Integrated neutralizing ion source based on pulsed beam modulation and ion beam polishing apparatus

Abstract

The application discloses an integrated neutralization ion source based on pulse beam current modulation and an ion beam polishing device.The integrated neutralization ion source comprises an ionization chamber, a three-grid ion optical assembly, a bipolar pulse power supply and a direct current voltage source.The three-grid ion optical assembly is arranged at an ion beam outlet of the ionization chamber.The three-grid ion optical assembly comprises a screen grid, an acceleration grid and a deceleration grid which are arranged in parallel and have a gap.The screen grid is arranged on one side close to the ionization chamber.The acceleration grid is connected with the direct current voltage source, and the deceleration grid is grounded.The screen grid is connected with the bipolar pulse power supply so as to control the proportion of positive ions and electrons in the pulse beam current in a single period by controlling the duty ratio of the positive voltage and the negative voltage of the bipolar pulse power supply, thereby achieving accurate neutralization.The application aims to realize the neutralization function of the neutralizer through the ion source, simplify the use of the neutralizer in the ion beam polishing device, simplify the structure of the ion beam polishing device, reduce the cost and achieve accurate neutralization.

Description

Technical Field

[0001] This invention belongs to the field of ion beam processing and etching technology for optical components and micro / nano structures, specifically relating to an integrated neutralizing ion source and ion beam polishing equipment based on pulsed beam modulation. Background Technology

[0002] With the continuous development of optical systems, the demand for precision optical components in various cutting-edge scientific research fields has been gradually increasing in recent years, such as EUV lithography objectives, synchrotron X-ray mirrors, and laser gyroscope resonators. Ion beam polishing (IBF) technology has the characteristics of high stability, no edge effect, non-contact non-destructive processing, and high processing accuracy, and is usually used as the final shaping process for high-precision optical parts. In conventional ion beam processing, the ion source can only extract positive ions, and an additional neutralizer is needed to provide electron current for neutralization compensation. Especially in the processing of insulating surfaces, if neutralization is not used, it will lead to a larger beam divergence angle, surface charging of the sample, affecting the shape of the ion beam removal function, and reducing processing accuracy. The ion beam is generated by an ion source, which consists of an ionization chamber and an ion optical system. In the ionization chamber, the gas is ionized into ions and electrons. The ion optical system extracts ions from the plasma boundary within the ion source, accelerates the ions, and finally focuses them into an ion beam with a certain energy. The surface of the ion optical system is covered with transparent small holes, and the diameter of the area formed by the distribution of these small holes is called the aperture of the ion optical system. Transmittance is the ratio of the area of ​​all vias on the gate to the area of ​​the open region. Based on the number of gates, ion optical systems are classified into single-gate, double-gate, and triple-gate ion optical systems. Currently used neutralizers primarily employ hollow cathodes made of barium tungsten and lanthanum hexaboride, achieving neutralization by emitting thermionic electrons. However, these cathodes readily react with reactive gases at high temperatures, losing their electron emission capability, resulting in high manufacturing costs, limited lifespan, and difficulty in switching operating modes quickly. A second method uses an additional ion source to emit electrons for neutralization, requiring an additional power supply, increasing costs, and causing uneven electron density distribution in space, affecting the degree of neutralization. Therefore, how to achieve precise neutralization during sub-nanometer precision shaping of the ion beam has become a critical technical problem that urgently needs to be solved. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to provide an integrated neutralizing ion source and ion beam polishing device based on pulsed beam modulation, which addresses the above-mentioned problems of the prior art. The present invention aims to realize the neutralization function of the neutralizer through the ion source, simplify the use of the neutralizer in the ion beam polishing device, simplify the structure of the ion beam polishing device, reduce costs, and achieve precise neutralization.

