Ion source

Abstract

This aims to increase the current flow rate of the ion beam containing aluminum ions drawn from the ion source, while also achieving stable ion beam extraction. [Solution] The ion source IS comprises a plasma generation chamber 3 and an aluminum-containing material 1 placed inside the plasma generation chamber 3. The aluminum-containing material 1 is an intermetallic compound, and the potential of the aluminum-containing material 1 is lower than the potential of the plasma generation chamber 3.

Description

Technical Field

[0001] It relates to an ion source for extracting an ion beam containing aluminum ions.

Background Art

[0002] Silicon carbide (SiC) devices are expected to be used in high-voltage and high-temperature applications such as electric vehicles, railways, and power plants. In addition, the manufacturing process of SiC devices uses an ion implantation process, similar to that of conventional silicon devices.

[0003] In the ion implantation process of SiC devices, when fabricating a PN junction, nitrogen ions or phosphorus ions are implanted as N-type dopants, and aluminum ions or boron ions are implanted as P-type dopants into a SiC wafer.

[0004] In the generation of nitrogen ions, phosphorus ions, and boron ions, generally, plasma is generated using a gas as a raw material. On the other hand, in the generation of aluminum ions, there is no optimal gas as a raw material, and an aluminum-containing material disposed inside the plasma generation chamber is sputtered.

[0005] Patent Document 1 discloses an ion source that sputters an aluminum-containing material disposed inside a plasma generation chamber to extract an ion beam containing aluminum ions.

[0006] The ion source of Patent Document 1 includes a reflection electrode structure. This reflection electrode structure is composed of an electrode body and a sputtered member. The sputtered member is an aluminum compound such as aluminum nitride or alumina.

[0007] An ionized gas containing fluorine is introduced into the plasma generation chamber. The introduced ionized gas is converted into plasma by an arc discharge. The generated plasma contains fluorine ions. The fluorine ions in the plasma sputter the material to be sputtered, causing aluminum ions and aluminum particles to be released from the sputtered material.

[0008] An ion extraction port is provided at one end of the plasma generation chamber. Near the ion extraction port, an extraction electrode system consisting of multiple electrodes is positioned. This extraction electrode system extracts an ion beam containing aluminum ions from the plasma. [Prior art documents] [Patent Documents]

[0009] [Patent Document 1] Japanese Patent Publication No. 2011-124059 [Overview of the Initiative] [Problems that the invention aims to solve]

[0010] The sputtered material in Patent Document 1 is made of an insulator. Therefore, the potential difference between the insulator and the plasma is small, and the sputtering of the sputtered material by ions in the plasma is insufficient. As a result, the beam current of the ion beam containing aluminum ions drawn from the ion source was not considered a high current.

[0011] A sheath is formed on the surface of the sputtered material, which is an insulator, and the surface potential of the sputtered material becomes positive. When ions in the plasma sputter the sputtered material, secondary electrons are emitted from the sputtered material. The surface of the sputtered material from which secondary electrons have been emitted charges up. When the sputtered material charges up, there is a concern that discharges will occur frequently in the plasma generation chamber, making ion beam extraction unstable.

[0012] The present invention aims to increase the current flow rate of an ion beam containing aluminum ions drawn from an ion source, while also achieving stable ion beam extraction. [Means for solving the problem]

[0013] The ion source is, Plasma generation chamber, The system comprises an aluminum-containing material placed inside the plasma generation chamber, The aforementioned aluminum-containing material is an intermetallic compound, The potential of the aluminum-containing material is lower than the potential of the plasma generation chamber. [Effects of the Invention]

[0014] By constructing the aluminum-containing material with intermetallic compounds, the potential difference between the aluminum-containing material and the plasma increases. This increased potential difference causes more aluminum ions and particles to be knocked out of the aluminum-containing material by ions in the plasma and released into the plasma. As a result, the amount of aluminum ions in the plasma increases, and the current of the ion beam containing aluminum ions drawn from the ion source increases. Furthermore, by constructing the aluminum-containing material with an intermetallic compound, the charging of the aluminum-containing material can be prevented, enabling stable ion beam extraction. [Brief explanation of the drawing]

[0015] [Figure 1] schematic cross-section of an ion source [Figure 2] Perspective view of an aluminum-containing material [Figure 3] Schematic cross-sectional view of a modified ion source. [Figure 4] Schematic cross-sectional view of other variations of the ion source [Modes for carrying out the invention]

[0016] Figure 1 is a schematic cross-sectional view of the ion source IS. This ion source IS is called a indirectly heated ion source. The filament 5 heats the cathode 4, and the heated cathode 4 emits thermoelectrons into the plasma generation chamber 3. This cathode 4 is called a thermoelectron emission member.

