Thin polymer films made of polystyrene-b-poly(ethylene oxide) (PS-PEO) diblock copolymer were deposited via spin-coating technique on thermally reconstructed sapphire substrates in order to obtain self-assembled polymer matrices characterized by long range domain ordering. This approach, under specific solvent vapor annealing conditions, enabled us to fabricate polymer films exhibiting quasi long-range crystalline organization of hexagonally packed PEO cylinders aligned perpendicularly with respect to the substrate surface. In order to find an optimal conditions for thin film fabrication, the influence of moisture annealing process on polymer films morphology was examined. Different drying conditions revealed semicrystalline nature of poly(ethylene oxide) block. Consequently, apart from regular amorphous layers, various crystalline forms were also observed, including dendritic crystals, densely branched structures and square shaped single crystals. Presented data show how strongly the polymer film morphology depends on annealing conditions.