[0004] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows:

[0005] An integrated neutralizing ion source based on pulsed beam modulation includes an ionization chamber, a three-grid ion optical assembly, a bipolar pulsed power supply, and a DC voltage source. The three-grid ion optical assembly is arranged at the ion beam outlet of the ionization chamber. The three-grid ion optical assembly includes a screen grid, an accelerating grid, and a decelerating grid arranged parallel to each other with gaps. The screen grid is arranged on the side closer to the ionization chamber. The accelerating grid is connected to the DC voltage source, and the decelerating grid is grounded. The screen grid is connected to the bipolar pulsed power supply to control the ratio of positive ions and electrons in the pulsed beam within a single cycle by controlling the duty cycle of the positive and negative voltages of the bipolar pulsed power supply to achieve precise neutralization. When the screen grid voltage is positive, a potential difference is formed between the screen grid and the low-potential accelerating grid, and the positive ion beam is extracted from the ion chamber under the action of the electric field. When the screen grid has no voltage, there is no potential difference between it and the decelerating grid, and the ion beam is not extracted. When the screen grid voltage is negative, a reverse accelerating electric field is formed, which extracts negatively charged electrons from the ion chamber of the ionization chamber.

[0006] Optionally, the voltage of the bipolar pulse power supply is adjustable from -300 to 1000V, the frequency is adjustable from 0 to 10kHz, and the duty cycle is adjustable from 0 to 100%.

[0007] Optionally, the voltage of the DC voltage source is 100V.

[0008] The present invention also provides an ion beam polishing device, including a machine tool and an ion source mounted on the machine tool, wherein the ion source is the aforementioned integrated neutralization ion source based on pulse beam modulation.

[0009] The present invention also provides a method for applying the aforementioned integrated neutralizing ion source based on pulsed beam modulation, comprising the following steps:

[0010] S101, Determine the electrical conductivity of the processed sample;

[0011] S102, determine the corresponding degree of neutralization based on the conductivity of the processed sample;

[0012] S103 controls the ratio of positive ions and electrons in the pulse beam within a single cycle by controlling the duty cycle of the positive and negative voltages of the bipolar pulse power supply according to the degree of neutralization, so as to achieve precise neutralization. The duty cycle of the positive and negative voltages of the bipolar pulse power supply is inversely related to the degree of neutralization, and the better the conductivity, the larger the duty cycle.

[0013] In step S101, determining the conductivity of the processed sample refers to determining the resistance of the processed sample. In step S103, when controlling the duty cycle of the positive and negative voltages of the bipolar pulse power supply according to the degree of neutralization to control the ratio of positive ions and electrons in the pulse beam within a single cycle to achieve precise neutralization, the smaller the resistance, the larger the duty cycle.

[0014] Compared with existing technologies, the present invention mainly achieves the following beneficial effects: The integrated neutralizing ion source based on pulsed beam modulation of the present invention can achieve pulsed cross-beaming of positive ion beams and negative electron beams through high-frequency pulse modulation of the ion optical system, and can be used for optical processing of various conductive and insulating materials. The method of controlling the ion / electron current ratio can change the current compensation state of the ion beam from no compensation to positive compensation or even overcompensation. Compared with traditional technologies, the integrated neutralizing ion source based on pulsed beam modulation of the present invention does not require an additional neutralizer, avoids tungsten filament contamination, has a compact processing system structure, reduces costs, and improves the surface quality of ion beam processing through precise neutralization. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the integrated neutralizing ion source in an embodiment of the present invention.

[0016] Figure 2 This is a schematic diagram illustrating the working principle of the integrated neutralizing ion source in an embodiment of the present invention.

[0017] Figure 3 These are the experimental results showing the effect of duty cycle on removal efficiency in embodiments of the present invention.

[0018] Figure 4 These are the experimental results of the effect of frequency on removal efficiency in the embodiments of the present invention.

[0019] Legend: 1. Ionization chamber; 2. Three-grid ion optical assembly; 21. Screen grid; 22. Accelerating grid; 23. Decelerating grid; 3. Bipolar pulse power supply; 4. DC voltage source. Detailed Implementation

[0020] This invention aims to replace the use of neutralizers, simplify the processing system, reduce costs, and achieve precise neutralization. To enable those skilled in the art to better understand the technical solution of this invention, the technical solution will be further described in detail below with reference to the accompanying drawings of the embodiments of this invention.

