Magnet for large-beam ion implanter and beam vertical angle control method

Abstract

The invention discloses a magnet for a large-beam ion implanter. The magnet comprises a magnet yoke and four coils arranged on the magnet yoke, each coil comprises a first coil and a second coil; all the first coils in the four coils are connected in series and then connected to the first power supply terminal group, and all the second coils in the four coils are connected in series and then connected to the second power supply terminal group. The invention also discloses a beam current vertical angle control method. The method comprises the following steps: adjusting the current of the PS1 and the PS2 until the current of the beam current reaches a stable maximum value; after the beam reaches the target chamber, measuring the vertical angle of each position of the beam, and calculating the average value of the vertical angles and the divergence of the vertical angles; and if the divergence of the vertical angle exceeds the process limit value, adjusting the current proportionality coefficient y of the PS2 relative to the PS1, generating a torsional magnetic field in the magnet Q1, and correcting the difference of the vertical angles at the two ends of the beam. The method has the advantages of improving the vertical angle difference between the two ends of the broadband ion beam and the like.

Description

Technical Field

[0001] This invention relates to the field of ion implanter technology, specifically to a magnet for a high-current ion implanter and a method for controlling the vertical angle of the beam. Background Technology

[0002] The key technical challenge of high-current ion implanters lies in controlling the high-current, low-energy beam, which is of great significance for the fabrication of ultra-shallow semiconductor junctions. The working process of a high-current ion implanter can be simply described as follows: Broadband continuous charged ions generated by the ion source are electrostatically extracted and accelerated, then focused vertically by magnet Q1 and fed into an analytical magnet. The analytical magnet filters the charged ions, deflecting ions of the required energy and type into the rear beamline drift region. In the drift region, ions are further focused or stretched horizontally or vertically by magnets Q2 and Q3 to reduce beam loss. Then, magnet Q4 adjusts the beam width, and a parallel lens magnet adjusts it into a parallel beam. Finally, the energy purification module performs final energy screening and filters out neutral particles.

[0003] For high-current ion implanters employing electrostatic acceleration technology, after ions are emitted from the ion source extraction system, the beam naturally diverges strongly due to the electrostatic repulsion between like charges and the electric field characteristics of the extraction module. Especially when the extraction current is high, without constraint, most of the beam will be lost on the beamline cavity wall during transmission. The magnetic field generated by the Q1 magnet applies an additional focusing force to the diverging beam, thereby maximizing beam transmission efficiency. Furthermore, under low-energy extraction voltages, the overall vertical angle of the beam will be further amplified by the distortion of the electric field of the extraction plates and the installation deviations of the subsequent optical path's electric or magnetic lenses, potentially leading to excessive vertical beam angle spread (VBAS) towards the target beam.

[0004] Unlike medium-current and high-energy ion implanters, which produce spot beams, high-current ion implanters produce a band-shaped ion beam of a certain width during beam extraction. This results in higher beam extraction current (ion density) and typically lower extraction energy.

[0005] Traditional high-current ion implanters use two symmetrical sets of coils at the ion source outlet to vertically focus the ion beam. Their advantages include simple structure and easy control. However, a disadvantage is that the magnetic field can only be linearly adjusted and cannot correct for the vertical angle difference between the two ends of the beam. When the VBAS of the low-energy beam reaching the target is too large, the overall optical path may lack adjustment capability.

[0006] The main considerations for correcting the beam vertical angle are as follows: Scenario 1: The beam drawn from the ion source may have a large difference in the vertical angle between the two ends of the beam, making it difficult for the VBAS process parameters of the beam reaching the target chamber to meet the standards. This is more likely to occur under low-energy, high-current beam conditions. Scenario 2: Due to slight alignment deviations in the installation of subsequent electromagnetic lens components in the optical path, or when the currents of magnets Q2 and Q3 are large and the center of the magnetic field does not completely coincide with the center of the optical path, deviations may also occur. Summary of the Invention

[0007] To address the technical problems existing in the prior art, this invention provides a magnet and a beam vertical angle control method for a high-current ion implanter to improve the overall angular difference of a broadband ion beam.

