Atom removal device for ion implantation process

Abstract

An atom screening device is used in the ion implantation process of a semiconductor manufacturing process, and includes a first atom screening module and a second atom screening module. The first atom screening module includes a sector mass analyzer, and the second atom screening module includes a first electrode plate pair, a second electrode plate pair, a first driver, and a second driver. The sector mass analyzer screens out elements whose deflection radius is greater than the outer wall of the sector mass analyzer or less than the inner wall of the sector mass analyzer, and the second atom screening module screens out elements whose deflection radius is between the outer wall and the inner wall of the sector mass analyzer. Thus, elements with similar atomic weights or isotopes to ions used for ion implantation are screened out, thereby improving the yield of the ion implantation process of high-end processes, while also converging the ion beam and reducing secondary electrons and radiation.

Description

Technical Field

[0001] The present application relates to an atom screening device for an ion implantation process in a semiconductor manufacturing process, and more particularly to an atom screening device capable of screening out atoms with a mass close to or isotopes of atoms implanted into an ion beam of a substrate in the ion implantation process. Background Art

[0002] In the semiconductor manufacturing process, ion doping is an important process for forming the PN junction of semiconductor components. Ion doping is completed by the ion implantation process. In the ion implantation process, since it is carried out under high temperature and high pressure, various elements of the environment or equipment will precipitate and mix into the ion beam used for the ion implantation process, which will affect the quality of the ion implantation process. The existing solution is to pass the ion beam through a mass analyzer. The magnetic field of the mass analyzer acts on the charge of the ion beam to generate the Lorentz force to deflect the ions, thereby screening out elements not used for the ion implantation process.

[0003] However, it is not easy to screen out atoms that are not used for ion implantation and have atomic weights similar to those of elements used in the ion implantation process or their isotopes by the mass analyzer. In the early low-end and mid-end processes, these elements have little effect on the yield, but with the gradual development of high-end processes (below 10nm), these atoms with similar atomic weights or their isotopes will affect the yield of the process to a considerable extent. Therefore, how to screen out these elements has become an important technical issue in high-end processes. Summary of the invention

[0004] An embodiment of the present application provides an atom screening device for an ion implantation process, which can screen out elements having similar atomic weights or isotopes to an ion beam used for the ion implantation process, thereby improving the yield of the ion implantation process in high-end processes.

[0005] In order to solve the above technical problems, this application provides solutions in the following ways:

[0006] The embodiment of the present application discloses an atom screening device for the ion implantation process of a semiconductor manufacturing process, which includes: a first atom screening module and a second atom screening module. The first atom screening module includes a sector-shaped mass analyzer, which includes an outer side wall and an inner side wall that are arc-shaped relative to the center of the circle, the outer side wall and the inner side wall are arranged opposite to each other and form an inlet end and an outlet end at both ends, respectively, and the second atom screening module includes a first electrode plate pair and a second electrode plate pair, and the first electrode plate pair and the second electrode plate pair are movably arranged near the outlet end of the sector-shaped mass analyzer. Wherein, the ion beam enters the sector-shaped mass analyzer from the inlet end, the sector-shaped mass analyzer of the first atom screening module screens out part of the ions, and the first electrode plate pair and the second electrode plate pair of the second atom screening module screen out part of the ions that leave the sector-shaped mass analyzer from the outlet end.

[0007] The outer side wall at the outlet end and the center of the circle have a first distance D1, the inner side wall at the outlet end and the center of the circle have a second distance D0, the difference between the first distance and the second distance is a first difference L, D1-D0 = L. The ion beam enters the sector-shaped mass analyzer from the inlet end, and the ion beam enters the sector-shaped mass analyzer from the inlet end and has a deflection radius R, the difference between the deflection radius and the second distance D0 is a second difference D, R-D0 = D, and the first atom screening module screens out ions whose second difference D>L or D<0 in the ion beam.

