A new generation of objective lens to achieve domestic high-speed scanning electron microscope

Electron microscopy moves from the laboratory to industrial applications. The key words are high speed and ease of use. The first intelligent automatic high-speed imaging scanning electron beam microscope was launched in Beijing, which is not only good for scientific research, but also good for engineering applications, expanding a micro-world exploration path.

This paper introduces how the domestic high-speed scanning electron microscope (High Throughput SEM) focuses on industrial applications, and has been updated to meet the requirements of use. Mainly from the five aspects of functional performance, key components, independent design, operation, manufacturing and maintenance, it focuses on explaining the first-generation objective concept and structure of the new generation, helping to achieve performance goals, providing a total solution and application platform.

First, performance optimization and upgrade

The laboratory pays more attention to seeing the fine results of the experiment, while the industrial scale production pays more attention to speed and efficiency. Therefore, high throughput can be listed as the first indicator. The rate is marked by the number of Pixels imaged per second. Conventional electron microscopes are mostly on the order of tens of M. The domestic industrial electron microscope imaging rate broke through the 100MPixels/s mark, which refreshed the technical performance index. For both SE and BSE dual channels, it reaches 200 MPixels/s. Imagine capturing 200 high-motion images per second, just like the magic of your camera turns into a camera. High-throughput industrial electron microscopes have turned from cameras that only observe still images to cameras that capture dynamic changes.

The reasons for achieving high throughput are manifold. Qualcomm's quantitative big data acquisition, derived from a unique electronic optical structure and system design, ensures high-speed acquisition of electronic information of samples, and the imaging speed is nearly 100 times that of traditional scanning electron microscopy.

The appearance of a high-throughput industrial scanning electron microscope is shown in Figure 1.

Figure 1. High-throughput industrial scanning electron microscope appearance

Second, the device is updated

Figure 2 shows the internal structure and main components of the industrial scanning electron microscope. In order to achieve high throughput, from the lens barrel to the sample stage, key components are fully integrated with a new generation of design and materials. The update cycle is still shrinking.

Figure 2 Schematic diagram of the internal structure of domestic industrial scanning electron microscope

The barrel itself is an unconventional "high" and becomes "short and thin". It is installed in the cabinet because the knob is not needed, and the user extends his finger to operate directly on the touch screen and the computer.

As shown, the source is the first of the electron microscope. The electron gun is launched by Schottky thermal field, the beam is large, and the customized tip is fine to the nanometer level to improve the emission efficiency.

A new generation of objective lenses is used to display the prestige in domestic industrial scanning electron microscopes. As we all know, the objective lens in the electron microscope plays an important role in connecting the upper and lower. But little known, from the early seventies to the present, the high-resolution large-field objective lens system has undergone several generations of changes. The previous generations were: MOL/ SOL/ BOL – VOIL/ SOIL – SORIL. The moving objective lens MOL (moving objective lens) and the swinging objective lens SOL (swinging objective lens) and the bending objective lens BOL (bent objective lens) can be said to be parallel three concepts, all belong to VOL (variable axis objective lens), and then structurally Developed to the variable objective immersion lens (VOIL), which includes MOIL and SOIL. After the immersion objective lens is used in a large amount, a structure of a swing objective retarding immersion lens (SORIL) is derived. Nowadays, the high-resolution large-field objective lens system has a new design idea, and the development is fixed as a new generation of composite deflection acquisition objective system.

The decelerating electrostatic lens assists in the collection of electronic signals, allowing more SE and BSE to be collected to achieve the desired high resolution. Because for non-conducting biological samples, it is necessary to avoid the accumulation of charge on the sample, otherwise it will affect the definition. When the biological sample is observed, the initial electrons decelerate between the objective lens and the sample after leaving the electron optical lens barrel, and the electron beam is in a low energy state, so that the charge effect is easily eliminated.

The new generation of composite deflection acquisition objective systems integrates unique signal acquisition methods and structures. Innovative detectors become key components. Take the lead and move the whole body. From the conventional scintillator + PMT update to the coaxial semiconductor type detector, with the gain amplifier circuit, the collection electron efficiency is greatly improved.

