A contact-reducing method over topography by combining the RELACS technique and bi-layer process

Abstract

Extending current lithography capability in the case of severe topography is desired in trench-first dual-damascene process. We demonstrate a solution of applying the RELACS process on DUV bi-layer resist system to provide a planarization material with CD shrinkage ability. By combining these two commercially available processes, the cost saving of contact-reducing techniques can be realized on wafers with aggressive topography. The main results presented in this study include (1) process window of the bi-layer/RELACS is comparable with that of the bi-layer only process. (2) Across wafer CD uniformity of the bi-layer/RELACS process is improved compared to that of the bi-layer process alone. Further etch steps does not degrade CD uniformity either. Nice post etch across CD uniformity and cross-section photos from post etch show the image resist still retains enough etch resistance after RELACS process. (3) Among all geometry in this study, the maximum difference from two orientations is 2nm in width and 5 nm in length. (4) Geometry size shows a bigger effect on shrinkage, for the ellipse contacts with aspect ratio 2, it shrinks 14 nm more in length direction than in width direction. For contacts with aspect ratio 1.3, the shrinkage difference between width and length is relative small (about 2 nm). (5) Total CD shrinkage in the range of 40 to 60 nm has been achieved. Baking temperature sensitivity is measured to be about 1.3 nm/°C. The value of temperature sensitivity suggests possible lot-to-lot, wafer-to-wafer and across wafer CD control for mass production. (6) A set of horizontal contacts is employed for pitch dependency studies. From pitch size changes from 450 nm to 700 nm in length direction, the length shrinkage changes by 8% of the target CD. And for pitch size changes from 450 nm to 850 nm in width direction, the width shrinkage changes by 9% of the CD target. Post RELACS OPC may be necessary for critical cases to compensate the pitch dependency of CD changes. © Society of Photo-Optical Instrumentation Engineers.