Ion source and method of operating the ion source

Abstract

The present invention provides an ion source capable of improving the extraction efficiency of an ion beam depending on the desired ion species, and a method for operating the ion source. [Solution] The ion source 10 comprises a cathode 12 that emits electrons, a plasma generation chamber 11 having an aperture region 14a through which electrons pass, and through which plasma containing desired ion species is generated from a source gas, and an electrode 19 positioned between the cathode 12 and the aperture region 14a and having a cylindrical portion 19a through which electrons pass, and the electrode 19 can be made negatively potential relative to the plasma generation chamber 11.

Description

[Technical Field]

[0001] The present invention relates to an ion source and a method for operating an ion source. [Background technology]

[0002] An ion source disclosed in Patent Document 1 is known as an ion source that generates an ion beam containing desired ion species. This ion source is used in an ion implantation apparatus and comprises an ionization chamber in which plasma is generated and an electron gun that supplies electrons to the ionization chamber.

[0003] This electron gun comprises a cathode that emits thermionic electrons when heated, an anode that is kept at a positive potential relative to the cathode by an anode power supply, and a control circuit that controls the anode power supply. This control circuit generates plasma within the electron gun by applying a positive voltage to the anode. Furthermore, the control circuit can also effectively eliminate the plasma within the electron gun by appropriately adjusting the anode voltage, for example by setting the anode voltage to zero.

[0004] This control circuit operates the ion source in monomer mode when the desired ion is a monatomic ion. It also operates the ion source in cluster mode when the desired ion is a molecular ion. When the ion source operates in monomer mode, i.e., when extracting monatomic ions, the electron beam emitted from the electron gun passes through the anode, ionizing the source gas more in the ionization chamber. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2014-183040 [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] In the ion source described in Patent Document 1, when extracting monatomic ions, the ion source operates in monomer mode. In this case, some of the electrons emitted from the electron gun flow from the anode to the anode electrode, reducing the electron transport efficiency. As a result, the efficiency of ionizing the source gas decreases, and the ion beam extraction efficiency decreases.

[0007] Furthermore, in the ion source described in Patent Document 1, if the anode is eliminated, the ion source cannot be operated in cluster mode, resulting in a decrease in the ion beam extraction efficiency when extracting molecular ions.

[0008] The present invention aims to provide an ion source that can improve the extraction efficiency of an ion beam depending on the desired ion species, and a method for operating the ion source. [Means for solving the problem]

[0009] The present invention provides an ion source for generating an ion beam containing predetermined ion species, comprising: a cathode that emits electrons; a plasma generation chamber having an aperture region through which the electrons pass, through which a plasma containing the ion species is generated from a source gas; and an electrode disposed between the cathode and the aperture region, having a cylindrical portion through which the electrons pass, wherein the electrode can be made negatively potential relative to the plasma generation chamber.

[0010] The ion source of the present invention comprises an electrode positioned between a cathode and an aperture region of a plasma generation chamber, and is configured to bring the electrode to a negative potential relative to the plasma generation chamber. In the ion source of Patent Document 1, the anode is either given a positive potential with respect to the ionization chamber or set to the same potential as the ionization chamber. In contrast, the inventor has confirmed that, depending on the desired ion species, an ion beam containing the ion species can be generated more efficiently when a negative potential is applied to this anode with respect to the ionization chamber. That is, according to the configuration of the present invention, in a specific ion species, the generation efficiency of the plasma containing the ion species is improved, and as a result, the extraction efficiency of the ion beam containing the ion species is improved.

[0011] Further, the ion source of the present invention may be configured to be able to make the electrode have a positive potential with respect to the plasma generation chamber.

[0012] According to this configuration, when an ion species for which a higher ion beam extraction efficiency can be obtained by making the electrode have a positive potential with respect to the plasma generation chamber is desired, the electrode can be made to have a positive potential with respect to the plasma generation chamber. That is, according to this configuration, it is possible to select whether to make the electrode have a negative potential or a positive potential with respect to the plasma generation chamber according to the desired ion species.

[0013] Further, the ion source of the present invention may be configured such that the ion species is a monoatomic ion, the electrode has a negative potential with respect to the plasma generation chamber, and the ion beam is generated.

