Recent advances in non-chemically amplified photoresists for next generation IC technology

While chemically amplified resists (CARs) have been dominating the semiconductor industries over the past few decades, particularly in the area of computer chip fabrication, the replacement of such resists has been realized in recent times as the CARs are approaching their resolution limit, and thus may not be able to fulfil the market demand that the semiconductor industries are looking for, particularly for sub-20 nm node technology using next generation lithography techniques. In this context, non-chemically amplified resists (n-CARs) are being anticipated as potential replacements of CARs. In the case of n-CARs, the photosensitive functionality is integrated into the resist backbone. Therefore, upon exposure to photons of suitable energy, the photosensitive group undergoes photochemical changes resulting in polarity switching between the exposed and unexposed regions. This polarity change helps in developing patterns in the presence of a suitable developer. Therefore, external chemical amplification using photoacid generators (PAGs) is not needed to bring in required polarity changes in the case of n-CARs. As the n-CARs do not require any additional chemical amplification, they are devoid of the most serious problem that almost all CARs face i.e. acid diffusion in the solid state causing considerable line-edge roughness (LER) and line-width roughness (LWR). Recently, several research groups have designed and developed various n-CARs with ultra-low resolution and LER/LWR. Although many n-CARs, sensitive to photons of various energies, have been developed over the last few decades for larger nodes (>60 nm) the n-CARs development for patterning sub-30 nm features is at the plinth level. This review article will focus on the recent developments in the area of n-CARs for sub-30 nm node technology using next generation lithography (NGL) techniques.