Conical filtering field negative hydrogen ion source structure

Abstract

The invention belongs to the technical field of accelerator and semiconductor ion implantation, and particularly relates to a conical filter field negative hydrogen ion source structure which comprises a lamp filament (13) arranged in a discharge chamber (7), the lamp filament (13) ionizes hydrogen introduced into the discharge chamber (7) into plasma, a cusping magnet (3) is arranged on the outer side of the discharge chamber (7), and a cusping field (15) is formed to constrain the plasma; a plasma electrode (8), an extraction electrode (10) and a ground electrode (14) are arranged on one side of the discharge chamber (7), and plasma is extracted from the discharge chamber (7) under the action of the plasma electrode (8), the extraction electrode (10) and the ground electrode (14); and a central magnet (4) and the like are arranged on the other side, opposite to the plasma electrode (8), of the discharge chamber (7). Negative hydrogen ion beams are obtained in a cusped field coupling axial symmetric filtering field mode, the extracted ion beams are symmetric about the central axis, the beam quality is good, and the transmission efficiency is high; and the service lives of the filament and the ion source are prolonged.

Description

Technical Field

[0001] The invention belongs to the technical field of accelerator and semiconductor ion implantation, and in particular relates to a conical filter field negative hydrogen ion source structure. Background Art

[0002] Ion implantation is an important process in the manufacture of semiconductor components. The ion implanter accelerates the ion beam generated by the ion source and implants it into the semiconductor wafer. The ion source is the component that generates the ion beam in the ion implanter. With the rapid development of power electronics technology, power semiconductor devices (IGBT) play a key role in the field of power conversion and control. The hydrogen ion high energy implanter is an important equipment for the production of IGBT ion implantation process.

[0003] The existing high-energy ion implanters mainly include tandem high-voltage type and high-frequency RF type. The Chinese patent application document with application number 202010515951.8 and titled "A device and method for high-energy hydrogen ion implantation" records a tandem high-voltage ion implanter. The tandem high-voltage type has the advantages of high energy stability and good beam quality. Since the tandem accelerator needs to use negative ion beam implantation, the negative hydrogen ion source is an important component of the high-energy ion implanter. There are two main existing technologies for generating negative hydrogen ion beams. One is to use the positive hydrogen ion beam charge exchange method. This method uses the positive hydrogen ion beam to collide with a certain concentration of gas to form negative ions through charge exchange. The ion beam energy is large and the beam quality is poor. The other is to use a negative hydrogen ion source to directly generate a negative hydrogen ion beam. The tangent field ion source is an effective means of generating negative hydrogen ion beams. Since negative hydrogen ions are extremely unstable, it is necessary to establish a filtering field near the extraction area to filter fast electrons and prevent fast electrons from colliding with negative hydrogen ions and decomposing them. The existing negative hydrogen ion sources all adopt the structure of axial multi-layer magnets, forming a multi-pole tangent field to confine the plasma in the discharge area, and a dipole magnetic field to form a filtering field in the extraction area, such as Figure 2 As shown. The Chinese patent application document with application number 202010515865.7 and titled “A cutting-edge field-shaped negative hydrogen ion source device for a high-energy ion implanter” records the structure in which the discharge zone and the filter zone are connected in series. The structure in which the discharge zone and the filter zone are connected in series makes the discharge chamber long, the gas utilization rate is low, the discharge power is large, and the filament life is short. At the same time, due to the presence of the dipole field near the extraction area, the discharge is asymmetric, the extraction beam quality is poor, and the transmission efficiency is low when passing through the tandem accelerator. This patent discloses an axisymmetric conical filter field ion source structure, which effectively solves the problems of short filament life of the ion source, asymmetric plasma discharge, and poor extraction beam quality. Summary of the invention

[0004] In view of the problems existing in the prior art, the purpose of the present invention is to provide a conical filter field negative hydrogen ion source structure to solve the problems of short filament life of the ion source, asymmetric plasma discharge, poor extraction beam quality and low transmission efficiency.

