A nanofocus x-ray source based on a single carbon nanotube electron source and a micro-nano focusing system

Abstract

The application discloses a kind of nanofocus X-ray sources based on single carbon nanotube electron source and micro-nano focusing system, it is related to X-ray source and micro-nano focusing field, including sequentially arranged in electron beam exit direction: single collimating carbon nanotube electron source cathode, micro-nano electrostatic pre-focusing system, magnetic focusing system and anode target material;Single collimating carbon nanotube electron source cathode is used to generate field emission electron beam;Micro-nano electrostatic pre-focusing system and magnetic focusing system are used to sequentially focus two stages to electron beam, so that electron beam bombardment anode target material forms nanoscale focal spot.Based on the above design, the application obtains a kind of high-resolution X-ray source device using carbon nanotube as field emission cathode, which realizes nanoscale focal spot size by combining electrostatic and electromagnetic focusing system made by micro-nano processing technology, while ensuring the high brightness of X-ray in realizing high resolution.

Description

Technical Field

[0001] This invention relates to the field of X-ray sources and micro / nano focusing technology, and more specifically to a nano-focus X-ray source based on a single carbon nanotube electron source and a micro / nano focusing system. Background Technology

[0002] X-ray inspection technology has wide applications in semiconductor chip defect detection, biomedical imaging, and materials science. As integrated circuit manufacturing processes evolve towards the nanometer scale, higher requirements are placed on the resolution of X-ray inspection equipment, the core of which lies in achieving nano-sized X-ray source focal spots (nano-focal points).

[0003] Currently, the realization of micro / nano-focused X-ray sources mainly relies on thermionic emission or traditional cold cathode electron sources, combined with electromagnetic lenses for focusing. However, existing technologies have the following main shortcomings: 1. Limitation of the virtual source radius: Traditional tungsten filament thermionic electron sources or conventional cold cathode electron sources have a large effective emission area, making it difficult to further reduce the radius of the electron beam's "virtual source." According to optical principles, the source size directly determines the ultimate focal spot size.

[0004] 2. Low electron source brightness leads to insufficient X-ray flux: Traditional macroscopic focusing lenses (electrostatic or electromagnetic) have large aberrations when reducing the electron beam. In order to obtain a very small focal spot, a large amount of beam intensity usually needs to be sacrificed, resulting in insufficient X-ray flux, which cannot meet the needs of rapid detection.

[0005] Therefore, how to solve the technical problem that existing X-ray sources cannot simultaneously achieve nanoscale focal spot size and high brightness is a technical problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0006] In view of this, the present invention provides a nanofocus X-ray source based on a single carbon nanotube electron source and a micro-nano focusing system, which solves the problems existing in the background technology.

[0007] To achieve the above objectives, the present invention provides the following technical solution: A nano-focus X-ray source based on a single carbon nanotube electron source and a micro-nano focusing system includes, in sequence along the electron beam emission direction: a single collimated carbon nanotube electron source cathode, a micro-nano electrostatic pre-focusing system, a magnetic focusing system, and an anode target. A single collimated carbon nanotube electron source cathode is used to generate a field emission electron beam; The micro-nano electrostatic pre-focusing system and magnetic focusing system are used to sequentially focus the electron beam in two stages, so that the electron beam bombards the anode target to form a nanoscale focal spot.

[0008] Optionally, a single collimated carbon nanotube electron source cathode is used to directionally grow multi-walled carbon nanotubes at the tip of a metal needle using plasma-assisted chemical vapor deposition, and excess carbon nanotubes are removed by focused ion beam etching to obtain a single multi-walled carbon nanotube collimated with the metal needle tip.

[0009] Optionally, the metal tip is a tungsten tip, and the catalyst for growing multi-walled carbon nanotubes is nickel.

[0010] Optionally, the micro-nano electrostatic prefocusing system includes an extraction stage and a focusing stage with micron-sized apertures, fabricated using microelectromechanical systems (MEMS) technology, for extracting and initially focusing electrons from the cathode of a single collimated carbon nanotube electron source to reduce the electron beam emission angle.

[0011] Optionally, the apertures of the electrostatic focusing electrodes in the micro-nano electrostatic pre-focusing system are 10 μm, 40 μm, and 10 μm from top to bottom, and the electrode plate spacing is 10 μm.

[0012] Optionally, a magnetic focusing system is located below the micro-nano electrostatic pre-focusing system to further compress the electron beam and reduce the focused spot size.

[0013] Optionally, the electron beam energy is set in the range of 30keV-180keV, ultimately forming a nanoscale focal spot with a diameter of less than 100nm on the anode target.

[0014] Optionally, the anode target is a metal target used to receive high-energy electrons after focusing to generate X-rays.

[0015] As can be seen from the above technical solution, compared with the prior art, the present invention discloses a nano-focus X-ray source based on a single carbon nanotube electron source and a micro-nano focusing system, which has the following beneficial effects: (1) Extremely small initial source size: Using carbon nanotubes as an electron source, the virtual source radius is much smaller than that of traditional hot cathodes or Schottky emission sources, providing a physical basis for obtaining nanofocuses.

