Improvement of gate CD imbalance for a 0.35 μm logic technology

Abstract

To obtain balanced gate final inspection critical dimension (FI CD) between dense and isolated pattern, negative photoresist (PR) instead of positive PR in gate photo process was applied and evaluated. Gate developed inspection critical dimension (DI CD) of isolated gate line pattern is larger than that of dense gate line pattern above 0.25 μm mask CD in positive PR process. That leads to extreme CD imbalance between isolated and dense pattern linewidth after etch because of much larger FI CD gain of isolated pattern. It was effective to do negative PR process in order to make gate DI CD of isolated pattern smaller than that of dense pattern and reducing FI CD gain difference between patterns. By applying 0.35 μm design rule to negative PR and positive PR, gate CD balance was shown to be dramatically enhanced as FI CD unbalance was measured to be 0.007 and 0.050 μm respectively. Negative PR is very effective to achieve stable gate CD balance without additional photo and etching recipe tuning above 0.25 μm gate process.