[0008] The first electrode plate pair can move to a position between a distance L and L / 2 from the inner side wall of the outlet end, and the second electrode plate pair can move to a position between a distance L / 2 and 0 from the inner side wall of the outlet end. Ions in the ion beam whose second difference value L>D>L / 2 leave the sector mass analyzer from the outlet end and are screened out by the first electrode plate pair, and ions in the ion beam whose second difference value L / 2>D>0 leave the sector mass analyzer from the outlet end and are screened out by the second electrode plate pair.

[0009] The first electrode plate pair includes a first proximal electrode plate and a first distal electrode plate, the first proximal electrode plate is closer to the exit end of the sector-shaped mass analyzer than the first distal electrode plate, and the second electrode plate pair includes a second proximal electrode plate and a second distal electrode plate, the second proximal electrode plate is closer to the exit end of the sector-shaped mass analyzer than the second distal electrode plate.

[0010] Optionally, in some embodiments, the potential of the first proximal electrode plate is lower than the potential of the first distal electrode plate, and the potential of the second proximal electrode plate is lower than the potential of the second distal electrode plate.

[0011] Optionally, in some embodiments, the potential of the first proximal electrode plate is equal to the potential of the second proximal electrode plate, and the potential of the first distal electrode plate is equal to the potential of the second distal electrode plate.

[0012] Optionally, in some embodiments, the first proximal electrode plate, the first distal electrode plate, the second proximal electrode plate and the second distal electrode plate are graphite plates.

[0013] Optionally, in some embodiments, the lengths of the first proximal electrode plate and the first distal electrode plate are both greater than L / 2, and the lengths of the second proximal electrode plate and the second distal electrode plate are both greater than L / 2.

[0014] Optionally, in some embodiments, the atom screening device further includes a mass spectrometry analysis unit, which derives the atomic weight of the element to be screened out by the second atom screening module based on the ion beam current intensity and the element mass distribution of the ion beam.

[0015] Optionally, in some embodiments, the atomic screening device also includes a computing control unit, which calculates the deflection radius R of the ions of the elements to be screened out relative to the center of the circle based on the atomic weight of the elements to be screened out provided by the mass spectrometry analysis unit, and calculates the second difference D between the deflection radius R and the second distance D0, and compares the second difference D with the first difference L to generate a control signal, and selects to drive the first driver to move the first electrode plate pair or to drive the second driver to move the second electrode plate pair.

[0016] Optionally, in some embodiments, the calculation control unit further calculates the deflection radius R relative to the center of the circle according to the speed at which the ions of the elements to be screened out enter the inlet end, the magnetic flux of the sector mass analyzer and the ion charge of the elements to be screened out.

[0017] Optionally, in some embodiments, a first driver and a second driver are further included, the first driver drives the first electrode plate pair to move, and the second driver drives the second electrode plate pair to move, the first driver includes a first stepper motor and a first encoder, the second driver includes a second stepper motor and a second encoder, the first encoder detects the rotation angle of the first stepper motor, and the second encoder detects the rotation angle of the second stepper motor.

[0018] The atom screening device of the present application sets up a second atom screening module, uses the first electrode pair to screen out elements whose second difference D between the deflection radius R and the second distance D0 is between L and L / 2, and uses the second electrode pair to screen out elements whose second difference D between the deflection radius R and the second distance D0 is between L / 2 and 0, thereby screening out elements with similar atomic weight or their isotopes to the ions used for ion implantation, while also converging the ion beam and reducing secondary electrons and radiation. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The drawings described herein are used to provide a further understanding of the present application and constitute a part of the present application. The illustrative embodiments of the present application and their descriptions are used to explain the present application and do not constitute an improper limitation on the present application. In the drawings:

[0020] Figure 1 is a schematic diagram of the main structure of an atom screening device according to an embodiment of the present application;

[0021] Figure 2 is a system block diagram of an atom screening device according to an embodiment of the present application;

[0022] Figure 3 It is a graph of the relationship between the ion beam current and the element mass after the ion beam with different elements passes through the sector mass analyzer;

[0023] Figure 4 It is a flow chart of using the atomic screening device of the present application to screen out elements.