[0021] like Figure 1As shown, this embodiment of the integrated neutralizing ion source based on pulsed beam modulation includes an ionization chamber 1, a three-grating ion optical assembly 2, a bipolar pulsed power supply 3, and a DC voltage source 4. The three-grating ion optical assembly 2 is arranged at the ion beam outlet of the ionization chamber 1. The three-grating ion optical assembly 2 includes a screen grating 21, an accelerating grating 22, and a decelerating grating 23 arranged parallel to each other with gaps. The screen grating 21 is arranged on the side closest to the ionization chamber 1 (as part of the plasma boundary). The accelerating grating 22 is connected to the DC voltage source 4, the decelerating grating 23 is grounded, and the screen grating 21 is connected to the bipolar pulsed power supply 3. This is used to control the ratio of positive ions and electrons in the pulse beam within a single cycle by controlling the duty cycle of the positive and negative voltages of the bipolar pulse power supply 3 to achieve precise neutralization. When the voltage of the screen 21 is positive, a potential difference is formed between the screen 21 and the low-potential accelerating grid 22, and the positive ion beam is extracted from the ion cavity under the action of the electric field. When the screen 21 has no voltage, there is no potential difference between it and the decelerating grid 23, and the ion beam is not extracted. When the voltage of the screen 21 is negative, a reverse accelerating electric field is formed, which extracts negatively charged electrons from the ion cavity of the ionization chamber 1.

[0022] For a three-grating ion optical system, the system consists of three parts: a screen grating 21, an accelerating grating 22, and a decelerating grating 23. The screen grating 21 is close to the plasma and forms part of the plasma boundary. The extraction of the ion beam is mainly achieved through the accelerating electric field between the screen grating 21 and the accelerating grating 22. The voltages on the accelerating grating 22 and the decelerating grating 23 are typically kept constant (the voltage of the accelerating grating 22 is negative, and the voltage of the decelerating grating 23 is zero). By changing the voltage of the screen grating 21, the energy and number of extracted ions are altered. If the potential difference between the screen grating 21 and the accelerating grating 22 is reduced to zero, the positive ions Ar+ will not be extracted by the accelerating electric field. If the field is reversed, electrons are accelerated and extracted. This study is based on this principle, replacing the DC power supply of the screen grating 21 with a bipolar pulsed power supply 3. This allows control of the type, energy, and duration of the extracted beam by controlling the voltage, duty cycle, and frequency of the pulsed power supply. Figure 2 As shown, when the voltage of the grid 21 is positive (+900V in the figure), a potential difference is formed between it and the low-potential accelerating grid 22, and the positive ion beam is extracted from the ion cavity under the action of the electric field. When the grid 21 has no voltage (0V), there is no potential difference between it and the decelerating grid 23, and the ion beam is not extracted. When the voltage of the grid 21 is negative (-500V in the figure), a reverse accelerating electric field is formed, which extracts negatively charged electrons from the ion cavity. By controlling the duty cycle and magnitude of the positive and negative voltages, the ratio of positive ions and electrons in the pulse beam within a single cycle can be controlled, achieving precise neutralization.

[0023] In this embodiment, the voltage of the bipolar pulse power supply 3 is adjustable from -300 to 1000V, the frequency is adjustable from 0 to 10kHz, and the duty cycle is adjustable from 0 to 100%. In this embodiment, the voltage of the DC voltage source 4 is 100V, the voltage of the accelerating grid 22 is constant at 100V, and the decelerating grid 23 is grounded to prevent electron backflow. The positive voltage directly determines the processing efficiency and is set according to the actual processing requirements. The neutralization ratio is adjusted by adjusting the duty cycle and the negative voltage of the grid 21.