[0014] The inventor has confirmed that when extracting a relatively light (having a relatively small molecular weight) monoatomic ion, the generation efficiency of the ion beam is improved when the electrode has a negative potential with respect to the plasma generation chamber. That is, according to this configuration, when the desired ion species is a monoatomic ion and the electrode has a negative potential with respect to the plasma generation chamber, the extraction efficiency of the ion beam is improved.

[0015] Further, the ion source of the present invention may be configured such that the ion species is a molecular ion, the electrode has a positive potential with respect to the plasma generation chamber, and the ion beam is generated.

[0016] According to this configuration, when the desired ion species is a molecular ion, the electrode can be set to a positive potential with respect to the plasma generation chamber.

[0017] The operation method of the ion source of the present invention is an operation method of an ion source that generates an ion beam containing a predetermined ion species, comprising a cathode that emits electrons, a plasma generation chamber that has an opening region through which the electrons pass and in which a plasma containing the ion species is generated from a source gas, and an electrode that is disposed between the cathode and the opening region and has a cylindrical portion through which the electrons pass. According to the ion species, it is selected whether to set the electrode to a positive potential or a negative potential with respect to the plasma generation chamber.

[0018] According to this method, it is possible to select whether to set the electrode disposed between the cathode and the opening region of the plasma generation chamber to a positive potential or a negative potential with respect to the plasma generation chamber according to the desired ion species.

Advantages of the Invention

[0019] According to the present invention, the extraction efficiency of the ion beam can be improved according to the desired ion species.

Brief Description of the Drawings

[0020] [Figure 1] Schematic diagram of an ion source in an embodiment of the present invention. [Figure 2] Diagram showing a cross-section around the cathode and the circuit configuration of the ion source in the same embodiment. [Figure 3] Diagram showing a cross-section around the cathode and the circuit configuration of the ion source in a first modification of the same embodiment. [Figure 4] Diagram showing a cross-section around the cathode and the circuit configuration of the ion source in a second modification of the same embodiment. [Figure 5] Diagram showing the relationship between the potential of the bias electrode with respect to the plasma generation chamber and the beam current value based on the test results in a test of extracting an ion beam of single atomic ions (H+) from H2 gas. [Figure 6] This figure shows the relationship between the potential of the bias electrode relative to the plasma generation chamber and the beam current value, based on test results from experiments in which ion beams of various monatomic ions (B+, Si+, C+, and P+) were extracted from various source gases. [Figure 7] This figure shows the relationship between the potential of the bias electrode relative to the plasma generation chamber and the beam current value, based on test results from experiments in which ion beams of various molecular ions (BF2+, CO2+ gas, and P2+) were extracted from various source gases. [Modes for carrying out the invention]

[0021] The ion source 10 in one embodiment of the present invention will be described. Figure 1 is a schematic diagram of the ion source 10. The ion source 10 of this embodiment is incorporated into an ion implantation apparatus used in, for example, a semiconductor manufacturing process, and generates an ion beam IB containing predetermined ion species, as shown in Figure 1. The predetermined ion species are those desired in the process in which the ion source 10 is used, and are appropriately changed depending on the target (not shown) to which the ion beam IB is irradiated and the purpose of irradiating with the ion beam IB.

[0022] The ion source 10 includes a plasma generation chamber 11 in which plasma is generated. The plasma generation chamber 11 in this embodiment has a substantially rectangular parallelepiped shape and has a pair of bottom walls 11a that face each other in the longitudinal direction of the plasma generation chamber 11.

[0023] Each bottom wall 11a has an opening 14 that penetrates through it. The opening 14 forms an opening region 14a through which electrons supplied from the cathode 12, which will be described later, pass. In other words, the plasma generation chamber 11 has an opening region 14a through which electrons supplied from the cathode 12 pass.

[0024] Furthermore, the ion source 10 includes a cathode 12 that emits electrons toward the plasma generation chamber 11. The cathode 12 is an indirectly heated cathode, and the ion source 10 further includes a filament 13 for heating the cathode 12.

