Limits of laser scattering defect inspection tools on patterned wafers

Many kinds of systems are available to detect defects on patterned wafers using very different technical methods. The fastest and most widespread of these use the laser scattering technique. Some suppliers have now introduced many improvements into this laser scattering tool technique. The latest of these improvements involves multi-thresholding and Fourier masking. We evaluate the quality and limitation of these techniques. The results are obtained on the one hand under real conditions on the 0.8 and 0.5 micron products. On the other hand we have developed a special design on a reticule to ensure good reproducibility and to help us understand the running of the equipment. Sensitivity has been extensively studied. This criterion is very dependent on many parameters. The tool is sensitive to the orientation of the wafer. The capture rate on the design of known simulated defects gives results when using repetitive designs. The optical signal is difficult to correlate with the dimensional parameter of the defect. This feature depends on the technology of the system. This point is crucial when moving from the role of monitoring tool to one of defect tool.