[0008] To solve the above-mentioned technical problems, the technical solution proposed by this invention is as follows: A magnet for a high-current ion implanter includes a yoke and four magnetic poles disposed on the yoke, each magnetic pole having an independent coil; each coil includes a first coil and a second coil, the first coil and the second coil being wound together on the same magnetic pole; All the first coils in the four coils are connected in series to the first power supply terminal group, and all the second coils are connected in series to the second power supply terminal group; wherein the first power supply terminal group is connected to the first power supply PS1 to provide the first excitation current to the first coils in the four coils, and the second power supply terminal group is connected to the second power supply PS2 to provide the second excitation current to the second coils in the four coils; wherein the first excitation current and the second excitation current are independently controlled.

[0009] Preferably, the upper and lower coils are wound with inner and outer first and second coils, and the number of turns of the first and second coils increases or decreases in a stepwise manner to form a symmetrical structure. The first and second coils of the left and right coils are divided into upper and lower groups.

[0010] Preferably, the first coil and the second coil in each coil are provided with independent current input ports and current output ports.

[0011] This invention also discloses a method for controlling the vertical angle of the beam based on the magnet used in a high-current ion implanter as described above, comprising the following steps: S1. During the beam initiation phase, adjust the currents of PS1 and PS2 until the beam current measured by the Setup Faraday cup reaches a stable maximum value; S2. After the beam reaches the target chamber, the vertical angle at a specified position of the beam is measured by multiple Faraday cups arranged in a straight line, and the average vertical angle VBAM and the vertical angle divergence VBAS are calculated. S3. If the vertical angle divergence VBAS exceeds the process limit, adjust the current ratio coefficient y of PS2 relative to PS1 to create a current difference between PS1 and PS2, thereby generating a torsional magnetic field in the Q1 magnet to correct the vertical angle difference between the two ends of the beam.

[0012] Preferably, in step S1, the currents of PS1 and PS2 are adjusted so that the current difference between them is less than a preset threshold, and the current magnitudes of PS1 and PS2 are adjusted synchronously until the beam current measured by the Setup Faraday cup reaches a stable maximum value.

[0013] Preferably, in step S1, when the change in PS1 current exceeds the calibration limit of the mass analyzer magnet, the calibration process of the mass analyzer magnet is triggered.

[0014] Preferably, in step S3, the y value is iteratively fine-tuned to form closed-loop control until VBAS is reduced to within the process requirements.

[0015] The present invention further discloses a computer program product, including a computer program that, when run by a processor, performs the steps of the method described above.

[0016] The present invention also discloses a computer-readable storage medium having a computer program stored thereon, the computer program performing the steps of the method described above when run by a processor.

[0017] The present invention further discloses a beam vertical angle control system, including a memory and a processor connected to each other, wherein the memory stores a computer program, and the computer program executes the steps of the method described above when run by the processor.

[0018] Compared with the prior art, the advantages of the present invention are as follows: This invention aims to improve the beam transmission efficiency of high-current ion implanters, achieving higher target beam current and a better overall vertical angle. A magnetic lens capable of adjusting the vertical angle of the beam is placed behind the ion source. This magnetic lens is constructed using two coupled coils, each powered by a separate power supply. The torsional magnetic field generated by a quadrupole electromagnet adjusts the vertical angle difference between the two ends of the beam. This magnet enhances the vertical beam focusing capability. The current in the two coils is controlled by an algorithm and supplied by two (or more) power supplies, causing a certain degree of torsion in the central magnetic field of the electromagnet. This torsional magnetic field improves the vertical angle difference between the two ends of the broadband ion beam, providing the ability to correct beam vertical angle divergence. This method can significantly reduce the vertical angle divergence of the low-energy beam in high-current ion implanters, better aligning the ion beam center path with the beamline cavity center path, and improving the terminal current intensity of the low-energy beam.

[0019] The control method of the present invention can enable more of the beam extracted from the ion source to enter the subsequent beamline region, thereby improving the beam extraction efficiency. Furthermore, since the Q1 magnet described in the present invention has a stronger vertical focusing capability, it can better overcome the repulsive force between like charges of ions when the ion source extraction current is high, which can support higher extraction current of the ion implanter. Combined with the higher beam extraction efficiency, this allows more beam to enter the target chamber region. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the magnet used in a high-current ion implanter according to the present invention.