[0024] Furthermore, this embodiment also provides an ion beam polishing apparatus, including a machine tool and an ion source mounted on the machine tool, wherein the ion source is the aforementioned integrated neutralizing ion source based on pulsed beam modulation. This embodiment also provides an application method for the aforementioned integrated neutralizing ion source based on pulsed beam modulation, comprising the following steps:

[0025] S101, Determine the electrical conductivity of the processed sample;

[0026] S102, determine the corresponding degree of neutralization based on the conductivity of the processed sample;

[0027] S103 controls the ratio of positive ions and electrons in the pulse beam within a single cycle by controlling the duty cycle of the positive and negative voltages of the bipolar pulse power supply 3 according to the degree of neutralization, so as to achieve precise neutralization. The duty cycle of the positive and negative voltages of the bipolar pulse power supply 3 is inversely related to the degree of neutralization, and the better the conductivity, the larger the duty cycle.

[0028] As an optional implementation, determining the conductivity of the processed sample in step S101 of this embodiment refers to determining the resistance of the processed sample. In step S103 of this embodiment, when controlling the duty cycle of the positive and negative voltages of the bipolar pulse power supply 3 according to the degree of neutralization to control the ratio of positive ions and electrons in the pulse beam within a single cycle to achieve precise neutralization, the smaller the resistance, the larger the duty cycle.

[0029] The following text will use common single-crystal silicon wafers as an example. N-type resistivity is 1-10 Ω·cm, which is a medium-resistivity material and requires low neutralization; fused silica material has a resistivity of 10 Ω·cm. 14 Ω.cm to 10 16 Ω.cm, belonging to insulating materials, requires high-temperature neutralization. The processing performance of an ion source is mainly evaluated by the removal function efficiency and stability. Currently, the spot method is more popular for obtaining ion beam removal functions. The spot test method refers to testing one or more removal function spots on an optical mirror. Based on the spots... Material removal amount at the location and test time Calculate the removal function :

[0030] .

[0031] The advantages of the spot test method are its simple experimental process, intuitive removal function spots, ease of calculation, and convenient residence time calculation after extraction of the removal function. Therefore, removal function experiments with different duty cycles and frequency parameters were conducted on single-crystal silicon and fused silica materials. A 5mm aperture was used for fixed-point removal for three minutes, and the peak removal efficiency was calculated.

[0032] Figure 3 Table 1 shows the effect of positive voltage duty cycle on the removal function, using a positive voltage of 800V, a negative voltage of -300V, and a frequency of 10kHz. A 100% duty cycle is equivalent to no electron extraction, i.e., no neutralization.

[0033] Table 1. Effect of duty cycle on removal efficiency (10 -3 mm 3 / min)

[0034]

[0035] Ion beam processing is essentially a type of CCOS (Collectively-Coated System). It calculates the expected material removal from the optical surface by convolving the removal function with the dwell time at each processing point along the processing path. Theoretically, a lower positive voltage duty cycle and dwell time result in lower removal efficiency. However, the neutralization ratio also affects removal efficiency. Without neutralization, the surface is charged, reducing the kinetic energy of ions bombarding the surface and decreasing removal efficiency. For single-crystal silicon, 100% duty cycle yields the highest efficiency, but the improvement compared to 90% is not significant. This is because this embodiment uses 3-minute fixed-point removal, where surface charging is not yet fully formed under medium-resistivity materials. Therefore, a 95% duty cycle is preferable for single-crystal silicon processing. See also... Figure 3 As shown in Table 1, the removal efficiency is highest at a 90% duty cycle for fused silica materials, indicating that this parameter effectively alleviates surface charging of insulating materials. Therefore, a 90% duty cycle is preferred.

[0036] Figure 4 Table 2 shows the effect of frequency on the removal function, using a positive voltage of 800V and a negative voltage of -300V. The duty cycle is 95% for monocrystalline silicon and 90% for fused silica.

