Ion beam irradiation device

Abstract

[Problem] To control a divergence angle of an ion beam when generating plasma and irradiating the ion beam. [Solution] An ion beam irradiation device 10 has a plasma generation unit 11 that generates a plasma 12 using a high frequency antenna 13 and further comprises, in an opening thereof, boundary electrodes 15 and extraction electrodes 16 for irradiating the ion beam from an irradiation hole H. Moreover, control electrodes 14 are provided further to the inner side of the plasma generation unit 11 than the boundary electrodes 15, and space potential probes 17 for detecting an electric field in the vicinity of the plasma interface are provided between the boundary electrodes 15 and the extraction electrodes 16. The detection result of the space potential probes 17 is amplified by an amplifier 20, the phase is adjusted by a phase adjustment circuit 21, and a high frequency transmitter 22 energizes the control electrodes 14 according to the signal.　A high-frequency electric field RF2 generated by the energizing of the control electrodes 14 interferes with a plasma generation electric field RF1, and thereby vibration at the plasma interface changes, and the divergence angle of the ion beam can be changed.

Description

Ion beam irradiation equipment

[0001] The present invention relates to an ion beam irradiation device that generates plasma and irradiates an ion beam, and more particularly to a technique for controlling the divergence angle of the ion beam.

[0002] Ion beams irradiated by generating plasma are used in various fields, such as nuclear fusion and accelerators, semiconductor processes, etching, film formation, and surface modification of metal materials. For example, Patent Document 1 discloses a technique for avoiding abnormal discharge that occurs when plasma film formation and ion beam irradiation are used in combination when generating plasma using a high-frequency power supply and extracting the ion beam using three or four ion beam extraction electrodes. Patent Document 2 discloses a technique for irradiating a large, parallel ion beam over a large area in the liquid crystal manufacturing process by changing the diameter and density of the extraction electrodes between the center and outer edge of the beam, thereby uniformly irradiating the diffused ion beam over the entire surface of the substrate. Known methods for generating plasma used in ion beam irradiation include the filament arc method and the radio frequency (RF) method. Compared to the filament arc method, the radio frequency (RF) method is said to have advantages in that it is not subject to limitations on continuous operation time due to filament wear and does not introduce filament material into the plasma as impurities.

[0003] JP-A No. 11-286781 JP-A No. 11-329335

[0004] When using ion beams in semiconductor manufacturing, etching, film formation, and the like, it is preferable to increase the divergence angle and irradiate the beam widely so that the beam is diffused, thereby achieving uniformity. Conversely, when using ion beams in fields such as accelerators, it is preferable to reduce the divergence angle and converge the beam to reduce beam loss. However, beams from radio frequency (RF) ion sources generally tend to have larger divergence angles than those from filament arc sources, and a technology for reducing the divergence angle and converging the beam has been desired. Such technology for controlling the divergence angle is not limited to radio frequency (RF) sources, but is also applicable to filament arc sources. In view of these problems, the present invention aims to enable the adjustment of the divergence angle of an ion beam irradiated using plasma.

[0005] The present invention can be an ion beam irradiation device that irradiates an ion beam, comprising: a plasma generation unit that generates plasma from a predetermined gas; a boundary electrode that is provided at an opening of the plasma generation unit as an electrode of a polarity opposite to that of the ion beam; an extraction electrode that is provided outside the boundary electrode as an electrode of the same polarity as that of the ion beam and that irradiates the ion beam; and a control electrode that is provided at the opening of the plasma generation unit for generating an electric field that changes at a predetermined frequency.

[0006] In the present invention, when irradiating an ion beam by extracting plasma using a boundary electrode and an extraction electrode, an electric field of a predetermined frequency (hereinafter referred to as the "control electric field") is generated in a control electrode placed in the plasma near the boundary electrode, and the plasma-beam interface near the boundary electrode opening is vibrated by the electric field, thereby varying the divergence angle. Therefore, according to the present invention, it is possible to adjust the divergence angle of the ion beam. The phase, frequency, and strength of the control electric field can be adjusted according to the required divergence angle. The electric field may be generated with a predetermined phase, frequency, and strength, or some or all of these may be adjustable or dynamically changed as appropriate. The predetermined frequency can be selected arbitrarily, such as a high frequency of 400 kHz or higher, or a lower frequency. In addition, in the present invention, plasma generation may be performed using either a filament arc method or a radio frequency (RF) method.

