Water immersion of model photoresists: Interfacial influences on water concentration and surface morphology

Bryan D. Vogt, Christopher L. Soles, Chla Ying Wang, Vivek M. Prabhu, Patricia M. Mcguiggan, Jack F. Douglas, Eric K. Lin, Wen Li Wu, Sushil K. Satija, Darío L. Goldfarb, Marie Angelopoulos

Research output: Contribution to journalArticlepeer-review

17 Scopus citations

Abstract

The emergence of immersion lithography as a potential alter-native for the extension of current lithography tools requires a fundamental understanding of the interactions between the photoresist and an immersion liquid such as water. The water concentration depth profile within the immersed photoresist films is measured with neutron reflectometry. The polymer/substrate interface affects both the water concentration near the interface and the surface morphology of the film. Immersed films are not stable (adhesive failure) over the course of hours when supported on a silicon wafer with a native oxide surface, but are stable when the substrate is first treated with hexamethyldisilazane (HMDS). The bulk of the polymer films swells to the equilibrium water concentration, however, a gradient in water concentration is observed near the polymer/HMDS substrate interface with a concentration of approximately 17% by volume fraction and extending up to 50 A into the film. Thus, polymers that absorb more than this amount exhibit depletion near the interface, whereas polymers that absorb less exhibit a water excess layer. These concentration gradients extend approximately 50 Å away from the interface into the film. As the total film thickness approaches this length scale, the substrate-induced concentration gradients lead to a film-thickness-dependent swelling; enhanced or suppressed swelling is witnessed for the excess or depleted interfacial concentrations, respectively. The substrate also influences the surface morphology of immersed thin films. The film surface is smooth for the HMDS-treated substrate, but pin-hole defects with an average radius of 19±9 nm are formed in the films supported on the native oxide substrates.

Original languageEnglish (US)
Article number013003
Pages (from-to)1-6
Number of pages6
JournalJournal of Microlithography, Microfabrication and Microsystems
Volume4
Issue number1
DOIs
StatePublished - Jan 1 2005

All Science Journal Classification (ASJC) codes

  • Atomic and Molecular Physics, and Optics
  • Electrical and Electronic Engineering

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