Impact of post-litho linewidth roughness smoothing processes on the post-etch patterning result

In the last years, interest in reducing linewidth roughness (LWR) in EUV lithography through a dedicated process step has significantly increased. Various post-litho processing techniques to improve LWR without compromising resolution or sensitivity have been proposed. While these techniques are giving smoothing levels up to 30% before etch, the important question is, of course, how efficient they are in the full patterning process. To evaluate the effectiveness of the smoothing techniques on the EUV resist process and the post-etch pattern, a few of the most promising techniques have been selected for evaluation. Post-develop rinse smoothing and solvent vapor smoothing can reduce the LWR by 10% to 15%. Ion-beam smoothing is giving higher smoothing values, but suffers some important limitations for its application. Two case studies of post-litho smoothing followed by a standard etch process reveal that a large portion of the LWR smoothing can remain after etch, but the LWR gain may also be completely lost. Finally, a plasma smoothing process combined with a layer deposition is proposed to optimize the etch process itself. Analysis of LWR in the spatial frequency domain at the different stages of the patterning process gives a better insight into the impact of the different steps.