The Synthesis of the High Resolution i Line Novolak Resist

Abstract

Semiconductors have continued to grow smaller alongside the development of shorter wavelength exposure sources and the development of photoresists optimized for such exposure wavelengths. For the g-line (436 nm) and i-line (365 nm) exposure wavelengths, novolak resists made of novolak resin have been used for patterning at pattern sizes of 0.5 μm-1 μm. For the exposure wavelength of 248 nm (KrF excimer laser), polyhydroxystyrene (PHS) has been used for patterning at pattern sizes of 0.2 μm-0.35 μm. For the exposure wavelength of 193 nm (ArF excimer laser), acrylic-based resin has been used for patterning at pattern sizes of 30 nm-0.2 μm. With the most advanced current lithography technologies, patterning at pattern sizes finer than 20 nm can be performed using exposure wavelengths of 13.5 nm (EUV). Apparently, then, lithography using novolak resists made of novolak resins is an outdated technology. However, it continues to be employed in LCD processes that involve TFT technology, where the development of higher definition LCDs continues to drive miniaturization. We studied the novolak resist, from synthesis to formulation and to evaluation of its resolution, to reexamine which factors are key to achieving high resolution in novolak resists.