[0037] Table 2: The effect of frequency on the removal function (10 -3 mm 3 / min)

[0038]

[0039] See Figure 4As shown in Table 2, the removal efficiency of both monocrystalline silicon and fused silica exhibits a consistent trend with frequency variation, initially decreasing, then increasing, and then decreasing again. For monocrystalline silicon processing, 2500Hz is preferred; 500Hz is not used because lower frequencies introduce spatial frequency errors during the processing trajectory. For fused silica processing, 7500Hz is preferred.

[0040] The above description is merely a preferred embodiment 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 also be considered within the scope of protection of the present invention.

Claims

1. A method of using an integrated neutralizing ion source based on pulsed beam modulation, characterized in that, The integrated neutralization ion source is installed on a machine tool for ion beam processing, and comprises an ionization chamber (1), a three-grid ion optical assembly (2), a bipolar pulse power supply (3) and a direct current voltage source (4). The three-grid ion optical assembly (2) is arranged at the ion beam outlet of the ionization chamber (1), and comprises a screen grid (21), an acceleration grid (22) and a deceleration grid (23) arranged in parallel and with a gap. The screen grid (21) is arranged close to one side of the ionization chamber (1), the acceleration grid (22) is connected to the direct current voltage source (4), the deceleration grid (23) is grounded, and the screen grid (21) is connected to the bipolar pulse power supply (3) for controlling the proportion of positive ions and electrons in the pulsed beam current in a single cycle by controlling the duty cycle of the positive voltage and the negative voltage of the bipolar pulse power supply (3) to achieve accurate neutralization to improve the surface quality of ion beam processing. When the voltage of the screen grid (21) is positive, a potential difference is formed between the screen grid (21) and the low-potential acceleration grid (22), and the positive ion beam current is extracted from the ion cavity under the action of the electric field; when the screen grid (21) has no voltage, there is no potential difference between the screen grid (21) and the deceleration grid (23), and the ion beam is not extracted; when the voltage of the screen grid (21) is negative, a reverse acceleration electric field is formed to extract negatively charged electrons from the ion cavity of the ionization chamber (1). The application method comprises the following steps: S101, determining the electrical conductivity of the processing sample, which refers to determining the electrical resistance of the processing sample; S102, determining the corresponding neutralization degree according to the electrical conductivity of the processing sample; S103, controlling the proportion of positive ions and electrons in the pulsed beam current in a single cycle by controlling the duty cycle of the positive voltage and the negative voltage of the bipolar pulse power supply (3) according to the neutralization degree to achieve accurate neutralization, and the duty cycle of the positive voltage and the negative voltage of the bipolar pulse power supply (3) is inversely proportional to the neutralization degree, and the better the electrical conductivity, the greater the duty cycle.

2. The method of claim 1, wherein the method is applied to an integrated neutralizing ion source based on pulsed beam modulation, characterized in that, The voltage of the bipolar pulse power supply (3) is adjustable from -300 to 1000V.

3. The method of claim 2, wherein the method is applied to an integrated neutralizing ion source based on pulsed beam modulation, characterized in that, The frequency of the bipolar pulse power supply (3) is adjustable from 0 to 10kHz.

4. The method of claim 3, wherein the method is applied to an integrated neutralizing ion source based on pulsed beam modulation, characterized in that, The duty cycle of the bipolar pulse power supply (3) is adjustable from 0 to 100%.

5. The method of claim 2, wherein the method is applied to an integrated neutralizing ion source based on pulsed beam modulation, characterized in that, The voltage of the direct current voltage source (4) is 100V.

6. The method of claim 1, wherein the method is used for an integrated neutralization ion source based on pulsed beam modulation, and the pulsed beam modulation is used for the ion source. In step S103, the smaller the resistance, the greater the duty cycle when controlling the proportion of positive ions and electrons in the pulsed beam current in a single cycle by controlling the duty cycle of the positive voltage and the negative voltage of the bipolar pulse power supply (3) according to the neutralization degree to achieve accurate neutralization.

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