Defect Inspection Device Using Dual Spatial Filters

The patent divides the light-blocking function into multiple spatial filters with different light-blocking patterns. Instead of using a single spatial filter that blocks all diffracted light (including defect signals), the system segments the filtering function across multiple filters, each blocking specific diffraction orders while preserving defect signals. This segmentation allows selective rejection of pattern diffraction while maintaining defect detection capability.

The patent applies different light-blocking patterns to different spatial filters, creating local quality variations in the filtering characteristics. Each spatial filter has a specific light-blocking pattern optimized for blocking certain diffraction orders, while the combination of all filters ensures comprehensive pattern rejection without sacrificing defect signals. This local differentiation of filtering properties resolves the contradiction between pattern suppression and defect signal preservation.

The patent segments the noise reduction function across multiple spatial filters, each targeting specific diffraction orders that constitute pattern noise. By dividing the noise rejection task among multiple filters with specialized light-blocking patterns, the system reduces pattern noise effectively while preserving defect scattered light that appears in different spatial frequencies, thereby maintaining detection reliability.

The patent converts the harmful effect of diffracted light from repetitive patterns into a beneficial filtering mechanism. By analyzing the diffraction pattern characteristics and designing spatial filters with complementary light-blocking patterns, the system transforms the problematic diffracted light into useful information for distinguishing defects from pattern noise, improving both noise reduction and detection reliability.