High-resolution low-aberration focusing system suitable for high-energy and low-energy focused ion beam processing

Abstract

The invention discloses a high-resolution low-aberration focusing system suitable for high-energy and low-energy focused ion beam processing, and belongs to the field of focused ion beam technology and micromachining application thereof. A new focusing system is designed to solve the problems that an existing focusing ion beam system is large in beam spot diameter in a low-energy mode, poor in resolution ratio, large in material damage in a high-energy mode and the like, and low-energy and high-energy modes are not coordinated. Under a low-energy condition, a method of accelerating first and then decelerating is adopted to effectively reduce aberration to obtain a fine ion beam, meanwhile, the resolution of the focused ion beam in a high-energy mode is ensured, and the application field of the focused ion beam is effectively expanded. The new focusing system comprises a collecting lens module, an objective lens module and a wiring sleeve, and an ion beam sequentially penetrates through the collecting lens module, the wiring sleeve and the objective lens module and then enters a sample to achieve the machining and etching functions. The collecting lens module forms a strong electric field through a specific assembly and an insulating ceramic design, and controls parallel or cross emission of ion beams. The objective lens module changes the focusing position and degree of the ion beam by optimizing the shape and potential of an electrode, controls the beam energy, beam current and beam spot size of the ion beam at the sample, and realizes the small-beam-spot high-resolution ion beam. According to the invention, the structure is compact, the electrode potential is flexible and adjustable, high-performance rapid switching of the focused ion beam in a high-energy mode and a low-energy mode is realized, the processing performance of the focused ion beam system in the two modes is improved, and an efficient and stable technical scheme is provided for micro-nano processing.

Description

Technical Field

[0001] The present invention relates to focused ion beam technology and its micromachining applications, and in particular to a high-resolution, low-aberration focusing system suitable for high-energy and low-energy focused ion beam machining; Background Art

[0002] Focused ion beam (FIB), a microdissection technology that uses electrostatic lenses to focus an ion beam to very small dimensions, is widely used in the semiconductor, materials, and biomedical fields. A FIB system primarily comprises an ion source, focusing system, deflection system, signal acquisition system, sample stage, and vacuum system. Typical ion beams are typically liquid metal ion sources, typically made of gallium (Ga), due to its low melting point, low vapor pressure, and excellent antioxidant properties. Under the influence of an external electric field at the top of the ion column, the liquid metal gallium ions form a tiny tip, from which a gallium ion beam is emitted under the pull of an extractor. This ion beam is focused to the nanometer scale by electrostatic lenses and an objective lens, and micro-nano patterning is achieved under the precise control of a deflection system.

[0003] The main applications of high-energy focused ion beam technology (usually 30-50keV) are: 1. Removal and etching of deep materials. High-energy ions have a large penetration depth and are suitable for rapid etching and deep structure processing, such as integrated circuit modification and MEMS manufacturing. 2. TEM sample preparation. High-energy ions can efficiently thin samples to an electron-transparent thickness to meet the needs of transmission electron microscopy analysis. 3. High-resolution imaging. Through secondary electron / ion signal imaging, it is suitable for material surface morphology analysis. 4. Ion implantation and modification. High energy can achieve deep ion implantation for semiconductor doping or material modification. The main applications of low-energy focused ion beam technology (usually <5keV) are: 1. Surface fine processing, low-energy ions reduce material damage and are suitable for nanoscale pattern etching (such as quantum device preparation); 2. Sensitive material processing, suitable for non-destructive processing of two-dimensional materials (graphene), organic materials or biological samples; surface cleaning and polishing, low-energy ions can remove surface contaminants or oxide layers to avoid damage to the underlying layer; 3. Precision deposition and repair, low-energy ion beam induced deposition (IBID) can accurately position the deposited material for circuit repair or nanostructure construction.

