| AVS 61st International Symposium & Exhibition | |
| Plasma Science and Technology | Tuesday Sessions |
| Session PS-TuA |
| Session: | Advanced BEOL/Interconnect Etching |
| Presenter: | Hisataka Hayashi, Toshiba Corporation Center for Semiconductor Research & Development, Japan |
| Authors: | H. Hayashi, Toshiba Corporation Center for Semiconductor Research & Development, Japan T. Imamura, Toshiba Corporation Center for Semiconductor Research & Development, Japan H. Yamamoto, Toshiba Corporation Center for Semiconductor Research & Development, Japan I. Sakai, Toshiba Corporation Center for Semiconductor Research & Development, Japan M. Omura, Toshiba Corporation Center for Semiconductor Research & Development, Japan |
| Correspondent: | Click to Email |
To meet the needs of the device scaling trend, patterning technologies for critical dimension control less than 20 nm is required. For 1X nm pattern formation beyond the conventional optical lithography limit, it is necessary to use double (or multiple) patterning process which increases the process cost. Directed-self assembly (DSA) of block copolymer is one of the most attractive candidates for 1X nm pattern formation process and 12.5 nm hp patterns were formed using polystyrene-block-poly(methyl methacrylate) (PS-b-PMMA) [1]. DSA lithography (DSAL) process using PS-b-PMMA needs selective removal of PMMA to PS, which is called “development process”. A wet development process was applied successfully for contact hole shrink process [2]. Although this method can remove PMMA selectively, pattern collapse will occur for line and space pattern resulting from surface tension of developer solvent.
On the other hand, although a dry development process is expected to solve this problem, selective removal of PMMA is difficult because PMMA is a similar organic polymer to PS. Dry development processes using Ar plasma and O2 plasma have been reported and their selectivities were 3.9 and 1.7, respectively [3]. However in our case, higher selectivity is needed for etching the underlayer with PS as mask.
In this study, we focused on differences of material composition of PS and PMMA. Our results concluded that the control of ion energy and design of gas chemistry were key factors for the selective etch.
The aromatic group in PS is more durable than the carbonyl group in PMMA for ion bombardment. A selectivity of around 8 was achieved by the control of ion energy in xenon plasma.
PMMA has more oxygen in the film than in PS, so we designed the gas chemistry to realize the selective PMMA etch by using this difference of the oxygen content. We studied carbon containing gas plasma, because carbon radical will deposit on PS which does not contain oxygen. On the other hand, carbon radical will react with the oxygen in the PMMA to make volatile COx, therefore selective PMMA etch to PS can be realized. A selectivity of over 20 was realized using CO gas plasma [4].
DSA lithography dry development was successfully realized by controlling ion energy and designing the etching gas chemistry based on the difference of material composition of PS and PMMA.
References
[1] C. Bencher et al., Proc. SPIE 7970, 79700F (2011)
[2] Y. Seino et al., Proc. SPIE 8323, 83230Y (2012)
[3] M. Satake et al., Proc. SPIE 8685, 86850T (2013)
[4] H. Yamamoto et al., Japanese Journal of Applied Physics 53, 03DD03 (2014)