FEP-171 resist is commonly used both together with 50 keV VSB and DUV laser mask writers. To improve resolution and other lithographic parameters, the industry has strived towards thinner resist and absorber films on the mask blank. The chrome thickness and etch resistance limit how thin the resist can be. The NTAR7 (730Å) chrome was optimized for binary masks for 193 nm lithography, while NTAR5 (590Å) chrome is used for attenuated PSM blanks with a MoSi absorber beneath the chrome film.
Resolution and lithographic performance can be improved further by integrating improved processes, including PEB, development and dry-etch. Micronic has in a series of papers described improvements to the FEP-171 process in combination with different chrome films and the SLM-based DUV (248 nm) Sigma7300 mask writer. The thickness of FEP-171 for Sigma7300 has been optimized for NTAR7 chrome and improvements have been described for the PEB and dry-etch process of the FEP-171/NTAR7 blanks.
In this paper we describe the FEP-171 process development further. We have investigated improvements to the develop process for FEP-171/NTAR7 blanks using Design of Experiments (DOE) and a Steag Hamatech ASP-5000. Improved performance on mask, especially for CD linearity and clear-field/dark-field deviation, was achieved using the resulting development recipe together with the Sigma7300. Better than 5 nm (range) CD linearity in chrome was demonstrated for isolated spaces in the range 200-1400 nm.
This work also covers a process study of FEP-171 on NTAR5 chrome. The resist thickness was optimized to 3200Å for the Sigma7300 and the performance was tested in terms of resolution, resist profile, CD linearity and CD uniformity. Resolution of 120 nm isolated lines and 140 nm isolated spaces was demonstrated, as well as 4 nm (range/2) global CD uniformity.