Measurement Sampling Frequency Impact on Determining Magnitude of Pattern Placement Errors on Photomasks

摘要

Current methodologies for determining pattern placement errors on production masks are based primarily on limited sample sizes and Gaussian statistics. These methodologies and accepted practices may not be indicative of the true nature of pattern placement errors actually occurring on the photomasks. Pattern placement errors can originate from a variety of sources on e-beam generated photomasks. Random shot placement errors, localized charging and heating, proximity effects, global charging, and writing strategies may all have an impact on overall pattern placement errors. It is suspected therefore that pattern placement errors on photomasks are not all well approximated as Gaussian, but include a number of significant errors with unique spatial signatures that need to be addressed differently. This paper investigates different measurement sampling strategies on a single leading edge poly layer to determine what level or amount of measurements might be necessary to more accurately determine the probabilities of the true placement errors on the photomask, and what spatially dependent components may or may not be accurately represented in the measurements.