Dissolution dynamics of poly(4-hydroxystyrene-co-methacrylic acid) in tetraalkylammonium hydroxide aqueous solutions

Abstract

The resist materials and their lithography processes are essential for achieving further miniaturization in the semiconductor microfabrication. In the sub-20 nm half-pitch region, the development process becomes particularly important due to the occurrence of stochastic defects (pinching and bridging). However, the details of dissolution dynamics are still unclear. In this study, we investigated the dissolution dynamics of poly(4-hydroxystyrene-co-methacrylic acid) (PHSMA) films in tetraalkylammonium hydroxide (TAAH) aqueous solutions using a quartz crystal microbalance method. PHSMA is a typical backbone polymer used in the extreme ultraviolet lithography. For poly(4-hydroxystyrene) films, it has been reported that the dissolution mode changed when the alkyl chain length of TAAH increased. However, the mode change was not observed for PHSMA films. This difference is considered to be caused by the formation of thick transient swelling layers of PHSMA films owing to the fast water intake and the molecular interaction of the hydroxyl groups of hydroxystyrene units.

Dissolution dynamics of poly(4-hydroxystyrene) in potassium hydroxide (KOH) and sodium hydroxide (NaOH) aqueous solutions investigated by quartz crystal microbalance (QCM) method

“…This shoulder is considered to be a short version of similar kinetics observed during the development of poly(4-hydroxystyreneco-methacrylic acid) (PHSMA) film. 35) It was clearly observed that the thickness of the transient swelling layer was kept constant for a while during the development of PHSMA in diluted TMAH developer. This is typical for the dissolution with Case II diffusion.…”

Dissolution dynamics of partially protected poly(4-hydroxystyrene) in organic developers investigated by a quartz crystal microbalance (QCM) method

“…13) The OH groups with pK a 4.76 are preferentially dissociated in the standard developer, while the OH groups with pK a 9.87 still maintain the hydrogen bonding. 15) This leads to the formation of a swelling layer thicker than in the case of PHS films. 15) Thus, in PHSMA, which is the most favorite base polymer for chemically amplified EUV resists, the OH groups that are not dissociated in the 2.38 wt% TMAH aqueous developer play an important role in the formation of the thick swelling layer.…”

“…15) This leads to the formation of a swelling layer thicker than in the case of PHS films. 15) Thus, in PHSMA, which is the most favorite base polymer for chemically amplified EUV resists, the OH groups that are not dissociated in the 2.38 wt% TMAH aqueous developer play an important role in the formation of the thick swelling layer. The control of the swelling layer caused by the phenolic OH groups is important for the suppression of resist pattern defects.…”