[0025] In this embodiment, the cathodes 12 are positioned outside each of the openings 14. That is, the ion source 10 of this embodiment comprises two cathodes 12 and two filaments 13. Alternatively, the ion source 10 may have an opening 14 formed on only one of the pair of bottom walls 11a, and may have one cathode 12 and one filament 13.

[0026] The plasma generation chamber 11 has an extraction opening 15 for extracting the ion beam IB. The extraction opening 15 is formed in the first side wall 11b, which is a side wall connecting the two bottom walls 11a. The plasma generation chamber 11 also has a plurality of gas inlet openings 16 for supplying raw material gas into the interior of the plasma generation chamber 11. Each gas inlet opening 16 is formed in the second side wall 11c, which is opposite the first side wall 11b. In this embodiment, the plasma generation chamber 11 has three gas inlet openings 16, but the number of gas inlet openings 16 is not limited to a specific number.

[0027] Inside the plasma generation chamber 11, a plasma containing desired ion species is generated by a raw material gas introduced from the outside through the gas inlet opening 16 and electrons emitted from the cathode 12. The type of raw material gas introduced into the plasma generation chamber 11 is changed according to the desired ion species.

[0028] The ion source 10 is positioned outside the plasma generation chamber 11 so as to face the extraction opening 15, and includes an extraction electrode 17 for extracting an ion beam IB from the plasma generated in the plasma generation chamber 11.

[0029] The ion source 10 can extract ions contained in the plasma generated inside the plasma generation chamber 11 as an ion beam IB through the extraction aperture 15. The ion beam IB extracted from the plasma generation chamber 11 is mass-separated, and the ion beam IB containing the desired ion species is irradiated onto a target (not shown) (e.g., a semiconductor wafer).

[0030] When the target is irradiated with the ion beam IB, the desired ions are implanted into the target. The purpose of irradiating the target with the ion beam IB using the ion source 10 of this embodiment may, for example, be to modify the surface of the target.

[0031] Figure 2 shows a cross-section of the ion source 10 around the cathode 12, and the configuration of the electrical circuit of the ion source 10. The ion source 10 in this embodiment is equipped with two cathodes 12, but since the configuration of each cathode 12 and its surroundings is identical, only the configuration of one cathode 12 and its surroundings is shown in Figure 2.

[0032] As shown in Figure 2, the ion source 10 includes a grounding element 18 attached to the opening 14 of the plasma generation chamber 11. The grounding element 18 is fixed to the plasma generation chamber 11 and is at the same potential as the plasma generation chamber 11. The grounding element 18 is cylindrical, and even when the grounding element 18 is attached to the opening 14, electrons emitted from the cathode 12 pass through the opening region 14a.

[0033] The ion source 10 further includes a bias electrode 19, which is an electrode positioned between the cathode 12 and the opening region 14a of the plasma generation chamber 11. The bias electrode 19 has a cylindrical portion 19a that can allow electrons emitted from the cathode 12 to pass through.

[0034] More specifically, the bias electrode 19 is positioned between the grounding element 18 and the cathode 12. An insulator (not shown) is positioned between the cathode 12 and the grounding element 18, and the grounding element 18 and the cathode 12 are positioned at a predetermined distance apart in the longitudinal direction of the plasma generation chamber 11.

[0035] Furthermore, the ion source 10 is equipped with an electromagnet (not shown) that forms a magnetic field B inside the plasma generation chamber 11 along the longitudinal direction of the plasma generation chamber 11. Some of the electrons emitted from the cathode 12 are trapped by the magnetic field B and supplied to the plasma generation chamber 11 by passing through the inside of the cylindrical portion 19a and the opening region 14a of the bias electrode 19.

[0036] The ion source 10 includes a filament power supply 21 that supplies a filament voltage Vf across the filament 13. The ion source 10 also includes a cathode power supply 22 that is placed between the cathode 12 and the filament 13 in the circuit and applies a cathode voltage Vc to the cathode 12 to maintain the cathode 12 at a positive potential relative to the filament 13.

[0037] The ion source 10 is positioned in the circuit between the plasma generation chamber 11 and the cathode 12, and includes an emitter power supply 23 that applies an emitter voltage Ve to the plasma generation chamber 11 to maintain the plasma generation chamber 11 at a positive potential relative to the cathode 12.

