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Bowen, Alan G.; Frommhold, Andreas; Lada, Tom; Bowen, J.; el Otell, Z. and Robinson, Alex P. G.
(2016).
DOI: https://doi.org/10.1117/12.2219212
URL: http://proceedings.spiedigitallibrary.org/proceedi...
Abstract
Spin-on-Carbon (SoC) hardmasks are an increasingly key component of the microchip fabrication process. Progress in lithographic resolution has made the adoption of extremely thin photoresist films necessary for the fabrication of “1x nanometre” linewidth structures to prevent issues such as resist collapse during development. While there are resists with high etch durability [1], ultimately etch depth is limited by resist thickness. A possible solution is the use of a multilayer etch stack. This allows for considerable increase in aspect ratio. For the organic hard mask base layer, a carbon-rich material is preferred as carbon possesses a high etch resistance in silicon plasma etch processes. A thin silicon topcoat deposited on the carbon film can be patterned with a thin photoresist film without feature collapse, and the pattern transferred to the underlying carbon film by oxygen plasma. This produces high aspect ratio carbon structures suitable for substrate etching. In terms of manufacturability it is beneficial to spin coat the carbon layer instead of using chemical vapor deposition [2], but the presence of carbon-hydrogen bonds in typical spin-on-carbon leads to line wiggling during the etch (a significant problem at smaller feature sizes). We have previously introduced a fullerene based SoC and reported on material characterization [3,4,5]. The materials low Ohnishi number provides high etch durability and the low hydrogen level allows for high resolution etching without wiggling. The use of the materials in such etch stacks is demonstrated (figures 1-3). A 20nm thin silicon film was sputtered on top of the carbon layers. Resist patterns are defined by e-beam, and in the case of figure 2, EUV lithography and transferred to the silicon thin film using SF6/CHF3 etch chemistry. The carbon layer was then etched by O2 plasma using the silicon mask and finally the pattern was transferred into the silicon substrate using the same process used to etch the topcoat. Recent advances in material development and work towards commercialization of the materials will be reported. Some results from external evaluations of the original 100 series will be presented, together with recent developments with the newer 200 and 300 series formulations (offering improved thermal stability and etch durability).
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[2] C.Y. Ho, X.J. Lin, H.R. Chien, C. Lien, Thin Solid Films 518 (2010) 6076
[3] A. Frommhold, J. Manyam, R.E. Palmer, and A.P.G. Robinson, Proc. SPIE 8328 (2012) 83280U
[4] A. Frommhold, R.E. Palmer, and A.P.G. Robinson, J. Micro/Nanolith. MEMS MOEMS. 12 (3), 033003 (2013)
[5] A Frommhold, A G. Brown, T Lada, A P. G. Robinson, Proc SPIE 9421-21 (2015)
