The principle of the Focused Ion Beam Scanning Electron Microscope (FIB-SEM)

A Focused Ion Beam-Scanning Electron Microscope (FIB-SEM) dual-beam system refers to a system that simultaneously possesses the functions of both a focused ion beam (FIB) and a scanning electron microscope (SEM). By integrating with corresponding gas deposition devices, nanomanipulators, various detectors, controllable sample stages, and other accessories, it becomes an analytical instrument that combines micro-area imaging, processing, and analysis into one. This makes it a versatile tool widely used in many fields, including physics, chemistry, biology, new materials, agriculture, environment, and energy.

Principle of FIB-SEM

The FIB-SEM dual-beam system combines the FIB system and a traditional scanning electron microscope (SEM) system at a specific angle within a single apparatus, adjusting the sample to a co-centric height position. This arrangement allows the sample surface to be perpendicular to either the electron beam or the ion beam during experiments by rotating the sample stage. This setup enables real-time observation with the electron beam and cutting or microfabrication with the ion beam.

In common dual-beam FIB-SEM systems, the electron beam is perpendicular to the sample stage, while the ion beam is set at a certain angle to the sample stage. During operation, the sample stage needs to be rotated to a 52-degree position, making the ion beam perpendicular to the sample stage, which facilitates processing. Meanwhile, the electron beam forms a specific angle with the sample stage, allowing observation of the internal structure of the cross-section.

Figure 1: A schematic diagram of the FIB-SEM dual-beam system structure

Refer to the attached diagram for the structure of the ion column. The liquid gallium (Ga) ion source is the most commonly used due to gallium's low melting point, low vapor pressure, and its ability to produce high-density ion beams that can etch most materials. When heated, gallium flows down to the tip of a tungsten needle. Due to surface tension and the opposing electric field force, gallium forms a cone with a tip radius of approximately 2 nm at the needle's apex. Subsequently, the enormous electric field at the tip (greater than 10^8 V/cm) ionizes the gallium atoms and emits them. The Ga ion beam is then focused onto the sample by electrostatic lenses and scanned across it. Interaction with the sample generates various signals, enabling precise machining and microscopic analysis of the sample.

Figure 2: Schematic Diagram of the Working Principle of the FIB-SEM Dual-Beam System

Functions and Applications of FIB-SEM

1. Main Functions of FIB-SEM:

① Electron beam imaging: Used for sample positioning, obtaining microstructural information, and monitoring the processing progress.

② Ion beam etching: Used for cross-sectional observation and patterning.

③ Gas deposition: Used for patterning and sample preparation.

④ Microscopic cutting: Preparation of ultra-thin sections with micrometer size and nanometer thickness (less than 100 nm) for subsequent TEM and synchrotron STXM analysis.

⑤ Microscopic cutting: Preparation of needle-shaped samples at the nanometer scale for subsequent APT analysis to obtain trace element and isotope information.

⑥ Integrated SEM imaging, FIB cutting, and EDXS chemical analysis: Used for micro-nano-scale three-dimensional reconstruction analysis of samples.

2. Main Applications of FIB-SEM:

① Micro- and nano-structural processing

② Cross-sectional analysis

③ TEM sample preparation

④ Three-dimensional atom probe sample preparation

⑤ Chip repair and circuit modification

⑥ Photomask repair

⑦ Three-dimensional reconstruction analysis

FIB-SEM Case Study

1. Micro- and Nano-Structural Processing

The FIB system can directly pattern or deposit the required shapes under the GIS system without the need for a mask. Using the FIB system, complex functional structures can be fabricated at the micro- and nano-scale, covering areas such as nano quantum electronic devices, sub-wavelength optical structures, surface plasmon devices, and photonic crystal structures. By adopting appropriate methods, it is possible to achieve not only the drawing of two-dimensional planar structures but also the fabrication of complex three-dimensional structures.

Figure 3: Case Study Images 1

2. Cross-Sectional Analysis

The FIB sputtering and etching function can precisely cut samples and observe the cross-section to characterize its morphology and dimensions. It can also be combined with systems for elemental analysis (EDS) to analyze cross-sectional composition. This technique is widely used in failure analysis of chips, LEDs, and other devices. For instance, when issues arise during the processing of standard IC chips, FIB can rapidly pinpoint and analyze the cause of defects, helping to improve the manufacturing process. The FIB system has become an indispensable tool in modern integrated circuit production lines.

Figure 4: Case Study Images 2

3. Three-Dimensional Reconstruction Analysis

The goal of three-dimensional reconstruction analysis is primarily achieved through software-controlled alternating FIB layer-by-layer cutting and SEM imaging, ultimately enabling 3D reconstruction. By efficiently combining FIB 3D reconstruction technology with EDS, researchers can characterize material structure, morphology, and composition in three-dimensional space. When combined with EBSD, it is possible to characterize the spatial organization, orientation, grain morphology, size, and distribution information of polycrystalline materials.

Figure 5: Case Study Images 3