[0007] In the present invention, the plasma generating unit may generate plasma by a radio frequency (RF) method.

[0008] Generally, radio frequency (RF) systems tend to produce ion beams with greater dispersion than filament arc systems, making the present invention particularly useful. The frequency used for plasma generation in RF systems can be determined arbitrarily, but is generally set to 400 kHz or higher. It is believed that the dispersion of the ion beam in RF systems is caused by the vibration of the plasma-beam interface due to the propagation of the radio frequency electric field (hereinafter referred to as the "plasma generating electric field") used to generate plasma. In the present invention, a control electric field is generated near the plasma-beam interface using a radio frequency electrode, thereby adjusting the influence of the plasma generating electric field and enabling the divergence angle of the ion beam to be controlled. In the above-described embodiment, the phase, frequency, and strength of the control electric field can be determined arbitrarily, including frequencies lower than the plasma generating electric field, but it is preferable to set them based on the high frequency of the plasma generating electric field. From this perspective, the frequency of the control electrode is preferably set to a high frequency of 400 kHz or higher, and more preferably to a frequency similar to that of the plasma generating electric field. Furthermore, since the divergence angle is controlled by the interference between the plasma generating electric field and the control electric field, it is preferable that the phases of the two fields be relatively adjustable.

[0009] When plasma is generated by a radio frequency (RF) method, the plasma generating unit may be provided with a detection unit that detects an electric field caused by the RF in the plasma generating unit, and a control unit that applies electricity to the control electrode in accordance with the detected electric field.

[0010] This allows current to be applied to the control electrode in response to fluctuations in the plasma-generating electric field, making it possible to effectively control the divergence angle. The control unit preferably controls all of the frequency, current, and phase of the control electric field, but may control only a part of them. The control according to the detection results can be, for example, feedback control, but various control rules can be applied. The control unit may be configured as software using a computer, or as hardware as a control circuit.

[0011] In the above aspect, the control unit may apply current so as to cancel out the detected electric field, thereby suppressing vibration of the plasma interface and reducing the divergence angle of the ion beam.

[0012] In the above aspect, the control unit may apply current in synchronization with the detected electric field, thereby amplifying the oscillation of the plasma interface and increasing the divergence angle of the ion beam.

[0013] In the above aspect, the detection unit may be installed between the boundary electrode and the extraction electrode. The detection unit can be installed in various locations, but according to the above aspect, it is possible to effectively detect the electric field that affects the plasma-beam interface.

[0014] In the present invention, the boundary electrode and the extraction electrode may have a shape in which a plurality of holes serving as irradiation holes for the ion beam are arranged.

[0015] This allows multiple ion beams to be irradiated in parallel. In this state, if the ion beams are diffused, it is possible to irradiate a wide area with the ion beams or obtain a large beam current.

[0016] In the case of the above shape, the control electrode may be disposed between the holes.

[0017] This allows the control electrodes to be positioned without interfering with the irradiation of the ion beam from the holes. The control electrodes may be positioned separately between the holes, or may be positioned as an integrated whole.

[0018] In the above aspect, the plasma generating unit may have an antenna disposed at a position facing the hole, and may generate plasma by passing the high frequency wave through the antenna.

[0019] In this configuration, the antenna for generating plasma is positioned opposite the hole, making it easy for the plasma-generating electric field to affect the plasma-beam interface. This makes the present invention extremely useful. Furthermore, because it is positioned opposite the hole, the electric field is thought to propagate perpendicular to the hole. This also has the advantage of making it easier to create uniform interference with the control electric field.