[0017] A filament power supply Vf is connected between the terminals of the filament 5. By flowing a current between the terminals of the filament 5 to heat the filament 5, thermoelectrons are emitted from the filament 5. A heat power supply Vc with the cathode 4 side as the positive electrode is connected between the filament 5 and the cathode 4. The thermoelectrons emitted from the filament 5 are accelerated by the voltage of the heat power supply Vc and collide with the cathode 4.

[0018] An ionization gas is supplied to the plasma generation chamber 3 through the gas inlet 7. The ionization gas is a noble gas such as argon or xenon, or a corrosive gas such as phosphorus trifluoride, phosphorus pentafluoride, boron trifluoride, silicon tetrafluoride, or chlorine.

[0019] An arc power supply Va with the plasma generation chamber 3 side as the positive electrode is connected between the cathode 4 and the plasma generation chamber 3. By applying an arc voltage between the cathode 4 and the plasma generation chamber 3 using the arc power supply Va, an arc discharge occurs. The ionization gas supplied to the plasma generation chamber 3 is ionized by the arc discharge, and plasma derived from the ionization gas is generated in the plasma generation chamber 3.

[0020] In the longitudinal direction of the plasma generation chamber 3 (the vertical direction in FIG. 1), an aluminum-containing material 1 is arranged facing the cathode 4. The aluminum-containing material 1 is fixed on a support member 2 made of a conductor material and is arranged at the inner end of the plasma generation chamber 3. Various methods such as screwing, fitting, and clamping are used to fix the aluminum-containing material 1 by the support member 2.

[0021] Aluminum-containing material 1 is an intermetallic compound containing aluminum. Specifically, Mo4Al 17 These are high-melting-point materials with a melting point of 1000°C or higher, such as WAl4 and TaAl3, and have an aluminum content of 30% or more by atomic percentage. Unlike conventional insulators such as AlN and Al2O3, these aluminum-containing materials 1 possess conductive properties.

[0022] A bias power supply Vx, with the plasma generation chamber 3 as the positive electrode, is connected between the plasma generation chamber 3 and the aluminum-containing material 1. This bias power supply Vx causes the potential of the aluminum-containing material 1 to be negative compared to the potential of the plasma generation chamber 3. The plasma generated in the plasma generation chamber 3 contains positively charged ions. These ions are attracted to the aluminum-containing material 1, which has a lower potential, and sputter the aluminum-containing material 1.

[0023] When the aluminum-containing material 1 is sputtered, aluminum ions and aluminum particles are released from the aluminum-containing material 1 into the plasma. The aluminum ions in the plasma pass through the ion extraction port 8 of the plasma generation chamber 3 and are extracted as an ion beam IB by an extraction electrode E consisting of one or more electrodes.

[0024] Since the aluminum-containing material 1 is composed of conductive intermetallic compounds, the potential difference between the plasma and the aluminum-containing material 1 is significantly larger than when using conventional insulators such as AlN and Al2O3. This larger potential difference causes more aluminum ions and particles to be knocked out of the aluminum-containing material 1 by ions in the plasma and released into the plasma. As a result, the amount of aluminum ions in the plasma increases, and the current of the ion beam IB containing aluminum ions drawn from the ion source IS increases.

[0025] Furthermore, by constructing the aluminum-containing material 1 with an intermetallic compound, charging of the aluminum-containing material 1 can be prevented, thus enabling stable extraction of the ion beam IB.

[0026] Furthermore, since the aluminum-containing material 1 is composed of an intermetallic compound, it functions as a reflective electrode, resulting in improved reflection efficiency compared to the configuration in Patent Document 1, which repels electrons emitted from the cathode 4 back to the cathode 4 side. As a result, the ionization efficiency of the ionized gas introduced into the plasma generation chamber 3 is improved, and consequently, the amount of ionized gas used can be reduced.

