Improving X-Ray Mask Pattern Placement Accuracy by Correcting Process Distortion in Electron Beam Writing

A new correction method named PAT (previous analysis of distortion and transformation of coordinates) has been developed for improving the pattern placement accuracy of completed X-ray masks. PAT compensates for total-process distortion in the electron beam writing step. In PAT, overall pattern position shifts are estimated using a send-ahead mask in advance of making working masks. Then the pattern position shifts obtained from the send-ahead mask are compensated for during electron beam writing. In an experiment, the pattern placement error of a completed X-ray mask represented by 3σ was reduced to below 0.07 µ m. This confirmed that highly accurate X-ray masks could be fabricated using PAT.