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In this paper, we investigated the several factors to affect systematic CD distribution error on intra field. First of all, localized mask CD variation caused by electron-beam scattering over local region, development loading and etch loading effect directly printed in wafer. Appropriate mask fabrication suppress CD variation at boundary region. Secondly, chemical flare effect is expected to make CD gradient at boundary region. Photo acid concentration change by sub-resolution assist feature (SRAF) can reduce the CD gradient. We demonstrated SRAF size dependency in positive tone develop (PTD) and negative tone develop (NTD) case. Thirdly, out-of-field stray light (OOFSL) due to adjacent exposed field causes CD gradient at field boundary. Exposure dose reduction is expected as a solution in this case. Even though we perfectly control CDU at boundary region after mask patterning, other process issues such as etch and CMP loading effect also make worse the CD distribution at boundary region. Through the consideration of above factors, we optimized systematic CD distribution error at boundary region before etch. Furthermore we compared several techniques to compensate post-etch systematic CD distribution. |
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Critical dimension metrology
Photomasks
Etching
SRAF
Semiconducting wafers
Chemical mechanical planarization
Lithography
