Extreme ultraviolet photoresists: Film quantum yields and LER of thin film resists

Extreme ultraviolet (EUV) is the leading candidate for a commercially viable solution for next generation lithography. The development of EUV chemically amplified photoresists and processes are critical to the future lithographic requirements of the microelectronics industry. To meet the necessary requirements for both integrated circuit (IC) specifications and cost, the resolution, line-edge roughness (LER) and sensitivity all need to be reduced. Unfortunately, a fundamental trade-off has been observed between these three crucial elements. We have predicted that the best way to obtain the required resolution, line-edge roughness and sensitivity (RLS) is to create more acid molecules per photon absorbed. This quantity is referred to as the film quantum yield (FQY). Utilizing increased photoacid generator (PAG) concentrations, the impact of FQY on the overall resist lithographic performance is characterized. However, despite significant improvements in RLS performance, LER continues to fall significantly short of industry requirements.;Lithographic exposures have shown that LER increases significantly as film thickness decreases (< 50 nm) for 193 nm and EUV wavelengths. LER degradation is a significant problem for future technology nodes where film thicknesses of 50 nm or less will be necessary to help mitigate pattern collapse. Understanding the mechanistic cause of the thickness dependent LER degradation is therefore very critical for future needs of the lithographic community. Investigations highlight key concerns related to the image degradation of ultra-thin film photoresists (< 50 nm) with the aim of better understanding the correlation between resist LER, acid diffusion and glass transition temperature.;Meeting the required LER will become increasingly difficult for future technology nodes due to thin film effects. Therefore, alternative processes and LER mitigation techniques are likely required for the implementation of EUV. Studies have demonstrated that underlayers improve resist LER and adhesion compared to primed silicon substrates. The exact cause of the performance improvement on underlayers is still unknown. We evaluated the thermal properties (glass transition temperature and coefficient of thermal expansion) and surface properties (H2O contact angle) of underlayers and determined their ability to support EUV imaging.