The evaluation of assist feature defect printability for sub-0.13-μm technology

Abstract

We demonstrated the impact of space between assist bar and main pattern, width of assist bar, defect size, and the location of defect between assist bar and main pattern on main pattern distortion. The sizes of designed defect on mask were 400, 1600, 3600, and 6400 nm2 (1X) and the locations of defect were varied with 20 nm intervals between assist bar and main pattern. The widths of assist bar were varied from 60nm to 100nm with 10nm intervals and the spacing between assist bar and main pattern with 130- and 150-nm-width were 200nm, 240nm, and 280nm. The ΔCD, which is the difference of CD values between normal main pattern and distorted main pattern adjacent to defects, values were decreased with increasing space between assist bar and main pattern, while width variation of assist bar does not affect on the ΔCD value. Concerning the effect of defect location, we observed that the isolated defects with ≥1600 nm2, located between assist bar and main pattern, were printed on wafer. In sharp contrast, the defect attached to assist bar were not printed at all for all sizes of defects. In addition, ΔCD values were linearly increased as the defect location is close to main pattern regardless of process conditions. These results indicate that the location of defect plays a major role to specify the defect criteria, especially for assist bar OPC mask. The change of process latitude and defect printability with the illumination conditions and mask bias was also investigated