[0021] Figure 2 This is a diagram showing the coil connection in the magnet of the high-current ion implanter of the present invention.

[0022] Figure 3 The flowchart is a representation of the beam vertical angle control method of the present invention in an embodiment. Detailed Implementation

[0023] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0024] like Figure 1 and Figure 2 As shown, the magnet for a high-current ion implanter provided in this embodiment of the invention is specifically a Q1 magnet, which includes a magnetic yoke and four independent coils disposed on the magnetic yoke; Each coil includes a first coil and a second coil, which are wound together on the same magnetic pole. All the first coils in the four coils are connected in series to the first power supply terminal group, and all the second coils are connected in series to the second power supply terminal group. The first power supply terminal group is connected to the first power supply PS1, which provides a first excitation current to the first coils in the four coils; the second power supply terminal group is connected to the second power supply PS2, which provides a second excitation current to the second coils in the four coils. The first excitation current and the second excitation current can be independently controlled to generate a composite magnetic field in the central region of the Q1 magnet, which is a superimposed quadrupole focusing magnetic field and a controllable torsional magnetic field.

[0025] Q1 Magnet coil winding method: The upper and lower coils are wound by two sets of inner and outer sub-coils. The number of turns of the inner and outer coils increases or decreases in a stepwise manner to form a symmetrical structure. The left and right coils are divided into upper and lower sets.

[0026] like Figure 1 As shown, the overall current direction is PS1: flowing into the upper coil C1T+ and out of C1T-, flowing into the left coil C3L+ and out of C3L-, flowing into the lower coil C1B+ and out of C1B-, and flowing into the right coil C3R+ and out of C3R-. PS2: Flow into the upper coil C2T+, flow out of C2T-, flow into the left coil C4L+, flow out of C4L-, flow into the lower coil C2B+, flow out of C2B-, flow into the right coil C4R+, flow out of C4R-.

[0027] The Q1 magnet is divided into four independent coils. C1T and C2T are a single coil, which is wound by two separate coils. C1B and C2B, C3L and C4L, and C3R and C4R are also single coils, which are connected to other coils through reserved interfaces.

[0028] The Q1 magnet of this invention is used to achieve vertical focusing of the beam extracted from the ion source and improve the divergence of the vertical angle of the beam to the target. The ultimate goal is to allow more beam to enter the subsequent optical path and reach the target chamber region, while ensuring that the various process parameters of the beam at the target end meet the requirements. In low-energy beam extraction, especially high-current extraction, due to the characteristics of the extraction system and the repulsion of ions in the beam by like charges, if the focusing force on the beam in the vertical direction is insufficient, most of the extracted ions will hit (i.e., be lost) on the vacuum cavity wall of the subsequent optical path components.

[0029] This invention aims to improve the beam transmission efficiency of high-current ion implanters, achieving higher target beam current and a better overall vertical angle. A magnetic lens capable of adjusting the vertical angle of the beam is placed behind the ion source. This magnetic lens is constructed using two coupled coils, each powered by a separate power supply. The torsional magnetic field generated by a quadrupole electromagnet adjusts the vertical angle difference between the two ends of the beam. This magnet enhances the vertical beam focusing capability. The current in the two coils is controlled by an algorithm and supplied by two (or more) power supplies, causing a certain degree of torsion in the central magnetic field of the electromagnet. This torsional magnetic field improves the vertical angle difference between the two ends of the broadband ion beam, providing the ability to correct beam vertical angle divergence. This method can significantly reduce the vertical angle divergence of the low-energy beam in high-current ion implanters, better aligning the ion beam center path with the beamline cavity center path, and improving the terminal current intensity of the low-energy beam.

[0030] Based on the above-described four-pole electromagnet structure, this embodiment of the invention further provides a method for controlling the vertical angle of the beam, such as... Figure 3 As shown, the specific steps include: S1. Beam setup stage: The beam is drawn out from the ion source and passes through magnets Q1, AMU, Q2, and Q3 before being collected by the setup Faraday cup.