[0020] The present invention does not need to include all of the various features described above, and may be configured by omitting or combining some of them as appropriate. Furthermore, the present invention can take various forms, such as not only the configuration as the ion beam irradiation device described above, but also an ion beam irradiation method for irradiating an ion beam using such an ion beam irradiation device.

[0021] Fig. 1 is an explanatory diagram showing the overall configuration of an ion beam irradiation device as an embodiment; Fig. 2 is an explanatory diagram showing the configuration of a boundary electrode and a high-frequency electrode; Fig. 3 is an explanatory diagram showing the influence of a high-frequency electric field on a divergence angle; Fig. 4 is an explanatory diagram showing an example of control of the divergence angle by a control electric field; Fig. 5 is an explanatory diagram showing the overall configuration of an ion beam irradiation device as a modified example;

[0022] An embodiment of the present invention will now be described. Fig. 1 is an explanatory diagram showing the overall configuration of an ion beam irradiation apparatus according to the embodiment. The ion beam irradiation apparatus 10 is an apparatus for generating plasma using a so-called radio frequency (RF) method, and the plasma generation unit 11 is a container for generating and holding plasma 12. A coil for generating plasma, i.e., a radio frequency antenna 13, is attached above the plasma generation unit 11. When a radio frequency is applied to the radio frequency antenna 13 to generate a radio frequency electric field, i.e., a plasma generation electric field, the gas inside the plasma generation unit 11 becomes plasma 12.

[0023] The plasma generation unit 11 has an opening at the bottom in the figure. A boundary electrode 15, an extraction electrode 16, and a ground electrode 17 are provided here for irradiating an ion beam from the plasma. When irradiating a positive ion beam, the boundary electrode 15 is connected to a power supply as a positive electrode and the extraction electrode 16 as a negative electrode. When irradiating a negative ion beam, the boundary electrode 15 is connected to a power supply as a negative electrode and the extraction electrode 16 as a positive electrode. By the action of the boundary electrode 15 and the extraction electrode 16, the plasma is irradiated from the irradiation hole H as an ion beam.

[0024] The angle at which the irradiated ion beam diverges (hereinafter referred to as the "divergence angle") is expressed as a half apex angle of the ion beam, with a state in which a parallel beam is irradiated (divergence angle of 0 degrees) as the reference. When the beam diverges, the angle is a positive value, and when the beam converges, the angle is a negative value. The plasma generating electric field RF1 generated by the radio frequency antenna 13 propagates toward the opening as shown in the figure, vibrating the interface between the plasma 12 at the boundary of the plasma generating section 11 and the outside air (hereinafter referred to as the "plasma interface"). As a result, in the radio frequency (RF) type ion beam irradiation device 10 as in the embodiment, the divergence angle of the ion beam is positive, and the ion beam tends to diverge.

[0025] The ion beam irradiation device 10 of this embodiment is provided with a control electrode 14 above the boundary electrode 15, i.e., inside the plasma generation section 11, as a mechanism for controlling the divergence angle. The control electrode 14 has the following role. When current is applied to the control electrode 14, a radio-frequency electric field, i.e., a control electric field RF2, is generated. This control electric field RF2 interferes with the plasma generation electric field RF1 and changes the effect of the plasma generation electric field RF1 on the plasma interface. As a result, the oscillation of the plasma-beam interface changes, and the divergence angle of the ion beam can be changed.

[0026] The control electrode 14 can be provided at any position, but in this embodiment, the height h2 to the center of the radio frequency antenna 13, based on the boundary electrode 15, is set to 350 mm, and the height h1 to the control electrode 14 is set to 10 mm. Since the plasma generating electric field RF1 attenuates at a distance from the radio frequency antenna 13, by providing the control electrode 14 at a distance from the radio frequency antenna 13 and in the vicinity of the boundary electrode 15, it is possible to achieve effective control while suppressing the strength of the control electric field. These dimensions are merely an example and are not intended to be limiting to those shown in the drawings.