[0038] Furthermore, the ion source 10 includes a bias power supply 24 that can maintain the bias electrode 19 at a positive potential relative to the cathode 12 while simultaneously making the bias electrode 19 at a negative potential relative to the plasma generation chamber 11. In this embodiment, the positive side of the bias power supply 24 is electrically connected to the bias electrode 19, and a bias voltage Vb is applied to the plasma generation chamber 11. The negative side of the bias power supply 24 is electrically connected to the negative side of the emitter power supply 23.

[0039] Therefore, the ion source 10 can make the bias electrode 19 negative relative to the plasma generation chamber 11 by adjusting the value of the bias voltage Vb to be less than the value of the emitter voltage Ve, that is, by making (bias voltage Vb) < (emitter voltage Ve).

[0040] Furthermore, the ion source 10 can be configured to make the bias electrode 19 positive relative to the plasma generation chamber 11 by adjusting the value of the bias voltage Vb to be greater than the value of the emitter voltage Ve, that is, by making (bias voltage Vb) > (emitter voltage Ve).

[0041] In other words, the ion source 10 can set the bias electrode 19 to either a negative or positive potential relative to the plasma generation chamber 11 by adjusting the bias voltage Vb applied by the bias power supply 24. Furthermore, the ion source 10 can also set the bias electrode 19 to the same potential as the plasma generation chamber 11 by adjusting the bias voltage Vb applied by the bias power supply 24.

[0042] In this embodiment, the configuration in which the bias power supply 24 is connected to the bias electrode 19 and the plasma generation chamber 11 is just one example. The ion source 10 can be configured in any way that allows the bias electrode 19 to be either negative or positive relative to the plasma generation chamber 11 while maintaining the plasma generation chamber 11 at a positive potential relative to the cathode 12.

[0043] Figure 3 shows a cross-section of the area around the cathode 12 and the circuit configuration of the ion source 10 in the first modified example of the ion source 10. In Figure 3, as in Figure 2, only the structure of one cathode 12 and its surrounding area is shown. In the first modified example, the bias power supply 24 is connected between the bias electrode 19 and the plasma generation chamber 11. Furthermore, the bias power supply 24 in the first modified example is configured to switch between positive and negative voltages. The bias power supply 24 in the first modified example may be, for example, a bipolar power supply. Alternatively, the bias power supply 24 in the first modified example may be configured by combining, for example, one or more DC power supplies and switches.

[0044] Figure 4 shows a cross-section around the cathode 12 and the circuit configuration of the ion source 10 in a second modified example of the ion source 10. In Figure 4, as in Figure 2, only the structure of one cathode 12 and its surrounding area is shown. As shown in Figure 4, in the second modification, the bias power supply 24 is located between the plasma generation chamber 11 and the bias electrode 19 via a switch 25 in the circuit. In this modification, the bias electrode 19 can be switched to a positive or negative potential relative to the plasma generation chamber 11 by switching the switch 25.

[0045] In this embodiment, the potential of the bias electrode 19 relative to the plasma generation chamber 11 may hereafter be simply referred to as "the potential of the bias electrode 19." Also, setting the bias electrode 19 to a positive potential relative to the plasma generation chamber 11 may be simply referred to as "setting the bias electrode 19 to a positive potential," and setting the bias electrode 19 to a negative potential relative to the plasma generation chamber 11 may be simply referred to as "setting the bias electrode 19 to a negative potential."

[0046] The inventor conducted tests in which the potential of the bias electrode 19 was changed with several types of raw material gases, and measured the beam current of the ion beam IB drawn at each potential.

[0047] In the ion source described in Patent Document 1, the anode can only be set to either a positive potential relative to the ionization chamber or to the same potential as the ionization chamber. In contrast, the inventor conducted the above test and confirmed that by setting the bias electrode 19 to a negative potential in the ion source 10, there are ion species for which the extraction efficiency of the ion beam IB is improved compared to conventional ion sources.

