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Semiconductor Wafer Inspection and Lasers
Wafer inspection, a critical process in semiconductor manufacturing, ensures the quality of foundational materials using both physical and optical methods. It involves non-destructive or minimally invasive testing of the wafer's surface topography, electrical properties, and internal structure, guaranteeing chip functionality and reliability—and ultimately having a direct impact on the yield of semiconductor devices.
Wafer Manufacturing and Inspection Process
Wafer inspection is the core of quality control in the front-end of semiconductor manufacturing, serving as a critical step to ensure process quality and chip performance throughout the semiconductor production process. It encompasses the following:
1. Includes graphic detection (Patterned Wafer Inspection)
For wafers with already-formed circuit patterns, image comparison technology is used to identify pattern defects such as open circuits and short circuits.
The system not only focuses on physical defects on the wafer surface but also on pattern defects, such as broken traces or short circuits in the circuit patterns. Typically, the inspection system compares images of test chips on the wafer with those of adjacent chips—or with a "golden" chip known to be free of defects. Using image-processing software and a subtraction process, the system precisely locates and distinguishes any defects. This critical step is performed during production to ensure that every wafer’s circuit patterns meet the design specifications. Additionally, pattern inspection of wafers is carried out at various stages of the manufacturing process to identify and address potential defects early on.
There is a graphical wafer inspection principle.
2. Non-patterned Wafer Inspection
The surface quality and cleanliness of wafers are critical to chip performance. During the wafer production process—including processes like single-crystal pulling, slicing, grinding, and polishing—redundant materials, crystal defects, and mechanical damage can inadvertently form on the wafer surface. Non-patterned wafer defect inspection is a key step used in both final product testing before shipment and front-end manufacturing processes. It detects and precisely locates defects such as particles, contamination, scratches, cracks, pits, and voids on silicon and epitaxial wafers, ultimately helping to enhance semiconductor yield and reliability.
During the inspection process, laser scanning technology is employed, where a laser beam performs radial scans across the rotating wafer surface. When the laser beam encounters particles or other defects on the wafer’s surface, these imperfections scatter a portion of the laser light. Based on the resulting light intensity distribution, either scattered light (using dark-field illumination) or the loss in reflected beam intensity (via bright-field illumination) can be directly detected—enabling manufacturers to verify whether the wafers meet quality standards before they leave the production line.
Schematic Diagram of Non-Graphic Wafer Inspection
Laser for wafer inspection
In semiconductor wafer inspection applications, the requirements for laser parameters are exceptionally stringent. Different wafer materials demand varying laser wavelengths, along with high power stability, precise spot stability, enhanced reliability, and minimal amplitude noise.
1. Continuous UV Laser
CNI offers a range of wavelengths including 261nm, 266nm, 313nm, 320nm, 325nm, 349nm, 355nm, 360nm, and 375nm. Continuous output power ranges from 1 to 6000 mW, with support for 7×24-hour continuous operation. It is primarily used for photoluminescence defect detection on SI or SiC wafers.
266/320/355nm Continuous UV Lasers
2. Picosecond UV Laser
CNI offers wavelengths such as 193 nm, 213 nm, 266 nm, and 355 nm. Among these, the laser power at 266 nm and 355 nm can reach up to 1–8000 mW, with repetition rates exceeding 80 MHz or even 120 MHz, and an M² factor lower than 1.2. High-power picosecond ultraviolet lasers are primarily used for Control and inspection of the Si manufacturing process.
266/355nm Picosecond UV Laser
3. Visible-light laser
CNI offers a range of laser wavelengths including 405nm, 450nm, 457nm, 520nm, 532nm, 633nm, and 671nm. Our standard visible-light lasers deliver output powers from 1 to 50W, featuring homogenized beam output, linear fan-shaped output, or single-mode fiber-coupled output—perfect for dark-field wafer defect detection—and support up to 7 × 24-hour continuous operation, with a lifespan exceeding 20,000 hours.
Ultra-high-stability visible-light laser
4. Infrared laser
CNI offers a range of infrared lasers with wavelengths including 808nm, 915nm, 940nm, 980nm, 1064nm, 1270nm, 1550nm, 2100nm, and 3800nm. With power levels reaching up to the hundred-watt range, these lasers are ideal for applications such as wafer inspection, wafer heating, and wafer debonding.
High-Power Infrared Laser with Fiber Coupling
As semiconductor processes advance to nodes below 3nm, the demand for wafer surface defect detection accuracy has risen to sub-nanometer levels. Laser technology, with its non-contact measurement capabilities, nanometer-level precision, and highly efficient automation features, has become the cornerstone supporting the entire wafer inspection process—from macroscopic defect screening to detailed microscopic morphology analysis.
Currently, laser technology is reshaping the boundaries of wafer inspection accuracy and efficiency by leveraging multi-dimensional sensing capabilities and optimizing with intelligent algorithms. To meet the semiconductor industry's ongoing demand for high yield rates and highly efficient detection, laser technology must also overcome critical challenges in precision, cost, and reliability through cross-disciplinary collaboration and seamless integration across the industrial value chain.
Changchun New Industries Optoelectronics Technology Co., Ltd.
Address: No. 888 Jinhu Road, High-Tech Zone, Changchun, 130103, P.R.China
International Tel:+86-431-85603799
Email: sales@cnilaser.com
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