[0005] In order to achieve the above-mentioned object of the invention, the technical solution of the present invention is as follows:

[0006] A conical filtering field negative hydrogen ion source structure comprises a filament arranged in a discharge chamber, the filament ionizes hydrogen gas introduced into the discharge chamber into plasma, a cusp magnet is arranged outside the discharge chamber to form a cusp field to confine the plasma; a plasma electrode, an extraction electrode and a ground electrode are arranged on one side of the discharge chamber, and the plasma is extracted from the discharge chamber under the action of the plasma electrode, the extraction electrode and the ground electrode; a central magnet is arranged on the other side of the discharge chamber relative to the plasma electrode, and the central magnet, a filtering iron ring arranged on the plasma electrode and the cusp magnets arranged on both sides of the discharge chamber jointly form a conical magnetic field for filtering fast electrons.

[0007] Furthermore, the cusp magnets include a plurality of first cusp magnets uniformly arranged along the circumference of the discharge chamber, and a plurality of second cusp magnets arranged on both sides of the discharge chamber, wherein the plurality of second cusp magnets on the same side are uniformly arranged along circumferences of different radii.

[0008] Furthermore, the polarities of the adjacent first cusp magnets on the same circumference are the same, and the polarities of the adjacent first cusp magnets on different circumferences are opposite.

[0009] Furthermore, the polarities of the adjacent second cusp magnets on the same circumference are the same, and the polarities of the adjacent second cusp magnets on different circumferences are opposite.

[0010] Furthermore, the plurality of second cusp magnets on one side are arranged on a fixed flange of the discharge chamber, and the plurality of second cusp magnets on the other side are arranged on a plasma electrode.

[0011] Furthermore, the central magnet is arranged in a central hole of the fixing flange (the rear flange in the fixing flange).

[0012] Furthermore, the filament is distributed in an annular shape, is coaxial with the conical magnetic field, and is arranged outside the conical magnetic field region.

[0013] Furthermore, the filament is a wave-shaped structure distributed in a ring shape, thereby increasing the electron emission area.

[0014] Furthermore, the filament is made of tantalum, molybdenum or tungsten.

[0015] Furthermore, the discharge voltage applied to the filament is 100-300V.

[0016] Furthermore, the cusp magnet is a samarium cobalt magnet.

[0017] Furthermore, the extraction electrode is trumpet-shaped, and its opening gradually increases along the plasma injection direction. Two groups of magnets and electron blocking rings are arranged in sequence at the end with the smaller opening of the extraction electrode. The two groups of magnets are arranged symmetrically up and down, and the electron blocking ring is arranged on the inner wall of the opening end along the circumference perpendicular to the central axis of the extraction electrode.

[0018] Furthermore, the fixing flange and the plasma electrode are made of copper material.

[0019] Furthermore, the fixing flange and the plasma electrode are both provided with cooling pipes.

[0020] Furthermore, the plasma electrode is negative high voltage, the lead-out electrode is 0.5-3 kV relative to the plasma electrode, and the ground electrode is at ground potential.

[0021] The beneficial effects of the present invention are as follows:

[0022] 1. The negative hydrogen ion beam is obtained by coupling the tangent field with the axisymmetric filtering field. The ion beam is symmetrical about the central axis, with good beam quality and high transmission efficiency.

[0023] 2. In addition to the cusp magnets arranged along the circumference of the outer side of the discharge chamber, cusp magnets are also arranged on the plasma electrode and the rear flange, which enhances the axial constraint of the cusp magnets on the plasma, reduces the size of the discharge chamber, reduces the discharge power of the ion source, improves the ionization efficiency, and prolongs the service life of the ion source;

[0024] 3. The filaments are distributed in a ring shape and are set outside the conical filter field. The plasma density is low, which reduces the sputtering of the plasma on the filaments, greatly prolongs the life of the filaments, reduces the maintenance time of the ion source, and improves the efficiency of the accelerator. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 Schematic diagram of the conical filter field negative hydrogen ion source structure

[0026] Figure 2 It is a schematic diagram of the traditional two-pole filtering field;

[0027] Figure 3 Schematic diagram of the axisymmetric conical filtration field.

[0028] In the above drawings, 1. cooling pipe; 2. rear flange; 3. tangent magnet; 4. center magnet; 5. magnet support; 6. end flange; 7. discharge chamber; 8. plasma electrode; 9. filter iron ring; 10. lead-out electrode; 11. conical magnetic field; 12. electron blocking ring; 13. filament; 14. ground electrode; 15. tangent field; 16. air inlet; 17. magnet. DETAILED DESCRIPTION

[0029] The present invention is described in detail below with reference to the accompanying drawings and embodiments.