[0027] To improve the ionization efficiency of the ionized gas, it is desirable to place the illustrated magnet 6 outside the plasma generation chamber 3 to generate a magnetic field B aligned with the opposing direction between the cathode 4 and the aluminum-containing material 1. The direction of the magnetic field B may be the opposite direction to that shown in the illustration, and the magnet 6 can be composed of an electromagnet or a permanent magnet.

[0028] Figure 2 is a perspective view of the aluminum-containing material 1. The aluminum-containing material 1 has a sputtered surface 1a that is sputtered by ions, a back surface 1b that faces the sputtered surface 1a, and a side surface 1c. The two opposing surfaces, the sputtered surface 1a and the back surface 1b, are connected only at the side surface 1c. In other words, there are no other parts connecting the sputtered surface 1a and the back surface 1b besides the side surface 1c, and there is no through hole provided approximately in the center of the sputtered member as in Patent Document 1. With such an aluminum-containing material 1, the capacity of the aluminum-containing material 1 itself increases, making it possible to operate the ion source IS for a longer period of time.

[0029] The aluminum-containing material 1 shown in Figure 2 has a cylindrical shape, but it is not limited to this shape. For example, the aluminum-containing material 1 may be a polygonal prism such as a rectangular prism or a hexagonal prism. Furthermore, the sputtered surface 1a and the back surface 1b do not necessarily have to be flat; they may have irregularities, either entirely or partially. Similarly, the side surface 1c may also have irregularities.

[0030] Figure 3 is a schematic cross-sectional view of a modified ion source IS. In the configuration shown in Figure 3, the arrangement of the aluminum-containing material 1 differs from the configuration in Figure 1. The arrangement of the aluminum-containing material 1 shown in Figure 3 may be adopted as the configuration of the ion source IS. Furthermore, the number of aluminum-containing material 1 may be more than one. In addition, in the configuration example in Figure 3, a reflective electrode made of molybdenum or tungsten may be placed in the position where the aluminum-containing material 1 was placed in Figure 1.

[0031] Figure 4 is a schematic cross-sectional view of another modification of the ion source IS. In Figure 4, the plasma generation chamber 3 is provided with a gas supply port 9 for supplying aluminum-containing gas. Here, the end of the first nozzle 11 of the vaporizer C is inserted into the gas supply port 9.

[0032] The vaporizer C includes a crucible 12 in which an aluminum-containing solid material 17 (for example, a solid material such as pure aluminum, aluminum nitride, or aluminum oxide, which may be in powder form) is placed.

[0033] The crucible 12 is a hollow member that is elongated in one direction. For example, the axis of the crucible 12 extends along the Z-axis direction as shown in the figure. An outlet 12b for supplying aluminum-containing gas to the plasma generation chamber 3 is provided at one end of the crucible 12 in the longitudinal direction. A reactive gas inlet 12a for introducing a reactive gas, a chlorine-containing gas, into the crucible 12 is provided at the other end of the crucible 12 in the longitudinal direction. The chlorine-containing gas is a gas containing chlorine components, such as chlorine gas (Cl2) or hydrogen chloride gas (HCl).

[0034] A first nozzle 11 is detachably attached to the crucible 12. A second nozzle 14 for supplying reactive gas to the crucible 12 is integrally formed with the crucible 12. Various methods (for example, fixing methods such as fitting or screwing) can be used to attach the first nozzle 11 to the crucible 12. The first nozzle 11, the second nozzle 14, and the crucible 12 are made of carbon material for reasons of heat resistance, processability, and cost.

[0035] Arrow J indicates the flow of chlorine-containing gas supplied to the crucible 12. The chlorine-containing gas flows from the gas supply source 20 through the valve 21, then sequentially through the second nozzle 14, the crucible 12, and the first nozzle 11, into the plasma generation chamber 3. When chlorine-containing gas flows into the crucible 12, it reacts with the aluminum-containing solid material 17. This reaction produces aluminum chloride (AlCl3) as a reaction product. When the reaction product is vaporized inside the high-temperature crucible 12, an aluminum-containing gas containing aluminum particles is generated. The aluminum-containing gas and chlorine-containing gas are supplied from the crucible 12 to the plasma generation chamber 3 via the first nozzle 11.

