| AVS 60th International Symposium and Exhibition | |
| Plasma Science and Technology | Monday Sessions |
| Session PS-MoM |
| Session: | Innovative Chemistries for Advanced Etch Processes |
| Presenter: | T. Imamura, Toshiba Corporation Semiconductor Company, Japan |
| Authors: | T. Imamura, Toshiba Corporation Semiconductor Company, Japan H. Yamamoto, Toshiba Corporation Semiconductor Company, Japan M. Omura, Toshiba Corporation Semiconductor Company, Japan I. Sakai, Toshiba Corporation Semiconductor Company, Japan H. Hayashi, Toshiba Corporation Semiconductor Company, Japan |
| Correspondent: | Click to Email |
As critical dimension (CD) continue to shrink, optical lithography has become increasingly difficult. Directed-self assembly (DSA) of block copolymer (BCP) is a promising candidate for a low cost 1X patterning process. CD of DSA lithography is determined by composition of the BCP. 12.5 nm hp patterns is formed using polystyrene-block-poly methyl methacrylate (PS-b-PMMA) [1]. DSA lithography process using PS-b-PMMA needs selective removal of PMMA to PS, which is called “development process”. Wet development process has enough selectivity, but there is a possibility of collapse of the remaining PS pattern. Because this problem arises due to surface tension of liquid, it is difficult to solve in principle. Dry development process has an advantage in that point. Generally, O2-based plasma is used for the PMMA removal and selectivity is around 2. Some have reported that the selectivity exceeds 4 by keeping the ion bombardment energy low in O2/Ar plasma. Also, because we use the remaining PS pattern as a mask of underlayer etch, high selectivity is needed to keep the PS pattern thick.
In this study, we focused on differences of material components of PS and PMMA. Based on that the PMMA has more oxygen in the film than in PS, we designed a new gas chemistry using carbon containing gas to realize high selective PMMA to PS etching.
Single layer film of PS and PMMA were spin-coated on a silicon wafer, and then baked. The thicknesses were 240 nm and 340 nm, respectively. We used 100 / 13.56 MHz dual frequency superimposed (DFS) capacitive coupled plasma (CCP) system. Plasma etching conditions were as follows. The pressure was 10 mTorr, 100MHz RF power 700W, 13.56 MHz RF power 70W, substrate temperature 40°C, and the total flow rate of the gas mixture of carbon containing gas and Ar was 300sccm. We changed the flow rate ratio of carbon containing gas and measured the film thickness by ellipsometry measurement.
When the carbon-containing gas ratio was increased from 7% to 10 % and 13 %, both the PMMA and PS etch rates decreased. The etch rate of PMMA decreased slightly, from 42.4 to 39.6 and 38.2 nm/min, while the rate of PS decreased drastically, from 5.4 nm/min to 1.8 and 0.3 nm/min. As a result, very high selectivity could be obtained at 13 %. We assumed that carbon atom from carbon containing gas was absorbed on PS and PMMA films. The carbon atoms on PMMA film reacted with oxygen in the film and volatilized as CO or CO2. On the other hand, the carbon remained on PS film and protected etching. As a result, carbon containing gas plasma achieved highly selective PMMA etching.
Reference
[1] C. Bencher et al., Proc. SPIE 7970, 79700F (2011)