused by the fluorine ion, the fluorine radical, and the like in the plasma4, the sputtering caused by the ions such as the fluorine ion, and the like in the plasma4, etc., the aluminum particles are emitted from the wall surface2aformed of the aluminum containing material into the plasma4. In other words, areas of the aluminum containing material, which undergo the erosion or the sputtering by the fluorine ions, etc. in the plasma4, can be increased in contrast to the case where only the opposing reflecting electrode20is formed of the aluminum containing material. As a result, an amount of aluminum ions contained in the ion beam34, i.e., an amount of aluminum ion beams, can be increased by increasing an amount of aluminum particles that are emitted into the plasma4.

Also, the hot cathode12(concretely, the cathode member36, etc.) is provided in vicinity of the wall surface2aformed of the aluminum containing material, and a temperature of the wall surface2ais increased by a radiant heat from the hot cathode12. As a result, like the case of the backside reflecting electrode44, an improvement of a sputter ratio of the wall surface2aand an increase of a vapor pressure of the aluminum containing material can be expected, and thus an amount of aluminum particles that are emitted into the plasma4can be increased. Therefore, an amount of aluminum ions contained in the ion beam34can be increased from this viewpoint.

Also, in the case of both embodiments shown inFIG. 6andFIG. 7, a part of the wall surface constituting the plasma generating chamber2, i.e., the wall surface2acontaining the opening portion3, is also used as the plate that is used to emit the aluminum particles. Therefore, unlike the ion source in the related art, there is no need that the plate used exclusively to generate the aluminum ions should be particularly provided. As a result, a reduction of the number of items and a simplification of the structure of the ion source can be attained rather than the case where such plate is particularly provided.

In the comparison between both embodiments inFIG. 6andFIG. 7, since the insulator50is not needed, a structure in the embodiment inFIG. 6is simpler than that in the embodiment inFIG. 7. Conversely, since the insulator50is provided, the electric isolation between the wall surface2aand the other wall surface of the plasma generating chamber2can be provided in the embodiment inFIG. 7more surely than that in the embodiment inFIG. 6.

Such a structure may be employed that a creeping distance is increased by providing a groove, for example, on a surface of the insulator50on the inside of the plasma generating chamber2. With such structure, it can be suppressed that the insulating performance is lowered due to a contamination on the surface of the insulator50.