Thin ZnO nanocomposite poly(styrene-acrylic acid) films on Si and SiO2 surfaces

The properties and formation of self-assembled ZnO nanoclusters using polystyrene-based diblock copolymers are reported. The polystyrene-polyacrylic acid copolymer consisting of a majority block (polystyrene) and a minority block (polyacrylic acid) with a block number average molecular weight ratio of 16,500/4500 and a block repeat unit ratio of 159/63 was used in order to obtain self-assembly due to microphase separation with spherical morphology. The self-assembly of the inorganic nanoparticles was achieved at room temperature in the liquid phase using a ZnCl2 precursor dopant attached to the minority block, and both dry and wet chemical processing techniques compatible with semiconductor manufacturing were developed in order to convert the ZnCl2 precursor into ZnO. The polymer films were applied by standard spin-on photolithographic techniques on Si wafers with and without thermally grown SiO2 surface films. A study by X-ray photoelectron spectroscopy (XPS) confirmed the conversion of the ZnCl2 dopant precursor into ZnO within the copolymer matrix, and atomic force microscopy (AFM) showed the spherical morphology of the resultant ZnO nanoclusters. Conversion of the precursor into ZnO was achieved both by a wet chemical treatment and by developing a new dry chemical treatment process based on ozone exposure. The study showed that the dry treatment has better stability and shorter conversion exposure times on the Si surfaces than the wet treatment approach, resulting in lateral size distribution between 250 and 350 nm and height distribution between 80 and 130 nm for the ZnO nanoclusters