Through-Focus Optical Scanning Microscopy for Embedded Defect Detection and Classification

It is important to detect and classify defects during the packaging process, especially when the defects of interest become smaller than the optical resolution limits, often called diffraction limits. We are currently investigating through-focus scanning optical microscopy (TSOM) for defect detection and classification, aiming to extract some critical 3D information of the defects of interests below the optical resolution limit without sacrificing throughput. Regarding underlayer or embedded defects, we found that NIR (near infrared) TSOM is valid for defects of size from tens of nm in wafer inspection to tens of microns in display panel inspection. We are also investigating the application of the TSOM in wafer-level packaging, such as TSV process control.