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Dry etching challenges for patterning smooth lines: LWR reduction of extreme ultra violet photo resist

We have investigated a H2 plasma smoothing process that improves the Line-Width-Roughness (LWR) and Line-Edge- Roughness (LER) of the EUV PR at 30 nm half pitch. This process reduces the LWR from ~5.8 to ~3.7 nm, a ~30% improvement. The main responsible for improving the LER/LWR under H2 plasma seems to be the vacuum ultraviolet light (VUV) below 120 nm together with the low energy hydrogen ions and radicals. The Fourier transform infrared (FTIR), X-ray photoelectron spectroscopy (XPS) and liquid proton nuclear magnetic resonance (NMR) analyses suggest a depletion of oxygen containing groups and reduction of the aromatic groups in the PR. XPS revealed that the PR surface is rapidly modified by the H2 plasma compared with the bulk (FTIR). Thus a cross-linked top surface is created which seems to be the limiting step for further LER/LWR improvement. The main challenge for dry etching is the EUV PR height which after lithography exposure and plasma smoothing, is less than 40 nm, provoking a low process window for subsequent etching steps. One strategy to open the process window is to encapsulate the PR with a more resistant material without destroying the lithography pattern. For this purpose a process was developed where 5-7nm of SiO2-like layer was deposited on top of the PR at low temperature (50 degrees Celsius). The main advantage of this deposited layer is that it is thicker on the top of the lines than in between them.