Resist reflow methodology development to investigate interfacial interactions

Abstract

BackgroundTo enable printing of smaller feature sizes, lithography has progressed into the extreme ultraviolet lithography (EUVL) regime. Alongside the wavelength scaling, a reduction in resist film thickness (FT) is observed to avoid large aspect ratios that would lead to pattern collapse. The further progression to high numerical aperture (NA) EUVL will require a further reduction in resist FT moving toward an ultra-thin film regime (<30-nm resist FT). This reduction in resist FT will make the interfacial interactions between resist and underlayer more dominant, potentially influencing material behavior and making resist design challenging.AimWe assess a reflow process as a means to investigate interfacial effects and in this way deconvolute the correlation between resist line volume, interfacial effects, and the reflow temperature (TR), defined as the temperature at which the resist line starts broadening, which is indicative of the glass transition temperature (Tg).ApproachWe pattern a model EUV chemically amplified resist at different nominal resist FTs and different critical dimensions (CDs) and half-pitch (HP) combinations to quantify changes in the TR.ResultsThe TR increases with the inverse of the CD, as well as the inverse of the resist FT. Moreover, the TR also scales with the area ratio (the ratio of the area in contact with the ambient to the area in contact with the underlayer).ConclusionsA linear relationship between TR and its volume factor (CD × FT) normalized for the area ratio (area in contact with the ambient to the area in contact with the underlayer) is found, revealing a combined dependency on line volume and interfacial interactions. This opens the potential for the use of the reflow methodology in investigating interfacial interactions.