Stabilization of thin polymeric bilayer films on top of semiconductor surfaces

The enhanced thermal stability of thin polymer bilayer films against dewetting is investigated. Stabilization results from the addition of a random functional copolymer. The model system consists of a silicon substrate covered with a bilayer of amorphous polyamide (PA), followed by a fully deuterated polystyrene (PSd). While the PA sublayer is stable against dewetting, the addition of a PSd homopolymer film allows dewetting to occur during annealing. By blending the PSd top layer with a fully protonated copolymer poly(styrene-co-maleic anhydride) (SMA2), containing 2% maleic anhydride groups in the chain, its dewetting process is retarded. This increase in stability is investigated as a function of copolymer and annealing time. Scanning force microscopy (SFM) is applied to determine the surface root-mean-square roughness and to check the stabilization effect. Information about the density profile is aquired from specular neutron reflectivity measurements. In addition, grazing incidence small angle neutron scattering (GISANS) is applied. GISANS utilizes the averaging capabilities of scattering methods, which is compared to local information obtained by SFM. Furthermore, GISANS enables the detection of buried structures in contrast to the SFM. An amount of 5% by volume SMA2 is sufficient to stabilize the bilayer film due to the creation of an enrichment layer of SMA2 at the PA:PSd interface. With creation of a brushlike interface, the mobility of the PSd molecules is decreased, which suppresses dewetting.