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Micro/Nano Lithography

Recent progress in chemically amplified extreme UV resist technology

Chemically amplified extreme UV resist has the potential to achieve 15nm half-pitch resolution.
31 January 2012, SPIE Newsroom. DOI: 10.1117/2.1201201.004102

Argon fluoride (ArF) immersion lithography techniques are shrinking the limits of resolution, making it possible to fabricate finer details than ever before. ArF immersion lithography is currently capable of achieving resolution of a line and space, or half-pitch, as small as 40–49nm. Double-patterning versions of the same technique will extend optical lithography limits to 30–39nm half-pitch. And multiple (triple or quadruple)-patterning technology has the potential to take optical lithography down to 10–19nm half-pitch. But such a complex process will increase manufacturing costs and decrease yields. And we are already reaching the limits of current technology. From a technical point of view, new lithography processes will be necessary for 10–19nm half-pitch resolution and smaller. Some leading candidates include extreme UV (EUV) lithography, directed self-assembly technology, and electron-beam (E-beam) lithography. At JSR, we have research and development programs in all of these technologies. Here we focus on the development of chemically amplified EUV resist.

Figure 1. Process window data of JSR extreme UV (EUV) resist evaluated using imec's NXE:3100 EUV lithography preproduction tool. hp: Half-pitch. UL: Underlayer. FT: Film thickness.

Figure 2. Process window data of JSR EUV resist, showing exposure latitude (EL) versus depth of focus (DOF).

Figure 3. Ultimate resolution data of JSR EUV resist on the Semiconductor Manufacturing Technology Consortium (SEMATECH) Berkeley Microfield Exposure Tool (MET). PSM: Phase-shift mask.

EUV lithography's extremely short wavelength (13.5nm) allows it to achieve 10–19nm half-pitch resolution in a single exposure. Requiring just a single exposure may give it a manufacturing cost advantage, depending on which high-volume manufacturing process is used. But EUV lithography will require new technical processes, different from traditional optical lithography systems. Since most of the materials used in lithography absorb 15.3nm light, EUV exposures must be performed under vacuum conditions with a reflective, instead of transmitting, type of photomask. The photoresist also requires a significant increase in resolution (R), linewidth roughness (L), sensitivity (S), and a large process window, or set of conditions under which it works well. Chemically amplified resist is the most promising EUV resist technology at present to achieve 10–19nm half-pitch patterns.

Photoresist materials' light absorption, and therefore the materials' acid-generation mechanism, is very different at EUV's 13.5nm wavelength than at 193nm (ArF) and 248nm (krypton fluoride, KrF) wavelengths. EUV photoresist development requires a different approach. Consequently, we are developing new materials such as molecular glass, photoacid generator (PAG) with short acid diffusion length, acid amplifier, and high-absorption resin, as well as resist processing methods to achieve RLS requirements simultaneously.1–3 JSR research especially focuses on developing short acid diffusion length PAGs to achieve significant improvements in RLS performance of chemically amplified resist. In a chemical amplified resist system, it is very important to maintain high optical contrast during the protective unit cleaving step catalyzed by the PAG acid during the post-exposure bake. Without a high optical contrast, PAG acid diffuses to the unexposed area and causes acid blur, reducing overall image contrast. Suppression of PAG acid diffusion length is one of the most important material design concepts needed to achieve superior RLS performance from chemically amplified EUV resist.

Figure 1 and Figure 2 show process window data for JSR EUV resist evaluated using imec's NXE:3100 EUV lithography preproduction tool. JSR EUV resist shows large exposure latitude (EL) and depth of focus (DOF) with high sensitivity. We believe that this result should encourage the lithography community to consider chemically amplified EUV resist for high-volume manufacturing at 20–29nm half-pitch.

Figure 3 shows ultimate resolution data for JSR EUV resist on the Semiconductor Manufacturing Technology Consortium (SEMATECH) Berkeley Microfield Exposure Tool. JSR EUV resist has the potential to achieve 15nm LS resolution. Our result shows that practical application of EUV lithography can realize 10–19nm-level pattern formation. But chemically amplified EUV resist technology incorporating new chemistries and process schemes must be explored to achieve the resolution, line-edge roughness, sensitivity and process latitude necessary for large-scale manufacturing of 16nm half-pitch and smaller devices.

The author is greatly indebted to imec for evaluation on its NXE:3100, and to SEMATECH and CXRO for evaluation on the SEMATECH Berkeley Microfield Exposure Tool.

Ken Maruyama
JSR Micro
Sunnyvale, CA

Ken Maruyama is a senior research engineer at JSR Micro. He received his MS and PhD in engineering from Kanagawa University, Japan. His current projects are focused on innovative materials development as well as accelerating advanced resist development for EUV lithography.

1. Ken Maruyama, Makoto Shimizu, Yuuki Hirai, Kouta Nishino, Tooru Kimura, Toshiyuki Kai, Kentaro Goto, Shalini Sharma, Development of EUV resist for 22nm half pitch and beyond, Proc. SPIE 7636, pp. 76360T, 2010. doi:10.1117/12.846332
2. Kouta Nishino, Ken Maruyama, Tooru Kimura, Toshiyuki Kai, Kentaro Goto, Shalini Sharma, Development of EUV resist for 22nm half pitch and beyond, Proc. SPIE 7969, pp. 79692I, 2011. doi:10.1117/12.879430
3. Hiroki Nakagawa, Tomohisa Fujisawa, Kentaro Goto, Tooru Kimura, Toshiyuki Kai, Yoshi Hishiro, Ultra-thin-film EUV resists beyond 20nm lithography, Proc. SPIE 7972, pp. 79721I, 2011. doi:10.1117/12.879303