Spin-coated PMMA films

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 8 krpm from a 1.25% solution on silicon substrates and postbaked at 200 °C for 2 min on a hot plate, while surface defects in the form of large circular pits with diameters between 10 and 20 μm and depth of ～2 nm dominate the surface morphologies of films spin coated at 7 krpm on glass substrates from a 2% solution and postbaked either at 200 °C for 2 min on a hot plate or at 170 °C for 30 min in an oven. Surface defects in the form of pinholes appear on the surfaces of films spin coated at 8 krpm on silicon substrates from a 1.25% solution (thickness of ～8 nm) and postbaked at 170 °C for 60 min 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.