[0004] However, since the proportion of lens chromatic aberration and inter-ion Coulomb force effects in the beam spot increases significantly with decreasing acceleration voltage, it is difficult to further improve the resolution of a focusing system suitable for FIB high-energy mode by directly switching to low-energy mode. At the same time, the ion beam brightness (current density per unit solid angle) decreases rapidly with decreasing energy, resulting in insufficient beam density and difficulty in achieving nanoscale focusing. In addition, on the one hand, the secondary electrons generated by low-energy ions have low energy, and the signal is easily interfered by noise, affecting imaging contrast and positioning accuracy; on the other hand, during the processing process, it is more likely to cause lateral scattering on the material surface, expanding the processing area and reducing lateral resolution. High-energy FIB excels in deep processing and efficient material removal, while low-energy FIB focuses on fine surface processing and sensitive material manipulation. Therefore, the FIB high-energy mode focusing system established by previous researchers is not suitable for FIB low-energy mode processing.

[0005] In order to achieve high-performance switching of the focused ion beam system between high-energy and low-energy modes, a high-resolution, low-aberration focusing system suitable for high-energy and low-energy focused ion beam processing is proposed. In the low-energy mode, the method of first accelerating and then decelerating is used to effectively reduce the aberration to obtain a fine ion beam while ensuring the resolution of the focused ion beam in the high-energy mode, effectively expanding the application of focused ion beams in semiconductors and sensitive materials. Summary of the Invention

[0006] In response to the problems of the existing focused ion beam system in the low-energy mode, such as large beam spot diameter and poor resolution, and large material damage in the high-energy mode, which are not coordinated between the low-energy and high-energy modes, the present invention proposes a high-resolution, low-aberration focusing system suitable for high-energy and low-energy focused ion beam processing. It comprehensively considers the goals that the focusing system needs to achieve in both high-energy and low-energy modes, optimizes the working mode, structure and electrical parameters of the condenser and objective lens, obtains a small beam spot, and realizes high-performance and fast switching of the FIB in high-energy and low-energy modes.

[0007] The present invention discloses a high-resolution, low-aberration focusing system suitable for high-energy and low-energy focused ion beam processing. In the low-energy working mode, a method of first accelerating and then decelerating is adopted, which greatly reduces the chromatic aberration of the focusing system and the Coulomb force effect between ions. By adjusting the potentials of the three electrodes of the objective lens, low aberration and small beam spot are achieved at a low landing voltage. On this basis, the electrical parameters of the condenser and lens are optimized to achieve high resolution in the FIB high-energy mode.

[0008] A high-resolution, low-aberration focusing system suitable for high-energy and low-energy focused ion beam processing comprises a condenser lens module, an objective lens module and a wiring sleeve.

[0009] The high-resolution focusing system is a cylindrical structure, consisting of a condenser module, an objective module, and a wiring sleeve, all located on the central axis of the focusing system. The wiring sleeve is a hollow tube made of duralumin, with various grooves designed on its outer surface for accommodating wires, screws, etc. The upper end of the wiring sleeve is connected to the condenser module, and the lower end is connected to the objective module. The upper end of the wiring sleeve has a clearance fit with the condenser module and is connected to the condenser flange of the condenser module via screws. The lower end of the wiring sleeve has a clearance fit with the objective module and is connected to the first electrode of the objective module via screws.

[0010] The ion beam passes through the condenser module, routing sleeve and objective lens module from top to bottom, and reaches the sample stage plane; it processes and etches by bombarding the sample on the sample stage.

[0011] The condenser module includes an ion source extraction electrode assembly, an ion source extraction electrode seat, a first condenser, insulating ceramic a, insulating ceramic b, a condenser flange, and a gas valve base assembly;

[0012] The extraction electrode assembly includes an extraction electrode, an extraction auroral diaphragm a, an extraction auroral diaphragm b, and an extraction electrode gasket; the extraction auroral diaphragm a and the extraction auroral diaphragm b are assembled into one by interference fit, and the assembled parts are then assembled into one by interference fit with the extraction electrode; the extraction electrode is connected to the ion source extraction electrode seat by screws, and the distance between the extraction electrode assembly and the ion source extraction electrode seat is changed by adjusting the thickness of the extraction electrode gasket.

