An optical constant calculation method capable of calculating an accurate
optical constant of an underlayer film to accurately identify a substrate
surface structure. After each of films is layered on a wafer, there are
measured the reflectivity of an oxide film under which an organic
insulation film is formed and the reflectivity of an organic insulation
film exposed after removal by plasma of the oxide film. Based on the
measured reflectivities, the optical constant of the organic insulation
film after being altered by heat treatment and the optical constant of
the organic insulation film after being altered by plasma are calculated.