Extendibility of EUV resists in the exposure wavelength from 13.5 down to 3.1 nm for next-generation lithography

The increasing density of semiconductor devices has required the development of high resolution exposure techniques. The miniaturization of feature sizes has been achieved mainly by shortening the exposure wavelength. Extreme ultraviolet (EUV) lithography at 13.5 nm exposure wavelength will be introduced into pilot lines in 2011, and high volume manufacturing is expected to be started in 2013/2014. Furthermore, the possibility of extending EUV lithography down to sub 5 nm has been proposed as next-generation lithography, by reducing the exposure wavelength to 6.x nm. ASML has estimated the throughput of exposure system for 6.x nm EUV lithography is comparable with 13.5 nm lithography, based on the experiments such as reflective multilayer optics. However, the estimation has not included the sensitivities of resist materials, which is one of the most important criteria for the practical lithography systems. Here, the sensitivities of several kinds of typical resists in EUV/soft X-ray wavelength down to 3.1 nm were actually evaluated by experiments. The sensitivities of resist materials were roughly proportional to the absorbed dose calculated by line absorption coefficients of resists. The dependence of the exposure wavelength on EUV resist sensitivity could be theoretically predicted for the next-generation lithography, if sensitivity at a certain EUV wavelength like 13.5 nm is experimentally obtained.