To provide a deposition diffusing agent which can be used over a wide range of methods for manufacturing semiconductor devices having various characteristics and which flexibly changes its deposition characteristics such as density and viscosity.

The deposition diffusing agent comprises raw materials for forming a silicon dioxide film, other raw materials of impurities, and alcohol as a solvent for the materials. Further, as the raw materials of the silicon dioxide film, silicon oxide represented by Si-X4 (X: a hydrocarbon compound) is used. Further, X the hydrocarbon compound has radicals which easily dissolve in the solvent, such as -OR (R: hydrocarbon group), -R and -OH, and the silicon compound hydrocarbon has a homohydrocarbon group and a heterohydrocarbon group.