[0027] In order to control the divergence angle, the ion beam irradiation device 10 has the following configuration. The space potential probe 18 is a sensor that detects the electric field near the plasma interface. The space potential probe 18 can be installed anywhere, but in this embodiment, it is installed between the boundary electrode 15 and the extraction electrode 16. This makes it possible to detect the result of interference between the plasma generation electric field RF1 and the control electric field RF2, and the detection result can be effectively used to control the divergence angle. The detection result of the space potential probe 18 is output as an electric signal, amplified by the amplifier 30, and phase-adjusted by the phase adjustment circuit 31, and input to the radio-frequency oscillator 32. The radio-frequency oscillator 32 energizes the control electrode 14 in accordance with this signal. In this way, a control electric field can be generated in accordance with the detection result of the space potential probe 18.

[0028] FIG. 2 is an explanatory diagram showing the configuration of the boundary electrode and the high-frequency electrode. FIG. 2(a) shows a perspective view, and FIG. 2(b) shows a side view. As shown, the boundary electrode 15 has a shape in which multiple irradiation holes 15h are arranged two-dimensionally. In the example shown, 16 irradiation holes 15h are shown, 4 vertically and 4 horizontally, but the number and arrangement can be determined arbitrarily. As shown in FIG. 1, a high-frequency antenna 13 is provided facing each of the irradiation holes 15h. This arrangement has the advantage that the plasma-generating electric field is incident perpendicularly to the irradiation holes 15h, allowing for uniform interference with the control electric field. However, this does not exclude the possibility of providing a high-frequency antenna 13 for multiple irradiation holes 15h or providing a high-frequency antenna 13 regardless of the position of the irradiation holes 15h.

[0029] As shown in the figure, the control electrode 14 is a flat electrode with through holes 14h provided at positions facing the irradiation holes 15h. In other words, the control electrode 14 is installed at a position facing the gaps between the multiple irradiation holes 15h. This makes it possible to avoid interference with the ion beam irradiation from the irradiation holes 15h. An insulator 19 is sandwiched between the control electrode 14 and the boundary electrode 15, integrating them while ensuring insulation between them. In the example shown in the figure, the control electrode 14 is composed of a single plate, but it may also be divided into multiple members.

[0030] A spatial potential probe 18 is inserted between the boundary electrode 15 and the control electrode 14. It is preferable that the spatial potential probe 18 is also inserted so as to avoid the position of the irradiation hole 15h.

[0031] The ion beam irradiation device 10 has the above-described structure, and is capable of irradiating an ion beam while controlling the divergence angle of the ion beam. The operation thereof will be described below.

[0032] FIG. 3 is an explanatory diagram showing the effect of a high-frequency electric field on the divergence angle. FIG. 3(a) shows the structure of the ion beam irradiation device used in the experiment, and FIG. 3(b) shows the experimental results. The ion beam irradiation device shown in FIG. 3(a) generates plasma using a filament arc method and irradiates an ion beam. A filament 13A is attached to the plasma generation unit 11A, and plasma 12A is generated by electrons emitted from the filament 13A. An opening is formed below the plasma generation unit 11A, and a boundary electrode 15A, an extraction electrode 16A, and a ground electrode 17A are attached thereto. In addition, a control electrode 14A is provided inside the plasma generation unit 11A from the boundary electrode 15A.

[0033] When plasma is generated by the filament arc method, unlike the radio frequency (RF) method, there is no plasma generation electric field, so there is no fluctuation in the plasma interface, and the ion beam is irradiated without much diffusion (the state of beam B2 shown by the dashed line in Figure 3(a)). When radio frequency power was applied to control electrode 14A in this state, the beam periodically fluctuated from a convergent state (negative divergence angle) like beam B1 shown by the solid line in Figure 3(a) to a diffused state (positive divergence angle) like beam B2, then to a dot-dash line like beam B3.