[0030] A conical filtering field negative hydrogen ion source structure comprises a filament 13 arranged in a discharge chamber 7, the filament 13 ionizes hydrogen gas introduced into the discharge chamber 7 into plasma, a cusp magnet 3 is arranged outside the discharge chamber 7 to form a cusp field 15 to confine the plasma; a plasma electrode 8, an extraction electrode 10 and a ground electrode 14 are arranged on one side of the discharge chamber 7, and the plasma is extracted from the discharge chamber 7 under the action of the plasma electrode 8, the extraction electrode 10 and the ground electrode 14; a central magnet 4 is arranged on the other side of the discharge chamber 7 relative to the plasma electrode 8, and the central magnet 4, a filtering iron ring 9 arranged on the plasma electrode 8 and the cusp magnets 3 arranged on both sides of the discharge chamber jointly form a conical magnetic field 11 for filtering fast electrons.

[0031] The specific technical solutions are as follows:

[0032] The present invention is a conical filter field negative hydrogen ion source structure, such as Figure 1 As shown. The negative hydrogen ion source is composed of a discharge chamber 7, a filament 13, an air inlet 16, a plasma electrode 8, a filter iron ring 9, a tangent magnet 3, a central magnet 4, a rear flange 2 and an extraction electrode 10. Among them, the tangent magnets 3 are evenly arranged along the circumference through the magnet support 5 outside the discharge chamber 7. The adjacent tangent magnets 3 on the same circumference have the same polarity, and the adjacent tangent magnets 3 on different circumferences have opposite polarities. The fixed flange is arranged at one end of the discharge chamber 7, including an end flange 6 for fixed connection and a rear flange 2 for installing the equipment. The tangent magnets 3 are also arranged on the plasma electrode 8 and the rear flange 2 in the fixed flange through the magnet support 5, and are evenly arranged along the circumferences of different radii on the plasma electrode 8 and the rear flange 2, respectively. The adjacent tangent magnets 3 on the same circumference have the same polarity, and the adjacent tangent magnets 3 on different circumferences have opposite polarities. The tangent magnets 3 are made of samarium cobalt magnets, which have a high Curie temperature and avoid high-temperature demagnetization. The block magnets used in the tangent magnets 3 are small in size and easy to install. The plasma electrode 8 and the rear flange 2 are both made of copper material with high thermal conductivity. A cooling pipe 1 is provided to force cooling and reduce the temperature of the ion source and the cusp magnet 3.

[0033] A central magnet 4 is arranged in the central hole of the rear flange 2 in the fixed flange, and the central magnet 4, the filtering iron ring 9 on the plasma electrode 8, and the tangent magnets 3 respectively arranged on the rear flange 2 and the plasma electrode 8 form an axisymmetric conical filtering magnetic field (conical magnetic field 11), as shown in FIG. Figure 3The axially symmetrical conical filtering magnetic field (conical magnetic field 11) is used to filter fast electrons and improve the extraction efficiency of negative hydrogen ion beams. The central magnet 4 is arranged outside the vacuum, and it can be easily replaced to adjust the ion source discharge parameters.

[0034] The filament 13 in the discharge chamber 7 is distributed in an annular shape and is made of materials such as tantalum, molybdenum or tungsten. It is arranged in an annular shape with a wavy structure outside the conical magnetic field 11. The filament 13 is coaxial with the conical magnetic field 11, which not only increases the electron emission area of ​​the filament 13, but also reduces the sputtering of the plasma on the filament 13, thereby greatly extending the life of the filament 13. Hydrogen is introduced into the discharge chamber 7 of the ion source through the air inlet 16. Under the action of high temperature, the filament 13 emits electrons. By applying a discharge voltage of 100-300V to the filament 13, the electrons are accelerated under the action of the electric field. The accelerated electrons collide with hydrogen molecules to form plasma. The cusp field 15 formed by the cusp magnet 3 outside the discharge chamber 7 is used to constrain the plasma, increase the plasma density, and increase the extraction beam intensity. In the conical field area at the center of the discharge chamber 7, fast electrons are filtered out under the action of the conical magnetic field 11, and negative hydrogen ion beams are extracted under the action of the electric field of the plasma electrode 8 and the extraction electrode 10.