[0024] 1 atom screening device; 10 first atom screening module; 11 sector mass analyzer; 20 second atom screening module; 21 first electrode plate pair; 22 second electrode plate pair; 23 first driver; 24 second driver; 30 mass spectrometry unit; 40 calculation control unit; 60 selection unit; 70 signal amplifier; 111 outer wall; 112 inner wall; 113 inlet end; 114 outlet end; 211 first proximal electrode plate; 212 first distal electrode plate; 2 21 second proximal electrode plate; 222 second distal electrode plate; 231 first stepper motor; 232 first encoder; 241 second stepper motor; 242 second encoder; 2311 gear; 2312 rack; 2313 insulation structure; 2411 gear; 2412 rack; 2413 insulation structure; D second difference; D1 first distance; D0 second distance; L first difference; O center of circle; P1 first peak; P2 second peak; P3 third peak; R deflection radius DETAILED DESCRIPTION

[0025] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0026] See also Figure 1 and Figure 2 ,in Figure 1 is a schematic diagram of the main structure of an atom screening device according to an embodiment of the present application, Figure 2 1 is a system block diagram of an atom screening device according to an embodiment of the present application. As shown in the figure, the atom screening device 1 according to an embodiment of the present application includes a first atom screening module 10 and a second atom screening module 20. The first atom screening module 10 includes a sector-shaped mass analyzer 11, which includes an outer wall 111 and an inner wall 112. The outer wall 111 and the inner wall 112 are arranged opposite to each other to form an ion beam channel, and an inlet end 113 and an outlet end 114 are formed at both ends, respectively. The outer wall 111 and the inner wall 112 are in an arc shape relative to the center O of the circle close to the inner wall. The inlet end 113 and the outlet end 114 have an angular distance of 90 degrees relative to the center of the circle. The outer wall 111 located at the outlet end 114 has a first distance D1 from the center O, and the inner wall 112 located at the outlet end 114 has a second distance D0 from the center O. The difference between the first distance D1 and the second distance D0 is a first difference L, and D1-D0=L.

[0027] The ion beam I enters the sector-shaped mass analyzer 11 from the entrance end 113. Under the action of the external magnetic field, the external magnetic field interacts with the charge of the ion beam to form a Lorentz force f on the ions I, f=qvB, where q is the charge of the ions, v is the speed of the ions I entering the entrance end 113, and B is the magnetic flux of the sector-shaped mass analyzer 11. The Lorentz force f acts as the centripetal force that deflects the ions I in the sector-shaped mass analyzer 11. Therefore, according to the formula of the centripetal force and the mass, speed and deflection radius of the ions I, f=mv 2 / R, where m is the element mass, v is the velocity of ions I entering the inlet end 113, and R is the deflection radius. From the above formula of Lorentz force and centripetal force, it can be obtained that the deflection radius R = mv / qB.

[0028] Different elements have different deflection radii in the sector mass analyzer 11. Under the same conditions of ion charge number q and magnetic flux B, the deflection radius R is positively correlated with the element mass. The difference between the deflection radius R and the second distance D0 is defined as the second difference D, D = R-D0. Figure 1 As shown, if the deflection radius R of element a is greater than the first distance D1, that is, the second difference D is greater than L, element a will collide with the outer wall 111 after entering the sector-shaped mass analyzer 11 from the inlet end 113, and will not pass through the outlet end 114. If the deflection radius R of element b is less than the second distance D0, that is, the second difference D is less than 0, element b will collide with the inner wall 112 after entering the sector-shaped mass analyzer 11 from the inlet end 113, and will not pass through the outlet end 114. Therefore, the sector-shaped mass analyzer 11 of the first atom screening module 10 can screen out ions with a deflection radius R greater than D1 or less than D0 in the ion beam, that is, it can screen out elements with a large difference in elemental mass from the ion beam used for the ion implantation process.

