The morphology of the film of polystyrene-block-poly(methyl methacrylate)(PS-b-PMMA) block copolymer having polystyrene(PS) cylinder forming composition spin-coated on a neutral brush modified silicon substrate has been investigated in this report. A mushroom-shaped morphology formed in the film with one period to two periods(L0-2L0) in thickness, which was spin-coated under a low humidity condition(RH ca. 13%) and then thermally annealed at an extreme high temperature(230℃). The results suggest that the spin-coating condition together with the confinement conditions plays a crucial role in the interesting morphology formation.