[0034] The measurement results are shown in Figure 3(b). The vertical axis represents the ion beam irradiation width W normalized by its average value W0. As shown in the figure, the normalized irradiation width fluctuates periodically within a range of 0.9 to 1.1. This period is synchronized with the period of the high-frequency power applied to the control electrode 14A. This confirms that the control electric field generated by applying current to the control electrode 14A causes the plasma interface to fluctuate from plane S1 to plane S2 as indicated by the arrow S in Figure 3(a), resulting in changes in the beams B1 to B3. Therefore, controlling the electric field acting on the plasma interface can control the ion beam divergence angle. The above experiment also demonstrates that control of the divergence angle using a high-frequency electrode is applicable not only to radio-frequency (RF) systems but also to plasma arc systems.

[0035] 4A and 4B are explanatory diagrams showing an example of controlling the divergence angle using a control electric field. FIG. 4A shows a state in which the phases of the plasma generating electric field RF1 and the control electric field RF2 are inverted. By doing so, the electric field acting on the plasma interface SS is suppressed by the interference between the two. Therefore, the ion beam B becomes almost parallel or convergent. In this state, the energy of the ion beam is concentrated, which is useful in fields that require effective energy application, such as nuclear fusion and accelerators.

[0036] 4(b) shows a state in which the phases of the plasma generating electric field RF1 and the control electric field RF2 are synchronized. By doing so, the influence of the electric field on the plasma interface SS increases due to the amplification effect of both fields, causing it to oscillate significantly as shown by the arrows in the figure. As a result, the ion beam B becomes diffused. This state is useful when irradiating a wide area with an ion beam, such as for irradiation of a semiconductor substrate, film formation, or etching.

[0037] 4 is merely an example, and by controlling the current supply to the control electrode 14, the interference state between the plasma generating electric field and the control electric field can be changed in various ways, and the divergence angle of the ion beam can be controlled accordingly. In actual use, the control electric field may be controlled by feedback control so that the electric field detected by the space potential probe 18 reaches a target state. Alternatively, without using feedback control, the phase may be adjusted by the phase adjustment circuit 31 so that a desired divergence angle is obtained.

[0038] According to the ion beam irradiation device of the embodiment described above, it is possible to control the divergence angle of the ion beam by controlling the current supplied to the control electrode. In the embodiment, the plasma is generated by a radio frequency (RF) method, but the present invention is also applicable to a filament arc method.

[0039] FIG. 5 is an explanatory diagram showing the overall configuration of a modified ion beam irradiation device. An example of application to a filament arc type ion beam irradiation device is shown. An outline of the device is shown in FIG. 5( a). In the modified device, plasma 12B is generated by electrons emitted from a filament (not shown) (see FIG. 3). An opening is formed at the bottom of the device, and a boundary electrode 15B, an extraction electrode 16B, and a ground electrode 17B are attached to these electrodes. An extraction power supply 20 and an acceleration power supply 21 are connected to these electrodes. A control electrode 14B is provided inside the boundary electrode 15B. A high-frequency oscillator 32 is connected to the control electrode 14B.

[0040] In the modified device, when a high frequency is applied from the high frequency oscillator 32, the interface of the plasma 12B is vibrated by the high frequency electric field, and the ion beam 12B is irradiated while changing in width from a narrow ion beam Bn to a wide ion beam Bw. Unlike the embodiment, the modified device does not have a high frequency for generating plasma, and therefore the convergence width is directly affected by the electric field from the control electrode 14.

[0041] The ion beam thus irradiated is then irradiated onto a sample 23 placed on a sample stage 22, thereby making it possible to control the distribution of the ion beam. Figure 5(b) is a plan view of the sample 23, showing the distribution of the ion beam. A narrow spot Sn and a wide spot Sw, each having a narrow convergence width, are generated by the irradiation of each ion beam. In this figure, the wide spot Sw is irradiated onto the entire surface of the sample, and the narrow spot Sn is irradiated in a dispersed state.

[0042] The range of the spot can be adjusted by moving the sample stage 22 vertically as shown by the arrow Mv in Figure 5(a). Furthermore, if the sample stage 22 can be moved one-dimensionally or two-dimensionally in the horizontal direction as shown by the arrow Mh, it is possible to alleviate bias in irradiation of the sample 23 and improve uniformity. Note that the configuration in which the sample stage 22 can be moved is not limited to the filament arc type, but can also be applied to a type in which plasma is generated by high frequency.

