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12 May 2005 A novel assist feature for contact holes to overcome problematic pitches
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Resolution and through-pitch common process window are two key factors to tackle for successful small contact process manufacturing. The off-axis illumination (OAI) in combination with assist feature and attenuated phase-shift mask (APSM) is the most common used solution. However, it is still difficult to avoid problematic pitches and get a sufficient through-pitch common process window for practical use unless forbidding the problematic pitches by design rule. A novel perpendicular assist feature (PAF) is proposed in this investigation, it is composed of a set of sub-resolution space perpendicular to the contact hole edge. The optical principles, design guidelines and tuning flow of PAF were described in this paper. The performance comparison between conventional assist feature (CAF) and PAF was also conducted in this study. Consequently, the PAF demonstrated better through-pitch photo performances on CD uniformity and mask error enhancement factor (MEEF), and most importantly, the problematic pitches issue occurred at CAF configuration was successfully eliminated.
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Mars Yang, Francis Lin, Elvis Yang, T. H. Yang, K. C. Chen, Joseph Ku, and C. Y. Lu "A novel assist feature for contact holes to overcome problematic pitches", Proc. SPIE 5754, Optical Microlithography XVIII, (12 May 2005);

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