Resist evaluation for EUV application at ASET

Although EUV lithography has been prepared for next generation litho-technique for several years, there are still lots of obstacles on its way. Especially, phase defect from the mask, and immaturity in the resist should be solved as soon as possible because they are directly related to realizing patterns on the wafer. ASET has been focusing on these two problems, that is, the mask-related defect control and the resist screening for EUV application. In this study, we concentrate on the resist evaluation for the EUV lithography application, mainly commercial CAR (Chemically- Amplified Resist) type resist, for example, ArF resist based on polymethacrylate and KrF resist based on poly(4- hydroxystyrene) (PHS). We screened tens of resists in viewpoint of resolution, photo-speed, and LWR (Line Width Roughness). We used two METs (Micro-Exposure Tools). The one is HiNA in ASET and the other is MET in Lawrence Berkeley National Lab. (LBNL) to evaluate resist. And we used EUV masks fabricated by DNP and ASET. Some resist showed modulation on the wafer for 28nm-hp line and space pattern and some resist showed very high photo-speed about 5mJ/cm2. Photo-speed could be improved about 25% by controlling the amount of additives, PAG and quencher. However, improvement in photo-speed caused degradation in resolution. This means there are trade-off relation between resolution and photo-speed. And we also evaluated polymer-bound PAG resist, which showed new possibility for EUV resist. And we encountered unexpected problem, pattern lifting, which was solved by using bufferlayer to increase attachment force between resist and wafer surface. We conclude that polymer bound PAG resist is a good approach to lower LWR of resist for EUVL application and bufferlayer tuning and matching with resist is also needed for low LWR. The EUVL masks were fabricated by Dai Nippon Printing Co., Ltd. The HiNA set-3 projection optics were developed and provided by Nikon Corporation. This work was supported by NEDO.