[0016] (2) Carbon nanotubes collimated with the needle tip: Whether the carbon nanotube is collimated directly determines the direction of electron beam emission. If the target needs to be hit accurately, the direction of the electron beam must be along the needle tip, which requires the carbon nanotube to be collimated with the direction of the needle tip. This invention obtains a collimated single carbon nanotube at the tip of the needle by combining PECVD and FIB cutting.

[0017] (3) High focusing efficiency and low aberration: The electrostatic and electromagnetic composite focusing system with micro-nano processing has a shorter focal length and stronger converging ability compared with traditional macro lenses, which effectively reduces geometric aberrations and allows most of the electron beam to be focused into the nanoscale focal spot, thus ensuring high brightness of X-rays while achieving high resolution.

[0018] (4) Solved key pain points: effectively solved the problem of "the focal spot size cannot be reduced" in the existing technology, and provided a core component solution for nanoscale high-resolution X-ray imaging. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0020] Figure 1 A structural diagram of a nanofocus X-ray source based on a single carbon nanotube electron source and a micro-nano focusing system provided by the present invention; Figure 2 A schematic diagram illustrating the method for obtaining a single collimated carbon nanotube electron source cathode provided by the present invention; Figure 3 This is a three-dimensional simulation diagram of the electron beam transmission trajectory provided by the present invention; Figure 4 The simulation diagram of the two-dimensional distribution of electron beam focal spot provided by the present invention. Detailed Implementation

[0021] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0022] This invention aims to address the technical challenge of achieving both nanometer-scale focal spot size and high brightness in existing X-ray sources, specifically including: 1) Overcome the physical limitation that the virtual source radius of traditional thermionic electron sources is too large, which prevents the final focal spot from being reduced to the nanometer level; 2) Solve the problem that macroscopic focusing systems suffer from large aberrations and low efficiency, resulting in severe electron beam loss when pursuing small focal spots.

[0023] Therefore, embodiments of the present invention disclose a nanofocus X-ray source based on a single carbon nanotube electron source and a micro / nano focusing system, such as... Figure 1 As shown, it includes, in sequence along the electron beam emission direction: a single collimated carbon nanotube electron source cathode, a micro-nano electrostatic pre-focusing system, a magnetic focusing system, and an anode target; A single collimated carbon nanotube electron source cathode is used to generate a field emission electron beam; The micro-nano electrostatic pre-focusing system and magnetic focusing system are used to sequentially focus the electron beam in two stages, so that the electron beam bombards the anode target to form a nanoscale focal spot.

[0024] refer to Figure 1 As can be seen, this embodiment uses a single multi-walled carbon nanotube (MWNT) as the field emission electron source, and utilizes its extremely small emission radius of curvature to obtain a near-ideal point electron source; at the same time, it combines micro-nano fabrication technology to fabricate micro-electrostatic lenses and micro-electromagnetic lenses to perform two-stage focusing of the electron beam, and finally form a nanoscale focal spot on the target material.

[0025] Furthermore, referring to Figure 2 The electron source cathode of a single collimated carbon nanotube is grown directionally on the tip of a metal needle using plasma-assisted chemical vapor deposition (PECVD). Excess carbon nanotubes are then removed by focused ion beam etching (FIB) to obtain a single multi-walled carbon nanotube collimated to the metal needle tip, which generates an electron beam through field emission. The tip curvature radius of the carbon nanotube can be controlled within tens of nanometers, greatly reducing the virtual source diameter of the electron beam.

[0026] Furthermore, the metal tip is a tungsten tip, and the catalyst for growing multi-walled carbon nanotubes is nickel. Specifically, during cathode preparation, nickel is used as a catalyst, and a large number of vertically grown multi-walled carbon nanotubes are grown on the tungsten tip using PECVD, with a tip diameter of approximately 10 nm-50 nm. Excess carbon nanotubes are removed using FIB, retaining only the central one. Finished products with the central axis of the carbon nanotube within 1° of the axis of the tungsten tip are selected. This carbon nanotube is perpendicular to the tip face of the tungsten tip and coaxial with the tungsten tip along the electron beam emission direction, which is the "collimated" single carbon nanotube described in this application.

[0027] Furthermore, the micro-nano electrostatic prefocusing system, located adjacent to the cathode, includes an extraction stage and a focusing stage with micron-sized apertures fabricated using microelectromechanical systems (MEMS) technology. These stages are used to extract electrons from the cathode of a single collimated carbon nanotube electron source and to initially focus them, thereby reducing the electron beam emission angle.

[0028] Furthermore, the apertures of the electrostatic focusing electrodes in the micro-nano electrostatic pre-focusing system are 10 μm, 40 μm, and 10 μm from top to bottom, and the electrode plate spacing is 10 μm.

