Semiconductor Wafer Inspection Using Dual-Angle Optical Scattering
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Solution Overview
Problem
Current optical scattering methods for semiconductor wafer surface inspection face challenges in accurately distinguishing between defects and particles, particularly in epitaxial wafers, with limited classification accuracy and unsuitability for mass production due to performance issues and potential damage from selective etching.
Innovation Solution
A semiconductor wafer inspection device employing dual optical sensors to detect narrowly and widely scattered light, with signal processing to calculate particle-like and defect-like sizes, enabling precise identification of defects and particles, including killer defects, without the need for selective etching.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If selective etching is performed as pretreatment for defect inspection, then the inspection accuracy is improved, but the throughput is lowered and the wafer surface quality is impaired
Solution Approach 1:
The patent extracts and eliminates the selective etching pretreatment step from the inspection process. By using optical scattering methods that can directly detect defects on the original wafer surface without chemical modification, the method removes the harmful pretreatment step while maintaining defect detection capability, thereby improving throughput and preserving wafer surface quality.
Solution Approach 2:
The patent replaces the chemical etching process with an optical detection method. Instead of using chemical reactions to enhance defect visibility, the system uses laser scattering techniques to directly detect defects on the unmodified surface, substituting a chemical-mechanical process with a non-contact optical method that preserves the wafer.
2Measurement precision
If selective etching is performed as pretreatment for defect inspection, then the inspection accuracy is improved, but the wafer surface quality is impaired
Solution Approach 1:
The patent removes the selective etching step that causes surface damage. By implementing direct optical scattering inspection on the original wafer surface, the method eliminates the source of surface degradation while maintaining the ability to detect defects, thus preserving wafer quality for subsequent processing.
Solution Approach 2:
The patent enables the wafer surface to serve itself for inspection purposes. The natural optical scattering properties of the wafer surface and its defects are utilized directly without requiring external chemical modification. The wafer's own surface characteristics provide the inspection signal, eliminating the need for harmful pretreatments.
3Device complexity
If a single threshold value of 1.6 μm is used to classify laser light scatterers, then the classification process is simplified, but the accuracy in distinguishing defects from particles is limited
Solution Approach 1:
The patent segments the classification process into multiple stages using different criteria. Instead of relying on a single size threshold, the system first classifies scatterers by size (≤1.6 μm vs. >1.6 μm), then further differentiates particles from defects using additional optical parameters such as scattering angle distribution and intensity ratios. This multi-stage segmentation improves classification accuracy while maintaining manageable complexity.
Solution Approach 2:
The patent transitions from one-dimensional classification (single size threshold) to multi-dimensional classification by incorporating additional measurement dimensions. The system measures scattering light intensity at multiple angles and uses ratios of these measurements to create a more nuanced classification space, enabling better differentiation between particles and defects beyond what a single threshold can provide.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Improves the accuracy of surface inspection, enhances the ability to differentiate between defects and particles, and is suitable for mass production without damaging the wafers, thus ensuring higher quality and yield.
Implementation Method 1
an abnormality inspection device employing an optical scattering method is widely employed for surface inspection of semiconductor wafers. Using such an abnormality inspection device, the surface of a semiconductor wafer is scanned with a laser beam of minute size and scattered light from laser light scatterers (defects or particles) on the surface of the semiconductor wafer is detected
Data Source
AI summary
The surface of an epitaxial wafer is inspected using an optical scattering method. The intensities of light scattered with a narrow scattering angle and light scattered with a wide scattering angle reflected from laser light scatterers (LLS) on the wafer surface are detected. If the intensifies of narrowly and widely scattered lights are within a prescribed sizing range, it is judged whether the laser light scatterer is a particle or killer defect by deciding into which zone (410, 414, 418, 439) within the sizing range the PLS size based on the narrowly scattered light intensity and the PLS size based, on the widely scattered light intensity fall. If the intensity of the narrowly or widely scattered light exceeds the sizing range (417, 420, 421, 423, 424, 425), or if a plenty of laser light scatterers are continuous or concentrated (422), the laser light scatterers are judged to be killer defects.