Polymeric and molecular resists for short wavelength lithography

Abstract

The technology for 193-nm lithography is developing rapidly to satisfy the requirements that envision printing features of 0.16 mm and below. However, high performance resists suitable for these exposure tools must be designed before they can be put into practical application. 193-nm photoresists should possess optimum range of transparency at 193 nm, high imaging property and etching resistance, and good adhesion property. Alicyclic polymers have the necessary transparency at 193 nm and etch resistance, but their incorporation gives rise to poor adhesion, cracks in resist film, and lowers resist sensitivity. Therefore, hydrophilic moiety such as hydroxyl group should be incorporated in the polymer. However, it was found that the resist formulated with the polymer containing hydroxyl group showed “foot” profiles, and this is suggested that the hydroxyl group causes cross-linking during a lithographic process. It was also found that hydroxyl group gave an undesirable effect on storage stability of polymers, especially when the monomer containing hydroxyl group copolymerized with maleic anhydride. In this study, we investigated which functional groups raise cross-linking reactions during lithographic process. 2-(2-Methoxyethoxy)ethyl ester, and 2-acetoxyethyl groups were introduced into side chains of the matrix polymer, respectively, in order to improve adhesion to a silicon substrate without causing cross-linking and storage stability. 2-(2-Methoxyethoxy)ethyl 5-norbornene-2-carboxylate (MENC) was synthesized and polymerized with t-butyl 5-norbornene-2-carboxylate (BNC), norbornene (NB), and maleic anhydride (MA). 2-Acetoxyethyl 5-norbornene-2-carboxylate (AENC) was also synthesized and polymerized with BNC, NB, and MA. These polymers showed comparable adhesion property to the polymer containing 2-hydroxyethyl 5-norbornene-2-carboxylate (HNC), and better storage stability than the polymer. Sub-micron line and space patterns were obtained with the resists ...