Spin-coated PMMA films

Abstract

Polymethylmethacrylate (PMMA) spin-coated thin films are commonly used as resist films in micro/nanofabrication processes. By using atomic force microscopy (AFM) imaging, scratching lithography and force–distance curves spectroscopy, the spin coating and post-processing conditions were determined, for obtaining films whose surface morphology appears featureless or is dominated by pinholes and other surface defects. Featureless appear the surfaces of films spin coated at 8krpm from a 1.25% solution on silicon substrates and postbaked at 200°C for 2min on a hot plate, while surface defects in the form of large circular pits with diameters between 10 and 20μm and depth of ∼2nm dominate the surface morphologies of films spin coated at 7krpm on glass substrates from a 2% solution and postbaked either at 200°C for 2min on a hot plate or at 170°C for 30min in an oven. Surface defects in the form of pinholes appear on the surfaces of films spin coated at 8krpm on silicon substrates from a 1.25% solution (thickness of ∼8nm) and postbaked at 170°C for 60min in an oven or left in a low vacuum chamber for a few days. The implication of the different film properties—depending on the preparation parameters—in lithographic techniques is explained and discussed in the paper.