Extreme ultraviolet (EUV) lithography is already being applied to the high-volume manufacturing of semiconductor devices. Although EUV lithography has enabled fine pitch scaling, such sub-20-nm-order fabrication has also imposed the issue of stochastic defects (in the form of randomly generated line bridges and breaks). To resolve such an issue, understanding the development process is essential. In this study, the dissolution dynamics of three types of EUV photoresist were investigated for four types of alkaline developer using a quartz crystal microbalance (QCM) method to clarify the swelling and dissolution kinetics during photoresist development. In experiments, tetramethylammonium hydroxide (TMAH), tetraethylammonium hydroxide (TEAH), tetrapropylammonium hydroxide (TPAH), and tetrabutylammonium hydroxide (TBAH) aqueous solutions were used as developers. Poly(4-hydroxystyrene) (PHS)-type, acryl-type, and hybrid-type photoresists were examined. The effect of the alkyl chain length of tetraalkylammonium cations depended on the type of photoresist. The dissolution dynamics depended on the combination of types of photoresist and developer.
The negative pressure atmosphere during the development process was investigated to mitigate the photoresist pattern collapse which is one of the traditional issues in the lithography processes for every generation of photoresists; i-line, KrF, ArF, ArF immersion, and recently extreme ultraviolet. The pattern collapse is caused by the capillary force between resist patterns during rinsing and drying in the development process. The main factors of capillary force are the surface tension and the contact angle of rinsing liquid and also the pattern structure (line width, space width, and height). On the other hand, the capillary force is influenced by the atmosphere pressure. In this paper, we controlled the chamber pressure during the rinsing and drying processes for the pattern collapse mitigation. The minimum critical dimension without pattern collapse under the negative pressure was found to be smaller (approximately 10% improvement) than that obtained with atmosphere pressure.
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