High-Speed Defect Classification for SEMs

Scanning electron microscopes are the natural successor to optical defect review tools. As defects get smaller, SEMs combine higher resolution with ease-of-use. SEM images are relatively easy to interpret and require minimal sample preparation.

SEM defect review is tricky, though. Contrast depends on the orientation of the sample relative to the detector, but also on the atomic number of the material. An operator may be able to see a defect more clearly by tilting the sample-and thus changing the relative position of the detector-but tilting forces the operator to refocus the image and reposition the defect in the field.

All of these tasks are difficult to automate, but manual defect review is too slow and error-prone for routine use.

Applied Materials' (Santa Clara, CA) new DR-SEM (See related article) takes a novel approach to the problem. Rather than tilting the sample, the SEMVision defect review SEM has multiple detectors with independent image processing. Some defects, like the microscratch shown below, will image better in one of the detectors. This multiple perspective imaging increases the range of detectable defects without the need for sample tilt, and allows the system to classify up to 300 defects/hour.

By Katherine Derbyshire

For more information: Applied Materials, Process Diagnostics and Control Group, 3203 Scott Blvd., Santa Clara, CA 95054-3209. Tel: 408-986-7194.