ADSORPTION AND GROWTH OF DIP-COATING PREPOLYMER FILMS ON SILICON-WAFERS - AN ATOMIC-FORCE MICROSCOPE STUDY

Ultrathin films of a prepolymer of the dicyanate of bisphenole A were made by dip-coating on commercial silicon wafers. The initial stages o f film formation could be characterized in detail by AFM (atomic force microscopy) in the tapping mode and in a newly developed deformation mapping mode. The interpretation is assisted by simple molecular model ling as well as surface analytical investigations. The thinnest films are discontinuous and have a mean thickness < 1 nm (ellipsometry). The y consist primarily of an amorphous deformable phase which probably re presents monomer. Even for the tiny roughness of the wafers (0.13 nm R MS), the initial adsorption is preferred in substrate depressions. Hig h resolution imaging could be reproducibly achieved even for this amor phous film surface. An extended contact time of the wafer with the pre polymer solution induces the adsorption of adsorbates, whose heights c orrespond to the next larger species of the prepolymer, the trimer. Fu rther increase in contact time results in a close packing of these ads orbates and such with double the height. After a contact time of about one minute, a steady state of the film morphology is reached, Then. t he mean film thickness can only be raised by increasing the concentrat ion of the solution. in addition, all films comprise large prepolymer agglomerates which represent conglomerates already present in the solu tion above a small, critical concentration.