[0036] The aluminum-containing solid material 17 is preferably pure aluminum with a purity of 99.90% or higher. Pure aluminum increases the proportion of aluminum in the aluminum-containing gas compared to other materials. By using pure aluminum, the ion beam current of the ion beam IB containing aluminum ions drawn from the ion source IS increases. However, the aluminum-containing solid material 17 is not limited to pure aluminum. Aluminum nitride, aluminum oxide, or other aluminum-containing solid materials may be used.

[0037] The supply of chlorine-containing gas to the second nozzle 14 may be carried out via a connecting member 19 fitted inside the second nozzle 14. Alternatively, a mass flow controller may be connected to the piping 22 connecting the gas supply source 20 and the connecting member 19 to control the flow rate of the chlorine-containing gas. However, the specific configuration for gas supply is not particularly limited as long as it can supply chlorine-containing gas to the connecting member 19.

[0038] The end portion 11a of the first nozzle 11 protrudes into the plasma generation chamber 3. Gas supply holes are formed in the end portion 11a. These supply holes are formed in a total of four directions: two along the X-axis and two along the Y-axis. This configuration allows for the multi-directional diffusion and supply of aluminum-containing gas within the plasma generation chamber 3. The number of gas supply holes formed at the end portion 11a is not limited to four; it may be less than four or more than four.

[0039] A heater 15 is positioned around the outer circumference of the crucible 12. The heater 15 is, for example, a coil heater or a sheet heater. However, various other heaters may be used. A first heat shield 16a is positioned around the outer circumference of the heater 15 to block heat radiation from the heater 15. In addition, a second heat shield 16b is positioned between the plasma generation chamber 3 and the first nozzle 11 to suppress excessive heat transfer from the plasma generation chamber 3 to the crucible 12.

[0040] A flange 18 is provided for attaching the vaporizer C to the ion source flange 23. The ion source flange 23 indirectly supports the plasma generation chamber 3 and other components such as the filaments 5 and cathode 4 surrounding the plasma generation chamber 3 by supporting components not shown.

[0041] The second nozzle 14 has a large-diameter portion 14a. A coil spring 10 is provided between the flange 18 and the large-diameter portion 14a of the second nozzle 14. The coil spring 10 biases the vaporizer C against the side wall of the plasma generation chamber 3 in order to maintain airtightness between the first nozzle 11 and the plasma generation chamber 3 and to prevent the outflow of aluminum-containing gas or chlorine-containing gas from between the components. The elastic member that biases the vaporizer C against the side wall of the plasma generation chamber 3 is not limited to the coil spring 10; other alternative means such as a leaf spring may also be used.

[0042] To maintain airtightness between the first nozzle 11 and the plasma generation chamber 3, one or more gaskets (not shown) may be provided between the vaporizer C and the side wall of the plasma generation chamber 3. Furthermore, to avoid excessive pressure due to the elastic force of the coil spring 10, a damper (for example, a spring clip) may be attached to the first nozzle 11.

[0043] If the crucible 12 is cylindrical, the cross-section of the aluminum-containing solid material 17 in the XY plane is semicircular. Furthermore, the height of the aluminum-containing solid material 17 is such that it does not block the reactive gas inlet 12a and outlet 12b. With such an aluminum-containing solid material 17, the chlorine-containing gas flows along the surface of the aluminum-containing solid material 17, allowing for efficient reaction between the chlorine-containing gas and the solid material 17.

[0044] Instead of having the end portion 11a of the first nozzle 11 protrude into the plasma generation chamber 3, the tip of the end portion 11a provided on the first nozzle 11 can be made flush with the wall of the plasma generation chamber 3. In this case, the number of gas supply holes formed at the end 11a of the first nozzle 11 is one in the Z-axis direction.

[0045] As shown in the example configuration in Figure 4, supplying an aluminum-containing gas to the plasma generation chamber 3 increases the concentration of the aluminum ion-containing plasma generated within the plasma generation chamber 3. This is expected to lead to a further increase in the beam current of the aluminum ion-containing ion beam IB.