[0013] The air valve base assembly includes an air valve base, an air valve pin, and an air valve seat gasket. The air valve base assembly is used in conjunction with external parts. The air valve pin is designed with a through hole, and the hole is coaxial with the outer contour of the air valve pin. The air valve base assembly is assembled into one with the condenser flange, and the two are clearance-matched on the mating surfaces and connected by screws. The screws pass through the air valve seat gasket and the air valve base and connect the two to the condenser flange. The air valve base and the air valve pin are threaded and sealed with a sealing ring.

[0014] The surface of insulating ceramic a is designed with 16 uniform through holes to improve vacuuming efficiency; the surface of insulating ceramic b is designed with a serrated structure to increase creepage distance; the upper end of insulating ceramic a is connected to the ion source extraction pole seat by vacuum glue; the lower end of insulating ceramic a is connected to the condenser flange by vacuum glue; the upper end of insulating ceramic b is connected to the first condenser by vacuum glue; and the lower end of insulating ceramic b is connected to the condenser flange by vacuum glue.

[0015] The central axis of the ion source extraction electrode assembly, the ion source extraction electrode seat, the first condenser, the condenser flange, and the gas valve seat assembly is consistent with the central axis of the wiring sleeve; the high-pressure screw cooperates with the threaded hole designed on the surface of the ion source extraction electrode seat to provide high pressure for the ion source extraction electrode seat; the high-pressure screw cooperates with the threaded hole designed on the surface of the first condenser to provide high pressure for the first condenser.

[0016] The objective lens module includes a first electrode, a second electrode, a third electrode and a second electrode insulating ceramic; the first electrode, the second electrode and the third electrode are all hollow cones and are made of titanium alloy material; the second electrode insulating ceramic is cylindrical with a groove designed on the lower surface and is made of alumina material; the first electrode and the second electrode insulating ceramic are connected by screws; the first electrode and the third electrode are connected by screws; the second electrode insulating ceramic and the second electrode are connected by vacuum glue; the axial symmetry center of the first electrode, the second electrode and the third electrode is the same as the central axis of the wiring sleeve.

[0017] The high-voltage screw cooperates with the threaded hole designed on the surface of the second electrode of the objective lens to provide high voltage for the second electrode of the objective lens.

[0018] The potential of the extraction electrode assembly in the focusing system is V1, the potential of the ion source extraction electrode seat is V2, the potential of the first condenser is V3, the potential of the condenser flange is V4, the potential of the first electrode is V5, the potential of the second electrode is V6, and the potential of the third electrode is V7.

[0019] The ion beam emitted by the ion source passes through the condenser module and forms a parallel beam or a cross beam under the action of the electric field formed by the ion source extraction electrode assembly, the ion source extraction electrode seat, the first condenser, and the condenser flange; when passing through the objective lens module, the position and degree of ion beam focusing are changed by adjusting the potential of each electrode of the objective lens, and the beam energy, beam current and beam spot size of the ion beam at the sample are controlled to achieve a small beam spot and high-resolution ion beam.

[0020] The advantages and positive effects of the present invention are:

[0021] (1) The high-resolution, low-aberration focusing system suitable for high-energy and low-energy focused ion beam processing of the present invention has a compact structure, and the positions of various components are coordinated, which can realize the external connection of various other functional components, thereby improving the functional diversity of the focusing system and laying a foundation for further reducing the aberration of the focusing system and improving the resolution.

[0022] (2) The present invention provides a high-resolution, low-aberration focusing system suitable for high-energy and low-energy focused ion beam processing. In the low-energy mode, the method of first accelerating and then decelerating is adopted, which effectively reduces the system chromatic aberration and the Coulomb force effect between ions, thereby reducing the beam spot and improving the low-energy FIB resolution.