[0048] The inventor conducted tests using an ion implanter equipped with an ion source 10 to generate ion beams of monatomic ions or molecular ions from multiple types of source gases and measure the beam current values. More specifically, for each ion beam generated from a source gas, the inventor sequentially changed only the potential of the bias electrode 19 relative to the plasma generation chamber 11 under predetermined conditions and measured the beam current values. This ion implanter is equipped with a mass spectrometry magnet for mass spectrometry of the ion beam extracted from the ion source 10, and this test measured the beam current of the ion beam containing the desired ions immediately after mass spectrometry.

[0049] Figures 5 to 7 show the results of the above test and illustrate the relationship between the potential of the bias electrode 19 relative to the plasma generation chamber 11 and the beam current value. In Figures 5 to 7, the measured beam current value is expressed as a ratio to the beam current value when the bias electrode 19 is at the same potential as the plasma generation chamber 11. In other words, Figures 5 to 7 show the relationship between the potential of the bias electrode 19 and the beam current value, with the beam current value measured when the potential of the bias electrode 19 relative to the plasma generation chamber 11 is 0V set to 1.

[0050] Figure 5 shows an ion beam of monatomic ions, i.e., hydrogen ions (H2), using hydrogen (H2) gas as the source gas. + This is the test result when the beam was extracted.

[0051] Figure 5 shows that when extracting a monatomic ion beam (hydrogen ion beam) from hydrogen gas, a higher beam current tends to be obtained when the potential of the bias electrode 19 relative to the plasma generation chamber 11 is negative rather than positive. Furthermore, Figure 4 shows that the beam current is maximized, particularly when the potential of the bias electrode 19 is -65V.

[0052] That is, when hydrogen ions are extracted using the ion source 10, by making the potential of the bias electrode 19 with respect to the plasma generation chamber 11 negative, compared with the conventional case, the generation efficiency of hydrogen ions in the plasma generation chamber 11 is improved, and the extraction efficiency of the ion beam is improved. In particular, when the potential of the bias electrode 19 is -65 V, the generation efficiency of the ion beam is maximized.

[0053] FIG. 6 shows the test results when BF3 gas, SiF4 gas, CO2 gas, and PH3 gas are used as the source gases, and single atomic ion beams are extracted from each source gas. More specifically, from BF3 gas, SiF4 gas, CO2 gas, and PH3 gas, the ion beams of B + , Si + , C + , and P + are the test results when the ion beams are extracted respectively.

[0054] From FIG. 6, when BF3 gas, SiF4 gas, CO2 gas, or PH3 gas is used as the source gas and single atomic ion beams, that is, B + , Si + , C + , or P + are extracted, it is understood that in any case, a higher beam current value tends to be obtained when the potential of the bias electrode 19 with respect to the plasma generation chamber 11 is negative rather than positive.

[0055] As understood from FIGS. 5 and 6, for single atomic ions H + , B + , Si + , C + , or P +When extracting an ion beam, setting the potential of the bias electrode 19 relative to the plasma generation chamber 11 to negative improves the generation efficiency of monatomic ions and thus the extraction efficiency of the ion beam compared to conventional methods. This is presumed to be due, for example, to improved electron confinement efficiency in the cylindrical portion 19a of the bias electrode 19 and improved electron transport efficiency to the plasma generation chamber 11.

[0056] Figure 7 shows the test results when molecular ion beams were extracted from BF3 gas, CO2 gas, and PH3 gas, respectively, using BF3 gas, CO2 gas, and PH3 gas as the source gases. More specifically, from BF3 gas, CO2 gas, and PH3 gas, BF2 + Ion beam, CO2 + The ion beam, and P2 + These are the test results when each of the ion beams was extracted. Figure 7 shows that when BF3 gas, CO2 gas, or PH3 gas is used as the source gas, the molecular ion BF2 + CO2 + , or P2 + When extracting an ion beam, it is understood that in all cases, a higher beam current value tends to be obtained when the potential of the bias electrode 19 relative to the plasma generation chamber 11 is set to a positive potential rather than a negative potential.

[0057] In this embodiment, the ion source 10 can either set the bias electrode 19 to a negative potential relative to the plasma generation chamber 11, or to a positive potential relative to the plasma generation chamber 11. Therefore, for ion species that yield a higher beam current value when the bias electrode 19 is at a negative potential, the bias electrode 19 should be set to a negative potential. Conversely, for ion species that yield a higher beam current value when the bias electrode 19 is at a positive potential, the bias electrode 19 should be set to a positive potential.

