Improving reticle quality through reticle blank inspection

We are jointly examining several aspects of reticle blank inspection. Previously, we have reported on our progress inspecting PBS blanks with the KLA-Tencor SL300 STARlight system. Using a simple test reticle we have measured, in a reproducible and qualitative way, the probability that a reticle blank defect will transfer to the finished reticle. Our study evaluated samples containing 452 blank defects. In some cases, the transfer probability is higher than 80 percent. We have now expanded our research to include reticles with optical resist such as 895I. Using eight optical blanks and a CD uniformity test pattern, we have found that the scanning process of the inspection does not measurably change the optical blank characteristics. However, there is clear evidence that the calibration process does impose some limitations on the use of non- destructive optical blank inspection. Our proposals to overcome those limitations are discussed.