Spin coating and characterization of thin high-density polyethylene films

The properties of thin films (0.03-2 mum) of high-density polyethylene spin -coated at elevated temperatures (100- 180 degreesC) onto silicon wafers an d evaporated gold films were investigated. The coatings were characterized with respect to thickness (ellipsometry, QCM), chemical composition (ESCA, TOFSIMS), and morphology (optical microscopy, AFM). Initial deposition temp erature was found to be an important process parameter that affected the cr ystal morphology, uniformity, and thickness of the films. The nucleation an d the crystal growth were found to depend on both the substrate type and su rface properties, especially at low supercooling. Below a film thickness of 0.1 mum, the morphology was composed of aggregates of edge-on oriented lam ellae instead of the flattened spherulitic structure observed in thicker fi lms. This thickness dependence of the morphology ceased when the spin-coati ng was performed at the lowest process temperature, since crystallization p robably occurred in the presence of solvent, rather than via a polymer melt , which promoted spherulitic growth. Low process temperatures also gave mor e uniform films and suppressed the formation of surface striations owing to lower solvent evaporation rate.