Surface and bulk chemistry of chemically amplified photoresists: Segregation in thin films and environmental stability issues

Abstract

The performance of chemically amplified photoresists, including next generation thin film 157 nm fluorinated copolymers and blends, is affected by such phenomena as polymer/substrate and polymer/air interfacial (surface energy) effects, blend miscibility, small molecule diffusion in thin films, permeability of airborne contaminants, and interactions with products from the deprotection reaction. Using near edge x-ray absorption fine structure (NEXAFS) spectroscopy, it is possible to simultaneously probe the surface and bulk chemistry of chemically amplified photoresists to determine possible causes of pattern degradation, including post exposure delay induced material failure, blend component and small molecule diffusion/segregation to the photoresist surface, and interactions between components of the photoresist formulation and developer. The surface and bulk chemistry of model photoresists were analyzed in the NEXAFS vacuum chamber, equipped with in situ processing capabilities for exposure, controlled dosing of a model contaminant gas (NMP or water vapor), and heating, to quantify component segregation and identify surface phenomena that may be responsible for pattern degradation. For model 157 nm blend films, it was found that there is segregation of one component to the surface of the photoresist film, in excess of the composition of that component in the blend. For polymer blends the more hydrophobic or lower surface tension species will typically wet the film surface when heated in air. Segregation of photo-acid generator has also been demonstrated and the effect of reducing film thickness investigated. As photoresist film thickness continually decreases and the photoresists become increasingly sensitive to environmental contaminants, the interfacial and surface regions dominate the behavior of the material and it is crucial to understand both their physical and chemical nature.