[0046] In the configuration example shown in Figure 4, unlike the configuration examples in Figures 1 and 3, it is not essential to supply the ionized gas into the plasma generation chamber 3 through the gas inlet 7. The reason for this is that chlorine-containing gas and aluminum-containing gas are introduced into the plasma generation chamber 3 from the vaporizer C side. In plasma generation chamber 3, chlorine-containing gas and aluminum-containing gas are converted into plasma, and positively charged ions contained in the plasma are used to sputter aluminum-containing material 1.

[0047] Instead of vaporizer C shown in Figure 4, a conventional vaporizer known as a vaporizer that does not use reactive gas may be used. In a conventional vaporizer, the components from the gas supply source 20 to the second nozzle 14 are unnecessary in the configuration example in Figure 4, and the reactive gas inlet 12a of the crucible 12 is closed.

[0048] The ion source IS in Figures 1, 3, and 4 is not limited to an indirectly heated ion source. The aluminum-containing material 1 described in previous embodiments can also be applied to a barn-type ion source in which the cathode 4 is removed from the ion source IS. In the case of a barn-type ion source, the thermionic emission member, which is the component that emits thermionic electrons into the plasma generation chamber 3, becomes the filament 5. Furthermore, although the cathode 4 and filament 5 are located inside the plasma generation chamber 3 in Figures 1, 3, and 4, they may also be located outside the plasma generation chamber 3.

[0049] In Figures 1 and 3, the bias power supply Vx was connected between the plasma generation chamber 3 and the aluminum-containing material 1, but connecting a power supply between them is not essential. As long as the potential of the aluminum-containing material 1 is lower than the potential of the plasma generation chamber 3, the power supply connection method and circuit configuration may differ from those shown.

[0050] As a specific example of an intermetallic compound containing aluminum, Mo4Al 17 Experiments were conducted to extract aluminum ions from an ion beam using WAl4 and TaAl3. According to the experimental results, Mo4Al 17 Furthermore, TaAl3 was able to obtain approximately twice the beam current compared to WAl4.

[0051] The reason why approximately twice the beam current was obtained is presumed to be due to the high proportion of aluminum elements bonded together. For example, Mo4Al 17 In TaAl3, the proportion of Al-Al bonds in the compound is approximately 70%. In contrast, in WAl4, the proportion of Al-Al bonds in the compound is very small, approximately 0%. The bond between Al and other elements (Mo, Ta, W) is ionic, and is stronger than the bond between Al and Al.

[0052] Due to these differences in bond strength between elements, the rate at which bonds are separated by halogen components (fluorine and chlorine) in the ionized gas differs. Simply put, Al-Al bonds separate faster than Al bonds with other elements. As a result, in compounds of Mo or Ta with Al, the beam current of aluminum ions drawn from the ion source increases compared to compounds of W with Al.

[0053] The melting point of a Ta-Al compound is higher than that of a Mo-Al compound. If the material has a sufficiently high melting point in a high-temperature plasma generation chamber, long-term stable operation of the ion source becomes possible. Considering this point, it is preferable to use a Ta-Al compound compared to a Mo-Al compound.

[0054] Furthermore, it goes without saying that the present invention is not limited to the embodiments described above, and various modifications are possible without departing from its spirit. [Explanation of symbols]

[0055] 1. Aluminum-containing materials 3. Plasma generation chamber 6 Magnets 9. Gas supply port IS Ion Source

Claims

1. Plasma generation chamber, An ion source comprising an aluminum-containing material disposed inside the plasma generation chamber, The aforementioned aluminum-containing material is an intermetallic compound, The potential of the aluminum-containing material is lower than the potential of the plasma generation chamber, which is an ion source.

2. A thermionic emission member is positioned opposite the aluminum-containing material, The ion source according to claim 1, further comprising a magnet that generates a magnetic field in the plasma generation chamber in a direction in which the thermionic emission member and the aluminum-containing material face each other.

3. The aforementioned aluminum-containing material is It has two opposing faces and sides, The ion source according to claim 1, wherein the two opposing surfaces are connected only at the side surfaces.

4. The ion source according to claim 1, wherein the plasma generation chamber is provided with a gas supply port for supplying an aluminum-containing gas.

5. The ion source according to any one of claims 1 to 5, wherein the aluminum-containing material is tantalum, molybdenum, or a compound of tungsten and aluminum.

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