|AVS 54th International Symposium|
|Plasma Science and Technology||Wednesday Sessions|
|Session:||Plasmas and Polymers|
|Presenter:||N. Vourdas, Institute of Microelectronics, NCSR "Demokritos", Greece|
|Authors:||N. Vourdas, Institute of Microelectronics, NCSR "Demokritos", Greece
G. Kokkoris, Institute of Microelectronics, NCSR "Demokritos", Greece
E. Gogolides, Institute of Microelectronics, NCSR "Demokritos", Greece
|Correspondent:||Click to Email|
In most cases of plasma processing of polymers, plasma etch rate (ER) is treated as being a constant value throughout the plasma process. However some studies have demonstrated that ER is actually a function of film thickness,1,2 process time3 or both. Similar observations have been recorded for the dissolution (development) rate (DR) of polymers, revealing a DR variation vs. film thickness. In this work we present plasma ER measurements via in situ spectroscopic ellipsometry (SE) of atactic (a-), isotactic (iso-) and syndiotactic (syndio-) poly(methyl methacrylate)-(PMMA) and poly(styrene)-(PS) films on Si and SiO2 under high density O2 plasma discharges, and observe variations of ER vs. time and thickness. Based on these findings along with data obtained from the literature we try to identify the reasons for these variations and deduce the key mechanisms controlling the plasma etching performance of thin and ultra thin polymeric films. Three kinds of ER variations are recorded: (a) ER increase (~8%) within the first stages of etching (~first 10 sec), followed by a gradual increase of ~20% until ~120 nm remaining film, (b) ~25% ER decrease after ~120 nm remaining film, and finally (c) ER drastic decrease at the final stages of etching (completion of etching) until ER=0. Variations (a) and (b) occur regardless the initial thickness, while the variation (c) strongly depends on process time, correlates with the surface roughness amplitude, and indicates means to control surface roughness of polymers (maximum surface roughness in this point). For ultra thin polymer films (less than ~100 nm) ER increase (region a) is not recorded; we attribute this to thin-film effects. These variations result in a decreased average ER of ultra-thin films compared to the ER of the thicker ones. These results are of interest both when ultra-thin polymers are used e.g. EUV lithography, chemical nano-patterning etc, or when high surface roughness is needed, e.g. antireflective coatings, super-hydrophobic coating fabrication etc.
1M. Tatoulian, O. Bouloussa, F. Moriere, F. Arefi-Khonsari et al, Langmuir 2004 20 p.10481
2N. Vourdas, A.G. Boudouvis, E. Gogolides, Microelectron. Eng. 2005 78-79 p.474
3X. Hua, S. Engelmann, G.S. Oehrlein et al, JVST B 2006 24 p.1850
4P. Paniez, M. Pons, O. Joubert, Microelectron. Eng. 1990 11 p.469.