A study of reactive adhesion promoters and their ability to mitigate pattern collapse in thin film lithography

Abstract

As integrated circuit fabrication continues to advance towards the 22 nm node and below, it has become clear that although line edge roughness and resolution are important, other issues such as pattern collapse must be addressed in order for technology to continue to progress. One of the primary modes of pattern collapse at small feature sizes is adhesion failure caused by loss of adhesion of the resist to the substrate during the drying process. The main forces which govern pattern collapse by adhesion failure are related to substrate/resist interactions. Significant research has been conducted to find methods for reducing capillary forces, such as use of surfactants in rinses, to reduce pattern collapse. However, the use of spin drying has also been observed to exhibit other collapse related effects that are not sensitive to such treatments. To this end, in this work a reactive adhesion promoter capable of covalently attaching to hydroxystyrene-based positive tone resist copolymers has been developed and demonstrated. A vinyl-ether-modified silane was prepared and effectively applied using a solution silanization reaction. A model hydroxystyrene-based positive tone resist was applied and subjected to post apply bake to cause reaction of the surface modifier with the photoresist to occur prior to patterning using e-beam lithography. Contact angle studies and ellipsometry were used to characterize the surface silanization reaction. Pattern collapse test structures were fabricated and analyzed after development and drying on the different surfaces to quantify the impact of the use of the covalent surface linker and compare it to more standard adhesion promoter processes such as those utilizing hexamethyldilazane (HMDS). The effect of soft bake condition on the performance of the reactive adhesion promoter has also been studied. Ultimately, the results of critical stress analysis and SEM studies of the resulting patterns confirm that use of surface priming agents that covalently attach the resist to the substrate can significantly enhance resist-substrate adhesion and dramatically reduce pattern collapse.