[0023] (3) The present invention provides a high-resolution, low-aberration focusing system suitable for high-energy and low-energy focused ion beam processing. By utilizing the flexible and adjustable characteristics of the electrode potential, high-performance rapid switching of the system under different high-energy and low-energy modes is achieved by setting different electrode potentials. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1This is an overall structural diagram of the focusing system device of the present invention;

[0025] Figure 2 Schematic diagram of the structure of the condenser module of the present invention;

[0026] Figure 3 2 is a structural diagram of the objective lens module of the present invention; DETAILED DESCRIPTION

[0027] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0028] A high-resolution, low-aberration focusing system suitable for high-energy and low-energy focused ion beam processing comprises a condenser lens module, an objective lens module and a wiring sleeve.

[0029] The high-resolution focusing system is a cylindrical structure as a whole. Figure 1 As shown, the condenser module, objective lens module, and wiring sleeve are integrally located on the central axis of the focusing system. The wiring sleeve 301 is a hollow tube made of duralumin, with various grooves designed on its outer surface for accommodating wires, screws, etc. The upper end of the wiring sleeve 301 is connected to the condenser, while the lower end is connected to the objective lens module. The upper end of the wiring sleeve 301 is clearance-fitted with the condenser module and screwed to the condenser flange 106 of the condenser module. The lower end of the wiring sleeve 301 is clearance-fitted with the objective lens module and screwed to the first electrode 201 of the objective lens module.

[0030] The ion beam is emitted by the filament of the ion source, passes through the condenser module, the routing sleeve and the objective lens module from top to bottom, and reaches the plane of the sample stage 401; finally, it is incident on the surface of the sample 4011 on the sample stage 401 for etching processing.

[0031] Condenser module such as Figure 2 As shown: it includes an ion source extraction electrode assembly 101, an ion source extraction electrode seat 102, a first condenser 103, an insulating ceramic a 104, an insulating ceramic b 105, a condenser flange 106, and a gas valve base assembly 107;

[0032] Lead-out pole assembly 101 Figure 2 As shown in a, it includes an extraction pole 1011, an extraction auroral diaphragm a1012, an extraction auroral diaphragm b1013, and an extraction pole gasket 1014; the extraction auroral diaphragm a1012 and the extraction auroral diaphragm b1013 are assembled into one by interference fit, and the assembled parts are then assembled into one with the extraction pole 1011 by interference fit; the extraction pole 1011 is connected to the ion source extraction pole seat 102 by screws, and the distance between the extraction pole assembly 101 and the ion source extraction pole seat 102 is changed by adjusting the thickness of the extraction pole gasket 1014.

[0033] Valve base assembly 107 as shown Figure 2 As shown in b, it includes an air valve base 1071, an air valve pin 1072, an air valve seat gasket 1073, and an air valve base assembly 107 for use with external parts; the air valve pin 1072 is designed with a through hole with a diameter of D11, and the hole is coaxial with the air valve pin; the air valve base assembly 107 and the condenser flange 106 are assembled into one, and the two are clearance-fitted on the mating surface, and the lower end of the condenser flange 106 and the upper end of the air valve base assembly 107 are connected by screws; the screws pass through the air valve seat gasket 1073 and the air valve base 1071, and connect the two to the condenser flange 106; the air valve base 1071 and the air valve pin 1072 are threaded together and sealed with a sealing ring a101.

[0034] The surface of insulating ceramic a 104 is designed with 16 uniform through holes to improve vacuuming efficiency; the surface of insulating ceramic b105 is designed with a serrated structure to increase creepage distance; the upper end of insulating ceramic a104 is connected to the ion source extraction pole seat 102 by vacuum glue; the lower end of insulating ceramic a104 is connected to the condenser flange 106 by vacuum glue; the upper end of insulating ceramic b105 is connected to the first condenser 103 by vacuum glue; the lower end of insulating ceramic b105 is connected to the condenser flange 106 by vacuum glue.

