ICE: Ionic contrast enhancement for organic solvent negative tone develop

Abstract

The use of organic solvents in the development of chemically amplified (CA) resists has been known since the introduction of DUV lithography into manufacturing over twenty years ago [1,2]. In this approach a negative tone image is produced using an aqueous base developable positive tone resist developed in an organic solvent. Recently there has been an increased interest in negative tone imaging due to superior performance for specific masking levels such as narrow trenches and contact holes [3]. Negative tone imaging of this type is based on differences in the polarity between the exposed and unexposed regions of the resist film. The dissolution contrast can be optimized by selecting a solvent with the proper match of solubility parameters (polarity, hydrogen bonding and dispersion) to attain good solubility of the relatively nonpolar unexposed resist and poor solubility of the deprotected acidic exposed film. Another approach is to tune the properties of the resist polymer for a given solvent, creating a new optimized resist. We have explored a third methodology to achieve a high contrast solvent developable system without a need to modify resist or solvent. In this report we describe a process that exploits the differences in solubility between ionic and organic materials. In this method an ionic species is introduced into the resist film following post-exposure bake to alter the polarity in such way that the resist contrast can be improved in organic solvent development. We describe processes using pre-rinses and developers containing salts. Lithographic response, characterized using contrast curves and imaging, is presented for a variety of resist platforms. We show evidence for ionic incorporation into the resist film using SIMS, XPS, QCM and FTIR characterization. We demonstrate the practical applicability of this method to 248nm, 193nm, e-beam and EUV exposures. © 2014 SPIE.