Correlation of lithographic performance of the electron beam resists SML and ZEP with their chemical structure

Gangnaik, Anushka, Georgiev, Yordan M. and Holmes, Justin D. (2015) Correlation of lithographic performance of the electron beam resists SML and ZEP with their chemical structure. Journal of Vacuum Science & Technology B, Nanotechnology and Microelectronics: Materials, Processing, Measurement, and Phenomena, 33 (4), 041601, [041601]. (doi:10.1116/1.4926387).

Abstract

Study of topographical and structural changes occurring in a positive resist known as SML after electron beam lithography are presented in this article. The authors also defined its chemical structure, which is very important for understanding the lithographic performance of the resist. The structural and lithographic properties of SML have been compared to the traditional ZEP resist. First, the change in the surface roughness with respect to the electron dose of SML and ZEP resists was measured. It was found that both resists start off with similar initial roughness values. However, ZEP was observed to have a higher roughness at the apex electron dose, thereafter a reduction in roughness was observed. The roughness variation in the two resists reflected on the resolution of the gratings that were patterned in both the resists. Gratings in SML showed smoother line edge roughness, and the patterns transferred using SML resist showed more even features than the ones transferred with ZEP. Subsequently, to understand the chemical composition of the new resist, Fourier transform infrared spectroscopy (FTIR) measurements were performed on both the resists as well as on poly(methyl methacrylate) (PMMA) and their spectra were compared. The FTIR spectra revealed that SML had a chemical structure similar to ZEP and PMMA polymers. The high sensitivity of ZEP is attributed to the Cl group in the compound, which is not present in SML and PMMA and can therefore explain their lower sensitivity to electron exposure in comparison to ZEP. Unlike PMMA but comparable to ZEP, SML shows an IR peak at a wavenumber close to 850 cm−1, suggesting the presence of α-methylstyrene group within its chemical structure, which accounts for the resist's high etch durability, similar to ZEP. Additional FTIR measurements of pre- and postexposed resists together with their attributions to the resolution of the SML and ZEP resists is also demonstrated in this article. The data presented in the study highlights the chemical properties of SML and ZEP resists polymers and correlates them to their lithographic performance.

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