[0035] The central axis of the ion source extraction electrode assembly 101, the ion source extraction electrode seat 102, the first condenser 103, the condenser flange 106, and the gas valve seat assembly 107 is the same as the central axis of the wiring sleeve 301; the high-pressure screw 501 cooperates with the D12 threaded hole designed on the surface of the ion source extraction electrode seat 102 to provide high pressure for the ion source extraction electrode seat 102; the high-pressure screw 502 cooperates with the D13 threaded hole designed on the surface of the first condenser 103 to provide high pressure for the first condenser 103.

[0036] Objective lens module such as Figure 3 As shown: it includes a first electrode 201, a second electrode 202, a third electrode 203 and a second electrode insulating ceramic 204; the first electrode 201, the second electrode 202, and the third electrode 203 are all hollow cones and are made of titanium alloy material; the second electrode insulating ceramic 204 is cylindrical with a groove designed on the lower surface and is made of alumina material; the first electrode 201 and the second electrode insulating ceramic 204 are connected by screws; the first electrode 201 and the third electrode 203 are connected by screws; the second electrode insulating ceramic 204 and the second electrode 203 are connected by vacuum glue; the axial symmetry center of the first electrode 201, the second electrode 202, and the third electrode 203 is the same as the central axis of the wiring sleeve 301.

[0037] The high-voltage screw 503 is engaged with the second electrode 202 of the objective lens via a pin, thereby providing high voltage to the second electrode 202 of the objective lens.

[0038] After emitting an ion beam from the ion source, it first enters the condenser module and exits in parallel or cross directions under the influence of the electric field formed by the ion source extraction electrode assembly 101 and the first condenser lens 103. It then enters the objective lens module, where the ion beam focus position and operating mode (high energy / low energy) are typically controlled by adjusting the potential of each electrode of the objective lens. This allows for low-aberration, high-resolution FIB at the sample, enabling high-resolution imaging and high-precision processing.

[0039] To verify the rationality of the electrode voltage configuration after the FIB system design was completed, evaluate the system's imaging and processing resolution, and confirm whether the system performance met the design specifications, the optimal conditions under different landing voltages were calculated. The beam spot diameter, chromatic aberration diameter, spherical aberration diameter, chromatic aberration coefficient, spherical aberration coefficient, beam brightness, and beam size of the FIB system were recorded. For low-energy conditions, the acceleration-then-deceleration mode and the normal mode were used.

[0040] The potential information of each electrode of the focusing system is listed in Table 1:

[0041] Table 1 Distribution of electrode potential (V) at different landing voltages

[0042]

[0043] The optimal results of the focusing system are listed in Table 2:

[0044] Table 2 shows the optimal results of the focusing system in the present invention.

[0045]

[0046]

[0047] Calculations in different modes show that the system can achieve a resolution of 2.8nm at 30kV at high energy. At low energy, the beam spot diameter in the acceleration-then-deceleration mode is significantly smaller than that in the standard mode, and the spherical and chromatic aberration coefficients are also significantly improved. In summary, the acceleration-then-deceleration method in the FIB low-energy mode not only significantly improves system resolution, but also significantly reduces chromatic aberration and inter-ion Coulomb effects, thereby improving beam stability.

