| AVS 54th International Symposium | |
| Plasma Science and Technology | Wednesday Sessions |
| Session PS1+NS-WeM |
| Session: | Plasmas in Nanotechnology |
| Presenter: | Y.-H. Ting, University of Wisconsin-Madison |
| Authors: | Y.-H. Ting, University of Wisconsin-Madison S.-M. Park, University of Wisconsin-Madison C.-C. Liu, University of Wisconsin-Madison X. Liu, University of Wisconsin-Madison F.J. Himpsel, University of Wisconsin-Madison P.F. Nealey, University of Wisconsin-Madison A.E. Wendt, University of Wisconsin-Madison |
| Correspondent: | Click to Email |
Polystyrene -block-poly(methyl methacrylate), (PS-b-PMMA) diblock copolymers are a promising lithography alternative for nanometer scale features. The two components segregate into nanoscale domains when the polymer solution is spun on to form a thin film and annealed above the glass transition temperatures of both components. Preferential removal of PMMA domains through plasma etching to leave behind a PS mask for subsequent etching of underlying layers is the focus of this work. The quality of the PS mask is characterized by the thickness and lateral dimension of the PS structures after removal of the PMMA, as well as the smoothness of its surfaces. We have characterized the effects of different plasma chemistries including O2, Ar/O2, Ar, CF4 and CHF3/O2 on etch selectivity and surface/sidewall roughness for PS and PMMA. The surface roughness of PS and PMMA after Ar/O2 plasma etching (which gave the best overall etch performance) was further examined as a function of ion bombardment energy to understand the roughening mechanisms, as the two polymers show different responses to changing plasma conditions. Specifically, the surface roughness of PMMA increases with increasing ion bombardment energy, while that of PS decreases. An oxidation-induced micro-masking process on PS surfaces upon plasma exposure has been proposed to explain the different in roughening of PS and PMMA. Surface chemical analysis using NEXAFS shows that chemical change occurs on the PS surface during exposure to oxygen containing plasmas. Evidence of inhomogeneities in the composition of the PS film suggests that surface inhomogeneities in chemical composition may persist and change chemically upon plasma exposure. Variations in etch resistance associated with the inhomogeneities may in turn be responsible for observed surface roughness. Roughening caused by this "micro-masking" effect is reduced under conditions that minimize selectivity, such as high ion bombardment energies. We acknowledge support from the UW NSF MRSEC for Nanostructured Materials.