[0031] Set the current of PS1 and PS2 to a small initial value and make them as close as possible (the current difference is less than a set preset threshold, such as 10%). Then, while keeping the current ratio between PS1 and PS2 roughly constant, the currents of PS1 and PS2 are increased or decreased synchronously in certain steps until the current value measured by the setup Faraday cup tends to a large value and basically stabilizes. The purpose of this process is to find the operating point that makes the setup Faraday cup reading reach its maximum value.

[0032] When the beam intensity measured by the Setup Faraday cup stabilizes and reaches its maximum value, the initial beam coarse adjustment is considered complete. This step ensures high beam extraction efficiency.

[0033] If the PS1 current value changes beyond the limit for AMU recalibration, an AMU calibration procedure is required.

[0034] S2. Adjustment after the beam reaches the target. At this point, the main focus is on addressing the issue of the vertical beam angle spread (VBAS) parameter exceeding process limitations.

[0035] The vertical angles at various positions of the beam are measured using seven Faraday cups arranged in a straight line, and the average vertical angle at the beam center (VBAM, Vertical Beam Angle Mean) is calculated, where VBAM is the average of the seven angle values. The VBAS is calculated by analyzing the divergence of seven angle values ​​(standard deviation or the difference between the maximum and minimum values, the calculation method is not limited). VBAS represents the overall vertical angle divergence of the beam, and a higher VBAS value indicates a larger difference in the overall vertical angle.

[0036] S3. A common operating condition for low-energy ion beams is that the VBAM value in the middle of the beam is close to 0, while the VBAM values ​​at both ends of the beam have opposite signs and a large difference, causing the VBAS parameter to exceed the limit (for example, Cup1 angle is positive and large, while Cup7 angle is negative and large). In this case, the following correction should be initiated: Correction is achieved by adjusting the current proportionality coefficient y of the second power supply PS2 relative to the first power supply PS1. Specifically, the control method for PS1 and PS2 is as follows: PS1 is given a current, and PS2 = PS1 * (1 + y), where the value of y ranges from -100% to unlimited. When the value of y is too large, due to the heat dissipation limitations of the power supply and magnet, PS2 will have an upper limit value for the current, which is controlled by the host computer program. By intentionally setting y to a positive or negative value (for example, adjusting y within the range of -30% to +50%), a torsional magnetic field in the desired direction can be generated in magnet Q1.

[0037] After adjusting the y-value, the angle difference between the two ends of the beam as it passes through magnet Q1 is pre-corrected. The corrected beam then reaches the target chamber again, and the angle Faraday cup remeasures and calculates a new VBAS. Based on the new VBAS value, the control system can further iteratively fine-tune the y-value until the VBAS is reduced to within the process requirements. This process forms a direct and proactive closed-loop control of the VBAS parameter.

[0038] Once VBAS meets the standard, record the optimal PS1 current and proportional coefficient y at this point, and save them as parameters for the process formulation.

[0039] The effectiveness of the invention is demonstrated through a specific adjustment example: In a certain low-energy, high-current process, the measurement data is shown in Table 1 before adjustment. It can be seen that the angle values ​​of Cup1 and Cup7 have opposite signs and large absolute values, with VBAS reaching as high as 1.63°. Based on the diagnostic results, the scaling factor y was automatically adjusted, and the results are shown in the adjusted row of Table 1. The angles at both ends of the beam (Cup1, Cup7) were significantly brought closer, the overall angle divergence was greatly reduced, and VBAS dropped to 0.41°, meeting the process requirements. Simultaneously, VBAM was also close to 0°, indicating good beam centerline alignment.

[0040] Table 1

[0041] The control method of the present invention can enable more of the beam extracted from the ion source to enter the subsequent beamline region, thereby improving the beam extraction efficiency. Furthermore, since the Q1 magnet described in the present invention has a stronger vertical focusing capability, it can better overcome the repulsive force between like charges of ions when the ion source extraction current is high, which can support higher extraction current of the ion implanter. Combined with the higher beam extraction efficiency, this allows more beam to enter the target chamber region.