[0043] As described above, the control of the divergence angle of the ion beam by using high frequency can be effectively applied to the filament arc method.

[0044] Although the device of the embodiment and the modified example have been described above, the ion beam divergence angle can be adjusted or controlled in various other ways. For example, the correlation between the phase and the divergence angle can be determined in advance by varying the phase of the high-frequency wave of the control electrode 14 using the phase adjustment circuit 31. This allows the phase to be quickly set according to the desired divergence angle. Alternatively, the correlation can be converted into data and stored in the control device, allowing the phase to be automatically determined. The control electrode 14 does not only control phase. It can also control frequency and current (electric field strength). Furthermore, a diode can be interposed between the control electrode 14 and the high-frequency oscillator 32, allowing only positive or negative current to flow. This can cancel or amplify only the positive or negative side of the plasma generating electric field, thereby enabling the beam to be changed between a parallel state and a diverging state, or between an equilibrium state and a convergent state. A low-frequency current, not just a high-frequency current, can also be passed through the control electrode 14. These controls may be realized in software by installing a program in a control device using a computer, or may be realized in hardware.

[0045] The present invention can be used to generate plasma and control the divergence angle of the ion beam when irradiating the plasma with the ion beam.

[0046] 10 Ion beam irradiation device 11, 11A Plasma generation unit 12, 12A Plasma 13 High frequency antenna 13A Filament 14, 14A, 14B High frequency electrode 14h Through hole 15, 15A, 15B Boundary electrode 15h Irradiation hole 16, 16A, 16B Extraction electrode 17, 17A, 17B Ground electrode 18 Space potential probe 19 Insulator 20 Extraction power supply 21 Acceleration power supply 22 Sample stage 23 Sample 30 Amplifier 31 Phase adjustment circuit 32 High frequency oscillator

Claims

1. An ion beam irradiation device that irradiates an ion beam, comprising: a plasma generation unit that generates plasma from a predetermined gas; a boundary electrode provided at an opening of the plasma generation unit as an electrode of opposite polarity to the polarity of the ion beam; an extraction electrode provided outside the boundary electrode as an electrode of the same polarity as the ion beam, for irradiating the ion beam; and a control electrode at the opening of the plasma generation unit for generating an electric field that changes at a predetermined frequency.

2. An ion beam irradiation device according to claim 1, wherein the plasma generating section generates plasma by a radio frequency (RF) method.

3. An ion beam irradiation device according to claim 2, comprising: a detection section for detecting an electric field generated by the high frequency in the plasma generation section; and a control section for passing current through the control electrode in response to the detected electric field.

4. An ion beam irradiation device according to claim 3, wherein the control unit applies electricity so as to cancel out the detected electric field.

5. An ion beam irradiation device according to claim 3, wherein the control unit applies electricity in synchronization with the detected electric field.

6. An ion beam irradiation device according to claim 3, wherein the detection unit is disposed between the boundary electrode and the extraction electrode.

7. An ion beam irradiation device according to claim 1, wherein the boundary electrode and the extraction electrode are shaped such that a plurality of holes serving as irradiation holes for the ion beam are arranged.

8. An ion beam irradiation device according to claim 7, wherein the control electrode is disposed between the holes.

9. An ion beam irradiation device according to claim 6, wherein the plasma generating section has an antenna disposed at a position facing the hole, and the plasma is generated by passing the high frequency wave through the antenna.

10. An ion beam irradiation method for irradiating an ion beam using an ion beam irradiation device having a plasma generation unit, and a boundary electrode and an extraction electrode provided at an opening of the plasma generation unit, comprising: a step of generating plasma from a predetermined gas in the plasma generation unit; a step of irradiating an ion beam by setting the boundary electrode and the extraction electrode to a predetermined potential; and a step of generating an electric field that changes at a predetermined frequency when irradiating the ion beam by passing electricity through a high-frequency electrode provided separately from the boundary electrode and the extraction electrode.

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