DENSITY PROFILE OF SPIN CAST POLYMETHYLMETHACRYLATE THIN-FILMS

The density profiles of polymethylmethacrylate ( PMMA) thin films on s ilicon (111) single crystal wafers were investigated via neutron refle ctivity measurements. Films were prepared by spin casting PMMA onto si licon wafers from o-xylene solution followed by annealing under vacuum at 90 degrees C for 5 h. A similar to 45 A thick layer at the free po lymer surface was observed in the as-prepared samples that has a densi ty about half the value of bulk PMMA. After heating above 110 degrees C, this diffuse layer disappeared and the thin film density profile wa s transformed to one with a sharp free polymer surface. This transitio n was found to be irreversible. (C) 1994 John Wiley and Sons, Inc.