Three-dimensional embedded defect detection and localization in a semi-transparent medium

The fabrication of new optical materials has many challenges that suggest the need for new metrology tools. To this purpose, the authors designed a system for localizing 10 micron embedded defects in a 10-millimeter thick semitransparent medium. The system, comprising a single camera and a motion system, uses a combination of brightfield and darkfield illumination. This paper describes the optical design and algorithm tradeoffs used to reach the desired detection and measurement characteristics using stereo photogrammetry and parallel-camera stereoscopic matching. Initial experiment results concerning defect detection and positioning, as well as analysis of computational complexity of a complete wafer inspection are presented. We concluded that parallel camera stereoscopic matching combined with darkfield illumination provides the most compatible solution to the 3D defect detection and positioning requirement, detecting 10 micron defects at a positioning accuracy of better than +/- 0.5 millimeters and at a speed of less than 3 minutes per part.