Investigation of systematic CD distribution error on intrafield

As feature size shrinks, better critical dimension uniformity (CDU) is highly demanded in aspects of device characteristics. Intra field CDU is one of main contributor in total CD variation budget. Especially systematic CD distribution in shot, bank and MAT boundary should be strongly considered to minimize repeated error to guarantee high yield even though it is not prominent in overall CDU value. 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.