Submicrometer defect detection in periodic structures by photorefractive holography: system design and performance

We have built an adaptive system capable of detecting submicrometer defects in periodic structures by using real-time holography in photorefractive crystals. We summarize the design and optimization of the defect-enhancement system. We present representative results of 0.2- to 0.5-µm diameter defect detection on two different periodic substrates: chrome-on-glass masks and patterned silicon wafers. On patterned silicon we detect 94% of the 0.5-µm diameter defects with three false positives, while inspecting an area greater than 1 mm(2) in 20 s or less. The throughput on the glass masks is somewhat less. To the best of our knowledge, these defects have an area 100 times smaller than those previously detected with any real-time holographic technique.