[0058] In particular, the above test results indicate that the desired ion species is H + B + Si + , C + , and P+ In the case of monatomic ions such as H2 gas, BF3 gas, SiF4 gas, CO2 gas, and PH3 gas, etc., as the source gas, the bias electrode 19 can be set to a negative potential relative to the plasma generation chamber 11. From the ion source 10 set in this way, an ion beam IB with a higher beam current value compared to conventional methods is generated. In other words, the ion beam extraction efficiency is improved compared to conventional methods.

[0059] Furthermore, if the desired ion species is a molecular ion, the ion source 10 can generate an ion beam IB by setting the bias electrode 19 to a positive potential relative to the plasma generation chamber 11, similar to conventional ion sources (ion sources disclosed in Patent Document 1).

[0060] Furthermore, when extracting monatomic ions from the ion source 10, the extraction efficiency of the ion beam IB does not necessarily improve when the bias electrode 19 is at a negative potential compared to when it is at a positive potential.

[0061] For example, Ar + The inventors have confirmed that when extracting an ion beam consisting of relatively heavy (relatively large) monatomic ions, such as those mentioned above, it is sometimes possible to generate an ion beam with a higher beam current value by setting the bias electrode 19 to a positive potential.

[0062] When operating the ion source 10 of this embodiment, whether to operate it with the bias electrode 19 at a negative potential or at a positive potential is determined by the desired ion species.

[0063] In other words, the operation method of the ion source 10 in this embodiment involves using the ion source 10 and selecting whether to set the bias electrode 19 to a positive potential relative to the plasma generation chamber 11, or to set the bias electrode 19 to a negative potential relative to the plasma generation chamber 11, depending on the desired ion species.

[0064] As mentioned above, the desired ion species is H + B +Si + , N + , and Ne + For relatively light (relatively small formula weight) monatomic ions, it is possible to choose to set the bias electrode 19 to a negative potential relative to the plasma generation chamber 11. This allows for the generation of an ion beam IB with a higher beam current value compared to when the bias electrode 19 is at a positive potential, thereby improving the extraction efficiency of the ion beam IB.

[0065] Furthermore, the desired ion species is a molecular ion, and Ar + When extracting relatively heavy (relatively large) monatomic ions, such as ion beams, it is advisable to set the bias electrode 19 to a positive potential.

[0066] Furthermore, it goes without saying that the present invention is not limited to the embodiments and modifications described above, and various modifications are possible without departing from the spirit of the invention. [Explanation of Symbols]

[0067] 10 Ion sources 11 Plasma generation chamber 12 Cathode 13 Filaments 14 Aperture 14a Opening area 19 Bias electrode 24 Bias power supply IB (Ion Beam)

Claims

1. An ion source that generates an ion beam containing a predetermined ion species, A cathode that emits electrons, A plasma generation chamber having an aperture region through which the electrons pass, and through which a plasma containing the ion species is generated from a source gas, An electrode having a cylindrical portion that allows electrons to pass through, which is positioned between the cathode and the opening region. Equipped with, An ion source capable of making the electrode negatively potential relative to the plasma generation chamber.

2. The ion source according to claim 1, wherein the electrode can be brought to a positive potential relative to the plasma generation chamber.

3. The aforementioned ion species is a monatomic ion, The ion source according to claim 1 or 2, wherein the electrode is made to a negative potential relative to the plasma generation chamber, and the ion beam is generated.

4. The aforementioned ion species is a molecular ion, The ion source according to claim 2, wherein the electrode is brought to a positive potential relative to the plasma generation chamber to generate the ion beam.

5. A method for operating an ion source that generates an ion beam containing a predetermined ion species, A cathode that emits electrons, A plasma generation chamber having an aperture region through which the electrons pass, and through which a plasma containing the ion species is generated from a source gas, An electrode having a cylindrical portion that allows electrons to pass through, which is positioned between the cathode and the opening region. Equipped with, A method for operating an ion source, in which, depending on the ion species, the electrode is set to a positive potential relative to the plasma generation chamber, or to a negative potential relative to the plasma generation chamber.

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