[0042] Explanation of related terms: Ion source: A device that generates a beam of charged ions, which are produced in an arc chamber and continuously extracted. Q1 (Quadrupole1) Magnet: A magnet component of a high-current ion implanter, installed at the ion source outlet for beam shaping.

[0043] Mass analyzer magnet: The ion source draws out a wide variety of ions, and different ions have different trajectories in the magnetic field. The mass analyzer current can be adjusted to filter out the desired ions according to the ion charge-to-mass ratio.

[0044] Setup Faraday: Located in the beamline region, it measures the target ions obtained after being extracted by the ion source and screened by the mass analyzer. Only ions that have passed through this location can enter the target chamber region.

[0045] Angle Faraday: Located in the target chamber region, it can measure the vertical and horizontal angles of the beam.

[0046] Target chamber: The area on a silicon wafer where ion implantation is performed.

[0047] The above are merely preferred embodiments of the present invention. The scope of protection of the present invention is not limited to the above embodiments. All technical solutions falling within the scope of the present invention's concept are within the scope of protection of the present invention. It should be noted that for those skilled in the art, any improvements and modifications made without departing from the principles of the present invention should be considered within the scope of protection of the present invention.

Claims

1. A magnet for use in a high-current ion implanter, characterized in that, It includes a magnetic yoke and four coils disposed on the magnetic yoke; each coil includes a first coil and a second coil, the first coil and the second coil being wound together on the same magnetic yoke; All the first coils in the four coils are connected in series to the first power supply terminal group, and all the second coils are connected in series to the second power supply terminal group; wherein the first power supply terminal group is connected to the first power supply PS1 to provide the first excitation current to the first coils in the four coils, and the second power supply terminal group is connected to the second power supply PS2 to provide the second excitation current to the second coils in the four coils; wherein the first excitation current and the second excitation current are independently controlled.

2. The magnet for a high-current ion implanter according to claim 1, characterized in that, The upper and lower coils are made of inner and outer first and second coils. The number of turns of the first and second coils increases or decreases in a stepwise manner to form a symmetrical structure. The first and second coils of the left and right coils are divided into upper and lower groups.

3. The magnet for a high-current ion implanter according to claim 1 or 2, characterized in that, Each of the first and second coils in the coils is provided with an independent current input port and a current output port.

4. A method for controlling the vertical angle of the beam in a magnet used in a high-current ion implanter, based on claim 1, 2, or 3, characterized in that, Including the following steps: S1. During the beam initiation phase, adjust the currents of PS1 and PS2 until the beam current measured by the Setup Faraday cup reaches a stable maximum value; S2. After the beam reaches the target chamber, measure the vertical angle at each position of the beam, and calculate the average vertical angle VBAM and the vertical angle divergence VBAS. S3. If the vertical angle divergence VBAS exceeds the process limit, adjust the current ratio coefficient y of PS2 relative to PS1 to create a current difference between PS1 and PS2, thereby generating a torsional magnetic field in the Q1 magnet to correct the vertical angle difference between the two ends of the beam.

5. The beam vertical angle control method according to claim 4, characterized in that, In step S1, the currents of PS1 and PS2 are adjusted so that the current difference between them is less than a preset threshold, and the current magnitudes of PS1 and PS2 are adjusted synchronously until the beam current measured by the Setup Faraday cup reaches a stable maximum value.

6. The beam vertical angle control method according to claim 4 or 5, characterized in that, In step S1, when the change in PS1 current exceeds the calibration limit of the mass analyzer magnet, the calibration process of the mass analyzer magnet is triggered.

7. The beam vertical angle control method according to claim 4 or 5, characterized in that, In step S3, the y value is iteratively fine-tuned to form a closed-loop control until VBAS is reduced to within the process requirements.

8. A computer program product, comprising a computer program, characterized in that, The computer program is executed by the processor to perform the steps of the method as described in any one of claims 4-7.

9. A computer-readable storage medium having a computer program stored thereon, characterized in that, The computer program, when run by a processor, performs the steps of the method as described in any one of claims 4-7.

10. A beam vertical angle control system, comprising a memory and a processor interconnected, wherein the memory stores a computer program, characterized in that, The computer program, when run by a processor, performs the steps of the method as described in any one of claims 4-7.

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