The high resolution of the image in the large field of view can meet the large-area observation requirements of materials and biological samples. After theoretical calculation and actual verification, when scanning large-area samples, the edge aberration is small and can still be focused, thus expanding the visual range.

Third, design system engineering

The self-designed electron microscope is completed by a full set of software modeling (Modeling). After various parameters are input into the system, simulation, virtual reality (VR), dynamic debugging, and comprehensive balance. The electron beam travels through the coaxial components in the barrel. In the data integration process, the fuzzy probability calculation achieves the effect of optimizing the overall performance. Finally, the height of the lens barrel is shortened as much as possible, the aperture size of the aperture is suitable, the height of the detector position and the radius of the aperture are moderate, the short magnetic objective lens and the electrostatic field are coupled, and the working distance is reduced from 20 mm to 4 mm.

The optical axis alignment of the electron microscope is a difficult problem for many years of deposition. To solve it from the source, it is to start with the design of the photovoltaic system itself. The electron beam is emitted from the electron source and always maintains the same high energy before moving quickly to the objective lens in the lens barrel. After entering the decompression electrostatic field, when the falling point energy and the changing beam are changed, the trajectory of the electron beam in the mirror is almost unchanged under different falling point energy conditions. So there is a basic guarantee in physical alignment. The special deflection centering coil also contributes to further fine adjustment.

Fourth, the use of automatic and simple

People-oriented, the use of automation, is a timeless task. With a series of actions such as power-on patrol, navigation and positioning, one-touch centering, focus adjustment, shifting and rectification, the SEM operation is almost as easy as playing the iPad.

The real-time focus tracking system consists of hardware and software. A set of light source height is set between the sample stage and the electron optical tube, and the working distance between the objective lens and the sample stage is corrected in real time. Moving the sample always maintains a clear image. It not only saves a lot of effort to debug and maintain the electron microscope, but also enables unattended continuous work. The amount of data in a day can reach 2 – 8TB.

The environmental conditions of the scanning electron microscope mainly involve several factors such as temperature, humidity, vibration, magnetic field strength, and grounding. The requirements of the SEM ground wire must be independent ground wire, that is, the grounding body to the terminal block are completely independent. Avoid noise from the internal thermal noise and grounding of the circuit. Increasing the signal-to-noise ratio is comparable to gold mining in sand, but it directly affects image quality.

V. Manufacturing is autonomously completed

It is challenging to master the design and manufacturing integration mechanism and master the complete set of electron microscope manufacturing technology. Especially in today's Internet age, post-80s researchers who are obsessed and proficient in microfabrication are rare.

The production precision of the core components of the electron microscope is in the order of micrometer and nanometer, and the processing complexity requires strict control. Self-manufactured parts are strategic deployments that master the design and manufacturing of electron microscopy. The world's most advanced CNC machine tools and well-organized instrument manufacturing assembly cleanroom are essential equipment.

Conclusion

At present, hot high-tech is developing in two directions: Internet, artificial intelligence, robots, drones, and nanomaterials. The other is life science, brain science, stem cells, and gene editing. The two directions are parallel. There is no cross between the two. What really makes the two directions interact is big data. Big data will be valued to form a data market. The acquisition of big data, which will use an electron microscope.

SEM, although it doesn't sound as tidal as AI, but she looks a little cute, especially when she takes you into an unknown world, when nanoscale big data in the materials industry, biomedicine, etc. becomes a must.

Different from the introduction of digestion and absorption roads, it has independent intellectual property rights in core technologies such as electro-optical design, electron beam scanning control circuit system and software system, and regards work as a business, which is the characteristic of domestic electron microscope people.

Runs are silent and sound, and the boutique is superior. Domestic electro-optical mirrors are based on high-throughput industrial scanning electron microscopy, which is the basis for realizing the reality and expanding into customized products such as portable and large samples to meet the emerging industries.

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