[0035] The plasma electrode 8 is set to negative high voltage, the extraction electrode 10 is 0.5-3kV relative to the plasma electrode 8, and the ground electrode 14 is at ground potential. In addition to the negative hydrogen ion beam, the electron beam will also be extracted at the same time. The extraction electrode 10 is trumpet-shaped, and the opening gradually increases along the plasma injection direction. Two groups of magnets 17 and electron blocking rings 12 are sequentially arranged on the horizontal side wall at the end of the extraction electrode 10 with a smaller opening. The two groups of magnets 17 are arranged symmetrically up and down, and the electron blocking ring 12 is arranged on the inner wall of the horizontal side wall along the circumference perpendicular to the central axis of the extraction electrode 10. The electron blocking ring 12 is annular. Since the mass of electrons is much lower than that of negative hydrogen ions, under the action of the magnetic field, the extracted electron beam can effectively deviate from the center and be blocked by the electron blocking ring 12, thereby obtaining a negative hydrogen ion beam with higher purity. Each group of magnets 17 facing each other up and down has opposite polarity, and the magnetic field is only about tens of Gauss, and the effect on the hydrogen ion beam can be ignored.

[0036] Example

[0037] A conical filter field negative hydrogen ion source structure of the present invention, such as Figure 1As shown. The negative hydrogen ion source is composed of a discharge chamber 7, a plasma electrode 8, a filter iron ring 9, a tangent magnet 3, a central magnet 4, a rear flange 2, an extraction electrode 10, etc. Five circles of tangent magnets 3 are arranged on the outer side of the cylinder wall of the discharge chamber 7, and are evenly arranged along the circumference. The adjacent magnets on the same circumference have the same polarity, and the adjacent magnets on different circumferences have opposite polarities. Five circles of tangent magnets 3 are evenly arranged on the circumferences of different radii on the plasma electrode 8, and five circles of tangent magnets 3 are evenly arranged on the circumferences of different radii on the rear flange 2. The adjacent magnets on the same circumference have the same polarity, and the adjacent magnets on different circumferences have opposite polarities. These magnets are 10 mm in diameter (cylindrical blocks) to form a tangent field 15 around the discharge chamber 7, effectively confining the plasma. A central magnet 4 is arranged at the center hole position of the rear flange 2, and the central magnet 4, the filter iron ring 9 on the plasma electrode 8, and the tangent magnets 3 on the rear flange 2 and the plasma electrode 8 simultaneously form a conical magnetic field 11. The filament 13 is made of tantalum material and is distributed in a wavy structure in an annular shape. It is arranged outside the conical magnetic field 11, which not only increases the electron emission area of ​​the filament 13, but also reduces the sputtering of the plasma on the filament 13, thereby extending the life of the filament 13. The filament 13 is heated by a current of 55-60 amperes to reach a high temperature and emit electrons. By applying a discharge voltage of 100-300V to the filament 13, the electrons are accelerated under the action of the electric field to obtain energy. Hydrogen is introduced into the discharge chamber 7 from the air inlet 16, and the accelerated electrons collide with hydrogen molecules to form plasma. In the central conical field area of ​​the discharge chamber 7, fast electrons are filtered out under the action of the conical magnetic field 11, and a large number of negative hydrogen ions are formed near the extraction area. A high voltage of 0.5-3kV is applied between the plasma electrode 8 and the extraction electrode 10, and a high voltage of 20kV is applied between the extraction electrode 10 and the ground electrode 14. The negative hydrogen ions are extracted by the high voltage electric field to form a negative hydrogen ion beam. When the diameter of the central lead-out hole of the plasma electrode 8 is 5 mm, the lead-out negative hydrogen ion beam is greater than 300 microamperes. The ion source is used to provide a negative hydrogen ion beam for a tandem accelerator with a terminal voltage of 1.7 MV. The acceleration and transmission efficiency of the negative hydrogen ion beam is better than 85%, and the transmission efficiency is improved by more than 30% compared with the traditional ion source. The life of the ion source filament is greater than 500 hours, which is significantly improved compared with the life of the conventional negative hydrogen ion source filament of about 100 hours.