[0029] In addition, elements with similar mass or isotopes to the element mass of the ion beam used for the ion implantation process, together with the element used for the ion implantation process, will leave the sector mass analyzer 11 from the outlet end 114. At this time, the second atom screening module 20 disposed at the outlet end 114 of the sector mass analyzer 11 is used to screen out elements or isotopes with similar atomic weights.

[0030] The second atom screening module 20 includes a first electrode plate pair 21, a second electrode plate pair 22, a first driver 23 and a second driver 24. The first electrode plate pair 21 and the second electrode plate pair 22 are arranged near the exit end 114 of the sector mass analyzer 11, and are used to capture or screen out elements not used for the ion implantation process that leave the sector mass analyzer 11 along with the ion beam of the ion implantation process. The first driver 23 drives the first electrode plate pair 21 to move to a position between the distance D1 and D0+L / 2 from the center of the circle, and the second driver 24 drives the second electrode plate pair 22 to move to a position between the distance D0+L / 2 and D0 from the center of the circle.

[0031] After the ion beam passes through the sector mass analyzer 11, the ions c in the ion beam whose deflection radius R is less than D1 and greater than D0+L / 2 leave the sector mass analyzer 11 from the outlet end 114 and are screened out by the first electrode plate pair 21, that is, the ions in the ion beam whose second difference value L>D>L / 2 leave the sector mass analyzer 11 from the outlet end 114 and are screened out by the first electrode plate pair 21. The ions d in the ion beam whose deflection radius R is less than D0+L / 2 and greater than D0 leave the sector mass analyzer 11 from the outlet end 114 and are screened out by the second electrode plate pair 22, that is, the ions in the ion beam whose second difference value L / 2>D>0 leave the sector mass analyzer 11 from the outlet end 114 and are screened out by the second electrode plate pair 22. In this way, the second atom screening module 20 can screen out elements with a mass close to that of the element or its isotope of the ion beam used for the ion implantation process, which cannot be screened out by the first atom screening module 10.

[0032] The first electrode plate pair 21 includes a first proximal electrode plate 211 and a first distal electrode plate 212, and the first proximal electrode plate 211 is closer to the outlet end 114 of the sector-shaped mass analyzer 11 than the first distal electrode plate 212. The second electrode plate pair 22 includes a second proximal electrode plate 221 and a second distal electrode plate 222, and the second proximal electrode plate 221 is closer to the outlet end 114 of the sector-shaped mass analyzer 11 than the second distal electrode plate 222. The first proximal electrode plate 211, the first distal electrode plate 212, the second proximal electrode plate 221 and the second distal electrode plate 222 of this embodiment are all graphite plates. In addition, in order to increase the reliability of screening out elements, the lengths of the first proximal electrode plate 211 and the first distal electrode plate 212 are both greater than L / 2, and the lengths of the second proximal electrode plate 221 and the second distal electrode plate 222 are both greater than L / 2, so as to screen out elements not used for the ion implantation process at the outlet end 114 of the sector-shaped mass analyzer 11 reliably.

[0033] The potential of the first proximal electrode plate 211 is lower than the potential of the first distal electrode plate 212, for example, the potential difference between the two is 2 kV. The potential of the second proximal electrode plate 221 is lower than the potential of the second distal electrode plate 222, for example, the potential difference between the two is 2 kV. The potential of the first proximal electrode plate 211 is equal to the potential of the second proximal electrode plate 221, and the potential of the first distal electrode plate 212 is equal to the potential of the second distal electrode plate 222. After the negatively charged ion beam leaves the exit end 114 of the sector mass analyzer 11, the elements of the ion beam not used for the ion implantation process can be repelled and excluded by the first proximal electrode plate 211 or the second proximal electrode plate 221, and at the same time, the negatively charged first proximal electrode plate 211 and the second proximal electrode plate 221 play a role in converging the ion beam used for the ion implantation process toward the center. In addition, the first proximal electrode plate 211 or the second proximal electrode plate 221 with a negative potential can exclude secondary electrons, or the secondary electrons are adsorbed by the first distal electrode plate 212 or the second distal electrode plate 222 with a positive potential, thereby playing a role in excluding secondary electrons.

