Application of substrate heating during deposition of CoPtCr-SiO2 granular medium on a bumpy-surface Ru underlayer to increase perpendicular anisotropy energy Ku⊥ of the media by promoting atomic diffusion in magnetic grains was investigated. At substrate temperature Tsub = 343 oC, magnetic grains epitaxially grew on a flat-surface Ru underlayer. And randomly oriented spherical magnetic grains surrounded by SiO2 were segregated on it. Reason of the surface flattening of the bumpy Ru underlayer was recrystallization of Ru grains promoted by desorption of oxygen from Ru grains. To prevent the oxygen desorption and the recrystallization, CoCr-SiO2 buffer layer was introduced onto the Ru underlayer. Consequently, the bumpy surface morphology of the underlayer is maintained and columnar growth of the granular layer was realized under Tsub < 380 oC.