[0038] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

Claims

1. A conical filter field negative hydrogen ion source structure, characterized in that: The invention comprises a filament (13) arranged in a discharge chamber (7), wherein the filament (13) ionizes hydrogen gas introduced into the discharge chamber (7) into plasma; a cusp magnet (3) is arranged outside the discharge chamber (7) to form a cusp field (15) to confine the plasma; a plasma electrode (8), an extraction electrode (10) and a ground electrode (14) are arranged on one side of the discharge chamber (7); the plasma is extracted from the discharge chamber (7) under the action of the plasma electrode (8), the extraction electrode (10) and the ground electrode (14); a central magnet (4) is arranged on the other side of the discharge chamber (7) relative to the plasma electrode (8); the central magnet (4), a filtering iron ring (9) arranged on the plasma electrode (8) and the cusp magnets arranged on both sides of the discharge chamber (7) together form a conical magnetic field (11) for filtering fast electrons.

2. A conical filter field negative hydrogen ion source structure as claimed in claim 1, characterized in that: The cusp magnets (3) include a plurality of first cusp magnets evenly arranged along the circumference of the discharge chamber (7), and a plurality of second cusp magnets arranged on both sides of the discharge chamber (7), wherein the plurality of second cusp magnets on the same side are evenly arranged along circumferences of different radii.

3. A conical filter field negative hydrogen ion source structure as claimed in claim 2, characterized in that: The polarities of the adjacent first cusp magnets on the same circumference are the same, and the polarities of the adjacent first cusp magnets on different circumferences are opposite.

4. A conical filter field negative hydrogen ion source structure as claimed in claim 2, characterized in that: The polarities of the adjacent second cusp magnets on the same circumference are the same, and the polarities of the adjacent second cusp magnets on different circumferences are opposite.

5. A conical filter field negative hydrogen ion source structure as claimed in claim 2, characterized in that: The plurality of second cusp magnets on one side are arranged on a fixed flange of the discharge chamber (7), and the plurality of second cusp magnets on the other side are arranged on a plasma electrode (8).

6. A conical filter field negative hydrogen ion source structure as claimed in claim 5, characterized in that: The central magnet (4) is arranged in the central hole of the fixing flange.

7. A conical filter field negative hydrogen ion source structure as claimed in claim 1, characterized in that: The filament (13) is distributed in an annular shape, is coaxial with the conical magnetic field (11), and is arranged outside the conical magnetic field (11).

8. A conical filter field negative hydrogen ion source structure as claimed in claim 7, characterized in that: The filament (13) is a wave-shaped structure distributed in an annular shape, thereby increasing the electron emission area.

9. A conical filter field negative hydrogen ion source structure as claimed in claim 8, characterized in that: The filament (13) is made of tantalum, molybdenum or tungsten.

10. A conical filter field negative hydrogen ion source structure as claimed in claim 9, characterized in that: The discharge voltage applied to the filament (13) is 100-300V.

11. A conical filter field negative hydrogen ion source structure as claimed in claim 1, characterized in that: The cusp magnet (3) is a samarium cobalt magnet.

12. The conical filter field negative hydrogen ion source structure according to claim 1, characterized in that: The extraction electrode (10) is trumpet-shaped, with an opening gradually increasing along the plasma injection direction. Two groups of magnets (17) and an electron blocking ring (12) are sequentially arranged at one end of the extraction electrode (10) with a smaller opening. The two groups of magnets (17) are symmetrically arranged up and down, and the electron blocking ring (12) is arranged on the inner wall of the opening end along a circumference perpendicular to the central axis of the extraction electrode (10).

13. A conical filter field negative hydrogen ion source structure as claimed in claim 5, characterized in that: The fixing flange and the plasma electrode (8) are made of copper material.

14. A conical filter field negative hydrogen ion source structure as claimed in claim 5, characterized in that: The fixed flange and the plasma electrode (8) are both provided with cooling pipes (1).

15. The conical filter field negative hydrogen ion source structure according to claim 1, characterized in that: The plasma electrode (8) is at negative high voltage, the lead-out electrode (10) is at 0.5-3 kV relative to the plasma electrode (8), and the ground electrode (14) is at ground potential.

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