[0034] like Figure 2 As shown, the atomic screening device 1 of the present application also includes a mass spectrometry unit 30, which obtains the atomic weight of the element to be screened out by the second atomic screening module according to the ion beam current intensity of each component element of the ion beam after passing through the sector mass analyzer 11 and the element mass distribution of the ion beam. Figure 3 As shown, the element used for the ion implantation process has a first peak value P1 of the ion beam current intensity, the element or isotope with a similar atomic weight to the element used for the ion implantation process has a second peak value P2 of the ion beam current intensity, and the other elements not used for the ion implantation process have a third peak value P3 of the ion beam current intensity. Therefore, the mass spectrometry unit 30 obtains the mass of the element that is desired to be screened out. The element with the third peak value P3 can be screened out after entering the sector mass analyzer 11 because its deflection radius is very different from that of the element used for the ion implantation process. The element with the second peak value P2 is the element that is desired to be screened out using the second atom screening module 20.

[0035] See also Figure 2The atomic screening device 1 of the present application also includes a calculation control unit 40, which calculates the deflection radius R of the ions of the element to be screened out relative to the center of the circle according to the atomic weight m of the element to be screened out provided by the mass spectrometry unit 30, and calculates the second difference D between the deflection radius R and the second distance D0, and compares the second difference D with the first difference L to generate a control signal. The control signal is transmitted to the analog-to-digital conversion unit 50, which converts the digital control signal into an analog control signal. The analog control signal is transmitted to the selection unit 60, which selects to drive the first driver 23 to move the first electrode plate pair 21 or to drive the second driver 24 to move the second electrode plate pair 22. The analog control signal is transmitted from the selection unit 60 to the signal amplifier 70, and the amplified analog control signal is transmitted to the first driver 23 or the second driver 24 to make it run. The first driver 23 includes a first stepper motor 231 and a first encoder 232. The second driver 24 includes a second stepper motor 241 and a second encoder 242. The first encoder 232 detects the rotation angle of the first stepper motor 231, and the second encoder 242 detects the rotation angle of the second stepper motor 241. The rotation angle data detected by the first encoder 232 and / or the second encoder 242 are fed back to the calculation control unit 40.

[0036] The output shaft of the first stepper motor 231 is provided with a gear 2311, and racks 2312 are provided on the first proximal electrode plate 211 and the first distal electrode plate 212, so that the first stepper motor 231 can drive the first proximal electrode plate 211 and the first distal electrode plate 212 to move synchronously. An insulating structure 2313 is provided at the connection between the first proximal electrode plate 211 and the first distal electrode plate 212 and the rack 2312, so that the first proximal electrode plate 211 and the first distal electrode plate 212 are electrically insulated from the first stepper motor 231. Similarly, the output shaft of the second stepper motor 241 is provided with a gear 2411, and racks 2412 are provided on the second proximal electrode plate 221 and the second distal electrode plate 222, so that the second stepper motor 241 can drive the second proximal electrode plate 221 and the second distal electrode plate 222 to move synchronously. An insulating structure 2413 is provided at the connection between the second proximal electrode plate 221 and the second distal electrode plate 222 and the rack 2412 , so that the second proximal electrode plate 221 and the second distal electrode plate 222 are electrically insulated from the second stepping motor 241 .

[0037] See also Figure 4 , Figure 4 This is a flow chart of using the atomic screening device of the present application to screen out elements not used in the ion implantation process. In step S1, after the ion beam is adjusted for uniformity and angle to reach the operating standard, the process then proceeds to step S2.

[0038] In step S2, the ion beam first enters the sector mass analyzer 11 and obtains Figure 3The corresponding relationship between the ion beam current intensity of each element shown and the atomic weight is obtained by the mass spectrometry unit 30 for the atomic weight of the element to be screened out, and then step S3 is entered.