Claims

1. A high-resolution, low-aberration focusing system suitable for high-energy and low-energy focused ion beam processing, characterized by: It includes a condenser module, an objective lens module and a wiring sleeve; the condenser module, the objective lens module and the wiring sleeve are coaxially arranged, and the ion beam passes through the condenser module, the wiring sleeve and the objective lens module in sequence from top to bottom to reach the sample surface; The condenser module includes an ion source extraction electrode assembly, an ion source extraction electrode seat, a first condenser, insulating ceramic a, insulating ceramic b, a condenser flange and an air valve base assembly; the ion source extraction electrode assembly includes an extraction electrode, an extraction aurora diaphragm a, an extraction aurora diaphragm b and an extraction electrode gasket, the extraction aurora diaphragm is first interference fit with the extraction aurora diaphragm b and then interference fit with the extraction electrode, the extraction electrode is connected to the extraction electrode seat by a screw, and the extraction electrode gasket is arranged between the extraction electrode and the extraction electrode seat; the upper and lower ends of the insulating ceramic a are respectively connected to the extraction electrode seat and the condenser flange by vacuum glue; the upper and lower ends of the insulating ceramic b are respectively connected to the condenser and the condenser flange by vacuum glue; the air valve base assembly is clearance-fitted with the condenser flange and connected by screws, and the air valve base is threaded with the air valve nail; The objective lens module includes a first electrode, a second electrode, a third electrode, and an insulating ceramic connector; the first electrode, the second electrode, and the third electrode are hollow cones made of titanium alloy; the insulating ceramic connector is cylindrical with a groove on the lower surface and is made of aluminum oxide; the first electrode is connected to the insulating ceramic connector and the third electrode by screws, and the insulating ceramic connector is connected to the second electrode by vacuum glue; The wiring sleeve is a hard aluminum hollow tube with a wire groove and a screw groove on the outer surface. The upper end of the wiring sleeve is gap-fitted with the condenser flange of the condenser module and connected by screws, and the lower end is gap-fitted with the first electrode of the objective lens module and connected by screws.

2. The high-resolution, low-aberration focusing system according to claim 1, wherein: In the condenser module, the central axis of the condenser lead-out pole assembly, lead-out pole seat, condenser, condenser flange and air valve base assembly coincides with the central axis of the wiring sleeve; the high-pressure screws respectively cooperate with the threaded holes on the lead-out pole seat and the condenser surface to provide high pressure for both.

3. The high-resolution, low-aberration focusing system according to claim 1, wherein: In the objective lens module, the axial symmetry centers of the first electrode, the second electrode, and the third electrode coincide with the central axis of the wiring sleeve; and the high-voltage screw cooperates with the threaded hole on the surface of the second electrode to provide high voltage for the second electrode.

4. The high-resolution, low-aberration focusing system according to claim 1, wherein: The condenser module focuses the ion beam into a parallel beam or a cross beam through the electric field formed by the condenser extraction electrode assembly, the extraction electrode seat, the condenser and the condenser flange; the objective lens module changes the position and degree of ion beam focusing by adjusting the potential of the first electrode, the second electrode and the third electrode, thereby controlling the beam energy, beam current and beam spot size of the ion beam at the sample.

5. The high-resolution, low-aberration focusing system according to claim 4, wherein: In the low-energy ion beam processing mode, the focusing system adopts an acceleration-then-deceleration working mode, which obtains a low landing voltage while reducing the chromatic aberration and Coulomb force effect between ions in the ion beam transmission process, thereby achieving a high-resolution low-energy ion beam.

6. The high-resolution, low-aberration focusing system according to claim 1, wherein: The air valve base assembly includes an air valve base, an air valve pin and an air valve seat gasket. The air valve pin is provided with a coaxial through hole. The air valve seat gasket is arranged between the air valve base and the condenser flange. The air valve base is fixed to the condenser flange by screws.

7. The high-resolution, low-aberration focusing system according to claim 1, wherein: The insulating ceramic a has 16 through holes evenly distributed on the ceramic surface, which are used to improve the vacuuming efficiency; the serrated structure of the insulating ceramic b is used to increase the creepage distance and improve the insulation performance.

8. The high-resolution, low-aberration focusing system according to any one of claims 1 to 7, wherein: By adjusting the potential (V1-V7) of each electrode in the condenser module and the objective lens module, high-performance fast switching between high-energy (30-50keV) and low-energy (<5keV) modes is achieved, significantly expanding the application range of focused ion beams.

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