[0029] Furthermore, the magnetic focusing system is located below the micro-nano electrostatic pre-focusing system and is used to further compress the electron beam to reduce the size of the focused spot.

[0030] Furthermore, the electron beam energy is set in the range of 30keV-180keV, ultimately forming a nanoscale focal spot with a diameter of less than 100nm on the anode target.

[0031] Furthermore, the anode target is a metal target, used to receive high-energy electrons after focusing to generate X-rays.

[0032] The specific implementation process of the nano-focus X-ray source based on a single carbon nanotube electron source and a micro-nano focusing system is as follows: (1) Carbon nanotubes are directionally grown at the tip of a metal needle by PECVD and excess carbon nanotubes are cut off by FIB to obtain a single carbon nanotube aligned with the metal needle tip.

[0033] (2) Electrons are emitted from the tip of carbon nanotubes under the action of a strong electric field. Due to the extremely small physical size of the carbon nanotubes themselves, the electron beam has an extremely small source point size in the initial stage. The emitted electrons first enter the micro-nano electrostatic pre-focusing system. By precisely controlling the electrode voltage, the electron beam is pre-focused, which significantly reduces the spherical aberration and chromatic aberration when it passes through the downstream lens.

[0034] (3) The electron beam then enters the magnetic focusing system. Under the action of a high gradient magnetic field, the electron trajectory is precisely controlled and eventually converges on the anode target to form a focal spot with a diameter on the nanometer scale (e.g., 100 nm).

[0035] Furthermore, particle simulation software was used to simulate electron beam tracking of the single collimated carbon nanotube electron source combined with the multi-level electrostatic focusing structure of this invention. The simulation results are as follows: Figure 3 , Figure 4 As shown. Figure 3 The complete transmission path of electrons emitted from the carbon nanotube cathode through multiple focusing electrodes is shown, with the electron beam converging and transmitting along the axis. The lateral position distribution of electrons is collected at the monitoring plane of the anode target at a distance of 33 mm from the cathode, yielding... Figure 4 The beam distribution shown indicates that the overall diameter of the electron focal spot formed on the anode target is close to 100 nm. The simulation results verify that the present invention can obtain nanoscale micro focal spots.

[0036] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0037] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A nanofocus X-ray source based on a single carbon nanotube electron source and a micro / nano focusing system, characterized in that, It includes, arranged sequentially along the electron beam emission direction: a single collimated carbon nanotube electron source cathode, a micro-nano electrostatic pre-focusing system, a magnetic focusing system, and an anode target; A single collimated carbon nanotube electron source cathode is used to generate a field emission electron beam; The micro-nano electrostatic pre-focusing system and magnetic focusing system are used to sequentially focus the electron beam in two stages, so that the electron beam bombards the anode target to form a nanoscale focal spot.

2. The nanofocus X-ray source based on a single carbon nanotube electron source and a micro / nano focusing system according to claim 1, characterized in that, The electron source cathode of a single collimated carbon nanotube uses plasma-assisted chemical vapor deposition to directionally grow multi-walled carbon nanotubes at the tip of a metal needle, and removes excess carbon nanotubes by focused ion beam etching to obtain a single multi-walled carbon nanotube collimated with the metal needle tip.

3. A nano-focus X-ray source based on a single carbon nanotube electron source and a micro / nano focusing system according to claim 2, characterized in that, The metal tip is a tungsten tip, and the catalyst for growing multi-walled carbon nanotubes is nickel.

4. A nanofocus X-ray source based on a single carbon nanotube electron source and a micro / nano focusing system according to claim 1, characterized in that, The micro-nano electrostatic prefocusing system includes an extraction stage and a focusing stage with micron-sized apertures, fabricated using microelectromechanical systems (MEMS) technology. These stages are used to extract electrons from the cathode of a single collimated carbon nanotube electron source and to initially focus them, thereby reducing the electron beam emission angle.

5. A nanofocus X-ray source based on a single carbon nanotube electron source and a micro / nano focusing system according to claim 4, characterized in that, The apertures of the electrostatic focusing electrodes in the micro-nano electrostatic pre-focusing system are 10μm, 40μm, and 10μm from top to bottom, and the electrode plate spacing is 10μm.

6. A nanofocus X-ray source based on a single carbon nanotube electron source and a micro / nano focusing system according to claim 1, characterized in that, The magnetic focusing system is located below the micro-nano electrostatic pre-focusing system and is used to further compress the electron beam to reduce the size of the focused spot.

7. A nanofocus X-ray source based on a single carbon nanotube electron source and a micro / nano focusing system according to claim 1, characterized in that, The electron beam energy is set in the range of 30keV-180keV, which ultimately forms a nanoscale focal spot with a diameter of less than 100nm on the anode target.

8. A nano-focus X-ray source based on a single carbon nanotube electron source and a micro / nano focusing system according to claim 1, characterized in that, The anode target is a metallic target used to receive high-energy electrons after focusing to generate X-rays.

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