[0039] In step S3, the mass spectrometry unit 30 transmits the atomic weight of the element to be screened out to the calculation and control unit 40. The calculation and control unit 40 calculates the deflection radius R of the element to be screened out according to the atomic weight m of the element to be screened out, the velocity v of the ion beam, the charge number q of the ion, and the magnetic flux B of the sector mass analyzer 11. Then, the calculation and control unit 40 calculates the second difference D between the deflection radius R and the second distance D0, R - D0 = D. If D > D1 or D < D0, step S4 is entered. If L > D > L / 2 or L / 2 > D > 0, step S5 is entered. If D = L / 2, step S6 is entered.

[0040] In step S4, the element to be screened out can be screened out by the sector mass analyzer 11. Therefore, the ion implantation process is being carried out, and it is not necessary to start the second atomic screening module 20.

[0041] In step S5, the element to be screened out must be screened out by the second atomic screening module 20. Therefore, the calculation and control unit 40 sends a control signal to the first driver 23 or the second driver 24 to move the first electrode plate pair 21 or the second electrode plate pair 22 to the position of the second difference D to block and screen out the element to be screened out.

[0042] In step S6, the element to be screened out has the same deflection radius as the ion used in the ion implantation process. At this time, the calculation and control unit 40 issues a warning and checks the calculation results of the mass spectrometry unit 30 to find problems.

[0043] The atomic screening device of the present application screens out elements with the second difference D between the deflection radius R and the second distance D0 between L and L / 2 by using the first electrode pair, and screens out elements with the second difference D between the deflection radius R and the second distance D0 between L / 2 and 0 by using the second electrode pair, so as to screen out elements with atomic weights or their isotopes similar to those of the ions used for ion implantation, and at the same time plays a role in converging the ion beam and reduces secondary electrons and radiation.

[0044] It should be noted that in this article, the term "including", "comprising" or any other variant thereof is intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements not only includes those elements, but also includes other elements not expressly listed, or also includes elements inherent to such process, method, article or device. Without further limitation, an element defined by the statement "including one..." does not exclude the existence of another identical element in the process, method, article or device including the element.

[0045] The embodiments of the present application are described above in conjunction with the accompanying drawings, but the present application is not limited to the above-mentioned specific implementation methods. The above-mentioned specific implementation methods are merely illustrative and not restrictive. Under the guidance of the present application, ordinary technicians in this field can also make many forms without departing from the purpose of the present application and the scope of protection of the claims, all of which are within the protection of the present application.

Claims

1. An atom screening device (1) for use in an ion implantation process of a semiconductor manufacturing process, characterized in that: include: A first atom screening module (10) comprises a sector-shaped mass analyzer (11), wherein the sector-shaped mass analyzer (11) comprises an outer wall (111) and an inner wall (112) which are arc-shaped relative to the center of the circle, wherein the outer wall (111) and the inner wall (112) are arranged opposite to each other and form an inlet end (113) and an outlet end (114) at both ends, respectively, wherein the center of the circle is close to the inner wall (112), and the outer wall (111) at the outlet end (114) is close to the center of the circle. The first distance between the inner side wall (112) and the center of the circle is D1, the second distance between the inner side wall (112) located at the outlet end (114) and the center of the circle is D0, the difference between the first distance and the second distance is a first difference value L, D1-D0=L; wherein the ion beam has a deflection radius R after entering the sector mass analyzer (11), the difference between the deflection radius R and the second distance D0 is a second difference value D, R-D0=D, and the first atom screening module (10) screens out ions in the ion beam whose second difference value D>L or D<0; A second atom screening module (20) comprises a first electrode plate pair (21) and a second electrode plate pair (22), wherein the first electrode plate pair (21) and the second electrode plate pair (22) are movably arranged near the outlet end (114) of the sector mass analyzer (11), wherein the first electrode plate pair (21) can move to a position between a distance L and L / 2 from the inner side wall (112) of the outlet end (114), and the second electrode plate pair (22) can move to a position between a distance L and L / 2 from the inner side wall (112) of the outlet end (114). The inner side wall (112) of the outlet end (114) moves to a position between a distance L / 2 and 0; wherein ions in the ion beam whose second difference value L>D>L / 2 leave the sector-shaped mass analyzer (11) from the outlet end (114) and are screened out by the first electrode plate pair (21), and ions in the ion beam whose second difference value L / 2>D>0 leave the sector-shaped mass analyzer (11) from the outlet end (114) and are screened out by the second electrode plate pair (22); The ion beam enters the sector-shaped mass analyzer (11) from the inlet end (113), the sector-shaped mass analyzer (11) of the first atom screening module (10) screens out a portion of the ions, and the first electrode plate pair (21) and the second electrode plate pair (22) of the second atom screening module (20) screen out a portion of the ions that leave the sector-shaped mass analyzer (11) from the outlet end (114).

