In a wafer fabrication plant, X-rays can be applied in X-Ray, XRD, XRF, and XPS. What are the functions and differences of these four instruments?
Although X-Ray, XRD, XRF, and XPS all use X-ray sources, their principles, targets, and application purposes are completely different.
01
X-Ray (CT)
Principle: Based on the transmission principle of X-rays: when X-rays penetrate a sample, they are absorbed to varying degrees depending on the sample’s internal density, thickness, and material composition. The detector records the changes in X-ray intensity after passing through the sample to form an image.
Function: Non-destructive inspection to visualize the internal structure of chip packaging. It does not provide elemental composition, only structural morphology, fractures, and misalignments. Capable of 2D or 3D reconstruction (CT scanning).
02
XRD (X-ray Diffraction)
Principle: Uses Bragg diffraction principles. When X-rays hit a crystal plane, elastic scattering occurs. When diffraction conditions are met, peak signals form at specific angles. By analyzing peak positions and intensities, one can determine crystal structure, orientation, stress, defects, etc.
Function: Determines the presence and orientation of crystals; measures lattice constants, stress, and grain size; checks whether epitaxial layers match the substrate lattice. Non-destructive and applicable to thin films, polycrystalline, and single crystal materials.
03
XRF (X-ray Fluorescence Spectroscopy)
Principle: X-rays bombard atoms in the sample → excite inner electrons → atoms become excited (creating vacancies) → outer electrons transition to fill inner vacancies and release excess energy → emit secondary X-rays (fluorescence) with characteristic energy.
Each element emits fluorescence with a unique energy → enabling qualitative and quantitative elemental analysis.
Function: Rapidly identifies types and concentrations of elements in samples (≥ ppm level); measures metal layer thickness. Non-destructive.
04
XPS (X-ray Photoelectron Spectroscopy)
Principle: X-rays irradiate the sample; photoelectric effect ejects inner electrons; by measuring the kinetic energy of these electrons, binding energy is calculated via energy conservation. Binding energy is element-specific → identifies element types, chemical states, and bonding states.
Function: Measures the elemental composition of the topmost 50–60 atoms or 5–10 nanometers of a surface. Destructive analysis.
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