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Molecular structure effects on dry etching behavior of Si-containing resists in oxygen plasma

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7 Author(s)
Bruce, R.L. ; Department of Material Science and Engineering and Institute for Research in Electronics and Applied Physics, University of Maryland, College Park, Maryland 20742 ; Lin, T. ; Phaneuf, R.J. ; Oehrlein, G.S.
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The authors have studied the influence of Si–O bonding in the polymer structure of Si-containing resists on O2 plasma etch behavior. Three polymers were synthesized with the same Si wt % (12.1%) and varying number of Si–O bonds (0, 1, or 2). The etch resistance during the plasma process was measured by monitoring the film thickness removed using real-time in situ ellipsometry. After plasma exposure, surface chemical changes and roughness were characterized by x-ray photoelectron spectroscopy and atomic force microscopy, respectively. For O2 plasma exposure without substrate bias, all polymers showed the formation of a ∼1 nm SiO2 layer at the surface that acted as a barrier to further oxygen etching. Adding Si–O bonds to the polymer structure at constant wt % Si greatly reduced the etch rate and Si loss during oxygen plasma etching relative to the case of no such bonds. Polymers with one Si–O bond in the polymer structure showed identical etch behavior to polymers with the same wt % Si and two Si–O bonds. However, increasing the number of Si–O bonds in the structure decreased the glass transition temperature of the polymer, leading to the formation of micron-sized wrinkles after plasma exposure. When a substrate bias was applied, the etch rate and the rate of Si loss increased due to sputtering of the SiO2 layer by energetic ions. For 90% N2/O2 discharges with substrate bias, a typical oxygen-based pattern transfer plasma condition, the etch rates of the polymers with the Si–O bond were lower and the SiO2 layer thickness formed was larger than that - - formed in pure O2 discharges with substrate bias. For all gas discharge conditions, polymers with pre-existing Si–O bonds showed less Si loss.

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Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures  (Volume:28 ,  Issue: 4 )