2. The atom screening device (1) according to claim 1, characterized in that: The first electrode plate pair (21) includes a first proximal electrode plate (211) and a first distal electrode plate (212), wherein the first proximal electrode plate (211) is closer to the outlet end (114) of the sector-shaped mass analyzer (11) than the first distal electrode plate (212), and the second electrode plate pair (22) includes a second proximal electrode plate (221) and a second distal electrode plate (222), wherein the second proximal electrode plate (221) is closer to the outlet end (114) of the sector-shaped mass analyzer (11) than the second distal electrode plate (222).

3. The atom screening device (1) according to claim 2, characterized in that: The potential of the first proximal electrode plate (211) is lower than the potential of the first distal electrode plate (212), and the potential of the second proximal electrode plate (221) is lower than the potential of the second distal electrode plate (222).

4. The atom screening device (1) according to claim 3, characterized in that: The potential of the first proximal electrode plate (211) is equal to the potential of the second proximal electrode plate (221), and the potential of the first distal electrode plate (212) is equal to the potential of the second distal electrode plate (222).

5. The atom screening device (1) according to claim 3, characterized in that: The first proximal electrode plate (211), the first distal electrode plate (212), the second proximal electrode plate (221) and the second distal electrode plate (222) are graphite plates.

6. The atom screening device (1) according to claim 3, characterized in that: The lengths of the first proximal electrode plate (211) and the first distal electrode plate (212) are both greater than L / 2, and the lengths of the second proximal electrode plate (221) and the second distal electrode plate (222) are both greater than L / 2.

7. The atom screening device (1) according to claim 1, characterized in that: It also comprises a mass spectrometry analysis unit (30), which obtains the atomic weight of the element to be screened out by the second atom screening module (20) according to the ion beam current intensity and the element mass distribution of the ion beam.

8. The atom screening device (1) according to claim 7, characterized in that: The method further comprises a calculation control unit (40), wherein the calculation control unit (40) calculates the deflection radius R of the ions of the element to be screened out relative to the center of the circle based on the atomic weight of the element to be screened out provided by the mass spectrometry analysis unit (30), and calculates the second difference D between the deflection radius R and the second distance D0, and compares the second difference D with the first difference L to generate a control signal, and selects to drive the first electrode plate pair (21) to move or to drive the second electrode plate pair (22) to move.

9. The atom screening device (1) according to claim 8, characterized in that: The calculation control unit (40) also calculates the deflection radius R relative to the center of the circle based on the speed at which the ions of the element to be screened out enter the inlet end (113), the magnetic flux of the sector mass analyzer (11) and the ion charge of the element to be screened out.

10. The atom screening device (1) according to claim 1, characterized in that: The invention also comprises a first driver (23) and a second driver (24), wherein the first driver (23) drives the first electrode plate pair (21) to move, and the second driver (24) drives the second electrode plate pair (22) to move, the first driver (23) comprises a first stepper motor (231) and a first encoder (232), and the second driver (24) comprises a second stepper motor (241) and a second encoder (242), the first encoder (232) detects the rotation angle of the first stepper motor (231), and the second encoder (242) detects the rotation angle of the second stepper motor (241).

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